Ground-State Copper(III) Stabilized by N-Confused/N-Linked Corroles: Synthesis, Characterization, and Redox Reactivity

Abstract

Stable square planar organocopper(III) complexes (CuNCC2, CuNCC4, and CuBN) supported by carbacorrole-based tetradentate macrocyclic ligands with NNNC coordination cores were synthesized, and their structures were elucidated by spectroscopic means including X-ray crystallographic analysis. On the basis of their distinct planar structures, X-ray absorption/photoelectron spectroscopic features, and temperature-independent diamagnetic nature, these organocopper complexes can be preferably considered as novel organocopper(III) species. The remarkable stability of the high-valent Cu(III) states of the complexes stems from the closed-shell electronic structure derived from the peculiar NNNC coordination of the corrole-modified frameworks, which contrasts with the redox-noninnocent radical nature of regular corrole copper(II) complexes with an NNNN core. The proposed structure was supported by DFT (B3LYP) calculations. Furthermore, a π-laminated dimer architecture linked through the inner carbons was obtained from the one-electron oxidation of CuNCC4. We envisage that the precise manipulation of the molecular orbital energies and redox profiles of these organometallic corrole complexes could eventually lead to the isolation of yet unexplored high-valent metal species and the development of their organometallic reactions.

Copper 1,19‐Diaza‐21,24‐dicarbacorrole: A Corrole Analogue with an N−N Linkage Stabilizes a Ground‐State Singlet Organocopper Species

“…[3,12] The core skeleton of Cu-5 adopted a quasi-planar geometry with a mean-plane deviation (m.p.d., defined by 23 core atoms) of 0.128 (Figure 2 d). More importantly, the N1-N19 bond length of Cu-5 was estimated to be 1.373 (4) , which was shorter than the corresponding C(sp 2 )-N(sp 2 ) bond length (1.377(3) ) in Cu-8 based on the intrinsic small radius of the nitrogen atom. [13] Furthermore, natural bond orbital (NBO) [14] analysis revealed that the Wiberg bond index of the N1-N19 bond moiety was 1.020, which was similar to that of the corresponding NÀC bond (1.072) in Cu-8.…”

“…Recently, we reported on a high-valent Cu III carbacorrole embedded with a peculiar a,b'-linked pyrrole unit. [4] Skeletal modification via the "N-confusion approach" resulted in the modulation of the Cu d x 2 Ày 2 orbital energy by the NNNC donor coordination environment. Copper benzonorrole (Cu-8, Figure 1 a) bearing an N(sp 2 )-C(sp 2 ) linkage, in turn, exhibited the characteristic features of a closed-shell singlet Cu III species, a highly planar geometry, diamagnetic property, and substantially up-shifted pre-edge energy in the X-ray absorption spectrum.…”

“…The observed irreversible oxidation wave at 0.54 V (vs. Fc + /Fc) and the quasi-reversible reduction wave at À1.49 V caused a large gap of 2.03 V ( Figure S18). [4,11] The one-electronoxidized cation (Cu-5 + ) revealed the emergence of a broad absorption band in the near-infrared region and a simple electron paramagnetic resonance (EPR) signal centered at g = 2.001 ( Figures S19 and S20). These results were in agreement with a doublet p-radical cation structure (Cu-5 + ) in the ground state, as evidenced by the spin-delocalized density map ( Figure S29).…”

“…) is almost identical to that of Cu-8 (Figure S21). The spectrum, thus, could be used to anticipate the innocent character of Cu-5 [3,4]. Lancaster and co-workers recently applied ligand field inversion for many reported d 8 Cu III organometallic complexes [21].…”

Bis‐copper(II) Complex of Triply‐linked Corrole Dimer and Its Dication

“…More recently, Furuta and co‐workers reported a variety of N‐confused corrole copper complexes ( CuNCC2 , CuNCC4 , CuBN ) in which the NNNC‐coordinated copper (i.e. organocopper species) preferably took high valent copper(III) states …”