Kinetics of photochemical alkane dehydrogenation catalyzed by Rh(PMe3)2(CO)Cl

Implications concerning the C-H bond activation step

Glen P. Rosini, Sobhi Soubra, Maxime Vixamar, Sheyi Wang, Alan S Goldman

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

The mechanism of photochemical alkane dehydrogenation catalyzed by Rh(PMe3)2(CO)Cl has been further probed with an emphasis on characterizing the initial C-H activation step and understanding the effect of added CO on selectivity. While pure cyclooctane and pure cyclohexane are dehydrogenated at the same rate (same quantum yields), cyclooctane shows much greater reactivity in mixtures of the two solvents. The product ratio (cyclooctene:cyclohexene) is highly dependent upon the partial pressure of CO, ranging from 12 in the absence of CO, to 75 in the limit of high CO pressure (>ca. 400 torr). The kinetic isotope effect for the dehydrogenation of c-C6H12/c-C6D12 is also found to be dependent upon CO pressure, ranging from 10 in the absence of CO to 4.2 under high CO pressure. The results support our earlier conclusion that the intermediate responsible for C-H activation is ground state [Rh(PMe3)2Cl]. It is also concluded that inhibition of the reaction by CO operates primarily via addition of CO to the intermediate alkyl hydrides, (R)(H)Rh(PMe3)2Cl. Addition of CO prior to C-H bond addition is apparently not a kinetically significant process, even under high CO pressure.

Original languageEnglish
Pages (from-to)41-47
Number of pages7
JournalJournal of Organometallic Chemistry
Volume554
Issue number1
Publication statusPublished - Mar 5 1998

Fingerprint

Alkanes
Dehydrogenation
Carbon Monoxide
dehydrogenation
Paraffins
alkanes
Chemical activation
activation
Kinetics
kinetics
cyclohexane
isotope effect
hydrides
partial pressure
Quantum yield
Cyclohexane
reactivity
selectivity
Hydrides
Partial pressure

Keywords

  • C-H bond activation step
  • CO pressure
  • Dehydrogenation

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry
  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Materials Chemistry

Cite this

Kinetics of photochemical alkane dehydrogenation catalyzed by Rh(PMe3)2(CO)Cl : Implications concerning the C-H bond activation step. / Rosini, Glen P.; Soubra, Sobhi; Vixamar, Maxime; Wang, Sheyi; Goldman, Alan S.

In: Journal of Organometallic Chemistry, Vol. 554, No. 1, 05.03.1998, p. 41-47.

Research output: Contribution to journalArticle

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AB - The mechanism of photochemical alkane dehydrogenation catalyzed by Rh(PMe3)2(CO)Cl has been further probed with an emphasis on characterizing the initial C-H activation step and understanding the effect of added CO on selectivity. While pure cyclooctane and pure cyclohexane are dehydrogenated at the same rate (same quantum yields), cyclooctane shows much greater reactivity in mixtures of the two solvents. The product ratio (cyclooctene:cyclohexene) is highly dependent upon the partial pressure of CO, ranging from 12 in the absence of CO, to 75 in the limit of high CO pressure (>ca. 400 torr). The kinetic isotope effect for the dehydrogenation of c-C6H12/c-C6D12 is also found to be dependent upon CO pressure, ranging from 10 in the absence of CO to 4.2 under high CO pressure. The results support our earlier conclusion that the intermediate responsible for C-H activation is ground state [Rh(PMe3)2Cl]. It is also concluded that inhibition of the reaction by CO operates primarily via addition of CO to the intermediate alkyl hydrides, (R)(H)Rh(PMe3)2Cl. Addition of CO prior to C-H bond addition is apparently not a kinetically significant process, even under high CO pressure.

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