Inverse Hypercorroles

Abstract

Ground-state and time-dependent density functional theory (TDDFT) calculations with the long-range-corrected, Coulomb-attenuating CAMY-B3LYP exchange-correlation functional and large, all-electron STO-TZ2P basis sets have been used to examine the potential "inverse hypercorrole" character of meso-p-nitrophenyl-appended dicyanidocobalt(III) corrole dianions. The effect is most dramatic for 5,15-bis(p-nitrophenyl) derivatives, where it manifests itself in intense NIR absorptions. The 10-aryl groups in these complexes play a modulatory role, as evinced by experimental UV-visible spectroscopic and electrochemical data for a series of 5,15-bis(p-nitrophenyl) dicyanidocobalt(III) corroles. TDDFT (CAMY-B3LYP) calculations ascribe these features clearly to a transition from the corrole's a_2u-like HOMO (retaining the D_4h irrep used for metalloporphyrins) to a nitrophenyl-based LUMO. The outward nature of this transition contrasts with the usual phenyl-to-macrocycle direction of charge transfer transitions in many hyperporphyrins and hypercorroles; thus, the complexes studied are aptly described as inverse hypercorroles.

Scheme 1. Structures of Species Computationally Modeled in This Study

In the Cn notation used, C refers ‘computational modeling’ and the numeral n to the number of nitrophenyl groups in the species.

Scheme 2. Mono-DMSO Cobalt Corroles Employed in This Study

Figure 1

UV–vis spectra of cobalt 5,15-di(4-nitrophenyl)corroles (at ∼10^–5 M) all in PhCN containing 0.1 M TBAP with 100 equiv of added TBACN.

Figure 2

Cyclic voltammograms of cobalt 5,15-di(4-nitrophenyl)corroles in PhCN/0.1 M TBAP with 100 equiv of added TBACN. The reduction process at −1.10 V in blue corresponds to overlapping electron additions at the two or three meso-nitrophenyl groups. Scan rate: 0.1 V/s.

Figure 3

(a) Hammett plots for the lowest-energy absorption band (above) and E_1/2 for the first oxidation process (below), for measurements in 0.1 M TBAP in PhCN with 100 equiv of added TBACN and (b) plot of wavenumber for the lowest energy absorption band vs E_1/2 for the first oxidation process in PhCN/0.1 M TBAP with 100 equiv of added TBACN.

Figure 4

CAMY-B3LYP-D3/STO-TZ2P-COSMO frontier MO energy levels along with C₂ irreps (a and b).

Figure 5

Simulated TD-CAMY-B3LYP-D3/STO-TZ2P-COSMO optical spectra (oscillator strengths vs wavelength in nm) in dichloromethane. The vertical lines represent calculated transitions which have then been broadened with Gaussians to generate the simulated spectra. The peak labels are cross-referenced in Table 2, which lists the MO compositions of the peaks in question. The MOs themselves are visually depicted in Figure 6.

Figure 6

Selected CAMY-B3LYP frontier MOs of dianions C0–C3, with C₂ irreps (a, b) and orbital energies in eV.