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. [ABSTRACT FROM AUTHOR]