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Unsymmetrical Pincer N-Heterocyclic Carbene–Nitrogen–Phosphine Chelated Palladium(II) Complexes: Synthesis, Structure, and Reactivity in Direct Csp2–H Arylation of Benzoxazoles
Organometallics ( IF 2.5 ) Pub Date : 2018-02-19 00:00:00 , DOI: 10.1021/acs.organomet.8b00005 Yaqiu Li 1 , Xiaojun Yu 1 , Yangdiandian Wang 1 , Haiyan Fu 1 , Xueli Zheng 1 , Hua Chen 1 , Ruixiang Li 1
Organometallics ( IF 2.5 ) Pub Date : 2018-02-19 00:00:00 , DOI: 10.1021/acs.organomet.8b00005 Yaqiu Li 1 , Xiaojun Yu 1 , Yangdiandian Wang 1 , Haiyan Fu 1 , Xueli Zheng 1 , Hua Chen 1 , Ruixiang Li 1
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An unsymmetrical pincer N-heterocyclic carbene–nitrogen–phosphine (CNP) and its palladium complexes PdCl2(κ2-CP) (4) and [PdCl(κ3-CNP)]PF6 (5·PF6) were synthesized. NMR spectra disclosed that the transformation of complex 4 structure occurred in the solution. Further NMR experimental and single crystal structure analysis of complex 4 provided unequivocal and structural evidence for the formation of complex [PdCl(κ3-CNP)]Cl (5·Cl) in the solution of complex 4. The catalytic performance of palladium complexes 4 and 5·PF6 was investigated with the direct Csp2–H arylation of benzoxazoles with aryl bromides. Notably, aryl bromides could give up to 97% arylation products in the presence of 0.5% complex 4. For ortho-substituted substrates, the steric hindrance had a significant impact, but product yields could be improved remarkably by extending reaction time. This result implied the catalytic active species in this system was stable and kept in a long lifetime. The flexible backbone and unsymmetrical pincer structure with a flank N-heterocyclic carbine should be a feasible strategy to realize an efficient catalytic transformation. This simple catalyst system first realized the direct arylation of aryl bromides with a catalyst loading as low as 0.25% without excessive base and copper as assistant catalyst.
中文翻译：
不对称的N型杂环卡宾-氮-膦螯合钯（II）配合物：苯并恶唑的直接Csp 2 -H芳构化反应的合成，结构和反应性
不对称钳形ñ -杂环卡宾-氮-膦（CNP）和它的钯络合物的PdCl 2（κ 2 -CP）（4）和[的PdCl（κ 3 -CNP）] PF 6（5·PF 6）的合成。NMR光谱揭示在溶液中发生了复合物4结构的转变。此外NMR实验和复杂的单晶结构分析4为复合物的形成提供明确和结构证据[的PdCl（κ 3 -CNP）] Cl（上5·氯）在复杂的解决方案4。钯配合物的催化性能通过苯并恶唑与芳基溴化物的直接Csp 2 -H芳基化研究了4和5·PF 6。值得注意的是，在0.5％的络合物4的存在下，芳基溴化物最多可提供97％的芳基化产物。对于邻位取代的底物，位阻具有显着影响，但可通过延长反应时间显着提高产物收率。该结果表明该体系中的催化活性物质是稳定的，并保持较长的寿命。灵活的主干和N侧面的不对称钳形结构-杂环卡宾应该是实现有效催化转化的可行策略。这种简单的催化剂系统首先实现了芳基溴化物的直接芳基化，其催化剂负载量低至0.25％，而没有过多的碱和铜作为辅助催化剂。
更新日期：2018-02-21
中文翻译：
不对称的N型杂环卡宾-氮-膦螯合钯（II）配合物：苯并恶唑的直接Csp 2 -H芳构化反应的合成，结构和反应性
不对称钳形ñ -杂环卡宾-氮-膦（CNP）和它的钯络合物的PdCl 2（κ 2 -CP）（4）和[的PdCl（κ 3 -CNP）] PF 6（5·PF 6）的合成。NMR光谱揭示在溶液中发生了复合物4结构的转变。此外NMR实验和复杂的单晶结构分析4为复合物的形成提供明确和结构证据[的PdCl（κ 3 -CNP）] Cl（上5·氯）在复杂的解决方案4。钯配合物的催化性能通过苯并恶唑与芳基溴化物的直接Csp 2 -H芳基化研究了4和5·PF 6。值得注意的是，在0.5％的络合物4的存在下，芳基溴化物最多可提供97％的芳基化产物。对于邻位取代的底物，位阻具有显着影响，但可通过延长反应时间显着提高产物收率。该结果表明该体系中的催化活性物质是稳定的，并保持较长的寿命。灵活的主干和N侧面的不对称钳形结构-杂环卡宾应该是实现有效催化转化的可行策略。这种简单的催化剂系统首先实现了芳基溴化物的直接芳基化，其催化剂负载量低至0.25％，而没有过多的碱和铜作为辅助催化剂。
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