N-Heterocyclic Olefin Stabilized Boron Cations

Boron mono- and di-cations featuring nucleophilic N-heterocyclic olefin (NHO) and pentamethylcyclopentadienyl (Cp*) substituent have been prepared and structurally characterized. Experimental and theoretical investigations show that [η5-Cp*B-NHO]2+ is considerably more Lewis acidic than [η5-Cp*B-IMes]2+ due to the steric congestion between NHO and Cp* leading much expose around the central boron atom. However, the weak interaction between NHO ligand and boron center result in the reaction product are generally unstable to isolate and characterize.