The reactions of RhCl(PBz3)3 with H2 and pyridine or 4-methylpyridine yield RhCl(H)2(PBz3) 2(py) and RhCl(H)2(PBz3)2(4-Me-py), respectively. These species undergo hydride site exchange via the loss of the pyridyl donor and formation of RhCl(H)2(PBz3)2 which contains equivalent hydride ligands; for the py system the activation free energy, ΔG300,‡ is 57.4 ± 0.1 kJ mol-1 while for 4-Me-py the value is 59.6 ± 0.3 kJ mol -1. These products only showed parahydrogen enhancement in the corresponding hydride resonances when a sacrificial substrate was added to promote hydrogen cycling. When RhCl(PPh3)3 was used as the precursor similar observations were made, while when RhCl(PCy 3)2(C2H4) was examined, H 2 addition led to the formation of the binuclear complex (H) 2Rh(PCy3)2(μ-Cl)2Rh(H) 2(PCy3)2 which was differentiated from RhCl(H)2(PCy3)2 on the basis of the similarity in diffusion coefficient (5.5 × 10-9 m2 s -1) to that of (H)2Rh(PPh3) 2(μ-Cl)2Rh(PPh3)2 (5.3 × 10-9 m2 s-1). The detection of RhCl(H) 2(PCy3)2(py) was facilitated when pyridine was added to a solution of RhCl(PCy3)2(C2H 4) before the introduction of H2. During these reactions trace amounts of the double substitution products, RhCl(H) 2(phosphine)(py)2, were also detected.