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

The selective fragmentation of internal alkynyl esters RC equivalent to CCO2Me into RC equivalent to C, C=O, and OMe fragments was investigated using a gallane(pyridyl)iron complex Cp*(OC)Fe{(eta(1)-HGaMes(2))(eta(1)-2-C5H4N)} (1, Cp*: eta(5)-C5Me5, Mes: 2,4,6-Me3C6H2). The reaction of complex 1 with RC equivalent to CCO2Me (R=Ph, CO2Me) in C7D8 (toluene) at 100 degrees C for 0.5 h proceeded via selective C-O and C-C bond cleavage to afford eta(1)-alkynyliron complex Cp*(OC)(2)Fe(C equivalent to CR) (R=Ph (5 a), CO2Me (5 b)) and 4-membered Ga2O2 cyclic gallane [Mes(2)GaOMe](2) (3). In contrast, the reaction of 1 with methyl propiolate HC equivalent to CCO2Me yielded a complex mixture, including gallane 3, Cp*(OC)(2)Fe(C equivalent to CH) (5 c), and Cp*(OC)Fe(C equivalent to CCO2Me)(GaMes(2))(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)(2)FeGaMes(2) (4) with TMSA to afford eta(1)-alkynyl(gallyl)(hydride)iron complex Cp*(OC)Fe(C equivalent to CSiMe3)(GaMes(2))(H) (6).