Synthesis of a New ChiralN,N,N-Tridentate Pyridinebisimidazoline Ligand Library and Its Application in Ru-Catalyzed Asymmetric Epoxidation

Abstract

A small ligand library of chiral tridentate N,N,N-pyridinebisimidazolines have been synthesized for the first time. This new class of ligands can be easily tuned and synthesized on multi g-scale. The usefulness of the ligands is shown in the ruthenium-catalyzed asymmetric epoxidation with hydrogen peroxide as oxidant. Excellent yields (>99%) and good enantioselectivities (up to 71% ee) have been obtained for the epoxidation of aromatic olefins. [reaction: see text]

Synthesis and catalytic application of novel binaphthyl-derived phosphorous ligands

“…After stirring the mixture for 2 h at room temperature and filtration of the precipitate the solvent is evaporated. The crude product is crystallized from ethanol/hexane (1) or THF/hexane (2). General procedure for the synthesis of 9 and 10 A suspension of 1 equiv.…”

Highly Diastereoselective Synthesis of 2,6‐Di[1‐(2‐alkylaziridin‐1‐yl)alkyl]pyridines, Useful Ligands in Palladium‐Catalyzed Asymmetric Allylic Alkylation

“…+ salts bearing the (S)-valinol-and (S)-phenylglycinol-derived ligands, 10ae' and 10ba', with PF 6 , SbF 6 or BF 4 counterions, were prepared by standard methodology. These salts were generally obtained as white or yellowish powders, and some of them appeared impure by 1 H NMR analysis.…”

“…[17] It was therein shown that terpyridine binds the (h 1 -allyl)Pd + fragment in the terdentate fashion and (h 3 -allyl)Pd + as a bidentate ligand. In fact, the two species are present both in the crystal and in a CD 2 Cl 2 solution in a dynamic equilibrium, which is strongly displaced towards the h 4 ] adopts the terdentate coordination mode both in the crystal and in solution, where the complex is fluxional through h 1 -h 3 equilibrium processes. [18,19] This is in contrast to the behaviour of (N,P,N) ligands which act as (P,N)-bidentate ligands in (h 3 -dimethylallyl)Pd + complexes.…”

“…The pyridine ring is present in most compounds of this type (Figure 1), where it has the role of a spacer between two identical N-containing moieties, e.g., the widely used, high-performing pyridine-bis(oxazolines) 1 (Pyboxs) [2] as well as the more recently developed pyridine-bisA C H T U N G T R E N N U N G (oxazines) (Pyboxazines) ligands 2 [3] and pyridine-bis(imidazolidines) 3. [4] Both ligands 1 and 2 are readily prepared from 2,6-pyridinedicarboxylic acids and enantiopure b-and gamino alcohols, respectively, without the need to construct new stereocenters. Pyridinediimines 4, which are similarly prepared from 2,6-pyridinedicarbaldehyde, have been also used as ligands in metal-catalyzed asymmetric reactions.…”

Ru(II) pyridyl-based NNN complex catalysts for (asymmetric) transfer hydrogenation of ketones at room temperature

“…Chiral imidazolines have been used in a number of applications in asymmetric synthesis [33], among which bidentate phosphine imidazolines have been used in the enantioselective hydrogenation of olefins [34] and allylic substitutions [35], tridentate benzene-bis(imidazolinyl) palladium complexes in asymmetric aza-Morita-Baylis-Hillman reactions [36] and Friedel-Crafts alkylations [37], and pyridinebisimidazoline NNN ligands in ATH [38], asymmetric epoxidation [39] and Henry reactions [40]. Herein, we report the synthesis of Ru(II) complexes bearing a tridentate NNN ligand containing benzimidazolyl and imidazolinyl moieties.…”