METHOD FOR PRODUCING SALTS HAVING HYDRIDOCYANOBORATE ANIONS

Abstract

The invention relates to a method for producing alkali metal salts having monohydrido-tricyanoborate anions from alkali metal monofluorotricyanoborates, and to a method for producing alkali metal salts having dihydrido-dicyanoborate anions from alkali metal difluorodicyanoborates.

Description

The invention relates to a process for the preparation of alkali metal salts having monohydridotricyanoborate anions from alkali metal monofluorotricyanoborates, and to a process for the preparation of alkali metal salts having dihydridodicyanoborate anions from alkali metal difluorodicyanoborates.

Alkali metal salts having monohydridotricyanoborate anions are known from published specification WO 2012/163489 and serve, for example, as starting materials for the synthesis of monohydridotricyanoborate salts having preferably organic cations. Ionic liquids of this type having monohydrido-tricyanoborate anions are suitable, for example, as electrolyte component for electrochemical cells, in particular for dye solar cells. WO 2012/163489 also describes the synthesis of these alkali metal salts, for example by the processes of Claims 4 to 6.

In these processes, the starting materials employed are either alkali metal tetracyanoborates or alkali metal tetrahydridoborates.

B. Györi et al, Journal of Organometallic Chemistry, 255, 1983, 17-28, describe, for example, the isomerisation of sodium triisocyanohydridoborate (adduct with 0.5 mol of dioxane) to sodium monohydridotricyanoborate in boiling n-dibutyl ether.

Alkali metal salts having dihydridodicyanoborate anions are known from published specifications WO 2012/163490 and WO 2012/163488 and likewise serve as starting materials for the synthesis of dihydridodicyanoborate salts having preferably organic cations, which are suitable, for example, for use as electrolyte component in electrochemical cells, in particular dye solar cells.

WO 2012/163488 describes processes for the preparation of alkali-metal diydridodicyanoborates, in which either an alkali metal tetrahydridoborate or an alkali metal trihydridocyanoborate are used as starting materials.

A synthesis of lithium [BH₂(CN)₂] is known, for example, from B. Györi et al, Journal of Organometallic Chemistry, 1983, 255, 17-28, where oligomeric 1/n (BH₂CN)_n is reacted with LiCN*CH₃CN in dimethyl sulfide.

A synthesis of sodium [BH₂(CN)₂] is known, for example, from B. F. Spielvogel et al, Inorg. Chem. 1984, 23, 3262-3265, where a complex of anilline with BH₂CN is reacted with sodium cyanide. Tetrahydrofuran is described as solvent. P. G. Egan et al., Inorg. Chem. 1984, 23, 2203-2204, also describe the synthesis of the dioxane complex Na[BH₂(CN)₂]*0.65(dioxane) based on the papers by Spielvogel et al. using another work-up variant.

Y. Zhang and J. M. Shreeve, Angew. Chem. 2011, 123, 965-967, describe, for example, the use of Ag[BH₂(CN)₂] for the preparation of ionic liquids having the dihydridodicyanoborate anion.

However, there continues to be a need for economical alternative synthetic methods for the preparation of alkali metal monohydridotricyanoborates or alkali metal dicyanodihydridoborates.

The object of the present invention is therefore to develop alternative preparation processes which start from readily accessible and comparatively cheaper starting materials. In particular, this need is for the synthesis of alkali metal monohydridotricyanoborates.

Surprisingly, it has been found that alkali metal monofluorotricyanoborates are excellent starting materials for the synthesis of the desired monohydridotricyanoborates, which are readily accessible.

Surprisingly, it has been found that alkali metal difluorodicyanoborates are excellent starting materials for the synthesis of the desired dihydridodicyanoborates, which are readily accessible.

This finding is surprising and unforeseeable, since boranes are generally strong acceptors for fluoride and the B—F bond formed is generally stronger than a B—H bond. N. N. Greenwood and A. Earnshaw, Chemistry of the Elements, Elsevier Science Ltd., 1997, indicate the bond energy E_(B—F) as 646 kJ/mol, whereas the bond energy E_(B—H is described as 381 kJ/mol.

The invention therefore relates to a process for the preparation of compounds of the formula I

[Me]⁺[BH_n(CN)_4-nn]⁻  I,

where
Me denotes an alkali metal and
n denotes 1 or 2,
by reaction of a compound of the formula II

[Me¹]⁺[BF_n(CN)_4-n]⁻  II,

where Me¹ denotes an alkali metal, which may be identical to or different from Me, and
n denotes 1 or 2, where n is identical in formula I and formula II, with either

• a) an alkali metal or alkaline-earth metal Me², where an alkali metal Me² may be identical to or different from Me or Me¹;
  • or a metal alloy Me²/Me or Me²/Me¹, where, in the case where Me² is an alkali metal, this alkali metal Me² is different from Me or Me¹; in an inert-gas atmosphere and
  • in the presence of a medium which is either capable of generating and/or stabilising solvated electrons or is capable of forming an anion free radical, if necessary with addition of a proton source, and
  • a metal cation exchange in the case where neither Me² nor Me¹ corresponds to Me,
  • or
• b) an alkali metal hydride of the formula III

Me³H  III

• • in an inert-gas atmosphere,
  • where Me³ may be identical to or different from Me or Me¹, without or in the presence of an F⁻-affinitive electrophilic reagent, and subsequent metal cation exchange in the case where neither Me³ nor Me¹ corresponds to Me.

The process according to the invention takes place in an inert-gas atmosphere, where the inert gases are preferably nitrogen or argon.

Alkali metals are the metals lithium, sodium, potassium, caesium or rubidium. Preferred alkaline-earth metals are calcium or barium.

In compounds of the formula I, Me is preferably sodium or potassium, particularly preferably potassium.

Accordingly, the process according to the invention is preferably suitable for the synthesis of sodium monohydridotricyanoborate or potassium monohydrido-tricyanoborate and for sodium dihydridodicyanoborate or potassium dihydridodicyanoborate.

The compounds of the formula II are commercially available or accessible by known synthetic processes. In the compounds of the formula II, Me¹ can be an alkali metal selected from the group lithium, sodium, potassium, caesium or rubidium, which is selected independently of the alkali metal of the end product of the formula I. Me¹ in formula II may be identical to or different from Me in formula I.

In compounds of the formula II, Me¹ is preferably sodium or potassium.

The preparation of the compounds of the formula II, as described above or as preferably described, can be carried out, for example, by reaction of an alkali metal cyanide with boron trifluoride etherate, as described in WO 2004/072089.

Alternatively, the compounds of the formula II in which n denotes 1 or 2 can be prepared by reaction of an alkali metal tetrafluoroborate with a trialkylsilyl cyanide. The reaction of a tetrafluoroborate with trimethylsilyl cyanide is described, for example, in B. H. Hamilton et al., Chem. Commun., 2002, 842-843 or in E. Bernhardt et al., Z. Anorg. Allg. Chem. 2003, 629, 677-685.

Trialkylsilyl cyanides are commercially available or are accessible by known synthetic processes.

The alkyl groups of the trialkylsilyl cyanide may be identical or different. The alkyl groups of the trialkylsilyl cyanide have 1 to 10 C atoms, preferably 1 to 8 C atoms, particularly preferably 1 to 4 C atoms. The alkyl groups of the trialkylsilyl cyanide are preferably identical in the case of alkyl groups having 1 to 4 C atoms. An alkyl group of the trialkylsilyl cyanide is preferably different if it is an alkyl group of 5 to 10 C atoms or of 5 to 8 C atoms. Suitable examples of trialkylsilyl cyanides are trimethylsilyl cyanide, triethylsilyl cyanide, triisopropylsilyl cyanide, tripropylsilyl cyanide, octyldimethylsilyl cyanide, butyldimethylsilyl cyanide, t-butyldimethylsilyl cyanide or tributylsilyl cyanide.

Particular preference is given to the use of trimethylsilyl cyanide, which is commercially available or can also be prepared in situ.

The trialkylsilyl cyanide can also be prepared in situ for the preparation of the compounds of the formula II. Many preparation methods have been described for the synthesis of trialkylsilyl cyanide.

Trialkylsilyl cyanide can be prepared, for example, from an alkali metal cyanide and a trialkylsilyl chloride. EP 76413 describes that this reaction was carried out in the presence of an alkali metal iodide and in the presence of N-methylpyrrolidone.

EP 40356 describes that this reaction was carried out in the presence of a heavy-metal cyanide.

WO 2008/102661 describes that this reaction was carried out in the presence of iodine and zinc iodide.

WO 2011/085966 describes that this reaction can be carried out in the presence of an alkali metal iodide or fluoride and optionally iodine. Preference is given here to the use of sodium cyanide and sodium iodide or potassium cyanide and potassium iodide, where the alkali metal iodide is preferably added in a molar amount of 0.1 mol, based on 1 mol of alkali metal cyanide and trialkylsilyl chloride. In general, this process for the preparation is based on the description by M. T. Reetz, I. Chatziiosifidis, Synthesis, 1982, p. 330; J. K. Rasmussen, S. M. Heilmann and L. R. Krepski, The Chemistry of Cyanotrimethylsilane in G. L. Larson (Ed.) “Advances in Silicon Chemistry”, Vol. 1, p. 65-187, JAI Press Inc., 1991 or WO 2008/102661.

The in-situ generation of trialkylsilyl cyanide for the synthesis of the compounds of the formula II is preferably carried out in accordance with the reaction conditions which are indicated in WO 2011/085966.

Working examples of the synthesis of representative compounds of the formula II are indicated in the example part.

Irrespective of which embodiment of process variant a) or b) of the process according to the invention is selected, it is preferred if the reaction of the reactants is followed by a purification step in order to separate the end product of the formula I, as described above, off from by-products or reaction products.

Suitable purification steps include the separation of readily volatile components by distillation or condensation, extraction with an organic solvent or a combination of these methods. Any known separation method can be used for this purpose or combined.

The invention therefore furthermore relates to the process according to the invention, as described above, where the reaction according to process variant a) or b) is followed by a purification step.

Should a metal cation exchange be necessary after the reaction of the compound of the formula II with the reactants indicated, as described above and below, has taken place, since the corresponding alkali metal cation Me for the target product of the formula I is not yet present in the reaction mixture, it is preferred in an embodiment of the invention if the metal cation exchange takes place during the purification step.

The metal cation exchange is preferably an alkali metal cation exchange.

A preferred method for the metal cation exchange or preferably the alkali metal cation exchange is, for example, the reaction of the reaction mixture obtained in accordance with variant a) or variant b) with a corresponding carbonate (Me)₂CO₃ and/or a corresponding hydrogencarbonate MeHCO₃, where Me corresponds to the alkali metal Me of the desired end product of the formula I.

If, for example, extraction is selected as purification step, an organic solvent is added to the aqueous reaction mixture in this case. The addition of the carbonate (Me)₂CO₃ and/or the hydrogencarbonate MeHCO₃ to the aqueous phase of the original reaction mixture and the suitable choice of solvent for the end product of the formula I facilitates in an advantageous manner the separation of reaction products and by-products from the end product of the formula I.

The invention therefore furthermore relates to the process according to the invention, as described above, where the metal cation exchange, preferably the alkali metal cation exchange, takes place during the purification step.

The invention therefore furthermore relates to the process according to the invention, as described above, where the metal cation exchange is carried out by reaction with the compound (Me₂)CO₃ and/or the compound MeHCO₃, where Me corresponds to the alkali metal Me of the desired end product of the formula I.

Irrespective of which embodiment of process variant a) or b) of the process according to the invention is selected, it is preferred if the reaction of the compound of the formula II, as described above or described as preferred, takes place in the presence of an organic solvent. The solvent respectively suitable for process variant a) or b) is indicated below.

The invention therefore furthermore relates to the process according to the invention, as described above, where the reaction of the compound of the formula II, as described above or described as preferred, both in variant a) and also in variant b), takes place in the presence of an organic solvent.

In process variant a) of the process according to the invention, as described above, a compound of the formula II, as described above, is reacted with an alkali metal or an alkaline-earth metal Me². If the metal Me² selected for use is an alkali metal, this may be identical to or different from the alkali metal cation of the compound of the formula II and may also be identical to or different from the alkali metal cation of the target product of the formula I.

If the alkali metal Me² used is different from Me¹ and Me, this reaction must be followed by an alkali metal cation exchange as process step in order to obtain the process end product of the formula I. If an alkaline-earth metal Me² is used, this reaction must be followed by a metal cation exchange as process step in order to obtain the process end product of the formula I. In a preferred process variant, the metal Me² is an alkali metal, as described above.

Alternatively, the process end product may also be a salt mixture of hydridocyanoborates with the alkali metal cations [Me]⁺, [Me¹]⁺ and/or the cation [Me²]⁺ or [Me²]²⁺. Depending on the desired subsequent reaction, separation of the salt mixture is not automatically necessary. The metal cation exchange to give the single process end product containing Me is then not necessary.

If a metal alloy Me²/Me or Me²/Me¹ is used in process variant a) a metal cation exchange is likewise necessary in order to obtain a single process end product containing the alkali metal Me.

The invention furthermore also relates to the process, as described above, in which, in process variant a), the medium for the generation and/or stabilisation of solvated electrons is selected from liquid ammonia, hexamethylphosphoric triamide (HMPA), amines, α,ω-diaminoalkanes, alcohols or diols.

Suitable amines are, for example, methylamine or ethylamine.

Suitable α,ω-diaminoalkanes are, for example, ethane-1,2-diamine, propane-1,3-diamine, butane-1,4-diamine or hexane-1,6-diamine.

Suitable alcohols are, for example, ethanol, n-propanol, i-propanol or butanol.

Suitable diols are, for example, ethylene glycol or 1,4-butanediol.

The preferred medium for the generation and/or stabilisation of solvated electrons is liquid ammonia.

Accordingly, the invention furthermore relates to a process as described above, characterised in that the medium for the generation and/or stabilisation of solvated electrons is liquid ammonia.

The invention furthermore also relates to the process, as described above, where, in process variant a), the medium which is capable of forming anion free radicals is selected from condensed aromatic compounds.

Condensed aromatic compounds form with an alkali metal Me² an anion free radical which acts as strong reducing agent.

Suitable condensed aromatic compounds are, for example, naphthalene, indene, fluorene, acenaphthylene, anthracene, phenanthrene or also polycyclic aromatic condensed hydrocarbons, for example tetracene, pentacene or hexacene.

The condensed aromatic compound selected is preferably naphthalene.

Accordingly, the invention furthermore relates to a process as described above, characterised in that the medium which is capable of forming anion free radicals is naphthalene.

In an embodiment of process variant a), a compound of the formula II, as described above, is reacted with an alkali metal Me² in liquid ammonia [NH₃(I)]. Lithium in NH₃(I), sodium in NH₃(I) or potassium in NH₃(I) is preferably used. Sodium in NH₃(I) or potassium in NH₃(I) is particularly preferably used.

Since the reaction with liquid NH₃ as only proton source is relatively slow, it is advantageous in this reaction procedure if a further proton source is added after the reaction with an alkali metal Me². A suitable proton source is selected, for example, from methanol, ethanol, butanol, aqueous mixtures of these alcohols, water or ammonium salts.

Suitable ammonium salts are, for example, ammonium chloride, ammonium sulfate or triethylammonium chloride.

In accordance with the invention, it is advantageous to use water as proton source.

The conditions of this embodiment of process variant a) also apply to the reaction of an alkaline-earth metal or a metal alloy Me²/Me or Me²/Me¹ in liquid ammonia. A preferred alkali metal alloy for the process according to the invention is Na/K.

The invention therefore furthermore relates to the process according to the invention, as described above, where the proton source is water.

The metal Me² employed or the metal alloy Me²/Me or Me²/Me¹ employed is preferably free from protecting agents which surround the metal or metal alloy, for example oil or paraffin.

It is also preferred in this embodiment of process variant a), as described above, if the reaction takes place in the presence of an organic solvent. Suitable solvents are diethyl ether, methyl t-butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-dimethoxyethane or diglyme. A preferred solvent is tetrahydrofuran.

Without being tied to the theory, the reaction in this embodiment of process variant a) in liquid ammonia will proceed in one or more steps, where the different anion species are able to form and are then ultimately converted into the monohydridotricyanoborate or dihydridodicyanoborate by reaction with the proton source.

It is therefore advantageous in this embodiment of process variant a) if the proton source is added separately or in the mixture with the organic solvent.

The addition of the proton source is preferably carried out at temperatures between −20° C. and 25° C., particularly preferably at 0° C.

It is therefore advantageous for this embodiment of process variant a) if the compound of the formula II, as described above or described as preferred, is initially introduced in a reaction vessel which is suitable for liquid ammonia, ammonia is condensed in at −78° C., and the metal Me² or the metal alloy Me²/Me or Me²/Me¹ is subsequently added in an inert-gas atmosphere. It may then be advantageous to stir this reaction mixture at −78° C. to −40° C. for 10 to 120 minutes and to allow the reaction mixture to warm to room temperature after the metal has been consumed. Corresponding precautionary measures for the ammonia evaporating must be observed.

After addition of the proton source, as described above, a metal cation exchange may follow if the corresponding alkali metal cation Me for the target product of the formula I is not yet present in the reaction mixture under the conditions, as described above.

In this embodiment of process variant a), it is preferred if the reaction is followed by a purification step in the form of an extraction. Preferred solvents can be selected from the group tetrahydrofuran, acetone, nitrile, such as, for example, acetonitrile, alcohol, such as, for example, methanol, ethanol or butanol, dialkyl ether, such as, for example, diethyl ether, monoglyme or diglyme.

Tetrahydrofuran is particularly preferably employed in this embodiment of process variant a).

In another embodiment of process variant a), a compound of the formula II, as described above, is reacted with a metal Me² or a metal alloy Me²/Me or Me²/Me¹ in the presence of naphthalene. In this variant, the metal Me² is an alkali metal, as defined above, or the metal alloy is an alkali metal alloy, as defined above.

Without being tied to the theory, the reaction in this alternative embodiment of process variant a) will proceed in one or more steps, where different anion species are able to form and are then ultimately converted into the monohydridotricyanoborate or dihydridodicyanoborate by reaction with a suitable proton source.

Suitable as proton source are, for example, methanol, ethanol, butanol, aqueous mixtures of these alcohols, aqueous solutions of carboxylic acids or mineral acids, water, or ammonium salts.

Suitable carboxylic acids are acetic acid, formic acid, glycolic acid or tartaric acid.

Suitable mineral acids are hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid.

Suitable ammonium salts are ammonium chloride, ammonium sulfate or triethylammonium chloride.

It is advantageous in accordance with the invention to use water as proton source.

The invention therefore furthermore relates to the process according to the invention, also in this alternative process variant a), as described above, where the proton source is water.

It is likewise preferred in this alternative embodiment of process variant a), as described above, if the reaction takes place in the presence of an organic solvent. Suitable solvents are diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, or 1,2-dimethoxyethane. A preferred solvent is tetrahydrofuran.

It is therefore advantageous in this embodiment of process variant a) if the proton source is added in the organic solvent. The addition of the proton source is preferably carried out at temperatures between −20° C. and 25° C., particularly preferably at 0° C.

It is advantageous for this alternative embodiment of process variant a) if naphthalene is added to a solution of the compound of the formula II, as described above or described as preferred, in a suitable organic solvent and the alkali metal Me² or the alkali metal alloy Me²/Me or Me²/Me¹ is subsequently added in excess in an inert-gas atmosphere. The suitable temperature range is 10° C. to 80° C., the reaction is preferably carried out at room temperature. It is advantageous if the same organic solvent is used for both steps.

The reaction of the compound of the formula II with Me²/naphthalene is preferably carried out at temperatures between 10° C. and 60° C., particularly preferably at room temperature. The reaction must be carried out in an inert atmosphere, preferably with exclusion of water and oxygen. Conditions for the exclusion of water and oxygen are described below and preferably also apply to this process variant.

After addition of the proton source, as described above in general terms and also for the first embodiment of process variant a), a metal cation exchange may follow if the corresponding alkali metal cation Me for the target product of the formula I is not yet present in the reaction mixture under the conditions, as described above.

In this embodiment of process variant a), it is preferred if the reaction is followed by a purification step in the form of an extraction. A preferred solvent for this purpose is tetrahydrofuran, dialkyl ether, acetone or acetonitrile. Tetrahydrofuran is particularly preferably employed in this embodiment of process variant a).

In this embodiment of process variant a), it is advantageous if the compound of the formula II, as described above or described as preferred, is taken up in an alcohol or in a diol, preferably in ethanol, and the alkali metal Me² or the alkali metal alloy Me²/Me or Me²/Me¹ is subsequently added in an inert-gas atmosphere. It may then be advantageous to stir this reaction mixture at −40° C. to 140° C., preferably at 0° C. to 80° C., for 10 minutes to a few hours and to work up the reaction mixture in accordance with the teaching of Example 10 after the alkali metal has been consumed. It is advantageous in this process variant to neutralise the metal alkoxide formed in excess using mineral acids, for example aqueous hydrochloric acid, before a subsequent metathesis reaction.

In process variant b) of the process according to the invention, as described above, a compound of the formula II, as described above, is reacted with an alkali metal hydride Me³H in an inert-gas atmosphere. The alkali metal cation [Me³]⁺ may be identical to or different from the alkali metal cation of the compound of the formula II and may also be identical to or different from the alkali metal cation of the target product of the formula I. If the alkali metal Me³ used is different from Me¹ and Me, this reaction must necessarily be followed by an alkali metal cation exchange as process step.

In an embodiment of process variant b), a compound of the formula II, as described above, is reacted with an alkali metal hydride Me³H in the presence of an F⁻-affinitive electrophilic reagent.

Without being tied to the theory, the mechanism of the nucleophilic substitution reaction is assumed for process variant b).

It has been found that the addition of an electrophilic reagent which has good affinity to F⁻ accelerates the substitution.

The term “affinity to F⁻” means that the reagent used preferably forms a bond to the F⁻. The bond here can be a covalent bond or also a bond which arises through electrostatic interaction.

In a preferred embodiment of process variant b), the (F⁻)-affinitive electrophilic reagent is a lithium salt or a magnesium salt.

Suitable lithium salts are lithium bromide, lithium iodide, lithium chloride, lithium triflate, lithium perchlorate or lithium tetrafluoroborate.

A suitable magnesium salt is magnesium triflate.

In a particularly preferred embodiment of process variant b), lithium bromide is employed as electrophilic reagent.

The invention therefore furthermore relates to the process according to the invention, as described above, where the (F⁻)-affinitive electrophilic reagent is a lithium salt or a magnesium salt.

The invention therefore furthermore relates to the process according to the invention, as described above, where the (F⁻)-affinitive electrophilic reagent is lithium bromide.

The reaction of the compounds of the formula II, as described above, with the alkali metal hydride of the formula III is preferably carried out in the presence of an organic solvent, for example in the presence of ethers. Preferred ethers are tetrahydrofuran, diethyl ether, methyl t-butyl ether or dimethoxyethane. Tetrahydrofuran is particularly preferably used.

The reaction according to the invention in accordance with process variant b) preferably takes place at temperatures between 10° C. and 200° C., in particular between 15° C. and 150° C., particularly preferably at 100° C. to 150° C., very particularly preferably at 80° C. The reaction takes place in an inert-gas atmosphere, preferably with exclusion of water and oxygen. Conditions for the exclusion of water and oxygen are described below and preferably also apply to this process variant.

It is preferred in this process variant b) if the work-up step, as described above, includes a combination of various separation methods.

It is, for example, preferred to decompose the possible excess of hydride of the formula III, as described above, by addition of water or an aqueous alcoholic solution of methanol, ethanol, isopropanol or butanol and to remove all volatile constituents under reduced pressure.

It is furthermore preferred to take up the reaction product obtained in an organic solvent and to remove the by-products by extraction with water or by filtration. In this step, the alkali metal cation exchange can also be carried out correspondingly, as described in detail above.

However, it is advantageous in process variant b) if the alkali metal cation [Me³]⁺ corresponds to the metal cation of the end product of the formula I.

Suitable organic solvents are tetrahydrofuran, dialkyl ethers, such as, for example, diethyl ether, acetonitrile or acetone.

It is therefore advantageous for this embodiment of process variant b) if the compound of the formula II, as described above or described as preferred, are stirred with the compound of the formula III, as described above, and a suitable solvent at the reaction temperature indicated and is subsequently worked up.

The process according to the invention may then be followed by a classical metathesis reaction, where a compound of the formula IV

[Kt]^z+z[BH_n(CN)_4-n]⁻  IV

in which
[Kt]^z+ is an inorganic or organic cation, z corresponds to the charge of the cation and
n denotes 1 or 2 and n has the same meaning as in the starting compound of the formula I, as described above,
is formed.

The invention therefore furthermore relates to a process for the preparation of compounds of the formula IV

[Kt]^z+z[BH_n(CN)_4-n]⁻  IV,

where
[Kt]^z+ is an inorganic or organic cation,
z corresponds to the charge of the cation and
n denotes 1 or 2,
by anion exchange, where a salt containing the cation [Kt]^z+ is reacted with a compound of the formula I

[Me]⁺[BH_n(CN)_4-n]⁻  I,

prepared by the process according to the invention, as described above, where Me denotes an alkali metal and n has the same meaning as in the compound of the formula IV.
[Kt]^z+ preferably has the meaning of an organic cation or an inorganic cation, where the cation [Kt]^z+ does not correspond to the cation Me⁺ employed in the compound of the formula I and
the anion A of the salt containing [Kt]^z+ denotes F⁻, Cl⁻, Br⁻, I⁻, HO⁻, [HF₂]⁻, [CN]⁻, [SCN]⁻, [R₁COO]⁻, [R₁OC(O)O]⁻, [R₁SO₃]⁻, [R₂COO]⁻, [R₂SO₃]⁻, [R₁OSO₃]⁻, [PF₆]⁻, [BF₄]⁻, [HSO₄]⁻, [NO₃]⁻, [(R₂)₂P(O)O]⁻, [R₂P(O)O₂]²⁻, [(R₁O)₂P(O)O]⁻, [(R₁O)P(O)O₂]²⁻, [(R₁O)R₁P(O)O]⁻, tosylate, malonate, which may be substituted by straight-chain or branched alkyl groups having 1 to 4 C atoms, [HOCO₂]⁻ or [CO₃]²⁻, where R₁ in each case, independently of one another, denotes a straight-chain or branched alkyl group having 1 to 12 C atoms and R₂ in each case, independently of one another, denotes a straight-chain or branched perfluorinated alkyl group having 1 to 12 C atoms and where electroneutrality is taken into account in the formula of the salt KtA.

A perfluorinated linear or branched alkyl group having 1 to 4 C atoms is, for example, trifluoromethyl, pentafluoroethyl, n-heptafluoropropyl, iso-heptafluoropropyl, n-nonafluorobutyl, sec-nonafluorobutyl or tert-nonafluorobutyl. R₂ defines analogously a linear or branched perfluorinated alkyl group having 1 to 12 C atoms, encompassing the above-mentioned perfluoroalkyl groups and, for example, perfluorinated n-hexyl, perfluorinated n-heptyl, perfluorinated n-octyl, perfluorinated ethylhexyl, perfluorinated n-nonyl, perfluorinated n-decyl, perfluorinated n-undecyl or perfluorinated n-dodecyl.

R₂ is particularly preferably trifluoromethyl, pentafluoroethyl or nonafluorobutyl, very particularly preferably trifluoromethyl or pentafluoroethyl.

R₁ is particularly preferably methyl, ethyl, n-butyl, n-hexyl or n-octyl, very particularly preferably methyl or ethyl.

Substituted malonates are, for example, the compounds—methyl or ethyl malonate.

The anion A of the of the salt containing [Kt]^z+ is preferably OH⁻, Cl⁻, Br⁻, I⁻, [CH₃SO₃]⁻[CH₃OSO₃]⁻, [CF₃COO]⁻, [CF₃SO₃]⁻, [(C₂F₅)₂P(O)O]⁻ or [CO₃]²⁻, particularly preferably OH⁻, Cl⁺, Br⁻, [CH₃OSO₃]⁻, [CF₃SO₃]⁻, [CH₃SO₃]⁻ or [(C₂F₅)₂P(O)O]⁻.

The organic cation for [Kt]^z+ is selected, for example, from iodonium cations, ammonium cations, sulfonium cations, oxonium cations, phosphonium cations, uronium cations, thiouronium cations, guanidinium cations, tritylium cations or heterocyclic cations.

Preferred inorganic cations are metal cations of the metals from group 2 to 12 or also NO⁺ or H₃O+⁺.

Preferred inorganic cations are Ag⁺, Mg²⁺, Cu⁺, Cu²⁺, Zn²⁺, Ca²⁺, Y³⁺, Yb³⁺, La³⁺, Sc³⁺, Ce³⁺, Nd³⁺, Tb³⁺, Sm³⁺ or complex (ligand-containing) metal cations which contain rare-earth, transition or noble metals, such as rhodium, ruthenium, iridium, palladium, platinum, osmium, cobalt, nickel, iron, chromium, molybdenum, tungsten, vanadium, titanium, zirconium, hafnium, thorium, uranium, gold.

The salt-exchange reaction of the salt of the formula I with a salt containing [Kt]^z+, as described above, is advantageously carried out in water, where temperatures of 0°-100° C., preferably 15-60° C., are suitable. The reaction is particularly preferably carried out at room temperature (25° C.).

However, the above-mentioned salt-exchange reaction may alternatively also be carried out in organic solvents at temperatures between −30° and 100° C. Suitable solvents here are acetonitrile, propionitrile, dioxane, dichloromethane, dimethoxyethane, dimethyl sulfoxide, tetrahydrofuran, dimethylformamide, acetone or alcohol, for example methanol, ethanol or isopropanol, diethyl ether or mixtures of the above-mentioned solvents.

In a further embodiment of the process according to the invention, the compound of the formula II is prepared in advance in situ from an alkali metal tetrafluoroborate and a trialkylsilyl cyanide, where the trialkylsilyl cyanide used can in turn be prepared before this reaction in situ from an alkali metal cyanide and a trialkylsilyl chloride, as described above.

The invention therefore furthermore relates to a process for the preparation of compounds of the formula I, as described above or described as preferred, where the compound of the formula II is prepared in situ.

The invention therefore furthermore relates to a process for the preparation of compounds of the formula I

[Me]⁺[BH_n(CN)_4-n]⁻  I,

where
Me denotes an alkali metal and
n denotes 1 or 2,
by reaction of a compound of the formula V

[Me¹]⁺[BF₄]⁻  V,

where Me¹ denotes an alkali metal, which may be identical to or different from Me,
with a trialkylsilyl cyanide, where the alkyl group of the trialkylsilyl cyanide in each case, independently of one another, denotes a linear or branched alkyl group having 1 to 10 C atoms, preferably having 1 to 8 C atoms, very particularly preferably having 1 to 4 C atoms, to give a compound of the formula II

[Me¹]⁺[BF_n(CN)_4-n]⁻  II,

where Me¹ corresponds to the alkali metal of the compound of the formula V and
n denotes 1 or 2, where n is identical in formula I and formula II,
where the conditions of the reaction are selected in such a way that both the water content and also the oxygen content are a maximum of 1000 ppm, and
reaction with either

• a) an alkali metal or alkaline-earth metal Me², where an alkali metal Me² may be identical to or different from Me or Me¹;
  • or a metal alloy Me²/Me or Me²/Me¹, where, in the case where Me² is an alkali metal, this alkali metal Me² is different from Me or Me¹; in an inert-gas atmosphere and
  • in the presence of a medium which is either capable of generating and/or stabilising solvated electrons or is capable of forming an anion free radical, if necessary with addition of a proton source, and
  • a metal cation exchange in the case where neither Me² nor Me¹ corresponds to Me,
  • or
• b) an alkali metal hydride of the formula III

Me³H  III

• • in an inert-gas atmosphere,
  • where Me³ may be identical to or different from Me or Me¹, without or in the presence of an electrophilic reagent which has affinity to F⁻ and subsequent metal cation exchange in the case where neither Me³ nor Me¹ corresponds to Me.

The reaction of the alkali metal tetrafluoroborate with trialkylsilyl cyanide, as described above, preferably takes place in the presence of a trialkylsilyl chloride, trialkylsilyl bromide and/or trialkylsilyl iodide, where the alkyl groups of the trialkylsilyl halide in each case, independently of one another, denote a straight-chain or branched alkyl group having 1 to 10 C atoms. Examples of trialkylsilyl cyanides are described above or described as preferred.

The alkyl groups of the trialkylsilyl halide may be identical or different. The alkyl groups of the trialkylsilyl halide preferably have 1 to 8 C atoms, particularly preferably 1 to 4 C atoms. The alkyl groups of the trialkylsilyl halide are preferably identical in the case of alkyl groups having 1 to 4 C atoms. An alkyl group of the trialkylsilyl halide is preferably different if it is an alkyl group of 5 to 10 C atoms or of 5 to 8 C atoms.

The trialkylsilyl halide is preferably a trialkylsilyl chloride.

Suitable trialkylsilyl chlorides are trimethylsilyl chloride (or synonymously trimethylchlorosilane), triethylsilyl chloride, triisopropylsilyl chloride, tripropylsilyl chloride, octyldimethylsilyl chloride, butyldimethylsilyl chloride, t-butyldimethylsilyl chloride or tributylsilyl chloride. Particular preference is given to the use of trimethylsilyl chloride. Very particular preference is given to the use of trimethylsilyl chloride alone.

Suitable trialkylbromosilanes are trimethylbromosilane (or synonymously trimethylsilyl bromide), triethylsilyl bromide, triisopropylsilyl bromide, tripropylsilyl bromide, octyldimethylsilyl bromide, butyldimethylsilyl bromide, t-butyldimethylsilyl bromide or tributylsilyl bromide. Particular preference is given to the use of trimethylsilyl bromide in a mixture with trimethylsilyl chloride.

Suitable trialkyliodosilanes are trimethyliodosilane (or synonymously trimethylsilyl iodide), triethylsilyl iodide, triisopropylsilyl iodide, tripropylsilyl iodide, octyldimethylsilyl iodide, butyldimethylsilyl iodide, t-butyldimethylsilyl iodide or tributylsilyl iodide. Particular preference is given to the use of trimethylsilyl iodide in a mixture with trimethylsilyl chloride.

The trialkylsilyl halide or a mixture of trialkylsilyl halides, as described above or described as preferred, is particularly preferably employed in a total amount of 1 to 20 mol %, based on the amount of trialkylsilyl cyanide employed. The trialkylsilyl halide or a mixture of trialkylsilyl halides is particularly preferably employed in a total amount of 3 to 12 mol %, based on the amount of trialkylsilyl cyanide employed. The trialkylsilyl halide or a mixture of trialkylsilyl halides is very particularly preferably employed in a total amount of 7 to 11 mol %, based on the amount of trialkylsilyl cyanide employed.

The reaction can be carried out both in an open apparatus and also in a closed apparatus.

It is preferred to mix the starting materials of the formula V, the trialkylsilyl cyanide and optionally the trialkylsilyl chloride in an inert-gas atmosphere whose oxygen content is a maximum of 1000 ppm. It is particularly preferred if the oxygen content is less than 500 ppm, very particularly preferably a maximum of 100 ppm.

The water content of the reagents and of the inert-gas atmosphere is a maximum of 1000 ppm. It is particularly preferred if the water content of the reagents and of the atmosphere is less than 500 ppm, very particularly preferably a maximum of 100 ppm.

The conditions with respect to the water content and oxygen content do not apply to the further reaction after process variants a) or b) or to the work-up after reaction of the compound of the formula II with the trialkylsilyl cyanide has taken place.

All further explanations of embodiments of the reaction according to the invention of the compound of the formula II to give compounds of the formula I, as described above, apply correspondingly in this respect to this one-pot process with the starting material of the compound of the formula V and can be combined in this respect without restriction.

In the case of in-situ generation of the trialkylsilyl cyanide, the invention relates to the following one-pot process.

The invention therefore furthermore relates to a process for the preparation of compounds of the formula I

[Me]⁺[BH_n(CN)_4-n]⁻  I,

where
Me denotes an alkali metal and
n denotes 1 or 2,
by reaction of a compound of the formula V

[Me¹]⁺[BF₄]⁻  V,

where Me¹ denotes an alkali metal, which may be identical to or different from Me,
with alkali metal cyanide and trialkylsilyl chloride under the conditions of in-situ generation of trialkylsilyl cyanide, where the alkyl group of the trialkylsilyl chloride and also of the trialkylsilyl cyanide formed in each case, independently of one another, denotes a linear or branched alkyl group having 1 to 10 C atoms, preferably having 1 to 8 C atoms, particularly preferably having 1 to 4 C atoms, to give a compound of the formula II

[Me¹]⁺[BF_n(CN)_4-n]⁻  II,

where Me¹ corresponds to the alkali metal of the compound of the formula V and
n denotes 1 or 2, where n in is identical formula I and formula II, and reaction with either

• a) an alkali metal or alkaline-earth metal Me², where an alkali metal Me² may be identical to or different from Me or Me¹;
  • or a metal alloy Me²/Me or Me²/Me¹, where, in the case where Me² is an alkali metal, this alkali metal Me² is different from Me or Me¹; in an inert-gas atmosphere and
  • in the presence of a medium which is capable of generating and/or stabilising solvated electrons or is capable of forming an anion free radical, if necessary with addition of a proton source, and
  • a metal cation exchange in the case where neither Me² nor Me¹ corresponds to Me,
  • or
• b) an alkali metal hydride of the formula III

Me³H  III

• • in an inert-gas atmosphere,
  • where Me³ may be identical to or different from Me or Me¹, without or in the presence of an electrophilic reagent which has affinity to F⁻ and subsequent metal cation exchange in the case where neither Me³ nor Me¹ corresponds to Me.

The in-situ generation of trialkylsilyl cyanide preferably takes place in the presence of an alkali metal iodide and optionally iodine, as described above. The in-situ generation of trialkylsilyl cyanide particularly preferably takes place in the presence of an alkali metal iodide. The conditions of the reaction for the in-situ generation are also selected in such a way that both the water content and also the oxygen content are less than 1000 ppm. The conditions mentioned above apply correspondingly.

The amount of alkali metal iodide is preferably 4 to 6 mol %, based on the amount of alkali metal cyanide, or 3 to 5 mol %, based on the amount of trialkylsilyl chloride. The amount of alkali metal iodide is particularly preferably 4.9 to 5.1 mol %, based on the amount of alkali metal cyanide, or 3.9 to 4.1 mol %, based on the amount of trialkylsilyl chloride.

The one-pot synthesis, as described above, is preferably carried out in a closed reaction vessel. During the reaction, a maximum pressure of 2.5 bar generally arises.

All further explanations of embodiments of the reaction according to the invention of the compound of the formula II to give compounds of the formula I, as described above, apply correspondingly in this respect to this one-pot process with the starting material of the compound of the formula V and the in-situ generation of trialkylsilyl cyanide and can be combined in this respect without restriction. Trimethylsilyl cyanide is particularly preferably generated in situ in the one-pot process.

The word choice “one-pot process” means that the compound of the formula II formed as an intermediate, as described above or described as preferred, is not isolated. It is also possible in the process variant of the “one-pot process” to separate off excess reactants and/or by-products and/or assistants, such as solvents, present.

The substances obtained are characterised by means of NMR spectra. The NMR spectra are measured on solutions in deuterated acetone-D₆ or in CD₃CN on a Bruker Avance 500 spectrometer with deuterium lock. The measurement frequencies of the various nuclei are: ¹H: 500.1 MHz, ¹¹B: 160.5 MHz and ¹³C: 125.8 MHz. The referencing is carried out using an external reference: TMS for ¹H and ¹³C spectra and BF₃.Et₂O— for ¹¹B spectra.

EXAMPLE 1

One-Pot Synthesis of Sodium Monofluorotricyanoborate; Na[BF(CN)₃]

6.0 g (40.0 mmol) of sodium iodide, NaI, and 40.0 g (816.3 mmol) of sodium cyanide, NaCN, are suspended in 20 ml of acetonitrile. 130 ml (1029 mmol) of trimethylsilyl chloride, (CH₃)₃SiCl, are added to the suspension. The reaction mixture is stirred vigorously at room temperature, during which the reaction mixture is kept in a sealed vessel with exclusion of light until the conversion of NaCN into (CH₃)₃SiCN has taken place. The reaction time can be one to two days. The reaction can be monitored via ¹³C-NMR measurements. 16.0 g (145.4 mmol) of sodium tetrafluoroborate, Na[BF₄], are then added. The reaction mixture is stirred and heated for a further 1.5 hours in a closed vessel, during which the oil-bath temperature is 100° C. During the reaction, (CH₃)₃SiF (boiling point 16° C.) forms. For this reason, the system is under pressure (max. 2.5 bar), and the reaction vessel must be opened carefully. After cooling to room temperature, crystals have formed, and all volatile components are removed in vacuo. Alternatively, the solids Na[BF(CN)₃] and NaCl may also be filtered. The solid residue or the filter residue is extracted with 150 ml of acetone. Acetone is then distilled off, and the residue is taken up in 70 ml of tetrahydrofuran (THF). After addition of 200 ml of dichloromethane, the product Na[BF(CN)₃] precipitates out and is filtered off and dried in vacuo, giving 17.61 g (134.5 mmol) of Na[BF(CN)₃]. This corresponds to a yield of 93%, based on Na[BF₄].

¹⁹F-NMR (solvent: acetone-D₆), δ, ppm: −212.2 q, ¹J_11B,19F=44 Hz, ¹J_10B,19F=14.5 Hz

¹¹B-NMR (solvent: acetone-D₆), δ, ppm: −17.8 d, ¹J_11B,19F=44 Hz.

NaI (0.60 g, 4.00 mmol) and NaCN (4.0 g, 81.6 mmol) are taken up in acetonitrile (2.0 ml), trimethylchlorosilane, (CH₃)₃SiCl (10.3 ml, 81.6 mmol), is added, and the mixture is stirred overnight at room temperature in a sealed vessel with exclusion of light. Sodium tetrafluoroborate, Na[BF₄](1.6 g, 14.54 mmol), and further trimethylsilyl chloride (2.5 ml, 19.79 mmol) are added to the suspension. The reaction mixture is heated at 1000 (oil-bath temperature) for 3 hours in a closed vessel (max. pressure 2.5 bar). All volatile constituents (trimethylsilyl chloride, trimethylsilyl fluoride, trimethylsilyl cyanide) are subsequently removed in vacuo. The residue is extracted with acetone (20 ml), and the filtrate is evaporated to dryness in vacuo.

Yield: 1.8 g (13.75 mmol), corresponding to 95%, based on the borate employed.

The ¹⁹F and ¹¹B NMR spectra are identical to those of Example A).

EXAMPLE 2

Synthesis of Sodium Monofluorotricyanoborate; Na[BF(CN)₃]

11.0 g (100 mmol) of sodium tetrafluoroborate, Na[BF₄], is initially introduced in a flask with PTFE spindle (Young, London). 100 ml of the mixture of trimethylsilyl cyanide, (CH₃)₃SiCN (75 mol %), trimethylsilyl chloride, (CH₃)₃SiCl (15 mol %) and trimethylsilyl fluoride, (CH₃)₃SiF (10 mol %), obtained in Example 1 (these and similar mixtures are recovered from the reactions described here during work-up) is added to the sodium tetrafluoroborate. The flask is closed, and the reaction mixture is stirred at 900 (oil-bath temperature) for 4 hours. 20 ml of fresh trimethylsilyl cyanide and 2 ml of trimethylsilyl chloride are then added, and the reaction mixture is stirred at 800 (oil-bath temperature) for a further 5 hours.

All volatile substances are then distilled off, and the residue is dried at 600 in vacuo for one day, giving 13.1 g (100 mmol) of Na[BF(CN)₃].

The ¹⁹F- and ¹¹B-NMR spectra are identical with those of Example 1.

EXAMPLE 3

Synthesis of Potassium Monofluorotricyanoborate; K[BF(CN)₃]

20.0 g (182 mmol) of sodium tetrafluoroborate, Na[BF₄], and 200 ml (1.5 mol) of trimethylsilyl cyanide, (CH₃)₃SiCN, are initially introduced, and 20 ml (158 mmol) of trimethylchlorosilane, (CH₃)₃SiCl, are added to this suspension. The reaction mixture is heated under reflux (oil-bath temperature 65° C. to 95° C.) for 96 hours. All volatile substances are then distilled off in vacuo. The mixture of trimethylsilyl cyanide, (CH₃)₃SiCN, trimethylsilyl chloride, (CH₃)₃SiCl, and trimethylsilyl fluoride, (CH₃)₃SiF, is collected in a cold trap and can be employed analogously to the mixture in Example 2 in a second synthesis. The residue is taken up in 100 ml of water, and hydrogen peroxide H₂O₂ (37% solution, about 200 ml) and K₂CO₃ (about 100 g) are carefully added until the solution is virtually no longer coloured. The excess peroxide is destroyed by addition of K₂S₂O₅. The water is distilled off, and the residue obtained is extracted with acetone (3×100 ml). The combined organic phases are reduced to 50 ml, and dichloromethane is then added until K[BF(CN)₃] precipitates out. Filtration and drying in vacuo gives 19.8 g (134.8 mmol) of K[BF(CN)₃]. The yield is 74%, based on sodium tetrafluoroborate.

¹⁹F-NMR (solvent: acetone-D₆), δ, ppm: −212.08 q, ¹J_11B,19F=44.4 Hz.

¹¹B-NMR (solvent: acetone-D₆), δ, ppm: −17.88 d, ¹J_11B,19F=44.4 Hz.

The spectra are identical to those of Example 1 and correspond to those from the literature [E. Bernhardt, M. Berkei, H. Willner, M. Schirmann, Z. Anorg. Allg. Chem., 2003, 629, 677-685].

Elemental Analysis:

found, %: C, 24.53, H, 0.00, N, 27.86;

calculated for C₃BFN₃K, %: C, 24.52, H, 0.00, N, 28.59.

EXAMPLE 4

Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃]

3.75 g of sodium fluorotricyanoborate (28.6 mmol) is initially introduced in a flask with PTFE spindle (Young, London), and ammonia (40 ml) is condensed in at −78° C. 1.32 g of sodium (57.4 mmol) is subsequently added with stirring in a counterstream of argon. The reaction mixture is slowly warmed to room temperature, so that the ammonia is able to escape. The residue is carefully taken up with a THF/water mixture (200 ml of THF, 50 ml of water) at 0° C. K₂CO₃ (about 5 g) is added until a clear phase separation is evident. The separated-off water phase is saturated with K₂CO₃ (about 50 g) and extracted with THF (3×50 ml). The combined THF phases are dried using K₂CO₃ and evaporated to a residual volume of 10 ml. Virtually colourless potassium hydridotricyanoborate can be precipitated by addition of CH₂Cl₂.

Yield: 2.38 g (18.5 mmol), 65%, based on the sodium fluorotricyanoborate employed.

¹H{¹¹B}-NMR (solvent: acetonintrile D₃), δ, ppm: 1.77 s.

¹¹B-NMR (solvent: acetonitrile D₃), δ, ppm: −40.2 d, ¹J_11B,H=98 Hz.

The spectra correspond to the spectra indicated in WO 2012/163489.

Elemental Analysis:

found, %: C, 27.94, H, 0.78, N, 32.58;

calculated for C₃HBN₃K, %: C, 27.93, H, 0.97, N, 32.54.

EXAMPLE 5

Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃]

Naphthalene (265 mg, 2.07 mmol) is dissolved in THF (8 ml), and an excess of sodium (about 1.00 g, 43.5 mmol) is added. The mixture is stirred at room temperature for 20 min, during which a dark-green solution forms. In another flask with PTFE spindle (Young, London), potassium fluorotricyanoborate (150 mg, 1.02 mmol) is dissolved in THF (10 ml); the sodium naphthalide solution is rapidly added dropwise to this solution. During this addition, the reaction solution rapidly changes colour to dark yellow, and a precipitate forms. Further sodium is added to the reaction solution until the latter becomes dark green. The suspension standing above the sodium is removed, and a saturated K₂CO₃ solution (5.6 g in 5 ml of H₂O) is carefully added. The lower aqueous phase formed is separated off and extracted with THF (10 ml). The combined organic phases are dried over K₂CO₃, and the solvent is removed. The solid residue is washed with CH₂Cl₂ (2×10 ml), filtered off, and the colourless solid substance is dried in vacuo.

The yield of potassium hydridotricyanoborate, K[BH(CN)₃], is 75 mg (0.582 mmol, 57%).

The ¹H and ¹¹B NMR spectra correspond to the data indicated in Example 4.

EXAMPLE 6

Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃]

1.0 g of Na[BF(CN)₃] (6.8 mmol), 1.0 g of potassium hydride, KH (25.0 mmol) and 0.7 g of LiBr (8.08 mmol) are taken up in THF (15 ml), and the suspension is stirred at 80° C. for 38 hours. i-PrOH and H₂O are added to the reaction mixture with cooling. Evolution of hydrogen is observed during this addition. All volatile constituents are subsequently removed under reduced pressure. The solid is taken up in acetone, a little H₂O and K₂CO₃ are added, and the mixture is stirred for 15 minutes. After the addition of further K₂CO₃, the organic phase is filtered off. The acetone is removed in vacuo, and the solid obtained is dried in vacuo.

The yield of K[BH(CN)₃] is 258 mg (2.0 mmol), corresponding to 29%, with respect to the borate employed.

The ¹H and ¹¹B NMR spectra correspond to those of Example 4.

EXAMPLE 7

Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃]

0.20 g of K[BF(CN)₃] (1.36 mmol), 0.15 g of KH (3.75 mmol) and 0.20 g of LiBr (2.30 mmol) are taken up in THF (5 ml) and stirred at 8000 for 2 days. The suspension is filtered, and the solvent is removed in vacuo. The solid is washed with dichloromethane on a glass frit and dried in vacuo. Yield of K[HB(CN)₃]: 40 mg (0.03 mmol), corresponding to 22% with respect to the K[BF(CN)₃]) employed.

The ¹H and ¹¹B NMR spectra correspond to those of Example 4.

EXAMPLE 8

Synthesis of Tetrabutylammonium Monohydridotricyanoborate; [n-Bu₄N][BH(CN)₃] Via Potassium Monohydridotricyanoborate Intermediate

K[BF(CN)₃](1.5 g, 10.20 mmol) is taken up in NH₃ (10 ml) at −78° C., and potassium (797 mg, 20.41 mmol) is added in portions. The suspension is stirred at −78° C. for a further 20 minutes and then slowly warmed to room temperature. The ammonia evaporating is discharged through a pressure control valve. The yellow solid obtained is subsequently dissolved in water (20 ml). An aqueous [n-Bu₄N]OH solution is added to the solution, and the mixture is extracted with CH₂Cl₂. The solvent is distilled off, and the residue is taken up in acetone. Undissolved material is filtered off, and the filtrate is evaporated to dryness.

The yield of [n-Bu₄][BH(CN)₃] is 1.57 g (4.72 mmol), corresponding to 46% with respect to the potassium tricyanofluoroborate employed.

¹H{¹¹B}-NMR (solvent: acetone-D₆), δ, ppm: 0.98 t (4CH₃, 12H; ³J_H,H=7.2 Hz), 1.45 m (4CH₂, 8H), 1.81 m (4CH₂+B—H, 9H). 3.44 m (4CH₂, 8H).

¹¹B-NMR (solvent: acetone-D₆), δ, ppm: −40.0 d, ¹J_11B,H=97 Hz.

EXAMPLE 9

One-Pot Synthesis of Potassium Monohydridotricyanoborate; K[BH(CN)₃] from Sodium Tetrafluoroborate by In-Situ Generation of Potassium Monofluorotricyanoborate

Na[BF₄](4.70 g, 42.78 mmol) is taken up in acetonitrile (6.25 ml), trimethylsilyl cyanide, (CH₃)₂SiCN, (30.0 ml, 225.0 mmol) and trimethylchlorosilane, (CH₃)₃SiCl, (7.5 ml, 59.4 mmol) are added, and the mixture is stirred at 100° C. for 3 hours. The reaction mixture is cooled to room temperature, and all volatile constituents are removed in vacuo (final pressure about 1·10⁻³ mbar). The residue obtained is dried in a fine vacuum at 120° C. for 12 hours and subsequently taken up in liquid ammonia (40 ml) at −78° C. Freshly cut, oil-free sodium (1.967 g, 85.56 mmol) is added in a counterstream of Ar, and the reaction mixture is stirred at −78° C. for one hour. The reaction mixture is subsequently warmed to room temperature. Ammonia evaporating is discharged. The solid remaining is taken up in tetrahydrofuran (THF; 200 ml), and H₂O (15 ml) is added to the suspension. The mixture is then stirred with K₂CO₃ (70 g) for 15 minutes. The THF phase is subsequently decanted and dried using K₂CO₃ (30 g) and filtered. The tetrahydrofuran is removed to a residual volume of about 5-10 ml using a rotary evaporator at a bath temperature of 70° C. and a pressure of about 600 mbar. Addition of CH₂Cl₂ (50 ml) causes K[BH(CN)₃] to precipitate out as brown crude product. This is filtered off, washed with dichloromethane (2×50 ml) and dried in a fine vacuum. According to the NMR data, the crude product contains 10% of K[BH₂(CN)₂]. The yield of K[BH(CN)₃]⁻ 0.36 THF is 66% (4.35 g, 28.08 mmol).

For the subsequent purification, the crude product is dissolved in 5 ml of acetone, and 50 ml of dichloromethane are added. The deposited precipitate is filtered off and dried in vacuo (final pressure is about 1×10-3 mbar).

The yield for the purified product (beige solid) is 2.61 g (47%).

The ¹H- and ¹¹B-NMR spectra correspond to those of Example 4.

EXAMPLE 10

Synthesis of Tetrabutylammonium Monohydridotricyanoborate; [n-Bu₄N][BH(CN)₃] Via Sodium Monohydridotricyanoborate Intermediate in a One-Pot Reaction in Ethanol

Na[BF(CN)₃](100 mg, 0.764 mmol) is dissolved in dry ethanol (4 ml), and elemental sodium (100 mg, 4.366 mmol) is added at 0° C. The reaction mixture is stirred at 0° C. for 8 hours. Further sodium (100 mg, 4.366 mmol) is subsequently added, and the reaction mixture is heated at the boil for 45 minutes. The reaction mixture is taken up in water (10 ml), and a solution of tetrabutylammonium bromide (350 mg, 1.08 mmol) in water (5 ml) is added. The tetrabutylammonium hydridotricyanoborate formed is extracted with CH₂Cl₂ (5·3 ml), and the combined organic phases are dried using MgSO₄. The suspension is filtered, and the filtrate is evaporated to dryness in vacuo, and the residue obtained is dried in a fine vacuum.

Yield: 227 mg (0.683 mmol, 89%)

The ¹H and ¹¹B NMR spectra correspond to those of Example 8.

EXAMPLE 11

Synthesis of Sodium Dihydridodicyanoborate; Na[BH₂(CN)₂]

Na[BF₂(CN)₂](100 mg, 0.80 mmol) is dissolved in NH₃ (2 ml) at −78° C., and sodium (74 mg, 3.23 mmol) is added. The dark-blue solution is slowly warmed to room temperature, and the ammonia evaporating in the process is discharged through a bubble counter. Water is added to the residue, and the solution is investigated by ¹¹B-NMR spectroscopy. The spectrum proves conversion to [BH₂(CN)₂] salt (about 55 mol %) and further unknown boron-containing species (about 40 mol %). The further purification is carried out by conversion to a [BH₂(CN)₂] salt having an organic cation, subsequent extraction with an organic solvent and washing with water and subsequent drying.

¹¹B NMR spectrum of [BH₂(CN)₂] anion:

¹¹B{¹H}-NMR (no lock; solvent: water), δ, ppm: −42.2 (s).

¹¹B-NMR (no lock; solvent: water), δ, ppm: −42.2 t, J_11B,H=94.6 Hz.

The NMR data are in accordance with the values of K[BH₂(CN)₂] described in the literature (WO 2012/163488A1).

EXAMPLE 12

Synthesis of Potassium/Sodium Dihydridodicyanoborate; K/Na[BH₂(CN)₂]

Na[BF₂(CN)₂] (20 mg) is taken up in THF together with KH and NaH (together about 30 equivalents) in an NMR tube with a glass valve having a Teflon spindle and warmed to 70° C. After 3 days, complete conversion into the dihydridodicyanoborate salt mixture is observed by NMR spectroscopy.

¹¹B NMR spectrum of [BH₂(CN)₂] anion:

¹¹B{¹H}-NMR (no lock; solvent: THF), δ, ppm: −42.6 (s).

¹¹B-NMR (no lock; solvent: THF), δ, ppm: −42.6 t, ¹J_11B,H=95 Hz.

The NMR data are in accordance with the values of K[BH₂(CN)₂] described in the literature (WO 2012/163488A1).

Claims

1. Process for the preparation of compounds of the formula I

[Me]+[BHn(CN)4-n]−  I,

where

Me denotes an alkali metal and

n denotes 1 or 2,

by reaction of a compound of the formula II [Me1]+[BFn(CN)4-n]−  II,

where Me1 denotes an alkali metal, which may be identical to or different from Me, and

n denotes 1 or 2, where n is identical in formula I and formula II,

with either

a) an alkali metal or alkaline-earth metal Me2, where an alkali metal Me2 may be identical to or different from Me or Me1; or a metal alloy Me2/Me or Me2/Me, where, in the case where Me2 is an alkali metal, this alkali metal Me2 is different from Me or Me; in an inert-gas atmosphere and in the presence of a medium which is either capable of generating and/or stabilising solvated electrons or is capable of forming an anion free radical, if necessary with addition of a proton source, and a metal cation exchange in the case where neither Me2 nor Me1 corresponds to Me, or

b) an alkali metal hydride of the formula III Me3H  III

in an inert-gas atmosphere, where Me3 may be identical to or different from Me or Me1, without or in the presence of an electrophilic reagent which has affinity to F−, and subsequent metal cation exchange in the case where neither Me3 nor Me1 corresponds to Me.

2. Process according to claim 1, characterised in that the reaction according to variant a) or b) is followed by a purification step.

3. Process according to claim 1, characterised in that the metal cation exchange takes place during the purification step.

4. Process according to claim 1, characterised in that the metal cation exchange is carried out by reaction with the compound (Me)2CO3 and/or the compound MeHCO3, where Me corresponds to the alkali metal Me of the compound of the formula I.

5. Process according to claim 1, characterised in that the reaction of the compound of the formula II, both in variant a) and in variant b), takes place in the presence of an organic solvent.

6. Process according to claim 1, characterised in that the compound of the formula II is prepared in situ.

7. Process according to claim 1, characterised in that the medium for the generation and/or stabilisation of solvated electrons is selected from liquid ammonia, hexamethylphosphoric triamide, amines, α,ω-diaminoalkanes, alcohols or diols.

8. Process according to claim 7, characterised in that the medium for the generation and/or stabilisation of solvated electrons is liquid ammonia.

9. Process according to claim 1, characterised in that the medium which is capable of forming anion free radicals is selected from condensed aromatic compounds.

10. Process according to claim 9, characterised in that the aromatic compound is naphthalene.

11. Process according to claim 1, characterised in that the proton source is water.

12. Process according to claim 1, characterised in that the (F−)-affinitive electrophilic reagent is a lithium or magnesium salt.

13. Process according to claim 12, characterised in that lithium bromide is used.

14. Process for the preparation of compounds of the formula IV

[Kt]z+z[BHn(CN)4-n]−  IV,

where

[Kt]z+ is an inorganic or organic cation,

z corresponds to the charge of the cation and

n denotes 1 or 2,

by anion exchange, where a salt containing the cation [Kt]z+ is reacted with a compound of the formula I [Me]+[BHn(CN)4-n]−  I,

prepared according to claim 1, where Me denotes an alkali metal and n has the same meaning as in the compound of the formula IV.