Syntheses and Characterization of Hydrotris(1-pyrazolyl)borate Dihydrogen Complexes of Ruthenium and Their Roles in Catalytic Hydrogenation Reactions

A series of new hydrotris(1-pyrazolyl)borate complexes of ruthenium were synthesized. Reaction of RuCl(HB(pz)3)(PPh3)2 with NaBH4 in ethanol produced the yellow monohydride complex RuH(HB(pz)3)(PPh3)2. Protonation of the monohydride complex RuH(HB(pz)3)(PPh3)2 with HBF4·Et2O in dichloromethane gave the molecular dihydrogen complex [Ru(HB(pz)3)(PPh3)2(H2)]BF4. Reactions of the dihydrogen complex [Ru(HB(pz)3)(PPh3)2(H2)]BF4 with L (L = CH3CN, H2O, N2) produced the adducts [Ru(HB(pz)3)(PPh3)2(L)]BF4. The dihydrogen complex [Ru(HB(pz)3)(PPh3)2(H2)]BF4 could be regenerated by reactions of [Ru(HB(pz)3)(PPh3)2(L)]BF4 (L = CH3CN, H2O) with pressurized H2. Deprotonation of the molecular dihydrogen complex [Ru(HB(pz)3)(PPh3)2(H2)]BF4 occurred with NEt3 or H2O under hydrogen pressure. Treatment of RuCl(HB(pz)3)(PPh3)2 with LiBF4 in acetonitrile produced the bis-solvento complex [Ru(HB(pz)3)(PPh3)(CH3CN)2]BF4. Heating a THF/CH3CN (9/1) solution of RuCl(HB(pz)3)(PPh3)2 at 60 °C led to the formation of RuCl(HB(pz)3)(PP...