Synthesis and Characterization of Nickel(II) and Palladium(II

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Synthesis and Characterization of Nickel(II) and Palladium(II) Complexes based on Tridentate [N−NP] and [N−NS] Ligands and Their Applications in Norbornene Polymerization Xiao-Chao Shi and Guo-Xin Jin* Shanghai Key Laboratory of Molecular Catalysis and Innovative Material, Department of Chemistry, Fudan University, 200433 Shanghai, People's Republic of China S Supporting Information *

ABSTRACT: The series of anilido-imine N−NP and N−NS tridentate nickel and palladium complexes [(ArNHC6H4CH NPh-2-XPh)MCl] (X = PPh, Ar = 2,6-Me2C6H3, M = Ni (2a), X = PPh, Ar = 2,6-Et2C6H3, M = Ni (2b); X = PPh, Ar = 2,6-iPr2C6H3, M = Ni (2c); X = S, Ar = Ph, M = Ni (2d); X = S, Ar = 2,6-Me2C6H3, M = Ni (2e); X = S, Ar = 2,6-i-Pr2C6H3, M = Ni (2f); X = PPh, Ar = 2,6-Me2C6H3, M = Pd (3a); X = PPh, Ar = 2,6-Et2C6H3, M = Pd (3b); X = PPh, Ar = 2,6-i-Pr2C6H3, M = Pd (3c)) were synthesized. All the complexes were fully characterized by IR, NMR and elemental analyses. X-ray diffraction analyses on complexes 2a,c and 3a revealed an almost square-planar coordination of the central metal. After activation with methylaluminoxane (MAO), the nickel(II) complexes 2a−f can be used as catalysts for norbornene polymerization to produce vinyl addition type polynorbornene (PNB) with high catalytic activities, up to 5.82 × 107 g of PNB (mol of Ni)−1 h−1, while poor catalytic activities are found for the palladium complexes 3a−c.

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INTRODUCTION Increasing attraction has been paid to the late-transition-metal catalysts for olefin polymerization in academic and industrial fields over the past few decades.1 Among these numerous catalysts, the nickel and palladium complexes have been the focus of extensive studies, especially complexes based on the αdiimine and salicylaldiminato ligands.2,3 The bulky α-diimine nickel(II) and palladium(II) complexes showed high catalytic abilities for olefin polymerization and produced linear to highly branched polymers.2a−f Single-component neutral nickel catalysts based on salicylaldiminato ligands showed excellent performance in ethylene polymerization and exhibited good tolerance to functional groups.3 The phosphine-sulfonate palladium(II) complexes have also been the target of intense research in recent years for their high tolerance toward polar functional groups, even those containing active protons.4 Recently, complexes containing chelating anilido-imine ligands have attracted much attention due to their ease of preparation as well as versatile modification of the steric and electronic demands.5−10 Nickel and palladium complexes bearing anilidoimine ligands have been prepared and tested for the vinyl addition polymerization of norbornene.8 For example, Wu reported cationic nickel complexes bearing anilido-imine ligands, which showed high activity toward the polymerization of norbornene.8a Jin reported unique three-coordinate nickel (I) complexes bearing an anilido-imine ligand which exhibited high activity to norbornene polymerization, up to 2.82 × 107 g of PNB (mol of Ni)−1 h−1, with high molecular weight.8b It has been demonstrated that the side-arm effect of an extra donor has a strong influence on catalytic polymerization.11−14 © 2012 American Chemical Society

The metal complexes coordinated by hard atoms (N, O) and soft atoms (P, S) atoms in the side arm were mainly studied. Gibson reported that group 4 metal complexes containing phenoxy-amide ligands bearing soft pendant donors exhibited ethylene polymerization catalysts more highly active than those of counterparts containing hard donors or systems without a pendant donor.12a A series of titanium complexes reported by the Tang research group having extra pendant S and P donors on salicylaldiminato ligands showed high abilities toward ethylene polymerization and copolymerization with 1-hexane.12b,c Modification of the anilido-imine ligands by the side arm approach has also been reported.7,8c,d,9,10 Rare-earth-metal complexes bearing quinolinyl group modified anilido-imine ligands were demonstrated to create a single active site to initiate the polymerization of ε-caprolactone (ε-CL).7 Anilidoimine ligands containing an S atom which attach via the amido nitrogen have been reported, and their nickel and palladium complexes showed higher catalytic activity than [N,N] bidentate anilido-imino nickel complexes toward norbornene polymerization.8c Magnesium and zinc complexes supported by an NNN-tridentate anilido-aldimine ligand which was modified via the imido nitrogen have also shown high performance for the ROP of ε-caprolactone (CL) and L-lactide (LA).9,10 Previously, our group have reported Ni and Ir complexes containing anilido-imine ligands for ethylene and norbornene polymerization.8b,15 Moreover, we have successfully obtained the group IV metal complexes bearing the ligands which Received: April 19, 2012 Published: June 15, 2012 4748

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Scheme 1. Synthesis of Ligands

providing a soft atom coordinated to the metal center and demonstrated the positive effect of the soft atom in the ligands for ethylene polymerization.12d,16,17 Despite the fact that the introduction of a soft S atom to anilido-imine ligands on the amido nitrogen has been reported,8c there have been no examples of modifying the anilido-imine liands on the imine nitrogen side with soft atoms. Following our interest in modifying anilido-imine ligands by the side arm using soft atoms and exploring the effect of a pendant arm on the imine nitrogen, a series of novel tridentate anilido-imine [N−NS] and [N−NP] ligands and their nickel(II) and palladium(II) complexes have been synthesized. After activation with MAO, these nickel(II) complexes can be used as catalysts for the polymerization of norbornene and show high activity up to 5.82 × 107 g of PNB (mol of Ni−1) h−1.

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Figure 1. Molecular structure of 1c (thermal ellipsoids at the 30% probability level). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): P1−C26, 1.832(2); P1− C9, 1.834(2); P1−C32, 1.836(2); N1−C1, 1.363(3); N1−C14, 1.424(2); N2−C7, 1.276(3); N2−C8, 1.420(3); C26−P1−C9, 103.42(9); C9−P1−C32, 102.81(9); C1−N1−C14, 126.30(18); C7−N2−C8, 120.75(17); N2−C7−C6, 125.15(19); N1−C1−C6, 120.15(18).

RESULTS AND DISCUSSION − N NP and N−NS tridentate ligands with various sterically hindered substituents were synthesized as described in Scheme 1. Condensation of 2-fluorobenzaldehyde with 1 molar equiv of 2-(diphenylphosphino)benzenamine and 2-aminophenyl phenyl sulfide in hexane gave A1 and A2 in high yields, respectively. The N−NP and N−NS tridentate ligands were obtained by nucleophilic aromatic displacement of fluorine in A1 and A2 by salt elimination in THF. Pure products of 1a−f were obtained as yellow crystals by initially chromatography and then crystallization from ethanol. All of these new ligands were characterized by 1H NMR and 13C NMR spectra and elemental analyses. In 1a, for example, new signals at 9.87 and 2.06 ppm in 1H NMR spectra, which were identified as −NH and −CH3, indicated the displacement of fluorine. The structures of 1c,f were further confirmed by single-crystal Xray diffraction analysis (Figures 1 and 2). In 1c, the C7−N2 bond distance is 1.276(3) Å, while for 1f, the C7−N2 bond distance is 1.288(3) Å, which is typical of a carbon−nitrogen double bond. The C1−N1 bond lengths in 1c,f are 1.363(3) and 1.367(3) Å, respectively. The C6−C7−N2 and C6−C1− N1 angles in 1c are 125.15(19) and 120.15(18)°, respectively, and there are nearly no differences from those same angles in 1f. Treatments of lithium salts of corresponding anilido-imino ligands with (DME)NiCl2 and (COD)PdCl2 in toluene at 80 °C afforded the desired nickel and palladium complexes as dark red powders (Scheme 2). In the solid state, all of the complexes were stable in dry air but the nickel complexes slowly decomposed in solution. The nickel and palladium complexes were well characterized by 1H NMR and IR spectra and

elemental analyses. The disappearance of the −NH signals around 10−11 ppm in the 1H NMR spectra and the variety in elemental analyses indicated the formation of the nickel and palladium complexes. To further confirm the structures of these complexes, crystals of 2a,c and 3c were obtained from CH2Cl2/ hexane solutions and analyzed by single-crystal X-ray diffraction (Figures 3−5, respectively). Single crystals of nickel complexes 2d−f suitable for X-ray structure determination were not obtained, but other analysis results testified to the purity of these complexes. Molecular structure analyses of complexes 2a,c reveal that these complexes adopt an almost square-planar geometry around the metal center, which is quite different from the case for their corresponding anilido-imino nickel complexes with tetrahedral geometries, due to the coordination of the P-donor side arm.8a,c The coordinated atoms of N1, N2, P1, and Cl1 around the nickel centers in 2a,c are almost coplanar, and the distances from the metal centers to the planes are 0.031(1) and 0.025(1) Å, respectively. The Ni1−N1 bond lengths (2a, 1.919(2) Å; 2c, 1.9215(18) Å) are slightly longer than those of Ni1−N2 (2a, 1.890(2) Å; 2c, 1.8894(17) Å) and the C7−N2 bond lengths (2a, 1.314(3) Å; 2c, 1.318(3) Å) are obviously shorter than those of C1−N1 (2a, 1.354(3) Å; 2c, 1.350(3) Å). 4749

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Figure 2. Molecular structure of 1f (thermal ellipsoids at the 30% probability level). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): S1−C25, 1.776(2); N1− C1, 1.367(3); N1−C8, 1.430(3); N2−C7, 1.288(3); N2−C20, 1.411(3); C25−S1−C26, 102.30(11); C1−N1−C8, 123.77(19); C7−N2−C20, 119.3(2); N1−C1−C6, 120.4(2); N(2)−C(7)−C(6), 124.5(2).

Figure 3. Molecular structure of 2a (thermal ellipsoids at the 30% probability level). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ni1−N2, 1.890(2); Ni1− N1, 1.919(2); Ni1−P1, 2.1452(9); Ni1−Cl1, 2.1889(10); P1−C13, 1.791(2); N1−C1, 1.354(3); N(2)−C(7), 1.314(3); N(2)−C(8), 1.448(3); N2−Ni1−N1, 94.86(8); N2−Ni1−P1, 86.12(6) ; N1− Ni1−P1, 175.80(6); N2−Ni1−Cl1, 170.47(7) ; N1−Ni1−Cl1, 94.66(6); P1−Ni1−Cl1, 84.39(3); C13−P1−Ni1, 101.46(9); N2− C7−C6, 127.8(2).

All of these data suggested that 2a,c are more localized than βdiketiminato complexes and the imino CN bonds in 2a,c retain double-bond character. The P1−Ni1 bond lengths in 2a,c are 2.1452(9) and 2.1449(8) Å, respectively, similar to that of reported pyrrole-imine nickel(II) complexes (P−Ni = 2.1458(2) Å).14,18 Despite the different steric effects of the N-aryl groups in complexes 2a,c, the bite angles N1−Ni1−N2 (2a, 94.86(8)°; 2c, 94.94(7)°) of the complexes are nearly the same. The variations in the imine and amine bonds between complex 2c (C7−N2 = 1.318(3) Å, C1−N1 = 1.350(3) Å) and the ligand 1c (C7−N2 = 1.276(3) Å, C1−N1 = 1.363(3) Å) are attributed to the coordination of the nitrogen atoms to the metal center. The molecular structure of complex 3a (Figure 5) is similar to that of complex 2a, which also has an almost square-planar geometry, with a deviation of the palladium atom from the plane constructed by the coordinated atoms of 0.027(1) Å. In contrast to 2a, longer bond distances are observed between Pd

and the coordinated atoms. The Pd1−P1 bond length is 2.2140(9) Å, which is normal in comparison with other Pd−P bonds.18 Norbornene Polymerization. With methylaluminoxane (MAO) as cocatalyst, complexes 2a−f and 3a−c were not able to catalyze ethylene polymerization at 1 atm, and no solid polymer was observed even at high pressures of ethylene. However, nickel complexes 2a−f could polymerize norbornene to afford vinyl addition type polynorbornene (PNB) with high activities (107 g of PNB (mol of Ni)−1 h−1) after activation with MAO and produced high-molecular-weight polymers (105 g mol−1). To investigate the reaction parameters affecting the polymerization of norbornene, the catalytic precursor 2c was studied

Scheme 2. Synthesis of Nickel and Palladium Complexes

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Table 1. Results of Norbornene Polymerization with 2c/ MAOa entry

Al/Ni

temp (°C)

NB (g)

yield (g)

activityb

Mvc

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

1000 3000 5000 7000 10000 5000 5000 5000 5000 5000 5000d 5000e 5000f

25 25 25 25 25 0 50 75 25 25 25 25 25

2 2 2 2 2 2 2 2 1 3 2 2 2

0.531 0.550 0.636 0.350 0.168 0.480 0.445 0.293 0.254 0.7163 0.233 0.349 0.886

1.25 1.32 1.53 0.84 0.40 1.15 1.07 0.71 0.61 1.72 2.80 2.09 1.06

7.01 6.91 6.08 6.48 6.43 7.12 6.52 6.02 6.24 6.44 6.17 6.76 6.53

Polymerization conditions: complex, 0.5 μmol; time, 5 min; Vtotal, 10 mL; solvent, chlorobenzene. bIn units of 107 g of PNB (mol of Ni)−1 h−1. cIn units of 105 g mol−1. d1 min. e2 min. f10 min. a

Figure 4. Molecular structure of 2c (thermal ellipsoids at the 30% probability level). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ni1−N2, 1.8894(17); Ni1−N1, 1.9215(18); Ni1−P1, 2.1449(8); Ni1−Cl1, 2.1831(8); P1− C13, 1.801(2); N1−C1, 1.350(3); N1−C14, 1.442(2); N2−C7, 1.318(3); N2−C8, 1.436(3); N2−Ni1−N1, 94.94(7); N2−Ni1−P1, 86.52(6); N1−Ni1−P1, 172.95(5); N2−Ni1−Cl1, 169.28(6); N1− Ni1−Cl1, 95.18(5); P1−Ni1−Cl1, 83.86(3); C13−P1−Ni1, 101.24(8); N2−C7−C6, 128.42(19).

increased, the catalytic ability of 2c first increased and then decreased sharply, while the molecular weights of the polymers varied irregularly. The highest catalytic capacity, 1.53 × 107 g of PNB (mol of Ni)−1 h−1 ,was observed when the Al/Ni ratio was 5000 with a molecular weight of 6.08 × 105 g mol−1 (run 3 in Table 1). A similar tendency of the catalytic abilities was also noted when the reaction temperature was increased from 0 to 75 °C, but the molecular weights of the obtained polymers decreased monotonously. Increasing the monomer concentration resulted in an improvement of polymerization rate and catalytic activity from 0.61 × 107 to 1.72 × 107 g of PNB (mol of Ni)−1 h−1, which is in agreement with other reports.8c,18,19 As seen in Table 1, with prolongation of the polymerization time, the activities monotonically decreased over the whole process. This observation suggested that the active species could be formed rapidly at the initial stage of the reaction on activation with MAO. The norbornene polymerization results of 2a−f are collected in Table 2. Under the same conditions, the nickel catalysts 2a−f Table 2. Results of Norbornene Polymerization with Ni Catalystsa

Figure 5. Molecular structure of 3a (thermal ellipsoids at the 30% probability level). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Pd1−N2, 2.018(3); Pd1−N1, 2.070(3); Pd1−P1, 2.2140(9); Pd1−Cl1, 2.3143(9); P1− C13, 1.803(3); P1−C22, 1.814(3); P1−C28, 1.816(4); N1−C1, 1.348(4); N1−C14, 1.433(4); N2−C7, 1.314(5); N2−C8, 1.447(4); N2−Pd1−N1, 92.04(11); N2−Pd1−P1, 85.09(9); N1−Pd1−P1, 176.27(8); N2−Pd1−Cl1, 173.11(9); N1−Pd1−Cl1, 94.81(8); P1− Pd1−Cl1, 88.03(3); N2−C7−C6, 128.3(3).

entry

cat.

temp (°C)

NB (g)

yield (g)

conversn (%)

activityb

Mvc

1 2 3 4 5 6

2a 2b 2c 2d 2e 2f

25 25 25 25 25 25

2 2 2 2 2 2

0.457 0.396 0.349 0.716 0.970 0.632

22.8 19.8 17.5 35.8 48.5 31.6

2.72 2.37 2.08 4.30 5.82 3.79

6.46 7.64 6.76 7.67 6.95 7.36

Polymerization conditions: complex, 0.5 μmol; time, 2 min; Vtotal, 10 mL; solvent, chlorobenzene. bIn units of 107 g of PNB (mol of Ni)−1 h−1. cIn units of 105 g mol−1. a

showed high catalytic abilities toward norbornene polymerization, while the palladium catalysts 3a−c only produced traces of polymer. Complexes 2d−f, which have an S atom on the side arm, had higher catalytic abilities than their corresponding analogues that contain a P atom as the third coordinated atom. In comparison to the nickel complexes reported by Wu, which also have an S atom attached to the anilido-imine ligands but via the amido nitrogen, complexes 2d−f displayed much higher

under different reaction conditions, and the results are collected in Table 1. For Ni(II) catalysts, an organoaluminum compound, such as MAO, has been determined to be an essential ingredient for high catalytic activity.19 Variation of the ratio of MAO to 2c, which is expressed here as Al/Ni ratio, had a considerable effect on the catalytic activities and the molecular weights of the obtained polymers. When the Al/Ni ratio was 4751

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catalytic abilities under similar conditions.8c The reason might be that the structures of complexes 2d−f are nearly coplanar and could provid more space in the axial direction for the coordination and insertion of norbornene in the procedure of polymerization. The steric structures of the ligands substituted on the amine had a great effect on their catalytic activities. When R = CH3, the highest catalytic abilities, 2.72 × 107 g of PNB (mol of Ni)−1 h−1 for 2a−c and 5.82 × 107 g of PNB (mol of Ni)−1 h−1 for 2d−f, were observed. All of the obtained polymers showed very similar IR and 1H NMR spectra. The absence of signals at 1620−1680, 966, and 735 cm−1 in the IR spectra revealed that there were no traces of double bonds, and signals only in the 0.9−3.0 ppm range observed in the 1H NMR spectra also supplied the same information.20 These data indicated that the polymers were vinyl addition type PNB. Attempts to determine the glass transition temperature (Tg) of PNB failed, and the DSC studies did not give an endothermic signal upon heating to the decomposition temperature (above 450 °C).

78.04; H, 4.91; N, 3.72. X = S: yield 89%; 1H NMR (500 MHz, CDCl3, ppm) δ 8.87 (s, 1H, CHN-Ph), 8.17 (t, 1H, Ph H), 7.23(s, 1H, Ph H), 7.18 (t, 1H, Ph H), 6.98−7.08 (m, 3H, Ph H), 6.93 (t, 2H, Ph H), 6.76 (t, 3H, Ph H), 6.70 (m, 2H, Ph H); 13C NMR (125 MHz, CDCl3, ppm) δ 164.2, 153.6, 149.9, 133.9, 133.5, 133.3, 133.2, 132.8, 129.4, 129.0, 128.3, 127.9, 127.2, 126.7, 124.6, 126.0, 118.3, 116.0, 115.8. Anal. Calcd for C19H14FNS: C, 74.24; H, 4.59; N, 4.56. Found: C, 73.98; H, 4.58; N, 4.67. Synthesis of Ligand 1a. A solution of nBuLi (6.87 mL, 11 mmol) in hexane was added to a solution of 2,6-dimethylaniline (1.21 g, 10 mmol) in THF (30 mL) at −78 °C. The mixture was warmed to room temperature and stirred overnight. The resulting solution of LiNHAr (Ar = C6H3Me2-2,6) was transferred dropwise into a solution of oC6H4F(CHNC6H4-2-PPh2) (3.83 g, 10 mmol) in THF (40 mL) at room temperature. After the reaction mixture was stirred for 12 h at 40 °C, it was quenched with H2O (25 mL) and extracted with n-hexane. The organic phase was dried over MgSO4 and evaporated to dryness in vacuo to give the crude product as a yellow-red solid. The solid was chromatographed on aluminum oxide with hexane/EtOAc 30/1 to obtain the pure product 1a (1.74 g, 36%) as a yellow powder. 1H NMR (500 MHz, CDCl3, ppm): δ 9.87 (s, 1H, Ph NH), 8.66 (s, 1H, NCH), 7.45 (t, 1H, Ph H), 7.38 (d, 1H, Ph H), 7.25 (m, 1H, Ph H), 7.08−7.16 (m, 15H, Ph H), 6.76 (m, 1H, Ph H), 6.66 (t, 1H, Ph H), 6.15 (d, 1H, Ph H), 2.06 (s, 6H, Ph CH3). 13C NMR (125 MHz, CDCl3, ppm): δ 162.3, 154.2, 148.5, 137.5, 137.2, 136.6, 136.5, 134.9, 133.8, 133.6, 133.0, 132.8, 132.4, 129.9, 128.3, 128.2, 128.1, 128.0, 126.2, 126.0, 117.0, 116.9, 115.1, 111.7, 18.4. Anal. Calcd for C33H29N2P: C, 81.79; H, 6.03; N, 5.78. Found: C, 81.68; H, 6.11; N, 5.62. Synthesis of Ligand 1b. A procedure similar to that used for the preparation of 1a was employed: nBuLi (6.87 mL, 11 mmol), 2,6diethylaniline (1.50 g, 10 mmol), and o-C6H4F(CHNC6H4-2-PPh2) (3.83 g, 10 mmol). Yield: 1.84 g (38%). 1H NMR (500 MHz, CDCl3, ppm): δ 10.05 (s, 1H, Ph NH), 8.67 (s, 1H, NCH), 7.48 (t, 1H, Ph H), 7.41 (d, 1H, Ph H), 7.10−7.32 (m, 16H, Ph H), 6.84 (m, 1H, Ph H), 6.69 (t, 1H, Ph H), 6.23 (d, 1H, Ph H), 2.54 (q, 4H, −CH2CH3), 2.06 (t, 6H, −CH2CH3). 13C NMR (125 MHz, CDCl3, ppm): δ 162.8, 154.6, 149.5, 142.9, 136.9, 136.5, 135.1, 134.0, 133.8, 133.3, 132.8, 132.7, 132.5, 130.2, 128.4, 126.9, 126.1, 126.0, 127.3, 117.0, 115.2, 112.2, 24.6, 14.5. Anal. Calcd for C35H33N2P: C, 82.00; H, 6.49; N, 5.46. Found: C, 82.08; H, 6.45; N, 5.50. Synthesis of Ligand 1c. A procedure similar to that used for the preparation of 1a was employed: nBuLi (6.87 mL, 11 mmol), 2,6diisopropylaniline (1.77 g, 10 mmol), and o-C6H4F(CHNC6H4-2PPh2) (3.83 g, 10 mmol). Yield: 2.32 g (43%). 1H NMR (500 MHz, CDCl3, ppm): δ 10.30 (s, 1H, Ph NH), 8.47 (s, 1H, NCH), 7.40 (t, 1H, Ph H), 7.04−7.32 (m, 17H, Ph H), 6.83 (m, 1H, Ph H), 6.60 (t, 1H, Ph H), 6.20 (d, 1H, Ph H), 3.16 (m, 2H, −CHCH3), 1.11(d, 6H, −CHCH3), 1.05 (d, 6H, −CHCH3). 13C NMR (125 MHz, CDCl3, ppm): δ 163.3, 155.1, 150.0, 147.6, 137.2, 137.1, 135.0, 134.8, 133.9, 133.8, 133.3, 132.2, 130.1, 128.4, 128.3, 128.2, 127.3, 125.7, 123.7, 117.6, 116.8, 115.0, 112.5, 28.4, 24.5, 23.6. Anal. Calcd for C37H37N2P: C, 82.19; H, 6.90; N, 5.18. Found: C, 82.08; H, 7.01; N, 5.23. Synthesis of Ligand 1d. A procedure similar to that used for the preparation of 1a was employed: nBuLi (6.87 mL, 11 mmol), aniline (0.93 g, 10 mmol), and o-C6H4F(CHNC6H4-2-SPh) (3.07 g, 10 mmol). Yield: 1.18 g (31%). 1H NMR (500 MHz, CDCl3, ppm): δ 11.44 (s, 1H, Ph NH), 8.52 (s, 1H, NCH), 7.60 (d, 1H, Ph H), 7.11−7.41 (m, 14H, Ph H), 7.05 (d, 1H, Ph H), 6.98 (t, 1H, Ph H), 6.80 (t, 1H, Ph H). 13C NMR (125 MHz, CDCl3, ppm): δ 161.8, 150.8, 145.3, 142.3, 136.0, 134.9, 134.8, 131.6, 129.5, 129.1, 129.0, 128.8, 126.6, 126.4, 125.9, 123.4, 121.4, 121.2, 119.9, 118.0, 113.6. Anal. Calcd for C25H20N2S: C, 78.91; H, 5.30; N, 7.36. Found: C, 78.82; H, 5.39; N, 7.31. Synthesis of Ligand 1e. A procedure similar to that used for the preparation of 1a was employed: nBuLi (6.87 mL, 11 mmol), 2,6diethylaniline (1.50 g, 10 mmol), and o-C6H4F(CHNC6H4-2-SPh) (3.07 g, 10 mmol). Yield: 1.22 g (30%). 1H NMR (500 MHz, CDCl3, ppm): δ 10.45 (s, 1H, Ph NH), 8.64 (s, 1H, NCH), 7.40 (d, 1H, Ph H), 7.10−7.31 (m, 13H, Ph H), 6.67 (t, 1H, Ph H), 6.22 (d, 1H, Ph

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CONCLUSION A series of nickel and palladium complexes bearing new tridentate anilido-imine N−NP and N−NS legands were synthesized and characterized. A combination of spectroscopic and X-ray crystallographic studies confirmed the molecular structures of these nickel and palladium complexes. By introduction of such a side arm, the nickel(II) complexes were demonstrated to be efficient catalytic precursors for the addition polymerization of norbornene. After being activated with methylaluminoxane (MAO), the nickel(II) complexes 2a− f could polymerize norbornene with high catalytic activities up to 5.82 × 107 g of PNB (mol of Ni)−1 h−1, while the palladium complexes 3a−c only produced traces of polymer.

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EXPERIMENTAL SECTION

General Considerations. All the operations were carried out under a pure argon atmosphere using standard Schlenk techniques. Tetrahydrofuran (THF), hexane, and toluene were distilled from sodium−benzophenone. Dichloromethane was distilled from calcium hydride. Commercial reagents, namely nBuLi, methylaluminoxane (MAO), 2-fluorobenzaldenyde (97%), 2,6-diisopropylaniline (92%), 2,6-diethylaniline (98%), 2,6-dimethylniline (95%), 2-aminophenyl phenyl sulfide (98%), and 2-(diphenylphosphino)benzenamine, were purchased from Acros Co. and used without further purification. Norbornene (bicyclo[2.2.1]hept-2-ene, Acros) was purified by distillation over sodium and used as a chlorobenzene solution. The complexes (DME)NiCl220a and (COD)PdCl220b complexes were synthesized according to the literature. Other commercially available reagents were purchased and used without purification. 1H (500 MHz) and 13C NMR (125 MHz) measurements were obtained on a Bruker AC500 spectrometer in CDCl3 solution. Elemental analyses for C, H, and N were carried out on an Elementar III Vario EI analyzer. Synthesis of Compound A. A solution of 2-fluorobenzaldehyde (1.86 g, 20 mmol), 2-substituted aniline (20 mmol), and 2 g of MgSO4 in n-hexane (50 mL) was stirred for 12 h at room temperature. The mixture was then filtered and washed with CH2Cl2. The combined bright yellow solution was concentrated to dryness and to give a yellow powder. Pure products were obtained as yellow crystals by recrystallization from ethanol in high yield. X = PPh: yield 92%; 1H NMR (500 MHz, CDCl3, ppm) δ 8.50 (s, 1H, CHN-Ph), 7.93 (t, 1H, Ph H), 7.69(m, 3H, Ph H), 7.46 (m, 6H, Ph H), 7.35 (m, 3H, Ph H), 7.13 (t, 3H, Ph H), 6.60 (t, 1H, Ph H), 6.91 (m, 1H, Ph H); 13C NMR (125 MHz, CDCl3, ppm) δ 161.9, 152.8, 136.9, 134.4, 134.2, 133.8, 133.6, 133.0, 132.9, 132.7, 132.3, 132.2, 132.1, 126.4, 126.1, 125.9, 124.4, 124.2, 117.2, 115.7, 115.5, 115.2, 114.9, 112.5, 111.5. Anal. Calcd for C25H19FNP: C, 78.32; H, 5.00; N, 3.65. Found: C, 4752

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H), 2.18 (s, 6H, Ph CH3). 13C NMR (125 MHz, CDCl3, ppm): δ 162.7, 150.0, 148.6, 137.5, 134.9, 134.3, 132.6, 131.6, 131.5, 130.6, 129.1, 128.3, 127.9, 127.1, 126.3, 117.9, 117.1, 115.4, 111.9, 18.5. Anal. Calcd for C27H24N2S: C, 79.37; H, 5.92; N, 6.86. Found: C, 79.45; H, 5.99; N, 6.85. Synthesis of Ligand 1f. A procedure similar to that used for the preparation of 1a was employed: nBuLi (6.87 mL, 11 mmol), 2,6diisopropylaniline (1.77 g, 10 mmol) and o-C6H4F(CHNC6H4-2SPh) (3.07 g, 10 mmol). Yield: 1.22 g (30%). 1H NMR (500 MHz, CDCl3, ppm): δ 10.66 (s, 1H, Ph NH), 8.68 (s, 1H, NCH), 7.19− 7.41 (m, 11H, Ph H), 6.26 (d, 1H, Ph H), 3.26 (m, 2H, −CHCH3), 1.14 (d, 6H, −CHCH3), 1.09 (d, 6H, −CHCH3). 13C NMR (125 MHz, CDCl3, ppm): δ 162.6, 150.2, 147.7, 138.8, 134.7, 133.6, 133.5, 132.4, 129.4, 128.3, 128.0, 127.5, 126.7, 126.3, 123.8, 117.5, 116.8, 115.2, 112.3, 28.5, 24.8, 23.3. Anal. Calcd for C31H32N2S: C, 80.13; H, 6.94; N, 6.03. Found: C, 80.05; H, 7.09; N, 6.05. Synthesis of Complex 2a. A solution of nBuLi (0.68 mL, 1.1 mmol) in hexane was added to a solution of 1a (0.48 g, 1.0 mmol) in dried toluene (10 mL) at −78 °C. The mixture was warmed to room temperature and stirred for 2 h. The resulting red solution was transferred dropwise into a suspension of (DME)NiCl2 (0.219 g, 1.0 mmol) in dried toluene (10 mL) at −78 °C, and the resulting mixture was slowly warmed to room temperature and stirred overnight at 80 °C. The crude reaction mixture was filtered under nitrogen and washed with toluene. The combined organic filtrates were concentrated under reduced pressure to ca. 2 mL, and then dry hexane (20 mL) was added. Solvent was removed from the precipitate via cannula filtration, and the residual red solid was washed with nhexane. Drying in vacuo produces the desired nickel complex in 45% yield (0.262 g). 1H NMR (500 MHz, CDCl3, ppm): δ 8.21 (s, 1H, NCH), 7.85 (t, 1H, Ph H), 7.24−7.46 (m, 12H, Ph H), 7.10 (d, 1H, Ph H), 7.02 (m, 3H, Ph H), 6.93 (m, 2H, Ph H), 6.34 (t, 1H, Ph H), 6.15 (d, 1H, Ph H), 2.32 (s, 6H, Ph CH3). IR (KBr): ν 1614, 1561, 1510, 1455, 1433, 1369, 1268, 1206, 1182, 1156, 1096, 1026, 752, 696 cm−1. Anal. Calcd for C33H28ClN2NiP: C, 68.61; H, 4.89; N, 4.85. Found: C, 68.88; H, 4.91; N, 4.72. Synthesis of Complex 2b. A procedure similar to that used for the preparation of 2a was employed: nBuLi (0.68 mL, 1.1 mmol), (DME)NiCl2 (0.219 g, 1.0 mmol), and 1b (0.51 g, 1.0 mmol). Yield: 0.215 g (35%). 1H NMR (500 MHz, CDCl3, ppm): δ 8.18 (s, 1H, NCH), 7.83 (t, 1H, Ph H), 7.08−7.44 (m, 17H, Ph H), 6.87 (m, 1H, Ph H), 6.31 (d, 1H, Ph H), 6.13 (d, 1H, Ph H), 2.68 (q, 4H, −CH2CH3), 1.22 (t, 6H, −CH2CH3). IR (KBr): ν 1613, 1564, 1514, 1457, 1434, 1340, 1255, 1178, 1160, 1097, 1028, 750, 693 cm−1. Anal. Calcd for C35H32ClN2NiP: C, 69.40; H, 5.32; N, 4.62. Found: C, 69.28; H, 5.31; N, 4.70. Synthesis of Complex 2c. A procedure similar to that used for the preparation of 2a was employed: nBuLi (0.68 mL, 1.1 mmol), (DME)NiCl2 (0.219 g, 1.0 mmol), and 1c (0.54 g, 1.0 mmol). Yield: 0.291 g (47%). 1H NMR (500 MHz, CDCl3, ppm): δ 8.27 (s, 1H, NCH), 7.84 (t, 1H, Ph H), 7.46 (m, 2H,Ph H), 7.36 (m, 3H, Ph H), 7.10−7.24 (m, 12H, Ph H), 6.82 (m, 1H, Ph H), 6.60 (t, 1H, Ph H), 6.32 (t, 1H, Ph H), 3.58 (m, 2H, −CHCH3), 1.04 (d, 6H, −CH− CH3), 0.99 (d, 6H, −CHCH3). IR (KBr): ν 1610, 1565, 1515, 1462, 1437, 1344, 1265, 1178, 1160, 1099, 1033, 748, 690 cm−1. Anal. Calcd for C37H36ClN2NiP: C, 70.11; H, 5.72; N, 4.42. Found: C, 69.99; H, 5.67; N, 4.59. Synthesis of Complex 2d. A procedure similar to that used for the preparation of 2a was employed: nBuLi (0.68 mL, 1.1 mmol), (DME)NiCl2 (0.219 g, 1.0 mmol), and 1d (0.383 g, 1.0 mmol). Yield: 0.073 g (15%). 1H NMR (500 MHz, CDCl3, ppm): δ 7.11−7.65 (m, 16H, Ph H and NCH overlap), 6.81 (t, 1H, Ph H), 6.66 (t, 1H, Ph H), 6.42 (d, 1H, Ph H). IR (KBr): ν 1604, 1577, 1524, 1450, 1426, 1323, 1154, 1125, 1024, 742, 690 cm −1 . Anal. Calcd for C25H19ClN2NiS: C, 63.40; H, 4.04; N, 5.91. Found: C, 63.59; H, 4.11; N, 5.89. Synthesis of Complex 2e. A procedure similar to that used for the preparation of 2a was employed: nBuLi (0.68 mL, 1.1 mmol), (DME)NiCl2 (0.219 g, 1.0 mmol), and 1e (0.41 g, 1.0 mmol). Yield: 0.095 g (19%). 1H NMR (500 MHz, CDCl3, ppm): δ 7.11−7.83 (m,

14H, Ph H and NCH overlap), 6.71 (t, 1H, Ph H), 6.50 (d, 1H, Ph H), 6.22 (m, 1H, Ph H). 2.19 (s, 6H, Ph CH3). IR (KBr): ν 1610, 1576, 1560, 1507, 1466, 1452, 1323, 1185, 1156, 1110, 752, 740, 690 cm−1. Anal. Calcd for C27H23ClN2NiS: C, 64.64; H, 4.62; N, 5.58. Found: C, 64.51; H, 4.51; N, 5.69. Synthesis of Complex 2f. A procedure similar to that used for the preparation of 2a was employed: nBuLi (0.68 mL, 1.1 mmol), (DME)NiCl2 (0.219 g, 1.0 mmol), and 1f (0.46 g, 1.0 mmol). Yield: 0.101 g (18%). 1H NMR (500 MHz, CDCl3, ppm): δ 7.08−7.30 (m, 14H, Ph H and NCH overlap), 6.90 (t, 1H, Ph H), 6.72 (t, 1H, Ph H), 6.12 (d, 1H, Ph H). 3.26 (m, 2H, −CHCH3), 1.12 (q, 12H, −CHCH3). IR (KBr): ν 1611, 1578, 1558, 1503, 1451, 1436, 1262, 1181, 1097, 1022, 801, 746, 688 cm −1 . Anal. Calcd for C31H31ClN2NiS: C, 66.75; H, 5.60; N, 5.02. Found: C, 66.51; H, 5.51; N, 5.11. Synthesis of Complex 3a. A procedure similar to that used for the preparation of 2a was employed: nBuLi (0.68 mL, 1.1 mmol), (COD)PdCl2 (0.300 g, 1.0 mmol), and 1a (0.48 g, 1.0 mmol). Yield: 0.406 g (65%). 1H NMR (500 MHz, DMSO, ppm): δ 8.96 (s, 1H, NCH), 8.13 (m, 1H, Ph H), 7.48−7.71 (m, 14H, Ph H), 7.28 (t, 1H, Ph H), 6.98 (m, 3H, Ph H), 6.86 (t, 1H, Ph H), 6.30 (t, 1H, Ph H), 5.89 (d, 1H, Ph H), 2.00 (s, 6H, Ph CH3). IR (KBr): ν 1612, 1581, 1566, 1508, 1455, 1436, 1261, 1159, 1099, 745, 692 cm−1. Anal. Calcd for C33H28ClN2PdP: C, 63.37; H, 4.51; N, 4.48. Found: C, 63.48; H, 4.59; N, 4.42. Synthesis of Complex 3b. A procedure similar to that used for the preparation of 2a was employed: nBuLi (0.68 mL, 1.1 mmol), (COD)PdCl2 (0.300 g, 1.0 mmol), and 1b (0.51 g, 1.0 mmol). Yield: 0.496 g (76%). 1H NMR (500 MHz, DMSO, ppm): δ 8.95 (s, 1H, NCH), 8.13 (t, 1H, Ph H), 7.45−7.70 (m, 15H, Ph H), 7.27 (t, 1H, Ph H), 7.01 (m, 3H, Ph H), 6.27 (t, 1H, Ph H), 5.87 (d, 1H, Ph H), 2.53 (m, 2H, −CH2CH3), 2.37 (m, 2H, −CH2CH3), 1.02 (t, 6H, −CH2CH3). IR (KBr): ν 1610, 1566, 1509, 1459, 1437, 1399, 1351, 1265, 1159, 1100, 1033, 748, 691 cm −1 . Anal. Calcd for C35H32ClN2PdP: C, 64.33; H, 4.94; N, 4.29. Found: C, 64.58; H, 4.99; N, 4.41. Synthesis of Complex 3c. A procedure similar to that used for the preparation of 2a was employed: nBuLi (0.68 mL, 1.1 mmol), (COD)PdCl2 (0.300 g, 1.0 mmol), and 1b (0.54 g, 1.0 mmol). Yield: 0.497 g (73%). 1H NMR (500 MHz, DMSO, ppm): δ 8.99 (s, 1H, NCH), 8.16 (m, 1H, Ph H), 7.44−7.72 (m, 13H, Ph H), 6.94−7.30 (m, 5H, Ph H), 6.28 (t, 1H, Ph H), 5.95 (d, 1H, Ph H), 3.14 (m, 2H, −CHCH3), 1.11 (d, 6H, −CHCH3), 0.88 (d, 6H, −CHCH3). IR (KBr): ν 1614, 1585, 1564, 1510, 1455, 1435, 1347, 1270, 1186, 1160, 1100, 1029, 749, 692 cm−1. Anal. Calcd for C37H36ClN2PdP: C, 65.20; H, 5.32; N, 4.11. Found: C, 65.31; H, 5.26; N, 4.15. X-ray Crystallography. Single crystals of complexes 1c,f, 2a,c, and 3a suitable for X-ray analysis were obtained from CH2Cl2/n-hexane solutions. The intensity data of the single crystals were collected on the CCD-Bruker Smart APEX system. All determinations of the unit cell and intensity data were performed with graphite-monochromated Mo Ka radiation (λ = 0.710 73 Å). All data were collected at room temperature or −100 °C using the ω scan technique. These structures were solved by direct methods using Fourier techniques and refined on F2 by a full-matrix least-squares method. All the non-hydrogen atoms were refined anisotropically, and all the hydrogen atoms were included but not refined. Polymerization of Norbornene. In a typical procedure (entry 3, Table 1), 0.5 μmol of nickel complex 2c in 1.0 mL of chlorobenzene, 2 g of norbornene in 4.0 mL of chlorobenzene, and another 3.4 mL of fresh chlorobenzene were placed in a special polymerization bottle (50 mL) with a strong stirrer under a nitrogen atmosphere. After the mixture was kept at 30 °C for 10 min, 1.66 mL of MAO was charged into the polymerization system via syringe and the reaction was initiated. Five minutes later, acidic ethanol (Vethanol/Vconcd HCl = 20/1) was added to terminate the reaction. The PNB was isolated by filtration, washed with ethanol, and dried at 80 °C for 48 h under vacuum. For all polymerization procedures, the total reaction volume was 10.0 mL, which can be achieved by varying the amount of 4753

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chlorobenzene when necessary. IR (KBr): ν 2947, 2867, 1475, 1453, 1375, 1294, 1258, 1146, 1107, 1040, 941, 891 cm−1.

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(7) (a) Shang, X.; Liu, X.; Cui, D. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 5662. (b) Gao, W.; Cui, D.; Liu, X.; Zhang, Y.; Mu, Y. Organometallics 2008, 27, 5889. (8) (a) Gao, H. Y.; Guo, W. J.; Bao, F.; Gui, G. Q.; Zhang, J. K.; Zhu, F. M.; Wu, Q. Organometallics 2004, 23, 6273. (b) Wang, H. Y.; Meng, X.; Jin, G. X. Dalton Trans. 2006, 2579. (c) Long, J. M.; Gao, H. Y.; Song, K. M.; Liu, F. S.; Hu, H.; Zhang, L.; Zhu, F. M.; Wu, Q. Eur. J. Inorg. Chem. 2008, 4296. (d) Long, J. M.; Gao, H. Y.; Liu, F. S.; Song, K. M.; Hu, H.; Zhu, F. M.; Wu, Q. Inorg. Chim. Acta 2009, 362, 3035. (9) Tsai, Y. H.; Lin, C. H.; Lin, C. C.; Ko, B. T. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 4927. (10) Liu, Y. C.; Lin, C. H.; Ko, B. T.; Ho, R. M. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 5339. (11) Jone, D. J.; Gibson, V. C.; Green, S.; Maddox, P. Chem. Commun. 2002, 1038. (12) (a) Oakes, D. C. H.; Kimberley, B. S.; Gibson, V. C.; Jones, D. J.; White, A. J. P.; Williams, D. Chem. Commun. 2004, 2174. (b) Hu, W. Q.; Sun, X. L.; Wang, C.; Gao, Y.; Tang, Y.; Shi, L. P.; Xia, W.; Sun, J.; Dai, H. L.; Li, X. Q.; Yao, X. L.; Wang, X. R. Organometallics 2004, 23, 1684. (c) Wang, C.; Ma, Z.; Sun, X. L.; Gao, Y.; Guo, Y. H.; Tang, Y.; Shi, L. P. Organometallics 2006, 25, 3259. (d) Jia, A. Q.; Wang, J. Q.; Hu, P.; Jin, G. X. Dalton Trans. 2011, 40, 7730. (13) Tshuva, E. Y.; Groysman, S.; Godbeg, I.; Kol, M. Organometallics 2002, 21, 662. (14) Siedle, G.; Lassabn, P. G.; Lozan, V.; Janiak, C.; Kersting, B. Dalton Trans. 2007, 52. (15) Meng, X.; Jin, G. X. J. Organomet. Chem. 2008, 693, 2597. (16) Zhang, J.; Lin, Y. J.; Jin, G. X. Organometallics 2007, 26, 4042. (17) Jia, A. Q.; Jin, G. X. Organometallics 2009, 28, 1872. (18) Han, F. B.; Zhang, Y. L.; Sun, X. L.; Li, B. G.; Guo, Y. H.; Tang, Y. Organometallics 2008, 27, 1924. (19) (a) Tang, G. R.; Lin, Y. J.; Jin, G. X. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 489. (b) Janiak, C.; Lassahn, P.-G. Polym. Bull. 2002, 47, 539. (c) Berchtold, B.; Lozan, V.; Lassahn, P.-G.; Janiak, C. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 3604. (d) Lassahn, P.-G.; Lozan, V.; Timco, G. A.; Christian, P.; Janiak, C.; Winpenny, R. E. P. J. Catal. 2004, 222, 260. (e) Lozan, V.; Lassahn, P.-G.; Zhang, C. G.; Wu, B.; Janiak, C.; Rheinwald, G.; Lang, H. Z. Naturforsch., B 2003, 58, 1152. (f) Blank, F.; Scherer, H.; Janiak, C. J. Mol. Catal. A: Chem. 2010, 330, 1. (20) (a) Ward, L. G. L. Inorg. Synth. 1972, 13, 154. (b) Rulke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; Van Leeuwen, W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

ASSOCIATED CONTENT

* Supporting Information S

A table giving a summary of crystallographic data and CIF files giving crystal data for 1c,f, 2a,c, and 3a. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +86-21-65641740. Tel: +8621-65643776. Notes

The authors declare no competing financial interest.

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REFERENCES

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dx.doi.org/10.1021/om3003202 | Organometallics 2012, 31, 4748−4754