Microwave irradiation and flow chemistry for a straightforward synthesis of piano-stool iron complexes

Article abstract of DOI:10.1016/j.jorganchem.2014.09.031

Two series of piano-stool iron(II) complexes bearing bidentate phosphine or mixed phosphorus-nitrogen ligands have been prepared upon reaction with CpFe(CO)₂I or [CpFe(naphthalene)][PF₆] under microwave irradiation or using flow chem

Full text of DOI:10.1016/j.jorganchem.2014.09.031

Journal of Organometallic Chemistry 774 (2014) 35e42
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Microwave irradiation and flow chemistry for a straightforward
synthesis of piano-stool iron complexes
Anastassiya Pagnoux-Ozherelyeva a, David Bolien b, Sylvain Gaillard a, Flavie Peudru a,
,
, *
Jean-François Lohier a, Richard J. Whitby b **, Jean-Luc Renaud a
a
ꢀ
Normandie University, University of Caen Basse Normandie, Laboratoire de Chimie Moleculaire et Thioorganique, CNRS, UMR, 6507,
ꢀ
6 boulevard du Marechal Juin, 14050 Caen, France
b Chemistry, University of Southampton, Southampton SO17 1BJ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Two series of piano-stool iron(II) complexes bearing bidentate phosphine or mixed phosphoruseni-
trogen ligands have been prepared upon reaction with CpFe(CO)2I or [CpFe(naphthalene)][PF6] under
microwave irradiation or using flow chemistry.
Received 24 July 2014
Received in revised form
16 September 2014
Accepted 23 September 2014
Available online 12 October 2014
© 2014 Elsevier B.V. All rights reserved.
Keywords:
Iron
Microwave
Flow chemistry
Organometallic synthesis
Introduction
piano-stool iron complexes is rare [8]. Flow chemistry provides
convenient access to high temperatures and pressures together
Driven by economic and environmental considerations, the use
of iron in catalysis has witnessed tremendous activity in recent years
[1,2]. Cyclopentadienyl iron complexes play a pivotal role in organic
[3] and organometallic chemistry [4] and materials science [5]. Due
to the potential of these organo-iron derivatives, several methods
have been reported for their preparation. One of the most used
procedures is a two step reaction involving addition of a bidentate
ligand onto iron(II) chloride followed by halide-cyclopentadienyl
anion exchange, but suffers from formation of ferrocene as a by-
product. An alternative is a ligand exchange on [CpFe(CO)2X] but
this generally requires long heating times or UV irradiation.
with very fast heat-up and cool-down, and hence precise control of
heating times [9,10]. The first examples of application of flow
chemistry to organometallic synthesis have recently appeared [11]
though it has not yet been used for the synthesis of iron complexes.
We report here a new and rapid methodology involving either
microwave irradiation or flow chemistry for the preparation of
piano-stool iron complexes bearing monodentate, bidentate
diphosphine or bidentate mixed PeN ligands.
Results and discussion
Microwave irradiation in polar solvents allows rapid heating to
high temperatures enabling short reaction times, and often
improved yields. Since its introduction, there has been tremendous
growth in applications to organic chemistry [6] but its use in
organometallic synthesis (namely for the preparation of organo-
metallic species) is still in its infancy [7]. Its use in the synthesis of
Organometallic synthesis using microwaves technology
The iron precursors [CpFeX(CO)2] (X ¼ I (2) and Br (3)) were
prepared using classical method from iron dimer, [CpFe(CO2)]2 (1)
[12]. Initially the replacement of the halogen ligand in complex 2 by
triphenylphosphine was investigated using the procedure
described by Wilson and co-workers [8a]. After optimization of the
reaction conditions, the green iron complex 4 was obtained in 90%
isolated yield (Scheme 1) [13]. Even if an excess of triphenylphos-
phine was used only one equivalent coordinated to the metal center
to give 4 as the only product.
* Corresponding author. Tel.: þ33 (0)231452842; fax: þ33 (0)231452877.
** Corresponding author. Tel.: þ44 (023)80592777; fax: þ44 (023)80593781.
E-mail addresses: R.J.Whitby@soton.ac.uk (R.J. Whitby), jean-luc.renaud@
ensicaen.fr, jean-luc.renaud@unicaen.fr (J.-L. Renaud).
http://dx.doi.org/10.1016/j.jorganchem.2014.09.031
0022-328X/© 2014 Elsevier B.V. All rights reserved.

36
A. Pagnoux-Ozherelyeva et al. / Journal of Organometallic Chemistry 774 (2014) 35e42
+ I-
Table 1
Synthesis of cationic iron complexes under microwave irradiation starting from
PR3 (1 eq), THF,
150W, 130 C, 6 min
PPh3 (1 eq), THF,
150W, 130 C, 6 min
precursors 2 or 3.a
°
°
Fe
Fe
Fe
PPh3
CO
CO
CO
Yieldb
R3P
I
I
Entry
X
Ligand
Complex
CO
CO
5
6
R = NMe2, 43%
R = Bu, 16%
4
, 90%
1
2
3
4
5
6
7
I
Br
I
I
Br
I
dppe
dppe
dppm
dppp
dppp
dppb
dppf
[CpFe(dppe)(CO)][I] (7)
[CpFe(dppe)(CO)][Br] (8)
[CpFe(dppm)(CO)][I] (9)
[CpFe(dppp)(CO)][I] (10)
[CpFe(dppp)(CO)][Br] (11)
[CpFe(dppb)(CO)][I] (12)
[CpFe(dppf)(CO)][I] (13)
54
21
10
60
20
47
66
2
Scheme 1. Synthesis of CpFePPh3(CO)(I) 4 and [CpFe(CO)2PR3][I].
I
However, repeating the synthesis with PBu3 and P(NMe2)3 gave
a
the bis-carbonyl cationic species 5 and 6 (Scheme 1). The lower
yields were due to difficulty in isolating the pure products. The
formation of either neutral or cationic iron complexes by reaction of
various neutral ligands with CpFe(CO)2X has been reported to give
either the neutral or cationic products, or both [8a,12a,13]. Catalysis
of conversion of cationic to neutral complexes by [CpFe(CO)2]2 has
been demonstrated [13a,f]. In our case the retention of liberated CO
in the microwave pressure tube seems to favor the cationic com-
plexes when electron rich monodentate ligands are used.
We next investigated the coordination of bidentate ligands.
Using the same reaction conditions, diphenylphosphinoethane
(dppe) gave the cationic iron complex, [CpFe(dppe)(CO)][I] (7) in
54% isolated yield (Scheme 2, Table 1). To attempt improving the
yield several solvents were tried. All gave diphosphine/CO ligand
exchange as monitored by 31P NMR spectroscopy but in DMSO and
DMF, purification was problematic and pure complex 7 could not be
isolated. In polar and protic solvents, such as methanol, ethanol,
iso-propanol and butanol, the control of the reaction temperature
turned out to be difficult. Nevertheless, in iso-propanol, we were
able to isolate 21% of complex 7. In non-polar solvents such as
toluene, the reaction time had to be increased to 15 min to obtain
7 in 30% isolated yield. Based on these experiments we identified
THF as the best solvent. To demonstrate the benefit of microwave
irradiation, the same ligand exchange was also carried out under
thermal conditions. Complex 7 was isolated in 67% yield but
required a two-day reaction time (Scheme 2).
Reaction conditions: [CpFe(CO)2X] (0.16 mmol), ligand (0.16 mmol), degassed
THF (1 mL) under an argon atmosphere, microwave irradiation (150 W) at 130 ꢁC for
6 min.
b
Isolated yield.
As the CO ligand is not labile and can be problematic for cat-
alytic activity, we investigated the possibility to replace it with
acetonitrile. To avoid the coordination of iodide to the metal
centre during this ligand exchange, we replaced it with PFꢀ6 . For
example reaction of 7 with KPF6 gave 14 in 95% isolated yield. The
oxidative carbonyl ligand removal from 14 was conducted in the
presence of Me3NO in acetonitrile within 3 h at room temperature
[14]. With these reaction conditions, complex 15 was obtained in
90% yield (Scheme 3).
Although we have defined a straightforward procedure for the
synthesis of several cyclopentadienyl iron complexes, we thought
to extend this methodology to a more direct synthesis of cationic
acetonitrile ligated complexes such as 15. The cyclopentadienyl
arene iron complex [CpFe(napth)][PF6] 16, described by Kündig
et al. [15], is a pertinent piano-stool iron precursor, as the arene
ligand is known to be labile at high temperature. Treatment of
ferrocene with aluminum chloride, aluminum powder and TiCl4
in heptane at 90 ꢁC for 3 h and subsequent addition of KPF6
afforded the expected sandwich complex 16 in 91% isolated yield
(Scheme 4).
We next examined the reaction between complex 16 and dppe.
The expected complex 15 was obtained in 92% isolated yield after
microwave irradiation (40 W) for 3.5 min in a 2:1 mixture of THF/
CH3CN (Scheme 5). This two-step procedure from ferrocene is a
much more convenient and efficient methodology for the synthesis
of substituted piano-stool iron complex 15 (84% overall yield) than
the four-step route from dimer [CpFe(CO)2]2 (47% overall yield).
The scope and limitation of the arene displacement were
studied with various diphosphine ligands, triphenylphosphine and
the mixed PeN ligand, dimethylaminophosphine 19 (Fig. 2) [16]
and the results are presented in Table 2.
With optimized conditions in hand, the scope of the reaction
was investigated using a variety of diphosphine ligands. Results are
presented in Table 1.
In all cases the cationic complexes were formed. The length of
the tether had an important effect on the isolated yield. Dppe, dppp,
dppf, and to a lesser extent dppb, led to the corresponding iron
complexes in better yields (54e66%, Table 1 entries 1, 4, 6, 7) than
dppm, (10% yield, entry 3, Table 1). The nature of the halide in the
iron precursor has also an impact on the reactivity, iodide 2 leading
to 33e40% higher yields than the corresponding bromide 3 (Table 1,
entries 1 vs. 2 and 4 vs. 5).
Under the reaction conditions above, complexes 15, 17 and 18
were obtained in high yields and purity (87e92%, entries 2e4,
Table 2). For complexation of 19, dppm or ddpf replacement of THF
by toluene was needed to obtain pure products. Thus in a 2/1
mixture of toluene/acetonitrile, complexes 20, 21 and 22, bearing
ligand 19, dppm and dppf, respectively, were prepared in 70, 89 and
55% yield (Table 2, entries 5e7). Unfortunately, either in the pres-
ence of one or two equivalents of triphenylphosphine, no complex
[CpFe(PPh3)(CH3CN)2][PF6] nor [CpFe(PPh3)2(CH3CN)][PF6] were
obtained (Table 1, entry 1).
To unambiguously establish the atom connectivity in the com-
plexes, single crystals for X-ray diffraction (XRD) were grown by
slow evaporation of a solution of [CpFe(dppp)(CO)][Br] 11 in
dichloromethane. An ellipsoid representation of complex 11 is
presented in Fig. 1. The X-ray diffraction analysis confirmed the
presence of one CO ligand in complex 11, and its cationic nature as
the bromine atom is an outer sphere counter-anion.
In order to unambiguously confirm the structure of these
complexes, a single crystal of complex [CpFe(dppb)(CH3CN)][PF6]
18 was grown for XRD analysis. The crystal was obtained by slow
evaporation of a solution of 18 in dichloromethane. An ellipsoid
representation of complex 18 is presented in Fig. 3. The presence of
only one molecule of acetonitrile coordinated to the metal center
was confirmed, as well as the presence of the outer sphere counter-
anion PFꢀ6 .
Scheme 2. Synthesis of [CpFe(dppe)(CO)][I] 7.

A. Pagnoux-Ozherelyeva et al. / Journal of Organometallic Chemistry 774 (2014) 35e42
37
Fig. 1. Ellipsoid representation of complex [CpFe(dppp)(CO)][Br] 11. Selected bonds (Å) and angles (ꢁ): Fe1eC33 1.757(2), Fe1eP2 2.2050(10), Fe1eP1 2.2143(8), P2eFe1eP1
91.99(4).
Organometallic synthesis using flow chemistry technology
Because microwave-assisted chemistry is mainly driven by
temperature phenomenon [7feh], we hypothesized that flow
chemistry would be an interesting alternative. Indeed, such
technology provides much faster heat-up and cool-down times
Scheme 3. Synthesis of cationic iron complex 15.
than microwave heating, with precisely defined residence times
at high temperature, and consequently may diminish thermal
decomposition [9e11]. We could only find two examples of the
use of flow chemistry for organotransition metal complex syn-
thesis, and neither deals with iron chemistry [11]. Our initial
explorations in this field concentrated on the reaction of
[CpFe(CO)2I] and phosphines (Schemes 1 and 2 above), but they
were hampered by the rapid release of gas and extrusion of
Scheme 4. Synthesis of complex [CpFe(napth)][PF6] 16.
-
PF6
PPh2
Ph2P
Fe
N
CH3
NMe2
NMe2
19
20
Fig. 2. Hemilabile bidentate monophosphine 19 and the corresponding iron complex
20.
Scheme 5. Synthesis of complex [CpFe(dppe)(CH3CN)][PF6] 15 from precursor 16.

38
A. Pagnoux-Ozherelyeva et al. / Journal of Organometallic Chemistry 774 (2014) 35e42
Table 2
The second route proved to be more robust and reliable. The
microwave procedure (Scheme 5) was transferred into a flow
process with minor adjustments. Introduction of in-line filtration
through alumina was needed to avoid blocking of the backpressure
regulator (Fig. 4).
Synthesis of cationic iron complexes under microwave irradiation.a
Entry
Ligand
Complex
Yield (%)b
1
2
3
4
PPh3
dppe
dppp
dppb
19
e
e
[CpFe(dppe)(CH3CN)][PF6] (15)
[CpFe(dppp)(CH3CN)][PF6] (17)
[CpFe(dppb)(CH3CN)][PF6] (18)
[CpFe(17)(CH3CN)][PF6] (20)
[CpFe(dppm)(CH3CN)][PF6] (21)
[CpFe(dppf)(CH3CN)][PF6] (22)
92
87
90
70
89
55
When scaling the synthesis from 50 mg (2 mL) to 150 mg (6 mL),
higher yields were obtained especially when a more concentrated
solution was used (150 mg in 2 mL), although precipitation in the
reactor became a problem. Under the lower concentration condi-
tions this corresponds to conversion of 2.5 mmol/h and of
12.5 mmol/h under the higher temperature conditions (160 ꢁC,
4 min). The reaction with dppf ligand required dichloromethane in
the solvent to prevent precipitation in the flow apparatus, and a
slightly higher temperature. The results are summarized in Table 3.
The flow chemistry method starting from cationic naphthalene
cyclopentadienyl iron complex allowed the synthesis of several
piano stool iron complexes with various bidentate phosphine
ligands and provides a useful alternative to the microwave proce-
dure with the potential for continuous production.
5c
6c
7c
dppm
dppf
a
Reaction conditions: [CpFe(napth)][PF6] (0.16 mmol), ligand (0.16 mmol),
degassed solution of THF/CH3CN (2/1) under an argon atmosphere, microwave
irradiation (40 W) at 130 ꢁC for 3.5 min.
b
Isolated yield.
c
Reaction performed in a 2/1 mixture of toluene/CH3CN.
reaction mixture during the thermal process, which occurred
beyond 90 ꢁC. With these experimental limitations, we decided
to focus on the displacement of the labile aromatic ligand from
16 (Scheme 5).
Fig. 3. Ellipsoid representation of complex [CpFe(dppb)(CH3CN)][PF6] 18. Selected bonds (Å) and angles (ꢁ): Fe1eN1 1.9167(18), Fe1eP2 2.2284(5), Fe1eP3 2.2353(6), P2eFe1eP3
98.11(2).

A. Pagnoux-Ozherelyeva et al. / Journal of Organometallic Chemistry 774 (2014) 35e42
39
Fig. 4. Modified flow setup with in-series filtration.
Table 3
diffractometer. Mo K
a
radiation at
l
¼ 0.71073 Å with a graphite
Synthesis of piano-stool iron complexes from 16 using flow-chemistry.
monochromator was used. Cell refinement and data reduction were
performed with SAINT (Bruker AXS). The structure was solved by
direct methods and refined using SHELXL-97 (Sheldrick). All non-H
atoms were refined by full-matrix least-squares with anisotropic
displacement parameters while hydrogen atoms were placed in
idealized positions.
Ligand Product Scale/isolated yield
50 mg, 160 ꢁC, 2 mL, 4 min 150 mg, 140 ꢁC, in 6 mL, 20 min
dppe 15
dppp 18
dppm 19
80%
57%
63%
17%b
72% (83%)a
77% (89%)a
55%
dppf
22
53%c
a
Synthesis of iron complexes 4e13
Values in brackets in 2 mL solvent.
CH2Cl2:THF:CH3CN ¼ 8:1:1, 140 ꢁC.
THF:CH3CN:CH2Cl2 ¼ 2:1:0.1, 160 ꢁC.
b
c
In a 10 mL dry microwave reactor were introduced [CpFe(CO)2I]
(49 mg, 0.16 mmol) and the ligand (0.16 mmol, 1 eq.) in degassed
THF (1 mL) under argon atmosphere. The homogeneous solution
was placed in a microwave reactor with a power fixed at 150 W, for
6 min at 130 ꢁC. The dark green solution was filtered through a pad
of deactivated alumina (3% H2O). Then, the cake was washed with
EtOH. The complex was recovered in the EtOH and transferred in a
Schlenk tube under argon atmosphere. The solvent was removed
under vacuum and the crude product was washed with dry and
degassed Et2O (3 ꢂ 10 mL). The supernatant liquid was removed
with Pasteur pipette and the resulting solid was dried under
vacuum.
Conclusions
We reported a straightforward synthesis of various cyclo-
pentadienyl iron complexes using either microwave or flow tech-
nologies. Since their introduction, there has been a tremendous
growth in applications to organic chemistry but their use in
organometallic synthesis (namely for the preparation of organo-
metallic species) are still rare, and flow technology had no prece-
dence in the literature for the synthesis of iron complexes.
Experimental
CpFe(PPh3)(CO)(I) 4
Following the general procedure above using PPh3 (42 mg,
0.16 mmol), complex 4 was obtained as green crystals (78 mg,
General considerations
90%). 1H NMR (400 MHz, CDCl3):
d
7.65e7.49 (m, 6H, HAr),
Reactions were carried out in Schlenk tube freshly with distilled
solvents under an atmosphere of dry Argon. All solvents were
degassed prior to use by freezeepumpethaw procedure (4 times).
Microwave synthesis was carried out using microwave reactor
(10 mL) with teflon lid under an atmosphere of dry Argon. The
reactions were realized using single-mode automatic microwave
synthesizers Synthesis System Explorer from CEM Corporation.
Organometallic commercial compounds and phosphine ligands
were used without purification. The starting materials [CpFe(CO)2I]
and [CpFe(CO)2Br] were prepared according to published methods
[12]. All other reagents were commercially available and were used
without further purification. NMR spectra were recorded on an ARX
Bruker 400 MHz spectrometer using solvent residual peak as
reference. HRMS analyses were performed on Q-TOF Micro
WATERS by electrospray ionization (ESI) by LCMT analytical ser-
vices. Infrared (IR) spectra were recorded with a Perkin Elmer 16 PC
FT-IR spectrometer. Crystallographic data sets were collected from
7.47e7.32 (m, 9H, HAr), 4.48 (s, 5H, HCp) ppm. 31P{1H} NMR
(162 MHz, CDCl3):
67.4 (s) ppm. 13C{1H} NMR (101 MHz, CDCl3):
d
d
220.8 (s, C, CCO), 135.9 (d, 3C, CqAr, J1
¼ 43.4 Hz), 133.8 (d,
(CeP)
6H, CHAr, J2
¼ 9.5 Hz), 130.3 (d, 3C, CHAr, J4
¼ 2.4 Hz),
(CeP)
(CeP)
128.4 (d, 6H, CHAr, J3
(neat):
¼ 9.8 Hz), 83.0 (s, 5H, CHCp) ppm. IR
(CeP)
n
1940 (large CO stretch) cmꢀ1. HRMS (m/z) ESIþ [M ꢀ Iꢀ]þ
calculated for C24H20FeOP 411.0601; found: [M]þ 411.0410 (7%).
HRMS (m/z) ESIþ [M ꢀ CO ꢀ Iꢀ]þ calculated for C23H20FeP:
383.0652; found: [M]þ 383.0460 (100%). Data consistent with
that previously reported [13e].
[CpFe(P(NMe2)3) (CO)2][I] 5
Following the general procedure for the synthesis of cationic
iron complex using P(NMe2)3 (26 mg, 0.16 mmol), complex 5 was
obtained as gray powder (78 mg, 43%). 1H NMR (400 MHz, CDCl3):
d
5.61 (s, 5H, HCp), 2.75 (s, 9H, HMe), 2.72 ppm (s, 9H, HMe) ppm. 31
P
single crystal samples using
a
Bruker Kappa APEXII CCD
{1H} NMR (162 MHz, CDCl3): d
140.6 (s) ppm. 13C{1H} NMR

40
A. Pagnoux-Ozherelyeva et al. / Journal of Organometallic Chemistry 774 (2014) 35e42
(126 MHz, CDCl3) (decoupled from phosphorus):
87.4 (5C, CHCp), 38.8 (6C, CH3) ppm. IR (neat):
stretch) cmꢀ1
HRMS (m/z) ESIþ [M
13H23FeN3O2P 340.0877; found 340.0863.
d
211.0 (2C, CCO),
2032, 1983 (CO
J3
¼ 7.0 Hz), 7.35e7.26 (m, 4H, HAr), 4.97 (s, 5H, HCp), 2.43e2.29
(HeH)
n
(m, 1H, CH2), 3.02e2.85 (m, 2H, CH2), 2.11 (t, 2H, CH2,
.
ꢀ
Iꢀ]þ calculated for
J3
¼ 13.8 Hz), 1.57e1.41 (m, 1H, CH2) ppm. 31P{1H} NMR
(HeH)
C
(162 MHz, CDCl3):
d6):
Cq, J1
d
52.0 (s) ppm. 13C{1H} NMR (126 MHz, DMSO-
d
215.8 (s, 1C, CCO), 137.1 (t, 2C, Cq, J1
¼ 26.1 Hz),133.2 (t, 2C,
(CeP)
[CpFe(P(n-Bu)3)(CO)2][I] 6
¼ 21.0 Hz), 132.7 (t, 4C,CHAr, J2
¼ 4.7 Hz), 131.4e131.1
(CeP)
(CeP)
Following the general procedure for the synthesis of cationic
iron complex using P(n-Bu)3 (32 mg, 0.16 mmol), complex 6 was
obtained as green powder (11 mg, 13%). 1H NMR (400 MHz, MeOD):
(m, 4C, CAr), 131.2 (s, 2C, CHAr), 130.8 (s, 2C, CHAr), 129.1 (t, 4C, CHAr
,
J3
¼ 4.9 Hz), 128.8 (t, 4C, CHAr, J3
¼ 4.7 Hz), 86.0 (s, 5C,
(CeP)
(CeP)
CHCp), 28.5 (t, 2C, CH2, J1
¼ 17.1 Hz), 19.9 (s, 1C, CH2) ppm. 13
C
(CeP)
d
5.52 (d, 5H, HCp, J ¼ 1.4 Hz), 2.04 (dd, 6H, CH2, J2
¼ 16.2 Hz,
{1H} NMR (126 MHz, DMSO-d6) (decoupled from phosphorus):
(HeP)
J3
¼ 9.9 Hz), 1.64e1.43 (m, 12H, CH2), 1.01 (t, 9H, CH3,
d
215.8 (1C, CCO), 137.1 (2C, Cq), 133.2 (2C, Cq), 132.7 (4C, CHAr), 131.2
J3(HeH) ¼ 7.0 Hz) ppm. 31P{1H} NMR (162 MHz, MeOD):
d
53.9 (s)
(4C, CAr), 131.2 (2C, CHAr), 130.8 (2C, CHAr), 129.1 (4C, CHAr), 128.8
(4C, CHAr), 86.0 (5C, CHCp), 28.5 (2C, CH2), 19.9 (1C, CH2) ppm. IR
(HeH)
ppm. 13C{1H} NMR (126 MHz, CDCl3) (decoupled from phos-
phorus):
CH2), 24.0 (3C, CH2), 13.9 (3C, CH3) ppm. IR (neat):
stretch) cmꢀ1 Iꢀ]þ calculated for
HRMS (m/z) ESIþ [M
19H32FeO2P: 379.1489; found: 379.1506.
d
210.4 (2C, CCO), 87.6 (5C, CHCp), 29.2 (3C, CH2), 26.2 (3C,
2041, 1996 (CO
(neat): n
1959 (CO stretch) cmꢀ1. Data consistent with those pre-
n
viously reported [13g].
.
ꢀ
C
[CpFe(dppp)(CO)][Br] 11
Following the general procedure for the synthesis of cationic
iron complex using [CpFe(CO)2Br] (41 mg, 0.16 mmol) and dppp
(66 mg, 0.16 mmol), complex 9 was obtained as a brown powder
[CpFe(dppe)(CO)][I] 7
Following the general procedure for the synthesis of cationic
iron complex using dppe (64 mg, 0.16 mmol), complex 7 was ob-
tained as yellow powder (58 mg, 54%). 1H NMR (400 MHz, DMSO-
(21 mg, 20%). 1H NMR (400 MHz, CDCl3):
d ,
7.55 (t, 2H, HAr
J3
¼ 7.5 Hz), 7.51e7.47 (m, 6H, HAr), 7.47e7.34 (m, 8H, HAr),
(HeH)
d6):
4H, HAr), 5.06 (s, 5H, HCp), 2.99e2.86 (m, 2H, CH2), 2.82e2.67 (m,
2H, CH2) ppm. 31P{1H} NMR (162 MHz, DMSO-d6):
92.9 (s) ppm.
d
7.85e7.77 (m, 4H, HAr), 7.64e7.49 (m, 12H, HAr), 7.36e7.27 (m,
7.31e7.24 (m, 4H, HAr), 4.81 (t, 5H, J3
¼ 1.3 Hz), 3.01e2.80 (m,
(HeH)
2H, CH2), 2.69e2.53 (m, 1H, CH2) 2.25e2.08 (m, 2H, CH2), 1.81e1.64
d
(m, 1H). 31P{1H} NMR (162 MHz, CDCl3):
d
52.0 (s) ppm. Data
13C{1H} NMR (126 MHz, DMSO-d6) (5 Cq are not observed): 132.6
consistent with those previously reported [13g].
(t, 4C, CHAr, J2
¼ 4.8 Hz), 131.5 (s, 2C, CHAr), 131.1 (t, 4C, CHAr
,
,
(CeP)
J2
¼
4.8 Hz), 131.0 (s, 2C, CHAr), 129.3 (t, 4C, CHAr
[CpFe(dppb)(CO)][I] 12
J3(CeP) ¼ 4.8 Hz), 129.1 (t, 4C, CHAr, J3
¼ 5.1 Hz), 85.0 (s, 5C,
Following the general procedure for the synthesis of cationic
iron complex using dppb (68 mg, 0.16 mmol), complex 12 was
obtained as yellow powder (53 mg, 47%). 1H NMR (400 MHz,
(CeP)
(CeP)
CHCp), 28.5 (t, 2C, CH2, J1
¼ 21.7 Hz) ppm. 13C{1H} NMR
(CeP)
(126 MHz, DMSO-d6) (decoupled from phosphorus):
d 214.2 (1C,
CCO) 135.3 (2C, Cq), 132.8 (2C, Cq), 132.6 (4C, CHAr), 131.5 (2C, CHAr),
DMSO-d6):
(m, 2H, CH2), 2.51e2.31 (m, 2H, CH2), 1.75e1.44 (m, 4H, CH2). 31P
{1H} NMR (162 MHz, DMSO-d6):
59.6 (s) ppm. 13C{1H} NMR
d
7.80e7.32 (m, 20H, HAr), 4.62 (s, 5H, HCp), 3.04e2.84
131.1 (4C, CHAr), 131.0 (2C, CHAr), 129.3 (4C, CHAr), 129.1 (4C, CHAr),
85.0 (5C, CHCp), 28.5 (2C, CH2) ppm. IR (neat):
n
1984 (CO stretch)
d
cmꢀ1. Data consistent with those previously reported [13g].
(126 MHz, CDCl3) (decoupled from phosphorus): d
217.9 (1C, CCO),
136.1 (2C, Cq),133.5 (2C, Cq),132.3 (2C, CHAr), 132.2 (4C, CHAr),131.6
(4C, CHAr), 131.4 (2C, CHAr), 130.0 (4C, CHAr), 129.7 (4C, CHAr), 86.9
[CpFe(dppm)(CO)][I] 8
Following the general procedure for the synthesis of cationic
iron complex using dppm (61 mg, 0.16 mmol), complex 8 was ob-
tained as yellow powder (10 mg, 10%). 1H NMR (400 MHz, DMSO-
(5C, CHCp), 32.3 (2C, CH2), 23.9 (2C, CH2) ppm. IR (neat):
n 1954 (CO
stretch) cmꢀ1. Data consistent with those previously reported [13g].
d6):
1H, CH2), 5.21 (s, 5H, HCp), 4.56e4.45 (m, 1H, CH2). 31P{1H} NMR
(162 MHz, DMSO-d6):
27.2 (s). 13C{1H} NMR (126 MHz, DMSO-d6)
(decoupled from phosphorus):
216.7 (1C, CCO), 133.2 (2C, Cq),
d
7.80e7.69 (m, 4H, HAr), 7.61e7.41 (m, 16H, HAr), 5.41e5.28 (m,
[CpFe(dppf)(CO)][I] 13
Following the general procedure for the synthesis of cationic
iron complex using dppf (89 mg, 0.16 mmol), complex 13 was ob-
tained as yellow powder (87 mg, 66%). 1H NMR (400 MHz, CD3CN):
d
d
132.6 (2C, Cq), 131.6 (4C, CHAr), 131.6 (2C, CHAr), 131.3 (2C, CHAr),
131.2 (4C, CHAr), 129.3 (4C, CHAr), 129.0 (4C, CHAr), 83.1 (5C, CCp),
d
7.71 (t, 2H, HAr, J3
¼ 7.4 Hz), 7.58e7.45 (m, 18H, HAr), 4.90 (s,
(HeH)
2H, HCp), 4.58 (s, 2H, HCp), 4.56e50 (m, 7H, HCp), 4.31 (s, 2H, HCp
)
41.89 (1C, CH2) ppm. IR (neat):
n
1967 (CO stretch) cmꢀ1. HRMS
ppm. 31P{1H} NMR (162 MHz, CD3CN):
d
68.9 (s) ppm. 13C{1H} NMR
(m/z) ESIþ [M]þ calculated for C31H27FeOP2: 533.0887; found:
(126 MHz, DMSO-d6) (decoupled from phosphorus): d 218.8 (1C,
533.0869. Data consistent with those previously reported [13g].
CCO), 138.4 (2C, Cq), 133.9 (4C, CHAr), 132.7 (2C, Cq), 131.7 (4C, CHAr),
131.6 (2C, CHAr), 130.5 (2C, CHAr), 128.7 (4C, CHAr), 128.6 (4C, CHAr),
89.0 (2C, CqCp), 86.6 (5C, CHCp), 84.5 (4C, CHCp), 74.4 (1C, CHCp), 73.4
[CpFe(dppe)(CO)][Br] 9
Following the general procedure for the synthesis of cationic
iron complex using [CpFe(CO)2Br] (41 mg, 0.16 mmol) and dppe
(64 mg, 0.16 mmol), complex 9 was obtained as a brown powder
(1C, CHCp), 73.3 (1C, CHCp), 70.4 (1C, CHCp) ppm. IR (neat):
n 1956
(CO stretch) cmꢀ1. HRMS (m/z) ESIþ calculated for C40H33Fe2OP2:
703.0705; found 703.0738.
(21 mg, 21%). 1H NMR (400 MHz, CDCl3):
d
7.72e7.66 (m, 4H, HAr),
7.59e7.54 (m, 4H, HAr), 7.54e7.50 (m, 4H, HAr), 7.36e7.29 (m, 8H,
Synthesis of cationic iron complexes 15, 17e18 and 20e22
HAr), 4.86 (s, 5H, HCp), 3.15e3.08 (m, 2H, CH2), 2.84e2.78 (m, 2H,
CH2) ppm. 31P{1H} NMR (162 MHz, DMSO-d6):
d
92.3 (s). Data
(Method A) In a 10 mL dry microwave reactor, [CpFe(naph-
thalene)][PF6] (63 mg, 0.16 mmol) and the ligand (0.16 mmol) were
introduced in a 2:1 mixture of degassed THF/CH3CN (1.5 mL) under
an argon atmosphere. The homogeneous solution was placed in a
microwave reactor (40 W) at 130 ꢁC for 3.5 min. The crude red
solution was filtered through a pad of deactivated alumina (3% H2O)
with dry and degassed CH3CN. This solution was transferred in a
Schlenk tube under argon atmosphere. The solvent was removed
consistent with those previously reported [13g].
[CpFe(dppp)(CO)][I] 10
Following the general procedure for the synthesis of cationic
iron complex using dppp (66 mg, 0.16 mmol), complex 10 was
obtained as a green powder (67 mg, 60%). 1H NMR (400 MHz,
DMSO-d6):
d ,
7.61e7.46 (m, 12H, HAr), 7.38 (t, 4H, HAr

A. Pagnoux-Ozherelyeva et al. / Journal of Organometallic Chemistry 774 (2014) 35e42
41
under vacuum and the crude product was dissolved in 1 mL of dry
CHA3cN) ppm. 31P{1H} NMR (162 MHz, CD3CN):
d
73.5 (s), ꢀ144.6
and degassed CH3CN. The naphthalene was eliminated by hot
extraction with pentane (60 ꢁC). The complex was precipitated with
Et2O (3 ꢂ 10 mL) and dried under vacuum.
(sept. J1
¼ 706.2) ppm. 13C{1H} NMR (126 MHz, CD3CN): (2C of
(PeF)
CH3CN, 4C of Cq and 4C of CAr are not observed): 135.0 (d, 2C, CHAr
d ,
J2
¼ 9.9 Hz), 133.4 (d, 2C, CHAr, J2
¼ 9.7 Hz), 132.0 (s, 1C,
(CeP)
(CeP)
(Method B) a 2:1 toluene/CH3CN (1.5 mL) was used.
CHAr), 131.5 (s, 1C, CHAr), 130.2 (d, 2C, CHAr, J3
¼ 8.6 Hz), 129.9
(CeP)
(d, 2C, CHAr, J3
¼ 10.3 Hz), 75.2 (s, 5C, CHCp), 63.0 (s, 1C, CH3),
(CeP)
[CpFe(dppe)(CH3CN)][PF6] 15
Following the general procedure (method A) using dppe (64 mg,
0.16 mmol), complex 15 was obtained as a red powder (103 mg, 92%).
55.8 (s, 1C, CH3) ppm. The complex is air sensitive and need to be
handled and stored under argon atmosphere.
1H NMR (CD3CN, 400 MHz):
d
7.87e7.79 (m, 4H, HAr), 7.58e7.52 (m,
[CpFe(dppm)(CH3CN)][PF6] 21
6H, HAr), 7.52e7.44 (m, 6H, HAr), 7.41e7.31 (m, 4H, HAr), 4.35 (t, 5H,
HCp, J ¼ 1.4 Hz), 2.59e2.49 (m, 2H, CH2), 2.43e2.34 (m, 2H, CH2),1.96
Following the general procedure (method B) using dppm
(61 mg, 0.16 mmol), complex 21 was obtained as a pink powder
(s, 3H, CH3) ppm. 31P{1H} NMR (CD3CN,162 MHz):
d
97.2 (s), ꢀ144.6
(61 mg, 55%). 1H NMR (400 MHz, CD3CN): 7.73e7.66 (m, 4H, HAr),
d
(sept, J1
¼ 706.2 Hz) ppm.13C{1H} NMR (CD3CN,100 MHz) (2C of
7.54e7.39 (m, 16H, HAr), 4.97e4.87 (m, 1H, CH2), 4.49 (s, 5H, HCp),
3.93e3.83 (m, 1H, CH2) ppm. 31P{1H} NMR (162 MHz, CD3CN):
(PeF)
CH3CN were not observed):
d
137.9 (t, 2C, Cq, J1
¼ 20.5 Hz),133.7
(t, 4C, CHAr, J2
4C, CHAr, J2
¼ 4.7 Hz), 133.1 (t, 2C, Cq, J1(CeP) ¼ 20.3), 132.5 (t,
d
36.0 (s), ꢀ144.6 (sept, J1
¼ 706.2 Hz) ppm. 13C{1H} NMR
(CeP)
(CeP)
(PeF)
¼ 4.8 Hz), 131.5 (s, 2C, CHAr) 131.3 (s, 2C,CHAr) 129.9
(101 MHz, CD3CN) (2C of CH3CN, 4Cq and 1C CH2 are not observed):
(CeP)
(t, 4C, CHAr, J3
¼ 4.8 Hz), 129.8 (t, 4C, CHAr, J3
¼ 4.8 Hz), 79.7
d
J2
133.1 (t, 4C, CHAr
,
J2
(CeP)
¼
5.7 Hz), 132.4 (t, 4C, CHAr
,
(CeP)
(CeP)
(s, 5C, CHCp) 28.4 (t, 2C, CH2, J1
¼ 21.3 Hz) ppm. IR (neat):
n
3059
¼ 5.0 Hz), 131.7 (s, 2C, CHAr), 131.6 (s, 2C, CHAr),130.0 (t, 4C,
(CeP)
(CeP)
(CeH Ar), 2268 (CN) cmꢀ1. HRMS (m/z) ESIþ [Mꢀ PFꢀ6 ]þ calculated
for C33H32FeNP2: 560.1359; found: 560.1346. HRMS (m/z) ESꢀ [M]þ
calculated for PF6, 144.9642; found 145.0724.
CHAr, J3
¼ 5.0 Hz), 129.8 (t, 4C, CHAr, J3
¼ 5.0 Hz), 77.9 (s, 5C,
(CeP)
(CeP)
CHCp) ppm. IR (neat): 3054 (CeH Ar), 2270 (CN) cmꢀ1. HRMS (m/z)
n
ESIþ [M]þ calculated for C32H30FeNP2: 546.1203; found: 546.1167
(32%). HRMS (m/z) ESIþ [M ꢀ CH3CN]þ calculated for C32H30FeNP2:
505.0937; found: 505.0846 (100%).
[CpFe(dppp)(CH3CN)][PF6] 17
Following the general procedure (method A) using dppp (66 mg,
0.16 mmol), complex 17 was obtained as a red powder (100 mg,
[CpFe(dppf)(CH3CN)][PF6] 22
87%). 1H NMR (CD3CN, 400 MHz):
d
7.68e7.61 (m, 4H, HAr),
Following the general procedure (Method B) using [CpFe(napht.)]
[PF6] (63 mg, 0.16 mmol) and dppf (89 mg, 0.16 mmol), complex 22
was obtained as a red powder (123 mg, 89%). 1H NMR (400 MHz,
7.55e7.47 (m, 8H, HAr), 7.34e7.28 (m, 4H, HAr), 7.28e7.22 (m, 4H,
HAr), 4.21 (s, 5H, HCp), 2.63e2.51 (m, 3H, CH2), 2.09 (s, 3H, CH3),
1.85e1.72 (m, 3H, CH2) ppm. 31P{1H} NMR (CD3CN, 162 MHz):
CD3CN): d
7.70e7.64 (m, 4H, HAr), 7.64e7.58 (m, 2H, HAr), 7.58e7.46
d
55.9 (s), ꢀ144.6 (sept, J1
¼ 706.2 Hz) ppm. 13C{1H} NMR
(m, 14H, HAr), 4.44 (s, 2H, HCp), 4.34 (s, 2H, HCp), 4.24e4.23 (m, 4H,
HCp), 3.93 (t, 5H, HCp, J ¼ 1.6 Hz),1.96 (s, 3H, CH3) ppm. 31P{1H} NMR
(PeF)
(CD3CN, 100 MHz) (2C of CH3CN were not observed): d 139.6 (t, 2C,
Cq, J1
¼ 20.6 Hz), 136.8 (t, 2C, Cq, J1
¼ 21.3 Hz), 133.9 (t, 4C,
(CD3CN, 162 MHz):
d
63.0 (s), ꢀ144.6 (sept, J1
¼ 706.2 Hz) ppm.
(CeP)
(CeP)
(PeF)
CHAr, J2
¼ 4.8 Hz), 132.6 (t, 4C, CHAr, J2
¼ 4.6 Hz), 131.4 (s,
13C{1H} NMR (CD3CN, 126 MHz) (2C of CH3CN are not observed):
(CeP)
(CeP)
2C, CHAr), 131.0 (s, 2C, CHAr), 129.7 (t, 4C, CHAr, J3
¼ 4.6 Hz),
139.7 (t, 2C, Cq, J1
¼ 19.7 Hz), 136.9 (t, 2C, Cq, J1
¼ 21.7 Hz),
(CeP)
(CeP)
(CeP)
129.4 (t, 4C, CHAr, J3
¼ 4.7 Hz), 80.7 (s, 5C, CHCp), 27.2 (t, 2C, CH2,
135.1 (t, 4C, CHAr, J2
¼ 5.1 Hz), 133.9 (t, 4C, CHAr, J2
¼ 4.8 Hz),
(CeP)
(CeP)
(CeP)
J1
¼ 13.3 Hz), 20.9 (s, 1C, CH2) ppm. IR (neat):
n
3058 (CeH Ar),
131.5 (s, 2C, CHAr), 130.8 (s, 2C, CHAr), 129.2 (t, 4C, CHAr,
(CeP)
2258 (CN) cmꢀ1. HRMS (m/z) ESIþ [M]þ calculated for C34H34FeNP2:
J3
¼ 4.5 Hz), 129.1 (t, 4C, CHAr, J3
¼ 4.7 Hz), 86.1 (t, 2C, Cq,
(CeP)
574.1516; found: 574.1513.
J1(CeP) ¼ 20.5 Hz), 80.7 (s, 5C, CHCp), 74.9 (s, 2C, CHCp), 74.8 (s, 2C,
(CeP)
CHCp), 73.3 (s, 2C, CHAr), 70.7 (s, 2C, CHAr) ppm. IR (neat):
n 3059
[CpFe(dppb)(CH3CN)][PF6] 18
(CeH Ar), 2260 (CN) cmꢀ1. HRMS (m/z) ESIþ [M ꢀ CH3CN]þ calcu-
Following the general procedure (method A) using [CpFe(-
napht.)][PF6] (63 mg, 0.16 mmol) and dppb (68 mg, 0.16 mmol),
complex 18 was obtained as a red powder (106 mg, 90%). 1H NMR
(CD3CN, 400 MHz): 7.63e7.50 (m, 16H, HAr), 7.44e7.32 (m, 4H, HAr),
3.93 (t, 5H, HCp, J ¼ 1.4 Hz), 2.68e2.60 (m, 2H, CH2), 2.25e2.20 (m,
2H, CH2), 1.96 (s, 3H, CH3), 1.59e1.50 (m, 2H, CH2), 1.41e1.31 (m, 2H,
lated for C39H33Fe2P2: 675.0756; found: 675.2050.
Representative procedure for flow chemistry
A solution of [CpFe(naphthalene)][PF6] (0.148 g, 0.375 mmol) and
1,2-bis(diphenylphosphino)ethane (0.164 g, 0.413 mmol) was pre-
pared in THF/CH3CN 2:1 (6 mL) and transferred to Vapourtec R2/R4
platform, which was set up for sample loop reactions (10 mL sample
loop). The sample loop was directly connected to a heated stainless
steel reactor (1 mm i.d.,10 mL capacity), followed by alumina column
(omnifit, x ¼ 6 mm, 5 cm, grade II, neutral alumina) and backpressure
regulator. The reactor was set to the indicated temperature and flow
rate. The collected sample was concentrated under reduced pressure,
re-dissolved in CH3CN (10 mL) and naphthalene was removed by hot
hexane extraction (5 ꢂ 10 mL, 60 ꢁC). The CH3CN layer was then
concentrated in vacuo, dry loaded on a column (neutral alumina,
grade II, 80 g) and the column flushed with ether (3 column vol-
umes). The title complex was then flushed off the column with
CH3CN and solvent removed in vacuo. The resulting red gum crys-
tallized after prolonged exposure to high vacuum. Characterisations
were carried out as described above.
CH2) ppm. 31P{1H} NMR (CD3CN, 162 MHz):
d
62.0 (s), ꢀ144.7 (sept,
J1
¼ 706.2 Hz) ppm. 13C{1H} NMR (CD3CN, 100 MHz) (2C of
(PeF)
CH3CN are not observed):
d
138.7 (t, 2C, Cq, J1
¼ 20.2 Hz), 136.7
(CeP)
(t, 2C, Cq, J1
¼ 19.9 Hz), 133.3 (t, 4C, CHAr, J2
¼ 4.5 Hz), 132.8
(CeP)
(CeP)
(t, 4C, CHAr, J2
¼ 4.3 Hz), 131.5 (s, 2C, CHAr), 130.8 (s, 2C, CHAr),
(CeP)
129.8 (t, 4C, CHAr
,
J3
¼
4.5 Hz), 129.6 (t, 4C, CHAr,
(CeP)
J3
¼ 4.5 Hz), 80.6 (s, 5C, CHCp), 30.1 (t, 2C, CH2, J1
¼ 11.0 Hz),
(CeP)
(CeP)
24.5 (s, 2C, CH2) ppm. IR (neat):
n .
3058 (CeH Ar), 2265 (CN) cmꢀ1
HRMS (m/z) ESIþ [M ꢀ CH3CN]þ calculated for C33H33FeP2:
547.1407; found: 547.1385.
[CpFe(19)(CH3CN)][PF6] 20
Following the general procedure (Method B) using [CpFe(-
napht.)][PF6] (79 mg, 0.20 mmol) and ligand 19 (61 mg, 0.20 mmol),
complex 20 was obtained as a violet powder (85 mg, 70%). 1H NMR
(400 MHz, CD3CN):
d
7.82e7.71 (m, 2H, HAr), 7.69e7.63 (m, 2H, HAr),
Remark: The flow chemistry was carried out with a backpressure
regulator (250 psi) to ensure that boiling did not occur. The system is
capable of up to 500psi pressure - limited by the pumps.
7.61e7.50 (m, 7H, HAr), 7.46e7.40 (m, 2H, HAr), 7.30e7.21 (m, 1H,
HAr), 4.27 (s, 5H, HCp), 3.57 (s, 3H, CH3), 2.90 (s, 3H, CH3), 1.96 (s, 3H,

42
A. Pagnoux-Ozherelyeva et al. / Journal of Organometallic Chemistry 774 (2014) 35e42
(c) A. Loupy (Ed.), Microwave in Organic Synthesis, second ed., Wiley-VCH,
Acknowledgements
Weinheim, Germany, 2006. For recent representative reviews on Microwave-
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(f) C.O. Kappe, Acc. Chem. Res. 46 (2013) 1579;
This work has been performed within the «CRUNCH» interre-
gional network. We gratefully acknowledge financial support from
the “Ministere de la Recherche et des Nouvelles Technologies” (PhD
grant for A.O.), CNRS (Centre National de la Recherche Scientifique),
the “Region Basse-Normandie”, the European Union (FEDER fund-
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(2009) 1003;
CCDC 856653 and 855917 contain the supplementary crystal-
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charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
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Appendix B. Supplementary data
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