Anionic phosph(in)ito (“phosphoryl”) ligands: Non-classical “actor” phosphane-type ligands in coordination chemistry

Accepted Manuscript Title: Anionic phosph(in)ito ( phosphoryl”) ligands: Non-classical “actor” phosphane-type ligands in coordination chemistry Author: P. Sutra A. Igau PII: DOI: Reference:

S0010-8545(15)00223-4 http://dx.doi.org/doi:10.1016/j.ccr.2015.07.002 CCR 112105

To appear in:

Coordination Chemistry Reviews

Received date: Revised date: Accepted date:

19-3-2015 1-7-2015 2-7-2015

Please cite this article as: P. Sutra, A. Igau, Anionic phosph(in)ito ( phosphoryl”) ligands: Non-classical “actor” phosphane-type ligands in coordination chemistry , Coordination Chemistry Reviews (2015), http://dx.doi.org/10.1016/j.ccr.2015.07.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Edited July 2

Anionic phosph(in)ito (“ phosphoryl “) ligands : Non-classical “actor” phosphane-type ligands in coordination chemistry O L nM

P

ip t

R1 R2

cr

P. Sutra,†,‡ A. Igau†,‡,*

Laboratoire de Chimie de Coordination, CNRS 205 route de Narbonne, 31077 Toulouse, France

‡

Université de Toulouse, UPS, INPT, 31077 Toulouse, France, e-mail: [email protected]

an

us

†

Graphical Abstract

d

M

Highlights

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 An overview of transition metal complexes with 1-P−metalated organophosphorus ligands of general formula {P(O)R1R2}

Ac ce p

 Recent experimental and theoretical studies on the electronic properties of O−anionic 1P(III)−phosph(in)ito ligands of general formula {P(O-)R1R2}  Main prevalent activities of transition metal complexes with 1-P−metalated organophosphorus ligands of general formula {P(O)R1R2}.

1. 2.

Introduction .................................................................................................................................................... 3 General synthetic pathways to metal complexes with ligands of general formula {P(O)R1R2}..................... 5 2.1. Dealkylation reactions via an Arbuzov-type reaction on phosphite transition metal complexes........... 5 2.2. Oxidation of terminal phosphanide metal complexes............................................................................ 7 2.3. Deprotonation reaction of secondary phosphane oxide (SPO) preligands............................................. 8 2.4. Silver P-metalated phosphonate species as transfer reagents ...............................................................10

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Ac ce p

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2.5. Oxidative addition of P(O)−R bonds to metal center ...........................................................................12 2.6. P−C and P−X (X=O,N) bonds cleavage with basic treatment ..............................................................14 2.7. Phosphonate Kläui type complexes ......................................................................................................15 2.8. Miscellaneous preparation ....................................................................................................................16 2.8.1. Hydrolysis of phosphite transition metal complexes ...................................................................16 2.8.2. P-C bond-breaking reaction via addition of MeOH/H2O.............................................................17 2.8.3. Elimination reactions ...................................................................................................................17 2.8.4. Oxidation reaction with nitrile oxides..........................................................................................17 2.8.5. Diverse preparations ....................................................................................................................18 3. Insight in the electronic properties of anionic phosph(in)ito ligands ............................................................18 4. Prevalent activities of anionic phosph(in)ite metal complexes......................................................................20 4.1. Phosphonate Kläui type complexes as mono-anionic six electron donors............................................20 4.2. Ligands of general formula {P(O)R1R2} as hydrogen-bond acceptor in supramolecular chemistry ....20 4.3. Prevalent activities in catalysis.............................................................................................................21 4.4. Prevalent activities for electrochemical and photophysical properties .................................................22 4.5. Miscellaneous prevalent activities ........................................................................................................23 5. Conclusions ...................................................................................................................................................25 Acknowledgements .......................................................................................................................................24 References .....................................................................................................................................................24

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1. Introduction Ligands are of central importance in transition metal chemistry [1-3]. The ligands directly influence the performance of transition metal chemical or electronic transformations through their electronic and steric effects

organophosphorus derivatives

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[4-6]. The design for the “ultimate” ligand giving rise to a catalyst with optimal activity and selectivity is a very challenging task. Organophosphorus derivatives are largely used as ligands in coordination chemistry. Phosphoryl is a term commonly used in organic chemistry to denote the fragment of general formula −P(O)R1R2 with the phosphorus atom attached to a carbon atom or to other elements from group 13 to 15. By inference, the term phosphoryl was applied in coordination chemistry when the organophosphorus group −P(O)R1R2 was used as a ligand and grafted to a metal center in 1-P-coordination mode. The electronic description of this ligand is depicted by the metal-phosphorus and phosphorus-oxygen formal bonding notations. In the literature, the ligand {P(O)(OR)(OR’)} in the corresponding P-metalated complex A2 has been named as phosphonato to emphasize the relationship with classic Arbuzov organophosphorus chemistry. As some authors reported, the formalism used in the description of the metal-phosphorus and phosphorus-oxygen in A type-complexes causes formal oxidation state ambiguities at the metal center. The nature of the phosphorus-oxygen bond in the fragment of general formula −P(O)R1R2 has been the subject of intense studies for many years. Experimental and theoretical calculations clearly suggest the absence of conventional multiple bonding in the P−O bond. The most recent investigations have emphasized that the P=O unit in phosphane oxides is better described with the highly polar canonical structure P+–O- [7-10]. According to the recent P−O bond electronic description, [LnM{P(O)R1R2}] complexes (Fig 1) may be considered as transition metal species B with O−anionic 1-P(III)−phosphano-type ligands. Thus, ligand {P(O)RR’}− is O−anionic phosphinito and {P(O)(OR)(OR’)}− is O−anionic phosphito, and, by inference, ligand {P(O)(NR2)R}− is O−anionic amidophosphinito and {P(O)(OR)(NR2)}− is O−anionic amidophosphito. For consistency with the recent experimental and theoretical studies reported in the literature on the structure of the fragment of general formula {P(O)R1R2}, the corresponding [LnM{P(O)R1R2}] complexes reported in this communication will be named as phosphane oxide A1/phosphonate A2 complexes and as anionic phosphinite B1/phosphite B2 complexes (Fig. 1) where the O−anionic phosph(in)ito ligand may be classified as a “non-classical” P(III)−phosphane-type ligand. O

R" P

R"

OR

Ac ce p O

Ln M

P

L nM

R

R

OR

R'

OR' phosphite

phosphinite

O

O P OR

R'

OR'

L nM

O

P

Ln M

R R'

P OR OR'

-P(V) phosphonate complexes

-P(III) O-anionic phosphinitecomplexes

-P(III) O-anionic phosphite complexes

(phosphano oxide ligands) (phosphonato ligands)

(O-anionic phosphinito ligands)

(O-anionic phosphito ligands)

-P(V) phosphane oxide complexes

(organophosphorus ligands)

P

OR' phosphonate

phosphane oxide

O R"

P

R

R'

organophosphorus metal complexes

O R"

O P

A1

A2

A

B1

B2

B

Fig. 1. 1-P−organophosphorus metal complexes A and B with ligands of general formula {P(O)R1R2} (R1,R2= R,R’ and OR,OR’ with R,R’= alkyl, aryl). Among all the classes of ligands that are both sterically and electronically tunable on a metal center, it is without a doubt that phosphanes PR3 are the most used ligands throughout inorganic and organometallic chemistry. The major application of metal complexes containing phosphane ligands is in homogeneous catalysis. Since Wilkinson’s [11] original work on the catalytic activity of [Rh(PPh3)3Cl] for hydrogenation reactions, transition metal complexes with 1-P(III)−phosphano-type ligands have been largely developed and are commonly in use in organic syntheses [12-15].

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H

O

Ln M

P

Ln M R

H O P

us

H H

cr

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Phosphanes are conventionally categorized as spectator ligands, meaning that they stay intact and keep their coordination to a metal center during chemical reactions. The concept of actor ligands, which dissociate or participate in a chemical or electronic reaction, has recently emerged for guiding ligand design [16]. Spectator and actor ligands can be either monodentate or multidentate. In addition, redox-active ligands [17-21], cooperative ligands [22-24], frustrated Lewis pair ligands [25-27], and hemilabile ligands [28-31] can behave as actor ligands. If a metal center can be coordinated by actor ligands, it is then interesting to examine the potential of the metal center to anchor the actor ligands, giving rise to ligand-based reactivity rather than metal-based reactivity. In the Pt-catalyzed hydrolysis of nitriles, an O−anionic 1-P−phosphinito ligand was proposed to act as a cooperative ligand, in which the oxygen reacts directly on a coordinated nitrile and activates it [32,33]. In early studies, van Leeuwen and co-workers have pointed out that O−anionic 1-P−phosphinite metal complexes could be ideal for the heterolytic splitting of dihydrogen (Scheme 1, [34,37]).

R

R'

R'

Scheme 1. Proposed heterolytic cleavage of H2 by  -P−phosphinite metal complex [34,37].

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1

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Recently, O−anionic bidentate phosphinite rhodium complexes were successfully tested in metal catalyzed transfer hydrogenation of ketones in isopropanol [38]. A transition state for the hydrogen-transfer was fully characterized by DFT calculations which highlighted a process occurring via a concerted outer-sphere mechanism similar to cyclopentadienone-ligated ruthenium complexes as described by Casey et al [39] for Shvo’s catalyst [40-43]. Shvo’s catalyst is a renowned H-transfer catalyst following a mechanism similar to that of the Noyori catalyst, akin to the heterolytic cleavage of dihydrogen [44-47]. Therefore, O−anionic 1P−phosph(in)ito ligands can be considered as actor “non-classical” 1-P(III)−phosphano-type ligands. O-Anionic 1-P−phosph(in)ito ligands possess different coordination modes (Scheme 2) which give rise to the formation of complexes which can be divided in three main families : the 1-O−metalated phosph(in)ite complexes C, the O−anionic 1-P(III)−metalated phosph(in)ite complexes B, and the 2-O,P(III)−metalated phosph(in)ite complexes D. This review is dedicated on the 1-P−metalated coordination chemistry of ligands of general formula {P(O)R1R2} recently described as O−anionic 1-P−phosph(in)ito ligands. Note that, to the best of our knowledge, interconversion of one isomer to the other between the O-metalated C and the O−anionic Pmetalated phosph(in)ite complexes B, has not been so far identified in the literature (Scheme 2). The O−anionic P-metalated phosph(in)ite complexes B have the propensity to adopt bridging modes to give the corresponding 2-O,P−phosph(in)ite complexes D. O−Anionic P−metalated phosph(in)ito ligands are well known to interact with donor hydrogen atom which make them an ideal choice for supramolecular structure formations which will be presented in section 4.2. O

MLn

P

R1

R

O L nM

R1

2

C

-O phosph(in)ite complexes

R

O

M'L'n

P

Ln M

R1

2

B

M'L'n

P 2

R

D

-P(III) O-anionic phosph(in)ite complexes

-O,P(III) phosph(in)ite complexes (bridging mode)

Scheme 2. Coordination modes B, C and D of phosph(in)ito ligands of general formula {P(O)R1R2}. The originality of this review lies in the fact that 1-P ligands of general formula {P(O)R1R2} are widespread in the literature and have been described for many different purposes in a large diversity of scientific communications. Consequently, a comprehensive review on these complexes is well beyond the present scope. The intend of this communication is to provide (i) a set of the general synthetic pathways of transition metal complexes incorporating 1-P ligands of general formula {P(O)R1R2}, (ii) an insight in the electronic properties

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of O−anionic 1-P−phosph(in)ito ligands, and (iii) some of the main prevalent activities of O−anionic 1 P−phosph(in)ito ligands observed in coordination chemistry.

2. General synthetic pathways to metal complexes with ligands of general formula {P(O)R1R2}

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2.1. Dealkylation reactions via an Arbuzov-type reaction on phosphite transition metal complexes

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Organophosphorus compounds containing P(O)-C(sp 3) bonds are typically prepared by the Arbuzov reaction [51]. The Arbuzov rearrangement is the thermal reaction of an alkylated nucleophile, R’X, with a phosphorus(III) ester, such as a trialkyl phosphite, P(OR)3, giving the corresponding organophosphorus compound R’P(O)(OR)2 with alkyl transfer RX. The reaction can be applied to the preparation of 1P−phosph(in)ite transition metal complexes. Starting from a transition-metal halide, LnMX, in place of R'X, induces the formation of the corresponding phosphonate complexes [LnM{P(O)(OR}2] (Scheme 3). R’X + P(OR)3 → R’P(O)(OR)2 + RX

an

LnMX + P(OR)3 → [LnM{P(O)(OR)2}] + RX

Scheme 3. Arbuzov-type reaction on phosphite transition metal complexes.

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There are a number of literature examples of transition metal-bound phosphito ligands undergoing dealkylation reactions via the Arbuzov (or Michaelis-Arbuzov)-type rearrangement. Phosphite transition metal dealkylation usually proceeds via either an ionic or a radical mechanism, with the former being more common in the presence of nucleophiles such as halides. The variety of metal complexes engaging in the reaction is broad [52]. This reaction has been reported for phosphites, P(OR)3, and few alkylsubstituted phosphites, namely the phosphonites, P(OR)2R, and the phosphinites, P(OR)R2 [53]. Examples of the reaction of amino-substituted phosphite, P(OR)(NR’2)2 were reported by Nakazawa and co-workers with cyclopentadienyl group iron complexes. Cationic complexes formed by replacement of the Cl ligand in 1 by amino-substituted phosphite, P(OMe)(R’)(NR2), are isolated as chloride salts 2, which undergo, on heating, dealkylation to afford the corresponding 1-P−amidophosphane oxide or 1-P−amidophosphonate iron complexes 3 (Scheme 4, [54-56]).

Cl

Ac ce p

(R 2N)R'P OMe

Fe

Cl

OC

Fe OC

CO 1

P



NR2

R' CO OMe 2

Fe - MeCl

OC

P

NR2 R'

CO O 3

R' = amino, alkoxy group

Scheme 4. Dealkylation reaction via an Arbuzov-type rearrangement on 1-P−amidophosphinite ( R’= amino group) or 1-P−amidophosphonite ( R’= alkoxy group) iron complexes 2 [54-56]. The reactivity of alcohols ROH with platinum complex 4 ligated by an N-heterocyclic phosphanido-containing diphosphane ligand has been investigated. The ability of 4 to interconvert between N-heterocyclic phosphanide, NHP-, and N-heterocyclic phosphenium, NHP+, configurations was experimentally and theoretically demonstrated and is related to oxidation/reduction reaction and ligand coordination/dissociation processes [57]. It was proposed that, in the presence of the nucleophilic Cl− anion, initial oxidative addition of ROH (R= Me, Et) to the neutral N-heterocyclic phosphenium/phosphanido diphosphane complex 4 leads to Pt-hydride amidophosphite species 5. The P–OR amidophosphite intermediates undergo an Arbuzov-like dealkylation reaction to release RCl and generate the 1-P−amidophosphonate product 6 (Scheme 5). The X-ray crystal 

Note that metallo-phosphonic Ln[M]−P(O)(OH)2 [48].and metallo-phosphinic Ln[M]−P(O)(R)(OH) acids [49] complexes are out of the scope of this review as well as metal organophosphonates in which the organic groups are covalently or ionically bound to an inorganic layer to form molecular composite solids [50].

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structure of the isolated compound 6 confirms its formulation as an N-heterocyclic 1-P−amidophosphonate Pthydride complex [58]. OR N

N

N

N

P

P ROH P Ph2

P Pt P Ph2 Ph 2 H Cl 5

O N

O

N

N

P P Ph 2

6

Pt P Ph2 H N

P Ph 2

an

P Pt Ph2 H



R

N Cl

us

P - RCl

cr

4

ip t

P Pt Ph 2 Cl

N

=

P

P

Scheme 5. Proposed mechanism for formation of  -P−amidophosphonate platinum hydride complex 6 [58]. 1

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The Arbuzov based synthetic pathway was extended to the preparation of chiral 1-P−phosphonate complexes. The preparation, resolution, and absolute stereochemistry assignments of a series of chiral methyl cobalt(III) phosphonate complexes which are potential P-chiral synthons were reported [59]. Treatment of cyclopentadienyl cobalt complex 7 with 1 equiv of dimethyl(diethylamido)phosphite at ambient temperature resulted in the formation of a reaction mixture from which amidophosphonate 9 and phosphonate 11 [60] diastereomeric cobalt complexes were isolated (Scheme 6). It is of particular interest to note that the amidophosphonate cobalt complex 9 was formed upon a dealkylation reaction on 8 via an Arbuzov rearrangement while the cationic 1P−dimethylphosphonate complex 11 was obtained from an hydrolysis mechanism.

I

Ac ce p

Et 2NP(OMe) 2

Co

I

HNP

I

Co HNP I

7

P

NEt2

Co - MeI

OMe OMe

HNP I

8

P

NEt 2 OMe

O

9

HNP= (S)-(-)-PPh2NHC*H(Me)Ph

H2 O

H O Co HNP I

P

I

O

NHEt2

OMe OMe

Co - H2 NEt2 I HNP I

I

P

OMe OMe

10 11 Scheme 6. Arbuzov and hydrolysis mechanism for formation of 1-P−amidophosphonate 9 and 1P−phosphonate 11 cobalt(III) complexes [60].

A solution of phosphite rhenium precursor 12 was irradiated for 15 min and immediate formation of the 1P−phosphonate complex 13 was observed in which a methyl group has migrated to the metal center presumably by an Arbuzov-like rearrangement. The tentatively proposed structure for the binuclear complex with the formal Re=Re double bond to fulfill an 18-electron count for each Re is in accord with the spectroscopic data. Unfortunately, all attempts to obtain an X-ray structure of 13 have failed [61]. As mentioned earlier, most Arbuzov-like rearrangements involving phosphite transition metal complexes are brought by nucleophiles, and

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ip t

both ionic and radical mechanisms have been proposed. However, there are some examples of methyl migration involving a phosphito ligand which are difficult to categorize under these mechanisms. As an example, the thermolysis of [Ru{(P(OMe)3}5] produces the 1-P−phosphonate complex [Ru{P(OMe)3}4{P(O)(OMe)2}Me] [62]. Inhibition of this rearrangement by the presence of free P(OMe)3 suggested that an equilibrium involving dissociation to [Ru{(P(OMe)3}4] may be involved. Note that methyl migration to the metal has occurred in this reaction. Perutz and co-workers have reported that a 1-P−phosphonate rhodium complex 15 was the major product under photochemical conditions in neat arenes of phosphite rhodium complex 14 [63]. Other metalphosphite complexes have been converted to the metal phosphonates by thermolysis [64].

Me CO O

h OC N2

OMe

Re

P

(MeO) 2P

OMe OMe

P(OMe) 2

O OC Me

13

an

12

h Rh (RO)3P

Re

us

Re

cr

There are few reports on [ CpCo(I)]- [52] as well as [CpRh(I)]-complexes [65] with phosphito ligands undergoing an Arbuzov rearrangement leading to phosphite decomposition and an alkylated metal center (Scheme 7). In general aliphatic phosphites are more prone to the Arbuzov rearrangement than arylphosphites.

Rh

P(OR) 3

(RO) 3P

15 O

M

14

R

P(OR) 2

R, R' = amino and/or alkoxy group

d

Scheme 7. Arbuzov rearrangements in the coordination sphere of rhenium 12 [61] and rhodium 14 [63] metal precursors to form the corresponding 1-P−phosphonate complexes 13 and 15.

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2.2. Oxidation of terminal phosphanide metal complexes

Ac ce p

Oxidation of the terminal phosphanido ligand {PR1R2–} in transition metal complexes is a convenient method for the synthesis of metal complexes with ligands of general formula {P(O)R1R2} (Scheme 8, [66,67]). The phosphorus lone pair of the phosphanido ligand {PR1R2–} possesses a strong nucleophilicity, a high bridging tendency and a remarkable flexibility. LnM

O

[O] PR1R2

LnM

PR1R2

[O] = O2 , H2 O2, air

Scheme 8. Oxidation of terminal phosphanide metal complexes [LnM{PR1R2}].

The selective synthesis of the hydrogen bonded complex 17 was obtained by reaction of the terminal phosphanide complex 16 with molecular dioxygen (Scheme 9, [68]). Starting from the same phosphanide platinum precursor 16, phosphane oxide complex 18 can be obtained by action of hydrogen peroxide (Scheme 9, [69]). Cy2 P O

Cy2 HP

H 2O 2 Pt

Cl

O2

- H 2O

Cl

H

Pt PHCy2

16

Cy2 P O

Cy2 HP

Pt PHCy2

18

Cy2 P

Cy2 HP

P O Cy2

Cl

17

Scheme 9. Selective oxidation of terminal phosphanide platinum secondary phosphane complex 16 [68,69]. Phosphane oxide platinum complex 20 was readily prepared by oxidation of the corresponding phosphanide complex 19 with either H2O2 or exposure to air (Scheme 10). Note that the crystal structure of the phosphane

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oxide platinum complex 20 showed distorted-tetrahedral geometry at phosphorus atom and the presence of a water molecule hydrogen-bonded to the oxygen atom of the PO unit [70]. Ph i

Bu

Ph i

Bu

P

P O

H2O2 (dppe)Pt

(dppe)Pt - H 2O

Me

19

ip t

Me

20

Scheme 10. Oxidation of terminal phosphanide alkyl platinum complex 19 [70].

M

an

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cr

In most of the cases, when air was added to the phosphanide complexes, oxidation reactions were completed within seconds. Phosphanide precursors 21a-c gave the corresponding phosphane oxide ruthenium complexes 22a−c in high spectroscopic yield (Scheme 11). Product 22a was isolated in >99% yield after workup. The 31P NMR signal of the Ph2P(O) organophosphorus fragment was 67 ppm downfield from that of the phosphanido ligand Ph2P, which is a typical shift for this functional transformation. Note that in the same reaction conditions, complexes 21a−c were treated with substoichiometric amounts of oxygen and were only partially converted to the corresponding phosphane oxide complexes 22a-c [71]. In marked contrast to what was observed for the former phosphanide ruthenium complexes, solutions of phosphanide rhenium precursor 23a gave intractable product mixtures when exposed to air. However, addition of only a few equivalents of O2 to the same starting compound 23a led to the formation of the corresponding phosphane oxide 24a in 45-70% yields (Scheme 11). The same complex 23a was also prepared in 60% yield with iodosobenzene, PhIO. Note that reaction of the di(tert-butyl)phosphanide complex 23b with iodosobenzene gave the phosphane oxide complex 24b in 34% yield after recrystallization [72].

air

Ru

PR2 PEt3

Et3 P

d

Et3 P

RT

te

21a-c

PR2

Ac ce p

O PR2

PEt3

22a-c

PhIO or O2

Re

ON

Ru

Re ON

PPh3

23a,b

O

PR 2 PPh3

24a,b

R= Ph (a), tBu (b), Cy (c)

Scheme 11. Oxidation of terminal phosphanide ruthenium 21a−c [71] and rhenium 23a,b [72] complexes. We lately prepared in a one-pot process, starting from the secondary phosphane ruthenium polypyridyl complex 25 and following the deprotonation/oxidation sequence, the corresponding O−anionic 1-P−phosphinite complex [Ru(tpy)(bpy){(Ph2P(O-)}]2+ 26 isolated in 92% yield as a red solid (Scheme 12, [73]). H

Ph 2P

N N

N Ru

N

2

2

O Ph2 P

1/ NEt3 2/ H 2 O2 CH 3CN

N N

N Ru

N

N

25

26

N

Scheme 12. One-pot synthesis of O−anionic 1-P−phosphinite ruthenium polypyridyl complex 26 [73].

2.3. Deprotonation reaction of secondary phosphane oxide (SPO) preligands 8 Page 8 of 33

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R1

P

O

H

O

Ln M

H

P

L nM

R1

R2

R

O

base Ln M

R1

2

R

2

R1

R

B

-P(III)

Phosphinous acid (PA)

P

2

Phosphinous acid transition metal complexes

 -P(III)

O-anionic

phosph(in)ite complexes

us

Secondary phosphane oxide (SPO)

H

P

cr

O

ip t

Tetracoordinated pentavalent () secondary phosphane oxides (SPOs, R1 R2P(O)H) have been known for 45 years as ligands for transition metals and introduced as catalysts by van Leeuwen and Roobeek in the early 1980s [34]. SPOs are generally easy to synthesize, and their air- and/or moisture stability allows long-term preservation and convenient handling [74-77]. Lately, these organophosphorus derivatives have drawn much attention. Tautomerization of SPOs to tricoordinated trivalent () phosphinous acids (PAs, R1R2P−OH) in the presence of a transition metal complex [MLn] allows the SPOs to act as P(III)−phosphane-like preligands (Scheme 13) [78,79].

Scheme 13. Tautomerization of secondary phosphane oxides (SPO) to phosphinous acids (PA) in the presence of a transition-metal precursor and deprotonation reaction to give B.

Ac ce p

te

d

M

an

The coordinated P(III)−phosphinous acid ligands stemming from SPOs are more than “classical” phosphanes and possess their own steric and electronic properties. Over the past few years, the knowledge of their coordination chemistry has significantly evolved but investigations on the understanding of their specificity, with respect to other P(III)-ligands, are scarce [80-82]. The presence of an acidic “hydroxy” substituent in −position to the phosphorus atom plays a critical role in some catalytic chemical transformations. P−metalated phosphinous acid are, in principle, deprotonated with an appropriate base to afford the corresponding O−anionic 1-P−phosph(in)ito ligand. Addition of triethylamine on phosphinous acid pentacarbonyl molybdenum precursor, yielded the corresponding triethylammonium O−anionic 1P−phosphinite pentacarbonyl molybdenum complex 27 (Scheme 14). The X-ray structure of this compound clearly revealed a strong N−H•••O hydrogen bridging interaction between the amonium and the PO unit, so that the ligand situation is intermediate between a phosphinous acid and a “true” naked O−anionic 1-P−phosphinito ligand as illustrated the value of the Tolman’s electronic parameter (TEP) of this complex. The air-stable O−anionic 1-P−phosphinite complexes [(CO)5M{Ph2P(O)}][Et3NH] (M = Cr, Mo (27), W) can be prepared from the corresponding chlorophosphane complexes [(CO)5M(Ph2PCl)] or from the diphosphoxane complexes [{(CO)5M(Ph2P)}2O] by base hydrolysis with triethylamine [84]. Hydrolysis of a coordinated halophosphane ligand followed by the addition of triethylamine gave an analogous O−anionic phosphite tungsten complex 28 (Scheme 14) [85]. Et 3N

Et 3N

H

H

O

(CO) 5 Mo

O

P

(CO) 5W

P

Ph

O O R

Ph

27

28

Scheme 14. O−anionic 1-P−phosphinite molybdenum 27 [84] and O−anionic 1-P−phosphite tungsten 28 [85] complexes in interaction with triethylammonium. When a solution of ruthenium complexes 29 are passed through a column charged with neutral Al2O3, the phosphinous acid Ph2POH ligand is deprotonated and the corresponding O−anionic 1-P−phosphinite complexes 30 are obtained (Scheme 15, [10]).

Ru

C

Ph2 P PhN

CH 2R NPh

Ph2 P H

-H + Ru +H+

H

Ph2 P PhN

OH

C

CH2 R NPh

Ph 2P H

H O

R= Ph, p-C6H4Me

29

30

9 Page 9 of 33

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Scheme 15. Interconversion of phosphinous acid ligand in 29 and O−anionic 1-P−phosphinito ligand in 30 over deprotonation/protonation chemical transformations [10].

ip t

On the basis of the 31P{1H} NMR data of complex 30, the phosphorus atom in the [Ph2P(O-)] fragment was considered as P(III)-organophosphorus derivative described as an O-anionic 1-P−phosphinito ligand. After addition of acids, formation of the phosphinite complexes is reversible. To unequivocally establish the ligand arrangement around the metal center, the structure of 30 was established by X-ray crystallography. The strong basicity of the anionic phosphinite oxygen atom are illustrated by the two outstandingly short intramolecular NH•••O hydrogen bonds which compares well with those between [HNEt3]+ cations and anionic phosphinite metal complexes [84,86].

R1 P

LnM

an

R2

us

cr

Among the coordinating modes of O−anionic 1-P−metalated phosph(in)ito, the self-assembled supramolecular phosphinous acid ligand and O-anionic 1-P−phosph(in)ito ligand held together by an intramolecular hydrogen bond have long been known in transition metal complexes B’ ([87], Fig. 2), and some of their corresponding complexes have been exploited in catalysis [35,88]. The synthesis of these bidentate O−anionic 1P−phosph(in)ito ligands can be accomplished by reaction of metal complexes with phosphane oxides [36,89-93] or mixed anhydrides of phosphinous and acrylic acids [94], by solvolysis of acetylenic phosphane [95], phosphazane [96], chlorophosphane [97] or phosphinite [98,99] complexes, or by treatment of suitable precursors with chlorophosphanes in protic solvents [100-103].

O

H

O

M

P

R2

R1

B'

Fig. 2. O−Anionic  -P−metalated bidentate phosphinous acid phosph(in)ite complexes B’.

d

1

Ac ce p

te

Deprotonation with an appropriate base of the cis-configured monoanion complex 32, featuring the quasichelating phosphinous acid O−anionic 1-P−phosphinito unit, R2P−O−H•••O−PR2, bridged by an hydrogen, is accompanied by a rearrangement to afford the trans-configured complex 33 with two O−negatively charged phosphinito units coordinated to one platinum center (Scheme 16). The NMR and the ESI mass data confirmed its formation. The crystal-structure analysis of 33 shows a square-planar platinum complex for this complex with a trans configuration. The removal of the proton of the cis-configured monoanion complex 32 leads to an additional shortening of the P−O distance of about 6 pm and an elongation of the Pt−P bond of about 3 pm. The increased Pt−P bond length can be attributed to the increased electron density at the phosphorus atom and therefore a reduced -backbonding contribution of the platinum. HO

P R2

Pt

R2 P

OH

31

Base/-HBase + HCl(g) /-Cl-

R2 P

Cl Pt Cl

Base/-HBase +

O H

P R2

O

O P R2

HCl(g) /-Cl-

F3C

32 R=

Pt

R2 P O

33 CF3

Scheme 16. Synthesis of bidentate 32 and monodentate 33 O−anionic 1-P−phosphinito platinum complexes by sequential deprotonation reactions [104]. Both deprotonation steps are reversible, as shown by the treatment of O−anionic 1-P−phosphinito complex 33 with one or two molar equivalents of gaseous hydrochloric acid to give cis-configured 32 or trans-configured 31 complexes respectively (Scheme 16, [104]).

2.4. Silver P-metalated phosphonate species as transfer reagents 10 Page 10 of 33

Edited July 2

t

Bu I

N

[Ag{P(O)(OR') 2}]

Bu

O

35

Pd - AgI

N t

N

R

Bu

P(OR')2

N

Pd

t

34

R

Bu

36

R'= alkyl, aryl

us

R= EDG, EWG

cr

t

ip t

Group 10 and 11 P-metalated phosphonate complexes, and more specifically palladium and gold phosphonate species, can be readily prepared from silver P-metalated phosphonate transfer reagents [Ag{P(O)R2}]. For example, treatment of precursors 34 with 1.0 equiv of [Ag{P(O)(OR’)2}] 35 generated the corresponding 1P−phosphonate palladium complexes 36 in high yields (Scheme 17) [105]. Simple filtration and removal of the volatiles typically afforded high yields of the desired complexes. Several phosphonate palladium complexes of the type [(NˆN)Pd(Ar){P(O)(OR’)2}] (NˆN= bipyridine-type ligands) and [(R2PˆPR2)Pd(Ar){P(O)(OR’)2}] (R2PˆPR2= chelating diphosphane ligands) [106] were characterized crystallographically. These complexes are intermediates in metal-catalyzed P-C bond forming reactions.

Scheme 17. Synthesis of 1-P−phosphonate palladium aryl complexes 36 from silver transfer reagents 35 [105].

Ac ce p

te

d

M

an

In the same way, 1-P−phosphonate complexes 38 were prepared by treatment of alkyl palladium precursors 37 with 1 equiv of [Ag{P(O)(OPh)2}]. Treatment of 37 with 2 equiv of a trialkylphosphane PR3, or with 1 equiv. of diphosphane R2PˆPR2 displaced the NˆN ligands and formed the corresponding complexes of the type [(PR3)2PdMe{P(O)(OPh)2}] (R= PMePh2, PMe2Ph, PEt3) and 1-P−phosphonate complexes 39 (R2PˆPR2 = dppe, dppp, dppb, dppf) respectively. Note that the trialkylphosphane complexes were also isolated by starting from [Pd(cod)MeCl]. These compounds are stable in solution or in the solid state for extended periods of time [107]. Treatment of 38 with HP(O)(OPh)2 afforded methane and a mixture of palladium-containing complexes. Addition of diethyl ether to this mixture precipitated the bis-phosphonate complexes 40 in good yields (Scheme 18) [108]. While complexes 38 are quite robust, the addition of weakly basic phosphane ligands promotes the formation of MeP(O)(OPh)2 due to reductive elimination [109].

Cl

N

[Ag{P(O)(OPh) 2}]

N

Me

37

- AgCl

R 2P O

-N

PR2 N

P R2

P(OPh) 2 Pd Me

39

P(OPh) 2

N

Pd

O R2 P

Pd N

Me

38

O

O H P(OPh) 2

P(OPh) 2

N Pd

- MeH

N N = bipy, tBu2 bipy

R2P PR2 = dppe, dppp, dppb, dppf

N

P(OPh) 2 O

40

Scheme 18. Synthesis of mono- 38, 39 and bis- -P−phosphonate 40 palladium complexes [107,108]. 1

Note that [Ag{P(O)(OPh)2}] undergoes significant decomposition within 48 hours at room temperature and partially dissolves in polar solvents [110-112]. In marked contrast, the synthesis of an hexane-soluble robust silver salt [Ag{P(O)(OC8H17)2}] was recently described and used as an effective transfer agent (Scheme 19, [113]). The unusually large silver−phosphorus coupling constants in NMR spectroscopy clearly established that the bonding mode of the phosphonate fragment is through phosphorus and not through oxygen. This silver salt can be stored at room temperature for several months with minimal decomposition and is soluble in most nonpolar solvents such as hexane, diethyl ether, toluene, and dichloromethane. As an example, a large number of organosoluble 1-P-phosphonate gold complexes [(Ar3P)Au{P(O)(OC8H17)2}] 42 can be prepared from gold precursors 41 using [Ag{P(O)(OC8H17)2}] as the transfer agent.

11 Page 11 of 33

Edited July 2

AgX [(Ar 3 P)Au{P(O)(OC 8 H 17)2 }]

(Ar3 P)AuX

41

42 [Ag{P(O)(OC 8H 17)2 }]

ip t

Scheme 19. Synthesis of hexane-soluble 1-P-phosphonate gold complexes 42 [113].

2.5. Oxidative addition of P(O)−R bonds to metal center

cr

Other salts than silver species are efficient transfer reagents. Lately, 1-P-phosphane oxide and 1P−phosphonate mercury complexes of general formula [Hg{R1R2P(O)}2] have been successfully synthesized after addition of the corresponding organophosphorus sodium salts {R1R2P(O)}Na to HgX2 (X=Cl, OAc) [114].

M

an

us

The addition of P(O)−H bonds to olefins is an alternative method for the preparation of organophosphorus compounds containing P(O)−C(sp3) bonds. The transition metal-catalyzed version of this reaction is attractive due to the ability of metal-containing catalysts to manipulate key reaction parameters such as regioselectivity and stereoselectivity by modification of ligand architecture and careful choice of metal center. For efficient atom economy, hydrogen phosphonates (RO)2P(O)H are attractive materials for this reaction ; however, few systems are known which successfully employ these substrates [115]. Tanaka reported the use of pinacol-derived hydrogen phosphonates in these reactions and in the hydrophosphorylation of alkynes, 1,3-dienes and allenes [116-118]. The hydrophosphorylation involves (i) oxidative addition of the P(O)−H bond, (ii) addition of the H−Pd bond to an alkene molecule, and (iii) reductive elimination to form the corresponding phosphonate. The oxidative addition of pinacol hydrogen phosphonate on the palladium precursor 43 readily proceeded at room temperature to generate the corresponding 1-P-phosphonate palladium complex 45 as the sole product of the reaction (Scheme 20). O

P(O)H

te

d

O

Cy3 P H

Pd

O O P

45

O

Cy3P

[(R 3P) nM]

M = Pd, R= Cy, n=2

Et 3 P

(EtO) 2 P(O)H

Ac ce p

43 44

M = Pt, R= Et, n=3

H

O

Pt P(OEt) 2

46

Et 3P

Scheme 20. Oxidative addition of P(O)−H phosphonates to palladium 43 [116] and platinum 44 [192] metal centers. Note that in the case of palladium starting compounds, the cyclic hydrogen phosphonate substrates have been successfully used, but simple reagents such as HP(O)(OPh)2 and HP(O)(OEt)2 are unreactive. This has been circumvented by the use of platinum precursor 44 in the preparation of the 1-P−phosphonate complex 46 (Scheme 20). Coordination to palladium(0) 50 of a diphosphane phosphane oxide ligand 47a was found to proceed with Ph– P(O) bond cleavage via an oxidative addition mechanism leading to an original 1-P−phosphane oxide PP(O)P– pincer complex 52a (Scheme 21, [119]). This reaction sequence was similarly observed for nickel reagents to give 53a. Activation of the P(O)−H bond, induced via the tautomerization of the tridentate secondary phosphane oxide (SPO) pre-ligand 47b upon coordination on iridium 48 and palladium 50 precursors, afforded the corresponding stable pincer hydride 1-P−phosphane oxide complexes, 49 and 52b, in good yields (Scheme 21) [120]. Note that 1-O−phosphane oxide complex 54 deprotonated by DBU undergo an oxidative addition of the P(O)−Ph bond to form the diphosphane 1-P−phosphane oxide pincer complex 52a which was also obtained via the deprotonation reaction of the corresponding phosphinous acid complex 55 (Scheme 21, [121]).

12 Page 12 of 33

Edited July 2

O [IrCl(COE)2] 2

48

P P

R'= H i

O

Cl

P i

Pr2

47

H

49 P

Ph

Pr 2

O

R'= Ph ( a) R'= H (b)

50 51

P

P

LnM P

LnM = Pd(PtBu3 )

i

M

i

Pr2

LnM = Ni(cod) 2

P

R' O P

= P

Pd

(M = Ni)

DBU

2

OH

P i

Pd

OTf

an

P

P

i

Pr2

Ph

Pr 2

M

55

P Pr 2

54

(M = Pd)

HOTf

P(O)R'

i

Pr2

H

P P

P i

Pr 2

R'

52a,b 53a

OTf

O

DBU

ip t

P

P Pr 2

cr

i

i

us

R'

Ir

Pr2

Scheme 21. Synthesis of 1-P-phosphane oxide iridium 49, palladium 52a,b and nickel 53a pincer complexes [119-121].

Ac ce p

te

d

Oxidative addition of a phosphorus-selenium bound to palladium(0) 56 and platinum(0) 57 precursors represents the first example of phosphorus-heteroatom bond additions to transition metal complexes [122]. Platinum(0) complex 57 was as reactive as its palladium(0) analogue 56 and reacted at room temperature, with (PhSe)P(O)(OR)2 for example, to form the corresponding seleno 1-P−phosphonate complexes 58 and 59 in excellent isolated yield (Scheme 22). On the basis of these studies, the catalytic addition of selenophosphates to alkynes was realized.

(Et 3P) 3M

56 , 57 ,

Et3P

O

+ PhSe P(OR) 2

PhSe

M

O P(OR) 2

Et3P

M= Pd M= Pt

58 , 59 ,

M= Pd, R= Ph, Et M= Pt, R= Ph

Scheme 22. Oxidative addition of the P(O)−Se bond of selenophosphates (RO)2P(O)SPh derivatives on palladium 56 and platinum 57 complexes [122].

The oxidative addition involving a P(O)−C bond has scarcely been observed. The ability of palladium complexes to activate the weak P(O)−C(O) bonds of -ketophosphonates was demonstrated early on by Nakazawa and Miyoshi [123,124]. The successful isolation of 1-P−phosphonate complexes 61 originates from the oxidative addition at the P−C bond of acyl phosphonate derivatives RC(O){P(O)(OR')2} to the formal "Pd(PMe3)2" intermediate obtained from the palladium precursor 60 (Scheme 23). O Me3 P

Et Pd

Et

PMe3

60

+

O

R

Me3 P

O

P(OR')2 Pd

P(OR')2

PMe3

R O

R= Ph, tol R'= Me, Et

61

Scheme 23. Oxidative addition involving a P(O)−C bond and palladium complex 60 [124].

13 Page 13 of 33

Edited July 2

2.6. P−C and P−X (X=O,N) bonds cleavage with basic treatment

Mn CO CO

PhNC

Me 2 P

PhNC

CO

OH

CH 2

PMe 2CH 2

CO

Mn

P Me2

CO

PMe2 OH

CO

CO

62

PMe 3

Mn

P O Me2

cr

PhNC CO

ip t

Reaction of chelate fac-diphosphane complex 62 with an excess of KOH produces the cleavage of a P–C bond of dmpm affording neutral 1-P−phosphane oxide complex 64. A mechanism of formation of this complex was proposed involving nucleophilic attack of OH- anion to a phosphorus atom forming a transient complex 63 containing phosphinous acid and dimethylphosphinomethanide (dmpm) ligands, followed by intramolecular proton transfer from oxygen to carbon (Scheme 24, [125]).

CO

63

64

us

Scheme 24. Cleavage of P−C bond in dmpm chelate ligand to form 1-P-phosphane oxide complex 64 [125].

d

M

an

Phosphane oxide or phosphonate derivatives containing P−N bond(s) undergo hydrolytic cleavage during the complexation reactions. This kind of P−N bond cleavage either can generate hydrogen P(O)−H species which can be excellent sources of catalyst precursors, or can covalently bind to the metal center via HCl elimination to produce neutral or anionic complexes which are very useful as potential catalysts. Treatment of nickel precursor 65 with 1 equiv. of the organophosphorus ligands 66 afforded the novel neutral pentacoordinate 1-P−phosphane oxide nickel complexes 67 (Scheme 25) with an isolated yields typically under 50%. The isolated yields could be only significantly improved up to 89% when 65 was treated with 1.5 equiv. of the diphosphane ligands 66. Over the course of this reaction, the P–N bonds of one diphosphane ligand were selectively cleaved to afford complexes 67 with one 1-P−phosphane oxide ligand and one intact 3(P,N,P)−coordinated diphosphane ligand [126,127].

N

HN

te

PR2

NH PR2

66

NiBr2 (DME)

N

65

Ac ce p

Br HN

PR2 Ni

PR2 O

HN PR 2

67

Scheme 25. P−N bond cleavage in the formation of phosphane oxide nickel complexes 67 [126].

Structurally related pincer-type platinum complexes 69 have been reported recently (Scheme 26, [128]). HN

N

HN

PR 2 Pt

HN

Cl

N

H

Cl Pt

DMF

PR2

HN PR 2

68

69

PR2 O

Scheme 26. P−N bond cleavage in the formation of neutral phosphane oxide platinum complexes 69 [128]. It was anticipated that the reactions of amidophosphite ligands 71 with palladium(II) precursor 70 in the presence of moisture would afford, after cleavage of the P-N bond followed by the oxidation of the P-center, the catalytically active P,S-chelated phosphonate complexes 72. The broken amine fragment gets protonated to form the countercation (Scheme 27, [129]). The structure of complexes 72 was definitively established by singlecrystal X-ray diffraction studies.

14 Page 14 of 33

Edited July 2

O P

S

N

X

X

O

O S O

71 X= O, NMe

P

O N H

H2 O

70

Cl

Cl

H

ip t

Pd

(PhCN) 2 PdCl2

72 Scheme 27. P−N bond cleavage in the formation of the P,S-chelated phosphonate palladium complexes72 [129].

P(OR)2

+

us

Cl (cod)Pd

cr

The chloro bridged dinuclear palladium(II) complex 76 is formed as a result of hydrolytic cleavage of the P–N bond of the chelating diphosphazane ligand of the corresponding polymeric metal complex 75 obtained from the reaction of palladium precursor 73 and the diphosphazane ligand 74 (Scheme 28, [130]). [PdCl2{ EtN(P(OR) 2) 2}] n

EtN

Cl

P(OR)2

73

75

74

an

R= 2,6-C6H3(i Pr)2

H 2O

M

(OR) 2 Cl O P Pd EtHN P 2 (OR) 2

+

O P(OR) 2

EtN P(OR) 2

76

te

d

Scheme 28. P–N bond cleavage of the diphosphazane ligand 74 in the formation of the dinuclear 1P−phosphonate palladium complex 76 [130].

2.7. Phosphonate Kläui type complexes

Ac ce p

The recent developments in the coordination and organometallic chemistry of the well-known phosphonate Kläui cobalt complexes was reviewed by Leung and co-workers [131]. These ligands represented below (Fig. 3) by [(5-C5R5)Co{P(O)X2}3]− 77 were first synthesized in 1977 by Wolfgang Kläui and co-workers [132]. R R

R R X 2P O

R

Co

X

X P

PX2 O

O

77

X = R, OR R = alkyl, aryl

Fig. 3. General structure of the phosphonate Kläui cobalt complexes 77. Here is a brief overview of the main synthetic pathways to prepare anionic phosphonate Kläui cobalt complexes (Scheme 29). Phosphonate Kläui cobalt complexes are commonly prepared by (i) reaction of the air sensitive cobaltocene [Cp2Co] 78 (method (a)), [Cp*Co(acac)] 79 (Cp* = 5-C5Me5) (method (b)), or [Cp2Co]+ 80/nBuLi (method (c)) with hydrogen phosphonates HP(O)(OR)2 followed by demetallation with NaCN in air, (ii) reaction of [CpCoI2(CO)2] 81 with P(OR)3 followed by Arbuzov dealkylation (see section 2.1.) with NaI (method (d)), or (iii) reaction of [CpCoI2(CO)2] 81 or [Cp*CoCl2]2 82 with NaP(O)(OR)2 salts (method e) [132-137]. The cobalt complexes 83 dissolve without decomposition in aqueous sulfuric acid, and are not oxidized by atmospheric oxygen or nitric acid [138]. Kläui cobalt phosphonate complexes bearing functional groups in pendant side

15 Page 15 of 33

Edited July 2

chains were also prepared [135,139]. Analogous 1-P−phosphonate Kläui iridium(III) [140] and ruthenium(II) [141,142] complexes have been prepared. (a)

R'

[Cp2 Co] R' R'

79 +

(ii) NaCN MeOH, air

(c)

n

(RO) 2 P

Co

P(OR)2

OR

RO P

O

[Cp2Co] + BuLi

R'

(i) Na[P(O)(OR) 2 ]

O

(ii) NaI Acetone

O

80

83

81

R= Me, Et, i Pr, Ph R'= H, Me

[CpCoI2 (CO)] 81 or [Cp*CoCl2] 2 82

cr

[Cp*Co(acac)]

[CpCoI2 (CO)] (ii) NaI Acetone

(i) HP(O)(OR) 2

(b)

ip t

78

(i) P(OR) 3 R'

Scheme 29. Synthetic routes to anionic phosphonate Kläui cobalt complexes 83.

us

All three of the R2P=O functions can be modified by changing the substituent R, therefore the preparation of chiral C3-symmetric Kläui cobalt phosphonate complexes were reported [143]. Note that sodium salts of phosphonate Kläui cobalt complexes tends to aggregate in both the solid state and solutions ; the structure of the corresponding aggregate is dependent upon the size of the R group [137,144,145].

an

2.8. Miscellaneous preparation 2.8.1. Hydrolysis of phosphite transition metal complexes

R

te

d

M

One of the main synthetic route to 1-P−phosphonate complexes starting from phosphite complexes results from nucleophilic displacement by a halide ion on a phosphite cation complex in an Arbuzov-like reaction [52]. However, the method is successful only for alkyl phosphite complexes ; it is not successful for their aryl phosphite analogues because of the reluctance of an unactivated aromatic nucleus to undergo nucleophilic addition or displacement. Gibson and co-workers have determined that the reactions of cationic iron complexes 84a,b and 85a, bearing aryl phosphite ligands, with the action of an aqueous base in acetone give the corresponding 1-P−phosphonate complexes 86a,b and 87a quickly and in good yields. A pathway involving intramolecular oxygen transfer to give 89 from intermediate metallocarboxylate anions 88 was suggested to account for the formation of aryl phosphonate iron complexes 86a,b and 87a (Scheme 30, [146]). R

R

R

R

Ac ce p

OH

R

Fe

R

R

P(OAr) 3

OC

R

Fe

R

Fe

OC

CO

84a,b (R= H) 85a (R= Me)

R

R

R P(OAr) 3 - ArO

OC

R

R

R

C

COO

O

88

R

R

R

P(OAr) 2

OC

Fe R CO

O

P(OAr) 2 O

86a,b (R= H) 87a (R= Me)

89

Ar= Ph (a), p-tolyl (b)

Scheme 30. Synthesis of 1-P−phosphonate iron complexes, 86a,b and 87a, via basic hydrolysis of their corresponding phosphite complexes 84a,b and 85a [146].

Reactions of aquacobalamine with phenylphosphonite PhP(OR)2 (R= Me, Ph) organophosphorus moieties lead after hydrolysis of the coordinating ligands to complexes 91 and 92 in which the O−anionic ligands [PhP(OR)(O)]− are P-bonded to the cobalt(III) ion of the cobalamine moiety (Scheme 31, [147]). An identical process was described with methyl diphenylphosphinite Ph2P−OMe. RO

RO

Ph

OR

O

P Co

O

Ph

Ph

P H 2O

Co

OR P

+

Co

- ROH - H+

90 R= Me, Ph

91

92

16 Page 16 of 33

Edited July 2

Scheme 31. Formation of diastereoisomers 91 and 92 of O−anionic 1-P−phosphinate cobalamine complexes (the cobalamine moiety is only diagrammatically represented) [147]. 2.8.2. P-C bond-breaking reaction via addition of MeOH/H2O

MeOH/H 2O

p-tolunitrile

OTf

P Ph 2

PPh2 OH

Ru

P Ru Ph2

solvent P(OMe) 2

93

94

O

us

P Ru Ph 2

cr

ip t

The mononuclear 1-P−phosphonate ruthenium complex 94 was prepared after P-C bond-breaking reaction via addition of MeOH/H2O on 93 and is most likely solvated in solution. Note that prolonged drying leads to removal of the solvate, the corresponding 16 electrons complex contains the phosphonato fragment {P(O)(OMe)2} as an anionic P-donor ligand. The presence of an open coordination position is demonstrated by the reaction with p-tolunitrile which affords the corresponding 18-electron 1-P−phosphonate complex 95 (Scheme 32, [148]).

95

NC p-tolyl P(OMe) 2 O

an

Scheme 32. Addition of MeOH/H2O to prepare 1-P−phosphonate ruthenium complexes 94 and 95 [148]. 2.8.3. Elimination reactions

te

d

M

Addition of gold precursors 96 on primary phosphinates (R2O)R1P(O)H gave after methane elimination the corresponding 1-P−phosphinate complexes 97 with P-coordination of O−anionic phosphinite [(R2O)R1PO] − ligands which undergo a ligand redistribution in solution, establishing equilibria that involve ionic isomers 98 (Scheme 33). Hydrogen phosphonates (RO)2P(O)H react with gold complex 99 in a molar ratio 2:1 to give after elimination of pentafluorobenzene and tetrahydrothiophene (tht) the neutral oligomeric 1-P−phosphonate species 100 which associate via cooperative action of hydrogen and aurophilic bonding (Scheme 33) as determined by singlecrystal X-ray diffraction. The degree of oligomerisation depends on the steric effect of the R groups [149]. O

P(R 1 )(OR 2)

H

Me

Ac ce p

(R 3 P)Au

96

(tht)Au

99

C 6F5

(R 3P)Au

- MeH

P(R 1 )(OR 2)

97

O

[(R3 P)2 Au]

[Au{ P(R 1 )(OR 2)} 2 ] O

98 H

P(OR) 2 O

1/n [{(RO) 2P(OH)}Au{ P(OR) 2}] n

- tht, - C 6HF5 R= Me, Ph, iPr

100

O

Scheme 33. 1-P−Phosphinate 97, 98 and 1-P−phosphonate 100 gold complexes via ligand elimination [149]. 2.8.4. Oxidation reaction with nitrile oxides Stable nitrile oxides ArCNO react with platinum precursors 101 (L = PPh3, C2H4) to give 1-P−phosphane oxide complex 102. X-ray studies show that the nitrile oxide is deoxygenated by triphenylphosphane and that a phenyl group migrates to the platinum metal center to give the corresponding complex 102 (Scheme 34, [150]).

17 Page 17 of 33

Edited July 2

Ph 3P [(Ph3 P)2 Pt(L)]

+ 2 ArCNO

Ph

O

Pt

PPh2

- ArCN

101

NCAr

102

L= PPh3, C2 H4

ip t

Scheme 34. 1-P−Phosphane oxide platinum complexes 102 from oxidation reaction with nitrile oxides [150]. 2.8.5. Diverse preparations

EtO EtO

O P

Fe OC

P

EtO O P

OEt OEt

OC



2

O P

EtO O P

OEt OEt

+

an

O C

us

cr

The thermal and photochemical reactions between [Fe2Cp2(CO)4] 103 and the diphosphite ligand (EtO)2POP(OEt)2 (tedip) proceed mainly through radical mechanism with C−O (ethoxy) or P−O (backbone) bond cleavages of the organophosphorus derivative. Note that no activation of the C-H bonds in the cyclopentadienyl ligand was observed. Under thermal activation, the known mononuclear compound 105 was formed and both the above cleavages occur to generate the 1-P−phosphonate complexes [{FeCp(CO)}2{(EtO)2POP(O)(OEt)}{-P(OEt)2}] as three isomers 104, 104’, and 104” (Scheme 35, [151]). In contrast, under photochemical conditions, none of the phosphonate complexes were formed.

Fe

Cp

103

Fe CO P (OEt) 2 Cp

OC

Fe

Cp

M

104

EtO

O P

O

OC Fe

OEt OEt

Fe Cp P (OEt) 2 CO

104'

OEt OEt O

Fe Cp

P (OEt) 2

P

+

Fe

CO

OC

104"

P(OEt)2 CO

105

te

d

Cp

P

O

Ac ce p

Scheme 35. Thermal activation of tepip ligand to prepare 1-P−phosphonate iron complexes 104, 104’, 104” and 105 [151]. The reaction between the bridge 2-P,O−phosphane oxide platinum(I) complex 106 bearing a Pt–Pt bond and an equimolar quantity of Brønsted acids HX led quantitatively to the synthesis of the corresponding P−phosphane oxide complex 107 (Scheme 36, [152]). PCy2

Cy2 HP Pt

Pt

O

HX

PCy2

Cy 2HP

PHCy2

Pt X

PCy2

106

H

107 X= Cl, Br, PhO, P(O)Cy2,

PHCy2 Pt PCy2 O

SiMe 3

Scheme 36. Reactivity of Brønsted acids on bridge 2-P,O−phosphane oxide platinum(I) complex 106 [152].

3. Insight in the electronic properties of O−anionic phosph(in)ito ligands Even though theoretical investigations are still scarce, experimental and DFT calculation data showed to be equally reliable in evaluating the electronic properties of mono-anionic monodentate and bidentate phosph(in)ito ligands . Although the theoretical values are evaluated in silico without taking account of the counter cation and the solvent, the trend observed with experimental data are in good correlation with theoretical data so far. Phosphinous acids R2P(OH) are less electron donating than their corresponding trisubstituted organophosphorus compounds PR3. In marked contrast, Buono, Martin and co-workers reported lately that O−anionic monodentate phosph(in)ito ligands of general formula {R1R2P(O)} are extremely electron-donating ligands [153]. For

18 Page 18 of 33

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2000

2030

2060

2090

CO(A1) in [LNi(CO)3 ]

cr

TEP (cm -1 ) NHCs PR2 OZ

PR3

PR2

us

PR2 O

ip t

instance, anionic P(III)−dialkylphosphinito {R2P(O−)} ligands outclass the recently described carbene ligands [2,154] in term of net electronic donation (Fig. 4). Theoretical investigations suggest that the destabilization of the phosphorus lone pair by an occupied poxygen orbital may be a key factor to explain the high electron donation of the O−anionic phosphinito ligand {R2P(O−)}. Mono-anionic bidentate phosphinous acid phosphinito ligands in B’ type complexes (Fig. 2), held together by an intramolecular hydrogen, are of intermediate donicity between phosphinous acids {R1R2POH} and anionic monodentate phosph(in)ito {R1R2P(O-)} ligands (Fig. 4). They exhibit very different electronic properties, depending on the organophosphorus substituents. The influence of counter cations on the electronic properties of ionic ligands is also dramatic and can be intuitively rationalized in terms of hard–soft interactions.

OH

Z= Na, K, Li

PR 2

an

R2 P

O

O

Z

Z= H, Na, K, Li

Fig. 4. “Tolman’s electronic parameter” (TEP) of  -P(III)−phosphinito O−anionic monodentate {R2P(O-)} and bidentate {R2P(O-)(R2POZ)} ligands [153].

M

1

+0.70

+1.00

+1.10

te

d

We lately reported the preparation of the O−anionic 1-P(III)−phosphinito complex [Ru(tpy)(bpy){(Ph2P(O-)}]2+ 26 (Scheme 12, [73]). The value of the oxidation potential of 26 is the lowest reported to date for a ruthenium complex with a P(III)−phosphano type ligand coordinated to the metal [Ru(tpy)(bpy)]2+ core (Fig. 5). Its value decreased drastically by 470 mV from that registered for the phosphane precursor [Ru(tpy)(bpy)(Ph2PH)] 2+ 25.

+1.20

Ph2PO PhP(OH)O

+1.30

Ac ce p N

V/ECS

+1.40

PCy3

" non-classical " P(III)-ligands

E0 (RuIII/RuII)

+1.50

PR 3

+1.6 0

+1.80

+2.00

P(OPh) 3

2+

L

" classical " P(III)-ligands

N N

Ru

N N

N

Ph-CN

N-ligands

[(tpy)(bpy)Ru] metal core

classical and " non-classical " P(III)-ligands

Ph2PO /Ph2PO

Ph2P(OH) /Ph2PO

n= 0

n+

L N

L

Ru

N N

N

n= 1

[(bpy) 2Ru] metal core

Fig. 5. Electrochemical properties of “classical” phosphano ligands {PR3} and “non-classical” O−anionic monoand bi-dentate 1-P(III)−phosph(in)ito ligands {R1R2P(O-)} on [(tpy)(bpy)Ru(II)] and [(bpy)2Ru(II)] metal cores. The nature of the phosphorus−oxygen and phosphorus−ruthenium bonds in the phosphinito ruthenium polypyridyl [Ru(tpy)(bpy){(Ph2P(O-)}]2+ 26 were investigated using electron localization function (ELF) and natural bond orbital (NBO) analysis. The population of the ELF basin V(Ru,P) lies in the range for dative metal−phosphane bonds. The oxygen atom of the phosphinito moiety exhibits a strong anionic character, as indicated by its negative charge from natural population analysis and its population of the ELF valence basin close to 6 electrons. As already proposed by Kirchner and co-workers [10], our theoretical study clearly suggests that the O−anionic 1-P(III)−phosphinito ligand {Ph2P(O-)} can be represented by the canonical structure corresponding to an L-type phosphane ligand with an anionic charge centered on the oxygen atom featuring a P−Ru dative bond with one lone pair of electrons at the phosphorus atom (Fig. 6).

19 Page 19 of 33

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2

O

Ph2 P N N

Ru

N N

ip t

N

26

cr

Fig. 6. Canonical structure and bonding description of the O−anionic 1-P(III)−metalated phosphinito ligand in [Ru(tpy)(bpy){(Ph2P(O−)}]2+ 26 complex [73].

4. Prevalent activities of anionic phosph(in)ito metal complexes

us

4.1. Phosphonate Kläui type complexes as mono-anionic six electron donors

Ac ce p

te

d

M

an

The extremely robust character of 1-P−phosphonate Kläui type complexes and their unique electronic properties allows them to coordinate to a variety of low and high oxidation state metals through the use of their three P−O oxygen atoms as donors. Phosphonate Kläui type complexes act as mono-anionic six-electron donors and their coordination chemistry resemble the unsubstituted tris(pyrazolyl)hydroborato six-electron ligand, (HB(pz)3)−. Phosphonate Kläui type stabilize a variety of organometallic fragments in high oxidation states that have not been previously stabilized by other oxygen donor ligands. In general, the Kläui ligand offers a wide range of possibilities as a versatile oxygen donor ligand. Here follow very few examples of some recent studies reported with transition metal complexes incorporating the Kläui ligand. Dinuclear phosphonate-bridged vanadium(IV) complexes 108 with the Kläui ligand have been prepared to model the catalytic activity of industrially used vanadium phosphate oxidation catalysts (Fig. 7). These complexes have been characterized via spectral and magnetic analyses and their structures determined by X-ray analyses [155]. Metal-mediated C−H amination coupled with cyclometalation of an alkylbenzene was first reported by ruthenium−imido catalysts 109 incorporating the 1-P−phosphonate Kläui tripodal ligand (Fig. 7, [156]). Diruthenium complexes 110 supported by the Kläui oxygen tripodal ligand and bridged by N2 were also synthesized [157]. Cerium complexes containing a tripodal 1-P−phosphonate ligand were efficient promoters of the aerobic oxidation of alkylbenzenes by a radical mechanism [158].

O

O

V

H2O

O

O

O

Ru

O

Cl

[BF4]2

O

O

O

N

O

Ad

N Ru

N

N

N

Ru

N

Cl

O N

108

O

O

110

109

O

O O

N

[(5-C 5R5)Co{P(O)X 2}3]

= bpy, phen

N

Kläui "ligands"

Fig. 7. Dinuclear P,O−phosphonate-bridged transition metal complexes 108-110 with Kläui “ligands”.

4.2. Ligands of general formula {P(O)R1R2} as hydrogen-bond acceptor in supramolecular chemistry Because of the presence of a strongly polarized hydrogen-bond acceptor P+−O- unit, phosphane oxides R3P(O) have a significant influence on the structural properties of the materials in which they are incorporated, both with regard to short-range interactions (such as hydrogen bonding) and long-range electrostatic interactions. Phosphane oxides have been investigated in strong intermolecular hydrogen bonding with proton H+ or Hbonded water molecule that link intermolecularly pairs of P+−O- entities [159-168]. Triphenylphosphane oxide

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ip t

(TPPO) has been widely exploited [169-171] in crystal engineering [172], particularly with regard to the design of hydrogen-bonded co-crystals. Trialkylphosphane oxides R3P(O) are one of the best hydrogen bond acceptors [173]. In coordination transition metal chemistry, O−anionic 1-P−phosph(in)ito ligands of general formula {P(O)R1R2} have similar properties. In recent work reported by Breit and co-workers, the concept of designing supramolecular bidentate ligands by utilizing hydrogen-bond interactions between substituents on two respective monodentate ligands has been realized [174,175]. We previously mentioned, in section 2.3. (see Fig. 2), the self-assembled supramolecular mono-anionic bidentate phosphinous acid and 1-P−phosph(in)ito ligands held together by an intramolecular hydrogen bond. These ligands act as a mono-anionic diphosphorus chelate for the metal center [80,82,176,177 and references cited in section 2.3]. The use of SPO preligands was recently recognized as the first use of a supramolecular bidentate ligand in catalysis [74].

3

O

Ph2 P

PPh2

111

[Ru]

O Ph 2P

Ph2 P

H

O

112

O

2

PPh 2 [Ru]

O

Ph2 P

H

base,

[Ru]

Ac ce p

O

[Ru]

O

[Ru]

te

[Ru]= (tpy)(bpy)Ru

H 2O

d

[Ru]

H

M

H O

an

us

cr

We lately reported an unprecedented intermolecular hydrogen-bonded dimer of O−anionic P(III)−metalated phosphinite complex [{(tpy)(bpy)Ru(Ph2PO-)}2H]3+ 111 [178]. Before our studies, this unusual coordination mode was not described for transition metal complexes incorporating O−anionic 1-P−phosphinito ligand {PR2(O-)}. After addition of water, formal substitution of the intermolecular hydrogen occurs to give an intermolecular H−bonded water molecule dimer complex [{(tpy)(bpy)Ru(Ph2PO-)}2H2O]2+ 112. It is noteworthy that the H−bonded water bridging intermolecularly two P−O- unit is a rare motif (Scheme 37, [179-182]). We also recently prepared the stable cis-configured O−mono-anionic 1-P−phosphinito chelate complex {[(bpy)2Ru(Ph2PO-)2}2H]+ 113. Deprotonation reaction with the addition of an appropriate base on the intramolecularly hydrogen bonded complex 113 led, after addition of water molecules, to the formation of an infinite chain of anionic phosphinito ruthenium polypyridyl metal fragment and H2O interconnected by strong P−O-...H hydrogen bonds 114 (Scheme 37). Note that the structure of this complex 114 has been established by X-ray studies [183].

PPh2

H2 O

113

[Ru]= (bpy) 2Ru

PPh 2

O O

H

H n

114 Scheme 37. Inter and intra hydrogen bonded supramolecular structures with mono- and bi-dentate O−anionic 1P(III)−phosphinite polypyridyles ruthenium complexes 111-114 [178,183].

4.3. Prevalent activities in catalysis The electronic tunability of “classical” P(III)-ligands has allowed for the design of a large variety of organometallic catalyzed reactions [184-186]. As mentioned in section 3., the value of the calculated TEPs of various O−anionic P(III)−phosphinito ligands corresponds to highly electron donating ligands, which compare with, and may outclass, the recently described carbene ligands [2,154,187]. It is therefore reasonable to anticipate that the use of strong donor O−anionic P(III)−phosphinito ligands may even expand the scope of catalytic processes which could be processed with those “non-classical” P(III)−phosphano type ligands. Phosphano-type P(III)−phosphinous acid and O−anionic P(III)−phosph(in)ito ligands, which may be simply inter-converted by protonation/deprotonation processes, are active catalysts for chemical transformations which usually requires electron acceptor ligands, such as phosphites [34,35,188], and extremely electron-donating ligands, such as carbenes [189].The ability of O−anionic P(III)−phosph(in)ito ligands to cleave and transfer heterolytically H2 in a metal complex has been also highlighted [38]. An outer-sphere mechanism, similar to the

21 Page 21 of 33

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an

us

cr

ip t

Shvo catalyst, has been proposed [39-43,190,191]. Interestingly, monodentate O−anionic 1-P(III)−phosphite palladium complexes have been successfully used by Tanaka and co-workers in the catalytic hydrophosphorylation of alkenes, alkynes and allenes [16,118,192,193]. The superiority of the self assembling mono-anionic chelate O−anionic 1-P(III)−phosph(in)ito ligands over non-assembled phosphane ligands in alkene hydroformylation [34,35,194,195] alkene, ketone and imine hydrogenation [196-198] and nitrile hydration [32,33,199] argues in favour of the bidentate coordination mode of the anionic phosph(in)ito/phosphinous acid chelate ligand being maintained during the catalytic process due to the strength of the intramolecular hydrogen bond. Lately, bidentate mono O−anionic 1-P(III)−phosph(in)ite complexes have been involved in a large number of catalytic transformations [176,177,200-206]. Note that recent studies have demonstrated the concept that secondary phosphane oxides preligands can be successfully used as strong ligands for the preparation of new air-stable ruthenium nanoparticles which are highly active for aromatic hydrogenation. The authors proposed that on a metal nanoparticle the oxygen atoms of the PO unit might mimic the role of an oxidic support and favour heterolytic cleavage of hydrogen as in molecular complexes of SPOs preligands [207]. Using a same approach, air-stable gold nanoparticles ligated by phosphinous acid were obtained and used for the chemoselective hydrogenation of aldehydes [208]. In view of the results obtained for molecular catalysts, it is reasonable to propose that the mechanism involved in these hydrogenation reactions may involve O−anionic 1-P(III)−phosphinito ligands grafted on the metallic surface of the nanoparticles.

4.4. Prevalent activities for electrochemical and photophysical properties

M

Because of their unique electrochemical and photophysical properties that can be fine-tuned by the adjacent ligands, ruthenium polypyridine complexes [209,210] have found notable applications in current organic electronics [211-215].

te

d

Incorporation of organophosphorus ligands in ruthenium polypyridine complexes is of particular interest because of the facile tuning of the phosphorus center; this ability has been widely demonstrated in catalysis [216]. Organophosphorus ligands, largely neglected in this domain, have the specific capacity in bringing up a large variety of electronic properties on the [Ru(tpy)(bpy)]2+ metal core never achieved so far by their corresponding nitrogen ligands [73,217]. We lately report experimental evidences of a long-lived room temperature luminescent complex [Ru(tpy)(bpy){Ph2P(O-)}]2+ 26 promoted by an O−anionic P-metalated phosphinito ligand (Fig. 8, [73]).

Ac ce p

Compared to “classical” P(III)-phosphane ligands [218], a significant increase of room temperature luminescence lifetime has been achieved with the O−anionic P−metalated phosphinite ruthenium polypyridyl complex 26. As suggested by ELF and NBO analysis, the organophosphorus fragment can be described as a strong -donor anionic P(III)-type ligand. This is the key point for the noteworthy electronic and photophysical properties of this complex. State-of-the-art free energy profile calculations on the excited states revealed that both favorable thermodynamic and kinetic factors are responsible for the remarkable luminescence properties of the anionic P−metalated phosphinite ruthenium polypyridine complex (Fig. 8). DFT calculations show that, in all cases, the HOMO is essentially a metallic orbital and the LUMO is a π* orbital localized on the tpy ligand, implying a Ru-based oxidation and a tpy-based reduction in the emitting excited state (MLCT). Destabilization of the HOMO in [Ru(tpy)(bpy){Ph2P(O-)}]2+ 26 was interpreted by the low π-acceptor ability of the O−anionic phosphinito ligand with respect to the primary phosphane Ph2PH ligand. The O−anionic P-metalated phosphinito ligand coordinated on the [Ru(bpy)(tpy)]2+ metal core has a major consequences on the electrochemical and optical properties of these species by destabilizing the non-emissive metal-centered triplet state (3MC) relative to the triplet metal-to-ligand charge-transfer excited state (3MLCT), responsible for luminescence.

22 Page 22 of 33

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cr

ip t

26

us

25

an

Fig. 8. Free energy profile on the excited states of O−anionic 1-P−phosphinite [Ru(tpy)(bpy){(Ph2P(O-)}]2+ 26 and [Ru(tpy)(bpy)(Ph2PH)] 2+ 25 complexes [73]. The ground state was omitted for clarity and the 3MLCT states were deliberately placed at the same energy origin for comparison between the 3MLCT and 3MC excited states.

4.5. Miscellaneous prevalent activities

M

Migration of the 1-P−(amido)phosphonate ligand in iron complex 115 to the cyclopentadienyl ring of the same metal fragment has been reported to induce the formation of 116 (Scheme 38, [219]).

O P

L

LDA, MeI

Me

L

Z

CO

116

115

Y

Fe

Y

te

CO

P

Z

d

Fe

O

L= CO, Y=Z= OEt Y= OMe, Z= NEt2 L= P(OMe)Ph2 , Y=Z= Ph

Ac ce p

Scheme 38. Migration of 1-P−(amido)phosphonato ligand in 115 on the cyclopentadienyl ring [219].

Reduction of CO ligand in the presence of boron reagents has been induced with 1-P−phosphonate iron complexes. Treatment of 1-P−phosphonate iron complex 117 with BF3•OEt2 and then PPh3 gave a sixmembered metalla-cyclic complex 119 through the formation of a phosphonate iron intermediate 118. The plausible reaction mechanism is illustrated in Scheme 39. BF3 induces migratory insertion of the CO ligand into the Fe-Me bond followed by an Arbuzov-like dealkylation with F- to give the corresponding 1-P−phosphonate complex 118 which is converted by PPh3 addition into 119 incorporating a bond between the phosphonate oxygen and the boron atoms in its structure [220]. The reaction of 1-P−phosphonate iron complex 120 with the hydroborane 9-BBN proceeds readily and quantitatively at room temperature resulting in the formation of the corresponding formyl complex 121. In this reaction, 9-BBN was proposed to attack first not the carbonyl oxygen but the PO oxygen atom because of the greater polarization of the phosphonate group. In this unusual reduction of terminal CO, the 1-P−phosphonato ligand play two important roles : (i) activation of the B-H bond in 9-BBN through the electron donation from the PO oxygen atom to the boron atom, (ii) anchoring the borane fragment to induce the strong coordination of the formyl oxygen (Scheme 39, [221]).

23 Page 23 of 33

Edited July 2

BF3 OEt2 P(OMe) 2

OC

Fe O P(OMe) 2 C O B F F

Ph3 P

Me - MeF

Me

117

Fe

Ph 3P Me

P(OMe) 2

C

O

O

118

B F

F

119 9-BBN

O

Fe

P(OMe) 2

OC

L

CO

H

120

P(OMe) 2

C

cr

Fe

O

O

ip t

Fe

O

us

B

an

121 Scheme 39. Reduction of CO ligand of 1-P−phosphonate iron complexes 117 [220] and 120 [221] with boron reagents.

P

OC CO

BCl3

2 BCl3

O NEt2 OMe

CH2Cl2

NEt2 Cl

THF,  or NEt3

123

Fe O P OC CO

NEt2 Cl

124

te

122

Fe O P OC CO

d

Fe

M

An halogenation reaction of an amidophosphonato ligand grafted on an iron metallic fragment was reported. Addition of boron trihalides BCl3 on P-metalated amidophosphonate complex 122 allowed the synthesis of the corresponding halogenated 1-P−amidophosphonate complexes 123 and 124 which are good precursors for future functionalization on the organophosphorus ligand (Scheme 40, [222]).

Ac ce p

Scheme 40. Halogenation reaction of the 1-P−amidophosphonato ligand in iron complex 122 [222].

Taking into account the unique properties of O−anionic monodentate and bidentate 1-P−phosph(in)ito ligands presented in this review, the results recently reported on the O,P-metalated phosphinite trinuclear complex 125 in which the six {Ph2P−O} arms bridge the Ti center with the two terminal Pd atoms [223]. Several tautomeric structures are conceivable for the trinuclear complex 125, but only tautomers having cationic 125’ or neutral five-coordinate Pd(II) 125” are thermodynamically stable (Fig. 9).

H

Pd

L

R2 R2 P O O P 2 R2 R2 P P Pd Ti O O P O O P R2 R2

L

H Pd

H

L

125'

R2 R2 P O O P R2 R2 P P Pd Ti O O O P P O R2 R2

L

125 H

(R= Ph)

125"

Fig. 9. Tautomeric zwitterionic 125’ and neutral 125” forms of the trinuclear complex 125 [223]. The structural data collected for the Pd-Ti-Pd trinuclear complex 125 indicated that both tautomers plays an important role in the electronic description of the six Ph2P−O bridging groups. In other words, some bridging Ph2P−O groups indicate appreciable contribution of the pentavalent form which coordinates to the Ti center as a neutral O−donor, but as an O−anionic P−donor to the Pd center and others adopt a trivalent form to which some Ph2P−O groups coordinate as an anionic O−donor and neutral P−donor.

24 Page 24 of 33

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5. Conclusions

Ac ce p

te

d

M

an

us

cr

ip t

In the midst of writing this review, it became clear that the “non-classical” phosphane-type ligands, namely the O−anionic 1-P−phosph(in)ito ligands, could easily fill much more pages that the originally contemplated. A number of examples of O−anionic 1-P−phosph(in)ito metal complexes have been left out and the prevalent activities of these entities were briefly discussed. The preparation of monodentate mono-anionic 1-P−phosph(in)ito ligands is easily achieved via a broad range of synthetic pathways. The synthesis of the bidentate mono-anionic phosphinous acid and 1-P−phosph(in)ito ligands held together by an intramolecular hydrogen bond can be also accomplished by reaction of metal complexes with various organophosphorus reagents. Recent studies, on the electronic properties of the O−anionic 1-P−phosph(in)ito ligands, report that these functionalized organophosphorus moieties are extremely electron-donating ligands which may outclass carbenes. O−Anionic 1-P−phosph(in)ito ligands may be considered as “non-classical actor” trivalent phosphanes which are both sterically and electronically tunable on a metal center. This review points out the ability of O−anionic P-metalated phosph(in)ito ligands to interconvert to the corresponding phosphinous acids upon protonation/deprotonation processes. This feature is quite unique and may explain the exceptional behavior of some phosphinous acid/phosph(in)ito catalysts in optimized pH conditions [224-229]. The application of phosph(in)ito transition metal complexes in catalysis is still underexplored and the promising results obtained so far pave the way for future investigations in challenging organic chemical transformations. Despite the growing interest in O−anionic 1-P−phosph(in)ito ligands, the development of these entities in coordination chemistry goes through a deeper understanding on the theoretical and spectroscopic features of their corresponding transition metal complexes. A large amount of fundamental data are still needed to be collected. In view of their electron donating properties, O−anionic 1-P−phosph(in)ito ligands have been largely neglected in many areas as in molecular electronics (sensors, field effect transistors, etc.). Incorporating anionic Pmetalated phosph(in)ito ligands, we may anticipate to induce a drastic change on the photophysical properties of their corresponding transition metal complexes. This is a promising basis in the future for the rational design of low cost sustainable phosph(in)ito-metal complexes with unprecedented properties for optoelectronic devices (dye sensitized solar cells, organic light emitting diodes, etc.). For the above-mentioned reasons, we can expect that O−anionic 1-P−phosph(in)ito ligands have still long way to go in transition metal chemistry. It is anticipated that another important feature which may be shown by these ligands is the possibility of combining physical properties, like magnetism and luminescence with properties easily found in the organic solid state, like semi-conducting properties, mesomorphism, nonlinear optics, polymerization, etc.

25 Page 25 of 33

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cr us an M

Ac ce p

te

d

Alk= alkyl Ar = aryl acac = acetylacetonate cod = 1,5-cyclooctadiene Cp = 5-C5H5 Cp* = 5-C5Me5 9-BBN = 9-borabicyclo[3.3.1]nonane LDA = lithium diisopropylamide, LiNiPr2 DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene DME = 1,2-dimethoxy-ethane bipy = 2,2’-bipyridine phen = 1,10-phenanthroline Nbipy = 4,4’-dinonyl-2,2’-bipyridine) dmpm = 1,2-bis(dimethylphosphino)methane dppm = 1,2-bis(diphenylphosphino)methane dppe = 1,2-bis(diphenylphosphino)ethane dmpe = 1,2-bis(dimethylphosphino)ethane depe = 1,2-bis(diethylphosphino)ethane dppp = 1,3-bis(diphenylphosphino)propane dppb = 1,3-bis(diphenylphosphino)butane dppf = 1,1’-bis(diphenylphosphino)ferrocene tol = toluene coe = cyclooctene tht = tetrahydrothiophene

ip t

Abbreviation

26 Page 26 of 33

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Acknowledgement We are grateful to the successive Directors of the Laboratoire de Chimie de Coordination. We warmly thank the technical and administrative staff of the laboratory for their support in our daily research activities. Our studies were supported by the CNRS, the Universite Paul Sabatier (Toulouse) and the French Ministry of Education and Research.

[15] [16] [17] [18] [19] [20] [21] [22] [23] [24]

[25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46]

cr

us

an

M

[7] [8] [9] [10] [11] [12] [13] [14]

d

[6]

te

[3] [4] [5]

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This contribution gives an overview of transition metal complexes with 1-P−metalated organophosphorus ligands of general formula { R1R2P(O)}. Their preparation is achieved via a wide range of synthetic pathways. Recent experimental and theoretical studies reported on O-anionic 1-P−phosph(in)ite complexes revealed that O-anionic 1-P−phosph(in)ito ligands {R1R2P(O-)} can be classified as electron donating P(III)−phosphane-type ligands which may outclass carbene ligands in term of net electronic donation. The promising results obtained in catalysis with these "non-classical" actor ligands pave the way for future investigations in challenging organic chemical transformations. In view of their electron donating properties and their ability to interact with donor hydrogen atom for supramolecular structure formations, O-anionic 1-P−phosph(in)ito ligands have still long way to go in transition metal chemistry.

Keywords

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Anionic ligand Posphinite ligand Posphite ligand Transition metal complex Catalysis Hydrogen bonding

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Table of Contents

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Mono- B and bi-dentate B' O-anionic -P(III) _phosph(in)ite complexes

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Graphical Abstract

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Mono- and bi-dentate O-anionic -P(III)-phosph(in)ite complexes

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