Extension of the Woodward-Hoffman rules to organometallic systems

It has been demonstrated that in the presence of catalytic amounts of certain metal ions or metal complexes, various strained derivatives of cyclobutene can undergo an extremely facile disrotatory ring opening to yield derivatives of butadiene. An explanation for the “apparent” break-down of the Woodward-Hoffman rules is offered in terms of the formation of intermediate organometallic pi complexes and consideration of the subsequent energetics involved for the ring opening reaction of these complexes.