To analyze this data further, we first look at single building block substitutions at each of the four sites shown in Fig. (a), i.e., building blocks used at all the remaining sites on the catalyst are held constant. For sites A and B, Fig. shows the change in free energy barriers (∆G in kcal/mol) due to the different building blocks. Although different building blocks are dominant at different steps of the reaction, we observe a substantial fluctuation in the ∆G even from single substitutions. In particular, substitutions on site B show larger fluctuations in ∆G across all reaction steps as compared to those on site A. This implies a stronger electronic effect of site B on the metal center compared to site A. We make similar observations for sites C and D, where a large number of cases arise as we also account for non-symmetric substitutions on the pincer arm.