Remote Oxidative Activation of a [Cp*Rh] Monohydride

Half-sandwich rhodium monohydrides are often proposed as intermediates in catalysis, but little is known regarding the redox-induced reactivity accessible to these species. Here, the κ2-bis-diphenylphosphinoferrocene (dppf) ligand has been used to explore the reactivity that can be induced when a [Cp*Rh] monohydride undergoes remote (dppf-centered) oxidation by 1e–. Chemical and electrochemical studies showed that one-electron redox chemistry is accessible to Cp*Rh(dppf), including a unique quasi-reversible RhII/I process at –0.96 V vs. ferrocenium/ferrocene (Fc+/0). This redox manifold was confirmed by isolation of an uncommon Rh(II) species that was characterized by EPR spectroscopy. Protonation of Cp*Rh(dppf) with anilinium triflate yielded an isolable and inert monohydride, and this species was found to undergo a quasireversible electrochemical oxidation at +0.41 V vs Fc+/0 that corresponds to iron-centered oxidation in the dppf backbone. Thermochemical analysis predicts that this dppf-centered oxidation drives a dramatic increase in acidity of the Rh–H moiety by 23 pKa units, a reactivity pattern confirmed by in situ 1H NMR studies. Taken together, these results show that remote oxidation can effectively induce M–H activation and suggest that ligand-centered redox activity could be an attractive feature for design of new systems relying on hydride intermediates.

U2 snRNA structure is influenced by SF3A and SF3B proteins but not by SF3B inhibitors

U2 snRNP is an essential component of the spliceosome. It is responsible for branch point recognition in the spliceosome A-complex via base-pairing of U2 snRNA with an intron to form the branch helix. Small molecule inhibitors target the SF3B component of the U2 snRNP and interfere with A-complex formation during spliceosome assembly. We previously found that the first SF3B inhibited-complex is less stable than A-complex and hypothesized that SF3B inhibitors interfere with U2 snRNA secondary structure changes required to form the branch helix. Using RNA chemical modifiers, we probed U2 snRNA structure in A-complex and SF3B inhibited splicing complexes. The reactivity pattern for U2 snRNA in the SF3B inhibited-complex is indistinguishable from that of A-complex, suggesting that they have the same secondary structure conformation, including the branch helix. This observation suggests SF3B inhibited-complex instability does not stem from an alternate RNA conformation and instead points to the inhibitors interfering with protein component interactions that normally stabilize U2 snRNP’s association with an intron. In addition, we probed U2 snRNA in the free U2 snRNP in the presence of SF3B inhibitor and again saw no differences. However, increased protection of nucleotides upstream of Stem I in the absence of SF3A and SF3B proteins suggests a change of secondary structure at the very 5′ end of U2 snRNA. Chemical probing of synthetic U2 snRNA in the absence of proteins results in similar protections and predicts a previously uncharacterized extension of Stem I. Because this stem must be disrupted for SF3A and SF3B proteins to stably join the snRNP, the structure has the potential to influence snRNP assembly and recycling after spliceosome disassembly.

Icosahedral Meta-Carboranes Containing Exopolyhedral B-Se and B-Te Bonds

Chalcogen-containing carboranes have been known for several decades and possess stable exopolyhedral B(9)-Se and B(9)-Te σ bonds despite the electron-donating ability of the B(9) vertex. While these molecules are known, little has been done to thoroughly evaluate their electrophilic and nucleophilic behavior. Herein, we report an assessment of the electrophilic reactivity of meta-carboranyl selenyl (II), tellurenyl (II), and tellurenyl (IV) chlorides and establish their reactivity pattern with Grignard reagents, alkenes, alkynes, enolates, and electron-rich arenes. These electrophilic reactions afford unique electron-rich B-Y-C (Y = Se, Te) bonding motifs not commonly found before. Furthermore, we show that meta-carboranyl selenolate, and even meta-carboranyl tellurolate, can be competent nucleophiles and participate in nucleophilic aromatic substitution reactions. Arene substitution chemistry is shown to be further extended to electron-rich species via the palladium mediated cross-coupling chemistry.

U2 snRNA structure is influenced by SF3A and SF3B proteins but not by SF3B inhibitors

U2 snRNP is an essential component of the spliceosome. It is responsible for branch point recognition in the spliceosome A-complex via base-pairing of U2 snRNA with an intron to form the branch helix. Small molecule inhibitors target the SF3B component of the U2 snRNP and interfere with A-complex formation during spliceosome assembly. We previously found that the first SF3B inhibited-complex is less stable than A-complex and hypothesized that SF3B inhibitors interfere with U2 snRNA secondary structure changes required to form the branch helix. Using RNA chemical modifiers, we probed U2 snRNA structure in A-complex and SF3B inhibited splicing complexes. The reactivity pattern for U2 snRNA in the SF3B inhibited-complex is indistinguishable from that of A-complex, suggesting that they have the same secondary structure conformation, including the branch helix. This observation suggests SF3B inhibited-complex instability does not stem from an alternate RNA conformation and instead points to the inhibitors interfering with protein component interactions that normally stabilize U2 snRNP's association with an intron. In addition, we probed U2 snRNA in the free U2 snRNP in the presence of SF3B inhibitor and again saw no differences. However, increased protection of nucleotides upstream of Stem I in the absence of SF3A and SF3B proteins suggests a change of secondary structure at the very 5′ end of U2 snRNA. Chemical probing of synthetic U2 snRNA in the absence of proteins results in similar protections and predicts a previously uncharacterized extension of Stem I. Because this stem must be disrupted for SF3A and SF3B proteins to stably join the snRNP, the structure has the potential to influence snRNP assembly and recycling after spliceosome disassembly.

New Acridone- and (Thio)Xanthone-Derived 1,1-Donor–Acceptor-Substituted Alkenes: pH-Dependent Fluorescence and Unusual Photooxygenation Properties

A synthetic route to new heterocyclic 1,1-donor–acceptor-substituted alkenes starting with N-methyl-acridone, xanthone, and thioxanthone was investigated, leading to the acridone- and xanthone-derived products methyl 2-methoxy-2-(10-methylacridin-9 (10H)-ylidene)acetate (7) and methyl 2-methoxy-2-(9H-xanthen-9-ylidene)acetate (10) in low yields with the de-methoxylated product methyl 2-(10-methylacridin-9 (10H)-ylidene)acetate (8) and the reduced compound methyl 2-methoxy-2-(9H-xanthen-9-yl)acetate (11) as the major products from N-methyl acridone and xanthone. From thioxanthone, only the rearrangement and reduction products (14) and (15) resulted. The photophysical properties of compounds (7), (8), and (10) were investigated in the presence and absence of the Brønsted acid TFA by NMR, UV–VIS absorption, and fluorescence spectroscopy. Protonation of the acridone-derived alkenes (7) and (8) led to strong bathochromic and hyperchromic fluorescence shifts and a substantial increase in Stokes shift. The photooxygenation experiments with these substrates showed an unusual reactivity pattern in the singlet oxygen processes: whereas the electron-rich enolether (7) was chemically unreactive, (8) and (10) were oxidatively cleaved, presumably via intermediate 1,2-dioxetanes.

Reactivity of NHC/diphosphene-coordinated Au(i)-hydride

We report the reactivity of NHC/diphosphene-stabilized Au(i)-hydride towards substrates with C–C and N–N multiple bonds. It reveals NHC/diphosphene-Au(i)-hydride is more reactive than NHC-Au(i)-hydride and also the reactivity pattern is different.

Hydroxido Supported and Differently Networked Octanuclear Ni6Ln2 [Ln = GdIII and DyIII] Complexes: Structural Variation, Magnetic Properties and Theoretical Insights

The design and synthesis of Schiff base H2L, (2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol) bearing ONOO donor set has been explored for its reactivity pattern with LnCl3∙6H2O (Ln = GdIII and DyIII) and Ni(CH3CO2)2∙4H2O in...