Pentamethylcyclopentadienyl-rhodium and -iridium complexes. Part IX. The formation of η-allyl-MIII and η-diene-MI complexes from µ-hydrido-compounds and acyclic dienes

Abstract

The reactions of the µ-hydrido-complexes [H(MC₅Me₅)₂Cl₃](4; M = Rh or Ir) with butadiene, penta-1,3-diene, isoprene, 1,1-dimethylallene, 2,3-dimethylbutadiene, trans-2-methylpenta-1,3-diene, and 2,5-dimethylhexa-2,4-diene are reported. η-Allylic complexes of varying stability are formed initially, but only the syn-1 (or 3-) alkyl isomer is formed where a choice is possible. The η-allylic complexes are of three types: (i) those that do not eliminate HCl under any conditions, (ii) those that eliminate HCl under forcing conditions, and (iii) those that eliminate HCl spontaneously to form the M^I(diene) complexes. The following conclusions are drawn: (a) the dienes react in the transoid form with these hydrides, and (b) in order for reductive elimination to occur, the η-allylic complex must have, or must easily be able to rearrange to a form bearing, an anti-1-alkyl group.