REACTIONS OF COORDINATED PHOSPHORUS TRICHLORIDE, PHENYLPHOSPHONOUS DICHLORIDE, 1-PHENYL-3,4-DIMETHYLPHOSPHOLE AND MESITYLPHOSPHINE IN OSMIUM(II) COMPLEXES

Substitution of a single labile triphenylphosphine ligand in OsHCl(CO)(PPh3)3 by PCl3, PCl2Ph, PhPCHCMeCMeCH or PH2(mesityl) [mesityl = 2,4,6-trimethylphenyl] gives complexes with the new ligand trans to the hydride ligand and mutually cis to the two triphenylphosphine ligands. The PCl3 and PCl2Ph complexes undergo slow substitution reactions at phosphorus, at temperatures > 50-degrees-C, with the nucleophiles methoxide, toluidine and hydride. The hydride ligand is readily cleaved either by acetonitrile solutions of aqueous perchloric acid, to give cationic acetonitrile containing complexes or by chlorine, to give neutral dichloride complexes. In all but one instance the products are isolated as mixtures of isomeric complexes with trans triphenylphosphine ligands. An exception to this dominant sterochemistry is observed for the complex containing the bulky mesitylphosphine ligand, OsHCl(PH2mesityl) (CO)(PPh3)2 for which the product of the hydride cleavage and subsequent carbonylation reaction consists of an almost equal mixture of isomers of [OsCl(PH2mesityl)(CO)2(PPh3)2]ClO4 with cis and trans triphenylphosphine ligands. The structure of one of these isomers, with a mesitylphosphine trans to triphenylphosphine, has been determined by X-ray crystallography.