Nickel-Catalyzed Suzuki Polycondensation for Controlled Synthesis of Ester-Functionalized Conjugated Polymers

Controlled synthesis of conjugated polymers with functional side chains is of great importance, affording well-defined optoelectronic materials possessing enhanced stability and tunability as compared to their alkyl-substituted counterparts. Herein, a chain-growth Suzuki polycondensation of an ester-functionalized thiophene is described using commercially available nickel precatalysts. Model compound studies were used to identify suitable catalysts, and these experiments provided guidance for the polymerization of the ester-substituted monomer. This is the first report of nickel-catalyzed Suzuki cross-coupling for catalyst-transfer polycondensation, and to further illustrate the versatility of this method, block and alternating copolymers with 3-hexyl­thiophene were synthesized. The presented protocol should serve as an entry point into the synthesis of other electron-deficient polymers and donor–acceptor copolymers with controlled molecular weights and low dispersity

TAML/H₂O₂ Oxidative Degradation of Metaldehyde: Pursuing Better Water Treatment for the Most Persistent Pollutants

The extremely persistent molluscicide, metaldehyde, widely used on farms and gardens, is often detected in drinking water sources of various countries at concentrations of regulatory concern. Metaldehyde contamination restricts treatment options. Conventional technologies for remediating dilute organics in drinking water, activated carbon, and ozone, are insufficiently effective against metaldehyde. Some treatment plants have resorted to effective, but more costly UV/H₂O₂. Here we have examined if TAML/H₂O₂ can decompose metaldehyde under laboratory conditions to guide development of a better real world option. TAML/H₂O₂ slowly degrades metaldehyde to acetaldehyde and acetic acid. Nuclear magnetic resonance spectroscopy (¹H NMR) was used to monitor the degradationthe technique requires a high metaldehyde concentration (60 ppm). Within the pH range of 6.5–9, the reaction rate is greatest at pH 7. Under optimum conditions, one aliquot of TAML <b>1a</b> (400 nM) catalyzed 5% degradation over 10 h with a turnover number of 40. Five sequential TAML aliquots (2 μM overall) effected a 31% removal over 60 h. TAML/H₂O₂ degraded metaldehyde steadily over many hours, highlighting an important long-service property. The observation of metaldehyde decomposition under mild conditions provides a further indication that TAML catalysis holds promise for advancing water treatment. These results have turned our attention to more aggressive TAML activators in development, which we expect will advance the observed technical performance

Monoplatinum Doping of Gold Nanoclusters and Catalytic Application

We report single-atom doping of gold nanoclusters (NCs), and its drastic effects on the optical, electronic, and catalytic properties, using the 25-atom system as a model. In our synthetic approach, a mixture of Pt₁Au₂₄(SC₂H₄Ph)₁₈ and Au₂₅(SC₂H₄Ph)₁₈ was produced via a size-focusing process, and then Pt₁Au₂₄(SC₂H₄Ph)₁₈ NCs were obtained by selective decomposition of Au₂₅(SC₂H₄Ph)₁₈ in the mixture with concentrated H₂O₂ followed by purification via size-exclusion chromatography. Experimental and theoretical analyses confirmed that Pt₁Au₂₄(SC₂H₄Ph)₁₈ possesses a Pt-centered icosahedral core capped by six Au₂(SC₂H₄Ph)₃ staples. The Pt₁Au₂₄(SC₂H₄Ph)₁₈ cluster exhibits greatly enhanced stability and catalytic activity relative to Au₂₅(SC₂H₄Ph)₁₈ but a smaller energy gap (<i>E</i>_g ≈ 0.8 eV vs 1.3 eV for the homogold cluster)

Stability and Reactivity of 1,3-Benzothiaphosphole: Metalation and Diels–Alder Chemistry

The synthesis and functionalization of the parent 1,3-benzothiaphosphole is reported. The phosphole could not be isolated, but the compound could be manipulated in solution to produce several new phosphorus compounds. Metalation of the 2-position using lithium diisopropylamide proceeded smoothly according to ³¹P NMR spectroscopy, and quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole. The PC bond of the thiaphosphole was also explored as a dienophile in Diels–Alder reactions with isoprene, 2,3-dimethylbutadiene, 2,3-dibenzylbutadiene, and cyclopentadiene. The fused-ring structures were fully characterized, and a solid-state molecular structure of the 2,3-dimethylbutadiene cycloadduct was obtained. Residual dipolar coupling (RDC) NMR experiments were used to assign major and minor products for the isoprene and cyclopentadiene adducts

Stability and Reactivity of 1,3-Benzothiaphosphole: Metalation and Diels–Alder Chemistry

The synthesis and functionalization of the parent 1,3-benzothiaphosphole is reported. The phosphole could not be isolated, but the compound could be manipulated in solution to produce several new phosphorus compounds. Metalation of the 2-position using lithium diisopropylamide proceeded smoothly according to ³¹P NMR spectroscopy, and quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole. The PC bond of the thiaphosphole was also explored as a dienophile in Diels–Alder reactions with isoprene, 2,3-dimethylbutadiene, 2,3-dibenzylbutadiene, and cyclopentadiene. The fused-ring structures were fully characterized, and a solid-state molecular structure of the 2,3-dimethylbutadiene cycloadduct was obtained. Residual dipolar coupling (RDC) NMR experiments were used to assign major and minor products for the isoprene and cyclopentadiene adducts

Stability and Reactivity of 1,3-Benzothiaphosphole: Metalation and Diels–Alder Chemistry

The synthesis and functionalization of the parent 1,3-benzothiaphosphole is reported. The phosphole could not be isolated, but the compound could be manipulated in solution to produce several new phosphorus compounds. Metalation of the 2-position using lithium diisopropylamide proceeded smoothly according to ³¹P NMR spectroscopy, and quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole. The PC bond of the thiaphosphole was also explored as a dienophile in Diels–Alder reactions with isoprene, 2,3-dimethylbutadiene, 2,3-dibenzylbutadiene, and cyclopentadiene. The fused-ring structures were fully characterized, and a solid-state molecular structure of the 2,3-dimethylbutadiene cycloadduct was obtained. Residual dipolar coupling (RDC) NMR experiments were used to assign major and minor products for the isoprene and cyclopentadiene adducts

Crystal Structure of Barrel-Shaped Chiral Au₁₃₀(<i>p</i>‑MBT)₅₀ Nanocluster

We report the structure determination of a large gold nanocluster formulated as Au₁₃₀(<i>p</i>-MBT)₅₀, where <i>p</i>-MBT is 4-methylbenzene­thiolate. The nanocluster is constructed in a four-shell manner, with 55 gold atoms assembled into a two-shell Ino decahedron. The surface is protected exclusively by –S–Au–S– staple motifs, which self-organize into five ripple-like stripes on the surface of the barrel-shaped Au₁₀₅ kernel. The Au₁₃₀(<i>p-</i>MBT)₅₀ can be viewed as an elongated version of the Au₁₀₂(SR)₄₄. Comparison of the Au₁₃₀(<i>p-</i>MBT)₅₀ structure with the recently discovered icosahedral Au₁₃₃(<i>p-</i>TBBT)₅₂ nanocluster (where <i>p-</i>TBBT = 4-<i>tert</i>-butyl­benzene­thiolate) reveals an interesting phenomenon that a subtle ligand effect in the para-position of benzenethiolate can significantly affect the gold atom packing structure, i.e. from the 5-fold twinned Au₅₅ decahedron to 20-fold twinned Au₅₅ icosahedron

Crystal Structure of Barrel-Shaped Chiral Au₁₃₀(<i>p</i>‑MBT)₅₀ Nanocluster

We report the structure determination of a large gold nanocluster formulated as Au₁₃₀(<i>p</i>-MBT)₅₀, where <i>p</i>-MBT is 4-methylbenzene­thiolate. The nanocluster is constructed in a four-shell manner, with 55 gold atoms assembled into a two-shell Ino decahedron. The surface is protected exclusively by –S–Au–S– staple motifs, which self-organize into five ripple-like stripes on the surface of the barrel-shaped Au₁₀₅ kernel. The Au₁₃₀(<i>p-</i>MBT)₅₀ can be viewed as an elongated version of the Au₁₀₂(SR)₄₄. Comparison of the Au₁₃₀(<i>p-</i>MBT)₅₀ structure with the recently discovered icosahedral Au₁₃₃(<i>p-</i>TBBT)₅₂ nanocluster (where <i>p-</i>TBBT = 4-<i>tert</i>-butyl­benzene­thiolate) reveals an interesting phenomenon that a subtle ligand effect in the para-position of benzenethiolate can significantly affect the gold atom packing structure, i.e. from the 5-fold twinned Au₅₅ decahedron to 20-fold twinned Au₅₅ icosahedron

Tri-icosahedral Gold Nanocluster [Au₃₇(PPh₃)₁₀(SC₂H₄Ph)₁₀X₂]⁺: Linear Assembly of Icosahedral Building Blocks

The [Au₃₇(PPh₃)₁₀(SR)₁₀X₂]⁺ nanocluster (where SR = thiolate and X = Cl/Br) was theoretically predicted in 2007, but since then, there has been no experimental success in the synthesis and structure determination. Herein, we report a kinetically controlled, selective synthesis of [Au₃₇(PPh₃)₁₀(SC₂H₄Ph)₁₀X₂]⁺ (counterion: Cl^– or Br^–) with its crystal structure characterized by X-ray crystallography. This nanocluster shows a rod-like structure assembled from three icosahedral Au₁₃ units in a linear fashion, consistent with the earlier prediction. The optical absorption and the electrochemical and catalytic properties are investigated. The successful synthesis of this new nanocluster allows us to gain insight into the size, structure, and property evolution of gold nanoclusters that are based upon the assembly of icosahedral units (<i>i.e.</i>, <i>cluster of clusters</i>). Some interesting trends are identified in the evolution from the monoicosahedral [Au₁₃(PPh₃)₁₀X₂]³⁺ to the bi-icosahedral [Au₂₅(PPh₃)₁₀(SC₂H₄Ph)₅X₂]²⁺ and to the tri-icosahedral [Au₃₇(PPh₃)₁₀(SC₂H₄Ph)₁₀X₂]⁺ nanocluster, which also points to the possibility of achieving even longer rod nanoclusters based upon assembly of icosahedral building blocks

Design of Bivalent Nucleic Acid Ligands for Recognition of RNA-Repeated Expansion Associated with Huntington’s Disease

We report the development of a new class of nucleic acid ligands that is comprised of Janus bases and the MPγPNA backbone and is capable of binding rCAG repeats in a sequence-specific and selective manner via, inference, bivalent H-bonding interactions. Individually, the interactions between ligands and RNA are weak and transient. However, upon the installation of a C-terminal thioester and an N-terminal cystine and the reduction of disulfide bond, they undergo template-directed native chemical ligation to form concatenated oligomeric products that bind tightly to the RNA template. In the absence of an RNA target, they self-deactivate by undergoing an intramolecular reaction to form cyclic products, rendering them inactive for further binding. The work has implications for the design of ultrashort nucleic acid ligands for targeting rCAG-repeat expansion associated with Huntington’s disease and a number of other related neuromuscular and neurodegenerative disorders