Modification of iron(II) tridentate bis(imino)pyridine complexes by a boryl group for the production of α-olefins at high temperature

Article abstract of DOI:10.1021/om800036b

A new series of boryl-substituted bis(imino)pyridine ligands [o-PinacolB-Ph-N=C(Me)-Py-C(Me)=N-Ph-o-BPinacol], Pinacol = (-O-(Me) ₂C-C(Me)₂-O-) (6), [2,4,6-tri-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph- o-BPinacol] (11), [4-bromo-2,6-di-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph-o-BPinacol] (12), [2,4,6-tri-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph-m-BPinacol](14), [2,4,6-tri-Me-Ph-N=C(Me) -Py-C(Me)=N-Ph-p-BPinacol] (17), and [4-Bromo-2,6-di-Me-Ph-N=C(Me)-Py-C(Me)=N- Ph-p-BPinacol] (18), and their corresponding Fe(II) complexes [{o-PinacolB-Ph-N=C(Me)-Py-C(Me)=N-Ph-o-BPinacol}FeCl₂] (3), [{2,4,6-tri-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph-o-BPinacol}FeCl₂] (19), [{4-bromo-2,6-di-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph-o-BPinacol}FeCl₂] (20), [{2,4,6-tri-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph-m-BPinacol}-FeCl₂] (21), [{2,4,6-tri-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph-p-BPinacol}FeCl₂] (22), and [{4-bromo-2,6-di-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph-p-BPinacol}FeCl₂] (23) were synthesized. According to X-ray analysis, the introduction of boryl groups in the ortho-positions of the complex as in 3 caused the shortening of the axial Fe-N bond lengths (up to 0.02 A) vs the analogous Fe(II) complex with ortho-methyl groups [{o-Me-Ph-N=C(Me)-Py-C(Me)=N-Ph-o-Me}FeCl₂], 1. The comparisons of the axial bond lengths in ortho-boryl-substituted isomer 19 with para-boryl-substituted 22 revealed that these bonds are shorter in the ortho-isomer (2.201(11) A) than in the para-isomer (2.232(2) A). An interesting structural feature of 3 is that it exists in the unexpected up-up conformer in the solid state, despite reasonable bulkiness of dioxaboranyl substituents in ortho-positions. Complexes 21-23 afforded very productive catalysts for the production of α-olefins with a more linear Schultz-Flory distribution and with the least amounts of the heavier insoluble fractions of α-olefins than the parent methyl-substituted Fe(II) complex 1.

Full text of DOI:10.1021/om800036b

1902
Organometallics 2008, 27, 1902–1911
Modification of Iron(II) Tridentate Bis(imino)pyridine Complexes by
a Boryl Group for the Production of r-Olefins at High
Temperature†
Alex S. Ionkin,* William J. Marshall, Douglas J. Adelman, Barbara Bobik Fones,
Brian M. Fish, and Matthew F. Schiffhauer
DuPont Central Research & DeVelopment, Experimental Station, Wilmington, Delaware 19880-0328
ReceiVed January 14, 2008
A new series of boryl-substituted bis(imino)pyridine ligands [o-PinacolB-Ph-NdC(Me)-Py-C(Me)dN-
Ph-o-BPinacol], Pinacol ) (-O-(Me)2C-C(Me)2-O-) (6), [2,4,6-tri-Me-Ph-NdC(Me)-Py-C(Me)dN-
Ph-o-BPinacol] (11), [4-bromo-2,6-di-Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-o-BPinacol] (12), [2,4,6-tri-
Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-m-BPinacol] (14), [2,4,6-tri-Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-p-
BPinacol] (17), and [4-Bromo-2,6-di-Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-p-BPinacol] (18), and their
corresponding Fe(II) complexes [{o-PinacolB-Ph-NdC(Me)-Py-C(Me)dN-Ph-o-BPinacol}FeCl2] (3),
[{2,4,6-tri-Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-o-BPinacol}FeCl2] (19), [{4-bromo-2,6-di-Me-Ph-NdC(Me)-
Py-C(Me)dN-Ph-o-BPinacol}FeCl2] (20), [{2,4,6-tri-Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-m-BPinacol}-
FeCl2] (21), [{2,4,6-tri-Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-p-BPinacol}FeCl2] (22), and [{4-bromo-2,6-
di-Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-p-BPinacol}FeCl2] (23) were synthesized. According to X-ray
analysis, the introduction of boryl groups in the ortho-positions of the complex as in 3 caused the shortening
of the axial Fe-N bond lengths (up to 0.02 Å) vs the analogous Fe(II) complex with ortho-methyl groups
[{o-Me-Ph-NdC(Me)-Py-C(Me)dN-Ph-o-Me}FeCl2], 1. The comparisons of the axial bond lengths in
ortho-boryl-substituted isomer 19 with para-boryl-substituted 22 revealed that these bonds are shorter in
the ortho-isomer (2.201(11) Å) than in the para-isomer (2.232(2) Å). An interesting structural feature of
3 is that it exists in the unexpected “up-up” conformer in the solid state, despite reasonable bulkiness
of dioxaboranyl substituents in ortho-positions. Complexes 21–23 afforded very productive catalysts for
the production of R-olefins with a more linear Schultz-Flory distribution and with the least amounts of
the heavier insoluble fractions of R-olefins than the parent methyl-substituted Fe(II) complex 1.
Scheme 1
Introduction
FeII catalysts with tridentate bis(imino)pyridine ligands were
reported to make R-olefin oligomers with perfect Schultz-Flory
distributions, exceptional purities (97–99%), and high
productivities.1b The results exceed the values reported for
catalysts used in the current commercial processes, including
the original Ziegler process and Shell’s SHOP technology.2 The
presence of sterically small substituents in the ortho-positions
of the imino aryl group, such as only one methyl group in the
ortho-positions in complex 1 or the fluorides in the ortho-
positions in complex 2 groups (Scheme 1), are crucial catalyst
structural features needed to produce R-olefins instead of
polyethylene.1,3
The FeII complex 1, with a tridentate bis(imino)pyridine
ligand, bearing only one methyl group in the ortho-positions
of the imino aryl group, was initially determined to be the best
for the R-olefin production.1c,e However, thorough analysis of
complex 1 as a precatalyst for R-olefin oligomerization at the
commercially desirable temperature of 120 °C revealed some
important shortcomings. Complex 1 is extremely productive,
but the lifetime of the catalyst is about 3 min at 120 °C. The
resulting exothermic effect is difficult to control. Also, the
Schultz-Flory distribution is not linear. The distribution was
curved with the light R-olefin fractions (C-4 and C-6) and
heavier fractions (C-14 and up) above the theoretical numbers.
These shortcomings for the industrial production needed to be
addressed through catalyst modifications.
In this study, we report FeII complexes with tridentate
bis(imino)pyridine ligands functionalized by boryl substituents,
which afford high-temperature catalysts for the production of
R-olefins. The four patterns of substitutions were envisioned to
make the complexes to produce R-olefins. Pattern A has two
ortho-boryl groups symmetrically placed in two aryl imino
groups. The nonsymmetrical patterns4 B, C, and D have two
ortho-methyls in one imino aryl group and one boryl group
placed in ortho-, meta-, and para-positions correspondingly
(Scheme 2).
Results and Discussion
Synthesis. Complex 3 of type A was prepared by the
following sequence. The condensation reaction between
commercially available 1-(6-acetylpyridin-2-yl)ethanone (4)
and 2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenyl-
† This is DuPont contribution #8695.
* Corresponding author. E-mail: alex.s.ionkin@usa.dupont.com.
10.1021/om800036b CCC: $40.75
2008 American Chemical Society
Publication on Web 03/20/2008

Modification of Iron(II) Tridentate Bis(imino)pyridine Complexes
Organometallics, Vol. 27, No. 8, 2008 1903
Scheme 2
Scheme 3
Figure 1. ORTEP drawing of 2,6-bis[1-(2-(4,4,5,5-tetramethyl-
[1,3,2]dioxaborolan-2-yl)phenylimino)ethyl]pyridineiron(II) chloride
(3). The crystal structure is drawn to the 50% probability level.
This is an “up-up” conformer.
(7) and 4-bromo-2,6-dimethylphenylaniline (8) led to nonsym-
metrical (imino)(keto)pyridines 9 and 10 respectively (Scheme
4).
The second set of selective condensations between precursors
9 and 10 from one side and borylated anilines 5, 13, and 16
from the other side led to the formation of the target ligands of
type B (11 and 12), type C (14), and type D (17 and 18).
Reactions between the above ligands and iron(II) chloride in
THF afforded the final complexes of types B-D (Scheme 5).
The structures of the nonsymmetrical complexes 19, 21, 22,
and 23 were determined by X-ray analysis. Their ORTEP
drawings are shown in Figures 2, 3, 4, and 5, respectively.
Solid State Structures of Fe Precatalysts. The complexes
3, 19, 22, and 23 have distorted bipyramidal geometry, which
is typical for iron(II) complexes with tridentate bis(imino)py-
ridine ligands with a ratio of 1:1.5 The planes of the aryl-
substituted arylimino groups of complex 3, 19, and 22 are
oriented orthogonally to the plane formed by iron and the three
nitrogen atoms. The meta-boryl-substituted arylimino groups
in 21 deviated mostly in this series from the orthogonality. The
angles between the mean planes of the nitrogens and iron vs
the meta-boryl-substituted phenyl rings are 65.7° and 67.4°. The
corresponding angles of the mesitylimino arm are 94.4° and
94.5°, which are essentially orthogonal. There are two sets of
angles for 21 because the crystal unit cell of complex 21 contains
two independent molecules.
amine (5) led to symmetrical bis(imino)pyridine (6), with
two boryl groups in the ortho-positions of the aryl imino
arms. The reaction between iron(II) chloride and ligand 6
led to complex 3 of type A (Scheme 3).
The structure of complex 3 was determined by X-ray analysis.
A crystal of 3 suitable for X-ray analysis was grown from
acetonitrile (Figure 1).
Nonsymmetrical complexes of types B, C, and D were
prepared by the following methods. Two sets of selective
condensations were used to prepare ligands of types B, C, and
D. The first condensation reactions between commercially
available 1-(6-acetylpyridin-2-yl)ethanone (4) and mesitylaniline
(1) For initial publications see (a): Bennett, A. M. A. (DuPont) PCT
Int. Appl. WO9827124 A1, 1998, 68 pp. (b) Britovsek, G. J. P.; Gibson,
V. C.; Kimberley, B. S.; Maddox, P. J.; McTavish, S. J.; Solan, G. A.;
White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 849. (c) Small,
B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143. (d) For recent
reviews and papers see: Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem.
ReV. 2000, 100, 1169. (e) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F.
Angew. Chem., Int. Ed. 1999, 38, 428. (f) Mecking, S. Coord. Chem. ReV.
2000, 203, 325. (g) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003,
103, 283. (h) Britovsek, G. J. P.; Cohen, S. A.; Gibson, V. C.; van Meurs,
M. J. Am. Chem. Soc. 2004, 126, 10701. (i) Barbaro, P.; Bianchini, C.;
Giambastiani, G.; Rios, I. G.; Meli, A.; Oberhauser, W.; Segarra, A. M.;
Sorace, L.; Toti, A. Organometallics 2007, 26, 4639. (k) Bart, S. C.;
Lobkovsky, E.; Bill, E.; Wieghardt, K.; Chirik, P. J. Inorg. Chem. 2007,
46, 7055. (l) Abu-Surrah, A. S.; Qaroush, A. K. Eur. Polym. J. 2007, 43,
2967. (m) Zhang, S.; Vystorop, I.; Tang, Z.; Sun, W.-H. Organometallics
2007, 26, 2456. (n) Small, B. L.; Rios, R.; Fernandez, E. R.; Carney, M. J.
Organometallics 2007, 26, 1744. (o) McTavish, S.; Britovsek, G. J. P.;
Smit, T. M.; Gibson, V. C.; White, A. J. P.; Williams, D. J. J. Mol. Catal.
A: Chem. 2007, 261, 293. (p) Seitz, M.; Milius, W.; Alt, H. G. J. Mol.
Catal. A: Chem. 2007, 261, 246. (q) Kaul, F. A. R.; Puchta, G. T.; Frey,
G. D.; Herdtweck, E.; Herrmann, W. A. Organometallics 2007, 26, 988.
(r) Mahdavi, H.; Badiei, A.; Zohuri, G. H.; Rezaee, A.; Jamjah, R.; Ahmadjo,
S. J. Appl. Polym. Sci. 2007, 103, 1517.
(2) Vogt, D. In Applied Homogeneous Catalysis with Organometallic
Compounds; Cornils, B., Herrmann, W. Eds.; VCH Publishers: 1996; Vol.
1, p 245.
(3) (a) Chen, Y.; Qian, C.; Sun, J. Organometallics 2003, 22, 1231. (b)
Chen, Y.; Chen, R.; Qian, C.; Dong, X.; Sun, J. Organometallics 2003, 22,
4312. (c) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskela, M.; Rieger, B.
Organometallics 2001, 20, 2321. (d) Moody, L. S.; MacKenzie, P. B.;
Killian, C. M.; Lavoie, G. G.; Ponasik, J. A.; Smith, T. W.; Pearson, J. C.;
Barrett, A. G. M. U.S. Pat. Appl. 0049135 A1, 2002. (e) Ionkin, A. S.
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Licht, A. I.; Schneider, K. J. Coord. Chem. ReV 2006, 250, 2.
(4) (a) Small, B. L.; Brookhart, M. Macromolecules 1999, 32, 2120.
(b) De Boer, E.; Johannes, M.; Deuling, H. H.; Van Der Heijden, H.;
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(5) Britovsek, G. J. P.; England, J.; Spitzmesser, S. K.; White, A. J. P.;
Williams, D. J. Dalton Trans. 2005, 5, 945.

1904 Organometallics, Vol. 27, No. 8, 2008
Scheme 4. Synthesis of Ligands 11, 12 (Type B); 14 (Type C); and 17, 18 (Type D)
Ionkin et al.
Scheme 5. Iron(II) Tridentate Bis(imino)pyridine Complexes
substituted analogue 1. This bond shortening can be explained
by enhanced pπ-dπ back-bonding interactions between iron
and the π-accepting boryl-substituted ligand7 (dioxaboranyl
groups are almost coplanar with phenylimino groups, to which
they are attached) and by the more σ-donating properties of
the boryl-substituted ligand8 compared with the alkyl-substituted
ligand in 1. It is next to impossible to separate impacts of the
of Types B-D
Both boron atoms in 3 remain three-coordinate. There are
no short contacts between chloride and boron atoms in complex
3, which could have resulted in four-coordinated boron atoms.
An interesting structural feature of 3 is that it exists as an
“up-up” conformer in the solid state despite reasonable
bulkiness of the dioxaboranyl substituents in ortho-positions.6
Selected bond lengths of 3 are presented in Table 1.
Figure 2. ORTEP drawing of [1-(6-{1-[2-(4,4,5,5-tetramethyl-
[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-yl)eth-
ylidene](2,4,6-trimethylphenyl)amineiron(II) chloride (19). The
crystal structure is drawn to the 50% probability level.
The axial Fe-N bonds in 3 are actually shorter by an average
of 0.015 Å than the corresponding bonds in the methyl-

Modification of Iron(II) Tridentate Bis(imino)pyridine Complexes
Organometallics, Vol. 27, No. 8, 2008 1905
Figure 5. ORTEP drawing of (4-bromo-2,6-dimethylphenyl)[1-(6-
{1-[4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]-
ethyl}pyridin-2-yl)ethylidene]amineiron(II) chloride (23). The crys-
tal structure is drawn to the 50% probability level.
Figure 3. ORTEP drawing of [1-(6-{1-[3-(4,4,5,5-tetramethyl-
[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-yl)eth-
ylidene](2,4,6-trimethylphenyl)amineiron(II) chloride (21). The
crystal structure is drawn to the 50% probability level.
the mesityl side is due to steric repulsion of the two ortho-
methyl groups and the iron core of the molecules. The boron
atoms in 19 and 22 remain tricoordinated and do not have short
contacts with chlorides or any other atoms. The rest of the
structural data are in agreement with the previous structural
studies of iron(II) complexes with tridentate bis(imino)pyridine
ligands.
The complexes 19 and 23 were analyzed by X-ray, however,
due to the small crystallite size; the overall structure quality is
poor and only serves to establish the connectivity for this study.
The correlations of the bond lengths in 19 and 23 with other
structures are not discussed for that reason here.
Oligomerization of Ethylene to r-Olefins by Fe(II)
Dichloride Complexes 19, 20, 21, 22, and 23. Ethylene
oligomerizations were done using the equipment and procedure
described in the Experimental Section. The purpose was to
evaluate the catalysts for the production of R-olefins. Catalyst
lifetimes, productivities, temperature stability, and product
distributions were of greatest interest. The performances of the
nonsymmetrical boryl-containing precatalysts are compared to
that of the standard symmetric ortho-methyl candidate, 1.
A catalyst lifetime was defined as the time from introduction
of ethylene to the reactor until its uptake was no longer detected
by the mass flow sensor. Since the catalysts have wide ranging
activities (speeds) and temperature sensitivities, the amounts of
precatalysts injected were adjusted until exothermic effects of
no greater than 2 °C were achieved and until similar amounts
of olefins were made for all precatalysts. The former ensured
that the lifetimes were not affected by catalysts being exposed
to temperatures more than 2 °C higher than the intended setpoint.
The latter was desired to make sure the data were not affected
by nonlinearities in the analytical methods.
Figure 4. ORTEP drawing of [1-(6-{1-[4-(4,4,5,5-tetramethyl-
[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-yl)eth-
ylidene](2,4,6-trimethylphenyl)amineiron(II) chloride (22). The
crystal structure is drawn to the 50% probability level.
above interactions, but the more electron-donating properties
of the boryl-substituted ligand seem to be the cause of the
shortening. The comparison of bond lengths of the imino groups
in 3 and 1 shows the reverse trends. The CdN bonds in 3 are
longer than in 1 by 0.01 Å. It may be an indication that Fe-N
bonds in 3 are stronger than in 1. The CdN bonds get longer
with the shortening of Fe-N bonds in X-ray-analyzed FeII
complexes with tridentate bis(imino)pyridine ligands.9
The axial Fe-N bonds from the mesityl imino arm in 22
(2.247(2) Å) is longer than those from the borylated imino arm
(2.232(2) Å for 22). This elongation of the Fe-N bonds from
Figure 6 is a plot of ethylene uptakes for several catalysts.
There is an initial rapid consumption of ethylene followed by
a tailing-off. The noise and larger perturbations in the tail
sections of the curves are a result of using a single ethylene
feed orifice to cover the large uptake range. The larger
(6) (a) Tellmann, K. P.; Gibson, V. C.; White, A. J. P.; Williams, D. J.
Organometallics 2005, 24, 280. (b) Ionkin, A. S.; Marshall, W. J.; Adelman,
D. J.; Bobik Fones, B.; Fish, B. M.; Schiffhauer, M. F. Organometallics
2006, 25, 2978.
(7) (a) Sakaki, S.; Biswas, B.; Musashi, Y.; Sugimoto, M. J. Organomet.
Chem. 2000, 611, 288. (b) Wrackmeyer, B.; Tok, O. L.; Ayazi, A.; Maisel,
H. E.; Herberhold, M. Magn. Reson. Chem. 2004, 42, 827. (c) Exner, O.;
Bose, R. Collect. Czech. Chem. Commun. 1974, 39, 2234. (d) Sakaki, S.;
Kai, S.; Sugimoto, M. Organometallics 1999, 18, 4825.
(9) (a) Britovsek, G. J. P.; Mastroianni, S.; Solan, G. A.; Baugh, S. P. D.;
Redshaw, C.; Gibson, V. C.; White, A. J. P.; Williams, D. J.; Elsegood,
M. R. J. Chem.-Eur. J. 2000, 6, 2221. (b) Bianchini, C.; Mantovani, G.;
Meli, A.; Migliacci, F.; Zanobini, F.; Laschi, F.; Sommazzi, A. Eur. J. Inorg.
Chem. 2003, 8, 1620.
(8) (a) Wrackmeyer, B.; Kerschl, S.; Klaus, U. Z. Naturforsch., B: Chem.
Sci. 2002, 57, 1251. (b) Sugihara, Y.; Takakura, K.; Murafuji, T.; Miyatake,
R.; Nakasuji, K.; Kato, M.; Yano, S. J. Org. Chem. 1996, 61, 6829.

1906 Organometallics, Vol. 27, No. 8, 2008
Ionkin et al.
Figure 6. Graph of ethylene uptake of complexes 1, 21, 22, and 23 in catalytic oligomerization of ethylene at 120 °C.
Table 1. Selected Bond Lengths (Å) for 1, 3, 19, 21, and 23
1
3
19
21
22
23
axial (imino) N-Fe bond
axial (imino) N-Fe bond
2.2303(16)
Fe-N1
2.220(4)
Fe-N1
2.225(10)
Fe-N1
mesityl side
2.201(11)
Fe-N3
boryl side
2.130(10)
Fe-N2
1.288(14)
N1-C1
2.259(3)
Fe-N1
mesityl side
2.272(3)
Fe-N3
boryl side
2.107(3)
Fe-N2
1.272(4)
N1-C1
2.247(2)
Fe-N1
mesityl side
2.232(2)
Fe-N3
boryl side
2.121(2)
Fe-N2
1.285(3)
N1-C1
2.220(11)
Fe-N1
4-bromo-2,6-dimethylphenyl side
2.234(13)
Fe-N3
boryl side
2.103(12)
Fe-N2
1.289(16)
N1-C1
2.2424(17)
Fe-N3
2.222(4)
Fe-N3
basel (central)
N-Fe bond
CdN
2.0943(16)
Fe-N2
1.281(2)
N1-C1
2.113(4)
Fe-N2
1.290(5)
N1-C1
mesityl side
1.261(15)
N3-C7
mesityl side
1.290(4)
N3-C7
mesityl side
1.288(3)
N3-C7
4-bromo-2,6-dimethylphenyl side
1.242(17)
N3-C7
boryl side
CdN
1.287(3)
N3-C7
1.272(5)
N3-C7
boryl side
boryl side
boryl side
Table 2. r-Olefins from Ethylene Oligomerizations by Iron(II) Complexes 1, 19, 20, 21, 22, and 23a
precatalyst and
amount, µmol
amount cocatalyst,
MMAO, mmol
temperature,
“K” value
Schultz-Flory distribution
kg of LAO
per g of catalyst
% solids
total LAO
SFD
b
c
entry
°C
R2
1
2
3
4
5
6
7
8
3, 0.15
2.26
2.26
2.26
2.26
2.26
2.26
2.26
2.26
2.26
2.26
1.13
120 and 100
120
100
120 and 100
120
100
120
100
120
100
traces
71
19, 0.16
19, 0.08
20, 0.15
21, 0.16
21, 0.08
22, 0.16
22, 0.08
23, 0.15
23, 0.07
1, 0.062
0.79
0.77
57.94
70.63
N/A
N/A
219
traces
122
178
168
855
266
752
458
0.66
0.68
0.64
0.67
0.63
0.65
0.59
4.00
3.87
3.01
3.54
1.13
2.53
3.44
0.9971
0.9902
0.9979
0.9989
0.9978
0.9992
0.9862
9
10
11
120
a Conditions: solvent, o-xylene, 600 mL; pressure, 700 psig. b Determined from GC, using extrapolated values for C-10 and C-12. c Xylenes insoluble
fraction of R-olefins.
disturbances are caused by the orifice opening slightly in
response to a small autoclave pressure drop. Considering the
individual traces in Figure 6, it appears that the boryl-containing
catalysts, 21–23, showed more activity beyond 800 s than did
the ortho-methyl, 1. This suggests the boryl group extended
the lifetime relative to that of the standard catalyst.
Results used to evaluate productivities, temperature stability,
and product distributions of the precatalysts are shown in Table
2. Complexes with ortho-borylated moieties, such as bis-
borylated complex 3 and nonsymmetrical monoborylated com-
plex 20, were found to have very low activities in R-olefin
oligomerization experiments within the tested range of temper-
atures (60–130 °C). The nonsymmetrical monoborylated com-
plex 19 behaved as a polymerization catalyst at high temper-
atures to some degree because it produced a lot of solids (Table
3, seventh column). The formation of up to 70% solids may be
an indication of the disproportionation of the catalyst 19 to
symmetrical tetra-ortho-methyl-substituted derivative 24 at this

Modification of Iron(II) Tridentate Bis(imino)pyridine Complexes
Organometallics, Vol. 27, No. 8, 2008 1907
Table 3. Summary of Crystal Data, Data Collection, and Structural Refinement Parameters for 1, 3, and 19
1
3
19
empirical formula
fw
cryst color, form
cryst syst
space group
a (Å)
C24H25Cl4FeN3
553.12
blue, needle
monoclinic
P2(1)/c
10.4140(5)
15.2465(8)
15.8488(8)
C37H47B2Cl2FeN5O4
774.17
C36H42BCl2FeN3O2
686.29
blue, needle
monoclinic
P2(1)/c
8.65(2)
23.25(6)
17.26(4)
90
90.99(4)
90
3471(14)
4
blue, rec. plate
monoclinic
P2(1)/n
12.6115(19)
16.284(2)
19.867(3)
90
104.933(3)
90
3942.1(10)
4
b (Å)
c (Å)
R (deg)
90
ꢀ (deg)
92.3650(10)
90
2514.3(2)
4
1.461
1.042
1136
γ (deg)
V (Å3)
Z
density (g/cm3)
1.304
0.562
1624
1.313
0.624
1440
abs µ (mm-1
F(000)
)
cryst size (mm)
temp (°C)
scan mode
detector
θmax (deg)
no. obsrvd reflns
no. uniq reflns
Rmerge
0.32 × 0.06 × 0.02
0.34 × 0.25 × 0.03
0.45 × 0.08 × 0.01
-100
-100
-100
ω
ω
ω
Bruker-CCD
Bruker-CCD
27.12
Bruker-CCD
25.98
27.96
37 670
6038
0.055
29 039
8687
0.147
17 417
6644
0.390
no. params
358
1.02
446
0.869
449
0.869
Sb
R indices [I > 2σ(I)]a
R indices (all data)a
max diff peak, hole (e/Å3)
wR2 ) 0.075, R1 ) 0.036
wR2 ) 0.084, R1 ) 0.060
0.288, -0.325
wR2 ) 0.126, R1 ) 0.068
wR2 ) 0.162, R1 ) 0.173
0.364, -0.342
wR2 ) 0.223, R1 ) 0.114
wR2 ) 0.367, R1 ) 0.386
0.703, -0.868
2
2 2
2
2 2
a R1 ) ∑|Fo - Fc|/∑Fo, wR2 ) {∑[w(Fo - Fc ) ]/∑[w(Fo2)2]}1/2 (sometimes denoted as wR2). b GooF ) S ) {∑[w(Fo - Fc ) ]/(n - p)}1/2, where
n is the number of reflections and p is the total number of refined parameters.
Scheme 6
needed. Also, a more stable catalyst will facilitate operation at
a higher temperature. This keeps the higher molecular weight
oligomers in solution to delay equipment fouling.
Of particular importance is the molecular weight distribution
of products made by a catalyst. The best that can be expected
is for the products to fit an ideal Schultz-Flory distribution.11
A single factor used to characterize this distribution is the
Schultz-Flory K value. It is defined as
high temperature, which is known to result in polymer
formation.1,10
K ) n(Cn+2 olefin)/n(Cn olefin)
Precatalysts 21–23, which have meta- or para-boryl imino
arm groups, show high activities. Comparisons of productivities
at 120 °C of the latter group to that of 1 indicate that 1 is nearly
2 times more productive than any of the boryl-containing
catalysts. While this may seem like a disadvantage, the amount
of precatalyst needed, even for the boryl-containing complexes,
adds insignificant expense to the cost of making R-olefins
because they are so active.
An indication of the temperature sensitivity of a catalyst can
be achieved by comparing its productivities at 100 and 120 °C.
Precatalyst 21 has nearly the same productivity at both tem-
peratures, whereas 22 and 23 are greatly different. This suggests
that 21 is much more thermally stable than are 22 and 23.
Support for this is seen in Figure 6. The ethylene uptake profiles
show that 21 continued to consume ethylene most steadily to
near the end of the experiment.
wherein n(Cn olefin) is the number of moles of olefin containing
n carbon atoms, and n(Cn+2 olefin) is the number of moles of
olefin containing n+2 carbon atoms, or in other words the next
higher oligomer of Cn olefin. From this, the weight fractions of
the various olefins in the resulting oligomeric reaction product
mixture can be determined. The K factor is usually preferred to
be in the range of about 0.6 to about 0.8 to make the R-olefins
of the most commercial interest. It is also desirable to be able
to vary this factor so as to make a range of products. As seen
in Table 2, small changes can be achieved by adjusting the
temperature.
Excluding the K values for 19, evaluation of the data in Table
2 indicates that precatalyst 21, with a meta-boryl group, gave
the highest K values of 0.68 at 100 °C and 0.66 at 120 °C
(entries 5 and 6 in Table 2). The meta-boryl group creates more
steric bulk around the metal center than para-substitution
patterns of 22 and 23. The increase of the steric bulk around
iron leads usually to an increase in the K value.9b,12,13a The drop
The temperature stability and productivities have implications
for R-olefin reactor design. For example, in a plug flow design,
an unstable but highly productive catalyst will require more
frequent injections of less catalyst than will a stable, less active
catalyst. While a less active but more stable catalyst will need
to be injected at a higher rate, fewer injection points will be
(11) Elvers, B., et al., Ed. Ullmann’s Encyclopedia of Industrial
Chemistry; VCH Verlagsgesellschaft mbH: Weinheim, 1989; Vol. A13, pp
243–247 and 275–276..
(12) Britovsek, G. J. P.; Gibson, V. C.; Mastroianni, S.; Oakes, D. C. H.;
Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Eur. J. Inorg.
Chem. 2001, 2, 431.
(10) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem. Soc.
1998, 120, 4049.

1908 Organometallics, Vol. 27, No. 8, 2008
Ionkin et al.
Table 4. Summary of Crystal Data, Data Collection, and Structural Refinement Parameters for 21, 22, and 23
21
22
23
empirical formula
fw
C61H74B2Cl6Fe2N6O4
1301.28
C30H36BCl2FeN3O2
608.18
C29H33BBrCl2FeN3O2
673.05
cryst color, form
cryst syst
space group
a (Å)
blue, rect plate
monoclinic
P2(1)/c
31.466(3)
blue, prism
monoclinic
P2(1)/c
14.116(4)
blue, needle
monoclinic
P2(1)
14.112(14)
b (Å)
8.8961(9)
15.902(5)
15.854(17)
c (Å)
25.037(3)
14.105(4)
13.830(15)
R (deg)
90
90
90
100.75(2)
90
3040(6)
ꢀ (deg)
111.985(2)
90
6498.8(12)
101.311(5)
90
3104.7(16)
γ (deg)
V (Å3)
Z
4
1.33
0.742
2712
4
4
density (g/cm3)
1.301
0.688
1272
1.471
2.017
1376
abs µ (mm-1
F(000)
)
cryst size (mm)
temp (°C)
scan mode
detector
0.50 × 0.18 × 0.06
0.50 × 0.24 × 0.15
0.12 × 0.04 × 0.01
-100
-100
-100
ω
ω
ω
Bruker-CCD
Bruker-CCD
Bruker-CCD
θmax (deg)
28.27
52 486
16 031
0.105
28.51
25 834
7769
0.084
26.99
22 463
6457
0.705
no. obsrvd reflns
no. uniq reflns
Rmerge
no. params
748
0.987
361
0.999
355
0.684
b
S
R indices [I > 2σ(I)]a
R indices (all data)a
wR2 ) 0.116, R1 ) 0.058
wR2 ) 0.144, R1 ) 0.144
0.690, -0.909
wR2 ) 0.125, R1 ) 0.052
wR2 ) 0.149, R1 ) 0.099
0.659, -0.793
wR2 ) 0.206, R1 ) 0.092
wR2 ) 0.350, R1 ) 0.366
0.859, -1.231
max diff peak, hole (e/Å3)
2
2 2
2
2 2
a R1 ) ∑|Fo - Fc|/∑Fo, wR2 ) {∑[w(Fo - Fc ) ]/∑[w(Fo2)2]}1/2 (sometimes denoted as wR2). b GooF ) S ) {∑[w(Fo - Fc ) ]/(n - p)}1/2, where
n is the number of reflections and p is the total number of refined parameters.
in K values by 0.02 upon increasing the temperature from 100
to 120 °C is normal dependency for the Versipol family of
catalysts.1 Precatalysts 22 and 23 have both para-boryl groups
in one imino arm and differ only by the para-substituent in
another imino arm (methyl in 22 and bromo in 23). The methyl
derivative 22 gave a set of K values of 0.64 and 0.67, which
are higher than 0.63 and 0.65 for the bromo derivative 23 at
the same two temperatures. Both sets of K values are quite
acceptable for commercial application. The parent catalyst from
complex 1, with two ortho-methyl groups on both imino arms,
gave R-olefins with a K value below 0.6.
(SFD R2) seen for the borylated precatalysts seen in Table 2 or
in Figure 7. The superior linearity of precatalysts 21-23 is
explained by the nonsymmetrical nature of the ligand.4
In conclusion, the Fe-based bis(imino)pyridine complexes
21-23 functionalized nonsymmetrically by the boryl groups
are more thermally stable but less productive than is the
symmetric parent complex 1. Additionally, they make more
desirable product distributions that are more ideal. Precatalyst
23 has the added advantage that it makes considerably less solids
than precatalyst 1.
In Table 2 is a column labeled “% solids of total LAO”. That
represents the weight percent of R-olefin made that was not
soluble in o-xylene at room temperature. Since these have very
limited commercial value, they represent an ethylene yield loss
and so should be minimized. The values for precatalyst 23 were
the lowest, with only 1.13 and 2.53 wt % at 120 and 100 °C,
respectively (entries 9 and 10 in Table 2).
The goodness-of-fit of the product distribution to the ideal
Schultz-Flory distribution was mentioned earlier as a measure
of the desirability of a catalyst. Using a form of the Schultz-Flory
equation given in previous work,13 a plot of the degree of
polymerization (Dp) minus 2 vs the logarithm of the quantity
the weight fraction with a certain degree of polymerization (MDp)
divided by that degree of polymerization is made to judge the
fit to the ideal distribution. Figure 7 shows the results for
precatalysts 21–23 and 1. Straight lines are drawn through all
of the sets of data. It is clear that the data points for precatalyst
1 deviate more from its line on the high and low Dp ends of the
plot. This is supported by the higher correlation coefficients
Experimental Section
All air-sensitive compounds were prepared and handled under a
N2/Ar atmosphere using standard Schlenk and inert-atmosphere box
techniques. Anhydrous solvents were used in the reactions. Solvents
were distilled from drying agents or passed through columns under
an argon or nitrogen atmosphere. Anhydrous iron(II) chloride, 1-(6-
acetylpyridin-2-yl)ethanone, 2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-
2-yl)phenylamine, 4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-
yl)phenylamine, 3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylamine, and THF were purchased from Aldrich. Complex 1
was prepared according to the literature.1,10
2,6-Bis[1-(2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylimino)ethyl]pyridine (6). A 1.77 g (0.0108 mol) sample
of 1-(6-acetylpyridin-2-yl)ethanone (4), 5.0 g (0.0228 mol) of
2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylamine (5), 100
mL of toluene, and 100 g of the fresh molecular sieves were kept
at 100 °C for 3 days. The molecular sieves were removed by
filtration. The solvent was removed in a rotary evaporator, and the
residue was recrystallized from 20 mL of ethanol. The yield of
2,6-bis[1-(2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimi-
1
(13) (a) Ionkin, A. S.; Marshall, W. J.; Adelman, D. J.; Bobik Fones,
B.; Fish, B. M.; Schiffhauer, M. F.; Soper, P. D.; Waterland, R. L.; Spence,
R. E.; Xie, T. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 585. (b)
Ionkin, A. S.; Marshall, W. J.; Adelman, D. J.; Shoe, A. L.; Spence, R. E.;
Xie, T. J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 2615.
no)ethyl]pyridine (6) was 4.48 g (73%) as a pale yellow solid. H
NMR (500 MHz, Tol-D8, TMS): δ 0.95 (s, 24H, Me), 2.31 (s, 6H,
Me), 6.63 (m, 2H, Arom-H), 6.90 (m, 2H, Arom-H), 7.21 (m, 2H,
Arom-H), 7.45 (t, 3JHH ) 7.8 Hz, 1H, Py-H), 8.05 (m, 2H, Arom-

Modification of Iron(II) Tridentate Bis(imino)pyridine Complexes
Organometallics, Vol. 27, No. 8, 2008 1909
Figure 7. Distribution of R-olefins from C-2 to C-14 for precatalysts 1, 21, 22, and 23.
H), 8.50 (d, 3JHH ) 7.8 Hz, 2H, Py-H). 13C NMR (500 MHz, Tol-
D8, (selected signals)): 165.8 (CdN). Anal. Calcd for
C33H41B2N3O4 (MW: 565.32): C, 70.11; H, 7.31; N, 7.43. Found:
C, 70.29; H, 7.33; N, 7.64.
2,6-Bis[1-(2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylimino)ethyl]pyridineiron(II) Chloride (3). A 1.31 g (0.0023
mol) sample of 2,6-bis[1-(2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-
2-yl)phenylimino)ethyl]pyridine (6) was dissolved in 40 mL of
THF. Iron(II) chloride (0.26 g, 0.0021 mol) was added in the
reaction mixture in one portion. The resultant blue precipitate was
filtered after 12 h of stirring, washed twice by 20 mL of pentane,
and dried at 1 mm vacuum. Yield of 2,6-bis[1-(2-(4,4,5,5-
tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino)ethyl]pyridineiro-
(500 MHz, CD2Cl2, TMS): δ 1.95 (s, 6H, Me), 2.22 (s, 3H, Me),
2.30 (s, 3H, Me), 6.80 (s, 2H, Arom-H), 7.95 (t, 3JHH)8.0 Hz, 1H,
Py-H), 8.15 (d, 3JHH ) 8.0 Hz, 1H, Py-H), 8.40 (d, 3JHH ) 8.0 Hz,
1H, Py-H). 13C NMR (500 MHz, CD2Cl2, TMS (selected signals)):
δ 168.4 (CdN), 199.5 (CdO). Anal. Calcd for C17H17BrN2O (MW:
345.23): C, 59.14; H, 4.96; N, 8.11. Found: C, 59.18; H, 5.07; N,
8.15.
δ
[1-(6-{1-[2-(4,4,5,5-Tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amine (11). A 5.0 g (0.0178 mol) sample of 1-{6-[1-(2,4,6-
trimethylphenylimino)ethyl]pyridin-2-yl}ethanone (9), 5.0 g (0.0228
mol) of 2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylamine
(5), 100 mL of toluene, and 100 g of fresh molecular sieves were
kept at 100 °C for 3 days. The molecular sieves were removed by
filtration. The solvent was removed in a rotary evaporator, and the
residue was recrystallized from 10 mL of ethanol. The yield of
[1-(6-{1-[2-4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}-
pyridin-2-yl)ethylidene](2,4,6-trimethylphenyl)amine (11) was 3.91 g
(71%) as a pale yellow solid. 1H NMR (500 MHz, Tol-D8, TMS):
δ 1.10 (s, 12H, Me), 2.00 (s, 6H, Me), 2.25 (s, 3 H, Me), 2.30 (s,
3H, Me), 2.45 (s, 3H, Me), 6.40 (m, 1H, Arom-H), 6.60 (m, 1H,
Arom-H), 7.00 (m, 1H, Arom-H), 7.20 (m, 1H, Arom-H), 7.50 (t,
n(II) chloride (3) was 1.31
g (92%). Anal. Calcd for
C33H41B2Cl2FeN3O4 (MW: 692.07): C, 57.27; H, 5.97; N, 6.07.
Found: C, 57.46; H, 6.09; N, 6.24. The structure was determined
by X-ray analysis.
1-{6-[1-(2,4,6-Trimethylphenylimino)ethyl]pyridin-2-yl}eth-
anone (9). A 20.0 g (0.123 mol) sample of 1-(6-acetylpyridin-2-
yl)ethanone (4), 14.92 g (0.110 mol) of 2,4,6-trimethylphenylamine
(7), and 300 mL of n-propanol with a few crystals of p-
toluenesulfonic acid were stirred at room temperature for 36 h in
a 500 mL flask under the flow of nitrogen. The resultant yellow
precipitate was filtered and washed by 20 mL of methanol. It was
then dried at 1 mm vacuum overnight. The yield of 1-{6-[1-(2,4,6-
trimethylphenylimino)ethyl]pyridin-2-yl}ethanone (9) was 9.01 g
3JHH ) 8.0 Hz, 1H, Py-H), 7.90 (s, 2H, Arom-H), 8.10 (d, 3JHH
)
8.0 Hz, 1H, Py-H), 8.55 (d, 3JHH ) 8.0 Hz, 1H, Py-H). 13C NMR
(500 MHz, Tol-D8, (selected signals)): δ 166.17 (CdN), 167.60
(CdN). Anal. Calcd for C30H36BN3O2 (MW: 481.44): C, 74.84;
H, 7.54; N, 8.73. Found: C, 75.05; H, 7.63; N, 8.92.
1
(26%) as a yellow solid. H NMR (500 MHz, CD2Cl2, TMS): δ
1.90 (s, 6H, Me), 2.20 (s, 3H, Me), 2.28 (s, 3H, Me), 2.75 (s, 3H,
(4-Bromo-2,6-dimethylphenyl)[1-(6-{1-[2-(4,4,5,5-tetrameth-
yl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-yl)eth-
ylidene]amine (12). A 6.30 g (0.0182 mol) sample of 1-{6-[1-(4-
bromo-2,6-dimethylphenylimino)ethyl]pyridin-2-yl}ethanone (10),
5.0 g (0.0228 mol) of 2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-
2-yl)phenylamine (5), 100 mL of toluene, and 100 g of fresh
molecular sieves were kept at 100 °C for 3 days. The molecular
sieves were removed by filtration. The solvent was removed in a
rotary evaporator, and the residue was recrystallized from 10 mL
of ethanol. The yield of (4-bromo-2,6-dimethylphenyl)[1-(6-{1-[2-
(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}-
pyridin-2-yl)ethylidene]amine (12) was 9.40 g (94%) as a pale
3
Me), 6.90 (s, 2H, Arom-H), 7.90 (t, JHH ) 8.0 Hz, 1H, Py-H),
3
3
8.09 (d, JHH ) 8.0 Hz, 1H, Py-H), 8.55 (d, JHH ) 8.0 Hz, 1H,
Py-H). 13C NMR (500 MHz, CD2Cl2, TMS (selected signals)): δ
167.3 (CdN), 200.0 (CdO). Anal. Calcd for C18H20N2O (MW:
280.36): C, 77.11; H, 7.19; N, 9.99. Found: C, 77.13; H, 7.20; N,
10.20.
1-{6-[1-(4-Bromo-2,6-dimethylphenylimino)ethyl]pyridin-2-
yl}ethanone (10). A 22.5 g (0.138 mol) sample of 1-(6-acetylpy-
ridin-2-yl)ethanone (4), 25.0 g (0.125 mol) of 4-bromo-2,6-
dimethylphenylamine (8), and 300 mL of n-propanol with a few
crystals of p-toluenesulfonic acid were stirred at room temperature
for 36 h in a 500 mL flask under the flow of nitrogen. The resultant
yellow precipitate was filtered and washed by 20 mL of methanol.
It was then dried at 1 mm vacuum overnight. The yield of 1-{6-
[1-(4-bromo-2,6-dimethylphenylimino)ethyl]pyridin-2-
1
yellow solid. H NMR (500 MHz, C6D6, TMS): δ 1.10 (s, 12H,
Me), 2.04 (s, 6H, Me), 2.20 (s, 3H, Me), 2.24 (s, 3H, Me), 6.90 (s,
2H, Arom-H), 7.15 (m, 1H, Arom-H), 7.20 (m, 1H, Arom-H), 7.30
3
(t, JHH ) 8.0 Hz, 1H, Py-H), 7.80 (s, 1H, Arom-H), 7.90 (s, 1H,
1
yl}ethanone (10) was 19.08 g (44%) as a yellow solid. H NMR
Arom-H), 8.45 (d, 3JHH ) 8.0 Hz, 1H, Py-H), 8.50 (d, 3JHH ) 8.0

1910 Organometallics, Vol. 27, No. 8, 2008
Ionkin et al.
Hz, 1H, Py-H). 13C NMR (500 MHz, C6D6, (selected signals)): δ
166.96 (CdN), 167.18 (CdN). Anal. Calcd for C29H33BBrN3O2
(MW: 546.31): C, 63.76; H, 6.09; N, 7.69. Found: C, 63.82; H,
6.18; N, 7.79.
[1-(6-{1-[2-(4,4,5,5-Tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amineiron(II) Chloride (19). A 6.10 g (0.0127 mol) sample
of [1-(6-{1-[2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phen-
ylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethylphenyl)-
amine (11) was dissolved in 50 mL of THF. Then 1.12 g (0.0088
mol) of iron(II) chloride was added in the reaction mixture in one
portion. The resultant blue precipitate was filtered after 12 h of
stirring, washed twice by 20 mL of pentane, and dried at 1 mm
vacuum. Yield of [1-(6-{1-[2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-
2-yl)phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amineiron(II) chloride (19) was 3.48 g (45%). Anal. Calcd
for C30H36BCl2FeN3O2 (MW: 608.19): C, 59.25; H, 5.97; N, 6.91.
Found: C, 59.34; H, 6.11; N, 7.03. The structure was determined
by X-ray analysis.
[1-(6-{1-[3-(4,4,5,5-Tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amine (14). A 5.76 g (0.0205 mol) sample of 1-{6-[1-(2,4,6-
trimethylphenylimino)ethyl]pyridin-2-yl}ethanone (9), 5.00 g (0.0228
mol) of 3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylamine
(13), 100 mL of toluene, and 100 g of fresh molecular sieves were
kept at 100 °C for 3 days. The molecular sieves were removed by
filtration. The solvent was removed in a rotary evaporator, and the
residue was recrystallized from 10 mL of ethanol. The yield of
[1-(6-{1-[3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]-
ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethylphenyl)amine (14) was
(4-Bromo-2,6-dimethylphenyl)[1-(6-{1-[2-(4,4,5,5-tetra-
methyl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-
yl)ethylidene]amineiron(II) Chloride (20). A 9.00 g (0.0165 mol)
sample of (4-bromo-2,6-dimethylphenyl)[1-(6-{1-[2-(4,4,5,5-
tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-
yl)ethylidene]amine (12) was dissolved in 50 mL of THF. Then
1.25 g (0.0099 mol) of iron(II) chloride was added in the reaction
mixture in one portion. The resultant blue precipitate was filtered
after 12 h of stirring, washed twice by 20 mL of pentane, and dried
at 1 mm vacuum. Yield of (4-bromo-2,6-dimethylphenyl)[1-(6-
{1-[2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}-
pyridin-2-yl)ethylidene]amineiron(II) chloride (20) was 3.19 g
(48%). Anal. Calcd for C29H33BBrCl2FeN3O2 (MW: 673.06): C,
51.75; H, 4.94; N, 6.24. Found: C, 51.92; H, 5.18; N, 6.37.
1
8.70 g (88%) as a pale yellow solid. H NMR (500 MHz, C6D6,
TMS): δ 1.05 (s, 12H, Me), 2.10 (s, 6H, Me), 2.30 (s, 3H, Me),
2.35 (s, 3H, Me), 2.40 (s, 3H, Me), 6.93 (s, 2H, Arom-H), 7.20
(m, 1H, Arom-H), 7.25 (m, 1H, Arom-H), 7.34 (t, 3JHH ) 8.0 Hz,
1H, Py-H), 7.91 (s, 1H, Arom-H), 7.98 (s, 1H, Arom-H), 8.40 (d,
3JHH ) 8.0 Hz, 1H, Py-H), 8.55 (d, 3JHH ) 8.0 Hz, 1H, Py-H). 13
C
NMR (500 MHz, C6D6, (selected signals)): δ 166.96 (CdN), 167.18
(CdN). Anal. Calcd for C30H36BN3O2 (MW: 481.44): C, 74.84;
H, 7.54; N, 8.73. Found: C, 74.96; H, 7.55; N, 8.75.
[1-(6-{1-[4-(4,4,5,5-Tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amine (17). A 3.20 g (0.0114 mol) sample of 1-{6-[1-(2,4,6-
trimethylphenylimino)ethyl]pyridin-2-yl}ethanone (9), 2.50 g (0.0114
mol) of 4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylamine
(16), 100 mL of toluene, and 100 g of fresh molecular sieves were
kept at 100 °C for 3 days. The molecular sieves were removed by
filtration. The solvent was removed in a rotary evaporator, and the
residue was recrystallized from 10 mL of ethanol. The yield of
[1-(6-{1-[4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]-
ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethylphenyl)amine (17) was
4.62 g (84%) as a pale yellow solid. 1H NMR (500 MHz, Tol-D8,
TMS): δ 1.15 (s, 12H, Me), 2.05 (s, 6H, Me), 2.20 (s, 3H, Me),
2.25 (s, 3H, Me), 2.30 (s, 3H, Me), 6.80 (m, 2H, Arom-H), 7.06
(m, 2H, Arom-H), 7.40 (t, 3JHH ) 8.0 Hz, 1H, Py-H), 8.20 (s, 2H,
Arom-H), 8.40 (d, 3JHH ) 8.0 Hz, 1H, Py-H), 8.50 (d, 3JHH ) 8.0
Hz, 1H, Py-H). 13C NMR (500 MHz, Tol-D8, (selected signals)):
δ 166.51 (CdN), 167.97 (CdN). Anal. Calcd for C30H36BN3O2
(MW: 481.44): C, 74.84; H, 7.54; N, 8.73. Found: C, 75.02; H,
7.59; N, 8.90.
[1-(6-{1-[3-(4,4,5,5-Tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amineiron(II) Chloride (21). A 8.00 g (0.0166 mol)
amountof[1-(6-{1-[3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phen-
ylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethylphen-
yl)amine (14) was dissolved in 50 mL of THF. Then 1.26 g (0.0099
mol) of iron(II) chloride was added in the reaction mixture in one
portion. The resultant blue precipitate was filtered after 12 h of
stirring, washed twice by 20 mL of pentane, and dried at 1 mm
vacuum. Yield of [1-(6-{1-[3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-
2-yl)phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amineiron(II) chloride (21) was 4.12 g (68%). Anal. Calcd
for C30H36BCl2FeN3O2 (MW: 608.19): C, 59.25; H, 5.97; N, 6.91.
Found: C, 59.36; H, 6.24; N, 7.08.
[1-(6-{1-[4-(4,4,5,5-Tetramethyl[1,3,2]dioxaborolan-2-yl)-
phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amineiron(II) Chloride (22). A 1.00 g (0.0021 mol) portion
of [1-(6-{1-[4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phen-
ylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethylphen-
yl)amine (17) was dissolved in 60 mL of THF. Then 0.25 g (0.0020
mol) of iron(II) chloride was added in the reaction mixture in one
portion. The resultant blue precipitate was filtered after 12 h of
stirring, washed twice by 20 mL of pentane, and dried at 1 mm
vacuum. Yield of [1-(6-{1-[4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-
2-yl)phenylimino]ethyl}pyridin-2-yl)ethylidene](2,4,6-trimethyl-
phenyl)amineiron(II) chloride (22) was 1.04 g (87%). Anal. Calcd
for C30H36BCl2FeN3O2 (MW: 608.19): C, 59.25; H, 5.97; N, 6.91.
Found: C, 59.48; H, 6.14; N, 7.05. The structure was determined
by X-ray analysis.
4-Bromo-2,6-dimethylphenyl)[1-(6-{1-[4-(4,4,5,5-tetramethyl-
[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-yl)eth-
ylidene]amine (18). A 7.10 g (0.0114 mol) sample of 1-{6-[1-(4-
bromo-2,6-dimethylphenylimino)ethyl]pyridin-2-yl}ethanone (10),
5.0 g (0.0228 mol) of 4-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-
2-yl)phenylamine (16), 100 mL of toluene, and 100 g of fresh
molecular sieves were kept at 100 °C for 3 days. The molecular
sieves were removed by filtration. The solvent was removed in a
rotary evaporator, and the residue was recrystallized from 10 mL
of ethanol. The yield of (4-bromo-2,6-dimethylphenyl)[1-(6-{1-[4-
(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}-
pyridin-2-yl)ethylidene]amine (18) was 8.20 g (73%) as a pale
yellow solid. 1H NMR (500 MHz, CD2Cl2, TMS): δ 1.30 (s, 12H,
Me), 2.00 (s, 6H, Me), 2.20 (s, 3H, Me), 2.45 (s, 3H, Me), 6.70
(m, 2H, Arom-H), 7.20 (s, 2H, Arom-H), 7.80 (m, 2H, Arom-H),
(4-Bromo-2,6-dimethylphenyl)[1-(6-{1-[4-(4,4,5,5-tetrameth-
yl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-yl)eth-
ylidene]amineiron(II) Chloride (23). A 2.00 g (0.00366 mol)
amount of (4-bromo-2,6-dimethylphenyl)[1-(6-{1-[4-(4,4,5,5-
tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}pyridin-2-
yl)ethylidene]amine (18) was dissolved in 50 mL of THF. Then
0.41 g (0.0032 mol) of iron(II) chloride was added in the reaction
mixture in one portion. The resultant blue precipitate was filtered
after 12 h of stirring, washed twice by 20 mL of pentane, and dried
3
3
7.90 (t, JHH ) 8.0 Hz, 1H, Py-H), 8.30 (d, JHH ) 8.0 Hz, 1H,
Py-H), 8.45 (d, JHH ) 8.0 Hz, 1H, Py-H). 13C NMR (500 MHz,
3
CD2Cl2, (selected signals)): δ 167.39 (CdN), 168.32 (CdN). Anal.
Calcd for C29H33BBrN3O2 (MW: 546.31): C, 63.76; H, 6.09; N,
7.69. Found: C, 63.91; H, 6.20; N, 7.83.

Modification of Iron(II) Tridentate Bis(imino)pyridine Complexes
Organometallics, Vol. 27, No. 8, 2008 1911
at 1 mm vacuum. Yield of (4-bromo-2,6-dimethylphenyl)[1-(6-{1-
[4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenylimino]ethyl}-
pyridin-2-yl)ethylidene]amineiron(II) chloride (23) was 1.96 g
(90%). Anal. Calcd for C29H33BBrCl2FeN3O2 (MW: 673.06): C,
51.75; H, 4.94; N, 6.24. Found: C, 51.93; H, 5.19; N, 6.31.
General Conditions of the Oligomerizations. Ethylene oligo-
merizations are done in a 1 L stainless steel Autoclave Engineers
Zipperclave. Catalyst and cocatalyst are charged separately using
stainless steel injection tubes. The complexes 1, 19, 20, 21, 22,
and 23 are activated by modified methylaluminoxane (MMAO).
The steps for a typical oligomerization are as follows. The injectors
are charged in a glovebox. The cocatalyst is obtained as a 7 wt %
solution in o-xylene and is charged as such into the injector
assembly along with a 10 mL chase of o-xylene. The catalysts are
prepared as suspensions in o-xylene (10 mg/100 mL). A sample is
pulled from a well-stirred suspension and is added to a 10 mL
charge of o-xylene. The injectors are attached to autoclave ports
equipped with dip tubes. Nitrogen is sparged through the loose
fittings at the attachment points prior to making them tight. The
desired charge of o-xylene is then pressured into the autoclave.
The agitator and heater are turned on. When the desired temperature
is reached, the cocatalyst is charged to the clave by blowing ethylene
down through the cocatalyst injector. After a significant pressure
rise is seen in the autoclave to indicate the cocatalyst and chase
solvent have entered, the injector is isolated from the process using
its valves. The pressure controller is then set to 5 psig below the
desired ethylene operating pressure and is put in the automatic mode
to allow it to control the operation of the ethylene addition valve.
When the pressure is 5 psig below the desired operating pressure,
the controller is put into manual mode and the valve is set to 0%
output. When the batch temperature is stable at the desired value,
the catalyst is injected using enough nitrogen such that the reactor
pressure is boosted to the desired pressure. At the same time as
the catalyst injection, the pressure controller is put in the automatic
mode and the oligomerization is started. The 5 psi boost is obtained
routinely by having a small reservoir between the nitrogen source
and the catalyst injector. A valve is closed between the nitrogen
source and the reservoir prior to injecting the catalyst so the same
volume of nitrogen is used each time to inject the catalyst
suspension. To stop the oligomerization, the pressure controller is
put into manual, the ethylene valve is closed, and the reactor is
cooled. The reaction time is 1 h.
X-Ray Diffraction Studies. Data for all structures were collected
using a Bruker CCD system at -100 °C. Structure solution and
refinement were performed using the Shelxtl14 set of programs.
The Platon-Squeeze15 program was used to correct the data where
the solvent molecules could not be correctly modeled.
Acknowledgment. The authors wish to thank Kurt Adams
for funding the X-ray research.
Supporting Information Available: Crystallographic informa-
tion (CIF file) for compounds 1, 3, 19, 21, 22, and 23. These
materialsareavailablefreeofchargeviatheInternetathttp://pubs.acs.org.
OM800036B
(14) Sheldrick, G. Shelxtl Software Suite, Version 5.1;Bruker AXS Corp.:
Madison, WI., 1997.
(15) Spek A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 2005.