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

Abstract

AbstractIn the first part of this work, a general method for the preparation of aryl, methyl, vinyl and alkynyl(vinyl‐idene)rhodium(I) 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(vinyl‐idene) 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') (PiPr3)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(η1‐O2CCH3)(PiPr3)2] (47) and the respective olefin.