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

2000-11-29T00:00:00Z (GMT) by Simon J. Webb Jeremy K. M. Sanders
A series of cyclic metalloporphyrin trimers containing one Ru(II)−CO porphyrin center are synthesized. A stepwise convergent route is used to synthesize <b>Ru(CO)Zn</b><b><sub>2</sub></b><b>2·Py</b><b><sub>3</sub></b><b>T</b>, where tripyridyltriazine (<b>Py</b><b><sub>3</sub></b><b>T</b>) templates the formation of the trimer and forces the CO group to the outside of the cavity. Three mixed-metal trimers, <b>Ru(CO)Zn</b><b><sub>2</sub></b><b>2</b>, <b>Ru(CO)Ni</b><b><sub>2</sub></b><b>2</b>, and <b>Ru(CO)Mg</b><b><sub>2</sub></b><b>2</b>, are synthesized from <b>Ru(CO)Zn</b><b><sub>2</sub></b><b>2·Py</b><b><sub>3</sub></b><b>T</b> and are characterized by NMR, UV−visible, and fluorescence spectroscopy. The <b>Ru(CO)Zn</b><b><sub>2</sub></b><b>2</b> trimer is found to bind <b>Py</b><b><sub>3</sub></b><b>T</b> very tightly (K ≈ 10<sup>12</sup> M<sup>-1</sup>), the resultant complex dissociating very slowly (<i>k</i><sub>dissoc</sub> ≈ 3 × 10<sup>-7</sup> s<sup>-1</sup>) in CDCl<sub>3</sub> at 60 °C. During the course of these studies, the binding selectivity of a ruthenium porphyrin monomer, <b>Ru(CO)3</b>, for pyridine over THF is estimated to be ca. 7 × 10<sup>4</sup>:1.