Alternating α-Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization

Article abstract of DOI:10.1021/acs.organomet.6b00671

The catalytic oligomerization of ethylene with chromium-based complexes containing bis(benzimidazolemethyl)amine (BIMA) ligands results in alternating distributions of linear α-olefins (LAOs). Extremely high activities are obtained (>100 000 g mmol^-1 h^-1 bar^-1) with N-alkyl-substituted BIMA ligands, whereas bulky groups on the central nitrogen or alternative central donors result in much lower activities. Variations in the ligand backbone, as well as methylation of the benzimidazole units, lead to reduction in activity. The alternating LAO distributions have been mathematically analyzed using second-order recurrence relations. The shape of the distributions is affected by ethylene pressure (1-4 bar) and by the cocatalyst to some degree. On the basis of the results and analysis presented herein, we propose that the alternating behavior originates from the ability of these chromium BIMA catalysts to undergo single as well as double ethylene insertion reactions. A minor second distribution (<5 wt %) of 2-ethyl-1-alkenes is obtained under certain conditions, resulting from incorporation of 1-butene. DFT studies (M06L) and experimental observations regarding the reaction between AlMe₃ and the N-methyl BIMA ligand 2 have shown that deprotonation of the benzimidazole N-H units can occur, which suggests a change in coordination of the BIMA ligand under oligomerization conditions.

Full text of DOI:10.1021/acs.organomet.6b00671

Article
pubs.acs.org/Organometallics
Alternating α‑Olefin Distributions via Single and Double Insertions in
Chromium-Catalyzed Ethylene Oligomerization
†
†
†
†
†
Atanas K. Tomov, James D. Nobbs, Juan J. Chirinos, Prabhjot K. Saini, Robert Malinowski,
†
†
‡
†
§
Sarah K. Y. Ho, Craig T. Young, David S. McGuinness, Andrew J. P. White, Mark R. J. Elsegood,
,
†
and George J. P. Britovsek*
†
Department of Chemistry, Imperial College London, Exhibition Road, London, SW7 2AZ, U.K.
School of Physical Sciences−Chemistry, University of Tasmania, Private Bag 75, Hobart 7001, Australia
Chemistry Department, Loughborough University, Loughborough, LE11 3TU, U.K.
‡
§
*
S Supporting Information
ABSTRACT: The catalytic oligomerization of ethylene with chromium-based complexes containing bis(benzimidazolemethyl)-
amine (BIMA) ligands results in alternating distributions of linear α-olefins (LAOs). Extremely high activities are obtained
−1
−1
−1
(
>100 000 g mmol
h
bar ) with N-alkyl-substituted BIMA ligands, whereas bulky groups on the central nitrogen or
alternative central donors result in much lower activities. Variations in the ligand backbone, as well as methylation of the
benzimidazole units, lead to reduction in activity. The alternating LAO distributions have been mathematically analyzed using
second-order recurrence relations. The shape of the distributions is affected by ethylene pressure (1−4 bar) and by the cocatalyst
to some degree. On the basis of the results and analysis presented herein, we propose that the alternating behavior originates
from the ability of these chromium BIMA catalysts to undergo single as well as double ethylene insertion reactions. A minor
second distribution (<5 wt %) of 2-ethyl-1-alkenes is obtained under certain conditions, resulting from incorporation of 1-butene.
DFT studies (M06L) and experimental observations regarding the reaction between AlMe and the N-methyl BIMA ligand 2
3
have shown that deprotonation of the benzimidazole N−H units can occur, which suggests a change in coordination of the BIMA
ligand under oligomerization conditions.
INTRODUCTION
■
Linear α-olefins (LAOs) are important chemical intermediates
for the production of detergents and lubricants and as co-
monomers in linear low-density polyethylene (LLDPE).
1
−4
Several commercial processes produce LAOs with different
distributions of chain lengths. The Alfen process involves
stepwise insertions of ethylene into the Al−C bonds of
aluminum alkyls, resulting in a range of LAOs that follow a
Poisson distribution. The Shell Higher Olefin Process (SHOP)
oligomerizes ethylene with a nickel-based catalyst (see Figure
5
Figure 1. Examples of commercial ethylene oligomerization catalysts
1
), where chain propagation competes with chain termination
(X = appropriate anion).
6
according to the Cossee mechanism, resulting in LAOs with a
Schulz−Flory distribution. Several chromium complexes have
been reported that oligomerize ethylene with high selectivity to
7
,8
1
5
Phillips Petroleum Company, and Sasol has recently
commercialized a tri/tetramerization technology based on
1
-hexene or 1-octene, for example, those based on PNP
9
−12
ligands
ligand systems.
and more recently with PNCN and PCN
1
3,14
The trimerization of ethylene to 1-hexene
Received: August 22, 2016
with a pyrrole/chromium-based catalyst is operated by the
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00671
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Article
Figure 2. GC-FID analysis of an alternating olefin distribution obtained with chromium BIMA catalyst [Cr(2)Cl ]/MAO (* = standard 2,2,4,4,6,8,8-
3
heptamethylnonane).
Figure 3. Overview of ligands 1−21.
PNP/chromium catalysts for the production of 1-hexene and 1-
geometry around chromium, reaction parameters such as
pressure, and the nature of the cocatalyst on catalytic activity
and product distribution have been investigated. Alternating
distributions can be mathematically described by second-order
recurrence relations, which are related to first-order recurrence
1
6
octene. Some examples of commercial oligomerization
catalysts are collected in Figure 1. Deuterium labeling studies
have shown that many chromium catalysts operate via a
metallacyclic mechanism rather than a Cossee chain growth
1
7−19
22
mechanism.
relations, for example, the Schulz−Flory distribution. Detailed
In 2006, Tomov et al. reported a chromium bis-
analysis of the product distribution, including all side products,
has led to a mechanistic proposal that involves a metallacyclic
mechanism whereby both single and double ethylene insertion
in the metallacycle are key steps in the oligomerization process.
(benzimidazolemethyl)amine (BIMA) complex that, in combi-
nation with methylaluminoxane (MAO) as the cocatalyst,
generates a highly active ethylene oligomerization catalyst with
−
1
−1
−1 20
activities of 100 000 g mmol
h
bar . An unusual
RESULTS AND DISCUSSION
alternating distribution of LAOs was obtained that was very
different from Schulz−Flory or Poisson distributions. The α-
olefins formed from an odd number of ethylene units (n = 1, 3,
■
Ligand and Complex Synthesis. A series of nitrogen-
based ligands 1−21 have been prepared, based on the original
bis(benzimidazolemethyl)amine ligand 2 (see Figure 3). The
synthesis and characterizing data of ligands 2, 6, 8, 9, 10, 11,
5, etc.) are significantly less abundant than the even-numbered
oligomers such as 1-butene (n = 2), 1-octene (n = 4), and 1-
dodecene (n = 6). An example of a chromatogram for a
distribution obtained with a BIMA chromium catalyst is shown
in Figure 2. Alternating distributions are still very rare and have
been observed only with chromium-based catalysts, but are not
23
24,25
13, and 16, as well as 4, 5, and 12,
have been previously
26
reported by us. The BIMA ligands 1, 14, and 15, as well as
2
7
28
29
17, 20, and 21, have been prepared by published
1
methods, and our H NMR values agree with those reported
21
exclusive to BIMA-type ligands.
previously. The extended ligands 18 and 19 were prepared
according to a published procedure by condensation of
phenylenediamine with 3,3′-iminodipropionitrile, and our
Here, we report a comprehensive study on these extremely
active and remarkable chromium BIMA oligomerization
catalysts. The effects of different ligands, the coordination
30,31
NMR data agreed with the data provided.
The new ligands
B
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Article
Figure 4. Molecular structures of the complexes fac-[Cr(15)Cl ] and mer-[Cr(21)Cl ].
3
3
−
Figure 5. Molecular structures of the cationic complex fac-[Cr(9)Cl (thf)](SbF ) (SbF anion has been omitted for clarity) and fac-[Cr(2)(CO)3].
2
6
6
3
and 7 were prepared by conventional condensation of
chromium source, [Cr(CO) ], was also investigated, which
6
phenylenediamine with N-alkyliminodiacetic acid diethyl ester
gave access to complex [Cr(2)(CO) ], which was characterized
3
(
see Experimental Section).
by NMR and X-ray diffraction (see Figure 5). Chromium(0)
carbonyl complexes with phosphine ligands have been oxidized
with silver salts to chromium(I) complexes and used as catalyst
The syntheses and characterization of complexes [Cr(2)-
2
0
27,32
Cl3] and [Cr(17)Cl3]
other chromium trichloride complexes [Cr(L)Cl ] were
have been described previously. All
33,34
precursors in ethylene oligomerization.
3
prepared by combining equimolar amounts of [CrCl (thf) ]
Bis(benzimidazole) ligands generally adopt a facial (fac)
3
3
and the relevant ligand in tetrahydrofuran. The resulting
paramagnetic Cr(III) complexes were insoluble in most
common organic solvents and were analyzed by mass
spectrometry, infrared spectroscopy, magnetic susceptibility
measurements, and elemental analyses. X-ray analysis was
carried out on crystals obtained from dimethylformamide
coordination mode around the chromium center, as seen
35
previously in [Cr(2)Cl3] and here in complexes [Cr(3)Cl3],
[Cr(15)Cl ], and [Cr(2)(CO) ], and in the cationic complexes
3
3
[Cr(5)Cl (dmf)]Cl and [Cr(9)Cl (thf)](SbF ). The chloro
2
2
6
ligand trans to one of the benzimidazole units is substituted in
these cationic fac complexes. Meridional (mer) coordination is
less common and is seen with smaller ligands, for example in
the bis(benzimidazole)amine complex [Cr(1)Cl (OH )]-
(
DMF) solutions for complexes [Cr(3)Cl ], [Cr(15)Cl ], and
3 3
[
Cr(21)Cl ]. The structure of complex [Cr(3)Cl ] is shown in
3
3
2
2
Figures S15 and S16, whereas the latter two complexes are
(SbF ) and the bis(pyrazole)butylamine complex [Cr(21)Cl ],
6
3
shown in Figure 4. In the case of ligand 5, the ionic complex
suggesting that the size of the ligands may affect the
coordination mode. The chloro ligand trans to the central
amine donor is substituted in the cationic mer complex. The
difference between the fac/mer coordination modes appears to
be rather subtle, as both can be obtained with seemingly similar
ligands. For example, the mer geometry is observed for the
[
Cr(5)Cl (dmf)]Cl crystallized from a DMF solution, rather
2
than the neutral complex [Cr(5)Cl ] (see Figure S21).
3
The poor solubility of the neutral complexes can be
improved by their conversion into ionic complexes, for example
with AgSbF . This enabled isolation and crystallization of the
6
cationic complexes [Cr(1)Cl (OH )](SbF ) and [Cr(9)-
bis(pyrazole) amine ligand 21 in [Cr(21)Cl ], whereas a fac
mode has been reported for the very similar N-methyl ligand.
2
2
6
3
36
Cl (thf)](SbF ), the molecular structures of which can be
2
6
found in Figure S20 and Figure 5, respectively. An alternative
Furthermore, the same ligand can show different coordination
C
DOI: 10.1021/acs.organomet.6b00671
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Article
a
Table 1. Ethylene Oligomerization Results with [Cr(L)Cl ]/MAO (L = 1−21)
3
solid PE
run
catalyst (μmol)
activity
liquid wt % (LAO)
Schulz−Flory α
Mn
Mw
PDI
1
2
3
4
5
6
7
8
9
[Cr(1)Cl ] (0.03)
15 000
102 000
96 000
97 000
39 000
20 000
27 000
11 000
11 000
5000
320
18 (99)
21 (99)
11 (97)
6 (92)
12 (97)
3 (98)
4 (99)
0
3
[Cr(2)Cl ] (0.03)
1920
1240
1,250
2550
7710
6310
8890
3930
2470
3530
4790
1.8
3.9
3
[Cr(3)Cl ] (0.03)
3
[Cr(4)Cl ] (0.03)
5620
4.5
3
[Cr(5)Cl ] (0.03)
9400
3.7
3
[Cr(6)Cl ] (0.03)
127 710
131 130
158 700
92 830
24 150
16.6
20.8
17.9
23.7
9.8
3
[Cr(7)Cl ] (0.03)
3
[Cr(8)Cl ] (0.03)
3
[Cr(9)Cl ] (0.03)
5 (99)
17 (98)
nd
3
10
11
12
13
14
15
16
17
18
19
20
21
[Cr(10)Cl ] (0.03)
3
[Cr(13)Cl ] (0.03)
3
[Cr(14)Cl ] (0.3)
2200
75
11
0.95
0.79
0.55
0.87
3
[Cr(15)Cl ] (0.4)
46
3
[Cr(16)Cl ] (2)
770
92
3
c
[Cr(17)Cl ] (1)
2500
44
79 (99)
20 (99)
9 (99)
0
710
3
[Cr(18)Cl ] (10)
3
[Cr(19)Cl ] (10)
21
0.62
3
b
[Cr(20)Cl ] (5)
16
3
c
c
[Cr(2)Cl (thf)](SbF ) (0.03)
16,000
16 000
88
21 (98)
9 (99)
96 (99)
1200
2800
2
6
[Cr(9)Cl (thf)](SbF ) (0.03)
2
6
d
[CrCl (thf) ] (25)
0.54
3
3
a
Conditions: 4 bar of ethylene pressure, 50 °C, MAO (5 mmol), toluene 200 mL, 1 h. Activity in g mmol h−1 bar . 1 barg (bar gauge) of
−1
−1
b
c
1
d
ethylene pressure. Determined by H NMR. 4 barg of ethylene pressure, 50 °C, MMAO-12 (500 equiv), toluene 100 mL, 1 h.
modes in different complexes; for example, ligand 2 coordinates
results are obtained for [Cr(9)Cl (thf)](SbF ) versus [Cr(9)-
2 6
in a fac mode in [Cr(2)Cl ], but a mer coordination is observed
Cl ] (runs 9 and 20). The catalyst precursor [CrCl (thf) ]
3 3 3
3
in [Cr(2)Cl(acac)](SbF ) when a bidentate acac ligand is
employed.
Ethylene Oligomerization Results. The chromium(III)
without any additional ligand gives a Schulz−Flory distribution
with very low activity (run 21). It appears that small alkyl
substituents such as methyl or higher linear alkyls at the central
nitrogen provide an optimal donor strength, both sterically and
electronically, for high catalytic activity.
6
2
0,35
complexes [Cr(L)Cl ], where L = 1−21, have been applied as
3
catalysts for the oligomerization of ethylene (Table 1). The
liquid fractions have been analyzed by FID-GC and the solid
fractions by GPC in selected cases. For those catalysts that give
an alternating olefin distribution, up to approximately 20 wt %
of the total product collected is in the liquid phase, consisting
of essentially pure C −C LAOs. The gas phase contains
Substitution at the benzimidazole nitrogens reduces the
activity dramatically. For example, complex [Cr(13)Cl ] with
3
−1
methylated benzimidazoles shows an activity of 320 g mmol
−1
−1
h
bar . The related complex [Cr(12)Cl ] with a central NH
3
amine donor was inactive under the conditions used. Changing
the central amine to other donors such as oxygen or sulfur in
complexes [Cr(14)Cl ] and [Cr(15)Cl ] or a noncoordinating
4
38
predominantly ethylene and butene, which were not quantified.
Solid polyethylene (80−100 wt %) constitutes the remainder of
3
3
the product spectrum, and the fraction with M values between
CH(CH ) unit in complex [Cr(16)Cl ] reduces the activity
n
3
3
1000 and 2000 is the tail end of the overall LAO distribution.
significantly compared with [Cr(2)Cl ]. Coordination of the
3
On the basis of several identical runs, the error in terms of
activity and product selectivity values was estimated to be
approximately 10% (see Table S1 and Figure S7).
central sulfur donor in [Cr(15)Cl ] is confirmed by X-ray
analysis (see Figure 4), but this coordination is weak judging
3
from the long Cr−S distance of 2.415(3) Å. Coordination of
−1
Extremely high activities of approximately 100 000 g mmol
the central oxygen donor in complex [Cr(14)Cl ] is unlikely,
3
h− bar can be obtained with chromium BIMA complexes, for
1
−1
considering the very long metal oxygen distances seen in other
n
37,38
example, ligands 2−4 with n-alkyl substituents (Me, Bu, or
complexes with this ligand.
A strongly coordinating central
n
Hex, runs 2−4). Catalytic activities are very sensitive to the
donor appears to be essential for high catalytic activity, and
3
nature of the substituent at the central amine. Complex
only sp -hybridized amine donors result in an alternating olefin
2
[
Cr(1)Cl ], with a hydrogen substituent at the central nitrogen,
distribution. An sp -hybridized nitrogen donor, such as pyridine
3
−1
−1
−1
is significantly less active at 15 000 g mmol
bulky substituents ( Pr, Bu, Cy, Ph, and Bz) at the central
h
bar . More
in complex [Cr(17)Cl ], shows a significantly lower activity
3
i
t
and, more importantly, gives a Schulz−Flory distribution of
39
nitrogen donor in complexes [Cr(6)Cl ]−[Cr(10)Cl ] lead to
LAOs with α = 0.87. A Schulz−Flory distribution is also
observed for the distributions obtained with complexes
[Cr(14)Cl ]−[Cr(16)Cl ], where α is 0.95, 0.79, and 0.55,
3
3
a reduced catalytic activity, less toluene-soluble olefins, and
higher molecular weight polyethylene. The 2,6-dimethylphenyl
3
3
complex [Cr(11)Cl ] was inactive under these conditions, and
respectively.
3
it is likely that the central amine is not coordinated in this case,
as seen for an analogous cobalt(II) complex. The cationic
Extending the bridge between the central donor and the
benzimidazole units with an extra methylene unit, as in
23
complex [Cr(2)Cl (thf)](SbF ) shows a lower activity
[Cr(18)Cl ], results in significantly lower activity compared
2
6
3
20
compared with [Cr(2)Cl ] (runs 2 and 19), whereas similar
with [Cr(1)Cl ]. The activity is further reduced for [Cr(19)-
3
3
D
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Article
Cl ], with N-methylated benzimidazole units, as seen for
The general solution to this recurrence relation takes the
3
n
n
[
Cr(12)Cl ] versus [Cr(1)Cl ]. Removal of the central donor
form mol(n) = c r + c r , whereby c and r1,2 are related to α
3
3
1 1 2 2 1,2
4
3
in [Cr(20)Cl ] or changing the benzimidazoles to pyrazole
and β. Experimental data obtained for an alternating
distribution can be fitted to this equation to determine c1,2
and r , and thereby α and β and 1 − α − β. Data fitting
3
units in [Cr(21)Cl ] results in very low polymerization activity.
3
Similar activities have been reported for related chromium
1,2
40,41
catalysts with bis(pyrazole)amine ligands,
whereas selective
analysis is performed using the C −C LAO fraction (n = 5−
10
34
2
ethylene trimerization was reported with facially coordinating
17), and the goodness of fit is expressed by the R values in the
last column in Table 2. The C −C oligomers are omitted
42
tridentate bis(pyrazolyl) ligands.
4
8
Distribution Analysis. Chain growth in ethylene oligome-
rization can occur via different mechanisms, depending on the
catalyst employed. For chromium complexes containing BIMA
ligands, a metallacyclic mechanism is implicated based on
because 1-butene (C ) is too volatile for quantitative analysis
4
and, as will be explained below, the experimental values for 1-
hexene (C ) and 1-octene (C ) can sometimes deviate from the
6
8
values calculated from the distribution analysis based on C −
1
0
20
deuterium labeling studies. If chain growth proceeds via the
coordination and insertion of single ethylene monomers, a
Schulz−Flory distribution is obtained, as seen for example for
the chromium complexes with ligands 14−17 and 19 (see
Table 1). Schulz−Flory distributions can be mathematically
described as first-order linear homogeneous recurrence relations
with a constant coefficient, and the solution to this relation
results in the typical Schulz−Flory equation: mol(n) = (1 −
C . The analysis for a selection of distributions is collected in
34
Table 2, and two graphical examples are shown in Figure 6. For
example, data fitting analysis of the oligomerization results from
C −C for complex [Cr(4)Cl ] (run 4, Table 1) provides the
1
0
34
3
n
n
equation mol%(n) = 15.75(0.91) + 15.62(−0.80) for this
particular distribution. The probabilities for single and double
coordination are determined as α = 0.11 and β = 0.72, and the
probability for termination is 1 − α − β = 0.17. Other
distributions can be found in the Supporting Information.
n−1
α)α R, where n is the number of ethylene units in the
n
n
2 2
oligomer and R is the total molar amount of oligomers
produced within the reaction time. The term α is the
probability of chain propagation, which is defined by the rate
of propagation divided by the sum of the rate of propagation
and termination. The term 1 − α represents therefore the
The relation mol%(n) = c1r1 + c r can be explained as an
exponential decay function c r with a positive decay parameter
n
1
1
r , combined with an alternating, exponential decay function
1
n
c r with a negative parameter r . The relative importance of
2
2
2
the various parameters c1,2 and r1,2 can be illustrated using the
two examples shown in Figure 6. The r1 and r2 factors
determine the steepness of the exponential decay functions.
The degree of alternation is indicated by the weighting factors
c and c , and the ratio c /c gives an indication of the extent of
probability of chain termination. The mol % fraction for each
n−1 43
oligomer equals mol%(n) = mol(n)/R = (1 − α)α
.
Alternating LAO distributions, as obtained here with
chromium complexes containing ligands 1−10, 13, and 18,
can be mathematically described as second-order linear
1
2
2
1
alternation. For example, for [Cr(1)Cl ] the relatively small
3
43
homogeneous recurrence relations with constant coefficients.
degree of alternation is indicated by the smaller value of c /c =
2
1
Each oligomer fraction is related to the previous fraction and
the one before by the parameters α and β, respectively, which
are the probabilities of chain growth via single ethylene
insertion (α) and double ethylene insertion (β) (see Scheme
0
[
.19, whereas alternation is much more pronounced for
Cr(4)Cl ], where c /c = 0.99.
3
2
1
In many cases, differences are observed between the
experimental amounts obtained for 1-hexene (C ) and 1-
6
1
). The term 1 − α − β represents the probability of
octene (C ) and those extrapolated from the C −C
8
10
34
termination.
distribution. These minor deviations are attributed to differ-
ences in the probabilities for metallacycle growth (α and β) and
termination (1 − α − β) for smaller metallacycles early on in
the oligomerization process. These differences become
negligible for larger metallacycles beyond metallacyclononane
Scheme 1. Ethylene Oligomerization Resulting in
Alternating Distributions
(
C ), and the propagation and termination probabilities
8
converge to constant values. The small deviations observed
here for C and C with chromium BIMA catalysts are probably
6
8
related to other chromium-based catalysts, where differences at
the early stages of metallacycle growth lead to oligomerizations
where 1-hexene or 1-octene become the major products of the
43
distribution. This is, for example, observed with chromium-
based selective oligomerization catalysts.
Effect of Pressure. Ethylene oligomerization with catalyst
[
Cr(17)Cl ], which contains a meridional ligand 17 with a
3
a
Table 2. Analysis of Alternating Distributions
b
mol%(n) = c1r1n + c r n
R2
c
catalyst
∑mmol(n)
α
β
1 − α − β
β/α
c2/c1
2 2
n
n
[
[
[
[
Cr(1)Cl3]
Cr(2)Cl3]
Cr(4)Cl3]
Cr(18)Cl3]
0.82
15.64
18.94
1.02
18.77(0.89) + 3.64(−0.82)
0.07
0.11
0.11
0.05
0.72
0.72
0.72
0.79
0.21
0.17
0.17
0.15
10.2
6.41
6.55
15.3
0.19
0.92
0.99
0.42
0.998
0.997
0.997
0.984
n
n
n
25.16(0.90) + 23.06(−0.79)
n
15.75(0.91) + 15.62(−0.80)
n
n
13.28(0.92) + 5.58(−0.87)
a
b
c
2
Conditions: see Table 1. Experimental total moles of LAOs from n = 3−17. R signifies the goodness of fit of the calculated values compared with
the experimental data.
E
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Figure 6. Experimental LAO distributions in mol%(n) versus n obtained with [Cr(1)Cl ] (left) and [Cr(4)Cl ] (right) together with calculated best-
3
3
fit distributions (n = number of ethylene units in oligomer).
central pyridine donor, results in a Schulz−Flory distribution of
difference between the orders for 1-octene and 1-hexene
formation is distinctly nonzero (see Figure S6). The higher
order for the formation of 1-octene with respect to 1-hexene
suggests a different mechanism involving both single and
double insertions of ethylene in the case of 1-octene formation,
whereas 1-hexene formation proceeds via single ethylene
insertions only.
From Table 3 it appears that the ratio between the
propagation probabilities for double versus single ethylene
insertion (β/α) is pressure dependent. The increase in β/α
shown in Figure 8 suggests that double insertion becomes more
likely than single insertion at higher pressure. While the trend
appears to be linear within this pressure regime, it is unclear at
this stage whether this trend continues at higher or lower
pressures.
3
9
LAOs. The total oligomer yield obtained at different gauge
pressures from 1 to 4 bar follows a first-order dependence on
ethylene concentration (see Figure S2). The order in ethylene
concentration for individual LAOs is conveniently determined
44
from the slope in a ln(rate) versus ln[ethylene] plot, whereby
ethylene pressure is a reliable proxy for concentration in
4
4,45
solution.
The rate can be approximated by the amount of
LAO produced within a given time. A first-order dependence
on ethylene pressure is observed for individual LAOs in this
case, and the difference for example between the orders for 1-
octene and 1-hexene formation is very close to zero (see Figure
S5). The LAO distribution is characterized by α = 0.87, which
is independent of ethylene pressure within the pressure range
of 1−4 bar. Because α is equal to the rate of propagation
divided by the rate of propagation plus the rate of termination,
this suggests that both the rate of propagation and the rate of
termination are affected in a similar manner by ethylene
concentration and that therefore chain transfer to monomer
must be the main termination pathway (rather than β-H
elimination).
Effect of Different Cocatalysts. Different cocatalysts have
been evaluated in combination with BIMA catalyst [Cr(2)Cl3].
All cocatalysts listed in Table 4 provide active catalyst systems,
and the activities can vary considerably. MAO provides the best
activity, but yields the lowest amount of oligomers in the liquid
fraction. The combination of an alkylating reagent (AlMe3)
with several abstracting reagents (B(C F ) , [Ph C][B(C F ) ],
6
5 3
3
6 5 4
The effect of pressure on alternating distributions has been
or [PhNMe H][B(C F ) ]) gives somewhat lower activities,
2
6 5 4
investigated for catalysts [Cr(1)Cl ] and [Cr(4)Cl ] at
3
3
but a larger oligomer fraction. Surprisingly, AlMe without an
3
ethylene gauge pressures between 1 and 4 bar. The total
yield of oligomers increases with a first-order dependence on
ethylene pressure in both cases (see Figures S3 and S4). Figure
abstractor also shows a reasonable activity with a comparable
oligomer distribution. Experimental and calculated distributions
can be found in Figures S8−12. While the differences between
the distributions appear to be small, given the 10% error margin
7
shows that the degree of alternation becomes more
pronounced at higher pressure such that individual oligomers
appear to have different orders in ethylene. Indeed, the
(
see Table S1), we do believe they are significant. It appears
that the nature of the cocatalyst can affect the oligomer
distribution to some degree and that a trialkyl aluminum in
general is an important aspect of the cocatalyst, something that
will be discussed in more detail in the last section.
Side Products. The selectivity for the formation of LAOs
obtained with chromium BIMA catalysts is generally very high,
typically in excess of 95% (see Table 1). In addition to the main
LAO distribution, a second minor distribution can sometimes
be observed, depending on the reaction conditions. This minor
distribution follows the opposite alternating pattern compared
to the main distribution; that is, oligomers derived from an odd
number of ethylene units are more abundant than those from
an even number, as can be seen in Figure 2. Because 1-butene is
the major product in these oligomerization reactions, the
second minor distribution is generated from incorporation of 1-
butene into the oligomerization reaction, as shown in eqs 1 and
2
. This was confirmed by oligomerization experiments of
Figure 7. Pressure dependence of the LAO distribution with
ethylene with additional 1-butene, using catalyst [Cr(2)Cl3]
[
Cr(4)Cl ]. Conditions: see Table 3.
(Table 5). In the absence of 1-butene, the wt % ratio between
3
F
DOI: 10.1021/acs.organomet.6b00671
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Table 3. Pressure Dependence of the LAO Distribution with [Cr(4)Cl ]/MAO
3
b
c
R2
d
P
olig/mmol
mol%(n)
α
β
1 − α − β
β/α
c2/c1
n
n
1
2
3
4
barg
barg
barg
barg
1.24
1.88
2.35
4.07
13.23(0.92) + 9.93(−0.79)
0.13
0.12
0.11
0.10
0.73
0.74
0.75
0.74
0.14
0.15
0.16
0.16
5.77
6.22
6.93
7.06
0.75
0.87
1.03
1.00
0.797
0.993
0.996
0.996
n
n
n
n
12.99(0.92) + 11.29(−0.81)
n
13.79(0.92) + 14.18(−0.81)
n
14.64(0.91) + 14.70(−0.81)
a
b
Conditions: [Cr(4)Cl ] 30 nmol, 50 °C, 1 h, 200 mL of toluene, MAO (5 mmol). 1 barg (bar gauge) = 2 bara (bar absolute) = 1 bar nitrogen + 1
bar ethylene. Oligomers from n = 3−19. R signifies the goodness of fit of the calculated values compared with the experimental data.
3
c
d
2
by ethylene before metallacycle growth can proceed. No
oligomers due to the oligomerization of 1-butene alone are
observed.
The distribution of the major 1-alkene fraction differs from
the 2-ethyl-1-alkene fraction in that, aside from the opposite
alternating behavior, the probability for termination (1 − α −
β) is significantly higher for the latter, cf., 0.36 versus 0.22 (0.28
versus 0.22 with additional 1-butene). As a result, the amount
of 2-ethyl-1-alkene isomer produced will decrease more rapidly
than the amount of 1-alkene, and therefore the selectivity to 1-
alkenes will increase across the product distribution. Termi-
nation via β-H transfer is expected to be faster for weaker
tertiary C−H bonds in the 2-ethyl metallacyclic complex in eq
2
. The addition of 1-butene affects the distribution in the 1-
Figure 8. Dependence of β/α on ethylene gauge pressure. Trendline:
alkene and 2-ethyl-1-alkene fractions, as seen from the β/α
ratios, which decrease from 5.89 to 3.99 and from 9.30 to 4.59,
respectively. Different distributions for both fractions imply that
2
linear (R = 0.944). Conditions: catalyst [Cr(4)Cl ] (30 nmol), 50 °C,
3
1
h, 200 mL of toluene, MAO (5 mmol).
1
-butene incorporation into the metallacycle affects the
distribution, and 1-butene must therefore be incorporated at
the beginning of metallacycle formation and not at the end. A
stronger binding of 1-butene, but lower reactivity compared to
ethylene provides an explanation for the observed behavior.
These observations made here for 1-butene may also apply to
other 1-alkenes and imply a general inhibition of the
oligomerization reaction by the higher alkene products.
Mechanistic Considerations. Single and Double Coor-
dination Mechanism. Chain growth in chromium-based BIMA
3
9
catalysts proceeds via a metallacyclic mechanism. A single
coordination mechanism, i.e., coordination and insertion of a
single ethylene unit at a time, results in a Schulz−Flory
distribution, which is observed for example with chromium
catalysts of ligands 14−17 that do not have a central amine
donor. An alternating distribution is obtained via a double-
insertion mechanism, whereby two ethylene monomers
the major and minor fraction is approximately 17:1, which
changes to 5:1 upon addition of an excess of 1-butene. The
identity of the minor products was confirmed as a distribution
of 2-ethyl-1-alkenes, based on NMR and GC analysis (see
Figure S13) and comparison with an authentic sample of the C6
product 2-ethyl-1-butene (m = 1 in eq 2). Co-oligomerization
of ethylene with higher 1-alkenes is known to occur with
chromium-type oligomerization catalysts that operate via a
43
coordinate to the chromium center and insert sequentially.
19,46−49
metallacyclic mechanism.
The activity of the catalyst system [Cr(2)Cl ]/MAO
In this case, the termination probability after the first insertion
is zero, and the metallacycle effectively grows by two ethylene
units at a time. The single- and double-insertion mechanisms
can operate in parallel, and the extent of each is determined by
the probabilities α and β, which are affected by the catalyst,
ethylene pressure, temperature, and the coordinating properties
3
−1
−1
decreases significantly from 55 900 to 8400 g mmol
h
−1
bar upon addition of a large excess of 1-butene. Additional 1-
butene is likely to slow down the rate of oligomerization due to
coordination to the metal center, which will require substitution
Table 4. Effect of Different Cocatalysts on the Oligomer Distribution with [Cr(2)Cl3]
b
R2
cocatalyst
activ
liq wt %
mol%(n)
α
β
1 − α − β
β/α
n
n
n
n
n
n
MAO
B(C F ) /AlMe
3
18 500
8000
8
32
35
46
32
17.60(0.89) + 19.03(−0.77)
0.12
0.13
0.15
0.09
0.16
0.69
0.68
0.66
0.69
0.64
0.20
0.20
0.19
0.22
0.20
5.92
5.39
4.49
8.00
3.91
0.994
0.998
0.999
0.998
0.996
n
17.81(0.89) + 10.61(−0.76)
6
5
3
F
n
[
[
Ph C][BAr ]/AlMe
12 000
13 200
4800
18.02(0.89) + 16.30(−0.74)
3
3
F
n
PhNMe H][BAr ]/AlMe
21.10(0.87) + 15.39(−0.79)
2
3
n
AlMe3
18.07(0.89) + 17.11(−0.72)
a
Conditions: catalyst [Cr(2)Cl ] 0.5 μmol, 4 barg, 1 h, 50 °C, 200 mL of toluene. Activity in g mmol h−1 bar . Cocatalysts: MAO: 3 mmol
b
−1
−1
3
F
F
F
−
−
(
6000 equiv); B(C F ) , [Ph C][BAr ], and [PhNMe H][BAr ]: 0.5 mmol (1 equiv); and AlMe : 0.5 mmol (1000 equiv) [BAr ] = [B(C F ) ] .
6 5 3 3 2 3 6 5 4
G
DOI: 10.1021/acs.organomet.6b00671
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Organometallics
Article
a
Table 5. Effect of Addition of 1-Butene on the 1-Alkene and 2-Ethyl-1-alkene Distributions with [Cr(2)Cl ]/MAO
3
c
d
e
R2
activ
wt%
mol%(n)
n
α
β
1 − α − β
β/α
b
n
n
n
n
1
2
1
2
-alkenes
55 900
8400
17
1
21.04(0.88) + 20.58(−0.76)
36.16(0.79) + 26.39(−0.73)
22.45(0.87) + 24.85(−0.71)
23.97(0.83) + 27.14(−0.71)
0.11
0.06
0.16
0.13
0.67
0.58
0.62
0.22
0.36
0.22
0.28
5.89
9.30
3.99
4.59
0.996
0.999
0.996
0.999
a
b
n
-ethyl-1-alkenes
b
n
-alkenes
29
6
n
-ethyl-1-alkenes
0.59
b
a
Conditions: catalyst [Cr(2)Cl ] (30 nmol), MAO (7 mmol), 4 bar, 1 h, 50 °C, 200 mL of toluene. Conditions: [Cr(2)Cl ] 150 nmol, MAO (7
mmol), 4 bar, 1 h, 50 °C, 200 mL of toluene, 1-butene (3.5 g) added. Activity in g mmol
polymer. Weight percentage of olefins in the liquid fraction, remainder is solid polyethylene. 1-Alkenes distribution: n = 1 is ethylene, n = 2 is 1-
butene etc.; 2-ethyl-1-alkenes distribution: n = 1 is 1-butene, n = 2 is 2-ethyl-1-butene, etc.
3
3
c
−1 −1
e
−1
h
bar , includes 1-alkenes, 2-ethyl-1-alkenes, and
d
Figure 9. Metallacycle growth via (a) single and (b) double ethylene coordination and insertion.
of the solvent and the anion (cocatalyst). We have previously
established a double-insertion route as the main mechanism in
ethylene tetramerization with Cr-PNP catalysts.
with benzimidazole pyridine 22 resulted in a Schulz−Flory
distribution of LAOs, similar to the oligomerization with the
bis(benzimidazole) pyridine ligand 17 (see Table 1, run 15).
The distribution obtained with ligand 23 showed alternating
behavior (Table 6). Tridentate BIMA ligands clearly give a
much better performance than the bidentate ligands 22 and 23.
Notwithstanding, partial dissociation of one donor during
metallacycle growth to provide the necessary coordination sites
for two ethylene monomers cannot be dismissed from these
results.
22
The growth of the metallacycle by single ethylene insertion
requires a facial arrangement of the metallacyle and the
ethylene monomer prior to insertion (Figure 9a). The insertion
of two ethylene monomers requires double ethylene coordina-
tion. This arrangement can lead to the sequential insertion of
two ethylene units without termination by β-H transfer after the
first insertion. For each insertion step, the metallacycle and the
ethylene monomer must be in facial orientation, as illustrated in
Figure 9b.
The Nature of the Active Species. It is very likely that
during the activation of the BIMA precatalyst with the
Structural studies (vide infra) have shown that BIMA ligands
can coordinate in a tridentate fac or mer fashion (see Figure 4),
and a strong binding of the central donor was found to be
essential for high catalytic activity. Coordination of two
ethylene units to a chromium BIMA metallacyclic complex
would generate a seven-coordinate complex, unless one of the
donors dissociates. To explore this further, we investigated two
related bidentate benzimidazole pyridine and benzimidazole
amine ligands, 22 and 23 (see eq 3). Combination of these
cocatalyst, which contains AlMe , the benzimidazole NH
3
functionalities become deprotonated to give anionic benzimi-
dazolide ligands. This proposal is supported by a separate
reaction carried out between BIMA ligand 2 and AlMe3
according to eq 4. The reaction of 2 with two equivalents of
AlMe3 in toluene resulted in deprotonation of both
benzimidazole NH groups, followed by trimerization to give a
hexanuclear aluminum complex, [(AlMe ) (2′)] , which was
2
2
3
characterized by NMR spectroscopy and X-ray diffraction (see
Figure S23). Related cyclic aluminum benzimidazole complexes
52,53
have been reported previously.
These observations suggest that the active species is
generated upon reaction of the cocatalyst (AlMe ) with the
3
chromium trichloride precatalyst via deprotonation of the
BIMA ligand. The requirement of AlMe in the cocatalyst seen
3
earlier is in agreement with this proposal. A polymerization
reaction carried out using a combination of [(AlMe ) (2′)] ,
2
2
3
[
CrCl (thf) ], and MAO resulted in a moderately active
3 3
polymerization system, giving an alternating distribution of
ligands with [CrCl (thf) ] is assumed to generate complexes of
LAOs (see Table 6).
3
3
the type [Cr(L)Cl (thf)], as reported for similar bidentate
The possibility of partial ligand dissociation was also
investigated by DFT calculations. The relative free energy
profile for a series of potential intermediates formed upon
3
49−51
nitrogen donor ligands.
Very low activities were observed
for both catalysts (see Table 6). Similar reduction in catalytic
activity was observed by McGuinness with tridentate versus
reaction of BIMA complex [Cr(2)Cl ] (I) with one or two
3
49
bidentate pyridine carbene ligands. The chromium complex
equivalents of AlMe is shown in Figure 10. Deprotonation by
3
H
DOI: 10.1021/acs.organomet.6b00671
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Table 6. Alkene Distributions with [CrCl (thf) ]/22, [CrCl (thf) ]/23, and [CrCl (thf) ]/[(AlMe ) (2′)]
3
3
3
3
3
3
2 2
3
b
c
d
R2
activ
10
wt %
mol%(n)
α
β
1 − α − β
β/α
[
[
[
Cr]/22
34
17
20
SF
n
0.62
0.16
0.09
0.999
0.964
0.996
n
n
Cr]/23
13
12.89(0.79) + 14.07(−0.63)
0.50
0.71
0.34
0.21
3.12
8.32
e
3
n
Cr]/[(AlMe ) (2′)]
2066
27.56(0.89) + 23.08(−0.80)
2
2
a
b
Conditions: catalyst [Cr] = [CrCl (thf) ]: 25 μmol, ligand 1 equiv, MMAO-12 (12.5 mmol), 4 bar, 1 h, 50 °C, 100 mL of toluene. Activity in g
3
3
−1
−1
−1
c
d
e
mmol
h
bar , includes polymer. Weight percentage of α-olefins in the liquid phase. SF = Schulz−Flory distribution. [CrCl (thf) ]/
3
3
[
(AlMe ) (2′)] : 100 nmol, MMAO-12 (24 mmol), 4 bar, 1 h, 50 °C, 200 mL of toluene.
2
2
3
Figure 10. Relative Gibbs free energy profile of potential intermediates formed upon reaction of complex I with AlMe . All energies are balanced for
3
AlMe and, in the case of ligand deprotonation, CH formation. See Supporting Information for details.
3
4
two AlMe units (complexes VI−VIII) clearly shows a dramatic
enediamine (7.56 g, 70.6 mmol) and N,N-diethyl acetate-N-butyl-
amine (8.66 g, 35.3 mmol). o-Phenylenediamine and the iminodiacetic
acid ethyl ester were stirred at 190 °C for 4 h. The water byproduct
was distilled from the reaction mixture, which was then allowed to cool
to room temperature. The product was triturated with water (120
mL), filtered, washed with water (4 × 20 mL), recrystallized from hot
3
lowering of the relative energies, which suggests that a
modifcation of the coordination environment around chromi-
um upon addition of AlMe is very likely. Further studies on the
3
nature of the active species are under way.
In conclusion, chromium-based BIMA complexes are a class
of ethylene oligomerization catalysts that, depending on the
ligand, can give extremely high catalytic activities and either a
Schulz−Flory or an alternating distribution of LAOs in the
liquid fraction, together with a major solid polyethylene
fraction. Schulz−Flory distributions are described by first-
order linear homogeneous recurrence relations with a constant
coefficient α, whereas alternating distributions are mathemati-
cally described by second-order linear homogeneous recurrence
relations with constant coefficients α and β, which represent the
probabilities for propagation via the insertion of one or two
ethylene monomers, respectively. The β/α ratio increases with
ethylene pressure within the range from 1 to 4 bar. A range of
different cocatalysts can be used, which affect the catalytic
activity and the LAO distribution. The presence of AlMe3
appears to be essential, and it is believed to react with the
facially coordinating BIMA ligand at the chromium center.
Incorporation of the most abundant LAO, 1-butene, can occur
during the oligomerization process, giving rise to a minor
alternating distribution of 2-ethyl-1-alkenes with opposite
alternating behavior. Further studies to understand this
intriguing class of oligomerization catalysts and our search for
new catalysts that will generate as yet unseen oligomer
distributions continue.
methanol/water (1:30), and finally dried at 60 °C under vacuum for 2
1
days. Yield: 5 g (43%). H NMR (400 MHz, DMSO-d , rt): δ 0.74 (t,
6
3
3
3
H, J 7.2, CH CH ), 1.18 (sept, 2H, J = 7.1, CH CH CH ),
HH 2 3 HH 2 2 3
3
1.45 (quint, 2H, JHH 7.4, CH CH CH ), 2.5 (overlapping with
2
2
2
solvent signal, 2H, CH
), 3.97 (s, 4H, NCH
C ), 7.13−7.17 (m, 4H,
2 q
13 1
2
J
HH 3.1, ArH), 7.53−7.56 (m, 4H, JHH 3.1, ArH). C{ H} NMR
(
(
(
3
100.6 MHz, DMSO-d , rt): δ 13.8 (CH ), 19.8 (CH CH ), 28.5
6 3 2 3
CH CH ), 52.1 (NCH C ), 53.4 (NCH CH ), 114.8 (ArC), 121.5
2
2
2
q
2
2
ArC), 138.6 (ArCipso), 152.68 (ArC ). Anal. Calcd for C H N (FW
33.4): C 72.04, H 6.95, N 21.00. Found: C 71.87, H 7.07, N 20.83%.
q
20 23
5
+
CI-MS (m/z): 334 [M + H] , 362.
N-Bis((1H-benzimidazol-2-yl)methyl)-N-tert-butylamine (7).
Compound 7 was synthesized by an analogous procedure to that
described for 3 using o-phenylenediamine (11.5 g, 106 mmol) and
N,N-diethyl acetate-N-tert-butylamine (13 g, 53 mmol). Yield: 11.5 g
1
(65%). H NMR (400 MHz, DMSO-d
, rt): δ 1.09 (s, CH(CH
)
2
),
6
3
4
.00 (s, (NCH ), 4.10 (s, NCH ), 7.14 (broad m, ArH), 7.53 (broad
2
2
13
1
m, ArH). C{ H} NMR (100.6 MHz, DMSO-d , rt): δ 26.1 (CH ),
6
3
4
6.1 (NCH C ), 54.4 (NC(CH ) ), 115.2 (ArC), 119.5 (ArC), 134.7
2 q 3 3
−
1
(
ArCipso), 152.8 (ArC ). IR (KBr, cm ): 3377 (NH, w), 3054 (Ar−H,
q
s), 1683−1538 (ArCC, CN, m), 1456, 1436 (N−H, s), 1271
(CN, s), 749 (CH, s). Anal. Calcd for C H N (FW 333.4): C 72.04,
20
23
5
H 6.95, N 21.00. Found: C 72.28, H 6.83, N 20.91. CI-MS (m/z), 334
+
[
M + H] .
Synthesis of Chromium Complexes. All Cr(III) complexes are
paramagnetic, and no NMR spectra could be recorded.
N,N-Bis((1H-benzimidazol-2-yl)methyl)amine Chromium(III)
Chloride [Cr(1)Cl ]. Equimolar quantities of 1 (1 g, 3.61 mmol) and
3
EXPERIMENTAL SECTION
■
[CrCl (THF) ] (1.35 g, 3.61 mmol) were stirred in 20 mL of THF for
3 3
Synthesis of Ligands. N-Bis((1H-benzimidazol-2-yl)methyl)-N-
n-butylamine (3). Compound 3 was synthesized using o-phenyl-
12 h. The product was isolated by filtration, washed twice with THF
(2 × 20 mL) and once with diethyl ether (20 mL), and dried under
I
DOI: 10.1021/acs.organomet.6b00671
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
vacuum. Yield: 1.49 g, 95%. Anal. Calcd for C H Cl CrN (FW
sized by an analogous procedure to that described for [Cr(1)Cl3]
using 8 (1 g, 2.79 mmol) and [CrCl (THF) ] (1.04 g, 2.79 mmol).
16
15
3
5
4
35.7): C 44.11, H 3.47, N 16.07. Found: C 44.25, H 3.74, N 15.84. IR
3
3
−1
(
(
(
(
KBr, cm ): 3202 (NH, s), 3120, 3110 (Ar−H, s), 1622−1544
Yield: 1.07 g (74%). Anal. Calcd for C H Cl CrN (FW 517.8): C
22 25 3 5
ArCC, CN, m), 1497, 1477, 1456 (N−H, s), 1278 (CN, s), 743
51.03, H 4.87, N 13.52. Found: C 50.93, H 4.72, N 13.64. IR (KBr,
CH, s). UV−vis (DMF), λ /nm (ε /dm3 mol cm ): 462
138), 635 (93), 721 (shoulder). FAB(+) MS (m/z): 399 ([M −
−1
−1
cm ): 3252 (NH, s), 3060 (Ar−H, s), 1622−1538 (ArCC, CN,
−1
max
max
m), 1496, 1477, 1454 (NH, s, m), 1276 (CN, m), 749 (CH, s). UV−
+
+
3
−1
−1
Cl] ), 363 ([M − 2Cl] ). μ = 3.77 μ .
vis (DMF), λ /nm (ε /dm mol cm ): 459 (160), 704 (65),
eff
B
max max
+
+
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-methylamine
731 (shoulder). FAB(+) MS (m/z): 481 [M − Cl] , 446 [M − 2Cl] ,
+
Chromium(III) Chloride [Cr(2)Cl ]. Complex [Cr(2)Cl ] was synthe-
360 [M − CrCl ] . μ = 3.87 μ .
3
3
3
eff
B
sized by an analogous procedure to that described for [Cr(1)Cl3]
using 2 (2 g, 6.87 mmol) and [CrCl (THF) ] (2.57 g, 6.87 mmol).
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-(phenyl)amine
Chromium(III) Chloride [Cr(9)Cl ]. Complex [Cr(9)Cl ] was synthe-
3
3
3
3
Yield: 2.87 g (93%). Anal. Calcd for C H Cl CrN (FW 449.7): C
sized by an analogous procedure to that described for [Cr(1)Cl3]
using N,N-bis(1H-benzimidazol-2-ylmethyl)-N-phenylamine (9) (0.20
g, 0.56 mmol) and [CrCl (THF) ] (0.21 g, 0.56 mmol). Yield: 0.23 g
17
17
3
5
4
5.40, H 3.81, N 15.57. Found: C 45.35, H 3.76, N 15.66. IR (KBr,
−
1
cm ): 3221 (NH, s),1622−1544 (ArCC, CN, m), 1497,
3
3
1
477,1455 (N−H, s), 1274 (CN, s), 753 (CH, s). UV−vis (DMF),
(87%). Anal. Calcd for C H Cl CrN (FW 511.8): C 51.63, H 3.74,
22 19 3 5
/nm (ε /dm3 mol cm )): 464 (156), 659 (75), 723
−1
−1
−1
λ
N 13.68. Found: C 51.49, H 3.95, N 13.58. IR (KBr, cm ): 3503
max
max
+
+
(
μ
shoulder). FAB(+) MS (m/z): 413 [M − Cl] , 291 [M − CrCl ] .
(NH, s), 3224, 3065, 1622−1545 (ArCC, CN, m), 1497, 1478,
3
= 3.87 μ .
1454 (NH, s), 1275 (CN, s), 748 (CH, s). UV−vis (DMF), λ /nm:
eff
B
max
+
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-butylamine
484, 678, 705 (shoulder). FAB(+) MS (m/z): 475 [M − Cl] , 440 [M
+
+
Chromium(III) Chloride [Cr(3)Cl ]. Complex [Cr(3)Cl ] was synthe-
− 2Cl] , 354 [M − CrCl ] . μ = 3.95 μ .
3
3
3
eff
B
sized by a procedure analogous to that described for [Cr(1)Cl ] using
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-(benzyl)amine
Chromium(III) Chloride [Cr(10)Cl ]. Complex [Cr(10)Cl ] was
synthesized by an analogous procedure to that described for
[Cr(1)Cl ] using 10 (0.63 g, 1.73 mmol) and [CrCl (THF) ] (0.65
g, 1.73 mmol). Yield: 0.79 g (88%). Anal. Calcd for C23 CrN
5
3
3
1
4
(1 g, 3.03 mmol) and [CrCl (THF) ] (1.13 g, 3.61 mmol). Yield:
3
3
3
3
.49 g, 84%. Anal. Calcd for C H Cl CrN (FW 491.8): C 48.85, H
2
0
23
3
5
−1
.71, N 14.24. Found: C 48.83, H 4.80, N 14.42. IR (KBr, cm ): 3440
3
3
3
(
1
NH, m), 3229, 3077 (Ar−H, s), 1623−1549 (ArCC, CN, m),
H21Cl
3
499, 1477, 1454, 1433 (N−H, m, s), 1276 (CN, m), 762, 748 (CH,
(FW 525.8): C 52.54, H 4.03, N 13.32. Found: C 52.43, H 4.03, N
+
+
−1
s). FAB(+) MS (m/z): 455 [M − Cl] , 420 [M − 2Cl] . μ = 3.89 μ .
13.23. IR (KBr, cm ): 3255 (NH, s), 1617−1550 (ArCC, CN,
eff
B
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-hexylamine
m), 1496, 1477, 1454 (NH, s, m), 1276 (CN, s), 749 (CH, s). UV−vis
3
−1
−1
Chromium(III) Chloride [Cr(4)Cl ]. Complex [Cr(4)Cl ] was synthe-
(DMF, 298 K, λ /nm (ε /dm mol cm )): 462 (162), 665 (75),
3
3
max max
+
+
sized by an analogous procedure to that described for [Cr(1)Cl3]
using 4 (1 g, 2.8 mmol) and [CrCl (THF) ] (1.05 g, 2.8 mmol). Yield:
726 (shoulder). FAB(+) MS: (m/z) 489 [M − Cl] , 454 [M − 2Cl] .
= 4.00 μ .
3
3
μ
μeff
B
1
5
.35 g, 93%. Anal. Calcd for C H Cl CrN (FW 519.8): C 50.83, H
.24, N 13.47. Found: C 51.05, H 5.30, N 13.38. IR (KBr, cm ): 3502
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-(2,6-dimethylphenyl)-
amine Chromium(III) Chloride [Cr(11)Cl ]. Complex [Cr(11)Cl ] was
synthesized by an analogous procedure to that described for
[Cr(1)Cl ] using N,N-bis(1H-benzimidazol-2-ylmethyl)-N-(2,6-
dimethylphenyl)amine (11) (0.20 g, 0.53 mmol) and [CrCl (THF)
22
27
3
5
−1
3
3
(
1
NH, m), 3228, 3073 (Ar−H, s), 1621−1542 (ArCC, CN, m),
498, 1477, 1454, 1431 (N−H, s), 1273 (CN, m), 752 (CH, s).
3
+
+
FAB(+) MS (m/z): 483 [M − Cl] , 448 [M − 2Cl] . μ = 3.83 μ .
3
]
3
eff
B
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-(3-phenylpropyl)amine
(0.19 g, 0.53 mmol). Yield: 0.23 g (81%). Anal. Calcd for
C H Cl CrN (FW 555.9): C 53.40, H 4.29, N 12.97. Found: C
Chromium(III) Chloride [Cr(5)Cl ]. Complex [Cr(5)Cl ] was synthe-
3
3
24 23
3
5
−
1
sized by an analogous procedure to that described for [Cr(1)Cl3]
53.51, H 4.39, N 12.82. IR (KBr, cm ): 3252 (NH, m), 3189 (Ar−
using 5 (1 g, 2.53 mmol) and [CrCl (THF) ] (0.95 g, 2.53 mmol).
H), 1622, 1591, 1520 (ArCC, CN, m), 1466, 1451 (NH, s), 1273
3
3
3
−1
Yield: 1.00 g (71%). Attempts to crystallize the complex from a
solution in DMF resulted in crystals that were found to be the cationic
complex [Cr(5)Cl (dmf)]Cl. Anal. Calcd for C H Cl CrN (FW
(CN, s), 742 (CH, s). UV−vis (DMF), λ /nm (ε /dm mol
max
max
−1
cm ): 482 (70), 678(58), 705 (shoulder). FAB(+) MS (m/z): 503
+
+
2
25 25
3
5
[M − Cl] , 468 [M − 2Cl] , 382 [M − CrCl ]. μ = 3.89 μB.
3
eff
5
53.9): C 54.21, H 4.55, N 12.64. Found: C 54.32, H 4.79, N 12.50. IR
N,N-Bis((1-Me-benzimidazol-2-yl)methyl)amine Chromium(III)
Chloride [Cr(12)Cl ]. A slurry of 0.50 g (1.64 mmol) of N,N-bis(2-
(1Me-benzimidazol-2-yl)methyl)amine (12) and 0.61 g (1.64 mmol)
of [CrCl (THF) ] in 20 mL of THF was stirred at reflux for 4 h. The
−1
(
1
KBr, cm ): 3231 (NH, s), 1622−1543 (ArCC, CN, m), 1498,
3
477, 1454 (N−H, s), 1274 (CN, m), 752 (CH, s). FAB(+) MS (m/
+
+
z): 517 [M − Cl] , 482 [M − 2Cl] . μ = 3.87 μ .
3
3
eff
B
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-(isopropyl)amine
obtained green solid was filtered, washed with THF (3 × 10 mL), and
dried under reduced pressure. Yield: 0.39 g (51.0%). Anal. Calcd for
C H N CrCl : C 46.62, H 4.13, N 15.10. Found: C 46.54, H 4.15, N
Chromium(III) Chloride [Cr(6)Cl ]. Complex [Cr(6)Cl ] was synthe-
3
3
sized by an analogous procedure to that described for [Cr(1)Cl3]
18
19
5
3
−1
using 6 (0.432 g, 1.35 mmol) and [CrCl (THF) ] (0.51 g, 1.35
15.01. FT-IR, cm : 3246 (s), 2857 (m), 1621 (m), 1541 (w), 1492
(m), 1474 (vs), 1465 (v.s), 1414 (m), 1382 (m), 1331 (m), 1272 (s),
1210 (w), 1147 (w), 1055 (s), 1003 (s), 981 (s), 944 (w), 919 (m),
977 (s), 752 (v.s), 702 (s), 654 (m), 558 (w), 518 (w), 510 (w), 431
(w), 418 (w). μeff = 3.91 μB.
3
3
mmol). Yield: 1.20 g (84%). Anal. Calcd for C H Cl CrN (FW
19
21
3
5
4
77.8): C 47.77, H 4.43, N 14.66. Found: C 47.87, H 4.35, N 14.46. IR
−1
(
KBr, cm ): 3440, 3226 (NH, s), 3067 (Ar−H), 1622−1545 (ArC
C, CN, m), 1496, 1478, 1455 (N−H, s, m), 1275 (CN, m), 752
CH, s). UV−vis (DMF), λ /nm: 459, 704, 731 (shoulder). FAB(+)
(
N,N-bIs((1-Me-benzimidazol-2-yl)methyl)-N-(methyl)amine
max
+
+
+
MS (m/z): 441 [M − Cl] , 406 [M − 2Cl] , 368 [M − 3Cl] , 320 [M
−
Chromium(III) Chloride [Cr(13)Cl ]. A slurry of 0.50 g (1.56 mmol) of
3
+
CrCl ] . μ = 3.46 μ .
N,N-bis(2-(1-Me-benzimidazol-2-yl)methyl)-N-(methyl)amine (13)
and 0.59 g (1.56 mmol) of [CrCl (THF) ] in 20 mL of THF was
3
eff
B
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-(tert-butyl)amine
3
3
Chromium(III) Chloride [Cr(7)Cl ]. Complex [Cr(7)Cl ] was synthe-
stirred at reflux for 4 h. The obtained green solid was filtered, washed
with THF (3 × 10 mL), and dried under reduced pressure. Yield: 0.64
g (85.8%). Anal. Calcd for C H N CrCl : C 47.77, H 4.43, N 14.66.
3
3
sized by an analogous procedure to that described for [Cr(1)Cl3]
using 7 (1 g, 3.00 mmol) and [CrCl (THF) ] (1.01 g, 3.00 mmol).
3
3
19 21
5
3
−1
Yield: 1.15 g (78%). Anal. Calcd for C H Cl CrN (FW 491.8): C
Found: C 47.59, H 4.40, N 14.64. FT-IR, cm : 3246 (v.s), 2857 (s),
1621 (m), 1595 (m), 1541 (w), 1492 (m), 1475 (v.s), 1462 (v.s), 1382
(m), 1382 (s), 1332 (m), 1272 (s), 1210 (w), 1146 (w), 1094 (w),
1055 (m), 1003 (s), 982 (s), 944 (w), 919 (m), 878 (s), 752 (v.s), 702
(s), 654 (m), 558 (w), 518 (w), 510 (w), 431 (w), 417 (w). μeff = 3.74
20
23
3
5
4
8.85, H 4.71, N 14.24. Found: C 48.97, H 4.90, N 14.37. IR (KBr,
−1
cm ): 3463 (NH, m), 3192, 3066 (Ar−H, s), 1653−1559 (ArCC,
CN, m), 1497, 1477, 1455 (N−H, m, s), 1275 (CN, m), 747 (CH,
+
+
s). FAB(+) MS (m/z): 455 [M − Cl] , 420 [M − 2Cl] , 334 [M −
+
CrCl ] . μ = 3.93 μ .
μ .
B
3
eff
B
N,N-Bis((1H-benzimidazol-2-yl)methyl)-N-(cyclohexyl)amine
O-Bis((1H-benzimidazol-2-ylmethyl) Ether Chromium(III) Chlor-
Chromium(III) Chloride [Cr(8)Cl ]. Complex [Cr(8)Cl ] was synthe-
ide [Cr(14)Cl ]. Complex [Cr(14)Cl ] was synthesized by a procedure
3
3
3
3
J
DOI: 10.1021/acs.organomet.6b00671
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
analogous to that described for [Cr(1)Cl ] using 14 (0.7 g, 2.5 mmol)
the reaction mixture changed from purple to green, and at the end of
the reaction a green precipitate was formed. The solid was filtered off,
washed with 5 mL of tetrahydrofuran and 3 × 10 mL of diethyl ether,
and dried at room temperature under reduced pressure for 5 h. Yield:
0.72 g (93.4%). Anal. Calcd (found): C 42.92 (42.83), H 6.08 (6.17),
N 15.64 (15.54). FT-IR (cm ): 574 (v.w), 600 (vw), 628 (w), 695
(w), 796 (s), 845 (m), 966 (w), 1031 (s), 1053 (v.s), 1119 (s), 1139
(w), 1258 (m), 1279 (s), 1300 (s), 1377 (vs), 1418 (v.s), 1422 (s),
1465 (v.s), 1492 (s), 1557 (vs), 2873 (m), 2932 (s), 2961 (vs), 3127
(w). μeff = 3.98 μB.
3
and [CrCl (THF) ] (0.94 g, 2.5 mmol) in 20 mL of THF. Yield: 0.96
3
3
g, 85%. Anal. Calcd for C H Cl CrN O (FW 436.7): C 44.01, H
1
6
14
3
4
−1
3
(
1
.23, N 12.83. Found: C 44.19, H 3.38, N 12.70. IR (KBr, cm ): 3232
NH, s), 1620−1540 (ArCC, CN, m), 1477−1454 (N−H, s),
054−1043 (C−O, s), 749 (CH, s). FAB(+) MS (m/z): 400 [M −
−1
+
+
+
Cl] , 365 [M − 2Cl] , 329 [M − 3Cl] . μ = 3.66 μ .
eff
B
S-Bis((1H-benzimidazol-2-yl)methyl) Thioether Chromium(III)
Chloride [Cr(15)Cl ]. Complex [Cr(15)Cl ] was synthesized by a
3
3
procedure analogous to that described for [Cr(1)Cl ] using 15 (0.58
3
g, 1.96 mmol) and [CrCl (THF) ] (0.73 g, 1.96 mmol). Yield: 0.75 g,
N-Bis((1H-benzimidazol-2-yl)methyl)-N-(methyl)amine Chromi-
3
3
8
5%. Anal. Calcd for C H Cl CrN S (FW 452.7): C 42.45, H 3.12,
um(0) Tricarbonyl [Cr(2)(CO) ]. Freshly prepared [Cr-
16
14
3
4
3
−1
N 12.38. Found: C 42.59, H 3.22, N 12.27. IR (KBr, cm ): 3448
Ar−H, s), 1622, 1593 (CC, CN, m), 1486, 1467, 1452 (N−H,
s), 1277 (C−N, s), 1046 (CS, s), 744 (CH, s). FAB(+) MS (m/z):
(CO) (NCMe) ] (0.08 g, 0.32 mmol), from [Cr(CO) ] (2.00 g,
3
3
6
(
9.10 mmol) heated at reflux for 24 h in acetonitrile (60 mL), and 2
(0.09 g, 0.32 mmol) were stirred overnight in THF at room
+
+
4
16 [M − Cl] , 381 [M − 2Cl] . μ = 3.89 μ .
temperature. The product was isolated by filtration, washed with Et O
eff
B
2
1
,1-Bis(1H-benzimidazol-2-ylmethyl)ethane Chromium(III) Chlor-
(3 × 10 mL), and dried under vacuum. [Cr(2)(CO) ] was obtained as
3
ide [Cr(16)Cl ]. Complex [Cr(16)Cl ] was synthesized by a procedure
an orange, air-sensitive solid. Recrystallization from a cold (−20 °C)
THF solution gave crystals suitable for X-ray analysis. Yield: 0.12 g,
85%. Anal. Calcd for C H CrN O (FW 427.4): C 56.21, H 4.01, N
3
3
analogous to that described for [Cr(1)Cl ] using 16 (0.6 g, 2.07
3
mmol) and [CrCl (THF) ] (0.78 g, 2.07 mmol). Yield: 0.86 g, 92%.
3
3
20 17
5
3
1
Anal. Calcd for C H Cl CrN (FW 448.7): C 48.18, H 4.04, N 12.49.
16.39. Found: C 56.17, H 4.15, N 16.42. H NMR (250 MHz, J = Hz,
DMSO-d ): δ 3.26 (s, 3H, NCH ), 4.19 (dd, J
1
8
18
3
4
−1
2
Found: C 48.10, H 4.17, N 12.31. IR (KBr, cm ): ν 3384 (Ar−H, s),
= 16.90, CH H ),
6
3
HaHb a b
n
ν 1626−1560 (ArCC, CN, s), δ 1488, 1460 (N−H, s), ν 1222
7.16 (m, 4H, J = 7.33, ArH), 7.34 (d, 2H, J = 7.33, ArH), 8.02
HH HH
+
13
1
(
2
NC, s), δ 757 (CH, s). FAB(+) MS (m/z): 412 [M − Cl] , 377 [M −
(d, 2H, JHH = 7.93, ArH). C{ H} NMR (62.9 MHz, DMSO-d ): δ
6
+
Cl] . μ = 3.88 μ .
25.1 (NCH ), 60.1 (NCH C ), 111.7 (ArC), 118 (ArC), 122.6 (ArC),
eff
B
3
2 q
N-Bis((1H-benzimidazol-2-yl)ethyl)amine Chromium Chloride
134.0 (ArC), 141.8 (ArC ), 153.9 (ArC ), 223.1 (CO). FAB(+)
ipso
q
[
Cr(18)Cl ]. Ligand 18 (0.20 g, 0.49 mmol), chromium(III) chloride
+
+
+
3
MS (m/z): 427 [M] , 358 [M − 2(CO) − Me] , 343 [M − 3(CO)] .
Cationic Complexes. trans-Dichloro(mer-N-bis((1H-benzimida-
zol-2-yl)methyl)amine)(tetrahydrofuran) Chromium(III) Hexafluor-
oantimonate [Cr(1)Cl (thf)]SbF . Silver hexafluoroantimonate (0.24 g,
tetrahydrofuran complex (0.246 g, 0.49 mmol), and 20 mL of dry THF
were stirred and heated at 60 °C for 16 h under a nitrogen
atmosphere. An insoluble solid formed, which was filtered off, washed
with 10 mL of dry THF, and dried in vacuo. The product was obtained
2
6
0.69 mmol) and complex [Cr(1)Cl ] (0.3 g, 0.69 mmol) were stirred
3
−1
as a light brown, amorphous solid: 0.151 g (66%). IR νmax/cm
in THF (20 mL) at room temperature overnight. The solution was
filtered, the solvent removed under reduced pressure, and the product
washed twice with diethyl ether (2 × 20 mL) and dried under vacuum.
Attempts to crystallize the complex from a THF solution resulted in
blue crystals that were analyzed as [Cr(1)Cl (OH )]SbF , probably
(
KBr): 3445 (m, N−H stretch), 3168, 2808 (s, aromatic and aliphatic
C−H stretch), 1619, 1540 (m, CN stretch), 1456, 1403 (s, aromatic
CC stretch and aliphatic C−H bending), 1260 (s, C−N stretch),
+
7
1
4
59 (s, aromatic C−H bending);. MS (LSIMS): m/z 427 ([M − Cl] ,
2
2
6
+
5%) and 392 ([M − 2Cl] , 10%). Anal. Calcd for C H N CrCl : C
due to adventitious moisture in the system. Yield: 0.375 g (77%). Anal.
Calcd for C H Cl CrF N OSb (FW 708.1): C 33.92, H 3.27, N 9.80.
18
19
5
3
6.60, H 4.13, N 15.11. Found: C 46.69, H 3.91, N 14.91. μeff = 3.5 μ .
B
20 23
2
6
5
−1
N-Bis((1H-benzimidazol-2-yl)ethyl)-N-(methyl)amine Chromium
Found: C 33.70, H 3.26, N 9.60. IR (KBr, cm ): 3202 (NH, m), 3164
Chloride [Cr(19)Cl ]. Compound 19 (0.20 g, 0.60 mmol), chromium-
(Ar−H), 1622−1544 (ArCC, CN, m), 1497, 1477, 1456 (N−H,
/
max
3
(
III) chloride tetrahydrofuran complex (0.225 g, 0.60 mmol), and 20
s), 1278 (CN, s), 748 (CH, s), 660 (Sb−F, s). UV−vis (DMF), λ
3
−1
−1
mL of dry DCM were stirred and heated at 35 °C for 16 h under a
nitrogen atmosphere. An insoluble solid formed, which was filtered off,
washed with 10 mL of dry THF and 10 mL of dry DCM, and dried in
vacuo. The product was obtained as a lilac, amorphous solid: 0.145 g
nm (ε /dm mol cm ): 440 (120), 647 (100), 726 (shoulder).
max
+
+
FAB(+) MS (m/z): 401 [M − THF] , 364 [M − THF − Cl] , 328
+
−
[M − THF − 2Cl] . FAB(−) MS (m/z): 235 [SbF ] . μ = 4.10 μ .
6
eff
B
cis-Dichloro(fac-N-bis(1H-benzimidazol-2-ylmethyl)-N-(phenyl)-
−
1
(
49%). IR νmax/cm (KBr): 3408 (m, N−H stretch), 3151, 2968 (s,
amine)(tetrahydrofuran) Chromium(III) Hexafluoroantimonate [Cr-
aromatic and aliphatic C−H stretch), 1618, 1560 (m, CN stretch),
(9)Cl
Cl (thf)]SbF
hexafluoroantimonate (0.06 g, 0.18 mmol) to afford [Cr(9)Cl
SbF as a green solid. Yield: 0.10 g (72%). Anal. Calcd for
CrF OSb (FW 784.2): C 39.82, H 3.47, N 8.93.
2 6
(thf)]SbF . The procedure used was as described for [Cr(1)-
1
1
(
485, 1458 (s, aromatic CC stretch and aliphatic C−H bending),
274 (s, C−N stretch), 746 (s, aromatic C−H bending). MS
2
6
, using ligand 9 (0.09 g, 0.18 mmol) and silver
(thf)]-
2
+
+
LSIMS): m/z 455 ([M − Cl] , 10%) and 420 ([M − 2Cl] , 5%).
6
Anal. Calcd for C H N CrCl : C 48.83, H 4.72, N 14.24. Found: C
C
26
H
27Cl
2
N
6 5
2
0
23
5
3
−1
4
8.69, H 4.61, N 14.03. μeff = 4.2 μB.
Found: C 39.72, N 3.58, N 8.73. IR (KBr, cm ): 3390 (NH, s),
3066 (Ar−H, s), 1623−1554 (ArCC, NC, m), 1498, 1479, 1454
(N−H, s), 1276 (CN, m), 1053 (C−O, m), 751 (CH, s), 665 (Sb−F,
Bis(1H-benzimidazol-2-yl)methane Chromium(III) Trichloride [Cr-
(
20)Cl ]. The ligand 20 (0.626g, 2.5 mmol) and [CrCl (THF) ]
3
3
3
3
−1
−1
(
0.943 g, 2.5 mmol) were combined in 30 mL of THF under nitrogen.
vs). UV−vis (DMF), λ /nm (ε /dm mol cm ): 441 (118), 644
max
max
+
The mixture was stirred for 3 days, and the intensely dark green
(103), 725. FAB(+) MS (m/z): 475 [M − (SbF ) − THF] , 440 [M
6
+
−
suspension was filtered, washed with THF, and dried, to leave the
− (SbF ) − THF − Cl] . FAB(−) MS (m/z): 235 [SbF ] . μ = 4.12
6
6
eff
−
1
product as a dark green powder (0.730 g, 78%). IR νmax/cm (KBr):
μ .
B
3
126 (br, N−H stretch), 1624 (m, CN stretch), 1595 and 1537 (m,
Bis(benzimidazol-2-ylmethyl)methylamine(dimethyl)aluminum
Trimer [(AlMe (2′)] . A solution of trimethylaluminum in heptane (2
aromatic CC stretch and aliphatic C−H bending), 1467 (s, NH,
2
)
2
3
bend), 1047 (m), 744 (s, aromatic C−H bending) 333 (s, N−Cr). MS
M, 1.7 mL, 3.4 mmol) was added to a suspension of 0.5 g (1.7 mmol)
of bis(benzimidazol-2-ylmethyl)methylamine (2) in 20 mL of dry
toluene, at −78 °C. The reaction mixture was stirred at −78 °C for 10
min, and the cooling bath removed. While warming up to room
temperature, the solid gradually dissolved, forming a pale blue
solution. The reaction mixture was stirred additionally for 2 h at room
temperature, and then approximately 3/4 of the solvent removed
under reduced pressure. The addition of 5 mL of dry n-heptane
resulted in the formation of an off-white precipitate, which was filtered,
washed with 5 mL of cold n-heptane, and dried under reduced
+
(
ESI): m/z 404 ([M + H + MeOH] , 15%). Anal. Calcd for
C H N CrCl : C 44.30, H, 2.97, N 13.78. Found: C 44.42, H 3.16, N
1
5
12
4
3
1
3.59.
N-Bis((3,5-dimethylpyrazol-1-yl)methyl)-N-(butyl)amine
Chromium(III) Chloride [Cr(21)Cl ]. A solution of 0.50 g (1.73 mmol)
of N-bis((3,5-dimethylpyrazol-1-yl)methyl)-N-(butyl)amine (21) in
3
1
0 mL of dry THF was added to a suspension of 0.65 g (1.73 mmol)
of [CrCl (THF) ] in 10 mL of THF, and the reaction mixture was
stirred at room temperature for 18 h. Shortly after the start the color of
3
3
K
DOI: 10.1021/acs.organomet.6b00671
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
pressure. Crystals suitable for X-ray analysis were obtained from a
toluene/heptane solution. Yield: 0.55 g (80%). H NMR (400 MHz,
(2) Forestier
̀
e, A.; Olivier-Bourbigou, H.; Saussine, L. Oil Gas Sci.
1
Technol. 2009, 64, 649.
̀
(3) Olivier-Bourbigou, H.; Forestiere, A.; Saussine, L.; Magna, L.;
Favre, F.; Hugues, F. Oil Gas Eur. Mag. 2010, 36, 97.
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6
6
2
13
1
N and CH −N), −0.88−1.58 (36H, CH −Al). C{ H} NMR (101
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3
3
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4
39.4, 138.9, 138.8, 137.7, 129.3, 128.5, 125.6, 123.9, 123.6, 123.4,
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(
(
(
200 mL) followed by addition of MAO as a moisture scavenger. The
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2
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2
3
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00671.
■
(
*
S
(
2
(
NMR spectra, GC chromatograms, additional graphs,
crystallographic details, and information regarding DFT
calculations (PDF)
Crystallographic data (CIF)
Optimized Cartesian coordinates (XYZ)
Ltd.), WO 2007/015074, 2007.
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(
(
AUTHOR INFORMATION
Corresponding Author
E-mail: g.britovsek@imperial.ac.uk.
■
*
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Notes
(
́
The authors declare no competing financial interest.
̀
̂
1
ACKNOWLEDGMENTS
■
Financial support from INEOS Technologies is kindly
acknowledged. We thank the Australian Research Council for
financial support through grant FT100100609 to D.S.M. We
thank the STFC for beam time at Daresbury Laboratory and
Drs. Jonathan E. Warren and Timothy J. Prior for scientific
support.
2
(
(
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