Two polymorphic hydrogen peroxide solvates of 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20; wurtzitane is an alternative name to iceane) were obtained using hydrated α‐CL‐20 as a ...guide. These novel H2O2 solvates have high crystallographic densities (1.96 and 2.03 g cm−3, respectively), high predicted detonation velocities/pressures (with one solvate performing better than ϵ‐CL‐20), and a sensitivity similar to that of ϵ‐CL‐20. The use of hydrated materials as a guide will be important in the development of other energetic materials with hydrogen peroxide. These solvates represent an area of energetic materials that has yet to be explored.
Supercharged solvates: Two polymorphic hydrogen peroxide solvates of 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20) were obtained with high crystallographic densities. Both solvates are predicted to have high detonation velocities/pressures (with one solvate performing better than ϵ‐CL‐20). H2O2 solvate formation allows for a simple method for improving the oxygen balance of existing materials.
This communication describes oxidatively induced Ar−CF3 bond-forming reductive elimination from new PdII complexes of general structure (L∼L)PdII(Ar)(CF3). The electrophilic fluorinating reagent ...N-fluoro-2,4,6-trimethylpyridinium triflate promotes these reactions in good to excellent yields. The palladium(IV) intermediate ( t Bu-bpy)PdIV(CF3)(F)(OTf)(C6H4F) has been isolated, characterized, and demonstrated to undergo high yielding Ar−CF3 coupling upon thermolysis. This work provides an attractive conceptual framework for the development of PdII/IV-catalyzed arene trifluoromethylation reactions.
Solvent dependence in the assembly of coordination driven macrocycles is a poorly understood phenomenon. This work presents the solvent dependent assembly of 8 lanthanide metallacrowns (LnMCs) in ...solution using picoline hydroxamic acid (picHA), Zn(II), and Ln(III) ions. ESI-MS and single-crystal X-ray crystallography reveal the selective assembly of LnZn4(picHA)4 3+, LnZn5(picHA)5 3+, LnZn8(picHA)8 3+, LnZn12(picHA)12 3+, LnZn16(picHA)16 3+, Ln2Zn3(picHA)4 4+, Ln2Zn7–9(picHA)8–10, and Ln4Zn4–5(picHA)8–9 complexes in five different solvents. The coordination preferences of the hard Ln(III) ion and relatively soft Zn(II) ion dictate the solvent selectivity in this system. The LnMCs assemble with open or closed Zn(II) and/or Ln(III) coordination sites based on the behavior of the solvent as an ancillary ligand. This structural promiscuity is attributed to the symmetry incompatible building blocks, which generate assemblies with substantial geometric strain such that no clear thermodynamic minimum exists between the different LnMCs. These LnMCs assemble from a Zn5(picHA)4 2+ intermediate, which is monitored using 1H NMR and ESI-MS to assess the stability of the complexes and possible assembly pathways based on kinetic considerations. LnMC assemblies that can be generated through central metal substitution reactions such as the LnZn4(picHA)4 3+, LnZn5(picHA)5 3+, and LnZn8(picHA)8 3+ effectively reach equilibrium after 24 h at room temperature. In contrast, LnMCs that must disrupt the Zn5L4 2+ structure to assemble, such as the LnZn16L16 3+, reach equilibrium after heating for 24 h at 65 °C. A pathway for LnMC assembly is presented where the Zn5L4 2+ is the key intermediate based on these reaction data and shared structural motifs in the complexes. These results correlate solvent dependent assembly to the building block geometry, highlighting synthetic approaches for generating novel complexes.
Boron clusters are proposed as a new concept for the design of magnesium‐battery electrolytes that are magnesium‐battery‐compatible, highly stable, and noncorrosive. A novel carborane‐based ...electrolyte incorporating an unprecedented magnesium‐centered complex anion is reported and shown to perform well as a magnesium‐battery electrolyte. This finding opens a new approach towards the design of electrolytes whose likelihood of meeting the challenging design targets for magnesium‐battery electrolytes is very high.
A b(o)rilliant improvement: An electrolyte incorporating an unprecedented magnesium‐centered complex anion was developed for use in rechargeable magnesium batteries. The carboranyl magnesium halide (see structure; B purple, Cl green, O red, C white, Mg orange) exhibited compatibility with magnesium‐metal anodes as well as remarkable oxidative stability (3.2 V vs. Mg) on non‐noble‐metal electrodes.
This report describes a detailed investigation of acetate-assisted C–H activation at PdIV centers supported by the tris(2-pyridyl)methane (Py3CH) ligand. Mechanistic information about this ...transformation has been obtained through the following: (i) extensive one- and two-dimensional NMR analysis, (ii) reactivity studies of a series of substituted analogues, and (iii) isotope effect studies. These experiments all suggest that C–H activation at (Py3CH)PdIV(biphenyl)Cl2+ occurs via a multistep process involving chloride-to-acetate ligand exchange followed by conformational and configurational isomerization and then C–H cleavage. The data also suggest that C–H cleavage proceeds via an acetate-assisted mechanism with the carboxylate likely serving as an intramolecular base. The viability of acetate-assisted C–H activation at high valent palladium has important implications for the design and optimization of catalytic processes involving this transformation as a key step.
This Article describes the synthesis and characterization of cyclometalated aminoquinoline NiII σ-aryl and σ-alkyl complexes that have been proposed as key intermediates in Ni-catalyzed C–H ...functionalization reactions. These NiII complexes serve as competent catalysts for the C–H functionalization of aminoquinoline derivatives with I2. They also react stoichiometrically with I2 to form either aryl iodides or β-lactams within minutes at room temperature. Furthermore, they react with AgI salts at −30 °C to afford isolable five-coordinate NiIII species. The NiIII σ-aryl complexes proved inert toward C(sp2)–I bond-forming reductive elimination under all conditions examined (up to 140 °C in DMF). In contrast, a NiIII σ-alkyl analogue underwent C(sp3)–N bond-forming reductive elimination at 140 °C in DMF to afford a β-lactam product. However, despite the ability of this latter NiIII species to participate in stoichiometric product formation, the complex was not a competent catalyst for β-lactam formation. Overall, these results suggest against the intermediacy of NiIII species in these C–H functionalization reactions.
This manuscript describes the design, synthesis, characterization, and reactivity studies of organometallic NiIII complexes of general structure TpNiIII(R)(R1) (Tp = tris(pyrazolyl)borate). With ...appropriate selection of the R and R1 ligands, the complexes are stable at room temperature and can be characterized by cyclic voltammetry, EPR spectroscopy, and X-ray crystallography. Upon heating, many of these NiIII compounds undergo C(sp2)–C(sp2) or C(sp3)–C(sp2) bond-forming reactions that are challenging at lower oxidation states of nickel.
The treatment of pyridine- and pyrazole-ligated NiII σ-aryl complexes with Selectfluor results in C(sp2)–F bond formation under mild conditions. With appropriate design of supporting ligands, ...diamagnetic NiIV σ-aryl fluoride intermediates can be detected spectroscopically and/or isolated during these transformations. These studies demonstrate for the first time that NiIV σ-aryl fluoride complexes participate in challenging C(sp2)–F bond-forming reductive elimination to yield aryl fluoride products.
A new series of bifunctional Ru complexes with pendent Lewis acidic boranes were prepared by late-stage modification of an active hydrogen-transfer catalyst. The appended boranes modulate the ...reactivity of a metal hydride as well as catalytic hydrogenations. After installing acidic auxiliary groups, the complexes become multifunctional and catalyze the cis-selective hydrogenation of alkynes with higher rates, conversions, and selectivities compared with the unmodified catalyst.
A Boronium Ion with Exceptional Electrophilicity Prokofjevs, Aleksandrs; Kampf, Jeff W.; Vedejs, Edwin
Angewandte Chemie (International ed.),
February 25, 2011, Letnik:
50, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Barely bidentate: The adduct of dimethylamino naphthalene (proton sponge) and 9‐BBN‐NTf2 is activated by steric hinderance for intermolecular borylation (see scheme). A contrasting ...addition/elimination pathway is favored when using monodentate triethylamine which gives the first observable borenium salt (9‐BBN‐NEt3+ Tf2N−) lacking any n‐ or π‐donor substitutents.
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