Copper Complexes with N,N,N-Tridentate Quinolinyl Anilido-Imine Ligands: Synthesis and Their Catalytic Application in Chan−Lam Reactions

The treatment of 2-(ArNC(H))C6H4-HNC9H6N with n-BuLi and the subsequent addition of CuCl2 afforded the anilido-aldimine Cu(II) complexes 1-5 Cu[{2-[ArN=C(H)]C6H4}N(8-C9H6N)]Cl (Ar = 2,6-iPr2C6H3 (1), 2,4,6-(CH3)3C6H2 (2), 4-OCH3C6H4 (3), 4-BrC6H4 (4), 4-ClC6H4 (5)), respectively. All the copper complexes were fully characterized by IR, EPR and HR-MS spectra. The X-ray diffraction analysis reveals that 2 and 4 are mononuclear complexes, and the Cu atom is sitting in a slightly square-planar geometry. These Cu(II) complexes have exhibited excellent catalytic activity in the Chan–Lam coupling reactions of benzimidazole derivatives with arylboronic acids, achieving the highest yields of up to 96%.


Introduction
The construction of C-N bonds is one of the most widely practiced reactions in synthetic chemistry.The name reactions, such as the Buchwald-Hartwig [1,2], Chan-Lam [3,4] and Ullmann [5] reactions, have been extensively explored for C-N bond formation.These reactions have a wide range of applications, such as in pesticide synthesis and pharmaceutical and material chemistry [6].Among these reactions, the Cu-promoted Chan-Lam coupling reaction features the advantages of low cost and operational simplicity and is an efficient synthetic method to construct various carbon-heteroatom bonds.In 1998, this name reaction was first reported to construct C-X bonds through the coupling between arylboronic acids and different nucleophiles in the presence of Cu(OAc) 2 as a catalyst (Scheme 1a) [7][8][9].Since then, Cu and other transition metal-catalyzed Chan-Lam reactions have contributed greatly to C-N bond formation [10][11][12][13].
In addition to metal salts, well-defined copper complexes were also rapidly developed as catalysts for these reactions.Representative examples can be found in Scheme 1b [14][15][16][17][18][19][20][21].In 2000, Collman and co-workers used 10 mol% of simple Cu complex [Cu(OH)•TMEDA] 2 Cl 2 (TMEDA = N,N,N ,N -Tetramethylethylenediamine) to produce a variety of N-arylimidazoles with good-to-excellent yields by cross-coupling arylboronic acids with imidazole compounds [14].In 2018, Schaper et al. synthesized a sulfonato-imino copper(II) complex that can efficiently catalyze the N-arylation or N-alkylation of amines and anilines with arylboronic acids without the need for any bases [18].Recently, Emerson's group reported a new tetradentate NHCcopper(II) complex, which showed good catalytic activity in the Chan-Lam coupling of aniline and phenylboronic acid [20].More recently, Jia et al. developed an efficient method for the copper-promoted Chan-Lam coupling of 1H-imidazole derivatives with arylboronic acids using an N, O-bidentate Cu complex (8.0 mol%) as a catalyst [21].Although considerable progress has been made in this field, there are still limitations, such as long reaction times, high catalyst loading, or the use of a base.Thus, developing novel and efficient catalysts for Chan-Lam coupling under mild conditions is in high demand.
showed good catalytic activity in the Chan-Lam coupling of aniline and phenylboronic acid [20].More recently, Jia et al. developed an efficient method for the copper-promoted Chan-Lam coupling of 1H-imidazole derivatives with arylboronic acids using an N, O-bidentate Cu complex (8.0 mol%) as a catalyst [21].Although considerable progress has been made in this field, there are still limitations, such as long reaction times, high catalyst loading, or the use of a base.Thus, developing novel and efficient catalysts for Chan-Lam coupling under mild conditions is in high demand.Moreover, it is well-accepted that ligands play an important role in catalysis.They can improve the solubility of transition-metal complexes in organic media and modify catalytic activity via the precise control of their electronic and geometric properties [22].Recently, our group has been focusing on synthesizing anilido-imine ligand-supported transition-metal complexes.The corresponding Ni [23], Fe [24], Cr [25] and Cu [26] complexes exhibit moderate to high activities in olefin polymerization and the atom transfer radical polymerization (ATRP) reaction, but studies on organic transformation are less reported.Herein, we report the synthesis of several copper complexes bearing N,N,N-tridentate anilido-imine ligands, which displayed excellent catalytic performance Moreover, it is well-accepted that ligands play an important role in catalysis.They can improve the solubility of transition-metal complexes in organic media and modify catalytic activity via the precise control of their electronic and geometric properties [22].Recently, our group has been focusing on synthesizing anilido-imine ligand-supported transitionmetal complexes.The corresponding Ni [23], Fe [24], Cr [25] and Cu [26] complexes exhibit moderate to high activities in olefin polymerization and the atom transfer radical polymerization (ATRP) reaction, but studies on organic transformation are less reported.Herein, we report the synthesis of several copper complexes bearing N,N,N-tridentate anilido-imine ligands, which displayed excellent catalytic performance in the Chan-Lam coupling of arylboronic acids with benzimidazole derivatives under base-free conditions (Scheme 1c).

Synthesis and Characterization of Ligands and Cu(II) Complexes
The tridentate anilido-imine ligands L1H, L2H, L4H, L5H and Cu(II) complex 1 were prepared according to the literature method [27] and our recent reports [26,28].The ligand L3H and other Cu complexes 2-5 were synthesized following the analogous methods.Cu(II) complex 1 was prepared using the literature method [26].The other Cu complexes (2)(3)(4)(5) were synthesized following the analogous methods.The reactions of ligands L2H-L5H with n-BuLi at −78 • C followed by adding CuCl 2 afforded complexes 2-5 as brown powders in 55-68% yields, respectively (Scheme 2).These complexes are air-and moisture-stable and soluble in common organic solvents (e.g., THF, CH 2 Cl 2 and toluene).Complexes 2-5 were all characterized by HR-MS, EPR (electron paramagnetic resonance) and IR spectroscopy.The HR-MS peaks at 427.1104 (2), 415.0740 (3), 462.9740 (4) and 419.0245 (5) match well with the calculated masses of the cationic species [M-Cl] + (Figures S1-S4).The EPR spectra of complexes 2-5 exhibit the values of g ⊥ around 2.04-2.09and g ⊥ around 2.11-2.16(Figure S5), which are comparable to the EPR data of some reported mononuclear Cu complexes [29] and our previous work [30].In their IR spectra, a strong vibration band at 1602-1613 cm −1 can be assigned to the imine group.The signals between 3100 and 3500 cm −1 of the N-H group in the ligands disappeared in the IR spectra of complexes 2-5, indicating the Cu-N bond formation through the deprotonation of the -NH group.

Synthesis and Characterization of Ligands and Cu(II) Complexes
The tridentate anilido-imine ligands L1H, L2H, L4H, L5H and Cu(II) com were prepared according to the literature method [27] and our recent reports The ligand L3H and other Cu complexes 2-5 were synthesized following the an methods.Cu(II) complex 1 was prepared using the literature method [26].The o complexes (2-5) were synthesized following the analogous methods.The reac ligands L2H-L5H with n-BuLi at −78 °C followed by adding CuCl2 afforded co 2-5 as brown powders in 55-68% yields, respectively (Scheme 2).These compl air-and moisture-stable and soluble in common organic solvents (e.g., THF, CH toluene).Complexes 2-5 were all characterized by HR-MS, EPR (electron param resonance) and IR spectroscopy.The HR-MS peaks at 427.1104 (2), 415.0740 (3), 4 (4) and 419.0245 (5) match well with the calculated masses of the cationic species (Figures S1-S4).The EPR spectra of complexes 2-5 exhibit the values of g⊥ aroun 2.09 and g║ around 2.11-2.16(Figure S5), which are comparable to the EPR data reported mononuclear Cu complexes [29] and our previous work [30].In their IR a strong vibration band at 1602-1613 cm −1 can be assigned to the imine group.The between 3100 and 3500 cm −1 of the N-H group in the ligands disappeared in the tra of complexes 2-5, indicating the Cu-N bond formation through the deproton the -NH group.

Description of the Crystal Structures of Complexes 2 and 4
Crystals 2 and 4 suitable for single-crystal X-ray diffraction were grown fro solutions in CH2Cl2/hexane.X-ray single-crystal diffraction analyses show that cr and 4 are monoclinic with space groups of Cc and P21/c, respectively.The crys are summarized in Table 1.Their molecular structures are depicted in Figures with selected bond

Description of the Crystal Structures of Complexes 2 and 4
Crystals 2 and 4 suitable for single-crystal X-ray diffraction were grown from their solutions in CH 2 Cl 2 /hexane.X-ray single-crystal diffraction analyses show that crystals 2 and 4 are monoclinic with space groups of Cc and P2 1 /c, respectively.The crystal data are summarized in Table 1.Their molecular structures are depicted in Figures 1 and 2, with selected bond lengths and angles.The unit cell of 4 contains two crystallographicallyindependent molecules with similar connectivity and only one molecule is depicted in Figure 2. The central metal Cu is coordinated by three nitrogen atoms and one chlorine atom, and the environment around the metal can be described as a distorted square-planar.The Cu-Cl bond lengths (2.2248(12) Å for 2 and 2.2529(13) Å for 4) are relatively longer than those of 2.1997(13)-2.2001(13)Å in complex [CuCl 2 (Mes-BIAN)] OEt 2 [31].The Cu-N amino bond lengths of 2 and 4 are 1.927(3) Å and 1.956(4) Å, respectively, which are similar to the Cu-N amino bond length (1.939(3) Å) in copper complex 1 [26].The Cu-N imino bond lengths (1.973(3) Å for 2 and 1.980(4) Å for 4) are slightly longer than that of 1 (1.967(3)Å) but much shorter than the bond length of 2.026(1) Å in the sulfonato-imine copper complex [18].

Catalytic Activity
In order to investigate the catalytic properties of copper complexes 1-5 in the C Lam coupling reaction, benzimidazole 6a and phenylboronic acid 7a were set as model substrates.The reaction parameters, such as solvents, reaction time, tempera and catalyst loading, were optimized using complex 1 as a catalyst, and the catalyti sults are shown in Table 2.At first, the solvent effect was investigated using 5 mol complex 1 under an air atmosphere and base-free conditions.The results showed the best catalytic activity was achieved when methanol was used as the solvent to the target product 8a with 90% yield at 50 °C for 20 h (Table 2, entry 1).Using other vents, such as i PrOH, 1,4-Dioxane, DMF, CH3CN, THF, and toluene, under the s conditions gave only trace or low yields (Table 2, entries 2-7).Next, the reaction and temperature were screened.When the reaction time was shortened from 20 h to and 12 h, the yields of 8a were 92% and 90%, respectively (Table 2, entries 8 and 9).ther reducing the reaction time to 8 h slightly decreased the yield to 83% (Table 2, e 10).Since the yields were almost the same at 20 h and 12 h, 12 h was considered the timized reaction time.Upon reducing the reaction temperature from 50 °C to 40 °C yield of 8a increased to 92% (Table 2, entry 11).When the reaction was performed e at 60 °C or room temperature, the yields of desired products dropped slightly (Tab entries 12 and 13).Thus, the best reaction temperature was selected to be 40 °C.A ward, the effect of catalyst loading on the reaction was explored.Changing the cat loading of 1 from 5 mol% to 3 mol%, 2 mol%, and 1 mol% resulted in yields of 93%, and 71%, respectively (Table 2, entries [14][15][16].Therefore, the most suitable catalyst l ing was decided to be 3 mol%.Subsequently, the catalytic activities of catalysts 2-5 tested under the optimized conditions, and complex 3 showed the highest activity, nishing product 8a with 96% yield (Table 2, entries [17][18][19][20].The CuCl2 was also teste the Chan-Lam coupling of 6a and 7a to afford the corresponding product with only yield, showing the important role of the ligand in the catalytic reaction (Table 2, e 21).The control experiment indicated that the coupling reaction did not occur in th sence of any catalyst (Table 2, entry 22).Finally, when the coupling reaction was

Catalytic Activity
In order to investigate the catalytic properties of copper complexes 1-5 in the Chan-Lam coupling reaction, benzimidazole 6a and phenylboronic acid 7a were set as the model substrates.The reaction parameters, such as solvents, reaction time, temperature and catalyst loading, were optimized using complex 1 as a catalyst, and the catalytic results are shown in Table 2.At first, the solvent effect was investigated using 5 mol% of complex 1 under an air atmosphere and base-free conditions.The results showed that the best catalytic activity was achieved when methanol was used as the solvent to give the target product 8a with 90% yield at 50 • C for 20 h (Table 2, entry 1).Using other solvents, such as i PrOH, 1,4-Dioxane, DMF, CH 3 CN, THF, and toluene, under the same conditions gave only trace or low yields (Table 2, entries 2-7).Next, the reaction time and temperature were screened.When the reaction time was shortened from 20 h to 16 h and 12 h, the yields of 8a were 92% and 90%, respectively (Table 2, entries 8 and 9).Further reducing the reaction time to 8 h slightly decreased the yield to 83% (Table 2, entry 10).Since the yields were almost the same at 20 h and 12 h, 12 h was considered the optimized reaction time.Upon reducing the reaction temperature from 50 • C to 40 • C, the yield of 8a increased to 92% (Table 2, entry 11).When the reaction was performed either at 60 • C or room temperature, the yields of desired products dropped slightly (Table 2, entries 12 and 13).Thus, the best reaction temperature was selected to be 40 • C. Afterward, the effect of catalyst loading on the reaction was explored.Changing the catalyst loading of 1 from 5 mol% to 3 mol%, 2 mol%, and 1 mol% resulted in yields of 93%, 84%, and 71%, respectively (Table 2, entries 14-16).Therefore, the most suitable catalyst loading was decided to be 3 mol%.Subsequently, the catalytic activities of catalysts 2-5 were tested under the optimized conditions, and complex 3 showed the highest activity, furnishing product 8a with 96% yield (Table 2, entries 17-20).The CuCl 2 was also tested in the Chan-Lam coupling of 6a and 7a to afford the corresponding product with only 48% yield, showing the important role of the ligand in the catalytic reaction (Table 2, entry 21).The control experiment indicated that the coupling reaction did not occur in the absence of any catalyst (Table 2, entry 22).Finally, when the coupling reaction was performed under an inert atmosphere, no product 8a was observed, indicating the key role of air in the catalytic reaction (Table 2, entry 23).
We next examined the substrate generality of this coupling reaction (Table 3).The phenylboronic acids with electron-deficient and electron-rich groups efficiently proceeded to afford the desired products (8a-8p) in 75-96% yields.Various substituents, including methyl, methoxyl, fluoro, chloro, bromo, phenyl, aceto, ester and cyano, were tolerated, indicating good functional group compatibility.The steric effect has relatively little influence on this coupling reaction, which can be seen from 8b-8d and 8g-8h.However, heteroaryl boronic acids such as furan-2-ylboronic acid and thiophen-2-ylboronic acid were not suitable for the present catalytic system, and only trace amounts of the desired products-8q and 8r-were obtained.Gratifyingly, disubstituted 1,4-phenylenediboronic acid was also smoothly coupled with benzimidazole 6a to produce the corresponding 8s in 76% yield.Further, the reaction of 6 with different monosubstituted and disubstituted groups with phenylboronic acid gave the corresponding products in good-to-excellent yields (8t-8y).The reaction between dimethylbenzimidazole and F-or OMe-substituted phenylboronic acid also afforded the corresponding products, 8x and 8y, in 88% and 90% yields, respectively.We next examined the substrate generality of this coupling reaction (Table 3).The phenylboronic acids with electron-deficient and electron-rich groups efficiently proceeded to afford the desired products (8a-8p) in 75-96% yields.Various substituents, including methyl, methoxyl, fluoro, chloro, bromo, phenyl, aceto, ester and cyano, were tolerated, indicating good functional group compatibility.The steric effect has relatively little influence on this coupling reaction, which can be seen from 8b-8d and 8g-8h.However, heteroaryl boronic acids such as furan-2-ylboronic acid and thiophen-2-ylboronic acid were not suitable for the present catalytic system, and only trace  Taking previous reports [19,[32][33][34] into account, a plausible mechanism for this Cucatalyzed Chan-Lam reaction is depicted in Scheme 3. Initially, phenylboronic acid 7a undergoes a transmetallation reaction with Cu II complex A to produce Cu II species B and ClB(OH) 2 .Species B reacts with benzimidazole 6a to form a Cu II intermediate C, which lowers the Cu III /Cu II reduction potential [35].Then, intermediate C undergoes a disproportionation process [18,[36][37][38]                        Taking previous reports [19,[32][33][34] into account, a plausible mechanism for this Cu-catalyzed Chan-Lam reaction is depicted in Scheme 3. Initially, phenylboronic acid 7a undergoes a transmetallation reaction with Cu II complex A to produce Cu II species B and ClB(OH)2.Species B reacts with benzimidazole 6a to form a Cu II intermediate C, which lowers the Cu III /Cu II reduction potential [35].Then, intermediate C undergoes a disproportionation process [18,[36][37][38]

General Considerations
All manipulations (except the catalytic reactions) under a nitrogen atmosphere were carried out using a Schlenk line.THF was distilled from Na and benzophenone under N2 before use.The other solvents for the catalytic reactions, CuCl2 and other reagents were obtained from commercial suppliers and used without further purification.IR spectra were recorded as KBr disks on a Thermo Fisher iS50 spectrometer (Thermo Fisher, Waltham, MA, USA).Mass spectroscopy was performed with an AB SCIEX 3200 Q-TRAP mass spectrometer (AB SCIEX, Framingham, MA, USA).The melting points were de- Taking previous reports [19,[32][33][34] into account, a plausible mechanism for this Cu-catalyzed Chan-Lam reaction is depicted in Scheme 3. Initially, phenylboronic acid 7a undergoes a transmetallation reaction with Cu II complex A to produce Cu II species B and ClB(OH)2.Species B reacts with benzimidazole 6a to form a Cu II intermediate C, which lowers the Cu III /Cu II reduction potential [35].Then, intermediate C undergoes a disproportionation process [18,[36][37][38]

General Considerations
All manipulations (except the catalytic reactions) under a nitrogen atmosphere were carried out using a Schlenk line.THF was distilled from Na and benzophenone under N2 before use.The other solvents for the catalytic reactions, CuCl2 and other reagents were obtained from commercial suppliers and used without further purification.IR spectra were recorded as KBr disks on a Thermo Fisher iS50 spectrometer (Thermo Fisher, Waltham, MA, USA).Mass spectroscopy was performed with an AB SCIEX 3200 Q-TRAP mass spectrometer (AB SCIEX, Framingham, MA, USA).The melting points were de- Taking previous reports [19,[32][33][34] into account, a plausible mechanism for this Cu-catalyzed Chan-Lam reaction is depicted in Scheme 3. Initially, phenylboronic acid 7a undergoes a transmetallation reaction with Cu II complex A to produce Cu II species B and ClB(OH)2.Species B reacts with benzimidazole 6a to form a Cu II intermediate C, which lowers the Cu III /Cu II reduction potential [35].Then, intermediate C undergoes a disproportionation process [18,[36][37][38]

General Considerations
All manipulations (except the catalytic reactions) under a nitrogen atmosphere were carried out using a Schlenk line.THF was distilled from Na and benzophenone under N2 before use.The other solvents for the catalytic reactions, CuCl2 and other reagents were obtained from commercial suppliers and used without further purification.IR spectra were recorded as KBr disks on a Thermo Fisher iS50 spectrometer (Thermo Fisher, Waltham, MA, USA).Mass spectroscopy was performed with an AB SCIEX 3200 Q-TRAP mass spectrometer (AB SCIEX, Framingham, MA, USA).The melting points were determined on an X-5 melting point apparatus (Beijing Tech Instrument Co., Ltd., Beijing, China).High-resolution mass spectra (HR-MS) were acquired using an Agilent 6210 ESI-TOF mass spectrometer (Agilent technology Co., Ltd, Santa Clara, CA, USA). 1 H Scheme 3. Proposed catalytic mechanism.

General Considerations
All manipulations (except the catalytic reactions) under a nitrogen atmosphere were carried out using a Schlenk line.THF was distilled from Na and benzophenone under N 2 before use.The other solvents for the catalytic reactions, CuCl 2 and other reagents were obtained from commercial suppliers and used without further purification.IR spectra were recorded as KBr disks on a Thermo Fisher iS50 spectrometer (Thermo Fisher, Waltham, MA, USA).Mass spectroscopy was performed with an AB SCIEX 3200 Q-TRAP mass spectrometer (AB SCIEX, Framingham, MA, USA).The melting points were determined on an X-5 melting point apparatus (Beijing Tech Instrument Co., Ltd., Beijing, China).High-resolution mass spectra (HR-MS) were acquired using an Agilent 6210 ESI-TOF mass spectrometer (Agilent technology Co., Ltd, Santa Clara, CA, USA). 1 H NMR and 13 C{ 1 H} NMR spectra were recorded on Zhongke-Niujin Quantum-I 400 MHz spectrometer (Zhongke-Niujin Co., Ltd., Wuhan, China).The EPR spectra were obtained at 77K in CH 2 Cl 2 (0.01 M) solution using a Bruker-A200 Electron Spin Paramagnetic Resonance instrument (Bruker Corporation, Karlsruhe, Germany).

X-ray Crystallographic Studies
Diffraction data of 2 and 4 were collected on an Oxford Diffraction SuperNova dual source diffractometer with graphite-monochromated Cu-Kα radiation (λ = 1.54178Å).The structures were solved by direct methods and refined by full-matrix least-squares on F 2 .All non-hydrogen atoms were refined anisotropically.The hydrogen atoms were introduced in calculated positions with the displacement factors of the host carbon atoms.Structure solution and refinement were performed using the SHELXL package [39].

Synthesis of Complex 3
Following the procedure as described for complex 1 using L3H as the ligand, complex 3 was obtained as a brown solid.Yield: 0.

Synthesis of Complex 4
Following the procedure as described for complex 1 using L4H as the ligand, complex 4 was obtained as a brown solid.Yield: 0.
in the presence of A to afford the high-valence Cu III intermediate D and Cu I species E, and a molecule of HCl is released.Subsequently, inter-mediate D yields the product 1-phenylbenzimidazole 8a and generates another molecule of intermediate E through a reductive elimination step.Finally, intermediate E is converted to Cu II complex A in the presence of air, HCl and ClB(OH) 2 to finish the catalytic cycle.
in the presence of A to afford the high-valence Cu III intermediate D and Cu I species E, and a molecule of HCl is released.Subsequently, intermediate D yields the product 1-phenylbenzimidazole 8a and generates another molecule of intermediate E through a reductive elimination step.Finally, intermediate E is converted to Cu II complex A in the presence of air, HCl and ClB(OH)2 to finish the catalytic cycle.
in the presence of A to afford the high-valence Cu III intermediate D and Cu I species E, and a molecule of HCl is released.Subsequently, intermediate D yields the product 1-phenylbenzimidazole 8a and generates another molecule of intermediate E through a reductive elimination step.Finally, intermediate E is converted to Cu II complex A in the presence of air, HCl and ClB(OH)2 to finish the catalytic cycle.

Table 1 .
Summary of the crystal data for complexes 2 and 4.

Table 2 .
Optimization of Chan-Lam coupling reaction a .

Table 2 .
Optimization of Chan-Lam coupling reaction a.

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .

Table 3 .
Substrate scope of Chan-Lam coupling reaction catalyzed by 3 a .
a a in the presence of A to afford the high-valence Cu III intermediate D and Cu I species E, and a molecule of HCl is released.Subsequently, intermediate D yields the product 1-phenylbenzimidazole 8a and generates another molecule of intermediate E through a reductive elimination step.Finally, intermediate E is converted to Cu II complex A in the presence of air, lytic cycle.