N-Heterotricyclic cationic carbene ligands. Synthesis, reactivity and coordination chemistry.

The direct dialkylation of triazolo[4,3-b]isoquinolin-3-ylidene structures readily affords dicationic N-heterotricyclic azolium salts. These are suitable starting materials for the synthesis of transition metal complexes containing N-heterotricyclic, cationic ligands characterized by extended charge delocalization. Silver and gold complexes as well as mono- and dicationic rhodium(i) complexes have been prepared and characterized, and the electronic properties of the ligand have been evaluated by using the TEP parameter and by comparison with a non-cationic analogue. X-Ray diffraction analysis of several carbene-metal complexes shows a negligible effect of the charge on the structures of the complexes. The catalytic activity of a tricationic gold complex has been evaluated in the intramolecular hydroarylation of a terminal alkyne.