Proline‐Derived Aminotriazole Ligands: Preparation and Use in the Ruthenium‐Catalyzed Asymmetric Transfer Hydrogenation

Abstract

The preparation of 2-triazolyl-and 2-tri-A C H T U N G T R E N N U N G azolylmethylpyrrolidines from l-proline and l-trans-4-hydroxyproline is described, along with their evaluation as chiral ligands in ruthenium-catalyzed asymmetric transfer hydrogenation. Modular evolution of the ligands by introduction of remote substituents is also presented, showing a surprisingly important effect on the performance of the ligands.

Nickel complexes with “click”-derived pyridyl-triazole ligands: weak intermolecular interactions and catalytic ethylene oligomerisation

“…5 Thus a host of metal centers have been coordinated to such "Click" derived ligands, and the metal complexes have found use in electrochemical [6][7][8][9][10][11][12] and photochemical studies, [11][12][13][14][15][16] in supramolecular chemistry, [17][18][19][20][21] magnetism, 22,23 metal-ion sensing 4a,24 and catalysis. [25][26][27][28][29][30] We have recently investigated metal complexes of substituted 1,2,3-triazole ligands for their electrochemical properties, 31 magnetic bistability 32 and their application in homogenous catalysis. 33,34 In this context, substituted pyridyl-triazoles were used in combination with d 8 metal centers like Pd(II) and Pt(II) by us 31,35 and others.…”

A Bis(Triazolecarboxamido) Ligand for Enantio‐ and Regioselective Molybdenum‐Catalyzed Asymmetric Allylic Alkylation Reactions

“…Recently, enantiopure 2‐triazolylpyrrolidines derived from 4‐hydroxyproline have been used as ligands for Ru in the transfer hydrogenation of ketones (structure VI in Figure 1). Chelation in the catalytically active species necessarily involves the triazole moiety, and the reduction process takes place with high TOF and enantioselectivity 5a. Even in cases where the triazole moiety was supposed to act as an innocent bystander (structure VII in Figure 1), NMR studies and theoretical calculations indicate that chelation involving the triazole moiety is preferred over standard P,N ‐coordination and leads to very high enantioselectivity in Pd‐catalyzed asymmetric allylic amination 5b.…”

Catalytic asymmetric transfer hydrogenation of ketones: recent advances

“…Results were in general very good and DFT calculations could explain the obtained stereochemistry. 49 Another triazole-derived ligand 45 was the best one from a family of diamine derivatives able to act together with a Ru-carbonyl complex as catalyst for the ATH of phenones, isopropanol being the hydrogen source under basic conditions. When an aliphatic ketone was reduced, namely cyclohexyl methyl ketone, conversion was excellent (93%) but, as expected, enantioselectivity was very poor (13% ee).…”