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-10214494-B2
Publication Date
2019-02-26
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; andX 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 these salts, as well as N-heterocyclic carbene (NHC) carbene-metal complexes derived from them. The backfunctionalized imidazolinium salts are described by a general formula wherein R1 is selected from ester, amide, or aromatic groups; R2 from hydrogen, ester, amide, or aromatic groups; R3 and R4 are aliphatic groups; and X is an anion. The synthesis method comprises cyclization of a halogenated acrylate with Hünig's base in a solvent, such as toluene or acetone.
The problem being addressed arises from limitations in chemical vapor deposition (CVD) and supercritical fluid deposition (SFD) methods used for metal film deposition, particularly on complex, tortuous internal structures. While SFD with backfluorinated NHC carbene complexes has been useful, existing synthesis methods for these complexes have been inefficient for industrial-scale production. Moreover, existing backfluorinated NHC carbene complexes provide limited additional functionalization options, restricting applications.
The invention overcomes these challenges by providing efficient, low-temperature methods for synthesizing backfunctionalized imidazolinium salts and their derivatives, including ionic liquids and metal complexes. These salts allow functionalization at the 'backside' of the imidazolinium ring, enabling diverse substituents including ester, amide, aromatic, and partially fluorinated groups on various ring positions. The synthetic methods employ cyclization reactions with halogenated acrylates or maleates using less nucleophilic bases such as Hünig's base, allowing milder reaction conditions and broader substrate scope. Additionally, the invention describes formation of backfluorinated NHC carbene-metal complexes via silver oxide mediated transmetallation, facilitating their use as metal precursors in supercritical fluid deposition and catalysis.
Claims Coverage
The patent includes one independent claim directed to an N-heterocyclic carbene-metal complex comprising specific structural features. The following are the main inventive features extracted from the claims.
NHC carbene-metal complex comprising a free NHC from a backfunctionalized imidazolinium salt
An N-heterocyclic carbene-metal complex including a metal coordinated to a first ligand that is a free NHC synthesized from a backfunctionalized imidazolinium salt according to a specified formula with defined R1, R2, R3, R4, and X substituents.
Metal selection for the NHC carbene-metal complex
The metal in the complex is selected from the group consisting of rhenium, ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, and gold.
Incorporation of second NHC ligand from backfunctionalized imidazolinium salt
The complex may additionally include a second ligand that is another free NHC synthesized from a backfunctionalized imidazolinium salt of the specified formula.
Inclusion of ancillary ligands coordinated to the metal
The complex may include a third ligand selected from acetylacetonate, alkoxy, alkyl, aryl, aryloxy, carbonyl, halide, imido, oxo, pyridine, trialkylphosphine, or triarylphosphine.
Free NHC synthesis method involving deprotonation with silver oxide
The free NHC is synthesized by deprotonation of the backfunctionalized imidazolinium salt, wherein deprotonation includes reaction with silver oxide to form the carbene-silver complex prior to metal coordination.
Synthesis method involving formamidine cyclization with Hünig's base
The free NHC is synthesized by formamidine cyclization of a halogenated acrylate with Hünig's base in a solvent such as acetone or toluene.
The claims cover the NHC carbene-metal complexes having free NHC ligands derived from backfunctionalized imidazolinium salts with defined substituents, coordination to specific transition metals, optional additional NHC ligands and ancillary ligands, and methods of synthesizing the free NHC ligands involving cyclization and deprotonation steps.
Stated Advantages
Efficient, mild synthesis methods enabling production of bulk quantities of backfunctionalized imidazolinium salts and NHC carbene complexes suitable for industrial use.
Capability to functionalize the 'backside' of the imidazolinium ring with diverse groups improving solubility and enabling additional chemical modifications.
Increased thermal stability of the organometallic precursors to hydrogen reduction at lower temperatures, improving deposition control in cold-wall supercritical fluid deposition processes.
Ionic liquids derived from imidazolinium salts offering utility as plasticizers for advanced propellants and potential for supported catalyst systems.
Improved solubility of NHC carbene-metal complexes in supercritical solvents, facilitating conformal metal deposition on complex substrate features.
Documented Applications
Use as precursors for cold-wall supercritical fluid deposition (SFD) processes to deposit noble metal films on substrates with complex internal geometries, enhancing deposition efficiency and selectivity.
Synthesis of backfluorinated second generation Grubbs' and Grubbs-Hoveyda catalysts active for olefin metathesis and ring-opening metathesis polymerization.
Formation of ionic liquids suitable as plasticizers in ammonium perchlorate-based, ammonium dinitramide-based, and furazan-based advanced propellant formulations.
Use in supported catalyst systems, employing transesterification to anchor complexes onto surfaces for heterogeneous catalysis.
Applications in biphasic fluorous catalysis improving catalytic efficiency and product separation due to solubility in fluorinated solvents.
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