Double stereoselective coordination of chiral N, S ligands: Synthesis, coordination chemistry and utilization in Pd‐catalyzed allylic alkylation. (21st December 2018)

• Record Type: Journal Article
• Authors: Major, Máté Miklós; Rövid, Gergő; Balogh, Szabolcs; Bényei, Attila; Lendvay, György; Frigyes, Dávid; Bakos, József; Farkas, Gergely
• Is Part Of: Applied organometallic chemistry. Volume 33:Number 2(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-12-21
• Subjects: asymmetric catalysis -- N -- S‐ligands -- stereoselective coordination; Organometallic chemistry -- Periodicals; Organometallic compounds -- Periodicals; 547.05
• DOI: 10.1002/aoc.4726
• Languages: English
• ISSNs: 0268-2605

Abstract

Abstract : A series of chiral pentane‐2, 4‐diyl‐based thioether‐amine ligands [4 and5 ; ( R, S )‐ and ( S, S )‐R 1 SCH(CH3 )CH2 CH(CH3 )NHR 2, respectively, where4a R 1 = i Pr, R 2 = Ph;4b R 1 = t Bu, R 2 = Ph;4c R 1 = 1‐Ad, R 2 = Ph;5a R 1 = i Pr, R 2 = Ph;5b R 1 = t Bu, R 2 = Ph;5c R 1 = 1‐Ad, R 2 = Ph;5d R 1 = i Pr, R 2 = 4‐MeOC6 H4 ;5e R 1 = i Pr, R 2 = 4‐MeC6 H4 ;5f R 1 = i Pr, R 2 = 3, 5‐Me2 C6 H3 ] 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 sets4 and5 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 ligands4a and5a 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 of5a resulted in the formation of a single chair conformation by the stereospecific locking of both stereolabile (N and S) donor atoms. In contrast, compound4a 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. Abstract : The unprecedented double stereoselective coordination of robust N, S‐type ligands resulted in high ee 's in asymmetric allylation reaction using green reaction media.