R. Qiu et al. / Journal of Organometallic Chemistry 695 (2010) 1182–1188
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of alcohols, phenols, thiols, and amines under solvent-free condi-
2.3.1. Table 1, Entries 1–12
tions, and found that this approach has merits such as operational
simplicity, solvent-free condition, mild reaction conditions, and
catalyst recyclability [47]. In view that Cp2Ti(OSO2C8F17)2 is higher
than Cp2Zr(OSO2C8F17)2 in Lewis acidity, the former should be cat-
alytically more efficient than the latter in acylation reactions. In
this study, we investigated the physiochemical properties (e.g.,
(a) Benzylacetae (Table 1, Entry 1): 1H NMR (400 MHz, CDCl3) d
2.04 (s, 3H), 5.06 (s, 2H), 7.20–7.31 (m, 5H); (b) 2-Phenylethyl ace-
tate (Table 1, Entry 2): 1H NMR (400 MHz, CDCl3) d 1.98 (s, 3H),
2.90 (t, J = 7.09 Hz, 2H), 4.25 (t, J = 7.2 Hz, 2H), 7.17–7.29 (m, 5H);
(c) 3-Phenylpropyl acetate (Table 1, Entry 3): 1H NMR (400 MHz,
CDCl3) d 1.95 (t, J = 7.2 Hz, 2H), 2.05 (s, 3H), 2.73 (t, J = 6.2 Hz,
2H), 4.12 (t, J = 6.0 Hz, 2H), 7.13–7.31 (m, 5H); (d) 1-Phenylpropyl
acetate (Table 1, Entry 4): 1H NMR (400 MHz, CDCl3) d 0.87 (t,
J = 7.4 Hz, 3H), 1.73–1.99 (m, 2H), 2.00 (s, 3H), 5.67 (t, J = 6.8 Hz,
1H), 7.28 (m, 5H); (e) Benzhydryl acetate (Table 1, Entry 5):
1HNMR (400 MHz, CDCl3) d 2.48 (s, 3H), 6.98 (s, 1H), 7.66–7.70
(m, 10H); (f) Trityl acetate (Table 1, Entry 6): 1H NMR (400 MHz,
CDCl3) 2.21 (m, 3H), 7.28–7.44 (m, 15H); (g) Undecyl acetate (Table
1, Entry 7): 1H NMR (400 MHz, CDCl3) d 0.86 (t, J = 6.0 Hz, 3H),
1.19–1.29 (m, 17H), 1.59 (t, J = 6.8 Hz, 2H), 2.02 (s, 3H), 4.03 (t,
J = 8.4 Hz, 2H); (h) Octyl acetate (Table 1, Entry 8): 1H NMR
(400 MHz, CDCl3) d 0.88 (t, J = 7.4 Hz, 3H), 1.36–1.27 (m, 10H),
1.62 (d, J = 7.6 Hz, 2H), 2.04 (s, 3H), 4.05 (t, J = 6.8 Hz, 2H); (i) n-bu-
tyl acetate (Table 1, Entry 9): 1H NMR (400 MHz, CDCl3) d 0.88 (t,
J = 7.2 Hz, 3H), 1.36 (m, 2H), 1.60 (m, 2H), 2.05 (s, 3H), 4.08 (t,
J = 6.4 Hz, 1H); (j) Sec-butyl acetate (Table 1, Entry 10): 1H NMR
(400 MHz, CDCl3) d 0.88 (t, J = 7.0 Hz, 3H), 1.36 (d, J = 7.2, 3H),
1.60 (m, 2H), 2.05 (s, 3H), 4.08 (m, 1H); (k) Cyclohexyl aceatate (Ta-
ble 1, Entry 11): 1H NMR (400 MHz, CDCl3) d 1.20–1.60 (m, 8H),
2.00 (s, 3H), 2.05–2.16 (m, 2H), 3.91(m, 1H); (l) Tert-butyl aceate
(Table 1, Entry 12): 1H NMR (400 MHz, CDCl3) 1.43 (s, 9H),
1.95(s, 3H).
acidity, solubility, thermal stability) of Cp2Ti(OSO2C8F17 2 and
)
examined its catalytic activities in the acylation of alcohols, phe-
nols, thiols, and amines under mild solvent-free conditions.
2. Experimental
2.1. General
The chemicals were purchased from Aldrich Co., Ltd., as well as
Acros Co., Ltd., and used as received unless otherwise specified.
NMR spectra were recorded at 25 °C on INOVA-400 MHz (USA) cal-
ibrated with tetramethysilane (TMS) as internal reference. Elemen-
tal analyses were performed using VARIO EL III (Germany). Catalyst
acidity was measured by the use of Hammett indicators. The em-
ployed indicators included dicinnamalalcetone (pKa = ꢀ3.0), crys-
tal violet (pKa = 0.8), dimethyl yellow (pKa = 3.3), and methyl red
(pKa = 4.8), as described elsewhere [48–50]. Acid strength was ex-
pressed in terms of Hammett acidity function (H0) that was scaled
by pKa value of the indicators. TG-DSC analysis was performed on
NETZSCH-STA-449C (Operation condition: O2, 5 °C/min heating
rate).
2.2. Typical procedure for preparation of Cp2Ti(OSO2C8F17 2
)
[44]
2.3.2. Table 2, Entries 1–7
(a) Geranyl acetate (Table 2, Entry 1): 1H NMR (400 MHz, CDCl3)
d 1.60 (s, 3H), 1.68 (s, 3H), 1.70 (s, 3H), 2.05–2.13 (m, 7H), 4.59 (d,
J = 7.2 Hz, 2H), 5.08 (t, J = 7.0 Hz, 1H), 5.35 (t, J = 7.0 Hz, 1H); (b)
Furan-2-yl-acetate (Table 2, Entry 2): 1H NMR (400 MHz, CDCl3)
d 2.08 (s, 3H), 5.06 (s, 2H), 6.37 (m, 1H), 6.40 (d, J = 3.2 Hz, 1H),
7.42 (bs, 1H); (c) Prop-2-ynyl acetate (Table 2, Entry 3): 1H NMR
(400 MHz, CDCl3) d 2.21(s, 3H), 3.32 (t, J = 5.6 Hz, 2H), 4.82 (d,
J = 5.8 Hz, 2H); (d) Cinnamyl acetate (Table 2, Entry 4): 1H NMR
(400 MHz, CDCl3) d 2.04 (s, 3H), 4.68 (d, J = 6.4 Hz, 2H), 6.19–6.29
(m, 1H), 6.58 (d, J = 16.2 Hz, 1H), 7.21–7.36 (m, 5H); (e) 1-(Pyri-
din-3-yl)allyl acetate (Table 2, Entry 5): 1H NMR (400 MHz, CDCl3)
d 2.13 (s, 3H), 2.68–2.77 (m, 2H), 5.10–5.03 (m, 2H), 5.70–5.78 (m,
1H), 5.87 (t, J = 6.6 Hz, 1H), 7.20 (t, J = 6.4 Hz, 1H), 7.31 (d,
J = 7.6 Hz, 1H), 7.67 (t, J = 8.5 Hz, 1H), 8.59 (d, J = 4.6 Hz, 1H); (f)
8-(Tetrahydro-2H-pyran-2-yloxy)octyl acetate (Table 2, Entry 6):
1H NMR (400 MHz, CDCl3) d 1.29 (bs, 12H), 1.50–1.63 (m, 8H),
1.69–1.73 (m, 1H), 1.81–1.85 (m, 1H), 2.05 (s, 3H), 3.36–3.41 (m,
1H), 3.48–3.50 (m, 1H), 3.70–3.76 (m, 1H), 3.85–3.89 (m, 1H),
4.05 (t, J = 6.8 Hz, 2H), 4.57 (t, J = 3.2 Hz, 1H); (g) 8-(Tert-butyldi-
methylsilyloxy)octyl acetate (Table 2, Entry 7): 1H NMR
(400 MHz, CDCl3) d 0.05 (s, 6H), 0.89 (s, 9H), 1.28 (bs, 12H),
1.46–1.53 (m, 2H), 1.57–1.64 (m, 2H), 2.04 (s, 3H), 3.59 (t,
J = 6.6 Hz, 2H), 4.05 (t, J = 6.8 Hz, 2H).
To a solution of Cp2TiCl2 (249 mg, 0.99 mmol) in THF (20 mL)
was added a solution of AgOSO2C8F17 [39] (1.21 g, 2.0 mmol) in
THF (10 mL). The mixture was stirred in darkness at room temper-
ature for 1 h, and then subject to filtration. The filtrate was com-
bined with dry hexane (40 mL), and kept refrigerated for 24 h to
furnish yellow needle crystals (693 mg, 54%): M.p. 206–210 °C.
1H NMR (400 MHz CD3CN) d = 1.78–1.83 (m, 4H, THF), 3.56 (s,
nH, H2O), 3.62 - 3.67 (m, 4H, THF), 6.95 (s, 10H, Cp). 19F NMR
(288 MHz CD3CN) d = ꢀ79.66–ꢀ79.75 (m, 3F, CFÞ3ꢀ), ꢀ113.28–
ꢀ113.38 (t, 2F, –CF2–), ꢀ119.36–ꢀ119.43 (t, 2F, –CF2–), ꢀ120.34–
ꢀ120.54 (m, 6F, –(CF2)–), ꢀ121.36–ꢀ121.41 (t, 2F, –CF2–),
ꢀ124.72–ꢀ124.87 (m, 2F, –CF2–). Elemental analysis results (%)
for C26H10F34O6S2Ti (as no hydrate and no THF molecule): C,
26.55; H, 0.86; found: C 26.60; H, 0.86 (After pumping at room
temperature for a week or at 80 °C for half an hour).
2.3. Typical procedure for acylation reaction catalyzed by
Cp2Ti(OSO2C8F17)2 (using acetylation of 2-phenylethanol as an
example)
To a round-bottom flask was added 2-phenylethanol (122 mg,
1.0 mmol) and equivalent acetic anhydride (102 mg, 1.0 mmol)
and
a desired amount of catalyst Cp2Ti(OSO2C8F17)2 (12 mg,
0.01 mmol, 1.0 mol% relative to 2-phenylethanol). The mixture
was stirred at room temperature for 2 min and monitored by
TLC. Then the mixture was diluted with petroleum ether
(10 mL ꢁ 3). By means of filtration, the catalyst was separated,
and the filtrate was washed twice with 10 mL of saturated brine,
and extracted by petroleum ether (10 mL ꢁ 2). Subsequently the
portions of petroleum ether were combined together, dried by so-
dium sulfate, and evaporated to obtain the crude ester. Finally, the
ester was subject to column chromatography on silica gel (petro-
leum ether: ethyl acetate = 8:1, Rf = 0.7) to afford the colorless li-
quid, 162 mg, yield, 99%. The following are the 1H NMR data for
desired ester.
2.3.3. Table 3, Entries 1–13
(a) Phenyl acetate (Table 3, Entry 1): 1H NMR (400 MHz, CDCl3)
d 2.29 (s, 3H), 7.07–7.09 (m, 2H), 7.19–7.24 (m, 1H), 7.34–7.40 (m.
2H); b) 2-Napthyl acetate (Table 3, Entry 3): 1HNMR (400 MHz,
CDCl3) d 2.42 (s, 3H), 7.22 (d, J = 8.8 Hz, 1H), 7.45 (m, 2H), 7.54
(s, 1H), 7.76 (m, 3H); (c) 1-Napthyl acetate (Table 3, Entry 4): 1H
NMR (400 MHz, CDCl3) d 2.42 (s, 3H), 7.23 (d, J = 6.4 Hz, 1H),
7.43–7.45 (m, 3H), 7.72 (d, J = 8.2 Hz, 1H), 7.84–7.88 (m, 2H); (d)
4-Methoxyphenyl acetate (Table 3, Entry 5): 1H NMR (400 MHz,
CDCl3) d 2.27 (s, 3H), 3.79 (s, 3H), 6.88 (d, J = 8.8 Hz, 2H), 7.00 (d,
J = 9.0 Hz, 2H); (e) 4-Cyanophenyl acetate (Table 3, Entry 6):
1HNMR (400 MHz, CDCl3) d 2.34 (s, 3H), 7.26 (d, J = 8.4 Hz, 2H),