The new polyhydrides [ReH5(PPh(3))(2)(L)] (1; L = 4-carbomethoxypyridine (a), pyridine (b), 4-picoline (c), 4-(dimethylamino)pyridine (d)), formed by reaction of L with [ReH7(PPh(3))(2)], are rigid on the NMR time scale at low temperature. The low-temperature spectrum is assigned by ROESY NMR studies, and turnstile and pseudorotation fluxionality mechanisms are suggested to account for the two successive coalescence events in the VT NMR spectra.