Organometallic electron reservoir sandwich iron complexes as potential agents for redox and electron transfer chain catalysis

Among the various properties of transition metal organometallic compounds is the ease with which they can withstand redox changes. This property led to the concept of 'organometallic electron-reservoir'. These organometallic electron-reservoirs are used to perform different types of catalytic reactions. The first mentioned is electron transfer chain (ETC) catalysis also called electrocatalysis, which uses them as initiators in reactions that implicate the electron itself as the real and effective catalyst. Examples will illustrate this principle in organometallic chemistry using Fe sandwich complexes: (i) ligand substitution in [Fe(II)Cp(arene)](+) PF6- by two-electron donors; (ii) intramolecular disproportionation of dinuclear fulvalene carbonyl complexes and selective discrimination of metal centers; (iii) design of a system in which both ETC and organometallic catalyses are coupled (the first known example concerns the polymerization of terminal alkynes by a W-0 complex); (iv) intramolecular dithiocarbamate ligand chelation in Fe(II) piano stool complexes which can be initiated either by reduction or by oxidation, both chain pathways being explained. A second application of these organometallic complexes in catalysis takes place in redox catalysis: when they are used in catalytic amount they act as electron carriers lowering the overpotential existing between an electrode and a substrate. Two cases were examined: (i) redox catalysis of the reduction of water and (ii) redox catalysis of the reduction of nitrogen derivatives: nitrates and nitrites. (C) 1999 Elsevier Science S.A. All rights reserved.