Carboxy Ester Hydrolysis Promoted by a Dicopper( II ) Macrocyclic Polyamine Complex with Hydroxypropyl Pendant Groups

A dinuclear Cu II complex containing a hexaaza macrocyclic ligand bearing two 2‐hydroxypropyl pendants, 3,6,9,16,19,22‐hexaaza‐6,19‐bis(2‐hydroxypropyl)tricyclo[22.2.2.2 11,14 ]triaconta‐1,11,13,24,27,29‐hexaene (L), was synthesized. The title complex [Cu 2 (H −2 L)Cl 2 ]·6.5H 2 O was isolated as a blue crystal, orthorhombic, space group Fddd , with a = 16.4581(12), b = 32.248(2), c = 35.830(2) Å, V = 19017(2) Å 3 , Z = 16, R 1 = 0.0690, and wR 2 = 0.1546 [ I > 2σ( I )]. The protonation constants of Cu 2 L were determined by potentiometric titration, and it was found that the alcoholic hydroxypropyl group of the complex Cu 2 L exhibits low p K a values of p K a1 = 7.31, p K a2 = 7.83 at 25 °C. The hydrolysis kinetics of 4‐nitrophenyl acetate (NA) promoted by the title complex have also been studied. The pH‐rate profile for Cu 2 L gave a sigmoidal curve and showed a second‐order rate constant of 0.39 ± 0.02 M −1 s −1 in 10% CH 3 CN/H 2 O(v/v), which is greater than that of the dinuclear Cu II complex formed by a hexaaza macrocycle without pendants. The reason for the higher catalytic activity of the title complex is discussed. We found that the volume of nucleophile RO − can effect the hydrolysis of the carboxy ester, the nucleophilicity of RO − and the Lewis acidity of the metal macrocycle also affect the carboxy ester hydrolysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)