摘要:

J. CHEM. SOC. DALTON TRANS. 1985 345Static and Dynamic Nuclear Magnetic Resonance Studies of Complexes ofTrimethylplatinum(iv) Halides with Olefinic Thio- and Seleno-ethers. X-RayCrystal Structures of [PtXMe,(MeSeCH=CHSeMe)] (X = CI or I) tEdward W. Abel, Suresh K. Bhargava, Keith G. Orrell," Andrew W. G. Platt, and Vladimir SikDepartment of Chemistry, University of Exeter, Exeter EX4 40 DT. Stanley CameronDepartment of Chemistry, Dalhousie University, Halifax B3 4J3, CanadaComplexes of general type [ PtXMe,( MeECH=CH EMe)] (E = S or Se; X = CI, Br, or I) have beenisolated and their solution and solid-state structures established. Static structures in solution werecharacterised by 'H, 13C, 77Se, and lMPt n.m.r. parameters; the dynamic stereochemistry of thesecomplexes, arising from low-temperature chalcogen inversion and hig h-temperature fluxionalrearrangements, was studied quantitatively by variable-temperature ' H n.m.r.spectroscopy.Correlations were found between lg5Pt and 77Se chemical shifts, and between lg5Pt shifts and'J( PtSe) values in these complexes. 'J(CPt) values can be interpreted in terms of trans influenceeffects. The solution invertomer populations are very halogen- and temperature-dependent. In thecase of selenium complexes, the predominant invertomer in solution corresponds to the single solid-state configuration as determined by X-ray crystallography. For the chloro-complex this is the meso-1form and for the iodo-complex the meso-2 species. The effects of n-conjugation on the energiesof the chalcogen inversion and platinum-methyl scrambling processes are discussed by comparingAG* (298.1 5 K) values with those for analogous complexes with aliphatic and aromatic chalcogenligands.In earlier studies on the structural dynamics of transition-metal complexes with Group 6B ligands, we have shown thatcomplexes of trimethylplatinum(1v) halides with aliphaticdithio-, diseleno-, and thio/seleno-ethers of general type[PtXMe,(MeECH,CH,E'Me)] (X = C1, Br, or I; E = E' = Sor Se and E = S, E' = Se) are highly stereochemically non-rigid, exhibiting temperature-variable n.m.r.spectra over a widetemperature range (often exceeding 100 "C). Similar observa-tions were made for complexes with aromatic dichalcogen etherligands,, namely [PtXMe,(o-MeEC,H,EMe)] (E = E' = S,X = C1; E = S, E' = Se, X = C1, Br, or I).However, the ratesof chalcogen inversion and other fluxional processes weresignificantly different in the two classes of complexes to suggestan influence of ligand backbone on the stereodynamics of thesemononuclear platinum(1v) complexes. In order to explorefurther this effect we have now synthesised analogous com-plexes with olefinic ligands, namely [PtXMe,(MeECH=CHE'Me)] (E = E' = S or Se; X = C1, Br, or I). n-Electronconjugation effects have previously been shown to influencestrongly the rates of pyramidal chalcogen inversion inrhenium(1) complexes (e.g. [ReX(CO),L] >, and palladium(r1)and platinum(I1) complexes (e.g. [PdX,L] and [PtX,L])with similar ether ligands (L). We therefore wished toinvestigate whether similar influences were operating in theseplatinum(rv) complexes, and whether the high-temperaturefluxional rearrangements, which are known to exist in thesecomplexes, are also affected.As these complexes, particularly those with selenium ligands,possess a variety of important n.m.r.nuclei, e.g. 'H, 13C, 77Se,and 195Pt, we have carried out a multinuclear investigation onthe low-temperature solutions of these complexes in order tocharacterise precisely the invertomer mixtures which arise.-f [ 1,2-Bis(methylseleno)ethene]chloro- and [ 1,2-bis(methylseleno)-etheneliodo-trimethylplatinum(~v).Supplementary data available (No. SUP 56081, 4 pp.): thermalparameters. See Instructions for Authors, J .Chem. SOC., Dalton Trans.,1985, Issue 1, pp. xvii-xix. Structure factors are available from theeditorial office.X-Ray crystallographic studies on some of these complexeshave been used to ascertain whether the predominant structuralisomer in solution can be closely identified with the solid-statestructure.ExperimentalMaterials.-The ligands cis-1,2-bis(methylthio)ethene andcis-1,2-bis(methylseleno)ethene were prepared by reportedmethod^.^'^The complexes were all prepared by the same general method.The preparation of [PtBrMe,(MeSeCH=CHSeMe)] describedbelow may be taken as typical.A slight excess of 1,2-bis(methylseleno)ethene (0.216 g, 0.57mmol) in chloroform (3 cm3) was added to trimethylplatinumbromide (0.125 3 g, 0.4 mmol) in chloroform (5 cm3) and theresulting solution heated to reflux for 2 h.The solution wasconcentrated under vacuum to ca. 1 cm3, and light petroleum(b.p. 40-60 "C; 1 cm3) was added to precipitate a white solid.The solvent was removed and the product recrystallised fromchloroform-light petroleum (b.p. 40-60 "C) to yield whitecrystals of [1,2-bis(methylseleno)ethene]bromotrimethyl-platinum(rv) (0.190 g, 91%).In view of the larger amounts of complex required for I3Cand 77Se n.m.r. studies, interconversions of complexes byhalogen-exchange reactions were also achieved in order tominimise the quantities of starting materials. Thus, the chlorideand bromide complexes were prepared from the iodide complexby reaction of the latter with the appropriate silver halide asdescribed previously.8All the complexes were white or pale yellow crystals whichwere readily soluble in common organic solvents.They werequite stable both in air and in solution. Analytical data arereported in Table 1.N.M.R. Spe~tra.-Hydrogen-l,'~C, and 77Se spectra wereobtained at 100.0, 25.1, and 19.1 MHz respectively on a JEOLPS/PFT-100 spectrometer in this Department operating in th346 J. CHEM. SOC. DALTON TRANS. 1985Table 1. Characterisation of the complexes [PtXMe,(MeECH=CHEMe)]Complex Colour(1) [PtClMe,(MeSCH=CHSMe)] White(2) [PtBrMe,(MeSCH=CHSMe)] White(3) [PtIMe,(MeSCH=CHSMe)] Paleyellow(4) [PtClMe,(MeSeCH=CHSeMe)] White(5) [PtBrMe,(MeSeCH=CHSeMe)] White(6) [PtIMe,(MeSeCH=CHSeMe)] PaleyellowM.p.("C)185190'-187191-192'170168161Calculated values are in parentheses.Decomposes.Analysis (I (%) - C H21.25 4.35(21.20) (4.30)19.10 3.90(19.05) (3.90)17.25 3.50(17.25) (3.55)17.15 3.45(17.10) (3.45)15.75 3.20(15.50) (3.10)14.45 2.95(14.45) (2.85)Fourier-transform mode. Probe temperature control was aspreviously described.' Platinum- 195 spectra were obtained at19.3 MHz on a JEOL FX 90Q spectrometer at the City ofLondon Polytechnic. All the complexes were dissolved inCD,Cl, for low-temperature n.m.r. studies, while C,D,NO, orC , D 5 N 0 2 ~ , D , were used as solvents in the high-temper-ature range (ca. 30-165 "C).Bandshape analyses of the 'H spectra were carried out usingour version of the original DNMR3 program of Kleier andB i n ~ c h .~X-Ray Structure Determinations.-Single-crystal structuredeterminations of [PtXMe,(MeSeCH=CHSeMe)] (X = C1 orI), compounds (4) and (6), were obtained.Crystal data for (4). C,H,,ClPtSe,, M = 489.7, ortho-rhombic, a = 12.146(2), b = 23.093(4), c = 9.219(2) A, spacegroup Pbca, 2 = 8, D, = 2.515 g cm-,, Mo-K, radiation(h = 0.7093 A), p = 16.7 mm-'.Crystal data for (6). C,H,,IPtSe,, M = 581.1, monoclinic,u = 11.962(4), b = 13.843(3), c = 8.126(2) A, p = 99.85(2)",space group P2,/n, Z = 4, D, = 2.910 g cm-,, Mo-K,radiation, p = 18.4 mm-'.A Picker four-circle diffractometer was used to obtain 768and 1 345 independent observable reflections with I > 3 4 0 for(4) and (6) respectively; 2 976 (4) and 3 195 (6) (h,k,l) reflectionswere scanned in the range 3 < 26 d 55".Crystals of dimensions0.1 x 0.2 x 0.33 and 0.1 x 0.12 x 0.13 mm were used;Lorentz, polarisation, and absorption corrections were applied.The structures were solved by Patterson and Fourier methods l oand were refined by full-matrix least squares to R = 0.052 (4)and 0.047 (6) with anisotropic thermal parameters for all non-hydrogen atoms; weights were given by w-' = a2(Fo) + 0.001(F,)'. The olefinic hydrogen atoms only could be located, andthe positions of these were not refined.ResultsStatic N.M.R. Parameters.-The two sulphur or seleniumatoms in these five-membered ring complexes are chiralcentres and thus, in the absence of any internal exchangeprocess, four diastereoisomers (two distinct meso forms and adegenerate pair of DL forms) may exist (Figure 1).This is totallyanalogous to the situation existing for the homochalcogen-aliphatic ' and -aromatic ligand complexes. The presence ofthese individual isomers (strictly termed, invertomers, as theyarise from the cessation of pyramidal inversion of the E atoms)is clearly shown in the low-temperature 'H n.m.r. spectra.The complex [PtClMe,(MeSCH=CHSMe)], whose 400-MHz 'H spectrum at -80 "C is shown in Figure 2, may betaken as representative of all the other complexes. The spectrumconsists of four main regions of absorption. The sulphur-methylregion (ii) consists of four signals (plus 195Pt satellites) due tothe three distinct invertomers. On warming the sample to ca.- 10 "C these signals coalesce to a single signal (plus lssPtsatellites) due to the onset of pyramidal sulphur inversion. Inthe platinum-methyl regions (iii/iv) at low temperature, sevensignals (plus 95Pt satellites) are expected and indeed detected at400 MHz.The three resonances due to Pt methyls trans tohalogen occur at lower frequencies (6 0.6--0.9), region (iv), andwith larger 'J( lg5Pt-H) values (72.3-74.0 Hz) compared tothose for Pt-methyls trans to chalcogen (6 1.1-1.2, 2J = 66.0-70.6 Hz), region (iii). These trends were noted originally inaliphatic chalcogen-ether complexes ',' and are useful assign-ments in the present complexes. Full proton chemical shift and'J(Pt-H) data for these complexes in the slow- and fast-inversion limits are presented in Table 2.No attempt was madeto assign individual Pt-methyl signals since this region was notsubsequently used for dynamic n.m.r. analysis despite the grosschanges (viz.,seven lines coalescing to two) which occurred onwarming to higher temperatures.The ligand olefinic region (i) (Figure 2) also showed thepresence of all invertomers at low temperature. Two singlets at 66.82 and 6.84 with 3J(Pt-H) values of 14.5 and 14.0 Hzrespectively were assigned to the meso-1 and meso-2 isomersrespectively, while an AB quartet centred at 6 6.75 (AvA, = 0.121p.p.m., 'JAB = 7.0 Hz) was due to the DL pair. This region of thespectrum was also not examined in further detail because of thevery small chemical shift differences involved, and because noadditional information to that obtained from the completeanalyses of the ligand-methyl region would ensue.Full assignments of the ligand-methyl region of the spectrawere made, prior to performing a dynamic n.m.r.bandshapeanalysis. Assignments for the selenium ligand complexes areshown in Figure 3 and the proton parameters for all the staticcomplexes are given in Table 3. Assignments were made on thebasis of previously observed trends ' in chemical shifts,,J(Pt-H) values, and invertomer populations. The two signals(neglecting lg5Pt satellites) at lower frequencies were assignedto methyl c (DL) and methyls dd' (meso-2). The signals at higherfrequencies were accordingly assigned to methyls aa' (meso- 1)and methyl b (DL).An examination of the trends in Figure 3 and Table 3 showsthat an increase in halogen mass/size favours the less stericallyhindered meso-2 and DL isomers at the expense of meso-I.Thesame trend was previously observed for the saturated ligandcomplexes, the main difference between the two series ofcomplexes being that in the olefinic ligand complexes theabundances of the DL species are considerably lower, the usualorder of populations being meso-1 > meso-2 % DL-1 = DL-2.By contrast, the usual order for the aliphatic ligand complexeswas meso-1 > DL-1 = DL-2 % meso-2, although in the case ofthe iodo-complex the DL isomers became the most abundantspecies. The halogen dependencies of the invertomer popula-tions for the two series of complexes are displayed graphically inFigure 4.chemical shifts and one- andtwo-bond 13C-195Pt coupling constants are given in Table 4.The labelling of the methyl carbons is shown in Figure 5.Thetrends in both chemical shifts and coupling constants areexactly analogous to those observed in the aliphatic ligandcomplexes, [PtXMe,(MeSeCH,CH,SeMe)].* In both series theexpected dependence of chemical shifts on electronegativity ofthe halogen is followed for Pt-methyl (trans E) carbons with6(Cl) > 6(Br) > &(I) but this trend is reversed for ligand-methyl and Pt-methyl (trans X) carbons. As far as the methyl-Carbon- 13 parameters. The J. CHEM. SOC. DALTON TRANS. 1985 347M e"MeMeD& k .H H H \H'Figure 1.Interconversion of meso and DL isomers of [PtXMe,(MeECH=CHEMe)]. Percentage populations refer to the complexes when E = S, (a)X = Cl, (b) X = Br, and (c) X = I at ca. -76 "C; Me*-Med refer to the E-methyl environments( i T I I(ii)I 11 1 * 1 ' I 1 1 1 1 1 l 1 1 1 I l L 1 1 1 1 1 1 1 1 1 1 1 1 I 1 I I 1 1 1 1 7 3 2 1 - 6/p. p.mFigure2. Hydrogen-1 n.m.r. spectrum (400 MHz) of [PtClMe,(MeSCH=CHSMe)] in CD,CI, at - 80 "C. The arrows in regions (iii/iv) indicate the mainPt-methyl signals. All lines not arrowed in these regions are lg5Pt satellitescarbon-platinum-195 coupling constants are concerned,'J,,(trans X) values are invariably greater than 'J,,(trans E).The variation of 'J(trans X) with halogen follows the trendexpected by the trans influence,' '*12 with values decreasing byapproximately 3% from chloro- to iodo-complexes.Within agiven complex, the magnitudes of 'J,,(trans X) showed nosimple dependence on invertomer, while values of 'J,,&transSe) were invariably greater in meso-1 than meso-2 implyingstronger Pt-C bonds and weaker Pt-Se bonds in meso-1compared to meso-2.The 2Jp,c values are expected to reflect changes in the Pt-Sebond strengths. However, the few values recorded in Table 4 donot indicate any significant trend. Difficulties in interpreting2Jcpt values were similarly encountered in the aliphatic ligandcomplexes.'Selenium-77 and platinum- 195 parameters. It is notable tha348 J. CHEM. SOC. DALTON TRANS. 1985Table 2. Chemical shifts and spin coupling constants of platinum-methyl protons in the slow- and fast-inversion limits"Pt-Me(trans to E) Pt-Me(trans to X)A hI I \Complex %/"C 6lp.p.m.' Jb/Hz 6lp.p.m. ,Jb/Hz(1) - 80.0- 15.1- 74.98.4(2)(3) - 74.58 .O- 55.877.7(4)(5) - 46.860.5- 46.777.7(6)1.21, 1.17, 1.15, 1.131.231.35, 1.31, 1.28, 1.161.331.48, 1.46, 1.36, 1.341 S O1.40, 1.37, 1.31, 1.281.371.47, 1.45, 1.44, 1.411.461.61, 1.59, 1.581.6265.81, 70.00, 68.00, 70.2370.5669.58, 70.55, 70.07, 71.070.6870.31, 71.00, 69.80, 69.6071.669.58, 69.83, 69.82, 69.8271.0569.83, 70.07, 70.20, 70.2070.8 170.80, 70.3 1, 7 1.0471.300.90, 0.70, 0.610.871.08, 0.89, 0.790.951.20, 1.04, 0.951.071.08, 0.80, 0.720.861.15, 0.90, 0.820.931.05, 0.96, 0.941.0573.91, 74.22, 73.0072.3072.88, 72.11, 72.7872.2870.70, 69.96, 70.7069.6073.74, 73.98, 73.7273.6172.51, 72.76, 73.6172.0270.80, 71.30, 70.807 1.04" Chemical shifts are relative to SiMe,.The solvent for sulphur complexes was CD,CI,, and for selenium complexes CDCl,. 2J(195Pt-C-'H).Table 3. Static parameters of the ligand methyl protons in the complexes [PtXMe,(MeECH=CHEMe)]meso- 1 isomer DL isomers meso-2 isomer - 3 r I-AX E v,' 3Jb p c 'b ,J P vc ,J P 'd ,J P 7-27sC1 S 276.97 13.92 0.746 270.60 12.10 0.049 233.76 13.68 0.049 244.26 15.86 0.156 0.212Br S 285.16 14.52 0.637 279.90 12.94 0.055 233.03 13.92 0.055 243.89 15.87 0.253 0.230I S 298.21 15.63 0.456 293.82 13.60 0.089 232.66 14.04 0.089 243.04 16.11 0.366 0.232C1 Se 269.80 10.74 0.518 261.50 9.80 0.086 219.72 11.22 0.086 231.40 12.45 0.310 0.205Br Se 275.02 11.23 0.405 267.94 10.38 0.112 216.43 11.35 0.112 227.17 12.32 0.371 0.300I Se 289.60 12.20 0.178 283.20 11.72 0.120 217.30 11.24 0.120 228.00 12.70 0.582 0.198" Chemical shifts (vi/Hz) of E methyls measured relative to SiMe,.3J('9sPt-E-C-'H)/Hz. Isomer population (kO.005).Table 4. Methyl I3C n.m.r. data" for [PtXMe,(MeSeCH=CHSeMe)]meso- 1 DL meso-2A A r I f > r A >X S(C') 'J 6(C2) ' J S(C3) 'J 6(C') 'J 6(C2) 'J S(C3) 'J S(C4) ' J S(Cs) ,J S(C') ' J 6(C2) 'J S(C3) zJBr -1.1 676.3 1.0 622.5 12.2 7.3 -1.3 676.2 0.4 636.0 0.4 623.3 13.0 4.9 4.9 b 0.5 682.4 1.1 618.9 8.1 b" At -40 "C in CDCl,. Shifts are to high frequency of SiMe,; J values are in Hz.Not measured.C1 -6.1 682.4 1.8 628.7 10.6 5.6 -5.7 686.0 1.2 632.3 1.4 629.9 11.4 9.8 9.4 b -3.6 688.5 2.4 626.5 7.8 bI 5.6 666.0 -0.4 633.0 15.7 9.8 7.4 - -1.8 620.3 -1.3 617.1 16.4 9.0 10.2 b 7.2 660.2 -1.4 621.3 8.8 bTable 5. Selenium-77 and 19'Pt n.m.r. data" for [PtXMe,(MeSeCH=CHSeMe)]meso- 1 DL meso-2A r A> I > I A-lX p b 6(Pt) 6(Se) 'J p b 6(Pt) S(Se') 'J 6(Se2) 'J p b 6(Pt) 6(Se) 'JC1 51.5 1 311.6 305.4 330.1 25.2 1 127.9 323.1 337.7 300.7 244.2 23.3 1276.6 299.5 246.6Br 35.5 1 204.0 299.1 339.9 28.1 985.5 319.4 346.7 296.3 256.8 36.4 1 104.1 298.0 256.6I 28.0 1001.6 286.1 353.5 23.5 729.8 310.6 361.6 287.4 271.5 48.5 807.1 295.0 283.0populations are appreciably temperature dependent such that p e = poOc + x(@/"C), where x = 0.13 (meso-1), 0.10 (DL), and -0.23 (meso-2).In CDCl,.Platinum-195 shifts to high frequency of 21.4 MHz at 0 "C. Selenium-77 shifts to high frequency of SeMe, at -30 "C. Invertomerthe 77Se and lg5Pt chemical shifts are significantly greater thanthose pertaining to the corresponding saturated ligandcomplexes ( c j Table 3 of ref. 8). This is presumably a result ofthe differing anisotropies associated with C-C and C=C bonds.In the case of the unsaturated ligand complexes, Table 5 revealsseveral unusual features. In particular, the Ig5Pt shifts for the DLspecies are to lower frequency of the shifts in the mesoinvertomers whereas in all other S/Se saturated ligand speciesstudied to date8 this signal lies between the two meso values.The temperature dependences of the DL shifts (ca.0.5 p.p.m."C') were also markedly higher than those of the meso shifts(ca. 0.024.1 p.p.m. 'C-'), and caused broadening andapparent splitting of the signals in some cases, as a result oftemperature gradients in the sample probably caused by 'Hdecoupling.Linear plots of 6(Se) versus 6(Pt) and lJSept uersus S(Pt)within each invertomer species were found to hold as in the caseof [PtXMe,(MeSeCH,CH,SeMe)].8 Figure 6 illustrates thelinear relationships of 6(Se) and 6(Pt) for the invertomers of[PtXMe,(MeSeCH=CHSeMe)] (X = C1, Br, or I).The trends in chemical shifts and coupling constants aregenerally as observed previously with increasing electroJ. CHEM. SOC. DALTON TRANS. 1985726048 - s x36-2L12349-----rneso-1 1X=CL1Figure 3.Ligand-methyl H spectra of [PtXMe,(MeSeCH=CHSeMe)]showing the halogen dependence of invertomer populationsnegativity of the halogen causing deshielding of a magneticenvironment, with a corresponding decrease in lJSep1. It shouldalso be noted that, for a given invertomer, the values of 'JSept areinvariably higher than in the corresponding saturated ligandanalogues. This would appear to reflect differing strengths ofPt-Se bonds as seemed to be the case for [PtXMe,{MeSe-(CH,),SeMe}] (n = 2 or 3). Accordingly, MeSeCH,CH,SeMewould not be expected to displace the unsaturated analoguefrom its complexes: equation (1). However, equation (1) lies well[PtXMe,(MeSeCH=CHSeMe)] + MeSeCH,CH,SeMe -to the right and occurs rapidly at room temperature.The ligandMeSe(CH,),SeMe reacts in a similar fashion. It thus appearsthat the Pt-Se bonds in these unsaturated ligand complexes arerelatively weak for mononuclear complexes, and '.ISepI values arenot direct reflections of these bond strengths. Changes in J,,?values may be primarily due to non-bonded electron-pairinteractions which mask smaller effects caused by changes inbond strength.A particularly notable feature of these systems is thepronounced dependence of invertomer populations ontemperature (Table 5, footnote b). This is in contrast tosaturated ligand complexes which are essentially temperatureindependent.,** This variation is particularly evident in thelg5Pt spectra and its magnitude depends only on the type ofinvertomer and not on the halogen.Temperature decreasecauses a decrease in meso-1 and DL abundances with acorresponding increase in meso-2 abundance. The effect oflowering the temperature will be slightly to shorten bondstrikingly illustrate how the predominant invertomer of these Secomplexes in solution becomes the sole invertomer in the solidstate. A similar trend is to be expected for the sulphur ligandcomplexes although this has not been confirmed to date. Thedifferent relative orientations of the SeMe groups in complexes(4) and (6) are reflected in the different mean torsional anglesX-Pt-Se-Me, being 25(2)" for (4) and 175(6)* for (6). The ringsin the two compounds also differ slightly.That in compound (4)is distinctly non-planar with the platinum atom 0.66 8, from theleast-squares best plane through the other four atoms whichthemselves deviate by < 0.01 8, from the plane, while the ring incompound (6) is essentially planar (maximum and meandeviations of 0.018 and 0.012 8, from the least-squares bestplane through all five atoms).The mean Pt-C, Pt-CI, and Pt-I distances of 2.06(3), 2.440(9),and 2.791(2) 8, are within the range of expected values. Themean Pt-Se distance of 2.531(3) 8, lies between two recentlyobserved values for this bond length, 2.598(7) 8, inmeso -1 DL meso-2 DLFigure 4. Variation of invertomer population with halogen and ligandbackbone in the complexes [PtXMe,(MeSRSMe)]: R = -CH=CH-,X = C1 (O), Br (H), or I (A); R = -CH,CH,-, X = C1 (O), Br (O),or 1 (A)lengths, and presumably the invertomer populations dependrather critically on this.Shortening bond lengths is likely toincrease interaction between ligand methyls and platinummethyls (trans X) or halogen X, depending on which isomer isconsidered. Changes in populations should reflect the relativeimportance of these interactions. Since a decrease intemperature produces an increase in meso-2 population, ligandmethyl-halogen interactions would seem to dominate thechanges in population. However, the lack of any dependence onhalogen type for this population change is difficult torationalise.X-Ray Data.-The low-temperature n.m.r. results indicated achangeover in the predominant invertomer in solution frommeso-1 to meso-2 as the halogen size increased.It was thereforeof considerable interest to examine which solid-state configur-ations existed for different halogen complexes. The complexes[PtClMe,(MeSeCH=CHSeMe)] (4) and [PtIMe,(MeSeCH=CHSeMe)] (6) were chosen for X-ray analysis since theydisplayed the greatest difference in invertomer mixtures insolution (see Figure 3 and Table 3).The atomic co-ordinates for complexes (4) and (6) are givenin Tables 6 and 7, and the stereoscopic views of the structuresare shown in Figures 7 and 8. In the chloro-derivative (4), theSe-Me groups are clearly on the same side of the five-memberedring as the chlorine atom (cJ: meso-1 invertomer) while in theiodo-derivative (6), these groups are on the opposite side of thering to the iodine atom (cJ meso-2 invertomer).These results[PtXMe,(MeSeCH,CH,SeMe)] + MeSeCHSHSeMe (1J. CHEM. SOC. DALTON TRANS. 1985M e'MMe'[rneso -1 I [DLI [meso -21Figure 5. Labelled invertomer species of [PtXMe,(MeSeCH=CHSeMe)]700 900 1100 13006(Pt)/p.p.m.Figure 6. Correlation of 77Se and 19'Pt shifts for invertomers of[PtXMe,(MeSeCH=CHSeMe)]: X = CI (a), Br (M), or I (A)[(PtBrMe,),(SeMe,),] and 2.426(3) A in [P~(S~,CNBU',),].'~Full details of bond distances and angles in complexes (4) and (6)are given in Table 8.Dynamic N.M. R. Dam-Chalcogen inversion energies werecomputed by examining the ligand-methyl regions of the 'Hspectra. The signals coalesce with increasing temperatureaccording to the scheme in Figure 1.The case of [PtClMe,-(MeSCHXHSMe)] is depicted in Figure 9 (N.B.: in this case,the DL signals are scarcely visible in the temperature rangeshown). Theoretical bandshapes were computed according tothe cyclic scheme for the interchanging E methyls shown below(X = 19'Pt). It will be noted that only single-site inversion isconsidered as previously 2*8 and two different magnitudes ofrate constant k,, and k,, are included to allow for the differentkinetic pathways rneso-1 --- DL and DL - rneso-2. Thespectra were found to be sensitive to both rate constants at mosttemperatures and gave more satisfactory fits with theoreticalspectra based on pairs of k values rather than on single k values(Figure 9). Theoretical spectra were based on the static 'Hparameters in Table 3.Arrhenius and Eyring plots of the 'bestfit' spectra yielded the energy data in Table 9.At temperatures well above those at which sulphur orselenium inversion had become rapid, additional spectralchanges were observed. These involved broadening, andTable 6. Atomic co-ordinates for [PtClMe,(MeSeCH=CHSeMe)] (4)Atom X Y Z0.161 03(9) 0.118 09(6) 0.101 09(15)0.042 8(3) 0.206 9(2) 0.141 6(3)0.007 9(3) 0.085 3(2) -0.065 l(4)0.264 2(8) 0.164 6(5) -0.093 9(10)0.249 5(33) 0.042 8(17) 0.068 9(36)0.279 l(24) 0.141 4(19) 0.255 7(41)0.086 5(25) 0.077 7(16) 0.270 q38)0.128 l(29) 0.274 2(15) 0.061 3(38)-0.055 7(23) 0.204 2(13) -0.015 2(38)-0.065 O(22) 0.157 1( 16) - 0.094 6(30)0.070 9(30) 0.073 q16) -0.257 l(45)- 0.106 3(0) 0.243 2(0) -0.041 4(0)-0.121 9(0) 0.159 7(0) -0.190 4(0)Table 7.Atomic co-ordinates for [PtIMe,(MeSeCH=CHSeMe)] (6)X Atom Y 20.220 83(7) 0.101 16(6)0.309 22( 15) 0.258 72( 13)0.196 51(20) 0.219 59(17)0.422 92( 18) 0.076 3 1( 18)0.241 4(20) 0.005 5(18)0.057 4(18) 0.128 6(17)0.115 4(21) 0.160 8(20)0.342 3(20) 0.218 7(16)0.430 O(19) 0.163 3(18)0.356 3(0) 0.269 O(0)0.509 2(0) 0.168 5(0)0.148 l(19) -0.015 O(19)0.436 3(21) -0.043 q19)0.376 78( 10)0.570 75(18)0.135 91(26)0.329 76(28)0.583 5(33)0.428 5(28)0.235 l(31)0.076 5(24)0.146 2(26)0.203 5(32)0.094 2(0)- 0.069 6(27)- 0.022 4(0)~~eventual coalescence of the two Pt-methyl signals to onesinglet (plus 19'Pt satellites). This change was perfectlyreversible with temperature and, in view of the retention of19'Pt-methyl coupling, was due to an intramolecular re-arrangement of Pt-met hyl environments.Exactly analogouschanges have been reported for saturated ligand ring complexesof platinum(~v).~.~*' 5.16 In the case of mononuclear platinum(1v)complexes 3*8 this scrambling process accompanied a 180"'pancake' rotation of the ligand moiety. However, it has notalways proved possible to confirm the separate existence of the'pancake' rotation process and the energy barrier of this processhas been assumed3 to be the same as that of the Pt-methylscrambling. We are forced to make the same assumption in thepresent complexes, where again we postulate a highly non-rigidpseudo-eight-co-ordinate platinum intermediate associatedwith the ligand rotation process, such a species possessingincipient methyl scrambling.More recent studies l 7 with Pt'"complexes of the ligand 2,4,6-trithiaheptane, MeSCH,SCH,S-Me, have provided direct confirmatory evidence for a ligand'pancake' rotation in PtJV complexes and yielded reliable energJ. CHEM. SOC. DALTON TRANS. 1985 35 1Figure 7. Stereoview of X-ray structure of [PtCIMe,(MeSeCH=CHSeMe)]Figure 8. Stereoview of X-ray structure of [PtIMe,(MeSeCH=CHSeMe)]Table 8. Bond distances (A) and angles (") for [PtCIMe,(MeSeCH=CHSeMe)] (4) and [PtIMe,(MeSeCH=CHSeMe)] (6)(a) Bond distancesPt-XPt-Se( 1)Pt-Se(2)Pt-C( 1)Pt-C(2)Pt-C(3)(6) Bond anglesX-Pt-Se( 1)X-P t-Se( 2)X-Pt-C( 1)X-Pt-C(2)X-Pt-C(3)Se( l)-Pt-C( 1) se( l)-Pt-C(2) se( l)-Pt-C(3)Se(2)-Pt-C( 1)Se(2)-Pt-C(2)Se(2)-Pt-C( 3)(4)2.440(9)2.532(4)2.525(4)2.07(4)2.09(3)2.03(3)(4)92.5(3)93.q3)89.9( 10)92.q11)175.6(9)176.8( 1 1)9441 1)90.3( 10)92.q 1 1)174.3( 1 1)90.q10)(6)2.79 1 (2)2.53 l(2)2.53 5( 3)2.12(2)2.10(2)2.08(2)(6)85.00(7)84.97(7)9347)91.2(6)177.5( 7)178.3(8)92.9(6)9 5.8(8)92.9(7)176.1(6)97.5(5)(4) (6)2.01(4) 1.96(2)1.88(3) 1.89(2)1.9q4) 1.93(2)1.95(3) 1.97(3)1.32(5) 1.34(3)(6)86.6(9)86.4(11)86.3(9)111.4(8)101.8( 6)110.9(7)101.6( 7)96(1)126(2)123(2)97.I( 10)data for the process. The assumption of ligand rotationinitiating Pt-methyl scrambling in the present complexes istherefore well founded.Computation of high-temperature bandshapes of the Pt-methyl signals was carried out in the usual way, using the staticparameters given in Table 10.The resulting energy data aretabulated in Table 11.Pyramidal 1noersion.-Most of the data in Table 9 are inaccordance with expectations from previous studies. Values ofASt are close to 0 J K-' mol-' and log,, (Als-') values areca. 13, both parameters therefore being supportive of purelyintramolecular processes. Pyramidal inversion of Se atomsoccurs less readily that at S atoms (AAG* ca. 10 kJ mol-') ashas been noted previously. 2*3*15*16 H owever, the main purposeof the present work was to examine relative rates of inversion inunsaturated and saturated ligand complexes.The relevant datafor comparison are included in Table 9. Replacement of analiphatic backbone by an olefinic backbone consistentlyreduces the A@ values for the chalcogen inversion by 9-15 kJmol-'. Comparisons are made slightly more difficult by the factthat the AG* values for the saturated ligand complexes werebased on single rate-constant fittings2 The pairs of data for E'and E2 inversion in the present complexes essentially reflect thedifferent ground-state populations of the meso-1 and DLspecies. The lowering of AG* values on introducingunsaturation into the ligand can almost certainly be attributedto ( 3 p 2 p ) x or ( 4 p 2 p ) n conjugation between the chalcoge352 J. CHEM. SOC. DALTON TRANS. 1985(a 1k Is-'260 08 5 0145 0-15 0.." - v l H zFigure 9.Experimental and computer-synthesised H spectra of [PtClMe,(MeSCH=CHSMe)] (ligand-methyl reglon) showlng the effects of using (a)one and (b) two independent rate constants to simulate the S inversionTable 9. Arrhenius and activation parameters' for sulphur and selenium inversion in the homochalcogen ligand complexes of trimethylplatinum(iv)halidesComplex Inversion EJkJ mol-' log,, A AG*/kJ mol-' AHS/kJ mol-' ASt/J K-' mol-'[PtClMe,(MeSCH=CHSMe)][PtClMe,(NeSCH,CH,SMe)][PtBrMe,( MeSCHXHSMe)][PtBrMe,(MeSCH,CH,SMe)][PtIMe,(MeSCH=CHSMe)][PtIMe,(MeSCH,CH,SMe)][PtBrMe,(MeSeCH=CHSeMe) J[PtBrMe,(MeSeCH,CH,SeMe)]57.9 f 1.450.8 f 1.663.4 f 0.756.4 f 0.550.2 f 1.969.8 f 2.258.6 f 2.655.5 f 1.866.9 & 2.064.4 f 1.362.2 f 0.577.3 f 4.213.7 f 0.313.2 f 0.412.8 f 0.113.3 f 0.113.0 & 0.414.0 f 0.413.6 f 0.614.1 f 0.413.5 k 0.312.9 f 0.213.2 f 0.113.6 f 0.7a At 298.15 K.s', Se': [ m s o - l ] - [DL-11. Sz, Se2: [DL-11 + [meso-21. ' Ref. 2.52.4 f 0.348.1 f 0.463.3 & 0.153.4 f 0.148.6 f 0.562.8 f 0.153.8 f 0.847.8 f 0.862.6 f 0.063.4 f 0.160.1 f 0.172.4 0.355.9 & 1.448.8 f 1.661.0 f 0.754.3 & 0.548.2 f 1.967.4 rf: 2.256.7 f 2.653.6 f 1.864.4 & 2.062.0 & 1.359.7 f 0.674.6 & 4.211.8 & 6.02.4 k 6.83.1 f 2.215.5 & 7.59.6 k 11.319.4 f 7.95.9 f 6.5-4.5 & 4.4-1.0 4 1.8-7.7 & 2.4-1.5 & 8.37.3 k 13.0lone pair and the ligand backbone, the interactions being more Similar results were obtained in cis-platinurn(rr) andeffective in the planar transition state that in the ground state, -palladium(II) complexes of type cis-[MX,L] [X = C1, Br, orand the ( 3 p - 2 ~ ) ~ interaction for S atoms being marginally more I; L = MeSCH,CH,SMe, o-(SMe),C,H,Me, or cis-pronounced than the (4p-2p)n interaction for Se atoms.MeSCH=CHSMe].' The change here on going from aliphatiJ. CHEM. SOC. DALTON TRANS. 1985 353Table 10. Static parameters used in calculating platinum-methyl scrambling energy barriers in the complexes [PtXMe,(MeEREMe)]Pt-Me (trans to S or Se) --- X E R Q/"C v"/Hz 'Jb/Hz v"/Hz 2Jb/Hz Main bandsPt satellitesCI S -CH=CH- 27.0 144.0' 70.56 88.86 72.27 0.344 0.344CI S -CH2CH2-d 71.2 136.23 ' 70.30 77.88 72.27 0.286 0.240Br Se -CH=CH- 60.5 146.24' 70.8 1 93.38 72.02 0.143 0.143Br Se -CH2CH2-d 91.6 154.8 70.56 84.22 71.53 0.160 0.143a Chemical shifts measured relative to SiMe,.2J('95Pt-C-'H). In CDCl,. See ref. 1 for preparative details. ' In C,D,NO,-C,D,.Pt-Me (trans to X) T2.hTable 11. Energy barriers a calculated for platinum-methyl scrambling in the homochalcogen ligand complexesComplex EJkJ mol-' log,, A AG*/kJ mol-' AM/kJ mol-' AS*/J K-' mol-'[PtClMe,(MeSCH=CHSMe)] 87.3 t- 0.8 13.9 f 0.1 80.4 k 0.1 84.3 f 0.8 13.1 f 2.2[PtCIMe,(MeSCH,CH,SMe)] 91.7 f 1.2 13.1 f 0.2 90.0 & 0.3 88.3 f 1.2 -5.8 k 2.9[PtBrMe,(MeSeCH=CHSeMe)] 75.9 & 0.3 12.1 * 0.1 79.7 & 0.1 72.9 f 0.3 -23.0 & 0.7[PtBrMe,(MeSeCH,CH,SeMe)] 86.3 f 0.7 12.4 f 0.1 88.2 & 0.2 82.8 & 0.6 -17.9 f 1.5[PtClMe,(o-MeSC,H,SMe)] 83.6 f 1.0 12.7 f 0.1 83.8 & 0.2 80.4 & 0.1 -11.4 f 2.5" At 298.15 K.See ref. 1 for preparative details. ' Ref. 3.to olefinic ligands was 10-12 kJ mol-', with the aromaticligands having intermediate values. An analogous trend wasalso noted4 in the two series of rhenium(1) complexes,[ReX(CO),L] (X = C1, Br, or I; L = MeECH,CH,EMe orMeECHXHEMe, E = S or Se). Here the sulphur inversionbarriers were lowered by 9-12 kJ mol-' and the seleniumbarriers by 6 - 8 kJ mol-'.Fluxional Rearrangement.-The platinum-methyl scramblingdata for the unsaturated ligand complexes are presented inTable 11 alongside comparisons with aliphatic- and aromatic-ligand data.The AGS values are ca. 20 kJ mol-' higher thanthose of chalcogen inversion and are essentially independent ofhalogen. There appears to be a small dependence on ligandbackbone with values for olefinic ligands being 8-10 kJ mol-'lower than for aliphatic ligands, the aromatic ligand complexagain being intermediate in magnitude. This is the samedependence that was found for the chalcogen inversion, andlends support to the two processes being at least indirectlyrelated. It suggests that only when pyramidal inversion issufficiently rapid will ligand rotation and platinum-methylscrambling become possible. Thus, if the chalcogen inversion isfacilitated by X-x conjugation then this will also act in favour ofthe platinum-methyl scrambling.AcknowledgementsWe are grateful to the S.E.R.C.for a postdoctoral researchassistantship (to A. W. G. P.), and to the CommonwealthScholarship Commission (U.K.) and the University GrantsCommission (India) for support (to S. K. B.). We also gratefullyacknowledge the use of the S.E.R.C. n.m.r. services at the City ofLondon Polytechnic and the University of Warwick.References1 E. W. Abel, A. R. Khan, K. Kite, K. G. Orell, and V. Sik, J. Chem.Soc., Dalton Trans., 1980, 1169.2 E. W. Abel, A. R. Khan, K. Kite, K. G. Orrell, and V. Sik, J. Chem.Soc., Dalton Trans., 1980, 1175.3 E. W. Abel, S. K. Bhargava, K. Kite, K. G. Orrell, V. Sik, and B. L.Williams, J. Chem. Soc., Dalton Trans., 1982, 583.4 E. W. Abel, S. K. Bhargava, M. B. Bhatti, K. Kite, M. A. Mazid, K. G.Orrell, V. Sik, B. L. Williams, M. B. Hursthouse, and K. M. A. Malik,J. Chem. Soc., Dalton Trans., 1982, 2065.5 E. W. Abel, S. K. Bhargava, K. Kite, K. G. Orrell, V. Sik, and B. L.Williams, Polyhedron, 1982, 1, 289.6 F. R. Hartley, S. G. Murray, W. Levason, H. E. Soutter, and C. A.McAuliffe, Inorg. Chim. Acta, 1979, 35, 265.7 L. M. Kataeva, E. G. Kataeva, and D. Ya Idiyatullina, Zh. Strukt.Khim., 1966, 7, 380.8 E. W. Abel, K. G. Orrell, and A. W. G. Platt, J. Chem. Soc., DaltonTrans., 1983, 2345.9 D. A. Kleier and G. Binsch, DNMR3 Program 165, QuantumChemistry, Program Exchange, Indiana University, 1970.10 D. F. Grant and E. J. Gabe, J. Appl. Crystallogr., 1978, 11, 114.11 D. E. Clegg, J. R. Hall, and C. A. Swile, 1. Organomet. Chem., 1971,12 M. H. Chisholm, H, C. Clarke, L. E. Manzer, J. B. Stothers, and13 E. W. Abel, A. R. Khan, K. Kite, K. G. Orrell, V. Sik, T. S. Cameron,14 W-H. Pan, J. P. Fackler, and H-W. Chen, Znorg. Chem., 1981,20,856.15 E. W. Abel, A. R. Khan, K. Kite, K. G. Orrell, and V. Sik, J. Chem.16 E. W. Abel, K. Kite, K. G. Orrell, V. Sik, and B. L. Williams, J. Chem.17 E. W. Abel, M. Z. A. Chowdhury, K. G. Orrell, and V. Sik, J.38, 403.J. E. H. Ward, J. Am. Chem. Soc., 1973, 95, 8574.and R. E. Cordes, J. Chem. Soc., Chem. Commun., 1979, 713.Soc., Dalton Trans., 1980, 2208, 2220.Soc., Dalton Trans., 1981, 2439.Organomet. Chem., 1983, 258, 109.Received 23rd March 1984; Paper 4147

ISSN:1477-9226    

DOI:10.1039/DT9850000345

出版商:RSC    

年代:1985

数据来源: RSC