The B–H–B bridging interaction in B-substituted oxazaborolidine–borane complexes: a theoretical study

Krzysztof Z Łączkowski,Angelika Baranowska-Łączkowska,Żaneta Czyżnikowska,Robert Zaleśny

doi:10.1007/s11224-012-0178-9

Abstract

Ten oxazaborolidine–borane complexes, nine among them boron-substituted (B–R, R=CH3, CF3, and OCH3), are carefully analysed using quantum-chemistry methods to determine their equilibrium geometries and the corresponding oxazaborolidine–borane interaction energies. It is observed that in all B-trifluoromethyl substituted oxazaborolidine–borane complexes and in one B-methyl substituted complex the B–H–B bond is formed and the interaction energies are 1.5–2.5 times as large as in other investigated complexes. We believe that the presented results may be helpful in experimental recognition of oxazaborolidine–borane complexes which may appear, inter alia, as reaction intermediates.

Highlights

Boron is known to form structures stabilized by strong delocalization of valence electrons [1]
During the last two decades an increasing interest has been observed in the asymmetric reduction of various types of organic compounds catalyzed by chiral oxazaborolidines, species recognized as catalysts in the Itsuno reaction [5] by Corey et al [6,7,8], and often referred to as CBS catalysts
The B–H–B bond is observed in all investigated B-trifluoromethyl substituted complexes and probably arises from the fact that the electron withdrawing CF3 group decreases the electron density on B1 atom

Summary

Introduction

Boron is known to form structures stabilized by strong delocalization of valence electrons [1]. It is observed that in all B-trifluoromethyl substituted oxazaborolidine–borane complexes and in one B-methyl substituted complex the B–H–B bond is formed and the interaction energies are 1.5–2.5 times as large as in other investigated complexes. Poland e-mail: angelika.baranowska@ukw.edu.pl keywords B-substituted oxazaborolidine–borane complexes Á B–H–B bond Á Ab initio calculations Á Density functional theory calculations Á Intermolecular interaction energy

Results

Conclusion