Transmetalation of a Primary Amino-Functionatized N-Heterocyclic Carbene Ligand from an Axially Chiral Square-Planar Nickel(II) Complex to a Ruthenium(II) Precatalyst for the Transfer Hydrogenation of Ketones

The first homoleptic nickel(II) complex with primary amino-functionalized N-heterocyclic carbene (C-NH(2)) ligands ([Ni(m-CH(2)NH(2))(2)](PF(6))(2), 2) was prepared under mild conditions by the reduction of a nitrile-functionalized imidazolium salt. This axially chiral, square-planar nickel(II) complex was characterized by NMR spectroscopy and an X-ray diffraction study. Enantiopure Delta-TRISPHAT was used as an NMR chiral shift reagent to observe the diastereotopic ion pairs by (1)H NMR in acetonitrile-d(3). A novel transmetalation reaction moved the primary amino-functionalized N-heterocyclic carbene ligand from the nickel(II) complex 2 to the [Ru(p-cymene)Cl](2) dimer, yielding the complex [Ru(p-cymene)(m-CH(2)NH(2))Cl]PF(6), (3), the first ruthenium(II) complex with such a chelating C-NH(2) ligand. Complex3 is a precatalyst for the transfer hydrogenation of acetophenone to 1-phenylethanol in basic 2-propanol at 75 degrees C with a turnover frequency of up to 880 h(-1) and conversion of 96%.