Rhodium(III) Azuliporphyrins

The
organometallic chemistry of azuliporphyrins has been extended
to the first syntheses of rhodium­(III) derivatives. Reaction of [Rh­(CO)2Cl]2 with an azuliporphyrin in refluxing xylenes
gave rhodium­(III) azuliporphyrins in 62–67% yield. These derivatives
incorporate solvent molecules as axial ligands and thereby introduce
two carbon–rhodium bonds in a three-component reaction. The
methylbenzyl ligands that are derived from xylenes overlie the π
system of the porphyrinoid macrocycle, and proton NMR spectra show
that these units are strongly shielded. The o-, m-, and p-xylene-derived complexes were
characterized by X-ray crystallography, and this confirmed the presence
of the central rhodium atom and the axial benzylic ligands. Additionally,
when the azuliporphyrin was reacted with [Rh­(CO)2Cl]2 in refluxing acetonitrile and then treated with acetone and
basic alumina, a rhodium­(III) azuliporphyrin with an acetone-derived
axial ligand was generated. These results demonstrate that azuliporphyrins
are superior organometallic ligands and therefore merit further investigation.