Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-02-22
2002-04-09
Higel, Floyd (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C568S631000, C568S797000, C585S427000, C585S435000, C585S457000
Reexamination Certificate
active
06369265
ABSTRACT:
TECHNICAL FIELD
This invention relates to Kumada coupling reactions, which can be used for chemical synthesis in the polymer and the fine chemical industry.
BACKGROUND
Metal catalyzed coupling reactions of aryl bromides, aryl iodides, and aryl pseudohalides (e.g., triflates) with various substrates is a general method employed for the formation of C—C bonds. Prior art methods generally cannot employ aryl chlorides as feedstock for these chemical transformations, and require the use of more expensive aryl bromides and aryl iodides. The use of aryl chlorides as chemical feedstock in coupling chemistry has proven difficult but would economically benefit a number of industrial processes. The few prior art methods that can employ aryl chlorides use expensive, air-sensitive phosphine ligands. In addition, phosphine ligands are often difficult to remove from the process product.
Nucleophilic N-heterocyclic carbenes, the imidazoline-2-ylidenes (sometimes commonly called imidazol-2-ylidenes) or so-called “phosphine mimics”, have attracted considerable attention as possible alternatives for the widely used phosphine ligands in homogeneous catalysis. A primary advantage of these ligands is that an excess of the ligand is not required. It appears that these ligands do not dissociate from the metal center, thus preventing aggregation of the catalyst to yield the bulk metal.
THE INVENTION
This invention provides a process for conducting Kumada coupling reactions. The catalyst system used in the present invention permits the use of aryl chlorides as substrates in Kumada coupling reactions while eliminating the need for phosphine ligands. Furthermore, both electron-donating and electron-withdrawing substituents on the aryl halide or pseudohalide, the Grignard reagent, or both, in the Kumada coupling reaction are tolerated by the catalyst system used in the present invention, and provide the corresponding Kumada coupling products in excellent yields. Homocoupling of aryl pseudohalides is also feasible using the processes of this invention.
An embodiment of this invention provides a process which comprises mixing, in a liquid medium, i) at least one aryl halide wherein the aryl halide has, directly bonded to the aromatic ring(s), at least one halogen atom selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom; ii) at least one Grignard reagent; iii) at least one metal compound comprising at least one metal atom selected from nickel, palladium, and platinum, wherein the formal oxidation state of the metal is zero or two; and iv) at least one N-heterocyclic carbene. The N-heterocyclic carbene is selected from the group consisting of an imidazoline-2-ylidene wherein the 1 and 3 positions are each, independently, substituted by a secondary or tertiary group which has at least three atoms, or a protonated salt thereof; an imidazolidine-2-ylidene wherein the 1 and 3 positions are each, independently, substituted by a secondary or tertiary group which hag at least three atoms, or a protonated salt thereof; a bis(imidazoline-2-ylidene) wherein abridging moiety is bound to one nitrogen atom of each ring, and wherein the remaining two nitrogen atoms are each, independently, substituted by a secondary or tertiary group which has at least three atoms, or a protonated salt thereof; and a bis(imidazolidine-2-ylidene) wherein a bridging moiety is bound to one nitrogen atom of each ring, and wherein the remaining two nitrogen atoms are each, independently, substituted by a secondary or tertiary group which has at least three atoms, or a protonated salt thereof, or mixtures of two or more of the foregoing.
Another embodiment of this invention provides a process for homocoupling. This process comprises mixing, in a liquid medium, i) at least one aryl pseudohalide; ii) at least one metal compound comprising at least one metal atom selected from nickel, palladium, and platinum, wherein the formal oxidation state of the metal is zero or two; and iii) at least one N-heterocyclic carbene selected from the group described in the first embodiment.
Further embodiments and features of this invention will be apparent from the ensuing description and appended claims.
As noted above, there are two fundamental aspects to this invention. One aspect is the provision of exceedingly efficient catalyzed Kumada coupling reactions. The other aspect involves the discovery of catalyzed homocoupling reactions in which aryl triflates or aryl tosylates are caused to homocouple even in the presence of a Grignard reagent.
The liquid medium for the processes of this invention can include any of a wide range of solvents, and mixtures of solvents are also usable. The exclusion of water is necessary because the processes of this invention use Grignard reagents. Types of solvents that can be used include hydrocarbons, ethers, and amides. Polar solvents are preferred. When a hydrocarbon solvent is included in the liquid medium, it is preferred that the hydrocarbon solvent is makes up less than a third (by volume) of the liquid medium. Ethers are a preferred solvent type. Ethers that may be used include, for example, diethyl ether, di-n-propyl ether, diisopropyl ether, tert-butyl ethyl ether, diheptyl ether, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, methyl tetrahydrofuran, glyme (the dimethyl ether of ethylene glycol), diglyme (the dimethyl ether of diethylene glycol), and the like. Cyclic ethers and polyethers are preferred, especially 1,4-dioxane and tetrahydrofuran. Mixtures comprising tetrahydrofuran are more preferred; a highly preferred liquid medium is a mixture of 1,4-dioxane and tetrahydrofuran.
Directly bonded to the aromatic ring(s) of the aryl halide or pseudohalide (i.e., aryl halide or aryl pseudohalide) is at least one halogen atom selected from a chlorine atom, a bromine atom, and an iodine atom, or at least one pseudohalide group. The term “pseudohalide group” includes such groups as p-toluene sulfonate (tosylate), trifluoromethanesulfonate (triflate), methanesulfonate (mesylate), nonaflate (ON
f
) and aryl diazonium salts (ArN
2
+
X
⊖
, where X
⊖
is halide, BF
4
⊖
, etc.). The aryl halide or pseudohalide can have two or more such halogen atoms with an atomic number greater than nine and/or pseudohalide groups, including combinations of halogen atoms and pseudohalide groups. However, when two or more such groups are present, the halogen atoms with an atomic number greater than nine and/or pseudohalide groups should all be different from each other. For example, when two such substituents are present, they may be a chlorine atom and a bromine atom, or an iodine atom and a tosylate group, or etc. It is preferred that there is only one chlorine atom, bromine atom, iodine atom, or pseudohalide group directly bound to the aryl ring of the aryl halide or pseudohalide. Aryl chlorides are more preferred as the aryl halide reactants.
The aryl moiety for the aryl halide or pseudohalide can be homocyclic or heterocyclic. Examples of suitable homocyclic aryl moieties include, but are not limited to, benzene, naphthalene, anthracene, phenanthrene, pyrene, biphenyl, acenaphthalene, fluorene, and indene. Heterocyclic aryl moieties that can be used include, for example, furan, thiophene, pyridine, indole, oxathiolane, isoxazole, thianthrene, isobenzofuran, phenoxathin, and the like. Benzene is a preferred aryl moiety for the aryl halide or pseudohalide.
For the aryl halide or pseudohalide, substituents other than a chlorine atom, a bromine atom, an iodine atom, and/or a pseudohalide group that may be present on the aromatic ring(s) include, but are not limited to, hydrogen atoms, fluorine atoms, nitro groups, hydrocarbyl groups, alkoxy groups, perfluorohydrocarbyl groups, silyl groups, amino groups, ether groups, ketone groups, and ester groups. When hydrocarbyl groups are present, they are preferably C
1
to C
18
alkyl groups or C
6
to C
20
aryl or aralkyl groups. Examples of suitable hydrocarbyl groups are methyl, ethyl, isopropyl, tert-butyl, cyclopentyl, methylcyclohexyl,
Huang Jinkun
Nolan Steven P.
Trudell Mark L.
Zhang Chunming
Higel Floyd
Sackey Ebenezer
Sieberth & Patty L.L.C.
University of New Orleans Research & Technology Foundation
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