Si-CN bond cleavage of silyl cyanides by an iron catalyst. A new route of silyl cyanide formation

Abstract

The reaction of silyl cyanide (R3SiCN) with hydrosilane (R'3SiH) in the presence of a catalytic amount of [(η5-C5H5)Fe(CO)2Me] formed R'3SiCN and R3SiH. This reaction involves Si?CN bond cleavage and provides a new method for the preparation of silyl cyanides. DFT calculation showed that coordinatively unsaturated [(η5-C5H5)Fe(CO)(SiMe3)] reacts exothermically with Me3SiCN to give the CN π-coordinated complex, [(η5-C5H5)Fe(CO)(η2-Me3SiCN)(SiMe3)], followed by exothermic silyl migration from the iron to the nitrogen atom of the η2-coordinated Me3SiCN with the activation energy of 8.8 kcal mol-1 to give [(η5-C5H5)Fe(CO)(Me3SiC=NSiMe3-κC,κN)]. The complex is one of the intermediates in the catalytic cycle. The related complex [(η5-C5Me5)Fe(CO)(κ-C,N-t-BuMe2SiC=NSiPh3)] was isolated in the reaction of [(η5-C5Me5)Fe(CO)(py)(SiPh3)] with t-BuMe2SiCN and characterized by 1H, 13C, and 29Si NMR spectroscopy. The activation energy of the Si?CN bond cleavage in [(η5-C5H5)Fe(CO)(κC,N-Me3SiC=NSiMe3)] was evaluated by DFT calculation to be 33.7 kcal mol-1 which is comparable to that in the reaction of acetonitrile (32.9 kcal mol-1).