Metallacyclic complexes with ortho-silylated triphenylphosphine ligands, LnOs(κ2(Si,P)-SiMe2C6H4PPh2), derived from thermal reactions of the coordinatively unsaturated trimethylsilyl, methyl complex, Os(SiMe3)(Me)(CO)(PPh3)2

Reaction between Os(SiCl3)Cl(CO)(PPh3)2 and five equivalents of MeLi produces a colourless intermediate, tentatively formulated as the lithium salt of the six-coordinate, dimethyl, trimethylsilyl-containing complex anion, Li[Os(SiMe3)(Me)2(CO)(PPh3)2]. Reaction of this material with ethanol releases methane and gives the red, coordinatively unsaturated methyl, trimethylsilyl-containing complex, Os(SiMe3)(Me)(CO)(PPh3)2 (1). An alternative synthesis of 1 is to add one equivalent of MeLi to Os(SiMe3)Cl(CO)(PPh3)2, which in turn is obtained by adding three equivalents of MeLi to Os(SiCl3)Cl(CO)(PPh3)2. Treatment of 1 with p-tolyl lithium, again gives a colourless intermediate which may be Li[Os(SiMe3)(Me)(p-tolyl)(CO)(PPh3)2], and reaction with ethanol gives the red complex, Os(SiMe3)(p-tolyl)(CO)(PPh3)2 (3). Complexes 1 and 3 are readily carbonylated to Os(SiMe3)(Me)(CO)2(PPh3)2 (2) and Os(SiMe3)(p-tolyl)(CO)2(PPh3)2 (4), respectively. Heating Os(SiMe3)Cl(CO)(PPh3)2 in molten triphenylphosphine results only in loss of the trimethylsilyl ligand and formation of the previously known complex containing an ortho-metallated triphenylphosphine ligand, Os(κ2(C,P)-C6H4PPh2)Cl(CO)(PPh3)2. In contrast, heating the five-coordinate osmium-methyl complex, Os(SiMe3)(Me)(CO)(PPh3)2 (1), in the presence of triphenylphosphine results mainly, not in tetramethylsilane elimination, but in ortho-silylation as well as ortho-metallation of different triphenylphosphine ligands giving, Os(κ2(Si,P)-SiMe2C6H4PPh2)(κ2(C,P)-C6H4PPh2)(CO)(PPh3) (5). A byproduct of this reaction is the non-silicon containing di-ortho-metallated complex, Os(κ2(C,P)-C6H4PPh2)2(CO)(PPh3) (6). A similar reaction occurs when Os(SiMe3)(Me)(CO)(PPh3)2 (1) is heated in the presence of tri(N-pyrrolyl)phosphine producing Os(κ2(Si,P)-SiMe2C6H4PPh2)(κ2(C,P)-C6H4PPh2)(CO)[P(NC4H4)3] (7) but a better synthesis of 7 is to treat 5 directly with tri(N-pyrrolyl)phosphine. Heating the six-coordinate complex, Os(SiMe3)(Me)(CO)2(PPh3)2 (2), gives two complexes both containing ortho-metallated triphenylphosphine, one with loss of the trimethylsilyl ligand, giving the known complex, Os(κ2(C,P)-C6H4PPh2)H(CO)2(PPh3), and the other with retention of the trimethylsilyl ligand, giving Os(SiMe3)(κ2(C,P)-C6H4PPh2)(CO)2(PPh3) (8). Crystal structure determinations for 5, 6, 7 and 8 have been obtained.