Document Type

Journal Article

Department/Unit

Department of Chemistry

Title

Helical complexes of chiral quaterpyridines – mononuclear cuII and dinuclear cuI complexes

Language

English

Abstract

Two series of chiral helical copper-quaterpyridine complexes were prepared by reacting chiral ligands L1-4 with CuI and CuII precursors. The CuII complexes, [Cu(L)(H2O)(ClO 4)2] or [Cu(L)(ClO4)2], were studied by ESI-MS, elemental analysis, and CD spectroscopy, and the CuI complexes, [Cu2(L)2](PF6)2, were examined by NMR, ESI-MS, elemental analysis, and CD spectroscopy. The crystal structures of [Cu(L1)(H2O)(ClO4)](ClO4) and [Cu(L3)(ClO4)2] were determined by X-ray diffraction. They are monomeric, distorted octahedral complexes with the quaterpyridine ligand coordinated at the four equatorial positions and one or two perchlorates at the apical position. The crystal structure of [Cu(L1m)(H2O)(ClO 4)](ClO4), which has an achiral quaterpyridine ligand L1m, the meso form of L1, was also determined. Comparison between [Cu(L1)(H 2O)(ClO4)](ClO4) and [Cu(L1m)(H 2O)(ClO4)](ClO4) shows small differences between the two structures. CD analyses of mononuclear CuII complexes of sterically demanding L2-4 indicate that these structures require a helical twist in the ligand. The crystal structure of [Cu2(L3) 2](PF6)2 shows that it is a two-metal two-ligand double-stranded helical structure. Solution NMR studies of the dinuclear CuI complexes show that each sample consists of two diastereomers with moderate to high diastereoselectivity (52-99 %). With L1m, head-to-head and head-to-tail configurational isomers were formed in an almost 1:1 ratio. Heterostranded helicates could also be formed with two different chiral ligands but selectivity favors the homostranded one. DFT calculations on the homostranded helicates yield evidence that interactions between the chiral groups of the ligand strands in the helicate are not solely responsible for determining the helical chirality of the CuI complexes. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Keywords

Circular dichroism, Copper, Helical structures, Quaterpyridine ligands

Publication Date

2011

Source Publication Title

European Journal of Inorganic Chemistry

Volume

2011

Issue

33

Start Page

5112

End Page

5124

Publisher

Wiley-VCH Verlag

DOI

10.1002/ejic.201100630

Link to Publisher's Edition

http://dx.doi.org/10.1002/ejic.201100630

ISSN (print)

14341948

ISSN (electronic)

10990682

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