Analysis of Electrolysis Reactions of Metal Complexes Using On-Line Electrospray Ionization Mass Spectrometry with a Compact Electrolytic Flow-Through Cell

An on-line electrospray ionization mass-spectrometric analysis for an electrolysis reaction was developed by the installation of a compact, efficient flow-through cell upstream of an electrospraying needle. The electrode was designed to avoid any reduction of the oxidation products formed during electrolysis. The electrolytic oxidation reaction of a Ru and Os metal complex was carried out to examine the performance of the system. From the electrolysis of [M(bpy)3](PF6)2 (where M = Ru and Os, and bpy = 2,2′-bipyridine) we detected the one-electron oxidation product, [M(bpy)3]3+. The electrolysis of [Ru(bpy)2(en)]-(ClO4)2 (en = ethylenediamine) formed two complex products along with the elimination of two and four hydrogen atoms from the en ligand. The structure of the two complex products was determined to be a monoimine and diimine complex, based on an electrolysis experiment using a deuterium-labeled complex, [Ru(bpy)2(ed)](ClO4)2 (ed = ethylene-d4-diamine, H2N–CD2–CD2–NH2). The results indicate that electrochemical oxidation occurs at the ethylenediamine ligand and that the monoimine complex is a reaction intermediate for the formation of a diimine complex