J. CHEM. SOC. DALTON TRANS. 1992 1991Synthesis, Structure and Reactions of a Palladium ClusterCompound containing Bound Acetonitrile, [ Pd4(p-S0,),-(i.,-so,)(MeCN)(PPh,)41%Andrew D. Burrows, Jonathan C. Machell and D. Michael P. Mingos**tInorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX 7 3QR, UKThe cluster compound [Pd,(p-SO,),(k-SO,),(PPh,),] 1 a reacts with acetonitrile to give a tetranuclearcompound [ Pd,(p-SO,),(p,-SO,) (MeCN) (PPh,),] 2a. Compound 2a has been characterised by a single-crystal X-ray analysis, and shown to have a butterfly arrangement of palladium atoms with Pd-Pd bonddistances between 2.754(1) and 2.969(1) 8. Comparison of the solid-state cross-polarisation magic anglespinning JIP-{lH} NMR spectrum with the low-temperature solution 3rP-{1H} spectrum indicates that thisstructure is maintained in solution.However, at room temperature, solutions of 2a revert back to 1 a. Likethe triangulo-osmium clusters [OsJCO),,(MeCN)] and [OS,(CO)~,( MeCN),], it has proved possible toreplace the labile acetonitrile ligand, and [Pd,(p-SO,),(p,-SO,),( PMePh,),] 1 b can be converted into[ Pd,(p-SO2),(~-SO2) (PMePh,)J 3 via the compound [Pd,(p-SO,),(k-SO,) (MeCN) (PMePh,),] 2b.The synthesis of carbonyl phosphine cluster compounds ofpalladium and platinum has attracted much attention.'-'Although the majority of work has concentrated on platinum,there has been considerable research into the synthesis ofpalladium carbonyl phosphine clusters. These compounds havebeen synthesised either from the reduction of palladium(1r)compounds, for example the conversion of palladium(I1) acetateinto [Pd lo(CO) 2(PB~3)6 or from palladium(0) monomers,including [Pd(o,$-C8H, ,)(PMe3)] in the synthesis of[Pd,(CO),(PMe,),] and [Pd2(dba),]=CHC1, (dba = diben-zylideneacetone) in the synthesis of [Pds(Co)8(PMe3),].7 Farless research has been reported for phosphine palladium clusterscontaining ligands other than CO.Recently, we reported thesynthesis of a series of pentapalladium cluster compounds withbridging sulfur dioxide ligands. Reaction of [Pd2(dba)3]=CHC1,with L (L = phosphine or arsine) under an atmosphere of SO2gives [Pd,(p-S02)2(p3-S02)2Ls].8 The related compound withL = PMe, has also been synthesised in the reaction of[Pd,(CO),(PMe,),] with S02.9 The chemistry of this series ofcompounds has been studied and the research described in thispaper demonstrates the reaction with acetonitrile, and thesubsequent replacement of the bound acetonitrile ligand with aphosphine.Results and DiscussionThe compound [Pd5(p-S02)2(p3-S02)2(PPh3)5] la is solublein dichloromethane, tetrahydrofuran (thf) and toluene to givered-green dichroic solutions, but attempts to dissolve it inacetonitrile led to a change in colour of the solid from darkgreen to orange-red. The IR spectrum of the red solid showedbands due to the v(S02) stretching modes at 1212m, 1174s,1062m and 1051s cm-'.These are shifted from those associatedwith la which were observed at 1214m, 1194m and 1064s cm-'.The presence of a co-ordinated acetonitrile molecule wasinferred from the observation of the v(CH,) stretching mode at2925m cm-' and the v(CN) stretching mode at 2275w m-'.Initial attempts to analyse the compound using 31P-(1H}NMR spectroscopy proved inconclusive, and spectra obtainedt Present address: Department of Chemistry, Imperial College ofScience, Technology and Medicine, South Kensington, London SW72AY, UK.$ Supplementary data available: see Instructions for Authors, J.Chem.SOC., Dalton Trans., 1992, Issue 1, pp. xx-xxv.1100 1080 1060 1040Wavenumberhn-'Fig. 1methane (i) 5, (ii) 15, (iii) 25 and (iv) 40 minTime-dependent infrared study of compound 24 in dichloro-in dichloromethane showed the presence of the starting materialla, and an additional broad singlet at 6 14.5.The d o u r of theCH2C12 solution changed slowly on standing from red to red-green dichroic and was associated with the reversion of thecompound to la. This was demonstrated by a time-dependentsolution IR study, the results of which are shown in Fig. 1. 1992 J. CHEM. SOC. DALTON TRANS. 1992I I 1 . 1 6 I . . , , -22 20 18 16 14 12 106Fig. 2 Low-temperature 31P-{ 'H} NMR spectrum of compound 2ab1 I 1 1 I I 1 I 135 30 25 20 15 10 56Fig. 3 CP MAS solid-state "P-{ 'H) NMR spectrum ofcompound h(774)Fig. 4 Molecular structure of compound 2a with phenyl groupsomitted for claritydichloromethane solution of the complex was made up, and theIR spectrum of this was recorded after 5,15,25 and 40 min.Thepeak at 1050 cm-' that disappears with time is associated withthe acetonitrile-containing compound 2a, whereas the peak at1063 cm-' that increases in intensity with time is due to [PdS(p-It has proved possxble to get 31P-{1H} NMR spectra ofS02)2(C13-S02)2(PPhJ!53Table 1 Crystal data for compound 2aFormulaMCrystal systemSpace groupa/AblAC I A u pZDc/g ~ m - ~F(o00)p/cm-'Crystal colourData collectionX-radiation*scan width/"total data collectedtotal unique and observeddata [ I > 3a(I)]merging R factorAbsorption correctionRefinementno. of parametersratio data: parametersweighting schemeL r , m i n / oC,4H63N0,P4Pd4S3-0.25CH2C121707.98 (1729.21 including solvent)OrthorhombicPbca (no.61)17.976(8)25.316(3)32.703(6)14 88381.55692011.71RedMo-Ka, h = 0.710 69 A1,22.50.85 + 0.35 tan012 13045880.01 63DIFABS lo48 19.54Chebyshev0.04920.0575(coefficients 5.954, -0.481,4.330)= { m w o I - I~c1)211~(wl~oIZ))f.compound 2a by dissolving it in dichloromethane at -20 "C.Spectra can be reicorded at this temperature and lower with noevidence of any decomposition to la. The low-temperaturespectrum in CD2C12 is shown in Fig. 2. Even at 180 K the staticno-exchange limit was not reached. At this temperature thespectrum showed two main features in a 3 : 1 intensity ratio. Themore intense resembles a triplet, but since there is nocomplementary multiplet in the spectrum it is more accuratelyrepresented as three singlets with similar chemical shifts.Thus2a contains four types of phosphorus atoms all in differentchemical environments.A cross-polarisation magic angle spinning (CP MAS) solid-state "P-('H) NMR spectrum for compound 2a was alsorecorded (Fig. 3). The spectrum shows one signal, at 6 24.1, in avery different phosphorus environment from the other three,which are centred at 6 18.1. A shoulder on this peak at 6 16.8may be attributed to one of these three environments, with theother two not resolved. This spectrum is very similar inappearance to the low-temperature solution 31P-( 'H} NMRspectrum, which suggests that the solid-state and solutionstructures of the compound are similar. Although someinformation has been obtained from spectroscopic methods ithas not been possible to characterise the compound completelyusing these techniques and therefore a single-crystal X-raydiffraction study was undertaken.Crystal and Molecular Structure of [Pd4(p-S02)2(p3-S02)-(MeCN)(PPh,),J 2a.-Single crystals of compound 2a weregrown from the slow diffusion of acetonitrile into a dichloro-methane solution of compound la.The details of the datacollection and structure solution are given in Table 1, thefractional atomic coordinates in Table 2 and important bondlengths and angles in Table 3. The cluster compound isillustrated in Fig. 4. The compound crystallises in the spacegroup Pbca and no disorder was apparent in the structure. Thestructure consists of well separated molecules of [Pd4(p-S02)2-(p 3-S0 2)( MeCN)( PPh 3)4] toget her with occluded solvenJ.CHEM. SOC. DALTON TRANS. 1992 1993Table 2 Fractional atomic coordinates for compound 2aXla0.359 29(5)0.291 90(5)0.373 88(5)0.248 97(5)0.410 l(2)0.266 O(2)0.264 8(2)0.436 7(2)0.276 l(2)0.439 6(2)0.150 2(2)0.439 2(5)0.458 4(5)0.264 5(5)0.226 4(5)0.279 2(5)0.212 3(5)0.1 15 8(9)0.037 3(9)0.176 l(6)0.529 6(8)0.564 5( 10)0.636 O( 13)0.664 4( 1 1)0.63 1 O( 1 1)0.561 3(9)0.399 2(7)0.355 2( 10)0.325 3( 1 1)0.339 5( 11)0.380 7( 10)0.414 l(9)0.457 3(9)0.527 6( 10)0.543 7( 1 1)0.485 4( 13)0.417 9( 12)0.400 8( 10)0.308 6(7)0.320 6(9)0.349 5( 12)0.357 O( 11)0.344 6( 12)0.3 19 6(9)0.176 6(7)0.138 5(8)0.063 2(9)0.024 5(9)Ylb0.023 02(4)- 0.070 64(4)-0.096 53(4)-0.019 83(4)-0.051 7(1)-0.104 3(1)0.064 7(1)0.090 3( 1)-0.146 7(1)-0.149 8(1)-0.001 7(1)- 0.056 O(4)- 0.078 8( 3)-0.105 2(4)-0.147 2(4)0.101 8(4)0.082 5(4)-0.042 l(6)-0.027 4(9)-0.051 5(4)0.065 5(6)0.085 l(7)0.063 6(9)0.024 l(8)0.005 9(8)0.027 7(7)0.121 6(5)0.093 l(7)0.1 15 9(8)0.167 3(8)0.195 8(7)0.147 6(7)0.145 l(7)0.1 54 2(7)0.194 l(8)0.221 O(9)0.215 4(8)0.147 6( 7)-0.144 2(5)- 0.098 2( 7)-0.099 2(9)-0.144 8(9)-0.191 3(9)-0.191 3(7)-0.161 5 ( 5 )-0.148 7(5)- 0.154 2(6)-0.174 3(6)Z I C0.339 99(3)0.318 51(3)0.390 92(3)0.392 81(3)0.31 1 9(1)0.419 5(1)0.370 9( 1)0.317 0(1)0.279 2( 1)0.435 5(1)0.436 7( 1)0.270 5(3)0.342 5(3)0.463 6(3)0.400 6(3)0.404 3(3)0.340 8(3)0.3 13 2(4)0.304 7(6)0.319 6(3)0.301 9(4)0.267 3(6)0.257 2(7)0.279 l(6)0.313 5(6)0.325 9(5)0.272 O(4)0.246 7(6)0.2 11 O(6)0.202 8(6)0.225 5(6)0.261 7(5)0.351 7(5)0.366 8(6)0.395 3(6)0.406 4(6)0.395 9(7)0.365 7(6)0.225 6(4)0.206 8(5)0.164 2(6)0.148 5(6)0.164 5(7)0.205 6(5)0.274 3(4)0.238 6(4)0.237 l(5)0.271 l(5)Xla0.061 9(8)0.138 8(8)0.317 O(7)0.389 4(7)0.428 l(9)0.393 3(9)0.324 q10)0.284 5(9)0.474 l(8)0.542 O(9)0.564 8( 10)0,526 5( 1 1)0.461 O( 12)0.436 9( 1 1)0.386 4(7!0.381 O(9)0.340 2( 12)0.304 3( 1 1)0.305 4(9)0.348 l(8)0.523 6(8)0.571 8(9)0.638 5( 1 1)0.656 3( 11)0.612 6(12)0.543 7( 10)0.099 8(7)0.077 4(7)0.037 l(9)0.024 5( 1 1)0.049 7( 10)0.085 4(8)0.180 4(7)0.253 9(8)0.278 4( 10)0.229 7( 1 1)0.156 5(11)0.130 8(9)0.073 5(7)0.090 O(9)0.036 9( 10)- 0.028 3( 10)-0.047 l(10)0.005 O(8)0.239 3(41)0.232 2( 16)0.236 9(26)Ylb-0.185 2(6)-0.179 3 5 )-0.207 6(5)-0.206 5(5)-0.250 9(7)-0.299 3(6)-0.302 9(7)-0.255 8(7)-0.115 6(6)-0.131 O(6)-0.102 3(7)-0.063 3(8)- 0.047 q9)-0.073 9(8)-0.205 5(5)-0.218 2(7)-0.263 6(8)- 0.292 4(8)- 0.278 9(7)- 0.236 2(6)- 0.179 8(6)-0.148 9(7)-0.172 8(8)-0.222 l(8)-0.252 7(9)- 0.230 4(7)-0.060 6(5)-0.095 1 ( 5 )-0.140 3(7)-0.152 l(8)-0.120 3(7)-0.073 4(6)0.029 7(5)0.031 3(6)0.057 4( 7)0.079 4(8)0.080 l(8)0.054 5(6)0.041 6(5)0.094 2(7)0.129 4(7)0.109 7(7)0.058 5(8)0.023 4(6)0.1 10 2(30)0.154 5(11)0.053 6( 1 1)Zlc0.306 3(4)0.308 9(4)0.296 9(4)0.3 10 q4)0.319 2(5)0.314 q5)0.303 l(6)0.293 3(5)0.481 l(4)0.500 3(5)0.535 2(5)0.549 2(6)0.531 7(7)0.496 3(6)0.454 2(4)0.494 8( 5 )0.507 O(7)0.477 l(6)0.438 2(5)0.426 3(5)0.414 5(4)0.391 3(5)0.376 6(6)0.386 8(6)0.41 1 2(7)0.424 7(6)0.451 8(4)0.421 6(4)0.43 1 4(5)0.471 9(6)0.502 l(5)0.492 7(5)0.483 5(4)0.491 9(4)0.528 O(6)0.553 7(6)0.544 5(6)0.509 8(5)0.41 7 8(4)0.4 12 O( 5 )0.397 7(5)0.385 7(5)0.390 7(6)0.407 4( 5 )0.067 l(23)0.098 7(9)0.085 l(14)molecules, best modelled as dichloromethane with a partialoccupancy.The metal geometry of the cluster may be described as a'butterfly', based on two edge-sharing metal triangles.Thepalladium-palladium bond lengths lie between 2.754( 1) and2.969( 1) A, which are all within the previously observed limitsfor Pd-Pd bonds. The distance between Pd(1) and Pd(3) is3.465(1) A, too long to represent any significant bondinginteraction. Each metal atom is bonded to a terminal tri-phenylphosphine ligand. Of the three SO2 ligands, two bridgetwo metal atoms in the conventional manner and the thirdbridges three metal atoms in the same fashion as observed for[ Pd 5( p S 0 2 ) 2 ( p3-S02)2( ASP h3) 5],8 with the sulfur atombridging two palladium atoms and an oxygen atom acting as atwo-electron donor to a third.An acetonitrile ligand boundterminally to one of the palladium atoms completes the ligandco-ordination sphere.Compound 2a is the first example of a palladium or'platinumcluster compound to contain the acetonitrile ligand. Examplesof mono- and di-meric palladium compounds containingbonded acetonitrile ligands are given in Table 4. The Pd-Nbond length in [Pd4(S02),(MeCN)(PPh3),] is 2.14(1) A, andthis therefore represents the longest bond thus far observedbetween palladium and acetonitrile. The ion [Pd(MeCN),]' +has been reported,' but not structurally characterised.Compound 2a has 58 valence electrons, and is thereforeisoelectronic with the other previously characterised tetra-palladium cluster compounds, [Pd,(CO)5L,] (L = PMePh,or PBu,),'~.' ' with 'butterfly' arrangements of palladiumatoms.The Pd-Pd bond lengths are greater in [Pd4(S02),-(MeCN)(PPh,),] presumably as a result of the larger biteangles associated with SO2 ligands. The butterfly array is alsomore open, with a non-bonded Pd Pd distance of 3.465(1) Acompared with 3.209(1) for [Pd,(CO),(PBu,),]. A relatedstructure has been postulated for the compound [Pd,(S02)3-(PMe3)5]8 in which the tetrapalladium butterfly core and theSO2 ligand co-ordination is the same as in 2a but the PPh, andMeCN ligands are all replaced by PMe, ligands.The osmium cluster compounds [Os3(CO), , (MeCN)] and[OS,(CO)~~(M~CM)~ J are both known,' and are synthesisedfrom the reaction of [OS~(CO),~] with acetonitrile in thepresence of Me,NO.Although neither has been characterise1994 J. CHEM. SOC. DALTON TRANS. 1992Table 3 Selected bond lengths (A) and angles (") for compound 2aPd( 1 )-Pd(2) 2.754(1) Pd(2)-S( 1) 2.189(3)Pd( 1 )-Pd(4) 2.845( 1) Pd(2)-P(2) 2.332(3)Pd( 1 )-S( 1) 2.292(3) Pd(2k-N 2.14(1)Pd( 1 FS(3) 2.241(3) Pd( 3)-Pd(4) 2.969( 1)Pd( 1 kP(1) 2.324(3) P d ( 3 H 1) 2.897( 3)Pd(2)-Pd(3) 2.865(1) Pd(3)-S(2) 2.162(3)Pd(2)-Pd(4) 2.855( I)Pd(4)-Pd( l)-Pd(2)S( 1 )-Pd( 1 )-Pd(2)S( 1 )-Pd( 1 )-Pd(4)S(3)-Pd(l )-Pd(2)S(3)-Pd( l)-Pd(4)S(3bP4 1 tS( 1)P( 1 )-Pd( 1 )-Pd(2)P( 1 )-Pd( 1 )-Pd(4)P( 1 )-Pd(l )-S( 1)P( 1 )-P4 1 )-S(3)Pd(3)-Pd(2)-Pd( 1)Pd(4)-Pd(2)-Pd( 1)Pd(4)-Pd(2 jPd(3)S( l)-Pd(2jPd( 1)S( l)-Pd(2)-Pd(3)S( I)-Pd(2)-Pd(4)P(2)-Pd(2)-Pd( 1)P(2)-Pd(2)-Pd(3)P(2)-Pd(2)-Pd(4)P(2)-Pd(2)-S( 1)61.3 l(3)50.41 (8)101.93(8)100.79(9)5 1.49(8)150.6( 1)144.3( 1)153.2( 1)103.7(1)1O4.7( 1)76.1 l(4)60.92(3)62.54(3)53.80(9)68.46(9)104,339)154.82(9)109.2q9)143.88(9)104.2(1)N-Pd(2)-Pd( 1)N-Pd(2)-Pd( 3)N-Pd(2)-Pd(4)N-Pd(2)-S( 1)N-Pd(2)-P(2)Pd(4)-Pd(3)-Pd(2)S( 1)-Pd( 3)-Pd(2)S( l)-Pd(3)-Pd(4)S(2)-Pd(3)-Pd(2)S(2)-Pd(3)-Pd(4)S(2Wd(3)-S( 1)P( 3)-Pd(3)-Pd(2)P(3)-Pd(3)-Pd(4)P(3tPd(3)-S( 1)P(3)-Pd(3)-S(2)0(2)-Pd(3)-Pd(2)O(2)-Pd( 3)-Pd(4)0(2)-Pd(3)-S( 1)0(2)-Pd(3)--S(2)0(2)-Pd(3)-P(3)103.2(3)122.7(3)67.7(3)153.7(3)9433)58.57(3)44.65(7)86.1 l(7)85.25(9)51.11(9)128.6( 1)156.6(1)139.0(1)132.6(1)97.6( I )73.7(2)113.3(2)30.5(2)158.8(2)102.5( 2)Pd(3FP(3)Pd(3)-0(2)W4)-S(2)Pd(4)-S(3)Pd(4)--P(4)S(1 W ( 1 )S(1 W ( 2 )Pd(2)-Pd(4)-Pd( 1)Pd(3)-Pd(4)-Pd( 1)Pd(3)-Pd(4)-Pd(2)S(2)-Pd(4)-Pd( 1 )S(2)-Pd(4)-Pd(2)S(2)-Pd(4bPd( 3)S(3)-Pd(4)-Pd( 1)S(3)-Pd(4)-Pd(2)S( 3)-Pd(4)-Pd( 3)P(4)-Pd(4)-Pd( 1)P(4)-Pd(4)-Pd(2)P(4)-Pd(4)-Pd( 3)S(3)-Pd(4)-S(2)P(4)-Pd(4)-S(2)P(4)-Pd(4)-S(3)Pd(2)-S( 1)-Pd( 1)Pd(3)-S( l)-Pd( 1)Pd(3)-S( 1 )-Pd( 2)O(1 )-S(1)-Pd(l)O( 1 )-S( 1 kPd(2)2.310(4)2.241(9)2.330(3)2.275(3)2.328(3)1.454(9)1.492(9)57.77( 3)73.1 l(3)58.89( 3)1 I9.07(9)82.54(9)46.23(8)50.42(8)97.01(8)120.94(9)164.8( 1)146.18(9)144.99(9)135.91(9)92.9( 1)96.0(1)75.q 1)82.9( 1)66.89(9)125.4(4)11544)1.44 l(9)1.44(1)1.462(9)1.44( 1)1.48(2)1.1 3(2)151.7(4)110.0(4)1 13.4(4)49.6(3)112.3(5)82.7( 1)1 16.8(4)1 12.7(4)109.0(4)1 17.8(4)114.1(6)78.1(1)120.3(4)1 13.0(4)109.7(4)1 15.4(4)115.3(6)177.6(17)168.5( 12)99.9(4)Table 4 Examples of palladium compounds containing bound aceto-nitrileCompound Pd-N/A Ref.[( MeCN)CI,Pd(p-L ')PdCIJ 2.065(14) 12[( MeCN), Pd( p-L2)PdCl,] 2.115(4), 13[Pd(q5-CH2CHCHMeCH2CH2CH= 2.086(7) 14C{Pd(~3-C3H,)(MeCN)2),(BloBr,,)l 2.10(1) 1 12.086(7)CMe,)(MeCN)]BF,L' = Bis(diphenylphosphinomethyl)phenylphosphine,(dipheny 1phosphino)-N-methylmaleimide.L2 = 2,3-bis-Table 5 Selected peaks in the FAB mass spectrum of [Pd,(SO,),-(PMePh,),lmlz Intensity Assignment1490 12 [M - 2S02]+1428 13 [M - 3S02]*1225 21 [M - 3S02 - PMePh2]+1025 27 [M - 3S02 - 2PMePh,]+948 32 [M - 3S0, - 2PMePh, - Ph]+871 31 [M - 3S0, - 2PMePh, - 2Ph]+M = Pd,(SO,),(PMePh,),.crystallographically, these compounds have been used assynthetic precursors to many triangufo-osmium clustercompounds, as the acetonitrile ligands are readily replacedby ligands such as PPh,, MeC,H4S0,CH2NC, C2H4 andpyridine.Reaction of [Pd4(S0,),(MeCN)(PMePh2)4] with PMe-Ph,.-The structure of compound 2a is very similar to thatobserved for [Pd4(S02)3(PMe3)5].8 As 2a is synthesised from[Pd5(S02)4(PPh3)5], it should be possible to convert a[Pd,(SO,),L,] cluster into a [Pd4(SO2),L5] cluster, via theacetonitrile complex, if the acetonitrile ligand is labile in asimilar manner to that reported for [Os,(CO), ,(MeCN)].Thisproved problematic with the PPh, group of compounds as theacetonitrile complex is not stable in solution. Fortunately, theequivalent PMePh, compound is soluble in acetonitrile, andhence it was decided to start from [Pd5(S02)4(PMePh2)5] lb.This has the additional advantage that the [Pd,(SO,),(PMe-Ph,),] cluster compound is well documented as it is formed as aby-product in the synthesis of [Pd,(SO,),(PMePh,),] from[Pd2(dba)3]-CHC13.8The compound [Pd,(SO,),(PMePh,),] was dissolved inacetonitrile giving a red solution of [Pd4(S0,),(MeCN)(PMe-Ph2)4] 2b. A toluene solution of PMePh, was added, and theacetonitrile removed under reduced pressure. Diethyl ether wasadded to precipitate a red solid, which was recrystallised fromthf-ether to give a red microcrystalline solid that analysed for[Pd4(S02)3(PMePh2)5] 3.The identity of the product wasconfirmed by 31P-(1H) NMR and IR spectroscopy and fastatom bombardment (FAB) mass spectrometry.The 31P-(*H) NMR spectrum, recorded at 240 K, was thesame spectrum as that observed for samples of compound 3synthesised directly from [Pd,(dba),]CHCI,. It has fiveresonances of equal intensity in the form of one doublet, threedoublets of doublets, and one doublet of doublet of doublets.'The IR spectrum showed v(S0,) stretching modes at 1204m,1 181m, 1055s and 1043vs em-', which again are identical tothose observed for samples of 3 synthesised directly from[Pd2(dba)3]=CHC13.8 Further confirmation of the identity ofthe compound was obtained by FAB mass spectrometry.Although the [MI' peak was not observed, other importantpeaks were and these are summarised in Table 5.The intensitiesare relative to the [Pd,(PMePh,),]+ peak, which was observedat m/z = 612. As in the other palladium cluster compoundsstudied using this techniques*" the SO2 ligands were lostfirst from the co-ordination sphere. Then came the removalof fragments from the phosphine ligands which occurredconcurrently with the loss of whole phosphine ligands. As with[Pd5(S02)3(C0)2(PMe2Ph)s] l9 the phenyl fragments werelost before the methyl fragments from the phosphine ligands.The synthesis of [Pd,(SO,),(PMePh,),] from [Pd4(S02)3-(MeCN)(PMePh,),] has shown that, as with the triangulo-osmium clusters, it is possible to replace the acetonitrile byligands which form stronger bonds to the cluster.It should alsoprove possible t o synthesise novel cluster compounds bytreating [ Pd4(S0 ,) , (MeCN)L,] clusters with mononucleaJ. CHEM. SOC. DALTON TRANS. 1992 1995metal carbonyls which are capable of replacing MeCN andforming additional metal-metal bonds.ExperimentalReactions were routinely carried out using Schienk-linetechniques under pure dry dinitrogen, with dry, dioxygen-freesolvents. Microanalyses (C, H and N) were carried out by Mr.M. Gascoyne and his staff at this laboratory. Infrared spectrawere recorded on a Perkin-Elmer FT-1710 or a MattsonPolaris spectrometer.Solid samples were mulled with Nujol orhexachlorobutadiene, and recorded between KBr or CsI discs.Spectra of solution samples were recorded in KBr cells. The31P-(1H} NMR spectra were recorded on a Briiker AM-300spectrometer operating at 121.49 MHz and referenced toP(OMe),O in D,O; computer simulations were carried outusing the Oxford University VAX computer system using aprogram developed by Professor R. K. Harris, then of theUniversity of East Anglia, and adapted for use in Oxford byDr. A. E. Derome. Solid-state spectra were recorded on a BrukerMSL-200 spectrometer operating at 80.96 MHz, using CP MAStechniques. The FAB mass spectra were recorded by Dr. J.Ballantine and his staff at the SERC Mass Spectrometry ServiceCentre at the University of Swansea.Experiments were carriedout using a VG ZAB-E high-resolution double-focusing massspectrometer. Samples were suspended in a matrix of 3nitrobenzyl alcohol (NOBA) and bombarded with a high-energy beam of xenon atoms to generate ions.Compounds la and l b were synthesised as reportedpreviously.*Syntheses.-[Pd4(p-S02)2(p3-S02)(MeCN)(PPh3)4J 2a.Acetonitrile (30 cm3) was added to [Pd5(S02)4(PPh3),] (0.30 g,0.14 mmol) and the suspension stirred for 2 h. The resultingorange-red precipitate of compound 2a was filtered off, washedwith acetonitrile, and dried by passing a stream of dinitrogenover it. Yield 0.24 g (79%) (Found: C, 50.5; H, 3.7; N, 1.0.C,,H,,N06P4Pd4S3~CH2c12 requires C, 50.2; H, 3.7; N, 0.8%).v(S0,) at 1212m, 1174s, 1062m and 1051s; v(CH3) at 2925w;v(NC) at 2275w cm-'.6(,'P) (CD2C12, 253 K) 17.1 (br s) and11.6 (br s); (CD2C12, 188 K) 6 21.6 (br s, lP), 11.34, 11.20 and11.05 (combined, 3P); 6('H) (CD2Cl,, 188 K) 1.96 (br s).[Pd4(p-S02)2(p3-S02)(PMePh2)s] 3. The compound [PdS-(S02),(PMePh2),] (0.20 g, 0.11 mmol) was dissolved inacetonitrile (20 cm3) giving a red solution of compound 2b, anda solution of PMePh, (0.022 g, 0.1 1 mmol) in toluene (20 cm3)was added. The mixture was stirred for 2 h, and the volume ofthe solution decreased under reduced pressure. Diethyl etherwas then added to precipitate a red solid, which wasrecrystallised from thf-ether to give compound 3. Yield 0.1 1 g48.2; H, 4.0%). v(S0,) at 1204m, 1181m, 1055s and 1043vs ern-'.(dd) and - 7.7 (dd).(61%) (Found: C, 47.7; H, 4.0.C ~ S H ~ , O ~ P S P ~ ~ S , requires C,S(,lP) (CD2C12, 250 K) 6.3 (ddd), -1.7 (d), -4.8 (dd), -5.0Crysral Structure Determination of [Pd4(p-S02)2(p3-S0,)-(MeCN)(PPh,),J 2a.--Crystals of compound 2a used in theanalysis were grown from a slow diffusion of acetonitrile intoa dichloromethane solution of compound la. A single crystalwas mounted in a Lindemann tube and transferred to thegoniometer head of an Enraf-Nonius CAD4 diffractometer.The experimental details associated with the crystallographicdetermination are summarised in Table 1. The structure wassolved by direct methods, with all non-hydrogen atoms locatedin subsequent Fourier difference syntheses. After assigninganisotropic thermal parameters to all of the palladium,phosphorus, oxygen and sulfur atoms, and the atoms of theacetonitrile, the hydrogens were generated geometrically.Onapplication of a Chebyshev weighting scheme the model con-verged at R 0.0492 and R' 0.0575. The programs and sources ofscattering factors used are given in refs. 10, 20 and 21. Thecarbon atoms are numbered such that C( I), C(7) and C( 13) arebonded to P(l), C(19), C(25) and C(31) to P(2), C(37), C(43)and C(49) to P(3), and C(55), C(61) and C(67) to P(4). AtomsC(73) and C(74) are associated with the acetonitrile ligand andC(75) with the dichloromethane molecule of solvation.Additional material available from the Cambridge Crystal-lographic Data Centre comprises H-atom coordinates, thermalparameters and remaining bond lengths and angles.AcknowledgementsThe SERC is thanked for financial support, Johnson Mattheyplc for generous loans of palladium salts, Sue Mason forrunning the solid-state NMR spectrum and Dr.J. Ballantine(Swansea) for the FAB mass spectrum.Referenceslo, 441.Rev., 1985,54,394.and Yu. T. Struchkov, J. Organomet. Chem., 1982,239,401.Struchkov, J. Organornet. Chem., 1986,301, C35.Struchkov, J. Chem. SOC., Chem. Commun., 1987,218.Organometallics, 1982,1, 1709.Polyhedron, 1987,6, 1987.Dalton Trans., 1992,261.Commun., 1988,1048.1 D. M. P. Mingos and R. W. M. Wardle, Transition Met. Chem., 1985,2 N. K. Eremenko, E. G. Mednikov and S. S. Kurasov, Rms- Chem.3 E. G. Mednikov, N. K. Eremenko, S. P. Gubin, Yu. L. Slovokhotov4 E. G. Mednikov, N. K. Eremenko, Yu. L. Slovokhotov and Yu. T.5 E. G. Mednikov, N. K. Eremenko, Yu. L. Slovokhotov and Yu. T.6 R. Goddard, P. W. Jolly, C. Kruger, K.-P. Schick and G. Wilke,7 M. Bochmann, I. Hawkins, M. B. Hursthouse and R. L. Short,8 A. D. Burrows, D. M. P. Mingos and H. R. Powell, J. Chem. Soc.,9 S. G. Bott, 0. J. Ezomo and D. M. P. Mingos, J. Chem. SOC., Chem.10 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983,39, 158.1 1 G. A. Kukina, V. S. Sergienko, Yu. L. Gait, I. A. Zakharova and12 M. M. Olmstead, R. R. Guimerans, J. P. Farr and A. L. Balch, Inorg.13 D. Fenske and W. Bensmann, 2. Naturforsch., Teil B, 1984,39,1819.14 R. Ciajolo, M. A. Jama, A. Tuzi and A. Vitagliano, J. Organomet.15 A. Sen and T.-W. Lai, J. Am. Chem. SOC., 1981,103,4627.16 J. Dubrawski, J. C. Kriege-Simondsen and R. D. Feltham, J. Am.Chem. Soc., 1980,102,2089.17 R. D. Feltham, G. Elbaze, R. Ortega, C. Eck and J. Dubrawski, Inorg.Chem., 1985,24,1503.18 B. F. G. Johnson, J. Lewis and D. A. Pippard, J. Chem. SOC., DaltonTrans., 1981,407.19 A. D. Burrows, J. C. Machell, D. M. P. Mingos and H. R. Powell,J. Chem. Soc., Dalton Trans., 1992,1521.20 D. J. Watkin, J. R. Carruthers and P. W. Retteridge, CRYSTALSUser Manual, Chemical Crystallography Laboratory, University ofOxford, 1985.2 1 International Tables for X-Ray Crystallography, Kynoch Press,Birmingham, 1974.M. A. Porai-Koshits, Inorg. Chim. Acfa, 1980,45, L257.Chim. Acta, 1983,75, 199.Chem., 1985,295,233.Received 3rd February 1992; Paper 2 jOO558