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

The direct metalation of phthalazinium halides with [Rh(^tBuO)(COD)]₂ or [Ir(^tBuO)(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 Å, shorter than the typical C(sp²)−C(sp²) single bond, indicating some electron density delocalization from the π system of the aryl ring over the vacant carbene orbital.