Mechanisms of Metal-Mediated Cyclizations

A complex of zirconocene with two rq2-alkynyl ligands is described. This complex is the first isolated example of the postulated intermediate in the zirconocene-mediated reductive coupling of alkynes. The development of a Bergman cyclization controlled by metal-ligand interactions is described. Upon complexation with palladium or platinum, phosphine-substituted enediynes rearrange to the aromatic diradical quickly at room temperature. Upon complexation with mercury, the Bergman cyclization is not observed at temperatures up to 450 C. The ligand undergoes a Bergman cyclization at 243 C in the absence of metals. A mechanism for this reaction is proposed. A new synthetic method for the catalytic conversion of organosilanes to organostannanes is described. This process utilizes the inexpensive bis(tributyltin) oxide, and produces the stannanes cleanly and in quantitative yield. Thesis Supervisor: Stephen L. Buchwald Title: Professor of Chemistry