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

A series of binuclear complexes [{CP*Ir(OOCCH2COO)}(2)-(Pyrazine)] (1b), [{Cp*Ir(OOCCH2COO)}(2)(bPY)] (2b; bpy = 4,4'-bipyridine), [{Cp*Ir(OOCCH2COO)}(2)(bpe)] (3b; bpe = trans-1,2-bis(4-pyridyl)ethylene) and tetranuclear metallamacrocycles [{(CP*Ir)(2)(OOC-C=C-COO)(Pyrazine)}(2)] (1c), [{(Cp*Ir)(2)(OOC-C=C-COO)(bpy)}(2)] (2c), [{(Cp*Ir)(2)(OOC-C=C-COO)(bpe)}(2)] (3c), and [{(CP*Ir)(2)[OOC(H3C6)-N=N-(C6H3)-COO](Pyrazine)}(2)] (1d), [{(Cp*Ir)(2)[OOC(H3C6)-N-N-(C6H3)COO]-(bpy)}(2)] (2d), [{(CP*Ir)(2)[OOC(H3C6)-N=N-(C6H3)COO](bpe)}(2)] (3d) were formed by reactions of 1a-3a {[(Cp*Ir)(2)(pyrazine)Cl-2] (1a), [(Cp*Ir)(2)(bpy)Cl-2] (2a), and [(Cp*Ir)(2)(bpe)Cl-2] (3a)} 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 C-H bonds from dicarboxylic acids. Interestingly, after exposure to UV/Vis light, 3c was converted to [2+2] cycloaddition complex 4. The molecular structures of 2b, 1c, 1d, 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 1c, 1d, and 4. All complexes were well characterized by H-1 NMR and ER spectroscopy, as well as elemental analysis.