MOLYBDENUM AND TUNGSTEN COMPLEXES OF S2CPME3 AND RELATED LIGANDS - CRYSTAL AND MOLECULAR-STRUCTURES OF W(ETA-3-S2CPME3)(CO)2(PME3)2, [MO(ETA-2-S2C(H)PME3)(CO)2(PME3)2]BF4, AND [MO(ETA-3-SC(SME)PME3)(CO)2(PME3)2]I

The known compound Mo(S2CPMe3)(CO)2(PMe3)2 (1a) and the newly prepared tungsten analog W(S2CPMe3)-(CO)2(PMe3)2 (1b), obtained by HCl elimination from WH(Cl)(CO)2(PMe3)3 upon treatment with CS2 and PMe3, contain a trihapto-bonded S,S',C-trimethylphosphonium dithiocarboxylate ligand as demonstrated by X-ray studies carried out with lb. Interaction of compounds 1 with protic acids affords the dithioformate species [M(eta2-S2C-(H)PMe3)(CO)2(PMe3)2]+ (M = Mo (2a), W (2b)) while alkyl-derived electrophiles X+ (X = Me, Et) furnish the cationic complexes [M(eta3-SC(SR)PMe3)(CO)2(PMe3)2]+ (isolated in the form of iodide salts; M = Mo, R = Me (3a), R = Et (4); M = W, R = Me (3b)). These contain unprecedented S-alkyl phosphonio dithioester ligands as a result of alkylation at one of the sulfur atoms. The protonation reactions are proposed to occur by initial attack of H+ at the strongly basic metal center followed by hydride migration to the electrophilic carbon atom. In accord with this, the reaction of the hydrides MH(Cl)(CO)2(PMe3)3 (M = MO, W) With CS2 gives, under appropriate conditions, the cationic species 2a and 2b. Compounds 1b, 2a[BF4], and 3a have been characterized by X-ray crystallography. Crystals of lb are orthorhombic, P2(1)2(1)2(1), with a = 11.957(4) angstrom, b = 12.724(3) angstrom, c = 13.758(2) angstrom, and Z = 4. 2a[BF4] possesses a triclinic space group P1 and has unit cell constants a = 6.935(3) angstrom, b = 13.372(3) angstrom, c = 13.722(2) angstrom, alpha = 103.49(2)-degrees, beta = 94.04(2)-degrees, gamma = 104.69(2)-degrees, and Z = 2. 3a is also triclinic, P1, with a = 11.193(2) angstrom, b = 12.988(7) angstrom, c = 8.791(4) angstrom, alpha = 99.81(4)-degrees, beta = 94.54(5)-degrees, gamma = 78.11(4)-degrees, and Z = 2.