In Figure , we also plot ∆∆E R P(c 4 ) for the model structures. The model complexes may provide insight into the origin of the reactivity differences, but we must first determine if they are a reasonable representation of the full complexes. The ∆∆E R of the dppm (θ ∼ 72 • ) and dppb (θ ∼ 84 • ) complexes is closely matched by the ∆∆E R P(c 4 ) of the θ = 70 • and 85 • c 4 model structures, respectively, for all reactions. The slopes between these complexes are also very similar, see Table in the SI. This suggests that the models are accurate representations of these complexes. It also seems that the bite angle is driving the difference in reactivity between the full complexes, as this is the only feature that changes in the minimal models. In contrast, ∆∆E R P(c 4 ) (θ = 95 • ), the closest model to the dppx complex, is in poor agreement with ∆∆E R dppx for all reactions. The agreement is even qualitatively incorrect for Reaction 3, with the ∆∆E R3 X values having different signs for the model and dppx complexes. The reason for these differences is that the ligand framework for the dppx complex is flexible, allowing it to twist into a significantly different (and more favorable) conformation compared to the other P ligands. Unlike the dppm and dppb complexes, for which the methyl and phenyl bridges remain beneath the rhodium, the xanthenyl group of the dppx complex folds up on one side, becoming almost parallel with the Cp * ring, see Figure . This leaves the opposite side of the molecule more open, promoting both hydrogen and solvent binding by reducing the steric bulk in the area. The minimal models, with their simple linker groups that only focus on the bite angle descriptor, clearly cannot reproduce effects arising from the extended structure of the ligand. In other words, the bite angle alone is not a good descriptor for this ligand.