NOVEL SE-O AND SI-N BOND METATHESES - MECHANISTIC PROBES, SPECTROSCOPIC STUDIES, AND STRUCTURAL EVIDENCE FOR REACTIVE OLIGOMERIC SELENOAZYL INTERMEDIATES

Mechanistic studies of the reaction of various seleninic anhydrides and hexamethyldisilazane have provided strong evidence for novel Se-O and Si-N bond metatheses. This reaction produces a reactive intermediate which readily oxidizes a variety of phenols to the corresponding o-alkyl or o-aryl selenoiminoquinones 1. The mechanism of this reaction has been identified as a new type of ligand coupling process on the basis of a tetravalent selenium-centered intermediate. The Se-77, Si-29, and N-15 NMR studies as well as reactions with pairs of different seleninic anhydrides give good evidence for a hitherto unknown class of cyclic oligomers (eight-membered rings) containing alternate Se-N single and double bonds.