Long‐Lived Excited States of Zwitterionic Copper(I) Complexes for Photoinduced Cross‐Dehydrogenative Coupling Reactions

Abstract

Four heteroleptic copper(I) complexes containing phenanthroline and monoanionic nido-carborane-diphosphine ligands have been prepared and structurally characterized by various spectroscopic techniques and X-ray diffraction. These complexes exhibit intense absorptions in the visible range and excited-state lifetimes on the microsecond scale. Their application in visible-light-induced cross-dehydrogenative coupling reactions was investigated. Preliminary studies showed that one of the four copper(I) complexes is an efficient catalyst for photoinduced oxidative C-H functionalization using oxygen as oxidant. Furthermore, α-functionalized tertiary amines were obtained in good-to-excellent yields by light irradiation (λ>420 nm) of a mixture of our Cu(I) complex, tertiary amines, and a variety of nucleophiles (nitroalkane, acetone, or indoles) under aerobic conditions. Electron paramagnetic resonance measurements provided evidence for the formation of superoxide radical anions (O2(-⋅)) rather than singlet oxygen ((1)O2) during these photocatalytic reactions.

Photoredox Catalysis with Metal Complexes Made from Earth‐Abundant Elements

“…The Che group discovered that aC u I complexw ith ap henanthroline and am onoanionic nido-carborane-diphosphine ligand (Scheme17a)i sa ble to mediate photoinduced crossdehydrogenative coupling reactions between tetrahydroisoquinolinesa nd nitroalkanes (Scheme 17 b). [41] The Cu I ÀPb onds were expected to be strong, and the steric bulkiness of the carborane ligand was anticipated to prevent significant excited-state distortions, yet in degassed CH 2 Cl 2 the Cu I complex from Scheme 17 ae xhibits an excited-statel ifetime of 1.4 ms, which is not longer than that of related [Cu(P^P)(N^N)] + species. [27] The respective complex is as trong photooxidant with an excited-state reduction potentialo f1 .01 Vv s. Ag/AgCl, and consequently it is able to mediate oxidative aza-Henry reactions of tertiary aminesw ith CH 3 NO 2 ,C 2 H 5 NO 2 and C 3 H 7 NO 2 under aerobic conditions (Scheme 17 b).…”

“…[27] The respective complex is as trong photooxidant with an excited-state reduction potentialo f1 .01 Vv s. Ag/AgCl, and consequently it is able to mediate oxidative aza-Henry reactions of tertiary aminesw ith CH 3 NO 2 ,C 2 H 5 NO 2 and C 3 H 7 NO 2 under aerobic conditions (Scheme 17 b). [41] Using [Cu(dap) 2 ] + as ap hotoredox catalyst, Bissember and co-workersw erea ble to perform direct a CÀHf unctionalization of amines. [42] Specifically,r eactions of N,N-dialkylanilines (67)a nd N-aryltetrahydroisoquinolines (69)w ith electron-deficient alkenes (66)y ieldedarange of annulated tetrahydroquinolines(68)a nd tetrahydroisoquinolines (70)a tr oom temperature under aerobic conditions (Scheme 18 aa nd b).…”

“…b) Photoinduced cross-dehydrogenative coupling reactions between tetrahydroisoquinolines and nitroalkanes using the complex from (a). [41] Scheme18. a, b) Direct a CÀHf unctionalization of N,N-dialkylanilines and Naryltetrahydroisoquinolines.…”

TADF Material Design: Photophysical Background and Case Studies Focusing on CuIand AgIComplexes

“…[4,9, Improvements were also stimulated in the fields of related functional materials based on metal complexes for sensing of oxygen or temperature [53][54][55][56][57][58][59] or for photocatalysis. [60][61][62][63][64][65][66] For luminescent materials to be applied in OLEDs, it is essential that all excitons generatedi nt he emission layer are harvesteda nd converted into photons. Since the statistic ratio of the formed excitons is one singlet to three triplets, [67,68] special mechanisms that allow to harvest all of them are required, as the two types of excitons show different relaxation properties.…”

Copper(I)-1,1,1-tris(diphenylphosphinomethyl)ethane complexes with different coordination modes tuned by auxiliary ligands and their spectroscopic properties

“…Copper(I) complexes containing aromatic diimine and/or phosphine ligands exhibit low-energy metal-to-ligand charge-transfer (MLCT) transitions and have been extensively studied because of their photophysical properties, photoinduced electron-transfer, and excited state substrate-binding reactions [1][2][3][4][5][6][7][8][9]. The steric and/or electronic effects of ligands in these complexes on excited state properties have been elaborated in the literature [10][11][12][13][14][15][16][17].…”