Immobilization of a Soluble Metal Complex in an Organic Network. Remarkable Catalytic Performance of a Porous Dialkoxyzirconium Polyphenoxide as a Functional Organic Zeolite Analogue

Abstract

Treatment of anthracenebisresorcinol 1 (a tetraphenol) with Zr(O t Bu) 4 in THF results in polycondensation to give an O−Zr−O network and affords a poly(dialkoxyzirconium phenoxide), 1 4 - ·2[Zr(O t Bu) 2 ] (Zr host), in quantitative yield as an insoluble, amorphous, microporous powder with a particle size of ∼0.7 μm, a pore size of ∼0.7 nm, and a specific surface area of ∼200 m 2 /g. The powder exhibits reversible Langmuir-type adsorption/desorption of N 2 at 77 K and hexane at 298 K. Adsorption and coadsorption of ethyl acetate, benzene, and other polar and apolar guests also occurs readily at 298 K. The Zr host catalyzes the Diels−Alder reaction of acrolein with 1,3-cyclohexadiene in a remarkable manner. As a solid metal−organic catalyst, it has a formula-based turnover rate constant of 40 h - 1, which far exceeds those of its components, i.e., the soluble Lewis acid Zr(O t Bu) 4 (0.1 h - 1 ) and the hydrogen-bonded insoluble organic network 1 (0.3 h - 1 ). The solid catalyst can be easily separated from the organic product, which is not contaminated with Zr or the reactants. The recovered catalyst can be used repeatedly without deactivation. The reaction can also be conducted in a flow system with the insoluble Zr host catalyst and a reactant mixture as a mobile phase. The remarkable catalytic performance of the Zr host and its easy preparation suggest that insoluble microporous metal−organic solid catalysts are workup-free and waste-free as well as resource- and energy-saving.