Dinuclear nickel(II) complexes of an unsymmetric 'end-off' compartmental ligand: Conversion of urea into cyanate at a dinuclear nickel core

摘要

A phenol-based "end-off" compartmental ligand, 2-[N,N-di(2-pyridylmethyl)aminomethyl]-6-{N[2-(dimethyl amino)ethyl]iminomethyl}-4-methylphenol (HL), having an iminic bidentate and an aminic tridentate chelating arms on the 2- and 6-positions of the phenolic ring, respectively, forms dinuclear nickel complexes [Ni-2(L)-(AcO)(NCS)(2)] (1), [Ni-2(L)(AcO)(2)(MeOH)]PF6 (2), and [{Ni-2(L)(OH)(MeOH)}(2)(CO3)](PF6)(2) (3). Complex 1 crystallizes in the monoclinic space group P2(1)/c, a = 14.165(5) Angstrom, b = 15.198(4) Angstrom, c = 17.395(8) Angstrom, beta = 100.62(4)degrees, V = 3680(2) Angstrom(3), and Z = 4. The pair of Ni ions present are bridged by the phenolic oxygen of L- and an acetate group in syn-syn mode (Ni-Ni: 3.373(3) Angstrom). An isothiocyanate nitrogen atom coordinates to each Ni providing an asymmetric dinuclear core with a mixed (5/6) coordination number set. Complex 2 crystallizes in the monoclinic space group P2(1)/c, a = 13.505(5) Angstrom, b = 12.028(4) Angstrom, c = 22.774(9) Angstrom, beta = 103.78(3)degrees, V = 3592(2) Angstrom(3), and Z = 4. It has a dinuclear core bridged by the phenolic oxygen of L- and two acetate groups in syn-syn mode, providing a mu-phenoxo-bis(mu-carboxylato)dinickel(II) core (Ni-Ni: 3.396(6) Angstrom). A methanol molecule coordinates to the Ni bound to the bidentate arm, forming a dinuclear core having a {6/6} coordination number set and an asymmetric donor atom environment. Complex 3 crystallizes in the orthorhombic space group Pbcn, a = 19.056(5) Angstrom, b = 18.997(4) Angstrom, c = 19.919(6) Angstrom, alpha = beta = gamma = 90 degrees, V = 7211(5) Angstrom(3), and Z = 8. In each dinuclear unit a pair of Ni ions are bridged by the phenolic oxygen of L- and a hydroxo oxygen (Ni-Ni: 3.087(2) Angstrom). A carbonate further bridges two of the dinuclear units to present a composite dimer. The Ni bound to the bidentate arm attains six-coordinate geometry by further interaction with two oxygens of the bridging carbonate group. The Ni bound to the tridentate arm assumes six-coordinate geometry by fu;ther coordination of a methanol oxygen. Complexes 1-3 react with urea in ethanof to form the isocyanate complexes [Ni-2(L)-(AcO)(NCS)(NCO)] (1'), [Ni-2(L)(AcO)(NCO)(EtOH)]PF6 (2'), and [{Ni-2(L)(NCO)(EtOH)}(2)(CO3)](PF6)(2) (3'), respectively. Complex 3' crystallizes in the triclinic space group , a = 20.072(7) Angstrom, b = 21.145(6) Angstrom, c = 18.688(6) Angstrom, alpha = 106.20(2)degrees, beta = 90.01(3)degrees, gamma = 88.73(3)degrees, V = 7614(4) Angstrom(3), and Z = 4. It has a dimeric structure very similar to that of 3, except for the replacement of the hydroxy bridge and the methanol ligand in 3 by isocyanate bridge and ethanol ligand, respectively, in 3'. [References: 42]