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-10981878-B2
Publication Date
2021-04-20
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 present invention relates to backfunctionalized imidazolinium salts and methods of synthesizing the same, as well as N-heterocyclic carbene (NHC) carbene-metal complexes derived therefrom. The synthesis involves cyclization of a halogenated acrylate with Hünig's base in a solvent to produce backfunctionalized imidazolinium salts having specific substituents at various positions on the imidazolinium ring. These salts may include ester, amide, or aromatic groups as backfunctionalizing functionalities, providing new chemical entities for further functionalization and metal complexation.
The problem addressed by the invention lies primarily in the difficulties associated with conventional chemical vapor deposition (CVD) and supercritical fluid deposition (SFD) processes, particularly in depositing metal coatings onto substrates with complex and tortuous internal structures. Conventional precursors are insufficiently soluble or thermally stable under SFD conditions, and existing backfluorinated NHC carbene complexes, while useful, require improved synthesis methods for bulk production and additional functionalization capabilities.
The invention provides improved synthesis methods that allow for backfunctionalized imidazolinium salts to be prepared using milder cyclization conditions (lower temperatures) with less nucleophilic bases such as Hünig's base or aromatic formamidines, increasing efficiency and expanding the scope to both aromatic and aliphatic side chains. These salts can be converted into free NHC carbenes and further coordinated into metal complexes suitable for applications including supercritical fluid deposition precursors and catalysts.
Claims Coverage
The patent includes multiple independent claims focused on novel backfunctionalized imidazolinium salts, methods of their synthesis, methods of forming NHC carbenes, and NHC carbene-metal complexes. The main inventive features relate to the chemical composition of the salts and complexes, the synthetic methodology, and the coordination to metals.
Backfunctionalized imidazolinium salts with specific substituents
Backfunctionalized imidazolinium salts selected from specific formula groups where R1 is an ester, amide, or aromatic group; R2 is hydrogen, ester, amide, or aromatic; R3 and R4 are aliphatic or aromatic groups including mesityl; and X is an anion.
Methods for synthesizing backfunctionalized imidazolinium salts by cyclization
Formamidine cyclization of halogenated styrenes using Hünig's base in solvents such as acetone or toluene to form backfunctionalized imidazolinium salts.
Methods for producing free NHC carbenes by deprotonation
Deprotonation of backfunctionalized imidazolinium salts using silver oxide or strong bases including potassium bis(trimethylsilyl)amide, potassium tert-butoxide, or alkali metal hydroxides to yield free NHC carbenes.
NHC carbene-metal complexes comprising backfunctionalized carbenes
Formation of metal complexes comprising a metal (selected from rhenium, ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, and gold) coordinated to one or more NHC carbene ligands derived from backfunctionalized imidazolinium salts, optionally comprising additional ligands such as acetylacetonate, alkoxy, alkyl, aryl, aryloxy, carbonyl, halide, imido, oxo, pyridine, trialkylphosphine, or triarylphosphine.
The independent claims collectively cover the novel chemical structure of backfunctionalized imidazolinium salts, their synthesis via cyclization methods with specific bases and solvents, methods to generate free NHC carbenes by deprotonation, and the formation of metal complexes with defined ligand sets and metal selections, enabling new applications.
Stated Advantages
Improved synthetic methodologies allow for bulk preparation of backfunctionalized NHC carbene complexes under milder conditions, enhancing efficiency and scalability.
The use of less nucleophilic bases at lower temperatures permits extension of functional groups beyond aromatic side chains to include aliphatic groups, broadening chemical versatility.
Backfunctionalized imidazolinium salts synthesized can form ionic liquids with unique solubility properties, useful as plasticizers and in various formulations.
Metal complexes formed from these backfunctionalized carbenes exhibit solubility and stability suitable for supercritical fluid deposition, enabling selective and efficient metal deposition.
The functionalization at the back of the imidazolinium ring allows for additional chemical transformations such as transesterification and transamination, facilitating catalyst modification and supported catalyst systems.
Documented Applications
Use as precursors in cold-wall supercritical fluid deposition (SCFD) processes for metallic coatings, particularly noble metals like ruthenium and copper, to achieve selective and conformal deposition on substrates.
Formation of second generation Grubbs' and Grubbs-Hoveyda olefin metathesis catalysts with backfluorinated NHC carbene ligands active in olefin metathesis and ring-opening metathesis polymerization.
Utilization of ionic liquids derived from backfunctionalized imidazolinium salts as plasticizers in advanced propellant formulations including ammonium perchlorate-based, ammonium dinitramide-based, and furazan-based propellants.
Application in biphase fluorous catalysis where the catalysts are soluble in fluorinated solvents, improving reaction efficiency and facilitating catalyst-product separation.
Preparation of supported catalyst systems by anchoring backfunctionalized imidazolinium salts onto solid supports for heterogeneous catalysis.
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