Copper(II) Carbaporphyrins: Oxygenation Reactivities Dependent upon Coordinating Structures

Abstract

Cu II metalations of carbaporphyrins 1−4 gave the corresponding Cu II complexes 1-Cu, 2-Cu, 3-Cu, and 4-Cu with varying degrees of distortions in Cu II square-planar coordination. Upon treatment with Cu(OAc) 2 , 1-Cu was inert but 2-Cu and 3-Cu gave the respective O-atom-inserted complexes 2-OCu and 3-OCu. Further, 3-Cu and 4-Cu were converted to mesomethoxynickel(II) porphyrins 3-OMe and 4-OMe, respectively, via treatment with Cu(OAc) 2 in methanol. meso-Hydroxynickel(II) porphyrin 3-OH was obtained by the treatment of 3-OCu by acetic acid. The treatment of 4-Cu with Cu(OAc) 2 in the presence of acetic acid gave 5,15-diketoporphyrinogen 4-O. Cu II complexes of carbaporphyrins became more reactive with an increased distortion in Cu II square-planar coordination.

BIII–Subporphyrins Bearing Distorted Metal-Coordinating Straps: CuII-Assisted meso-Fabrications

“…Further, 2-OCu was converted to meso -oxygenated products, such as 2-OMe or 2-OH (Scheme ). These results indicate that the oxidative functionalization of C–H bond has been accomplished in an indirect manner. It may also be suggested that earring porphyrins that will force a more distorted coordination of Cu II carbaporphyrins may be viable to enable catalytic C–H-activating functionalization.…”

“…In 2016, we explored earring Ni II porphyrin 1 bearing a tripyrrin strap linked at the 3,7-positions, which has a carbaporphyrins pocket and serves as an effective ligand toward transition metals to allow metalations by chelate-directed C–H bond metalation . Actually, 1 gave Pd II and Cu II complex 1-Pd and 1-Cu under suitable metalation conditions in good yields (Scheme ). Since then, various earring porphyrins have been explored. − Through these studies, it has been revealed that oxygenation reactivities of Cu II carbaporphyrins become more reactive with increased distortion of the square planar Cu II coordination .…”

“…Actually, 1 gave Pd II and Cu II complex 1-Pd and 1-Cu under suitable metalation conditions in good yields (Scheme ). Since then, various earring porphyrins have been explored. − Through these studies, it has been revealed that oxygenation reactivities of Cu II carbaporphyrins become more reactive with increased distortion of the square planar Cu II coordination . While 1-Cu was stable and did not induce an oxygenation reaction, distorted earring porphyrin 2 bearing a 2,5-di­(pyrid-2-yl)­pyrrole strap at the 3,7-positions gave 2-Cu in the reaction with Cu­(OAc) 2 in high yield.…”