Synthesis and Characterization of Water-Soluble Zinc, Cobalt(II) and Copper(II) Complexes with a Neutral Tripodal N,N,N-Ligand: Crystal Structures of [(κ3N-4-TIPOiPr)Co(H2O)(κ2O-NO3)]NO3 and [(κ3N-4-TIPOiPr)Cu(H2O)(κO-SO4)], 4-TIPOiPr = tris(2-isopropylimidazol-4(5)-yl)phosphane oxide

The development of ligands bearing substituents to model a hydrophobic enzyme cavity and concurrently showing sufficient solubility in aqueous media seems somehow paradox. The zinc and cobalt(II) nitrato (4, 5) and copper(II) sulfato (6) complexes of the new tris(2‐isopropylimidazol‐4(5)‐yl)phosphane oxide ligand (4‐TIPOiPr, 2a) show exactly these properties; in addition, the structure of the CoII complex 5·MeOH·Et2O shows striking similarity to the active site of CoII‐substituted carbonic anhydrase. 2a and its metal complexes are stable towards hydrolysis which is in contrast to the known sensitivity of (imidazol‐2‐yl)phosphane oxides.