Electronic and steric modification of divalent group 14 compounds using peripheral boryl substituents

This thesis examines the use of sterically demanding boryl groups as peripheral substituents on N-heterocyclic carbenes and Group 14 tetrelenes. Chapter III focuses on the syntheses of borylated imidazoles and imidazolium salts. With the aim of accessing an N,Nâ-bisborylated NHC or its metal complexes, the reactivity of bisborylated imidazolium salts with Brønsted bases and metal complexes was studied. The results highlight the lability of the NâB bond and electrophilicity of the boryl group as displacement of the boryl group was repeatedly observed. Chapter IV deals with the syntheses and reactivity of unsymmetrical borylated imidazolium salts and the corresponding carbenes. An unsymmetrical bisborylated carbene has been observed and characterized both in situ and with a range of trapping experiments. This system is however characterized by a 1,2-shift of the N-bound boryl group to the C2 position. Slow rearrangement allowed for assessment of the kinetic properties of the reaction experimentally; computational studies provide consistent activation barriers and suggest an intramolecular migration pathway. Structural and spectroscopic studies of transition metal complexes and a selenium adduct of the carbene allowed for investigation of the steric and electronic properties of the carbene. Chapter V examines the attempts to synthesize N,Nâ-bisborylated saturated N-heterocyclic carbenes and tetrelenes. Bisborylated N-heterocyclic germylenes and stannylenes were successfully synthesized and structurally characterized. Their reactivity towards small molecules was examined, with the pursuit of a germanone being of particular interest.