SYNTHESIS AND STRUCTURE OF OSMIUM AND RUTHENIUM COMPLEXES CONTAINING TETRAFLUOROETHYLENE AND MALEIC-ANHYDRIDE AS LIGANDS

The d8 complexes, M(CO)(L)(PPh3)3 (M = Ru, Os; L = CO, CNR; R = p-tolyl) and OsCl(NO)(PPh3)3, all form simple 1 : 1 π-adducts with tetrafluoroethylene and maleic anhydride, with the overall coordination geometry being dependent upon the relative electron-withdrawing properties of the olefin and the relative electron richness of the metal fragment. In all the tetrafluoroethylene complexes of ruthenium examine, the geometry of the complex involves cis-triphenylphosphine ligands. The X-ray crystal structure of Ru(C2F4(CO)2(PPh3)2 is presented as an example of this structural class. Ru(C2F4)(CO)2(PPh3)2 crystallises in the monoclinic space group P21/a with a cell having dimensions a = 35.940(2), b = 10.655(7), c = 18.559(6) Å and β = 93.21(3)°, with two crystallography independently molecules in the asymmetric unit (Z = 8). The osmium complexes do not display this strong preference for cis-triphenylphosphine ligands and Os(C2F4)(CO)2(PPh3)2 exists as two separate but interconvertible isomers in solution. One isomer has the same relative geometry as Ru(C2F4)(CO)2(PPh3)2 . The other has trans-triphenylphosphine ligands. This temperature-dependent equilibrium has been studied by variable-temperature NMR and has ΔH° = -15 kJ mol-1 and ΔS° = -60 J K-1 mol-1. The maleic anhydride complexes also show a variation in geometry from the usual trans triphenylphosphine arrangement. The X-ray crystal structure of Os(maleic anhydride)(CO)2(PPh3)2 is reported along with the solution structures of other maleic anhydride complexes. Os(maleic anhydride)(CO)2(PPh3)2 crystallises in the monoclinic space group P21/c with a cell having dimensions a = 23.667(2), b = 20.306(1), c = 16.147(1) Å and β = 93.20(1)°, with two crytallographically independent molecules in the asymmetric unit (Z = 8). The triphenylphosphine ligands are again cis but only one lies in the plane of the osmium and the coordinated olefin. © 1990.