Ethylene polymerization characteristics of an electron-deficient nickel(II) phenoxyiminato catalyst modulated by non-innocent intramolecular hydrogen bonding

Article abstract of DOI:10.1021/om100251j

The synthesis and characterization of the neutrally charged electron-deficient nickel(II) phenoxyiminato catalyst {2-(hydroxydiphenylmethyl) -4-tert-butyl-[6-(2,6-diisopropylphenyl)]salicylaldiminato} methyl(trimethylphosphine)nickel(II) (1b) with an intr

Full text of DOI:10.1021/om100251j

5040 Organometallics 2010, 29, 5040–5049
DOI: 10.1021/om100251j
Ethylene Polymerization Characteristics of an Electron-Deficient
Nickel(II) Phenoxyiminato Catalyst Modulated by Non-Innocent
Intramolecular Hydrogen Bonding†
Massimiliano Delferro, Jennifer P. McInnis, and Tobin J. Marks*
Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113
Received March 31, 2010
The synthesis and characterization of the neutrally charged electron-deficient nickel(II) phenoxy-
iminato catalyst {2-(hydroxydiphenylmethyl)-4-tert-butyl-[6-(2,6-diisopropylphenyl)]salicylaldiminato}-
methyl(trimethylphosphine)nickel(II) (1b) with an intramolecular hydrogen bond directed toward the
active catalytic site is reported. At room temperature, catalyst 1b exhibits 2.5ꢀ greater ethylene
polymerization activity and 2ꢀ greater polyethylene product branching than an analogous catalyst
without the hydrogen bond (2b). Furthermore, catalyst 1b produces substantially greater polyethylene
yields in the presence of polar additives such as ethyl ether, acetone, and water than does 2b under
identical conditions. This enhanced polymerization activity in the presence of polar additives suggests
that the hydrogen bonding proximate to the metal center significantly modifies the relative rates of
competing enchainment and chain transfer processes.
Introduction
comonomers such as acrylates.5 Our laboratory previously
demonstrated that cooperative effects in single-site6 bime-
tallic olefin polymerzation catalysts (group 47 and group
101c,d) selectively enhance bulky/polar comonomer enchain-
ment and branch formation versus the corresponding mono-
metallic catalysts. The nature and density of branching in
In the past several years, late-transition-metal catalysts for
olefin polymerization, in particular Ni(II) complexes,1 have
attracted much research interest.2 Due to their functional
group tolerance, such catalysts can effect ethylene polymer-
ization in the presence of polar additives3 and in aqueous
emulsions4 or can readily copolymerize ethylene with polar
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Guo, N.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 2008, 130, 2246–2261.
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† Part of the Dietmar Seyferth Festschrift. In honor of Professor Dietmar
Seyferth for his outstanding contributions in the field of Organometallic
Chemistry.
*To whom correspondence should be addressed. Tel: (þ1) 847 491
5658. Fax: (þ1) 847 491 2990. E-mail: t-marks@nortwestern.edu.
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2009, 41, 8929–8934. (b) Guironnet, D.; Goettker-Schnetmann, I.; Mecking,
S. Macromolecules 2009, 42, 8157–8164. (c) Rodriguez, B. A.; Delferro,
M.; Marks, T. J. J. Am. Chem. Soc. 2009, 131, 5902–5919. (d) Rodriguez,
B. A.; Delferro, M.; Marks, T. J. Organometallics 2008, 27, 2166–2168.
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r
pubs.acs.org/Organometallics
Published on Web 06/17/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 21, 2010 5041
Scheme 1. General Pathway for Nickel-Catalyzed Ethylene Polymerization
Chart 1
Ni(II)-mediated polymerization processes is known to de-
pend on competition between chain propagation and rever-
sible β-H elimination/addition (Scheme 1),8 which in turn
modifies the product microstructure and, hence, processing
and mechanical properties.9
To facilitate β-hydrogen elimination/re-insertion during
the propagation and thus favor highly branched polyolefins,
several approches have been demonstrated: (1) decrease the
ethylene concentration,1c (2) increase the reaction temperature,2j
(3) use cationic complexes,8m,o,p,10 and (4) decrease the electron
density at the metal center by introducing electron-withdrawing
ligand substituents.11 In this regard, electron deficiency at the Ni
center significantly increases ethylene polymerization rates,12 due
to a lowered ethylene-insertion barrier, and enhances β-agostic
interactions with Ni-alkyl species, as suggested by DFT
calculations.13 New ways to manipulate electron density at the
Ni center would be of great interest, and in the present contribu-
tion we present structural and solution studies along with olefin
polymerization catalytic chemistry of a novel phenoxyiminato
Ni(II) catalyst with a non-innocent intramolecular hydrogen
bond14 directed at the active catalytic center (1b; Chart 1). This
catalyst exhibits 2.5ꢀ increased polymerization activity in com-
parison to the control phenoxyiminato Ni(II) catalyst analogue
without an intramolecular hydrogen bond (2b). Furthermore,
this enhanced activity is mantained in the presence of polar
additives, such as water, acetone, and diethyl ether.
(8) (a) McCord, E. F.; McLain, S. J.; Nelson, L. T. J.; Ittel, S. D.;
Tempel, D.; Killian, C. M.; Johnson, L. K.; Brookhart, M. Macro-
molecules 2007, 40, 410–420. (b) Zhang, L.; Brookhart, M.; White, P. S.
Organometallics 2006, 25, 1868–1874. (c) Collins, S.; Ziegler, T. Organo-
metallics 2007, 26, 6612–6623. (d) Cherian, A. E.; Rose, J. M.; Lobkovsky,
E. B.; Coates, G. W. J. Am. Chem. Soc. 2005, 127, 13770–13771. (e) Liu,
W.; Brookhart, M. Organometallics 2004, 23, 6099–6107. (f) Jenkins, J. C.;
Brookhart, M. J. J. Am. Chem. Soc. 2004, 126, 5827–5842. (g) Leatherman,
M. D.; Svejda, S. A.; Johnson, L. K.; Brookhart, M. J. Am. Chem. Soc. 2003,
125, 3068–3081. (h) Gottfried, A. C.; Brookhart, M. Macromolecules 2003,
36, 3085–3100. (i) Shultz, L. H.; Tempel, D. J.; Brookhart, M. J. Am. Chem.
Soc. 2001, 123, 11539–11555. (j) Shultz, L. H.; Brookhart, M. Organome-
tallics 2001, 20, 3975–3982. (k) Gottfried, A. C.; Brookhart, M. Macro-
molecules 2001, 34, 1140–1143. (l) Tempel, D. J.; Johnson, L. K.; Huff, R. L.;
White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6686–6700. (m)
Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; Johnson, L. K.; White,
P. S.; Brookhart, M. Macromolecules 2000, 33, 2320–2334. (n) Guan, Z.;
Cotts, P. M.; McCord, E. F.; McLain, S. J. Science 1999, 283, 2059–2062. (o)
Killian, C. M.; Tempel, D. J.; Johnson, L. K.; Brookhart, M. J. Am. Chem.
Soc. 1996, 118, 11664–11665. (p) Johnson, L. K.; Killian, C. M.; Brookhart,
M. J. Am. Chem. Soc. 1995, 117, 6414–6415.
Experimental Section
Materials and Methods. All manipulations of air-sensitive
materials were performed with rigorous exclusion of oxygen
and moisture in flamed Schlenk-type glassware on a dual-
manifold Schlenk line, interfaced to a high-vacuum line (10-5
Torr), or in a nitrogen-filled Vacuum Atmospheres glovebox
with a high-capacity recirculator (<1 ppm of O2). Argon and
ethylene (Matheson, polymerization grade) were purified by
passage through a supported MnO oxygen-removal column and
an activated Davison 4A molecular sieve column. Ether and
THF solvents were purified by distillation from Na/K alloy/
benzophenone ketyl. Hydrocarbon solvents (n-pentane and
(9) (a) Brookhart, M. S.; Johnson, L. K.; Killian, C. M.; Arthur,
S. D.; Feldman, J.; McCord, E. F.; McLain, S. J.; Kreutzer, K. A.;
Bennett, M. A.; Coughlin, E. B.; Ittel, S. D.; Parthasarathy, A.; Tempel,
D. J. WO 9623010, 1996. (b) Simpson, D. M.; Vaughan, G. A. Ethylene
Polymers: LLDPE. In Encyclopedia of Polymer Science and Technology;
Mark, H. F., Ed.; Wiley: New York, 2003; Vol. 2, pp 441-482.
(10) (a) Leatherman, M. D.; Brookhart, M. Macromolecules 2001, 34,
2748. (b) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am.
Chem. Soc. 1998, 120, 888. (c) Johnson, L. K.; Mecking, S.; Brookhart, M. J.
Am. Chem. Soc. 1996, 118, 267.
ꢀ
(11) Kuhn, P.; Semeril, D.; Jeunesse, C.; Matt, D.; Neuburger, M.;
(13) Chan, M. S. W.; Deng, L.; Ziegler, T. Organometallics 2000, 19,
2741–2750.
Mota, A. Chem. Eur. J. 2006, 12, 5210–5219.
(12) Soula, R.; Broyer, J. P.; Llauro, M. F.; Tomov, A.; Spitz, R.;
Claverie, J.; Drujon, X.; Malinge, J.; Saudemont, T. Macromolecules
2001, 34, 2438–2442 and references therein.
(14) For reviews of hydrogen-bonding interactions in transition
metal complexes, see: Natale, D.; Mareque-Rivas, J. C. Chem. Commun.
2008, 425–437 and references therein.

5042 Organometallics, Vol. 29, No. 21, 2010
Delferro et al.
toluene) were dried using activated alumina columns according
to the method described by Grubbs15 and were additionally
vacuum-transferred from Na/K alloy immediately before
vacuum line manipulations. All solvents for high-vacuum-line
manipulations were stored in vacuo over Na/K alloy in Teflon-
valve-sealed bulbs. Other nonhalogenated solvents were dried
over Na/K alloy, and halogenated solvents were distilled from
Preparation of 1-(Methoxymethoxy)-4-tert-butylbenzene. To
a suspension of NaH (2.4 g, 100 mmol, 95%) in dry THF (30 mL)
was added dropwise a solution of 4-tert-butylphenol (10 g, 66.6
mmol) in dry THF (20 mL) at 0 ꢀC. The mixture was than warmed
to room temperature and stirred for 2 h. To the resulting mixture
was added dropwise chloromethyl methyl ether (MOMCl,
7.59 mL, 100 mmol) at 0 ꢀC over a period of 2 h. The reaction
mixture was next warmed to room temperature, and stirring was
continued for 4 h. A saturated solution of NH4Cl (50 mL) was
added to quench the reaction. The mixture was extracted with ethyl
ether (3 ꢀ 30 mL), and the organic phase was washed with brine
and dried over Na2SO4. After filtration, the volatiles were removed
in vacuo to yield a colorless oil. The product 1-(methoxymethoxy)-
4-tert-butylbenzene can be immediately used without further
purification. Yield: 96%. Anal. Calcd for C12H18O2 (M = 194.27):
C, 74.19; H, 9.34. Found: C, 73.74; H, 9.71. 1HNMR(25ꢀC, CDCl3,
500 MHz): δ 7.41-7.08 (m, 4H, Ph), 5.24 (s, 2H, -OCH2O-), 3.56
(s,3H,-OCH3),1.40(s,9,CH3) ppm. 13CNMR(25ꢀC, CDCl3,125
MHz): δ 155.1, 144.6, 126.3, 115.81, 94.5, 55.9, 34.2, 31.6 ppm.
Preparation of [5-tert-Butyl-2-(methoxymethoxy)phenyl]dip-
henylmethanol. To a dry THF (20 mL) solution of 1-(methoxy-
methoxy)-4-tert-butylbenzene (5.00 g, 25.7 mmol) were added
dropwise n-BuLi (10.30 mL, 25.7 mmol, 2.5 M in hexane) and
TMEDA (3.85 mL, 25.7 mmol) at 0 ꢀC. The reaction mixture
was stirred for 3 h at room temperature. Next, a solution of
benzophenone (4.68 g, 25.7 mmol) in dry THF (10 mL) was
added to the resulting slurry solution at 0 ꢀC and the reaction
mixture was stirred at room temperature overnight before
quenching with saturated aqueous NH4Cl solution. The THF
was then removed in vacuo, and the aqueous solution was
extracted with CH2Cl2 (3 ꢀ 20 mL). The organic phase was
dried over Na2SO4, filtered, and evaporated to dryness. The
residue was recrystallized from methanol to give [5-tert-butyl-
2-(methoxymethoxy)phenyl]diphenylmethanol as a white solid.
Yield: 88%. Anal. Calcd for C25H28O3 (M = 376.49): C, 79.75;
H, 7.50. Found: C, 80.01; H, 7.44. 1H NMR (25 ꢀC, CDCl3, 500
MHz): δ 7.31-6.57 (m, 13H, Ph), 5.19 (s, 1H, OH), 4.96 (s, 2H,
˚
CaH2 and stored over activated Davison 4 A molecular sieves.
Deuterated solvents were obtained from Cambridge Isotope
Laboratories (all g99 atom % D), were freeze-pump-
thaw degassed, were dried over Na/K alloy (C6D6) or CaH2
(CD2Cl2), and were stored in a storage tube. The reagents
trans-[NiMeCl(PMe3)2],16 [2-(tert-butyl)-6-(2,6-diisopropylphe-
nyl)imino]phenol, [2-(tert-butyl)-6-(2,6-diisopropylphenyl)imino]-
phenolato sodium salt,17 and {[2-(tert-butyl)-6-(2,6-diisopropyl-
phenyl)imino]phenolato}methyl(trimethylphosphine)nickel(II) (3)1d
were prepared according to literature procedures. For the pre-
paration of Schiff bases 1 and 2, the procedure of Skarzewski
and co-workers was modified.18 The reagents 4-tert-butylphenol,
NaH (95%), chloromethyl methyl ether (MOMCl), n-BuLi
(n-butyllithium, 2.5 M in hexane), N,N,N0,N0-tetramethylethane-
1,2-diamine (TMEDA), benzophenone, methyl iodide, N,N-di-
methylformamide (DMF), 2,6-diisopropylaniline, and (trimethyl-
silyl)methyl lithium salt (LiCH2TMS) were purchased from Sigma-
Aldrich, and [Ni(cod)2] (cod = 1,5-cyclooctadiene) was purchased
from Strem Chemicals.
Physical and Analytical Measurements. NMR spectra were
recorded on Bruker AVANCEIII (FT; 500 MHz, 1H; 125 MHz,
13C), Varian UNITYInova-500 (FT; 500 MHz, 1H; 125 MHz, 13C),
and Mercury-400 spectrometers (FT; 400 MHz, 1H; 100 MHz, 13C;
1
162 MHz, 31P). Chemical shifts (δ) for H and 13C spectra were
referenced using internal solvent resonances and are reported
relative to tetramethylsilane (TMS). Chemical shifts (δ) for 31P
spectra are reported relative to an external 85% H3PO4 standard.
NMR experiments on air-sensitive samples were conducted in
Teflon-valve-sealed sample tubes (J. Young). Solution magnetic
susceptibility was determined by 1H NMR using Evans’ method.19
Elemental analyses were performed by Midwest Microlab, India-
napolis, IN. 1H and 13C NMR spectra of polymers were acquired
in 1,1,2,2-tetrachloroethane-d2 at 120 ꢀC. In ethylene polymeriza-
tions, spectral assignments were made as described in the
literature.20 Melting temperatures of polymers were measured by
differential scanning calorimetry (DSC, Mettler Toledo DSC 822)
from the second scan with a heating rate of 10 ꢀC/min. Gel
permeation chromatography (GPC) was carried out in 1,2,4-
trichlorobenzene (stabilized with 125 ppm of BHT) at 150 ꢀC on
a Polymer Laboratories 220 instrument equipped with a set of
three PLgel 10 μm mixed-B columns with differential refractive
index, viscosity, and light scattering (15 and 90ꢀ) detectors. Data
reported were determined via triple detection.
-OCH2O-), 3.08 (s, 3H, -OCH3), 1.13 (s, 9H, CH3) ppm. 13
C
NMR (25 ꢀC, CDCl3, 125 MHz): δ 152.5, 146.5, 143.9, 135.2,
127.8, 127.0, 125.3, 114.0, 94.1, 82.2, 56.0, 34.1, 31.2 ppm.
Preparation of [(5-tert-Butyl-2-(methoxymethoxy)phenyl)]-
diphenylmethoxymethylene. To a suspension of NaH (0.38 g,
15.8 mmol, 95%) in dry THF (30 mL) was added a solution of
[5-tert-butyl-2-(methoxymethoxy)phenyl]diphenylmethanol (3 g,
7.09 mmol) in dry THF (20 mL) at 0 ꢀC. The mixture was stirred at
room temperature for 2 h. Methyl iodide (4.41 mL, 70.9 mmol) was
then added, and the mixture was heated at 60 ꢀC for another 2 h.
The reaction was next quenched with water (30 mL). The THF was
removed in vacuo, and the aqueous solution was extracted with
diethyl ether (3 ꢀ 20 mL). The organic phase was dried over
Na2SO4, filtered, and evaporated to dryness. The residue was rec-
rystallized from cold methanol to afford [(5-tert-butyl-2-(methoxy-
methoxy)phenyl)]diphenylmethoxymethylene as a white powder.
Yield: 79%. Anal. Calcd for C26H30O3 (M = 390.51): C, 79.97; H,
(15) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.
(16) Klein, H.-F.; Karsch, H. H. Chem. Ber. 1972, 105, 2628–2636.
(17) Wang, C.; Friedrich, S. K.; Younkin, T. R.; Li, R. T.; Grubbs,
R. H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149–
3151.
(18) Skarzewski, J.; Ostrycharz, E.; Siedlecka, R.; Zielinska-Blajet,
M.; Pisarski, B. J. Chem. Res., Synop. 2001, 7, 263–264.
(19) (a) Evans, D. F. J. Chem. Soc. 1957, 2003–2005. (b) Sur, S. K. J.
Magn. Reson. 1989, 82, 169–174.
1
7.74. Found: C, 80.56; H, 8.30. H NMR (25 ꢀC, CDCl3, 500
MHz): δ 7.83-6.94 (m, 13H, Ph), 4.69 (s, 2H, -OCH2O-), 3.04
(s, 3H, -OCH3), 2.99 (s, 3H, -PhOCH3), 1.31 (s, 9H, CH3) ppm.
13C NMR (25 ꢀC, CDCl3, 125 MHz): δ 152.5, 143.9, 142.9, 131.5,
128.9, 127.3, 126.7, 125.6, 125.3, 114.0, 94.1, 85.9, 55.9, 52.1, 34.4,
31.7 ppm.
(20) Polyethylene methyl branching densities were determined by 1H
NMR spectroscopy. The formula used to calculate branching was (CH3/
3)/[(CH þ CH2 þ CH3)/2] ꢀ 1000 = branches per 1000 carbons. CH3,
CH2, and CH refer to the integrations obtained for the methyl, methy-
lene, and methine resonances, respectively. (a) Jenkins, J. C.; Brookhart,
M. Organometallics 2003, 22, 250–256. (b) Chen, Q.; Yu, J; Huang, J
Organometallics 2007, 26, 617–625. (c) Hu, T.; Tang, L.; Li, X.; Li, Y.; Hu,
N. Organometallics 2005, 24, 2628–2632. (d) Zhang, D.; Jin, G. Organo-
metallics 2003, 22, 2851–2854. (e) Liu, W.; Ray, D. G., III; Rinaldi, P. L.
Macromolecules 1999, 32, 3817–3819. (f) Pooter, M. D.; Smith, P. B.;
Dohrer, K. K.; Bennett, K. F.; Meadows, M. D.; Smith, C. G.; Schouwenaars,
H. P.; Geerards, R. A. J. Appl. Polym. Sci. 1991, 42, 399–408.
Preparation of 5-tert-Butyl-3-(methoxydiphenylmethyl)-2-(methoxy-
methoxy)benzaldehyde. A solution of n-BuLi (2.5 M in hexane, 4.6
mL, 11.7 mmol) and TMEDA (1.75 mL, 11.7 mmol) were added to
a solution of [(5-tert-butyl-2-(methoxymethoxy)phenyl)]dipheny-
lmethoxymethylene (2.61 g, 7.8 mmol) in diethyl ether (50 mL) at
0ꢀC over 30 min. The mixture was stirred at this temperature for 4 h.
DMF (1.2 mL, 15.6 mmol) was then added at 0 ꢀC, and the reaction
mixture was warmed to room temperature and stirred overnight.
Water (50 mL) was next added, and the pH was adjusted to 7-8
with HCl. The organic phase was separated, and the aqueous layer

Article
Organometallics, Vol. 29, No. 21, 2010 5043
was extracted with diethyl ether (3 ꢀ 30 mL). The combined organic
phases were dried over Na2SO4, filtered, and evaporated to dryness.
The residue was recrystallized from methanol to give 5-tert-butyl-
3-(methoxydiphenylmethyl)-2-(methoxymethoxy)benzaldehyde as
a pale yellow powder. Yield: 76%. Anal. Calcd for C27H301O4 (M =
418.52): C, 77.48; H, 7.22. Found: C, 77.42; H, 7.26. H NMR
(25 ꢀC, CDCl3, 500 MHz): δ 10.22 (s, 1H, CHO), 7.04-7.24 (m,
13H, Ph), 4.31 (s, 2H, -OCH2O-), 3.29 (s, 3H, -OCH3), 3.06 (s,
3H, -PhOCH3), 1.33 (s, 9H, CH3) ppm. 13C NMR (25 ꢀC, CDCl3,
125 MHz): δ 192.0, 157.6, 146.5, 143.2, 136.9, 134.0, 130.9, 127.9,
127.0, 124.7, 101.0, 86.0, 77.1, 57.2, 52.1, 34.8, 31.3 ppm.
Preparation of 5-tert-Butyl-2-hydroxy-3-(hydroxydiphenyl-
methyl)benzaldehyde. Degassed HClconc (25 mL) in i-PrOH
(125 mL) at 0 ꢀC was added to a CH2Cl2 (125 mL) solution of
5-tert-butyl-3-(methoxydiphenylmethyl)-2-(methoxymethoxy)-
benzaldehyde (5.00 g, 11.9 mmol). The resulting solution was
warmed to room temperature over the course of 4 h, and the
stirring was continued overnight. Water (50 mL) was then added
to the resulting solution. The organic phases were separated,
and the aqueous layer was extracted with CH2Cl2 (3 ꢀ 30 mL).
The organic phase was dried over Na2SO4, filtered, and evapo-
rated to dryness. The residue was recrystallized from pentane
to give 5-tert-butyl-2-hydroxy-3-(hydroxydiphenylmethyl)ben-
zaldehyde as a pale yellow powder. Yield: 89%. Anal. Calcd for
C24H24O3 (M = 360.45): C, 79.97; H, 6.71. Found: C, 79.73; H,
6.71. 1H NMR (25 ꢀC, CDCl3, 500 MHz): δ 11.77 (s, 1H,
Ph-OH), 9.94 (s, 1H, CHO), 7.52-6.89 (m, 13H, Ph), 5.25 (s,
1H, C-OH), 1.17 (s, 9H, CH3) ppm. 13C NMR (25 ꢀC, CDCl3,
125 MHz): δ 197.3, 157.3, 145.7, 142.4, 135.5, 134.7, 129.3,
128.1, 127.8, 127.6, 120.3, 82.0, 34.3, 31.2 ppm.
Preparation of 5-tert-Butyl-2-hydroxy-3-(methoxydiphenylmethyl)-
benzaldehyde. Degassed HClconc (5 drops) in MeOH (15 mL) at
room temperature was added to a MeOH (10 mL) suspension of
5-tert-butyl-3-(methoxydiphenylmethyl)-2-(methoxymethoxy)ben-
zaldehyde (3.80 g, 9.01 mmol). The mixture was stirred at room
temperature for 50 min. Water (50 mL) was then added. The
MeOH was removed in vacuo, and the aqueous solution was
extracted with CH2Cl2 (3 ꢀ 30 mL). The organic phase was dried
over Na2SO4, filtered, and evaporated to dryness. The residue was
recrystallized from cold methanol to give 5-tert-butyl-2-hydroxy-
3-(methoxydiphenylmethyl)benzaldehyde as a pale yellow powder.
Yield: 60%. Anal. Calcd for C25H26O3 (M = 374.47): C, 80.18; H,
7.00. Found: C, 80.26; H, 7.10. 1HNMR(25ꢀC, CDCl3, 500 MHz):
δ 11.01 (s, 1H, Ph-OH), 9.91 (s, 1H, CHO), 8.06-7.31 (m, 13H,
Ph), 3.04 (s, 3H, OMe), 1.32 (s, 9H, CH3) ppm. 13C NMR (25 ꢀC,
CDCl3, 125 MHz): δ 195.9, 157.3, 142.2, 141.2, 133.6, 131.6, 129.0,
128.7, 127.6, 127.4, 121.0, 86.2, 51.9, 34.4, 31.4 ppm.
Preparation of 2-(Hydroxydiphenylmethyl)-4-tert-butyl-[6-(2,6-
diisopropylphenyl)]salicylaldimine (1). To a MeOH solution (20 mL)
of 5-tert-butyl-2-hydroxy-3-(hydroxydiphenylmethyl)benzaldehyde
(2.2 g, 6.1 mmol) were added formic acid (5 drops) and 2,6-
diisopropylaniline (1.73 mL, 9.15 mmol) at room temperature.
The mixture was stirred for 2 days, during which time a yellow
solid formed. The solid was next collected by filtration, washed
with cold methanol, and dried under vacuum. Yield: 96%.
Yellow crystals of 2-(hydroxydiphenylmethyl)-4-tert-butyl-[6-(2,
6-diisopropylphenyl)]salicylaldimine (1) suitable for X-ray stud-
ies were obtained by layering hexane onto a CH2Cl2 solution.
Anal. Calcd for C36H41NO2 (M = 519.72): C, 83.20; H, 7.95; N,
2.70. Found: C, 83.57; H, 7.91; N, 2.80. 1H NMR (25 ꢀC, CDCl3,
500 MHz): δ 14.22 (s, 1H, Ph-OH), 8.33 (s, 1H, CHN),
7.37-6.75 (m, 13H, Ph), 5.92 (s, 1H, C-OH), 2.97 (sept, 2H,
CHiso, 3JH,H = 6.5 Hz), 1.175 (d, 12H, CH3(iso), 3JH,H =6.5 Hz),
1.16 (s, 9H, CH3(tert)) ppm. 13C NMR (25ꢀC, CDCl3, 125 MHz):
δ 167.1, 157.6, 146.2, 145.2, 140.8, 139.0, 134.2, 131.9, 127.8,
127.7, 127.2, 125.7, 123.3, 117.8, 82.3, 34.0, 31.2, 28.1, 23.7 ppm.
Preparation of 2-(Methoxydiphenylmethyl)-4-tert-butyl-[6-(2,6-
diisopropylphenyl)]salicylaldimine (2). To a methanol solution
(100 mL) of 5-tert-butyl-2-hydroxy-3-(methoxydiphenylmethyl)-
benzaldehyde (2.0 g, 5.4 mmol) were added formic acid (5 drops)
Table 1. Crystal Data and Structure Refinement Details for
1 and 1b
1
1b
formula
fw
C36H41NO2
519.72
C40H52NNiO2P
668.49
cryst syst
space group
T, K
triclinic
P1
170(2)
triclinic
P1
100(2)
˚
a, A
9.6595(2)
11.1247(2)
14.6231(3)
100.354(1)
102.299(1)
95.643(1)
1494.98(5)
2
11.6789(1)
12.5998(2)
14.3988(2)
109.437(1)
106.588(1)
95.916(1)
1868.34(4)
2
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
Dcalcd, g cm-3
F(000)
1.154
560
1.188
716
cryst size, mm3
0.33 ꢀ 0.11 ꢀ 0.09 0.32 ꢀ 0.27 ꢀ 0.09
μ, mm-1
0.070
18 359
6075
0.595
42 449
10 836
8730
421
R1 = 0.0351
(wR2 = 0.0826)
R1 = 0.0495
(wR2 = 0.0892)
P
no. of rflns collected
no. of unique rflns
no. of rflns obsd (I > 2σ(I)) 3110
no. of params
R indices (I > 2σ(I))a
356
R1 = 0.0490
(wR2 = 0.0995)
R1 = 0.1063
(wR2 = 0.1418)
P
R indices (all data)a
P
P
a R1 = ||Fo| - |Fc||/ |Fo|. wR2 = [ [w(Fo2 - Fc2)2]/ [w(Fo2)2]].
and 2,6-diisopropylaniline (1.33 mL, 7.1 mmol). The mixture was
stirred for 2 h at reflux, and then overnight at room temperature.
The volatiles were next removed in vacuo to yield a yellow oil.
MeOH (10 mL) was added and the solution left in the refrigerator
at -20 ꢀC overnight. A yellow solid was formed. The solid was
collected by filtration, washed with cold methanol, and dried
under vacuum. Yield: 60%. Anal. Calcd for C37H43NO2 (M =
533.74): C, 83.26; H, 8.12; N, 2.62. Found: C, 83.17; H, 8.30; N,
2.73. 1H NMR (25 ꢀC, CDCl3, 500 MHz): δ 13.44 (s, 1H,
Ph-OH), 8.39 (s, 1H, CHN), 8.14-7.37 (m, 13H, Ph), 3.21 (s,
3
1H, -OMe), 3.02 (sept., 2H, CHiso, JH,H = 6.5 Hz), 1.25 (d,
3
12H, CH3iso, JH,H = 6.5 Hz), 1.49 (s, 9H, CH3tert) ppm. 13C
NMR (25 ꢀC, CDCl3, 125 MHz): δ 166.8, 157.0, 146.2, 142.6,
140.9, 138.8, 130.2, 128.9, 128.2, 127.4, 126.9, 125.3, 123.2, 118.4,
85.9, 52.0, 34.3, 31.6, 28.1, 23.6 ppm.
Preparation of 2-(Hydroxydiphenylmethyl)-4-tert-butyl-[6-(2,6-
diisopropylphenyl)]salicylaldiminate Li(THF)þ Salt (1a). Com-
pound 1 (2 g, 3.85 mmol) and LiCH2TMS (0.398 g, 4.23 mmol)
were combined in a reaction flask in the glovebox. Dry THF
(15 mL) was added at -78 ꢀC and the mixture was stirred for
30 min, followed by stirring at room temperature overnight. The
volatiles were next removed in vacuo and the residue was recrys-
tallized from pentane to give 2-(hydroxydiphenylmethyl)-4-tert-
butyl[6-(2,6-diisopropylphenyl)]-salicylaldiminate lithium salt (1a)
as a white powder. Yield, 89%. Anal. Calcd for C40H48LiNO3
(M = 597.76): C, 80.37; H, 8.09; N, 2.34. Found: C, 80.62; H, 7.83;
N, 2.66. 1H NMR (25 ꢀC, C6D6, 500 MHz): δ 8.06 (s, 1H, CHN),
7.18-6.77 (m, 13H, Ph), 5.24 (s, br, 1H, C-OH), 3.41 (m, 4H,
3
THF), 3.02 (sept., 2H, CH(iso), JH,H = 7.0 Hz), 1.35 (m, 4H,
THF), 1.16 (s, 9H, CH3(tert)), 1.04 (d, 6H, CH3(iso), 3JH,H = 7.0
3
Hz), 0.855 (d, 6H, CH3(iso), JH,H = 7.0 Hz) ppm. 13C NMR
(25 ꢀC, C6D6, 125 MHz): δ 169.1, 168.3, 151.1, 147.3, 140.2, 136.7,
132.7, 132.5, 132.3, 127.9, 127.4, 125.2, 124.0, 122.3, 84.9, 68.1
(THF), 34.8, 32.0, 28.5, 26.1 (THF), 25.8 ppm.
Preparation of 2-(Methoxydiphenylmethyl)-4-tert-butyl-[6-(2,6-
diisopropylphenyl)]salicylaldiminate Liþ Salt (2a). Compound 2
(1.63 g, 3.05 mmol) and LiCH2TMS (0.316 g, 3.36 mmol) were
combined in a reaction flask in the glovebox. Dry THF (15 mL)
was added at -78 ꢀC, and the mixture was stirred for 30 min,
followed by stirring at room temperature overnight. The volatiles
were next removed in vacuo, and the residue was recrystallized

5044 Organometallics, Vol. 29, No. 21, 2010
Delferro et al.
Scheme 2. Ligand Synthesis
from pentane to give 2-(methoxydiphenylmethyl)-4-tert-butyl-
[6-(2,6-diisopropylphenyl)]salicylaldiminate lithium salt (2a) as a
white powder. Yield: 80%. Anal. Calcd for C37H42LiNO2 (M =
539.68): C, 82.34; H, 7.84; N, 2.60. Found: C, 82.62; H, 7.59; N,
1
2.61. H NMR (25 ꢀC, C6D6, 500 MHz): δ 8.19 (s, 1H, CHN),
7.47-6.85 (m, 13H, Ph), 3.26 (sept., 2H, CH(iso), 3JH,H = 6.5 Hz),
2.78 (s, 3H, -OMe), 1.24 (s, 9H, CH3(tert)), 1.42 (d, 12H, CH3-
(iso), 3JH,H = 6.5 Hz) ppm. 13C NMR (25 ꢀC, C6D6, 125 MHz): δ
169.7, 167.6, 151.6, 144.3, 139.7, 134.1, 132.5, 131.9, 129.9, 126.5,
124.9, 123.6, 122.1, 90.4, 52.8, 34.3, 31.6, 28.4, 22.6 ppm.
Preparation of {2-(Hydroxydiphenylmethyl)-4-tert-butyl-[6-(2,6-
diisopropylphenyl)]salicylaldiminato}methyl(trimethylphosphine)-
nickel(II) (1b). A solution of 7a (0.400 g, 0.67 mmol) in benzene
(30mL) was added dropwiseatroomtemperaturetoa solutionof
trans-[NiMeCl(PMe3)2] (0.175 g, 0.67 mmol) in benzene (25 mL).
The orange mixture was stirred for 6 h at room temperature.
After this time, the reaction mixture was filtered by cannula. The
filtrate was then evaporated in vacuo, and the solid residue was
washed with pentane. A light orange microcrystalline powder
of {2-(hydroxydiphenylmethyl)-4-tert-butyl-[6-(2,6-diisopropyl-
phenyl)]salicylaldiminato}methyl(trimethylphosphine)nickel(II)
(1b) was obtained. Yield: 92%. Orange crystals of 1b suitable for
X-ray studies were obtained by slow evaporation of pentane
solutions. Anal. Calcd for C40H52NiNO2P (M = 668.51): C,
Figure 1. ORTEP plot of the molecular structure of ligand 1.
Thermal ellipsoids are drawn at the 50% probability level. Selected
distances (A): C1-O1 = 1.361(3), C24-O2 = 1.443(3), C11-
N1 = 1.278(3).
˚
1
71.87; H, 7.84; N, 2.10. Found: C, 71.68; H, 7.81; N, 2.08. H
NMR (25 ꢀC, C6D6, 500 MHz): δ 8.22 (s, 1H, C-OH), 7.89 (s,
1H, CHN), 7.62-6.98 (m, 13H, Ph), 3.88 (m, 2H, CH(iso),
After this time, the reaction mixture was filtered by cannula. The
filtrate was then evaporated in vacuo, and the solid residue was
washed with pentane. A light orange microcrystalline powder of
{2-(methoxydiphenylmethyl)-4-tert-butyl-[6-(2,6-diisopropylphenyl)]-
salicylaldiminato}methyl(trimethylphosphine)nickel(II) (2b) was
obtained. Yield: 89%. Anal. Calcd for C41H54NiNO2P (M =
682.54): C, 72.15; H, 7.97; N, 2.05. Found: C, 72.47; H, 7.92; N,
1.99. 1H NMR (25 ꢀC, C6D6, 500 MHz): δ 7.98 (d, 1H, CHdN,
4JP,H=9.5 Hz), 7.59-6.97(m, 13H, Ph), 4.02 (sept., 2H, CH(iso),
3JH,H = 7 Hz), 3.32 (s, 3H, C-OMe), 1.38 (d, 6H, CH3(iso),
3JH,H = 7 Hz), 1.20 (s, 9H, CH3(tert)), 1.09 (d, 6H, CH3(iso),
3JH,H = 7 Hz), 0.71 (d, 9H, PMe3, 4JP,H = 9.5 Hz), -1.13 (d, 3H,
3
3JH,H = 6.5 Hz), 1.31 (d, 6H, CH3(iso), JH,H = 6.5 Hz), 1.11
(s, 9H, CH3(tert)), 0.97 (d, 6H, CH3(iso), 3JH,H = 6.5 Hz), 0.59
(d, 9H, PMe3, 4JP,H = 9 Hz), -1.14 (s, 3H, Ni-CH3) ppm. μeff
=
1.08 μB in CD2Cl2. 13C NMR (25 ꢀC, C6D6, 125 MHz): δ 166.3,
163.7, 149.0, 141.3, 136.9 136.2, 134.2, 129.3, 126.9, 123.7, 119.8,
83.5, 33.8, 31.4, 28.6, 25.0, 23.2, 13.3 (d, PMe3, 1JC,P = 28 Hz),
-12.5 (d, Ni-CH3, 2JC,P = 43 Hz). 31P{1H} NMR (25 ꢀC, C6D6,
162 MHz): δ -15.7 ppm.
Preparation of {2-(Methoxydiphenylmethyl)-4-tert-butyl-[6-(2,6-
diisopropylphenyl)]salicylaldiminato}methyl(trimethylphosphine)-
nickel(II) (2b). A solution of 2a (0.500 g, 0.92 mmol) in benzene
(30mL) was added dropwiseatroomtemperaturetoa solutionof
trans-[NiMeCl(PMe3)2] (0.242 g, 0.92 mmol) in benzene (25 mL).
The orange mixture was stirred for 2 days at room temperature.
3
Ni-CH3, JP,H = 7.5 Hz) ppm. 13C NMR (25 ꢀC, C6D6, 125
MHz): δ 165.7, 149.9, 147.5, 141.4, 137.5, 134.2, 131.2, 126.1,
123.6, 119.9, 88.2, 53.0, 33.8, 31.4, 28.6, 25.0, 23.2, 12.9 (d, PMe3,
2
1JC,P = 26 Hz), -13.5 (d, Ni-CH3, JC,P = 52 Hz). 31P{1H}
NMR (25 ꢀC, C6D6, 162 MHz): δ -8.7 ppm.

Article
Organometallics, Vol. 29, No. 21, 2010 5045
Figure 2. ORTEP plots of the molecular structure of 1b: (A) view perpendicular to the molecular plane; (B) view in the molecular plane.
Thermal ellipsoids are drawn at the 50% probability level. H atoms are omitted for clarity, except for the H2 atom, which is involved in
˚
a hydrogen bond. Selected distances (A) and angles (deg): Ni1-O1 = 1.925(1), Ni1-C1 = 1.932(1), Ni1-N1 = 1.937(1), Ni1-P1 =
2.147(4), O2-H2 = 0.81(2), N1-C11 = 1.305(2), C5-O1 = 1.312(1), C28-O2 = 1.440(2); —O1-Ni1-C1 = 164.4(1),
—O1-Ni1-N1 = 93.6(1), —C1-Ni1-N1 = 94.5(1), —O1-Ni1-P1 = 88.3(1), —C1-Ni1-P1 = 87.0(1), —N1-Ni1-P1 =
166.0(1), —C28-O2-H2 = 104.2(2), —C11-N1-Ni1 = 123.6(1), —O2-H2 O1 = 145.1(1).
3 3 3
Scheme 3. Synthesis of Catalysts 1b and 2b
X-ray Data Collection, Structure Solution, and Refinement.
Intensity data for compounds 1 and 1b were collected at 170 and
100 K, respectively, on a Bruker AXS Smart 100021 single-
crystal diffractometer equipped with an area detector using
Chart 2
˚
graphite-monochromated Mo KR radiation (λ = 0.710 73 A).
Crystallographic and experimental details of the structure are
summarized in Table 1. An empirical correction for absorption
was made. The structures were solved by direct methods and
refined by full-matrix least-squares procedures (based on Fo2),22
first with isotropic thermal parameters and then with anisotro-
pic thermal parameters in the last cycles of refinement for all the
non-hydrogen atoms. The hydrogen atoms, introduced into the
geometrically calculated positions, were refined riding on the
corresponding parent atoms, except for the hydrogen H2 in 1b
that was found in the ΔF2 maps and refined isotropically.
General Procedure for Ethylene Polymerization by Ni Cata-
lysts. A 350 mL glass pressure vessel (dried in a 120 ꢀC oven
overnight prior to use) was loaded with a solution of 10 μmol of
catalyst and 20 μmol of [Ni(cod)2] in 25 mL of dry toluene inside
the glovebox. A large magnetic stir bar was added to the vessel,
and it was sealed, taken out of the glovebox, and attached to a
high-pressure/high-vacuum line. The solution was then de-
gassed and brought to the required temperature with an external
bath, and the temperature of the bath was monitored by a
thermocouple to ensure minimal mass transfer effects. The
reactor was then quickly charged with 8.0 atm of ethylene and
polymerization was allowed to proceed for 40 min with rapid
stirring. After the desired run time, the reactor was vented, and
the reaction mixture was quickly quenched with 10% HCl in
methanol. The precipitated polymer was stirred for several
hours, collected by filtration, and washed with methanol. It
was then dried under high vacuum at 80 ꢀC overnight.
General Procedure for Ethylene Polymerization by Ni Cata-
lysts in Polar Solvents. A 350 mL glass pressure vessel (dried in a
120 ꢀC oven overnight prior to use) was loaded with a solution of
10 μmol of catalyst and 20 μmol of [Ni(cod)2] in 25 mL of dry
toluene inside the glovebox. A large magnetic stir bar was added
to the vessel, and it was sealed, taken out of the glovebox, and
attached to a high-pressure/high-vacuum line. The solution was
than degassed and brought to the required temperature with an
external bath, and the temperature of the bath was monitored by
a thermocouple to ensure minimal mass transfer effects. The
reactor was pressurized with 1.0 atm of ethylene, and 1500 equiv
(21) SAINT Software Users Guide, Version 6.0; Bruker Analytical
X-ray Systems: Madison, WI, 1999.
(22) Sheldrick, G. M. SADABS; Bruker Analytical X-ray Systems,
Madison, WI, 1999. Sheldrick, G. M. SHELXL-97, Program for Crystal
€
€
Structure Refinement; University of Gottingen, Gottingen, Germany, 1997.

5046 Organometallics, Vol. 29, No. 21, 2010
Table 2. Ethylene Homopolymerization Data at 25 ꢀC and at 50 ꢀC with Catalysts 1b, 2b, and 3
Delferro et al.
c
entry
catalysta
T (ꢀC)
time (min)
polymer yield (g)
activityb
Mw
Mw/Mn
branches/1000 Cd
Tm (ꢀC)e
1
2
3
4
5
6
1b
2b
3
1b
2b
3
25
25
25
50
50
50
40
40
40
40
40
40
7.82
3.12
3.50
5.21
6.32
6.72
148(1)
59(2)
65(3)
99(5)
120(3)
125(2)
6700
7400
62700
1400
3100
5600
1.8
2.0
2.8
2.4
2.2
1.9
60
44
27
104
77
77
75
77
105
31
33
31
a Polymerizations carried out with 10 μmol of catalyst and 2.0 equiv of cocatalyst/Ni at 25 ꢀC in 25 mL of toluene at 8.0 atm ethylene pressure. Each
entry is the average of at least two runs. b In units of kg of polyethylene/((mol of Ni) h atm). c Determined by GPC (triple detection). d Determined by
1H NMR.20 e Melting temperature determined by DSC.
of the desired rigorously degassed polar solvent additive was
Table 3. Ethylene Homopolymerization Data at 50 ꢀC with
Catalyst 1b
quickly syringed in. The pressure was then swiftly brought to 8.0
atm of ethylene for 40 min with rapid stirring. After the desired
run time, the reactor was vented, and the reaction mixture was
quickly quenched with 10% HCl in methanol. The precipitated
polymer was stirred for several hours, collected by filtration, and
washed with methanol. It was then dried under high vacuum at
80 ꢀC overnight.
entry catalysta T (ꢀC) time (min) polymer yield (g) activityb
4
5
6
7
8
1b
1b
1b
1b
1b
50
50
50
50
50
10
20
30
40
60
1.87
3.22
4.33
5.21
6.84
140(3)
120(4)
108(4)
99(5)
85(4)
Decomposition Mechanism Experiment. A J. Young NMR
tube was charged with catalyst 1b (0.007 g, 10.5 μmol), ligand 1
(0.0055 g, 10.5 μmol), and C6D6 (0.7 mL) at room temparature.
Conversion to the bis-ligation product at 50 ꢀC was not observed
a Polymerizations carried out with 10 μmol of catalyst and 2.0 equiv of
cocatalyst/Ni at 50 ꢀC in 25 mL of toluene at 8.0 atm ethylene pressure.
Each entry is the average of at least two runs. b In units of kg of
polyethylene/((mol of Ni) h atm).
1
via H NMR spectroscopy, only the formation of free ligand,
Ni(0), and a trace amount of unidentified products.
to low field of the hydroxyl protons (δ 14.22 (O1H1) and 5.92
(O2H2) ppm in CDCl3). The 1H NMR spectrum of 2 shows a
similar chemical shift for the phenol proton (δ 13.44 ppm in
CDCl3), again suggesting significant intramolecular hydrogen
bonding.
Results
The goal of this research was to investigate the effects of
installing a hydrogen bond directed toward the active site of
a Ni(II) phenoxyiminato olefin polymerization catalyst (1b)
and to compare the ethylene polymerization properties with
those of analogous catalysts without intramolecular hydro-
gen bonding (catalyst 2b). Ethylene homopolymerizations
were also carried out in the presence of polar additives, and it
is found that introduction of the proximate -OH group
substantially increases catalyst activity tolerance.
Catalysts Synthesis and Characterization. The ligand
2-(hydroxydiphenylmethyl)-4-tert-butyl-[6-(2,6-diisopropyl-
phenyl)]salicylaldimine (1) is efficiently synthesized by con-
densation of 5-tert-butyl-2-hydroxy-3-(hydroxydiphenylmethyl)-
benzaldehyde18 with 2,6-diisopropylaniline in methanol
(Scheme 2). The analogous ligand 2-(methoxydiphenylmethyl)-
4-tert-butyl-[6-(2,6-diisopropylphenyl)]salicylaldimine (2), de-
signed as a non-hydrogen-bonded control, is prepared in a similar
manner via selective deprotection of the MOM-protected
phenol by stirring with dilute HCl in MeOH for 50 min at
room temperature (see Scheme 2).
Monodeprotonation of 1 and 2 with 1.1 equiv of LiCH2TMS
in THF affords the 2-(hydroxydiphenylmethyl)-4-tert-butyl-
[6-(2,6-diisopropylphenyl)]salicylaldiminate lithium salt 1a
and 2-(methoxydiphenylmethyl)-4-tert-butyl-[6-(2,6-diisopro-
pylphenyl)]salicylaldiminate lithium salt 2a, respectively
(Scheme 3). Deprotonation is selective at the 1 phenol due to
the large pKa difference of the two hydroxyl groups.25 The 1H
NMR spectrum of 1a in C6D6 still exhibits the hydroxyl proton
H2 resonance at δ 5.239 ppm, and two new signals at δ 3.412
and 1.349 ppm are assigned to a single THF molecule co-
ordinated to the Liþ ion. Instead, in compound 2a, no THF
molecules are coordinated to the lithium atom, as confirmed
by 1H NMR spectroscopy. In both cases, salts 1a and 2a were
isolated prior to reaction with the Ni(II) reagent. Reaction of
lithium salt 1a and 2a with 1.0 equiv of trans-[NiMeCl(PMe3)2]
in benzene yields the Ni(II) phenoxyiminato complexes 1b and
2b, respectively (Scheme 3).
The solid-state structure of complex 1b was determined by
X-ray diffraction, and experimental details are summarized
in Table 1. ORTEP views of the crystal structure (Figure 2)
reveal that the phenoxyiminato ligand chelates the Ni center
in a N,O-κ2 fashion. The structure of 1b can be compared
(vide infra) to these of related hydrogen-bonded complexes
(Chart 2) {[Ph2PCHCO)(2-OH-C6H4)]Ni(PPh3)Ph} (4),26
Yellow crystals of 1 suitable for X-ray diffraction were
obtained by layering hexane onto a CH2Cl2 solution. The
ORTEP plot of the structure of 1 is depicted in Figure 1, and
experimental details are summarized in Table 1. In the solid
state, two intramolecular hydrogen bonds are present in
ligand 1 (O1-H1 N1 and O2-H2 O1), which form
3 3 3
3 3 3
two six-membered pseudorings.23 The distance between phe-
nol atom O1 and phenyl methanol O2 is unexceptional
˚
(2.781(2) A), while that between the phenol O1 atom and
(25) The pKa of phenolin water at 25 ꢀC is 9.95: Torres-Lapasio, J. R.;
Garcia-Alvarez-Coque, M. C.; Bosch, E.; Roses, M. J. Chromatogr. A
2005, 1089, 170–186. In contrast, the pKa of triphenylmethanol is 12.73:
Nishiura, Y.; Omatsu, T.; Nakayama, H.; Matsufuji, A.; Takahashi, O.;
Nimura, S. PCT Int. Appl. WO2006016667 A1, 2006.
24
imine N1 atom is 2.617(2) A. These two hydrogen bonds
˚
persist in solution, as confirmed by the 1H NMR displacement
(23) Filarowski, A.; Koll, A.; Sobczyk, L. Curr. Org. Chem. 2009, 13,
172–193.
(24) In the Cambridge Crystallographic DataBase, the meandistance
(26) Braunstein, P.; Chauvin, Y.; Mercier, S.; Saussine, L.; De Cian,
A.; Fischer, J. J. Chem. Soc., Chem. Commun. 1994, 2203–2204. This is a
SHOP-type ethylene oligomerization catalyst; the presence of an intramole-
cular hydrogen bond influences the product oligomer molecular mass
distribution: C4-C8 = 95-97%.
˚
˚
(A) for an intramolecular hydrogen bond O(H) O is 2.44 A and for
3 3 3
˚
O(H) N is 2.68 A.
3 3 3

Article
Organometallics, Vol. 29, No. 21, 2010 5047
Scheme 4
Table 4. Ethylene Homopolymerization Data at 25 ꢀC in the Presence of 1500 Equiv of Polar Additive
c
entry
catalysta
polar additive
polymer yield (g)
activityb
Mw
Mw/Mn
branches/1000 Cd
Tm (ꢀC)e
1
2
3
4
5
6
7
8
9
1b
2b
3
1b
2b
3
1b
2b
3
ethyl ether
ethyl ether
ethyl ether
acetone
acetone
acetone
water
5.93
2.20
2.83
2.77
1.20
2.11
1.93
0.62
0.45
112(2)
42(2)
60(4)
52(1)
23(2)
39(2)
37(3)
12(2)
10(1)
5300
7900
53800
4900
8000
58000
2600
8100
2.1
2.1
2.8
1.7
2.1
2.6
2.1
2.3
1.6
59
48
33
54
52
26
50
41
30
66
73
104
61
69
105
79
water
water
75
108
66200
a Polymerizations carried out with 10 μmol of catalyst and 2.0 equiv of cocatalyst/Ni at 25 ꢀC and 1500 equiv of polar additive for 40 min in 25 mL of
toluene at 8.0 atm ethylene pressure. b In units of kg of polyethylene/((mol of Ni) h atm). Each entry is the average of at least two runs. c Determined by
GPC (triple detection). d Determined by 1H NMR.20 e Melting temperature determined by DSC.
{(2,6-iPr2-C6H3)NdCH[2-(20-(OH)-C6H4)C6H3O)]Ni(PPh3)Ph}
(5),27 and [NiMe(OPh)(HOPh)(PMe3)2] (6).28 Note, however,
that the Ni-O bond in 1b (1.925(1) A) is significantly longer
than those found in the Cambridge Structural Database for
˚
analogous compounds (mean value 1.900(1) A), suggesting
that the proximate hydrogen bond weakens the O1 donor
power.
The above structural results are also in accord with the
DFT calculations of Ziegler for N,O-chelated Ni catalysts,
which argue that reduced electron density at the O atom
depresses the ethylene insertion barrier,13 and the experimental
results of Matt et al. with Ni(II) phosphanylenolates having
electron-withdrawing substituents.11 The intramolecular O2-
respectively, from the Ni1-O1-N1 mean plane. This distor-
tion is due to the intramolecular hydrogen bond and is
accompanied by a slight paramagnetism in solution, as evi-
denced by 1H NMR (μeff ≈ 1.0 μB in CD2Cl2 at room
temperature).19 However, complex 2b is diamagnetic in solu-
tion, which suggests that the distortion caused by the intra-
molecular hydrogen bonding in 1b is responsible for the
paramagnetism. The 1H-1H 2D NOESY NMR spectrum of
1b (C6D6 at 25 ꢀC) displays cross-peaks between the Ni-CH3
group and one iPr group (CH3 and CH) (see Figure S1 in the
Supporting Information). Close proximity between the OH
group and trimethylphosphine is also evident and is consistent
with the solid-state distorted-square-planar coordination geo-
˚
1
H2 O1 hydrogen bond is preserved in 1b, with —O2-
metry. Furthermore, the H NMR spectrum exhibits a large
3 3 3
3 3 3
˚
H2 O1 = 145.0(1)ꢀ. The H2 atom is located ∼0.81(1) A
downfield OH signal displacement from δ 5.239 ppm in 1a to
8.292 ppm in 1b. Complex 2b shows the same spatial arrange-
ment of the PMe3 and Me groups as in compound 1b, as is
evident in the 1H-1H 2D NOESY NMR spectrum.
˚
from O2 of the hydroxyl group and 1.98(1) A from O1 of the
salicylideniminato ligand. The distance between the O1
(hydroxyl group) and O2 (salicylideniminato ligand) is
˚
2.68(1) A. The intramolecular hydrogen-bonding parameters
Ethylene Homopolymerization Experiments. Ethylene
homopolymerizations were carried out at room temperature
with catalysts 1b, 2b, and 3 in the presence of the phosphine
scavenger/cocatalyst Ni(cod)2, using conditions minimizing
mass transport and exotherm effects.7e,g-j Most notable is
that catalyst 1b exhibits, at room temperature, 2.5ꢀ greater
polymerization activity than do 2b and 3 (Table 2). The
microstructures of the polyethylenes produced by all cata-
lysts were characterized by 1H and 13C NMR spectroscopy.20
The 13C NMR spectra show prominent non polyethylene
backbone resonances assignable to methyl and hexyl
branches (see Supporting Information), except for polyethy-
lenes produced by catalyst 1b, where small amounts of ethyl
branches are also evident. 1H NMR spectra of the polyethy-
lenes produced by catalysts 1b and 2b also exhibit vinyl end
groups -CH2CHdCH2, internal olefinic subunits -CHdCH-,
and vinylidene groups -CH2C(Me)dCH2. The polyethylene
are significantly different from those found in the crystal
˚
structure of complex 5 (O-H O bond distance 2.62 A;
3 3 3
—O-H O = 158ꢀ)27 and complex 6 (O-H O bond
3 3 3
3 3 3
distance 2.61 A; —O-H O = 165ꢀ).28 With regard to
˚
3 3 3
complex 5, the distance between the two oxygen atoms is
shorter than in 1b, while —O-H O is greater. These
3 3 3
variations in bond distance and angle, as well as the higher
acidity of the free hydroxyl group in 5 versus 1b,25 correlate
with notable differences in ethylene polymerization properties
(vide infra). The trimethylphosphine and the Ni-methyl
˚
group are displaced approximately 0.515(2) and 0.443(3) A,
(27) Hu, T.; Li, Y. G.; Liu, J. Y.; Li, Y. S. Organometallics 2007, 26,
2609–2615. The ethylene polymerization activity of this salicylaldimine-
based Ni(II) catalyst is reported to be 3.33 kg/((mol of Ni) h atm) at 25 ꢀC.
(28) Kim, Y. J.; Osakada, K.; Takenaka, A.; Yamamoto, A. J. Am.
Chem. Soc. 1990, 112, 1096–1104.

5048 Organometallics, Vol. 29, No. 21, 2010
Delferro et al.
Figure 3. Plot of activity (kg of PE/((mol Ni) h atm)) vs time (min) for ethylene polymerization with 1b at 50 ꢀC.
Figure 4. Ethylene polymerization activity (kg of PE/((mol Ni) h atm)) in toluene solution with the indicated cosolvents, mediated by
1b (blue b), 2b (red [), and 3 (green 2) Ni phenoxyiminato catalysts.
product branch density by 1H NMR20 obtained with 1b is 2ꢀ
greater than that achieved by catalysts 2b and 3 under
identical reaction conditions, which is also supported by
melting temperature depression data (DSC).
were carried out in toluene solutions containing 1500 equiv of
polar additives (Table 4). Polymerization activities decrease in
the order toluene > ethyl ether > acetone > water (Figure 4).
Note that catalyst 1b remains ∼4ꢀ more active in the presence
of water than do catalysts 2b and 3 and retains significantly
greater branch density.
Ethylene Homopolymerization as a Function of Tempera-
ture. Homopolymerizations at higher temperatures (g50 ꢀC)
yield polyethylenes with lower molecular weights and higher
branching densities (Table 2). Only in the case of complex 1b
does precipitation of black Ni(0) occur, and ethylene con-
sumption falls after ca. 10 min (Table 3).29 Accordingly,
catalyst 1b deactivation experiments were conducted at
50 ꢀC. Treatment of complex 1b with an equimolar amount
of ligand 1 in an NMR tube at 50 ꢀC does not form the
inactive species A, only Ni(0) and the free ligand (Scheme 4).
Ethylene Homopolymerization in Presence of Polar Additives.
Catalysts 1b, 2b, and 3 are also polymerization active in the
presence of polar additives. Ethylene homopolymerizations
Discussion
Ethylene Homopolymerization. Comparing the ethylene
homopolymerization characteristics of catalyst 1b with those
of 2b and 3 reveals significant differences that are attributed
to the intramolecular hydrogen bond directed toward the
catalyst active site. At room temperature, the 1b cata-
lyst activity and product polyethylene branch density are
2.5ꢀ and 2.0ꢀ greater, respectively, than that achieved by
analogous catalysts 2b and 3 under identical conditions. The
significant differences in activity and microstructure reason-
ably reflect decreased electron density at the Ni center, which
should decrease the ethylene insertion barrier.13 Catalyst 1b
(29) Berkefeld, A.; Mecking, S. J. Am. Chem. Soc. 2009, 131, 1565–
1574 and references therein.

Article
Organometallics, Vol. 29, No. 21, 2010 5049
Scheme 5. Possible Influence of Hydrogen Bonding on the Interactions of Polar Additives (S) with a Ni Catalytic Center
produces polyethylenes with molecular weights comparable
to those afforded by catalyst 2b, but dissimilar by 10ꢀ from
reduce activity, note that catalyst 1b remains 2ꢀ more active
than catalysts 2b and 3. The polar additives (S) in the reaction
medium may act as ligands, coordinating to the metal center,
thus competing with ethylene and slowing the chain propa-
gation. We suggest that the intramolecular hydrogen bond
directed toward the catalyst active site acts as a local
scavenger for the polar additives, shifting the equilibrium
toward chain walking scenarios (Scheme 5).
those obtained with catalyst 3 (1b, Mw = 6700; 3, Mw
=
62 700); all polydispersities are consistent with single-site pro-
cesses. This 1b vs 3 Mw difference is presumably a consequence
of catalyst 1b kinetically favoring reversable β-hydrogen
elimination versus chain propagation and/or the different steric
hindrance around the metal centers.
At high temperatures (g50 ꢀC) all of the present catalysts
yield polyethylenes with lower molecular weights and higher
branching densities (Table 2). A shorter catalyst lifetime (ca.
10 min) is observed with 1b (Figure 3), which corresponds to
the formation of Ni(0) and free ligand detected by 1H NMR.
On the other hand, negligible Ni(0) and bis-ligating deacti-
vation processes are observed for 2b and 3 at 50 ꢀC, indicat-
ing that the intramolecular hydrogen bonding reduces the
thermal stability of catalyst 1b.
The decomposition mechanism for 1b presumably in-
volves the formation of a Ni-H intermediate, which can
either undergo ethylene insertion and reinitiate the cata-
lytic cycle or reductively eliminate Ni(0) and free ligand
(Scheme 1). In addition, free ligand in the reaction medium
could react with the Ni active species to afford the inactive
bis-ligated Ni(II) complex. In the case of compound 1b, the
formation of the Ni-H intermediate is more favorable than
for 2b and 3, as reflected in the polyethylene microsctructures
obtained. At higher temperatures, reductive elimination
dominates, but the formation of the bis-ligated species is
not observed.
Conclusions
These results show that hydrogen-bonded complex 1b
displays high catalytic activity for ethylene polymerizations
with respect to the analogous non-hydrogen-bonded com-
plexes 2b and 3. The intramolecular hydrogen bond directed
toward the catalyst active site promotes fine tuning of
product branch density and appears to accelerate β-hydro-
gen elimination/re-insertion processes. Moreover, the polar
functionality proximate to the Ni center significantly stabi-
lizes catalyst activity during ethylene homopolymerization in
the presence of polar additives. Further studies are underway
to clarify the scope and mechanisms of such directed electro-
phile effects on olefin activation and catalytic enchainment.
Acknowledgment. Financial support by the DOE
(Grant 86ER13511) is gratefully acknowledged. We
thank Mr. M. P. Weberski, Jr., and Mr. C. J. Stephenson
for helpful discussions.
Supporting Information Available: Figures giving the 1H-1H
2D NOESY NMR spectrum of 1b and NMR (1H and 13C)
spectra of polymer samples and CIF files giving crystallographic
data for 1 and 1b. This material is available free of charge via the
Internet at http://pubs.acs.org.
Ethylene homopolymerization experiments in presence of
polar additives reveal that catalyst 1b is more polar additive
tolerant than catalysts 2b and 3. Polymerization activities
decline in the order toluene > diethyl ether > acetone >
water (Figure 4). While the polar additives significantly