Transition Metal Complexes of an (S,S)‑1,2-Diphenylethylamine-Functionalized N‑Heterocyclic Carbene: A New Member of the Asymmetric NHC Ligand Family

By a simple SN2 reaction between N-methylimidazole and a chiral sulfamidate, the first proligand of a new class of enantiopure NHC-CHPh-CHPh-NH2 ligands can be prepared in high yield. This proligand, with the molecular formula [(S,S)-H2NCHPhCHPh-NC3H3N-CH3]­(PF6), when reacted with a slight excess of lithium or potassium bis­(trimethylsilyl)­amide, produces the corresponding NHC-CHPh-CHPh-NH2 ligand, “kaibene”. In the presence of the silver­(I) starting material AgPF6 or AgI, two Ag­(kaibene)2X complexes (X = PF6 or I) and one helical kaibene silver polymer, [Ag­(kaibene)]n(PF6)n, can be prepared. Using the suitable silver complex, we successfully transferred kaibene to ruthenium­(II), iridium­(I), and nickel­(II). The ruthenium complex [Ru­(p-cymene)­(kaibene)­(Cl)]­PF6 with a base in THF is a moderately active catalyst at 50 °C and 25 bar of H2 for the hydrogenation of acetophenone but with no enantioselectivity.