Reactivity and Catalytic Activity of a Robust Ruthenium(II)−Triphos Complex

The ruthenium(II)−triphos acetato complex [RuCl(OAc)(κ3-triphos)] (triphos = (PPh2CH2)3CMe) has been found to
be an active catalyst precursor for the hydrogenation of 1-alkenes under relatively mild conditions (5−50 bar H2,
50 °C). In contrast to related triphenylphosphine complexes, [RuCl(OAc)(κ3-triphos)] is much less air sensitive and
high catalytic activities were achieved when catalyst samples were prepared without exclusion of air or moisture.
Substitution of the acetato ligand can be effected by treatment of acid, affording [Ru2(μ-Cl)3(κ3-triphos)2]Cl and
[RuCl(κ3-triphos)]2(BF4)2 with aqueous HCl and [Et2OH]BF4, respectively, or by heating with dmpm in the presence
of [NH4]PF6, resulting in formation of [RuCl(κ2-dmpm)(κ3-triphos)]PF6 (dmpm = PMe2CH2PMe2). A hydride complex,
[RuHCl(κ3-triphos)], formed by acetato-mediated heterolytic cleavage of dihydrogen is proposed as the active catalytic
species. An inner-sphere, monohydride mechanism is suggested for the catalytic cycle, with chloro and triphos
ligands playing a spectator role. These mechanistic proposals are consistent with reactivity studies carried out on
[RuCl(OAc)(κ3-triphos)] and [RuH(OAc)(κ3-triphos)] and supported by a computational analysis. The solid-state
structures of [RuCl(OAc)(κ3-triphos)], [RuCl(κ3-triphos)]2(BF4)2, and [RuCl(κ2-dmpm)(κ3-triphos)]PF6 have been
established by X-ray diffraction.