Backfunctionalized imidazolinium salts and NHC carbene-metal complexes
Inventors
Blanski, Rusty L. • Grubbs, Robert H.
Assignees
United States Department of the Air Force
Publication Number
US-10538494-B2
Publication Date
2020-01-21
Expiration Date
2035-10-09
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Abstract
Backfunctionalized imidazolinium salts and methods of synthesizing the same and NHC carbene-metal complexes therefrom. For backfunctionalized imidazolinium salts of the formula: Wherein R1 is selected from the group consisting of an ester group, an amide group, and an aromatic group; R2 is selected from the group consisting of hydrogen, an ester group, an amide group, and an aromatic group; R3 and R4 are each selected from the group consisting of a C1-C20 alkyl group, C1-C20 partially fluorinated alkyl group, an aryl group, an aryl group with para CF3 functionality, an aryl group having C1-C20 partially fluorinated alkyl groups or partially fluorinated alkoxy groups, and a C1-C20 partially fluorinated aliphatic group, and a C1-C20 aryl group; and X is an anion. The method comprises cyclization of a halogenated acrylate with a formamidine with Hünig's base in a solvent.
Core Innovation
The invention relates to backfunctionalized imidazolinium salts and methods of synthesizing these salts along with NHC carbene-metal complexes derived from them. The backfunctionalized imidazolinium salts have a general formula where R1 is an ester, amide, or aromatic group; R2 is hydrogen, ester, amide, or aromatic group; R3 and R4 are selected from various alkyl, partially fluorinated alkyl, aryl groups, or combinations thereof; and X is an anion. The methods of synthesis involve cyclization of halogenated acrylates with formamidine and a base such as Hünig's base in a solvent.
The background problem addressed is the limitations in chemical vapor deposition (CVD) processes for metal deposition, particularly with respect to coating internal or tortuous surfaces effectively and avoiding metal deposition on undesired areas of processing chambers. While supercritical fluid deposition (SFD) offers improvements, existing precursors lack efficient synthesis methods for bulk production and lack mechanisms for additional functionalization of NHC carbene complexes, especially backfluorinated NHC carbene complexes.
The invention provides improved synthesis methods that enable bulk production of backfunctionalized imidazolinium salts and associated NHC carbene-metal complexes. These methods utilize cyclization of halogenated fluorinated acrylates or maleates with formamidine in polar aprotic solvents at moderate temperatures with bases like Hünig's base or triethylamine. This contrasts with earlier methods requiring elevated temperatures and limited to aromatic side chains. Additionally, the invention includes ionic liquids derived from these salts and methods for attaching these NHC carbenes to various metals for improved solubility, stability, and use in supercritical fluid deposition and catalysis.
Claims Coverage
The patent includes one independent method claim focused on the synthesis of backfunctionalized imidazolinium salts. The inventive features relate to chemical components and synthesis conditions.
Method of synthesizing backfunctionalized imidazolinium salts by cyclization
A method of synthesizing a backfunctionalized imidazolinium salt by cyclization of a halogenated acrylate with formamidine using Hünig's base in a solvent, including acetone and toluene as solvents.
Use of secondary bases in the formamidine cyclization
The method further comprises introducing secondary bases during the formamidine cyclization, wherein the secondary base is selected from triethylamine, formamidine, and Hünig's base.
Preparation of halogenated acrylate ester prior to cyclization
The method can include preparing a halogenated acrylate ester from an acrylate ester before performing the cyclization.
Specific substitution pattern and anion choice
The backfunctionalized imidazolinium salt obtained has a configuration with R1 in trans-configuration relative to R2, and X is a halogen anion.
The independent claim covers a method for synthesizing backfunctionalized imidazolinium salts featuring cyclization of halogenated acrylates with formamidine and specific bases under defined solvent and stereochemical conditions, enabling efficient production of these compounds.
Stated Advantages
Improved synthesis methods occur at lower temperatures compared to conventional methods, enabling use of alternative, less nucleophilic, and more economical bases such as triethylamine, thereby increasing productivity and minimizing costs.
The methods facilitate bulk production of backfunctionalized NHC carbene complexes suitable for industrial use.
The synthesized backfunctionalized imidazolinium salts yield ionic liquids with solubility in non-polar solvents and suitable physical properties as plasticizers for advanced propellant formulations.
Backfunctionalized NHC carbene-metal complexes derived using these methods have improved solubility in supercritical solvents and stability at lower temperatures, enhancing their utility for supercritical fluid deposition processes.
The invention enables additional functionalization of NHC carbene complexes through transesterification and other modifications, expanding versatility and potential applications.
Documented Applications
Use of backfunctionalized NHC carbene-metal complexes as precursors in supercritical fluid deposition (SCFD) for metal coating of substrates, including noble metals such as copper and ruthenium, utilizing cold-wall processing systems.
Use of the synthesized imidazolinium salts and their complexes as catalysts in transition metal catalyzed reactions, including olefin metathesis and ring opening metathesis polymerization, especially for catalysts active in fluorous catalysis.
Ionic liquids derived from the backfunctionalized imidazolinium salts used as plasticizers in advanced propellant formulations, such as ammonium perchlorate-based, ammonium dinitramide-based, and furazan-based propellants.
Supported catalysts systems where the backfunctionalized salts are anchored onto surfaces (e.g., silica-supported catalysts) for catalytic and industrial applications.
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