Rhodium(I)-assisted stereoselective coupling of an alkyl, aryl or vinyl group with a vinylidene ligand: A novel synthetic route to π-allyl and π-butadienyl rhodium complexes

Article abstract of DOI:10.1002/chem.19970030120

In the first part of this work, a general method for the preparation of aryl, methyl, vinyl and alkynyl(vinylidene)rhodium(1) complexes trans-[Rh(R')-(=C=CHR)(PiPr₃)₂] (8-14, 18-22) and trans-[Rh(R')(=C=CMe₂)(PiPr₃)₂] (16, 17) from the corresponding chloro(vinylidene) derivatives and Grignard reagents is described Whilst compounds 8 and 10-13 react with pyridine to give trans-[Rh(C≡CR)(py)(PiPr₃)₂] (23-25) by elimination of R'H, treatment of 8-11, 16, and 18 with carbon monoxide yields the square-planar η¹-vinyl and η¹-butadienylrhodiumcarbonyl complexes trans-[Rh{η¹-(Z)-C(R')=CHR}(CO)(PiPr³)²] (27-32). The reaction of 8 or 18 with methyl or tert-butylisocyanide leads stereoselectively to the isocyaniderhodium(I) compounds trans-[Rh{η¹-(Z)C(R)=CHPh}(CNR')(PiP₃)₂] (33-35). Acid-induced cleavage of the rhodium carbon σ bond of 27, 30, or 31 with CH₃CO₂H gives trans-[Rh(η¹-O₂CCH₃)-(CO)(PiPr₃)₂] (38) and the corresponding olefin or diene, respectively. In the absence of a Lewis base such as pyridine, CO, or CNR', compounds 18-20 rearrange in benzene at 40-50°C to afford the isomeric π-allyl complexes [Rh(η³-1-RC₃H₄)(PiPr₃)₂] (40-42) almost quantitatively. The vinyl(vinylidene) compounds 11 and 12 also undergo an intramolecular rearrangement that leads to the η³-2,3,4-butadienyl- or to the alkynyl(ethene)rhodium(I) isomers, depending on the reaction conditions. In an analogous manner to the η¹-vinyl- and η¹-butadienyl(carbonyl) derivatives 27, 30, and 31, the π-allyl and π-butadienyl complexes also react with acetic acid to give [Rh(η²-O₂CCH₃)(PiPr₃)₂] (47) and the respective olefin.