New Bifunctional Bis(azairidacycle) with Axial Chirality via Double Cyclometalation of 2,2'-Bis(aminomethyl)-1,1'-binaphthyl.

As a candidate for bifunctional asymmetric catalysts containing a half-sandwich C-N chelating Ir(III) framework (azairidacycle), a dinuclear Ir complex with an axially chiral linkage is newly designed. An expedient synthesis of chiral 2,2'-bis(aminomethyl)-1,1'-binaphthyl () from 1,1-bi-2-naphthol (BINOL) was accomplished by a three-step process involving nickel-catalyzed cyanation and subsequent reduction with Raney-Ni and KBH. The reaction of ()- with an equimolar amount of [IrClCp*] (Cp* = η-C(CH)) in the presence of sodium acetate in acetonitrile at 80 °C gave a diastereomeric mixture of new dinuclear dichloridodiiridium complexes () through the double C-H bond cleavage, as confirmed by H NMR spectroscopy. A loss of the central chirality on the Ir centers of was demonstrated by treatment with KOC(CH) to generate the corresponding 16e amidoiridium complex . The following hydrogen transfer from 2-propanol to provided diastereomers of hydrido(amine)iridium retaining the bis(azairidacycle) architecture. The dinuclear chlorido(amine)iridium can serve as a catalyst precursor for the asymmetric transfer hydrogenation of acetophenone with a substrate to a catalyst ratio of 200 in the presence of KOC(CH) in 2-propanol, leading to ()-1-phenylethanol with up to an enantiomeric excess (ee) of 67%.