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Dinuclear copper(II) complexes with the new ligand 1,6-bis[[bis(1-methyl-2-benzimidazolyl)methyl]amino]-n-hexane (EBA) have been synthesized, and their reactivity as models for tyrosinase has been investigated in comparison with that of previously reported dinuclear complexes containing similar aminobis(benzimidazole) donor groups. The complex [Cu2(EBA)(H2O)4]4+, five-coordinated SPY, with three nitrogen donors from the ligand and two water molecules per copper, can be reversibly converted into the bis(hydroxo) complex [Cu2(EBA)(OH)2]2+ by addition of base (pKa1 = 7.77, pKa2 = 9.01). The latter complex can also be obtained by air oxidation of [Cu2(EBA)]2+ in methanol. The X-ray structural characterization of [Cu2(EBA)(OH)2]2+ shows that a double μ-hydroxo bridge is established between the two Cu(II) centers in this complex. The coordination geometry of the coppers is distorted square planar, with two benzimidazole donors and two hydroxo groups in the equatorial plane, and an additional, lengthened and sev...

A series of organometallic complexes derived by organocobaloximes and organorhodoximes in which either one or both the hydrogen bridges have been replaced by BPh 2 groups, RM(DH)(DBPh 2 ) N -MeIm and RM((DBPh 2 ) 2 N -MeIm, respectively, have been synthesised and characterised, both in solution and in solid state. 1 H NMR spectra show that they assume different interconverting conformations in solution. With increasing steric bulk of R, the axial phenyls of the BPh 2 group tend to face N -MeIm, forcing the latter in an orientation which is quite unusual in organocobaloximes and causing a lengthening of the Co-N bond. Some possible implications on the strength of the trans Co-C bond are discussed.

Crystallization and crystal structure analysis of chlorohydrates of either tri- or tetracationic copper porphyrins, namely copper(5,-10,15-tris(N-methyl-pyridinium-4-yl)-20-pyridine-porphyrinato) (1) and copper(5,10,15,20-tetrakis(N-methyl-pyridinium-4-yl)-porphyrinato), respectively, have been performed. Two crystalline forms, 2 and 3, of the latter have been obtained under different preparation conditions. A novel kind of slipped stack chains of these cationic porphyrins has been detected. The pronounced saddle conformation of the porphyrin reveals π-like interactions between the peripheral pyrrole C b -C b "double bond" and the metal center. DFT calculations on the isolated porphyrins clearly show the HOMO orbitals with the correct topology to yield a bonding interaction among the stacked porphyrin units. To our knowledge, a slipped stack chain of positively charged porphyrins has never been previously reported, if the arrangement of faced units of monocationic metalloporphyrins or phthalocyanins is excluded.

Protein design provides an attractive approach to test the essential features required for folding and function. Previously, we described the design and structural characterization in solution of mimochromes, a series of miniaturized metalloproteins, patterned after the F-helix of the hemoglobin beta-chain. Mimochromes consist of two medium-sized helical peptides, covalently linked to the deuteroporphyrin. CD and NMR characterization of the prototype, mimochrome I, revealed that the overall structure conforms well to the design. However, formation of Delta and Lambda diastereomers was observed. To overcome the problem of diastereomer formation, we re-designed mimochrome I, by engineering intramolecular, interchain interactions. The resulting model was mimochrome IV: the solution structural characterization showed the presence of the Lambda isomer as a unique form. To examine the extent to which the stereochemical stability and uniqueness of mimochrome IV was retained in the solid state, the crystal structure of Co(III)-mimochrome IV was solved by X-ray diffraction, and compared to the solution structure of the same derivative. Co(III)-mimochrome IV structures, both in solution and in the solid state, are characterized by the following common features: a bis-His axial coordination, a Lambda configuration around the metal ion, and a predominant helical conformation of the peptide chains. However, in the crystal structure, intrachain Glu1-Arg9 ion pairs are preferred over the designed, and experimentally found in solution, interchain interactions. This ion pairing switch may be related to strong packing interactions.

This report contains the chemistry of the ruthenium−carbene functionality bonded to the dibenzotetramethyltetraaza[14]annulene dianion, tmtaa. [{Ru(tmtaa)}2(μ-C8H12)], 1, was the most appropriate starting material, as it contains a labile olefin, which can be displaced by a number of ligands to give [Ru(tmtaa)(L)(L‘)] [L = L‘ = Py, 2; L = CO, L‘ = thf, 3; L = ButNC, L‘ = thf, 4; L = L‘ = ButNC, 5]. Reaction of 1 with diazoalkanes led to the displacement of the olefin and gave the corresponding carbene derivatives [Ru(tmtaa)(CRR‘)] [R = R‘ = Ph, 6; R = Ph, R‘ = H, 7; R = Ph, R‘ = COOMe, 8], which have square-pyramidal structures. Complexes 7 and 8 underwent a remarkable labilization of the carbene functionality in the reaction with carbon monoxide, while 6 was only converted to the corresponding carbonyl [Ru(tmtaa)(CPh2)(CO)], 10, by CO. The reaction of 7 with both CO and ButNC led to the migration of the carbene to one of the metalladiimino rings of the ligands in 12 and 13, while the reaction of 8 with b...