A Sterically Hindered Derivative of 2,1,3-Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium–Nitrogen Radical Anion

Interaction of the tetradentate redox-active 6,6′-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H₄L) with TeCl₄ leads to neutral diamagnetic compound TeL ( 1 ) in high yield. The molecule of 1 has a nearly planar TeN₂O₂ fragment, which suggests the formulation of 1 as Te^IIL²⁻, in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp₂] leads to quantitative formation of the paramagnetic salt [CoCp₂]⁺[ 1 ]^.−, which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp₂]⁺[ 1 ]^.− at room temperature features a quintet due to splitting on two equivalent ¹⁴N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the ¹²⁵Te nucleus. Two-component relativistic DFT calculations perfectly reproduce the a(¹⁴N) HFI constants and A_∥(¹²⁵Te) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in 1 ^.− is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1 ^.− can be regarded as the first example of a structurally characterised monomeric tellurium–nitrogen radical anion.     

Modeling the effect of ion-induced shock waves and DNA breakage with the reactive CHARMM force field

Ion-induced DNA damage is an important effect underlying ion beam cancer therapy. This article introduces the methodology of modeling DNA damage induced by a shock wave caused by a projectile ion. Specifically it is demonstrated how single- and double strand breaks in a DNA molecule could be described by the reactive CHARMM (rCHARMM) force field implemented in the program MBN Explorer. The entire workflow of performing the shock wave simulations, including obtaining the crucial simulation parameters, is described in seven steps. Two exemplary analyses are provided for a case study simulation serving to: (a) quantify the shock wave propagation and (b) describe the dynamics of formation of DNA breaks. The article concludes by discussing the computational cost of the simulations and revealing the possible maximal computational time for different simulation set-ups.     

A long Nb=O double bond in bis(pyridinium) tetra­chlorooxo(pyridine‐κN)niobate(V) chloride

The asymmetric unit of the title compound, (C₅H₆N)₂[NbCl₄O(C₅H₅N)]Cl or (pyH)₂[O=NbCl₄(py)]Cl (py is pyridine), contains a discrete anionic niobium(V) complex, [O=NbCl₄(py)]⁻, and two protonated pyridine mol­ecules, which form medium–strong hydrogen bonds with the Cl⁻ counter‐ion. The Nb=O distance of 1.7643 (17) Å is the longest among those in congener niobium complexes reported to date. Extensive density functional theory studies of conformations of [O=NbCl₄(py)]⁻ and structural data mining raise doubts regarding the reliability of the length of this Nb=O double bond.     

Unusual equilibria involving group 4 amides, silyl complexes, and silyl anions via ligand exchange reactions

Silyl anion SiButPh2- (2) was found to substitute an amide ligand in Zr(NMe2)4 (3) to give the disilyl complex Zr(NMe2)3(SiButPh2)2- (1a) and Zr(NMe2)5- (1b) in THF. The reaction is reversible, and nucleophilic amide NMe2- attacks the Zr-SiButPh2 bonds in 1a or Zr(NMe2)3(SiButPh2) in the reverse reaction, leading to an unusual ligand exchange equilibrium 2 3 + 2 2 right harpoon over left harpoon 1a + 1b (eq 1). The silyl anion 2 selectively attacks the -N(SiMe3)2 ligand in Zr(NMe2)3[N(SiMe3)2] (6) to give 1a and N(SiMe3)2- (7). Reversible reaction occurs as well, where 7 selectively substitutes the silyl ligand in Zr(NMe2)3(SiButPh2)2- (1a) or Zr(NMe2)3(SiButPh2), giving the equilibrium 6 + 2 2 right harpoon over left harpoon 1a + 7 (eq 3). The thermodynamics of these equilibria has been studied: For eq 1, DeltaH degrees = -8.3(0.2) kcal/mol, DeltaS degrees = -23.3(0.9) eu, and DeltaG degrees 298K = -1.4(0.5) kcal/mol at 298 K; for eq 3, DeltaH degrees = -1.61(0.12) kcal/mol, DeltaS degrees = -2.6(0.5) eu, and DeltaG degrees 298K = -0.8(0.3) kcal/mol. In both equilibria, the enthalpy changes for the forward reactions outweigh the entropy changes, and therefore the substitutions of amide ligands in Zr(NMe2)4 (3) and Zr(NMe2)3[N(SiMe3)2] (6) to afford the disilyl complex 1a are thermodynamically favored. The following equilibria were also observed and studied: Zr(NMe2)3[N(SiMe3)2] (6) + Si(SiMe3)3- (9) right harpoon over left harpoon Zr(NMe2)3[Si(SiMe3)3] (10) + N(SiMe3)2- (7) and Zr(NMe2)4 (3) + 9 right harpoon over left harpoon 10 + Zr(NMe2)5- (1b).     

Solid‐state 11B and 13C NMR,IR, and X‐ray crystallographic characterization of selected arylboronic acids and their catechol cyclic esters

Nine arylboronic acids, seven arylboronic catechol cyclic esters, and two trimeric arylboronic anhydrides (boroxines) are investigated using ¹¹B solid‐state NMR spectroscopy at three different magnetic field strengths (9.4, 11.7, and 21.1 T). Through the analysis of spectra of static and magic‐angle spinning samples, the ¹¹B electric field gradient and chemical shift tensors are determined. The effects of relaxation anisotropy and nutation field strength on the ¹¹B NMR line shapes are investigated. Infrared spectroscopy was also used to help identify peaks in the NMR spectra as being due to the anhydride form in some of the arylboronic acid samples. Seven new X‐ray crystallographic structures are reported. Calculations of the ¹¹B NMR parameters are performed using cluster model and periodic gauge‐including projector‐augmented wave (GIPAW) density functional theory (DFT) approaches, and the results are compared with the experimental values. Carbon‐13 solid‐state NMR experiments and spectral simulations are applied to determine the chemical shifts of the ipso carbons of the samples. One bond indirect ¹³C‐¹¹B spin‐spin (J) coupling constants are also measured experimentally and compared with calculated values. The ¹¹B/¹⁰B isotope effect on the ¹³C chemical shift of the ipso carbons of arylboronic acids and their catechol esters, as well as residual dipolar coupling, is discussed. Overall, this combined X‐ray, NMR, IR, and computational study provides valuable new insights into the relationship between NMR parameters and the structure of boronic acids and esters. Copyright © 2012 John Wiley & Sons, Ltd.     

An angularly fused three‐ring precursor to phytuberin

The title compound, 3,3a,5,5a,6,7,8,9‐octahydro‐3a‐hydroxy‐5a‐methyl‐8‐(2‐prop­enyl)­furo­[3,2‐c]­iso­benzo­furan‐2‐one, C₁₄H₂₀O₄, crystallizes with two independent molecules in the asymmetric unit. The molecules have similar metric parameters but differ in the conformations of the isopropenyl groups. The hydroxyl groups form one‐dimensional chains of hydrogen bonds.     

Synthesis of Phosphorus Containing Polymers by Phase Transfer Catalysis (PTC). I. Comparative Study between Liquid-Liquid and Liquid-Vapor Systems

Abstract

Polyphosphonates were synthesized by interfacial alkaline polycondensation of bispheml A (BA) with phenyldichlorophosphonate (PPD) and cyclohexyl-dichlorophosphonate (CPD) in liquid-liquid[1] (1–1) and Iiquid-vapoR[2] (I-v) systems.