Special Issue “Progress in Synthesis and Applications of Phosphorus-Containing Compounds”

Organophosphorus compounds, due to their interesting physicochemical properties, have found wide applications in many important areas of the chemical industry, such as the synthesis of utility chemicals (e.g., flame retardants, anticorrosive coatings, and adhesives), ligands for catalysis, agrochemicals (e.g., insecticides, herbicides, and fungicides), and, finally, pharmaceutically active compounds. Unsurprisingly, owing to the importance of phosphorus-containing compounds, several methods have emerged for their effective synthesis, including in an asymmetric fashion.

This Special Issue of Organics aims to provide an overview of the latest progress in the Synthesis and Applications of Phosphorus-Containing Compounds. It contains experimental contributions, including full papers, as well as reviews describing the synthesis and applications of organophosphorus compounds. The articles collected nicely highlight many of the aspects of organophosphorus chemistry and will help to update the latest knowledge in this exciting and wide field of research. The gathered contributions are excellent proof that the passion for phosphorus and its diverse chemistry remains as strong as ever.

In their contribution to this Special Issue, Petro P. Onys’ko et al. presented the synthesis of new NH-iminophosphonates bearing 2-, 3-, and 4-pyridyldifluoromethyl groups at the imine carbon. The obtained building blocks were converted into highly functionalized acyclic and heterocyclic aminophosphonates and phosphonic acids combining biorelevant aminophosphonic fragments, difluoromethyl groups, and pyridyl, piperidyl, thiazolidin-4-one, or thiazinan-4-one heterocyclic moieties in their structure.

In the contribution of Alexander B. Rozhenko and Petro P. Onys’ko et al., the authors demonstrated that the esters of iminophosphonic acids, depending on the character of the substitution, can possess a Z- or E-configuration, which in turn can influence the stereochemistry of the products and their further chemical transformations. The Z/E-isomerism in a broad series of iminophosphonates was studied using quantum chemical methods to better understand the factors stabilizing a definite isomer.

In line with “green chemistry” principles, the article by Didier Villemin et al. reported on environmentally friendly multicomponent reactions of various amines (including primary and secondary amines as well as polyamines), glyoxylic acid, and phosphorous acid performed under microwave irradiation and leading to new 2-amino bis(2-phosphonoacetic) acids. The developed protocol was carried out in water and often no organic solvent was used for the separation and purification steps.

As a contribution to the field of asymmetric synthesis of organophosphorus compounds, Toshiaki Murai et al. reported on an elegant generation of primary phosphines and their oxides with a stereogenic carbon center adjacent to the phosphorus atom and their radical addition reaction to alkenes to give P-stereogenic secondary phosphine oxides. The primary phosphines with a stereogenic carbon atom adjacent to the phosphorus atom were synthesized through the reduction in phosphonates and phosphonoselenoates containing a binaphthyl group. Their oxidized products were found to undergo BEt₃-mediated radical addition to cyclohexene and a range of alkenes in an anti-Markovnikov fashion to give P-stereogenic secondary phosphine oxides with high dr values.

To highlight the long-standing relationship between phosphorus and metals, Arturo Espinosa Ferao and Rainer Streubel et al. reported on quantum chemical calculations and the synthesis of P-tert-butyl substituted aminophosphane W(CO)₅ complexes obtained via formal N-H insertion reactions of a Li/Cl phosphinidenoid complex into NH bonds of ammonia and different amines. Further regioselective deprotonation of the obtained 1,2-bifunctional aminophosphane complex was also studied.

A representative example for the utility of phosphorus-based ligands in asymmetric homogenous catalysis was reported by David Sémeril and Shaima Hkiri, who disclosed the synthesis of optically pure diphosphite in which the two phosphorus atoms were grafted on two proximally phenolic rings of calix [4]arene. The latter compound and two related calixarenyl diphosphites were employed as ligands in the rhodium-catalyzed asymmetric hydrogenation of α-dehydroamino esters, resulting in ee up to 95% being obtained.

In turn, an application of organophosphorus compounds as building blocks in organic synthesis was reported by R. Alan Aitken and Ryan A. Inwood, who presented the synthesis of aryl benzyl ethers bearing the phosphonamidate group EtO-P(=O)-NHBu on the aryl ring, either para- or meta- to a benzylic ether, and their successful Wittig rearrangement to afford the corresponding new phosphonamidate-functionalised diarylmethanols.

To demonstrate the practical utility of organophosphorus compounds, Claire Negrell et al. reported on a phosphorylated cardanol additive for use as a chain stopper, flame retardant, and reactive diluent for greener alkyd coatings. The use of phosphorylated cardanol was responsible for reduction in solvent content and brought flame-retardant properties to the alkyd resins. The most effective product that was associated with excellent flame-retardant properties and excellent coating properties was obtained with phosphate-cardanol added at 2%wt of P.

Comprehensive reviews were also published in this Special Issue. Anne-Marie Caminade et al. presented a review on specific bifunctionalization on the surface of phosphorus dendrimers and focused on the syntheses of such molecules and their properties and applications, especially in catalysis, material science, and as biological tools.

In a review article, Paul Joseph et al. presented a comprehensive overview of some reactive routes to flame-retardant fiber-forming polymers, namely, polypropylene and polyacrylonitrile containing modifying groups that were incorporated into polymeric chains and include phosphorus- or phosphorus/nitrogen-containing moieties in different chemical environments.

As a Guest Editor of this Special Issue, it was a great pleasure and honor to collaborate with such excellent researchers working in the fascinating and wide field of organophosphorus chemistry. The edition of this Special Issue has coincided with the COVID-19 pandemic and research operations were shuttered around the globe, making this task even more demanding. I wish to thank the Editorial Office and especially Ms. Stella Mao and Mr. Stephen Wang for their professional support and patience. It was a pleasure to serve as Guest Editor of this of Special Issue of Organics entitled “Progress in Synthesis and Applications of Phosphorus-Containing Compounds” [1] and I extend my gratitude to all the authors for their excellent contributions. Enjoy reading them!