Systematic studies of 17-electron rhenium(II) carbonyl phosphine complexes

Oxidative electrochemical properties in dichloromethane have been examined for compounds of the types cis- or trans-[Re(CO)(2)(P-P)(2)](+) and trans-Re(CO)(P-P)(2)X (P-P = diphosphine ligand, X = Cl, Br) which exhibit a range of charge and ligand types. In all cases 17e Re(II) species are formed, although the oxidation potentials vary over a reasonably wide range. The Re(II) compounds have been characterized by spectroelectrochemical (IR) and electrospray mass spectrometry (ESMS) studies. The stabilities of the Re(II) species are dependent upon charge and ligand types. The trans configuration is strongly preferred in the Re(II) state, so when the starting material is cis, there is rapid isomerization following electron transfer. The major form of reactivity detected is facile reduction of the trans-[Re(CO)(2)(P-P)(2)](2+) species. The particularly high stability of trans-[Re(CO)(dpe)(2)X](+) (dpe = Ph2P(CH2)(2)PPh2) allows solid-state studies to be undertaken for the trans-[Re(CO)( dpe)(2)X](+/0) couple when the compounds are mechanically attached to a graphite electrode immersed in water (electrolyte).