PREPARATION AND REACTIVITY OF SOME ETA-2-S2 AND ETA-2-SE2 COMPLEXES OF OSMIUM AND THE X-RAY CRYSTAL-STRUCTURE OF OS(ETA-2-SE2)(CO)2(PPH3)2

The compounds Os(η2-Se2)(CO)2(PPh3)2, Os(η2-Se2)(CO)(CNR)(PPh3)2 where R = p-tolyl, and Os(η2-S2)-(CO)2(PPh3)2 have been prepared. The reactivity of the (η2-S2) and (η2-Se2) iigands has been investigated and, in contrast to that of the (η2-O2) analogues, which are oxidizing in character, has been found to be reducing in nature. Thus the Iigands are readily attacked by alkylating agents to give cations of the type [Os(η2-Se2Me)(CO)2(PPh3)2]+ which react further with borohydride to yield complexes of the type [Os(H)(η1-Se2Me)(CO)2(PPh3)2. Reaction with iodine or dinitrogen tetroxide yields the known complexes Osl2(CO)2(PPh3)2 and Os(NO3)2(CO)2(PPh3)2, respectively, with elemental selenium or sulfur being liberated. Reactions involving electrophiles such as NO+ and RN2+ have been observed in which nitric oxide and nitrogen are evolved with elemental sulfur or selenium being deposited, followed by subsequent decomposition of the osmium residue in the absence of suitable Iigands. The structure of dicarbonylbis(triphenylphosphine)diseleniumosmium(0) has been determined from three-dimensional X-ray data collected by counter methods. The compound crystallizes in the triclinic space group Pl, with two molecules in a cell of dimensions a = 10.479 (1) Å, b = 17.933 (3) Å, c = 10.416 (2) Å, a = 103.49 (3)°, β = 1 15.10 (1)°, and γ = 75.72 (2)°. Refinement by least-squares techniques, using 5319 observations above background, gave a final agreement factor on F of 0.034. The coordination geometry at the Os atom is that of a distorted octahedron, with trans phosphine Iigands and the Se2 ligand “sideways” bonded. The Se-Se distance is lengthened to 2.321 (1) Å upon coordination. ESCA spectra show that the S2 and Se2 Iigands are very effective at removing electron density from the Os atom. © 1979, American Chemical Society. All rights reserved.