Hugo Vazquez-Lima

Ligand Noninnocence in Coinage Metal Corroles: A Silver Knife-Edge.

A silver β-octabromo-meso-triarylcorrole has been found to exhibit a strongly saddled geometry, providing the first instance of a strongly saddled corrole complex involving a metal other than copper. The Soret maxima of the Ag octabromocorroles also redshift markedly in response to increasingly electron-donating para substituents on the meso-aryl groups. In both these respects, the Ag octabromocorroles differ from simple Ag triarylcorrole derivatives, which exhibit only mild saddling and substituent-insensitive Soret maxima. These results have been rationalized in terms of an innocent M(III)-corrole(3-) description for the simple Ag corroles and a noninnocent M(II)-corrole(·2-) description for the Ag octabromocorroles. In contrast, all copper corroles are thought to be noninnocent, while all gold corroles are innocent. Uniquely among metallocorroles, silver corroles thus seem poised on a knife-edge, so to speak, between innocent and noninnocent electronic structures and may tip either way, depending on the exact nature of the corrole ligand.

Synthesis and Reactivity Studies of a Tin(II) Corrole Complex

A series of tris(pentafluorophenyl)corrole (TPFC) tin(IV) and tin(II) complexes were prepared and studied by various characterization techniques including (1)H, (19)F, and (119)Sn NMR and UV-vis spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The unusual 4-coordinate, monomeric, divalent tin(II) complex [(TPFC)Sn(II)](-) (2a) showed highly efficient reactivity toward alkenes and alkyl halides via a nucleophilic addition pathway leading to the quantitative formation of alkyl stannyl corrole compounds. DFT calculations confirmed the divalent nature of the tin center in 2a, and an NBO analysis showed about 99.99% Sn lone pair character, of which 83.6% was Sn 5s and 16.35% was Sn 5p character.

Tungsten Biscorroles: New Chiral Sandwich Compounds

The oxidative metalation method, involving the interaction of free-base meso-triarylcorroles and W(CO)6 in refluxing decalin, led to a set of three tungsten(VI) biscorroles, the first homoleptic sandwich compounds involving corroles. Single-crystal X-ray structures of two of the complexes revealed square-antiprismatic coordination and strongly domed corroles with long W-N distances of 2.15-2.22 Å and a substantial displacement of ∼1.17 Å of the metal relative to the mean N4 planes of the ligands. The structures correspond to approximate C2 symmetry and are thus chiral. DFT calculations strongly indicate that the enantiomers are configurationally stable and hence amenable to chiral resolution. Their other notable properties include a strongly blueshifted Soret band at (357±2) nm, a relatively intense π→W(dz2 ) near-IR feature at (781±3) nm, and a low electrochemical HOMO-LUMO gap of approximately 1.3 V. The results obtained herein suggest that metallobiscorroles may emerge as a new class of inherently chiral chromophores with novel optical and electrochemical properties.

Metallocorrole Interactions with Carbon Monoxide, Nitric Oxide, and Nitroxyl—A DFT Study of Low-Energy Bound States

Presented herein is a first DFT survey of metallocorrole (M = Mn, Fe, Co) adducts of CO, NO, NO(-), and HNO. Bound states with relatively short M-N(O) distances <1.9 Å are predicted for both [M(Cor)(NO)](-) and [M(Cor)(HNO)] derivatives for all three metals. The calculations also confirm the existence of moderately stable charge-neutral CoCO corrole adducts.

Ligand noninnocence in FeNO corroles: insights from β-octabromocorrole complexes

The first FeNO octabromocorroles have been synthesized including four β-octabromo-meso-tris(p-X-phenyl)corrole derivatives Fe[Br8TpXPC](NO) (X = CF3, H, CH3, OCH3) and the β-octabromo-meso-tris(pentafluorophenyl)corrole complex, Fe[Br8TPFPC](NO). The last complex, which proved amenable to single-crystal X-ray structure determination, exhibits the geometry parameters: Fe-N(O) 1.643(8) Å, N-O 1.158(9) Å, and a FeNO angle of 176.4(6)°. The more electron-deficient complexes exhibit increased instability with respect to NO loss and also higher infrared NO stretching frequencies (νNO). Interestingly, DFT calculations and IR marker bands indicate a noninnocent {FeNO}(7)-(corrole˙(2-)) formulation for all FeNO corroles, both β-H8 and β-Br8, with essentially the same degree of corrole radical character. Instead, an electron-deficient corrole appears to exert a field effect resulting in reduced Fe-to-NO backdonation, which accounts for both the increased instability with respect to NO loss and the higher νNOs.

Stepwise Deoxygenation of Nitrite as a Route to Two Families of Ruthenium Corroles: Group 8 Periodic Trends and Relativistic Effects

Given the many applications of ruthenium porphyrins, the rarity of ruthenium corroles and the underdeveloped state of their chemistry are clearly indicative of an area ripe for significant breakthroughs. The tendency of ruthenium corroles to form unreactive metal-metal-bonded dimers has been recognized as a key impediment in this area. Herein, by exposing free-base meso-tris(p-X-phenyl)corroles, H3[TpXPC] (X = CF3, H, Me, and OMe), and [Ru(COD)Cl2]x in refluxing 2-methoxyethanol to nitrite, we have been able to reliably intercept the series Ru[TpXPC](NO) in a matter of seconds to minutes and subsequently RuVI[TpXPC](N), the products of a second deoxygenation, over some 16 h. Two of the RuVIN complexes and one ruthenium corrole dimer could be crystallographically analyzed; the Ru-Nnitrido distance was found to be ∼1.61 Å, consistent with the triple-bonded character of the RuVIN units and essentially identical with the Os-Nnitrido distance in analogous osmium corroles. Spectroscopic and density functional theory (DFT) calculations suggest that the RuNO corroles are best viewed as innocent {RuNO}6 complexes, whereas the analogous FeNO corroles are noninnocent, i.e., best viewed as {FeNO}7-corrole•2-. Both RuVIN and OsVIN corroles exhibit sharp Soret bands, suggestive of an innocent macrocycle. A key difference between the two metals is that the Soret maxima of the OsVIN corroles are red-shifted some 25 nm relative to those of the RuVIN complexes. Careful time-dependent DFT studies indicate that this difference is largely attributable to relativistic effects in OsVIN corroles. The availability of two new classes of mononuclear ruthenium corroles potentially opens the door to new applications, in such areas as catalysis and cancer therapy.

Stabilization and Structure of the Cis Tautomer of a Free-Base Porphyrin

Single-crystal X-ray analysis of the β-heptakis(trifluoromethyl)-meso-tetrakis(p-fluorophenyl)porphyrin, H2 [(CF3 )7 TpFPP], has revealed the first example of a stable cis tautomer of a free-base porphyrin, the long-postulated intermediate of porphyrin tautomerism. The stability of the unique molecule appears to reflect a dual origin: a strongly saddled porphyrin skeleton, which alleviates electrostatic repulsion between the two NH protons, and two polarization-enhanced, transannular N-H⋅⋅⋅O-H⋅⋅⋅N hydrogen bond chains, each involving a molecule of water. DFT calculations suggest that the observed tautomer has a lower energy than the alternative, doubly hydrated trans tautomer by some 8.3 kcal mol-1 . A fascinating prospect thus exists that H2 [(CF3 )7 TpFPP]⋅2 H2 O and cognate structures may act as supramolecular synthons, which, given their chirality, may even be amenable to resolution into optically pure enantiomers.

Synthesis and Molecular Structure of99Tc Corroles

The first 99 Tc corroles have been synthesized and fully characterized. A single-crystal X-ray structure of a 99 TcO triarylcorrole revealed nearly identical geometry parameters as the corresponding ReO structure. A significant spectral shift between the Soret maxima of TcO (410-413 nm) and ReO (438-441 nm) corroles was observed and, based on two-component spin-orbit ZORA TDDFT calculations, ascribed to relativistic effects in the Re case. The syntheses reported herein potentially pave the way toward 99m Tc-porphyrinoid-based radiopharmaceuticals.

Rare and Nonexistent Nitrosyls: Periodic Trends and Relativistic Effects in Ruthenium and Osmium Porphyrin-Based {MNO}7 Complexes

Relativistic and nonrelativistic density functional theory calculations were used to investigate rare or nonexistent ruthenium and osmium analogues of nitrosylhemes. Strong ligand field effects and, to a lesser degree, relativistic effects were found to destabilize {RuNO}7 porphyrins relative to their {FeNO}7 analogues. Substantially stronger relativistic effects account for the even greater instability and/or nonexistence of {OsNO}7 porphyrin derivatives.

Synthesis and Molecular Structure of 99Tc Corroles

The first 99 Tc corroles have been synthesized and fully characterized. A single-crystal X-ray structure of a 99 TcO triarylcorrole revealed nearly identical geometry parameters as the corresponding ReO structure. A significant spectral shift between the Soret maxima of TcO (410-413 nm) and ReO (438-441 nm) corroles was observed and, based on two-component spin-orbit ZORA TDDFT calculations, ascribed to relativistic effects in the Re case. The syntheses reported herein potentially pave the way toward 99m Tc-porphyrinoid-based radiopharmaceuticals.