Reaction of a metal alkyl with ethylene as a model for Ziegler-Natta polymerization. Evidence for the olefin insertion mechanism

A labeling study was carried out which demonstrates (in agreement with the classical view) that insertion, rather than ..cap alpha..-elimination, is the critical step in the mechanism of this reaction. A 0.13M benzene-d/sub 6/ solution of 1(cobalt complex) was heated under 4 atm of ethylene for 30 hours at 76/sup 0/C in a sealed NMR tube, the absorptions characteristic of 1 (..sigma..4.49, 0.61 ppM) and ethylene (5.27) were replaced by those from methane (0.22) and propene (1.58, CH/sub 3/), as well as by a new cyclopentadienyl signal (5.50, 5H) and two new multiplets at 1.11 (2H) and 2.09 (2H) ppM.