VARIABLE-TEMPERATURE H-1-NMR SPECTRA AND T1 MEASUREMENTS ON THE DINUCLEAR OCTAHYDRIDE COMPLEXES RE2H8(PR3)4 (PR3 = PPH3, PET2PH, PME2PH, PME3) AND THE MONOHYDRIDE COMPLEXES CP2REH AND RE2HCL3(CO)2(DPPM)2 (DPPM = PH2PCH2PPH2)

The variable-temperature spectra and T1 1H NMR data for the dinuclear complexes Re2H8(PR3)4 (PR3 = PPh3, PEt2Ph, PMe2Ph, PMe3) are reported in CD2Cl2. The room-temperature spectra consist of a quintet in the hydride region. In all cases, at very low temperatures, it was possible to obtain spectra indicative of a frozen-out species; the quintet for the metal-bonded hydrogen atoms resolved into two distinct resonances of equal intensity. Definitive assignments as to which peak was due to the terminal and which to the bridging hydrogen atoms were made on the basis of an isotopic perturbation of resonance experiment, and thus the peak at higher field was assigned as due to the terminal hydrogen atoms. Furthermore, all of the Re2H8(PR3)4 complexes exhibited minimum T1 times around ca. 140 ms at 400 MHz. A minimum T1, value of 280 ms at 400 MHz was found for Cp2ReH in toluene-d8. In the case of Re2HCl3(CO)2(dppm)2, the value of ca. 85 ms was obtained at 200 MHz and −80 °C in CD2Cl2. These results suggest, at least in the case of Re2HCl3(CO)2(dppm)2, that other relaxation mechanisms, in addition to the H-H dipolar one, can operate in these rhenium complexes. © 1990, American Chemical Society. All rights reserved.