NMR spectroscopy as a unique tool for the quantification of weak interactions between trivalent phosphorus compounds and diphenyliodonium ions

Abstract

The interaction of a diphenyliodonium salt with trivalent phosphorus compounds and the relevance of these interactions in visible light induced reactions were studied using {¹H,¹⁹F,³¹P} NMR and DFT calculations. In the case of diphenyliodonium salt and triethylphosphite, a comparison of the thermal and photocatalytic pathways highlighted the importance of blue light in this reaction and the phosphonium intermediate was identified in kinetic monitoring by both pathways. The formation of an EDA complex was well characterised by an {¹H,¹⁹F,³¹P} NMR study at low temperature and the significance of acetonitrile for the formation of this EDA complex was evidenced by a comparative study in several solvents (MeCN-d₃, DMF, and CD₂Cl₂). The mechanistic study was then extended to phosphonium salt formation reactions involving triphenylphosphine and diphenylmethylphosphine and the EDA complexes were identified. DFT calculations were used to support these findings by probing the stability of the complexes by measuring the P–I distance on the calculated structures and TD-DFT calculations showed the absorbance of the EDA complexes in the visible range, which explain their photoreactivity. Finally, the stoichiometry of these complexes and the binding constants of their formation were determined and compared with the experimental result.