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 o f aryl, methyl, vinyl and alkynyl(vinylidene)rhodium(I) complexes tran s-[Rh(R')-(=C=CHR)(PiPr(3))(2)] (8-14, 18-22) and trans-[Rh(R')(=C=CMe 2)(PiPr(3))(2)] (16, 17) from the corresponding chloro(vinylidene) der ivatives 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 w ith carbon monoxide yields the square-planar eta(1)-vinyl and eta(1)-b utadienylrhodiumcarbonyl 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-but ylisocyanide leads stereoselectively to the isocyaniderhodium(I) compo unds 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 3 1 with CH3CO2H gives trans-[Rh(eta(1)-O2CCH3)(CO)(PiPr(3))(2)] (38) an d the corresponding olefin or diene, respectively. In the absence of a Lewis base such as pyridine, CO, or CNR', compounds 18-20 rearrange i n benzene at 40 - 50 degrees C to afford the isomeric pi-allyl complex es [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 alk ynyl(ethene)rhodium(I) isomers, depending on the reaction conditions. In an analogous manner to the eta(1)-vinyl- and eta(1)- butadienyl(car bonyl) derivatives 27, 30, and 31, the pi-allyl and pi-butadienyl comp lexes also react with acetic acid to give [Rh(eta(2)-O2CCH3)(PiPr(3))( 2)] (47) and the respective olefin.