What Is the Difference between the Manganese Porphyrin and Corrole Analogues of Cytochrome P450's Compound I?

Abstract

Density functional calculations on oxo-manganese complexes of corrole (1) and porphyrin (2 and 3) show a fundamental difference. The ground state of I is the singlet manganese(V) state, 1A(MnV), in which corrole is a closed shell. In contrast, 2 and 3 have high-spin manganese(IV) states, 1A1u and 3A2u respectively. This difference and the state ordering for each system are rationalized based on the competition between the intrinsic tendency of manganese to prefer high-spin electronic configurations, vis-à-vis the general tendency to prefer double occupancy in the low-lying orbitals. The outcome of this competition is determined primarily by the identity of the macrocycle, corrole versus porphyrin. Corrole with a small cavity holds the MnO moiety with a high off-plane displacement, and thereby prefers the low-spin state. On the other hand, porphyrin with the wider cavity holds the MnO moiety closer to the plane, and thereby prefers high-spin states.

Ab initio multiconfiguration reference perturbation theory calculations on the energetics of low-energy spin states of iron(III) porphyrins

“…In unpublished work (Ghosh A, Dey A, unpublished results) we have found that B3LYP calculations with comparable basis sets favor the diamagnetic Mn(V) state by a smaller margin of about 0.3 eV. In contrast, Gross, Shaik and co-workers [39] [40]. B3LYP calculations on Mn(corrolato)(O) predicts a closed-shell Mn(V) state as the ground state-a qualitatively correct result-but the Mn(IV)-oxo corrole p-cation radical states lie barely about 0.1-0.2 eV higher in energy [36].…”

Kinetic studies of reactions of iron(IV)-oxo porphyrin radical cations with organic reductants

“…The chemistry of porphyrin-metal-oxo [10], corrole-metal-oxo [7,[11][12][13][14][15], and corrolazine-metaloxo species [16,17] have received considerable attention. Iron(IV)-oxo porphyrin radical cation models of Compound I have been known for more than two decades [18], and they have been characterized by various spectroscopic methods, such as UV-vis, EPR, Mö ssbauer, EXAFS and Raman spectroscopies [19].…”

Electronic Structure and Reactivity of Transition Metal Complexes

“…4 We also averaged the error of the GGAþU and GGA splittings for each intermediate with respect to the CCSD(T) splittings for that intermediate. The average error for the five spin splittings along the reaction coordinate is 0.04 eV in GGAþU, to be compared with GGA, which exhibits an average error of 0.20 eV, or B3LYP that performs even more poorly with an average error of 0.30 eV in the splittings.…”

“…In biological systems, mid-row 3d transition metals facilitate reactions as diverse as methane-to-methanol conversion at an antiferromagnetically coupled dimetal center [1,2], unactivated alkane halogenation by a highenergy, high-spin ferryl-oxo center in the halogenase SyrB2 [3], and oxygen binding at iron porphyrins in hemoglobin [4]. In inorganic catalysts, many transition metal complexes have been designed to carry out synthetic pathways that mimic active biological catalytic cycles.…”