Synthesis and Recognition Properties of a Ruthenium(II)−Bis(zinc) Cyclic Porphyrin Trimer

A series of cyclic metalloporphyrin trimers containing one Ru(II)−CO porphyrin center are synthesized. A stepwise convergent route is used to synthesize Ru(CO)Zn₂2·Py₃T, where tripyridyltriazine (Py₃T) templates the formation of the trimer and forces the CO group to the outside of the cavity. Three mixed-metal trimers, Ru(CO)Zn₂2, Ru(CO)Ni₂2, and Ru(CO)Mg₂2, are synthesized from Ru(CO)Zn₂2·Py₃T and are characterized by NMR, UV−visible, and fluorescence spectroscopy. The Ru(CO)Zn₂2 trimer is found to bind Py₃T very tightly (K ≈ 10¹² M^-1), the resultant complex dissociating very slowly (k_dissoc ≈ 3 × 10^-7 s^-1) in CDCl₃ at 60 °C. During the course of these studies, the binding selectivity of a ruthenium porphyrin monomer, Ru(CO)3, for pyridine over THF is estimated to be ca. 7 × 10⁴:1.