AB-INITIO STUDY OF SUBSTITUTED 2-AMINOETHYLBORINATES

A series of 2-aminoethylborinate derivatives has been studied by ab in itio calculations at the HF/6-31G* level in order to obtain informati on about the substituent effects around the coordinative N --> B bond. Their geometries were fully optimized and the electrostatic charge, t he bond order of the Mulliken population analysis and the hybridizatio n of the different atoms were determined. Based on these data it can b e shown that the N --> B bond strength depends on two factors: the pol arization along the N --> B bond and the electrostatic repulsive inter actions between the substituents around this bond. It was determined t hat the bond strength can be increased by the introduction of electron egative substituents at the nitrogen atom. Also, it was concluded that the conformations adopted by the five-membered heterocyclic rings dep end on the electrostatic interactions around the O-B-N fragment: As a consequence of these interactions, the boron atom is displaced out of the molecular plane, when the nitrogen atom is substituted by at least one methyl group. Otherwise it is one of the carbon atoms of the ring . (C) 1998 Elsevier Science B.V.