Migratory-insertion reactions involving the thiocarbonyl ligand. dihapto-thioacyl complexes from the rearrangement of arylthiocarbonyl complexes of osmium(II). Structure of Os(η2-CSR)(η1-O2CCF3)(CO)(PPh3)2

Abstract Reaction of HgR 2 with OsHCl(CS)(PPh 3 ) 3 yields red, five-coordinate, OsRCl-(CS)(PPh 3 ) 2 (R = p -tolyl). From this have been derived the compounds OsRX(CS)(PPh 3 ) 2 with X = Br, I, S 2 CNEt 2 , O 2 CMe, O 2 CCF 3 . These compounds add an additional ligand, MeCN, CO or CNR to form colourless, six coordinate arylthiocarbonyl complexes, which undergo migratory-insertion reactions to form red, dihapto -thioacyl complexes. The crystal structure of a representative example, Os(η 2 -CSR)(η 1 -O 2 CCF 3 )(CO)PPh 3 ) 2 has been determined. The red equant crystals are orthorhombic, space group P 2 1 2 1 2 1 , a 11.584(1), b 19.184(2), c 18.90(1) A, V 4199 A 3 , Z  4. The structure was solved by conventional heavy-atom methods and refined by full-matrix least-squares employing anisotropic thermal parameters for all non-hydrogen atoms except the carbon atoms of the triphenylphosphines. The final R factor is 0.057 for 2868 observed reflections. The coordination geometry in the monomeric complex is that of an octahedron distorted by the constraints of the ligands. The triphenyl phosphine ligands are mutually trans ; the equatorial plane contains carbonyl, monohapto -trifluoroacetate, and dihapto -thioacyl ligands. Bond distances and angles are OsP 2.405, 2.407(4) A; POsP 173.9(1)°; OsCO 1.83(2) A; Os-O (trifluoroacetate) 2.206(11) A; OsC (thioacyl) 1.91(2); OsS 2.513(6); CS 1.72 A. The CS bond length implies a reduction in bond order from 2.0 to approx. 1.5 upon coordination to the metal. The η 2 -thioacyl ligand in Os(η 2 -CSR)Cl(CNR)(PPh 3 ) 2 is methylated with methyl triflate and further reaction with LiCl produces the thiocarbene complex OsCl 2 (C[SMe]R)(CNR)(PPh 3 ) 2 .