Photoactive Chiral Metal鈥揙rganic Frameworks for Light-Driven Asymmetric 伪-Alkylation of Aldehydes

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• 作者：Pengyan Wu ; Cheng He ; Jian Wang ; Xiaojun Peng ; Xuezhao Li ; Yonglin An ; Chunying Duan
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：September 12, 2012
• 年：2012
• 卷：134
• 期：36
• 页码：14991-14999
• 全文大小：578K
• 年卷期：v.134,no.36(September 12, 2012)
• ISSN：1520-5126

文摘

Chiral metal鈥搊rganic frameworks (MOFs) with porous and tunable nature show promise as heterogeneous asymmetric catalysts. Through incorporating the stereoselective organocatalyst l- or d-pyrrolidin-2-ylimidazole (PYI) and a triphenylamine photoredox group into a single framework, we have developed two enantiomeric MOFs, Zn鈥?b>PYI1 and Zn鈥?b>PYI2, to prompt the asymmetric 伪-alkylation of aliphatic aldehydes in a heterogeneous manner. The strong reductive excited state of the triphenylamaine moiety within these MOFs initiated a photoinduced electron transfer, rendering an active intermediate for the 伪-alkylation. The chiral PYI moieties acted as cooperative organocatalytic active sites to drive the asymmetric catalysis with significant stereoselectivity. Control experiments using the lanthanide-based metal鈥搊rganic frameworks Ho鈥?b>TCA and MOF鈥?b>150, assembled from 4,4鈥?4鈥?nitrilotribenzoic acid, as catalysts suggested that both the photosensitizer triphenylamine moiety and the chiral organocatalyst d-/l-PYI moiety were necessary for the light-driven 伪-alkylation reactions. Further investigations demonstrated that the integration of both photocatalyst and asymmetric organocatalyst into a single MOF makes the enantioselection superior to that of simply mixing the corresponding MOFs with the chiral adduct. The easy availability, excellent stereoselectivity, great separability, and individual components fixed with their well-defined porous and repeating structures make the MOF a versatile platform for a new type of tandem catalyst and cooperative catalyst.