Carbon-sulfur reductive elimination from palladium(IV) sulfinate complexes.
Carbon-sulfur reductive elimination from palladium(IV) sulfinate complexes.
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DOI：
10.1002/anie.201005489
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发表时间：
2011-01
影响因子：
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通讯作者：
Xiaodan Zhao;V. Dong
中科院分区：
文献类型：
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作者：
Xiaodan Zhao;V. Dong
钯配合物是最通用的催化剂之一，能够构建各种键。[1，2]因此，钯配合物的基础研究对实际催化过程的设计和理解产生了很大影响。近年来，人们对钯Ⅳ络合物还原消除形成C <$X键（X= CF_3、C、O、Cl、F）进行了研究。[3-5]尽管含硫产物的重要性，[6]有关C？S键形成反应的机理研究很少。[7]本文报道了新型亚磺酸钯配合物的合成、表征和研究。我们描述了第一次直接观察到的C-S键形成还原消除钯IV配合物。[1c]磺酰氯是钯催化的交叉偶联反应和钯催化的C <$H键氧化的方便和通用的试剂。[8-10] Dubbaka和Vogel已经报道了涉及磺酰氯的交叉偶联反应，该反应通过C <$C还原消除发生，并损失SO2。[9]相反，我们观察到C <$H键氧化，推测是通过C <$S还原消除产生砜。[10]虽然Vogel的交叉偶联反应通过Pd 0/PdII物种发生，但螯合辅助的C？H键氧化反应被认为通过高价Pd物种发生。[11然而，从高价Pd物种中还原消除C？S的直接证据一直难以捉摸。[13]受这一挑战的启发，我们的目标是1）探索磺酰氯作为PdII的氧化剂，2）研究亚磺酸钯（IV）络合物的还原消除。基于以前的报道，[4，5]我们选择[Pd（phpy）2]（1，phpy= 2-苯基吡啶基）作为我们初步研究的模型配合物。已知刚性和富电子的C，N配体稳定PdIV中心并促进碳-碳和碳-杂原子键的形成。[4，5]实际上，在室温下用二氯甲烷中的4-甲基苯磺酰氯（2a）处理络合物1 20分钟得到所需的亚磺酸钯（IV）络合物3a，其分离为黄色固体（66%产率;表1，
Palladium complexes are among the most versatile catalysts that are capable of constructing a variety of bonds.[1, 2] Consequently, fundamental studies on palladium complexes have a great impact on the design and understanding of practical catalytic processes. Studies on reductive elimination to form C¿ X bonds (X= CF3, C, O, Cl, F) from PdIV complexes have recently been achieved.[3–5] Despite the importance of sulfur-containing products,[6] related mechanistic studies on C¿ S bond-forming reactions are rare.[7] Herein we report the synthesis, characterization, and study of novel palladium (IV) sulfinate complexes. We describe the first direct observation of C¿ S bond-forming reductive elimination from PdIV complexes.[1c] Sulfonyl chlorides are convenient and versatile reagents for both palladium-catalyzed cross-coupling reactions and palladium-catalyzed C¿ H bond oxidation.[8–10] Dubbaka and Vogel have reported cross-coupling reactions involving sulfonyl chlorides that occur by C¿ C reductive elimination with loss of SO2.[9] In contrast, we have observed C¿ H bond oxidations that presumably occur by C¿ S reductive elimination to produce sulfones.[10] While Vogel s cross-coupling reaction occurs via Pd0/PdII species, chelation-assisted C¿ H bond oxidation reactions are thought to occur via high-valent Pd species.[11, 12] However, direct evidence for C¿ S reductive elimination from high-valent Pd species has been elusive.[13]Inspired by this challenge, we aimed to 1) explore sulfonyl chlorides as oxidants for PdII and 2) study reductive elimination from palladium (IV) sulfinate complexes. Based on the previous reports,[4, 5] we chose [Pd (phpy) 2](1, phpy= 2-phenylpyridyl) as the model complex for our initial investigations. Rigid and electron-rich C, N ligands are known to stabilize PdIV centers and promote the formation of carbon–carbon and carbon–heteroatom bonds.[4, 5] Indeed, treatment of complex 1 with 4-methylbenzenesulfonyl chloride (2a) in dichloromethane at room temperature for 20 minutes resulted in the desired palladium (IV) sulfinate complex 3a, which was isolated as a yellow solid (66% yield; Table 1,