New Enantioselective Reactions catalysed by cinchonidine-modified platinum

Inversion of enantioselectivity in the platinum-catalyzed hydrogenation of substituted acetophenones

“…4). The selectivity could not be improved by working below room temperature, as it was observed in several other reactions catalyzed by the Pt-cinchona system [7,9,11,20,50]. The negative effect of increasing temperature above room temperature on the ee is a general feature of hydrogenations over cinchona-modified Pt.…”

“…Thoroughly investigated reactions are the hydrogenation of α-ketoesters and α-ketolactones [3,[5][6][7][8], α-diketones [9][10][11][12][13], α, α, α-trifluoroketones [14][15][16][17], and linear and cyclic α-ketoamides [18][19][20]. In these reactions over 90% ee could be achieved after optimization of catalyst pretreatment and reaction conditions.…”

Adsorption of activated ketones on platinum and their reactivity to hydrogenation: a DFT study

“…This effect of stabilization of the transition state and the half-hydrogenated species is possible also for other molecules that contain an oxygen atom in the same position. Indeed it has been experimentally observed that molecules such as diketones and α-keto alcohols [43][44][45][46] can be catalytically hydrogenated on platinum, as well as α-keto acetals [47,48]. This is further supported by the observation that the hydrogenation of α-keto ethers occurs more efficiently when the conformation of the molecule is fixed in cis position in a cyclic molecule rather than when the ether is free to rotate, in which case the activating effect of the oxygen may occur to a lesser extent [49].…”

Non‐Zeolitic Standard Catalysts

“…The coadsorption of another strongly adsorbing molecule such as either oxygen or an alkyne favored the desired reaction by governing the number of desired sites and removing some that gave non-selective behavior [23]. A remarkable feature of this work has been the rate enhancement that accompanies enantioselective reaction; factors of up to 100 were recorded, attributable to the role of the modifier in assisting the chemisorption of the reactant in the best possible way [24]. Recent studies, involving doping by Bi, have shown that the enantioselectivity achieved at sites at or near steps in the Pt surface of EUROPT-1 is higher than that achieved at terrace sites [25b].…”

“…The effects on its catalytic properties of the addition of silver, titania and alumina [14], chlorine, oxygen, sulfur, ammonia, and carbon monoxide have all been examined [7], but of particular interest is its extensive use in studies of enantioselective hydrogenation [16][17][18][19][20][21][22][23][24][25], where its long-term stability has been an asset over some 20 years of experimentation. Its metallic function has always maintained the same dispersion and other particle characteristics, while being modified in a number of different ways to impart enantioselectivity.…”