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The cathodic reduction of the bischelated manganese carbonyl cation iran.r-Mn(CO)2(?)2-DPPE)2+ (I+, where DPPE = PPh2-(CH2)2PPh2) produces the metastable anion Mn(CO)2(jt2-DPPE)(n1-DPPE)" ( ) via an overall 2e process at a Pt electrode in either tetrahydrofuran or acetonitrile solution. The unusual observation of a cathodic curve crossing and two isopotential points in the cyclic voltammogram of I+ can be traced to an electron transfer with II" to afford a pair of neutral radicals, i.e., the 19e I' and the 17e II'. The former (which is also generated during the initial step in the reduction of I+) is a metastable species and spontaneously extrudes an end of one DPPE ligand to afford the second radical IP with the rate constant kT == 4 X 106 s"1. The structures of the anionic and radical intermediates II", IP, and P are discussed in the context of their transient electrochemical behavior as well as their 31P NMR and ESR spectra. The rather slow rate of electron transfer between I+ and II" is ascribed to steric effects in carbonylmanganese ions encumbered with a pair of DPPE ligands.

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