Electrostatically Enhanced 3-and 4-Pyridyl Borate Salt Nucleophiles and Bases

A variety of electrostatically enhanced 3- and 4-pyridylboratesalt catalysts are reported and show significant improvement overan activated noncharged neutral control compound. Their nucleophilicityin a stoichiometric S(N)2 reaction and catalytic performancein a urethane synthesis are evaluated along with three methods forrapidly evaluating the basicity of these species. That is, qualitativetitrations in CH2Cl2 and CHCl3 werecarried out, two separate solution-state IR studies in CCl4 and CDCl3 are reported, and the proton affinities ofthe anionic components of the salts were computed. Charge differencesbetween the anion and its protonated zwitterionic conjugate acid areevaluated along with the highest occupied molecular orbitals of theanions in relationship to some of the surprising reactivity findingsthat were observed in the two kinetic studies.

Automated summary

A range of electrostatically enhanced 3- and 4-pyridylboratesalt catalysts are reported, which show significant improvement compared to an activated noncharged neutral control compound. Their nucleophilicity and catalytic performance are evaluated in different reactions, along with three methods for rapidly evaluating their basicity. The charge differences between the anion and its protonated zwitterionic conjugate acid are also assessed, as well as the highest occupied molecular orbitals of the anions.