Synthesis of (Imido)vanadium(V) Complexes Containing 8-(2,6

Article pubs.acs.org/Organometallics

Synthesis of (Imido)vanadium(V) Complexes Containing 8‑(2,6Dimethylanilide)-5,6,7-trihydroquinoline Ligands: Highly Active Catalyst Precursors for Ethylene Dimerization Xiao-Yan Tang,†,‡,∥ Atsushi Igarashi,†,∥ Wen-Hua Sun,§ Akiko Inagaki,† Jingyu Liu,‡ Wenjuan Zhang,§ Yue-Sheng Li,‡ and Kotohiro Nomura*,† †

Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 minami Osawa, Hachioji, Tokyo 192-0397, Japan ‡ State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China § Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China S Supporting Information *

ABSTRACT: A series of (imido)vanadium(V) dichloride complexes containing 8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligands of the type V(NR)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (R = Ad (3), 2-MeC6H4 (4), 2,6-Me2C6H3 (Ar, 5)) have been prepared and identified, and their structures have been determined by X-ray crystallographic analysis. The ethylene dimerization catalyst generated from complex 3 upon treatment with an excess amount of MAO exhibited remarkable catalytic activities (e.g. TOF = 9600000 h−1 (2670 s−1), Al/V = 4000 (molar ratio)), affording 1-butene as the major product (95.0− 99.4%). The activities of 3 and 4 were higher than those exhibited by the corresponding 2-(anilide)methylpyridine analogues; 3 showed higher 1-butene selectivity than the others and the activity did not decrease remarkably at 50 °C. Complex 5 afforded a mixture of polymer and oligomers with low activities, suggesting that a fine tuning of both the imido and the anionic donor ligands plays an essential role in this catalysis.

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1).12,17e We also reported that the 2,6-dimethylphenylimido analogue V(NAr)Cl2[2-ArNCH2(C5H4N)] showed moderate activity for ethylene polymerization (Scheme 1).18d Notably, related aryloxo-modified complexes, such as V(N-2,6Me2C6H3)Cl2(O-2,6-Me2C6H3), exhibited remarkable catalytic activities for ethylene (co)polymerization.18a−c As summarized in Scheme 1, the steric bulk of the imido ligand influences the level of catalytic activity and plays a key role in the extent of chain growth (dimerization vs polymerization).12a,c Catalysts based on 1 and 2 showed remarkable activity. In contrast, the reaction with ethylene by V(NAd)Cl2 [2ArNCH2(2-Me-C5H3N)] afforded a mixture of polymer and oligomers: the reaction with the quinoline analogues also afforded a mixture of polymer and oligomers (Scheme 1). On the basis of ESR and 51V NMR data, it appears that the anionic chelating ligand helps maintain the vanadium oxidation state in the catalyst solution, even in the presence of excess aluminum alkyl.12b

INTRODUCTION Linear α-olefins are important intermediates for a variety of products (such as detergents, polymers, lubricants, surfactants, etc.)1 and are largely produced by ethylene oligomerization.2−12 In particular, recent examples of ethylene oligomerization, especially using nickel4 and iron complexes,5 or ethylene trimerization, especially using chromium complex catalysts,6−8 are well-known. The development of vanadium-based catalysts for olefin polymerization/oligomerization is potentially attractive, considering that classical Ziegler-type catalysts derived from either V(acac)3 or VOCl3 and Et2AlCl, EtAlCl2, or nBuLi are known to display high reactivity toward olefin polymerization.13−17 We recently prepared (imido)vanadium(V) complexes containing an anionic donor ligand of the type V(NR)Cl2(Y) (Y = anionic ancillary donor ligands; R = aryl, 1-adamantyl (Ad), cyclohexyl, etc.)12,17c−e,18 and subsequently demonstrated that (imido)vanadium(V) complexes containing the (2anilidomethyl)pyridine ligand, V(NR)Cl2[2-ArNCH2(C5H4N)] (R = Ad, cyclohexyl, phenyl, etc.; Ar = 2,6-Me2C6H3), exhibited both notable catalytic activities and high selectivities for ethylene dimerization in the presence of MAO cocatalyst (Scheme © XXXX American Chemical Society

Received: November 19, 2013

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dx.doi.org/10.1021/om401119y | Organometallics XXXX, XXX, XXX−XXX

Organometallics

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Scheme 1. Effect of Ligands in the Reaction of Ethylene12

Chart 1

Scheme 2

precursors for reactions with ethylene. During the course of our investigations, we discovered that the catalyst derived from 3 exhibits the highest catalytic activity for ethylene dimerization of those that were tested.20

Taking into account the above facts, we assumed that the steric bulk of the imido ligand directly affects the ethylene reactivity (dimerization vs polymerization) and that electronic factors also play a role in the activity (in dimerization).12a,c Moreover, a f ine tuning of substituents in both the imido ligand and the chelate anionic donor ligand plays an essential role for exhibiting notable activity with high selectivity.12c Recently, nickel complexes containing 8-arylimino-5,6,7-trihydroquinolyl ligands showed remarkable reactivity with ethylene,19 and a placement of the fused ring thus seems promising in terms of better catalyst design. In this paper, we thus focus on synthesis of the vanadium(V) dichloride complexes containing 8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligands of the type V(NR)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (R = Ad (3), 2-MeC6H4 (4), 2,6-Me2C6H3 (Ar, 5); Chart 1) and explored their use as catalyst

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RESULTS AND DISCUSSION 1. Synthesis and Structural Analysis of V(NR)Cl2[8-(2,6Me2C6H3)N(C9H10N)] (R = 1-Adamantyl (Ad), 2-MeC6H4, 2,6-Me2C6H3). The V(NR)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] complexes (R = Ad (3), 2-MeC6H4 (4), 2,6-Me2C6H3 (5)) were prepared in toluene by reacting the corresponding vanadium(V) imido trichloride complexes (R = Ad,21 2-MeC6H4,12c 2,6Me2C6H322) with 8-ArNH(C9H10N) (Ar = 2.6-Me2C6H3) in the presence of NEt3 (Scheme 2). The substituted aniline 8ArNH(C9H10N) was prepared by reduction of the imine B


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Figure 1. ORTEP drawings for V(NAd)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (3), V(N-2-MeC6H4)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (4), and V(N2,6-Me2C6H3)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (5). Thermal ellipsoids are drawn at the 50% probability level, and H atoms are omitted for clarity.23

Table 1. Selected Bond Distances and Angles for V(NAd)Cl2[2-ArNCH2(C5H4N)] (1), V(N-2-MeC6H4)Cl2[2-ArNCH2(C5H4N)] (2), V(NAd)Cl2[8-ArN(C9H10N)] (3), V(N-2-MeC6H4)-Cl2[8-ArN(C9H10N)] (4), V(NAr)Cl2[8-ArN(C9H10N)] (5), and V(NAr)Cl2[2-(2,6-iPr2C6H3)NCH2(C5H4N)] (Ar = 2,6-Me2C6H3)a 1b

2c

V−N(1) V−N(2) V−N(3) V−Cl(1) V−Cl(2)

1.6517(12) 2.2241(11) 1.8580(12) 2.2677(3) 2.2709(4)

1.6697(19) 2.1790(19) 1.8524(18) 2.2776(7) 2.2695(7)

Cl(1)−V−Cl(2) N(1)−V−N(2) V−N(1)−C(1) Cl(1)−V−N(3) Cl(2)−V−N(3)

119.953(16) 174.90(4) 170.94(10) 116.92(4) 118.18(3)

125.45(3) 173.47(9) 176.42(17) 115.31(6) 114.22(6)

3

4

5

V(NAr)Cl2[2-Ar′-NCH2(C5H4N)]d

1.679(3) 2.214(3) 1.870(3) 2.2646(17) 2.2789(16)

1.679(2) 2.211(2) 1.850(2) 2.2645(10) 2.2868(9)

119.48(4) 174.56(11) 176.9(2) 117.71(9) 117.18(10)

121.87(3) 175.93(10) 176.2(2) 114.55(7) 116.98(8)

Bond Distances (Å)

a

1.645(2) 1.674(3) 2.202(3) 2.200(3) 1.857(3) 1.863(3) 2.2604(10) 2.2648(15) 2.2748(9) 2.2783(18) Bond Angles (deg) 119.60(4) 119.79(5) 175.05(12) 176.65(12) 168.7(2) 173.5(3) 118.52(8) 116.20(11) 117.56(8) 119.57(10)

Detailed analysis data are shown in the Supporting Information.23 bData from ref 12a. cData from ref 12c. dData from ref 18e.

analogue19 with NaBH4. The V(NR)Cl3 complexes were obtained from VOCl3 by treatment with the corresponding aryl or adamantyl isocyanate in n-octane. The same synthetic strategy was previously used to prepare the 2-anilidomethylenepyridine vanadium(V) analogues 1 and 2. Complexes 3−5 were characterized by solution 1H, 13C, and 51V NMR measurements and C/H/N elemental analyses. The structures of 3−5 were determined by X-ray crystallography (Figure 1).23 The molecular structures were determined by X-ray crystallography, and selected bond distances and angles are shown in Table 1.23 Selected results for V(NAd)Cl2[2A r N C H 2 ( C 5 H 4 N ) ] ( 1 ) , 1 2 a V ( N -2 - M eC 6 H 4 ) C l 2 [ 2ArNCH2(C5H4N)] (2),12c and V(NAr)Cl2[2-(2,6-iPr2C6H3)NCH2(C5H4N)]18e are also included for comparison. These complexes display a distorted-trigonal-bipyramidal geometry around the vanadium with the pyridyl N donor of the bidentate 8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline

ligand and the imido N atom lying on the axis. The two chloride ligands and the anilido N atom occupy the three equatorial sites. The axial N(1)−V−N(2) bond angles are 175.0(1)° (3), 176.65(12)° (4), and 174.56(11)° (5); the sums of the equatorial Cl(1)−V−Cl(2), Cl(1)−V−N(3), and Cl(1)−V− N(3) bond angles are 355.7° (3), 355.6° (4), and 354.4° (5). The V−Cl bond distances in 3−5 range from 2.260(1) to 2.279(2) Å, similar to the V−Cl distances in 1 and 2 (2.2677(3)−2.2776(7) Å),12a,c and their Cl(1)−V−Cl(2) bond angles (119.48(4)−119.79(5)°) are also close to that in 1 (119.79(5)°) but smaller than that in 2 (125.45(3)°). The V−N(1) distance of 3 of 1.645(2) Å is comparable to that in 1 of 1.6517(12) Å,12a and these distances are shorter than those in the arylimido analogues 4 (1.674(3) Å), 5 (1.679(3) Å), and 2 (1.6697(19) Å).12a,c The V−N(1)−C(1) imido bond angle in 3 (168.7(2)°) is smaller than that in 4 (173.5(3)°), and this is the same as the trend that the bond angle in 1 C


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(170.94(10)°) is smaller than that in 2 (176.42(17)°). The V− N(2) imino bond distances in 3−5 (2.200(3)−2.214(3) Å) are slightly longer than that in 2 (2.1790(19) Å),12c but slightly shorter than that in 1 (2.2241(11) Å).12a These are, however, apparently shorter than those in the (1-adamantlyimido)vanadium(V) dichlorido complexes containing 2- or 8(anilidomethyl)quinoline ligands, V(NAd)Cl2[2ArNCH2 (C 9H6 N)] and V(NAd)Cl2 [8-ArNCH2 (C 9H 6N)] (2.2911(14) and 2.3338(18) Å, respectively),12c suggesting fairly strong coordination of the imino nitrogen to the vanadium in complexes 3−5. 2. Reaction of V(NR)Cl2[8-(2,6-Me2C6H3)N(C9H10N)]− MAO Catalyst Systems with Ethylene (R = Ad (3), 2MeC6H4 (4), 2,6-Me2C6H3 (5)) . We recently demonstrated that V(NR)Cl2[2-ArNCH2(C5H4N)] upon activation with excess methylaluminoxane (MAO) (R = Ad (1), 2-MeC6H4 (2)) exhibited significant catalytic activities for ethylene dimerization, affording 1-butene with high selectivity (>90%).12 It was also demonstrated that 1-hexene was formed by the subsequent reaction of ethylene with 1-butene accumulated in the reaction mixture.12a,b In order to evaluate the influence of the substitution of the 8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligand for the 2-(2,6-dimethylanilide)methylpyridine ligand, reactions with ethylene using V(NR)Cl2[8-ArN(C9H10N)] (R = Ad (3), 2MeC6H4 (4); Ar = 2,6-Me2C6H3) in the presence of MAO were conducted under conditions similar to those reported previously.12 The results are summarized in Table 2 and are compared with those for 112a and 2,12c conducted under the same conditions for this study. Additional results for complexes 3 and 4 in the presence of MAO are given in the Supporting Information.24 Note that complex 3 exhibited higher catalytic activities than 1 (e.g. TOF (turnover frequency, h−1) on the basis of reacted ethylene 1830000 by 1 (run 1) vs 4130000 by 3 (run 6), 2730000 by 1 (run 2) vs 9600000 by 3 (run 13)) and afforded 1-butene as the major product. A TOF of 10640000 h−1 (2960 s−1, activity 304000 (kg of ethylene reacted)/((mol of V) h)) with 97.9% 1butene selectivity was achieved (run 14), which should be, as far as we know, the highest value ever reported. As reported previously for 1,12a,b the catalytic activity is dependent upon the Al/V molar ratios employed, and the selectivity of 1-butene decreases upon increasing the amount of 1-butene in the reaction mixture, suggesting that 1-hexene would be produced from a subsequent reaction of 1-butene with ethylene.25 It should be noted that the selectivity of 1-butene by 3 becomes higher than that by 1 even under similar conditions (e.g. 95.9% (run 6), 97.7% (run 13) by 3 vs 92.5% (run 1), 97.0% (run 2) by 1), although the 1-butene concentration in the mixture with 3 should be higher than that with 1 due to higher activity (because, as reported previously in the reaction by 1, an increase of 1-butene concentration should afford 1-hexene by subsequent reaction of ethylene with 1-butene12b). These experimental results indicate that the structure of the chelate anionic ligand (placement of a fused ring) affects both the activity and the selectivity of 1-butene (reactivity toward subsequent reaction of 1-butene with ethylene). Complex 4 also showed higher catalytic activities with high selectivity of 1-butene in comparison to those of complex 2 under the optimized conditions (e.g. TOF (h−1) 2160000 by 2 (run 3) vs 2830000 by 3 (run 23)). However, the activity was lower than that with the 1-adamantylimido analogue (3), suggesting that the electronic nature of the imido ligand plays a role in the activities. The activities were also affected by the Al/V molar ratios. The

Table 2. Ethylene Dimerization by V(NR)Cl2[2ArNCH2(C5H4N)]−MAO (R = Ad (1), 2-MeC6H4 (2)) and V(NR)Cl2[8-(2,6-Me2C6H3)N(C9H10N)]−MAO Catalyst Systems (R = Ad (3), 2-MeC6H4 (4))a run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

cat. (amt /μmol) f

1 (0.5) 1 (0.1)f 2 (0.2) 3 (0.5) 3 (0.5) 3 (0.5) 3 (0.5) 3 (0.5) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 4 (0.5) 4 (0.5) 4 (0.5) 4 (0.5) 4 (0.5) 4 (0.2) 4 (0.2) 4 (0.2) 4 (0.2)

Al/Vb

time /min

activityc × 10−3

TOFd × 10−4/ h−1

500 1500 3000 200 500 1000 2000 3000 500 1000 2000 3000 4000 4000 5000 200 500 1000 2000 3000 1000 2000 3000 4000

10 10 10 10 10 10 10 10 10 10 10 10 10 5 10 10 10 10 10 10 10 10 10 10

51.1 76.5 61.7 42.6 53.8 117.9 100.1 71.9 2.0 23.7 165.7 205.4 274.0 303.6 190.6 4.3 30.7 38.0 50.9 44.5 21.9 55.9 80.9 40.5

183 273 216 149 189 413 351 252 7.08 83.1 580 719 960 1064 668 15.1 108 133 178 156 76.7 196 283 142

C4′e/% C6′e/% 92.5 97.0 91.1 99.4 95.0 95.9 95.9 95.1 99.3 99.1 98.7 97.7 97.7 97.9 97.3 98.5 98.0 97.0 95.9 94.1 98.0 97.3 96.9 95.6

7.5 3.0 8.9 0.6 5.0 4.1 4.1 4.9 0.7 0.9 1.3 2.3 2.3 2.1 2.7 1.5 2.0 3.0 4.1 5.9 2.0 2.7 3.1 4.4

Conditions: ethylene 8 atm, toluene 30 mL, 25 °C, d-MAO white solid (methylaluminoxane prepared by removing AlMe3, toluene from TMAO). bAl/V molar ratio. cActivity in (kg of ethylene reacted)/ ((mol of V) h). dTOF (turnover frequency) = (molar amount of ethylene reacted)/((mol of V) h). eBy GC analysis vs internal standard. fFrom ref 12a. a

selectivity of 1-butene with 4 is higher than that with 2 under similar conditions (e.g. 96.9% (run 23) with 3 vs 91.1% (run 2) with 2), as observed in 3: this would also suggest that the structure of the chelate anionic ligand (placement of a fused ring) affects the selectivity. Ethylene dimerizations with 2−4 in the presence of MAO were conducted at different temperatures and ethylene pressures, and the results are summarized in Table 3. It turned out that the activity with 3 slightly decreased at 0 °C as well as at 50 °C (runs 13, 30, and 31), and the 1-butene selectivity found at 50 °C was apparently lower than those found at 0 or 25 °C. The activity at 4 atm (run 29) was lower than that found at 8 atm (run 13), as observed in 1 (a first-order dependence between the activity and the ethylene pressure),12b although no obvious difference was observed in the selectivity of 1-butene. Because of the high productivity by 3, we chose conditions exhibiting moderate activity with the Al/V molar ratio of 1000 (amount of the catalyst in feed 0.10 μmol) to conduct a study for exploring the time course dependence. As reported previously,12a,b the selectivity of 1-butene seems to decrease at prolonged times upon an increase of 1-butene accumulated in the reaction mixture. This again suggests that the initial product was 1-butene, and 1-hexene was formed from 1-butene that accumulated in the reaction mixture.12a,b It should be noted that the activity stayed at the same level in the first 30 min (runs 10, 32, and 33) but decreased D


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Table 3. Effect of Ethylene Pressure and Temperature on Ethylene Dimerization by V(NR)Cl2[2-ArNCH2(C5H4N)]−MAO (R = Ad (1), 2-MeC6H4 (2)) and V(NR)Cl2[8-(2,6-Me2C6H3)N(C9H10N)]−MAO (R = Ad (3), 2-MeC6H4 (4)]) Catalyst Systemsa run 25 1 26 3 27 28 29 30 13 31 10 32 33 34 35 19 36 37 23

cat. (amt/μmol) f

1 (0.5) 1 (0.5)f 1 (0.5)f 2 (0.2) 2 (0.2) 2 (0.2) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 3 (0.1) 4 (0.5) 4 (0.5) 4 (0.5) 4 (0.2) 4 (0.2)

Al/Vb

ethylene/atm

temp/°C

time/min

activityc × 10−3

TOFd × 10−5

C4′e/%

C6′e/%

500 500 500 3000 3000 3000 4000 4000 4000 4000 1000 1000 1000 1000 2000 2000 2000 3000 3000

8 8 8 8 8 8 4 8 8 8 8 8 8 8 8 8 8 8 8

0 25 50 25 0 50 25 0 25 50 25 25 25 25 0 25 50 0 25

10 10 10 10 10 10 10 10 10 10 10 20 30 60 10 10 10 10 10

17.5 51.1 8.16 61.7 99.7 26.2 103 150 274 176 23.7 23.6 23.5 16.4 69.6 50.9 9.70 111 80.9

6.25 18.3 2.91 21.6 34.9 9.19 36.0 52.4 96.0 61.8 8.31 8.26 8.22 5.73 24.4 17.8 3.41 38.9 28.3

97.9 92.5 95.2 91.1 86.4 96.7 97.5 98.9 97.7 95.5 99.1 99.1 98.4 97.7 88.7 95.9 96.9g 93.0 96.9

2.1 7.5 4.8 8.9 13.6 3.3 2.5 1.1 2.3 4.5 0.9 0.9 1.6 2.3 11.3 4.1 3.1 7.0 3.1

a

Conditions: toluene 30 mL, d-MAO white solid (methylaluminoxane prepared by removing AlMe3, toluene from TMAO). bAl/V molar ratio. Activity in (kg of ethylene reacted)/((mol of V) h). dTOF (turnover frequency) = (molar amount of ethylene reacted)/((mol of V) h). eBy GC analysis vs internal standard. fFrom ref 12a. gA trace amount of polyethylene was also obtained.

c

Table 4. Reactions with Ethylene by V(N-2,6-Me2C6H3)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (5)−MAO Catalyst Systemsa oligomerd b

run

cat. (amt/μmol)

Al/V

temp/°C

activity

38 39 40 41 42 43 44 45

5 (2.0) 5 (2.0) 5 (2.0) 5 (2.0) 5 (2.0) 5 (2.0) 5 (2.0) 5 (2.0)

200 500 1000 1500 2000 3000 1500 1500

25 25 25 25 25 25 0 50

61 121 169 304 299 267 382 599

c

PE

C4′/%

C6′/%

yield/mg

activitye

92.9 95.5 96.5 96.1 96.2 95.4 97.4 85.6

7.1 4.5 3.5 3.9 3.8 4.6 2.6 14.4

7 15 25 34 29 28 8 192

21 45 74 101 87 85 23 578

a

Conditions: toluene 30 mL, ethylene pressure 8 atm, 10 min, d-MAO white solid (methylaluminoxane prepared by removing AlMe3, toluene from TMAO). bAl/V molar ratio. cActivity in (kg of ethylene reacted(/((mol of V) h). dBy GC analysis vs internal standard. eActivity in (kg of PE)/ ((mol of V) h).

butene concentration in the mixture with 3 should be higher than that with the others due to higher activity. The facts indicate that the structure of the chelate anionic ligand in addition to the nature of the imido ligand affects the selectivity of 1-butene, especially the reactivity toward the subsequent reaction of 1butene with ethylene. Reactions with ethylene using the 2,6-dimethylphenylimido analogue 5 were conducted in the presence of MAO, and the results are summarized in Table 4.24 It turned out that the 5− MAO catalyst system exhibited low to moderate activities, affording a mixture of 1-butene and polyethylene, whereas the 2(anilidomethyl)pyridine analogue V(NAr)Cl2[2ArNCH2(C5H4N)] (Ar = 2,6-Me2C6H3) showed moderate activity for ethylene polymerization.17e The molecular weights of the resulting polymers could not be measured by ordinary GPC analysis (in o-dichlorobenzene at 140 °C), suggesting the formation of ultrahigh-molecular-weight polymers.12b,18 The activity was affected by the Al/V molar ratio employed, but the ratio does not affect the oligomer/PE ratio. The activity was also affected by the reaction temperature, and the activity at 50 °C was

gradually after 60 min (run 34), probably due to an accumulation (increased degree) of the reaction product. In contrast to the temperature dependence with 3, the activity with the 2-methylphenyl analogues (2, 4) increased at 0 °C along with apparent decreases in the 1-butene selectivity in comparison to reactions conducted at 25 °C (e.g., with 2 86.4% (run 27) vs 91.1% (run 3) and with 4 88.7% (run 35) vs 95.9% (run 19)]. This is in interesting contrast to what is observed for the adamantyl analogues (1, 3).12a Moreover, the activity apparently decreased at 50 °C (run 36), whereas a significant decrease in the activity was not observed with 3; the activity with 2 at 50 °C (run 28) was also lower than that at 25 °C (run 3). Moreover, a trace amount of polyethylene, the weight of which was difficult to measure, was also obtained with 4 at 50 °C. These would suggest that the thermal stability of the active species generated from the 2-phenylimido analogue (4) would be inferior to that from the adamantylimido analogue (3). It should also be noted that, as described above, the selectivity of 1-butene with 3 (especially at 0 and 25 °C) was higher than those with 2 and 4 under similar conditions, although the 1E


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higher than those at 0 and 25 °C. Moreover, the PE/oligomer ratio was rather strongly affected by the reaction temperature: the ratio of PE increased at higher temperature. These results suggest that there are several (at least two) catalytically active species generated in the reaction mixture of 5 and MAO under these conditions, and the ratio would be affected by the reaction temperature. On the basis of these facts, we can thus at least say it is clear that f ine tuning of substituents in both the imido ligand and the chelate anionic donor ligand plays an essential key role in exhibiting remarkable activity with high selectivity. In summary, we have shown that V(NAd)Cl2[8-(2,6Me2C6H3)N(C9H10N)] (3) exhibited remarkable catalytic activities, affording 1-butene as the major product (e.g. TOF 9600000 h−1 (2670 s−1, run 13)), and the highest initial activity of 10640000 h−1 (2960 s−1) with 97.9% selectivity of 1-butene has been achieved after 5 min, which should be the highest value ever obtained. The observed activities with the (imido)vanadium(V) complexes containing 8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligands (3, 4) were higher than those with the corresponding 2-(anilidomethyl)pyridine analogues (1, 2). The results of this study reveal that both the imido ligand and the nature of the anionic donor ligand affect the activity and the 1butene selectivity. Promising catalyst performances demonstrated by 3 should be noteworthy, and we believe that the information here is potentially important for designing efficient molecular vanadium catalysts. We are now exploring the structure/activity/selectivity relationship for better catalyst design and the mechanistic details, including isolation of dimethyl and/or cationic species proposed as the key intermediate/precursors.

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Table 5. Crystal Data and Collection Parameters of V(NAd)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (3), V(N-2MeC6H4)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (4), and V(N2,6-Me2C6H3)Cl2[8-(2,6-Me2C6H3)-N(C9H10N)] (5)a 3b formula formula wt cryst color, habit cryst size (mm) cryst system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g/cm3) F000 temp (K) μ(Mo Kα) (cm−1) total, unique no. of rflns measd (Rint) 2θmax (deg) no. of observations (I > 2.00σ(I)) no. of variables R1 (I > 2.00σ(I)) wR2 (I > 2.00σ(I)) goodness of fit

EXPERIMENTAL SECTION

General Procedure. All experiments were carried out under a nitrogen atmosphere in a Vacuum Atmospheres drybox. Anhydrous grade toluene and n-hexane (Kanto Kagaku Co., Ltd.) were transferred into a bottle containing molecular sieves (a mixture of 3A 1/16, 4A 1/8, and 13X 1/16) in the drybox under a nitrogen stream and were passed through a short alumina column under an N2 stream prior to use. V(NAd)Cl321 (Ad = 1-adamantyl), V(N-2-MeC6H4)Cl3,12c and V(N2,6-Me2C6H3)Cl322 were prepared according to a published method. Triethylamine was purchased from TCI Co., Ltd. Polymerization grade ethylene (purity >99.9%, Sumitomo Seika Co. Ltd.) was used as received. Toluene and AlMe3 in the commercially available methylaluminoxane (TMAO, 9.5 wt % (Al) toluene solution, Tosoh Finechem Co.) were removed under reduced pressure (at ca. 50 °C for removing toluene and AlMe3 and then at >100 °C for 1 h for completion) in the drybox to give white solids. GC analysis was performed with a Shimadzu GC-2025AF gas chromatograph (Shimadzu Co. Ltd.) equipped with a flame ionization detector. Elemental analyses were performed by using an EAI CE-440 CHN/ O/S Elemental Analyzer (Exeter Analytical, Inc.). All 1H, 13C, and 51V NMR spectra were recorded on a Bruker AV500 spectrometer (500.13 MHz for 1H, 125.77 MHz for 13C, and 131.55 MHz for 51V). All spectra were obtained in the solvent indicated at 25 °C unless otherwise noted. Chemical shifts are given in ppm and are referenced to SiMe4 (δ 0.00 ppm, 1H, 13C) and VOCl3 (δ 0.00 ppm, 51V). Coupling constants and half-width values, Δν1/2, are given in Hz. Synthesis of N-(2,6-Dimethylphenyl)-5,6,7-trihydroquinolin8-amine. The synthetic procedure of the imine (before reduction using NaBH4) is analogous to that reported previously.19 In a sealed Schlenk glass tube, were placed sequentially 5,6,7-trihydroquinolin-8-one (2.36 g, 16.0 mmol), toluene (100 mL), 2,6-dimethylaniline (2.00 g, 16.5 mmol), and p-toluenesulfonic acid hydrate (28 mg). The mixture was placed in an oil bath that had been preheated to 110 °C and was stirred overnight. After the reaction, the mixture was filtered through a alumina pad, and the filter cake was washed with toluene several times. The

a b

4b

5

C55H70Cl6N6V2 1129.75 yellow, block 0.20 × 0.19 × 0.17 monoclinic C2/c (No. 15) 32.189(5) 10.1323(16) 16.883(3) 90 104.380(6) 90 5333.9(15) 4 1.407 2360 93(2) 6.95 18194, 6084 (0.0431) 55.0 6084

C49H54Cl6N6V2 1041.56 orange, block 0.18 × 0.13 × 0.10 monoclinic P21/c (No. 14) 9.303(6) 15.039(11) 17.140(12) 90 90.433(8) 90 2398(3) 2 1.443 1076 93(2) 7.66 25043, 5495 (0.0564) 55.0 5495

C25H29Cl2N3V 493.35 red, block 0.22 × 0.19 × 0.04 monoclinic P21/c (No. 14) 19.131(14) 13.533(10) 9.120(7) 90 96.377(10) 90 2347(3) 4 1.396 1028 93(2) 6.68 22416, 5375 (0.0549) 55.0 5375

421 0.0570 0.1442 1.071

361 0.0617 0.1360 1.054

366 0.0524 0.1227 1.084

Detailed structural data are given in the Supporting Information.23 Structures for 3 and 4 were solved as two crystals containing CH2Cl2.

combined filtrate and the wash were dried under reduced pressure to remove toluene. The residue was dissolved in methanol (50 mL). To the reaction mixture was added sodium borohydride (NaBH4, 8 g, 210 mmol) slowly, and the mixture was stirred overnight at room temperature. The mixture was quenched by the addition of water. The reaction mixture was concentrated in a rotary evaporator and extracted with chloroform. The organic volatiles were removed with a rotary evaporator. The residue was subjected to column chromatography (silica gel, n-hexane/ethyl acetate 2/1 v/v). The resultant mixture containing 8-(2,6-Me2C6H3)NH(C9H10N) was placed in vacuo at 150 °C to remove aniline. The residue was dissolved in the minimum amount of n-hexane, and yellow crystals (1.45 g, 5.75 mmol) were obtained at −40 °C. Yield: 35.8%. 1H NMR (CDCl3): δ 8.48 (d, 1H, J = 4.70, quino-H), 7.42 (d, 1H, J = 7.65, quino-H), 7.12 (dd, 1H, J = 7.65 and 4.70, quino-H), 7.03 (d, 2H, J = 7.45, Ar-H), 6.87 (t, 1H, J = 7.45, ArH), 4.38 (m, 1H, NCH), 4.04 (br, 1H, NH), 2.83 (m, 2H, quino-H), 2.34 (s, 6H, ArCH3), 1.95 (m, 2H, quino-H), 1.78 (m, 2H, quino-H). 13 C NMR (CDCl3): δ 157.7, 147.3, 145.0, 136.9, 132.1, 131.2, 128.8, 122.2, 122.1, 57.3, 29.8, 28.7, 19.6, 19.1. Synthesis of V(NAd)Cl2[8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline] (3). To a toluene solution (60 mL) containing V(NAd)Cl3 (613 mg, 2.00 mmol) was added a toluene solution (20 mL) containing N-(2,6-dimethylphenyl)-5,6,7-trihydroquinolin-8amine (505 mg, 2.00 mmol) and triethylamine (222 mg, 2.20 mmol) at −30 °C. The reaction mixture was warmed slowly to room temperature, and the mixture was then stirred overnight. The solution was passed through a Celite pad, and the filter cake was washed with hot toluene. The combined filtrate and wash were placed in a rotary evaporator to remove the volatiles. The resultant solid was dissolved in a minimum amount of CH2Cl2, and the solution was layered with nF


Organometallics

Article

hexane. The chilled solution placed in the freezer (−30 °C) afforded yellow-orange microcrystals (815 mg, 1.60 mmol). Yield: 80.2%. 1H NMR (CDCl3): δ 8.70 (d, 1H, J = 5.20, quino-H), 7.65 (dd, 1H, J = 7.64 and 1.00, quino-H), 7.45 (dd, 1H, J = 7.64 and 5.20, quino-H), 7.14− 7.08 (m, 3H, Ar-H), 5.29 (dd, 1H, J = 12.0 and 4.75, NRH), 2.98−2.92 (m, 1H, quino-H), 2.88−2.81 (m, 1H, quino-H), 2.28 (s, 3H, ArCH3), 2.19 (s, 3H, ArCH3), 2.00−1.93 (m, 1H, quino-H), 1.89 (s, 3H, Ad-H), 1.77−1.71 (m, 7H, Ad-H and quino-H), 1.61−1.56 (m, 1H, quino-H), 1.52−1.41 (m, 7H, Ad-H and quino-H). 13C NMR (CDCl3): δ 162.6, 157.4, 146.8, 131.8, 131.5, 128.6, 128.5, 128.0, 126.7, 124.2, 76.2, 41.2, 35.8, 29.0, 27.8, 26.3, 21.1, 20.5, 18.7. 51V NMR (CDCl3): δ −75.26 (Δν1/2 = 2118 Hz). Anal. Calcd for C27H34Cl2N3V: C, 62.07 (59.77 + VC, vanadium carbide); H, 6.56; N, 8.04. Found: C, 61.04; H, 6.39; N, 7.74. Synthesis of V(N-2-MeC6H4)Cl2[8-(2,6-dimethylanilide)-5,6,7trihydroquinoline] (4). To a toluene solution (22 mL) containing V(N-2-MeC6H4)Cl3 (228 mg, 0.869 mmol) was added a toluene solution (7 mL) containing N-(2,6-dimethylphenyl)-5,6,7-trihydroquinolin-8-amine (219 mg, 0.868 mmol) and triethylamine (100 mg, 0.988 mmol) at −30 °C. The reaction mixture was warmed slowly to room temperature, and the mixture was then stirred overnight. The solution was passed through a Celite pad, and the filter cake was washed with hot toluene. The combined filtrate and wash were placed in a rotary evaporator to remove the volatiles. The solid was dissolved in a minimum amount of CH2Cl2. The CH2Cl2 solution was layered with nhexane, and deep orange block microcrystals (180 mg, 0.376 mmol) were obtained at −30 °C. Yield: 43.4%. 1H NMR (CDCl3): δ 8.86 (d, 1H, J = 4.95, quino-H), 7.73 (d, 1H, J = 7.55, quino-H), 7.54−7.51 (m, 1H, quino-H), 6.99 (d, 1H, J = 7.30, Ar-H), 6.93−6.82 (m, 6H, Ar-H), 5.46 (dd, 1H, J = 11.90 and 4.20, NRH), 3.03−2.99 (m, 1H, quino-H), 2.94−2.87 (m, 1H, quino-H), 2.61 (s, 3H, ArCH3), 2.28 (s, 3H, ArCH3), 2.15 (s, 3H, ArCH3), 2.04−1.99 (m, 1H, quino-H), 1.85−1.76 (m, 1H, quino-H), 1.69−1.64 (m, 1H, quino-H), 1.59−1.51 (m, 1H, quino-H). 13 C NMR (CDCl3): δ 160.4, 157.5, 147.0, 139.7, 138.1, 132.0, 131.1, 130.5, 129.4, 128.2, 128.1, 127.6, 126.8, 126.6, 125.3, 124.3, 77.6, 27.8, 26.3, 21.0, 20.1, 18.7, 18.6. 51V NMR (CDCl3): δ 62.2 (Δν1/2 = 1894 Hz). Anal. Calcd for C24H26Cl2N3V: C, 60.26; H, 5.48; N, 8.78. Found: C, 60.28; H, 5.59; N, 8.42. Synthesis of V(N-2,6-Me2C6H3)Cl2[8-(2,6-dimethylanilide)5,6,7-trihydroquinoline] (5). To a toluene solution (22 mL) containing V(N-2,6-C6H3)Cl3 (553 mg, 2.00 mmol) was added a toluene solution (60 mL) containing N-(2,6-dimethylphenyl)-5,6,7trihydroquinolin-8-amine (505 mg, 2.00 mmol) and triethylamine (101 mg, 2.24 mmol) at −30 °C. The reaction mixture was warmed slowly to room temperature, and the mixture was then stirred overnight. The solution was passed through a Celite pad, and the filter cake was washed with hot toluene. The combined filtrate and the wash were placed in a rotary evaporator to remove the volatiles. The solid was dissolved in a minimum amount of CH2Cl2. The CH2Cl2 solution was layered with nhexane, and red microcrystals (673 mg, 1.37 mmol) were obtained at −30 °C. Yield: 68.3%. 1H NMR (CDCl3): δ 8.88 (d, 1H, J = 5.47, quinoH), 7.72 (d, 1H, J = 7.40, quino-H), 7.52 (dd, 1H, J = 5.47 and 7.40, quino-H), 6.95−6.93 (m, 1H, Ar-H), 6.88−6.82 (m, 2H, Ar-H), 6.70 (br, 3H, Ar-H), 5.45 (dd, 1H, J = 4.53 and 12.0, NR-H), 3.02−2.88 (m, 2H, quino-H), 2.62 (s, 6H, Ar-CH3), 2.23 (s, 3H, ArCH3), 2.14 (s, 3H, ArCH3), 2.02−1.97 (m, 1H, quino-H), 1.86−1.76 (m, 1H, quino-H), 1.69−1.64 (m, 1H, quino-H), 1.59−1.51 (m, 1H, quino-H). 13C NMR (CDCl3): δ 159.8, 157.5, 147.3, 143.2, 137.9, 132.0, 130.6, 129.2, 128.2, 128.1, 127.4, 127.3, 126.7, 126.6, 124.2, 78.0, 27.9, 26.3, 21.0, 20.2, 19.6, 19.2. 51V NMR (CDCl3): δ 102.0 (Δν1/2 = 1763 Hz). Anal. Calcd for C25H28Cl2N3V: C, 60.99; H, 5.73; N, 8.53. Found: C, 60.81; H, 5.75; N, 8.46. Reaction with Ethylene. Ethylene oligomerizations were conducted in a 100 mL scale stainless steel autoclave, and the typical reaction procedure is as follows. Toluene (29.0 mL) and the prescribed amount of MAO were placed in the autoclave in the drybox. The reaction apparatus was then filled with ethylene (1 atm), and the prescribed amount of the complex in toluene (1.0 mL) was placed in the autoclave. The reaction apparatus was then immediately pressurized to 7 atm (total 8 atm), and the mixture was magnetically stirred for 10 min

(the ethylene pressure was kept constant during the reaction). After the above procedure, the ethylene that remained was purged at −30 °C, and 0.5 g of n-heptane was added as an internal standard. The solution was then analyzed by GC to determinate the activity and the product distribution. After the above oligomerization procedure, the remaining mixture in the autoclave was poured into MeOH containing HCl, and the resultant polymer (white precipitate) was collected on a filter paper by filtration and was adequately washed with MeOH. The resultant polymer was then dried in vacuo at 60 °C for 2 h. Crystallographic Analysis. All measurements were carried out on a Rigaku XtaLAB mini imaging plate diffractometer with graphitemonochromated Mo Kα radiation. The crystal collection parameters are given in Table 5. All structures were solved by direct methods and expanded using Fourier techniques,26 and the non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined using the riding model. All calculations were performed using the Crystal Structure27 crystallographic software package, except for refinement, which was performed using SHELXL-97.28

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ASSOCIATED CONTENT

S Supporting Information *

A table giving additional results for reactions with ethylene and tables and CIF files giving crystallographic data for V(NAd)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (3), V(N-2-MeC6H4)Cl2[8(2,6-Me2C6H3)N(C9H10N)] (4), and V(N-2,6-Me2C6H3)Cl2[8(2,6-Me2C6H3)N(C9H10N)] (5). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*K.N.: tel, +81-42-677-2547; fax, +81-42-677-2547; e-mail, [email protected]. Author Contributions ∥

These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This project was partly supported by Bilateral Joint Projects between Japan Society of Promotion of Sciences (JSPS) and National Natural Science Foundation of China (NSFC, No. 21011140068). This project is also supported partly by an international joint research program sponsored by Tokyo Metropolitan University, TMU), and by NSFC (No. 20923003 for Y.L.). We are also grateful to Tosoh Finechem Co. for donating MAO. A.I. expresses his thanks to TMU for a predoctoral fellowship.

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REFERENCES

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(11) For V complex catalysts, see: (a) Brussee, E. A. C.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2000, 497. (b) Schmidt, R.; Welch, M. B.; Knudsen, R. D.; Gottfried, S.; Alt, H. G. J. Mol. Catal. A 2004, 222, 17 Vanadium complexes containing chelate bis(imino) pyridine ligands yielded polymers/oligomers with Schultz-Flory distribution.. (12) (a) Zhang, S.; Nomura, K. J. Am. Chem. Soc. 2010, 132, 4960. (b) Igarashi, A.; Zhang, S.; Nomura, K. Organometallics 2012, 31, 3575. (c) Nomura, K.; Igarashi, A.; Zhang, W. J.; Sun, W.-H. Inorg. Chem. 2013, 52, 2607. (13) (a) Carrick, W. L. J. Am. Chem. Soc. 1958, 80, 6455. (b) Carrick, W. L.; Kluiber, R. W.; Bonner, E. F.; Wartman, L. H.; Rugg, F. M.; Smyth, J. J. J. Am. Chem. Soc. 1960, 82, 3883. (c) Phillips, G. W.; Carrick, W. L. J. Polym. Sci. 1962, 59, 401. (14) (a) Junghanns, E.; Gumboldt, O.; Bier, G. Makromol. Chem. 1962, 58, 18. (b) Natta, G.; Mazzanti, G.; Valvassori, A.; Sartori, G.; Fiumani, D. J. Polym. Sci. 1961, 51, 411. (15) For example, Christman, D. L.; Keim, G. I. Macromolecules 1968, 1, 358. (16) (a) Doi, Y.; Ueki, S.; Keii, T. Macromolecules 1978, 12, 814. (b) Doi, Y.; Koyama, T.; Soga, K. Makromol. Chem. 1985, 186, 11. (17) For recent reviews (vanadium catalysts), see: (a) Hagen, H.; Boersma, J.; van Koten, G. Chem. Soc. Rev. 2002, 31, 357. (b) Gambarotta, S. Coord. Chem. Rev. 2003, 237, 229. (c) Nomura, K.; Zhang, W. Chem. Sci. 2010, 1, 161. (d) Redshaw, C. Dalton Trans. 2010, 39, 5595. (e) Nomura, K.; Zhang, S. Chem. Rev. 2011, 111, 2342 and related references cited therein. (18) (a) Nomura, K.; Sagara, A.; Imanishi, Y. Macromolecules 2002, 35, 1583. (b) Wang, W.; Nomura, K. Macromolecules 2005, 38, 5905. (c) Wang, W.; Nomura, K. Adv. Synth. Catal. 2006, 348, 743. (d) Onishi, Y.; Katao, S.; Fujiki, M.; Nomura, K. Organometallics 2008, 27, 2590. (e) Zhang, S.; Katao, S.; Sun, W.-H.; Nomura, K. Organometallics 2009, 28, 5925. (19) (a) Yu, J.; Hu, X.; Zeng, Y.; Zhang, L.; Ni, C.; Hao, X.; Sun, W.-H. New J. Chem. 2011, 35, 178. (b) Yu, J.; Zeng, Y.; Huang, W.; Hao, X.; Sun, W.-H. Dalton Trans. 2011, 40, 8436. (c) Zhang, L.; Hao, H.; Sun, W.-H.; Redshaw, C. ACS Catal. 2011, 1, 1213. (d) Hou, X.; Liang, T.; Sun, W.-H.; Redshaw, C.; Chen, X. J. Organomet. Chem. 2012, 708−709, 98. (e) Hou, X.; Cai, Z.; Chen, X.; Wang, L.; Redshaw, C.; Sun, W.-H. Dalton Trans. 2012, 41, 1617. (20) The results were partially introduced by K.N. at the Sixth AsiaPacific Congress on Catalysis (APCAT-6), Taipei, Taiwan, October 2013. (21) Zhang, W.; Nomura, K. Inorg. Chem. 2008, 47, 6482. (22) Buijink, J.-K. F.; Teubin, J. H.; Kooijman, H.; Spek, A. L. Organometallics 1994, 13, 2922. (23) Structural reports including CIF files for V(NR)Cl2[8-(2,6Me2C6H3)N(C9H10N)] (R = Ad (3), 2-MeC6H4 (4), 2,6-Me2C6H3 (5)) are given in the Supporting Information. (24) Additional results in reactions of ethylene with V(NAd)Cl2[8(2,6-Me 2 C 6 H 3 )N(C 9 H 10 N)] (3), V(N-2-MeC 6 H 4 )Cl 2 [8-(2,6Me 2C6H3)N(C9H10N)] (4), and V(N-2,6-Me2C 6H3)Cl2[8-(2,6Me2C6H3)N(C9H10N)] (5) are given in the Supporting Information. (25) The reaction with ethylene in the presence of Et2AlCl afforded polyethylene with a trace amount of oligomers (observed as a tiny trace in the GC chromatogram). The activity was 14 (kg of PE)/((mol of V) h) (at 0 °C) or 8 (kg of PE)/((mol of V) h) (at 25 °C) (conditions: 3, 5.0 μmol; Et2AlCl, 0.50 mmol (Al/V = 100); toluene, 30 mL; ethylene, 8 atm; 10 min). The results with the 3−Et2AlCl catalyst system are highly analogous to those observed with the 1−Et2AlCl catalyst system.12b (26) SIR2008: Burla, M. C.; Calandro, R.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Siliqi, D.; Spagna, R. J. Appl. Crystallogr. 2007, 40, 609. (27) Crystal Structure 4.0: Crystal Structure Analysis Package; Rigaku and Rigaku Americas, Tokyo, Japan, 2000−2010; pp 196−8666. (28) SHELX97: Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.

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Synthesis of (Imido)vanadium(V) Complexes Containing 8-(2,6

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