Controlling the chirality of molecule-surface systems is essential for applications ranging from heterogeneous catalysis to biosensing.N-heterocyclic carbenes(NHCs)are quickly becoming a dominant ligand for noble meta...Controlling the chirality of molecule-surface systems is essential for applications ranging from heterogeneous catalysis to biosensing.N-heterocyclic carbenes(NHCs)are quickly becoming a dominant ligand for noble metal surface passivation,but the potential of chiral NHC scaffolds remains untapped.In this work,two stereoisomers,one C_(2) symmetric and one C_(s) symmetric,of saturated N-heterocyclic carbenes(NHCs)and a structurally related unsaturated NHC(C_(2v) symmetric)were synthesized as NHC-CO_(2) adducts.These CO_(2)-protected NHCs were deposited on gold films and their presence on the films was confirmed by laser desorption ionization mass spectrometry(LDI-MS)and surface enhanced Raman spectroscopy(SERS).Surprisingly,the C_(s) NHC,but not the chiral C_(2) NHC,partially degrades to the independently synthesized unsaturated NHC upon binding to the gold.Theoretical calculations assist in explaining this phenomenon by showing that the NHCs primarily lie flat on the gold surfaces,which exposes the backbone protons on the C_(s)-symmetric NHC to a formal elimination of H_(2),while the C_(2)-symmetric NHC remains protected from this elimination reaction.These results raise critical questions as to how the structure of NHC ligands may be tuned to influence binding and reactivity on gold surfaces.展开更多
基金supported by the National Science Foundation under Grants CHE-2108328(G.K.,P.N.,and D.M.J.)CHE-2108330(N.L.D.,R.L.T.,and J.P.C.)+1 种基金CHE-1856419CHE-2312222(G.H.and L.J.)。
文摘Controlling the chirality of molecule-surface systems is essential for applications ranging from heterogeneous catalysis to biosensing.N-heterocyclic carbenes(NHCs)are quickly becoming a dominant ligand for noble metal surface passivation,but the potential of chiral NHC scaffolds remains untapped.In this work,two stereoisomers,one C_(2) symmetric and one C_(s) symmetric,of saturated N-heterocyclic carbenes(NHCs)and a structurally related unsaturated NHC(C_(2v) symmetric)were synthesized as NHC-CO_(2) adducts.These CO_(2)-protected NHCs were deposited on gold films and their presence on the films was confirmed by laser desorption ionization mass spectrometry(LDI-MS)and surface enhanced Raman spectroscopy(SERS).Surprisingly,the C_(s) NHC,but not the chiral C_(2) NHC,partially degrades to the independently synthesized unsaturated NHC upon binding to the gold.Theoretical calculations assist in explaining this phenomenon by showing that the NHCs primarily lie flat on the gold surfaces,which exposes the backbone protons on the C_(s)-symmetric NHC to a formal elimination of H_(2),while the C_(2)-symmetric NHC remains protected from this elimination reaction.These results raise critical questions as to how the structure of NHC ligands may be tuned to influence binding and reactivity on gold surfaces.
