Variable Reaktivität eines N‐heterocyclischen Phosphenium‐Komplexes: P‐C‐Bindungsaktivierung oder “abnormale” Deprotonierung

Oxophosphoniumionen (R2P=O)+ sind faszinierende chemische Intermediate, die mit den bekannten Acyliumkationen (RC=O)+ verwandt sind. Sie bestehen aus einem dreifach koordinierten Phosphor(V)‐Zentrum mit einer Phosphor‐Sauerstoff‐Doppelbindung. Hier wird die Synthese zweier Oxophosphoniumionen vorgestellt, die durch sterisch anspruchsvolle Imidazolin‐2‐imin‐ und Imidazolidin‐2‐olefin‐Substituenten am Phosphorzentrum stabilisiert sind. Diese neuen Verbindungen wurden durch NMR‐Spektroskopie und Einkristallröntgenstrukturanalyse charakterisiert, und die Bindungssituation wurde mittels DFT‐Rechnungen untersucht. Die Bestimmung der Akzeptornummer und der Fluoridionenaffinität zeigte, dass die Wahl der Substituenten starken Einfluss auf die Elektrophilie des Phosphorzentrums hat. Darüber hinaus wurden die Bildung von Lewis‐Base‐Addukten mit Pyridinderivaten sowie die Reaktivität gegen Isopropylalkohol untersucht.

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Lewis‐Basen‐freie Oxophosphoniumionen: variable, trigonal‐planare Lewis‐Säuren

Wünsche

Witteler

Dielmann

2018

Angewandte Chemie

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Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues

et al. 2018

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Muonium (Mu), an H atom analogue, is employed to probe the addition of free radicals to the P=C bond of a phosphaalkene. Specifically, two unprecedented muoniated free radicals, MesP •-CMu(Me)2 (1a, minor product) and MesPMu-C • Me2 (1b, major product), were detected by muon spin spectroscopy (µSR) when a solution of MesP=CMe2 (1: Mes = 2,4,6trimethylphenyl) was exposed to a beam of positive muons (µ +). The µ + serves as a source of Mu (i.e. Mu = µ + + e-). To confirm the identity of the major product 1b, its spectral features were compared to its isotopologue, MesPH-C • (Me)CH2Mu (2a). Conveniently, 2a is the sole product of the reaction of MesPH(CMe=CH2) (2) with Mu. For all observed radicals, muon, proton and phosphorus hyperfine coupling constants were determined by µSR and compared to DFTcalculated values.

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Reversible Silylium Transfer between P‐H and Si‐H Donors

et al. 2020

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The Mo=PR2 π* orbital in a Mo phosphenium complex acts as acceptor in a new PIII‐based Lewis superacid. This Lewis acid (LA) participates in electrophilic Si‐H abstraction from E3SiH to give a Mo‐bound secondary phosphine ligand, Mo‐PR2H. The resulting Et3Si+ ion remains associated with the Mo complex, stabilized by η1‐P‐H donation, yet undergoes rapid exchange with an η1‐Si‐H adduct of free silane in solution. The equilibrium between these two adducts presents an opportunity to assess the role of this new LA in catalytic reactions of silanes: is the LA acting as a catalyst or as an initiator? Preliminary results suggest that a cycle including the Mo‐bound phosphine‐silylium adduct dominates in the catalytic hydrosilylation of acetophenone, relative to a putative cycle involving the silane‐silylium adduct or “free” silylium.

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Variable Reaktivität eines N‐heterocyclischen Phosphenium‐Komplexes: P‐C‐Bindungsaktivierung oder “abnormale” Deprotonierung

Cited by 7 publications

References 40 publications

Lewis‐Basen‐freie Oxophosphoniumionen: variable, trigonal‐planare Lewis‐Säuren

Lewis‐Basen‐freie Oxophosphoniumionen: variable, trigonal‐planare Lewis‐Säuren

Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues

Reversible Silylium Transfer between P‐H and Si‐H Donors

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