EP0201365A1 - Process for the electrosynthesis of alcohols and epoxide compounds - Google Patents

Abstract

The invention relates to a process for the electrosynthesis of alcohols and epoxy compounds by electrochemical reduction of organic halides in the presence of carbonyl derivatives in an organic solvent medium containing a supporting electrolyte. The organic halides contain an atom or a functional group which stabilizes carbon-ions, preferably fixed to the carbon carrying the halogen. The anode is made of a reducing metal preferably chosen from the group consisting of magnesium, aluminium, zinc, iron and their alloys. This process has the advantage of being simple, readily convertible to an industrial scale, especially as a result of the possibility of using a single-compartment cell and low-toxicity solvents. It can be applied to the electrosynthesis of numerous alcohols.

Description

The invention relates to a process for the electrosynthesis of alcohols and epoxy compounds by electrochemical reduction of organic halides in the presence of carbonyl derivatives, process carried out in an electrolysis cell in an organic solvent medium containing an indifferent electrolyte.

Alcohols are compounds commonly used in the chemical industry, in particular as synthesis intermediates; they are also used in pharmacy, perfumery, etc.

• -SHONO et collaborateurs, d'une part dans Te- trahedron Letters, Vol 22, pages 871-874 (1981) et d'autre part dans J. Am. Chem. Soc. 1984, 106, 259-260 décrivent un tel procédé dans le cas d'aldéhydes comme dérivés carbonylés. La cellule d'électrolyse comporte deux compartiments séparés par un diaphragme en céramique et les électrodes sont en carbone. L'aldéhyde et l'halogénure organique sont introduits dans le compartiment cathodique, en milieu solvant (chloroforme ou N,N-diméthylformamide).

Several processes for the electrosynthesis of alcohols by electrochemical reduction of organic halides in the presence of carbonyl derivatives are known:

• -SHONO et al., On the one hand in Tetrahron Letters, Vol 22, pages 871-874 (1981) and on the other hand in J. Am. Chem. Soc. 1984, 106, 259-260 describe such a process in the case of aldehydes as carbonyl derivatives. The electrolysis cell has two compartments separated by a ceramic diaphragm and the electrodes are made of carbon. The aldehyde and the organic halide are introduced into the cathode compartment, in a solvent medium (chloroform or N, N-dimethylformamide).

The reaction is only described for two polyhalides which are particularly easy to reduce (CCI, and CCl ₃ COOCH ₃ ).

• -KARRENBROCK et SCHAFER dans Tetrahe- dron Letters, N° 17, pages 1521-1522 (1978) décrivent également un tel procédé dans lequel la cellule d'électrolyse comporte deux compartiments séparés. Le dérivé carbonylé et l'halogénure organique sont introduits dans le compartiment cathodique, en milieu N,N-diméthylformamide (DMF) comme solvant. La réaction n'est décrite que pour CCI,, polyhalogénure particulièrement facile à réduire.

The yields vary between 20 and 89% depending on the products and the operating conditions.

• -KARRENBROCK and SCHAFER in Tetrahedron Letters, N ° 17, pages 1521-1522 (1978) also describe such a process in which the electrolysis cell has two separate compartments. The carbonyl derivative and the organic halide are introduced into the cathode compartment, in N, N-dimethylformamide (DMF) medium as solvent. The reaction is only described for CCI, polyhalide particularly easy to reduce.

In the case of aldehydes, the yields vary between 30 and 70%. In the case of ketones, the yields are much lower (10 and 25%).

SATOH, SUGINOME, TOKUDA in Bull. Chem., Soc. Jpn., 56, 1791-1794 (1983) describe the electrosynthesis of tertiary alcohols by electrochemical reduction of allylic or benzylic halides in the presence of acetone in an un-compartmentalized electrolysis cell; the electrodes are made of platinum, the cathode can also be made of mercury or carbon.

Only the use of hexamethylphosphorotriamide - (HMPT) as solvent makes it possible to obtain acceptable yields (13 to 53% depending on the operating conditions). The use of DMF and THF as solvent instead of HMPT is particularly inappropriate, since, all other conditions being identical, the yield then drops from 53% to less than 10%.

However, HMPT is a particularly toxic and in particular carcinogenic solvent, which excludes its use in an industrial process.

To the knowledge of the

Applicant, of a simple process, transposable on an industrial scale, of electrosynthesis of alcohols or of epoxy compounds by electrochemical reduction of organic halides in the presence of carbonyl derivatives in an electrolysis cell in organic solvent medium containing an indifferent electrolyte, having a high yield and of sufficiently general scope, that is to say applicable, as regards carbonyl derivatives, both to aldehydes and to ketones, the reactivity of which is known to be lower than that of aldehydes, and applicable to other halogenated derivatives which are more difficult to reduce than the few polyhalides which are particularly easy to reduce, mentioned above in the prior art.

The object of the present invention is such a method.

The process according to the invention for electrosynthesis of alcohols and epoxy compounds by electrochemical reduction of organic halides in the presence of carbonyl derivatives in an electrolysis cell provided with electrodes, in an organic solvent medium containing an indifferent electrolyte is characterized in using an anode consumable in a metal chosen from the group of reducing metals and in that the organic halides have at least one atom or a functional group stabilizing carbanions.

• 1) Ce procédé est très simple de mise en oeuvre puisqu'il peut être mis en oeuvre dans une cellule d'électrolyse à un seul compartiment, sans diaphragme ni fritté, ce qui est très important, notamment au stade industriel.
• 2) Ce procédé peut être mis en oeuvre avec des solvants relativement peu toxiques, utilisables et utilisés de façon courante dans l'industrie (DMF par exemple).
• 3) Ce procédé a une portée relativement large et est applicable à l'électrosynthèse de nombreux alcools et compsés époxydes.

It has been observed, as the description which follows shows, that in a completely unexpected manner, high yields are thus obtained while:

• 1) This process is very simple to implement since it can be implemented in a single compartment electrolysis cell, without diaphragm or sintered, which is very important, especially at the stage industrial.
• 2) This process can be carried out with relatively low-toxic solvents which can be used and commonly used in industry (DMF for example).
• 3) This process has a relatively wide scope and is applicable to the electrosynthesis of many alcohols and epoxy compounds.

It should also be noted that, unlike the methods described in the state of the art for which an inert anode is used, there is not, in the method according to the invention, degradation of the solvent at the anode. This feature is particularly interesting and advantageous.

The electrolysis cell is a conventional cell, well known to those skilled in the art, comprising only one compartment. This possibility of using a single compartment cell is a major advantage as already mentioned.

According to the invention, the organic halides have at least one atom or one functional group stabilizing carbanions. Preferably, this atom or group is attached to the carbon carrying the halogen, that is to say located in position a relative to the halogen.

The atoms and functional groups which stabilize carbanions are well known to those skilled in the art. Mention may be made, for example, of halogens, ester, ketone, allyl, benzyl, alkoxy or nitrile groups.

• -un groupement benzylique, substitué ou non substitué
  
  , Ar représentant un groupement aromatique)
• -un groupement allylique, substitué ou non substitué
  
  \
• -un groupement a monohalogéné (- C -X), gem. dihalogéné
  
• ou α trihalogéné (CX,)
• -un groupement a ester
  
• -un groupement a cétonique
  
• -un groupement aryle substitué par des groupements stabilisateurs de carbanions.

Preferably, the organic halides which can be used in the context of the present invention correspond to the general formula RX in which X represents a halogen atom and R represents

• a benzyl group, substituted or unsubstituted
  
  , Ar representing an aromatic group)
• an allylic group, substituted or unsubstituted
  
  \
• -a monohalogenated group (- C -X), gem. dihalogenated
  
• or α trihalogenated (CX,)
• - an ester group
  
• -a keto group
  
• an aryl group substituted by carbanion stabilizing groups.

dans laquelle R, et R₂, identiques ou différents, représentent :

• -un atome d'hydrogène,
• -une chaîne aliphatique ou cycloaliphatique, substituée ou non substituée, saturée ou non saturée,
• -un groupement aryle, substitué ou non substitué,
• ou bien encore, R, et R₂. conjointement avec l'atome de carbone auquel ils-sont attachés, forment un cycle, saturé ou non saturé, substitué ou non substitué, comportant éventuellement un ou plusieurs hétéroatomes comme l'azote, l'oxygène, le phosphore ou le soufre. A titre illustratif et non limitatif, on peut citer par exemple l'acétone, la cyclohexa- none, la méthyléthylcétone, l'acétaldehyde, la ben- zophénone et la dichlorobenzophénone.

By way of illustration and without limitation, there may be mentioned for example benzyl chloride, benzyl bromide, allyl chloride, 3-chloro 2 methyl propene, 3-chloro 1 butene, 1 chloro 1 methyl acetate d ethyl, carbon tetrachloride, dichlorophenyl-methane, 1-phenyl 3-chloro propene and 1-methyl 3 chloropropene: According to a particular embodiment of the invention, the carbonyl derivatives correspond to the general formula

in which R, and R ₂ , identical or different, represent:

• -a hydrogen atom,
• - an aliphatic or cycloaliphatic chain, substituted or unsubstituted, saturated or unsaturated,
• an aryl group, substituted or unsubstituted,
• or again, R, and R ₂ . together with the carbon atom to which they are attached, form a ring, saturated or unsaturated, substituted or unsubstituted, optionally comprising one or more heteroatoms such as nitrogen, oxygen, phosphorus or sulfur. By way of illustration and without limitation, mention may be made, for example, of acetone, cyclohexanone, methyl ethyl ketone, acetaldehyde, benzophenone and dichlorobenzophenone.

dans laquelle R, R, et R₂ ont la signification précitée.According to a preferred variant, the alcohols obtained according to the process which is the subject of the present invention correspond to the general formula

wherein R, R, and R ₂ have the above meaning.

Particularly preferably, when the carbonyl derivatives are ketones, that is to say when R. and R ₂ are different from hydrogen, tertiary alcohols are obtained.

Epoxy compounds are obtained when an organic halide compound is used as the organic halides. An elimination of a halogenated acid molecule then occurs.

As a general rule, in order to carry out the present invention, it is quite obvious to those skilled in the art that the carbonyl derivative must be more difficult to reduce than the organic halide and none of the substituents carried by R, and R2 must be more electrophilic than the carbonyl group itself.

The process which is the subject of the present invention is characterized in that an anode consumable in a metal chosen from the group consisting of reducing metals is used.

Preferably, the metal is chosen from the group comprising magnesium, aluminum, zinc, iron and their alloys. The term "their alloys" means any alloy containing at least one of the above-mentioned metals, namely magnesium, aluminum, zinc and iron. This anode can have any shape and in particular all the classic forms of metal electrodes well known to those skilled in the art (twisted wire, flat bar, cylindrical bar, renewable bed, balls, fabric, grid, etc.).

Preferably, a cylindrical bar of diameter adapted to the dimensions of the cell is used. For example, for a cell whose total volume is 45 cm3, the diameter of the bar is of the order of 1 cm.

Before use, it is preferable to clean the surface of the anode, chemically (by diluted HCI for example) or mechanically (file, Emeri cloth for example) so as to remove in particular the metal oxide often present on the surface of the metal.

The cathode is any metal such as stainless steel, nickel, platinum, gold, silver, or carbon. It is preferably formed by a grid or a cylindrical plate arranged concentrically around the anode.

The electrodes are supplied with direct current via a stabilized power supply.

The organic solvents used in the context of the present invention are all the low-protic solvents usually used in organic electrochemistry. Examples include DMF, acetonitrile, tetramethylurea (TMU), tetrahydrofuran (THF) and THF-HMPT mixtures. Preferably, DMF is used.

Acetone can also be used. In this case it plays both the role of solvent and of carbonyl derivative.

The indifferent electrolytes used can be those usually used in organic electrochemistry. Mention may be made, for example, of the salts whose anion is a halide, a carboxylate, an alcoholate, a perchlorate or a fluoroborate and the cation a quaternary ammonium, lithium, sodium, potassium, magnesium, zinc or aluminum.

Among these salts, mention may in particular be made of tetraalkyl ammonium tetrafluoroborates - (tetrabutylammonium tetrafluoroborate, for example), tetrabutylammonium perchlorate, tetraalkyl ammonium halides (tetrabutylammonium chloride or tetrabutylammonium iodide, for example tetrabutylammonium iodide) lithium.

Preferably, the concentration of indifferent electrolyte in the organic solvent is between 0.01 M and 0.5 M.

Also preferably, the concentration of organic halides in the organic solvent is between 0.2 M and 2 M.

The ratio of concentrations in the organic solvent between the carbonyl derivative and the organic halide can be arbitrary. It is preferable to use an excess of carbonyl derivative and in particular a concentration ratio of between 0.5 and 10.

The electrosynthesis reaction of the invention can be catalyzed by an organometallic complex of the transition metals such as for example the bipyridyl complexes of metal halides and more particularly the nickel bromide complex 2,2'bipyridine.

The use of such a catalyst proves to be very advantageous when the alkyl halide is difficult to reduce or the anhydride is easy to reduce.

• 1) à une température généralement comprise entre -20 °C et + 30°C,
• 2) sous une densité de courant sur la cathode variant de préférence entre 0,1 et 10 A/dm2. On opère en général à intensité constante, mais on peut également opérer à tension constante, à potentiel contrôlé ou avec intensité et potentiel variables,
• 3) sous agitation de la solution, par exemple par l'intermédiaire d'un barreau aimanté, après avoir désoxygéné la solution par barbotage d'un gaz inerte, azote ou argon par exemple.

The following procedure is given by way of example:
Electrolysis is conducted

• 1) at a temperature generally between -20 ° C and + 30 ° C,
• 2) at a current density on the cathode preferably varying between 0.1 and 10 A / dm2. We generally operate at constant intensity, but we can also operate at constant voltage, with controlled potential or with variable intensity and potential,
• 3) with stirring of the solution, for example by means of a magnetic bar, after having deoxygenated the solution by bubbling with an inert gas, nitrogen or argon for example.

After passing a quantity of current corresponding to 2 Faraday (2 X 96500C) per mole of halogenated derivatives (or possibly until complete transformation of these) _; the electrolysis is stopped.

To verify the total transformation of the halogenated derivatives, an aliquot part of the solution is taken. After hydrolysis then extraction with ether, the absence of the starting halogenated derivatives and the formation of the corresponding alcohols is verified by gas chromatography (GC). At this stage, the determination of the halogenated derivatives still present makes it possible to know the rate of transformation of these halogenated derivatives and the determination of the alcohols to know the yield of alcohols formed.

The rest of the solution is then hydrolyzed (for example with water, ammonium chloride or hydrochloric acid). The alcoholate formed is then transformed into alcohol which is then extracted according to conventional methods, with ether for example.

After evaporation of the extraction solvent and of the light products, the crude alcohol is isolated, which is identified by its NMR and IR spectra, and the purity of which is determined by GC. We then deduce the yield of the reaction in * pure alcohol isolated with respect to the starting organic halide.

The isolated raw alcohol is then purified either by distillation or by separation on a silica column. The pure alcohol thus isolated (purity verified by CPG) is identified by its IR and NMR spectra.

The invention is illustrated by the nonlimiting examples which follow. To carry out these examples, a conventional electrolysis cell is used, consisting of two parts.

The upper glass part is equipped with 5 tubes allowing the arrival and the exit of the inert gas, the possible samples of solution during electrolysis, the electrical passages. The lower part consists of a stopper fitted with a seal, screwed onto the upper glass part.

The total volume of the cell is 45 cm3.

The anode is formed by a cylindrical bar 1 cm in diameter. It is introduced into the cell through the central tube and is thus located approximately in axial position relative to the cell. It dips into the solution over a length of about 2.5 cm.

The cathode consists of a cylindrical fabric arranged concentrically around the anode. The "working" surface of the cathode is of the order of 20 cm 2.

The cell is immersed in a thermostatic bath set to the chosen temperature.

The particular operating conditions (nature of the electrodes, of the indifferent electrolyte, of the solvent used, the temperature of the bath, etc.) are also specified for each example.

Free 1 - Synthesis of dimethylbenzylcarbinol.

The anode is a cylindrical bar of magnesium, diameter 1 cm. The cathode is a cylindrical fabric of nickel foam, arranged concentrically around the anode. Its apparent surface is 20 cm2.

20 cm3 of anhydrous DMF are introduced into the cell. 10 cm3 (or 136 mmol) of acetone, 3.29 g (26 mmol) of benzyl chloride and 0.78 g (2 mmol) of tetrabutylammonium tetrafluoroborate.

Nitrogen is bubbled through the solution for about 15 min and then the nitrogen is kept at atmospheric pressure above the solution.

The solution is stirred using a magnetic bar and then the cell is immersed in a thermostatic bath maintained at -20 ° C. The electrodes are supplied with direct current via a stabilized power supply and a constant current density is imposed, equal to 2 A / dm2 on the cathode.

After passing 2 Faraday per mole of benzyl chloride, an aliquot of the solution is taken. After hydrolysis then extraction with ether, analysis by GPC shows that all of the benzyl chloride has been transformed and that dimethylbenzylcarbinol of formula has been formed

To isolate the alcohol formed from the entire solution, the excess acetone is first evaporated and then hydrolyzed with an aqueous ammonium chloride solution, then extracted 3 times with ether.

After evaporation of the ether and of the light products, the dimethylbenzylcarbinol is isolated, which is identified by its NMR and IR spectra. This crude dimethylbenzylcarbinol has a purity of 70%, determined by CPG. Among the impurities, mention may be made of bibenzyl, toluene and DMF and diacetone alcohol.

The isolated crude dimethylbenzylcarbinol is then purified by distillation. Pure dimethylbenzylcarbinol is obtained (purity greater than 95% according to analysis by GPC), identified by its IR and NMR spectra. The yield dimethylbenzylcarbinol ^p ur so obtained is 56%

EXAMPLES 2 TO 32 Synthesis of dimethylbenzylcarbinol

The same tests were carried out as that described in Example 1, but modifying certain operating conditions. especially the nature of the anode. The operating conditions, compared with those of Example 1, as well as the results obtained are specified in Table 1.

It is found that the yields obtained are relatively high, between 50 and 70% in the majority of cases. These yields are expressed as pure alcohol present in the isolated raw alcohol, relative to the starting benzyl chloride.

Free 33 to 57 -Synthesis of various alcohols

The same general operating conditions for preparation, isolation, dosing and purification as those followed for the previous examples were applied. The indications relating to the starting materials and to the conditions specific to each test as well as the results obtained are specified in table 2.

In Examples 41 and 42, the alcohols formed were isolated from the crude product obtained by chromatographic separation on silica gel and identified by their IR and NMR spectra.

Unless otherwise indicated, the yields indicated are those of alcohols formed, relative to the starting organic halide.

EXAMPLES 58 TO 65 Preparation of epoxy compounds

By conducting electrosynthesis under the same general conditions of preparation, isolation, dosage and purification as those followed for the previous examples, but taking as organic halide, a gem.dihalogenated compound, for example benzy chloride lidene, on the one hand the expected alcohol is obtained but also on the other hand and in majority the epoxy compound by elimination of a molecule of HX acid from the alcohol formed.

Table 3 lists the indications relating to the starting materials and the conditions specific to each test as well as the results obtained.

Examples 66 to 71

These electrosyntheses are carried out under the same conditions as those of the previous examples. However, a catalyst was added to the solution in proportions of 1.5 mmol.

This catalyst is a nickel-2,2 'bipyridyl bromide complex (NiBrzBipy).

This complex is prepared by adding 2 x 10- ^Z mole of NiBr ₂ .2H ₂ O and 2 x 10 ^-2 mole of 2-2'bipyridine (Bipy), in 120 ml of absolute ethanol.

This mixture is stirred for 24 hours at a temperature of 20 ° C. The mixture is filtered to recover the NiBr ₂ .2-2'Bipy complex which has precipitated.

This precipitate is washed with acetone and after drying under vacuum at 20 ° C., 1.8 × 10 ^-2 mole of NiBr ₂ Bipy are recovered. or a weight yield of 90%.

Table 4 brings together the operating conditions and the nature of the starting products and of the products obtained in examples 66 to 71. The yields of alcohol produced and isolated are expressed relative to the carbonylated starting product.

présent à une concentration de 35 mmol, dans 30 ml de DMF et en utilisant comme électrolyte inerte une solution de N(Bu)₄l à une concentration de 10-² mole/litre pour les essais 66, 67 et 69, ou une solution à 10^-1 mole/litre de (N(Bu)₄Br pour les essais 70,71. Pour l'essai 68, l'électrolyte inerte est le N(Et)4Br à une concentration de 10-² mole/litre.These tests were carried out using an organic halide of formula

present at a concentration of 35 mmol in 30 ml of DMF and by using as inert electrolyte a solution of N (Bu) ₄ l at a concentration of 10- ² mole / liter for tests 66, 67 and 69, or a solution to 10 ^-1 mol / l (N (Bu) ₄ Br 70.71 for testing. for testing 68, the inert electrolyte is N (Et) 4Br at a concentration of 10- ² mole / liter.

The electrolysis is carried out with a carbon cathode and a current density of 1 A / dm ² .

The electrosynthesis process of the invention makes it possible to synthesize compounds which are particularly useful in the field of perfumery such as dimethylbenzylcarbinol, methylethylbenzylcarbinol, for example, or that of pharmacy such as parachlorobenzyl-dimethylcarbinol which is used to manufacture chlortermine.

Claims (17)

1-Process for the electrosynthesis of alcohols by electrochemical reduction of organic halides in the presence of carbonyl derivatives in an electrolysis cell provided with electrodes, in an organic solvent medium containing an indifferent electrolyte characterized in that a consumable anode is used in a metal chosen from the group consisting of reducing metals and in that the organic halides have at least one atom or a functional group stabilizing carbanions. 2-Alcohol electrosynthesis method according to claim 1 characterized in that an anode consumable in a metal chosen from the group consisting of magnesium, aluminum, zinc, iron and their alloys is used. 3-A process for the electrosynthesis of alcohols according to any one of the preceding claims, characterized in that the organic halides have at least one atom or a functional group stabilizing carbanions, attached to the carbon carrying the halogen. 4-Alcohol electrosynthesis process according to any one of the preceding claims, characterized in that the carbonnylated derivatives correspond to the general formula

in which R, and R ₂ , identical or different, represent ^* a hydrogen atom ^* an aliphatic or cycloaliphatic chain, substituted or unsubstituted, saturated or unsaturated ^* an aryl group, substituted or unsubstituted
or again, R, and R ₂ . together with the carbon atom to which they are attached, form a ring, saturated or unsaturated, substituted or unsubstituted, optionally comprising one or more heteroatoms. 5-Process for the electrosynthesis of tertiary alcohols according to any one of the preceding claims, characterized in that the carbonyl derivatives are ketones. 6-Process for the electrosynthesis of alcohols according to any one of the preceding claims, characterized in that the organic halides correspond to the general formula RX in which X represents a halogen atom and R represents a benzyl group, substituted or unsubstituted, an allylic group, substituted or unsubstituted, -a monohalogenated, dihalogenated or α trihalogenated group, - an ester group, -a keto group, an aryl group substituted by carbanion stabilizing groups. 7-Alcohol electrosynthesis process according to any one of the preceding claims, characterized in that the organic solvent is N, N-dimethylformamide (DMF). 8-Alcohol electrosynthesis method according to any one of the preceding claims, characterized in that the indifferent electrolyte is chosen from the group consisting of tetraalkylammonium tetrafluoroborates, tetraalkylammonium halides, tetrabutylammonium perchlorate and perchlorate of lithium. 9-A process for the electrosynthesis of alcohols according to any one of the preceding claims, characterized in that the concentration of indifferent electrolyte in the organic solvent is between 0.01 M and 0.5 M. 10-Process for the electrosynthesis of alcohols according to any one of the preceding claims, characterized in that the concentration of ha organic logures in the organic solvent is between 0.2 M and 2 M. 11-Process for the electrosynthesis of alcohols according to any one of the preceding claims, characterized in that the ratio of the concentrations in the organic solvent between the carbonyl derivative and the organic halide is between 0.5 and 10. 12-Alcohol electrosynthesis method according to any one of the preceding claims, characterized in that the electrolysis temperature is between -20 ° C and + 30 ° C. 13-Alcohol electrosynthesis method according to any one of the preceding claims, characterized in that the current density on the cathode is between 0.1 A / dm ² and 10 A / dm ² . 14-Alcohol electrosynthesis process according to any one of the preceding claims, characterized in that the electrolysis is carried out at constant intensity. 15-Process for the electrosynthesis of epoxy compounds characterized in that the process according to one of the preceding claims is used and in that the abovementioned organic halides are chosen from gem.dihalogenated compounds. 16-Electrosynthesis process according to one of the preceding claims, characterized in that the electrolysis is carried out in the presence of a catalyst chosen from the organometallic complexes of the transition metals, preferably the bipyridyl complexes of metal halides. 17-electrosynthesis process according to claim 16, characterized in that the aforementioned catalyst is the bipyridyl complex of nickel bromide.