Unusual pathways for metal-assisted C-C and c-p coupling reactions using allenylidenerhodium complexes as precursors

The rhodium allenylidenes trans-[RhCl{CCC(Ph)R}(PiPr3)2] [R = Ph (1), p-Tol (2)] react with NaC5H5 to give the half-sandwich type complexes [(η5-C5H5)Rh{CCC(Ph)R}(PiPr3)] (3, 4). The reaction of 1 with the Grignard reagent CH2CHMgBr affords the η3-pentatrienyl compound [Rh(η3-CH2CHCCCPh2)(PiPr3)2] (6), which in the presence of CO rearranges to the η1-pentatrienyl derivative trans-[Rh{η1-C(CHCH2)CCPh2}(CO)(PiPr3)2] (7). Treatment of 7 with acetic acid generates the vinylallene CH2CH−CHCCPh2 (8). Compounds 1 and 2 react with HCl to give the five-coordinate allenylrhodium(III) complexes [RhCl2{CHCC(Ph)R}(PiPr3)2] (10, 11). An unusual [C3 + C2 + P] coupling process takes place upon treatment of 1 with terminal alkynes HC⋮CR‘, leading to the formation of the η3-allylic compounds [RhCl{η3-anti-CH(PiPr3)C(R‘)CCCPh2}(PiPr3)] [R‘ = Ph (12), p-Tol (13), SiMe3 (14)]. From 12 and RMgBr the corresponding phenyl and vinyl rhodium(I) derivatives 15 and 16 have been obtained. The previously unknown unsaturated ylide iPr3...