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Synthesis and structural characterization of homochiral coordination polymers with imidazole-based monocarboxylate ligands

Abstract

Chiral Na[(S)-LR] (R = Me, 1a; iPr, 1b; CH2iPr, 1c, and (S)-secBu, 1d) and Na[(R) LR] (R = Me, 1a’) compounds were synthesised following standard procedures. New compounds 1d and 1a’ were analytical and spectroscopically characterised. 1a and 1c were structurally identified by single-crystal X ray diffraction methods as homochiral 2D coordination polymers {Na(H2O)[(S)-LMe]}n and {Na[(S)-LCH2iPr]}n, respectively. Both (S) 2alkyl,2-(1H-imidazol-1-yl)acetate anions displayed unprecedented coordination modes in these coordination polymers: 32OO’ for 1a and 42O2O’ for 1c. Enantiomeric species 1a’, {Na(H2O)[(R)-LMe]}n, showed the same X ray powder diffractogram (XRPD) that 1a, in agreement with a similar crystal structure. DFT calculations on the [LR]- anions confirmed their coordination capabilities as ditopic linkers. In fact, the reaction of Na[LR] with several metal salts yielded the following coordination polymers: {Ag[(S)-LMe]}n, 2a, {Ag[(R)-LMe]}n, 2a’, {Cu[(S)-LR]2}n (R = Me, 3a; iPr, 3b), {Cu[(R)-LMe]}n, 3a’, {Zn[(S)-LR]2}n (R = Me, 4a; iPr, 4b; (S)-secBu, 4d) and {Zn[(R)-LMe]2}n, 4a’. For known 3a and 4a, this procedure is a new synthetic route that avoided high temperature reaction conditions. New complexes 2, 3a’,b, and 4a’,b,d were characterised by elemental analysis, infrared, XRPD methods and single-crystal X-ray for 2a. This complex is also a two-dimensional coordination polymer in which the [(S) LMe]- anion acts as µ4N,2O,2O’ bridging ligand. Compounds 1-4a’ are the first examples of homochiral coordination polymers with imidazole-monocarboxylate ligands based on non-natural amino acids. Preliminary studies in the metal-catalysed preparation of chiral α aminophosphonates were carried out but, unfortunately, no enantioselectivity was observed.

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Publication details

The article was received on 22 Mar 2019, accepted on 15 May 2019 and first published on 15 May 2019


Article type: Paper
DOI: 10.1039/C9DT01237K
Dalton Trans., 2019, Accepted Manuscript

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    Synthesis and structural characterization of homochiral coordination polymers with imidazole-based monocarboxylate ligands

    E. Borrego-Blanco, A. I. Nicasio, E. Alvarez González, F. Montilla, J. M. Córdoba and A. Galindo, Dalton Trans., 2019, Accepted Manuscript , DOI: 10.1039/C9DT01237K

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