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-10913723-B2
Publication Date
2021-02-09
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 an aliphatic group; and X is an anion; the method comprises cyclization of a halogenated acrylate with Hünig's base in a solvent.
Core Innovation
The invention relates to backfunctionalized imidazolinium salts and methods of synthesizing them, as well as NHC carbene-metal complexes derived from these salts. The key feature of the backfunctionalized imidazolinium salts is their formula, where R1 is selected from ester, amide, and aromatic groups; R2 is selected from hydrogen, ester, amide, and aromatic groups; R3 and R4 are aliphatic groups; and X is an anion. The method for synthesis involves cyclization of a halogenated acrylate with Hünig's base in a solvent.
The background identifies challenges with conventional chemical vapor deposition (CVD) methods for depositing metals, particularly in coating internal structures with tortuous features. Supercritical fluid deposition (SFD) processes have been used to address some limitations by using supercritical fluids, such as carbon dioxide, to enhance precursor solubility and conformal penetration. However, existing SFD methods like hot-wall systems are inefficient due to unwanted metal deposition on all chamber surfaces. Cold-wall systems improve efficiency but require organometallic precursors that are thermally stable to hydrogen reduction at lower temperatures and reducible at elevated temperatures. Prior backfluorinated NHC carbene complexes improved some deposition issues but lacked efficient bulk synthesis methods and routes for additional functionalization.
This invention addresses these shortcomings by providing a method for synthesizing backfunctionalized imidazolinium salts with various functional groups via cyclization of halogenated acrylates using Hünig's base under mild conditions. These salts serve as precursors for NHC carbene-metal complexes with selected metals like rhenium, ruthenium, iridium, palladium, platinum, silver, and gold. The synthesis permits modification of side chains including fluorinated groups and aliphatic chains, enabling production of ionic liquids and catalysts. Moreover, the invention discloses techniques to prepare second generation Grubbs' and Grubbs-Hoveyda catalysts by reacting backfluorinated NHC carbenes with first generation catalysts, facilitating functional versatility and industrial scalability.
Claims Coverage
The patent includes one independent claim encompassing a method of synthesizing NHC carbene-metal complexes by synthesizing backfunctionalized imidazolinium salts through specific cyclization steps, with several dependent claims specifying additional features.
Method of synthesizing backfunctionalized imidazolinium salt
Synthesizing a backfunctionalized imidazolinium salt via formamidine cyclization of a halogenated acrylate with Hünig's base as the primary base in a solvent.
Coordination of second ligand to metal
Coordinating a second ligand to the metal, where the ligand is a second free N-heterocyclic carbene.
Coordination of third ligand to metal
Coordinating a third ligand to the metal, the third ligand being selected from acetylacetonate, alkoxy, alkyl, aryl, aryloxy, carbonyl, halide, imido, oxo, pyridine, trialkylphosphine, and triarylphosphine.
Metal selection for carbene-metal complex
Selecting the metal from rhenium, ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, and gold.
Use of polar aprotic solvent for cyclization
Using a polar aprotic solvent for the formamidine cyclization of the halogenated acrylate.
Specific polar aprotic solvents
Selecting the polar aprotic solvent from ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.
Use of Hünig's base as primary base
Specifying Hünig's base as the primary base used in formamidine cyclization of the halogenated acrylate.
The claims collectively cover a method of preparing backfunctionalized imidazolinium salts by cyclization using Hünig's base in specified solvents and forming NHC carbene-metal complexes by coordinating various ligands and metals suitable for deposition and catalytic applications.
Stated Advantages
The method enables efficient synthesis of backfunctionalized imidazolinium salts at lower temperatures than conventional methods, allowing use of less nucleophilic and less costly bases such as Hünig's base, triethylamine, or aromatic formamidines.
The synthesis provides access to a wider variety of functional groups including aliphatic, aromatic, ester, amide, and fluorinated substituents, which were difficult to achieve using conventional methods.
Backfunctionalized imidazolinium salts can form ionic liquids soluble in non-polar solvents and viscous oils at room temperature with potential utility as plasticizers in advanced propellant formulations.
Preparation of NHC carbene-metal complexes using these salts facilitates targeted metal precursors that are soluble and stable in supercritical fluids and suitable for selective metal deposition in cold-wall SFD systems, improving process efficiency.
Methods enable production of second generation Grubbs' and Grubbs-Hoveyda catalysts with backfluorinated NHC carbenes, affording catalytically active species for olefin metathesis and ring opening polymerization.
Documented Applications
Use as precursors for supercritical fluid deposition (SCFD) to deposit noble metals such as copper and ruthenium with improved solubility and stability in supercritical solvents.
Application in catalysis, including preparation of second generation Grubbs' and Grubbs-Hoveyda catalysts for olefin metathesis and ring opening metathesis polymerization.
Use as ionic liquids serving as plasticizers for advanced propellant formulations including ammonium perchlorate-based, ammonium dinitramide-based, and furazan-based propellants.
Supported catalyst systems via transesterification with anchoring groups for preparing silica-supported backfunctionalized NHC carbene-metal complexes.
Biphase fluorous catalysis enhancing chemical reaction efficiency by improving separation of catalysts and products in fluorinated solvent systems.
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