title: Urea metal-organic frameworks as effective and size-selective hydrogen-bond catalysts.
abstract: A new urea-containing metal-organic framework (MOF) was synthesized to act as a heterogeneous catalyst. Ureas are well-known for self-recognition and aggregation behavior, resulting in loss of catalytic competency. The catalyst spatial isolation achievable in a porous MOF environment suggests a potentially general solution. The combination of a symmetrical urea tetracarboxylate strut, 4,4'-bipyridine, and Zn(NO(3))(2)·6H(2)O under solvothermal conditions afforded a new microporous MOF (NU-601). This material is indeed an effective hydrogen-bond-donor catalyst for Friedel-Crafts reactions between pyrroles and nitroalkenes, whereas a homogeneous urea is much less competent. The higher rates of reaction of small substrates relative to larger ones with NU-601 strongly suggest that catalysis primarily occurs within the pores of this new material rather than on its exterior. To the best of our knowledge, this approach is the first example of specific engineering of successful hydrogen-bonding catalysis into a MOF material.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Roberts
authors.forename: Branden M
authors.initials: BM
authors.lastname: Fini
authors.forename: Amy A
authors.initials: AA
authors.lastname: Sarjeant
authors.forename: Omar K
authors.initials: OK
authors.lastname: Farha
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Hupp
authors.forename: Karl A
authors.initials: KA
authors.lastname: Scheidt
mesh_terms: D002384:Catalysis; D006860:Hydrogen Bonding; D008670:Metals / Q000138:chemical synthesis / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D014508:Urea / Q000138:chemical synthesis / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D008670:Metals; D009942:Organometallic Compounds; D011725:Pyridines; D014508:Urea; D015032:Zinc; C034306:4,4'-bipyridyl