Coupling of two phosphaalkynes via a carbonyl group in the addition across a rhrh double bond

Phosphaalkynes, RCP (R = Bu^t, Adamantyl), add across the RhRh double bond of [Rh₂Cpequation/tex2gif-stack-1.gif(CO)₂] to give either [Rh₂Cpequation/tex2gif-stack-2.gif(μ-CO)(COPCR)] or [Rh₂Cpequation/tex2gif-stack-3.gif(CO){PCRC(O)CRP}] depending on the stoichiometry of the reaction (Cp* = η⁵-C₅Me₅). The structures of these complexes have been elucidated by NMR spectroscopy and by a single crystal X-ray study on [Rh₂Cpequation/tex2gif-stack-4.gif(CO){PCAdC(O)CPAd}]. Small amounts of the 1,3-diphosphacyclobutadiene complexes [RhCp*(P₂C₂R₂)] and the trinuclear compound [Rh₃Cpequation/tex2gif-stack-5.gif(CO)₂] are also formed in these reactions. The reactions of RCP with [CoRhCp₂*(CO)₂] are also described.

1 A preliminary account of part of this work has appeared in J. Chem. Soc., Chem. Commun., 1987, 658.