Reductive Elimination at Pb(II) Center of an (Amino)plumbylene-Substituted Phosphaketene: New Pathway for Phosphinidene Synthesis

A stable (amino)plumbylene-substituted phosphaketene 3 was synthesized by the successive reactions of PbCl₂ with two anionic reagents (lithium amidophosphine and NaPCO). Of particular interest, the thermal evolution of 3 , at 80 °C, leads to the transient formation of corresponding amino- and phosphanylidene-phosphaketenes ( 6 and 7 ), via a reductive elimination at the Pb^II center forming new N−P and P−P bonds. Further evolution of 6 gives a new cyclic (amino)phosphanylidene phosphorane 4 , which shows a unique reactivity as a phosphinidene. This result provides a new synthetic route to phosphinidenes, extending and facilitating further their access.     

Step‐by‐Step Synthesis of the Endohedral Stannaspherene [Ir@Sn12]3− via the Capped Cluster Anion [Sn9Ir(cod)]3−

The endohedral stannaspherene cluster anion [Ir@Sn₁₂]^3? was synthesized in two steps. The reaction of K₄Sn₉ with [IrCl(cod)]₂ (cod: 1,5‐cyclooctadienyl) in ethylenediamine (en) solution first yielded the [K(2,2,2‐crypt)]⁺ salt (2,2,2‐crypt: 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) of the capped cluster anion [Sn₉Ir(cod)]^3?. Subsequently, crystals of this compound were dissolved in en, followed by the addition of triphenylphosphine or 1,2‐bis(diphenylphosphino)ethane and treatment at elevated temperatures. [Ir@Sn₁₂]^3? was obtained and characterized as the [K(2,2,2‐crypt)]⁺ salt. The isolation of [Sn₉Ir(cod)]^3? as an intermediate product establishes that the formation of the stannaspherene [Ir@Sn₁₂]^3? occurs through the oxidation of [Sn₉Ir(cod)]^3?. Among the structurally characterized tetrel cluster anions, [Ir@Sn₁₂]^3? is a unique example of a stannaspherene, and one of the rare spherical clusters encapsulating a metal atom that is not a member of Group 10. Single‐crystal structure determination shows that the novel Zintl ion cluster has nearly perfect icosahedral I_h point symmetry.     

Tandem mass spectrometry of intact GroEL-substrate complexes reveals substrate-specific conformational changes in the trans ring

It has been suggested that the bacterial GroEL chaperonin accommodates only one substrate at any given time, due to conformational changes to both the cis and trans ring that are induced upon substrate binding. Using electrospray ionization mass spectrometry, we show that indeed GroEL binds only one molecule of the model substrate Rubisco. In contrast, the capsid protein of bacteriophage T4, a natural GroEL substrate, can occupy both rings simultaneously. As these substrates are of similar size, the data indicate that each substrate induces distinct conformational changes in the GroEL chaperonin. The distinctive binding behavior of Rubisco and the capsid protein was further investigated using tandem mass spectrometry on the intact 800-914 kDa GroEL-substrate complexes. Our data suggest that even in the gas phase the substrates remain bound inside the GroEL cavity. The analysis revealed further that binding of Rubisco to the GroEL oligomer stabilizes the chaperonin complex significantly, whereas binding of one capsid protein did not have the same effect. However, addition of a second capsid protein molecule to GroEL resulted in a similar stabilizing effect to that obtained after the binding of a single Rubisco. On the basis of the stoichiometry of the GroEL chaperonin-substrate complex and the dissociation behavior of the two different substrates, we hypothesize that the binding of a single capsid polypeptide does not induce significant conformational changes in the GroEL trans ring, and hence the unoccupied GroEL ring remains accessible for a second capsid molecule.     

Facile introduction of SH group on aromatic substrates via electrophilic substitution reactions

Herein, we describe a mild and efficient two-step procedure to introduce a thiol group on aromatic substrates. First, reaction with an activated sulfoxide leads to an arylsulfonium salt intermediate. Then, two successive beta-elimination-based dealkylation reactions afford the desired arylthiols in good to excellent yields.     

Synthese sowie Kristall- und Molekülstruktur von Tetrafluoro[2-(pyrrolidinio)ethyl]silicat

Synthesis and Crystal and Molecular Structure of Tetrafluoro[2-(pyrrolidinio)ethyl]silicate The zwitterionic tetrafluoro[2-(pyrrolidinio)ethyl]silicate ( 4 ) was synthesized by reaction of trimethoxy(2-pyrrolidinoethyl)silane ( 5 ) with hydrogen fluoride in ethanol/hydrofluoric acid at 0°C. The crystal and molecular structure of 4 was studied at ?100°C by single-crystal X-ray diffraction. In addition, 4 was characterized by solution-state NMR studies (CD₃CN: ¹H, ¹³C).     

New materials from telechelic polyacetals

Telechelic polyacetals, obtained by cationic ring-opening polymerization of 1,3-dioxolane (DXL) and 1,3-dioxepane (DXP), have been used as building blocks for polymer materials. In the first part of this paper, the synthesis and the properties of networks based on polyDXL α,ω-bis(methacrylates) are discussed. The second part deals with the synthesis and the properties of polyacetal polyurethanes. A thermoplastic polyurethane was prepared with poly(DXL-co-DXP) α,ω-diol as soft segment and the combination butane-1,4-diol and hexamethylene diisocyanate as hard segment. Polyurethane networks were obtained from polyacetal polyols and diphenylmethane diisocyanate (MDI). Some physical properties of these new materials are reported.     

Volumen-Druck-Temperatur-Beziehungen bei Polyoxyäthylenen mit verschiedenem Molekulargewicht

Colloid and Polymer Science - An handelsüblichen Polyoxyäthylenen mit zahlenmittleren Molekulargewichten größer als 200 g/Mol wurde das spezifische Volumen in Abhängigkeit...