Torsten Sixt

Iron versus ruthenium oxidation in 1,1′-bis(diphenylphosphino)ferrocene–ruthenium(II) complexes: EPR and spectroelectrochemical evidence

Abstract Oxidation of [Cp * RuH(dppf)] ( 1 ), dppf=1,1′-bis(diphenylphosphino)ferrocene, and [(Cym)RuCl(dppf)](PF 6 ) ( 2 ), Cym= p -cymene, occurs at ruthenium for 1 but yields a ferrocenium species for compound 2 .

Iron(II) versus osmium(II) oxidation in 1,1′-bis(diorganophosphino)ferrocene–osmium(II) complexes

Abstract The compounds [(Cym)OsCl(dxpf)](PF6), Cym=p-cymene and dxpf: 1,1′-bis(diphenylphosphino)ferrocene (dppf), 1,1′-bis(diethylphosphino)ferrocene (depf) or 1,1′-bis(diisopropylphosphino)ferrocene (dippf), were synthesized and characterized by NMR (1H, 31P) and, in the case of [(Cym)OsCl(dppf)](PF6), by X-ray structure analysis of the acetonitrile solvate. EPR and UV–vis spectroelectrochemistry indicate the formation of an osmium(II)–ferrocenium species on reversible one-electron oxidation. The second oxidation and the reduction are electrochemically irreversible.

Copper(I) complexes with N,O-donor Schiff base ligands related to intermediate forms of the TPQ cofactor in amine oxidases

Neutral complexes (PPh 3 ) 2 Cu(L) were obtained from (PPh 3 ) 2 Cu(NO 3 ) and the deprotonated forms of the three Schiff base ligands 2-(benzylideneimino)phenol (BimOH), 4-(benzylideneimino)resorcinol (Bim(OH) 2 ) and N -(2,4-dihydroxy-5-isopropylphenyl)acetamide (DipaH 3 ). The ligands were designed to model aminated intermediate forms of the topaquinone (TPQ) cofactor in the enzymatic cycle of copper-dependent amine oxidases. The ligands L are coordinated to the metal centers through imineN and phenolateO donor atoms to form five-membered chelate rings, in contrast to the six-membered chelate rings of salen-type Schiff base ligands. Compound (Bim(OH)O)Cu(PPh 3 ) 2 ·0.5CH 3 OH was structurally analyzed, it exhibits intramolecular aryl–aryl interactions between the ligands and intermolecular hydrogen bonds involving the free phenolic hydroxyl substituent, the coordinated phenolate oxygen atom and the methanol solvate molecule.

Structures and properties of complexes [MCl(C5Me5)(N∧S)](PF6), M=Rh, Ir, with N∧S=1-methyl-2-(alkylthiomethyl)-1H-benzimidazole ligands

Abstract The four complexes [MCl(C5Me5)(N∧S)](PF6), M=Rh, Ir; N∧S=1-methyl-2-(methylthiomethyl)-1H-benzimidazole (mmb) and 1-methyl-2-(tert-butylthiomethyl)-1H-benzimidazole (mtb) were synthesized and characterized by spectroscopy, electrochemistry and X-ray crystallography (as methanol solvates). The essential coordination features, viz., longer M–S (ca. 2.38 A) and shorter M–N bonds (ca. 2.09 A) in five-membered chelate rings are common to all four species. Cyclic voltammetry reveals irreversible two-electron reduction to MI complexes and partially reversible oxidation to IrIV species for [IrCl(C5Me5)(mtb)]+. The results are discussed in comparison with those obtained for α-diimine (N∧N) complexes of the [MCl(C5Me5)]+ fragments.

A copper(I) dimer [Cu(L)(CH3CN)]2(BF4)2 with the new chelating and bridging tridentate ligand 1-(2-pyridylmethyl)-2-(2-pyridyl)benzimidazole (L)

Abstract Reaction of 1,2-phenylenediamine with 2-pyridinecarboxaldehyde gave the new compound 1-(2-pyridylmethyl)-2-(2-pyridyl)benzimidazole (L) which reacted with [Cu(CH3CN)4](BF4) to form the title complex. Although the imine/2-(2-pyridyl) (‘α-diimine’) coordination setting in L appears well suited for forming a five-membered chelate ring, the crystal structure analysis of the bis(methanol) solvate revealed that the system rather opts for the formation of a partially saturated eight-membered chelate ring involving both pyridyl groups with a twist angle of 61.8° between the benzimidazole and 2-(2-pyridyl) moieties. In addition, L acts as a tridentate ligand, effecting dimerization of two chelate rings through the imine nitrogen centers of the imidazole groups. This dimerization gives rise to a ten-membered dimetalla ring. Tetracoordination at copper(I) is complemented by acetonitrile. The preference for this structure is attributed to the formation of unstrained metal centers with N–Cu–N angles between 105° and 118° and Cu–N distances of 2.03–2.05 A.