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The polarographic behavior of N,N′-ethylenebis(acetylacetoniminato) (baen) and N,N′-ethylenebis(salicylaldehydeiminato) (bisaen) complexes of cobalt(III), nickel(II), and copper(II) in DMF solutions was studied thoroughly. At the dropping mercury electrode, these metal complexes give well-defined cathodic waves corresponding to the reduction of metal(II) to metal(I). A careful and systematic study of the polarographic behavior of β-cis and trans cobalt(III)-baen and -bisaen complexes of the general formulae: CoZY1−a and CoZX21−2b, and that of nickel(II)- and copper(II)-baen complexes, revealed that the unusual stability of the metal(I)-baen and -bisaen complexes can be ascribed mainly to the stable square-planar nature of baen and bisaen. The effect of the replacement of the ligand by the halogen atom was also investigated.
Abstract Under air-oxidation conditions, the reaction of [Co(α-Me-sal2en)] with l-aaH, where α-Me-sal2en represents the dianion of N,N′-ethylenebis(α-niethylsalicylideneaniine) and where l-aaH denotes l-proline, hydroxy-l-proline, or allo-hydroxy-l-proline, proceeded rapidly to yield Λ-cis-β2–[Co(α-Me-sal2en)(l-aa)] stereoselectively, followed by the slow isomerization of the Λ-cis-β2-isomer thus formed to give the corresponding Δ-cis-β2-isomer in a yield of almost 100% under equilibrium conditions. The complexes thus formed were isolated and characterized by the use of their absorption, circular dichroism, and 1H-NMR spectra. The preferential formation of the Λ-cis-β2-isomer in the initial reaction was found to be kinetic in origin. The kinetic stereoselectivity was determined to be 87% for l-proline, 56% for hydroxy-l-proline, and 23% for allo-hydroxy-l-proline by the measurement of the rotation at 435 nm of the reaction solutions. On the other hand, no kinetic differentiation was observed for the formation of the similar cis-β2-complexes with l-alanine, l-valine, l-methionine, l-phenylalanine, l-tryptophan, N-benzyl-l-alanine, and N-methyl-l-alanine. On the basis of these data, the mechanism of the initial complexation was discussed. The high thermodynamic stereoselectivity for Δ-cis-β2-isomer was explained in terms of the intramolecular steric interaction between the pyrrolidine ring of the coordinated l-aa and the distorted α-Me-sal2en ligand in the complex.
Abstract The stability constants, K1, of Δ-β2-diastereomers of mixed ligand cobalt(III) complexes with a chiral quadridentate Schiff base (sal-(R,R)-chxn), derived from salicylaldehyde and (R,R)-1,2-cyclohexanediamine, and d- or l-amino acidate (aa−=gly, ala, val, leu, thr, phe, trp, pro, asp, asn, and glu) were determined spectrophotometrically in water–methanol (2:3 by volume) containing acetate buffer (0.3 mol dm−3) at 22°C: trans-[Co{sal-(R,R)-chxn}(H2O)2]++aa−\oversetK1\ightleftharpoonsΔ-β2-[Co{sal-(R,R)-chxn}(aa)]. The K1 values range from 5.6×106 to 1.2×109 mol−1 dm3 and obey a linear free energy relationship except for d-phe, d-trp, d-asp, d-asn, and d-pro. In the cases of d-phe, d-trp, d-asp, and d-asn, their stability constants are 5–30 times as high as those for the corresponding l-aa. Extraordinary stabilization of the d-phe and d-trp complexes is discussed in terms of the interligand stacking of the aromatic rings between the Schiff base ligand and a side chain of amino acidate on the basis of conformational analysis and 1H NMR spectra.
Abstract Ausgehend von trans‐Diaquokomplexen der beiden Schiffschen Basen wurden bei Reaktion mit zweizähnigen Liganden nur die β‐cis‐Formen als Komplexe (I) und (II) in hohen Ausbeuten erhalten, während bei Umsetzung mit einzähnigen Liganden sich nur die trans‐planaren Komplexe (IIIa) bzw. (IIIb) bildeten, von denen (IIIb) bei Auflösung in Wasser zu (IIIc) und dieser bei Zugabe von Pyridin zu (IIId) reagiert.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNovel nucleophilic substitution reaction by radical cation intermediates. Photosensitized transacetalization via SON1 mechanismS. Hashimoto, I. Kurimoto, Y. Fujii, and R. NoyoriCite this: J. Am. Chem. Soc. 1985, 107, 5, 1427–1429Publication Date (Print):March 1, 1985Publication History Published online1 May 2002Published inissue 1 March 1985https://pubs.acs.org/doi/10.1021/ja00291a062https://doi.org/10.1021/ja00291a062research-articleACS PublicationsRequest reuse permissionsArticle Views485Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Abstract Photosensibilisierte Transacetalisierung der Ether (I) mit Alkoholen wie (II) gibt die Produkte (III), (VI) bzw. (VII) [als Sensibilisatorsystem dient ein binäres System aus einem lichtabsorbietenden kondensierten Kohlenwasserstoff und einem nicht‐lichtabsorbierenden Cyanaromaten, z.B. (IV)/(V) (effektivstes System]: unabhängig, ob von reinem Isomeren (Ib) oder (Ic) oder einem (Ib)/(Ic)‐Gemisch ausgegangen wird, werden stets die trans‐Produkte (VIa) bzw. (V IIa) bzw. (VIIc) bevorzugt gebildet.
