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

Recent Advances in the Synthesis of Commercially Available Phosphite Antioxidants

Phosphite antioxidants exhibit superior anti-aging and color-stabilizing properties when incorporated into polymer materials. Their synergistic antioxidative effects are particularly noteworthy when used in combination with hindered phenol antioxidants and other primary antioxidants, serving as effective secondary antioxidants, displaying noteworthy synergistic antioxidation effects. This review systematically classifies the synthetic methods for phosphite antioxidants into three distinct categories based on the types of starting materials: synthesis from phosphorus trichloride, phosphorus-containing esters, and white phosphorus. Additionally, it delineates the reaction mechanisms associated with these approaches and provides an overview of future potential research directions and applications for organophosphorus antioxidants.

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.

Chemodivergent phosphonylation of diazocarboxylates: light-on vs. light-off reactions

By tapping into the divergent reactivity of diazocarboxylates under thermal and photocatalytic conditions, we could develop chemodivergent phosphonylation protocols for α-diazocarboxylates with trialkyl phosphites. While the thermal reaction led to N-P bond formation affording phosphonylated hydrazones, the visible light-mediated reaction furnished phosphonylated aryl carboxylates through C-P bond formation. Both reactions are notable for their operational simplicity and mild conditions affording products in good yields without the requirement of a metal, base or photocatalyst.

Recent progress on the functionalization of white phosphorus in China

Direct synthesis of organophosphorus compounds from white phosphorus represents a significant but challenging subject, especially in the context of ongoing efforts to comprehensively improve the phosphorus-derived chemical industry driven by sustainability and safety concerns. China is the world's largest producer of white phosphorus, creating a significant demand for the green transformation of this crucial feedstock. This review provides an overview of advancements in white phosphorus activation by Chinese research teams, focusing on the direct construction of P‒C/N/O/S/M bonds from white phosphorus. Additionally, we offer some insights into prospective directions for the activation and transformation of white phosphorus in the future. This review paper aims to attract more researchers to engage in this area, stimulating follow-up exploration and fostering enduring advances.

Controlled Ring Opening of a Tetracyclic Tetraphosphane with Twofold Metallocene Bridging

A direct route to a doubly ferrocene bridged tetracyclic tetraphosphane 1 was developed via reductive coupling of Fe(CpPCl2)2 (2 a), where a chlorine terminated linear P4-compound 3 could be identified as an intermediate. Selective P-P bond activation was further achieved by reacting 1 with elemental selenium or [Cp*Al]4, where regioselective insertion of Se or Al atoms resulted in ferrocenylene bridged [P4Se] (4) or [P4Al] (7) moieties. Compound 7 can be transformed to a hydrogen terminated linear P4 species, 8, with protic solvents. Methylation of compound 1 with MeOTf, proceeds via intermediate formation of monomethylated species 5, which gradually produced Me2-terminated dicationic 6, again containing a linear P4-unit. Besides spectroscopic characterization, the structural details of compounds 1, 4, 6, and 8 could be determined by SC-XRD. Moreover, DFT calculations were used to rationalize the reactivity of 1, derived compounds and intermediates. As a key feature, 1 undergoes ring opening polymerization to a linear polyphosphane 9.

Cobalt-Mediated [3+1] Fragmentation of White Phosphorus: Access to Acylcyanophosphanides

Despite the accessibility of numerous transition metal polyphosphido complexes through transition-metal-mediated activation of white phosphorus, the targeted functionalization of Pn ligands to obtain functional monophosphorus species remains challenging. In this study, we introduce a new [3+1] fragmentation procedure for cyclo-P4 ligands, leading to the discovery of acylcyanophosphanides and -phosphines. Treatment of the complex [K(18c-6)][(Ar*BIAN)Co(η4 -P4 )] ([K(18c-6)]3, 18c-6=[18]crown-6, Ar*=2,6-dibenzhydryl-4-isopropylphenyl, BIAN=1,2-bis(arylimino)acenaphthene diimine) with acyl chlorides results in the formation of acylated tetraphosphido complexes [(Ar*BIAN)Co(η4 -P4 C(O)R)] (R=tBu, Cy, 1-Ad, Ph; 4 a-d). Subsequent reactions of 4 a-d with cyanide salts yield acylated cyanophosphanides [RC(O)PCN]- (9 a-d- ) and the cyclo-P3 cobaltate anion [(Ar*BIAN)Co(η3 -P3 )(CN)]- (8- ). Further reactions of 4 a-d with trimethylsilyl cyanide (Me3 SiCN) and isocyanides provide insight into a plausible mechanism of this [3+1] fragmentation reaction, as these reagents partially displace the P4 C(O)R ligand from the cobalt center. Several potential intermediates of the [3+1] fragmentation were characterized. Additionally, the introduction of a second acyl substituent was achieved by treating [K(18c-6)]9b with CyC(O)Cl, resulting in the first bis(acyl)monocyanophosphine (CyC(O))2 PCN (10).

Direct Synthesis of Phosphoryltriacetates from White Phosphorus via Visible Light Catalysis

Organophosphorus compounds (OPCs) are widely used in many fields. However, traditional synthetic routes in the industry usually involve multistep and hazardous procedures. Therefore, it's of great significance to construct such compounds in an environmentally-friendly and facile way. Herein, a photoredox catalytic method has been developed to construct novel phosphoryltriacetates. Using fac-Ir(ppy)3 (ppy=2-phenylpyridine) as the photocatalyst and blue LEDs (456 nm) as the light source, white phosphorus can react with α-bromo esters smoothly to generate phosphoryltriacetates in moderate to good yields. This one-step approach features mild reaction conditions and simple operational process without chlorination.

An Isolable Radical Anion Featuring a 2-Center-3-Electron π-Bond without a Clearly Defined σ-Bond

Featuring an extra electron in the π* antibonding orbital, species with a 2-center-3-electron (2c3e) π bond without an underlying σ bond are scarcely known. Herein, we report the synthesis, isolation and characterization of a radical anion salt [K(18-C-6)]+ {[(HCNDipp)2 Si]2 P2 }⋅- (i.e. [K(18-C-6)]+ 3⋅- ) (18-C-6=18-crown-6, Dipp=2,6-diisopropylphenyl), in which 3⋅- features a perfectly planar Si2 P2 four-membered ring. This species represents the first example of a Si- and P-containing analog of a bicyclo[1.1.0]butane radical anion. The unusual bonding motif of 3⋅- was thoroughly investigated via X-ray diffraction crystallography, electron paramagnetic resonance spectroscopy (EPR), and calculations by density functional theory (DFT), which collectively unveiled the existence of a 2c3e π bond between the bridgehead P atoms and no clearly defined supporting P-P σ bond.

Bicyclic (alkyl)(amino)carbene (BICAAC)-supported phosphinidenes

Herein, the synthesis and characterization of bicyclic (alkyl)(amino)carbene (BICAAC)-stabilized phosphinidenes (1-4) are reported. Compounds 1-3 were obtained by reacting trihalophosphine [PX3, X = Cl (1), Br (2), I (3)] with BICAAC in THF. A BICAAC-stabilized bis-phosphinidene (4) was obtained from the reduction of compound 2. All four compounds were characterized by X-ray crystallography and heteronuclear NMR spectroscopy. Theoretical calculations indicated the predominant C(carbene)P double bond characteristic in compounds 1-4.

Isolation of (Aryl)-(Imino) Phosphide and (Aryl)-(Phosphaalkene) Amide Complexes of Alkali Metals from Carbene-Phosphinidenes under Reductive-Thermal Rearrangements

Two-electron reduction of cyclic alkyl(amino) carbene (cAAC)-supported chloro-phosphinidene cAAC=P-Cl (1) followed by unprecedented thermal rearrangements afforded the alkali metal complexes of (aryl)-(cyclic alkyl(imino)) phosphides 3 a-3 c, 4 a-4 b through migration of the 2,6-diisopropylphenyl (dipp) group from N to the P centre, and the (aryl)-(cyclic alkyl(phosphaalkene)) amide 5 through cleavage of the CMe2 -N bond followed by energetically favoured 5-exo-tet ring-closure in the presence of the alkali metals Cs (3 a-3 c), K (4 a, 4 b), and Li (5). Compound 3 a was found to be photoluminescent (PL), emitting bright orange light under a laboratory UV lamp of wavelength 365 nm with PL quantum yield (ϕPL ) of 2.6 % (λem =600 nm), and an average lifetime (τ) of 4.8 μs. Reaction of 3 a with CuCl and AgOTf afforded (aryl)-(cyclic alkyl(imino)) phosphide-stabilized tetra-nuclear CuI (6), and octa-nuclear AgI (7) clusters, respectively. Moreover, complexes 3 a-3 c provided a direct route for the stabilization of cyclic alkyl(aminoboryl) phosphaalkenes 8 a-8 c when treated with 1-bromo-N,N,N',N'-tetraisopropylboranediamine.

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.

Electrochemical Late-Stage Functionalization

Late-stage functionalization (LSF) constitutes a powerful strategy for the assembly or diversification of novel molecular entities with improved physicochemical or biological activities. LSF can thus greatly accelerate the development of medicinally relevant compounds, crop protecting agents, and functional materials. Electrochemical molecular synthesis has emerged as an environmentally friendly platform for the transformation of organic compounds. Over the past decade, electrochemical late-stage functionalization (eLSF) has gained major momentum, which is summarized herein up to February 2023.

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.

C- and N-Phosphorylated Enamines-An Avenue to Heterocycles: NMR Spectroscopy

The review presents extensive data (from the works of the author and literature) on the structure of C- and N-chlorophosphorylated enamines and the related heterocycles obtained by multipulse multinuclear ¹H, ¹³C, and ³¹P NMR spectroscopy. The use of phosphorus pentachloride as a phosphorylating agent for functional enamines enables the synthesis of various C- and N-phosphorylated products that are heterocyclized to form various promising nitrogen- and phosphorus-containing heterocyclic systems. ³¹P NMR spectroscopy is the most convenient, reliable and unambiguous method for the study and identification of organophosphorus compounds with different coordination numbers of the phosphorus atom, as well as for the determination of their Z- and E-isomeric forms. An alteration of the coordination number of the phosphorus atom in the phosphorylated compounds from 3 to 6 leads to a drastic screening of the ³¹P nucleus from about +200 to -300 ppm. The unique structural features of nitrogen-phosphorus-containing heterocyclic compounds are discussed.

Electrochemically Oxidative Phosphating of Aldehydes and Ketones

Disclosed herein is the first protocol for the electrochemically oxidative phosphating of aldehydes and ketones to generate α-hydroxyphosphine oxides with diphenylphosphine as the phosphine source. Various phosphating products containing P-C bonds are basically assembled in modest to excellent yields. This electrochemical phosphating was achieved by utilizing a simple undivided cell with foam nickel electrodes at room temperature without the addition of any oxidant or metal catalyst. The prepared α-hydroxyphosphine oxides possess potential application in pharmacological research.

One-Step Synthesis of Benzophosphole Derivatives from Arylalkynes by Phosphenium-Dication-Mediated Sequential C-P/C-C Bond Forming Reaction

A metal-free, phosphenium-dication-mediated sequential C-P and C-C bond forming reaction has been developed. This protocol can provide concise access to the (di)benzophosphole derivatives in one synthetic operation from the readily available and simple arylalkynes and phosphinic acids. Application to the multiple cyclization reaction and the fully intermolecular three-component-coupling-type reaction are also described.

Hydrostannylation of Red Phosphorus: A Convenient Route to Monophosphines

The preparation of valuable and industrially relevant organophosphorus compounds currently depends on indirect multistep procedures involving difficult-to-handle white phosphorus as a common P atom source. Herein, we report a practical and versatile method for the synthesis of a variety of monophosphorus compounds directly from the bench-stable allotrope red phosphorus (Pred ). The relatively inert Pred was productively functionalised by using the cheap and readily available radical reagent tri-n-butyltin hydride, and subsequent treatment with electrophiles yields useful P1 compounds. Remarkably, these transformations require only modest inert-atmosphere techniques and use only reagents that are inexpensive and commercially available, making this a convenient and practical methodology accessible in most laboratory settings.

Synthesis, Structure and Reactivity of a Cyapho(dicyano)methanide Salt

We describe the synthesis of a cyapho(dicyano)methanide salt, [K(18-crown-6)][C(CN)2 (CP)], from reaction of [Na(18-crown-6)][PH2 ] (18-crown-6=1,4,7,10,13,16-hexaoxacyclooctadecane) with 1,1-diethoxy-2,2-dicyanoethylene (EtO)2 C=C(CN)2 . The reaction proceeds through a Michael addition-elimination pathway to afford [Na(18-crown-6)][HP{C(OEt)=C(CN)2 }]. Addition of a strong, non-nucleophilic base (KHMDS) to this intermediate results in the formation of [K(18-crown-6)][C(CN)2 (CP)]. Subsequent reactivity studies reveal that the cyapho(dicyano)methanide ion is susceptible to protonation with strong acids to afford the parent acid HC(CN)2 (CP). The reactivity of the cyaphide moiety in [C(CN)2 (CP)]- was explored through coordination to metal centers and in cycloaddition reactions with azides.

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.