Design and synthesis of new alkyl-based chiral phosphoric acid catalysts

Amplification of enantiomeric excess by dynamic inversion of enantiomers in deracemization of Au38 clusters

Symmetry breaking and amplification processes have likely played a fundamental role in the development of homochirality on earth. Such processes have not been much studied for inorganic matter at the nanoscale. Here, we show that the balance between left- and right-handed intrinsically chiral metal clusters can be broken by adsorbing a small amount of a chiral molecule in its ligand shell. We studied the amplification of enantiomeric excess of the Au₃₈(2-PET)₂₄ cluster (2-PET = 2-phenylethylthiolate). By exchanging a small fraction of the achiral 2-PET ligand by chiral R-1,1′-binaphthyl-2,2′-dithiol (R-BINAS), a mixture of species is obtained composed of anticlockwise (A) and clockwise (C) versions of Au₃₈(2-PET)₂₄ and Au₃₈(2-PET)₂₂(R-BINAS)₁. At 70 °C, the system evolves towards the anticlockwise clusters at the expense of the clockwise antipode. It is shown that the interplay between the diastereospecific ligand exchange, which introduces selectivity but does not change the A/C ratio, and the fast racemization of the Au₃₈(2-PET)₂₄ is at the origin of this observation.

Symmetry breaking and amplification processes play a fundamental role in nature and technology. Here, the authors show that the interplay between racemization and ligand exchange leads to amplification of enantiomeric excess of intrinsically chiral metal clusters.