Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp³)–H arylation with iodoarenes were carried out, to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes undergo the key C–H activation step. The ubiquitous base Na₂CO₃ is found to hinder catalysis; replacement of Na₂CO₃ with NaO^tBu gave improved catalytic turnovers under milder conditions. Deprotonation of the 8-aminoquinoline derivative N-(quinolin-8-yl)pivalamide (1a) at the amide nitrogen using NaH, followed by reaction with NiCl₂(PPh₃)₂ allowed for the isolation of complex Ni([AQ^piv]-κN,N)₂ (3) with chelating N-donors (where [AQ^piv] = C₉NH₆NCO^tBu). Complex 3 is a four-coordinate disphenoidal high-spin Ni(II) complex, excluding short anagostic Ni--^tBu hydrogen interactions. Complex 3 reacts with the paddle-wheel [Ph₃PNi(μ-CO₂^tBu)₂]₂ (6·PPh₃) or ^tBuCO₂H to give insoluble {[AQ^piv]Ni(O₂C^tBu)}₂ (5). Dissolution of 5 in donor solvents L (L= DMSO and DMF) gave a paramagnetic intermediate assigned by NMR as [AQ^piv]Ni(O₂C^tBu)L (5·L) and equilibrium reformation of 3 and 6·L. DFT calculations support this equilibrium in solution. Both 3 and 5 undergo C–H activation at temperatures as low as 80 °C and in the presence of PR₃ (PR₃ = PPh₃, PⁱBu₃) to give Ni(C₉NH₆NCOCMe₂CH₂-κN,N,C)PR₃ (7·PR₃). The C–H functionalization reaction orders with respect to 7·PⁱBu₃, iodoarenes, and phosphines were determined. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C–H functionalization step; DFT calculations were also carried out to support this finding. When Na₂CO₃ is used as the base, the rate determination step for C–H functionalization appears to be 8-aminoquinoline deprotonation and binding to Ni. The carbonate anion was also observed to provide a deleterious NMR-inactive low-energy off-cycle resting state in catalysis. Replacement of Na₂CO₃ with NaO^tBu improved catalysis at milder conditions and made carboxylic acid and phosphine additives unnecessary. Complex 3 and its functionalized analogues were observed as the catalyst resting state under these conditions.

中文翻译：

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8-氨基喹啉导向的镍催化 C(sp3)-H 官能化的机制：顺磁性 Ni(II) 物种和碳酸盐作为碱的有害影响

研究了 8-氨基喹啉导向的镍催化 C(sp ³ )-H 与碘芳烃的芳基化机理，以确定催化剂的静止状态并优化催化性能。顺磁性配合物经历关键的 C-H 激活步骤。发现无处不在的碱 Na ₂ CO ₃会阻碍催化；在较温和的条件下，用 NaO ^t Bu替代 Na ₂ CO ₃提高了催化转化率。使用 NaH 在酰胺氮处对8-氨基喹啉衍生物N- (quinolin-8-yl)pivalamide ( 1a ) 进行去质子化，然后与 NiCl ₂ (PPh ₃ ) _{2 反应}允许分离复合物 Ni([AQ ^piv ]-κ N , N ) ₂ ( 3 ) 与螯合 N 供体（其中 [AQ ^piv ] = C ₉ NH ₆ NCO ^t Bu）。配合物3是一个四配位的蝶形高自旋 Ni(II) 配合物，不包括短的 Anagostic Ni-- ^t Bu 氢相互作用。配合物3与桨轮反应 [Ph ₃ PNi(μ-CO ₂ ^t Bu) ₂ ] ₂ ( 6·PPh ₃ ) 或^t BuCO ₂H 得到不溶性 {[AQ ^piv ]Ni(O ₂ C ^t Bu)} ₂ ( 5 )。5在供体溶剂 L（L = DMSO 和 DMF）中的溶解产生了一种顺磁性中间体，由 NMR 指定为 [AQ ^piv ]Ni(O ₂ C ^t Bu)L ( 5·L ) 和3和6·L 的平衡重整。DFT 计算支持解决方案中的这种平衡。两个3和5经受C-H活化在温度低至80℃，并在PR的存在₃（PR ₃ = PPH ₃，P^我Bu ₃ ) 得到Ni(C ₉ NH ₆ NCOCMe ₂ CH ₂ -κ N , N , C )PR ₃ ( 7·PR ₃ )。确定了关于7·P ⁱ Bu ₃、碘芳烃和膦的 C-H 官能化反应顺序。使用电子上不同的芳基碘化物进行的哈米特分析表明，C-H 功能化步骤存在协同氧化加成机制；还进行了 DFT 计算以支持这一发现。当 Na ₂ CO ₃用作基础，C-H 功能化的速率确定步骤似乎是 8-氨基喹啉去质子化并与 Ni 结合。还观察到碳酸根阴离子在催化中提供有害的 NMR 非活性低能量非循环静止状态。用 NaO ^t Bu代替 Na ₂ CO ₃改善了在温和条件下的催化作用，并且不需要羧酸和膦添加剂。在这些条件下观察到复合物3及其功能化类似物作为催化剂的静止状态。