An Investigation into the Tether Length and Substitution Pattern of Arene-Substituted Complexes for Asymmetric Transfer Hydrogenation of Ketones

Abstract

A series of Ru(II) catalysts were prepared and tested in the asymmetric transfer hydrogenation of ketones. The catalyst containing a "4-carbon" tether gave the fastest rates of ketone reduction. This is due to both increased rate of regeneration of hydride "Ru-H" and increased rate of ketone reduction. Several classes of ketone were reduced in enantiomeric excesses of up to 97%. Substituents on the arene ring of the catalyst influence the reaction rate and enantioselectivity.

Side chain functionalized η5-tetramethyl cyclopentadienyl complexes of Rh and Ir with a pendant primary amine group

“…Among the many developments, side chain functionalization particularly has added new facets to the chemistry of this class of compounds [2][3][4]. The emerging reactivity patterns have been utilized to tailor solubility [4,5], control the electronic properties of the metal center via hemi-labile coordination [5][6][7][8], introduce chirality [9], or to accelerate catalytic reactions with bifunctional mechanism [10]. Compounds with pendant amino groups have attracted considerable attention, with (2-dimethylamino)ethyl tethered g 5 -cyclopentadienyl derivatives of Ru, Rh, or Ir being prominent examples [4,10].…”

Ruthenium(II) complex catalysts bearing a pyridyl-supported pyrazolyl-imine ligand for transfer hydrogenation of ketones

“…Among the most efficient catalyst systems are the Ru(II) complexes bearing a monotosylated 1,2-diamine or aminoalcohol ligand discovered by Noyori and co-workers, which can offer high catalytic activity and selectivity due to a N-H effect [2]. Following their pioneering work, a lot of related ligands and transition metal complexes have been reported in this area [3,4]. Baratta et al recently reported highly active ruthenium(II) 2-(aminomethyl)pyridine (ampy) phosphane complex catalysts for TH of ketones which have shown an acceleration effect by the N-H functionality in the ampy ligand [5][6][7][8].…”

Asymmetric Hydrogenation and Transfer Hydrogenation of Ketones

“…In this respect, the covalent linkage from the diamine to the  6 -arene unit in the ''tethered'' catalysts C9 provide extra stability and a significant increase in rate relative to the ''unthetered'' catalyst in some cases ( Fig. 8) (Cheung et al, 2007). With these catalysts, ring-substituted acetophenones, -chloroacetopehones, dialkyl ketones and ketopyridines were converted to the corresponding chiral alcohols in FA/TEA, mostly near to room temperature.…”