Chemical Papers
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for the acceptorless dehydrogenation of amines into imines.
This reaction occurs eꢂciently in the oxidant free condi-
tion and is accompanied by liberation of hydrogen gas as a
by-product.
septum in a NMR tube ꢀlled with toluene-d8. HNMR result
showed the presence of hydrogen at 4.65 ppm.
Results and discussion
Experimental
Primary results on the dehydrogenation of benzylamine
using diꢁerent percentages of iron complexes with phos-
phine as a ligand in several conditions such as diꢁerent
additives and diꢁerent amounts of PPh and FeCl are
General
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All reagents were purchased from Sigma-Aldrich and used
without further purification. Column chromatography
separations were performed on silica gel (220−440 mesh)
and aluminium oxide (100–200). The NMR spectra were
determined on a Bruker Avance DRX-400 MHz. Elemental
microanalysis was performed on a Thermo Finnigan Flash
EA 1112 series CHN analyzer. The physical, analytical and
spectral data for all compounds are given in the Supplemen-
tary material to this paper.
shown in Table 1.
At ꢀrst, the catalytic activity was investigated in diꢁer-
ent amounts of metal and ligand. When 2 mol% of FeCl
2
was used, the product was formed in low yield (Table1,
entry1). Increasing the loading of the catalyst to 9 mol%
has improved the yield to 90% (entries 2–5). But, when the
catalyst loading was increased over (above) the 9 mol%,
no signiꢀcant change was observed in the eꢂciency of
reaction (Table1, entry 6). Then, diꢁerent amounts of
ligand were investigated, which only 18 mol% of ligand
was approved and had good eꢂciencies (Table1, entries
General Procedure
5
, 7 and 9). Further optimization of the reaction was per-
FeCl (11.4 mg, 0.09 mmol), triphenylphosphine (47.2 mg,
formed by studding the eꢁect of additive on the reaction
yields. We understood that in the additive-free condition,
the yields are not more than 78% (Table1, entry 17). No
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0
.18 mmol) and t-BuOK (11.2 mg, 0.10 mmol (and 2 mmol
aniline derivatives in the case of heterocoupling reaction)
were placed in a dry Schlenk tube and connected to the
vacuum line. The tube was evacuated and ꢀlled with nitro-
gen three times. Freshly degassed mesitylene (3 mL) was
injected into the mixture, which was then heated to 160 °C
improvement was observed by adding 10% MgSO , NaH,
4
Na CO and K CO (Table1, entries 10 and 12–14). By
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3
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adding 10 mol% of DABCO as an organic additive, an
improvement was observed (Table1, entry 11). Finally,
with 10% of t-BuOK the yield changed to 90% (Table1,
entry 5) clearly showing that additional reactivity by
t-BuOK as an additive can be useful.
under a N atmosphere and then benzylic amine (2 mmol)
2
was added. The progress of reaction was monitored by thin
layer chromatography. After ꢀnishing the reaction, the mix-
ture was cooled to room temperature and the product was
puriꢀed by aluminium oxide (activated) or silica gel col-
Additionally, in the absence of PPh , the reaction yield
3
was decreased (Table1, entry18). Also, in FeCl -free
2
umn chromatography (96/4 hexane/Et N) to give the prod-
condition, the reaction was prevented and no product was
isolated (Table 1, entry 19). Optimization studies showed
that FeCl (9 mol%), PPh (18 mol%), t-BuOK (10 mol %)
3
uct. In the case of heterocoupling reaction, benzylic amins
(
1 mmol) and aniline derivatieves (2 mmol) were applied.
2
3
and mesitylene (3 ml) at 160 °C are the best combinations
Procedure for hydrogen detection
for this catalytic system in this reaction.
After optimizing the reaction conditions, the various
amines were examined under the mentioned reaction con-
ditions (Table 2). In all the cases, benzylic amines contain-
ing electron-withdrawing groups gave lower yields than
that with electron-donating groups. (Table2, entries 4–7).
As shown as in the Table 2, the substituted benzylamine
with methyl group has an excellent yield. In addition, the
existence of reactivity diꢁerent between benzylamines
and aniline derivatives can make it possible to do hetero-
coupling reaction (Table 2, entries 8 and 9). In order to
prevent of forming homocoupling products, 2 mmol of
aniline derivatives have been employed. Additionally, the
further investigations have been done for the all entries in
An oven-dried Schlenk tube was charged with FeCl
2
(
11.4 mg, 0.09 mmol), triphenylphosphine (47.2 mg,
0
.18 mmol) and t-BuOK (11.2 mg, 0.10 mmol. The tube
was then inserted into an oil bath, vacuum was used and
the tube was ꢀlled with nitrogen (repeated 3 times). Freshly
degassed mesitylene (3 mL) was injected into the mixture
and the mixture was heated to 160 °C and then benzylamine
(
2 mmol) was added. Subsequently, the tube was discon-
nected from the nitrogen atmosphere and connected to a
burette ꢀlled with water. After completion of reaction, the
hydrogen gas collected in the burette was bubbled through a
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Nazarahari, Maryam
