Reduction of Tertiary Phosphine Oxides with DIBAL-H

A Triphenylphosphine-Based Microporous Polymer for a Wittig Reaction Cycle in the Solid State

The Wittig reaction is a key step in industrial processes to synthesise large quantities of vitamin A and various other important chemicals that are used in daily life. This article presents a pathway to achieve the Wittig reaction in a solid network. A highly porous triphenylphosphine-based polymer was applied as a solid Wittig reagent that undergoes, in a multi-step cycle, in total six post-synthetic modifications. This allowed for regeneration of the solid Wittig reagent and reuse for the same reaction cycle. Of particular industrial relevance is that the newly developed material also enables a simple way of separating the product by filtration. Therefore, additional costly and difficult separation and purification steps are no longer needed.

Deoxygenation of Phosphine Oxides by PIII/PV═O Redox Catalysis via Successive Isodesmic Reactions

Deoxygenation of phosphine oxides is of great significance to synthesis of phosphorus ligands and relevant catalysts, as well as to the sustainability of phosphorus chemistry. However, the thermodynamic inertness of P═O bonds poses a severe challenge to their reduction. Previous approaches in this regard rely primarily on a type of P═O bond activation with either Lewis/Brønsted acids or stoichiometric halogenating reagents under harsh conditions. Here, we wish to report a novel catalytic strategy for facile and efficient deoxygenation of phosphine oxides via successive isodesmic reactions, whose thermodynamic driving force for breaking the strong P═O bond was compensated by a synchronous formation of another P═O bond. The reaction was enabled by P^III/P═O redox sequences with the cyclic organophosphorus catalyst and terminal reductant PhSiH₃. This catalytic reaction avoids the use of the stoichiometric activator as in other cases and features a broad substrate scope, excellent reactivities, and mild reaction conditions. Preliminary thermodynamic and mechanistic investigations disclosed a dual synergistic role of the catalyst.

Soft QPCs: Biscationic Quaternary Phosphonium Compounds as Soft Antimicrobial Agents

Quaternary ammonium compounds (QACs) serve as a first line of defense against infectious pathogens. As resistance to QACs emerges in the environment, the development of next-generation disinfectants is of utmost priority for human health. Balancing antibacterial potency with environmental considerations is required to effectively counter the development of bacterial resistance. To address this challenge, a series of 14 novel biscationic quaternary phosphonium compounds (bisQPCs) have been prepared as amphiphilic disinfectants through straightforward, high-yielding alkylation reactions. These compounds feature decomposable or "soft" amide moieties in their side chains, anticipated to promote decomposition under environmental conditions. Strong bioactivity against a panel of seven bacterial pathogens was observed, highlighted by single-digit micromolar activity for compounds P6P-12A,12A and P3P-12A,12A. Hydrolysis experiments in pure water and in buffers of varying pH revealed surprising decomposition of the soft QPCs under basic conditions at the phosphonium center, leading to inactive phosphine oxide products; QPC stability (>24 h) was maintained in neutral solutions. The results of this work unveil soft QPCs as a potent and environmentally conscious new class of bisQPC disinfectants.

Reduction of Triphenylphosphine Oxide to Triphenylphosphine by Phosphonic Acid

A novel method for the iodine-mediated reduction of phosphine oxides (sulfides) to phosphines using phosphonic acid under solvent-free conditions is described. By using a combination of H₃PO₃ and I₂, both tertiary monophosphine oxides and bis-phosphine oxides were reduced under this system, readily producing monodentate and bidentate phosphines, respectively, in good yields. Notably, chiral (R)-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl dioxide could be also tolerated without racemization. This new approach is inexpensive and features simple conditions and a wide substrate scope.

Nickel-catalysed diversification of phosphine ligands by formal substitution at phosphorus

We report a diversification strategy that enables the direct substituent exchange of tertiary phosphines. Alkylated phosphonium salts, prepared by standard alkylation of phosphines, are selectively dearylated in a nickel-catalysed process to access alkylphosphine products via a formal substitution at the phosphorus center. The reaction can be used to introduce a wide range of alkyl substituents into both mono- and bisphosphines. We also show that the alkylation and dearylation steps can be conducted in a one-pot sequence, enabling accelerated access to derivatives of the parent ligand. The phosphine products of the reaction are converted in situ to air-stable borane adducts for isolation, and versatile derivatisation reactions of these adducts are demonstrated.

Phosphine substituents can be exchanged by standard alkylation of a phosphine and a subsequent dearylation of the resulting phosphonium salt. A wide variety of alkyl groups can be introduced into both mono- and bidentate ligands using this method.

A Mild One-Pot Reduction of Phosphine(V) Oxides Affording Phosphines(III) and Their Metal Catalysts

The metal-free reduction of a range of phosphine(V) oxides employing oxalyl chloride as an activating agent and hexachlorodisilane as reducing reagent has been achieved under mild reaction conditions. The method was successfully applied to the reduction of industrial waste byproduct triphenylphosphine(V) oxide, closing the phosphorus cycle to cleanly regenerate triphenylphosphine(III). Mechanistic studies and quantum chemical calculations support the attack of the dissociated chloride anion of intermediated phosphonium salt at the silicon of the disilane as the rate-limiting step for deprotection. The exquisite purity of the resultant phosphine(III) ligands after the simple removal of volatiles under reduced pressure circumvents laborious purification prior to metalation and has permitted the facile formation of important transition metal catalysts.

Photoinduced Dearomatizing Three-Component Coupling of Arylphosphines, Alkenes, and Water

A unique photoinduced reaction that couples a triarylphosphine, an alkene, and water to produce 2-(cyclohexa-2,5-dienyl)ethylphosphine oxide is reported herein. The alkene inserts into a C(aryl)-P bond of the arylphosphine, the aryl ring is dearomatized into the cyclohexadienyl ring, and the phosphorus is oxidized. The three components are all readily available, and their intermolecular coupling significantly increases molecular complexity. The products formed are applicable to the Wittig olefination.

Phosphorus-Recycling Wittig Reaction: Design and Facile Synthesis of a Fluorous Phosphine and Its Reusable Process in the Wittig Reaction

This study shows that phosphorus sources can be recycled using the appropriate fluorous phosphine in the Wittig reaction. The designed fluorous phosphine, which has an ethylene spacer between its phosphorus atom and the perfluoroalkyl group, was synthesized from air-stable phosphine reagents. The synthesized phosphine can be used for the Wittig reaction process to obtain various alkenes in adequate yields and stereoselectivity. The concomitantly formed fluorous phosphine oxide was extracted from the reaction mixture using a fluorous biphasic system. The fluorous phosphine was regenerated by reducing the fluorous phosphine oxide with diisobutylaluminum hydride. Finally, a series of gram scale phosphorus recycling processes were performed, which included the Wittig reaction, separation, reduction, and reuse.

Trivalent Rare-Earth Metal Amide Complexes as Catalysts for the Hydrosilylation of Benzophenone Derivatives with HN(SiHMe2 )2 by Amine-Exchange Reaction

The rare-earth metal complexes Ln(L1 )[N(SiHMe2 )2 ](thf) (Ln=La, Ce, Y; L1 =N,N''-bis(pentafluorophenyl)diethylenetriamine dianion) were synthesized by treating Ln[N(SiHMe2 )2 ]3 (thf)2 with L1 H2 . The lanthanum and cerium derivatives are active catalysts for the hydrosilylation of benzophenone derivatives with HN(SiHMe2 )2 . An amine-exchange reaction was revealed as a key step of the catalytic cycle, in which Ln-Si-H β-agostic interactions are proposed to promote insertion of the carbonyl moiety into the Si-H bond.

Asymmetric Friedel–Crafts Alkylation of Indoles Catalyzed by Chiral Aziridine-Phosphines

Over the course of the present studies, a series of optically pure phosphines functionalized by chiral aziridines was synthesized in reasonable/good chemical yields. Their catalytic activity was checked in the enantioselective Friedel–Crafts alkylation of indoles by β-nitrostyrene in the presence of a copper(I) trifluoromethanesulfonate benzene complex. The corresponding Friedel–Crafts products were achieved efficiently in terms of chemical yield and enantioselectivity (up to 85% in some cases).

Convergent Synthesis of Polysubstituted Furans via Catalytic Phosphine Mediated Multicomponent Reactions

Tri- or tetrasubstituted furans have been prepared from terminal activated olefins and acyl chlorides or anhydrides by a multicomponental convergent synthesis mode. Instead of stoichiometric nBu₃P, only catalytic nBu₃P or nBu₃P=O is needed to furnish the furans in modest to excellent yields with a good functional group tolerance under the aid of reducing agent silane. This synthetic method features a silane-driven catalytic intramolecular Wittig reaction as a key annulation step and represents the first successful application of catalytic Wittig reaction in multicomponent cascade reaction.

Dearylation of arylphosphine oxides using a sodium hydride–iodide composite

A new protocol for the dearylative functionalization of arylphosphine oxides was developed using NaH in the presence of LiI.

Intramolecular Nucleophilic Substitution of ω-Haloalkylphosphine Derivatives

ω-Haloalkylphosphine derivatives undergo the intramolecular nucleophilic substitution reaction upon treatment with a strong base, yielding either cycloalkylphosphine derivatives or heterocyclic phosphine derivatives. The selectivity of the cyclization of (ω-haloalkyl)alkylarylphosphine derivatives depends strongly on the distance between the electrophilic and nucleophilic carbon atoms and the structure of the phosphorus moiety. The desymmetrization of dimethylphenylphosphine sulfide followed by haloalkylation and cyclization led to the enantiomerically enriched tertiary phosphine sulfide, possessing a cyclohexyl fragment at the phosphorus.

A clean and simple method for deprotection of phosphines from borane complexes

Simple, efficient, clean, and stereospecific protocols of protection of phosphorus atom with borane and deprotection from the borane complexes of the tertiary phosphines in mild conditions are reported. The proposed protection/deprotection reactions tolerate a range of functional groups and lead to pure products with excellent yield with no need for application of chromatographic or crystallisation purification procedures. For the first time mechanisms of the reactions of phosphine protection and deprotection have been studied based on experimental kinetic data as well as quantumchemical calculations, which allows designing reaction conditions suitable for a given substrate.

Efficient access to a designed phosphapalladacycle catalyst via enantioselective catalytic asymmetric hydrophosphination

A chiral phosphine auxiliary was generated with excellent ee via catalytic asymmetric hydrophosphination of 3-(naphthalen-1-ylmethylene)pentane-2,4-dione. The subsequent metal complexation of the monophosphine yielded two different coordination complexes depending on the reaction conditions. The ortho-palladation of both coordination complexes resulted in the formation of a single dimeric phosphapalladacycle complex that could be further converted to the monomeric bisacetonitrile derivative. Moreover, the palladium complex exhibits interesting oxophilicity as the stable bisaquo derivative could be isolated and characterized crystallographically. The catalytic potential of the phosphapalladacycle was also demonstrated.

A theoretical study on the mechanism of ruthenium(ii)-catalyzed phosphoryl-directed ortho-selective C–H bond activations: the phosphoryl hydroxy group triggered Ru(ii)/Ru(0) catalytic cycle

A theoretical study on the mechanism of ruthenium(ii)-catalyzed phosphoryl-directed ortho-selective C–H bond activations has been reported.

Understanding the mechanism, thermodynamic and kinetic features of the Kukhtin–Ramirez reaction in carbamate synthesis from carbon dioxide

In this article, thermodynamic and kinetic aspects of the Kukhtin–Ramirez reaction of the carbamate formation from carbon dioxide have been investigated in the presence of various phosphorous reagents (PRs), theoretically.

Disilanes as oxygen scavengers and surrogates of hydrosilanes suitable for selective reduction of nitroarenes, phosphine oxides and other valuable substrates

In this report, we demonstrate that the reaction of nitroarenes with hexamethyldisilane under various conditions affords a different range of compounds with excellent selectivity.

Mechanistic insights into the role of PC- and PCP-type palladium catalysts in asymmetric hydrophosphination of activated alkenes incorporating potential coordinating heteroatoms

The impact of the structural attributes of chiral PC- and PCP-palladium catalysts was investigated in the asymmetric hydrophosphination of various heterocycle-functionalized enone substrates. Due to the architecture of the catalysts, they are confronted with potential catalyst deactivation arising from the coordination of the electron-rich heteroatoms (P, O, N and S) to the metal center. A systematic variation of the location and identity of the heteroatoms demonstrated the impact of structural modifications on the substrates, which have a significant influence on both yields (16-99%) and enantioselectivities (0-99%). A detailed discussion on the distinct catalytic mechanisms (intra- vs. inter-molecular addition) provides important information to explain the results obtained.