C-H activation is a powerful strategy for forming C-C bonds without the need for prefunctionalization. In this paper, we present a general, direct, and regioselective palladium-catalyzed functionalization of a phosphorus heterocycle, 2-phenyl-1H-isophosphinoline 2-oxide. The mild reaction conditions enabled the introduction of various functionalized alkenes. Moreover, the flame-retardant properties of selected products clearly highlighted the synergy between the phosphine oxide and another heteroatom-based group, even in the condensed phase.

This study focuses on the synthesis, properties, and comparative analysis of new flame-retardant compounds: coumarins and isophosphinolines. These compounds feature a diarylphosphine oxide (DAPO) substituent at the β-position relative to both the carbonyl and the phosphoryl groups. Various derivatives with halogens, phosphorus, and/or aromatics substituents were synthetized and their thermal stability and flammability were evaluated at the microscale by thermogravimetric analysis (TGA) and pyrolysis–combustion flow calorimetry (PCFC) in order to identify the most promising molecules for use as flame-retardant (FR) additives or comonomers. FTIR-coupled PCFC analysis was also carried out to study the combustion profiles of the molecules. Beyond the confirmation of some expected trends, such as the char promotion of phosphorus and flame inhibition of halogens, the study revealed some unexpected findings that warrant further investigation. These include the prominent role of the chlorine substitution position on the aromatic ring, as well as significant differences in FR performance between diastereoisomers.

This study to evaluate the tautomeric stability of diphenylphosphine oxides using density functional theory (DFT/B3LYP/6-31+G*) calculation in dichloromethane solution. The results reveal that stability of the tautomers is closely dependent on the electronic nature of the substituents. Specifically, the trivalent pentavalent form (PV) is favored when the substituents exert an electron-donating effect. Conversely, the trivalent form (PIII) becomes more stable in the presence of electron-withdrawing groupe. PIII tautomer, characterized by its nucleophilic nature, exhibits enhanced nucleophilicity when the phosphorus moiety is present as the deprotonated phosphinite anion. The deprotonation reaction leading to this ionic form allowed the estimation of pKa values for diphenylphosphine oxides. These pKa values also show a significant dependence on substituent nature, highlighting the influence of electronic effects on the acidity of these compounds.