Monitoring the formation 3c/3d as a function of time revealed no change in the 1:1 product ratio with conversion suggesting that these products do not interconvert at 80 °C. Furthermore, manual separation of crystals of 3c and 3d allowed isolation of a sample enriched in 3d (2.4:1). Re-exposing the enriched mixture to reaction conditions did not result in an equilibriation to a 1:1 mixture of 3c : 3d. Similarly, an experiment in which 3g was heated with allylbenzene to 80 °C did not lead to the formation of the cross-over products These findings strongly suggest that the hydrozincation step is non-reversible and b-hydride elimination is not in operation for either alkyne or alkene substrates up to temperatures of 80 °C.