NiII, CuII and ZnII complexes with a sterically hindered scorpionate ligand (TpmsPh) and catalytic application in the diasteroselective nitroaldol (Henry) reaction.

The Ni(II) and Zn(II) complexes [MCl(Tpms(Ph))] (Tpms(Ph) = SO3C(pz(Ph))3, pz = pyrazolyl; M = Ni 2 or Zn 3) and the Cu(II) complex [CuCl(Tpms(Ph))(H2O)] (4) have been prepared by treatment of the lithium salt of the sterically demanding and coordination flexible tris(3-phenyl-1-pyrazolyl)methanesulfonate (Tpms(Ph))(-) (1) with the respective metal chlorides. The (Tpms(Ph))(-) ligand shows the N3 or N2O coordination modes in 2 and 3 or in 4, respectively. Upon reaction of 2 and 3 with Ag(CF3SO3) in acetonitrile the complexes [M(Tpms(Ph))(MeCN)](CF3SO3) (M = Ni 5 or Zn 6, respectively) were formed. The compounds were obtained in good yields and characterized by analytic and spectral (IR, (1)H and (13)C{(1)H} NMR, ESI-MS) data, density functional theory (DFT) methods and {for 4 and [(n)Bu4N](Tpms(Ph)) (7), the latter obtained upon Li(+) replacement by [(n)Bu4N](+) in Li(Tpms(Ph))} by single crystal X-ray diffraction analysis. The Zn(II) and Cu(II) complexes (3 and 4, respectively) act as efficient catalyst precursors for the diastereoselective nitroaldol reaction of benzaldehydes and nitroethane to the corresponding β-nitroalkanols (up to 99% yield, at room temperature) with diastereoselectivity towards the formation of the anti isomer, whereas the Ni(II) complex 2 only shows a modest catalytic activity.