Organometallic complexes of Schiff bases: Recent progress in oxidation catalysis

Accepted Manuscript Organometallic complexes of Schiff bases: Recent progress in oxidation catalysis Wail Al Zoubi, Young Gun Ko PII:

S0022-328X(16)30357-6

DOI:

10.1016/j.jorganchem.2016.08.023

Reference:

JOM 19602

To appear in:

Journal of Organometallic Chemistry

Received Date: 21 May 2016 Revised Date:

30 July 2016

Accepted Date: 23 August 2016

Please cite this article as: W. Al Zoubi, Y.G. Ko, Organometallic complexes of Schiff bases: Recent progress in oxidation catalysis, Journal of Organometallic Chemistry (2016), doi: 10.1016/ j.jorganchem.2016.08.023. 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.

ACCEPTED MANUSCRIPT

Organometallic Complexes of Schiff Bases: Recent progress in oxidation catalysis Wail Al Zoubi, and Young Gun Ko

RI PT

School of Materials Science & Engineering, Yeungnam University, Gyeongsan 712-749, South Korea.

SC

O Mn(V) R

R'

N

N

Mn +

O

O-

Oxgen Donor

ZEMS

or

R-CH2-R'

O Mn(III)

EP

TE

D

R'

AC C

R

O

M AN U

O

1

or

CH3CN/H2O/NaIO4

O

OH R

R' H

+

R

C

R'

ACCEPTED MANUSCRIPT

Organometallic Complexes of Schiff Bases: Recent progress in

Wail Al Zoubi, and Young Gun Ko

RI PT

oxidation catalysis

School of Materials Science & Engineering, Yeungnam University, Gyeongsan 712-749,

SC

South Korea.

Abstract

M AN U

Schiff bases were versatile compounds synthesized from the condensation of a primary amino compound with aldehydes or ketones and widely used for industrial purposes and also exhibit catalytic oxidation in the oxidation of organic compounds and polymers. Oxidation reactions (oxidation of alkanes, alcohols, epoxidation of alkenes and sulfoxidation etc.) of organic

TE D

compounds were the most relevant ones and were reviewed considering the recent advances in the last years. Recent researches of Schiff bases and their complexes in oxidation catalysis had focused on employing metal catalyzed oxidation of organic compounds. This review

EP

summarizes the developments in the last decade for oxidation of organic substrates and polymers that proceed through Schiff base complexes.

AC C

Keywords: Epoxidation, Schiff base, Polystyrene, alkanes, Oxidation, Homogeneous.

1

ACCEPTED MANUSCRIPT

Introduction Imines(Schiff bases) were most widely used organic compounds that coordinate to metal ions

RI PT

via imine or azomethine nitrogen (C=N) and have a wide variety of applications in many fields including analytical, biological, medicinal, organic, inorganic chemistry and as catalyst in several reactions such as polymerization reaction, reduction of thionyl chloride of ketone, oxidation of organic compounds, reduction reaction of ketones, aldol reaction, Henry reaction,

SC

epoxidation of alkenes, hydrosilylation of ketones, synthesis of bis(indole) methanes and Diels-Alder reaction. It was usually prepared by condensation of an aldehyde or ketone with

O

R

+

NH2

R

C

M AN U

amine according to the following equation [1].

R

R

C

N

R

+

H 2O

R

Primary amine

Aldehyde or ketone

TE D

Schiff base

R in this equation may be an alkyl or an aryl group. However, aromatic Schiff bases were more stable, important class of compounds, and more readily synthesized, where, the

EP

aromatic aldehydes or primary amines having effective stereochemistry tutorials were more stable, while those, which contained alkyl substituents were relatively unstable and readily

AC C

polymerizable [2]. The synthesis of Schiff base was a reversible reaction and generally takes place under acid or base catalysis, or upon heating with suitable polar or non-polar solvents.

2

ACCEPTED MANUSCRIPT

O R

OH

C

R

R

Aldehyde or ketone

NH2

R

Primary amine

C

R

NHR

NR C

R

+

H2O

SC

R

RI PT

Carbinolamine

Water

M AN U

N-subtituted imine

Also, the mechanism of imine formation was another variation on the theme of neucleophilic addition (NH2) to the carbonyl group (CO), where, the amine reacted with aldehyde or ketone to give unstable carbinolamine (N+-CO-). After that the carbinolamine lost water by either acid or base catalyzed pathways, where, the reaction occurred faster and require less activation energy. Since the

OH2

OH R 2C

TE D

carbinolamine was an alcohol, it undergoes acid catalyzed dehydration [3].

N

H

AC C

EP

H

R'

R 2C

N

R'

H

(acid-catalyzed dehydration) R N R

R'

+ H 2O

H

R

R' C

R

3

N

+ H3O+

ACCEPTED MANUSCRIPT

Hence, the need for a review article highlighting the uses as homogenous or heterogeneous (supported) catalyst in oxidation processes of industrial interest in the presence of a suitable




RI PT

oxidant e.g., alkyl hydro peroxides, H2O2 or O2, and under mild conditions. Schiff base complexes as catalysts

Many Schiff base complexes of metal ions show high catalytic activity and played a

SC

significant role in various reactions to enhance their yield and product selectivity. The convenient route of synthesis and thermal stability of Schiff base ligands have contributed

1.

polymerization reaction

M AN U

significantly for their possible applications in catalysis as metal complexes [4].

The polymerization reactions were catalyzed with various catalysts and based on experimental observations: the following conditions apply to the efficient use of catalysts in

TE D

the polymerization of different compounds [4]

The typical Salen-type Schiff base ligand H2L(H2L=N.N’-bis(salicylidene)cyclohexane-1.2diamine) and an excess of Zn(OAc)2.2H2O in the presence of Et3N, a new tetranuclear

EP

complex [Zn4(L)2(OAc)3(OH)] with multiple active species and self-owned normal initiator was obtained and shown to efficiently catalyze the bulk solvent free melting ring opening

AC C

polymerization (ROP)(Fig. 1) of L-lactide giving the uniformly isotactic poly-l-lactides (PLLAs) [5].

Yan et al. [6] have reported the synthesis a series of mononuclear asymmetric Salen-type Schiff base complexes [Cu(Ln)] by the Cu(II)-templated approach in the presence of one of five salicylaldehyde derivatives, respectively. These complexes could effectively catalyze the

4

ACCEPTED MANUSCRIPT

metal-coordinative polymerization pf MA for the formation of syndio-enriched PMMAs (poly(methyl methacrylates)(Fig.2) in the presence of AIBN, where the Cu(II) to chelateplane distances were positively relative to the catalytic activity. Moreover, the introduction of

RI PT

the encumbering substituent ortho to the phenoxide ring of the ligands plays a much more important and influential role on the tacticity and chain-growth of the obtained PMMAs than the variation of reaction conditions under the controllable polymerization.

SC

Therefore, Coordination compounds derived from polymeric Schiff bases could be used as catalytic precursors for the polymerization of ethylene. After the activation with monomer,

M AN U

these systems were of heterogeneous nature and can prevent reactor fouling. The structure of the ligand backbone had strong influence on the polymerization activities and the properties of the resulting polyethyenes [7].

Lihui et al. [8] have reported the synthesis and characterization a zinc complex with the base

[(CH3)2NCH2CH2N=CHC6H3(OH)(OMe)],

TE D

Schiff

derived

from

2-

dimethylaminoethylamine and o-vanillin [Zn2L2(OB)2] by X-ray crystallography and NMR spectroscopy. Besides, this zinc complex initiated the ring opening polymerization (ROP)

EP

(Fig. 3) of L-lactide (L-LA), and the polymerization runs were well controlled, giving polylactide end-capped with benzyl ester and hydroxyl groups. The result indicated that the

AC C

structure of the ancillary ligands showed some influence on the catalytic activity, the introduction of electron-rich methoxy at ortho phenoxy substitute resulted in a decrease of the polymerization rate.

A monometallic (Ni(II),1) and a series of heterometallic (Ni(II)-Ln(II), Ln Ce(2); Ln=Nd (3); Ln=Sm (4); Ln=Eu(5); Ln =Tb (6) Ho(7); Ln=Tm(8)) complexes based on the acyclic Salen 5

ACCEPTED MANUSCRIPT

type Schiff base ligands H2L (H2L= N,N′-bis(3-methoxysalicylidene)propane-1,2-diamine) were synthesized and characterized by FT- IR, ESI-MS and X-ray crystallography. The catalysis results indicated that two kinds of complexes with different active species could

RI PT

efficiently catalyze the bulk solvent free melt ring opening polymerization (ROP) (Fig. 4) llactide with moderate molecular weights and narrow molecular weight distribution. Especially for the series of bimetallic complexes 2-8, the involvement of rare ions slightly

SC

decreased the catalytic activities on the ROP of l-lactide, while was in favor of the increase of polymeric molecular weights (Mw or Mn) and the polymerization controllability, and the

[9]. Lanthanide

Schiff

base

M AN U

type of rare ions was important and influential factor contributing to the catalytic behaviors

complexes

with

the

formula

[3.5-tBu2-2-(O)C6H2CH=N

C6H5]3Ln(THF) (Ln=Sc, Y, La, Na, and Gd) were synthesized by the metathesis reaction of

TE D

anhydrous LnCl3 with a Schiff base sodium salt good yield(˃80%). The ring opening polymerization (ROP) of ɛ-caprolactone (Cl) was successfully carried out using the lanthanide Schiff base complexes as catalysts and the neodymium complex leads to a

EP

controlled ROP of Cl [10].

Bob et al. [11] have reported the preparation a novel series of Schiff base ruthenium

AC C

complexes that were active catalysts in the field of atom transfer radical polymerization (ATRP). Moreover, when activated with trimethylsilyldiazomethane (TMSD), these species exhibit good catalytic activity in the ring opening metathesis polymerization (ROMP) of norbornene and cycloocten. The activity for both the ROMP and ATRP reaction is dependent on the steric bulk and electron donating ability of the Schiff base ligand. The control over polymerization in ATRP was verified for the two substrates that exhibit the highest activity, 6

ACCEPTED MANUSCRIPT

namely MMA and styrene. The results showed that the optimal ATRP equilibrium leading to a controlled polymerization could be established by adjusting the steric and electronic

RI PT

properties of the Schiff base ligand [11]. 2. Alkenes reaction

Alkenes (CH=CH) were a family of hydrocarbons (compounds containing carbon and

SC

hydrogen only) containing a carbon-carbon double bond, highly abundant, cheap, and thus very attractive potential substrates for the direct synthesis of added value functionalized

M AN U

products. Mover, imines and their complexes were useful and efficient catalysts or catalyst precursors for the functionalization for the selective oxidation of alkanes under mild conditions and using environmentally benign oxidants remains a serious challenge. Hence, epoxides, and cyclic ether with a three-membered ring, particularly ethylene and propene oxides, were key raw materials for the synthesis of a variety of chemicals such as, glycols,

TE D

glycol ethers, complex glycols, polyglycol ethers, alkylene glycol and alkanolamines and also act as building blocks in different polymers, such as, polyesters, polylactic acid and polyurethanes [2,3].

EP

The simplest epoxide, ethylene oxide, properly called oxirane by IUPAC, was the organic

AC C

compound with the formula C2H2O, was produced commercially by Union Carbide (1937), and Shell (1958) by vapor-phase oxidation of ethylene with air or oxygen using an alkali metal promoted supported silver catalyst. However, this silver catalyzed process was applicable to olefins lacking allylic and other reactive C-H bonds, such as ethylene (CH=CH), 1.3-butadiene (CH2=CH-CH=CH2) and styrene but other olefins, such as propene, have displayed low yields due to competitive oxidation of allylic C–H bonds. The 7

ACCEPTED MANUSCRIPT

hydrochlorination route was traditionally used in the production of propene oxide (Scheme 1). But due to the application of expensive, toxic and emitting corrosive hydrogen chloride, the process was being criticized by environmentalists. Currently, polymer-supported Schiff base

RI PT

complexes were promising catalysts in the oxidation of alkenes [12].

In the past two decades, the field of catalysts has seen a boom with numerous groups successfully developing newer and better complexes, therefore, transition metal complexes

SC

based on Schiff base ligands have received a bigger proportion of attention due to their diverse structural features. Currently, many transition metal ions complexes with Schiff base

M AN U

ligands have been identified as very efficient catalysts in both heterogeneous and homogeneous reactions, which showed high homogeneity, reproducibility, selectivity, and high activity to catalyze reactions under mild conditions [13-18].

Bahram et al. [19,20] have reported the evaluation of mg (III)-salophen complex (scheme 2)

TE D

as oxidation catalyst [19, 20]. The results have showed that these composite exhibit significant catalytic activities for epoxidation of linear alkenes, and alkane hydroxylation using sodium periodate as oxidant. Therefore, the results of oxidation were showed in Fig. 5.

EP

This catalyst efficiently converted both cyclic and linear alkenes to their corresponding epoxides with NaIO4. Therefore, alkyl aromatic and cycloalkanes were oxidized efficiently to

AC C

their corresponding alcohols and ketones in the presence of this catalyst (Scheme 3). In the present work, it was shown that the Schiff base Mg(III) complex was able to transfer an oxygen to an alkene

organic substrate, using mainly NaIO4 as source of oxygen,

exhibiting significant catalytic activity with higher yields [8]. In addition, the catalytic results shown that the activity of the catalyst was dependent on reaction parameters such as solvent 8

ACCEPTED MANUSCRIPT

in which the complexes was dissolved, the composition of Schiff bases, oxidant and axial donor ligand in the epoxidation of cis-cyclooctene [20].

RI PT

Valiollah at al. [21] have reported the bonding an account of biomimetic oxidation (Scheme 4), magnesium (III) salophen to imidazole modified polystyrene. Mn(salophen)Cl-PSI catalyze alkene epoxidation with sodium periodate under agitation with magnetic stirring. Alkyl aromatic and cycloalkanes were oxidized efficiently to their corresponding alcohols

SC

and ketones in the presence of this catalyst (Scheme 4). This new heterogenized catalyst was of high stability and reusability in the oxidation reactions. This heterogenized system showed

M AN U

the higher selectivity and stability in comparison with the homogeneous system. Therefore, the effect of reaction parameters such as terminal oxidants, solvent, and oxidant in the epoxidation of cis-cyclooctene were also investigated. In this work, the authors investigated the ability of different oxidants such as, NaOCl, NaIO4, Bu4NIO4, H2O2, KHSO5, tert-

TE D

butylhydroperoxide, urea–H2O2 (UHP) in the epoxidation of cyclooctene, catalyzed by the heterogeneous Mn(III) salophen. Where, sodium periodate (NaIO4) was used as the oxygen source. In addition, the epoxidation of cyclooctene was studied in various solvents. The

EP

results indicated that the best solvent was acetonitrile, this was attributed to polarity of solvent which tend to have large dipole moments, better swelling of the polymer and

AC C

solubility of NaIO4 in the solvent.

All complexes [MoO2L]2 (scheme 5) were tested as oxidation catalyst for the epoxidation of the made substrate cyclooctene and cyclohexene under organic solvent-free conditions using aqueous TBHP as oxidant at 80°C. Three main products detected for the oxidation of cyclohexene are cyclohexene oxide (CHO) from epoxidation, trans-1.2-cyclohexanediol (CHD) (due to CHO hydrolysis) and small traces of 2-cyclohexen-1-ol (CHol) from allylic 9

ACCEPTED MANUSCRIPT

oxidation (Scheme 6). Further in the catalyst, the OH addition at the ortho (L1) and para (L3) positions of the salicylic ring increased the catalytic activity relative to the reference SAP

RI PT

catalyst, while the substitution at the meta (L2) position had essentially no effect [22]. Valiollah et al. have reported (Scheme 7) the efficient biomimetic epoxidation of alkenes and hydroxylation of alkanes with sodium periodate catalyzed by zeolite-encapsulated Mn

SC

(III)-salophen, ZEMS. This catalytic system showed a good activity in the epoxidation of linear alkenes. Alkyl aromatic and cycloalkanes were oxidized efficiently to their

M AN U

corresponding alcohols and ketones in the presence of this catalyst [23].

In this study, the authors chose different oxidants such as, NaOCl, NaIO4, Bu4NIO4, H2O2, KHSO5, tert-BuOOH, urea–H2O2 (UHP) in the oxidation reactions. The results in the epoxidation of cyclooctene were summarized in Fig. 6, when NaOCl, H2O2, tertbutylhydroperoxide and urea–H2O2 (UHP) were used as the oxygen source, either in CH3CN

TE D

or CH2Cl2, the catalyst produces low cyclooctene epoxide [23]. Bahram et al. [24] have reported the suppurating dicationic Mn(III)-salen, containing

EP

phosphonium groups at 5.5’-positions of salen ligand (Fig. (a)7), on an ion-exchange resin, Dowex MSC1, via electrostatic interaction. This heterogenized homogeneous manganese

AC C

(III)-salen complex could be used as catalyst in the alkene epoxidation with sodium periodate. This catalytic system shown a good activity in the epoxidation of cyclic, aromatic and especially linear alkenes and exhibits a high selectivity in epoxidation of a-pinene and R-(+)-limonene. Alkyl aromatic and cycloalkanes were oxidized efficiently to their corresponding alcohols and ketones in the presence of this catalyst. In the another work was similar to above, Mn(III) salophen has been successfully bonded to 10

ACCEPTED MANUSCRIPT

1.4-phenylenediamine modified polystyrene, PSP. Mn(salophen)ClPSP catalyzes alkene epoxidation with sodium periodate under agitation with magnetic stirring. This catalytic system showed a good activity in the epoxidation of alkenes. Alkyl aromatic and

RI PT

cycloalkanes were oxidized efficiently to their corresponding alcohols and ketones in the presence of this catalyst (Fig. (b)7). The effect of reaction parameters such as terminal oxidants, solvent and oxidant in the epoxidation of cis-cyclooctene were investigated. The

SC

results showed that NaIO4 was the best oxygen source, because of good oxidation conversions, inertness in the absence of catalyst and high solubility in the CH3CN/H2O

M AN U

mixture. Also, the best solvent was an aqueous acetonitrile, because of the polarity of the solvent, better swelling of the polymer and solubility of NaIO4 in the CH3CN. Further, this catalytic system showed a good activity in the epoxidation of linear alkenes [25]. The work of Jacobson and coworkers expanded the scope of alkene epoxidation by using

TE D

chiral manganese Schiff’s base complexes [26]. These enabled asymmetric epoxidation with high stereochemical control. Synthesis of a chiral (salen) Mn(III) which was analogous to that developed by Jacobsen (Fig 8), has been tested within the supercages of zeolite Y [27].

EP

Using NaOCl as the oxidant, alkene epoxidations were tested in the present of dichloromethane. By having the active catalyst in a confined environment good

AC C

enantioselectivity could be achieved. The complexes have also been carried out on clays [28] and used for olefin epoxidation with PhIO as the oxidant. Mg (II) bipyridine complexes immobilized in mesoporous Al–MCM-41 have also shown activity for the oxidation of styrene using iodosylbenzene, hydrogen peroxide and tert-butyl hydroperoxide as the oxidants [29].

11

ACCEPTED MANUSCRIPT

Kureshy et al. [30]

have reported the preparation Co(II) chiral salen complexes (Fig. 9) 1-4

derived from α-naphthyl salicylaldehyde with 1S, 2S(+) diaminocyclohexane, 1R, 2R(-) diaminodiphenylethane and S(+)1.2-diaminopropane. Epoxidation of non-functionalized

RI PT

prochiral olefins viz. styrene, trans 3-nonene and trans 4-octene was screened by the combined use of an atmospheric pressure of molecular oxygen and sacrificial reductant isobutyraldehyde catalyzed by the above synthesized Co(II) chiral salen complexes with and

SC

without pyridine N-oxide as cooxidant by GLC to give corresponding epoxide and carboxylic acid as coproduct. However, in the presence of pyridine N-oxide was improved

M AN U

by maintaining the absolute configuration [30].

An eco-friendly and cheap Fe(III)-ferrocene Schiff base catalyst(Fig 10) has been designed for the efficient oxidation of alkanes and alcohols. Hence, oxidation reactions of previous compounds were done by using greener oxidant hydroxide peroxide in acetonitrile medium.

TE D

The alkanes and alcohols have been selectively oxidized to their corresponding aldehydes and ketones. In addition, this complex has shown excellent catalytic activity with high selectivity and recyclability [31].

EP

Norma at al. [32] have reported chiral the synthesis Schiff base ligands from aromatic aldehydes and chiral and chiral amino alcohols. Complexes of Schiff bases were then

AC C

screened as catalyst in the asymmetric ring opening of meso-cyclohexene epoxide with phenyllithium to give (1S, 2R)-phenylcyclohexanol in 9-67 % (Fig. 11).Therefore, a new microporous metal–organic framework compound featuring chiral (salen)Mn struts is highly effective as an asymmetric catalyst for olefin epoxidation(Scheme 8)[ 33]. Reza et al.[34] have reported the synthesis and transformed a new chiral linear tetramine 12

ACCEPTED MANUSCRIPT

(N1-(1-(2-aminophenylamino) propan-2-yl) benzene-1,2-diamine) (scheme 9), CLT, and its Schiff base ligand, which was derived from CLT with 2-hydroxybenzaldehyde into the corresponding manganese (III) complex. In this study, manganese complex catalyzes the

RI PT

oxidation of alcohols using 30% H2O2 as an oxide. Over-oxidation of aldehydes to carboxylic acid and the formation of by-products were not observed. Study indicated that the effect of different amounts of the catalyst, various amounts of the catalyst were used and

SC

detected (Fig. 12) [34].

Many works have proved that oxidation of cyclohexane catalyzed by Schiff base complexes

M AN U

using H2O2 as the oxidant was studied [34]. However, to choose the best solvent, the oxidation reactions were carried out in common solvents under the same conditions. The results indicate that acetonitrile provided the best oxidation medium for higher substrate conversion and selectivity of cyclohexanol. It was interesting to note that acetonitrile was

TE D

successfully used for many oxidation reactions [35-38]. Furthermore, the volatility of acetonitrile was lower than that of other solvents under open-wide system, so the utilization factor of acetonitrile was more here than that of other solvents. Therefore a lower

EP

environmental contamination was expected in such cases and acetonitrile was a suitable solvent for the oxidation of cyclohexane. The products obtained for the oxidation reaction

AC C

were cyclohexanol, cyclohexanone and adipic acid as shown by scheme 10. Jin et al. [39] have reported the synthesis and characterization two new ligands, 1-hydroxy5-[4-(2-hydroxybenzylideneamino)phenoxy]-3-oxapentane(HL1) and 1-methoxy-5-[4-(2hydroxybenzylideneamino)phenoxy]-3-oxapentane(HL2), and their Mn(III) complexes (Scheme 11). New Schiff base Mn (III) complexes were used to mimic peroxidase in the

13

ACCEPTED MANUSCRIPT

oxidation of phenol by hydrogen peroxide. Therefore, the effect of the mole ratio of H2O2/catalyst, pH and temperature on the reaction rate was investigated.

RI PT

A series of nickel (II) complexes containing N, O donor Schiff base ligand have been synthesized and characterized by analytical and spectral methods. In this investigation, catalytic system offered an efficient oxidation of primary and secondary alcohols to corresponding carbonyl compounds. From this study, it was shown that the activity

SC

decreases with increasing of bulkiness of the substituents (Fig. 13). This may be attributed to steric hindrance caused by the substituent, which could affect the planarity of the ligand in

M AN U

the complexes. Therefore, in order to work the effect of time of reaction on the activity, the product analysis was done at regular intervals of time under similar reaction conditions. The result in the present study indicates that the optimization of the reaction conditions was studied by taking benzyl alcohol as substrate with NiL1 in EMIM-NaOCl system (Fig. 14).

TE D

The benzaldehyde formed was quantified by GC [40].

Partha et al.[41] have reported the synthetization and characterization of new Cu (II) complexes,

[Cu4(O)(Ln

)2(CH3COO)4]

where

HL1=4-methyl-2,6-bis(2-

EP

fluoroethyliminomethyl) phenol, HL2=4-methyl-2.6-bis(2-chloroethyliminomethyl)phenol and HL3=4-methyl-2,6-bis(2-bromoethyliminomethyl) phenol(Scheme 12) by element

AC C

analysis, FT-IR, UV-vis spectroscopy, and electrospray ionization mass spectroscopy. This work indicates that complexes have been found to be active catalysts (Scheme 13) for the oxidation of cyclohexane and toluene in the presence of hydrogen peroxide as the oxidant under mild conditions. Where, cyclohexane is oxidized to yield cyclohexanol and cyclohexanone, whereas toluene is oxidized to benzyl alcohol and benzaldehyde. In this

14

ACCEPTED MANUSCRIPT

work, the authors have verified that presence of nitric acid is important in such oxidation reactions. The amount of oxidized products almost does not alter in the 5-15 range of

RI PT

n(HNO3)/n(catalyst) ratio, whereas if the ratio is further increased, the yield decreases[41]. A hydrazone Schiff base ligand derived from salicylaldehyde and benzhydrazide has been synthesized and reacted with vanadium (IV) leading to the corresponding vanadium (V) complex. The complex has been anchored on the surface of functionalized silica gel by N.O-

SC

coordination to the covalently Si–O bound modified salicylaldiminato ligand. The supported complex has been evaluated as a catalyst for hydrocarbon oxidation with hydrogen peroxide

M AN U

in acetonitrile. The heterogeneous system proved to be an efficient catalyst and was able to activate hydrogen peroxide toward the oxidation of alkenes, alkanes, benzene, and

TE D

alkylaromatic compounds with more than 2,500 h-1 activity [42].

The classical Fenton system, a stoichiometric mixture of Fe (II) with H2O2, was transformed gradually into the catalytic Fe(III)-Fe(II)-H2O2 system in the course of the hydrogen peroxide decomposition, generating hydroxyl radicals. D. H. R. Barton have described other

EP

catalytic systems for the selective oxyfunctionalization of hydrocarbons with oxygen atom

AC C

donors (Gif systems, i.e. iron complexes in pyridine/acetic acid) [40], L Que Jr et al. have studied dioxygen Activation at Mononuclear Nonheme iron active sites [41], G. J. P. Britovsek have reported the preparation a series of Fe(II), Mn(II), Co(II) and Ru(II) complexes containing bis(imino)pyridine or bis(amino)pyridine ligands and weakly coordinating triflate (OTf−) or non-coordinating SbF6- anions, and the results indicate that the

Fe (II) complexes have shown catalytic activity for the oxidation of cyclohexane with 15

ACCEPTED MANUSCRIPT

H2O2. [45] (nonheme transition metal catalysts containing polydentate nitrogen ligands), D. Mansuy [46] (Mg and Fe porphyrins with imidazole are much better catalysts than Fe

RI PT

porphyrins for oxygen-atom transfer from H202 to hydrocarbons), E. N. Jacobsen [44, 45] A (salen) manganese (III) complex bearing a chiral binaphthyl strapping unit catalyzes the enantioselective hydroxylation of indane and the epoxidation of alkenes (Scheme 4) and W.

SC

Herrmann [49] (methyltrioxorhenium/H2O2, Scheme 14).

Gholamhossein was synthesized an asymmetric tetradentate ONN’O’ Schiff base ligand

M AN U

(H2L)(scheme 15) followed by reaction of the synthesized H2L with an equimolar mixture of methanolic solutions of the VO(acac)2, a new oxidovanadium(IV) Schiff base complex (VOL). The catalytic activity of the Schiff base complex was investigated in the epoxidation reaction of cyclooctene and different reaction parameters such as solvent, oxidant, and the amount of oxidant and catalyst were optimized, showing that it can be active and selective

TE D

under the optimized conditions. The results showed that the cyclic alkenes were efficiently converted to the corresponding epoxides, whereas the VOL did not appreciably convert the linear alkenes. The epoxidation of cyclooctene was studied in se solvents CH3Cl, CH2Cl2,

EP

CCl4, CH3CN, THF, and MeOH in the presence of tert-butylhydroperoxide (TBHP) as an oxidant and VOL as a catalyst (Fig 15) [50].

AC C

A new magnetically separable catalyst consisting of binuclear Mn (II) complex [Mn2(HL)2 (H2O)4],

HL=2-[(2-hydroxy-benzylidene)-amino]-3-(4-hydroxyphenyl)-propionic

acid,

supported on (3-chloropropyl)-trimethoxysilane (CPTMS) functionalized silica-coated magnetic nanoparticles (MNPs) was prepared. This immobilized complex was found to be an efficient heterogeneous catalyst for the oxidation of different sulfides and hydrocarbons using

16

ACCEPTED MANUSCRIPT

hydrogen peroxide (H2O2) as an oxidant and should be used carefully, due to the possibility of overoxidation. Where, table show the sulfoxidation, the conversion and selectivity drastically increased with the molecular ratio of H2O2 to methyl phenyl sulfide, the catalytic

RI PT

oxidation gave 75% sulfoxide (Table 1), but the excess H2O2 required in this catalytic system can be attributed to its decomposition in the presence of the catalyst [51].

In the present studies, a hydrazone Schiff base ligand was prepared by the condensation of

SC

benzhydrazide and salicylaldehyde and reacted with vanadium (IV) leading to the corresponding vanadium(V) complex(Scheme 16). Therefore, the previous complex has been

M AN U

evaluated as a catalyst for cis-cyclooctene oxidation with H2O2 and the researchers were very interested to combine the advantages of hydrogen peroxide as a terminal oxidant with the possibility to recover and recycle the vanadium oxo catalyst. The catalyzed oxidation of ciscyclooctene was carried out with hydrogen peroxide to give cis-cyclooctene oxide. In this

TE D

present study, excellent conversions with good selectivities were achieved for both alkenes and alkanes. This solid catalys was easily separated from reaction mixture via filtration, which made the work-up procedure simple [52].

EP

Nasim et al hve reported the synthesization characterization a cis-dioxomolybdenum(VI) Schiff base complex [MoO2L]. Also, homogeneous oxidation of olefins using the complex as

AC C

a catalyst with hydrogen peroxide as oxidant in ethanol solution showed high catalytic activity. Under reflux conditions, the oxidation of cyclooctene, styrene, α-methyl styrene, 4-methyl styrene and 1-methyl cyclohexene with hydrogen peroxide gave the corresponding epoxides as the sole products [53]. Conclusion 17

ACCEPTED MANUSCRIPT

Schiff bases were considered as a very important class of organic compounds because of their capacity to bind metal ions from environmental media and as an efficient catalyst for the oxidation of alkanes and alcohols, epoxidation of alkenes, sulfoxidation of organic

RI PT

compounds in the presence of a suitable oxidant e.g., alkyl hydroperoxides, H2O2 or O2, under mild conditions.

The results shown that the Schiff bases and their complexes exhibited an efficient catalytic

SC

activity toward the selective epoxidation of simple alkenes, as well as of primary and

the separation and catalyst recycle.

M AN U

secondary alcohols. Their immobilization on solid supports was a good strategy to facilitate

The reviewed topics were rather promising in the field of catalysis with multi and interdisciplinary approaches and had industrial significance. Interesting developments have already been achieved in oxidation catalysis with Schiff base complexes, as discussed herein,

TE D

but there were still challenges that need to be further addressed, namely toward the development of “greener” processes.

In conclusion, using H2O2 as mild oxidant in the presence of the synthesized catalysts

EP

provides an efficient, easy and safe approach the oxidation of alcohols to corresponding

AC C

compounds. It seemed these heterogeneous catalysts could run other organic reactions which need Lewis acid.

Finally, we recommend this green (H2O2), simple, clean, and economical procedure for the oxidation of different organic compounds.

18

ACCEPTED MANUSCRIPT

References W. Al Zoubi, J.Coord.Chem 66(13) (2013) 2264-2289. W. Al Zoubi, Spectrochim. Acta 132 (2014) 854–870. W. Al Zoubi, Inter. J. Org Chem 3(2013)73-95. K.C. Gupta, AK. Sutar, Coord Chem Rev 252(2008)1420-1450. Q. Shi, J. Yang, X. Lu, Inorg. Chem. Commun 59(2015) 61-62. Y. Chen, Y. Liu, X. Zhang, Z. Zhang, L. Liu, D. Fan, L. Ding, X. Lu, Inorg. Chem. Commun 53(2015) 1-3. 7. M. Seitz, H.G. Alt, J. Mol. Catal. A: Chem 257 (2006)73-77. 8. L. Yao. L. Wang, J. Zhang, N. Tang, J. Wu., J. Mol. Catal. A: Chem 352 (2012)57-62. 9. L. Ding, W. Jin, Z. Chu, L. Chen, X. Lu, G. Yuan, J. Song, D. Fan, F. Bao., Inorg. Chem. Commun 14(8)(2011)1274-1278. 10. X. Ni, W. ZHU, Z. Shen, Chin. J. Chem Catal 31(8)(2010) 965-971. 11. B D. Clercq, F. Verpoort, J. Mol. Catal. A: Chem. 180 (2002)67-76.

SC

RI PT

1. 2. 3. 4. 5. 6.

M AN U

12. R.A. Sheldon, in: B. Cornils, W.A. Herrrmann (Eds.), Applied Homogeneous Catalysis with Organometallic Compounds A comprehensive Handbook, vol. 1, Wiley-VCH, Weinheim, 1996, p. 411. 13. D.C. Sherrington, Catal. Today 57 (2000) 87.

14. S. Kulkarni, M. Alurkar, A. Kumar, Appl. Catal. A: Gen. 142 (1996) 243. 15. L.K. Doraiswamy, M.M. Sharma, Heterogeneous Reactions, Analysis and Reactor Design, Wiley, New York, 1984.

17.

TE D

16. Y. Goldberg, Phase Transfer Catalysis, Gordon and Breach, Switzerland, 1992. P. Hodge, D.C. Sherrington, Polymer Supported Reactions in Organic Synthesis, John Wiley, Chichester, 1980.

18. F. Helfferich, Ion Exchange, McGraw Hill, New York, 1962.

EP

19. B. Bahramian, F D. Ardejani, V. Mirkhani, K. Badii., Appl. Catal 97–103.

A: General 345 (2008)

AC C

20. B. Bahramian, V. Mirkhani, M. Moghadam, S. Tangestaninejad, Catal. Commun 7 (2006) 289–296.

21. W. Wang, J C. Darana, R. Poli, D. Agustina, J. Mol. Catal. A: Chemical 416 (2016) 117-126.

22. V. Mirkhani, M. Moghadam, S. Tangestaninejad, B. Bahramian, Appl. Catal., A: General 311 (2006) 43–50.

23. V Mirkhani, M. Moghadam, S. Tangestaninejad, B. Bahramian, A. Mallekpoor-Shalamzari, Appl. Catal A: General 321 (2007) 49–57. 24. B. Bahramian, V. Mirkhani, M. Moghadam, S. Tangestaninejad, Appl. Catal., A: General 301 19

ACCEPTED MANUSCRIPT

(2006) 169–175. 25. V. Mirkhani, M. Moghadam, S. Tangestaninejad, B. Bahramian., Polyhedron 25 (2006) 2904–2914.

27.

RI PT

26. E.N. Jacobsen, W. Zhang, J. Org. Chem. 56 (1991) 2296. M.J. Sabater, A. Corma, A. Domenech, V. Fornés, H. Garc´ıa, Chem. Commun. (1997) 1285.

28. J.M. Fraile, J.I. Garc´ıa, J. Massam, J.A. Mayoral, J. Mol. Catal 136 (1998) 47. 29.

S. Kim, W. Zhang, T.J. Pinnavaia, Catal. Lett 43 (1997) 149.

SC

30. R.I. Kureshy, N.H. Khan, S.H.R. Abdi, A.K. Bhatt, P. Iyer, J. Mol. Catal. A: Chemical 121(1997)25–31.

M AN U

31. S.K.M. Islam, S. Paul, A. Singha Roy, P. Mondal., J Inorg Organomet Polym 23 (2013) 560570. 32. G. Ujaque, J. E. Norton, K. N. Houk, J. Org. Chem 67(2002)7179-7184. 33. G.A. Morris, S.T. Nguyen, J.T. Hupp, J. Mol. Catal. A. Chem 174 (2001) 15. 34. R. Azadbakht, A.A. Manesh, M. Malayeri, B. Dehghani., Cite this: New J. Chem., 39(2015)6459.

TE D

35. M.R. Maurya, A.K. Chandrakar, S. Chand, J. Mol. Cat. A: Chem.263 (2007) 227. 36. Y. Iamamoto, M.D. Assis, K.J. Ciuffi, C.M.C. Prado, B.Z. Prellwitz, M. Moraes, O.R. Nascimento, H.C. Sacco, J. Mol. Cat. A: Chem 116 (1997) 365. 37. Y.Y. Karabach, A.M. Kirillov, M. Haukka, M.N. Kopylovich, A.J.L. Pombeiro, J. Inorg. Biochem 102 (2008) 1190.

EP

38. C. Adhikary, R. Bera, B. Dutta, S. Jana, G. Bocelli, A. Cantoni, S. Chaudhuri, S. Koner, Polyhedron 27 (2008) 1556.

AC C

39. J. Zhang. Y. Tang, J.Q. Xie, J.Z. Li, W. Zeng, C.W. Hu, J. Serb. Chem. Soc. 70(10)(2005)1137–1146.

40. D. Ramakrishna, B. Ramachandra Bhat, R. Karvembu, Catal. Commun 11(2010)498-501.

41. P. Roy, M. Manasserob., Dalton Trans., 39(2010)1539-1545.

42. H. H. Monfared, V. Abbasi, A. Rezaei, M. Ghorbanloo, A. Aghaei., Transition Met Chem. 37(2012)85–92.

43. D. H. R. Barton, Tetrahedron 54(1998)5805. 20

ACCEPTED MANUSCRIPT

44. M. Costas, M. P. Mehn, M. P. Jensen, L. Que, Jr., Chem. Rev 104(2)(2004)939-986. 45. G. J. P. Britovsek, J. England, S. K. Spitzmesser, A. J. P. White, D. J. Williams, Dalton Trans. 24(2005)945-955.

RI PT

46. P. Battioni, J. P. Renaud, J. F. Bartoli, M. Reina-Artiles, M. Fort, D. Mansuy, J. Am. Chem. Soc 110(1988)8462. 47. E. N. Jacobsen, W. Zhang, A. R. Muci, J. R. Ecker, L. Deng, J. Am. Chem. Soc.113(1991) 7063. 48. S.-I. Murahashi, S. Noji, N. Komiya, Adv. Synth. Catal. 346(2004)195.

SC

49. R. W. Murray, K. Iyanara, J. Chenb, J. T. Wearing, Tetrahedron Lett 36(1995)6415.

50. G. Grivani, A. Ghavami, V. Eigner, M. Dusˇek, A. D. Khalaji., Chin. Chem. Lett. 26 (2015) 779-784.

M AN U

51. M. Ghorbanloo, R. Tarasi, J. Tao, H. Yahiro, Turkish Journal of Chemistry 38(2014)488–503. 52. H, Hosseini Monfared, V. Abbasi, A, Rezaei, M. Ghorbanloo, A. Aghaei., Transition Met Chem 37 (2012)85–92.

AC C

EP

TE D

53. N. Tadayanompour, S. Rayati, M. Hossaini Sadr, K. Zare, A. Wojtczak., Transition Metal Chem., 40(8)(2015) 891-897.

21

ACCEPTED MANUSCRIPT

O

O

O

[Zn4(L)2(OAc)3(OH)] O

OH O

ROP

n

O

O

L-Lactide

PLA

RI PT

O

Figure 1. Representative reaction opening polymerization (ROP) of L-lactide

N

N

Cu O

O

SC

R1

COOCH3

n H 2C

R2

COOCH3

H2 C

*

AIBN

*

n

CH3

M AN U

CH3

Figure 2. Representative reaction polymerization of poly (methyl methacrylates) (PMMAs) O

O

O d[lactide]/dt=kp[lctide]1[Zn2L2(OBn)2]1

Zn- Schiff base

O

Bn

O

O

O

O

O n

OH

TE D

O

O

O

EP

Figure 3. Representative reaction opening polymerization (ROP) of L-lactide

O

O

O

O

Schiff Base complex O *

O

OH O

PLLA

n O

AC C

L-LA

Figure 4. Representative reaction opening polymerization (ROP) of L-lactide

22

ACCEPTED MANUSCRIPT

(a) The traditional route proceeds via the conversation of propylene to chloropropanols Cl

H3 C

CH2

Cl2

+

+

OH

H2O

+

Cl

H3C

H3C

RI PT

2

OH

(b)The reaction produces a mixture of 1-chloro-2-propanol and 2-chloro-1-propanol, which is then dehyrochlorinated. For example:

OH

O Cl

+

OH

+

-

H3C

+

H2O

SC

H3C

Cl-

AC C

EP

TE D

M AN U

Scheme 1. The hydrochlorination route

Figure 5. The effect of different oxidant on the epoxidation of cyclooctene catalyzed by [Mn(salophen)diatomite at room temperature

23

ACCEPTED MANUSCRIPT

Mn O

RI PT

O

+ O

M AN U

SC

Scheme 2. Structure of the complex (Mn (salophen)

OH

Verbenone

Verbonol

O

OH

alpha-Pinene

alpha-Pinene oxide

AC C

EP

TE D

Scheme 3. Alkyl aromatic and cycloalkanes were oxidized efficiently to their corresponding alcohols

24

ACCEPTED MANUSCRIPT

O

[Mn(salophen-PSI]/NaIO4 CH3CN/H2O

OH

or R

R-CH2-R'

O R'

+

R

C

R'

H N

RI PT

N

Mn

O

H N Cl

+

CH3CN reflux (48)

N

N

reflux

SC

N

O

Cl

TE D

M AN U

N

N

N

N

Mn O

Cl

O

AC C

EP

Scheme 4. Preparation of polymer supported catalyst, Mn (III) salophen-PSI

25

ACCEPTED MANUSCRIPT

H O

R3

OH

R2

+

R1

H2 N

OH

MeOH, r.t.

RI PT

H2SAP; R1+R2=R3=H H2L1:R1=OH H H2L2: R+OH H2L3: R3+OH

+ [MoO2(acac)2)] MeOH, r.t

H

N

N

OH

+ [MoO2(acac)2] 1) MeOH (R3 =OH), reflux 2) 80 C under vacuum

OH

R2

R3

R1

[MoO2(SAP)]2 [MoO2L1] [MoO2L2]2 [MoO2L3]2

under vacuum 80 C

H O

M AN U

N

O

O

O

R2

R1

+ [MoO2(acac)2] MeOH(R1=OH), reflux EtOH(R2=OH), reflux

O

Mo

SC

R3

O

Mo

R3

O

O

HO

R

R2

R1

[MoO2(SAP)(MeOH)]2 [MoO2L1(MeOH)] [MoO2L2(EtOH)]2

TE D

Scheme 5 . Access routes to the H2 L Pro-ligands and molybdenum complexes

OH OH

0.1% Mo

EP

TBHP aq

O

+

+

OH

But

CHO

O

CHD

O

AC C

Mo

H

O

O

Scheme 6. Epoxidation of cyclohexene

26

CHol

2

ACCEPTED MANUSCRIPT

O Mn(V) R

R'

N

N Mn +

O

O O

or R-CH2-R'

RI PT

O-

Oxgen Donor

ZEMS

or

CH3CN/H2O/NaIO4

R

O Mn(III)

R'

+

H

R'

SC

R

M AN U

Scheme 7. Alkyl aromatic and cycloalkanes were oxidized efficiently to their corresponding alcohols and

AC C

EP

TE D

ketones in the presence of zeolite-encapsulated Mn (III)-salophen

27

O

OH

R

C

R'

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

TE D

Figure 6. The effect of oxidant on the epoxidation of cyclooctene catalyzed by ZEMS at room temperature

N

N

EP

Mn

O

OAc O

AC C

ClPh3P

PPh3Cl O [Mn(salen)-Dowex]/NaIO4 CH3CN/H2O/Imidazole R

R-CH2-R'

O

OH C

R' + R

R'

H

Figure (a)7. The water-soluble Mn (III)-salen used in this study

28

ACCEPTED MANUSCRIPT

N

N Mn

O

CH3CN

NH2

NH

reflux (48)

Cl

RI PT

+ H2N

O

Cl

reflux (48)

SC

NH2

M AN U

NH

NH

alpha-Pinen

N

O

N Mn Cl

O

TE D

O

OH

O

Verbenone

Verbenol

alphe-Pinene oxide

Figure (b)7. Cycloalkanes were oxidized efficiently to their corresponding alcohols and ketones in the

AC C

EP

presence of Mn(salophen)ClPSP with sodium periodate under agitation with magnetic stirring

N

N Mn

O

O

Figure 8. Chiral (salen) manganese (III) complex

29

ACCEPTED MANUSCRIPT

NO2

NO2

NO2

Naohthalene

1

1.NaNO2/HCl

+

Zinc dust

2.ZnCl

(a)

(b)

2

1.Sn?HCl 2.NaNO2/H2SO4 3.bioling H2O

OH

OH OHC

CHCl3/NaOH

3

4

R1

R2

N

N

SC

Chiral diamine

R1

R2

N

N

M AN U

Co OH

O

RI PT

NH2

O

HO

Co(CH3COO)2.4H2O

Figure 9. Co(II) chiral salen complexes1–4 derived from α-naphthyl salicylaldehyde with 1S,2S(+)

TE D

diaminocyclohexane, 1R,2R(-) diaminodiphenylethane and S(+)1.2-diaminopropane

NH2

NH2

HN

THF

+

EP

CH2Cl

H2N

1

room temperature

3

AC C

2

NH

N

Fe

Cl

Cl

OH2

C H

Ferrocene carboxadehyde

Ethanol, 70 C

NH

ferrocene

N

FeCl3 Ethanol, 70 C

4

Cl

5

Figure 10. Synthesis of polymer supported metal complex 30

C H

ferrocene

ACCEPTED MANUSCRIPT

O

O

O

Mo3SIN3

O

N

N3

N

Cr O

SC

O

94%

Me3SiO

RI PT

Me3SiO

Figure 11. Complexes of Schiff bases were then screened as catalyst in the asymmetric ring opening of meso-

M AN U

cyclohexene epoxide with phenyllithium to give (1S, 2R)-phenylcyclohexanol in 9-67%.

N

N

Mn

O

O

Cl

O

TE D

N

N

O

SO2tBu

O

O

EP

I

AC C

Scheme 8. Epoxidation of conjugated olefins by managanese (III) complexes

31

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Figure 12. Optimization of catalyst and oxidant for the oxidation of diphenylmethanol to benzophenone alcohol (1mmol), various amounts of oxidant and catalyst in CH3CN under reflux.

O

TE D

O

N

-2HCl

NH

HO

MnCl2 N(CH2CH3)3

M

N

OH

N

N

NH

NH

HN

EP

[Mn(III)L]+

AC C

M=Mn(III)

CH2OH

CHO

[Mn(III)L]Cl

COOH

+

CH3CN, H2O2

Cl

Cl

86%

Cl

0%

Scheme 9. Selective oxidation of the benzylic group to the aldehyde.

32

ACCEPTED MANUSCRIPT

HOOC OH

O

H2O2/Catalyst

+

+

CH3CN

1

2

RI PT

COOH

3

Scheme 10. Oxidation of cyclohexane to cyclohexanol (1), cyclohexanone (2) and adipic acid (3).

N

O

O

+

H2O

O

OH

SC

H C

OH

Mn O

H2O2

OH

O

O

N

C H

M AN U

HO

H+

MnL2

k

H+

H C

N

O

O

OH

H O

O

Mn

O

HO

O

O

N

C H

MnL2S

TE D

O

OH

O

N

O

O

OH

H O

O

Mn

O

O

O

N

C H

MnL2 OH

K

OH

+ H2O

H2O2

EP

+

HO

H C

OH

AC C

Scheme 11. 1-hydroxy-5-[4-(2-hydroxybenzylideneamino) phenxy]-3-oxapentane (HL1) and 1-methoxy-5-[4(2-hydroxybenzylideneamino) phenoxy]-3-oxapentane (HL2 ), and their Mn (III) complexes used to mimic peroxidase in the oxidation of phenol by hydrogen peroxide

33

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Figure 13. Effect of time on conversion of benzyl alcohol to benzaldehyde (1 mmol benzyl alcohol, 0.02 mmol

AC C

EP

TE D

NiL1, 1 mmol oxidant, 0.3 mL EMIM).

Figure 14. Optimization of reaction conditions for oxidizing benzyl alcohol to benzldhyde

34

ACCEPTED MANUSCRIPT

CH3

CH3

Reflux 4 h CH3CN

+ 2 H NCH CH X 2 2 2

N OH

OH

O

N

RI PT

O

X

X

Cu(OAc)2

M AN U

SC

CH3

O

N

O

X

Cu

O

= acetate O

N O

X

O

O

O

X

N

TE D

X = For for 1 X = Cl for 2 X = Br for 3

Cu

Cu

O Cu

O

O O

N

X

CH3

EP

Scheme 12 the synthetization of new Cu (II) complexes, [Cu4(O)(Ln )2(CH3COO)4] where HL1=4-methyl-2,6bis(2-fluoroethyliminomethyl) phenol, HL2=4-methyl-2.6-bis(2-chloroethyliminomethyl)phenol and HL3=4-

AC C

methyl-2,6-bis(2-bromoethyliminomethyl) phenol.

35

ACCEPTED MANUSCRIPT

(L)CuII-OOH

CuII(L) + H2O2

R

O-D bond Cleavage

O-H bond cleavage ROO

RO RH

RI PT

ROOH + (L)CuI

decomposition

ROH

SC

ROH + CO

AC C

EP

TE D

M AN U

Scheme 13. Probable mechanistic pathway of catalytic reaction

36

ACCEPTED MANUSCRIPT

(a)

NaOCl CH3

CH3

N

N

H3CO

O Cl O Bu-t

OCH3

t-Bu

H2O2

+

(b)

SC

OH

RI PT

Mn

OH CH3

88%

O

O

6-8%

M AN U

Re O

OH

OH

Mn(salen)(1)(cat) (c)

PhIO 1.5-dicycohexylimidazole CH2Cl, -30C

34 % ee

TE D

O Mn(salen) (1) (cat.)

4-phenylpyridine N-oxide CH2Cl2, -30 C

EP

(d)

93 % ee (3S, 4S)

AC C

Scheme 14. (a) Enantioselective epoxidation of cis- -methylstyrene catalyzed by Jacoben’s catalyst, (b) Oxidation of admantane catalyzed by methyltrioxothenium, (C) Enantioselective oxidation of indane with Mn (Salen) catalyst 1, (d) Enantioselective oxidation of 2.2’-dimethylchromene with Mn(salen) catalyst 1

37

ACCEPTED MANUSCRIPT

O

O N

CHCl3

+ H2N

NH2

NH2

r.t/3h OH

acacen

N

NH2

MeOH OH Ref/ 2h

Br

Br

OH

N

OH

RI PT

O

N

HO

N

MeOH + VO(acac) Ref/1h 2

OH

HO

H2L

N

M AN U

Br

SC

H2L

Br

O

N

V

O

O

VOL

Scheme 15. Preparation procedure of the asymmetric tetradentate ONN’O’ Schiff base Ligand (H2L) and its

AC C

EP

TE D

vanadyl complex (VOL).

Figure 15. The effect of solvent on the conversion of the cyclooctene to cyclooctene epoxide in the presence of TBHP as oxidant by the catalytic amount of VOL in refluxed conditions. 38

RI PT

ACCEPTED MANUSCRIPT

Table 1

Oxidation of methyl phenyl sulfides by the Fe3O4@SiO2/ ([Mn2L(HL)(H2O)4]/H2O2 Sulfoxide/Sulfone Yield (%) 23.4

1

S

2

S

52.0

3

S

75.0

4

S

11.25

5

S

0

2:1a

Sulfoxide Selectivity (%) c 91

100

3:1a

100

3:1d

30

3:1e

-

Reaction conditions: catalyst 6.4 mg (0.0016 mmol), MeSPh 1 mmol, CH3CN3 mL, temperature 60 ± 1◦C, time 60 min, bConversions are based on the starting substrate; csulfoxide selectivity:%sulfoxide/(sulfoxide+sulfone);dWithout catalyst; reaction temperature 60◦C, MeSPh 1.0 mmol, CH3CN3 mL, reaction time 2h, H2O2 3mmol; Fe3O4 @SiO2 (0.0016 mmol), MeSPh 1.0 mmol, CH3CN3 mL, time 2 h, temperature 60 ± 1 ◦C.

AC C

EP

TE D

a

H2O2:Substrate molar ratio 1:1a

SC

Substrate

M AN U

No

39

ACCEPTED MANUSCRIPT

(a) O

NH2

Si(OEt)3

N

MeOH

SiH(OEt)3

Reflux

HL1

+

silica gel

Toluene Reflux, 24 h

silica gel

O O Si O

RI PT

OH

HO

SC

(silica gel-O2)EtO) si-L1H

M AN U

(b)

N

(silica-O2)EtO)Si-L1H = [VO(acac)2] +

N

O

O

(L2)2-

TE D

CH2Cl2 Reflux 19 h

silica gel

O O Si O

O

O

V

O O

N

(Silica gel-O2)EtOSi-L1-VO(L2)

AC C

EP

N

N

Scheme 16. A Modification of the silica gel surface by organosilane to (silica gel–O2)EtO)Si-L1H and b immobilization of vanadium oxide on the surface of the functionalized silica gel to give the catalyst

40

ACCEPTED MANUSCRIPT

RI PT

Organometallic Complexes of Schiff Bases: Recent progress in oxidation catalysis Wail Al Zoubi, and Young Gun Ko

SC

School of Materials Science & Engineering, Yeungnam University, Gyeongsan 712-749, South Korea.

1. The results shown that the Schiff bases and their complexes exhibited an efficient

M AN U

catalytic activity toward the selective epoxidation of simple alkenes, as well as of primary and secondary alcohols.

2. Their immobilization on solid supports was a good strategy to facilitate the

AC C

EP

TE D

separation and catalyst recycle.