Stepwise Deoxygenation of Nitrite as a Route to Two Families of Ruthenium Corroles: Group 8 Periodic Trends and Relativistic Effects.

Given the many applications of ruthenium porphyrins, the rarity of ruthenium corroles and the underdeveloped state of their chemistry are clearly indicative of an area ripe for significant breakthroughs. The tendency of ruthenium corroles to form unreactive metal-metal-bonded dimers has been recognized as a key impediment in this area. Herein, by exposing free-base meso-tris(p-X-phenyl)corroles, H3[TpXPC] (X = CF3, H, Me, and OMe), and [Ru(COD)Cl2]x in refluxing 2-methoxyethanol to nitrite, we have been able to reliably intercept the series Ru[TpXPC](NO) in a matter of seconds to minutes and subsequently RuVI[TpXPC](N), the products of a second deoxygenation, over some 16 h. Two of the RuVIN complexes and one ruthenium corrole dimer could be crystallographically analyzed; the Ru-Nnitrido distance was found to be ∼1.61 Å, consistent with the triple-bonded character of the RuVIN units and essentially identical with the Os-Nnitrido distance in analogous osmium corroles. Spectroscopic and density functional theory (DFT) calculations suggest that the RuNO corroles are best viewed as innocent {RuNO}6 complexes, whereas the analogous FeNO corroles are noninnocent, i.e., best viewed as {FeNO}7-corrole•2-. Both RuVIN and OsVIN corroles exhibit sharp Soret bands, suggestive of an innocent macrocycle. A key difference between the two metals is that the Soret maxima of the OsVIN corroles are red-shifted some 25 nm relative to those of the RuVIN complexes. Careful time-dependent DFT studies indicate that this difference is largely attributable to relativistic effects in OsVIN corroles. The availability of two new classes of mononuclear ruthenium corroles potentially opens the door to new applications, in such areas as catalysis and cancer therapy.