An official website of the United States government
Abstract Arynes are fleeting, high‐energy intermediates that undergo myriad trapping reactions by nucleophiles. Their unusual reactivity compared to other electrophiles can spur unexpected mechanistic pathways enroute to the formation of benzenoid products. Herein we explore a particularly unique case of thermally generated arynes reacting with phosphoranes to form helical dibenzothiophenes and ‐selenophenes. Multiple new helical polycyclic aromatic products are reported. DP4+ and X‐ray crystallographic analysis were used in tandem to confirm the structural topologies of selected products and to demonstrate the utility of DP4+ for distinguishing between isomeric polycyclic aromatic compounds. Lastly, we discuss a plausible mechanism consistent with DFT computations that accounts for the product formation; namely, ligand coupling (i.e., reductive elimination) within a hypervalent, pentacarbon‐ligated σ‐phosphorane furnishes the dibenzothio‐ or dibenzoselenophene.
more »
« less
Gold‐Catalyzed C−H Functionalization Polycondensation for the Synthesis of Aromatic Polymers
Abstract Homogeneous gold (Au) complexes have demonstrated tremendous utility in modern organic chemistry; however, their application for the synthesis of polymers remains rare. Herein, we demonstrate the first catalytic application of Au complexes toward the polycondensation of alkyne‐containing comonomers and heteroarene nucleophiles. Polymerization occurs through successive intermolecular hydroarylation reactions to produce high molecular weight aromatic copolymers with 1,1‐disubstituted alkene backbone linkages. Clear correlations between the rate and degree of polymerization (DP) were established based on catalyst structure and counterion pairing, thus enabling polymerization reactions that proceeded with remarkable efficiency, high reactivity, and exceptional DPs. The reactivity is broad in scope, enabling the copolymerization of highly functionalized aromatic and aliphatic monomers. These results highlight the untapped utility of Au catalysis in providing access to new macromolecular constructs.
more »
« less
- Award ID(s):
- 1632825
- PAR ID:
- 10236003
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 59
- Issue:
- 49
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 21971-21975
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Redox-switchable polymerizations of lactide and epoxides were extended to the solid state by anchoring an iron-based polymerization catalyst to TiO 2 nanoparticles. The reactivity of the molecular complexes and their redox-switching characteristics were maintained in the solid-state. These properties resulted in surface-initiated polymerization reactions that produced polymer brushes whose chemical composition is dictated by the oxidation state of the iron-based complex. Depositing the catalyst-functionalized TiO 2 nanoparticles on fluorine-doped tin oxide resulted in an electrically addressable surface that could be used to demonstrate spatial control in redox-switchable polymerization reactions. By using a substrate that contained two electrically isolated domains wherein one domain was exposed to an oxidizing potential, patterns of surface-bound polyesters and polyethers were accessible through sequential application of lactide and cyclohexene oxide. The differentially functionalized surfaces demonstrated distinct physical properties that illustrated the promise for using the method to pattern surfaces with multiple, chemically distinct polymer brushes.more » « less
-
Mechanically-induced redox processes offer a promising alternative to more conventional thermal and photochemical synthetic methods. For macromolecule synthesis, current methods utilize sensitive transition metal additives and suffer from background reactivity. Alternative methodology will offer exquisite control over these stimuli-induced mechanoredox reactions to couple force with redox-driven chemical transformations. Herein, we present the iodonium-initiated free-radical polymerization of (meth)acrylate monomers under ultrasonic irradiation and ball-milling conditions. We explore the kinetic and structural consequences of these complementary mechanical inputs to access high molecular weight polymers. This methodology will undoubtedly find broad utility across stimuli-controlled polymerization reactions and adaptive material design.more » « less
-
Fourteen Ag( i ), Au( i ), Ni( ii ), Pd( ii ), and Pt( ii ) complexes with macrocyclic tetradentate N-heterocyclic carbene (NHC) ligands were prepared via reactions between three macrocyclic tetrabenzimidazolium salts and metal precursors. All except two Au complexes were characterized using single-crystal X-ray diffraction. Three different structures, including a trinuclear one containing a NHC–Ag–(H 2 O) moiety and a hexanuclear propeller-like supramolecular assembly, are found for Ag–NHC complexes. Nine complexes of group 10 metal ions adopt square-planar geometry, in which the different ring-sizes of the macrocyclic tetracarbene ligands lead to a variation of metal–carbene bond lengths. π–π stackings are observed between the rigid aromatic benzimidazole rings in the nickel group complexes.more » « less
-
Abstract The synthesis of vinyl alcohol copolymers is limited due to the poor radical reactivity of vinyl acetate (VAc), the traditional precursor to polyvinyl alcohol (PVA). Main group monomers such as BN 2‐vinylnaphthalene (BN2VN) have attracted attention as alternatives to VAc to form side chain hydroxyls via oxidation, but outstanding questions of molecular weight control remain. Herein we report systematic investigation of solvent, temperature, and initiator concentration as factors influencing BN2VN degree of polymerization. We find increased chain transfer to toluene, hypothesized to arise from differences in radical stabilization and reactivity by aromatic and BN aromatic rings. As a result of these combined efforts, high molecular weight (Mw ~ 105 g mol−1) BN2VN homopolymers and BN2VN‐styrene copolymers were obtained.more » « less
