THEORETICAL INVESTIGATION OF ALUMINUM OXYGEN PI-BONDING IN 3-COORDINATE AND 4-COORDINATE ALUMINUM ALKOXIDES

A number of munomeric 3- and 4-coordinate aluminum aryloxides have been observed to exhibit unusually short Al-O bonds and very obtuse Al-O-C angles. We have explored the bonding in models for these complexes using ab initio molecular orbital theory. Both the shortening of the Al-O bonds and the large Al-O-C angles are attributed to pi-symmetry interactions between the oxygen lone pair and the empty aluminum p-orbital in the 3-coordinate compounds, a not unexpected result for group III elements. The equally large angles in the 4-coordinate complexes are attributed to donation from oxygen into the sigma* donor-acceptor orbital.