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

Abstract

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(+)/1(2+) in dichloromethane/0.05 M [NBu4][B(C6F5)(4)] (E-1/2 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 x-organic (diphenylolefin) makeup in 1 to increasingly organic based fractions in 1(+) and 1(2+). 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)2 P(OPh) 3 (eta(5)-C5H4(Et)C=C(C6H5)(2)) was prepared by the "electrochemical switch" method, wherein [Mn(CO)(2)P(OPh)(3) (eta(5)-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.