Synthesis of zinc, copper, nickel, cobalt, and iron complexes using tris(pyrazolyl)methane sulfonate ligands:: A structural model for N,N,O binding in metalloenzymes

Ligands of intermediate steric bulk were designed to mimic metalloenzymes with histidine and carboxlyate binding sites. The reaction between tris(3-isopropylpyrazolyl) methane and butyllithium followed by SO3NMe3 in THF yielded the new ligand lithium tris(3-isopropylpyrazolyl) methane sulfonate (LiTpms(iPr)). Various metal salts reacted with LiTpms(iPr) to give the octahedral complexes M(TpMS(iPr))(2) (M = Zn, Cu, Ni, Co, Fe) in which each ligand has N,N,O binding to the metal. In the reaction between LiTpms(iPr) and ZnCl2, in addition to the major product Zn(Tpms(iPr))(2), [LiTpms(iPr)-ZnCl2]center dot 2THF was also formed as a minor product with a tetrahedral zinc atom coordinated to either N,N,Cl,Cl in the solid phase or N,N,N,Cl in acetonitrile solution. Although Tpms(iPr) is coordinatively flexible and can act as a bipodal or tripodal ligand, it appears to favor the formation of octahedral L2M complexes.