Figure 2.

Top: Three isomers (A, B, C) are observed for the Ni^II-peptide complexes, which contain a fifth ligand, a coordinated solvent molecule (acetonitrile) designated by an open square. Bottom: ³¹P{¹H} NMR spectra of the Ni^II-parent complexes show only three isomers as shown for Meth. The Prop-peptide complexes also show all three isomers plus a down-up isomer with restricted structural mobility (D) as shown for Prop-R10. The Meth-peptide complexes show only the D isomer as shown for Meth-K10. The unlabeled resonances at ~45 ppm are oxidized phosphine.