120
R.U. Islam et al. / Catalysis Communications 12 (2010) 116–121
Table 1
We also tested the coupling reaction between aryl chlorides with
different alkenes, but no formation of a coupled product could be
detected. The products were purified by chromatography and
identified from their spectroscopic data. These compounds were
found to be identical with those reported by others. The TOF value
indicates that the polymer nanocomposite is a potential candidate
for this kind of reaction, TOF being defined as the mol product/(mol
catalyst. hour) and this was calculated from the isolated yield, the
amount of palladium used and the reaction time. The recyclability of
the catalyst was practically not feasible due to the minute quantity of
the material used for the reaction and as a consequence of the nature
of the support which was soluble in organic solvent and thus is not
recoverable from the system. An ICPMS study indicated that the Pd
loading in the coupled organic products was less than 0.4 wt.% while
an XPS study of the same sample failed to reveal any signal for Pd
which indicates an absence of Pd at the surface or near surface
region.
Heck coupling reactions of aryl iodides with different olefins.
4. Conclusions
Reagents and reaction conditions: aryl iodides (1.0 mmol), alkenes (1.5 mmol), triethyl
amine (1.5 mmol), DMF (5 ml) and catalyst [Pd–poly-(1,8-diaminonaphthalene)] (4 mg),
80 °C, 8 h.
The present paper reports a synthesis route for the preparation of a
metal–polymer composite material that successfully served as an
efficient catalyst for a Heck coupling reaction under phosphine-free
conditions. The process of the formation of the C–C bond by our
catalyst without the use of a phosphine ligand, is eco-friendly, easy to
handle especially since the poly-(1,8-diaminonaphthalene) sup-
ported palladium catalyst is air-stable, all our reactions having been
conducted in air. Such a phosphine-free production process thus has
potential importance in industry as well as in small scale laboratories
from both an environmental and economic point of view. All these
merits indicate that the composite material has potential as a
promising catalyst in Heck reactions. Furthermore, we also believe
that this polymer based composite catalyst is a very promising
candidate for developing other kinds of carbon–carbon coupling
reactions.
temperature did not affect the reaction. Before reaching the melting
temperature the polymer would undergo a phase transition process,
polymer softening at about 95 °C and physical and chemical cross
linking at around 110 °C. As a result of cross linking the active site of
the catalyst could reorient and thus this would be expected to affect
the reaction. For the Heck cross-coupling reactions Pd(0) is the
catalytic species and the possible mechanism is the interaction of aryl
halide (R1X) and Pd(0) to form the aryl-palladium halide complex [R1
(Pd2+)X], which then couples with aryl (R2) alkenes in presence of a
base to produce the [R1–(Pd2+)–R2] intermediate and finally the biaryl
product (R1–R2) is produced via the reductive elimination of Pd2+ to
Pd(0).
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Table 2
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