Method for the reduction of metal halides

Abstract

The invention relates to a method for producing a compound of formula MX.sub.n from a precursor compound of formula MX.sub.m, where M is a metal, X is a halide selected from F, Cl, Br, J, m is a number selected from the range 2 to 8, and n is a number selected from the range 1 to 7, with the condition that n<m, comprising a method step in which the precursor compound is reduced with a silane compound to the compound of formula MX.sub.n.

Claims

1. A method for production of a compound of formula MX.sub.n comprising providing a precursor compound of formula MX.sub.m, wherein M is tungsten, X is a halide, selected from F, Cl, Br, I, m is 6, and n is 5, reducing the precursor compound with a silane compound to form a compound of formula MX.sub.n, and optionally, purifying the MX.sub.n compound via sublimation after the reducing step, wherein at least 10 kg of the precursor compound of formula MX.sub.m are used, wherein, after the reduction and/or after the sublimation, the metal halide of formula MX.sub.n is obtained in a yield of >90% relative to the molar quantity of precursor compound that was used, and wherein the reducing step is performed for a time period of 5 min to 60 min.

2. The method according to claim 1, wherein X=Cl.

3. The method according to claim 1, for the production of WCl.sub.5 from WCl.sub.6.

4. The method according to claim 1, wherein the silane compound selected from the group consisting of organosilanes, silanes, halosilanes, and organohalosilanes.

5. The method according to claim 1, wherein the silane compound is an organosilane that has at least one methyl group that is bound to a silicon atom.

6. The method according to claim 1, wherein the silane compound is an oligosilane or a disilane.

7. The method according to claim 1, wherein the reduction is performed in a solvent that has aromatic hydrocarbons.

8. The method according to claim 1, wherein the molar substance amount ratio of the precursor compound to the reducing agent is between 2:1 and 1:2 and/or wherein the reduction is performed at a temperature of 10° C. to 50° C.

9. The method according to claim 1, wherein the metal halide of formula MX.sub.n is purified via sublimation after the reduction.

10. The method according to claim 9, wherein the metal halide of formula MX.sub.n has a purity of greater than 99.9 wt. %.

Description

EXEMPLARY EMBODIMENT

(1) Chemicals

(2) The chemicals used in Examples 1 through 3 are compiled in Table 1.

(3) TABLE-US-00001 TABLE 1 Chemicals used in Examples 1 through 3 Total Molar mass Compound formula CAS Nr. Note g/mol Tungsten WCl.sub.6 13283-01-7 99.9% purity, store in glove box 396.61 hexachloride Hexamethyldisilane Si.sub.2C.sub.6H.sub.18 1450-14-2 99.5% purity (determined via GC), 146.38 (HMDSi) store via molecular sieve 4 Å Toluene C.sub.7H.sub.8 108-88-3 anhydrous, distilled via 92.14 Na/benzophenone, store via molecular sieve 4 Å and Al.sub.2O.sub.3 Pentane C.sub.5H.sub.12 anhydrous 72.15 Tungsten WCl.sub.5 13470-14-9 Reaction product 43.67 pentachloride
Thermogravimetry (TGA) with simultaneous differential thermoanalysis (SDTA)

(4) Thermogravimetric analyses (TGA), as well as the weigh-ins for them, took place under nitrogen atmosphere in a glove box with a device of make TGA 3+ (Manufacturer: Mettler Toledo; evaluation with software branded as Stare). For the measurement, approximately 6-12 mg of a sample were weighed in an aluminum oxide crucible. The TGA (mass loss) and SDTA (heat flow) curves were obtained as results. The first derivation (DTG curve, speed of the mass variation) was respectively calculated from the TGA curve. The heating rate was 10 K/min or 20 K/min.

Example 1

(5) Tungsten hexachloride was reduced with hexamethyldisilane (HMDSi) to tungsten pentachloride according to the following reaction equation. Chemicals and substance amounts as indicated in Table 2 were thereby used. The reaction time was 24 h.

(6) ##STR00001##

(7) TABLE-US-00002 TABLE 2 Chemicals and substance amounts according to Example 1 Initial Volumes Substance Equivalents Chemicals quantity (g) (mL) amount (mmol) (eq) WCl.sub.6 0.907 — 2.287 1.00 HMDSi 0.184 — 1.258 0.55 Toluene — 25 — —

(8) In a heated 250 mL Schlenk flask placed under nitrogen, WCl.sub.6 was weighed into a glove box. Outside of the glove box, toluene and, then, the hexamethyldisilane were added under N.sub.2 flow, and the tube was sealed tightly. It was stirred at room temperature.

(9) The created solid was subsequently filtered under nitrogen through a reversion frit (G4, ca. 10-16 μm pore diameter) and flushed again with dry toluene (2× with 10 mL), and, subsequently, was flushed with dry n-pentane (2× with 10 mL). Then, it was dried for several hours at room temperature and in fine vacuum (10.sup.−3 mbar). Storage took place in a glove box under nitrogen atmosphere.

(10) Approximately half of the product was weighed into a sublimation apparatus and sublimated for approximately 5 h at 160° C. oil bath temperature in fine vacuum (10.sup.−3 mbar). Violet crystals formed at the cooling finger.

Example 2

(11) Tungsten hexachloride was reduced with hexamethyldisilane to tungsten pentachloride, as described in Example 1, with the following modifications: The substance amounts according to Table 3 were used. The reaction time was 1 h.

(12) TABLE-US-00003 TABLE 3 Chemicals and substance amounts according to Example 2 Initial Volumes Substance Equivalents Chemicals quantity (g) (mL) amount (mmol) (eq) WCl.sub.6 16.089 — 40.566 1.00 HMDSi 2.850 — 19.472 0.48 Toluene — 100 — —

Example 3

(13) Tungsten hexachloride was reduced with hexamethyldisilane to tungsten pentachloride, as described in Example 1, with the following modifications: The substance amounts according to Table 4 were used. The reaction time was 20 h.

(14) TABLE-US-00004 TABLE 4 Chemicals and substance amounts according to Example 3 Initial Volumes Substance Equivalents Chemicals quantity (g) (mL) amount (mmol) (eq) WCl.sub.6 13.917 — 35.094 1.00 HMDSi 2.465 — 16.845 0.48 Toluene — 100 — —
Results:

(15) The yields of tungsten pentachloride before and after sublimation are compiled in Table 5.

(16) TABLE-US-00005 TABLE 5 Overview of the yields of tungsten pentachloride Total yield of raw product after Sublimate Sublimation Example Conditions precipitation (%) yield (%) residue (%) 1 0.55 eq, 24 h 77.7 —* —* 2 0.48 eq, 1 h 87.3 92.1 2.7 3 0.48 eq, 20 h 89.4 93.8 1.4 *Reaction on a small scale; therefore, no sublimation was initially performed.

(17) The missing percentages from the addition of “sublimate yield” and “residue” are possibly solvent residues that were not removed upon drying the raw product, and losses in the scraping of the sublimate from the sublimation tube.

(18) The results show that, with hexamethyldisilane as a reducing agent, the desired product may already be obtained at high yield and purity after a relatively short time (1 h). A nearly residue-free, sublimable raw product may be obtained after approximately 20 h. An over-reduction almost never occurs with use of stoichiometrically equivalent quantities (or a slight shortfall), with respect to the ratio of metal to Si.

(19) Product that has once sublimated sublimates completely in a second sublimation under vacuum, which means that no decomposition occurs under vacuum at high temperatures (up to at least 160° C.). With measurements of the thermal decomposition under normal pressure (nitrogen atmosphere, TGA measurement), a decomposition may be detected at different heating rates (=“residence times”). This is apparent from the mass loss in the TGA measurement. An increase in the heating rate in the TGA measurement promotes the complete mass loss of the product.

Example 4: Implementation on a Large Scale

(20) Tungsten hexachloride was reduced with hexamethyldisilane to tungsten pentachloride. Chemicals according to Table 1 were thereby used, wherein HMDSi and solvent, obtained in high-purity form as from the manufacturer, were used. 66 L toluene are placed in a 100 L reactor rendered inert with nitrogen. 19.0 kg (47.86 mol, 2.03 eq.) tungsten hexachloride are added while stirring at 100 R/min and subsequently washed with 10 L toluene. The flow temperature is set to 30° C. 3.47 kg (23.56 mol, 1 eq) hexamethyldisilane are dosed in within 1 h and subsequently washed with 5 L toluene. Subsequent stirring takes place for 1 hour at 100 R/min and a flow temperature of 20° C.

(21) The reaction mixture is filtered, and the filter cake is displacement washed with 10 L toluene. The filter cake is subsequently washed three times—each time with 10 L pentane. The product is dried in a vacuum at 40° C. The yield was 16.2 kg (94%, relative to WCl.sub.6).

(22) The result shows that the reaction can be scaled up without significant loss of yield and product quality, wherein chemicals that are typically readily available may be used. These advantages are highly significant in industrial production.

Example 5: Reduction of FeBr.SUB.3 .and CuBr.SUB.2

(23) FeBr.sub.3 and CuBr.sub.2 were reduced with HMDSi (hexamethyldisilane, (CH3).sub.6Si.sub.2) to the respective next lowest stable oxidation number.

(24) General Experimental Procedure

(25) 0.2 g FeBr.sub.3 were weighed into a heated Schlenk flask under inert gas atmosphere. 3 mL HMDSi were added under nitrogen flow. It was briefly heated to boiling and was subsequently stirred for 8 hours at 70° C.

(26) Although, with CuBr.sub.2, the process proceeds analogously, deviating from the method with FeBr.sub.3, it was filled up under air and subsequently evacuated, and was not warmed.

(27) With iron bromide, a discoloration of the yellow-brown fluid occurred after the warming. After warming to 70° C. for eight hours, solution and solid have a yellow color. With copper bromide, a discoloration already took place after a few minutes at room temperature, such that a warming was omitted.

(28) The created solids were then filtered at room temperature through a G4 filter frit under nitrogen atmosphere. Drying subsequently took place in fine vacuum (10.sup.−3 mbar) at room temperature for several hours, and the samples were kept under inert gas.

(29) Using micro-X-ray fluorescence spectroscopy (μRFA, Bruker Tornado M4 with rhodium and tungsten x-ray tubes, two silicon drift detectors), it was established that FeBr.sub.2 and CuBr were obtained as reaction products.

Example 6: Reduction of WCl.SUB.5 .and TaCl.SUB.4 .in Dichloromethane as a Solvent

(30) The metal halides (MH) were weighed into an inert gas atmosphere (glove box) in Schlenk flasks and filled outside the glove box with approx. 40 mL dried dichlormethane. The calculated amount of silane was added in a stream of nitrogen while stirring. The input weight (EW) and yields (AW) per test are documented in Table 6.

(31) The processing took place at room temperature after 24 h of stirring, by filtration under inert gas using a G4 frit. The precipitate was washed with dry hexane and dried under vacuum (10.sup.−3 mbar) at room temperature. The products were stored in the glove box until further use.

(32) TABLE-US-00006 TABLE 6 Input and output weights of the tests in methylene chloride AW Equivalents EW MH EW silane product AW No. Reaction (silane) Silane g (mmol) g (mmol) g % 1 WCl.sub.6 −> WCl.sub.5 0.48 HMDSi 0.952 (2.40) 0 169 (1.15) 0.659 76.0 2 WCl.sub.6 −> WCl.sub.5 0.48 TESi 0.870 (2.19) 0.122 (1.05) 0.299 37.8 3 WCl.sub.6 −> WCl.sub.5 1 TESi 0.990 (2.50) 0.290 (2.50) 0.630 69.8 4 WCl.sub.6 −> WCl.sub.5 1 DMCSi 0.995 (2.51) 0.240 (2.53) 0.754 83 2 5 TaCl.sub.5 −> TaCl.sub.4 0.48 TESi 0.917 (2.56) 0.143 (1.23) 0.563 68.2 Annotations: EW—input weight, AW—output weight, MH—metal halide, HMDSi—hexamethyldisilane, TESi—triethylsilane (Et.sub.3SiH), DMCSi—dimethylchlorosilane (Me.sub.2SiHCl)

(33) Observations:

(34) Test 1: In the filtration, a portion of the product passed through the frit, such that the output weight initially appeared to be lower; after separation of this precipitate, the total yield of >90% was determined.

(35) Test 2: Gas development, reaction slow.

(36) Test 4: Reaction slow, concluded only after 24 h.

(37) The identification of the reaction products was performed via x-ray diffractometry of the powders obtained as a product, and confirmed that WCl.sub.5 or TaCl.sub.4 were obtained as reaction products.