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

Four new binucleating ligands featuring a hydroxytrimethylene linker between two coordination sites (1,3-bis{N-[3-(dimethylamino)propyl]-N-methylamino}propan-2-ol, HL1; 1,3-bis{N-[2-(dimethylamino)ethyl]-N-methylamino}propan-2-ol, HL2; 1,3-bis[bis(2-methoxyethyl)amino]propan-2-ol, HL3; and 1-bis[(2-methoxyethyl)amino]-3-{N-[2-(dimethylamino)ethyl]-N-methylamino}propan-2-ol, HL4) were synthesized, along with the corresponding zinc complexes. The structures of three dinuclear zinc complexes ([Zn2L1(μ-CH3COO)2]BPh4 (1), [Zn2L3(μ-CH3COO)2]BPh4 (3), and [Zn2L4(μ-CH3COO)(CH3COO)(EtOH)]BPh4 (4)) and a tetranuclear zinc complex ({[Zn2L2(μ-CH3COO)]2(μ-OH)2}(BPh4)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.