title: Synthesis of an adj-dicarbaporphyrin and the formation of an unprecedented tripalladium sandwich complex.
abstract: An adj-dicarbaporphyrin was prepared by carrying out a base-catalyzed MacDonald reaction between bis(3-indenyl)methane and a dipyrrylmethane dialdehyde. The porphyrinoid system exhibited highly diatropic characteristics, and the proton NMR spectrum gave resonances at -5.74 and -6.24 ppm for the internal NH and CH protons, respectively. The UV-vis spectrum was also porphyrin-like, giving a Soret band at 455 nm and a series of Q bands at longer wavelengths. Addition of trifluoroacetic acid gave a C-protonated monocation, and at higher acid concentrations a dicationic species was observed. Addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded a monodeprotonated porphyrinoid anion. All of these species retained highly diatropic characteristics. Density functional theory calculations showed that a nonplanar tautomer with four internal hydrogens was favored, in agreement with the spectroscopic data. Nucleus-independent chemical shift calculations also confirmed the aromatic characteristics of the free-base, cationic, and anionic structures. The dicarbaporphyrin reacted with palladium(II) acetate in refluxing acetonitrile to give an unusual tripalladium sandwich complex consisting of two dianionic palladium(II) dicarbaporphyrin units surrounding a palladium(IV) cation with unique η(5) interactions involving meso-carbon atoms.
authors.affiliation: Department of Chemistry, Illinois State University , Normal, Illinois 61790-4160, United States.
authors.forename: Deyaa I
authors.initials: DI
authors.lastname: AbuSalim
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Ferrence
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Lash