Controlling Photoreactions with Restricted Spaces and Weak Intermolecular Forces: Exquisite Selectivity during Oxidation of Olefins by Singlet Oxygen
作者:Arunkumar Natarajan、Lakshmi S. Kaanumalle、Steffen Jockusch、Corinne L. D. Gibb、Bruce C. Gibb、Nicholas J. Turro、V. Ramamurthy
DOI:10.1021/ja070086x
日期:2007.4.1
Highly regioselectivephotooxidation of methyl cycloalkenes has been performed in an aqueous medium by selectively blocking two of the three allylic hydrogens through supramolecular steric effect. Hydrophobic, steric, and weak intermolecular C−H−π interactions are suggested to be responsible for the specific orientation of the olefin within a water-soluble, deep-cavity cavitand with eight carboxylic
Kinetics of the Oxygenation of Unsaturated Organics with Singlet Oxygen Generated from H<sub>2</sub>O<sub>2</sub> by a Heterogeneous Molybdenum Catalyst
作者:Bert F. Sels、Dirk E. De Vos、Pierre A. Jacobs
DOI:10.1021/ja065849f
日期:2007.5.1
A heterogeneous catalyst containing MoO42- exchanged on layered double hydroxides (Mo-LDHs) is used to produce O-1(2) from H2O2, and with this dark O-1(2), unsaturated hydrocarbons are oxidized in allylic peroxides. The oxidation kinetics are studied in detail and are compared with the kinetics of oxidation by O-1(2), formed from H2O2 by a homogeneous catalyst. A model is proposed for the heterogeneously catalyzed O-1(2) generation and peroxide formation. The model divides the reaction suspension in two compartments: (1) the intralamellar and intragranular zones of the LDH catalyst; (2) the bulk solution. The 2-compartment model correctly predicts the oxidant efficiency and peroxide yield for a series of olefin peroxidation reactions. O-1(2) is generated at a high rate by the heterogeneous catalyst, but somewhat more O-1(2) is lost by quenching with the heterogeneous catalyst than using the homogeneous catalyst. Quenching occurs mainly as a result of collision with the LDH hydroxyl surface, as is evidenced by using LDH supports containing strong O-1(2) deactivators such as Ni2+. A total of 15 organic substrates were peroxidized on a preparative scale using the best Mo-LDH catalyst under optimal conditions.