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

In 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')‐(CCHR)(P i Pr 3 ) 2 ] ( 8–14, 18–22 ) and trans ‐[Rh(R')(CCMe 2 )(P i Pr 3 ) 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(CCR)(py)(P i Pr 3 ) 2 ] ( 23–25 ) by elimination of R'H, treatment of 8–11 , 16 , and 18 with carbon monoxide yields the square‐planar η 1 ‐vinyl and η 1 ‐butadienylrhodiumcarbonyl complexes trans ‐[Rh{η 1 ‐( Z )‐C(R')CHR}(CO)(P i Pr 3 ) 2 ] ( 27–32 ). The reaction of 8 or 18 with methyl or tert ‐butylisocyanide leads stereoselectively to the isocyaniderhodium(I) compounds trans ‐ [Rh{η 1 ‐( Z )‐C(R)CHPh}(CNR') (P i Pr 3 ) 2 ] ( 33–35 ). Acid‐induced cleavage of the rhodium‐carbon σ bond of 27, 30 , or 31 with CH 3 CO 2 H gives trans ‐[Rh(η 1 ‐O 2 CCH 3 )‐(CO)(P i Pr 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 °C to afford the isomeric π‐allyl complexes [Rh(η 3 ‐1‐RC 3 H 4 )(P i Pr 3 ) 2 ] ( 40–42 ) almost quantitatively. The vinyl(vinylidene) compounds 11 and 12 also undergo an intramolecular rearrangement that leads to the η 3 ‐2,3,4‐butadienyl‐ or to the alkynyl(ethene)rhodium(I) isomers, depending on the reaction conditions. In an analogous manner to the η 1 ‐vinyl‐and η 1 ‐butadienyl(carbonyl) derivatives 27, 30 , and 31 , the π‐allyl and π‐butadienyl complexes also react with acetic acid to give [Rh(η 1 ‐O 2 CCH 3 )(P i Pr 3 ) 2 ] ( 47 ) and the respective olefin.