Carbonylation of Boranes ¿ A Computational Study

Abstract

The classical simple picture of stepwise B-to-C migratory insertion of all three alkyl groups in the carbonylation reaction of trialkyl boranes with CO was shown not to be correct, except for the first alkyl group shift affording an acyl borane. The second and third direct alkyl shifts turned out to be kinetically hampered due to the non-activated character of the B C bond in electron-poor B atoms. The latter can only be achieved by either the autocatalytic action of the final alkyl boron oxide or by formation of dimeric species with weakened B-alkyl bonds at borate centres. Both thermodynamic and several NICS-related parameters pointed to scarce, even “negative”, aromatic character for boroxines, the final cyclotrimerization products of alkyl-boron oxides