1H NMR Direct Observation of Enantiomeric Exchange in Palladium(II) and Platinum(II) Complexes Containing N,N' Bidentate Aryl-pyridin-2-ylmethyl-amine Ligands

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• 作者：Virginia Diez ; José ; V. Cuevas ; Gabriel Garcí ; a-Herbosa ; Gabriel Aull&oacute ; n ; Jonathan P. H. Charmant ; Arancha Carbayo ; Asunci&oacute ; n Mu&ntilde ; oz
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：January 22, 2007
• 年：2007
• 卷：46
• 期：2
• 页码：568 - 577
• 全文大小：198K
• 年卷期：v.46,no.2(January 22, 2007)
• ISSN：1520-510X

文摘

The complexes [MCl₂(G SRC="/images/gifchars/kappa.gif" BORDER=0 >²-N~N')] (N~N' = 2-C₅H₄N-CH₂-NHAr; Ar = 4-MeC₆H₄, a; 2,6-Me₂C₆H₃, b; 4-MeOC₆H₄,c; 4-CF₃C₆H₄, d; M = Pd, 1a-d; Pt, 2a-d) have been prepared and fully stereochemically characterized both inthe solid state and in solution. Their behavior in DMSO-d₆ solution is dependent on the substituents of the arylgroup and on the metal. Complexes of palladium with substituents at the para position (1a, 1c, 1d) display adynamic ¹H NMR pattern when the solutions are heated. An enantiomeric exchange Sges/gifchars/lambda.gif" BORDER=0 >/Rges/gifchars/delta.gif" BORDER=0 > is suggested to explainsuch behavior. On the basis of the calculated negative ges/gifchars/Delta.gif" BORDER=0 >S^{ges/entities/thermod.gif">} values, an associative mechanism involving the solventis proposed. Under the same conditions, analogous complexes of platinum (2a, 2c, 2d) proved to be unstable, andrelease of the N~N' ligand was observed. Complexes 1b and 2b show temperature-variable ¹H NMR spectrawithout any evidence accounting for enantiomeric exchange or decoordination. DFT calculations on models of 1aand 1b show that diastereomeric exchange Sges/gifchars/delta.gif" BORDER=0 >/Sges/gifchars/lambda.gif" BORDER=0 > is a process where the complex with the higher sterical hindrance,1b, has a lower energy barrier.