Visible Photodissociation Spectra of Gaseous Rhodamine Ions: Effects of Temperature and Tagging

See the paper

Mechanism of Gas Phase Ethene-Ozone Reaction and Concomitant Processes. Theoretical Study

A theoretical analysis of the gas phase ethene-ozone reaction is presented. A complete survey of low energy channels reveals several new intermediates, and provides a rationale for the efficient formation of OH radicals in the gas phase ozonolysis of ethene

Proton Affinities of Organocatalysts Derived from Pyridine N-oxide

Proton affinities of several efficient organocatalysts METHOX, QUINOX, ANETOX, KOTOX, FUREOX, and FUROOX bearing a pyridine N-oxide or 2,2′-bipyridyl N,N′-dioxide moiety were de-termined by using extended kinetic method and density functional theory calculations. Proton affinities are in the range of 1030–1060 kJ mol–1. Using isodesmic reactions, the effect of combining two pyridine N-oxide units in the neutral and the protonated molecule was studied: The combination of an unfavorable interaction in the former case and a favorable interaction in the latter accounts for the superbasic proper¬ties of 2,2′-bipyridyl N,N′-dioxides. Last but not least, the theoretically predicted pKa in ethanol are 0.1, –2.7, 0.9, 1.8, 1.9, and 2.3 for the METHOX, QUINOX, ANETOX, FUROOX, FUREOX, and KOTOX, respectively

Assembling Screws: Large Preference for the Homochiral Combination in the Proton-Bound Dimers of 1-Aza[6]helicene in the Gas Phase

By means of selective deuterium labeling combined with separation of enantiomers, chiral discrimination in the proton-bound dimers of 1-aza[6]helicene is probed by electrospray mass spectrometry. The analysis of the results reveals a pronounced preference for the formation of homochiral dimers (P,P and M,M) over the heterochiral variant (P,M)

Photochemistry of a 9-Dithianyl-Pyronin Derivative: A Cornucopia of Reaction Intermediates Lead to Common Photoproducts

Leaving groups attached to themeso-methyl position of many common dyes, such as xanthene, BODIPY, or pyronin derivatives, can be liberated upon irradiation with visible light. However, the course of phototransformations of such photoactivatable systems can be quite complex and the identification of reaction intermediates or even products is often neglected. This paper exemplifies the photochemistry of a 9-dithianyl-pyronin derivative, which undergoes an oxidative transformation at themeso-position to give a 3,6-diamino-9H-xanthen-9-one derivative, formic acid, and carbon monoxide as the main photoproducts. The course of this multi-photon multi-step reaction was studied under various conditions by steady-state and time-resolved optical spectroscopy, mass spectrometry and NMR spectroscopy to understand the effects of solvents and molecular oxygen on individual steps. Our analyses have revealed the existence of many intermediates and their interrelationships to provide a complete picture of the transformation, which can bring new inputs to a rational design of new photoactivatable pyronin or xanthene derivatives

Gas-phase Fragmentation of Deprotonated p-Hydroxyphenacyl Derivatives

Electrospray ionization of methanolic solutions of p-hydroxyphenacyl derivatives HO-C6H4-C(O)-CH2-X (X = leaving group) provides abundant signals for the deprotonated species which are assigned to the corresponding phenolate anions −O-C6H4-C(O)-CH2-X. Upon collisional activation in the gas phase, these anions inter alia undergo loss of a neutral “C8H6O2” species concomitant with formation of the corresponding anions X−. The energies required for the loss of neutral roughly correlate with the gas phase acidities of the conjugate acids (HX). Extensive theoretical studies performed for X = CF3COO in order to reveal the energetically most favorable pathway for the formation of neutral “C8H6O2” suggest three different routes of similar energy demands, involving a spirocyclopropanone, epoxide formation, and a diradical, respectively

Spektroskopische Charakterisierung eines reaktiven [Cu2(μ‐OH)2]2+ Intermediates in Cu/TEMPO‐katalysierten aeroben Alkoholoxidationen

CuI/TEMPO-Katalysatorsysteme (TEMPO=2,2,6,6-Tetramethylpiperidinoxyl) sind vielseitige Katalysatoren für aerobe Alkoholoxidationsreaktionen zur selektiven Synthese von Aldehyden. Jedoch sind mehrere Aspekte des Reaktionsmechanismus noch nicht aufgeklärt, was hauptsächlich daran liegt, dass bisher keine reaktiven Intermediate identifiziert werden konnten. Wir zeigen hier die Synthese und Charakterisierung eines dinuklearen Komplexes [L12Cu2]2+ (1), der in Gegenwart von TEMPO die katalytische 4 H+/4 e− Reduktion von O2 zu Wasser an die Oxidation von benzylischen und aliphatischen Alkoholen koppeln kann. Die Mechanismen der katalytischen O2-Reduktion und der Alkoholoxidation wurden sowohl durch spektroskopische Detektion der reaktiven Intermediate in der Gas- und der kondensierten Phase als auch durch kinetische Studien an jedem Reaktionsschritt in den Katalysezyklen aufgeklärt. Die intermediären Bis(μ-oxido)dikupfer(III)- (2) und Bis(μ-hydroxido)dikupfer(II)-Spezies (3) wurden als wichtige Reaktanden in beiden Reaktionen identifiziert. Die vorliegende Studie ermöglicht tiefgehende mechanistische Einblicke in die aerobe Alkoholoxidation, die eine wertvolle Grundlage bieten um übergangsmetallkatalysierte Reaktionen mit redoxaktiven Cokatalysatoren besser zu verstehen.DFG, 390540038, EXC 2008: Unifying Systems in Catalysis "UniSysCat"EC/H2020/682275/EU/Mass Spectrometry of Isomeric Ions/IsoM

Electrospray ionization as a convenient new method for the generation of catalytically active iron-oxide ions in the gas phase

Abstract Electrospray ionization (ESI) of aqueous iron(III) nitrate solutions can be used as an easy route for the generation of bare iron-oxide and hydroxide cations such as FeO + , FeOH + , and Fe(OH) 2 + in the gas phase. Analysis of the ESI mass spectra obtained under variable conditions in combination with complementary collision experiments suggest that the iron-oxo species are formed by collision-energy driven replacements of nitrato-ligands by water stemming from the sprayed solution. It is demonstrated that the gas-phase reactivity of methane with the iron-oxide cation FeO + generated via ESI is in good agreement with the well-documented literature data for this reaction

Gold(I) and Silver(I) π-Complexes with Unsaturated Hydrocarbons.

Gold π-complexes have been studied largely in the past 2 decades because of their role in gold-catalyzed reactions. We report an experimental and theoretical investigation of the interaction between a wide range of unsaturated hydrocarbons (alkanes, alkynes, alkadienes, and allenes) and triphenylphosphine-gold(I), triphenylphosphine-silver(I), and acetonitrile-silver(I) cations. The bond dissociation energies of these complexes were determined by mass spectrometry collision-induced dissociations and their structures were studied by density functional theory calculations and infrared photodissociation spectroscopy. The results show that with the same phosphine ligand, gold binds stronger to the π-ligands than silver and thereby activates the unsaturated bond more effectively. Ligand exchange of phosphine by acetonitrile at the silver complexes increases the binding energy as well as the activation of the π-ligands. We also show that the substitution of an unsaturated bond is more important than the bond type