10.1002/cctc.201900392
ChemCatChem
FULL PAPER
a stir bar. The tube was inserted into a Radleys carousel, vacuum was
applied and the tube was filled with nitrogen (repeated 3 times).
Degassed mesitylene (3 mL) was added with a syringe through the
septum and the reaction vessel was heated to 164 °C with stirring. The
alcohol (1.0 mmol) and the amine (1.0 mmol) were added with a syringe
and the reaction was stirred for 24 h under a flow of nitrogen. The
mixture was then concentrated under reduced pressure and the residue
purified by silica gel flash chromatography eluting with 98/2 hexane/Et3N
(the column was first treated with pure Et3N).
Acknowledgements
The project was supported by the Villum Fonden (grant 12380).
We thank Freja Kjelmann Grauslund and Karoline Hauberg
Rasmussen for their contribution to the substrate scope in Table
2 and Jan-Georges Jersild Balin and Mathias Dircks Olander for
determining the KIE and the Hammett value.
Keywords: Alcohols • Cobalt • Dehydrogenation • Imines •
Homogeneous catalysis
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Figure 4. Proposed mechanism for cobalt-catalyzed dehydrogenation.
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Experimental Section
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General Information: All commercially available reagents were
purchased from Sigma-Aldrich or Strem Chemicals and were used as
received. Mesitylene was reagent grade, stored over activated 4Å
molecular sieves for 24 to 48 h and degassed through 3 freeze-pump-
thaw cycles under an atmosphere of nitrogen. Gas chromatography was
performed on a Shimadzu GCMS-QP2010S instrument fitted with an
Equity 5, 30 m × 0.25 mm × 0.25 m column. Helium was used as the
carrier gas and ionization was performed by electron impact (70 eV).
Flash column chromatography separations were performed on silica gel
60 (40 – 63 m). NMR spectra were recorded on a Bruker Ascend 400
and a Bruker Avance 800 spectrometer. Chemical shifts were measured
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relative to the signals of residual CHCl3 (H = 7.26 ppm) and CDCl3 (C
=
77.16 ppm). LCMS analysis was carried out on a Waters ACQUITY
UPLC system with a PDA and SQD2 electrospray detector and a Thermo
Accucore C18 2.6 m, 2.1 × 50 mm column.
General Procedure: An oven-dried Schlenk tube (24 x 150 mm) was
charged with CoBr2 (11 mg, 0.05 mmol), acid-activated Zn dust (7 mg,
0.10 mmol), Mg3N2 (10 mg, 0.10 mmol), ligand 6 (43 mg, 0.10 mmol) and
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