Polyhedron Vol. 9, No. 14, pp. 1659-1666, 1990 0277-5387/90 $3.00+ .oO

Printed in Great Britain Pergamon Press plc

CONTRIBUTIONS TO THE CHEMISTRY OF SILICON- SULPHUR COMPOUNDS-LVII.” SYNTHESIS, MOLECULAR

STRUCTURE AND PROPERTIES OF CYCLO-TETRAKIS- [TRI-~~~~-B~OXYSIL~ETHIOLATOCOPPER~~,

[(t-C4H90),SiSCu],, THE FIRST EXAMPLE OF A SQUARE PLANAR Cu.& RING

BARBARA BECKER and WIESLAW WOJNOWSKI

Department of Chemistry, Technical University of Gdansk, PL-80-952 Gdatisk, Poland

KARL PETERS,? EVA-MARIA PETERS and HANS GEORG VON SCHNERING

Max-Planck-Institut fiir Festkijrperforschung, D-7000 Stuttgart 80, F.R.G.

(Received I2 December 1989 ; accepted 1 march 1990)

Abstract-The preparation of cyclo-tetrakis[tri-rert-butoxysiianethiolatocop~r(I)] from tri-terr-butoxysilanethiol and copper(I1) acetate or CuCl or Cu,O is described. The com- pound crystallizes as colourless monoclinic rods. The molecular structure is characterized by a nearly planar alternating ~u4S4-eight-mem~red ring with three-fold coo~i~t~ sulphur and two-fold coordinated copper atoms. According to the mass spectrum the tetrameric molecule is also preserved in the vapour phase. The compound was characterized s~ctroscopically by 29Si, I%, ‘H NMR, IR and UV. Reactions with triphenylphosphine, 1, IO-phenanthroline, and 2,2’-bipyridine afforded three adducts with formal stoichiometries RSCu- (PPh3)2, RSCu* phen and (RSCU)~ * bipy, respectively.

Many of the recent developments in metal thiolate chemistry were stimulated by studies on metallo- thioneins, a unique class of metalloproteins which are polyme~llic with exclusive coordination by the cysteine thiolate function.2 As copper is one of the most abundant metallic elements in nature, copper-thiolate chemistry is of considerable current interest.

Complexes formed by copper(I) and alkyl or aryl thiolate ligands are numerous and their structures show a great variety. Insoluble compounds with RSCu stoichiometry are presumed to be non-molec- ular in structure. 3*4 On the other hand, the struc- tures of monometallic linear [Cu(SC,HMe,- 2,3,5,6)& li and trigonal planar [Cu(SPh);]*- 6.7 anions, oligomeric copper(I) thiolate species such as tetrametallic [CU,(SR),]~- (R = Ph,6*8

* For part LVI, see ref. 1. t Author to whom correspondence should be addressed.

Me8), ~CU~[(SCH*)~~~H~]~~*- ’ and pen~metallic [Cu5(SPh)7]2-,‘0 [Cu,(SBu-t),]- “*I2 anions or octametallic neutral aggregates such as [Cu(SC,H2 Pr3-&13 are known. Molecular structures were also determined for several copper thiolates bearing additional ligands such as triphenylphosphine in Cu~(SPh)~(PPh~~4,‘4 Cu~(SPh)~(PPh~)4,‘5 Cu4 (SBu-t)4(PPh3)2,3 Cu4(SPh)4(PPh,)4,*6 bis(di- phenylphosphino)methane in Cu4[SC(CH&C2 H~l4[(PPh*)~CH212,” thioxanthate in Cu@&

HI 1)4(S2C%H11)4,‘~ pyridine nitrogen as in Cu6 (SC5H3NSiMe&19 or tetrathiomolybdate group as in [(PhS)CuS2MoSzf2- and [(PhS)CuSzMoSz Cu(SPh)12- anions.20

Some years ago we reported the preparation and molecular structure of the first silanethio- late, namely cyclotetrakis[tri-tert-butoxysilanethio- latosilver(I)], [(t-C4H90)$iSAg]4,2’ obtained by a reaction of tri-tert-butoxysilanethiol with silver nitrate in benzene-water. This was followed by syn- theses and molecular structure determinations of

16.59

1660 B. BECKER et al.

tri-zert-butoxysilanethiolates of thallium [(r-BuO), SiST112,** mercury [(t-Bu0)3SiS]2Hg,23 and lead {[(t-BuO)3SiS]2Pb}2. 24 All these silanethiolates were obtained with quantitative yields and in any case other products such as higher oligomers or polymers were found, suggesting that it is steric demand of the bulky (t-BuO),SiS ligand which probably reduces the tendency of thiolate sulphur to bridge metal centres and/or prevents close approach to thiolate units thus limiting the for- mation of oligomeric aggregates.

Copper complexes with silanethiolate ligands were never investigated. Herein, we report the preparation, molecular structure and some pro- perties of cyclo-tetrakisltri-rert-butoxysilanethio- latocopper(I)], [(t-C4H9@3SiSCu]4 structurally characterized copper complex.

EXPERIMENTAL

Syntheses

(i), the first silanethiolate

Tri-tert-butoxysilanethiol, (t-BuO),SiSH, was pre- pared as described previously. * 5 All other chemicals were commercial products. Solvents, if necessary, were dried according to common procedures.

Preparation of [(t-BuO)3SiSCu]4 (1)

Three synthetic routes to the title complex were developed :

Method A. To a solution of (t-BuO),SiSH (7 g, 25 mmol) in 50 cm3 of benzene, a solution of copper(II)ace (5 g, 25 mmol) in 25 cm3 of water was added and the resulting two-phase mixture shaken vigorously for ca 2 h until the silanethiol disappeared, as verified by TLC. The benzene layer was separated, washed twice with water, dried over magnesium sulphate and finally the benzene was removed in uacuo. The solid residue, contain- ing in addition to 1 also bis(tri-tert-butoxy- silyl)disulphide, was twice crystallized from iso- propanol-benzene (3 : 1 v/v) yielding 2.12 g of pure colourless 1; m.p. 222-223°C yield 50%.

Method B. Copper(I) chloride (1.070 g, 10.7 mmol), (t-BuO),SiSH (2.772 g, 9.9 mmol), anhy- drous Et,N (1.05 g, 10.5 mmol) and 20 cm3 of anhydrous benzene were mixed together under argon atmosphere and stirred for ca 30 min. Insol- uble material was then removed by filtration and washed with a further 20 cm3 portion of benzene. Both liquid phases were combined and evaporated to dryness in vacua. The solid residue was recry- stallized from i-PrOH-benzene, yielding 2.622 g of pure 1; m.p. as above, yield 74%.

Method C. A solution of (t-BuO),SiSH (0.560 g, 2 mmol) in 2 cm3 of anhydrous benzene was added to copper(I) oxide (0.144 g, 1 mmol) and the mixture refluxed with stirring under Ar for ca 7 h. Then 5 cm3 of benzene was added and traces of the remain- ing Cu20 were removed by filtration. Evaporation to dryness and subsequent recrystallization from i-PrOH-benzene afforded 0.585 g of pure 1; m.p. as above, yield 84%. Found : C, 42.0 ; H, 7.9. Calc. for Cu$4Si4012C48H10B: C, 42.0; H, 7.9%.

Reaction of 1 with triphenylphosphine

To a solution of l(l.370 g, 1 mmol) in 10 cm3 of anhydrous benzene, Ph3P (2.1 g, 8 mmol) was added, the mixture refluxed for 2.5 h under argon and then left overnight at room temperature. The deposited solid material was separated by filtration, washed with n-hexane and then recrystallized from hexane-ethanol (7: 5 v/v) affording 3.366 g of colourless plates; m.p. 154154.5”C. ‘H NMR spectrum : 7.20 ppm (m, 30H, CsHS), 1.35 and 1.15 ppm ; (two broad poorly separated singlets, 27H, CH3), and microanalytical data consistently indi- cated the composition (t-C4H90)3SiSCu*(PPh3)2; yield 97%. When the 1 to Ph3P molar ratio was only 1: 4 the same product was obtained with a yield of ca 45%. Found: C, 66.6; H, 6.6. Calc. for CuSSi03P2C48HS7: C, 66.4; H, 6.6%.

Reaction of 1 with 1, IO-phenanthroline monohydrate (phen - H *O)

Phen. H20 (0.396 g, 2 mmol) was added to 5 cm3 of anhydrous benzene and refluxed until a clear solution was obtained. Then to the hot solution a solution of 1 (0.685 g, 0.5 mmol) in 3 cm3 of an- hydrous benzene was added. The mixture which rapidly turned deep red was left to stand for 1 day at room temperature. The dark red crystals which grew were collected, washed with hexane and dried in vacua. 0.986 g of product was obtained ; m.p. 164166°C. Attempts to recrystallize the product from hot benzene resulted in partial decomposition. Microanalytical data suggested the composition (t- C4H90)$iSCu*phen; yield 94%. Found: C, 55.1; H, 6.7. Calc. for CuSSiN203C24H35: C, 55.1 ; H, 6.7%.

Reaction of 1 with 2,2’-bipyridine (bipy)

To a solution of l(0.785 g, 0.573 mmol) in 5 cm3 of anhydrous hexane a solution of bipy (0.358 g, 2.292 mmol) in 10 cm3 of anhydrous benzene was added. The mixture turned orange and after ca l- 2 min, fine pink-red crystals began to deposit. After 3 h, when the solution over the solid was colourless,

Contributions to the chemistry of silicon-sulphur compounds-LVII

Sil the crystals were collected, washed with hexane and dried in uacuo. 0.961 g of product was obtained, m.p. 186-188°C. From the hexane fraction, which analysed by TLC did not show the presence of starting I, the solvent was evaporated affording 0.175 g (- 50%) of unreacted bipy, identified by a mixed melting point. According to the above result aIso microanalytica data pointed to the com- position [(t-C4HgO),SiSCu]2 - bipy. Yield quan- titative. Found: C, 48.7; H, 7.5. Calc. for CuzSz Si2N206C34H62 : C, 48.5 ; H, 7.4%.

ANALYTICAL PROCEDURES

lh4ayer Enroma’rografiny

TLC was performed on Silufo1254 + 366 (Kaval- ier, Csss\) #ales wjti hexane-benzene ( 4 : 5 V}Y) as a mobile phase. The spots were visualized by UV (a pink-red spot of 1, RF = 0.85) and silver nitrate solution (in EtOH-Hz0 1 : 1) {black spot for 1 and trown spats Ear {(c-BuO)&!$, RF = a.66 aud (t-BuO),SiSH, RF = 0.57).

Carbon and hydrogen contents were determined by the microcombustion method.26 Melting points are uncorrected.

Spectral tnea.swemeenCs

Spectral measurements were performed as fol- lows : IR : 4000-400 cm-‘, Specord 751R (C.Zeiss), sorution in cc<4; UTd: sz$X.@-W,W cm-), Spe- CCDFh uu-YiS )C,ZP,,SS>, ~sxm--= M SCh%Dn h

hexane, argon atmosphere ; ‘H NMR : Varian 360A (60 MHz), solution in CC& (TMS int.) ; 13C NMR : Bruker AM 250 (v,, = 62.896 MHz), solution in (cDlJ3 /TMS i&J; ‘9sj WQR : IW.&er AM 25D (I vg = 49.689 MHz>, solution in CDcl, I’IWS int.), Cr(acac), as a relaxation reagent at room tem- perature with inverse gated broad band proton n&e decoupting; Mass spectrum: Vatian Mat 8230 (??.I., 70 eV), direct inlet.

SllO

Fig. I. Atom labeKing for the central Si4S4Cu4 part of the molecule of 1.

Crystal and molecular structure determination of 1

The crystal and molecular structure of 1 was ~e~ernirne~uya~m~ecry~~lr~rffraction~~~~.Fig-

ure 1 shows a perspective drawing of the central Si4S4Cu4 part of 1 with the atom labelling, and Fig. 2 a stereo pair of the whole molecule.

Atomic coordinates, displacement factor co- efficients, full lists of bond lengths and angles and Xjsrs oE F,,}Fc v&es ha,ave been deposited as supplementary data with the Editor, from whom copies are available on request. Atomic coordinates have also been deposited with the Cambridge Crys1allographic Data CenXre.

RESULTS AND DISCUSSION

The preparation of a new tetracopper(1) silane- thio’rate complex I@-C&O),SiSCuj, (13 is readily acGeue& commenting from e&z sopper(11) or copper(I), however, the synthesis of I starting from

Fig. 2. Stereo pair of the molecule of 1, hydrogen atoms are omitted for clarity.

1662 B. BECKER et al.

Table 1. Summary of crystal data, intensity collection and structural refinement for 1

Crystallographic section

Compound Empirical formula Molecular mass

a (pm) b (pm) c (pm) B (“) V(pm3 x 10e6) z d(calc) [g cm- ‘1 Crystal system Space group

Data collection

Diffractometer Radiation Monochromator Crystal size (mm) Data collection mode 0 range (“) Recip. latt. segment

Number of reflections measured Number of unique reflections Number of reflections F > 30(F) Linear abs. coefficient (mm- ‘) Abs. Correction

Structural analysis and refinement

Solution by Method of refinement

Parameter/F, ratio

K, K, Program used

1

Cu&Si40~JhH,08 1372.25 2478.7(15) 2472.1(27) 1271.4(7) 100.99(4) 7648(9) 4 1.192 Monoclinic c2/c

Nicolet R3m/V MO-K, Graphite 0.35 x 0.45 x 4.0 Wyckoff-scan 1.75-27.5 h=&32 k=0-32 I= -16-16 4091 3889 3878 1.31 *-scan

Direct phase determination Full-matrix LSQ. Hydrogen positions were calculated and refined isotropically 0.084 0.059, 0.064 Nicolet SHELXTL PLUS

copper(H) substrate as in eq. (1) :

4 Cu(OAc),+ 8 (t-BuO),SiSH-+

[(t-BuO)SiSCu14+2 [(t-BuO)$iS12

+8AcOH (1)

seems to be of minor preparative importance since the half amount of introduced silanethiol is con- verted to the appropriate disulphide, which must be subsequently separated from the desired copper(I) silanethiolate 1. On the other hand, the easy oxi- dation of silanethiol by copper(I1) salts, analogous to those known for organic thiols, may also serve as a source of bis(tri-tert-butoxysilyl)disulphide, prepared by us previously using the more con- venient oxidation of sodium silanethiolate by iodine, and characterized structurally.27

Much better results were obtained starting from copper(I) compounds. The route from copper(I) chloride and silanethiol, in the presence of tertiary amine as the HCl acceptor [eq. (2)], can be regarded

4CuCl+4(6BuO),SiSH+4 Et3N-

[(t-Bu0)3SiSCu]4+4Et,N*HCI (2)

as a classical one and gives a good yield of 1. The best results, however, were obtained for the simplest case where silanethiol reacts with copper(I) oxide forming 1 and water only as a byproduct [eq. (3)] :

2 CuO + 4 (t-BuO) ,SiSH -

[(t-Bu0)$iSCu14 + 2H20. (3)

This route has never been used before for the syn- thesis of copper thiolate complexes, maybe because

Contributions to the chemistry of silicon-sulphur compounds-LVII 1663

organic thiols are far less acidic than silanethiols.28 As we have shown previously, mercury23 and lead24 molecular tri-rert-butoxysilanethiolates can also be obtained by the same method with quantitative yields.

Crystal and molecular structure of 1

Cycle - tetrakis[tri - tert - butoxysilanethiolato- copper(I)] (1) crystallizes monoclinically as colour- less rods, melting at 222-223°C without decom- position. The crystal lattice parameters are given in Table 1, and the molecular structure of 1 is illustrated in Figs 1 and 2.

The molecule consists of four (t-BuO),SiSCu units, where every sulphur atom is triply coordinated and thus serves as a bridge for two adjacent, doubly coordinated copper atoms. The Cu4S4 core is almost planar since the mean shift of sulphur atoms from the Cu, plane was found to be only 32 pm. Such a structure type has never been observed previously for copper(I) thiolates although similar Cu4X4 cores have been found in other homoleptic

copper(I) complexes, namely (~-BuOCU)~,‘~ (Me3SiCH2Cu)430 and [CUCO(CO)~]~~’ (here the

Table 2. Selected bond lengths (pm) and

Cu4C04 cycle is distinctly non-planar). The mol- ecule of 1 is of 2-C2 symmetry (the two-fold axis passes through Cu(1) and Cu(3) atoms) and iso- morphous with tetrameric silver tri-tert-butoxy- silanethiolate, [(~-BuO)~S~SA~]~, whose prepara- tion and,molecular structure were described by us previously. 2 ’

For both copper and silver silanethiolates the discrete eight-membered cyclic molecular units of alternating metal and sulphur atoms exhibit no secondary metal . . . S interactions. This reflects the steric demand of the bulky tri-tert-butoxy- silanethiolate ligand which prevents any close approach of the molecules and precludes any sec- ondary bridging interaction to form oligomeric aggregates. In this sense the above silanethiolate ligand can be compared with the thiolate ligands which originate from (PhMe,Si),CSH and (Me,Si),CSH which, as it was shown recently by their investors Block and Zubieta,32 behave simi- larly affording silver thiolates with small Ag,& and Ag,S, cores, respectively.

Table 2 lists the selected interatomic distances and interatomic angles determined for the molecule ofl.

angles (“) for 1 (standard deviations in . .

parentheses)

Bond lengths

Cu(l)-cu(2) Cu(l)--Cu(2a) Cu(l>-S(1)

285.5( 1) 285.4( 1) 217.2(2)

Cu(2~~(3) Cu(2)_S( 1) Cu(2)-S(2a) Cu(3>-S(2)

284.6( 1) 217.5(2) 217.0(2) 216.1(2)

Si-S S&O C-O C-C

Cu(2)-Cu( I)-S( 1) Cu(Z)-Cu(l)---S(la) Cu(lt-cu(2~uu) cu(3)-cu(2bS(l) Cu(3)-Cu(2)--S(2a) cu(2)--cu(3tiS(2) Cu(2)-Cu(3)--S(2a) Cu(l>-S(lWu(2) Cu(2)--S( l)-Si( 1) Cu(3)-+2)--Cu(2a)

!&-Si-0 O-%-O Si-O-C o-c-c C-G-C

212.7(3k213.8(2); 150.7(6k161.6(8); 135.2(9)--142.6( 12) ; 137.4(19k150.5(20);

mean 213.2(2) mean 155.0(3) mean 138.7(5) mean 143.3(4)

Bond angles

49.0( 1) Cu(2)-Cu( l)-Cu(2a) 137.6(l) S(l)--Cu(l)_S(la) 90.5( 1) Cu(l)-Cu(2)-S(1)

138.7(l) Cu( l)--Cu(2)-S(2a) 48.8( 1) S(l>--Cu(2)_S(2a)

136.8(l) Cu(2)-Cu(3)-Cu(2a) 49.1(l) S(2)-Q(3)_S(2a) 82.1(l) Cu(l)-S(l)--Si(1) 94.5( 1) Cu(3)-S(2)-Si(2) 82.1(l) Si(2)--S(2)-Cu(2a)

104.8(3k112.9(2); mean 109.9( 1) 106.6(4k111.6(5); mean 109.0(2) 144.6(6)-157.0(9); mean 149.6(3) 103.2(9)-l 14.2(12) ; mean 109.0(5) 101.2(13)--117.7(12); mean 109.8(5)

89.3(l) 173.4(l) 48.9( 1)

137.4(l) 172.0(2) 89.7(l)

174.0(l) 95.8( 1)

100.4(l) 100.9( 1)

1664 B. BECKER et al.

As observed previously for the isomorphous silver silanethiolate, *’ for copper(I)silanethiolate (1) the displacement of copper atoms from linear co- ordination towards the centre of the Cu& ring (S-&-S, average 172.8”) decreases the metal- metal distances. The d(Cu-Cu) value (285 pm), which is the same as determined for the closed [Cul&J4- cage,33 is, however, substantially larger than the Cu-Cu single bond distance (234 pm). Significant deviations from co-linear S-Cu-S bonds were reported for the [CU,&]~- cage anion (S-Cu-S angle, 166.9-170.9”),33 the neutral thiolate [Cu(SC6H2Pr3-z)ls, (S-&-S, average 177.5”),‘3 and also for the anionic thiolate com- plexes containing not only triply but also doubly coordinated copper-[Cu5(SBu-t)J (S-Cu-S angles 169.2-173.4”)” and [Cu,(SPh),12- (S-Cu-S angle 175.2”). ‘* These similarities are not restricted to the S-Cu-S angles since the Cu-S bonds forming these angles are also of com- parable lengths. For 1 the Cu-S distances are 216.1 and 217.0 pm, and for the compounds mentioned above’0*‘2,‘3,33 the d(Cu-S) values are within the same limits.

It is remarkable that although in 1 sulphur is triply coordinated, the Si-S bond lengths, d(Si-S) 213.3 pm, are similar to those determined for two- fold bonded sulphur compounds (e.g. d(Si-S), 213.2 pmz7 in [(t-BuO),SiS],).

Due to great similarities between the molecular structures of silver2’ and copper (this work) tri-tert- butoxysilanethiolates, a more detailed discussion about the latter is not necessary. The reader is asked to consult our previous paper” where all structural details are thoroughly discussed, since the general conclusions formulated there can be, in our opinion, applied also to the present case.

Properties of 1

Cycle - tetrakis[tri - tert - butoxysilanethiolato- copper(I)] (1) shows very good solubility in benzene, hexane and carbon tetrachloride. The solubility however falls with growing solvent polarity, so 1 is poorly soluble in acetonitrile and lower alcohols, and insoluble in water.

The IR spectrum of 1 (4000400 cm- ‘) contains only features typical for the (t-C4H90)3SiS group (v = 2970,1470,1385,1360,1235,1200,1185,1060, 1015, 685, 635 and 530 cm-‘). This is consistent with previously reported7q9 data for copper(I) thiolates pointing out that v(Cu-S) stretching modes are at lower frequencies (35&300 cm- ‘).

The UV absorption spectrum of 1 consists of a broad asymmetric band (A,,, 202 nm, E - 4600) with a distinct shoulder (A,,,,, 225 nm, E N 2000) and

a second, well separated symmetric band (&,,, 285 nm, E N 1400). The shortest wavelength maximum at ca 200 nm is attributed to the o(Si-S) + o*(Si-S) transition, however, any detailed dis- cussion on this interesting spectrum cannot be given without further investigations on the other silane- thiolates. Such investigations are now in progress.

The ‘H, 13C and 29Si NMR spectra of 1 are very simple-only one singlet for CH3 hydrogens at 1.35 ppm, two singlets for two different carbon atoms at 31.78 ppm (CH,) and 74.46 ppm (CMe,), and one singlet at -72.73 ppm for silicon atoms were detected, respectively. The above values are similar to those reported by us previously for Ag, Tl, Hg and Pb tri-tert-butoxysilanethiolates.2’-24

The mass spectrum of 1 shows a group of peaks at m/z 1368-I 379 (max. abundance 20%) which can be attributed to the ions originating from the parent molecule with four copper atoms, on the basis of identity of both experimental and calculated isotope patterns. In the region above m/z 1000, two other groups of peaks were found-the group centred at m/z 1090 (5%) [M-(t-BuO),SiS] and the group at CCI m/z 1030 (lo%), most probably corresponding to the ions with [(t-Bu0)$iSCu13 composition. Some other peaks with abundances greater than 5% were found at m/z 586 (8%), 265 (23%), 209 (12%), 153 (33%) 135 (40%) 95 (25%) and 79 (27%), and the base peak at m/z 58 (100%). No peaks which could be attributed to ions with the [(t-BuO),SiSCu], (n = 1 or 2) composition were detected. The mass spectrum indicates that not only in the solid but also in the vapour phase the molecule of 1 is quite stable. The existence of [(t-BuO)3SiSCu]3 molecules also seems possible. Although a homoleptic copper thiolate with a cyclic Cu3S3 core has not yet been prepared, the six-membered cycle of alternat- ing silver and sulphur atoms was found in the [(PhMe,Si),CSAg], molecule.32

Compound 1 is stable to water and does not hydrolyse even in the presence of acetic acid, as has been seen from method (A) of its synthesis. An attempt however to prepare 1 from CuCl and (t- BuO),SiSH in benzene, in the absence of a hydrogen chloride acceptor, failed. Although the transient formation of small amounts of 1 was observed on TLC, it was quickly destroyed by evolving HCI finally giving a mixture of black copper sulphides.

In 1 copper is only doubly coordinated and it was thus interesting to investigate if it can further react with compounds which are known to be the good donor ligands. Reaction of 1 with tri- methylphosphine was performed producing a high yield of colourless crystals of a new complex for which the formuia [(t-BuO)3SiSCu(PPh3)2]n could be attributed on the basis of elemental analysis and

Contributions to the chemistry of silicon-sulphur compounds-LVII 1665

‘H NMR spectrum, however, the value of n remains unknown. From steric considerations it is of very low probability that the Cu&, core of 1 is preserved in the phosphine adduct. Although three complexes containing the Cu& core and phosphine as an additional ligand are known--(t-BuSCu),(PPh3)2,3 (&HI 1SCu)4(PhzPCHzPPh2)2’7 and (PhSCu), (PPh3),16--in all of them a maximum of one phosphorus atom is coordinated to the copper atom. The same SCuP, stoichiometry as our phos- phine ligated copper silanethiolate was found by Dance et ~1.‘~ for (Ph,P),Cu(SPh),Cu (PPh3)2, whose molecular structure is characterized by pseudo-tetrahedral coordination on copper (PZCuSZ) and the unique planar stereochemistry at the sulphur atoms which is enforced by crowding of the 12 phenyl rings on the surface of the molecule. A similar structure could also be expected for [(t-BuO)3SiSCu(PPh3)2]n (n = 2) but, taking into account the steric hindrance caused by the very bulky (t-BuO,)SiS ligand, much greater than that of benzenethiolate, it seems doubtful.

The ‘H NMR spectrum of [(t-BuO)$iSCu (PPh)J, in the methyl region consists of two broad singlets (ratio ca 2: 1) separated by only 0.2 ppm, suggesting that the methyls are in different en- vironments. This could be easily realized in the monometallic structure depicted below, where steric requirements are also minimized.

(C”3)FO

(CH&CO 4\S./°C(CH3)3 1

I ,PG”sh s-cu

‘%“3~3

The structure has no precedents in the chemistry of neutral copper thiolate derivatives and requires further verification.

Compound 1 reacts also with l,lO-phen- anthroline affording, almost quantitatively, dark red crystals of a new complex, poorly soluble in common organic solvents, with formal stoi- chiometry (t-Bu0)3SiSCu * phen, similar to that found for the phosphine complex if phosphorus atoms are substituted for the nitrogen atoms of phenanthroline.

Reaction of 1 with 2,2’-bipyridine gave, however, a different result, the formal stoichiometry of a pink-red complex, also formed quantitatively, was found to be [(t-BuO),SiSCu], * bipy. Its solubility is even lower than that of the phenanthroline complex.

The most intriguing question arises from com- parison of the stoichiometries of both amine com- plexes, which are completely different despite the great similarities exhibited by these ligands. Pre-

sently, the molecular structure of the phen- anthroline and bipyridine derivatives of copper(I) silanethiolate are unknown, but the possibility that 2,2’-bipyridine does not act as a chelate ligand but forms a bridge between two metal centres cannot be excluded on consideration of recent results of Craven et al. 34 They reported a molecular structure of 4,4’-dimethyl-2,2’-bipyridylbis[pentacarbonyl- chromium(O)] where the orientation of the ligand pyridyl rings is mutually perpendicular and every nitrogen atom coordinates one chromium form- ing a bridged, binuclear structure. It is the first reported example of this type of coordination which, although possible for 2,2’-bipyridine, cannot be realized for 1, lo-phenanthroline and, therefore, in particular cases can account for significant differences between complexes formed by both these ligands.

Acknowledgements-The authors are grateful to Pro- fessor A. Meller (University of Gottingen, F.R.G.) for determination of NMR and mass spectra. B.B. and W.W. acknowledge the Polish Academy of Sciences (CPBP 01.13.3.6) for financial support.

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