Curved π-conjugated molecules have attracted considerable interest because of the unique properties originating from their curved π surface. However, the synthesis of such distorted molecules requires harsh conditions, which hamper easy access to heteroatom-containing curved π systems. Here we report the synthesis of a π-extended azacorannulene with nitrogen in its centre. The oxidation of 9-aminophenanthrene provides tetrabenzocarbazole, which is converted to the azabuckybowl through palladium-catalysed intramolecular coupling. The electron-donating nature and curved π surface of the azabuckybowl enable its tight association with C60 in solution and solid states. High charge mobility is observed for the azabuckybowl/C60 assembly. This compound may be of interest in the fields of curved π systems as fullerene hosts, anisotropic π donors and precursors to nitrogen-containing nanocarbon materials.
Four new cobalt(ii) complexes [Co(6-MeTPA)Cl]ClO4/PF6 (2/2a), [Co(6-Me2TPA)Cl]ClO4/PF6 (3/3a), [Co(BPQA)Cl]ClO4/PF6 (4/4a) and [Co(BQPA)Cl]ClO4/PF6 (5/5a) as well as [Co(TPA)Cl]ClO4 (1) where TPA = tris(2-pyridylmethyl)amine, 6-MeTPA = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine, 6-Me2TPA = bis(6-methyl-2-pyridyl)methyl)-(2-pyridylmethyl)amine, BPQA = bis(2-pyridylmethyl)-(2-quinolylmethyl)-amine and BQPA = bis(2-quinolylmethyl)-(2-pyridylmethyl)amine were synthesized and structurally characterized. Single crystal X-ray crystallography confirmed the distorted trigonal bipyramidal geometries of complexes 2a-5a. Spectrophotometric titrations and conductivity measurements of the complexes in the CH3CN-H2O mixture showed that the chloro complexes exist in equilibrium with the corresponding hydrolyzed aqua species, [Co(L)(H2O)](2+). The pKa values of the coordinated H2O in aqua complexes vary from 8.4 to 8.7 (37 °C). The interactions of the complexes (1-5) with DNA have been investigated at pH = 7.0 and 9.0 (10 mM Tris-HCl buffer) and 37 °C where very high catalytic cleavage was observed. Under pseudo Michaelis-Menten kinetic conditions, the catalytic rate constants, kcat, decrease in the order 4>2>5>1>3. At pH 7.0 (10 mM Tris-HCl buffer) and 37 °C, the kcat value for complex 4 (6.02 h(-1)), where [Co(BPQA)(H2O)](2+) is the major species, corresponds to 170 million rate enhancement over the non-catalyzed DNA. Electrophoretic experiments conducted in the presence and absence of radical scavengers (DMSO, KI, NaN3) ruled out the oxidative mechanistic pathway of the reaction and suggested that the hydrolytic mechanism is the preferred one. This finding was in agreement with the observed increase in the kcat values at pH 9.0 compared to the corresponding values at pH 7.0 as a result of the increased concentration of the reactive hydroxo species, [Co(L)(OH)](+). The reactivity of the synthesized complexes in catalyzing the DNA cleavage is discussed in relation to the steric effect imposed by the coordinated pyridyl ligand around the central cobalt(ii) center.
Fused benzene rings to antiaromatic compounds generally improve their stability but attenuate their antiaromaticity. The opposite case is now reported. NiII benzonorcorroles were synthesized and the effect of benzo‐fusion on the antiaromaticity was elucidated. The benzo‐fusion resulted in significant decrease of the HOMO–LUMO gaps and enhancement of the paratropic ring current effect. Furthermore, the introduction of the benzo groups induced singlet diradical character in the antiaromatic porphyrinoid.
A large up-field shift (-763 ppm) has been observed for the carboxyl carbons of the dichlorido complex TBA[Ru(2)(O(2)CCH(3))(4)Cl(2)] (TBA(+) = tetra(n-butyl)ammonium cation) in the (13)C NMR spectrum (CD(2)Cl(2) at 25 °C). The DFT calculations showed spin delocalization from the paramagnetic Ru(2)(5+) core to the ligands, in agreement with the large up-field shift.
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