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 MI(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.