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

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.

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.

Photocatalytic functionalization of white phosphorus with aryl bromides and chlorides

We report the implementation of a consecutive photoinduced electron transfer (conPET) strategy for the functionalization of white phosphorus (P4) with inexpensive and widely available aryl bromides and chlorides. By employing a well-known acridinium-based photocatalyst under near-UV irradiation, this protocol gives direct access to valuable triarylphosphines and tetraarylphosphonium salts. The reaction mechanism is elucidated by NMR spectroscopic studies and model reactions.

Metal Fluorides Passivate II-VI and III-V Quantum Dots

Quantum dots (QDs) with metal fluoride surface ligands were prepared via reaction with anhydrous oleylammonium fluoride. Carboxylate terminated II-VI QDs underwent carboxylate for fluoride exchange, while InP QDs underwent photochemical acidolysis yielding oleylamine, PH3, and InF3. The final photoluminescence quantum yield (PLQY) reached 83% for InP and near unity for core-shell QDs. Core-only CdS QDs showed dramatic improvements in PLQY, but only after exposure to air. Following etching, the InP QDs were bound by oleylamine ligands that were characterized by the frequency and breadth of the corresponding ν(N-H) bands in the infrared absorption spectrum. The fluoride content (1.6-9.2 nm-2) was measured by titration with chlorotrimethylsilane and compared with the oleylamine content (2.3-5.1 nm-2) supporting the formation of densely covered surfaces. The influence of metal fluoride adsorption on the air stability of QDs is discussed.

Synthesis and Characterization of a Terminal Iron(II)-PH2 Complex and a Series of Iron(II)-PH3 Complexes

Reported is the reaction of a series of iron(II) bisphosphine complexes with PH3 in the presence of NaBArF4 [where BArF4 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate]. The iron(II) bisphosphine reagents bear two chlorides or a hydride and a chloride motif. We have isolated six different cationic terminal-bound PH3 complexes and undertaken rigorous characterization by NMR spectroscopy, single crystal X-ray diffraction, and mass spectrometry, where the PH3 often remains intact during the ionization process. Unusual bis- and tris-PH3 complexes are among the compounds isolated. Changing the monophosphine from PH3 to PMe3 results in the formation of an unusual Fe7 cluster, but with no PMe3 being ligated. Finally, by using an iron(0) source, we have provided a rare example of a terminally bound iron-PH2 complex.

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.

Mechanistic Insights and Synthetic Explorations of the Photoredox-Catalyzed Activation of Halophosphines

The light-driven activation of halophosphines R2PX (R = alkyl- or aryl, X = Cl, Br) by an IrIII-based photocatalyst is described. It is shown that initially formed secondary phosphines R2PH react readily with the remaining R2PX in a parent-child reaction to form diphosphines R2P-PR2. Aryl-containing diphosphines can be further reduced to secondary phosphines RAr2PH under identical photoredox conditions. Dihalophosphines RPX2 are also activated by the photoredox protocol, giving rise to unusual 3-, 4-, and 5-membered cyclophosphines. Transient absorption studies show that the excited state of the Ir photocatalyst is reductively quenched by the DIPEA (N,N-di-iso-propylethylamine) electron donor. Electron transfer to R2PX is however unexpectedly slow and cannot compete with recombination with the oxidized donor DIPEA•+. As DIPEA is not a perfectly reversible donor, a small proportion of the total IrII population escapes recombination, providing the reductant for the observed transformations.

Photochemical Benzylation of White Phosphorus

Organophosphorus compounds (OPCs) have wide application in organic synthesis, material sciences, and drug discovery. Generally, the vast majority of phosphorus atoms in OPCs are derived from white phosphorus (P4). However, the large-scale preparation of OPCs mainly proceeds through the multistep and environmentally toxic chlorine route from P4. Herein, we report the direct benzylation of P4 promoted by visible light. The cheap and readily available benzyl bromide was used as a benzylation reagent, and tetrabenzylphosphonium bromide was directly synthesized from P4. In addition, the metallaphotoredox catalysis strategy was applied to functionalize P4 for the first time, which significantly improved the application range of the substituted benzyl bromide.

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.

Study of pnictides for photovoltaic applications

For the transition into a sustainable mode of energy usage, it is important to develop photovoltaic materials that exhibit better solar-to-electricity conversion efficiencies, a direct optimal band gap, and are made of non-toxic, earth abundant elements compared to the state-of-the-art silicon photovoltaics. Here, we explore the non-redox-active pnictide chemical space, including binary A₃B₂, ternary AA'₂B₂, and quaternary AA'A''B₂ compounds (A, A', A'' = Ca, Sr, or Zn; B = N or P), as candidate beyond-Si photovoltaics using density functional theory calculations. Specifically, we evaluate the ground state configurations, band gaps, and 0 K thermodynamic stability for all 20 pnictide compositions considered, besides computing the formation energy of cation vacancies, anion vacancies, and cation anti-sites in a subset of candidate compounds. Importantly, we identify SrZn₂N₂, SrZn₂P₂, and CaZn₂P₂ to be promising candidates, exhibiting optimal (1.1-1.5 eV) hybrid-functional-calculated band gaps, stability at 0 K, and high resistance to point defects (formation energies >1 eV), while other possible candidates include ZnCa₂N₂ and ZnSr₂N₂, which may be susceptible to N-vacancy formation. We hope that our study will contribute to the practical development of pnictide semiconductors as beyond-silicon light absorbers.

Tris(bicyclo[1.1.1]pentyl)phosphine: An Exceptionally Small Tri-tert-alkylphosphine and Its Bis-Ligated Pd(0) Complex

Tris(bicyclo[1.1.1]pentyl)phosphine can be prepared by radical addition of PH₃ to [1.1.1]propellane, giving the smallest tri-tert-alkylphosphine known. PBcp₃ is substantially smaller than PCy₃ and is comparable in electron-donating power to PEt₃. It gives a bis-ligated Pd(0) complex Pd(PBcp₃)₂ that is exceptionally reactive toward alkyl halide oxidative addition and functions as a general ligand for palladium-catalyzed cross-coupling of sp³ electrophiles. Radical addition of [1.1.1]propellane to phenylphosphine gives the bis(bicyclo[1.1.1]pentyl)phosphine derivative PBcp₂Ph, illustrating the generality of this approach to bicyclopentylphosphine synthesis.

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.

Taming PH3: State of the Art and Future Directions in Synthesis

Appetite for reactions involving PH₃ has grown in the past few years. This in part is due to the ability to generate PH₃ cleanly and safely via digestion of cheap metal phosphides with acids, thus avoiding pressurized cylinders and specialized equipment. In this perspective we highlight current trends in forming new P–C/P–OC bonds with PH₃ and discuss the challenges involved with selectivity and product separation encumbering these reactions. We highlight the reactivity of PH₃ with main group reagents, building on the early pioneering work with transition metal complexes and PH₃. Additionally, we highlight the recent renewal of interest in alkali metal sources of H₂P^– which are proving to be useful synthons for chemistry across the periodic table. Such MPH₂ sources are being used to generate the desired products in a more controlled fashion and are allowing access to unexplored phosphorus-containing species.

Binding, Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes

The bridging MeCN ligand in the dicopper(I) complexes [(DPFN)Cu2 (μ,η1  : η1 -MeCN)][X]2 (X=weakly coordinating anion, NTf2 (1 a), FAl[OC6 F10 (C6 F5 )]3 (1 b), Al[OC(CF3 )3 ]4 (1 c)) was replaced by white phosphorus (P4 ) or yellow arsenic (As4 ) to yield [(DPFN)Cu2 (μ,η2  : η2 -E4 )][X]2 (E=P (2 a-c), As (3 a-c)). The molecular structures in the solid state reveal novel coordination modes for E4 tetrahedra bonded to coinage metal ions. Experimental data and quantum chemical computations provide information concerning perturbations to the bonding in coordinated E4 tetrahedra. Reactions with N-heterocyclic carbenes (NHCs) led to replacement of the E4 tetrahedra with release of P4 or As4 and formation of [(DPFN)Cu2 (μ,η1  : η1 -Me NHC)][X]2 (4 a,b) or to an opening of one E-E bond leading to an unusual E4 butterfly structural motif in [(DPFN)Cu2 (μ,η1  : η1 -E4 Dipp NHC)][X]2 (E=P (5 a,b), E=As (6)). With a cyclic alkyl amino carbene (Et CAAC), cleavage of two As-As bonds was observed to give two isomers of [(DPFN)Cu2 (μ,η2  : η2 -As4 Et CAAC)][X]2 (7 a,b) with an unusual As4 -triangle+1 unit.

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.

Photocatalytic stannylation of white phosphorus

Organophosphorus compounds (OPCs) are highly important chemicals, finding numerous applications in both academia and industry. Herein we describe a simple photocatalytic method for the stannylation of white phosphorus (P₄) using a cheap, commercially-available distannane, (Bu₃Sn)₂, and anthraquinone as a simple photocatalyst. Subsequent ‘one pot’ transformation of the resulting stannylated monophosphine intermediate (Bu₃Sn)₃P provides direct, convenient and versatile access to valuable OPCs such as acylated phosphines and tetraalkylphosphonium salts.

A simple, mechanistically unique photochemical procedure is reported for the efficient, direct, catalytic stannylation of P₄ and ‘one pot’ transformation into valuable monophosphorus compounds.

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.

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.

Photochemical transformation of chlorobenzenes and white phosphorus into arylphosphines and phosphonium salts

Chlorobenzenes are important starting materials for the preparation of commercially valuable triarylphosphines and tetraarylphosphonium salts, but their use for the direct arylation of elemental phosphorus has been elusive. Here we describe a simple photochemical route toward such products. UV-LED irradiation (365 nm) of chlorobenzenes, white phosphorus (P₄) and the organic superphotoreductant tetrakis(dimethylamino)ethylene (TDAE) affords the desired arylphosphorus compounds in a single reaction step.