Electronic Structure of Manganese Corroles Revisited: X-ray Structures, Optical and X-ray Absorption Spectroscopies, and Electrochemistry as Probes of Ligand Noninnocence

Abstract

Presented herein is a detailed multitechnique investigation of ligand noninnocence in S = / manganese corrole derivatives at the formal Mn oxidation state. The Soret maxima of Mn[T pXPC]Cl (T pXPC = meso-tris( p-X-phenyl)corrole, where X = CF, H, Me, and OMe) were found to red-shift over a range of 37 nm with increasing electron-donating character of X. For Mn[T pXPC]Ph, in contrast, the complex Soret envelopes were found to be largely independent of X. These observations suggested a noninnocent corrole-like ligand for the MnCl complexes and an innocent corrole ligand for the MnPh complexes. Single-crystal X-ray structures of three Mn[T pXPC]Cl complexes revealed skeletal bond-length alternations indicative of a noninnocent corrole, while no such alternation was observed for Mn[T pOMePC]Ph. B3LYP density functional theory (DFT) calculations on Mn[TPC]Cl yielded strong spatial separation of the α and β spin densities, consistent with an antiferromagnetically coupled Mn-corrole description. By comparison, relatively little spatial separation of the α and β spin densities was found for Mn[TPC]Ph, consistent with an essentially Mn-corrole description. X-ray absorption of near-edge spectroscopy (XANES) revealed a moderate blue shift of 0.6 eV for the Mn K-pre-edge of Mn[T pCFPC]Ph and a striking enhancement of the pre-edge intensity, relative to Mn[T pCFPC]Cl, consistent with a more oxidized, i.e., Mn, center in Mn[T pCFPC]Ph. Time-dependent DFT calculations indicated that the enhanced intensity of the Mn K-pre-edge of Mn[T pCFPC]Ph results from the extra 3d hole, which mixes strongly with the Mn 4p orbital. Combined with similar results on Fe[TPC]Cl and Fe[TPC]Ph, the present study underscores the considerable potential of metal K-edge XANES in probing ligand noninnocence in first-row transition-metal corroles. Cyclic voltammetry measurements revealed highly negative first reduction potentials for the Mn[T pXPC]Ph series (∼-0.95 V) as well as large electrochemical HOMO-LUMO gaps of ∼1.7 V. The first reductions, however, are irreversible, suggesting cleavage of the Mn-Ph bond.

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

“…Recently, Nocera and Kar independently reported that several copper complexes of meso ‐aryl‐substituted corroles consist of the central copper(II) ion and the divalent corrole π‐radical ligand with strong antiferromagnetic interaction between the copper(II) and the π‐radical fragment, thereby behaving as an overall singlet spin‐state even at room temperature. Similar ligand non‐innocent behaviors have also been known for silver octabromocorroles, chloroiron and nitrosoiron corroles, triphenylphosphine cobalt corroles, and chloromanganese corroles . Another important observation is the metal‐ligand interaction depending on the size of the ligand.…”

Heavy-element–ligand covalence: ligand noninnocence in molybdenum and tungsten Viking-helmet Corroles

“…The Mo(4d z 2)-corrole("a 2u ") interaction evident in the HOMO−2 and LUMO (Fig. 5) is, topologically, exceedingly similar to analogous interactions involving the 3d z 2 orbital in MnCl, 23 FeCl, [10][11][12][13][14][15] FeNO, 27 and Co-PPh 3 31 corroles. Importantly, this picture was fully borne out by an examination of the 4d-based natural bond orbitals (NBOs) of the molecule.…”

“…To gain an estimate of the strength of the Mo(4d z 2)corrole •2− antiferromagnetic coupling, we optimized the corresponding ferromagnetically-coupled (S = 3/2) state of Mo[TPC]O and found its energy to be ∼0.9 eV above the ground state (for the B3LYP functional). In stark contrast, the ferromagnetically coupled states of MnCl, 23 FeCl, [10][11][12][13][14][15] FeNO, 27 and Co-PPh 3 31 corroles were invariably found to occur only a few tenths of an eV higher in energy relative to the antiferromagnetically-coupled ground state, a testament to much stronger metal-ligand orbital interactions for the heavier transition elements. This result provides a rare Paper Dalton Transactions measure of metal-ligand magnetic coupling for a 4d transition metal.…”

“…In recent years, metallocorroles have provided many examples of well-characterized noninnocent systems. [19][20][21][22] Key examples include MnCl, 23 FeCl, [9][10][11][12][13][14][15] FeNO, [24][25][26][27] Fe 2 (μ-O), 28 Copy 29 /DMSO 30 ( py = pyridine), Co-PPh 3 , 31 and Cu [32][33][34][35][36][37][38][39][40] corrole derivatives. It is worth noting that all these involve first-row transition metals.…”

X-ray absorption spectroscopy of archetypal chromium porphyrin and corrole derivatives

“…The sterically hindered TMP ligands was chosen to improve the stability of the Cr(IV) complex, but the differences in peripheral transition metal d electron counts, XAS has only been infrequently applied to Cr porphyrins and indeed to metalloporphyrin-type complexes in general, except for those involving Mn and Fe. [1][2][3][4][5][6][7][8] Indeed, only one directly relevant study has been reported in the literature, focusing on Cr IV [TTP]O and Cr V [TTP]N, where TTP 2À is the dianion of meso-tetra(p-tolyl) porphyrin. 9 Understandably, we have used substantially improved theoretical methods in the present study to model the Cr K-edge XAS data on the high-valent compounds 2 and 3, and where appropriate, we will point out similarities and differences relative to the earlier study.…”