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 (LiTpmsiPr). Various metal salts reacted with LiTpmsiPr
to give the octahedral complexes M(TpmsiPr)2 (M = Zn, Cu, Ni, Co, Fe) in which each ligand has N,N,O binding
to the metal. In the reaction between LiTpmsiPr and ZnCl2, in addition to the major product Zn(TpmsiPr)2, [LiTpmsiPrZnCl2]·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 TpmsiPr is coordinatively flexible and can act as a
bipodal or tripodal ligand, it appears to favor the formation of octahedral L2M complexes.