Phosphate diester hydrolysis promoted by Zinc(II) complexes with alkoxide pendants

Abstract

Two new Zn(II) complexes of tripodal pyridyl-amine ligands with alcohol pendants, 2-[bis-(2-pyridin-2-yl-ethyl)-amino]-ethanol (L 1) and 3-[bis-(2-pyridin-2-yl-ethyl)-amino]-propan-1-ol (L 2), have been synthesized and structurally characterized. The reactivities of ZnL 1 ( 1) and ZnL 2 ( 2) for promoting the hydrolysis of bis( p-nitrophenyl)phosphate (BNPP) have been investigated, and both complexes are highly active in catalyzing the hydrolysis of BNPP, with 2 ( k = 1.8 × 10 −1 M −1 s −1) being about two orders of magnitude more active than 1 ( k = 2.7 × 10 −3 M −1 s −1) in promoting the hydrolysis of BNPP. The differences in reactivity can be attributed to the disparate abilities of the alkoxide nucleophiles in the pendant groups in ligands L 1 and L 2 to attack the substrate phosphate diester BNPP due to differences in their tether lengths. X-ray crystal structures of 1 and 2 are also reported, which show that the complexes form dimers with bridging alkoxide ligands in the solid state.