title: Annulated boron substituted N-heterocyclic carbenes: theoretical prediction of highly electrophilic carbenes.
abstract: Theoretical calculations were carried out to understand the effect of annulation on the electronic and ligand properties of boron substituted N-heterocyclic carbenes (B-NHCs). Annulation results in a decrease in stability as indicated by the calculated values of singlet-triplet separations and stabilization energies as well as HOMO-LUMO gaps. Annulated B-NHCs are found to be weaker σ-donors but better π-acceptors than the parent ones. The decrease in σ-donation ability and the increase in π-accepting ability are further supported by the calculated values of proton affinities, nucleophilicity and electrophilicity indices as well as (31)P NMR chemical shifts of the corresponding NHC-PPh adducts. Most of the annulated B-NHCs are found to have significantly enhanced electrophilicity than the other known carbenes.
authors.affiliation: Department of Chemical Sciences, Tezpur University, Napaam 784028, Assam, India. ashwini@tezu.ernet.in.
authors.forename: Priyam
authors.initials: P
authors.lastname: Bharadwaz
authors.forename: Bitupon
authors.initials: B
authors.lastname: Borthakur
authors.forename: Ashwini K
authors.initials: AK
authors.lastname: Phukan