Zinc enzyme modelling with zinc complexes of polar pyrazolylborate ligands

The Zn-OH₂ and Zn-OH complexes of the new tris(pyrazolyl)borate ligands with pyridyl and carboxamido substituents were investigated for their reactivity towards hydrolyzeable substrates. Tp^4−Py,MeZn-OH inserted CO₂ and CS₂ in methanol forming the Zn-OCOOMe and Zn-SCSOMe products. In non-aqueous media, both types of complexes with both types of substituents on the Tp ligands effected stoichiometric cleavage of tris(p-nitrophenyl)phosphate and p-nitrophenyl acetate. In solutions containing water and the MOPS buffer, up to eight p-nitrophenyl groups per equivalent of zinc complex could be cleaved from the esters, and the resulting bis(p-nitrophenyl)phosphate was also degraded to mono(p-nitrophenyl)phosphate. This is the first time that pyrazolylborate-zinc complexes have shown catalytic activity in hydrolytic reactions.