Coordination–Insertion of Norbornene at Gold: A Mechanistic Study

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• 作者：Feriel Rekhroukh ; Laura Estevez ; Christian Bijani ; Karinne Miqueu ; Abderrahmane Amgoune ; Didier Bourissou
• 刊名：Organometallics
• 出版年：2016
• 出版时间：April 11, 2016
• 年：2016
• 卷：35
• 期：7
• 页码：995-1001
• 全文大小：418K
• 年卷期：0
• ISSN：1520-6041

文摘

A detailed experimental/theoretical study of the migratory insertion of norbornene into gold(III)–carbon bonds of discrete (P,C)-cyclometalated gold(III) alkyl complexes is reported. The generation of cationic gold(III) methyl complex 2 by methide abstraction with B(C₆F₅)₃ has been confirmed spectroscopically at low temperature. The DFT-optimized structure of this highly electrophilic species indicates a three-coordinate gold(III) species with T-shaped geometry. In the presence of norbornene, the corresponding gold(III)–olefin complex 3 is formed, and it has been fully characterized by NMR spectroscopy at low temperature. Bonding analysis of this key intermediate confirmed the significantly weaker contribution of metal-to-olefin back-donation with gold compared with the other late transition metals. Upon warm-up, the π complex 3 evolves by insertion of the olefin into the Au(III)–Me bond to form the cationic (P,C)gold(III)–norbornyl complex 4. The mechanism of the double addition has been extensively explored by DFT calculations, and the results strongly support a two-step coordination–migratory insertion pathway. The influence of the unsymmetrical (P,C) bidentate ligand on the kinetic and thermodynamic parameters of the reaction is also discussed. This comprehensive organometallic study provides new important insights into the coordination, structure, and reactivity of gold(III) complexes. It highlights some fundamental similarities but also points out some significant differences with isolobal Pd(II) alkyl complexes.