Mechanisms and applications of oxidative coupling catalyzed by a ruthenium(0) complex

What is it about?

Aspects of the chemistry of zero-valent ruthenium complexes having a cyclic diene ligand, and their use for homo- and cross-dimerizations are reviewed. The naphthalene ligand in [Ru(6-naphthalene)(4-1,5-COD)] is readily removed to generate a formal 12e species, “Ru(4-1,5-COD)”, having 6e coordination sites. These 6e coordination sites can be divided into 4e and 2e sites, and a conjugated compound and substituted alkene therefore selectively coordinate to them to satisfy the 18e rule. The zero-valent ruthenium center is highly Lewis basic and the oxidative coupling reaction readily occurs to form a ruthenacycle. The ruthenium(0) complexes catalyze homo- and cross-dimerizations by the oxidative coupling mechanism and some of the solid evidence in support of the mechanism is summarized. The coordination of substrates is prochiral-selective and when a chiral cyclic diene is incorporated in the catalyst, the first enantioselective cross-dimerizations are achieved.

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Why is it important?

This review shows the detailed mechanistic insights of catalytic homo- and cross-dimerizations catalyzed by a ruthenium(0) complex. Two significant findings are that: a) isolation of ruthenacyclopentane by the stoichiometric reactions, and b) the first enantioselective cross-dimerization between substituted alkenes, or between substituted alkene and conjugated dienes. This is the solid evidence for the mechanism and an important application of present catalyses.

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