The σ–π transmitted coupling over five and six bonds in pyridine–borane complexes. MO calculations on structure and spin–spin couplings

Abstract

The spin–spin coupling over six bonds between borane and ring protons in the borane complexes of pyridine and 2,6-lutidine has the same magnitude as in toluene. This σ–π transmitted coupling suggests that the hyperfine parameters QCCH and QNBH have the same magnitude. Comparison of INDO MO FPT calculations of 6J for these compounds and the methyl borazines with experiment indicates the relative degree of electron delocalization in these systems. An STO-3G structure is calculated for pyridine–borane. Almost free rotation about the B—N bond is predicted (sixfold barrier). The calculated [Formula: see text]depends exponentially on the B—N bond length. Solvent effects on the proton chemical shift are in qualitative agreement with the reaction field model.