Redox Reactions in Palladium Catalysis: On the Accelerating and/or Inhibiting Effects of Copper and Silver Salt Additives in Cross-Coupling Chemistry Involving Electron-rich Phosphine Ligands
Redox Reactions in Palladium Catalysis: On the Accelerating and/or Inhibiting Effects of Copper and Silver Salt Additives in Cross-Coupling Chemistry Involving Electron-rich Phosphine Ligands
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DOI：
10.1002/anie.201202504
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Schoenebeck, Franziska
中科院分区：
文献类型：
--
作者：
Aufiero, Marialuisa;Proutiere, Fabien;Schoenebeck, Franziska
钯催化的交叉偶联反应广泛用于构建碳-碳或碳-杂原子键。[1]这些转变通常由一种以上的金属辅助，Cu/Pd可能是最常用的组合之一，例如在Sonogashira和Stille反应中。[2]Cu盐在这些转化中的确切作用尚未完全了解，但CuI被认为在Sonogashira偶联中在炔基向Pd的转移中起催化、加速作用（通过形成有机铜物质[Cu（C CR）]，其进而更容易转移到PdII，方案1）。[3]其他的报道也表明在Stille和Suzuki反应中，CuI盐通过有机铜物种促进金属转移。[4，5]另一方面，CuI也具有清除配体的作用。[6，7] Chen及其同事最近补充了铜效应的另一种可能性，他们报告了铂上甲基的金属转移，涉及PtII-CuI双金属物种。[8]与Cu盐的这些“加速”作用相反，Buchwald和同事还报道了Cu盐在芳基氯的Sonogashira交叉偶联反应中的抑制作用。[9]近年来，随后开发了许多替代的Sonogashira转化的无Cu变体，或涉及Ag盐的过程[10]。[11]我们在此报告我们的观察结果的氧化还原转换的Pd 0催化剂双核PdI配合物的存在下，铜和银盐，并解决的起源增强和/或抑制的交叉偶联反应的存在下，氧化性盐。我们的研究结果表明，替代交叉偶联循环的可能性，涉及Pd 0/PdII和Cu（如图1所示），目前公认的共存，协同循环，涉及Pd 0/PdII和铜。
Palladium-catalyzed cross-coupling reactions are widely used to construct carbonÀcarbon or carbonÀheteroatom bonds.[1] These transformations are frequently assisted by more than one metal, and Cu/Pd is probably one of the most frequently applied combinations, for example, in the Sonogashira and Stille reactions.[2] The precise effects of Cu salts in these transformations are not fully understood, but CuI is thought to play a catalytic, accelerating role in the transfer of an alkynyl group to Pd in the Sonogashira coupling (through formation of an organocopper species,[Cu (C CR)], which in turn is more readily transferred to PdII, Scheme 1).[3] Other reports suggest the facilitation of transmetalation by CuI salts via organocopper species in the Stille and Suzuki reactions also.[4, 5] On the other hand, a ligand-scavenging effect was also ascribed to CuI.[6, 7] Another possibility of Cu effect was added by Chen and co-workers recently, who reported a transmetalation of a methyl group at platinum, involving a PtII-CuI bimetallic species.[8] In contrast to these “accelerating” effects of Cu salts, Buchwald and co-workers also reported an inhibitory effect of Cu salts in Sonogashira cross-coupling reactions of aryl chlorides.[9] A number of alternative, Cu-free variants of the Sonogashira transformation, or processes involving Ag salts instead,[10] were subsequently developed in recent years.[11] We herein report our observations of redox transformations of Pd0 catalysts to dinuclear PdI complexes in the presence of Cu and Ag salts, and address the origin of enhancement and/or inhibition of cross-coupling reactivity in the presence of oxidizing salts. Our results suggest the possibility of alternative cross-coupling cycles involving bimetallic PdI over the currently accepted co-existing, synergistic cycles involving Pd0/PdII and Cu (as shown in Scheme 1).