Amine-functionalised hexagonal mesoporous silica as support for copper(II) acetylacetonate catalyst

Copper(II) acetylacetonate was anchored onto a hexagonal mesoporous silica (HMS) material using a two-step procedure: (i) functionalisation of the surface hydroxy groups with (3-aminopropyl)triethoxysilane (AMPTSi) and then (ii) anchoring of the copper(II) complex through Schiff condensation with free amine groups, using two different metal complex loadings. Upon the first step, nitrogen elemental analysis, XPS and DRIFT showed the presence of amine groups on the surface of the HMS material, and porosimetry indicated that the structure of the mesoporous material remained unchanged, although a slight decrease in surface area was observed. Atomic absorption, XPS and DRIFT showed that copper(II) acetylacetonate was anchored onto the amine-functionalised HMS by Schiff condensation between the free amine groups and the carbonyl groups of the copper(II) complex; using EPR an NO3 coordination sphere was proposed for the anchored copper(II) complex. The new [Cu(acac)2]-AMPTSi/HMS materials were tested in the aziridination of styrene at room temperature, using PhI=NTs as nitrogen source and acetonitrile as solvent. The styrene conversion and total TON of the heterogeneous phase reaction are higher than those of the same reaction catalysed in homogeneous phase by [Cu(acac)2]; nevertheless, the initial activity decreases and the reaction time increases due to substrate and product diffusion limitations. The heterogeneous catalyst showed a successive slight decrease in catalytic activity when reused for two more times. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

The structural and electrochemical consequences of hydrogenating Copper N2S2 Schiff base macrocycles

A series of cis and trans tetradentate copper macrocyclic complexes, of ring size fourteen - sixteen, which employ amine and thioether donor groups are reported. Apart from 5,6,15,16-bisbenzo-8,13-diaza-1,4-dithia-cyclohexadecane copper(I) (cis-[Cu(H4NbuSen)]+) all of the complexes are obtained in the copper(II) form. Crystallographic analysis shows that the copper(II) complexes all adopt a distorted planar geometry around the copper. In contrast, cis-[Cu(H4NbuSen)]+ is found to adopt a distorted tetrahedral geometry. The complexes were subjected to electrochemical analysis in water and acetonitrile. The effect of the solvent, positions of the donor atoms (cis/trans) on E1/2 is discussed as is the comparison of the electrochemical behaviour of these complexes with their parent Schiff base macrocycles.

Copper(II) complexes with unsymmetrical pentadentate ed3a-type diamino-tricarboxylate ligands. Crystal structures, configurational analysis and DFT study of complexes

The O–O–N–N–O-type pentadentate ligands H3ed3a, H3pd3a and H3pd3p (H3ed3a stands ethylenediamine-N,N,N′-triacetic acid; H3pd3a stands 1,3-propanediamine-N,N,N′-triacetic acid and H3pd3p stands 1,3-propanediamine-N,N,N′-tri-3-propionic acid) and the corresponding novel octahedral or square-planar/trigonal-bipyramidal copper(II) complexes have been prepared and characterized. H3ed3a, H3pd3a and H3pd3p ligands coordinate to copper(II) ion via five donor atoms (three deprotonated carboxylate atoms and two amine nitrogens) affording octahedral in case of ed3a3− and intermediate square-pyramidal/trigonal-bipyramidal structure in case of pd3a3− and pd3p3−. A six coordinate, octahedral geometry has been established crystallographically for the [Mg(H2O)6][Cu(ed3a)(H2O)]2 · 2H2O complex and five coordinate square-pyramidal for the [Mg(H2O)5Cu(pd3a)][Cu(pd3a)] · 2H2O. Structural data correlating similar chelate Cu(II) complexes have been used for the better understanding the pathway: octahedral → square-pyramidal ↔ trigonal- bipyramid geometry. An extensive configuration analysis is discussed in relation to information obtained for similar complexes. The infra-red and electronic absorption spectra of the complexes are discussed in comparison with related complexes of known geometries. Molecular mechanics and density functional theory (DFT) programs have been used to model the most stable geometric isomer yielding, at the same time, significant structural data. The results from density functional studies have been compared with X-ray data.