Indian Journal of Chemistry Vol. 44A. November 2005, pp. 2240-2246

Synthesis, characterization and catalytic activity of fl-phenoxodicopper complexes with bi-Schiff bases derived from a-amino acids

Jun-Fa Wei* & Xian-Ying Shi School of Chemistry and Material s Science, Shaanxi Normal University, Xi ' an 710062, P R ChinJ

Email: weijf@snnu .ed u.cn;shixy @snnu .edu.cn

Received /3 July 2005; revised 3 Septelllber 2005

Several dicopper compl exes and re le vant dimetal complexes have been sy nthesized with the bi -Schiff base ligands formed by 2,6-diformyl-4- methy lphenol (HDFA) with g lyci ne, L-phenylalanine, L-hi stidine or hi stamine, and characteri zed by e lemental analys is, IR, UV-v is, CD, EPR , and XPS. Using the CU2 co mplexes as mode ls of dopamine fi- hydroxy lase (D,BH) and peptidylg lyc ine a-hydroxylation monooxygen a ~e (PHM), we have in vestigated the epox idation of styrene with PhlO as the monooxygen donor. The results show that styrene oxide is the main product of epoxidatio n of sty rene, and that no benzaldehyde is formed as the by-product. Turnover numbers (TNs) of each model comp lex in epoxidat ion o f styrene are 4.7, 3. L 2.S, and 2 .5 mol- I C Uz. fo r the complex de ri ved from g lyc ine, pheny lalan ine, L-hi stidine, and hi stam ine, respec­tive ly . EPR study reveals that a hypervale nt iodine oxo inte rmediate C uCu <--o-lPh mi ght be formed as the active spec ies. ruling o ut the poss ibility of fo rmation of the hyperva le nt meta l-oxo species C u(III)=O in thc oxidation course .

IPC Code: Int. C I7 C07C25 1/02; C07F I lOS

Copper-containing proteins and enzymes, such as he­mocyanin (Hc), tyrosinase (Tyr), dopamine fJ­hydroxylase (OfJH), peptidylglycine a-hydroxylation monooxygenase (PHM), and particulate methane monooxygenase (pMMO) have biological importance. For applications related to biological oxidations and developing biomimetic catalysts employed in selec­tive oxidation of organics, these copper-containing proteins, enzymes and the complexes mimicking them have been continuously an active and spectacu lar re­search area 1-4. In the past two decades, many ingenu­ity model complexes with a binuclear cupric core have been reported. Most of them mimic hemocyanin and tyros inase5

.6

. However, only a few reports involve the model complexes towards CU2 core containing monooxygenases such as OfJH and PHM . Recently , Blain et al. 5 have reported a model system in which intramolcular hydroxylation takes place on the ligand of model complex itself.

OfJH is a monooxygenase containing a dicopper core existing in the renicapsule marrow of mammal3

.

Its biological function is catalyzing the fJ-hydroxyla­tion of dopamine to noradrenalin , one of the renicap­su le hormones. PHM is a dicopper core containing monooxygenase existing in the body of mammals, responsible for the C-terminal a-amidation of bioac­tive polypeptides and neuropeptides2. [n add ition, OfJH and PHM can catalyze epoxidation of alkenes and hydroxylation of alkanes7

- '2, which are generally

considered to be of great importance in organic sy n­theses and petro-chemical industry. As a conti nuati on of our research on mimicking OfJH and MMO, we report here some dicopper complexes of the bi s-Schiff base ligand derived from 2,6-diform yl-4-methylphenol with some amino acids, and their cata­lytic ability as models of OfJH and PHM in styrene epoxidation us ing PhlO as a terminal oxidant.

Materials and Methods All the reagents used were of AnalaR grade. 2,6-

Oiformyl-4 -methylphenol was prepared by catalytic oxidation of 2,6-di(hydroxymethyl )-4-methy Ipheno l, as described previously' 3. M.pt. 130°C (Ref 8 ; m.pt. 127-129D C). [odosylbenzene was also prepared by reported procedure. M.pt. 2l0D C (decom) (Re f 9 ; m.pt. 2 10°C (decom). Solvents used for physical measurements and epoxidation were purified before use.

Carbon, hydrogen and nitrogen analyses were per­formed with a Cario-Erba-l106 elemental analyzer. Halides were determined by the Volhard titration. Conductivity measurements were carried out with a ~~S- II A mol ar conductometer in ethanol soluti on at 25 DC. IR spectra were recorded on a Nicolet 10 OX Fourier transform infrared spectrophotometer. Elec­tronic spectra were performed on a Sh imadzLl UV365 spectrophotometer using a so luti on sealed in quartz cell s, and EPR spectra in X-band (ca . 9.5 GHz) were

WEI & SHI : /.l-PHENOXODICOPPER COMPLEXES OF a-AM INO ACID BI -SCHI FF BASES 2241

performed on a Varian E-115 instrument using DPPH as reference material. XPS spectra were obtained on a Perkin-Elmer PHI-550 spectrometer using Mg K" ra­diation and operating at a pressure of 10-8 Pa and cov­ering the energy region for all elements contained . The binding energies were referenced to the hydro­carbon component in C I s envelope defined at 284.6 eV to compensate for surface charging.

Synthesis of complexes

CulDFAgly)Cl (J )

This complex was prepared as already reported 14 .

0.420 g of greeni sh powder was obtained (Yield 96%).

Cuz(DFAphe)Cl·H]O (2)

HDFA (0 . 164 g, 1.00 mmol) was dissolved in ethanol (20 mL). To this soluti on, an aqueous so lution containing 0 .330 g (2.00 mmol) of L-phenyla lanine and 0 . 12 g (3 :00 mmol) of NaOH was added. After the solution was reflu xed for 30 min wi th stilTing, an ethano lic solut ion containing 0.34 1 g (2.00 mmol) of CuCb·2H20 was added . Then, the solution was heated and stirred for 2 h. After the resulting mixture was cooled to room temperature, water (100 mL) was added to the reaction mixture. The light greenish powder was obtained by filtration , which washed with I : 1 ethanol-water. Yield 0.490 g (77 %).

Cuz(DFAhist)Cl·UhO (3 )

HDFA (0.164 g, 1.00 mmol) was di ssolved in ethano l (20 mL). To this solutio n, an aqueous solution containing 0. 3 11 g (2.00 mmol) of L-histidine and 0 .12 g (3.00 mmol) of NaOH was added, followed by stirring al ambient temperature for 15 min . Then , an ethanolic solu tion contai ning CuCh ·2 H20 (0 .34 1 g, 2.00 mmol) was added, and the resulting mixture was stirred for 2 h. After cooling it to the room tempera­ture, the light green powder was obtained by fi ltra­tion , washed with water and ethanol. Yield 0.533 g (84%).

Cuz(iso-DFAhist)Cl·3H 10 (4)

HDFA (0.164 g, 1.00 mmol) , L-hi stidine (0.31 1 g, 2 .00 mmol), and NaOH (0. 12 g, 3.00 mmol) were mixed in I : 1 ethanol-water (25 mL) and stirred at 60°C for 2 h. After the reaction mixture was kept

standing at 60°C for 2 days, an ethanolic so lu tion of CuCb·2H20 (0 .341 g, 2.00 mmol) was added and stirred at the same temperature for 2 h. The green

crystalline powder was collected by vacuum filtration , washed with I : 1 ethanol -water, recrystalli zed in etha­nol. Yie ld 0.587 g (90%).

Cuz(DFAhim)ClJ·H ]O (5)

HDFA (0.164 g, 1.00 mmol) was di ssolved in ethanol (20 mL). To this solu tion, histamine hydrogen chloride (0 .368 g , 2.00 mmol ) in an aqueous solution containing NaOH (0.08 g, 2.00 mmol) was added while warmed and stirred for 15 min . An ethanol so­lution of CuCI2·2H20 (0.34 1 g, 2.00 mmol) was added to this mixture. The reaction mi xture was stirred at 65°C for 2 h and then kept standing at room tem­perature overnight. The green crystalline powder was collected by vacuum filtration, washed with 1: I etha­no l-water, recrystallized in ethano l. Yi eld 0.445 g (74%).

ZIlz(DFAhist)CI·3H10 (6)

This complex was prepared as a white coloured powder (y ie ld 85%) according to the same procedure as complex 3 except substituting C uCb·2H20 by ZnCb.

Zllliso-DFAhisl)C/·3H 20 (7)

This complex was prepared as a white coloured powder (yie ld 8 1 %) according to the same procedure as complex 4 except substituting CuCb·2H20 by ZnCb.

Catalytic epoxidation and analyses of the reaction mixture

Catalyti c epox idation and analyses of reacti on . d d · I 1011 5 00 mIxture were o ne as repo rte prev Ious Y . . . .

mL purified acetonitrile, 0.005 mmol complex and 0 .5 mL freshly disti lled styrene were added to a 10 mL Schlenk tube. A high-puri fied ni trogen stream was bubbled to the mi xture to remove the resolved oxy­gen. Then, 0.45 mmol PhlO (0. 100 g) was added to the resulting mixture and electromagneticall y stirred

at room temperature (22°C) under nitrogen atmos­phere. After continuous stirring for 14 h, the resulting mi xture was left to stand for 30 min and 1.0 ~IL clear so luti on was extracted for GC analys is .

GC ana lyses were done wi th temperature pro­gram ming in the range of 130-230°C at a rate of 20°Chni n, FlO detection, and a 30 m quartz capillary coated with 2% PEG20M. Identificati o n and calibra­tions were performed using standard co mpounds and peak area and calibrati ng fac to r method. Every sam­ple was determined three times and the mean was adopted.

2242 INDIAN J CHEM, SEC A, NOVEMBER 2005

Results and Discussion Synthesis and structure of the complexes

Okawa and his coworkers had previously prepared CU2 complexes of the bi -Schiff base derived from g ly­cine and from alanine and the sy nthes is of analog complexes failed with other ami no acids'~. After care­fully repeating thi s experiment, we consider the exis­tence of equilibrium in such a template synthesis:

HDFA+2 NH2CHRCOOH+2 CuCb~

CU2C1 +3HCI

For the amino acids with a bulky group, such as phenyl in L-phenylalanine, the equi librium position shifts to left. As a result, the complexes are not eas i Iy obtained for those amino acids. Upon neutralization of HCI with equal molar of an alkali metal hydroxide, the equi librium reaction proceeds to right to give the CU2 complexes in higher yie lds. The complex can also be obtained successfu lly by using copper(IJ) salt of weak acid, such as cupric acetate, as the Cu(ll) source.

The li gand derived from L-histidine and 2,6-diformyl-4-methylphenol can form stab le C U2 com­plexes due to its poly-dentate coordination e nviron­ment. However, the y ields of the complexes increase along with addition of sto ichiometric amount of so­dium hydroxide. In our attempt to prepare this com­plex, the products obtained are different from each other both in appearance and spectrum . Light green coloured product was obtained with shorter reaction time, but a dark green product was obtained with longer reaction time and at higher temperature. The IR spectra of two complexes are different sign ifi ­cantly from each other. The former has a sharp peak at 1622 cm - I attributab le to imine C N groups, while the laller has no peak belonging to imine g roups. We have noted that the C=N group of the Schiff base formed from condensation of L-histid ine and a-hydroxyl benzaldehyde cou ld further carry out an intramolecular addition with imidazole group to give six-membered ring

,s.' 6 . Therefore, we suggest that the complexes obtained with longer reaction time wou ld have a structure shown in Fig. I (4, 7 ), while the complexes obtained in shorter time have the expected structure shown in Fig. I (2).

All of the complexes are stable in so lid state and insol uble in water except complex 5 and 6 . The com­plex 1 and 2 are soluble in methanol , ethanol, DMF, and DMSO. The complexes of bi-Schiff base of L-histidi ne with 2,6-diformyl-4-methylphenol and the annulated derivative are sparing soluble in ethanol, DMF, and DMSO.

The analytical data of each complex satisfies its expected s tructure well , as is shown in Table I . The data of molar conductivity indicate that all of the complexes belong to non-electrolyte, and are in agreement with the expected structures. It is worthy to note that complex 5 is of a 1:2 electrolyte in methano l with a molar conductivity of 22 1 S·cm2·moI- I

. Never­theless, in water the molar conductivity is even higher than those of 1:2 electrolytes perhaps due to ioniza­tion of the bridged chloride atom. However, the value of molar conductivity is 26 S'cm2 'mol ' l for the same comp lex in e thanol , indicating that it belongs to non­electrolyte (Geary '7indicated that the molar conduc­tivities are in the range of 35 to 45 S·cm2·mor l for I : 1 electrolytes, and of 70 to 90 S'cm2 'mor l for 1:2 elec­trolytes in ethanol). This means that each non­bridging C I atom in the complex is capable of main­taining its coordination to a Cu(l I) core as the fifth ligand in ethanol so lutio n. But in more polar so lvents, these C I atoms could not keep its linkage to metal at­oms, librat ing free Cl anions. In water, which is a more polar solvent, even the bridged C I may be sub­stituted by OH-, so that the molar conductivity is much higher.

TG-DT A curves of CU2 and Zn2 co mplexes (3 and 6) of the bis-Schiff's base derived from L-hi stidine

show a weight-loss of 6.02% at 65-1 20°C for 3 and of

1 M=C .. R=H, X-CI

2 M=C ... R=PhCH1, X=el

4 M=C .. X~I

7 M-Zn,X=C1

Fig . I - T he sugges ted structures of the model complexes.

WEI & SHI: )l-PH ENOXODICOPPER COMPLEXES OF a-AMINO ACID BI-SCHI FF BASES 2243

Table I - Elemental analysis. electronic spectra and molar conducti vities of the complexes (25°C in DMSO)*

No.

1

2

3

4

5

6

7

C

35 .54

50.77

39.59

38.7 1

38.05

38.41

38.29

Detd

H

2.58

4.05

3.73

3.89

3.90

3.8 1

3.78

Mi croanal:tsis

N X C

6.33 8. 17 35.66

4.36 5.69 50.98

13.22 5.65 39.78

12.83 5.4 1 38.68

13.87 17.8 1 37 .98

12.69 5.5 1 38.68

12.77 5.48 38.68

*The data in parentheses are those determined in ethanol.

H

2.53

3.96

3.66

3.86

3.85

3.86

3.86

8.46% at 60-1 10°C for 6, corresponding to 2 (calcd wt. loss 5 .68%) and 3 mol H20 (8.24%), respective ly. The low temperature for loss of water molecules means they do not coordinate to metal cores in the complexes. The weights of residues are 24.58 and 23.98%, corresponding to 2 mol of CuO (cal cd wt 25.09%) and 2 mol of ZnO (24.82% calcd wt) , pro­viding another support for the composition of these complexes . These results and the JR , UV-vis, XPS , and EPR inves tigations indicate that the complexes have the structure showed in Fig. I .

IR spectra

The bands occurring at 1680 and 1667 cm-- I which are attributable to Vc =o of two -CHO in 2,6-diformyl-4-methylphenol disappear in the complexes, meaning that two -CHO groups transform to Schiff's bases. The IR spectra of complexes 1 and 2 are similar to each other due to their similar structure. The absorp­tions between 1650 and 1630 cm - I are contri bu ted to Vc=o of - COO- and to VC=N of imine groups, respec­tively . A separation of 234 cm- I between Vns and Vs

implies that the carboxylic groups participate in the coordi nation 18. The peaks appeari ng at 1600 and 1450 cm - I can be assigned to the skeleta l vibration of ben­zene ri ng, and the peaks in the range of 1450- 1440 cm - I to VC-D. For compl ex 5, a peak appears at 1633 cm - I, similar to the complexes reported in the lite ra­ture l6 and our prev ious paper 'o. The bands observed at 3264 and 3120 cm- I are attributed to VN-H and Ve -I I of imidazole groups .

The IR spectrum of compl ex 3 , which contain s both carboxy li c groups and imidazole groups, shows the characteristic peaks both of complex 1 or 2 and of complex 5, such as the peaks at 323 1 cm- I and 3 140 cm - I attribu table to VN-H and VC-I-I of imidazole, the

UV -v is Am •• Conductivity, 1\ Calcd (nm ) (S'cm2'mol- ')

N X

6.40 8.10 390 693 8. 10

4.43 5.57 39 1 (388) 673(650) 7.49

3.26 5.59 430 498 3.26

12.89 5.44 4.68

13.99 17 .70 378(380) 680(663) (26 .0)

12.89 5.44 397 450 6.11

12.89 5.44 4.23

broad band at 1622 cm - I to VC=N and Vas coo- , and a peak at 1433 cm- I to Vc-o. In other words, the IR spectrum of complex 3 is commensurate to a super­imposition of the spectra of complex 1 and 5. The IR spectrum of the Zn2 analogue complex is similar to those of CU2 complexes.

Electronic spectra and circular dichroism (CD)

On the e lectronic spectra of complexes 2 , 5 , and 3 , there is an absorption band at 393, 373, and 430 nm (Table 1), contributing to imine groups C=N. The complex 3 shows an addition absorption band at 498 nm . On the spectra of complexes 4 and 7, these ab­sorption bands disappear as imine groups disappear. The dod transition of 1 appears at 693 nm in DMSO compared with previously reported 680 nml4. Thi s mi ght be ex plained as that DMSO coordinates to cu­pric atoms at axial position of CU2 coordination plane to form an di storted octahedral geometry . r n contrast, the coordination of DMSO was hindered by benzyl groups in 2 to maintain the planarity of square coordi­nati on so that the dod transition appears in the region of hi gher frequency 19. Complex 5 shows a dod transi ­tion at 672 nm in ethanol so lution, and at 687 nm in DMSO solution, cOITesponding to quadrilateral plane geometry and di storted octahedral geometry caused by ax ial coordinated so lvent molecules, respectively .

Com plexes 2, 3 , 4, 6, and 7 are asymmetric mole­cu les in which there ex ists a ch iral axia l C2 along the linkage of C H j of benzene ring to phenoxo atom. They are , ~h erefo re, active in circu lar dichroi sm. For complex 3, the negative Cotton effect at 418 11m is attributed to imine (C=N) groups. The shoulder at 520 nm corresponds to the band at 498 nm in its elec­tron ic spectrum. The Cotton effect occurring at 700 nm is assigned to the dod transition .

2244 IND IAN J CHEM, SEC A, NOVEMBER 2005

XI}S studies

It can be seen from Tabl e 2 and Fig. 2 that the electro n binding energies (E' ) of CU2P3!2 in the com­pl exes decrease in compari son with that in C uC I2.

This might be ex plained as that CuO I) cores accept the lone pairs of e lectrons from the coordinati o n at­oms of the ligand and bridging C I or 0 ato m to en­large the e lectric c louds of out-sphere. As a result, the E' of CU2P3/2 depresses upon the complex formation . The most negative chemical shi ft (!1E!') of CU2P3/2 in 3 would be due to the fact that it has more coordina­tion ato ms in the ligand .

As ex pected, the coordination atoms exhibit posi­tive chemical shifts in complex formation. The bridging CI atom in 2 and in 3 shows a more positi ve chemical shi ft since the bridg ing Cl ato m donates two lone pairs to two Cu cores, leading the e lectron cloud more depressed. The three CI atoms in 5 show a broad dissymmetric peak which can be resolved into two peaks with a ratio of 1:2 by Gauss 's method. The cor­responding t.~'s are 199.6 and 198. 1 eV respectively . The former is assigned to the bridgi ng CI ato m, which shifts to the end of higher energy by 0.2 eV in com­pari son with that of Cl anion in CuCI2. The latter is assigned to the two axial coordinated CI atoms of which the E' falls in the region between that of CuCh

Table 2 - The characteristic e lectron binding energ ies (£') and chemical shifts (I'!.£') of several elements in CuCI2 and some of

the complexes (in eV)

Compo CU2PJI2

CuCI2 E!' 936.0

2 E' (I'!.£') 935.6 (- 0.4)

5 £' (I'!.£') 935.2 (- 0.8)

3 E!' (t'J.£') 935.0(-1.0)

a

::=~ ~

950

b

CI2p

199.4

199.7 (+0.3)

199.6 (+0.2), 198. 1 (- I.3)

199.8 (+ 0.4)

Nl s

400.2

399.4

400.0

5

Fig. 2 - XPS of (a) CU2P312 in the complexes 2, 5, 3, and CuCI2;

(b) CI2p ill complex 2.

( 199.4 eV) and that of KCl ( 197 .8 eV according to the standard spectrum2U

), but more close to that of KCI. T hi s means that these two fifth ligands coordinate to cupri c atom too weakly to maintain the linkage with meta l ions. In other words , these CI atoms are c lose to free cr anions in ionic compounds.

The N Is of a ll complexes are higher than those of uncoordinated N atoms in com mon organ ics (Eb of N Is of amino nitrogen ;::; 398 eV20

), indicat ing that the N ato ms of ligands parti c ipate the coordination.

EPR studies

EPR spectrum of complex 2 shows a sy mmetric broad signal centered at g=2. 1 t6 (Figs 3 and 4) having a line shape characteristic of a planar dinuclear

--2J22 3

Fig . 3 - EPR spectra of the complexes 2, 5, and 3 (293K*X-band).

---

-----

Fig. 4 - EPR spectra of complex 2 before and after reaction with PhIO.

WEI & SHI: ~-PHENOXODICOPPER COMPLEXES OF a-AMINO ACID BI-SCHIFF BASES 2245

Cu(lI) core. Complex 5, g>gj>2, which is the char­acter of D4h field, indicates it has a pyramid structure. The EPR spectrum of complex 3 is quite complicate, but has the shape characteristic of binuclear cupric complexes.

Catalytic activity With iodosylbenzene PhIO as the monooxygen do­

nor, the styrene was epoxidized to styrene oxide alone using the CU2 complexes modeling D,BH as catalyst. There is no benzaldehyde formed as the concomitant by-product. A controlled experiment shows that no oxygenated product was observed in absence of PhIO or of model complex, indicating that both monooxy­gen donor and model complex are indispensable to the oxidation reaction. Based on the turnover numbers (TNs), the catalytic abilities of model complexes 1, 2, 3, and 5 (See Fig. 5 for structures) are 8.7, 6.1, 2.8, and 2.5 mol- J

, respectively . Complex 1 is the most active one. But, structurally similar complex 2 is slightly less active. This might be explained as that the coordination of PhIO to the CU2 core of complex 2 is influenced by phenyl rings of the complexing arms derived from phenylalanine, while in complex 1, there is no bulky groups on complexing arms derived from glycine.

Complexes 3 and 5 are rather less active perhaps due to their structure. For complex 3, the imidazole groups of complexing arms coordinate favourably to cupric atom from the axial direction . Thus, the axially coordinated imidazole group on one Cu(Il) nuclear has certain hindrance to the empty site on the neigh­bouring Cu(n) nuclear, unfavourable for PhIO to ac­cess to Cu(U) to form high-valent iodine oxo coordi­nation compound CuCu~O=IPh.

In complex 5, two non-bridged CI atoms coordinate axially to each cupric core. Although, this coordina­tion is too weak to keep the coordination in high polar solvent such as water and methanol solution (it be­haves as a 1:2 electrolyte because these coordinated chloride atoms can be ionized completely in aqueous or methanolic solution), it is strong enough to keep the CI atoms in coordinate sphere in ethanol and in less polar solvent-acetonitrile, in which the epoxida­tion reaction occurs. Thus, the influence of axially coordinated CI atoms on the coordination of PhIO is similar to that of imidazole groups in complex 3 .

EPR is one of the most powerful tools to obtain the information of reaction intermediates. For complex 2, EPR splits to multi peaks with hyperline structure (see

2

3 (1m; imidazole group) 4

Fig. 5- The suggested structures of the model complexes 1,2,3,5.

Fig. 3) from the broad singlet peak upon PhlO addi­tion. This means that a hypervalent iodine-oxo inter­mediate CuCu~o-IPh might form as the active spe­cies when complex 2 reacts with PhIO, rather than the high-valent metal oxo M=O intermediate existing in metalloprophin, metallophthalocyanin, and dinuclear complexes of Cr(lII), Mn(IIJ), or Fe(IIl)8-9. From the theoretical viewpoint, if a Cu(lII)=O species were formed as an intermediate in the course of reaction , it might be EPR silence because the Cu(III) nuclear with d8 structure is an antimagnetic species due to the fact that all of the d electrons are coupled whether in square field or square pyramid field. We noted that Cu(III) peptide complex formed by oxidation of Cu(n) peptide complex with an Ir(III) compound has EPR silence21 . In contrast, EPR signal of complex 2 does not disappear upon reaction with PhIO. Hence, the Cu(III)=O species are impossible to be the active intermediate in the course of epoxidation of olyfins by using PhIO as monooxygen donor.

Conclusions The CU2 complexes described herein mimiC D,BH

and PHM nicely on the aspect of catalyzing epoxida­tion reaction of external alkenes with PhIO as termi­nal oxidant. The formation of Cu(III)=O as the inter­mediate active species in the reaction course is ruled out. This would be helpful to clarify the argument on the CuCu~o-IPh or Cu(JII)=O as the active inter­mediate.

2246 INDI AN J CHEM, SEC A, NOVEMBER 2005

Acknowledgement This work was financially supported by the Na­

tional Natural Science Foundation of China (Grant 20172036), and Sino-France Cooperation Project of Ministration of Education and Natural Science Foun­dation of Shaanxi Province (Grant 2002810).

References I Klinman J P, Chem Rev, 96 (1996) 2541. 2 Kaim W & Rail J, Angew Chem. Int Ed Engl, 108 (1996) 43. 3 Prigge S T. Kolhekar A S, Eipper B A, Mains R E & Mario

A L, Science, 278 (1997) 1300. 4 Mukherjee R N, Indian J Chem, 42A (2003) 2175. 5 Blain I, Patrick S, Michel G, Thierry T & Marius R, Rev Mol

Biotech, 90 (2002) 95. 6 Patrick L H & William B T, Coord Chelll Rev, ( 1999) 190. 7 Blain r, Giorgi M, Riggi I D & Reg lier M, Ellrop J Inorg

Chem, (2000) 393. 8 Itho S, Nakao H & Berreau L M, J Alii Chelll Soc, 120 ( 1998)

2890. 9 Padgette S R, Wimalassena K & Herman H H, Biochelll. 24

( 1985) 5826.

10 Wei J F, Yu X D & Jin D S, Chin J Mol Catal. 12 (1998) 27 1 (in Chinese).

11 Ailludha P, Akilan P & Kandaswamy M, Polyhedron. 19, 2000, 1769.

12 Amudha P, Thirumavalavan M & KaIldaswalllY M, Polyhe­dron , 18 (1999) 1363.

13 Wei J F, Yu X D & Jin D S, Sci China (B) , 41 (1998) 247. 14 Okawa H, Kida S , Muto Y & Tokii T , Bull Chelll Soc Japall ,

46 ( 1973) 1462. 15 Casella L, Gullotti M & Pintar A, In org Chem, 26 ( 1987)

103 1. 16 Grzybowski J J, Merrell P H & Urbach F L, Inorg Chem, 17

(1978) 3078. 17 Geary W J, Coord Chem Rev, 7 ( 1971) 81. 18 Nakmoto K, Infrared and Raman Spectra of Inorganic alld

Coordination Compounds, 4th Edn (John Wiley and Sons, New York) 1986.

19 Chen J T, Liao D Z, Zhang R H, Chen H & Liu W X, Chem J Ch in Vniv, 13 ( 1992) 6 (in Chinese).

20 Ghosh P K, IlIIroduction to Photoelectron Spectroscopy (John Wiley and Sons, New York) 1983 .

2 1 Margerum D W, Chel1appa K L & Bossu F P, J Am Chelll Soc, 97 ( 1975) 6894.