UV-vis, ir and epr spectroelectrochemical study of the ec redox transition [( pr3) n(co) 3(r′-pz) m]+/0; m = mo, w; r′-pz = n-alkylpyrazinium; r = isopropyl, cyclohexyl; n = 1 or 2

Article abstract of DOI:10.1016/0022-328X(95)05933-G

The title complexes, isolated as trans,mer-configurated salts [(PR₃)₂(CO)₃(R′-pz)M](PF₆), display a strong π interaction between the zerovalent metal center and the excellent π acceptor ligands R-pz⁺. The solvatochromism of the long-wavelength metal-to-ligand charge transfer (MLCT) absorption as analyzed in particular for [(PCy₃)₂(CO)₃(CH₃(CH₂)₁₇-pz)W](PF₆) correlates not with established MLCT parameters but with the donor numbers of the solvents. The seemingly reversible one-electron oxidation and reduction processes were studied by spectroelectrochemical techniques with regard to EPR, carbonyl vibrational and UV-vis/NIR spectroscopic features. Whereas oxidation leads to labile M(I) species with 17 valence electrons, the reduction is centered at the R′-pz+ ligand and causes a rapid reversible dissociation of one PR₃ group from the metal (EC_rev process). Both EPR and IR data suggest pentacoordination at the 16 + δ valence electron centers in the neutral species [(PR₃)(CO)₃(R′-pz)M]'.