Asymmetric Synthesis of <i>P</i>‑Stereogenic Diarylphosphinites by Palladium-Catalyzed Enantioselective Addition of Diarylphosphines to Benzoquinones

The reaction of phenyl­(2,4,6-tri­methyl­phenyl)­phosphine with a substituted benzoquinone in the presence of a chiral phosphapalladacycle complex as a catalyst and triethylamine in chloroform at −45 °C proceeded in a new type of addition manner to give a high yield of a 4-hydroxyphenyl phenyl­(2,4,6-tri­methyl­phenyl)­phosphinite with 98% enantioselectivity, which is a versatile intermediate readily convertible into various phosphines and their derivatives with high enantiomeric purity

Asymmetric Synthesis of <i>P</i>‑Stereogenic Diarylphosphinites by Palladium-Catalyzed Enantioselective Addition of Diarylphosphines to Benzoquinones

The reaction of phenyl­(2,4,6-tri­methyl­phenyl)­phosphine with a substituted benzoquinone in the presence of a chiral phosphapalladacycle complex as a catalyst and triethylamine in chloroform at −45 °C proceeded in a new type of addition manner to give a high yield of a 4-hydroxyphenyl phenyl­(2,4,6-tri­methyl­phenyl)­phosphinite with 98% enantioselectivity, which is a versatile intermediate readily convertible into various phosphines and their derivatives with high enantiomeric purity

Palladacycle-Catalyzed Asymmetric Hydrophosphination of Enones for Synthesis of C*- and P*-Chiral Tertiary Phosphines

A highly reactive and stereoselective hydrophosphination of enones catalyzed by palladacycles for the synthesis of C*- and P*-chiral tertiary phosphines has been developed. When Ph₂PH was employed as the hydrophosphinating reagent, a series of C*-chiral tertiary phosphines were synthesized (C*–P bond formation) in high yields with excellent enantioselectivities, and a single recrystallization provides access to their enantiomerically pure forms. When racemic secondary phosphines <i>rac</i>-R³(R⁴)­PH were utilized, a series of tertiary phosphines containing both C*- and P*-chiral centers were generated (C*–P* bond formation) in high yields with good diastereo- and enantioselectivities. The stereoelectronic factors involved in the catalytic cycle have been revealed

Metal Effects on the Asymmetric Cycloaddition Reaction between 3,4-Dimethyl-1-phenylphosphole and Sulfoxide

The orthometalated [1-(dimethylamino)­ethyl]­naphthalene platinum­(II) complex has been used successfully to promote the asymmetric cycloaddition reaction between 3,4-dimethyl-1-phenylphosphole and sulfoxide in high selectivity. The <i>exo</i>-cycloadduct coordinated to the platinum template as bidentate chelates via their phosphorus and sulfur atoms. The dichloro platinum complexes could be crystallized and were stable in the solid state as well as in solution. Optically pure P–S bidentate ligands could be liberated from these dichloro complexes by treatment with aqueous potassium cyanide. The study also highlights the difference in reactivity and mode of substrate activation between an earlier study involving a Pd analogue of the template and the current results

Asymmetric Synthesis of Enaminophosphines via Palladacycle-Catalyzed Addition of Ph₂PH to α,β-Unsaturated Imines

A highly reactive, chemo- and enantioselective addition of diphenylphosphine to α,β-unsaturated imines catalyzed by a palladacycle has been developed, thus providing the access to a series of chiral tertiary enaminophosphines in high yields. A putative catalytic cycle has also been proposed

Asymmetric Synthesis of Enaminophosphines via Palladacycle-Catalyzed Addition of Ph₂PH to α,β-Unsaturated Imines

A highly reactive, chemo- and enantioselective addition of diphenylphosphine to α,β-unsaturated imines catalyzed by a palladacycle has been developed, thus providing the access to a series of chiral tertiary enaminophosphines in high yields. A putative catalytic cycle has also been proposed

Versatile Syntheses of Optically Pure PCE Pincer Ligands: Facile Modifications of the Pendant Arms and Ligand Backbones

A series of chiral C-stereogenic PCP and PCN ligand precursors were prepared in situ from inexpensive achiral starting materials via a simple catalytic asymmetric P–H addition reaction in good overall yields. This facile catalytic method of preparing the ligand backbones renders easy and economical modifications of the electronically crucial <i>para</i>-substituent, chiral functionalities, and donor atoms for different transition metal ions. A one-pot synthetic procedure was used efficiently to prepare the corresponding optically pure pincer complexes. All the new complexes were characterized by NMR and mass spectroscopy. The molecular structures of several selected complexes have also been elucidated by X-ray crystallography. Preliminary studies indicated that minor structural changes on these novel pincer complexes affect their chemical properties significantly when they were applied as catalysts for the reaction between diphenylphosphine and chalcone

Asymmetric 1,4-Conjugate Addition of Diarylphosphines to α,β,γ,δ-Unsaturated Ketones Catalyzed by Transition-Metal Pincer Complexes

An enantioselective asymmetric 1,4-addition of diarylphosphines to linear α,β,γ,δ-unsaturated dienones was developed. A series of chiral PCP- and PCN-transition-metal (Pd, Pt and Ni) pincers, themselves prepared catalytically via asymmetric hydrophosphination, were sequentially screened to reveal the roles of backbone architecture and metal ion in catalyst design. The selected ester-functionalized PCP-palladium pincer afforded the chiral 1,4-phosphine adducts in excellent yields with up to >99% <i>ee</i>. The same catalyst when utilized for the hydrophosphination of an α,β,γ,δ-unsaturated malonate ester also revealed the critical role played by the ester functionality on the ligand backbone in dictating the enantioselectivity of the 1,6-adduct

Stereogenic Lock in 1‑Naphthylethanamine Complexes for Catalyst and Auxiliary Design: Structural and Reactivity Analysis for Cycloiridated Pseudotetrahedral Complexes

A series of optically active pseudo-tetrahedral five-membered cyclometalated 1-naphthylethanamine iridium­(III) complexes were prepared and characterized to analyze the efficacy of the stereogenic conformational lock in both solid and solution phases. The synthesis of the iridacycles was diastereoselective, and the compounds were found to be conformationally rigid. In comparison to its phenyl derivative, the structural lock prevented oxidation of the amine moiety within the five-membered organometallic ring during its synthesis. With up to three stereogenic centers in one of the naphthalene complexes, the stereochemistry of the metallacycle remained stable to both thermal and chemical changes. In terms of catalytic performance, the complexes displayed excellent activity for the asymmetric hydrogen transfer reaction, albeit with modest enantioselectivities

Synthesis of Stereoprojecting, Chiral N‑C(sp³)‑E Type Pincer Complexes

A synthetic strategy to generate chiral N-C­(sp³)-E (E = S, O) pincer complexes incorporating enhanced stereoprojecting groups at the N-arm site has been established. The synthesis of the tridentate pincer ligand was carried out via palladacycle-catalyzed asymmetric hydrophosphination of N-chelating enones. The chelation properties of the substrates were initially demonstrated on C­(sp²)-N type palladacycles. The extended substrate scope allows versatile structural modifications on the ligand backbone. Subsequent cyclometalation provided N-C­(sp³)-E complexes in a diastereoselective reaction