Palladacycle from Cyclometalation of the Unsubstituted

Oct 15, 2014 - Theresa Sperger , Italo A. Sanhueza , Indrek Kalvet , and Franziska Schoenebeck. Chemical Reviews 2015 115 (17), 9532-9586. Abstract | ...
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Palladacycle from Cyclometalation of the Unsubstituted Cyclopentadienyl Ring in Ferrocene: Synthesis, Characterization, Theoretical Studies, and Application to Suzuki−Miyaura Reaction Hengyu Qian,† Zhigang Yin,*,† Tongyan Zhang,† Shihai Yan,‡ Quanling Wang,† and Chunxia Zhang† †

Key Laboratory of Surface & Interface Science of Henan, School of Material & Chemical Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, People’s Republic of China ‡ College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao 266109, People’s Republic of China S Supporting Information *

ABSTRACT: The ferrocenylimines of general formula [(η5-C5H5)Fe(η5-C5H4)-CH2NCH-C(R)CH-C6H5] with R = H (2a) and CH3 (2b) were conveniently prepared from ferrocenylmethylamine. Reaction of 2a,b with lithium tetrachloropalladate in methanol in the presence of anhydrous sodium acetate resulted in the formation of the di-μ-chloro-bridged heteroannular cyclopalladated complexes 3a,b via the unsubstituted ferrocenyl C−H bond activation of the related ligands. Treatment of 3a,b with triphenylphosphine gave Pd{[(η5-C5H4)Fe(η5-C5H4)CH2NCH-CHCH-C6H5]}ClPPh3 (4a) and Pd{[(η5-C5H4)Fe(η5-C5H4)-CH2NCH-C(CH3)CH-C6H5]}ClPPh3 (4b), respectively. The crystal structures of 4a,b confirmed the formation of a carbon−palladium bond by using a carbon atom in the unsubstituted cyclopentadienyl ring. Additionally, theoretical studies using density functional theory calculations were carried out in order to account for the regioselectivity of cyclometalation. As for the catalysts, using 0.1% of palladacycles 4a,b in the presence of K3PO4·7H2O as base exhibited excellent yields in the Suzuki− Miyaura coupling reaction of aryl bromides with phenylboronic acid.

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Fe(η5-C5H4)CH2NCH-C4H3S]ClPPh3} in the Mizoroki− Heck reaction has been described.5b,e,f Although pioneering strides have been made, the development of heteroannular cyclopalladation of ferrocene compounds and their applications in cross-coupling reactions still remain a major challenge, probably because of the inherent difficulty in the course of cyclometalation. In light of this and the potential application of heteroannular cyclopalladated complexes in organic synthesis, the ligands (η5C5H5)Fe(η5-C5H4)-CH2NCH-C(R)CH-C6H5 [R = H (2a), CH3 (2b)] are described in this paper. In compounds 2a,b, the −NCH− moiety was not coplanar with the substituted cyclopentadienyl ring. This might provide three different activations of the σ C−H bond in cyclometalation. The activation of the σ C−H bond of the substituted C5H4 ring would result in the formation of ortho-palladated derivatives

INTRODUCTION

Recent studies of the fundamental chemistry of organopalladium compounds have generated new impetus for the construction of novel palladacycles and their potential applications in organic synthesis,1 new molecular materials,2 and medical and biological chemistry.3 In particular, ferrocenyl derivatives have been cyclopalladated at the substituted cyclopentadienyl ring since the 1960s,4 where the Pd−C bond was stabilized by the intramolecular coordination of donor atoms (N, P, O, or S). Moreover, palladation at the unsubstituted cyclopentadienyl ring gave heteroannular cyclopalladated derivatives, in which the carbon nitrogen double bond was not coplanar with the substituted cyclopentadienyl ring and might direct the palladium atom toward the lower one.5 Only scattered attention had been paid to the study of their properties. In 2005, Moyano et al. reported the first heteroannular palladacycle that promoted the aza-Claisen rearrangement with excellent enantioselectivity.5d Meanwhile, the application of heteroannular palladacycle {Pd[(η5-C5H4)© 2014 American Chemical Society

Received: September 3, 2014 Published: October 15, 2014 6241

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substituted cyclopentadienyl ring. Notably, from their 13C NMR spectra there exists some evidence for the formation of heteroannular complexes. For example, one signal for the carbon atoms in the unsubstituted cyclopentadienyl ring appears at 68.8 and 67.3 ppm for ligands 2a and 2b, while five carbon signals corresponding to the unsubstituted cyclopentadienyl ring are found in complexes 4a,b, among which a new quarternary C-signal for the metalated carbon atom resonates at 81.7 and 82.7 ppm, respectively. For the palladium complexes 4a and 4b, the 31P NMR signal appears at 34.1 ppm (4a) and 35.3 ppm (4b), which is in accordance with those reported for the trans disposition of the phosphorus ligand and the nitrogen atom.8 Molecular Structures of Palladium Complexes 4a,b. Suitable crystals of palladium complexes 4a,b were obtained from dichloromethane/methanol. The structures, as shown in Figures 2 and 3, indicate that the unsubstituted cyclo-

(Figure 1 A), while palladation of the C5H5 ring would produce the unexpected heteroannular palladacycles (Figure 1 B).

Figure 1. Schematic view of three different types of palladacycles.

Moreover, the palladacycles with a σ Pd−Csp2,phenyl bond due to the “endo effect” in cyclometalation (Figure 1 C) could not be ruled out.6 Our experimental results showed that only the heteroannular palladacycles were obtained (Figure 1 B). in order to explain these results, a theoretical investigation on these palladium(II) complexes is presented. The detailed results are discussed below.

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RESULTS AND DISCUSSION The Ligands. The required ligands 2a,b were prepared by the condensation of ferrocenylmethylamine and cinnamaldehyde or α-methyl cinnamaldehyde in 75.8% and 72.3% yields, and the carbon nitrogen double bond in the IR spectra displays an intense band at 1625 cm−1 for 2a and 1630 cm−1 for 2b, respectively, as shown in Scheme 1. The 1H NMR spectra of Scheme 1. Synthesis of the Heteroannular Palladacycles 4a,b

Figure 2. Molecule drawing for 4a. All H atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Pd1−C19, 2.030(4); Pd1−N1, 2.130(4); Pd1−P1, 2.2392(15); Pd1−Cl1, 2.4089(12); N1−C30, 1.274(6); C19−Pd1−N1, 88.27(16); C19− Pd1−P1, 90.00(14); N1−Pd1−Cl1, 91.07(10); P1−Pd1−Cl1, 91.05(5).

2a,b exhibit peaks for the ferrocene moiety with a proton ratio of 2:2:5 in the range 4.20−4.39 ppm, showing that they are monosubstituted ferrocene derivatives. Synthesis and Characterization of Palladacycles 4a,b. With the expected ligands in hand, the corresponding palladation was carried out following the procedure4e that afforded the dimeric cyclopalladated complex. Due to its poor solubility in all common organic solvents, it was subjected to a bridge-splitting reaction with PPh3 in dichloromethane for 2 h. The unexpected heteroannular palladacycles 4a,b with σ Pd− Csp2,ferrocene bond by using a carbon atom in the remote unsubstituted cyclopentadienyl ring were obtained in 68.2% and 65.8% yields. In their IR spectra, the CN absorptions are shifted to lower wave numbers by 14−17 cm−1 (1611 cm−1 for 4a and 1613 cm−1 for 4b), when compared with the corresponding starting ligands, indicating the existence of N→Pd coordination. In addition, the two absorption bands at around 1100 and 1000 cm−1, a feature of the monosubstituted ferrocene derivatives,7 are not detected in complexes 4a,b, indicating the disappearance of the unsubstituted cyclopentadienyl ring in this molecule. Moreover, in comparison with the 1H NMR spectra of the corresponding ligands 2a,b, the resonance of the unsubstituted cyclopentadienyl ring in the upfield region (around 3−5 ppm) in complexes 4a,b is absent, indicating that palladation occurs on the remote, non-

pentadienyl ring is palladated, forming an unexpected metallacycle, and the remaining coordination sites are occupied by a chloride, the imine nitrogen, and the phosphorus atom of the PPh3, showing the tetracoordinate palladium(II) complexes. The Pd(II) center in each complex is in a slightly distorted square-planar environment, with the largest deviation from the mean plane being −0.1002 Å at N(1) for 4a and 0.0918 Å at C(19) for 4b, and the dihedral angles between the planes C(19)Pd(1)N(1) and P(1)Pd(1)Cl(1) are 7.1° and 8.0° for 4a and 4b, respectively. Due to the existence of intramolecular N→Pd coordination,9 the plane bearing the −NC−CC− group is twisted from its attached phenyl ring with a dihedral angle of 7.0° in 4a and 9.7° in 4b. The N(1)−Pd(1)−P(1) angles are 173.6° and 178.9°, in agreement with a trans arrangement between the PPh3 and the imine nitrogen, as indicated by the 31P NMR feature of complexes 4a and 4b. The Pd−N bond length (2.130(4) Å for 4a; 2.138(4) Å for 4b) is appreciably longer than that reported for the endo-type cyclopalladated ferrocenylimines, but the Pd(1)−C(19) bond length (2.030(4) Å for 4a; 1.997(6) Å for 4b) falls comfortably within the range found for these palladium(II) complexes.10 6242

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Table 1. Comparison of the Calculated (Lower Row) Bond Distances (Å) and Bond Angles (deg) around the Pd Atoms with Those Obtained by X-ray Diffraction (Upper Row) Pd1−C19 Pd1−N1 Pd1−P1 Pd1−Cl1 C19−Pd1−N1 C19−Pd1−P1 N1−Pd1−Cl1

Figure 3. Molecule drawing for 4b. All H atoms and the methanol molecule have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Pd1−C19, 1.997(6); Pd1−N1, 2.138(4); Pd1−P1, 2.2576(17); Pd1−Cl1, 2.4176(19); N1−C30, 1.255(7); C19−Pd1− N1, 90.40(19); C19−Pd1−P1, 88.86(16); N1−Pd1−Cl1, 84.82(12); P1−Pd1−Cl1, 95.82(6).

P1−Pd1−Cl1

4a

4b

2.030(4) 2.0257 2.130(4) 2.1921 2.2392(15) 2.3550 2.4089(12) 2.4887 88.27(16) 89.47 90.00(14) 91.57 91.07(10) 86.10 91.05(5) 93.46

1.997(6) 2.034 2.138(4) 2.2160 2.2576(17) 2.3526 2.4176(19) 2.4963 90.04(19) 90.37 88.86(16) 91.62 84.82(12) 85.10 95.82(6) 93.25

Moreover, the values of the torsion angles Cphenyl−CC− C(30) and CC−C(30)−N(1) [179.85° and 177.61° in model B, 179.47° and 176.99° in model E] compare well to the observed values for the corresponding ligands [179.74° and 179.75° in model A, 179.16° and 179.89° in model D], so the imine moiety was coplanar with the phenyl ring in models A and D. Additionally, the C(29)−N(1)−C(30) angles obtained for the optimized geometries were 117.5° [model A] and 117.7° [model D], respectively. Therefore, this conformation for these ligands might direct the donor atom toward the lower, nonsubstituted cyclopentadienyl ring. Further, it is well known that cyclometalation of the nitrogen-donor ligands proceeds in two steps:4e,11 (1) the coordination of the nitrogen atom to the metal; (2) the electrophilic attack of metal at the carbon atom. Once the donor atom is coordinated to the metal, the C−H bond susceptible to the metalation must be in close proximity to the metal and adopt a suitable position to form the corresponding metallacycles. On this basis, the geometries of model complexes {Pd[(η5-C5H5)Fe(η5-C5H4)-CH2-NCH-C(R)CH-C6H5]Cl3}− (where nitrogen is coordinated to palladium through its lone pair exclusively; R = H, model E and R = CH3, model J) were undertaken using the B3LYP methods. For the optimized geometry, the electron density on C(19) in the unsubstituted cyclopentadienyl ring is higher than on C(28) in the substituted cyclopentadienyl ring and C(38 or 39) in the phenyl ring (Table 2). In addition, the distances between the palladium and the carbon atoms (C19, C28, C38, or C39), being inclined to undergo metalation, are 3.428, 3.863, and 5.291 Å in model C and 3.418, 3.847, and 6.280 Å in model F, respectively. For this

The two cyclopentadienyl rings are nearly eclipsed with a dihedral angle of 2.4° and 3.7° for 4a and 4b, respectively. Computational Studies on the Regioselectivity of Cyclopalladation. In an effort to explain the unexpected formation of palladium(II) complexes (4a and 4b), molecular geometries were calculated for the ligands and the palladium complexes. The detailed results are shown in Figure 4. As shown in Table 1, the predicted geometries for models B and E from density functional theory (DFT) calculations are in good agreement with the X-ray experimental parameters.

Table 2. Partial Mulliken Charges and the Distances between Palladium and the Carbon Atoms Involved in Cyclometalation atom Mulliken charge distance (Å)

Figure 4. Optimized structures of models A−F. The hydrogen atoms have been omitted. Models A and D: ligand; models B and E: the heteroannular palladacycle; models C and F: the intermediate.

C19

C28

C38a/C39b

−0.153a/− b

−0.141a/− b

−0.118a/− 0.114b 5.291a/6.280b

0.158 3.428a/3.418b

0.130 3.863a/3.847b

a

The atom number is listed in model C. bThe atom number is listed in model F.

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arrangement it shows that the C−H bond in the unsubstituted cyclopentadienyl ring is extremely close to the palladium and has the proper orientation to be suitable for activation. These findings may be responsible for the formation of the heteroannular palladium(II) complex via an unexpected cyclometalation at the unsubstituted cyclopentadienyl ring. Catalytic Studies for the Suzuki−Miyaura Reaction. The Suzuki−Miyaura cross-coupling reaction of aryl halides and aryl boronic acids is one of the most versatile and powerful synthetic tools for carbon−carbon bond formation.12 Some palladium complexes were developed and displayed good efficiency in this kind of reaction.13 Despite the progress in this field, the search for novel palladium complexes remains a major challenge in the development of high catalytic activity with wide substrate tolerance. Thus, we wonder whether the present novel heteroannular palladium complexes 4a and 4b can proceed in carbon−carbon bond forming reactions. Initially, the Suzuki−Miyaura coupling between bromobenzene and phenylboronic acid in the presence of palladacycle 4a was selected as the model reaction to examine the catalytic efficiency, and the results are outlined in Table 3. After optimization of the

Table 4. Suzuki Coupling of Aryl Halides with Phenylboronic Acida Aryl Bromide + PhB(OH)2 → Ar-Ph yieldb (%)

base

solvent/temp

yieldb(%)

1 2 3 4 5 6 7 8 9 10 11

K3PO4·7H2O K3PO4·7H2O K3PO4·7H2O K3PO4·7H2O K3PO4·7H2O Cs2CO3 K2CO3 KF·2H2O KOH NaOH Et3N

tetrahydrofuran/66 °C dioxane/100 °C methanol/65 °C toluene/110 °C toluene/110 °C toluene/110 °C toluene/110 °C toluene/110 °C toluene/110 °C toluene/110 °C toluene/110 °C

43.8 70.2 55.2 91.5 92.8c 82.5 55.4 32.5 75.2 71.8 36.5

aryl bromide

catalyst 4a

catalyst 4b

1 2 3 4 5 6 7 8 9 10 11 12 13 14

bromobenzene 4-bromoethylbenzene 2-bromotoluene 1-bromo-2,4-dimethoxybenzene 4-bromofluorobenzene 4-bromobenzotrifluoride 4-bromobenzotrifluoride 1-bromo-4-nitrobenzene 1-bromo-4-nitrobenzene chlorobenzene chlorobenzene 1-chloro-4-nitrobenzene 1-chloro-4-nitrobenzene 1-chloro-4-nitrobenzene

91.5 86.3 80.2 36.4 89.6 94.6 92.3c 96.8 94.5c 7.2 21.8d 17.5 40.3d 60.4e

93.6 85.2 83.4 35.2 88.5 95.8 91.2c 97.2 93.4c 8.3 19.4d 18.4 39.8d 58.2e

a

Reaction conditions: ArBr (1 mmol), PhB(OH)2 (1.2 mmol), catalyst (0.5 mol %), base (1 mmol), solvent (5 mL), reaction time (2 h). b Isolated yield (average of two runs). cCatalyst: 0.1 mol %. dCatalyst: 2 mol %. eCatalyst: 2 mol %; reaction time: 10 h.

Table 3. Effect of Base and Solvent on the Suzuki−Miyaura Reaction of Bromobenzene with Phenylboronic Acida entry

entry

4, entry 10). Finally, the coupling of the activated chloride (1chloro-4-nitrobenzene) with phenylboronic acid afforded a moderate yield (Table 4, entries 12 and 13). On increasing the catalyst loading to 2 mol % and prolonging the reaction time to 10 h, the yield of the biaryl could reach 60.4% and 58.2% (Table 4, entry 14), respectively.

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CONCLUSION In summary, reaction of Schiff bases derived from ferrocenylmethylamine with Li2PdCl4 led to the formation of the unexpected heteroannular palladium complexes 4a and 4b, resulting from cyclometalation of the unsubstituted cyclopentadienyl ring. Single-crystal X-ray analysis confirmed that the carbon−palladium bond was formed by using a carbon atom in the unsubstituted ferrocene ring. Theoretical studies based on DFT show a reasonable agreement with these observation. In addition, these palladacycles exhibit high activity for the Suzuki−Miyaura reaction of aryl bromides with phenylboronic acid, giving the biaryl products in high yields. This protocol provides a promising method for the formation of heteroannular cyclometalated complexes. Further studies are in progress centered on the mechanism of cyclometalation and their applications in organic synthesis.

a Reaction conditions: PhBr (1 mmol), PhB(OH)2 (1.2 mmol), catalyst 4a (0.5 mol %), base (1 mmol), solvent (5 mL), reaction time (2 h). bIsolated yields (average of two runs). cReaction time: 4 h.

reaction conditions with bromobenzene, it was found that K3PO4·7H2O and toluene were the most appropriate base and solvent, and the reaction was stopped after 2 h instead of 4 h. To gain insight into the broad functional group tolerance of this system, a representative range of aryl bromides and chlorides were tested in the presence of palladacycles 4a and 4b. An electron-deficient aryl bromide bearing an electronwithdrawing −CF3 or −NO2 group reacted with phenylboronic acid with the reduction of catalyst loading to 0.1% and yielded the corresponding products almost quantitatively for both palladium complexes 4a and 4b (Table 4, entries 6−9). In the case of 4-bromoethylbenzene, the electron-rich counterparts could couple with phenylboronic acid in excellent yield (Table 4, entry 2). In addition, reaction of 2-bromotoluene with phenylboronic acid gave the corresponding product in 80.2% and 83.4% yields for palladacycles 4a and 4b. A comparatively lower yield was obtained employing 1-bromo-2,4-dimethoxybenzene instead of 2-bromotoluene as the substrate (Table 4, entries 3 and 4). This result suggested a strong steric effect of the substituted group of the phenyl ring on the catalytic activity in this reaction. When chlorobenzene was used as the coupling partner, only a trace amount of the biaryl was obtained (Table

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EXPERIMENTAL SECTION

General Procedures. Melting points were measured on an microscopic apparatus and were uncorrected. IR spectra were obtained as KBr disks on a spectrophotometer. Elemental analyses were carried out with a microanalyzer. NMR spectra were recorded on a DPX 400 spectrometer in CDCl3. Chemical shifts were cited relative to SiMe4. Solvents were dried and distilled under nitrogen prior to use. Synthesis of Ligands 2a,b. A mixture of ferrocenylmethylamine (903 mg, 4.2 mmol), the corresponding aldehyde (4 mmol) [cinnamaldehyde (528 mg) or α-methylcinnamaldehyde (584 mg)], and 10 mL of methanol was stirred for 2 h at room temperature. The mixture was concentrated to dryness and purified by chromatography on a silica gel plate (petroleum/CH2Cl2 = 10:1). (η5-C5H5)Fe(η5-C5H4)-CH2-NCH-CHCH-C6H5 (2a): orange oil (997 mg, 75.8%). IR (KBr pellet): 3084, 2915, 1649, 1625, 1601, 1429, 6244

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1350, 1105, and 810 cm−1. 1H NMR: δ 4.23 (5H, s, C5H5), 4.30 (2H, s, C5H4), 4.39 (2H, s, C5H4), 4.88 (2H, s, CH2), 7.01−7.04 (1H, m, CHCHPh), 7.25−7.28 (2H, m, Ph-H), 7.31−7.32 (1H, m, CHCHPh), 7.32−7.34 (1H, m, Ph-H), 7.53−7.57 (2H, m, Ph-H), 8.21−8.25 (1H, m, NCH). 13C NMR: δ 60.2 (CH2), 69.2, 69.4, 70.5, 70.6, 80.5 (C5H4C), 68.8 (C5H5-C), 126.0 (CHCHPh), 128.1, 128.9, 134.9, 147.7 (PhC), 134.9 (CHCHPh), 166.7 (NCH). Anal. Calcd for C20H19FeN: C 72.95, H 5.78, N 4.26. Found: C 72.51, H 5.62, N 4.52. (η5-C5H5)Fe(η5-C5H4)-CH2-NCH-C(CH3)CH-C6H5 (2b): orange oil (992 mg, 72.3%). IR (KBr pellet): 3096, 2911, 1652, 1630, 1598, 1425, 1345, 1101, and 809 cm−1. 1H NMR: δ 1.82 (1H, s, CH3), 4.25 (5H, s, C5H5), 4.32 (2H, s, C5H4), 4.37 (2H, s, C5H4), 4.85 (2H, s, CH2), 7.24−7.28 (2H, m, Ph-H), 7.31 (1H, s, CCHPh), 7.32−7.35 (1H, m, Ph-H), 7.54−7.57 (2H, m, Ph-H), 8.23 (1H, s, NCH). 13C NMR: δ 21.7 (CH3), 58.3 (CH2), 68.3, 68.4, 70.1, 70.2, 81.3 (C5H4C), 67.3 (C5H5-C), 124.1 (CCHPh), 127.1, 128.8, 132.5, 146.5 (PhC), 133.8 (CCHPh), 167.2 (NCH). Anal. Calcd for C21H21FeN: C 73.47, H 6.12, N 4.08. Found: C 73.01, H 6.41, N 4.23. Synthesis of the Cyclopalladated Complexes 4a,b. A solution of the ferrocenylimines 2a,b (1 mmol), Li2PdCl4 (1 mmol, 10 mL), and NaOAc (0.082 g, 1 mmol) in dry methanol was stirred for 20 h at room temperature. The resulting precipitate was collected by filtration and washed several times with methanol. A 1.5 mmol amount of triphenylphosphine was added to a CH2Cl2 suspension of the above precipitate, the mixture was stirred at room temperature for 3 h, and the monomeric derivatives 4a,b were purified by chromatography on a silica gel plate developed using CH2Cl2/CH3OH (20:1) as the eluent and recrystallized from CH3OH. Pd{[(η5-C5H4)Fe(η5-C5H4)-CH2-NCH-CHCH-C6H5]}ClPPh3 (4a): red solid (499 mg, 68.2%). Mp: 187−188 °C. IR (KBr pellet): 3038, 1611, 1598, 1420, and 780 cm−1. 1H NMR: δ 3.78 (2H, s, CH2), 3.33, 3.49, 3.83, 3.87, 3.93, 4.02, 4.31, 4.58 (8H, s, Cp-H), 7.29−7.31 (1H, m, CHCHPh), 7.31−7.64 (15H, m, PPh3-H), 7.31−7.40 (5H, m, PhH), 7.87−7.92 (1H, m, CHCHPh), 8.16−8.22 (1H, m, NCH). 13C NMR: δ 58.6 (CH2), 66.0, 66.4, 66.6, 67.3, 69.1, 71.7, 72.9, 74.3, 74.4, 81.7 (Cp-C), 127.0 (CHCHPh), 127.9, 128.9, 130.1, 134.9 (Ph-C), 128.0, 128.1, 130.1, 131.5, 134.8, and 135.2 (PPh3-C), 145.4 (CHCHPh), 162.7 (NCH). 31P NMR: δ 34.1. Anal. Calcd for C38H33ClFeNPPd: C 62.29, H 4.51, N 1.91. Found: C 62.58, H 4.92, N 1.94. Pd{[(η5-C5H4)Fe(η5-C5H4)-CH2-NCH-C(CH3)CH-C6H5]}ClPPh3 (4b): red solid (512 mg, 65.8%). Mp: 181−182 °C. IR (KBr pellet): 3038, 1613, 1595, 1410, and 775 cm−1. 1H NMR: δ 3.19 (3H, s, CH3), 3.52 (2H, s, CH2), 3.29, 3.79, 3.83, 3.86, 3.97, 4.03, 4.34, 4.98 (8H, s, Cp-H), 7.26−7.59 (15H, m, PPh3-H), 7.37−7.45 (5H, m, Ph-H), 7.35−7.36 (1H, m, CCHPh), 7.85−7.88 (1H, m, NCH). 13C NMR: δ 16.3 (CH3), 50.8 (CH2), 66.1, 66.4, 66.7, 66.8, 67.5, 69.2, 71.6, 73.3, 74.6, 82.7 (Cp-C), 127.8 (CCHPh), 128.0, 128.4, 130.2, 134.0 (Ph-C), 128.4, 129.7, 131.0, 131.5, 134.6, and 135.8 (PPh3-C), 145.2 (CCHPh), 167.5 (NCH). 31P NMR: δ 35.3. Anal. Calcd for C39H35ClFeNPPd·CH3OH: C 61.69, H 5.01, N 1.80. Found: C 61.32, H 5.42, N 1.91. General Procedure for Suzuki−Miyaura Cross-Coupling Reaction of Aryl Bromide or Aryl Chloride with Phenylboronic Acid. A 1 mmol amount of aryl bromide or chloride, 1.2 mmol of phenylboronic acid, 1 mmol of K3PO4·7H2O, and catalyst were dissolved in 5 mL of toluene and stirred at 110 °C for 2 h. The reaction mixture was diluted with water and extracted with CH2Cl2. After the removal of the solvent, the residue was purified by TLC on a silica gel plate (petroleum/CH2Cl2 = 5:1). X-ray Crystallographic Studies of the Cyclopalladated Complexes 4a,b. Suitable single crystals of complexes 4a,b for Xray diffraction were obtained from a CH2Cl2/CH3OH solution. X-ray single-crystal diffraction data for complexes 4a,b were collected on an Oxford Xcalibur, Gemini, Eos CCD diffractometer at 291(2) K with Mo Kα radiation (λ = 0.710 73 Å) by the ω scan mode. All the structures were solved by direct methods using the SHELXS program of the SHELXTL package and refined by full-matrix least-squares methods with SHELXL.14 CCDC Nos. 920661 and 920662 contain the supplementary crystallographic data for complexes 4a and 4b,

respectively. This material can be obtained free of charge via http:// www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Theoretical Details. Geometry optimizations and orbital calculations were performed using the hydrid B3LYP method.15 The 631G(d,p) basis set was employed for C, H, N, Cl, and S atoms, while for Pd and Fe atoms, the Lanl2dz basis set was used. The optimized geometry for the model complexes was in a good agreement with experimental results.

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ASSOCIATED CONTENT

S Supporting Information *

1

H and 13C NMR spectra of the heteroannular palladium complexes, typical 1H NMR spectra of biaryl products, and CIF files for the complexes 4a,b. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*(Z.-G. Yin) E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work is supported by National Natural Science Foundation of China (No. 21406209), Key Science and Technology Research for Henan Projects (No. 122102210046), and National Training Programs of Innovation and Entrepreneurship for Undergraduates (Nos. 201310462001 and 201310462024).

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