Preparation and Characterization of Metalloporphyrin Tröger's and Spiro-Tröger's Base Derivatives.

A series of metalloporphyrin dimers as Tröger's bases or spiro-Tröger's bases was prepared starting from five different -symmetry porphyrin derivatives substituted in -positions by Ph, 3-MeO-Ph, 4-MeO-Ph, 3,4-(MeO)-Ph, or 3,5-(MeO)-Ph. Free-base porphyrins were converted to metalloporphyrins, which were subsequently nitrated with nickel(II), copper(II), or zinc(II) nitrate to give β-nitrometalloporphyrins. These were further reduced to β-aminometalloporphyrins and treated with a methanal equivalent under acidic conditions to selectively obtain Tröger's base , spiro-Tröger's base , or a mixture of both, in yields up to 41% of and 45% of depending on the reaction conditions used. The ratio of to was influenced by the methanal equivalent used, the strength of the acid, and, above all, the solvent. The presence of a metal ion within the porphyrin core and the use of a chlorinated solvent were found to be essential for the formation of spiro-Tröger's base . The molecular structure of spiroTB was proven by electron diffraction.