Synthesis of (imido)vanadium(V) complexes containing 8-(2,6- dimethylanilide)-5,6,7-trihydroquinoline ligands: Highly active catalyst precursors for ethylene dimerization

Article abstract of DOI:10.1021/om401119y

A series of (imido)vanadium(V) dichloride complexes containing 8-(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligands of the type V(NR)Cl ₂[8-(2,6-Me₂C₆H₃)N(C ₉H₁₀N)] (R = Ad (3), 2-MeC

Full text of DOI:10.1021/om401119y

Article
pubs.acs.org/Organometallics
Synthesis of (Imido)vanadium(V) Complexes Containing 8‑(2,6-
Dimethylanilide)-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-trihydroqui-
noline 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.
1).12,17e We also reported that the 2,6-dimethylphenylimido
INTRODUCTION
■
analogue V(NAr)Cl2[2-ArNCH2(C5H4N)] showed moderate
Linear α-olefins are important intermediates for a variety of
activity for ethylene polymerization (Scheme 1).18d Notably,
products (such as detergents, polymers, lubricants, surfactants,
etc.)1 and are largely produced by ethylene oligomerization.2−12
related aryloxo-modified complexes, such as V(N-2,6-
Me2C6H3)Cl2(O-2,6-Me2C6H3), exhibited remarkable catalytic
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 attrac-
tive, considering that classical Ziegler-type catalysts derived from
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[2-
ArNCH2(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
n
either V(acac)3 or VOCl3 and Et2AlCl, EtAlCl2, or BuLi are
known to display high reactivity toward olefin polymer-
ization.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 (2-
anilidomethyl)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
Received: November 19, 2013
© XXXX American Chemical Society
A
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Scheme 1. Effect of Ligands in the Reaction of Ethylene12
Chart 1
Scheme 2
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 fine
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-dimethy-
lanilide)-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
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
RESULTS AND DISCUSSION
■
1. Synthesis and Structural Analysis of V(NR)Cl2[8-(2,6-
Me2C6H3)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 2,6-
Me2C6H322) with 8-ArNH(C9H10N) (Ar = 2.6-Me2C6H3) in the
presence of NEt3 (Scheme 2). The substituted aniline 8-
ArNH(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(N-
2,6-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
a
V(NAr)Cl2[2-(2,6-iPr2C6H3)NCH2(C5H4N)] (Ar = 2,6-Me2C6H3)
b
c
d
1
2
3
4
5
V(NAr)Cl2[2-Ar′-NCH2(C5H4N)]
Bond Distances (Å)
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)
1.645(2)
2.202(3)
1.857(3)
2.2604(10)
2.2748(9)
1.674(3)
1.679(3)
1.679(2)
2.211(2)
1.850(2)
2.2645(10)
2.2868(9)
2.200(3)
2.214(3)
1.863(3)
1.870(3)
2.2648(15)
2.2783(18)
2.2646(17)
2.2789(16)
Bond Angles (deg)
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)
119.60(4)
175.05(12)
168.7(2)
119.79(5)
176.65(12)
173.5(3)
119.48(4)
174.56(11)
176.9(2)
121.87(3)
175.93(10)
176.2(2)
118.52(8)
116.20(11)
117.71(9)
114.55(7)
117.56(8)
119.57(10)
117.18(10)
116.98(8)
Detailed analysis data are shown in the Supporting Information.23 Data from ref 12a. Data from ref 12c. Data from ref 18e.
a
b
c
d
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-anilidomethylene-
pyridine 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[2-
ArNCH2 (C5H4N)] (1),12a V(N-2-MeC6 H4 )Cl2[2-
ArNCH2(C5H4N)] (2),12c and V(NAr)Cl2[2-(2,6-iPr2C6H3)-
NCH2(C5H4N)]18e are also included for comparison.
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
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
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 [2-
ArNCH2(C9H6N)] and V(NAd)Cl2[8-ArNCH2(C9H6N)]
(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), 2-
MeC6H4 (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), 2-
MeC6H4 (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% 1-
butene 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
Table 2. 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 Catalyst
a
Systems (R = Ad (3), 2-MeC6H4 (4))
d
cat.
(amt
TOF
× 10−4
h−1
c
time activity ×
/
b
e
e
run /μmol) Al/V
/min
10−3
C4′ /% C6′ /%
f
1
2
3
4
5
6
7
8
9
1 (0.5)
1 (0.1)
500
10
10
10
10
10
10
10
10
10
10
10
10
10
5
51.1
76.5
61.7
42.6
53.8
117.9
100.1
71.9
2.0
183
273
216
149
189
413
351
252
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
f
1500
3000
200
2 (0.2)
3 (0.5)
3 (0.5)
3 (0.5)
3 (0.5)
3 (0.5)
3 (0.1)
500
1000
2000
3000
500
7.08
83.1
580
10 3 (0.1)
11 3 (0.1)
12 3 (0.1)
13 3 (0.1)
14 3 (0.1)
15 3 (0.1)
16 4 (0.5)
17 4 (0.5)
18 4 (0.5)
19 4 (0.5)
20 4 (0.5)
21 4 (0.2)
22 4 (0.2)
23 4 (0.2)
24 4 (0.2)
1000
2000
3000
4000
4000
5000
200
23.7
165.7
205.4
274.0
303.6
190.6
4.3
719
960
1064
668
10
10
10
10
10
10
10
10
10
10
15.1
500
30.7
38.0
50.9
44.5
21.9
55.9
80.9
40.5
108
133
178
156
1000
2000
3000
1000
2000
3000
4000
76.7
196
283
142
a
Conditions: ethylene 8 atm, toluene 30 mL, 25 °C, d-MAO white
solid (methylaluminoxane prepared by removing AlMe3, toluene from
b
c
TMAO). Al/V molar ratio. Activity in (kg of ethylene reacted)/
((mol of V) h). TOF (turnover frequency) = (molar amount of
ethylene reacted)/((mol of V) h). By GC analysis vs internal
standard. From ref 12a.
d
e
f
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
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
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 =
a
Ad (1), 2-MeC6H4 (2)) and V(NR)Cl2[8-(2,6-Me2C6H3)N(C9H10N)]−MAO (R = Ad (3), 2-MeC6H4 (4)]) Catalyst Systems
b
c
d
e
e
run
cat. (amt/μmol)
Al/V
ethylene/atm
temp/°C
time/min
activity × 10−3
TOF × 10−5
C4′ /%
C6′ /%
f
25
1
1 (0.5)
500
500
8
8
8
8
8
8
4
8
8
8
8
8
8
8
8
8
8
8
8
0
25
50
25
0
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
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
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
f
1 (0.5)
f
26
3
1 (0.5)
500
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)
3000
3000
3000
4000
4000
4000
4000
1000
1000
1000
1000
2000
2000
2000
3000
3000
27
28
29
30
13
31
10
32
33
34
35
19
36
37
23
50
25
0
150
25
50
25
25
25
25
0
274
176
23.7
23.6
23.5
16.4
69.6
50.9
9.70
111
25
50
0
g
96.9
93.0
25
80.9
96.9
a
b
Conditions: toluene 30 mL, d-MAO white solid (methylaluminoxane prepared by removing AlMe3, toluene from TMAO). Al/V molar ratio.
c
d
e
Activity in (kg of ethylene reacted)/((mol of V) h). TOF (turnover frequency) = (molar amount of ethylene reacted)/((mol of V) h). By GC
f
g
analysis vs internal standard. From ref 12a. A trace amount of polyethylene was also obtained.
a
Table 4. Reactions with Ethylene by V(N-2,6-Me2C6H3)Cl2[8-(2,6-Me2C6H3)N(C9H10N)] (5)−MAO Catalyst Systems
d
oligomer
PE
b
c
e
run
cat. (amt/μmol)
Al/V
temp/°C
activity
C4′/%
C6′/%
yield/mg
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
25
25
25
25
25
25
0
61
121
169
304
299
267
382
599
92.9
95.5
96.5
96.1
96.2
95.4
97.4
85.6
7.1
4.5
7
15
25
34
29
28
8
21
45
1000
1500
2000
3000
1500
1500
3.5
74
3.9
101
87
3.8
4.6
85
2.6
23
50
14.4
192
578
a
Conditions: toluene 30 mL, ethylene pressure 8 atm, 10 min, d-MAO white solid (methylaluminoxane prepared by removing AlMe3, toluene from
b
c
d
e
TMAO). Al/V molar ratio. Activity in (kg of ethylene reacted(/((mol of V) h). By GC analysis vs internal standard. Activity in (kg of PE)/
((mol of V) h).
gradually after 60 min (run 34), probably due to an accumulation
(increased degree) of the reaction product.
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 1-
butene 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 [2-
ArNCH2(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
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 1-
E
dx.doi.org/10.1021/om401119y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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 fine 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.
Table 5. Crystal Data and Collection Parameters of
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-
a
2,6-Me2C6H3)Cl2[8-(2,6-Me2C6H3)-N(C9H10N)] (5)
b
b
3
4
5
formula
C55H70Cl6N6V2
1129.75
C49H54Cl6N6V2
1041.56
C25H29Cl2N3V
493.35
formula wt
cryst color, habit
cryst size (mm)
yellow, block
orange, block
red, block
0.20 × 0.19 ×
0.17
0.18 × 0.13 ×
0.10
0.22 × 0.19 ×
0.04
In summary, we have shown that V(NAd)Cl2[8-(2,6-
Me2C6H3)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-trihydroqui-
noline 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 1-
butene selectivity. Promising catalyst performances demonstra-
ted 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.
cryst system
space group
a (Å)
monoclinic
C2/c (No. 15)
32.189(5)
10.1323(16)
16.883(3)
90
monoclinic
P21/c (No. 14)
9.303(6)
15.039(11)
17.140(12)
90
monoclinic
P21/c (No. 14)
19.131(14)
13.533(10)
9.120(7)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
104.380(6)
90
90.433(8)
90
96.377(10)
90
5333.9(15)
4
2398(3)
2
2347(3)
4
D
calcd (g/cm3)
1.407
1.443
1.396
F000
2360
1076
1028
temp (K)
μ(Mo Kα) (cm−1
93(2)
93(2)
93(2)
)
6.95
7.66
6.68
total, unique no. of 18194, 6084
rflns measd (Rint)
25043, 5495
(0.0564)
22416, 5375
(0.0549)
(0.0431)
2θmax (deg)
55.0
55.0
55.0
no. of observations 6084
(I > 2.00σ(I))
5495
5375
no. of variables
421
361
366
R1 (I > 2.00σ(I))
0.0570
0.0617
0.1360
1.054
0.0524
0.1227
1.084
wR2 (I > 2.00σ(I)) 0.1442
EXPERIMENTAL SECTION
■
goodness of fit 1.071
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.
a
Detailed structural data are given in the Supporting Information.23
Structures for 3 and 4 were solved as two crystals containing CH2Cl2.
b
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 chromatog-
raphy (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, Ar-
H), 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).
13C NMR (CDCl3): δ 157.7, 147.3, 145.0, 136.9, 132.1, 131.2, 128.8,
21
V(NAd)Cl3 (Ad = 1-adamantyl), V(N-2-MeC6H4)Cl3,12c and V(N-
22
2,6-Me2C6H3)Cl3 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 methyl-
aluminoxane (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 51
V
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-trihydroquinolin-
8-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
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-trihy-
droquinoline] (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-8-
amine (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 n-
F
dx.doi.org/10.1021/om401119y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
hexane. The chilled solution placed in the freezer (−30 °C) afforded
(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 graphite-
monochromated 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
1
yellow-orange microcrystals (815 mg, 1.60 mmol). Yield: 80.2%. H
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)-5,6,7-
trihydroquinoline] (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-trihydroqui-
nolin-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 n-
hexane, 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).
13C NMR (CDCl3): δ 160.4, 157.5, 147.0, 139.7, 138.1, 132.0, 131.1,
ASSOCIATED CONTENT
* Supporting Information
■
S
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.
AUTHOR INFORMATION
Corresponding Author
*K.N.: tel, +81-42-677-2547; fax, +81-42-677-2547; e-mail,
ktnomura@tmu.ac.jp.
■
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.
Author Contributions
∥These authors contributed equally.
Notes
The authors declare no competing financial interest.
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)-5,6,7-
trihydroquinolin-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 n-
hexane, 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, quino-
H), 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.
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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■
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H
dx.doi.org/10.1021/om401119y | Organometallics XXXX, XXX, XXX−XXX