Ti and Zr bidentate bis-phosphinimide complexes

Article abstract of DOI:10.1039/b308114a

The diphosphines m-C₆H₄(CH₂Pt-Bu₂)₂ 1 and m-C₆H₄(CH₂PCy₂)₂ 2 were prepared and oxidized with Me₃SiN₃ to m-C₆H₄(CH₂(t-Bu₂)PNSiMe₃) ₂ 3 and m-C₆H₄(CH₂(Cy₂) PNSiMe₃)₂ 4, and subsequently converted to m-C₆H₄(CH₂-(t-Bu)₂PNH)₂ 5 and m-C₆H₄(CH₂(Cy)₂PNH)₂ 6. Reaction of 5 and 6 with Ti(NMe₂)₄ afforded the yellow compounds m-C₆H₄(CH₂(t-Bu)₂ PN)₂Ti(NMe₂)₂ 7 and m-C₆H₄(CH₂(Cy)₂PN)₂ Ti(NMe₂)₂ 8, and the low abundance by-product m-C₆H₄(CH₂(t-Bu)₂PN)₂TiBr (NMe₂) 9. In a similar manner, the species m-C₆H₄(CH₂(t-Bu)₂PN)₂Zr(N Et₂)₂ 10 was prepared from Zr(NEt₂)₄. Compounds 8, 9 and 10 were converted to C₆H₄(CH₂(t-Bu)₂PN)₂ TiBr₂ 11, m-C₆H₄(CH₂-(Cy)₂PN)₂ TiCl₂ 13 and C₆H₄(CH₂(t-Bu)₂PN)₂ ZrCl₂ 14 via reaction with Me₃SiX (X = Br, Cl). Alternatively, m-C₆H₄(CH₂ (t-Bu)₂PN)₂TiCl₂ 12 and 13 were prepared in low yield from reaction of 3 or 4 with TiCl₄. Alkylation of 11 with MeMgBr and PhCH₂MgBr proceeded to give m-C₆H₄(CH₂(t-Bu)₂PN)₂ TiMe₂ 15 and m-C₆H₄(CH₂- (t-Bu)₂PN)₂Ti(CH₂Ph)₂ 16, respectively. The species (m-C₆H₄(CH₂ (t-Bu)₂PN)₂)₂Zr 17 was prepared from Zr(CH₂Ph)₄. These synthetic routes are described and the implications for applications in olefin polymerization catalysis are considered. X-Ray structural data for compounds 1, 3, 4, 5, 8, 9 and 16 are reported.

Full text of DOI:10.1039/b308114a

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Ti and Zr bidentate bis-phosphinimide complexes
Emily Hollink, Jeffrey C. Stewart, Pingrong Wei and Douglas W. Stephan*
Department of Chemistry & Biochemistry, University of Windsor, Windsor, Ontario,
Canada N9B3P4. E-mail: stephan@uwindsor.ca
Received 16th July 2003, Accepted 20th August 2003
First published as an Advance Article on the web 4th September 2003
The diphosphines m-C6H4(CH2Pt-Bu2)2 1 and m-C6H4(CH2PCy2)2 2 were prepared and oxidized with Me3SiN3 to
m-C6H4(CH2(t-Bu2)PNSiMe3)2 3 and m-C6H4(CH2(Cy2)PNSiMe3)2 4, and subsequently converted to m-C6H4(CH2-
(t-Bu)2PNH)2 5 and m-C6H4(CH2(Cy)2PNH)2 6. Reaction of 5 and 6 with Ti(NMe2)4 afforded the yellow compounds
m-C6H4(CH2(t-Bu)2PN)2Ti(NMe2)2 7 and m-C6H4(CH2(Cy)2PN)2Ti(NMe2)2 8, and the low abundance by-product
m-C6H4(CH2(t-Bu)2PN)2TiBr(NMe2) 9. In a similar manner, the species m-C6H4(CH2(t-Bu)2PN)2Zr(NEt2)2 10 was
prepared from Zr(NEt2)4. Compounds 8, 9 and 10 were converted to C6H4(CH2(t-Bu)2PN)2TiBr2 11, m-C6H4(CH2-
(Cy)2PN)2TiCl2 13 and C6H4(CH2(t-Bu)2PN)2ZrCl2 14 via reaction with Me3SiX (X = Br, Cl). Alternatively,
m-C6H4(CH2(t-Bu)2PN)2TiCl2 12 and 13 were prepared in low yield from reaction of 3 or 4 with TiCl4. Alkylation
of 11 with MeMgBr and PhCH2MgBr proceeded to give m-C6H4(CH2(t-Bu)2PN)2TiMe2 15 and m-C6H4(CH2-
(t-Bu)2PN)2Ti(CH2Ph)2 16, respectively. The species (m-C6H4(CH2(t-Bu)2PN)2)2Zr 17 was prepared from Zr(CH2Ph)4.
These synthetic routes are described and the implications for applications in olefin polymerization catalysis are
considered. X-Ray structural data for compounds 1, 3, 4, 5, 8, 9 and 16 are reported.
analyses were performed employing a Waters 150C GPC using
Introduction
1,2,4-trichlorobenzene as the mobile phase at 140 ЊC and were
A large number of phosphinimide ligand complexes have been
performed at NOVA Chemicals Corporation research facilities
prepared and characterized. Much of the earlier work has been
in Calgary. The samples were prepared by dissolving the poly-
reviewed by Dehnicke and co-workers.1,2 In more recent work,
we have reported a series of phosphinimide complexes of Ti
mer in the mobile phase solvent in an external oven at 0.1%
(w/v) and were filtered before injection. Molecular weights are
expressed as polyethylene equivalents with a relative standard
and Zr in which the monodentate phosphinimide ligands act
as steric equivalents to cyclopentadienyl groups.3–6 Molecular
deviation of 2.9% and 5.0% for Mn and Mw respectively.
orbital considerations also infer an electronic analogy.1,2 This
Reagent grade solvents and NEt3 were purchased from Aldrich
strategy has lead to the development of commercially viable
Chemical Co. Benzene, toluene and Et2O were dried over Na/
ethylene polymerization catalyst precursors.7 Thus, complexes
benzophenone, MeOH dried over Mg, and NEt3 dried over
of the form CpTi(NPR3)X2 and (R3PN)2TiX2 exhibit similar
KOH prior to distillation. C6D6 and CD2Cl2 were purchased
reactivity to the corresponding metallocene systems. In an
from Canadian Isotopes Laboratories and degassed by at least
effort to further extend this analogy to include ansa-metallo-
cene systems, it is logical to consider analogous chelating bis-
phosphinimide ligands. Clearly one would envision synthetic
routes to such complexes from bis-phosphines, a class of ligand
4 freeze/pump/thaw cycles before storing over 4 Å molecular
sieves. The reagents MeMgBr, Me3SiCl, Me3SiBr, Me3SiN3, and
α,αЈ-dibromo-m-xylene were purchased from Aldrich Chemical
Co., Zr(NEt2)4, HPt-Bu2, HPCy2 and Ti(NMe2)4 were pur-
that is well known. While commercially available bis-phos-
chased from Strem Chemical Co.; all were used without further
phines have been converted to bis-phosphinimines and further
purification. Zr(CH2Ph)4 was prepared by a literature method.14
employed to prepare Group IV phosphinimide complexes by
MAO, t-i-BAl (Akzo Nobel) and B(C6F5)3 and [Ph3C][B(C6F5)4]
were generously donated by NOVA Chemicals Corporation and
the research groups of Cavell8–10 and Bochmann,11 the resulting
species are either bimetallic complexes, or have resulted in
polymerization-inactive carbene derivatives. In contrast, it has
were used as received. The phosphine m-C6H4(CH2Pt-Bu2)2 1
was prepared by known methods.15
only been very recently reported that complexes containing
di-anionic, bis-phosphinimides as chelating ligands have been
prepared.12,13 In this manuscript, we address the paucity of
chelating bis-phosphinimide ligands, in the development of
synthetic routes to their corresponding Ti and Zr complexes.
Synthesis of m-C6H4(CH2PCy2)2 2. Method 1. α,αЈ-Dibromo-
m-xylene (5.71 g, 21.6 mmol) was added to a Schlenk flask.
MeOH was added via a cannula to generate a slurry, and
HPCy2 (9.43 g, 47.5 mmol) was added via a syringe at 25 ЊC.
The mixture was stirred for 16 h during which time the solution
became homogeneous. NEt3 (4.80 g, 47.5 mmol) was added via
a syringe, and the solution was cooled to Ϫ30 ЊC to afford the
phosphine as fine, colourless needles (9.65g, 89%).
Experimental
General considerations
The syntheses were performed employing an atmosphere of
dry, oxygen-free nitrogen in a Vacuum Atmospheres inert
atmosphere glove box or standard Schlenk techniques. 1H
NMR data were acquired on a Bruker Avance 500 MHz spec-
trometer, and 13C{1H} and 31P{1H} NMR data on a Bruker
Method 2. α,αЈ-Dibromo-m-xylene (130 mg, 0.49 mmol)
was dissolved in THF (20 mL), and the solution was cooled to
Ϫ78 ЊC. A clear solution of LiPCy2 (210 mg, 1.03 mmol) in the
same solvent (10 mL) was added dropwise, and the mixture was
stirred for 4 h before it was gradually warmed to 25 ЊC. The
solvent was removed in vacuo, and the product was extracted
with hexanes. Following filtration through Hyflo Super Cel ®,
the solution was concentrated, and the product was recrystal-
lized to afford colourless needles (180 mg, 72%). The spectro-
1
Avance 300 MHz spectrometer. H and 13C NMR chemical
shifts are listed downfield from tetramethylsilane in parts per
million, and were referenced to the residual proton or carbon
peak of the solvent. 31P NMR data were referenced using an
external standard relative to 85% H3PO4. Spectra were reported
in C6D6 unless otherwise noted. University of Windsor
Analytical Services performed the combustion analyses. GPC
1
scopic data were consistent with literature values. H NMR δ:
7.51 (s, 1H, C6H4 (oЈ-H)), 7.18 (m, 2H, C6H4 (o-H)), 7.17 (m,
1H, C6H4 (m-H)), 2.77 (s, 4H, CH2), 1.84–1.16 (m, 44H, Cy).
D a l t o n T r a n s . , 2 0 0 3 , 3 9 6 8 – 3 9 7 4
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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3
13C{1H} NMR δ: 140.8 (s, C6H4 (ipso-C)), 130.9 (s, C6H4 (o-C)),
128.5 (s, C6H4 (oЈ-C)), 127.0 (s, C6H4 (m-C)), 34.0 (d, 1JP–C = 24
Hz, CH2), 30.3 (d, 1JP–C = 13 Hz, Cy (ipso-C)), 29.8 (d, 2JP–C = 10
Hz, Cy (o-C)), 27.7 (br s, Cy (m-C)), 26.9 (s, Cy (p-C)). 31P{1H}
NMR δ: 1.9 (s).
8.46 (s, 1H, C6H4 (oЈ-H)), 7.09 (t, 1H, JH–H = 8 Hz, C6H4 (m-
3
H)), 6.89 (d, 2H, JH–H = 8 Hz, C6H4 (o-H)), 3.45 (s, 12H,
NMe2), 2.85 (d, 4H, 2JP–H = 9 Hz, CH2P), 1.19 (d, 36H, 3JP–H
=
13 Hz, t-Bu). 13C{1H} NMR δ: 134.9 (s, C6H4 (o-C)), 134.5 (s,
C6H4 (ipso-C)), 127.4 (s, C6H4 (o-C)), 127.1 (s, C6H4 (m-C)),
47.3 (s, NMe2), 37.1 (d, 1JP–C = 56 Hz, t-Bu), 30.0 (d, 1JP–C = 44
Hz, CH2P), 27.7 (s, t-Bu). 31P{1H} NMR δ: 12.7 (s). Anal. Calcd
for C28H56N4P2Ti: C, 60.21; H, 10.10; N, 10.03. Found: C,
60.61; H, 10.30; N, 9.93%. 8: Yellow solid. Yield: 322 mg, 73%.
1H NMR δ: 8.60 (s, 1H, C6H4 (o-H)), 7.11 (t, 1H, 3JH–H = 8 Hz,
Synthesis of m-C6H4(CH2(t-Bu2)PNSiMe3)2 3 and m-C6H4-
(CH2(Cy2)PNSiMe3)2 4. Solid 1 (2.06 g, 5.22 mmol) and
Me3SiN3 (3.01 g, 26.10 mmol) were combined in a Schlenk flask
to generate a slurry. The mixture was heated at reflux for 15 h,
after which time the excess Me3SiN3 was removed in vacuo. The
resulting beige solid was crushed with a mortar and pestle into a
fine powder, washed with pentanes (3 × 5 mL), and dried for an
additional 5 h. Yield of 3: 2.30 g (94%). 1H NMR δ: 7.53 (s, 1H,
3
C6H4 (m-H)), 7.86 (d, 2H, JH–H = 8 Hz, C6H4 (o-H)), 3.57 (s,
12H, NMe2), 2.69 (d, 4H, JP–H = 11 Hz, CH2P), 1.95 (m, 4H,
2
PCy2), 1.60 (br, 12H, PCy2), 1.44 (m, 4H, PCy2), 1.35 (m, 8H,
PCy2), 1.32 (m, 4H, PCy2), 1.11 (m, 12H, PCy2). 13C{1H} NMR
δ: 134.0 (s, C6H4 (ipso-C)), 133.9 (s, C6H4 (o-C)), 127.3 (s, C6H4
(o-C)), 127.1 (s, C6H4 (m-C)), 48.1 (s, NMe2), 37.8 (d, 1JP–C = 62
Hz, PCy2 (ipso-C)), 33.1 (d, 1JP–C = 48 Hz, CH2P), 27.4 (d, 2JP–C
= 12 Hz, PCy), 26.6 (s, PCy2), 26.5 (s, PCy2). 31P{1H} NMR δ:
1.6 (s). Anal. Calcd for C36H64N4P2Ti: C, 65.24; H, 9.73; N,
8.45. Found: C, 65.16; H, 9.91; N, 8.46%.
3
C6H4 (oЈ-H)), 7.32 (d, 2H, JH–H = 5 Hz, C6H4 (o-H)), 7.23 (d,
3
2
1H, JH–H = 5 Hz, C6H4 (m-H)), 2.93 (d, 4H, JP–H = 10 Hz,
CH2), 1.09 (d, 36H, 3JP–H = 10 Hz, t-Bu), 0.36 (s, 18H, SiMe3).
13C{1H} NMR δ: 135.3 (s, C6H4 (ipso-C)), 132.7 (s, C6H4 (o-C)),
128.8 (s, C6H4 (oЈ-C)), 127.6 (s, C6H4 (m-C)), 37.2 (d, JP–C
60 Hz, t-Bu), 31.0 (d, JP–C = 56 Hz, CH2P), 27.4 (s, t-Bu), 4.9
(s, SiMe3). 31P{1H} NMR δ: 24.8 (s). Anal. Calcd for C30H62-
N2P2Si2: C, 63.33; H, 10.98; N, 4.92. Found: C, 63.38; H, 10.89;
N, 4.90%. Crystals suitable for X-ray diffraction were grown by
1
=
1
Synthesis of m-C6H4(CH2(t-Bu)2PN)2TiBr(NMe2) 9. This yel-
low solid was isolated as a by-product (minimal solubility in
pentanes) from the above reaction; its presence was due to HBr
salts that originated from the phosphine synthesis (typical
yields ranged from 3–10%). 1H NMR δ: 8.67 (s, 1H, C6H4
1
slow evaporation from benzene. 4: (2.30 g, 94%). H NMR δ:
7.57 (s, 1H, C6H4 (oЈ-H)), 7.22 (br, 2H, C6H4 (o-H)), 7.16 (br,
1H, C6H4 (m-H)), 2.82 (d, 4H, 2JP–H = 12 Hz, CH2P), 1.82–1.50
(m, 18H, PCy2), 1.48–1.05 (m, 26H, PCy2), 0.38 (s, 18H, SiMe3).
13C{1H} NMR δ: 134.9 (s, C6H4 (ipso-C)), 132.3 (s, C6H4 (o-C)),
128.3 (s, C6H4 (oЈ-C)), 128.0 (s, C6H4 (m-C)), 37.8 (d, 1JP–C = 65
Hz PCy2 (ipso-C)), 34.0 (d, 1JP–C = 60 Hz, CH2P), 27.1 (br, PCy2
(o-C)), 26.4 (s, PCy2 (m-C)), 25.7 (s, PCy2 (p-C)), 5.2 (s, SiMe3).
31P{1H} NMR δ: 13.5 (s). Anal. Calcd for C38H70N2P2Si2: C,
67.81; H, 10.48; N, 4.16. Found: C, 67.66; H, 10.60; N, 4.03%.
Crystals suitable for X-ray diffraction were grown by slow
evaporation from pentanes.
3
(oЈ-H)), 7.07 (t, 1H, JH–H = 8 Hz, C6H4 (m-H)), 6.86 (d, 2H,
3JH–H = 8 Hz, C6H4 (o-H)), 3.67 (s, 6H, NMe2), 2.89 (d, 2H, 2JP–H
=
14 Hz, CH2P), 2.80 (d, 2H, 2JP–H = 14 Hz, CH2P), 1.24 (d, 18H,
3JP–H =14Hz, CMe3), 1.04(d, 18H, 3JP–H =14Hz, CMe3). 13C{1H}
NMR δ: 174.9 (s, C6H4 (ipso-C)), 129.5 (s, C6H4 (o-C)), 128.3 (s,
C6H4 (o-C)), 127.7 (s, C6H4 (m-C)), 48.6 (s, NMe2), 38.2 (d, 1JP–C
=
56 Hz, t-Bu), 36.2 (d, 1JP–C = 56 Hz, t-Bu), 29.2 (d, 1JP–C = 44 Hz,
CH2P), 27.3(s, t-Bu), 27.2(s, t-Bu). 31P{1H}NMRδ:17.2(s). Due
to the presence of 7, 9 could not be isolated cleanly for micro-
analyses, consequently repeated analyses gave high C and H
values. Anal. Calcd for C26H50BrN3P2Ti: C, 52.54; H, 8.48; N,
7.07. Found: C, 55.04; H, 8.81; N, 7.11%. Recrystallization from
benzene/pentanes afforded a few X-ray quality, pale yellow
crystals of 9.
Synthesis of m-C6H4(CH2(t-Bu)2PNH)2 5 and m-C6H4(CH2-
(Cy)2PNH)2 6. Solid 3 (0.57 g, 1.2 mmol) and MeOH (30 mL)
were heated at reflux for 16 h, after which time the volatile
products were removed in vacuo. The oily residue was washed
with hexanes (3 × 10mL) to afford a fine white powder (0.32g,
1
81%). 5: H NMR δ: 7.75 (s, 1H, C6H4 (o-H)), 7.29 (d, 2H,
3JH–H = 4 Hz, C6H4 (o-H)), 7.12 (br, 1H, C6H4 (m-H)), 2.86 (d,
Synthesis of m-C6H4(CH2(t-Bu)2PN)2Zr(NEt2)2 10. Zr(NEt2)4
(0.199 g, 0.53 mmol) was diluted in PhH (15 mL), and a clear
solution of 5 (223 mg, 0.53 mmol) in the same solvent (10 mL)
was added dropwise at 25 ЊC. The solution was stirred for 24 h,
after which time the volatile products were removed in vacuo to
afford an oily residue. Pentanes were added to precipitate a pale
yellow solid, which was subsequently filtered off, washed with
2
3
4H, JP–H = 18 Hz, CH2P), 1.11 (d, 36H, JP–H = 22 Hz, t-Bu).
13C{1H} NMR δ: 135.8 (s, C6H4 (ipso-C)), 132.6 (s, C6H4 (o-C)),
128.3 (s, C6H4 (oЈ-C)), 128.0 (s, C6H4 (m-C)), 36.2 (d, JP–C
56 Hz, t-Bu), 30.1 (d, JP–C = 39 Hz, CH2P), 27.9 (s, CMe3).
31P{1H} NMR δ: 48.2 (s). Anal. Calcd for C24H46N2P2: C, 67.89;
H, 10.92; N, 6.60. Found: C, 67.82; H, 10.93; N, 6.61%. 6: (0.91
g, 96%). 1H NMR (CD2Cl2) δ: 10.67 (br, 2H, N–H), 8.30 (s, 1H,
1
=
1
1
pentanes and dried. Yield: 302 mg, 87%. H NMR δ: 8.20 (s,
3
1H, C6H4 (oЈ-H)), 7.09 (t, 1H, 3JH–H = 8 Hz, C6H4 (m-H)), 6.88
C6H4 (oЈ-H)), 7.38 (t, 1H, JH–H = 8 Hz, C6H4 (m-H)), 7.15 (d,
3
3
3
2
(d, 2H, JH–H = 8 Hz, C6H4 (o-H)), 3.59 (q, 8H, JH–H = 7 Hz,
2H, JH–H = 8 Hz, C6H4 (o-H)), 3.51 (d, 4H, JP–H = 12 Hz,
CH2P), 2.34–1.72 (m, 18H, PCy2), 1.52–1.23 (m, 26H, PCy2).
13C{1H} NMR (CD2Cl2) δ: 140.8 (s, C6H4 (ipso-C)), 130.9 (s,
C6H4 (o-C)), 128.5 (s, C6H4 (oЈ-C)), 127.0 (s, C6H4 (m-C)), 34.0
(d, 1JP–C = 24 Hz, CH2P), 30.3 (d, 1JP–C = 13 Hz, PCy2 (ipso-C)),
29.8 (br, PCy2 (o-C)), 27.7 (s, PCy2 (m-C)), 26.9 (s, PCy2 (p-C)).
31P{1H} NMR (CD2Cl2) δ: 36.2 (s). Anal. Calcd for C32H54N2P2:
C, 72.69; H, 10.29; N, 5.30. Found: C, 72.61; H, 10.13; N,
5.01%.
NCH2), 2.83 (d, 4H, 2JP–H = 10 Hz, CH2P), 1.38 (t, 12H, 3JH–H
=
7 Hz, CH2Me), 1.17 (d, 36H, JP–H = 13 Hz, t-Bu). 13C{1H}
3
3
NMR δ: 134.9 (d, JP–C = 9 Hz, C6H4 (o-C)), 133.7 (s, C6H4
(ipso-C)), 127.5 (s, C6H4 (o-C)), 127.4 (s, C6H4 (m-C)), 45.8 (s,
NCH2), 37.1 (d, JP–C = 56 Hz, t-Bu), 30.4 (d, JP–C = 44 Hz,
CH2P), 27.9 (s, t-Bu), 17.1 (s, CH2Me). 31P{1H} NMR δ: 16.0
(s). Anal. Calcd for C32H64N4P2Zr: C, 58.41; H, 9.80; N, 8.51.
Found: C, 58.66; H, 9.60; N, 8.33%.
1
1
Synthesisofm-C6H4(CH2(t-Bu)2PN)2Ti(NMe2)2 7andm-C6H4-
(CH2(Cy)2PN)2Ti(NMe2)2 8. These compounds were prepared
in a similar fashion and thus one preparation is detailed.
Ti(NMe2)4 (0.25 mL, 1.08 mmol) was dissolved in PhH (40
mL), and a clear solution of 5 (460 mg, 1.08 mmol) in the same
solvent (10 mL) was added dropwise at 25 ЊC. The clear yellow
solution was stirred for 18 h, after which time the volatile prod-
ucts were removed in vacuo. The residue was extracted with
pentanes (3 × 10 mL), filtered, and the solvent was removed
in vacuo to afford a yellow solid (412 mg, 68%). 7: 1H NMR δ:
Synthesis of m-C6H4(CH2(t-Bu)2PN)2TiBr2 11, m-C6H4(CH2-
(Cy)2PN)2TiCl2 13 and m-C6H4(CH2(t-Bu)2PN)2ZrCl2 14. These
compounds were prepared in a similar fashion, with use of the
appropriate silyl reagent Me3SiX (X = Br, Cl), thus a represent-
ative experiment is described. A crude mixture of 7 and 9 (551
mg, ca. 1.1 mmol) was dissolved in PhH (40 mL) to give a clear
yellow solution, and Me3SiBr (0.30 mL, 2.2 mmol) was added
dropwise at 25 ЊC. The solution was stirred for 20 h, during
which time it became heterogeneous. The beige solid that pre-
cipitated was filtered off, washed with pentanes (3 × 5 mL) and
D a l t o n T r a n s . , 2 0 0 3 , 3 9 6 8 – 3 9 7 4
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dried in vacuo. Yield: 522 mg (ca. 76%). 11: 1H NMR (CD2Cl2)
Hyflo Super Cel ®. The solvent was removed in vacuo to
3
1
δ: 8.70 (s, 1H, C6H4 (o-H)), 7.19 (t, 1H, JH–H = 7 Hz, C6H4
afford a white solid 75 mg (62%). 15: H NMR δ: 8.48 (s, 1H,
3
3
(m-H)), 7.12 (d, 2H, JH–H = 7 Hz, C6H4 (o-H)), 3.27 (d, 4H,
C6H4 (oЈ-H)), 7.05 (t, 1H, JH–H = 8 Hz, C6H4 (m-H)), 6.84 (d,
2JP–H = 10 Hz, CH2P), 1.34 (d, 36H, 3JP–H = 14 Hz, t-Bu). 1H NMR
δ:8.92(s,1H,C6H4 (oЈ-H)),7.04(t,1H,3JH–H =8Hz,C6H4 (m-H)),
6.80 (d, 2H, 3JH–H = 8 Hz, C6H4 (o-H)), 2.78 (d, 4H, 2JP–H = 10 Hz,
2H, JH–H = 8 Hz, C6H4 (o-H)), 2.84 (d, 4H, JP–H = 10 Hz,
3
2
3
CH2P), 1.17 (d, 36H, JP–H = 14 Hz, t-Bu), 0.88 (s, 6H, TiMe).
13C{1H} NMR δ: 134.0 (s, C6H4 (ipso-C)), 128.2 (s, C6H4 (o-C)),
3
1
CH2P), 1.10 (d, 36H, JP–H = 14 Hz, t-Bu). 13C{1H} NMR
127.8 (s, C6H4 (o-C)), 127.2 (s, C6H4 (m-C)), 37.9 (d, JP–C
=
(CD2Cl2) δ: 135.4 (s, C6H4 (oЈ-C)), 133.0 (d, 2JP–C = 8 Hz, C6H4
(ipso-C)), 128.6 (s, C6H4 (o-C)), 128.2 (s, C6H4 (m-C)), 39.1 (d,
1JP–C = 54 Hz, t-Bu), 29.4 (d, 1JP–C = 45 Hz, CH2P), 27.8 (s, t-Bu).
31P{1H} NMR (CD2Cl2) δ: 24.7 (s). 31P{1H} NMR δ: 22.4. Anal.
Calcd for C24H44Br2N2P2Ti: C, 45.74; H, 7.04; N, 4.44. Found: C,
45.31; H, 7.11; N, 4.25%. Preliminary X-ray data: C2/c, Z = 8;
a = 24.20(1) Å, b = 15.02(1) Å, c = 19.79(1) Å, β = 94.89(1)Њ. 13:
White solid (342 mg, 73%). 1H NMR δ: 8.94 (s, 1H, C6H4
57 Hz, t-Bu), 36.9 (s, TiMe), 29.7 (d, 1JP–C = 44 Hz, CH2P), 27.6
(s, t-Bu). 31P{1H} NMR δ: 12.4 (s). Anal. Calcd for
C26H50N2P2Ti: C, 62.37; H, 10.08; N, 5.60. Found: C, 62.59; H,
10.06; N, 5.22%. 16: Yield: 62 mg, 74%. 1H NMR δ: 8.20 (s, 1H,
C6H4 (o-H)), 7.28 (m, 8H, CH2Ph (o,m-H)), 7.04 (t, 1H, 3JH–H
=
3
7 Hz, C6H4 (m-H)), 6.89 (t, 2H, JH–H = 7 Hz, CH2Ph (p-H)),
3
6.82 (d, 2H, JH–H = 7 Hz, C6H4 (o-H)), 2.86 (s, 4H, CH2Ph),
2.75 (d, 4H, 2JP–H = 10 Hz, CH2P), 1.02 (d, 36H, 3JP–H = 13 Hz,
t-Bu). 13C{1H} NMR δ: 151.9, 134.0, 133.6, 128.9, 128.2, 127.4,
127.0, 120.1, 67.5 (s, CH2Ph), 37.4 (d, 1JP–C = 55 Hz, t-Bu), 29.7
3
(oЈ-H)), 7.09 (t, 1H, JH–H = 8 Hz, C6H4 (m-H)), 6.83 (d, 2H,
3JH–H = 8 Hz, C6H4 (o-H)), 2.64 (d, 4H, 2JP–H = 11 Hz, CH2), 2.10–
0.99 (m, 44H, Cy). 13C{1H} NMR δ: 135.1 (s, C6H4 (ipso-C)),
132.4(s,C6H4 (o-C)),128.1(s,C6H4 (oЈ-C)),128.0(s,C6H4 (m-C)),
37.3 (d, 1JP–C = 62 Hz, Cy (ipso-C)), 31.4 (d, 1JP–C = 49 Hz, CH2),
26.9 (d, 2JP–C = 8 Hz, Cy (o-C)), 26.7 (d, 2JP–C = 6 Hz, Cy (o-C)),
26.2 (br s, Cy (m-C)), 26.1 (br s, Cy (m-C)), 25.9 (s, Cy, (p-C)).
31P{1H} NMR δ: 8.8 (s). Anal. Calcd for C32H52Cl2N2P2Ti: C,
59.54; H, 8.12; N, 4.34. Found: C, 59.92; H, 8.45; N, 4.43%.
Colourless crystals suitable for X-ray diffraction were grown by
slow evaporation from benzene/pentanes. 14: Yield: 120 mg,
(d, JP–C = 43 Hz, CH2P), 27.7 (s, t-Bu). 31P{1H} NMR δ: 15.4
1
(s). Anal. Calcd for C38H58N2P2Ti: C, 69.92; H, 8.96; N, 4.29.
Found: C, 69.59; H, 8.76; N, 4.22%.
Synthesis of (m-C6H4(CH2(t-Bu)2PN)2)2Zr 17. Solid
Zr(CH2Ph)4 (100 mg, 0.22 mmol) was added at RT to a clear
solution of 5 (191 mg, 0.45 mmol) in PhH (20 mL). The slurry
became dark brown and homogeneous upon stirring for 16 h.
Following filtration through Hyflo Super Cel ®, the solvent was
removed in vacuo, affording a yellow solid. It was washed with
pentanes (3 × 5 mL) and dried in vacuo. Yield: 96 mg, 47%. 1H
75%. 1H NMR δ: 7.56 (s, 1H, C6H4 (o-H)), 7.31 (d, 2H, 3JH–H
=
3
7 Hz, C6H4 (o-H)), 7.23 (t, 1H, JH–H = 7 Hz, C6H4 (m-H)),
2
3
3
2.92 (d, 4H, JP–H = 11 Hz, CH2), 1.05 (d, 36H, JP–H = 13 Hz,
t-Bu). 13C{1H} NMR (CD2Cl2) δ: 129.3 (s, C6H4 (oЈ-C)), 135.0
(s, C6H4 (ipso-C)), 127.1 (s, C6H4 (o-C)), 125.6 (s, C6H4 (m-C)),
37.2 (d, 1JP–C = 60 Hz, t-Bu), 31.0 (d, 1JP–C = 56 Hz, CH2), 27.6
(s, t-Bu). 31P{1H} NMR δ: 24.5. Anal. Calcd for C24H44-
Cl2N2P2Zr: C, 49.30; H, 7.59; N, 4.79. Found: C, 49.31; H, 7.11;
N, 4.25%.
NMR δ: 8.34 (s, 1H, C6H4 (oЈ-H)), 7.12 (t, 1H, JH–H = 7 Hz,
3
C6H4 (p-H)), 6.97 (d, 2H, JH–H = 7 Hz, C6H4 (o-H)), 3.00 (d,
2
3
4H, JP–H = 10 Hz, CH2P), 1.28 (d, 36H, JP–H = 13 Hz, t-Bu).
13C{1H} NMR δ: 135.7 (s, C6H4 (ipso-C)), 133.4 (s, C6H4 (o-C)),
127.3 (s, C6H4 (o-C)), 126.9 (s, C6H4 (m-C)), 37.4 (d, JP–C
56 Hz, t-Bu), 31.9 (d, JP–C = 44 Hz, CH2P), 28.7 (s, t-Bu).
31P{1H} NMR δ: 11.7 (s). Anal. Calcd for C48H88N4P4Zr: C,
61.57; H, 9.47; N, 5.98. Found: C, 61.82; H, 9.93; N, 5.61%.
1
=
1
Synthesis of m-C6H4(CH2(t-Bu)2PN)2TiCl2 12 and m-C6H4-
(CH2(Cy)2PN)2TiCl2 13. These compounds were prepared in a
similar manner and thus one preparation is detailed. TiCl4
(0.252 mL, 2.3 mmol) was diluted in PhMe (50 mL), and a clear
solution of 4 (1.546 g, 2.3 mmol) in the same solvent (30 mL)
was added dropwise at 25 ЊC. The solution became dark brown
and heterogeneous immediately, and was then heated at reflux-
ing temperature for 12 h. Upon cooling, the solution was fil-
tered through Hyflo Super Cel ®, and the solvent was removed
in vacuo. The crude mixture was purified by recrystallization in
PhMe/hexanes at Ϫ35 ЊC to afford colourless crystals. 12: Yield
244 mg, 30%. 1H NMR δ: 9.05 (s, 1H, C6H4 (oЈ-H)), 7.04 (t, 1H,
Polymerization protocols
Ethylene was purchased from BOC Gas Co., and was dried over
alumina and 3 Å molecular sieves. A dried 1 L Büchi autoclave
was charged with PhMe (50 mL) and MAO (1000 eq, 10% in
PhMe) or t-i-BAl (20 eq, 25% in heptanes) and the solution was
presaturated with the monomer by briefly venting/backfilling
(×4) and then stirring under an atmosphere of C2H4 for 5 min.
The temperature was controlled at 30 ЊC (to ca. ϩ2 ЊC), the
pressure of C2H4 set to 12 psig, and the solvent stirred at a rate
of 1000 rpm. A solution of the catalyst precursor (PhMe, 350
µmol LϪ1) was injected, and the mixture was stirred at 25 ЊC for
10 min. The reaction was quenched with 1 M HCl in MeOH,
and the precipitated polymer was washed with HCl, HCl/
MeOH and PhMe before drying at 50 ЊC for at least 48 h prior
to weighing.
3
3JH–H = 7 Hz, C6H4 (m-H)), 6.79 (d, 2H, JH–H = 7 Hz, C6H4
(o-H)), 2.76 (d, 4H, 2JP–H = 9 Hz, CH2P), 1.07 (d, 36H, 3JP–H = 14
Hz, t-Bu). 13C{1H} NMR δ: 134.2 (s, C6H4 (ipso-C)), 127.9 (s,
C6H4 (o-C)), 127.9 (s, C6H4 (oЈ-C)), 127.3 (s, C6H4 (m-C)), 37.8
1
1
(d, JP–C = 57 Hz, t-Bu), 29.9 (d, JP–C = 44 Hz, CH2P), 27.5 (s,
t-Bu). 31P{1H} NMR δ: 20.7 (s). Anal. Calcd for C24H44Cl2-
N2P2Ti: C, 53.24; H, 8.21; N, 5.17. Found: C, 53.41; H, 8.35; N,
5.20%. Crystals suitable for X-ray diffraction were grown by
slow evaporation from benzene. Preliminary X-ray data: P21/c,
Z = 8; a = 23.5658(2) Å, b = 14.7449(2) Å, c = 18.6175(2) Å,
β = 113.267(1)Њ. 13: Yield: 235 mg, 16%. NMR as described
above.
X-Ray crystallography
Data collection and reduction. Crystals were manipulated and
mounted in capillaries in a glove box, thus maintaining a dry,
O2-free environment for each crystal. Diffraction experiments
were performed on a Siemens SMART System CCD diffract-
ometer. The data were collected in a hemisphere of data in 1329
frames with 10 second exposure times. The observed extinctions
were consistent with the space groups in each case. The data sets
were collected (4.5Њ<2θ <45–50.0Њ). A measure of decay was
obtained by re-collecting the first 50 frames of each data set.
The intensities of reflections within these frames showed no
statistically significant change over the duration of the data
collections. The data were processed using the SAINT and
XPREP processing packages.16 An empirical absorption correc-
tion based on redundant data was applied to each data set.
Subsequent solution and refinement was performed using the
Synthesis of m-C6H4(CH2(t-Bu)2PN)2TiMe2 15 and m-C6H4-
(CH2(t-Bu)2PN)2Ti(CH2Ph)2 16. These compounds were pre-
pared in a similar manner using the appropriate Grignard
reagent, thus one preparation is detailed. MeMgBr (3.0 M solu-
tion in Et2O, 0.17 mL, 0.50 mmol) was added dropwise to a
heterogeneous solution of 11 (153 mg, 0.24 mmol) in Et2O (30
mL). The solution was stirred for 12 h, after which time the
solvent was removed in vacuo. The product was extracted with
pentanes (3 × 10 mL), and the extracts were filtered through
D a l t o n T r a n s . , 2 0 0 3 , 3 9 6 8 – 3 9 7 4
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SHELXTL16 solution package operating on
computer.
a Pentium
Structure solution and refinement. Non-hydrogen atomic scat-
tering factors were taken from the literature tabulations.17 The
heavy atom positions were determined using direct methods
employing the SHELXTL direct methods routine. The remain-
ing 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
2
function ω(|Fo| Ϫ |Fc|)2 where the weight ω is defined as 4Fo /
2
2σ(Fo ) and Fo and Fc are the observed and calculated structure
factor amplitudes. 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 posi-
tions were calculated and allowed to ride on the carbon to
which they are bonded assuming a C–H bond length of 0.95 Å.
H-atom temperature factors were fixed at 1.10 times the iso-
tropic temperature factor of the C-atom to which they are
bonded. The H-atom contributions were calculated, but not
refined. In the case of compounds 9 and 16 the geometry of the
benzene of crystallization was constrained such that the C–C
bonds were 1.39 Å. Similarly, for 8, the geometry of the dis-
ordered cyclohexyl groups were constrained with C–C bond
lengths of 1.54 Å. 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. Crystallographic data are reported in Table 1.
CCDC reference numbers 215279–215286.
See http://www.rsc.org/suppdata/dt/b3/b308114a/ for crystal-
lographic data in CIF or other electronic format.
Results and discussion
We have previously described the synthesis and structure of
bis-phosphinimide titanium complexes. In (R3PN)2TiX2, as in
related complexes of the form Cp(R3PN)TiX2, the Ti–N–P
angle approaches linearity, ranging from 160–180Њ.3,4,6 Thus, in
order to construct a chelating bis-phosphinimide ligand and
preclude bridging phosphinimide fragments, the link between
the phosphorus atoms must be long enough to tolerate this
linearity at N. To this end, we have employed a linkage derived
from the α,αЈ-m-xylene fragment. Preliminary molecular mech-
anics computations supported the view that such a linkage
would be flexible enough to permit chelation and yet not
deform the nature of the approximately linear P–N–Ti linkage.
The diphosphines m-C6H4(CH2Pt-Bu2)2 1 and m-C6H4(CH2-
PCy2)2 2 were prepared according to literature methods.15
Subsequent oxidation with Me3SiN3 afforded m-C6H4(CH2-
(t-Bu2)PNSiMe3)2 3 and m-C6H4(CH2(Cy2)PNSiMe3)2 4 in 94%
yield. The formulations of these species were consistent with
the observed NMR spectral data. Treatment of 3 and 4 with
methanol resulted in cleavage of the N–Si bonds to generate
m-C6H4(CH2(t-Bu)2PNH)2 5 and m-C6H4(CH2(Cy)2PNH)2 6 in
81% and 96% yield, respectively. In addition, compounds 1, 3, 4
and 5 were characterized crystallographically (Fig. 1). The
structural data confirmed the formulation and the metric
parameters were as expected. P–N bond lengths were ranged
from 1.531(2) Å to 1.577(2) Å while the P–N–Si angles varied
from 162.49(16)Њ to 175.12(17)Њ. This is typical of trimethylsilyl
or parent phosphinimines.2
Reaction of the ligands 5 and 6 with Ti(NMe2)4 afforded the
yellow compounds m-C6H4(CH2(t-Bu)2PN)2Ti(NMe2)2 7 and
m-C6H4(CH2(Cy)2PN)2Ti(NMe2)2 8 in yields of 68% and 73%,
respectively ( Scheme 1). In the case, of 8, X-ray quality crystals
were obtained ( Fig. 2). The pseudo-tetrahedral coordination
sphere about titanium comprised of four nitrogen atoms. The
two Ti–N bond lengths for the phosphinimide scaffold were
found to be 1.866(4) Å and 1.879(5) Å. These compare with the
D a l t o n T r a n s . , 2 0 0 3 , 3 9 6 8 – 3 9 7 4
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Fig. 2 ORTEP drawing of 8, 30% thermal ellipsoids are shown.
Hydrogen atoms are omitted for clarity. Selected distances (Å) and
angles (Њ): Ti(1)–N(2) 1.866(4), Ti(1)–N(1) 1.879(5), Ti(1)–N(4)
1.902(4), Ti(1)–N(3) 1.926(5), P(1)–N(1) 1.553(4), P(2)–N(2) 1.567(4);
N(2)–Ti(1)–N(1) 115.61(18), N(2)–Ti(1)–N(4) 109.68(18), N(1)–Ti(1)–
N(4) 109.08(19), N(2)–Ti(1)–N(3) 109.65(19), N(1)–Ti(1)–N(3)
109.64(19), N(4)–Ti(1)–N(3) 102.3(2), P(1)–N(1)–Ti(1) 151.3(3), P(2)–
N(2)–Ti(1) 157.7(3).
shorter titanium–phosphinimide bond lengths are consistent
with the stronger donor character of the phosphinimide
ligands. The bite angle of the 10-membered chelating ring of
the bis-phosphinimide was found to be 115.61(18)Њ, which
accommodated P–N–Ti angles at the phosphinimide nitrogen
atoms of 151.3(3)Њ and 157.7(3)Њ. These angles are less than
those seen in the related bulky bis-phosphinimide complex
(t-Bu3PN)2TiCl2 (175.5(2)Њ)4 as well as the related monodentate
phosphinimide species CpTi(NPR2CH2Ph)Cl2 (175.16(11)Њ).18
The P–N bond distances are 1.553(4) Å and 1.567(4) Å, similar
to those seen in (t-Bu3PN)2TiX2 (X = Cl 1579(4) Å, Me 1.561(3)
Å).4 The titanium-bound amido groups exhibit typical planar
geometry at nitrogen, although it is interesting to note that the
amido ligands are oriented such that the planes are orthogonal
to one another.
Fig. 1 ORTEP16 drawings of (a) 1, (b) 3, (c) 4, (d) 5, 30% thermal
ellipsoids are shown. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (Њ): 3: P(1)–N(1) 1.538(2), P(2)–N(2) 1.531(2),
Si(1)–N(1) 1.663(3), Si(2)–N(2) 1.662(3); P(1)–N(1)–Si(1) 165.05(16),
P(2)–N(2)–Si(2) 175.12(17). 4: P(1)–N(1) 1.533(2), P(2)–N(2) 1.533(2),
Si(1)–N(1) 1.664(2), Si(2)–N(2) 1.668(2); P(1)–N(1)–Si(1) 163.07(15),
P(2)–N(2)–Si(2) 162.49(16). 5: P(1)–N(1) 1.577(2), P(2)–N(2) 1.581(2).
A low abundance by-product, typically present in 3–10%,
was also isolated from the reaction to prepare complex 7.
NMR data and X-ray data confirmed that this latter species
was m-C6H4(CH2(t-Bu)2PN)2TiBr(NMe2) 9 (Fig. 3). It was
determined that this species formed as a result of the presence
of a residual amount of HBr that was carried through as an
impurity from the preparation of the original phosphine 1.
X-Ray data for 9 showed a pseudo-tetrahedral geometry about
titanium, with a bidentate bis-phosphinimide ligand, a di-
methylamido ligand and a bromide ligand completing the co-
ordination sphere. Titanium–nitrogen bond distances of
1.818(4) Å and 1.827(4) Å were seen for the phosphinimide
nitrogen atoms, while the Ti–amido distance was 1.905(5) Å.
The increased titanium–nitrogen bond distance in the amido
ligand, also observed in the structure of 8, is consistent with
the stronger donor character of the phosphinimide ligand. The
chelate ring of the bis-phosphinimide is large enough to allow
the angles at nitrogen to approach linearity, and as a result, the
Ti–N–P angles are 170.9(3)Њ and 172.3(3)Њ. The larger Ti–N–P
angles in 9 compared to 8 may be related to a more Lewis
acidic titanium center due to the presence of only one
ancillary amido ligand. In addition, the t-Bu substituted bis-
phosphinimide chelating ligand may be a slightly better donor
than the Cy-analog. The bite angle of the N–Ti–N in the chelat-
ing phosphinimide ligand is 117.1(2)Њ. In addition, the aromatic
ring in the chelate backbone is canted with respect to the TiN2
plane at an angle of 25.3Њ. This orients the nearest hydrogen
atom on the arene ring 3.105 Å from the Ti center. The planar
amido group and the Ti–Br distance of 2.5202(19) Å are typi-
cal of Group IV amido complexes.19 In a similar fashion,
related zirconium derivatives were prepared. Reaction of 5 with
Scheme 1
Ti–N bond lengths of 1.789(4) Å and 1.792(4) Å found in
(t-Bu3PN)2TiCl2.4 The amido-ligands gave rise to longer Ti–N
bond distances of 1.902(4) Å and 1.926(5) Å, respectively. The
D a l t o n T r a n s . , 2 0 0 3 , 3 9 6 8 – 3 9 7 4
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Fig. 4 ORTEP drawing of 16, 30% ellipsoids are shown, hydrogen
atoms have been omitted for clarity. Selected bond distances (Å) and
angles (Њ): Ti(1)–N(2) 1.805(7), Ti(1)–N(1) 1.831(7), Ti(1)–C(32)
2.129(8), Ti(1)–C(25) 2.172(8), P(1)–N(1) 1.562(7), P(2)–N(2) 1.576(7);
N(2)–Ti(1)–N(1) 117.7(3), N(2)–Ti(1)–C(32) 106.3(4), N(1)–Ti(1)–
C(32) 113.2(3), N(2)–Ti(1)–C(25) 103.8(3), N(1)–Ti(1)–C(25) 110.1(4),
C(32)–Ti(1)–C(25) 104.6(4), P(1)–N(1)–Ti(1) 168.9(5), P(2)–N(2)–Ti(1)
175.2(5).
Fig. 3 ORTEP drawing of 9, 30% thermal ellipsoids are shown.
Hydrogen atoms are omitted for clarity. Selected distances (Å) and
angles (Њ): Ti(1)–N(1) 1.818(4), Ti(1)–N(2) 1.827(4), Ti(1)–N(3)
1.905(5), Ti(1)–Br(1) 2.5202(19), N(1)–P(1) 1.578(5), N(2)–P(2)
1.570(5); N(1)–Ti(1)–N(2) 117.1(2), N(1)–Ti(1)–N(3) 108.9(2), N(2)–
Ti(1)–N(3) 109.8(2), N(1)–Ti(1)–Br(1) 109.10(16), N(2)–Ti(1)–Br(1)
107.03(17), N(3)–Ti(1)–Br(1) 104.16(17), P(1)–N(1)–Ti(1) 170.9(3),
P(2)–N(2)–Ti(1) 172.3(3), C(26)–N(3)–C(25) 109.6(5), C(26)–N(3)–
Ti(1) 124.3(4), C(25)–N(3)–Ti(1) 125.8(4).
(t-Bu)2PN)2)2Zr 17. Similarly reaction of Zr(CH2Ph)4 with one
equivalent of a chelating diamido ligand, resulted in cleavage of
all alkyl ligands to afford the tetrakis-amido derivatives.20 The
yield of 17 was optimized using a 1 : 2 stoichiometry of metal
precursor : ligand precursor.
Zr(NEt2)4 gave the species m-C6H4(CH2(t-Bu)2PN)2Zr(NEt2)2
10 in 87% yield.
Reaction of a crude mixture of 7 and 9 with Me3SiBr resulted
in selective cleavage of the titanium amido bonds, affording the
species m-C6H4(CH2(t-Bu)2PN)2TiBr2 11 in 76% yield. Pre-
liminary X-ray data for 11 confirmed the connectivity, however
the data were of too poor quality for detailed discussion. In a
similar manner, treatment of 8 with Me3SiCl gave m-C6H4-
(CH2(Cy)2PN)2TiCl2 13 and m-C6H4(CH2(t-Bu)2PN)2ZrCl2 14
in similarly good yields of 73–75%. Attempts to prepare the Ti–
chloride species directly from TiCl4 upon reaction with the tri-
methylsilyl phosphinimines 3 and 4 was also attempted. Despite
the general utility of the Me3SiCl elimination reaction in the
preparation of compounds of the form CpTi(NPR3)Cl2,6 this
strategy was found to provide low (typically 10–20%) and
unreliable yields of C6H4(CH2(t-Bu)2PN)2TiCl2 12 and m-
C6H4(CH2(Cy)2PN)2TiCl2 13. Nonetheless, crystalline samples
of these colorless compounds were obtained from numerous
attempts to optimize the reaction conditions. In the case of 12
and 13 several X-ray data sets were obtained. Although these
data once again confirmed the connectivity, the solutions were
of poor quality.
Alkylation of 11 with precise control of the stoichiometry of
MeMgBr and PhCH2MgBr proceeded in a straightforward
manner to prepare m-C6H4(CH2(t-Bu)2PN)2TiMe2 15 and
m-C6H4(CH2(t-Bu)2PN)2Ti(CH2Ph)2 16 in yields of 62% and
74%, respectively. X-Ray data for 16 (Fig. 4) revealed slightly
longer titanium–nitrogen phosphinimide bond distances, aver-
aging 1.818(7) Å. The titanium–carbon bond distances were
found to be 2.129(8) Å and 2.172(8) Å. The bite angle of the
chelating ligand was found to be 117.7(3)Њ, while the P–N–Ti
angles approached linearity at 168.9(5)Њ and 175.2(5)Њ.
Preliminary evaluation of compounds 12, 13 and 15 as
ethylene polymerization catalysts was performed in a Büchi
autoclave (30 2 ЊC, 1.82 atm of ethylene). Several activation
conditions were attempted. Use of MAO resulted in only traces
of polymer while use of a solution of t-i-BAl/[Ph3C][B(C6F5)4]
gave poor polymerization activities (1–200 g PE mmolϪ1 hϪ1
atmϪ1) relative to zirconocene standards. These data stand in
marked contrast to that reported for the species (t-Bu3PN)2-
TiMe2, despite the structural similarity with the present chelate
compounds.4 This suggests that use of the m-xylyl linkage
between the phosphorus atoms significantly reduces the steric
protection about the phosphinimide-N atoms. This would, in
turn, permit attack of the phosphinimide nitrogen centers by
Lewis acid activators, ultimately generating polymerization-
inactive species. Similar conclusions have been inferred in
studies of deactivation pathways for the related titanium bis-
phosphinimide species.21–23 Efforts are continuing to explore the
utility of Ti and Zr complexes of chelating bis-phosphinimide
ligands. The results of these studies will be reported in due
course.
Acknowledgements
Financial support from NSERC of Canada and NOVA
Chemicals Corporation is gratefully acknowledged. E. H. is
grateful for the award of an Ontario Graduate Scholarship.
D. W. S. is grateful for the award of a Forschungpreis from
the AvHumboldt Foundation.
In a related strategy targeting the Zr analog of 16, reaction of
Zr(CH2Ph)4 with 5 resulted in the formation of (m-C6H4(CH2-
D a l t o n T r a n s . , 2 0 0 3 , 3 9 6 8 – 3 9 7 4
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12 U. Siemeling, L. Koelling, O. Kuhnert, B. Neumann, A. Stammler,
H.-G. Stammler, G. Fink, E. Kaminski, A. Kiefer and R. R.
Schrock, Z. Anorg. Allg. Chem., 2003, 629, 781.
13 U. Siemeling, L. Koelling, A. Stammler and H.-G. Stammler,
J. Chem. Soc., Dalton Trans., 2002, 3277.
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