The Rh NBO charges for the reactant species are plotted in Figure . First, we note that the Rh charge for the P complexes and the minimal model systems are virtually identical. This indicates that neither the bite angle nor the steric bulk significantly alter the electron density around the metal for a specific choice of linker element. Second, the charge for Rh(III) is more positive (or less negative with P) with acetonitrile than with H, compare green and red markers in Figure . This is reasonable because the solvent molecule is a better electronwithdrawing group than H. Third, Rh(I) has the same charge on the metal as in the Rh(III)H complex with P ligands, and it is more positive than in the Rh(III)H complex with the bpy ligand. This may seem counterintuitive, but it is consistent with the fact that P is a very polarizable element, and it readily donates charge to the Rh center. The addition of a proton to the metal increases this donation (see the linker charges in Figure of the SI) with a minimal net change for the charge of the metal. On the other hand, the N center in bpy is considerably more electronegative than P, leaving less electron density around the Rh. However, it seems that when the Rh shares electrons with the proton to form the hydride complex, there is less electron density for the bpy ligand to pull, which results in a slightly negative charge on the Rh atom. Finally and most importantly, Rh is surrounded by a higher electron density with P-based ligands than with N ligands. This is consistent with the difference in electronegativity of the linker atoms, and it is confirmed by the linker charges in Figure of the SI. These results point to electronic effects, related to the choice of linker atom in the ligand, possibly playing a more important role than the bite angle in the reactivity of the complex. Repeating this analysis with Hirshfeld or CM5 charges leads to qualitatively the same result, see Figures S3 and S4 in the SI.