Stepwise reduction of the thiocarbonyl ligand: hydride transfer to CS: thioformyl, thioformaldehyde, methylthiolato, secondary carbene, formyl and iminoformyl complexes of osmium

Abstract

The complexes OsHX(CS)L(PPh 3) 2 (X  Cl, Br; L  CO and X  Cl; L  CN- p-tolyl), which contain mutually cis hydrido and thiocarbonyl ligands, undergo transfer of the hydrido ligand to CS when treated with CO to give blue complexes containing the thioformyl ligand [OsCHS]. OsCl(CHS)(CO) 2(PPh 3) 2 reacts with borohydride to give the first metal complex of the thioformaldehyde monomer, viz. Os(η 2-CH 2S)(CO) 2(PPh 3) 2, which reacts rapidly with HCl to give OsCl(SCH 3)(CO) 2(PPh 3) 2 and then, by a slower reaction, OsCl 2(CO) 2(PPh 3) 2 and CH 3SH. The ligands produced in this stepwise reduction have possible relevance as models for postulated intermediates in the Fischer—Tropsch synthesis. Synthetic routes to formyl [OsCHO], iminoformyl [OsCHNMe] and secondary carbene complexes [OsCHSMe, OsCHNMe 2, OsCHOMe] are also demonstrated.