Oxidation and Oxygenation of Carbonyl Ruthenium(II) Azuliporphyrin

Chemical
oxidation and oxygenation of carbonyl ruthenium­(II) azuliporphyrin
[Ru­(TPAP)­(CO)] were explored. [Ru­(TPAP)­(CO)] reacts with
dioxygen giving carbonyl ruthenium­(II) 21-oxyazuliporphyrin [Ru­(TPAP-O)­(CO)]
revealing the activation the Ru–C bond inside azuliporphyrin
coordination cavity. Solution and X-ray structural studies confirmed
the tendency of [Ru­(TPAP-O)­(CO)] to form dimeric [Ru­(TPAP-O)­(CO)]2. The dimer adopts a head-to-tail structure with the azulenolate
groups forming bridges from one macrocycle to the ruthenium­(II) in
the adjacent unit. One-electron oxidation of [Ru­(TPAP)­(CO)]
gives the first π-cation radical of metallo­carbaporphyrinoid[Ru­(TPAP)­(CO)]+•with extraordinary participation of the azulene
unit in the spin delocalization. The most characteristic 1H NMR features of the radical are large, sign-alternating isotropic
shifts of resonances assigned to meso-aryl, azulene,
and pyrrolic hydrogen atoms. The spin distribution determined by density
functional theory confirmed the π-cation radical electronic
structure reproducing the diagnostic spectroscopic features including
π-delocalization at meso-aryl resonances and
very characteristic sign alternation of contact shifts for an azulene
moiety.