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 fbr 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-d(4)-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.