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

[RuCl 2 (dcypb)(CO)] 2 2 (dcypb = 1,4-bis(dicyclohexylphosphino)butane) was prepared in high yield via phosphine exchange between dcypb and RuCl 2 (CO)(PPh 3 ) 2 (DMF) ( 1 ). Reaction of 2 with 8 equiv of KBH s Bu 3 affords [ fac -RuH 3 (CO)(dcypb)] - ( 3 ), stabilized by interactions with a K + counterion and an intact KBH s Bu 3 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 H 2 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(C 6 H 4 )(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.