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Corroles on metal surfaces show substantial reactivity and aromaticity-driven interfacial electron transfer of their transient σ/π-radicals. These effects are much more pronounced than for the clos...

Chromyl(V) complexes of eleven different meso-aryl- and [Formula: see text]-alkylcorrole ligands have been prepared and characterized by analytical, spectroscopical, electrochemical and structural means. All seven new complexes show the expected optical spectra of chromyl(V) corroles with the Soret band situated slightly above (meso-arylcorroles) or below ([Formula: see text]-alkylcorrole) 400 nm, and with an isotropic room temperature EPR signal for the [Formula: see text] ion Cr(V) at about [Formula: see text]. Cyclic voltammetry evidences two or three quasi-reversible one-electron redox steps, which are characterized as two ligand-centered processes and one metal-centered process based on spectroelectrochemical measurements and a Hammett analysis. Chemical reduction to a chromyl(IV) corrolate was successfully performed using NaHg and NEt3. Citric acid, however, produces a different reduction product, for which an isocorrole structure is proposed. Six chromyl(V) corroles could be analysed by seven single crystal diffraction analyses. The obtained molecular data prove the presence of remarkably similar CrN4O coordination units independent of the corrole substitution pattern, and of macrocyclic conformations which can be understood as comprised mainly of a doming mode, a more or less pronounced saddling mode, and one out of two different and dominating ruffling modes.

Chemically inert oxidometal(V) corrols of molybdenum and rhenium undergo clean ligand-exchange reactions upon the action of SiCl4 . The resulting dichlorido complexes show trigonal prismatic coordination of the metal ion with the chlorine atoms residing in a cis configuration, and were studied by optical and resonance spectroscopy as well as DFT calculations. In situ reactivity studies with carbon nucleophiles indicate high reactivity for chlorine replacement. Treatment with sodium cyclopentadienide paves the way to robust molybdenum corrolocene half-sandwich complexes. These organometallic compounds are the first corrole species that stabilize an air-stable and diamagnetic low spin d2 -MoIV center. Structural, spectroelectrochemical, and chemical investigations prove a reversible MoIV /MoV redox couple close to the Fc/Fc+ potential for these systems. The high stability of the compounds in both redox states calls for future applications in catalysis and as redox switch.

Under oxygen-limiting conditions, the marine bacterium Dinoroseobacter shibae DFL12T generates energy via denitrification, a respiratory process in which nitric oxide (NO) is an intermediate. Accumulation of NO may cause cytotoxic effects. The response to this nitrosative (NO-triggered) stress is controlled by the Crp/Fnr-type transcriptional regulator DnrF. We analyzed the response to NO and the mechanism of NO sensing by the DnrF regulator. Using reporter gene fusions and transcriptomics, here we report that DnrF selectively repressed nitrate reductase (nap) genes, preventing further NO formation. In addition, DnrF induced the expression of the NO reductase genes (norCB), which promote NO consumption. We used UV-visible and EPR spectroscopy to characterize heme binding to DnrF and subsequent NO coordination. DnrF detects NO via its bound heme cofactor. We found that the dimeric DnrF bound one molecule of heme per subunit. Purified recombinant apo-DnrF bound its target promoter sequences (napD, nosR2, norC, hemA, and dnrE) in electromobility shift assays, and we identified a specific palindromic DNA-binding site 5′-TTGATN4ATCAA-3′ in these target sequences via mutagenesis studies. Most importantly, successive addition of heme as well as heme and NO to purified recombinant apo-DnrF protein increased affinity of the holo-DnrF for its specific binding motif in the napD promoter. On the basis of these results, we propose a model for the DnrF-mediated NO stress response of this marine bacterium.

10-Heterocorrole complexes with oxygen, sulfur, and selenium at position 10 of the macrocycle, and with the divalent ions of nickel, copper, and palladium were prepared and investigated. The focus was set onto the size adaptation and matching mechanisms of cavity sizes vs. ionic radii in corrole-type macrocycles. A full set of single crystal X-ray analyses was obtained and revealed that in all but one case the N4 binding site of the ring-contracted tetrapyrrole is larger than necessary to bind the metal ion without deformation. In plane size adaptation through M-N bond length elongation of 2.5%-3.2% is effective, in addition to pronounced out-of-plane ruffling of the macrocycle for those compounds with a more severe size mismatch. Such ruffling had been excluded for corroles before but is apparently the most efficient mechanism to adapt to small central ions.

The pyrrolyl-based iron pincer compounds [(tBuPNP)FeCl] (1), [(tBuPNP)FeN2] (2), and [(tBuPNP)Fe(CO)2] (3) were prepared and structurally characterized. In addition, their electronic ground states were probed by various techniques including solid-state magnetic susceptibility and zero-field 57Fe Mossbauer and X-band electron paramagnetic resonance spectroscopy. While the iron(II) starting material 1 adopts an intermediate-spin (S = 1) state, the iron(I) reduction products 2 and 3 exhibit a low-spin (S = 1/2) ground state. Consistent with an intermediate-spin configuration for 1, the zero-field 57Fe Mossbauer spectrum shows a characteristically large quadrupole splitting (ΔEQ ≈ 3.7 mm s–1), and the solid-state magnetic susceptibility data show pronounced zero-field splitting (|D| ≈ 37 cm–1). The effective magnetic moments observed for the iron(I) species 2 and 3 are larger than expected from the spin-only value and indicate an incompletely quenched orbital angular momentum and the presence of spin–orbit co...

A novel synthesis for dialkyl cobalt compounds [(tmeda)CoR2] is presented. In these complexes tmeda is readily replaced by an NHC or a bidentate phosphine ligand to form 3- and 4-coordinate compounds, respectively. [(ItBu)Co(CH2SiMe3)2] (ItBu = 1,3-di-tert-butylimidazolin-2-ylidene) serves as an efficient, homogeneous olefin hydrogenation pre-catalyst and allows the preparation of the novel cobalt bis(alkyne) complex [(ItBu)Co(η2-PhCCPh)2].

The half-sandwich complex [Cp'Fe(μ-I)]

The heme synthase AhbD catalyzes the oxidative decarboxylation of two propionate side chains of iron-coproporphyrin III to the corresponding vinyl groups of heme during the alternative heme biosynthesis pathway occurring in sulfate-reducing bacteria and archaea. AhbD belongs to the family of Radical SAM enzymes and contains two [4Fe–4S] clusters. Whereas one of these clusters is required for substrate radical formation, the role of the second iron–sulfur cluster is not known. In this study, the function of the auxiliary cluster during AhbD catalysis was investigated. Two single cluster variants of AhbD from M. barkeri carrying either one of the two clusters were created. Using these enzyme variants it was shown that the auxiliary cluster is not required for substrate binding and formation of the substrate radical. Instead, the auxiliary cluster is involved in a late step of AhbD catalysis most likely in electron transfer from the reaction intermediate to a final electron acceptor. Moreover, by using alternative substrates such as coproporphyrin III, Cu-coproporphyrin III and Zn-coproporphyrin III for the AhbD activity assay it was observed that the central iron ion of the porphyrin substrate also participates in the electron transfer from the reaction intermediate to the auxiliary [4Fe–4S] cluster. Altogether, new insights concerning the completely uncharacterized late steps of AhbD catalysis were obtained.

Nickel(II) complexes of ring-contracted 9-methylisocorroles were prepared by templated macrocyclisation and act as the first porphyrinoid catalysts for C–C cross-coupling., Cationic nickel(ii) complexes of two ring-contracted porphyrinoid ligands distantly related to the corrins were prepared by metal templated macrocyclisation. The compounds show reversible electron transfer processes and were found to be the first porphyrinoid-based catalysts for C–C cross-coupling.

The reaction of 5,10,15-trimesitylcorrole (H3 cor) with tungsten hexachloride and tungsten hexacarbonyl resulted in the unexpected formation of the 3,17-dichloro-5,10,15-trimesitylcorrole radical (H2 cor*) as an air-stable product. X-ray crystallography proved the planarization of the corrole radical structure, which was rationalized by the reduced steric hindrance of two versus three hydrogen atoms inside the N4 cavity. Although the aromaticity was lost, no specific changes in C-C or C-N bond distances could be observed. The regioselectivity of the two-fold chlorination is the result of the nucleophilic attack of chloride ions to an oxidized corrole macrocycle, and is supported by DFT results. The corrole radical acts as a dianionic ligand and allows the insertion of the divalent zinc(II) cation, which usually does not form neutral corrole complexes.

The coordination chemistry of the previously neglected 2,4-di(tert-butyl)pentadienyl (Pdl′) ligand with transition metals is explored. Several open metallocenes [(η5-Pdl′)2M] (M = Ti (3), V (4) and Cr (5)) were prepared and characterized by various spectroscopic techniques and X-ray diffraction. Attempts to prepare the open ferrocene [(η5-Pdl′)2Fe] were hampered by its high thermal instability, which leads to the formation of iron metal and 2,4,7,9-tetra-tert-butyl-1,3,7,9-decatetraene (2). Nevertheless, the half-open ferrocene [(η5-Pdl′)Fe(η5-Cp″)] (Cp″ = 1,2,4-(Me3C)3C5H2, 6) and mono(pentadienyl) iridium complex [(η5-Pdl′)Ir(η4-cod)] (9) were successfully synthesized. The electronic and molecular structures of the half-open ferrocene [(η5-Pdl′)Fe(η5-Cp″)] (6) and its closed analogue [(η5-Cp′)Fe(η5-Cp″)] (7, Cp′ = 1,3-(Me3C)2C5H3) were compared. Complex 6 is significantly more encumbered than 7, as shown by the short Pdl′cent–Fe distance. Clean oxidation of 6 and 7 can be accomplished electrochemically and chemically to give the half-open ferrocenium 6+ and closed ferrocenium 7+, respectively, and in both cases steric strain is released upon oxidation. On heating of 6+ to 152 °C in the solid state H2 and isobutene is eliminated to give [(η5-Cp′)2Fe]+ (8).