The Reaction of Carbon Dioxide with Palladium−Allyl Bonds

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• 作者：Jianguo Wu ; Jennifer C. Green ; Nilay Hazari ; Damian P. Hruszkewycz ; Christopher D. Incarvito ; Timothy J. Schmeier
• 刊名：Organometallics
• 出版年：2010
• 出版时间：December 13, 2010
• 年：2010
• 卷：29
• 期：23
• 页码：6369-6376
• 全文大小：923K
• 年卷期：v.29,no.23(December 13, 2010)
• ISSN：1520-6041

文摘

A family of palladium allyl complexes of the type (2-methylallyl)₂Pd(L) (L = PMe₃ (1), PEt₃ (2), PPh₃ (3), NHC (4); NHC = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) have been prepared through the reaction of (2-methylallyl)₂Pd with the appropriate free ligand. Compounds 1−4 contain one η¹- and one η³-2-methylallyl ligand, and 3 was characterized by X-ray crystallography. These complexes react rapidly with CO₂ at low temperature to form well-defined unidentate palladium carboxylates of the type (η³-2-methylallyl)Pd(OC(O)C₄H₇)(L) (L = PMe₃ (6), PEt₃ (7), PPh₃ (8), NHC (9)). The structure of 9 was elucidated using X-ray crystallography. The mechanism of the reaction of 1−4 with CO₂ was probed using a combination of experimental and theoretical (density functional theory) studies. The coordination mode of the allyl ligand is crucial, and whereas nucleophilic η¹-allyls react rapidly with CO₂, η³-allyls do not react. We propose that the reaction of palladium η¹-allyls with CO₂ does not proceed via direct insertion of CO₂ into the Pd−C bond but through nucleophilic attack of the terminal olefin on electrophilic CO₂, followed by an associative substitution at palladium.