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,Me)Zn-OH inserted CO2 and CS2 in methanol forming the Zn-OCO-OMe 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. (c) 2006 Elsevier B.V. All rights reserved.