Abstract:
The synthesis and characterization of some new binucleating tetraarylporphyrin ligands is reported. The potentially most useful example is α,α,5,15-bis[N-(2-methylbenzimidazolyl)acetamidophenyl]-α, α,10,20-bis(pivalamidophenyl)porphine (8). The ligands have two appended benzimidazole arms which are designed to chelate a second metal directly above the porphyrin. The synthetic methodology for obtaining both the 5,15 (i.e., trans) and the 5,10 (i.e., cis) bis-appended ligand from an α, α, α, α,5,10,15,20 tetra-functionalized starting material is described in detail. A key design feature of the ligand system is amenability to single-crystal X-ray structure determination and this is demonstrated with an X-ray structure of a copper(II) complex. Crystal data for CuC74H66N12O4·1.5(diethyl ether)·toluene are the following: monoclinic, C2/c, a = 31.240 (4) Å, b = 16.769 (5) Å, c = 35.199 (4) Å, β = 121.4 (1)°; R = 0.0823, Rw = 0.0826. H bonding between the benzimidazole moieties and the pivalamido pickets is seen to determine the structural disposition of the appendages lying above the porphyrin ring. Iron(III) porphyrin complexes of these new ligands exist in a hydroxo monomer form as well as the familiar μ-oxo dimer form.
