Synthesis and Molecular Structure of a Copper Octaiodocorrole

Although rather delicate on account of their propensity to undergo deiodination, β-octaiodoporphyrinoids are of considerable interest as potential precursors to novel β-octasubstituted macrocycles. Presented herein are early results of our efforts to synthesize β-octaiodocorrole derivatives. Oxidative condensation of 3,4-diiodopyrrole and aromatic aldehydes failed to yield free-base octaiodocorroles. Treatment of copper <i>meso</i>-tris­(<i>p</i>-cyanophenyl)­corrole with <i>N</i>-iodosuccinimide and trifluoroacetic acid over several hours, however, yielded the desired β-octaiodinated product in ∼22% yield. Single-crystal X-ray structure determination of the product revealed a strongly saddled corrole macrocycle with metrical parameters very close to those of analogous Cu octabromocorrole complexes. The compound was also found to exhibit an exceptionally red-shifted Soret maximum (464 nm in dichloromethane), underscoring the remarkable electronic effect of β-octaiodo substitution

Molecular Structure of a Free-Base β‑Octaiodo<i>-meso</i>-tetraarylporphyrin. A Rational Route to <i>cis</i> Porphyrin Tautomers?

Although a <i>cis</i> tautomer has long been invoked as an intermediate in porphyrin tautomerism, the first such species was only recently isolated and structurally characterized in the form of a β-heptakis­(trifluoromethyl)-<i>meso</i>-tetraarylporphyrin. Reported herein is the molecular structure of a β-octaiodo-<i>meso</i>-tetraarylporphyrin solvate, which also exhibits a <i>cis</i> tautomeric structure. Both structures implicate two factors as critical to the stabilization of the <i>cis</i> tautomeric forma free-base porphyrin that is naturally strongly saddled on steric grounds and a hydroxylic or amphiprotic solvent that can provide hydrogen-bonded N–H···X-H···N (X = O in both the above examples) straps connecting the central NH groups with the antipodal unprotonated nitrogens. The results raise the prospect that a rational strategy affording <i>cis</i> porphyrin tautomers in a predictable manner may be within reach

Electronic Structure of Cobalt–Corrole–Pyridine Complexes: Noninnocent Five-Coordinate Co(II) Corrole–Radical States

Two sets of complexes of Co–triarylcorrole–bispyridine complexes, Co­[T<i>p</i>XPC]­(py)₂ and Co­[Br₈T<i>p</i>XPC]­(py)₂ have been synthesized, where T<i>p</i>XPC refers to a <i>meso</i>-tris­(<i>para</i>-X-phenyl)­corrole ligand with X = CF₃, H, Me, and OMe and Br₈T<i>p</i>XPC to the corresponding β-octabrominated ligand. The axial pyridines in these complexes were found to be labile and, in dilute solutions in dichloromethane, the complexes dissociate almost completely to the five-coordinate monopyridine complexes. Upon addition of a small quantity of pyridine, the complexes revert back to the six-coordinate forms. These transformations are accompanied by dramatic changes in color and optical spectra. ¹H NMR spectroscopy and X-ray crystallography have confirmed that the bispyridine complexes are authentic low-spin Co­(III) species. Strong substituent effects on the Soret maxima and broken-symmetry DFT calculations, however, indicate a Co^II–corrole^•2– formulation for the five-coordinate Co­[T<i>p</i>XPC]­(py) series. The calculations implicate a Co­(d_<i>z</i>²)–corrole­(“a_2u”) orbital interaction as responsible for the metal–ligand antiferromagnetic coupling that leads to the open-shell singlet ground state of these species. Furthermore, the calculations predict two low-energy <i>S</i> = 1 intermediate-spin Co­(III) states, a scenario that we have been able to experimentally corroborate with temperature-dependent EPR studies. Our findings add to the growing body of evidence for noninnocent electronic structures among first-row transition metal corrole derivatives

Electronic Structure of Cobalt–Corrole–Pyridine Complexes: Noninnocent Five-Coordinate Co(II) Corrole–Radical States

Two sets of complexes of Co–triarylcorrole–bispyridine complexes, Co­[T<i>p</i>XPC]­(py)₂ and Co­[Br₈T<i>p</i>XPC]­(py)₂ have been synthesized, where T<i>p</i>XPC refers to a <i>meso</i>-tris­(<i>para</i>-X-phenyl)­corrole ligand with X = CF₃, H, Me, and OMe and Br₈T<i>p</i>XPC to the corresponding β-octabrominated ligand. The axial pyridines in these complexes were found to be labile and, in dilute solutions in dichloromethane, the complexes dissociate almost completely to the five-coordinate monopyridine complexes. Upon addition of a small quantity of pyridine, the complexes revert back to the six-coordinate forms. These transformations are accompanied by dramatic changes in color and optical spectra. ¹H NMR spectroscopy and X-ray crystallography have confirmed that the bispyridine complexes are authentic low-spin Co­(III) species. Strong substituent effects on the Soret maxima and broken-symmetry DFT calculations, however, indicate a Co^II–corrole^•2– formulation for the five-coordinate Co­[T<i>p</i>XPC]­(py) series. The calculations implicate a Co­(d_<i>z</i>²)–corrole­(“a_2u”) orbital interaction as responsible for the metal–ligand antiferromagnetic coupling that leads to the open-shell singlet ground state of these species. Furthermore, the calculations predict two low-energy <i>S</i> = 1 intermediate-spin Co­(III) states, a scenario that we have been able to experimentally corroborate with temperature-dependent EPR studies. Our findings add to the growing body of evidence for noninnocent electronic structures among first-row transition metal corrole derivatives

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

Presented herein is a detailed multitechnique investigation of ligand noninnocence in <i>S</i> = ³/₂ manganese corrole derivatives at the formal Mn^IV oxidation state. The Soret maxima of Mn­[T<i>p</i>XPC]Cl (T<i>p</i>XPC = <i>meso</i>-tris­(<i>p</i>-X-phenyl)­corrole, where X = CF₃, 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<i>p</i>XPC]­Ph, in contrast, the complex Soret envelopes were found to be largely independent of X. These observations suggested a noninnocent corrole^•2–-like ligand for the MnCl complexes and an innocent corrole^3– ligand for the MnPh complexes. Single-crystal X-ray structures of three Mn­[T<i>p</i>XPC]­Cl complexes revealed skeletal bond-length alternations indicative of a noninnocent corrole, while no such alternation was observed for Mn­[T<i>p</i>OMePC]­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^III-corrole^•2– 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^IV-corrole^3– 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<i>p</i>CF₃PC]­Ph and a striking enhancement of the pre-edge intensity, relative to Mn­[T<i>p</i>CF₃PC]­Cl, consistent with a more oxidized, i.e., Mn^IV, center in Mn­[T<i>p</i>CF₃PC]­Ph. Time-dependent DFT calculations indicated that the enhanced intensity of the Mn K-pre-edge of Mn­[T<i>p</i>CF₃PC]­Ph results from the extra 3d_<i>z</i>² hole, which mixes strongly with the Mn 4p_<i>z</i> 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<i>p</i>XPC]­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

Coordination Polymers of 5‑Alkoxy Isophthalic Acids

The topology of coordination polymers containing 5-alkoxy isophthalic acids and first row transition metals was found to be dependent on the combination of solvent system used and length of the alkyl chain. Four different framework types were identified: Phase A, M₆­(ROip)₅­(OH)₂­(H₂O)₄·​<i>x</i>H₂O (M = Co and R = Et, Pr, or ^<i>n</i>Bu, or M = Zn and R = Et); Phase B, M₂­(ROip)₂­(H₂O) (M = Co or Zn and R = Et, Pr, ^<i>n</i>Bu, or ^<i>i</i>Bu, or M = Mn and R = ^<i>n</i>Bu or ^<i>i</i>Bu); Phase C, Zn₃­(EtOip)₂­(OH)₂; and Phase D, Zn₂­(EtOip)₂­(H₂O)₃. Preliminary screening of the NO storage and release capabilities of the Co-containing materials is also reported

Synthesis, Structure and Cation-Binding Properties of Some [4 + 4] Metallocyclic MO₂²⁺ (M = Mo or W) Derivatives of 9‑Phenyl-2,3,7-trihydroxyfluor-6-one

The trianion Z^3– obtained from 9-phenyl 2,3,7-trihydroxyfluor-6-one, ZH₃, affords dioxomolybdenum and dioxotungsten derivatives which contain [4 + 4] metallocycles of composition [(MO₂)₄Z₄]^4– (M = Mo, W) in combination with a variety of counter cations. The syntheses, structures and ESMS of the following compounds are presented: compound <b>1</b>, (MePPh₃)₃(NBu₄)­[(MoO₂)₄Z₄]; compound <b>2</b>, (MePPh₃)₃(NBu₄)­[(WO₂)₄Z₄]; compound <b>3</b>, (MePPh₃)₄[(WO₂)₄Z₄]; compound <b>4</b>, (PPh₄)₂(NBu₄)₂[(MoO₂)₄Z₄]; compound <b>5</b>, (AsPh₄)₃(NBu₄)­[(MoO₂)₄Z₄]; compound <b>6</b>, (AsPh₄)₂(NBu₄)₂[(WO₂)₄Z₄]; compound <b>7</b>, (Ph₃PNPPh₃)­(NBu₄)₃[(MoO₂)₄Z₄]; compound <b>8</b>, (Ph₃PNPPh₃)­(NBu₄)₃[(WO₂)₄Z₄]; compound <b>9</b>, (NEt₄)­(NBu₄)₃[(MoO₂)₄Z₄]. The metallocycles in all of these compounds have similar structures, with the four metal centers located at the corners of a square slightly distorted, to varying degrees, toward a rhombus and also toward a tetrahedron. Various cations are bound inside the anionic metallocycles. ESI mass spectrometry shows that the metallocycles remain intact in the gas phase, forming [(MO₂)₄Z₄]^4–, {X-[(MO₂)₄Z₄]}^3– and in some cases {X₂-[(MO₂)₄Z₄]}^2– where X⁺ is an organic cation

Cobalt- and Rhodium-Corrole-Triphenylphosphine Complexes Revisited: The Question of a Noninnocent Corrole

A reinvestigation of cobalt–corrole–triphenylphosphine complexes has yielded an unexpectedly subtle picture of their electronic structures. UV–vis absorption spectroscopy, skeletal bond length alternations observed in X-ray structures, and broken-symmetry DFT (B3LYP) calculations suggest partial Co^II–corrole^•2– character for these complexes. The same probes applied to the analogous rhodium corroles evince no evidence of a noninnocent corrole. X-ray absorption spectroscopic studies showed that the Co K rising edge of Co­[TPC]­(PPh₃) (TPC = triphenylcorrole) is red-shifted by ∼1.8 eV relative to the <i>bona fide</i> Co­(III) complexes Co­[TPC]­(py)₂ and Co­[TPP]­(py)Cl (TPP = tetraphenylporphyrin, py = pyridine), consistent with a partial Co^II–corrole^•2– description for Co­[TPC]­(PPh₃). Electrochemical measurements have shown that both the Co and Rh complexes undergo two reversible oxidations and one to two irreversible reductions. In particular, the first reduction of the Rh corroles occurs at significantly more negative potentials than that of the Co corroles, reflecting significantly higher stability of the Rh­(III) state relative to Co­(III). Together, the results presented herein suggest that cobalt–corrole–triphenylphosphine complexes are significantly noninnocent with moderate Co^II–corrole^•2– character, underscoringyet againthe ubiquity of ligand noninnocence among first-row transition metal corroles

Enhancement of CO₂ Uptake and Selectivity in a Metal–Organic Framework by the Incorporation of Thiophene Functionality

The complex [Zn₂(tdc)₂dabco] (H₂tdc = thiophene-2,5-dicarboxylic acid; dabco = 1,4-diazabicyclooctane) shows a remarkable increase in carbon dioxide (CO₂) uptake and CO₂/dinitrogen (N₂) selectivity compared to the nonthiophene analogue [Zn₂(bdc)₂dabco] (H₂bdc = benzene-1,4-dicarboxylic acid; terephthalic acid). CO₂ adsorption at 1 bar for [Zn₂(tdc)₂dabco] is 67.4 cm³·g^–1 (13.2 wt %) at 298 K and 153 cm³·g^–1 (30.0 wt %) at 273 K. For [Zn₂(bdc)₂dabco], the equivalent values are 46 cm³·g^–1 (9.0 wt %) and 122 cm³·g^–1 (23.9 wt %), respectively. The isosteric heat of adsorption for CO₂ in [Zn₂(tdc)₂dabco] at zero coverage is low (23.65 kJ·mol^–1), ensuring facile regeneration of the porous material. Enhancement by the thiophene group on the separation of CO₂/N₂ gas mixtures has been confirmed by both ideal adsorbate solution theory calculations and dynamic breakthrough experiments. The preferred binding sites of adsorbed CO₂ in [Zn₂(tdc)₂dabco] have been unambiguously determined by in situ single-crystal diffraction studies on CO₂-loaded [Zn₂(tdc)₂dabco], coupled with quantum-chemical calculations. These studies unveil the role of the thiophene moieties in the specific CO₂ binding via an induced dipole interaction between CO₂ and the sulfur center, confirming that an enhanced CO₂ capacity in [Zn₂(tdc)₂dabco] is achieved without the presence of open metal sites. The experimental data and theoretical insight suggest a viable strategy for improvement of the adsorption properties of already known materials through the incorporation of sulfur-based heterocycles within their porous structures