Role of the Ligand and of the Size and Flexibility of the Palladium-Ancillary Ligand Cycle on the Reactivity of Substituted Alkynes toward Palladium(0) Complexes Bearing Potentially Terdentate Nitroge

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• 作者：Luciano Canovese ; Fabiano Visentin ; Gavino Chessa ; Paolo Uguagliati ; Carlo Levi ; Alessandro Dolmella ; Giuliano Bandoli
• 刊名：Organometallics
• 出版年：2006
• 出版时间：October 23, 2006
• 年：2006
• 卷：25
• 期：22
• 页码：5355 - 5365
• 全文大小：310K
• 年卷期：v.25,no.22(October 23, 2006)
• ISSN：1520-6041

文摘

The reaction between palladium(0) complexes bearing potentially terdentate ligands and dimethylacetylenedicarboxylate (DMA) to give the corresponding palladacyclopentadiene complexes was studiedunder kinetic conditions. The reactivity of the complexes was markedly influenced by the nature of theancillary ligand. Thus, when pyridyldithioether (SNS) and dipyridylthioether (NSN) ligands are used,the reactivity and the rate law of the corresponding derivatives are similar to those of the unsubstitutedbidentate pyridylthioether substrates and, therefore, a marked rate increase can be obtained only byreduction of the olefin steric requirement. When terdentate NNN ligands are used, an apparent differencein reactivity between the derivatives bearing the pyridine-amine-pyridine and pyridine-amine-quinolineligands is observed. On the basis of a detailed structural study (NMR, X-ray) and on kinetic investigations,an interpretation which takes into account the flexibility of the cycle formed between the ligand andpalladium is proposed. Thus, irrespective of the size of the cycle, the complexes in which the ligandforms flexible cycles undergo ring opening less easily, with a consequent reduction of reactivity.Conversely, rigid rings cannot undergo associative attack without companion ring opening, thisphenomenon being crucial in favoring the alkyne attack.