Preparation of silylium salts

Abstract: Silylium salts corresponding to the formula: R 3 Si(X') q + A - wherein R independently each occurrence is selected from hydrocarbyl, silyl, hydrocarbyloxy, dihydrocarbylamino, and combinations thereof having up to 30 nonhydrogen atoms, X' is an optional Lewis base having up to 20 nonhydrogen atoms, q is 0 or 1, and A - is a noncoordinating, compatible anion, are prepared by oxidizing, preferably electrolytically, a solution comprising a disilane compound corresponding to the formula: R 3 SiSiR 3 wherein R is as previously defined, in the presence of a source of the noncoordinating counter ion, A - .

Description: This invention relates to an improved method for preparing silylium salts. J. B. Lambert, et al., Organometallics , 13, 2430-2443 (1994), disclosed a process for preparing silylium borate salts by reaction of carbenium borates with silanes. Lewis base adducts of silylium borates, especially ether and acetonitrile adducts of silylium borates, are disclosed in S. R. Bahr, et al., J. Am. Chem. Soc. , 115, 4514-4519 (1993) and in M. Kira, et al., J. Am. Chem. Soc. , 114, 6697-6700 (1992), respectively. None of the foregoing references discloses a utility for such silylium compounds in the formation of polymerization catalysts. The copending European Patent Application (EP-A-0781299) from which the present Application is divided claims catalyst systems useful for polymerization of addition polymerizable monomers, said systems comprising: A) a metal complex corresponding to the formula: L k MX m X' n X" p , or a dimer thereof wherein: L is an anionic, delocalized, π-bonded group that is bound to M, containing up to 50 nonhydrogen atoms, optionally two L groups may be joined together forming a bridged structure, and further optionally one L may be bound to X; M is a metal of Group 4 of the Periodic Table of the Elements in the +2, +3 or +4 formal oxidation -state; X is an optional, divalent substituent of up to 50 non-hydrogen atoms that together with L forms a metallocycle with M; X' is an optional neutral Lewis base having up to 20 non-hydrogen atoms; X" each occurrence is a monovalent, anionic moiety having up to 40 non-hydrogen atoms, optionally, two X" groups may be covalently bound together forming a divalent dianionic moiety having both valences bound to M, or form a neutral, conjugated or nonconjugated diene that is π-bonded to M (whereupon M is in the +2 oxidation state), or further optionally one or more X and one or more X' groups may be bonded together thereby forming a moiety that is both covalently bound to M and coordinated thereto by means of Lewis base functionality; k is 1 or 2; m is 0 or 1; n is a number from 0 to 3; p is an integer from 0 to 3; and the sum, k+m+p, is equal to the formal oxidation state of M, and B) a silylium salt corresponding to the formula: R 3 Si(X') q + A - , wherein R independently each occurrence is selected from hydrocarbyl, silyl, hydrocarbyloxy, dihydrocarbylamino, and combinations thereof having up to 30 nonhydrogen atoms, X' is as previously defined, q is zero or one, and A - is a noncoordinating, compatible anion. The copending Application also claims processes for forming catalyst systems comprising contacting the foregoing components A) and B) in an inert diluent, optionally in the presence of one or more addition polymerizable monomers. Certain of the above described catalyst systems, especially those in which the metal M is initially in the +4 formal oxidation state, are believed to exist in the form of the corresponding cationic metal complex having the formula: (L k M*X m X' n X" p-1 ) + A - , or a dimer thereof wherein: M* is a metal of Group 4 of the Periodic Table of the Elements in the +4 formal oxidation state; L, X, X', X", A - , k, m, n and p are as previously defined. According to the present invention there is provided a novel method of forming the silylium salts, comprising electrolyzing a solution comprising a disilane compound corresponding to the formula: R 3 SiSiR 3 wherein R is as previously defined, in the presence of a source of the noncoordinating counter ion, A - . To form the catalyst system of EP-A-0781299, the resulting silylium salt is contacted with the metal complex, L k MX m X' n X" P , or a dimer thereof. The term "silylium ion" refers to cationic species that possess an electron deficient tri-coordinate silicon atom. Stable silylium ions are such cationic species that are able to exist in solution without decomposition for a time period sufficient to undergo the reactions desired of the present invention. Preferred silylium ions are those ions that are incapable of coordination with the metal atom or only weakly coordinate thereto. Further preferably such ions are capable of abstracting an X" group from the metal complex. The silylium ion may also exist in the form of an adduct with a neutral Lewis base, for example as an ether adduct. Examples of suitable silylium ions include trimethylsilylium, triethylsilylium, triisopropylsilylium, triisobutylsilylium, trihexylsilylium, methyldiphenylsilylium, methyldiisopropylsilylium, dimethyldodecylsilylium, dimethyloctadecylsilylium, tris(trimethylsilyl)silylium, and ether adducts thereof. As used herein, the recitation "noncoordinating, compatible anion" means an anion which either does not coordinate to the metal containing portion of the complex (or with respect to the electrochemical formation of the silylium cation explained hereinafter, does not coordinate to the silylium complex) or which is only weakly coordinated thereto thereby remaining sufficiently labile to be displaced by a neutral Lewis base, such as an olefin compound. A noncoordinating, compatible anion specifically refers to a compatible anion which, within the time frame of the desired end use, when functioning as a charge balancing anion in the catalyst system of EP-A-0781299 does not transfer an anionic substituent or fragment thereof to the Group 4 metal complex portion thereby forming neutral byproducts. "Compatible anions" are also anions that are not degraded to neutrality when the initially formed complex decomposes and that are noninterfering with the desired subsequent polymerization or other uses of the complex. More particularly the noncoordinating, compatible anion may comprise a single coordination complex comprising a charge-bearing metal or metalloid core, which anion is both bulky and non-nucleophilic. The recitation "metalloid", as used herein, includes non-metals such as boron and phosphorus which exhibit semi-metallic characteristics. Preferred compatible noncoordinating anions, A - , are those containing a single coordination complex comprising a charge-bearing metal or metalloid core, which anion is capable of stabilizing the catalyst system and sufficiently labile to be displaced by olefinic, diolefinic and acetylenically unsaturated substances or other neutral Lewis bases such as ethers or nitriles. Suitable metals include, but are not limited to, aluminum, gold and platinum. Suitable metalloids especially include boron, phosphorus, silicon and germanium. Compounds containing anions which comprise coordination complexes containing a single metal or metalloid atom are, of course, well known and many, particularly such compounds containing a single boron atom in the anion portion, are available commercially. In light of this, salts containing anions comprising a coordination complex containing a single boron atom are preferred. Most preferred compatible non-coordinating anions are tetrakis(pentafluorophenyl)borate, tetrakis (2,3,5,6-tetrafluorophenyl)borate, tetrakis(2,3,4,5-tetrafluorophenyl)borate, tetrakis(3,4,5-trifluorophenyl)borate, tetrakis(1,2,2-trifluoroethenyl)borate, methyltris(perfluorophenyl)borate and phenyltris(perfluorophenyl)borate. Examples of silylium salts usefully prepared according to the present invention include: trimethylsilylium tetrakispentafluorophenylborate, triethylsilylium tetrakispentafluorophenylborate, triphenylsilylium tetrakispentafluorophenylborate, tribenzylsilylium tetrakispentafluorophenylborate, trimethylsilylium methyltrispentafluorophenylborate, trimethylsilylium benzyltrispentafluorophenylborate, triethylsilylium phenyltrispentafluorophenylborate, triethylsilylium methyltrispentafluorophenylborate, triphenylsilylium methyltrispentafluorophenylborate, tribenzylsilylium benzyltrispentafluorophenylborate, tribenzylsilylium methyltrispentafluorophenylborate, trimethylsilylium tetrakis(2,3,5,6-tetrafluorophenyl)borate, triphenylsilylium tetrakis(2,3,5,6-tetrafluorophenyl)borate, trimethylsilylium tetrakis(3,4,5-trifluorophenyl)borate, tribenzylsilylium tetrakis(3,4,5-trifluorophenyl)aluminate, triphenylsilylium methyltris(3,4,5-trifluorophenyl)aluminate, triethylsilylium tetrakis(1,2,2- trifluoroethenyl)borate, tricyclohexylsilylium tetrakis(2,3,4,5-tetrafluorophenyl)borate, dimethyloctadecylsilylium tetrakis(pentafluorophenyl)borate, tris(trimethylsilyl)silylium methyltris(2,3,4,5-tetrafluorophenyl)borate, or ether adducts thereof. According to the present invention, the previously identified disilane compound, R 3 SiSiR 3 , is oxidized under inert oxidizing conditions and converted into two cationic products each having the formula: R 3 Si + . The term "inert oxidizing conditions" as used herein refers to the use of solvents, oxidizing agents and oxidizing conditions such that byproducts that would render inactive the catalyst system of the present invention are not formed during the reaction. More particularly, suitable solvents are materials that are: liquids under the conditions of the oxidation (generally temperatures from 0 to 100°C), capable of dissolving the reactants and inert. "Inert solvents" are those that are not reduced or oxidized under the reaction conditions employed. Examples of preferred solvents include difluorobenzene (all isomers). and C 1-6 dialkyl ethers of(poly)alkylene glycols, especially dimethoxyethane, and mixtures of the foregoing. Generally, solvents that are Lewis bases, especially nitrile, ether, amine, and phosphine compounds may be used. A preferred process involves the electrolytic oxidation of the disilane compound. General techniques and equipment for electrolysis that are previously well known in the art are used. A disilane that oxidizes at a potential higher than that of the metal complex is preferably employed. A preferred oxidizing potential for such disilane is at least +0.50 volts versus a saturated calomel electrode, more preferably at least +1.50 volts versus a saturated calomel electrode. Cell potentials can be calculated using a known potential reference such as ferrocene. From these potentials, potentials from a saturated calomel electrode may be calculated using well known techniques. The electrolysis may be conducted in a standard electrolytic cell containing an anode and cathode (also referred to as the working electrode and counter electrode, respectively). Suitable materials of construction for the cell include glass, plastic, ceramic, glass coated metal, etc. The electrodes are prepared from inert conductive materials, by which are meant conductive materials that are unaffected by the reaction mixture or reaction conditions. Platinum or palladium are preferred inert conductive materials. Normally an ion permeable membrane such as a fine glass frit separates the cell into separate compartments, the working electrode compartment and counter electrode compartment. A third, buffering or spacer, compartment may further separate the working electrode compartment and counter electrode compartment. The working electrode is immersed in a reaction medium comprising the disilane compound, solvent, supporting electrolyte, and any other materials desired for moderating the electrolysis or stabilizing the resulting complex. The counter electrode is immersed in a mixture of the solvent and an electrolyte comprising the A - anion, which electrolyte may also be the supporting electrolyte. The desired voltage may be determined by theoretical calculations or determined experimentally by sweeping the cell using a reference electrode such as a silver electrode immersed in the cell electrolyte. The background cell current, the current draw in the absence of the desired electrolysis, is also determined. The electrolysis is completed when the current drops from the desired level to the background level. In this manner, nearly complete conversion of the disilane can be easily detected. Desirably, conversions from 50 to 80 percent of theoretical are utilized to avoid contamination of the desired reaction product with further electrolytic decomposition products. Suitable supporting electrolytes more preferably include salts corresponding to the formula: G + A - ; wherein: G + is a cation which is nonreactive towards the starting disalane and resulting complex, and A - is as previously defined. Examples of cations, G + , include tetrahydrocarbyl substituted ammonium or phosphonium cations wherein each hydrocarbyl group has up to 10 carbon atoms. Preferred supporting electrolytes are tetraalkylammonium salts of tetrakis(perfluoroaryl) borates, especially tetra-n-butylammonium tetrakis(pentafluorophenyl)borate. During the electrolysis the cation of the supporting electrolyte passes to the counter electrode and the noncoordinating compatible anion, A - , migrates to the working electrode to become the anion of the resulting oxidized product. Either the solvent or the cation of the supporting electrolyte is reduced at the counter electrode in equal equivalent quantity with the amount of oxidized silylium cation formed at the working electrode. Also, since two moles of silylium complex are formed for each mole of disilane compound employed, the molar amount of disilane compound used is generally approximately one-half the molar quantity of Group 4 metal complex used. The following Example is provided as further illustration of the invention and is not to be construed as limiting. Unless stated to the contrary all parts and percentages are expressed on a weight basis. Example 1 Electrochemical Generation of Trimethylsilylium Tetrakispentafluorophenylborate A standard H-cell for electrolysis comprising two electrode wells separated by a fine glass frit, platinum mesh working and counter electrodes, and a silver wire reference electrode was placed inside an inert atmosphere glove box filled with argon. Each half of the cell was filled with 1,2-difluorobenzene solvent (5 ml in the working compartment, 4 ml in the counter compartment) and tetra(n-butylammonium) tetrakis(pentafluorophenyl)borate supporting electrolyte (15 mmole in each compartment). Hexamethyldisilane was added to the working compartment (10 mmole). The solution was stirred and the potential stepped to the appropriate value to start oxidation of the Si-Si bond, +2.4 V versus a saturated calomel electrode. The reaction was stopped when 10 mmole of (CH 3 ) 3 Si + were produced. The working compartment solution was then pipetted into a round bottom flask and the solvent was removed under vacuum. The product was dissolved in toluene to form a 0.005 M solution used as cocatalyst for the polymerization. Polymerization A two liter stirred reactor was charged with 714 g of mixed alkane solvent (Isopar-E™ available from Exxon Chemicals Inc.) and 107 g of 1-octene comonomer. Hydrogen (32 Δpsi, Δ220 kPa) was added to the reactor by differential pressure expansion from a 80 mL addition tank. The reactor was heated to 140°C, stirred at 1200 rpm and saturated with ethylene at 3.5 MPa. Catalyst and cocatalyst were mixed in a dry box by pipetting toluene solutions of (N-t-butylamido)dimethyl(η 5 -cyclopentadienyl)silanetitanium (IV) dimethyl (prepared as described in Example 1, part A of EP-A-0781299) and trimethylsilylium tetrakispentafluorophenyl borate (prepared by electrolysis as above) to provide 1.0 µmol of each compound. The resulting solution was transferred to a catalyst addition tank and injected into the reactor and the addition line washed with toluene which was also injected into the reactor. The polymerization was allowed to proceed with ethylene being added on demand. After 15 minutes the polymer solution was removed from the reactor. A hindered phenol antioxidant (Irganox™ 1010 available from Ciba Geigy Corp.), 100 mg, was added to the resulting ethylene/1-octene copolymer. Volatiles were removed from the polymer solution under reduced pressure in an oven at about 130°C for approximately 18 hours. The yield of ethylene/1-octene copolymer was 99.1 g.

Claims: A process for preparing a silylium salt corresponding to the formula: R 3 Si(X') q + A - wherein R independently each occurrence is selected from hydrocarbyl, silyl, hydrocarbyloxy, dihydrocarbylamino, and combinations thereof having up to 30 nonhydrogen atoms, X' is an optional Lewis base having up to 20 nonhydrogen atoms, q is 0 or 1, and A - is a noncoordinating, compatible anion, said process comprising oxidizing a solution comprising a disilane compound corresponding to the formula: R 3 SiSiR 3 wherein R is as previously defined, in the presence of a source of the noncoordinating counter ion, A - . A process according to Claim 1, wherein the oxidation is conducted in an inert solvent selected from difluorobenzenes, C 1-6 dialkyl ethers of (poly)alkylene glycols or mixtures thereof. A process according to Claim 1 or Claim 2, wherein the oxidation is electrolytic oxidation. A process according to Claim 3, wherein the oxidation is an electrolysis conducted at a potential of at least +0.5 volts versus a saturated calomel electrode. A process according to Claim 4, wherein the potential is at least +1.50 volts versus a saturated calomel electrode. A process according to any one of Claims 3 to 5, wherein the electrolysis is conducted until conversion of disilane compound is from 50 to 80 percent of theoretical. A process according to any one of Claims 3 to 6, wherein the supporting electrolyte corresponds to the formula: G + A - , wherein G + is selected from tetrahydrocarbyl substituted ammonium or phosphonium cations wherein each hydrocarbyl group has up to 10 carbon atoms, and A - is as defined in Claim 1. A process according to Claim 7, wherein the supporting electrolyte is selected from tetraalkylammonium salts of tetrakis(perfluoroaryl)borates. A process according to Claim 8, wherein the supporting electrolyte is selected from tetra-n-butylammonium tetrakis(perfluoroaryl)borate. A process according to any one of the preceding claims, wherein the silylium ion is selected from trimethylsilylium, triethylsilylium, triisopropylsilylium, triisobutylsilylium, trihexylsilylium, methyldiphenylsilylium, methyldiisopropylsilylium, dimethyldodecylsilylium, dimethyloctadecylsilylium, tris(trimethylsilyl)silylium, and ether adducts thereof. A process according to any one of the preceding claims, wherein A - is tetrakis(pentafluorophenyl)borate, tetrakis (2,3,5,6-tetrafluorophenyl)borate, tetrakis(2,3,4,5-tetrafluorophenyl)borate, tetrakis(3,4,5-trifluorophenyl)borate, tetrakis(1,2,2-trifluoroethenyl)borate, methyltris(pentafluorophenyl)borate or phenyltris(pentafluorophenyl)borate. A process according to Claim 11, wherein the silylium salt is trimethylsilylium tetrakispentafluorophenylborate, triethylsilylium tetrakispentafluorophenylborate, triphenylsilylium tetrakispentafluorophenylborate, tribenzylsilylium tetrakispentafluorophenylborate, trimethylsilylium methyltrispentafluorophenylborate, trimethylsilylium benzyltrispentafluorophenylborate, triethylsilylium phenyltrispentafluorophenylborate, triethylsilylium methyltrispentafluorophenylborate, triphenylsilylium methyltrispentafluorophenylborate, tribenzylsilylium benzyltrispentafluorophenylborate, tribenzylsilylium methyltrispentafluorophenylborate, trimethylsilylium tetrakis(2,3,5,6-tetrafluorophenyl)borate, triphenylsilylium tetrakis(2,3,5,6-tetrafluorophenyl)borate, trimethylsilylium tetrakis(3,4,5-trifluorophenyl)borate, tribenzylsilylium tetrakis(3,4,5-trifluorophenyl)aluminate, triphenylsilylium methyltris(3,4,5-trifluorophenyl)aluminate, triethylsilylium tetrakis(1,2,2-trifluoroethenyl)borate, tricyclohexylsilylium tetrakis(2,3,4,5-tetrafluorophenyl)borate, dimethyloctadecylsilylium tetrakis(pentafluorophenyl)borate, tris(trimethylsilyl)silylium methyltris(2,3,4,5-tetrafluorophenyl)borate, or an ether adduct thereof.

Inventors: DEVORE DAVID D, LAPOINTE ROBERT E, MUSSELL ROBERT D, NEITHAMER DAVID R, DEVORE, DAVID D., LAPOINTE, ROBERT E., MUSSELL, ROBERT D., NEITHAMER, DAVID R.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1995
Main classification: C07F7
IPC codes: C07F17, C07F7, C25B3