10.1002/anie.201809199
Angewandte Chemie International Edition
COMMUNICATION
Though 1 is an effective HDF catalyst, mixtures of excess
Et3SiH and SZO300 (2) also catalyze the HDF of triflurotoluene to
give 180 TON at 80 oC over 4 h (Table 1, entry 2). However, 2 is
less active than 1 in this reaction due to faster deactivation of 2
(Figure S21). Consistent with the spectral properties of 1, the 29Si
CPMAS spectrum of 2 contains signals at 57, 41, and 18 ppm
(Figure S11), and the electrophilic silicon species also bind TEPO
(Dd = 43 and 21 ppm, Figure S12). These results indicate that
electrophilic R3Si+ sites are present in 2. SZO300 does not catalyze
HDF in the absence of silane (Table 1, entry 3).
interactions in R3Si•••Ox may result in more reactive R3Si+ sites
on oxides to activate these substrates.
Acknowledgements
M. P. C. is a member of the UCR Center for Catalysis. This work
was supported by the University of California, Riverside and the
National Science Foundation (CHE-1800561). The solid-state
NMR measurements at 14.1 T were recorded on an instrument
supported by the National Science Foundation (CHE-1626673).
Table 2. Hydrodefluorination reactions catalyzed by 1.a
nsubstrate
ncat
Conv
(%)
t
Entry
Cat.
Substrate
TONc
Keywords: C-F activation • Heterogeneous Catalysis • Lewis
(µmol)b
(h)
(mmol)
acids• Surface chemistry • Silanes
1
2
1
2
C6H5CF3
C6H5CF3
0.5
0.5
0.5
0.2
0.24
0.4
0.5
0.5
2
2
12
4
42
20
0
330
180
0
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3
SZO
1
C6H5CF3
na
4.9
4.9
2
12
504
30
24
12
24
4e
5e
6f
7
C6F5CF3
56
67
80
0
93
112
160
0
1
C4F9CHCH2
1
C10H15F
3
C6H5CF3
C6H5CF3
3.4
13
8
4
0
0
a – Reactions at 80 oC with neat substrate and Et3SiH at 80 oC; b
– active silicon in 1 and total silicon in 2 and 3; c – mol Et3SiF/mol
active Si determined by 19F NMR and GC analysis; – reaction
e
run at 120 oC; f – reaction run at 25 oC. na = not applicable
At 120 oC 1 also is active in HDF of neat Et3SiH/C6F5CF3 to form
C6F5CH3 (TON = 93, 504 h), though at much slower rates than
trifluorotoluene. 1-Adamantylfluoride is more reactive in HDF than
o
C6F5CF3 with 1, giving a TON of 160 after 24 h at 25 C. 1 also
activates one allylic C–F bond in 1H, 2H, 2H-perfluorohexene at
120 oC to form Z-CH3CHCFCF2CF2CF3 as a major product (TON
= 112, 30 h). 1 does not catalyzed the HDF of perfluorohexane or
hexafluorobenzene at elevated temperatures.
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also prepared TIPS/Al2O3 (3) from the reaction of
allyltriisopropylsilane and partially dehydroxylated alumina,12 and
TMS/SiO2 (4) from the reaction of partially dehydroxylated silica
and HN(SiMe3)2 (see the Supporting Information for details).22
The 29Si CPMAS spectrum of both materials contains signals at
~0 ppm, consistent with the formation of R3Si–Ox surface species.
Both 2 and 3 are inactive in HDF of trifluorotoluene in the
presence of Et3SiH after 24 h at 80 oC.
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This study shows that electrophilic R3Si+ sites can be formed
on oxide surfaces. This study also shows that not all oxides are
capable of forming these sites. Oxides containing sites that
promote the formation of weakly coordinating ion pairs, which are
present on SZO300, form R3Si+ species that are active in HDF.
Oxides that promote a formation of R3Si–Ox, such as silica and
alumina, are not active in HDF because R3Si+ sites are not
formed. Though [TIPS][SZO300] sites in 1 are very active in C–F
bond activation, they are unreactive towards sp2 C–F bonds and
the C–F bonds in perfluorohexane. Further optimization of the
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