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η5-Rhodium(I) Complexes of a λ4-Phosphinine Anion:  Syntheses, X-ray Crystal Structures, and Application in the Catalyzed Hydroformylation of Olefins

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journal contribution
posted on 14.02.2005 by Audrey Moores, Nicolas Mézailles, Louis Ricard, Pascal Le Floch
2,6-Bis(trimethylsilyl)-4,5-diphenylphosphinine 1 and 2,3,5,6-tetraphenylphosphinine 2 react with tert-butyllithium to afford the expected λ4-phosphinine anions 3 and 4. These anions react with [Rh(COD)Cl]2 to yield the corresponding η5-complexes 5 and 6, in which coordination occurs through the anionic carbocyclic π-system of the ring. Both complexes were fully characterized by conventional spectroscopic techniques, and their X-ray crystals structures were recorded. The catalytic activity of 5 and 6 was tested in the hydroformylation of olefins. Good conversion yields and turnover frequencies were obtained in the hydroformylation of styrene and cyclohexene under mild conditions with low catalyst loading. The hydroformylation of styrene occurs with a high regioselectivity (93/7) in favor of the branched isomer. Interestingly, catalyst 6 catalyzes the transformation of 2,3-dimethyl-2-butene into 3,4-dimethylpentanal through a tandem isomerization/hydroformylation process.