Syntheses and structures of non-symmetric guanidinato zirconium and hafnium complexes and their catalytic behavior for ethylene polymerization

Article abstract of DOI:10.1016/j.jorganchem.2007.07.051

Equivalent addition reactions of PhN(Li)SiMe₃ to nitriles, RCN (R = dimethylamido, 1-piperidino), generated non-symmetric guanidinato lithium [(Et₂O)LiN(SiMe₃)C(NMe₂)N(Ph)]₂ (1) or [(THF)LiN(SiMe

Full text of DOI:10.1016/j.jorganchem.2007.07.051

Journal of Organometallic Chemistry 692 (2007) 5195–5202
www.elsevier.com/locate/jorganchem
Syntheses and structures of non-symmetric guanidinato zirconium
and hafnium complexes and their catalytic behavior for
ethylene polymerization
*
Meisu Zhou, Hongbo Tong, Xuehong Wei, Diansheng Liu
Institute of Applied Chemistry, Shanxi University, Taiyuan 030006, PR China
Received 9 July 2007; received in revised form 30 July 2007; accepted 31 July 2007
Available online 6 August 2007
Abstract
Equivalent addition reactions of PhN(Li)SiMe3 to nitriles, RCN (R = dimethylamido, 1-piperidino), generated non-symmetric
guanidinato lithium [(Et2O)LiN(SiMe3)C(NMe2)N(Ph)]2 (1) or [(THF)LiN(SiMe3)C(NMe2)N(Ph)]2 (2) and [(Et2O)LiN(SiMe3)C-
(N(CH2)5)N(Ph)]2 (5) which further reacted with zirconium or hafnium tetrachloride to form Zr and Hf guanidinato complexes with
the general formula [PhNC(R)NSiMe3]3MCl (R = dimethylamido, M = Zr (3), Hf (4); R = 1-piperidino, M = Zr (6), Hf (7)). Complexes
1–4, 6 and 7 were well characterized by 1H, 13C NMR and microanalysis, the single crystal X-ray diffraction analysis data for complexes
1, 3, 4 and 7 were also provided. Furthermore, complexes 3, 4, 6 and 7 were found to be active for ethylene polymerization. The influ-
ences of cocatalyst, pressure, reaction temperature and Al/M ratio on activity were investigated.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Guanidinato complexes; Synthesis; Structure; Ethylene polymerization
1. Introduction
plexes of group IVB, the wide investigations have recog-
nized that they could be used as the alternatives of
unique cyclopentadienyl species in order to form suitable
catalytic sites for the polymerization of a-olefins [5–8], fur-
thermore, zirconium complexes with co-ligands of amidi-
nato and Cp ring showed some special intramolecular
reactivity and extreme activities for the living polymeriza-
tion of (sterically encumbered) a-olefins at low temperature
[9]. Guanidinate-supported titanium imido complexes were
prepared and firstly used as a catalyst for alkyne hydroam-
ination [10]. Recently, zirconium-amido guanidinato com-
plex was used as a potential precursor for the CVD of
ZrO2 thin films [11].
The first linked guanidinato ligand system and its Ti and
Zr complexes were synthesized and demonstrated that the
two of guanidinato moieties resulted in changes to ligand
geometry and metal coordination behavior and difference
of the reactivity from unlinked analogues [12]. Our previ-
ous works involved the b-diketiminato and amidinato
metal complexes, which were prepared from the reaction
Both of guanidine and amidine compounds have
received increased attentions from 1980s because of their
steric and electronic flexibility, the variety of possible coor-
dination modes. Especially for guanidines, they can form
neutral, monoanionic [(RN)2CNR2]ꢀ or dianionic
[(RN)3C]2ꢀ forms. These features mean that guanidinates
have the potential to develop into valuable ancillary
ligands in coordination and organometallic chemistry [1].
Beyond the fundamental investigation of guanidinate com-
plexes related to their structural features, some guanidinato
complexes have been identified as initiators or catalysts for
polymerization reactions, e.g., trimethylene carbonate and
its copolymerization with e-caprolactone [2], the polymeri-
zation of lactide [3], the polymerization of a-olefins [3], or
the polymerization of styrene [4]. Regarding to the com-
*
Corresponding author. Tel.: +86 351 7018091; fax: +86 351 7016048.
E-mail address: dsliu@sxu.edu.cn (D. Liu).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.051

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M. Zhou et al. / Journal of Organometallic Chemistry 692 (2007) 5195–5202
of amido anions with nitriles and had the electronic prop-
erties of the delocalized p-electrons [13–18]. Some early and
late transition metal complexes were studied for the consid-
eration of potential precursors in ethylene polymerization
[13]. In this work, the addition reactions of PhN(Li)SiMe3
to nitriles were carried out to generate non-symmetric
guanidinato lithium, which reacted with zirconium and
hafnium tetrachloride provides a series of triguanidinato
Zr(IV) or Hf(IV) chloride, respectively. The zirconium
and hafnium metal complexes showed moderate catalytic
activity in ethylene polymerization.
Treatment of PhN(Li)SiMe3 with (CH3)2NCN in n-hex-
ane and recrystallization from Et2O gave complex 1 as col-
orless crystals in 80% yield. Complex 2 was obtained in
44% yield from the reaction of PhN(Li)SiMe3 with
(CH3)2NCN in THF and recrystallized from THF as well.
The colorless crystalline complex 2 was very air-sensitive
and changed into red when it exposed to air. The lithium
salt 5 was not isolated but was generated in situ in similar
procedure to complex 1.
The non-symmetric guanidine ligands were designed to
form complex with zirconium and hafnium for the consid-
eration of potential precursor for the polymerization of
ethylene. However, attempts for the equivalent ligand/
metal complexes with formula of LMCl3 (M = Zr or Hf)
from the reactions of 1 with an equivalent portion of
MCl4 in THF at ꢀ78 ꢁC were not successful. So did the
equivalent reaction of 5 with ZrCl4 or HfCl4, even no mat-
ter THF or Et2O as solvent could not help the reaction for
available complexes. Therefore the reactions with different
molar ratio of guanidinato ligands to MCl4 are explored
and finally reproducible reaction with good yield of com-
plexes with molar ratio of guanidinato lithium to MCl4
as 3:1 was carried out in THF or hexane. The reaction of
1 with one third molar ratio of ZrCl4 or HfCl4 in THF at
ꢀ78 ꢁC led to colorless crystalline complexes [PhNC-
2. Results and discussion
2.1. Synthesis and characterization of complexes 1–7
The symmetric guanidinate ligand and complexes were
commonly studied because they could be easily formed
by an insertion reaction of carbodiimides RN@C@NR into
a metal alkyl amide bond [19–22]. Our non-symmetric gua-
nidine ligands, [N(Ph)–C(R)–N(SiMe3)]Li (1, R = NMe2,
5, 1-piperidino), were prepared from the reaction of
PhN(Li)SiMe3with dimethylcyanmide or 1-piperidinecar-
bonitrile. The synthetic routes to complexes 1–7 are illus-
trated in Scheme 1.
R'
R'
N R
Ph N
R
1/3 MCl4
Et2O
R
N
N
Ph
Cl
Li
N
M
Ph
R'
THF
CH2Cl2
N
N
R'
N
Li
N
Ph
Ph
OEt2
N
R
R
R'
3 M = Zr, R = SiMe3, R' =Me2N
4 M = Hf, R = SiMe3, R' =Me2N
1
R = SiMe3, R' =Me2N
Hexane
Et2O
R'CN
R'
R
THF
Li
N
R'CN
Hexane
THF
N
Ph
Ph NLi(R)
R = SiMe3
Ph
N
N
Li
THF
R
R'
2
R = SiMe3, R' =Me2N
R''CN
Hexane
R''
N R
Ph N
R''
R
N
Cl
1/3 MCl4
Hexane
M
Ph
R''
N
N
R''
Ph N
N
R
Ph
Li+
2
N
R
5
N
R = SiMe3, R'' =
6 M = Zr, R = SiMe3, R'' =1-piperidino
7 M = Hf, R = SiMe3, R'' =1-piperidino
(1-piperidino)
Scheme 1. Synthetic routes to complexes 1–7.

M. Zhou et al. / Journal of Organometallic Chemistry 692 (2007) 5195–5202
5197
˚
(NMe2)NSiMe3]3ZrCl (3) and [PhNC(NMe2)NSiMe3]3
HfCl (4), respectively. These complexes could be easily
recrystallized to get single crystals suitable for X-ray anal-
ysis in dichloromethane. Similarly, the complexes
[PhNC(N(CH2)5)NSiMe3]3ZrCl (6) and [PhNC(N(CH2)5)-
NSiMe3]3HfCl (7) were obtained by treatment of 5 with
one third portion of ZrCl4 or HfCl4 in hexane at ꢀ78 ꢁC
and the single crystals of 7 were obtained from recrystalli-
zation in hexane.
the C–N distances [N(1)–C(1) = 1.323(5) A, N(2)–C(1) =
1.340(5) A].
˚
The X-ray data for complex 2 is enough to confirm the
outline of the molecule but does not meet the standards of
the Journal.
An X-ray study of complex 3 (Fig. 2, Table 2) reveals a
‘‘propeller’’-like structure, in which three ligands as leaf
blades with the metal–chloride bond as leafstalk. Owing
to the propeller-like structure, three trimethylsilyl groups
are located close to the chlorine atom and the three phenyl
groups are arranged on the trans-position to the chlorine.
2.2. Molecular structures of complexes 1–4 and 7
˚
In complex 3, the Zr–Cl bond distance [2.515(15) A] is
The molecular structure of crystalline 1 is illustrated in
Fig. 1 and the selected bond lengths and angles are listed
in Table 1. The molecular structure of 1 is a dimmer built
around planar LiNLiN ring and the angles at the nitrogen
atom are narrower [73.5(3)ꢁ] than those at the Li atom
[106.5(3)ꢁ]. One lithium atom is coordinated with three N
and one O atom (Et2O). The core of the centrosymmetric
molecule 1 has a fused tricyclic ladder motif comprising a
central planar N2Li1N20Li10 ring flanked by planar
N1C1N2Li1 and N10C10N20Li10 rings. The dihedral angle
between them is 63.6ꢁ. The electronic delocalization
throughout the guanidinate moiety is observed from
longer than the corresponding values found for the earlier
examples having such structure as L3ZrCl including sym-
metric zirconium benzamidinate [(Siam)3ZrCl] [Siam =
N,N bis(trimethylsilyl)benzamidinat]] [Zr–Cl 2.464(2) A]
[23] and non-symmetric chiral zirconium benzamidinate
complex [{C6H5C(N-TMS)(N-myrtanyl)}3ZrCl] [Zr–Cl
0
˚
˚
˚
2.475(3) A] [24]. The Zr–N bond lengths of 2.216(4)–
2.292(4) A are consistent with the values previously
reported [24,25]. For the CN3 framework, the three C–N
bond distances in the guanidinate ligand are N1–C7
Fig. 2. Molecular structure of compound 3.
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) of compound 3
˚
Bond lengths (A)
Bond angles (ꢁ)
Fig. 1. Molecular structure of compound 1.
Zr(1)–Cl(1)
Zr(1)–N(1)
Zr(1)–N(2)
Zr(1)–N(4)
Zr(1)– N(5)
Zr(1)–N(7)
Zr(1)–N(8)
N(1)–C(7)
N(2)–C(7)
N(3)–C(7)
N(6)–C(19)
N(9)–C(31)
2.5151(15)
2.291(4)
2.219(4)
2.285(4)
2.216(4)
2.292(4)
2.217(4)
1.343(6)
1.334(6)
1.378(6)
1.381(6)
1.371(6)
N(1)–Zr(1)–N(2)
N(4)–Zr(1)–N(5)
N(7)–Zr(1)–N(8)
N(1)–C(7)–N(2)
N(4)–C(19)–N(5)
N(7)–C(31)–N(8)
N(1)–Zr(1)–Cl(1)
N(2)–Zr(1)–Cl(1)
N(4)–Zr(1)–Cl(1)
N(5)–Zr(1)–Cl(1)
N(7)–Zr(1)–Cl(1)
N(8)–Zr(1)–Cl(1)
59.24(15)
59.36(14)
59.06(14)
112.8(5)
113.3(5)
112.9(5)
128.55(11)
83.17(11)
129.54(11)
83.65(11)
128.65(10)
83.37(11)
Table 1
˚
Selected bond lengths (A) and angles (ꢁ) of compound 1
˚
Bond lengths (A)
Bond angles (ꢁ)
C(1)–N(1)
C(1)–N(2)
C(1)–N(3)
N(1)–Li(1)
N(2)– Li(1)
N(20)–Li(1)
Li(1)–O(1)
1.323(2)
1.341(2)
1.391(2)
1.997(3)
2.201(3)
2.057(3)
1.977(3)
N(1)–C(1)–N(2)
N(1)–C(1)–N(3)
N(1)–Li(1)–N(2)
Li(1)–N(2)–Li(10)
118.20(14)
120.95(12)
65.79(9)
73.56(14)

5198
M. Zhou et al. / Journal of Organometallic Chemistry 692 (2007) 5195–5202
˚
˚
˚
1.343(6) A, N2–C7 1.334(6) A and N3–C7 1.378(6) A,
respectively. All of these bond distances are roughly in
possibility of p overlap between these two moieties. In
the case of 3 and 4, the torsional angles between these
two planes are 40.3ꢁ (3) and 39.8ꢁ (4), respectively. They
are much smaller than that in [{iPrNC[N(SiMe3)2]-
NiPr}2ZrCl2] [88.2ꢁ], [{CyNC[N(SiMe3)2]NCy}2ZrCl2]
[86.3ꢁ] or [{CyNC[N(SiMe3)2]NCy}2HfCl2] [85.8ꢁ] [25],
suggest that the steric interaction between the phenyl or tri-
methylsilyl and the dimethylamido group is somewhat lim-
ited and is not big enough to eliminate the p conjugation.
In fact, the sum of 359.8ꢁ (3) and 359.9ꢁ (4) for the three
bond angles around N atom in dimethylamido group are
consistent with the sp2 hybridization necessary for
conjugation.
Crystals of 6, obtained from hexane, were of poor qual-
ity but the data were adequate to establish its structure as
shown in Scheme 1. In complex 7 (Fig. 4, Table 4), there
are two independent molecules in the unit cell and the bond
distances and angles have no significant differences. There-
fore, bond lengths and angles in one molecule were listed.
The molecule shows similar geometric and structural fea-
tures to those of 3 and 4, i.e. a capped octahedral structure
2
2
˚
the range for C(sp )–N(sp ) bonds (ca. 1.36 A) [26]. This
is an indication of lone pair donation from the nitrogen
atom (dimethylamido group) to the central carbon and
concomitant electron delocalization involving all three
nitrogen atoms of the chelating ligand. Complex 4 exhib-
ited geometric and structural feature similar to those of
3. The molecular structure of crystalline 4 is shown in
Fig. 3 and selected bond distances and angles are listed in
Table 3. In complex 4, the bond length of Hf–Cl
˚
[2.497(2) A] is normal as in symmetric guanidinato Hf com-
˚
plex [Hf–Cl = 2.41–2.52 A] [25]. The bond lengths of Hf–N
are in the range of 2.18–2.27 A; bond lengths of C–N in the
guanidinate moiety are in the range of 1.32–1.34 A. The
bond angles of N–C–N are 110.5 (8)ꢁ, 112.4 (7)ꢁ and
113.1 (7)ꢁ, respectively. The dihedral angle between N(1)–
Hf(1)–N(3) and N(4)–Hf(1)–N(6) , N(1)–Hf(1)–N(3) and
N(7)–Hf(1)–N(9), and N(4)–Hf(1)–N(6) and N(7)–Hf(1)–
N(9) are 91.2ꢁ, 91.3ꢁ and 88.6ꢁ, respectively.
˚
˚
The dihedral angle formed by the planar NMe2 function
and the MNCN plane offers a means of evaluating the
Fig. 4. Molecular structure of compound 7.
Table 4
Fig. 3. Molecular structure of compound 4.
˚
Selected bond lengths (A) and angles (ꢁ) of compound 7
˚
Bond lengths (A)
Bond angles (ꢁ)
Hf(1)–Cl(1)
Hf(1)–N(1)
Hf(1)–N(2)
Hf(1)–N(4)
Hf(1)–N(5)
Hf(1)–N(7)
Hf(1)–N(8)
N(3)–C(1)
N(6)–C(16)
N(9)–C(31)
N(1)–C(1)
N(2)–C(1)
N(4)–C(16)
N(5)–C(16)
N(7)–C(31)
N(8)–C(31)
2.475(3)
2.240(8)
2.214(8)
2.244(7)
2.229(8)
2.248(8)
2.224(8)
1.401(12)
1.387(13)
1.369(13)
1.330(12)
1.309(11)
1.346(11)
1.328(12)
1.343(12)
1.356(13)
N(1)–Hf(1)–N(2)
N(4)–Hf(1)–N(5)
N(7)–Hf(1)–N(8)
N(1)–C(1)–N(2)
N(4)–C(16)–N(5)
N(7)–C(31)–N(8)
N(1)–Hf(1)–Cl(1)
N(2)–Hf(1)–Cl(1)
N(4)–Hf(1)–Cl(1)
N(5)–Hf(1)–Cl(1)
N(7)–Hf(1)–Cl(1)
N(8)–Hf(1)–Cl(1)
59.3(3)
59.3(3)
59.5(3)
113.3(10)
111.5(10)
110.6(10)
127.1(2)
82.7(2)
129.4(2)
84.4(2)
130.7(2)
83.7(2)
Table 3
˚
Selected bond lengths (A) and angles (ꢁ) of compound 4
˚
Bond lengths (A)
Bond angles (ꢁ)
Hf(1)–Cl(1)
Hf(1)–N(1)
Hf(1)–N(3)
Hf(1)–N(4)
Hf(1)–N(6)
Hf(1)–N(7)
Hf(1)–N(9)
N(1)–C(7)
N(3)–C(7)
N(2)–C(7)
N(5)–C(19)
N(8)–C(31)
2.497(2)
2.265(6)
2.194(7)
2.276(6)
2.199(6)
2.262(7)
2.186(7)
1.346(11)
1.326(11)
1.365(11)
1.381(11)
1.349(12)
N(1)–Hf(1)–N(3)
N(4)–Hf(1)–N(6)
N(7)–Hf(1)–N(9)
N(1)–C(7)–N(3)
N(4)–C(19)–N(6)
N(7)–C(31)–N(9)
N(1)–Hf(1)–Cl(1)
N(3)–Hf(1)–Cl(1)
N(4)–Hf(1)–Cl(1)
N(6)–Hf(1)–Cl(1)
N(7)–Hf(1)–Cl(1)
N(9)–Hf(1)–Cl(1)
59.7(2)
59.6(2)
59.7(2)
112.4(7)
113.1(7)
110.5(8)
128.56(18)
82.79(19)
128.59(18)
82.94(18)
129.36(18)
83.32(19)

M. Zhou et al. / Journal of Organometallic Chemistry 692 (2007) 5195–5202
5199
with the coordination number 7 at the hafnium. The bond
shown in Table 5, complex 3, 4, 6 and 7 were active for
the polymerization of ethylene with the order of
4 > 6 > 3 > 7. So complex 4 was selected for a series of
polymerizations at varied reaction temperature from 20
to 80 ꢁC while other reaction parameters were not chan-
ged. Apparently, the activity of the catalyst decreased in
this whole process with increased reaction temperature.
With the temperature from 20 to 80 ꢁC, the activity of 4
˚
distance of C(central)–N(1-piperidino) [1.401(12) A] in 7 is
˚
longer than C(central)–N(dimethylamido) [1.3786 A] in 3
˚
and [1.365(11) A] in 4, but similar to that in Hf{[C6H11NC-
˚
(N(Si(CH3)3)2)NC6H11]Cl4}{Li(THF)3} [1.41(2) A] [25].
The 1-piperidino ring in 7 adopts a chair conformation.
Although the dihedral angle [48.9ꢁ] between the chelating
core N–C–N and its adjacent C–N–C plane of 1-piperidino
group is larger than that in 3 and 4, which suggests more
bulky 1-piperidino group than dimethylamido group, the
sum of 355.4ꢁ for the three bond angles around 1-piperidi-
no N atom indicates the strong p-bonding interaction
between the two moieties as well.
decreased from 2.92 · 104 to 1.15 · 104 g PE molꢀ1 hꢀ1
.
Overall, the catalytic system displays good activity over
a wide range of reaction temperature. Molecular weight,
on the other hand, increased as temperature was raised.
This suggests that single molecule might show higher cat-
alytic activity at higher temperature, although deactiva-
tion or decomposition proceeds faster at higher
temperature.
2.3. The ethylene polymerization reaction activated by
3, 4, 6 and 7
In our case, the change of ligands and central metals did
not affect the catalytic activity of the compounds signifi-
cantly. Complex 6 with 1-piperidino group on guanidine
showed a catalytic activity of 1.52 · 104 g molꢀ1 hꢀ1 while
3 with N,N-dimethyl group on guanidine showed a rela-
tively lower value of 1.05 · 104 g molꢀ1 hꢀ1; as for com-
plexes 3 and 4, the hafnium guanidine 4 showed a
relatively higher catalytic activity of 2.92 · 104 g molꢀ1 hꢀ1
than the corresponding zirconium guanidine 3 (1.05 ·
104 g molꢀ1 hꢀ1). The angle between the propeller flaps in
complex 4 [91.2ꢁ] is larger by 2.4ꢁ than that in complex 3
[88.8ꢁ], resulting in a more exposed chloride ligand. This
opened coordination is likely partially responsible for the
different catalytic activity.
Comparing with the analogue zirconium benzamidinate
complex [Zr(j2-L)3Cl] (L = [N(SiMe3)C(C6H4Me-4)NPh]ꢀ)
[27], complex 3 exhibited lower activity for ethylene poly-
merization. The difference between the activities of the
two complexes could be due to the electronic factor of
the ligands. In complex 3, dimethylamido group could be
a stronger donor (more basic) than the analogue amidinate
complex and, for the given zirconium metal, replacement of
The influences of various catalytic systems formed from
3, 4, 6 and 7 in the presence of cocatalysts such as methyl-
aluminoxane (MAO) or Et2AlCl on the ethylene activation
were evaluated. To demonstrate what factors, and how
they may affect the ethylene polymerization, the activity
of catalyst precursor 4 was particularly investigated at var-
ied Al/Hf molar ratio and temperature. The detailed results
are summarized in Table 5.
At atmospheric pressure of ethylene, complex 3 has not
been found to be active for the polymerization of ethyl-
ene, no matter activated with MAO or Et2AlCl, neither
with Et2AlCl under 10 atm of ethylene. Based on this
observation, 10 atm pressure of ethylene was employed
in the experiments, in which other reaction parameters
were varied. For complexes 3 and 4, larger amounts of
MAO were found to decrease the activity, at a ratio of
Al/M 1000 reaching higher activities 1.05 · 104 and
2.92 · 104 g molꢀ1 hꢀ1, respectively. Therefore, ethylene
polymerization reactions were carried out under 10 atm
of ethylene at Al/M ratio of 1000 at room temperature
for complexes 3, 4, 6 and 7, activated with MAO. As
Table 5
Data for ethylene polymerization catalyzed by complexes 3, 4, 6 and 7/cocat system
Entry
Cat
Cocat
P (atm)
T (ꢁC)
Al/Zr(Hf)
Yield (mg)
Activitya
Mg (104)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
3
3
3
3
3
4
4
4
4
4
4
4
6
7
MAO
Et2AlCl
Et2AlCl
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
1
1
20
20
20
20
20
20
20
20
20
40
60
80
20
20
1000
500
500
1000
2000
500
1000
1500
2000
1000
1000
1000
1000
1000
–
–
–
26.2
–
No
No
No
1.05 · 104
Trace
–
–
–
1.8
–
10
10
10
10
10
10
10
10
10
10
10
10
–
Trace
–
73.0
26.9
26.7
69.4
41.6
28.7
38.0
23.7
2.92 · 104
1.08 · 104
1.07 · 104
2.78 · 104
1.67 · 104
1.15 · 104
1.52 · 104
9.48 · 103
1.1
1.3
4.9
28
35
34
–
0.35
Conditions: 5 lmol catalyst, 30 ml toluene for 1 atm ethylene pressure, 100 ml toluene for 10 atm ethylene pressure, 0.5 h.
a
g molꢀ1 hꢀ1
.
b
Measured in decahydronaphthalene at 135 ꢁC using an Ubbelohde viscometer according to ½gꢁ ¼ 62 ꢂ 10ꢀ3M0g:7
.

5200
M. Zhou et al. / Journal of Organometallic Chemistry 692 (2007) 5195–5202
an amidinate by a guanidinate increased the electron
density on the metal and reduced its catalytic activity for
ethylene polymerization.
9H, SiMe3), 2.40 (s, 6H, NMe), 6.8–7.1 (m, 5H, Ph). 13C
NMR (CDCl3): d 2.37 (s, SiMe3), 39.6 (s, NMe), 121 (s,
Ph), 123 (s, Ph), 127 (s, Ph), 147 (s, C(C5H5)), 167 (s,
NC(NMe2)N).
3. Experimental
3.2.3. [PhNC(NMe2)NSiMe3]3HfCl Æ 2CH2Cl2 (4)
3.1. General remarks
(CH3)2NCN (0.30 ml, 3.68 mmol) was added to a
solution of PhN(Li)SiMe3 (0.63 g, 3.68 mmol) in THF
(30 cm3) at ꢀ78 ꢁC. The resulting mixture was warmed to
ca. 25 ꢁC and stirred for overnight. HfCl4 (0.39 g,
1.23 mmol) was added at ꢀ78 ꢁC. The resulting mixture
was warmed to ca. 25 ꢁC and stirred for 60 h. The volatiles
were removed in vacuo, and the residue was extracted with
dichloromethane and filtered. The filtrate was concentrated
to give colorless crystals of 4 (0.48 g, 36%). Anal. Cacl. for
C38H64Cl5N9Si3Hf: C, 41.99; H, 5.93; N, 11.60. Found: C,
All manipulations were performed under argon using
standard Schlenk and vacuum line techniques [28,29]. Sol-
vents were dried and distilled over Na or Na/K alloy under
argon prior to use. Methylaluminoxane (MAO, 1.46 M
solution in toluene) was purchased from Akzo Nobel Corp.
Diethylaluminum chloride (Et2AlCl, 1.7 M in toluene) and
other reagents were purchased from Acros or Aldrich.
PhNHSiMe3 was prepared according to the literature
[30]. The NMR spectra were recorded on a Bruker DKX-
300 instrument, and solvent resonances were used as the
internal references for 1H spectra and 13C spectra. Elemen-
tal analyses were carried out using a Vario EL-III analyzer
(Germany).
1
41.79; H, 6.10; N, 11.42%. H NMR (CDCl3): d 0.05 (s,
9H, SiMe3), d 2.40 (s, 6H, NMe), d 6.8–7.2 (m, 5H, Ph).
13C NMR (CDCl3): d 2.51 (s, SiMe3), d 39.7 (s, NMe), d
121 (s, Ph), d 123 (s, Ph), d 127 (s, Ph), d 147 (s,
C(C5H5)), d 167 (s, NC(NMe2)N).
(6)
3.2. Preparations
3.2.4.
[PhNC(N(CH ) CH )NSiMe ] ZrCl
2 4
3 3
1-Piperidinecarboni2trile (0.39 ml, 3.38 mmol) was added
to a solution of PhN(Li)SiMe3 (0.58 g, 3.38 mmol) in hex-
ane (30 cm3) at ꢀ78 ꢁC. The resulting mixture was warmed
to ca. 25 ꢁC and stirred for overnight. ZrCl4 (0.262 g,
1.13 mmol) was added at ꢀ78 ꢁC. The resulting mixture
was warmed to ca. 25 ꢁC and stirred for 12 h, then filtered.
The filtrate was concentrated to ca. to 15 cm3 to give color-
3.2.1. [(Et2O)LiN(SiMe3)C(NMe2)N(Ph)]2 (1) and
[(THF)LiN(SiMe3)C(NMe2)N(Ph)]2 (2)
The reaction of PhNHSiMe3 with n-butyllithium at the
ratio of 1:1 in hexane at 0 ꢁC affords PhN(Li)SiMe3 in
80% yield. (CH3)2NCN (0.73 ml, 9.08 mmol) was added
to a solution of PhN(Li)SiMe3 (1.5 g, 9.08 mmol) in hexane
(20 ml) at ꢀ78 ꢁC. The resulting mixture was warmed to ca.
25 ꢁC and stirred for overnight. The volatiles were removed
in vacuo and the residue was recrystallised from Et2O yield-
ing colorless crystals of compound 1 (0.96 g, 44%). 1H
NMR (C6D6): d 0.23 (s, 9H, SiMe3), 2.70 (s, 6H, NMe),
6.91–7.07 (m, 2H, Ph), 7.27–7.50 (m, 3H, Ph). 13C NMR
(C6D6): d 5.5 (s, SiMe3), 40.3 (s, NMe), 127–130 (m, Ph),
155.8 (s, C(C5H5)), 183.6 (s, NC(NMe2)N). Crystallization
from THF yielded colorless crystals of compound 2 (80%).
1H NMR (C6D6): d 0.42 (s, 9H, SiMe3), 2.71–2.80 (d, 6H,
NMe), 1.43, 1.45, 1.47 (thf), 3.61, 3.64, 3.66 (thf), 6.85–7.32
(m, 5H, Ph). 13C NMR (C6D6): d 5.74 (s, SiMe3), 41.1–41.9
(s, NMe), 28.1, 70.4 (thf), 120.7–156.0 (m, Ph), 166.8 (s,
C(C5H5)), 170.4 (s, NC(NMe2)N).
less crystals of
6 (0.48 g, 45%). Anal. Cacl. for
C45H72ClZrN9Si3: C, 56.89; H, 7.64; N, 13.27. Found: C,
56.67; H, 7.65; N, 13.03%. H NMR (CDCl3): d 0.196 (s,
9H, SiMe3), d 1.16 (s, 2H, CH2), d1.31 (s, 4H, CH2), d
2.57–2.61 (d, 2H, CH2), d 2.74–2.80 (t, 2H, CH2), d 6.83–
6.88 (t, 1H, Ph), d 7.01–7.04 (d, 2H, Ph), d 7.08–7.13 (t,
2H, Ph). 13C NMR (CDCl3): d 3.13 (s, SiMe3), d 23.8,
24.1, 48.2(3s, CH2), d 121, 124, 127 (3s, Ph), d 147 (s,
C(C5H5)), d 167 (s, NC(1-piperidino)N).
1
3.2.5.
[PhNC(N(CH2)4CH2)NSiMe3]3HfCl
(7)
1-Piperidinecarbonitrile (0.32 ml, 2.77 mmol) was added
to a solution of PhN(Li)SiMe3 (0.47 g, 2.77 mmol) in hex-
ane (30 cm3) at ꢀ78 ꢁC. The resulting mixture was warmed
to ca. 25 ꢁC and stirred for overnight. HfCl4 (0.30 g,
0.92 mmol) was added at ꢀ78 ꢁC. The resulting mixture
was warmed to ca. 25 ꢁC and stirred for 12 h, then filtered.
The filtrate was concentrated to ca. to 15 cm3 to give color-
7 (0.32 g, 33%). Anal. Cacl. for
C45H72ClHfN9Si3: C, 52.10; H, 7.00; N, 12.15. Found: C,
52.00; H, 7.03; N, 11.98%. H NMR (CDCl3): d 0.19 (s,
9H, SiMe3), d 1.15 (s, 2H, CH2), d1.32 (s, 4H, CH2), d
2.58–2.62 (d, 2H, CH2), d 2.75–2.81 (t, 2H, CH2), d 6.83–
6.87 (t, 1H, Ph), d 7.02–7.05 (d, 2H, Ph), d 7.09–7.14 (t,
2H, Ph). 13C NMR (CDCl3): d 3.72 (s, SiMe3), d 24.2,
24.5, 48.7 (3s, CH2), d 121, 125, 127 (3s, Ph), d 147 (s,
C(C5H5)), d 167 (s, NC(1-piperidino)N).
3.2.2. [PhNC(NMe2)NSiMe3]3ZrCl Æ 2CH2Cl2 (3)
(CH3)2NCN (0.32 ml, 4.00 mmol) was added to a solu-
tion of PhN(Li)SiMe3 (0.68 g, 4.00 mmol) in THF
(30 cm3) at ꢀ78 ꢁC. The resulting mixture was warmed to
ca. 25 ꢁC and stirred for overnight. ZrCl4 (0.10 g,
1.33 mmol) was added at ꢀ78 ꢁC. The resulting mixture
was warmed to ca. 25 ꢁC and stirred for 60 h. The volatiles
were removed in vacuo, and the residue was extracted with
dichloromethane and filtered. The filtrate was concentrated
to give colorless crystals of 3 (0.49 g, 44%). Anal. Cacl. for
C38H64Cl5N9Si3Zr: C, 45.74; H, 6.46; N, 12.60. Found: C,
less crystals of
1
1
46.00; H, 6.52; N, 12.84%. H NMR (CDCl3): d 0.04 (s,

M. Zhou et al. / Journal of Organometallic Chemistry 692 (2007) 5195–5202
5201
Table 6
Crystal and refinement data for 1, 3, 4 and 7
Compound
1
3
4
7
Formula
M
C32H60Li2N6O2Si2
630.92
C38H64Cl5N9Si3Zr
999.72
C38H64Cl5HfN9Si3
1086.99
C45H72ClHfN9Si3
1037.33
Crystal system
Space group
Monoclinic
p2(1)/c
10.052(8)
20.114(19)
10.926(12)
90.00
114.967(11)
90.00
2003(3)
Triclinic
Triclinic
Monoclinic
P2(1)/c
22.209(13)
23.699(14)
19.699(12)
90.00
92.057(10)
90.00
10362(11)
8
ꢀ
ꢀ
P1 (No. 2)
P1 (No. 2)
˚
a (A)
11.953(3)
12.995(3)
17.508(4)
71.048(3)
76.964(3)
81.753(3)
2498.6(9)
2
11.894(2)
12.961(3)
17.507(3)
70.939(2)
77.232(3)
81.657(3)
2480.0(9)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
U (A )
Z
2
Absorption coefficient (mmꢀ1
)
0.121
0.596
2.482
2.173
Unique reflections [Rint
Reflections with I > 2r(I)
]
3519 [0.098]
1544
8632 [0.061]
4500
8559 [0.036]
7594
18178 [0.130]
1081
Final R indices [I > 2r(I)] R1, wR2
R indices (all data) R1, wR2
0.074, 0.1228
0.1720, 0.1527
0.061, 0.1043
0.1147, 0.1188
0.070, 0.1543
0.080, 0.1594
0.062, 0.1218
0.1640, 0.1660
3.2.6. Procedure for ethylene polymerization
map. All non-H atoms were refined with anisotropic dis-
placement parameters, while the H atoms were constrained
to parent sites, using a riding mode (SHELXTL) [33]. Crystal
data and processing parameters for 1, 3, 4 and 7 are sum-
marized in Table 6.
Ethylene polymerization at 1 atm of ethylene pressure
was carried out as follows: The catalyst precursor was dis-
solved in toluene in a Schlenk tube and the reaction solu-
tion was stirred at 1 atm of ethylene. The reaction was
initiated by adding the desired amount of cocatalyst. After
30 min, the solution was quenched with HCl–acidified eth-
anol (5%), and the precipitated polyethylene was filtered,
washed with ethanol, and dried in vacuum at 60 ꢁC to con-
stant weight.
Ethylene polymerization at higher ethylene pressure was
carried out in a 500 ml autoclave stainless steel reactor
equipped with a mechanical stirrer and a temperature con-
troller. Briefly, toluene, the desired amount of cocatalyst,
and a toluene solution of the catalytic precursor (the total
volume was 100 ml) were added to the reactor in this order
under an ethylene atmosphere. When the desired reaction
temperature was reached, ethylene at 10 atm pressure was
introduced to start the reaction, and the ethylene pressure
was maintained by constant feeding of ethylene. After
30 min, the reaction was stopped. The solution was
quenched with HCl–acidified ethanol (5%), and the precip-
itated polyethylene was filtered, washed with ethanol, and
dried in vacuum at 60 ꢁC to constant weight.
Acknowledgements
We thank the Natural Science Foundation of China
(No. 20672070 and 20572065), the Natural Science
Foundation of Shanxi (2007011020), the Foundation for
the Returned Overseas Chinese Scholars (2006, M.S.
ZHOU), Shanxi Key Lab for Functional Molecules (No.
20053002) for the financial support. We are also grateful
to Prof. Wen-Hua Sun for providing the polymerization
data and for the related useful discussions.
Appendix A. Supplementary material
CCDC 195471, 203550, 603753, 603754 and 631436 con-
tain the supplementary crystallographic data for 1, 2, 3, 4
and 7. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK, fax: (+44) 1223-336-
033, or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online
version, at doi:10.1016/j.jorganchem.2007.07.051.
3.3. X-ray crystal data and refinement for 1, 3, 4 and 7
Diffraction data for each of 1, 3,4 and 7 were collected
on a Bruker SMART APEX diffractometer/CCD area
detector using monochromated Mo Ka radiation,
References
˚
k = 0.71073 A. Crystals were coated in oil and then directly
mounted on the diffractometer under a stream of cold
nitrogen gas. A total of N reflections were collected by
using x scan mode. Corrections were applied for Lorentz
and polarization effects as well as absorption using multi-
scans (SADABS) [31]. The structure was solved by direct
method (SHELXS-97) [32]. Then the remaining non-hydrogen
atoms were obtained from the successive difference fourier
[1] (a) P.J. Bailey, S. Pace, Coord. Chem. Rev. 214 (2001) 91;
(b) F.T. Edelmann, Coord.Chem. Rev. 137 (1994) 403.
[2] Li-Ying Zhou, Hong-Mei Sun, Jing-Lei Chen, Ying-Ming Yao, Qi
Shen, J. Polym. Sci. Part A: Polym. Chem. 43 (2005) 1778.
[3] P. Bazinet, D. Wood, G.P.A. Yap, D.S. Richeson, Inorg. Chem. 42
(2003) 6225.
[4] Yun-Jie Luo, Ying-Ming Yao, Qi Shen, Macromolecules 35 (2002)
8670.

5202
M. Zhou et al. / Journal of Organometallic Chemistry 692 (2007) 5195–5202
[5] M.P. Coles, Dalton Trans. (2006) 985.
[19] Jie Zhang, Rui-Fang Cai, Lin-Hong Weng, Xi-Geng Zhou, J.
Organomet. Chem. 672 (2003) 94.
[20] B.W. Corey, L.R. Laurel, A.A. Khalil, M.W. Lisa, Inorg. Chem. 45
(2006) 263.
[21] R. Daniel, B. Arne, W. Manuela, A.F. Roland, Inorg. Chem. 45
(2006) 269.
[22] M.P. Coles, P.B. Hitchcock, Eur. J. Inorg. Chem. (2004) 2662.
[23] D. Walther, R. Fischer, H. Go¨rls, J. Koch, B. Schweder, J.
Organomet. Chem. 508 (1996) 13.
[24] C. Averbuj, E. Tish, M.S. Eisen, J. Am. Chem. Soc. 120 (1998)
8640.
[25] D. Wood, G.P.A. Yap, D.S. Richeson, Inorg. Chem. 38 (1999)
5788.
[26] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen,
R. Taylor, J. Chem. Soc., Perkin Trans. 2 (1987) S1.
[27] P.B. Hitchcock, M.F. Lappert, P.G. Merle, Dalton Trans. (2007)
585.
[6] J. Barker, M. Kilner, Coord. Chem. Rev. 133 (1994) 219.
[7] D.H. Korine, M.S. Eisen, J. Organomet. Chem. 503 (1995) 307.
[8] A.P. Duncan, S.M. Mullins, J. Arnold, R.G. Bergman, Organomet-
allics 20 (2001) 1808.
[9] (a) R.J. Keaton, L.A. Koterwas, J.C. Fettinger, L.R. Sita, J. Am.
Chem. Soc. 124 (2002) 5932;
(b) R.J. Keaton, L.R. Sita, Organometallics 21 (2002) 4315;
(c) R.J. Keaton, K.C. Jayaratne, D.A. Henningsen, L.A. Koterwas,
L.R. Sita, J. Am. Chem. Soc. 123 (2001) 6197.
[10] Tiow-Gan Ong, G.P.A. Yap, D.S. Richeson, Organometallics 21
(2002) 2839.
[11] A. Devi, R. Bhakta, A. Milanov, M. Hellwig, D. Barreca, E.
Tondello, R. Thomas, P. Ehrhart, M. Winter, R. Fischer, Dalton
Trans. (2007) 1671.
[12] Tiow-Gan Ong, G.P.A. Yap, D.S. Richeson, Organometallics 22
(2003) 387.
[13] Mei-Su Zhou, Shu-Ping Huang, Lin-Hong Weng, Wen-Hua Sun,
Dian-Sheng Liu, J. Organomet. Chem. 665 (2003) 237.
[14] Sheng-Di Bai, Jian-Ping Guo, Dian-Sheng Liu, Dalton Trans. (2006)
2244.
[28] D.F. Shriver, M.A. Drezdon, The Manipulation of Air Sensitive
Compounds, second ed., Wiley, New York, 1986.
[29] S. Herzog, J. Dehnert, K. LuhderTechnique of Inorganic Chemistry,
vol. VII, Interscience, New York, 1969.
[15] Sheng-Di Bai, Jian-Ping Guo, Dian-Sheng Liu, W.Y. Wong, Eur.
J. Inorg. Chem. (2006) 4903.
[16] Jian-Feng Li, Shu-Ping Huang, Lin-Hong Weng, Dian-Sheng Liu,
J. Organomet. Chem. 691 (2006) 3003.
[17] S.E. Schaus, J. Branalt, E.N. Jacobsen, J. Org. Chem. 63 (1998) 403.
[18] B.M. Trost, M.J. Krische, R. Radinov, G. Zanoni, J. Am. Chem.
Soc. 118 (1996) 6297.
[30] H.H. Anderson, J. Am. Chem. Soc. 73 (1951) 5802.
[31] G.M. Sheldrick, Correction Software, University of Go¨ttinggen,
Germany, 1996.
[32] G.M. Sheldrick, Program for the Solution of Crystal Structures,
University of Go¨ttinggen, Germany, 1997.
[33] Program for Crystal Structure Refinement, Bruker Analytical X-ray
Instruments Inc., Madison, WI, USA, 1998.