Monoradical-containing four-coordinate Co(iii) complexes: homolytic S–S and Se–Se bond cleavage and catalytic isocyanate to urea conversion under sunlight

Abstract

Four-coordinate, monoradical-containing Co(iii) complexes participated in the non-innocent ligand driven homolytic cleavage of S-S and Se-Se bonds and catalyzed the conversion of RNCO (R = phenyl and naphthyl) to the corresponding urea derivatives (TON 480) in dry CHCl under sunlight stimulus.

Assigning Ligand Redox Levels in Complexes of 2-Aminophenolates: Structural Signatures

“…43b Noninnocent redox-active ligand-driven homolytic cleavage of S−S and Se−Se bonds was observed, as a result of the reaction between PhX−XPh (X = S, Se) and four-coordinate complex 71 with two different redox levels, and with X = S, a squarepyramidal cobalt(III) (ls, S Co = 0) complex 59 was isolated. 52 The complex is diamagnetic owing to strong antiferromagnetic coupling between the two (L ISQ ) •− -centered π radicals (S rad = 1 / 2 ). Complex 59 experienced homolytic Co−XPh (X = S, Se) bond cleavage under exposure to sunlight, and 71 was regenerated.…”

“…Notably, 71 catalyzed the conversion of aromatic isocyanates [RNCO] (R = phenyl and naphthyl) to the corresponding urea derivatives in dry CH 2 Cl 2 under sunlight. 52 Exposure to chlorine gas to zirconium(IV) complex 8 27a resulted in an oxidative addition reaction at the metal center, affording a dichloro complex 42, 27 via 1e − oxidation of each (L AP ) 2− ligand. Zr IV −C bond formation (complex 9) was also accomplished.…”

“…A set of three square-planar Pd II complexes (22, 62, and 85) with an invariant metal–ligand coordination environment, where 2-aminophenolate ligands are present in (L •– , L •– ), (L 0 , L 0 ), and (L •– , L 0 ) redox levels, respectively, have been reported. Complexes 1 – 15 , with square-planar, distorted-octahedral, and capped-octahedral geometry, where ligands are coordinated in the L 2– redox level, have been reported. ,− A sizable number of complexes, 16 – 59 , with distorted-tetrahedral, square-planar, and octahedral geometry have also been reported, where ligands are coordinated in the L •– redox level. ,,,,,− The PPh 3 -bound complexes 5 with 2-aminophenolate in the L 2– redox level and 38 in the L •– redox level provided examples of proof-of-concept of hemilability. , The distorted-tetrahedral 47 and 48 are the first examples of radical-bound high-spin hs-Co II and hs-Ni II . Complexes 56 – 59 of the composition [Co III (L •– ) 2 X] (X = monodentate anionic ligand) with five-coordinate geometry, where ligands are coordinated in the L •– redox level, have also been reported. ,− Four/six-coordinate complexes 60 – 66 with ligands in the L 0 redox level have also been reported. ,,,,,, Notably, using a tridentate and a hexadentate ligand, complexes have also been synthesized with two coordinated ligands in two different redox levels (tridentate), 89 , or two arms in two different redox levels (hexadentate), 91 .…”

“…Complex 59 experienced homolytic Co–XPh (X = S, Se) bond cleavage under exposure to sunlight, and 71 was regenerated. Notably, 71 catalyzed the conversion of aromatic isocyanates [RNCO] (R = phenyl and naphthyl) to the corresponding urea derivatives in dry CH 2 Cl 2 under sunlight …”

Cobalt–Carbon Bond Formation Reaction via Ligand Reduction of Porphycene–Cobalt(II) Complex and Its Noninnocent Reactivity

“…Aiming for further improvement, it is necessary to utilize not only the valence change of the cobalt, but also the effect of the ligands. Recently, there have been several examples of the reaction of cobalt complexes with redox-active ligands. − In the case of cobalt­(III) bis­(amidophenolate), the cobalt center acts as a strong nucleophile and reacts with alkyl halides under gentle conditions to generate the Co–C bond without a valence change in the cobalt ion but with the one-electron oxidations of two amidophenolate ligands. The reaction mechanism was estimated to be the S N 2-type oxidative addition of alkyl halides to the Co­(III) center.…”