α‐Amino‐iso‐Butyric Acid Foldamers Terminated with Rhodium(I) N‐Heterocyclic Carbene Catalysts

• Published in: Chemistry : a European journal 2022-02, Vol.28 (9), p.e202104293-n/a
• Main Authors: Tilly, David P., Cullen, William, Zhong, Heng, Jamagne, Romain, Vitórica‐Yrezábal, Inigo, Webb, Simon J.
• Format: Article
• Language: English
• Subjects: Butyric Acid; carbene ligands; Carbenes; Catalysis; Catalysts; Chemistry; Chirality; conformation analysis; Crystallography; Diastereoisomers; foldamers; Heterocyclic Compounds - chemistry; homogeneous catalysis; Hydrosilylation; Iridium - chemistry; Magnetic resonance spectroscopy; Methane - analogs & derivatives; Models, Molecular; Molecular Structure; NMR; NMR spectroscopy; Nuclear magnetic resonance; Organometallic complexes; Organometallic Compounds - chemistry; Remote control; Residues; Rhodium; Rhodium - chemistry; Stereoisomerism; Stereoselectivity
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202104293

To investigate how remotely induced changes in ligand folding might affect catalysis by organometallic complexes, dynamic α‐amino‐iso‐butyric acid (Aib) peptide foldamers bearing rhodium(I) N‐heterocyclic carbene (NHC) complexes have been synthesized and studied. X‐ray crystallography of a foldamer with an N‐terminal azide and a C‐terminal Rh(NHC)(Cl)(diene) complex showed a racemate with a chiral axis in the Rh(NHC) complex and a distorted 310 helical body. Replacing the azide with either one or two chiral L‐α‐methylvaline (L‐αMeVal) residues gave diastereoisomeric foldamers that each possessed point, helical and axial chirality. NMR spectroscopy revealed an unequal ratio of diastereoisomers for some foldamers, indicating that the chiral conformational preference of the N‐terminal residue(s) was relayed down the 1 nm helical body to the axially chiral Rh(NHC) complex. Although the remote chiral residue(s) did not affect the stereoselectivity of hydrosilylation reactions catalysed by these foldamers, these studies suggest a potential pathway towards remote conformational control of organometallic catalysts. Another twist: α‐Amino‐iso‐butyric acid foldamers terminated with rhodium(I) N‐heterocyclic carbene complexes have been shown to possess point, helical and axial chirality. Communication from chiral residues at the N‐termini of these 1 nm long foldamers to rhodium(I) complexes at the C‐termini led to unequal ratios of diastereoisomers, although this did not alter the stereoselectivity of hydrosilylation reactions catalyzed by these foldamers.