Synthesis of Highly Enantioenriched Sulfonimidoyl Fluorides and Sulfonimidamides by Stereospecific Sulfur–Fluorine Exchange (SuFEx) Reaction

Sulfonimidamides present exciting opportunities as chiral isosteres of sulfonamides, with potential for additional directional interactions. Here, we present the first modular enantioselective synthesis of sulfonimidamides, including the first stereoselective synthesis of enantioenriched sulfonimidoyl fluorides, and studies on their reactivity. A new route to sulfonimidoyl fluorides is presented from solid bench-stable, N-Boc-sulfinamide (Boc=tert-butyloxycarbonyl) salt building blocks. Enantioenriched arylsulfonimidoyl fluorides are shown to be readily racemised by fluoride ions. Conditions are developed, which trap fluoride and enable the stereospecific reaction of sulfonimidoyl fluorides with primary and secondary amines (100 % es, es=enantiospecificity) generating sulfonimidamides with up to 99 % ee. Aryl and alkyl sulfonimidoyl fluoride reagents are suitable for mild late stage functionalisation reactions, exemplified by coupling with a selection of complex amines in marketed drugs.     

Nucleophilic Substitution at Heteroatoms—Identity Substitution Reactions at Phosphorus and Sulfur Centers: Do They Proceed in a Concerted (SN2) or Stepwise (A–E) Way?

The mechanisms of three selected identity substitution reactions at phosphorus and sulfur occurring with stereospecific inversion have been investigated using density functional theory (DFT). The first identity reaction between methoxyl anion and methyl ethylphenylphosphinate 1 reported in 1963 has been shown to proceed in a stepwise fashion according to the addition–elimination (A–E) mechanism involving formation of a pentacoordinate phosphorus intermediate (TBI-1). In contrast, the results of DFT studies of the identity chloride exchange reaction in (ethoxy)ethylphosphonochloridothionate 3 in acetone solution provided evidence that it proceeds synchronously according to the classical Ingold’s S_N2-P mechanism. DFT calculations of the methoxyl–methoxy exchange reaction at sulfur in methyl p-toluenesulfinate 4 catalyzed by trifluoroacetic acid in methanol revealed that it proceeds stepwise (A–E mechanism), involving the formation of the high-coordinate sulfurane intermediate. In both identity transesterification reactions, 1 and 4, the transiently formed trigonal bipyramidal intermediates with the two methoxyl groups occupying apical positions (TBI-1 and TBI-4) have higher free energy barriers for the Berry-type pseudorotation than those for direct decomposition to starting phosphinate and sulfinate ensuring stereospecific inversion of configuration at the phosphinyl and sulfinyl centers. Thus, the DFT method proved its usefulness in the distinction between both mechanisms that are often indistinguishable by kinetic measurements.     

Two‐Step Oxidation Synthesis of Sulfur with a Red Aggregation‐Induced Emission

Sulfur is not normally considered a light‐emitting material, even though there have been reports of a dim luminescence of this compound in the blue‐to‐green spectral region. Now, it is shown how to make red‐emissive sulfur by a two‐step oxidation approach using elemental sulfur and Na₂S as starting materials, with a high photoluminescence quantum yield of 7.2 %. Polysulfide is formed first and is partially transformed into Na₂S₂O₃ in the first step, and then turns back to elemental S in the second step. The elevated temperature and relatively oxygen‐deficient environment during the second step transforms Na₂S₂O₃ into Na₂SO₃ incorporated with oxygen vacancies, thus resulting in the formation of a solid‐state powder consisting of elemental S embedded in Na₂SO₃. It shows aggregation‐induced emission properties, attributed to the influence of oxygen vacancies on the emission dynamics of sulfur by providing additional lower energy states that facilitate the radiative relaxation of excitons.     

ChemInform Abstract: Broken Symmetry Analysis of Spin Coupling in Iron-Sulfur Clusters.

On the basis of broken symmetry molecular orbital calculations, a method is developed to estimate antiferromagnetic coupling constants for polynuclear transition metal complexes containing three or more metal sites.     

Sulfur-Containing Bent N-Heteroacenes

A series of novel sulfur-containing bent N-heteroacenes were constructed and characterized by NMR and UV/Vis spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction. By introducing sulfur-containing groups (thio, sulfinyl, and sulfonyl) into bent azaacenes, their electronic delocalization was improved and frontier energy levels were modulated. The target products displayed tunable optical and electronic properties through altering the valence of sulfur and fused length of the azaacenes. For the first time, typical products were utilized as organic field effect transistor materials, affording promising results.     

Protein–Metal-Ion Networks: A Unique Approach toward Metal Sulfide Nanoparticles Embedded In Situ in Nanocomposites

Nanoscale metal sulfides are of tremendous potential in biomedicine. Generally, the properties and performances of metal sulfide nanoparticles (NPs) are highly related to their structures, sizes and morphologies. Recently, a strategy of using sulfur-containing protein–metal-ion networks for preparing metal sulfide embedded nanocomposites was proposed. Within the networks, proteins can play multiple roles to drive the transformation of these networks into protein-encapsulated metal sulfide NPs with ultrasmall size and defined structure (as both a template and a sulfur provider) or metal sulfide NP–protein hydrogels with injecting and self-healing properties (as a template, a sulfur provider, and a gelator) in a controlled manner. In this Concept, the synthesis strategy, the formation mechanism, and the biomedical applications of the gained nanocomposites are presented. Moreover, the challenges and opportunities of using protein–metal ion networks to construct functional materials for biomedical applications are analyzed.     

An economic model for investing in sulfur oxide control technology development

The model estimates, subject to restrictions, the functional relationship between national sulfur dioxide discharges and investment in control technology development. Estimates may be made for different product demands, allowed cost increases, and clean fuel availabilities. Control technology development may be accelerated by increased investment. Both optimal and sub-optimal solutions are calculated for an example problem. A general computing method is provided.The model was presented at the Industrial Process Design for Pollution Control Workshop, Chicago, Illinois, Oct. 1973; copyright released by the American Institute of Chemical Engineers for publication for the first time in the monographNormative Analysis in Policy Decisions: Public and Private.     

Über die Isotopenzusammensetzung des Schwefels in seinem natürlichen Kreislauf

Es wird ein Modell des globalen Kreislaufs der Isotope des Schwefels erarbeitet, auf dessen Grundlage die säkularen Veränderungen der Isotopenzusammensetzung des Schwefels in sedimentären Sulfiden, in organisch gebundenem Schwefel und in sedimentären Sulfaten verstanden werden können. Das Modell berücksichtigt die Venwitterung von Magmatiten und sedimentärem Schwefel unter Oxydation von Sulfid zu Sulfat, die Verwitterung sedimentärer Sulfate, die Bildung sedimentärer Sulfide und organisch gebundenen Schwefels, die Bildung sedimentärer Sulfate, die Metamorphose der Sedimente und die Überführung sedimentären Schwefels in die Ozeane durch vulkanische Prozesse. Es wird gezeigt, daß nur die Isotopieeffekte bei der mikrobiellen Reduktion von Sulfat zu Sulfid, bei der Assimilation von Sulfaten durch die Pflanze und bei der Verwitterung sedimentärer Sulfide und organisch gebundenem Schwefel unter Oxydation von Sulfid zu Sulfat Einfluß auf die globale Isotopenzusammensetzung des Schwefels in den Sedimenten haben können. Im Wechselspiel dieser Prozesse kommen die säkularen Verānderungen der δ³⁴S-Werte, insbesondere die charakteristischen Schwankungen der δ³⁴S-Werte zustande. Dabei begünstigen starke Meeresbedeckungen der Erdoberfläche und warmes Klima die mikrobielle Reduktion von Sulfat zu Sulfid in den Ozeanen und führen zum Sinken bzw. Steigen der δ³⁴S-Werte in den sedimentären Sulfiden und im organisch gebundenen Schwefel bzw. in den sedimentären Sulfaten. Regressionen der Ozeane und kaltes Klima, insbesondere Vereisungen begünstigen die Verwitterung und Oxydation von Sulfiden zu Sulfaten und führen zu einem Steigen bzw. Sinken der δ³⁴S-Werte in den sedimentären Sulfiden und im organisch gebundenen Schwefel bzw. in den sedimentären Sulfaten.     

Cyano Derivatives of Bis(cyclopentadienyl)titanium(IV). The crystal and molecular structure of μ-Oxo-bis[bis(cyclopentadienyl)cyanotitanium(IV)], [(η5-C5H5)2TiCN]2O

By the reaction of KCN with Cp₂TiCl₂ (Cp = η⁵-C₅H₅) in boiling methanol, bis(cyclopentadienyl)-methoxytitanium(IV) cyanide, Cp₂Ti(OCH₃)CN, is formed which in air is converted into the dinuclear oxygen-bridged derivative (Cp₂TiCN)₂O. By the same procedure, the bis(methylcyclopentadienyl) analogue [MeCp₂TiCN]₂O has been obtained. An X-ray diffraction study of (Cp₂TiCN)₂O has shown that the CN group acts as a unidentate ligand with a Ti? C bond length of 2.158 Å and a Ti? C? N bond angle of 177.7°, very close to linearity. The Ti? O bond distance, 1.836 Å, and the bond angle at the bridging O atom, 174.1°, are normal. The ligands are arranged in a nearly tetrahedral way around the Ti atoms. The structural results are compared to those for similar dinuclear titanium complexes.