SYNTHESIS AND REDOX STUDIES ON RUTHENIUM AND OSMIUM COMPLEXES WITH PRIMARY AND SECONDARY PHOSPHINES - SINGLE-CRYSTAL STRUCTURES OF TRANS-[RUCL2(PPHH(2))(4)] AND TRANS-[OSCL2(PPH(2)H)(4)]CENTER-DOT-CH2CL2

Reaction of RUCl(3).3H(2)O or [NH4](2)[OsCl6] with 5-7 molar equivalents of PR(2)H (R = Ph or C6H11) or PPhH(2) in degassed refluxing EtOH solution (or EtOH-water for Os) gave [MCl(2)(PR(2)H)(4)] and [MCl(2)(PPhH(2))(4)] in high yield as yellow solids. Ultraviolet-visible and P-31 NMR spectroscopic studies confirm that these species exist as trans isomers in solution and the integrity of the PH functions. Prolonged standing of trans-[RuCl2 (PPh(2)H)(4)] in CH2Cl2 solution led to partial isomerisation to the cis isomer as confirmed by P-31 NMR R spectroscopy. The crystal structure of trans-[RuCl2(PPhH(2))(4)] has been determined. It confirms a trans arrangement of the Cl- ligands with the Ru-II occupying a crystallographic inversion centre with four precisely coplanar equatorial PPhH(2) ligands, Ru-Cl2.422(3), Ru-P(1) 2.319(3) and Ru-P(2) 2.318(3) Angstrom. The lower steric demands of the PPhH(2) ligands compared to PPh(2)H are reflected in the more regular octahedral arrangement seen in trans-[RuCl2(PPhH(2))(4)] compared to trans-[RuCl2(PPh(2)H)(4)].O.5CHCl(3). The crystal-structure determination of trans-[OsCl2(PPh(2)H)(4)].CH2Cl2 showed two independent half molecules in the asymmetric unit with each Os-II occupying an inversion centre and co-ordinated to a trans arrangement of two Cl- and four PPh(2)H ligands. Os(1)-Cl 2.448(2), Os(2)-Cl 2.443(2), Os(1)-P 2.357(2). 2.349(2), Os(2)-P 2.355(2), 2.333(2) Angstrom. With the exception of [RuCl2(PPhH(2))(4)] (irreversible), cyclic voltammetric studies on the complexes trans-[MCl(2)(PR(2)H)(4)] and trans-[MCl(2)(PPhH(2))(4)] show a reversible oxidation in each case, which is assigned to a M(II)-M(III) redox couple.