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Carbon−Oxygen Bond Formation between a Terminal Alkoxo Ligand and a Coordinated Olefin. Evidence for Olefin Insertion into a Rhodium Alkoxide

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posted on 02.08.2006, 00:00 by Pinjing Zhao, Christopher D. Incarvito, John F. Hartwig
Preparation and reactivity of a series of bis(phosphine) rhodium(I) alkoxides stabilized by intramolecular olefin coordination are reported. {Rh(PEt3)2[κ:η-OCRR‘(CH2)nCHCH2]} (n = 1, 2) were prepared via alcoholysis of {Rh(PEt3)2[N(SiMe3)2]} by the corresponding alcohols HOCRR‘(CH2)nCHCH2. The in situ generated {Rh(PEt3)212-OCRR‘(CH2)2CHCH2]} were not stable at ambient temperatures and decomposed in the presence of added PEt3 to afford 2,2-disubstituted-5-methylenetetrahydrofurans and [(PEt3)4Rh−H] in good to high yields. Kinetic and deuterium labeling results support a syn-oxyrhodation pathway via direct olefin insertion into a Rh−O bond, followed by rapid β-hydride elimination. In comparison, {Rh(PEt3)212-OCRR‘CH2CHCH2]} are isolated as stable crystals, and the Rh−olefin interactions are evidenced by an X-ray structure. Heating of these complexes generated [Rh(PEt3)22-allyl)] and the corresponding ketones in high yields following an apparent β-allyl elimination pathway.