| Recently there has been a great interest in the hydrolytic chemistry of binuclear metal complexes. Herein I report the catalytic hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) with the bimetallic copper complex dibromo(1,6-bis(1,4,7-triaza-1-cyclononyl)-p-xylene) dicopper(II) (Cu2(pL1)Br4 ). Half-order dependence of the rate of BNPP hydrolysis on the concentration of Cu2(pL1)Br4 is indicative of a monomer-dimer equilibrium in which the inactive hydroxide-bridged dimer is the prevalent species. The pH rate profile for the hydrolysis of BNPP by Cu2(pL1)Br4 is consistent with two catalytically competent protonation states contributing to the hydrolysis reaction. Interestingly, the hydrolysis of BNPP by the metal complex, Cu2( pL1)Br4, showed a similar rate enhancement over the background hydrolysis rate to that of the mononuclear Cu([9]aneN 3)Cl2. There does not appear to be significant cooperation between the two copper centers of Cu2(pL 1)Br4 in the hydrolysis of BNPP.; The syntheses and characterizations by x-ray crystallography, EPR, and electronic absorption spectroscopy are reported for [Cu([9]aneN3) 2][CF3SO3]2·H2O [Cu([9]aneN 2O)2][BF4]2, and [Cu([9]aneN2 O)2][NO3]2. The dynamic Jahn-Teller distortion present in the Cu([9]aneN3)22+ cation is removed upon replacement of one nitrogen donor with oxygen. The pseudooctahedral structures of [Cu([9]aneN2O)2][BF 4]2, and [Cu([9]aneN2O)2][NO3 ]2, determined crystallographically, exhibit a strong tetragonal distortion with the two oxygen atoms in the elongated axial positions. In contrast, crystallographic characterizations of a number of Cu([9]aneN 3)22+ salts reveal that the octahedral-like coordination about the Cu(II) is dependent on crystal packing forces, and the degree of tetragonal distortion varies with the identity of the counter ion. A room temperature powder EPR spectrum of [Cu([9]aneN2O) 2]Br2 exhibits a static Jahn-Teller distortion while that of [Cu([9]aneN3)2][CF3SO3] 2 is dynamically averaged. Solution EPR and electronic absorption spectra of [Cu([9]aneN2O)2][CF3SO3] 2 indicate a strong interaction between the equatorial nitrogen atoms and the Cu(II) as evidenced by the observation of nitrogen hyperfine splitting in gx and a shift of the ligand-field absorption to higher energy. The absence of a dynamic Jahn-Teller effect in the presence of the [9]aneN 2O ligand correlates with a lowered reactivity for phosphodiester hydrolysis, suggesting that ligand fluxionality may be important in accessing the transition state in copper-promoted hydrolysis. |
