Stereoelectronic Effects in Dihapto-Coordinated Complexes of TpW(NO)(PMe₃) and Their Manifestation in Diels−Alder Cycloaddition of Arenes

Abstract

The addition of singly and doubly activated dienophiles to TpW(NO)(PMe 3 )(5,6 - η 2 -anisole) and TpW(NO)(PMe 3 )(5,6 - η 2 -1,3-dimethoxybenzene) to generate dihapto-coordinated [2.2.2]bicyclooctadienes and -trienes is explored. The highly functionalized bicyclic scaffolds are isolated from the metal fragment intact. Although moderate yields hinder their synthetic application, a unique stereoelectronic effect is uncovered. Coordination diastereomers of anisoles with the methoxy substituent distal to the PMe 3 ligand have faster reaction rates relative to the proximal diastereomer. DFT calculations reveal the metal fragment possesses a dipole that directs positive charge away from the PMe 3 ligand, and a polarized cycloaddition transition state is invoked to explain this observation.