Copper catalysis with redox-active ligands

Abstract

Copper catalysis finds applications in various synthetic fields by utilizing the ability of copper to sustain mono- and bielectronic elementary steps. Further to the development of well-defined copper complexes with classical ligands such as phosphines and N-heterocyclic carbenes, a new and fast-expanding area of research is exploring the possibility of a complementing metal-centered reactivity with electronic participation by the coordination sphere. To achieve this electronic flexibility, redox-active ligands can be used to engage in a fruitful “electronic dialogue” with the metal center, and provide additional venues for electron transfer. This review aims to present the latest results in the area of copper-based cooperative catalysis with redox-active ligands.

Use of Crown Ether Functions as Secondary Coordination Spheres for the Manipulation of Ligand–Metal Intramolecular Electron Transfer in Copper–Guanidine Complexes

“…The second oxygen atom of the other acetate group is furthera way from the coppera tom (3.011(4) for CuÀO10). As expected, the imino N = Cb ond distances of the guanidino groups (N1-C7/N4-C12) are elongatedu pon copperc oordination (from 1.282(2)/ 1.286(2) in L to 1.341(7)/1.335 (7) in [L{Cu(OAc) 2 }]). On the other hand, the structural data do not argue for ligand oxidation by IET to the copper atom.…”

“…Coordination compounds with redox-active organic (or non-innocent) ligandsa re attractive fors everal applications.I nc atalysis, they could act as an electron reservoir that provides electrons for the activation of substrate bonds. [1][2][3][4][5][6][7][8][9][10] Because the different redoxs tates of the ligandsu sually display distinct colors, applications in electrochromic or thermochromic devices could be envisioned. Several applicationsr ely on at unable and reversible intramolecular electron transfer (IET) between the redox-active ligand and the metal.…”

Stimulation of Redox‐Induced Electron Transfer by Interligand Hydrogen Bonding in a Cobalt Complex with Redox‐Active Guanidine Ligand

“…Cobalt complexes with redox-active ligands have been the subject of intense research over the last decades, [1][2][3][4][5][6] Especially,m ononuclear complexes with one or two dioxolenetype ligands and dinuclear complexes with abridging tetraoxolene ligand were thoroughly studied, in part due to the huge potential of complexes with redox-active ligands for catalysis. [7][8][9][10][11][12][13] Intramolecular electron transfer in such complexes could be triggered by various stimulants.I n1 980, the first complex showing temperature-dependent equilibrium between two redox isomers in solution was synthesized, converting alow-spin Co III complex preferred at low temperature into ah igh-spin Co II complex favoured at higher temperature. [14] Thet erm valence tautomerism (VT) was coined for equilibria between redox isomers.In1993, the first complex showing VT in the solid state was reported, [15] and several other examples followed, [16] with various conversion temperatures,n arrow or wide temperature regions for interconversion, and small or large thermal hysteresis.…”

Stimulierung eines redoxinduzierten Elektronentransfers durch Interligand‐Wasserstoffbrücken in einem Cobaltkomplex mit redoxaktivem Guanidin‐Liganden

“…[1][2][3][4][5][6] Insbesondere einkernige Komplexe mit einem oder zwei Liganden vom Dioxolen-Typ und zweikerne Komplexe mit einem verbrückenden Te traoxolen-Liganden wurden umfassend untersucht, zum Te il auch aufgrund ihres großen Potentials als Komplexe mit redoxaktiven Liganden in der Katalyse. [7][8][9][10][11][12][13] Intermolekularer Elektronentransfer konnte in solchen Komplexen durch verschiedene Stimulanzien ausgelçst werden. 1980 wurde der erste Komplex synthetisiert, der ein temperaturabhängiges Gleichgewicht zwischen zwei Re-doxisomeren in Lçsung zeigt.…”