Double stereoselective coordination of chiral N,S ligands: Synthesis, coordination chemistry and utilization in Pd-catalyzed allylic alkylation

Máté Miklós Major, Gergő Rövid, Szabolcs Balogh, Attila Bényei, György Lendvay, Dávid Frigyes, József Bakos, Gergely Farkas

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

A series of chiral pentane-2,4-diyl-based thioether-amine ligands [4 and 5; (R,S)- and (S,S)-R1SCH(CH3)CH2CH(CH3)NHR2, respectively, where 4a R1 = iPr, R2 = Ph; 4b R1 = tBu, R2 = Ph; 4c R1 = 1-Ad, R2 = Ph; 5a R1 = iPr, R2 = Ph; 5b R1 = tBu, R2 = Ph; 5c R1 = 1-Ad, R2 = Ph; 5d R1 = iPr, R2 = 4-MeOC6H4; 5e R1 = iPr, R2 = 4-MeC6H4; 5f R1 = iPr, R2 = 3,5-Me2C6H3] with stereogenic S- and N-donor atoms has been prepared starting from cyclic sulfates via optically pure γ-aminoalcohol or 2,4-dimethylazetidine intermediates. The synthesis of the novel diastereomerically related ligand sets 4 and 5 was accomplished starting from the same source of chirality. The modular ligand structure and the novel synthetic strategies developed for their synthesis allowed the easy modification of the ligands’ (i) S- and (ii) N-substituents, as well as (iii) the relative stereochemistry within the ligand backbone. Six-membered [Pd(N,S)Cl2]-type chelate complexes of the diastereomerically related ligands 4a and 5a were synthesized and characterized by X-ray crystallography in the solid phase, by density functional theory calculations and in solution by NMR spectroscopy. The coordination of 5a resulted in the formation of a single chair conformation by the stereospecific locking of both stereolabile (N and S) donor atoms. In contrast, compound 4a forms rapidly equilibrating palladium species due to the fast inversion of the sulfur donor. Ligands with stereochemically fixed donor atoms provided robust and efficient catalytic systems that can be effectively applied in alkylene carbonates as green reaction media. Remarkably, the phosphine-free catalysts are air-stable, and at room temperature in the presence of moisture gave excellent ee’s (up to 93%) in asymmetric allylation processes thanks to the double stereoselective coordination.

Original languageEnglish
Article numbere4726
JournalApplied Organometallic Chemistry
Volume33
Issue number2
DOIs
Publication statusPublished - Feb 2019

Keywords

  • N
  • S-ligands
  • asymmetric catalysis
  • stereoselective coordination

ASJC Scopus subject areas

  • Chemistry(all)
  • Inorganic Chemistry

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