Titanium "constrained geometry" complexes with pendant arene groups

Article abstract of DOI:10.1039/c0dt01530j

The synthesis of the proligands C₅Me₄HSiMe ₂N(H)R) (R = CMe₂Ph 1, 2-C₆H₄Ph 2) was accomplished via a straightforward salt metathesis reaction of the appropriate lithium amide and ClSiMe₂(C₅Me₅H). Generation of the dilithio salt and reaction with TiCl₃·(THF) ₃ followed by oxidation gave C₅Me₄SiMe ₂N(C₆H₄Ph)TiCl₂ (3) in low yield. In contrast, deprotonation of 1 and 2 and reaction with (Me₂N) ₂TiCl₂ afforded C₅Me₄(SiMe ₂NR)Ti(NMe₂)₂ (R = CMe₂Ph 4, 2-C₆H₄Ph 5), respectively, in good yields Treatment with MeI gave the analogs C₅Me₄(SiMe₂NR)TiI ₂ (R = CMe₂Ph 6, 2-C₆H₄Ph 7). Reduction of 7 with potassium graphite afforded C₅Me ₄(SiMe₂NC₆H₄Ph)Ti 8. Treatment of 6 and 7 with MeMgBr afforded C₅Me₄(SiMe₂NR) TiMe₂ (R = CMe₂Ph 9, 2-C₆H₄Ph 10). Complexes 9 and 10 in combination with the activator [Ph₃C][B(C ₆F₅)₄] catalyzed the polymerization of styrene and ethylene. Copolymerization was also investigated. While the catalyst derived from 10 showed poor activity, compound 9 showed markedly higher activity than 10 and (C₅Me₄)SiMe₂(NtBu)]TiMe₂. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c0dt01530j

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PAPER
Titanium “constrained geometry” complexes with pendant arene groups†
Meghan A. Dureen, Christopher C. Brown, Jason G. M. Morton and Douglas W. Stephan*
Received 3rd November 2010, Accepted 18th January 2011
DOI: 10.1039/c0dt01530j
The synthesis of the proligands C5Me4HSiMe2N(H)R) (R = CMe2Ph 1, 2-C6H4Ph 2) was accomplished
via a straightforward salt metathesis reaction of the appropriate lithium amide and ClSiMe2(C5Me5H).
Generation of the dilithio salt and reaction with TiCl3·(THF)3 followed by oxidation gave
C5Me4SiMe2N(C6H4Ph)TiCl2 (3) in low yield. In contrast, deprotonation of 1 and 2 and reaction with
(Me2N)2TiCl2 afforded C5Me4(SiMe2NR)Ti(NMe2)2 (R = CMe2Ph 4, 2-C6H4Ph 5), respectively, in good
yields Treatment with MeI gave the analogs C5Me4(SiMe2NR)TiI2 (R = CMe2Ph 6, 2-C6H4Ph 7).
Reduction of 7 with potassium graphite afforded C5Me4(SiMe2NC6H4Ph)Ti 8. Treatment of 6 and 7
with MeMgBr afforded C5Me4(SiMe2NR)TiMe2 (R = CMe2Ph 9, 2-C6H4Ph 10). Complexes 9 and 10 in
combination with the activator [Ph3C][B(C6F5)4] catalyzed the polymerization of styrene and ethylene.
Copolymerization was also investigated. While the catalyst derived from 10 showed poor activity,
compound 9 showed markedly higher activity than 10 and (C5Me4)SiMe2(NtBu)]TiMe2.
variety of ligand scaffolds that incorporate an assortment of
main group elements bonded to various early transition metals.8
Introduction
While metallocenes of the type Cp¢2MR2 (M = Ti or Zr; R = alkyl)
remain precursors of the most active and well understood olefin
polymerisation catalysts systems, new catalysts are continually
sought to provide new polymer microstructures and circumvent
existing patents.1,2 Soon after Bercaw and coworkers reported
the synthesis and olefin polymerization activity of an ansa-
bridged cyclopentadienyl-amido (Cp-amido) scandium complex,
(Fig. 1(a)),3,4 Okuda reported the synthesis of a related complex of
titanium (Fig. 1(b),(c)),5 and patents for processes utilizing similar
group IV systems in ethylene homo- and copolymerisations were
filed.6,7 Such Cp-amido systems have been dubbed “constrained
geometry catalysts” (CGCs), as the ansa-bridge necessitates an
“opening-up” of the metal centre that is believed to enhance
monomer coordination.
An application where the use of CGCs offers enhanced produc-
tivity over classical group IV metallocenes is that of ethylene
copolymerisations with a-olefins.9 CGCs have been shown to
effect superior comonomer incorporation in copolymerisations
of ethylene and styrene, in contrast to copolymersations with
classical metallocenes.7,10 This is surprising considering typical
CGCs demonstrate poor activities in the homopolymerisation of
styrene.7 In this case, catalyst deactivation is believed to result from
intramolecular coordination of the phenyl ring of a 2,1 inserted
monomer.11 This seems plausible given the intramolecular arene
coordination observed in related CGC benzyl cations.12
Marks and coworkers have developed catalyst systems with
higher activities than prototypical CGC systems for the poly-
merization of styrene. They have found that binuclear CGC
systems are more active in these polymerizations and hypothesized
that arene coordination of the growing polymer chain occurs
at the opposite metal centre, thereby allowing for monomer
coordination to the metal centre that is the site of propagation.11
This group has also demonstrated that typical CGC catalysts can
be used to promote the polymerization of styrene in the presence
of multiple equivalents of secondary and tertiary silanes; here
amplification of the polymerization activity is believed to be a
result of displacement of Ti ◊ ◊ ◊ Ph interactions via the formation of
weak Ti ◊ ◊ ◊ H–SiR3 contacts.13 A variety of substituted CGC-based
catalysts have been developed and examined.14,15 For example,
Waymouth and co-workers have explored the impact of electron-
withdrawing substituents on N,16 while Yang et al. have employed
sterically demanding arene substituents on N.17 While in these
cases the arene fragment modifies the donor capacity, the groups
of Hessen18–27 and Bochmann28,29 have probed the interactions of
Fig. 1 CGC Complexes.
The prototypical CGC is a titanium catalyst incorporating a
permethylated Cp¢ group and a tert-butyl group on the nitrogen
centre (Fig. 1), but the term CGC has been applied to a wide
Department of Chemistry, University of Toronto, 80 St. George St. Toronto,
Ontario, Canada, M5S 3H6. E-mail: dstephan@chem.utoronto.ca; Tel: +1
416-946-3294
† CCDC reference numbers 808875–808880. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt01530j
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early metal systems with pendant arenes on Cp ligands. Arriola
and coworkers have developed CGC polymerization catalysts
with arene systems extending from the Cp unit (Fig. 1).30 These
catalysts were found to increase styrene incorporation in ethylene–
styrene copolymerisations presumably a result of interaction of
the extended p-system with the phenyl ring of an incoming
monomer.31 The Stephan group showed that the pendant arene in
biphenylphosphinimide complexes of group IV metals stabilized
metal cations.32 The synthesis of CGC-type precatalysts with
pendant phenyl groups on the nitrogen substituent were targeted
with these precedents in mind. Synthetic methods to obtain
these species have been developed and an initial assessment of
the derived catalysts in ethylene and styrene polymerization is
described.
7 Hz, m-C6H4); 7.21 (tt, 1H, 3JH–H = 8 Hz, 4JH–H = 1 Hz, p-C6H4);
2.86 (s, 1H, Cp¢H); 2.03 (s, 6H, Cp¢Me); 1.89 (s, 6H, Cp¢Me);
1.51 (s, 6H, CMe2Ph); 0.91 (s, 1H, NH); 0.06 (s, 6H, SiMe2).
1
13C{ H} NMR (CD2Cl2): 153.0, 135.9, 133.8, 128.4, 128.4, 126.3,
126.0, 57.5, 54.6, 34.1 (CMe2Ph), 15.2 (Cp¢Me), 11.6 (Cp¢Me), 1.8
(SiMe2).
2: White crystalline solid, 2.15 grams, 65%. 1H NMR (CD2Cl2):
7.4 (t, 2H, 3JH–H = 7 Hz, m-Ph), 7.3 (m, 3H), 7.2 (t, 1H, 3JH–H = 7
Hz), 7.1 (dd, 1H, 3JH–H = 7 Hz,4JH–H = 2 Hz), 6.9 (d, 1H, 3JH–H = 8
Hz), (td, 1H, 3JH–H = 7 Hz,4JH–H = 1 Hz), 3.6 (s, 1H, NH), 3.0 (s, 1H
Cp¢H), 1.8 (s, 6H, Cp¢Me), 1.7 (s, 6H, Cp¢Me), 0.2 (s, 6H, SiMe2).
1
13C{ H} NMR (CD2Cl2): 145.0, 140.4, 136.8, 132.7, 131.1, 130.3,
129.8, 129.4, 128.8, 127.7, 118.0 (Cp¢), 116.0 (Cp¢), 55.0 (Cp¢), 14.5
(Cp¢Me), 11.4 (Cp¢Me), -1.5 (SiMe2). EA calc’d for C23H29NSi
(347.577) C, 79.48; H, 8.41; N, 4.03; Found: C, 79.25, H, 9.24,
N, 3.95. X-ray quality crystals were grown by slow cooling of a
solution in pentane.
Experimental section
General considerations
Synthesis of C5Me4SiMe2N(C6H4Ph)TiCl2 (3). A solution of
2 (815 mg, 2.34 mmol) in THF (250 mL) was cooled to -78 C,
◦
All preparations were done under an atmosphere of dry, O2-
free N2 employing both Schlenk line techniques and a Vacuum
Atmospheres inert atmosphere glove box. Solvents (pentane,
hexanes, toluene, diethyl ether, THF and methylene chloride) were
purified employing a Grubbs’ type column systems manufactured
by Innovative Technology and stored over either a potassium
mirror (toluene, diethyl ether, and pentane) or molecular sieves
at which point nBuLi (1.5 mL, 4.8 mmol) was added dropwise
while the reaction mixture was stirred with a magnetic stirrer
bar. After the addition was complete the reaction mixture was
warmed to room temperature with a water bath, then subsequently
cooled to -78 ◦C. This mixture was then transferred dropwise, via
cannula, to a stirring slurry of TiCl3(THF)3 (869 mg, 2.34 mmol)
in THF (200 mL) which had also been cooled to -78 ◦C. After
the addition was complete, the reaction mixture was warmed
to room temperature and the solvent removed in vacuo. The
reaction mixture was then transferred to the glovebox, where the
mixture was re-dissolved in diethyl ether (200 mL) and filtered
through Celite, at which point silver chloride (336 mg, 2.34 mmol)
was added. The solvent was removed under reduced pressure
and the mixture extracted into toluene (100 mL) and filtered
through Celite. The solution was cooled to -35 ◦C after which the
supernatant liquid was removed from yellow, needle-like crystals
(105 mg, 10%). Removal of solvent in vacuo from the supernatant
˚
˚
(4 A). Molecular sieves (4 A) were purchased from Aldrich
Chemical Company and dried at 200 ◦C under vacuum for 3 h prior
to use. Deuterated solvents were dried over Na/benzophenone
(C6D6, C7D8, THF-d8) or CaH2 (CD2Cl2, C6D5Br) and vacuum
distilled prior to use. All common organic reagents were purified
by conventional methods unless otherwise noted. H, 13C, 11B,
1
19F and 31P nuclear magnetic resonance (NMR) spectroscopy
spectra were recorded on a Bruker Avance-400 spectrometer at
300 K unless otherwise noted. 1H and 13C NMR spectra are
referenced to SiMe4 using the residual solvent peak impurity
of the given solvent. 31P, 11B and 19F NMR experiments were
referenced to 85% H3PO4, BF3(OEt2), and CFCl3, respectively.
Chemical shifts are reported in ppm and coupling constants in
Hz as absolute values. Combustion analyses were performed in-
house employing a Perkin Elmer CHN Analyzer. [Ph3C][B(C6F5)4]
and [(C5Me4)SiMe2(NtBu)]TiCl2 were generously donated by
NOVA Chemicals Corporation. PhCMe2NH2 was purchased from
TCI Chemicals and used as received. ClSiMe2(C5Me5H) and
PhC6H4NH2 were purchased from Aldrich chemicals and used
1
liquid afforded an oil that contained little of 3, evidenced by H
1
3
NMR spectroscopy. H NMR (CD2Cl2): 7.5 (dm, 2H, JH–H = 7
Hz), 7.3–7.2 (m, 5H), 7.2–7.1 (m, 2H), 2.3 (s, 6H, Cp¢Me), 2.1 (s,
6H, Cp¢Me), 0.1 (s, 6H, SiMe2). 13C{ H} NMR (CD2Cl2): 148.9,
1
143.9, 141.5, 139.0, 134.9, 132.1, 128.54, 128.46, 127.5, 125.8,
125.4, 106.5, 16.7 (Cp¢Me), 13.7 (Cp¢Me), 2.2 (SiMe2). EA calc’d
for C23H27NSiCl2Ti (464.345) C, 59.49; H, 5.86; N, 3.02; Found:
C, 59.0, H, 5.82, N, 2.59.
33
7
as received. (Me2N)2TiCl2 and [(C5Me4)SiMe2(NtBu)]TiMe2
Synthesis of C5Me4(SiMe2NR)Ti(NMe2)2 (R = CMe2Ph 4, 2-
C6H4Ph 5). These compounds were synthesized via a similar
procedure, therefore only one synthesis is described. A soluti◦on
of 1 (544 mg, 1.8 mmol) in THF (20 mL) was cooled to -35 C
at which point nBuLi (2.25 mL, 1.6 M in hexanes) was added
dropwise, with stirring, over a period of 3 min, during which time
the solution went from colourless to a clear, deep yellow. This
solution was allowed to warm to room temperature over a period
of 45 min after which it was cooled to -35 ◦C and added dropwise
were synthesized via literature procedures. High temperature GPC
data were provided by the Department of Chemistry, Cornell
University, Ithaca, NY.
Synthesis of (C5Me4HSiMe2N(H)R) (R = CMe2Ph 1, 2-C6H4Ph
2). These compounds were synthesized via a similar proce-
dure, therefore only one synthesis is described. A solution of
PhMe2CN(H)Li (prepared via the 1 : 1 reaction of nBuLi and
cumyl amine: 4.5 g, 4.25 mmol) in THF (100 mL) was cooled to
-78 ◦C and added slowly, via cannula, to a solution of Cp¢Me2SiCl
(9.131 g, 4.25 mL), also at -78 ◦C. After the addition was complete
the solvent was removed in vacuo and the product distilled under
vacuum to afford a bright yellow-green oil (12.0 g, 94%). 1H NMR
33
to a solution of (Me2N)2TiCl2 (373 mg, 1.8 mmol) in THF
(35 mL) which was also at -35 ◦C. The reaction mixture changed
from a dark red solution to an orange/white slurry over the course
of the addition. The reaction was warmed to room temperature
and stirred for an additional hour. The solvent was removed under
(CD2Cl2) : 7.50 (d, 2H 3JH–H = 8 Hz, o-C6H4); 7.32 (t, 2H, 3JH–H
=
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reduced pressure after which dichloromethane was added (10 mL)
and the mixture filtered through Celite. Removal of the solvent
in vacuo and subsequent washing with cold (-35 ◦C) pentane (2 ¥
3 mL) afforded an orange crystalline solid (632 mg, 78%) 1H NMR
(CD2Cl2) (300.048 MHz): 7.39 (m, 2H, o-C6H4); 7.24 (m, 2H, m-
C6H4); 7.16 (m, 1H, p-C6H4); 3.11 (s, 12H, NMe2); 2.10 (s, 6H,
Cp¢Me); 2.02 (s, 3H, Cp¢Me); 1.70 (s, 6H, CMe2Ph); 0.07 (s, 6H,
added and the mixture filtered through Celite to afford a dark
brown solution, which was concentrated under reduced pressure
to approximately half the original volume. This solution was
cooled to -35 ◦C overnight to afford dark brown crystals (55 mg,
31%). The supernatant hexanes were concentrated and cooled to
◦
-35 C overnight to afford a second crop of crystals (17 mg) for
1
3
an overall yield of 41%. H NMR (C6D6): 6.92 (dd, 1H, JH–H
=
1
4
3
4
SiMe2). 13C{ H} NMR (CD2Cl2): 153.00(ipso-Ph); 128.03 (Ph);
8 Hz, JH–H = 2 Hz), 6.84 (td, 1H, JH–H = 8 Hz, JH–H = 2 Hz),
3 4
127.78 (Cp¢); 127.39 (Cp¢); 126.99(Ph); 126.20 (Ph); 101.30 (ipso-
Cp¢); 64.36 (CMe2); 50.44 (NMe2); 33.49 (CMe2); 14.11 (Cp¢Me);
12.59 (Cp¢Me); 5.89 (SiMe2). EA calc’d for C24H41N3SiTi (447.576)
C, 64.01; H, 9.23; N, 9.39. Found: C, 64.18, H, 9.24, N, 9.27.
X-ray quality crystals were grown by slow cooling of a solution in
pentane.
6.30 (td, 1H, JH–H = 7 Hz, JH–H = 1 Hz), 6.24 (dm, 1H, 3JH–H
=
3 4
8 Hz), 3.99 (dd, 2H, JH–H = 6 Hz, JH–H = 1 Hz), 3.22 (dd, 2H,
3JH–H = 7 Hz, JH–H = 6 Hz), 2.43 (s, 6H, Cp¢Me), 1.63 (tt, 1H,
4
3JH–H = 7 Hz, JH–H = 1 Hz), 0.99 (s, 6H, Cp¢Me), 0.49 (s, 6H,
4
SiMe2). 13C{ H} NMR (C6D6): 156.0, 144.2, 126.4, 124.6, 124.4,
1
121.2, 117.5, 114.1, 113.0, 111.0, 34.8, 23.1, 16.8 (Cp¢Me), 14.6,
11.0 (Cp¢Me), 4.5 (SiMe2). EA calc’d for C23H27NSiTi (393.440)
C, 70.22; H, 6.92; N, 3.56. Found: C, 69.80, H, 7.45, N, 3.58.
5: Bright orange crystals, 731 mg, 94%. 1H NMR (CD2Cl2): 7.4
3
3
(dm, 2H, JH–H = 7 Hz), 7.3 (t, 2H, JH–H = 7 Hz), 7.2 (tm, 1H,
3JH–H = 7 Hz), 7.1 (tm, 2H, JH–H = 7 Hz), 6.9 (td, 2H, JH–H
=
3
3
8 Hz, 4JH–H = 1 Hz), 6.8 (d, 1H, 3JH–H = 8 Hz), 2.9 (s, 12H, NMe2);
Synthesis of C5Me4SiMe2N(R)TiMe2 (R = CMe2Ph 9, 2-C6H4Ph
10). These compounds were synthesized via a similar procedure,
therefore only one synthesis is described. A solution of 6 (382 mg,
0.63 mmol) in THF (30 mL) was cooled to -35 ◦C and MeMgBr
(3 M in diethyl ether, 0.436 mL) was added in one portion. The
ethereal solution changed from a dark orange to a yellow solution
with a white precipitate. The solvent was removed under reduced
pressure and the product was extracted with pentane (20 mL) and
filtered through a plug of Celite. The pentane was removed in vacuo
to afford a yellow solid (215 mg, 89%). 1H NMR (C6D6): 7.5 (dm,
2.2 (s, 6H, Cp¢Me); 2.1 (s, 3H, Cp¢Me); 0.2 (s, 6H, SiMe2).13C{ H}
1
NMR (CD2Cl2): 153.8, 143.5, 136.1, 131.6, 131.0, 130.9, 129.4,
128.2, 128.0, 127.9, 127.5, 126.6, 121.6, 102.2, 48.2 (NMe2), 14.6
(Cp¢Me), 12.1 (Cp¢Me), 3.96 (SiMe2). EA calc’d for C27H39N3SiTi
(481.593) C, 67.34, H, 8.16; N, 8.73. Found: C, 67.42, H, 8.42,
N, 8.82. X-ray quality crystals were grown by slow cooling of a
solution in pentane.
Synthesis of C5Me4(SiMe2NR)TiI2 (R = CMe2Ph 6, 2-C6H4Ph
7). These compounds were synthesized via a similar procedure,
therefore only one synthesis is described. 6: To a solution of 4
(1.525 g, 3.4 mmol) in CH2Cl2 (10 mL) was added iodomethane
(0.5 mL, 80.2 mmol) in one portion. The solution darkened from
yellow orange to dark red, concomitant with the formation of a
white precipitate. The mixture was stirred for 12 h, after which
the solution was filtered through Celite and the solvent removed
from the filtrate in vacuo. The resulting solid was washed with
cold pentane (2 ¥ 5 mL) to afford a red microcrystalline solid
3
3
2H, JH–H = 8 Hz, o-Ph), 7.2–7.1 (m), 7.1 (tt, 1H, JH–H = 7 Hz,
4JH–H = 2 Hz, p-Ph), 2.05 (s, 6H, CMe2), 2.0 (s, 6H, Cp¢Me), 1.9 (s,
6H, Cp¢Me), 0.5 (s, 6H, TiMe2) 0.1 (s, 6H, SiMe2). 13C{ H} (C6D6,
1
partial) : 149.2, 132.2, 128.0, 124.9, 124.8, 97.0, 60.1, 50.3, 32.0,
13.4, 10.3, 3.4. EA calc’d for C22H35NSiTi (389.493) C, 67.84; H,
9.06; N, 3.60 Found: C, 67.32; H, 8.65; N, 3.12.
10: Pale yellow crystals, 122 mg, 82%.1H NMR (CD2Cl2): 7.4
3
3
4
(dm, 2H, JH–H = 8 Hz), 7.3 (dd, 1H, JH–H = 7 Hz, JH–H = 2
1
3
4
(2.01 g, 96%). H NMR (CD2Cl2) (300.048 MHz): 7.5 (dm, 2H,
Hz), 7.3–7.2 (m, 4H), 7.1 (td, 1H, JH–H = 7 Hz, JH–H = 2 Hz),
3JH–H = 8 Hz, o-Ph), 7.3 (tm, 2H, 3JH–H = 8 Hz, m-Ph), 7.2 (tm, 1H,
3JH–H = 8 Hz, p-Ph), 2.6 (s, 6H, Cp¢Me), 2.3 (s, 6H, CMe2), 2.1 (s,
6.9 (dd, 1H, 3JH–H = 7 Hz, 4JH–H = 2 Hz), 2.2 (s, 6H, Cp¢Me), 1.9
(s, 6H, Cp¢Me), 0.3 (s, 6H, TiMe2) 0.03 (s, 6H, SiMe2). 13C{ H}
1
1
6H, Cp¢Me), 0.1 (s, 6H, SiMe2). 13C{ H} NMR (CD2Cl2): 150.8,
NMR (CD2Cl2): 149.8, 142.2, 137.0, 135.9, 131.7, 130.8, 130.3,
128.5, 128.1, 128.1, 127.0, 126.9, 123.6, 98.0, 56.3, 15.4, 12.4, 2.8
(SiMe2). EA calc’d for C25H33NSiTi (423.510) C, 70.90; H, 7.85;
N, 3.31; Found: C, 70.42, H, 8.37, N, 3.06. X-ray quality crystals
were grown by slow cooling of a solution in pentane.
146.6, 143.0, 130.9, 129.8, 129.0, 107.9 (ipso-Cp¢); 69.5 (CMe2),
35.3 (CMe2), 21.6 (Cp¢Me), 18.7 (Cp¢Me), 6.2 (SiMe2). EA calc’d
for C20H29NSiTiI2(613.232) C, 39.17; H, 4.77; N, 2.28 Found: C,
39.21; H, 4.86; N, 2.50. X-ray quality crystals were grown by slow
evaporation of a solution in dichloromethane.
7: Bright red crystals, 935 mg, 98%. 1H NMR (CD2Cl2): 7.7 (dd,
1H, 3JH–H = 7 Hz, 4JH–H = 2 Hz), 7.6 (m, 2H), 7.4–7.2 (m, 6H), 2.6
Styrene polymerizations. In the glovebox, a 500 mL round-
bottom Schlenk flask was charged with a magnetic stir bar, toluene
(50 mL), and styrene (10 g) that had been filtered though activated
neutral alumina immediately prior to use. The flask was removed
1
(s, 6H, Cp¢Me), 2.1 (s, 6H, Cp¢Me), 0.1 (s, 6H, SiMe2). 13C{ H}
NMR (CD2Cl2): 149.2, 146.4, 141.4, 133.7, 132.5, 131.9, 128.6,
128.4, 128.3, 127.5, 125.9, 106.8, 19.4 (Cp¢Me), 16.9 (Cp¢Me), 2.4
(SiMe2). EA calc’d for C23H27NSiTiI2 (647.249) C, 42.68; H, 4.20;
N, 2.16. Found: C, 42.45, H, 4.48, N, 2.06. X-ray quality crystals
were grown by slow evaporation of a solution in dichloromethane.
ꢀ
C
from the glovebox and attached to a Schlenk line via Tygon
tubing which was evacuated and flushed with N2 (5¥) before the
flask was opened to one atmosphere of N2. In the glovebox, the
titanium precatalyst (11 mmol) and [Ph3C][B(C6F5)4] (10 mmol)
were combined in toluene (4 mL) and loaded into a plastic syringe,
removed from the glovebox and injected into the stirring toluene–
styrene mixture. After one hour, acidified methanol (10 mL) was
injected to quench the reaction, and methanol (400 mL) was added
to precipitate the polymer. The polymeric solids were collected by
vacuum filtration and dried in a vacuum oven at 60 ◦C for 48 h.
Synthesis of C5Me4SiMe2N(C6H4Ph)Ti (8). Potassium
graphite (122 mg, 0.9 mmol) was added to a solution of 7 (292 mg,
0.45 mmol) in THF (35 mL) in portions over a period of 5 min
during which time the red solution became a dark brown slurry.
This reaction mixture was stirred for an additional 2 h after
which the solvent was removed in vacuo. Hexanes (15 mL) were
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Ethylene polymerizations. In the glovebox, a 500 mL round-
bottom Schlenk flask was charged with a magnetic stir bar, toluene
(50 mL), and tri-iso-butylaluminium (40 mg). The flask was
removed from the glovebox and attached to a Schlenk line via
ꢀ
C
Tygon tubing which was evacuated and flushed with N2 (5¥)
before the flask evacuated and refilled with ethylene (3¥). In the
glovebox, the titanium precatalyst (10 mmol) and [Ph3C][B(C6F5)4]
(10 mmol) were separately dissolved in toluene (3 mL) and loaded
into separate plastic syringes, removed from the glovebox and the
precatalyst solution was injected into the toluene–styrene mixture
immediately followed by the activator solution. After ten minutes,
acidified methanol (10 mL) was injected to quench the reaction,
and methanol (400 mL) was added to precipitate the polymer. The
polymeric solids were collected by vacuum filtration and dried in
a vacuum oven at 60 ◦C for 72 h.
Scheme 1 Synthesis of 1, 2 and 4–7, 9 and 10.
X-ray data collection and reduction. Crystals were manipulated
and suspended in Paratone inside a glovebox, mounted on a
MiTegen Micromount, and placed under a N2 stream, thus
maintaining a dry, O2-free environment for each crystal. The data
for crystals were collected on a Bruker Apex II diffractometer
confirmed crystallographically (Fig. 2 and Table 1). The metrical
parameters of this species are unexceptional. Complexation of
these ligands with titanium was initially attempted by reaction
of TiCl4·(THF)2 with the dilithio species generated by the in situ
deprotonation of 1 and 2 with nBuLi. This reaction generated
a mixture of unidentified products, which is not surprising as
low yields were reported in the synthesis of related Cp-amido
titanium complexes synthesized in this fashion.5,36 In a modified
synthetic attempt, the Me3Si-derivatives of 1 or 2 were generated
in situ by deprotonation with two equivalents of nBuLi followed
by treatment with Me3SiCl, but treatment of these species with
TiCl4·(THF)2 also resulted in mixtures of unidentified products.
˚
with MoKa radiation (l = 0.71069 A). The frames were integrated
with the Bruker SAINT software package using a narrow-frame
algorithm. Data were corrected for absorption effects using the
empirical multi-scan method (SADABS). Subsequent solution
and refinement were performed using the SHELXTL solution
package.
Structure solution and refinement. Non-hydrogen atomic scat-
tering factors were taken from the literature tabulations.34 The
heavy atom positions were determined using direct methods
employing the SHELXTL direct methods routine. The remaining
non-hydrogen atoms were located from successive difference
Fourier map calculations. The refinements were carried out by
using full-matrix least squares techniques on F, minimizing the
function w(Fo - Fc)2 where the weight w is defined as 4Fo2/2s(Fo
)
2
and Fo and Fc are the observed and calculated structure factor
amplitudes, respectively. In the final cycles of each refinement,
all non-hydrogen atoms were assigned anisotropic temperature
factors in the absence of disorder or insufficient data. In the
latter cases atoms were treated isotropically. C–H atom positions
were calculated and allowed to ride on the carbon to which
˚
they are bonded assuming a C–H bond length of 0.95 A. H-
atom temperature factors were fixed at 1.10 times the isotropic
temperature factor of the C-atom to which they are bonded.
The H-atom contributions were calculated, but not refined. The
locations of the largest peaks in the final difference Fourier map
calculation as well as the magnitude of the residual electron
densities in each case were of no chemical significance. Additional
details are provided in the supplementary data.†
Fig. 2 POV-Ray depiction of 2. Hydrogen atoms are omitted for
clarity. Selected bond distances (A) and angles (◦): Si(1)–N(1),
˚
1.7312(19); Si(1)–C(22), 1.859(3); Si(1)–C(23), 1.867(3); Si(1)–C(13),
1.896(2); N(1)–Si(1)–C(13), 102.74(10); C(1)–N(1)–Si(1), 131.04(14).
An alternative metathetical avenue to such complexes is
treatment of the dilithio ligand precursor with TiCl3·(THF)3
followed by subsequent oxidation to the desired Ti(IV) precatalyst
with AgCl or PbCl2.7 This synthetic strategy was attempted
using 2 and afforded the desired titanium dichloride species
C5Me4SiMe2N(C6H4Ph)TiCl2 (3) albeit in low yield (10%).
Seeking a higher yield synthetic strategy to titanium com-
plexes, deprotonation of 1 and 2 in situ followed by treat-
ment with (Me2N)2TiCl2 afforded C5Me4(SiMe2NR)Ti(NMe2)2
Results and discussion
Synthesis of the proligands C5Me4HSiMe2N(H)R) (R = CMe2Ph
1, 2-C6H4Ph 2) was accomplished via
salt metathesis reaction of the appropriate lithium amide
and ClSiMe2(C5Me5H) (Scheme 1). Complex 1 was isolated
a straightforward
in good yield as
a yellow oil, similarly to the related
(C5Me4H)SiMe2(N(H)tBu).3,35 Complex 2 was isolated in mod-
erate yield as a waxy crystalline solid and the formulation was
2864 | Dalton Trans., 2011, 40, 2861–2867
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(R = CMe2Ph 4, 2-C6H4Ph 5), respectively, in good yield
(Scheme 1). These compounds were isolated as highly soluble,
large crystals; the solid state molecular structures were determined
via X-ray analysis (Fig. 3). The constrained-geometry ligand
Ti–N distances were found to be 1.985(2) A and 2.013(2) A
and the average Ti–N bond distances for the NMe2 groups were
96 and 98% yield, respectively. X-ray diffraction studies allowed
for the determination of the solid-state molecular structures of
both 6 and 7 (Fig. 4). The metrical parameters of these complexes
are unexceptional, although, to the best of our knowledge, the
molecular structures of similar (Cp-amido)TiI2 complexes have
not been reported. “Constrained geometry” titanium diiodides
have been reported in the literature, but these complexes were
synthesized from impure (Cp-amido)TiMe2 and reconverted to
such dialkyl complexes as a purification strategy.38
˚
˚
˚
˚
˚
1.927(2) A and 1.925(2) A in 4 and 5. These are longer than
˚
1.972(4) A and 1.915(5) A seen for the corresponding distances
in C5H4SiMe2N(tBu)Ti(NMe2)2 Interestingly, the centroid–Ti
˚
distances in 4 and 5 are found to be 2.104(3) and 2.065(3) A,
bracketing that found in C5H4SiMe2N(tBu)Ti(NMe2)2 (Ti–Ct,
35
˚
2.083 A).
Fig. 4 POV-Ray depiction of (a) 6 and (b) 7. Hydrogen atoms are
◦
˚
omitted for clarity. Selected bond distances (A) and angles ( ) 6:
Ti(1)–Ct, 2.045(8); Ti(1)–N(1), 1.919(5); I(1)–Ti(1), 2.6544(12); I(2)–Ti(1),
2.6812(13); Si(1)–N(1), 1.764(5); Si(1)–C(12), 1.889(8); N(1)–Ti(1)–Ct,
108.70(10); N(1)–Si(1)–C(12), 90.8(3); I(1)–Ti(1)–I(2), 105.70(4). 7:
Ti(1)–Ct, 2.025(7); Ti(1)–N(1), 1.946(7); I(1)–Ti(1), 2.6390(16); I(2)–Ti(1),
2.6495(18); Si(1)–N(1), 1.773(7); Si(1)–C(13), 1.866(9); N(1)–Ti(1)–Ct,
107.23(10); N(1)–Si(1)–C(13), 89.4(3); I(1)–Ti(1)–I(2), 100.73(5).
Fig. 3 POV-Ray depiction of (a) 4 and (b) 5. Hydrog◦en atoms are
˚
omitted for clarity. Selected bond distances (A) and angles ( ) 4: Ti(1)–Ct,
2.104(3); Ti(1)–N(1), 1.985(2); Ti(1)–N(2), 1.942(2); Ti(1)–N(3), 1.915(2);
Si(1)–N(1), 1.730(2); Si(1)–C(12), 1.861(3); N(1)–Ti(1)–Ct, 106.18(10);
N(1)–Si(1)–C(12), 93.63(12); N(3)–Ti(1)–N(2), 100.48(10). 5: Ti(1)–Ct,
2.065(3); Ti(1)–N(1), 2.013(2); Ti(1)–N(2), 1.925(2); Ti(1)–N(3), 1.925(2);
Si(1)–N(1), 1.732(2); Si(1)–C(13), 1.869(3); N(1)–Ti(1)–Ct, 105.12(10);
N(1)–Si(1)–C(13), 93.10(11); N(2)–Ti(1)–N(3), 99.76(11).
Previous work in the Stephan group with biphenyl-
phosphinimide ligands has shown that reduction of titanium
complexes of this ligand results in reoxidation of the metal
centre via activation of this pendant arene.39 Treatment of 7 with
two equivalents of potassium graphite afforded a similar arene-
activation product, C5Me4(SiMe2N C6H4Ph)Ti, 8 (Scheme 2).
X-ray quality crystals of 8 could not be obtained after repeated
recrystallizations but the 1H NMR spectrum contained resonances
at 4.0, 3.2, and 1.6 ppm in a 2 : 2 : 1 ratio attributable to the
hydrogens from the former phenyl substituent (Fig. 5). The
relative ratios and multiplicity of these resonances verify the
Cummins and coworkers have previously reported the cleavage
of Ti–N bonds with MeI to give TiI2 derivatives.37 Analogous
treatment of either 4 or 5 with >20 equivalents of MeI in CH2Cl2
afforded C5Me4(SiMe2NR)TiI2 (R = CMe2Ph 6, 2-C6H4Ph 7). The
1H NMR spectra of these reactions in CD2Cl2 revealed these
reactions to be quantitative and these products were isolated in
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were obtained. X-ray data did confirm the structure of 10 (Fig. 6)
although the poor quality of the crystals precluded a meaningful
discussion of metrical parameters.
Scheme 2 Synthesis of 8.
Fig. 6 POV-Ray depiction of 10. Hydrogen atoms are omitted for clarity.
Reactions of 9 and 10 with [Ph3C][B(C6F5)4] generated
cations that were used as catalysts in polymerisation reactions
of styrene and ethylene (Table 2). Polymerisations were also
conducted using [(C5Me4)SiMe2(NtBu)]TiMe2 under identical
conditions for comparative purposes. Cations derived from
[(C5Me4)SiMe2(NtBu)]TiMe2 have been shown to exhibit very
poor productivities in the polymerization of styrene,7 a result
that was reproduced here. Polymerization of styrene using 9 as a
precatalyst afforded higher activity than the catalyst derived from
complex 10, while this latter catalyst exhibited similar activity to
[(C5Me4)SiMe2(NtBu)]TiMe2 under these conditions. While use of
these catalysts in the polymerisation of ethylene gave higher activi-
ties as expected, the catalyst derived from 9 exhibited good activity.
The resulting polyethylene has polydispersity that is consistent
with a single-site catalyst. In contrast, the catalyst derived from 10
was inactive. It is interesting to note that the catalyst derived from
Fig. 5 1H NMR spectrum of 8 in C6D6.
formulation of 8. Attempts to effect analogous reduction of 6 with
potassium graphite afforded a mixture of products which were not
identified.
In order to generate the dialkyl precatalysts required for
polymerization, 6 and 7 were treated with two equivalents of
MeMgBr in THF, affording C5Me4(SiMe2NR)Ti(NMe2)2 (R =
CMe2Ph 9, 2-C6H4Ph 10), respectively (Scheme 1). The solid-state
molecular structure of 9 was not determined, but a resonance at 0.1
ppm attributable to two equivalent titanium methyl groups verified
the alkylation had proceeded to completion. Single crystals of 10
Table 1 Crystallographic data
2
4
5
6
7
10
Formula
C23H29NSi
347.56
C24H41N3SiTi
447.59
Monoclinic
P21/n
8.9918(18)
32.057(6)
9.6600(19)
90
117.73(3)
90
2464.8(8)
4
150(2)
1.206
0.411
22 740
0.0799
5597
C27H39N3SiTi
481.60
C20H29I2NSiTi
613.23
Monoclinic
Cc
19.434(4)
8.4193(17)
14.943(3)
90
111.49(3)
90
2275.0(8)
4
150(2)
1.790
3.147
7620
0.0313
3837
C23H27I2NSiTi
647.25
Monoclinic
P21/c
15.316(3)
7.7666(16)
21.150(4)
90
108.64(3)
90
2383.9(8)
4
150(2)
1.803
3.009
16 159
0.0929
5413
C25H33NSiTi
423.51
Formula weight
Crystal system
Space group
Triclinic
Triclinic
Triclinic
¯
¯
¯
P1
P1
P1
˚
a (A)
9.3969(19)
10.297(2)
12.440(3)
68.91(3)
82.78(3)
64.73(3)
1015.0(4)
2
8.7355(17)
12.022(2)
12.655(3)
85.17(3)
82.55(3)
79.94(3)
1295.0(4)
2
7.5742(15)
11.756(2)
13.062(3)
80.73(3)
85.90(3)
83.85(3)
1139.5(4)
2
˚
b (A)
˚
c (A)
a (◦)
b (◦)
g (◦)
3
˚
V (A )
Z
T (K)
150(2)
1.137
0.121
4542
0.0426
3144
150(2)
1.235
0.396
12 539
0.0586
5897
150(2)
1.234
0.438
10 730
0.1237
5127
dcalc (g cm-1)
Rint
m (cm-1)
Total data
Data > 3s(F
Variables
R (>3s)
Rw
2
)
O
226
274
299
226
253
261
0.0600
0.1644
1.090
0.0552
0.1575
0.996
0.0548
0.1551
1.028
0.0333
0.0775
1.096
0.0590
0.1364
1.021
0.1179
0.3469
1.070
GOF
˚
Data collected with Mo Ka radiation (l = 0. 0.71073 A).
2866 | Dalton Trans., 2011, 40, 2861–2867
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Table 2 Polymerization and copolymerization data
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Mw
PDI
CGC
9
10
Styrene
Styrene
Styrene
3
16
3
13 620
11 650
11 360
158 400
177 000
—
1.64
1.52
1.51
2.06
2.91
—
CGC
9
Ethylene
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308
770
0
10
9
Negligible
—
—
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1H NMR spectroscopy. While the abstraction of methyl from
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arene substituent. Nonetheless, this postulate is supported to
some extent by the preparation of 8, where the generation of
unsaturation at the Ti center prompts interaction with the arene
fragment.
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CGCs with pendant arene groups. While the complex bearing
a biphenyl substituent demonstrated generally low activities in
the polymerisation of styrene and ethylene, the complex bearing
a cumyl substituent exhibited moderately increased activities in
comparison to the benchmark CGC under similar conditions.
Nonetheless, this catalyst was inactive in coplymerization of
ethylene/styrene.
10100–10101.
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The financial support from NSERC of Canada is gratefully
acknowledged. DWS is also grateful for the award of a Canada
Research Chair and a Killam Research Fellowship.
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Notes and references
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2861–2867 | 2867
©