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|Title:||Intramolecular Se center dot center dot center dot N nonbonding interactions in low-valent organoselenium derivatives: A detailed study by H-1 and Se-77 NMR spectroscopy and X-ray crystallography|
|Keywords:||Monomeric Selenolato Complexes|
|Publisher:||WILEY-V C H VERLAG GMBH|
|Citation:||CHEMISTRY-A EUROPEAN JOURNAL, 5(5), 1411-1421|
|Abstract:||A series of novel low-valent organoselenium compounds stabilized by Se...N intramolecular interactions has been synthesized. The existence of Se...N nonbonding interactions was determined by H-1 and Se-77 NMR spectroscopy and X-ray crystallography. These interactions result in an apparent downfield shift of the Se-77 NMR signals; the shift values roughly correspond with the strength of the Se...N interaction. Single-crystal X-ray studies show that the strength of the Se...N interactions depends on the relative electronegativity of the group attached to the selenium and the nature of the heteroatom. These interactions lengthen the Se-X (X = Se, Cl, Br, I, CH2-) bond trans to the N...Se bond and increase the possibility of nucleophilic attack on the selenium. In addition to the Se...N intramolecular interaction, Se...X (X = Cl, Br, I) intermolecular interactions were observed in [2-(4,4-dimethyl-2-oxazolinyl)phenyl]-selenenyl chloride (4), bromide (5), and iodide (6), indicative of the hypervalent (pseudo-high-valent) nature of the selenium. The strength of the Se...N intramolecular interaction decreases in the order RSeCl, RSeBr, RSeI, whereas the Se...X intermolecular interaction increases in the same order. The aryl benzylic compounds [2-(4,4-dimethyl-2-oxazolinyl)phenyl]benzyl selenide (7), alpha,alpha'-di[2-(4,4-dimethyl-2-oxazoliny1)-phenylselenenyl]-m-xylene (8), alpha,alpha'-di[2-(4,4-dimethyl-2-oxazolinyl)phenyl-selenenyl]-o-xylene (9), and 1,3,5-tri[2-(4,3-dimethyl-2-oxazolinyl)phenylselenenyl]-2,4,6-trimethylbenzene (10) are unusually stable and also show weak Se...N interactions in the solid state. The strong Se...N interactions in all the compounds suggest that the sp(2) nitrogen may coordinate with the selenium more strongly than the sp(3) nitrogen and the resonance contributions from the five-membered heterocyclic rings further increase the extent of Se...N interactions between selenium and tertiary nitrogen. A correlation between the Se...N intramolecular distance and the Se-77 chemical shift was attempted.|
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