To compare the effect of the element, namely their differing ability to direct electron density to and from rhodium, the reactivity trends for N(c 3 ) and N(c 4 ) linkers are also shown in Figure . The effect of the linker atom is noticeable when comparing the P(c 4 ) and N(c 4 ) scans; the N(c 4 ) scans exhibit the same bite angle trends as the corresponding P(c 4 ) reactions, but the slopes are smaller, and the ∆∆E R N(c 4 ) curves for each reaction change by no more than 3 kcal/mol. The N-H bond lengths in these model systems are 0.4 Å smaller than the corresponding P-H bonds, so the smaller bite angle dependence of the N(c 4 ) ligands could be attributed to a reduced steric impact. Similar to the P(c 3 ) scans, the ∆∆E R N(c 3 ) curves are quadratic for R1 and R3, with steep changes as the ligands approach each other (6 kcal/mol from 85 • to 70 • for R3) or the Cp * ring (9 kcal/mol from 85 • to 110 • for R1). This is a result of the Rh(I) species being highly strained at extreme bite angles. The N(c 3 ) structures actually exhibit more steric hindrance than the P(c 3 ) ones as they approach Cp * ; since the nitrogen ligands are about 0.5 Å shorter (end to end), wide bite angles force the methylene groups towards the center of the Cp * , while for phosphorus they only approach the less crowded exterior of the ring.