Cofactor-Controlled Chirality of Tropoisomeric Ligand

Abstract

A new tropos ligand with an integrated anion receptor site has been prepared. Chiral carboxylate and phosphate anions that bind in the anion receptor unit proved capable of stabilizing chiral conformations of the achiral flexible bidentate biaryl phosphite ligand, as shown by variable temperature 1 H and 31 P NMR spectroscopical studies of palladium(0) olefin complexes. Palladium allyl complexes of the supramolecular ligand-chiral cofactor assemblies catalyzed asymmetric allylic substitutions of rac-(E)-1,3-diphenyl-2propenyl carbonate and rac-3-cyclohexenyl carbonate with malonate and benzylamine as nucleophiles to provide nonracemic products. Although moderate enantioselectivities were observed, (ee:s up to 66%), the results confirm the ability of the anionic guests to affect the conformation of the ligand.

Supramolecularly fine-regulated enantioselective catalysts

“…and Error! Reference source not found.. 35 The addition of an enantiopure acid derivative as the RA (or "cofactor" as referred to by the authors) broke the symmetry of the diamidodiindolylmethane fragment in ligand L14 and generated preferred conformations in the conformationally labile phosphite groups. NMR spectroscopy studies showed that hydrogen bonding between the NH groups in ligand L14 and the oxyanions was at the origin of the chirogenesis processes taking place.…”

Inducing Axial Chirality in a Supramolecular Catalyst

“…Rhodium and platinum complexes were analyzed through ac ombination of NMR studies,E SI-MS measurements,a sw ell as UV-VIS and circular dichroism spectroscopy. This transfer has been achieved by coordination of achiral co-ligand or anion, [7][8][9][10][11] or control of the backbone by acovalently bound chiral auxiliary (Scheme 1). [1][2][3][4] However, the asymmetric synthesis of such an inflexible (atropos) backbone is often long and difficult.…”

“…This transfer has been achieved by coordination of achiral co-ligand or anion, [7][8][9][10][11] or control of the backbone by acovalently bound chiral auxiliary (Scheme 1). [9,28] Also chiral phosphoric acids have been used for supramolecular stereoregulation through ion pairing in asymmetric catalysis. [17,18] In this manner, ab y-design nonlinear amplification of stereoselectivity was achieved.…”

“…[1][2][3][4] However, the asymmetric synthesis of such an inflexible (atropos) backbone is often long and difficult. This transfer has been achieved by coordination of achiral co-ligand or anion, [7][8][9][10][11] or control of the backbone by acovalently bound chiral auxiliary (Scheme 1). [5,6] In such adynamic system, the resolution into one of the diastereomers is dependent on transfer of chiral information from as tereoregulating unit.…”

“…[25,26] Theg roup of Reek demonstrated that stereocontrol in asupramolecular catalyst system could be achieved by either entrapment of the rhodium center in asupramolecular metallocage [27] or by molecular recognition of ac hiral cofactor in ab identate ligand. [9,28] Also chiral phosphoric acids have been used for supramolecular stereoregulation through ion pairing in asymmetric catalysis. [29,30] Our group has previously developed self-organizing ligand systems based on self-assembly of monodentate building blocks through hydrogen bonding (6-DPPon = 6-diphenylphosphino pyridone,see Scheme 2f or R = Ph and S* = H), [31] and these bidentate ligands were successfully employed in hydroformylation and hydrocyanation of alkenes.…”