Chromium(III) complexes of sterically crowded bidentante {ONR} and Tridentate {ONNR} Naphthoxy-Imine tigands: Syntheses, structures, and use in ethylene oligomerization

Article abstract of DOI:10.1021/om801196d

bidentate {ONR}H (R = C6F5, 2c) and tridentate {ONNR}H (R = quinolyl, 2a; 2-pyridylmethyl, 2b} naphthol-imine and phenol-imine (R = quinolyl, 2d) pro-ligands sterically encumbered by an ortho- triphenylsilyl moiety have been prepared and converted to the

Full text of DOI:10.1021/om801196d

Organometallics 2009, 28, 2401–2409
2401
Chromium(III) Complexes of Sterically Crowded Bidentante {ONR}
and Tridentate {ONNR} Naphthoxy-Imine Ligands: Syntheses,
Structures, and Use in Ethylene Oligomerization‡
Evgueni Kirillov,*,† Thierry Roisnel,† Abbas Razavi,# and Jean-Franc¸ois Carpentier*,†
Catalysis and Organometallics, UMR 6226 Sciences Chimiques de Rennes, CNRS-UniVersity of Rennes 1,
35042 Rennes Cedex, France, and Total Petrochemicals Research, Zone Industrielle C,
7181 Feluy, Belgium
ReceiVed December 18, 2008
New bidentate {ONR}H (R ) C6F5, 2c) and tridentate {ONNR}H (R ) quinolyl, 2a; 2-pyridylmethyl,
2b} naphthol-imine and phenol-imine (R ) quinolyl, 2d) pro-ligands sterically encumbered by an ortho-
triphenylsilyl moiety have been prepared and converted to the corresponding naphthoxy-imino (3a-c)
and phenoxy-imino (3d) CrBr2{ON(N)R}(CH3CN) complexes, respectively, via reaction with (p-
tolyl)CrBr2(THF)3 and subsequent recrystallization from acetonitrile. The molecular structures of 2a, 2d,
3a, and 3b have been established by single-crystal X-ray diffraction studies. Upon activation with MAO,
complexes 3a, 3b, and 3d, despite the presence of coordinated acetonitrile in those precursors, lead to
highly active catalysts for the oligomerization of ethylene (activities up to 23 730 kg mol-1 h-1 at 25-100
°C, 6 bar), yielding selectively linear R-olefins (89-96% vinyl-end; Mn ) 600-1450 g mol-1, Mw/Mn )
1.9-2.3).
Chart 1. Typical Cr(III) Phenoxy-Imine Compounds
Disclosed in the Literature7 That Are Suitable for the
Oligomerization or Polymerization of Ethylene
Introduction
Discrete group 3-6 metal complexes bearing various chelat-
ing aryloxide-based ligands have demonstrated astonishing
performances in the oligomerization/polymerization of ethylene
and R-olefins.1 In particular, phenoxy-imine type ligands have
attracted considerable attention due to the flexibility these ligand
platforms afford for tuning the stereoelectronic properties of
the precatalysts and, in turn, control the catalytic performances.2,3
Although these Schiff base ligands have been used mostly with
group 4 metals, they have led also to very valuable catalyst
systems when associated with chromium. Chromium holds a
quite interesting position among transition metals, since effective
catalysts for both ethylene polymerization and oligomerization,4
including selective tri-5 and tetramerization,6 have been reported
for this element. Recently, Gibson et al. identified via high-
throughput screening of a 205-member Schiff base salicylaldi-
mine ligand library, reacted in situ with (p-tolyl)CrCl2(THF)3,
two new classes of highly active chromium-based systems for
the oligomerization and polymerization of ethylene, respectively
(Chart 1).7 The polymerization system comprised bidentate
ortho-substituted anthracenyl Schiff bases bearing small primary
or secondary alkyl-imine substituents, while the oligomerization
catalysts were based on tridentate ortho-triptycenyl-substituted
Schiff bases with pyridylmethyl or quinolyl substituents.
(2) (a) Matsugi, T.; Fujita, F. Chem. Soc. ReV. 2008, 37, 1264. (b) Makio,
H.; Fujita, T. Macromol. Rapid Commun. 2007, 28, 698. (c) Terao, H.;
Ishii, S.; Saito, J.; Matsuura, S.; Mitani, M.; Nagai, N.; Tanaka, H.; Fujita,
T. Macromolecules 2006, 39, 8584. (d) Nakayama, Y.; Saito, J.; Bando,
H.; Fujita, T. Chem.-Eur. J. 2006, 12, 7546. (e) Saito, J.; Suzuki, Y.; Makio,
H.; Tanaka, H.; Onda, M.; Fujita, T. Macromolecules 2006, 39, 4023. (f)
Mitani, M.; Nakano, T.; Fujita, T. Chem.-Eur. J. 2003, 9, 2396. (g) Mitani,
M.; Furuyama, R.; Mohri, J.; Saito, J.; Ishii, S.; Terao, H.; Nakano, T.;
Tanaka, H.; Fujita, T. J. Am. Chem. Soc. 2003, 125, 4293. (h) Makio, H.;
Kashiwa, N.; Fujita, T. AdV. Synth. Catal. 2002, 344, 477. (i) Mitani, M.;
Furuyama, R.; Mohri, J.; Saito, J.; Ishii, S.; Terao, H.; Kashiwa, N.; Fujita,
T. J. Am. Chem. Soc. 2002, 124, 7888. (j) Mitani, M.; Mohri, J.; Yoshida,
Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui, S.; Furuyama, R.; Nakano, T.;
Tanaka, H.; Kojoh, S.; Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem.
Soc. 2002, 124, 3327. (k) Saito, J.; Mitani, M.; Mohri, J.; Yoshida, Y.;
Matsui, S.; Ishii, S.; Kojoh, S.; Kashiwa, N.; Fujita, T. Angew. Chem., Int.
Ed. 2001, 40, 2918. (l) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio,
H.; Matsukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.;
Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2001, 123, 6847.
(3) (a) Mason, A. F.; Coates, G. W. J. Am. Chem. Soc. 2004, 126, 10798.
(b) DeRosa, C.; Circelli, T.; Auriemma, F.; Mathers, R. T.; Coates, G. W.
Macromolecules 2004, 37, 9034. (c) Mason, A. F.; Coates, G. W. J. Am.
Chem. Soc. 2004, 126, 16326. (d) Reinartz, S.; Mason, A. F.; Lobkovsky,
E. B.; Coates, G. W. Organometallics 2003, 22, 2542. (e) Hustad, P. D.;
Tian, J.; Coates, G. W. J. Am. Chem. Soc. 2002, 124, 3614. (f) Tian, J.;
Coates, G. W. Angew. Chem., Int. Ed. 2000, 39, 3626.
‡ Dedicated to Prof. M. N. Bochkarev on the occasion of his 70th
birthday.
* Corresponding authors. Fax: (+33)(0)223-236-939. E-mail: evgueni.kirillov@
univ-rennes1.fr; jean-francois.carpentier@univ-rennes1.fr.
† CNRS-University of Rennes 1.
# Total Petrochemicals Research.
(1) For leading reviews on “post-metallocene” complexes of groups 3-
6 and the lanthanides related to olefin oligo/polymerization, see: (a)
Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed.
Engl. 1999, 38, 428. (b) Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew.
Chem., Int. Ed. 2002, 41, 2236. (c) Edelmann, F. T.; Freckmann, D. M. M.;
Schumann, H. Chem. ReV. 2002, 102, 1851. (d) Gibson, V. C.; Spitzmesser,
S. K. Chem. ReV. 2003, 103, 283. (e) Gromada, J.; Mortreux, A.; Carpentier,
J.-F. Coord. Chem. ReV. 2004, 248, 397. (f) Corradini, P.; Guerra, G.;
Cavallo, L. Acc. Chem. Res. 2004, 37, 231. (g) Kol, M.; Segal, S.;
Groysman, S. In StereoselectiVe Polymerization with Single-Site Catalysts;
CRC Press LLC: Boca Raton, FL, 2008; pp 345-361. (h) Okuda, J. Stud.
Surf. Sci. Catal. 2007, 172, 11. (i) Domski, G. J.; Rose, J. M.; Coates,
G. W.; Bolig, A. D.; Brookhart, M. Prog. Polym. Sci. 2007, 32, 30.
10.1021/om801196d CCC: $40.75
2009 American Chemical Society
Publication on Web 03/30/2009

2402 Organometallics, Vol. 28, No. 8, 2009
KirilloV et al.
Scheme 1. Synthetic Route Used for the Preparation of Naphthol-Imine {ONNR}H and {ONR}H Pro-ligands
In this contribution, we report derivatives of these known
ligands, but with a naphthol platform sterically encumbered by
a bulky ortho-triphenylsilyl substituent. Cr(III) complexes
derived from these new bi- and tridentate naphthol-imine pro-
ligands have been prepared and structurally characterized. For
comparative studies, a related ortho-SiPh3-substituted phenol-
imine pro-ligand and its chromium complex were also synthe-
sized. The valuable performances of some of these complexes
in ethylene oligomerization, yielding eventually vinyl-end-
capped C∼50 oligoethylenes in high selectivity, upon activation
with alkylaluminum reagents, are discussed as well.
Results and Discussion
Synthesis of Pro-Ligands. The synthesis of bidentate
({ONR}H; R ) C6F5, 2a) and tridentate ({ONNR}H; R )
2-pyridylmethyl, 2b, or quinolyl, 2c) naphthol-imine pro-ligands
was achieved starting from commercially available and inex-
pensive 2-methoxynaphthalene (Scheme 1). The initial four-
step procedure ended up with the formation of 3-triphenylsilyl-
substituted 2-hydroxy-1-naphthaldehyde (1) in high overall yield
(82%). The latter compound can be straightforwardly condensed
with aromatic or aliphatic primary amines to the corresponding
naphthol-imines 2a-c under standard conditions, using either
HCOOH (cat.) in MeOH or PTSA (p-toluenesulfonic acid) (cat.)
in toluene (see the Experimental Section for details). The phenol-
based tridentate ligand ({ONNR}H, R ) quinolyl, 2d) was
prepared by an analogous condensation reaction (HCOOH (cat.)
in MeOH) from 2-hydroxy-5-methyl-3-(triphenylsilyl)benzal-
dehyde8 and 8-aminoquinoline.
(4) (a) MacAdams, L. A.; Buffone, G. P.; Incarvito, C. D.; Rheingold,
A. L.; Theopold, K. H. J. Am. Chem. Soc. 2005, 127, 1082. (b) Theopold,
K. H. Eur. J. Inorg. Chem. 1998, 15. (c) Bhandari, G.; Kim, Y.; McFarland,
J. M.; Rheingold, A. L.; Theopold, K. H. Organometallics 1995, 14, 738.
(d) Do¨hring, A.; Go¨hre, J.; Jolly, P. W.; Kryger, B.; Rust, J.; Verhovnik,
G. P. J. Organometallics 2000, 19, 388. (e) Rogers, J. S.; Bu, X. H.; Bazan,
G. C. Organometallics 2000, 19, 3948. (f) Enders, M.; Fernandez, P.;
Ludwig, G.; Pritzkow, H. Organometallics 2001, 20, 5005. (g) Gibson,
V. C.; Maddox, P. J.; Newton, C.; Redshaw, C.; Solan, G. A.; White,
A. J. P.; Williams, D. J. Chem. Commun. 1998, 1651. (h) MacAdams, L. A.;
Kim, W. K.; Liable-Sands, L. M.; Guzei, I. A.; Rheingold, A. L.; Theopold,
K. H. Organometallics 2002, 21, 952. (i) Gibson, V. C.; Mastroianni, S.;
Newton, C.; Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J.
J. Chem. Soc., Dalton Trans. 2000, 1969. (j) Vidyaratne, I.; Scott, J.;
Gambarotta, S.; Duchateau, R. Organometallics 2007, 26, 3201. (k)
Albahily, K.; Koc¸, E.; Al-Baldawi, D.; Savard, D.; Gambarotta, S.; Burchell,
T. J.; Duchateau, R. Angew. Chem., Int. Ed. 2008, 47, 1. (l) Albahily, K.;
Al-Baldawi, D.; Gambarotta, S.; Koc¸, E.; Duchateau, R. Organometallics
2008, 27, 5943. (m) Junges, F.; Kuhn, M. C. A.; dos Santos, A. H. D. P.;
Rabello, C. R. K.; Thomas, C. M.; Carpentier, J.-F.; Casagrande, O. L.
Organometallics 2007, 26, 4010.
(5) (a) Reagan, W. K. (Phillips Petroleum Co.) Eur. Pat. 0417477, 1991.
(b) Mimura, H.; Aoyama, T.; Yamamoto, T.; Oguri, M.; Koie, Y. (Tosoh
Corp.) Jap. Patent 09268133, 1997. (c) Emrich, R.; Heinemann, O.; Jolly,
P. W.; Krueger, C.; Verhovnik, G. P. J. Organometallics 1997, 16, 1511.
(d) Kohn, R. D.; Haufe, M.; Kociok-Kohn, G.; Grimm, S.; Wasserscheid,
P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 4337. (e) Wass, D. F. (BP
Chemicals Ltd) WO Patent 004119, 2002. (f) Carter, A.; Cohen, S. A.;
Cooley, N. A.; Murphy, A.; Scutt, J.; Wass, D. F. Chem. Commun. 2002,
858. (g) Yoshida, T.; Yamamoto, T.; Okada, H.; Murakita, H. (Tosoh Corp.)
U.S. Patent 0035029, 2002. (h) Mohamed, H. A.; Bollmann, A.; Dixon, J.;
Gokul, V.; Griesel, L.; Grove, J. J. C.; Hess, F.; Maumela, H.; Pepler, L.
Appl. Catal., A 2003, 255, 355. (i) Grove, J. J. C.; Mohamed, H. A.; Griesel,
L. (Sasol Technology Ltd) WO Patent 03/004158, 2002. (j) Dixon, J. T.;
Wasserscheid, P.; McGuinness, D. S.; Hess, F. M.; Maumela, H.; Morgan,
D. H.; Bollmann, A. (Sasol Technology Ltd) WO Patent 03053890, 2001.
(k) McGuinness, D.; Wasserscheid, P.; Keim, W.; Morgan, D.; Dixon, J. T.;
Bollmann, A.; Maumela, H.; Hess, F.; Englert, U. J. Am. Chem. Soc. 2003,
125, 5272. (l) McGuinness, D. S.; Wasserscheid, P.; Keim, W.; Hu, C.;
Englert, U.; Dixon, J. T.; Grove, C. Chem Commun. 2003, 334. (m) Agapie,
T.; Day, M. W.; Henling, L. M.; Labinger, J. A.; Bercaw, J. E. Organo-
metallics 2006, 25, 2733. (n) Schofer, S. J.; Day, M. W.; Henling, L. M.;
Labinger, J. A.; Bercaw, J. E. Organometallics 2006, 25, 2743. (o) Jabri,
A.; Temple, C.; Crewdson, P.; Gambarotta, S.; Korobkov, I. V.; Duchateau,
R. J. Am. Chem. Soc. 2006, 128, 9238. (p) Temple, C.; Gambarotta, S.;
Korobkov, I. V.; Duchateau, R. Organometallics 2007, 26, 4598. (q)
Albahily, K.; Al-Baldawi, D.; Gambarotta, S.; Duchateau, R.; Koc¸, E.;
Burchell, T. J. Organometallics 2008, 27, 5708.
The obtained products were authenticated by elemental
1
analysis, H and 13C{1H} NMR spectroscopy, and an X-ray
diffraction study for 2a and 2d. It is noteworthy that, in striking
contrast with the quinolyl-based imino-phenol {ONN}H pro-
ligand molecule disclosed by Gibson et al.,7a the most stable
tautomeric form found for molecules of 2a and 2b is the keto-
enamine one. This keto-enamine structure persists not only in
the solid state, as evidenced for 2a (Vide infra), but also in
CD2Cl2 solution. In fact, the room-temperature 13C{1H} NMR
spectra of both 2a and 2b display a single set of signals that
include resonances at δ 185.2 and 180.6 ppm, respectively,
which are unambiguously assigned to CdO groups. The 13C{1H}
NNR spectra of 2c and 2d at 25 °C (in CD2Cl2 and/or CDCl3)
feature a different pattern indicative of an imino-phenol structure
on the NMR time scale, that is, no signal in the carbonyl region
but two resonances at δ 166.7 (ipso-C phenol) and 164.7 ppm
(6) (a) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H.; McGuinness, D. S.; Morgan, D. H.; Neveling, A.; Otto, S.;
Overett, M.; Slawin, A. M. Z.; Wasserscheid, P.; Kuhlmann, S. J. Am. Chem.
Soc. 2004, 126, 14712. (b) Jabri, A.; Crewdson, P.; Gambarotta, S.;
Korobkov, I. V.; Duchateau, R. Organometallics 2006, 25, 715.
(7) (a) Jones, D. J.; Gibson, V. C.; Green, S. M.; Maddox, P. J.; White,
A. J. P.; Williams, D. J. J. Am. Chem. Soc. 2005, 127, 11037. (b) van Meurs,
M.; Britovsek, G. J. P.; Gibson, V. C.; Cohen, S. A. J. Am. Chem. Soc.
2005, 127, 9913. (c) Gibson, V. C.; O’Reilly, R. K. U.S. Pat. Appl. 0258867,
2006. (d) Gibson, V. C.; Mastroianni, S.; Newton, C.; Redshaw, C.; Solan,
G. A.; White, A. J. P.; Williams, D. J. Dalton Trans. 2000, 1969.
(8) Thadani, A. N.; Huang, Y.; Rawal, V. H. Org. Lett. 2007, 9, 3873.

Chromium(III) Complexes of Naphthoxy-Imine Ligands
Organometallics, Vol. 28, No. 8, 2009 2403
Scheme 2. Synthesis of Cr(III) Dibromide Naphthoxy- and
Phenoxy-Imino Complexes 3a-d
Figure 1. Molecular structure of pro-ligand 2a (ellipsoids drawn
at the 50% probability level; all hydrogen atoms, except H(1)-N(1),
removed for the sake of clarity).
Figure 2. Molecular structure of pro-ligand 2d (ellipsoids drawn
at the 50% probability level; all hydrogen atoms, except H(1)-O(1),
removed for the sake of clarity).
(CdN), and δ 168.5 (ipso-C phenol) and 165.9 ppm (CdN),
respectively. This observation is further corroborated by the
solid-state structure of 2d (Vide infra). Apparently, stabilization
of either keto-enamine or imino-phenol tautomer results from
a delicate balance between electronic effects induced by the
substituent at the imino nitrogen atom, the additional ring of
the naphthoxy (vs phenoxy) platform, and possibly the ꢀ-effect
of silicon9 induced by the SiPh3 substituent as well.
One-Step Synthesis of Cr(III) Complexes by σ-Bond
Metathesis. A direct approach toward the targeted chromium
complexes was used, which involves the protonolysis reaction
of the (p-tolyl)CrBr2(THF)310 precursor with the corresponding
naphthol-imine pro-ligand 2a-c in toluene.7a Complex 3d,
bearing the phenoxy-imino ligand, was similarly obtained. After
evaporation and recrystallization of the resultant materials from
acetonitrile, Cr(III) dibromide complexes were isolated in high
yields (Scheme 2). Elemental analyses indicated that complex
3c, which is based on the bidentate ligand, contains two
coordinated acetonitrile molecules, while complexes 3a, 3b, and
3d, which are based on tridentate ligands, contain a single
coordinated acetonitrile molecule. The latter feature was further
confirmed by single-crystal X-ray diffraction studies for 3a and
3b. In addition, complexes 3a-d were authenticated by UV-vis
spectroscopy, FAB-MS, and SQUID methods (see Experimental
Section and Supporting Information for details).
Figure 3. Molecular structure of complex 3a (ellipsoids drawn at
the 50% probability level (all hydrogen atoms removed for the sake
of clarity).
Solid-State Molecular Structures. Single-crystal X-ray
diffraction studies were performed for pro-ligands 2a and 2d
and chromium dibromide complexes 3a and 3b (Figures 1-4).
Crystallographic data and structural determination details are
summarized in Table 1, and important bond distances and angles
are given in Table 2.
The distribution of formally single and double bonds in pro-
ligand 2a in the solid state (Figure 1) is in agreement with the
aforementioned keto-enamine solution structure of this molecule.
Thus, the O(1)-C(1) bond distance in 2a (1.265(2) Å) is
significantly shorter than the corresponding bond distances
(9) Lambert, J. B.; Yan, Z.; Emblidge, R. W.; Salvador, L. A.; Xiaoyang,
L.; So, J.-H.; Chelius, E. C. Acc. Chem. Res. 1999, 32, 183, and references
therein.
(10) (p-tolyl)CrBr2(THF)3 was obtained from the transmetalation/
transhalogenation reaction of CrCl3 and (p-tolyl)MgBr, carried out in THF.
This compound was isolated in 18% yield after two consecutive recrystal-
lizations; see ref 19.

2404 Organometallics, Vol. 28, No. 8, 2009
KirilloV et al.
almost inactive, using either MAO or AlEt2Cl as the activator,
respectively (entries 8 and 9). These observations are in line
with those made by Gibson et al.7a,11 On the other hand,
activation of Cr(III) precursors 3a and 3b with MAO (500-800
equiv) afforded stable and very productive catalytic systems
(entries 3-7). Activities up to 14 160 and 12 600 kg mol-1 h-1
were observed for complexes 3a and 3b, respectively, under 6
bar of ethylene at a temperature of 50 °C. Performing the
reaction with 3a from room temperature for a shorter reaction
time gave a very high activity of 23 730 kg mol-1 h-1 (entry
6). Complex 3d, which is based on a triphenylsilyl-substituted
phenoxy-imine ligand, was ca. 2 times less active than its
naphthoxy analogues 3a,b under the same conditions (entry 10).
Those reactions are quite exothermic due to the very high
activity even with low catalyst loadings, and the temperature
of the reaction mixture is hard to control, often reaching up to
80-100 °C after a few minutes (see Table 3). Monitoring of
the ethylene uptake indicated that the activity is quite steady
under such conditions and thus that the catalysts are thermally
stable in this temperature range. Not surprisingly, the activity
(and productivity) observed at 100 °C is, however, somewhat
lower than under the previous conditions (entry 5).
The catalytic performance of complexes 3a,b, and even those
of the somehow less active complex 3d, contrasts sharply with
those of the acetonitrile complexes based on tridentate phenoxy-
imine reported by Gibson et al., which all proved to be
inactive.7a In this case, it was suggested that the acetonitrile
ligand may interfere with the activation process or may even
be retained by the metal center. Obviously, our results evidence
that the apparently innocent replacement of the triptycenyl for
a triphenylsilyl ortho-substituent (despite the aforementioned
similar steric protection they seem to confer) in those Schiff
base chromium acetonitrile complexes drastically affects their
catalytic performance. In this respect, it is noteworthy that no
significant change in activities of complexes 3a and 3d was
observed when an excess of donor (acetonitrile, THF, or
pyridine; 4 equiv vs Cr) was deliberately introduced in the
polymerization medium (entries 12, 16-18).
Figure 4. Molecular structure of complex 3b (ellipsoids drawn at
the 50% probability level; all hydrogen atoms removed for the sake
of clarity).
observed in imino- and keto-phenols described by Gibson et
al. (1.323-1.354(2) Å).7a Also, the C(1)-C(11) bond distance
is shorter than the endocyclic C(1)-C(2) (1.384(2) vs 1.460(2)
Å), and the C(11)-N(1) bond distance (1.336(2) Å) is elongated
as compared to the value (1.288(2) Å) observed for a typical
CdN bond in an imino-phenol molecule, such as in 2d. In fact,
the imino-phenol structure of 2d, determined by NMR in
solution (Vide supra), was confirmed in the solid state by X-ray
analysis (Figure 2).
Both complexes 3a and 3b feature a mononuclear structure
in the solid state, with the chromium center in a slightly distorted
octahedral environment (Figures 3 and 4). The tridentate ligand
adopts a meridional coordination, with the two bromide ligands
occupying mutually trans positions and the acetonitrile molecule
coordinated trans to the imino nitrogen donor. In fact, these
molecular structures reveal that coordination of 2a and 2b onto
Cr(III) eventually results in the formation of naphthoxy-imino
complexes. The Cr(1)-O(1) bond distances in 3a and 3b
(1.912(4), 1.905(2) Å, respectively) are in the range (1.890(3)-
1.923(3) Å) of those determined for related phenoxy-based
{ONNR}CrCl2(solvent) (solvent ) MeCN, THF, pyridine)
complexes.7a Also, the C(11)-N(1) bond distance in 3a is
shortened, while the C(1)-C(11) bond distance is elongated,
as compared to those in pro-ligand 2a. The O(naphthoxy)-Cr-
N(acetonitrile) bond angles (3a, 91.8(2)°; 3b, 85.81(10)°) are
similar to the corresponding O(phenoxy)-Cr-N(solvent) bond
angles (R ) quinolyl, solvent ) pyridine, 87.51(2)°; R )
2-pyridylmethyl, solvent ) acetonitrile, 90.49(2)-92.55(2)°)
observed in the ortho-triptycenyl-phenoxy CrCl2(ONNR)-
(solvent) complexes reported by Gibson et al.7a This observation
may indicate that the ortho-triptycenyl and -triphenylsilyl
substituents bring similar steric crowding around the salicyla-
ldiminato oxygen and Cr(III) center.
Studies on the Reactivity toward Ethylene. Selective
Preparation of Vinyl End-Capped Higher Oligoethylenes.
The catalytic activity of combinations based on Cr(III) dibromo
complexes 3a-d and a coactivator was evaluated in the oligo/
polymerization of ethylene. Three different possible coactivators,
namely, MAO, AlEt2Cl, and Al(iBu)3, were used. The reaction
conditions and representative examples of catalytic activity and
polymer analyses data are summarized in Table 3.
Activation of complexes 3a,b with AlEt2Cl or Al(iBu)3 as
cocatalyst (500 equiv vs Cr) was found to be inefficient (entries
1 and 2). Also, systems based on precursor 3c, which incorpo-
rates a bidentate ligand, proved to be very poorly active or
Products obtained with catalyst systems based on 3a, 3b, and
3d are all solid oligomers with Tm ) 114-122 °C.12 The Mn
values are typically in the range 600-1600 g mol-1 as
determined by 1H NMR and HT GPC, with monomodal
distributions (Mw/Mn ) 1.9-2.3) as shown by HT GPC (Figure
1
5). H and 13C{1H} NMR analyses revealed linear oligomers
with remarkably high contents of vinyl ends (ca. 90 mol %)
(Figures 6 and 7), that is, essentially linear R-olefins.13,14 The
catalyst system derived from preformed 3d (entry 10), or
generated in situ from 2d with (p-tolyl)CrBr2(THF)3 (entry 15),
showed a slightly higher propensity to produce terminal olefins
(92-96 mol %). As aforementioned in terms of activity,
(11) Gibson et al. have shown on related Cr-{phenoxy-imine} systems
that (i) substitution of the salicylaldehyde in the para-position with the
electron-withdrawing CF3 substituent and (ii) replacement of a phenyl for
a 3-F-4-BrC6H3 group at the imino N atom generally results in slightly
decreased catalytic activity (see ref 7a). We thus assume that the inactivity
of complex 3c is likely a consequence of the general poor ability of systems
based on aryloxy-imine bidentate ligands derived from arylamines, combined
with the electron-withdrawing effect of the C6F5 substituent.
(12) Only minor amounts (<5% of consumed ethylene) of low oligomers
(1-hexene, 1-octene) were also detected by GLC and GLC-MS.
(13) Small amounts (ca. 2-6 mol %) of internal olefins were also
detected; see Figure 6. A small percentage of alkanes, which likely arise
by chain transfer to aluminum, accounts for the balance.
(14) (a) Vinyl end-capped (g90%) low molecular weight polyethylenes
(Mw ) 1000-10 000 g mol-1) were obtained with FI catalysts bearing
phenoxy-cycloalkylimine ligands: (b) Ishii, S.; Mitani, M.; Saito, J.;
Matsuura, S.; Kojoh, S.; Kashiwa, N.; Fujita, T. Chem. Lett. 2002, 740.

Chromium(III) Complexes of Naphthoxy-Imine Ligands
Organometallics, Vol. 28, No. 8, 2009 2405
Table 1. Summary of Crystal and Refinement Data for Compounds 2a, 2d, 3a, and 3b
2a · CH2Cl2
2d
3a · toluene
3b · 0.5toluene
empirical formula
fw
temp, K
C38H28N2OSi · CH2Cl2
641.64
100(2)
C35H28N2OSi
520.68
100(2)
C40H30Br2CrN3OSi · C7H8
808.58
100(2)
C37H30Br2CrN3OSi · 0.5C7H8
825.63
100(2)
wavelength, Å
cryst system
space group
a, Å
b, Å
c, Å
0.71073
0.71073
triclinic
P21a
10.9845(5)
12.1870(6)
20.0955(10)
94.952(2)
2680.1(2)
4
0.71073
monoclinic
P21a
19.245(2)
10.3843(11)
20.931(2)
116.442(3)
3745.4(7)
4
0.71073
triclinic
P1
11.5073(8)
11.5843(8)
13.8235(11)
90
1789.5(2)
2
triclinic
j
j
P1
9.2733(16)
9.9482(15)
17.772(3)
90
1591.6(5)
2
ꢀ, deg
volume, Å3
Z
density (calc), Mg/m3
absorp coeff, mm-1
cryst size, mm3
reflns collected
indep reflns
max. and min. transmn
data/restraints/params
1.339
0.277
1.29
0.120
1.434
2.505
1.532
2.624
0.34 × 0.21 × 0.19
0.45 × 0.28 × 0.23
0.22 × 0.18 × 0.04
0.27 × 0.20 × 0.08
22 065
19 151
38 517
36 633
7218 [R(int) ) 0.0390]
0.949 and 0.905
7218/0/409
6071 [R(int) ) 0.0445]
0.973 and 0.857
6071/0/354
8586 [R(int) 0.1003]
0.905 and 0.567
8586/0/434
8119 [R(int) 0.0396]
0.811 and 0.485
8119/0/444
final R indices [I > 2σ(I)] R1 ) 0.0416, wR2 ) 0.0999 R1 ) 0.0438, wR2 ) 0.0996 R1 ) 0.0808, wR2 ) 0.2367 R1 ) 0.0427, wR2 ) 0.1220
R indices (all data)
R1 ) 0.0526, wR2 ) 0.1062 R1 ) 0.0514, wR2 ) 0.1054 R1 ) 0.1434, wR2 ) 0.2666 R1 ) 0.0529, wR2 ) 0.1286
goodness-of-fit on F2
largest diff peak, e Å-3
1.034
1.036
1.059
1.025 and -1.102
0.419 and -0.474
0.321 and -0.329
1.217 and -1.481
Table 2. Selected Bond Distances (Å) and Angles (deg) for Compounds 2a, 2d, 3a, and 3b
2a
2d
3a
3b
O(1)-C(1)
C(1)-C(2)
C(1)-C(11)
C(11)-N(1)
Cr(1)-O(1)
Cr(1)-Br(1)
1.265(2)
1.460(2)
1.384(2)
1.336(2)
1.350(2)
1.414(2)
1.449(2)
1.288(2)
1.316(7)
1.409(9)
1.416(9)
1.304(8)
1.912(4)
2.4360(14)
2.4498(15)
2.4498(15)
1.999(5)
2.053(3)
2.076(6)
90.0(2)
171.5(2)
91.8(2)
81.5(2)
177.5(2)
96.7(2)
1.316(4)
1.413(4)
1.439(4)
1.299(4)
1.905(2)
2.4675(6)
2.4819(6)
2.4819(6)
1.974(3)
2.062(3)
2.096(3)
90.77(10)
172.95(10)
85.81(10)
82.18(10)
176.49(10).
101.24(10)
90.61(8)
87.94(7)
90.30(7)
94.32(7)
173.41(2)
Cr(1)-Br(2)
Cr(1)-N(1)
Cr(1)-N(2)
Cr(1)-N(3)
O(1)-Cr(1)-N(1)
O(1)-Cr(1)-N(2)
O(1)-Cr(1)-N(3)
N(1)-Cr(1)-N(2)
N(1)-Cr(1)-N(3)
N(2)-Cr(1)-N(3)
N(1)-Cr(1)-Br(1)
N(2)-Cr(1)-Br(1)
N(3)-Cr(1)-Br(1)
O(1)-Cr(1)-Br(2)
Br(1)-Cr(1)-Br(2)
93.75(16)
87.72(17)
87.92(17)
91.97(14)
174.68(6)
changing the nature of the donor (acetonitrile, THF, or pyridine;
4 equiv vs Cr) had no significant effect on properties of the
isolated oligoethylenes (entries 12, 16-18). The observation
that different donor molecules have the same effect as aceto-
nitrile suggests that the donor is not implicitly involved in the
active catalytic species. Rather, we assume that, by ensuring
only monomeric Cr is present, it has a role in affecting the
activation pathway followed with MAO.15
pared to the related triptycenyl-substituted phenoxy-imino
complexes reported by Gibson, namely, the tolerance of
coordinated acetonitrile in the precursor and even of excess
added donors such as acetonitrile, THF, or pyridine. Those
catalyst systems afford selectively linear R-olefins. The latter
products can serve as valuable macromers in copolymerization
reactions with ethylene or R-olefins for the production of long-
chain branched polymers.16,17
Conclusions
Experimental Section
New bulky bidentate and tridentate naphthol-imine pro-
ligands have been straightforwardly prepared and easily installed
onto Cr(III) as dibromide acetonitrile adducts. The chromium
complexes bearing tridentate ligands, upon activating with
MAO, showed very high activities in the oligomerization of
ethylene to afford selectively vinyl end-capped oligoethylenes.
Those triphenylsilyl ortho-substituted naphthoxy-imino and
phenoxy-imino Cr systems feature some peculiarities as com-
All experiments were performed under a purified argon atmo-
sphere using standard Schlenk techniques or in a glovebox. Solvents
were distilled under nitrogen from Na/benzophenone (THF and
Et2O), CaH2 (acetonitrile), or Na/K alloy (toluene, pentane),
degassed thoroughly, and stored under nitrogen prior to use.
(16) (a) Komon, Z. J. A.; Bu, X.; Bazan, G. C. J. Am. Chem. Soc. 2000,
122, 1830. (b) Komon, Z. J. A.; Bu, X.; Bazan, G. C. J. Am. Chem. Soc.
2000, 122, 12379. (c) Diamond, G. M.; Leclerc, M. K.; Murphy, V.;
Okazaki, M.; Bazan, G. C. J. Am. Chem. Soc. 2002, 124, 15280.
(17) Dong, J.-Y.; Hu, Y. Coord. Chem. ReV. 2006, 250, 47.
(15) We thank a reviewer for suggesting this hypothesis.

2406 Organometallics, Vol. 28, No. 8, 2009
KirilloV et al.
Table 3. Ethylene Oligomerization Catalyzed by CrBr2{ON(N)R}(CH3CN) (3a-d)/Alkylaluminum Combinationsa
c
d
e
cat.
(µmol)
co-cat.
([Al]/[Cr])
tempb
(°C)
P(C2H4) time product
activity
Mn,NMR
Mn,GPC
vinylc
Tm
d
entry
(bar)
(min)
(g)
(kg mol-1 h-1
)
(g mol-1
)
(g mol-1
)
Mw/Mn
(mol %) (°C)
1
2
3
4
5
6
7
8
3a (5.0)
AlEt2Cl (500) 50
Al(iBu)3 (500) 50
6
6
1
6
6
6
6
6
6
6
1
1
6
1
6
6
6
6
60
60
20
10
10
5
10
60
60
10
60
60
10
60
10
10
10
10
0.11
0
22
0
3a (5.0)
3a (5.0)
3a (5.0)
3a (5.0)
3a (5.0)
3b (5.0)
3c (5.0)
3c (5.0)
3d (5.0)
2a/Cr (23.0)f
MAO (500)
MAO (500)
MAO (500)
MAO (500)
MAO (500)
MAO (500)
50
50 (90)
100
25 (107)
50 (83)
50
4.29
11.80
2.24
9.89
10.50
0.20
traces
5.57
3.50
1.15
9.22
0.62
0.20
8.75
12.43
5.68
2 570
14 160
2 690
23 730
12 600
40
1 450
1 140
1 300
1 100
1 340
nd
800
nd
nd
850
nd
2.23
nd
nd
2.22
90
90
89
87
91
119
118
118
119
122
9
AlEt2Cl (500) 50
10
MAO (500)
MAO (800)
50 (83)
50
6 680
150
55
11 060
27
1 140
ndj
nd
630
nd
nd
800
nd
nd
nd
nd
nd
1.99
nd
nd
2.10
nd
nd
nd
nd
93
<40j
90
85
67
96
88
88
92
116
114
119
118
119
121
118
118
117
11f
12f,g 2a/Cr (21.0)f,g MAO (800)
50
1 130
1 070
1 430
1 290
1 320
1 210
1 200
13f
14f
15f
16h
17i
18g
2a/Cr (5.0)
2b/Cr (23.0)f
2d/Cr (5.0)
3a (5.0)h
MAO (500)
MAO (800)
MAO (500)
MAO (500)
MAO (500)
MAO (500)
50 (93)
50
50
50 (94)
50 (93)
50 (74)
240
10 500
14 900
6 820
3a (5.0)i
3d (5.0)g
a Unless otherwise stated, reactions were performed in a 300 mL double-mantled glass reactor using toluene (80 mL) as solvent. b Temperature of
circulating water in the double mantle of the reactor; data in brackets are the maximal temperature reached in the reactor, due to the exothermicity of
the reaction. c Determined from the 1H NMR spectrum in C2D2Cl4 at 100 °C. d Determined by GPC at 150 °C in trichlorobenzene vs polystyrene
standards. e Determined by DSC; the Tm values refer to peak maxima. f Reactions conducted in a Schlenk flask (1 atm) or in an autoclave (6 atm), by
mixing pro-ligand 2a,b,d with (p-tolyl)CrBr2(THF)3 (1:1). g MeCN (4 equiv vs Cr) was added. h THF (4 equiv vs Cr) was added. i Pyridine (4 equiv vs
Cr) was added. j Internal olefin products (CH3-CHdCH-) amounted to ca. 50%, and the presence of alkanes was also observed but could not be
quantified, hampering exact determination of Mn,NMR
.
mL). The organic part was extracted with Et2O (3 × 50 mL). The
combined organic extracts were dried over MgSO4 and evaporated
to dryness. The crude residue was recrystallized from heptane and
dried under vacuum to give (3-methoxy-2-naphthyl)(triphenyl)silane
1
(7.11 g, 90%). H NMR (200 MHz, CDCl3, 25 °C): δ 7.80 (m,
2H), 7.67 (m, 7H), 7.55-7.23 (m, 12 H), 3.69 (s, 3H, OCH3). Anal.
Calcd for C29H24OSi: C, 83.61; H, 5.81. Found: C, 82.15; H, 5.23.18
(4-Bromo-3-methoxy-2-naphthyl)(triphenyl)silane. A 150 mL
Schlenk flask was charged with (3-methoxy-2-naphthyl)(triphenyl)-
silane (4.68 g, 11.23 mmol) and N-bromosuccinimide (NBS, 2.20 g,
12.36 mmol) under argon, followed by addition of DMF (10 mL).
The resultant mixture was stirred overnight at room temperature,
then diluted with water (ca. 500 mL) and extracted with CH2Cl2 (3
× 50 mL). The combined organic extracts were washed with water
(ca. 200 mL) and brine and dried over Na2SO4. The product was
purified by passing through a short silica column using heptane/
EtOAc (15:1) as the eluent to afford the product as an off-white
Figure 5. Typical HT-GPC (SEC) traces for oligoethylenes prepared
with 3a/MAO (top) and 3b/MAO (bottom) systems. The * marker
stands for the solvent signal.
Deuterated solvents (benzene-d6, toluene-d8, Eurisotop) were
vacuum-transferred from Na/K alloy into storage tubes. Starting
materials were purchased from Acros, Strem, and Aldrich and used
as received. NMR spectra of diamagnetic compounds were recorded
on Bruker AC-300 and AM-500 spectrometers. 1H and 13C chemical
shifts are reported in ppm vs SiMe4 and were determined by
reference to the residual solvent peaks. Assignment of resonances
for pro-ligands was made from 1H-13C HMQC and HMBC NMR
experiments. Coupling constants are given in Hertz. Elemental
analyses (C, H, N) were performed using a Flash EA1112 CHNS
Thermo Electron apparatus and are the average of two independent
determinations. Magnetic moment data were obtained on a Quantum
Design SQUID MPMS magnetometer, operating with a constant
magnetic field of 1000 Oe. UV spectra were recorded on a Varian
Cary 5000 UV-vis-NIR spectrophotometer. FAB-HRMS spectra
were recorded on a high-resolution MS/MS Micromass ZAB-
SpecTOF spectrometer.
1
solid (5.28 g, 96%). H NMR (200 MHz, CDCl3, 25 °C): δ 8.29
(d, J ) 8.4 Hz, 1H), 7.80 (s, 1H), 7.66 (m, 8H), 7.52-7.27 (m, 10
H), 3.18 (s, 3H, OCH3). Anal. Calcd for C29H23BrOSi: C, 70.30;
H, 4.68. Found: C, 68.99; H, 4.56.18
2-Hydroxy-3-(triphenylsilyl)-1-naphthaldehyde (1). tert-BuLi
(16.1 mL of a 1.5 M solution in pentane, 24.10 mmol) was added
dropwise to a stirred solution of (4-bromo-3-methoxy-2-naphthyl)-
(triphenyl)silane (6.02 g, 12.1 mmol) in Et2O (50 mL) at -78 °C.
The reaction mixture was stirred for 1.5 h at -78 °C and then 30
min at 0 °C, followed by addition of DMF (0.94 mL, 12.1 mmol).
The resultant mixture was stirred overnight at room temperature
and diluted with water (ca. 200 mL). The organic part was extracted
with CH2Cl2 (3 × 50 mL), and the combined organic extracts were
dried over MgSO4. The resultant solution was transferred into a
Schlenk flask under argon, and a solution of BBr3 (24.1 mL of 1
M solution in CH2Cl2, 24.1 mmol) was added dropwise at -78
(3-Methoxy-2-naphthyl)(triphenyl)silane. sec-BuLi (15.3 mL
of a 1.3 M solution in hexane/cyclohexane, 19.91 mmol) was added
dropwise, over a period of time of 15 min, to a stirred solution of
2-methoxynaphthalene (3.00 g, 18.96 mmol) in THF (70 mL) at
-30 °C. The reaction mixture was stirred overnight at room
temperature, and a solution of Ph3SiCl (5.87 g, 19.91 mmol) and
hexamethylphosphoramide (HMPA, 3.46 mL, 19.88 mmol) in THF
(50 mL) was added. The reaction mixture was refluxed for 20 h,
then cooled to room temperature and diluted with water (ca. 500
(18) Low carbon values were repetitively obtained. We ascribe this
problem to the presence of silicon, which is known to form noncombustible
SiC. Similar difficulty in obtaining satisfactory elemental analyses for
silicon-containing complexes of group 3 metals has been encountered by
other workers; see e.g.: (a) Arredondo, V. M.; Tian, S.; McDonald, F. E.;
Marks, T. J. J. Am. Chem. Soc. 1999, 121, 3633. (b) Mitchell, P.; Hajela,
S.; Brookhart, S. K.; Hardcastle, K. I.; Henling, L. M.; Bercaw, J. E. J. Am.
Chem. Soc. 1996, 118, 1045. (c) Kirillov, E.; Toupet, L.; Lehmann, C. W.;
Razavi, A.; Carpentier, J.-F. Organometallics 2003, 22, 4467.

Chromium(III) Complexes of Naphthoxy-Imine Ligands
Organometallics, Vol. 28, No. 8, 2009 2407
1
Figure 6. Typical H (500 MHz) NMR spectrum (C2D2Cl4, 373 K) of vinyl end-capped oligoethylenes produced with 3a/MAO (Table 3,
entry 4); Mn,NMR ) 1140 g mol-1, n ≈ 38. The * markers in the 1H NMR spectrum stand for resonances of internal olefin (CH3-CHdCH-)
products.
Figure 7. Typical 13C{1H} (125 MHz) NMR (high-field region) spectrum (C2D2Cl4, 373 K) of vinyl end-capped oligoethylenes produced
with 3a/MAO (Table 3, entry 4); n ≈ 38.
°C. The reaction mixture was stirred overnight at room temperature
and carefully hydrolyzed with water (ca. 500 mL). The mixture
was extracted with CH2Cl2 (3 × 50 mL), and the combined organic
extracts were dried over MgSO4 and evaporated to dryness. The
crude residue was recrystallized from methanol at room temperature
and dried under vacuum to give 1 as an off-white solid (5.44 g,
1-[(Quinolin-8-ylamino)methylene]-3-(triphenylsilyl)naphtha-
len-2-one (2a). To a stirred mixture of 1(1.09 g, 2.53 mmol) and
8-aminoquinoline (0.37 g, 2.53 mmol) in methanol (40 mL) was
added a catalytic amount of formic acid (ca. 10 mg) at room
temperature. The mixture was refluxed for 25 h, over which time
period the product precipitated as a microcrystalline powder. The
reaction mixture was transferred onto a Schott filter and filtered.
The orange solid obtained was washed with a minimal amount of
cold methanol and dried under vacuum to give 2a as an orange
solid (0.77 g, 55%). Crystals of 2a suitable for X-ray diffraction
1
95%). H NMR (200 MHz, CDCl3, 25 °C): δ 13.58 (s, 1H, OH),
10.88 (s, 1H, dCHO), 8.40 (d, J ) 8.4 Hz, 1H), 8.03 (s, 1H), 7.67
(m, 6H), 7.43 (m, 12H). Anal. Calcd for C29H22O2Si: C, 80.90; H,
5.15. Found: C, 80.17; H, 4.67.18

2408 Organometallics, Vol. 28, No. 8, 2009
KirilloV et al.
studies were obtained by recrystallization from CH2Cl2 at room
temperature. 1H NMR (500 MHz, CD2Cl2, 25 °C): δ 15.31 (d, J )
11.1 Hz, 1H, NH), 9.31 (d, J ) 11.1 Hz, 1H, dCHN), 9.02 (dd, J
) 1.8 Hz, J ) 4.4 Hz, 1H), 8.26 (dd, J ) 1.8 Hz, J ) 8.2 Hz, 1H),
8.07 (d, J ) 8.2 Hz, 1H), 7.81 (m, 2H), 7.73 (m, 7H), 7.66 (m,
1H), 7.57-7.40 (m, 12H), 7.27 (m, 1H). 13C{1H} NMR (125 MHz,
CD2Cl2, 25 °C): δ 185.2 (CdO), 151.7, 150.1, 146.4, 139.8, 137.4,
136.4, 136.1, 135.8, 135.0, 133.2, 130.0, 129.3, 129.2, 129.0, 127.7,
126.6, 126.5, 124.4, 123.5, 122.3, 118.3, 113.9, 108.2. Anal. Calcd
for C38H28N2OSi: C, 81.98; H, 5.07; N, 5.03. Found: C, 81.04; H,
4.98; N, 5.1.18
mixture was stirred overnight at room temperature and evaporated
to dryness under vacuum. The deep pink residue was recrystallized
from dry acetonitrile (ca. 20 mL) to give 3a as a violet crystalline
solid (0.187 g, 86%). Crystals suitable for X-ray diffraction analysis
were obtained from this batch. UV-vis (CH2Cl2, 298 K, mol-1
dm3 cm-1): ε527 5660, ε500 5296, ε371 6455. FAB-HRMS (CHCl3,
m/z): calcd for C76H54N4O2Si252Cr ([CrL2]+•)20 1162.3190; found
1162.3201. µ(BM) ) 3.87. Anal. Calcd for C40H30Br2CrN3OSi: C,
59.42; H, 3.74; N, 5.20. Found: C, 58.65; H, 3.52; N, 5.12.18
(ONNPy)CrBr2(MeCN) (3b). Complex 3b was prepared in a
similar manner to that described above for 3a, starting from 2b
(0.100 g, 0.192 mmol) and (p-tolyl)CrBr2(THF)3 (0.100 g, 0.192
mmol). 3b was recovered as a green crystalline solid (0.135 g, 91%).
Crystals suitable for X-ray diffraction analysis were obtained from
this batch. UV-vis (CH2Cl2, 298 K, mol-1 dm3 cm-1): ε456 2865,
1-{[(Pyridin-2-ylmethyl)amino]methylene}-3-(triphenylsilyl)-
naphthalen-2-one (2b). Using the same protocol as the one
described above for 2a, pro-ligand 2b was prepared as a yellow
solid in 60% yield (0.78 g), starting from 1 (1.08 g, 2.51 mmol)
ε
319 7384. FAB-HRMS (CHCl3, m/z): calcd for C70H54N4O2Si252Cr
1
and 2-aminomethylpyridine (0.29 g, 2.50 mmol). H NMR (500
([CrL2]+•)20 1090.3190; found: 1090.3181. Anal. Calcd for
C37H30Br2CrN3OSi: C, 57.52; H, 3.91; N, 5.44. Found: C, 57.1; H,
3.75; N, 5.35.18
MHz, CD2Cl2, 25 °C): δ 14.44 (br m, 1H, NH), 8.96 (d, J ) 8.8
Hz, 1H), 8.63 (d, J ) 4.1 Hz, 1H), 7.95 (d, J ) 8.8 Hz, 1H), 7.79
(s, 1H), 7.70 (m, 1H), 7.67 (m, 6H), 7.60-7.35 (m, 11H), 7.32 (d,
J ) 8.0 Hz, 1H), 7.25 (m, 1H), 7.23 (m, 1H), 4.88 (m, 2H, CH2Py).
13C{1H} NMR (125 MHz, CD2Cl2, 25 °C): δ 180.6 (CdO), 158.6,
156.4, 149.8, 149.3, 136.9, 136.3, 135.6, 135.1, 131.5, 129.8, 129.2,
128.9, 127.7, 126.1, 122.8, 122.6, 121.9, 117.8, 106.1, 57.7. Anal.
Calcd for C35H28N2OSi: C, 80.73; H, 5.42; N, 5.38. Found: C, 79.94;
H, 5.00; N, 5.3.18
(ONC6F5)CrBr2(MeCN)2 (3c). Complex 3c was prepared in a
similar manner to that described above for 3a, starting from 2c
(0.100 g, 0.168 mmol) and (p-tolyl)CrBr2(THF)3 (0.087 g, 0.168
mmol). 3c was recovered as a golden crystalline solid (0.101 g,
68%). UV-vis (CH2Cl2, 298 K, mol-1 dm3 cm-1): ε438 6500, ε337
10035, ε303 9626. FAB-HRMS (C2H4Cl2, m/z): calcd for
C70H42N2O2F10Si252Cr ([CrL2]+•)20 1240.2030; found 1240.2039.
µ(BM) ) 3.87. Anal. Calcd for C39H27Br2CrF5N3OSi: C, 52.72;
H, 3.06; N, 4.73. Found: C, 51.89; H, 2.78; N, 4.80.18
Synthesis of 1-[(Pentafluorophenyl)imino]methyl}-3-(triph-
enylsilyl)-2-naphthol (2c). Pro-ligand 2c was synthesized by
condensation of 1 (1.04 g, 2.42 mmol) and pentafluorophenylaniline
(0.44 g, 2.42 mmol) in toluene at reflux for 40 h in the presence of
PTSA (ca. 5 wt %), using a Dean-Stark apparatus. The final
reaction mixture was evaporated to dryness, and the solid residue
was recrystallized from methanol to give 2c as a yellow solid (0.93
g, 65%). 1H NMR (500 MHz, CDCl3, 25 °C): δ 14.49 (s, 1H, OH),
9.76 (s, 1H), 8.13 (d, J ) 8.5 Hz, 1H), 7.96 (s, 1H), 7.71 (d, J )
6.7 Hz, 6H), 7.69 (d, J ) 10.2 Hz, 1H), 7.62 (t, J ) 10.2 Hz, 1H),
7.52-7.30 (m, 10H). 13C{1H} NMR (125 MHz, CDCl3, 25 °C): δ
168.5, 165.9 (ipso-C phenol and CdN), 148.1, 136.4, 134.2, 134.0,
130.2, 129.6, 129.4, 127.9, 127.7, 126.3, 123.9, 118.9, 108.8 (signals
from the C6F5 group were not observed). 19F{1H} NMR (188 MHz,
CDCl3, 25 °C): δ -152.4 (m, 2F), -159.1 (t, 1F), -162.8 (m, 2F).
Anal. Calcd for C35H22F5NOSi: C, 70.58; H, 3.72; N, 2.35. Found:
C, 69.89; H, 3.52; N, 2.45.18
(OPhenNNQuin)CrBr2(MeCN) (3d). Complex 3d was prepared
in a similar manner to that described above for 3a, starting from
2d (0.186 g, 0.357 mmol) and (p-tolyl)CrBr2(THF)3 (0.185 g, 0.357
mmol). 3d was isolated as a deep pink crystalline solid (0.223 g,
81%). UV-vis (CH2Cl2, 298 K, mol-1 dm3 cm-1): ε505 3636, ε358
7684. FAB-HRMS (CHCl3, m/z): calcd for C70H54N4O2Si252Cr
([CrL2]+•)20 1090.3197; found 1090.3190. Anal. Calcd for
C37H30Br2CrN3OSi: C, 57.52; H, 3.91; N, 5.44. Found: C, 56.93;
H, 3.88; N, 5.36.18
Crystal Structure Determination of 2a, 2d, 3a, and 3b.
Crystals of 2a, 2d, 3a, and 3b suitable for X-ray diffraction analysis
were obtained by recrystallization of purified products (see Ex-
perimental Section). Diffraction data were collected at 100 K using
a Bruker APEX CCD diffractometer with graphite-monochroma-
tized Mo KR radiation (λ ) 0.71073 Å). A combination of ω and
φ scans was carried out to obtain at least a unique data set. The
crystal structures were solved by means of the Patterson method;
remaining atoms were located from difference Fourier synthesis
followed by full matrix least-squares refinement based on F2
(programs SHELXS-97 and SHELXL-97).21 Many hydrogen atoms
could be found from the Fourier difference analysis. Carbon- and
nitrogen-bound hydrogen atoms were placed at calculated positions
and forced to ride on the attached atom. The hydrogen atom
contributions were calculated but not refined. All non-hydrogen
atoms were refined with anisotropic displacement parameters.
Crystals of 3a were found to contain lattice disordered solvent
molecules, which could not be sufficiently modeled in the refine-
ment cycles. These molecules were removed using the SQUEEZE
procedure22 implemented in the PLATON package.23 The locations
of the largest peaks in the final difference Fourier map calculation
as well as the magnitude of the residual electron densities were of
Synthesis of 4-Methyl-2-[(quinolin-8-ylimino)methyl]-6-(triph-
enylsilyl)phenol (2d). Using the same protocol as the one described
above for 2a, pro-ligand 2d was prepared as a pink solid in 66%
yield (7.34 g), starting from 2-hydroxy-5-methyl-3-(triphenylsilyl)-
benzaldehyde8 (8.47 g, 21.46 mmol) and 8-aminoquinoline (3.10
1
g, 21.46 mmol). H NMR (500 MHz, CDCl3, 25 °C): δ 13.62 (s,
1H, NH), 9.04 (s, 1H, dCHN), 8.93 (dd, J ) 2.0 Hz, J ) 4.0 Hz,
1H), 8.19 (dd, J ) 2.0 Hz, J ) 8.5 Hz, 1H), 7.69 (m, 7H), 7.57
(m, 2H), 7.45-7.38 (m, 13H), 7.17 (d, J ) 2.0 Hz,), 2.26 (s, 3H,
CH3). 13C{1H} NMR (125 MHz, CDCl3, 25 °C): δ 166.7, 164.7
(ipso-C phenol and CdN), 150.4, 145.7, 143.2, 141.9, 136.5, 136.1,
135.5, 135.3, 135.2, 134.8, 129.8, 129.3, 127.7, 126.6, 125.8, 121.6,
121.0, 118.7, 20.5. Anal. Calcd for C35H28N2OSi: C, 80.73; H, 5.42;
N, 5.38. Found: C, 80.00; H, 5.28; N, 5.30.18
(4-CH3C6H4)CrBr2(THF)3. The synthesis of (p-tolyl)-
CrBr2(THF)3 was performed using a modified literature procedure,19
starting from CrCl3 and (p-tolyl)MgBr in THF (18% yield after
two recrystallizations from THF at 0 °C). Anal. Calcd for
C19H31Br2CrO3: C, 43.95; H, 6.02. Found: C, 43.81; H, 5.78.
(ONNQuin)CrBr2(MeCN) (3a). A Schlenk flask was charged with
2a (0.150 g, 0.269 mmol) and (p-tolyl)CrBr2(THF)3 (0.140 g, 0.269
mmol), and toluene (5 mL) was vacuum transferred in. The reaction
(20) The bis(ligand) complex fragment has been also observed as the
most intense peak in MS spectra of some related phenoxy-imino Cr(III)
dichloride complexes; see ref 7a.
(21) (a) Sheldrick, G. M. SHELXS-97, Program for the Determination
of Crystal Structures; University of Goettingen: Germany, 1997. (b)
Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal
Structures; University of Goettingen: Germany, 1997.
(19) Daly, J. J.; Sneeden, R. P. A.; Zeiss, H. H. J. Am. Chem. Soc. 1966,
88, 4287.
(22) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(23) Spek, A. L. Acta Crystallogr. 1990, A46, C-34.

Chromium(III) Complexes of Naphthoxy-Imine Ligands
Organometallics, Vol. 28, No. 8, 2009 2409
no chemical significance. Crystal data and details of data collection
and structure refinement for the different compounds are given in
Table 1. Main crystallographic data (excluding structure factors)
are available as Supporting Information, as cif files.
1.5Ia)/2If], where If and Ia are the relative intensities for CH2CH3
and CHdCH2, respectively (see Figure 6). The average number
molecular weight determined by NMR was calculated from the
following formula: Mn,NMR ) vinyl content(%) × [(Id + Ie - Ia)/
2(Ia)] × M(C2H4) + M(C5H10), where Id, Ie, and Ia are the relative
intensities for (CH2CH2)n, CH2CH3, and CHdCH2, respectively (see
Oligomerization of Ethylene. In a typical procedure, a 300 mL
glass high-pressure reactor (Top Industrie) was charged with 80
mL of freshly distilled toluene under argon flash. Mechanical stirring
(Pelton turbine, 1000 rpm) was started. The reactor was then purged
with ethylene, loaded with a solution of cocatalyst/scavenger
selected from MAO, AlEt2Cl, or Al(iBu)3, at atmospheric pressure,
and then kept at the desired temperature by circulating thermostatted
water in the reactor double wall. A solution of precatalyst 3a-d in
5 mL of toluene was injected in by syringe. The gas pressure in
the reactor was immediately set up at the desired pressure and kept
constant with a back regulator throughout the experiment. The
ethylene consumption was monitored via an Aalborg flowmeter.
After a given time period, the reactor was depressurized and the
reaction was quenched by adding about 5 mL of a 10% solution of
HCl in methanol. The oligomeric materials were further precipitated
by adding 500 mL of methanol, washed, and dried under vacuum
overnight at room temperature. The reaction conditions are sum-
marized in Table 3.
Figure 6), and M(C2H4) ) 28 g mol-1 and M(C5H10) ) 70 g mol-1
.
Acknowledgment. This work was financially supported
by Total Petrochemicals (grant to E.K.). We gratefully thank
Prof. Richard F. Jordan (The University of Chicago) for the
HT-GPC analyses. We are also grateful to Thierry Guizouarn
for SQUID measurements and Philippe Jehan for FAB-MS
analysis. J.F.C. thanks the Institut Universitaire de France
for a Junior IUF fellowship (2005-2009).
Supporting Information Available: Crystallographic data for
2a, 2d, 3a, and 3b as CIF files; NMR spectra for pro-ligands 2a,d,
UV-vis and FAB-MS spectra for complexes 3a-d, magnetic data
for complexes 3a,c. This material is available free of charge via
the Internet at http://pubs.acs.org.
The percentage of vinyl termination was determined by 1H NMR,
according to the following formula: vinyl content ) 1 - [(If -
OM801196D