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CONSPECTUS: 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.

A porphyrin cis tautomer, where the two central NH protons are on adjacent pyrrole rings, has long been invoked as an intermediate in porphyrin tautomerism. Only recently, however, has such a species been isolated and structurally characterized. Thus, single-crystal X-ray structure determinations of two highly saddled free-base porphyrins, beta-heptakis(trifluoromethyl)-mesotetrakis(p-fluorophenyl)porphyrin, H-2[(CF3)(7)TFPP], and beta-octaiodo- 5,10,15,20- tetrakis(4'-trifluoromethylphenyl) porphyrin, H-2[I8TCF3PP], unambiguously revealed cis tautomeric structures, each stabilized as a termolecular complex with a pair of ROH (R = CH3 or H) molecules that form hydrogen-bonded N-H center dot center dot center dot O-H center dot center dot center dot N straps connecting the central NH groups with the antipodal unprotonated nitrogens. The unusual substitution patterns of these two porphyrins, however, have left open the question how readily such supramolecular assemblies might be engineered, which prompted us to examine the much more synthetically accessible beta-octabromo-meso-tetraphenylporphyrins. Herein, single-crystal Xray structures were obtained for two such compounds, 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4'-trifluoromethylphenyl)porphyrin, H-2[Br8TCF3PP], and 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4'-fluorophenyl)porphyrin, H-2[Br8TFPP], and although the central hydrogens could not all be located unambiguously, the electron density could be convincingly modeled as porphyrin cis tautomers, existing in each case as a bis-methanol adduct. In addition, a perusal of the Cambridge Structural Database suggests that there may well be additional examples of porphyrin cis tautomers that have not been recognized as such. We are therefore increasingly confident that porphyrin cis tautomers are readily accessible via supramolecular engineering, involving the simple stratagem of crystallizing a strongly saddled porphyrin from a solvent system containing an amphiprotic species such as water or an alcohol. Research Council of NorwayResearch Council of Norway [262229]; U.S. National Science FoundationNational Science Foundation (NSF) [CHE-1726077] This work was supported by the Research Council of Norway (grant no. 262229) and the U.S. National Science Foundation (grant no. CHE-1726077). We thank Dr. Laura J. McCormickMcPherson for helpful discussions.

Metallocorroles wherein the metal ion is MnIII and formally FeIV are studied here using field- and frequency-domain electron paramagnetic resonance techniques. The MnIII corrole, Mn(tpfc) (tpfc = 5...

A combination of Pt L

Single-crystal X-ray structures were obtained for the copper and μ-oxodiiron complexes of 2,3,7,8,12,13,17,18-octafluoro-5,10,15-triphenylcorrole, hereafter denoted as Cu[F8TPC] and {Fe[F8TPC]}2O. A comparison with the crystal structures of other undecasubstituted Cu corroles, including those with H, Ar, Br, I, and CF3 as β-substituents, showed that the degree of saddling increases in the order: H ≲ F < Ar ≲ Br ≲ I < CF3. In other words, Cu[F8TPC] is marginally more saddled than β-unsubstituted Cu triarylcorroles, but substantially less saddled than Cu undecaarylcorroles, β-octabromo-meso-triarylcorroles, and β-octaiodo-meso-triarylcorroles, and far less saddled than Cu β-octakis(trifluoromethyl)-meso-triarylcorroles. As for {Fe[F8TPC]}2O, the moderate quality of the structure did not allow us to draw firm conclusions in regard to bond length alternations in the corrole skeleton and hence also the question of ligand noninnocence. The Fe-O bond distances, 1.712(8) and 1.724(8), however, are essentially identical to those observed for {Fe[TPFPC]}2O, where TPFPC3- is the trianion of 5,10,15-tris(pentafluorophenyl)corrole, suggesting that a partially noninnocent electronic structural description may be applicable for both compounds.

A porphyrin cis tautomer, where the two central NH protons are on adjacent pyrrole rings, has long been invoked as an intermediate in porphyrin tautomerism. Only recently, however, has such a species been isolated and structurally characterized. Thus, single-crystal X-ray structure determinations of two highly saddled free-base porphyrins, β-heptakis(trifluoromethyl)-meso-tetrakis(p-fluorophenyl)porphyrin, H2[(CF3)7TFPP], and β-octaiodo-5,10,15,20-tetrakis(4′-trifluoromethylphenyl)porphyrin, H2[I8TCF3PP], unambiguously revealed cis tautomeric structures, each stabilized as a termolecular complex with a pair of ROH (R = CH3 or H) molecules that form hydrogen-bonded N–H···O–H···N straps connecting the central NH groups with the antipodal unprotonated nitrogens. The unusual substitution patterns of these two porphyrins, however, have left open the question how readily such supramolecular assemblies might be engineered, which prompted us to examine the much more synthetically accessible β-octabromo-meso-tetraphenylporphyrins. Herein, single-crystal X-ray structures were obtained for two such compounds, 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4′-trifluoromethylphenyl)porphyrin, H2[Br8TCF3PP], and 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4′-fluorophenyl)porphyrin, H2[Br8TFPP], and although the central hydrogens could not all be located unambiguously, the electron density could be convincingly modeled as porphyrin cis tautomers, existing in each case as a bis-methanol adduct. In addition, a perusal of the Cambridge Structural Database suggests that there may well be additional examples of porphyrin cis tautomers that have not been recognized as such. We are therefore increasingly confident that porphyrin cis tautomers are readily accessible via supramolecular engineering, involving the simple stratagem of crystallizing a strongly saddled porphyrin from a solvent system containing an amphiprotic species such as water or an alcohol.

Metallocorroles wherein the metal ion is Mn

BACKGROUND: Levels of physical activity and variation in physical activity and sedentary time by place and person in European children and adolescents are largely unknown. The objective of the study was to assess the variations in objectively measured physical activity and sedentary time in children and adolescents across Europe. METHODS: Six databases were systematically searched to identify pan-European and national data sets on physical activity and sedentary time assessed by the same accelerometer in children (2 to 9.9¿years) and adolescents (=10 to 18¿years). We harmonized individual-level data by reprocessing hip-worn raw accelerometer data files from 30 different studies conducted between 1997 and 2014, representing 47, 497 individuals (2-18¿years) from 18 different European countries. RESULTS: Overall, a maximum of 29% (95% CI: 25, 33) of children and 29% (95% CI: 25, 32) of adolescents were categorized as sufficiently physically active. We observed substantial country- and region-specific differences in physical activity and sedentary time, with lower physical activity levels and prevalence estimates in Southern European countries. Boys were more active and less sedentary in all age-categories. The onset of age-related lowering or leveling-off of physical activity and increase in sedentary time seems to become apparent at around 6 to 7¿years of age. CONCLUSIONS: Two third of European children and adolescents are not sufficiently active. Our findings suggest substantial gender-, country- and region-specific differences in physical activity. These results should encourage policymakers, governments, and local and national stakeholders to take action to facilitate an increase in the physical activity levels of young people across Europe.

X-ray structures of gold corroles, which are still rather uncommon, afford significant insights into intermolecular interactions involving Au(III), a subject that has been much less studied than aurophilic and metallophilic interactions involving Au(I). The X-ray structure of gold [Formula: see text]-octabromo-meso-tris(para-pentafluorosulfanylphenyl)corrole, reported herein, has revealed two Au···Br interactions (∼4.2 Å) per Au atom. We suggest that analogous but somewhat stronger Au···Br interactions are a key factor underlying the remarkable insolubility of gold octabromocorrole derivatives.

Two new series of iron meso-tris(para-X-phenyl)corrole (TpXPC) complexes, Fe[TpXPC]Ph and Fe[TpXPC]Tol, in which X=CF3 , H, Me, and OMe, and Tol=p-methylphenyl (p-tolyl), have been synthesized, allowing a multitechnique electronic-structural comparison with the corresponding FeCl, FeNO, and Fe2 (μ-O) TpXPC derivatives. Optical spectroscopy revealed that the Soret maxima of the FePh and FeTol series are insensitive to the phenyl para substituent, consistent with the presumed innocence of the corrole ligand in these compounds. Accordingly, we may be increasingly confident in the ability of the substituent effect criterion to serve as a probe of corrole noninnocence. Furthermore, four complexes-Fe[TPC]Cl, Fe[TPC](NO), {Fe[TPC]}2 O, and Fe[TPC]Ph-were selected for a detailed XANES investigation of the question of ligand noninnocence. The intensity-weighted average energy (IWAE) positions were found to exhibit rather modest variations (0.8 eV over the series of corroles). The integrated Fe-K pre-edge intensities, on the other hand, vary considerably, with a 2.5 fold increase for Fe[TPC]Ph relative to Fe[TPC]Cl and Fe[TPC](NO). Given the approximately C4v local symmetry of the Fe in all the complexes, the large increase in intensity for Fe[TPC]Ph may be attributed to a higher number of 3d holes, consistent with an expected FeIV -like description, in contrast to Fe[TPC]Cl and Fe[TPC](NO), in which the Fe is thought to be FeIII -like. These results afford strong validation of XANES as a probe of ligand noninnocence in metallocorroles. Electrochemical redox potentials, on the other hand, were found not to afford a simple probe of ligand noninnocence in Fe corroles.

Electrochemical and acid-base properties of four free-base triarylcorroles were examined in nonaqueous media. These compounds are represented here as (tdcc)H[Formula: see text], (tpfc)H[Formula: see text], (Br[Formula: see text]tdcc)H[Formula: see text] and (Br[Formula: see text]tpfc)H[Formula: see text], where tdcc and tpfc are the trianions of tris(2,6-dichlorophenyl)corrole and tris(pentafluorophenyl)corrole, respectively. Different spectroscopic and electrochemical properties were observed for the [Formula: see text]-brominated corroles as compared to the non-brominated derivatives, due in part to the corrole ring distortion and in part to the strong electron-withdrawing properties of the Br groups. The brominated free-base corroles are easier to deprotonate than the non-brominated corroles in solution, which was confirmed by electrochemistry and spectroelectrochemistry as well as protonation/deprotonation reactions of the compounds with acid or base in PhCN. The electrochemistry of the protonated and deprotonated corroles is presented and comparisons made with previously published data for other protonated and deprotonated free-base corroles under the same solution conditions.

An inherently chiral metallocorrole has been resolved for the first time by means of HPLC on a chiral stationary phase. For the compound in question, a homoleptic tungsten biscorrole, the absolute configurations of the enantiomers were assigned using online HPLC-ECD measurements in conjunction with time-dependent CAM-B3LYP calculations, which provided accurate simulations of the ECD spectra.

Correction for ‘X-ray absorption spectroscopy of exemplary platinum porphyrin and corrole derivatives: metal- versus ligand-centered oxidation’ by Benjamin D. Matson et al., RSC Adv., 2021, 11, 32269–32274. DOI: 10.1039/D1RA06151H

Two amphiphilic corroles-5,10,15-tris(3-carboxyphenyl)corrole (H3[mTCPC]) and 5,10,15-tris(4-carboxyphenyl)corrole (H3[pTCPC])-and their gold complexes have been synthesized, and their photophysical properties and photovoltaic behavior have been investigated. Like other nonpolar gold corroles, Au[mTCPC] and Au[pTCPC] were both found to exhibit room temperature phosphorescence in deoxygenated solutions with quantum yields of ∼0.3% and triplet lifetimes of ∼75 μs. Both compounds exhibited significant activity as dyes in photodynamic therapy experiments and in dye-sensitized solar cells. Upon irradiation at 435 nm, both Au corroles exhibited significant phototoxicity against AY27 rat bladder cancer cells while the free-base corroles proved inactive. Dye-sensitized solar cells constructed using the free bases H3[mTCPC] and H3[pTCPC] exhibited low efficiencies (≪1%), well under that obtained with 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin, H2[pTCPP] (1.9%, cf. N719 9.5%). Likewise, Au[pTCPC] proved inefficient, with an efficiency of ∼0.2%. By contrast, Au[mTCPC] proved remarkably effective, exhibiting an open-circuit voltage (Voc) of 0.56 V, a short-circuit current of 8.7 mA cm(-2), a fill factor of 0.72, and an efficiency of 3.5%.

In spite of significant applications as starting materials for a variety of metallocorrole derivatives, free-base β-octabromo-meso-triarylcorroles continue to be viewed as inaccessible. The reasons range from the need for tedious column-chromatographic purification to limitations of the reductive demetallation protocol for selected systems. Here we report that column chromatography may be entirely avoided for a number of β-octabromo-meso-tris(p-X-phenyl)corrole derivatives, where X=CF3, NO2, F, H, CH3, and OCH3; instead, analytically pure products may be obtained by recrystallization from chloroform/methanol. In addition, we have presented an optimized synthesis of the heretofore inaccessible, sterically hindered ligand β-octabromo-meso-tris(2,6-dichlorophenyl)corrole, H3[Br8TDCPC], via reductive demetallation of the corresponding Mn(III) complex. With our earlier report of β-octabromo-meso-tris(pentafluorophenyl)corrole, H3[Br8TPFPC], a comprehensive set of optimized synthetic protocols are thus in place for a good number of β-octabromo-meso-triarylcorrole ligands. Furthermore, we have illustrated the use of these ligands by synthesizing the iron complexes Fe[Br8TDCPC]Cl and Fe[Br8TDCPC](py)2, of which the latter lent itself to single-crystal X-ray structure determination.

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.

The first example of a diboryl corrole complex, [(BF2)2(Br8T(4-F-P)C)](-) (Br8T(4-F-P)C = trianion of 2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(4-fluorophenyl)corrole), has been isolated using the strongly electron-withdrawing and sterically crowded triaryl octabromocorrole ligand. Density functional theory (DFT) calculations show that the hydrolysis reaction producing the partially hydrolyzed complexes [B2OF2(Cor)](-) is more favored for the less sterically crowded triaryl corrole complexes. Monoboryl complexes BF2(H2Cor) (Cor = trianions of 5,10,15-triphenylcorrole (TPC), 5,10,15-tris(4-methylphenyl)corrole (T(4-CH3-P)C), 5,10,15-tris(4-trifluoromethylphenyl)corrole (T(4-CF3-P)C), and 5,10,15-tris(pentafluorophenyl)corrole (TPFPC)) were prepared and characterized. The experimental data are consistent with an out-of-plane dipyrrin coordination mode for these complexes, and DFT optimizations suggest that internal BF···HN hydrogen bonding may be significant in stabilizing these complexes. Further examples of the anionic diboron corrole [B2OF2(Cor)](-) containing the electron-withdrawing 5,10,15-tris(pentafluorophenyl)corrole (TPFPC) and the sterically hindered 10-(4-methoxyphenyl)-5,15-dimesitylcorrole (Mes2(4-MeOP)C) trianions are reported.

Copper corroles exhibit inherent saddling, driven by ligand non-innocence, which may be viewed as a form of multideterminantal character. The saddling is enhanced by sterically hindered peripheral substituents. The sterically hindered complex Cu[(CF3)8T(pFP)C] (wherein the ligand is β-octakis(trifluoromethyl)-meso-tris(p-fluorophenyl)corrolato) is thus exceedingly saddled with adjacent pyrrole rings nearly orthogonal to one another. By contrast, Au[(CF3)8T(pFP)C] has a nearly planar corrole macrocycle, implying an innocent corrole ligand.

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 β-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 β-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.

In contrast to sterically hindered metalloporphyrins, which are almost always strongly nonplanar, similarly substituted metallocorroles are generally relatively planar. A crystal structure of a copper β-octakis(trifluoromethyl)-meso-triarylcorrole, however, has revealed a corrole macrocycle with an unprecedented degree of saddling. With the exception of the bipyrrole unit, any two adjacent pyrrole rings are essentially orthogonal to each other. Furthermore, the C2-symmetric molecular structure is chiral and NMR spectroscopy and DFT calculations suggest that the enantiomers do not interconvert readily. Once resolved, the molecule may provide us with a novel example of an inherently chiral chromophore.

Although the chemistry of corroles has grown spectacularly in recent years, the field has been marred by the lack of convenient protocols for demetalation of metallocorroles. Reported herein is a superior procedure for demetalating copper corroles with concentrated H 2SO4 and 5-200 equiv FeCl 2 or SnCl 2. The yields obtained with this reductive procedure are generally substantially better than with CHCl 3/ H 2SO4, CH 2Cl2/ H 2SO4, or H 2SO4 alone. With an oxidation-prone metallocorrole such as Cu [ T (p- OMeP ) C ], the reductive protocol was essential for obtaining any measurable yield of the free base at all. Free-base β-octabromo-meso-triarylcorroles were also obtained in pure form, in good yields, and with relative ease via this procedure.

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.

A first major study of undecaphenylcorrole (UPC) derivatives is presented. Three different Cu-UPC derivatives with different para substituents X (X = CF(3), H, CH(3)) on the β-aryl groups were synthesized via Suzuki-Miyaura coupling of Cu[Br(8)TPC] and the appropriate arylboronic acid. A single-crystal X-ray structure of the X = CF(3) complex revealed a distinctly saddled macrocycle conformation with adjacent pyrrole rings tilted by ~60-66° relative to one another (within the dipyrromethane units), which is somewhat higher than that observed for β-unsubstituted Cu-TPC derivatives but slightly lower than that observed for Cu[Br(8)TPC] (~70°) derivatives. Electrochemical and electronic absorption measurements afforded some of the first comparative insights into meso versus β substituent effects on the copper corrole core. The Soret maxima of the Cu-UPC complexes (~440-445 nm), however, are comparable to those of Cu[Br(8)TPC] derivatives and are considerably red-shifted relative to Cu-TPC derivatives. Para substituents on the β-phenyl groups were found to tune the redox potentials of copper corroles more effectively than those on meso-phenyl substituents, a somewhat surprising observation given that neither the HOMO nor LUMO has significant amplitudes at the β-pyrrolic positions.

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 β-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−).

The cover picture shows a variety of nonplanar aromatics, including corannulene, fullerenes, helicenes and nonplanar porphyrins against a background of the midnight sun near Tromso, Norway. The molecule at the center is a new member of this intriguing family of compounds – an exceedingly strongly saddled, chiral copper corrole. These have been synthesized by Prof. A. Ghosh and co-workers at the University of Tromso; details are discussed in the Short Communication on p. 1865 ff.

X-ray structures of Co(III)[(CF(3))(3)Cor](PPh(3)) [(CF(3))(3)Cor = meso-tris(trifluoromethyl)corrolato] and Cu[(CF(3))(4)Por] [(CF(3))(4)Por = meso-tetrakis(trifluoromethyl)porphyrinato] revealed planar and highly ruffled macrocycle conformations, respectively, in line with analogous observations for a handful of other meso-perfluoroalkylated porphyrins and corroles reported in the literature. To gain insights into the difference in conformational behavior, we evaluated DFT (BP86-D/TZP) ruffling potentials for a variety of corrole complexes, as well as their porphyrin analogues. The calculations led us to conclude that corrole derivatives, in essence, cannot ruffle.

The reaction of copper beta-octabromo- meso-triarylcorrole derivatives with methyl 2,2-difluoro-2-(fluorosulfonyl)acetate has provided four beta-octakis(trifluoromethyl)corrole complexes, Cu[(CF 3) 8T( p-XP)C] (X = F, H, Me, OMe), in moderate yields. The new complexes present a conglomeration of remarkable substituent effects, both steric and electronic. DFT (OLYP/TZP) geometry optimization of Cu[(CF 3) 8TPC] (i.e., X = H) indicates a sterically hindered, strongly saddled geometry, with numerous short F...F nonbonded contacts of 2.5-2.9 A and certain beta carbons displaced by over 1.5 A relative to the mean corrole plane. The CF 3 groups generally appear as quartets in the (19)F NMR spectra, with unexpectedly large (5) J FF coupling constants of about 14 Hz, apparently a manifestation of the highly crowded structure. The eight CF 3 groups together exert a powerful influence on the redox potentials of the copper corrole core. Thus, the E 1/2ox of Cu[(CF 3) 8TPC] (1.4 V vs saturated calomel electrode) is a full half of a volt above that of Cu(TPC) (0.9 V) and a quarter of a volt above that of Cu(Br 8TPC) (1.14 V). Intriguingly, the beta CF 3 groups also greatly intensify the influence of the meso aryl substituents on the redox potentials, relative to the other Cu[Y 8T( p-XP)C] series, where Y = H, F, and Br. The Cu[(CF 3) 8T( p-XP)C] complexes also exhibit the most red-shifted optical spectra of any series of metallocorroles synthesized to date. Thus, between Cu(TPC) and Cu[(CF 3) 8T( p-MeO-P)C], the Soret maximum shifts by nearly 100 nm. The observed red-shifts are attributed in part to charge-transfer transitions of the Soret region and in part to the extreme nonplanar distortions.