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

In the first part of this work, a general method for the preparation of aryl, methyl, vinyl and alkynyl(vinylidene)rhodium(I) complexes trans-[Rh(R')-(=C=CHR)(PiPr(3))(2)] (8-14, 18-22) and trans-[Rh(R')(=C=CMe2)(PiPr(3))(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 equivalent to CR)(py)(PiPr(3))(2)] (23-25) by elimination of R'H, treatment of 8-11, 16, and 18 with carbon monoxide yields the square-planar eta(1)-vinyl and eta(1)-butadienylrhodiumcarbonyl complexes trans[Rh{eta(1)-(Z)-C(R')= CHR}(CO)(PiPr(3))(2)] (27-32). The reaction of 8 or 18 with methyl or tert-butylisocyanide leads stereoselectively to the isocyaniderhodium(I) compounds trans-[Rh(Rh{eta(1)-(Z)-C(R)= CHPh} (CNR')(PiPr(3))(2)] (33-35). Acid-induced cleavage of the rhodium-carbon sigma bond of 27, 30, or 31 with CH3CO2H gives trans-[Rh(eta(1)-O2CCH3)(CO)(PiPr(3))(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 degrees C to afford the isomeric pi-allyl complexes [Rh(eta(3)-1-RC3H4)(PiPr(3))(2)] (40-42) almost quantitatively. The vinyl(vinylidene) compounds 11 and 12 also undergo an intramolecular rearrangement that leads to the eta(3)-2,3,4-butadienyl- or to the alkynyl(ethene)rhodium(I) isomers, depending on the reaction conditions. In an analogous manner to the eta(1)-vinyl- and eta(1)- butadienyl(carbonyl) derivatives 27, 30, and 31, the pi-allyl and pi-butadienyl complexes also react with acetic acid to give [Rh(eta(2)-O2CCH3)(PiPr(3))(2)] (47) and the respective olefin.