Hafnium-phosphinimide complexes

Article abstract of DOI:10.1139/V09-082

A series of phosphinimide complexes of Hf are prepared and characterized. Reaction of the phosphinimine t-Bu₃PNH with Hf(NEt₂) ₄ gave (t-Bu₃PN)Hf(NEt₂)₃ (1) but this species was not readily

Full text of DOI:10.1139/V09-082

1163
Hafniumꢀphosphinimide complexes
Osamah Alhomaidan, Gregory C. Welch, Guangcai Bai, and Douglas W. Stephan
Abstract: A series of phosphinimide complexes of Hf are prepared and characterized. Reaction of the phosphinimine t-Bu3PNH
with Hf(NEt2)4 gave (t-Bu3PN)Hf(NEt2)3 (1) but this species was not readily converted to the corresponding HfCl3-derivative.
The reaction of 2 equiv. of t-Bu3PNH with Hf(NEt2)4, however, gave (t-Bu3PN)2Hf(NEt2)2 (2), which was readily converted to
(t-Bu3PN)2HfCl2 (3) and (t-Bu3PN)2HfMe2 (4). Employing t-Bu3PNLi and HfCl4 afforded (t-Bu3PN)3HfCl (5) while reaction
with CpHfCl3 gave rise to ligand redistribution reactions affording (t-Bu3PN)2HfCl2 and Cp2HfCl2. However, Cp(t-Bu3PN)2HfCl
(7) was prepared by treating (t-Bu3PN)2HfCl2 with CpNa. The related species of Cp2(t-Bu3PN)HfCl (8) was synthesized by the re-
action of Cp2HfCl2 and t-Bu3PNLi. Ligand redistribution was avoided in the reaction of Cp*HfCl3 as Cp*(t-Bu3PN)HfCl2 (9) and
Cp*(i-Pr3PN)HfCl2 (10) were readily obtained and derivatized as Cp*(t-Bu3PN)Hf(NMe2)2 (11) and Cp*(t-Bu3PN)HfMe2 (12),
respectively. Similarly, ((Me3Si)2C5H3)(t-Bu3PN)HfCl2 (13) was converted to ((Me3Si)2C5H3)(t-Bu3PN)HfMe2 (14). Reactions
with Lewis acid activators were used to prepare Cp*(t-Bu3PN)HfMe(THF)MeB(C6F5)3 (15), (Cp*(t-Bu3PN)HfMe)(B(C6F5)4)
(16), and (t-Bu3PN)2Hf(H2B(C6F5)2)2 (17). Preliminary testing of 3, 9, and 13 in ethylene polymerization is reported. Compounds
3, 4, 7, 9, and 17 are characterized crystallographically.
Key words: hafnium, phosphinimide, ligand redistribution, cyclopentadienyl ligands, ethylene polymerization.
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Resume : On a prepare et caracterise une serie de complexes de Hf avec le phosphinimide. La reaction de la phosphinimine
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t-Bu3PNH avec le Hf(NEt2)4 conduit a la formation du compose (t-Bu3PN)Hf(NEt2)3 (1); toutefois, cette espece ne se transforme
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pas facilement en derive HfCl3 corrrespondant. Toutefois, la reaction de 2 equiv. de t-Bu3PNH avec du Hf(NEt2)4 conduit a la
formation de (t-BuPN)2Hf(NEt2)2 (2) qu’on peut facilement transformer en (t-Bu3PN)2HfCl2 (3) et en (t-Bu3PN)2HfNe2 (4).
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L’utilisation de (t-BuPNLi) et de HfCl4 conduit a la formation de (t-Bu3PN)2HfCl (5) alors que la reaction avec du CpHfCl3
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conduit a une reaction de redistribution de ligand conduisant au (t-Bu3PN)2HfCl2 et au Cp2HfCl2. Toutefois, on a pu preparer
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le Cp(t-Bu3PN)2HfCl (7) par traitement du (t-Bu3PN)2HfCl2 avec du CpNa. On a effectue la synthese de l’espece apparentee
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Cp2(t-Bu3PN)HfCl (8) par reaction du Cp2HfCl2 avec le t-Bu3PNLi. La reaction de redistribution des ligands a ete evitee dans
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la reaction du Cp*HfCl3 et il a ete possible d’obtenir facilement de Cp*(t-Bu3PN)HfCl2 (9) et Cp*(t-BuPN)HfCl2 (10) et de
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les transformer en derives Cp*(t-Bu3PN)Hf(NMe2)2 (11) et Cp*(t-BuPN)Hf(NMe2)2 (12) respectivement. De la meme maniere,
on a pu transformer le produit [(Me3Si)2C5H3](t-Bu3PN)HfCl2 (13) en [(Me3Si)2C5H3](t-Bu3PN)HfCl2Me2 (14). On a fait appel
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a des reactions avec des activateurs d’acide de Lewis pour preparer les produits Cp*(t-BuPH)HgMe(THF)MeB(C6F5)3 (15),
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(Cp*(t-Bu3PN)HfMe)(B(C6F5)4) (16) et (t-Bu3PN)Hf(H2B(C6F5)2)2 (17). On rapporte les resultats preliminaires de l’evaluation
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des composes 3, 9 et 13 dans des polymerisations de l’ethylene. Les structures des composes 3, 4, 7, 9 et 17 ont ete caracteri-
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sees par cristallographie.
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Mots-cles : hafnium, phosphonimide, redistribution de ligand, ligands cyclopentadienyles, polymerisation de l’ethylene.
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[Traduit par la Redaction]
affording the so-called ‘‘constrained geometry cata-
lysts’’.12ꢀ15 Another system that has drawn considerable re-
cent attention is that based on the ‘‘FI’’ catalysts developed
by researchers at the Mitsui Chemical Co.7,16ꢀ20 During the
last decade, we have studied olefin polymerization cata-
lysts based on Ti-phosphinimide complexes and exam-
ined in detail the structureꢀactivity relationship,21ꢀ33 as
well as the mechanisms of deactivation.34ꢀ39 These systems
yield highly active olefin polymerization catalysts10,40 and
indeed, some of these systems are also operative under
commercially relevant conditions.10,31,40
While the majority of early metal catalysts have been de-
rived from Ti or Zr complexes,1ꢀ9 we have also probed the
reactivity of V41 and Cr42 phosphinimide complexes. Deriva-
tives of the third-row element Hf have drawn much less at-
tention, presumably due to the high stability of HfꢀC
bonds.43 Nonetheless, recent publications have described
nonmetallocene Hf complexes, which are highly active for
olefin polymerization. These systems incorporated bis(phe-
noxy-imine) ligands (Fig. 1a),44ꢀ47 first introduced by Mitsui
Introduction
The drive to discover new homogeneous catalysts for ole-
fin polymerization has stimulated much research over the last
25 years. Several reviews have described such studies.1ꢀ9
While synthetic routes to a large number of potential cata-
lysts have been developed, only very few have been shown
to operate effectively under commercial conditions.10 One
system that has indeed been commercialized is based on the
early metal derivatives of a cyclopentadienyl-amide ligand,11
Received 19 March 2009. Accepted 14 May 2009. Published on
the NRC Research Press Web site at canjchem.nrc.ca on 28 July
2009.
O. Alhomaidan, G.C. Welch, G. Bai, and D.W. Stephan.1,2
Department of Chemistry & Biochemistry, University of
Windsor, Windsor, ON N9B 3P4, Canada.
1Corresponding author (e-mail: dstephan@chem.utoronto.ca).
2Present address: Department of Chemistry, University of
Toronto, 80 St. George St. Toronto, ON M5S 3H6, Canada.
Can. J. Chem. 87: 1163–1172 (2009)
doi:10.1139/V09-082
Published by NRC Research Press

1164
Can. J. Chem. Vol. 87, 2009
researchers for the FI catalysts. In addition, researchers at
Dow have described Hf systems based on the pyridyl-amido
ligand depicted in Fig. 1b.48ꢀ50 In this paper, we describe
synthetic routes to a series of Hfꢀphosphinimide derivatives.
The reactivity of these species with Lewis acid activators is
considered and a preliminary evaluation of the polymeriza-
tion activity is presented.
Fig. 1. Recent examples of Hf olefin-polymerization catalysts.
Experimental section
General considerations
All preparations were performed under an atmosphere of
dry O2-free N2 employing either Schlenk-line techniques or
a Vacuum Atmospheres inert atmosphere glovebox. Solvents
were purified employing Grubbs-type column systems man-
ufactured by Innovative Technologies or were distilled from
Anal. calcd. for C32H74N4P2Hf: C 50.88, H 9.87, N 7.42;
found: C 50.73, H 10.13, N 6.99.
Synthesis of (t-Bu3PN)2HfCl2 (3)
1
the appropriate drying agents under N2. H and 13C NMR
Compound 2 (1.00 g, 1.323 mmol) was dissolved in
10 mL of toluene. Me3SiCl (1.40 mL, 10.590 mmol) was
added dropwise to the clear solution at room temperature. A
white solid started forming in a few minutes. It was stirred
for 8 h and the volatiles removed under vacuum. The white
solid was washed with hexanes (5 mL) and then dried under
spectra were recorded on Bruker Avance 300 and 500 spec-
trometers. Deuterated benzene, toluene, and methylene
chloride were purchased from Cambridge Isotopes Laborato-
ries, vacuum distilled from the appropriate drying agents,
and freeze-pump-thaw degassed (three times). Trace
amounts of protonated solvents were used as references, and
1H and 13C{1H} NMR chemical shifts are reported relative
to SiMe4. 31P{1H}, 11B{1H}, and 19F NMR spectra were
referenced to external 85% H3PO4, BF3ꢁEt2O, and CFCl3,
respectively. Combustion analyses were performed at the
University of Windsor Chemical Laboratories employing a
PerkinElmer CHN Analyzer. High temperature gel permea-
tion chromatography (GPC) data were provided by the tech-
nical staff at NOVA Chemicals Corporation. t-Bu3PNLi51
1
vacuum (0.85 g, 1.257 mmol, 95%). H NMR (C6D6): 1.28
3
(d, JPH = 10.0 Hz, 54H, P-t-Bu). 13C{1H} NMR (C6D6):
1
41.0 (d, JPC = 48 Hz, P-t-Bu), 30.0 (P-t-Bu). 31P NMR
(C6D6): 41.3. Anal. calcd. for C24H54N2P2HfCl2: C 42.26, H
7.98, N 4.11; found: C 42.68, H 8.11, N 4.28.
Synthesis of (t-Bu3PN)2HfMe2 (4)
Compound 3 (0.10 g, 0.147 mmol) was dissolved in
10 mL of diethyl ether. MeMgBr (3 mol/L, 0.19 mL;
0.588 mmol) was added dropwise at room temperature. The
solution was stirred overnight and then pumped to dryness.
The product was extracted with hot hexanes (10 mL) and
then filtered through celite. Removing hexanes under vac-
uum gave a white solid (0.09 g, 0.145 mmol, 93%). 1H
52
and (Me3SiC5H4)HfCl3 were prepared as previously re-
ported.
Synthesis of (t-Bu3PN)Hf(NEt2)3 (1)
t-Bu3PNH (0.46 g, 2.119 mmol) was dissolved in 5 mL of
toluene and then added dropwise to a toluene solution
(10 mL) containing Hf(NEt2)4 (1.0 g, 2.119 mmol) at room
temperature. The light yellow solution was heated overnight
at 70 8C. Toluene was removed under vacuum to give a
3
NMR (C6D6): 1.33 (d, JPH = 10.5 Hz, 54H, P-t-Bu), 0.42
(s, 6H, HfMe2). 13C{1H} NMR (C6D6): 41.6 (HfMe2), 40.7
1
(d, JPC = 45 Hz, P-t-Bu), 30.1 (P-t-Bu). 31P NMR (C6D6):
37.2. Anal. calcd. for C26H60N2P2Hf: C 48.70, H 9.43, N
4.37; found: C 48.54, H 9.79, N 4.28.
1
crystalline white solid (1.27 g, 2.077 mmol, 96%). H NMR
3
3
(C6D6): 3.60 (q, J = 7.3 Hz, 12H, NCH2CH3), 1.29 (t, J =
3
7.3 Hz, 18H, NCH2CH3), 1.28 (d, JPH = 13.0 Hz, 27H, P-t-
Synthesis of (t-Bu3PN)3HfCl (5)
Bu). 13C{1H} NMR (C6D6): 44.3 (NCH2CH3), 40.4 (d, 1JPC
=
HfCl4 (0.50 g, 1.561 mmol) was suspended in 5 mL of
THF. t-Bu3PNLi (1.05 g, 4.685 mmol) in 5 mL of THF was
added quickly at room temperature. The suspension became
clear within 30 min. It was stirred for another 8 h and the
volatiles removed under vacuum. The product was dissolved
in 15 mL of toluene and then filtered through celite. The
solution was concentrated to ca. 3 mL and then stored in a
freezer at ꢀ35 8C for 48 h. A white solid precipitated,
48 Hz, P-t-Bu), 30.0 (P-t-Bu), 16.9 (NCH2CH3). 31P NMR
(C6D6): 38.5. Anal. calcd. for C24H57N4PHf: C 47.16, H
9.40, N 9.17; found: C 46.88, H 9.24, N 9.59.
Synthesis of (t-Bu3PN)2Hf(NEt2)2 (2)
t-Bu3PNH (0.93 g, 4.279 mmol) was dissolved in 5 mL of
toluene and then added dropwise to toluene solution
(10 mL) containing Hf(NEt2)4 (1.0 g, 2.119 mmol) at room
temperature. The solution was refluxed for 12 h. Toluene
was removed under vacuum to give an orange oil. It was
dissolved in pentane (5 mL) and stirred for 10 min. Remov-
ing pentane under vacuum gave a colorless crystalline solid
which was isolated and dried under vacuum (0.83 g,
3
0.961 mmol, 62%). 1H NMR (C6D6): 1.44 (d, JPH
=
12.0 Hz, 81H, P-t-Bu). 13C{1H} NMR (C6D6): 41.1 (d, JPC
= 45 Hz, P-t-Bu), 30.7 (P-t-Bu). 31P NMR (C6D6): 36.0.
Anal. calcd. for C36H81N3P3HfCl: C 50.11, H 9.46, N 4.87;
found: C 50.13, H 9.71, N 4.95.
1
1
3
(1.55 g, 2.052 mmol, 96%). H NMR (C6D6): 3.79 (q, J =
3
7.3 Hz, 8H, NCH2CH3), 1.38 (d, JPH = 12.5 Hz, 54H, t-Bu),
1.36 (t, 3J = 7.3 Hz, 12 H, NCH2CH3). 13C{1H} NMR
Synthesis of (t-Bu3PN)3HfMe (6)
Compound 5 (0.20 g, 0.231 mmol) was dissolved in 5 mL
of diethyl ether. MeMgBr (3 mol/L, 0.23 mL, 0.693 mmol)
1
(C6D6): 44.8 (NCH2CH3), 40.7 (d, JPC = 45 Hz, P-t-Bu),
30.4 (P-t-Bu), 16.9 (NCH2CH3). 31P NMR (C6D6): 35.8.
Published by NRC Research Press

Alhomaidan et al.
1165
was added dropwise at room temperature. The solution was
stirred for 4 h and the volatiles removed under vacuum. The
product was extracted with hexanes (2 ꢂ 5 mL) and then
filtered through celite. Removing hexanes under vacuum
was removed under vacuum to give a white solid (94 mg,
1
0.168 mmol, 64%). H NMR (C6D6): 2.19 (s, 15H, Cp*),
3
3
1.64 (m, 3H, PCH), 0.95 (dd, JPH = 14.0 Hz, J = 7.0 Hz,
18H, i-Pr). 13C{1H} NMR (C6D6): 120.9 (Cp*), 26.9 (d, JPC
1
1
gave a white solid (0.17 g, 0.201 mmol, 87%). H NMR
= 58 Hz, PCH), 17.3 (P-i-Pr), 12.3 (Cp*). 31P NMR (C6D6):
35.3. Anal. calcd. for C19H36NPHfCl2: C 40.83, H 6.49, N
2.51; found: C 41.22, H 6.64, N 2.48.
3
(C6D6): 1.44 (d, JPH = 12.0 Hz, 81H, P-t-Bu), 0.36 (s, 3H,
1
HfMe). 13C{1H} NMR (C6D6): 41.0 (d, JPC = 45 Hz, P-t-
Bu), 30.7 (P-t-Bu), 29.1 (HfMe). 31P NMR (C6D6): 34.1.
Anal. calcd. for C37H84N3P3HfCl: C 52.75, H 10.05, N
4.99; found: C 52.63, H 9.99, N 4.95.
Synthesis of Cp*(t-Bu3PN)Hf(NMe2)2 (11)
Compound 9 (100 mg, 0.166 mmol) was dissolved in
3 mL of THF. Me2NLi (50 mg, 0.980 mmol) was dissolved
in 3 mL of THF and then added dropwise to the above sol-
ution at room temperature. The solution was stirred for 36 h
and the volatiles removed under vacuum. The product was
extracted with hexanes (10 mL) and then filtered through
celite. Hexanes were removed under vacuum to give a crys-
Synthesis of Cp(t-Bu3PN)2HfCl (7)
Compound 3 (0.13 g, 0.191 mmol) was dissolved in 5 mL
of THF. Solid CpNa (16.78 mg, 0.191 mmol) was added to
the above at ꢀ35 8C. The solution was stirred at room tem-
perature for 8 h and the volatiles removed under vacuum.
The product was dissolved in 7 mL of toluene and then fil-
tered through celite. Toluene was removed under vacuum to
1
talline solid (91 mg, 0.147 mmol, 88%). H NMR (C6D6):
3
3.10 (s, 12H, NMe2), 2.19 (s, 15H, Cp*), 1.28 (d, JPH
=
1
give a white solid (0.13 g, 0.183 mmol, 95%). H NMR
12.0 Hz, 27H, P-t-Bu). 13C{1H} NMR (C6D6): 116.9 (Cp*),
3
1
(C6D6): 6.57 (s, 5H, Cp), 1.31 (d, JPH = 12.5 Hz, 54H, P-t-
46.4 (NMe2), 40.3 (d, JPC = 45 Hz, P-t-Bu), 30.1 (P-t-Bu),
1
Bu). 13C{1H} NMR (C6D6): 110.7 (Cp), 41.1 (d, JPC
=
12.1 (Cp*). 31P NMR (C6D6): 38.1. Anal. calcd. for
C26H54N3PHf: C 50.51, H 8.80, N 6.80; found: C 50.28, H
8.54, N 6.64.
48 Hz, P-t-Bu), 30.4 (P-t-Bu). 31P NMR (C6D6): 37.4. Anal.
calcd. for C29H59N2P2HfCl: C 48.94, H 8.36, N 3.94; found:
C 48.86, H 8.61, N 3.71.
Synthesis of Cp*(t-Bu3PN)HfMe2 (12)
Synthesis of Cp2(t-Bu3PN)HfCl (8)
Compound 9 (0.71 g, 1.181 mmol) was suspended in
8 mL of diethylether. MeMgBr (3 mol/L, 1.97 mL,
5.905 mmol) was added dropwise at room temperature. The
cloudy solution was stirred for 12 h and the volatiles re-
moved under vacuum. The product was extracted with hot
hexanes (2 ꢂ 8 mL) and then filtered through celite. Re-
moving hexanes under vacuum gave a white solid (0.62 g,
Cp2HfCl2 (0.85 g, 2.24 mmol) was dissolved in 10 mL of
THF. Solid t-Bu3PNLi (0.50 g, 2.24 mmol) was added in
portions at room temperature. The cloudy solution was
stirred for 24 h and then pumped to dryness. The product
was dissolved in 10 mL of toluene and then filtered through
celite. The solution was concentrated to *5 mL and then
stored in a freezer at ꢀ35 8C for 48 h. A pale yellow solid
precipitated, which was isolated and dried under vacuum
1
1.107 mmol, 95%). H NMR (C6D6): 2.11 (s, 15H, Cp*),
3
1.24 (d, JPH = 11.0 Hz, 27H, P-t-Bu), ꢀ0.03 (s, 6H,
1
(0.97 g, 1.73 mmol, 77%). H NMR (C6D6): 6.15 (s, 10H,
HfMe2). 13C{1H} NMR (C6D6): 116.5 (Cp*), 41.7 (HfMe2),
3
1
Cp), 1.18 (d, JPH = 12.5 Hz, 27H, P-t-Bu). 13C{1H} NMR
41.0 (d, JPC = 45 Hz, P-t-Bu), 30.1 (P-t-Bu), 11.9 (Cp*). 31P
1
(C6D6): 111.9 (s, Cp), 41.3 (d, JPC = 45 Hz, P-t-Bu), 30.3
NMR (C6D6): 40.3. Anal. calcd. for C24H48HfNP: C 51.46,
H 8.64, N 2.50; found: C 51.07, H 8.59, N 2.43.
(s, P-t-Bu). 31P{1H} NMR (C6D6): 40.8. Anal. calcd. for
C22H37NPHfCl: C 47.15, H 6.65, N 2.50; found: C 46.90, H
6.30, N 2.23.
Synthesis of (Me3Si)2Cp(t-Bu3PN)HfCl2 (13)
(Me3Si)2CpHfCl3 (0.10 g, 0.202 mmol) was dissolved in
5 mL of toluene. Solid t-Bu3PNLi (0.45 g, 0.202 mmol)
was added to the above at room temperature. The clear sol-
ution was stirred at room temperature for a week upon
which it became cloudy and the volatiles removed under
vacuum. The product was extracted with hot hexanes
(5 mL) and then filtered through celite. Hexanes were re-
moved to give a colorless oil, which solidified on standing
for a few hours as a white material (0.08 g, 0.118 mmol,
Synthesis of Cp*(t-Bu3PN)HfCl2 (9)
Cp*HfCl3 (1.09 g, 2.595 mmol) was suspended in 10 mL
of toluene. Solid t-Bu3PNLi (0.58 g, 2.597 mmol) was added
in portions at room temperature. The cloudy solution was
stirred for 24 h and then filtered through celite. The solution
was concentrated to *5 mL and then stored in a freezer
at ꢀ35 8C for 48 h. A white solid precipitated, which was
isolated, washed with pentane, and then dried under vacuum
1
1
4
(1.30 g, 2.163 mmol, 83%). H NMR (C6D6): 2.19 (s, 15H,
59%). H NMR (C6D6): 7.01 (t, J = 2.1 Hz, 1H, H2 of
3
4
Cp*), 1.21 (d, JPH = 12.5 Hz, 27H, P-t-Bu). 13C{1H} NMR
Cp@), 6.81 (d, J = 2.1 Hz, 2H, H3 and H4 of Cp@), 1.17 (d,
1
(C6D6): 121.0 (Cp*), 41.3 (d, JPC = 45 Hz, P-t-Bu), 30.0 (P-
3JPH = 13.0 Hz, 27H, P-t-Bu), 0.46 (s, 18H, SiMe3). 13C{1H}
NMR (C6D6): C1, C2, and C3 of Cp@ not seen, 120.9 (C4
t-Bu), 12.3 (Cp*). 31P NMR (C6D6): 46.3. Anal. calcd. for
C22H42NPHfCl2: C 43.97, H 7.04, N 2.33; found: C 44.08,
H 7.07, N 2.34.
1
and C5 of Cp@), 41.4 (d, JPC = 45 Hz, P-t-Bu), 30.0 (P-t-
Bu), 0.73 (SiMe3). 31P NMR (C6D6): 45.0. Anal. calcd. for
C23H48NPSi2HfCl2: C 40.91, H 7.17, N 2.07; found: C
40.59, H 7.06, N 1.94.
Synthesis of Cp*(i-Pr3PN)HfCl2 (10)
Cp*HfCl3 (0.11, 0.262 mmol) was suspended in 3 mL of
toluene. Solid i-Pr3PNLi (0.05 g, 0.276 mmol) was added in
portions at room temperature. The cloudy solution was
stirred overnight and then filtered through celite. Toluene
Synthesis of (Me3Si)2Cp(t-Bu3PN)HfMe2 (14)
Compound 13 (0.15 g, 0.222 mmol) was dissolved in
3 mL of diethylether. MeMgBr (3 mol/L, 0.37 mL,
Published by NRC Research Press

1166
Can. J. Chem. Vol. 87, 2009
Table 1. Crystallographic data.
Crystal
Formula
3
4
7
9
17 0.5(C6H5Me)
C51.5H62B2F20HfN2P2
1351.08
Monoclinic
P21/n
15.423(10)
15.819(5)
24.116(10)
C24H54Cl2HfN2P2
682.02
Triclinic
P-1
13.185(4)
15.486(5)
16.407(5)
89.845(4)
89.878(4)
73.037(4)
3204.4(17)
4
C26H60HfN2P2
641.19
Monoclinic
P21/n
13.2389(11)
16.5993(13)
15.5844(13)
C36H81ClHfN3P3
862.89
Monoclinic
P21/c
21.720(6)
12.784(4)
17.046(5)
C22H42Cl2HfNP
600.93
Monoclinic
P21/n
11.855(7)
16.683(10)
13.521(8)
Formula weight
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (deg)
b (deg)
106.5240(10)
108.883(3)
97.072(6)
102.001(19)
g (deg)
3
˚
V (A )
3283.3(5)
4
1.297
3.289
31134
5785
4479(2)
4
2654(3)
4
5755(5)
4
Z
D(calcd.) (g cm-1)
1.414
1.280
2.521
42099
7884
397
0.0280
0.0825
0.762
1.504
4.200
22502
4623
244
0.0630
0.1744
1.297
1.545
2.013
54604
10154
712
0.0326
0.0816
1.029
Absorption coeff.,m (cm-1) 3.536
Data collected
36389
14392
559
0.0335
0.0792
1.043
Data F2o > 3s (F2o)
Variables
R
Rw
280
0.0240
0.0597
1.037
GOF
P
P
1=2
2
2
Note: Data collected at 20 8C with Mo Ka radiation (l = 0.71069 A). R = S(Fo ꢀ Fc)/SFo. Rw ¼ f ½wðFo2 ꢀ Fc2Þ ꢃ= ½wðFoÞ ꢃg
˚
1.110 mmol) was added dropwise at room temperature. The
solution was stirred for 8 h and the volatiles removed under
vacuum. The product was extracted with hexanes (5 mL)
and then filtered through celite. Hexanes were removed to
give a crystalline white solid (0.12 g, 0.189 mmol, 86%).
Synthesis of (Cp*(t-Bu3PN)HfMe)(B(C6F5)4) (16)
Compound 12 (50 mg, 0.09 mmol) and (Ph3C)(B(C6F5)4)
(82 mg, 0.09 mmol) were dissolved in 2 mL of CH2Cl2 in
two separate vials. The borate solution was added dropwise
to the other at ꢀ35 8C. The clear yellow solution was stirred
for 15 min and the volatiles removed under vacuum to give
an orange foam. It was washed with benzene (3 ꢂ 3 mL)
4
1H NMR (C6D6): 6.75 (t, J = 1.6 Hz, 1H, H2 of Cp@), 6.54
4
3
(d, J = 1.6 Hz, 2H, H3 and H4 of Cp@), 1.22 (d, JPH
=
1
12.5 Hz, 27H, P-t-Bu), 0.38 (s, 18H, SiMe3), 16 (s, 6H,
and then dried under vacuum for 12 h. H NMR (CD2Cl2):
HfMe2). 13C{1H} NMR (C6D6): 125.2 (C1 and C3 of Cp@),
3
2.07 (s, 15H, Cp*), 1.40 (d, JPH = 13.0 Hz, 27H, t-Bu),
1
0.03 (s, HfMe). 13C{1H} NMR (CD2Cl2): 148.7 (d, JCF
=
1
123.4 (C2 of Cp@), 41.1 (d, JPC = 47 Hz, P-t-Bu), 39.9
(HfMe2), 30.1 (P-t-Bu), 1.0 (SiMe3). 31P NMR (C6D6): 39.8
Anal. calcd. for C25H54NPSi2Hf: C 42.58, H 7.72, N 1.99;
found: C 42.50, H 7.60, N 1.93.
1
240 Hz, o-C6F5), 138.8 (dm, JCF = 240 Hz, p-C6F5), 136.9
(d, JCF = 247 Hz, m-C6F5), 120.1 (s, Cp*), 41.8 (s, HfMe),
1
1
41.5 (d, JPC = 45 Hz, t-Bu), 30.0 (s, t-Bu), 11.7 (s,
C5(CH3)5). 19F NMR (CD2Cl2): ꢀ133.5 (s, 8F, o-F), ꢀ164.1
(t, JFF = 20 Hz, 4F, p-F), ꢀ168.0 (m, 8F, m-F). 31P NMR
3
Synthesis of Cp*(t-Bu3PN)HfMe(THF)MeB(C6F5)3 (15)
Compound 12 (50 mg, 0.089 mmol) was dissolved in
2 mL of CH2Cl2 containing 72 mL of THF (10 equiv.).
B(C6F5)3 (45 mg, 0.088 mmol) was dissolved in 2 mL of
CH2Cl2 and then added dropwise to the above solution at
room temperature. The colorless solution was stirred for
30 min and then pumped to dryness to give a white solid,
washed with pentane (3 mL), and then dried under vacuum
(CD2Cl2): 48.2. 11B NMR (CD2Cl2, 96 MHz): ꢀ16.9. The
extreme air sensitivity of this species precluded satisfactory
elemental analysis.
Synthesis of (t-Bu3PN)2Hf(H2B(C6F5)2)2 (17)
Compound 4 (15 mg, 0.023 mmol) and HB(C6F5)2
(33 mg, 0.093 mmol) were combined in a small vial con-
taining 1 mL of benzene. The vial was capped and sonicated
for 10 min at room temperature. The cloudy solution was
heated at 50 8C for 30 min until it became clear. The prod-
uct precipitated as colorless crystals on cooling to room
temperature. The solvent was removed under vacuum to
give a white solid. The solid was washed thoroughly with
hexanes (5 ꢂ 2 mL) to remove MeB(C6F5)2 and side prod-
ucts and then dried under vacuum (25 mg, 0.019 mmol,
1
(91 mg, 0.079 mmol, 89%). H NMR (CD2Cl2): 4.13 (br,
4H, OCH2CH2), 2.11 (s, 15H, Cp*), 2.03 (br, 4H,
3
OCH2CH2), 1.39 (d, JPH = 13.5 Hz, 27H, P-t-Bu), 0.47 (br
s, 3H, MeB(C6F5)3), 0.27 (s, 3H, HfMe). 13C{1H} NMR
1
(CD2Cl2): 149.0 (dm, JCF = 225 Hz, o-C6F5), 138.1 (dm,
1
1JCF = 240 Hz, p-C6F5), 137.1 (dm, JCF = 240 Hz, m-
C6F5), 121.9 (Cp*), 121.9 (Cp*), 75.9 (OCH2CH2), 41.1 (d,
1JPC = 46 Hz, P-t-Bu), 29.8 (P-t-Bu), 29.1 (HfMe), 26.0
(OCH2CH2), 11.7 (Cp*), 11.0 (br, CH3B(C6F5)3). 19F NMR
1
83%). H NMR (C6D6): 4.67 (br q, m-H, JHB = 65 Hz, 4H),
3
3
(CD2Cl2, 282 MHz): ꢀ133.59 (d, JFF = 22 Hz, 6F, o-
0.92 (d, JPH = 10 Hz, 54H, t-Bu). 13C{1H} NMR (C6D6):
3
1
1
F), ꢀ165.71 (t, JFF = 20 Hz, 3F, p-F), ꢀ168.25 (m, 6F, m-
148.3 (d, JCF = 241 Hz, o-C6F5), 139.5 (dm, JCF =
F). 31P NMR (CD2Cl2): 51.3. 11B NMR (CD2Cl2, 96 MHz):
ꢀ14.9. The extreme air sensitivity of this species precluded
satisfactory elemental analysis.
250 Hz, p-C6F5), 138.1 (d, JCF = 245 Hz, m-C6F5), 40.2 (d,
1
1JPC
=
45 Hz, t-Bu), 29.2 (s, t-Bu). 19F NMR
3
(C6D6): ꢀ130.7 (s, 8F, o-F), ꢀ157.8 (t, JFF = 28 Hz, 4F, p-
Published by NRC Research Press

Alhomaidan et al.
1167
F), ꢀ163.9 (m, 8F, m-F). 31P NMR (C6D6): 47.2. 11B NMR
Scheme 1. Synthetic routes to 1ꢀ4.
(C6D6): ꢀ15.0 (t, JBH
= 65 Hz). Anal. calcd. for
C48H58B2F20N2P2Hf: C 44.18, H 4.48, N 2.15; found: C
44.09, H 4.33, N 2.03.
X-ray data collection and reduction
Crystals were manipulated and mounted in capillaries in a
glovebox, thus maintaining a dry, O2-free environment for
each crystal. Diffraction experiments were performed on a
Siemens SMART System CCD diffractometer. The data
(4.58 < 2q < 458ꢀ50.08) were collected in a hemisphere of
data in 1329 frames with 10 s exposure times. The observed
extinctions were consistent with the space groups in each
case. A measure of decay was obtained by recollecting 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 proc-
essed using the SAINT and SHELXTL processing packages.
An empirical absorption correction based on redundant data
was applied to each data set. Subsequent solution and refine-
ment was performed using the SHELXTL solution package.
were freshly prepared and loaded into syringes in a glove-
box, then transferred to the reactor immediately before in-
jection to limit the possibility of catalyst decomposition. A
prepared solution of TiBAl (3.0 mL) was injected into the
reaction vessel through the catalyst injection inlet and al-
lowed to stir for 5 min. The prepared precatalyst solution
(1.0 mL) was injected, followed immediately with the injec-
tion of the B(C6F5)3 solution (1.5 mL) into the reactor ves-
sel. The mixture was stirred at 1500 5 rpm at 30 8C under
2 atm (1 atm = 101.325 kPa) of dynamic ethylene flow for
10 min. The temperature and ethylene flow rate were re-
corded manually at regular intervals. After 5ꢀ10 min, the
polymerization was stopped by closing the ethylene inlet
valve and venting the reactor, the stirring was stopped, and
the reactor was disassembled. The contents of the reactor
were emptied into a 4 L beaker containing approximately
100 mL of 10% HCl (v/v) in MeOH. The precipitated poly-
mer was collected by filtration, washed with toluene and
acetone, and dried overnight. The resulting polymer was
weighed and polymerization activity calculated.
Structure solution and refinement
Non-hydrogen atomic scattering factors were taken from
the literature tabulations.53 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 calcu-
lations. The refinements were carried out by using full-ma-
trix least-squares techniques on F, minimizing the function
u(Fo ꢀ Fc)2 where the weight, u, is defined as 4F2=2sðF2Þ
and Fo and Fc are the observed and calculated strucoture faoc-
tor amplitudes, respectively. In the final cycles of each re-
finement, 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.
CꢀH atom positions were calculated and allowed to ride on
the carbon to which they are bonded assuming a CꢀH bond
Results and discussion
The dehalosilylation reaction of silyl-phosphinimides and
a titanium halide proved to be a simple and successful
method for the preparation of titanium-phosphinimide com-
plexes. However, this method does not work well for zirco-
nium.54 Previously, several phosphinimide complexes of Zr
and Hf have been prepared at high temperature using an
equimolar amount of KF to remove a N-silyl substituent as
the by-product Me3SiF.54,55 However, the most convenient
route to Zr compounds involves either salt metathesis (LiCl)
or alkane or amine elimination. Thus, using these latter
methods we targeted Hfꢀphosphinimide complexes.
˚
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 cal-
culated, 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 pro-
vided in the Supplementary data.
Polymerization protocol
The parent phosphinimine, t-Bu3PNH, was reacted stoi-
chiometrically with Hf(NEt2)4 to afford (t-Bu3PN)Hf(NEt2)3
(1) in 96% yield (Scheme 1). Subsequent treatment of 1
with excess Me3SiCl in an effort to affect amide cleavage
and prepare (t-Bu3PN)HfCl3 proved to be problematic.
Based on spectroscopic data it appeared Me3SiCl effects
nonselective HfꢀN bond cleavage.
For comparable results, routine standards were run regu-
larly to ensure reproducibility. The polymerizations were
performed in a 1 L Buchi reactor system. Following assem-
bly, the reactor vessel and solvent storage unit were refilled
with nitrogen via four refill and evacuation cycles over at
least 90 min. Approximately 600 mL of toluene was trans-
ferred to the solvent storage container from the purification
column. The solvent was purged with dry nitrogen for
20 min and then transferred to the reactor vessel by differ-
ential pressure. The solvent was stirred at 1500 5 rpm and
the temperature was kept constant at 30 2 8C. The system
was then exposed to ethylene via five vent and refill cycles.
The precatalyst, cocatalyst, and scrubber stock solutions
Similarly, reaction of t-Bu3PNH with Hf(NEt2)4 in a 2:1
ratio afforded the species (t-Bu3PN)2Hf(NEt2)2 (2) in 96%
yield. In contrast to the above species, 2 reacts cleanly at
room temperature with excess Me3SiCl to give (t-
Bu3PN)2HfCl2 (3). This compound showed a singlet at
1
41.3 ppm and a doublet at 1.28 ppm in the 31P NMR and H
Published by NRC Research Press

1168
Can. J. Chem. Vol. 87, 2009
Scheme 2. Synthetic routes to 5 and 6.
Fig. 2. ORTEP drawings of (a) 3 and (b) 4; 20% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Selected bond
˚
distances (A) and angles (8): 3: Hf(1)—N(2) 1.922(3), Hf(1)—N(1)
1.927(3), Hf(1)—Cl(1) 2.3855(13), Hf(1)—Cl(2) 2.3856(14),
P(1)—N(1) 1.569(3), P(2)—N(2) 1.570(4); N(2)ꢀHf(1)ꢀN(1)
111.22(15), N(2)ꢀHf(1)ꢀCl(1) 109.81(12), N(1)ꢀHf(1)ꢀCl(1)
108.87(12), N(2)ꢀHf(1)ꢀCl(2) 109.70(12), N(1)ꢀHf(1)ꢀCl(2)
109.89(12). Cl(1)ꢀHf(1)ꢀCl(2) 107.27(6), P(1)ꢀN(1)ꢀHf(1)
175.0(3), P(2)ꢀN(2)ꢀHf(1) 168.3(2); 4: Hf(1)—N(2) 1.946(3),
Hf(1)—N(1) 1.948(3), Hf(1)—C(26) 2.237(4), Hf(1)—C(25)
2.251(5), N(1)—P(1) 1.554(3), N(2)—P(2) 1.555(3);
N(2)ꢀHf(1)ꢀN(1) 114.92(13), N(2)ꢀHf(1)ꢀC(26) 108.74(15),
N(1)ꢀHf(1)ꢀC(26) 110.11(15), N(2)ꢀHf(1)ꢀC(25) 109.69(17),
N(1)ꢀHf(1)ꢀC(25) 109.06(18), C(26)ꢀHf(1)ꢀC(25) 103.73(17),
P(1)ꢀN(1)ꢀHf(1) 170.8(2), P(2)ꢀN(2)ꢀHf(1) 175.7(2).
Fig. 3. ORTEP drawing of 5; 20% thermal ellipsoids are shown.
Hydrogen atoms are omitted for clarity. Selected bond distances
˚
(A) and angles (8): Hf(1)—N(3) 1.969(3), Hf(1)—N(2) 1.971(3),
Hf(1)—N(1) 1.983(3), Hf(1)—Cl(1) 2.4272(13), P(1)—N(1)
1.551(4), P(2)—N(2) 1.557(3), P(3)—N(3) 1.561(3);
N(3)ꢀHf(1)ꢀN(2) 111.16(16), N(3)ꢀHf(1)ꢀN(1) 112.93(16),
N(2)ꢀHf(1)ꢀN(1) 110.95(15), Hf(1)ꢀCl(1) 107.64(11),
N(2)ꢀHf(1)ꢀCl(1) 106.50(11), N(1)ꢀHf(1)ꢀCl(1) 107.31(11),
P(1)ꢀN(1)ꢀHf(1) 164.8(2), P(2)ꢀN(2)ꢀHf(1) 165.0(2),
P(3)ꢀN(3)ꢀHf(1) 168.1(2).
NMR spectra, respectively. The pseudotetrahedral arrange-
ment around Hf was confirmed by X-ray crystallography
˚
(Fig. 2a). The HfꢀN distances were found to be 1.922(3) A
˚
˚
and 1.927(3) A and the HfꢀCl distances were 2.3855(13) A
˚
and 2.3856(14) A. The PꢀNꢀHf angles (175.0(3)8 and
˚
168.3(2) 8) are approximately linear and typical of early
metal phosphinimide complexes.54,56 This geometry suggests
the presence of some degree of multiple bonding character in
the HfꢀN bond.
5 (1.969(3), 1.971(3), and 1.983(3) A) were longer than
those seen in 3, presumably a result of reduced Lewis acidity
and greater steric congestion at Hf. The methylated analog
(t-Bu3PN)3HfMe (6) was obtained from the treatment of 5
with MeMgBr. This species exhibited a sharp 31P NMR sig-
nal at 34.1 ppm and two 1H NMR signals, a doublet at
1.44 ppm for tert-butyl groups and a singlet at 0.36 ppm for
methyl protons, consistent with the formulation.
Compound 3 was subsequently alkylated with MeMgBr to
give (t-Bu3PN)2HfMe2 (4) as a white solid in 93% yield. An
upfield shift in 31P NMR at 37.2 ppm is consistent with the
presence of electron donating methyl substituents. The struc-
ture of 4, determined by X-ray crystallography (Fig. 2b),
was similar to 3, although the HfꢀN bonds were longer
Complexes of the form Cp(t-Bu3PN)MCl2 (M = Ti, Zr)
have been shown to be active olefin polymerization
catalysts.30,56,57 Thus, the Hf analog was targeted. Reaction
of 1equiv. of t-Bu3PNLi with CpHfCl3 was performed. The
product showed a single 31P NMR resonance at 41.3 ppm
and two 1H NMR signals, a singlet at 5.82 ppm for the
cyclopentadienyl group and a doublet at 1.28 ppm for tert-
˚
at 1.946(3) and 1.948(3) A. In addition, the PꢀN bonds
˚
(1.554(3) and 1.555(3) A) were shorter, a consequence of
the more electron-rich Hf.
It has been previously shown that efforts to prepare Zr
analogs of 3 and 4 employing (t-Bu3PNLi) and ZrCl4 were
unsuccessful as the tris ligand complexes, (t-Bu3PN)3ZrCl,
were preferentially formed.36 In a similar fashion, reactions
of the lithium phosphinimide with HfCl4 in a 1:1 ratio did
not give (t-Bu3PN)HfCl3. Instead, a product mixture was
evidenced by 31P NMR spectroscopy. However, by em-
ploying a 3:1 ratio of reagents the phosphinimide com-
pound (t-Bu3PN)3HfCl (5) was prepared and isolated in
62% yield. The structure of this white product (5) was also
confirmed crystallographically (Fig. 3). The HfꢀN bonds in
1
butyl protons. The 31P and H NMR spectra for the phosphi-
nimide ligand correspond to those observed for 3 while the
1H NMR resonance attributed to the cyclopentadienyl group
corresponds to that seen for Cp2HfCl2. Indeed, 3 was iso-
lated as a crystalline product from this reaction mixture and
its identity confirmed crystallographically. It is noteworthy
that the reaction of IndHfCl3 with t-Bu3PNLi proceeding in
a similar fashion yielded 3 and Ind2HfCl2. Attempts to probe
the mechanism of this ligand redistribution reaction were
Published by NRC Research Press

Alhomaidan et al.
1169
Scheme 3. Proposed ligand redistribution process to 3.
Fig. 4. ORTEP drawing of 9; 20% thermal ellipsoids are shown.
Hydrogen atoms are omitted for clarity. Selected bond distances
˚
(A) and angles (8): Hf(1)—N(1) 1.925(7), Hf(1)—Cl(2) 2.398(3),
Hf(1)—Cl(1) 2.402(3), N(1)—P(1) 1.574(8); N(1)ꢀHf(1)ꢀCl(2)
104.3(2), N(1)ꢀHf(1)ꢀCl(1) 103.3(2), Cl(2)ꢀHf(1)ꢀCl(1)
103.46(12), P(1)ꢀN(1)ꢀHf(1) 163.2(4).
performed by a variable temperature 31P NMR spectroscopy.
Although solubility was problematic, on mixing at 15 8C, a
broad resonance at 56.6 ppm was observed, which slowly
transformed to a sharp signal at 41.3 ppm corresponding to
3. One possible mechanism could involve metathesis
generating Cp(t-Bu3PN)HfCl2,which then undergoes ligand
redistribution to give (t-Bu3PN)2HfCl2 and Cp2HfCl2. Alter-
natively, the improved solubility of Cp(t-Bu3PN)HfCl2 could
result in a second metathesis to give Cp(t-Bu3PN)2HfCl,
which could then react with CpHfCl3 to give the two redis-
tribution products (Scheme 3). This would suggest that the
initial species giving rise to the resonance at 56.6 ppm could
be Cp(t-Bu3PN)HfCl2, although the mechanistic details of
this disproportionation were not confirmed.
Scheme 4. Synthetic routes to 9ꢀ14.
The proposed intermediate in the latter mechanism,
Cp(t-Bu3PN)2HfCl (7), was prepared independently in 95%
yield by treating (t-Bu3PN)2HfCl2 with an equimolar
amount of CpNa. Compound 7 gave rise to 31P resonance
at 37.4 ppm and a 1H NMR signal at 6.57 ppm arising
from the cyclopentadienyl protons. This species is stable
on its own at elevated temperature. However, upon addi-
tion of a stoichiometric amount of CpHfCl3, 7 reacts to
give 3 and Cp2HfCl2, thus supporting the role of 7 in the
ligand redistribution process described above. In a related
and analogous synthesis, the species Cp2(t-Bu3PN)HfCl (8)
was readily synthesized in 77% isolated yield by reacting
Cp2HfCl2 with t-Bu3PNLi.
While the species Cp(t-Bu3PN)HfCl2 was not accessible,
use of substituted cyclopentadienyl groups afforded the
target species that were stable with respect to ligand redis-
tribution. For example, Cp*HfCl3 reacts with t-Bu3PNLi
smoothly to give Cp*(t-Bu3PN)HfCl2 (9) as evidenced by
NMR data. The pseudotetrahedral arrangement about Hf was
unambiguously confirmed by X-ray crystallography (Fig. 4).
Bu3PN)Hf(NMe2)2 (11) and Cp*(t-Bu3PN)HfMe2 (12) in
yields of 88% and 95%, respectively (Scheme 4).
In a procedure similar to that employed for the synthesis
of 8, other cyclopentadienyl derivatives could be employed.
For example, ((Me3Si)2C5H3)HfCl3 reacted stoichiometri-
cally with t-Bu3PNLi to form ((Me3Si)2C5H3)(t-Bu3PN)HfCl2
(13). This reaction proceeded slowly, presumably as a result
of the sterically demanding substituents on the Cp-ring.
Nonetheless, this afforded 13 in 59% isolated yield. Com-
pound 13 exhibits a sharp 31P NMR signal at 45.0 ppm and
˚
The HfꢀN distance was found to be 1.925(7) A while the
˚
˚
HfꢀCl distances were 2.398(3) A and 2.402(3) A, which are
quite similar to those in 3. Additionally, the approximately
linear PꢀNꢀHf vector (163.2(4)8) in 9 is significantly larger
than that observed in (Hf3Cl6(NPMe3)5)+(Hf2Cl7(NPMe3)2)ꢀ
(133.1(8)8, 125.9(6)8, and 132.6(8)8),55 where the phosphini-
mide ligand bridges two Hf atoms.
1
four H NMR resonances at 7.01, 6.81, 1.17, and 0.46 ppm
attributable to the Cp, tert-butyl, and trimethylsilyl groups,
respectively. This species was readily alkylated with
MeMgBr to give ((Me3Si)2C5H3)(t-Bu3PN)HfMe2 (14) as a
crystalline white solid in a high yield of 86% (Scheme 4).
The reactions of Lewis acid activators are commonly used
to generate cationic species, which serve as single-site cata-
lysts in olefin polymerization.58 Reaction of 12 with B(C6F5)3
in CH2Cl2 under various conditions, showed no clear indica-
In addition, reaction of Cp*HfCl3 with i-Pr3PNLi afforded
1
Cp*(i-Pr3PN)HfCl2 (10). The H NMR signal attributable to
the Cp* group was observed at 2.19 ppm, downfield from
that seen for Cp*2HfCl2 (1.88 ppm). The halide atoms in
9 could be readily replaced with amides or methyl groups
via reaction with LiNMe2 or MeMgBr, affording Cp*(t-
Published by NRC Research Press

1170
Can. J. Chem. Vol. 87, 2009
Scheme 5. Reactions of Hfꢀdialkyls with boranes.
Fig. 5. ORTEP drawing of 17; 20% thermal ellipsoids are shown.
Hydrogen atoms are omitted for clarity. Selected bond distances
˚
(A) and angles (8): Hf(1)—N(1) 1.909(3), Hf(1)—N(2) 1.921(3),
Hf(1)—B(1) 2.588(5), Hf(1)—B(2) 2.655(4), Hf(1)—F(16)
2.678(3), P(1)—N(1) 1.594(3), P(2)—N(2) 1.587(3);
N(1)ꢀHf(1)ꢀN(2) 112.85(14), N(1)ꢀHf(1)ꢀB(1) 104.05(14),
N(2)ꢀHf(1)ꢀB(1) 111.07(15), N(1)ꢀHf(1)ꢀB(2) 101.36(14),
N(2)ꢀHf(1)ꢀB(2) 113.45(14), B(1)ꢀHf(1)ꢀB(2) 113.32(15),
P(1)ꢀN(1)ꢀHf(1) 177.4(2), P(2)ꢀN(2)ꢀHf(1) 173.3(2).
tion of the formation of a cationic species by NMR spectro-
scopy. However, reaction in the presence of THF afforded
[Cp*(t-Bu3PN)HfMe(THF)][MeB(C6F5)3] (15) in 89% yield
1
(Scheme 5). The H NMR spectrum showed a broad singlet
at 0.47 ppm attributable to the Me-B and a sharp singlet at
0.27 ppm attributable to the HfꢀMe. The sharp 11B NMR
signal at ꢀ14.9 ppm confirmed a tetracoordinate boron
environment.59 In a similar fashion, methyl-abstraction by
[Ph3C][B(C6F5)4] from 12 affords the cationic species [Cp*(t-
Bu3PN)HfMe][B(C6F5)4] (16). In this species, the HfꢀMe
gave rise to a broad singlet at 0.03 ppm in the 1H NMR spec-
same condition. The insolubility of the resulting polyethylene,
which precluded GPC data infers high molecular weight. Sim-
ilar observations have been made for other phosphinimide-
based olefin polymerization catalysts.54
trum, while
a
sharp 11B NMR signal was observed
at ꢀ16.9 ppm. This reactivity towards Lewis acids resembles
that of the analogous Zr species, Cp(t-Bu3PN)ZrMe2.60
The corresponding reactions of 4 with B(C6F5)3 or
[Ph3C][B(C6F5)4] gave complex mixtures of unidentified
products. However, 4 was found to react cleanly with
(C6F5)2BH at room temperature. The resulting product was
Conclusions
Phosphinimide complexes of hafnium can be synthesized
either by salt metathesis or amine elimination. Cyclopenta-
dienyl redistribution precludes the synthesis of Cp(t-
Bu3PN)HfCl2, although use of bulkier substituted cyclopen-
tadienyl ligands readily affords the analogous derivatives.
Activation of several Hfꢀphosphinimide-dihalide species
proved to be inactive in olefin polymerization upon activa-
tion by MAO. In contrast, activation of dimethyl analogs by
[Ph3C][B(C6F5)4] generate catalysts of moderate activity.
1
isolated as a white solid (17) in 89% yield. The H NMR
spectrum exhibited a resonance centered at 4.67 ppm con-
sisting of four broad peaks separated by 65 Hz. The 11B
NMR showed a triplet at ꢀ15.00 ppm. This complex (17)
was further confirmed by X-ray crystallography and con-
firmed to be (t-Bu3PN)2Hf(H2B(C6F5)2)2 (Scheme 5, Fig. 5).
˚
The HfꢀN distances in 17 were found to be 1.909(3) A and
˚
1.921(3) A, while the PꢀNꢀHf angles were nearly linear at
Supplementary data
˚
177.4(2)8 and 173.3(2)8. The HfꢀB distances of 2.588(5) A
˚
Supplementary data for this article are available on the
journal Web site (canjchem.nrc.ca) or may be purchased
from the Depository of Unpublished Data, Document Deliv-
ery, CISTI, National Research Council Canada, Ottawa, ON
K1A 0R6, Canada. DUD 3979. For more information on ob-
taining material, refer to cisti-icist.nrc-cnrc.gc.ca/cms/
unpub_e.shtml. CCDC 732437ꢀ732441 contain the X-ray
data in CIF format for this manuscript. These data can be
obtained, free of charge, via www.ccdc.cam.ac.uk/conts/
retrieving.html (Or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
and 2.655(4) A were consistent with the close proximity of
˚
one ortho-F of a C6F5 group (HfꢁꢁꢁF 2.678(3) A). This inter-
action was not seen in the related zirconocene complex,
Cp2Zr(H2B(C6F5)2)2.61
Preliminary testing of the ability of compounds 3, 9, and 13
to effect ethylene polymerization was probed. The polymer-
izations were performed for 5 min at 30 8C, under 2 atm of
ethylene, and using Al(i-Bu)3 as a scavenger. Employing
500 equiv. of methylaluminoxane (MAO) as the alkylatingand
activating reagent, negligible amounts of polyethylene were
obtained. Similarly, using 12 and 14 while employing 2 equiv.
of B(C6F5)3 as the activator, no polymer formation occurred.
However, activation of 12 and 14 with [Ph3C][B(C6F5)4]
gave rise to activities of 5900 and 5800 g/mol/h/atm, respec-
tively. This compares to 6400 and 8000 g/mol/h/atm, obtained
for Cp2HfMe2 and Cp(t-Bu3PN)TiMe2, respectively, under the
Acknowledgements
Financial support from the Natural Sciences and Engineer-
ing Research Council of Canada (NSERC) and NOVA
Published by NRC Research Press

Alhomaidan et al.
1171
(21) Beddie, C.; Hollink, E.; Wei, P.; Gauld, J.; Stephan, D. W.
Organometallics 2004, 23 (22), 5240ꢀ5251. doi:10.1021/
om049545i.
(22) Brown, S. J.; Gao, X.; Harrison, D. G.; McKay, I.; Koch, L.;
Wang, Q.; Xu, W.; Spence, R. E.; Stephan, D. W. Chem.
Abstr. 2000, 132, 123057a.
Chemicals Corporation is gratefully acknowledged. OA is
grateful for the financial support from the Saudi Basic
Industries Corporation (SABIC). DWS is grateful for the
award of a Canada Research Chair.
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