Robust, chiral, and porous BINAP-based metal-organic frameworks for highly enantioselective cyclization reactions.
We report here the design of BINAP-based metal-organic 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·Rh(BF4) and I·Rh(SbF6) efficiently catalyzed highly enantioselective (up to 99% ee) reductive cyclization and Alder-ene cycloisomerization of 1,6-enynes, respectively. I·Rh catalysts afforded cyclization products at comparable enantiomeric excesses (ee's) and 4-7 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·Rh is inactive in the more sterically encumbered Pauson-Khand reactions between 1,6-enynes and carbon monoxide. In contrast, with a more open structure, Rh-functionalized BINAP-dMOF, II·Rh, effectively catalyzed Pauson-Khand cyclization reactions between 1,6-enynes and carbon monoxide at 10 times higher activity than the homogeneous control. II·Rh was readily recovered and used three times in Pauson-Khand cyclization reactions without deterioration of yields or ee's. 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.
Department of Chemistry, University of Chicago , 929 E. 57th Street, Chicago, Illinois 60637, United States.
Takahiro
T
Sawano
Department of Chemistry, University of Chicago , 929 E. 57th Street, Chicago, Illinois 60637, United States.
Nathan C
NC
Thacker
Department of Chemistry, University of Chicago , 929 E. 57th Street, Chicago, Illinois 60637, United States.
Zekai
Z
Lin
Department of Chemistry, University of Chicago , 929 E. 57th Street, Chicago, Illinois 60637, United States.
Alexandra R
AR
McIsaac
Department of Chemistry, University of Chicago , 929 E. 57th Street, Chicago, Illinois 60637, United States.
Wenbin
W
Lin
D003500:Cyclization; D008958:Models, Molecular; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010316:Particle Size; D016062:Porosity; D013237:Stereoisomerism; D013499:Surface Properties
C406943:BINAP, 2-naphthol; D009281:Naphthalenes; D009942:Organometallic Compounds