Ni(II)-mediated synthesis of the novel tripodal aminopyridyl ligand tamepyr: Coordination geometry and rigidity of complexes with the divalent 3d metals Fe–Zn and with In(III)

Abstract

The synthesis of the novel chelator ‘tamepyr’ ( N, N′, N″-tris(2-pyridylmethyl)-1,1,1-tris(aminomethyl)ethane) and properties of its complexes with Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and In(III) are reported. Tamepyr was prepared as a complex with Ni(II) by the NaBH 4 reduction of the tamepyr-trisimine complex, [Ni((2-py-C(H) NCH 2) 3CMe)] 2+. The decomposition of [Ni(tamepyr)] 2+ with excess sodium cyanide affords tamepyr in 40% overall yield from tame. Structural study of [Zn(tamepyr)](ClO 4) 2 shows similar Zn–N distances with reference to the aminopyridyl tripod tachpyr ( N, N′, N″-tris(2-pyridylmethyl)- cis, cis-1,3,5-triaminocyclohexane), being d(Zn–N amine,py) = 216.9(2), 212.8(2) pm versus 216.0(3), 216.5(4) pm for [Zn(tachpyr)](ClO 4) 2. However, the [Zn(tamepyr)] 2+ data indicate a greater propensity to octahedral coordination in a tame-framework chelator compared to a tach-framework chelator: the trigonal twist angle in the ZnN 6 coordination sphere of [Zn(tamepyr)] 2+ is 46.5(2)° versus 43.7(2)° for [Zn(tachpyr)] 2+. When presented with larger metals such as In(III), tamepyr shows greater flexibility than tachpyr, thus, [In(tamepyr)] 3+ is completely fluxional at ambient temperature while [In(tachpyr)] 3+ is static up to 107 °C as shown by 1H NMR in DMSO- d 6.