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.