Exploring benzylic gem-C(sp3)–boron–silicon and boron–tin centers as a synthetic platform

A stepwise build-up of multi-substituted C_sp³ carbon centers is an attractive, conceptually simple, but often synthetically challenging type of disconnection. To this end, this report describes how gem-α,α-dimetalloid-substituted benzylic reagents bearing boron/silicon or boron/tin substituent sets are an excellent stepping stone towards diverse substitution patterns. These gem-dimetalloids were readily accessed, either by known carbenoid insertion into C–B bonds or by the newly developed scalable deprotonation/metallation approach. Highly chemoselective transformations of either the C–Si (or C–Sn) or the C–B bonds in the newly formed gem-C_sp³ centers have been achieved through a set of approaches, with a particular focus on exploiting the synthetically versatile polarity reversal in organometalloids by λ³-aryliodanes. Of particular note is the metal-free arylation of the C–Si (or C–Sn) bonds in such gem-dimetalloids via the iodane-guided C–H coupling approach. DFT calculations show that this transfer of the (α-Bpin)benzyl group proceeds via unusual [5,5]-sigmatropic rearrangement and is driven by the high-energy iodine(iii) center. As a complementary tool, the gem-dimetalloid C–B bond is shown to undergo a potent and chemoselective Suzuki–Miyaura arylation with diverse Ar–Cl, thanks to the development of the reactive gem-α,α-silyl/BF₃K building blocks.

This work explores divergent reactivity of the benzylic gem-boron–silicon and boron–tin double nucleophiles, including the arylation of the C–B bond with Ar–Cl, along with a complementary oxidative λ³-iodane-guided arylation of the C–Si/Sn moiety.     

Square-Planar Heteroleptic Complexes of α-Diimine-NiII-Catecholate Type: Intramolecular Ligand-to-Ligand Charge Transfer

Two heteroleptic Ni^II complexes combined the redox-active catecholate and 2,2′- bipyridine ligand platforms were synthesized to observe a photoinduced intramolecular ligand-to-ligand charge transfer (LL’CT, HOMO_catecholate → LUMO_α-diimine). A molecular design of compound [Ni^II(3,6-Cat)(bipy)]∙CH₃CN (1) on the base of bulky 3,6-di-tert-butyl-o-benzoquinone (3,6-DTBQ) was an annelation of the ligand with an electron donor glycol fragment, producing derivative [Ni^II(3,6-Cat^gly)(bipy)]∙CH₂Cl₂ (2), in order to influence the energy of LL’CT transition. A substantial longwave shift of the absorption peak was observed in the UV-Vis-NIR spectra of 2 compared with those in 1. In addition, the studied Ni^II derivatives demonstrated a pronounced negative solvatochromism, which was established using a broad set of solvents. The molecular geometry of both compounds can be ascribed as an insignificantly distorted square-planar type, and the π–π intermolecular stacking of the neighboring α-diimines is realized in a crystal packing. There is a lamellar crystal structure for complex 1, whereas the perpendicular T-motifs with the inter-stacks attractive π–π interactions form the packing of complex 2. The redox-active nature of ligand systems was clearly shown through the electrochemical study: a quasi-reversible one-electron reduction of 2,2′-bipyridine and two reversible successive one-electron oxidative conversations (“catecholate dianion—o-benzosemiquinonato radical anion—neutral o-benzoquinone”) were detected.     

Structure of penetrable-rod fluids: exact properties and comparison between Monte Carlo simulations and two analytic theories

Bounded potentials are good models to represent the effective two-body interaction in some colloidal systems, such as the dilute solutions of polymer chains in good solvents. The simplest bounded potential is that of penetrable spheres, which takes a positive finite value if the two spheres are overlapped, being 0 otherwise. Even in the one-dimensional case, the penetrable-rod model is far from trivial, since interactions are not restricted to nearest neighbors and so its exact solution is not known. In this paper the structural properties of one-dimensional penetrable rods are studied. We first derive the exact correlation functions of the penetrable-rod fluids to second order in density at any temperature, as well as in the high-temperature and zero-temperature limits at any density. It is seen that, in contrast to what is generally believed, the Percus-Yevick equation does not yield the exact cavity function in the hard-rod limit. Next, two simple analytic theories are constructed: a high-temperature approximation based on the exact asymptotic behavior in the limit T--> infinity and a low-temperature approximation inspired by the exact result in the opposite limit T--> 0. Finally, we perform Monte Carlo simulations for a wide range of temperatures and densities to assess the validity of both theories. It is found that they complement each other quite well, exhibiting a good agreement with the simulation data within their respective domains of applicability and becoming practically equivalent on the borderline of those domains. A comparison with numerical solutions of the Percus-Yevick and the hypernetted-chain approximations is also carried out. Finally, a perspective on the extension of our two heuristic theories to the more realistic three-dimensional case is provided.     

Equitable versus nearly equitable coloring and the Chen-Lih-Wu conjecture

Chen, Lih, and Wu conjectured that for r ≥ 3, the only connected graphs with maximum degree at most r that are not equitably r-colorable are K _r,r (for odd r) and K _r+1. If true, this would be a strengthening of the Hajnal-Szemerédi Theorem and Brooks’ Theorem. We extend their conjecture to disconnected graphs. For r ≥ 6 the conjecture says the following: If an r-colorable graph G with maximum degree r is not equitably r-colorable then r is odd, G contains K _r,r and V(G) partitions into subsets V ₀, …, V _t such that G[V ₀] = K _r,r and for each 1 ≤ i ≤ t, G[V _i ] = K _r . We characterize graphs satisfying the conclusion of our conjecture for all r and use the characterization to prove that the two conjectures are equivalent. This new conjecture may help to prove the Chen-Lih-Wu Conjecture by induction.     

Collective magnetic response of inhomogeneous nanoisland FeNi films around the percolation transition

By using superconducting quantum interference device (SQUID) magnetometry, we investigated anisotropic high-field (H ? 7T) low-temperature (10 K) magnetization response of inhomogeneous nanoisland FeNi films grown by rf sputtering deposition on Sitall (TiO₂) glass substrates. In the grown FeNi films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the percolation transition at the d _c ? 1.8 nm. We discovered that, beyond conventional spin-magnetism of Fe₂₁Ni₇₉ permalloy, the extracted out-of-plane magnetization response of the nanoisland FeNi films is not saturated in the range of investigated magnetic fields and exhibits paramagnetic-like behavior. We found that the anomalous out-of-plane magnetization response exhibits an escalating slope with increase in the nominal film thickness from 0.6 to 1.1 nm, however, it decreases with further increase in the film thickness, and then practically vanishes on approaching the FeNi film percolation threshold. At the same time, the in-plane response demonstrates saturation behavior above 1.5–2T, competing with anomalously large diamagnetic-like response, which becomes pronounced at high magnetic fields. It is possible that the supported-metal interaction leads to the creation of a thin charge-transfer (CT) layer and a Schottky barrier at the FeNi film/Sitall (TiO₂) interface. Then, in the system with nanoscale circular domains, the observed anomalous paramagnetic-like magnetization response can be associated with a large orbital moment of the localized electrons. In addition, the inhomogeneous nanoisland FeNi films can possess spontaneous ordering of toroidal moments, which can be either of orbital or spin origin. The system with toroidal inhomogeneity can lead to anomalously strong diamagnetic-like response. The observed magnetization response is determined by the interplay between the paramagnetic- and diamagnetic-like contributions.     

New tin(IV) complexes with sterically hindered o‐iminobenzoquinone ligand: Synthesis and structure

The reduction of 4,6‐di‐tert‐butyl‐N‐(2, 6‐di‐iso‐propylphenyl)‐o‐iminobenzoquinone (imQ) by tin amalgam in hexane solution leads to new six‐coordinated o‐iminoquinonato tin(IV) complex (iSQ)₂SnAP ( 1 ) (where iSQ and AP are o‐iminosemiquinolate and dianion o‐amidophenolate, respectively). Variable temperature magnetic susceptibility measurements of 1 have shown that this complex possesses a weak ferromagnetic exchange between o‐iminosemiquinonate ligands. The oxidation of 1 with air oxygen produces new o‐iminoquinonolate tin(IV) derivatives [(iSQ)Sn(AP)]₂O ( 2 ) and (iSQ)₂Sn(OH)₂ ( 3 ) containing μ‐oxo‐ and hydroxo‐ligands, respectively. The electronic structure of 1 was examined by DFT analysis. Complexes 1–3 have been investigated using single‐crystal X‐ray diffraction. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:332–340, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20555     

Low temperature subband 2D electron mobilities in heavy delta- and modulation doped GaAs/GaAlAs heterostructures

We synthesised high-2D electron-density GaGs/GaAlAs heterostructures with different distance L_σ of Si delta-layer in GaAs from the heterojunction and uniform doped GaAlAs. The quantum Hall effect and Shubnikov-de Haas effect were measured for temperatures down to 0.4 K in magnetic fields up to 40 T. The enhanced 2D electron concentration achieved was 1.1^*10¹³ cm^?2 in six filled subbands. The Hall mobility depends on L_σ and has maximum for L_σ=600÷750Å. From the amplitudes of the SdH oscillations and Fourier transforms the subband mobilities and electron concentration in each subband have been extracted. According to calculations intersubband electron scattering appears to be important and reduces mobilities in subbands.     

Extraribosomal cyclic tetradepsipeptides beauverolides: profiling and modeling the fragmentation pathways

Profiling of cyclic tetradepsipeptides beauverolides was tested as a chemotaxonomic tool for fungal strain identification/discrimination. Two new tetradepsipeptides, beauverolides Q and R, were characterized by tandem mass spectrometry. Specific elimination of 113 atomic mass units from both protonated and sodiated molecules of beauverolides is ubiquitous for all 12 most dominant congeners evaluated in this profiling study. Reconstruction of the total ion chromatogram, according to this neutral fragment release, was used for data filtering and selectivity enhancement. Selective ring opening and fragment ion formation of beauverolide I are discussed in detail utilizing high-level theoretical modeling of the fragmentation pathways.     

Convolution Structures and Arithmetic Cohomology

Convolution structures are group-like objects that were extensively studied by harmonic analysts. We use them to define H ⁰ and H ¹ for Arakelov divisors over number fields. We prove the analogs of the Riemann–Roch and Serre duality theorems. This brings more structure to the works of Tate and van der Geer and Schoof. The H ¹ is defined by a procedure very similar to the usual ech cohomology. Serres duality becomes Pontryagin duality of convolution structures. The whole theory is parallel to the geometric case.