APPLICATIONS OF THIN-LAYER FTIR, UV-VIS, AND ESR SPECTROELECTROCHEMISTRY FOR EVALUATING (TPP)RU(CO) REDOX REACTIONS IN NONAQUEOUS MEDIA

In situ FTIR, UV-vis, and ESR spectroelectrochemistry were combined with microvoltammetry and classical electrochemical techniques in order to elucidate the prevailing electron-transfer mechanism for the oxidation and reduction of (TPP)Ru(CO) (where TPP is the dianion of tetraphenylporphyrin) in six different nonaqueous solvents. (TPP)Ru(CO) undergoes four reversible oxidation/reduction reactions at a 25-µm microelectrode. All four electrode reactions were investigated with respect to the site of electron transfer, the stability of the electrooxidation/reduction product, the fate of the axially bound CO ligand, and the presence or absence of other axial ligands. A CO ligand remains coordinated to the singly oxidized, singly reduced, and doubly reduced forms of (TPP)Ru(CO)(L) (where L is a solvent molecule). The doubly oxidized species is only stable on the cyclic voltammetry time scale, and a rapid chemical reaction occurs after electrogeneration of [(TPP)Ru(CO)(L)]. The CO vibration frequencies of [(TPP)Ru(CO)(L)]+, [(TPP)Ru(CO)]+, (TPP)Ru(CO), (TPP)Ru(CO)(L), [(TPP)Ru(CO)(L)r, and [(TPP)Ru(CO)(L)]2- vary between 1985 and 1853 cm-1. The CO vibration frequency of [(TPP)Ru(CO)(L)]n (where n varies from +1 to -2) depends upon the overall charge of the complex and shifts by 27-52 cm-1 per unit change in n. The binding of a solvent molecule to [(TPP)Ru(CO)]+ shifts the CO vibration to a higher frequency by 2-25 cm depending upon the ligand, but no systematic trend in the CO vibration was observed upon ligand binding by neutral (TPP)Ru(CO). © 1990, American Chemical Society. All rights reserved.