Chemical and Electrochemical Generation of Hydride-Forming Catalytic Intermediates (bpy)M(CnRn): M = Rh, Ir (n = 5); M = Ru, Os (n = 6). Coordinatively Unsaturated Ground State Models of MLCT Excited States?

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Inorganic Chemistry, 33 (20): 4453--4459 (1994)
DOI: 10.1021/ic00098a009


The d6 metal complex ions (bpy)MCl(CnRn)+ bpy = 2,2'-bipyridine; M = Rh, Ir (n = 5, R = Me); M = Ru (n = 6; C6R6 = C6H6, p-MeC6H4CHMe2, C6Me6); M = Os (n = 6; C6R6 = p-MeC6H4CHMe2, C6Me6) were prepd. as hexafluorophosphate salts and studied by cyclic voltammetry. In each case, a two-electron redn. produced highly colored coordinatively unsatd. species (bpy)M(CnRn) which could also be obtained via chem. redn. 1H- and 13C-NMR high field shifts by bpy resonances, cathodically shifted secondary 1-electron redn. waves, and the vibrationally structured long-wavelength absorption features in the visible region of these neutral compds. all suggest an oxidn. state distribution involving a partially reduced bpy ligand. Such an electronic structure would correspond to the typical formulation of low-lying MLCT excited states in conventional d8 metal complexes and may be relevant for the functioning of the systems as catalysts for hydride transfer, including H2 evolution. Stable hydride intermediates of this catalysis were isolated and characterized in the case of the 5d systems (bpy)MH(CnRn)+ M = Ir (n = 5) and Os (n = 6) which could be reversibly reduced to neutral radical complexes as evident from a resolved EPR spectrum. on SciFinder(R)



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