Preparation and characterization of iminopyrrolyl hafnium complexes as catalyst precursors for α-olefin polymerization

Article abstract of DOI:10.1016/j.molcata.2006.01.070

Amido, chloro, and benzyl hafnium complexes bearing 2-(N-aryliminomethyl)pyrrole [(R-pyr)H, 1a: R = DIP = 2-{N-(2,6-diisopropylphenyl)iminomethyl}, 1b: R = XYL = 2-{N-(2,6-dimethylphenyl)iminomethyl}, 1c: R = ANI = 2-{N-(4-methoxyphenyl)iminomethyl}, 1d: R = TOL = 2-{N-(4-methylphenyl)iminomethyl}] were prepared and characterized. The coordination modes of (R-pyr)₂Hf(NMe₂)₂ (2a-d) depend on the bulkiness of the aromatic substituent at the imine nitrogen of the ligands. In contrast, all (R-pyr)₂HfCl₂ (3a-d) have a C₂-symmetric octahedral structure. These diamido- and dichloro-bis(iminopyrrolyl)hafnium complexes, when combined with MMAO, become active catalysts for ethylene polymerization. Two types of hafnium benzyl complexes, (DIP-pyr)Hf(CH₂Ph)₃ (4a) and (DIP-pyr)₂Hf(CH₂Ph)₂ (5a), were prepared by the alkane elimination reaction from reactions of Hf(CH₂Ph)₄ with controlled amounts of iminopyrrole (1a). The mono(iminopyrrolyl)hafnium tribenzyl complex (4a) exhibited a high catalytic activity for 1-hexene polymerization.

Full text of DOI:10.1016/j.molcata.2006.01.070

Journal of Molecular Catalysis A: Chemical 254 (2006) 131–137
Preparation and characterization of iminopyrrolyl hafnium complexes
as catalyst precursors for ␣-olefin polymerization
Hayato Tsurugi, Yutaka Matsuo, Kazushi Mashima∗
Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
Available online 24 April 2006
Abstract
Amido, chloro, and benzyl hafnium complexes bearing 2-(N-aryliminomethyl)pyrrole [(R-pyr)H, 1a: R = DIP = 2-{N-(2,6-diisopropylphenyl)-
iminomethyl}, 1b: R = XYL = 2-{N-(2,6-dimethylphenyl)iminomethyl}, 1c: R = ANI = 2-{N-(4-methoxyphenyl)iminomethyl}, 1d: R = TOL = 2-
{N-(4-methylphenyl)iminomethyl}] were prepared and characterized. The coordination modes of (R-pyr)2Hf(NMe2)2 (2a–d) depend on the
bulkiness of the aromatic substituent at the imine nitrogen of the ligands. In contrast, all (R-pyr)2HfCl2 (3a–d) have a C2-symmetric octahedral
structure. These diamido- and dichloro-bis(iminopyrrolyl)hafnium complexes, when combined with MMAO, become active catalysts for ethylene
polymerization. Two types of hafnium benzyl complexes, (DIP-pyr)Hf(CH2Ph)3 (4a) and (DIP-pyr)2Hf(CH2Ph)2 (5a), were prepared by the alkane
elimination reaction from reactions of Hf(CH2Ph)4 with controlled amounts of iminopyrrole (1a). The mono(iminopyrrolyl)hafnium tribenzyl
complex (4a) exhibited a high catalytic activity for 1-hexene polymerization.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Polymerization; Ethylene; 1-Hexene; Hafnium; Iminopyrrole
1. Introduction
2. Experimental
Recently there has been increasing interest in the develop-
ment of ␣-olefin polymerization using well-defined transition
metal complexes. A promising candidate is the combination of
an anionic non-Cp ligand and group 4 metals [1–3]. Studies of
nitrogen-based ligand modification have led to the introduction
of sterically and electronically demanding features on the ancil-
lary ligand [4,5]. Monoanionic N-aryliminopyrrole ligands have
attracted attention in the last 5 years [6,7], as a system compa-
rable to phenoxyimine complexes of group 4 metals, complexes
that contain a similar steric feature and have ultra-high catalytic
activity and living characteristics for ethylene polymerization
[8]. Our continuing efforts to generate group 4 metal complexes
having iminopyrrolyl ligands have been extended to hafnium as
the central metal. Here we report the preparation of hafnium
complexes bearing mono- and bis(iminopyrrolyl) ligands and
the catalyst performance for ethylene and 1-hexene polymeriza-
tions.
2.1. General
All manipulations involving air- and moisture-sensitive
organometallic compounds were carried out using the standard
Schlenk techniques under argon. Hexane and toluene were dried
and deoxygenated by distillation over sodium benzophenone
ketyl under argon. Benzene-d6 and toluene-d8 were distilled
from P2O5 and thoroughly degassed by trap-to-trap distilla-
tion before use. 1-Hexene, bromobenzene, bromobenzene-d5,
and chloroform-d3 were distilled from CaH2 and deoxygenated.
Tetrabenzyl complex Hf(CH2Ph)4 [9] and tetraamido complex
Hf(NMe2)4 [10] were prepared according to the literature. 2-
{N-(aryl)iminomethyl}pyrrole ligands 1a–d were prepared by
condensation of the 2-formylpyrrole with the corresponding ani-
line derivatives [11].
1
The H NMR (400 and 300 MHz) and 13C NMR (100 and
75 MHz) spectra were measured on a JEOL JNM-AL400 and a
VARIAN Mercury-300 spectrometer. Elemental analyses were
recorded by Perkin-Elmer 2400 at Faculty of Engineering Sci-
ence, Osaka University. All melting points were measured in
sealed tubes under argon atmosphere and were not corrected.
∗
Corresponding author. Fax: +81 6 6850 6296.
E-mail address: mashima@chem.es.osaka-u.ac.jp (K. Mashima).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.01.070

132
H. Tsurugi et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 131–137
1
2b: 92% yield, mp 197–199 ◦C (dec). H NMR (400 MHz,
The gel permeation chromatographic analyses were carried out
at 40 ◦C by using a Shimadzu LC-10A liquid chromatograph
system and a RID 10A refractive index detector, equipped with
a Shodex KF-806L column which was calibrated versus com-
mercially available polystyrene standards (Showa Denko).
CDCl3, 308 K): δ 1.23 (s, 3H, Ar-CH3), 1.28 (s, 3H, Ar-
CH3), 2.47 (s, 6H, N(CH3)2), 2.96 (br s, 3H, N(CH3)2),
3.25 (br s, 3H, N(CH3)2), 6.14 (br s, 1H, 5-pyr), 6.16 (br
s, 1H, 4-pyr), 6.47 (br s, 1H, 4-pyr), 6.73 (br s, 1H, 3-pyr),
3
6.83 (d, 1H, JH H = 2.9 Hz, 3-pyr), 6.8–7.1 (m, 6H, C6H3),
2.2. Preparation of diamido complexes,
Hf(R-pyr)2(NMe2)2 (2a–d) [(R-pyr)H = 1a–d]
7.39 (br s, 1H, 5-pyr), 7.80 (s, 1H, N = CH), 7.81 (s, 1H,
N = CH). 13C NMR (100 MHz, CDCl3, 308 K): δ 15.5 (q,
1JC H = 126 Hz, Ar-CH3), 17.1 (q, JC H = 127 Hz, Ar-CH3),
1
39.8 (q, 1JC H = 133 Hz, N(CH3)2), 43.1 (br q, 1JC H = 136 Hz,
To a solution of Hf(NMe2)4 (393 mg, 1.11 mmol) in toluene
(6 mL) was added a toluene solution of 1c (444 mg, 2.22 mmol)
in toluene (8 mL) at room temperature. After the reaction mix-
ture was heated at 50 ◦C for 4 h, all volatiles were removed
under reduced pressure. The resulting yellow product was
washed with three portions of hexane (4 mL), and then dried
under reduced pressure. 2c: 96% yield, mp 210–212 ◦C (dec).
1H NMR (CDCl3, 308 K): δ 3.13 (s, 12H, NMe2), 3.74 (s,
1
N(CH3)2), 46.0 (br q, JC H = 136 Hz, N(CH3)2), 112.9 (d,
1JC H = 168 Hz, 4-pyr), 114.4 (d, 1JC H = 168 Hz, 4-pyr), 118.7
1
1
(d, JC H = 168 Hz, 3-pyr), 120.8 (d, JC H = 168 Hz, 3-pyr),
125.1 (d, JC H = 160 Hz, p-C6H3), 125.5 (d, JC H = 159 Hz,
1
1
1
p-C6H3), 127.6 (d, JC H = 158 Hz, m-C6H3), 127.8 (d,
1JC H = 158 Hz, m-C6H3), 128.2 (d, 1JC H = 158 Hz, m-C6H3),
1
128.3 (d, JC H = 158 Hz, m-C6H3), 131.5 (s, o-C6H3), 131.6
(s, o-C6H3), 132.3 (s, o-C6H3), 132.5 (s, o-C6H3), 137.7
(d, JC H = 181 Hz, 5-pyr), 137.9 (s, 2-pyr), 138.1 (s, 2-pyr),
139.9 (d, JC H = 181 Hz, 5-pyr), 149.2 (s, ipso-C6H3), 150.0
3
6H, OMe), 6.22 (dd, 2H, JH H = 2.0 and 3.4 Hz, 4-pyr),
3
1
6.58 (d, 2H, JH H = 3.4 Hz, 3-pyr), 6.60 (s, 8H, o- and m-
C6H4), 7.20 (br s, 2H, 5-pyr), 7.93 (s, 2H, N = CH). 13C NMR
1
1
1
(CDCl3, 308 K): δ 44.6 (q, JC H = 133 Hz, NMe2), 55.5 (q,
(s, ipso-C6H3), 160.7 (d, JC H = 163 Hz, N = CH), 163.8 (d,
1JC H = 143 Hz, OMe), 113.2 (d, 1JC H = 168 Hz, 4-pyr), 113.7
1JC H = 163 Hz, N = CH). Anal. Calcd for C30H38HfN6: C,
(d, 1JC H = 160 Hz, m-C6H4), 119.8 (d, 1JC H = 168 Hz, 3-pyr),
54.50; H, 5.79; N, 12.71. Found: C, 54.79; H, 6.10; N, 12.39.
1
1
2d: 89% yield, mp 145–150 ◦C (dec). H NMR (toluene-
1
122.2 (d, JC H = 160 Hz, o-C6H4), 137.7 (d, JC H = 178 Hz,
5-pyr), 138.6 (s, 2-pyr), 143.1 (s, ipso-C6H4), 157.0 (s, p-
d8, 308 K): δ 2.09 (s, 6H, Ar-Me), 3.23 (s, 12H, NMe2),
1
3
C6H4), 157.8 (d, JC H = 163 Hz, N = CH). Anal. Calcd for
6.34 (dd, 2H, JH H = 3.6 and 1.9 Hz, 4-pyr), 6.57 (d, 2H,
3JH H = 3.6 Hz, 3-pyr), 6.62 (d, 4H, 3JH H = 8.0 Hz, C6H4), 6.82
C28H34HfN6O2: C, 50.56; H, 5.15; N, 12.64. Found: C, 50.84;
H, 5.24; N, 12.25.
(d, 4H, C6H4), 7.34 (br s, 2H, 5-pyr), 7.63 (s, 2H, N = CH). 13
C
1
Similar treatment of Hf(NMe2)4 with the corresponding lig-
and was operated for 2a, 2b, and 2d.
NMR (toluene-d8, 308 K): δ 20.8 (q, JC H = 125 Hz, Ar-Me),
1
1
41.1 (q, JC H = 130 Hz, NMe2), 114.0 (d, JC H = 168 Hz, 4-
pyr), 120.9 (d, 1JC H = 169 Hz, 3-pyr), 121.8 (d, 1JC H = 160 Hz,
o-C6H4), 129.3 (d, 1JC H = 161 Hz, m-C6H4), 134.6 (s, p-C6H4),
2a: 97% yield, mp 162–164 ◦C (dec). H NMR (400 MHz,
1
C6D6, 308 K): δ 0.67 (d, 3H, 3JH H = 6.8 Hz, CH(CH3)2), 0.69
(d, 3H, 3JH H = 6.7 Hz, CH(CH3)2), 0.82 (d, 3H, 3JH H = 6.8 Hz,
1
138.6 (d, JC H = 173 Hz, 5-pyr), 139.2 (s, 2-pyr), 147.9 (s,
3
ipso-C6H4), 158.6 (d, 1JC H = 163 Hz, N = CH). Anal. Calcd for
C28H34HfN6: C, 53.12; H, 5.41; N, 13.27. Found: C, 53.03; H,
5.73; N, 13.21.
CH(CH3)2), 1.02 (d, 3H, JH H = 6.7 Hz, CH(CH3)2), 1.08 (d,
3
3
3H, JH H = 6.8 Hz, CH(CH3)2), 1.16 (d, 3H, JH H = 6.8 Hz,
3
CH(CH3)2), 1.21 (d, 3H, JH H = 6.7 Hz, CH(CH3)2), 1.33
(d, 3H, JH H = 6.7 Hz, CH(CH3)2), 1.70 (m, 1H, CH(CH3)2),
3
2.28 (m, 1H, CH(CH3)2), 2.56 (s, 6H, N(CH3)2), 2.93 (s, 3H,
N(CH3)2), 3.15(m, 1H, CH(CH3)2), 3.32(s, 3H, N(CH3)2), 3.59
(m, 1H, CH(CH3)2), 6.09 (br s, 1H, 4-pyr), 6.19 (br s, 1H, 4-
pyr), 6.46 (br s, 1H, 5-pyr), 6.75 (d, 1H, 3JH H = 3.2 Hz, 3-pyr),
6.80 (d, 1H, 3JH H = 2.8 Hz, 3-pyr), 7.0–7.2 (m, 6H, C6H3), 7.34
(br s, 1H, 5-pyr), 7.80 (s, 1H, N = CH), 7.87 (s, 1H, N = CH).
13C NMR (100 MHz, C6D6, 308 K): δ 22.7, 22.7, 23.0, 24.1,
26.5, 26.5, 26.5, and 26.7 (q, 1JC H = 125–127 Hz, CH(CH3)2),
27.0, 27.2, 27.2, and 28.4 (d, 1JC H = 125–128 Hz, CH(CH3)2),
40.5, 44.9, and 46.2 (q, 1JC H = 131–134 Hz, N(CH3)2), 112.9
2.3. Preparation of dichloro complexes Hf(R-pyr)2Cl2
(3a–d) [(R-pyr)H = 1a–d]
To 2c (300 mg, 0.451 mmol) suspended in hexane (5.0 mL)
was added trimethylsilyl chloride (0.57 mL, 4.5 mmol) via
syringe. After the reaction mixture was stirred for 4 h at 40 ◦C.
Removal of all volatile afforded orange microcrystals, which
were washed with hexane (4× 5 mL) and dried in vacuo, giv-
ing 3c (265 mg, 0.409 mmol, 91% yield), mp 120–121 ◦C (dec).
1H NMR (CDCl3, 308 K): δ 3.76 (s, 6H, OMe), 6.24 (dd,
3JH H = 2.0 and 3.4 Hz, 2H, 4-pyr), 6.67 (2H, 3-pyr), 6.69 (d, 4H,
3JH H = 8.9 Hz, m-C6H4), 6.84 (d, 4H, o-C6H4), 7.43 (br s, 2H,
5-pyr), 7.94 (s, 2H, N = CH). 13C NMR (CDCl3, 308 K): δ 55.5
(q, 1JC H = 143 Hz, OMe), 113.9 (d, 1JC H = 161 Hz, m-C6H4),
1
1
(d, JC H = 168 Hz, 4-pyr), 114.3 (d, JC H = 168 Hz, 4-pyr),
1
1
118.8 (d, JC H = 168 Hz, 3-pyr), 121.7 (d, JC H = 168 Hz,
3-pyr), 123.3, 123.4, 123.5, 123.6, 125.8, and 126.4 (d,
1JC H = 156–160 Hz, p- and m-C6H3), 137.1 (s, 2-pyr),
1
1
1
137.3 (s, 2-pyr), 137.6 (d, JC H = 181 Hz, 5-pyr), 140.2 (d,
115.1 (d, JC H = 172 Hz, 4-pyr), 123.0 (d, JC H = 162 Hz, o-
1JC H = 181 Hz, 5-pyr), 141.9 (s, o-C6H3), 141.9 (s, o-C6H3),
142.8 (s, o-C6H3), 143.1 (s, o-C6H3), 147.1 (s, ipso-C6H3),
149.4 (s, ipso-C6H3), 161.9 (d, 1JC H = 163 Hz, N = CH), 163.9
(d, 1JC H = 164 Hz, N = CH). Anal. Calcd for C38H54HfN6: C,
59.02; H, 7.04; N, 10.87. Found: C, 58.76; H, 7.44; N, 10.52.
C6H4), 123.5 (d, 1JC H = 171 Hz, 3-pyr), 138.2 (s, 2-pyr), 141.6
(s, ipso-C6H4), 143.0 (d, JC H = 185 Hz, 5-pyr), 157.9 (s, p-
C6H4), 160.2 (d, JC H = 168 Hz, N = CH). Anal. Calcd for
1
1
C24H22Cl2HfN4O2: C, 44.49; H, 3.42; N, 8.65. Found: C, 44.21;
H, 3.71; N, 8.70.

H. Tsurugi et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 131–137
133
Similar treatment with Me3SiCl afforded the corresponding
dichloro complexes.
3.6 Hz, 1H, 4-pyr), 6.61 (3-pyr overrapped with other reso-
3
nance), 6.63 (d, JH H = 7.1 Hz, 6H, o-Ph of HfCH2Ph), 6.83
3a: 85% yield, mp 115–117 ◦C (dec). H NMR (400 MHz,
(t, 3JH H = 7.4 Hz, 3H, p-Ph of HfCH2Ph), 6.95–7.10 (aromatic
1
3
CDCl3, 308 K): δ 0.88 (d, 12H, JH H = 6.7 Hz, CH(CH3)2),
protons and 5-pyr), 7.57 (s, 1H, N = CH). 13C NMR (75 MHz,
1
0.90 (br s, 6H, CH(CH3)2), 1.13 (br s, 6H, CH(CH3)2),
2.66 (m, 2H, CH(CH3)2), 2.88 (br s, 2H, CH(CH3)2),
6.38 (br s, 2H, 4-pyr), 6.92 (br s, 2H, 5-pyr), 6.96 (d,
C6D5CD3, 308 K) δ 22.9 (q, JC H = 126 Hz, CHMe2), 25.5
(q, 1JC H = 126 Hz, CHMe2), 28.7 (d, 1JC H = 127 Hz, CHMe2),
85.6 (t, 1JC H = 122 Hz, HfCH2Ph), 115.3 (d, 1JC H = 170 Hz, 4-
pyr), 122.5 (d, 1JC H = 169 Hz, 3-pyr), 122.8 (d, 1JC H = 161 Hz,
p-Ph of HfCH2Ph), 123.6, 125.2, 127.1, 128.1, 128.8, 129.0
3
2H, JH H = 3.5 Hz, 3-pyr), 7.13–7.26 (6H, 2 C6H3), 8.00
(s, 2H, N = CH). 13C NMR (100 MHz, CDCl3, 308 K): δ
1
1
1
26.7 (q, JC H = 128 Hz, CH(CH3)2), 28.0 (d, JC H = 126 Hz,
(d, JC H = 154 Hz, o-Ph of HfCH2Ph), 138.3, 141.5, 142.5
1
1
1
CH(CH3)2), 115.3 (d, JC H = 168 Hz, 4-pyr), 124.1 (d,
(d, JC H = 181 Hz, 5-pyr), 147.5, 164.9 (d, JC H = 167 Hz,
N = CH). Anal. Calcd for C38H42N2Hf1: C, 64.72; H, 6.00; N,
3.97. Found: C, 65.31; H, 6.18; N, 3.76.
1JC H = 171 Hz, 3-pyr), 124.3 (d, JC H = 158 Hz, m-C6H3),
1
1
127.4 (d, JC H = 160 Hz, p-C6H3), 137.6 (s, o-C6H3), 142.4
(s, 2-pyr), 144.2 (d, JC H = 177 Hz, 5-pyr), 145.4 (s, ipso-
C6H3), 168 (d, JC H = 164 Hz, N = CH). Anal. Calcd for
1
1
2.5. Preparation of dibenzyl complex (R-pyr)2Hf(CH2Ph)2
C34H42Cl2HfN4: C, 54.01; H, 5.60; N, 7.41. Found: C, 53.61;
H, 5.99; N, 7.48.
(5a)
1
3b: 80% yield, mp 110–112 ◦C (dec). H NMR (400 MHz,
To a solution of Hf(Ch2Ph)4 (142 mg, 0.261 mmol) in toluene
(10 mL), cooled to −78 ◦C, was added a solid of 1a (123 mg,
0.482 mmol). The reaction mixture was stirred overnight at room
temperature. The color of the solution turned to yellow–brown.
After removal of insoluble products by centrifugation, all
volatiles were removed in vacuo. The resulting yellow–brown
oil was dissolved in small amount of hexane and stored at
−20 ◦C. Complex 5a was obtained as yellow microcrystals in
CDCl3, 308 K): δ 1.98 (s, 12H, Ar-CH3), 6.33 (m, 2H, 4-pyr),
6.93 (m, 4H, 3-pyr and 5-pyr), 7.00 (m, 6H, C6H3), 8.01 (s,
2H, N = CH). 13C NMR (100 MHz, CDCl3, 308 K): δ 18.5
(q, 1JC H = 127 Hz, Ar-CH3), 115.5 (d, 1JC H = 172 Hz, 4-pyr),
1
1
124.3 (d, JC H = 171 Hz, 3-pyr), 126.5 (d, JC H = 159 Hz, p-
1
C6H3), 128.5 (d, JC H = 157 Hz, m-C6H3), 132.2 (s, 2-pyr),
1
138.2 (s, o-C6H3), 144.5 (d, JC H = 186 Hz, 5-pyr), 147.7 (s,
ipso-C6H3), 164.5(d, 1JC H = 168 Hz, N = CH). Anal. Calcd for
C26H26Cl2HfN4: C, 48.50; H, 4.07; N, 8.70. Found: C, 48.24;
H, 4.16; N, 9.02.
76% yield (mp 115–119 ◦C). H NMR (300 MHz, C6D5CD3,
1
3
308 K): δ 0.90 (d, JH H = 6.6 Hz, 12H, CH(CH3)2), 0.96 (d,
3JH H = 6.9 Hz, 12H, CH(CH3)2), 2.15 (s, 4H, Hf-CH2Ph), 2.93
3d: 80% yield, mp 93–95 ◦C (dec). 1H NMR (CDCl3,
(br m, 4H, CH(CH3)2), 6.13 (dd, JH H = 2.2 and 3.6 Hz, 2H,
3
3
308 K): δ 2.26 (s, 6H, Ar-Me), 6.24 (dd, 3JH H = 1.6 and 4.0 Hz,
4-pyr), 6.47 (d, JH H = 7.4 Hz, 4H, o-Ph of Hf-CH2Ph), 6.70
3
3
3
2H, 4-pyr), 6.68 (d, 2H, 3-pyr), 6.79 (d, 4H, JH H = 8.3 Hz,
(d, JH H = 3.6 Hz, 2H, 5-pyr), 6.72 (t, JH H = 7.4 Hz, 2H, p-
Ph of Hf-CH2Ph), 6.78 (br, 2H, 3-pyr), 6.97 (t, 3JH H = 8.0 Hz,
6H, m-Ph of Hf-CH2Ph), 7.05–7.15 (m, 6H, Ph), 7.85 (s, 2H,
N = CH). 13C NMR (75 MHz, C6D5CD3, 308 K) δ 23.2 (q,
o-C6H4), 6.97 (d, 4H, m-C6H4), 7.42 (br s, 2H, 5-pyr),
7.95 (s, 2H, N = CH). 13C NMR (CDCl3, 308 K): δ 21.0 (q,
1JC H = 127 Hz, Ar-Me), 115.1(d, 1JC H = 172 Hz, 4-pyr), 121.8
(d, 1JC H = 161 Hz, o-C6H4), 123.7 (d, 1JC H = 170 Hz, 3-pyr),
1JC H = 125 Hz, CHMe2), 27.6 (q, JC H = 126 Hz, CHMe2),
29.3 (d, JC H = 134 Hz, CHMe2), 90.3 (t, JC H = 118 Hz,
HfCH2Ph), 115.7, 122.9, 123.6, 124.8, 127.8, 128.5, 128.6,
1
1
1
1
129.2 (d, JC H = 160 Hz, m-C6H4), 136.0 (s, p-C6H4), 138.3
1
(s, 2-pyr), 143.8 (d, JC H = 184 Hz, 5-pyr), 145.8 (s, ipso-
1
1
C6H4), 160.5 (d, JC H = 168 Hz, N = CH). Anal. Calcd for
139.4, 143.0, 143.4, 147.5, 148.5, 164.4 (d, JC H = 165 Hz,
C24H22Cl2HfN4: C, 46.81; H, 3.60; N, 9.10. Found: C, 47.06;
H, 3.47; N, 9.32.
N = CH). Anal. Calcd for C48H56N4Hf1: C, 66.46; H, 6.51; N,
6.46. Found: C, 66.59; H, 6.59; N, 6.40.
2.4. Preparation of tribenzyl complex (R-pyr)Hf(CH2Ph)3
2.6. Polymerization of ethylene
(4a)
The precatalyst (1.0–3.0 mg) was dissolved in toluene and
then 1000 equiv. of methylaluminoxane (MAO) in toluene was
added at 25 ◦C. The orange solution (1.0 mmol/L) was magnet-
ically stirred and maintained under ethylene (1 atm). The poly-
merization was carefully terminated by the addition of methanol
and aqueous hydrogen chloride. The resulting white polymer
was collected by filtration and dried in vacuo at 60 ◦C.
In a schlenk, Hf(Ch2Ph)4 (1.631 g, 3.00 mmol) was dis-
solved in toluene (20 mL) at room temperature. To the solution,
cooled to −78 ◦C, was added a solid of 1a (0.695 g, 2.73 mmol).
The reaction mixture was allowed to warm to room temper-
ature and then stirred overnight. The color of the solution
turned to yellow–brown. After removal of insoluble products
by centrifugation, most of volatiles were removed in vacuo.
The resulting yellow–brown solution was added hexane (2 mL)
and stored at −20 ◦C, giving 4a as yellow microcrystals in
61% yield, mp 80–94 ◦C (dec). 1H NMR (300 MHz, C6D5CD3,
2.7. Polymerization of 1-hexene
A solution of precatalyst (20 ␮mol) in C6H5Br (1.5 mL) was
added to a solution of [Ph3C][B(C6F5)4] (20 ␮mol) in C6H5Br
(1.0 mL) at 0 ◦C. After 1-hexene (2.5 mL) was added, the reac-
tion mixture was stirred. The polymerization was quenched by
3
308 K): δ 0.92 (d, JH H = 6.8 Hz, 6H, CH(CH3)2), 1.12 (d,
3JH H = 6.8, 6H, CH(CH3)2), 1.98 (s, 6H, HfCH2Ph), 2.61 (sep,
3JH H = 6.8 Hz, 2H, CH(CH3)2), 6.25 (dd, JH H = 1.9 Hz and
3

134
H. Tsurugi et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 131–137
adding 1N HCl in MeOH. The polymer was extracted by hexane
and washed by MeOH. The hexane solution was filtered through
silica gel, and then dried under vacuum.
3. Results and discussion
3.1. Diamido- and dichloro-bis(iminopyrrolyl) complexes
of hafnium
2.8. Crystallographic data collection and structure
determination of 4a
Bis(iminopyrrolyl) hafnium complexes, (R-pyr)2Hf(NMe2)2
(2a–d), were prepared by treating Hf(NMe2)4 with the corre-
sponding iminopyrroles 1a–d in toluene (Eq. (1)). Two equiv.
of dimethylamine were released. The geometry of the products
highly depended on the bulkiness of the aromatic substituent at
the imine nitrogen of the ligands. Treatments of Hf(NMe2)4 with
bulky ligands 1a and 1b afforded bis(iminopyrrolyl)hafnium
complexes 2a and 2b with dissymmetric structures, respectively,
while reactions with the less bulky ligands 1c and 1d produced
the corresponding six coordinated C2-symmetric cis-diamido
complexes 2c and 2d.
Crystals of 4a suitable for the X-ray diffraction study were
mounted on glass fibers. All measurements were made on
a Rigaku R-AXIS-RAPID Imaging Plate diffractometer with
graphite monochromated Mo K␣ radiation (λ = 0.71095). Index-
ing was performed from three oscillations. The camera radius
was 127.40 mm. Readout was performed in the 0.100 mm pixel
mode. A symmetry-related absorption correction using the pro-
gram ABSCOR was applied. The data were corrected for
Lorentz and polarization effects.
The structures were solved by direct methods (SIR92)
[12] and refined on F2 by full-matrix least-squares meth-
ods, using SHELXL-97 [13]. The non-hydrogen atoms
were refined anisotropically by the full-matrix least squares
method. All hydrogen atoms were included in the refine-
ment on calculated positions riding on their carrier atoms.
ꢀ
ꢀ
The function R1 and wR2 were
||Fo| − |Fc||/ |Fo| and
ꢁ
ꢂ
w(Fo2 − Fc2)2/ w(Fo2)2 1/2. All calculations of least-
ꢀ
ꢀ
squares refinements were performed with SHELXL-97 pro-
grams on an Origin 3400 computer of Silicon Graphics Inc., at
the Research Center for Structural Biology Institute for Protein
Research, Osaka University. Structural parameters and X-ray
structure analysis are summarized in Table 1.
(1)
The 1H NMR spectra of complexes 2a and 2b displayed two
sets of resonances due to the two magnetically nonequivalent
iminopyrrolyl ligands together with signals of two nonequiva-
lent two NMe2 ligands. Two imino protons appeared separately
at δH 7.80 and 7.87 for 2a, and δH 7.80 and 7.81 for 2b. Because
the chemical shift differences for each complex are small, two
iminopyrrolyl ligands coordinated in a bidentate fashion to the
hafnium atom. In the 13C NMR spectra of complexes 2a and
2b, two imino carbons were observed at δC 161.9 and 163.9 for
2a and δC 160.7 and 163.8 for 2b. The downfield shift of two
imino carbons, compared to the corresponding free ligands, also
indicated that both imino groups coordinated to the metal. The
2D NOESY analyses of 2a and 2b confirmed that they possessed
the cis-diamido moiety. These results indicated that the hafnium
complexes 2a and 2b adopt structure C shown in Fig. 1. On
Table 1
Crystal data and data collection parameters of (DIP-pyr)Hf(CH2Ph)3
(C6H5CH3) (4a)
Formula
C45H50N2Hf
797.39
Formula weight
Crystal system
Space group
Triclinic
¯
P1 (No. 2)
˚
a (A)
10.835(2)
11.013(3)
15.988(4)
108.584(9)
100.329(8)
95.738(9)
1753.6(7)
47425 (6.0–55.2◦)
2, 1.510
˚
b (A)
˚
c (A)
α (◦)
β (◦)
γ (◦)
3
1
˚
V (A )
the other hand, the H NMR spectra of complexes 2c and 2d
displayed rather simple signals due to a C2-symmetric configu-
ration (A or B).
No. of reflections for cell det. (2θ range)
Z, Dcalcd (g/cm−3
F(0 0 0)
)
812.00
30.04
120
µ [Mo K␣] (cm−1
T (K)
)
Two amido moieties of complexes 2a–d were able to be
replaced by two chloride atoms. Treatments of complexes 2a–d
with trimethylsilyl chloride in hexane for 4 h at 40 ◦C resulted
in quantitative formations of the corresponding dichloro com-
Crystal size (mm)
2θmax (◦)
No. of reflections measured
Unique data (Rint
0.35 × 0.10 × 0.20
55.0
55841
8019 (0.074)
7285
1
plexes (R-pyr)2HfCl2 (3a–d) (Eq. (2)). The H NMR spectra
)
of all dichloro complexes 3a–d exhibited sharp signals due to
the C2-symmetric octahedral structure. We previously reported
that the zirconium analogue (ANI-pyr)2ZrCl2 has an octahe-
dral geometry where the two chloride atoms are located in a
cis-fashion [7f]. This observation suggested that the two chlo-
ride atoms of bis(iminopyrrolyl)hafnium complexes have a cis-
No. of observations (I > 2.0σ(I))
No. of variables
R1, wR2 (I > 2.0σ(I))
R1, wR2 (all data)
GOF on−F32
433
0.0357, 0.0809
0.0401, 0.0830
1.11
1.36, −1.48
˚
ꢀρ (e A
)

H. Tsurugi et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 131–137
135
Fig. 1. Five isomeric octahedral structures (A–E) [A–C: cis-X geometry; D and E: trans-X geometry].
configuration.
amounts of iminopyrrole (1a). On the other hand, a reaction
of Hf(CH2Ph)4 with 1 equiv. of a less sterically hindered
iminopyrrole (1b) only afforded a mixture of mono- and
bis(iminopyrrolyl) hafnium benzyl complexes. In the case
of iminopyrrole ligands with para-aromatic substituents
(1c, d), bis(iminopyrrolyl)hafnium dibenzyl complexes
were the only products after treatment of Hf(CH2Ph)4
with 1 equiv. of the iminopyrrole ligands. Preparations of
bis(iminopyrrolyl)hafnium dibenzyl complexes in which
aromatic or alkyl substituents are located at the imino-nitrogen
of the ligands were reported by Okuda and co-workers [7h,7i].
The complex 4a was characterized by spectral data, combus-
tion analysis, and X-ray analysis. The 1H NMR spectrum of 4a
displayed one singlet signal due to benzyl protons and one set of
signals due to the iminopyrrolyl ligand in an expected integral
ratio. The benzyl proton resonance could be frozen to become
a broad signal by cooling the sample solution to approximately
−60 ◦C. In the 13C NMR spectrum, the three-benzyl carbons
(2)
Because the diamido and dichloro moieties of hafnium com-
plexes 2a–d and 3a–d have the cis-diamido and cis-dichloro
geometry suitable for olefin polymerization activity, these com-
plexes, upon activation by excess amounts of methylalumi-
noxane, were tested as catalysts for ethylene polymerization
(Table 2). Although these complexes exhibited catalytic activ-
ity, their activities were lower than that found for other group 4
metal bis(iminopyrrolyl) complexes [7b,7h,7i].
1
3.2. Hafnium benzyl complexes bearing iminopyrrolyl
ligands
were equal and the value of JC H for the benzyl methylene
carbons was 122 Hz, consistent with the typical η1-coordination
mode of the benzyl ligand [14].
Scheme
1
shows the preparation of mono- and
bis(iminopyrrolyl) hafnium benzyl complexes, 4a and 5a,
starting from Hf(CH2Ph)4. These two hafnium complexes
were isolated by the reactions of Hf(CH2Ph)4 with controlled
Table 2
Polymerization of ethylene catalyzed by 2a–d and 3a–d
Catalyst Temperature Time (h) ␮mol-cat
PE (mg) Activity (kg-
PE/mol-cat h)
(◦C)
(␮mol)
2a
2b
2c
2d
3a
3b
3c
3d
20
20
20
20
0
0
0
0
9
9
9
2
9
9
9
2
12.2
16.8
17.6
6.3
10.7
16.9
19.4
10.6
42.0
65.5
53.7
3.4
3.9
3.1
8.8
1.4
141.5
257.2
218.2
89.2
13.2
15.2
11.2
8.4
Scheme 1.
In toluene: [Hf] = 1.0 mM; MMAO 1000 eq.; ethylene 1 atm.

136
H. Tsurugi et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 131–137
Table 3
Selected bond distances and angles in complex 4a
˚
Bond distances (A)
Hf N1
Hf C18
Hf C25
N1 C1
C1 C2
C3 C4
N2 C5
Hf N2
Hf C19
Hf C32
N1 C4
C2 C3
C4 C5
2.214(3)
2.222(4)
2.252(4)
1.365(5)
1.388(7)
1.381(6)
1.302(5)
2.289(3)
2.663(4)
2.261(3)
1.382(6)
1.390(7)
1.408(5)
Bond angles (◦)
N1 Hf N2
72.0(1)
88.6(1)
N1 Hf C25
N2 Hf C18
C18 Hf C25
Hf C25 C26
N1 Hf C18
N1 Hf C32
N2 Hf C25
Hf C18 C19
Hf C32 C33
109.0(2)
123.0(2)
107.3(3)
101.6(1)
149.8(1)
127.2(1)
89.8(3)
Fig. 2. The molecular structure of complex 4a. All hydrogen atoms and a solvent
molecule (toluene) were omitted for clarity.
110.7(2)
complex 5a possesses a C2-symmetric geometry (A in Fig. 1).
This structure is in contrast to our previous report that (DIP-
pyr)2Zr(CH2Ph)2 possessed a dissymmetric structure [7g] (C
in Fig. 1), but consistent with a dibenzyl complex of bis{2-N-
(adamantly)iminomethylpyrrolyl}hafnium, which adopts a C2-
symmetric structure (A in Fig. 1) [7i].
The structure of 4a is shown in Fig. 2 and selected bond
distances and angles are summarized in Table 3. The hafnium
atom of 4a adopts a distorted trigonal bipyramidal geometry,
in which a pyrrolyl nitrogen atom (N1) and one benzyl carbon
(C32) occupy apical positions. The short distance (2.663(4) A)
of Hf-C19 and the acute angle (89.8(3)◦) of Hf-C18-C19 clearly
indicate that one benzyl ligand is in an η2-coordination mode
to the hafnium atom, while the other two benzyl ligands are
normal η1-coordination ligands, which is in sharp contrast to the
structure depicted by the NMR spectral data, presumably due to
the rapid interconversion process of the three benzyl ligands in
solution.
We examined the catalytic activity of 4a and 5a, upon combi-
nation with MMAO, for ethylene polymerization. Their catalytic
activities were negligible. On the other hand, complex 4a, when
[Ph3C][B(C6F5)4] was used as a cocatalyst, became a cata-
lyst for the polymerization of 1-hexene. The results conducted
at room temperature and 60 ◦C are summarized in Table 4.
The tri(benzyl) complex 4a at room temperature had high cat-
alytic activity for 1-hexene polymerization; however, the cat-
alyst system afforded a mixture of polymers and oligomers,
strongly suggesting that the chain transfer reaction, including
␤-hydrogen elimination, proceeded readily. At an elevated tem-
perature (60 ◦C), the catalytic activity increased and the molec-
ular weights of both polymers and oligomers decreased. The 1H
NMR spectra of these products displayed olefinic resonances
around 4.7 and 5.4 ppm. The resonances around 4.7 ppm are
due to 1,1-disubstituted olefins that result from ␤-elimination
in a 1,2-insertion product, and the resonances around 5.4 ppm
The 1H NMR spectrum of 5a displayed signals assignable to
one set of iminopyrrolyl and that of benzyl in an expected 1:1
ratio. In the 1H NMR spectrum, the two-iminopyrrolyl ligands
were magnetically equivalent within the temperature range of
−50 to 35 ◦C. Benzyl methylene protons were observed as a sin-
glet at room temperature, and then became broad as the tempera-
ture was cooled below −40 ◦C, presumably due to the restricted
rotation around the hafnium–carbon bond. It is assumed that
Table 4
1-Hexene polymerization catalyzed by 2a/[Ph3C][B(C6F5)4]
Run
1
Temperature (◦C)
r.t.a
Time (min)
15
Yield (%)
78
Activity (kg-polymer/mol-cat h)
262
Mw
Mw/Mn
313800b
2900b
2.12b
2.41b
2
60
3
86
1446
92200b
1300b
1.90b
1.49b
Conditions: [cat] = 5.0 mM; solvent = C6H5Br; catalyst = 20 ␮mol; [1-hexene]/[cat] = 1000.
a
The reaction mixture was boiling in 10 min.
Bimodal molecular weight distribution.
b

H. Tsurugi et al. / Journal of Molecular Catalysis A: Chemical 254 (2006) 131–137
137
are due to internal olefins that result from ␤-elimination in a
2,1-insertion product [15]. The sterically less demanding cata-
lyst could not control the 1,2 versus 2,1-insertion and, moreover,
facilitated ␤-elimination. When bis(iminopyrrolyl) complex 5a
was used as a catalyst precursor, the catalyst system was far
less active than the tri(benzyl) complex 4a/[Ph3C][B(C6F5)4]
catalyst.
[7] For group 4 metal iminopyrrolyl complexes: Use of Ti:
(a) Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, M. Nitabaru, T. Nakano,
H. Tanaka, T. Fujita, Chem. Lett. (2000) 1270;
(b) Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, T. Nakano, H. Tanaka,
N. Kashiwa, T. Fujita, Organometallics 20 (2001) 4793;
(c) Y. Yoshida, J. Saito, M. Mitani, Y. Takagi, S. Matsui, S. Ishii, T.
Nakano, N. Kashiwa, T. Fujita, Chem. Commun. (2002) 1298;
(d) Y. Yoshida, J. Mohri, S. Ishii, M. Mitani, J. Saito, S. Matsui, H.
Makio, T. Nakano, H. Tanaka, M. Onda, Y. Yamamoto, A. Mizuno, T.
Fujita, J. Am. Chem. Soc. 126 (2004) 12023;
4. Conclusions
Use of Zr and Hf:
(e) D.M. Dawson, D.A. Walker, M. Thornton-Pett, M. Bochmann, J.
Chem. Soc., Dalton Trans. (2000) 459;
(f) Y. Matsuo, K. Mashima, K. Tani, Chem. Lett. (2000) 1114;
(g) H. Tsurugi, T. Yamagata, K. Tani, K. Mashima, Chem. Lett. 32
(2003) 756;
(h) S. Matsui, T.P. Spaniol, Y. Takagi, Y. Yoshida, J. Okuda, J. Chem.
Soc., Dalton Trans. (2002) 4529;
(i) S. Matsui, Y. Yoshida, Y. Takagi, T.P. Spaniol, J. Okuda, J.
Organomet. Chem. 689 (2004) 1155;
We demonstrated the preparation and characterization
of mono- and bis(iminopyrrolyl) hafnium complexes. From
Hf(NMe2)4, amine elimination reaction was used to pre-
pare bis(amido)-bis(iminopyrrolyl) hafnium complexes (2a–d).
Simple treatment with Me3SiCl led to the quantitative for-
mation of dichloro derivatives (3a–d). On the other hand,
from Hf(CH2Ph)4, mono(iminopyrrolyl) hafnium complex 4a
was isolated by a 1:1 reaction with sterically demanding
iminopyrrole 1a. The activity of bis(iminopyrrolyl) hafnium
complexes 2a–d and 3a–d for ethylene polymerization was
very low (0.7–15.2 kg-PE/mol-cat h); however, complex 4a
became a highly active catalyst for 1-hexene polymeriza-
tion (262–1446 kg-polymer/mol-cat h), upon activation with
[Ph3C][B(C6F5)4].
(j) T. Yasumoto, T. Yamagata, K. Mashima, Organometallics 24 (2005)
3375.
[8] (a) H. Makio, N. Kashiwa, T. Fujita, Adv. Synth. Catal. 344 (2002) 477;
(b) M. Mitani, T. Nakano, T. Fujita, Chem. Eur. J. 9 (2003) 2396;
(c) Y. Suzuki, H. Terao, T. Fujita, Bull. Chem. Soc. Jpn. 76 (2003)
1493;
(d) J. Tian, G.W. Coates, Angew. Chem. Int. Ed 39 (2000) 3626;
(e) J. Tian, P.D. Hustad, G.W. Coates, J. Am. Chem. Soc. 123 (2001)
5134;
(f) P.D. Hustad, G.W. Coates, J. Am. Chem. Soc. 124 (2002) 11578;
(g) M. Fujita, G.W. Coates, Macromolecule 35 (2002) 9640;
(h) S. Reinartz, A.F. Mason, E.B. Lobkovsky, G.W. Coates, Organomet-
gallics 22 (2003) 2542;
Acknowledgements
H.T. thanks the Japan Society for the Promotion of Science
(JSPS) research fellowships for Young Scientists.
(i) A.F. Mason, G.W. Coates, J. Am. Chem. Soc. 126 (2004) 16326.
[9] (a) U. Zucchini, E. Albizzati, U. Giannini, J. Organomet. Chem. 26
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