Ring-strain effects on the oxidation potential of enediynes and enediyne complexes

Abstract

The metal–enediyne complexes [(η⁵-C₅H₅)Fe{η⁵-1,2-C₅H₃CC(CH₂)_nCC}] (4, n = 4; 5, n = 5) and [(η⁵-C₅H₅)Fe{η⁵-1,2-C₅H₃(CCMe)₂}] (6) were prepared from 1,2-diethynylferrocene (3). Complexes 4 and 5 were characterized in the solid state by X-ray crystallographic analysis. The structures of 4 and 6 were determined by computation using ab initio methods. A correlation was observed between ring-strain and increased ease of electrochemical oxidation along the series 6 (+0.164 V) to 5 (+0.152 V) to 4 (+0.123 V). A similar trend in ionization potentials was identified in both the gas phase and in solution by computational methods.