Enantioselective Addition of Secondary Phosphines to Methacrylonitrile: Catalysis and Mechanism

Enantioselective Hydrophosphination of Terminal Alkenyl Aza-Heteroarenes

This paper presents a Mn(I)-catalysed methodology for the enantioselective hydrophosphination of terminal alkenyl aza-heteroarenes. The catalyst operates through H-P bond activation, enabling successful hydrophosphination of a diverse range of alkenyl-heteroarenes with high enantioselectivity. The presented protocol addresses the inherently low reactivity and the commonly encountered suboptimal enantioselectivities of these challenging substrates. As an important application we show that this method facilitates the synthesis of a non-symmetric tridentate P,N,P-containing ligand like structure in just two synthetic steps using a single catalytic system.

Copper(I)-Catalyzed Asymmetric Hydrophosphination of 3,3-Disubstituted Cyclopropenes

Herein, a copper(I)-catalyzed asymmetric hydrophosphination of 3,3-disubstituted cyclopropenes is reported. It provides a series of phosphine derivatives in high to excellent diastereo- and enantioselectivities. The methodology enjoys broad substrate scope on both 3,3-disubstituted cyclopropenes and diarylphosphines. The high stereoselectivity is attributed to both the high stability of the Cu(I)-(R,R)-QUINOXP* complex in the presence of stoichiometric HPPh2 and the produced phosphines, and the high-performance asymmetric induction of the Cu(I)-(R,R)-QUINOXP* complex. Finally, the method is used for the synthesis of new chiral phosphine-olefin compounds built on a cyclopropane skeleton, one of which serves as a wonderful ligand in Rh-catalyzed asymmetric conjugate addition of phenylboronic acid to various α,β-unsaturated compounds.

Manganese(I)-Catalyzed Asymmetric Hydrophosphination of α,β-Unsaturated Carbonyl Derivatives

Here we report catalytic asymmetric hydrophosphination of α,β-unsaturated carbonyl derivatives using a chiral Mn(I) complex as a catalyst. Through H-P bond activation, various phosphine-containing chiral products can be accessed via hydrophosphination of various ketone-, ester-, and carboxamide-based Michael acceptors.

Enantioselective copper-catalyzed hydrophosphination of alkenyl isoquinolines

An enantioselective Cu-catalyzed hydrophosphination of alkenyl quinolines was developed to access a variety of potential chiral bidentate P,N-ligands.

Сatalytic Asymmetric Synthesis of C-Chiral Phosphonates

The current review is devoted to the achievements in the development of methods for the catalytic asymmetric synthesis of phosphonates containing a chiral center in the side chain. C-chiral phosphonates are widely represented among natural compounds with various biological activities as insecticides, herbicides, antibiotics, and bioregulators. Synthetic representatives of this class have found practical application as biologically active compounds. The review summarizes methods of asymmetric metal complex catalysis and organocatalysis as applied to such reactions as phospha-aldol reaction, two-component and three-component phospha-Mannich reaction, phospha-Michael reaction, as well as hydrogenation of unsaturated phosphonates and phosphine oxides, ketophosphonates, and iminophosphonates. Methods for the asymmetric hydride reduction of C=X phosphonates (X=O, S, NR) are also discussed in detail. The review presents updated literature reports, as well as original research by the author.

Broken Promises? On the Continued Challenges Faced in Catalytic Hydrophosphination

In this Perspective, we discuss what we perceive to be the continued challenges faced in catalytic hydrophosphination chemistry. Currently the literature is dominated by catalysts, many of which are highly effective, that generate the same phosphorus architectures, e.g., anti-Markovnikov products from the reaction of activated alkenes and alkynes with diarylphosphines. We highlight the state of the art in stereoselective hydrophosphination and the scope and limitations of chemoselective hydrophosphination with primary phosphines and PH₃. We also highlight the progress in the chemistry of the heavier homologues. In general, we have tried to emphasize what is missing from our hydrophosphination armament, with the aim of guiding future research targets.

Direct visible-light-induced synthesis of P-stereogenic phosphine oxides under air conditions

Over the past two decades, visible-light-induced transformations have been regarded as being among the most environmentally benign and powerful strategies for constructing complex molecules and diverse synthetic building blocks in organic synthesis. However, the development of efficient photochemical processes for assembling enantiomerically pure molecules remains a significant challenge. Herein, we describe a simple and efficient visible-light-induced C-P bond forming reaction for the synthesis of P-chiral heteroaryl phosphine oxides in moderate to high yields with excellent ee values (97-99% ee). Even in the absence of transition metal or photoredox catalysts, a variety of P-chiral heteroaryl phosphine oxides, including chiral diphosphine oxide 41, have been directly obtained under air conditions. Density functional theory (DFT) calculations have shown that the reaction involves intersystem crossing and single electron transfer to give a diradical intermediate under visible light irradiation.

Manganese(i)-catalyzed access to 1,2-bisphosphine ligands

Chiral bisphosphine ligands are of key importance in transition-metal-catalyzed asymmetric synthesis of optically active products. However, the transition metals typically used are scarce and expensive noble metals, while the synthetic routes to access chiral phosphine ligands are cumbersome and lengthy. To make homogeneous catalysis more sustainable, progress must be made on both fronts. Herein, we present the first catalytic asymmetric hydrophosphination of α,β-unsaturated phosphine oxides in the presence of a chiral complex of earth-abundant manganese(i). This catalytic system offers a short two-step, one-pot synthetic sequence to easily accessible and structurally tunable chiral 1,2-bisphosphines in high yields and enantiomeric excess. The resulting bidentate phosphine ligands were successfully used in asymmetric catalysis as part of earth-abundant metal based organometallic catalysts.

Chiral bisphosphine ligands are of key importance in transition-metal-catalyzed asymmetric synthesis of optically active products. Mn(i)-catalyzed hydrophosphination offers a two-step, one-pot synthetic sequence to access chiral 1,2-bisphosphines.

Manganese(I)-Catalyzed H-P Bond Activation via Metal-Ligand Cooperation

Here we report that chiral Mn(I) complexes are capable of H–P bond activation. This activation mode enables a general method for the hydrophosphination of internal and terminal α,β-unsaturated nitriles. Metal−ligand cooperation, a strategy previously not considered for catalytic H–P bond activation, is at the base of the mechanistic action of the Mn(I)-based catalyst. Our computational studies support a stepwise mechanism for the hydrophosphination and provide insight into the origin of the enantioselectivity.

Carbene-Catalyzed Enantioselective Hydrophosphination of α-Bromoenals to Prepare Phosphine-Containing Chiral Molecules

Disclosed herein is the first carbene-organocatalyzed asymmetric addition of phosphine nucleophiles to the in situ generated α,β-unsaturated acyl azolium intermediates. Our reaction enantioselectively constructs carbon-phosphine bonds and prepares chiral phosphines with high optical purities. The phosphine products are suitable for transforming to chiral ligands or catalysts with applications in asymmetric catalysis. The diarylalkyl or trialkyl phosphine products from our catalytic reactions, air-sensitive and reactive in nature, can be trapped (and stored) in their sulfur-oxidized form for operational simplicities.

Nickel Complexes in C‒P Bond Formation

This review is a comprehensive account of reactions with the participation of nickel complexes that result in the formation of carbon-phosphorus (C‒P) bonds. The catalytic and non-catalytic reactions with the participation of nickel complexes as the catalysts and the reagents are described. The various classes of starting compounds and the products formed are discussed individually. The several putative mechanisms of the nickel catalysed reactions are also included, thereby providing insights into both the synthetic and the mechanistic aspects of this phosphorus chemistry.

Diverse C-P Cross-Couplings of Arylsulfonium Salts with Diarylphosphines via Selective C-S Bond Cleavage

Diverse C-P cross-couplings of arylthianthrenium salts with diarylphosphines producing various triarylphosphines via highly selective C-S bond cleavage are reported. In the absence of catalyst, the reaction of arylthianthrenium salts with diarylphosphines undergoes phosphinative ring opening exclusively via the cleavage of an endocyclic C-S bond of a thianthrene skeleton. The use of a palladacycle catalyst under otherwise the same conditions enables the phosphination via the cleavage of an exocyclic C-S bond with significantly higher speed.

Synthesis and characterization of enantiopure planar-chiral phosphorus-linked diferrocenes

Six new homochiral diferrocenyl derivatives have been synthesized, one of which is purely planar–chiral. Even if the two diferrocene subunits are identical, they are distinguished due to their positions relative to the substituents at the phospho­rous prochiral centre.

In the course of an ongoing synthetic project on cyclic diferrocenylphosphines, we obtained a group of planar–chiral diferrocenyl com­pounds useful as precursors for subsequent cyclization. Here we report the crystal structures of two sym­metric com­pounds [(Fc^A)₂(Ph)P], one of which contains four stereogenic centres (two C chiral and two planar chiral centres), i.e. 1,1′-(phenyl­phos­phane­di­yl)bis­{(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferrocene}, [Fe₂(C₅H₅)₂(C₂₄H₂₅O₄P)], and the other phosphine sulfide is a purely planar–chiral com­pound (two planar chiral centres), i.e. bis[(2S_p)--2-ethenylferrocen-1-yl]phenylphosphane sulfide, [Fe₂(C₅H₅)₂(C₂₀H₁₇PS)]. Owing to the stereocentres present, reactions performed on [(Fc^A)₂(Ph)P]-type com­pounds strongly favour one ferrocene unit over the other due to diastereoselectivity. Furthermore, we present four related structures where the ferrocene units are not identical [(Fc^A)(Fc^B)(Ph)P]. These are {(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferrocen-1-yl}[(2S_p)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₂H₂₁O₂PS)], [(2S_p)-2-ethenylferrocen-1-yl]{(2S_p)-2-[(1R)-1-hy­droxy­eth­yl]ferrocen-1-yl}phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₀H₁₉OPS)], {(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferro­cen-1-yl}{(2S_p)-2-[(1R)-1-hy­droxy­eth­yl]ferrocen-1-yl}phenyl-(R)-phos­phine sulfide, [Fe₂(C₅H₅)₂(C₂₂H₂₃O₃PS)], and {(2S_p)-2-[(1R)-1-benzyl­amino)­eth­yl]ferrocen-1-yl}[(2S_p)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₇H₂₆NPS)]. All of the structures are accessible in one step from known precursors.

Organocatalytic 1,6-hydrophosphination of para-quinone methides: enantioselective access to chiral 3-phosphoxindoles bearing phosphorus-substituted quaternary carbon stereocenters

An efficient organocatalytic enantioselective 1,6-hydrophosphonylation of para-quinone methides has been achieved for the construction of phosphorus-substituted quaternary carbon stereocenters.

Planar-Chiral P and N-bridged Diferrocenes

We describe the synthesis of planar-chiral diferrocene compounds 4, 7 and 12, intended as key precursors for a new family of asymmetric catalyst ligands with less complex structures than their popular equivalents. In contrast to conventional 1,2-disubstituted ferrocenes containing center-chiral and planar-chiral elements, these compounds are purely planar-chiral due to the absence of α-substiuted ethyl groups. The title compounds 4, 7 and 12 were obtained from known precursors in 87%, 59% and 60% yields, respectively.

Synthesis of P-chiral phosphine compounds by palladium-catalyzed C–P coupling reactions

An efficient C–P coupling reactions of enantiopure tert-butylmethylphosphine-boranes with aryl and heteroaryl halides is developed by using Pd(OAc)₂/dppf as a catalyst, affording a series of P-chiral phosphines (up to 99% ee).

Catalytic and Mechanistic Developments of the Nickel(II) Pincer Complex-Catalyzed Hydroarsination Reaction

Synthetic challenges have significantly slowed the development of the catalytic asymmetric hydroarsination reaction despite it being a highly attractive C-As bond formation methodology. In addition, there is a poor understanding of the main reaction steps in such reactions which limit further development in the field. Herein, key intermediates of the hydroarsination reaction catalyzed by a PCP Ni^II -Cl pincer complex are presented upon investigating the reaction with DFT calculations, conductivity measurements, NMR spectroscopy, and catalytic screening. The novel Ni-Cl-As interaction proposed was then contrasted against known Ni^II -catalyzed hydrophosphination reactions to highlight dissimilarities between them even though P and As share a close group relationship. Lastly, the asymmetric hydroarsination of nitroolefins was further developed to furnish a library of chiral organoarsines in up to 99 % yield and 80 % ee under mild conditions (-20 °C to RT) between 5 to 210 mins.

A Nucleophilicity Scale for the Reactivity of Diazaphospholenium Hydrides: Structural Insights and Synthetic Applications

Nucleophilicity parameters (N, s_N ) of a group of representative diazaphospholenium hydrides were derived by kinetic investigations of their hydride transfer to a series of reference electrophiles with known electrophilicity (E) values, using the Mayr equation log k₂ =s_N (N+E). The N scale covers over ten N units, ranging from the most reactive hydride donor (N=25.5) to the least of the scale (N=13.5). This discloses the highest N value ever quantified in terms of Mayr's nucleophilicity scales reported for neutral transition-metal-free hydride donors and implies an exceptional reactivity of this reagent. Even the least reactive hydride donor of this series is still a better hydride donor than those of many other nucleophiles such as the C-H, B-H, Si-H and transition-metal M-H hydride donors. Structure-reactivity analysis reveals that the outstanding hydricity of 2-H-1,3,2-diazaphospholene benefits from the unsaturated skeleton.

Room Temperature Ni(II) Catalyzed Hydrophosphination and Cyclotrimerization of Alkynes

The catalytic activity of nickel complexes in hydrophosphination involving secondary phosphines is not a commonly studied transformation. Beyond a small number of stand-out examples, many reports in the literature focus on the use of simple nickel salts. β-Diketiminates have been proven to be incredibly effective ligands for catalysis using a range of metal centers. This synthetic study investigates the catalytic ability of a Ni(II) β-diketiminate complex in the hydrophosphination of alkenes and alkynes, with a serendipitous discovery of its ability to effect alkyne cyclotrimerization and phosphine dehydrocoupling.

Rhodium-Catalyzed Enantioposition-Selective Hydroarylation of Divinylphosphine Oxides with Aryl Boroxines

The rhodium-catalyzed hydroarylation of divinylphosphine oxides (RP(O)(CH=CH₂ )₂ ) with aryl boroxines ((ArBO)₃ ) gives the corresponding monoarylation products (RP(O)(CH=CHAr)CH₂ CH₃ ) in high yields. One of the two vinyl groups in the phosphine oxide undergoes oxidative arylation while the other one is reduced to an ethyl moiety. These reactions proceed with high selectivity in terms of the enantiotopic vinyl groups in the presence of (R)-DTBM-segphos/Rh to give the P-stereogenic monoarylation products with high enantioselectivity.

From Mechanistic Study to Chiral Catalyst Optimization: Theoretical Insight into Binaphthophosphepine-catalyzed Asymmetric Intramolecular [3 + 2] Cycloaddition

Density functional M11 was used to study the mechanism and enantioselectivity of a binaphthophosphepine-catalyzed intramolecular [3 + 2] cycloaddition reaction. The computational results revealed that this reaction proceeds through nucleophilic addition of the phosphine catalyst to the allene, which yields a zwitterionic phosphonium intermediate. The subsequent stepwise [3 + 2] annulation process, which starts with the intramolecular nucleophilic addition of the allenoate moiety to the electron-deficient olefin group, determines the enantioselectivity of the reaction. This step is followed by a ring-closing reaction and water-assisted proton-transfer process to afford the final product with concomitant regeneration of the phosphine catalyst. Theoretical predictions of the enantioselectivity for various phosphine catalysts were consistent with experimental observations, and 2D contour maps played an important role in explaining the origin of the enantioselectivity. Moreover, on the basis of our theoretical study, new binaphthophosphepine catalysts were designed and that are expecting to afford higher enantioselectivity in this cycloaddition reaction.

Nickel catalyzed enantioselective hydroarsination of nitrostyrene

A catalytic asymmetric hydroarsination reaction of an activated alkene viz. (E)-nitrostyrene was developed using chiral PCP Pt-, Pd- and Ni-pincer complexes as catalysts. The corresponding chiral tertiary arsine adduct was obtained in ees of up to 80% under mild reaction conditions using the PCP Ni-Cl pincer catalyst. The arsine adduct was furnished with catalyst loadings of 1-5 mol% and the reaction duration ranging from <5 min to 180 min. The subsequent coordination of the hydroarsination product to gold(i) chloride allowed for the confirmation of the stereochemistry of the arsine adduct via crystallographic analysis.

Synthesis, characterization and catalytic activity of rare-earth metal amides incorporating cyclohexyl bridged bis(β-diketiminato) ligands

The bridged bis(β-diketiminato) ligands supported rare-earth amides exhibited high catalytic activity towards the hydrophosphination of β-nitroalkene and α,β-unsaturated carbonyl derivatives with an excellent regioselectivity.

Synthesis and molecular structures of divalent bridged bis(guanidinate) europium complexes and their application in intermolecular hydrophosphination of alkenes and alkynes

Bimetallic Eu^IIcomplexes supported by bridged bis(guanidinate) ligands are efficient precatalysts for the intermolecular hydrophosphination of alkenes and alkynes.

Computational assessment of electron density in metallo-organic nickel pincer complexes for formation of PC bonds

Hydrophosphination is an atomically efficient method for introducing new carbon-phosphorous bonds in organic synthesis. New late-transition metal catalytic complexes are proposed to facilitate this process. These nickel-based complexes are analyzed using semiempirical (SE), Hartree-Fock (H-F), and density functional theory (DFT) models. H-F proves to be ineffective, while the SE approach has limited, qualitative use. DFT shows electron density at the metal center suitable for catalyzing bond formation in the proposed, reductive hydrophosphination mechanism. It also shows that the pincer complexes under investigation are relatively insensitive to solvent dielectric constant and to the chemical character of the monodentate ligand, both in terms of electron distribution and in terms of molecular orbital energies.