| dc.description.abstract | In order to mimic the active site structure and function of copper proteins, the N,N,O-hetroscorpionate ligand, Lithium 2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetate (3) has been synthesized. Pyrazole rings of ligand were used to mimic imidazole of histidine. A sterically constrained group like tert-butyl group is added to each pyrazole rings that in order to mimic the bulky protein peptide chains. Treatment of ligand Li(bdtbpza) (3) with divalent cupric salt, Cu(NO3)2．2.5H2O, resulted in the formation of two complexes [CuII(bdtbpza)(NO3)] (4) and [CuII2(bdtbpza)2(NO3)2] (5). The conversion between complexes (4) and (5) is temperature-dependent. Complex (4) was achieved at ambient temperature while complex (5) was obtained at low temperature (< −20 oC). The reaction of complex (4) and zinc amalgam in different solvents led to different structures i.e. [ZnII2(bdtbpza)2(NO3)2] (6) from DMF and [CuI3(bdtbpza)3ZnII(NO3)2] (7) from THF. On the other hand, copper(I) complex [CuI3Li(bdtbpza)3(MeOH)](PF6) (8) was synthesized by using [Cu(CH3CN)4](PF6) as the starting metal source.
To study copper oxygenases, reduction of complex (4) or (5) and further conducting with O2(g) process C−H activation and oxygenation to [Cu2II(bdtbpzaO)2] (9), which was also got from a reaction of CuI-containing complex (7) or (8) with O2(g). Interestingly, the reaction of complex (8) and O2(g) not only achieved the dimeric product, (9), but isolated another monomeric product, [CuII(bdtbpzaOH)(DMF)](PF6) (10) was. The activation process is monitored by UV-Vis spectra and ESI-Mass spectra. In the activation of complex (4) at ambient temperature, the time-course UV-Vis showed the absorbance of d−d transition increasing with lengthening time, and the wavelength shifted to higher energy gradually. In the time-course UVVis spectra at −55 oC, the activation of complex (8) exhibited an increasing intensity of the absorption band at 357 and 659 nm. This absorption spectrum was similar to that of complex (9); therefore, it cannot be absolutely assigned as the result from neat CuII−superoxide, CuII−peroxide, complex (9) or (10). In the experiment of tracking ESI-Mass, the fragement, m/z = 599.3, was considered to be copper(II)peroxide. The demetallation of the product (9) from CH activation gave a new ligand, [Na2(bdtbpzaO)2] (11), which allows us to extent another new model chemistry. | en_US |