New chiral catalysts for reduction of ketones

Ruthenium(II)-assisted asymmetric hydrogen transfer reduction of acetophenone using chiral tridentate phosphorus-containing ligands derived from (1R, 2R)-1,2-diaminocyclohexane

“…However, ligands 4 probably bind to ruthenium metal in a bidentate fashion resembling the salen-like chelation [25] (Fig. 1a), while ligands 5, with the imine reduced form [NNHCP], bind in a tridentate fashion leading to a ruthenium intermediate like that proposed by Kwong and coworkers [38] (Fig.…”

“…In their work they also showed the remarkable difference in activity between sp 2 -N and sp 3 -N ligands [24][25][26]31]. In an attempt to mimic enzymes, Liese and coworkers [32] have bound the above ligands to a polymer and have demonstrated that it could behave like enzymes in the asymmetric hydrogen transfer reduction of acetophenone.…”

“…Similar tetradentate ligands of the [NNNN]-type with 1,2-diaminocyclohexane backbone containing oxazolines have been synthesized by Zhu and coworkers; interestingly, the catalytic application of these ligands have not yet been explored [22]. Tetradentate salen ligands in which the hard oxygen donor atom is replaced by a soft phosphorus donor atom of the type [OPNNPO], [SPNNPS] [23], [PNNP], [PNHNHP] bearing C 2 symmetry, and [PNHNHNR 2 ]-type of ligands, have also been extensively studied as catalysts with metals such as titanium [23a], iridium [23b], ruthenium [24][25][26], rhodium [23b], molybdenum [27,28] and palladium [29,30].…”

A ruthenium(II) bipyridine complex containing a 4,5-diazafluorene moiety: Synthesis, characterization and its applications in transfer hydrogenation of ketones and dye sensitized solar cells

“…Conversely, the most electrondonating substituents, (2-or 4-methoxy) led to lower conversions. It is well-known that the presence of an electron withdrawing group can ease hydrogen transfer reactions [46,47], which has been attributed to the hydridic nature of the reducing species involved. As such, substrates with fluoro or nitro groups undergo higher conversions owing to rapid hydride transfer, while substrates with electron-donating substituents (2-or 4-methoxy) undergo a slower reaction in a more controlled manner [48,49].…”

Asymmetric transfer hydrogenation of acetophenone derivatives with novel chiral phosphinite based η6-p-cymene/ruthenium(II) catalysts

“…It was found that the activity is highly dependent on the steric bulkiness of the alkyl group [51]. When the size of alky group is increased, the activity was remarkable decreased [52,53]. However, enantioselectivity was not significantly influenced by increasing the bulkiness of the alkyl group.…”