Transient Phosphenium and Arsenium Ions versus Stable Stibenium and Bismuthenium Ions.

Marian Olaru,Stefan Mebs,Daniel Duvinage,Enno Lork,Jens Beckmann

doi:10.1002/chem.201902520

Marian Olaru, Stefan Mebs + Show 3 more

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https://doi.org/10.1002/chem.201902520

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Journal: Chemistry	Publication Date: Oct 24, 2019
Citations: 14	License type: CC BY 4.0

Affiliation: University of Bremen, Freie Universität Berlin

Abstract

Fluoride abstraction from bis‐m‐terphenylelement fluorides (2,6‐Mes2C6H3)2EF (E=P, As) generated the highly reactive phosphenium ion [(2,6‐Mes2C6H3)2P]+ and the arsenium ion [(2,6‐Mes2C6H3)2As]+, which immediately underwent intramolecular electrophilic substitution and formation of an 1,2,4‐trimethyl‐6‐mesityl‐5‐m‐terphenyl‐benzo[b]phospholium ion and an 1,2,4‐trimethyl‐6‐mesityl‐5‐m‐terphenyl‐benzo[b]arsolium ion, respectively. The formation of the latter involved a methyl group migration from the ortho‐position of a flanking mesityl group to the meta‐position. This reactivity of [(2,6‐Mes2C6H3)2E]+ (E=P, As) is in sharp contrast to the related stibenium ion [(2,6‐Mes2C6H3)2Sb]+ and bismuthenium ion [(2,6‐Mes2C6H3)2Bi]+, which have been recently isolated and fully characterized (Angew. Chem. Int. Ed. 2018, 57, 10080–10084). On the basis of DFT calculations, a mechanism for the rearrangement of the phosphenium and arsenium ions into the phospholium and arsolium ions is proposed, which is not feasible for the stibenium and bismuthenium ions.

Highlights

Fluoride abstraction from bis-m-terphenylelement fluorides (2,6-Mes2C6H3)2EF (E = P, As) generated the highly reactive phosphenium ion [(2,6-Mes2C6H3)2P]+ and the arsenium ion [(2,6-Mes2C6H3)2As]+, which immediately underwent intramolecular electrophilic substitution and formation of an 1,2,4-trimethyl-6-mesityl-5-m-terphenylbenzo[b]phospholium ion and an 1,2,4-trimethyl-6-mesityl-5-m-terphenyl-benzo[b]arsolium ion, respectively
The vast majority of phosphenium and arsenium ions known in condensed phase are intra- or intermolecularly stabilized by substituents or ligands that compensate the electron deficiency by conjugation with donor atoms possessing electron lone pairs, which dramatically reduces the Lewis acidity and reactivity.[1]
The preparation of divalent phosphenium and arsenium ions from neutral trivalent precursors involves the abstraction of one substituent and replacement by a weakly coordinating anion

Summary

Introduction

Unlike the indefinitely stable [1 c]+ and [1 d]+, the transient [1 a]+ and [1 b]+, immediately undergo intramolecular electrophilic substitution and formation of the 1,2,4-trimethyl-6-mesityl-5-m-terphenyl-benzo[b]phospholium ion, [2 a]+, and the The reaction of (2,6-Mes2C6H3)2PF with EtAlCl3 at À90 8C provided a dark solution, reminiscent of the color of solutions containing the stibenium ion [(2,6-Mes2C6H3)2Sb]+, [1 c]+ or the bismuthenium ion [(2,6-Mes2C6H3)2Bi]+, [1 d]+.[14] Above À80 8C, the dark color rapidly faded away to give a yellow solution, which contained the 1,2,4-trimethyl-6-mesityl5-m-terphenyl-benzo[b]phospholium ion, [2 a]+ as the major product (Figure 2).

Results

Conclusion