Synthesis of iron hydrides by selective C-F/C-H bond activation in fluoroarylimines and their applications in catalytic reduction reactions

Article abstract of DOI:10.1002/ejic.201500313

The reactions of Fe(PMe₃)₄ with different 2,6-diflurophenylarylimines 1-5 were explored. Fluoroarylimines 1-3, the aryl rings of which are substituted with electron-withdrawing groups, reacted with Fe(PMe₃)₄ to afford the C-H activation products 6-8. However, if the aryl rings of the fluoroarylimines were substituted with electron-donating groups, the iron hydrides 9 and 10 were obtained from the reactions of the fluoroarylimines with Fe(PMe₃)₄ through C-F bond activation. In a further study, silanes, especially triethoxysilane, were found to benefit the reactions and improve the yields of the hydridoiron complexes. The three-component reaction of Fe(PMe₃)₄, a fluoroarylimine, and a silane could also be utilized in reactions involving 2,6-(CH₃)₂C₆H₃-C(=NH)-2,6-F₂C₆H₃ (13) and 2,6-F₂C₆H₃-C(=NH)-C₆F₅ (16) to synthesize iron hydrides (15 and 18). The hydridoiron complexes could be utilized as efficient catalysts in the hydrosilylation of aldehydes and ketones. Furthermore, cinnamaldehydes were selectively reduced to the corresponding cinnamyl alcohols in high yields. The mechanism of the catalytic reduction reaction was studied extensively through operando IR spectroscopy.

Full text of DOI:10.1002/ejic.201500313

FULL PAPER
DOI:10.1002/ejic.201500313
Synthesis of Iron Hydrides by Selective C–F/C–H Bond
Activation in Fluoroarylimines and Their Applications in
Catalytic Reduction Reactions
[
a]
[a]
[a]
Lin Wang, Hongjian Sun, and Xiaoyan Li*
Keywords: C–H activation / C–F activation / Hydrosilylation / Hydride ligands / Iron
The reactions of Fe(PMe
arylimines 1–5 were explored. Fluoroarylimines 1–3, the aryl
rings of which are substituted with electron-withdrawing
3
)
4
with different 2,6-diflurophenyl-
of Fe(PMe
utilized in reactions involving 2,6-(CH
6 5
(13) and 2,6-F –C(=NH)–C F
3
)
4
, a fluoroarylimine, and a silane could also be
–C(=NH)–2,6-
(16) to synthesize
3 2 6 3
) C H
F
2
C
6
H
3
2
C
6
H
3
groups, reacted with Fe(PMe
3
)
4
to afford the C–H activation
iron hydrides (15 and 18). The hydridoiron complexes could
be utilized as efficient catalysts in the hydrosilylation of
aldehydes and ketones. Furthermore, cinnamaldehydes were
selectively reduced to the corresponding cinnamyl alcohols
in high yields. The mechanism of the catalytic reduction re-
action was studied extensively through operando IR spec-
troscopy.
products 6–8. However, if the aryl rings of the fluoroarylim-
ines were substituted with electron-donating groups, the iron
hydrides 9 and 10 were obtained from the reactions of the
3 4
fluoroarylimines with Fe(PMe ) through C–F bond acti-
vation. In a further study, silanes, especially triethoxysilane,
were found to benefit the reactions and improve the yields
of the hydridoiron complexes. The three-component reaction
Introduction
different valence state, can also result in the selective acti-
[
4]
vation of C–F or C–H bonds.
The activation of inert bonds attracts continuous atten-
tion because of its significance in organic synthesis, the
degradation of hazardous substance, the preparation of
organometallics, and so forth. Among numerous inert bond
activations, the activation of C–F and C–H bonds has been
a research hotspot in recent years. There are thousands of
publications on the activation of C–H bonds.[1] Meanwhile,
the cleavage and functionalization of C–F bonds has also
been intensively studied in spite of the difficulty caused by
the strength of the bond.[ However, the selective activation
of C–F/C–H bonds is still a great challenge.
There are several methods to realize the selective acti-
vation of C–F/C–H bonds. Firstly, the difference between
the C–F and C–H bond energies can be used to achieve this
aim. For example, owing to the low bond energy and high
acidity of the C–H bond of pentafluorobenzene, many
metal complexes such as palladium complexes activate the
C–H bond rather than the C–F bonds.[ Secondly, the utili-
zation of different metal complexes, including those with
different metal centers or the same metal center with a
[5]
[6]
Special ligands and additives are often used to im-
prove the C–F/C–H selectivity. Compounds containing sili-
con, boron, phosphorus or Lewis acids benefit the acti-
[7]
vation of C–F bonds. The design of substrate molecules is
also an effective method to promote the selective activation.
Locating the fluorine or hydrogen atom at “active site” is
[8]
the simplest strategy. However, few examples of selective
activation through the adjustment of the electronic proper-
ties of the substrates have been reported.
Metal hydrides are important intermediates with a broad
range of applications in catalytic reactions such as hydrode-
2]
[9]
[10]
[11]
fluorination, hydrosilylation, hydrogenation, and de-
[12]
hydrogenation reactions.
The direct activation of C–H
[13]
[14]
bonds and the hydrogenation of metal halides are the
two common methods to obtain metal hydrides. However,
the one-pot reaction involving the activation of C–F bonds
and the hydrogenation of metal fluorides is rarely used in
the synthesis of metal hydrides.
3]
In our previous work, the reaction of Fe(PMe ) with
3
4
(
2,6-difluorophenyl)(phenyl)methanimine resulted in selec-
[
4b]
tive C–H bond activation. As a continuation, we will re-
port the successful selective activation of C–F and C–H
bonds from the reactions of Fe(PMe ) with fluoroarylim-
[
a] School of Chemistry and Chemical Engineering, Key
Laboratory of Special Functional Aggregated Materials,
Ministry of Education, Shandong University,
Shanda Nanlu 27, 250199 Jinan, P. R. China
E-mail: xli63@sdu.edu.cn
3
4
ines controlled by the substituents on the aryl ring. Further-
more, a series of iron hydrides were prepared. In the pres-
ence of silanes, the yields of iron hydrides obtained through
C–F bond activation could be greatly promoted (Scheme 1).
The iron hydrides performed well in the catalytic hydro-
http://www.chemnew.sdu.edu.cn/tea-44.html
Supporting information for this article is available on the
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silylation of aldehydes and ketones, especially α,β-unsatu- plexes, the signals of two types of PMe groups were re-
3
rated aldehydes.
corded in 1:2 ratios. The 19F NMR spectra showed three
singlets at δ = –110.6 (6), –110.4 (7), and –110.6 ppm (8).
From the IR and NMR spectra, it can be concluded that
these three hydridoiron complexes (6–8) have an octahedral
Scheme 1. The selective activation of the C–F/C–H bonds of
fluoroarylimines through the control of the substituents on the aryl
ring.
Results and Discussion
Selective Activation of C–H Bonds
A series of fluoroarylimines with different substituents
(compounds 1–5) were synthesized to react with Fe-
(
PMe ) to explore the influence of the substituents upon
3
4
the selectivity of C–F/C–H bond activation. The reactions
of imines 1, 2, and 3 with Fe(PMe ) in diethyl ether at
3
4
20 °C afforded the C–H bond activation products 6–8 in
high yields (Scheme 2). Complexes 6–8 crystallized as violet
blocks from pentane solutions at –20 °C. The IR spectra of
6
–8 show typical ν(Fe–H) signals at ν˜ = 1738 (6), 1744 (7),
–
1
[13c]
1
and 1741 cm (8).
The H NMR spectra of 6–8 pro-
vided the hydrido signals at δ ≈ –15 ppm as doublets of
3
1
triplets (dt). In the P NMR spectra of these three com-
Figure 1. Molecular structures of 6 (top), 7 (middle), and 8
(bottom). Most of the hydrogen atoms are omitted for clarity, and
thermal ellipsoids are drawn at 50% probability.
Scheme 2. Synthesis of hydridoiron complexes 6–8 through selec-
tive C–H bond activation.
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coordination geometry around the iron atom. The struc-
tures obtained from the single-crystal X-ray diffraction of
–8 confirm this conjecture (Figure 1). In the molecular
6
structure of 6, with P1–Fe1–P3 identified as the axial direc-
tion, the five atoms Fe1, P2, N1, C18, and H100 are in the
equatorial plane. The angle P1–Fe1–P3 [153.97(4)°] deviates
significantly from 180° because of the steric bulk of the li-
gand. The Fe–H bond length is 1.51(3) Å. The structures
of 7 and 8 are similar to that of 6. The Fe–H bond lengths
in 7 and 8 are 1.40(2) and 1.44(3) Å, respectively.
In the process of C–H bond activation, the nitrogen atom
of the imine group plays a role as an anchoring atom. This
makes it feasible for the Fe center to approach the C–H
bond at the ortho position.
Figure 2. The molecular structure of 9. Most of the hydrogen atoms
are omitted for clarity, and thermal ellipsoids are drawn at 50%
probability.
Selective C–F Bond Activation
bond at the ortho position rather than the C–H bond. This
Instead of the C–H bond activation products (Scheme 2), means that the selective activation of C–H and C–F bonds
two iron hydrides 9 and 10 formed through C–F bond acti- can be realized by the same metal complex through control
vation were isolated from the reactions of 4 and 5 with of the substituents on the aryl ring of 2,6-difluorophen-
Fe(PMe ) (Scheme 3). The IR spectra show typical ν(Fe– ylarylimine ligands. Furthermore, hydridoiron complexes
3
4
–
1
1
H) signals at ν˜ = 1754 (9) and 1747 cm (10). In the H were obtained through C–F bond activation. This is dif-
NMR spectra, the significant hydrido signals appear at δ = ferent from previous results.
16.3 (9) and –16.7 ppm (10) as doublets of triplets with
To improve the yields of 9 and 10, additives were intro-
coupling constants J(P,H)trans = 18.0, 23.8 Hz and duced into the reactions. Silanes have been used as
J(P,H)cis = 84.0, 81.3 Hz, respectively.
[
4b]
–
2
2
[15]
hydrogen sources in hydrodefluorination reaction. Owing
to the strong binding between silicon and fluorine, the
[
16]
silane could benefit the C–F bond activation.
After it had been experimentally confirmed that
Fe(PMe ) did not react with HSi(OEt) , the three-compo-
3
4
3
nent reaction of Fe(PMe ) , 4 or 5, and triethoxysilane in
3
4
diethyl ether was performed. As expected, the yields of 9
and 10 improved significantly (Scheme 4).
Scheme 3. Synthesis of hydridoiron complexes 9 and 10 by selective
C–F bond activation.
Single crystals of 9 were obtained to confirm that the
hydridoiron complex was produced through C–F bond acti-
vation (Figure 2). As in 6, two phosphorus atoms (P1 and
P3) are located at the axial direction with a bond angle of
Scheme 4. Synthesis of 9 and 10 through the three-component reac-
150.23(3)°. The imine ligand coordinates to the iron center
tion.
through cyclometalation (N1 and C10) owing to the chelate
effect. The five atoms Fe1, N1, C17, C15, and C10 consti-
To determine the destination of the fluorine atom in the
tute a five-membered metallacycle with a sum of internal three-component reaction, Fe(PMe ) , 4, HSi(OEt) , and
3
4
3
angles of 540.03° [N1–Fe1–C10 79.84(8)°, Fe1–C10–C15 solvent were sealed in an NMR tube, and the reaction was
1
13.92(1)°, C10–C15–C17 113.18(18)°, C15–C17–N1 monitored after 24 h. In the 19F NMR spectrum of this
1
12.65(17)°, and C17–N1–Fe1 120.40(15)°]. The hydrogen reaction solution, a singlet at δ = –153.7 ppm could be iden-
[
17]
19
atom connected to the C19 atom is still present. The Fe–H tified as the signal of (CH CH O) SiF.
The F NMR
3
2
3
bond length is 1.44(3) Å. The structural characteristics of signal of 9 appears at δ = –114.8 ppm. The relative integral
iron hydrides 9 and 10 are similar to those of 6–8. ratio of these two signals is ca. 1:1. This provides strong
From the formation of 6–10, it can be concluded that for evidence that triethoxysilane participates in the C–F bond
the imines 1–3 with an electron-withdrawing group (EWG) activation.
on the nonfluorinated aryl ring, the C–H bond activation
On the basis of these results, a possible mechanism for
is favorable. In contrast, the reactions of Fe(PMe ) with the reaction in Scheme 4 is proposed (Scheme 5). After the
3
4
the imines 4 and 5 with an electron-donating group (EDG) coordination of the imine group, the C–F bond activation
on the nonfluorinated aryl ring tend to activate the C–F through ortho-cyclometalation affords intermediate A. Ac-
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cording to previous reports,[18] there are two feasible paths (Table 1). With 10 mol-% of Fe(PMe ) as the catalyst in a
3
4
to obtain the final product. The first path (Scheme 5, mixture of 4 and HSi(OEt) , the conversion of the fluoro-
3
Path a) is a σ-bond metathesis model. Triethoxysilane coor- imine after 5 h at 60 °C was 52%. Compound 11 is the only
dinates to the Fe center after PMe dissociation to form product, and the resonance of (CH CH O) SiF was found
3
3
2
3
intermediate B with a four-membered ring. In the presence at δ = –152.62 ppm in the in situ 19F NMR spectrum. The
of PMe , complex 9 is generated with the formation of hydrodefluorination reaction catalyzed by Fe(PMe3)4
3
(
EtO) SiF as a byproduct. The second path (Scheme 5, showed an interesting color change. At the beginning of the
3
Path b) is an oxidative addition/reductive elimination reaction, the mixture changed from tan to violet, which is
model. The intermediate C, an iron(IV) hydride, is obtained the color of 9. On the basis of this phenomenon, it can
through the dissociation of PMe and the oxidative addition be inferred that the hydridoiron complex is not only the
3
of the silane. With the assistance of PMe , the reductive significant intermediate in the catalytic cycle but also the
3
elimination affords 9. In consideration of the rationality of real catalyst for the hydrodefluorination reaction.[ Fur-
20]
the activation energy and the stability of the intermediate, ther studies under the same conditions indicated that the
the first path (Scheme 5, Path a) is more reasonable.
reaction catalyzed by 10 mol-% of 9 leads to a 71% conver-
sion of 4, but the yield of 11 is only 25%. Compound 12
and other unknown reduction products are produced.
Table 1. Catalytic hydrodefluorination reaction of 4.[a]
Entry
Catalyst
–
Fe(PMe )
3 4
Conversion/yield of 11[b] [%]
1
2
3
20/20
52/52
71/25
9
[
1
[
a] Reaction conditions: 4 (0.231 g, 1 mmol), HSi(OEt)
3
(0.197 g,
.2 mmol), catalyst (0.1 mmol) in THF (2 mL) at 60 °C for 5 h.
1
9
b] Determined by F NMR spectroscopy, trifluorotoluene as the
Scheme 5. The possible mechanism for the three-component reac-
tions.
standard.
In addition to triethoxysilane, other additives that could
This three-component reaction provides not only an
effective method to synthesize hydridoiron complexes
through C–F bond activation but also evidence for the
mechanism of hydrodefluorination reactions, because hyd-
benefit the generation of the hydridoiron complexes were
also investigated. Triethylsilane, triphenylsilane, and di-
phenylmethylsilane were chosen as the hydrogen sources.
The results indicated that all three of these silanes could
improve the yields with different efficiencies (Figure 3).
Among these silanes, triethylsilane has the lowest efficiency.
The reaction needs 48 h to reach completion, and the yield
of the hydridoiron complex is only 65%. Diphenylmethylsil-
ane and triphenylsilane have similar activities. However, tri-
phenylsilane is a solid and difficult to remove. Finally,
triethoxysilane is the best additive among these silanes.
Other fluoroarylimines were selected to expand the scope
of the reaction. Instead of the expected hydridoiron com-
plex, the bischelate complex 14 was obtained in 83% yield
from the reaction of 13 with Fe(PMe ) (Scheme 7).
ridoiron complexes are regarded as important intermediates
in the proposed catalytic cycle.[
15,19]
Under the conditions
used for previous hydrodefluorination reactions, PMe3
(
1 equiv.) was added to a tetrahydrofuran (THF) solution
[
15]
of 9 at 60 °C. The mixture changed from violet to blue-
purple. After the removal of the solvent under reduced pres-
sure, the residue was extracted with n-pentane. Compounds
11 and 12 were identified through mass spectrometric detec-
tion of the extract (Scheme 6).
3
4
1
In the H NMR spectrum of 14, the relative integral ratio
of the signals of the C=NH group (δ = 8.94 ppm) and the
PMe ligand (δ = 0.71 ppm) is 1:9. This indicates that the
3
31
ratio of imine ligand to PMe is 1:1 in 14. In the P NMR
3
spectrum of 14, there is only one signal at δ = 10.3 ppm.
Therefore, it can concluded that 14 has an octahedral
coordination geometry around the iron atom with two
Scheme 6. The stoichiometric hydrodefluorination reaction of the
fluoroarylimine started from the hydridoiron complex.
On the basis of these experimental results, a hydrode- phosphorus atoms at the axial positions and two imine li-
fluorination reaction catalyzed by Fe(PMe ) was designed gands in the equatorial plane.
3
4
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Scheme 8. Synthesis of the hydridoiron complex 15 from the three-
component reaction.
in a yield of 35% (Scheme 9). In the 31P NMR spectrum of
1
7, there is only one singlet at δ = 19.0 ppm. In addition,
19
the F NMR spectrum shows five signals at δ = –112.1,
–127.4, –138.9, –155.1, and –165.0 ppm with a relative inte-
gral ratio of 2:1:1:1:1. These NMR spectroscopic data indi-
Figure 3. The relationship between the yield of 9 and the activity cate that 17 is also a bischelate complex formed by the C–
of different silanes.
F bond activation of the pentafluorophenyl moiety. When
the strategy of the three-component method was used in
this reaction, the hydridoiron complex 18 was obtained in
56% yield as violet crystals, which were characterized by IR
and NMR spectroscopy (Scheme 9). The X-ray diffraction
analysis of 18 suggests that the activation of the C–F bond
indeed occurs at the pentafluorophenyl group (Figure 4).
Scheme 7. The bischelate complex 14 obtained from the reaction
of 13 with Fe(PMe
3 4
) .
If triethoxysilane was added into the reaction shown in
Scheme 7, hydridoiron complex 15 was obtained rather
than the bischelate complex 14 (Scheme 8). A typical ν(Fe–
–
1
H) peak at ν˜ = 1753 cm was observed in the IR spectrum
1
of 15. In the H NMR spectrum of 15, a doublet of triplets
2
with coupling constants J(P,H)trans
= 15.0 Hz and
2
J(P,H)cis = 84.0 Hz at δ = –16.76 ppm supports the exis-
tence of the Fe–H bond.
Compound 16 was designed to study the selective acti-
vation of different C–F bonds because there are two types
of C–F bonds at the ortho positions to the imine group. The
Figure 4. The molecular structure of 18. Most of the hydrogen
atoms are omitted for clarity, and thermal ellipsoids are drawn at
reaction of 16 with Fe(PMe ) afforded 17 as blue crystals 50% probability.
3
4
Scheme 9. The bischelate complex 17 and hydridoiron complex 18 obtained from the three-component reaction.
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The structure of 18 is similar to those of the other hyd- Table 3. Catalytic activity of iron hydrides in the hydrosilylation of
PhCOMe.[
a]
ridoiron complexes (Figure 2).
The Reduction Reactions of Aldehydes and Ketones
Catalyzed by the Hydridoiron Complexes
Iron complexes often have the potential to catalyze many
types of reactions. According to previous reports, iron com-
plexes play significant roles in the hydrosilylation reactions
Entry
[Fe–H]
Conversion [%][b]
1
2
3
4
5
6
6
8
9
10
15
18
44
35
52
90
57
99
[
21]
[22]
[23]
[24]
of aldehydes, ketones,
esters,
alkenes,
alkynes,
In addition, hydrogenation reac-
tions of carbonyl compounds with H as the hydrogenation
amides,
[
25]
[26]
and even CO2.
2
[
27]
[28]
source,
hydroboration reactions,
transfer hydrogen-
[
29]
[30]
ation reactions, reductive amination reactions and de- [a] Reaction conditions: PhCOMe (1 mmol), HSi(OEt)3
[
31]
(1.2 mmol), and iron hydride (0.01 mmol) in THF (1 mL) at 55 °C
for 10 h. [b] Determined by GC with n-dodecane as the standard.
hydrogenative silylation reactions of alcohols can also be
catalyzed by iron complexes. Among them, iron hydrides
have been intensively studied in recent years owing to
their catalytic activity in the hydrosilylation reactions of Table 4. The reduction of aldehydes and ketones catalyzed by 18.[a]
aldehydes and ketones.[ Therefore, the six hydridoiron
32]
complexes 6, 8, 9, 10, 15, and 18 were tested in the hydro-
silylation of PhCHO with HSi(OEt) (Table 2). As for the
3
hydrosilylation of PhCOMe, the six iron hydrides exhibited
different activities (Table 3). Complexes 10 and 18 showed
excellent activity with conversions of 99 and 90%, whereas
6
and 8 exhibited poor activity.
Table 2. Catalytic activity of iron hydrides in the hydrosilylation of
[
a]
PhCHO.
Entry
[Fe–H]
Conversion [%][b]
1
2
3
4
5
6
6
8
Ͼ99
Ͼ99
Ͼ99
Ͼ99
Ͼ99
Ͼ99
9
10
15
18
[
a] Reaction conditions: PhCHO (1 mmol), HSi(OEt)
3
(1.2 mmol),
[a] Reaction conditions: (1) aldehyde or ketone (1 mmol), HSi-
and iron hydride (0.01 mmol) in THF (1 mL) at 55 °C for 5 h. [b]
Determined by GC with n-dodecane as the standard.
(OEt)3 (1.2 mmol), and 18 in THF (1 mL) at T °C for t h. (2)
CH OH (3 mL) and 10% NaOH (5 mL) added to the mixture,
3
60 °C for 24 h. [b] Complex 18 (0.003 mmol), T = 45 °C, t = 2 h.
On the basis of the results in Tables 2 and 3, 18 was [c] Isolated yield. [d] Complex 18 (0.006 mmol), T = 45 °C, t = 3 h.
[
e] Complex 18 (0.01 mmol), T = 60 °C, t = 12 h. [f] Determined
chosen as the catalyst for the optimization of the conditions
for the reduction reactions of aldehydes and ketones. The
optimized catalytic conditions for the hydrosilylation of
by GC with n-dodecane as the standard.
most aldehydes are 0.3 mol-% catalyst loading, 45 °C and of 18 with 4-FC H CHO and HSi(OEt) was explored.
6
4
3
2
h. For ketones, the conditions for the reduction reactions However, no changes were observed during these reactions.
are slightly harsher owing to the low activity of ketones. Operando IR spectroscopy was utilized to monitor the re-
With 1 mol-% of catalyst, the conversions reached 99% af- action process (Figure 5). A mixture of 4-FC H CHO and
6
4
ter 10 h at 60 °C. The reduction reactions of aldehydes and 20 mol-% of 18 in THF (2 mL) was placed in the reaction
ketones with different functionalities were catalyzed under container at 20 °C. The reaction was kept at 20 °C during
the optimized condition. After workup, the corresponding the initial stages. As shown in Figure 5, the IR absorption
–1
alcohols were obtained in good yields (Table 4).
( ν˜ = 1703 cm ) for the C=O bond of 4-FC H CHO re-
6 4
The mechanism for the hydrosilylation of carbonyl com- mained unchanged until the reaction mixture was heated to
[
12,33]
pounds catalyzed by metal hydrides is controversial.
45 °C after 10 min. At a reaction temperature of 45 °C, the
To understand the mechanism, the stoichiometric reaction signal at ν˜ = 1703 cm–1 became weaker, and the IR absorp-
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–
1
tion band for the C–O bond (1133 cm ) was enhanced. As
In addition to the simple aromatic aldehyde and ketone,
the reaction proceeded, these two signals gradually became the selective reduction reactions of α,β-unsaturated alde-
stable. After 25 min, HSi(OEt) was added into the reaction hydes were also studied, because the selectivity of the re-
3
solution. At the same time, the signal of C=O bond dis- duction of C=C and C=O bonds is always regarded as a
appeared immediately, and that of the C–O bond increased challenge for α,β-unsaturated aldehydes. The [1,4] and [1,2]
sharply.
addition are the two common modes for the hydrosilylation
[
35,36]
of unsaturated aldehydes.
Cinnamaldehyde was se-
lected as a substrate to explore this catalytic system. Cinna-
myl alcohol was the only product with all six of the cata-
lysts (Table 6). In the presence of 2 mol-% of 15, cinnamyl
alcohol was obtained in a yield of 83% after 7 h at 60 °C.
Table 6. Catalytic activity of iron hydrides in the hydrosilylation of
cinnamaldehyde.[
a]
Entry
Catalyst
Yield [%][b]
1
2
3
4
5
6
6
8
67
66
70
77
83
80
Figure 5. The changes of IR absorption with time.
9
10
15
18
This information reveals that the C=O bond of 4-
FC H CHO can insert into the Fe–H bond of the iron
6
4
hydride at high temperature. The reaction reaches an equi- [a] Reaction conditions: (1) cinnamaldehyde (1 mmol), HSi(OEt)
3
(
1.2 mmol), and iron hydride (0.02 mmol) in THF (1 mL) at 60 °C
librium in a short time. With the synergy of the silane, the
hydrosilylation reaction can be completed rapidly. On this
basis, the synergy between the iron hydride and the silane
is the key point of the mechanism.
3
for 7 h. (2) CH OH (3 mL) and 10% NaOH (5 mL) added to the
mixture, 60 °C for 24 h. [b] Isolated yield.
To explore the scope of this catalytic application, dif-
As different catalytic conditions were needed for the re- ferent substituted cinnamaldehydes were tested as sub-
duction reactions of aldehydes and ketones, the selective re- strates (Table 7). If the phenyl ring of cinnamaldehyde was
duction of a mixture of aldehydes and ketones was ex- substituted with halogen atoms such as fluorine or chlorine
[
34]
plored. Enough HSi(OEt) was added into a mixture of
3
PhCHO and PhCOMe (1:1) dissolved in THF in the pres- Table 7. The selective reduction of cinnamaldehydes catalyzed by
[a]
15.
ence of 0.3 mol-% of 18, and the conversion of PhCHO
reached 81% after 2 h at 45 °C. No hydrosilylation product
of PhCOMe was found in the reaction mixture. However,
with 1 mol-% of 18 at 60 °C, the conversions of the
aldehyde and ketone are both more than 75% (Table 5).
Table 5. Selective reduction of aldehyde and ketone with 18 as cata-
[
a]
lyst.
Entry
Catalyst Temperature Time [h] Yield D
Yield E
[%][
b]
[%]
[b]
[mol-%]
[°C]
1
2
0.3
1
45
60
2
12
81
85
0
78
[
(
a] Reaction conditions: (1) cinnamaldehyde (1 mmol), HSi(OEt)
3
1.2 mmol), and 15 (0.02 mmol) in THF (1 mL) at 60 °C for 7 h.
[a] Reaction conditions: (1) PhCHO (1 mmol), PhCOMe (1 mmol),
3
(2) CH OH (3 mL) and 10% NaOH (5 mL) added to the mixture,
HSi(OEt)
3
(2.5 mmol), and 18 in THF (2 mL) at T °C for t h. (2) 60 °C for 24 h. [b] Isolated yield. [c] (1) α-Bromocinnamaldehyde
(1 mmol), HSi(OCH CH (1.2 mmol) and 15 (0.02 mmol) in THF
(1 mL) at 60 °C for 7 h. (2) CH OH (3 mL) and 10% NaOH (5 mL)
added to the mixture, 60 °C for 24 h.
CH
3
OH (3 mL) and 10% NaOH (5 mL) added to the mixture,
2
3 3
)
60 °C for 24 h. [b] Determined by GC with n-dodecane as the
3
standard.
Eur. J. Inorg. Chem. 2015, 2732–2743
2738
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
atoms, the corresponding cinnamyl alcohol was obtained in Experimental Section
a lower yield. The corresponding cinnamyl alcohols could
General Methods: All operations were conducted by utilizing stan-
dard Schlenk techniques under a nitrogen atmosphere. Pentane, di-
ethyl ether, THF, toluene, and dioxane were dried by distillation
be obtained in higher yields if the cinnamaldehydes had
substituents at the α position, despite the possible steric hin-
drance. With α-bromocinnamaldehyde as the substrate, 3-
phenyl-2-propyn-1-ol was isolated in a yield of 88%. It can
be deduced that the reaction process has two steps. The
first step is the hydrosilylation of the aldehyde group with
6 6
from Na–benzophenone under nitrogen before use. C D for NMR
spectroscopy was degassed and dehydrated with sodium.
[
37]
Fe(PMe
,6-difluorophenylarylimines were obtained by the addition reac-
tions of 2,6-difluorobenzonitrile and arylmagnesium bromides in
the siloxane with NaOH in CH OH at 60 °C was ac- diethyl ether solutions and subsequent quenching with meth-
3 4
) was prepared according to the literature method. The
2
HSi(EtO) to afford the related siloxane. The hydrolysis of
3
3
companied by the elimination of HBr to deliver the final anol.[ Infrared spectra (4000–400 cm ) were obtained from Nu-
38]
–1
product.
jol mulls between KBr disks and recorded with a Bruker ALPHA
FTIR instrument. The H, C, and P NMR spectra (300, 75,
and 121.5 MHz, respectively) were recorded with a Bruker Avance
1
13
31
3
6 6
00 spectrometer with C D as the solvent without an internal ref-
Conclusions
1
3
31
erence at room temperature. The C and P NMR resonances
were obtained with broadband proton decoupling. Elemental
analyses were performed with an Elementar Vario ELIII analyzer.
Melting points were measured in capillaries sealed under nitrogen.
The MS spectra were recorded with an Agilent Technologies 6510
QTOF LC/MS instrument. The operando IR spectra were recorded
with an IC 15 instrument from Mettler–Toledo, and the Auto
Chem iC software (version 4.2) was utilized to perform the data
treatment.
We have explored the reactions of different kinds of 2,6-
difluorophenylarylimines with Fe(PMe ) and realized the
selective activation of C–H and C–F bonds by controlling
the substituents. As a result, two types of iron hydrides were
obtained. The iron hydrides obtained through the activation
of C–F bonds aroused our interest. Three-component reac-
3
4
tions of Fe(PMe ) , 2,6-difluorophenylarylimines and
3
4
silanes were proposed. From the three-component reac-
tions, the hydridoiron complexes from the activation of C– X-ray Crystal-Structure Determinations: The single-crystal X-ray
F bonds could be obtained in high yields. This finding pro- diffraction data of the complexes were collected with a Bruker
SMART Apex II CCD diffractometer equipped with a graphite-
monochromated Mo-K radiation source (λ = 0.71073 Å). During
α
vides not only an efficient method to synthesize iron
hydrides but also strong evidence for the mechanism of
catalytic hydrodefluorination reactions. By taking advan-
tage of this method, a series of hydridoiron complexes were
prepared. These hydridoiron complexes can be used as the
catalysts in the hydrosilylation reactions of aldehydes and
ketones, especially the selective hydrosilylation of α,β-unsat-
the collection of the intensity data, no significant decay was ob-
served. The intensities were corrected for Lorentz polarization
effects and empirical absorption with the SADABS program. The
structures were solved by direct or Patterson methods with the
2
SHELXS-97 program and refined on F with SHELXTL. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
urated aldehydes. This is an improvement over previous re- included in calculated positions and refined by using a riding model
[
32]
sults.
(Table 8).
Table 8. Selected X-ray crystallographic data.
6
7
8
9
18
Formula
C
22
H
35ClF
535.72
monoclinic
P2 /c
2
FeNP
3
C
535.72
triclinic
P1
9.9447(3)
11.3923(3)
13.2459(5)
66.567(2)
76.723(3)
71.777(3)
1298.26(7)
150(2)
22
H
35ClF
2
NP
3
C
20
H
34
F
2
3
FeNP S
C
496.30
triclinic
P1
9.2049(5)
9.2843(5)
14.8935(8)
95.224(4)
92.419(4)
94.133(4)
1262.71(12)
143(2)
23
H
38FFeNP
3
22 32 6 3
C H F FeNP
M
z
507.30
triclinic
P1
573.25
triclinic
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
¯
¯
¯
¯
P1
1
9.662(10)
23.54(2)
12.004(12)
90.00
98.212(15)
90.00
2703(5)
273(2)
4
9.2937(19)
11.375(2)
13.260(3)
66.56(3)
79.31(3)
74.38(3)
1233.7(4)
293(2)
2
9.7470(14)
11.2899(16)
13.594(2)
65.499(9)
79.516(14)
74.761(10)
1308.8
296(2)
2
0.813
γ [°] 3
V [Å ]
T [K]
Z
2
2
–
1
μ [mm ]
0.858
0.893
0.912
0.805
Total reflections
Unique reflections
10780
4663
8757
4423
6102
4282
13491
7230
0.0434
0.0370
0.0599
0.0838
0.0676
0.758
31878
6223
0.1765
0.1190
0.1942
0.2705
0.2700
1.082
R
R
int
0.0257
0.0362
0.1048
0.0479
0.1186
1.128
0.0232
0.0267
0.0765
0.0296
0.0783
1.031
0.0180
0.0333
0.0805
0.0453
0.0886
1.062
1
[IϾ2σ(I)]
2
wR(F ) [IϾ2σ(I)]
(all data)
R
1
2
wR(F ) (all data)
GOF on F2
Eur. J. Inorg. Chem. 2015, 2732–2743
2739
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
CCDC-975062 (for 6), -1041484 (for 7), -975060 (for 8), -975061 (dt, 2JP,H = 24.0, 82.5 Hz, 1 H, Fe–H), 1.02 [m, 27 H, P(CH
)
],
3
3
3
1
(
for 9), and -1046641 (for 18) contain the supplementary crystallo-
6.66–8.21 (m, 5 H, Ar-H), 9.65 (s, 1 H, C=NH) ppm. P NMR
2
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_ request/cif.
(121.5 MHz, C
P, P(CH ], 18.0 [d, JP,P = 37.5 Hz, 2 P, P(CH
(282.4 MHz, C , 298 K): δ = –110.6 (s) ppm. C NMR
75 MHz, C
11.8 (CAr), 124.1 (d,
Ar), 159.5 (d, 1JF,C = 187.5 Hz, F–CAr), 204.3 (C=NH) ppm.
6
D
6
, 298 K): δ = 23.2 [t,
JP,P = 37.5 Hz, 1
2
19
3
)
3
3 3
) ] ppm. F NMR
1
3
6
D
6
1
(
1
(
6
D
6
, 298 K): δ = 22.2 [d,
J
P,C = 10.5 Hz, (CH
JF,C = 11.2 Hz, CAr), 136.4 (CAr), 145.2
3 3
) P],
[
(
2,6-F
2
C
6
H
3
–C(=NH)–C
6
H
3
4-Cl]Fe(H)(PMe
3
)
3
(6): Fe(PMe
3
)
4
4
0.50 g, 1.39 mmol) dissolved in diethyl ether (20 mL) was added
C
to a diethyl ether solution (30 mL) of (2,6-difluorophenyl)(4-
chlorophenyl)methanimine (1; 0.26 g, 1.18 mmol) at 20 °C. The
mixture was stirred at the same temperature for 24 h. During this
period, the mixture changed from deep yellow to violet. After the
removal of the solvent under reduced pressure, the solid residue
was extracted with pentane (30 mLϫ2). Violet crystals of 6 crys-
tallized from the pentane solution at –20 °C, yield 0.49 g, 78%;
[
2-CH –C(=NH)–6-FC ]Fe(H)(PMe (9). Method A:
3
C
6
H
4
6
H
3
3 3
)
Fe(PMe (0.50 g, 1.39 mmol) dissolved in diethyl ether (20 mL)
was added to a diethyl ether solution (30 mL) of (2,6-difluoro-
phenyl)(2-methylphenyl)methanimine (4; 0.27 g, 1.18 mmol) at
2
During this period, the mixture changed from deep yellow to violet.
After the removal of the solvent under reduced pressure, the solid
residue was extracted with pentane (30 mLϫ2). Violet crystals of
3 4
)
0 °C. The mixture was stirred at the same temperature for 24 h.
m.p. 135 °C (dec). C22
9.08, H 9.51, N 1.86; found C 59.10, H 8.65, N 1.86. IR (Nujol):
ν˜ = 3300 [ν(N–H)], 1738 [ν(Fe–H)], 1617 [ν(C=N)], 1580, 1556
2 3 5
H35ClF FeNP ·3C H12 (752.20): calcd. C
5
9
crystallized from the pentane solution at –20 °C, yield 0.19 g,
–
1 1
32%. Method B: Fe(PMe ) (0.50 g, 1.39 mmol), HSi(OEt) (0.23 g,
[
ν(C=C)], 938 [ρ
δ = –15.39 (br t,
P(CH ], 6.55–8.26 (m, 6 H, Ar-H), 9.30 (s, 1 H, C=NH) ppm.
1
(PCH
3
)] cm . H NMR (300 MHz, C
6
D
6
, 298 K):
3 4
3
2
1.39 mmol), and (2,6-difluorophenyl)(2-methylphenyl)methanimine
4; 0.27 g, 1.18 mmol) were dissolved in diethyl ether (20, 10, and
J
P,H = 73.5 Hz, 1 H, Fe–H) 0.85 [m, 27 H,
(
3 3
)
3
1
2
30 mL, respectively). The three components were mixed at 20 °C.
The mixture was stirred at the same temperature for 24 h. During
this period, the mixture changed from deep yellow to violet. After
the removal of the solvent under reduced pressure, the solid residue
was extracted with pentane (30 mLϫ2). Violet crystals of 9 crys-
tallized from the pentane solution at –20 °C, yield 0.44 g, 75%;
6 6
P NMR (121.5 MHz, C D , 298 K): δ = 23.5 [t, JP,P = 37.1 Hz,
P,P = 37.1 Hz, 2 P, P(CH
NMR (282.4 MHz, C D , 298 K): δ = –110.6 (s) ppm. C NMR
], 18.5 [d, 2
19
1
P, P(CH
3
)
3
J
3
)
3
] ppm.
F
1
3
6 6
1
(
(
1
(
75 MHz, C
6
D
6
, 298 K): δ = 21.9 [d, JP,C = 9.8 Hz, (CH
3 3
) P], 112.0
2
d,
40.6 (CAr), 149.2 (CAr), 166.7 (d, JF,C = 198 Hz, F–CAr), 215.5
C=NH) ppm.
JF,C = 24.8 Hz, CAr), 119.2 (CAr), 126.1 (CAr), 129.5 (CAr),
1
m.p. 120 °C (dec). C23
H 9.03, N 2.46; found C 58.45, H 8.47, N 2.50. IR (Nujol): ν˜ =
278 [ν(N–H)], 1754 [ν(Fe–H)], 1617 [ν(C=N)], 1587 [ν(C=C)], 932
3 5
H39FFeNP ·C H12 (569.49): calcd. C 59.05,
[
2,6-F –C(=NH)–C
2
C
6
H
3
6
H
3
3-Cl]Fe(H)(PMe
3
)
3
3 4
(7): Fe(PMe )
3
(0.50 g, 1.39 mmol) dissolved in diethyl ether (20 mL) was added
–1 1
[
(
2
ρ
1
(PCH
3
)] cm . H NMR (300 MHz, C
dt, JP,H = 18.0, 84.0 Hz, 1 H, Fe–H), 1.09 [m, 27 H, P(CH
.44 (s, 3 H, CH ) 6.78–8.06 (m, 6 H, Ar-H), 8.89 (s, 1 H, C=NH)
ppm. 31P NMR (121.5 MHz, C
8.1 Hz, 1 P, P(CH ], 18.8 [m, 2 P, P(CH
282.4 MHz, C , 298 K): δ = –113.7 (s) ppm. C NMR
75 MHz, C
0.2 (CH ), 123.4 (CAr), 125.6 (CAr), 130.1 (CAr), 146.7 (CAr),167.2
d, JF,C = 235.5 Hz, F–CAr) 177.0 (CAr), 201.9 (C=NH) ppm.
6
D
6
, 298 K): δ = –16.26
to a diethyl ether solution (30 mL) of (2,6-difluorophenyl)(3-
chlorophenyl)methanimine (2; 0.26 g, 1.18 mmol) at 20 °C. The
mixture was stirred at the same temperature for 24 h. During this
period, the mixture changed from deep yellow to violet. After the
removal of the solvent under reduced pressure, the solid residue
was extracted with pentane (30 mLϫ2). Violet crystals of 7 crys-
tallized from the pentane solution at –20 °C, yield 0.45 g, 71%;
2
3 3
)
],
3
2
6
6 P,P
D , 298 K): δ = 24.1 [t, J =
19
3
(
(
3
(
3
)
3
3 3
) ] ppm. F NMR
13
6 6
D
1
6
6 3 3
D , 298 K): δ = 22.0 [d, JP,C = 12.8 Hz, (CH ) P],
3
m.p. 138 °C (dec). C22
6.52, H 8.74, N 2.06; found C 56.70, H 8.85, N 2.03. IR (Nujol):
ν˜ = 3301 [ν(N–H)], 1744 [ν(Fe–H)], 1617 [ν(C=N)], 1582, 1556
H
35ClF
2
FeNP
3
·2C
5
H
12 (680.05): calcd. C
1
5
[3-OCH –C(=NH)–6-FC ]Fe(H)(PMe (10). Method A:
3
C
6
H
4
6
H
3
3 3
)
–
1
1
3 4
Fe(PMe )
(0.50 g, 1.39 mmol) dissolved in diethyl ether (20 mL)
[
ν(C=C)], 935 [ρ
1
2
(PCH
3
)] cm . H NMR (300 MHz, C
δ = –15.60 (dt, JP,H = 24.0, 84.0 Hz, 1 H, Fe–H), 1.15 [m, 27 H,
P(CH ], 6.71–7.58 (m, 6 H, Ar-H), 9.06 (s, 1 H, C=NH) ppm.
6 6
D , 298 K):
was added to a diethyl ether solution (30 mL) of (2,6-difluoro-
phenyl)(4-methoxyphenyl)methanimine (5; 0.29 g, 1.18 mmol) at
20 °C. The mixture was stirred at the same temperature for 24 h.
During this period, the mixture changed from deep yellow to violet.
After the removal of the solvent under reduced pressure, the solid
residue was extracted with pentane (30 mLϫ2). Violet crystals of
10 crystallized from the pentane solution at –20 °C, yield 0.26 g,
43%. Method B: Fe(PMe
1
ine (5; 0.29 g, 1.18 mmol) were dissolved in diethyl ether (20, 10,
and 30 mL, respectively). The three components were mixed at
20 °C. The mixture was stirred at the same temperature for 24 h.
During this period, the mixture changed from deep yellow to violet.
3 3
)
3
1
2
6 6
P NMR (121.5 MHz, C D , 298 K): δ = 26.8 [t, JP,P = 43.0 Hz,
P,P = 41.1 Hz, 2 P, P(CH
NMR (282.4 MHz, C D , 298 K): δ = –110.4 (s) ppm. C NMR
, 298 K): δ = 21.8 [d, JP,C = 12 Hz, (CH
JF,C = 24.0 Hz, CAr), 119.7 (CAr), 125.6 (CAr),
29.4 (CAr), 147.1 (CAr), 152.3 (CAr), 165.9 (d, JF,C = 154.5 Hz,
], 19.1 [d, 2
19
1
P, P(CH
3
)
3
J
3
)
3
] ppm.
F
1
3
6 6
1
(
(
1
75 MHz, C
C
6
D
6
3
)
3
P], 99.6
Ar), 111.9 (d, 2
1
3 4 3
) (0.50 g, 1.39 mmol), HSi(OEt) (0.23 g,
.39 mmol), and (2,6-difluorophenyl)(4-methoxyphenyl)methanim-
F–CAr), 214.3 (C=NH) ppm.
[
2,6-F –C(=NH)–C S]Fe(H)(PMe
2
C
6
H
3
4
H
2
3
)
3
(8):
3 4
Fe(PMe )
(0.50 g, 1.39 mmol) dissolved in diethyl ether (20 mL) was added
to a diethyl ether solution (30 mL) of (2,6-difluorophenyl)(thienyl)-
methanimine (3; 0.26 g, 1.18 mmol) at 20 °C. The mixture was After the removal of the solvent under reduced pressure, the solid
stirred at the same temperature for 24 h. During this period, the
mixture changed from deep yellow to violet. After the removal of
the solvent under reduced pressure, the solid residue was extracted
residue was extracted with pentane (30 mLϫ2). Violet crystals of
10 crystallized from the pentane solution at –20 °C, yield 0.51 g,
85%; m.p. 124 °C (dec). C23H39FFeNOP (513.34): calcd. C 53.81,
3
with pentane (30 mLϫ2). Violet crystals of 8 crystallized from the H 7.66, N 2.73; found C 54.11, H 7.80, N 2.66. IR (Nujol): ν˜ =
pentane solution at –20 °C, yield 0.48 g, 80%; m.p. 149 °C (dec). 3238 [ν(N–H)], 1746 [ν(Fe–H)], 1620 [ν(C=N)], 1572 [ν(C=C)], 934
FeNP S·2C 12 (651.63): calcd. C 55.50, H 8.97, N 2.15; [ρ
found C 55.17, H 9.19, N 2.06. IR (Nujol): ν˜ = 3314 [ν(N–H)], (dt, JP,H = 23.8, 81.3 Hz, 1 H, Fe–H), 0.94 [m, 27 H, P(CH
742 [ν(Fe–H)], 1624 [ν(C=N)], 1582 [ν(C=C)], 1560 [ν(C=C)], 935 3.61 (s, 3 H, OCH ), 6.54–7.82 (m, 7 H, Ar-H), 8.88 (s, 1 H,
C=NH) ppm. P NMR (121.5 MHz, C , 298 K): δ = 29.5 [t,
–
1 1
C
20
H
34
F
2
3
5
H
1
(PCH
3
)] cm . H NMR (300 MHz, C
6
D
6
, 298 K): δ = –16.66
],
2
3 3
)
1
3
–1
1
31
[ρ
1
(PCH
3
)] cm . H NMR (300 MHz, C
6
D
6
, 298 K): δ = –14.62
6 6
D
Eur. J. Inorg. Chem. 2015, 2732–2743
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
2JP,P = 57.8 Hz, 1 P, P(CH
)
], 18.4 [d, 2JP,P = 57.8 Hz, 2
, 298 K): δ = –110.5
31
P NMR (121.5 MHz, C
D
, 298 K): δ = 19.0 [s, 2 P, P(CH
, 298 K): δ = –112.1 (s, 2 F, 2,6-
), –127.4 (m, 1 F), –138.9 (m, 1 F), –155.1 (m, 1 F), –165.0
(m, 1 F) ppm.
3
3
6
6
3 3
) ]
] ppm. 19F NMR (282.4 MHz, C
19
P, P(CH
3
)
3
6
D
6
6 6
ppm. F NMR (282.4 MHz, C D
F C H
2 6 3
13
1
(s) ppm. C NMR (75 MHz, C
6
D
6
, 298 K): δ = 22.2 [d, JP,C
=
=
2
9
2
1
2
3 3 3 F,C
.0 Hz, (CH ) P], 54.6 (OCH ), 107.8 (CAr), 111.8 (d, J
6.3 Hz, CAr), 112.0 (CAr), 126.2 (CAr), 129.2 (CAr), 132.9 (CAr),
40.2 (d, 2 F,C = 1.7 Hz, CAr), 155.6 (CAr), 163.9 (d, 1
88.7 Hz, F–CAr), 200.8 (C=NH) ppm.
[
2,6-F –C(=NH)–3,4,5,6-F
Fe(PMe (0.50 g, 1.39 mmol), HSi(OEt)
2,6-difluorophenyl)(pentafluorophenyl)methanimine (16; 0.36 g,
.18 mmol) were dissolved in THF (20, 10, and 30 mL, respec-
2
C
6
H
3
4
C
6
H
3
]Fe(H)(PMe
3
)
3
(18):
J
F,C
J =
3
)
4
3
(0.23 g, 1.39 mmol), and
(
1
[2,6-(CH
3
)
2
C
6
H
3
–C(=NH)–6-FC Fe(PMe
6
H
3
]
2
3
)
2
(14): Fe(PMe
3 4
)
tively). The three components were mixed at 20 °C. The mixture
was stirred at the same temperature for 24 h. During this period,
the mixture changed from deep yellow to violet. After the removal
of the solvent under reduced pressure, the solid residue was ex-
tracted with diethyl ether (30 mLϫ2). Violet crystals of 18 crys-
tallized from the diethyl ether solution at –20 °C, yield 0.38 g, 56%;
(
0.50 g, 1.39 mmol) dissolved in diethyl ether (20 mL) was added
to a diethyl ether solution (30 mL) of (2,6-difluorophenyl)(2,6-di-
methylphenyl)methanimine (13; 0.29 g, 1.18 mmol) at 20 °C. The
mixture was stirred at the same temperature for 24 h. During this
period, the mixture changed from deep yellow to blue. After the
removal of the solvent under reduced pressure, the solid residue
was extracted with pentane (30 mLϫ2). Violet crystals of 14 crys-
tallized from the pentane solution at –20 °C, yield 0.30 g, 78%;
m.p. 110 °C (dec). C22
8.24, H 6.54, N 2.16; found C 48.21, H 7.77, N 1.71. IR (Nujol):
ν˜ = 3295 [ν(N–H)], 1760 [ν(Fe–H)], 1622 [ν(C=N)], 1584 [ν(C=C)],
32 6 3 4
H F FeNP ·C H10O (647.38): calcd. C
4
m.p. Ͼ280 °C. C36
N 4.24; found C 65.41, H 7.83, N 3.55. IR (Nujol): ν˜ = 1587
44 2 2 2
H F FeN P (660.55): calcd. C 65.46, H 6.71,
–
1 1
1556 [ν(C=C)], 936 [ρ
1 3 6 6
(PCH )] cm . H NMR (300 MHz, C D ,
–
1
1
298 K): δ = –13.25 (br s, Fe–H), 0.93 [br s, P(CH ) ], 9.66 (br s,
[
ν(C=C)], 1527 [ν(C=C)], 932 [ρ
300 MHz, C , 298 K): δ = 0.71 [s, 18 H, P(CH
CH ), 2.56 (s, 6 H, CH ), 6.62–7.44 (m, 12 H, Ar-H), 8.94 (s, 2 H,
C=NH) ppm. P NMR (121.5 MHz, C , 298 K): δ = 10.3 [s, 2
] ppm. 19F NMR (282.4 MHz, C
P, P(CH , 298 K): δ = –114.2
s) ppm.
1
(PCH
3
)] cm .
H
NMR
3 3
3
1
6 6
C=NH) ppm. P NMR (121.5 MHz, C D , 298 K): δ = 25.8 [t,
JP,P = 47.2 Hz, 2
P, P(CH ) ] ppm. F NMR (282.4 MHz, C D , 298 K): δ = –112.2
(
6
D
6
3 3
)
], 2.25 (s, 6 H,
2
2
J
P,P = 47.8 Hz, 1 P, P(CH
3
)
3
], 19.3 [d,
3
3
1
9
31
6
D
6
3 3
6
6
(s, 2 F, 2,6-F C H ), –109.4 (m, 1 F), –143.6 (m, 1 F), –158.4 (m,
2
6
3
3
)
3
6
D
6
1
F), –167.0 (m, 1 F) ppm.
(
Representative Experimental Procedure for the Catalytic Reduction
of Aldehydes and Ketones: A 25 mL Schlenk tube was charged with
[
(
(
2,6-(CH
3
)
2
C
6
H
3
–C(=NH)–6-FC
(0.50 g, 1.39 mmol), HSi(OEt)
2,6-difluorophenyl)(2,6-dimethylphenyl)methanimine (13, 0.29 g,
.18 mmol) were dissolved in diethyl ether (20, 10, and 30 mL,
6
H
3
]Fe(H)(PMe
3
)
3
(15):
Fe-
PMe
3
)
4
3
(0.23 g, 1.39 mmol), and
a mixture of PhCHO (1.0 mmol), HSi(OEt)
3
(1.2 mmol), and 18
(
0.003 mmol) in THF (2 mL). The reaction vessel was stirred at
1
45 °C for 2 h. The progress of the reaction was monitored by GC.
respectively). The three components were mixed at 20 °C. The mix-
ture was stirred at the same temperature for 24 h. During this
period, the mixture changed from deep yellow to violet. After the
removal of the solvent under reduced pressure, the solid residue
was extracted with pentane (30 mLϫ2). Violet crystals of 15 crys-
tallized from the pentane solution at –20 °C, yield 0.49 g, 82%;
After the reaction mixture cooled to the room temperature,
CH OH (3 mL) and 10% NaOH (5 mL) were added to the tube.
The mixture was stirred for 24 h at 60 °C, and the product was
extracted with Et O (30 mLϫ2). The combined organic phases
were dried with anhydrous NaSO and filtered, and the solvent was
3
2
4
evaporated under reduced pressure. The product was purified by
column chromatography with silica gel [petroleum ether (60–
m.p. 130 °C (dec). C24
H 9.16, N 2.40; found C 59.80, H 8.97, N 2.12. IR (Nujol): ν˜ =
300 [ν(N–H)], 1753 [ν(Fe–H)], 1584 [ν(C=C)], 1525 [ν(C=C)], 936
3 5
H41FFeNP ·C H12 (583.51): calcd. C 59.69,
2
90 °C)/ethyl acetate 5:1 v/v] to afford PhCH OH as a colorless
3
[
(
2
liquid (0.096 g, 90.2%).
–1 1
ρ
1
(PCH
3
)] cm . H NMR (300 MHz, C
dt, JP,H = 15.0, 85.5 Hz, 1 H, Fe–H), 1.09 [m, 27 H, P(CH
.33 (s, 6 H, CH
6 6
D , 298 K): δ = –16.76
2
3
)
3
], Representative Experimental Procedure for the Catalytic Reduction
), 6.75–8.05 (m, 6 H, Ar-H), 8.80 (s, 1 H, C=NH) of α,β-Unsaturated Aldehydes: A 25 mL Schlenk tube was charged
3
31
2
ppm. P NMR (121.5 MHz, C
6
D
6
, 298 K): δ = 24.3 [t,
J
P,P
=
with a mixture of cinnamaldehyde (1.0 mmol), HSi(OEt)
3
2
3
8.7 Hz, 1 P, P(CH
3
)
3
], 16.5 [d, JP,P = 38.7 Hz, 2 P, P(CH
F NMR (282.4 MHz, C
NMR (75 MHz, C , 298 K): δ = 21.4 (CH
3
)
3
] ppm.
(1.2 mmol), and 15 (0.02 mmol) in THF (2 mL). The reaction vessel
was stirred at 60 °C for 7 h. The progress of the reaction was moni-
tored by TLC. After the mixture cooled to the room temperature,
1
9
13
6
D
6
, 298 K): δ = –114.7 (s) ppm.
C
=
=
1
6
D
6
3
), 22.1 [d,
J
P,C
1
2
1
4.2 Hz, (CH
3
)
3
P], 103.9 (CAr), 122.8 (CAr), 133.9 (d, 3JF,C
3
CH OH (3 mL) and 10% NaOH (5 mL) were added to the tube.
4.0 Hz, CAr), 136.0 (CAr), 141.2 (d, 2JF,C = 8 Hz, CAr), 146.3 (CAr), The mixture was stirred for 24 h at 60 °C, and the product was
61.6 (d, 1
J
F,C = 257.2 Hz, F–CAr), 176.3 (CAr), 208.3 (C=NH) extracted with Et
2
O (30 mLϫ2). The combined organic phases
ppm.
were dried with anhydrous NaSO
4
and filtered, and the solvent was
evaporated under reduced pressure. The product was purified by
column chromatography with silica gel [petroleum ether (60–
[
(
2,6-F
2
C
6
H
3
–C(=NH)–3,4,5,6-F
4 6 3 2 3 2 3 4
C H ] Fe(PMe ) (17): Fe(PMe )
0.50 g, 1.39 mmol) dissolved in THF (20 mL) was added to a THF
90 °C)/ethyl acetate 3:1 v/v] to afford cinnamyl alcohol as pale
solution (30 mL) of (2,6-difluorophenyl)(pentafluorophenyl)meth-
animine (16; 0.36 g, 1.18 mmol) at 20 °C. The mixture was stirred
at the same temperature for 24 h. During this period, the mixture
yellow crystals (0.11 g, 83.0%).
changed from deep yellow to purple. After the removal of the sol- Acknowledgments
vent under reduced pressure, the solid residue was extracted with
pentane (30 mLϫ2). Blue crystals of 17 crystallized from the pent-
ane solution at 0 °C, yield 0.12 g, 25%; m.p. Ͼ280 °C.
C H F12FeN P ·3C H12 (1000.80): calcd. C 56.41, H 6.24, N
32 26 2 2 5
The authors gratefully acknowledge the financial support by the
National Science Foundation of China (NSFC) (grant number
21172132/21372143), the K. C. Wong Education Foundation, and
2
.80; found C 56.52, H 6.38, N 2.57. IR (Nujol): ν˜ = 3284 [ν(N– Deutscher Akademischer Austauschdienst (DAAD) and the sup-
H)], 1624 [ν(C=N)], 1586 [ν(C=C)], 1524 [ν(C=C)], 944 [ρ (PCH )] port from Prof. Dr. Dieter Fenske and Dr. Olaf Fuhr [Karlsruhe
, 298 K): δ = 1.00 [m, 18 H, Nano-Micro Facility (KNMF), KIT] for the X-ray diffraction
], 6.52–7.50 (m, 6 H, Ar-H), 10.8 (s, 2 H, C=NH) ppm. analysis.
1
3
–1
1
cm . H NMR (300 MHz, C
P(CH
6 6
D
3 3
)
Eur. J. Inorg. Chem. 2015, 2732–2743
2741
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
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