Construction of Tetranuclear Macrocycles through CH Activation and Structural Transformation Induced by [2+2] Photocycloaddition Reaction

A series of binuclear complexes [{Cp*Ir(OOCCH 2 COO)} 2 (pyrazine)] ( 1 b ), [{Cp*Ir(OOCCH 2 COO)} 2 (bpy)] ( 2 b ; bpy=4,4′‐bipyridine), [{Cp*Ir(OOCCH 2 COO)} 2 (bpe)] ( 3 b ; bpe= trans ‐1,2‐bis(4‐pyridyl)ethylene) and tetranuclear metallamacrocycles [{(Cp*Ir) 2 (OOC‐CC‐COO)(pyrazine)} 2 ] ( 1 c ), [{(Cp*Ir) 2 (OOC‐CC‐COO)(bpy)} 2 ] ( 2 c ), [{(Cp*Ir) 2 (OOC‐CC‐COO)(bpe)} 2 ] ( 3 c ), and [{(Cp*Ir) 2 [OOC(H 3 C 6 )‐NN‐(C 6 H 3 )COO](pyrazine)} 2 ] ( 1 d ), [{(Cp*Ir) 2 [OOC(H 3 C 6 )‐NN‐(C 6 H 3 )COO](bpy)} 2 ] ( 2 d ), [{(Cp*Ir) 2 [OOC(H 3 C 6 )‐NN‐(C 6 H 3 )COO](bpe)} 2 ] ( 3 d ) were formed by reactions of 1 a – 3 a {[(Cp*Ir) 2 (pyrazine)Cl 2 ] ( 1 a ), [(Cp*Ir) 2 (bpy)Cl 2 ] ( 2 a ), and [(Cp*Ir) 2 (bpe)Cl 2 ] ( 3 a )} with malonic acid, fumaric acid, or H 2 ADB (azobenzene‐4,4′‐chcarboxylic acid), respectively, under mild conditions. The metallamacrocycles were directly self‐assembled by activation of CH bonds from dicarboxylic acids. Interestingly, after exposure to UV/Vis light, 3 c was converted to [2+2] cycloaddition complex 4 . The molecular structures of 2 b , 1 c , 1 d , and 4 were characterized by single‐crystal x‐ray crystallography. Nanosized tubular channels, which may play important roles for their stability, were also observed in 1 c , 1 d , and 4 . All complexes were well characterized by 1 H NMR and IR spectroscopy, as well as elemental analysis.