Rhenium Biscorrole Sandwich Compounds: XAS Evidence for a New Coordination Motif.

The interaction of three free-base meso-tris(p-X-phenyl)corroles H3[TpXPC] (X = H, CH3, OCH3) with Re2(CO)10 at 235 °C in the presence of K2CO3 in o-dichlorobenzene has led to putative rhenium biscorrole sandwich compounds with the formula ReH[TpXPC]2. Density functional theory calculations and Re L3-edge extended X-ray absorption fine structure measurements suggest a seven-coordinate metal center, with the "extra" hydrogen located on one of the corrole nitrogens. The complexes can be deprotonated by a base such as 1,8-diazabicyclo[5.4.0]undec-7-ene, resulting in a substantial sharpening of the UV-vis spectra and split Soret bands, consistent with the generation of C2-symmetric anions. Both the seven-coordinate neutral and eight-coordinate anionic forms of the complexes represent a new coordination motif in the field of rhenium-porphyrinoid interactions.

The Story of 5d Metallocorroles: From Metal-Ligand Misfits to New Building Blocks for Cancer Phototherapeutics.

Porphyrin chemistry is Shakespearean: over a century of study has not withered the field's apparently infinite variety. Heme proteins continually astonish us with novel molecular mechanisms, while new porphyrin analogues bowl us over with unprecedented optical, electronic, and metal-binding properties. Within the latter domain, corroles occupy a special place, exhibiting a unique and rich coordination chemistry. The 5d metallocorroles are arguably the icing on that cake.New Zealand chemist Penny Brothers has used the word "misfit" to describe the interactions of boron, a small atom with a predilection for tetrahedral coordination, and porphyrins, classic square-planar ligands. Steve Jobs lionized misfits as those who see things differently and push humanity forward. Both perspectives have inspired us. The 5d metallocorroles are misfits in that they encapsulate a large 5d transition metal ion within the tight cavity of a contracted porphyrin ligand.Given the steric mismatch inherent in their structures, the syntheses of some 5d metallocorroles are understandably capricious, proceeding under highly specific conditions and affording poor yields. Three broad approaches may be distinguished.(a) In the metal-alkyl approach, a free-base corrole is exposed to an alkyllithium and the resulting lithio-corrole is treated with an early transition metal chloride; a variant of the method eschews alkyllithium and deploys a transition metal-alkyl instead, resulting in elimination of the alkyl group as an alkane and insertion of the metal into the corrole. This approach is useful for inserting transition metals from groups 4, 5, and, to some extent, 6, as well as lanthanides and actinides.(b) In our laboratory, we have often deployed a low-valent organometallic approach for the middle transition elements (groups 6, 7, 8, and 9). The reagents are low-valent metal-carbonyl or -olefin complexes, which lose one or more carbon ligands at high temperature, affording coordinatively unsaturated, sticky metal fragments that are trapped by the corrole nitrogens.(c) Finally, a metal acetate approach provides the method of choice for gold and platinum insertion (groups 10 and 11).This Account provides a first-hand perspective of the three approaches, focusing on the last two, which were largely developed in our laboratory. In general, the products were characterized with X-ray crystallography, electrochemistry, and a variety of spectroscopic methods. The physicochemical data, supplemented by relativistic DFT calculations, have provided fascinating insights into periodic trends and relativistic effects.An unexpected feature of many 5d metallocorroles, given their misfit character, is their remarkable stability under thermal, chemical, and photochemical stimulation. Many of them also exhibit long triplet lifetimes on the order of 100 µs and effectively sensitize singlet oxygen formation. Many exhibit phosphorescence in the near-infrared under ambient conditions. Furthermore, water-soluble ReO and Au corroles exhibit impressive photocytotoxicity against multiple cancer cell lines, promising potential applications as cancer phototherapeutics. We thus envision a bright future for the compounds as rugged building blocks for new generations of therapeutic and diagnostic (theranostic) agents.

Rhenium Corrole Dimers: Electrochemical Insights into the Nature of the Metal-Metal Quadruple Bond.

The interaction of free-base triarylcorroles with Re2(CO)10 in 1,2-dichlorobenzene in the presence of 2,6-lutidine at 180 °C under strict anerobic conditions afforded approximately 10% yields of rhenium corrole dimers. The compounds exhibited diamagnetic 1H NMR spectra consistent with a metal-metal quadruple bond with a σ2π4δ2 orbital occupancy. One of the compounds proved amenable to single-crystal X-ray structure determination, yielding a metal-metal distance of ∼2.24 Å, essentially identical to that in triple-bonded osmium corrole dimers. On the other hand, the electrochemical properties of Re and Os corrole dimers proved to be radically different. Thus, the reduction potentials of the Re corrole dimers are some 800 mV upshifted relative to those of their Os counterparts. Stated differently, the Re corrole dimers are dramatically easier to reduce, reflecting electron addition to δ* versus π* molecular orbitals for Re and Os corrole dimers, respectively. The data also imply electrochemical HOMO-LUMO gaps of only 1.0-1.1 V for rhenium corrole dimers, compared with values of 1.85-1.90 V for their Os counterparts. These HOMO-LUMO gaps rank among the first such values reported for quadruple-bonded transition-metal dimers for any type of supporting ligand, porphyrin-type or not.

Rhenium-Imido Corroles.

Metallocorroles involving 5d transition metals are currently of interest as near-IR phosphors and as photosensitizers for oxygen sensing and photodynamic therapy. Their syntheses, however, are often bedeviled by capricious and low-yielding protocols. Against this backdrop, we describe rhenium-imido corroles, a new class of 5d metallocorroles, synthesized simply and in respectable (∼30%) yields via the interaction of a free-base corrole, Re2(CO)10, K2CO3, and aniline in 1,2,4-trichlorobenzene at ∼190 °C in a sealed vial under strict anaerobic conditions. The generality of the method was shown by the synthesis of six derivatives, including those derived from meso-tris(pentafluorophenyl)corrole, H3[TPFPC], and five different meso-tris(p-X-phenyl)corroles, H3[TpXPC], where X = CF3, F, H, CH3, OCH3. Single-crystal X-ray structures obtained for two of the complexes, Re[TpFPC](NPh) and Re[TpCF3PC](NPh), revealed relatively unstrained equatorial Re-N distances of ∼2.00 Å, a ∼ 0.7-Å displacement of the Re from the mean plane of the corrole nitrogens, and an Re-Nimido distance of ∼1.72 Å. Details of the corrole skeletal bond distances, diamagnetic 1H NMR spectra, relatively substituent-independent Soret maxima, and electrochemical HOMO-LUMO gaps of ∼2.2 V all indicated an innocent corrole macrocycle. Surprisingly, unlike several other classes of 5d metallocorroles, the Re-imido complexes proved nonemissive in solution at room temperature and also failed to sensitize singlet oxygen formation, indicating rapid radiationless deactivation of the triplet state, presumably via the rapidly rotating axial phenyl group. By analogy with other metal-oxo and -imido corroles, we remain hopeful that the Re-imido group will prove amenable to further elaboration and thereby contribute to the development of a somewhat challenging area of coordination chemistry.

Electrophilic Activation of Osmium-Nitrido Corroles: The OsN Triple Bond as a π-Acceptor Metallaligand in a Heterobimetallic OsVIN-PtII Complex.

Presented herein is a first investigation of the chemical reactivity of osmium-nitrido corroles, which are known for their unusual thermal, chemical, and photochemical stability. Elemental chlorine perchlorinates the ß-positions of the triarylcorrole but leaves the OsN unit untouched. The OsN unit is also unaffected by a variety of other electrophilic and nucleophilic reagents. Upon photolysis, however, the anion of Zeise's salt associates with the nitrido ligand to generate an OsVI≡N-PtII complex. The very short OsN-Pt linkage [1.895(9)-1.917(8) Å] and the downfield 195Pt NMR resonance (-2702 ppm) suggest that the OsN corrole acts as a π-accepting ligand toward the Pt(II) center. This finding represents a rare example of the successful photochemical activation of a metal-ligand multiple bond that is too kinetically inert to exhibit any appreciable reactivity under thermal conditions.

Infrared Spectroelectrochemistry of Iron-Nitrosyl Triarylcorroles. Implications for Ligand Noninnocence.

Recent DFT calculations have suggested that iron nitrosyl triarylcorrole complexes have substantial {FeNO}7-corrole•2- character. With this formulation, reduction of Fe(C)(NO) complexes, where C = triarylcorrole, should be centered on the corrole macrocycle rather than on the {FeNO}7 moiety. To verify this proposition, visible and infrared spectroelectrochemical studies of Fe(C)(NO) were carried out and the results were interpreted using DFT (B3LYP/STO-TZP) calculations. The first reduction of Fe(C)(NO) led to significant changes in the Soret and Q-band regions of the visible spectrum as well as to a significant downshift in the νNO and changes in the corrole vibrational frequencies. DFT calculations, which showed that the electron was mostly added to the corrole ligand (85%), were also able to predict the observed shifts in the νNO and corrole bands upon reduction. These results underscore the importance of monitoring both the corrole and nitrosyl vibrations in ascertaining the site of reduction. By contrast, the visible spectroelectrochemistry of the second reduction revealed only minor changes in the Soret band upon reduction, consistent with the reduction of the FeNO moiety.

Ambient-temperature near-IR phosphorescence and potential applications of rhenium-oxo corroles.

Presented herein is a first photophysical investigation of a series of rhenium(v)-oxo tris(p-X-phenyl)corroles, Re[TpXPC](O), where X = CF3, F, H, CH3, and OCH3. The complexes all exhibit near-IR phosphorescence in anoxic toluene at room temperature, with emission maxima at 780 ± 10 nm, phosphorescence decay times of 56-74 µs and quantum yields of 1.07-1.52%, the highest reported to date for phosphorescent corrole derivatives. We have also demonstrated that the dyes may serve as indicators in optical oxygen sensors and as sensitizers in triplet-triplet-annihilation-based upconversion. Although the ReO corroles are not superior to benchmark benzoporphyrin complexes that are currently used in these applications, they may prove useful in certain areas such as optical multianalyte sensing owing to improved flexibility in the available spectral properties of the dyes. The high thermal and photochemical stability of the complexes also bodes well for their deployment as new, phosphorescent sensitizers in photodynamic therapy.

Relativistic Effects on a Metal-Metal Bond: Osmium Corrole Dimers.

A series of metal-metal bonded osmium corrole dimers, {Os[T pXPC]}2, were synthesized in reasonably good yields (35-46%) via the interaction of the corresponding free-base meso-tris( p-X-phenyl)corroles (H3[T pXPC], X = CF3, H, CH3, and OCH3), Os3(CO)12, and potassium carbonate in 1,2,4-trichlorobenzene under an inert atmosphere at 180 °C over several hours. The complexes are only the second class of Os corroles reported to date (the first being OsVIN corroles) and also the second class of metal-metal bonded metallocorrole dimers (the other being Ru corrole dimers). Comparison of the X-ray structures, redox potentials, and optical spectra of analogous Ru and Os corrole dimers, along with scalar-relativistic DFT calculations, has provided an experimentally calibrated account of relativistic effects in these complexes. Three of the Os corrole dimers (X = CF3, H, and OCH3) were analyzed with single-crystal X-ray diffraction analysis, revealing inversion-related corrole rings with eclipsed Os-N bonds and Os-Os distances of ∼2.24 Å that are ∼0.06 Å longer than the Ru-Ru distances in the analogous Ru corrole dimers. Interestingly, a comparison of scalar-relativistic and nonrelativistic DFT calculations indicates that this difference in metal-metal bond distance does not, in fact, reflect a differential relativistic effect. For a given corrole ligand, the Ru and Os corrole dimers exhibit nearly identical oxidation potentials but dramatically different reduction potentials, with the Os values ∼0.5 V lower relative to Ru, suggesting that whereas oxidation occurs in a ligand-centered manner, reduction is substantially metal-centered, which indeed was confirmed by scalar-relativistic calculations. The calculations further indicate that approximately a third of the ∼0.5 V difference in reduction potentials can be ascribed to relativity. The somewhat muted value of this relativistic effect appears to be related to the finding that reduction of an Os corrole dimer is not exclusively metal-based but that a significant amount of spin density is delocalized over to the corrole ligand; in contrast, reduction of an Ru corrole dimer occurs exclusively on the Ru-Ru linkage. For isoelectronic complexes, the Ru and Os corrole dimers exhibit substantially different UV-vis spectra. A key difference is a strong near-UV feature of the Os series, which in energy terms is blue-shifted by ∼0.55 V relative to the analogous feature of the Ru series. TDDFT calculations suggest that this difference may be related to higher-energy Os(5d)-based LUMOs in the Os case relative to analogous MOs for Ru.

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.

Determinants of delayed care seeking for TB suggestive symptoms in Seru district, Oromiya region, Ethiopia: a community based unmatched case-control study.

BACKGROUND: Early tuberculosis (TB) case finding and adequate chemotherapy are essential for interrupting disease transmission and preventing complications due to delayed care seeking. This study was undertaken in order to provide insights into the magnitude and determinants of patient delay. METHODS: The study was conducted in rural Seru district, employing a population based unmatched case-control study design. The WHO standardized TB screening tool was used to identify presumptive TB cases among the district population ages > 15 years. Presumptive TB cases who sought care in a health facility more than 14 days after the onset of symptoms were considered cases while those who sought care within the first 14 days were classified as controls. A structured interview questionnaire was used to capture socio demographic characteristics and health care service utilization related data from the study participants. A multiple binary logistic regression model was used to identify any factor associated with patient care seeking delay. RESULT: A total of 9,782 individuals were screened, of which 980 (10%, 95% CI; 9.4-10.5%) presumptive TB cases were identified. From these cases 358 (76%, 95% CI; 75.6%-76.4%) sought care within the first 14 days of the onset of symptoms with a median patient delay of 15 days, IQR (5-30 days). The most common TB suggestive symptom mentioned by the participants was night sweat 754 (76.4%) while the least common was a history of contact with a confirmed TB case in the past one year 207 (21.1%). Individuals in the 45-54 age range had lower odds of delay (AOR 0.31, 95%CI 0.15, 0.61) as compared to those 15-24 years old. First TB treatment episode (AOR16.2, 95% CI 9.94, 26.26) and limited access to either traditional or modern modes of transportation (AOR 2.62, 95% CI 1.25, 5.49) were independently associated with patient care delay. CONCLUSION: Increasing community awareness about the risks of delayed care seeking and the importance of accessing health services close to the community can help decrease patient care delay.

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 Šand a substantial displacement of ∼1.17 Šof 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.

Metal-Ligand Misfits: Facile Access to Rhenium-Oxo Corroles by Oxidative Metalation.

With the exception of a single accidental synthesis, rhenium corroles are unknown, but of great interest as catalysts and potential radiopharmaceuticals. Oxidative metalation of meso-triarylcorroles with [Re2 (CO)10 ] in refluxing decalin has provided a facile and relatively high-yielding route to rhenium(V)-oxo corroles. The complexes synthesized could all be fully characterized by single-crystal X-ray structure analyses.

Oxidative metalation as a route to size-mismatched macrocyclic complexes: osmium corroles.

Heavy-element corroles are of great interest as optical sensors, near-IR dyes, phosphors, organic light-emitting diodes, and anticancer compounds. Insertion of 5d metals into corroles, however, is often a difficult and unpredictable process. Against this backdrop, oxidative metalation of meso triarylcorroles with [Os3 (CO)12 ]/NaN3 in refluxing 1:2 diethylene glycol monomethyl ether/glycol has provided a convenient and relatively high-yielding route to nitridoosmium(VI) corroles, three of which could be characterized with single-crystal X-ray structure analysis.

Inverse Photoemission Spectroscopy of Coinage Metal Corroles: Comparison with Solution-Phase Electrochemistry.

A combined direct and inverse photoemission study of coinage metal corroles suggests that the latter technique, in favorable cases, can provide some additional information relative to electrochemical measurements. Thus, whereas inverse photoemission spectroscopy (IPES) provides relative electron affinities for electron addition to different unoccupied orbitals, electrochemical reduction potentials shed light on the energetics of successive electron additions. While all three coinage metal triphenylcorrole (TPC) complexes exhibit similar ionization potentials, they exhibit dramatically different inverse photoemission spectra. For Cu[TPC], the lowest-energy IPES feature (0.74 eV) is found to be exceedingly close to the Fermi level; it is significantly higher for Ag[TPC] (1.65 eV) and much higher for Au[TPC] (2.40 eV). These differences qualitatively mirror those observed for electrochemical reduction potentials and are related to a partially metal-centered LUMO in the case of Cu- and Ag[TPC] and a fully corrole-based LUMO in the case of Au[TPC]; the latter orbital corresponds to the LUMO+1 in the case of Ag[TPC].

The structural chemistry of metallocorroles: combined X-ray crystallography and quantum chemistry studies afford unique insights.

Although they share some superficial structural similarities with porphyrins, corroles, trianionic ligands with contracted cores, give rise to fundamentally different transition metal complexes in comparison with the dianionic porphyrins. Many metallocorroles are formally high-valent, although a good fraction of them are also noninnocent, with significant corrole radical character. These electronic-structural characteristics result in a variety of fascinating spectroscopic behavior, including highly characteristic, paramagnetically shifted NMR spectra and textbook cases of charge-transfer spectra. Although our early research on corroles focused on spectroscopy, we soon learned that the geometric structures of metallocorroles provide a fascinating window into their electronic-structural characteristics. Thus, we used X-ray structure determinations and quantum chemical studies, chiefly using DFT, to obtain a comprehensive understanding of metallocorrole geometric and electronic structures. This Account describes our studies of the structural chemistry of metallocorroles. At first blush, the planar or mildly domed structure of metallocorroles might appear somewhat uninteresting particularly when compared to metalloporphyrins. Metalloporphyrins, especially sterically hindered ones, are routinely ruffled or saddled, but the missing meso carbon apparently makes the corrole skeleton much more resistant to nonplanar distortions. Ruffling, where the pyrrole rings are alternately twisted about the M-N bonds, is energetically impossible for metallocorroles. Saddling is also uncommon; thus, a number of sterically hindered, fully substituted metallocorroles exhibit almost perfectly planar macrocycle cores. Against this backdrop, copper corroles stand out as an important exception. As a result of an energetically favorable Cu(d(x2-y2))-corrole(π) orbital interaction, copper corroles, even sterically unhindered ones, are inherently saddled. Sterically hindered substituents accentuate this effect, sometimes dramatically. Thus, a crystal structure of a copper ß-octakis(trifluoromethyl)-meso-triarylcorrole complex exhibits nearly orthogonal, adjacent pyrrole rings. Intriguingly, the formally isoelectronic silver and gold corroles are much less saddled than their copper congeners because the high orbital energy of the valence d(x2-y2) orbital discourages overlap with the corrole π orbital. A crystal structure of a gold ß-octakis(trifluoromethyl)-meso-triarylcorrole complex exhibits a perfectly planar corrole core, which translates to a difference of 85° in the saddling dihedral angles between analogous copper and gold complexes. Gratifyingly, electrochemical, spectroscopic, and quantum chemical studies provide a coherent, theoretical underpinning for these fascinating structural phenomena. With the development of facile one-pot syntheses of corrole macrocycles in the last 10-15 years, corroles are now almost as readily accessible as porphyrins. Like porphyrins, corroles are promising building blocks for supramolecular constructs such as liquid crystals and metal-organic frameworks. However, because of their symmetry properties, corrole-based supramolecular constructs will probably differ substantially from porphyrin-based ones. We are particularly interested in exploiting the inherently saddled, chiral architectures of copper corroles to create novel oriented materials such as chiral liquid crystals. We trust that the fundamental structural principles uncovered in this Account will prove useful as we explore these fascinating avenues.

Influence of Fluorinated Substituents on the Near-Infrared Phosphorescence of 5d Metallocorroles.

The influence of fluorinated substituents on the luminescent properties of rhenium-oxo, osmium-nitrido, and gold triarylcorroles was studied via a comparison of four ligands: triphenylcorrole (TPC), tris(p-trifluoromethylphenyl)corrole (TpCF3PC), tris{3,5-bis(trifluoromethyl)phenyl}corrole (T3,5-CF3PC), and tris(pentafluorophenyl)corrole (TPFPC). For each metal series examined, fluorinated substituents were found to enhance the luminescent properties, with the phosphorescence quantum yields and triplet decay times increasing in the order TPC < TpCF3PC < T3,5-CF3PC < TPFPC. Among the 11 complexes examined, the highest phosphorescence quantum yield, 2.2%, was recorded for Re[TPFPC](O).

Phenol- and resorcinol-appended metallocorroles and their derivatization with fluorous tags.

Boron tribromide-mediated demethylation of rhenium-oxo and gold meso-tris(4-methoxyphenyl)corrole and meso-tris(3,5-dimethoxyphenylcorrole), M[TpOMePC] and M[T(3,5-OMe)PC] (M = ReO, Au), have yielded the corresponding phenol- and resorcinol-appended metallocorroles, M[TpOHPC] and M[T(3,5-OH)PC], in good yields. The latter compounds proved insoluble in dichloromethane and chloroform but soluble in THF. The M[T(3,5-OH)PC] derivatives also proved moderately soluble in 0.05 M aqueous KOH. Unlike oxidation-prone aminophenyl-substituted corroles, the phenol- and resorcinol-appended metallocorroles could be readily handled in air without special precautions. The phenolic metallocorroles could be readily alkylated with 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecyl iodide ("FtI") to afford the fluorous-tagged metallocorroles M[TpOFtPC] and M[T(3,5-OFt)PC] in > 90% yields. The simplicity of the synthetic protocols promise a wide range of phenolic and fluorous-tagged porphyrin analogues with potential applications to diverse fields such as sensors, catalysis, and photodynamic therapy, among others.

Iridium(VII)-Corrole Terminal Carbides Should Exist as Stable Compounds.

Scalar-relativistic DFT calculations with multiple exchange-correlation functionals and large basis sets foreshadow the existence of stable iridium(VII)-corrole terminal carbide derivatives. For the parent compound Ir[Cor](C), OLYP/STO-TZ2P calculations predict a short Ir-C bond distance of 1.69 Å, a moderately domed macrocycle with no indications of ligand noninnocence, a surprisingly low electron affinity of ∼1.1 eV, and a substantial singlet-triplet gap of ∼1.8 eV. These results, and their essential invariance with respect to the choice of the exchange-correlation functional, lead us to posit that Ir(VII)-corrole terminal carbide complexes should be isolable and indefinitely stable under ambient conditions.

Comparing Isoelectronic, Quadruple-Bonded Metalloporphyrin and Metallocorrole Dimers: Scalar-Relativistic DFT Calculations Predict a >1 eV Range for Ionization Potential and Electron Affinity.

A scalar-relativistic DFT study of isoelectronic, quadruple-bonded Group 6 metalloporphyrins (M = Mo, W) and Group 7 metallocorroles (M = Tc, Re) has uncovered dramatic differences in ionization potential (IP) and electron affinity (EA) among the compounds. Thus, both the IPs and EAs of the corrole derivatives are 1 eV or more higher than those of the porphyrin derivatives. These differences largely reflect the much lower orbital energies of the δ- and δ*-orbitals of the corrole dimers relative to those of the porphyrin dimers, which in turn reflect the higher (+III as opposed to +II) oxidation states of the metals in the former compounds. Significant differences have also been determined between Mo and W porphyrin dimers and between Tc and Re corrole dimers. These differences are thought to largely reflect greater relativistic destabilization of the 5d orbitals of W and Re relative to the 4d orbitals of Mo and Tc. The calculated differences in IP and EA should translate to major differences in electrochemical redox potentials-a prediction that in our opinion is well worth confirming.

Synthesis and molecular structure of gold triarylcorroles.

A number of third-row transition-metal corroles have remained elusive as synthetic targets until now, notably osmium, platinum, and gold corroles. Against this backdrop, we present a simple and general synthesis of ß-unsubstituted gold(III) triarylcorroles and the first X-ray crystal structure of such a complex. Comparison with analogous copper and silver corrole structures, supplemented by extensive scalar-relativistic, dispersion-corrected density functional theory calculations, suggests that "inherent saddling" may occur for of all coinage metal corroles. The degree of saddling, however, varies considerably among the three metals, decreasing conspicuously along the series Cu > Ag > Au. The structural differences reflect significant differences in metal-corrole bonding, which are also reflected in the electrochemistry and electronic absorption spectra of the complexes. From Cu to Au, the electronic structure changes from noninnocent metal(II)-corrole(•2-) to relatively innocent metal(III)-corrole(3-).