A detailed NMR study of the solution stereodynamics in tricarbonylrhenium(I) halide complexes of the non-racemic chiral ligand 2,6-bis[(4R,5R)-dimethyl-1,3-dioxan-2-yl]pyridine (L1) and the molecular structure of fac-[ReBr(CO)3(L1)]

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J.-Chem.-Soc.-Dalton-Trans.-1999-4495–4501Download

Author(s): Heard Peter J. | King Paul M. | Bain Alex. D. | Hazendonk Paul | Tocher Derek A.

Type of publication: Journal paper

Abstract: Tricarbonylrhenium(I) halide complexes of the non-racemic chiral ligand 2,6-bis[(4R,5R)-dimethyl-1,3-dioxan-2-yl]pyridine (L1), namely fac-[ReX(CO)3(L1)] (X = Cl, Br or I), have been prepared. In these complexes the ligand is bound in a bidentate fashion, with the N atom of the pyridine ring and an O atom of one of the acetal rings co-ordinated to the octahedral metal centre. The bidentate mode is confirmed by the crystal structure of fac-[ReBr(CO)3(L1)]. There are four possible diastereoisomers, depending on the configuration at the metal centre and at the acetal-carbon atom of the co-ordinated ring; the crystal structure of fac-[ReBr(CO)3(L1)] shows that the SR diastereoisomer is present in the solid-state. In solution, three of the four possible diastereoisomers are observed, namely SR, RR and SS; their relative populations are in the order SR > RR > SS. Above ambient temperature the complexes are stereochemically non-rigid. The fluxional kinetics have been measured by a combination of standard band shape analysis and selective inversion experiments. Two distinct processes are present: an acetal ring flip and exchange of the pendant and co-ordinated acetal rings. The latter process occurs via two independent mechanisms, namely tick-tock and rotation pathways. The activation energies for the stereodynamics are in the ranges 72–73 kJ mol–1 (tick-tock), 77–78 kJ mol–1 (acetal ring flip) and 83–90 kJ mol–1 (rotation) at 298 K.

Published URL: https://pubs.rsc.org/en/content/articlelanding/1999/dt/a904026i

Date Published: November 11 1999

Publication title: Journal of the Chemical Society | Dalton Transactions

Publisher: Royal Society of Chemistry

Place of publication: London

Pages: 4495-4501

Subject(s): Chemistry

DOI: https://doi.org/10.1039/A904026I

Keywords: tricarbonylrhenium(I) | halide complexes | fac-[ReBr(CO)3(L1)] | 2,6-bis[(4R,5R)-dimethyl-1,3-dioxan-2-yl]pyridine

Depositing User: Hasnah Patel