Symmetrical and Mixed Tris(acyl)phosphines: Synthesis, Oxidation and Photochemistry

Herein, we present a convenient synthesis for symmetrical and mixed substituted tris(acyl)phosphines (TAPs) starting from red phosphorus. All TAPs exhibit a phosphaalkene-acylphosphine equilibrium, which was investigated in detail by variable-temperature (VT) NMR spectroscopy supported by density-functional theory (DFT) calculations. Depending on the substituents, two phosphaalkene derivatives and ten acylphosphine derivatives could be isolated. NMR spectroscopy and single-crystal X-ray crystallography enabled a clear structural assignment of these compounds. Oxidation of selected TAPs led to the formation of the corresponding tris(acyl)phosphine oxides (TAPOs). Furthermore, their spectroscopic properties as well as their photochemistry was investigated. Especially, the TAPO compounds were evaluated for their suitability as photoinitiators by CIDNP spectroscopy, photobleaching measurements and by storage stability tests.