Zirconium and hafnium complexes supported by linked bis(β- diketiminate) ligands: Synthesis, characterization and catalytic application in ethylene polymerization

Article abstract of DOI:10.1039/b905392a

Zirconium and hafnium complexes bearing new 1,2-ethanediyl- or 1,3-propanediyl-linked bis(β-diketiminate) ligands, [{C_nH _2n-(BDI^Ar)₂}MCl₂] (Ar = 2,6-Me ₂-C₆H₃, 2,6-Cl₂-C₆H ₃, 2,6-ⁱPr₂-C₆H₃; M = Zr, n = 2 (4a-c), n = 3 (5a-c); M = Hf, n = 2 (6b)), were synthesized via the reaction of MCl₄·2THF and one equivalent of dilithium salt of the corresponding ligand. Distorted trigonal prismatic and octahedral coordination geometries as well as C₁-symmetric structures are found for zirconium complexes 4c and 5c in the solid state. Variable temperature ¹H NMR spectra indicated the fluxional nature of 4a and 5a in solution. Upon activation with methylaluminoxane (MAO), all these complexes except hafnium complex 6b displayed moderate catalytic activities for ethylene polymerization. 1,2-Ethanediyl-linked complexes 4a and 4b are generally more active than their 1,3-propanediyl-linked analogues. The substituents at the ortho-positions of the phenyl rings have different effect on the catalytic activities of 1,2-ethanediyl-linked series or 1,3-propanediyl-linked series. It is noteworthy that even at a low Al/Zr molar ratio of 500, the catalytic activities of these zirconium complexes could be retained. Polyethylenes with broad molecular weight distributions (MWD = 15.3-20.3) were produced, which might result from the fluxional character of the zirconium complexes. The linear structure of obtained polyethylenes was further determined by ¹³C NMR spectroscopy and DSC analysis. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b905392a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Zirconium and hafnium complexes supported by linked bis(b-diketiminate)
ligands: synthesis, characterization and catalytic application in ethylene
polymerization†
Shaogang Gong, Haiyan Ma* and Jiling Huang*
Received 17th March 2009, Accepted 7th July 2009
First published as an Advance Article on the web 10th August 2009
DOI: 10.1039/b905392a
Zirconium and hafnium complexes bearing new 1,2-ethanediyl- or 1,3-propanediyl-linked
bis(b-diketiminate) ligands, [{CnH2n-(BDIAr)2}MCl2] (Ar = 2,6-Me2-C6H3, 2,6-Cl2-C6H3,
2,6-iPr2-C6H3; M = Zr, n = 2 (4a–c), n = 3 (5a–c); M = Hf, n = 2 (6b)), were synthesized via the
reaction of MCl4·2THF and one equivalent of dilithium salt of the corresponding ligand. Distorted
trigonal prismatic and octahedral coordination geometries as well as C1-symmetric structures are found
for zirconium complexes 4c and 5c in the solid state. Variable temperature 1H NMR spectra indicated
the fluxional nature of 4a and 5a in solution. Upon activation with methylaluminoxane (MAO), all
these complexes except hafnium complex 6b displayed moderate catalytic activities for ethylene
polymerization. 1,2-Ethanediyl-linked complexes 4a and 4b are generally more active than their
1,3-propanediyl-linked analogues. The substituents at the ortho-positions of the phenyl rings have
different effect on the catalytic activities of 1,2-ethanediyl-linked series or 1,3-propanediyl-linked series.
It is noteworthy that even at a low Al/Zr molar ratio of 500, the catalytic activities of these zirconium
complexes could be retained. Polyethylenes with broad molecular weight distributions (MWD =
15.3–20.3) were produced, which might result from the fluxional character of the zirconium complexes.
The linear structure of obtained polyethylenes was further determined by 13C NMR spectroscopy and
DSC analysis.
and 1-hexene (2.6 ¥ 107 g copolymer/mol-Zr·h), and the molar
Introduction
percentage of 1-hexene incorporation increased while the feed
Among a variety of polydentate ligands adopted for synthesiz-
of 1-hexene was enhanced. Recently, we found that zirconium
ing non-metallocene complexes, b-diketiminate ligands attract
considerable attention due to their isoelectronic relationship
with the cyclopentadienyl anion, and convenient preparation
in high yields from cheap and readily available materials, as
well as versatile modulation of steric and electronic require-
ments by varying the amine moieties and the backbone.1
For example, Collins’ and Andres’ groups2,3 reported group 4
metal complexes bearing b-diketiminate ligands with electron-
withdrawing groups, which displayed high catalytic activities
for ethylene polymerization (1.1 ¥ 107 g PE/mol-Zr·h) and
afforded polyethylenes with narrow molecular weight distribu-
tions (MWD = ~2.7). Bis(b-diketiminate) titanium complexes,4
[(BDIAr)2TiCl2] (Ar = 2,6-iPr2-C6H3), showed moderate cat-
alytic activities both in ethylene homo-polymerization and in
ethylene/norbornene copolymerization. Xie’s group5 prepared
mono(b-diketiminate) titanium trichloride complexes, which dis-
played high catalytic activities for the copolymerization of ethylene
complexes bearing symmetrically or unsymmetrically substituted
b-diketiminate ligands could provide ultra-high molecular weight
polyethylenes (UHMWPE) or polyethylenes with broad molecular
weight distribution via the modulation of N-aryl moieties.6 All
these facts show that the versatile b-diketiminate ligand sets afford
great opportunity to produce polyolefins with variable properties
when binding with group 4 metals.7
More recently, bridged-bis(phenolate)-type dianionic tetraden-
tate ligands have been developed and thoroughly introduced
to group 4 metals; versatile catalytic behavior and stereose-
lectivities for a-olefin8 or styrene9 polymerization have been
gained through fine-tuning the phenoxide ortho-substituents or
the bridging unit sterically and electronically. Grassi’s group10
revealed that the bridged bis(phenoxy-iminate) zirconium com-
plexes could produce polyethylene with narrow MWD (MWD =
~2.0) and regioregular 1,2-insertion of a-olefin took place
during the copolymerization of ethylene with propylene or
1-hexene. Kol et al.8a,8b and Busico et al.8c,8d found that, with
bulky ortho-substituents on the phenolate rings, the tetradentate
diamino bis(phenolate) zirconium complexes catalyzed the isos-
elective polymerizations of propylene or 1-hexene. For titanium
complexes with [OSSO]-type bis(phenolate) ligands, the elonga-
tion of the bridging unit from 1,2-ethanediyl to 1,3-propanediyl
switched the selectivity for styrene polymerization from isotactic
to syndiotactic.9 In most of the cases, such linear tetradentate
Laboratory of Organometallic Chemistry, East China University of Science
and Technology, 130 Meilong Road, Shanghai, 200237, People’s Republic of
China. E-mail: haiyanma@ecust.edu.cn, qianling@online.sh.cn; Fax: +86
21 64253519
† Electronic supplementary information (ESI) available: 1H NMR spectra
of 4a and 4c, variable temperature spectra of 4a and 5a, 13C NMR spectrum
of typical polyethylene sample. CCDC reference numbers for 4c and 5c
724272 and 724273. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b905392a
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ligands were capable of generating rigid chirality at a metal
center and hence achieved stereoselective olefin enchainment. It
is conceivable that a [NN«NN]-type tetradentate dianionic ligand
formed by linking two b-diketiminate moieties with a bridging unit
may also provide a rigid ligand framework for group 4 metals to
construct most likely a C2-symmetric configuration, thus affording
the potential of stereoselective polymerization of a-olefin by
elegantly modifying the ortho-substituents on the phenolate rings
and/or the bridge between the two b-diketiminate moieties, in
addition to the single-site character. Some examples of linked
bis(b-diketimine)s have been synthesized11 and adopted for rare
earth metals to catalyze the copolymerization of epoxides and
CO2.12 Here, we would like to expand the ligand categories and
report a series of 1,2-ethanediyl and 1,3-propanediyl-linked bis(b-
diketiminate) zirconium and hafnium dichloride complexes and
their catalytic behavior in ethylene polymerization.
Attempts at synthesizing 1,2-ethanediyl-linked bis(b-diketimine)
with meta-trifluoromethyl substitution on the phenyl rings via
the reaction of corresponding enaminoketone and diamine failed
to give any target product. Only meta-trifluoromethylaniline,
N-(meta-trifluoromethyphenyl) substituted b-diketimine (3-CF3–
=
=
C6H4N C(Me)CH C(Me)NHC6H4-CF3-3), and some unknown
compounds with high boiling points were detected in the reaction
mixture. Previously, we found that successful synthesis of b-
diketimines with two different N-aryl moieties was limited to those
having bulky ortho-substituents on at least one of the two phenyl
i
13
=
=
rings, such as (2,6- Pr2C6H3N C(Me)CH C(Me)NHC6H5).
Therefore, it seems that a sufficient space hindrance arising from
substituents at the ortho-positions of the N-phenyl moiety is
crucial to prevent the undesired recomposition reaction.
The profound influence of a bridging unit on the polymer-
ization performance of resultant metal complexes9 also encour-
aged us to use an aromatic group as bridge. Thus, enam-
inoketone 1b pretreated with [Et3O]+[BF4]-, was reacted with
1,2-diaminobenzene in the presence of Et3N. However, only
Results and discussion
=
=
compound 7 (2,6-Cl2–C6H3N C(Me)CH C(Me)OC2H3), and
unreacted 1,2-diaminobenzene were isolated from the reaction
mixture (Scheme 2). Obviously, no reaction occurred between the
generated borate intermediate and 1,2-diaminobenzene.
Synthesis of linked bis(b-diketiminate) zirconium and hafnium
complexes
As depicted in Scheme 1, in order to investigate in detail the effect
of ligand framework on the catalytic behavior of the corresponding
metal complexes, a series of linked bis(b-diketimine)s 2a–d and
3a–c with different ortho-substituents and alkanediyl bridges were
synthesized in reasonable yields of 62–76% by using a classic two-
step condensation route.12
Scheme 2
Zirconium and hafnium complexes 4a–c, 5a–c and 6b bear-
ing linked bis(b-diketiminate) ligands were synthesized via the
reaction of ZrCl4·2THF or HfCl4·2THF and one equivalent of
dilithium salt of the corresponding ligand in toluene under mild
conditions (Scheme 1). Analytically pure complexes were obtained
as yellow to orange yellow crystalline solids in moderate yields
after recrystallization from hot toluene. Spectroscopic data and
elemental analysis results are consistent with the stoichiometry of
one linked bis(b-diketiminate) ligand per metal. The monomeric
nature of this series of complexes was further confirmed by X-ray
diffraction studies (vide post).
Scheme 1
The synthesis of analogous linked bis(b-diketimine)s with
meta-substituted N-phenyl groups was, however, unsuccessful.
Great effort was made to prepare zirconium complex bearing
ortho-trifluoromethyl substituted 2d. The H NMR spectrum of
1
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the reddish solids isolated from the reaction mixture indicated
an unknown structure containing b-diketiminate fragment but
without the 1,2-ethanediyl bridge; a decomposition reaction was
then deduced accordingly. The lithium salt of ligand 2d prepared
either in toluene or in diethyl ether was hydrolyzed, which
gave an untraceable mixture rather than 2d. Most likely, the
existence of strong electron-withdrawing ortho-CF3 groups led to
the decomposition of 2d when treated with n-BuLi.
Complexes 4a–6b are quite sensitive to air and moisture. Partial
decomposition occurred when isolated crystalline solids were re-
dissolved in dry toluene. It is of note that a counterintuitive
influence of ortho-substituents on the phenyl rings on the solubility
of resultant complexes was observed: complexes 4c and 5c with
ortho-isopropyl substitution were sparingly soluble in toluene,
whereas the rest with either ortho-methyl or chlorine substituents
were smoothly dissolvable. In general, 1,3-propanediyl-linked
complexes 5a–c show better solubility in aromatic solvents than
4a–c containing 1,2-ethanediyl bridge. When compared with
the non-linked b-diketiminate zirconium congeners,6 complexes
4a–6b in this work exhibit superior solubility in toluene.
ically demanding diisopropyl groups in 4c effectively hinders the
fluxional interconversion between D and K-isomers.14 Due to the
partial overlapping of N-CH2 and isopropyl methine resonances
1
in the H NMR spectrum, detailed investigation concerning the
solution behavior of 4c at higher temperature was cumbered.
1
The H NMR spectra of complexes 5a (R1 = R2 = CH3), 5b
i
(R1 = R2 = Cl) and 5c (R1 = R2 = Pr) also indicate two symmetry-
related b-diketiminate fragments in each case at room temperature.
The fluxionality of the 1,3-propanediyl-bridge in 5a and 5b is
somewhat frozen out on the NMR time scale, showing two broad
signals for the four protons of N–CH2; whereas only one multiple
signal is displayed for the two N–CH2 units in 5c, which is in
contrast to the rigidity observed for 4c. The restricted rotation of
aromatic rings is further observed for 5a and 5c, with more than
one set of resonances being displayed for the Ar-alkyl groups.
Variable-temperature 1H NMR spectra of 5a (in toluene-d8) give
evidence of a gradual coalescence of two N–CH2 signals to a
broad singlet at d = 3.8 ppm at elevated temperatures up to 60 ◦C
(Fig. 1).15 When cooled to -60 ◦C, in spite of slight sharpening of
these two resonances, no identifiable fine-coupling patterns could
be observed. From line broadening analysis, the activation energy
for 5a of this process is found to be DGπ = 59.2 kJ mol-1 (for
N–CH2 signals, Dn = 599.5 Hz, Tc = 319 K). Likewise, by using
the Erying equation to plot ln(K/T) versus 1/T, DHπ = 5.1 kcal
mol-1, DSπ = -28.5 kcal mol-1 K-1 can be obtained.
Structures of zirconium complexes in solution
For a linear tetradentate ligand, depending on the nature of
donors, the size of metal ion, and the spatial requirements of
the ligand framework, a number of structural isomers can form
when wrapping around a gro◦up 4 metal (Scheme 3). From the
1H NMR spectra (C6D6, 25 C) of complexes 4a (R1 = R2 =
CH3) and 4b (R1 = R2 = Cl) with 1,2-ethanediyl-bridged ligands,
only a single isomer is observed in each case, which is highly
symmetric in solution, as is evident from the symmetry-related
two b-diketiminate fragments. Complexes 4a and 4b appear to
be C2v symmetric in solution according to the sharp singlet
1
displayed by the four N-CH2 protons in the H NMR spectra.
All of the above mentioned features observed at 25 ◦C are still
present at -70 ◦C (C7D8) for 4a. Such symmetry could result
either from a trans-Cl,Cl, cis-N1,N1, cis-N2,N2 isomer of C2v-
symmetric octahedral configuration (trans in Scheme 3) or from
fast-exchanging cis-Cl,Cl, trans-N1,N1, cis-N2,N2 C2-symmetric
octahedral enantiomers of D and K-configuration (cis-a). Based on
the most reasonable coordination of tetradentate ligands and the
X-ray crystal structure of 4c, we assume a C2-symmetric ground
state for 4a and 4b.14
Fig. 1 Variable temperature 1H NMR spectra of complex 5a (R1 = R2 =
Me) (toluene-d8). Only the –NCH2CH2CH2N– moiety is shown.
Fluxional behavior of octahedral complexes with linear
tetradentate ligand was often observed for those having soft-
donor-containing ligands (such as S14,16,17 and P18). Depending
on the ligand framework, different processes have been suggested.
For instance, the solution behavior of titanium complexes with
[OSSO]-type bisphenolate ligands might involve either a rapid
enantiomerization between the D and K-isomers occurring likely
via a tetrahedrally coordinated transition state or an intercon-
version between cis-Cl,Cl, trans-N1,N1, cis-N2,N2 C2-symmetric
(cis-a) and cis-Cl,Cl, cis-N1,N1, cis-N2,N2 C1-symmeric (cis-b)
configurations via a Bailar twist process.14,16a,17 As shown in
Scheme 4, being different from the case of octahedral complexes
with two bidentate or three bidentate ligands, a single Bailar
twist process of an octahedral complex wrapped by a “linear”
Scheme 3 The possible stereoisomers of metal complex with general
formula of [N1N2«N2N1]ZrCl2 (only diastereomers are shown).
i
In contrast to them, complex 4c (R1 = R2 = Pr) displays
two separate resonances in AA¢BB¢ spin pattern for the four N-
1
CH2 protons in the H NMR spectrum as well as four doublets
for the methyl protons of isopropyl groups, two multi-peaks for
the methine protons, apparently suggesting a rigid C2-symmetric
configuration in solution. It seems that the introduction of ster-
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Scheme 4 Possible interconversion among stereoisomers via Bailar twist process.
tetradentate ligand (for example, [N1N2«N2N1]-type) with cis-a
Crystal structures of zirconium complexes 4c and 5c
configuration (K-isomer) will, however, lead to the other isomers,
instead of direct enantiomerization between the D- and K-isomers.
Thus, more than one set of resonances accounting for the N1–N2
units might be observed in addition to the decoalescence of the
bridging moiety in the 1H NMR spectra at decreased temperature.
Single crystals of zirconium complexes 4c and 5c suitable for
X-ray diffraction measurement were obtained by slowly cooling
a saturated toluene solution to -20 ◦C. Crystallographic data,
results of structure refinements, selected bond lengths and angles
are summarized in Tables 1, 2 and 3.
1
The variable temperature H NMR spectra of 5a show that,
The X-ray crystal structure of 4c (Fig. 2) shows that
the zirconium center is six coordinated with the tetradentate
bis(diketiminate) ligand and two chloride atoms. Although con-
sisting of cis-N(2), N(4), trans-N(1), N(3) and cis-Cl(1), Cl(2)
orientation (cis-a), the geometry around Zr atom in 4c is
distorted significantly from octahedral coordination, which is
more likely trigonal prismatic as evidenced by the consider-
ably large angles of N(1)–Zr–N(4) = 119.91(10)◦ and N(2)–
Zr–N(3) = 118.89(10)◦. The slight differences between the
besides the gradual decoalescence of two broad N–CH2 signals,
the two b-diketiminate fragments keep symmetric and only one
singlet is displayed for the two g-protons within the temperature
range of -60–60 ◦C, giving no convincing evidence for a Bailar
twist process. According to the obtained dynamic and variable 1H
NMR spectroscopic data, the observed fluxionality of 5a might
be caused by the rapid enantiomerization between the D and K-
isomers in solution likely via a tetrahedrally coordinated transition
state (Scheme 5).14 This might also be the case for 4a in solution.
Table 1 Crystal data and structure refinement details for 4c and 5c
4c
5c
Formula
C36H52Cl2N4Zr·0.5C7H8 C37H54Cl2N4Zr·0.5C7H8
Formula weight
Crystal size/mm3
Crystal system
Space group
749.00
763.03
0.498 ¥ 0.419 ¥ 0.347
monoclinic
P2(1)/c
0.293 ¥ 0.262 ¥ 0.204
monoclinic
P2(1)/c
˚
a/A
11.4820(11)
31.485(3)
11.7046(11)
90.00
111.609(2)
90.00
11.6509(13)
31.598(4)
11.6510(13)
90.00
110.906(2)
90.00
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
Volume/A
3933.9(6)
4
4006.9(8)
4
1.264
Z
Calcd density/mg m-3 1.265
Absorp coeff/mm-1
F(000)
0.447
1580
0.440
1610
q range for data
1.91 to 27.00
1.87 to 25.50
collection/◦
Scheme 5 Possible interconversion of K- and D-isomers via tetrahedrally
coordinated transition state assumed for 5a (Ar = 2,6-Me2-C6H3).
Limiting indices
-14 ≤ h ≤ 13, -35 ≤
k ≤ 40, -14 ≤ l ≤ 14
22563/8553 [R(int) =
0.0853]
-14 ≤ h ≤ 12, -38 ≤
k ≤ 36, -14 ≤ l ≤ 14
21032/7437 [R(int) =
0.1133]
No. of reflns
collected/unique
Data/restrains/
parameters
From VT-NMR experiments, it is unusual that the 1,2-
ethanediyl-linked complex 4a seems configurationally more flexi-
ble than 1,3-propanediyl-linked 5a.14 This behavior however may
be rationalized if we take into account the considerable strain of
the 6–5–6 chelating skeleton arising from the short 1,2-ethanediyl
linkage in complex 4a (evident from the X-ray crystal structures of
4c and 5c), which should facilitate the weakening or detachment
of N (middle)-Zr bonds.
8553/4/446
7437/8/426
Goodness-of-fit on F2 1.011
0.799
Final R indices
[I > 2s(I)]
R indices (all data)
R1 = 0.0552
R1 = 0.0565
wR2 = 0.1133
R1 = 0.1237
wR2 = 0.1296
0.824 and -0.596
wR2 = 0.1165
R1 = 0.0796
wR2 = 0.1255
0.738 and -0.680
Largest diff.
peak/hole/e A
-3
˚
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◦
˚
zirconium complexes, probably due to the bulky steric hindrance
of two ortho-isopropyls on the phenyl rings.
Table 2 Selected bond distances (A) and angles ( ) for complex 4c
Zr–N(1)
Zr–N(3)
Zr–Cl(1)
N(1)–C(1)
2.314(3)
2.322(2)
2.4241(9)
1.337(4)
Zr–N(2)
Zr–N(4)
Zr–Cl(2)
N(2)–C(3)
C(2)–C(3)
2.176(3)
2.174(3)
2.4187(9)
1.347(4)
1.374(5)
The modification of the linkage within the ligand leads to
considerable change in the coordination geometry around the
metal center. In the solid state, complex 5c possesses C1-symmetric
structure (cis-a, Fig. 3) and has a distorted octahedral coordina-
tion geometry with two cis-Cl atoms at an angle of 112.89(5)◦,
which is smaller than that of 4c (117.40(4)◦). The bigger angle of
N(1)–Zr–N(3) = 167.15(14)◦ in 5c than that of 4c (160.03(9)◦)
further shows the more crowded space structure of the whole
ligand framework. The angle of N(2)–Zr–N(4) = 76.71(16)◦ is
bigger than that in 4c, but still smaller than those in non-
linked bis(b-diketiminate) zirconium complexes, indicative of the
presence of strains to a certain degree. The other bond distances
and angles in 5c are, however, similar to those of 4c.
C(1)–C(2)
1.398(5)
N(1)–C(14)
N(1)–Zr–N(2)
N(2)–Zr–N(4)
N(1)–Zr–N(4)
Cl(1)–Zr–Cl(2)
N(4)–Zr–Cl(1)
1.453(4)
78.15(10)
72.68(11)
119.91(10)
117.40(4)
92.13(8)
N(3)–Zr–N(4)
N(1)–Zr–N(3)
N(2)–Zr–N(3)
N(2)–Zr–Cl(2)
77.42(10)
160.03(10)
118.89(10)
90.35(8)
◦
˚
Table 3 Selected bond distances (A) and angles ( ) for complex 5c
Zr–N(1)
Zr–N(3)
Zr–Cl(1)
N(1)–C(1)
2.303(4)
2.282(4)
2.4238(14)
1.328(6)
Zr–N(2)
Zr–N(4)
Zr–Cl(2)
N(2)–C(3)
C(2)–C(3)
2.193(4)
2.204(4)
2.4282(16)
1.325(6)
1.393(7)
C(1)–C(2)
1.406(7)
N(1)–C(14)
N(1)–Zr–N(2)
N(2)–Zr–N(4)
N(1)–Zr–N(4)
Cl(1)–Zr–Cl(2)
N(4)–Zr–Cl(1)
1.488(6)
81.89(15)
76.71(16)
107.41(15)
112.89(5)
87.50(12)
N(3)–Zr–N(4)
N(1)–Zr–N(3)
N(2)–Zr–N(3)
N(2)–Zr–Cl(2)
82.13(16)
167.15(14)
109.16(15)
87.90(12)
i
Fig. 3 ORTEP diagram of the molecular structure of 5c (R1 = R2 = Pr).
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms
and solvent molecule are omitted for clarity.
Polymerization of ethylene with complexes 4a–6b/MAO systems
Ethylene polymerization by these linked bis(b-diketiminate) zirco-
nium complexes 4a–c, 5a–c and hafnium complex 6b was investi-
gated under different conditions using excess methylaluminoxane
(MAO) as the cocatalyst. The results of zirconium complexes are
collected in Tables 4 and 5. Hafnium complex 6b (R1 = R2 = Cl)
showed hardly any activity for the polymerization of ethylene.
It is of note that, due to the extreme sensitivity, the toluene
solution of zirconium pre-catalyst had to be prepared freshly and
consumed within 1–2 hours, otherwise visible decomposition of
the zirconium complexes would lead to significant uncertainty of
the polymerization data.
Optimization of polymerization parameters showed that the
polymerization temperature and adopted molar ratio of Al/Zr
had a significant influence on the catalytic activities of these
zirconium complexes. All complexes kept moderate activities when
polymerization temperature was increased from 30 to 90 ◦C, but
the range of 50–70 ◦C seemed to be superior conditions. For most
of the complexes, the highest catalytic activity was reached at about
70 ◦C. It is notable that considerable activities could be retained for
4a and 5a with ortho-dimethyl substitution even at 90 ◦C (Entries
i
Fig. 2 ORTEP diagram of the molecular structure of 4c (R1 = R2 = Pr).
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms
and solvent molecule are omitted for clarity.
two b-diketiminate parts in bond lengths and angles suggest
a C1-symmetric configuration of 4c in the solid state. The
angle of N(2)–Zr–N(4) = 72.68(11)◦ is rather small when
compared to those in non-linked◦ bis(b-diketiminate) zirco-
nium complexes (83.19(6)–91.21(3) ).6,7c On the other hand,
the angle of Cl(1)–Zr–Cl(2) (117.40(4)◦) is significantly en-
larged (ca. 90◦ in six coordinate non-linked bis(b-diketiminate)
zirconium complexes).2a,7c All these features imply significant
strains of the tetradentate ligand possibly arising from the
short 1,2-ethanediyl linkage. The obviously longer Zr–N(1) and
Zr–N(3) bonds in comparison with those of Zr–N(2) and
Zr–N(4) are typical for six coordinate bis(b-diketiminate)
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Table 4 The polymerization of ethylene with 4a–c/MAO catalytic systemsa
Entry
Catalyst
[Al]/[Zr]
Temp/◦C
Yield/g
Activity/kg PE (mol-Zr)-1 [C2H4]-1 h-1
Mhb/105 g mol-1
1
2
4a
1000
1000
1000
1000
500
2000
1000
1000
1000
300
30
50
70
90
70
70
30
70
90
70
70
70
30
50
70
90
70
70
0.2188
0.3669
0.3152
0.3002
0.2990
0.1066
0.3017
0.3520
0.1463
0.3381
0.4827
0.2412
0.1900
0.1833
0.2122
0.1563
0.2769
0.1874
72
156
336
196
160
57
98
188
97
180
257
128
62
18.32
6.13
n.d.d
0.66
2.82
6.14
4.51
4.96e
1.88
5.65
4.96
6.18
26.85
12.05
8.67f
0.36
9.09
2.13
3c
4
5
6
7
8
4b
4c
9
10
11
12
13
14
15
16
17
18
500
2000
1000
1000
1000
1000
500
78
113
103
148
100
2000
a In toluene, V = 25 mL, [Zr] = 2 ¥ 10-4 mol/L, Pethylene = 1.0 MPa, tp = 0.5 h. b Intrinsic viscosity was determined in decahydronaphthalene at 135 ◦C
and molecular weight was calculated using the relation: [h] = 6.77 ¥ 10-4Mh
Mw = 7.83 ¥ 105 g mol-1, Mw/Mn = 16.9.
.
c tp = 0.25 h. d Not determined, polymer sample only partially dissolved
0.67
in decahydronaphthalene at 135 ◦C. e Mw and Mw/Mn were determined by GPC. For Entry 8, Mw = 4.17 ¥ 105 g mol-1, Mw/Mn = 15.3. f For Entry 15,
Table 5 The polymerization of ethylene with 5a–c/MAO catalytic systemsa
Entry
Catalyst
[Al]/[Zr]
Temp/◦C
Yield/g
Activity/kg-PE (mol-Zr)-1 [C2H4] -1 h-1
Mhb/105 g mol-1
19
20
21
22
23
24
25
26
27
28
29
30
31
32e
33
34
5a
1000
1000
1000
1000
2000
1000
1000
1000
1000
500
2000
1000
1000
1000
500
30
50
70
90
70
30
50
70
90
70
70
30
50
70
70
70
0.1197
0.2309
0.3208
0.2136
0.2630
0.1401
0.2590
0.2188
0.1357
0.3364
0.1720
0.1492
0.2931
0.2296
0.3239
0.0623
40
98
170
139
140
46
110
117
89
180
92
n.d.c
n.d.c
5.31
1.80
3.94
8.76
6.58
8.60d
2.17
4.63
7.70
9.64
7.88
n.d.c
5.58
2.16
5b
5c
49
125
245
173
33
2000
a In toluene, V = 25 mL, [Zr] = 2 ¥ 10-4 mol/L, Pethylene = 1.0 MPa, tp = 0.5 h. b Intrinsic viscosity was determined in decahydronaphthalene at
◦
0.67
135 C and molecular weight was calculated using the relation: [h] = 6.77 ¥ 10-4 Mh
.
c Not determined, polymer sample only partially dissolved in
decahydronaphthalene at 135 ◦C. d Mw and Mw/Mn were determined by GPC, for Entry 26, Mw = 5.04 ¥ 105 g mol-1, Mw/Mn = 20.3. e tp = 0.25 h.
4 and 22). Comparably, zirconium complexes 4b and 5b with
ortho-dichlorine substituents are somewhat thermally unstable;
they displayed higher activities than 4a and 5a within the temper-
ature range of 30–50 ◦C but lower activities at higher temperature.
This is, however, consistent with the thermal instability of these
complexes observed during their synthesis. Some b-diiminato
titanium complexes were reported to exhibit optimized catalytic
further increasing of the [Al]/[Zr] molar ratio to 2000 led to
a decrease of catalytic activity. Probably, as suggested in the
literature,10a,19 the surface of active species being overlaid with
an excess of MAO and the increased amount of AlMe3 embodied
in MAO led to the deactivation of the active species. As is well-
understood, when MAO is used as the cocatalyst, a large excess
amount has to be adopted to ensure a good activation of the metal
complex pre-catalyst; especially for non-metallocene group 4 metal
complexes, the value of the Al/Zr molar ratio could be higher than
10 000 occasionally.20 For example, group 4 metal complexes with
[O,N]-type phenoxy-iminate ligands were reported to be activated
with large amounts of MAO ([Al]/[M] > 2000–62500) to reach the
optimum catalytic activities;20 we found that the non-linked bis(b-
diketiminate) zirconium complexes6 displayed optimum catalytic
activities for ethylene polymerization at [Al]/[Zr] = 2000. It
◦
activities at about 25 C.4,5,7k In our previous work, zirconium
complexes bearing non-linked b-diketiminate ligands exhibited a
maximal value of catalytic activities at about 50 ◦C.6 This series of
alkanediyl-linked bis(b-diketiminate) zirconium complexes seem
to be able to abide higher polymerization temperature.
As shown in Tables 4 and 5, in general, good catalytic activities
of these zirconium pre-catalysts could be obtained with the
enhancement of [Al]/[Zr] molar ratio from 500 to 1000. However,
8242 | Dalton Trans., 2009, 8237–8247
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is noteworthy that, in this work, in spite of different ortho-
substituents or bridging units being introduced to the ancillary
ligands, all of the formed zirconium complexes could display
comparatively high catalytic activities for ethylene polymerization
at a low [Al]/[Zr] molar ratio of 500.
introduction of two differient N-aryl moieties to the ligand
backbone led to the existence of multiple active species under
polymerization conditions.6 As mentioned above, the VT-NMR
experiments of complexes 4a and 5a suggestedthat these zirconium
complexes are highly fluxional in solution, possibly involving the
weakening or partial detachment of the Zr–N bonds; it becomes
conceivable that different active species might have formed under
polymerization conditions, hence producing polyethylenes with
broad MWD.22
Due to the difficulty encountered in the synthesis of linked
bis(b-diketimine)s, the modification of the ligand framework was
limited to introducing ortho-substitution on the phenyl rings.
Nearly similar activities were observed for all the zirconium
complexes, as listed in Tables 4 and 5; the steric and electronic
nature of the ortho-substituents on the phenyl rings exhibited
some influence on the polymerization of ethylene. When Al/Zr =
500–1000, in general, for complexes 4a–c, the catalytic activities
for◦ethylene polymerization within the temperature range of 30–
Indicated by the single peak at d = 29.7 ppm in the
1
13C{ H} NMR spectrum (Fig. S6, ESI†) and small resonances of
d = 31.9, 22.6 and 13.8 ppm assignable to the terminal n-propyl
group, linear character without any branch is evident for the
obtained PE samples, which is in agreement with previous reports
of group 4 complexes with N,N-bidentate ligands.23 Melting
temperatures (sample of Entry 8, 134.6◦; sample of entry 26,
137.1 ◦) measured by DSC also prove the polymers are typical
linear polyethylene. Moreover, complexes 4b and 5b were applied
to study the polymerization of propylene or 1-hexene in the
presence of MAO as the cocatalyst, but no polymer could be
obtained.
i
70 C increased in the order of 4c (R1 = R2 = Pr) < 4a (R1 =
R2 = Me) < 4b (R1 = R2 = Cl) (see Entries 1, 7, 13 and Entries
5, 11, 17). The introduction of bulky ortho-isopropyl groups to
the aryl rings in complex 4c was not favored, which might have
cumbered remarkably the coordination sphere of the metal center
and restrained the coordination/insertion of ethylene monomer.
In the case of previously reported non-linked bis(b-
diketiminate) zirconium complexes,6 the introduction of para-
chlorine substituents led to a decrease of catalytic activity, prob-
ably due to the dominant electron-donating behavior via the p–p
conjugated effect from chlorine to phenyl ring. An improvement
of catalytic activity for ethylene polymerization was observed
for a mono-diiminato titanium complex with ortho-fluorine
substituents on the aromatic rings, where the strong electron-
withdrawing effect of fluorine atoms enhanced the electrophilicity
of metal center and led to the increase of activity.5 Herein, we
think that the higher activity of 4b (R1 = R2 = Cl) than 4a (R1 =
R2 = Me) at a lower temperature range could result from the
electron-withdrawing effect of ortho-chlorine substituents, which
might become dominant when a chlorine atom is situated at
the ortho-positions of the phenyl ring versus the para-position.
Owing to the thermal instability, complex 4b lost its advantage
at higher polymerization temperatures, despite bearing electron-
withdrawing ortho-chloro substituents.
Conclusions
Novel linked bis(b-diketiminate) zirconium and hafnium com-
plexes 4a–6b were prepared via the reaction of ZrCl4·2THF or
HfCl4·2THF and the dilithium salt of corresponding ligand at
1 : 1 molar ratio in toluene. Either a distorted trigonal prismatic
geometry or a distorted octahedral geometry around the metal
center was found for 4c and 5c, respectively, via X-ray crystal
structure analysis. In the solid state, both 4c and 5c possess C1-
symmetry, which however could be regarded as quasi-C2 symmetry
when taking into account the very slight differences between the
two b-diketiminate parts. In the presence of MAO, the zirconium
complexes showed moderate catalytic activities for ethylene poly-
merization. The influence of substituents at the ortho-positions of
the aromatic rings on the catalytic activities was significant. When
a low Al/Zr molar ratio of 500 was adopted, these zirconium
complexes could retain comparatively high catalytic activities.
Although the mechanism is still ambiguous, we consider that the
production of polyethylenes with broad MWD (MWD = 15.3–
20.3) by these complexes was related with the fluxional property
of these complexes, which was confirmed by variable temperature
1H NMR measurements.
A similar trend of the influence of ortho-substituents on ethylene
polymerization was also found for complexes 5a and 5b, but not
for 5c (Table 5). Complex 5c with ortho-isopropyl substituents
displayed the highest catalytic activity among the three 1,3-
propanediyl bridged bis(b-diketiminate) zirconium complexes,
unexpectedly. At present we do not have a reasonable explanation
for this counterintuitive phenomenon. Besides, the length of the
bridging unit also had some effect on the catalytic properties of the
corresponding complexes; complexes 5a–b showed slightly lower
catalytic activities than complexes 4a–b with the 1,2-ethanediyl-
bridge, which might result from the more hindered coordination
sphere in 5a–b.21
In our opinion, the introduction of an alkanediyl linkage may
provide a rigid ligand framework and consequently afford zir-
conium complexes with a stereorigid C2-symmetric configuration
capable of catalyzing a stereoselective a-olefin polymerization with
single-site nature. However, selective GPC analysis results revealed
the production of polyethylenes with very broad MWD (MWD =
15.3–20.3). In our previous work, polyethylenes with broad MWD
(14.8) were obtained by zirconium complexes bearing non-linked
asymmetrically substituted bis(b-diketiminate) ligands, where the
Experimental
General considerations and materials
All manipulations were carried out under a dry argon atmosphere
using dry-box or standard Schlenk techniques unless otherwise
stated. Toluene was refluxed over sodium benzophenone ketyl
prior to use. Benzene-d6 and toluene-d8 were dried over sodium
under argon. n-BuLi (Chemetall, 2.5 M in n-hexane) was used
as received. Methylaluminoxane (MAO, 1.53 M in toluene) was
purchased from Witco. ZrCl4·2THF,24 HfCl4·2THF,24 enaminoke-
tones 1a and 1c,1b and linked bis(b-diketimine) 2c12 were pre-
pared according to the literature procedures. NMR spectra were
recorded on Bruker AVANCE-300, 400 and 500 spectrometers
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1
with CDCl3, C6D6 or C7D8 as solvent. Chemical shifts for H
another 0.5 h at room temperature. A solution of ethylene diamine
(1.503 g, 25.00 mmol) in Et3N (15.15 g, 150.0 mmol) was added
to the reaction solution and the stirring was continued overnight.
The volatiles were removed in vacuo and the obtained residue was
treated with 50 mL of toluene for 2 h. [Et3NH]+[BF4]- precipitated
as an oily solid. After filtration, toluene was removed under
reduced pressure to afford a yellow solid. After recrystallization
from ethanol at -20 ◦C, colorless crystals were obtained (7.751 g,
72%) (Found: C, 78.11; H, 8.97; N, 13.1. Calc. for C28H38N4: C,
78.10; H, 8.89; N, 13.01%); mp 140.5–141.5 ◦C; dH (500 MHz,
CDCl3) 1.57 (s, 6H, CH3), 1.95 (s, 6H, CH3), 2.00 (s, 12H,
Ar-CH3), 3.34 (s, 4H, N-CH2), 4.59 (s, 2H, g -CH), 6.84 (t,
NMR spectra were referenced internally using the residual solvent
resonances and reported relative to tetramethylsilane (TMS).
Melting points were determined in sealed glass capillaries under
argon and reported without correction. Elemental analyses were
performed on an EA-1106 instrument. ESI-MS spectra were
recorded on a Micromass LCT mass instrument. Polymeric grade
ethylene was directly used for polymerization without further
purification. 13C NMR spectra of polymers were recorded on a
Bruker AVANCE-500 spectrometer with 1,2-dichlorobenzene-d4
as solvent at 100 ◦C. The intrinsic viscosities [h] of polyethylenes
(PE) were measured with an Ubbelohde viscometer in decahydron-
aphthalene at 135 ◦C. The viscosity average molecular weights of
PE were calculated according to the equation:25 [h] (dL g-1) =
6.77 ¥ 10-4 Mh0.67. Differential scanning calorimetry (DSC) was
perfo◦rmed on a Universal V2.3C TA instrument at a heating rate
of 10 C min-1. Gel permeation chromatography (GPC) performed
on a Waters 150 ALC/GPC system in a 1,2-dichlorobenzene
solution at 135 ◦C was used to determine the weight-average
molecular weights (Mw) and the molecular weight distributions
(Mw/Mn) of the polymers.
3
3J = 7.5 Hz, 2H, p-Ar-H), 7.01 (d, J = 7.5 Hz, 4H, m-Ar-H),
10.77 (br s, 2H, NH); dC (100 MHz, CDCl3) 18.6 (Ar-Me), 19.6
(CMe), 21.5 (CMe), 44.8 (N-CH2), 94.0 (CH), 122.2 (Ar-C),
127.8 (Ar-C), 128.2 (Ar-C), 149.8 (Ar-C), 155.5 (NCMe), 166.24
(NCMe).
N,N¢-(1,2-Ethanediyl)-bis[2-(2,6-dichlorophenyl)amino-4-imino-
2-pentene] (2b). Ligand 2b was synthesized similarly as 2a.
9.501 g (50.00 mmol) of [Et3O]+[BF4]-, 12.21 g (50.00 mmol) of 1b
and 1.503 g (25.00 mmol) of ethylene diamine were used to give
2b as colorless crystals (9.733 g, 76%) (Found: C, 56.38; H, 5.11;
N, 11.02. Calc. for C24H26Cl4N4: C, 56.27; H, 5.12; N, 10.94%);
mp 179–180 ◦C; dH (500 MHz, CDCl3) 1.69 (s, 6H, CH3), 1.99
(s, 6H, CH3), 3.41 (s, 4H, N-CH2), 4.66 (s, 2H, g -CH), 6.85 (t,
Syntheses of zirconium and hafnium complexes
4-(2,6-Dichlorophenyl)amino-3-penten-2-one (1b). 2,6-Dichlo-
roaniline (16.20 g, 100.0 mmol) was mixed with 2,4-pentanedione
(20.02 g, 200.0 mmol) in 100 mL of toluene containing a catalytic
amount of p-toluenesulfonic acid. The reaction solution was
refluxed for 24 h with water removed using a Dean–Stark trap. All
the volatiles were removed in vacuo, and the residue was distilled
under 110–113 ◦C/(0.05 Torr). The obtained pale yellow solids
were recrystallized with ethanol to give 1b as pale yellow crystals
(20.01 g, 82%); mp 77–79 ◦C; dH (500 MHz, CDCl3) 1.74 (s, 3H,
CH3), 2.14 (s, 3H, CH3), 5.32 (s, 1H, g -CH), 7.20 (t, 3J = 8.0 Hz,
1H, p-Ar-H), 7.39 (d,3J = 8.0 Hz, 2H, m-Ar-H), 12.06 (br s, 1H,
NH); dC (100 MHz, CDCl3) 19.0 (NCMe), 29.3 (OCMe), 97.4
(CH), 127.8 (Ar-C), 128.4 (Ar-C), 128.8 (Ar-C), 135.0 (Ar-C),
161.3 (NCMe), 197.1 (OCMe).
3
3J = 8.0 Hz, 2H, p-Ar-H), 7.27 (d, J = 8.0 Hz, 4H, m-Ar-H),
10.61 (br s, 2H, NH); dC (100 MHz, CDCl3) 19.8 (CMe), 22.4
(CMe), 44.7 (N-CH2), 94.1 (CH), 123.1 (Ar-C), 127.7 (Ar-C),
128.1 (Ar-C), 146.8 (Ar-C), 157.74 (NCMe), 169.1 (NCMe).
N,N¢-(1,2-Ethanediyl)-bis[2-(2-trifluoromethylphenyl) amino-4-
imino-2-pentene] (2d). Ligand 2d was synthesized similarly as
2a. 9.501 g (50.00 mmol) of [Et3O]+[BF4]-, 12.16 g (50.00 mmol)
of 1d and 1.503 g (25.00 mmol) of ethylene diamine were used to
give 2d as yellow crystals (8.679 g, 68%) (Found: C, 60.77; H, 5.51;
N, 10.98. Calc. for C26H28F6N4: C, 61.17; H, 5.53; N, 10.97%); mp
144.5–145.5 ◦C; dH (500 MHz, CDCl3) 1.80 (s, 6H, CH3), 1.96
(s, 6H, CH3), 3.35 (s, 4H, N-CH2), 4.64 (s, 2H, g -CH), 6.77 (d,
4-(2-Trifluoromethylphenyl)amino-3-penten-2-one (1d). Enam-
inoketone 1d was synthesized similarly as 1b. 16.11 g (100.0 mmol)
of 2-trifluoromethylaniline and 20.02 g of 2,4-pentanedione
(200.0 mmol) were used to give 1d as light yellow crystals (20.67 g,
85%); mp 57–58 ◦C; dH (500 MHz, CDCl3) 1.88 (s, 3H, CH3),
3
3J = 7.6 Hz, 2H, o-Ar-H), 7.04 (t, J = 7.6 Hz, 2H, p-Ar-H),
3
3
7.40 (t, J = 7.6 Hz, 2H, m-Ar-H), 7.58 (d, J = 7.6 Hz, 2H, m-
Ar-H), 10.68 (br s, 2H, NH); dC (100 MHz, CDCl3) 19.4 (CMe),
21.5 (CMe), 44.5 (N-CH2), 95.1 (CH), 121.6 (Ar-C), 121.9 (Ar-C),
122.5 (q, 1JC-F = 275.1 Hz, CF3), 123.2 (Ar-C), 126.4 (q, 2JC-C-F
=
3
2.13 (s, 3H, CH3), 5.28 (s, 1H, g -CH), 7.23 (d, J = 7.7 Hz, 1H,
52.0 Hz, Ar-C), 132.3 (Ar-C), 150.1 (Ar-C), 157.1 (NCMe), 167.1
(NCMe).
o-Ar-H), 7.35 (t, 3J = 7.7 Hz, 1H, p-Ar-H), 7.54 (t, 3J = 7.7 Hz,
1H, m-Ar-H). 7.70 (d, 3J = 7.7 Hz, 1H, m-Ar-H), 12.45 (br s, 1H,
NH); dC (100 MHz, CDCl3) 19.4 (NCMe), 29.1 (OCMe), 98.5
N,N¢-(1,3-Propanediyl)-bis[2-(2,6-dimethylphenyl)amino-4-imino-
2-pentene] (3a). Ligand 3a was synthesized similarly as 2a.
9.501 g (50.00 mmol) of [Et3O]+[BF4]-, 10.15 g (50.00 mmol) of 1a
and 1.851 g (25.00 mmol) of propylene diamine were used to give
3a as light yellow crystals (6.892 g, 62%) (Found: C, 78.31; H,
8.88; N, 12.54.◦Calc. for C29H40N4: C, 78.33; H, 9.07; N, 12.60%);
mp 80.5–81.5 C; dH (500 MHz, CDCl3) 1.58 (s, 6H, CH3), 1.73
1
(CH), 123.4 (q, JC-F = 271.3 Hz, CF3), 126.2 (Ar-C), 126.6 (q,
2JC-C-F = 39.0 Hz, Ar-C), 128.7 (Ar-C), 132.4 (Ar-C), 136.9 (Ar-C),
137.0 (Ar-C), 159.8 (NCMe), 196.8 (OCMe).
N,N¢-(1,2-Ethanediyl)-bis[2-(2,6-dimethylphenyl)amino-4-imino-
2-pentene] (2a). Following the procedure reported for 2c.12
Under an argon atmosphere, a solution of [Et3O]+[BF4]- (9.501 g,
50.00 mmol) in CH2Cl2 (40 mL) was slowly added to a solution
of 4-(2,6-dimethylphenyl)amino-3-penten-2-one (1a) (10.19 g,
50.00 mmol) in CH2Cl2 (40 mL) at 0 ◦C, then the reaction solution
was stirred overnight at ambient temperature. Et3N (5.051 g,
3
(p, J = 6.7 Hz, 2H, -CH2-CH2-CH2-), 1.87 (s, 6H, CH3), 2.01
3
(s, 12H, Ar-CH3), 3.29 (t, J = 6.7 Hz, 4H, -CH2-CH2-CH2-),
3
4.60 (s, 2H, g -CH), 6.84 (t, J = 7.5 Hz, 2H, p-Ar-H), 7.01 (d,
3J = 7.5 Hz, 4H, m-Ar-H), 10.72 (br s, 2H, NH); dC (100 MHz,
CDCl3) 18.7 (Ar-Me), 19.4 (CMe), 21.5 (CMe), 32.1 (CH2), 40.5
◦
50.00 mmol) was added at 0 C and the mixture was stirred for
8244 | Dalton Trans., 2009, 8237–8247
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(N-CH2), 93.5 (CH), 122.1 (Ar-C), 127.9 (Ar-C), 128.3 (Ar-C),
149.9 (Ar-C), 155.9 (NCMe), 166.3 (NCMe).
dropwise n-BuLi (2.5 M in hexane, 0.80 mL, 2.0 mmol) at
-78 ◦C. The mixture was stirred and allowed to warm to ambient
temperature slowly. After being stirred for an additional 12 h,
the obtained yellow solution was added dropwise to a stirred
suspension of ZrCl4·2THF (0.755 g, 2.00 mmol) in 20 mL of
toluene at -78 ◦C. The reaction mixture was warmed to room
temperature and stirred overnight. The mixture was evaporated
to dryness under reduced pressure and the obtained yellow solid
was extracted several times with hot toluene. All the filtrates were
combined and concentrated to ca. 30 mL under vacuum. Yellow
crystals were obtained after deposition at -20 ◦C overnight
(0.662 g, 56%) (Found: C, 56.73; H, 6.17; N, 9.22. Calc. for
C28H36Cl2N4Zr: C, 56.93; H, 6.14; N, 9.48%); mp 185–190 ◦C
(Dec.); dH (500 MHz, C6D6) 1.34 (s, 6H, CH3), 1.65 (s, 6H, CH3),
2.04 (s, 12H, Ar-CH3), 3.31 (s, 4H, N-CH2), 5.25 (s, 2H, g -CH),
N,N¢-(1,3-Propanediyl)-bis[2-(2,6-dichlorophenyl)amino-4-imino-
2-pentene] (3b). Ligand 3b was synthesized similarly as 2a.
9.501 g (50.00 mmol) of [Et3O]+[BF4]-, 12.21 g (50.00 mmol) of 1b
and 1.851 g (25.00 mmol) of propylene diamine were used to give
3b as yellow crystals (8.947 g, 68%) (Found: C, 56.81; H, 5.45;
N, 10.55. Calc. for C25H28Cl4N4: C, 57.05; H, 5.36; N, 10.64%);
mp 109–110 ◦C; dH (500 MHz, CDCl3) 1.70 (s, 6H, CH3), 1.78
(p, 3J = 6.7 Hz, 2H, -CH2-CH2-CH2-), 1.85 (s, 6H, CH3), 3.35 (t,
3J = 6.7 Hz, 4H, -CH2-CH2-CH2-), 4.66 (s, 2H, g -CH), 6.84 (t,
3
3J = 8.0 Hz, 2H, p-Ar-H), 7.25 (d, J = 8.0 Hz, 4H, m-Ar-H),
10.55 (br s, 2H, NH); dC (100 MHz, CDCl3) 19.6 (CMe), 22.4
(CMe), 31.3 (CH2), 40.4 (N-CH2), 93.4 (CH), 123.1 (Ar-C),
127.8 (Ar-C), 128.1 (Ar-C), 146.9 (Ar-C), 158.1 (NCMe), 169.9
(NCMe).
3
3
6.88 (d, J = 7.5 Hz, 4H, m-Ar-H), 6.97 (t, J = 7.5 Hz, 2H,
p-Ar-H); dC (125 MHz, C6D6) 20.2 (Ar-Me), 24.6 (CMe), 24.7
(CMe), 54.0 (N-CH2), 105.4 (g -CH), 127.4 (Ar-C), 130.3 (Ar-C),
137.9 (Ar-C), 144.5 (Ar-C), 165.5 (NCMe), 166.7 (NCMe).
N,N¢-(1,3-Propanediyl)-bis[2-(2,6-diisopropylphenyl) amino-4-
imino-2-pentene] (3c). Ligand 3c was synthesized similarly as 2a.
9.501 g (50.00 mmol) of [Et3O]+[BF4]-, 12.97 g (50.00 mmol) of
1c and 1.851 g (25.00 mmol) of propylene diamine were used to
give light yellow crystals (9.051 g, 65%) (Found: C, 79.98; H, 9.91;
N, 10.00. Calc. for C37H56N4: C, 79.80; H, 10.14; N, 10.06%); mp
114.5–115.5 ◦C; dH (500 MHz, CDCl3) 1.07 (d, 3J = 6.9 Hz, 12H,
{N,N¢-(1,2-Ethanediyl)-bis[pent-2-ene-4-imino-2-(2,6-dichloro-
phenyl)aminate]} zirconium dichloride (4b). Complex 4b was
synthesized similarly as 4a. 1.024 g (2.000 mmol) of 2b, 0.80 mL
of n-BuLi (2.5 M in hexane, 2.0 mmol), and 0.755 g (2.00 mmol)
of ZrCl4·2THF were used to give yellow crystals (0.739 g, 55%)
(Found: C, 42.87; H, 3.60; N, 8.33. Calc. for C24H24Cl6N4Zr: C,
42.88; H, 3.71; N, 8.14%); mp 168–172 ◦C (Dec.); dH (500 MHz,
C6D6) 1.60 (s, 6H, CH3), 1.63 (s, 6H, CH3), 3.47 (s, 4H, N-CH2),
3
CH(CH3)2), 1.14 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.60 (s, 6H,
3
CH3), 1.69 (p, J = 6.7 Hz, 2H, -CH2-CH2-CH2-), 1.88 (s, 6H,
CH3), 2.84 (sep, 3J = 6.9 Hz, 4H, CH(CH3)2), 3.27 (t, 3J = 6.7 Hz,
3
4H, -CH2-CH2-CH2-), 4.60 (s, 2H, g -CH), 7.01 (t, J = 7.5 Hz,
3
5.44 (s, 2H, g -CH), 6.42 (t, J = 8.0 Hz, 2H, p-Ar-H), 7.06 (d,
3
2H, p-Ar-H), 7.08 (d, J = 7.5 Hz, 4H, m-Ar-H), 10.83 (br s,
3J = 8.0 Hz, 4H, m-Ar-H); dC (125 MHz, C6D6) 23.6 (CMe), 25.4
(CMe), 56.4 (N-CH2), 108.2 (g -CH), 126.9 (Ar-C), 129.7 (Ar-C),
133.1 (Ar-C), 152.3 (Ar-C), 167.9 (NCMe), 168.5 (NCMe).
2H, NH); dC (100 MHz, CDCl3) 19.5 (CMe), 21.9 (CMe), 23.1
(CHMe2), 24.1 (CHMe2), 28.3 (CHMe2), 31.9 (CH2), 40.5 (N-
CH2), 93.4 (CH), 122.8 (Ar-C), 123.0 (Ar-C), 138.3 (Ar-C), 147.1
(Ar-C), 156.0 (NCMe), 166.5 (NCMe).
{N,N¢-(1,2-Ethanediyl)-bis[pent-2-ene-4-imino-2-(2,6-diisopro-
pylphenyl)aminate]} zirconium dichloride (4c). Complex 4c was
synthesized similarly as 4a. 1.085 g (2.000 mmol) of 2c,
0.80 mL of n-BuLi (2.5 M in hexane, 2.0 mmol), and 0.755 g
(2.00 mmol) of ZrCl4·2THF were used to give yellow crystals
(0.829 g, 59%) (Found: C, 62.81; H, 7.78; N, 7.33. Calc. for
C36H52Cl2N4Zr·0.4(C7H8): C, 62.99; H, 7.52; N, 7.57%); mp 204–
Reaction of 1b with 1,2-diaminobenzene. Under an argon
atmosphere, a solution of [Et3O]+[BF4]- (9.501 g, 50.00 mmol)
in CH2Cl2 (40 mL) was slowly added to a solution of 4-(2,6-
dichlorophenyl)amino-3-penten-2-one (1b) (12.15 g, 50.00 mmol)
in CH2Cl2 (40 mL) at 0 ◦C, then the reaction solution was stirred
overnight at room temperature. Et3N (5.051 g, 50.00 mmol) was
added at 0 ◦C and the mixture was stirred for another 0.5 h at
ambient temperature. A solution of 1,2-diaminobenzene (2.703 g,
25.00 mmol) in Et3N (15.15 g, 150.0 mmol) was added to the
reaction solution and the stirring was continued for 48 h. All
the volatiles were removed in vacuo and the obtained residue was
treated with 50 mL of toluene for 2 h. [Et3NH]+[BF4]- precipitated
as an oily solid. After filtration, toluene was removed under
reduced pressure to afford a brown solid. Colorless crystals of
7 (4.551 g) were obtained by column chromatography on silica gel
with petroleum ether as eluent. dH (500 MHz, CDCl3) 1.30 (t, 3J =
7.0 Hz, 3H, OCH2CH3), 1.80 (s, 3H, CH3), 2.38 (s, 3H, CH3),
3.85 (q, 3J = 7.0 Hz, 2H, OCH2CH3), 5.26 (s, 1H, g -CH), 6.87 (t,
3J = 8.0 Hz, 1H, p-Ar-H), 7.27 (t, 3J = 8.0 Hz, 2H, m-Ar-H); dC
(CDCl3, 100 MHz) 14.8 (CH2CH3), 20.6 (CMe), 23.6 (CMe), 63.5
(CH2CH3), 100.1 (CH), 123.4 (Ar-C), 125.5 (Ar-C), 128.3 (Ar-C),
147.0 (Ar-C), 166.4 (NCMe), 169.0 (NCMe).
◦
3
210 C (Dec.); dH NMR (500 MHz, C6D6) 1.04 (d, J = 6.5 Hz,
3
6H, CH(CH3)2), 1.26 (d, J = 6.5 Hz, 6H, CH(CH3)2), 1.31 (d,
3J = 6.5 Hz, 6H, CH(CH3)2), 1.61 (s, 6H, CH3), 1.63 (d, J =
3
6.5 Hz, 6H, CH(CH3)2), 1.72 (s, 6H, CH3), 2.89 (sep,3J = 6.5 Hz,
2H, -CH(CH3)2), 3.10 (d, 2J = 6.7 Hz, 2H, N-CH2), 3.64 (sep,3J =
6.7 Hz, 2H, -CH(CH3)2), 3.86 (d, 2J = 6.7 Hz, 2H, N-CH2), 5.40
(s, 2H, g -CH), 7.01–7.22 (m, 6H, Ar-H); dC (125 MHz, C6D6)
22.9 (CHMe2), 24.9 (CMe), 25.3 (CHMe2), 25.4 (CHMe2), 26.2
(CHMe2), 26.7 (CMe), 29.4 (CHMe2), 29.6 (CHMe2), 56.3 (N-
CH2), 108.4 (g -CH), 123.9 (Ar-C), 125.4 (Ar-C), 126.3 (Ar-C),
126.7 (Ar-C), 129.9 (Ar-C), 140.5 (Ar-C), 142.9 (Ar-C), 152.5
(Ar-C), 165.5 (NCMe), 168.6 (NCMe).
{N,N¢-(1,3-Propanediyl)-bis[pent-2-ene-4-imino-2-(2,6-dimethyl-
phenyl)aminate]} zirconium dichloride (5a). Complex 5a was
synthesized similarly as 4a. 0.899 g (2.00 mmol) of 3a, 0.80 mL
of n-BuLi (2.5 M in hexane, 2.0 mmol), and 0.755 g (2.00 mmol)
of ZrCl4·2THF were used to give yellow crystals (0.556 g, 46%)
(Found: C, 57.88; H, 6.71; N, 8.45. Calc. for C29H38Cl2N4Zr: C,
57.59; H, 6.33; N, 9.26%); mp 175–179 ◦C (Dec.); dH (500 MHz,
{N,N¢-(1,2-Ethanediyl)-bis[pent-2-ene-4-imino-2-(2,6-dimethyl-
phenyl)aminate]} zirconium dichloride (4a). To a solution of
ligand 2a (0.861 g, 2.00 mmol) in 10 mL of toluene was added
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Dalton Trans., 2009, 8237–8247 | 8245
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C7D8, 60 ◦C) 1.37 (s, 6H, CH3), 1.48 (p, 3J = 6.5 Hz, 2H, -CH2-),
1.79 (s, 6H, CH3), 1.94 (br s, 12H, Ar-CH3), 3.79 (br s, 4H,
of 4c and 5c were solved by direct methods and refined using
Fourier techniques. An absorption correction based on SADABS
was applied.26 All non-hydrogen atoms were refined by full-matrix
least-squares on F2 using the SHELXTL program package.27
Hydrogen atoms were located andrefinedbythe geometrymethod.
The cell refinement, data collection, and reduction were done by
Bruker SAINT.28 The structure solution and refinement were per-
formed by SHELXS-9729 and SHELXL-97,30 respectively. Both in
4c and 5c, inclusion of solvent molecule was detected; the quality
of the crystals was not good enough to allow a satisfactory location
of the solvent molecules at ambient temperature. Hydrogen atoms
of solvent molecules in 4c and 5c that could not be located
were included directly. Molecular structures were generated using
ORTEP-III.31
3
N-CH2), 5.32 (s, 2H, g -CH), 6.86 (d, 4H, J = 7.5 Hz, Ar-H),
6.97 (t, 2H, 3J = 7.5 Hz, Ar-H); dH (500 MHz, C7D8, 20 ◦C) 0.92
(s, 6H, CH3), 1.34 (s, 6H, CH3), 1.58 (m, 2H, -CH2-), 1.70 (s, 12H,
Ar-CH3), 3.25 (br s, 2H, N-CH2), 4.35 (br s, 2H, N-CH2), 5.36
(s, 2H, g -CH), 6.90–7.02 (m, 6H, Ar-H); dC (125 MHz, C7D8,
25 ◦C) 20.8 (-CH2-), 23.3 (CMe), 23.7 (Ar-Me), 24.5 (CMe), 47.3
(N-CH2), 106.5 (CH), 126.5 (Ar-C), 127.5 (Ar-C), 138.1 (Ar-C),
145.1 (Ar-C), 166.5 (NCMe), 168.9 (NCMe).
{N,N¢-(1,3-Propanediyl)-bis[pent-2-ene-4-imino-2-(2,6-dichlo-
rophenyl)aminate]} zirconium dichloride (5b). Complex 5b was
synthesized similarly as 4a. 1.052 g (2.000 mmol) of 3b, 0.80 mL
of n-BuLi (2.5 M in hexane, 2.0 mmol), and 0.755 g (2.00 mmol)
of ZrCl4·2THF were used to give yellow crystals (0.578 g, 43%)
(Found: C, 43.30; H, 3.95; N, 7.87. Calc. for C25H26Cl6N4Zr: C,
43.74; H, 3.82; N, 8.16%); mp 211–220 ◦C (Dec.); dH (500 MHz,
C6D6) 1.00 (br s, 2H, -CH2-), 1.57 (s, 6H, CH3), 1.72 (s, 6H, CH3),
3.60 (br s, 2H, N-CH2), 4.04 (br s, 2H, N-CH2), 5.36 (s, 2H, g -
CH), 6.40 (m, 2H, p-Ar-H), 7.03 (br s, 4H, m-Ar-H); dC (125 MHz,
C6D6) 19.7 (-CH2-), 23.4 (CMe), 27.0 (CMe), 46.9 (N-CH2), 107.7
(CH), 123.7 (Ar-C), 127.0 (Ar-C), 129.9 (Ar-C), 158.5 (Ar-C),
166.7 (NCMe), 168.7 (NCMe).
Typical procedure for ethylene polymerization
A 100 mL autoclave, equipped with a magnetic stirrer, was heated
at 100 ◦C under vacuum for 30 min and then cooled to the
desired temperature by immersing into a thermostatically heated
bath, then filled with ethylene. The appropriate amount of MAO
solution, toluene solution of zirconium complex, and toluene to
bring the final volume to 25 mL were added to the autoclave in
that sequence; the reactor was then pressurized with ethylene. The
ethylene pressure was kept constant during the polymerization.
The reaction mixture was stirred vigorously for a certain time and
the ethylene pressure in the autoclave was slowly vented. Then the
polymerization was quenched with 3% HCl in ethanol (50 mL).
The contents of the reactor were transferred to a beaker and then
separated from the solution by filtration. The collected polymer
was washed to neutral with ethanol and then dried overnight in a
vacuum oven at 60 ◦C to constant weight.
{N,N¢-(1,3-Propanediyl)-bis[pent-2-ene-4-imino-2-(2,6-diis-
opropylphenyl)aminate]} zirconium dichloride (5c). Complex 5c
was synthesized similarly as 4a. 1.114 g (2.000 mmol) of 3c,
0.80 mL of n-BuLi (2.5 M in hexane, 2.0 mmol), and 0.755 g
(2.00 mmol) of ZrCl4·2THF were used to give yellow crystals
(0.760 g, 53%) (Found: C, 63.75; H, 7.24; N, 7.78. Calc. for
C37H54Cl2N4Zr·0.3C7H8: C, 63.44; H, 7.65; N, 7.42%); mp 211–
216 ◦C (Dec.); dH (500 MHz, C6D6) 1.04 (br s, 2H, -CH2-, partially
overlapped), 1.06 (d, 3J = 6.5 Hz, 6H, CH(CH3)2), 1.22 (d, 3J =
The concentration of ethylene in toluene was evaluated accord-
ing to Herry’s law:32
3
6.5 Hz, 6H, CH(CH3)2), 1.26 (d, J = 6.5 Hz, 6H, CH(CH3)2),
1.60 (d,3J = 6.5 Hz, 6H, CH(CH3)2), 1.63 (s, 6H, CH3), 1.71 (s,
6H, CH3), 2.83 (sep, 3J = 6.5 Hz, 2H, CH(CH3)2), 3.67 (m, 4H, N-
CH2), 3.92 (sep, 3J = 6.5 Hz, 2H, CH(CH3)2), 5.30 (s, 2H, g -CH),
7.01–7.19 (m, 6H, Ar-H); dC (125 MHz, C6D6) 23.9 (-CH2-), 25.4
(CHMe2), 25.5 (CHMe2), 26.9 (CMe), 27.7 (CMe), 28.9 (CHMe2),
29.3 (CHMe2), 46.9 (N-CH2), 106.8 (g -CH), 123.9 (Ar-C), 125.6
(Ar-C), 126.9 (Ar-C), 129.2 (Ar-C), 130.0 (Ar-C), 141.3 (Ar-C),
143.7 (Ar-C), 152.5 (Ar-C), 165.9 (NCMe), 169.2 (NCMe).
Cethylene = PethyleneH0exp(DHL/(RT))
where Cethylene = ethylene concentration (mol L-1), Pethylene = ethylene
pressure (atm), H0 = the Herry coefficient, 0.00175 mol L-1 atm-1,
DHL = enthalpy of salvation of ethylene in toluene, 2569 cal
mol-1, R = universal gas constant, 1.989 cal mol-1 K-1) and T =
polymerization temperature (K).
Acknowledgements
{N,N¢-(1,2-Ethanediyl)-bis[pent-2-ene-4-imino-2-(2,6-dichloro-
phenyl)aminate]} hafnium dichloride (6b). Complex 6b was
synthesized similarly as 4a. 1.024 g (2.000 mmol) of 2b,
0.80 mL of n-BuLi (2.5 M in hexane, 2.0 mmol), and 0.928 g
(2.00 mmol) of HfCl4·2THF were used to give yellow crystals
(1.018 g, 67%) (Found: C, 40.89; H, 3.55; N, 6.91. Calc. for
C24H24Cl6N4Hf·0.5(C7H8): C, 40.98; H, 3.49; N, 6.96%); mp 180–
185 ◦C (Dec.); dH (500 MHz, C6D6) 1.58 (s, 6H, CH3), 1.62 (s,
6H, CH3), 3.52 (s, 4H, N-CH2), 5.40 (s, 2H, g -CH), 6.42 (t, 3J =
8.0 Hz, 2H, p-Ar-H), 7.06 (d, 3J = 8.0 Hz, 4H, m-Ar-H).
This work is subsidized by the National Basic Research Program
of China (2005CB623801), National Natural Science Foundation
of China (NNSFC, 20604009 and 20774027), the Program for
New Century Excellent Talents in University (for H. Ma, NCET-
06-0413), Shanghai Rising-Star Program (06QA14014). All the
financial supports are gratefully acknowledged. Authors also
thank the very kind donation of a Braun glove-box by AvH
foundation.
Notes and references
X-Ray diffraction measurements of 4c and 5c
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8246 | Dalton Trans., 2009, 8237–8247
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The Royal Society of Chemistry 2009
©

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21 Herein an exception was again observed for 5c. At present we have
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with the fluxionality of 5c in solution.
22 The reaction of zirconium complex 4a with excess MAO (30 quiv.)
1
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