Article
EXPERIMENTAL SECTION
■
General Procedures. Reactions for the synthesis of complexes
were performed using Schlenk techniques or a glovebox under an
atmosphere of dry nitrogen. Solvents were predried over sodium wire
and distilled under nitrogen from sodium (toluene and n-hexane)
sodium-benzophenone (THF). Deuterated solvents were stored over
activated 4 Å molecular sieves and degassed by several freeze−thaw
cycles. The starting materials allyl(chloro)dimethylsilane and 2-(5-
n
norbornen-2-yl)ethylchlorodimethylsilane, Zr(NMe ) , and BuLi
2
4
were used as purchased (Aldrich). The compounds bdmpzm
2
9
[
(
(
bdmpzm = bis(3,5-dimethylpyrazol-1-yl)methane] and bpzsimeH
19
1) were prepared as previously reported. (R)-(+)-Limonene oxide
cis and trans mixture) was distilled from calcium hydride under
vacuum. The remaining epoxide substrates were used as received
unless specified otherwise (Aldrich, Across). CO2 (99,99%) was
commercially obtained and used without further purification.
Instruments and Measurements. NMR spectra were recorded
1
13
on a Bruker Advance Neo 500 ( H NMR 500 MHz and C NMR
25 MHz) spectrometer and were referenced to the residual
1
deuterated solvent signal. The NOESY-1D spectra were recorded
with the following acquisition parameters: irradiation time 2 s and
number of scans 256 using standard VARIAN-FT software. 2D NMR
spectra were acquired using the same software and processed using an
IPC-Sun computer. Microanalyses were performed with a PerkinElm-
er 2400 CHN analyzer.
Preparation of Compounds 2−6. Synthesis of bpzsialiH (2). In
a 250 mL Schlenk tube, bdmpzm (2.00 g, 9.79 mmol) was dissolved
in dry THF (70 mL) and cooled to −70 °C. A 1.6 M solution of
Figure 4. Plausible mechanism for the conversion of epoxides and
CO into cyclic carbonates catalyzed by the system 4/TBAB.
2
n
BuLi (6.12 mL, 9.79 mmol) in hexane was added, and the suspension
was stirred for 1 h. The reaction mixture was warmed to −20 °C, and
the resulting yellow suspension was treated with a solution of
allyl(chloro)dimethylsilane (1.48 mL, 9.79 mmol) in dry THF (20
mL), after which the solution was stirred for 30 min. The reaction
mixture was warmed to room temperature and was stirred for an
additional hour. The solvent was removed under reduced pressure,
and the residual solid was extracted in hexane (70 mL) to give a
yellow solid of 2. Yield: (2.72 g, 92%). Anal. Calcd for C H N Si: C,
process in CDCl or CD Cl produced degradation of complex
3
2
2
4
possibly as a consequence of protic traces in solution,
whereas the use of thf-d or C D did not afford enough
8
6
6
solubility to the TBAB. The proposal is consistent with the
initial coordination of the epoxide to the zirconium center,
with expansion of the coordination sphere, as recently reported
1
6
26
4
1
6
3.53; H, 8.66; N, 18.52. Found: C, 63.49; H, 8.63; N, 18.50. H
28
a
in analog octahedral zirconium-based catalysts, subsequent
nucleophilic attack of the bromide to the less sterically
NMR (C D , 297 K), δ 6.02 (s, 1H, CH ), 5.78 (m, 1H, −CH −
6
6
2
4
CHCH ), 5.63 (s, 2H, H ), 4.88 (m, 2H, −CH −CHCH ), 2.14
2
2
2
3
5
hindered carbon atom of the epoxide, CO insertion into the
(s, 6H, Me ), 1.87 (m, 1H, −CH
2
−CHCH
), 1.81 (s, 6H, Me ),
2
2
1
3
1
3
0
1
1
.35 (s, 6H, SiMe ). C { H} NMR (C D , 297 K), δ 146.5 (C ),
Zr−O bond, and final ring closing of the cyclic carbonate with
stereochemistry retention.
2
6
6
5
39.3 (C ), 134.3 (−CH −CHCH ), 113.5 (−CH −CHCH ),
2
2
2
2
4
a
3
06.1 (C ), 66.9 (C ), 22.7 (−CH −CHCH ), 13.3 (Me ), 10.4
2
2
5
(Me ), −3.2 (SiMe ).
2
CONCLUSIONS
■
Synthesis of bpzsinbH (3). The synthesis of 3 was carried out in an
We have designed a simple strategy for the preparation of a
novel family of zirconium complexes containing organosilyl
derived bis(pyrazol-1-yl)methanides that act as robust
identical manner to 2, using bdmpzm (2.00 g, 9.79 mmol), 1.6 M
n
solution of BuLi (6.12 mL, 9.79 mmol) in hexane and 2-(5-
norbornen-2-yl)ethylchlorodimethylsilane (2.12 mL, 9.79 mmol), to
give 3 as a yellow solid. Yield: (3.33 g, 89%). Anal. Calcd for
C H N Si: C, 69.06; H, 8.96; N, 14.64. Found: C, 69.01; H, 8.82;
3
monoanionic κ -NNC scorpionate ligands. X-ray diffraction
2
2
34
4
analysis indicated that these species are very strained, forming
four-membered heterometallacycles in the molecule.
1
3
3
N, 14.69. H NMR (C D , 297 K), δ 6.07 (dd, J
6.2 Hz, 1H, H ), 6.06 (s, 1H, CH ), 5.92 (dd, J
JH−H = 6.2 Hz, 1H, H ), 5.65 (s, 2H, H ), 2.76 (s, 1H, H ), 2.66 (s,
H, H ), 2.19 (s, 6H, Me ), 1.89 (m, 1H, H ), 1.84 (s, 6H, Me ),
= 10.9 Hz, J
6
6
H−H
H−H
d
a
3
=
= 10.9 Hz,
3
H−H
These κ -NNC-scorpionate zirconium amides in the
3
e
4
f
presence of a cocatalyst showed to be effective catalysts for
c
3
b
5
1
CO fixation into five-membered cyclic carbonates. The study
h
2
1.50, 0.52 (m, 2H, H ), 1.15 (m, 2H, Si−CH −CH −), 0.90 (m, 2H,
2
2
g
3
allowed the development of a new zirconium-based system
consisting of a combination of the complex 4 and TBAB,
which resulted in being efficient and selective for the
H ), 0.39, 0.37 (s, 6H, SiMe ), 0.22 (t, 2H, J
= 7.1 Hz, Si−CH −
2
H−H
2
1
3
1
3
5
CH −). C { H} NMR (C D , 297 K), δ 146.3 (C ), 139.3 (C ),
136.7 (C ), 132.2 (C ), 106.1 (C ), 67.6 (C ), 49.5 (C ), 45.0 (C ),
2.6 (C ), 32.3 (C ), 28.5 (Si−CH −CH −), 13.9 (C ), 13.4 (Me ),
0.5 (Me ), −2.7 (Si−CH −CH −), −2.8 (SiMe ).
2
6
6
d
e
4
a
f
c
b
h
g
3
4
1
cycloaddition of CO to epoxides in good to excellent yields.
2
2
2
5
Kinetic studies revealed apparent first-order dependence on
the catalyst and cocatalyst concentrations. Furthermore, this
bicomponent system displayed very broad substrate scope,
including terminal, internal, and disubstituted substrates, as
well as the challenging biorenewable terpene derived limonene
oxide, under mild and solvent-free conditions. The presence of
a chiral fragment in complex 6 exerted a slight stereoselective
trans-influence for limonene oxide.
2
2
2
Synthesis of [Zr(NMe ) (bpzsime)] (4). In a 250 mL Schlenk tube,
2
3
bpzsimeH (1.0 g, 3.62 mmol) was dissolved in dry toluene (60 mL).
A solution of Zr(NMe ) (0.97 g, 3.62 mmol) in toluene (30 mL) was
2
4
added, and the mixture was stirred during 12 h at room temperature.
The solvent was evaporated to dryness under reduced pressure to
yield a yellow product. The product was washed with n-hexane (1 ×
25 mL) to give compound 4 as a yellow solid. Crystals suitable for X-
ray diffraction were obtained by recrystallization from toluene at −26
F
Inorg. Chem. XXXX, XXX, XXX−XXX
Fernández-Baeza, Juan
