Tricarbonylrhenium(I) halide complexes of chiral non-racemic 2-(dioxolanyl)-(dioxanyl)pyridine ligands: synthesis, NMR and DFT calculations.

Heard, Peter J, King, Paul M, Sroisuwan, Phunrawie and Kaltsoyannis, Nikolas (2003) Tricarbonylrhenium(I) halide complexes of chiral non-racemic 2-(dioxolanyl)-(dioxanyl)pyridine ligands: synthesis, NMR and DFT calculations.

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Abstract

The chiral non-racemic O/N/O donor ligands 2-[(4R,5R)-4,5-dimethyl-1,3-dioxolan-2-yl]-6-[(4R,6R)-4,6-dimethyl-1,3-dioxan-2-yl]pyridine and 2-[(4R,5R)-4,5-dimethyl-1,3-dioxolan-2-deuteryl]-6-[(4R,6R)-4,6-dimethyl-1,3-dioxan-2-yl]pyridine were prepared in a stepwise fashion form 2,6-dibromopyridine. Reaction with the pentacarbonylhalogenorhenium(I) compounds yields the complexes [ReX(CO)3L], in which the ligands act in a N/O bidentate chelate fashion. There are eight possible diastereoisomers, three of which are observable in solution. DFT calculations indicate that the relative stability of the diastereoisomers is SR5>RR5>SS5≈RS5>RS6>SS6>RR6>SR6. Above ambient temperature, a dynamic process leads to the exchange of 2 of the 3 diastereoisomers: the free energy of activation is ca. 79 kJ mol−1. The results of the DFT calculations and the magnitude of ΔG‡ suggest the dynamic process to be the flip of the co-ordinated acetal ring. DFT calculations on the [ReX(CO)3] complexes of chiral non-racemic 2-(dioxolanyl)-6-(dioxanyl)pyridines, in which the ligands coordinate in a bidentate N/O fashion, indicate that binding of the five-membered dioxolanyl ring is strongly favoured over that of the six-membered dioxanyl ring. In solution 3 of the 8 possible diastereoisomers are observed, two of which undergo exchange above ambient temperature.

Item Type: Article
Additional Information: This is the author's final version of the work after peer review. This article was originally published in the Polyhedron Journal in 2003 by Elsevier. The published article can be found at http://dx.doi.org/10.1016/j.poly.2003.08.012
Keywords: Tricarbonylrhenium(I) halide complexes, Diastereoisomers, 1H NMR, DFT calculations, Acetal ligands
Divisions: ?? GlyndwrUniversity ??
Depositing User: ULCC Admin
Date Deposited: 05 Oct 2011 09:13
Last Modified: 11 Dec 2017 20:05
URI: http://glyndwr.repository.guildhe.ac.uk/id/eprint/140

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