Compositions – Electrically conductive or emissive compositions – Metal compound containing
Reexamination Certificate
2001-12-20
2004-10-26
Wong, Edna (Department: 1753)
Compositions
Electrically conductive or emissive compositions
Metal compound containing
C205S457000
Reexamination Certificate
active
06808655
ABSTRACT:
The present invention relates to a novel process for synthesizing aryl organozinc derivatives. The invention relates more particularly to the electrolytic synthesis of aryl organozinc derivatives, in the catalytic presence of the element cobalt.
The reactivity of organozinc reagents, especially aryl organozinc reagents, shows many specificities which would make them particularly advantageous in many organic synthesis operations. However, they are difficult to obtain and are often prepared from organometallic reagents made with more electronegative metals, that is to say more reductive metals.
In addition, most of the techniques require the use of highly aprotic and especially very dry media.
In particular, reactions for the electrolytic synthesis of organozinc reagents present the risk of two unwanted reactions: firstly, the reduction reaction to give a hydrogenated derivative, and secondly, a coupling reaction (formation of biaryl)
A certain number of tests have been conducted in an attempt to perform this synthesis electrolytically. The tests that were the most conclusive were performed by some of the authors of the present invention.
Mention may be made more particularly, firstly, of the general textbook “Organozinc reagent, a practical approach” (Paul KNOCHEL and Philip JONES Editors, Oxford University Press, December 1998). More particularly, a synthetic route is described therein in chapter 8 by S. SIBILLE, V. RATOVELOMANANA and J. PERICHON (see also Journal of Chemical Society Chemical Communications, 1992, 283-284) and the article by C. GOSMINI, J. Y. NEDELEC and J. PERICHON (Tetrahedron Letters, 1997, 38, 1941-1942).
In these articles, the only route that is described therein is the use of very specific nickel complexes as electrolytic synthesis catalysts, in a limited number of media. However, the use of these nickel complexes, although constituting an important innovation, does not generally make it possible to achieve high yields relative to the haloaryl substrate.
Accordingly, one of the aims of the present invention is to provide a process for obtaining organozinc derivatives in good yields, both in terms of reaction yields (RY) and degrees of conversion (DC). In other words, one of the aims of the present invention is to provide a technique which allows the conversion of the substrate with good selectivity (CY).
Another aim of the present invention is to provide a technique for reducing the reduction and coupling reactions.
Another aim of the present invention is to provide a route that is capable of catalyzing the electrolytic synthesis reaction of aryl organozinc reagents, starting with the corresponding halo derivatives.
These aims and others, which will emerge hereinbelow, are achieved by means of using cobalt as a catalyst in the electrolytic synthesis of arylzinc compounds.
According to the present invention, it has been shown that cobalt can be introduced especially into the electrolyte in oxidation state II. Admittedly, cobalt can also be introduced in the form of cobalt III, but, since the medium is a reductive medium, this form will have a tendency to disappear very rapidly to be converted into various species, and especially into cobalt II. The state and form of the catalytically active cobalt have not been completely elucidated.
According to one preferred embodiment of the present invention, it is desirable to use cobalt in the presence of at least one of its ligands.
The coordination of the cobalt is advantageously performed with compounds (solvents or solvating agents) that have a high donor number. More specifically, it may be pointed out that it is preferable that the donor number D of these solvents should be greater than or equal to 10, preferably less than or equal to 30, and advantageously between 20 and 30, the limits being included. The said donor number corresponds to the &Dgr;H (variation in enthalpy), expressed in kilocalories, of the combination of said aprotic polar solvent or of said ligand, with antimony pentachloride. This is described more specifically in the book by Christian REINHARDT: “Solvents and Solvent Effects in Organic Chemistry—VCH, page 19, 1988”. Said page gives a definition of the donor number.
It has been shown, in the course of the study which led to the present invention, that very good results are obtained when the atom coordinating to the cobalt is an atom from the nitrogen column, and advantageously nitrogen. In this case, it is preferable that the ligand atom should not bear an electric charge.
When a specific coordinating agent is used, which does not act as solvent, pyridine, nitrile, phosphine, stibine and imine, or even oxime, functions or groups may be mentioned.
When unidentate (or monodentate) ligands are used, it is desirable to use in the electrolyte a molar ratio between the ligand(s) and the cobalt which is high ([lig]/[Co] of about 10 and advantageously ≧about 100); there is usually no upper limit since the ligands may serve as solvent.
When bidentate or multidentate ligands are used, it is possible to decrease the lower limit to ratios at least equal to 2, advantageously to 4 and preferably to 6, but more preferably to 8.
To be efficient, it is desirable that the cobalt should be present at a minimum concentration at least equal to 10
−3
M. To be economical, it is preferable that the cobalt should not be too concentrated; thus, it is preferred that the cobalt content should be not more than 0.2 M.
The reaction medium advantageously comprises a solvent; this solvent should be polar enough to dissolve the metals or, more exactly, the metal salts used, and it should be lipophilic enough to at least partially dissolve the substrates from which it is desired to form the organozinc reagent.
It is preferable to use solvents that are sufficiently low in acidity (it is desirable that their pKa should be at least equal to 16, advantageously to 20 and preferably to 25), so that the reactions with hydrogen are as limited as possible. Thus, primary alcohols are too acidic to give very good results.
More specifically, the solvents that will be preferred are “polar aprotic” solvents such as, for example, alone or as a mixture:
purely oxygenated solvents, in particular ethers, preferably polyethers such as 1,2-dimethoxyethane or cyclic ethers such as THF or dioxane;
amides or ureas (DMF, N-methyl-2-pyrrolidone, imidazolidone, tetramethylurea, dimethoxypropyleneurea, etc.);
sulfones (for example sulfolane) or sulfoxides (such as DMSO); and
provided that they are liquid under the operating conditions, nitrogenous derivatives, nitrogenous heterocycles, especially pyridine, and compounds containing a nitrile function (for those that are preferred, see below); and
a provided that they are liquid under the operating conditions, complexing agents (crown ether, HMPT, tris(3,6-dioxaheptyl)amine (TDA-1)), which improve the correct functioning of the reaction by increasing the conductivity, increasing the reactivity of the anion and preventing the deposition of metal at the cathode.
Without this explanation being limiting, it would appear that these advantageous phenomena are correlated with the ability to complex the metal cations or as a mixture.
As has been mentioned previously, the solvents used may themselves act as complexing agents or ligands. They may especially, and advantageously, contain one or more of the coordination functions mentioned above.
The solvent may be a mixture of an apolar solvent and a polar solvent as defined above by the donor number.
To make the products easier to separate from the reaction media, it is preferable that said solvent should have a boiling point that is substantially different from the compound to be synthesized and from the starting compound.
To facilitate the reaction and to improve the conductivity of the medium, saline electrolytes, occasionally referred to as base salts, optionally modified by the presence of complexing agents, are generally used. These electrolytes are chosen so as not to disrupt the reactions at the anode and the cathode.
Accordi
Gosmini Corinne
Perichon Jacques
Rollin Yolande
Rhodia Chimie
Wong Edna
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