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)Zn(2)2.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)Zn(2)2, Ru(CO)Ni(2)2, and Ru(CO)Mg(2)2, are synthesized from Ru(CO)Zn(2)2.Py3T and are characterized by NMR, UV-visible, and fluorescence spectroscopy. The Ru(CO)Zn(2)2 trimer is found to bind Py3T very tightly (K approximately 10(12) M-1), the resultant complex dissociating very slowly (kdissoc approximately 3 x 10(-7) s-1) in CDCl3 at 60 degrees 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 x 10(4):1.