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(PPh₃)(CH₃CN) (Tp = hydrotris(pyrazolyl)borate) with NaBH₄ in ethanol did not yield the expected hydride complex TpRuH(PPh₃)(CH₃CN) (2) but rather the methyl carbonyl complex TpRu(CH₃)(CO)(PPh₃) (1b). Formation of Ib was due to decarbonylation of ethanol by 2 generated in situ by NaBH₄ reduction of TpRuCl(PPh₃)(CH₃-CN). Analogous reactions in the presence of other primary alcohols RCH₂OH (R = H, C₂H₅, n-C₃H₅, C₆H₅, C₆H₄CH₃-4, and C₆H₄Cl-4) led to the corresponding σ-organyl complexes TpRuR(CO)(PPh₃). A common feature of the reactions is that the R groups of alcohols RCH₂-OH become the σ-organyl groups in the final metal complexes. A mechanism involving metal-η²-aldehyde and -η²-dihydrogen intermediates is proposed for the decarbonylation reaction. This is supported by the observation of the η²-dihydrogen complex TpRuH(H₂)-(PPh₃) (3) during the decarbonylation reaction. 3 was synthesized independently by heating a THF solution of 2 under 40 atm of H₂ at 60 °C for 48 h or by heating 2 in CH₃OH at 60 °C under 6 atm of H₂ for 5-6 h.