μ2,η1- N -[(N, N -Dimethylamino)dimethylsilyl] -2,6-diisopropylanilido metal (Li, Zr, Hf) compounds and the catalytic behaviors of the IVB compounds in ethylene (Co)polymerization

Article abstract of DOI:10.1021/om100044b

The dimer of lithium μ₂,η¹-N-[(N,N- dimethylamino)dimethylsilyl]-2,6-diisopropylanilidate [1c, [LiN(2,6- ⁱPr₂C₆H₃)Si(CH₃) ₂N(CH₃)₂]₂ represented as (LiL) ₂] reacted with group 4 chlorides to form corresponding compounds, which were crystallized and confirmed by X-ray diffraction analysis as compounds of pseudotetrahedral ZrL₂Cl₂ (2) and chloro-bridged dinuclear tetrahedral compounds ZrLCl₂(μ-Cl)₂Li'2THF (3), ZrLCl₂(μ-Cl)₂Li'2Et₂O (4), HfLCl ₂(μ-Cl)₂Li'2Et₂O (5), and [ZrLCl ₂(μ-Cl)]₂ (6). The catalytic behaviors of group 4 compounds were investigated in the presence of MAO as a cocatalyst. Compound 4 exhibited high activity for ethylene polymerization, while compounds 2 and 6 showed good activities for both ethylene polymerization and ethylene/1-hexene copolymerization.

Full text of DOI:10.1021/om100044b

Organometallics 2010, 29, 2085–2092 2085
DOI: 10.1021/om100044b
μ2,η1-N-[(N,N-Dimethylamino)dimethylsilyl]-2,6-diisopropylanilido
Metal (Li, Zr, Hf) Compounds and the Catalytic Behaviors of the IVB
Compounds in Ethylene (Co)Polymerizationξ
Shifang Yuan,†,‡ Xuehong Wei,† Hongbo Tong,† Liping Zhang,†,‡ Diansheng Liu,*,† and
Wen-Hua Sun*,‡
†Institute of Applied Chemistry, Shanxi University, Taiyuan 030006, People’s Republic of China, and
‡Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
Received January 20, 2010
The dimer of lithium μ2,η1-N-[(N,N-dimethylamino)dimethylsilyl]-2,6-diisopropylanilidate [1c,
[LiN(2,6-iPr2C6H3)Si(CH3)2N(CH3)2]2 represented as (LiL)2] reacted with group 4 chlorides to form
corresponding compounds, which were crystallized and confirmed by X-ray diffraction analysis
as compounds of pseudotetrahedral ZrL2Cl2 (2) and chloro-bridged dinuclear tetrahedral com-
pounds ZrLCl2(μ-Cl)2Li 2THF (3), ZrLCl2(μ-Cl)2Li 2Et2O (4), HfLCl2(μ-Cl)2Li 2Et2O (5), and
3
3
3
[ZrLCl2(μ-Cl)]2 (6). The catalytic behaviors of group 4 compounds were investigated in the presence
of MAO as a cocatalyst. Compound 4 exhibited high activity for ethylene polymerization, while
compounds 2 and 6 showed good activities for both ethylene polymerization and ethylene/1-hexene
copolymerization.
Introduction
IVB compounds have been extensively explored such as
metallocene derivatives4 and half-metallocene derivatives;5
moreover, the so-called constrained-geometry catalysts
(CGC) of the half-metallocene compounds were finally
commercialized.6 Recently the nonbridged half-metallocene
compounds were found to show high efficiency both in
catalytic activity and in precisely controlling copolymer
properties.7 In addition, the bis(imino)titanium compounds
performed with high activities toward either ethylene poly-
merization or ethylene copolymerization with R-olefins.8
The catalytic behavior of transition metal compounds bear-
ing the silylamido motifs9 acting as versatile ligands in
various reactive patterns10 has been widely explored.11 In
our recent work regarding silylamidolithium and group 4 metal
compounds,12 the highly sensitive μ2,η1-N-[(N,N-dimethy-
lamino)dimethylsilyl]-2,6-diisopropylanilidometal (Li, Zr, Hf)
Organoamidolithium compounds have been extensively
studied for their reactivities and transformation of organo-
amido-metal compounds,1 in which some of them provide
efficient procatalysts in olefin polymerization.2 In trials of
organometallic procatalysts for olefin polymerization,3 the
ξ Dedicated to Prof. Dr. Uwe Rosenthal of the University of Rostock,
Germany, on the occasion of his 60th birthday.
*Corresponding authors. Tel: þ86-10-62557955. Fax: þ86-10-62618239.
E-mail: whsun@iccas.ac.cn (W.-H.S.); dsliu@sxu.edu.cn (D.L.).
(1) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C.
Metal and Metalloid Amides; Ellis Horwood Ltd.: England, 1980.
(2) (a) Guram, A. S.; Jordan, R. F In Comprehensive Organometallic
Chemistry II; Lappert, M. F., Ed.; Elsevier Scientific Ltd: Oxford, 1995; Vol.
4, p 589. (b) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255. (c)
Brintzinger, H. H.; Fischer, D.; M€ulhaupt, R.; Rieger, B.; Waymouth, R. M.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (d) McKnight, A. L.;
Waymouth, R. M. Chem. Rev. 1998, 98, 2587. (e) Resconi, L.; Cavallo,
L.; Fait, A.; Piemontesi, F. Chem. Rev. 2000, 100, 1253.
(3) (a) Ziegler, K.; Gellert, H. G.; Zosel, K.; Lehmkuhl, W.; Pfohl, W.
Angew. Chem. 1955, 67, 424. (b) Ziegler, K.; Holzkamp, E.; Breil, H.;
Martin, H. Angew. Chem. 1955, 67, 541. (c) Natta, G. J. Polym. Sci. 1955,
16, 143. (d) Natta, G.; Pino, P.; Corradini, P.; Danusso, F.; Mantica, E.;
Mazzanti, G.; Moraglio, G. J. Am. Chem. Soc. 1955, 77, 1708. (e) Groppo,
E.; Lamberti, C.; Bordiga, S.; Spoto, G.; Zecchina, A. Chem. Rev. 2005, 105,
115.
(7) (a) Nomura, K. Dalton Trans. 2009, 8811. (b) Nomura, K.; Liu, J.;
Padmanabhan, S.; Kitiyanan, B. J. Mol. Catal. A: Chem. 2007, 267, 1. (c)
Liu, S.; Yi, J.; Zuo, W.; Wang, K.; Wang, D.; Sun, W.-H. J. Polym. Sci., Part
A: Polym. Chem. 2009, 47, 3154. (d) Zuo, W.; Zhang, S.; Liu, S.; Liu, X.;
Sun, W.-H. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 3396. (e) Liu,
S.; Zuo, W.; Zhang, S.; Hao, P.; Wang, D.; Sun, W.-H. J. Polym. Sci., Part A:
Polym. Chem. 2008, 46, 3411.
(8) (a) Matsugi, T.; Fujita, T. Chem. Soc. Rev. 2008, 37, 1264. (b)
Yoshida, Y.; Matsui, S.; Takagi, Y.; Mitani, M.; Nakano, T.; Tanaka, H.;
Kashiwa, N.; Fujita, T. Organometallics 2001, 20, 4793. (c) Yoshida, Y.;
Mohri, J.; Ishii, S.; Mitani, M.; Saito, J.; Matsui, S.; Makio, H.; Nakano, T.;
Tanaka, H.; Onda, M.; Yamamoto, Y.; Mizuno, A.; Fujita, T. J. Am. Chem.
Soc. 2004, 126, 12023. (d) Zuo, W.; Sun, W.-H.; Zhang, S.; Hao, P.; Shiga, A.
J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 3415.
(4) (a) Sinn, H.; Kaminsky, W.; Vollmer, H.-J.; Woldt, R. Angew.
Chem., Int. Ed. Engl. 1980, 19, 390. (b) Kaminsky, W. Macromol. Chem.
Phys. 1996, 197, 3907. (c) Brintzinger, H. H.; Fischer, D.; M€ulhaupt, R.;
Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
€
(d) Alt, H. G.; Koppl, A. Chem. Rev. 2000, 100, 1205.
(5) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587.
(6) (a) Stevens, J. C.; Timmers, F. J.; Wilson, D. R.; Schmidt, G. F.;
Nickias, P. N.; Rosen, R. K.; McKnight, G. W.; Lai, S. Eur. Pat. Appl.
0416815A2, 1991. (b) Shapiro, P. J.; Bunel, E.; Schaefer, W. P.; Bercaw, J. E.
Organometallics 1990, 9, 867. (c) Shapiro, P. J.; Cotter, W. D.; Schaefer,
W. P.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1994, 116, 4623.
(9) Braunschweig, H.; Breitling, F. M. Coord. Chem. Rev. 2006, 250,
2691.
(10) (a) Chomitz, W. A.; Arnold, J. Chem. Commun. 2007, 4797. (b)
Ferreira, H.; Dias, A. R.; Duarte, M. T.; Ascenso, J. R.; Martins, A. M. Inorg.
Chem. 2007, 46, 750. (c) Passarelli, V.; Benetollo, F.; Zanella, P. Eur. J.
Inorg. Chem. 2004, 1714.
r
2010 American Chemical Society
Published on Web 04/16/2010
pubs.acs.org/Organometallics

2086 Organometallics, Vol. 29, No. 9, 2010
Scheme 1. Synthesis of Ligands 1a-c
Yuan et al.
Scheme 2. Synthesis of the Metal Compounds 2-6
compounds were prepared and structurally confirmed. These
Zr and Hf compounds show good activities toward ethylene
(co)polymerization. Here we report the synthesis and charac-
terization of such NSiN chelate complexes in detail and
describe the catalytic activities of the Zr and Hf compounds
toward ethylene (co)polymerizations.
in Scheme 1, and all newly synthesized compounds were
characterized by elemental analyses and NMR spectra, and
by single-crystal X-ray diffraction for colorless crystals of
1a and 1c.
The lithium μ2,η1-N-[(N,N-dimethylamino)dimethylsilyl]-
2,6-diisopropylanilidate dimer (1c) reacted with appropriate
amounts of Zr or Hf chlorides to form corresponding metal
compounds (2-6) (Scheme 2). The reaction of 2 equiv of 1c
to zirconium tetrachloride in THF resulted in a light-colored
solution, which was extracted into toluene and crystallized at
-20 °C to provide colorless crystals of ZrL2Cl2 (2) in a nice
yield. Reactions with a ligand/metal ratio of 1:1 gave com-
pounds of which the molecular structures showed solvent
molecules used in crystallization. For zirconium, the
extracted solution of toluene/THF (4:1) was crystallized at
-10 °C to give red crystals of complex 3, ZrLCl2(μ-
Results and Discussion
Synthesis and Characterization. The reactions of N-sub-
stituted anilines with lithium derivatives commonly formed
anilidolithium dimers.13 The potassium hydrido-anilidate,
without evidence of crystal structure, was proposed as a
reactive intermediate in organic synthesis.14 Although the
acidic properties of the N-H are observed, the stoichio-
metric reaction of 2,6-diisopropylaniline with nBuLi quanti-
tatively formed the dimeric lithium anilide [LiNH(2,6-iPr2-
C6H3) Et2O]2 (1a), with an isolated yield of 97%. Further
3
treatment of [LiNH(2,6-iPr2C6H3) Et2O]2 (1a) with two
Cl)2Li 2THF, which contains trichlorozirconium μ2,η1-
3
3
equivalents of (CH3)2N(CH3)2SiCl in Et2O quantitatively
produced the compound (CH3)2N(CH3)2SiNH(2,6-iPr2-
C6H3) (HL, 1b). The stoichiometric reaction of (CH3)2N-
(CH3)2SiNH(2,6-iPr2C6H3) (HL, 1b) with nBuLi in tetrahy-
drofuran (THF) gave the μ2,η1-N-[(N,N-dimethylamino)-
dimethylsilyl]-2,6-diisopropylanilido lithium dimer [(LiL)2,
1c]. The synthetic procedure of compounds 1a-c is illustrated
N-[(N,N-dimethylamino)dimethylsilyl]-2,6-diisopropylani-
lidate and lithium chloride with two THF molecules. Using
ether to extract metal compounds, both zirconium and
hafnium compounds gave the analogous ether adducts
MLCl2(μ-Cl)2Li 2Et2O (M = Zr, 4; M = Hf, 5). Meanwhile
3
using dichloromethane to extract the zirconium compound
for crystallization at -10 °C, dimer 6, [ZrLCl2(μ-Cl)]2, was
isolated in good yield. Unlike compounds 3-5 crystallized
with an adduct of LiCl, the dichloromethane provided the
chloro interaction with zirconium for cleaving lithium chlor-
ide, and two cationic zirconium units aggregated through
bridging chlorides as dimer 6 in the solid state. The synthetic
procedures and transformation of compounds 2-6 are illu-
strated in Scheme 2.
(11) (a) Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics 2006,
25, 3486. (b) Morello, L.; Yu, P. H.; Carmichael, C. D.; Patrick, B. O.; Fryzuk,
M. D. J. Am. Chem. Soc. 2005, 127, 12796. (c) Kim, S.-J.; Jung, I. N.; Yoo,
B. R.; Cho, S.; Ko, J.; Kim, S. H.; Kang, S. O. Organometallics 2001, 20,
1501. (d) Kim, S.-J.; Jung, I. N.; Yoo, B. R.; Kim, S. H.; Ko, J.; Byun, D.;
Kang, S. O. Organometallics 2001, 20, 2136. (e) Kim, S.-J.; Lee, Y.-J.; Kim,
S. H.; Ko, J.; Cho, S.; Kang, S. O. Organometallics 2002, 21, 5358. (f)
Barroso, S.; Cui, J. L.; Dias, A. R.; Duarte, M. T.; Ferreira, H.; Henriques, R.
T.; Oliveira, M. C.; Ascenso, J. R.; Martins, A. M. Inorg. Chem. 2006, 45,
3532. (g) Passarelli, V.; Benetollo, F.; Zanella, P.; Carta, G.; Rossetto, G.
Dalton Trans. 2003, 1411. (h) Chomitz, W. A.; Minasian, S. G.; Sutton,
A. D.; Arnold, J. Inorg. Chem. 2007, 46, 7199. (i) Brauer, D. J.; B€urger, H.;
Liewald, G. R.; Wilke, J. J. Organomet. Chem. 1986, 310, 317. (j) Veith, M.;
Crystal Structures. X-ray diffraction analysis indicated
that the compound [(2,6-iPr2C6H3)HN Li Et2O]2, 1a, crys-
3
tallized as a centrosymmetric dimer with a planar Li2N2 core
(Figure. 1) with its bond lengths and angles collected in Table
S1 of the Supporting Information. The lithium atoms are
bonded to two bridging NHAr groups with one coordinated
Et2O molecule per lithium. The Li-N distances
€
Frank, W.; Tollner, F.; Lange, H. J. Organomet. Chem. 1987, 326, 315. (k)
Horton, A. D.; With, J. Organometallics 1997, 16, 5424. (l) Shattenmann,
F. J.; Schrock, R. R.; Davis, W. M. Organometallics 1998, 17, 989. (m)
Schumann, H.; Gottfriedsen, J.; Dechert, S.; Girgsdies, F. Z. Anorg. Allg.
Chem. 2000, 626, 747. (n) Hill, M. S.; Hitchcock, P. B. Organometallics
2002, 21, 3258.
(12) (a) Bai, S.-D.; Tong, H. B.; Guo, J. P.; Zhou, M.-S.; Liu, D.-S.;
Yuan, S.-F. Polyhedron 2010, 29, 262. (b) Zhou, M. S.; Zhang, S.; Tong, H.
B.; Sun, W.-H.; Liu, D.-S. Inorg. Chem. Commun. 2007, 10, 1262.
(13) (a) Kennepohl, D. K.; Brooker, S.; Sheldrick, G. M.; Roesky,
H. W. Chem. Ber. 1991, 124, 2223. (b) Ren, G. M.; Shang, D. L.; Guo, J. P.
Acta Crystallogr. E 2007, E63, m793.
˚
(1.997(6)-2.020(6) A) were normal between the Li-N dis-
tances within 1.961-1.962 A and 2.01-2.18 A.15-19 The
13a
˚
˚
(15) Cetinkaya, B.; Hitchcock, P. B.; Lappert, M. F.; Misra, M. C.;
Thorne, A. J. J. Chem. Soc., Chem. Commun. 1984, 148.
(16) Bartlett, R. A.; Chen, H.; Dias, H. V. R.; Olmstead, M. M.;
Power, P. P. J. Am. Chem. Soc. 1988, 110, 446.
(14) (a) Turaeva, D. A.; Kurbatov, Y. V. Russ. J. Org. Chem. 2004,
38, 1691. (b) Turaeva, D. A.; Kurbatov, Y. V. Russ. J. Org. Chem. 2004, 40,
1787.
(17) Tang, Y. J.; Zakharov, L. N.; Rheingold, A. L.; Kemp, R. A.
Inorg. Chim. Acta 2006, 359, 775.
(18) Cole, M. L.; Jones, C.; Junk, P. C. New J. Chem. 2002, 26, 89.

Article
Organometallics, Vol. 29, No. 9, 2010 2087
Figure 1. Molecular structure of compound 1a with thermal
ellipsoids at 30% probability. Hydrogen atoms have been
omitted for clarity.
Figure 2. Molecular structure of compound 1c with thermal
ellipsoids at 30% probability. Hydrogen atoms have been
omitted for clarity.
planar Li2N2 core formed a rhombus. It was also noted that
an agostic interaction between Li and H atoms on the
coordinated CH(CH3)2 was found in this molecule, based
˚
on a short Li H distance of 2.220 A, which was shorter
3 3 3
than that in the related structure [(ad-Dipp)NHLi Et2O]2
3
17
˚
(2.32 A).
The molecular structure of compound 1c formed a chair-
type arrangement of three fused four-membered lithiocyclic
rings with the central Li2N2 and two LiSiN2 rings (Figure 2),
and its bond lengths and angles are collected in Table S2 of
the Supporting Information. The interplanar angle between
the four-membered rings in the backbone of 1c is 87.49°.
Each lithium atom is bonded by three nitrogen atoms in the
N4Li2 core, which gives rise to approximate trigonal-pyra-
midal geometry around both lithium atoms. Four atoms of
two lithium and two nitrogen in the central Li2N2 ring are
˚
coplanar and form a rhombus with sides of 2.02 A and
Figure 3. Molecular structure of compound 2 with thermal
ellipsoids at 30% probability. Hydrogen atoms have been
omitted for clarity.
Li-N-Li0 angles of 73.6(3)°. The Li Li distance
3 3 3
˚
[2.419(11) A] is longer than the previously reported Li Li
3 3 3
[2.397(11) A] in [LiN(SiMe2NMe2)(2,6-Me2C6H3)]2,13b
˚
˚
shorter than that [2.465(7) A] in 1a and those
center is located in an octahedral environment composed by
two anionic μ2,η1-N-[(N,N-dimethylamino)dimethylsilyl]-2,
6-diisopropylanilidates, which were puckered rather than
in a trans arrangement. The dihedral angle of planes
N(1)-Zr-N(2) and N(3)-Zr-N(4) is 86.41°; that of N(1)-
Zr-N(2) and N(1)-Si-N(2) is 7.06° (average vertical dis-
20,21
˚
[2.494(6)-2.521(7) A] in [(XMe2Si)2N]2Li2.
gen donors in 1c do effectively bind to lithium, so that the
The nitro-
Li-N bonding in the central ring is weakened and the
Li Li distance is increased. The dihedral angles between
the aryl ring and the Li2N2 or LiSiN2 ring are 78.48° and
70.74°, respectively. In addition, there were weak interac-
tions between Li and other atoms because of relatively
shorter distances observed for examples of Li-C(l)
3 3 3
˚
tance from Si to the N(1)-Zr-N(2) plane is ca. 0.143 A). The
˚
distances between Zr Si (3.0682(19)-3.0844(18) A) are
3 3 3
˚
too long to form bonds, while the Zr-N bond lengths [2.15 A
for Zr-N(1) and Zr-N(3), 2.50 A for Zr-N(2) and Zr-N-
(4)] indicated differences of direct or coordination bonds.
The shorter Si-N distances [1.71 A for Si-N(1) and 1.77 A
for Si-N(2)] show some double-bond character, indicating a
nonconjugated μ2,η1-N-Si-N group. The aryl ring and
ZrSiN2 ring are approximately vertical, at 84.33°. An analo-
gous situation was identified to take place with the average
Cs symmetry zirconium compounds.11b
˚
˚
˚
(2.485(10) A) and Li-H(11a) (2.669 A).
In the molecular structure of compound 2 (Figure 3) with
its bond lengths and angles collected in Table S3 of
the Supporting Information, the six-coordinate zirconium
˚
˚
(19) Khvorosta, A.; Shutova, P. L.; Harmsa, K.; Lorbertha, J.;
Sundermeyera, J.; Karlovb, S. S.; Zaitseva, G. S. Z. Anorg. Allg. Chem.
2004, 630, 885.
(20) (a) Veith, M.; Koban, A.; Fries, K.; Spaniol, P.; Elsasser, R.;
Rammo, A.; Huch, V.; Kleinsteuber, U. Organometallics 1998, 17, 2612.
(b) Chen, H.; Ruth, A.; Bartlett, H. V.; Dias, R.; Olmstead, M. M.; Philip, P. P.
Inorg. Chem. 1991, 30, 2487.
(21) (a) Antolini, F.; Hitchcock, P. B.; Lappert, M. F.; Merle, P. G.
Chem. Commun. 2000, 1301. (b) Bezombes, J. P.; Hitchcock, P. B.; Lappert,
M. F.; Merle, P. G. J. Chem. Soc., Dalton Trans. 2001, 816. (c) Engelhardt,
L. M.; Jacobsen, G. E.; Junk, P. C.; Raston, C. L.; Skelton, B. W. J. Chem.
Soc., Dalton Trans. 1988, 1011.
The X-ray diffraction study showed that compounds 3-5
have a similar structure to the “ate” complex, and the
molecular structure of compound 3 is illuminated in Figure 4,
while the molecular structures of compounds 4 and 5 are
shown in the Supporting Information, with Tables S4-S6
collecting the bond lengths and angles for compounds 3-5,
respectively. The metal (Zr or Hf) is six-coordinated as a

2088 Organometallics, Vol. 29, No. 9, 2010
Yuan et al.
Figure 5. Molecular structure of compound 6 with thermal
ellipsoids at 30% probability. Hydrogen atoms have been
omitted for clarity.
Figure 4. Molecular structure of compound 3 with thermal
ellipsoids at 30% probability. Hydrogen atoms have been
omitted for clarity.
˚
observed in the above compounds (1.717(5)-1.775(5) A in
˚
˚
2, 1.724(3)-1.778(3) A in 3, and 1.727(4)-1.789(4) A in 4).
The dihedral angle between planes N(1)-Zr-N(2) and N-
(1)-Si-N(2) is 10.78°. The plane N(1)-Si-N(2)-Zr is
nearly perpendicular to the Zr2Cl2 plane with a dihedral
angle of 87.61°, and the dihedral angle between the aryl ring
and N(1)-Si-N(2)-Zr is 88.54°. As a consequence, the aryl
rings and the Zr2Cl2 plane formed a small dihedral angle of
29.83°.
distorted octahedron by one bidentate aminosilylamidate
and four chlorides. The N-M-N angles of 2 [67.47(16)° and
68.05(17)°], 3 [69.64(11)°], 4 [69.51(13)°], and 5 [69.99(15)°]
are far smaller than the right angle for an ideal octahedral
geometry. As observed in compound 2, the μ2,η1-N-Si-N
group is a nonconjugated group that forms one direct Zr-N
˚
bond [2.06 A in both 3 and 4] and one coordination Zr-N
Catalytic Behavior of the Procatalysts 2 and 4-6. The
compounds 2, 4, 5, and 6 were investigated for their catalytic
behaviors of ethylene (co)polymerization. The procatalyst 4
was studied for optimum conditions (entries 1-13 in
Table 1). AlEt3 or Et2AlCl as activator gave little activity
for ethylene polymerization (entries 1, 2 in Table 1). Using
1000 molar ratios of Al to Zr under ambient pressure of
ethylene at 30 °C, the activities observed for ethylene poly-
merization were 1.30 ꢀ 104 g mol(Zr)-1 h-1 atm-1 for
˚
˚
bond [2.41 A in 3, 2.44 A in 4], in which the direct Zr-N bond
˚
length is similar to the data [Zr-N 2.05-2.12 A] for
[HC(Me2SiNR)3Zr(μ-Cl)2Li(Et2O)2].22 The distances of
˚
Zr Si [3.0150(15) A, 3; 3.0071(15) A, 4] prove no interac-
˚
3 3 3
tion between them. Similar structural features are observed
in compound 5. The dihedral angles N(1)-Zr-N(2) and
N(1)-Si-N(2) in 3 are 0.36°, meaning N(1)-Zr-N(2)-Si is
virtually coplanar. The dihedral angles N(1)-M-N(2) and
N(1)-Si-N(2) are 13.79° in 4 and 13.74° in 5 (average
vertical distance from Si to the plane N(1)-M-N(2) is ca.
3
3
3
MMAO (entry 3 in Table 1) and 2.10 ꢀ 104 g mol-
3
(Zr)-1 h-1 atm-1 for MAO (entry 4 in Table 1). Employing
˚
˚
3
3
0.287 A in 4 and ca. 0.285 A in 5).
1000 equiv of MAO, the optimum reaction temperature at 1
bar was 50 °C (entries 4-6 in Table 1), and the best
performance was 2.70 ꢀ 104 g mol(Zr)-1 h-1 atm-1 with
The molecular structure of dinuclear zirconium com-
pound [ZrLCl2(μ-Cl)]2 (6) consists of a discrete centrosym-
metric center (Figure 5), with its bond lengths and angles
collected in Table S7 of the Supporting Information.
The association interactions between two zirconium atoms
are four common bridging zirconium-chlorine bonds
3
3
3
the resulting polyethylene (PE) having a molecular weight
of 337 kg mol-1 and a broad polydispersity (15) (entry 5
3
in Table 1). When the ethylene pressure was increased to
10 atm, both catalytic activities and the molecular weight of
resultant PEs were enhanced (entries 7-13 in Table 1).
Under 10 atm of ethylene pressure at 30 °C, the optimum
Al/Zr ratio was 1000 (entry 8 in Table 1). Increasing the
reaction temperature from 30 to 80 °C gave the highest
activity of 1.73 ꢀ 105 g mol(Zr)-1 h-1 atm-1 at 70 °C
[2.5736(11)-2.6997(11) A].23-26 Each zirconium unit is six-
˚
coordinated and possesses a distorted octahedral geometry.
The benzylamido nitrogen atom and the bridging chloride
ion occupy the axial sites N(1)-Zr-Cl(3) [158.54(9)°]. The
main distortion results from the acute angle Cl(3)-Zr-Cl-
(3)0 [74.15(3)°] in the planar bridging Zr2Cl2 core, while the
amino ligand chelating angle N(1)-Zr-N(2) [70.58(11)°] as
well as the other bond angles around the zirconium center are
3
3
(entry 12 in Table 1). Similarly, the hafnium procatalyst 5
also showed the highest activity of 2.40 ꢀ 104 g mol-
3
(Hf)-1 h-1 atm-1 at 70 °C (entry 17 in Table 1). In general,
˚
3
3
within the usual ranges. The Zr-N direct bond [2.023(3) A]
and coordination bond [2.394(3) A] in 6 are shorter than the
the hafnium procatalyst 5 showed lower activity than its
zirconium analogue 4 did. In both catalytic systems of
zirconium and hafnium, the catalytic activities were greatly
improved with an increase of ethylene pressure, which were
consistent with our former observations because higher
ethylene pressure enhanced the coordination and insertion
of ethylene for fast polymerization.8d,27 The obtained PEs
possessed melting points in the range 133-136 °C, typical for
high-density polyethylene (HDPE). The Tm and Mw values
˚
corresponding values for 2-4; however, the bond lengths of
˚
N-Si [1.738(3)-1.806(3) A] in 6 are longer than those
(22) (a) Gade, L. H.; Memmler, H.; Kauper, U.; Schneider, A.; Fabre,
S.; Bezougli, I.; Lutz, M.; Galka, C.; Scowen, I. J.; McPartlin, M.
Chem.;Eur. J. 2000, 6, 692. (b) Memmler, H.; Walsh, K.; Gade, L. H.
Inorg. Chem. 1995, 34, 4062.
(23) Shafir, A.; Arnold, J. Organometallics 2003, 22, 567.
(24) Zhang, Y. H.; Kissounko, D. A.; Fettinger, J. C.; Sita, L. R.
Organometallics 2003, 22, 21.
(25) Ramos, C.; Royo, P.; Lanfranchi, M.; Pellinghelli, M. A.;
Tiripicchio, A. Eur. J. Inorg. Chem. 2005, 3962.
(26) Gauvin, R. M.; Lorber, C.; Choukroun, R.; Donnadieu, B.;
Kress, J. Eur. J. Inorg. Chem. 2001, 2337.
(27) (a) Zuo, W.; Zhang, M.; Sun, W.-H. J. Polym. Sci., Part A:
Polym. Chem. 2009, 47, 357. (b) Zhang, S.; Sun, W.-H.; Xiao, T.; Hao, X.
Organometallics 2010, 29, 1168.

Article
Organometallics, Vol. 29, No. 9, 2010 2089
Table 1. Ethylene Polymerization with Procatalysts 4 and 5e
Al/Ma
activityb
Tm (°C)c
Mw
Mw/Mn
d
d
entry
procat.
cocat.
P(atm)
T (°C)
1
4
4
4
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
Et2AlCl
AlEt3
MMAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
1
1
30
30
30
30
50
70
30
30
30
50
60
70
80
30
50
60
70
80
200
200
trace
trace
1.30
2.10
2.70
0.80
5.26
5.92
4.43
7.21
10.6
17.3
13.8
0.23
0.83
1.05
2.40
0.96
2
3
1
1000
1000
1000
1000
500
135.3
135.1
134.1
133.3
135.5
134.9
133.5
134.6
134.2
133.7
133.2
135.7
135.2
134.8
134.7
134.5
6.18
3.37
56
15
4
1
5
1
6
1
7
10
10
10
10
10
10
10
10
10
10
10
10
8
1000
1500
1000
1000
1000
1000
1000
1000
1000
1000
1000
16.7
8.2
9
10
11
12
13
14
15
16
17
18
9.07
4.20
3.37
13
9.1
8.7
13.0
24
21
8.12
4.21
15
a M = Zr or Hf. b 104 g mol(M) -1 h-1 atm-1 c Determined by DSC. d 105 g mol-1. Determined by GPC. e Conditions: 5 μmol of procat., 30 min;
.
total volume: 30 mL of toluene at 1 atm or 100 mL of toluene at 10 atm.
3
3
3
3
Table 2. Ethylene Polymerization with Procatalysts 2/MAO and 6/MAOd
activitya
Tm (°C)b
Mw
Mw/Mn
c
c
entry
procat.
P (atm)
T (°C)
Al/Zr
1
2
3
4
5
6
7
8
2
2
2
2
2
2
2
2
6
6
6
6
6
6
6
6
1
10
10
10
10
10
10
10
1
50
30
50
50
50
60
70
80
30
50
70
30
50
60
70
80
1000
1000
500
trace
2.96
2.65
3.36
2.84
5.00
6.92
4.32
trace
0.80
trace
2.84
4.52
6.68
9.76
5.96
135.8
135.6
135.0
133.1
133.8
133.3
133.1
5.43
4.9
1000
1500
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
2.22
2.53
4.6
4.2
9
10
11
12
13
14
15
16
1
1
133.8
4.72
65
10
10
10
10
10
135.4
135.1
134.8
134.2
133. 8
6.37
6.12
24
13
4.11
11
a 104 g mol(Zr) -1 h-1 atm-1 b Determined by DSC. c 105 g mol-1. Determined by GPC. d Conditions: 5 μmol of Zr, 30 min; total volume: 30 mL of
.
toluene at 1 atm of ethylene or 100 mL of toluene at 10 atm of ethylene.
3
3
3
3
of PEs gradually decreased with an increase in the reaction
temperature (entries 1-18 in Table 1).
Ziegler-Natta catalytic system). The resultant PEs have
high molecular weights; for example, with the 1000 Al/Zr
molar ratios under 10 atm of ethylene at 30 °C, procatalyst 4
The procatalysts 2 and 6 were investigated in parallel in the
presence of MAO, and their results were tabulated in Table 2.
In a comparison with results by procatalyst 4, both proca-
talysts 2 and 6 showed relatively lower activities for ethylene
polymerization. Varying the reaction conditions (entries 1-8
for procatalyst 2 and entries 9-16 for procatalyst 6 in
Table 2), the optimum condition was the 1000 Al/Zr molar
ratios under 10 atm of ethylene at 70 °C with the highest
activity of 6.92 ꢀ 104 g mol(Zr)-1 h-1 atm-1 by 2 (entry 7
produced PE with the molecular weight 1670 kg mol-1
3
(entry 8 in Table 1), while PE by 2 showed a molecular
weight of 543 kg mol-1 (entry 2 in Table 2), 1300 kg mol-1
3
3
for PE by 5 (entry 14 in Table 1), and 637 kg mol-1 for PE by
3
6 (entry 12 in Table 2). Moreover, the resultant PEs have
broader molecular weight distributions at lower reaction
temperature, indicating that uniform formation of active
sites requires higher reaction temperatures. Since the poly-
merization is a highly exothermic reaction, the reaction
temperature will rise and accelerate the formation of the
active species.
3
3
3
in Table 2) and 9.76 ꢀ 104 g mol(Zr)-1 h-1 atm-1 by 6
3
3
3
(entry 15 in Table 2), respectively. Given that the only
difference between compounds 3 and 4 is the coordinated
solvent (THF vs Et2O), procatalyst 3 was not investigated
because it was believed to create the same active zirconium
species as its analogue 4.
Although the ethylene polymerization was conducted in a
homogeneous catalytic system, the resultant PEs showed
broad molecular weight distributions (4.2-65) (Tables 1 and 2).
Regarding zirconium procatalysts, procatalyst 2 produced
PE with a low molecular weight and narrow molecular
weight distribution, while 4 produced PE with the highest
molecular weight but slightly broader polydispersity, and
6 gave PE with moderate molecular weight and even
wider molecular distribution. In complex 2, there are two
In all cases, the best activities were observed with the 1000
Al/Zr molar ratio under 10 atm of ethylene at 70 °C. In order
to reduce viscosity of the solution and improve mass trans-
portation at elevated temperatures, the procatalysts should
be activated at 70 °C. Such temperatures are favored for
commercially applicable catalysts (about 80 °C for the

2090 Organometallics, Vol. 29, No. 9, 2010
Yuan et al.
Table 3. Ethylene/1-Hexene Copolymerization with Procatalysts
2/MAO and 6/MAOd
activitya
Tm (°C)b
Mw
Mw/Mn
c
c
entry procat.
T (°C)
1
2
3
4
5
6
7
8
2
2
2
2
6
6
6
6
30
60
70
80
30
60
70
80
3.84
6.98
8.28
6.28
4.84
9.68
10.3
8.96
130.9
129.8
129.1
128.6
130.5
129.2
128.6
127.3
6.07
3.39
17
16
10.6
3.34
33
26
a 104 g mol(Zr) -1 h-1 atm-1 b Determined by DSC. c 105 g mol-1
. .
3
3
3
3
Determined by GPC. d Conditions: 5 μmol of Zr, 30 min, Al/Zr = 1000;
total volume: 100 mL of toluene at 10 atm.
μ2,η1-N-[(N,N-dimethylamino)dimethylsilyl]-2,6-diisopropylani-
lidates occupying spaces around zirconium; therefore the
active species is likely to be uniform, giving PEs with narrow
Mw/Mn. On the other hand, a bulky environment surround-
ing active zirconium caused slow coordination of ethylene
and potentially terminated chain growth, so the PEs ob-
tained by 2 had low molecular weights. It is likely that the
LiCl adduct is removed when forming its active species of
procatalyst 4 with zirconium coordinated with one μ2,η1-
N-[(N,N-dimethylamino)dimethylsilyl]-2,6-diisopropylani-
lidate, which provided more space for monomer coordina-
tion and resulted in PEs showing high molecular weights. In
comparison with 2, procatalyst 4 seems to form a less stable
active species, and although a higher activity was observed
for 4, multiple active sites were formed, leading to PEs with
wide molecular weight distributions. However, the PEs by 6
have wider molecular distributions with molecular weights
between PEs by procatalysts 2 and 4.28,29 Procatalyst 6, being
symmetrically split, is likely to provide the same active sites
as 2, which produced PEs with high molecular weights;
beyond that, dimeric active sites and other mononuclear
active sites may be responsible for PEs with different molec-
ular weights. This would result in PE samples produced with
6 showing wide molecular weight distributions, which is
observed.
Figure 6. 13C NMR spectrum of poly(ethylene-co-1-hexene)
prepared by 6/MAO (entry 7 in Table 3).
values of the copolymers decrease gradually with the reaction
temperatures (entries 1-8 in Table 3), while the copolymers’
molecular weight distributions are broader than polymers in
homopolymerization. Again, copolymers by 2 showed narrow
molecular distributions. Changing copolymerization para-
meters and using a different procatalyst, the molecular weights
and weight distributions of copolymers obtained could be
controlled.
13C NMR analysis of the resultant poly(ethylene-co-1-
hexene) revealed a 13C NMR spectrum of butyl-branched
polyethylene, indicating a typical linear low-density poly-
ethylene (LLDPE).30 It showed about 3% branched carbon
incorporated polymer resulted from 6/MAO (Figure 6).
Summary
The new lithium μ2,η1-N-[(N,N-dimethylamino)dimethylsilyl]-
2,6-diisopropylanilidate dimer (1c) and the μ2,η1-N-[(N,N-
dimethylamino)dimethylsilyl]-2,6-diisopropylanilidometal (zirco-
nium or hafnium) procatalysts 2-6 are synthesized and char-
acterized. The procatalysts 2 and 4-6 showed good activity
Ethylene/1-Hexene Copolymerization. Regarding the high
performance of branched polyolefins,27a,29 the copolymer-
izations of ethylene/1-hexene by 2/MAO and 6/MAO were
successfully carried out, and the results are illustrated in
Table 3. At 10 atm of ethylene pressure, with the Al/Zr molar
ratio of 1000 and 1-hexene (6 mL), the catalytic reactions
were monitored at different temperatures for procatalysts 2
(entries 1-4 in Table 3) and 6 (entries 5-8 in Table 3). The
copolymerization activity is higher than those observed in
homopolymerization of ethylene (Table 2). The best active
values are obtained at 70 °C in the range 20 to 80 °C: 8.28 ꢀ
105 g mol(Zr)-1 h-1 atm-1 for the procatalyst 2 (entry 3 in
toward ethylene polymerization (up to 1.73 ꢀ 105 g mol-
3
(Zr)-1 h-1 atm-1) and gave PEs with broad molecular weight
3
3
distributions. Procatalyst 2, containing two ligands, produced
polymers with relatively narrow molecular weight distributions
because of better stability of its active species, while procatalyst
4, bearing one ligand, showed high activity and produced
polymers with high molecular weights but wider molecular
weight distributions. The dimeric procatalyst 6 apparently
provides multiple active species and produces polymers with
wider molecular weight distributions. In the copolymerization
of ethylene with 1-hexene, the resultant copolymers indicated
nice incorporation of 1-hexene, and these procatalysts are
promising for further investigation. More importantly, the
current zirconium procatalysts exhibited excellent thermal
stability at 70 °C regarding the aspect of industrial requirement.
3
3
3
Table 3) and 1.03 ꢀ 105 g mol(Zr)-1 h-1 atm-1 for the
3
3
3
procatalyst 6 (entry 7 in Table 3). The introduction of 1-hexene
produces butyl branches, which results in lower melting points
(127-131 °C) than linear polyethylene. Both Tm and Mw
(28) (a) Vollmerhaus, R.; Rahim, M.; Tomaszewski, R.; Xin, S.;
Taylor, N. J.; Collins, S. Organometallics 2000, 19, 2161. (b) Xie, G.;
Qian, C. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 211. (c) Kim,
W. K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.; Theopold, K. H.
Organometallics 1998, 17, 4541.
(29) (a) Hong, H.; Zhang, Z.; Chung, T. C.; Lee, R. W. J. Polym. Sci.,
Part A: Polym. Chem. 2007, 45, 639. (b) Smit, M.; Zheng, X.; Loos, J.;
Chadwick, J. C.; Koning, C. E. J. Polym. Sci., Part A: Polym. Chem. 2006,
44, 6652.
(30) (a) Yano, A.; Gasegawa, S.; Kaneko, T.; Sone, M.; Sato, M.;
Akimoto, A. Macromol. Chem. Phys. 1999, 200, 1542. (b) Quijiada, R.;
Galland, G. B.; Mauler, R. S.; de Menezes, S. C. Macromol. Rapid
Commun. 1996, 17, 607. (c) Chu, K.-J.; Soares, J. B. P.; Penlidis, A.
Macromol. Chem. Phys. 2000, 201, 340. (d) Zhang, Y.; Yang, X.; Yu, Y.;
Qian, Y.; Huang, J. Chin. J. Chem. 2005, 23, 1081. (e) Czaja, K.; Bialek, M.
Polymer 2001, 42, 2289.

Article
Organometallics, Vol. 29, No. 9, 2010 2091
Experimental Section
was layered on the yellow solution to obtain the product 1c (0.55 g)
in 97% isolated yield as colorless crystals. H NMR (300 MHz
1
3
General Procedures. All manipulations were carried out under
an atmosphere of argon using standard Schlenk techniques.
Deuterated solvents C6D6 and CDCl3 were dried over activated
C6D6): δ 0.38 (s, 6H, Si(CH3)2), 1.34, 1.49 (q, 12H, JHH
=
6.0 Hz, CH(CH3)2), 2.46 (s, 6H, N(CH3)2), 3.87 (m, 2H, CH-
(CH3)2), 7.32-7.35 (m, 2H, m-Ph), 7.42 (m, 1H, p-Ph). 13C NMR
(75 MHz C6D6): δ -0.08 (Si(CH3)2), 24.04, 25.14 (CH(CH3)2),
27.33 (CH(CH3)2), 40.08 (N(CH3)2), 119.23 (p-Ph), 122.99, 123.63
(m-Ph), 142.66 (o-Ph), 148.66 (ipso-CPh).
˚
molecular sieves (4 A) and vacuum transferred before use.
Hexane was dried over sodium potassium alloy. Diethyl ether
was dried and distilled from sodium/benzophenone and stored
over a sodium mirror under argon. Dichloromethane was
Bis{μ2,η1-N-[(N,N-dimethylamino)dimethylsilyl]-2,6-diisopropyl-
anilido}zirconium Dichloride [ZrL2Cl2, 2]. To a solution of 1c
(0.57 g, 1 mmol) in 25 mL of THF at -78 °C was added ZrCl4
(0.23 g, 1 mmol). The resulting mixture was stirred for a while,
then warmed to room temperature and kept stirring for 24 h.
Volatile compounds were removed in vacuo, and the resulting
residue was extracted with toluene and filtered. The filtrate was
concentrated in vacuo to ca. 10 mL. The compound 2 was
crystallized at -20 °C as colorless crystals (0.49 g) in 69% yield.
Mp: 57-58 °C (dec). Anal. Calcd for C32H58Cl2N4Si2Zr: C,
˚
distilled from activated molecular sieves (4 A). Toluene was
refluxed in the presence of sodium/benzophenone and distilled
under nitrogen prior to use. The NMR spectra were recorded on
a Bruker DKX-300 spectrometer with TMS as the internal
standard. Elemental analyses were performed with a Flash EA
1112 microanalyzer. The polymerization-grade ethylene was
supplied by Beijing Yansan Petrochemical Co. Et2AlCl (1.90
M in toluene) and AlEt3 (2.0 M in hexane) were purchased from
Acros Chemicals, while methylaluminoxane (MAO, 1.46 M in
toluene) and modified methylaluminoxane (MMAO, 1.93 M in
heptane) were purchased from Ablemarle Corp. 13C NMR
spectra of the copolymers were recorded on a Bruker DMX-
300 MHz instrument at 135 °C in deuterated 1,2-dichloroben-
zene with TMS as an internal standard. The GPC curves were
obtained by plotting detector response versus elution volume
using polystyrene standards (with an approximate polydisper-
sity index). Further fractionalization of fractions was not per-
formed. Melting points of polyolefins were measured on a
Perkin-Elmer DSC-7 differential scanning calorimetry (DSC)
analyzer. Under a nitrogen atmosphere, a sample of about
2.0-6.0 mg was heated from 50 to 160 °C at a rate of 10 °C/
min and kept for 5 min at 160 °C to remove the thermal history,
then cooled at a rate of 10 °C/min to 50 °C. The DSC trace and
the melting points of the samples were obtained from the second
scanning run.
1
53.53; H, 8.09; N, 7.84. Found: C, 53.50; H, 8.12; N, 7.86. H
NMR (300 MHz CDCl3): δ 0.39-0.66 (d, 12 H, Si(CH3)2), 1.11,
1.24 (m, 24H, JHH = 6.6 Hz, CH(CH3)2), 3.59 (m, 4H, CH-
3
(CH3)2), 2.80-3.02 (d, 12H, N(CH3)2), 6.97-7.01(m, 4H, m-Ph),
7.09-7.11 (m, 2H, p-Ph). 13C NMR (75 MHz CDCl3): δ 3.55
(Si(CH3)2), 22.50, 23.09, 23.44, 24.29, 24.71, 25.11, 25.42, 25.67
(CH(CH3)2), 26.26, 26.93, 36.49, 41.46 (CH(CH3)2), 43.90, 45.09
(N(CH3)2), 121.78, 122.49 (p-Ph), 122.88, 123.18 (m-Ph), 140.50,
141.54, 142.47, 145.31 (ipso-CPh).
μ2,η1-N-[(N,N-Dimethylamino)dimethylsilyl]-2,6-diisopropylani-
lidozirconium Chloride-Lithium Chloride THF Adduct [ZrLCl2-
(μ-Cl)2Li 2THF, 3]. Using a similar procedure to that for 2 but
3
with equimolar reactants of lithium and zirconium, the resultant
residue was extracted with toluene and filtered. The filtrate was
dried in vacuo and dissolved in a mixture of toluene and THF (4:1)
at -10 °C to obtain compound 3 as red crystals (1.03 g) in 78%
yield. Mp: 149-151 °C (dec). Anal. Calcd for C24H43Cl4LiN2O2-
SiZr: C, 43.52; H, 6.80; N, 4.28. Found: C, 43.46; H, 6.82; N, 4.31.
1H NMR (300 MHz CDCl3): δ 0.36 (s, 6H, Si(CH3)2), 1.17, 1.27
(q, 12H, 3JHH = 6.3 Hz, CH(CH3)2), 1.89 (s, 8H, THF), 2.33 (m,
2H, 3JHH = 6.3 Hz, CH(CH3)2), 2.90 (s, 6H, N(CH3)2), 3.90 (s,
8H, THF), 7.03-7.23 (m, 3H, Ph). 13C NMR (75 MHz CDCl3): δ
1.56 (Si(CH3)2), 27.06, 28.16 (CH(CH3)2), 29.45 (CH(CH3)2),
30.02 (THF), 49.07 (N(CH3)2), 72.30 (THF), 127.97 (p-Ph),
131.34 (m-Ph), 145.43, 147.80 (ipso-CPh).
Lithium μ2-2,6-Diisopropylhydridoanilidoanilidate Dimer Ether
Adduct ([(2,6-iPr2C6H3)HNLi Et2O]2, 1a). To a solution of
2,6-diisopropylbenzenamine (2.0 mL, 10 mmol) in 25 mL
3
n
of Et2O at 0 °C was added dropwise BuLi (3.50 mL, 2.86 M,
10 mmol) to form a colorless solution. The mixture was warmed
to room temperature and kept stirring for 6 h. Hexane (25 mL)
was layered on the solution to obtain the product 1a (2.48 g) in
1
97% yield as colorless crystals. H NMR (300 MHz C6D6): δ
3
1.04-1.09 (t, 6H, CH3, Et2O), 1.22, 1.26 (q, 12H, JHH
=
μ2,η1-N-[(N,N-Dimethylamino)dimethylsilyl]-2,6-diisopropylani-
lidozirconium Chloride-Lithium Chloride Ether Adduct [ZrLCl2-
6.9 Hz, CH(CH3)2), 1.45 (s, 1H, NH), 2.94-2.98 (m, 2H, CH-
(CH3)2), 3.21-3.28 (m, 4H, CH2, Et2O), 6.86 (m, 1H, p-Ph),
7.20-7.22 (m, 2H, o,m-Ph). 13C NMR (75 MHz C6D6): δ
15.96 (CH3, Et2O), 23.92, 24.29 (CH(CH3)2), 28.14, 29.24
(CH(CH3)2), 66.53 (CH2, Et2O), 112.61, 119.73, 123.82,
124.35, 132.74, 156.92 (Ph).
(μ-Cl)2Li 2Et2O, 4]. The same procedure as the synthesis of
3
compound 3 was used; however, its product was dissolved in ether
and crystallized to give yellow crystals of compound 4 (0.84 g) in
63% yield. Mp: 82-83 °C (dec). Anal. Calcd for C24H49Cl4Li-
N2O2SiZr: C, 43.26; H, 7.36; N, 4.23. Found: C, 43.23; H, 7.34; N,
4.27. 1H NMR (300 MHz CDCl3): δ 0.17 (s, 6H, Si(CH3)2), 1.01
(d, 12H, 3JHH = 7.2 Hz, CH(CH3)2), 1.23 (s, 12H, Et2O), 2.71 (s,
6H, N(CH3)2), 3.32 (s, 8H, Et2O), 3.63 (m, 2H, CH(CH3)2),
6.87 (m, 3H, Ph). 13C NMR (75 MHz CDCl3): δ -0.09 (Si(CH3)2),
25.25, 28.27 (CH(CH3)2), 27.75, 28.69 (CH(CH3)2),46.88(N(CH3)2),
124.86 ( p-Ph), 125.16 (m-Ph), 143.49, 146.25 (ipso-CPh).
N-[(N,N-Dimethylamino)dimethylsilyl]-2,6-diisopropylaniline
((CH3)2N(CH3)2SiNH(2,6-iPr2C6H3) as HL, 1b). To a solution
of 1a (2.54 g, 5 mmol) in 25 mL of hexane at 0 °C was dropwise
transferred Me2NMe2SiCl (1.49 mL, 10 mmol) to form a color-
less solution, which gradually turned to a white, cloudy solu-
tion. The mixture was warmed to room temperature and stirred
for 12 h. The resulting white residue was filtered, and the filtrate
was concentrated. Oily compound 1b was formed (2.78 g) in
98% yield. Attempts to purify the product by extraction with
hexanes were unsuccessful because of the high solubility of the
yellow oil in all these solvents. 1H NMR (300 MHz CDCl3): δ
μ2,η1-N-[(N,N-Dimethylamino)dimethylsilyl]-2,6-diisopropylani-
lidohafnium Chloride-Lithium Chloride Ether Adduct [HfLCl2-
(μ-Cl)2Li 2Et2O, 5]. Using the same procedure of synthesis as
3
compound 3, with hafnium chloride instead of zirconium chloride,
light yellow crystals of compound 5 (0.89 g, 59% yield) were
obtained from its ether solution. Mp: 63-64 °C (dec). Anal. Calcd
for C24H49Cl4LiN2O2SiHf: C, 38.25; H, 6.51; N, 3.72. Found: C,
38.21; H, 6.53; N, 3.76. 1H NMR (300 MHz CDCl3): δ 0.37 (s, 6H,
Si(CH3)2), 1.20 (d, 12H, 3JHH = 7.2 Hz, CH(CH3)2), 1.27 (t, 12H,
3
0.13 (s, 6H, Si(CH3)2), 1.18, 1.20 (d, 12H, JHH = 6.9 Hz, CH-
(CH3)2), 2.52 (s, 6H, N(CH3)2), 3.34-3.41 (m, 2H, CH(CH3)2),
6.95-6.99 (m, 1H, p-Ph), 7.04-7.09 (m, 2H, o,m-Ph).
Lithium μ2,η1-N-[(N,N-Dimethylamino)dimethylsilyl]-2,6-di-
isopropylanilidate Dimer ([Li(CH3)2N(CH3)2SiN(2,6-iPr2C6H3)]2
as (LiL)2, 1c). To a solution of 1b (0.59 g, 2 mmol) in 25 mL of THF
at 0 °C was dropwise added nBuLi (0.7 mL, 2.86 M, 2 mmol) to
form a colorless solution, which gradually disappeared and chan-
ged to a yellow solution. The mixture was warmed to room
temperature and kept stirring for 12 h. Then 25 mL of hexane
3JHH = 6.6 Hz, Et2O), 2.97 (s, 6H, N(CH3)2), 3.50 (q, 8H, 3JHH
=
6.9 Hz, Et2O), 3.92 (m, 2H, CH(CH3)2), 7.08 (m, 1H, p-Ph), 7.11
(m, 2H, m-Ph). 13C NMR (75 MHz CDCl3): δ -0.09 (Si(CH3)2),
24.57 (CH(CH3)2), 27.24 (CH(CH3)2), 46.48 (N(CH3)2), 123.75
(o-Ph), 144.17 (ipso-CPh).

2092 Organometallics, Vol. 29, No. 9, 2010
Yuan et al.
μ2,η1-N-[(N,N-Dimethylamino)dimethylsilyl]-2,6-diisopropylani-
lidozirconium Chloride Dimer {[ZrLCl2(μ-Cl)]2, 6}. The same
procedure as the synthesis of compound 3 was used; however,
its product was dissolved in dichloromethane and crystallized at
-10 °C to give yellow crystals of compound 6 (0.77 g) in 81%
yield. Mp: 52-53 °C (dec). Anal. Calcd for C32H58Cl6N4Si2Zr2:
C, 40.68; H, 6.14; N, 5.93. Found: C, 40.71; H, 6.12; N, 5.90. 1H
NMR (300 MHz CDCl3): δ 0.10 (s, 6H, Si(CH3)2), 1.12 (d, 12H,
3JHH = 7.2 Hz, CH(CH3)2), 3.34 (m, 2H, CH(CH3)2), 2.06 (s, 6H,
N(CH3)2), 6.65 (m, 3H, Ph). 13C NMR (75 MHz CDCl3): δ -0.01
(Si(CH3)2), 25.54, 28.69 (CH(CH3)2), 27.51, 28.88 (CH(CH3)2),
46.78 (N(CH3)2), 124.60 (p-Ph), 125.57 (m-Ph), 143.47, 146.51
(ipso-CPh).
Procedures for Ethylene Polymerization. Polymerization at 1
atm of Pressure. The metal compound (5 μmol) was added to a
Schlenk-type flask under nitrogen. This flask was backfilled
three times with nitrogen and twice with ethylene, then charged
with the required amount of freshly distilled toluene. At the
chosen temperature, the reaction solution was vigorously stirred
under 1 atm of ethylene for the desired period of time after
adding the desired amount of MAO solution. The polymeriza-
tion reaction was quenched by adding 10% HCl-ethanol solu-
tion (60 mL), and then the mixture was poured into 100 mL of
ethanol to precipitate the polymer, which was further washed
with ethanol and water followed by drying under vacuum at
60 °C to its constant weight. In the case of ethylene/1-hexene
copolymerization, 1-hexene (dried with calcium hydride) in
toluene was added prior to the addition of MAO.
recharged with ethylene three times, then cooled to room
temperature. A toluene solution of the catalysts (and monomer)
was transferred to the reactor, which was then maintained at
the desired temperature. MAO solution to give a final volume of
100 mL was then added to start the polymerization; then the
autoclave was immediately pressurized to the desired pressure.
After 30 min, the autoclave was placed in a water-ice bath for
an hour, then opened with adding 10% HCl-acidic ethanol.
The solid polyolefin was washed with ethanol and water several
times and then dried under vacuum to constant weight.
X-ray Crystallography. Data collection of 1a, 1c, and 2-6 was
˚
performed with Mo KR radiation (λ = 0.71073 A) on a Bruker
Smart Apex CCD diffractometer at 173(2) or 213(2) K. Crystals
were coated in oil and then directly mounted on the diffract-
ometer under a stream of cold nitrogen gas. A total of N
reflections were collected by using the ω scan mode. Intensities
were corrected for Lorentz and polarization effects and empiri-
cal absorption. The structures were solved by direct methods and
refined by full-matrix least-squares on F2. All non-hydrogen
atoms were refined anisotropically. Structure solution and refine-
ment were performed by using the SHELXL-97 package.31
Crystal data collection and refinement details for all compounds
are available in Table S8 of the Supporting Information.
Acknowledgment. We thank the Natural Science Foun-
dation of China (20772074 and 20874105) and SXNSF
(2008011021 and 2008012013-2).
Polymerization at 10 atm of Pressure. For polymerization at
higher ethylene pressure, a stainless steel autoclave (0.5 L
capacity) equipped with gas ballast through a solenoid clave
for continuous feeding of ethylene at constant pressure was
used. The autoclave was heated under vacuum to over 80 °C and
Supporting Information Available: The GPC diagrams of
corresponding polyolefins, molecular structures of compounds
4 and 5, bond lengths and angles of compounds 1a, 1c, and 2-6,
crystal data and processing parameters for compounds 1a, 1c,
and 2-6, and a CIF file giving crystallographic data. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(31) Sheldrick, G. M. SHELXL-97, Program for the Solution of
€
€
Crystal Structures; University of Gottingen: Gottingen, Germany, 1997.