Synthesis of Alkyl- and Aryl[hydrotris(pyrazolyl)borato]carbonylruthenium Complexes by Decarbonylation of Alcohols. Synthesis of TpRuH(H2)(PPh3) [Tp = Hydrotris(pyrazolyl)borate], an Observable Intermediate in the Decarbonylation Reaction

Treatment of TpRuCl(PPh 3 )(CH 3 CN) (Tp = hydrotris(pyrazolyl)borate) with NaBH 4 in ethanol did not yield the expected hydride complex TpRuH(PPh 3 )(CH 3 CN) ( 2 ) but rather the methyl carbonyl complex TpRu(CH 3 )(CO)(PPh 3 ) ( 1b ). Formation of 1b was due to decarbonylation of ethanol by 2 generated in situ by NaBH 4 reduction of TpRuCl(PPh 3 )(CH 3 CN). Analogous reactions in the presence of other primary alcohols RCH 2 OH (R = H, C 2 H 5, n -C 3 H 7, C 6 H 5, C 6 H 4 CH 3 -4, and C 6 H 4 Cl-4) led to the corresponding σ-organyl complexes TpRuR(CO)(PPh 3 ). A common feature of the reactions is that the R groups of alcohols RCH 2 OH become the σ-organyl groups in the final metal complexes. A mechanism involving metal−η 2 -aldehyde and −η 2 -dihydrogen intermediates is proposed for the decarbonylation reaction. This is supported by the observation of the η 2 -dihydrogen complex TpRuH(H 2 )(PPh 3 ) ( 3 ) during the decarbonylation reaction. 3 was synthesized independently by heating a THF solution of 2 under 40 atm of H 2 at 60 °C for 48 h or by heating 2 in CH 3 OH at 60 °C under 6 atm of H 2 for 5−6 h.