Design of a Dinuclear Nickel(II) Bioinspired Hydrolase to Bind Covalently to Silica Surfaces: Synthesis, Magnetism, and Reactivity Studies

Presented herein is the design of a dinuclear NiII synthetic
hydrolase [Ni2(HBPPAMFF)­(μ-OAc)2(H2O)]­BPh4 (1) (H2BPPAMFF
= 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)­aminomethyl)])-4-methyl-6-formylphenol)
to be covalently attached to silica surfaces, while maintaining its
catalytic activity. An aldehyde-containing ligand (H2BPPAMFF)
provides a reactive functional group that can serve as a cross-linking
group to bind the complex to an organoalkoxysilane and later to the
silica surfaces or directly to amino-modified surfaces. The dinuclear
NiII complex covalently attached to the silica surfaces
was fully characterized by different techniques. The catalytic turnover
number (kcat) of the immobilized NiIINiII catalyst in the hydrolysis of 2,4-bis­(dinitrophenyl)­phosphate
is comparable to the homogeneous reaction; however, the catalyst interaction
with the support enhanced the substrate to complex association constant,
and consequently, the catalytic efficiency (E = kcat/KM) and the
supported catalyst can be reused for subsequent diester hydrolysis
reactions.