Preface

This volume is number 52 of a very long series, first published in 1970 under the editorship of Professor Stuart Trippet and which subsequently has involved a wide range of contributors to the literature of organophosphorus chemistry. This volume provides a selective review of papers in this area, published in the period from January 2021 to January 2022, and continues our efforts to provide an up-to-date survey of progress in this topic, which continues to generate a vast amount of research. We have again been fortunate in securing contributions from a team of international authors from the UK, Germany, Poland, Portugal, Italy, Hungary and India. Unfortunately, as a result of the international situation between Russia and Ukraine, we have not been able to secure a chapter on the chemistry of Phosphines for this volume.

In Chapter 1, Mariette Pereira and colleagues have covered some of the most relevant literature published during 2021 relating to tervalent phosphorus acid derivatives. Areas covered include synthetic methodologies to halogenophosphorus compounds, phosphorus esters (phosphinite, phosphonite and phosphites), phosphorus amides (aminophosphines, phosphoramidites and diamidophosphites) and phosphorus compounds bearing two different tervalent phosphorus moieties. Also included is a critical selection of their applications with an emphasis on the catalytic applications of phosphorus(iii) donor ligands and their metal complexes.

In Chapter 2, György Keglevich gives an account of new developments in the synthesis and reactivity of phosphine chalcogenides, mainly oxides and sulfides, published during 2021. A series of new synthetic methods for phosphine oxides are discussed, followed by preparations utilizing simple P-reagents such as P(iii)- and P(v)-chlorides, and >P(O)H species. Their additions to unsaturated substrates and P–C coupling reactions, involving interesting variations, represent an important topic. The modification of P-chalcogenides including deoxygenations are also shown. Optically active phosphine oxides and their complexes also form a usual part of this chapter.

In Chapter 3, Maurizio Selva and his group describe the literature on the preparation, characterisation and applications of phosphonium salts and ylides, published between January and December 2021. The large number of reviewed references highlights the importance of such P-based derivatives in synthetic and non-synthetic applications. For the reader’s convenience, topics are organized to offer an introductory survey on the methods of preparation and characterisation of each type of compound, followed by an analysis of applicative and curiosity driven research. Recent advances on the synthesis and applications of phosphonium-based ionic liquids (PILs) are summarised in a dedicated section, highlighting, in particular, the ever-increasing number of extraction and energy storage applications reported for these P-based ionic liquids.

In Chapter 4, Balczewski, and Owsianik cover aspects of the chemistry of quinquevalent P(v) acid compounds, the chapter showing the most important achievements of the 2021 year. As in previous years, the report is structured to show achievements in the area of organophosphorus compounds containing: three P–O bonds (Section 2: phosphoric acids and their derivatives), two P–O and one P–C bonds (Section 3: phosphonic acids and their derivatives) as well as one P–O and two P–C bonds (section 4: phosphinic acids and their derivatives), in addition to the phosphoryl group P═O present in all three groups of compounds. Each of the main sections covers “synthesis and reactions” including pure synthesis without applications, “synthesis and biological applications” and “synthesis and miscellaneous applications” including synthesis directed towards non-biological applications. At the end of each subsection, the corresponding achievements are shown for hetero-analogues in which phosphorus–oxygen bonds have been replaced by phosphorus-heteroatom P–X and/or P═Y bonds (X, Y = N, S or Se). The subsection on quinquevalent phosphorus acids and their derivatives as catalysts has been placed, as usual, at the end of the entire chapter, after a review of all three main groups of compounds. As in previous years, the area devoted to phosphoric and phosphonic acids and their derivatives dominated over a smaller section of phosphinic acids and their derivatives, and literature references for these sections remained at a ratio of 4 : 12 : 1. A dynamic, five-fold increase in the number of works, in the subject of chiral phosphoric acids as catalysts, has been recorded this year.

In Chapter 5, Gerd-V. Roeschenthaler and Romana Pajkert have shown that, during 2021, the chemistry of penta- and hexa-coordinated phosphorus compounds has continued to expand in its breadth and application.

The synthesis, properties and structural investigations on novel cage-phosphoranes, spirophosphoranes, fluorophosphoranes, metallophosphoranes and pentacoordinated corroles have been briefly described. Pentacoordinated phosphoranes have been also postulated as intermediates and transition states in the synthesis of isoquinolines, indolizines,1,3-dienes and furan-monogenes as well as in a carbamate version of the Kabachnik–Field reaction. Furthermore, studies on hexacoordinated phosphorus(v) corroles, carbene-fluorophosphorane adducts and transition metal complexes stabilized by a FAP anion have been reported.

In Chapter 6, Chandrasekhar and Chakraborty provide a review of research carried out in the calendar year 2021 on phosphazenes. These are compounds having a formal P═N motif in their skeleton. In these compounds the phosphorus centre is pentavalent and tetracoordinate while the nitrogen centre is trivalent and dicoordinate. These compounds can be categorized into three broad families: (a) acyclic phosphazenes, (b) cyclophosphazenes and (c) polyphosphazenes. Although there is another class of compound usually called hybrid polymers containing a cyclophosphazene skeleton, in this chapter they are included in the family of polyphosphazenes.

Finally, in Chapter 7, Goutam Brahmachari has provided an update on recent key developments during 2021 in the areas of green and sustainable chemistry and engineering, reviewing progress in green and energy-efficient synthetic approaches in organophosphorus chemistry. Organophosphorus chemistry is a broad and exciting field, with potential opportunities for researchers involved in multi-disciplinary areas of scientific endeavour, including organic, medicinal, pharmaceutical, agricultural, and industrial chemistry. Organophosphorus compounds find extensive applications in all these fields owing to their inherent physical and biological properties. Since its first development in the 90s, green and sustainable chemistry has grown considerably over the past two decades. It has become much more prevalent among researchers working in all branches of chemical science. As part of these noteworthy developments, synthetic organic chemists have been motivated to develop eco-friendly methodologies for generating phosphorus-functionalised compounds of potential interest, focusing on various green chemistry principles. As a result, considerable progress towards green and sustainable chemistry has been accomplished during the last decade. In continuation of our earlier contributions, this present chapter also aims to offer an overview of such developments in green synthetic approaches in organophosphorus chemistry reported in 2021.

D. W. Allen

L. J. Higham