New tricks for an old ligand: cyclometallated and didentate co-ordination of 2,2′ : 6′,2″-terpyridine to ruthenium( II )

Monomethylation of 2,2′ : 6′,2″-terpyridine (terpy) afforded the N-methyl-2,2′ : 6′,2″-terpyridinium cation, [Hmterpy]+. With one of the terminal pyridine ring nitrogen atoms thus protected, it co-ordinates to ruthenium(II) either as a didentate N,N′-donor giving [Ru(terpy)(Hmterpy-N,N′)Cl][PF6]2, or as a cyclometallating terdentate ligand giving [Ru(terpy)(mterpy-N,N′,C)][PF6]2, depending upon the reaction conditions. Both complexes have been fully characterised by spectroscopic and electrochemical methods, and the crystal structures of [Ru(terpy)(mterpy-N,N′,C)][BF4]2·2MeCN and [Ru(terpy)(Hmterpy-N,N′)Cl][PF6]2·2MeCN determined.