Copper and manganese complexes with C2-multitopic ligands. X-ray crystal structure of [Cu(N,N′-bis[(S)-prolyl]phenylenediamine)H2O]. Catalytic properties

Inorganica Chimica Acta 333 (2002) 83 /92 www.elsevier.com/locate/ica

Copper and manganese complexes with C2-multitopic ligands. X-ray crystal structure of [Cu(N,N?-bis[(S)-prolyl]phenylenediamine)H2O]. Catalytic properties M.J. Alco´n a, Marta Iglesias a,*, F. Sa´nchez b,* a

Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid, Spain b Instituto de Quı´mica Orga´nica, CSIC, Juan de la Cierva, 33 28006 Madrid, Spain Received 19 September 2001; accepted 14 January 2002

Abstract Eight mononuclear complexes with multitopic C2-symmetry ligands, [Cu(L)]ClO4, [Mn(L)Cl(H2O)]PF6, (L/N ,N?- bis[(S )prolyl]phenylenediamine (1), N ,N? -bis[(S )-N -benzylprolyl]phenylenediamine (2), N ,N?- bis{[(S )-pyrrolidin-2-yl]methyl}phenylenediamine (3), N ,N?- bis-{[(S )-N -benzyl-pyrrolidin-2-yl]methyl}phenylenediamine (4)) have been prepared and characterised by analytical (elemental analysis, and mass spectroscopy) and FT IR, NMR and electronic spectroscopies. The data show that the ligands are neutral and coordinate to the metal in a tetradentate manner. The N ,N?- bis[(S )-prolyl]phenylenediamine ligand also appears as an anionic species, (LH-2), and the single crystal structure determination of the respective complex, [Cu(1)]H2O, is reported. This new family of Cu-complexes catalyse the cyclopropanation of styrene with ethyl and t -butyl diazoacetate to afford cis /trans 2-phenylcyclopropan-1-carboxylates with good yields and selectivity against dimerisation and low ee ( B/10%). On the other hand, the manganese and copper complexes also catalyse the oxidation of organic sulfides to sulfoxides with high selectivity, and moderate to low enantioselectivity. If an excess of oxidant were used the reaction yields sulfone as only product with excellent yield. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Copper complexes; Multitopic ligand; Manganese complexes; Cyclopropanation; Oxidation

1. Introduction The development of new transition metal catalysts designed to facilitate simple organic transformations in high yields with high degrees of enantioselection is an increasingly important goal. The success of metal complexes for enantioselective catalysis is largely dependent on the structure and electronic properties of the chiral ligands [1]. The most commonly studied and employed organometallic complexes contain phosphorus ligands. This is mainly due to the excellent results obtained with phosphines in different catalytic reactions. However, interest in nitrogen ligands has increased over the last few years because of the promising results [2]. Nitrogen-containing ligands pre-

* Corresponding authors. Tel.: 34-91-334 9032; fax: 34-91-372 0623. E-mail address: [email protected] (M. Iglesias).

sent several distinct advantages. First, they are largely available in enantiomerically pure form, both in the chiral pool and as cheap industrial chemical intermediates. The second advantage lies in the chemistry of the nitrogen functional group itself. The chemistry of nitrogen is not always easy but has received abundant attention so that there exist, in most cases, numerous synthetic solutions to each possible transformation of these compounds. As a result, these synthetic facilities allow tailor-made modifications toward the preparation of ligands with specific physicochemical properties. C2-symmetric diamines could be used in carbonyl reduction by hydride transfer with more than 99% ee [3]. It is noticeable that even groups known for their work on the use of chiral phosphines have turned their attention to nitrogen-containing ligands. Thus, in 1995, Noyori and his group used a synergetic effect of diamines and phosphines in carbonyl reduction by hydrogenation with molecular H2 [4]. Chiral diureas

0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 7 6 8 - 5

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with the C2-diamine basic structure gave also promising results [5]. Nitrogen-containing ligands may be used in asymmetric catalysis with transition metals less expensive than noble metals. Thus, semicorrins were used in cobalt complexes by Pfaltz and co-workers [6] for the reduction of a,b-unsaturated molecules with NaBH4. We recently initiated a systematic investigation of the structural and electronic factors that regulate the catalytic activity of various cationic complexes in hydrogenation and cyclopropanation reactions [7]. Previously, we described the utility of a series of highly flexible C2-multidentate-ligated rhodium, iridium or copper complexes in catalytic hydrogenation or cyclopropanation of prochiral alkenes. Herein we present the synthesis and characterisation of a family of new cationic copper and manganese complexes, with multidentate C2-symmetry ligands (Fig. 1) derived from (S )proline, and the results of their ability to catalyse the cyclopropanation of styrene with ethyl and t-butyl diazoacetate and the oxidation of sulfides to sulfoxides and sulfones.

2. Results and discussion Recently, we had prepared a series of tetradentate ligands constituted by two units of (S )-proline attached to a very flexible ethylene bridge, where the spectroscopic studies would not assure that the ligand occupy the four equatorial coordination positions around the metal, as can be suggested by molecular mechanic calculations. Now we have synthesised new ligands where the ethylene bridge has been changed for a more planar demanding o-phenylene bridge. This structural modification permits assure a ‘cuasi’ square-planar (copper-complexes) or octahedral (manganese complexes) with the four nitrogen-donor atoms on the equatorial co-ordination sites. We reasoned that such an arrangement would facilitate the reaction of the metal complexes with substrates, as dissociation of one strongly N-donating ligand would not be required prior to the formation of the putative metal/substrate intermediate, maintaining the stereo-

Fig. 1. C2-symmetry ligands.

chemical features through reaction coordinates and promoting improved stereo- and enantio-selectivities. 2.1. Copper-complexes To avoid the formation of dinuclear species, the Cucomplexes 5 /8 were formed according to the simple substitution reaction shown in Scheme 1. The reaction of ligands 1/4 with [Cu(MeCN)4]ClO4 provided microcrystalline solids of [Cu(ligand)(solvent)]ClO4 (Fig. 2), which lacks coordinated ClO4 ions, perhaps due to unfavourable steric interactions of the ligand with potential axial ligands. The reaction of N ,N?-bis [(S )-prolyl]phenylenediamine (1) with [Cu(MeCN)4]ClO4 beside the expected complex, provided red crystals of a paramagnetic Cu-complex, [Cu(N ,N?-bis [(S )-prolyl]phenylenediamine-2)]H2O (5a), in 48% yield, which present the ligand as a deprotonated anionic species. The complexes were characterised by analytical (elemental analysis, mass spectroscopy, FAB, ESI MS and APCI MS), spectroscopic, and X-ray crystallography analysis in the case of 5a. A suitable red crystal for a crystallographic study was obtained from a crystallisation in acetonitrile. The crystal selected for the crystallographic study was sealed in a capillary containing oil that prevents decomposition. The Cu-complexes (5 /8) described herein involve the ligands functioning as a neutral, tetradentate chelate through its amine, amide groups (except for 5a) as characterised by a combination of analytical, spectroscopic and X-ray crystallographic methods. The FT IR spectra of the free ligands exhibit the characteristic bands of amides and amines. The amide I band appears at about 1650/1670 cm 1 and amide II at 1530 /1550 cm 1. The solid-state FT IR spectra of the copper complexes are consistent with their proposed structures. Uncoordinated ClO4 is indicated by the presence of a fine structure and no splitting in the strong ClO4 vibrations observed near 1100 cm 1. The H2O ligands exhibit strong absorption near 3500 cm 1. The FT IR spectra of complexes lack any vibrations attributable to a coordinated CH3CN ligand, which is consistent with the planar tetracoordinated proposed structure. The spectrum of 5a shows absorption bands at 3373 and 3211 cm 1 for the N /H and lacks any vibration due to a ClO4 group, which is consistent with its tetracoordinated structure, with free axial co-ordination sites as defined by X-ray crystallography. In all complexes the keto group is not involved in the coordination to the metal, only one C /O stretching

Scheme 1. Preparation of copper complexes.

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are very close to those reported for similar ligands and their corresponding complex [8]. In order to obtain information about the nuclearity, the FAB, ESI-MS and APCI-MS mass spectra of Cu complexes were examined. All the complexes examined provided nice quality ionspray mass spectra. The molecular weight of the complex has been confirmed in all cases, and MS MS granted the structural information necessary for the complete characterisation of the compounds examined. The nuclearity for complex 5a was confirmed by X-ray analysis. The dark colour of the complexes could be indicative of the presence of the intermolecular metal/metal interaction [9]. In fact the planarity of the ligand 1 and the square-planar coordination of the metal centre confer on these molecules a reasonable planarity suitable for the formation of stacked arrangements with potential intermetallic interactions. X-ray analysis confirms these interactions. Fig. 2. Structure of new complexes.

frequency at approximately 1670/1682 cm 1 appears and a strong broad band at 1584 and 1542 cm1 as expected for C /C and N/C /O groups. The IR spectra of Cu /amine complexes show n(N /H) bands shifted at higher frequencies (3440 /3280 cm1) and bands due to n (Cl /O) at 1100 cm 1. The n(Cl/O) frequency appears at 1087 cm 1. The 13C MAS and CP/MAS NMR spectra of powdered samples 5, 6 show broad signals due to partial deprotonation of NH /amide ligands which gives [Cu(LH 2)]  species as demonstrated by the X-ray crystal structure 5a. For complexes 7, 8 the 13C NMR spectrum shows well defined signals as corresponds at Cu(I), [Cu(L)], species. The general trend is for a downfield of the resonances when comparing the complexes to the free ligands. This phenomenon is most pronounced for the carbons close to the coordinated atoms. Properties of the complexes in acetonitrile solutions were investigated by means of electrical conductance, and electronic spectroscopy. The conductance measurements in 1 mM solutions of Cu-complexes (160 /180 V 1 cm2 mol 1) correspond to 1:1 electrolytic behaviour for all complexes. Solutions of amide Cu-complexes in CH3CN are indistinguishable by UV /Vis spectroscopy from those of amine complexes, respectively, suggesting a common solution structure for pairs of complexes supported by the same type of ligand. In addition to intense transitions between 200 and 300 nm, assigned as LMCT transitions, the complexes 5, 6 each exhibit a single ligand field transition between 500 and 600 nm. This d / d band exhibits a smooth hypsochromic shift as a function of increasing ligand size, occurring at 603 and 545 nm for solutions of 6, 5, respectively. These values

2.2. X-ray structure determination of {[Cu(N ,N? Bis[(S )-prolyl]phenylenediamine)H2O] (5a) X-ray crystallographic data for the complex 5a are collected in Table 1, while significant interatomic Table 1 Crystal data and structure refinement for [Cu(N ,N? -bis[(S )-prolyl]phenylenediamine)H2O] (5a) Empirical formula Formula weight Temperature (K) ˚) Wavelength (A Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) Volume, Z Density (calculated) Absorption coefficient F (000) Crystal size (mm) u range for data collection (8) Limiting indices

C16H18CuN4O3 377.88 143 (2) 0.71073 orthorhombic P 212121

7.6570 (11) 10.349 (2) 39.877 (6) 90 90 90 ˚ 3, 8 3160.0 (8) A 1.589 Mg m 3 1.405 mm 1 1560 0.04 0.12 0.08 2.71 /20.82 75 h 5 3, 105 k 5 9, 21 5 l 5 39 Reflections collected 5782 Independent reflections 3080 (Rint  0.0971) Absorption correction None Refinement method full-matrix least squares on F 2 Data/restraints/parameters 3080/0/193 Goodness-of fit on F 2 0.980 Final R indices [I  2s (I )] R1  0.0935, wR2  0.2119 R indices (all data) R1  0.1456, wR2  0.2445 Absolute structure parameter 0.02 (6) ˚ 3) 1.683 and 0.699 Largest diff. Peak and hole (e A

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Table 2 ˚ ) and angles (8) in [Cu(N ,N? -bis[(S )Selected bond lengths (A prolyl]phenylenediamine)H2O] (5a) Bond lengths Cu(1) N(1) Cu(1) N(2) N(1) C(5) N(2) C(6) C(6) O(1) Cu(1?)  N(1?) Cu(1?)  N(2?) N(1?)  C(5?) N(2?)  C(6?) C(6?) O(1?)

2.04 (2) 1.90 (2) 1.52 (2) 1.32 (2) 1.26 (2) 2.01(2) 1.91(2) 1.47(2) 1.36(2) 1.21(2)

Cu(1) N(3) Cu(1) N(4) N(4) C(14) N(3) C(13) C(13) O(2) Cu(1?)  N(3?) Cu(1?)  N(4?) N(4?)  C(14?) N(3?)  C(13?) C(13?)  O(2?)

1.915 (14) 1.97 (2) 1.54 (2) 1.27 (2) 1.24 (2) 1.97(2) 1.98(2) 1.55(3) 1.34(3) 1.27(3)

Bond angles N(2) Cu(1) N(3) N(3) Cu(1) N(4) N(2) Cu(1) N(1) C(2) N(1) Cu(1) C(6) N(2) Cu(1) C(12) N(3) Cu(1) C(17) N(4) Cu(1) N(2?)  Cu(1?) N(3?) N(3?)  Cu(1?) N(4?) N(2?)  Cu(1?) N(1?) C(2?) N(1?)  Cu(1?) C(6?)  N(2?)  Cu(1?) C(12?) N(3?)  Cu(1?) C(17?) N(4?)  Cu(1?)

84.4 85.1 85.4 117.4 118.0 114.9 118.0 82.4 87.5 84.2 116.7 117.2 113.5 117.9

N(2) Cu(1) N(4) N(3) Cu(1) N(1) N(4) Cu(1) N(1) C(5) N(1) Cu(1) C(7) N(2) Cu(1) C(13) N(3) Cu(1) C(14) N(4) Cu(1) N(2?)  Cu(1?)  N(4?) N(3?)  Cu(1?)  N(1?) N(4?)  Cu(1?)  N(1?) C(5?)  N(1?)  Cu(1?) C(7?)  N(2?)  Cu(1?) C(13?)  N(3?)  Cu(1?) C(14?)  N(4?)  Cu(1?)

168.4 167.3 105.6 105.4 114.1 119.9 106.7 169.7 163.7 106.1 107.5 116.0 113.6 107.0

(7) (6) (6) (12) (12) (11) (10) (7) (6) (6) (12) (13) (12) (11)

(7) (6) (6) (11) (11) (13) (11) (7) (6) (6) (11) (12) (14) (12)

distances and angles are compiled in Table 2. Single crystals of 5a are obtained after crystallisation from acetonitrile at room temperature. The monomeric structure of 5a (with the two-associated lattice water molecules omitted) is depicted in Fig. 3, with nonhydrogen atoms numbered. [Cu(N ,N?-Bis[(S)-prolyl]phenylenediamine 2)]H2O is characterised by the presence of square planar copper(II) in which the tetradentate ligand defines the equatorial plane of the metal and a H2O molecule acts a solvate (Fig. 3). While two crystallographic independent but chemically similar formula units are found in the asymmetric unit of orthorhombic crystals of 5a, the present discussion focuses on only one. There are no significant axial bonding interactions between the central copper(II) and the uncoordinated H2O and the

Fig. 3.

ORTEP

representation of the X-ray structure of 5a.

metal ion is only minimally displaced from the equator˚ ). The Cu /N bond lengths exhibit a ial plane (0.01 A slight asymmetry, such that the Cu /Namine bonds ˚ ] are slightly longer than the Cu / [average 2.00(2) A ˚ ]. The N /Cu /N, ‘bite Namide bonds [average 1.90(2) A angles’ [of 84.4 (7)8, 85.1 (6)8, 85.4 (6)8 105.6 (6)8 are as expected for a relatively rigid diamide /diamine ligand. 2.3. Manganese-complexes MnCl2 ×/4H2O reacted with ligands 1 /4 in presence of NH4PF6 to yield the cationic complexes, [Mn(ligand)Cl(H2O)]PF6 ×/x H2O, (9/12). Acetonitrile solutions of these complexes were highly conductive [10]; this implied that there was extensive dissociation of the chloride ligand upon dissolution of complexes and consequent formation of the respective cation [Mn(ligand)(solvent)2]2. Unfortunately, we could not grow any single crystals suitable for X-ray crystallographic studies. The Mn-complexes (9 /12) described herein all involve the ligands functioning as a neutral, tetradentate chelate through its amine, amide groups occupying the four equatorial sites (Fig. 2). The axial coordinating solvents have been verified by the appropriate losses in their thermogravimetric (TG) analyses. The IR spectrum of complex (9) shows a n (N /H) band at 3370 cm 1, shifted to higher frequencies, due to Mn-coordinated NH of pyrrolidine ring and a broad band at 3186 cm 1 shifted to lower frequencies that corresponds to n (N /H) amide band. The amide bands appears splitted at 1682, 1638 cm 1, close to the free ligand position and corresponds to the uncoordinated keto function. The amide II band appears in the same position as the free ligand. The n(P /F) frequency appears at 842 cm 1. The IR spectrum of complex 11 shows n (N /H) bands at 3371, 3186 cm 1 shifted at higher frequencies. A strong intensity absorption band at 1686 cm 1 attributable to the n (C /O) vibration, appears in the same position that the free ligand that excludes coordination to the C /O. The IR spectra of Mn/amine complexes show n (N /H) bands shifted at higher frequencies and bands due to n(P /F) at 830 cm 1. The compounds show a broad band at 3300/ 3500 cm 1 indicative of coordinated and lattice water. The electronic spectra of all the complexes, in DMF, show intraligand transition bands at 320 and 280 nm, while the MLCT bands fall near 350 nm. The position of the MLCT band depends on functional group amide or amine. As expected for Mn(II) complexes, d/d transition bands are not observed in dilute solution because of their being doubly forbidden. The FAB, ESI-MS and APCI-MS mass spectra of complexes were recorded. All the complexes examined provided nice quality ionspray mass spectra and the molecular weight of the complex has been confirmed in all cases. The ionisation of these compounds occurs with

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loss of PF6 ion, finding in all cases a cationic [Mn(L)Cl]  complex. Also, these complexes tend to give a heterolitic breakage of the M /X bond. The Mn / Cl bond present in these complexes is indeed quite polarised and it breaks affording the complexes metal cation by loss of a chloride anion. 2.4. Catalytic experiments 2.4.1. Catalytic activity on cyclopropanation reactions Over more than two decades transition-metal-catalysed cyclopropanation of olefins with a diazoacetate have received much attention of synthetic chemists due, mainly to the great importance of cyclopropanes as insecticides and drugs intermediates [11]. The selectivity towards cyclopropanation versus diazoalkane dimerisation, cis /trans selectivity and the differentiation of the enantiotopic faces of double bond are the main target in this reaction. The simultaneous control of selectivity and two stereochemical problems is indispensable for achieving highly efficient cyclopropanation [12], besides the availability and stability of the catalysts and possibility for reuse in several runs. Recently, we have described that some copper complexes with pyrrolidine derivatives as chiral ligand catalyse the asymmetric cyclopropanation of olefins with alkyl diazoacetates, and moderate enantiomeric excesses have been achieved [13,7b]. To evaluate the new class of bis-pyrrolidine ligands 1/4, we tested their copper complexes in a usual reaction model as the cyclopropanation of styrene with ethyl and t-butyl diazoacetates; the results are reported in Table 3. In the reaction of styrene with an alkyl diazoacetate, the main products are alkyl cis and trans 2-phenylcyclopropanecarboxylates, and alkyl maleate and alkyl fu-

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marate as by-products in different extension. The reaction takes place through a nearly synchronous carbene insertion generating two new asymmetric centres, causing a total of two pairs of enantiomers as depicted in Scheme 2. In the standard cyclopropanation reaction, ethyl diazoacetate is added slowly dropwise to a solution or suspension of styrene and catalyst (1 mol%) to avoid excess diazoacetate at any moment during the reactions, that would increase the formation of diethyl maleate and fumarate. As shown in Table 3, the structure of the ligands does not have a significant effect on the selectivity and enantioselectivity. Different substituents of the ligand did not change the cis /trans ratio of the cyclopropanation products, which only appears to depend on the ester group of the diazoacetate, corresponding to the results reported by others [14,15]. 2.4.2. Catalytic activity in oxidation of sulfides The selective oxidation of sulfides to sulfoxides and sulfones has been an active target for many years, due, mainly, to the increasing importance of sulfoxides as auxiliaries in organic synthesis [16] and for the increasing number of sulfoxides and sulfones as active drugs in the recent pharmacology [17]. Recently, we have described that some copper and manganese complexes with pyrrolidine derivatives as chiral ligand catalyse the sulfoxidation reaction with high yield, and moderate enantiomeric excess [18]. In order to determine the performance of new manganese and copper-complexes as catalysts, the oxidation of methylphenylsulfide and (2-ethylbutyl)phenylsulfide)

Table 3 Asymmetric cyclopropanation of styrene with diazoacetates catalysed by copper complexes Cat.

N2CHCO2R?

Yield [%] (h)

5a 5b 6 7 8 5a 5b 6 7 8

R? Et R? Et R? Et R? Et R? Et R? t -Bu R? t -Bu R? t -Bu R? t -Bu R? t -Bu

69(24) 66(20) 75(22) 72(24) 62(20) 58(24) 67(18) 75(20) 80(23) 76(24)

a

Selectivity 80 79 76 68 60 78 47 65 65 70

b

Trans /cis

a

2.04 1.67 1.82 1.89 1.83 2.17 2.56 2.54 2.94 2.77

Reaction conditions: Styrene/cat. 100/1, styrene/diazoacetate: 8/ 11, temp. 50 8C. a Determined by GC analysis on a 25 m capillary column (methylsilicone-2,3-dipentyl-6-(t -butyldimethylsilil)-b-cyclodextrin), ee B 10%. b Yield of cyclopropanes versus ester fumarate and maleate.

Scheme 2. Cyclopropanation reaction. Table 4 Oxidation of methylphenylsulfide catalysed by copper complexes in homogeneous conditions at 0 8C Cat.

[%] conv. (h)

Sel. SO (%)

TOF

Cu1a Cu1b Cu2 Cu3 Cu4

85 (3) 100 (3) 93 (3) 82 (3) 90 (3)

34 13 35 48 49

57 112 100 125 68

a

mmol subs./mmol cat. min.

a

ee (%) 3.2 24.0 25.1 21.1 20.3

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Table 5 Oxidation of alkylphenylsulfides catalysed by manganese complexes Substrate

Cat.

T (8C)

[%] conv. (h)

Sel. SO (%)

TOF

Phenylmethylsulfide

Mn1 Mn1 Mn2 Mn2 Mn3 Mn3 Mn4 Mn4 Mn1 Mn2 Mn3 Mn4

0 8C r.t. 0 8C r.t. 0 8C r.t. 0 8C r.t. r.t. r.t r.t r.t

82 (1.5) 80 (0.5) 80 (2) 85 (1) 75 (3) 80 (2) 80 (2) 85 (2) 100 (1) 100 (2) 100 (2) 100 (2)

50 33 45 30 53 45 68 33 80 75 77 78

99 487 124 503 145 569 200 600 440 500 550 625

(2-Ethylbutyl)phenylsulfide

a

a

ee (%) 18.1 23.3 19.7 18.5 27.7 22.7 23.5 20.4 13.0 15.1 20.1 17.2

mmol subs./mmol cat. min.

Fig. 4. Kinetic profile of oxidation of (2-ethylbutyl)phenylsulfide with Mn-catalysts (room temperature).

was tested. The activities, selectivity and enantiomeric excesses attained are collected in Tables 4 and 5 and Figs. 4 and 5. The experimental conditions were established by varying the nature of the oxidant among those used in preparative scale. First, hydrogen peroxide (H2O2) was examined as oxidant in acetonitrile in different conditions and little formation of sulfoxide was detected at ambient temperature in spite of excess amount of oxidant used. Thus, NaOCl was employed as an oxidant in the present study since we have obtained high yields at low temperature. By varying the pH of NaOCl solution we have determined that pH 11.3 is the optimum for oxidation reactions. The 4-methylmorpholine N-oxide is used, as promoter, to stabilise the Mn(V) /O complex formed in the oxidation cycle. Finally, low temperature (0 8C) was chosen when a small molecule was oxidised; when a large molecule was oxidised no reaction was observed and the reaction temperature was raised to room temperature to increase the reaction rate.

The oxidations were usually carried out in the presence of catalytic amounts of the catalyst (1% based on experimental metal content) and 4-methylmorpholine N-oxide monohydrate (0.1 mmol) by using aqueous solution of NaOCl as sacrificial oxidant in CH2Cl2 at 0 8C for methylphenylsulfide or 25 8C for (2-ethylbutyl)phenylsulfide. Higher reaction temperatures lead to a significant loss of the asymmetric induction as well as a dramatic decrease in the selectivity to sulfoxide. A series of blank experiments revealed that each component is essential for an effective catalytic reaction and the system is relatively unaffected by changing the order of mixing. The reactions showed a high chemoselectivity for larger (2-ethylbutyl)phenylsulfide (Table 5, Fig. 5). Indeed, in most of the cases, sulfoxides were obtained as the main or sole products as detected by NMR and GC analysis. The lower selectivity presented for methylphenylsulfide, in the general selected conditions to compare the catalysts, corresponds with the much higher extent of the reaction obtained for this substrate,

Fig. 5. Selectivity to (2-ethylbutyl)phenylsulfoxide for the oxidation reactions carried out with Mn-catalysts.

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but when we monitored the parameters of the reaction for a pair catalyst-substrate, we have afforded at sulfoxide as only product. As far as the catalyst is concerned, it can be seen that for the oxidation of alkylphenylsulfides (Table 5), the amide-compounds are more effective catalysts than the amine-ones and similar selectivity was found in both cases. The copper complexes show less activity and similar selectivity (Table 4) as manganese ones (Table 5).

3. Conclusion We have described the synthesis and characterisation of a family of well-defined copper and manganese complexes with a series of tetradentate ligands derived from L-proline. We have shown that these new copper complexes can be valuable in the catalysed enantioselective cyclopropanation of olefins with ethyl and tbutyl diazoacetate. The main product was a mixture of alkyl cis /trans -2-cyclopropanecarboxylate. The chemical yield is high (in the range 60 /90%). Also the manganese and copper complexes are suitable catalysts for the selective oxidation of sulfides exclusively sulfoxides or sulfones, by tuning the reaction conditions, in high yield and showed high TOF. The results presented herein serve as a foundation for our continued efforts to rationally design the high efficient catalysts for the asymmetric synthesis.

4. Experimental 4.1. General remarks All preparation of complexes was carried out under dinitrogen by conventional Schlenk-tube techniques. The starting complexes [Cu(CH3CN)4]X (X /ClO4, PF6) were prepared according to the literature methods [19]. All solvents were carefully degassed before use. C, H and N analysis were carried out by the analytical department of the Institute of Materials Science (C.S.I.C.) with a Perkin/Elmer 240C apparatus. Metal contents were analysed by atomic absorption using a Unicam Philips SP9 apparatus. Mass spectra were performed on a Hewlett /Packard 1100 MSD mass spectrometer (ESI MS, APCI MS) with positive mode and VG-Autospec (FAB ). FT IR spectra were recorded with a Nicolet XR60 spectrophotometer (range 4000 /200 cm 1) in KBr pellets; 1H, 13C spectra were taken on Varian XR300 and Bruker 200 spectrometers. 1 H NMR chemical shifts are given in ppm using tetramethylsilane as an internal standard. High resolution 13C MAS or CP/MAS NMR spectra of powdered samples, in some cases also with a Toss sequence, in order to eliminate the spinning side bands, were

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recorded at 100.63 MHz, 6 ms 908 pulse width, 2 ms contact time and 5/10 recycle delay, using a Bruker MSL 400 spectrometer equipped with an FT unit. The spinning frequency at the magic angle (54844?) was 4 KHz. Optical rotation values were measured at the sodium-D line (589 nm) with a Perkin /Elmer 241 MC polarimeter. Gas chromatography analysis was performed using a Hewlett /Packard 5890 II with a flame ionisation detector in a cross-linked methylsilicone column. X-ray diffraction experiment was made with a Siemens/Bruker SMART diffractometer equipped with a CCD bidimensional detector. Caution ! Perchlorate salts of transition metal complexes containing organic ligands are potentially explosive and should be prepared in small quantities and handled with appropriate precautions. While no difficulties were encountered with the complexes reported herein, due caution should be exercised. 4.2. Synthesis of ligands The ligands N ,N? -bis[(S)-prolyl]phenylenediamine (1), N ,N?-bis[N-benzyl-(S)-prolyl)phenylenediamine (2), N ,N?-bis[2(S)-2-pyrrolidinylmethyl]phenylenediamine (3), N ,N? -bis-[N-benzyl-2(S)-pyrrolidinylmethyl]phenylenediamine (4), were synthesised according to methods previously published [20]. 4.3. Synthesis of metal complexes (5 /12) 4.3.1. Copper complexes: general procedure To a solution of [Cu(CH3CN)4]ClO4 (1 mmol) in dry acetonitrile (20 ml) was added a solution of the corresponding ligand (1 mmol); the mixture was stirred for 3 h at room temperature (r.t.) and the crystalline precipitate filtered. The filtrate was evaporated under reduced pressure to a volume of 5 ml and a careful addition of diethyl ether caused the precipitation of a microcrystalline solid, which was collected by filtration, washed and dried in vacuo (10 3 mmHg) to give the desired complex. 4.3.1.1. [Cu(1)]H2O (5a). Red. Yield: 48%. Melting point (m.p.) /230 8C */C16H20CuN4O2 ×/H2O (381): Calc. C 50.0; H 6.3; N 14.7; Cu 16.6; Found C 50.2; H 6.6; N 14.6; Cu 16.3% */IR (KBr, cm 1): n/3373, 3211 (NH); 1584 (C /C); 1544 (N /C /O)*/UV /Vis (10 3 M, DMF): l nm (log  /)/492, 292 (3.9) */MS (m /z ): 367 ([Cu(1)]), 303 (1)*/TG analysis: 0.194 mg weight loss (4.53% of 4.28 mg complex; expected weight loss: 4.72%) at 94 8C (H2O). 4.3.1.2. [Cu(1)]ClO4 ×/2H2O (5b). Brown */Yield: 40% */m.p.: 210 (d) */LM (10 3 M, V1 cm2 mol1, CH3CN) /126 */C16H22ClCuN4O6 ×/2H2O (501): Calc. C 38.3; H 5.2; N 11.2; Cu 12.7; Found C 38.0; H 5.4; N

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10.9; Cu 12.4% */IR (KBr, cm 1): n /3392, 3193 (N / H); 1682 (C /O); 1586 (C /C); 1542 (N /C /O); 1104 (Cl /O) */UV/Vis (103 M, DMF): l nm (log  /)/545 (w), 290.0 (3.8) */MS (m /z): 466 ([Cu(1)]ClO4), 383 ([Cu(1)(H2O)] ), 367 ([Cu(1)] ), 303 (1)*/TG analysis: 0.328 mg weight loss (6.96% of 4.71 mg complex; expected weight loss: 7.18%) at 103 8C (H2O). 4.3.1.3. [Cu(2)]ClO4 ×/2H2O (6). Dark brown */Yield: 70% */m.p.:/200 */LM (10 3 M, V1 cm2 mol 1, CH3CN)/130*/C16H26ClCuN4O6 ×/2H2O (473): Calc. C 40.6; H 6.3; N 11.8; Cu 13.4; Found C 41.0; H 6.1; N 11.4; Cu 13.0% */IR (KBr, cm 1): n /3380, 3200 (N / H); 1598 (C/C); 1090 (Cl /O) */UV /Vis (10 3 M, DMF): l nm (log  /)/603 (w), 292.0 (3.8) */MS (m / z ): 438 ([Cu(2)]ClO4), 274 (2)*/TG analysis: 0.379 mg weight loss (7.52% of 5.04 mg complex; expected weight loss: 7.60%) at 108 8C (H2O). 4.3.1.4. [Cu(3)]ClO4 ×/2H2O (7). Light green */Yield: 55% */m.p.:/230 (d) */LM (103 M, V1 cm2 mol 1, CH3CN)/136*/C30H34ClCuN4O6 ×/2H2O (681): Calc. C 52.9; H 5.6; N 8.2; Cu 9.3; Found C 52.6; H 5.1; N 7.9; Cu 8.9% */IR (KBr, cm 1): n /3510 (O /H); 3414 (N / H); 1676 (C /O); 1600 (C /C); 1528 (N /C /O); 1104 (Cl /O) */1H NMR(CD3CN, 50 8C): d /7.8 /6.6 (m, 14H, Ph.); 4.3 /4.0 (m, 2H, CH2Ph); 3.50 /3.48 (m, 2H, CH2Ph); 2.95 /1.50 (m, H5, H3, H4)*/13C-NMR (solid) d /176.20 (C /O); 142.07 (CPh /NH); 129.45 (CPh /C); 64.02 (C2); 61.22 (CH2Ph); 51.07 (C5); 33.89 (C3); 22.33 (C4)*/UV /Vis (103 M, DMF): l nm (log  /)/290.0 (3.8)*/MS (m /z): 543 ([Cu(3)] )*/TG analysis: 0.267 mg weight loss (5.23% of 5.10 mg complex; expected weight loss: 5.28%) at 114 8C (H2O). 4.3.1.5. [Cu(4)(NCCH3)]ClO4 (8). Brown */Yield: 80% */m.p.: 240 (d) */LM (103 M, V1 cm2 mol 1, CH 3 CN) / 126 / 130 */ C 3 0 H 3 8 ClCuN 4 O 4 ×/ CH 3 CN (658): Calc. C 58.3; H 6.2; N 10.6; Cu 9.7; Found C 58.6; H 6.1; N 10.4; Cu 10.0% */IR (KBr, cm 1): n /3200 (N /H); 1596 (C /C); 1076 (Cl /O) */13C NMR (solid) d /142.01, 141.28 (Carom /NH); 129.40, 118.35 (Carom.); 62.42 (C2); 53.93 (C H2Ph); 48.95(C5); 37.55 (C8, C3); 22.26 (C4); 2.73 (C H3CN) */UV /Vis (103 M, DMF): l nm (log  /)/296.0 (3.7) */MS (m /z)(MeOH / CH3CN): 648 ([Cu(4)(MeOH)]ClO4), 571 ([Cu(4)(MeOH)]ClO4-Ph), 91 */TG analysis: 0.300 mg weight loss (6.13% of 4.89 mg complex; expected weight loss: 6.23%) at 78 8C (NCCH3). 4.3.2. Manganese complexes 4.3.2.1. General procedure. To a solution of ligand (1 mmol) in ethanol (30 cm3) was added MnCl2 ×/4H2O (198 mg, 1 mmol) and NH4PF6 (162 mg, 1 mmol) and the mixture was refluxed for 3 h. In the case of amide

ligands, the precipitated white product was filtered and the filtrate was concentrated by rotary evaporation to give other crop of the white solid. The combined solids were washed with small portions of ethanol and then dried in vacuo. For amine ligands the solvent was evaporated until 5 ml and the addition of ethyl ether causes the precipitation of a brown solid which is filtered, washed and dried in vacuo. 4.3.2.2. [Mn(1)Cl(H2O)]PF6 (9). White */Yield: 57% */m.p.: 194.7 8C */LM (10 3 M, V1 cm2 mol 1, CH3CN) /136 /147 */C16H24ClF6MnN4O3P (556): Calc. C 34.6; H 4.3; N 10.1; Mn 9.9; Found: C 34.5; H 4.5; N 10.0; Mn 9.9% */IR (KBr, cm1): n/ 3370, 3186 (N /H); 1682, 1638 (C /O); 1598 (C /C); 842 (P /F) */UV /Vis (10 3 M, DMF): l nm (log  /)/ 287.0 (3.0)*/MS (m /z ): 357 ([Mn(1)]2); 303 (1/1) */ TG analysis: 0.158 mg weight loss (3.10% of 4.97 mg complex; expected weight loss: 3.22%) at 104 8C (H2O). 4.3.2.3. [Mn(2)Cl(H2O)]PF6 (10). Brown */Yield: 69% */m.p.: 184.7 8C */LM (10 3 M, V1 cm2 mol 1, CH3CN) /160 /170 */C16H28ClF6MnN4OP (527.5): Calc. C 36.4; H 5.3; N 10.6; Mn 10.4; Found: C 36.5; H 4.9; N 10.2; Mn 9.9% */IR (KBr, cm 1): n/ 3394, 3200 (N /H); 1618 (C /C); 836 (P /F) */UV /Vis (10 3 M, DMF): l nm (log  /) /340.0 (2.8); 290.0 (2.9)*/MS (MeOH /H2O)(m /z ): 455 ([Mn(2)]PF6 /F); 382 ([Mn(2)Cl(H2O)] ); 329 ([Mn(2)]); 275 (2/1) */ TG analysis: 0.170 mg weight loss (3.38% of 5.03 mg complex; expected weight loss: 3.41%) at 98/102 8C (H2O). 4.3.2.4. [Mn(3)Cl(H2O)]PF6 (11). White */Yield: 70% */m.p.:/200 8C */LM (10 3 M, V 1 cm2 mol 1, CH3CN) /156 /167 */C30H34ClF6MnN4O3P (735.5): Calc. C 49.0; H 4.9; N 7.6; Mn 7.5; Found: C 49.5; H 4.9; N 7.2; Mn 7.9% */IR (KBr, cm1): n/ 3486 (O /H); 3371, 3186 (N /H); 1686 (C /O); 1598 (C /C); 836 (P /F) */UV/Vis (103 M, DMF): l nm (log  /)/290.0 (2.9) */MS (m /z)(MeOH /CH3CN): 729 ([Mn(3)Cl(MeOH)]PF6 /F); 537 ([Mn(3)]); 483 (3/ 1) */TG analysis: 0.109 mg weight loss (2.34% of 4.64 mg complex; expected weight loss: 2.45%) at 114 8C (H2O). 4.3.2.5. [Mn(4)Cl(H2O)]PF6 ×/H2O (12). Brown */ Yield: 60% */m.p.: 165.8 8C */LM (103 M, V 1 cm2 mol 1, CH3CN) /146 /150 */C30H42ClF6MnN4O2P (725.5): Calc. C 49.6; H 5.8; N 7.7; Mn 7.6; Found: C 49.3; H 5.9; N 7.4; Mn 7.4% */IR (KBr, cm1): n/ 3496 (O /H); 3271, 3200 (N /H); 1600(C /C); 840 (P/ F) */UV /Vis (10 3 M, DMF): l nm (log  /)/326.0 (2.3); 284.0 (2.5)*/MS (m /z ): 509 ([Mn(4)]); 455 (3/ 1) */TG analysis: 0.259 mg weight loss (4.87% of 5.32

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mg complex; expected weight loss: 4.96%) at 108 / 119 8C (H2O).

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all goodness of fit S are based on F 2, conventional R factors (R ) are based on F .

4.4. Catalytic experiments 4.4.1. Cyclopropanation: general method To a stirred mixture of styrene (3 mmol) and a catalyst (0.02 mmol), alkyl diazoacetate (alkyl /ethyl, t-butyl) (4.12 mmol) was added dropwise with a syringe over a period of 2 h in an N2 atmosphere at 50 8C. After the evolution of N2 ceased, a mixture of ethyl cis / trans -2-phenylcyclopropanecarboxylates was obtained. Chemical yields were determined by GC and the enantiomeric excesses were measured by gas chromatography with a chiral glass capillary column (mixture of methylsilicone (OV-1701) and methylsilicone-heptakis[2,3-dipentyl-6-(t-butyldimethylsilyl)]-b-cyclodextrin as stationary phase) [21]. 4.4.2. Oxidation of sulfides: general method In a typical oxidation reaction the catalyst (0.01 mmol) was added to a dichloroethane solution of the substrate (sulfide, 1 mmol) and 4-methylmorpholine Noxide monohydrate (0.1 mmol). The mixture was allowed to desired temperature and the oxidant NaOCl (pH 11.3, 1.9 mmol) was added. Chemical yields and the enantiomeric excesses of methylphenylsulfide were measured by gas chromatography with a chiral glass capillary column [21]. The ee for (2-ethylbutyl)phenylsulfide was determined by 1H NMR using (/)MPPA ((R )-(/)-a-methoxyphenylacetic acid) [22] as chiral shifting agent. 4.5. X-ray crystallographic study A summary of the fundamental crystal and refinement data is given in Table 1. A red crystal of 5a showing well defined faces gave a poor spectrum at 143 K, but good enough to solve the structure. That crystal was mounted on a Brucker /Siemens Smart CCD diffractometer equipped with a normal focus, 2.4 kW sealed tube X-ray source (Molybdenum radiation, l/ ˚ ) operating at 50 kV and 20 mA. Data were 0.71073 A collected over a quadrant of the reciprocal space by a combination of two frame sets. The cell parameter was determined and refined by least-squares fit of all reflection collected. Each frame exposure time was of 10 s covering 0.38 in v . The crystal to detector distance was 6.05 cm. Coverage of the unique set was over 92% complete to at least 238 in u. The first 50 frames were recollected at the end of the data collection to monitor crystal decay showing a lack of around a 60% of the intensities. The structure was solved by Multan and Fourier methods using SHELXTL [23]. Full matrix leastsquare refinement was carried out using SHELXTL [23] minimising w (F02/Fc2)2. Weighted R factors (Rw) and

5. Supplementary material Crystallographic data (excluding structure factors) for the structure(s) reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC167020. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: int. code / 44(1223)336-033; E-mail: [email protected]].

Acknowledgements The authors acknowledge the valuable help of Mr. J.A. Esteban Perales for the preparation of ligands and the financial support from the Direccio´n General de Investigacio´n Cientı´fica y Te´cnica of Spain (Project MAT2000-1768-C02-02).

References [1] (a) R. Noyori, Asymmetric Catalysis in Organic Synthesis (ch. 2), Wiley, New York, 1994, p. 16; (b) H. Takaya, T. Onta, R. Noyori, in: I. Ojima (Ed.), Catalytic Asymmetric Synthesis (ch. 1), VCH, New York, 1993; (c) J. Halpern, in: J.D. Morrison (Ed.), Asymmetric Synthesis, Academic Press, New York, 1985, p. 5; (d) E.N. Jacobsen, A. Pfaltz, H. Yamamoto (Eds.), Comprehensive Asymmetric Catalysis, Springer, Berlin, 1999. [2] (a) F. Fache, E. Schulz, M. Lorraine Tommasino, M. Lemaire, Chem. Rev. 100 (2000) 2159 /2231; (b) A. Togni, L.M. Venanzi, Angew. Chem., Int. Ed. Engl. 33 (1994) 497 (and references therein); (c) F. Fache, B. Dunjic, P. Ga´mez, M. Lemaire, Topics in Catalysis 4 (1997) 201. [3] P. Ga´mez, F. Fache, P. Mangeney, M. Lemaire, Tetrahedron Lett. 34 /43 (1993) 6897. [4] (a) T. Ohkuma, H. Ooka, S. Hashiguchi, T. Ikariya, R. Noyori, J. Am. Chem. Soc. 117 (1995) 2675; (b) T. Ohkuma, H. Ooka, S. Hashiguchi, T. Ikariya, R. Noyori, J. Am. Chem. Soc. 117 (1995) 10417. [5] P. Ga´mez, B. Dunjic, M. Lemaire, J. Org. Chem. 61 (1996) 5196. [6] U. Leutenegger, A. Madin, A. Pfaltz, Angew. Chem., Int. Ed. Engl. 28 (1989) 60. [7] (a) M.J. Alco´n, M. Iglesias, F. Sa´nchez, I. Viani, J. Organomet. Chem. 601 (2000) 284; (b) M.J. Alco´n, E. Gutierrez-Puebla, M. Iglesias, A. Monge, F. Sa´nchez, Inorg. Chim. Acta 306 (2000) 116. [8] F. Dallavalle, G. Folesani, G. Pelosi, M.B. Ferrari, G. Galaverna, R. Corradini, R. Marchelli, J. Coord. Chem. Rev. 51 (2000) 135. [9] A. Elduque, F. Aguilera, F.J. Lahoz, J.A. Lo´pez, L.A. Oro, M.T. Pinillos, Inorg. Chim. Acta 274 (1998) 15. [10] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.

92

M.J. Alco´n et al. / Inorganica Chimica Acta 333 (2002) 83 /92

[11] M.F. Doyle, M.A. McKervey, T. Ye, Modern Catalytic Methods for Organic Synthesis with Diazo Compounds, Wiley, New York, 1998. [12] A. Pfaltz, K.M. Lydon, M.A. Mckervey, H. Charette, H. Lebel, Cyclopropanation and C /H insertion reaction, in: E.N. Jacobsen, A. Pfaltz, H. Yamamoto (Eds.), Comprehensive Asymmetric Catalysis, vol. 2 (Ch. 16), Springer, Berlin, 1999. [13] (a) A. Carmona, A. Corma, M. Iglesias, F. Sa´nchez, Inorg. Chim. Acta 244 (1996) 79; (b) A. Carmona, A. Corma, M. Iglesias, F. Sa´nchez, Inorg. Chim. Acta 244 (1996) 239; (c) M.J. Alco´n, A. Corma, M. Iglesias, F. Sa´nchez, J. Mol. Catal., A: Chem. 144 (1999) 337. [14] (a) D. Mu¨ller, G. Umbrich, B. Weber, A. Pfatz, Helv. Chim. Acta 74 (1991) 232; (b) T. Ichiyanagi, M. Shimizu, T. Fujisawa, Tetrahedron 53 (1997) 9599. [15] (a) M.M. Diaz-Requejo, T.R. Belderraı´n, M.C. Nicasio, P.J. Pe´rez, Organometallics (2000) 285 /289;

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

(b) M.M. Diaz-Requejo, T.R. Belderraı´n, M.C. Nicasio, P.J. Pe´rez, Organometallics 2601 (1998) (1999) 351. J. Drabowki, P. Kielbasinki, M. Mikolayczyk, Synthesis of Sulfoxides, Wiley, New York, 1994. P. Lindberg, P. Nordberg, T. Alminger, A. Bra¨ndstro¨m, B. Wallmark, J. Med. Chem. 29 (1986) 1327. M.J. Alco´n, A. Corma, M. Iglesias, F. Sa´nchez, J. Mol. Catal. A, Chem. 178 (2002) 253. I. Cso¨regh, P. Kierkegaard, R. Norestam, Acta Crystallogr., Sect. B 31 (1975) 314. M.J. Alco´n, M. Iglesias, F. Sa´nchez, I. Viani, J. Organomet. Chem. 634 (2001) 25. E. Miranda, F. Sa´nchez, J. Sanz, M.I. Jimenez, I. MartinezCastro, J. High Resol. Chromatogr. 21 (1998) 225. P.H. Buist, D. Marecak, Tetrahedron: Asymmetry 6 (1995) 7. G.M. Sheldrick, SHELXTL Program for the Refinement of Crystal Structures, University of Go¨ttingen, Go¨ttingen, Germany, 1997.