Trialkylphosphines having a bulky phosphacyclopentane backbone: Structural and redox properties depending on the exocyclic alkyl groups and EPR observation of a persistent trialkylphosphine radical cation

Fumiya Hirakawa, Hiroshi Nakagawa, Shunya Honda, Shintaro Ishida, Takeaki Iwamoto

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

Bulky phosphines and their redox properties have received increased attention in the view of useful auxiliary ligands for transition metal catalysts and Lewis-base components of frustrated Lewis pairs for chemical transformations. Herein we report the synthesis, structure, and properties of a series of trialkylphosphines 2R (R = methyl, ethyl, isopropyl, tert-butyl, 1- adamantyl) that possess the bulky 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane as a structural backbone. Among these phosphines, 2Ad, which contains an adamantyl moiety, has a very large buried volume (%Vbur) for a trialkylphosphine (62.0) and shows a quasi-reversible oxidative wave at a lower oxidation potential (-0.12 V in CH2Cl2, vs ferrocene/ferrocenium couple) by cyclic voltammetry. The reaction of 2Ad with AgPF6 afforded a cationic silver aquo complex [Ag(2Ad)(H2O)]+[PF6]-, whereas the reaction with NOSbF6 gave a persistent phosphine radical cation [2Ad]•+. Based on the EPR spectra and DFT studies, the spin and positive charge of [2Ad]•+ are localized on the phosphorus atom.

Original languageEnglish
Pages (from-to)14634-14642
Number of pages9
JournalJournal of Organic Chemistry
Volume85
Issue number22
DOIs
Publication statusPublished - 2020 Nov 20

ASJC Scopus subject areas

  • Organic Chemistry

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