An efficient titanium amidinate catalyzed version of Ziegler's "aufbaureaktion"

Article abstract of DOI:10.1002/ejic.201201194

Diethylamidotitanium trichloride reacts with a variety of bulky amidines ArN(H)C(Ar′)NAr [Ar = 2,6-diisopropylphenyl; Ar′ = Ph, p-Me ₂NC₆H₄, p-MeOC₆H₄, p-(2,5-dimethylpyrrole)C₆H₄

Full text of DOI:10.1002/ejic.201201194

FULL PAPER
DOI:10.1002/ejic.201201194
An Efficient Titanium Amidinate Catalyzed Version of
Ziegler’s “Aufbaureaktion”
Johannes Obenauf,[a] Winfried P. Kretschmer,[a] Tobias Bauer,[a] and
Rhett Kempe*[a]
Keywords: Polymerization / Titanium / N ligands / Amidinates
Diethylamidotitanium trichloride reacts with a variety of
bulky amidines ArN(H)C(ArЈ)NAr [Ar 2,6-diisoprop-
ylphenyl; ArЈ = Ph, p-Me2NC6H4, p-MeOC6H4, p-(2,5-di-
methylpyrrole)C6H4] to form ammonium titanates. These
new titanium complexes undergo polyethylenyl chain trans-
fer polymerization to aluminium alkyls after activation with
d-MAO (“dry methylaluminoxane”). Ethylene is polymerized
with an activity of up to 1000 kgPE molcat–1 h–1 bar–1 in the
presence of 1000 equiv. of triethylaluminium. Linear alumin-
ium-terminated polyethylene is the only product observed.
This polymerization process can be viewed as an efficient
catalytic version of Ziegler’s “Aufbaureaktion”.
=
documented. Furthermore, enhancements of the CCTP
concept such as “chain shuttling”[9] and “ternary CCTP”[12]
Introduction
Ziegler’s “Aufbaureaktion”,[1] the rather slow oligomer- have been developed (Scheme 1).
ization of ethylene mediated by triethylaluminium (TEA),
is an important industrial process. Initially, aluminium-ter-
minated linear alkyl chains are produced, which can be
oxidized with O2. After hydrolytic workup aliphatic
alcohols are formed with a chain length of (for instance) 6
to 22 carbon atoms and are usually referred to as Ziegler
or fatty alcohols. These alcohols have a wide range of appli-
cations in personal care, polymer/leather/metal processing,
agriculture, cosmetics, flavours, fragrances, plastics (as sof-
teners), paints, coatings, industrial cleaning materials and
biocides.[2] Unfortunately, the chain growth in the “Aufbau-
reaktion” is very slow and limited in terms of higher molec-
ular weight products. At temperatures at which faster inser-
tion could be expected, competitive β-H elimination/trans-
fer processes become dominant so that OH group termin-
ated polyethylene (PE-OH) cannot be obtained by this
method. A polymerization method that produces metal ter-
Scheme 1. Net reaction and mechanism of CCTP involving alumin-
minated polyethylene is coordinative chain transfer polyme-
rization (CCTP).[3,4] Pioneering work in this field was re-
ported by Samsel et al.[5] as well as by Mortreux and co-
workers.[6] Recently, a variety of ethylene/propylene CCTP
catalyst systems with rare earth (RE) metals and transition
metals in combination with different chain transfer agents
(CTAs) such as Mg,[6] Zn[7–9] and Al alkyls[10,11] have been
ium alkyls; top: CTS (chain transfer state); bottom: CGS (chain
growing state). [M] = cationic or neutral transition metal or RE
complex; R1, R2 = alkyl moiety; n, m = natural numbers.
In CCTP, the chain growing state (CGS) elongates the
polymer chain and the chain transfer state (CTS) exchanges
the polymeryl chain between the catalyst and the CTA. In
this way, a catalyst can grow more than one “living” chain.
Bochmann and Lancaster reported that the exchange of
alkyl chains between group 4 metal cations and Al occurs
via bimetallic complexes in the CTS.[13] Norton and co-
workers described a detailed mechanistic picture of zircon-
ium complex catalyzed chain growth of Al alkyls.[14,15] The
kinetics of chain growth have been studied when catalyzed
[a] Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Fax: +49-921-552-157
E-mail: kempe@uni-bayreuth.de
Homepage: http://www.ac2.uni-bayreuth.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201201194.
by [(EBI)Zr(μ-Me)2AlMe2][B(C6F5)4] [EBI
= ethylene
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bridged bis(indenyl)]. This reaction is first order in [olefin] propylphenyl)carbodiimide to obtain the corresponding
and [catalyst] and inverse first order in [AlR3].[14] This in- lithium amidinates. After hydrolysis with water or saturated
verse first order dependence prohibits the use of high CTA/ ammonium chloride solution and recrystallization from hot
catalyst ratios. High amounts of CTA result in poor overall ethanol, amidines 1a–1d were obtained in good yields.
polymerization activity. As a consequence, most of the de- Owing to the substituent in the para position, these ligands
scribed CCTP catalyst systems work with CTA/catalyst ra- are considered to donate more electron density to the metal
tios Ͻ 500 and fail with significantly higher CTA/catalyst centre as illustrated in Figure 1.
ratios. A possible solution to this problem is the design of
new catalyst systems that undergo fast chain growth in
comparison to chain exchange and still suppress β-H elimi-
nation/transfer processes. In such a regime, multiple inser-
tions may compensate efficiency loss caused by high CTA/
catalyst ratios.[16] We recently developed rare earth (RE)
based CCTP catalysts[10,17] and varied the nature as well as
the steric demand of the monoanionic ligand used to stabi-
lize the organo RE cations. In addition, the size of the RE
Scheme 2. Synthesis of N,NЈ-bis(2,6-diisopropylphenyl)benzamid-
ines; Ar = 2,6-diisopropylphenyl.
atom was varied to find a catalyst system that tolerates high
CTA/catalyst ratios.[11a–11d,18] Unfortunately, these varia-
tions did not lead to CTA/catalyst ratios above 500. Thus,
we shifted our attention to group 4 metals, and titanium
catalysts in particular. Titanium catalysts stabilized by
bulky aminopyridinato (Ap) ligands showed very attractive
polymerization activities but suffered from ligand transfer
problems.[19] The Ap ligand is transferred to the CTA (alk-
ylaluminium compounds) and the increased electron-donor
ability of the ligand increased ligand transfer rates instead
of decreasing them.[20] Guanidinates[21,22] and amidinates[23]
are chemically related to Ap ligands and were expected to
significantly alter ligand transfer rates but to maintain high
polymerization activity. Herein, we report a new titanium
amidinate based catalyst system that is highly active in the
presence of high CTA/catalyst ratios and undergoes poly-
Figure 1. Higher electron donating ability owing to the introduc-
tion of functional groups in the backbone of the ligand.
Complex Synthesis
Amidines 1a–1d were treated with one equivalent of di-
ethylenyl chain transfer to TEA. No β-H elimination/trans- ethylamidotitanium trichloride [(Et2N)TiCl3] in toluene at
fer products were observed under the conditions applied room temperature to form the corresponding amidinatoti-
here.
tanium trichloride complexes by amine elimination. How-
ever, NMR experiments and X-ray crystal structure analysis
showed that the reactions of 1a–1d with [(Et2N)TiCl3] lead
to the amidinatotitanium trichloride only as an intermedi-
ate product, along with one equivalent of diethylamine
(Scheme 3). The released amine reacts with the amidinatoti-
Results and Discussion
Ligand Synthesis
Various synthetic protocols for the synthesis of amidines tanium trichloride to form equal amounts of an amidinato-
are known from the literature.[24] For the synthesis of 1a, diethylamidotitanium dichloride and diethylammonium
the protocol according to Boeré[24b] was slightly modified chloride. The latter reacts with the remaining amidinatoti-
(Scheme 2, top) by using a simplified workup procedure. tanium trichloride to form a diethylammonium amidinato-
2,6-Diisopropylaniline was treated with one equivalent of tetrachlorotitanate. Treatment of these anionic complexes
benzoyl chloride in an aqueous potassium hydroxide solu- 2a–2d with (trimethylsilyl)methyllithium or butyllithium se-
tion. The resulting amide was converted into the corre- lectively leads to the neutral amidinato diethylamidotitan-
sponding imidoyl chloride, which was treated with a further ium dichloride complexes (Scheme 3).
equivalent of 2,6-diisopropylaniline in the presence of tri-
All complexes were analyzed by NMR spectroscopy and
ethylamine to give N,NЈ-bis(2,6-diisopropylphenyl)benzam- elemental analysis. Single crystal structure analyses were
idine (1a). Colourless crystals were obtained by crystalli- carried out for selected complexes. Crystals suitable for X-
zation from hot ethanol. Amidines substituted in the para ray analysis were obtained by layering concentrated toluene
position of the phenyl backbone were prepared by insertion solutions with hexane or by recrystallization from hot hex-
reactions of the lithiated arene and N,NЈ-bis(2,6-diisoprop- ane. The molecular structures of complexes 2a, 2b, 2d and
ylphenyl)carbodiimide (Scheme 2, bottom). 4-Bromoan- 3b are presented in Figures 2, 3 and 4. Selected bond
isole, 4-bromo-N,N-dimethylaniline or 1-(4-bromophenyl)- lengths and angles are listed in Table 1. Crystallographic
2,5-dimethyl-1H-pyrrole were lithiated with an excess of details are available in the Supporting Information (Table
nBuLi and subsequently reacted with N,NЈ-bis(2,6-diiso- S1).
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Scheme 3. Synthesis of the complexes 2a–2d and 3b.
Figure 2. Dimeric structure of 2b. Carbon-bonded hydrogen atoms are omitted for clarity.
These new diethylammonium amidinato-tetrachloro- NH···Cl hydrogen bonds (illustrated for 2b in Figure 2). In
titanates form dimeric structures. Two complex anions are complexes 2a–2d, the titanium centres are pseudo-octa-
bridged by the diethylammonium counterions through hedrally coordinated by four chloro and two nitrogen atoms
to yield an anion accompanied by the diethylammonium
Table 1. Selected bond lengths [Å] and angles [°].
2a
2b
2d
3b
Ti1–N1
Ti1–N2
Ti1–Cl1
Ti1–Cl2
Ti1–Cl3
Ti1–Cl4
C1–N1
C1–N2
C1–C2
C2–C3
C3–C4
C4–C5
C5–N3
N1–C1–N2
N1–Ti1–N2
ΣϽ(C1)
ΣϽ(N3)
2.1032(16) 2.040(2)
2.0540(16) 2.088(2)
2.093(3)
2.053(3)
2.3541(13) 2.272(3)
2.3253(12) 2.272(3)
2.0758(19)
2.0730(18)
2.3287(6)
2.3418(6)
2.3601(6)
2.2774(6)
1.335(2)
1.337(3)
1.483(6)
–
2.3381(8)
2.2686(9)
2.3711(8)
2.3917(8)
1.352(3)
1.338(3)
1.468(4)
1.396(4)
1.372(4)
1.402(4)
1.361(3)
2.2677(13)
2.3545(11)
1.328(5)
1.355(5)
1.488(6)
1.386(6)
1.399(6)
1.376(6)
1.438(6)
109.2(4)
63.66(13)
359.9
–
–
1.351(3)
1.343(3)
1.472(3)
1.392(3)
1.377(3)
1.409(4)
1.365(3)
108.19(19)
63.47(7)
359.99
359.9
–
–
–
109.66(16) 108.3(2)
63.37(6)
359.99
–
63.72(8)
359.8
360.1
Figure 3. Molecular structure of 3b. Carbon-bonded hydrogen
atoms are omitted for clarity.
359.4
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Figure 4. Molecular structures of 2a, 2b and 2d (from left to right). Carbon-bonded hydrogen atoms are omitted for clarity.
counterion. The two Ti–N bond lengths are in the range resulted in no significant difference in activity, but a nearly
found for benzamidinatotitanium complexes.[25] The N1– sevenfold increase in molecular weight accompanied by a
C1, N2–C1 and C5–N3 bond lengths are significantly broadening of the polydispersity was obtained (Table 2, En-
shorter than C(sp2)–N single bonds and slightly longer than try 3). Increasing the temperature to 80 °C led to a signifi-
C–N double bonds. The sums of the bond angles around cant decrease in the polymerization ability (Table 2, En-
N3 are 360.1 (2b), 359.4 (2d) and 359.9° (3b), which con- try 4). The low activity at 80 °C could result from catalyst
firms that the nitrogen atoms are sp2 hybridized. Further- decomposition at this temperature. As a consequence, fur-
more, the introduction of electron donating groups leads to ther studies were conducted at 50 °C. To rule out ligand
a quinoid π-electron system, which results in significantly transfer from Ti to trimethylaluminium (TMA),[18,26] fur-
shorter C3–C4 bond lengths than the C2–C3 and C4–C5 ther experiments were also done with d-MAO, MAO from
bond lengths, as suggested in Figure 1. This clearly indi- which free TMA was removed. Alteration of the ligand
cates that the lone pair of the introduced substituents par- backbone did not give greatly different polymerization re-
ticipates in the ligand π system and can increase the electron sults at this stage. Polymerization with 3b leads to a clearly
density at the titanium centre, which results in closer bond- bimodal distribution. This indicates that two active sites are
ing to the ligand. The N1–Ti1–N2 bond angle is smaller operating if 3b is used as a precatalyst. One of the distribu-
than that in [{PhC(NSiMe3)2}TiCl3], which indicates the tions is identical to the one observed for precatalyst 2b un-
higher steric demand of the 2,6-diisopropylphenyl moieties. der identical conditions (Figure 5). One of these active sites
Compound 3b crystallizes in the monoclinic space group could be identical to the single site catalyst that is generated
P21/n. The metal centre is coordinated by the amidinate li- by MAO activation of 2b. The other one could result from
gand, a diethylamido ligand and two chloro ligands to form a diethylamido-containing species. The activity of the com-
a neutral complex (Figure 3). The N1–Ti1–N2 bond angle plexes increases if activated with d-MAO (Table 3) instead
[62.4(3)°] is slightly smaller than those in 2a–2d.
of MAO. Higher molecular weight polyethylene, roughly
one order of magnitude higher than for the MAO runs, was
observed for all catalysts, which indicates that a polymeryl
chain transfer to TMA occurs if MAO is used as an acti-
Polymerization Studies
The activation of the precatalysts 2a–c and 3b with vator. The addition of defined amounts of TEA to the d-
methylaluminoxane (MAO) leads to active polymeri- MAO runs supports this hypothesis. The variation of the
zation catalysts at 50 °C with activities of up to 900 TEA-to-Ti ratio from 500 to 1000 to 2000 to 10000 resulted
kgPE mol–1 h–1 bar–1 and polyethylene with molecular in a decrease of the molecular weight, activity and polydis-
weights between 23 and 90 kgmol–1 (Table 2). We suppose persity. The activation of 3b with d-MAO leads to a mono-
that the diethylammonium ion is deprotonated and ends up modal but broad distribution and shows evidence of a bi-
at the aluminium species. The temperature influences the modal distribution; the distribution is clearly bimodal with
polymerization rather strongly (Table 2, Entries 2–4). At MAO. The influence of functional groups in the backbone
50 °C, 2b produces polyethylene with a molecular weight of of the ligands was also examined. NMR investigations of
29 kgmol–1 with an activity of 900 kgPE mol–1 h–1 bar–1 the polymers obtained showed that all polymer chains are
(Table 2, Entry 2). A decrease of the temperature to 30 °C fully saturated as there are no olefinic resonances (Figure
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S1 in the Supporting Information). This can only be ex- donating groups to the backbone of the ligands gives rise
plained by the exclusive presence of metal-terminated poly- to increased electron-donating ability of these ligands. Only
mer before hydrolysis with acidified ethanol.
marginal influences of that electron donor ability towards
the polymerization performance were observed. These
mono(amidinato) titanium complexes gave rise to highly
active polymerization catalysts after activation with d-
MAO. The polymerization can be viewed as a catalyzed ver-
sion of Ziegler’s “Aufbaureaktion”.
Table 2. Ethylene polymerization using MAO.[a]
Entry Precat.[a] mPE
[g] [kgPE molcat–1 h–1 bar–1
Activity
Mw
Mw/Mn
]
[kgmol–1
]
1
2
3
4
5
6
7
2a
2b
0.90
0.90
0.80
0.13
0.60
0.70
0.80
900
900
800
130
600
700
800
24.2
28.6
197.8
6.3
49.4
22.3
91.6
2.8
6.0
16.8
2.3
6.0
4.8
2b[b]
2b[c]
2c
Experimental Section
2d
3b
General Comments: All manipulations and reactions were carried
out under dry argon by using standard Schlenk and glovebox tech-
niques. Solvents were purified by distillation from LiAlH4, potas-
sium, Na/K alloy or sodium ketyl of benzophenone under argon
immediately before use. Toluene (Aldrich, anhydrous, 99.8%) was
passed over columns of Al2O3 (Fluka), BASF R3-11 supported Cu
oxygen scavenger and molecular sieves (Aldrich, 4 Å). Ethylene
(AGA polymer grade) was passed over BASF R3-11 supported Cu
oxygen scavenger and molecular sieves (Aldrich, 4 Å). [(Et2N)-
TiCl3] was prepared according to literature procedures.[27] Com-
mercial nBuLi (2.5 m in hexane) and all other chemicals were used
as received. Elemental analyses were carried out with a Vario ele-
mentar EL III apparatus.
11.4
[a] Conditions: precatalyst 2.0 μmol; MAO 1.3 mmol; toluene
150 mL; p = 2 bar; t = 15 min; T = 50 °C. [b] T = 30 °C. [c] T =
80 °C.
NMR Spectroscopy: NMR spectra were obtained with a Varian
INOVA 400, Varian INOVA 300 or Bruker ARX250 spectrometer.
Chemical shifts are reported in ppm relative to the residual proton
signals of the deuterated solvent. Deuterated solvents were ob-
tained from Cambridge Isotope Laboratories and were degassed,
dried and distilled prior to use.
Figure 5. Mw distribution plots of polymers (Table 2, Entries 2 and
7).
Table 3. Ethylene polymerization using d-MAO.[a]
Gel Permeation Chromatography (GPC): Gel permeation
chromatography (GPC) analysis was carried out with a PL-GPC
220 (Agilent, Polymer Laboratories) high temperature chromato-
graphic unit equipped with differential pressure (DP) and refractive
index (RI) detectors and two linear mixed bed columns (Olexis, 13-
micron particle size). GPC analysis were performed at 150 °C and
with 1,2,4-trichlorobenzene as the mobile phase. The samples were
prepared by dissolving the polymer (0.05 wt.-%, c = 1 mgmL–1) in
the mobile phase solvent in an external oven, and the solutions
were run without filtration. The molecular weights of the samples
Entry Precat.[a] TEA mPE
(equiv.) [g] [kgPE molcat–1 h–1 bar–1] [kgmol–1]
Activity
Mw
Mw/Mn
1
2
3
4
5
6
7
8
2a
2a
2b
2b
2b
2b
2b
2c
2c
2d
2d
3b
0
1.40
500 0.80
1.60
1400
800
1600
1200
1000
700
350
800
300
1300
800
232.9
8.0
228.4
7.4
3.5
1.9
1.0
310.3
8.4
86.2
6.9
384.4
8.9
2.1
4.5
4.1
2.3
1.7
1.3
2.2
2.3
10.0
3.0
4.9
0
500 1.20
1000 1.00
2000 0.70
10000 0.35
0
0.80
500 0.30
1.30
500 0.80
3.50
were referenced to PE (Mw = 520–3200000 gmol–1) and PS (Mw
=
580–2800000 gmol–1) standards. The reported values are the
average of at least two independent determinations.
9
10
11
12
0
X-ray Crystallography: X-ray crystal structure analyses were per-
0
3500
formed with
a STOE-IPDS II diffractometer [λ(Mo-Kα) =
[a] Conditions: precatalyst 2.0 μmol; d-MAO 1.0 mmol; toluene
150 mL; p = 2 bar; t = 15 min; T = 50 °C.
0.71073 Å] equipped with an Oxford Cryostream low-temperature
unit. Structure solution and refinement were accomplished with
SIR97,[28] SHELXL-97[29] and WinGX.[30] Selected details of the
X-ray crystal structure analyses are listed in Table 1.
Conclusions
CCDC-902396 (for 2a), -903295 (for 2b), -902394 (for 2d) and
-903293 (for 3b) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk./data_request/cif.
Several conclusions can be drawn from the present study.
Mono(amidinato) titanium complexes can be synthesized
by amine elimination. The treatment of amidines with di-
ethylamidotitanium trichloride leads to anionic mono-
(amidinato) titanium tetrachloride complexes with dieth-
ylammonium counterions and mono(amidinato) diethyl-
amidotitanium dichloride complexes. The titanates can also
be converted selectively into neutral dichloride complexes
Ethylene Polymerization: The polymerizations were carried out in
a 300 mL Büchi glass autoclave with an ethylene flow display
equipped with external heating (water bath) at 2 bar ethylene pres-
sure. The autoclave was evacuated and purged with ethylene. Tolu-
ene (150 mL) was added into the autoclave and saturated with eth-
by addition of strong bases. The introduction of electron- ylene. The stock solutions of catalyst and cocatalyst were prepared
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in a glovebox. After addition of the cocatalyst and complete satura-
tion with ethylene, the catalyst was added. After 15 min of reaction
time, the reactor was vented and acidified ethanol was added. The
polymers were filtered and dried at 80 °C.
[d, J = 6.4 Hz, 6 H, CH(CH3)2], 0.92 [d, J = 6.2 Hz, 6 H, CH-
(CH3)2], 1.38 [d, J = 6.6 Hz, 6 H, CH(CH3)2], 1.39 [d, J = 6.7 Hz,
6 H, CH(CH3)2], 3.08 (s, 3 H, OCH3), 3.31 [m, 2 H, CH(CH3)2],
3.49 [m, 2 H, CH(CH3)2], 5.88 (s, 1 H, NH), 6.51–7.65 (m, 10 H,
ArH) ppm.
Ligand Synthesis
N,NЈ-Bis(2,6-diisopropylphenyl)-4-(2,5-dimethylpyrrole-1-yl)benz-
amidine (1d): To a solution of 1-(4-bromophenyl)-2,5-dimethylpyr-
role[31] (2.00 g, 8.0 mmol) in hexane (30 mL), nBuLi (3.4 mL,
8.5 mmol) was added dropwise at –78 °C. Stirring of the mixture
for four hours at room temperature resulted in a white solid. The
supernatant solution was decanted, and the solid was washed twice
with hexane. After removal of the supernatant solution, the solid
was dried in vacuo. To the obtained [4-(2,5-dimethyl-1H-pyrrole-
1-yl)phenyl]lithium (1.00 g, 5.64 mmol) in diethyl ether (30 mL) a
solution of N,NЈ-bis(2,6-diisopropylphenyl)carbodiimide (1.84 g,
5.08 mmol) in diethyl ether (15 mL) was added dropwise at –78 °C.
The reaction mixture was warmed to room temperature and stirred
overnight. Saturated ammonium chloride solution (3 mL) was
added and stirred vigorously for 1 h. The organic phase was sepa-
rated, and the aqueous phase was extracted several times with
ether. The combined organic phases were dried with anhydrous so-
dium sulfate, filtered and the solvent was removed under reduced
pressure. Recrystallization from hot ethanol led to orange crystals
(1.08 g, 62 %). 1H NMR (300 MHz, CDCl3): δ = 0.84 [d, J =
6.8 Hz, 6 H, CH(CH3)2], 0.92 [d, J = 6.7 Hz, 6 H, CH(CH3)2], 1.18
[d, J = 6.7 Hz, 6 H, CH(CH3)2], 1.29 [d, J = 7.0 Hz, 6 H, CH-
(CH3)2], 1.87 (s, 6 H, CH3-pyrrole), 3.13 [m, 4 H, CH(CH3)2], 5.68
(s, 1 H, NH), 5.78 (s, 2 H, CH-pyrrole), 6.89–7.40 (m, 10 H, ArH)
ppm.
N,NЈ-Bis(2,6-diisopropylphenyl)benzamidine (1a): To a solution of
2,6-diisopropylaniline (10 mL, 9.4 g, 53 mmol) in potassium hy-
droxide solution (100 mL, 10% in water), benzoyl chloride (6.7 mL,
8.19 g, 58 mmol) was added with vigorous stirring. The purple pre-
cipitated solid was collected by filtration and washed with water
and hexane. The resulting N-2,6-diisopropylphenylbenzamide
(10.00 g, 50.7 mmol) was heated at reflux for one hour in thionyl
chloride (20 mL). The excess thionyl chloride was removed under
reduced pressure, and N-(2,6-diisopropylphenyl)benzimidoyl chlor-
ide was obtained as a yellow oily residue. To a solution of this
intermediate (5 g, 16.7 mmol) and triethylamine (2.3 mL, 1.7 g,
16.7 mmol) in toluene (50 mL), 2,6-diisopropylaniline (3.1 mL,
3.8 g, 16.7 mmol) was added. The mixture was heated to reflux for
two hours. Subsequently, the reaction mixture was poured into
water. The organic phase was separated, washed twice with water
and dried with anhydrous sodium sulfate. After removal of the sol-
vent, the residue was recrystallized from hot ethanol (5.4 g, 69%
1
with respect to the imidoyl chloride). H NMR (250 MHz, C6D6):
δ = 0.95 [d, J = 6.4 Hz, 6 H, CH(CH3)2], 1.02 [d, J = 6.2 Hz, 6 H,
CH(CH3)2], 1.37 [d, J = 6.6 Hz, 6 H, CH(CH3)2], 1.49 [d, J =
6.7 Hz, 6 H, CH(CH3)2], 3.35 [m, 2 H, CH(CH3)2], 3.52 [m, 2 H,
CH(CH3)2], 5.70 (s, 1 H, NH), 6.50–7.63 (m, 11 H, ArH) ppm.
N,NЈ-Bis(2,6-diisopropylphenyl)-4-dimethylaminobenzamidine (1b):
nBuLi (2.5 m in hexane, 4.0 mL, 10 mmol) was slowly added to a
solution of 4-bromo-N,N-dimethylaniline (2.01 g, 10 mmol) in
THF (40 mL) at –78 °C. After stirring for 3 h, a solution of N,NЈ-
bis(2,6-diisopropylphenyl)carbodiimide (3.31 g, 8.6 mmol) in THF
(20 mL) was added dropwise. The solution was warmed to room
temperature and stirred overnight. The solvent was removed under
reduced pressure, and the residue was dissolved in ether. To this
solution, a saturated ammonium chloride solution (5 mL) was
added, and the mixture was stirred for 1 h. The aqueous phase was
separated and washed twice with ether. The organic phases were
combined and dried with anhydrous sodium sulfate. After filtration
and removal of the solvent, the residue was recrystallized from hot
ethanol. The obtained colourless crystals were isolated, washed
Complex Synthesis
Diethylammonium [N,NЈ-Bis(2,6-diisopropylphenyl)benzamidinato-
tetrachlorotitanate] (2a): Diethylamidotitanium trichloride (0.350 g,
1.55 mmol) and 1a (0.60 g, 1.35 mmol) were dissolved in toluene
(20 mL), and the solution was stirred for 24 h at room temperature.
The solvent was removed under reduced pressure, and the dark
brown residue was dissolved in toluene and filtered. Dark red crys-
tals were obtained by layering the filtrate with hexane (0.41 g,
1
43%). H NMR (400 MHz, C6D6): δ = 1.03 [d, J = 6.8 Hz, 12 H,
CH(CH3)2], 1.49 [t, J = 6.8 Hz, 6 H, H2N(CH2CH3)2], 1.74 [d, J =
6.5 Hz, 12 H, CH(CH3)2], 2.69 [q, J = 7.2 Hz, 4 H, H2N(CH2-
CH3)2], 3.87 [m, 4 H, CH(CH3)2], 6.63–7.30 (m, 11 H, ArH), 7.73
[s, 2 H, H2N(CH2CH3)2] ppm. 13C NMR (100 MHz, C6D6): δ =
13.2 [H2N(CH2CH3)2], 23.8 [CH(CH3)2], 24.0 [CH(CH3)2], 28.8
1
with cold ethanol and dried under vacuum (3.9 g, 74%). H NMR
(250 MHz, C6D6): δ = 0.81 [d, J = 6.7 Hz, 6 H, CH(CH3)2], 0.90
[d, J = 6.8 Hz, 6 H, CH(CH3)2], 1.14 [d, J = 6.7 Hz, 6 H, CH- [CH(CH3)2], 49.2 [H2N(CH2CH3)2], 124.57, 131.5, 130.9, 131.0,
(CH3)2], 1.24 [d, J = 6.9 Hz, 6 H, CH(CH3)2], 2.81 [s, 6 H,
N(CH3)2], 3.08 [m, 2 H, CH(CH3)2], 3.37 [m, 2 H, CH(CH3)2], 5.51
(s, 1 H, NH), 6.38–7.20 (m, 10 H, ArH) ppm.
143.0, (ArC), 177.7 (NCN) ppm. C35H51Cl4N3Ti (703.49): calcd. C
59.76, H 7.31, N 5.97; found C 58.97, H 7.45, N 5.82.
Diethylammonium [N,NЈ-Bis(2,6-diisopropylphenyl)-4-dimethyl-
amidobenzamidinato-tetrachlorotitanate] (2b): Compound 1b
(0.214 g, 0.44 mmol) and diethylamidotitanium trichloride (0.10 g,
0.44 mmol) were dissolved in toluene (20 mL), and the solution was
stirred for one hour at room temperature. Dark red crystals were
obtained by layering with hexane (0.150 g, 48 %). 1H NMR
(300 MHz, C6D6): δ = 0.94 [t, J = 6.9 Hz, 6 H, H2N(CH2CH3)2],
1.49 [d, J = 6.6 Hz, 12 H, CH(CH3)2], 1.60 [d, J = 6.4 Hz, 12 H,
CH(CH3)2], 1.96 [s, 6 H, N(CH3)2], 3.80 [m, 4 H, CH(CH3)2], 4.09
[q, J = 6.9 Hz, 4 H, H2N(CH2CH3)2], 7.09–7.25 (m, 10 H, ArH),
7.41 [s, 2 H, H2N(CH2CH3)2] ppm. 13C NMR (75 MHz, C6D6): δ
= 13.1 [H2N(CH2CH3)2], 24.3 [CH(CH3)2], 25.6 [CH(CH3)2], 29.1
[CH(CH3)2], 38.7 [N(CH3)2], 48.8 [H2N(CH2CH3)2], 110.2, 124.8,
126.8, 133.5, 143.4, 144.4, 145.7, 157.3 (ArC), 182.6 (NCN) ppm.
C37H56Cl4N4Ti (746.55): calcd. C 59.53, H 7.56, N 7.50; found C
59.40, H 7.64, N 7.61.
N,NЈ-Bis(2,6-diisopropylphenyl)-4-methoxybenzamidine (1c): To a
solution of 4-bromoanisole (2.0 mL, 16 mmol) in hexane (40 mL),
nBuLi (6.4 mL, 16 mmol) was added dropwise at room tempera-
ture. Stirring of the solution for 4 h produced a white precipitate.
The supernatant solution was decanted, and the residue was
washed twice with hexane, dried under vacuum and subsequently
dissolved in ether. A solution of N,NЈ-bis(2,6-diisopropylphenyl)-
carbodiimide (3.55 g, 13.8 mmol) in ether was added dropwise, and
the mixture was stirred overnight. To this solution, a saturated am-
monium chloride solution (5 mL) was added, and the mixture was
stirred for 1 h. The aqueous phase was separated and washed twice
with ether. The combined organic phases were dried with anhy-
drous sodium sulfate and filtered. The solvent was removed in
vacuo. Recrystallization of the residue from hot ethanol led to pale
1
yellow crystals (1.3 g, 65%). H NMR (300 MHz, C6D6): δ = 0.91
Eur. J. Inorg. Chem. 2013, 537–544
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FULL PAPER
Diethylammonium [N,NЈ-Bis(2,6-diisopropylphenyl)-4-methoxy-
benzamidinatotetrachlorotitanate] (2c): Compound 2c was prepared
according to the procedure for 2b by using the following amounts:
1c (0.208 g, 0.44 mmol) and diethylamidotitanium trichloride
(0.10 g, 0.44 mmol), yield 0.141 g, 46 %. 1H NMR (300 MHz,
C6D6): δ = 1.21 [t, J = 6.6 Hz, 6 H, H2N(CH2CH3)2], 1.31 [d, J =
6.5 Hz, 12 H, CH(CH3)2], 1.45 [d, J = 6.4 Hz, 12 H, CH(CH3)2],
2.49 [q, J = 7.0 Hz, 4 H, H2N(CH2CH3)2], 2.92 (s, 3 H, OCH3),
3.55 [sept, J = 6.6 Hz, 4 H, CH(CH3)2], 7.18–7.30 (m, 10 H, Ar–
H) ppm. 13C NMR (75 MHz, C6D6): δ = 13.2 [H2N(CH2CH3)2],
24.2 [CH(CH3)2], 25.7 [CH(CH3)2], 29.0 [CH(CH3)2], 49.1
[H2N(CH2CH3)2], 54.6 (OCH3), 113.3, 120.9, 124.7, 127.0, 133.3,
143. 5, 144. 9, 162.2, 162.7 (ArC), 177. 3 (NCN) ppm.
C36H53Cl4N3OTi + C7H8 (825.64): calcd. C 62.55, H 7.45, N 5.09;
found C 61.07, H 7.79, N 5.37.
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Diethylammonium [N,NЈ-Bis(2,6-diisopropylphenyl)-4-(2,5-dimeth-
ylpyrrole-1-yl)benzamidinatotetrachlorotitanate] (2d): Compound
2d was prepared according to the procedure for 2b by using the
following amounts: 1d (0.400 g, 0.70 mmol) and diethylamido-
titanium trichloride (0.169 g, 0.70 mmol). Dark red crystals were
obtained by layering with hexane (0.270 g, 47 %). 1H NMR
(300 MHz, CD2Cl2): δ = 0.75 [d, J = 6.7 Hz, 12 H, CH(CH3)2],
1.13 [d, J = 6.6 Hz, 12 H, CH(CH3)2], 1.25 [m, 6 H, H2N(CH2-
CH3)2], 3.17 [q, J = 7.3 Hz, 4 H, H2N(CH2CH3)2], 3.75 [m, 4 H,
CH(CH3)2], 5.74 (s, 6 H, CH3-pyrrole), 6.81–7.87 (m, 12 H, ArH),
7.59 [s, 2 H, H2N(CH2CH3)2] ppm. 13C NMR (75 MHz, CD2Cl2):
δ = 11.4 (CH3-pyrrole), 13.1 [N(CH2CH3)2], 24.0 [CH(CH3)2], 25.9
[CH(CH3)2], 29.1 [CH(CH3)2], 43.1 [N(CH2CH3)2], 107.2, 125.2,
125.8, 128.2, 128.6, 128.7, 129.5, 132.3, 136.6, 138.5, 143.5, 144.0
(ArC) ppm. C103H140Cl8N8Ti2 (1869.63): calcd. C 66.17, H 7.55, N
5.99; found C 65.97, H 7.81, N 5.81.
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[N,NЈ-Bis(2,6-diisopropylphenyl)-4-dimethylamino-benzamidinato]-
dichlorodiethylamidotitanium(IV) (3b): Compound 1b (0.30 g,
0.62 mmol) and diethylamidotitanium trichloride (0.14 g,
0.62 mmol) were dissolved in toluene (20 mL), and the solution was
stirred for 1 h at room temperature. (Trimethylsilyl)methyllithium
(0.058 g, 0.62 mmol) was added, and the mixture was stirred over-
night, which brightened the dark red solution. The solution was
filtered, and the residue was extracted twice with toluene. The sol-
vent was removed under reduced pressure. Recrystallization from
hot hexane led to bright red crystals (0.40 g, 80 %). 1H NMR
(300 MHz, C6D6): δ = 1.08 [t, J = 6.9 Hz, 6 H, N(CH2CH3)2], 1.20
[d, J = 6.8 Hz, 12 H, CH(CH3)2], 1.64 [d, J = 6.7 Hz, 12 H,
CH(CH3)2], 2.04 [s, 6 H, N(CH3)2], 3.95 [sept, J = 6.7 Hz, 4 H,
CH(CH3)2], 4.23 [q, J = 7.0 Hz, 4 H, N(CH2CH3)2], 7.00–7.52 (m,
10 H, ArH) ppm. 1 3 C NMR (75 MHz, C6 D6 ): δ = 13.2
[N(CH2CH3)2], 24.3 [CH(CH3)2], 25.6 [CH(CH3)2], 28.9 [CH-
(CH3)2], 38.7 [N(CH3)2], 48.9 [N(CH2CH3)2], 110.0, 114.8, 124.6,
126.8, 133.3, 143.4, 151.7 (ArC), 177.8 (NCN) ppm.
C37H54Cl2N4Ti + 0.5 C6H14 (716.71): calcd. C 67.03, H 8.58, N
7.82; found C 65.08, H 8.78, N 7.40.
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Acknowledgments
Financial support from the Deutsche Forschungsgemeinschaft
(DFG) SFB 840 and from SASOL Germany GmbH is gratefully
acknowledged.
Eur. J. Inorg. Chem. 2013, 537–544
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Received: October 2, 2012
Published Online: December 7, 2012
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