Oxidation of Cymantrene Analogues of Ferrocifen: Electrochemical, Spectroscopic, and Computational Studies of the Parent Complex 1,1′-Diphenyl-2-cymantrenylbutene

The
oxidative electrochemical behavior of 1,1′-diphenyl-2-cymantrenylbutene
(1), a cymantrene analogue of the breast cancer drug
ferrocifen, was shown to involve the sequential electron-transfer
series 1/1+/12+ in dichloromethane/0.05 M [NBu4]­[B­(C6F5)4] (E1/2 values
0.78 and 1.18 V vs ferrocene). By a combination of spectroscopic and
computational techniques, it was shown that the cymantrene functionality
plays an important role in dissipating the positive charges in the
oxidized compounds and is therefore an active participant in the redox
events. The redox-active orbital goes from roughly equal degrees of
organometallic and π-organic (diphenylolefin) makeup in 1 to increasingly organic based fractions in 1+ and 12+. Structural changes
mimicking those of oxidized tetrakis­(aryl)­ethylenes accompany the
one-electron oxidations. There is sufficient unpaired electron density
on the manganese center in 1+ to allow for
oxidatively induced ligand exchange of one or more of the carbonyl
ligands with donor ligands, including phosphites and pyridine. The
complex Mn­(CO)2P­(OPh)3(η5-C5H4(Et)­CC­(C6H5)2) was prepared by the “electrochemical switch”
method, wherein [Mn­(CO)2P­(OPh)3(η5-C5H4(Et)­CC­(C6H5)2)]+, produced by the oxidation of 1 in the presence of P­(OPh)3, was reduced back
to the neutral CO-substituted complex.