(Pyrazolylborate)zinc Organophosphate Complexes Resulting from Hydrolytic Cleavage of Phosphate Esters

Abstract

Five different (pyrazolylborate)zinc hydroxide complexes Tp*Zn−OH (1) were used as hydrolytic reagents towards esters of various acids of phosphorus. Trimethyl phosphate and trimethyl phosphite could not be cleaved. Dimethyl and diphenyl phosphite yielded TptBu,MeZn−OPHO(OR) (2, 3). Triphenyl phosphate reacted slowly producing moderate yields of Tp*Zn−OPO(OPh)2 (4). Tris(p‐nitrophenyl) phosphate was cleaved rapidly, forming Tp*Zn−OPO(OC6H4NO2)2 (5) and Tp*Zn−OC6H4NO2 (6). Alkylbis(p‐nitrophenyl) phosphates showed intermediate reactivity, losing p‐nitrophenolate upon hydrolysis and producing Tp*Zn−OPO(OR)(OC6H4NO2) (7, 8). When phosphorus acid diesters were employed, condensation between the Zn−OH and P−OH functions occurred. This proved to be the convenient way of preparing the organophosphate complexes Tp*Zn−OPO(Ph)2 (9), Tp*Zn−OPO(OPh)2 (4), and Tp*Zn−OPO(OC6H4NO2)2 (5). Six structure determinations showed the structural variability of the resulting complexes.

Why does nature use zinc-a personal view

“…As a result, the hydrolytic agent water and the organophosphate, employed to model the substrate, are attached to zinc at the same time. 30 The Tp*Zn-OH complexes were shown to be able to perform, in a stoichiometric way, all hydrolytic reactions catalyzed by zinc enzymes, as outlined elsewhere. 20, 25 Bearing voluminous organic substituents, they suffer from two limitations with respect to catalytic action.…”

Structure and physical properties of several pseudotetrahedral zinc complexes containing a new alkyl thiolate heteroscorpionate ligand

“…Thus far, the most successful metalloprotein models have utilized tris(pyrazolyl)borate ligands, Tp R , as a template, which provides a facial array of three nitrogen donors from which a number of pseudotetrahedral zinc complexes of the form LZnX have been prepared. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, the tris(pyrazolyl)borate ligand is restricted to providing an all nitrogen (N 3 ) donor set around the zinc ion, inappropriate for many zinc-containing biomolecules. Recently efforts to synthesize unsymmetrical ligands with mixed N, O, S donor atoms has been undertaken with some success.…”

Kinetics and mechanism of the catalytic dehydration of HCO3− by zinc(II) complexes of tripod ligands

“…According to the previous studies 2–23, the mechanism for dehydration of HCO 3 − catalyzed by the Zn(II) complexes of tripods is shown in Scheme . In the catalyst [Zn(H 2 O) 2 ] 3 L each arm of tripod bind one zinc(II) ion using two nitrogen atoms to form complex (I), in which the other coordination sites of Zn(II) are occupied by water molecules.…”

“…This is probably due to the formation of a stable bicarbonate intermediate through ring‐closure for Zn(12aneN3) and the inhibition of this effect for the five‐coordinate complex Zn(12aneN4) 10. Vahrenkamp and coworkers have investigated the kinetics thoroughly 15, 16 to describe the properties of interconversion reactions catalyzed by L 3 Zn‐OH or L 3 Zn‐OH 2 species. The L 3 indicates a tris(pyrazolylborate), a chelating ligand that binds zinc through three coordinate bonds provided by the heterocycle pyrazole.…”