Xu X, Doyle MP. Enantiomer recognition of amides by dirhodium(II) tetrakis[methyl 2-oxopyrrolidine-5(S)-carboxylate].
Inorg Chem 2011;
50:7610-7. [PMID:
21736309 DOI:
10.1021/ic200609u]
[Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Association constants of the chiral dirhodium(II) carboxamidate Rh(2)(5S-MEPY)(4) with Lewis bases including acetonitrile and amides have been determined by UV-vis titration experiments. With chiral lactams and acyclic acetamides in their R- and S-configurations equilibrium constants with chiral dirhodium carboxamidates are measures of chiral differentiation, and equilibrium constant ratios as high as three have been determined. From equilibrium associations with acetamide, N-methylacetamide, and N,N-dimethylacetamide, as well as equilibrium constants for lactams and acyclic amides, higher values occur when both the amide carbonyl oxygen and N-H are bound to Rh(2)(5S-MEPY)(4). This cooperative bonding mode is confirmed by NMR measurements that show a distinctive shift of a N-H absorption, as well as perturbation of the ligands on dirhodium compound, and they suggest N-H association with a ligated oxygen of Rh(2)(5S-MEPY)(4). Measurements were made on the dirhodium(II) compound from which protective axial ligands have been removed to enhance their reliability.
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