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mixture was hot, further reaction was observed and the yield
increased from 48 to 56% (Table 1, entry 14). Thus, at high
temperatures, some leaching occurs and the catalysis is partly
performed by soluble rhenium species. However, the re-depo-
sition of soluble Re species at room temperature allows the re-
use of the recovered catalyst for batch applications. To exclude
the theory that these reactions are entirely the result of homo-
geneous catalysis, the yields that were obtained with the ReOx-
C catalyst were compared with those from reference com-
pounds that were able to produce dissolved oxorhenium spe-
cies. NH4ReO4 catalyzes the DODH reaction of tetradecanediol,
but with lower yields than ReOx-C, likely as a result of its poor
solubility in benzene. Re2O7 dissolved and showed high initial
DODH rates, but quickly became deactivated. Overall, the
yields of tetradecene were much lower than with the hetero-
geneous catalyst (17–19% versus 36% in Table 1, entry 8). The
lower productivity with the oxorhenium reference compounds
Figure 3. Concentrations of the reactant and the product, as determined by
in situ ATR-IR spectroscopy, and the pressure during the DODH of diethyl
tartrate catalyzed by ReOx-C at 1508C.
support the notion that
a
stabilized, catalytically active
The change in total pressure, which can be largely ascribed
to H2 consumption under these conditions, follows the profile
of the tartrate consumption, as would be expected from the
reaction stoichiometry (Scheme 4). An induction period of 2 h
was found when the ReOx-C sample was pre-reduced for only
10 min prior to the addition of diethyl tartrate, whereas the in-
duction period was shorter when the catalyst was reduced for
a longer time. These results indicate that the catalyst first has
to be transformed into a reduced active state.
perrhenate species exists on the carbon support. Interestingly,
the solubility of both reference compounds increased in the
presence of diols, thus suggesting complexation of the rheni-
um by the diol.
The deoxydehydration of (+)-diethyl tartrate by ReOx-C re-
sulted in an efficient and highly selective conversion into the
trans olefin, diethyl fumarate, in excellent yield (>95%)
(Scheme 4), with no detectable reduction or hydrolysis of the
Finally, we also assessed the ability of ReOx-C to catalyze hy-
drogen-transfer DODH reactions of glycols. Heating a mixture
of the C14-glycol and diisopropyl carbinol with ReOx-C (about
10 mol%, 1508C, benzene) over a few days cleanly afforded
1,2-tetradecene (43% yield, 165 h, Scheme 5). With benzyl alco-
Scheme 4. The deoxydehydration of (+)-diethyl tartrate by ReOx-C.
carboxy groups. Diethyl fumarate is the expected product if
the catalytic reaction proceeds through stereoselective syn
elimination of the vicinal hydroxy groups, which can be realiz-
ed through the formation and concerted retrocyclization of
a Re-O,O-glycolate intermediate, as proposed for the homoge-
neous rhenium-catalyzed DODH reaction.[5–10] Some caution
must be applied to this result, because diethyl maleate (cis)
was partially converted into diethyl fumarate under catalytic
conditions (ReOx-C, 1.4 MPa H2, 1508C, 24 h).
Scheme 5. Yields of the olefin in the DODH reaction with various hydrogen-
transfer reagents.
To gain an initial insight into the reaction kinetics, the DODH
of diethyl tartrate was spectroscopically monitored in an auto-
clave with an integrated ATR-IR probe in the reactor wall. The
specific IR bands of the reactant (diethyl tartrate) and product
(diethyl fumarate) were used to calculate their respective con-
centrations (for details of the reactor and calibration proce-
dures, see the Supporting Information). No other products
except for diethyl fumarate were observed by in situ IR spec-
troscopy, consistent with the high selectivity that was ob-
served by GC and NMR spectroscopy. Figure 3 shows excellent
correlation between the rate of conversion of the tartrate and
the rate of formation of fumarate.
hol as the co-reactant under the same conditions, a faster reac-
tion ensued with 52% of the olefin detected after 70 h, along
with benzaldehyde as a co-product. The H-donor tetrahydro-
naphthalene, which is abundant in petroleum, was also effec-
tive under the same conditions in the DODH reaction catalyzed
by ReOx-C, thereby affording 40% of tetradecene (and naph-
thalene) after 161 h. In all cases, no alkane product was
detected.
Herein, we have reported the first polyol-into-olefin DODH
reactions catalyzed by supported ReOx, by employing both H2
and hydrogen-transfer reductants. It appears that DODH catal-
ysis is promoted by both soluble and surface-bound Re spe-
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