Syntheses and reactions of coordinatively unsaturated silyl, aryl osmium(II) complexes and the crystal structures of Os[Si(OEt)3]R(CO)(PPh3)2 and Os[Si(OEt)3]R(CO)2(PPh3)2 (R=phenyl or o-tolyl)

Reaction between OsPhCl(CO)(PPh3)2 and HSi(OEt)3 gives the five-coordinate complex, Os[Si(OEt)3]Cl(CO)(PPh3)2 (1), the crystal structure of which reveals a square pyramidal geometry with the triethoxysilyl ligand at the apical site and the two triphenylphosphine ligands arranged mutually trans. Addition of CO gives the six-coordinate complex, Os[Si(OEt)3]Cl(CO)2(PPh3)2 (2), but this addition is thermally reversible. The chloride ligand in 1 is replaced easily and reaction with LiR gives the stable, five-coordinate complexes, Os[Si(OEt)3]R(CO)(PPh3)2 (3a, R=phenyl; 3b, R=o-tolyl). Crystal structure determinations for 3a and 3b reveal a coordination geometry almost unchanged from that of 1 with Cl replaced by phenyl and o-tolyl, respectively. Addition of CO to 3a and 3b gives the six-coordinate complexes, Os[Si(OEt)3]R(CO)2(PPh3)2 (4a, R=phenyl) (4b, R=o-tolyl). Crystal structure determinations for 4a and 4b confirm octahedral geometry for each compound. Despite having adjacent aryl and silyl ligands neither 3a, 3b nor 4a, 4b show any tendency to undergo reductive elimination of RSi(OEt)3. IR, 1H-, 13C- and 29Si-NMR data for all new complexes are presented.