Inorganic Chemistry
Article
Scheme 2. CO2 Capture by Supported Lewis Acid (S3) and Dissolved Lewis Base (3) mixtures (Left) or by Supported Lewis Base
(S4) and Dissolved Lewis Acid (4) Mixtures (Right) to Give the FLP/CO2 Adducts S5 and S6, Respectively
The contact time was 2 ms. A recycle delay of 5 s and an acquisition
time of 33.9 ms were used. 13C resonances are referenced vs
adamantane as an external standard.
with dry O2-free toluene (3×) before the residual solvent was allowed to
evaporate in the glovebox over 2 days. Final solvent removal was by
vacuum evaporation (P < 10−3 mmHg) to afford 0.303 g of silica
nanopowder supported allyltriethoxysilane S2 as a white powder. ATR
FTIR/cm−1: ν(C=C) 1633, ν(C−H) 2898−3084. 13C CP MAS NMR
δC (100.6 MHz)/ppm: 21.23 (C5), 23.02 (C3), 62.74 (C4), 119.07
(C1), 135.52 (C2).
The 11B NMR spectra were recorded at 128.4 MHz, with a contact
time of 5 ms, a recycle delay of 2 s, and an acquisition time of 49.9 ms.
The 31P NMR spectra were recorded at 162.0 MHz, with a contact time
of 5 ms, a recycle delay of 2 s, and an acquisition time of 49.9 ms. The
11B CP MAS NMR spectra are referenced vs NaBH4 as an external
Silica Nanopowder Supported Diphenylborane (S3a) and Bis-
(pentafluorophenyl)borane (S3b). The boranes 1a (0.026 g, 0.156
mmol) and 1b (0.014 g, 0.040 mmol) were added to slurries of S2
(0.199 g for 1a or 0.123 g for 1b) in dry O2-free toluene (10 mL)
(Scheme 1, step 2). The resulting mixtures were stirred at room
temperature in a glovebox for 3 days. The mixtures were then filtered,
the resulting white powders were washed with dry O2-free toluene
(3×), and residual solvent was allowed to evaporate in the glovebox
over 2 days. Further solvent removal was carried out by vacuum
evaporation (P < 0.001 mmHg) to afford either S3a (0.157 g) or S3b
(0.036 g) as a white powder.
standard, and the 31P CP MAS NMR spectra are referenced vs H3PO4
as an external standard.
Attenuated Total Reflectance Fourier Transform Infrared Spec-
troscopy. ATR FTIR spectra of samples in the solid or liquid phase
were recorded as neat samples on a Nicolet IS50 FTIR spectrometer
equipped with a single-bounce ATR diamond.
Syntheses. Scheme 1 illustrates the syntheses of 1 and S1−S4.
Diphenylborane (1a) and Bis(pentafluorophenyl)borane (1b). In
a glovebox, either triphenylborane (0.504 g, 2.082 mmol) or
tris(pentafluorophenyl)borane (1.001 g, 1.95 mmol) were transferred
to a flask containing 10 mL of dry O2-free toluene. The two separate
mixtures were stirred until the boranes were fully dissolved. This was
followed by the slow dropwise addition of a 10 mL oxygen-free toluene
solution of triethylsilane (0.243 g, 0.33 mL, 2.097 mmol) to the
B(C6H5)3 solution or of triethylsilane (0.230 g, 0.31 mL, 1.980 mmol)
to the B(C6F5)3 solution. The mixtures were heated to 80 °C and stirred
at this temperature for 6 days. As 1a and 1b formed, the solutions
turned yellow and brown, respectively. The solutions were then cooled
to room temperature and subsequently concentrated to ca. 15 mL. This
caused immediate precipitation of the desired products. Solid 1a and 1b
were isolated by filtration and washed three times with dry, O2-free
toluene to remove residual Et3SiH.
Solid (C6H5)2BH (1a) was obtained as a fluffy, fibrous white powder
(0.067 g, 27.7%), mp 214.3 °C, and was stored in a glovebox. ATR
FTIR/cm−1: ν(B−H) 1574. 1H NMR δH (300 MHz, C6D6)/ppm: 4.02
(1 × 1H, s, B−H), 7.35−7.38 (6H, m, 2 × C6H5), 8.25−8.27 (4H, m, 2
× C6H5).
Solid (C6F5)2BH (1b) was obtained as a white crystalline powder
(0.12 g, 17.8%), mp 114.0 °C, and was stored in a glovebox. ATR
FTIR/cm−1: ν(B−H) 1564 (characteristic of a B−(μ-H)2−B
function).30 1H NMR δH (300 MHz, C6D6)/ppm: 4.18 (1 × 1H, s,
spectra, respectively).
Data for S3a are as follows. ATR FTIR/cm−1: ν(B−phenyl) = 1440,
ν(C−H) 2872−3076. 13C CP MAS NMR δC (100.6 MHz)/ppm:
19.82 (C2), 21.78 (C5), 22.94 (C3), 40.76 (C1), 62.55 (C4), 130.67
(C8,8′; C9,9′; C10,10′), 134.25 (C7,7′; C11,11′), 138.52 (C6,6′). 11B
CP MAS NMR δB (128.4 MHz)/ppm: −0.31.
Data for S3b are as follows. ATR FTIR/cm−1: ν(B−Phenyl) 1486,
ν(C−H) 2894−3011. 13C CP MAS NMR δC (100.6 MHz)/ppm:
17.68 (C2), 19.34 (C5), 22.46 (C3), 33.10 (C1), 62.34 (C4), 128.89
(C6,6′), 131.86 (C8,8′; C9,9′; C10,10′), 132.44 (C7,7′; C11,11′). 11B
CP MAS NMR δB (128.4 MHz): −0.44.
Silica Nanopowder Supported 2-(Diphenylphosphino)-
ethyltriethoxysilane (S4a) and 2-(Dicyclohexylphosphino)-
ethyltriethoxysilane (S4b). The phosphine silanes, either 2-
(diphenylphosphino)ethyltriethoxysilane 2a (1.01 g, 2.68 mmol for
S4a) or 2-dicyclohexylphosphinoethyltriethoxysilane 2b (1.011 g, 2.60
mmol for S4b) were added to a slurry of hydroxy-covered silica
nanopowder S1 (see synthesis of S2 for how to obtain S1; 0.152 g for
S4a or 0.145g for S4b) in dry O2-free toluene (10 mL) (Scheme 1, step
3). The resulting solutions were stirred at room temperature in a
glovebox for 3 days. The solutions were then filtered, the recovered
white powder was washed with dry O2-free toluene (3×), and the
adsorbed solvent on the powder was allowed to evaporate in a glovebox
over 2 days. Final solvent removal was carried out by vacuum
evaporation to afford either S4a (0.118 g) or S4b (0.107 g) as a white
powder.
Silica Nanopowder Supported Allyltriethoxysilane (S2). Silica
nanopowder was boiled for 1 h in double-distilled water to generate
surface S1 (Scheme 1, step 2) bearing hydroxyl groups and then dried
for 16 h under vacuum (10−3 mm Hg) at 60 °C. Allyltriethoxysilane (1
g, 4.89 mmol) was then added to a slurry of the hydroxylated silica
nanopowder (S1, 0.28g) in dry O2-free toluene (10 mL). The resulting
mixture was stirred at room temperature in a glovebox for 3 days. The
mixture was then filtered, and the recovered white powder waswashed
Data for S4a are as follows. ATR FTIR/cm−1: ν(P−C) 1447, ν(C−
H) 2855−2969. 13C CP MAS NMR δC (100.6 MHz)/ppm: 9.97 (C2),
21.45 (C1), 24.28 (C4), 62.33 (C3), 131.86 (C7,7′; C8,8′; C9,C9′),
136.16 (C6,6′; C10,10′), 138.43 (C5,5′). 31P CP MAS NMR δP (162.0
MHz)/ppm: δ −5.56.
Data for S4b are as follows. ATR FTIR/cm−1: ν(C−H) 2883−3054
cm−1. 13C CP MAS NMR δC (100.6 MHz)/ppm: 6.52 (C2), 10.16
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Inorg. Chem. 2021, 60, 55−69