Synthesis and structures of zinc complexes with new binucleating ligands containing alkoxide bridges, and their activities in the hydrolysis of tris( p-nitrophenyl)phosphate

Abstract

Four new binucleating ligands featuring a hydroxytrimethylene linker between two coordination sites (1,3-bis{ N-[3-(dimethylamino)propyl]- N-methylamino}propan-2-ol, HL 1 ; 1,3-bis{ N-[2-(dimethylamino)ethyl]- N-methylamino}propan-2-ol, HL 2 ; 1,3-bis[bis(2-methoxyethyl)amino]propan-2-ol, HL 3 ; and 1-bis[(2-methoxyethyl)amino]-3-{ N-[2-(dimethylamino)ethyl]- N-methylamino}propan-2-ol, HL 4 ) were synthesized, along with the corresponding zinc complexes. The structures of three dinuclear zinc complexes ([Zn 2 L 1 (μ-CH 3COO) 2]BPh 4 ( 1), [Zn 2 L 3 (μ-CH 3COO) 2]BPh 4 ( 3), and [Zn 2 L 4 (μ-CH 3COO)(CH 3COO)(EtOH)]BPh 4 ( 4)) and a tetranuclear zinc complex ({[Zn 2 L 2 (μ-CH 3COO)] 2(μ-OH) 2}(BPh 4) 2 ( 2)) were revealed by X-ray crystallography. Hydrolysis of tris( p-nitrophenyl)phosphate (TNP) by these zinc complexes in an acetonitrile solution containing 5% Tris buffer (pH 8.0) at 30 °C was investigated spectrophotometrically and by 31P NMR. Although zinc complexes 1, 3, and 4 did not show hydrolysis activity, the tetranuclear zinc complex 2, containing μ-hydroxo bridges, was capable of hydrolyzing TNP. This suggests that the hydroxide moiety in the complex may have an important role in the hydrolysis reaction.