Viking Helmet Corroles: Activating Inert Oxidometal Corroles.

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.

Metal-Assisted One-Pot Synthesis of Isoporphyrin Complexes.

Zinc and cadmium complexes of meso-arylisoporphyrins carrying a pyrrolyl or dipyrrinyl substituent at the sp(3) carbon atom were obtained through a simple one-pot variation of the Alder-Longo porphyrin synthesis. Key to the formation and stabilization of isoporphyrins is the presence of metal acetates during the oxidative macrocyclization step. The characteristic Q-bands of isoporphyrins are found in the NIR region between 750 nm and 880 nm. All of the isolated pyrrolyl- and dipyrrinyl-appended isoporphyrins are stable under typical laboratory conditions and allow chemical transformations like BF2 coordination, transmetalation, and ligand exchange.

Acidic Condensation of BODIPYs with Aldehydes: A Quick and Versatile Route to Alkenyl-BODIPYs and C(sp(3) )-Connected DYEmers.

The condensation of aldehydes with BODIPY (boron dipyrrin) luminophores was investigated. Formaldehyde can be used to connect two BODIPYs at each of the three pyrrolic C positions (α-, ß-, and ß'-positions) in a quick and highly selective manner, yielding new DYEmers (di- and oligomeric BODIPY derivatives) with varied photophysical properties. Benzaldehydes form DYEmers only at the ß- and the ß'-positions. For aliphatic aldehydes the DYEmer formation competes with the elimination of water from a proposed alcohol intermediate, leading to the formation of α- and ß-alkenyl-BODIPYs. 2-Phenylacetaldehyde and similar precursors exclusively yield elimination products. These acid-mediated transformations are valuable alternatives to the well-established, base-promoted Knoevenagel condensation protocol that is typically employed in the preparation of BODIPYs with near infrared (NIR)-shifted absorptions.

The Corrole Radical.

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.

Charge transfer tuning by chemical substitution and uniaxial pressure in the organic complex tetramethoxypyrene-tetracyanoquinodimethane.

In the search for novel organic charge transfer salts with variable degrees of charge transfer we have studied the effects of two modifications of the recently synthesized donor-acceptor system [tetramethoxypyrene (TMP)]-[tetracyanoquinodimethane (TCNQ)]. One is of chemical nature by substituting the acceptor TCNQ molecules by F4TCNQ molecules. The second consists in simulating the application of uniaxial pressure along the stacking axis of the system. In order to test the chemical substitution, we have grown single crystals of the TMP-F4TCNQ complex and analyzed its electronic structure via electronic transport measurements, ab initio density functional theory (DFT) calculations and UV/VIS/IR absorption spectroscopy. This system shows an almost ideal geometrical overlap of nearly planar molecules stacked alternately (mixed stack) and this arrangement is echoed by a semiconductor-like transport behavior with an increased conductivity along the stacking direction. This is in contrast to TMP-TCNQ which shows a less pronounced anisotropy and a smaller conductivity response. Our band structure calculations confirm the one-dimensional behavior of TMP-F4TCNQ with pronounced dispersion only along the stacking axis. Infrared measurements illustrating the C≡N vibration frequency shift in F4TCNQ suggest however no improvement in the degree of charge transfer in TMP-F4TCNQ with respect to TMP-TCNQ. In both complexes about 0.1e is transferred from TMP to the acceptor. Concerning the pressure effect, our DFT calculations on the designed TMP-TCNQ and TMP-F4TCNQ structures under different pressure conditions show that application of uniaxial pressure along the stacking axis of TMP-TCNQ may be the route to follow in order to obtain a much more pronounced charge transfer.

Synthesis and characterization of hexa-coordinated Sn(IV) complexes of meso-aryl dipyrrins.

Our successful synthesis of the first examples of Sn(IV) complexes of meso-aryl dipyrrins is reported. Sn(IV) dipyrrins are synthesized by treating meso-aryl dipyrrins with readily available SnCl2·2H2O in pyridine at reflux temperature and isolated as pure complexes by recrystallization. The X-ray structure revealed that the complex is hexa-coordinated and the Sn(IV) ion is coordinated to two dipyrrin units and two chlorides with overall appearance of a butterfly like structure. The complexes are stable in solution and characterized by spectral and electrochemical techniques.