Proton-coupled O-O activation on a redox platform bearing a hydrogen-bonding scaffold.
Porphyrin architectures bearing a hydrogen-bonding scaffold have been synthesized. The H-bond pendant allows proton-coupled electron transfer (PCET) to be utilized as a vehicle for effecting catalytic O-O bond activation chemistry. Suzuki cross-coupling reactions provide a modular synthetic strategy for the attachment of porphyrins to a rigid xanthene or dibenzofuran pillar bearing the H-bond pendant. The resulting HPX (hanging porphyrin xanthene) and HPD (hanging porphyrin dibenzofuran) systems permit both the orientation and acid-base properties of the hanging H-bonding group to be controlled. Comparative reactivity studies for the catalase-like disproportionation of hydrogen peroxide and the epoxidation of olefins by the HPX and HPD platforms with acid and ester hanging groups reveal that the introduction of a proton-transfer network, properly oriented to a redox-active platform, can orchestrate catalytic O-O bond activation. For the catalase and epoxidation reaction types, a marked reactivity enhancement is observed for the xanthene-bridged platform appended with a pendant carboxylic acid group, establishing that this approach can yield superior catalysts to analogues that do not control both proton and electron inventories.
Chang
Christopher J
CJ
Department of Chemistry, 6-335, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA.
Chng
Leng Leng
LL
Nocera
Daniel G
DG
D001572:Benzofurans / Q000737:chemistry*; D002374:Catalase / Q000737:chemistry / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000378:metabolism; D004852:Epoxy Compounds / Q000737:chemistry; D006860:Hydrogen Bonding; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism; D011166:Porphyrins / Q000138:chemical synthesis* / Q000737:chemistry; D011522:Protons; D014966:Xanthenes / Q000737:chemistry*
D001572:Benzofurans; D004852:Epoxy Compounds; D011166:Porphyrins; D011522:Protons; D014966:Xanthenes; C023614:dibenzofuran; D003577:Cytochrome P-450 Enzyme System; D010544:Peroxidases; D002374:Catalase