The protonation of ruthenium- and rhodium-bridged carboxylates and their use as homogeneous hydrogenation catalysts for unsaturated substances

The protonation of rhodium(II) acetate by non-complexing, non-oxidising acids such as fluoroboric acid gives the green rhodium(II) cation Rh4+2. The interaction with triphenylphosphine and carbon monoxide lead to the complexes Rh(PPh3)3BF4 and Rh(CO)(PPh3)3BF4.The new ruthenium(II) acetate Ru2(OCOMe)4 and its adducts with triphenylphosphine and pyridine have been characterised.The methanolic fluoroboric acid solutions of RhII and RuII acetates and of Ru2(OAc)4Cl, in the presence of triphenylphosphine, are active catalysts for the homogeneous hydrogenation of alkenes, alkynes, and other unsaturated substances.