Aromatic molecules can be dearomatized by ?2-coordination to the chiral metal group {TpW(NO)(PMe3)}. With 2,5-dimethyl- or 2-methylpyrrole, a 3H-?2-W-pyrrole complex is formed, which can be trapped with weak acid as a 3H-?2-W-pyrrolium complex, while with pyrrole or 2,4-dimethylpyrrole, a 7-coordinate W-pyrrolyl-hydride results. With 2-methylpyrrole, in the absence of weak acid, the initially formed W-?2-pyrrole complex converts to a 7-coordinate pyrrolyl-hydride complex, which, upon addition of strong acid, yields a 2H-?2-W-pyrrolium complex, as a single coordination diastereomer. Stereoselective hydride addition to the iminium carbon was achieved with both of the ?2-W-2-methylpyrrolium complexes, however, attempts to add other nucleophiles in a parallel manner were unsuccessful. In the presence of H�nig's base, the 2H-?2-W-pyrrolium complex reacts with a number of Michael acceptors forming N-substituted products in about 1 day. In the case of methyl vinyl ketone or ethyl vinyl ketone, and in the presence of pyrrolidine, this product reacts further to yield a bicyclic product with an indolizine core.Separately, pyrrole and substituted pyrroles have been found to undergo novel Friedel-Crafts-like alkylation with benzene bound to the {TpW(NO)(PMe3)} group. In the presence of a trimethylphosphine/trimethylphosphonium buffer, the pyrrole adds across one exposed double bond of the ?2-tungsten-benzene complex while trimethylphosphonium adds across the other.

Exploration of reactivity of a novel tungsten-bound 2H-pyrrolium

245th National Meeting (2013)

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