J.A. van Rijn et al. / Journal of Catalysis 272 (2010) 220–226
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2.5. GLC method
Quantitative gas liquid chromatography analyses were carried
out on a Varian CP-3800 apparatus equipped with a VF-1 ms
(25 m  0.25 mm) column with decane as internal standard. The
temperature gradient used was as follows: isothermal for 5 min
at 40 °C, heating 10 °C/min to 250 °C and finally isothermal for
5 min at 250 °C.
2.6. Phosphonium salt formation
Into the reaction vessel were charged 2.5
lmol of
Scheme 1. Reaction of 4-tert-butylphenol (1) with allyl alcohol (2) catalyzed by
different [RuCp(PP)]+ complexes.
[RuCpCl(PPh3)2], 5 mol of AgOTs, 0.05 mmol of triphenylphos-
l
phine and 0.05 mmol of HOTs and flushed with argon. Degassed
and dried toluene was added (2.5 ml), and the mixture was stirred
for 5 min. Allyl alcohol was added (5 mmol), and the reaction was
stirred at 60 °C for 5 min. Reaction was cooled to room tempera-
ture, and the mixture was concentrated in vacuo to yield a colorless
oil in 24 mg (100%). 1H NMR (CDCl3): d 7.76–7.62 (m, 17H, ArH),
7.06 (d, 2H, J = 7 Hz, ArH), 5.73–5.59 (m, 1H, H-allyl), 5.40 (dd,
1H, J = 6 Hz, 30 Hz, @CHH), 5.35 (dd, 1H, J = 6 Hz, 24 Hz, @CHH),
4.38 (dd, 2H, J = 9 Hz, 12 Hz, CH2), 2.30 (s, 3H, Me). 31P{1H} NMR
(CDCl3): d 21.6 (s).
[13], [RuCpCl(dppp)] [14] (dppp = 1,3-bis[diphenylphosphino]pro-
pane) and [RuCpCl(dppb)] [15] were prepared according to litera-
ture procedures.
1H NMR spectra (300 MHz) and 31P{1H} NMR spectra
(121.4 MHz) were measured on a Bruker DPX-300. Chemical shifts
are reported in ppm. Proton chemical shifts are relative to TMS,
and phosphorus chemical shifts are relative to 85% aqueous
H3PO4. The spectra were taken at room temperature.
2.2. Synthesis of [RuCpCl(dpppe)]
(dpppe = bis(diphenylphosphinophenyl) ether)
2.7. Kinetic data on experiments with extra triphenylphosphine
addition
A solution of RuCpCl(PPh3)2 (72 mg, 0.1 mmol) and the biden-
tate dpppe phosphine ligand (0.1 mmol) in 5 ml toluene was stir-
red for 16 h at 90 °C. The solution was cooled to room
temperature and flushed over a column of silica gel (3 g, d = 1
cm) with 15 ml of toluene to remove the triphenylphosphine. Fi-
nally, the orange product was eluted with ethyl acetate until the
eluens was colorless. The solution was then concentrated in vacuo
to approximately 1 ml, and the product precipitated with petro-
leum ether and [RuCpCl(dpppe)] was obtained as a yellow solid
in a yield of 69 mg (93%). Anal. Calcd for C41H33ClOP2RuÁ0.25(hex-
ane): C, 67.01; H, 4.83. Found: C, 66.62; H, 4.92. 1H NMR (CDCl3): d
7.50 (m, 2H, ArH), 7.36 (m, 8H, ArH), 7.26–7.13 (m, 8H, ArH), 7.01
(m, 4H, ArH), 6.92–6.90 (m, 2H, ArH), 6.84–6.71 (m, 4H, ArH), 4.10
(s, 5H, Cp). 31P NMR (CDCl3): d 44.6 (s).
The general procedure for catalytic reactions was followed, but
with addition of the indicated amount of triphenylphosphine to
the mixture prior to flushing with argon.
2.8. Procedure for ‘‘second batch” experiments
The general procedure for catalytic reactions was followed, but
after 3 h, a second batch of substrates was added (2.5 mmol of 4-
tert-butylphenol and 5.0 mmol of allyl alcohol). Samples were ta-
ken at one and 3 h after addition of the first batch and at one
and 3 h after addition of the second batch (4 h total reaction time).
3. Results and discussion
In an earlier study, we have shown that the catalytic allyl ether
formation is enhanced by addition of two equivalents of acid on
ruthenium [6]. However, under those conditions (at 100 °C), the
use of [RuCp(PPh3)2](OTs) results in only low conversion of phenol,
and propanal is still produced as the major product. It was found
that at lower reaction temperatures and higher acid concentra-
tions, the production of propanal can be effectively prevented
and the catalyst becomes extremely active and selective in the
O-allylation of phenols (Table 1).
As expected, in the absence of acid, no reactivity for allylation is
observed (entry 1). Gradually increasing the acid concentration re-
sults in higher yields of the desired allyl ether, but still propanal is
the major product (entries 2–4). In a reaction mixture with 20 mM
of HOTs (2 mol% on phenol), the production of propanal is com-
pletely blocked and a high conversion of 1 is achieved. The selectiv-
ity for O-allyl ether 3 is very high for this acid concentration, and
the catalyst remains selective also after longer reaction times
(6 h). When the concentration of HOTs is increased beyond
20 mM, the selectivity drops significantly, with only marginal in-
crease in the conversion of 1. Therefore, 20 mM HOTs at 60 °C
was used in the further experiments. Without the ruthenium com-
plex but with the acid only, no allylation or allyl alcohol isomeriza-
tion is observed, thus clearly providing evidence for ruthenium
complex catalyzed reactions that can be tuned by the acid.
2.3. General procedure for catalytic reactions
Into the reaction vessel were charged 2.5 mmol of 4-tert-butyl-
phenol (or another nucleophilic substrate if indicated), 2.5
the ruthenium-chloride catalyst precursor complex, 5.0
l
mol of
lmol of
AgOTs (to displace chloride anions with tosyl through formation
of AgCl) and 0.05 mmol of HOTs and flushed with argon. Degassed
and dried toluene was added (2.5 ml), and the mixture was stirred
for 5 min. Allyl alcohol was added (5 mmol), and the reaction was
stirred at 60 °C. Samples were taken at certain time intervals with
an airtight syringe and analyzed by gas chromatography [6].
The spectroscopic data of allyl phenyl ether [16], allyl 2,4,6-tri-
methylphenyl ether [17] and allyl phenyl sulfide [18] corre-
sponded with the data reported in literature.
2.4. High turnover number experiments
The catalyst amount ([RuCpCl(PPh3)2] and AgOTs) was kept
constant while increasing the amounts of the reactants (4-tert-
butylphenol and allyl alcohol), acid (HOTs) and solvent (toluene)
by a factor 20. A similar reaction was conducted, but the amount
of ruthenium complex was reduced to 0.25
turnover number of 75,000 was reached.
lmol. After 72 h, a