The ligands 2-(dimethoxymethyl)pyridine (L1) and 2,6-bis(dimethoxymethyl)pyridine (L2) formed bidentate chelate complexes with the isoelectronic transition metal moieties ReIX(CO)3 and PtIVXMe3 (X = halide). The complexes [ReX(CO)3L1] (X = Cl or Br), [PtXMe3L1] (X = Br or I) and [ReBr(CO)3L2] in organic solvents were shown by NMR to undergo fluxional processes which interconvert co-ordinated and pendant OMe groups. Rates and activation energies of these fluxions were measured by NMR methods (1-dimensional bandshape analysis or 2-dimensional exchange spectroscopy). Magnitudes of ΔG‡ (298.15 K) for the fluxions were in the range 59–85 kJ mol−1 with the order being ReI–L1 > ReI–L2 > PtIV–L1. A carbon–carbon bond rotation mechanism is proposed for the fluxions in the L1 complexes and concerted C–C bond rotation/metallotropic shift processes for the L2 complexes. Crystal structures of [ReCl(CO)3L1] and [PtIMe3L1] revealed distorted octahedral metal centres with N–M–O ‘bite’ angles of 73–75° and a trans relationship of the axial halide and pendant OMe group.