10.1002/ejic.201800462
European Journal of Inorganic Chemistry
FULL PAPER
Conclusions
initial sample is taken for GC analysis. Addition of 0.5 M H2SO4 in
dry, degassed diethyl ether turns the solution orange, indicating
activation of the catalyst. Samples (0.3 ml aliquots) were taken at
predetermined time points from the reaction mixture and
quenched in 1ml H2O and 2 ml Et2O, and then exposed to air. The
ether layer was extracted and taken for GC analysis.
A previously undetected autocatalytic profile of the homogeneous
[Ni(P(OEt)3)4] (NiL4) alkene isomerisation reaction has been
discovered and is supported by a very high correlation between
the experimental data and that of a previously published kinetic
model for an autocatalytic reaction.15 31P NMR studies suggest
that the uncoordinated triethylphosphite, generated during the
catalytic cycle and representing the rate-limiting step, inhibits the
initial protonation of the nickel pre-catalyst significantly (acting as
a proton scavenger), thus decreasing the reaction rate. This
hypothesis was tested using mercury(II) sulfate as a phosphite
scavenger. In terms of reaction engineering, the deactivation can
be overcome by maintaining a high acid concentration as none of
the free ligand is available to react with H+. Furthermore, it may
be possible that the Hg(II) is able to remove phosphite directly
from the catalyst.
Given that added phosphite slows the reaction considerably it is
likely the product of the reaction, beta-methylstyrene, complexes
with nickel to give a more active catalyst for the isomerisation of
allylbenzene. This work suggests it is possible to produce a more
active and stable source of homogeneous nickel(0) by forming
active nickel catalysts in-situ.
Gas Chromatography
Gas chromatograph analysis was collected using a Shimadzu
GC-17A fitted with an RTX-5MS column (30 m x 0.25 mm x 0.25
µm), using the following method: Injection temperature and FID
detector set at 250 oC, initial column temperature 130 oC for 5 min,
ramped to 210 oC at a rate of 40 oC per min and held for 2 mins.
Retention times: allylbenzene (2.2 mins), cis-beta-methylstyrene
(2.45 mins, minor), trans-beta-methylstyrene (2.65 min),
dodecane (3.7 min, internal standard).
Keywords: Homogenous Catalysis • Autocatalysis• Alkene
Isomerisation • Nickel • Allylbenzene
Experimental Section
[1]
[2]
[3]
[4]
[5]
[6]
[7]
C. A. Tolman, J. Am. Chem. Soc., 1972, 94, 2994-2999.
C. A. Tolman, J. Am. Chem. Soc., 1970, 92, 6785-6790.
C. A. Tolman, J. Am. Chem. Soc., 1970, 92, 6777-6784.
C. A. Tolman, J. Am. Chem. Soc., 1970, 92, 4217-4222.
M. F. Perutz, Nature, 1970, 288, 726-734.
Allylbenzene, triethylphosphite and diethylamine were used as
obtained from Sigma Aldrich. The nickel(II) chloride hexahydrate
and methanol were reagent grade. The synthesised catalyst was
stored under N2 at -18 oC.
K. Soai, T. Shibata, H. Morioka, K. Choji, Nature, 1995, 378, 767-768.
I. Sato, D. Omiya, T. Saito, K. Soai, J. Am. Chem. Soc., 2000, 122,
11739-11740.
Synthesis of Tetrakistriethylphosphitenickel(0),
[Ni(P(OEt)3)4]
[8]
[9]
I. Sato, H. Urabe, S. Ishiguro T. Shibata, K. Soai, Angew. Chem. Int. Ed.,
2003, 42, 315-317.
Adapted from a literature method.17 A 50 mL round bottom flask
is loaded with ground NiCl2 ·6 H2O (0.5 g, 2.1 mmol) and a
magnetic stirrer bar. At 0 oC, 2.7 ml (2.6 g, 15.8 mmol) of
triethylphosphate is added to give a dark red solution. After 5
minutes, diethylamine (0.4 ml, 0.3 g, 4.2 mmol) in 5 ml methanol
is added very slowly dropwise (The solution heats upon addition
but must stay at low temperature in order to inhibit the formation
of green Ni(II) species). The solution changes from red to a
white/yellow slurry. Once the reaction has completed (after ca. 5
mins stirring), with the use of a Pasteur pipette, the mixture can
be filtered and dried on a glass-fritted funnel. At this point
methanol at 0 oC or lower is used to wash the solids using small
aliquots (3 x 5 ml, care: the catalyst has partial solubility in
methanol). The resultant white solid is dried in vacuo using a
vacuum desiccator. Yield: 0.9 g (72 %). 1H NMR (Tol-D8): 1.5 ppm
(CH3), 4.3 ppm (CH2). 31P{1H} NMR (Tol-D8): +159 ppm.
K. Soai, I. Sato, Chirality, 2002, 14, 548-554.
[10] M. Szlosek, B. Figadère, Angew. Chem. Int. Ed., 2000, 39, 1799-1801.
[11] E. Ferrer-Flegeau, C. Bruneau, P. H. Dixneuf, A. Jutand, J. Am. Chem.
Soc., 2011, 133, 10161–10170;
[12] I. Fabre, N. von Wolff, G. Le Duc, E. Ferrer-Flegeau,
C. Bruneau, P. H. Dixneuf, A. Jutand, Chem. Eur. J., 2013, 19, 7595 –
7604.
[13]
F. Barrios-Landeros, B. P. Carrow, J. F. Hartwig, J. Am. Chem. Soc.,
2008, 130, 5842–5843.
[14] P. Peringer, D. Obendorf, Inorg. Chim. Acta., 1983, 77, 147-148.
[15] M. A. Watzky, R. G. Finke, J. Am. Chem. Soc., 1997, 119, 10382-10400.
[16] E. J. Nurminen, J. K. Mattinen, H. Lönnberg, J. Chem. Soc. Perkin Trans.
2, 2000, 2238-2240.
[17] K. R. Birdwhistell, J. Lanza, J. Chem. Ed., 1997, 74, 579-581.
General catalytic isomerisation of allylbenzene to beta-
methylstyrene.
[Ni(P(OEt)3)4] (60 mg, 0.083 mmol) was added to a 50-mL 3-neck
round bottom flask, under Schlenk conditions. Dry and degassed
diethyl ether (30 ml) was added via syringe, resulting in a
colourless solution. To this, allylbenzene and dodecane (0.5 ml)
were added, the latter used as an internal standard, where an
This article is protected by copyright. All rights reserved.