One electron oxidation of triferrocenylmethanol: Synthesis, metal atom dynamics, electron delocalization, and the crystal structure of [Fc 3COH]+ PF6 -

The title compound 2 was prepared and its crystal structure was determined at 100 K. The neat solid was examined by temperature dependent 57Fe Mössbauer effect (ME) spectroscopy over the interval 92 < T < 318 K, and evidences two diamagnetic Fe(II) sites and one paramagnetic Fe(III) site. The latter shows spin–lattice relaxation, but there is no evidence of electron delocalization among the three iron sites in the above temperature interval. The mean-square-amplitude-of-vibration of the diamagnetic iron site has been determined from the recoil-free fraction ME resonance, and compared to the neutral Fc3COH homologue (1). The ME dynamical data are in good agreement with the Ui,j value at 100 K extracted from the crystallographic results. The ME parameters at 5 K have also been determined with the sample compound embedded in a paraffin wax matrix as well as pelletized with BN

Regio- and Stereoselective 1,2-Carboboration of Ynamides with Aryldichloroboranes.

AbstractCatalyst‐free 1,2‐carboboration of ynamides is presented. Readily available aryldichloroboranes react with alkyl‐ or aryl‐substituted ynamides in high yields with complete regio‐ and stereoselectivity to valuable β‐boryl‐β‐alkyl/aryl α‐aryl substituted enamides which belong to the class of trisubstituted alkenylboronates. The 1,2‐carboboration reaction is experimentally easy to conduct, shows high functional group tolerance and broad substrate scope. Gram‐scale reactions and diverse synthetic transformations convincingly demonstrate the synthetic potential of this method. The reaction can also be used to access 1‐boraphenalenes, a class of boron‐doped polycyclic aromatic hydrocarbons

Direct Light-Enabled Access to α-Boryl Radicals: Application in the Stereodivergent Synthesis of Allyl Boronic Esters

Operationally simple strategies to assemble boron containing organic frameworks are highly enabling in organic synthesis. While conventional retrosynthetic logic has engendered many platforms focusing on the direct formation of C−B bonds, α-boryl radicals have recently reemerged as versatile open-shell alternatives to access organoborons via adjacent C−C bond formation. Direct light-enabled α-activation is currently contingent on photo- or transition metal-catalysis activation to efficiently generate radical species. Here, we disclose a facile activation of α-halo boronic esters using only visible light and a simple Lewis base to enable homolytic scission. Intermolecular addition to styrenes facilitates the rapid construction of highly versatile E-allylic boronic esters. The simplicity of activation permits the strategic merger of this construct with selective energy transfer catalysis to enable the complimentary stereodivergent synthesis of Z-allylic boronic esters

Inverting Small Molecule-Protein Recognition by the Fluorine Gauche Effect: Selectivity Regulated by Multiple H→F Bioisosterism

Fluorinated motifs have a venerable history in drug discovery, but as C(sp3 )@F-rich 3D scaffolds appear with increasing frequency, the effect of multiple bioisosteric changes on molecular recognition requires elucidation. Herein we demonstrate that installation of a 1,3,5-stereotriad, in the substrate for a commonly used lipase from Pseudomonas fluorescens does not inhibit recognition, but inverts stereoselectivity. This provides facile access to optically active, stereochemically well-defined organofluorine compounds (up to 98% ee). Whilst orthogonal recognition is observed with fluorine, the trend does not hold for the corresponding chlorinated substrates or mixed halogens. This phenomenon can be placed on a structural basis by considering the stereoelectronic gauche effect inherent to F@C@C@X systems (s!s*). Docking reveals that this change in selectivity (H versus F) with a common lipase results from inversion in the orientation of the bound substrate being processed as a consequence of conformation. This contrasts with the stereochemical interpretation of the biogenetic isoprene rule, whereby product divergence from a common starting material is also a consequence of conformation, albeit enforced by two discrete enzymes

Toward a Neutral Single-Component Amidinate Iodide Aluminum Catalyst for the CO₂ Fixation into Cyclic Carbonates

A new iodide aluminum complex ({AlI(κ⁴-naphbam)}, 3) supported by a tetradentate amidinate ligand derived from a naphthalene-1,8-bisamidine precursor (naphbamH, 1) was obtained in quantitative yield via reaction of the corresponding methyl aluminum complex ({AlMe(κ⁴-naphbam)}, 2) with 1 equiv of I₂ in CH₂Cl₂ at room temperature. Complexes 2 and 3 were tested and found to be active as catalysts for the cyclic carbonate formation from epoxides at 80 °C and 1 bar of CO₂ pressure. A first series of experiments were carried out with 1.5 mol % of the alkyl complex 2 and 1.5 mol % of tetrabutylammonium iodide (TBAI) as a cocatalyst; subsequently, the reactions were carried out with 1.5 mol % of iodide complex 3 as a single-component catalyst. Compound 3 is one of the first examples of a nonzwitterionic halide single-component aluminum catalyst producing cyclic carbonates. The full catalytic cycle with characterization of all minima and transition states was characterized by quantum chemistry calculations (QCCs) using density functional theory. QCCs on the reaction mechanism support a reaction pathway based on the exchange of the iodine contained in the catalyst by 1 equiv of epoxide, with subsequent attack of I⁻ to the epoxide moiety producing the ring opening of the epoxide. QCCs triggered new insights for the design of more active halide catalysts in future explorations of the field

Synthesis and Characterization of Poly-NHC-Derived Silver(I) Assemblies and Their Transformation into Poly-Imidazolium Macrocycles

Part of the “RSEQ-GEQO Prize Winners” Special CollectionThree metallosupramolecular assemblies composed of two bis-NHCs and two silver atoms, [4](PF6)2, two tetra-NHCs and foursilver atoms, [7](PF6)4, and two tri-NHCs and three silver atoms[8](BF4)3, have been prepared. Assemblies [4](PF6)2and [7](PF6)4feature NHC ligands decorated with terminal olefin groups.Irradiation of [4](PF6)2yielded complex [5](PF6)2with twoterminal cyclobutane rings linking the two bis-NHC ligands.Liberation of the macrocyclic tetrakisimidazolium salt H4-6(PF6)4was achieved by reaction of [5](PF6)2with NH4Cl/NH4PF6. No [2+2] cycloaddition was observed upon irradiation of [7](PF6)4,apparently due to an unfavorable orientation of the olefingroups. Irradiation of complex [8](BF4)3with three internal pairsof olefin groups leads to [9](BF4)3as a mixture of two isomersthat differ on the relative orientation of the internal cyclobutanerings. Reaction of [9](BF4)3with NH4Cl/NH4BF4yields an isomermixture of the novel cage-line hexakisimidazolium salt H6-10(BF4)6Three poly-imidazolium salts with appended olefins were obtained. Subsequent reaction with Ag2O enabled the preparation of the related poly-NHC-derived silver assemblies, which, depending on the relative orientation of the pendant olefins, underwent [2+2] cyclization of the olefins upon irradiation. The macrocyclic poly-imidazolium salts can be achieved by de-metallation using NH4Cl.Funding for open access charge: CRUE-Universitat Jaume

Synthesis, crystal structure and thermolysis kinetics of [Co(H2O)6](ClO4)2.(HMTA)2.2H2O (HMTA = hexamethylenetetramine)

676-681A new compound, [Co(H2O)6](ClO4)2.(HMTA)2.2H2O; HMTA = hexamethylenetetramine) has been synthesized and characterized with the assistance of X-ray crystallography, elemental analysis, FT-IR spectroscopy, TG-DTA and DSC (N2 atmosphere). Both TG data model-fitting method as well as method of model free isoconversional have been employed to observe the kinetics of thermolysis of the compound. In order to understand the effect of sudden high heat, measurements of explosion delay are undertaken at regular five unique temperatures and the kinetics of explosion has also been explored using Arrhenius equation

rac-(2R,3S)-2-Phenyl-3-(3-phenyl-1,2,3,4-tetra­hydro­quinoxalin-2-yl)quinoxaline

The title compound, C28H22N4, is the unexpected by-product of the reaction of 2-hydroxy­acetophenone and 1,2-diamino­benzene under iodine catalysis, during which a carbon–carbon σ-bond between two quinoxaline units was formed. Although a fully oxidized title compound should sterically be possible, only one quinoxaline ring is fully oxidized while the second ring remains in the reduced form. As expected, the tetra­hydro­quinoxaline unit is not planar; it adopts a sofa conformation, whereby the atom joining the two heterocyclic systems lies out of the plane of the other atoms. The quinoxaline ring system makes a dihedral angle of 53.61 (4)° with its phenyl ring substituent. The crystal packing is determined by pairs of N—H⋯N, N—H⋯π and weak C—H⋯N hydrogen bonds, forming a chain parallel to the a axis