REDUCTION OF [RE(X)(CO)(3)(R'-DAB)] (X=OTF(-), BR- DAB EQUALS DIAZABUTADIENE R'=IPR, PTOL, PAN) AND [RE(R)(CO)(3)(IPR-DAB)] (R=ME, ET, BZ) COMPLEXES - A COMPARATIVE (SPECTRO)ELECTROCHEMICAL STUDY AT VARIABLE TEMPERATURES

This article describes the reduction routes of the complexes [Re(X)(CO )(3)(R'-DAB)] (X = Br-, Otf(-); R' = pAn, pTol, iPr) and the metal-alk yl complexes [Re(R)(CO)(3)(iPr-DAB)] (R = Me, Et, Bz), using data obta ined from IR and UV-vis spectroelectrochemical measurements and cyclic voltammetry at variable temperatures. Oneelectron reduction of the co mplexes [Re(Br)(CO)(3)(R'-DAB)] in nPrCN results in the establishment of an equilibrium between the radical anions [Re(Br)(CO)3(R'-DAB)](.-) and the solvento radical [Re(nPrCN)(CO)(3)(R'-DAB)](.). The ratio bet ween these radical species could be tuned by changing the character of the R' substituents on the R'-DAB ligand and by variation of the temp erature. The radicals could be reduced in a subsequent one-electron st ep to give the five-coordinate anions [Re(CO)(3)(R'-DAB)](-) together with the six-coordinate anions [Re(nPrCN)(CO)(3)(R'-DAB)](-) as the mi nor products. The bonding properties of the five-coordinate anions are discussed on the basis of a qualitative MO scheme and compared with t hose of the related complex [Mn(CO)(3)(iPr-DAB)](-). The main feature of the [Re(CO)(3)(R'-DAB)](-) complexes is a strong delocalization of their HOMOs, which rules out application of the localized-valence conc ept in this case. The complexes [Re(R)(CO)(3)(iPr-DAB)] were found to be reduced in an electrochemically and chemically reversible one-elect ron step to give radical anionic products, tentatively formulated as { [Re(CO)(3)(iPr-DAB)](-)... R(.)}. The radical nature of the products h as been confirmed by ESR spectroscopy whereas the IR and UV-vis data c orrespond with the presence of the [Re(CO)(3)(iPr-DAB)](-) moiety.