ALCETYLENE HYDROSILATION USING CYCLOALKADIENE-PLATINUM COMPLEX AS CATALYST

Abstract: A process is described for hydrosilating alkynes with hydridosilane using a cycloalkadiene-platinum complex as catalyst. The use of the cycloalkadiene-platinum complex as catalyst in our process surprisingly reduces the formation of the bis-silated adduct of the alkynes, when compared to the use of standard platinum-based hydrosilation catalysts.

Description: The present invention is a process for hydrosilating acetylene with hydridosilanes using a cycloalkadiene-platinum complex as catalyst. The use of the cycloalkadiene-platinum complex as catalyst in our process reduces formation of the bis-silated adduct of the acetylene, when compared to the preivous use of standard platinum-based hydrosilation catalysts. Virtually any compound which contains a ≡SiH group is reacted with compounds containing aliphatic unsaturation in the presence of a platinum compound, such as chloroplatinic acid, to effect a reaction typically referred to as hydrosilation or hydrosilylation. U.S. Patent 2,823,218 discusses such hydrosilation reactions in greater detail. U.S. Patent 3,419,593 describes a group of catalysts that are the reaction product of chloroplatinic acid with organosilicon compounds having terminal unsaturation that are particularly useful in hydrosilation processes. U.S. Patent 4,292,434 discloses a hydrosilation catalyst obtained by dissolving a platinum halide in at least 20 parts by weight of an olefin, such as 1,5-cyclooctadiene, for each part by weight of platinum halide and subsequently heating and mixing the solution obtained with from 0.5 to one mole of a primary or secondary amine for each gram atom of platinum. The catalyst is reported as useful in the reaction of acetylene with methyldichlorosilane to produce vinylmethyldichlorosilane. However, we have found that at the 1,5 cycloalkadiene to platinum molar ratio described by U.S. Patent 4,292,435 (approximately 80:1), the 1,5 cyclooctadiene will act as an inhibitor of the reaction. Kopylova L. et al., Russian Journal of General Chemistry, 63(6), Part 01 (1993), 900-903 describe hydrosilylation reactions of monosubstituted acetylene and ethylene which proceed to give two isomeric adducts (α and β) in the presence of square-planar complexes of Pt(II) with triethyl-, triethoxy-, trichloro-, and alkylchlorosilanes. Lewis L.N. et al., Organometallics, 10 (10), (1991), 3750-9 describe reactions of terminal alkynes including phenylacetylene and 1-pentyne, with several SiH compounds selected from triphenylsilane, diphenylmethylsilane, phenyldimethylsilane, triethylsilane, and triethoxysilane. A common problem associated with the hydrosilation of an alkyne with a hydridosilane, in the presence of a platinum halide or platinum olefin complex as catalyst, is the formation of the bis-silated adduct of the alkyne as a by-product. Typically, such hydrosilation processes are run under high pressure to increase the concentration of alkyne in the reaction mixture, relative to the alkenyl substituted product, thereby minimizing the formation of the bis-silated adduct. However, alkynes such as acetylene are explosive at high pressures, thereby making those processes dangerous. We have surprisingly found that in processes where an alkyne is silated with a hydridosilane in the presence of a cycloalkadiene-platinum complex as catalyst, the amount of the bis-silated adduct formed is reduced, when compared to standard platinum-based hydrosilation catalysts. This allows such processes to be run at near normal atmospheric pressure while still providing an acceptable ratio of alkenyl substituted product to bis-silated adduct by-product. The present invention is a process for hydrosilation of acetylene. The process comprises: contacting at a temperature within a range of 40 to 150°C. acetylene with a hydridosilane described by formula (R 2 ) n HSiX 3-n (2) where each R 2 is independently selected from alkyl groups comprising one to 20 carbon atoms or aryl groups, each X is an independently selected halogen atom and n=0 to 3; in the presence of a platinum catalyst consisting of a cycloalkadiene-platinum complex, described by formula PtR 3 2 or Pt(R 3 )X 2 , where R 3 is a cycloalkadiene comprising 6 to 20 carbon atoms and X is as previously described. The acetylene is contacted with the hydridosilane in standard low-pressure type reactors suitable for reacting such compounds. The pressure at which our process is conducted is not critical and is varied within a wide range. However, the present process is unexpectedly advantageous in that it is conducted at near normal atmospheric pressure while still providing an acceptable ratio of alkenyl-substituted product to bis-silated by-product. Therefore, it is preferred that the process is conducted at a pressure within a range of 10.1 to 303.9 kPa (0.1 to 3 atmospheres). More preferred is when the process is conducted at 101.3 to 303.9 kPa (1 to 3 atmospheres). The present process can be conducted in either a gas or liquid phase. However, it is preferred that the process is conducted in a liquid phase using a liquid hydrocarbon solvent in which the acetylene and hydridosilane are soluble. It is preferred that the liquid hydrocarbon solvent have a boiling point greater than the boiling point of the alkenyl substituted product of our process to facilitate separation of the product from the solvent. The solvent is, for example, an aromatic hydrocarbon such as xylene or a mixture of the isomers of xylene, toluene or benzene. A demonstration of such a liquid phase process is provided in the examples herein. The present process is conducted at a temperature within a range of 40 to 150°C. A preferred temperature is 60 to 100°C. The optimal temperature for conducting the process will depend upon such factors as the acetylene and hydridosilane to be reacted. For example, when acetylene is reacted with methyldichlorosilane a preferred temperature for conducting the process is within a range of 70 to 80°C. and when acetylene is reacted with dimethylchlorosilane a preferred temperature is within a range of 60 to 70°C. Hydridosilanes useful in our process are described by formula (2), where R 2 is selected from alkyl groups comprising 1 to 20 carbon atoms or aryl groups, each X is an independently selected halogen atom and n has a value of zero, one, two or three. R 2 is, for example, alkyl groups such as methyl, ethyl, propyl and tert-butyl; halogen substituted alkyl groups such as chloromethyl or 3,3,3-trifluoropropyl; aryl groups such as phenyl, tolyl and xylyl; and halogen substituted aryl groups such as chlorophenyl. Preferred is when R 2 is methyl. Also, preferred is when X is a chlorine atom. The preferred hydridosilane is selected from methyldichlorosilane or dimethylchlorosilane. In the present process, it is preferred that the mole ratio of the acetylene to the hydridosilane fed to the process is within a range of 0.5:1 to 3:1. Preferred is when the mole ratio of acetylene to hydridosilane is within a range of 1:1 to 1.3:1. The present process is conducted in the presence of a platinum catalyst, consisting of a cycloalkadiene-platinum complex described by formula PtR 3 2 or Pt(R 3 )X 2 , where R 3 is a cycloalkadiene comprising 6 to 20 carbon atoms and each X is an independently selected halogen atom. Preferred is when the cycloalkadiene has 6 to 10 carbon atoms. The cycloalkadiene is cyclohexadiene, cycloheptadiene, cyclooctadiene, norbornadiene and cyclodecadiene. The preferred cycloalkadiene is 1,5-cyclooctadiene. Preferred is when X is chlorine. The most preferred platinum catalyst is described by formula Pt(R 3 )Cl 2 , where R 3 is 1,5-cyclooctadiene. Procedures for making platinum catalysts useful in the present process are found, for example, in Drew et al., Inorg. Synth. 28 :346-349 (1990) and in Crascall et al., Inorg. Synth. 28 :126-132 (1990). The concentrations of platinum catalyst used in our process are varied within wide limits. In general, when the process is run as a batch process in the liquid phase, the catalyst concentration in the liquid phase is that providing 1 to 20,000 parts per million (ppm) of platinum. Preferred is when the catalyst provides about 20 to 10,000 ppm platinum in the liquid phase. The present process further comprises the presence of non-complexed cycloalkadiene comprising 6 to 20 carbon atoms with the proviso that the ratio of total moles of cycloalkadiene per g·atom of platinum be five or less. Where, the "total moles of cycloalkadiene" is that provided to the process by the cycloalkadiene-platinum complex plus any additional non-complexed cycloalkadiene present in our process. The additional non-complexed cycloalkadiene may be added to the process separate from the cycloalkadiene-platinum complex or it may be provided to the process as a mixture with the cycloalkadiene-platinum complex. Preferred is when the ratio of total moles of cycloalkadiene to g·atom of platinum is less than 3. Even more preferred is when the ratio is less than 2.5. When present, it is preferred that the non-complexed cycloalkadiene is the same as that complexed with the platinum to form the cycloalkadiene-platinum complex. The following examples are provided to illustrate the present invention. The apparatus set-up for running the examples is as follows. Commercially acquired acetylene was purified to remove stabilizing agents. The purified acetylene was introduced via a coarse glass-frit gas dispersion tube into a 500 mL, 3-neck, round-bottom flask containing liquid hydridosilane. This flask, termed the "SiH reservoir", was fitted with a thermometer and equipped with Teflon™ adapters at the necks for entry of delivery and exit tubes. The exit tube from the SiH reservoir was a 6 mm outside diameter (O.D.) polypropylene tube leading to a 500 mL flask used as a safety trap between the SiH reservoir and the reaction flask. The tubing exiting the safety trap was a 3 mm O.D. Teflon" tube. This exit tube was connected to a second gas dispersion tube which entered a 1 L, 3-neck, round-bottom flask termed the "reactor". The reactor was equipped with a stirring bar and fitted with a thermometer at one neck and a claisen adapter on the center neck. The straight neck of the claisen adaptor was equipped with a rubber septum for the periodic withdrawal of samples from the reactor for analysis by gas chromatography using a thermal conductivity detector (GC-TCD). The second neck of the claisen adapter was fitted with a dewar condenser cooled with a dry ice/isopropyl alcohol (IPA) bath. The Tygon™ tubing exiting this condenser led to a mineral oil double-bubbler via a dry ice/IPA trap. Provisions were made for blanketing and or purging the apparatus with nitrogen gas from just before the SiH reservoir to between the last dry ice/IPA trap and the bubbler. The experimental procedure for running the examples was as follows. Methyldichlorosilane or dimethylchlorosilane was added to the SiH reservoir, which was maintained at a constant temperature of 18°C. when the hydridosilane was methyldichlorosilane and 13°C. when the hydridosilane was dimethylchlorosilane. A preweighed quantity of catalyst and where indicated 1,5-cyclooctadiene (COD) was added to the reactor. Based on approximately one g-mol of product formed during a run, the amount of catalyst used provided a final Pt/SiH g·atom to mole ratio of 6 X 10 -5 :1 in each example. Methylvinyldichlorosilane or dimethylvinylchlorosilane (as a means of varying the average vinylsilane concentration in the reactor) and xylenes in the amounts described in each example were transferred to the reactor under a slow nitrogen purge. The reaction apparatus was purged with acetylene and then the gas dispersion tube in the SiH reservoir was slowly lowered into the hydridosilane to bubble acetylene through the hydridosilane. The acetylene flow rate was maintained at 115 to 120 mL minute to yield approximately 120 to 170 g of vinylsilane product in a three to four hour run time. The gas exiting the SiH reservoir comprised acetylene and hydridosilane at a molar ratio within a range of 1.2:1 to 1.25:1. The gaseous mixture was next passed into the stirring catalyst solution in the reactor. In those examples where a reaction occurred, an exotherm was evident within three minutes. The temperature of the reactor was controlled by means of a silicone oil bath to maintain the temperatures reported for each example. The exotherm usually peaked in 30 to 45 minutes. The reaction temperature was then maintained at a constant temperature as reported for each example for the remainder of the run. When the level of liquid in the reactor reached a preset mark on the flask, corresponding to the approximate product weight as described in each example, the gas dispersion tube in the SiH reservoir was raised above the liquid level to stop any further hydrosilation. Acetylene flow was continued for an additional two to five minutes. The reactor was cooled to room temperature under nitrogen atmosphere and the product mixture was removed under nitrogen pressure into a preweighed bottle. The weight of all products formed was obtained by subtracting the weight of the initial reaction mixture (i.e. catalyst, catalyst modifier, vinylsilane and xylenes) from that of the final product mixture. Analysis of the mixture was performed by GC-TCD. The catalysts used in the examples are as follows. A catalyst comprising a Pt(COD)Cl 2 complex was acquired from Strem Chemicals, Inc., Newbury, MA. The catalyst designated as "CPA/IPA/MeViSiCl 2 " was prepared by the following method. A 500 mL, round-bottom flask, equipped with a stirring bar, was flushed with nitrogen and charged with 296.2 g of distilled methylvinyldichlorosilane. 3.77 g of a solution comprising chloroplatinic acid in 1-propanol and containing 4.39 percent by weight of platinum, obtained from Johnson-Matthey, Ward Hill, MA, were slowly added to the flask. This mixture was stirred for 15 hours under nitrogen and then transferred to a clean, stoppered glass bottle for storage. The catalyst designated as "CPA/IPA/Me 2 ViSiCl" was prepared by adding 2.51 g of the solution comprising chloroplatinic acid in 2-propanol, as described above, to 197.5 g of distilled Me 2 ViSiCl. The resulting mixture was treated by a method similar to that described for preparing the CPA/IPA/MeViSiCl 2 catalyst. In the examples the following labels apply. "Hydridosilane" describes the hydridosilane tested; "Catalyst" is the type of catalyst used, as previously described; "Catalyst Conc" is the initial g·atoms of platinum per mole of SiH added to the reactor; "COD" is the weight of 1,5-cyclooctadiene added to the reactor; "Additional MeViSiCl 2 " and "Additional Me 2 ViSiCl" is the weight of methylvinyldichlorosilane or dimethylvinylchlorosilane initially added to the reactor to vary the average concentration of vinylsilane in the reactor; "Xylenes" is the amount of a mixture of xylene isomers added to the reactor; "Temperature Range" describes the temperature range of the reactor that occurred from initiation of the exotherm to temperature stabilization; "Hold Temp" is the constant temperature the content of the reactor was held at after temperature stabilization. "Average MeViSiCl 2 Conc" and "Average Me 2 ViSiCl Conc" is the average concentration by weight of these compounds in the reactor during a run; "Weight MeViSiCl 2 " and "Weight Me 2 ViSiCl" is the weight of methylvinyldichlorosilane or dimethylvinylchlorosilane made by the process, as determined by GC-TCD and corrected for any such compound initially added to the reactor; "Weight Bis-Silated Derivative" is the amount of the bis-silated acetylene made during conduct of the process; "P/B Weight Ratio" is the weight ratio of product MeViSiCl 2 or Me 2 ViSiCl made during the run to bis-silated acetylene adduct; "Me" is methyl and "Vi" is vinyl. Example 1 (Reference example) Hydridosilane MeHSiCl 2 Catalyst CPA/IPA/MeViSiCl 2 Catalyst Conc 6 X 10 -5 g·atom Pt/mol SiH COD 0 g Additional MeViSiCl 2 127 g Xylenes 148 g Temperature Range 67-79°C Hold Temperature 77°C Average MeViSiCl 2 Conc 58 Wt% Weight Product MeViSiCl 2 165 g Weight Bis-Silated Derivative 11 g P/B Weight Ratio 15.4:1 Example 2 Hydridosilane MeHSiCl 2 Catalyst Pt(COD)Cl 2 Catalyst Conc 6 X 10 -5 g·atom Pt/mol SiH COD 0 g Additional MeViSiCl 2 149 g Xylenes 148 g Temperature Range 72-82°C Hold Temperature 76°C Average MeViSiCl 2 Conc 58 Wt% Weight Product MeViSiCl 2 164 g Weight Bis-Silated Derivative 8 g P/B Weight Ratio 21:1 Example 3 (Reference example) Hydridosilane MeHSiCl 2 Catalyst Pt(COD)Cl 2 Catalyst Conc 6 X 10 -5 g·atom Pt/mol SiH COD 0.013 g Additional MeViSiCl 2 149 g Xylenes 149 g At a ratio of 3:1 moles of COD to g·atom of platinum used in this example, the reaction did not initiate at 70°C. and only a minor amount of methylvinyldichlorosilane was formed in the process. Example 4 (Reference example) Hydridosilane Me 2 HSiCl Catalyst CPA/IPA/Me 2 ViSiCl Catalyst Conc 6 X 10 -5 g·atom Pt/mol SiH COD 0 g Additional Me 2 ViSiCl 0 g Xylenes 275 g Temperature Range 56-69°C Hold Temperature 63°C Average Me 2 ViSiCl Conc 20 Wt% Weight Product Me 2 ViSiCl 118 g Weight Bis-Silated Derivative 6 g P/B Weight Ratio 19:1 Example 5 Hydridosilane Me 2 HSiCl Catalyst Pt(COD)Cl 2 Catalyst Conc 6 X 10 -5 g·atom Pt/mol SiH COD 0 g Additional Me 2 ViSiCl 22 g Xylenes 275 g Temperature Range 60-70°C Hold Temperature 66°C Average Me 2 ViSiCl Conc 21 Wt% Weight Product Me 2 ViSiCl 128 g Weight Bis-Silated Derivative 5 g P/B Weight Ratio 25.6:1

Claims: A process for hydrosilation of acetylene, the process comprising contacting at a temperature within a range of 40 to 150°C. acetylene with a hydridosilane described by formula (R 2 ) n HSiX 3-n , where each R 2 is independently selected from alkyl groups comprising one to 20 carbon atoms or aryl groups, each X is an independently selected halogen atom and n=0 to 3; in the presence of a platinum catalyst, consisting of a cycloalkadiene-platinum complex described by formula PtR 3 2 or Pt(R 3 )X 2 , where R 3 is a cycloalkadiene comprising 6 to 20 carbon atoms and X is as previously described. A process according to claim 1 further comprising a non-complexed cycloalkadiene comprising 6 to 20 carbon atoms, with the proviso that the ratio of moles of total cycloalkadiene to g·atom of platinum is 5:1 or less. A process according to claims 1 or 2 where the contacting is effected at a pressure within a range of 10.1 to 303.9 kPa (0.1 to 3 atmospheres). A process according to claims 1 or 2 where the contacting is conducted in a liquid phase using a liquid hydrocarbon solvent in which the acetylene and hydridosilane are soluble. A process according to claims 1 or 2 where the hydridosilane is selected from methyldichlorosilane or dimethylchlorosilane. A process according to claim 5 where the hydridosilane is methyldichlorosilane and the contacting is effected at a temperature within a range of 60 to 100°C. A process according to claim 5 where the hydridosilane is dimethylchlorosilane and the contacting is effected at a temperature within a range of 60 to 100°C. A process according to claims 1 or 2 where the mole ratio of the acetylene to the hydridosilane is within a range of 0.5:1 to 3:1. A process according to claims 1 or 2 where the cycloalkadiene substituent of the platinum catalyst is 1,5-cyclooctadiene. A process according to claim 9 where the platinum catalyst is described by formula Pt(R 3 )Cl 2 and R 3 is 1,5-cyclooctadiene. A process according to claim 4 where the liquid phase comprises 20 to 10,000 ppm platinum.

Inventors: ROY AROOP KUMAR, ROY, AROOP KUMAR
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1997
Main classification: C07F7
IPC codes: B01J31, C07B61, C07F7