New H-bond accepting tris(pyrazolyl)borates: stabilization of metal aquo species as models for the vicinal oxygen chelate enzyme superfamily

The hydrogen-bond accepting ligand K[TpCO2Et,Me] was prepared and its complexes with divalent Ni, Co, Mn and Cu reveal a stabilization of penta- or hexa-coordinate metal aquo complexes of the general form [TpCO2Et,MeM(H2O)x] (x = 2 or 3) which are unprecedented for the alkyl substituted Tp analogs. These complexes make good structural models for many of the enzymes of the vicinal oxygen chelate superfamily.