Curtin-Hammett principle to evaluate alkene insertion

Given an unsymmetrical alkene in a simple non-stereoselective catalytic hydrogenation reaction. If one would want to investigate the nuances in the catalytic cycle of a dihydride complex leading to the alkane, there are two important transition-states that have to be considered.


1. Insertion of the alkene into one metal-hydride bond
2. Reductive elimination of the alkyl and remaining hydride to give the alkane.


We assume the boundary condition that the transition-state for the second step (**TS-2**) is always higher in energy than the transition-state for the first step (**TS-1**).


Moreover, I want to look at the elementary steps of the insertion, e.g. a 1,2-insertion (1-position of alkene binds to the metal and the hydride is transferred to the 2-position of said alkene) or 2,1-insertion (2-position of alkene binds to the metal and the hydride is transferred to the 1-position of the alkene).


If I now have a catalyst where the transition state for the first step (**TS-1**) lies lower in energy for a 2,1-insertion compared to a 1,2-insertion, but the transition-state for the second step (**TS-2**) lies higher in energy for the 2,1-insertion product than for the 1,2-insertion product, which pathway is the *right* one? E.g. does the mechanism proceed through the 2,1-insertion since **TS-1** favors this pathway, or does the mechanism proceed through a 1,2-insertion since **TS-2** is lower for this pathway.


