Synthesis, characterization, and marked polymerization selectivity characteristics of binuclear phenoxyiminato organozirconium catalysts

Article abstract of DOI:10.1021/ja076857e

The new binuclear phenoxyiminato zirconium complex {1,7-(O)₂C₁₀H₄-2,7-[CH=N(2,6-ⁱPr₂C₆H₃)]₂}Zr₂Cl₆(THF)₂ (FI²-Zr₂) polymerizes ethylene with greater activity (8×) than the mononuclear analogue. Also, this catalyst produces high molecular weight ethylene + 1-hexene copolymers, while the mononuclear analogue yields only traces of copolymer under identical conditions. This ability to produce copolymers suggests cooperativity between the two Zr centers which promotes 1-hexene co-enchainment. Copyright

Full text of DOI:10.1021/ja076857e

Synthesis, Characterization, and Marked Polymerization
Selectivity Characteristics of Binuclear Phenoxyiminato
Organozirconium Catalysts.
Michael R. Salata and Tobin J. Marks*
Department of Chemistry, Northwestern University, Evanston, Illinois
60208-3113
t-marks@northwestern.edu
Supporting Information
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, or interfaced to a high-vacuum line (10-5 Torr), or in a
nitrogen-filled Vacuum Atmospheres glove box with a high capacity recirculator (<1
ppm 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 solvents were purified by distillation from Na/K
alloy/benzophenone ketyl. Hydrocarbon solvents were distilled under nitrogen from Na/K
alloy. All solvents for high-vacuum line manipulations were stored in vacuo over Na/K
alloy in Teflon-valve sealed bulbs. Deuterated solvents were obtained from Cambridge
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Isotope Laboratories (all 99 atom %D), were freeze pump- thaw degassed, dried over
Na/K alloy and were stored in resealable flasks. Other non-halogenated solvents were
dried over Na/K alloy, and halogenated solvents were distilled from CaH2 and stored over
activated Davison 4A molecular sieves. The reagents 2,6-di-iso-propylaniline, and
chlorotrimethylsilane were purchased from Aldrich and used as received. The
comonomer 1-hexene (Aldrich) was dried over CaH2. The reagents LiCH2TMS and
ZrCl4 (Aldrich) were sublimed before use. Methylaluminoxane (MAO, obtained as a
10% toluene solution from Aldrich) was dried under high vacuum for 24 h to remove
1
excess volatile aluminum alkyls before use. The reagents ZrCl4(THF)2 and Zr{3-tBu-2-
(O)C6H3CH=N(2,6-iPr2C6H3)}Cl3(THF)2 (FI-Zr1) were prepared according to literature
procedures, however, for the latter, heating at reflux for 16 h was required for complete
reaction.
Physical and Analytical Measurements. NMR spectra were recorded on Varian
UNITYInova-500 (FT, 500 MHz, 1H; 125 MHz, 13C) or UNITYInova-400 (FT, 400
MHz, 1H; 100 MHz, 13C). Chemical shifts for 1H and 13C spectra were referenced using
internal solvent resonances and are reported relative to tetramethylsilane. NMR
experiments on air-sensitive samples were conducted in Teflon valve-sealed sample tubes
(J.Young). Elemental analyses were performed by Midwest Microlab, Indianapolis,
Indiana. 13C NMR assays of polymer microstructure were conducted in mixture (1:1 in
volume) of 1,2,4-trichlorobezene (containing 0.1 M Cr(acac)3 solution) and 1,1,2,2-
tetrachloroethane-d2 at 130°C. Signals were assigned according to the literature for
polyethylene and ethylene + α-olefin copolymers.3 Melting temperatures of polymers
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were measured by DSC (DSC 2920, TA Instruments, Inc.) from the second scan with a
heating rate of 10 °C/min. GPC measurements were performed on a Polymer
Laboratories PL-GPC 220 instrument using 1,2,4-trichlorobenzene solvent (stabilized
with 125 ppm BHT) at 150 °C. A set of three PLgel 10 m mixed columns was used.
Samples were prepared at 160 °C. Molecular weights were determined by GPC using
narrow polystyrene standards and are not corrected. Laser desorption mass spectra were
obtained with a Perseptive BioSystems time-of-flight MALDI mass spectrometer using a
dithranol matrix.
Synthesis of 2,7-di(2,6-diisopropylphenyl)imino-1,8-dihydroxynaphthalene (1).
Under N2, the reagent 2,7-diformyl-1,8-dihydroxynaphthalene (2.15 g, 9.93 mmol) was
dissolved in 50 mL dry dichloromethane. Activated molecular sieves (2 g) were then
added, followed by formic acid (5 drops), and 2,6-di-iso-propylaniline (8.0 mL, 42
mmol). The reaction was heated under reflux for 3 h during which time the 2,7-diformyl-
1,8-dihydroxynaphthalene gradually dissolved, and the reaction mixture color changed
from yellow to dark red. The reaction mixture was then cooled and filtered. The
volatiles were removed from the filtrate in vacuo, and the resulting red oily solid was
washed with hexanes (3 x 15 mL) and collected by filtration to give a pure orange solid.
X-ray quality single crystals were obtained by slow evaporation of a dichloromethane
solution. Yield, 4.5 g (86%).
1H NMR (CDCl3, 23°C, 499.447 MHz): 14.56 (s, OH), 13.48 (s, OH), 8.75 (s), 8.34
(s), 7.66 (d, J = 11.3 Hz), 6.78-7.35 (m), 3.08 (d, CHMe2), 1.20 (d, CHMe2).
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Anal. Found: C, 80.84; H, 7.90; N, 5.25. Calcd. for C36H42N2O2: C, 80.86; H, 7.92; N,
5.24.
Synthesis of 2,7-Di(2,6-diisopropylphenyl)imino-1,8-di(trimethylsiloxy)naphthalene
(2). The reagents 2,7-di(2,6-diisopropylphenyl)imino-1,8-dihydroxynapthalene (589 mg,
1.10 mmol) and LiCH2TMS (228.2 mg, 2.424 mmol) were combined in a reaction flask
in the glovebox. On the vacuum line, dry THF (25 mL) was added at -78°C and the
mixture was stirred for 30 min, followed by stirring for 30 min at 0°C. The volatiles
were next removed in vacuo, and the resulting solid was dissolved in 20 mL dry
dichloromethane. Next, chlorotrimethylsilane (0.35 mL, 2.7 mmol) was added with
stirring, and the resulting solution became hazy over a period of 4.5 h. The reaction
mixture was then filtered, and volatiles were removed from the filtrate in vacuo. Pure
orange product was obtained by washing the resulting orange/brown solid with cold
pentane (5 mL). X-ray quality single crystals were obtained by cooling a saturated
pentane solution at -10°C. Yield, 598 mg (80%).
1H NMR (CDCl3, 23°C, 499.447MHz): 8.762 (s, 2H, HC=N), 8.475 (d, 2H, 3JH-H
8.457 Hz, naph C3), 7.639 (d, 2H, 3JH-H = 8.641 Hz, naph C4), 7.297 (d, 2H, 3JH-H
=
=
7.537 Hz, dipp p), 7.231 (t, 4H, 3JH-H = 7.354 Hz, dipp m), 3.152 (sept, 4H, 3JH-H = 6.802
Hz, CHMe2), 1.307 (s, 24H, CHMe2), 0.227 (s, 18H, SiMe3). 13C NMR (CDCl3, 23°C,
100.745 MHz) 158.447, 154.442, 150.080, 140.512, 138.032, 125.771, 124.647,
124.214, 123.351, 123.267, 122.460, 28.111, 24.214, 23.564, 0.387.
Anal. Found: C, 74.26; H, 8.60; N, 4.15. Calcd. for C36H42N2O2: C, 74.28; H, 8.61; N,
4.13.
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Synthesis of {1,7-(O)2C10H4-2,7-[CH=N(2,6-iPr2C6H3)]2}Zr2Cl6(THF)2 (FI2-Zr2).
Under N2, the reagent 2,7-di(2,6-diisopropylphenyl)imino-1,8-
di(trimethylsiloxy)naphthalene (484 mg, 0.713 mmol) in 20 mL dry dichloromethane was
added dropwise with stirring to a solution of ZrCl4(THF)2 (538 mg, 1.43 mmol) in 20 mL
dry dichloromethane at -78°C. The solution was then allowed to warm to room
temperature and stirred for 1 h before heating to reflux for 24 h. The volatiles were then
removed in vacuo, and the residue was redissolved in 25 mL dichloromethane and
filtered. Next, 20 mL dry toluene was added to the filtrate, and the resulting pure orange
product was isolated by filtration. Attempts at isolating single crystals of FI2-Zr2 using
standard methods gave powders. Yield, 762 mg (79%).
1H NMR (CD2Cl2, 23°C, 499.447MHz): 12.953 (s, 2H, HC=N), 8.162 (d, 2H,
3JH-H=14.668 Hz, naph C3), 7.620 (d, 2H, 3JH-H = 8.149 Hz, naph C4), 7.501 (t, 2H, 3JH-H
= 7.335 Hz, dipp p), 7.330 (m, 4H, 3JH-H = 8.964 Hz, dipp m), 3.193 (sept, 4H, 3JH-H
=
6.520 Hz, CHMe2), 1.286 (s, 24H, 3JH-H = 6.519 Hz, CHMe2). 13C NMR (CD2Cl2, 23°C,
100.745 MHz): 171.281, 167.466, 147.524, 144.200, 142.764, 136.481, 134.094,
130.865, 124.656, 119.707, 110.889, 29.032, 23.436.
Anal. Found: C, 49.68; H, 5.48; N, 2.65. Calcd. for C36H42N2O2: C, 49.29; H, 5.26; N,
2.61.
MALDI-TOF-MS: m/z 1074.2 (parent ion calcd 1070.04), 921.9 (-2 THF calcd 925.93),
731.8 (-2 THF and -ZrCl3 calcd 730.13).
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Ethylene Homopolymerization Experiments. On the high vacuum line (10-5 Torr),
ethylene polymerizations were carried out in 250 mL round-bottom three-neck flasks
equipped with a large magnetic stirring bar, Morton indentations, and a thermocouple
probe. In a typical experiment, a pre-assembled, degassed reactor containing toluene (50
mL) and MAO (1000 eq relative to Zr) was pre-saturated under of ethylene (1.0 atm) and
equilibrated at the desired reaction temperature using an external bath. The catalytically-
active species was freshly generated in toluene (4.0 mL) and MAO (500 equiv relative to
metal). After an activation time (~30 min), the catalyst solution was then quickly injected
into the rapidly stirred flask using a gas-tight syringe equipped with a flattened spraying
needle. The temperature of the toluene solution was monitored in representative
experiments using a thermocouple (OMEGA Type K thermocouple with a Model HH21
microprocessor thermometer). The reaction exotherm temperature rise was invariably less
than 5°C during these polymerizations. After a measured time interval, the
polymerization was quenched by the addition of 2% acidified methanol (15 mL). More
methanol (100 mL) was then added, and the polymer was collected by filtration, washed
with methanol and 10% aqueous HCl, and dried on the high vacuum line overnight to a
constant weight.
Ethylene + Olefin Copolymerization Experiments. On the high vacuum line (10-5
Torr), ethylene polymerizations were carried out in 250 mL round-bottom three-neck
flasks equipped with a large magnetic stirring bar, Morton indentations, and a
thermocouple probe. In a typical experiment, 10 mL of comonomer was vacuum-
transferred into a graduated flask at –78°C, then the comonomer was injected into a pre-
S6

assembled, degassed reactor containing toluene (50 mL) and MAO (500 equiv relative to
Zr). The mixture was pre-saturated under of ethylene (1.0 atm) and equilibrated at the
desired reaction temperature using an external bath. The catalytically-active species was
freshly generated in toluene (4.0 mL) and MAO (500 eq relative to metal). After an
activation time (~30 min), the catalyst solution was then quickly injected into the rapidly
stirred flask using a gas-tight syringe equipped with a flattened spraying needle. The
temperature of the toluene solution was monitored in representative experiments using a
thermocouple (OMEGA Type K thermocouple with a Model HH21 microprocessor
thermometer). The reaction exotherm temperature rise was invariably less than 5°C
during these polymerizations. After a measured time interval, the polymerization was
quenched by the addition of 2% acidified methanol (15 mL). More methanol (100 mL)
was then added, and the polymer was collected by filtration, washed with methanol and
10% aqueous HCl, and dried on the high vacuum line overnight to a constant weight.
Crystal Structures of 1 and 2.
A. 2,7-Di(2,6-diisopropylphenyl)imino-1,8-dihydroxynaphthalene (1). A
summary of crystal structure data for compound 1 is presented in Table S1. Selected
bond distances and angles for 1 are summarized in Table S2. Figure S1 shows the solid
state structure of the binucleating ligand precursor 1. The asymmetric crystal structure
reveals that O(2) actually is in essence deprotonated by the proximate imine functionality
N(2). A proton was located in the difference map between O(1) and O(2) in a pseudo-
chelating fashion which causes the anilino group to assume a trans geometry due to the
S7

steric demand of the isopropyl groups. The crystal structure explains the asymmetry and
room temperature broadness of the 1H NMR spectrum.
B. 2,7-Di(2,6-diisopropylphenyl)imino-1,8-di(trimethylsiloxy)naphthalene
(2). A summary of crystal structure data for compound 2 is presented in Table S1.
Selected bond distances and angles for 2 are summarized in Table S3. Figure S2 shows
the solid state structure of 2. The crystal structure reveals the symmetric nature of the
molecule, and as expected, the bulky trimethylsiloxy groups have close nonbonded
contacts with the di-isopropylanilino groups.
References
1 Manzer, L. E. Inorg. Synth. 1982, 21, 136.
2 Pennington, D. A.; Clegg, W.; Coles,S. J.; Harrington, R. W.; Hursthouse, M. B.;
Hughes, D. L.; Light, M. E.; Schormann, M.; Bochmann, M.; Lancaster, S. J. Dalton
Trans. 2005, 3, 561-571.
3 Pooter, M. De.; Smith, P. B.; Dohrer, K. K.; Bennett, K. F.; Meadows, M. D.; Smith, C.
G.; Schouwenaars, H. P.; Geerards, R. A. J. App. Polym. Sci. 1991, 42, 399-408.
S8

Figure Captions
Figure S1. ORTEP plot and atom numbering scheme for 2,7-di(2,6-di-
isopropylphenyl)imino-1,8-dihydroxynaphthalene (1). Thermal ellipsoids are drawn at
the 50% probability level.
Figure S2. ORTEP plot and numbering scheme for 2,7-di(2,6-diisopropylphenyl)imino-
1,8-di(trimethylsiloxy)naphthalene (2). Thermal ellipsoids are drawn at the 50%
probability level.
Figure S3. 1H NMR spectrum (CDCl3, 500 MHz) of 2,7-di(2,6-diisopropylphenyl)imino-
1,8-dihydroxynaphthalene (1).
Figure S4. 1H NMR spectrum (CDCl3, 400 MHz) of 2,7-di(2,6-diisopropylphenyl)imino-
1,8-dihydroxynaphthalene (1) at -33°C.
Figure S5. 1H NMR spectrum (CDCl3, 500 MHz) of 2,7-di(2,6-diisopropylphenyl)imino-
1,8-di(trimethylsiloxy)naphthalene (2).
Figure S6. 13C NMR spectrum (CDCl3, 100 MHz) of 2,7-di(2,6-diisopropylphenyl)imino-
1,8-di(trimethylsiloxy)naphthalene (2).
Figure S7. 1H NMR spectrum (CD2Cl2, 500 MHz) of {1,7-(O)2C10H4-2,7-[CH=N(2,6-
iPr2C6H3)]2}Zr2Cl6(THF)2 (FI2-Zr2).
Figure S8. 13C NMR spectrum (CD2Cl2, 100 MHz) of {1,7-(O)2C10H4-2,7-[CH=N(2,6-
iPr2C6H3)]2}Zr2Cl6(THF)2 (FI2-Zr2).
Figure 9. MALDI mass spectrum of {1,7-(O)2C10H4-2,7-[CH=N(2,6-
iPr2C6H3)]2}Zr2Cl6(THF)2 (FI2-Zr2) with dithranol as the supporting matrix.
S9

Figure S1.
Figure S2.
S10

Figure S3.
S11

Figure S4.
S12

Figure S5.
S13

Figure S6.
S14

Figure S7.
S15

Figure S8.
S16

Figure S9.
Pr
Pr
Pr
Pr
Pr
N
Pr
Cl
Zr
Cl
Cl
Zr
Cl
Cl
Zr
Cl
Cl
Zr
Cl
Cl
Zr
Cl
THF
O
Cl
THF
O
Cl
Cl
Cl
N
Cl
N
N
N
O
O
OH
O
N
Pr
Pr
Pr
Pr
Pr
Pr
Chem ical Formula: C44H54Cl6N2O4Zr2
Molecular Weight: 1070.08
Chemical Formula: C36H40Cl6N2O2Zr2
Exact Mass: 921.93
Chemical Formula: C36H41Cl3N2O2Zr
Molecular Weight: 731.31
S17

Table 1. Summary of the Crystal Structure Data for Complexes 1 and 2.
Complex
1
2
Formula
Formula Weight
C36H42N2O2
534.72
C42H58N2O2Si2
679.08
Crystal Dimensions (mm)
Crystal System
a, Å
b, Å
c, Å
0.506 x 0.326 x 0.186
Monoclinic
10.0592(8)
23.0731(18)
13.9928(11)
90
0.598 x 0.232 x .070
Monoclinic
26.914(6)
9.765(2)
16.289(4)
90
, deg
109.4350(10)
90
3062.6(4)
P2(1)/n
109.311(3)
90
4040.1(15)
Cc
β, deg
, deg
V, Å3
Space group
Z value
4
4
Dcalc, mg/m3
Temp K
, mm-1
1.160
153(2)
0.071
1.116
153(2)
0.123
MoK
MoK
Radiation
2 range, deg
Intensities (unique, (Rint)
R
1.77 to 28.91
7436, 0.0299
0.0616
1.60 to 28.78
9137, 0.0828
0.0462
0.1614
0.1123
wR2
S18

Table 2. Selected Bond Distances (Å) and Angles (deg) for compound 1.
------------------------------------------------------------------------------------------------------------
Distances
O(2)-C(20)
O(1)-C(14)
C(20)-C(23)
C(20)-C(19)
C(19)-C(18)
C(19)-C(14)
C(14)-C(15)
C(15)-C(16)
C(15)-C(13)
N(2)-C(24)
1.289(2)
1.3472(19)
1.436(2)
1.449(2)
1.414(2)
1.428(2)
1.399(2)
1.408(2)
1.464(2)
1.306(2)
N(2)-C(25)
C(18)-C(17)
C(18)-C(21)
C(12)-N(1)
C(22)-C(21)
C(22)-C(23)
N(1)-C(13)
C(16)-C(17)
C(23)-C(24)
1.438(2)
1.412(2)
1.435(2)
1.4286(19)
1.353(2)
1.426(2)
1.279(2)
1.372(2)
1.409(2)
Angles
O(2)-C(20)-C(23)
O(2)-C(20)-C(19)
C(23)-C(20)-C(19)
C(18)-C(19)-C(14)
C(18)-C(19)-C(20)
C(14)-C(19)-C(20)
O(1)-C(14)-C(15)
O(1)-C(14)-C(19)
C(15)-C(14)-C(19)
C(14)-C(15)-C(16)
121.84(13)
120.39(13)
117.76(14)
119.48(13)
120.29(13)
120.23(14)
119.10(14)
120.50(13)
120.40(14)
118.74(14)
C(14)-C(15)-C(13)
C(16)-C(15)-C(13)
C(24)-N(2)-C(25)
C(1)-C(12)-N(1)
C(8)-C(12)-N(1)
C(13)-N(1)-C(12)
N(2)-C(24)-C(23)
C(26)-C(25)-N(2)
C(33)-C(25)-N(2)
N(1)-C(13)-C(15)
119.49(14)
121.77(13)
128.79(14)
120.36(14)
117.93(14)
116.33(13)
122.35(14)
118.65(14)
117.90(14)
122.81(15)
------------------------------------------------------------------------------------------------------------
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Table 3. Selected Bond Distances (Å) and Angles (deg) for compound 2.
------------------------------------------------------------------------------------------------------------
Distances
C(1)-N(1)
1.421(3)
1.274(3)
1.471(3)
1.396(3)
1.411(3)
1.356(3)
1.417(3)
1.370(2)
1.427(3)
1.856(2)
1.846(2)
1.849(2)
1.426(3)
1.441(2)
C(22)-C(23)
C(23)-C(24)
C(24)-C(25)
C(25)-C(26)
C(25)-C(30)
C(26)-O(2)
C(27)-Si(2)
C(28)-Si(2)
C(29)-Si(2)
C(30)-N(2)
C(31)-N(2)
O(1)-Si(1)
1.412(3)
1.367(3)
1.415(3)
1.386(3)
1.470(3)
1.361(2)
1.857(3)
1.843(3)
1.851(3)
1.262(3)
1.425(2)
1.6822(15)
1.6765(15)
C(13)-N(1)
C(13)-C(14)
C(14)-C(17)
C(14)-C(15)
C(15)-C(16)
C(16)-C(22)
C(17)-O(1)
C(17)-C(21)
C(18)-Si(1)
C(19)-Si(1)
C(20)-Si(1)
C(21)-C(22)
C(21)-C(26)
O(2)-Si(2)
Angles
C(9)-C(1)-N(1)
C(2)-C(1)-N(1)
117.48(17)
O(2)-C(26)-C(21)
C(25)-C(26)-C(21)
N(2)-C(30)-C(25)
C(32)-C(31)-C(39)
C(32)-C(31)-N(2)
C(39)-C(31)-N(2)
C(13)-N(1)-C(1)
C(30)-N(2)-C(31)
C(17)-O(1)-Si(1)
C(26)-O(2)-Si(2)
O(1)-Si(1)-C(19)
O(1)-Si(1)-C(20)
C(19)-Si(1)-C(20)
O(1)-Si(1)-C(18)
C(19)-Si(1)-C(18)
C(20)-Si(1)-C(18)
O(2)-Si(2)-C(28)
O(2)-Si(2)-C(29)
C(28)-Si(2)-C(29)
O(2)-Si(2)-C(27)
C(28)-Si(2)-C(27)
C(29)-Si(2)-C(27)
120.45(17)
120.93(18)
120.58(18)
119.24(17)
121.30(17)
119.44(17)
121.30(18)
120.59(18)
118.46(17)
120.89(16)
120.64(17)
117.73(16)
117.54(17)
124.72(17)
120.16(17)
120.11(17)
119.73(18)
120.51(18)
121.04(18)
119.60(17)
121.15(16)
119.25(17)
118.88(16)
120.67(16)
121.31(17)
121.03(17)
119.48(18)
119.21(17)
121.56(18)
120.28(17)
124.56(12)
127.82(12)
104.29(10)
111.42(9)
N(1)-C(13)-C(14)
C(17)-C(14)-C(15)
C(17)-C(14)-C(13)
C(15)-C(14)-C(13)
C(16)-C(15)-C(14)
C(15)-C(16)-C(22)
O(1)-C(17)-C(14)
O(1)-C(17)-C(21)
C(14)-C(17)-C(21)
C(22)-C(21)-C(17)
C(22)-C(21)-C(26)
C(17)-C(21)-C(26)
C(23)-C(22)-C(16)
C(23)-C(22)-C(21)
C(16)-C(22)-C(21)
C(24)-C(23)-C(22)
C(23)-C(24)-C(25)
C(26)-C(25)-C(24)
C(26)-C(25)-C(30)
C(24)-C(25)-C(30)
O(2)-C(26)-C(25)
110.55(12)
109.54(9)
111.01(12)
109.92(11)
102.82(11)
109.12(11)
109.70(15)
111.30(11)
115.21(17)
108.49(14)
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