Protonolysis reactions in the series RMn(CO) 5 and RC(O)Mn(CO) 5

Abstract

Proton cleavage (protonolysis) of the RMn bond in RMn(CO) 5 complexes occurs readily and cleanly with CF 3SO 3H to give the corresponding RH compounds. The relative order of reactivity in the series of RMn(CO) 5 compounds we have prepared is R  H, CH 3, Ph, p-CH 3C 6H 4, p-BrC 6H 4, p-CF 3C 6H 4 > PhCH 2 > p-ClC 6H 4CH 2 ≅ p-CH 3OC 6H 4CH 2 ⪢ PhCH 2CH 2. Protonolysis with HBF 4 is much slower than with triflic acid in every case. The reaction with both acids very likely proceeds by attack of the proton on Mn followed by reductive elimination. Surprisingly, the corresponding RC(O)Mn(CO) 5 compounds on treatment with triflic acid do not undergo protonolysis to aldehydes. Instead, hydroxycarbenes are formed reversibly and the acyls are slowly decarbonylated to RMn(CO) 5 which then undergo protonolysis and reductive elimination to give quantitative yields of RH.