Let's Make White Phosphorus Obsolete

Cu/Ag-Mediated Three-Component Synthesis of Dibenzophosphole under Mild Conditions

We report a one-pot, three-component synthesis of dibenzophosphole under mild conditions, facilitated by a copper-silver bimetallic system. This method employs readily available cyclic diaryliodonium salts as arylation reagents and sodium phosphaethynolate (NaOCP) as a phosphorus source, eliminating the need for lithium reagents and energy-intensive chlorophosphines. The resulting dibenzophosphole derivatives exhibit strong fluorescence, highlighting their potential as fluorescent materials.

Closing the Loop: Low-Waste Phosphorus Functionalization Enabled by Simple Disulfides

Useful monophosphorus products are obtained from both white and red phosphorus via a simple strategy involving initial oxidation by aryl disulfides followed by quenching with nucleophiles. Direct transformations of elemental phosphorus are usually very challenging, forcing chemists to instead rely on inefficient and hazardous multi-step methods. However, here they are achieved using inexpensive and easy-to-handle reagents, providing access to diverse P-C, P-N and P-O bonded products in good yields. By isolating the thiolate byproducts of these reactions, a simple, closed loop can be achieved that produces only minimal, benign waste byproducts, in contrast to other direct methods. This closed loop can even be elaborated into a true (electro)catalytic cycle, which is extremely rare in the field of elemental phosphorus functionalization.

Palladium-catalyzed coupling of aryl sulfonium salts with [TBA][P(SiCl3)2] for the construction of tertiary phosphines

We present a strategy for the synthesis of triarylphosphines via palladium-catalyzed C-P cross-coupling reactions of aryl sulfonium salts with [TBA][P(SiCl3)2]. This method utilizes [TBA][P(SiCl3)2], a phosphorus derivative of phosphoric acid, as the phosphorus source. This approach circumvents the hazards and intricate pathways associated with white phosphorus.

One-Step Esterification of Phosphoric, Phosphonic and Phosphinic Acids with Organosilicates: Phosphorus Chemical Recycling of Sewage Waste

Global concerns regarding the depletion and strategic importance of phosphorus resources have increased demand for the recovery and recycling. However, waste-derived phosphorus compounds, primarily as chemically inert phosphoric acid or its salts, present a challenge to their direct conversion into high-value chemicals. We aimed to develop an innovative technology that utilizes the large quantities of sewage waste, bypasses the use of white phosphorus, and enables esterification of phosphoric acid to produce widely applicable phosphate triesters. Tetraalkyl orthosilicates emerged as highly effective reagents for the direct triple esterification of 85 % phosphoric acid, as well as the esterification of organophosphinic and phosphonic acids. Furthermore, we achieved esterification of recovered phosphoric acid with tetraalkyl orthosilicate, thus pioneering a recycling pathway from sewage waste to valuable phosphorus chemicals. Experimental and theoretical investigations revealed a novel mechanism, wherein tetraalkyl orthosilicates facilitate multimolecular aggregation to achieve alkyl transfer from tetraalkylorthosilicate to phosphoric acid via multiple proton shuttling.

Adduct-catalyzed tandem electro-thermal synthesis of organophosphorus (III) compounds from white phosphorus

Electrooxidation strategies for synthesizing readily oxidizable products face notable challenges, especially when the oxidation potential of the products is lower than that of the reactants or when high current densities are necessary. The electrooxidation synthesis of trivalent organophosphorus compounds (OPCs (III)) from white phosphorus (P4) has demonstrated potential but is hindered by selectivity issues due to over-oxidation. Herein, we report a tandem electro-thermal synthesis pathway that addresses these challenges in producing OPCs (III) from P4. The process begins with an electrooxidation step that generates a stable trivalent phosphorus transfer reagent, then thermochemically converted into various high-value OPCs (III). Utilizing hexafluoroisopropanol (HFIP) as the nucleophile and optimizing a tetrabutylammonium iodide (TBAI)-4-dimethylaminopyridine (DMAP)-adduct catalytic system, we developed an efficient electrophilic phosphorus transfer reagent via electrosynthesis. The adduct facilitates the oxidation of P4 and enhances the nucleophilicity of HFIP, thereby improving the electrooxidation process. This approach supports high current density, scales up to the hundred-gram level without yield loss, and remains compatible with fluctuating green electricity.

Nucleophilic Functionalization of Activated P4 in [CpFe(CO)2-(η1-P4)][Al(ORF)4] with Alcohols R-OH

The bonding situation in [Fp-P4][Al(ORF)4] (1) (Fp = (CO)2CpFe, RF = C(CF3)3) gives rise to an Umpolung of the P4 fragment, which should make it accessible for nucleophiles. To investigate this projected reactivity, the complex was combined with a series of hydroxy-nucleophiles - that all do not react with free P4 - leading to a variety of P1 building blocks. With excess of R-OH (R = Me, Et, Ph), the thermodynamically more stable complex salts [Fp-P(H)x(OR)3-x)][Al(ORF)4] (x=2,1,0) (2b-2d) are formed and show that the phosphonium type pathway is accessible. Quantum chemical calculations display a variety of reaction pathways that all lead very rapidly to the P1 building blocks. With stoichiometric amounts of R-OH, [Fp-PH3][Al(ORF)4] (2 a) as well as [HP(OR)3][Al(ORF)4] (2 f) were observed as products. Hence, activation of the P4-cage in complex 1 was confirmed.

Two P, Ten P, White P, Red P: Mechanistic Exploration of the Oligomerization of Red Phosphorus from Diphosphorus with the Ab Initio Nanoreactor

Phosphorus is critical to humans on many fronts, yet we do not have a mechanistic understanding of some of its most basic transformations and reactions─namely the oligomerization of white phosphorus to red. With heat or under ultraviolet (UV) exposure, it has been experimentally demonstrated that white phosphorus dissociates into diphosphorus units which readily form red phosphorus. However, the mechanism of this process is unknown. The ab initio nanoreactor approach was used to explore the potential energy surface of phosphorus clusters. Density functional theory and metadynamics simulations were used to characterize potential reaction pathways. A mechanism for oligomerization is proposed to take place via diphosphorus additions at π-bonds and weak σ-bonds through three membered ring intermediates. Downhill paths through P6 and P8 clusters eventually result in P10 clusters that can oligomerize into red phosphorus chains. The initial, rate limiting step for this process has an energy barrier of 24.2 kcal/mol.

Unravelling White Phosphorus: Experimental and Computational Studies Reveal the Mechanisms of P4 Hydrostannylation

The hydrostannylation of white phosphorus (P4) allows this crucial industrial precursor to be easily transformed into useful P1 products via direct, 'one pot' (or even catalytic) procedures. However, a thorough mechanistic understanding of this transformation has remained elusive, hindering attempts to use this rare example of successful, direct P4 functionalization as a model for further reaction development. Here, we provide a deep and generalizable mechanistic picture for P4 hydrostannylation by combining DFT calculations with in situ 31P NMR reaction monitoring and kinetic trapping of previously unobservable reaction intermediates using bulky tin hydrides. The results offer important insights into both how this reaction proceeds and why it is successful and provide implicit guidelines for future research in the field of P4 activation.

Metal-doped biochar for selective recovery and reuse of phosphate from water: Modification design, removal mechanism, and reutilization strategy

Phosphorus (P) plays a crucial role in plant growth, which can provide nutrients for plants. Nonetheless, excessive phosphate can cause eutrophication of water, deterioration of aquatic environment, and even harm for human health. Therefore, adopting feasible adsorption technology to remove phosphate from water is necessary. Biochar (BC) has received wide attention for its low cost and environment-friendly properties. However, undeveloped pore structure and limited surface groups of primary BC result in poor uptake performance. Consequently, this work introduced the synthesis of pristine BC, parameters influencing phosphate removal, and corresponding mechanisms. Moreover, multifarious metal-doped BCs were summarized with related design principles. Meanwhile, mechanisms of selective phosphate adsorption by metal-doped BC were investigated deeply, and the recovery of phosphate from water, and the utilization of phosphate-loaded adsorbents in soil were critically presented. Finally, challenges and prospects for widespread applications of selective phosphate adsorption were proposed in the future.

Synthetic Methods for Azaheterocyclic Phosphonates and Their Biological Activity: An Update 2004-2024

The increasing importance of azaheterocyclic phosphonates in the agrochemical, synthetic, and medicinal field has provoked an intense search in the development of synthetic routes for obtaining novel members of this family of compounds. This updated review covers methodologies established since 2004, focusing on the synthesis of azaheterocyclic phosphonates, of which the phosphonate moiety is directly substituted onto to the azaheterocyclic structure. Emphasizing recent advances, this review classifies newly developed synthetic approaches according to the ring size and providing information on biological activities whenever available. Furthermore, this review summarizes information on various methods for the formation of C-P bonds, examining sustainable approaches such as the Michaelis-Arbuzov reaction, the Michaelis-Becker reaction, the Pudovik reaction, the Hirao coupling, and the Kabachnik-Fields reaction. After analyzing the biological activities and applications of azaheterocyclic phosphonates investigated in recent years, a predominant focus on the evaluation of these compounds as anticancer agents is evident. Furthermore, emerging applications underline the versatility and potential of these compounds, highlighting the need for continued research on synthetic methods to expand this interesting family.

An Air-Stable Storage Compound for White Phosphorus: Reversible Addition to a Stannylene and Chemical Release of P4

Controlled insertion into a single P-P bond of white phosphorus (P4) was achieved by employing a diaryl stabilized stannylene, Ar*2Sn (Ar*=2,6-bis(benzhydryl)-4-iPr-phenyl). Conversions of the stannylene with P4 gave a non-pyrophoric, air-stable storage compound, which releases P4 quantitively upon irradiation with light (354 or 455 nm). Alternatively, the phosphorus cage is detached by reacting the storage compound with PhChChPh (Ch=Se, Te). Despite the recent advances in the directed conversion of P4 using main group element compounds, Ar*2Sn constitutes only the second structurally characterized example of a stannylene capable of performing controlled, reversible addition and release of white phosphorus.

Beyond Triphenylphosphine: Advances on the Utilization of Triphenylphosphine Oxide

Triphenylphosphine oxide is a well-known industrial waste byproduct, and thousands of tons of it are generated every year. Due to its chemical stability and limited applications, settlement of this waste issue has drawn extensive attention from chemists. The reduction of triphenylphosphine oxide to triphenylphosphine is heretofore the most employed solution, and is well reviewed. In view of our recent studies on the selective and efficient conversion of Ph3P(O) to other valuable organophosphorus chemicals by using sodium, the present perspective mainly highlights the advances on the utilization of Ph3P(O) to prepare a diverse range of functional organophosphorus compounds, except Ph3P, via selective P-C, C-H, and P-O bond cleavages.

Sustainable Photo- and Electrochemical Transformation of White Phosphorous (P4 ) into P1 Organo-Compounds

Elemental white phosphorous (P4 ) is a crucial feedstock for the entire phosphorus-derived chemical industry, serving as a common precursor for the ultimate preparation of high-grade monophosphorus (P1 ) fine chemicals. However, the corresponding manufacturing processes generally suffer from a deep reliance on hazardous reagents, inputs of immense energy, emissions of toxic pollutants, and the generation of substantial waste, which have negative impacts on the environment. In this context, sustainability and safety concerns provide a consistent impetus for the urgent overall improvement of phosphorus cycles. In this Concept, we present an overview of the most recent growth in photo- and electrochemical synthesis of P1 organo-compounds from P4 , with special emphasis on sustainable features. The key aspects of innovations regarding activation mode and mechanism have been comprehensively analyzed. A preliminary look at the possible future direction of development is also provided.

Synthesis of Black Phosphorene Quantum Dots from Red Phosphorus

Black phosphorene quantum dots (BPQDs) are most commonly derived from high-cost black phosphorus, while previous syntheses from the low-cost red phosphorus (Pred ) allotrope are highly oxidised. Herein, we present an intrinsically scalable method to produce high quality BPQDs, by first ball-milling Pred to create nanocrystalline Pblack and subsequent reductive etching using lithium electride solvated in liquid ammonia. The resultant ~25 nm BPQDs are crystalline with low oxygen content, and spontaneously soluble as individualized monolayers in tertiary amide solvents, as directly imaged by liquid-phase transmission electron microscopy. This new method presents a scalable route to producing quantities of high quality BPQDs for academic and industrial applications.

Mechanochemical Phosphorylation of Acetylides Using Condensed Phosphates: A Sustainable Route to Alkynyl Phosphonates

In pursuit of a more sustainable route to phosphorus-carbon (P-C) bond-containing chemicals, we herein report that phosphonates can be prepared by mechanochemical phosphorylation of acetylides using polyphosphates in a single step, redox-neutral process, bypassing white phosphorus (P4) and other high-energy, environmentally hazardous intermediates. Using sodium triphosphate (Na5P3O10) and acetylides, alkynyl phosphonates 1 can be isolated in yields of up to 32%, while reaction of sodium pyrophosphate (Na4P2O7) and sodium carbide (Na2C2) engendered, in an optimized yield of 63%, ethynyl phosphonate 2, an easily isolable compound that can be readily converted to useful organophosphorus chemicals. Highly condensed phosphates like Graham's salt and bioproduced polyphosphate were also found to be compatible after reducing the chain length by grinding with orthophosphate. These results demonstrate the possibility of accessing organophosphorus chemicals directly from condensed phosphates and may offer an opportunity to move toward a "greener" phosphorus industry.

Isopropenyl phosphate as an atom efficient reagent for phosphorylation of alcohols with catalytic base

The atom efficient transesterification of phosphate esters with catalytic base was investigated using an isopropenyl leaving group, generating acetone as the only by-product. The reaction proceeds in good yields at room temperature, with excellent chemoselectivity towards primary alcohols. Mechanistic insights were obtained by obtaining kinetic data using in operando NMR-spectroscopy.

UV induced hydrophosphination of dimethyl 2-vinylcyclopropane-1,1-dicarboxylate towards phosphine chalcogenides

Dimethyl 2-vinylcyclopropane-1,1-dicarboxylate underwent a hydrophosphination reaction with either a primary or secondary phosphine under photolytic conditions. Notably, a free radical initiator was not required. The resulting tertiary phosphines were derivatized using S₈ to afford moisture and air stable yellow or colorless oils in a 27%-73% isolated yield. A series of control reactions were performed, and we propose that this UV induced hydrophosphination reaction proceeds through a radical mechanism.

Direct synthesis of phosphorotrithioates from [TBA][P(SiCl3)2] and disulfides

Sulfur-containing organophosphorus molecules have played a pivotal role in organic synthesis, pharmaceutical pesticides and functional materials, thereby motivating researchers worldwide to establish S-P bonds from more environmentally friendly phosphorus sources. In this study, a novel method was developed for constructing S-P bonds, specifically by reacting the inorganic phosphorus derivative TBA[P(SiCl₃)₂] with sulfur-containing compounds under mild conditions. This method demonstrates the advantages of low energy consumption, mild reaction conditions and environmental friendliness. Moreover, this protocol-as a green synthesis method to replace the use of white phosphorus in the production of organophosphorus compounds (OPCs)-achieved the functional conversion of "inorganic phosphorus to organic phosphorus", in line with the national green development strategy.

Electrolytic Synthesis of White Phosphorus Is Promoted in Oxide-Deficient Molten Salts

Elemental white phosphorus (P₄) is a key feedstock for the entire phosphorus-derived chemicals industry, spanning everything from herbicides to food additives. The electrochemical reduction of phosphate salts could enable the sustainable production of P₄; however, such electrosynthesis requires the cleavage of strong, inert P-O bonds. By analogy to the promotion of bond activation in aqueous electrolytes with high proton activity (Brønsted-Lowry acidity), we show that low oxide anion activity (Lux-Flood acidity) enhances P-O bond activation in molten salt electrolytes. We develop electroanalytical tools to quantify the oxide dependence of phosphate reduction, and find that Lux acidic phosphoryl anhydride linkages enable selective, high-efficiency electrosynthesis of P₄ at a yield of 95% Faradaic efficiency. These fundamental studies provide a foundation that may enable the development of low-carbon alternatives to legacy carbothermal synthesis of P₄.

Processing of Phosphoric Solid Waste by Humic Acid Leaching Method

This article presents the results of research on the leaching of solid phosphorus-containing waste with humic acid. Such waste includes the by-products of the electrothermal processing of phosphate raw materials—phosphorus sludge and cottrel dust. Chemical and X-ray diffraction analyses have been used to study their composition and phase structure, according to which these substances have an amorphous structure. The leaching of phosphoric sludge and cottrel dust was investigated by varying the main parameters. The obtained data were processed using the method of formal kinetics to study the features of the process. The reaction rate constants and the apparent activation energy were calculated, and the values found made it possible to determine that the process under study is limited by diffusion. The scientific novelty of the article is the use of humic acid for leaching phosphoric solid waste as opposed to traditional methods. This new method may offer improved efficiency, reduced environmental impact, and a potential alternative solution for the processing of phosphoric waste.

Advances in the Synthesis and Analysis of Biologically Active Phosphometabolites

Phosphorus-containing metabolites cover a large molecular diversity and represent an important domain of small molecules which are highly relevant for life and represent essential interfaces between biology and chemistry, between the biological and abiotic world. The large but not unlimited amount of phosphate minerals on our planet is a key resource for living organisms on our planet, while the accumulation of phosphorus-containing waste is associated with negative effects on ecosystems. Therefore, resource-efficient and circular processes receive increasing attention from different perspectives, from local and regional levels to national and global levels. The molecular and sustainability aspects of a global phosphorus cycle have become of much interest for addressing the phosphorus biochemical flow as a high-risk planetary boundary. Knowledge of balancing the natural phosphorus cycle and the further elucidation of metabolic pathways involving phosphorus is crucial. This requires not only the development of effective new methods for practical discovery, identification, and high-information content analysis, but also for practical synthesis of phosphorus-containing metabolites, for example as standards, as substrates or products of enzymatic reactions, or for discovering novel biological functions. The purpose of this article is to review the advances which have been achieved in the synthesis and analysis of phosphorus-containing metabolites which are biologically active.

The Backbone of Success of P,N-Hybrid Ligands: Some Recent Developments

Organophosphorus ligands are an invaluable family of compounds that continue to underpin important roles in disciplines such as coordination chemistry and catalysis. Their success can routinely be traced back to facile tuneability thus enabling a high degree of control over, for example, electronic and steric properties. Diphosphines, phosphorus compounds bearing two separated PIII donor atoms, are also highly valued and impart their own unique features, for example excellent chelating properties upon metal complexation. In many classical ligands of this type, the backbone connectivity has been based on all carbon spacers only but there is growing interest in embedding other donor atoms such as additional nitrogen (-NH-, -NR-) sites. This review will collate some important examples of ligands in this field, illustrate their role as ligands in coordination chemistry and highlight some of their reactivities and applications. It will be shown that incorporation of a nitrogen-based group can impart unusual reactivities and important catalytic applications.

Photochemical Alkene Hydrophosphination with Bis(trichlorosilyl)phosphine

Bis(trichlorosilyl)phosphine (HP(SiCl₃)₂, 1) was prepared from [TBA][P(SiCl₃)₂] ([TBA]2, TBA = tetra-n-butylammonium) and triflic acid in 36% yield. Phosphine 1 is an efficient reagent for hydrophosphination of unactivated terminal olefins under UV irradiation (15-60 min) and gives rise to bis(trichlorosilyl)alkylphosphines (RP(SiCl₃)₂, R = (CH₂)₅CH₃, 88%; (CH₂)₇CH₃, 98%; (CH₂)₂C(CH₃)₃, 76%; CH₂Cy, 93%; (CH₂)₂Cy, 95%; CH₂CH(CH₃)(CH₂)₂CH₃, 82%; (CH₂)₃O(CH₂)₃CH₃, 95%; (CH₂)₃Cl, 83%; (CH₂)₂SiMe₃, 92%; (CH₂)₅C(H)CH₂, 44%) in excellent yields. The products require no further purification beyond filtration and removal of volatile material under reduced pressure. The P-Si bonds of prototypical products RP(SiCl₃)₂ (R = -(CH₂)₅CH₃, -(CH₂)₇CH₃) are readily functionalized to give further phosphorus-containing products: H₃C(CH₂)₇PCl₂ (56%), [H₃C(CH₂)₅P(CH₂Ph)₃]Br (84%), H₃C(CH₂)₇PH₂ (61%), H₃C(CH₂)₅P(O)(H)(OH) (81%), and H₃C(CH₂)₅P(O)(OH)₂ (55%). Experimental mechanistic investigations, accompanied by quantum chemical calculations, point toward a radical-chain mechanism. Phosphine 1 enables the fast, high-yielding, and atom-efficient preparation of compounds that contain phosphorus-carbon bonds in procedures that bypass white phosphorus (P₄), a toxic and high-energy intermediate of the phosphorus industry.

Halogenation and Nucleophilic Quenching: Two Routes to E-X Bond Formation in Cobalt Triple-Decker Complexes (E=As, P; X=F, Cl, Br, I)

The oxidation of [(Cp'''Co)2 (μ,η2  : η2 -E2 )2 ] (E=As (1), P (2); Cp'''=1,2,4-tri(tert-butyl)cyclopentadienyl) with halogens or halogen sources (I2 , PBr5 , PCl5 ) was investigated. For the arsenic derivative, the ionic compounds [(Cp'''Co)2 (μ,η4  : η4 -As4 X)][Y] (X=I, Y=[As6 I8 ]0.5 (3 a), Y=[Co2 Cl6-n In ]0.5 (n=0, 2, 4; 3 b); X=Br, Y=[Co2 Br6 ]0.5 (4); X=Cl, Y=[Co2 Cl6 ]0.5 (5)) were isolated. The oxidation of the phosphorus analogue 2 with bromine and chlorine sources yielded the ionic complexes [(Cp'''Co)2 (μ-PBr2 )2 (μ-Br)][Co2 Br6 ]0.5 (6 a), [(Cp'''Co)2 (μ-PCl2 )2 (μ-Cl)][Co2 Cl6 ]0.5 (6 b) and the neutral species [(Cp'''Co)2 (μ-PCl2 )(μ-PCl)(μ,η1  : η1 -P2 Cl3 ] (7), respectively. As an alternative approach, quenching of the dications [(Cp'''Co)2 (μ,η4  : η4 -E4 )][TEF]2 (TEF=[Al{OC(CF3 )3 }4 ]- , E=As (8), P (9)) with KI yielded [(Cp'''Co)2 (μ,η4  : η4 -As4 I)][I] (10), representing the homologue of 3, and the neutral complex [(Cp'''Co)(Cp'''CoI2 )(μ,η4  : η1 -P4 )] (11), respectively. The use of [(CH3 )4 N]F instead of KI leads to the formation of [(Cp'''Co)2 (μ-PF2 )(μ,η2  : η1  : η1 -P3 F2 )] (12) and 2, thereby revealing synthetic access to polyphosphorus compounds bearing P-F groups and avoiding the use of very strong fluorinating reagents, such as XeF2 , that are difficult to control.

Recent Breakthroughs in P4 Chemistry: Towards Practical, Direct Transformations into P1 Compounds

For several decades, academic researchers have been intensively studying the chemistry of white phosphorus (P4 ) in the hope of developing direct methods for its transformation into useful P-containing products. This would bypass the hazardous, multistep procedures currently relied on by industry. However, while academically interesting P4 activation reactions have become well established, their elaboration into useful, general synthetic procedures has remained out of reach. Very recently, however, a series of independent reports has begun to change this state of affairs. Each shows how relatively simple and practical synthetic methods can be used to access academically or industrially relevant P1 compounds from P4 directly, in "one pot" or even in a catalytic fashion. These reports mark a step change in the field of P4 chemistry, and suggest its possible transition from an area of largely academic interest to one with the promise of true synthetic relevance.

Direct conversion of white phosphorus to versatile phosphorus transfer reagents via oxidative onioation

The main feedstock for the value-added phosphorus chemicals used in industry and research is white phosphorus (P₄), from which the key intermediate for forming P(III) compounds is PCl₃. Owing to its high reactivity, syntheses based on PCl₃ are often accompanied by product mixtures and laborious work-up procedures, so an alternative process to form a viable P(III) transfer reagent is desirable. Our concept of oxidative onioation, where white phosphorus is selectively converted into triflate salts of versatile P₁ transfer reagents such as [P(L_N)₃][OTf]₃ (L_N is a cationic, N-based substituent; that is, 4-dimethylaminopyridinio), provides a convenient alternative for the implementation of P-O, P-N and P-C bonds while circumventing the use of PCl₃. We use p-block element compounds of type R_nE (for example, Ph₃As or PhI) to access weak adducts between nitrogen Lewis bases L_N and the corresponding dications [R_nEL_N]²⁺. The proposed equilibrium between [R_nEL_N]²⁺ + L_N and [R_nE(L_N)₂]²⁺ allows for the complete oxidative onioation of all six P-P bonds in P₄ to yield highly reactive and versatile trications [P(L_N)₃]³⁺.

Sustainable Production of Reduced Phosphorus Compounds: Mechanochemical Hydride Phosphorylation Using Condensed Phosphates as a Route to Phosphite

In pursuit of a more sustainable production of phosphorous acid (H₃PO₃), a versatile chemical with phosphorus in the +3 oxidation state, we herein report that condensed phosphates can be employed to phosphorylate hydride reagents under solvent-free mechanochemical conditions to furnish phosphite (HPO₃ ^2-). Using potassium hydride as the hydride source, sodium trimetaphosphate (Na₃P₃O₉), triphosphate (Na₅P₃O₁₀), pyrophosphate (Na₄P₂O₇), fluorophosphate (Na₂PO₃F), and polyphosphate ("(NaPO₃) _n ") engendered phosphite in optimized yields of 44, 58, 44, 84, and 55% based on total P content, respectively. Formation of overreduced products including hypophosphite (H₂PO₂ ^-) was identified as a competing process, and mechanistic investigations revealed that hydride attack on in-situ-generated phosphorylated phosphite species is a potent pathway for overreduction. The phosphite generated from our method was easily isolated in the form of barium phosphite, a useful intermediate for production of phosphorous acid. This method circumvents the need to pass through white phosphorus (P₄) as a high-energy intermediate and mitigates involvement of environmentally hazardous chemicals. A bioproduced polyphosphate was found to be a viable starting material for the production of phosphite. These results demonstrate the possibility of accessing reduced phosphorus compounds in a more sustainable manner and, more importantly, a means to close the modern phosphorus cycle.

Facile Synthesis of the Dicyanophosphide Anion via Electrochemical Activation of White Phosphorus: An Avenue to Organophosphorus Compounds

Organophosphorus compounds (OPCs) have gained tremendous interest in the past decades due to their wide applications ranging from synthetic chemistry to materials and biological sciences. We describe herein a practical and versatile approach for the transformation of white phosphorus (P₄) into useful OPCs with high P atom economy via a key bridging anion [P(CN)₂]^-. This anion can be prepared on a gram scale directly from P₄ through an electrochemical process. A variety of OPCs involving phosphinidenes, cyclophosphanes, and phospholides have been made readily accessible from P₄ in a two-step manner. Our approach has a significant impact on the future preparation of OPCs in laboratory and industrial settings.

Generation of a π-Bonded Isomer of [P4 ]4- by Aluminyl Reduction of White Phosphorus and its Ammonolysis to PH3

By employing the highly reducing aluminyl complex [K{(NON)Al}]₂ (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene), we demonstrate the controlled formation of P₄ ^2- and P₄ ^4- complexes from white phosphorus, and chemically reversible inter-conversion between them. The tetra-anion features a unique planar π-bonded structure, with the incorporation of the K⁺ cations implicit in the use of the anionic nucleophile offering additional stabilization of the unsaturated isomer of the P₄ ^4- fragment. This complex is extremely reactive, acting as a source of P^3- : exposure to ammonia leads to the release of phosphine (PH₃ ) under mild conditions (room temperature and pressure), which contrast with those necessitated for the direct combination of P₄ and NH₃ (>5 kbar and >250 °C).

Photocatalytic Arylation of P4 and PH3 : Reaction Development Through Mechanistic Insight

Detailed 31 P{1 H} NMR spectroscopic investigations provide deeper insight into the complex, multi-step mechanisms involved in the recently reported photocatalytic arylation of white phosphorus (P4 ). Specifically, these studies have identified a number of previously unrecognized side products, which arise from an unexpected non-innocent behavior of the commonly employed terminal reductant Et3 N. The different rate of formation of these products explains discrepancies in the performance of the two most effective catalysts, [Ir(dtbbpy)(ppy)2 ][PF6 ] (dtbbpy=4,4'-di-tert-butyl-2,2'-bipyridine) and 3DPAFIPN. Inspired by the observation of PH3 as a minor intermediate, we have developed the first catalytic procedure for the arylation of this key industrial compound. Similar to P4 arylation, this method affords valuable triarylphosphines or tetraarylphosphonium salts depending on the steric profile of the aryl substituents.

Pentaphosphaferrocene-mediated synthesis of asymmetric organo-phosphines starting from white phosphorus

The synthesis of phosphines is based on white phosphorus, which is usually converted to PCl₃, to be afterwards substituted step by step in a non-atomic efficient manner. Herein, we describe an alternative efficient transition metal-mediated process to form asymmetrically substituted phosphines directly from white phosphorus (P₄). Thereby, P₄ is converted to [Cp*Fe(η⁵-P₅)] (1) (Cp* = η⁵-C₅(CH₃)₅) in which one of the phosphorus atoms is selectively functionalized to the 1,1-diorgano-substituted complex [Cp*Fe(η⁴-P₅R'R″)] (3). In a subsequent step, the phosphine PR'R″R‴ (R' ≠ R″ ≠ R‴ = alky, aryl) (4) is released by reacting it with a nucleophile R‴M (M = alkali metal) as racemates. The starting material 1 can be regenerated with P₄ and can be reused in multiple reaction cycles without isolation of the intermediates, and only the phosphine is distilled off.

Reversing Lewis acidity from bismuth to antimony

Investigations on the boundaries between the neutral and cationic models of (Mesityl)₂EX (E = Sb, Bi and X = Cl^-, OTf^-) have facilitated reversing the Lewis acidity from bismuth to antimony. We use this concept to demonstrate a higher efficiency of (Mesityl)₂SbOTf over (Mesityl)₂BiOTf in the catalytic reduction of phosphine oxides to phosphines. The experiments supported with computations described herein will find use in designing new Lewis acids relevant to catalysis.

Fragmentation, catenation, and direct functionalisation of white phosphorus by a uranium(IV)-silyl-phosphino-carbene complex

Room temperature reaction of the uranium(iv)-carbene [U{C(SiMe3)(PPh2)}(BIPMTMS)(μ-Cl)Li(TMEDA)(μ-TMEDA)0.5]2 (1, BIPMTMS = C(PPh2NSiMe3)2) with white phosphorus (P4) produces the organo-P5 compound [P5{C(SiMe3)(PPh2)}2][Li(TMEDA)2] (2) and the uranium(iv)-methanediide [U{BIPMTMS}{Cl}{μ-Cl}2{Li(TMEDA)}] (3). This is an unprecedented example of cooperative metal-carbene P4 activation/insertion into a metal-carbon double bond and also an actinide complex reacting with P4 to directly form an organophosphorus species. Conducting the reaction at low temperature permits the isolation of the diuranium(iv) complex [{U(BIPMTMS)([μ-η2:η2-P2]C[SiMe3][PPh2])}2] (4), which then converts to 2 and 3. Thus, surprisingly, in contrast to all other actinide P4 reactivity, although this reaction produces catenation overall it proceeds via P4 cleavage to functionalised P2 units. Hence, this work establishes a proof of concept synthetic cycle for direct fragmentation, catenation, and functionalisation of P4.

Synthesis of monophosphines directly from white phosphorus

Monophosphorus compounds are of enormous industrial importance due to the crucial roles they play in applications such as pharmaceuticals, photoinitiators and ligands for catalysis, among many others. White phosphorus (P₄) is the key starting material for the preparation of all such chemicals. However, current production depends on indirect and inefficient, multi-step procedures. Here, we report a simple, effective 'one-pot' synthesis of a wide range of organic and inorganic monophosphorus species directly from P₄. Reduction of P₄ using tri-n-butyltin hydride and subsequent treatment with various electrophiles affords compounds that are of key importance for the chemical industry, and it requires only mild conditions and inexpensive, easily handled reagents. Crucially, we also demonstrate facile and efficient recycling and ultimately catalytic use of the tributyltin reagent, thereby avoiding the formation of substantial Sn-containing waste. Accessible, industrially relevant products include the fumigant PH₃, the reducing agent hypophosphorous acid and the flame-retardant precursor tetrakis(hydroxymethyl)phosphonium chloride.

Reversible Activation and Transfer of White Phosphorus by Silyl-Stannylene

Use of a silyl supported stannylene (Mes TerSn(Sit Bu3 ) [Mes Ter=2,6-(2,4,6-Me3 C6 H2 )2 C6 H3 ] enables activation of white phosphorus under mild conditions, which is reversible under UV light. The reaction of a silylene chloride with the activated P4 complex results in facile P-atom transfer. The computational analysis rationalizes the electronic features and high reactivity of the heteroleptic silyl-substituted stannylene in contrast to the previously reported bis(aryl)stannylene.

Transition-Metal-Mediated Functionalization of White Phosphorus

Recently there has been great interest in the reactivity of transition-metal (TM) centers towards white phosphorus (P4 ). This has ultimately been motivated by a desire to find TM-mediated alternatives to the current industrial routes used to transform P4 into myriad useful P-containing products, which are typically indirect, wasteful, and highly hazardous. Such a TM-mediated process can be divided into two steps: activation of P4 to generate a polyphosphorus complex TM-Pn , and subsequent functionalization of this complex to release the desired phosphorus-containing product. The former step has by now become well established, allowing the isolation of many different TM-Pn products. In contrast, productive functionalization of these complexes has proven extremely challenging and has been achieved only in a relative handful of cases. In this review we provide a comprehensive summary of successful TM-Pn functionalization reactions, where TM-Pn must be accessible by reaction of a TM precursor with P4 . We hope that this will provide a useful resource for continuing efforts that are working towards this highly challenging goal of modern synthetic chemistry.

Phosphorus recovery and recycling – closing the loop

The natural phosphorus cycle has been disrupted by human activity, which necessitates the development of new methods for the sustainable production of phosphorus compounds, and efficient recovery and recycling schemes.