Intramolecular C–C Coupling Reactions of Alkynyl, Vinylidene, and Alkenylphosphane Ligands in Rhodium(III) Complexes

Electrophilic attack with methyl trifluoro­methane­sulfonate or tetrafluoro­boric acid, to new alkynyl rhodium complexes containing alkenylphosphanes, leads to butenynyl coupling products or to the unprecedented rhodaphosphacycle complexes [Rh­(η5-C5Me5)­{κ4-(P,C,C,C)-iPr2PCH2C­(CH2)­C­(CH2R)­CC­(R)}]­[BF4] (R = Ph (11a), p-tol (11b)). These complexes 11a,b can be explained as a result of the coupling of three organic fragments in the molecule, the alkynyl, the vinylidene, generated in situ by reaction with HBF4 (A), and the C–C double bond from the alkenylphosphane. DFT computational studies on the formation of complex 11a suggest the [2 + 2] intramolecular cycloaddition between the double bond of the allylphosphane and the Cα–Cβ of the vinylidene A as the most plausible pathway for this reaction.