FR2681866A1 - Process for the synthesis of organosilicon compounds and organosilicon compounds - Google Patents

Abstract

The subject of the present invention is a new process for the synthesis of organosilicon compounds and the latter. This synthetic process is characterised in that a halogenated aryl substrate, preferably polyhalogenated or fluorinated, is electrolysed at a consumable (or soluble) metal anode(s) consisting of an anodic metal in an aprotic medium containing: a) a support electrolyte (nature immaterial), advantageously at a concentration of the order of 1 to 5% (mol) with respect to the halogenated substrate when a solvent is present and 0.0001 to 0.01% when electrolysis is carried out without solvent; b) optionally a complexing agent; c) a silicon compound of formula: R'3R'2R'1SiY (II) where R'3, R' 2 and R'1 represent hydrocarbon chains, advantageously of C1 to C10, preferably of C1 to C6, heavy halogens, preferably chlorine. Application to organic synthesis.

Description

PROCESS FOR THE SYNTHESIS OF ORGANOSILICIES AND ORGANOSILICIAL COMPOUNDS
The present invention relates to a novel process for the synthesis of organosilicon compounds, more specifically fluorinated aryl compounds. It also relates to the synthesis of compounds which until now could not have been obtained by conventional techniques.

 For the synthesis of organosilicon compounds of the arylsilane type, two main methods are known apart from direct synthesis: the first is to form carbanions which are then reacted with halogenated derivatives of the chlorosilane type. This technique has many disadvantages. It gives good results in some cases, with alkali metals (mainly lithium) which are both expensive and difficult to handle, but the method is not general especially with polyhalogenated derivatives. In addition, it is often necessary to use excess over stoichiometry, which increases the amount of metals and rejects to be treated.

The method is also usable, in some cases, with magnesium but here again it has many drawbacks (use of solvents very strongly electron donors such as hexamethylphosphorotriamide with polychlorarines, existence of side reactions).

 In addition, this technique requires, for yields to be suitable, the use of metals which must have a very high surface area morphology.

 The other method developed is the use of disilanes which are reacted with a halogenated aryl derivative in the presence of a catalyst, generally consisting of a complex of palladium, at high temperature (160 ° C.) in a solvent. reputedly toxic, HMPT.

 These two techniques have the disadvantage in common of being relatively selective when several halogens are substitutable with silicon groups.

 This problem is even more acute when there are fluorine atoms in the molecule, for example in the benzyl position. This is why one of the aims of the present invention is to provide a method which overcomes the disadvantages mentioned above.

 Another object of the present invention is to provide compounds which can not be produced by conventional techniques in the field.

où R'3, R'2, R'i représentent des chaînes hydrocarbonées, avantageusement de C1 à C1o, de préférence de C1 à C6, des halogènes lourds, de préférence le chlore.These and other objects, which will appear later, are achieved by means of an electrolytic process useful for the synthesis of silicon derivatives, characterized in that a halogenated aryl substrate, preferably polyhalogenated or fluorinated, is subjected to to an electrolysis with anode (s) consumable metal (s) (or soluble) constituted (s) of anodic metal in an aprotic medium containing a) a support electrolyte (said indifferent), preferably at a concentration of the order of 1 to 5% (mol) relative to the halogenated substrate when there is a solvent and 0.0001 to 0.01% when operating without solvent b) optionally a complexing agent c) a compound Silicon formula

wherein R'3, R'2, R'i represent hydrocarbon chains, preferably C1 to C1o, preferably C1 to C6, heavy halogens, preferably chlorine.

 Advantageously R'3, R'2, R'1 are most often at least one, preferably at least 2 hydrocarbon chains. When using halosilanes which are readily reducible (potential) of reduction below 2.5 V in absolute value, such as those having less than 3 hydrocarbon chains, or having aromatic groups, a catalyst should be provided, for example a elemental nickel complex (O).

The halogenated substrate to be silylated advantageously has the formula
Ar [C ((R1) 3-pHp)] nXm (I) with the exception of monochlorotoluene
where Ar is a homo- or hetero-aromatic radical, mono- or
polycyclic
where p = 0, 1, 2, 3
where n is an integer at most equal to the number of free vertices,
preferably at 0, 1, 2, 3 when Ar is monocyclic
where m is an integer less than or equal to 6, with m + na 6
with benzene but m, and a fortiori mtn being able to be superior
in the case of polyaromatic derivatives
- where groups X, similar or different, represent a
heavy halogen (Cl, Br, I), preferably chlorine
where the groups R 1, which are similar or different, represent a
hydrocarbon chain, preferably C1 to Ciao, preferably
from C1 to C6, a hydrogen or a halogen, preferably a fluorine
Thus, according to the present invention, using a technique based on electrosynthesis, it has been shown that one could carry out very selective silylations; it is thus possible to replace one halogen selectively with respect to another, whether it is different, or that it is similar, but then of a different environment. Said technique preferably uses constant intensity electrolysis, without diaphragm with consumable anode.

 It made it possible to carry out silylations of fluorobenzene to initially give a disilylated diene derivative which, after rearrangement, gives the silylated fluorobenzene at the 2- and 5-positions.

 The reaction can take place in the presence or absence of solvent.

When a solvent is used (in the remainder of the present description solvent refers to both a pure compound and a mixture), it is appropriate to choose a solvent which has a field of electrical inactivity between the oxidation potential of the anode and about -3 volts.

If solvents are used, it is preferable that they are aprotic (to avoid protonation) and polar, such as, alone or as a mixture, oxygenated solvents, in particular ethers, preferably polyethers such as dimethoxy-1, 2 ethane or cyclic ethers such as
THF; amides or ureas (DMF, N-methylpyrrolidone-2, imidazolidone, tetramethylurea, dimethoxypropylene urea, etc.), sulfones or sulfoxides and, insofar as they are liquid under the operating conditions, complexing agents (crown ethers, HMPT, tris (3,6-dioxa-heptyl) amine (TDA-1)) that improve the smooth running of the reaction by increasing the conductivity, increasing the reactivity of the anion, preventing metal deposition at the cathode.

Without this explanation being limiting, it seems that these phenomena are correlated with the ability to complex metal cations, alone or in mixture (s).

 The solvents used can themselves act as complexing agents.

 The electrolysis can also be carried out in environments where no solvents are used, provided electrolytes are used which, alone or in the presence of conductivity aids, are soluble therein.

 To facilitate the separation of the products from the reaction media, it is preferable that said solvent has a boiling point substantially different from the compound to be synthesized and the starting compound.

 The electrolyte, optionally modified by the presence of complexing agent, is chosen so as not to disturb the reactions at the anode and at the cathode.

 The electrolyte may be chosen to have as cations those corresponding to the metals of the anode.

 The electrolyte may be chosen so as to have as cation metals with high carrier capacity such as the divalent, advantageously trivalent aluminum type. Metals having, in addition to the zero degree, only one degree of oxidation are preferred.

 The electrolyte may be chosen so that its cations are directly soluble in the reaction medium. Thus, when the medium is slightly polar, rather than making the metal cations soluble by means of adjuvant (s), it may be advantageous to use stable "oniums" in the field of electrical inactivity.

 Onium is understood to mean the organic compounds which in the name assigned to them by the nomenclature include an affix, generally suffix, "onium".

The most used are tetraalkylammoniums. Alkyl groups, taken in the etymological sense, generally have 1 to 12 carbon atoms, preferably 1 to 4 carbon atoms; it is also possible to use phase transfer agents.

 The anions may be anions customary for indifferent electrolytes, but it is preferable that they be chosen from those released by the reaction, essentially halides, or, for example, complex anions of the BF 4 -, PF 6 -, Cl 4 type. -.

 The complexing agents, adjuvants of conductivity, are chosen from known compounds for solvating the cations at least partly comprising the electrolyte and / or those which correspond to the metals of the anode. They can play an important role by increasing the field of inactivity of the cation, especially when the adjuvant is a very complexing agent such as crown ethers; in addition to these and the complexing agents capable of acting as solvent "lato sensu" as indicated above, we can cite as examples (or more exactly as paradigms), the derivatives whose preparation is described in the patent published under No. FR-A 2,450,120, those described in the titles published under numbers FR-A 2,026,481 and 2,052,947 and in a general manner the compounds known by the term "encryptors".

 Said anodic metal is advantageously chosen so that the chemical species it releases, possibly modified by the presence of adjuvant (s), does not disturb the reactions at the anode and the cathode.

 Said anode metal is advantageously chosen from aluminum, zinc, magnesium, silver, iron, cobalt, nickel, mercury, copper, alkaline earth metals or their alloys.

In the case of easily reducible metal salts, a complexing agent should be added to make their reduction potential more cathodic.

 The cathode is preferably inert under the conditions of the experiment; it is advantageously made of material selected from those containing the metals of the platinum group, among the glassy carbon and so-called stainless steels, this list not being limiting.

 However, the cathode can also in many cases be made of the same metal as the anode, which facilitates the periodic reversal of polarity, which is used to prevent or prevent passivation.

This technique made it possible to prepare derivatives that could not be accessed by the other methods: PhCF2SiMe3, PhCF (SiMe3) 2,
O-F3C-C6H4-SiMe3 which could not be prepared even by the disilane route, but this list is obviously not limiting.

Note that o, m, p, F3C-C6H4Li are very dangerous (risk of explosion), as well as the corresponding magnesians except p-F3C-C6H4-MgX, which seems more stable.

The subject of the present invention is also new silyl compounds corresponding to the formula
Ar [C ((R1) 3-p 'Hp Zp)] nXmtZm "(III) - where Ar is a homo- or hetero-mono- or polycyclic aromatic residue - where p = 0, 1, 2, 3 - where p "= 0, 1, 2, 3 - where n is an integer equal to 0, 1, 2, 3 - where m 'is an integer equal to 0, 1, 2, 3; where m "is an integer equal to 0, 1, 2, 3 - where m '+ m" = m is an integer less than or equal to 6, with m + n <6 - where X = Cl, Br, I.

where Z represents

where R'3, R'2, R'1 represent hydrocarbon chains,
preferably from C1 to C10, preferably from C1 to C6, halogens
heavy, preferably chlorine - where R1 represents a hydrocarbon chain, preferably C1 to C10, preferably C1 to C6, hydrogen or fluorine with 4> p + p "> 0
The techniques described above can be used to make the disilyl addition derivatives on aryl ethers, generally alkoxybenzenes, see the example on anisole.

Good results are obtained by working without solvent or with salts allowing to descend very low in potential such as the ammoniums associated with the anion phosphorus hexafluoride. Aryl ethers react more easily, but in an equivalent manner to the fluorobenzene-type fluorinated aryl derivatives.

 The following nonlimiting examples illustrate the invention.

Example 1
The single compartment cell, equipped with five tubes, is equipped with a consumable anode (aluminum bar), a cylindrical cathode made of stainless steel mesh (30 cm2 surface) or glassy carbon fabric and magnetic stirring; it is constantly maintained under a light sweep of dry inert gas (argon or nitrogen).

The solvent and the complexing agent are preliminarily purified and dried by conventional chemical means: THF over Na / benzophenone, HMPT over CaH 2, before distillation in both cases.

Prior to the introduction of the halogenated derivative, the medium is treated in the following manner: 40 ml of solvent, 7 ml of HMPT, 0.02 mmol.ll of carrier electrolyte (NBu4Br), 22 ml (172 mmol) of Trimethylchlorosilane (freshly distilled over magnesium and used in excess) is placed in the cell and then degassed with ultrasound for 20 minutes.

Pre-electrolysis (0.5 h to 100 m A) is then performed to remove the hydrogen chloride formed by reaction of trimethylchlorosilane with residual water traces. The formation of Me6Si20, not electroactive, in the solution, does not disturb the electrolysis.

At the end of the pre-electrolysis, 33 mmol of accurately weighed trifluoromethylbenzene are introduced by means of a syringe into the cell. A constant intensity of 100 mA is applied by means of a stabilized and regulated supply for 19.5 h until there has been 2.2 F per mole of PhCF3.

After the electrolysis, the crude medium is transferred by cannula under argon into a 150 ml flask. The cell is rinsed with 3 times 40 ml of dry pentane. The partially precipitated salts (due to residual solubility in THF) are decanted at the bottom of the cell.

After removal of the volatile products (pentane, excess chlorosilane and a part of Me6Si20) with the water pump, the residual salts end up precipitating. A 40 ml addition of dry pentane makes it possible to decant them completely. The pentane is then evaporated under vacuum and the product distilled. 4.62 g of pure PhCF 2 SiMe 3 are obtained (bp = 95% under 40 mm).
Hg, Yield: 70%) identified by 1H NMR, 13c, 29Si, IR and mass spectrometry, as well as by elemental analysis.

Study of the selectivity of the monosilylation of benzene polychiorides by electrosynthesis with consumable anode: numerous tests on the electrosilylation of polyhalides including benzene polychlorides by the method of the consumable anode, constant current and without diaphragm showed that these reactions seemed to meet the rules Empirical studies: 1 ") that electrosynthesis was feasible even without solvent, 2") that monosilylation was always selective for disilylation, 3) that the regioselectivity of monosilylation was generally good when at least 2 non-equivalent chlorines were present.

Example No. 2
A - In solution in THF. Experimental conditions - single compartment cell of 100 cm3, - intensity: 100 mA; current density: 0.1-0.4 A / dm 2 - solvent: THF, 40 ml - co-solvent: HMPT, 8 ml - carrier electrolyte: Bu4NBr 100 mg approximately - substrate: ex. C6H4Cl2: 3g or 2.3 ml - reagent: Me3SiCl, 20 ml - molar ratio (reagent / substrate) = 7 - amount of current: 2.2 F / mol - aluminum anode (bar diameter: 1 cm, length: 8 cm ) - cathode: cylindrical stainless steel cloth.

o-trimethylsilylchlorobenzène
Rdt = 98% (isolé 95%) à comparer avec la voie chimique (31%) F.EFFENBERGER et D. HABICH Liebigs
Ann. Chem., 1979, 842. Me3Si Cl o-dichlorobenzene

o trimethylsilylchlorobenzène
Yield = 98% (isolated 95%) compared with the chemical route (31%) F.EFFENBERGER and D. HABICH Liebigs
Ann. Chem., 1979, 842.

dichlorotriméthylsilylbenzènes
Rdt = 90% répartition : 2,5 : 82 % ; 3,4 : 9%; 2,4 : 9 % (les 2 chiffres indiquent la place des deux atomes de chlore, le groupe Me3Si étant en 1.) Me3SiC1 tétrachloro -1,2,4,5 benzène

trichloro-2,4,5 triméthylsilylbenzène
Rdt = 78% à comparer avec la voie chimique (rendement 4 20 % J. DUNOGUES, travaux non publiés).Me3SiCl 1,2,4-trichlorobenzene

dichlorotriméthylsilylbenzènes
Yield = 90% distribution: 2.5: 82%; 3.4: 9%; 2.4: 9% (the 2 digits indicate the position of the two chlorine atoms, the Me3Si group being in 1.) Me3SiC1 tetrachloro -1,2,4,5 benzene

2,4,5-trichloro-trimethylsilylbenzene
Yield = 78% compared with the chemical route (yield 4 20% J. DUNOGUES, unpublished work).

pentachlorotriméthylsilylbenzène
Rdt = 90%
B - Sans solvant . Conditions expérimentales - cellule à compartiment unique de 100 cm3 - intensité : 100 mA ; densité de courant : 0,1-0,4 A/dm2 - quantité de courant non optimisée correspondant à un taux de transformation du substrat de 35 % - anode aluminium ou magnésium (barreau diamètre : lcm, longueur : 8 cm) - co-solvant : HMPT, 8 ml - électrolyte support : Bu4NBr 100 mg environ - substrat : ex. C6H4Cl2 : 26g soit 20 ml - réactif ; Me3SiCl , 40 ml - cathode : toile cylindrique d'acier inox.MerSiCl hexachlorobenzene

pentachlorotriméthylsilylbenzène
Yield = 90%
B - Without solvent. Experimental conditions - 100 cm3 single compartment cell - intensity: 100 mA; current density: 0.1-0.4 A / dm2 - amount of non-optimized current corresponding to a 35% conversion rate of the substrate - aluminum or magnesium anode (bar diameter: 1 cm, length: 8 cm) - co- solvent: HMPT, 8 ml - carrier electrolyte: Bu4NBr 100 mg approximately - substrate: ex. C6H4Cl2: 26g, ie 20 ml - reagent; Me3SiCl, 40 ml - cathode: stainless steel cylindrical cloth.

o-trimethyl si lyl chl orobenzène
Rdt = 94% à comparer avec la voie chimique (31%) F.EFFENBERGER et D. HRBICH Liebigs
Ann. Chem., 1979, 842.Assays are performed by gas chromatography (GC)
Me3SiCl o-dichlorobenzene

o-trimethyl if lyl chl orobenzene
Yield = 94% compared with the chemical route (31%) F.EFFENBERGER and D. HRBICH Liebigs
Ann. Chem., 1979, 842.

m-triméthylsilylchlorobenzène
Rdt = 73%
Lorsqu'on opère sans solvant, les rendements indiqués sont des rendements faradiques cathodiques, c'est-à-dire par rapport à la quantité d'électricité engagée.Me3Si Cl m-dichlorobenzene

m-triméthylsilylchlorobenzène
Yield = 73%
When operating without a solvent, the yields indicated are faradic cathodic yields, that is to say with respect to the quantity of electricity engaged.

Example N- 3
1 - Case of anisole
Work done at the Laboratory has shown that compound 5, obtained from anisole, could be a particularly interesting intermediate for the synthesis of ketoprofen (powerful analgesic)

Unfortunately, the use of lithium in this step was too expensive for the method to be competitive. So we tried the electro-chemical way to get this compound.

After numerous negative tests with various support electrolytes, the disilicinated cyclohexadiene of anisole could be obtained in the mixture
THF / HMPT in the presence of NBu4PF6 (electrodes: Al / stainless) with a yield of 70%.

Table No. 5: Experimental conditions of negative tests.

<Tb>

<SEP> TESTS <SEP> NEGATIVE
<tb> Solvents <SEP> I <SEP> Electrode <SEP> I <SEP><SEP> Electrolytes <SEP> supports <SEP>
<tb> i <SEP> THF-TDA-i <SEP><SEP> Al / C <SEP> i <SEP> NEt4BF4 <SEP> i
<tb><SEP> THF-HMPT <SEP> THE-HMPT <SEP> Al / C <SEP> J <SEP><SEP> NEt4BF4 <SEP> i
<tb> THF-HMPT <SEP> Al / C <SEP> J <SEP><SEP> NBu4Br <SEP> I
<tb> THF-HMPT <SEP> Mg / stainless steel <SEP> NBU4Br
<Tb>
The difficulties encountered in obtaining this diene under the usual conditions of synthesis led to attempt electrolyses without solvent.

Under these conditions, the diene 5 could be synthesized with a faradic cathodic efficiency of the order of 70%:
Experimental conditions:
Al / stainless steel
Anisole: 20 ml Me3SiCl: 40 ml
HMPT: 10 ml

<tb><SEP> QMe <SEP> OMe
<tb><<SEP><<SEP> SiMe3 <SEP> 70 <SEP>%
<tb><SEP> Me3SiC1-HMPT, <SEP> ss
<tb><SEP> Al / stainless steel
<tb><SEP> Me3Si
<Tb>
95% non-insulated chemical yield
The NMR spectra are in agreement with those obtained in the laboratory by chemical means.

Claims (6)

1). Electrolytic process useful for the synthesis of silicon derivatives, characterized in that a halogenated, preferably polyhalogenated or fluorinated aryl substrate is subjected to an electrolysis with anode (s) which is consumable (or s)) constituted of an anode metal in an aprotic medium containing a) a supporting electrolyte (said indifferent), advantageously at a concentration of about 1 to 5% (mol) relative to the halogenated substrate when there is a solvent and 0.0001 to 0.01% when operating without solvent b) optionally a complexing agent; c) a silicon compound of formula

 where R'3, R'2, R'1 represent hydrocarbon chains, preferably C1 to C10, preferably C1 to C6, heavy halogens, preferably chlorine. 2). Process according to Claim 1, characterized in that said halogenated silyl substrate advantageously has the formula  Ar [C ((R 1) 3-p Hp)] nXm (I)  where Ar is a homo- or hetero-aromatic radical, mono- or  polycyclic  where p = 0, 1, 2, 3  where n is an integer equal to 0, 1, 2, 3  where m is an integer less than or equal to 6, with m + n <6 with  benzene but m, and a fortiori m + n can be higher in the case  polyaromatic derivatives  - where groups X, similar or different, represent a  heavy halogen (Cl, Br, I), preferably chlorine  where the groups R1, which are similar or different, represent a  hydrocarbon chain, advantageously from C1 to C10, preferably  from C1 to C6, a hydrogen or a halogen, preferably a fluorine 3) .A method according to claims 1 and 2 characterized in that said solvent has a boiling point substantially different from the compound to be synthesized. 4). Process according to one of Claims 1 to 3, characterized in that the said solvent is an oxygenated solvent chosen from ethers, amides, including ureas, phosphorotriamides, sulphones and sulphoxides, and mixtures thereof. 5). Process according to one of Claims 1 to 4, characterized in that the conductivity additives are chosen from compounds known to solvate the constituent cations of the electrolyte and / or corresponding to the metals of the anode. 6). Process according to one of Claims 1 to 5, characterized in that the electrolyte is chosen in such a way as to have as cation those corresponding to the metals of the anode. 7). Process according to one of Claims 1 to 6, characterized in that the anion of the electrolyte is the chloride ion or a mixture of anions containing it. 8) Method according to one of claims 1 to 7 characterized in that the constituent metal of the cathode is selected from platinum group metals, glassy carbon and stainless steels 9) Compounds of formula  Ar [C ((R1) 3-pp "Hp Zp)] nXmtZm" (III) - where Ar is a homo- or hetero-mono- or polycyclic aromatic residue - where p = 0, 1, 2, 3 - where p "= 0, 1, 2, 3 - where n is an integer equal to 0, 1, 2,3 - where m 'is an integer equal to 0, 1, 2, 3 - where m" is an integer equal to 0, 1, 2, 3 - where m '+ m "= m is an integer less than or equal to 6, with m + n 46 - where X = Cl, Br, I. where Z represents

 where R'3, R'2, R'1 represent hydrocarbon chains, preferably C1 to C10, preferably C1 to C6, heavy halogens, preferably chlorine. - where R1 represents a hydrocarbon chain, preferably C1 to C10, preferably C1 to C6, a hydrogen or a fluorine with 4> p + p "> 0 10) compound according to claim 9 characterized in that p" = 1 or 2.