Robust, Chiral, and Porous BINAP-Based Metal鈥揙rganic Frameworks for Highly Enantioselective Cyclization Reactions

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• 作者：Takahiro Sawano ; Nathan C. Thacker ; Zekai Lin ; Alexandra R. McIsaac ; Wenbin Lin
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：September 30, 2015
• 年：2015
• 卷：137
• 期：38
• 页码：12241-12248
• 全文大小：628K
• ISSN：1520-5126

文摘

We report here the design of BINAP-based metal鈥搊rganic frameworks and their postsynthetic metalation with Rh complexes to afford highly active and enantioselective single-site solid catalysts for the asymmetric cyclization reactions of 1,6-enynes. Robust, chiral, and porous Zr-MOFs of UiO topology, BINAP-MOF (I) or BINAP-dMOF (II), were prepared using purely BINAP-derived dicarboxylate linkers or by mixing BINAP-derived linkers with unfunctionalized dicarboxylate linkers, respectively. Upon metalation with Rh(nbd)₂BF₄ and [Rh(nbd)Cl]₂/AgSbF₆, the MOF precatalysts I路Rh(BF₄) and I路Rh(SbF₆) efficiently catalyzed highly enantioselective (up to 99% ee) reductive cyclization and Alder-ene cycloisomerization of 1,6-enynes, respectively. I路Rh catalysts afforded cyclization products at comparable enantiomeric excesses (ee鈥檚) and 4鈥? times higher catalytic activity than the homogeneous controls, likely a result of catalytic site isolation in the MOF which prevents bimolecular catalyst deactivation pathways. However, I路Rh is inactive in the more sterically encumbered Pauson鈥揔hand reactions between 1,6-enynes and carbon monoxide. In contrast, with a more open structure, Rh-functionalized BINAP-dMOF, II路Rh, effectively catalyzed Pauson鈥揔hand cyclization reactions between 1,6-enynes and carbon monoxide at 10 times higher activity than the homogeneous control. II路Rh was readily recovered and used three times in Pauson鈥揔hand cyclization reactions without deterioration of yields or ee鈥檚. Our work has expanded the scope of MOF-catalyzed asymmetric reactions and showed that the mixed linker strategy can effectively enlarge the open space around the catalytic active site to accommodate highly sterically demanding polycyclic metallocycle transition states/intermediates in asymmetric intramolecular cyclization reactions.