European Journal of Organic Chemistry
10.1002/ejoc.201701173
COMMUNICATION
ruthenium catalysts showing the presence of a ruthenium
dihydride species in the catalytic cycle.[12] As a result, the
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measured KIE value of 2.15 is too small, but it does show that
cleavage of the C-H bond is a slow step in the overall
transformation. The KIE for the decarbonylation step was
measured with 2-naphthaldehyde and 2--[D]-naphthaldehyde
and found to be 1.16.[13] This rather modest value suggests that
C-H cleavage in the aldehyde (e.g. by oxidative addition to
ruthenium) is not the rate-determining step and the KIE for the
overall transformation therefore relates to the alcohol
dehydrogenation. Although, these kinetic experiments do not
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ruthenium(II) phosphine complex as the catalytically active
species responsible for both the dehydrogenation and the
decarbonylation in two separate catalytic cycles as determined
for the corresponding iridium-catalyzed transformation.[5]
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[
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a
biorenewable compound and was recently
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In conclusion, we have described a ruthenium-catalyzed
protocol for the dehydrogenative decarbonylation of primary
alcohols where dihydrogen and carbon monoxide are released.
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[
13] The reaction time necessary for the complete decarbonylation of 2-
naphthaldehyde was compatible to the reaction time for the overall
dehydrogenative decarbonylation of 2-naphthylmethanol, i.e. about 7 h.
The transformation employs 5% of Ru(COD)Cl
2
and 15% of P(o-
tolyl) in refluxing p-cymene and can be applied to both benzylic
3
and non-benzylic primary alcohols. The intermediate aldehyde
can be observed during the reaction, which is therefore believed
to proceed through two separate catalytic cycles.
Experimental Section
General procedure
The primary alcohol (1.0 mmol), Ru(COD)Cl
2
(14 mg, 0.05 mmol), P(o-
tolyl) (45 mg, 0.15 mmol) and a stir bar were placed in a dry Schlenk
3
tube equipped with a cold finger and connected to the vacuum line. The
tube was evacuated and filled with nitrogen three times, followed by
addition of decane (50 mg, internal standard) and p-cymene (2 mL). The
mixture was heated on an oil bath to reflux under a flow of nitrogen and
the reaction was monitored by GCMS. The yield was determined by
GCMS via the internal standard or by evaporation of the solvent and
purification of the residue by flash chromatography (pentane/EtOAc,
95:5).
Acknowledgements
We thank the Villum Fonden for financial support (grant 12380).
Keywords: alcohols • decarbonylation • dehydrogenation •
ruthenium • syngas
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