Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02261518 1999-02-12
FIELD OF THE INVENTION
This invention relates to a novel synthetic method to prepare bulky
trialkyl aminophosphonium halides.
BACKGROUND OF THE INVENTION
Olefin polymerization catalysts having phosphinimine ligands
("phosphinimine catalysts") are disclosed in co-pending and commonly
to assigned patent applications. See, for example, Canadian patent
applications 2,206,944; 2,210,131; 2,243,783; 2,243,775; and 2,243,726,
the disclosures of which are incorporated herein by reference.
The prior art preparation of these phosphinimine catalysts uses an
azide as an intermediate as disclosed in the above referenced patent
applications. As will be appreciated by those skilled in the art, azides may
explosively decompose.
It is an object of this invention to mitigate a problem associated with
the prior art preparation of phosphinimine catalysts. We have now
discovered a synthetic method which enables the production of
phosphinimine catalysts without using an azide.
SUMMARY OF THE INVENTION
In one embodiment, there is provided a process to prepare a
molecule
defined by the formula:
R3P
NH2
X
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wherein X is a halogen and each R is an alkyl group, with the proviso that
at least one R is selected from isopropyl and cyclohexyl;
wherein said process comprises the reaction of ammonia with a dihalide
defined by the formula:
R3PX2
wherein X and each R are as defined above, characterized in that said
to reaction is undertaken in a protic medium at a temperature of from -
40°C
to 200°C.
In another embodiment, there is provided a process to prepare
tri(tertiary-butyl) Aminophosphonium chloride, wherein said process
comprises the reaction of ammonia with tri(tertiary-butyl) phosphonium
dichloride.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
The present process is undertaken under very mild conditions.
Preferred temperatures are from -40°C to 200°C, most
preferably from 20
to 100°C. A positive ammonia pressured of from 1 to 13 atmospheres is
also preferred.
It is preferred to use a protic reaction medium, especially ethanol or
methanol.
3 o The products of the process of the present invention, namely bulky
trialkyl aminophosphonium halides, may be reacted with a base (such as
sodium hydroxide, sodium methoxide or butyl lithium) to give a trialkyl
phosphinimine R3P=NH. The phosphinimine may then be used to prepare
the phosphinimine catalysts (described in the above noted patent
applications) by reacting it with a metal halide.
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The term "bulky trialkyl" refers to the steric bulk of the alkyl
substituents on the phosphines atom. As used herein, the term "bulky
alkyl" means that the steric bulk should be greater than the steric bulk
provided by three phenyl substituents. The use of so-called "Tolman cone
angles" is conventionally employed to describe the bulk of phosphines.
Triphenyl phosphine is typically described as having a Tolman cone angle
to of 145° (see, for example, Chemistry of the Elements, by Greenwood
and
Earnshaw, published by Pergamon Press). The bulky alkyl substituents
preferably provide a cone angle (on the precursor phosphine - i.e. the R3P
fragment) of at least 150°, most preferably at least 160°.
Exemplary bulky
alkyl groups include isopropyl, cyclohexyl, and tertiary butyl. It is
particularly preferred that each R group be tertiary butyl.
Further details are provided in the following, non-limited examples.
EXAMPLES
Preparation of Tri-isopropyl Aminophosphonium Bromide,
iPr3P(NH2)Br
To a solution of tri-isopropylphosphine (10g, 62 mmol) in acetonitrile
(100 mL) at 0°C was added bromine, Br2 (3.2 mL, 62 mmol). The reaction
was stirred for 1-2 hours and ammonia gas was then added to the reaction
3o flask. An exothermic reaction ensued. After the reaction was complete,
the volatiles were removed in vacuo to leave a white solid residue. The
solid was treated with methylene chloride and then filtered to remove the
insoluble NH4Br by-product. The methylene chloride was removed in
vacuoto leave the desired product in >95% purity as determined by'H
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NMR spectroscopy. Yield = 14.6 g, 91%. 'H NMR [200 MHz, CDC13, 8]:
5.34 (br, s, NH2), 2.7 (m, 3H), 1.46 (d, 9H), 1.38 (d, 9H).
Preparation of N-trimethylsilyl Tri-isopropylphosphinimine, iPr3P(=N-
SiMe3) from Tri-isopropyl Aminophosphonium Bromide, iPr3P(NH2)Br
To a slurry of iPr3P(NH2)Br (14.4 g, 56 mmol) in THF (250 mL) at
~0°C was added a hexane solution of BuLi (45 mL, 2.5 M., 112.5 mmol).
1o During the addition the iPr3P(NH2)Br was observed to dissolve. The
reaction was stirred for 60 minutes. It was then added to a solution of
trimethylsilyl chloride (10.7 mL, 84 mmol) in THF (200 mL). After 60
minutes the reaction mixture volatiles were removed in vacuo. The
resulting oily residue was then treated with hexane and the reaction
filtered. Removal of the hexane yielded the desired product in >95% purity
as determined by'H NMR spectroscopy. Yield = 13.5g, 98%. 'H NMR
[200 MHz, C~DB]: 1.61 (m, 3H), 0.97 (d, 9H), 0.87 (d, 9H) 0.28 (s, 9H,
SiMe3).
Preparation of Tri-tert-butylphosphonium dichloride, tBu3PCl2, in
Ether
To a solution of tBu3P (5.2 g) in ether (100 ml) at -50°C was
slowly
added chlorine gas. The reaction was very exothermic and immediately
3o gave a white solid that dissolved as the reaction warmed to 0°C over
the
one hour chlorine addition period. Once the reaction complete the
volatiles were removed in vacuo. The resulting white solid product was
then isolated as a pure material in quantitative yield. Yield = 7 g. 'H NMR
[200 MHz, CDC13, 8]: 1.79 (d, J= 17.4 Hz)
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Preparation of Tri-tert=butyl Aminophosphonium Chloride,
tBu3P(NH2)CI in Methanol
To a solution of tBu3PCl2 (2g) in methanol (30 mL) at 0°C was
added ammonia gas at atmospheric pressure. After about 30 minutes it
appeared that the solution was saturated with ammonia and the gas
addition was terminated. The reaction was then stirred overnight at room
to temperature. The reaction volatiles were removed in vacuo to yield a
white solid. 'H NMR spectroscopic analysis of this solid demonstrated the
formation of the desired product although some starting tBu3PCl2
remained. Consequently, the solid was redissolved in methanol (30 mL)
and the solution placed in a stainless steal pressure vessel. The solution
was cooled to -40°C and ammonia (10 g) added. The vessel was then
sealed and warmed to 50°C for 16 hours.
~H NMR analysis of solution at that time revealed that the reaction had
gone to completion with only tBu3P(NH2)CI present. Yield = 1.60 g. 'H
NMR [200 MHz, CDC13, 8]: 5.5 (br, NH2), 1.55 (d, J= 14.1 Hz, tBu)
Preparation of Tri-tent butyl Aminophosphonium Chloride,
tBu3P(NH2)CI in Methanol
To a solution of tBu3P (2.874 g, 14.2 mmol) in methanol (40 ml) at
0°C was added tert-butyl hypochlorite, tBuOCI (1.67 g, 14.2 mmol).
After
30 minutes, the volatiles were removed in vacuo from clear reaction
mixture and the resulting solid treated with toluene. The toluene was then
removed in vacuo to leave a white solid. (The toluene was added to help
ensure removal of all methanol). The white solid was isolated (yield = 2.88
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g) and characterized by'H NMR spectroscopy. It was found to contain
only tBu3PCl2 (~60%) and tBu3P=O (~40%).
To a solution of the tBu3PCl2/tBu3P=O mixture (2 g) in methanol (30
ml) at -40°C in a stainless steal pressure vessel was added ammonia (5
g).
The vessel was sealed and then warmed to 50°C for 64 hours. The
reaction was depressurized and the reaction solution transferred to a glass
to Schlenk vessel. The volatile components were then removed in vacuo to
leave a white solid. This was treated with methylene chloride and the
solution filtered. The methylene chloride was removed in vacuo and the
resulting solid washed with toluene to remove residual tBu3P0. The
product was then dried in vacuo. Yield = 684 mg. ' H NMR [200 MHz,
CD2C12, 8]: 5.9 (br, NH2), 1.57 (d, J= 14.1 Hz). The NMR spectrum
revealed ~10% residual tBu3P0 remained in the product.
Preparation of N-trimethylsilyl Tri-tert-butylphosphinimine, tBu3P(=N-
SiMe3) from Tri-tert-butyl Aminophosphonium Chloride
A sample of tBu3P(NH2)CI (400 mg, 1.6 mmol) contaminated with a
small amount of tBu3PCl2 was slurried in tetrahydrofuran (30 mL) at -
78°C
and a solution of BuLi in hexane (1.6 M, 2.2 ml, 3.5 mmol) was added.
After 45 minutes, trimethylsilyl chloride (0.4 mL) was added and then the
3o reaction was allowed to warm to room temperature. The reaction mixture
volatiles were removed in vacuo to yield a sticky solid. Hexane was added
and the reaction filtered. Removal of the hexane gave the desired product
as a white solid in >95% purity as determined by'H NMR spectroscopy.
Yield = 443 mg, 97%. 'H NMR [200 MHz, C~D8, 8]: 1.16 (d, J= 12.7 Hz),
0.33 (s, SiMe3).
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COMPARATIVE EXAMPLES
Reaction of tBu3PBr2 with Ammonia in Methanol
To a solution of tBu3PBr2 (1 g) in methanol (25 ml) at 0°C was
added
ammonia gas at atmospheric pressure. After about 30 minutes, it
appeared that the solution was saturated with ammonia and the gas
addition was terminated. The reaction was then stirred overnight at room
to temperature. The reaction volatiles were removed in vacuo to yield a
white solid. 'H NMR spectroscopic analysis of this solid demonstrated that
it consisted primarily of starting material with a large number of other
materials. None of these other materials had NMR spectra consistent with
tBu3P(NH2)Br.
Reaction of tBu3PBr2 with Ammonia in Acetonitrile
To a solution of tBu3PBr2 (2g) in acetonitrile (50 ml) at 25°C was
30
added ammonia gas at atmospheric pressure. Gas addition was
continued for 2 hours. The reaction volatiles were removed in vacuo to
yield a white solid. 'H NMR spectroscopic analysis of this solid
demonstrated that it was starting tBu3PBr2.
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