Electrochemistry and spectroelectrochemistry of [Re(1,2-bis(dimethylphosphino)ethane)(3)](+)

The electrochemical properties of [Re(dmpe)(3)](+), where dmpe is 1,2-bis(dimethylphosphino)ethane, have been investigated in aqueous and non-aqueous solutions by cyclic and square wave voltammetry as well as by thin-layer electrochemical and spectroelectrochemical techniques. The redox behavior in N,N-dimethylformamide (DMF) is described in terms of three interrelated one-electron oxidations and the chemistry from decomposition of electrogenerated Re(III) species. The first and third redox processes are assigned to the oxidation of [Re(dmpe)(3)](+) to [Re(dmpe)3](2+) and [Re(dmpe)(3)](2+) to [Re(dmpe)(3)](3+); the corresponding E-p values from square wave voltammetry are +0.336 and +1.120 V versus Ag/AgCl (3 M NaCl). The second redox process (+0.884 V) is described as the oxidation of an Re(II) species, [Re(dmpe)(2)(eta(1)-dmpe)S](2+) (S = a solvent molecule), which is proposed as an intermediate in the dissociation of a dmpe ligand. Complete dissociation of dmpe occurs from the Re(III) complexes to yield a species denoted as [Re(dmpe)(2)S-2](3+), which is reduced with a peak potential from square wave voltammetry at -0.288 V in DMF. Identification of this species as a bis(dmpe) complex is accomplished by comparison of its FAB mass spectrum UV-Vis spectrum, HPLC retention time, and electrochemical properties to those of an independently synthesized complex, where S is replaced by Cl-.