Abstract
The photochemical dehydrogenation of alkanes is catalyzed in solution by trans-Rh(PMe3)2(CO)Cl with high efficiency; quantum yields up to 0.10 and turnover numbers as high as 5000 are achieved with cyclooctane as substrate. The intramolecular regioselectivity of the reaction is investigated with methyl-, ethyl-, and isopropylcyclohexane. In competition experiments, cyclooctane is found to be 17 times as reactive as cyclohexane; under carbon monoxide atmosphere, the selectivity is enhanced to a factor of 130. A kinetic isotope effect, kH/kD = 5.3, is found for the dehydrogenation of C6H12/C6D12. Both intra- and intermolecular selectivities are consistent with a pathway involving a reversible C-H oxidative addition followed by a β-hydrogen elimination. trans-Rh(PMe3)2(CO)Cl is demonstrated to be the only significant photoactive species in solution. The dehydrogenation reaction is quenched by carbon monoxide with Stern-Volmer kinetics. On the basis of these results, a mechanism is proposed in which the energy needed to drive these thermodynamically unfavorable dehydrogenations is obtained only from Rh-CO bond photolysis.
| Original language | English |
|---|---|
| Pages (from-to) | 7088-7093 |
| Number of pages | 6 |
| Journal | Journal of the American Chemical Society |
| Volume | 111 |
| Issue number | 18 |
| Publication status | Published - 1989 |
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Photochemical dehydrogenation of alkanes catalyzed by trans-carbonylchlorobis(trimethylphosphine)rhodium : Aspects of selectivity and mechanism. / Maguire, John A.; Boese, William T.; Goldman, Alan S.
In: Journal of the American Chemical Society, Vol. 111, No. 18, 1989, p. 7088-7093.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Photochemical dehydrogenation of alkanes catalyzed by trans-carbonylchlorobis(trimethylphosphine)rhodium
T2 - Aspects of selectivity and mechanism
AU - Maguire, John A.
AU - Boese, William T.
AU - Goldman, Alan S
PY - 1989
Y1 - 1989
N2 - The photochemical dehydrogenation of alkanes is catalyzed in solution by trans-Rh(PMe3)2(CO)Cl with high efficiency; quantum yields up to 0.10 and turnover numbers as high as 5000 are achieved with cyclooctane as substrate. The intramolecular regioselectivity of the reaction is investigated with methyl-, ethyl-, and isopropylcyclohexane. In competition experiments, cyclooctane is found to be 17 times as reactive as cyclohexane; under carbon monoxide atmosphere, the selectivity is enhanced to a factor of 130. A kinetic isotope effect, kH/kD = 5.3, is found for the dehydrogenation of C6H12/C6D12. Both intra- and intermolecular selectivities are consistent with a pathway involving a reversible C-H oxidative addition followed by a β-hydrogen elimination. trans-Rh(PMe3)2(CO)Cl is demonstrated to be the only significant photoactive species in solution. The dehydrogenation reaction is quenched by carbon monoxide with Stern-Volmer kinetics. On the basis of these results, a mechanism is proposed in which the energy needed to drive these thermodynamically unfavorable dehydrogenations is obtained only from Rh-CO bond photolysis.
AB - The photochemical dehydrogenation of alkanes is catalyzed in solution by trans-Rh(PMe3)2(CO)Cl with high efficiency; quantum yields up to 0.10 and turnover numbers as high as 5000 are achieved with cyclooctane as substrate. The intramolecular regioselectivity of the reaction is investigated with methyl-, ethyl-, and isopropylcyclohexane. In competition experiments, cyclooctane is found to be 17 times as reactive as cyclohexane; under carbon monoxide atmosphere, the selectivity is enhanced to a factor of 130. A kinetic isotope effect, kH/kD = 5.3, is found for the dehydrogenation of C6H12/C6D12. Both intra- and intermolecular selectivities are consistent with a pathway involving a reversible C-H oxidative addition followed by a β-hydrogen elimination. trans-Rh(PMe3)2(CO)Cl is demonstrated to be the only significant photoactive species in solution. The dehydrogenation reaction is quenched by carbon monoxide with Stern-Volmer kinetics. On the basis of these results, a mechanism is proposed in which the energy needed to drive these thermodynamically unfavorable dehydrogenations is obtained only from Rh-CO bond photolysis.
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UR - http://www.scopus.com/inward/citedby.url?scp=0001562807&partnerID=8YFLogxK
M3 - Article
VL - 111
SP - 7088
EP - 7093
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 18
ER -