Fiber-optic infrared reflectance spectroelectrochemistry: isomerization of a manganese pyranyl complex

A simple apparatus for fiber-optic reflectance FTIR spectroelectrochemical measurements is described. The method is useful for observing the products of electrode reactions generated in steady-state at an electrode surface, and the problem of large thin-layer resistance in non-aqueous solvents is minimized. Cyclic voltammetry (CV) and FTIR spectroelectrochemical measurements on five compounds ([(η5-C5H5)Fe(CO)2]2 (Fp2), Fp(CCPh), Mn2(CO)10, BrMn(CO)5 and (η5-2,4-diphenyl-6-methylpyranyl)tricarbonylmanganese (PyrMn(CO)3) are presented. As expected, Mn2(CO)10 and BrMn(CO)5 are both reduced to the known Mn(CO)5− anion, but Fp2 is reduced in CH2Cl2 to form FpCH2Cl, and Fp(CCPh) forms a [μ2–η1:η2-Fp2CCPh]+ cation. Upon oxidation of the PyrMn(CO)3 complex, the Mn(CO)3+ unit undergoes migration from the pyranyl ring to a phenyl ring to form an η6-arene complex which has a pyrylium ion as a substituent on the arene ligand.