P-Stereogenic PCP Pincer–Pd Complexes: Synthesis and Application in Asymmetric Addition of Diarylphosphines to Nitroalkenes

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.

Synthesis and Characterization of Palladium Pincer Bis(carbene) CCC Complexes

The metalation of the DIPPCCC (DIPPCCC = bis(diisopropylphenyl-imidazol-2-ylidene)phenyl) ligand platform with Pd was achieved under mild conditions by reacting [H3(DIPPCCC)]Cl2 with Pd(OAc)2 at room temperature in the presence of 3.1 equiv of LiN(SiMe3)2. The resulting complexes (DIPPCCC)PdX (X = Cl or Br) were oxidized by two-electron oxidants PhICl2, Br2, and BTMABr3. All the complexes were crystallographically characterized, and analysis of structural parameters around the ligand scaffold show no evidence of a ligand-centered radical, rendering the metal center in the oxidized species, (DIPPCCC)PdX3 (X = Cl or Br), a formal PdIV oxidation state. Unlike their NiIV analogues, these PdIV complexes are stable to air and moisture. The addition of styrene to (DIPPCCC)PdBr3 resulted in the clean reduction of PdIV to PdII, along with the formation of the halogenated alkane. The oxidation to PdIV and subsequent return to PdII upon reduction, as opposed to formation of PdIII species, showcases the accessibility of high-valent palladium DIPPCCC complexes.

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.

Lipase-Catalyzed Phospha-Michael Addition Reactions under Mild Conditions

Organophosphorus compounds are the core structure of many active natural products. The synthesis of these compounds is generally achieved by metal catalysis requiring specifically functionalized substrates or harsh conditions. Herein, we disclose the phospha-Michael addition reaction of biphenyphosphine oxide with various substituted β-nitrostyrenes or benzylidene malononitriles. This biocatalytic strategy provides a direct route for the synthesis of C-P bonds with good functional group compatibility and simple and practical operation. Under the optimal conditions (styrene (0.5 mmol), biphenyphosphine oxide (0.5 mmol), Novozym 435 (300 U), and EtOH (1 mL)), lipase leads to the formation of organophosphorus compounds in yields up to 94% at room temperature. Furthermore, we confirm the role of the catalytic triad of lipase in this phospha-Michael addition reaction. This new biocatalytic system will have broad applications in organic synthesis.

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.

Chiral (phosphine)-(imidazoline) PCN pincer palladium(II) complexes: synthesis and application in asymmetric hydrophosphination of 2-alkenoylpyridines with diphenylphosphine

A series of new chiral PCN pincer Pd(II) complexes 3a−l with aryl-based (phosphine)-(imidazoline) ligands were conveniently synthesized from readily available starting materials with the key step being phosphination/C−H palladation reaction....

Racemization mechanism of lithium tert-butylphenylphosphido-borane: A kinetic insight

The racemization mechanism of tert-butylphenylphosphido-borane is investigated experimentally and theoretically. Based on this converging approach, it is shown, first, that several phosphido-borane molecular species coexist at the time of the reaction and, second, that one particular of both initially assumed reactive routes most significantly contribute to the overall racemization process. From our converging modeling and experimental measurement, it comes out that the most probable species to be here encountered is a phosphido-borane-Li (THF)₂ neutral solvate, whose P-stereogenic center monomolecular inversion through a Y-shaped transition structure (Δ_r G°^≠ : 81 kJ mol^-1 ) brings the largest contribution to the racemization process.

Ruthenium-Catalyzed Enantioselective Propargylic Phosphinylation of Propargylic Alcohols with Phosphine Oxides

The development of transition metal-catalyzed enantioselective propargylic substitution reactions has gained much progress in recent years, however, no successful example with phosphorus-centered nucleophiles has yet been reported until now. Herein, we report the first successful example of ruthenium-catalyzed enantioselective propargylic substitution reactions of propargylic alcohols with diarylphosphine oxides as phosphorus-centered nucleophiles. This synthetic approach provides a new method to prepare chiral phosphorus-containing organic compounds.

Synthesis and application in asymmetric catalysis of P-stereogenic pincer–metal complexes

P-stereogenic pincer: synthesis and application in asymmetric catalysis.

Chiral palladium pincer complexes for asymmetric catalytic reactions

Palladium pincer complexes, containing a monoanionic terdentate ligand composed of an anionic aryl carbon atom and two mutually compatible donor sites, have aroused considerable interest since their first reports in the late 1970s. The high stability of the Pd pincer complexes and particularly their high modularity make these species ideal candidates for catalysis. Furthermore, the nature of the meridional coordination of the pincer ligands, and along with this their ability to enforce a stereo-specific environment around the Pd center, provide a good opportunity for developing chiral Pd pincer catalysts. Thus, a broad variety of chiral Pd pincer complexes have been prepared by the introduction of various stereochemical centers in the pincer skeletons. These chiral Pd pincer complexes have been successfully applied to many asymmetric catalytic reactions such as hydrophosphination reactions, allylation of aldehydes and imines, Michael and aldol reactions, Suzuki-Miyaura reactions as well as reactions of nitrile compounds with imines. This review focuses on the synthetic methods and the applications of chiral Pd pincer complexes in asymmetric catalysis.

Investigating palladium pincer complexes in catalytic asymmetric hydrophosphination and hydroarsination

Given the periodic relationship of phosphines and arsines, is remodeling the catalytic asymmetric hydrophosphination reaction an efficient manner to develop the corresponding hydroarsination reaction? Herein, a chiral PCP-Pd(ii) pincer complex adept at generating enantioenriched phosphines was examined in the asymmetric hydroarsination reaction. Under distinct conditions, tertiary phosphines and arsines were generated in excellent yields (P: 96%, As: 91%) and ees (P: 90%, As: 85%). While secondary arsine reagents were not direct substitutes for the analogous phosphines, important parameters were identified which increased yield and ee of the hydroarsination reaction. Unlike the PCP-PdOAc pincer complex commonly used for hydrophosphinations, hydroarsination reactions involved a PCP-PdCl catalyst with 10 equiv. of CsF for optimal performance. Notable differences between the two reactions and their workup procedures were highlighted to guide further developments in the field. Lastly, respective mechanisms were proposed and contrasted for the activation of HEPh2 (E = P, As).

Which future for stereogenic phosphorus? Lessons from P* pincer complexes of iron(ii)

Locking the chelate conformation and supplying steric bulk for enantiodiscrimination: a tough task for stereogenic phosphorus in multidentate ligands.

Recent Advances in Metal-Catalyzed Asymmetric 1,4-Conjugate Addition (ACA) of Nonorganometallic Nucleophiles

The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

Synthesis and coordination chemistry of new asymmetric donor/acceptor pincer ligands, 1,3-C6H4(CH2PtBu(Rf))2 (Rf = CF3, C2F5)

Syntheses of new asymmetric pincer precursors 1,3-C₆H₄{CH₂P(^tBu,X)}₂ (^tBu,XPCPH; X = Cl, SiMe₃, OPh) and a new class of hybrid donor/acceptor pincer ligands 1,3-C₆H₄{CH₂P(^tBu,R_f)}₂ (^tBu,RfPCPH; R_f = CF₃, C₂F₅) are reported.

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.

Computational and carbon-13 NMR studies of Pt-C bonds in P-C-P pincer complexes

A (13)C{(1)H} NMR based investigation was conducted to examine the electronic properties of C(aryl)-M bonds and their trans influence in P-C(aryl)-P pincer complexes. A series of structurally related platinum pincer complexes were rationally designed and their corresponding (13)C-(195)Pt coupling constants were systematically examined. By methodical substitution of the ligand trans to the organometallic C(aryl)-Pt bond, this study revealed the significant influence of the ligands on the nature of the C(aryl)-M bonds. The single crystal X-ray analysis of the complexes and computational studies further confirmed the observations that the C-M bond exhibits significant π-character.

Applications and stereoselective syntheses of P-chirogenic phosphorus compounds

This review reports the best stereoselective or asymmetric syntheses, the most efficient P*-building blocks and functionalisation of P-chirogenic compounds, in the light of chiral phosphorus compound applications.

Heterometallic rare-earth metal complexes with imino-functionalized 8-hydroxyquinolyl ligands: synthesis, characterization and catalytic activity towards hydrophosphinylation of trans-β-nitroalkene

The heterobimetallic complexes exhibited high catalytic activities on the hydrophosphinylation of β-nitroalkenes.

P-stereogenic PNP pincer-Pd catalyzed intramolecular hydroamination of amino-1,3-dienes

A new P-stereogenic PNP pincer-Pd complex was readily prepared and was used in the asymmetric intramolecular hydroamination of amino-1,3-dienes, with the desired products being obtained in good yields and with excellent regioselectivities and up to moderate enantioselectivities.