Zirconium complexes incorporated with asymmetrical tridentate pincer type mono- and di-anionic pyrrolyl ligands: Mechanism and reactivity as catalytic precursors

Article abstract of DOI:10.1039/c2dt30417a

The reactions of Zr(NR₂)₄ (1, R = Me; 2, R = Et) with an asymmetrical tridentate pincer type pyrrole ligand precursor [C ₄H₂NH(2-CH₂NH^tBu)(5-CH ₂NMe₂)] and treatment o

Full text of DOI:10.1039/c2dt30417a

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PAPER
Zirconium complexes incorporated with asymmetrical tridentate pincer type
mono- and di-anionic pyrrolyl ligands: mechanism and reactivity as catalytic
precursors†
Jia-Wei Hsu,a Yu-Chun Lin,a Ching-Sheng Hsiao,a Amitabha Datta,a Chia-Her Lin,b Jui-Hsien Huang,*a
Jing-Cherng Tsaic and Wei-Che Hsuc
Received 22nd February 2012, Accepted 18th April 2012
DOI: 10.1039/c2dt30417a
The reactions of Zr(NR2)4 (1, R = Me; 2, R = Et) with an asymmetrical tridentate pincer type pyrrole
ligand precursor [C4H2NH(2-CH2NHtBu)(5-CH2NMe2)] and treatment of the derivatives with either
PhNCS or PhNCO have been carried out and characterized. Reacting Zr(NR2)4 (1, R = Me; 2, R = Et)
with [C4H2NH(2-CH2NHtBu)(5-CH2NMe2)] generates Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)](NR2)2
(3, R = Me; 4, R = Et) in high yield along with the elimination of 2 equiv of dimethylamine or
diethylamine, respectively. Interestingly, while changing the solvent from Et2O to CH2Cl2, the complex
Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)][C4H2N(2-CH2NHtBu)(5-CH2NMe2)]Cl (5) is produced by
undergoing C–Cl bond cleavage. Furthermore, reaction of either 3 or 4 with 1 or 2 equiv of PhNCS
or PhNCO yields Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)](NMe2)[PhNC(NMe2)S] (6), Zr[C4H2N-
(2-CH2NtBu)(5-CH2NMe2)](NEt2)[PhNC(NEt2)O] (7) and Zr[C4H2N(2-CH2NHtBu)(5-CH2NMe2)]-
[PhNC(NEt2)O]3 (8), respectively. All the aforementioned complexes were characterized by 1H and
13C NMR spectrometry and the molecular structures of 5, 6, and 8 have been determined by single-crystal
X-ray diffractometry. Complexes 4, 5, and 7 initiated the ethylene polymerization in the presence of MAO
as the co-catalyst.
high thermal stability and the unusual reactivity that they confer
to the metal complexes they form stand out. It is due to these
Introduction
The control of the properties of metal centers by a well defined
ligand system is an ultimate goal of inorganic and organo-
metallic chemistry. From the point of view of ligand design,
nitrogen donor ligands, for which in principle a great variety of
synthetic strategies is available, may generate catalytically active
complexes.1 A large number of metallocene complexes that have
a nitrogen atom directly bonded at the cyclopentadieneyl (Cp)
ring, have been prepared and characterized physicochemically
and theoretically.2 Different Cp ligand mediated organometallic
complexes have been reported previously.3 Excepting the Cp
ligand systems, various non-Cp ligand types have been adopted
in organometallic complexes.4 Among these non-Cp ligands,
pincer type ligands5 have been used and reviewed in the past
decades. Pincer complexes are a group of species with very
particular and interesting physical properties, among which their
characteristics of robustness and thermal stability that pincer
compounds have attracted the continuous attention of the
chemistry community for multiple applications, this being par-
ticularly true in the case of homogeneous catalysis.6 Pincer type
ligands can bind to metals in versatile modes by means of rigid
or flexible tridendate mono-anionic, di-anionic, or tri-anionic
ligands. Early transition metal complexes containing various
pincer type ligands have been observed in the literature, as
depicted in Scheme 1, where most of the pincer type ligands
show symmetrical geometries.7–16
We have been interested in using substituted pyrrolyl as sup-
porting ligands with various metals17 since the pyrrolyl entity
has the capability to bring metal atoms into close proximity and
provides an intramolecular or intermolecular pathway for
bonding interactions. Recently we have published one paper
using a tridentate asymmetrical pyrrole ligand, [C4H2NH-
(2-CH2NHtBu)(5-CH2NMe2)], to react with aluminum hydride
complexes in which the pyrrolyl ligand acted as a tridentate
mono-anionic ligand.18 As part of our continuing interest in
developing systems using the asymmetrical pyrrole ligands, the
present contribution focuses on the versatile bonding modes of
our designed ligand and the C–Cl bond cleavage promotion by
the di-anionic pyrrolyl ligands.
aDepartment of Chemistry, National Changhua University of Education,
Changhua 50058, Taiwan. E-mail: juihuang@cc.ncue.edu.tw
bDepartment of Chemistry, Chung-Yuan Christian University,
Chun-Li 320, Taiwan
cDepartment of Chemical Engineering, National Chung Cheng
University, Minhsiung, Chiayi 62102, Taiwan
†CCDC 867477 (5), 867478 (6) and 867479 (8). For crystallographic
data in CIF or other electronic format see DOI: 10.1039/c2dt30417a
7700 | Dalton Trans., 2012, 41, 7700–7707
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Scheme 1 Early transition metal complexes containing various pincer type ligands.
Results and discussion
Synthesis and characterization
The reactions of Zr(NR2)4 (1, R = Me; 2, R = Et) with asymme-
trical tridentate pyrrole ligands are summarized in Scheme 2.
Reacting 1 and 2 with 1 equiv of [C4H2NH(2-CH2NHtBu)-
(5-CH2NMe2)] in diethyl ether, methylene chloride, or heptane gen-
erates Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)](NR2)2 (3, R = Me;
4, R = Et) in high yield by elimination of 2 equiv of dimethyl-
amine or diethylamine, respectively. The 1H NMR spectrum of 3
shows appropriate signals corresponding to the different binding
modes of the tridentate pyrrolyl ligand to the zirconium atom.
The anionic amido and neutral amine nitrogen of the correspond-
ing CH2NtBu and CH2NMe2 arms are connected to zirconium
via covalent and coordination modes, respectively. The methyl-
ene protons of the CH2NtBu and CH2NMe2 fragments show res-
onances at δ = 4.80 and 3.41, which belong to a downfield shift
comparable to the neutral precursor. The crystallographic data of
complexes 3 and 4 are not suitable for publication; however, the
spectral results confirm the geometries of these complexes.
Scheme 2 Reactions of Zr(NR2)4 (1, R = Me; 2, R = Et) with asym-
metrical tridentate pyrrole ligands.
While adding
2
equiv of [C4H2NH(2-CH2NHtBu)-
(5-CH2NMe2)] to Zr(NR2)4 in diethyl ether, one unit of pyrrolyl
ligand mediated complexes 3 and 4 was isolated, leaving another
equiv of unreacted species. Interestingly, an unexpected complex,
Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)][C4H2N(2-CH2NHtBu)-
(5-CH2NMe2)Cl (5) has been produced during the reaction of 1
and 2 with 2 equiv of tridentate pyrrolyl ligands in methylene
chloride with moderate yield. Complex 5 can also be produced
from the reactions of 3 and 4 with an additional equiv of
[C4H2NH(2-CH2NHtBu)(5-CH2NMe2)] in methylene chloride.
Scheme 3 Insertion of an NCS fragment into a Zr-amide bond to gen-
erate complex 6, Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)](NMe2)[PhNC-
(NMe2)S].
1
The geometrically rigid complex 5 shows complicated H NMR
due to the intramolecular hydrogen bonding with the nitrogen
atom of the non-coordinated CH2NMe2 fragment.19
spectra in C6D6, where the methylene protons of Zr-bonded
CH2NMe2, CH2NtBu, and CH2NHtBu stand for the diastereo-
topic coupling of doublets of doublet span in a range of δ from
5.00 to 2.72. The non-coordinated CH2NMe2 fragment shows
one singlet at δ = 2.47 for the methylene protons. Additionally,
The treatment of complex 4 with 1 or 2 equiv of PhNCS
resulted in several products, which made isolation and purifi-
cation difficult. Fortunately, we refined the complexation
between 3 and 1 equiv of PhNCS, which resulted in the insertion
of an NCS fragment into a Zr-amide bond to generate complex
6, Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)](NMe2)[PhNC(NMe2)S],
in moderate yield (Scheme 3). Insertion involving isothiocyanate
into M–E bonds (where E can be carbon or heteroatoms) are
1
the structure of 5 is also identified by H homonuclear decou-
1
pling and H-13C HSQC 2-D NMR spectra. It is worthy to note
that the amino proton of Zr-bonded NHtBu fragment shows a
1
downfield shift in the H NMR spectrum (δ = 7.47), presumably
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well known in the literature.20 In 6, the methyl protons of Zr–
NMe2 appear as two singlets at δ = 2.26 and 2.50, and the
methyl group of PhNC(NMe2)S appears as one singlet at δ =
2.33. The 13C NMR chemical shift for the quaternary carbon of
thioureato PhNC(NMe2)S appears at δ = 179.6, which is consist-
ent with previous results in the literature.21
Similarly, the reactions of complex 4 with PhNCO and PhNC-
(NEt2)OH are summarized in Scheme 4. Reacting complex 4
with 1 equiv of PhNCO generates a zirconium mono-(ureato)
complex 7, Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)](NEt2)[PhNC-
(NEt2)O], in moderate yield via insertion. As evidenced by the
13C NMR spectra of complex 7, the chemical shift for the qua-
ternary carbon of ureato PhNC(NEt2)O remains at δ = 166.3.
Complex 7 can also be initiated by the interaction of 4 with
1 equiv of PhNC(NEt2)OH, derived from the condensation of
PhNCO and HNEt2.
Unexpectedly, the reaction of 4 and 2 equiv of PhNC(NEt2)-
OH in diethyl ether resulted in tris(ureato) zirconium complex 8,
Zr[C4H2N(2-CH2NHtBu)(5-CH2NMe2)][PhNC(NEt2)O]3,
in
moderate yield. It is notable that no bis(ureato) zirconium
complex was isolated while reacting 2 equiv of PhNC(NEt2)OH
with 4, but surprisingly the complexation between 3 equiv of
PhNC(NEt2)OH and 4 ultimately led to the formation of the tri-
dentate pyrrole ligand, tetrakis(ureato) zirconium complex22 and
several un-identified products. Complex 8 can also be detected
1
from the H NMR spectra from the reaction of 7 with 1 equiv of
PhNC(NEt2)OH in C6D6 in a J. Young NMR tube. The 1H
NMR signals of 8 are quite broad at room temperature; therefore,
1
we applied variable temperature H NMR as shown in Fig. 1.
The diethyl group of the PhNC(NEt2)O fragments exhibit as a
triplet and a quartet at δ = 2.95 and 0.81, respectively, at 373 K.
However, while lowering temperature to 250 K, the ethyl groups
exhibit broad resonance signals, an indication of fast exchange
among the three ureato fragments.23 In addition, the character-
istic 13C NMR signal for the quaternary carbons of ureato PhNC
(NEt2)O belongs at δ = 166.4 at 373 K.22
Molecular geometries of complexes 5, 6 and 8
The molecular geometries of 5, 6 and 8 were determined by
X-ray single-crystal diffractometry and their data collections and
selected bond lengths and angles are summarized in Tables 1
and 2, respectively. The crystal structure of 5, as shown in
Fig. 2, adopts a distorted octahedron constructed with two sub-
stituted pyrrolyl ligands and one chlorine atom, and represents a
mer-isomer. One of the substituted pyrrolyl ligands behaves as a
mono-anionic pincer type ligand where the nitrogen atoms of the
NHtBu and NMe2 fragments occupy trans positions with the
angle of N(1)–Zr(1)–N(3) at 138.85(6)°, and the Npyrrolyl is trans
to NtBu of another pyrrolyl ligand having an N(2)–Zr(1)–N(5)
angle of 163.12(6)°. It is worth noting that the bidentate coordi-
nation mode of the second pyrrolyl ligand, which results in a
chelating angle formed by participation of Npyrrolyl, NtBu and Zr
atoms N(5)–Zr(1)–N(4) of 79.74(6)°, subsequently leaves
Scheme 4 Reactions of complex 4, Zr[C4H2N(2-CH2NtBu)(5-CH2-
NMe2)](NEt2)2, with PhNCO and PhNC(NEt2)OH.
Fig. 1 Variable temperature 1H NMR spectra of complex 8 in d8-toluene using a 300 M Hz NMR spectrometer.
7702 | Dalton Trans., 2012, 41, 7700–7707
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Table 1 Summary of the data collection for complexes 5, 6, and 8
5
6
8
Formula
Fw
Cryst syst
Space group
a (Å)
b (Å)
c (Å)
C24H43ClN6Zr
542.31
Monoclinic
P21/n
15.384(3)
9.8710(18)
18.687(3)
90
110.323(9)
90
C23H38N6SZr
521.87
Monoclinic
P21/n
9.4590(6)
26.1531(16)
10.9676(7)
90
109.209(3)
90
C45H67N9O3Zr
873.30
Triclinic
ˉ
P1
11.3294(5)
12.1455(5)
17.9863(8)
90.132(2)
96.703(2)
109.661(2)
2312.43(17)/2
1.254
α (°)
β (°)
γ (°)
V (Å3)/Z
2661.1(8)/4
1.354
0.536
2562.1(3)/4
1.353
0.532
D
calc (g cm−3
)
μ (mm−1
F(000)
)
0.286
928
Fig. 2 The molecular geometry of complex 5. The thermal ellipsoids
are drawn at the 30% probability level. The hydrogen atoms are omitted
for clarity.
1144
1096
Size (mm)
0.40 × 0.21 ×
0.15
1.48 to 28.85
45 256
0.40 × 0.30 ×
0.25
1.56 to 29.47
36 264
0.40 × 0.21 ×
0.15
1.14 to 28.76
37 208
2θ range (°)
Reflns,
collected
Reflns, ind
6956 [R(int) =
0.0577]
7075 [R(int) =
0.0562]
11 975 [R(int) =
0.0321]
Abs corr
(Tmax, Tmin
0.7738 and
0.5327
0.875 and
0.826
0.7738 and
0.5327
)
GOF
1.037
1.008
1.080
R [I > 2σ(I)]
R (all data)
R1 = 0.0321,
wR2 = 0.0740
R1 = 0.0475,
wR2 = 0.0808
R1 = 0.0385,
wR2 = 0.0803
R1 = 0.0690,
wR2 = 0.0911
R1 = 0.0339,
wR2 = 0.0853
R1 = 0.0433,
wR2 = 0.0935
Table 2 Selected bond lengths (Å) and angles (°) for complexes 5, 6,
and 8
Fig. 3 The molecular geometry of complex 6. The thermal ellipsoids
are drawn at the 30% probability level. The hydrogen atoms are omitted
for clarity.
5
Zr(1)–Cl(1)
Zr(1)–N(2)
Zr(1)–N(4)
N(4)–Zr(1)–Cl(1)
N(1)–Zr(1)–N(3)
N(2)–Zr(1)–N(1)
6
Zr(1)–N(1)
Zr(1)–N(3)
Zr(1)–N(6)
S(1)–C(7)
N(2)–Zr(1)–N(3)
N(2)–Zr(1)–N(1)
N(4)–C(7)–S(1)
8
Zr(1)–O(1)
Zr(1)–O(2)
Zr(1)–O(3)
Zr(1)–N(8)
O(2)–Zr(1)–N(1)
O(1)–Zr(1)–N(7)
N(1)–Zr(1)–N(5)
N(4)–Zr(1)–N(7)
2.4590(6)
2.1289(16)
2.1837(15)
168.93(4)
138.85(6)
69.40(6)
Zr(1)–N(1)
Zr(1)–N(3)
Zr(1)–N(5)
N(5)–Zr(1)–N(2)
N(5)–Zr(1)–N(4)
N(2)–Zr(1)–N(3)
2.4027(16)
2.4120(16)
2.1060(16)
163.12(6)
79.74(6)
Fig. 3. Complex 6 contains a highly distorted octahedral geo-
metry, surrounded by a tridentate pyrrolyl ligand, an additional
NMe2 fragment and a bidentate PhNCS unit and comprises the
bond angles of the three axes N(2)–Zr(1)–N(3), N(6)–Zr(1)–
N(4) and N(1)–Zr(1)–S(1) of 142.50(7), 148.23(7) and
150.76(6)°, respectively. The molecule possesses a four-mem-
bered thioureato plane, which is consistent with obtuse and acute
bond angles N(4)–C(7)–S(1) of 112.70(17)° and N(4)–Zr(1)–
S(1) of 61.54(5)°. The bond lengths and angles of the thioureato
plane towards the Zr atom are rather similar to those in the litera-
ture.21 The molecule itself is arranged as a mer-isomer with the
coordination of the tridentate pyrrolyl ligand the same as in 5,
and the corresponding Zr–Npyrrolyl distance [2.1387(19) Å] is
comparable to the former.
69.99(6)
2.1387(19)
2.0864(19)
2.0736(19)
1.751(2)
142.50(7)
69.19(7)
Zr(1)–N(2)
Zr(1)–N(4)
Zr(1)–S(1)
N(1)–Zr(1)–S(1)
N(4)–Zr(1)–S(1)
N(3)–Zr(1)–N(1)
N(6)–Zr(1)–N(4)
2.541(2)
2.2790(18)
2.7012(6)
150.76(6)
61.54(5)
73.54(7)
148.23(7)
112.70(17)
2.2068(12)
2.1999(11)
2.2178(11)
2.2826(13)
58.87(4)
152.83(5)
164.26(5)
148.14(5)
Zr(1)–N(1)
Zr(1)–N(4)
Zr(1)–N(5)
Zr(1)–N(7)
O(1)–Zr(1)–N(4)
N(7)–Zr(1)–N(8)
O(3)–Zr(1)–N(5)
2.2593(12)
2.2668(13)
2.2524(12)
2.4863(14)
58.64(5)
72.31(5)
58.70(4)
Crystals of 8 were obtained from a diethyl ether solution at
−20 °C and its molecular structure is shown in Fig. 4.
In complex 8, the central Zr atom lies on an eight-coordinated
environment featuring bidentate orientation of the nitrogen and
oxygen donor atoms from the corresponding pyrrolyl and three
ureato ligands. Two of the four-membered ureato rings belong
on one plane and the third one is on the same plane as a five-
membered bidentate pyrrolyl metallacycle. Fig. 5 depicts a clear
representation of two perpendicular planes. The pyrrolyl ligand
mediated N–Zr–N acute angle is 72.31(5)°, similar to those of
the NMe2 fragment dangling outside of the coordination sphere.
The comparison of the corresponding Zr–Npyrrolyl bond lengths,
[Zr(1)–N(2) and Zr(1)–N(4), 2.1289(16) and 2.1837(15) Å], is a
clear indication that the tridentate pincer type pyrrolyl ligand
holds to Zr more strongly than the bidentate one.
Pale yellow crystals of 6 were obtained from a saturated
diethyl ether solution and its molecular structure is depicted in
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reported bidentate pyrrole zirconium complexes.24 The N–C
(1.332(2) to 1.336(2) Å) and C–O (1.2929(18) to 1.332(2) Å)
bond lengths of the ureato fragments both correspond to the
range of a partially double bond, indicating that the π electrons
of the ureato fragments are equally delocalized in the NC(N)O
core.25
Mechanism of the formation of complex 5
Complex 5 shows its versatility in being generated from path-
ways of complexes 1–4 with different equivalent amounts of the
tridentate pyrrolyl ligand precursor in methylene chloride.
However, complex 5 could not be generated while using THF,
heptanes or toluene as the reacting solvents. Excess [C4H2NH-
(2-CH2NHtBu)(5-CH2NMe2)] with Zr(NR2)4 in diethyl ether
solution only produces complexes 3 and 4 along with unreacted
ligand. This consequence indicates that the second equiv of tri-
dentate pyrrole ligand is too bulky to bind the Zr atom or most
likely, forms a highly reactive bis-pyrrolyl Zr intermediate,
which presumably does not remain stable in non-hydrochloroalk-
ane solvents and quickly reforms the starting materials. Besides
this, the presence of methylene chloride provides exothermic
conditions for the bis-pyrrolyl Zr species with C–Cl bond
cleavages.26 Mechanistically, this possibility can be considered
to explain the formation of this derivative, as proposed
in Scheme 5. The reaction of [C4H2NH(2-CH2NHtBu)-
(5-CH2NMe2)] with Zr(NR2)4 in CD2Cl2 in a J. Young NMR
Fig. 4 The molecular geometry of complex 8. The thermal ellipsoids
are drawn at the 30% probability level. The hydrogen atoms are omitted
for clarity.
1
tube is performed and monitored with H NMR spectroscopy.
As expected, the reaction pathway is derived via an intermediate
route. The second equiv sterically hindered pyrrole ligand reacts
with complex 4 forming bis-(pyrrolyl)Zr amide intermediate.
Due to the highly reactive steric congestion of the intermediate,
it simultaneously undergoes C–Cl bond cleavage from the adja-
cent CD2Cl2 bound Zr center via eliminating Et2NCD2Cl to
form complex 5.
Ethylene polymerization
Complexes 4, 5, and 7 were used as catalyst precursors for ethyl-
ene polymerization in the presence of MAO as the co-catalyst,
and the outcomes are presented in Table 3. All the complexes
show moderate activity27 towards ethylene polymerization.
Complex 5 shows higher catalytic activity than complexes 4
and 7. The polyethylenes obtained by using complexes 4, 5, and
Fig. 5 A schematic drawing of the two perpendicular planes of 8. One
plane is formed by two ureato rings and the other is formed by one
ureato ring and one chelated metallocycle ring.
Scheme 5 The presence of methylene chloride provides exothermic conditions for the bis-pyrrolyl Zr species with C–Cl bond cleavages.
7704 | Dalton Trans., 2012, 41, 7700–7707 This journal is © The Royal Society of Chemistry 2012

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1
Table 3 Ethylene polymerization data using complexes 4, 5, and 7 in
the presence of MAO
pale orange compounds (0.195 g, yield 84%). H NMR (C6D6):
0.99 (t, 12H, JHH = 6.9 Hz, NCH2CH3), 1.41 (s, 9H, NtBu),
2.09 (s, 6H, CH2NMe2), 3.02 (m, 4H, JHH = 6.9 Hz
NCHaHbCH3), 3.25 (m, 4H, JHH = 6.9 Hz, NCHaHbCH3), 3.47
(s, 2H, CH2NMe2), 4.77 (s, 2H, CH2NtBu), 6.23 (s, 1H, pyrrolyl
CH), 6.30 (s, 1H, pyrrolyl CH). 13C{1H}NMR(C6D6): 15.0,
30.2, 43.1, 48.6, 52.9, 55.1, 64.0, 100.6, 104.6, 131.3, 142.7.
Elem. Anal.: Calcd: C, 54.25; H, 9.33; N, 15.82. Found: C,
54.67; H, 9.05; N, 15.15.
b
Cat
[MAO]/[cat]
Activitya
Tm
ΔHc
Mn
Mw/Mn
4
5
7
2000
2000
2000
47
69
39
133
130
133
149.0
126.5
162.5
187 000
146 000
272 000
2.8
2.6
3.0
a [g (polymer) mmol−1 (zirconium) h−1 bar−1 (ethylene)]. b Crystalline
melting temperature [°C]. c Heat of fusion [J g−1]. Tm and ΔH were
determined by DSC. Mn and Mw/Mn were determined by high
temperature GPC (in trichlorobezene at 135 °C).
Synthesis of ZrCl[C4H2N(2-CH2NHtBu)(5-CH2NMe2)]-
[C4H2N(2-CH2NtBu)- (5-CH2NMe2)] (5))
7 have rather narrow Mw/Mn values (2.6–3.0) indicating the
To a solution of Zr(NEt2)4 (0.5 g, 1.31 mmol) in CH2Cl2
(15 mL) was added a [C4H2NH(2-CH2NHtBu)(5-CH2NMe2)]
(0.55 g, 2.62 mmol)/CH2Cl2 (15 mL) solution at 0 °C. The
resulting solution was stirred at room temperature for 14 h and
volatiles were removed in vacuo. The residue was recrystallized
from a saturated CH2Cl2 solution at −20 °C to generate 0.358 g
single site behaviors of these catalysts.28
Experimental
General procedure
1
red crystals (yield 53%). H NMR (C6D6): 0.99 (s, 9H, NHtBu),
All reactions were performed under a dry nitrogen atmosphere
using standard Schlenk techniques or in a glove box. Heptane
and diethyl ether were dried by refluxing over sodium benzophe-
none ketyl. CH2Cl2 was dried over P2O5. All solvents were dis-
tilled and stored in solvent reservoirs which contained 4 Å
molecular sieves and were purged with nitrogen. 1H and
13C NMR spectra were recorded on a Bruker Avance 300
spectrometer. Chemical shifts for 1H and 13C spectra were
recorded in ppm relative to the residual protons of CDCl3 (δ =
7.24, 77.0) and C6D6 (δ = 7.15; 128.0). Elemental analyses were
performed on a Heraeus CHN-OS Rapid Elemental Analyzer at
the Instrument Center of the NCHU. Zr(NMe2)4 were purchased
from Aldrich and used as received. [C4H2NH(2-CH2NHtBu)-
1.55 (s, 9H, NtBu), 1.85 (s, 6H, NMe2), 2.03 (s, 3H, NMe2),
2.33 (s, 3H, NMe2), 2.47 (s, 2H, CH2NMe2), 2.72 (d, 1H, JHH
=
12.6 Hz, CHaHbNMe2), 3.56 (d, 1H, JHH = 12.6 Hz,
CHaHbNMe2), 3.83 (d, 1H, JHH = 12.6 Hz, CHaHbNHtBu), 4.35
2
3
(dd, 1H, JHH = 12.6 Hz, JHH = 7.8 Hz, CHaHbNHtBu), 4.71
(d, 1H, JHH = 16.5 Hz, CHaHbNtBu), 4.98 (d, 1H, JHH = 16.5
Hz, CHaHbNtBu), 6.04 (s, 1H, pyrrolyl CH), 6.05 (s, 1H, pyrro-
lyl CH), 6.16 (s, 1H, pyrrolyl CH), 6.18 (s, 1H, pyrrolyl CH),
7.47 (d, 1H, JHH = 7.8 Hz, CH2NHtBu). 13C{1H} NMR (C6D6):
28.7, 32.9, 44.6, 47.6, 49.9, 49.9, 50.2, 53.7, 57.2, 57.9, 65.9,
101.4, 103.1, 105.0, 112.8, 133.9, 134.7, 136.4, 143.0.
29
(5-CH2NMe2)],18 Zr(NEt2)4 and PhNC(NEt2)OH30 were pre-
Synthesis of Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)]-
[PhNC(NMe2)S](NMe2) (6))
pared using similar procedures as those reported in the literature.
To a solution of 3 (0.2 g, 0.51 mmol) in diethyl ether (15 mL)
was added PhNCS (0.062 mL, 0.51 mmol) in diethyl ether
(15 mL) at −78 °C. The resulting solution was stirred at room
temperature for 14 h and dried in vacuo to remove all the vola-
tiles. The yellow–orange residue was recrystallized from a satu-
rated diethyl ether solution at −20 °C to generate 0.13 g of pale
yellow solid (yield 48.0%). 1H NMR (C6D6): 1.10 (s, 9H,
NtBu), 2.26 (s, 3H, NMe2), 2.33 (broad, 6H, NCSNMe2), 2.50
(s, 3H, NMe2), 3.13 (d, 1H, JHH = 12.9 Hz, CH2NMe2), 3.19
(s, 6H, Zr-NMe2), 3.82 (d, 1H, JHH = 12.9 Hz, CH2NMe2), 4.26
(d, 1H, JHH = 15.3 Hz, CH2NtBu), 4.63 (d, 1H, JHH = 15.3 Hz,
CH2NtBu), 6.24–6.31 (4H, pyrrolyl CH + PhCH), 6.72 (t, 1H,
JHH = 7.5 Hz, PhCH), 7.00 (t, 2H, JHH = 7.5 Hz, PhCH).
13C{1H} NMR (C6D6): 28.8, 41.1, 45.1, 48.7, 50.5, 52.2, 55.6,
65.1, 100.8, 104.4, 121.9, 122.6, 128.8, 133.0, 142.7, 148.6,
179.6.
Synthesis of Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)](NMe2)2 (3))
To a solution of Zr(NMe2)4 (0.2 g, 0.75 mmol) in 15 mL
pentane was added [C4H2NH(2-CH2NHtBu)(5-CH2NMe2)]
(0.156 g, 0.75 mmol) in pentane (15 mL) at 0 °C. The mixture
was stirred at room temperature for 3 h and the volatiles were
removed under vacuum. The residue was re-crystallized from a
saturated pentane solution at −20 °C to produce 0.22 g of pale
1
yellow needle shaped crystals (yield 77.0%) H NMR (C6D6):
1.39 (s, 9H, NtBu), 1.92 (s, 6H, CH2NMe2), 2.75 (s, 12H,
Zr-NMe2), 3.41 (s, 2H, CH2NMe2), 4.80 (s, 2H, CH2NtBu),
6.31 (s, 1H, pyrrolyl CH), 6.36 (s, 1H, pyrrolyl CH). 13C{1H}
NMR(C6D6): 30.3, 41.4, 47.5, 53.1, 55.2, 63.8, 100.7, 104.8,
131.5, 143.1.
Synthesis of Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)](NEt2)2 (4))
To a solution of Zr(NEt2)4 (0.2 g, 0.52 mmol) in heptane
(15 mL) was added [C4H2NH(2-CH2NHtBu)(5-CH2NMe2)]
(0.11 g, 0.52 mmol) in heptane (15 mL) at room temperature.
After the solution was stirred at room temperature for 3 h, the
resulting solution was dried in vacuo. The orange solid was pro-
pagated from a saturated heptane solution at −20 °C to produce
Synthesis of Zr[C4H2N(2-CH2NtBu)(5-CH2NMe2)]-
[PhNC(NEt2)O](NEt2) (7))
To a solution of 4 (0.2 g, 0.45 mmol) in diethyl ether (15 mL)
was added PhNC(NEt2)OH (0.086 g, 0.45 mmol) in diethyl
ether (15 mL) at 0 °C. The resulting solution was stirred at room
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 7700–7707 | 7705

View Article Online
temperature for 12 h and volatiles were removed in vacuo. The
orange solid was recrystallized from a saturated diethyl ether
solution to give orange crystals (0.183 g, yield 72.0%). 1H NMR
(C6D6): 0.76 (t, 6H, JHH = 6.9 Hz, ZrNCH2CH3), 1.11 (t, 6H,
JHH = 6.9 Hz, CNCH2CH3), 1.21 (s, 9H, NtBu), 2.24 (s, 3H,
NMeaMeb), 2.45 (s, 3H, NMeaMeb), 2.86 (m, 2H, JHH = 7.2 Hz,
Zr-NCH2CH3), 2.99 (m, 2H, JHH = 7.2 Hz, Zr-NCH2CH3), 3.23
(d, 1H, JHH = 12.6 Hz, CH2NMe2), 3.24 (m, 2H, JHH = 6.9 Hz,
CNCH2CH3), 4.00 (d, 1H, JHH = 12.6 Hz, CH2NMe2), 4.10 (m,
2H, JHH = 6.9 Hz, CNCH2CH3), 4.58 (d, 1H, JHH = 15.3 Hz,
CH2NtBu), 4.75 (d, 1H, JHH = 15.3 Hz, CH2NtBu), 6.30 (s, 1H,
displacement parameters. For all the structures, the hydrogen
atom positions were calculated and they were constrained to
idealized geometries and treated as riding where the H atom dis-
placement parameter was calculated from the equivalent isotro-
pic displacement parameter of the bound atom. An absorption
correction was performed with the program SADABS31 and the
structures of both complexes were determined by direct method
procedures in SHELXS32 and refined by full-matrix least-squares
methods, on F2’s, in SHELXL.33 All the relevant crystallo-
graphic data and structure refinement parameters for 5, 6, and 8
are summarized in Table 1.
pyrrolyl CH), 6.34 (s, 1H, pyrrolyl CH), 6.62 (d, 2H, JHH
=
Crystallographic data for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publications nos. CCDC-867477 (5),
CCDC-867478 (6) and CCDC-867479 (8).
7.5 Hz, PhCH), 6.75 (t, 1H, JHH = 7.2 Hz, PhCH), 7.04 (t, 2H,
JHH = 7.8 Hz, PhCH). 13C{1H} NMR(C6D6): 13.3, 15.5, 28.3,
41.3, 43.6, 48.7, 49.3, 52.0, 54.6, 64.9, 100.8, 104.1, 121.9,
122.0, 128.7, 132.4, 142.5, 146.9, 166.3.
Acknowledgements
Synthesis of Zr[C4H2N(2-CH2NHtBu)(5-CH2NMe2)]-
[PhNC(NEt2)O]3 (8))
The authors express their appreciation to the National Science
Council of Taiwan for financial assistance. We would also like to
thank the National Changhua University of Education for provid-
ing the X-ray diffractometer and NMR spectrometer.
To a solution of 4 (0.2 g, 0.45 mmol) in diethyl ether (15 mL)
was added PhNC(NEt2)OH (0.165 g, 0.9 mmol) in diethyl ether
(15 mL) at 0 °C. The solution was stirred at room temperature
for 12 h and all the volatiles were removed in vacuo. The solid
was recrystallized from a saturated diethyl ether solution to
produce 0.165 g of orange crystals (yield 44.0%). 1H NMR
(d8-toluene, 373 K): 0.81 (t, 18H, JHH = 7.2 Hz, NCH2CH3),
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This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 7700–7707 | 7707