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Catalytic dehydrogenation of ethane over mononuclear Cr(III)–silica surface sites. Part 2: CH activation by oxidative addition
Author(s) -
Lillehaug Sindre,
Jensen Vidar R.,
Børve Knut J.
Publication year - 2006
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.990
Subject(s) - dehydrogenation , chemistry , catalysis , activation energy , potential energy surface , chromium , oxidative phosphorylation , catalytic cycle , oxidative addition , reaction rate constant , spin states , transition state , photochemistry , medicinal chemistry , kinetics , inorganic chemistry , organic chemistry , molecule , biochemistry , physics , quantum mechanics
Models of Cr(III)–silica were used to study CH activation in ethane by oxidative addition as a possible route to catalytic dehydrogenation. This mechanism involves a formal double oxidation of chromium and a minimum energy crossing point (MECP) was located on the seam between the quartet spin potential energy surface of Cr(III) and the doublet spin potential energy surface of Cr(V). Subsequent to the change of spin state, the CH activation path passes through a transition state on the doublet potential surface, leading to the formation of an ethylhydridochromium(V) complex. This complex represents only a shallow minimum on the potential energy surface and β‐hydrogen transfer to complete the catalytic cycle must therefore take place in the extension of the CH activation step. The combination of a significant activation energy and a small pre‐exponential factor in the rate constant makes CH activation by oxidative addition an unlikely mechanism for dehydrogenation in this system. Copyright © 2005 John Wiley & Sons, Ltd.