Br?nsted Base-Induced Rearrangement and Nucleophilic Addition of O/N-Functionalized NHCs and Relative Group 4 Metal Complexes for Ethylene Polymerization Catalysis

Article abstract of DOI:10.1021/acs.organomet.5b00862

The O/N-functionalized NHC precursors 1-[RNHC(O)CH₂]-3-[2-OH-3,5-^tBu₂-(C₆H₂)CH₂]-imidazolium bromide, [H₃(1a-f)]Br (a: R = 2,6-ⁱPr₂-(C₆H₃); b: R = 2,4,6-Me₃-(C₆H₂); c: R = 2,6-Me₂-(C₆H₃); d: R = 4-Me-(C₆H₄); e: R = 4-Cl-(C₆H₄); f: R = ^tBu), have been synthesized and characterized. Reactions between the aryloxy/amido-NHC precursors [H₃(1a-e)]Br and Ag₂O resulted in the NHC rearrangement to compounds [2-OH-3,5-(^tBu)₂-(C₆H₂)CH₂][R]NC(O)-CH₂-(C₃N₂H₃) (4a-e) in 68-89% yield. The preliminary study suggested that, after deprotonation, the o-quinone methide (o-QM) intermediate was in situ generated by the C-N cleavage and proton transfer of the resultant aryloxybenzyl NHCs, followed by the nucleophilic attack of o-QM to the nitrogen atom of the amido group. Treatment of salicylaldimine-functionalized NHC precursor 1-ⁱPr-3-[2-HO-C₆H₂-3,5-^tBu₂-C(H)? - ?N-CH₂CH₂]-imidazolium bromide, [H₂(2)]Br, with sodium hydride and group 4 metal sources MCl₄(THF)₂ (M = Ti, Zr) step by step afforded rare zwitterionic complexes [M(13)Cl₄] (M = Ti, 10; Zr, 11) in 50-53% yield. The formation of phenolate-amine 13 was attributed to the nucleophilic addition of the formed NHC to the imine carbon after deprotonation. The corresponding products 4a and {[Ti(13)Cl₄]₂(μ-O)} (12) from the controlled hydrolysis of 10 have been confirmed by X-ray single-crystal analysis. Two novel NHC precursors, {H₂(5)}Br and [H₃(7)]Br, together with silver complex [Ag₂(5)₂] (6) were conveniently derived. Several relative group 4 metal complexes, [MX₂(k²-N,O-OC₆H₂-3,5-^tBu₂-C(H)? - ?N - CH₂CH₂-Im)₂][Br]₂ (M = Zr, X = Cl, 8; M = Hf, X = OSiMe₃, 9) and [Ti(7)Cl₂] (14), have been prepared and tested for ethylene polymerization with MAO as cocatalyst. Complex 14 showed the highest catalytic activity of up to ca. 114 kg PE/(mol Ti·h·atm) to produce linear polymer.

Full text of DOI:10.1021/acs.organomet.5b00862

Article
pubs.acs.org/Organometallics
Brønsted Base-Induced Rearrangement and Nucleophilic Addition of
O/N-Functionalized NHCs and Relative Group 4 Metal Complexes for
Ethylene Polymerization Catalysis
Li Wan and Dao Zhang*
Department of Chemistry, Fudan University, 220 Handan Road, Shanghai, 200433, People’s Republic of China
S
* Supporting Information
ABSTRACT: The O/N-functionalized NHC precursors 1-
[RNHC(O)CH2]-3-[2-OH-3,5-tBu2-(C6H2)CH2]-imidazo-
lium bromide, [H3(1a−f)]Br (a: R = 2,6-iPr2-(C6H3); b: R =
2,4,6-Me3-(C6H2); c: R = 2,6-Me2-(C6H3); d: R = 4-Me-
t
(C6H4); e: R = 4-Cl-(C6H4); f: R = Bu), have been
synthesized and characterized. Reactions between the
aryloxy/amido-NHC precursors [H3(1a−e)]Br and Ag2O
resulted in the NHC rearrangement to compounds [2-OH-
3,5-(tBu)2-(C6H2)CH2][R]NC(O)-CH2-(C3N2H3) (4a−e) in
68−89% yield. The preliminary study suggested that, after
deprotonation, the o-quinone methide (o-QM) intermediate
was in situ generated by the C−N cleavage and proton transfer
of the resultant aryloxybenzyl NHCs, followed by the
nucleophilic attack of o-QM to the nitrogen atom of the amido group. Treatment of salicylaldimine-functionalized NHC
precursor 1-iPr-3-[2-HO-C6H2-3,5-tBu2-C(H)N-CH2CH2]-imidazolium bromide, [H2(2)]Br, with sodium hydride and group
4 metal sources MCl4(THF)2 (M = Ti, Zr) step by step afforded rare zwitterionic complexes [M(13)Cl4] (M = Ti, 10; Zr, 11) in
50−53% yield. The formation of phenolate-amine 13 was attributed to the nucleophilic addition of the formed NHC to the
imine carbon after deprotonation. The corresponding products 4a and {[Ti(13)Cl4]2(μ-O)} (12) from the controlled hydrolysis
of 10 have been confirmed by X-ray single-crystal analysis. Two novel NHC precursors, {H2(5)}Br and [H3(7)]Br, together with
silver complex [Ag2(5)2] (6) were conveniently derived. Several relative group 4 metal complexes, [MX2(k2-N,O-OC6H2-
3,5-tBu2-C(H)N−-CH2CH2-Im)2][Br]2 (M = Zr, X = Cl, 8; M = Hf, X = OSiMe3, 9) and [Ti(7)Cl2] (14), have been
prepared and tested for ethylene polymerization with MAO as cocatalyst. Complex 14 showed the highest catalytic activity of up
to ca. 114 kg PE/(mol Ti·h·atm) to produce linear polymer.
center by the covalent tethering of the two anionic functional
groups.
INTRODUCTION
■
N-Heterocyclic carbene (NHC) ligands have been studied
intensely in recent years and are now used widely as strongly
basic phosphine analogues, to support early and late transition
metal complexes.1 The overwhelming majority of NHCs are
functionalized (with respect to the N and N′ substituents) by
incorporating neutral donor or anionic groups such as pyridyl,
phosphine, NHC, amide, alkoxide, aryloxide, and cyclo-
pentadienyl. It is well known that pincer ligands are ubiquitous
in transition and main group metal catalysis due to the stability
offered to the metal complex and the ease with which the
pincer framework can be modified.2 Recently several anionic
pincer-type tridentate ligands, A−G (Figure 1), featuring the
NHC carbene donor in the central position were developed to
stabilize transition metal complexes.3−9 It has been proven that
the NHC moiety could be held in proximity of the metal center
with the help of such covalent tethering to produce incredibly
robust complexes, which are generally more stable than similar
complexes featuring monodentate NHC ligands. In particular
the symmetric pincer NHC ligands (A, B, and E) sufficiently
force the binding of the soft NHC to the hard early metal
Group 4 metal NHC complexes are of interest because of
their unique structural properties1a and their potential
applications in olefin (co)polymerization,3,4b,10 ring-opening
polymerization of rac-lactide,4,11 copolymerization of epoxides
and CO2,12 and hydroamination/cyclization of amino-
alkenes.13,14 In our previous study, several mono- and bis-
aryloxy-modified NHC multidentate hybrid ligand precursors,
[H3(A)]Br (Figure 1) and [H2(J)]Br (Scheme 1), have been
successfully developed, and some early transition Ti(IV),
Zr(IV), and S-block Mg(II) metal compounds have been
synthesized and characterized by X-ray single-crystal analysis.3
However, when the in-situ-generated anionic NHC derivatives
(A)2− and (J)− at low temperature (−78 °C) were slowly
warmed to room temperature, 1,2-migration15 occurred to give
1,2-bisaryloxy-substituted imidazole (A*) and (J*), respectively
(Scheme 1).3 Moreover, if (A)2− was directly hydrated at very
Received: October 21, 2015
© XXXX American Chemical Society
A
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Figure 1. Typical examples of anionic pincer-type tridentate NHC ligands.
Several relative IVB metal complexes were obtained and their
catalytic property for ethylene polymerization has been
explored. Here we wish to report these results.
Scheme 1. 1,2-Migration Rearrangement of Aryloxy-NHCs
(A)2− and (J)−
RESULTS AND DISCUSSION
■
Synthesis of O/N-Functionalized NHC Precursors
[H3(1a−f)]Br and [H2(2)]Br. As shown in Scheme 2, the
aryloxy/amido-NHC precursors [H3(1a−f)]Br were obtained
as white powders in good unoptimized yields (83−89%) by the
reaction of 2-(1H-imidazol-1-yl)-N-(R)-acetamide (3a−f) with
2-(bromomethyl)-4,6-di-tert-butylphenol, a route analogous to
that for [H3(A)]Br.3b Formation of [H3(1a−f)Br was
confirmed by 1H and 13C NMR spectroscopy and high-
resolution mass spectra (HRMS).
The amido-NH resonance in [H3(1a−f)Br was identified by
1
D2O exchange study using H NMR and HSQC spectroscopy
analysis (Table 1; also see Figure S3). For example, the H
low temperature, the monoaryloxy-substituted imidazole was
observed by H NMR due to the C−N bond cleavage.
1
1
Recently we prepared aryloxy/amido-functionalized NHC
precursors [H3(1a−f)]Br and phenoxyimine-modified NHC
precursor [H2(2)]Br.9 We are hopeful that, after deprotonation,
these nonsymmetric pincer NHC ligands (1a−f)2− and (2)−
will efficiently stabilize IVB early transition metal catalysts
(Figure 1). Although (2)− has already been employed in the
synthesis of NHC complexes of nickel(II) and lanthanide
(III),9 no IVB metal NHC example has been reported.
Unexpectedly, when these imidazolium salts were deprotonated
with Brønsted bases, such as Ag2O or NaH, the C−N bond
cleavage, rearrangement (for [H3(1a−f)]Br), and nucleophilic
addition (for [H2(2)]Br) of the formed NHCs occurred.
a
1
Table 1. Selected H NMR Data of H3(1a−f)]Br
NHC precursor
NH
OH
NCHN
H3(1a)]Br
H3(1b)]Br
H3(1c)]Br
9.87
9.88
9.73
10.5
9.09
8.06
6.67
6.67
6.74
7.14
7.10
6.94
9.59
9.59
9.52
9.10
8.84
9.33
b
H3(1d)]Br
b
H3(1e)]Br
H3(1f)]Br
a
b
In ppm in CDCl3. In DMSO-d6.
Scheme 2. Synthesis of Aryloxy/Amido-NHC Precursors [H3(1a−f)]Br
B
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Figure 2. Molecular structures of compound [H3(1a)]Br·(H2O). The bromides, solvent molecules, and all hydrogen atoms are omitted for clarity.
Selected distances (Å) and angles (deg): C(1)−N(2) = 1.306(6), C(1)−N(1) = 1.336(5), N(3)−C(21) = 1.446(5), C(19)−C(20) = 1.530(5),
C(6)−O(1) = 1.379(4), N(1)−C(4)−C(5) = 109.3(3), N(2)−C(19)−C(20) = 112.1(3), O(2)−C(20)−N(3) = 125.9(3), C(20)−N(3)−C(21) =
124.4(3).
1
NMR spectrum of [H3(1a)]Br exhibits three resonances at δ =
9.87, 6.67, and 9.59 ppm for the protons of the amido-NH
group, phenoxy-OH, and imidazolium-CH, respectively; its 13C
NMR spectrum shows the characteristic resonances for the
imidazolium-C2 carbon atom at δ = 151.4 ppm. Crystals of
[H3(1a)]Br·(H2O) (Figure 2) and [H3(1f)]Br·(CH2Cl2)
(Figure S30) obtained by slow diffusion of hexane into their
saturated dichloromethane solution at ambient temperature
were analyzed by X-ray single-crystal diffraction.
The H NMR spectrum of 4a showed the expected absence
of two downfield peaks of the NCHN proton and the amide
(NH) proton of the reactant imidazolium bromide salt. In
comparison with [H3(1a)]Br, the resonances at δ = 0.84 and
1.21 ppm appear as two broad signals and can therefore be
i
assigned to the methyl protons of Pr groups, owing to the
hindered rotation of the C−N bond of the N-2,6-diisopropyl-
phenylacetamido moiety. For the same reason, the −COCH2−
proton resonates as a very broad singlet at δ = 4.78 ppm, which
is quite different from the −NCH2− proton, with a sharp
singlet at δ = 4.78 ppm.
Crystals of 4a·2(C7H8) suitable for X-ray diffraction analysis
were obtained by cooling a saturated toluene solution at −20
°C. The molecular structure (Figure 3) clearly revealed the C−
The phenoxyimine-functionalized NHC precursor [H2(2)]Br
was prepared as a white powder in high yield using a modified
literature procedure.9,16 Notably, recrystallization was proved to
be a good way to purify the crude product, while the gel
chromatography usually made it decompose to 3,5-di-tert-
butylsalicylaldehyde. This ligand was also confirmed by its well-
1
resolved H NMR spectrum.
Silver Oxide-Induced C−N Cleavage and NHC Re-
arrangement of [H3(1a−e)]Br. It is well known that the Ag-
NHC reagent is a useful route to transition metal−NHC
compounds.17 We first tried to deprotonate the NHC precursor
[H3(1a)]Br using silver oxide. After the mixture of [H3(1a)]Br,
Ag2O, and 4 Å molecular sieves in dichloromethane was stirred
in the dark at room temperature for 24 h, no expected NHC-Ag
compound could be obtained after workup. Surprisingly, and in
contrast to other similar reactions, the unexpected imidazole
product 4a was isolated in 80% yield (Scheme 3). Compound
4a was full characterized by 1H and 13C NMR, DEPT, HMBC,
and HRMS.
Figure 3. Molecular structure of compound 4a·2(C7H8). The solvent
molecules and all hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): N(3)−C(10) = 1.311(3), N(2)−
C(10) = 1.343(2), C(11)−C(12) = 1.352(3), N(1)−C(8)−C(9) =
114.96(14), C(7)−N(1)−C(21) = 118.05(13), C(7)−N(1)−C(21) =
118.05(13).
Scheme 3. Ag2O-Induced Rearrangement of [H3(1a−f)]Br
N bond cleavage and migration of the benzyl group. An
important structural feature of compound 4a is its rigid
conformation. The rotation of the C(16)−N(1) bond of the
2,6-diisopropylphenyl group was blocked, which can also be
1
observed in its H NMR spectrum.
Other similar N-arylacetamide-NHC precursors [H3(1b−e)]
Br gave the same result (Table 2). Compounds 4b−e could be
achieved in 68−89% yields employing the same synthetic
methodology as applied for 4a (entries 1−4 and 6). The size of
the N-aryl groups in [H3(1a−e)]Br seemed to lack an obvious
C
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the C−N cleavage product 3d (100 mg) was isolated in 33%
yield (entry 5). Interestingly, for [H3(1e)]Br in DMSO and
DMF, both 3e (54 mg, 21% and 40 mg, 16%) and 4e (61 mg,
20% and 85 mg, 28%) could be obtained in low yield,
respectively (entries 7 and 8). The formation of 3d−e indicates
that the C−N bond cleavage occurs concomitantly during their
reactions with Ag2O. Moreover, in most cases 3,5-di-tert-butyl-
2-hydroxybenzaldehyde could be found in the reaction mixture.
The in situ NMR experiments of [H3(1a)]Br with Ag2O in
CDCl3 were carried out (Figure 4). At the beginning, the signal
at δ = 9.87 ppm for the proton of the amido-NH group quickly
disappeared within 30 min (from (a) to (c)). Later the
deprotonation of imidazolium-CH at δ = 9.59 ppm occurred
slowly; at the same time the signal of isopropyl-CH3 at δ = 0.84
ppm of 4a appears before the complete disappearance of the
imidazolium-CH of [H3(1a)]Br (from (d) to (e)), which
suggests that transformation of [H3(1a)]Br into 4a is rapid and
does not allow any isolation of intermediates species. Moreover,
the resonance at δ = 208.6 ppm in the in situ 13C NMR spectra
of the in situ mixture can be assigned to the generated NHCs
(see Supporting Information).
Table 2. Ag2O-Induced NHC Rearrangement Results of
[H3(1a−f)]Br
a
b
entry
subtract
solvent
product
yield (%)
1
2
3
4
5
6
7
8
9
[H3(1a)]Br
[H3(1b)]Br
[H3(1c)]Br
[H3(1d)]Br
[H3(1d)]Br
[H3(1e)]Br
[H3(1e)]Br
[H3(1e)]Br
[H3(1f)]Br
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DMSO
CH2Cl2
DMF
4a
4b
4c
4d
4d
4e
4e
4e
4f
80
89
68
c
79
d
trace
c
77
e
21
f
DMSO
CH2Cl2
16
cg
,
0
a
Conditions: 5.0 mmol of [H3(1a−e)]Br, 2.75 mmol of Ag2O, several
b
c
4 Å molecular sieves, 10 mL of solvent, rt, 24 h. Isolated yield. 72 h.
d
3d (100 mg) was isolated in 33% yield based on H3(1d)]Br (300
e
mg). Besides 4e (54 mg), 3e (61 mg) was isolated in 20% yield based
on H3(1e)]Br (300 mg). Besides 4e (40 mg), 3e (85 mg) was isolated
in 28% yield based on H3(1e)]Br (300 mg). 3f (55 mg) was isolated
f
g
in 48% yield based on H3(1f)]Br (300 mg) after the solution was
heated to remove silver black.
We protected the phenoxy-OH with a benzyl group to
prepare [H2(5)]Br, a monobenzyl derivative of [H3(1a)]Br
(Scheme 4). When [H2(5)]Br was treated with Ag2O in the
dark, no rearrangement product but the NHC-Ag compound
[Ag2(5)2] (6) was obtained in 35% yield, which is similar to
that previously reported by Ghosh et al.18 This result suggests
that the rearrangement reaction facilitates the proton transfer
and the phenoxy-OH is necessary for this transformation.
All of these observations are in agreement with a plausible
rearrangement pathway proposed in Scheme 5. When the
aryloxybenzyl NHC precursor I was treated with Ag2O, there
exists a slow C−N bond cleavage equilibrium between the
effect on their yields (for example, 80% for 4a and 79% for 4d).
Notably, the N-alkylacetamide-NHC precursor [H3(1f)]Br
gave a different picture (entry 9 and Scheme 3). Treatment
of [H2(1f)]Br with Ag2O in dichloromethane clearly suggested
the formation of an unidentified Ag complex, whose solution
was heated to give silver black and C−N cleavage product 3f
(54 mg, 48% yield).
The sparing solubility of imidazolium salts [H3(1d−e)]Br in
dichloromethane has little impact on their rearrangement
reactions (entries 4, 6 vs 1−3). However, solvent has an
obvious influence (entries 4 vs 5; 6 vs 7, 8). When the reaction
of [H3(1d)]Br (300 mg) was carried out in DMSO, no 4d but
Figure 4. In situ 1H NMR spectra of [H3(1a)]Br (a), [H3(1a)]Br/Ag2O (the molar ratio is 1/0.55) at 10 min (b), 30 min (c), 2 h (d), and 24 h (e),
and 4a (f) in CDCl3 at 20 °C.
D
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phosphorylated imidazoles.21a The N−C migration ability of
N-functionalized NHCs usually depends on their thermal
stability from sterics and the effects of substituents at the
nitrogen atoms. The rate of migration is faster for phosphoryl
than for alkyl such as methyl, which is similar to that occurring
for the N-aryloxy NHC system.
Scheme 4. Synthesis of NHC Precursor [H2(5)]Br and Its
Silver Complex 6
As mentioned above, we have been studying the use of
anionic functional groups pendant on the NHC to provide a
“tether” by which an electropositive metal may be bound more
strongly to the soft carbene center.3 As shown in Scheme 6, a
Scheme 6. Synthesis of NHC Precursor [H3(7)]Br
Scheme 5. Possible Pathway for the NHC Rearrangement of
[H3(1a−f)]Br
new type of bisphenol-linked imidazolium salt, [H3(7)]Br,
which incorporates a bulky N-arylamide linker, has been
derived from 4a; its titanium complex showed high activity for
ethylene polymerization with MAO as cocatalyst (see below).
Sodium Hydride-Induced NHC Nucleophilic Addition
of [H2(2)]Br to Imines. For [H2(2)]Br, we began our research
on the synthesis of group 4 complexes similar to “FI
catalysts”.22 The corresponding group 4 metal complexes
[MX2(k2-N,O-OC6H2-3,5-tBu2-C(H)N-CH2CH2-Im)2][Br]2
(M = Zr, X = Cl, 8; M = Hf, X = OSiMe3, 9) were prepared
with a moderate yield of ca. 55% as shown in Scheme 7. After
Scheme 7. Synthesis of “FI”-like Titanium and Zirconium
Complexes 8 and 9
aryloxybenzyl-NHC II and o-quinone methide (o-QM).1920
Hydrolyzing the mixture at this moment clearly promoted
positive dissociation of II to afford the imidazoles 3a−e
together with 2,4-di-tert-butyl-6-(hydroxymethyl)phenol due to
the nucleophilic attack of water molecule to o-QM. The
nucleophilic N-alkylation of III by o-QM took place on the
nitrogen of the amido group to produce 4a−e together with the
generation of another o-QM. This process was always
accompanied by the proton transfer from the OH of aryloxy
to the carbon of NHC. For [H3(1f)]Br, the acidity of N-
alkylacetamide tert-BuNHCO is too weak to form the
corresponding amido anion in the presence of Ag2O as base;
on the other hand, the o-QM was consumed by the formed
water. As a result, the C−N cleavage product 3f slowly formed.
Besides the above-mentioned C−N cleavage and rearrange-
ment of the N-functionalized imidazolium salts, the related
rearrangements involving a phosphorus group from N to C
have also been observed via a “carbene mechanism” recently.21
Bronsted bases are necessary and NHCs are formed as
intermediates. For example, treatment of N-phosphorylated
imidazolium salts with trimethylamine afforded the 2-
continuing workup, both of them were purified by recrystalliza-
tion in dichloromethane/hexane several times and character-
ized by NMR and elemental analysis. In comparison to
[H2(2)]Br, their NMR spectroscopy shows several significant
changes that are indicative of κ2-O,N-ligand coordination. For
1
example, in the H NMR spectrum of 9 the chemical shift of
the NC(H)N proton was observed significantly upfield at δ
10.31 ppm, whereas the signal of the imine C(H)N proton
was shifted downfield to a resonance at δ = 8.99 ppm (ppm) if
compared with those (10.86 and 8.44 ppm, respectively) of
[H2(2)]Br. The OSiMe3 signal observed at δ −0.17 ppm is
similar to that of [Hf(thd)2(OSiMe3)2].23a
The colorless single crystals of 9 suitable for X-ray diffraction
were obtained by layering hexane on its dichloromethane
solution. In the solid state, complex 9 has an octahedral
geometry around the metal Hf(IV) (Figure 5). Two OSiMe3
ligands are found cis to each other, while the rest of the donors
of two imine nitrogen atoms and two phenolic oxygen atoms
E
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Figure 5. Molecular structure of the hafnium complex 9. All solvent molecules and hydrogen atoms are omitted for clarity. Selected distances (Å)
and angles (deg): Hf(1)−O(1) = 2.035(6), Hf(1)−O(2) = 2.020(6), Hf(1)−O(3) = 1.953(6), Hf(1)−O(4) = 1.922(7), Hf(1)−N(1) = 2.332(6),
Hf(1)−N(4) = 2.338(9), N(1)−C(7) = 1.323(10), O(4)−Hf(1)−O(3) = 104.8(3), O(4)−Hf(1)−O(2) = 95.9(3), O(3)−Hf(1)−O(2) = 92.7(2),
O(4)−Hf(1)−O(1) = 94.3(3), O(3)−Hf(1)−O(1) = 98.2(2), O(2)−Hf(1)−O(1) = 162.6(2), O(4)−Hf(1)−N(1) = 163.3(3), O(3)−Hf(1)−
N(1) = 90.7(2), O(2)−Hf(1)−N(1) = 89.5(2), O(1)−Hf(1)−N(1) = 76.9(2), O(4)−Hf(1)−N(4) = 88.6(4), O(3)−Hf(1)−N(4) = 163.8(3),
O(2)−Hf(1)−N(4) = 76.5(3), O(1)−Hf(1)−N(4) = 89.8(3), N(1)−Hf(1)−N(4) = 77.4(3), C(1)−O(1)−Hf(1) = 145.1(6).
take a cis-N/trans-O geometry due to the significantly shorter
M−O bonds than M−N bonds. It has been proven that such a
structure will be beneficial to the coordination and insertion of
olefins.
Scheme 8. Synthesis of Zwitterionic Group 4 Metal
Complexes 10−12
When [H2(2)]Br was treated with excess NaH (ca. 5 equiv)
in dichloromethane, a clear solution was obtained after
centrifugation and continuously reacted with 1.0 equiv of
MCl4(THF)2 (M = Ti, Zr) in THF to afford complex
[M(13)Cl4] (M = Ti, 10; Zr, 11) in 50−53% yield (Scheme
1
8). Although well-resolved H and 13C NMR spectra of these
complexes could be obtained, we failed to obtain suitable
crystals for X-ray single-crystal diffraction to confirm their
structures. Later an oxygen-bridged binuclear titanium complex,
{[Ti(13)Cl4]2(μ-O)} (12), was successfully achieved in 37%
yield by the controlled hydrolysis of complex 10 in diethyl
ether (Scheme 8).
X-ray analysis of 12 revealed its dinuclear titanium structure
to be linked by one μ-oxygen atom; the geometry around each
titanium atom is distorted octahedral (Figure 6). The most
notable feature of this structure is the zwitterionic amine-
phenoxide ligands that are bound to titanium centers in a k2-
O,N fashion. The imine CN double bond [also see N(1)−
C(7) = 1.323(10) Å in complex 9] of [H2(2)]Br disappeared;
two new typical single bonds of C(7)−N(1) [1.493(4) Å] and
C(7)−C(8) [1.496(4) Å] emerged to form a six-membered
piperazine ring, N(1)−C(7)−C(8)−N(3)−C(11)−C(12).
Both bond distances and angles of the imidazolium moiety
N(2)−C(8)−N(3)−C(10)−C(9) are almost the same as those
in complex 9 (also see Figure 5).
Zwitterionic group 4 complexes without a cyclopentadienyl
(Cp) group and borate are very rare.23b Among these, a
F
DOI: 10.1021/acs.organomet.5b00862
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 6. Molecular structure of the binuclear titanium complex {[Ti(13)Cl4]2(μ-O)} (12). All hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ti(1)−O(1) = 1.818(2), Ti(2)−O(1) = 1.790(2), Ti(1)−O(2) = 1.819(2), Ti(1)−N(1) = 2.792(2), Ti(1)−Cl(1)
= 2.4447(9), Ti(1)−Cl(2) = 2.3053(9), Ti(1)−Cl(3) = 2.3899(9), N(1)−C(12) = 1.468(4), N(1)−C(7) = 1.493(4), N(2)−C(8) = 1.334(4),
N(2)−C(9) = 1.380(4), N(3)−C(8) = 1.325(4), N(3)−C(10) = 1.390(4), N(3)−C(11) = 1.459(4), C(7)−C(8) = 1.496(4), C(9)−C(10) =
1.316(5), C(11)−C(12) = 1.503(4), N(1)−Ti(1)−Cl(2) = 175.60(7), O(1)−Ti(1)−Cl(3) = 167.57(7), Cl(1)−Ti(1)−O(2) = 165.32(7), Cl(3)−
Ti(1)−Cl(1) = 85.96(3), O(1)−Ti(1)−N(1) = 81.56(9) O(1)−Ti(1)−O(2) = 94.55(9), Cl(2)−Ti(1)−Cl(3) = 95.21(4), Cl(1)−Ti(1)−N(1) =
81.26(6). N(3)−C(8)−N(2) = 108.4(3), C(8)−N(2)−C(9) = 107.9(3), C(8)−N(3)−C(10) = 108.3(3), C(10)−C(9)−N(2) = 108.2(3), C(9)−
C(10)−N(3) = 107.2(3).
1
Figure 7. H NMR (CDCl3 at 20 °C) and HRMS spectra of zwitterionic 13.
zwitterionic phenolate titanium example, [Ti(OiPr)Cl3(THF)
nucleophilic attack at its imine group,15c,25 we hypothesized
that the formation of 10 goes through a nucleophilic attack of
NHC to the imine CN bond. Next we turned to the direct
isolation and characterization of the zwitterionic amine-
phenoxide 13. Treatment of [H2(2)]Br with excess sodium
hydride in dichloromethane afforded the desired product 13 as
a yellow powder in 75% yield. Compound 13 has been
characterized spectroscopically by NMR and HRMS as shown
in Figure 7. New signals for the formed CH are observed at
5.85 and 52.9 ppm in the 1H and 13C NMR, respectively. It also
is in good agreement with the results by HRMS; a base peak at
m/z 370.2886 (100%) was observable at the position
corresponding to the parent molecule [M + H]+.
+
(L)] (L = 2-−O(C6H4)NH3 ), has been characterized by X-ray
analysis, although the neighboring nitrogen is not coordinated
with the metal center in both cases.23c Its Ti−O(phenolato)
distance of 1.879(3) Å is longer than Ti(1)−O(2) [1.819(2) Å]
in complex 12. Noticeably, the bond between Ti(1) and the
amine nitrogen atom N(1) is 2.792(2) Å, which is much longer
than the values [2.245(6)−2.323(5) Å] typically observed for
group 4 metal complexes we previously reported.24 The
possible explanation for this is that the interaction between
titanium Ti(1) and sp3-hybridized nitrogen N(1) is very weak.
Considering the fact that the aminophenoxo-functionalized
NHC ligand could be derived from [H2(2)]Br via a
G
DOI: 10.1021/acs.organomet.5b00862
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Concerning the reaction mechanism (Scheme 9), after
deprotonation there existed a proton transfer between the
Scheme 10. Synthesis of Titanium NHC Complex [Ti(7)Cl2]
(14)
Scheme 9. Proposed Pathway for the Formation of
Zwitterionic 13
7 NHC ligand, and the open coordination site was occupied by
two chlorides.
The catalytic behavior of titanium complex 14 for ethylene
polymerization was systemically studied at low pressure (50
psig) in the presence of MAO as cocatalyst (Table 3). Complex
initially formed intermediate phenoxide A with its NHC-imine
tautomer B.26 Subsequent cyclization of B to an imidazolium
amide C27 occurred by the nucleophilic addition of NHC to
imine, which followed by formal proton migration to give 13.
Catalytic Property for Ethylene Polymerization of
Relative Group 4 Metal Complexes. Zirconium complex 8/
MAO was first used as a catalyst for ethylene polymerization
because it has a similar structure to the famous “FI catalyst”.22
However, it revealed only a very low activity of 8.16 kg·
mol−1Zr·h−1·bar−1 under our reaction conditions (10 μmol of
[Zr], 2.0 bar of ethylene, Al/Zr = 500, 50 mL of toluene, 22 °C,
2 h). Moreover, the GC analysis of the reaction mixture
suggested the existence of oligomers besides a solid polymer.
This might be attributed to the two imidazolium moieties that
are independent and far away from the coordination shell of the
metal center (Figure 5). Thus, they were deprotonated to
afford aluminum NHC adducts when complex 8 was activated
with MAO.28 As a result, more than one active species existed
in the catalytic system to afford polymerization with multi-
modal molecular weight distributions.
Next we considered the phenol-imine-modified NHC
precursor [H2(2)]Br and bisphenol-linked NHC precursor
[H3(7)]Br, which incorporates a bulky N-arylamide linker
because they are similar to the NHC ligands (A)2− and (J)−
(Figure 1) we previously designed for titanium catalysts. The
anionic functional groups pendant on the NHC will provide a
“tether” by which an electropositive group 4 metal may be
bound more strongly to the soft carbene center.2 It is well
known that one of the efficient approaches to group 4 metal
NHC complexes is amine elimination by reactions of NHC
precursors with metal precursors such as M(NR2)4 and
MCl2(NR2)4 (M = Ti, Zr, Hf).1a By this strategy, the in situ
mixture of Ti(NMe2)4 and NHC precursor [H2(2)]Br or
[H3(7)]Br was primarily investigated for its potential as an
ethylene polymerization catalyst at low pressure (50 psi). The
combination of Ti(NMe2)4/[H2(7)]Br revealed a higher
catalytic activity (ca. 42 kg PE/(mol Ti·h·atm)) than
Ti(NMe2)4/[H2(2)]Br (ca. 11 kg PE/(mol Ti·h·atm)) under
experimental conditions (10 mmol of [Ti], 50 mL of toluene,
30 min).
Table 3. Results of Ethylene Polymerization Using 14/
MAO
a
b
entry
[Al]/[Ti]
T (°C)
polymer (g)
activity
1
2
3
4
5
6
7
1000
1000
1000
1000
500
10
30
50
70
50
50
50
50
50
0.102
0.393
0.798
0.557
0.666
0.711
0.687
1.354
0.622
14.5
56.1
114.0
79.5
95.1
101.6
98.1
96.7
88.9
1500
2000
1000
1000
c
8
d
9
a
Polymerization conditions: 4 μmol of [Ti] (the concentration of [Ti]
is 8 × 10−5 mol/L), MAO as cocatalyst, 50 mL of toluene, 50 psig of
b
c
ethylene pressure, 30 min. kg PE/(molTi·h·atm). 100 psig of
ethylene pressure. The titanium complex is [Ti(A)Cl2].3b
d
14 revealed a catalytic activity of up to ca. 114 kg PE/(mol Ti·
h·atm), which is higher than that of [Ti(A)Cl2]3b (ca. 89 kg
PE/(mol Ti·h·atm)) (entry 3 vs 9) that we previously reported.
It is possible that the bulk of the N-Dipp-amide linker provides
more steric hindrance and protects the catalyst active site at
that position. Reinforcing this hypothesis is the fact that the
polymer produced by 14/MAO has a higher number-average
molecular weight (Mn) of ca. 4545 g mol−1 than that of
1
[Ti(A)Cl2]/MAO (3830 g mol−1) according to their H NMR
spectra at 120 °C. The 13C NMR spectrum of polyethylene
produced by 14 (Table 3, entry 3) revealed a linear polymer,
and no methyl or long-chain branches could be observed.
Overall, the activities of this catalytic system are moderate
compared to other reported examples of the NHC-Ti complex
catalyzed polymerization of ethylene.3b,3 29−31 Using pyridy-
c,
lene bis-NHC (L) as a symmetric pincer ligand, Gibson and co-
workers prepared the titanium NHC complex [TiIII(L)Cl3],
which showed much higher activity (791 kg /(mol Ti·h·atm))
than 14 to produce an ultrahigh molecular weight polyethylene
(>2 M). The melting temperature (141 °C) of the polymer is
consistent with high-density polyethylene with no significant
branching. Besides pincer ligands, the bidentate NHC hybrid
ligands have also been used to construct titanium catalysts such
as the imino-NHC complex [Ti(L)Cl4] (ca. 40 kg /(mol Ti·h))
and “salicylaldimine-like” aryloxy-NHC complex [M(L)2Cl2]
(ca. 24 kg /(mol Ti·h·atm)). Similar to 14, these NHC-Ti
complexes catalyzed ethylene polymerization to afford linear
polymers.
As shown in Scheme 10, titanium complex [Ti(7)Cl2] (14)
was prepared as an orange-red solid in 77% yield in a similar
fashion to [Ti(A)Cl2] previously reported. Although the quality
of the obtained lamellar crystals from its hexane/THF/CH2Cl2
solution was poor, the outline of the solid-state structure of 14
clearly indicates its mononuclear structure with the k3-(O,C,O)-
H
DOI: 10.1021/acs.organomet.5b00862
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Organometallics
Article
3-(3,5-Di-tert-butyl-2-hydroxybenzyl)-1-(2-((2,6-dimethylphenyl)-
amino)-2-oxoethyl)-1H-imidazol-3-ium bromide ([H3(1c)]Br): white
solid (1.94 g, 87% yield). Mp: 174−176 °C. Anal. Calcd for
C28H38BrN3O2 [528.52 g/mol]: C, 63.63; H, 7.25; N, 7.95. Found:
CONCLUSIONS
■
In summary, we present an unexpected rearrangement and
nucleophilic addition of O/N-functionalized NHC precursors
promoted by a Brønsted base. A new type of multidentate
NHC precursors could be conveniently derived from these
rearrangement products. The nucleophilic addition of NHCs to
imines not only yields a rare zwitterionic phenolate-amine
ligand and metal complexes but also provides a convenient
route to novel heterocyclic compounds. Most importantly, the
early transition metal complexes supported by such NHC
hybrid ligands we obtained revealed high catalytic activities for
ethylene polymerization.
1
C, 63.55; H, 7.21; N, 7.88. H NMR (400 MHz, CDCl3): δ 1.29 (s,
9H, C(CH3)3), 1.36 (s, 9H, C(CH3)3), 2.15 (s,6H, 2CH3), 5.45 (s,
2H, CH2), 5.55 (s, 2H, COCH2),6.67 (s, 1H, OH), 6.95 (s, 1H,
PhCH), 6.97 (s, 1H, PhCH), 7.00−7.02 (m, 1H, PhCH), 7.11 (s, 1H,
PhCH), 7.14 (s, 1H, PhCH), 7.37 (s, 1H, imidazolH), 7.58 (s, 1H,
imidazolH), 9.59 (s, 1H, NCHN), 9.88 (s, 1H, NH). 13C NMR (100
MHz, CDCl3): δ 18.7, 30.1, 31.6, 34.4, 34.9, 51.1, 51.8, 121.2, 123.2,
125.8, 126.0, 127.4, 128.0, 133.2, 135.4, 136.7, 139.0, 143.8, 151.5,
163.6. IR (KBr pellets, cm−1): ν 3417, 3147, 3098, 3063, 2959, 2864,
1688, 1557, 1526, 1477, 1361, 1221, 1202, 1145, 1090, 1020, 996, 851,
791, 748, 619. HRMS (positive ions): m/z 448.2990 (calcd for [M −
Br]+ 448.2964).
3-(3,5-Di-tert-butyl-2-hydroxybenzyl)-1-(2-oxo-2-(p-tolylamino)-
ethyl)-1H-imidazol-3-ium bromide ([H3(1d)]Br): white solid (1.75 g,
85% yield). Mp: 164−166 °C. Anal. Calcd for C27H36BrN3O2 [514.50
g/mol]: C, 63.03; H, 7.05; N, 8.17. Found: C, 62.97; H, 7.11; N, 8.04.
1H NMR (400 MHz, DMSO): δ 1.24 (s, 9H, C(CH3)3), 1.37 (s, 9H,
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were performed
under an inert atmosphere of dry argon by using vacuum line and
Schlenk tube techniques. All chemical reagents were purchased from
commercial sources (Acros, Aldrich, Alfa Aesar, or Fluka) and used as
received unless otherwise indicated. The phenoxyimine-modified
NHC precursor [H2(2)]Br was prepared using the literature
method.15,16 The solvents were dried and distilled prior to use by
C(CH3)3), 2.25 (s, 3H, CH3), 5.22 (s, 2H, CH2), 5.49 (s, 2H,
COCH2),7.14 (m, 3H, OH + 2PhCH), 7.26 (s, 1H, PhCH), 7.45 (m,
2H, 2PhCH), 7.72 (m, 2H, PhCH + imidazolH), 8.68 (s, 1H, imidazolH),
9.10 (s, 1H, NCHN), 10.50 (s, 1H, NH). 13C NMR (100 MHz,
DMSO): δ 20.9, 30.3, 31.8, 34.5, 35.4, 49.3, 51.6, 119.5, 122.5, 123.5,
124.6, 125.2, 129.8, 133.2, 136.4, 137.8, 138.9, 142.8, 151.7, 164.0. IR
(KBr pellets, cm−1): ν 3418, 3148, 3096, 3063, 2961, 2868, 1684,
1526, 1475, 1362, 1203, 1148, 1025, 998, 791, 747, 618. HRMS
(positive ions): m/z 434.2818 (calcd for [M − Br]+ 434.2808).
1-(2-((4-Chlorophenyl)amino)-2-oxoethyl)-3-(3,5-di-tert-butyl-2-
hydroxybenzyl)-1H-imidazol-3-ium bromide ([H3(1e)]Br): white solid
(1.93 g, 90% yield). Mp: 206−208 °C. Anal. Calcd for
C26H33BrClN3O2 [534.92 g/mol]: C, 58.38; H, 6.22; N, 7.86.
1
literature methods. H and 13C NMR spectra were recorded on Jeol
ECA-400 or Bruker AV500 spectrometers. 1H and 13C chemicals shifts
(δ) are given in ppm (the residual peak of deuterated solvents was
used as a reference). Elemental analyses and high-resolution mass
spectra were achieved by the Analysis Center, Fudan University.
General Procedure for Synthesis of NHC Precursors [H3(1a−
f)]Br. Under a N2 atmosphere a flask was charged with 2-(1H-
imidazol-1-yl)-N-(2,6-R1-4 -R2-phenyl)acetamide (4.0 mmol) and
THF (5 mL). A solution of 2-bromomethyl-4,6-di-tert-butylphenol
(1.26 g, 4.2 mmol) in THF (5 mL) was slowly added at reflux
temperature. After stirring for 12 h, the solution was evaporated to
dryness to give the crude product. The product was washed with
diethyl ether and dried in vacuo, which yielded white solids of
[H3(1a−e)]Br.
1
Found: C, 58.33; H, 6.31; N, 7.93. H NMR (400 MHz, DMSO): δ
1.23 (s, 9H, C(CH3)3), 1.36 (s, 9H, C(CH3)3), 5.25 (s, 2H, CH2),
5.48 (s, 2H, COCH2),7.10 (s, 1H, PhCH), 7.25 (s, 1H, PhCH), 7.38 (s,
1H, PhCH), 7.40 (s, 1H, PhCH), 7.60 (s, 1H, PhCH), 7.62 (s, 1H,
PhCH), 7.72 (s, 1H,imidazolH), 7.76 (s, 1H,imidazolH), 8.84 (s, 1H,
3-(3, 5-Di-tert-butyl-2-hydroxybenzyl)-1-(2-((2, 6-
diisopropylphenyl)amino)-2-oxoethyl)-1H-imidazol-3-ium bromide
([H3(1a)]Br): white solid (2.08 g, 89% yield). Mp: 218−220 °C. Anal.
Calcd for C32H46BrN3O2 [584.63 g/mol]: C, 65.74; H, 7.93; N, 7.19.
NCHN), 9.09 (s, 1H, NH). 13C NMR (100 MHz, DMSO): δ 30.3,
31.8, 34.5, 35.3, 49.4, 51.9, 121.1, 122.5, 123.5, 124.6, 125.3, 127.8,
129.3, 137.1, 138.9, 142.9, 151.7, 164.5. IR (KBr pellets, cm−1): ν
3421, 3149, 3100, 3060, 2961, 2868, 1685, 1555, 1526, 1474, 1459,
1363, 1220, 1201, 1147, 1087, 1022, 999, 854, 791, 746, 619. HRMS
(positive ions): m/z 454.2273 (calcd for [M − Br]+ 454.2261).
1-(2-(tert-Butylamino)-2-oxoethyl)-3-(3,5-di-tert-butyl-2-
hydroxybenzyl)-1H-imidazol-3-ium bromide ([H3(1f)]Br). N-(tert-
Butyl)-2-(1H-imidazol-1-yl)acetamide (3f) was obtained as a white
solid in 90% yield. 1H NMR (400 MHz, CDCl3): δ 1.29 (s, 9H,
C(CH3)3), 4.55 (s, 2H, CH2), 5.29 (br, 1H, NH), 6.96 (s, 1H,
NCHN), 7.43 (s, 1H, imidazolH), 7.52(s, 1H, imidazolH). 13C NMR (100
MHz, CDCl3): δ 29.7, 51.8, 120.7, 131.8, 139.2, 166.9. [H3(1f)]Br was
obtained from 3f as a white solid in 86% yield using a similar route to
compound [H3(1a)]Br. Mp: 146−148 °C. Anal. Calcd for
C24H38BrN3O2 [480.48 g/mol]: C, 59.99; H, 7.97; N, 8.75. Found:
1
Found: C, 65.62; H, 8.01; N, 7.12. H NMR (400 MHz, CDCl3): δ
1.09 (s, 12H, CH(CH3)2), 1.29 (s, 9H, C(CH3)3), 1.36 (s, 9H,
C(CH3)3), 3.02 (sept, 2H, CH(CH3)2), 5.49 (s, 2H, CH2), 5.59 (s,
2H, COCH2), 6.73 (s, 1H, OH), 7.10−7.13 (m, 3H, PhCH), 7.19 (s,
1H, PhCH), 7.23−7.26 (m, 1H, PhCH), 7.37 (s, 1H, imidazolH), 7.58 (s,
1H, imidazolH), 9.57 (s, 1H, NCHN), 9.87 (s, 1H, NH). 13C NMR (100
MHz, CDCl3): δ 23.8, 23.9, 28.7, 30.3, 31.5, 34.4, 34.8, 51.3, 52.1,
121.1, 121.4, 122.9, 123.4, 125.6, 126.3, 128.5,130.6, 136.7, 138.8,
144.0, 146.0, 151.4, 164.4. HRMS (m/z): 503.3415 [M − Br − H]+
(100%). IR (KBr pellets, cm−1): ν 3418, 3189, 3012, 2959, 2867, 1668,
1559, 1527, 1458, 1444, 1248, 1217, 1201, 1154, 1091, 1029, 999, 855,
791, 745, 619. HRMS (positive ions): m/z 504.3594 (calcd for [M −
Br − H]+ 504.3590).
3-(3,5-Di-tert-butyl-2-hydroxybenzyl)-1-(2-(mesitylamino)-2-ox-
oethyl)-1H-imidazol-3-ium bromide ([H3(1b)]Br): white solid (1.80 g,
83% yield). Mp: 178−180 °C. Anal. Calcd for C29H40BrN3O2 [542.55
g/mol]: C, 64.20; H, 7.43; N, 7.74. Found: C, 64.22; H, 7.41; N, 7.82.
1H NMR (400 MHz, CDCl3): δ 1.28 (s, 9H, C(CH3)3), 1.34 (s, 9H,
C(CH3)3), 2.08 (s,6H, 2CH3), 2.18 (s,3H, CH3), 5.45 (s, 2H, CH2),
5.52 (s, 2H, COCH2),6.74 (s, 3H, OH + 2PhCH), 7.09 (s, 1H, PhCH),
7.13 (s, 1H, PhCH), 7.35 (s, 1H, imidazolH), 7.58 (s, 1H, imidazolH), 9.52
(s, 1H, NCHN), 9.73 (s, 1H, NH). 13C NMR (100 MHz, CDCl3): δ
18.6, 20.9, 30.1, 31.5, 34.4, 34.9, 51.2, 51.8, 121.1, 121.3, 123.2, 125.6,
126.1, 128.7, 130.5, 135.0, 136.8, 137.0, 139.0, 143.9, 151.6, 163.7. IR
(KBr pellets, cm−1): ν 3419, 3149, 3099, 3062, 2961, 2868, 1683,
1555, 1526, 1475, 1362, 1221, 1201, 1147, 1088, 1022, 998, 853, 792,
747, 618. HRMS (positive ions): m/z 462.3165 (calcd for [M − Br]+
462.3121).
1
C, 59.88; H, 7.92; N, 8.81. H NMR (400 MHz, CDCl3): δ 1.29 (s,
9H, C(CH3)3), 1.36 (s, 9H, C(CH3)3), 1.39 (s, 9H, C(CH3)3), 5.22 (s,
2H, CH2), 5.58 (s, 2H, COCH2), 6.94 (bs, 1H, OH), 7.14−7.21 (m,
2H, PhCH), 7.38 (s, 1H, imidazolH), 7.48 (s, 1H, imidazolH), 8.06 (s, 1H,
NH), 9.33 (s, 1H, NCHN). 13C NMR (100 MHz, CDCl3): δ 28.6,
30.2, 31.5, 34.4, 34.9, 51.3, 52.3, 121.2, 121.4, 123.1, 125.6, 126.1,
136.4, 139.2, 143.9, 151.6, 163.5. IR (KBr pellets, cm−1): ν 3419, 3257,
3099, 3084, 2961, 2869, 1685, 1559, 1526, 1481, 1456, 1393, 1363,
1278, 1219, 1156, 1089, 1022, 999, 854, 791, 748, 620. HRMS
(positive ions): m/z 400.2995 (calcd for [M − Br]+ 400.2964).
General Procedure for Rearrangement of [H3(1a−e)]Br to
4a−e. Under a N2 atmosphere a flask was charged with [H3(1a−e)]Br
(5.0 mmol), Ag2O (2.75 mmol), several 4 Å molecular sieves, and
dichloromethane (10 mL). After the mixture was stirred at room
temperature for 24 h (for [H3(1a−c)]Br) or 72 h (for [H3(1d−e)]Br)
I
DOI: 10.1021/acs.organomet.5b00862
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in the dark, solvent was evaporated in vacuo to dryness. The crude
product was purified using gel column chromatography to give
compounds 4a−e as white solids.
2959, 2867, 1685, 1554, 1525, 1475, 1457, 1361, 1219, 1201, 1145,
1086, 1022, 997, 853, 791, 747, 619. HRMS (positive ions): m/z
454.2272 (calcd for [M + H]+ 454.2261).
N-(3,5-Di-tert-butyl-2-hydroxybenzyl)-N-(2,6-diisopropylphenyl)-
2-(1H-imidazol-1-yl)acetamide (4a): white solid (2.27g, 80% yield).
Mp: 152−154 °C. Anal. Calcd for C32H45N3O2 [503.72 g/mol]: C,
Synthesis of [H2(5)]Br3b: white solid (2.29g, 85% yield). Mp:
164−166 °C. Anal. Calcd for C39H52BrN3O2 [674.75 g/mol]: C,
1
69.42; H, 7.77; N, 6.23. Found: C, 69.33; H, 7.70; N, 6.32. H NMR
1
76.30; H, 9.00; N, 8.34. Found: C, 76.22; H, 9.01; N, 8.22. H NMR
(400 MHz, CDCl3): δ 1.09 (s, 12H, CH(CH3)2), 1.30 (s, 9H,
C(CH3)3), 1.46 (s, 9H, C(CH3)3), 3.01 (sept, 2H, CH(CH3)2), 4.94
(s, 2H, CH2), 5.30 (s, 2H, CH2), 5.58 (s, 2H, CH2), 7.04 (s, 1H,
PhCH), 7.10 (s, 1H, PhCH), 7.12 (s, 1H, PhCH),7.20−7.24 (m, 2H,
PhCH), 7.41−7.44 (m, 5H, PhCH),7.51 (s, 1H, imidazolH), 7.57 (s, 1H,
imidazolH), 9.58 (s, 1H, NCHN), 10.00 (s, 1H, NH). 13C NMR (100
MHz, CDCl3): δ 23.8, 28.7, 31.4, 34.7, 35.7, 50.0, 51.8, 121.2, 123.3,
123.5, 123.7, 126.1, 126.3, 126.6, 127.2, 128.3, 128.4, 129.0, 130.7,
136.6, 143.7, 146.0, 148.1, 154.2, 164.3. IR (KBr pellets, cm−1): ν
3419, 3023, 3012, 2958, 2869, 1667, 1559, 1528, 1455, 1445, 1249,
1220, 1219, 1155, 1100, 1030, 997, 857, 792, 747, 618. HRMS
(positive ions): m/z 594.4074 (calcd for [M − Br]+ 594.4060).
Synthesis of Silver Complex [Ag2(5)2] (6).18a Compound 6 was
obtained as a white solid (0.379g, 35% yield) after several
recrystallizations from hexane/dichloromethane. Anal. Calcd for
C78H100Ag2N6O4 [2077.16 g/mol]: C, 66.85; H, 7.19; N, 6.00.
(400 MHz, CDCl3): δ 0.84 (m, 6H, CH(CH3)2), 1.09 (s, 9H,
C(CH3)3), 1.21 (d, 6H, CH(CH3)2), 1.42 (s, 9H, C(CH3)3), 2.74
(sept, 2H, CH(CH3)2), 4.39 (s, 2H, CH2), 4.72 (bs, 2H, COCH2),6.31
(d, 1H, PhCH), 6.95 (s, 1H, PhCH), 7.10 (s, 1H, PhCH), 7.23 (m, 3H,
2PhCH + imidazolH), 7.43 (m, 2H,NCHN + imidazolH), 8.49 (s, 1H, OH).
13C NMR (100 MHz, CDCl3): δ 24.3, 24.9, 28.4, 29.5, 29.7, 31.4, 33.8,
35.2, 47.8, 53.0, 119.0, 120.1, 125.3, 125.5, 126.6, 129.6, 130.3, 133.6,
136.6, 138.0, 140.8, 146.2, 152.4, 169.8. IR (KBr pellets, cm−1): ν
3420, 3015, 2960, 2867, 1669, 1560, 1524, 1458, 1445, 1250, 1217,
1219, 1154, 1090, 1030, 997, 857, 790, 745, 619. HRMS (positive
ions): m/z 504.3594 (calcd for [M + H]+ 504.3590).
N-(3,5-Di-tert-butyl-2-hydroxybenzyl)-2-(1H-imidazol-1-yl)-N-
mesitylacetamide (4b): white solid (1.57g, 68% yield). Anal. Calcd for
C29H39N3O2 [461.64 g/mol]: C, 75.45; H, 8.52; N, 9.10. Found: C,
1
75.38; H, 8.61; N, 8.98. H NMR (400 MHz, CDCl3): δ 1.12 (s, 9H,
C(CH3)3), 1.41 (s, 9H, C(CH3)3), 1.82 (s, 6H, 2CH3), 2.33 (s,3H,
CH3), 4.29 (s, 2H, CH2), 4.66 (bs, 2H, COCH2),6.34 (d, 1H, PhCH),
6.89 (s, 1H, PhCH), 6.96 (s, 2H, PhCH), 7.05 (s, 1H, imidazolH), 7.22 (s,
1H, imidazolH), 7.25 (s, 1H, NCHN), 8.80 (s, 1H, OH). 13C NMR (100
MHz, CDCl3): δ 17.4, 21.0, 29.6, 31.4, 31.6, 33.9, 35.2, 47.9, 50.6,
119.9, 120.5, 124.4, 126.4, 129.6, 130.3, 134.8, 135.5, 137.3, 137.9,
139.4, 141.1, 152.3, 168.7. IR (KBr pellets, cm−1): ν 3419, 3100, 3061,
2960, 28678, 1687, 1554, 1527, 1473, 1363, 1220, 1119, 1150, 1089,
1020, 997, 851, 791, 749, 618. HRMS (positive ions): m/z 462.3125
(calcd for [M + H]+ 462.3121).
1
Found: C, 66.68; H, 7.07; N, 6.13. H NMR (400 MHz, CDCl3): δ
1.09 (s, 12H, CH(CH3)2), 1.29 (s, 9H, C(CH3)3), 1.47 (s, 9H,
C(CH3)3), 3.07 (sept, 2H, CH(CH3)2), 4.97 (s, 2H, CH2), 5.34 (s,
2H, CH2), 5.55 (s, 2H, CH2),7.04 (s, 1H, PhCH), 7.10 (s, 1H, PhCH),
7.13 (s, 1H, PhCH),7.18−7.24 (m, 2H, PhCH), 7.41−7.43 (m, 5H,
PhCH),7.51 (s, 1H, imidazolH), 7.56 (s, 1H, imidazolH). 13C NMR (100
MHz, CDCl3): δ 23.8, 28.7, 31.4, 34.7, 35.7, 50.0, 51.8, 121.2, 123.3,
123.5, 123.7, 126.1, 126.3, 126.6, 127.2, 128.3, 128.4, 129.0, 130.7,
136.6, 143.7, 146.0, 148.1, 154.2, 170.8, 176.0.
Synthesis of [H3(7)]Br. Under a N2 atmosphere a flask was
charged with 4a (4.0 mmol) and THF (5 mL). A solution of 2-
bromomethyl-4,6-di-tert-butylphenol (1.26 g, 4.2 mmol) in THF (5
mL) was slowly added at reflux temperature. After stirring for 12 h, the
solution was evaporated to dryness to give the crude product. The
product was washed with diethyl ether and dried in vacuo to give pure
[H3(7)]Br as a white solid (2.89 g, 90% yield). Mp: 230−232 °C.
Anal. Calcd for C47H68BrN3O3 [802.97 g/mol]: C, 70.30; H, 8.54; N,
5.23. Found: C, 70.17; H, 8.44; N, 5.32. 1H NMR (400 MHz, CDCl3):
δ 0.85 (m, 6H, CH(CH3)2), 1.08 (s, 9H, C(CH3)3), 1.22 (m, 6H,
CH(CH3)2), 1.30 (s, 9H, C(CH3)3), 1.39 (s, 9H, C(CH3)3), 1.40 (s,
9H, C(CH3)3), 2.66 (sept, 2H, CH(CH3)2), 4.79 (bs, 4H, 2CH2), 5.66
(s, 2H, CH2), 6.30 (d, 1H, PhCH), 7.06 (s, 1H, OH), 7.13 (s, 1H,
PhCH),7.24 (m, 4H, PhCH), 7.32 (s, 1H, PhCH),7.37 (s, 1H, imidazolH),
N-(3,5-Di-tert-butyl-2-hydroxybenzyl)-N-(2,6-dimethylphenyl)-2-
(1H-imidazol-1-yl)acetamide (4c): white solid (1.99 g, 89% yield).
Anal. Calcd for C28H37N3O2 [447.61 g/mol]: C, 75.13; H, 8.33; N,
9.39. Found: C, 75.02; H, 8.54; N, 9.28. 1H NMR (400 MHz, CDCl3):
δ 1.11 (s, 9H, C(CH3)3), 1.41 (s, 9H, C(CH3)3), 1.86 (s, 6H, 2CH3),
4.30 (s, 2H, CH2), 4.70 (bs, 2H, COCH2),6.31 (d, 1H, PhCH), 6.89 (s,
1H, PhCH), 7.06 (s, 1H, PhCH), 7.15 (s, 1H, PhCH), 7.17 (s, 1H,
PhCH), 7.22 (s, 1H, imidazolH), 7.25 (m, 2H,NCHN + imidazolH), 8.76 (s,
1H, OH). 13C NMR (100 MHz, CDCl3): δ 17.5, 29.6, 31.4, 35.2, 48.0,
50.5, 120.0, 120.3, 124.5, 126.3, 129.4, 129.6, 136.0, 137.2, 137.4,
138.0, 141.1, 152.3, 168.6. IR (KBr pellets, cm−1): ν 3415, 3140, 3100,
3065, 2960, 2861, 1670, 1555, 1525, 1477, 1362, 1219, 1201, 1147,
1090, 1019, 997, 851, 791, 747, 620. HRMS (positive ions): m/z
448.2964 (calcd for [M + H]+ 448.2964).
7.43 (s, 1H, imidazolH), 8.20 (s, 1H, OH), 9.81 (s, 1H, NCHN). 13C
NMR (100 MHz, CDCl3): δ 25.4, 26.4, 29.5, 30.7, 31.3, 32.4, 32.7,
34.9, 35.5, 36.2, 51.6, 52.6, 54.3, 119.7, 123.0, 123.2, 123.6, 126.5,
126.7, 126.8, 127.0, 127.9, 131.8, 133.6, 137.7, 139.1, 141.2, 142.2,
144.9, 147.2, 153.3, 168.7. HRMS (m/z): [M − Br]+ (100%). HRMS
(positive ions): m/z 722.5253 (calcd for [M − Br]+ 722.5261).
Synthesis of Zirconium Complex [ZrCl2(k2-N,O-OC6H2-
3,5-tBu2-C(H)N-CH2CH2-Im)2][Br]2 (8). A THF solution of
NaN(SiMe3)2 (1.0 M, 1.0 mL, 1.0 mmol) was added to a suspension
of [H2(L1)]Br (450 mg, 1.0 mmol) in THF (15 mL) at −78 °C. The
ligand solution was cannulated into a THF (10 mL) solution of
ZrCl4(thf)2 (188 mg, 0.5 mmol) keeping the temperature below −78
°C. The mixture was allowed to warm to ambient temperature and
stirred for a further 6 h. After removal of volatiles in vacuo, the residue
was extracted with dichloromethane (15 mL) and centrifuged to
remove insoluble materials. The resulting supernatant was concen-
trated, and hexane (15 mL) was added to give 8 as a light yellow
powder (292 mg, 55% yield). 1H NMR (400 MHz, CDCl3): δ 1.13 (s,
18H, C(CH3)3), 1.41 (s, 18H, C(CH3)3), 1.53 (d, 12H, CH(CH3)2),
3.25 (m, 2H, CH2), 4.24 (m, 2H, CH2), 4.30 (m, 2H, CH(CH3)2),
4.68 (m, 4H, CH2), 6.34 (s, 2H, NCHCHN), 7.10 (s, 2H,
NCHCHN), 7.34 (s, 2H, ArCH), 7.60 (s, 2H, ArCH), 8.63 (s, 2H,
CHN), 9.80 (s, 2H, imidCHC). 13C NMR (100 MHz, CDCl3): δ
23.8 (CH(CH3)2), 30.6, 31.7 (CH(CH3)3), 34.2, 35.3 (CH(CH3)3),
N-(3,5-Di-tert-butyl-2-hydroxybenzyl)-2-(1H-imidazol-1-yl)-N-(p-
tolyl)acetamide (4d): white solid (1.71g, 79% yield). Anal. Calcd for
C27H35N3O2 [433.59 g/mol]: C, 74.79; H, 8.14; N, 9.69. Found: C,
1
74.77; H, 8.14; N, 9.70. H NMR (400 MHz, CDCl3): δ 1.16 (s, 9H,
C(CH3)3), 1.42 (s, 9H, C(CH3)3), 2.44 (s,3H, CH3), 4.44 (s, 2H,
CH2), 4.73 (bs, 2H, COCH2), 6.47 (d, 1H, PhCH), 6.87 (s, 1H,
PhCH), 6.96 (s, 1H, PhCH), 6.98 (s, 2H, PhCH), 7.24−7.28 (m, 4H,
2imidazolH + NCHN + PhCH), 8.83 (s, 1H, OH). 13C NMR (100 MHz,
CDCl3): δ 21.2, 29.7, 31.5, 34.0, 35.3, 48.2, 51.8, 119.8, 121.5, 124.5,
126.6, 127.9, 129.5, 130.9, 137.6, 137.7, 137.8, 139.8, 141.0, 152.0,
168.0. IR (KBr pellets, cm−1): ν 3419, 3145, 3097, 3063, 2962, 2870,
1684, 1527, 1475, 1362, 1205, 1150, 1025, 997, 792, 749, 619. HRMS
(positive ions): m/z 434.2805 (calcd for [M + H]+ 434.2808).
N-(4-Chlorophenyl)-N-(3,5-di-tert-butyl-2-hydroxybenzyl)-2-(1H-
imidazol-1-yl)acetamide (4e): white solid (1.75 g, 77% yield). Anal.
Calcd for C26H32ClN3O2 [454.00 g/mol]: C, 68.78; H, 7.10; N, 9.26.
1
Found: C, 68.71; H, 7.15; N, 9.18. H NMR (400 MHz, CDCl3): δ
1.16 (s, 9H, C(CH3)3), 1.42 (s, 9H, C(CH3)3), 4.45 (s, 2H, CH2),
4.74 (bs, 2H, COCH2), 6.44 (s, 1H, PhCH), 6.85 (s, 1H, PhCH), 7.02−
7.04 (m, 3H, PhCH), 7.26−7.28 (m, 2H, imizolH + NCHN), 7.46 (d,
2H, imizolH + PhCH), 8.62 (s, 1H, OH). 13C NMR (100 MHz, CDCl3):
δ 29.6, 29.7, 31.5, 31.6, 34.0, 35.3, 48.3, 51.9, 119.8, 121.0, 124.7,
126.4, 129.6, 130.6, 135.8, 137.8, 138.5, 141.2, 151.9, 167.9. HRMS
(m/z): (M+, 100%). IR (KBr pellets, cm−1): ν 3421, 3132, 3099, 3060,
J
DOI: 10.1021/acs.organomet.5b00862
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 4. Crystal Data and Structure Refinements of [H3(1a)]Br, 4a, 9, and 12
[H3(1a)]Br·(H2O)
4a·2(C7H8)
C46H61N3O2
9·(CH2Cl2)
12·3(CHCl3)
formula
C32H48BrN3O3
602.64
C53H90Br2Cl2HfN6O4Si2
1340.70
C49H71Cl15N6O3Ti2
1419.67
fw
687.98
cryst size/mm3
cryst syst
space group
a/Å
0.39 × 0.06 × 0.05
triclinic
0.21 × 0.21 × 0.19
monoclinic
P21/c
0.15 × 0.08 × 0.07
triclinic
0.38 × 0.35 × 0.27
tetragonal
14(1)/a
P1
̅
P1
̅
9.591(2)
10.870(3)
16.325(4)
74.296(4)
76.993(4)
87.310(4)
1596.3(7)
2
10.3474(8)
23.8857(18)
16.5887(13)
90
12.8602(15)
13.7192(16)
19.785(2)
78.314(2)
80.812(2)
80.869(2)
3345.5(7)
2
44.813(3)
44.813(3)
16.8439(11)
90
b/Å
c/Å
α/deg
β/deg
93.1840(10)
90
90
γ/deg
V/Å3
90
4093.6(5)
4
33827(4)
16
Z
ρcalcd/Mg·m−3
F(000)
1.254
1.116
1.331
1.115
640
1496
1372
11680
μ/mm−1
θ range/deg
reflns collected
R(int)
1.322
0.068
2.911
0.696
1.95−26.10
10 516
1.71−27.00
28 931
1.62−25.10
20 380
0.91−27.53
124 524
0.0350
0.0362
0.0465
0.0740
data/restraints/params
goodness of fit
6259/5/379
1.049
8940/0/476
1.153
11 731/81/651
1.124
19 456/78/745
0.988
a
R indices (I > 2σ(I))
R1 = 0.0536
wR2 = 0.1451
R1 = 0.0793
wR2 = 0.1705
1.057/−0.493
R1 = 0.0573
wR2 = 0.1646
R1 = 0.0870
wR2 = 0.1848
0.884/−0.332
R1 = 0.0626
wR2 = 0.1594
R1 = 0.1007
wR2 = 0.1918
2.028/−0.911
R1 = 0.0602
wR2 = 0.1570
R1 = 0.0975
wR2 = 0.1727
0.710/−0.616
a
R indices (all data)
lgst diff peak and hole/e/Å3
R1 = ∑∥Fo| − |Fc∥/∑|Fo|. wR2 = [∑(|Fo|2 − |Fc|2)2/∑(Fo )]1/2
a
2
.
51.1, 52.6 (CH2), 59.8 (CH(CH3)2), 118.9 (NCHC), 121.4, 125.3,
128.2, 129.0, 137.8, 140.4, 143.1, 157.7, 168.8 (CHimine). Anal. Calcd
for C46H70Br2Cl2N6O2Zr [1061.02 g/mol]: C, 52.07; H, 6.65; N, 7.92.
Found: C, 51.92; H, 6.54; N, 7.88.
ArCH), 7.91 (s, 1H, ArCH). 13C NMR (100 MHz, CDCl3): δ 21.4,
23.3, 30.1, 31.5, 34.4, 35.1, 41.1, 46.2, 50.7, 52.6, 117.5, 120.1, 123.5,
125.5, 137.9, 142.8, 143.3, 160.0. Anal. Calcd for C23H35Cl4N3OTi
[559.22 g/mol]: C, 49.40; H, 6.31; N, 7.51. Found: C, 49.64; H, 6.35;
N, 7.62.
Synthesis of Zirconium Complex [Zr(13)Cl4] (11). Complex 11
was obtained as a yellow powder (207 mg, 52% yield) from hexane/
dichloromethane in a similar manner to 10 using ZrCl4(THF)2 (248
mg, 0.66 mmol). 1H NMR (400 MHz, CDCl3): δ 1.13 (s, 9H,
C(CH3)3), 1.30 (s, 12H, C(CH3)3 + CH(CH3)2), 1.51 (d, 3H,
CH(CH3)2), 3.10 (m, 1H, CH2), 3.26 (m, 1H, CH2), 3.81 (m, 1H,
CH2), 4.24 (m, 2H, CH(CH3)2 + CH2), 4.78 (br, 1H, NH), 5.84 (s,
1H, OPhCH), 6.21 (s, 1H, imidazolH), 7.24 (s, 1H, imidazolH), 7.68 (s, 1H,
ArCH), 7.89 (s, 1H, ArCH). 13C NMR (100 MHz, CDCl3): δ 21.5,
23.8, 29.7, 31.7, 34.2, 35.3, 38.6, 46.3, 50.7, 52.6, 117.6, 120.9, 123.4,
125.3, 137.8, 140.4, 143.0, 157.7. Anal. Calcd for C23H35Cl4N3OZr
[602.58 g/mol]: C, 45.84; H, 5.85; N, 6.97. Found: C, 45.92; H, 6.06;
N, 7.03.
Synthesis of Hafnium Complex [Hf(OSiMe3)2(k2-N,O-OC6H2-
3,5-tBu2-C(H)N-CH2CH2-Im)2][Br]2 (9). Complex 9 was obtained
as colorless crystals (351 mg, 56% yield) from hexane/dichloro-
methane in a similar manner to 8 using HfCl4 (160 mg, 0.5 mmol) and
1
NaOSiMe3 (113 mg, 1.0 mmol). H NMR (400 MHz, CDCl3): δ
−0.17 (s, 18H, OSi(CH3)3), 1.29 (s, 18H, C(CH3)3), 1.45 (s, 18H,
C(CH3)3), 1.53 (d, 12H, CH(CH3)2), 3.97 (m, 2H, CH2), 4.21 (m,
2H, CH2), 4.29 (m, 2H, CH(CH3)2), 4.60 (m, 4H, CH2), 6.30 (s, 2H,
NCHCHN), 7.06 (s, 2H, NCHCHN), 7.37 (s, 2H, ArCH), 7.60 (s,
2H, ArCH), 8.96 (s, 2H, CHN), 10.28 (s, 2H, imidCHC). 13C NMR
(100 MHz, CDCl3): δ 1.1, 2.5 (OSi(CH3)3), 23.0 (CH(CH3)2), 30.0,
31.6 (CH(CH3)3), 34.3, 35.4 (CH(CH3)3), 49.4, 53.6 (CH2), 59.1
(CH(CH3)2), 118.9 (NCHC), 121.9, 123.0, 130.5, 131.3, 136.4, 139.2,
140.5, 160.1, 174.8 (CHimine). Anal. Calcd for C52H88Br2HfN6O4Si2
[1255.76 g/mol]: C, 49.74; H, 7.06; N, 6.69. Found: C, 49.55; H, 6.91;
N 6.81.
Synthesis of Titanium Complex {[Ti(13)Cl3]2(μ-O)} (12). Water
(1.0 M in Et2O) (134 μL, 0.134 mmol) was added dropwise to a
CH2Cl2 solution (20 mL) of 10 (150 mg, 0.268 mmol) with an ice−
water bath. The mixture was stirred overnight at room temperature
and was evaporated to dryness. The crude mixture was recrystallized
from CH2Cl2/hexane to give dark red block microcrystals (53 mg, 37%
Synthesis of Titanium Complex [Ti(13)Cl4] (10). A dichloro-
methane (20 mL) solution of L (300 mg, 0.66 mmol) was added
dropwise to a Schlenk tube containing sodium hydride (80 mg, 2.20
mmol) at 0 °C. The mixture was allowed to warm to ambient
temperature, stirred for a further 1 h, and centrifuged to remove excess
sodium hydride. The resulting supernatant was cannulated into a THF
(10 mL) solution of TiCl4(thf)2 (220 mg, 0.66 mmol) keeping the
temperature below −78 °C. After stirring for a further 48 h at room
temperature the mixture was centrifuged to remove insoluble
materials. The resulting supernatant was concentrated to ca. 2.0 mL,
and hexane (15 mL) was added to give 10 as a reddish-brown powder
1
yield). H NMR (400 MHz, CDCl3): δ 1.09 (s, 9H, C(CH3)3), 1.29
(s, 12H, C(CH3)3 + CH(CH3)2), 1.48 (d, 3H, CH(CH3)2), 3.07 (m,
1H, CH2), 3.22 (m, 1H, CH2), 4.16 (m, 1H, CH2), 4.42 (m, 2H,
CH(CH3)2 + CH2), 4.72 (br, 1H, NH), 5.74 (s, 1H, OPhCH), 6.13 (s,
1H, imidazolH), 7.21 (s, 1H, imidazolH), 7.70 (s, 1H, ArCH), 7.94 (s, 1H,
ArCH). 13C NMR (100 MHz, CDCl3): δ 21.6, 23.6, 29.4, 31.5, 34.2,
35.1, 37.5, 46.2, 50.8, 53.0, 117.6, 121.4, 123.2, 125.0, 138.8, 141.8,
142.3, 153.0. Anal. Calcd for C46H70Cl6N6O3Ti2 [1063.54 g/mol]: C,
51.95; H, 6.63; N, 7.90. Found: C, 51.88; H, 6.53; N, 7.82.
1
(184 mg, 50% yield). H NMR (400 MHz, CDCl3): δ1.16 (s, 9H,
C(CH3)3), 1.28 (s, 12H, C(CH3)3 + CH(CH3)2), 1.59 (d, 3H,
CH(CH3)2), 3.13 (m, 1H, CH2), 3.31 (m, 1H, CH2), 3.94 (m, 1H,
CH2), 4.29 (m, 2H, CH(CH3)2 + CH2), 4.80 (br, 1H, NH), 5.87 (s,
1H, OPhCH), 6.23 (s, 1H, imidazolH), 7.24 (s, 1H, imidazolH), 7.68 (s, 1H,
Synthesis of Zwitterionic Ligand 13. A dichloromethane (20
mL) solution of L (200 mg, 0.44 mmol) was added dropwise to a
Schlenk tube containing sodium hydride (80 mg, 2.20 mmol) at 0 °C.
K
DOI: 10.1021/acs.organomet.5b00862
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
The mixture was allowed to warm to ambient temperature, stirred for a
further 1 h, and centrifuged to remove excess sodium hydride. The
resulting supernatant was concentrated to a residue, which was washed
with hexane (15 mL) and dried under vacuum to afford 13 as a yellow
solid (183 mg, 75% yield). Mp: 116−118 °C. Anal. Calcd for
C23H35N3O [369.54 g/mol]: C, 74.75; H, 9.55; N, 11.37. Found: C,
74.66; H, 9.59; N, 11.29. 1H NMR (400 MHz, CDCl3): δ 1.18 (s, 9H,
C(CH3)3), 1.39 (s, 12H, C(CH3)3 + CH(CH3)2), 1.62 (d, 3H,
CH(CH3)2), 3.18 (m, 1H, CH2), 3.39 (m, 1H, CH2), 4.17 (m, 1H,
CH2), 4.30 (sep, 1H, CH(CH3)2), 4.60 (m, 2H, CH2 + NH), 5.85 (s,
1H, OPhCH), 6.16 (s, 1H, imidazolH), 7.30 (s, 1H, imidazolH), 7.55 (s, 1H,
ArCH), 7.74 (s, 1H, ArCH). 13C NMR (100 MHz, CDCl3): δ 21.8,
23.6 (CH(CH3)2), 29.6, 31.5 (CH(CH3)3), 34.2, 35.1 (CH(CH3)3),
37.4, 46.1 (CH2), 50.8 (CH(CH3)2), 52.9 (CH), 117.6 (NCHC),
120.9, 121.4, 123.2, 125.0, 138.5, 141.7, 142.2, 153.2. HRMS (positive
ions): m/z 370.2886 (calcd for [M + H]+ 370.2864).
Synthesis of Titanium Complex [Ti(7)Cl2] (14). Complex
[Ti(7)Cl2] (14) (0.75 g) was prepared as an orange-red solid in
77% yield in a similar fashion to [Ti(A)Cl2] that we previously
reported.3b 1H NMR (400 MHz, CDCl3): δ 0.85 (m, 6H, CH(CH3)2),
1.11 (s, 9H, C(CH3)3), 1.25 (m, 6H, CH(CH3)2), 1.33 (s, 9H,
C(CH3)3), 1.42−1.44 (b, 18H, C(CH3)3), 2.69 (sept, 2H,
CH(CH3)2), 4.82 (bs, 4H, 2CH2), 5.70 (bs, 2H, CH2), 6.33 (d, 1H,
PhCH), 7.13 (s, 1H, PhCH),7.25 (m, 4H, PhCH), 7.32 (s, 1H,
PhCH),7.39−7.43 (m, 2H). 13C NMR (100 MHz, CDCl3): δ 25.5,
26.3, 29.6, 31.0, 31.2, 32.3, 32.9, 35.0, 35.5, 36.4, 51.8, 52.9, 54.6,
120.1, 123.2, 123.5, 123.6, 126.5, 126.8, 127.0, 127.9, 132.0, 133.7,
137.9, 139.4, 141.0, 142.8, 145.1, 147.3, 153.7, 165.4. Anal. Calcd for
C47H65Cl2N3O3Ti [838.81 g/mol]: C, 67.30; H, 7.81; N, 5.01. Found:
C, 67.18; H, 7.55; N, 4.72.
Typical General Procedure for Ethylene Polymerization. A
stainless steel autoclave (100 mL) equipped a mechanical stirrer and a
temperature controller was heated under vacuum at 120 °C for 2 h and
cooled to the desired reaction temperature under a nitrogen
atmosphere. After the desired amount of MAO and toluene (with
50 mL total volume maintained through adding toluene) were
transferred into the reactor, the solution was saturated under a
pressure somewhat higher than atmospheric pressure at 30 °C. A
solution of precatalyst in toluene was added to the reactor, and the
pressure of the autoclave was immediately raised to 5 atm and
maintained until the reactor was vented. The polymer was precipitated
in acidic methanol (VHCl/Vmethanol = 1/20), filtered, washed with
methanol, and then dried at 50 °C under vacuum to constant weight.
X-ray Crystallography. The single crystals suitable for X-ray
analysis were sealed into a glass capillary, and the intensity data of a
single crystal were collected on the CCD Bruker Smart APEX system.
Data obtained with the ω−2θ scan mode were collected on a Bruker
SMART 1000 CCD diffractometer with graphite-monochromatic Mo
Kα radiation (λ = 0.710 73 Å) at 293(2) K. The structures were solved
using direct methods, while further refinement with full-matrix least-
squares on F2 was obtained with the SHELXTL program package.32
All non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were introduced in calculated positions with the displacement factors
of the host carbon atoms. Four crystal structures have been deposited
as CCDC-937146 ([H3(1a)]Br), -937147 (4a), -1423419 (9), and
-1423420 (12) at the Cambridge Crystallographic Data Centre. The
crystallographic data of these compounds are summarized in Table 4.
AUTHOR INFORMATION
Corresponding Author
*E-mail: daozhang@fudan.edu.cn (D. Zhang). Fax: 86 21 6564
1740. Tel: 86 21 6564 3021.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the National Natural Science
Foundation of China (No. 21272040) for the financial support.
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ASSOCIATED CONTENT
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* Supporting Information
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