Structural determination of ruthenium-porphyrin complexes relevant to catalytic epoxidation of olefins

A reproducible synthesis of a competent epoxidation catalyst, Ru(VI)(TPP)(O)2)] (TPP = tetraphenylporphyrin dianion), starting from Ru(II)(TPP)(CO)L] (L = none or CH3OH), is described. The molecular structure of the complex was determined by using ab initio X-ray powder diffraction (XRPD) methods, and its solution behavior was in detail investigated by NMR techniques such as PGSE (pulsed field gradient spin-echo) measurements. Ru(IV)(TPP)(OH)]2O, a reported byproduct in the synthesis of Ru(VI)(TPP)(O)2], was synthesized in a pure form by oxidation of Ru(II)(TPP)(CO)L] or by a coproportionation reaction of Ru(VI)(TPP)(O)2] and Ru(II)(TPP)(CO)L], and its molecular structure was then determined by XRPD analysis. Ru(VI)(TPP)(O)2] can be reduced by dimethyl sulfoxide or by carbon monoxide to yield Ru(II)(TPP)(S-DMSO)2] or Ru(II)(TPP)(CO)(H2O)], respectively. These two species were characterized by conventional single-crystal X-ray diffraction analysis.