Organometallics
Article
(s, 6H, Ar-CH3), 0.56 (s, 6H, Nb−CH3). 13C{1H} NMR (CDCl3): δ
162.2, 155.2, 153.3, 148.0, 137.9, 135.4, 131.9, 128.1, 126.7, 124.2,
123.1, 121.6, 121.3, 64.0, 40.5, 19.2, 18.4. Anal. Calcd for C24H30N3Nb:
C, 63.57; H, 6.67; N, 9.27. Found: C, 63.48; H, 6.58; N, 9.15.
0.0485 mmol). Yield: 70.6%. 1H NMR (C6D6): δ 8.75 (d, 1H, J = 5.10
Hz, Ar-H), 6.93 (d, 3H, J = 7.50 Hz, Ar-H), 6.89 (t, 2H, J = 7.28 Hz, Ar-
H), 6.81 (t, 1H, J = 7.15 Hz, Ar-H), 6.72 (t, 1H, J = 7.55 Hz, Ar-H), 6.65
(t, 1H, J = 6.33 Hz, Ar-H), 6.54 (d, 1H, J = 8.05 Hz, Ar-H), 4.42 (s, 2H,
NCH2), 2.55 (s, 6H, Ar-CH3), 2.21 (s, 6H, Ar-CH3), 1.99 (d, 2H, J =
10.8 Hz, CH2SiCH3), 0.53 (d, 2H, J = 10.8 Hz, CH2SiCH3), 0.085 (s,
18H, CH2SiCH3). Anal. Calcd for C30H46N3NbSi2: C, 60.28; H, 7.76;
N, 7.03. Found: C, 60.18; H, 7.67; N, 6.99.
4.8. Synthesis of Nb(N-2,6-iPr2C6H3)Me2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (4b). Into a toluene solution (30 mL) containing
Nb(N-2,6-i Pr2 C6 H3 )[OCH(CF3 )2 ]2 [2-(2,6-Me2 C6 H3 )-
NCH2(C5H4N)] (3b, 400 mg, 0.492 mmol) was added a toluene
solution (10 mL) containing MeMgBr (410 μL, 1.23 mmol, 3.0 M in
diethyl ether) slowly at −30 °C. The reaction mixture was warmed
slowly to room temperature, and the mixture was then stirred for 1 h. To
the solution was added CH2Cl2, and the mixture was placed in a rotary
evaporator to remove the volatiles. The resultant residue was extracted
with CH2Cl2 and the solution was passed through a celite pad, and the
filtercake was washed with CH2Cl2. 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 was layered
with toluene. The chilled solution placed in the freezer (−30 °C)
afforded yellow microcrystals (202 mg, 0.396 mmol). Yield: 80.6%. 1H
NMR (CDCl3): δ 8.89 (d, 1H, J = 5.15 Hz, Ar-H), 7.97 (t, 1H, J = 7.25
Hz, Ar-H), 7.59 (t, 1H, J = 6.40 Hz, Ar-H), 7.51 (d, 1H, J = 7.95 Hz, Ar-
H), 6.90−6.87 (m, 4H, Ar-H), 6.80 (t, 1H, J = 7.58 Hz, Ar-H), 6.71 (t,
1H, J = 7.50 Hz, Ar-H), 4.85 (s, 2H, NCH2), 3.82 (sep, 2H, J = 6.80 Hz,
CH(CH3)2), 2.18 (s, 6H, Ar-CH3), 1.14 (d, 12H, J = 6.80 Hz,
CH(CH3)2), 0.53 (s, 6H, Nb−CH3). 13C{1H} NMR (CDCl3): δ 162.1,
154.8, 150.7, 148.1, 145.4, 137.8, 131.8, 128.2, 124.0, 123.1, 122.2,
121.6, 121.3, 64.3, 40.8, 27.8, 24.4, 18.1. Anal. Calcd for C28H38N3Nb:
C, 66.00; H, 7.52; N, 8.25. Found: C, 65.72; H, 7.29; N, 8.02.
4.11. Reaction of Nb(N-2,6-Me2C6H3)Me2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (4a) with Borate (6a). Into a Et2O solution (10 mL)
containing Nb(N-2,6-Me2 C6 H3 )Me2 [2-(2,6-Me2 C6 H3 )-
NCH2(C5H4N)] (4a, 20 mg, 0.0441 mmol) was added a Et2O solution
(4 mL) containing [Ph3C][B(C6F5)4] (40 mg, 0.0441 mmol) at −30
°C. The reaction mixture was warmed slowly to room temperature, and
the mixture was then stirred for 1 h. After the reaction, the solution was
placed in a rotary evaporator to remove the solvent. The residue was
dissolved in Et2O and dropped into n-hexane. Removal of the n-hexane
layer and washing by n-hexane afforded the residue (33 mg). 1H NMR
(CDCl3): δ 8.67 (d, 1H, J = 4.80 Hz, Ar-H), 8.17 (t, 1H, J = 7.80 Hz, Ar-
H), 7.73 (d, 1H, J = 8.05 Hz, Ar-H), 7.67 (t, 1H, J = 6.50 Hz, Ar-H),
6.94 (d, 1H, J = 7.35 Hz, Ar-H), 6.90−6.82 (m, 4H, Ar-H), 6.76 (t, 1H, J
= 7.48 Hz, Ar-H), 5.24 (d, 1H, J = 21.11 Hz, NCH2), 5.16 (d, 1H, J =
21.10 Hz, NCH2), 3.80 (br s, 8H, OCH2CH3), 2.31 (s, 6H, Ar-CH3),
2.22 (s, 3H, Ar-CH3), 2.13 (s, 3H, Ar-CH3), 1.35 (s, 3H, Nb−CH3),
1.32 (t, 12H, J = 6.85 Hz, OCH2CH3). 13C{1H} NMR (CDCl3): δ
161.3, 154.2, 151.6, 148.3 (br d, 1JCF = 240.5 Hz), 146.0, 141.5, 138.3
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(br d, JCF = 245.1 Hz), 136.3 (br d, JCF = 239.7 Hz), 136.1, 130.6,
129.1, 128.9, 128.7, 127.6, 126.5, 125.7, 125.0, 123.3, 68.2, 65.7, 47.9,
19.1, 18.4, 18.3, 14.9 (signals ascribed to ipso-C6F5 carbon were not
observed). 19F NMR (CDCl3): δ −132.6, −162.9 (t, 3JFF = 20.5 Hz),
4.9. Synthesis of Nb(N-2-MeC6H4)Me2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (4c). Into a toluene solution (25 mL) containing
Nb(N-2-MeC6H4)[OCH(CF3)2]2[2-(2,6-Me2C6H3)NCH2(C5H4N)]
(3c, 302 mg, 0.406 mmol) was added a toluene solution (6 mL)
containing MeMgBr (320 μL, 0.96 mmol, 3.0 M in diethyl ether) slowly
at −30 °C. The reaction mixture was warmed slowly to room
temperature, and the mixture was then stirred for 1 h. To the solution
was added CH2Cl2, and the mixture was placed in a rotary evaporator to
remove the volatiles. The resultant residue was extracted with CH2Cl2.
The solution was passed through a celite pad, and the filtercake was
washed with CH2Cl2. 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 was layered with
toluene. The chilled solution placed in the freezer (−30 °C) afforded
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−166.8 (t, JFF = 18.5 Hz). These NMR spectra strongly suggest the
formation of the cationic methyl complex, [Nb(N-2,6-Me2C6H3)Me-
{2-(2,6-Me2C6H3)NCH2(C5H4N)}]+ [B(C6F5)4]−(Et2O)2 (6a), and
4.12. Reaction of Nb(N-2,6-iPr2C6H3)Me2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (4b) with Borate (6b). Into a Et2O solution (20
mL) containing Nb(N-2,6-iPr2C6H3)Me2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (4b, 20 mg, 0.0392 mmol) was added a Et2O
solution (8 mL) containing [Ph3C][B(C6F5)4] (35 mg, 0.0392 mmol)
at −30 °C. The reaction mixture was warmed slowly to room
temperature, and the mixture was then stirred for 1 h. After the reaction,
the solution was placed in a rotary evaporator to remove the solvent.
The residue was dissolved in Et2O and dropped into n-hexane. Removal
of the n-hexane layer and washing by n-hexane afforded the residue (17
mg). 1H NMR (CDCl3): δ 8.50 (d, 1H, J = 5.35 Hz, Ar-H), 8.16 (t, 1H,
J = 7.68 Hz, Ar-H), 7.72 (d, 1H, J = 7.95 Hz, Ar-H), 7.66 (t, 1H, J = 6.45
Hz, Ar-H), 6.93 (t, 5H, J = 8.30 Hz, Ar-H), 6.84 (t, 1H, J = 7.50 Hz, Ar-
H), 5.22 (d, 1H, J = 21.16 Hz, NCH2), 5.15 (d, 1H, J = 21.16 Hz,
NCH2), 3.63−3.57 (m, 2H, CH(CH3)2), 3.60 (br s, 8H, OCH2CH3),
2.24 (s, 3H, Ar-CH3), 2.14 (s, 3H, Ar-CH3), 2.13 (s, 3H, Ar-CH3), 1.33
(s, 3H, Nb−CH3), 1.30 (br s, 12H, OCH2CH3), 1.16 (dd, 12H, J = 6.98
and 9.65 Hz, CH(CH3)2). 13C{1H} NMR (CDCl3): δ 161.1, 153.8,
148.8, 148.3 (br d, 1JCF = 246.0 Hz), 146.7, 146.0, 141.5, 138.3 (br d,
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yellow microcrystals (90 mg, 0.205 mmol). Yield: 50.4%. H NMR
(CDCl3): δ 8.88 (d, 1H, J = 5.20 Hz, Ar-H), 7.97 (t, 1H, J = 7.70 Hz, Ar-
H), 7.59 (t, 1H, J = 6.40 Hz, Ar-H), 7.53 (d, 1H, J = 7.95 Hz, Ar-H),
6.98 (t, 3H, J = 8.73 Hz, Ar-H), 6.86 (t, 1H, J = 7.48 Hz, Ar-H), 6.76 (t,
1H, J = 7.45 Hz, Ar-H), 6.70 (t, 1H, J = 7.33 Hz, Ar-H), 6.06 (d, 1H, J =
7.70 Hz, Ar-H), 4.87 (s, 2H, NCH2), 2.42 (s, 3H, Ar-CH3), 2.20 (s, 6H,
Ar-CH3), 0.50 (s, 6H, Nb−CH3). 13C{1H} NMR (CDCl3): δ 162.4,
155.7, 154.6, 147.9, 137.9, 133.9, 132.1, 129.0, 128.2, 125.6, 125.2,
124.2, 123.1, 121.8, 121.4, 64.0, 38.6, 18.8, 18.4. Anal. Calcd for
C23H28N3Nb: C, 62.87; H, 6.42; N, 9.56. Found: C, 61.95; H, 6.12; N,
9.36. Rather low C values would be due to incomplete combustion
(formation of NbC) during the analysis run.
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1JCF = 241.5 Hz), 136.4 (br d, JCF = 240.0 Hz), 130.5, 129.3, 129.0,
128.9, 126.5, 126.4, 125.1, 123.3, 122.6, 66.1, 47.9, 28.4, 24.6, 24.1,
18.4, 18.0, 14.9 (signals ascribed to ipso-C6F5 carbon were not
observed). 19F NMR (CDCl3): δ −132.5, −162.8 (t, 3JFF = 20.6 Hz),
4.10. Synthesis of Nb(N-2,6-Me2C6H3)(CH2SiMe3)2[2-(2,6-
Me2C6H3)NCH2(C5H4N)] (5a). Into a toluene solution (10 mL)
containing Nb(N-2,6-Me2C6H3)[OCH(CF3)2]2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (3a, 52 mg, 0.0686 mmol) was added a toluene
solution (5 mL) containing Me3SiCH2MgCl (162 μL, 0.164 mmol, 1.0
M in diethyl ether) at −30 °C. The reaction mixture was warmed slowly
to room temperature, and the mixture was then stirred for 1 h. To the
solution was added CH2Cl2, and the mixture was placed in a rotary
evaporator to remove the volatiles (addition of CH2Cl2 into the
solution would improve the efficiency of the subsequent extraction).
The resultant residue was extracted with CH2Cl2. The solution was
passed through a celite pad, and the filtercake was washed with CH2Cl2.
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 toluene and was layered with n-hexane. The chilled solution
placed in the freezer (−30 °C) afforded yellow crystals of 5a (29 mg,
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−166.8 (t, JFF = 18.2 Hz). These NMR spectra strongly suggest the
formation of the cationic methyl complex, [Nb(N-2,6-iPr2C6H3)Me{2-
(2,6-Me2C6H3)NCH2(C5H4N)}]+[B(C6F5)4]−(Et2O)2 (6b), and the
4.13. Oligomerization/Polymerization of ethylene. Ethylene
oligomerizations were conducted in a 100 mL scale stainless steel
autoclave. The typical reaction procedure is as follows. Toluene (29
mL) and the prescribed amount of MAO solid (prepared from ordinary
MMAO-3AH by removing n-hexane, AliBu3 and AlMe3) were added
into the autoclave in the drybox. The reaction apparatus was then filled
with ethylene (1 atm), and Nb(N-2,6-Me2C6H3)Me2[2-(2,6-
Me2C6H3)NCH2(C5H4N)] (4a) (3.0 μmol) in toluene (1.0 mL) was
then added into the autoclave, the reaction apparatus was then
K
Organometallics XXXX, XXX, XXX−XXX