Reactions of a Gallane(pyridyl)iron Complex with Internal and Terminal Alkynyl Esters: C−O and C−C Bond Cleavage and Oxidative Addition of C−H Bond

Abstract

The selective fragmentation of internal alkynyl esters RC≡CCO2Me into RC≡C, C=O, and OMe fragments was investigated using a gallane(pyridyl)iron complex Cp*(OC)Fe{(η1‐HGaMes2)(η1‐2‐C5H4N)} (1, Cp*: η5‐C5Me5, Mes: 2,4,6‐Me3C6H2). The reaction of complex 1 with RC≡CCO2Me (R=Ph, CO2Me) in C7D8 (toluene) at 100 °C for 0.5 h proceeded via selective C−O and C−C bond cleavage to afford η1‐alkynyliron complex Cp*(OC)2Fe(C≡CR) (R=Ph (5 a), CO2Me (5 b)) and 4‐membered Ga2O2 cyclic gallane [Mes2GaOMe]2 (3). In contrast, the reaction of 1 with methyl propiolate HC≡CCO2Me yielded a complex mixture, including gallane 3, Cp*(OC)2Fe(C≡CH) (5 c), and Cp*(OC)Fe(C≡CCO2Me)(GaMes2)(H) (F). The oxidative addition of the terminal H−C bond to the iron center occurred via the reaction of complex 1 with trimethylsilylacetylene (TMSA) and the photochemical reaction of dimesitylgallyliron complex Cp*(OC)2FeGaMes2 (4) with TMSA to afford η1‐alkynyl(gallyl)(hydride)iron complex Cp*(OC)Fe(C≡CSiMe3)(GaMes2)(H) (6).