Synthesis, Structures, and Norbornene Polymerization Behavior of N

Article pubs.acs.org/Organometallics

Synthesis, Structures, and Norbornene Polymerization Behavior of N‑Heterocyclic Carbene-Sulfonate-Ligated Palladacycles Minliang Li,† Haibin Song,† and Baiquan Wang*,†,‡,§ †

State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, and ‡Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Nankai University, Tianjin 300071, People’s Republic of China § State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s Republic of China S Supporting Information *

ABSTRACT: A series of new N-heterocyclic carbene-sulfonate (NHC-sulfonate) ligands 5a−e were synthesized. Treatment of the NHC-sulfonate ligands with Ag2O and palladacycles {[Pd(OAc)(8-Me-quin-H)]2 or [Pd(dmba)(μ-Cl)]2 (dmba = Me2NCH2C6H5)} yielded the desired C(sp3),Nchelated and C(sp2),N-chelated NHC-sulfonate palladacycles 6a−e and 7a−e in high yields. All these complexes were fully characterized by 1H and 13C NMR, high-resolution mass spectrometry, and elemental analysis. The molecular structures of compounds 5a, 6d, 6e, and 7e were determined by singlecrystal X-ray diffraction analysis. In the presence of MAO, the C(sp3),N-chelated NHC-sulfonate palladacycles 6a−e showed excellent catalytic activities [107 g of polynorbornene (PNB) (mol of Pd)−1 h−1], while the C(sp2),N-chelated palladacycles 7a−e showed moderate catalytic activities [106 g of PNB (mol of Pd)−1 h−1] in the vinyl polymerization of norbornene. The C(sp2),N-chelated palladacycles 7a−e showed high thermal stability and reached the highest activities at high temperature (100 °C).

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INTRODUCTION In the past decades, considerable attention has been paid to a kind of phosphine-sulfonate ligand. It was first synthesized by Murray and Charleston and subsequently used for the nickelcatalyzed ethylene oligomerization.1 Since it was reported by Pugh and co-workers for palladium-catalyzed copolymerization of ethylene with methyl acrylate2 and CO,3 intensive studies have been focused on the unique characteristics of these phosphine-sulfonate palladium catalysts,4 and several types of polymers have been produced including polyethylene,5 copolymers of ethylene with polar vinyl monomers,6 copolymers of ethylene with CO,7 and copolymers of polar vinyl monomers with CO.8 In addition, some phosphinesulfonate complexes of other transition metals such as ruthenium,9 nickel,10 iridium,9g,11 and rhodium12 were also synthesized (Chart 1, A). The phosphine-sulfonate species has electronic asymmetry: the phosphine ligand is a strong donor, while the sulfonate ligand is a very weak one. N-Heterocyclic carbenes (NHCs) are even stronger donors compared with phosphines: they can stabilize the complexes and have been widely used in organometallic chemistry.13 Substituting NHCs for the phosphines will make the ligands potentially suitable for catalysis. However, reports of such a NHC-sulfonate are rather rare due to the difficulty in the synthesis of the ligands. Hoveyda and co-workers reported a series of chiral saturated NHC-arenesulfonate ligands and their silver complexes (Chart 1, B), which were used in copper-catalyzed asymmetric © XXXX American Chemical Society

Chart 1. Phosphine-Sulfonate and NHC-Sulfonate Complexes

conjugate addition, allylic alkylation, hydroboration, and diboronation reactions.14 Jordan and co-workers reported similar saturated NHC-arenesulfonate ligands and their Pd(II) complexes (Chart 1, C) and studied the dynamic properties and insertion reactivity.15 Also, palladium alkyl complexes in which the NHC and sulfonate units were linked by a methylene spacer (Chart 1, D) were reported by Nozaki’s group.16 However, to the best of our knowledge, the unsaturated NHCReceived: March 13, 2015

A

DOI: 10.1021/acs.organomet.5b00214 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 1. Synthesis of NHC-Sulfonate Ligands

sulfonate ligands and their transition metal complexes have not been reported. Since the synthesis of cyclopalladated azobenzene by Cope and Siekman in 1965,17 palladacycles have become an important class of catalysts because of their versatile frameworks, remarkable catalytic activity, synthetically easy accessibility, extra stability toward air and moisture, and relatively low toxicity.18 Although a wide variety of phosphorus-, nitrogen-, sulfur-, and oxygen-derived palladacycles were synthesized and utilized in catalytic formation of carbon−carbon and carbon− heteroatom bonds,19 palladacycles with NHCs have been less studied.20 Recently, we succeeded in developing a series of aryloxide-NHC-ligated palladacycles, and these complexes showed excellent catalytic properties in the vinyl polymerization of norbornene.21 Inspired by these studies, we decided to explore the behavior of palladacycles bearing NHC-sulfonate ligands containing unsymmetric strong/weak σ donors similar to the widely studied phosphine-sulfonate ligands. This kind of palladacycles combines the characteristics of the NHC-sulfonate ligands and the stability of the palladacycle complexes and may potentially be regarded as polymerization catalysts. Herein, we report the synthesis and structures of a series of C(sp3),N-chelated and C(sp2),N-chelated NHC-sulfonate palladacycle complexes. The vinyl polymerization of norbornene with these complexes is also studied in the presence of methylaluminoxane (MAO).

Figure 1. ORTEP diagram of 5a. Thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): S(1)−O(1) 1.4509(10), S(1)−O(2) 1.4465(11), S(1)−O(3) 1.4507(11), S(1)−C(2) 1.7839(14), N(1)−C(13) 1.3289(18), N(2)−C(13), 1.3227(17), N(2)−C(13)−N(1) 108.39(12).

these complexes are air and moisture stable and have been fully characterized by 1H NMR, 13C NMR, HRMS, and elemental analysis. In their 1H NMR spectra, the signals of the imidazole proton at the C-2 position, appearing in compound 5, completely disappeared. For complexes 6a−e, the characteristic signals of the carbene carbons in their 13C NMR spectra appeared at 171.8 (6a), 170.9 (6b), 171.3 (6c), 172.6 (6d), and 171.5 (6e) ppm, while in complexes 7a−e, the corresponding signals appeared at 172.6 (7a), 172.1 (7b), 172.3 (7c), 173.5 (7d), and 172.3 (7e) ppm. The molecular structures of 6d, 6e, and 7e were determined by single-crystal X-ray diffraction analysis. As shown in Figures 2−4, complexes 6d, 6e, and 7e possess spiro structures consisting of the seven-membered {C−O}Pd chelate rings and the five-membered C,N-chelated palladacycles with palladium as the spiroatom. The seven-membered {C−O}Pd chelate rings in 6d, 6e, and 7e adopt twist-boat conformations,23 with angles of 86.8(4)°, 84.5(6)°, and 85.6(2)° between the Pd square planes [O(1)−Pd(1)−C(1) for 6d, O(3)−Pd(1)−C(23) for 6e, O(1)−Pd(1)−C(1) for 7e] and the backbone planes of the {C−O} ligands [S(2)−C(5)−C(4)−N(1) for 6d, S(3)− C(29)−C(24)−N(3) for 6e, S(1)−C(5)−C(4)−N(1) for 7e], respectively. The NHC ligands are rotated out of the Pd square planes by 60.4(3)° for 6d as measured by the angle between the N(1)−C(1)−N(2) and O(1)−Pd(1)−C(1) planes, 65.4(5)° for 6e as measured by the N(2)−C(23)− N(3) and O(3)−Pd(1)−C(23) planes, and 62.9(8)° for 7e as measured by the [N(1)−C(1)−N(2) and O(1)−Pd(1)−C(1) planes. The Pd−N bond lengths in C(sp3),N-chelated palladacycles [2.0600(12) Å for 6d, 2.054(3) Å for 6e] are much shorter than that in the C(sp2),N-chelated palladacycle 7e [2.1138(15) Å], while the Pd−C(sp3) bonds [2.0192(15) Å for 6d, 2.011(3) Å for 6e] are much longer than the Pd−C(sp2) bond [1.9767(17) Å for 7e]. The Pd−C(NHC) bond lengths

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RESULTS AND DISCUSSION Synthesis of NHC-Sulfonate Ligands. The synthesis of NHC-sulfonate ligands 5 is outlined in Scheme 1. The commercially available 4-tert-butylaniline (1) was reacted with concentrated sulfuric acid to provide 2 in 95% yield. Compound 2 was diazotized, followed by iodination to provide 3 in 67% yield.22 Treatment of 3 with imidazole in the presence of CuI yielded sodium 5-tert-butyl-2-(1H-imidazol-1-yl)benzenesulfonate (4). Compound 4 was then reacted with different halohydrocarbons to afford the desired ligands 5a−e. For 5c−e the bromo-hydrocarbons were used, but for 5a,b the liquid methyl iodide and more active isopropyl iodide were used, respectively. All the compounds were characterized by 1H NMR, 13C NMR, and high-resolution mass spectrometry (HRMS). In DMSO-d6 all the 1H NMR spectra exhibited the characteristic singlets at 9−10 ppm for the imidazolium. The molecular structure of 5a was also confirmed by single-crystal X-ray diffraction analysis (Figure 1). Synthesis of NHC-Sulfonate Palladacycles. A series of C(sp3),N-chelated NHC-sulfonate palladacycles 6a−e and C(sp2),N-chelated palladacycles 7a−e were synthesized by the reactions of NHC-sulfonate ligands 5a−e with Ag2O, [Pd(OAc)(8-Me-quin-H)]2, or [Pd(dmba)(μ-Cl)]2 (dmba = Me2NCH2C6H5) in good yields, respectively (Scheme 2). All B


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Organometallics Scheme 2. Synthesis of the NHC-Sulfonate Palladacycles

Figure 4. ORTEP diagram of 7e. Thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Pd(1)−C(1) 1.9772(18), Pd(1)−C(24) 1.9767(17), Pd(1)−N(3) 2.1138(15), Pd(1)−O(1) 2.1442(12), S(1)−O(1) 1.4804(14), S(1)−O(2) 1.4417(15), S(1)− O(3) 1.4437(14), C(24)−Pd(1)−C(1) 95.12(7), C(24)−Pd(1)− N(3) 83.65(7), C(1)−Pd(1)−N(3) 177.81(7), C(24)−Pd(1)−O(1) 170.96(6), C(1)−Pd(1)−O(1) 92.42(6), N(3)−Pd(1)−O(1) 88.65(5).

Figure 2. ORTEP diagram of 6d. Thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Pd(1)−C(1) 1.9843(14), Pd(1)−C(21) 2.0192(15), Pd(1)−N(3) 2.0600(12), Pd(1)−O(1) 2.1698(11), S(2)−O(1) 1.4783(11), S(2)−O(2) 1.4512(13), S(2)− O(3) 1.4432(13), C(1)−Pd(1)−C(21) 90.71(6), C(1)−Pd(1)−N(3) 174.67(5), C(21)−Pd(1)−N(3) 84.07(5), C(1)−Pd(1)−O(1) 95.02(5), C(21)−Pd(1)−O(1) 173.52(5), N(3)−Pd(1)−O(1) 90.24(5).

Norbornene Polymerization Catalyzed by C,N-Chelated Palladacycles. Vinyl polynorbornene has received considerable attention due to its good mechanical strength, heat resistivity, and optical transparency.24 Recently, some Nheterocyclic carbene nickel and palladium complexes have been utilized in the vinyl polymerization of norbornene with excellent activities.25 In order to explore the potential applications of the C(sp3),N-chelated NHC-sulfonate palladacycles, the vinyl polymerizations of norbornene with these palladacycles were studied. Complex 6b was chosen as the precatalyst for the study of the polymerization in detail. First, no polymer was obtained without cocatalyst. To ascertain the suitable cocatalyst, various reagents such as Et2AlCl, Et3Al, i Bu3Al, MAO, B(C6F5)3, and [Ph3C]+[B(C6F5)4]− were examined under different conditions, but only MAO could activate the precatalyst. So complex 6b was used to optimize the catalytic parameters in the presence of MAO, and the results are listed in Table 1. Higher temperatures (from 20 to 60 °C) enhanced the catalytic activity (entries 1−3, Table 1); however, the catalytic activity decreased slightly when the temperature was further increased (entries 4, 5, Table 1). Variation of the ratio of MAO to 6b, which is expressed here as Al/Pd ratio, had a considerable effect on the catalytic activities. On increasing the Al/Pd ratios, the catalytic ability of 6b first increased sharply and then decreased slightly (entries 6−11, Table 1). The maximum activity, 5.637 × 10 7 g of polynorbornene (PNB) (mol of Pd)−1 h−1, was observed

Figure 3. ORTEP diagram of 6e. Thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Pd(1)−C(23) 1.979(3), Pd(1)−C(1) 2.011(3), Pd(1)−N(1) 2.054(2), Pd(1)−O(3) 2.182(2), S(3)−O(1) 1.444(2), S(3)−O(2) 1.446(2), S(3)−O(3) 1.482(2), C(23)−Pd(1)−C(1) 91.25(11), C(23)−Pd(1)−N(1) 175.58(10), C(1)−Pd(1)−N(1) 84.36(11), C(23)−Pd(1)−O(3) 93.72(9), C(1)−Pd(1)−O(3) 173.75(9), N(1)−Pd(1)−O(3) 90.63(10).

are similar in all complexes [1.9843(14) Å for 6d, 1.979(3) Å for 6e, 1.9772(18) Å for 7e]. C


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Organometallics

temperature. Along with an increase of Al/Pd ratio at 100 °C, the catalytic ability of 7b first increased to reach a maximum activity of 2.921 × 106 g of PNB (mol of Pd)−1 h−1 at a Al/Pd ratio of 2500 (entriy 4, Table 2) and then decreased gradually (entries 4−8, Table 2). Long reaction time results in high yield, but the activity decreased rapidly (entries 4, 9−11, Table 2). The color of the PNB obtained at 30 min is slightly black, indicating that the active species decomposes at 100 °C for a long time. The optimal polymerization conditions for the catalytic system are 100 °C with an Al/Pd molar ratio of 2500 in 3 min. Similarly, complexes 7a and 7c−e also exhibited moderate activities [106 g of PNB (mol of Pd)−1 h−1] in the polymerization of norbornene (entries 12−15, Table 2). There is no detailed report on the mechanism study in the vinyl polymerization of norbornene by an anion-tethered Pd catalyst in the presence of MAO. From our catalytic systems, we also cannot obtain any useful information. However, there are some mechanism studies on the vinyl polymerization of norbornene by an anion-tethered Ni catalyst in the presence of MAO in previous reports,26 and it has been accepted that the role of MAO is to create an empty site for coordination and insertion of the norbornene.26,27 Analogous to the aniontethered Ni catalyst, we proposed a possible mechanism for the Pd-catalyzed vinyl polymerization of NBE as shown in Scheme 3. First, the N ligand is released from the palladium and a cationic palladium species may also be formed by the effect of the MAO; then NBE is coordinated to the Pd center and inserted into the Pd−C bond to initiate the polymerization. In general, the steric hindrance may promote the release of the ligand from the Pd center but is not in favor of the coordination of NBE to the Pd center and insertion into the Pd−C bond in the catalytic process. The Pd−C(sp3) bonds in 6a−e are more active for insertion and less crowded than the Pd−C(sp2) bonds in 7a−e. For the C(sp3),N-chelated palladacycles 6a−e, the key factor may be the release of the less crowded ligand from the Pd center. So the steric hindrance may slightly promote the process, and a high Al/Pd ratio (up to 7000) is needed. But for the C(sp2),N-chelated palladacycles 7a−e, the main factors may be the coordination of NBE to the Pd center and insertion into the Pd−C bond. So the steric hindrance may depress the processes and showed a different activity order from that for 6a−e. The crowded ligand and less active Pd−C(sp2) bond in the C(sp2),N-chelated palladacycles 7a−e also resulted in a lower Al/Pd ratio (2500), lower catalytic activities, but higher thermal stability than those for 6a−e. The polymers obtained are insoluble in most organic solvents, such as hexane, chloroform, benzene, chlorobenzene, dichlorobenzene, acetone, dioxane, methanol, tetrahydrofuran, and tetrachloroethane. Therefore, we cannot measure the molecular weights of the polymers by GPC. According to the TGA study, the polymers are thermally stable up to 400 °C. The determination of the glass transition temperature (Tg) of vinyl polynorbornene has been described as difficult, since it is apparently located close to the temperature range where decomposition tends to set in.28 DSC studies did not show an endothermic signal upon heating up to 400 °C. It was reported in the literature that there were three types of polymerization of norbornene, which are ROMP type, cationic or radical type, and vinyl type.24a,29 The missing absorption of a double bond at 1600−1700 cm−1 in the IR spectra of the polymers indicates that the polymerization initiated by the palladacycles/MAO system is not ROMP type. The cationic or radical polymer-

Table 1. Vinyl Polymerization of Norbornene with C(sp3),NChelated Palladacycles Activated by MAOa entry

cat.

T (°C)

Al/Pd

PNB (g)

activityb

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6a 6c 6d 6e

20 40 60 80 100 60 60 60 60 60 60 60 60 60 60

3000 3000 3000 3000 3000 2000 4000 5000 6000 7000 8000 7000 7000 7000 7000

0.0184 0.1199 0.6150 0.6055 0.4722 0.0206 0.6782 0.8809 0.9208 0.9395 0.9287 0.8678 0.9140 0.9737 0.9482

1.10 7.19 36.90 36.33 28.33 1.24 40.69 52.85 55.25 56.37 55.72 52.07 54.84 58.42 56.89

Polymerization conditions: catalyst, 1 μmol; solvent, toluene; Vtotal, 10 mL; norbornene, 1.0 g; reaction time, 1 min; MAO, 1.4 M in toluene. bIn units of 106 g of PNB (mol of Pd)−1 h−1. a

when the temperature was 60 °C and the Al/Pd ratio was 7000 (entry 10, Table 1). The catalytic behaviors toward norbornene polymerization for the other complexes (6a, 6c−e) were also investigated under the optimum conditions with an Al/Pd ratio of 7000 at 60 °C (entries 12−15, Table 1), confirming high activities in all cases. The vinyl polymerizations of norbornene with C(sp2),Nchelated palladacycles were also studied, and the results are listed in Table 2. Similar to the C(sp3),N-chelated palladaTable 2. Vinyl Polymerization of Norbornene with C(sp2),NChelated Palladacycles Activated by MAOa entry

cat.

T (°C)

Al/Pd

PNB (g)

activityb

1 2 3 4 5 6 7 8 9c 10d 11e 12 13 14 15

7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7b 7a 7c 7d 7e

40 60 80 100 100 100 100 100 100 100 100 100 100 100 100

2500 2500 2500 2500 1500 2000 3000 4000 2500 2500 2500 2500 2500 2500 2500

0.0599 0.1449 0.2797 0.4382 0.1149 0.2522 0.4346 0.4176 0.5206 0.6813 0.9084 0.4448 0.3671 0.3221 0.3299

0.399 0.966 1.865 2.921 0.766 1.681 2.897 2.784 2.082 1.363 0.606 2.965 2.447 2.147 2.199

a Polymerization conditions: catalyst, 3 μmol; solvent, toluene; Vtotal, 10 mL; norbornene, 1.0 g; reaction time, 3 min; MAO, 1.4 M in toluene. bIn units of 106 g of PNB (mol of Pd)−1 h−1. cReaction time, 5 min. dReaction time, 10 min. eReaction time, 30 min.

cycles, the C(sp2),N-chelated palladacycles could be activated only by MAO. The catalytic conditions for norbornene polymerization were optimized by precatalyst 7b in the presence of MAO. It was found that the activity increased with increasing temperature from 40 to 100 °C (entries 1−4, Table 2). The highest activity was found at 100 °C (entry 4, Table 2), indicating that the active species is stable at high D


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Organometallics Scheme 3. Proposed Mechanism for Pd-Catalyzed Vinyl Polymerization of NBE with MAO

white powder (21.78 g, 95.0 mmol, 95%). Mp: >300 °C. 1H NMR (400 MHz, DMSO-d6): δ 8.26 (br, 2H, NH2), 7.63 (d, J = 2.3 Hz, 1H, Ar-H), 7.31 (dd, J = 8.3, 2.3 Hz, 1H, Ar-H), 6.96 (d, J = 8.3 Hz, 1H, Ar-H), 1.25 (s, 9H, C(CH3)3). 13C NMR (100 MHz, DMSO-d6): δ 144.5, 135.3, 132.8, 126.9, 123.7, 120.1, 33.9, 31.1. HRMS (ESI, m/z): calcd for C10H15NO3S [M − H]− 228.0700, found 228.0702. Sodium 5-tert-Butyl-2-iodobenzenesulfonate (3).22 To a suspension of 2 (11.5 g, 50.0 mmol) in water (30 mL) was added anhydrous Na2CO3 (2.65 g, 25 mmol) with stirring until a homogeneous solution was obtained. NaNO2 (3.62 g, 52.5 mmol) in water (20 mL) was then added to this solution slowly at 0 °C, and the mixture was stirred for 20 min at below 5 °C. To the resulting mixture were added crushed ice (20 g) and concentrated HCl (10 mL) at 0 °C (immediate precipitation of the diazonium salt was observed). A solution of NaI (8.24 g, 55.0 mmol) in water (20 mL) was then added slowly with stirring at 0 °C. After addition was completed, stirring was continued for ca. 10 min at 0 °C, and the resulting mixture was allowed to warm to room temperature and then heated to 50 °C for 12 h to remove all N2. The mixture was then refrigerated, and the insoluble component was separated. After the solid was treated with boiling EtOH (some Et2O then added), the mixture was allowed to cool to separate the insoluble solid. The solid was washed with cold EtOH and Et2O, leaving the product as a white solid (12.1 g, 33.4 mmol, 67%). Mp: >300 °C. 1H NMR (400 MHz, DMSO-d6): δ 7.98 (s, 1H, Ar-H), 7.78 (d, J = 7.8 Hz, 1H, Ar-H), 7.04 (d, J = 7.8 Hz, 1H, Ar-H), 1.25 (s, 9H, C(CH3)3). 13C NMR (100 MHz, DMSO-d6): δ 150.0, 149.4, 140.4, 127.1, 125.0, 89.6, 34.2, 30.8. HRMS (ESI, m/z): calcd for C10H12INaO3S [M − Na]− 338.9557, found 338.9560. Sodium 5-tert-Butyl-2-(1H-imidazol-1-yl)benzenesulfonate (4). Compound 3 (5.43 g, 15 mmol), CuI (0.29 g, 1.5 mmol), Cs2CO3 (9.77 g, 30 mmol), and 50 mL of dried DMSO were added to a round-bottom flask. The reaction mixture was stirred at 100 °C for 36 h, then cooled to room temperature, filtered through Celite, and washed with DMSO (10 mL × 3). After removal of solvent under reduced pressure the residue was recrystallized from MeOH and Et2O. The obtained solid (4.07 g, 13.5 mmol, 90%) might contain some Cs2CO3 and was used in the subsequent step without further purification. Mp: >300 °C. 1H NMR (400 MHz, DMSO-d6): δ 7.96 (d, J = 2.2 Hz, 1H, Ar-H), 7.91 (s, 1H, NCHN), 7.44 (dd, J = 8.2, 2.2 Hz, 1H, Ar-H), 7.41 (s, 1H, im-H), 7.13 (d, J = 8.2 Hz, 1H, Ar-H), 6.87 (s, 1H, im-H), 1.27 (s, 9H, C(CH3)3). 13C NMR (100 MHz, DMSO-d6): δ 149.7, 141.6, 138.5, 131.5, 127.1, 126.9, 126.6, 125.3, 121.6, 34.3, 30.9. HRMS (ESI, m/z): calcd for C13H15N2NaO3S [M − Na]− 279.0809, found 279.0814. General Procedures for Preparation of the NHC-Sulfonate Liagands 5a−e. The mixture of 4 (3.02 g, 10 mmol), an exact amount of RX (CH3I for 5a, iPrI for 5b, nBuBr for 5c, PhCH2Br for 5d, MesCH2Br for 5e), and 30 mL of dried DMF was stirred at 100 °C for 12 h. After removal of solvent under reduced pressure, the residue was dissolved in CH3OH and purified by column chromatography (alumina, CH2Cl2/CH3OH = 6:1) to give 5 as a white solid. Compound 5a (R = Me). Yield: 0.88 g (3.0 mmol, 30%). Mp: >300 °C. 1H NMR (400 MHz, DMSO-d6): δ 9.36 (s, 1H, NCHN), 7.98 (d, J = 2.3 Hz, 1H, Ar-H), 7.90 (s, 1H, im-H), 7.78 (s, 1H, im-H), 7.62 (dd, J = 8.2, 2.3 Hz, 1H, Ar-H), 7.44 (d, J = 8.2 Hz, 1H, Ar-H), 3.93 (s,

izations of norbornene generally result in soluble polymers with low molecular weight (300 °C. 1H NMR (400 MHz, DMSO-d6): δ 9.48 (s, 1H, NCHN), 7.98− 7.97 (m, 2H, Ar-H and im-H), 7.92 (t, J = 1.7 Hz, 1H, im-H), 7.63 (d, J = 8.2 Hz, 1H, Ar-H), 7.49 (d, J = 8.2 Hz, 1H, Ar-H), 4.75−4.65 (m, 1H, −CH(CH3)2), 1.51 (d, J = 6.7 Hz, 6H, −CH(CH3)2), 1.33 (s, 9H, C(CH3)3). 13C NMR (100 MHz, DMSO-d6): δ 152.9, 142.8, 136.9, 129.0, 127.2, 127.0, 124.8, 124.7, 119.1, 52.2, 34.6, 30.8, 22.2. HRMS (ESI, m/z): calcd for C16H22N2O3S [M − H]− 321.1278, found 321.1280. Compound 5c (R = nBu). Yield: 1.01 g (3.0 mmol, 30%). Mp: >300 °C. 1H NMR (400 MHz, DMSO-d6): δ 9.42 (s, 1H, NCHN), 7.98 (s, 1H, Ar-H), 7.90 (s, 1H, im-H), 7.87 (s, 1H, im-H), 7.63 (d, J = 8.2 Hz, 1H, Ar-H), 7.47 (d, J = 8.2 Hz, 1H, Ar-H), 4.23 (t, J = 6.8 Hz, 2H, NCH2−), 1.85−1.78 (m, 2H, CH2-CH2-CH2), 1.33 (br, 11H, −CH2CH3 and C(CH3)3), 0.92 (t, J = 7.3 Hz, 3H, CH3). 13C NMR (100 MHz, DMSO-d6): δ 152.9, 142.8, 138.0, 128.9, 127.3, 127.0, 124.9, 124.7, 120.9, 48.6, 34.6, 31.3, 30.8, 18.4, 13.3. HRMS (ESI, m/z): calcd for C17H24N2O3S [M − H]− 335.1435, found 335.1435. Compound 5d (R = CH2Ph). Yield: 1.42 g (3.8 mmol, 38%). Mp: >300 °C. 1H NMR (400 MHz, DMSO-d6): δ 9.62 (s, 1H, NCHN), 7.99 (d, J = 2.3 Hz, 1H, Ar-H), 7.93 (t, J = 1.7 Hz, 1H, im-H), 7.82 (t, J = 1.7 Hz, 1H, im-H), 7.63 (dd, J = 8.3, 2.3 Hz, 1H, Ar-H), 7.51 (d, J = 8.3 Hz, 1H, Ar-H), 7.46−7.38 (m, 5H, Ph-H), 5.53 (s, 2H, N-CH2Ph), 1.34 (s, 9H, C(CH3)3). 13C NMR (100 MHz, DMSO-d6): δ 153.0, 142.8, 138.4, 134.7, 128.8, 128.7, 128.4, 127.8, 127.3, 127.1, 125.4, 124.7, 121.0, 51.8, 34.6, 30.8. HRMS (ESI, m/z): calcd for C20H22N2O3S [M − H]− 369.1278, found 369.1277. Compound 5e (R = CH2Mes). Yield: 1.44 g (3.5 mmol, 35%). Mp: >300 °C. 1H NMR (400 MHz, DMSO-d6): δ 9.23 (s, 1H, NCHN), 7.94 (d, J = 2.3 Hz, 1H, Ar-H), 7.88 (t, J = 1.7 Hz, 1H, im-H), 7.60 (dd, J = 8.3, 2.3 Hz, 1H, Ar-H), 7.57 (t, J = 1.7 Hz, 1H, im-H), 7.43 (d, J = 8.2 Hz, 1H, Ar-H), 6.95 (s, 2H, Ar-H), 5.43 (s, 2H, N-CH2-Ar), 2.31 (s, 6H, Ar-CH3), 2.24 (s, 3H, Ar-CH3), 1.31 (s, 9H, C(CH3)3). 13 C NMR (100 MHz, DMSO-d6): δ 152.8, 142.6, 138.4, 138.3, 137.6, 129.2, 128.8, 127.3, 127.0, 126.4, 125.2, 124.6, 120.5, 46.9, 34.6, 30.8, 20.5, 19.2. HRMS (ESI, m/z): calcd for C23H28N2O3S [M − H]− 411.1748, found 411.1740. General Procedures for Preparation of the C(sp3),NChelated NHC-Sulfonate Palladacycles 6a−e. A mixture of 5 (1.0 mmol) and 3 equiv of silver oxide (0.696 g, 3 mmol) was placed in a round-bottom flask equipped with a cooler and dissolved in 30 mL of chloroform. The reaction mixture was stirred at reflux for 24 h under dark and then cooled to room temperature. The reaction mixture was filtered through Celite, and [Pd(OAc)(8-Me-quin-H)]2 (0.308 g, 0.5 mmol) was added. After stirring for 36 h at room temperature under dark, the reaction mixture was filtered through Celite. After removal of solvent under reduced pressure the residue was dissolved in CH2Cl2 and purified by column chromatography (silica gel, CH2Cl2/EtOAc = 8:1) to give 6 as a white solid. Compound 6a (R = Me). Yield: 380 mg (0.70 mmol, 70%). Mp: 265 °C (dec). Anal. Calcd for C24H25N3O3PdS: C, 53.19; H, 4.65; N, 7.75. Found: C, 53.30; H, 4.69; N, 7.80. 1H NMR (400 MHz, CDCl3): δ 8.90 (d, J = 4.1 Hz, 1H, Ar-H), 8.34 (d, J = 2.1 Hz, 1H, Ar-H), 8.20 (d, J = 8.3 Hz, 1H, Ar-H), 7.54−7.47 (m, 3H, Ar-H), 7.42−7.38 (m, 2H, Ar-H), 7.30 (d, J = 8.2 Hz, 1H, Ar-H), 7.17 (d, J = 1.4 Hz, 1H, imH), 7.14 (d, J = 1.4 Hz, 1H, im-H), 4.09 (s, 3H, N-CH3), 3.16 (d, J = 15.1 Hz, 1H, Ar-CH2-Pd), 3.06 (d, J = 15.1 Hz, 1H, Ar-CH2-Pd), 1.34 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ 171.8, 152.2, 150.5, 148.7, 148.4, 140.9, 137.6, 134.4, 128.7, 128.7, 128.2, 127.6, 126.9, 125.7, 123.7, 123.5, 122.6, 121.3, 38.3, 35.0, 31.2, 15.5. HRMS (ESI, m/z): calcd for C24H25N3O3PdS [M + H]+ 542.0724, found 542.0734. Compound 6b (R = iPr). Yield: 520 mg (0.91 mmol, 91%). Mp: 275 °C (dec). Anal. Calcd for C26H29N3O3PdS: C, 54.78; H, 5.13; N, 7.37. Found: C, 54.94; H, 5.40; N, 7.08. 1H NMR (400 MHz, CDCl3): δ 8.92 (dd, J = 4.8, 1.4 Hz, 1H, Ar-H), 8.34 (d, J = 2.2 Hz, 1H, Ar-H),

8.21 (dd, J = 8.4, 1.4 Hz, 1H, Ar-H), 7.55−7.49 (m, 3H, Ar-H), 7.43− 7.40 (m, 2H, Ar-H), 7.32 (d, J = 8.2 Hz, 1H, Ar-H), 7.20 (d, J = 2.0 Hz, 1H, im-H), 7.18 (d, J = 2.0 Hz, 1H, im-H), 5.53−5.43 (m, 1H, CH(CH3)2), 3.11−3.03 (m, 2H, Ar-CH2-Pd), 1.60 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.34 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ 170.9, 152.2, 150.6, 148.9, 148.5, 141.3, 137.6, 134.6, 128.9, 128.7, 128.1, 127.6, 126.9, 125.5, 124.1, 123.6, 121.4, 117.2, 53.1, 35.0, 31.2, 24.8, 23.0, 15.4. HRMS (ESI, m/z): calcd for C26H29N3O3PdS [M + H]+ 570.1037, found 570.1052. Compound 6c (R = nBu). Yield: 360 mg (0.62 mmol, 62%). Mp: 203−205 °C. Anal. Calcd for C27H31N3O3PdS: C, 55.53; H, 5.35; N, 7.19. Found: C, 55.49; H, 5.62; N, 6.94. 1H NMR (400 MHz, CDCl3): δ 8.89 (d, J = 4.7 Hz, 1H, Ar-H), 8.34 (d, J = 2.2 Hz, 1H, Ar-H), 8.17 (d, J = 8.3 Hz, 1H, Ar-H), 7.53−7.45 (m, 3H, Ar-H), 7.40−7.36 (m, 2H, Ar-H), 7.31 (d, J = 8.2 Hz, 1H, Ar-H), 7.18 (d, J = 1.8 Hz, 1H, imH), 7.15 (d, J = 1.9 Hz, 1H, im-H), 4.59−4.51 (m, 1H, N-CH2CH2), 4.34−4.27 (m, 1H, N-CH2CH2), 3.10−3.02 (m, 2H, Ar-CH2-Pd), 2.11−2.00 (m, 1H, N-CH2CH2), 1.99−1.88 (m, 1H, N-CH2CH2), 1.55−1.46 (m, 2H, CH2CH2CH3), 1.33 (s, 9H, C(CH3)3), 1.00 (t, J = 7.3 Hz, 3H, CH2CH3). 13C NMR (100 MHz, CDCl3): δ 171.3, 152.1, 150.5, 148.7, 148.4, 141.2, 137.5, 134.5, 128.7, 128.6, 128.1, 127.6, 126.8, 125.7, 123.8, 123.5, 121.3, 120.9, 50.9, 35.0, 33.4, 31.1, 19.6, 15.5, 13.7. HRMS (ESI, m/z): calcd for C27H31N3O3PdS [M + H]+ 584.1194, found 584.1210. Compound 6d (R = CH2Ph). Yield: 480 mg (0.78 mmol, 78%). Mp: 270 °C (dec). Anal. Calcd for C30H29N3O3PdS: C, 58.30; H, 4.73; N, 6.80. Found: C, 58.17; H, 4.65; N, 6.72. 1H NMR (400 MHz, CDCl3): δ 8.93 (s, 1H, Ar-H), 8.37 (s, 1H, Ar-H), 8.21 (d, J = 8.3 Hz, 1H, ArH), 7.56−7.53 (m, 2H, Ar-H), 7.47−7.34 (m, 9H, Ar-H), 7.20 (s, 1H, im-H), 6.97 (s, 1H, im-H), 5.97 (d, J = 15.2 Hz, 1H, CH2-Ph), 5.52 (d, J = 15.2 Hz, 1H, CH2-Ph), 3.16 (d, J = 15.2 Hz, 1H, Ar−CH2-Pd), 3.08 (d, J = 15.2 Hz, 1H, Ar−CH2-Pd), 1.36 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ 172.6, 152.3, 150.4, 148.7, 148.2, 141.2, 137.6, 135.9, 134.4, 129.0, 128.8, 128.6, 128.2, 128.1, 127.7, 127.6, 126.8, 125.7, 124.4, 123.5, 121.3, 121.3, 54.9, 35.0, 31.2, 16.3. HRMS (ESI, m/z): calcd for C30H29N3O3PdS [M + H]+ 618.1037, found 618.1049. Compound 6e (R = CH2Mes). Yield: 460 mg (0.7 mmol, 70%). Mp: 285 °C (dec). Anal. Calcd for C33H35N3O3PdS: C, 60.04; H, 5.34; N, 6.37. Found: C, 59.95; H, 5.18; N, 6.22. 1H NMR (400 MHz, CDCl3): δ 8.93 (d, J = 3.9 Hz, 1H, Ar-H), 8.36 (s, 1H, Ar-H), 8.18 (d, J = 8.1 Hz, 1H, Ar-H), 7.52−7.51 (m, 3H, Ar-H), 7.41−7.38 (m, 2H, Ar-H), 7.32 (d, J = 8.1 Hz, 1H, Ar-H), 7.07 (s, 1H, im-H), 6.91 (s, 2H, Ar-H), 6.62 (s, 1H, im-H), 6.04 (d, J = 14.0 Hz, 1H, CH2-Mes), 5.28 (d, J = 14.0 Hz, 1H, CH2-Mes), 3.36 (d, J = 15.0 Hz, 1H, Ar-CH2-Pd), 3.14 (d, J = 15.0 Hz, 1H, Ar-CH2-Pd), 2.48 (s, 6H, Ar-CH3), 2.28 (s, 3H, Ar-CH3), 1.33 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ 171.5, 152.1, 150.5, 148.7, 148.4, 141.1, 138.6, 138.4, 137.6, 134.5, 129.5, 128.8, 128.6, 128.1, 128.0, 127.6, 126.7, 125.8, 123.5, 123.4, 121.3, 119.8, 49.0, 35.0, 31.1, 21.0, 20.1, 15.2. HRMS (ESI, m/z): calcd for C33H35N3O3PdS [M + H]+ 660.1507, found 660.1521. General Procedures for Preparation of the C(sp2),NChelated NHC-Sulfonate Palladacycles 7a−e. A mixture of 5 (1.0 mmol) and 3 equiv of silver oxide (0.696 g, 3 mmol) was placed in a round-bottom flask equipped with a cooler and dissolved in 30 mL of chloroform. The reaction mixture was stirred at reflux for 24 h under dark and then cooled to room temperature. The reaction mixture was filtered through Celite, and [Pd(dmba)(μ-Cl)]2 (0.276 g, 0.5 mmol) was added. After stirring for 36 h at room temperature under dark, the reaction mixture was filtered through Celite. After removal of solvent under reduced pressure the residue was dissolved in CH2Cl2 and purified by column chromatography (silica gel, CH2Cl2/ EtOAc = 4:1) to give 7 as a white solid. Compound 7a (R = Me). Yield: 300 mg (0.56 mmol, 56%). Mp: 250 °C (dec). Anal. Calcd for C23H29N3O3PdS: C, 51.73; H, 5.47; N, 7.87. Found: C, 51.53; H, 5.61; N, 8.05. 1H NMR (400 MHz, CDCl3): δ 8.32 (d, J = 2.2 Hz, 1H, Ar-H), 7.54 (dd, J = 8.2, 2.2 Hz, 1H, Ar-H), 7.31 (d, J = 8.2 Hz, 1H, Ar-H), 7.22 (d, J = 1.9 Hz, 1H, im-H), 7.16 (d, J = 1.9 Hz, 1H, im-H), 6.94−6.90 (m, 2H, Ar-H), 6.77−6.73 (m, 1H, Ar-H), 6.19 (d, J = 7.5 Hz, 1H, Ar-H), 4.19 (d, J = 14.0 Hz, 1H, ArF


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Organometallics CH2-N), 3.86 (s, 3H, NCH3), 3.42 (d, J = 14.0 Hz, 1H, Ar-CH2-N), 2.75 (s, 3H, N(CH3)2), 2.36 (s, 3H, N(CH3)2), 1.36 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ 172.6, 152.4, 148.4, 143.6, 140.7, 136.3, 134.2, 128.2, 126.5, 125.9, 125.8, 124.2, 123.1, 122.8, 122.5, 70.7, 49.9, 48.6, 39.0, 35.0, 31.1. HRMS (ESI, m/z): calcd for C23H29N3O3PdS [M + H]+ 534.1037, found 534.1040. Compound 7b (R = iPr). Yield: 280 mg (0.55 mmol, 55%). Mp: 240 °C (dec). Anal. Calcd for C25H33N3O3PdS: C, 53.43; H, 5.92; N, 7.48. Found: C, 53.34; H, 6.05; N, 7.51. 1H NMR (400 MHz, CDCl3): δ 8.33 (d, J = 2.2 Hz, 1H, Ar-H), 7.53 (dd, J = 8.2, 2.2 Hz, 1H, Ar-H), 7.32 (d, J = 8.2 Hz, 1H, Ar-H), 7.24 (d, J = 1.9 Hz, 1H, im-H), 7.21 (d, J = 1.9 Hz, 1H, im-H), 6.94−6.90 (m, 2H, Ar-H), 6.77−6.73 (m, 1H, Ar-H), 6.23 (d, J = 7.5 Hz, 1H, Ar-H), 5.19−5.09 (m, 1H, CH(CH3)2), 4.17 (d, J = 14.1 Hz, 1H, Ar-CH2-N), 3.43 (d, J = 14.1 Hz, 1H, Ar-CH2-N), 2.76 (s, 3H, N(CH3)2), 2.36 (s, 3H, N(CH3)2), 1.59 (d, J = 6.7 Hz, 3H, CH(CH3)2), 1.41 (d, J = 6.7 Hz, 3H, CH(CH3)2), 1.36 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ 172.1, 152.4, 148.4, 143.6, 141.3, 136.8, 134.5, 128.1, 126.5, 125.7, 125.6, 124.2, 123.3, 122.5, 117.5, 70.8, 53.3, 50.0, 48.6, 35.1, 31.2, 25.1, 21.5. HRMS (ESI, m/z): calcd for C25H33N3O3PdS [M + H]+ 562.1350, found 562.1359. Compound 7c (R = nBu). Yield: 460 mg (0.80 mmol, 80%). Mp: 230 °C (dec). Anal. Calcd for C26H35N3O3PdS: C, 54.21; H, 6.12; N, 7.29. Found: C, 54.41; H, 6.07; N, 7.52. 1H NMR (400 MHz, CDCl3): δ 8.33 (d, J = 2.2 Hz, 1H, Ar-H), 7.53 (dd, J = 8.2, 2.2 Hz, 1H, Ar-H), 7.32 (d, J = 8.2 Hz, 1H, Ar-H), 7.22 (d, J = 1.8 Hz, 1H, im-H), 7.15 (d, J = 1.8 Hz, 1H, im-H), 6.94−6.90 (m, 2H, Ar-H), 6.77−6.73 (m, 1H, Ar-H), 6.22 (d, J = 7.5 Hz, 1H, Ar-H), 4.49−4.42 (m, 1H, NCH2CH2), 4.15 (d, J = 14.0 Hz, 1H, Ar-CH2-N), 3.97−3.90 (m, 1H, N-CH2CH2), 3.44 (d, J = 14.0 Hz, 1H, Ar-CH2-N), 2.75 (s, 3H, N(CH3)2), 2.37 (s, 3H, N(CH3)2), 2.06−1.95 (m, 1H, N-CH2CH2), 1.92−1.82 (m, 1H, N-CH2CH2), 1.56−1.43 (m, 2H, CH2CH2CH3), 1.36 (s, 9H, C(CH3)3), 1.01 (t, J = 7.3 Hz, 3H, CH2CH3). 13C NMR (100 MHz, CDCl3): δ 172.3, 152.4, 148.4, 143.9, 141.1, 136.5, 134.4, 128.1, 126.4, 125.8, 125.7, 124.1, 123.1, 122.4, 121.2, 70.8, 51.1, 50.1, 48.6, 35.0, 32.8, 31.2, 19.1, 13.6. HRMS (ESI, m/z): calcd for C26H35N3O3PdS [M + H]+ 576.1507, found 576.1521. Compound 7d (R = CH2Ph). Yield: 500 mg (0.82 mmol, 82%). Mp: 248 °C (dec). Anal. Calcd for C29H33N3O3PdS: C, 57.09; H, 5.45; N, 6.89. Found: C, 57.24; H, 5.74; N, 7.10. 1H NMR (400 MHz, CDCl3): δ 8.35 (d, J = 2.2 Hz, 1H, Ar-H), 7.55 (dd, J = 8.2, 2.2 Hz, 1H, Ar-H), 7.40−7.32 (m, 6H, Ar-H), 7.23 (d, J = 1.6 Hz, 1H, im-H), 7.02 (d, J = 1.6 Hz, 1H, im-H), 6.97−6.90 (m, 2H, Ar-H), 6.81 (t, J = 7.1 Hz, 1H, Ar-H), 6.34 (d, J = 7.5 Hz, 1H, Ar-H), 5.78 (d, J = 15.1 Hz, 1H, CH2Ph), 5.03 (d, J = 15.1 Hz, 1H, CH2-Ph), 4.09 (d, J = 14.0 Hz, 1H, ArCH2-N), 3.38 (d, J = 14.0 Hz, 1H, Ar-CH2-N), 2.66 (s, 3H, N(CH3)2), 2.36 (s, 3H, N(CH3)2), 1.37 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): 173.5, 152.6, 148.6, 144.1, 141.2, 136.5, 135.8, 134.2, 129.0, 128.2, 128.2, 126.5, 126.0, 125.7, 124.3, 123.5, 122.5, 121.7, 70.8, 55.6, 49.9, 48.6, 35.1, 31.2. HRMS (ESI, m/z): calcd for C29H33N3O3PdS [M + H]+ 610.1350, found 610.1362. Compound 7e (R = CH2Mes). Yield: 570 mg (0.87 mmol, 87%). Mp: 237 °C (dec). Anal. Calcd for C32H39N3O3PdS: C, 58.93; H, 6.03; N, 6.44. Found: C, 58.87; H, 6.08; N, 6.47. 1H NMR (400 MHz, CDCl3): δ 8.34 (d, J = 2.2 Hz, 1H, Ar-H), 7.53 (dd, J = 8.2, 2.2 Hz, 1H, Ar-H), 7.32 (d, J = 8.2 Hz, 1H, Ar-H), 7.12 (d, J = 2.0 Hz, 1H, imH), 6.98−6.93 (m, 2H, Ar-H), 6.90 (s, 2H, Ar-H), 6.85−6.80 (m, 1H, Ar-H), 6.67 (d, J = 2.0 Hz, 1H, im-H), 6.36 (d, J = 7.4 Hz, 1H, Ar-H), 5.78 (d, J = 14.5 Hz, 1H, CH2-Mes), 4.94 (d, J = 14.5 Hz, 1H, CH2Mes), 4.22 (d, J = 14.1 Hz, 1H, Ar-CH2-N), 3.45 (d, J = 14.1 Hz, 1H, Ar-CH2-N), 2.78 (s, 3H, N(CH3)2), 2.40 (s, 3H, N(CH3)2), 2.38 (s, 6H, Ar-CH3), 2.28 (s, 3H, Ar-CH3), 1.37 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ 172.3, 152.4, 148.6, 143.8, 141.1, 138.6, 138.4, 136.7, 134.5, 129.5, 128.1, 127.9, 126.5, 125.9, 125.7, 124.2, 122.7, 122.6, 120.2, 70.9, 50.1, 48.6, 35.1, 31.2, 21.0, 20.2. HRMS (ESI, m/z): calcd for C32H39N3O3PdS [M + H]+ 652.1820, found 652.1832. Crystallographic Studies. Single crystals suitable for X-ray diffraction were obtained from CH3OH/toluene for 5a and CH2Cl2/ hexane for 6d, 6e, and 7e. Data collections were carried out on a Rigaku Saturn 724 CCD (for 5a, 6d, and 7e) or Rigaku Saturn 70

CCD (for 6e) diffractometer equipped with a rotating anode system at 113(2) K by using graphite-monochromated Mo Kα radiation (ω−2θ scans, λ = 0.710 73 Å for 5a and 6e, λ = 0.710 75 Å for 6d and 7e). Semiempirical absorption corrections were applied for all complexes. The structures were solved by direct methods and refined by fullmatrix least-squares. Calculations were performed by using the SHELXL-97 program system. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were assigned idealized positions and were included in structure factor calculations. Norbornene Polymerization. In a typical procedure, 1.00 g of norbornene in 5 mL of toluene and the exact amount of MAO (1.4 M) were added into a flask (100 mL) with stirring under an Ar atmosphere. After the mixture was kept at the desired temperature for 2 min, the right amount of the palladium complex in 1 mL of toluene was injected into the flask via syringe, and the reaction was started. After the desired time, 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 in vacuo to a constant weight. For all the polymerization procedures, the total reaction volume was 10 mL, which can be achieved by variation of the added toluene when necessary.

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ASSOCIATED CONTENT

S Supporting Information *

A CIF file giving X-ray structure information for 5a, 6d, 6e, and 7e. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00214.

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AUTHOR INFORMATION

Corresponding Author

*Tel and fax: +86-22-23504781. E-mail: [email protected]. cn. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the National Natural Science Foundation of China (Nos. 21174068, 21421062) and Specialized Research Fund for the Doctoral Program of Higher Education of China (20110031110009) for financial support.

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REFERENCES

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