Electron transfer in organonickel complexes of α-diimines: Versatile redox catalysts for C–C or C–P coupling reactions – A review

Exploring Mechanisms in Ni Terpyridine Catalyzed C–C Cross-Coupling Reactions—A Review

“…Their completely reversible first electrochemical reductions are centered at potentials near −1.5 V, and by using spectroelectrochemical (UV-Vis and EPR) methods, the reduced species [Ni(tpy)(aryl)] could be generated and studied. As found before for the Me derivate [Ni(tpy)(Me)], the aryl complexes [Ni(tpy)(aryl)] were best described as divalent nickel bound to a radical anionic (tpy) •− ligand [Ni(II)(tpy •− )(aryl)], and not as [Ni(I)(tpy)(aryl)] [50,51].…”

“…Single electron transfer (SET) from the nickel complex 6 to alkyl iodides forms alkyl radicals and the nickel(II) complex 7. These radicals add oxidatively [46,49] [50][51][52][53], and aryl derivatives [Ni(tpy)(aryl)]. Cationic complexes [Ni(II)(R-tpy)(aryl)] + (R-tpy = substituted terpyridines) have been prepared from suitable precursors and studied structurally and spectroscopically in detail [51].…”

“…Both the high giso value and the high g anisotropy ∆g observed for [Ni(tpy)Br] • characterize this complex as having the unpaired electron largely centered at the metal in contrast to the Me and aryl derivatives [50,51].…”

“…The authors ascribed this to the high reactivity of [Ni(III)(tpy) 3 ] 3+ in air, decomposing the isolated compound upon workup and isolation. in detail [50,[78][79][80][81][82][83]. Nickel complexes of α-diimines in high oxidation states catalyze ligand-directed C-H functionalization under electrochemical conditions [84].…”

“…In contrast to this, monovalent halide complexes [Ni(tpy)(X)] with X = Cl, Br, or I are best described as Ni(I) (d 9 ) systems [41][42][43]45,49,50].…”