Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-02-16
2003-09-30
Aulakh, Charanjit S. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C548S312700, C548S324500, C548S325100, C548S326100, C548S335100, C548S111000
Reexamination Certificate
active
06627758
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to ligands, transition metal complexes including the ligands, and methods of using the ligands and transition metal complexes. More particularly, the invention relates to ligands including first and second heteroatoms, transition metal complexes of such ligands, and methods of using the ligands and complexes, for example, to facilitate chemical reactions, such as hydration of terminal alkynes.
Medicinal chemists and biochemists want to know how amino acids are arranged in proteins, so that they can better understand the correlation between structures and the functions of drugs. One of the techniques used to accomplish the task of protein structure determination requires the breaking of amide bonds to liberate the amino acids. However, at physiological temperatures and pH 9, it takes an impractical length of time, for example, 168 years, to break half the amide bonds in a sample. In contrast, organisms found in nature have remarkably efficient systems to make and break amide bonds. Scientists have used natural enzymes such as carboxypeptidase to do the task of amide bond cleavage.
In some cases, it is believed that the crucial step involves proton transfer between imidazole, a carboxylate, and the amide undergoing hydrolysis, while other enzymatic systems involve a metal-catalyzed amide bond cleavage such as that seen in the zinc(II)-metalloprotease. However, existing enzymatic systems can be very complicated and sometimes difficult to handle due to their sensitivity to temperature and pH.
Amide hydrolysis has been catalyzed not only by enzymes, but also by acids, bases, and metal ions. These systems take advantage of one or more possible factors, which facilitate amide bond cleavage. First, the amide bond cleaving reagent or catalyst could act as a proton transfer reagent, which can be an important factor in amide bond hydrolysis. Secondly, a metal may catalyze or mediate amide hydrolysis by acting as a Lewis acid through O-complexation, delivery of a metal-coordinated hydroxide or a combination of the latter two processes.
Considerable work has been directed toward studying the amide hydrolysis reaction and the development of reagents that assist amide hydrolysis. Some work toward the development of an amide hydrolysis catalyst has been published by Kostic. For example, Kostic and coworkers have found that a palladium(II) complex can accomplish the hydrolysis of a number of dipeptides, but with only a modest 4 catalytic turnovers.
It would be advantageous to provide reaction facilitators, e.g., catalysts, promoters and the like, that mimic enzymatic systems in their hydrogen-bonding and/or proton transfer abilities, but are robust, simple to handle, and have useful reactor facilitation.
Industrial hydrolysis of acrylonitrile is used to make acrylic acid which, in turn, can be converted to a variety of esters such as methyl, ethyl, butyl, and 2-ethylhexyl acrylates. The acrylates can then be used as comonomers with methyl methacrylate and/or vinyl acetate to give polymers for water-based paints, among other products. A number of industrial methods exist for obtaining acrylic acids from nitriles and one of the more economical methods is the direct hydrolysis of the acrylonitrile to the acrylic acid. However, this synthetic route involves the use of a stoichiometric amount of sulfuric acid to produce the acrylamide sulfate, which is then treated with an alcohol to give the acrylic ester. It would be advantageous to provide a direct route from the acrylonitrile and alcohol to yield the desired acrylate without the need to use and then neutralize a strong acid.
As petroleum resources dwindle and the need to control the emissions of carbon dioxide into the environment increases, use of carbon dioxide as a feedstock becomes more desirable. It would be advantageous to provide materials useful to facilitate carbon dioxide conversion, for example, to carbonates, carbamates and ureas.
A further example of environmentally desirable methods of conducting organic synthesis involves the use of water in the oxidation of unsaturated hydrocarbons. For example, the metal-catalyzed hydration of alkynes is an important route to carbonyl compounds. The use of water in such syntheses has the additional advantages of ease of use, safety, and economic savings. Most metal-catalyzed hydrations of 1-alkynes follow Markovnikov addition to give ketones. Recently, anti-Markovnikov addition has been reported, which gives aldehydes and a small amount of ketones [Tokunaga, M., et al.
Angew. Chem. Int. Ed.,
37(20), 2867-2869 (1998); JP 11319576].
It is desirable to identify and exploit the novel cooperativities afforded by metal ions and suitable organic ligands in additional industrial processes, for example, in the hydration of terminal alkynes. It is preferred that such reactions be catalytic in nature so that the organometallic complex is not consumed during the reaction.
SUMMARY OF INVENTION
New organic ligands, transition metal complexes including such ligands and methods for using the ligands and complexes have been discovered. The present ligands and transition metal complexes can be produced using relatively straightforward synthetic chemistry techniques. Moreover, the structures of the present ligands and metal complexes can be effectively selected or even controlled, for example, in terms of proton transfer ability and/or hydrogen bonding ability, thereby providing ligands and complexes with properties effective to facilitate one or more chemical reactions. Thus, the present metal complexes can be effectively used to facilitate, for example, catalyze, promote, and the like, various chemical reactions, such as hydrolysis, alcoholysis, aminolysis, carbon dioxide conversion, and hydration reactions, which provide useful benefits.
In one broad aspect of the present invention, compositions are provided which comprise at least one organic ligand and a transition metal moiety partially complexed by the organic ligand.
The present organic ligands, many of which themselves are novel and within the scope of the invention, include a first heteroatom and a second heteroatom. The first and second heteroatoms are covalently bonded to each other or separated from the other by at least one atom, for example, a carbon atom. Whenever the present organic ligands are complexed to a transition metal moiety, one or both of the first and second heteroatoms is/are covalently bonded to the transition metal moiety. In particular, each of the first and second heteroatoms presents a lone pair of electrons that can be free (unbonded), protonated, occasionally or temporarily bonded to an aforementioned transition metal moiety, e.g., through a coordinate covalent bond, or hydrogen bonded to a second molecule, e.g., water. It is this variability in functionality that affords the desired cooperativity sought in a ligand of the invention, especially whenever catalytic activity is desired.
In one embodiment of the invention, a composition includes an organic ligand having the following structure:
In this molecule, one or more of the pyridyl N atoms binds to a transition metal moiety, for example, containing ruthenium.
In a further aspect of the invention, an organic compound includes at least two different types of heteroatoms selected from among N, P, and S, and further includes at least one substituted or unsubstituted heterocycle selected from imidazole, pyrazole, and pyridine groups. In this molecule, the at least two different types of heteroatoms are separated from each other by at least one atom, e.g., a carbon atom. The heteroatoms are preferably selected so that at least one is capable of binding to a transition metal and another has a binding affinity for water through a hydrogen bond.
In another preferred embodiment, a ligand of the invention includes an N-heterocycle covalently linked to a P-atom. A particularly preferred ligand in this regard is a P-linked imidazole having the formula shown below:
Whenever an aforementioned P-linked imidazole is coo
Aulakh Charanjit S.
San Diego State University Foundation
Stout, Uxa Buyan & Mullins, LLP
Uxa Frank J.
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