Estimated Rate Constants for Hydrogen Abstraction from N-Heterocyclic Carbene−Borane Complexes by an Alkyl Radical

Abstract

Rate constants for hydrogen abstraction by a nonyl radical from 20 complexes of N-heterocyclic carbenes and boranes (NHC-boranes) have been determined by the pyridine-2-thioneoxycarbonyl (PTOC) competition kinetic method at a single concentration point. The rate constants range from <1 x 10(4) to 8 x 10(4) M(-1) s(-1). They show little dependence on the electronic properties of the carbene core, but there is a trend for increasing rate constants with decreasing size of the carbene N-substituents. Two promising new reagents with small N-substituents (R = Me) have been identified.