Highly Enantioselective Adsorption of Small Prochiral Molecules on a Chiral Intermetallic Compound

Abstract

Intrinsically chiral surfaces of intermetallic compounds are shown to be novel materials for enantioselective processes.T heir advantage is the significantly higher thermal and chemical stability,and therefore their extended application range for catalyzedc hiral reactions compared to surfaces templated with chiral molecular modifiers or auxiliaries.O n the Pd 1 -terminated PdGa(111) surface,r oom-temperature adsorption of as mall prochiral molecule (9-ethynylphenanthrene) leads to exceptionally high enantiomeric excess ratios of up to 98 %. Our findings highlight the great potential of intrinsically chiral intermetallic compounds for the development of novel, enantioselective catalysts that can be operated at high temperatures and potentially also in harsh chemical environments.

Near‐Enantiopure Trimerization of 9‐Ethynylphenanthrene on a Chiral Metal Surface

“…The chirality of Pd 1 manifests itself in enantioselective adsorption at 300 K with an enantiomeric excess ee =100 % 96±2 % for prochiral 9‐Ethynylphenanthrene (9‐EP, Figure b) . However, no enantioselective reaction between molecules could be demonstrated on that surface …”

“…Owing to the ensemble effect, the temperature evolution of the enantiomeric excess of 9‐EP structures and reaction products on PdGa{111}Pd 3 are in stark contrast to those on PdGa{111}Pd 1 . Specifically, whereas on PdGa{111}Pd 3 , 9‐EP monomers occur in a racemic mixture at 300 K, they appear with an enantiomeric excess of 96 % on PdGa{111}Pd 1 due to a lower energy barrier for the conversion between R and S monomers and the enantiospecific van der Waals interaction with the substrate's second layer Ga trimer .…”

“…[22][23][24] The chirality of Pd 1 manifests itself in enantioselective adsorption at 300 K with an enantiomeric excess ee = 100 % #RÀ#S j j #Rþ#S ¼96 AE 2 % for prochiral 9-Ethynylphenanthrene (9-EP, Figure 1 b). [25] However, no enantioselective reaction between molecules could be demonstrated on that surface. [25] Here, we study the near-enantiopure trimerization from an initial racemic mixture of 9-EP on PdGa:A( " 1 " 1 " 1)Pd 3 (A:Pd 3 ) by scanning tunneling microscopy (STM), COsensitized non-contact atomic force microscopy (nc-AFM), and density functional theory (DFT) calculations.…”

“…[25] However, no enantioselective reaction between molecules could be demonstrated on that surface. [25] Here, we study the near-enantiopure trimerization from an initial racemic mixture of 9-EP on PdGa:A( " 1 " 1 " 1)Pd 3 (A:Pd 3 ) by scanning tunneling microscopy (STM), COsensitized non-contact atomic force microscopy (nc-AFM), and density functional theory (DFT) calculations.…”

Absolute Structure from Scanning Electron Microscopy

“…In case of crystalline materials, both enantiomorphs of a non-centrosymmetric phase crystallize in different absolute structures with complementary chirality [1][2][3] or polarity. Absence of centrosymmetry is a necessary condition of various physical and chemical properties which are subject of highly active research areas such as unusually ordered magnetic 4,5 and superconducting states 6,7 , topological surface properties 8,9 or enantioselective catalysis on non-centrosymmetric materials [10][11][12][13] . Respective experiments crucially depend on efficient methods to reliably identify the chirality, enantiomorphic purity, and crystallographic orientation of crystals and crystallites.…”