Kinetic Insights into Cyanosilylation of Aldehydes Catalyzed by a Covalently Bridged Dinuclear (Salen)titanium Complex

Enantioselective addition of trimethylsilyl cyanide (TMSCN) to aldehydes is one of the most extensively studied organic reactions in asymmetric catalysis. Herein, we report our intensive kinetic investigation on the asymmetric addition of TMSCN to benzaldehyde, catalyzed by a covalently bridged dinuclear (salen)titanium complex 2, which has been one of the most efficient artificial chiral catalysts reported so far for this reaction. It was found that the method of initial rates for kinetic investigation is not appropriate in this case because of the presence of a significant incubation period in the catalysis, while the method of progress rates proved to be more reliable and efficient for judging the kinetic orders of this catalytic system. The kinetic results revealed that the reaction follows first order with respect to the catalyst and is nearly independent of concentrations of both benzaldehyde and TMSCN. A detailed catalytic mechanism for cyanosilylation of benzaldehyde in the presence of 2 was proposed, wherein the key active dinuclear species works in a cooperative manner for dual activation of both reactants.