Synthesis, Structures, and Norbornene Polymerization Behavior of

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

Synthesis, Structures, and Norbornene Polymerization Behavior of Neutral Nickel(II) and Palladium(II) Complexes Bearing Aryloxide Imidazolidin-2-imine Ligands Mingyuan Li,† Xin Shu,† Zhengguo Cai,*,† and Moris S. Eisen*,‡ †

State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, People’s Republic of China ‡ Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa, 32000, Israel S Supporting Information *

ABSTRACT: A series of novel aryloxide imidazolidin-2-imine bidentate neutral Ni(II) and Pd(II) complexes bearing fiveand six-membered chelate ring structures were synthesized and characterized. X-ray diffraction analysis results revealed that all of the Ni(II) complexes (Ni1−Ni3) and Pd(II) complexes (Pd1 and Pd3) adopted an almost square-planar geometry. In the presence of various cocatalysts such as MAO, MMAO, Et2AlCl, and EtAlCl2, all of the Ni(II) and Pd(II) complexes exhibited remarkably high activities (up to 2.6 × 107 g of PNB (mol of M)−1 h−1) toward the addition polymerization of norbornene. These catalyst systems produced high-molecularweight polynorbornene (PNB) with narrow molecular weight distribution, except for the insoluble PNB obtained with Pd1−Pd3/MAO systems. The Pd(II) complexes showed particularly good thermostability with a high activity of 1.56 × 107 g of PNB (mol of Pd)−1 h−1 even at 80 °C. These complexes are rare examples of neutral Ni(II) and Pd(II) complexes bearing aryloxide-functionalized imidazolidin-2-imine ligands in the field of olefin polymerization.

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INTRODUCTION In 1995, cationic Ni(II) and Pd(II) complexes bearing bulky αdiimine ligands reported by Brookhart et al.1 made it possible to produce various branched polyethylenes with excellent activities and high molecular weight and copolymerize ethylene with polar monomers such as methyl acrylate. Since then, latetransition-metal catalysts have aroused a great deal of research. Later at the end of the 20th century, Grubbs et al.2 reported a series of neutral Ni(II) complexes bearing salicylaldimine ligands (a, Chart 1) that showed high activities in ethylene polymerization to give high-molecular-weight linear polyethylene even without any cocatalyst and exhibited excellent tolerance toward heteroatoms. These unique features make neutral Ni(II) catalysts an attractive choice for olefin (co)polymerization, and therefore have attracted great interest in the modification and design of novel neutral Ni(II) catalysts with analogous scaffolds.3 In the past few decades, N-heterocyclic carbenes (NHCs), due to their various distinctive capabilities, have been given wide attention and regarded as a powerful class of ligands in organometallics since the precursory work of Arduengo.4 Grubbs et al.5 first reported a series of chelating NHC-ligated Pd(II) complexes (b, Chart 1) in 2004, which is analogous to the salicylaldimine framework and may have the potential to enhance the reactivity of metal-based catalysts. The extensive © XXXX American Chemical Society

Chart 1. Analogy between Salicylaldimine, Aryloxide NHCs, and Aryloxide Imidazolidin-2-imine Ligands

modification of NHC ligands was then applied in various transition-metal complexes that showed excellent performance in catalytic transformations, including olefin polymerization catalyzed by group 4 and 10 transition-metal catalysts.6 A class of NHC derivatives formed by an exocyclic nitrogen atom attached at the 2-position of the N-heterocycle, imidazolin-2-iminato ligands, which can be described by the Received: January 30, 2018

A

DOI: 10.1021/acs.organomet.8b00059 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics mesomeric structures shown in Chart 2, indicate that these ligands may act as strong 2σ,4π-electron N-donor ligands.7,8

Scheme 1. Synthesis of Aryloxide Imidazolidin-2-imine Ligands and Complexes

Chart 2. Mesomeric Forms of Imidazolin- and Imidazolidin2-iminato Ligands

In addition, their parallels containing five-membered Nheterocycles, but with a saturated 4,5-CH2CH2 moiety, affording imidazolidines instead of imidazolines should also have the same mesomeric structures (Chart 2).7−10 These imidazolin- and imidazolidin-2-iminato ligands are widely used in organometallic chemistry. Excellent performance of their early-transition-metal complexes is increasingly being observed in the field of olefin polymerization.9 However, there are few reports on latetransition-metal complexes bearing these ligands for olefin polymerization catalysis.8 Moreover, these imidazolin- and imidazolidin-2-iminato ligands are generally coordinated to the metal center in their monoanionic forms.7−9 The study of the coordination applications of their neutral forms in olefin polymerization is still very limited, although they have already been used in organometallic and coordination chemistry.10 Stimulated by the bridged neutral bis- and mono(imidazolinand imidazolidin-2-imine) ligands,10 we think that the bidentate ligands formed by appending an additional functional donor group to these neutral forms could have promising applications in late-transition-metal catalysts in olefin polymerization. Here, we report an efficient way to synthesize a series of aryloxide imidazolidin-2-imine bidentate ligands and also their Ni(II) and Pd(II) complexes (Chart 1), and the catalytic behaviors toward norbornene polymerization. This is the first example, to the best of our knowledge, of neutral Ni(II) and Pd(II) complexes bearing aryloxide-functionalized imidazolidin2-imine ligands in the field of olefin polymerization.

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RESULTS AND DISCUSSION Synthesis and Characterization of the Ligands and Complexes. As shown in Scheme 1, the ligands L1−L3 were synthesized by the reaction of substituted o-aminophenol (1 and 2) or substituted 2-(aminomethyl)phenol (3) with 2chloro-1,3-dimethyl imidazolinium chloride (4, DMC) in the presence of trimethylamine in acetonitrile. DMC can be easily obtained by refluxing 1,3-dimethyl-2-imidazolidinone (DMI) with excess oxalyl chloride in chloroform.11 After deprotonation of each ligand with 1.5 equiv of KH, reaction with the appropriate metal precursor (trans-[NiPhCl(PPh3) 2] or [PdMeCl(PPh3)]2) led to the formation of the expected neutral Ni(II) complexes (Ni1−Ni3) and Pd(II) complexes (Pd1−Pd3) in good yields, respectively. All of the Ni(II) complexes and Pd(II) are sensitive to air and moisture when they are in solution. The solid-state forms of these complexes are stable in air and moisture for several hours. In addition, Ni(II) complexes Ni1−Ni3 and Pd(II) complexes Pd1 and Pd3 were suitable for X-ray diffraction analysis (Figure 1). The selected bond lengths and angles of these complexes are shown in Table 1. The structures revealed that all of the complexes adopted an almost square-planar geometry, in which the distances from the

Figure 1. Structures of complexes Ni1−Ni3, Pd1, and Pd3. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms have been omitted for clarity.

metal center to the coordination plane are 0.085 Å (Ni1), 0.121 Å (Ni2), 0.062 Å (Ni3), 0.048 Å (Pd1), and 0.058 Å (Pd3), respectively. The PPh3 group in the complexes Ni1−Ni3 and Pd1 is trans to the imidazolidin-2-imine group, while the PPh3 group was found to be cis in complex Pd3. Interestingly, the Pd−C bond (2.032(3) Å for Pd3) is much shorter than that in complex Pd1 (2.1781(18) Å), indicating that the Pd−C bond in this cis configuration is stronger than that in the trans configuration. The Ni−O bond lengths (1.90−1.92 Å) are much shorter than the Pd−O bond lengths (∼2.06 Å). The Ni−N(imidazolidin-2-imine) bond lengths (1.92−1.94 Å) in the Ni(II) complexes are also much shorter than those in the Pd(II) complexes (2.12−2.13 Å) and similar to those in the neutral salicylaldiminato Ni(II) complexes (a1, ∼1.937(4) Å B


Article

Organometallics Table 1. Selected Bond Lengths (Å) and Angles (deg) for Ni(II) and Pd(II) Complexes M−O M−N M−P M−C O−M−P O−M−N N−M−P C−M−P C−M−O C−M−N a

Ni1

Ni2

Ni3a

Pd1

Pd3

1.9096(11) 1.9368(13) 2.1412(4) 1.8865(16) 92.05(4) 84.61(5) 173.47(4) 89.04(5) 175.62(6) 93.88(6).

1.9051(13) 1.9260(16) 2.1322(6) 1.897(2) 91.80(4) 84.94(6) 174.25(5) 87.69(6) 170.74(8) 94.76(7)

1.902(4)/1.915(4) 1.936(5)/1.919(5) 2.1462(19)/2.1572(18) 1.882(7)/1.884(6) 86.94(13)/88.10(12) 91.35(18)/91.09(18) 174.23(15)/177.30(16) 90.7(2)/91.66(19) 177.2(3)/176.7(2) 90.9(2)/89.0(2)

2.0587(17) 2.1206(18) 2.2312(6); 2.1781(18) 93.58(5) 80.75(7) 172.75(5) 89.38(5) 170.32(7) 96.94(7);

2.0576(18) 2.134(2) 2.2063(8) 2.032(3) 169.33(6) 87.18(7) 101.17(6) 87.59(9) 84.13(10) 171.24(10)

There are two independent molecules in the unit cell.

for Ni−N(imine))2a but longer than those in the bis(aryloxideNHC) Ni(II) complexes (b1, 1.838(2)−1.866(2) Å for Ni− C(carbine)).6l The Pd−N(imidazolidin-2-imine) bond lengths are also analogous to those in the neutral salicylaldimine Pd(II) complexes (a2, 2.088(3)−2.103(3) Å for Pd−N(imine))12 and longer than those in the aryloxide-NHC Pd(II) complexes (b2, 1.950(3)−2.030(3) Å for Pd−C(carbene)),5,6n respectively. These results revealed that the coordination ability of the neutral form of the imidazolidin-2-imine ligand is similar to that of the salicylaldimine ligand and slightly weaker than that of the carbene ligand, because the tendency of the metal−ligand interaction is usually indicated by the length of the metal− ligand bonds.8 The O−M−N angles in all of the Ni(II) complexes (84.61(5)° for Ni1; 84.94(6)° for Ni2; 91.35(18)/ 91.09(18)° for Ni3) are larger than those of the Pd(II) complexes with the same ligand (80.75(7)° for Pd1; 87.18(7)° for Pd3). With the same two t-Bu groups on the ligand, the O− Ni−N angle in complex Ni3 bearing a six-membered chelate ring is larger than that in the complex Ni2 bearing a fivemembered chelate ring. Norbornene Polymerization. Polynorbornene (PNB) obtained by vinyl-type polymerization of norbornene shows unique properties, such as high glass transition and decomposition temperatures, good chemical and UV resistance, excellent transparency, low optical birefringence and dielectric loss, and high refractive index.13 Ni(II) and Pd(II) complexes are the most outstanding catalysts toward norbornene polymerization due to their excellent performance, such as high activity and high molecular weight of the PNBs.13a Neutral salicylaldimine-ligated Ni(II) catalysts upon the activation of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO) exhibited very high activities up to 107 g of PNB (mol of Ni)−1 h−1 to produce high-molecular-weight vinyl-type PNB.14 Neutral Ni(II) catalysts bearing bis(o-aryloxide NHC) ligands showed moderate catalytic activities (106 g of PNB (mol of Ni)−1 h−1) in the addition polymerization of norbornene. Neutral Pd(II) catalysts bearing salicylaldimine ligands and oaryloxide NHCs ligands also exhibited great performance in this field.6 As analogues of these complexes, the complexes presented in this work should have potential application in olefin polymerization. Therefore, their catalytic behaviors toward norbornene polymerization were studied. The polymerization results with Ni(II) catalysts and Pd(II) catalysts are summarized in Tables 2 and 3, respectively. Moreover, the selected molecular weights and distributions of soluble PNBs are given in Table 4. In the absence of cocatalysts, all of the complexes were inactive, which implies that phosphine scavengers are crucial for these catalytic systems. In the

Table 2. Polymerization of Norbornene with Ni(II) Complexes Activated by Different Cocatalystsa entry

cat.

cocat.

Al/Ni

T (°C)

yield (g)

Ab

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

Ni1 Ni1 Ni1 Ni1 Ni1 Ni1 Ni1 Ni1 Ni1 Ni1 Ni1 Ni2 Ni3

MAO MAO MAO MAO MMAO Et2AlCl EtAlCl2 MAO MAO MAO MAO MAO MAO

4000 5000 6000 7000 6000 6000 6000 6000 6000 6000 6000 6000 6000

10 10 10 10 10 10 10 20 40 60 80 10 10

0.176 0.208 0.247 0.238 0.210 0.155 0.020 0.213 0.188 0.119 0.084 0.227 0.223

1.06 1.25 1.48 1.43 1.26 0.93 0.12 1.28 1.13 0.71 0.50 1.36 1.34

Polymerization conditions: complex, 0.5 μmol; norbornene, 20 mmol; MAO, 1.4 M in toluene; MMAO, 2.43 M in toluene; Et2AlCl, 0.9 M in n-hexane; EtAlCl2, 1.8 M in toluene; t = 20 min; Vtotal(toluene) = 15 mL. bAcitivity in units of 106 g of PNB (mol of Ni)−1 h−1. a

presence of various cocatalysts such as MAO, MMAO, Et2AlCl, and EtAlCl2, Ni(II) complexes showed high activities, producing soluble vinyl-type PNBs with high molecular weight and narrow molecular weight distribution. Pd(II) complexes showed much higher activities, although PNB produced by the Pd/MAO system was insoluble even at 150 °C in trichlorobenzene. We selected Ni(II) complex Ni1 to investigate the effects of the cocatalyst used and a series of polymerization conditions in detail. On activation with MAO at 10 °C, the activity of catalyst Ni1 increased from 1.06 × 106 to 1.48 × 106 g of PNB (mol of Ni)−1 h−1 with an increase in the Al/Ni ratio from 4000 to 6000 (entries 1−3, Table 2). Further increase in the Al/Ni ratio to 7000 slightly decreased the activity (entry 4, Table 2). It was found that MMAO, Et2AlCl, and EtAlCl2 showed lower activities than MAO in the same Al/Ni ratio in the following order: MAO (1.48 × 106 g of PNB (mol of Ni)−1 h−1) > MMAO (1.26 g of PNB (mol of Ni)−1 h−1) > Et2AlCl (0.93 g of PNB (mol of Ni)−1 h−1) > EtAlCl2 (0.12 g of PNB (mol of Ni)−1 h−1) (entries 3 and 5−7, Table 2). The molecular weight Mn of the PNB obtained by complex Ni1 with different cocatalysts decreased in the order 74.5 × 104 (MAO) > 71.5 (MMAO) > 17.2 (Et2AlCl) > 4.6 (EtAlCl2), with a narrow molecular weight distribution of 1.22−1.58 (entries 1−4, Table 4), indicating the single-site catalytic behavior of the catalysts. It C


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Organometallics

3 and 12, Table 2) and a lower Mn value of 52.1× 104 (entry 5, Table 4), indicating that the greater steric hindrance and stronger electron-donating effect caused by t-Bu groups may slightly hinder the coordination and insertion process of norbornene monomers. The steric and electronic effects of substituents on the ligand were proved to show negligible influence on the activities and molecular weights of the reported salicylaldimine Ni complexes.3 In addition, reduced activities caused by slightly bulkier substituents on the ligand were observed in the bis(aryloxide-NHC) Ni system.6l This is different from the case for the polymerization of ethylene, in which bulky groups in the ortho position could generally improve both the activities of the catalysts and the molecular weight of polyethylene.3 There is not much difference in the activities and molecular weights between complex Ni2 with a five-membered ring and complex Ni3 with a six-membered ring (entries 12 and 13, Table 2; entries 5 and 6, Table 4), and both the activities and molecular weights were slightly lower than those of complex Ni1. The activities obtained in the Ni1−Ni3/ MAO systems are similar to those of the aryloxide-NHC Ni/ MAO syetem (∼106 g of PNB (mol of Ni)−1 h−1)6l and lower than those of typical salicylaldimine Ni/MMAO systems (∼107 g of PNB (mol of Ni)−1 h−1).14a On the basis of the norbornene polymerization results with Ni(II) catalysts, Pd(II) complex Pd1 was chosen as the precatalyst to study the effects of cocatalyst and a series of conditions of polymerization in detail. On activation with MAO, the activity of catalyst Pd1 increased from 1.15 × 106 to 2.13 × 106 and then decreased to 1.80 × 106 g of PNB (mol of Ni)−1 h−1 with an increase in the Al/Pd ratio from 5000 to 10000 (entries 14−17, Table 3). An increase in the polymerization temperature resulted in an increase in the activity of 1 order of magnitude (up to 26.28 × 106 g of PNB (mol of Pd)−1 h−1 at 60 °C) and maintained high activity even at 80 °C (entries 18−21, Table 3). Complexes Pd2 and Pd3 also showed very high activities of 23.35 × 106 and 24.59 × 106 g of PNB (mol of Pd)−1 h−1 at 60 °C (entries 22 and 23, Table 3), respectively, indicating that Pd(II) catalysts showed better thermostability than Ni(II) catalysts. The highest activity obtained in this Pd1−Pd3/MAO system is comparable to those of the Pd/MAO system based on typical salicylaldimine ligands12 and aryloxide-NHC ligands,6q in both of which the activities are usually around (20−50) × 106 g of PNB (mol of Pd)−1 h−1 at elevated temperature, indicating the excellent performance of Pd complexes and also the negligible influence of steric effects in Pd/MAO systems. As in the same cases described in many previous reports, the PNBs obtained by Pd/ MAO systems here are also insoluble in most common organic solvents.6 When EtAlCl2 was used as a cocatalyst, complex Pd1 showed the highest activity of 7.09 × 106 g of PNB (mol of Pd)−1 h−1 at an Al/Pd ratio of 4500 at 10 °C (entry 26, Table 3), whereas Et2AlCl exhibited significantly low activity (entry 28, Table 3). The highest activity of Pd1 with EtAlCl2 (12.12 × 106 g of PNB (mol of Pd)−1 h−1) was observed at 40 °C (entry 30, Table 3). Most importantly, soluble PNBs were obtained by the Pd1/EtAlCl2 system with a high molecular weight Mn of 32.7 × 104 and narrow PDI of 1.58 (entry 7, Table 4). Complexes Pd2 and Pd3 also showed high activities of 12.05 × 106 and 11.64 × 106 g of PNB (mol of Pd)−1 h−1 at 40 °C (entries 33 and 34, Table 3), respectively, to yield highmolecular-weight PNBs (entries 8 and 9, Table 4). The highest activity of the Pd/EtAlCl2 system here is similar to that of the tridentate o-aryloxide-NHC Pd/Et2AlCl system (12.29 × 106 g

Table 3. Polymerization of Norbornene with Pd(II) Complexes Activated by Different Cocatalystsa entry 14c 15c 16c 17c 18 19 20 21 22 23 24 25 26 27 28c 29 30 31 32 33 34

cat. (amt (μmol)) Pd1 Pd1 Pd1 Pd1 Pd1 Pd1 Pd1 Pd1 Pd2 Pd3 Pd1 Pd1 Pd1 Pd1 Pd1 Pd1 Pd1 Pd1 Pd1 Pd2 Pd3

(0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (1.0) (1.0) (1.0) (1.0) (1.0) (1.0) (1.0) (1.0) (1.0) (1.0) (1.0)

cocat.

Al/Pd

T (°C)

yield (g)

Ab

MAO MAO MAO MAO MAO MAO MAO MAO MAO MAO EtAlCl2 EtAlCl2 EtAlCl2 EtAlCl2 Et2AlCl EtAlCl2 EtAlCl2 EtAlCl2 EtAlCl2 EtAlCl2 EtAlCl2

5000 7000 9000 10000 9000 9000 9000 9000 9000 9000 3500 4000 4500 5000 4500 4500 4500 4500 4500 4500 4500

10 10 10 10 20 40 60 80 60 60 10 10 10 10 10 20 40 60 80 40 40

0.191 0.255 0.355 0.300 0.265 0.587 1.095 0.650 0.973 1.021 0.523 0.536 0.591 0.585 0.040 0.967 1.010 0.963 0.793 1.004 0.959

1.15 1.53 2.13 1.80 6.36 14.09 26.28 15.60 23.35 24.59 6.28 6.43 7.09 7.02 0.12 11.60 12.12 11.56 9.52 12.05 11.64

a

Polymerization conditions unless specified otherwise: norbornene, 20 mmol; MAO, 1.4 M in toluene; Et2AlCl, 0.9 M in n-hexane; EtAlCl2, 1.8 M in toluene; t = 5 min; Vtotal(toluene) = 15 mL. bAcitivity in units of 106 g of PNB (mol of Ni)−1 h−1. ct = 20 min.

Table 4. Selected Molecular Weight and Distribution of PNBsa entry

entry in Table2 or 3

cat.

cocat.

Ab

Mn (104)

PDI

1 2 3 4 5 6 7 8 9

3 5 6 7 12 13 30 33 34

Ni1 Ni1 Ni1 Ni1 Ni2 Ni3 Pd1 Pd2 Pd3

MAO MMAO Et2AlCl EtAlCl2 MAO MAO EtAlCl2 EtAlCl2 EtAlCl2

1.48 1.26 0.93 0.12 1.36 1.34 12.12 12.05 11.64

74.5 71.5 17.2 4.6 52.1 52.9 32.7 23.4 18.2

1.31 1.34 1.22 1.58 1.21 1.38 1.58 2.00 1.90

a

Conditions: molecular weight and distribution were determined by high-temperature GPC in 1,2,4-trichlorobenzene at 150 °C with polystyrene standards. bAcitivity in units of 106 g of PNB (mol of Ni)−1 h−1.

should be emphasized that the activities obtained by different cocatalysts are from single-point kinetic measurements; the real difference between these cocatalysts still needs more detailed research. Despite all this, MAO was chosen to act as the optimized cocatalyst to continue the studies on other polymerization parameters because of the high activity and high molecular weight obtained in this system. The polymerization temperature also showed a significant influence on the activity. When the temperature was increased from 10 to 80 °C, the activity showed a drastic reduction from 1.48 × 106 to 0.50 × 106 (entries 3 and 8−11, Table 2). In comparison to complex Ni1, complex Ni2 containing two additional t-Bu groups on ortho and para positions showed a lower activity of 1.36 × 106 g of PNB (mol of Ni)−1 h−1 in comparison to 1.48 × 106 (entries D


Organometallics

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of PNB (mol of Pd)−1 h−1) reported by Wang’s group.6q However, a higher molecular weight of PNB was obtained by the Pd1−Pd3/ EtAlCl2 systems ((18.2−32.7) × 104 vs (3.8− 16.4) × 104 g of PNB (mol of Pd)−1 h−1).6q The polymers obtained by the Pd/MAO system are insoluble in common organic solvents even at elevated temperature and therefore cannot be characterized by NMR and GPC methods. In addition, for soluble PNBs, although different molecular weights and distributions were obtained by changing the reaction conditions, similar 1H NMR spectra were observed in C2D2Cl4 at 80 °C. As shown in Figure 2, the typical 1H NMR

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EXPERIMENTAL SECTION

All operations involving oxygen- and moisture-sensitive compounds were carried out under an atmosphere of dried and purified nitrogen using standard Schlenk or glovebox techniques. Materials. Dichloromethane, tetrahydrofuran, diethyl ether, toluene, and n-hexane were purified by a PS-MD-5 (Innovative Technology) solvent purification system. Chloroform was distilled from anhydrous calcium chloride under nitrogen. 1,3-Dimethyl-2imidazolidinone (DMI), oxalyl chloride, 2,4-bis(1,1-dimethylethyl)phenol, 2-chloro-N-(hydroxymethyl)acetamide, 1,2-benzenediol, 2chloro-2-methylpropane, 2-aminophenol, Et2AlCl (0.9 M in n-hexane), and AlEtCl2 (1.8 M in toluene) were purchased from Energy Chemical and used without any purification. Anhydrous nickel(II) chloride and PdClMe(COD) were purchased from The Great Wall Chemicals and used as received. Potassium hydride was purchased from J&K Chemicals and washed with n-hexane before use. Norbornene (NB) was purchased from J&K Chemicals, dried over calcium hydride, and freshly distilled before use. MMAO and MAO as cocatalysts were donated by Tosoh-Finechem Co. Other commercially available reagents were purchased and used as received. Norbornene Polymerization. Norbornene polymerization was performed in a 100 mL flask equipped with a magnetic stirrer and carried out by the following methods. At first, the flask was charged with a certain amount of norbornene, cocatalyst, and toluene under nitrogen. After the mixture was kept at the desired temperature for 10 min, polymerization was initiated by introduction of the nickel or palladium complex in toluene (0.5 μmol/mL) into the flask via syringe, and the reaction was started. At the desired time later, the polymerization was terminated by addition of 10% HCl in ethanol. The precipitated polymer was washed with ethanol and water and dried at 60 °C under vacuum to a constant weight. For all of the polymerization procedures, the reaction volume in total was constant, which can be achieved by variation of the added toluene when necessary. Measurements. The molecular weights and molecular weight distributions of polymers were determined by a Polymer Laboratory PL GPC-220 instrument equipped with a triple-detection array consisting of a differential refractive index (DRI) detector, a twoangle (45, 90°) light scattering (LS) detector at a laser wavelength of 658 nm, and a four-bridge capillary viscosity detector. This system included one guard column (PL# 1110-1120) and three 30 cm columns (PLgel 10 μm MIXED-B 7.5 × 300 mm). Polymer characterization was carried out at 150 °C using 1,2,4-trichlorobenzene as eluent and calibrated by polystyrene standards. The NMR spectra were measured on Bruker Avance 300, Bruker Avance III 400 and 500, and Bruker Ascend 600 spectrometers. Elemental analysis was performed using an Elementar Vario EL III instrument. Crystal Structure Determinations. A single crystal was mounted under a nitrogen atmosphere at low temperature, and data collection was performed on a Bruker APEX2 diffractometer using graphitemonochromated Mo Kα radiation (λ = 0.71073 Å).The determination of the unit cell parameters was carried out by the SMART program package. The absorption correction was applied using the SADABS program. All structures were solved by direct methods and refined on F2 by full-matrix least-squares techniques with anisotropic thermal parameters for non-hydrogen atoms. Hydrogen atoms were placed at calculated positions and were included in the structure calculation. Calculations were carried out using the SHELXL-97, SHELXL-2014, and Olex2 programs. Synthesis of Aryloxide Imidazolidin-2-imine Ligands. 2Chloro-1,3-dimethylimidazolinium chloride (DMC), 2-(aminomethyl)-4,6-bis(1,1-dimethylethyl)phenol, and 2-amino-4,6-bis(1,1-dimethylethyl)-phenol were prepared according to literature procedures.11,15,16 Ligand L1. To 2-aminophenol (20 mmol) and triethylamine (40 mmol) in MeCN (40 mL) was added a solution of 2-chloro-1,3dimethylimidazolinium chloride (DMC) (20 mmol) in MeCN (20 mL) at 0 °C with strong agitation. After the mixture was refluxed for 3 h, sodium hydroxide (40 mmol) in 10 mL of H2O was added. Volatiles

Figure 2. 1H NMR spectra of polynorbornene obtained by (1) Ni1/ MAO and (2) Pd1/EtAlCl2 systems (asterisks denote solvent impurities).

spectra of PNB obtained by Ni1/MAO (entry 3, Table 2) and Pd1/EtAlCl2 (entry 30, Table 3) catalytic systems both showed that signals only appear in the 0.9−3.0 ppm range and no vinyl hydrogen atoms are observed, indicating that the polymers were vinyl addition type products.

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CONCLUSION In summary, the first example of neutral Ni(II) and Pd(II) complexes bearing aryloxide imidazolidin-2-imine bidentate ligands and their catalytic behavior toward norbornene polymerization were reported. Upon activation with various cocatalysts, all of the Ni(II) and Pd(II) complexes are highly active toward norbornene polymerization. The metal center, the chelating ligand, the type and ratio of cocatalyst, and temperature also showed significant influences on the polymerization activities and the properties of PNB in these catalytic systems. The performances of the Pd(II) complexes were excellent, and the activities of the Pd(II) complexes were about 1 order of magnitude higher than those of the Ni(II) complexes even at 80 °C. However, the activities of Ni(II) complexes are fairly high among the Ni(II) complexes ever reported. Moreover, soluble PNBs were also obtained by the Pd/EtAlCl2 system. The vinyl-type PNBs obtained by Ni(II) and Pd(II) complexes were further confirmed by NMR spectra. Further studies on late-transition-metal complexes based on modified aryloxide imidazolidin-2-imine ligands and on their behaviors toward other α-olefin (co)polymerization processes are in progress. E


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Organometallics

Complex Ni2. This complex was prepared by the same method as for complex Ni1 with L2, giving an orange-red powder. Yield: 80.7%. Single crystals for XRD were obtained in n-hexane/THF (3/1; v/v). 1 H NMR (300 MHz, C6D6): δ 7.90−7.78 (m, 6H, Ar-CH), 7.23−6.99 (m, 12H, Ar-CH), 6.62−6.53 (m, 1H, Ar-CH), 6.52−6.42 (m, 3H, ArCH), 2.48 (s, 6H, NCH3), 2.27 (t, J = 8.3 Hz, 2H, NCH2CH2N), 2.03 (t, J = 8.3 Hz, 2H, NCH2CH2N), 1.51 (s, 9H, C(CH3)3), 1.34 (s, 9H, C(CH3)3). 13C NMR (75 MHz, C6D6): δ 168.4, 160.3, 160.2, 156.6, 156.0, 143.0, 140.0, 135.2, 135.0, 133.6, 133.2, 133.0, 129.6, 124.2, 120.9, 113.9, 109.6, 45.9, 34.9, 34.4, 34.2, 32.8, 30.2. 31P NMR (120 MHz, C6D6): δ 33.85. Anal. Calcd for C43H50N3NiOP: C, 72.28; H, 7.05; N, 5.88. Found: C, 71.89; H, 7.01; N, 5.60. MS (ESI, m/z): calcd for C43H50N3NiOP [M] 713.3045, found 713.3050. Complex Ni3. This complex was prepared by the same method as for complex Ni1 with L3, giving a yellow powder. Yield: 84.3%. Single crystals for XRD were obtained in n-hexane/THF (5/1; v/v). Clear NMR spectra could not be obtained because of broadened signals. Anal. Calcd for C44H52N3NiOP: C, 72.54; H, 7.19; N, 5.77. Found: C, 72.16; H, 7.29; N, 5.58. MS (ESI, m/z): calcd for C44H52N3NiOP [M + H]+ 728.3280, found 728.3250. Complex Pd1. To a solution of L1 (1.0 mmol) in dry CH2Cl2 (30 mL) was added KH (1.5 mmol). After it was stirred at room temperature for 1 h, the resulting mixture was filtered, and the filtrate was evaporated. The yellow residue was washed with n-hexane (30 mL) and dried in vacuo. This salt was used for the next synthesis immediately without further purification. Then a solution of this salt in dry CH2Cl2 (20 mL) was added dropwise at room temperature to a stirred solution of [PdMeCl(PPh3)]2 (1.0 mmol) in dry CH2Cl2 (20 mL). After 6 h, the reaction mixture was filtered. The volatiles were then partially removed from the filtrate in vacuo, and to the residue was added excess n-hexane. A yellow powder of complex Pd1 was obtained by filtration. Yield: 88.5%. Single crystals for XRD were obtained in n-hexane/CH2Cl2 (4/1; v/v). 1H NMR (500 MHz, CDCl3): δ 7.82−7.71 (m, 6H, Ar-CH), 7.44−7.35 (m, 9H, Ar-CH), 6.74−6.61 (m, 2H, Ar-CH), 6.53−6.43 (m, 1H, Ar-CH), 6.39−6.28 (m, 1H, Ar-CH), 3.68 (s, 4H, NCH2CH2N), 2.97 (s, 6H, NCH3), −0.14 (d, J = 3.3 Hz, 3H, Pd-CH3). 13C NMR (126 MHz, CDCl3): δ 166.1, 141.8, 135.1, 135.0, 132.8, 132.4, 130.1, 129.2, 128.4, 128.2, 128.1, 125.5, 120.9, 117.9, 116.4, 112.0, 47.5, 35.2, −1.9 (d, J = 10.2 Hz, Pd-CH3). 31P NMR (200 MHz, CDCl3): δ 36.08. Anal. Calcd for C30H32N3OPPd: C, 61.28; H, 5.49; N, 7.15. Found: C, 61.18; H, 5.46; N, 7.09. MS (ESI, m/z): calcd for C30H33N3OPPd [M + H]+ 588.1396, found 588.1390. Complex Pd2. This complex was prepared by the same method as for complex Pd2 with L2, giving a yellow powder. Yield: 82.6%. 1H NMR (300 MHz, C6D6): δ 8.11−7.96 (m, 6H, Ar-CH), 7.31−7.23 (m, 1H, Ar-CH), 7.16−7.04 (m, 9H, Ar-CH), 6.72−6.60 (m, 1H, Ar-CH), 2.53 (s, 4H, NCH2CH2N), 2.50 (s, 6H, NCH3), 1.64 (s, 9H, C(CH3)3), 1.56 (s, 9H, C(CH3)3), 0.16 (d, J = 3.4 Hz, 3H, Pd-CH3). 13 C NMR (75 MHz, C6D6): δ 165.0, 162.4, 162.3, 140.4, 135.5, 135.0, 134.8, 133.3, 132.7, 131.9, 129.6, 115.0, 112.4, 46.3, 35.1, 34.5, 33.8, 32.3, 29.8, −1.7 (d, J = 11.1 Hz Pd-CH3). 31P NMR (120 MHz, C6D6): δ 38.13. Anal. Calcd for C38H48N3OPPd: C, 65.18; H, 6.91; N, 6.00. Found: C, 64.92; H, 6.85; N, 5.96. MS (ESI, m/z): calcd for C38H49N3OPPd [M + H]+ 700.2648, found 700.2683. Complex Pd3. This complex was prepared by the same method as for complex Pd3 with L3, giving an off-white powder. Yield: 81.8%. Single crystals for XRD were obtained in n-hexane/CH2Cl2 (5/1 v/v). 13 C NMR (75 MHz, CDCl3, −20 °C): δ 164.3, 163.8, 163.2, 161.2, 137.3, 137.2, 135.2, 135.0, 134.7, 134.6, 133.8, 133.1, 132.5, 131.9, 131.6, 130.2, 130.0, 129.9, 129.2, 128.4, 128.1, 128.0, 127.9, 127.2, 126.9, 125.5, 123.4, 122.7, 122.3, 53.4, 49.3, 38.2, 35.7, 34.9, 33.9, 32.2, 32.1, 29.9, 297, 3.1, −4.5. Isomer 1 (25%) 1H NMR (300 MHz, CDCl3, −20 °C): δ 7.79−7.68 (m, 6H, Ar-CH), 7.46−7.29 (m, 9H, Ar-CH), 7.05−7.00 (m, 1H, Ar-CH), 6.74−6.67 (m, 1H, Ar-CH), 3.32 (s, 4H, NCH2CH2N), 3.12 (s, 6H, NCH3), 2.36 (s, 2H, CH2), 1.26 (s, 9H, C(CH3)3), 0.87 (s, 9H, C(CH3)3), −0.24 (d, 3H, Pd−CH3). 31P NMR (120 MHz, CDCl3, −20 °C): δ 36.18. Isomer 2 (75%) 1H NMR (300 MHz, CDCl3, −20 °C): δ 7.67−7.57 (m, 6H, Ar-CH), 7.46−7.28 (m, 9H, Ar-CH), 7.13−7.07 (m, 1H, Ar-CH), 6.64−6.57 (m, 1H, Ar-

were removed by evaporation under vacuum. Then, 50 wt % potassium hydroxide in H2O (10 mL) was added. The products were extracted with MeCN, and the organic phase was collected and dried with anhydrous MgSO4. Then the dry MeCN solution was evaporated under vacuum. The crude product was dissolved in the minimum amount of MeCN (∼30 mL) and stored at −20 °C overnight to recrystallize. The ligands were used as crystals or a microcrystalline powder. Yield: 48.7%. 1H NMR (400 MHz, CDCl3): δ 6.89−6.84 (m, 1H, Ar-CH), 6.82−6.76 (m, 2H, Ar-CH), 6.76−6.70 (m, 1H, Ar-CH), 3.36 (s, 4H, NCH2CH2N), 2.72 (s, 6H, NCH3). 13C NMR (150 MHz, CDCl3): δ 158.1, 149.4, 135.5, 121.6, 121.1, 119.4, 113.2, 48.7, 35.3. Anal. Calcd for C11H15N3O: C, 64.37; H, 7.37; N, 20.47. Found: C, 64.26; H, 7.24; N, 20.68. MS (ESI, m/z): calcd for C11H15N3O [M + H]+ 206.1293, found 206.1298. Ligand L2. This ligand was prepared by the same method as for L1 with 2-amino-4,6-bis(1,1-dimethylethyl)phenol. Yield: 45.8%. Anal. Calcd for C19H31N3O: C, 71.88; H, 9.84; N, 13.24. Found: C, 71.93; H, 10.06; N, 13.09. MS (ESI, m/z): calcd for C19H31N3O [M + H]+ 318.2545, found 318.2548. 13C NMR (150 MHz, CDCl3): δ 162.8, 157.4, 146.9, 145.5, 144.9, 143.5, 140.1, 134.8, 132.9, 131.8, 116.0, 115.6, 114.9, 111.3, 50.5, 49.6, 48.7, 36.6, 35.3, 35.1, 34.8, 34.4, 34.2, 32.0, 31.9, 30.1, 29.7. Isomer 1 (34.5%) 1H NMR (400 MHz, CDCl3): δ 6.88−6.84 (m, 1H, Ar-CH), 6.75−6.72 (m, 1H, Ar-CH), 3.39 (s, 4H, NCH2CH2N), 2.73 (s, 6H, NCH3), 1.40 (s, 9H, C(CH3)3), 1.27 (s, 9H, C(CH3)3). Isomer 2 (65.5%) 1H NMR (400 MHz, CDCl3): δ 7.29−7.27 (m, 1H, Ar-CH), 6.98−6.96 (m, 1H, Ar-CH), 3.70 (t, J = 6.2 Hz, 2H, NCH2CH2N), 3.24 (s, 3H, NCH3), 2.96 (t, J = 6.2 Hz, 2H, NCH2CH2N), 2.51 (s, 3H, NCH3), 1.44 (s, 9H, C(CH3)3), 1.34 (s, 9H, C(CH3)3). Ligand L3. This ligand was prepared by the same method as for L1 with 2-(aminomethyl)-4,6-bis(1,1-dimethylethyl)phenol. Yield: 37.5%. 1 H NMR (400 MHz, CDCl3): δ 7.18−7.12 (m, 1H, Ar-CH), 6.86− 6.80 (m, 1H, Ar-CH), 4.82 (s, 2H, CH2), 3.23 (s, 4H, NCH2CH2N), 2.88 (bs, 6H, NCH3), 1.44 (s, 9H, C(CH3)3), 1.28 (s, 9H, C(CH3)3). 13 C NMR (100 MHz, CDCl3): δ 157.6, 155.4, 139.7, 136.2, 124.2, 122.1, 121.9, 52.4, 35.1, 34.2, 31.9, 29.8. Anal. Calcd for C20H33N3O: C, 72.46; H, 10.03; N, 12.68. Found: C, 72.55; H, 10.13; N, 12.84. MS (ESI, m/z): calcd for C20H33N3O [M + H]+ 332.2702, found 332.2697. Synthesis of Complexes. The nickel(II) precursor used in this work is trans-[NiPhCl(PPh3)2], which was prepared according to the work reported earlier.17 The palladium(II) precursor [PdMeCl(PPh3)]2 was prepared according to the work reported by the Anderson group.18 Complex Ni1. To a solution of L1 (1.0 mmol) in dry THF (30 mL) was added KH (1.5 mmol). After it was stirred at room temperature for 3 h, the resulting mixture was filtered, and the filtrate was evaporated. The yellow residue was washed with n-hexane (30 mL) and dried in vacuo. This salt was used for the next synthesis immediately without further purification. Then a solution of this salt in dry THF (30 mL) was added dropwise at room temperature to a flask equipped with trans-[NiPhCl(PPh3)2] (1.0 mmol). A rapid color change from yellow to dark red was observed. After it was stirred overnight at room temperature, the reaction mixture was filtered. The volatiles were then partially removed from the filtrate in vacuo, and to the residue was added excess n-hexane. A light orange powder of complex Ni1 was obtained by filtration. Yield: 87.9%. Single crystals for XRD were obtained in n-hexane/THF (5/1; v/v). 1H NMR (600 MHz, CDCl3): δ 7.69−7.61 (m, 6H, Ar-CH), 7.35−7.27 (m, 3H, ArCH), 7.24−7.19 (m, 6H, Ar-CH), 6.99−6.93 (m, 2H, Ar-CH), 6.55− 6.51 (m, 1H, Ar-CH), 6.49−6.46 (m, 1H, Ar-CH), 6.46−6.42 (m, 1H, Ar-CH), 6.40−6.36 (m, 2H, Ar-CH), 6.28−6.20 (m, 2H, Ar-CH), 3.28 (t, J = 8.6 Hz, 2H, NCH2CH2N), 2.87 (s, 6H, NCH3), 2.76 (t, J = 8.6 Hz, 2H, NCH2CH2N). 13C NMR (150 MHz, CDCl3): δ 168.4, 163.4, 153.5, 153.1, 143.5, 139.0, 134.6, 134.5, 132.5, 132.2, 129.3, 127.6, 127.5, 123.8, 120.9, 118.9, 115.2, 112.4, 111.8, 46.3, 34.3. 31P NMR (120 MHz, CDCl3): δ 32.67. Anal. Calcd for C35H34N3NiOP: C, 69.79; H, 5.69; N, 6.98. Found: C, 69.45; H, 5.71; N, 6.96. MS (ESI, m/z): calcd for C35H35N3NiOP [M + H]+ 602.1871, found 602.1870. F


Article

Organometallics CH), 4.74 (s, 2H, CH2), 2.89 (s, 6H, NCH3), 2.65 (s, 4H, NCH2CH2N), 1.54 (s, 9H, C(CH3)3), 1.24 (s, 9H, C(CH3)3), 0.60 (d, 3H, Pd−CH3). 31P NMR (120 MHz, CDCl3, −20 °C): δ 41.48. Anal. Calcd for C39H50N3OPPd: C, 65.58; H, 7.06; N, 5.88. Found: C, 65.29; H, 6.91; N, 5.73. MS (ESI, m/z): calcd for C39H50N3OPPd [M + H]+ 714.2805, found 714.2810.

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(3) Mu, H.; Pan, L.; Song, D.; Li, Y. Neutral Nickel Catalysts for Olefin Homo- and Copolymerization: Relationships between Catalyst Structures and Catalytic Properties. Chem. Rev. 2015, 115, 12091− 12137. (4) (a) Arduengo, A. J.; Harlow, R. L.; Kline, M. A Stable Crystalline Carbene. J. Am. Chem. Soc. 1991, 113, 361−363. (b) Arduengo, A. J.; Dias, H. V. R.; Harlow, R. L.; Kline, M. Electronic Stabilization of Nucleophilic Carbenes. J. Am. Chem. Soc. 1992, 114, 5530−5534. (5) Waltman, A. W.; Grubbs, R. H. A New Class of Chelating NHeterocyclic Carbene Ligands and Their Complexes with Palladium. Organometallics 2004, 23, 3105−3107. (6) (a) Waltman, A. W.; Ritter, T.; Grubbs, R. H. Rearrangement of N-Heterocylic Carbenes Involving Heterocycle Cleavage. Organometallics 2006, 25, 4238−4239. (b) Yagyu, T.; Oya, S.; Maeda, M.; Jitsukawa, K. Syntheses and Characterization of Palladium(II) Complexes with Tridentate N-Heterocyclic Carbene Ligands Containing Aryloxy Groups and Their Application to Heck Reaction. Chem. Lett. 2006, 35, 154−155. (c) Dang, L.; Guo, J.; Song, H.; Liu, B.; Wang, B. Synthesis, Structures, and Norbornene Polymerization Behavior of C(Sp3), N-Chelated Palladacycles Bearing o-Aryloxide-NHeterocyclic Carbene Ligands. Dalton Trans. 2014, 43, 17177−17183. (d) Romain, C.; Choua, S.; Collin, J. P.; Heinrich, M.; Bailly, C.; Karmazin-Brelot, L.; Bellemin-Laponnaz, S.; Dagorne, S. Redox and luminescent properties of robust and air-stable N-heterocyclic carbene group 4 metal complexes. Inorg. Chem. 2014, 53, 7371−7376. (e) Nirmala, M.; Prakash, G.; Viswanathamurthi, P.; Malecki, J. G. An attractive route to transamidation catalysis: Facile synthesis of new o-aryloxide-N-heterocyclic carbene ruthenium(II) complexes containing trans triphenylphosphine donors. J. Mol. Catal. A: Chem. 2015, 403, 15−26. (f) Bellemin-Laponnaz, S.; Welter, R.; Brelot, L.; Dagorne, S. Synthesis and structure of V(V) and Mn(III) NHC complexes supported by a tridentate bis-aryloxide-N-heterocyclic carbene ligand. J. Organomet. Chem. 2009, 694, 604−606. (g) ElBatta, A.; Waltman, A. W.; Grubbs, R. H. Bis-ligated Ti and Zr complexes of chelating N-heterocyclic carbenes. J. Organomet. Chem. 2011, 696, 2477−2481. (h) Ren, H.; Yao, P.; Xu, S.; Song, H.; Wang, B. A new class of o-hydroxyaryl-substituted N-heterocyclic carbene ligands and their complexes with palladium. J. Organomet. Chem. 2007, 692, 2092−2098. (i) Zhang, J.; Zhang, M.; Bai, T.; Ni, X.; Shen, Z. Synthesis and characterization of heterobimetallic organo rare earth complexes bearing aryloxide-N-heterocyclic carbene ligands. J. Organomet. Chem. 2017, 843, 1−6. (j) Borré, E.; Dahm, G.; Aliprandi, A.; Mauro, M.; Dagorne, S.; Bellemin-Laponnaz, S. Tridentate Complexes of Group 10 Bearing Bis-Aryloxide N-Heterocyclic Carbene Ligands: Synthesis, Structural, Spectroscopic, and Computational Characterization. Organometallics 2014, 33, 4374−4384. (k) Dang, L.; Song, H.; Wang, B. Synthesis, Structures, and Norbornene Polymerization Behavior of o-Aryloxide-Substituted NHC-Ligated σ, π-Cycloalkenyl Palladium Complexes. Organometallics 2014, 33, 6812−6818. (l) Kong, Y.; Cheng, M.; Ren, H.; Xu, S.; Song, H.; Yang, M.; Liu, B.; Wang, B. Synthesis, Structures, and Norbornene Polymerization Behavior of Bis(aryloxide-N-heterocyclic carbene) Nickel Complexes. Organometallics 2011, 30, 1677−1681. (m) Kong, Y.; Ren, H.; Xu, S.; Song, H.; Liu, B.; Wang, B. Synthesis, Structures, and Norbornene Polymerization Behavior of Bis(aryloxide-N-heterocyclic carbene) Palladium Complexes. Organometallics 2009, 28, 5934−5940. (n) Kong, Y.; Wen, L.; Song, H.; Xu, S.; Yang, M.; Liu, B.; Wang, B. Synthesis, Structures, and Norbornene Polymerization Behavior of Aryloxide-N-Heterocyclic Carbene Ligated Palladacycles. Organometallics 2011, 30, 153−159. (o) Kong, Y.; Xu, S.; Song, H.; Wang, B. Synthesis, Structures, and Norbornene ROMP Behavior of oAryloxide-N-Heterocyclic Carbenep-Cymene Ruthenium Complexes. Organometallics 2012, 31, 5527−5532. (p) Yang, D.; Tang, Y.; Song, H.; Wang, B. o-Aryloxide-N-heterocyclic Carbenes: Efficient Synthesis of the Proligands and Their p-Cymene Ruthenium Complexes. Organometallics 2015, 34, 2012−2017. (q) Yang, D.; Tang, Y.; Song, H.; Wang, B. Synthesis, Structures, and Norbornene Polymerization Behavior of Palladium Complexes Bearing Tridentate o-Aryloxide-Nheterocyclic Carbene Ligands. Organometallics 2016, 35, 1392−1398.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00059. NMR spectra and ESI-MS report of the ligands and complexes and X-ray crystallographic data (PDF) Accession Codes

CCDC 1820062, 1820064, 1820066, 1820068, and 1820070 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc. cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for Z.C.: [email protected]. *E-mail for M.S.E.: [email protected]. ORCID

Zhengguo Cai: 0000-0001-5784-3920 Moris S. Eisen: 0000-0001-8915-0256 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (21774018), the Program for New Century Excellent Talents in University, the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, and “Shu Guang” project supported by Shanghai Municipal Education Commission and Shanghai Education Development Foundation and the Fundamental Research Funds for the Central Universities. We thank Dr. Heng Liu (Technion-Israel Institute of Technology) for his helpful discussions.

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REFERENCES

(1) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. New Pd(II)- and Ni(II)-Based Catalysts for Polymerization of Ethylene and α-Olefins. J. Am. Chem. Soc. 1995, 117, 6414−6415. (b) Johnson, L. K.; Mecking, S.; Brookhart, M. Copolymerization of Ethylene and Propylene with Functionalized Vinyl Monomers by Palladium(II) Catalysts. J. Am. Chem. Soc. 1996, 118, 267−268. (c) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. Mechanistic Studies of the PalladiumCatalyzed Copolymerization of Ethylene and α-Olefins with Methyl Acrylate. J. Am. Chem. Soc. 1998, 120, 888−899. (2) (a) Wang, C. M.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben, D. A.; Day, M. W. Neutral Nickel(II)-Based Catalysts for Ethylene Polymerization. Organometallics 1998, 17, 3149−3151. (b) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Banleben, D. A. Neutral, SingleComponent Nickel (II) Polyolefin Catalysts That Tolerate Heteroatoms. Science 2000, 287, 460−462. G


Article

Organometallics (r) Yang, D.; Dong, J.; Wang, B. Homo- and copolymerization of norbornene with tridentate nickel complexes bearing o-aryloxide-Nheterocyclic carbene ligands. Dalton Trans 2018, 47, 180−189. (7) (a) Petrovic, D.; Bannenberg, T.; Randoll, S.; Jones, P. G.; Tamm, M. Synthesis and reactivity of copper(I) complexes containing a bis(imidazolin-2-imine) pincer ligand. Dalton Trans. 2007, 26, 2812−2822. (b) Tamm, M.; Randoll, S.; Herdtweck, E.; Kleigrewe, N.; Kehr, G.; Erker, G.; Rieger, B. Imidazolin-2-iminato titanium complexes: synthesis, structure and use in ethylene polymerization catalysis. Dalton Trans. 2006, 3, 459−467. (c) Tamm, M.; Randoll, S.; Bannenberg, T.; Herdtweck, E. Titanium complexes with imidazolin-2iminato ligands. Chem. Commun. 2004, 7, 876−877. (d) Panda, T. K.; Trambitas, A. G.; Bannenberg, T.; Hrib, C. G.; Randoll, S.; Jones, P. G.; Tamm, M. Imidazolin-2-iminato Complexes of Rare Earth Metals with Very Short Metal-Nitrogen Bonds: Experimental and Theoretical Studies. Inorg. Chem. 2009, 48, 5462−5472. (8) Wu, X.; Tamm, M. Transition metal complexes supported by highly basic imidazolin-2-iminato and imidazolin-2-imine N-donor ligands. Coord. Chem. Rev. 2014, 260, 116−138. (9) (a) Randoll, S.; Jones, P. G.; Tamm, M. Chromium Complexes with Me2Si-Bridged Cyclopentadienyl-imidazolin-2-imine Ligands: Synthesis, Structure, and Use in Ethylene Polymerization Catalysis. Organometallics 2008, 27, 3232−3239. (b) Nomura, K.; Bahuleyan, B. K.; Zhang, S.; Veeresha Sharma, P. M.; Katao, S.; Igarashi, A.; Inagaki, A.; Tamm, M. Synthesis and structural analysis of (imido)vanadium(V) dichloride complexes containing imidazolin-2-iminato- and imidazolidin-2-iminato ligands, and their use as catalyst precursors for ethylene (co)polymerization. Inorg. Chem. 2014, 53, 607−623. (c) Sharma, M.; Yameen, H. S.; Tumanskii, B.; Filimon, S. A.; Tamm, M.; Eisen, M. S. Bis(1,3-di-tert-butylimidazolin-2-iminato) titanium complexes as effective catalysts for the monodisperse polymerization of propylene. J. Am. Chem. Soc. 2012, 134, 17234−17244. (d) Shoken, D.; Sharma, M.; Botoshansky, M.; Tamm, M.; Eisen, M. S. Mono(imidazolin-2-iminato) titanium complexes for ethylene polymerization at low amounts of methylaluminoxane. J. Am. Chem. Soc. 2013, 135, 12592−12595. (e) Nomura, K.; Fukuda, H.; Apisuk, W.; Trambitas, A. G.; Kitiyanan, B.; Tamm, M. Ethylene copolymerization by half-titanocenes containing imidazolin-2-iminato ligands-MAO catalyst systems. J. Mol. Catal. A: Chem. 2012, 363−364, 501−511. (f) Apisuk, W.; Trambitas, A. G.; Kitiyanan, B.; Tamm, M.; Nomura, K. Efficient ethylene/norbornene copolymerization by half-titanocenes containing imidazolin-2-iminato ligands and MAO catalyst systems. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2575−2580. (g) Stelzig, S. H.; Tamm, M.; Waymouth, R. M. Copolymerization behavior of titanium imidazolin-2-iminato complexes. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 6064−6070. (h) Shoken, D.; Shimon, L. J. W.; Tamm, M.; Eisen, M. S. Synthesis of Imidazolin-2-iminato Titanium Complexes Containing Aryloxo Ligands and Their Catalytic Performance in the Polymerization of α-Olefins. Organometallics 2016, 35, 1125−1131. (10) (a) Jess, K.; Derdau, V.; Weck, R.; Atzrodt, J.; Freytag, M.; Jones, P. G.; Tamm, M. Hydrogen Isotope Exchange with Iridium(I) Complexes Supported by Phosphine-Imidazolin-2-imine P, N Ligands. Adv. Synth. Catal. 2017, 359, 629−638. (b) Petrovic, D.; Hill, L. M.; Jones, P. G.; Tolman, W. B.; Tamm, M. Synthesis and reactivity of copper(I) complexes with an ethylene-bridged bis(imidazolin-2-imine) ligand. Dalton Trans. 2008, 7, 887−894. (c) Filimon, S. A.; Petrovic, D.; Volbeda, J.; Bannenberg, T.; Jones, P. G.; Freiherr von Richthofen, C. G.; Glaser, T.; Tamm, M. 3d Metal Complexes Supported by a Bis(imidazolin-2-imino)pyridine Pincer Ligand-Synthesis, Structural Characterisation, and Magnetic Properties. Eur. J. Inorg. Chem. 2014, 2014, 5997−6012. (d) Jess, K.; Baabe, D.; Freytag, M.; Jones, P. G.; Tamm, M. Transition-Metal Complexes with Ferrocene-Bridged Bis(imidazolin-2-imine) and Bis(diaminocyclopropenimine) Ligands. Eur. J. Inorg. Chem. 2017, 2017, 412−423. (e) Petrovic, D.; Glöge, T.; Bannenberg, T.; Hrib, C. G.; Randoll, S.; Jones, P. G.; Tamm, M. Synthesis and Reactivity of 16-Electron PentamethylcyclopentadienylRuthenium(II) Complexes with Bis(imidazolin-2-imine) Ligands. Eur. J. Inorg. Chem. 2007, 2007, 3472−3475. (f) Tönnemann, J.; Scopelliti,

R.; Severin, K. (Arene)ruthenium Complexes with Imidazolin-2-imine and Imidazolidin-2-imine Ligands. Eur. J. Inorg. Chem. 2014, 2014, 4287−4293. (g) Jess, K.; Baabe, D.; Bannenberg, T.; Brandhorst, K.; Freytag, M.; Jones, P. G.; Tamm, M. Ni-Fe and Pd-Fe Interactions in Nickel(II) and Palladium(II) Complexes of a Ferrocene-Bridged Bis(imidazolin-2-imine) Ligand. Inorg. Chem. 2015, 54, 12032−12045. (h) Volbeda, J.; Jones, P. G.; Tamm, M. Preparation of chiral imidazolin-2-imine ligands and their application in rutheniumcatalyzed transfer hydrogenation. Inorg. Chim. Acta 2014, 422, 158− 166. (i) Massai, L.; Pratesi, A.; Bogojeski, J.; Banchini, M.; Pillozzi, S.; Messori, L.; Bugarcic, Z. D. Antiproliferative properties and biomolecular interactions of three Pd(II) and Pt(II) complexes. J. Inorg. Biochem. 2016, 165, 1−6. (j) Börner, J.; Flörke, U.; Glöge, T.; Bannenberg, T.; Tamm, M.; Jones, M. D.; Döring, A.; Kuckling, D.; Herres-Pawlis, S. New insights into the lactide polymerisation with neutral N-donor stabilised zinc complexes: Comparison of imidazolin2-imine vs. guanidine complexes. J. Mol. Catal. A: Chem. 2010, 316, 139−145. (k) Bogojeski, J.; Volbeda, J.; Bugarčić, Ž . D.; Freytag, M.; Tamm, M. Platinum(II) complexes with hybrid amine-imidazolin-2imine ligands and their reactivity toward bio-molecules. New J. Chem. 2016, 40, 4818−4825. (l) Todd, A. D. K.; McClennan, W. L.; Masuda, J. D. Organoaluminum(III) complexes of the bis-N,N’-(2,6diisopropylphenyl)imidazolin-2-imine ligand. RSC Adv. 2016, 6, 69270−69276. (m) Filimon, S. A.; Hrib, C. G.; Randoll, S.; Neda, I.; Jones, P. G.; Tamm, M. Quinine-Derived Imidazolidin-2-imine Ligands: Synthesis, Coordination Chemistry, and Application in Catalytic Transfer Hydrogenation. Z. Anorg. Allg. Chem. 2010, 636, 691−699. (n) Glöge, T.; Aal, F.; Filimon, S.-A.; Jones, P. G.; Michaelis de Vasconcellos, J.; Herres-Pawlis, S.; Tamm, M. Transition Metal Complexes Containing C2-Symmetric Bis(imidazolin-2-imine) Ligands Derived from a 1-Alkyl-3-arylimidazolin-2-ylidene. Z. Anorg. Allg. Chem. 2015, 641, 2204−2214. (11) Maronna, A.; Hubner, O.; Enders, M.; Kaifer, E.; Himmel, H. J. Bisguanidines with biphenyl, binaphthyl, and bipyridyl cores: protonsponge properties and coordination chemistry. Chem. - Eur. J. 2013, 19, 8958−8977. (12) Hu, T.; Li, Y. G.; Li, Y. S.; Hu, N. H. Novel highly active binuclear neutral nickel and palladium complexes as precatalysts for norbornene polymerization. J. Mol. Catal. A: Chem. 2006, 253, 155− 164. (13) (a) Blank, F.; Janiak, C. Metal Catalysts for the Vinyl/Addition Polymerization of Norbornene. Coord. Chem. Rev. 2009, 253, 827− 861. (b) Ahmed, S.; Bidstrup, S. A.; Kohl, P. A.; Ludovice, P. J. Development of a New Force Field for Polynorbornene. J. Phys. Chem. B 1998, 102, 9783−9790. (c) Grove, N. R.; Kohl, P. A.; Allen, S. A. B.; Jayaraman, S.; Shick, R. Functionalized Polynorbornene Dielectric Polymers: Adhesion and Mechanical Properties. J. Polym. Sci., Part B: Polym. Phys. 1999, 37, 3003−3010. (d) Janiak, C.; Lassahn, P. G. Metal Catalysts for the Vinyl Polymerization of Norbornene. J. Mol. Catal. A: Chem. 2001, 166, 193−209. (e) Ma, R.; Hou, Y.; Gao, J.; Bao, F. Recent Progress in the Vinylic Polymerization and Copolymerization of Norbornene Catalyzed by Transition Metal Catalysts. Polym. Rev. 2009, 49, 249−287. (14) (a) Li, X. F.; Li, Y. S. Vinylic Polymerization of Norbornene by Neutral Nickel(II)-Based Catalysts. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2680−2685. (b) Sun, W. H.; Yang, H. J.; Li, Z. L.; Li, Y. Vinyl Polymerization of Norbornene with Neutral Salicylaldiminato Nickel(II) Complexes. Organometallics 2003, 22, 3678−3683. (c) Zhang, D.; Jin, G. X.; Weng, L. H.; Wang, F. S. Synthesis, Molecular Structures, and Norbornene Addition Polymerization Activity of the Neutral Nickel Catalysts Supported by β-Diketiminato [N,N], Ketiminato [N,O], and Schiff-Base [N,O] Ligands. Organometallics 2004, 23, 3270−3275. (d) Wang, W. H.; Jin, G. X. Synthesis, Molecular Structures and Norbornene Addition Polymerization Activity of the Neutral Nickel Catalysts Supported by N-NaphthylSalicylaldiminato Ligands. Inorg. Chem. Commun. 2005, 8, 109−112. (e) Song, D. P.; Li, Y. G.; Lu, R.; Hu, N. H.; Li, Y. S. Synthesis and Characterization of Novel Neutral Nickel Complexes Bearing Fluorinated Salicylaldiminato Ligands and Their Catalytic Behavior H


Article

Organometallics for Vinylic Polymerization of Norbornene. Appl. Organomet. Chem. 2008, 22, 333−340. (15) Stokker, G. E.; Deana, A. A.; DeSolms, S. J.; Schultz, E. M.; Smith, R. L.; Cragoe, E. J., Jr; Baer, J. E.; Ludden, C. T.; Russo, H. F. 2(Aminomethyl)phenols, a New Class of Saluretic Agents. 1. Effects of Nuclear Substitution. J. Med. Chem. 1980, 23, 1414−1427. (16) Dulong, F.; Bathily, O.; Thuery, P.; Ephritikhine, M.; Cantat, T. A N-aryloxy-β-diketiminate ligand in 4d, 4f and 5f-metals complexes. Dalton Trans. 2012, 41, 11980−11983. (17) Zeller, A.; Herdtweck, E.; Strassner, T. Structural Characterization and a New One-Pot Synthesis of trans-Chloro(phenyl)bis(triphe-nylphosphane)nickel(II). Eur. J. Inorg. Chem. 2003, 2003, 1802−1806. (18) Ladipo, F. T.; Anderson, G. K. Convenient method for the synthesis of chloro-bridged methyl- and acetylpalladium(II) dimers. Organometallics 1994, 13, 303−306.

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