Preparation and Characterization of the Triflate Complex [Cp*(dppe)FeOSO2CF3]: A Convenient Access to Labile Five- and Six-Coordinate Iron(I) and Iron(II) Complexes

Article abstract of DOI:10.1002/ejic.201901086

Treatment of the iron hydride [Cp*(dppe)FeH] (1) with methyl triflate (CH₃OSO₂CF₃) yielded the iron triflate adduct [Cp*(dppe)FeOSO₂CF₃] (4, 85 %). In the solid state, the triflate is coordinated at t

Full text of DOI:10.1002/ejic.201901086

A Journal of
Accepted Article
Title: Preparation and characterization of the triflate complex
[Cp*(dppe)Fe-OSO2CF3]: a convenient access to labile five- and
six-coordinate Fe(I) and Fe(II) complexes
Authors: Paul Hamon, Loic Toupet, Thierry Roisnel, Jean-René
Hamon, and Claude Lapinte
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201901086
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
FULL PAPER
Preparation and characterization of the triflate complex
[Cp*(dppe)FeOSO2CF3]: a convenient access to labile five- and
six-coordinate Fe(I) and Fe(II) complexes
Paul Hamon,[a] Loic Toupet,[b] Thierry Roisnel,[a] Jean-René Hamon,*[a] and Claude Lapinte,*[a]
This article is dedicated to our friend and colleague Dr. Jean-François Halet on the occasion of his 60th birthday, and recognizes his
scientific achievements in the field of molecular and solid-state theoretical chemistry.
Abstract: Treatment of the iron hydride [Cp*(dppe)FeH] (1) with methyltriflate (CH3OSO2CF3) yielded the iron triflate adduct
[Cp*(dppe)FeOSO2CF3] (4, 85 %). In the solid state, the triflate is coordinated at the iron center as shown by XRD (dFe-O = 2.118(4)Å) and IR
spectroscopy (νSO = 1305 cm-1). In solution, 4 is in equilibrium with the 16-electron species [Cp*(dppe)Fe]OSO2CF3 (5(OSO2CF3)), 4 /
5(OSO2CF3) = 2:1). The CV of 4 displays two waves (E1 = -0.74 V, E2 = 0.24 V vs SCE) assigned to the [Cp*(dppe)Fe(I)]/[Cp*(dppe)Fe(II)]+
and [Cp*(dppe)Fe(II)]+/[Cp*(dppe)Fe(III)]2+ redox couples. Reduction of 4 with Cp2Co provided the complex [Cp*(dppe)Fe(I)] (6, 95 %) and
oxidation of 6 with [Cp2Fe]PF6 gave [Cp*(dppe)Fe]PF6 (5(PF6), 98 %). XRD established the pseudo-trigonal bipyramidal geometry for the
five-coordinated cation 5+. The reactivity of 5(PF6) and 6 toward small molecules (CH2Cl2, H2O, CO, H2, N2) is reported.
complex [Cp*(dppe)FeCl] is less labile than in many other
related iron(II) complexes. Indeed, it has been shown that the
Introduction
chloride atom can be abstracted with sodium tetraphenylborate
Incorporation of the Cp*(dppe)Fe or, more generally, Cp*(P2)Fe
in the case of many iron(II) chloro complexes like trans-
{Cp* = η5-C5(CH3)5, P2 = bis-monodentate or chelating bidentate
[(depe)2Fe(H)Cl],
[Cp*(dippe)FeCl] (depe
dmpe
trans-[(dmpe)2FeCl2],
[Cp(dippe)FeCl],
phosphine} moieties in various unsaturated organic architectures
led to the realization of a wealth of interesting molecules for
molecular electronics.[1-3] The development of this synthetic
chemistry allowing selective and easy introduction of the
organoiron units in various organic environments has been
based on the reactivity of the chloro complex [Cp*(dppe)FeCl]
=
1,2-bis(diethylphosphino)ethane;
=
1,2-bis(dimethylphosphino)ethane; dippe
=
1,2-
bis(diisopropylphosphino)ethane) allowing the generation of the
corresponding 16-electron species which can be eventually
stabilized by labile ligands like dihydrogen or dinitrogen.[9, 10]
Many years ago we found that the protonation of the
hydride complex [Cp*(dppe)FeH] (1) with HBF4•(O(C2H5)2 occurs
at the Fe-H bond and gives the η2-H2 complex [Cp*(dppe)Fe(η2-
H2)]BF4 (2(BF4)) faster than the protonation at the metal atom,
as it had been predicted previously.[11, 12] The dihydrogen adduct
was isolated, stored as lemon yellow microcrystals for several
weeks at -50 °C, and characterized. The presence of the
coordinated η2-H2 ligand was definitively established by the
determination of the hydrogen-deuterium coupling constant (JHD
= 27 Hz) for the isotopomer [Cp*(dppe)Fe(η2-HD)]BF4.[11] As
soon as the temperature increases above -50 °C, the color
becomes orange indicating that the dihydrogen complex is
converted into the iron(IV) dihydride [Cp*(dppe)Fe(H)2]BF4
(3(BF4)).
5]
{dppe = 1,2-bis(diphenylphosphanyl)ethane} with alkynes.[4,
Despite a rather strong Fe-Cl bond, the rich chemistry of
[Cp*(dppe)FeCl] with terminal alkynes and terminal polyalkynes
comes from the 1,2-migration of the terminal hydrogen atom
which constitutes the driving force for the irreversible formation
of the corresponding vinylidene complexes.[6]
Interestingly, the complex [Cp*(dppe)FeCl] can be handled
in air in the solid state.[4] The chloride ligand is displaced by
bromide and iodide.[4] It can also be quickly displaced by
molecular white phosphorus,[7] and good two-electron ligands
like nitriles, in the presence of salts with a large counter anions
-
-
(i.e. PF6 , BPh4 , ...), to give [Cp*(dppe)Fe(NC-R)]PF6. The
complex [Cp*(dppe)FeCl] does not react with KF and small
molecules such as H2, N2, or H2O.[8] The chloride ligand of the
In a previous papers, we briefly reported that the triflate
complex [Cp*(dppe)FeOSO2CF3] (4) available from its chloro
relative in two steps constitutes a valuable precursor to the
coordinatively unsaturated complex [Cp*(dppe)Fe]PF6 (5(PF6))
and an alternative to [Cp*(dppe)FeCl] for the coordination of
alkynyl ligands containing carbon-silicon bonds.[13, 14] We also
found that compound 4 opened the route to the iron(I) 17-
electron derivative [Cp*(dppe)Fe] (6).[15] We now report the full
characterization and some reactivity of 4, a convenient access to
5 and 6 together with their basic chemical properties including
Paul Hamon,[a] Dr. Loic Toupet,[b] Dr. Thierry Roisnel,[a] Dr. Jean-René
Hamon,*[a] and Dr. Claude Lapinte,*[a]
[a]
Univ Rennes, CNRS, ISCR-UMR 6226, F-35000 Rennes, France
E-mail: jean-rene.hamon@univ-rennes1.fr
claude.lapinte@univ-rennes1.fr
https://iscr.univ-rennes1;fr/omc/
[b]
Univ Rennes, CNRS, IPR-UMR 6251, F-35000 Rennes, France
Supporting information for this article is given via a link at the end of the
document.
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
FULL PAPER
the preparation of the water complex [Cp*(dppe)Fe(OH2)]PF6
As expected for 18-electron iron(II) complexes, 4 is
diamagnetic. This was confirmed by the SQUID measurement
of the corrected molar magnetic susceptibility of a powdered
sample of 4. In the range 4-300 K, the plot of the product χMT vs
T is linear and the intercept is very close to zero, in agreement
with the diamagnetic nature of the complex.[17] In solution, the
1H NMR spectrum of a d8-THF solution of 4 shows three broad
bands at δ = 26.3 (W1/2 = 375 Hz), 22.3 (W1/2 = 375 Hz), and 0.9
(W1/2 = 250 Hz) ppm (W1/2 = half-height width). Based on their
relative intensities, the signals can be assigned to the CH2, CH3,
and phenyl resonances, respectively (Figure S1, Supporting
Information). The broadness of the bands and the chemical
(12), and the nitrogen adduct [Cp*(dppe)Fe(η1-N2)]PF6 (13).
Results and Discussion
1. Synthesis and reactivity of [Cp*(dppe)FeOSO2CF3] (4)
Treatment of the iron hydride [Cp*(dppe)FeH] (1) with 1.1 equiv
of methyl triflate (CH3OSO2CF3) at -80 °C causes the formation
of a yellow suspension which quickly turns green even if the
temperature is maintained at -80 °C. The solid material isolated
by filtration and purified by crystallization from a THF/pentane
mixture was identified as the iron triflate adduct
[Cp*(dppe)FeOSO2CF3] (4, 85 % yield, Scheme 1). When the
reaction is performed at 20 °C, the yellow intermediate is still
briefly observed and the yield of the reaction is unchanged. We
assumed that the transient yellow intermediate could be the η2-
methane adduct, but the very short lifetime of this putative
intermediate precluded the collection of any experimental
evidence. This reaction is reminiscent with the reaction of the
hydride 1 with acidic reagents (HBF4•(O(C2H5)2 or HOSO2CF3)
which also gave yellow intermediates identified as the η2-H2
complex [Cp*(dppe)Fe(η2-H2)]X (2(X)).[11] However, the final
product is different here, since the oxidative addition of methane
was not observed.
The IR spectrum of 4 (KBr disk, Figure S4, Supporting
Information) displays a series of bands below 1300 cm-1
characteristic of the presence of triflate anion. However, these
bands are useless to establish the existence of a Fe-O bond
between the anion and the metal center. Interestingly, the
presence of the sulfonyl stretching mode at 1305 cm-1 can be
regarded as the spectroscopic signature of coordinated triflate.
In this respect, it can be noted that the IR spectrum of the
closely related complex [Cp*(dppp)Fe]OSO2CF3 (dppp = 1,2-
bis(diphenylphosphanyl)propane) in which the triflate is not
bound to the iron atom, does not show this sulfonyl stretching
mode.[16] The triflate anion was definitely demonstrated to be
coordinated to the metal by an X-ray diffraction analysis on
shifts indicate
a paramagnetic behavior of the solution.
Accordingly, the chemical shifts strongly vary with the
temperature and move to positions expected for diamagnetic
derivatives as the temperature decreases. Thus, at 193 K, the
resonances of the phenyl, CH2, and CH3 groups are found at δ =
7.3, 3.7, and 2.6 ppm, respectively. The magnetic moment
determined in solution by the Evans method (μeff = 1.9 μB, d8-
THF, 307 K)[18] is much smaller than the value expected for a
complex carrying two unpaired electron (S = 1, 2.83 μB).[19]
Based on this result, one can assume that the triflate ligand is
partially dissociated in solution, providing an equilibrium
between the 18-electron neutral complex
4
and the
paramagnetic 16-electron salt [Cp*(dppe)Fe]OSO2CF3
(5(OSO2CF3)) (Scheme 2). Indeed, as a consequence of its
pseudo trigonal-bipyramidal geometry, complex 5(OSO2CF3) has
a triplet ground state (S = 1, see below). The percentage of
diamagnetic triflate complex 4 present in the THF solution at 307
K can be calculated using the relationship proposed by Puerta et
al. (eq 1).[20] In eq. 1, the value of 3.3 µB corresponds to the
magnetic moment determined for pure [Cp*(dppe)](PF6) (see
below). Thus, one can estimate that THF solution of 4 contains
67 % of the triflate adduct in equilibrium with 33 % of the salt
5(OSO2CF3).
% diamagnetic species = 100 x [1 - (µeff/3.3 µB)2]
1
Scheme 2. Dissociation of the triflate complex 4 in solution (The
phenyl groups of the dppe ligand have been omitted for clarity).
The partial dissociation of 4 in THF solution was also
validated by a series of 1H NMR spectra of 4 in THF with
increasing quantities of lithium triflate. For instance, the methyl
resonances of the Cp* ligand are observed at δ = 22.3, 19.7,
15.4, and 14.8 ppm with 0, 1, 10, and 20 equiv of lithium triflate,
respectively.
single crystal (see Section 6).
Scheme 1. Synthesis of complex [Cp*(dppe)FeOSO2CF3] (4)
(The phenyl groups of the dppe ligand have been omitted for
clarity).
Assuming that the 16-electron cation 5+ can be easily
reduced into its 17-electron counterpart [Cp*(dppe)Fe] (6) by a
base, and subsequently quenched by a good hydrogen atom
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
FULL PAPER
donor like methanol, the iron triflate complex 4 was reacted with
one equiv of sodium methoxyde in methanol. As expected, the
V) indicate that both electron transfers are associated with
significant reorganizations of the coordination sphere around the
metal center.[2] From the CV data, the preparation of the
[Cp*(dppe)Fe(I)] constitutes a viable synthetic target, while the
isolation of the product resulting from the chemical evolution of
[Cp*(dppe)Fe(III)]2+ can also be expected. It is assumed that the
additional wave observed in reduction (Ep = -0.48 V) constitutes
the electrochemical signature of the in situ generated species
(Figure 1).
reaction gives back the starting iron hydride
1 almost
quantitatively (Scheme 1). The 16-electron complex
5(OSO2CF3) can also be quenched in situ by dihydrogen. To a
THF solution of 5(OSO2CF3) a pressure of 0.1 bar of dihydrogen
was introduced at -80 °C. Readily, a lemon yellow color
characteristic of the dihydrogen complex [Cp*(dppe)Fe(η2-
H2)]OSO2CF3 (2(OSO2CF3)) appears and persists until the
temperature increases above - 50 °C. Then, the color turns
progressively orange indicating the formation of dihydride
complex 3(OSO2CF3) (Scheme 1).
3. Reduction and oxidation of 4
Thus, complex 4 was reacted with 1 equiv of cobaltocene in THF
at -80 °C (Scheme 3). As the reaction proceeds, the original
dark green color turns orange in less than one hour. After work
up, the 17-electron iron(I) complex 6 was isolated in pure form
as very air and moisture sensitive orange crystals (95 % yield)
from cold pentane. The molecular structure of 6 was confirmed
by X-ray diffraction study.[15]
2. Redox properties of [Cp*(dppe)FeOSO2CF3] (4) in THF
The initial scan in the cyclic voltammetry (CV) of 4 was run from
-1.2 V to 0.8 V [vs. a standard calomel electrode (SCE)] in THF
at 20 °C. The cyclic voltammogram displays two mono-
electronic waves and one additional wave in the reduction
process (Figure 1). The potentials for the two redox couples are
found at E1 = -0.74 and E2 = +0.24 V. The two redox systems
originate from the dissociation of the triflate complex 4 in THF,
the redox active species being the [Cp*(dppeFe]+ cation and not
complex 4. Indeed, it has been invariably observed that all
mononuclear
complexes
with
the
general
formula
[Cp*(dppe)FeX] show a unique reversible oxidation wave in their
CV between -1V and +1 V vs SCE.[2-4]
Scheme 3. Preparation of 5(PF6) via 6, and 7, from 4 (The
phenyl groups of the dppe ligand have been omitted for clarity).
Complex 6 was first characterized by CV analysis. As expected,
its cyclic voltammogram was found identical to that of 4. The
characterization of 6 by 1H and 31P NMR was not successful.
However, The presence of an odd electron in 6 was probed by
the measurement of the magnetic moment in solution by 1H
NMR using the Evans method.[18] The effective magnetic
moment (μeff = 1.48 ± 01 μB, C6D6) is not far from the theoretical
spin-only value (μB = 1.73). The X-band ESR spectrum for 6 run
at 77 K in a pentane glass displays three features (g1 = 1.9934;
g2 = 2.1911; g3 = 2.1971) in accord with its pseudo octahedral
geometry. The iron(I) complex 6 was also characterized in the
solid state by 57Fe Mössbauer spectroscopy. The Mössbauer
spectrum run for samples stored at 20 °C for several weeks
under argon atmosphere exhibits a single doublet confirming the
Figure 1. Cyclic voltammogram of 4 (THF, 0.1 M [n-Bu4N]PF6,
20 °C, platinum electrode, sweep rate = 0.1 V s-1, potentials in V
vs SCE; the ferrocene-ferrocenium couple (0.56 V vs SCE)[21]
was used as an internal reference.
The two electrochemical processes can be assigned to the
redox
couples
[Cp*(dppe)Fe(I)]/[Cp*(dppe)Fe(II)]+
and
[Cp*(dppe)Fe(II)]+/[Cp*(dppe)Fe(III)]2+, respectively. The ratio of
the anodic and cathodic peak current (ipa/ipc = 1) establishes the
thermal stability at 20 °C of the redox species
[Cp*(dppe)Fe(I)]/[Cp*(dppe)Fe(II)]+ at the platinum electrode. In
the case of the second redox event which corresponds to the
[Cp*(dppe)Fe(II)]+/[Cp*(dppe)Fe(III)]2+ system, the current peak
ratio is less than one (ipa/ipc = 0.8) indicating that the 15-electron
dicationic iron(III) species is not chemically stable at the
platinum electrode. The measured peak-to-peak separations
(ΔEp1 = 0.16 V, ΔEp2 = 0.15 V) which are larger than the value
expected for reversible electrochemical processes (ΔEp = 0.060
thermal stability of this 17-electron iron(I) species.
The
Mössbauer parameters and their analysis are given below in the
Mössbauer section.
The neutral complex 6 was oxidized with 1 equiv of
ferrocenium hexafluorophosphate in THF at -40 °C for 2 h
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
FULL PAPER
(Scheme 3). Its 16-electron counterpart [Cp*(dppe)Fe]PF6
(5(PF6)) was quantitatively isolated (98 % yield) as air and
moisture sensitive red-orange crystals after recrystallization from
a THF/pentane mixture. It is interesting to note that in the
closely related series [(η5-C5H5)(dppe)Fe]+,[22] and [(η5-
C5Me4Et)(CO)2Fe]+,[23] THF coordinates to the metal and the
corresponding THF adducts were isolated. The molecular
structure of 5(PF6) was definitely established by an X-ray
diffraction analysis on single crystal (see Section 6). In accord
with its pseudo C2v symmetry, the 16-electron cation shows a
magnetic moment μeff = 3.3 ± 0.2 μB (THF, 307 K, Evans
method) not far from the value expected for a transition metal
ion bearing two unpaired electron (μeff = 2.83 μB).[19] The ESR
spectrum of 5(OSO2CF3) was obtained from a frozen THF
solution of 4. The spectrum displayed three well resolved
features (g1 = 2.0677, g2 = 2.1051, g3 = 2.3730) with an
hyperfine splitting due to the coupling with the two phosphorus
nuclei of the dppe ligand for the low field tensor g3 (a3 = 21 G).
Furthermore, the Δms = 2 transition characteristic of the triplet
state was found at g = 4.264.
or CH2Cl2. The methyl radical might be stable enough under the
experimental conditions to be quenched by a second molecule
of 6. In contrast, the radical •CH2Cl probably reorganizes by
itself instead of reacting with a second molecule of 6.
The addition by syringe of 1 equiv of HBF4•(O(C2H5)2)2 to a
pentane solution of 6 cooled at -80 °C produces the immediate
formation of a lemon-yellow solid which slowly precipitates. This
color is characteristic of the dihydrogen complex
[Cp*(dppe)Fe(η2-H2)]BF4 (2(BF4)) which is stable at -80 °C as
previously obtained from the protonation of the hydride 1.[11]
Above -50 °C, the precipitate turns orange indicating the
dihydrogen derivative is converted to the Fe(IV) dihydride
counterpart [Cp*(dppe)Fe(H)2]BF4 (3(BF4)). After work up, the
dihydride 3(BF4) is isolated in 95 % yield and identified by its
2
characteristic sharp triplet (δ = -7.89 ppm, JPH = 68 Hz) in the
1H NMR spectrum. It is surprising that 6 can be converted in
3(BF4) with only one equiv of HBF4•(O(C2H5)2)2. The proton is
probably reduced by 6 to generate the 16-electron species 5+
and one hydrogen atom. It is possible that H• catches another
hydrogen atom from the diethyl ether in the solvent cage to form
one molecule of H2 which instantaneously reacts with the 16-
electron 5+ to form the dihydrogen complex 3(BF4).
1
The H NMR spectrum of 5(PF6) run at 300 K in d8-THF
exhibits two broad resonances at δ = 67.6 (W1/2 = 990 Hz), 56.5
(W1/2 = 720 Hz), and a broad multiplet at δ -10.2 ppm which can
be assigned to the CH2, CH3 and phenyl groups of the Cp* and
dppe ligands. The 31P NMR spectrum shows one well resolved
resonance at δ = 85.1 ppm corresponding to the phosphorus
nuclei of the dppe ligand. Surprisingly enough, the 13C NMR
spectrum is well resolved and displays resonances
corresponding to the two ligands bound to the metal (see Exp.
Sect. and Figures S5-S7 in Supporting Information).
Fe
PF6
5(PF6)
Fe Cl
P P
P
8
P
P
CH2Cl2
[(C5H5)2Fe]PF6
In accord with its redox potential, complex 5(PF6) can
easily be oxidized by treatment of a THF solution at -80 °C with
1 equiv of [Cp2Fe]PF6 (Scheme 3). After warming up to 20 °C,
the mixture is filtered and the obtained red liquor is evaporated
to dryness to give the known iron(III) fluoride complex
[Cp*(dppe)Fe-F]PF6 (7, 90 % yield).[24] In agreement with the
observation made in cyclic voltammetry (see above), the in situ
generated 15-electron species [Cp*(dppe)Fe]2+ activates the
HBF4
THF
Fe
P
H
Fe
BF4
Fe
P
H
H
-20 °C
P
P P
3(BF4)
1
6
CH3I
CO
-
PF6 counter anion by capturing a fluoride anion. It can also be
O
noted that this very reactive intermediate does not react with the
THF and no trace of polymerization of the solvent was detected.
CO
C
Fe
P
I
Fe CH3
Fe
Fe
+
C
O
OC
9
10
P
P
4. Reactivity of [Cp*(dppe)Fe] (6)
P
11
Microcrystals of the complex 6 can be stored at 20 °C for days
under vacuum or argon pressure. In solution, it behaves as a
highly reactive species as expected for a 17-electron iron(I)
radical. For instance, it can be stored in THF at -50 °C for a
while, but as the temperature reached -20 °C, it readily abstracts
a hydrogen atom from the solvent to give back the iron hydride 1
(Scheme 4). Complex 6 also reacts with CH2Cl2 to afford
quantitatively and specifically the iron chloride [Cp*(dppe)FeCl]
(8). Treatment of a cold THF solution of 6 with an excess of
CH3I under similar conditions, immediately results in the
quantitative formation of a 1:1 mixture of [Cp*(dppe)FeI] (9) and
[Cp*(dppe)FeCH3] (10).[4] Probably, in the first step of these two
reactions, the Fe(I) complex 6 abstracts a halide atom from CH3I
Scheme 4. Some examples of the reactivity of 6 (The phenyl
groups of the dppe ligand have been omitted for clarity).
The Fe(I) complex 6 also reacts very quickly with CO.
Indeed, when an excess of carbon monoxide was introduced in
a Schlenk tube containing an orange pentane solution of 6,
immediately the color turned to dark purple. After work up, the
binuclear complex [Cp*(CO)2Fe]2 (11) was isolated as a purple
powder and identified by IR and NMR spectroscopy.[25] It can be
assumed that the 17-electron species 6 reacts with CO to
generate the 19-electron intermediate [Cp*(η2-dppe)Fe(CO)]•
which can easily relaxes by decoordination of one phosphorus
atom of the dppe ligand, generating [Cp*(η1-dppe)Fe(CO)]• as a
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10.1002/ejic.201901086
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17-electron second intermediate. Reaction with
a
second
[Cp*(dppe)Fe(O=C(CH3)2)]OSO2CF3 (14) was reported to be
paramagnetic.[13] A careful reinvestigation of the dependence of
the magnetic susceptibility with temperature have shown that the
bulk crystalline samples of 14 is a diamagnetic material polluted
by a paramagnetic impurity containing two unpaired electrons (S
= 1). Examination of crystalline samples of 14 with microscope
allowed to found few red small crystals among the dark green
bulk material. Further investigation were not carried out.
molecule of CO liberates the diphosphane from the metal and
dimerization of the [Cp*Fe(CO)2]• species gives 11. It is
interesting to observe that a sequence of 17-electron and 19-
electron intermediates easily produces the displacement of the
chelating dppe by CO.
5. Reactivity of [Cp*(dppe)Fe]PF6 (5(PF6))
It was also found that upon addition of water to an orange
THF solution of [Cp*(dppe)Fe]PF6 (5(PF6)) the color turned dark
green, immediately. Slow diffusion of pentane into this mixture
provides green crystals identified by an X-ray diffraction analysis
as the water complex [Cp*(dppe)Fe(H2O)]PF6 (12) as a solvate
with two molecules of THF (see Section 6). The presence of the
water molecule is evidenced by the observation of a νOH band in
the IR spectrum at 3402 cm-1 (KBr disk). Analytically pure
microcrystalline samples of the 18-electron complex 12 were
found diamagnetic. The determination of the magnetic moment
in d8-THF at 307 K by the Evans method (µeff = 0.4 µB) showed
that the complex 12 is partially dissociated in solution (See
Figure S8-S10, Supporting Information). According to eq. 1, the
solution contains 88 % of the water adduct in equilibrium with
12 % of 16-electron complex 5(PF6). In solution, the water
adduct is more stable than the triflate complex 4, in accord with
a shorter FeO bond distance in the former derivative (see
Section 6). The 1H NMR spectrum (d8-THF, 25 °C) of 12
resembles that of 4 with three broad resonances at δ = 8.2, 6.4
and 5.9 ppm assigned to the CH2, CH3, and phenyl resonances,
respectively. The protons of the water molecule could not be
found. A single resonance is observed in the 31P NMR spectrum
(δ = 89.6 ppm (d8-THF, 25 °C).
The coordinatively unsaturated complex 5(PF6) behaves as a
strong Lewis acid. It reacts cleanly and quickly with small
molecules like water, dihydrogen, dinitrogen, and methylene
dichloride as well (Scheme 5). As 4 is in equilibrium with
5(OSO2CF3) (Scheme 2), the reactivity of 4 and 5(PF6) are
absolutely identical. Depending on the reactions and the
experimental conditions, the isolation of the products as triflate
or hexafluorophosphate salts can lead to different yields of the
isolated pure products. As a general rule, better yields are
obtained in the hexafluorophosphate series, and the reactions
reported below are described in this series.
Similarly to 4, 5(PF6) reacts with H2 and provides the
dihydride derivative [Cp*(dppe)Fe(H)2]PF6 (3(PF6)), 95 % yield,
Scheme 5). The reaction of 5(PF6) with CH2Cl2 is also very
quick and specific, leading to the formation of the iron(III)
chloride [Cp*(dppe)FeCl]PF6 (8(PF6)), Scheme 5) that was
isolated in 92 % yield after crystallization.[4]
It is now well recognized that dinitrogen molecule can act
as a ligand to a transition metal complex.[26] In particular, a large
variety of iron-dinitrogen complexes have been reported. They
all display an η1, or end-on, binding geometry.[27]
Upon
exposure to nitrogen gas, an orange THF solution of 5(PF6)
turns progressively to yellow. After work up, the new salt
[Cp*(dppe)Fe(η1-N2)]PF6 (13) was isolated as yellow
microcrystals in 92 % yield. The dinitrogen complex 13 is
thermally stable when stored under argon or under vacuum.
The [Cp*(dppe)Fe]+ framework of this compound was
characterized by 1H, 31P, and 13C NMR. The presence of the N2
molecule attached to the iron nucleus was probed by elemental
analysis and IR spectroscopy (Figure S11, Supporting
Information).
The IR spectrum displays a relatively intense νN2 stretching
band at 2120 cm-1, characteristic of a mononuclear complex
end-bonded to a molecule of dinitrogen.[27] The IR frequency
compares well with those found for the iron(II) complexes as for
examples [(dppe)2Fe(η1-N2)]BPh4 (2130 cm-1), [(dmpe)2Fe(H)(η1-
N2)]BPh4 (2112 cm-1, dNN = 1.13 Å), and [Cp(dippe)Fe(H)(η1-
N2)]BPh4 (2112 cm-1, dNN = 1.13 Å).[10, 27, 28] It is worthy to note
that the bulky Cp* ligand plays here a decisive role on the
specificity of the reaction. Indeed, it has been shown that the
binuclear complex [(C5H5)(dppe)Fe-NN-Fe(dppe)(C5H5)}](PF6)2
is formed when the C5 ring is not methylated.[29] The cyclic
voltammogram of 13 recorded in THF between -1.0 V and +1.0
Scheme 5. Some examples of the reactivity of 5(PF6) (The
phenyl groups of the dppe ligand have been omitted for clarity).
Although the 16-electron complex does not coordinate
THF in contrast with its [(η5-C5H5)(dppe)Fe]+
and [(η5-
23]
C5R5)(CO)2Fe]+ relatives,[22,
it can nevertheless give adduct
with oxygenated molecules. For instance, it was shown that
5(PF6) gives a stable adduct with acetone.[13] It can be
mentioned
here,
that
the
acetone
adduct
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
FULL PAPER
V does not show any wave. This result clearly indicates that the
nitrogen ligand is well-coordinated to the iron atom and its
dissociation in THF does not occur.
Figure 2. Molecular structures of the triflate adduct 4 (top), the
cationic 16-electron Fe(II) complex 5(PF6) (middle), and the
water complex 12•2(C4H8O) (bottom) with their respective partial
numbering scheme. Hydrogen atoms, except those involved in
H-bonding interactions in 12•2(C4H8O), and counter anions have
been omitted for clarity. Thermal ellipsoids are drawn at 20 %
probability.
6. Molecular structures of 4, 5(PF6), and 12•2(C4H8O)
Slow diffusion of pentane into concentrated THF solutions of the
triflate adduct 4, the 16-electron Fe(II) complex 5(PF6) and the
water complex 12•2(C4H8O) provided suitable crystals for X-ray
analyses. Diffraction parameters for these compounds are
available in Table S1 (Suporting Information). ORTEP views are
given in Figure 2, while pertinent bond lengths and angles for
these three complexes are collected in Table 1. The structures
of the six-coordinated complexes 4 and 12•2(C4H8O) show for
the iron centers the expected pseudo-octahedral geometry with
three sites occupied by the Cp* ligand, two sites by the chelating
bis-phosphane; the triflate or the water molecules being
coordinated at the remaining sixth position. The Fe-C and Fe-P
bond distances, and the bond angles are in the previously
However, these bonds are slightly longer than that determined
for the closely related complex [Cp*(dppe)Fe(O=C(CH3)2)]PF6
(14) (dFe-O = 2.031(4) Å) and significantly longer than those
reported
for
other
iron
complexes
like
[(η5-
C5Me4Et)(CO)2Fe(OH2)]BF4 (dFe-O = 2.022(9) and 2.043(9) Å).[23]
The X-ray analysis of 12•2(C4H8O) also revealed the
presence of two molecules of solvent per cation with hydrogen
bonding interactions between the protons of the water molecule
and the oxygen atoms of the molecules of THF (Table 2). The
hydrogen atoms of the water ligand were not located or refined.
The Fe-O...OC4H8 distances are 2.710(4) Å and 2.781(4) Å.
The Fe-O bond length determined for 4 (2.118(4) Å) and
12•2(C4H8O) (2.077(2) Å) are much shorter than the sum of the
van der Waals radii (2.67 Å),[30, 31] and very close to the average
of the distances reported in the literature showing that the triflate
and water ligands are well bound to the metal atom.[31, 32]
established ranges for cationic iron(II) derivatives of this series.[2-
4]
Table 1. Selected bond distances [Å] and angles [°] for 4, 5(PF6),
and 12•2(C4H8O).
4
5(PF6)
12•2(C4H8O)
Bond lengths
Fe(1)-O(1)
2.118(4)
-
2.077(2)
Fe(1)-P(1)
Fe(1)-P(2)
2.2682(17) 2.233(3)
2.2238(17) 2.256(3)
2.2339(11)
2.2219(14)
Fe(1)-CCp* av.
Fe-Cp*cent
2.129(6)
1.748
2.134(10) 2.112(3)
1.770
1.793
Bond angles
P(1)-Fe(1)-O(1)
P(2)-Fe(1)-O(1)
P(1)-Fe(1)-P(2)
94.22(13)
84.29(13)
84.20(6)
-
-
89.84(8)
86.61(8)
86.39(11) 85.01(4)
The view of 5(PF6) in Figure 2 clearly shows that the iron
atom is in a formally five-coordinate environment and the data
does not reveal any indications of stabilization by means of intra-
or intermolecular agostic interaction. The Cp* ring is pentahapto
bonded and the plane defined by the phosphorus nuclei of dppe
ligand and the iron atom is almost perpendicular to the Cp*
plane. The molecule is close to the C2v symmetry. The angle
defined by the ring centroid, the Fe atom, and the centroid of the
P(1) - P(2) segment is close to 180 ° (175.2 °) in accord with the
pseudo-trigonal bipyramidal geometry for the coordination of the
complex cation. The bond distances and angles found for
5(PF6) compare well with those found for the related X-ray
characterized 16-electron species [Cp*(dippe)Fe]BPh4 and
[(pentadienyl)(PEt3)2Fe]PF6.[33]
Table 2. Hydrogen bond interaction parameters for 12•2(C4H8O)
D-HꞏꞏꞏA
D-H [Å]
HꞏꞏꞏA [Å] DꞏꞏꞏA [Å]
1.84 2.710(4)
D-HꞏꞏꞏA [°]
O1-H1AꞏꞏꞏO2
0.93
156
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
FULL PAPER
O1-H1BꞏꞏꞏO3
0.94
0.97
1.94
2.58
2.781(4)
3.511(5)
149
162
with 8, complexes 4 and 5(PF6) react with small molecules like
dihydrogen, dinitrogen, carbon monoxide, and water. Further
synthetic efforts from our group are in progress to take
advantage of the rich reactivity of 4 for the elaboration of new
molecular architectures.
C12-H12AꞏꞏꞏO3
7. 57Fe Mössbauer Spectroscopy of 4-6, 12 and 14
The 57Fe Mössbauer spectra of the complexes 4-6, 12, and 14
were run at 80 K and least-square fitted with Lorentzian line
shapes.[34] The spectra of all complexes show a single doublet
which clearly establishes the spectroscopic purity of the samples
and the chemical stability of these complexes over weeks. The
isotropic shift (IS) and quadrupole splitting (QS) are reported in
Table 3. The line broadening (Γ) are in line with the value
observed for half sandwich iron complexes, except in the case of
Experimental Section
General Data: Manipulations of air-sensitive compounds were performed
under an argon atmosphere using standard Schlenk techniques or in a
argon-filled Jacomex 532 drybox. All glassware was oven-dried and
vacuum or argon flow-degassed before use. Reagent grade
tetrahydrofuran (THF), diethyl ether, and pentane were dried and
deoxygenated by distillation from sodium/benzophenone ketyl.
Dichloromethane was distilled under argon from P2O5 and then from
the five-coordinated complex 5(PF6).
phenomenon due to the magnetic properties of this complex (S
= 1) is at the origin of the broad lines.[35]
Probably, relaxation
Na2CO3. [Cp*(dppe)FeH] (1),[4] [Cp*(dppe)FeCl] (8),[4] and ferricinium
The Mössbauer parameters depend on several factors
including the oxidation and the spin states, the atoms
coordinated at the Mössbauer nucleus, and the coordination
numbers.[35, 36] In the present case, only the comparison of IS
and QS between the iron(II) with oxygen ligands 4, 12, and 14
makes sense. In this series of complexes, the IS and QS
parameters decrease in the order 4, 12, 14 while the iron-
oxygen bond distances decrease continuously. It is interesting
to note that the strength of the Fe-O bond determined in the
solid state is in line with the thermodynamic stability of the
complexes in solution. It can also be noted that, the five-
coordinated complexes 5(PF6) and 6 display much smaller
values for both the IS and QS parameters.[2]
hexafluorophosphate [Fe(5-C5H5)2]PF6
were prepared following
[21]
published procedures. Methyl triflate (CH3O3SCF3) and ammonium
hexaflorophosphate were commercially available and used as received
without further purification. Caution: Methyl trifluoromethanesulfonate is
toxic and a suspected carcinogen, and must be handled in a well-
ventilated fume hood. FT-IR spectra were recorded using a Bruker
IFS28 spectrophotometer (range 4000-400 cm-1) as solids dispersed in
KBr pellets. 1H, 13C, 19F and 31P NMR spectra were recorded on a Bruker
DPX200 NMR multinuclear spectrometer at 298 K, unless otherwise
noted. Chemical shifts are reported in parts per million () relative to
tetramethylsilane (TMS) for 1H and 13C NMR spectra, external 85 %
H3PO4 for 31P NMR spectra, and external CFCl3 for 19F spectra. Coupling
constants (J) are reported in hertz (Hz), and integrations are reported as
number of protons. EPR spectra were recorded on a Bruker EMX-8/2.7
(X-band) spectrometer. Magnetic susceptibility measurements were
conducted in solution according to the Evans' method.[18] Mössbauer
spectra were recorded with a 2.5 x 10-2 C (9.25 x 108 Bq) 57Co source
using a symmetric triangular sweep mode. Computer fitting of the
Mössbauer data to Lorentzian line shapes was carried out with a
previously reported computer program.[34] The isomer shift values are
reported relative to iron foil at 298 K. The electrochemical analyses were
performed with use of an EG&G-PAR Model 263 potentiostat/galvanostat.
Cyclic voltammetry (CV) measurements were performed at room
temperature (ca. 20 °C) with a normal three-electrode configuration
consisting of a Pt-disk (d = 1.0 mm) working electrode, a saturated
Table 3. 57Fe Mössbauer data for the new and some closely
related complexes (80 K)
Cmpd
1[4]
4
5(PF6)
6
12
IS (mm/s) QS (mm/s) Γ (mm/s) dFe-O (Å)
0.20
2.08
0.13
0.713
0.499
0.436
0.591
0.567
0.553
2.336
1.728
1.241
2.233
2.191
1.752
0.124
0.257
0.136
0.118
0.128
0.130
2.128(4)
2.076(2)
2.031(4)
not bound
14[13]
15[16]
14
calomel reference electrode (SCE), and
a platinum-wire counter
electrode. The ferrocene/ferrocenium redox couple (E1/2 = 0.560 V in
THF) was used as an internal calibrant for the potential
measurements.[21] Elemental analyses were conducted on a Thermo-
Finnigan Flash EA 1112 CHNS/O analyser by the Microanalytical Service
of the Centre Régional de Mesures Physiques de l'Ouest (CRMPO) at
the University of Rennes 1, France.
=
[Cp*(dppe)Fe(O=C(CH3)2)]OSO2CF3,
15
=
[Cp*(dppp)Fe]OSO2CF3
Conclusions
In this contribution, we described the synthesis, spectroscopic
and structural characterization, and redox properties of the
triflate adduct [Cp*(dppe)FeOSO2CF3] (4). The triflate anion is
well coordinated at the iron nuclus in the solid state, but partially
dissociates in solution to liberate the highly reactive cationic 16-
electron [Cp*(dppe)Fe]+ (5+). As a result, the 17-electron iron(I)
derivative [Cp*(dppe)Fe] (6) is accessible by a one electron
reduction with Cp2Co, and the 15-electron iron(III) counterpart
[Cp*(dppe)FeOSO2CF3] (4): A Schlenk tube was loaded with 0.590 g
(1.0 mmol) of [Cp*(dppe)FeH], 150 mL of diethyl ether and a magnetic
stirbar. Methyl triflate (125 µL, 1.1 mmol) was then added by syringe to
the red-orange solution. A yellow suspension appeared immediately
which quickly gave a green precipitate. The dark solid was filtered by
cannula, washed with 3 x 20 mL portion of pentane and dried under
vacuum. Recrystallization from THF/pentane mixture provided 0.630
g
(85 % yield) of [Cp*(dppe)FeOSO2CF3] as air and moisture sensitive
dark-green crystals. A crystal from this crop was used for an X-ray
structure determination. Anal. Calcd for C37H39F3FeO3P2S: C, 60.17; H,
5.32. Found : C, 59.82; H, 5.33%. FT-IR (KBr): ν = 1305, 1267, 1234,
1169, 1153, 1094, 1032 cm-1. µeff (d8-THF, 307 K) = 1.9 µB. 1H NMR (200
MHz, d8-THF, 300 K): δ = 26.3 (br s, CH2, w1/2 = 375 Hz); 22.3 (br s,
[Cp*(dppe)Fe](PF6)2 can be generated by
a one electron
oxidation with [Cp2Fe]PF6. However, the dication reacts with the
-
PF6 anion to yield [Cp*(dppe)FeF]PF6 (7). The reactivity of 4 is
richer than that of its precursor [Cp*(dppe)FeCl] (8). In contrast
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10.1002/ejic.201901086
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C5Me5, w1/2 = 375 Hz); 0.9 (br s, Ph) ppm. 13C NMR (50 MHz, d8-THF,
193 K): δ = 137.7-129.3 (m, Ph), 95.1 (br s, C5Me5), 34.2 (br s, CH2), 8.5
(s, C5Me5) ppm. 31P NMR (81 MHz, d8-THF, 193 K): δ = 89.8 (s, dppe)
ppm. 19F NMR (188 MHz, d8-THF): δ = -72.5 (s, CF3O2SO) ppm.
of diethyl ether. The extracts were taken to dryness and [Cp*(dppe)FeCl]
(8) was collected in 95 % yield as a pure microcrystalline powder. The
compound was identified by comparison of its 1H NMR and CV data with
those of an authentic sample.[4]
Preparation of the hydride 1 from 4: A Schlenk tube was charged with
0.738 g (1 mmole) of 4, 30 mL of methanol and a stirbar. The solution
was cooled to -80 °C before adding NaOCH3 (0.065 g, 1.2 mmol). The
solution changed slowly from green to orange while the temperature was
allowed to increase to 20 °C. The solvent was removed under reduced
pressure, and the solid residue extracted with 3 x 15 mL portion of
pentane. After removal of the solvent and drying under vacuum, the
complex [Cp*(dppe)FeH] (1) was isolated (0.56 g, 95 % yield), and
identified by 1H nmr spectroscopy with its characteristic triplet at δ = -16.8
ppm (2JHP = 67 Hz) with comparison with an authentic sample.[4]
Reaction of 6 with CH3I: A Schlenk tube was charged with 0.290 g (0.5
mmol) of [Cp*(dppe)Fe] (6) and 10 mL of THF. The solution was cooled
to -80 °C and 4 μL of CH3I (0.6 mmol) was added by syringe. The
solvent was then removed at 20 °C. The solid residue was extracted with
2 x 10 mL portions of pentane. The extract taken to dryness contained
[Cp*(dppe)FeI] (9) and [Cp*(dppe)FeCH3] (10) formed in the 1:1 ratio and
quantitative yield. The products were identified by 1H, 31P NMR and
cyclic voltammetry (CV) and comparison of the data with those of
authentic samples.[4]
Reaction of 6 with HBF4•OEt2: A Schlenk tube was loaded with 0.590 g
(1.0 mmol) of [Cp*(dppe)Fe] (6) and 20 mL of pentane at -80 °C. Then,
150 μL (1.1 mmol) of HBF4•OEt2 were added by syringe. Immediately, a
lemon-yellow solid precipitated. The resulting solid was filtered off,
washed with 2 x 10 mL portions of diethyl ether and dried under vacuum
at 20 °C. The complex [Cp*(dppe)Fe(H)2]BF4 (3(BF4)) was recovered as
a yellow powder (0.64 g, 95 % yield), and identified by comparison of its
[Cp*(dppe)Fe] (6): A Schlenk tube cooled to -80 °C was loaded with
0.738 g (1.0 mmol) of [Cp*(dppe)FeOSO2CF3], 30 mL of THF and a
magnetic stirbar. Cobaltocene (0.170 g, 0.9 mmol) was then added in
one go to the green solution. The color slowly turned orange and at -
20 °C the solvent was removed under vacuum. At room temperature, the
solid residue was extracted with
Crystallization from cold pentane gave 0.50
[Cp*(dppe)Fe] as very air and moisture sensitive orange
3
x
10 mL portion of pentane.
2
g
(95 yield) of
%
characteristic 1H NMR spectrum (δFe-H = -7.9 ppm (t, JHP = 68 Hz) with
a
that of an authentic sample.[11]
microcrystalline solid. Anal. Calcd for C36H39FeP2: C, 73.35; H, 6.67.
Found : C, 72.87; H, 6.65. µeff (C6H6, 307 K) = 1.48 ± 0.1 µB.
Reaction of 6 with CO: A Schlenk tube was charged with 0.590 g (1.0
mmol) of [Cp*(dppe)Fe] (6) and 20 mL of pentane at 20 °C. The
glassware was purged under reduced pressure and refilled with 2 bars of
CO. The orange solution became instantaneously purple. The stirring
was continued for 15 min. The solvent was then removed under reduced
pressure and the solid residue washed with 3 x 10 mL portion of diethyl
ether to remove free dppe that was identified by 1H and 31P NMR
spectroscopy. The remaining purple residue was dried under vacuum to
provide 0.38 g (98 % yield) of [Cp*(CO)2Fe]2 (11). Complex 11 was
identified spectroscopically (IR and NMR) by comparison with literature
data.[25]
[Cp*(dppe)Fe]PF6 (5(PF6)): A Schlenk tube cooled to -40 °C was
charged with 1.35 g (2.3 mmol) of [Cp*(dppe)Fe], 20 mL of THF and a
magnetic stirbar. Ferricinium hexafluorophosphate (0.685 g, 2.07 mmol)
was then added in one go to the orange solution. The reaction mixture
was stirred for 2 h while it slowly warmed up to 20 °C. The solvent was
evaporated under vacuum and the solid residue washed with 5 x 50 mL
portion of a pentane/diethyl ether mixture (1:1, v/v). Recrystallization from
THF/pentane mixture provided 1.50 g (98 % yield) of [Cp*(dppe)Fe]PF6
as very air and moisture sensitive orange-red crystals. A crystal from this
crop was used for an X-ray structure determination. Anal. Calcd for
C
36H39F6FeP3: C, 58.87; H, 5.35 . Found : C, 58.55; H, 5.63 . µeff (THF,
Reaction of 5(PF6) with H2: A Schlenk tube was charged with 0.734 g
(1.0 mmol) of [Cp*(dppe)Fe]PF6 and 30 mL of THF at 20 °C. The argon
atmosphere was partially removed under reduced pressure before
introducing 1.2 bar of H2. The orange solution turned immediately yellow.
The solution was stirred for 15 min and the solvent was removed under
reduced pressure. The solid residue was washed with 3 x 20 mL portion
of pentane. The complex [Cp*(dppe)Fe(H)2]PF6 (3(PF6)) was recovered
as a yellow powder (0.64 g, 95% yield) and identified by comparison of
its characteristic 1H NMR spectrum with that of an authentic sample.[11]
307 K) = 3.3 ± 0.2 µB. 1H NMR (200 MHz, d8-THF, 297 K): δ = 67.6 (br s,
CH2, w1/2 = 990 Hz), 56.5 (br s, CH3, w1/2 = 720 Hz), -10.2 (br s, o-Ph)
ppm. 31P NMR (81 MHz, d8-THF, 297 K): δ = 85.1 (s, dppe), -140.6 (sept.,
PF6) ppm. 19F NMR (188 MHz, d8-THF, 297 K): δ = -69.5 (d, J = 714
Hz, PF6) ppm.
P-F
Chemical oxidation of [Cp*(dppe)Fe]PF6 (5(PF6)): To a 50 mL orange
THF solution of 5(PF6) (0.734 g, 1.0 mmol), cooled at -80 °C, was added
in one go a solid sample of ferrocenium hexafluorophosphate (0.320 g,
0.97 mmol). The color turned immediately dark red, and stirring was
continued while the mixture was allowed to warm to room temperature.
The solvent was evaporated under reduced pressure and the solid
material extracted with 5 x 20 mL portion of acetone. The extracts were
combined and evaporated to dryness. The dark red residue was washed
with 2 x 20 mL portion of diethyl ether to remove the ferrocene.
Crystallization from acetone/pentane mixture afforded 0.601 g (90 %
yield based on [Cp2Fe]PF6) of [Cp*(dppe)FeF]PF6 (7) isolated as a
thermally air stable dark red powder. Complex 7 was authenticated by
Reaction of 5(PF6) with CH2Cl2: A Schlenk tube was charged with
0.734 g (1.0 mmol) of [Cp*(dppe)Fe]PF6 and 15 mL of CH2Cl2 at 20 °C.
The resulting solution was stirred for 10 min and the solvent was
removed under reduced pressure. The solid residue was washed with 3
x 15 mL portion of pentane and dried under vacuum. The complex
[Cp*(dppe)FeCl]PF6 (8(PF6)) was recovered as red garnet cristals (0.710
g, 92 % yield) and identified by comparison with an authentic sample.[4]
Reaction of 5(PF6) with H2O: A Schlenk tube was loaded with 0.734 g
(1.0 mmol) of [Cp*(dppe)Fe]PF6, 30 mL of THF and a magnetic stirbar.
Degased water (0.09 g, 5.0 mmol) was then added by syringe to the
orange solution. The reaction mixture was stirred for 15 min during which
time the color changed to dark green. The solvent was removed under
reduced pressure, the solid residue washed with 3 x 20 mL portion of
pentane, and dried under vacuum to provide 0.76 g (85% yield) of
[Cp*(dppe)FeOH2•2THF]PF6 (12) as an air sensitive black powder.
comparison of its 19F NMR (CD2Cl2)broad signal at δFe-F = -60.0 (w1/2
=
360 Hz) ppm with literature data.[24]
Reaction of 6 with CH2Cl2: In a Schlenk tube containing 20 mL of
CH2Cl2 under argon was added 0.290 g (0.5 mmol) of [Cp*(dppe)Fe] (6)
at 20 °C. The solution turned instantaneously green, and the stirring was
maintened for 15 min. The solvent was removed under reduced
pressure and the dark green solid was extracted with 2 x 10 mL portions
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
FULL PAPER
2009, 28, 1878-1890; (f) Y. Tanaka, T. Ishisaka, A. Inagaki, T. Koike, C.
Lapinte, M. Akita, Chem. Eur. J. 2010, 16, 4762-4776; (g) A. Burgun, F.
Gendron, C. Sumby, T. Roisnel, O. Cador, K. Costuas, J.-F. Halet, M. I.
Bruce, C. Lapinte, Organometallics 2014, 33, 2613-2627; (h) M. Lohan, F.
Justaud, T. Roisnel, P. Ecorchard, H. Lang, C. Lapinte, Organometallics
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2010, 29, 4628-4638.
Single crystals suitable for X-ray analysis were grown by slow diffusion of
pentane into a THF solution. Anal. Calcd for C44H57F6FeO3P3: C, 58.94;
H, 6.41; P, 10.36. Found: C, 58.97; H, 6.49; P, 9.50. µeff (d8-THF, 307 K)
= 0.4 µB. FT-IR (KBr): νOH = 3402 cm-1. 1H NMR (200 MHz, d8-THF, 298
K): δ = 8.2 (br s, CH2), 6.4 (br s, w1/2 = 150 Hz, CH3), 5.9 (br s, w1/2 = 50
Hz, o-Ph) ppm. 13C NMR (50 MHz, d8-THF, 298 K): δ = 179.0-146.0 (Ph),
132.0 (C5Me5), 51.9 (CH2), 0.5 (C5Me5) ppm. 31P NMR (81 MHz, d8THF,
193 K): δ = 89.6 (s, dppe) ppm.
[2] F. Paul, C. Lapinte, Coord. Chem. Rev. 1998, 178-180, 427-505.
[3] J.-F. Halet, C. Lapinte, Coord. Chem. Rev. 2013, 257, 1584-1613.
[4] C. Roger, P. Hamon, L. Toupet, H. Rabaâ, J.-Y. Saillard, J.-R. Hamon,
C. Lapinte, Organometallics, 1991, 10, 1045-1054.
[5] N. G. Connelly, M. P. Gamasa, J. Gimeno, C. Lapinte, E. Lastra, J. P.
Maher, N. Le Narvor, A. L. Rieger, P. H. Rieger, J. Chem. Soc., Dalton
Trans. 1993, 2575-2578.
[6] (a) M. I. Bruce, P. J. Low, Adv. Organomet. Chem. 2004, 50, 179-444;
(b) N. Le Narvor, L. Toupet, C. Lapinte, J. Am. Chem. Soc. 1995, 117,
7129-7138.
[7] I. de Los Rios, J.-R. Hamon, P. Hamon, C. Lapinte, L. Toupet, A.
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Reaction of 5(PF6) with N2: A Schlenk tube was charged with 0.734 g
(1.0 mmol) of [Cp*(dppe)Fe]PF6 and 30 mL of THF at 20 °C. The argon
atmosphere was partially removed under reduced pressure before
introducing 1.2 bar of N2. The orange solution turned immediately yellow.
The solution was stirred for 15 min and the solvent was removed under
reduced pressure. The solid residue was washed with 3 x 20 mL portion
of pentane. The complex [Cp* (dppe)(Fe(N2)]PF6 (13) (0.705 g, 92 %
yield) was recovered as yellow microcrystals.
Anal. Calcd. for
C36H39F6FeN2P3 : C, 56.71; H, 5.16; N, 3.67. Found : C, 56.92; H, 5.13;
N, 3.55. 1H NMR (200 MHz, CD3COCD3, 300 K): δ = 8.26-7.41 (m, 20H,
Ph dppe), 2.07-1.99 (2m, 4H, CH2, dppe), 1.61 (s, 15H, C5Me5) ppm.
13C NMR (50 MHz, CD3COCD3, 300 K): δ = 133.9-129.7 (m, Ph dppe),
92.5 (s, C5Me5), 28.6 (tm, CH2 dppe, 1JCH 136 Hz), 9.3 (q, CH3, 1JCH= 128
Hz) ppm. 31P NMR (81 MHz, CD3COCD3, 300 K): δ = 85.5 (s, dppe) ppm.
FT-IR (KBr): νNN = 2120 cm-1.
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X-ray Crystal Structure Determinations: A suitable X-ray single crystal
of compound 4, 5(PF6) and 12•2(C4H8O) obtained as described above,
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1957164 (for 4), 1957165 (for 5(PF6)), and 1957166 (for 12•2(C4H8O))
contain the supplementary crystallographic data for this paper. These
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
FULL PAPER
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10.1002/ejic.201901086
European Journal of Inorganic Chemistry
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FULL PAPER
The new complex
Key Topic*: Organoiron complexes
[Cp*(dppe)FeOSO2CF3] was
prepared by treatment of the hydride
[Cp*(dppe)FeH] with CH3OSO2CF3
(85 % yield). This compound
dissociates in THF opening the
route to the five-coordinated
complexes [Cp*(dppe)Fe], and
[Cp*(dppe)Fe]PF6, and to the six-
coordinated derivatives
Paul Hamon, Loic Toupet, Thierry
Roisnel, Jean-René Hamon*, Claude
Lapinte*
Page No. – Page No.
Preparation and characterization of
the triflate complex
[Cp*(dppe)FeOSO2CF3]: a
convenient access to labile five-
and six-coordinate Fe(I) and Fe(II)
complexes
[Cp*(dppe)Fe-L]PF6 (L = CO, H2, N2,
H2O).
This article is protected by copyright. All rights reserved.