Access to a Chiral Phosphine–NHC Palladium(II) Complex via the Asymmetric Hydrophosphination of Achiral Vinyl Azoles

Abstract

Enantioenriched phosphine azoles were synthesized in high yields via palladium-catalyzed asymmetric hydrophosphination with excellent yields and enantioselectivities under mild reaction conditions. One of the phosphine azoles was methylated and complexed to palladium(II) cleanly to give a chiral phosphine−NHC palladium(II) complex with excellent overall conversion.

Chelating Phosphine–N-Heterocyclic Carbene Platinum Complexes via Catalytic Asymmetric Hydrophosphination and Their Cytotoxicity Toward MKN74 and MCF7 Cancer Cell Lines

“…In a preliminary proof-of-concept biological study to probe the potential benefits associated with the novel molecular scaffold as anticancer drugs, a series of nine racemic phosphine–NHC platinum­(II) complexes was synthesized from the corresponding vinyl azoles using ( rac )-[Pd]. Similar to our previously reported synthetic protocol, the phosphine azoles were methylated and directly coordinated to bis (acetonitrile)­platinum­(II) chloride (Table ). Interestingly, the coordination between the phosphine azolium cation derived from 1a and PtCl 2 (NCMe) 2 gave rise to a new pair of resonance singlets at 26.39 and 25.81 ppm with equal intensities in the 31 P­{ 1 H} NMR spectrum.…”

“…Using the same synthetic route previously reported by our group, a series of nine new vinyl azoles were synthesized from benzaldehyde and its derivatives (Scheme ). These vinyl azoles were hydrophosphinated in the presence of a chiral palladacyle and TMEDA to afford enantioenriched phosphine azoles.…”

“… a Reactions were carried out with diphenylphosphine (0.0575 mmol), ( R )-[Pd] (2.5 mol %), and TMEDA (0.0575 mmol) in CH 2 Cl 2 (2 mL) and the listed vinyl azoles (0.0575 mmol) before being oxidized with 30% w/w aqueous hydrogen peroxide at the stated temperature (optimized). b The reaction was carried out at −78 °C for 8 h (reported) c Isolated yield. d Determined by chiral HPLC. …”

“…Interestingly, the Pt–Cl trans to the phosphine was significantly longer, at 2.371 Å, than the Pt–Cl trans to the NHC, at 2.349 Å. Since NHCs are known to exert a stronger trans influence than phosphines, this unexpected difference in bond length could be attributed to the steric repulsion induced by the methyl group on the NHC pendant arm since this group pointed directly into the coordination sphere, a unique steric feature of NHCs that has also been observed in another previously reported palladium analogue …”

Metal-free synthesis of β-aminoketones by the reductive hydroamination of ynones

“…2A). 10 The direct hydroboration products also could be obtained when employing HBpin as reducing agents to react with alkynes in the presence of metal catalysts (Fig. 2B).…”