Modular, Homochiral, Porous Coordination Polymers: Rational Design, Enantioselective Guest Exchange Sorption and Ab Initio Calculations of Host–Guest Interactions

摘要

Two new, homochiral, porous metal–organic coordination polymers [Zn₂(ndc){(R)-man}(dmf)]3DMF and [Zn₂(bpdc){(R)-man}(dmf)]2DMF (ndc=2,6-naphthalenedicarboxylate; bpdc=4,4′-biphenyldicarboxylate; man=mandelate; dmf=N,N′-dimethylformamide) have been synthesized by heating ZnII nitrate, H₂ndc or H₂bpdc and chiral (R)-mandelic acid (H₂man) in DMF. The colorless crystals were obtained and their structures were established by single-crystal X-ray diffraction. These isoreticular structures share the same topological features as the previously reported zinc(II) terephthalate lactate [Zn₂(bdc){(S)-lac}(dmf)]DMF framework, but have larger pores and opposite absolute configuration of the chiral centers. The enhanced pores size results in differing stereoselective sorption properties: the new metal–organic frameworks effectively and stereoselectively (ee up to 62 %) accommodate bulkier guest molecules (alkyl aryl sulfoxides) than the parent [Zn₂(bdc){(S)-lac}(dmf)]DMF, while the latter demonstrates decent enantioselectivity toward precursor of chiral anticancer drug sulforaphane, CH₃SO(CH₂)₄OH. The new homochiral porous metal–organic coordination polymers are capable of catalyzing a highly selective oxidation of bulkier sulfides (2-NaphSMe (2-C₁₀H₇SMe) and PhSCH₂Ph) that could not be achieved by the smaller-pore [Zn₂(bdc){(S)-lac}(dmf)]DMF. The sorption of different guest molecules (both R and S isomers) into the chiral pores of [Zn₂(bdc){(S)-lac}(dmf)]DMF was modeled by using ab initio calculations that provided a qualitative explanation for the observed sorption enantioselectivity. The high stereo-preference is accounted for by the presence of coordinated inner-pore DMF molecule that forms a weak CHO bond between the DMF methyl group and the (S)-PhSOCH₃ sulfinyl group.