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

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posted on 2009-08-24, 00:00 authored by Rebecca J. Salomon, Edward C. Lis,, Monica U. Kasbekar, Kimberley C. Bassett, William H. Myers, Carl O. Trindle, Michal Sabat, W. Dean Harman
The addition of singly and doubly activated dienophiles to TpW(NO)(PMe3)(5,6-η2-anisole) and TpW(NO)(PMe3)(5,6-η2-1,3-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 PMe3 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 PMe3 ligand, and a polarized cycloaddition transition state is invoked to explain this observation.