Oxidative coupling reactions at ruthenium(0) and their applications to catalytic homo- and cross-dimerizations¶

• The homo- and cross-dimerizations by transition-metal compounds are reviewed.
• The first solid evidence for the tail-to-tail dimerizations of substituted alkenes by the oxidative coupling mechanism is described.
• The first enantioselective cross-dimerizations using substituted alkenes are described.

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(η6-naphthalene)(η4-1,5-COD)] is readily removed to generate a formal 12e species, “Ru(η4-1,5-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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