Cycloaddition of salicylaldehyde to nitrile: Synthesis and characterization of new macrocyclic copper(II) complexes bearing a heterobicyclic functional pendant arm

Salicylaldehyde reacts with one of the N-CH2CN pendant arms of [CuL1]2+ (L1 = 2,13-bis(N-cyanoethyl)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docosane) to produce [CuL2]2+ bearing one 1-hydroxy-2-aza-4-oxanaphthalene ring. Interestingly, [CuL2]2+ readily reacts with methanol to yield [CuL3]2+ bearing one 1-methoxy-2-aza-4-oxa-3-naphthyl ring. The heterobicyclic functional pendant arms of [CuL2]2+ and [CuL3]2+ are involved in coordination, and each complex has distorted square-pyramidal coordination geometry. Both [CuL2]2+ and [CuL3]2+ are hydrolyzed to [CuL4]2+ bearing one N-CH2CN and one N-CH2CONH2 pendant arms in basic aqueous solutions, though they are quite stable in acidic aqueous solutions.