Selective C-F and C-H Activation of Fluoroarenes by Fe(PMe3)4 and Catalytic Performance of Iron Hydride in Hydrosilylation of Carbonyl Compounds

Article abstract of DOI:10.1021/acs.organomet.6b00546

The reactions of perfluorinated toluene (CF₃C₆F₅), pentafluoropyridine (C₅NF₅), and hexafluorobenzene (C₆F₆) with the iron(0) complex Fe(PMe₃)₄ were investigated. The Fe(I) complexes (4-CF₃C₆F₄)Fe(PMe₃)₄ (1), (4-C₅NF₄)Fe(PMe₃)₄ (2), and (C₆F₅)Fe(PMe₃)₄ (3) were obtained by selective activation of the C-F bonds. However, under similar reaction conditions, the reaction of Fe(PMe₃)₄ with perfluoronaphthalene (C₁₀F₈) afforded a π-coordinated Fe(0) complex, (η⁴-1,2,3,4-C₁₀F₈)Fe(PMe₃)₃ (4), and the expected C-F bond activation reaction was not observed. The expected iron hydride (C₆F₅)FeH(PMe₃)₄ (6) could be obtained in a yield of 80% by the reaction of bromopentafluorobenzene with Fe(PMe₃)₄ and subsequent reduction with NaBH₄. The molecular structures of complexes 2, 4, and 6 were determined by single-crystal X-ray diffraction. Complexes 1-4 and 6 could be used as catalysts for the hydrosilylation of carbonyl compounds. Among them, complex 6 is the best catalyst. The selective reduction of carbonyl groups of α,β-unsaturated aldehydes and ketones was also realized with 6 as catalyst.

Full text of DOI:10.1021/acs.organomet.6b00546

Article
pubs.acs.org/Organometallics
Selective C−F and C−H Activation of Fluoroarenes by Fe(PMe ) and
3
4
Catalytic Performance of Iron Hydride in Hydrosilylation of Carbonyl
Compounds
†
,‡,#
†,§,#
⊥
Shumiao Zhang,†,∥,# Benjing Xue,†,# Hongjian Sun, Xiaoyan Li,*
†
,†
Tingting Zheng,
Junye Li,
⊥
Olaf Fuhr, and Dieter Fenske
†School of Chemistry and Chemical Engineering, Key Laboratory of Special Functional Aggregated Materials, Ministry of Education,
Shandong University, Shanda Nanlu 27, 250199 Jinan, People’s Republic of China
‡
Department of Chemistry, Capital Normal University, 100037 Beijing, People’s Republic of China
§
Department of Pharmaceutical Engineering, Heze University, DaXue Road, 274015 Heze, People’s Republic of China
∥
School of Chemistry and Chemical Engineering, Qufu Normal University, 273165 Qufu, People’s Republic of China
⊥
̈ ̈
Institut fur Nanotechnologie (INT) und Karlsruher Nano-Micro-Facility (KNMF), Karlsruher Institut fur Technologie (KIT),
Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
*
S Supporting Information
ABSTRACT: The reactions of perfluorinated toluene (CF C F ), pentafluoropyr-
3
6 5
idine (C NF ), and hexafluorobenzene (C F ) with the iron(0) complex Fe(PMe )
5
5
6
6
3 4
were investigated. The Fe(I) complexes (4-CF C F )Fe(PMe ) (1), (4-C NF )-
3
6
4
3 4
5
4
Fe(PMe ) (2), and (C F )Fe(PMe ) (3) were obtained by selective activation of
3
4
6
5
3 4
the C−F bonds. However, under similar reaction conditions, the reaction of
Fe(PMe ) with perfluoronaphthalene (C F ) afforded a π-coordinated Fe(0)
3
4
10 8
4
complex, (η -1,2,3,4-C F )Fe(PMe ) (4), and the expected C−F bond activation
reaction was not observed. The expected iron hydride (C F )FeH(PMe ) (6)
1
0
8
3 3
6
5
3 4
could be obtained in a yield of 80% by the reaction of bromopentafluorobenzene
with Fe(PMe ) and subsequent reduction with NaBH . The molecular structures
3
4
4
of complexes 2, 4, and 6 were determined by single-crystal X-ray diffraction.
Complexes 1−4 and 6 could be used as catalysts for the hydrosilylation of carbonyl
compounds. Among them, complex 6 is the best catalyst. The selective reduction of
carbonyl groups of α,β-unsaturated aldehydes and ketones was also realized with 6 as catalyst.
INTRODUCTION
enes and catalytic hydrodefluorination of perfluoroarenes with
■
sodium formate as the reducing agent under mild con-
In recent years, more and more methods have been developed
for the preparation of organic fluorine compounds.
1
−7
22−24
The
ditions.
We also demonstrated C−F bond activation by
comprehensive research on C−F bond activation by transition-
metal complexes has provided a new way to explore the
selective synthesis of new organic fluorides and to access novel
electron-rich cobalt and iron complexes using imine as an
anchoring group.
In this paper, we expand the scope of the C−F and C−H
bond activation of perfluoroarenes and polyfluoroarenes with
electron-rich low-valent iron complexes. The Fe(I) complexes
1−3 were formed by the reactions of tetrakis-
25−27
8
−19
methodologies for the defluorination of organic fluorides.
2
Nickel complexes were selected as catalysts in the C(sp )−F
activation and functionalization of organic fluorides by
1
9d,e
19f
Ackermann
and Herrmann. However, there have been
(
trimethylphosphine)iron(0) with perfluorinated toluene,
few reports on C−F bond activation and functionalization
promoted by electron-rich low-valent iron complexes. Although
Milstein in 1994 reported the C−F bond activation of
pentafluorobenzene utilizing a rhodium complex as the catalyst
pyridine, and benzene via selective C−F bond cleavage. In
the case of perfluoronaphthalene (C F ), the π-coordinated
10 8
Fe(0) complex 4 was formed by the reaction of Fe(PMe3)4
20
at room temperature, the first exmples of C−F bond
with perfluoronaphthalene. The novel iron(II) hydride 6 was
synthesized and used as an efficient catalyst for the hydro-
silylation of carbonyl compounds.
21
activation by iron were published in 1997.
We are interested in research on C−F bond activation and
functionalization mediated by electron-rich iron, cobalt, and
nickel complexes. Recently, we reported the synergistic effect of
the complex tetrakis(trimethylphosphine)cobalt(0) and trime-
thylphosphine on selective C−F bond activation of fluoroar-
Received: July 20, 2016
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00546
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Article
RESULTS AND DISCUSSION
The molecular structures of complexes 1 and 3 are similar to
that of complex 2. Although the structures of complexes 1 and
■
Selective C−F Bond Activation of Perfluorinated
Toluene, Pyridine, Benzene, and Naphthalene.
Organocobalt(I) complexes could be obtained through
selective C−F bond activation, while the reaction of
perfluorotoluene with Co(PMe ) provided a cobalt benzyne
3
were also supported by single-crystal X-ray diffraction, the
poor crystallographic data prevent their publication. The ball
and stick representations of these two structures along with
their Cartesian coordinates are provided in the Supporting
Information.
3
4
2
2,23
complex via double C−F bond activation.
In place of
22
On the basis of the similar chemistry on cobalt, a proposed
mechanism for the formation of complexes 1−3 is given with
complex 1 as an example (Scheme 1). The precoordination of
Co(PMe ) , the reactions of Fe(PMe ) with CF C F , C NF ,
3
4
3 4
3
6
5
5
5
and C F were studied under similar reaction conditions. The
6
6
three pentacoordinate iron(I) complexes 1−3 were isolated (eq
1
). In the case of CF C F and C NF , the C−F bond
3
6
5
5
5
Scheme 1. Proposed Mechanism of Formation of Complex 1
activation occurred at the 4-position for both Fe(PMe ) and
3
4
2
2,23
Co(PMe ) .
In the IR spectra, the vibrations of the PMe
the aromatic ring to the Fe(0) center to form the intermediate
3
4
3
−
1
2
23
ligands were found at 938 (1), 933 (2) and 948 (3) cm .
Complexes 1−3 are paramagnetic because they have an iron(I)
center with a d configuration.
1a with an η -coordinated perfluorotoluene ligand under
elimination of a trimethylphosphine ligand is the first possible
step. The C−F bond activation is promoted by the
nucleophilicity of the active electron-rich low-valent Fe-
7
The molecular structure of complex 2 is shown in Figure 1.
In complex 2 the iron atom is located at the center of a
(PMe ) . Selective oxidative addition of the C−F bond of
3 3
perfluorotoluene at the para position at the Fe(0) center occurs
to give rise to intermediate 1b. The radical FPMe formed
3
through one-electron reductive elimination disproportionates
to PMe and F PMe with the formation of the final product 1.
3
2
3
The calculation showed that this process is thermodynamically
2
8
favorable. The formation of F PMe in solution was
2
3
confirmed via 19F and P NMR.
31
29
It is important to note that the para C−F bond was activated
for both perfluorotoluene and perfluoropyridine. This is
consistent with our early reports on C−F bond activation
2
2,24
with Co(PMe ) .
Because the C−F bond activation is
3
4
realized by nucleophilic attack by Fe(PMe3)3 with the
assistance of PMe , the C−F bond activation occurs only at
3
the ortho or para position in both perfluorotoluene and
perfluoropyridine with electron-withdrawing groups (CF3
group in perfluorotoluene and N atom in pyridine). Obviously,
the 3,4-position π-coordination is better than 1,2-position π
coordination in terms of both electronegativity and stereo-
chemistry. In addition, the DFT calculations on the mechanism
of the C−F bond activation of perfluorotoluene by Co(PMe )
Figure 1. Molecular structure of 2 (all of the hydrogen atoms are
omitted for clarity). Selected bond distances (Å) and angles (deg):
Fe1−C1 2.031(2), Fe1−P3 2.2251(6), Fe1−P4 2.2291(6), Fe1−P2
3
4
28
indicated that para C−F bond activation is preferred.
Interestingly, the reaction of perfluoronaphthalene with
Fe(PMe ) is completely different from the aforementioned
2
.2441(6), Fe1−P1 2.2656(8); C1−Fe1−P3 87.27(5), C1−Fe1−P4
64.83(5), P3−Fe1−P4 93.78(3), C1−Fe1−P2 81.64(5), P3−Fe1−
3
4
1
reactions (eq 1). Under similar reaction conditions, a π-
P2 158.09(2), P4−Fe1−P2 92.17(3), C1−Fe1−P1 99.46(5), P3−
Fe1−P1 95.52(2), P4−Fe1−P1 95.51(2), P2−Fe1−P1 104.88(2).
4
coordinated Fe(0) complex, (η -1,2,3,4-C F )Fe(PMe ) (4),
10
8
3 3
was confirmed (eq 2). Complex 4 is stable in air for more than
1
/2 h. The expected C−F bond activation product was not
tetragonal pyramid with the P1 atom at the vertex position. The
Fe1−C1 bond distance in complex 2 is 2.031(2) Å. All of the
Fe−P bond distances are in the normal range. In complex 2 the
aromatic plane is almost perpendicular to the corresponding
square plane.
found on extending the reaction time (48 h) or increasing the
reaction temperature (50 °C). The 18-valence-electron
configuration of penta-coordinate iron(0) species confers
upon complex 4 this stability. In the infrared spectrum of
complex 4 the characteristic ρ(PMe ) band was recorded at 948
3
B
DOI: 10.1021/acs.organomet.6b00546
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Article
(
1.380(3) Å), C13−C14 (1.379(3) Å), C17−C18 (1.376(3)
Å), and C16−C17 (1.385(3) Å). According to this
configuration, the eight fluorine atoms can actually be divided
into four different types: F1 and F2; F3 and F8; F4 and F7; F5
and F6. This result is consistent with the analysis of NMR data.
4
Owing to this η -coordination the four C−F bonds C10−F1
(
1.363(3) Å), C11−F2 (1.367(2) Å), C12−F3 (1.392(2) Å),
and C19−F8 (1.380(2) Å) were activated because they are
obviously longer than the other four C−F bonds C14−F4
−1
1
cm . In the H NMR spectrum, the proton resonances of the
(
1.349(3) Å), C15−F5 (1.346(3) Å), C16−F6 (1.346(3) Å),
PMe groups were recorded at 1.31 ppm as a pseudotriplet and
3
3
1
and C17−F7 (1.348(3) Å). The Fe−P and Fe−C distances are
both in the normal regions.
1
.40 ppm as a doublet in the ratio of 2:1. The P NMR signals
are observed at 18.3 and 20.1 ppm as multiplets with an
1
9
Selective C−H Bond Activation of 2,3,5,6-Tetrafluor-
integration ratio of 2:1. In the F NMR spectra the resonances
at −200.5, −195.6, −163.8, and −154.4 ppm were registered in
the integration ratio of 1:1:1:1. This indicates that the eight
fluorine atoms of perfluoronaphthalene are divided into four
opyridine. The reaction of Fe(PMe ) with 2,3,5,6-tetrafluor-
3 4
opyridine (pK = −10.94) in pentane at room temperature
a
selectively gave rise to the C−H bond activation product 2 with
release of hydrogen (Scheme 2). Hydride complex 5 as the
expected intermediate was not isolated.
4
types after η -coordination. However, in free perfluoronaph-
thalene there are two types of fluorine atoms.
In the molecular structure of complex 4 the iron atom is
coordinated with a η -1,2,3,4-perfluoronaphthalene molecule
4
Scheme 2
and three trimethylphosphine ligands (Figure 2). The
Figure 2. Molecular structure of 4 (all of the hydrogen atoms are
omitted for clarity). Selected bond distances (Å) and angles (deg):
Fe1−C10 2.003(2), Fe1−C11 1.994(2), Fe1−C12 2.068(2), Fe1−
C19 2.075(2), Fe1−P1 2.2231(6), Fe1−P3 2.2398(6), Fe1−P2
Synthesis of Pentafluorophenyl Iron Hydride Com-
plex 6. The reaction of pentafluorobenzene with Fe(PMe3)4
also failed to give the corresponding hydrido iron complex 6. A
hydrido cobalt intermediate as a possible C−H bond activation
product in the study of selective C−F/C−H bond activation of
C F H with Co(PMe ) was proposed on the basis of the
2
.2536(6); C11−Fe1−P1 141.03(7), C19−Fe1−P1 90.90(6), C11−
Fe1−P3 116.83(7), C19−Fe1−P3 97.85(6), P1−Fe1−P3 99.01(2),
C11−Fe1−P2 95.89(7), P1−Fe1−P2 96.83(3), P3−Fe1−P2
6
5
3 4
93.31(2).
1
observation of in situ IR and H NMR spectra, but an
experiment to isolate the hydrido cobalt intermediate also
23
failed. Except for the C−H activation pathway, direct
reduction is also feasible in synthesizing metal hydrides
according to refs 30 and 31. The reaction of bromopenta-
fluorobenzene with Fe(PMe3)4 in diethyl ether at room
temperature gave a red solution. The solvent was then changed
configuration of complex 4 can be considered as a distorted-
trigonal-bipyramidal coordination geometry with P2 and the
midpoint of the C10−C19 bond in the axial positions, while P1,
P3, and the midpoint of the C11−C12 bond are in the
4
triangular plane. Owing to the η -coordination, the deviation of
to THF, and NaBH was added. Yellow crystals of complex 6
4
the plane [C19−C10−C11−C12] from the original naph-
could be obtained from pentane at −20 °C in a yield of 80%
thylene ring is 44.97(9)°. The distance from the central iron
(
eq 3).
4
atom to this plane is 1.6047 Å. Owing to the η -1,2,3,4-
coordination of the naphthylene molecule the corresponding
four C−F bonds (F1−C10 = 1.363(3), F2−C11 = 1.367(2),
F3−C12 = 1.392(2), and F8−C19 = 1.380(2) Å) are longer
than the other four C−F bonds (F4−C14 = 1.349(3), F5−C15
=
1.346(3), F6−C16 = 1.346(3), and F7−C17 = 1.348(3) Å).
For the same reasons, the bond distances C10−C11 (1.373(3)
Å), C11−C12 (1.429(3) Å), C12−C13 (1.481(3) Å), C18−
C19 (1.482(3) Å), and C10−C19 (1.425(3) Å) are longer than
the related bond distances C15−C16 (1.356(4) Å), C14−C15
C
DOI: 10.1021/acs.organomet.6b00546
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Organometallics
Article
4
1
The ν(Fe−H) stretching band of complex 6 was found at
iron hydrides as catalysts were published. Recently, we have
found that several pincer iron(II) hydrides and bidentate
iron(II) hydrides can be used as catalysts in the reduction of
952 cm− in the IR spectrum, and the hydrido signal as a
1
1
1
multiplet was found at −12.94 ppm in the H NMR spectrum.
31
Three P NMR resonances (22.9, 19.3, and 5.98 ppm) showed
carbonyl groups with triethyloxysilane as the reduction
19
42−47
the four PMe ligands in a ratio of 2:1:1. In the F NMR
reagent.
As a continuation of our study in this direction,
3
spectrum, four signals (−95.40, −99.35, −163.99, and −164.80
ppm) in a ratio of 1:1:2:1 indicate the five fluorine atoms.
The molecular structure of complex 6 confirms a
hexacoordinate octahedral geometry in the crystals (Figure
complexes 1−4 and 6 were used as catalysts to explore their
performance in the hydrosilylation of carbonyl compounds.
It can be seen from Table 1 that with complex 6 as catalyst
(EtO) SiH is the best hydrogen source among the tested
3
3). The iron atom is located at the center of the octahedron.
Table 1. Different Silanes as Hydrogen Sources with 1−4
a
and 6 as Catalysts
b
entry
cat.
hydrogen source
time (h)
yield (%)
1
2
3
4
5
6
7
8
9
6
6
6
6
6
6
6
6
1
1
2
2
3
3
4
4
(EtO) SiH
3
3
94
37
0
3
Et SiH
3
Ph SiH
3
3
Me PhSiH
3
0
2
Ph SiH2
2
3
71
89
23
0
PhSiH3
TMDS
PMHS
3
3
3
(EtO) SiH
3
48
93
33
98
33
93
83
94
3
1
1
1
1
1
1
1
0
1
2
3
4
5
6
(EtO) SiH
7
3
(EtO) SiH
3
3
(EtO) SiH
12
3
3
(EtO) SiH
3
(EtO) SiH
10
3
3
(EtO) SiH
3
(EtO) SiH
20
3
a
Catalytic reaction conditions: PhCHO (1.0 mmol), (EtO) SiH (1.2
3
mmol), n-dodecane (internal standard) (1.0 mmol), THF (2 mL),
catalyst (0.5 mol %). Determined by GC analysis.
Figure 3. Molecular structure of 6 (most of the hydrogen atoms are
omitted for clarity). Selected bond distances (Å) and angles (deg):
Fe2−P6 2.231(2), Fe2−P7 2.212(1), Fe2−P9 2.227(1), Fe2−P8
b
silanes. Although complexes 1−4 could also catalyze this
process, their activities are relatively weak because the
transformation needed a longer time.
As shown in Table 2, the reaction conditions of hydro-
silylation reactions catalyzed by iron hydrido complex 6 were
2
.257(2), Fe2−C19 2.055(4), Fe2−H2 1.42(4); P8−Fe2−H2
70.5(14), P9−Fe2−P6 160.02(5), C19−Fe2−P7 160.06(12), C19−
1
Fe2−H2 85.8(13), C9−Fe2−H2 81.9(14), C6−Fe2−H2 82.8(14).
When P8−Fe2−H2 (170.5(14)°) is designated as the axial
direction, iron and the four atoms [C19−P9−P7−P6] are in
the equatorial plane. The Fe1−H1 distance (1.42 Å) is in the
normal region, and the Fe−H bond lies in the plane of the
pentafluorobenzene. Fe2−P8 (2.257(2) Å) is slightly longer
than the other three Fe−P bonds (Fe2−P6 = 2.231(2), Fe2−
P7 = 2.212(1), Fe2−P9 = 2.227(1) Å) because of the strong
trans-influence of the hydrido ligand.
Table 2. Optimization of Reaction Conditions for
Hydrosilylation
a
3
2
b
entry
amt of cat. (mol %)
T (°C)
conversion (%)
1
2
3
4
5
1
60
40
40
40
40
>99
>99
>99
96
Catalytic Application of Complexes 1−4 and 6 in
Hydrosilylation of Aldehydes and Ketones. Iron com-
plexes, especially iron hydrides, are involved in many chemical
processes, such as polymerization, insertion, addition, and
reduction. Recently, there have been some examples of iron
1
0.5
0.3
0.1
25
a
33−36
Reaction conditions: 0.5 mmol of benzaldehyde, 0.6 mmol of
hydrides as catalysts in reduction reactions.
Guan reported
b
HSi(OEt) , 2 mL of THF, 3 h. GC conversion.
a catalytic hydrosilylation of carbonyl compounds by hydrido
3
37
[
PCP]-pincer iron complexes. The hydrogenation of ketones
by an iron catalyst under low hydrogen pressure with high
chemoselectivity at room temperature was disclosed by
optimized. With a 0.5 mol % catalyst loading of 6, the reaction
was complete in 3 h in THF at 40 °C (entry 3). Further
decrease of the catalyst loading reduced the conversion (entries
4 and 5).
In accord with the optimized reaction conditions, complex 6
was chosen as the catalyst. The scope of the reduction of
3
8
Casey. The selective hydrogenation of alkyne to trans-alkene
and selective reduction of the carbonyl group of α,β-
unsaturated ketones were realized with iron hydries by
39,40
Bianchini’s group.
Several reports on hydrosilylation with
D
DOI: 10.1021/acs.organomet.6b00546
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Article
a
aldehydes and ketones is shown in Table 3. With aldehydes as
substrates, the yields are good. The molecules containing
Table 4. Hydrosilylation of Unsaturated Aldehydes
a
Table 3. Scope of Hydrosilylation Reactions
a
Reaction conditions unless specified otherwise: 0.5 mmol of
substrate, 0.6 mmol of HSi(OEt) , 2 mL of THF, catalyst loading 2
3
mol %, 3 h, at 40 °C. Then 3 mL of methanol and 1 mL of 10%
b
NaOH(aq) were added, reacted at 60 °C for 24 h. Isolated yields.
c
With α-bromocinnamaldehyde as substrate, the product is 3-phenyl-
2
-propyn-1-ol because the elimination of HBr occurred during the
d e
basic hydrolysis. Catalyst loading 3 mol %, 24 h, at 40 °C. Catalyst
loading 3 mol %, 24 h, at 40 °C, GC yield.
48
unsaturated aldehydes and ketones. In the literature, most
reports on the reduction of α,β-unsaturated aldehydes and
ketones detail the selective reduction of the CC bonds with
the CO bonds unchanged. Obviously, complex 6 is a good
catalyst for the selective reduction of CO bonds of α,β-
unsaturated aldehydes and ketones. This selectivity is similar to
a
Reaction conditions: 0.5 mmol of substrate, 0.6 mmol of HSi(OEt)3,
2
1
mL of THF, reacted at 40 °C. Then 3 mL of methanol and 1 mL of
46
b
that of our earlier reported system. Regrettably, the yields
0% NaOH(aq) were added, reacted at 60 °C for 24 h. Isolated
c
(
Table 4) are not as good as those of Beller with fluoro(tris(2-
yields. GC yields.
(
diphenylphosphino)phenyl)phosphino)iron tetrafluoroborate
49
electron-withdrawing groups need longer reaction times
as catalyst.
(
entries 3 and 4) or higher catalyst loadings (entries 6−8).
CONCLUSIONS
For ketones, even with 3 mol % of catalyst and reaction for 24
h, the yields are still moderate. This catalytic system is also
suitable for an aliphatic aldehyde (entry 5), but the yield is
moderate. The scope of this catalytic system could be extended
to other aromatic compounds bearing functional reducible
groups, such as nitro, nitrile, ester, etc. (entries 9−11).
α,β-Unsaturated aldehydes and ketones are also applicable to
this catalytic system (Table 4). An electron-withdrawing group
on the benzene ring influenced the reaction negatively (entry
■
In summary, the three novel perfluorinated aryl iron(I)
complexes 1−3 were synthesized through C−F bond activation
by the reaction of perfluorinated toluene, pyridine, and benzene
with Fe(PMe ) . Under similar reaction conditions, the
3
4
reaction of Fe(PMe3)4 with perfluoronaphthalene (C F )
afforded a stable π-coordinated Fe(0) complex, (η -1,2,3,4-
10
8
4
C F )Fe(PMe ) (4). The expected C−F bond cleavage
10
8
3 3
reaction was not observed. The complex (4-C NF )Fe(PMe )
5
4
3 4
6
). These results showed that the reductions occurred
(2) could also be obtained from the selective C−H bond
activation of 2,3,5,6-pentafluoropyridine with Fe(PMe ) . The
selectively at the carbonyl groups and the CC bond
remained unchanged. The selectivity of the reduction of C
C and CO bonds is always regarded as a challenge for α,β-
3
4
iron hydride (C F )FeH(PMe ) (6) could be obtained from
6
5
3 4
the reaction of pentafluorophenyl bromide with Fe(PMe ) in
3
4
E
DOI: 10.1021/acs.organomet.6b00546
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Organometallics
Article
CFarom), −195.6 (m, 2F, CFarom), −200.5 (m, 2F, CFarom). 13C NMR
the presence of NaBH in a yield of 80%. Complexes 1−4 and
4
1
3
(
100 MHz, (CD ) CO, 298 K): δ 20.78 (dt, J(PC) = 23 Hz, J(PC) =
6
could be used as catalysts for the hydrosilylation of carbonyl
3 2
1
3
2
Hz, PCH ), 21.84 (t′, | J(PC) + J(PC)| = 24 Hz, PCH ), 93.34 (m,
1
compounds. Among them, complex 6 is the best catalyst. The
selective reduction of the carbonyl groups of α,β-unsaturated
aldehydes and ketones was also realized with 6 as catalyst.
3
3
1
J(FC) = 194 Hz, Ar−C), 120.14 (m, J(FC) = 242 Hz, Ar−C),
1
1
25.04 (m, Ar−C), 135.73 (m, J(FC) = 232 Hz, Ar−C), 140.58 (m,
1
J(FC) = 229 Hz, Ar−C).
Synthesis of Complex 6. A solution of Fe(PMe ) (0.77 g, 2.1
3
4
EXPERIMENTAL SECTION
■
mmol) in 30 mL of diethyl ether was combined with a solution of
bromopentafluorobenzene (0.39 g, 2.1 mmol) in diethyl ether (20
mL) at room temperature. The reaction mixture was stirred for 3 h.
General Procedures and Materials. Standard vacuum techni-
ques were used in manipulations of volatile and air-sensitive materials.
Solvents were dried by known procedures and distilled under nitrogen
before use. Literature methods were used in the preparation of
Then the solvent was changed to THF and NaBH (0.19 g, 5 mmol)
4
was added. During this period the red solution turned light yellow.
The THF was removed, and the solid was extracted by pentane.
Crystallization from pentane at −20 °C afforded yellow single crystals
of 6 (0.89 g, 80%). Anal. Found (calcd) for 6, C H FeF P , 528.21
50
Fe(PMe ) . CF C F , C NF , C F , and C F were obtained from
3
4
3
6
5
5
5
6
6
10 8
ABCR. All other chemicals were used as purchased. Infrared spectra
−
1
(
4000−400 cm ), as obtained from Nujol mulls between KBr disks,
1
8
37
5 4
−
1
were recorded on a Bruker ALPHA FT-IR spectrometer. The in situ IR
g/mol: C, 41.27 (40.93); H, 6.89 (7.06). IR (Nujol, cm ): 1952,
1
was carried out on a METTLER TOLEDO React IR IC 15
ν(Fe−H); 1614, 1585 ν(CC); 940, ρ(PMe ). H NMR (300 MHz,
3
1
31
13
19
instrument. H, P, C, and F NMR spectra were recorded on
Bruker Avance 300, Bruker Avance 400, and Bruker Avance 500 MHz
spectrometers. 31P and C NMR resonances were obtained with
broad-band proton decoupling. Elemental analyses were carried out on
an Elementar Vario EL III instrument. GC-MS were recorded on a
TRACE-DSQ instrument.
benzene-d , 300 K): δ −12.94 (m, 1H, Fe-H), 0.97 (s, 18H, PCH ),
6
3
31
1
.13 (s, 9H, PCH ), 1.26 (s, 9H, PCH ). P NMR (121.4 MHz,
3
3
13
2
benzene-d , 300 K): δ 22.9 (t, J = 40 Hz, 2P, PCH ), 19.3 (s, 1P,
PCH ), 5.98 (m, 1P, PCH ). F NMR (282 MHz, benzene-d , 300
6
PP
3
19
3
3
6
K): δ −95.40 (1F, CF ), −99.35 (1F, CFarom), −163.99 (2F,
arom
CF ), −164.80 (1F, CFarom).
arom
Caution! (EtO) SiH is flammable and highly toxic by inhalation and
3
General Procedure for the Catalytic Hydrosilylation of
may cause skin irritation and blindness. Even though during our
studies on the dehydration of amides we used it without incident,
triethoxysilane should be used with precaution. Indeed, due to possible
silane disproportionation, the formation of an extremely pyrophoric
Aldehydes and Ketones. By standard Schlenk techniques, the
aldehyde or ketone (0.5 mmol), (EtO) SiH (0.6 mmol), and the
3
corresponding amount of complex 6 in THF were combined. Then 2
mL of THF was added. The reaction mixture was stirred at 40 °C. To
the reaction mixture was then added MeOH (3 mL) and a 10%
aqueous solution of NaOH (1 mL) with vigorous stirring at 60 °C for
gas (possibly SiH ) has led to several fires and explosions, as reported
4
5
1
in the literature.
Synthesis of Complex 1. A solution of Fe(PMe ) (1.00 g, 2.70
3
4
about 24 h. The organic product was extracted with Et O (15 mL ×
2
mmol) in 50 mL of pentane was combined with a solution of CF C F
3
6 5
3
), dried over anhydrous MgSO , and concentrated under vacuum.
4
(0.63 g, 2.70 mmol) in pentane (30 mL) at −80 °C. The reaction
The alcohol product was further purified by silica column
mixture was warmed to ambient temperature and stirred for 18 h.
During this period the pale yellow mixture turned brown-yellow. The
reaction mixture was filtered. Crystallization from pentane at −4 °C
afforded red single crystals of 1 (0.75 g, 48%). Anal. Found (calcd) for
chromatography (with petroleum/ethyl acetate 10/1 as eluent).
1
Finally, all products were confirmed by H NMR.
X-ray Structure Determinations. Intensity data were collected
on a STOE STADI VARI diffractometer with graphite-monochro-
mated Mo Kα radiation (λ = 0.71073 Å). The structures were solved
1
, C H FeF P , 577.21 g/mol: C, 39.33 (39.54); H, 5.99 (6.29). IR
19 36 7 4
−
1
(
Nujol, cm ): 1609, 1561 ν(CC); 938 ρ(PMe ).
2
3
by direct methods and refined with full-matrix least-squares on all F
Synthesis of Complex 2. A solution of Fe(PMe ) (1.20 g, 3.30
3
4
(SHELXL-97) with non-hydrogen atoms anisotropic. Each hydride
mmol) in 50 mL of pentane was combined with a solution of C NF5
5
was located directly from the difference map and the position refined.
The remaining H atoms were either located or calculated and
subsequently treated with a riding model. CCDC-946453 (2), CCDC-
(0.55 g, 3.30 mmol) in pentane (30 mL) at −80 °C. The reaction
mixture was warmed to ambient temperature and stirred for 18 h.
During this period the pale yellow mixture turned brown-yellow. The
reaction mixture was filtered. Crystallization from pentane at −4 °C
afforded red single crystals of 2 (0.89 g, 53%). Anal. Found (calcd) for
8
71948 (4), and CCDC-1483882 (6) contain supplementary
crystallographic data for this paper. Copies of the data can be
obtained free of charge on application to the CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax(+44)1223−336−033; e-mail:
deposit@ccdc.cam.ac.uk).
2
, C H FeF P , 510.20 g/mol: C, 39.77 (40.02); H, 7.00 (7.11); N,
17 36 4 4
−1
2.70 (2.75). IR (Nujol, cm ): 1607, 1589 ν(CC); 933 ρ(PMe ).
3
Synthesis of Complex 3. A solution of Fe(PMe ) (1.10 g, 3.00
3
4
Crystallographic data of complex 2: C H F FeNP , 510.20 g/
17
36
4
4
mmol) in 50 mL of pentane was combined with a solution of C6F6
0.60 g, 3.00 mmol) in pentane (30 mL) at −80 °C. The reaction
mol, 0.22 × 0.20 × 0.18 mm, monoclinic, P2 /n, a = 9.3973(19) Å, b =
1
(
3
1
2
6.146(3) Å, c = 15.785(3) Å, β = 91.16(3)°, V = 2394.6(8) Å , T =
93(2) K, Z = 4, Dcalc = 1.415 Mg/m , μ = 0.931 mm , data collection
mixture was warmed to ambient temperature and stirred for 18 h.
During this period the pale yellow mixture turned brown-yellow. The
reaction mixture was filtered. Crystallization from pentane at −4 °C
afforded red single crystals of 3 (0.40 g, 25%). Anal. Found (calcd) for
3
−1
range 2.50 < 2θ < 27.54°, −12 ≤ h ≤ 12, −19 ≤ k ≤ 20, −20 ≤ l ≤ 20,
no. of unique data 5470 (R(int) = 0.0210), parameters 256, GOF on
2
F 1.041, R1 (I > 2σ(I)) = 0.0293, wR2 = 0.0821 (all data).
3
, C H FeF P , 527.20 g/mol: C, 41.20 (41.01); H, 6.72 (6.88). IR
18 36 5 4
−
1
Crystallographic data of complex 4: C H F FeP , 556.17 g/mol,
(
Nujol, cm ): 1555 ν(CC); 948 ρ(PMe ).
19 27
8
3
3
0
1
=
.15 × 0.12 × 0.10 mm, orthorhombic, Pbca, a = 12.8431(8) Å, b =
Synthesis of Complex 4. A solution of Fe(PMe ) (0.60 g, 1.70
3
4
3
1.9957(7) Å, c = 30.6007(19) Å, V = 4714.4(5) Å , T = 273(2) K, Z
mmol) in 50 mL of pentane was combined with a solution of C F
10 8
3
−1
8, Dcalc = 1.567 Mg/m , μ = 0.911 mm , data collection range 1.33<
(0.50 g, 1.70 mmol) in pentane (30 mL) at −80 °C. The reaction
2
θ < 25.05°, −15 ≤ h ≤ 15, −14 ≤ k ≤ 14, −36 ≤ l ≤ 34, no. of
mixture was warmed to ambient temperature and stirred for 18 h.
During this period the pale yellow mixture turned brown-yellow. The
reaction mixture was filtered. Crystallization from pentane at −4 °C
afforded red single crystals of 4 (0.60 g, 62%). Anal. Found (calcd) for
2
unique data 4180 (R(int) = 0.0262), parameters 281, GOF on F
1.079, R1 (I > 2σ(I)) = 0.0279, wR2 = 0.0745 (all data).
Crystallographic data of complex 6: C18
0.15 × 0.10 × 0.08 mm, monoclinic, P2 /c, a = 23.694(8) Å, b =
12.609(3) Å, c = 18.059(5) Å, β = 112.301(2)°, V = 4992(2) Å , T =
H F FeP , 528.21 g/mol,
37 5 4
4
, C H FeF P , 556.17 g/mol: C, 41.22 (41.03); H, 4.97 (4.89). IR
1
19
27
8 3
−1
1
3
(
Nujol, cm ): 1625 ν(CC); 948 ρ(PMe ). H NMR (300 MHz,
3
2
4
3
−1
acetone-d , 300 K): δ 1.31 (t′, 18H, | J(PH) + J(PH)| = 6 Hz, PCH ),
173(2) K, Z = 8, Dcalc = 1.406 Mg/m , μ = 0.900 mm , data collection
range 2.78< 2θ < 27.46°, −27 ≤ h ≤ 28, −14 ≤ k ≤ 14, −21 ≤ l ≤ 21,
no. of unique data 8621 (R(int) = 0.0483), parameters 534, GOF on
6
3
2
31
1
.40 (d, J(PH) = 6 Hz, 9H, PCH ). P NMR (121.4 MHz, acetone-
3
19
d , 297 K): δ 18.3 (m, 2P, PCH ), 20.1 (m, 1P, PCH ). F NMR (282
6
3
3
2
MHz, acetone-d , 300 K): δ −154.4 (m, 2F, CFarom), −163.8 (m, 2F,
F 1.043, R1 (I > 2σ(I)) = 0.0397, wR2 = 0.0929 (all data).
6
F
DOI: 10.1021/acs.organomet.6b00546
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
14) Sladek, M. I.; Braun, T.; Neumann, B.; Stammler, H.-G. J. Chem.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
■
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NMR spectra of the complexes and the catalytic products
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(
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complexes 1 and 3 (PDF)
Cartesian coordinates of complexes 1 and 3 (XYZ)
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Lachicotteand, R. J.; Holland, P. L. J. Am. Chem. Soc. 2005, 127, 7857−
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870.
AUTHOR INFORMATION
Corresponding Author
E-mail for X.L.: xli63@sdu.edu.cn.
Author Contributions
These authors contributed equally to this work.
(19) (a) Dugan, T. R.; Goldberg, j. M.; Brennessel, W. W.; Holland,
■
P. L. Organometallics 2012, 31, 1349−1360. (b) Hu, J.-Y.; Zhang, J.;
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#
Notes
̈
̈
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
We gratefully acknowledge support by the NSF of China (No.
1172132/21372143) and Beijing Municipal Education
Commission (No.201510028008).
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DOI: 10.1021/acs.organomet.6b00546
Organometallics XXXX, XXX, XXX−XXX