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 <i>o</i>-, <i>m</i>-, and <i>p</i>-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