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1.
Angew Chem Int Ed Engl ; 61(31): e202200334, 2022 Aug 01.
Article in English | MEDLINE | ID: mdl-35594167

ABSTRACT

We report here "sandwich" diimine-copper(I) catalysts for C(sp3 )-H bond functionalization. Reactions of alkanes and ethers with trimethylsilyldiazomethane, ethyl diazoacetate, and trifluoromethyl-diazomethane have been demonstrated. We also report C(sp3 )-H bond methylation, benzylation, and diphenylmethylation by diazomethane, aryldiazomethanes, and diphenyldiazomethane. These reactions are rare examples of base-metal catalyzed, intermolecular C(sp3 )-H functionalizations by employing unactivated diazo compounds. Electrophilicity and unique steric environment of "sandwich"-copper catalysts are likely reasons for their catalytic efficiency.

2.
ACS Macro Lett ; 9(8): 1161-1166, 2020 Aug 18.
Article in English | MEDLINE | ID: mdl-35653207

ABSTRACT

The compatibilization of polyethylene (PE) and isotactic polypropylene (iPP) blends is of particular interest due to the challenges associated with recycling these plastics from mixed waste streams. Polyethylene-graft-iPP copolymers (PE-g-iPP) were prepared using a grafting-through strategy by copolymerization of ethylene with allyl-terminated iPP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths (Mn = 6-28 kg/mol), graft numbers, and graft spacings were prepared. These graft copolymers were melt-blended with high-density polyethylene (HDPE) and iPP (iPP/HDPE = 30/70 w/w), and the blend properties were evaluated by tensile testing. The blends showed enhanced tensile strength at 5 and 1 wt % loading, with higher tensile strength observed for larger block numbers and graft lengths. These results indicate that graft copolymers are efficient compatibilizers for blends of HDPE and iPP.

3.
Organometallics ; 35(17): 2938-2943, 2016 Sep 12.
Article in English | MEDLINE | ID: mdl-27642213

ABSTRACT

Synthesis and full characterization of cationic isostructural "sandwich" diimine-coinage metal ethylene complexes are reported. Ethylene self-exchange kinetics proceeds by an associative exchange mechanism for Cu and Au complexes. The fastest ligand exchange was observed for Ag complex 8a. The upper limit of ΔG‡, assuming associative ligand exchange, was found to be ca. 5.0 kcal/mol. Ethylene self-exchange in Cu complex 7b proceeds with ΔG298‡ = 12.9 ± 0.1 kcal/mol, while the exchange is the slowest in Au complex 9, with ΔG298‡ = 16.7 ± 0.1 kcal/mol. Copper complex 7b is unusually stable and can survive in air for years.

4.
J Org Chem ; 80(11): 5934-43, 2015 Jun 05.
Article in English | MEDLINE | ID: mdl-25941908

ABSTRACT

A diastereoselective synthesis of 4-vinyl oxazolines syn-2 was developed based on an acid-catalyzed cyclization of bistrichloroacetimidates (E)-1. The reaction likely involves an allyl carbenium ion intermediate in which the adjacent stereocenter directs the stereoselectivity for C-N bond formation. Oxazolines syn-2 were transformed to C-quaternary threoninol, threoninal, and threonine derivatives which can be further incorporated into complex natural compounds.


Subject(s)
Allyl Compounds/chemistry , Amino Alcohols/chemistry , Butylene Glycols/chemistry , Imidoesters/chemical synthesis , Oxazoles/chemical synthesis , Vinyl Compounds/chemistry , Cyclization , Imidoesters/chemistry , Molecular Structure , Oxazoles/chemistry , Stereoisomerism
5.
J Am Chem Soc ; 136(20): 7213-6, 2014 May 21.
Article in English | MEDLINE | ID: mdl-24773453

ABSTRACT

While traditional polymerization of linear α-olefins (LAOs) typically provides amorphous, low T(g) polymers, chain-straightening polymerization represents a route to semicrystalline materials. A series of α-diimine nickel catalysts were tested for the polymerization of various LAOs. Although known systems yielded amorphous or low-melting polymers, the "sandwich" α-diimines 3-6 yielded semicrystalline "polyethylene" comprised primarily of unbranched repeat units via a combination of uncommon regioselective 2,1-insertion and precision chain-walking events.


Subject(s)
Alkenes/chemistry , Alkenes/chemical synthesis , Imines/chemistry , Nickel/chemistry , Organometallic Compounds/chemistry , Catalysis , Crystallography, X-Ray , Models, Molecular , Molecular Structure , Polymerization
6.
J Am Chem Soc ; 135(25): 9342-5, 2013 Jun 26.
Article in English | MEDLINE | ID: mdl-23758609

ABSTRACT

We have developed a method for direct, copper-catalyzed, auxiliary-assisted fluorination of ß-sp(2) C-H bonds of benzoic acid derivatives and γ-sp(2) C-H bonds of α,α-disubstituted benzylamine derivatives. The reaction employs a CuI catalyst, a AgF fluoride source, and DMF, pyridine, or DMPU solvent at moderately elevated temperatures. Selective mono- or difluorination can be achieved by simply changing reaction conditions. The method shows excellent functional group tolerance and provides a straightforward way for the preparation of ortho-fluorinated benzoic acids.


Subject(s)
Benzoic Acid/chemistry , Benzylamines/chemistry , Copper/chemistry , Halogenation , Organometallic Compounds/chemistry , Catalysis , Molecular Structure
7.
J Org Chem ; 75(22): 7897-900, 2010 Nov 19.
Article in English | MEDLINE | ID: mdl-20973520

ABSTRACT

Cationic Pd(II) catalysts generated from chiral biphenyl diphosphine complexes or from COP-Cl promote enantioselective cyclization of E- and Z-configured allylic bis-trichloroacetimidates to highly enantioenriched 2-trichloromethyl-4-vinyloxazoline. This represents an exclusive example for olefin amination in high yield and enantioselectivity with trichloroacetimidate as the N-nucleophile by using a cationic palladium(II) complex as a catalyst providing an easy-to-deprotect enantioenriched vinylglycinol derivative.


Subject(s)
Acetamides/chemistry , Chloroacetates/chemistry , Glycine/analogs & derivatives , Oxazoles/chemical synthesis , Palladium/chemistry , Catalysis , Cyclization , Glycine/chemistry , Molecular Structure , Oxazoles/chemistry , Stereoisomerism
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