A bulky silyl shift-directed synthesis of a silyl-linked amidinate-amidine and its Zr(iv) complex

Article abstract of DOI:10.1039/c0dt01177k

A novel silyl-linked amidinate-amidine monoanionic ligand 3 was synthesized by double additions of PhCN starting from silyl-linked bis(amino) monoanion 2, which underwent an intramolecular Li/H metathesis and double silyl shift. The related Zr(iv) complex

Full text of DOI:10.1039/c0dt01177k

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PAPER
A bulky silyl shift-directed synthesis of a silyl-linked amidinate-amidine and
its Zr(IV) complex†
Hong-Bo Tong, Min Li, Sheng-Di Bai, Shi-Fang Yuan, Jian-Bin Chao, Shuping Huang* and Dian-Sheng Liu*
Received 6th September 2010, Accepted 3rd February 2011
DOI: 10.1039/c0dt01177k
A novel silyl-linked amidinate-amidine monoanionic ligand 3 was synthesized by double additions of
PhCN starting from silyl-linked bis(amino) monoanion 2, which underwent an intramolecular Li/H
metathesis and double silyl shift. The related Zr(IV) complex 4 was prepared and confirmed by X-ray
diffraction revealing a structural rearrangement from its precursor. The mechanisms for the reaction
processes have been proposed. Each of compounds 2, 3 and 4 was characterized by NMR spectroscopy,
elemental analysis and X-ray diffraction. Complex 4 exhibited moderate activity for ethylene
polymerization in the presence of methylalumoxane (MAO).
of the silyl by linking with a electron donor group led to an
Introduction
unusual monoanionic analogue of type II. To the best of our
Amidinate compounds are well known and have been paid
knowledge, this is the first example of a silyl-linked amidinate-
considerable attention in searching for novel spectator ligands.1–3
amidine monoanion.
The ease of tuning the electronic and steric properties by variation
Herein, the synthesis of a silyl-linked amidinate-amidine ligand
of substituents on the conjugated N–C–N backbone make these
with an electron donor group (here NMe2) has been described.
ligands versatile and comparable with the ubiquitous cyclopen-
The mechanisms of the reaction processes are proposed and
tadienyl species. Also based on the similar convenience, a special
configuration changes of the ligand caused by the donor group
branch of linked bis(amidinate) ligands has attracted our interest
discussed. The corresponding Zr(IV) complex 4 was tested as a
in recent years. This new family of bianionic ligands has been
catalyst for ethylene polymerization.
explored because of the advantage of affording both dinuclear and
mononuclear complexes, such as types I and II (Chart 1) which
were investigated in our laboratory.4,6 The related transition metal
derivatives were assumed to be useful in asymmetric synthesis.4,5
Type II complexes display close contact between the two amidinate
moieties.6–9 For relevant work on the isomerization processes
of organosilyl groups in silylamines, a combined experimental–
theoretical study has been made recently by Klingebiel and co-
workers.10
Experimental
All manipulations and reactions were performed under an inert at-
mosphere of nitrogen using standard Schlenk techniques. Solvents
were pre-dried over sodium, distilled from sodium–potassium
alloy (hexane), sodium–benzophenone (diethyl ether, tetrahydro-
˚
furan) and stored over molecular sieves (4 A). Deuterated solvent
(C6D6) was dried over sodium–potassium alloy. All solvents were
degassed prior to use. Chemicals were purified by distillation
before use except for the commercial sample of n-butyllithium
in hexane (2.72 mol dm-3, Alfa Aesar Corporation). 1H, 13C
NMR spectra were recorded on a Bruker DRX-300 spectrometer.
Elemental analyses were performed on a Vario instrument.
Synthesis and characterization
Chart 1
[SiMe(NMe2)(PhNH)2] (1). A stirred solution of aniline (9.3
g, 100 mmol) in hexane (150 cm3) w◦as treated with LiBun (37 cm3,
100 mmol, 2.72 M in hexane) at 0 C. The reaction mixture was
stirred at room temperature for 3 h and then Cl2SiMe(NMe2)
(7.9 g, 50 mmol) was slowly added at -78 ◦C. After stirring for
a further 10 h at room temperature, the mixture was filtered, and
the filtrate was distilled by distillation at 120 ◦C under 5–6 mmHg
to give a very viscous oil [(Me2N)SiMe(PhNH)2].
There have been no monoanionic analogues of type II reported
so far, due to the tendency of intermolecular Li/H metathesis.6
In our further research of type II complexes, the modification
Institute of Applied Chemistry, Shanxi University, Tiayuan, 030006, China
† CCDC reference numbers 761269–761271. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt01177k
4236 | Dalton Trans., 2011, 40, 4236–4241
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Table 1 Crystal and refinement data for 2–4
2
3
4
Chemical formula
Mr
C38H60Li2N6O2Si2
702.98
C58H60Li2N10Si2
967.22
C37H46Cl3N5O2SiZr
818.45
Crystal system
Triclinic
P1
Triclinic
P1
Monoclinic
P21/c
¯
¯
Space group
˚
a/A
11.089(3)
12.471(3)
17.197(4)
81.586(4)
75.624(4)
67.478(4)
2124.5(9)
2
213(2)
8820
7344
0.0370
0.0700
0.1176
0.1288
0.1375
761269
10.660(4)
11.667(6)
12.924(7)
115.39(4)
97.71(3)
105.45(4)
1341.5(11)
1
213(2)
6270
4518
0.0271
0.0705
0.1652
0.0823
0.1728
761270
14.7016(17)
20.676(2)
26.029(3)
90.00
90.506(2)
90.00
7911.6(16)
8
213(2)
32332
13925
0.0529
0.0732
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
T/K
No. reflections measured
No. independent reflections
Rint
Final R1 values (I > 2s(I))
Final wR(F2) values (I > 2s(I))
Final R1 values (all data)
Final wR(F2) values (all data)
CCDC number
0.1432
0.1048
0.1557
761271
1
1.93 g (66.5%), H NMR (300 MHz, 298 K, C6D6): d 0.19 (s,
3H, SiCH3), 1.17 (m, JHH = 7.2, 4H, THF), 2.25 (s, NHPh),
2.74 (s, 6H, N(CH3)2), 3.43 (m, JHH = 7.2, 4H, THF), 6.58–7.47
(m, 10H, Ph); 13C NMR (75.1 MHz, 298 K, C6D6): d (ppm)
149.6 (NCN of amidinate), 149.99 (NCN of amidine), 116.50,
122.43, 122.8, 123.1, 124.6, 125.0, 126.1, 126.3, 126.5, 126.7, 127.3,
127.5, 127.6, 127.8, 127.9, 128.1, 129.0, 134.6, 134.9, 149.27 (Ph),
90.8 (N(CH3)2), 67.6 (OCH2CH2 of THF), 25.5 (OCH2CH2 of
THF), 3.6 (SiCH3). Found: C, 54.5; H, 5.3; N, 8.5. Calc. for
C37H46Cl3N5O2SiZr: C, 54.3; H, 5.7; N, 8.6%.
{[SiMe(NMe2)(PhNH)PhNLi(OEt2)]2} (2). To a stirred solu-
tion of 1 (1.56 g, 10 mmol) in hexane (30 cm3) was slowly added
◦
LiBun (3.7 cm3, 10 mmol, 2.72 M in hexane) at -78 C and the
reaction mixture was warmed to room temperature and stirred
for 10 h, then solvent was carefully removed in vacuo after which
the residue was recrystallized in E◦t2O to give colorless crystals
1
of 2. Yield: 3.12 g (89%), 136–138 C. H NMR (300 MHz, 298
K, C6D6): d (ppm) 0.46 (s, 3H, SiCH3), 1.09–1.13 (t, JHH = 1.8
Hz, 6H, OCH2CH3), 2.19 (s, 1H, NHPh), 2.46 (s, 6H, N(CH3)2),
3.21 (q, JHH = 1.8 Hz, 4H, OCH2CH3), 6.83–7.17 (m, 10H, 2Ph);
13C NMR (75.1 MHz, 298 K, C6D6): d (ppm) 146.3, 129.2,
127.7, 127.38, 127.1 (Ph), 65.2 (OCH2CH3), 36.0 (N(CH3)2), 14.9
(OCH2CH3), -5.1 (SiCH3). Found: C, 64.0; H, 8.1; N 12.0. Calc.
for (C19H30LiN3OSi)2: C, 64.1; H, 8.2; N, 11.95%.
X-Ray crystallography
X-Ray diffraction data of 2, 3 and 4 were collected with graphite-
monochromated Mo-Ka radiation (l = 0.71073 A) on a Bruker
˚
{[SiMe(NMe2){NC(Ph)NH(Ph)}{(NC(Ph)N(Ph)Li)}]2} (3).
To a stirred solution of 2 (1.05 g, 3 mmol) in Et2O (20 cm3)
was added PhCN via syringe (0.3/0.6 cm3, 3/6 mmol) at 0 ◦C
and the mixture was slowly warmed to room temperature and
stirred for a further 5 h. Then the mixed solution was carefully
concentrated in vacuo to afford colourless crystals of 3. Filtering
the solution of unreacted starting material purified the product 3.
Yield: 0.60/1.28 g (41.5/88.5%); mp 173–175 C. H NMR (300
MHz, 298 K, C6D6): d (ppm) 0.36 (s, 6H, SiCH3), 2.55 (s, 12H,
N(CH3)2), 2.76 (s, 2H, NHPh), 6.83–7.47 (m, 20H, C6H5); 13C
NMR (75.1 MHz, 298 K, C6D6): d 165.1 (NCN of amidinate),
164.2 (NCN of amidine), 120.2, 124.6, 124.7, 124.8, 125.0, 127.4,
127.5, 127.6, 127.8, 127.9, 128.1, 128.3, 128.3, 128.5, 128.6, 128.8,
129.2, 137.0, 142.9, 150.6, 152.2, 152.8 (Ph), 38.4 (N(CH3)2),
37.41 (N(CH3)2), 1.2 (SiCH3). Found: C, 72.1; H, 6.1; N, 15.0.
Calc. for C58H60Li2N10Si2: C, 72.0; H, 6.25; N, 14.5%.
Smart Apex CCD diffractometer, equipped with an Oxford
Cryosystems CRYOSTREAM device. The collected frames were
processed with the proprietary software SAINT and an absorption
correction was applied (SADABS) to the collected reflections.11
The structures of the molecules were solved by direct methods
and expanded by standard difference Fourier syntheses using the
software SHELXTL.12,13 Structure refinements were made on F2
using the full-matrix least-squares technique. All non-hydrogen
atoms were refined with anisotropic displacement parameters.
Hydrogen atoms were placed in idealized positions and allowed
to ride on the respective parent atoms. Pertinent crystallographic
data and other experimental details are summarized in Table 1.
Compound 2 exhibits a severely disordered Et2O of the carbon
atoms (C37a, C37b, C38a, C38b) which was resolved by using
SIMU, DELU and EADP restraints. Compound 4 shows a slightly
disordered THF of the carbon atoms (C67–C70, C71–C74) which
was treated by using DFIX restraints.
◦
1
SiMe(NMe2){NC(Ph)NH(Ph)}{(NC(Ph)N(Ph)ZrCl3(THF))·
THF} (4). To a solution of 3 (1.45 g, 3.0 mmol) in Et2O (20 cm3)
◦
at -78 C was added ZrCl4 (0.70 g, 3.0 mmol) and the reaction
Results and discussion
mixture was warmed to room temperature and stirred for a further
10 h, then the solvent was removed in vacuo and extracted with
CH2Cl2. The volatiles were evaporated in vacuo and the residue
was recrystallized in THF to give yellow crystals of 4. Yield:
The silyl-linked diamine [(Me2N)SiMe(PhNH)2] 1 (Scheme 1) was
chosen as precursor and was prepared by a common procedure
reported in literature.6 The synthesis of 1–4 is shown in Scheme 1.
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promoted an intramolecular Li/H metathesis before a further
addition to PhCN, and led to the silyl-linked amidinate-amidine
monoanion 3 (Scheme 1). In contrast, for the dimethylsilyl-linked
monoanion analogue, such a result had not been observed in
our previous work.6 This strongly suggests an intimate relation
between NMe2 group modification and the intramolecular Li/H
metathesis.
The proposed mechanism for the formation of 3 is described
as following (Scheme 2): (1) addition of PhCN to 2 led to the
silyl-linked amino-amidine intermediate a, (2) a subsequent 1,3-
silyl group shift (N to N¢) to form a silyl linked amino-amidinate
intermediate b, (3) an intramolecular Li/H metathesis leading to
c, (4) a further addition reaction of PhCN to give the final product
3
3 with a h -conjugated skeleton by a 1,3-silyl shift (N to N¢). The
result strongly suggests that compound 3 is a thermodynamically
favourable product and d may exist as an intermediate in this
process.
As illustrated in Scheme 1, treatment of 3 with ZrCl4 gave
the corresponding Zr(IV) complex 4. Interestingly, X-ray analysis
showed that 4 has a different molecular skeleton from its precursor
3. The proposed mechanism for the formation of 4 is illustrated
in Scheme 3. First, the reaction might lead to the amidinated
Zr intermediate coordinated with one of N atoms which is
less hindered; second, it undergoes a cleavage of a Si–N¢ bond
and formation of a Si–N bond corresponding to a bulky silyl
group shift (N to N¢) leading to the N–C–N–Si–N–C–N skeletal
rearrangement. The driving force is probably steric as it leads to
coordination of the less bulky amino group.
Scheme 1 Synthesis of compounds 2–4. Reagents and conditions: (i) 1
equiv. LiBun, hexane and Et2O, -78 ◦C; (ii) 1 or 2 equiv. PhCN, Et2O,
0
◦C; (iii) ZrCl4, -78 ◦C, extraction with CH2Cl2, recrystallization from
THF.
Treatment of diamine 1 with 1 equiv. of LiBun gave compound
2. Compound 2 was crystallized in Et2O and characterized by
single-crystal X-ray diffraction. Compound 2 reacted with PhCN
to provide 3 (silyl-linked amidinate-amidine ligand), which was
characterized by single-crystal X-ray diffraction. Interestingly,
the expected silyl-linked bis(amidinate) ligand (type II, Chart 1)
was not isolated from the addition reaction of 2 to PhCN. In
addition, the monoanion 3 was always isolated whether using a
1 : 1 molar ratio (41.5% yield) or 1 : 2 molar ratio (88.5% yield)
of 2 to PhCN. Our original design was to introduce a electron
donor group (NMe2) on the silyl-bridge, however, the NMe2
group changed the basicity of the terminal PhNH group, which
In order to gain further insight into the reaction process, a
7
variable-temperature Li NMR study of compound 3 has been
performed in d8-toluene. As illustrated in Fig. 1, from -20 to 20
◦
7
C, there was only one Li signal at ~1.62 ppm for compound
◦
7
3. From 20 to 70 C, no other Li signals were found; the only
change was in the width of signal. Thus, we believe that compound
3 can not transfer to intermediate d without ZrCl4. Hence we
propose a mechanism for the conversion from compound 2 to
3 via a double 1,3-silyl shift and a Li/H metathesis step. When
3 reacted with ZrCl4, the ligand moved back via a 1,3-silyl
shift to form 4 (Scheme 3). The rearrangement interaction of
Scheme 2 Synthesis mechanism of silyl-linked amidinate-amidine lithium compound 3, a–d are proposed as intermediates in this process.
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Fig. 1 Variable-temperature 7Li NMR studies of compound 3 in
d8-toluene.
Fig. 2 ORTEP view of 2 with thermal ellipsoids at 30% probability level.
Scheme 3 Proposed mechanism of skeletal rearrangement of 4.
the silyl-linked-bis(amidinate) ligand with MCl4 (M = Zr, Ti) is
not an unprecedented case. In previous studies, the interactions
of silyl-linked-bis(amidinato)lithium with ZrCl4 or TiCl4 have
been reported to give similar rearrangement of the molecular
framework.8,9
Compound 2 is a dimer of silyl-linked bis(amino)lithium in
which each Li atom is coordinated by three aniline N atoms
and one O atom from Et2O (Fig. 2). The central Li atoms
and their coordinated N atoms compose three four-membered
rings which adopt a nonplanar saddle-shaped conformation. The
˚
two Li–O bonds are 1.966(6) and 1.924(7) A. The three Li–
˚
N bonds are in the range of 2.08–2.26 A. Each of Li1 or Li2
forms a distorted tetrahedral core with the ligands. One of the
solvated Et2O molecules is disordered over two positions (Fig. 2).
Selected bond lengths and angles for compound 2 are collected in
Table 2.
Compound 3 was crystallized as colorless crystals in the
solid state. The molecular structure of 3 (Fig. 3) shows a
centrosymmetric dimeric arrangement consisting of two lithium
silyl-linked amidinate-amidine moieties. Each Li atom is co-
ordinated by an amidinate moiety, a terminal N atom of an
amidine moiety and an NMe2 moiety with N–Li distances of
Fig. 3 ORTEP view of 3 with thermal ellipsoids at 30% probability level
(symmetry code: -x, -y, -z for atoms A).
˚
2.091(6), 2.111(5), 2.059(6) and 2.130(6) A, respectively. The
coordination geometry around the central Li atoms is distorted
tetrahedral with a sum of angles of 649.6◦ around Li atoms.
Selected bond lengths and angles for compound 3 are collected in
Table 3.
Compound 4 was crystallized in THF as yellow crystals in the
solid state. X-Ray analysis shows that it is converted as a linked
iminoamidinate mononuclear species. Selected bond lengths and
angles for compound 4 are collected in Table 4. The ligand around
the Zr has a different N–C–N–Si–N–C–N backbone from its
precursor 3. The two N–C–N moieties (amidinate and amidine)
exhibit different coordination modes to the metal center; one is
ionic chelating and the other is neutral monodentate. Around the
central Zr atoms, the three Zr–N bonds are in the range of 2.22–
˚
2.28 A. Atoms Cl(1), Zr(1) and Cl(3) are closely linear and this
line is perpendicular to Zr(1)–Cl(2). In the presence of a THF
molecule, the Zr adopts a pentagonal bipyramid configuration
(Fig. 4).
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◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for compound 2
Li(1)–N(1)
Li(1)–N(4)
Li(1)–N(5)
Li(1)–O(1)
2.100(6)
2.115(6)
2.200(6)
1.966(6)
Li(2)–N(1)
Li(2)–N(2)
Li(2)–N(4)
Li(2)–O(2)
2.080(7)
2.266(6)
2.076(7)
1.924(7)
N(1)–Li(1)–N(4)
N(1)–Li(1)–N(5)
N(4)–Li(1)–N(5)
101.5(3)
109.0(3)
78.4(2)
N(4)–Li(2)–N(1)
N(4)–Li(2)–N(2)
N(1)–Li(2)–N(2)
103.6(3)
112.1(3)
77.4(2)
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) for compound 3
Li–N(1)
Li–N(3)
2.091(6)
2.130(6)
Li–N(4A)
Li–N(5A)
2.111(5)
2.059(6)
N(1)–Li–N(4A)
N(5A)–Li–N(1)
N(5A)–Li–N(4A)
128.9(3)
123.5(3)
65.98(2)
N(5A)–Li–N(3)
N(1)–Li–N(3)
N(4A)–Li–N(3)
102.7(2)
100.3(2)
128.2(3)
Fig. 4 ORTEP view of 4 with thermal ellipsoids at 30% probability level.
In order to select appropriate co-catalysts, four common co-
catalysts (AlEt3, AlEt2Cl, MAO or MMAO) have been used at
the same temperature (entries 1–4 in Table 5). As illustrated in
Table 5, in the study of the compound 4 as catalyst at 1 atm of
ethylene pressure (entries 1–4 in Table 5), almost no absorption
of ethylene was observed with AlEt3 and AlEt2Cl as co-catalysts
using Al/Zr of 200 (entries 1 and 2 in Table 5); by using Al/Zr
of 1000, MAO and MMAO were promising as activities increased
to 0.21 ¥ 104 g mol (Zr)-1 h-1 with MMAO (entry 3 in Table 5)
and to 0.32 ¥ 104 g mol (Zr)-1 h-1 (entry 4 in Table 5) with MAO,
respectively.
◦
˚
Table 4 Selected bond lengths (A) and angles ( ) for compound 4
Zr(1)–N(1)
Zr(1)–N(4)
Zr(1)–N(5)
2.278(4)
2.222(4)
2.238(4)
Zr(1)–Cl(1)
Zr(1)–Cl(2)
Zr(1)–Cl(3)
Zr(1)–O(1)
2.450(2)
2.546(2)
2.456(2)
2.288(4)
N(5)–Zr(1)–N(1)
N(4)–Zr(1)–N(5)
N(4)–Zr(1)–N(1)
135.5(2)
59.1(2)
76.5(2)
Cl(1)–Zr(1)–Cl(3)
Cl(1)–Zr(1)–Cl(2)
Cl(3)–Zr(1)–Cl(2)
178.8(1)
87.9(1)
93.1(1)
Ethylene polymerization
In almost all cases, the best activities were observed with a 1000
◦
Recently, the catalytic behavior of transition metal compounds
bearing silylamido motifs14 acting as versatile ligands in various
reactive patterns15–17 has been widely explored.18–27 Some metal
complexes based on diamine ligands have shown to be valuable
as olefin polymerization catalysts.28–33 Here we report the silyl-
linked amidinate-amidine chelate Zr(IV) complex 4 and describe
its catalytic activity for such application.
The general procedures for ethylene polymerization were
adopted as reported in literature.34 Compound 4 was dissolved
in toluene and transferred into an autoclave via a syringe. The
solution of co-catalyst (AlEt3, AlEt2Cl, MAO or MMAO) in
toluene was added via a syringe for activation. While stirring,
ethylene gas was filled into the reactor at 1 (or 10) atm of ethylene
pressure. After stirring for a fixed period of time, the reaction
mixture was quenched with 5% HCl/EtOH. The polymer was
filtered, washed with ethanol and dried in vacuo.
Al/Zr molar ratio under 10 atm of ethylene at 70 C.34 Such
temperatures are favored for commercially applicable catalysts
(about 80 ◦C for the Ziegler–Natta catalytic system). Since the
polymerisation is a highly exothermic reaction, the reaction
temperature will rise and accelerate the formation of the active
species.34
As illustrated in Table 5, in the study of complex 4 as catalyst
at 10 atm of ethylene pressure in the presence of MAO as co-
catalyst (entries 4–7 in Table 5), much higher catalytic activities
were observed than those obtained at 1 atm (entries 1–4 in Table
5). Increasing the reaction temperature from 30 to 70 ◦C (entries
5–7 in Table 5) gave the highest activity of 80.8 ¥ 104 g mol (Zr)-1
h-1 with Mw value of 12.7 ¥ 104 g mol-1 and molecular weight
distribution (MWD) of 5.76 (entry 7 in Table 5). The obtained PEs
possessed melting points (Tm) in the range 133–136 ◦C (entries 3–7
in Table 5), typical for high-density polyethylene (HDPE). The Tm
Table 5 Ethylene polymerization by complex 4
T/◦C
Al/Zr
Activitya
Tmb/◦C
10-4Mw
Mw/Mn
c
c
Entry
Co-cat.
p/atm
1
2
3
4
5
6
7
AlEt3
1
1
1
30
30
30
30
30
50
70
200
200
1000
1000
1000
1000
1000
None
None
0.21
0.32
0.91
2.40
80.8
—
—
136.5
136.1
134.9
134.3
133.2
—
—
—
—
—
—
12.7
—
—
—
—
—
—
5.76
AlEt2Cl
MMAO
MAO
MAO
MAO
MAO
1
10
10
10
Conditions: 5 mmol cat, 30 min, 30 ml toluene for 1 atm or 100 ml toluene for 10 atm. a 104 g mol (Zr)-1 h-1. b Determined by DSC. c Determined by GPC.
4240 | Dalton Trans., 2011, 40, 4236–4241
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values of PEs gradually decreased with an increase in the reaction
temperature (entries 3–7 in Table 5).
8 S.-D. Bai, J.-P. Guo, D.-S. Liu and W.-Y. Wong, Eur. J. Inorg. Chem.,
2006, 4903.
9 S.-D. Bai, H.-B Tong, J.-P Guo and D.-S Liu, Inorg. Chim. Acta, 2009,
362, 114.
In
a
comparison with results by recently explored
precatalysts,33,34 compound 4 showed relatively higher activities
for ethylene polymerisation at 10 atm of ethylene pressure, and
produced similar high-density polyethylene (HDPE). However,
compared with the most commonly used precatalyst Cp2ZrCl2
(about 105 g mol (Zr)-1 h-1),35,36 the catalytic activity of compound
4 is relatively lower under similar conditions. In conclusion, com-
pound 4 exhibited moderate activity for ethylene polymerization
in the presence of methylalumoxane (MAO).
10 C. Matthes, M. Noltemeyer and U. Klingebiel, Organometallics, 2007,
26, 838–845.
11 Bruker SMART (Version 5.0) and SAINT (Version 6.02), Bruker AXS
Inc., Madison, WI, 2000.
12 G. M. Sheldrick, SADABS, SHELXS97 and SHELXL97, University
of Go¨ttingen, Germany, 1997.
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Conclusions
A synthetic pathway for the silyl-linked amidinate-amidine
monoanion 3 had been developed. To the best of our knowledge
it is the first example of a silyl-linked amidinate-amidine ligand.
The processes of double addition of PhCN through bulky silyl
shifts and an intramolecular Li/H metathesis were described. A
related zirconium complex 4 with a structural rearrangement from
its precursor had been obtained and showed moderate activity for
ethylene polymerization in our primary tests.
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Acknowledgements
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We are grateful for the financial support from the Natural Science
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D. Bai) and the Natural Science Foundation of Shanxi Province
(2009011059-1 to H.-B. Tong). We especially acknowledge Prof.
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