DOI: 10.1002/cctc.201600257
Full Papers
Heterogeneous Catalytic Hydroarylation of Olefins at
a Nanoscopic Aluminum Chlorofluoride
We report on hydroarylation reactions of arenes with olefins
under very mild conditions catalyzed heterogeneously by alu-
minum chlorofluoride (ACF; AlClxF3Àx, xꢀ0.05–0.25). The reac-
tions of benzene and toluene with ethylene or propylene pro-
ceed with high conversions to afford various alkylated arenes.
For cyclohexene and 1-hexene, the reactions require higher
temperatures and the conversions are lower. ACF also catalyzes
the hydroarylation of 1,3,5-trifluorobenzene and pentafluoro-
benzene with ethylene and propylene. The alkylations of
arenes with non-fluorinated olefins resemble typical Friedel–
Crafts chemistry to give rise to Markovnikov regioselectivity.
The reaction of CF3CH=CH2 with benzene proceeds with anti-
Markovnikov regioselectivity to give the fluorinated olefin
PhCHCH=CF2 and the alkylation product PhCH2CH2CF3 as prod-
ucts of CÀF and CÀH activation.
Introduction
The hydroarylation of olefins is a process for the generation of
CÀC bonds to access molecules of particular importance. For
example, the hydrophenylation of ethylene produces ethylben-
zene, which is the key reactant to manufacture styrene,[1] an
important monomer in polymer chemistry.[2] Likewise, the addi-
tion of benzene to the C=C bond of propylene affords
cumene, which is another molecule in high demand as it is the
intermediate for the production of phenol and acetone.[3]
These two reactions, the ethylation and isopropylation of ben-
zene, account for the production of around 20106 tonnes of
PhCH2CH3 and 8106 tonnes of PhCH(CH3)2 per year.[4]
temperatures and pressures and they typically involve non-flu-
orinated arenes and olefins.[9] It is of current interest to devel-
op new catalysts that are able to catalyze the hydroarylation of
olefins under mild conditions.
Previously, we have studied the reactivity of aluminum
chlorofluoride (ACF; AlClxF3Àx, xꢀ0.05–0.25).[10] This material is
an amorphous solid with an extraordinary Lewis acid strength
that is able to catalyze the activation of CÀF bonds in fluoro-
methanes in the presence of triethylsilane[11] as well as H/D ex-
change reactions between aromatic and aliphatic hydrocar-
bons.[10b]
Lewis and Brønsted acids catalyze the alkylation of arenes
that use olefins as reactants.[5] The catalysts enhance the elec-
trophilic character of the olefins that react with the arenes.
This type of Friedel–Crafts chemistry leads to the synthesis of
the Markovnikov addition products because the regioselectivi-
ty is driven by the stability of the olefinic substrates that inter-
act with the catalyst, which then exhibit a significant carbocat-
ion character.[6]
In this contribution we report the hydroarylation of olefins
catalyzed heterogeneously under remarkably mild conditions.
The reaction routes were extended to fluorinated arenes such
as trifluorobenzene and pentafluorobenzene. The reaction of
benzene with 3,3,3-trifluoropropene led to CÀF activation.
Results and Discussion
HF, H2SO4, and AlCl3 are examples of catalysts chosen for
many industrial processes. However, the need for more selec-
tive, safe, environmentally friendly, and sustainable processes
has promoted an intensive search for new types of cata-
lysts.[6c,7] This led to the use of a variety of zeolites as cata-
lysts.[8] The optimization of zeolite-catalyzed processes resulted
in the efficient alkylation of aromatic substrates such as ben-
zene; however, these catalytic processes take place at high
The room-temperature reaction of deuterated benzene with
ethylene and propylene in a Young’s tap NMR tube in the pres-
ence of catalytic amounts of ACF gave the monoalkylated
products ethylbenzene and cumene with 100% conversion ac-
cording to the NMR spectra (Scheme 1; Table 1, entries 1 and
2), whereas 1-hexene afforded a mixture of hexylbenzene and
(1-methylpentyl)benzene (Table 1, entry 4). The treatment of
benzene with cyclohexene yielded a mixture of mono-, di-, and
trialkylated products with C6D5C6H10D as the main product
(75%, entry 5; Figure S5).
[a] Dr. B. Calvo, J. Wuttke, Prof. Dr. T. Braun, Prof. Dr. E. Kemnitz
Humboldt-Universität zu Berlin
Department of Chemistry
In the case of the addition of 3,3,3-trifluoropropene to C6D6
(Table 1, entry 3) the reaction time was much longer than for
propylene and the conversion was lower. The 1H NMR spec-
trum of the reaction mixture showed the presence of two
Brook-Taylor-Straße 2
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Supporting Information and the ORCID identification number(s) for the
compounds:
the
anti-Markovnikov
addition
product
C6D5CH2CHDCF3 and the fluorinated olefin C6D5CH2CH=CF2
ChemCatChem 2016, 8, 1945 – 1950
1945
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