Multifunctional Ruthenium Catalysts: A Novel Borohydride-Stabilized Polyhydride Complex Containing the Basic, Chelating Diphosphine 1,4-Bis(dicyclohexylphosphino)butane and Its Application to Hydrogenation and Murai Catalysis

Abstract

[RuCl2(dcypb)(CO)]2 2 (dcypb = 1,4-bis(dicyclohexylphosphino)butane) was prepared in high yield via phosphine exchange between dcypb and RuCl2(CO)(PPh3)2(DMF) (1). Reaction of 2 with 8 equiv of KBHsBu3 affords [fac-RuH3(CO)(dcypb)]- (3), stabilized by interactions with a K+ counterion and an intact KBHsBu3 molecule in the third coordination sphere. Substantial ion pairing accounts for the stability and high hydrocarbon solubility of 3. Complex 3 effects reduction of benzophenone under unprecedentedly mild conditions, at 1 atm of H2 in refluxing 2-propanol. It is also active for ortho functionalization of benzophenone under 20 atm of ethylene. Stoichiometric experiments reveal facile formation of ortho-metalated RuH(CO)[OC(C6H4)(Ph)](dcypb) (5), an intermediate proposed in both types of catalysis. The catalytic activity of isolated 5 supports this hypothesis in the case of hydrogenation but not of Murai catalysis. The X-ray crystal structures of 3 and 5 are reported.