Pyracenebis(imidazolylidene): A New Janus-Type Biscarbene and Its Coordination to Rhodium and Iridium

A pyracene-linked bis-azolium compound has been obtained from the bis-annulation of tetrakis(iminopyracene) (TIP) with chloromethyl methyl ether. The resulting bis-azolium salt was readily coordinated to rhodium and iridium, affording bis-NHC complexes with 2-fold symmetry. The X-ray structural characterization of the Rh complex containing the pyracenebis(imidazolylidene) ligand is also reported. The new bis-NHC ligand consists of two linearly opposed (Janus-type) imidazolylidenes annulated to both sides of a pyracene skeleton.