Carboxy ester hydrolysis promoted by two new bimetallic macrocyclic complexes. Synthesis, characterization and catalytic activity Yan-Wei Ren, Hui Guo, Chen Wang, Jing-Jing Liu, Hua Jiao, Jun Li* and Feng-Xing Zhang Shaanxi Key Laboratory of Physico-inorganic Chemistry, Department of Chemistry, Northwest University, Xi’an, Shaanxi, 710069, China Received 17 January 2006; accepted 2 March 2006 Abstract A dinuclear macrocyclic ligand containing [12]aneN 3 and its two transition metal complexes, [Zn 2 L(OAc) 2 ](ClO 4 ) 2 (1) and [Cu 2 L(OAc) 2 ](ClO 4 ) 2 (2) have been synthesized and characterized on the basis of elemental analyses, molar conductivities, 1 H-n.m.r, IR spectra, electronic spectra and thermal analysis. In addition, the studies on the hydrolysis of a caboxy ester, 4-nitrophenyl acetate (NA), promoted by the two complexes were also investigated. The experimental results indicated that the two complexes can efficiently catalyze hydrolysis of NA, and the k NA for complexes (1) and (2) at pH 7.25, 25 °C, were calculated to be 4.46 Â 10 )2 and 4.21 Â 10 )2 M )1 s )1 , respectively, which are better than those of the corresponding mononuclear complex in the same conditions. Introduction Dinuclear metallohydrolases are a class of ubiquitous enzymes that catalyze the hydrolytic cleavage of target bond in a substrate-specific manner, such as nuclease P1 and purple acid phosphate [1, 2], in which the most important and distinguishing features are that the two ions are connected to each other through one solvent molecule (OH ) or H 2 O) as well as the carboxylate function from amino acid side chains [3–5]. The cata- lytic role of metal ion is ascribed to the orientation and activation of substrates; the bridging groups keep the ions at a suitable distance and give a fundamental contribution to substrate activation. Much effort has been devoted to the study of metal complexes with 1,4,7-triazacyclononane ([9]aneN 3 ) and bis(1,4,7-triazacyclononane) ligands [6–8]. This reflects the well-known, and excellent coordinating properties of [9]aneN 3 ligands. However, much less attention has been paid to the analogous compound 1,5,9-triazacy- clododecane ([12]aneN 3 ). Although the synthesis was reported several years ago, the coordination properties of bis([12]aneN 3 ) still remain relatively undeveloped. Recent studies using ([12]aneN 3 ) have shown that this larger macrocyclic ligand provides interesting biomi- metic properties on some of its complexes [9, 10], quite different from their [9]aneN 3 analogs. To elucidate whether the bis([12]aneN 3 ) ligand can mimic the chemical surrounding of Zn(II) or Cu(II) in the active site of Zn(II) or Cu(II)-containing enzymes and also to seek better and more practical hydrolysis catalysts, herein we synthesized and characterized a di- nuclear macrocyclic ligand L containing [12]aneN 3 , as well as two new bimetallic complexes [Zn 2 L(OAc) 2 ] (ClO 4 ) 2 (1) and [Cu 2 L(OAc) 2 ](ClO 4 ) 2 (2). Further- more, the studies on the hydrolysis of a carboxy ester, 4-nitrophenyl acetate (NA), promoted by the two com- plexes have also been carried out. Experimental Materials and general methods Most of the reagents purchased were of the highest commercial quality and were used without further purification. Solvents were dried by conventional pro- cedures and all samples were thoroughly dried prior to elemental analyses. Orthodiaminde (III) (see Scheme 1) was prepared according to previous literature [11]. The C, H and N elemental analyses were performed on a Vario EL-III instrument. Transition metal contents were determined using a TAS986 atomic absorption spectrophotometer. The IR spectra were recorded on an Equinox 55 spectrophotometer in the 4000–400 cm )1 region using a powdered sample on a KBr plate. Electronic spectra were recorded on a TU- 1800 spectrophotometer in water solution. Molar conductances were determined on a DDS-11A conductance instrument in water solution. Thermal decomposition was performed on a Netzsch STA 449C instrument, with a heating rate of 10 °C/min, in nitro- gen. 1 H-n.m.r. was recorded on a Varian INOVA- 400 MHz spectrometer with TMS as internal standard in D 2 O solution at room temperature. * Author for correspondence: E-mail: junli@nwu.edu.cn Transition Metal Chemistry (2006) 31:611–615 Ó Springer 2006 DOI 10.1007/s11243-006-0037-x