Organometallic Electron-Reservoir Complexes. Concepts and Applications

Abstract

The 19-electron complexes [FeI(η5-C5R5)(η6-arene)] (R=H, arene = C6Me6, 1,3,5-tBu3C6H3; R=Me, arene = C6Me6, C6Et5H) are thermally stable and serve as strong single-electron reductant in a variety of stoichiometric and catalytic electron-transfer processes that are detailed in this review (prototype: [FeI(η5-C5H5)(η6-C6Me6)]). They are electron-reservoirs because their redox potential is very negative and they form a redox system for which both redox forms are stable. In this sense, they are Green redox reagents, since the oxidized form is recovered after use and is even frequently catalytically used. Symmetrically, the 17-electron complex [FeIII(η5-C5R5)(η6-C6Me6)][SbCl6]2, the strongest organometallic single-electron oxidant with a redox potential 1 V more positive than that of its isoelectronic ferrocenium analog, is a reservoir of electron hole.

Artificial Photosynthesis: Learning from Nature

“…A first principle for the accumulative electron transfer in APS is to store multiple electrons in one molecule to run the catalytic cycles. Molecular electron‐reservoirs are compounds, which can store and transfer multi‐electrons stoichiometrically or catalytically without decomposition or side reaction . However, the electron reservoir property in organometallic compounds is restricted to some classes of compounds that can withstand multiple redox changes without molecular disruption.…”

Correlation between Density Functional Studies and Experimental Data of Three New 19-Electron Metal Sandwich Complexes Containing Amido, Ester, and Thioester Cyclopentadienyl Substituents

“…These complexes were characterized by UV/vis spectroscopy, cyclic voltammetry, EPR, and Mössbauer spectroscopy, and the most commun one, CpFe I (η 6 -C 6 Me 6 ), was characterized by X-ray diffraction . This stable 19-electron electron-reservoir complex gave rise to a particularly rich chemistry, especially in the field of electron-transfer reactions . The electron-reservoir properties of this family of complexes (η 5 -C 5 R 5 )Fe I (η 6 -C 6 R′ 6 ) (R = H or Me; R′ = Me or Et) rely on the localization of the extra electron on the metal center protected by the ligand shell.…”

“…Besides electron-transfer chemistry, ,, the [CpFe(η 6 -arene)] complexes are useful for dendritic construction subsequent to photolytic ligand substitution . The electron-transfer properties can be transferred to dendrimers if the appropriate linkage is used to connect the sandwich compound to the dendrimer branches.…”

A New, Facile, and General Synthesis of Functional and Heterodifunctional Ferrocenes

“…Ferrocene derivatives are useful in many areas including anticancer drugs and other biomedical applications, electrochemistry, redox biosensors, reagents and standards, mediators of enzyme reactions, resins, fuel additives, paints, ligand scaffold, catalysis, liquid crystals, nonlinear optical materials, self-assembled monolayers, magnetic materials, polymers, and dendrimers . The major synthetic routes that have been extensively reported and used for ferrocene derivatives are (i) direct synthesis of 1,1′-disubstituted ferrocenes from substituted cyclopentadienyls, (ii) electrophilic Friedel−Crafts-type reactions, and (iii) metalation with n -butyllithium followed by electrophilic reactions .…”