Facile rearrangement and electron transfer of 19-electron radicals from the reduction of the bischelated manganese carbonyl cation Mn(CO)2[PPh2(CH2)2PPh2]2+

Abstract

The cathodic reduction of the bischelated manganese carbonly cation trans-Mn(CO)/sub 2/(/eta//sup 2/-DPPE)/sub 2//sup +/ (I/sup +/, where DPPE = PPh/sub 2/(CH/sub 2/)/sub 2/PPh/sub 2/) produces the metastable anion Mn(CO)/sub 2/(/eta2/-DPPE)(/eta//sup 1/-DPPE)/sup /minus// (II/sup /minus//) 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/sup +/ can be traced to an electron transfer with II/sup /minus// 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/sup +/) is a metastable species and spontaneously extrudes an end of one DPPE ligand to afford the second radical II* with the rate constant k/sub r/ /approximately/ 4 /times/ 10/sup 6/ s/sup /minus/1/. The structures of the anionic and radical intermediates II/sup /minus//, II*, and I* are discussed in the context of their transient electrochemical behavior as well as their /sup 31/P NMR and ESR spectra. The rather slow rate of electron transfer between I/sup +/ and II/sup /minus// is ascribed to steric effects in carbonylmanganese ions encumbered with a pair ofmore » DPPE ligands. 59 refs., 7 figs., 1 tab.« less