Synthesis and redox studies on ruthenium and osmium complexes with primary and secondary phosphines. Single-crystal structures of trans-[RuCl2(PPhH2)4] and trans-[OsCl2(PPh2H)4]·CH2Cl2

Abstract

Reaction of RuCl3·3H2O or [NH4]2[OsCl6] with 5–7 molar equivalents of PR2H (R = Ph or C6H11) or PPhH2 in degassed refluxing EtOH solution (or EtOH–water for Os) gave [MCl2(PR2H)4] and [MCl2(PPhH2)4] in high yield as yellow solids. Ultraviolet-visible and 31P 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(PPh2H)4] in CH2Cl2 solution led to partial isomerisation to the cis isomer as confirmed by 31P NMR spectroscopy. The crystal structure of trans-[RuCl2(PPhH2)4] has been determined. It confirms a trans arrangement of the Cl– ligands with the RuII occupying a crystallographic inversion centre with four precisely coplanar equatorial PPhH2 ligands. Ru–Cl 2.422(3), Ru–P(1) 2.319(3) and Ru–P(2) 2.318(3)A. The lower steric demands of the PPhH2 ligands compared to PPh2H are reflected in the more regular octahedral arrangement seen in trans-[RuCl2(PPhH2)4] compared to trans-[RuCl2(PPh2H)4]·0.5CHCl3. The crystal-structure determination of trans-[OsCl2(PPh2H)4]·CH2Cl2 showed two independent half molecules in the asymmetric unit with each OsII occupying an inversion centre and co-ordinated to a trans arrangement of two Cl– and four PPh2H 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)A. With the exception of [RuCl2(PPhH2)4](irreversible), cyclic voltammetric studies on the complexes trans-[MCl2(PR2H)4] and trans-[MCl2(PPhH2)4] show a reversible oxidation in each case, which is assigned to a MII–MIII redox couple.