Structure and Reactivity of the Orthocarbonic and Orthosilicic Acid Esters of Pyrocatechol

The first compound found to contain planar tetracoordinated silicon is the orthosilicic ester (2) . In contrast, the bondilg geometry of the central atom of the analogous orthocarbonic ester deviates only slightly from a tetrahedron. Quantum mechanical studies [ e.g . on the model compound (3) ] showed that planar tetracoordination is easier for silicon than for carbon. The ability of silicon to engage in sixfold coordination [type (4) ] even makes such planar structures easier to achieve than the tertahedral structure.