Aluminum alkyl-mediated route to novel N,N,O-chelates for five-coordinate Iron(II) chloride complexes: Synthesis, structures, and ethylene polymerization studies

Article abstract of DOI:10.1021/om700611q

Two five-coordinate iron(II) chloride complexes bearing 2-imine-6-(methyl alcohol)pyridine chelates have been prepared via an aluminum-mediated methyl migration route from the corresponding 2-acetyl-6-iminopyridine. Both iron complexes display moderate ac

Full text of DOI:10.1021/om700611q

Organometallics 2007, 26, 5119-5123
5119
Notes
Aluminum Alkyl-Mediated Route to Novel N,N,O-Chelates for
Five-Coordinate Iron(II) Chloride Complexes: Synthesis,
Structures, and Ethylene Polymerization Studies
Vernon C. Gibson,† Carl Redshaw,*,‡ Gregory A. Solan,*,§ Andrew J. P. White,† and
David J. Williams†
Department of Chemistry, Imperial College, South Kensington, London SW7 2AY, U.K., Wolfson Materials
and Catalysis Centre, School of Chemical Sciences and Pharmacy, UniVersity of East Anglia, NR4 7TJ,
U.K., and Department of Chemistry, UniVersity of Leicester, UniVersity Road, Leicester, LE1 7RH, U.K.
ReceiVed July 11, 2007
Chart 1. 2,6-Bis(imino)pyridine (A), 2-Imino-6-
(methylamino)pyridine (B), 2-Acetyl-6-iminopyridine (L1),
and 2-Imine-6-(methyl alcohol)pyridine (L2)
Summary: Two fiVe-coordinate iron(II) chloride complexes
bearing 2-imine-6-(methyl alcohol)pyridine chelates haVe been
prepared Via an aluminum-mediated methyl migration route
from the corresponding 2-acetyl-6-iminopyridine. Both iron
complexes display moderate actiVity for ethylene polymerization
on treatment with excess methylaluminoxane, affording highly
linear polymers along with some oligomeric products.
Introduction
Since the discovery that sterically bulky 2,6-bis(arylimino)-
pyridine ligands (A, Chart 1) can impart late transition metals,
and in particular iron, with extremely high activities for ethylene
oligomerization and polymerization,1,2 considerable effort has been
devoted to catalyst modification with a view to enhancing both
activity and control of the microstructure of the resulting poly-
mer.3 In particular, changes to the basic bis(imino)pyridine ligand
motif have been targeted, with modifications to the N-imine sub-
stituents,1-3 the C-imino substituents,3a,4 and the central pyridine
substituents at the forefront.3a,5 More significant variations includ-
ing substitution of one of the imino groups in A for an amino (B,
Chart 1),6 pyridyl,7 thiophenyl,8 furanyl,8 acetyl (L1, Chart 1),9
or ethylcarboxylato10 group have also been reported, with the
corresponding iron (and cobalt) catalysts showing low to high
activities for both ethylene oligomerization and polymerization.
During the development of these new ligand systems, a
number of elegant organometallic synthetic strategies have come
to the fore including the use of trimethylaluminum to modify
A to give, following hydrolysis, the selectively reduced B.6,11
Indeed, the reactivity of A toward a range of alkylaluminums
alone has proved most intriguing, with aluminum-based products
* To whom correspondence should be addressed. E-mail:
Carl.Redshaw@uea.ac.uk (C.R.) and gas8@le.ac.uk (G.A.S.).
† Imperial College.
‡ University of East Anglia.
§ University of Leicester.
(1) (a) Small B. L.; Brookhart, M.; Bennet, A. M. A. J. Am. Chem. Soc.
1998, 120, 4049. (b) Small, B. L.; Brookhart, M. Macromolecules 1999,
32, 2120. (c) Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143.
(2) (a) 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. (b) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.;
Kimberley, B. S.; Maddox, P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw,
C.; Solan, G. A.; Stro¨mberg, S.; White, A. J. P.; Williams, D. J. J. Am.
Chem. Soc. 1999, 121, 8728.
(3) For reviews see: (a) Gibson, V. C.; Redshaw, C.; Solan, G. A. Chem.
ReV. 2007, 107, 1745. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV.
2003, 103, 283. (c) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew.
Chem., Int. Ed. 1999, 38, 428. (d) Ittel, S. D.; Johnson, L. K.; Brookhart,
M. Chem. ReV. 2000, 100, 1169. (e) Mecking, S. Angew. Chem., Int. Ed.
2001, 40, 534. (f) Bianchini, C.; Giambastiani, G.; Rios, G. I.; Mantovani,
G.; Meli, A.; Segarra, A. M. Coord. Chem. ReV. 2006, 250, 1391.
(4) (a) Kleigrewe, N.; Steffen, W.; Blo¨mker, T.; Kehr, G.; Fro¨hlich, R.;
Wibbeling, B.; Erker, G.; Wasilke, J.-C.; Wu G.; Bazan, G. C. J. Am. Chem.
Soc. 2005, 127, 13955. (b) Smit, T.; Tomov, A. K.; Gibson, V. C.; White,
A. J. P.; Williams, D. J. Inorg. Chem. 2004, 43, 6511.
(6) (a) Britovsek, G. J. P.; Gibson, V. C.; Mastroianni, S.; Redshaw, C.;
Solan, G. A.; White, A. J. P.; Williams, D. J. Eur. J. Inorg. Chem. 2001, 431.
(b) Gibson, V. C.; Kimberley, B. S.; Solan, G. A. (BP) WO0020427, 2000.
(7) Britovsek, G. J. P.; Baugh, S. P. D.; Hoarau, O.; Gibson, V. C.; Wass,
D. F.; White, A. J. P.; Williams, D. J. Inorg. Chim. Acta 2003, 345, 279.
(8) (a) Bianchini, C.; Mantovani, G.; Meli, A.; Migliacci, F.; Laschi, F.
Organometallics 2003, 22, 2545. (b) Bianchini, C.; Giambastiani, G.;
Mantovani, G.; Meli, A.; Mimeau, D. J. Organomet. Chem. 2004, 689,
1356. (c) Bianchini, C.; Gatteschi, D.; Giambastiani, G.; Rios, I. G.; Ienco,
A.; Laschi, F.; Mealli, C.; Meli, A.; Sorace, L.; Toti, A.; Vizza, F.
Organometallics 2007, 26, 726.
(9) (a) Kaul, F. A. R.; Puchta, G. T.; Frey, G. D.; Herdtweck, E.;
Herrmann, W. A. Organometallics 2007, 26, 988. (b) Fernandes, S.;
Bellabarba, R. M.; Ribeiro, A. F. G.; Gomes, P. T.; Ascenso, J. R.; Mano,
J. F.; Dias, A. R.; Marques, M. M. Polym. Int. 2002, 51, 1301. (c) Bennett,
A. M. A. (DuPont) U.S. Patent 5955555, 1999. (d) Sommazzi, A.; Milani,
B.; Proto, A.; Corso, G.; Mestroni, G.; Masi, F. (Enichem) WO0110875,
2001. (e) de Boer, E. J. M.; Deuling, H. H.; van der Heijden, H.; Meijboom,
N.; van Oort, A. B. (Shell) W00158874, 2001.
(10) (a) Sun, W. -H.; Tang, X.; Gao, T.; Wu, B.; Zhang, W.; Ma, H.
Organometallics 2004, 23, 5037. (b) Su, B.-Y.; Zhao, J.-S. Polyhedron 2006,
25, 3289.
(11) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan, G. A.; White, A. J.
P.; Williams, D. J. Chem. Commun. 1998, 2523.
(5) (a) Nu¨ckel, S.; Burger, P. Organometallics 2001, 20, 4345. (b) Seitz,
M.; Milius, W.; Alt, H. G. J. Mol. Catal. A: Chem. 2006, 261, 246. (c)
Kim, I.; Heui Han, B.; Ha, C.-S.; Kim, J. -K.; Suh, H. Macromolecules
2003, 36, 6689.
10.1021/om700611q CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/24/2007

5120 Organometallics, Vol. 26, No. 20, 2007
Notes
a
Scheme 1
Figure 1. Molecular structure of one (A) of the two independent
molecules present in the crystals of 1a (50% probability ellipsoids);
hydrogen atoms omitted for clarity. Selected bond lengths (Å) and
angles (deg): Al(1)-O(7) 1.907(3), Al(1)-N(1) 1.994(4), Al(1)-
C(24) 1.952(5), Al(1)-C(25) 1.959(5), Al(1)‚‚‚N(10) 2.427(4), Al-
(2)-O(7) 1.917(3), Al(2)-C(26) 1.984(5), Al(2)-C(27) 1.983(5),
Al(2)-C(28) 1.986(5), C(7)-O(7) 1.436(5), C(10)-N(10) 1.288-
(5), C(24)-Al(1)-C(25) 125.2(3), O(7)-Al(1)‚‚‚N(10) 152.82(13),
O(7)-C(7)-C(8) 110.2(4), O(7)-C(7)-C(9) 109.4(4), O(7)-Al-
(2)-C(26) 106.2(2), C(26)-Al(2)-C(27) 112.2(3), C(27)-Al(2)-
C(28) 111.4(2).
a
Reagents and conditions: (i) ArNH2, EtOH, H+; (ii) 2AlMe3, 100
°C, 12 h, toluene; (iii) H2O, room temperature; (iv) FeCl2, 90 °C, 15
min, n-BuOH.
full structural description see the Supporting Information. The
geometry at Al(1) is best described as trigonal pyramidal, the
metal lying ca. 0.19 Å [0.20 Å] out of the basal {N(1),C(24),C-
(25)} plane in the direction of the apical atom O(7). The imino
nitrogen N(10) approaches the opposite face of the basal plane
at a distance of 2.427(4) Å [2.472(4) Å], a value significantly
shorter than that of 2.575(4) Å seen in the closely related imino-
amide-pyridine species [2-(ArNdCH)-6-(ArNCHMe)C5H3N]-
AlMe2 (Ar ) 2,4,6-Me3C6H2).11 The Al-N(1)pyridine distance
of 1.994(4) Å [1.978(3) Å] is significantly shorter than that seen
in the imino-amide-pyridine complex11 [2.029(4) Å], probably
reflecting the difference between the 6-(OCMe2) unit here in
1a and the corresponding 6-(ArNCHMe) moiety in the literature
species. The Al-O(7) separations do not differ significantly,
being 1.907(3) Å [1.915(3) Å] to Al(1) and 1.917(3) Å [1.911-
(3) Å] to Al(2); the geometry at O(7) is trigonal planar. The
geometry at Al(2) is only slightly distorted tetrahedral, with
angles in the range 106.2(2)-112.2(3)° [105.3(2)-114.9(3)°].
being isolated from alkyl migration to not only the imine carbon
but also the pyridine C2 and C4 positions.12-14
In this note we are concerned with employing trimethylalu-
minum to mediate the formation of 2-imine-6-(methyl alcohol)-
pyridine (L2, Chart 1) from L1. In addition, full characterization
of the resultant iron(II) halide complexes is reported and their
application as precatalysts for ethylene oligomerization/polym-
erization probed.
Our entry point into this work is the 2-acetyl-6-iminopy-
ridines, 2-(OdCMe)-6-(ArNdCMe)C5H3N (Ar ) 2,6-i-Pr2C6H3,
L1a; 2,4,6-Me3C6H2, L1b), which are readily accessible by the
condensation reaction of equimolar amounts of the correspond-
ing aniline.1b,6b,9,15 On treatment with Me3Al (2 equiv), both
L1a and L1b undergo alkylation of the ketone moiety of the
ligand backbone and concomitant adduct formation to afford
the air-sensitive bimetallic 2-imino-6-methoxidepyridine com-
plexes [2-(ArNdCMe)-6-{(Me3Al)OCMe2}C5H3N]AlMe2 (Ar
) 2,6-i-Pr2C6H3, 1a; 2,4,6-Me3C6H2, 1b) in good yield (>70%)
(Scheme 1). Complexes 1a and 1b have been both characterized
by 1H NMR spectrocopy and give satisfactory microanalytical
data (see Experimental Section). In addition, a single-crystal
X-ray diffraction study was performed on 1a.
Green-yellow crystals of 1a suitable for a structure determi-
nation were grown by the slow cooling of a saturated hot aceto-
nitrile solution. The complex crystallizes with two independent
molecules (A and B) in the asymmetric unit with only minor
variations apparent between molecules. A perspective view of
molecule A in 1a is depicted in Figure 1, along with selected
bond distances and angles. The following discussion refers to
one of the independent molecules (A), the values in square
brackets being for the second independent molecule (B); for a
1
In the H NMR spectra of 1a and 1b, the Me2C-O protons
are seen as singlets at ca. δ 1.82, while the aluminum-methyl
resonances are observed more upfield as two distinct singlets
(1a δ-0.67, -0.83; 1b δ-0.70, -0.83). The presence of inequiv-
alent aluminum-methyl environments is further supported in the
13C{1H} NMR spectrum of 1b with two resonances at δ -3.2
and -4.5 for the Al-Me carbon atoms. While the FAB mass spec-
trum of 1b gave little information, the spectrum for 1a displayed
a peak corresponding to the molecular ion; as expected, this
peak is short-lived and decays over a period of minutes.
Hydrolysis of 1a and 1b smoothly generates the protonated
ligands 2-(ArNdCMe)-6-{(HO)CMe2}C5H3N (Ar ) 2,6-i-
Pr2C6H3, L2a; 2,4,6-Me3C6H2, L2b) as pale yellow solids in
1
good yield (>70%) (Scheme 1). Characterization by H and
13C NMR and IR spectroscopy and EI mass spectrometry
supports the formulations (see Experimental Section). Reaction
of L2 with FeCl2 in n-BuOH at elevated temperature gives the
high-spin N,N,O-chelate iron complexes [2-(ArNdCMe)-6-
{(HO)CMe2}C5H3N]FeCl2 (Ar ) 2,6-i-Pr2C6H3, 2a; 2,4,6-
Me3C6H2, 2b), in high (2a, ca. 77%) and moderate (2b, ca. 32%)
isolated yield (Scheme 1). Complexes 2a and 2b have been
characterized by FAB mass spectrotrometry and magnetic
susceptibility measurements and give satisfactory microanalyti-
(12) Milione, S.; Cavallo, G.; Tedesco, C.; Grassi, A. J. Chem. Soc.,
Dalton Trans. 2002, 1839.
(13) Knijnenburg, Q.; Smits, J. M. M.; Budzelaar, P. H. M. C. R. Chim.
2004, 7, 865. (b) Knijnenburg, Q.; Smits, J. M. M.; Budzelaar, P. H. M.
Organometallics 2006, 25, 1036.
(14) Knijnenburg, Q.; Gambarotta, S.; Budzelaar, P. H. M. Dalton Trans.
2006, 5442.
(15) Small, B. L.; Carney, M. J.; Holman, D. M.; O’Rourke, C. E. Halfen,
J. A. Macromolecules 2004, 37, 4375.

Notes
Organometallics, Vol. 26, No. 20, 2007 5121
tively.1,2 Indeed a pronounced bimodal distribution is seen with
2a/MAO, a feature that is common for bis(imino)pyridine iron
precatalysts in the presence of large excesses of MAO.1-3 It is
probable that as with precedents in this area,1,2 the lower
molecular weight peak corresponds (Mpk ) 1340) to an almost
1
fully saturated material. This is supported by the H NMR
spectra of the oligomeric fractions obtained during both runs,
which show significantly enhanced levels of methyl chain ends
(with regard to the vinylic ends). Furthermore, analysis of the
vinylic region of the spectra reveals the presence of greater than
99% R-olefins. It is apparent that these systems, as with bis-
(imino)pyridine iron catalysts,2b can facilitate chain-transfer
reactions by both â-H elimination and chain transfer to
aluminum.
In conclusion, we have successfully employed trimethylalu-
minum to promote the formation of a new family of tridentate
2-arylimino-6-(methylalcohol)pyridine N,N,O-ligands (L2), which
can be readily complexed with iron(II) chloride. Moderate
activities in ethylene polymerization are displayed for the
resultant catalysts with values significantly lower than in related
bis(arylimino)pyridine iron systems.
Figure 2. Molecular structure of 2a (50% probability ellipsoids);
hydrogen atoms (apart from H7) omitted for clarity. Selected bond
lengths (Å) and angles (deg): Fe-O(7) 2.173(6), Fe-N(1) 2.096-
(7), Fe-N(10) 2.201(7), Fe-Cl(1) 2.266(3), Fe-Cl(2) 2.304(2),
C(7)-O(7) 1.458(10), C(10)-N(10) 1.293(10), O(7)-Fe-N(10)
139.4(2), N(1)-Fe-Cl(1) 101.8(2), N(1)-Fe-Cl(2) 148.2(2), Cl-
(1)-Fe-Cl(2) 109.84(12), C(8)-C(7)-C(9) 110.2(9), N(10)-
C(10)-C(11) 125.2(8).
cal data (see Experimental Section). In addition, 2a has been
the subject of a single-crystal X-ray diffraction study.
Experimental Section
General Techniques and Materials. All manipulations were
carried out under an atmosphere of nitrogen using standard Schlenk
and cannula techniques or in a conventional nitrogen-filled glove-
box. Solvents were refluxed over an appropriate drying agent16 and
distilled and degassed prior to use. Elemental analyses were
performed by the microanalytical services of the Department of
Chemistry at Imperial College, London Metropolitan University,
and Medac Ltd. GPC data were recorded at Rapra Technology using
a Polymer Labs/Varian GPC220 instrument [with PLgel guard +
2 × mixed bed-B columns (30 cm, 10 µm)] at 160 °C in 1,2,4-
trichlorobenzene with a refractive index detector. NMR spectra were
recorded on a Bruker spectrometer at 250 MHz (1H) and 62.9 MHz
(13C) at 293 K; chemical shifts are referenced to the residual protio
impurity of the deuterated solvent; coupling constants are quoted
in Hz. IR spectra (Nujol mulls) were recorded on Perkin-Elmer
577 and 457 grating spectrophotometers. The EI (electron impact)
and FAB (fast atom bombardment) mass spectra were recorded
using a Kratos Concept spectrometer with NBA as the matrix.
Magnetic susceptibility studies were performed using an Evans
balance (Johnson Matthey) at room temperature. The magnetic
moment was calculated following standard methods,17 and correc-
tions for underlying diamagnetism were applied to data.18
Dark blue crystals of the iron complex 2a were grown from
a saturated solution of acetonitrile on prolonged standing at ambi-
ent temperature. A perspective view of 2a is shown in Figure
2 along with selected bond distances and angles (see Supporting
Information for a full structural discussion). The geometry at the
iron center is distorted square pyramidal with Cl(1) occupying
the apical site; the basal atoms Cl(2), N(1), O(7), and N(10)
are coplanar to within 0.01 Å with the metal lying ca. 0.59 Å
out of this plane in the direction of the apical atom. The Fe-
imine bond length of 2.201(7) Å is slightly shorter than that
typically seen in related species,1,2 possibly as a consequence
of the relatively long distance to the neutral donor O(7) [2.173-
(6) Å]; the Fe-pyridine separation is unexceptional.1,2,4-7
For both 2a and 2b, molecular ions along with peaks corres-
ponding to the loss of a chloride ligand are evident in their respec-
tive FAB mass spectra. In their IR spectra the ν(CdN) absorp-
tion bands are seen at ca. 1593 cm-1 and shifted (by ca. 28 cm-1)
to a lower wavenumber in comparison with that seen in the cor-
responding free ligand (L2). The magnetic susceptibility measure-
ments for 2a and 2b reveal magnetic moments of ca. 4.62 µB
(Evans balance at ambient temperature), which are consistent
with high-spin configurations possessing four unpaired electrons
(S ) 2).
The results of ethylene polymerization tests at 1 bar with
precatalysts 2a and 2b with methylaluminoxane (MAO) as
activator are collected in Table 1 (runs 1 and 2). The tests were
carried out in a Schlenk flask with toluene as the solvent. The
results show that both the new 2-imino-6-(methylalcohol)-
pyridine iron complexes on treatment with MAO are active
ethylene polymerization catalysts. The highest activity of 276
g mmol-1 h-1 bar-1 is obtained with 2b, which under similar
conditions is significantly less than that observed for the closest
related bis(imino)pyridine catalyst [2,6-{(2,4,6-Me3C6H2)Nd
CMe}2C5H3N]FeCl2/MAO,1,2 while in a similar range to the
imino-amine-pyridine catalyst [2-{(2,6-i-Pr2C6H3)NdCMe}-6-
{(2,6-i-Pr2C6H3)NHCMe2}C5H3N]FeCl2/MAO.6 The difference
in activity between 2a and 2b mirrors the trend seen for 2,6-
diisopropylphenyl versus mesityl bis(imino)pyridine catalysts.1-3
Inspection of the molecular weight data reveals very broad
molecular weight distributions for the polyethylene obtained
using 2a and 2b with Mw values comparable to those obtained
with [2,6-{(2,6-i-Pr2C6H3)NdCMe}2C5H3N]FeCl2/MAO and
[2,6-{(2,4,6-Me3C6H2)NdCMe}2C5H3N]FeCl2/MAO, respec-
Iron dichloride, trimethylaluminum (2.0 M in toluene), and
methylaluminoxane (10% solution in toluene) were purchased from
Aldrich Chemical Co. 2-Acetyl-6{1-((2,6-diisopropylphenyl)imino)-
ethyl}pyridine (L1a) and 2-acetyl-6{1-((2,4,6-trimethylphenyl)-
imino)ethyl}pyridine (L1b) were prepared using previously reported
procedures.9 CP grade ethylene (99.9%) was purchased from BOC
and used without further purification. All other chemicals were
obtained commercially and used as received unless stated otherwise.
Synthesis of [2-{(2,6-i-Pr2C6H3)NdCMe}-6-{(Me3Al)OCMe2}-
C5H3N]AlMe2 (1a). Trimethylaluminum (1.24 mL, 2.48 mmol) was
added dropwise to a solution of L1a (0.40 g, 1.24 mmol) in toluene
(40 mL) and the solution heated to reflux overnight. The volatiles
were removed under reduced pressure, and the product was
extracted into acetonitrile. Filtration followed by concentration and
prolonged standing at room temperature afforded green-yellow
1
blocks of 1a. Yield: 0.46 g, 79%. H NMR (CDCl3, 293 K): δ
2
2
8.30 (t, 1H, JHH ) 7.9 Hz, py-H), 8.01 (dd, 1H, JHH ) 7.8 Hz,
(16) Armarego W. L. F.; Perrin, D. D. In Purification of Laboratory
Chemicals, 4th ed.; Butterworth Heinemann, 1996.
(17) Mabbs, F. E.; Machin, D. J. Magnetism and Transition Metal
Complexes; Chapman and Hall: London, 1973.
(18) (a) O’Connor, C. J. Prog. Inorg. Chem. 1982, 29, 203. (b) Handbook
of Chemistry and Physics, 70th ed.; Weast, R. C., Ed.; CRC Press: Boca
Raton, FL, 1990; p E134.

5122 Organometallics, Vol. 26, No. 20, 2007
Table 1. Results of Ethylene Polymerization Runs Using Precatalysts 2a and 2ba
Notes
b
Mpk
mass of
polymer (g)
mass of
oligomer (g)
activity
run
precatalyst
(g mmol-1 h-1 bar-1
)
Mn
Mw
Mw/Mn
peak 1 (%)
1340 (59)
37 400 (100)
peak 2 (%)
81 400 (41)
b
b
b
1
2
2a
2b
1.699
2.755
0.037
0.064
170
276
2050
2820
13 4000
77 000
66
27
b
a Toluene solvent, 1 bar of ethylene, reaction time 1 h, 25 °C, 500 equiv of MAO as activator. GPC performed in 1,2,4-trichlorobenzene at 160 °C.
2
3JHH ) 0.8 Hz, py-H), 7.75 (d, 1H, JHH ) 8.2 Hz, py-H), 7.3 -
for C22H30Cl2N2OFe: C, 56.77; H, 6.45; N, 6.02. Found: C, 56.91;
H, 6.51; N, 5.91. µeff: 4.67 µΒ.
2
7.2 (m, 3H, Ar-H), 2.65 (sept, 2H, JHH ) 7.0 Hz, CHMe2), 2.31
2
(s, 3H, MeCdN), 1.83 (s, 6H, Me2C-O), 1.26 (d, 6H, JHH ) 6.3
Synthesis of [2-{(2,4,6-Me3C6H2)NdCMe}-6-{(HO)CMe2}-
C5H3N]FeCl2 (2b). By using the same procedure described for 2a,
compound 2b was obtained as a blue powder. Yield: 0.37 g, 32%.
2
Hz, CHMe2), 1.01 (d, 6H, JHH ) 6.3 Hz, CHMe2), -0.67 (s, 6H,
Me2Al), -0.83 (s, 9H, Me3Al). MS (FAB): m/z 467 [M + H]+.
Anal. Calcd for C27H44N2OAl2 (sample dried for 12 h in Vacuo):
C, 69.49; H, 9.51; N, 6.01. Found: C, 69.40; H, 9.47; N, 6.13.
IR (cm-1), ν(CdN) 1590. MS (FAB): m/z 423 [M+], 388 [M+
Cl]. Anal. Calcd for C19H24Cl2N2OFe: C, 53.90; H, 5.67; N, 6.62.
-
Synthesis of [2-{(2,4,6-Me3C6H2)NdCMe}-6-{(Me3Al)OCMe2}-
C5H3N]AlMe2 (1b). By using the same procedure described for
1a, compound 1b was obtained as a green-yellow powder. Yield:
0.41 g, 75%. 1H NMR (CDCl3, 293 K): δ 8.28 (t, 1H, 2JHH ) 8.8
Found: C, 54.11; H, 5.81; N, 6.41. µeff 4.57 µΒ.
Ethylene Polymerization/Oligomerization Evaluation. An oven-
dried 200 mL Schlenk vessel equipped with a magnetic stir bar was
evacuated and backfilled with nitrogen. The vessel was charged with
the precatalyst (0.01 mmol) and dissolved or suspended in toluene
(40 mL). MAO (5.0 mmol, 500 equiv) was introduced, and the
reaction mixture left to stir for 5 min. The vessel was purged with
ethylene, and the contents were magnetically stirred under 1 bar of
ethylene pressure at room temperature for the duration of the test.
After 1 h, the test was terminated by the addition of dilute aqueous
hydrogen chloride (5 mL) and the polymer collected, washed with
MeOH/H+ and then water, and dried in a vacuum oven at 40 °C
overnight. The yield of the polymer was recorded and the activity
calculated (g PE mmol-1 h-1 bar-1) for the 1 h period. The organic
soluble phase was separated, dried over magnesium sulfate, and
filtered, the solvent was removed under reduced pressure, and the
Hz, py-H), 7.98 (d, 1H, 2JHH ) 7.8 Hz, py-H), 7.74 (d, 1H, 2JHH
)
8.6 Hz, py-H), 6.92 (s, 2H, Ar-H), 2.30 (s, 3H, MeCdN), 2.22 (s,
3H, p-Ar-Me), 1.99 (s, 6H, o-Ar-Me), 1.82 (s, 6H, Me2C-O), -0.70
(s, 6H, Me2Al), -0.83 (s, 9H, Me3Al). 13C{1H} NMR (CDCl3, 293
K): δ 171.4 (Me2C-O), 163.7 (MeCdN), 147.7, 143.5, 142.2,
138.3, 135.4, 129.4, 128.6, 127.6, 125.7, 123.9, 123.2 (Ar/py), 31.1,
21.9, 21.1, 18.9, 16.9 (Me), -3.2, -4.5 (Al-Me). MS (FAB): 296
[M + H - Al2Me5]+. Anal. Calcd for C24H38N2OAl2: C, 67.92;
H, 8.96; N, 6.60. Found: C, 67.59; H, 8.71; N, 6.39.
Synthesis of 2-{(2,6-i-Pr2C6H3)NdCMe}-6-{(HO)CMe2}-
C5H3N (L2a). Degassed water (20 mL) was added to a stirred
solution of 1a (0.45 g, 0.97 mmol) in diethyl ether (30 mL). After
stirring for 30 min the aqueous layer was separated and extracted
with diethyl ether (2 × 30 mL). The combined organic extracts
were dried over MgSO4 and filtered, and the volatiles were removed
under reduced pressure to give L2a as a yellow powder. Yield:
1
residue was analyzed by H NMR spectroscopy.
X-ray Crystal Structure Determinations. For 1a. Diffraction
data were collected at 183 K using Cu KR radiation (λ ) 1.54178
Å). Solution and refinement of the structure were carried out using
the SHELXTL program system.19 For 1a: C27H44N2OAl2‚0.5MeCN,
M ) 487.13 g/mol; monoclinic; space group P2(1)/n; a ) 15.5098-
(9) Å, b ) 17.722(2) Å, c ) 22.2233(9) Å, â ) 99.838(4)°; V )
6018.7(9) Å3; Z ) 8; D(calcd) ) 1.075 g/cm3; absorption coefficient
) 1.027 mm-1; F(000) ) 2120. Crystal size 0.80 × 0.23 × 0.06
mm. Reflections collected ) 9304 and 8930 independent reflections
with R(int) ) 0.0484. Restraints/parameters ) 0/604; goodness-
of-fit on F2 ) 1.035; R(I > 2σ(I)) ) 0.0652, wR2 ) 0.1320; R(all
data) ) 0.1296, wR2 ) 0.1637. Figure 1 shows an ORTEP diagram
and gives selected bond lengths and angles.
1
2
0.26 g, 81%. H NMR (CDCl3, 293 K): δ 8.29 (dd, 1H, JHH
7.8 Hz, JHH ) 0.8 Hz, py-H), 7.84 (t, 1H, JHH ) 7.8 Hz, py-H),
)
3
2
2
3
7.47 (dd, 1H, JHH ) 7.9 Hz, JHH ) 0.9 Hz, py-H), 7.2-7.1 (m,
3H, Ar-H), 5.24 (s, br, 1H, OH), 2.74 (sept, 2JHH ) 6.9 Hz, CHMe2),
2.24 (s, 3H, MeCdN), 1.61 (s, 6H, C(OH)Me2), 1.15 (d, 12H, 2JHH
) 6.9 Hz, CHMe2). 13C{1H} NMR (CDCl3, 293 K): δ 166.4 (Cd
N), 164.9, 154.0, 146.3, 137.7, 135.7, 123.7, 123.0, 119.9, 119.4
(Ar/py), 30.8, 28.3, 23.2, 17.3 (Me). IR (Nujol mull, cm-1): ν-
(O-H) 3599, ν(CdN) 1622. MS (EI): m/z 338 [M]+. Anal. Calcd
for C22H30N2O: C, 78.11; H, 8.88; N, 8.28. Found: C, 78.41; H,
9.02; N, 8.11.
For 2a. Diffraction data were collected at room temperature using
Mo KR radiation (λ ) 0.71073 Å). Solution and refinement of the
structure were carried out using the SHELXTL program system19
For 2a: C22H30N2OCl2Fe‚MeCN, M ) 506.28 g/mol; monoclinic;
space group P2(1)/n; a ) 12.481(2) Å, b ) 12.229(2) Å, c )
18.486(3) Å, â ) 109.22(2)°; V ) 2664.2(8) Å3; Z ) 4; D(calcd)
) 1.262 g/cm3; absorption coefficient ) 0.786 mm-1; F(000) )
1064. Crystal size 0.30 × 0.15 × 0.13 mm. Reflections collected
) 3662 and 3476 independent refelections with R(int) ) 0.0582.
Restraints/parameters ) 1/284; goodness-of-fit on F2 ) 0.990; R(I
> 2σ(I)) ) 0.0698, wR2 ) 0.1278; R(all data) ) 0.1506, wR2 )
0.1690. Figure 2 shows an ORTEP diagram and gives selected bond
lengths and angles.
Synthesis of 2-{(2,4,6-Me3C6H2)NdCMe}-6-{(HO)CMe2}-
C5H3N (L2b). By using the same procedure described for L2a, com-
pound L2b was obtained as a yellow powder. Yield: 0.24 g, 74%.
1H NMR (CD2Cl2, 293 K): δ 8.20 (dd, 1H, 3JHH ) 7.9 Hz, 4JHH
)
3
0.5 Hz, py-H), 7.76 (app. t, 1H, JHH ) 7.9 Hz, py-H), 7.38 (dd,
1H, 3JHH ) 7.9 Hz, 4JHH ) 0.5 Hz, py-H), 6.81 (s, 2H, Ar-H), 6.81
(s, 2H, Ar-H), 5.14 (s, br, 1H, OH), 2.21 (s, 3H, m-Ar-Me), 2.12
(s, 3H, MeCdN), 1.92 (s, 3H, o-Ar-Me), 1.52 (s, 6H, (OH)CMe2).
13C{1H} NMR (CDCl3, 293 K): δ 166.4 (CdN), 164.5, 154.3,
146.1, 137.8, 135.8, 123.6, 123.1, 120.0, 119.5 (Ar/py), 30.8, 28.3,
18.1, 16.3 (Me). IR (Nujol mull, cm-1): ν(O-H) 3597, ν(CdN)
1620. MS (EI): m/z 296 [M]+. Anal. Calcd for C19H24N2O: C,
77.03; H, 8.11; N, 9.46. Found: C, 77.19; H, 8.33; N, 9.34.
Synthesis of [2-{(2,6-i-Pr2C6H3)NdCMe}-6-{(HO)CMe2}-
C5H3N]FeCl2 (2a). FeCl2 (0.050 g, 0.39 mmol) was dissolved in
n-BuOH (10 mL) at 90 °C, and L2a was introduced (0.132 g, 0.39
mmol) to yield a blue solution. After being stirred at 90 °C for 15
min, the reaction was allowed to cool to room temperature. Hexane
(30 mL) was added to precipitate the product, which was subse-
quently washed with hexane (3 × 10 mL), filtered, and dried to
afford 2a as a pale blue solid. Yield: 1.06 g, 77%. IR (cm-1), ν-
(CdN) 1595. MS (EI): m/z 465 [M]+, 430 [M - Cl]+. Anal. Calcd
Acknowledgment. We are grateful to Rapra Technology
(UK) for obtaining the gel permeation chromatographic data.
Dr. Graham Eaton (Leicester) is thanked for help with the FAB
mass spectrometry.
(19) SHELXTL PC, version 5. 03.; Siemens Analytical X-Ray Instru-
ments, Inc.: Madison, WI, 1994. SHELXTL PC, version 5; Bruker AXS:
Madison, WI, 1997.

Notes
Supporting Information Available: Tables giving detailed
crystallographic data, atomic positional parameters, and complete
bond lengths and angles for 1a and 2a. This material is available
free of charge via the Internet at http://pubs.acs.org. These data
Organometallics, Vol. 26, No. 20, 2007 5123
have also been deposited at the Cambridge Crystallographic Data
Centre (reference numbers: 643859 and 643860).
OM700611Q