VINYLOXYBORANE AND ITS ISOMERS - AN ABINITIO STUDY OF THE C2H5BO POTENTIAL-ENERGY SURFACE, THE BARRIER TO 1,3-SHIFTS IN BETA-KETOBORANES, AND THE MECHANISM OF THE CARBONYLATION REACTION OF BORANES

Vinyloxyboranes, CH2 = CH-O-BR2, are shown by ab initio molecular orbital theory to be more stable than the isomeric beta-aldoboranes, R2B-CH2-CH = O, by ca. 19 kcal/mol. The MP2/6-31G*/6-31G* + ZPE barrier for the [ 1,31 boron shift is only 10.9 kcal/ mol (R = Me) relative to the aldoborane. Other C2H5BO isomers (alpha-ketoboranes, boraepoxides and organoboron oxides), which are related to the proposed stages in the carbonylation reaction of boranes, are shown to be plausible intermediates. However, some of the computed barriers for methyl group migrations are unrealistically large, up to ca. 63 kcal/mol.