EFFECTS OF CHELATE RING RIGIDITY ON INTRAMOLECULAR HYDROGEN-EXCHANGE IN HYDRIDO(DIHYDROGEN)BIS(DIPHOSPHINE)RUTHENIUM(II) IONS [RUH(ETA(2)-H-2)(DIPHOSPHINE)(2)](+) (DIPHOSPHINE=BINAP AND DPBP)

The molecular hydrogen complex [RuH(eta(2)-H-2)(dpbp)(2)](+) (2f) was prepared in situ by reaction of H-2 gas with five-coordinate complex [RuH(dpbp)(2)]PF6 (1f) (dpbp = 2,2'-bis(diphenylphosphino)-1,1'-biphenyl). H-1 and P-31(H-1) NMR behaviour of 2f was measured in the temperature range 303-183 K, and compared with that of [RuH(eta(2)-H-2)-(binap)(2)](+) (2e; binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl). In the H-1 NMR spectrum, 2f showed a single broad signal in the hydride region due to a rapid hydrogen exchange between molecular hydrogen and terminal hydride at 303 K. The signal separated into two peaks at lower temperatures and the characteristic resonances of Ru-(H-2) and Ru-H were detected below 213 K. In contrast, 2e showed two signals of Ru-(H-2) and Ru-H even at 303 K. The differences in the NMR features between dpbp complexes and binap complexes were discussed on the basis of the flexibility or rigidity of diphosphine chelate rings.