title: Masked imidazolyl-dipyrromethanes in the synthesis of imidazole-substituted porphyrins.
abstract: Imidazole-substituted metalloporphyrins are valuable for studies of self-assembly and for applications where water solubility is required. Rational syntheses of porphyrins bearing one or two imidazol-2-yl or imidazol-4-yl groups at the meso positions have been developed. The syntheses employ dipyrromethanes, 1-acyldipyrromethanes, and 1,9-diacyldipyrromethanes bearing an imidazole group at the 5-position. The polar, reactive imidazole unit was successfully masked by use of (1) the 2-(trimethylsilyl)ethoxymethyl (SEM) group at the imidazole pyrrolic nitrogen, and (2) a dialkylboron motif bound to the pyrrole of the dipyrromethane and coordinated to the imidazole imino nitrogen. The nonpolar nature of such doubly masked imidazolyl-dipyrromethanes facilitated handling. Selected masked dipyrromethanes were characterized by 11B and 15N NMR spectroscopy. Five distinct methods were examined to obtain trans-A2B2-, trans-AB2C-, and trans-AB-porphyrins. Each porphyrin contained one or two SEM-protected imidazole units. The SEM group could be removed with TBAF or HCl. Two zinc(II) porphyrins and a palladium(II) porphyrin bearing a single imidazole moiety were prepared and subjected to alkylation (with ethyl iodide, 1,3-propane sultone, or 1,4-butane sultone) to give water-soluble imidazolium- porphyrins. This work establishes the foundation for the rational synthesis of a variety of porphyrins containing imidazole units.
authors.affiliation: Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
authors.forename: Jayeeta
authors.initials: J
authors.lastname: Bhaumik
authors.forename: Zhen
authors.initials: Z
authors.lastname: Yao
authors.forename: K Eszter
authors.initials: KE
authors.lastname: Borbas
authors.forename: Masahiko
authors.initials: M
authors.lastname: Taniguchi
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Lindsey
mesh_terms: D007093:Imidazoles / Q000737:chemistry*; D008968:Molecular Conformation; D011166:Porphyrins / Q000138:chemical synthesis* / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D007093:Imidazoles; D011166:Porphyrins; D011758:Pyrroles; C512015:dipyrromethane; C029899:imidazole