SYNTHESIS AND STRUCTURAL STUDIES OF SOME NEW RHENIUM PHOSPHINE HEPTAHYDRIDE COMPLEXES - EVIDENCE FOR CLASSICAL STRUCTURES IN SOLUTION

A series of new rhenium phosphine heptahydride complexes ReH7L2(L2= a chelating bidentate phosphine) have been synthesized and characterized by IR and 1H, 31P, and 13C NMR spectroscopy. The hydride resonances of ReH7(dppf) (1, dppf = 1, 1'-bis(diphenylphosphino) ferrocene), ReH7(dppb) (2, dppb = 1,4-bis(diphenylphosphino)butane), and ReH7{(+)-diop} (3, (+)-diop = (4S,5S)-4,5-bis((diphenylphosphino)methyl)-2,2-dimethyl-1,3-dioxolane) undergo decoalescence upon cooling. The low-temperature hydride patterns suggest classical 9-coordinate tricapped trigonal prismatic structures. Consistent with the classical structures, 1H NMR spectra of deuterated ReH7L2complexes show very small and temperature-independent upfield isotope shifts in the hydride region and no change in 2JHP. Sequential treatment of 1, 2, and 3 with NaH and Me2SO4in the presence of Ph3SiH leads to ReH6(SiPh3)L2(L2= dppf, dppb, (+)-diop). Variable-temperature 1H NMR studies of these silyl derivatives provide further support for the classical formulation of their parent heptahydrides. Theoretical T1(min) values are calculated for some polyhydrides on the basis of different structural models and are compared with the experimental numbers. Precautions to be taken in interpreting 71data are discussed. © 1990, American Chemical Society. All rights reserved.