Molecular building block approaches to chiral porous zirconium phosphonates for asymmetric catalysis

Porous zirconium phosphonates containing chiral dihydroxy functionalities have been synthesized via a building block approach. Enantiopure atropisomeric bisphosphonic acids of various lengths, L-1-L-3, were first synthesized starting from 1,1'-bi-2-naphthol (BINOL) in multi-step sequences. Amorphous chiral porous zirconium phosphonates were then obtained by refluxing BINOL-derived bisphosphonic acids with Zr((OBu)-Bu-n)(4) in n-BuOH, and have been characterized by powder X-ray diffraction, solid-state CP-MAS P-31 NMR, IR, TGA, adsorption measurements, circular dichroism spectroscopy, and microanalyses. These zirconium phosphonates have empirical formulae of (Zr-L1-3).xH(2)O (X = 4 or 5), and exhibit BET surface areas ranging from 431 to 586 m(2)/g. In combination with Ti((OPr)-Pr-i)(4), these zirconium phosphonates have been used to heterogeneously catalyze the additions of diethylzinc to a wide range of aromatic aldehydes with high conversions and e.e. of up to 72%. This work represents a novel approach towards heterogeneous asymmetric catalysis. The tunability of such a molecular building block approach promises to lead to practically useful heterogeneous asymmetric catalytic processes. (C) 2004 Elsevier B.V. All rights reserved.