Inorganic Chemistry
Article
Characterization of Products. All of the synthesized formamide
products are known, and their characterization data are in good
agreement with those reported in the literature.16,20,23
filtration test during one formylation of morpholine. After 21 h,
the hot reaction mixture was filtered through diatomaceous
earth. The filtrate was found to be catalytically active,
suggesting that the catalyst is homogeneous.
Hot Filtration Test. This test relies on a comparison of catalytic
activity before and after filtering the active catalyst solution.24,25 In this
experiment, in a glovebox under a N2 atmosphere, precatalyst
Ni(acac)2 (0.019 mmol), dmpe (0.058 mmol), morpholine (9.70
mmol), and 1 mL of DMSO were placed in a glass vial within a 31 mL
steel pressure vessel. This vessel was closed, removed from the
glovebox, connected to a CO2 line, and flushed with CO2 three times
to replace most of the nitrogen. The reagents were stirred and allowed
to react with each other in dry DMSO under CO2 pressure (10 bar) at
room temperature for 10−15 min. The mixture was heated to 100 °C
in an oil bath for 20−30 min and then pressurized to 60 bar of CO2.
H2 was added until the total pressure was 100 bar. The reaction was
allowed to proceed for 21 h. After this time, the vessel was cooled to
about 50 °C and cleaned to remove residual heating oil. Inside a
glovebox, the vessel was depressurized slowly and opened, and the hot
solution was passed through a short column of diatomaceous earth in a
fritted-glass filter. DMSO (1 mL) was used to rinse the filter. A small
portion of the filtrate was tested by NMR spectroscopy to confirm the
formylation. The remainder of the filtrate was transferred into a new
glass vial in the steel vessel, fresh morpholine (9.70 mmol) was added,
the vessel was closed, and the hydrogenation of CO2 was resumed in
the same way mentioned above. After 21 h, the vessel was cooled in an
ice bath and depressurized, and the reaction vessel was opened under
air. The filtration process was done through a Celite filter again.
Finally, the filtrate was analyzed by 1H NMR spectroscopy with
cyclohexane as an internal standard, confirming the formylation of the
second batch of morpholine.
In summary, the in situ catalytic activity of complexes
prepared from combinations of an abundant-metal salt and a
phosphine ligand has been investigated for the catalytic
formylation of morpholine, 2-ethylhexylamine, and dimethyl-
amine using CO2 and H2. Fe(II) and Ni(II) phosphine
complexes showed good catalytic activity. The catalytic
formylation of morpholine with CO2 and H2 has been found
to exhibit a TON value of 18000. To the best of our knowledge,
this is the highest TON reported using any abundant-metal
catalyst for formylation using CO2. These studies of CO2
hydrogenation are continuing, with current efforts focused on
the synthesis, structural identification, and testing of isolated Ni
catalyst precursors. So far, repeated attempts at isolating Ni
species simultaneously containing both acac and dmpe ligands
have been unsuccessful.
EXPERIMENTAL METHODS
■
General Considerations. All metal precursors and ligands were
purchased from Sigma-Aldrich, Alfa Aesar, and Strem Chemicals and
used without further purification, unless otherwise specified. All
manipulations involving air- and moisture-sensitive compounds were
carried out using high vacuum and standard Schlenk techniques or in a
glovebox under N2. The organic solvents were distilled under argon
after drying over an appropriate drying agent. All solvents were
degassed by freeze−pump−thaw cycles before use. CO2 (research
grade, 4.8) and H2 (ultrahigh purity, 5.0) were supplied by Praxair
(Canada) and used without further purification. All reagents for the
catalytic reactions were loaded into a 31 or 160 mL high-pressure
reaction vessel in the glovebox. Aliquots were removed from the crude
reaction mixtures immediately after depressurization following the
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
Preliminary screening data (PDF)
specified reaction time and analyzed by a 400 MHz Bruker Advance
̈
NMR spectrometer equipped with an autosampler. Chemical shifts are
indicated in ppm relative to tetramethylsilane (TMS). FT-IR spectra
were recorded as KBr disks or in CHCl3 as a solvent with a Bruker FT-
IR spectrophotometer.
AUTHOR INFORMATION
Corresponding Author
■
Standard Procedure for the Hydrogenation of Carbon
Dioxide. The catalysts were prepared in situ from 3d metal(II) salts
and added phosphines. The reactions were performed in glass vials
within a 31 or 160 mL Parr vessel. The gas pressure was measured by a
pressure gauge, and a burst disk was installed for safety. The reaction
vessel (31 or 160 mL) was loaded with a glass vial containing a stir bar,
57 μmol of the metal salt, monophosphine ligand (228.8 μmol),
diphosphine (114.2 μmol), and 0.5 mL of morpholine in 0.5 mL of
DMSO under an inert atmosphere in a nitrogen-filled glovebox. The
vessel was closed, removed from the glovebox, connected to a CO2
line, and flushed three times with CO2 to remove the nitrogen. The
reagents were then allowed to react with each other in dry DMSO
under CO2 pressure (10−15 bar) at room temperature for 10−15 min.
This time delay was intended to allow ligand/metal salt reactions to
begin before the introduction of H2. The mixture was then heated to
100 °C in an oil bath for 20−30 min, and then the system was
pressurized with 60 bar of CO2. H2 was added until the total pressure
was 100 bar. The 20−30 min delay is required in order for the vessel
to attain the desired temperature before the final gas addition. The
reaction was then allowed to proceed for 21 h. After this time, the
vessel was cooled in an ice bath and depressurized. The crude product
was filtered through diatomaceous earth and analyzed by NMR
spectroscopy using the appropriate deuterated solvents, with cyclo-
hexane as an internal standard.
ORCID
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Sciences and Engineering Research
Council, CREATE/413798-2012, and the Canada Research
Chairs Program for financial support.
REFERENCES
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The determination of the extent of conversion of dimethylamine to
DMF was not possible due to the volatility of the unreacted amine.
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