Iron piano-stool phosphine complexes for catalytic hydrosilylation reaction

Article abstract of DOI:10.1016/j.ica.2011.10.048

A family of six cyclopentadienyl-iron carbonyl complexes bearing phosphine ligands (PPh₃, PMe₂Ph and PCy₃) with iodide or PF₆ as a counter-anion were prepared and used as catalysts for the hydrosilylation of carbonyl derivatives. Aldehydes were reduced at 30 °C, using PMHS as the silane, whereas ketones were reduced at 70 °C using PhSiH₃.

Full text of DOI:10.1016/j.ica.2011.10.048

Inorganica Chimica Acta 380 (2012) 301–307
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Iron piano-stool phosphine complexes for catalytic hydrosilylation reaction
Jianxia Zheng a, Luis C. Misal Castro a, Thierry Roisnel b, Christophe Darcel a, Jean-Baptiste Sortais a,
⇑
a UMR 6226 CNRS, Université de Rennes 1, ‘‘Sciences Chimiques de Rennes’’ (Catalysis and Organometallics), Campus de Beaulieu, Bat 10C, 263 avenue du Général Leclerc,
35042 Rennes Cedex, France
b UMR 6226 CNRS, Université de Rennes 1, ‘‘Sciences Chimiques de Rennes’’(Centre de Diffractométrie X), Campus de Beaulieu, Bat 10B, 263 avenue du Général Leclerc,
35042 Rennes Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 20 October 2011
A family of six cyclopentadienyl–iron carbonyl complexes bearing phosphine ligands (PPh3, PMe2Ph and
PCy3) with iodide or PF6 as a counter-anion were prepared and used as catalysts for the hydrosilylation of
carbonyl derivatives. Aldehydes were reduced at 30 °C, using PMHS as the silane, whereas ketones were
reduced at 70 °C using PhSiH3.
Young Investigator Award Special Issue
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Iron
Hydrosilylation
Reduction
Ketones
Aldehydes
1. Introduction
cyclic carbene as ligands for the reduction of carbonyl derivatives
[34–37].
The decrease in non-renewable natural resources has become a
global concern for the future, and it is usually the main issue asso-
ciated with fossil fuel feedstock. However, precious transition met-
als, such as palladium, rhodium or ruthenium which are
extensively used for catalytic processes in the chemical industry
are also limited, and their costs have already increased tremen-
dously over the last decade. New directions for homogeneous
catalysis should not only address energy issues by developing
highly reactive catalysts, but should also favour the use of earth-
abundant materials as the catalysts. Iron, in terms of its abundance,
low cost and low toxicity is especially attractive surrogate for pre-
cious transition metals. During the last decade, the use of iron as an
efficient catalyst has dramatically increased and efficient processes
are now able to compete with other transition metals [1–7]. In the
field of reduction, important breakthroughs have recently been
achieved, mainly in hydrogenation, hydrogen transfer reaction
and hydrosilylation reactions [8–10]. Since the pioneering report
from Brunner [11,12], important contributions have been made
using either a combination of iron salts and ligands to generate
in situ catalysts [13–21] or well-defined complexes as pre-
catalysts [22–31]. As part of our research on iron-catalysed
transformations [32,33], we have recently described the use of
well-defined iron complexes, neutral or cationic, bearing N-hetero-
Building on our work on piano-stool iron complexes, we de-
scribe in the present study the synthesis, characterisation and cat-
alytic activity of a family of iron complexes bearing phosphine
ligands with two different counter-anions iodide and PF6
(Scheme 1). These complexes are the phosphorus analogs of the
previously studied complex [CpFe(CO)2(IMes)]I.
2. Experimental
2.1. General considerations
All reagents were obtained from commercial sources and used
as received, excepted liquid aldehydes which were distilled prior
to use. Toluene was distilled following conventional methods (so-
dium/benzophenone) and stored under an argon atmosphere. All
reactions were carried out under argon atmosphere. Technical
grade petroleum ether (40–60 °C bp) and ethyl acetate were used
for column chromatography. 1H NMR spectra were recorded in
CDCl3 at ambient temperature on Bruker DPX-200, AVANCE I 300
spectrometers at 200.1, and 300.1 MHz, respectively, using the sol-
vent as an internal standard (7.26 ppm). 13C NMR spectra were ob-
tained at 50 or 75 MHz and referenced to the internal solvent
signals (central peak is 77.1 ppm). Chemical shift (d) and coupling
constants (J) are given in ppm and in Hz, respectively. The peak
patterns are indicated as follows: (s, singlet; d, doublet; t, triplet;
q, quartet; m, multiplet, and br. for broad). GC analysis were per-
⇑
Corresponding author. Tel.: +33 2 23 23 62 88; fax: +33 2 23 23 69 39.
E-mail address: jean-baptiste.sortais@univ-rennes1.fr (J.-B. Sortais).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.10.048

302
J. Zheng et al. / Inorganica Chimica Acta 380 (2012) 301–307
(m, 5H), 5.59 (d, J = 1.2 Hz, 5H), 2.25 (d, J = 11.2, 6H). 31P{1H}
NMR (81 MHz, acetone-d6): d 38.4 (s), À142.9 (sept, J = 707).
13C{1H} NMR (125 MHz, acetone-d6): d 209.7 (d, J = 24.8), 135.3
(d, J = 53.0), 131.5 (d, J = 2.6), 129.4 (d, J = 9.0), 129.3 (d, J = 7.4),
87.9 (s), 18.0 (d, J = 35.4). HRMS (ESI): m/z calcd for C15H16O2P56Fe
[MÀPF6]+ 315.0237; found 315.0236.
Fe
Fe
CO
Fe
CO
CO
I
CO
CO
R3P
Ph3P
R3P
PF6
I
1 : PR3 = PMe2Ph
2 : PR3 = PCy3
3
4 : PR3 = PMe2Ph
5 : PR3 = PCy3
6 : PR3 = PPh3
[CpFe(CO)2(PCy3)]PF6 (Complex 5). 93% yield. IR (CH2Cl2, cmÀ1):
2005, 2048. 1H NMR (300 MHz, acetone-d6): d 5.80 (s, 5H), 2.83–
1.40 (m, 33H). 31P{1H} NMR (81 MHz, acetone-d6): d 79.5 (s),
À143.0 (sept, J = 707). 13C{1H} NMR (75 MHz, acetone-d6):
d
Scheme 1. Structure of the complexes 1–6.
212.8 (d, J = 22.6), 88.2 (s), 39.2 (d, J = 21.4), 31.1 (d, J = 2.8), 27.9
(d, J = 10.8), 26.5 (d, J = 1.5). HRMS (ESI): m/z calcd for
C
25H38O2P56Fe [MÀPF6]+ 457.1959; found 457.1958.
formed with GC-2014 (Shimadzu) 2010 equipped with a 30-m cap-
illary column (Supelco, SPBTM-20, fused silica capillary column,
30 M  0.25 mm  0.25 mm film thickness), which was used with
N2/air as the vector gas. The following GC conditions were used:
initial temperature 80 °C for 2 min, then heating rate 10 °C/min
up to 225 °C then 225 °C for 15 min. [CpFe(CO)2I] [38], [Cp2Fe]PF6
[39], and [CpFe(CO)2(THF)]PF6 [40] were prepared according to
the published procedures. HR–MS spectra were carried out by
the corresponding facilities at the CRMPO (Centre Régional de Me-
sure Physiques de l’Ouest), University Rennes 1. FTIR spectra were
recorded at room temperature in solution between KBr plates on
an IR Affinity-1 Shimadzu apparatus.
The complex 6 was prepared according to the modified pub-
lished procedures [44,45]: [CpFe(CO)2]2 (0.18 g, 0.5 mmol), ferrice-
nium salt [Cp2Fe]PF6 (0.33 g, 1.0 mmol) and PPh3 (0.29 g,
1.1 mmol) were added into 10 mL CH2Cl2 solution and stirred for
30 min. The colour of reaction mixture turned from dark brown
to orange. After removing the solvent under vacuum, the complex
was further purified by recrystallization from CH2Cl2 and Et2O.
[CpFe(CO)2(PPh3)]PF6 (Complex 6). 80% yield. IR (CH2Cl2, cmÀ1):
2017, 2058. 1H NMR (300 MHz, acetone-d6): d 7.75–7.51 (m, 15H),
5.63 (d, J = 1.4 Hz, 5H). 31P{1H} NMR (121 MHz, acetone-d6): d 61.5
(s), À144.2 (sept, J = 707). 13C{1H} NMR (75 MHz, acetone-d6): d
210.9 (d, J = 24.3), 133.8 (d, J = 10.4), 133.1 (d, J = 2.8), 132.2 (d,
J = 52.2), 130.5 (d, J = 11.0), 89.8 (s). HRMS (ESI): m/z calcd for
25H20O2P56Fe [MÀPF6]+ 439.0550; found 439.0551.
2.2. Syntheses and characterisations of complexes 1–6
C
Complexes 1 and 2 were prepared according to modified pub-
lished procedures [41,42]: [CpFe(CO)2I] (1.22 g, 4.0 mmol) and
phosphine (4.8 mmol) were stirred overnight at room temperature
in toluene (10 mL). The supernatant was removed by cannula
transfer, the yellow solid was then washed with toluene and
recrystallized with CH2Cl2 and diethyl ether.
2.3. X-ray structure determinations
Suitable crystals (obtained by slow diffusion of Et2O in CH2Cl2
solution of the complexes) were collected on an APEXII, Bruker-
AXS diffractometer equipped with a CCD detector, using graph-
ite-monochromated Mo
K
a
radiation (k = 0.71073 Å) at
[CpFe(CO)2(PMe2Ph)]I (Complex 1). 63% yield. IR (CH2Cl2,
cmÀ1): 2006, 2049. 1H NMR (300 MHz, CDCl3): d 7.74–7.41 (m,
5H, Ph), 5.47 (s, 5H, Cp), 2.24 (d, J = 10.7, 6H, CH3). 31P{1H} NMR
(121 MHz, CDCl3): d 37.0. 13C NMR (75 MHz, CDCl3): d 209.0 (d,
J = 25.0), 134.4 (d, J = 52.9), 131.6 (d, J = 3.0), 129.7 (d, J = 10.9),
128.9 (d, J = 9.5), 87.9 (s), 20.2 (d, J = 34.7). HRMS (ESI): m/z calcd
for C15H16O2P56Fe [MÀI]+ 315.0237; found 315.0236.
T = 150(2) K. The structure was solved by direct methods using
the SIR97 program [46], and then refined with full-matrix least-
square methods based on F2
(SHELX-97) [47] with the help of the
WINGX [48] program. All non-hydrogen atoms were refined with
anisotropic atomic displacement parameters. H atoms were finally
included in their calculated positions. For the complex 1, the con-
tribution of the disordered solvents to the calculated structure fac-
tors was estimated following the BYPASS algorithm [49],
implemented as the SQUEEZE option in PLATON [50]. A new data
set, free of solvent contribution, was then used in the final refine-
ment. The Refinement of the Flack parameter, for the complex 3,
lead to a value of 0.53(5). Due to the presence of anomalous atoms
(I and Fe) in the complex and a suitable data collection (high
redundancy and high completeness), accuracy on this refined Flack
parameter is quite large, leading to an unambiguous meaning of
this parameter. Thus, the value of the Flack parameter is the signa-
ture of the presence of racemic twin (two enantiomer molecules in
identical quantity) in the crystal. Crystal data and collection
parameters as well as the selected bond distances and angles are
collected in Tables 1 and 2, respectively.
[CpFe(CO)2(PCy3)]I (Complex 2). 60% yield. IR (CH2Cl2, cmÀ1):
2004, 2048. 1H NMR (300 MHz, CDCl3): d 5.63 (s, 5H), 2.29–1.13
(m, 33H). 31P{1H} NMR (81 MHz, CDCl3): d 80.4. 13C{1H} NMR
(75 MHz, CDCl3): d 211.1 (d, J = 22.2), 87.0 (s), 38.5 (d, J = 20.4),
30.6 (d, J = 2.4), 27.2 (d, J = 10.4), 25.8 (s). HRMS (ESI): m/z calcd
for C25H38O2P56Fe [MÀI]+ 457.1959; found 457.1960.
The complex 3 was prepared according to the published proce-
dure [43].
[CpFe(CO)(PPh3)I] (Complex 3). 58% yield. IR (CH2Cl2, cmÀ1):
1952. 1H NMR (200 MHz, CDCl3): d 7.63–7.52 (m, 6H), 7.44–7.33
(m, 9H) 4.48 (d, J = 1.1, 5H). 31P{1H} NMR (81 MHz, CDCl3): d
68.6. 13C{1H} NMR (75 MHz, CD2Cl2): d 136.2 (d, J = 44.8), 134.0
(d, J = 9.3), 130.5 (d, J = 1.8), 128.5 (d, J = 9.6), 83.3 (s). HRMS: m/z
calcd for C24H20OINaP56Fe [M+Na]+ 560.9543; found 560.9541.1
Complexes 4 and 5 were prepared according to the modified
published procedure [40]:
2.4. Procedure for hydrosilylation of aldehydes
[CpFe(CO)2(THF)]PF6
(197 mg,
0.5 mmol),
phosphine
A 10 mL oven dried Schlenk tube containing a stirring bar, was
loaded with [CpFe(CO)2(PPh3)]PF6 (0.015 g, 0.025 mmol), THF
(0.5 mL) was then added followed by aldehyde (0.5 mmol) and
(0.60 mmol) were stirred in 10 mL of CH2Cl2 for 30 min at room
temperature. After filtration, the solution was concentrated under
vacuum, the complexes were obtained after recrystallization by
CH2Cl2 and Et2O.
PMHS (119 lL, 2.0 mmol). The reaction mixture was stirred in a
preheated oil bath at 30 °C for 24 h under visible light irradiation
(24 Watt compact fluorescent lamp). Then 1 mL of MeOH was
added followed by 1 mL of 2 M NaOH aqueous solution with
vigorous stirring. The reaction mixture was further stirred for 1 h
at room temperature and extracted with diethyl ether
[CpFe(CO)2(PMe2Ph)]PF6 (Complex 4). 90% yield. IR (CH2Cl2,
cmÀ1): 2009, 2054. 1H NMR (200 MHz, acetone-d6): d 7.88–7.61
The 13C{1H} NMR signal for the carbonyl ligands were not detected.
1

J. Zheng et al. / Inorganica Chimica Acta 380 (2012) 301–307
303
Table 1
Crystal data and data collection parameters.
Complex
1
2
3
4
5
Formula
C
15H16FeO2PI
C25H38FeO2PI
584.27
C24H20FeIOP
538.12
orthorhombic
Pc21n
8.7065 (3)
13.7633 (5)
17.2369 (6)
90
C15H16F6FeO2P2
460.07
monoclinic
P21/n
10.8531 (8)
13.6501 (11)
12.0929 (9)
90
90.108 (4)
90
2(C25H20F6FeO2P2)
1204.69
Formula weight
Crystal system
space group
a (Å)
b (Å)
c (Å)
442.01
triclinic
P1
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
9.6568 (10)
10.1855 (11)
11.0017 (12)
88.056 (7)
65.179 (6)
89.511 (6)
981.57 (18)
2
9.5701 (4)
11.6070 (4)
11.6957 (5)
89.6710 (10)
82.8080 (10)
80.9860 (10)
1272.89 (9)
2
11.3616 (8)
14.6952 (12)
16.5388 (12)
97.930 (3)
93.846 (3)
90.079 (3)
2728.6 (4)
2
a
(°)
b (°)
90
90
c
(°)
V (Å3)
2065.50 (13)
4
1.73
1791.5 (2)
4
1.706
Z
qcalcd (gcmÀ3
)
1.495
2.420
1.524
1.886
1.466
0.732
l
(mmÀ1
)
2.314
1.087
F(000)
432
596
1064
928
1256
Crystal size (mm3)
h range (°)
0.32 Â 0.27 Â 0.24
3.06–27.5
À12 6 h 6 12
À13 6 k 6 13
À14 6 l 6 13
11267
4397/0.0345
97.1
183
0.34 Â 0.13 Â 0.08
3.51–27.4
À12 6 h 6 10
À14 6 k 6 15
À15 6 l 6 15
20643
5764/0.0316
99.3
271
0.14 Â 0.12 Â 0.08
2.62–27.49
À9 6 h 6 11
À17 6 k 6 15
À16 6 l 6 22
10307
4535/0.0319
99.9
140
0.38 Â 0.27 Â 0.05
1.49–27.47
À14 6 h 6 11
À15 6 k 6 17
À15 6 l 6 12
8529
3931/0.0494
95.7
238
0.38 Â 0.29 Â 0.1
2.97–27.48
À14 6 h 6 14
À19 6 k 6 19
À21 6 l 6 20
35921
12380/0.047
98.9
649
Index ranges
No. of reflections collected
No. of independent reflections collected (Rint
Completeness to dmax (%)
No. of refined parameters
GOF (F2)
)
1.088
1.051
1.056
0.783
1.039
R1(F) (I > 2d(I))
0.0564
0.1506
0.0192
0.0511
0.0507
0.116
0.0354
0.0909
0.0413
0.0985
wR2(F2) (I > 2d(I))
Absolute structural parameters
0.53 (5)
1.75/À0.857
Largest diff peak/hole (eÅÀ3
)
3.535/À1.065
0.789/À0.523
0.373/À0.429
0.845/À0.686
(2 Â 10 mL). The combined organic layers were dried over anhy-
drous MgSO4, filtered and concentrated under vacuum. The con-
version was determined by 1H NMR. The residue was then
purified by silica gel column chromatography using a petroleum
ether–ethyl acetate mixture (10–40%) to achieve the desired prod-
uct. 1H and 13C NMR of the products were in accordance with those
described in the literature.
due was purified by silica gel column chromatography using a
petroleum ether–ethyl acetate mixture (10–20%) to achieve the de-
sired product. 1H and 13C NMR of the products were in accordance
with those described in the literature.
3. Results and discussion
2.5. Procedure for hydrosilylation of ketones
3.1. Synthesis of the catalysts
A 10 mL oven-dried Schlenk tube containing a stirring bar, was
loaded with [CpFe(CO)PPh3I] (0.014 g, 0.025 mmol). The ketone
(0.5 mmol) was added followed by PhSiH3 (74 lL, 0.6 mmol). The
reaction mixture was stirred in a preheated oil bath at 70 °C for
30 h. Then 1 mL of MeOH was added followed by 1 mL of 2 M
NaOH aqueous solution with vigorous stirring. The reaction mix-
ture was further stirred for 1 h at room temperature and was ex-
tracted with diethyl ether (2 Â 10 mL). The combined organic
layers were dried over anhydrous MgSO4, filtered and concentrated
under vacuum. Conversion was determined by 1H NMR. The resi-
Cyclopentadienyl iron carbonyl complexes have been studied
extensively as models in coordination chemistry [51] to investi-
gate, for example, the properties of phosphines [42] or NHC-car-
bene ligands [52,53] and the chirality at the metal center [54]. To
start our investigation on iron–phosphine complexes as potential
catalysts for hydrosilylation, we selected three phosphine ligands
for their steric and electronic properties: PPh3, PMe2Ph, and PCy3.
Various iron derivatives were prepared according to established
pathways. For the first family, which uses iodide as a counter-
anion, complexes 1 and 2, respectively with PMe2Ph and PCy3,
Table 2
Selection of bonds and distances of the complexes 1–5.
Complex
1
2
3
4
5
Distances (Å)
Fe–P
Fe–Cp
2.2183 (16)
1.722
2.2675 (4)
1.725
2.2275 (15)
1.686
2.2234 (8)
1.725
2.2646 (6)
1.729
Fe–CO
Fe–CO
Fe–I
1.789 (6)
1.777 (6)
–
1.7892 (16)
1.7799 (16)
–
1.847 (11)
–
2.6298 (8)
1.782 (3)
1.785 (3)
–
1.785 (2)
1.782 (2)
–
Angles (°)
P–Fe–CO
P–Fe–CO
OC–Fe–CO
P–Fe–I
92.6 (2)
90.2 (2)
93.6 (3)
–
93.44 (5)
93.88 (5)
96.11 (7)
–
92.7 (3)
–
–
97.62 (4)
87.5 (3)
91.61 (10)
91.45 (11)
92.56 (13)
–
–
94.05 (7)
91.60 (7)
95.34 (10)
I–Fe–CO
–
–
–

304
J. Zheng et al. / Inorganica Chimica Acta 380 (2012) 301–307
I
toluene
r.t., 16h
+
PR3
Fe
CO
Fe
PR3
I
OC
OC
CO
1
2
PR3 = PMe2Ph
PR3 = PCy3
Scheme 2. Synthesis of the complexes 1 and 2.
PF6
PF6
CH2Cl2
+
PR3
Fe
Fe
r.t., 30 min
CO
CO
Fig. 2. ORTEP view of the complexes 4–5, drawn at 50% of probability. Hydrogen
atoms and PF6 moities were omitted for clarity.
CO
CO
THF
R3P
PR3 = PMe2Ph,
PR3 = PCy3,
4
5
O
OH
1) [Fe], silane, solvent
visible light irradiation
Scheme 3. Synthesis of the complexes 4 and 5.
H
H
H
2) hydrolysis
respectively, were obtained in moderate yields (60%) by direct
reaction of the phosphine with the iron precursor [CpFe(CO)2I] in
toluene at rt [41,42] (Scheme 2). When the same conditions were
applied to PPh3 as the phosphine, a mixture of the desired cationic
compound [CpFe(CO)2PPh3]I (<20%) and the neutral complex 3,
[CpFe(CO)(PPh3)I] was obtained [55]. Thus, the neutral complex 3
selectively was prepared from [CpFe(CO)2I] and triphenylphos-
phine according to Coville [56,57] and Aime’s [43] procedures
using [CpFe(CO)2]2 dimer as a catalyst to favour the substitution
of the carbonyl ligand.
Scheme 4. Hydrosilylation of benzaldehyde catalyzed by the iron complexes 1–6.
ence was observed between the iodide and PF6 series. With those
complexes in hand, we then started to investigate their catalytic
properties.
3.2. Catalytic hydrosilylation reaction
In order to study the effect of the nature of the counter-anion in
the course of the catalytic reaction, the analogous complexes with
PF6 as non-coordinative anion were prepared following the meth-
odology described by Schumann [40]. Complexes 4 and 5 were ob-
tained in one step by reaction of the corresponding phosphine with
the precursor [CpFe(CO)2(THF)]PF6 in CH2Cl2 (Scheme 3). Although
the same conditions could be applied for the preparation of the
complex 6, this compound was obtained by the direct oxidation
of [CpFe(CO)2]2 by [Cp2Fe]PF6 in the presence of PPh3 in CH2Cl2
at rt [45,58].
We performed studies of the catalytic activities of [CpFe(phos-
phine)] complexes to explore their potential in the hydrosilylation
reaction of aldehydes (Scheme 4).
The optimization of the hydrosilylation reaction was carried out
with benzaldehyde as the model substrate. As illustrated in Table 3,
the preliminary survey was carried out using 5 mol.% of [CpFe
(CO)2(PMe2Ph)]I 1 as the catalyst, and 1.2 equiv. of diphenylsilane
as the reducing agent, under exposure to visible light in toluene.
After a 16 h reaction at 70 °C, 53% conversion was observed after
basic cleavage of the silyl ether intermediate (Table 3, entry 1).
When the reaction was performed with phenylsilane as the hy-
dride source, the conversion increased to 80% (Table 3, entry 2).
Interestingly, the conversion was improved to 98% when THF
was chosen as the reaction solvent (Table 3, entry 4). When the
reaction temperature was decreased to 30 °C and the concentra-
tion of the catalyst increased, 92% conversion was observed
(Table 3, entry 5). However, with 2 mol.% of the catalyst under neat
All complexes have been characterized by 1H, 13C and 31P NMR,
IR, HR–MS and X-ray diffraction studies. To the best of our knowl-
edge, only the crystallographic structure of 6 has been described
[59]. Singles crystals suitable for X-ray diffraction studies were ob-
tained for all the other complexes. Representative molecular struc-
tures are displayed in Figs. 1 and 2 for complexes 1–3 and 4–5,
respectively. Typical piano-stool geometries were observed for this
family of catalysts (See Table 2) and no significant structural differ-
Fig. 1. ORTEP view of the complexes 1–3, drawn at 50% of probability. Hydrogen atoms and iodide atom for 1 and 2 were omitted for clarity.

J. Zheng et al. / Inorganica Chimica Acta 380 (2012) 301–307
305
Table 3
Optimisation of the hydrosilylation of benzaldehyde with catalyst 1. Typical conditions: benzaldehyde (0.5 mmol), silane and catalyst were stirred under visible light irradiation,
conversions were determined by GC after methanolysis (MeOH, NaOH 2 M).
Entry
Catalyst loading (mol.%)
Silane (equiv.)
Solvent
Temp. (°C)
Time (h)
Conversion (%)
1
2
3
4
5
6
7
8
5
5
5
5
5
2
5
5
5
5
5
Ph2SiH2 (1.2)
PhSiH3 (1.2)
Ph2SiH2 (1.2)
PhSiH3 (1.2)
PhSiH3 (1.2)
PhSiH3 (1.2)
PhSiH3 (1.2)
PMHS (4)
Toluenea
Toluenea
THFa
70
70
70
70
30
30
30
30
30
30
30
16
16
16
16
16
16
16
16
24
16
16
53
80
70
98
92
83
87
68
>98
96
98
THFa
THFb
THFb
b
CH2Cl2
THFb
THFc
Neat
Neat
9
10
11
PMHS (4)
Ph2SiH2 (1.2)
PhSiH3 (1.2)
a
b
c
2 mL.
1 mL.
0.5 mL.
Table 4
O
OH
Comparison of the different catalysts 1–6 for the reduction of benzaldehyde. Typical
conditions: benzaldehyde (0.5 mmol), catalyst (5 mol%), silane (PhSiH3, 0.6 mmol or
PMHS 2 mmol) and solvent were stirred at 30 °C under visible light irradiation for
16 h. Conversions were determined by GC after methanolysis (MeOH, 2 M NaOH).
1) [Fe], silane, solvent
visible light irradiation
2) hydrolysis
Entry
Catalyst
PhSiH3
THF
PMHS
THF
Scheme 5. Hydrosilylation of acetophenone catalyzed by the iron complexes 1–6.
Neat
1
2
3
4
5
6
1
2
3
4
5
6
92
95
>98
94
95
95
96
92
91
97
97
91
68
42
85
95
95
88
Table 5
Optimisation of the hydrosilylation of acetophenone with catalyst 1. Typical
conditions: acetophenone (0.5 mmol), silane (1.2 equiv.), THF (2 mL) or neat, under
visible light irradiation, conversion determined by GC after methanolysis (MeOH,
NaOH 2 M).
Entry Catalyst loading Silane
(mol.%)
Solvent Temp.
Time
(h)
Conversion
(%)
(°C)
1
2
3
4
5
5
5
5
5
2
Ph2SiH2 THF
70
70
70
70
50
16
16
16
30
16
1
2
66
73
41
condition, the reaction slowed down, and only 83% conversion was
obtained (Table 3, entry 6). Replacing the solvent by CH2Cl2 also re-
duced the conversion to 87% (Table 3, entry 7). Therefore, THF was
employed as the solvent for all following reactions. It is notewor-
thy that the cheap and convenient silane PMHS could be employed
as the silane at 30 °C in THF, since the reaction reached the comple-
tion after 24 h (Table 3, entries 8–9). These results show the poten-
tial advantage of this family of catalysts over similar systems
which usually require higher temperature with PMHS [16,32].
Notably, the reactions could also be performed in neat condition
with diphenylsilane or phenylsilane (Table 3, entries 10–11) with-
out decomposition of the catalyst.
Further screening of the catalysts 1–6 using the optimized con-
ditions (catalyst loading 5%, THF or neat conditions, phenylsilane
or PMHS as the hydride source, Table 4) revealed that for the reac-
tions performed with PMHS catalysts with PF6 as the counter anion
usually worked better than catalysts with iodide as the counter
PhSiH3
PhSiH3
PhSiH3
PhSiH3
THF
Neat
Neat
Neat
Table 6
Comparison of the different catalysts 1–6 for the reduction of
acetophenone. 5 mol.% of catalyst, 0.5 mmol of acetophenone,
1.2 equiv. of PhSiH3, no solvent, 70 °C, 30 h, conversion deter-
mined by GC.
Entry
Catalyst
Conversion (%)
1
2
3
4
5
6
1
2
3
4
5
6
73
69
88
43
50
87
O
O
O
O
O
H
H
H
H
H
MeO
N
Cl
>98 (65)
>98 (80)
>98 (69)
>98 (87)
>98 (86)
O
O
O
H
H
O
H
Fe
H
Me2N
>98a
>98 (95)
>98 (76)
>98 (88)b
Fig. 3. Scope of iron-catalysed hydrosilylation of aldehydes using [CpFe(CO)2PPh3]PF6 as the catalyst. Conversions are determined by 1H NMR and isolated yields are given in
parentheses. (a) Conversion determined by GC. (b) At 70 °C.

306
J. Zheng et al. / Inorganica Chimica Acta 380 (2012) 301–307
O
O
O
O
O
Br
Cl
93 (73)
85 (71)
92 (72)
88
96
98
93
48
O
O
O
O
O
7
F3C
MeO
91 (57)
85 (66)
Fig. 4. Scope of iron-catalysed hydrosilylation of ketones using [CpFe(CO)(PPh3)I] as the catalyst. Conversions are determined by 1H NMR and isolated yields are given in
parentheses.
anion. Since PPh3 is economical and easy to handle, the catalyst 6
[CpFe(CO)2(PPh3)]PF6 was chosen as the catalyst for the scope of
aldehydes, albeit the conversion is slightly lower than when with
PMe2Ph and PCy3 are used as ligands (Table 4, entries 6, versus 4
and 5).
3 was selected as the catalyst for the scope of the reaction. Several
ketones were subjected to the best reaction conditions optimized
for the scope of this reaction (Fig. 4). It turned out that this iron-
catalyzed hydrosilylation could adapt to various ketones. In con-
trast to aldehydes, aryl methyl ketones bearing substituents in
the ortho-position of the aryl ring led to the corresponding alcohols
in 48% conversion, which probably means that ortho-hindered sub-
stituents can hamper the reaction. The hydrosilylation reaction
was suitable to both electron-rich and electron-poor substituted
(Me, OMe, Cl, and Br) aromatic methyl ketones, and the reaction re-
sulted in corresponding alcohols with good to excellent yields. The
principle of this iron-catalyzed transformation can also be ex-
tended to alkyl methyl ketones such as 4-phenyl-2-butanone and
To investigate the scope of the reaction, a variety of aldehydes
were then tested using the optimized mild conditions (PMHS,
THF, 24 h at 30 °C, 5 mol.% of 6, under visible light irradiation). Sev-
eral aldehydes were reduced with good to excellent yields (Fig. 3).
The electronic effects on the reactivity were limited. Electron-defi-
cient as well as electron-donating groups on the aryl ring did not
show any significant influence on the activity of the iron catalyst.
Interestingly, functional groups such as chloride remained un-
changed under such reaction conditions. The chemoselectivity of
the hydrosilylation of aldehyde versus alkene was also demon-
strated: the catalyzed hydrosilylation of enal derivatives such as
cinnamaldehyde led exclusively to the corresponding allyl alcohol
resulting in an exclusive 1,2-addition with no GC-detectable
amounts of 1,4-addition products and the isolated yield was up
to 76%. Extension of the procedure to heterocyclic aromatic alde-
hydes, such as 2-pyridinecarboxaldehyde, was also possible. Inter-
estingly, ferrocenecarboxaldehyde could also be reduced using this
catalyst (at 70 °C, 24 h) and the corresponding alcohol was ob-
tained with a good isolated yield (88%).
Based on the promising results obtained with [CpFe(phos-
phine)] complexes as catalysts for the hydrosilylation of aldehydes,
we also tested these compounds with ketones which are usually
more difficult to reduce (Scheme 5).
The optimisation was carried out using catalyst 1 as the model
catalyst and acetophenone as the model substrate (Table 5). When
reactions were performed in THF, after 16 h under irradiation, no
conversion was observed for either types of hydride source, diphe-
nylsilane or phenylsilane (Table 5, entries 1 and 2). Under solvent-
free conditions, the conversion could reach 73% at 70 °C after 30 h
(Table 5, entries 3 and 4).
2-undecanone. In the case of the cyclic ketone,
a-tetralone, the
reaction led to the corresponding 1,2,3,4-tetrahydro-1-naphthol
with moderate yield (57%).
4. Conclusion
In conclusion, we have demonstrated that cationic and neutral
cyclopentadienyl iron carbonyl complexes bearing a phosphine as
the ligand could be successfully used as catalysts for the hydrosily-
lation of aldehydes and ketones. Interestingly, we observed that
compared to complexes bearing a NHC-carbene as the ligand,
phosphine analogs proceeded more slowly (5 mol.% were required
instead of 1 mol.%), but PMHS could be used as the silane for the
reduction of aldehydes at 30 °C. We also showed that simple
PPh3 could be a good ligand for this family of catalysts. More de-
tailed studies directed towards a precise mechanism are currently
under investigation in our group.
Acknowledgements
We are grateful to CNRS, Rennes Métropole and Ministère de la
recherche for support, the Ministère des affaires étrangères and the
Fundacion Gran Mariscal de Ayacucho for a grant to L.C.M.C., and
the European Union through network IDECAT.
The different catalysts were tested using the best conditions for
the reduction of acetophenone (5 mol.% of catalyst, 1.2 equiv. of
PhSiH3, no solvent, 70 °C, 30 h, under irradiation). (Table 6) By con-
trast with the results obtained for the reduction of benzaldehyde,
the complexes bearing a non-coordinative counter-anion were
not found to be more efficient than the ones with iodide as the
counter-ion (Table 6, entries 1,2 versus 4–6). Only complexes 3
and 6, derived from PPh3, gave satisfactory conversion rates above
85% (Table 6, entries 3 and 6). Following these encouraging results,
we performed reactions in the absence of light. The reaction only
worked well with the neutral complex 3, whereas no conversion
was observed for complex 6.
Appendix A. Supplementary material
Crystallographic data for complexes 1–5 are summarised in
Table 1. CCDC-836108 (for 1), -836109 (for 2), -836110 (for 3),
-836111 (for 4) and -836112 (for 5) contain the supplementary
crystallographic 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. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.10.048.
Given the cheapness of phosphine (PPh3), the easy preparation
of the catalyst and the fact that no irradiation was needed, complex

J. Zheng et al. / Inorganica Chimica Acta 380 (2012) 301–307
307
[29] T. Muraoka, Y. Shimizu, H. Kobayashi, K. Ueno, H. Ogino, Organometallics 29
(2010) 5423.
References
[30] S. Hosokawa, J. Ito, H. Nishiyama, Organometallics 29 (2010) 5773.
[31] L.C. Misal Castro, D. Bézier, J.-B. Sortais, C. Darcel, Adv. Synth. Catal. 353 (2011)
1279.
[32] X.-F. Wu, C. Darcel, Eur. J. Org. Chem. 1 (2009) 1144.
[33] X.-F. Wu, D. Bezier, C. Darcel, Adv. Synth. Catal. 351 (2009) 367.
[34] F. Jiang, D. Bézier, J.-B. Sortais, C. Darcel, Adv. Synth. Catal. 353 (2011) 239.
[35] D. Bézier, G.T. Venkanna, J.-B. Sortais, C. Darcel, ChemCatChem (2011)
doi:10.1002/cctc.201100202.
[36] D. Bézier, F. Jiang, T. Roisnel, J.-B. Sortais, C. Darcel, Eur. J. Inorg. Chem. (2011)
doi:10.1002/ejic.201100762.
[37] L.C. Misal Castro, J.-B. Sortais, C. Darcel, Chem. Commun. (2011). doi:10.139/
C1CC14403K.
[38] S. Yasuda, H. Yorimitsu, K.O. Yasuda, H. Yorimitsu, K. Oshima, Organometallics
27 (2008) 4025.
[39] T.C. Lehman, C. Thorpe, Biochemistry 29 (1990) 10594.
[40] H. Schumann, J. Organomet. Chem. 304 (1986) 341.
[41] P.M. Treichel, R.L. Shublin, K.W. Barnett, D. Reichard, Inorg. Chem. 5 (1966)
1177.
[1] C. Bolm, J. Legros, J. Le Paih, L. Zani, Chem. Rev. 104 (2004) 6217.
[2] B. Plietker (Ed.), Iron Catalysis in Organic Chemistry, Wiley VCH Verlag,
Weinheim, 2008.
[3] S. Enthaler, K. Junge, M. Beller, Angew. Chem., Int. Ed. 47 (2008) 3317.
[4] A. Correa, O. Garcia Mancheño, C. Bolm, Chem. Soc. Rev. 37 (2008) 1108.
[5] B.D. Sherry, A. Fürstner, Acc. Chem. Res. 41 (2008) 1500.
[6] W.M. Czaplik, M. Mayer, J. Cvengros, A. Jacobi Von Wangelin, ChemSusChem 2
(2009) 396.
[7] C.-L. Sun, B.-J. Li, Z.-J. Shi, Chem. Rev. 111 (2011) 1293.
[8] R.H. Morris, Chem. Soc. Rev. 38 (2009) 2282.
[9] M. Zhang, A. Zhang, Appl. Organometal. Chem. 24 (2010) 751.
[10] K. Junge, K. Schorder, M. Beller, Chem. Commun. 47 (2011) 4849.
[11] H. Brunner, K. Fisch, Angew. Chem., Int. Ed., Engl. 29 (1990) 1131.
[12] H. Brunner, K. Fisch, J. Organomet. Chem. 412 (1991) C11.
[13] H. Nishiyama, A. Furuta, Chem. Commun. (2007) 760.
[14] A. Furuta, H. Nishiyama, Tetrahedron Lett. 49 (2008) 110.
[15] N.S. Shaikh, K. Junge, M. Beller, Org. Lett. 9 (2007) 5429.
[16] N.S. Shaikh, S. Enthaler, K. Junge, M. Beller, Angew. Chem., Int. Ed. 27 (2008)
2497.
[17] S. Zhou, K. Junge, D. Addis, S. Das, M. Beller, Angew. Chem., Int. Ed. 48 (2009)
9507.
[18] D. Addis, N. Shaikh, S. Zhou, S. Das, K. Junge, M. Beller, Chem. Asian J. 5 (2010)
1687.
[19] T. Inagaki, L.T. Phong, A. Furuta, J. Ito, H. Nishiyama, Chem. Eur. J. 16 (2010)
3090.
[20] Y. Sunada, H. Kawakami, Y. Motoyama, H. Nagashima, Angew. Chem., Int. Ed.
48 (2009) 9511.
[21] K. Muller, A. Schubert, T. Jozak, A. Ahrens-Botzong, V. Schünemann, W.R. Thiel,
ChemCatChem 3 (2011) 887.
[22] S. Zhou, D. Addis, S. Das, K. Junge, M. Beller, Chem. Commun. 1 (2009) 4883.
[23] A.M. Tondreau, E. Lobkovsky, P.J. Chirik, Org. Lett. 10 (2008) 2789.
[24] D.V. Gutsulyak, L.G. Kuzmina, J.A.K. Howard, S.F. Vyboishchikov, G.I. Nikonov, J.
Am. Chem. Soc. 130 (2008) 3732.
[42] N.J. Coville, E.A. Darling, A.W. Hearn, P. Johnston, J. Organomet. Chem. 328
(1987) 375.
[43] S. Aime, M. Botta, R. Gobetto, D. Osella, Organometallics 4 (1985) 1476.
[44] D.L. Reger, C. Coleman, J. Organomet. Chem. 131 (1977) 153.
[45] D. Catheline, D. Astruc, J. Organomet. Chem. 266 (1984) C11.
[46] A. Altomare, M.C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi,
A.G.G. Moliterni, G. Polidori, R. Spagna, J. Appl. Cryst. 32 (1999) 115.
[47] G.M. Sheldrick, Acta Crystallogr., Sect. A64 (2008) 112.
[48] L.J. Farrugia, J. Appl. Cryst. 32 (1999) 837.
[49] P.V.D. Sluis, A.L. Spek, Acta Crystallogr., Sect. A46 (1990) 194.
[50] A.L. Spek, J. Appl. Cryst. 36 (2003) 7.
[51] V. Guerchais, Eur. J. Inorg. Chem. (2002) 783.
[52] P. Buchgraber, L. Toupet, V. Guerchais, Organometallics 22 (2003) 5144.
[53] L. Mercs, G. Labat, A. Neels, A. Ehlers, M. Albrecht, Organometallics 25 (2006)
5648.
[54] H. Brunner, H. Ike, M. Muschiol, T. Tsuno, N. Umegaki, M. Zabel,
Organometallics 30 (2011) 414.
[25] B.K. Langlotz, H. Wadepohl, L.H. Gade, Angew. Chem., Int. Ed. 47 (2008)
4670.
[26] A.M. Tondreau, J.M. Darmon, B.M. Wile, S.K. Floyd, E. Lobkovsky, P.J. Chirik,
Organometallics 28 (2009) 3928.
[27] J. Yang, T.D. Tilley, Angew. Chem., Int. Ed. 49 (2010) 10186.
[28] V.V.K.M. Kandepi, J.M.S. Cardoso, E. Peris, B. Royo, Organometallics 29 (2010)
2777.
[55] V.N. Pandey, Inorg. Chim. Acta 22 (1977) L39.
[56] N.J. Coville, M.O. Albers, E. Singleton, J. Chem. Soc., Dalton Trans. (1983) 947.
[57] N.J. Coville, M.O. Albers, E. Singleton, J. Organomet. Chem. 232 (1982) 261.
[58] B.D. Dombek, R.J. Angelici, Inorg. Chim. Acta 7 (1973) 345.
[59] T.S. Janik, L.M. Krajkowski, M.R. Churchill, J. Chem. Crystallogr. 25 (1995) 751.