Syntheses and reactions of coordinatively unsaturated silyl, aryl osmium(II) complexes and the crystal structures of Os[Si(OEt)(3)]R(CO)(PPh3)(2) andOs[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-coordin ate complex, Os[Si(OEt)(3)]Cl(CO)(PPh3)(2) (1), the crystal structure of wh ich reveals a square pyramidal geometry with the triethoxysilyl ligand at t he apical site and the two triphenylphosphine ligands arranged mutually tra ns. 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 lig and in 1 is replaced easily and reaction with LiR gives the stable, five-co ordinate complexes, Os[Si(OEt)(3)[R(CO)(PPh3), (3a, R = phenyl; 3b, R = o-t olyl). 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 c omplexes, 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 geomet ry for each compound. Despite having adjacent aryl and silyl ligands neithe r 3a, 3b nor 4a, 4b show any tendency to undergo reductive elimination of R Si(OEt)(3). IR, H-1-,C-13- and Si-29-NMR data for all new complexes are pre sented. (C) 2001 Elsevier Science B.V. All rights reserved.