Organometallic Nucleophiles and Pd: What Makes ZnMe2 Different? Is Au Like Zn?

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• 作者：Juan delPozo ; Estefan铆a Gioria ; Juan A. Casares ; Rosana 脕lvarez ; Pablo Espinet
• 刊名：Organometallics
• 出版年：2015
• 出版时间：July 13, 2015
• 年：2015
• 卷：34
• 期：13
• 页码：3120-3128
• 全文大小：532K
• ISSN：1520-6041

文摘

The cis/trans isomerization of [PdMeAr(PR₃)₂] complexes (Ar = C₆F₅, C₆F₃Cl₂) can take place spontaneously (via dissociation and topomerization, studied experimentally) or be catalyzed by ZnMe₂. The latter mechanism, studied by DFT methods, involves methyl exchange between Pd and Zn. The study of this catalyzed isomerization shows that, in contrast with the typical acidic behavior of Zn in ZnMeCl, Zn in ZnMe₂ (or, more exactly, the ZnMe bond) behaves as a strong basic center, able to attack the relatively high in energy acceptor orbital at Pd in fairly electron rich Pd complexes such as [PdArMeL₂] or [PdMe₂L₂]. This makes the two reagents very different in Negishi couplings. The catalyzed isomerization occurs via transmetalation; thus, both processes are connected. A comparison of the Pd/Zn intermediates and transition states with those found previously for Pd/Au transmetalations reveals very similar structures with intermetallic distances in the order of or noticeably shorter than the sum of the vdW radii, regardless of the nature of the metal (metallophilic Au or nonmetallophillic Zn). These short distances are associated with the involvement of the metals in 3c2e electron deficient bonds during R group transmetalation. In this respect, there is a remarkable similarity to the structurally known behavior of main-group electron-deficient compounds, which supports a unified view of the transmetalation processes.