A Coordination-Induced 1,4→1,2-Quinonediimine Isomerization

Hitherto unused in coordination compounds , the para-quinonoid azophenine (p-ap) has now been applied for the synthesis of Cu(PPh₃)₂(o-ap)](BF₄) ( 1 ), in which the ligand exists as its ortho-quinonoid tautomer. Additional stabilization of this metal–π donor/ligand–π acceptor arrangement occurs through chelate-like hydrogen bonding between the NH functionalities, which are both now ortho-positioned, and the BF₄^? counterion.