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Isolation of Singlet Carbenes Derived 2-Phospha-1,3-butadienes and their Sequential One-electron Oxidation to Radical Cations and Dications

Abstract

A synthetic strategy for the 2-phospha-1,3-butadiene derivatives [{(IPr)C(Ph)}P(cAACMe)] (3a) and [{(IPr)C(Ph)}P(cAACCy)] (3b) (IPr = C{(NDipp)CH2}2, Dipp = 2,6-iPr2C6H3; cAACMe = C{(NDipp)CMe2CH2CMe2}; cAACCy = C{(NDipp)CMe2CH2C(Cy)}, Cy = cyclohexyl) containing a C=C‒P=C framework has been established. Compounds 3a and 3b have a remarkably small HOMO-LUMO energy gap (3a: 5.09; 3b: 5.05 eV) with a very high-lying HOMO (‒4.95 eV for each). Consequently, 3a and 3b readily undergo one-electron oxidation with the mild oxidizing agent GaCl3 to afford radical cations [{(IPr)C(Ph)}P(cAACR)]GaCl4 (R = Me 4a, Cy 4b) as crystalline solids. The main UV-vis absorption band for 4a and 4b is red-shifted with respect to that of 3a and 3b, which is associated with the SOMO related transitions. The EPR spectrum of compounds 4a and 4b each exhibits a doublet due to coupling with the 31P nucleus. Further one-electron removal from the radical cations 4a and 4b is also feasible with GaCl3, affording the dications [{(IPr)C(Ph)}P(cAACR)](GaCl4)2 (R = Me 5a, Cy 5b) as yellow crystals. The molecular structures of compounds 3-5 have been determined by X-ray diffraction and analyzed by DFT calculations.

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Article information


Submitted
05 Nov 2019
Accepted
05 Jan 2020
First published
06 Jan 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020, Accepted Manuscript
Article type
Edge Article

Isolation of Singlet Carbenes Derived 2-Phospha-1,3-butadienes and their Sequential One-electron Oxidation to Radical Cations and Dications

R. S. Ghadwal, M. Sharma, S. Blomeyer, B. Neumann, G. Stammler, A. Hinz, M. van Gastel and T. Glodde, Chem. Sci., 2020, Accepted Manuscript , DOI: 10.1039/C9SC05598C

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