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 SO ₃NMe₃ 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'pr)2, [LiTpms ^iPr-ZnCl₂]·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.