English

• The cross-coupling of organic halides and organoboron reagents, known as the Suzuki-Miyaura coupling stands out as one of the most powerful, convenient, and versatile methods to create carbon-carbon bonds and thus has found widespread applications in advanced materials, natural products and organic synthesis.^[1~9] Most published examples concern the use of aryl iodides and bromides in the reaction, but the application of aryl chlorides^[10~13] has recently attracted much attention mainly due to their economic reason of low cost, availability and stability. Recently, N-heterocyclic carbene (NHC)-palladium complexes, ^[14~18] as an important and fascinating subclass of palladium catalysts, have been developed and shown good catalytic activity in the Suzuki-Miyaura coupling of aryl chlorides. For example, the PEPPSI (pyridine, enhanced, precatalyst, preparation, stabilization, initiation) NHC-palladium complexes^[19~22] readily catalyzed the Suzuki-Miyaura coupling reaction of aryl chlorides with arylboronic acids in good yields. The NHC-Pd(Ⅱ)-Im complexes^[23~28] acting as highly effective pre-catalysts can perform the Suzuki-Miyaura coupling of aryl as well as benzyl chlorides with arylboronic acids under mild conditions. Strassner et al.^[29] have explored the applications of the NHC-Pd(Ⅱ)-2-phenylimidazole complexes for the Suzuki-Miyaura cross-coupling reaction of aryl chlorides and the reaction was found to tolerate a wide range of substrates at low catalyst loadings. The catalytic activities of imine-Pd-NHC complexes were evaluated for more challenging Suzuki-Miyaura cross-coupling reaction of aryl chlorides.^[30] Dinuclear NHC-palladium complexes containing various bridging ligands have also been reported to be active catalyst precursors for the coupling reactions.^[31~33] In our previous work, the N-heterocyclic carbene-palladium(Ⅱ) complexes with benzoxazole or benzothiazole ligands were developed, which were used as effective catalysts for the Suzuki-Miyaura coupling of aryl as well as benzyl chlorides with arylboronic acids.^[34] Although these species have been found to be particularly useful as catalysts in the Suzuki-Miyaura coupling of aryl chlorides, the development of easily prepared, and highly reactive NHC-Pd(Ⅱ) complexes still constitutes a challenging endeavor in current organometallic chemistry. Encouraged by the results mentioned above and also in continuation of our interest in the construction of functionalized complexes, herein we would like to report the synthesis and structural characterization of N-heterocyclic carbene palladium(Ⅱ) complexes with acridine as ancillary ligands (Eq. 1). The application of the obtained complexes in the Suzuki-Miyaura coupling of aryl and benzyl chlorides with arylboronic acids is also presented below.

  1   Results and disscussion

  1.1   Synthesis and characterization of the palladium(Ⅱ) complexes

  According to our previous report, ^[34] the synthesis of the required N-heterocyclic carbene-palladium(Ⅱ) complexes 3 was easily done in a one-step sequence from commercially available imidazolium salts, palladium chloride, and acridine as shown in Eq. 1. The expected palladium(Ⅱ) complexes 3 were isolated in good yields after purification and fully characterized by ¹H NMR, ¹³C NMR, and elemental analysis. The molecular structures of Pd complexes 3a and 3b were unambiguously determined by X-ray single crystal analysis. The molecules are illustrated in Figures 1 and 2, respectively. Complexes 3a and 3b showed slightly distorted-square-planar configuration for the central palladium atom. The two chloride anions perpendicular to the plane of the NHC ligands and the acridine is trans to it. All of the bond lengths and angles around the Pd(Ⅱ) center in the two complexes are similar. The values of bond lengths and angles also compare well to those of the related NHC-Pd(Ⅱ) complexes with N-containing compounds.^[34] The Pd—N bond lengths (around 2.100 Å) in complexes 3a and 3b are slightly longer than that of Pd—C_carbene (around 1.975 Å), the Pd—Cl(1) and Pd—Cl(2) bond lengths are nearly identical. The angles of C_carbene—Pd—N and Cl(1)—Pd—Cl(2) are almost close to 180°, while the C_carbene—Pd—Cl(1) angles, C_carbene—Pd—Cl(2) angles, N—Pd—Cl(1) angles and N—Pd—Cl(2) angles are almost close to 90°.

  Figure 1.  Molecular structures of the Pd(Ⅱ) complexes 3a

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  Figure 2.  Molecular structures of the Pd(Ⅱ) complexes 3b

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  1.2   Suzuki-Miyaura coupling reaction

  In order to test the catalytic activities of the N-hetero-cyclic carbene-palladium(Ⅱ) complexes 3a and 3b, initial experiments were carried out using 1-chloro-4-methoxy-benzene and phenylboronic acid as the reactants, plus complex 3a as the catalyst, in i-PrOH-H₂O at 80 ℃, with the results shown in Table 2. The choice of base proved to have an important influence on the reaction (Table 2, Entries 1~9).^[35] Cs₂CO₃ was found to be the most effective among the tested bases in this case (Table 2, Entries 6 and 9). When 1.0 mol% complex 3awas tested, the yield decreased (Table 2, Entry 10). In addition, i-PrOH mixed with an equal volume of water was found to be the most appropriate solvent, giving the biaryl product in a > 99% yield (Table 2, Entry 6 vs. Entries 11~13). The complex 3b was less efficient than 3a under identical conditions (Entry 6 vs. Entry 14). Fortunately, in this system, the N-heterocyclic carbene-palladium(Ⅱ) complexes 3 were found to exhibit better catalytic activity compared with a related NHC-Pd(Ⅱ) catalyst (complex Ⅰ or Ⅱ) in the Suzuki-Miyaura coupling reaction. For example, in the presence of 2.0 mol% N-heterocyclic carbene-palladium(Ⅱ) complex Ⅰ, very low yield of the corresponding product 6a was obtained (Entry 15). While similar results were also observed when the palladium(Ⅱ) complex Ⅱ was used as the catalyst (Entry 16). We speculate that the possible reasons were ascribed to the different coordination ability acridine and benzoxazole. However, the other N-heterocyclic carbene-palladium(Ⅱ) complex Ⅲ was examined, and similar yield was also achieved (95% yield, Entry 17).

  Table 1.  Summary of crystallographic details for complexes 3a annd 3b

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  	3a·CH2Cl2	3b·CH2Cl2
  Empirical formula	C41H47Cl4N3Pd	C35H35Cl4N3Pd
  Mr	830.02	745.86
  Temperature/K	301(2)	298(2)
  Wavelength/Å	0.71073	0.71073
  Crystal system	Monoclinic	Monoclinic
  Cryst size/mm3	0.35×0.32×0.28	0.28×0.26×0.13
  a/Å	13.3144(17)	12.6455(4)
  b/Å	14.7975(18)	16.2574(5)
  c/Å	21.804(3)	17.324(6)
  α/(o)	90	90
  β/(o)	103.742(4)	96.6480(10)
  γ/(o)	90	90
  V/Å3	4172.8(9)	3537.2(2)
  Z	4	4
  Space group	P2(1)/n	P2(1)/c
  Dcalcd/(g·cm－3)	1.321	1.401
  μ/mm－1	0.732	0.854
  θ range/(o)	2.92~25.00	2.98~26.00
  F(000)	1712	1520
  No. of data collected	46724	55414
  No. of unique data	7313	6923
  R(int)	0.0827	0.0613
  Final R indices [I > 2σ(I)]	R1＝0.1047	R1＝0.0517
  R indices (all data)	R1＝0.1342	R1＝0.0763

  Table 2.  Optimization of reaction conditions for Suzuki-Miyaura reaction of 1-chloro-4-methoxybenzene with phenylboronic acid catalyzed by the NHC-Pd(Ⅱ) complexes^a

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  Entry	Cat.	Base	Solvent (V:V)	Yieldb/%
  1	3a	KOBu-t	i-PrOH/H2O (1:1)	> 99
  2	3a	K2CO3	i-PrOH/H2O (1:1)	89
  3	3a	K3PO4	i-PrOH/H2O (1:1)	800
  4	3a	Na2CO3	i-PrOH/H2O (1:1)	88
  5	3a	NaOBu-t	i-PrOH/H2O (1:1)	97
  6	3a	Cs2CO3	i-PrOH/H2O (1:1)	> 99
  7	3a	NaHCO3	i-PrOH/H2O (1:1)	31
  8c	3a	KOBu-t	i-PrOH/H2O (1:1)	54
  9c	3a	Cs2CO3	i-PrOH/H2O (1:1)	81
  10d	3a	Cs2CO3	i-PrOH/H2O (1:1)	89
  11	3a	Cs2CO3	i-PrOH/H2O (1:2)	74
  12	3a	Cs2CO3	i-PrOH/H2O (1:3)	48
  13	3a	Cs2CO3	EtOH/H2O (1:1)	85
  14	3b	Cs2CO3	i-PrOH/H2O (1:1)	81
  15	Ⅰ	Cs2CO3	i-PrOH/H2O (1:1)	54
  16	Ⅱ	Cs2CO3	i-PrOH/H2O (1:1)	35
  17	Ⅲ	Cs2CO3	i-PrOH/H2O (1:1)	95
  aAll reactions were carried out using 4a (0.20 mmol), 5a (0.30 mmol), base (2.0 equiv.), Cat. (2.0 mol%) in solvent (2.0 mL) at 80 ℃ for 3 h. bIsolated yields. cReaction time was 2 h. dCat. (1.0 mol%).

  With the optimized conditions in hand, a series of aryl chlorides were first used as reactants with phenylboronic acid to test the generality of the reaction. As shown in Table 3, most of the coupling reactions proceeded efficiently to give the corresponding biaryl products 6a~6j in good to excellent yields. Both electron-donating and withdrawing substitutets on the aryl chlorides were tolerated and yields of 79%~ > 99% were obtained for 6a~6h. Whilst the ortho-substituents showed some negative effect on the yields of the catalysis products 6c and 6f. To our pleasure, when heteroaromatic aryl chlorides such as 2-chloropyri-dine and 3-chloropyridine were used as the substrates, high yields of the corresponding products were observed (6i and 6j). Subsequently, the scope of complex 3a catalytic system was further investigated with respect to arylboronic acids (Entries 11~17). In most cases, the reaction worked well and approached to corresponding products in good to almost quantitative yields under identical conditions. However, sterically hindered boronic acid such as 2, 6-dime-thylphenylboronic acid resulted in a significant decrease in yield (100% yield). In addition, in the case of 3-pyridinylboronic acid or 4-pyridinylboronic acid afforded trace amounts of product under the present reaction conditions (data not shown in Table 3). Overview, the results indicated that complex 3a was still efficient in the catalytic process.

  Table 3.  Substrate scope for the catalytic Suzuki-Miyaura reaction of aryl chlorides using the NHC-Pd(Ⅱ) complex 3a as the catalyst^a

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  Entry	Ar1	Ar2	Product	Yieldb/%
  1	4-MeOC6H4	Ph	6a	> 99
  2	3-MeOC6H4	Ph	6b	99
  3	2-MeOC6H4	Ph	6c	93
  4	4-MeC6H4	Ph	6d	99
  5	3-MeC6H4	Ph	6e	95
  6	2-MeC6H4	Ph	6f	79
  7	4-CH3COC6H4	Ph	6g	99
  8	4-O2NC6H4	Ph	6h	99
  9	2-Pyridyl	Ph	6i	98
  10	3-Pyridyl	Ph	6j	86
  11	4-MeOC6H4	4-MeC6H4	6k	99
  12	4-MeOC6H4	3-MeC6H4	6l	96
  13	4-MeOC6H4	2-MeC6H4	6m	91
  14	4-MeOC6H4	4-FC6H4	6n	99
  15	4-MeOC6H4	4-CF3C6H4	6o	98
  16	4-MeOC6H4	1-Naphthyl	6p	91
  17	4-MeOC6H4	2-Naphthyl	6q	99
  aAll reactions were carried out using 4 (0.20 mmol), 5 (0.30 mmol), Cs2CO3 (2.0 equiv.), Cat. 3a (2.0 mol%) in i-PrOH/H2O [V:V＝1:1 (2.0 mL)] at 80 ℃ for 3 h. bIsolated yields.

  Inspired by these successful results, we then turned our interest to such transformations using the benzyl chlorides as the substrates. As shown in Table 4, all reactions proceed smoothly to afford diarylmethanes in good to almost quantitative yields under identical conditions. Particularly, when sterically hindered boronic acids such as 2-methylphenylboronic acid were used as the substrates, high yield of the corresponding product was always observed (99% yield, Entry 3). Overview, the above results confirm that the present N-heterocyclic carbene-palladium(Ⅱ) complexes are highly efficient catalysts for the Suzuki-Miyaura coupling of aryl as well as benzyl chlorides with arylboronic acids.

  Table 4.  Substrate scope for the catalytic Suzuki-Miyaura reaction of benzyl chlorides using the NHC-Pd(Ⅱ) complex 3a as the catalyst^a

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  Entry	Ar3	Ar2	Product	Yieldb/%
  1	Ph	4-MeC6H4	8a	> 99
  2	Ph	3-MeC6H4	8b	99
  3	Ph	2-MeC6H4	8c	99
  5	Ph	4-FC6H4	8d	99
  6	Ph	4-CF3C6H4	8e	98
  7	Ph	1-Naphthyl	8f	96
  8	4-t-BuC6H4	Ph	8g	99
  9	4-MeC6H4	Ph	8h	99
  10	3-MeC6H4	Ph	8i	99
  11	2-MeC6H4	Ph	8j	99
  12	4-FC6H4	Ph	8k	98
  aAll reactions were carried out using 7 (0.20 mmol), 5 (0.30 mmol), Cs2CO3 (2.0 equiv), Cat. 3a (2.0 mol%) in i-PrOH/H2O [V:V＝1:1 (2.0 mL)] at 80 ℃ for 3 h. bIsolated yields.

  2   Conclusion

  In summary, the easily available, well-defined N-hetero-cyclic carbene-palladium(Ⅱ) complexes 3a and 3b, being derived from the corresponding imidazolium salts, palladium chloride and acridine, showed good catalytic activity in the Suzuki-Miyaura coupling of aryl chlorides and benzyl chlorides with arylboronic acids. Further ex ploration of these N-heterocyclic carbene-palladium(Ⅱ) complexes and their catalytic applications in other reactions is in progress.

  3   Experimental

  3.1   Apparatus and reagents

  Melting points were measured on a XT4A melting point apparatus and uncorrected. ¹H NMR and ¹³C NMR spectra were recorded on a Bruker DPX 400 instrument using TMS as an internal standard. Elemental analyses were measured on a Thermo Flash EA 1112 elemental analyzer. Reactions for the preparation of N-heterocyclic carbene-palladium(Ⅱ) complexes were carried out under nitrogen atmosphere. Solvents were dried with standard methods and freshly distilled prior to use if needed. All other chemicals were used as purchased.

  3.2   Synthesis of N-heterocyclic carbene-palladium (Ⅱ) complexes

  Under an N₂ atmosphere, the mixture of imidazolium salts (1.1 mmol), acridine (2.0 mmol, 358.4 mg), PdCl₂ (1.0 mmol, 177.3 mg) and K₂CO₃ (1.1 mmol, 152.0 mg) was stirred in anhydrous tetrahydrofuran (THF) (10 mL) under reflux for 16 h. After cooling, filtration and evaporation, the residue was purified by preparative thin layer chromatography (TLC) on silica gel plates eluting with CH₂Cl₂ to afford the corresponding N-heterocyclic carbene-palladium(Ⅱ) complexes 3a and 3b.

  trans-[1, 3-Bis(2, 6-diisopropylphenyl)imidazol-2-ylidene]-(acridine)-palladium(Ⅱ) dichloride (3a): 67% yield, orange solids. m.p. 143~145 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 9.17 (d, J＝8.7 Hz, 2H, ArH), 8.61 (s, 1H, ArH), 7.77 (d, J＝5.2 Hz, 2H, ArH), 7.71~7.67 (m, 2H, ArH), 7.55~7.54 (m, 6H, ArH), 7.40 (s, 2H, ArH), 7.29 (s, 2H, ArH), 3.32~3.30 [m, 4H, CH(CH₃)₂], 1.44 (d, J＝5.8 Hz, 12H, CH₃CHCH₃), 1.15 (d, J＝6.1 Hz, 12H, CH₃CHCH₃); ¹³C NMR (100 MHz, CDCl₃) δ: 158.6, 147.6, 147.5, 138.7, 135.3, 131.2, 130.2, 128.9, 127.9, 127.2, 125.8, 124.8, 123.9, 29.0, 26.7, 22.6; IR (KBr) ν: 3118, 3085, 2960, 2925, 2865, 1621, 1522, 1460, 1442, 1383, 1363, 1348, 1333, 1268, 926, 800, 756, 731, 707, 602, 499 cm^－1; MS (ESI⁺) m/z: 708.1 (M－Cl). Anal. calcd for C₄₀H₄₅Cl₂N₃Pd: C 64.48, H 6.09, N 5.64; found C 64.43, H 6.10, N 5.66.

  trans-[1, 3-Bis(2, 4, 6-trimethylphenyl)imidazol-2-ylidene]-(acridine)-palladium(Ⅱ) dichloride (3b): 55% yield, orange solids. m.p. 135~138 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 9.15 (d, J＝8.7 Hz, 2H, ArH), 8.66 (s, 1H, ArH), 7.82 (d, J＝8.0 Hz, 2H, ArH), 7.56 (t, J＝7.4 Hz, 2H, ArH), 7.45 (t, J＝6.9 Hz, 2H, ArH), 7.25 (s, 6H, ArH), 2.56 (s, 6H, CH₃), 2.46 (s, 12H, CH₃); ¹³C NMR (100 MHz, CDCl₃)δ: 156.6, 147.7, 139.2, 138.8, 137.2, 135.2, 131.4, 129.2, 128.5, 128.0, 127.2, 125.9, 123.8, 21.4, 19.3; IR (KBr) ν: 3160, 3127, 2917, 1620, 1570, 1521, 1484, 1460, 1411, 1369, 1339, 1279, 1231, 1154, 1038, 1010, 910, 861, 783, 733, 707, 601 cm^－1; MS (ESI⁺) m/z: 624.0 (M－Cl)⁺. Anal. calcd for C₃₄H₃₃Cl₂N₃Pd: C 61.78, H 5.03, N 6.36; found C 61.73, H 5.10, N 6.39.

  3.3   General procedure for the catalytic Suzuki-Miyaura reaction

  A Schlenk flask was charged with aryl chlorides (0.20 mmol), arylboronic acids (0.30 mmol), N-heterocyclic carbene-palladium(Ⅱ) complex 3 (2.0 mol%), Cs₂CO₃ (2.0 equiv., 651.6 mg), i-PrOH (1.0 mL) and H₂O (1.0 mL). The mixture was stirred at 80 ℃ for 3 h. After cooling, the reaction mixture was evaporated and the product was isolated by preparative TLC on silica gel plates.

  3.4   Crystal structure determination and data co-llection

  Crystals of 3a and 3b were obtained by recrystallization from CH₂Cl₂/n-hexane at ambient temperature. Their data were collected on an Oxford Diffraction Gemini E diffractometer with graphite-monochromated Mo Kα radiation (λ＝0.7107 Å). The structures were solved by direct methods using the SHELXS-97 program, and all non-hydrogen atoms were refined anisotropically on F² by the full-matrix least-squares technique, which used the SHELXL-97 crystallographic software package.^{[36, 37]} The hydrogen atoms were included but not refined. Details of the crystal structure determination of the Pd(Ⅱ) complexes are summarized in Table S1 in the Supporting Information. CCDCs 1499311 and 1499312 contain the crystallographic data for complexes 3a and 3b, respectively.

  Supporting Information ¹H NMR, ¹³C NMR spectra of compounds 3a and 3b and the ¹H NMR spectra of catalysis products. The Supporting Information is available free of charge via the Internet at http://sioc-journal.cn.

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  Figure 1  Molecular structures of the Pd(Ⅱ) complexes 3a

  Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (°) in complex 3a: Pd(1)—C(14) 1.981(10), Pd(1)—N(1) 2.109(10), Pd(1)—Cl(1) 2.313(3), Pd(1)—Cl(2) 2.290 (3); C(14)—Pd(1)—Cl(1) 91.6(3), N(1)—Pd(1)—Cl(1) 88.7(3), C(14)—Pd(1)—Cl(2) 90.2(3), N(1)—Pd(1)—Cl(2) 89.7(3), C(14)—Pd(1)—N(1) 176.7(4), Cl(1)—Pd(1)—Cl(2) 175.73(13).

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  Figure 2  Molecular structures of the Pd(Ⅱ) complexes 3b

  Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (°) in complex 3b: Pd(1)—C(14) 1.972(4), Pd(1)—N(1) 2.095(3), Pd(1)—Cl(1) 2.3005(12), Pd(1)—Cl(2) 2.2993(12); C(14)—Pd(1)—Cl(1) 90.30(11), N(1)—Pd(1)—Cl(1) 87.54(10), C(14)—Pd(1)—Cl(2) 93.16(11), N(1)—Pd(1)—Cl(2) 89.11(10), C(14)—Pd(1)—N(1) 176.66(15), Cl(1)—Pd(1)—Cl(2) 175.81(5).

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  Table 1.  Summary of crystallographic details for complexes 3a annd 3b

  	3a·CH2Cl2	3b·CH2Cl2
  Empirical formula	C41H47Cl4N3Pd	C35H35Cl4N3Pd
  Mr	830.02	745.86
  Temperature/K	301(2)	298(2)
  Wavelength/Å	0.71073	0.71073
  Crystal system	Monoclinic	Monoclinic
  Cryst size/mm3	0.35×0.32×0.28	0.28×0.26×0.13
  a/Å	13.3144(17)	12.6455(4)
  b/Å	14.7975(18)	16.2574(5)
  c/Å	21.804(3)	17.324(6)
  α/(o)	90	90
  β/(o)	103.742(4)	96.6480(10)
  γ/(o)	90	90
  V/Å3	4172.8(9)	3537.2(2)
  Z	4	4
  Space group	P2(1)/n	P2(1)/c
  Dcalcd/(g·cm－3)	1.321	1.401
  μ/mm－1	0.732	0.854
  θ range/(o)	2.92~25.00	2.98~26.00
  F(000)	1712	1520
  No. of data collected	46724	55414
  No. of unique data	7313	6923
  R(int)	0.0827	0.0613
  Final R indices [I > 2σ(I)]	R1＝0.1047	R1＝0.0517
  R indices (all data)	R1＝0.1342	R1＝0.0763

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  Table 2.  Optimization of reaction conditions for Suzuki-Miyaura reaction of 1-chloro-4-methoxybenzene with phenylboronic acid catalyzed by the NHC-Pd(Ⅱ) complexes^a

  Entry	Cat.	Base	Solvent (V:V)	Yieldb/%
  1	3a	KOBu-t	i-PrOH/H2O (1:1)	> 99
  2	3a	K2CO3	i-PrOH/H2O (1:1)	89
  3	3a	K3PO4	i-PrOH/H2O (1:1)	800
  4	3a	Na2CO3	i-PrOH/H2O (1:1)	88
  5	3a	NaOBu-t	i-PrOH/H2O (1:1)	97
  6	3a	Cs2CO3	i-PrOH/H2O (1:1)	> 99
  7	3a	NaHCO3	i-PrOH/H2O (1:1)	31
  8c	3a	KOBu-t	i-PrOH/H2O (1:1)	54
  9c	3a	Cs2CO3	i-PrOH/H2O (1:1)	81
  10d	3a	Cs2CO3	i-PrOH/H2O (1:1)	89
  11	3a	Cs2CO3	i-PrOH/H2O (1:2)	74
  12	3a	Cs2CO3	i-PrOH/H2O (1:3)	48
  13	3a	Cs2CO3	EtOH/H2O (1:1)	85
  14	3b	Cs2CO3	i-PrOH/H2O (1:1)	81
  15	Ⅰ	Cs2CO3	i-PrOH/H2O (1:1)	54
  16	Ⅱ	Cs2CO3	i-PrOH/H2O (1:1)	35
  17	Ⅲ	Cs2CO3	i-PrOH/H2O (1:1)	95
  aAll reactions were carried out using 4a (0.20 mmol), 5a (0.30 mmol), base (2.0 equiv.), Cat. (2.0 mol%) in solvent (2.0 mL) at 80 ℃ for 3 h. bIsolated yields. cReaction time was 2 h. dCat. (1.0 mol%).

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  Table 3.  Substrate scope for the catalytic Suzuki-Miyaura reaction of aryl chlorides using the NHC-Pd(Ⅱ) complex 3a as the catalyst^a

  Entry	Ar1	Ar2	Product	Yieldb/%
  1	4-MeOC6H4	Ph	6a	> 99
  2	3-MeOC6H4	Ph	6b	99
  3	2-MeOC6H4	Ph	6c	93
  4	4-MeC6H4	Ph	6d	99
  5	3-MeC6H4	Ph	6e	95
  6	2-MeC6H4	Ph	6f	79
  7	4-CH3COC6H4	Ph	6g	99
  8	4-O2NC6H4	Ph	6h	99
  9	2-Pyridyl	Ph	6i	98
  10	3-Pyridyl	Ph	6j	86
  11	4-MeOC6H4	4-MeC6H4	6k	99
  12	4-MeOC6H4	3-MeC6H4	6l	96
  13	4-MeOC6H4	2-MeC6H4	6m	91
  14	4-MeOC6H4	4-FC6H4	6n	99
  15	4-MeOC6H4	4-CF3C6H4	6o	98
  16	4-MeOC6H4	1-Naphthyl	6p	91
  17	4-MeOC6H4	2-Naphthyl	6q	99
  aAll reactions were carried out using 4 (0.20 mmol), 5 (0.30 mmol), Cs2CO3 (2.0 equiv.), Cat. 3a (2.0 mol%) in i-PrOH/H2O [V:V＝1:1 (2.0 mL)] at 80 ℃ for 3 h. bIsolated yields.

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  Table 4.  Substrate scope for the catalytic Suzuki-Miyaura reaction of benzyl chlorides using the NHC-Pd(Ⅱ) complex 3a as the catalyst^a

  Entry	Ar3	Ar2	Product	Yieldb/%
  1	Ph	4-MeC6H4	8a	> 99
  2	Ph	3-MeC6H4	8b	99
  3	Ph	2-MeC6H4	8c	99
  5	Ph	4-FC6H4	8d	99
  6	Ph	4-CF3C6H4	8e	98
  7	Ph	1-Naphthyl	8f	96
  8	4-t-BuC6H4	Ph	8g	99
  9	4-MeC6H4	Ph	8h	99
  10	3-MeC6H4	Ph	8i	99
  11	2-MeC6H4	Ph	8j	99
  12	4-FC6H4	Ph	8k	98
  aAll reactions were carried out using 7 (0.20 mmol), 5 (0.30 mmol), Cs2CO3 (2.0 equiv), Cat. 3a (2.0 mol%) in i-PrOH/H2O [V:V＝1:1 (2.0 mL)] at 80 ℃ for 3 h. bIsolated yields.

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