Controlling the Sense of Enantioselection on Surfaces by Conformational Changes of Adsorbed Modifiers

Novel Evidence on the Role of the Nucleophilic Intermediate Complex in the Orito-Reaction: Unexpected Inversion in the Enantioselective Hydrogenation of 2,2,2-Trifluoroacetophenone on Pt-Cinchona Chiral Catalyst Using Continuous-Flow Fixed-Bed Reactor

“…In the case of TFAP bound to the protonated quinuclidine moiety, namely in solvent mixture with TFA the formation of the (R)-and (S)-products in excess are interpreted through the so-called O-H-N complexes (see Fig. 5, A1) [11,[70][71][72] or by the two point H-bonding model (A2 complex) [27,73]. Unexpected formation of the (R)-product in excess in higher amount in the presence of CN in solvent mixture without TFA may be envisaged by the formation of the less widely accepted nucleophilic complex illustrated in Fig.…”

Crucial aspects in the design of chirally modified noble metal catalysts for asymmetric hydrogenation of activated ketones

“…36 A striking example for the effect of subtle changes of the modifier is provided by comparing the enantioselectivities achieved in the asymmetric hydrogenation over Pt/Al 2 O 3 modified by cinchonidine, O-phenylcinchonidine and ether derivatives of cinchonidine bearing differently substituted phenyl rings, as shown in Fig. 38 O-Phenylcinchonidine (PhOCD) is known to efficiently induce inversion of enantioselectivity with respect to cinchonidine (CD) in the enantioselective hydrogenation of various activated ketones on Pt/Al 2 O 3 . 38 O-Phenylcinchonidine (PhOCD) is known to efficiently induce inversion of enantioselectivity with respect to cinchonidine (CD) in the enantioselective hydrogenation of various activated ketones on Pt/Al 2 O 3 .…”

Electrochemical studies of irreversibly adsorbed ethyl pyruvate on Pt{hkl} and epitaxial Pd/Pt{hkl} adlayers

“…Although several models have been proposed to explain the mechanism of enantioselection under reaction conditions [9,22,[27][28][29][30][31] no one theory appears to account satisfactorily for all of the unusual experimental features of this complex surface reaction, for example; the rate acceleration associated with the modified hydrogenation reaction [32][33][34][35][36][37][38][39], its solvent dependency [40][41][42][43][44], the effect of modifier [31,41,[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] and substrate [52,[64][65][66] structure and concentration [37,39] together with catalyst pr...…”