Synthesis and reactivity of heterobimetallic complexes with phenolic oxygens bridged ligands
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A new efficient method for the synthesis of dicompartmental ligands enalH 2 8 and of tnalH2, 10 is described. This method is essentially a concise one-step route via the Mannich condensation, from 4-methyl 2-formylphenol and paraformaldehyde with appropriate amines. A series of macrocyclic heterobimetallic complexes of type [Mc(tntnam)M o](PF6)n and [Mc'(tntnim)Ni](PF 6)n where Mc = Co(III) and Zn(II), Mc ' = Co(II), Co(III) and Zn(II) and Mo = Ni(II), Cu(II) and Zn(II) have been synthesized and characterized. The macrocyclic ligands tntnim 12 and tntnam 13 contain two geometrically distinct 6-coordinate (closed-site) and 4-coordinate (open-site) compartments which are bridged by phenolic oxygens. The heterobimetallic complexes with Zn(II) or Ni(II) in the open-site are primarily formed as 5-coordinate with a chloride ion as a fifth ligand; the latter can be removed by Ag+ ion. The 1H NMR and 13C NMR of diamagnetic complexes and [Co(tntnam)ZnCl](PF6)2, 27 and [Co(tntnam)Zn](PF6)3, 28 demonstrate that the expected trans pyridine structures are formed. Solution magnetic moments of heterobimetallic complexes indicate that all Co(III) ions are spin paired, but the Ni(II) ions are spin free. The electronic absorption and emission spectra and redox couples are reported. The crystal structures of [Zn(tntnim)NiCl]PF 6•C2H5OH, 16, [Zn(tntnam)Ni](PF 6)2, 22, [Zn(tntnam)Cu](PF6) 2, 23, and [Co(tnmam)Ni(H2O)](PF6) 3•4H2O, 25 were determined. The crystal structures demonstrate that the expected 'trans' pyridine structures are formed. Photoreactivity of heterobimetallic complexes towards molecular oxygen showed that, in spite of sensitivity of these complexes to molecular oxygens no singlet molecular oxygen, O2 (1[Delta]g ), or peroxide species were generated as a result of irradiation with visible light. A series of acyclic ligands analogous to the dialdehyde ligand enalH 2, but containing different ligating groups instead of the aldehyde moieties were prepared. These include dialcoholic ligands of enolH4 and tnolH4, diimine ligand of enmimH2, and diamine ligand of enmamH2. Exploration of the coordination chemistry of these ligands revealed that the presence of an "en" in the closed-site solely provides a C2 symmetrical isomer among the three possible topological isomers. Monometallic complexes of [Co(enolH2)] +, [Co(tnolH2)]+, [Cr(tnolH2)] +, (Zn(enmim)(H+)2]2+, [Zn(enmam)(H +)2]2+ and [Cr(enmam)(H+) 2]3+ and heterobimetallic complexes [Zn(enmam)Cu] 2+ and [Cr(enmam)Cu]3+ have been prepared and characterized. Syntheses of [Zn(enmam)(H+)2]2+ through two different routes reveals that introduction of a metal into free ligand enmamH2 selectively occupies the closed-site cavity and leaves the open-site cavity intact.