Small-molecule activation chemistry catalyzed by proton-coupled electron transfer

Proton-coupled electron transfer (PCET) is the basic mechanism for bioenergetic conversion. Consummate examples include water oxidation in photosynthesis and oxygen reduction in respiration. Despite the importance of PCET in such catalytic bond-making and bond-breaking reactions, the underlying mechanisms of coupled proton and electron transport in these processes is not well understood. To address mechanistic issues surrounding the role of PCET in catalytic chemical transformations, we have begun characterizing PCET events at a molecular level in a broad spectrum of small-molecule activation reactions for the first time. Two distinct structural scaffolds have been elaborated to study the PCET chemistry of 0-0 bond forming and cleaving reactions. The first consists of platforms containing two redox sites linked face-to-face by a rigid xanthene (DPX) or dibenzofuran (DPD) spacer - Pacman porphyrins. A comparative structural study demonstrates that DPD has the unprecedented ability to open and close its binding pocket by a vertical distance of over 4 A upon substrate binding, providing the first direct observation of the Pacman effect in a single cofacial platform. Moreover, efficient oxygen-activation chemistry is preserved when such cofacial motifs exhibit a large range of vertical motion; for example, dicobalt(II) complexes of both DPX and DPD are effective electrocatalysts for the direct four- electron reduction of oxygen to water despite their ca. 4 A difference in metal-metal distances.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Chang, Christopher J., 1974-

Advisor dc:contributor.advisor

• Daniel G. Nocera.

• Chemistry.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/29928

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/29928