Triphenylphosphonium and trimethyl-phosphonium hexachloroosmates (IV) and their reactions with alkylating agents; Methyl and trimethylsilylmethyl osmium compounds; trans-di-chlorotetrakis(trimethylphosphine)-osmium(II); Tetrakis(trimethyl-silylmethyl)oxoosmium(VI)

Polyhedm Vol. 1, No. I, pp. 8341, Printed in Great Britain.

1982

02~-5387/82/01008M5f03.0010 Pergamon Press Ltd.

TRIPHENYLPHOSPHONIUM AND TRIMETHYLPHOSPHONIUM HEXACHLOROOSMATES (IV) AND THEIR REACTIONS WITH ALKYLATING AGENTS; METHYL AND TRIMETHYLSILYLMETHYL OSMIUM COMPOUNDS; TRANS-DICHLOROTETRAKIS(TRIMETHYLPHOSPHINE)OSMIUM(I1); TETRAKIS(TRIMETHYLSILYLMETHYL)OXOOSMIUM(VI) ALFRED0 S. ALVES, DAVID S. MOORE, RICHARD A. ANDERSEN and GEOFFREY WILKINSON* Chemistry Department, Imperial College, London, SW7 2AY, and Chemistry Department, University of California, Berkeley, CA 94721,U.S.A. (Received 6 August 1981) Abstract-The reported synthesis of tetrachlorobis(triphenylphosphine) osmium(IV) is shown to proceed via initial formation of a salt, [PhsPH]x[OsCIJ, from which the corresponding [Me,PH]+ salt can be obtained by exchange; the latter salt reacts with acetone to give [MesPC(OH)Me&[OsClJ. The action of methyl and trimethylsilylmethyl alkylating agents on the hexachloroosmates and on OsCls(PPhs)s to give u-alkyls is reported. The complex trons-OsMe,(PPhs)., reacts with carbon monoxide to give the corresponding bis acetyl. The complex trunsOsCI,(PMe,), is resistant to attack by alkylating agents. The interaction of bis(trimethylsiIylmethyl)magnesiumwith 0~0, in pentane at -70°C yields (Me,SiCHr),OsO.

INTRODUCTION Osmium compounds with metal-carbon u bonds have been recently reviewed.’ Relatively few tertiary phos-

phine complexes with alkyl or aryl groups are known: these are mainly chelating diphosphine complexes of the type OsXR(diphos), (where X may be Cl, R = Me, Et, X, R = Me, Ph) hydrido, alkyl or aryl compounds derived from the halides by LiAlH4 reduction: and carbonyl compounds OsClR(CO)(PPh,),? We now report some alkyls derived from phosphonium ion, from salts of the hexachloroosmate(IV) OsCl,(PPh,), and from 0~0,. A. OShfIIJh4(W)HALIDE COMPLKKKSAND TIIBIR ALKYLATIONRKACTIONS 1. Triphenylphosphine complexes

On attempting to prepare truns-OsCl,(PPh,), by the method of Kahar et 01.~a yellow solid was isolated and shown to be the salt [Ph,PH],[OsClJ. Thus, the IR spectrum has a band at 2425 cm-’ [ u(P-H)] and a strong OS-C] stretch at 301 cm-‘. The conductivity in nitromethane corresponded to that of a 2 : 1 electrolyte. X-ray crystallographic stud? has confirmed the salt formulation; the two phosphonium ions are located at opposite faces of the octahedra1 ion and orientated so that the hydrogen bound to phosphorus points towards the face as in (1). The P-H bond length is 1.22A. On crystallisation of this salt from hot acetone, the dark brown crystals of 0sC14(PPh&, identical with those reported4 are obtained and X-ray studg contirms the octahedra1 geometry with trans-PPhs groups. The conversion of the phosphonium salt to the neutral complex in acetone can be monitored by “C NMR spectra; there is no evidence of any stable intermediates. The reaction of [Ph3PH],[OsClJ with an excess of

MeLi and PhpP in benzene produces two products that can be separated either by low temperature extraction with petroleum or by chromatography. These compounds were identified spectroscopically and analytically as truns-OsMea(PPh&, and OsH(Me)(GH,PPh,)(PPh&. The presence of the ortho metallated group in the latter was confirmed by bands in the IR spectrum at 1590,1085 and 740 cm-’ .6 The dimethyl compound reacts readily at ambient temperature with carbon monoxide (2 atm) and the reaction can be monitored by IR and NMR spectra. Thus, the ‘H NMR spectrum shows the disappearance of the OsMe resonance at 6 0.02ppm and the appearance of an acetyl resonance at S 1.3ppm. In the IR spectrum a new band at 1940cm-’ (OS-CO) appears initially but disappears with the concommitant appearance of the acyl band at 1830cm-‘. We have been unable to isolate the carbonyl or monoacyl intermediates, however, but it seems likely that the first species formed is 0sMe2(PPh&(CO) resulting from dissociation of PPh, and coordination of CO to which methyl is then transferred. The two methyl groups are transferred successively since they are in trans positions and there is no evidence for the formation of acetone which might have been expected from a group transfer of methyl in cis positions.’ By contrast with the above alkylations giving OS” and OS” species the interaction of [Ph,PH]a[OsClJ with MeMgI in diethylether gives a red-brown solution from which OsMe,(PPh,), can be isolated as an air-sensitive solid. The interaction of [Ph~PH]a[OsC16] with Me,SiCH,MgCl in diethyl ether also produces an orthometahated osmium(II1) species OsH(CHaSiMe3 (&H.,PPha)(PPhJ similar to the methyl compound noted 83

A. S. ALVESef al.

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above; the IR spectrum again has typical bands at 1585, 1430, 1085 and 730 cm-‘. 2. Trimethylphosphine complexes The interaction of [Ph,PH],[OsCL] with excess PMe, in toluene at 80°C produces the exchanged salt [MesPH],[OsC&] which has a conductance corresponding to a 2 : 1 electrolyte. The IR spectrum shows the P-H stretch at 2470 cm-’ and an OS-Cl stretch at 305 cm-‘. The 31P NMR spectrum has a main doublet [J(P-H) = 513 Hz] each line split into a 10 line multiplet [J(PCH) = 10 Hz] due to coupling with the methyl group protons. On recrystallisation from acetone, a second phosphonium salt is obtained. This shows IR bands at 3448 and 3394cm-‘(OH); 1380-70, 1360-50, 1122cm-’ (R,COH); and 305 cm-’ (OsCl). The 3’P NMR spectrum has a multiplet at S t41.3 ppm [J(P-CZQ= 16.88Hz] while the ‘H NMR spectrum has lines corresponding to Me,P (S 1.7, d, J = 11Hz), PCMe,OH (S 1.2, .d, J = 12 Hz) and OH (6 6.2, d, .I = 3.8 Hz). The spectroscopic data suggests that the salt is [Me,PCMe20Hlz[OsCL] and this formulation has been substantiated by a full X-ray crystallographic study.s In the crystal the hydroxyl hydrogen is hydrogen-bonded to one of the chlorines of the [OsC@ anion [H . . . Cl = 2,49A] in which there is a corresponding lengthening of the Os-Cl bond [2.345A compared to 2.270& as in (2). The interaction of P-H bonds with acetone has been suggested to proceed by nucleophilic attack at the carbonyl carbon followed by proton transfer in reactions of the type:9

metric structures in PMe, complexes.” Unfortunately, we have been unable to obtain crystals suitable for X-ray crystallography. B. REACTIONS OF TlUCHI.OltOZRZS(TRlPHRNYL

PHOSPmNE) OsrvnuM The complex fac-OsC1B(PPh&4 and MepSiCHIMgCl

in toluene react to produce what is clearly according to analytical and spectroscopic data an orthometallated triphenylphosphine osmium(IV) complex, 0sHCl(CH5SiMe3)(C&PPh2XPPhs), presumable via initial reduction to an OS” intermediate which then undergoes oxidative-addition. On attempting to convert OsCl,(PPh,), into 0sC1#‘Ph~)~r3 by the same procedure used to prepare the latter from (NH&OS& and Ph3P, namely refluxing in aqueous t-butanol, the product was a yellow solid, OsC&(PPh&. Neither this complex nor OsCl,(PPh,), appear to undergo exchange with PMe, under conditions we have tried but OsCl,(PPh,), does so quite readily to give trans-OsC12(PMe3)4.The structure of the latter has been confirmed by X-ray diffraction study: the four PMea ligands adopt a pseudo tetrahedral arrangement about the osmium atom. This complex is extremely resistant to attack and may be recovered unchanged after treatment in toluene, ether or tetrahydrofuran with Li, Mg and Al methyls, NaBH,, LiAIH, and Na/K liquid alloy. P h.

P

PhzPH t R,R# = 0 +PhzP-C(OH)R,R2. In the present case, the following reactions seem reasonable: bPh.

MePH’ * Me3P t H’ Me*COt H’ $ Me2C’OH MeC’OH t :PMes + [Me,C(OH)PMe$. Unlike the case with triphenylphosphonium hexachloroosmate no neutral species is formed even on prolonged reaction. The failure of the [PhpPH]+ ion to react is probably due to the lower basicity of Ph3P. In anhydrous acetone ReCI, and PPhs react to give [Ph,PC(Me),CH2C(0)Me]‘[ReCI,PPh,]- and the cation was also obtained from K*ReCL, PPh, and HCI in acetone but here the reaction was proposed to proceed via acid catalysed condensation of acetone to mesityl oxide followed by Michael addition to PPh+” [Me3PH12[0sC&] with The interaction of Me,SiCH,MgCI produces two products. When the salt is in excess, OsCl,(CH,SiMe,)(PMe& is obtained and when the Grignard reagent is in excess, a dimer, 0s2C1(CHSiMe&(PMes)~. The latter appears to have lost a hydrogen from the Me$iCH2 groups” to form bridges as in (3); the ‘H NMR spectrum has resonances at S -0.1 and -0.3 ppm with a ratio of 1 : 9 (CH and SiMe,) while the methyl groups of the non-equivalent PMe3 groups have resonances at S 1.8 t, 1.3 d and 1.15ppm. The compound thus appears to have two fivecoordinate osmium atoms in different (11,111)formal oxidation states wth a different number of PMe, groups on each atom. There are precedents for unusual asym-

86

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toluene. Yields are essentially quantitative. [Found: C, 68.0 (68.8); H, 5.1 (5.0); P, 9.4 (9.4)%]. The formulation as the truns-bis(acety1) is confirmed by the o&o to meta separation of the phenyl protons (0.3ppm)‘g in the ‘H NMR spectrum and by the 3’P NMR spectrum, S - 4.22 ppm (s). 6 Tetramethylbis(triphenylphosphine) osmium(IV) To a stirred solution of [Ph3PHl~[OsCl~I (0.21 g) in Et,0 (10cm3) at -70°C was added dropwise MeMgI (1.5 cm3 of 1.3 M solution in Et,O) and the mixture stirred at ambient temperature for 3 d. The solution was filtered and the solvent removed; extraction of the oily residue with petroleum (3 x 10cm3), concentration to 15cm3 and cooling at - 20°C gave a brown-red crystalline solid which was collected, washed with petroleum and dried in vacuum. Yield O.O3g, 17%; m.p. (decomp.) 80°C. [Found: C, 62.5 (62.2); H, 5.7 (5.4); P, 7.0 (8.0)%. M 700 (774)]. NMR: ‘H 0.31 (4 x Me), 7.09 m (6 x Ph); the trans formulation of PPh, groups is established by the same criterion’9 as above (0.65 ppm). The compound is soluble in hydrocarbons decomposes in CHC13, CH& Me&O and thf and is insoluble in pyridine, MeOH and EtOH. 7 Hydrido (trimethylsilylmethyl)

(9’ - diphenylphos phinophenyl) triphenylphosphine osmium(III)

-

To [Ph,PH],[OsC&] (0.86 g) in Et,0 (20 cm3) at - 70°C was added MeaSiCHzMgCl (5 cm3 of 1.6 M solution in Et,O). After 1 hr the solution was allowed to warm to room temperature and after 12 hr stirring the solvent was removed and the residue extracted with petroleum (3 x 20cm3). The extract was filtered, concentrated (10cm3), and cooled to - 20°C for 12 hr when the yellow-brown crystals were collected, washed with petroleum and dried in vacuum. Yield 0.3 g, 40%; m.p. 170°C. [Found: C, 59.4 (59.8); H, 5.1 (5.1); P, 7.6 (7.7)%]. NMR: ‘H; - 10.6m (H); 0.3 (SiMe3), 0.75 (CH,), 7.7-7.0 (Ph). 8 Hydrido (chloro) (trimethylsilylmethyl) ($ - diphenyl phosphinophenyl) triphenylphosphineosmium(III) To fat-0sC13 (PPh3)3 (0.84g) in toluene (40 cm3) was added Me$iCH&C1(3.5 cm3, 1.65M in EtzO) and the solution stirred for 30 min at - 70°C and again at room temperature for 2d. Work up as in 7, but extracting with toluene gave a microcrystalline brown solid. Yield 0.15g (24%); m.p. (decomp.) 140°C. [Found: C, 56.9 (56.9); H, 4.8 (4.8); Cl, 3.8 (4.1); P, 7.1 (7.9)%. M 720 (836)]. NMR: ‘H, -9.2 m (H); 0.3 (SiMe,); 0.7 (CH,); 6.5-8.0 br (Ph). The compound is soluble in aromatic solvents and cyclohexane, slightly soluble in petroleum and reacts with Me,SO, CHCl, and CH,Cl,. 9 Tn’chloro(trimethylsilylmethyl)bis(trimethylphosphine)

10 Chloro bis (u-trimethylsilylmethylidene) (trimethylphosphine) di - osmium(II, III)

pentakis

To [Me3PH],[OsC&](1.Og) in tetrahydrofuran (80 cm’) at -70°C was added Me,SiCH,MgCl (6 cm3 of 1.3 M solution in Et,O) and the solution stirred for 3 min at - 70°C and ca. 1 d at room temperature. After removal of solvent the residue was extracted with petroleum (50cm3) which was concentrated to cu. 5cm’. Elution from a cellulose column with toluene gave a yellow-red fraction which was collected, concentrated to cu. 3 cm3 and cooled to -40°C to give red microcrystals which were washed with chilled petroleum and dried in vacuum. Yield 0.25g, 30%; m.p. (decomp.) 130°C. [Found: C, 29.0 (28.5); H, 6.7 (6.9); Cl, 3.7 (3.7); P, 14.5 (15.4)%. M 880 (968)]. 11 Trichlorobis(triphenylphosphine) osmium(III) A solution of fac-OsC13(PPh3)34 (1 g) in Bu’OH (25 cm’) and water (1 cm3) was refluxed for 3 d. The resulting yellow solid was collected, washed with water (3 x 5 cm’), methanol (3 x 5 cm3) and ether (2 x 10cm3) and dried in vacuum over NaOH pellets. Yield 0.7 g, 83% m.p. 160°C. [Found: C, 52.0 (52.5); H, 3.8 (3.8), Cl, 12.8 (12.8); P, 6.3 (6.8)%. M 800 (820)]. 12 trans-Dichlorotetrakis(trimethylphosphine) osmium(H) The complex 0sC12(PPh3)3’3 (l.Og, 1.8 mmol) and PMe, (2 cm4 in toluene (20 cm3) were dried at 80°C in a pressure bottle for 20 hr after which the solvent was removed and the yellow solid washed with petroleum (3 x 15cm3). Recrystallisation from toluene-petroleum (1 : 1) gave a yellow-gold crystals of quality suitable for X-ray study. Yield, 0.5 g, 83%; m.p. > 350°C. [Found: C, 25.8 (25.5); H, 6.4 (6.3); Cl, 12.6 (12.5); P, 20.6 (21.6)%. M 600 (565)]. 13 Tetrukis(trimethylsilymethy1) oxoosmium( VI) Bis(trimethylsilylmethy1) magnesium (6.7 cm3 of a 1.0 M Et20 solution, 0.0067 mol) was added to osmium tetraoxide (0.85g, 0.0033 mol) in pentane (50cm3) at -70°C. The dark brown suspension was stirred for an additional 2hr. The volatile material was removed in vacuum and residue was extracted with pentane (50 cm3), filtered, and concentrated to ca. 10 cm3. Chromatography on silica gel with pentane, elution followed by concentration to cu. 2 cm3 and cooling to -70°C gave the brown-yellow needles which were collected and dried in vacuum. Yield: 0.45g, 12%, m.p., cu. 15°C. [Found: C, 34.3 (34.5); H, 8.0 (7.9)%]. Acknowledgements-We thank the Brazilian Science Research Council IA.S.A.) and S.E.R.C. (D.S.M.) for suoaort. Dr. J. F. Gibson for epr measurements and Johnson Mat&y Ltd. for loan of osmium salts.

osmium(IV)

To [Me3PH]2[OsC&](0.89 g) in thf (60 cm3) at - 70°C was added Me,SiCH,MgCl (3 cm3 of 1.3 M solution in Et,O) and the solution stirred for 20 min followed by 2 d at room temperature. The filtered solution was evaporated and the oily residue extracted with petroleum (2 x 20cm’) which was evaporated in vacuum and the residue crystallised from toluene at -40°C to give redbrown crystals. Yield, 0.42 g, 44%; m.p. > 340°C. [Found: C, 24.4 (24.0); H, 6.1 (5.8); Cl, 21.0 (21.0); P, 6.3 (8.3)%]. M 400 (535)]. NMR: -0.22 (CH2); -0.1 (SiMe3); 1.1 (PMe,).

REFJZRENCRS

‘D. S. Moore, Coord. Chem. Revs. 1982,in press. ‘J. Chatt and R. G. Hayter, Z. Chem. Sot. 1%3,6017. ‘W. R. Roper and L. J. Wright, Z. Organometal.Chem. 1977,142, Cl. ‘hf. M. T. Kahar, S. S. Ahamedand R. A. Levenson, Z. Znorg. Nuclear Chem. 1976,38, 1135. ‘A. C. Skapski, Imperial College, private communication. 6D. J. Cole-Hamilton and G. Wilkinson, J. Chem. Sot., Dalton Trans. 1977,797;W. Keir, J. Organometal. Chem. 1%8,14,179. ‘See, e.g. E. Carmona-Guzman and G. Wilkinson, Z. Chem. Sac., Dalton Trans. 1978, 1139.

Triphenylphosphonium and trimethylphosphonium hexachloroosmates(IV) %I. B. Hursthouse, Queen Mary College, private communication. 9E. Evargelidou-Tsolis, F. Ramirez, J. F. Pilot and C. P. Smith, Phosphorus 1974,4,109. u’I-I.Gerkke Jr., and G. Eastland, Znorg. Chem. 1970,9,2722, J. Znorg.Nuclear Chem. 1970,32,867. I’M. Bochmann, G. Wilkinson, A. M. R. Galas, K. M. A. Malik and M. B. Hursthouse, 1. Chem. Sot. D&n Trans. 1980,1797. “See, e.g., R. A. Andersen, R. A. Jones and G. Wilkinson, 1. Chem. Sot., Dalton Trans. 1978,466. i3P. R. Hoffman and K. G. Caulton, .Z.Am. Chem. Sot., 1975,15, 4221.

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“D . S. Moore, A. Alves and G. Wilkinson, .Z.Chem. Sot., Chem. Commwr. 1982,in press. “J F. Gibson, K. Mertis and G. Wilkinson, Z. Chem. Sot., Zkon Trans. 1975,1093. “E. C. Ashby, J. Laemmle and H. M. Neumann, Accts. Chem. Res. 1974,I, 272. “P. S. Braterman and R. J. Cross, Chem. Sot. Revs. 1973,2,271. ‘*K Mertis and G. Wilkinson, J. Chem. Sot., DaltonTrans. 1976, 1488. ‘9. S. Moore and S. D. Robinson, Znorg. Chim. Acta 1981,53, L171.