Phthalazin-2-ylidenes As Cyclic Amino Aryl Carbene Ligands in Rhodium(I) and Iridium(I) Complexes

The direct metalation of phthalazinium halides with [Rh('BuO)(COD)](2) or [Ir('BuO)(COD)](2) led to the isolation of stable [MCl(phthalazin-2-ylidene)X(COD)] (M = Rh, Ir) as a new family of cyclic amino aryl carbene transition metal complexes. The X-ray diffraction analysis of several representatives systematically revealed a relatively short C(aryl)-C(carbene) bond distance of 1.44-1.46 angstrom, shorter than the typical C(sp(2))-C(sp(2)) single bond, indicating some electron density delocalization from the pi system of the aryl ring over the vacant carbene orbital.