First synthesis and spectroscopic characterization of isolated butatrienylidene complexes of transition metals

Article abstract of DOI:10.1016/S0022-328X(98)01107-3

The complex Cp*Fe(dippe)Fe(C≡CC≡C)Fe(CO)₂Cp* (3b, dippe = 1,2-bis(diisopropylphosphino)ethane, Cp* = pentamethylcyclopentadienyl) was prepared by activation of the terminal butadiyne Cp*(CO)₂FeC≡CC≡CH (2) with the chloro iron complex

Full text of DOI:10.1016/S0022-328X(98)01107-3

Journal of Organometallic Chemistry 578 (1999) 76–84
First synthesis and spectroscopic characterization of isolated
butatrienylidene complexes of transition metals
Franc¸oise Coat, Maud Guillemot, Fre´de´ric Paul, Claude Lapinte *
UMR CNRS 6509, ‘Organome´talliques et Catalyse: Chimie et Electrochimie Mole´culaires’, Uni6ersite´ de Rennes 1, Campus de Beaulieu,
35042 Rennes Cedex, France
Received 7 July 1998
Abstract
The complex Cp*Fe(dippe)Fe(CꢀCCꢀC)Fe(CO)2Cp* (3b, dippe=1,2-bis(diisopropylphosphino)ethane, Cp*=pentamethylcy-
clopentadienyl) was prepared by activation of the terminal butadiyne Cp*(CO)2FeCꢀCCꢀCH (2) with the chloro iron complex
Cp*(dippe)FeCl (1b) in the presence of KPF6 and KOBut. Treatment of Cp*(P2)Fe((CꢀCCꢀC)Fe(CO)2Cp* (3a, P2=dppe,
dppe=1,2-bis(diphenylphosphinoethane); 3b, P2=dippe) with HBF4 · Et2O produced the secondary iron butatrienylidene com-
plexes [Cp*(P2)Fe{ꢁCꢁCꢁCꢁC(H)Fe(CO)2Cp*}][BF4] (4a, P2=dppe, 75%; 4b, P2=dippe, 93%). The slightly more stable tertiary
butatrienylidene iron derivatives [Cp*(P2)Fe{ꢁCꢁCꢁCꢁC(CH3)Fe(CO)2Cp*}][OSO2CF3] (5a, P2=dppe, 22%; 5b, P2=dippe, 75%)
were made by reacting the precursor complexes 3a–b with methyl triflate under similar conditions. All the compounds 4a–b and
5a–b are almost stable in solution at 20°C. They are light and air sensitive, even in solid state. The solid samples can be stored
under argon for few days in the dark at 5°C. The complexes 4a–b and 5a–b were characterized by multinuclear NMR, IR,
UV–vis, and Mo¨ssbauer spectroscopies, mass spectrometry and cyclic voltammetry. Their electronic structures are discussed in
connection with the spectroscopic data. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Organoiron(II); Iron; Butatrienylidene complex
1. Introduction
cally characterized. These compounds are usually
reported to be reactive intermediates in different reac-
tions. Thus, a ruthenium butatrienylidene was trapped
as a trifluoroacetate adduct [10] whereas a wide variety
of compounds were prepared by addition of protic and
aprotic nucleophiles to such intermediates [11,12]. For
instance, reactions of transient butatrienylidene deriva-
tives with aromatic imines has allowed the access to
complexes containing 1-azabuta-1,3-diene or ethynyl-
quinoline ligands [13].
We have previously reported the synthesis and the
physical properties of a ‘D–CꢀC–CꢀC–A’ carbon
chain. The termini were an organometallic donor (D=
Cp*(dppe)Fe) and an organometallic acceptor (A=
Cp*(CO)2Fe) with quite different electronic densities.
We have found that the electrochemical and spectro-
scopic properties of this molecular assembly are distinct
from those of the individual organoiron building
A large variety of mononuclear transition metal com-
plexes containing highly unsaturated carbon chains are
known:
[M]ꢁ(C)xR2
The importance of metal stabilized carbene (x=1),
vinylidene (x=2), and allenylidene (x=3) complexes
in organometallic chemistry, organic synthesis and
catalysis is now well established and has been the
subject of several reviews [1–6]. Complexes with pen-
tatetraenylidene (x=5) ligands coordinated to Ru [7],
Ir [8], Cr, and W [9] centers were also synthesized.
However, metal complexes containing a butatrienyli-
dene (x=4) ligand were never isolated or spectroscopi-
* Corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01107-3

F. Coat et al. / Journal of Organometallic Chemistry 578 (1999) 76–84
77
Scheme 1.
blocks. This establishes the key role played by the
all-carbon spacer which acts as a polarized molecular
wire [14,15]. We now report the reactivity of the D–
CꢀC–CꢀC–A core (D=Cp*(dppe)Fe, Cp*(dippe)Fe
and A=Cp*(CO)2Fe) towards different electrophiles
(HBF4, CH3OSO2CF3) together with the synthesis, the
isolation, and the characterization of the first thermally
stable butatrienylidene complexes.
with a diethylether solution of HBF4 · Et2O immediately
darkens the initially ruby-red solution from which a
precipitate can be recovered by addition of n-pentane.
After removal of the supernatant liquor, the solid was
washed with diethylether. Compound 4a was isolated in
a 75% yield as purple powder and identified as iron
butatrienylidene complex [Cp*(P2)Fe{ꢁCꢁCꢁCꢁC(H)Fe-
(CO)2Cp*}][BF4] (Scheme 2). Complex 4b was prepared
in a similar way using diethylether as solvent. Both
compounds 4a and 4b are unstable and light sensitive in
solution at 20°C. They are also very air and moisture
sensitive even in solid state. Nevertheless, the solid
samples can be stored for few weeks in the dark at 5°C.
Complexes 4a–b were characterized by NMR, IR,
UV–vis, and Mo¨ssbauer spectroscopies, mass spec-
trometry and cyclic voltammetry. Attempts to grow
crystals and to prepare analytically pure samples were
unsuccessful due to the slow but unavoidable decompo-
sition of these compounds in solution even at low
temperature.
In order to gain more information from an analog
likely to be more stable, synthesis of the tertiary buta-
trienylidene iron derivatives, [Cp*(P2)Fe{ꢁCꢁCꢁCꢁC-
(CH3)Fe(CO)2Cp*}][OSO2CF3] (5a–b) was undertaken.
These complexes were made by methylation of the
precursors 3a–b, using methyl triflate as the elec-
trophilic reagent. Whereas 5b was obtained easily in
Et2O, the complex in the dppe series 5a was quite
difficult to recover from the reaction medium. The
microcrystalline solid went partly through the glass and
paper filters used. The complexes 5a and 5b appear
slightly more stable in solution and less moisture sensi-
tive than the secondary butatrienylidene 4a and 4b.
2. Results and discussion
2.1. Synthesis and characterization of binuclear v-buta-
diyndiyl complex Cp*(dippe)Fe(CꢀCCꢀC)Fe(CO)2Cp*
(3b)
Complex 3b was prepared by activation of the termi-
nal butadiyne Cp*(CO)2FeCꢀCCꢀCH (2) with the
chloro iron complex Cp*(dippe)FeCl (1b) in the pres-
ence of KPF6 and KOBut following the procedure
previously described for Cp*(dppe)Fe(CꢀCCꢀC)Fe-
(CO)2Cp* (3a, Scheme 1) [14]. The binuclear complex
3b was isolated as a red powder after recrystallization
from pentane at −20°C in a 77% yield. Interestingly,
similar reactions of the trimethylsilylbutadiyne or the
bis(trimethylsilyl)butadiyne with Cp*(dppe)FeCl (1a)
did
not
afford
the
mononuclear
complex
Cp*(dppe)FeCꢀC–CꢀCR (R=H, or SiMe3) but the
binuclear symmetric compound Cp*(dppe)FeCꢀC–
CꢀCFe(dppe)Cp*. This latter complex was also at the
origin of very interesting properties [16]. The second
activation of a s-metallated butadiynyl ligand is a very
favored reaction. On the other hand, our attempts to
isolate a monometallated precursor in the absence of
base were not successful either. The reaction of the
chloro complex 1a with Me3SiCꢀCCꢀCH under neutral
conditions produces the allenylidene complex
[Cp*(dppe)Fe(ꢁCꢁCꢁC(OCH3)CH3][BPh4] (6) which re-
sults from an addition of methanol to the putative
butatrienylidene intermediate [Cp*(dppe)Fe(ꢁCꢁCꢁ
CꢁCH2)][BPh4] [17].
However,
attempts
to
grow
crystals
from
dichloromethane/pentane or THF/pentane mixtures (at
5°C in dark) also failed, with only decomposition mate-
rials being recovered.
2.3. IR and NMR characterization of the
butatrienylidene complexes
[Cp*(P2)Fe{ꢁCꢁCꢁCꢁC(E)Fe(CO)2Cp*}][BF4]
(P2=dppe, E=H, 4a; P2=dippe, E=H, 4b;
P2=dppe, E=CH3, 5a; P2=dippe, E=CH3, 5b)
2.2. Synthesis of the butatrienylidene complexes
[Cp*(P2)Fe{ꢁCꢁCꢁCꢁC(E)Fe(CO)2Cp*}][BF4]
(P2=dppe, E=H, 4a; P2=dippe, E=H, 4b;
P2=dppe, E=CH3, 5a; P2=dippe, E=CH3, 5b)
Comparison of the IR spectra of 3a–b with those of
the corresponding cationic complexes 4a–b and 5a–b
Treatment of a dichloromethane solution of 3a [14]

78
F. Coat et al. / Journal of Organometallic Chemistry 578 (1999) 76–84
Scheme 2.
reveals a weak decrease of the two wCO frequencies (ca.
3–15 cm−1). Thus, the electron density on the
Cp*Fe(CO)2 moiety decreases slightly, but the fre-
quency is still suggestive of a neutral iron(II) center.
The IR bands corresponding to the butatrienylidene
stretch are difficult to assign with certainty. A vibration
mode is observed in the IR spectrum of these com-
pounds at (w, cm−1, Nujol) 1952, 1945, 1942, 1946 for
4a, 4b, 5a, and 5b, respectively. The position of this
band is quite close to that of the wCꢁCꢁC observed for the
metal–allenylidene complexes [3]. This band is not
present in the spectra of 3a–b and could be attributed
to CꢁC band stretching of the butatrienylidene. How-
ever, in the dppe series, the spectra display other ab-
sorption bands at {w, cm−1, Nujol (CH2Cl2)} 1776
(1892, 1905) and 1830, 1882 (1863, 1882) for 4a and 4b,
respectively. Similar bands were not observed in the
spectra of the corresponding complexes of the dippe
series, but it cannot be excluded that these bands also
originate from another vibration mode of the buta-
trienylidene ligand. At this point, it is also important to
emphasize the absence of a band in the 1500–1650
cm−1 range. This allows us to exclude the presence of
an ethynylvinylidene bridge between the iron centers
(vide infra).
butatrienylidene group than for the secondary one. In
the complexes 4a and 4b, the four resonances of the
carbon chain were assigned making the assumption that
Ca would have the lowest field shift and the chemical
shifts of the carbon atoms would gradually move upfi-
eld as one moves along the chain and on the basis of
the JCP and JCH coupling constants. Note that only the
2JCP coupling was observed whereas the 1JCH, 2JCH, and
3JCH were clearly visible in the 13C-NMR spectra of 4a
2
3
and 4b. The difference between the JCH and JCH
coupling constants is small, therefore the Cb and Cg
resonances cannot be definitely assigned.
Assignment of the carbon resonances for the
methylbutatrienylidene ligands are achieved on the ba-
2
sis of the JCH which indicates that the methyl group is
bound to the Cd atom. The Cb and Cg resonances of 5a
and 5b were assigned by analogy to the compounds 4a
and 4b. The Ca, Cb, and Cg resonances of the buta-
trienylidene are upfield shifted relative to the corre-
sponding resonances of butadiynediyl bridge in the
binuclear precursors 3a and 3b [14]. In contrast, and in
agreement with its sp2 hybridization, the Cd is
downfield shifted with respect to 4a and 4b.
2.4. Mo¨ssbauer characterization of the butatrienylidene
complexes
The 13C-NMR resonances of the –C4– chain were
easily observed, and are quite similar for the four
butatrienylidene iron complexes (Table 1). The carbon
resonances are downfield shifted when the dppe ligand
is replaced by the dippe. Moreover, all the resonances
of the –C4– spacer are less shifted for the tertiary
The Mo¨ssbauer spectra of microcrystalline samples
of the iron complexes 3a, 4a, 5a and 5b are characteris-
tic of pure bis(iron) complexes with two different envi-
ronments around the metal centers. As depicted (Fig. 1)
for complex 4a, the experimental Mo¨ssbauer spectra of
these compounds display two quadrupole doublets. As-
suming that the two doublets have the same surface, a
single set of fitting parameters was obtained (Table 2).
The doublet with the larger isomeric shift, l, was
assigned to the Cp*Fe(P2) iron center. Indeed, larger l
values were invariably observed in this series, either for
neutral or cationic mononuclear complexes, than in the
Cp*Fe(CO)2 series [17]. Moreover, the isomeric shift of
the Cp*Fe(P2) unit in the butatrienylidene complexes is
smaller than the value determined for the same iron
unit in the neutral complex 3a. As l is generally related
to the electronic density on the metal center, this obser-
Table 1
13C-NMR chemical shifts (ppm), coupling constants (Hz) for the
butatrienylidene ligands
Compound
Ca
Cb
Cg
Cd
(solvent, T °C)
4a
258.7
167.4
128.3
58.4
(CDCl3, 20)
2JCP=36
260.8
3JCH=8.1 2JCH=8.4 1JCH=180.2
4b
170.9
133.3
59.0
(CD2Cl2, −40) 2JCP=34.8 3JCH=5.7 2JCH=6.0 1JCH=176.6
5a
250.5
149.8
121.6
69.3
(CDCl3, 20)
2JCP=35
264.9
2JCH=18
73.6
5b
166.2
131.9
(Acetone, −40) 2JCP=36
4JCH=6.5 3JCP=2.4 2JCH=7.8

F. Coat et al. / Journal of Organometallic Chemistry 578 (1999) 76–84
79
Fig. 1. Mo¨ssbauer spectrum of 4a at 80 K.
vation is strongly indicative of the localization of the
positive charge on the Cp*Fe(P2) fragment in 4 and 5.
On the other hand, the Mo¨ssbauer parameters of the
Cp*Fe(CO)2 group in the butatrienylidene complexes
are characteristic of the Fp* fragment and compare
very well with those of the complex Cp*Fe(CO)2Me
taken as a reference compound [18]. The parameters
determined for the Cp*Fe(P2) moiety are quite close to
those previously obtained for the allenylidene
[Cp*(dppe)Fe{ꢁCꢁCꢁC(OCH3)CH3}][BPh4] (6) in the
same iron series. In the Cp*Fe(dppe)L series, we have
found that a quadrupole splitting in the range 1.0–1.5
is diagnostic of an iron–carbon double bond between
the metal and the terminal sp hybridized carbon atom
of the ligand L. Moreover, we observed that the larger
the quadrupole separation is, the weaker the strength of
the iron–carbon p-bond will be [17]. Accordingly, the
decrease of DEQ from 5a to 5b constitutes an indication
of the increase of the bond order between the iron and
the carbon ligand concomitantly with the electron re-
leasing properties of the coordinated organometallic.
Note that significantly smaller DEQ were found for the
stable vinylidene complexes in the same series [17].
Finally, since most of the organometallic fragments are
less electron rich than the Cp*Fe(P2) group, they possi-
Scheme 3.
bly coordinate butatrienylidene ligands less strongly,
and consequently the C4 ligand may be more reactive
(see below).
Comparison of the spectroscopic data of the buta-
trienylidene with those of allenylidene transition metal
complexes for which both X-ray and spectroscopic data
are available, is instructive. Several studies suggested
that there is a significant contribution to electron distri-
bution from two mesomeric forms: [MꢁCꢁCꢁCR2]+
and [M–CꢀC–CR2]+ [11,19,20]. Thus, the electron
delocalization for the butatrienylidene derivatives 4 and
5 can be depicted by the three resonance structures A,
B and C of Scheme 3. These were previously proposed
to account for the reactivity of related compounds as
intermediates [13]. In agreement with a relatively weak
FeꢁC p-bond suggested by the Mo¨ssbauer quadrupole
splitting parameters, a significant contribution of the
forms B and C in the description of the electron
delocalization for the butatrienylidene complexes ap-
pears plausible. It is noteworthy that the 13C chemical
shifts of the butatrienylidene fragment compare well
with those of the hetero allenylidene 6 and other al-
lenylidenes reported from other groups [11,17,21]. Such
a comparison between allenylidene and butatrienylidene
complexes has however to be regarded with caution
since these two kinds of compounds have different
stabilities. It has been pointed out, from X-ray data for
purely organic molecules, that there is a clear difference
between cumulenes with even and odd numbers of
double bonds. In both cases some triple bond character
was observed for internal bonds [22].
Table 2
57Fe Mo¨ssbauer fitting parameters determined at 80 K for com-
pounds 3–5
Compound
Cp*Fe(P2)
Cp*Fe(CO)2
l
DEQ
l
DEQ
(mm s−1
)
(mm s−1
)
(mm s−1
)
(mm s−1
)
3aa
4a
5a
5b
6b
0.257
0.161
0.163
0.170
0.160
1.973
1.316
1.424
1.264
1.451
0.029
0.087
0.103
0.094
1.974
1.888
1.786
1.778
c
Fp*CH3
0.120
1.88
a From Ref. [14].
b From Ref. [17].
c From Ref. [18].

80
F. Coat et al. / Journal of Organometallic Chemistry 578 (1999) 76–84
2.5. UV–6is absorption of the complexes 4a–b and
5a–b
All the new compounds show a deep purple color
that has no counterpart in the corresponding
monometallic species. For example alkynyl and bu-
tadiynyl complexes show only an intense UV absorp-
tion that tails into the visible and accounts for the
orange color of these complexes [23]. The visible spectra
of the butatrienylidene compounds show a characteris-
tic absorption at (u, nm; m/103, M−1 cm−1) 527 (15.5),
546 (15.6), and 538 (13.6) for 4a, 5a, 5b, respectively.
Due to the high sensitivity of these compounds to light,
air and moisture, the real values of the molecular
extinction coefficient m are certainly higher than the
determined values. Indeed, the intensity of the absorp-
tion band decreases during the measurement and con-
comitantly a new absorption band appears in the red
(Fig. 2). The evolution is particularly fast for the sec-
ondary iron butatrienylidene complexes 4a–b. In the
Schlenk cell, the disappearance of the spectrum of 3a is
complete in ca. 30 min and the final spectrum corre-
sponds to a mixture of unidentified species. In the
initial spectrum of 4a, the mixed valence complex
[Cp*(dppe)Fe–CꢀC–CꢀC–Fe(CO)2Cp*][PF6] (3a+) is
clearly detected (see Fig. 2 and Section 2.6). The solvent
effects were probed with 4a as a representative complex
in this series (u, nm; toluene/CH2Cl2/acetonitrile; 528/
527/524). The position of the maxima varied only very
slightly with polarity indicating similar ground and
excited state polarities. Some allenylidene and related
complexes are also intensely colored with a strong
absoptions in the 500–600 nm region assigned to
charge-transfer bands [24]. In our series of iron buta-
trienylidene complexes, the optical transition centered
in the 520–550 nm range would be consistent with
charge transfer from an iron (of the Cp*(dppe)Fe unit)
based orbital.
Fig. 3. Cyclic voltammograms for 3a, 4a, and 5a in 0.1
[nBu4N][PF6]/CH2Cl2 (Pt electrode, V vs. SCE, scan rate 0.100 V
−1).
M
s
THF. After 15 min of reaction, the dimetallabu-
tadiynediyl complex 3a was almost quantitatively re-
covered and identified by 1H-NMR, IR and cyclic
voltammetry (CV). The facile deprotonation of 4a indi-
cates that the butatrienylidene complexes should be
more acidic than the corresponding allenylidene de-
scribed as resistant to deprotonation in the Ru series
[21]. More surprisingly, we found by CV that 4a is
partly deprotonated by water.
The initial scans in the CV of the complex 4a be-
tween 1.0 and −1.5 V at a platinum electrode
(dichloromethane, 0.1 M tetrabutylammonium hex-
afluorophosphate, 0.100 V s−1, 20°C, Fig. 3) display a
complex behavior corresponding to the presence of
both the complexes 3a and 4a in the electrochemical cell
(Scheme 4). Starting from −0.600 V the oxidation
waves a and c belong to the redox couple 3a/3a+ and
3a+/3a+ +, respectively, as previously described [14].
The waves b and d are characteristic of the butatrienyli-
dene complex 4a. The surprising formation of 3a in the
electrochemical cell is attributed to the reaction of 4a
with adventitious traces of water. This assumption was
confirmed by addition of small amounts of water which
produced the decrease in the current corresponding to
the waves b and d and, conversely, the increase of the
waves a and c. Addition of a base like DBU or NEt3 in
the cell also produced the total disparition of the waves
b and d. An irreversible reduction of 4a is also observed
on the CV (Fig. 3, Table 3) in addition to the reversible
oxidation of 4a.
2.6. Acidic and redox properties of the butrienylidene
iron complexes 4a–b and 5a–b
In order to gain information on the acidity of the
hydrogen atom on Cd of the butatrienylidene ligand, 4a
was reacted with one equivalent of DBU at −80°C in
In the case of 4b, the CV displays a similar behavior
with a shift of the potential towards the negative values
(Table 3). The deprotonation of the butatrienylidene
complex 4b by water is more difficult and the wave a is
Fig. 2. Visible spectra of 3a, 4a, and 5a (CH2Cl2, 20°C, 10−4 M).

F. Coat et al. / Journal of Organometallic Chemistry 578 (1999) 76–84
81
Scheme 4.
Table 3
tron-rich as one moves along the chain from the metal
atom [24,25]. Considering a polyyne with two different
organometallic building blocks s-bound at both ends
there are formally two different electronic structures for
the carbon chain (A1, A2, Scheme 5). The terminal
electron-poor and electron-rich carbon could be con-
nected either to the more or the less electron releasing
metal centers. From this work, it is strongly suggested
that the most electron rich terminal carbon atom is
bound to the electron poor metal center and conversely,
the most electron poor one is connected to the most
electron-rich iron atom (structure A1). A steric control
of the reaction cannot definitely be excluded, however
we think this alternative unlikely, especially for the
protonation reaction in the dippe series.
Electrochemical data for compounds 3–5, in CH2Cl2 (0.1
M
[nBu4N][PF6]; 20°C; Pt electrode; sweep rate 0.100 V s−1 a
)
c
Compound
E0
DEp
ic/ia
3ab
3b
4a
4b
5a
5b
−0.36
+0.74
−0.53
+0.69
−1.13
+0.40
−0.88
0.35
0.07
0.07
0.06
0.06
1
0.9
1
1
NR
1
0.07
0.09
0.07
0.08
NR
0.9
−1.13
+0.40
1
1
c
+0.28
The reaction is highly specific since only the buta-
trienylidene compounds were observed even after anal-
ysis of the isolated crude materials. We have no
experimental evidence to know whether the isolated
material is the kinetic or the thermodynamic product of
the reaction. In fact, both molecules C and B should
have almost the same stability, as was shown by ab
initio calculations for the related ligands :CꢁCHCꢀCH
and :CꢁCꢁCꢁCH2 [26].
From a molecular electronics point of view the reac-
tions depicted in Scheme 4 are relevant from the con-
cept of molecular switches [27–29]. Indeed, the study of
physical properties of the mixed-valence complex 3a+
allowed evidence that this molecule acts as a wire [14].
The reduction of 3a+ followed by its protonation
switches off the electronic exchange between the remote
ends and also locks it chemically. Thus this communi-
cation can be restored either by the reverse operations,
i.e. chemical deprotonation and one-electron oxidation
at the same potential, or by another one-electron oxida-
tion at a more positive potential, producing a sponta-
neous deprotonation to give back 3a+.
a V versus SCE, ferrocene–ferrocenium couple (0.460 V/SCE) was
used as an internal reference for the potential measurements.
b From Ref. [14].
c Reduction wave not observed.
c
For the non reversible systems the peak potential is reported
instead of the E0 value.
not clearly observed in the initial scan. The water seems
not to be a strong enough base to deprotonate this
complex. However, in the reverse reduction and in the
following scans, the wave a is present in the voltam-
mogram. For both complexes 4a and 4b, we found that
the current ratio ic/ia for the waves a is always above
unity and increases with the scan rate. This result
’
’
indicates that the radical dication 4a+ + and 4b++
decompose in 3a+ and 3b+, respectively, by sponta-
neous loss of a proton (Scheme 4). The CVs of the
tertiary butatrienylidene complexes 5a and 5b display a
reversible one-electron oxidation process and an irre-
versible reduction process (Fig. 1).
In a related and simultaneous work, we have found
that the formally cumulene complex [Cp*(dppe)-
FeꢁCꢁCꢁCꢁCꢁFe(dppe)Cp*][PF6]2 is in thermal equi-
librium with the paramagnetic diradical form [Cp*-
3. Conclusions
Theoretical calculations on unsaturated carbon
chains s-bound to transition metals indicates that the
carbon atoms are alternatively electron-poor and elec-
’
’
(dppe)Fe – C ꢀ C – C ꢀ C – Fe(dppe)Cp*][PF6]2 [16,30].

82
F. Coat et al. / Journal of Organometallic Chemistry 578 (1999) 76–84
Scheme 5.
The energy gap between the diamagnetic ground state
and the ferromagnetic excited state is small enough to
render the complex paramagnetic at liquid nitrogen
temperature. At that time, we were curious about the
spectroscopic properties of the iron complexes with non
ambiguous metal–butatrienylidene structure. In this re-
spect, this work contributes greatly to our knowledge of
0.194 g of KPF6 (1.056 mmol) and 0.120 g of tBuOK
(1.056 mmol). The mixture was stirred overnight and
allowed to warm up to room temperature. After re-
moval of the solvent under vacuum, the crude residue
was extracted with pentane (2×25 ml). Crystallization
from cold pentane (−20°C) yielded a red powder
which was identified as Cp*(dippe)Fe(CꢀC–CꢀC)Fe-
(CO)2Cp* (0.507 g, 0.67 mmol, 77%). Anal. Calc. for
C40H62P2O2Fe2: C, 64.18, H, 8.35, P, 8.3. Found: C,
such carbon rich bridges. In particular, it is now more
+ +
’
’
and more clear that the {Fe –CꢀC–CꢀC– Fe}
and {FeꢁCꢁCꢁCꢁCꢁCꢁCꢁCꢁCꢁFe}+ + might be distin-
guished from their Mo¨ssbauer quadrupole splittings.
This point is of importance, since a cumulenic structure
was found for the related rhenium complex [31]. Cur-
rent work is now underway in order to control the
magnetic properties of these molecules and their evolu-
tion either upon bridge extension or upon tuning of
electronic properties of the terminal ends.
64.36, H, 8.31, P, 8.0. FTIR (Nujol, cm−1): 2112(w,
1

CꢀC), 2019,1969 (vs, CO). H-NMR: (300 MHz, C6D6,
25°C): lH=3.08, 2.08 (m, 2×2H, CH isopropyl); 1.75
(m, 4H, CH2); 1.75 (s, 15H, [Fe(C5Me5)(dippe)]); 1.49
(s, 15H, [Fe(C5Me5)(CO)2]); 1.44, 1.25 and 0.92, 1.05
(m, 2×12H, CH3 isopropyl). 13C-NMR {1H} (75
MHz, C6D6, 25°C): lC=216.0 (s, CO); 111.7 (t, Ca,
3
2JCP=39 Hz); 106.5 (t, Cb, JCP=2 Hz); 102.5 (t, Cg,
4JCP=2 Hz); 65.0 (s, Cd); 96.5 (s, [Fe(C5Me5)(CO)2]);
85.9 (s, [Fe(C5Me5)(dippe)]); 27.4, 25.5 (m, CH iso-
propyl); 22.0, 19.9 and 21.1, 19.2 (m, CH3 isopropyl);
19.6 (m, CH2–P); 11.6 (q, [Fe(C5Me5)(CO)2]); 9.74 (m,
[Fe(C5Me5)(dippe)]). 31P-NMR (121.5 MHz, C6D6,
25°C): lP=98.9 (s).
4. Experimental
4.1. General data
Reagent grade THF, diethylether and n-pentane were
dried and distilled from sodium benzophenone ketyl
prior to use. Pentamethylcyclopentadiene was prepared
according to the published procedure [32] and other
chemicals were used as received. All the manipulations
were carried out under an argon atmosphere using
Schlenk techniques or in a Jacomex 532 dry box under
nitrogen. The FTIR spectra were recorded using Nico-
let instrument (Model 205) and KBr windows. High
field NMR spectra experiments were performed on a
4.3. [Cp*(dppe)Fe{ꢁCꢁCꢁCꢁCꢁ(H)Fe(CO)2Cp*}][OTf]
(4a)
Complex 3a (0.270 g, 0.30 mmol) was dissolved in
dichloromethane (20 ml, −70°C). To this cold solution
48 ml of a commercial solution of HBF4 · Et2O 85% in
diethylether (0.27 mmol) was added under argon and
the reaction medium was allowed to come back to
−20°C with stirring over 1 h. The purple solution was
subsequently concentrated (5 ml) and an excess of
n-pentane was added to precipitate the complex 4a as a
purple powder, which was washed with several frac-
tions of 10 ml diethylether and dried in vacuo to give
0.210 g of [{Fe(h5-C5Me5)(h2-dppe)}(m2ꢁCꢁCꢁCꢁCH)-
{Fe(h5-C5Me5)(CO)2}][BF4] (75%). FTIR (KBr/Nujol,
cm−1) w 2015, 1966 (s, CO); 1952, 1882, 1830 (w,
CꢁCꢁC); 1052 (vs, BF4−). (KBr/CH2Cl2, cm−1) w 2015,
1964 (s, CO); 1882, 1863 (w, CꢁCꢁC), 1060 (vs, s,
BF4−). 31P-NMR (121 MHz, CDCl3, 20°C) lP=94.4 (s,
dppe). 19F-NMR (188 MHz, CDCl3) lF= −154.8 (s,
multinuclear
Bruker
300
MHz
instrument
(AM300WB). Chemical shifts are given in ppm relative
to TMS for 1H- and 13C-NMR spectra, H3PO4 for
31P-NMR spectra. Elemental analyses were performed
at the Center for Microanalyses of the CNRS at Lyon-
Solaise, France. Mo¨ssbauer spectra were recorded with
a 2.5×10−2 C (9.25×108 Bq) 57Co source using a
symmetric triangular sweep mode.
4.2. Cp*(dippe)Fe(CꢀC–CꢀC)Fe(CO)2Cp* (3b)
1
To a solution of 0.260 g Cp*Fe(CO)2(CꢀC–CꢀCH)
(0.88 mmol) in MeOH (50 ml) at −80°C was added
successively 0.440 g of Cp*Fe(dippe)Cl (0.88 mmol),
BF4−). H-NMR (300 MHz, CDCl3, 20°C) lH 7.60−
7.10 (m, 20H, Ph); 3.86 (s, 1H, CdH–); 2.90; 2.55 (2m,
4H, CH2(dppe)); 1.72 (s, 15H, {(C5Me5)Fe(dppe)}); 1.42

F. Coat et al. / Journal of Organometallic Chemistry 578 (1999) 76–84
83
1
(s, 15H, {(C5Me5)Fe(CO)2}). 13C-NMR (75 MHz,
MHz, CDCl3, 20°C) lF= −78.2 (s, CF3(O)2SO−). H-
NMR (300 MHz, CDCl3, 20°C) lH 7.60–7.10 (m, 20H,
Ph); 2.95; 2.55 (2m, 4H, CH2(dppe)); 2.07 (s, 3H,
ꢁCꢁC(CH3)–Fe); 1.62 (s, 15H, (C5Me5)Fe(dppe)); 1.42
(s, 15H, (C5Me5)Fe(CO)2). 13C-NMR (75 MHz, CDCl3)
lC 250.5 (t, 2JCP=35 Hz, Ca); 215.1 (s, CO); 149.8
(s,Cb); 136.1–128.6 (m, Phdppe); 121.5 (q, 1JCF=321
2
CDCl3, −40°C) lC 258.7 (t, JCP=36 Hz, Ca); 215.5
(s, CO); 167.5 (s, 3JCH=8.1, Cb); 135.0–133.1 (m, Cipso
,
,
Ph); 133.6 (m, Cortho, Ph); 131.3 (d, 3JCP=26 Hz, Cmeta
2
Ph); 128.8 (s, Cpara, Ph); 128.5 (s, JCH=168.4, Cg);
97.2 (s, {(C5Me5)Fe(CO)2}); 97.0 (s, {(C5Me5)Fe-
1
(dppe)}); 58.6 (s, JCH=183 Hz, Cd); 30.9 (m, CH2);
10.0 (q, 1JCH=128 Hz, {(C5Me5)Fe(dppe)} and
{(C5Me5)Fe(CO)2}). UV–vis (CH2Cl2) umax (m dm3
M−1 cm−1) 526 nm (]15200). MS (FAB+, m-NBA)
m/z 885 (M–BF4−, 70%); 828 (M–{BF4+H+2CO},
35%); 638 (M–{BF4+Fp}, 30%); 589 (M–{BF4+
H+CꢀCCꢀC–Fp}, 100%).
Hz, CF3S(O)2O− and Phdppe); 121.6 (q, JCH=7 Hz,
Cg); 97.9 (s, (C5Me5)Fe(CO)2); 96.4 (s, (C5Me5)-
Fe(dppe)); 69.3 (s, JCH=183 Hz, Cd(Me)); 31.0 (m,
3
2
1
CH2); 16.5 (q, JCH=127 Hz, ꢁCꢁCꢁCꢁC(Me)–); 10.2
(q, 1JCH=127 Hz, (C5Me5)Fe(dppe)); 9.8 (q, JCH
=
1
128 Hz, (C5Me5)Fe(CO)2}). UV–vis (CH2Cl2) umax (m
dm3 M−1 cm−1) 546 nm (]15540). MS (FAB+, m-
NBA) m/z, 889.3 (M–{CF3S(O2)O−}), 652.2 (M–
4.4. [Cp*(dippe)Fe{ꢁCꢁCꢁCꢁC(Me)Fe(CO)2Cp*}][BF4]
(4b)
{CF3S(O2)O−}–{Cp*Fe(CO)2}),
(dppe)+).
589.0
(Cp*Fe-
To a −60°C solution of 3b (0.446 g, 0.59 mmol) in
diethylether (20 ml), were added 111 ml of HBF4 · Et2O
(0.65 mmol) and the solution was allowed to warm up
to 20°C upon stirring (1 h). After additon of pentane
(75 ml), the solution was removed and the precipitate
washed with pentane (2×20 ml). Complex 4b was
isolated as a pink powder (0.460 g, 93%). FTIR (Nujol,
cm−1): 2003, 1962 (vs, CO), 1945 (w, CꢁCꢁC). 1H-NMR
(300 MHz, CD2Cl2, −40°C) lH 3.54 (s, CꢁCH); 1.71
(s, 15H, (C5Me5)Fe(dippe)); 1.65 (s, 15H, (C5Me5)-
Fe(CO)2); 1.40–1.02 (m, isopropyl). 13C-NMR (75
4.6. [Cp*(dippe)Fe{ꢁCꢁCꢁCꢁC(Me)Fe(CO)2Cp*}]-
[OSO2F3] (5b)
To a −80°C diethyl ether solution (20 ml) of 3b
(0.360 g, 0.48 mmol) 59.8 ml (0.53 mmol) of
MeOSO2CF3 were added and the solution was allowed
to warm up upon stirring. A pink suspension was
formed at −60°C, but the compound essentially re-
mained in solution. An excess of pentane (100 ml) was
added at 20°C to precipitate the salt. After filtration a
purple powder was obtained and washed twice with
pentane (20 ml) to give 0.330 g of 5b (75%). FTIR
(Nujol, cm−1): 2004, 1957 (CO), 1946 (CꢁCꢁC). 1H-
NMR (300 MHz, C3D6O, −40°C) lH 2.09 (s, 3H,
Me–CꢁC); 1.85 (s, 15H, (C5Me5)Fe(dippe)); 1.77 (s,
15H, (C5Me5)Fe(CO)2); 1.06–1.50 (m, dippe). 13C-
NMR (75 MHz, C3D6O, −40°C): lC=264.9 (t, Ca,
2
MHz, CD2Cl2, −40°C) lC=260.8 (t, Ca, JCP=34.8
3
Hz); 216.5 (s, CO); 170.9 (d, Cb, JCH=5.7 Hz); 133.3
2
(d, Cg, JCH=6 Hz); 97.2 (s, [(C5Me5)Fe(CO)2]); 96.9
1
(s, [(C5Me5)Fe(dippe)]); 59.0 (d, Cd, JCH=176.6 Hz);
29.5, 25.1 (m, CH isopropyl); 22.0, 19.5, 19.0, 18.8 (m,
1
CH3 isopropyl); 10.3 (q, [(C5Me5)Fe(CO)2], JCH=127
Hz); 9.9 (s, [(C5Me5)Fe(dippe)], 1JCH=128 Hz). 31P-
NMR (121.5 MHz, CD2Cl2, −40°C, H3PO4 ext): lP=
94.3 (s, dippe).
3
2JCP=35.8 Hz); 217.0 (s, CO); 166.2 (tq, Cb, JCP=2.4
Hz, 4JCH=6.5 Hz); 131.9 (s, Cg); 98.4 (s,
[(C5Me5)Fe(CO)2]); 96.9 ([(C5Me5)Fe(dippe)]); 73.6 (q,
4.5. [Cp*(dppe)Fe{ꢁCꢁCꢁCꢁC(Me)Fe(CO)2Cp*}]-
[OSO2CF3] (5a)
Cd, 2JCH=7.8 Hz); 29.5, 25.6 (m, CH isopropyl, 1JCP
=
5.7 Hz); 22.6 (q, CH3, 1JCH=128 Hz); 20.0, 19.5, 18.9,
18,7 (m, CH3 isopropyl); 19.7, 19.2 (m, CH2–P); 10.9
(q, [(C5Me5)Fe(CO)2], 1JCH=127 Hz); 9.9 (q,
[(C5Me5)Fe(dippe)], 1JCH=128 Hz). 31P-NMR (121.5
MHz, C3D6O, −40°C): lP=95.2 (s, dippe).
Complex 3a (0.270 g, 0.97 mmol) was dissolved in
dichloromethane (20 ml) and the solution was cooled to
−70°C. To this solution 30 ml of methyl triflate (0.28
mmol) were added and the reaction medium was al-
lowed to come back to −20°C upon stirring over 1 h.
The ruby-red color of the reaction medium darkens
upon addition. The purple solution was subsequently
concentrated (5 ml) and an excess of n-pentane was
added to precipitate the complex 5a as a purple pow-
der, which was washed with two fractions of 5 ml
diethylether and dried in vacuo to give 0.070 g of 5a
(22%). FTIR (KBr/Nujol, cm−1) w 2015, 1949 (s, CO);
4.7. Deprotonation of 4a
To a −80°C THF solution (10 ml) of 4a (0.070 g,
0.07 mmol.) 1.0 equivalent of 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU, 0.011 g) were added. After
stirring 15 min the solution was warmed up to 20°C
and the solvent removed under reduced pressure. After
extraction of the crude residue with diethyl ether a red
1942, 1905, 1892 (w, CꢁCꢁC). IR (KBr/CH2Cl2, cm−1
)
w 2016, 1964 (s, CO); 1949 (w, CꢁCꢁC). 31P-NMR (121
MHz, CDCl3, 20°C) lP=95.2 (s, dppe). 19F-NMR (188
powder characterized by H-NMR, IR and CV as 3a
1
was quantitatively recovered.

84
F. Coat et al. / Journal of Organometallic Chemistry 578 (1999) 76–84
[15] F. Paul, C. Lapinte, Coord. Chem. Rev. 178–180 (1998) 427.
Acknowledgements
[16] N. Le Narvor, L. Toupet, C. Lapinte, J. Am. Chem. Soc. 117
(1995) 7129.
[17] V. Guillaume, P. Thominot, F. Coat, A. Mari, C. Lapinte, J.
Organomet. Chem. 565 (1998) 75.
We thank the French Ministe`re MENESER for
award thesis grant to F. Coat and M. Guillemot.
[18] D. Catheline, D. Astruc, Organometallics 3 (1984) 1094.
[19] A. Wolinska, D. Touchard, P.H. Dixneuf, A. Romero, J.
Organomet. Chem. 420 (1991) 217.
[20] J.P. Selegue, Organometallics 1 (1982) 217.
[21] N. Pirio, D. Touchard, P.H. Dixneuf, M. Fettouhi, L. Ouahab,
Angew. Chem. Int. Ed. Engl. 31 (1992) 651.
[22] H. Irngartinger, W. Gotzmann, Angew. Chem. Int. Ed. Engl. 25
(1986) 340.
References
[1] M.I. Bruce, A.G. Swincer, Adv. Organomet. Chem. 22 (1983) 59.
[2] M.I. Bruce, A.G. Swincer, Adv. Organomet. Chem. 52 (1987)
3940.
[3] M.I. Bruce, Chem. Rev. 91 (1991) 197.
[23] H.P. Xia, W.F. Wu, W.S. Ng, I.D. Williams, G. Jia,
Organometallics 16 (1997) 2940.
[24] N.M. Kostic, R.F. Fenske, Organometallics 1 (1982) 974.
[25] B.E.R. Schilling, R. Hoffmann, D.L. Lichtenberger, J. Am.
Chem. Soc. 101 (1979) 585.
[26] C.E. Dykstra, C.A. Parsons, C.L. Oates, J. Am. Chem. Soc. 101
(1979) 1962.
[27] S.L. Gilat, S.H. Kawai, J.M. Lehn, Chem. Eur. J. 1 (1995) 275.
[28] S.H. Kawai, S.L. Gilat, R. Ponsinet, J.-M. Lehn, Chem. Eur. J.
1 (1995) 285.
[29] S.L. Gilat, S.H. Kawai, J.-M. Lehn, Mol. Cryst. Liq. Cryst. 246
(1994) 232.
[30] N. Le Narvor, C. Lapinte, C.R. Acad. Sci. Paris, T1, Se´r. IIc,
(1998) 745.
[31] M. Brady, W. Weng, Y. Zhou, J.W. Seyler, A.J. Amoroso, A.M.
Arif, M. Bo¨hme, G. Frenking, J.A. Gladysz, J. Am. Chem. Soc.
119 (1997) 775.
[4] H. Werner, Nachr. Chem. Tech. Lab. 40 (1992) 435.
[5] H. Werner, J. Organomet. Chem. 475 (1994) 45.
[6] M.I. Bruce, Coord. Chem. Rev. 166 (1997) 91.
[7] D. Touchard, P. Haquette, A. Daridor, L. Toupet, P. Dixneuf, J.
Am. Chem. Soc. 116 (1994) 11157.
[8] R.W. Lass, P. Steinert, J. Wolf, H. Werner, Chem. Eur. J. 2
(1996) 19.
[9] G. Roth, H. Fischer, T. Meyer-Friedrichsen, J. Heck, S. Hou-
brechts, A. Persoons, Organometallics 17 (1998) 1511.
[10] J.R. Lomprey, J.P. Selegue, Organometallics 12 (1993) 616.
[11] M.I. Bruce, P. Hinterding, P.J. Low, B.W. Skelton, A.H. White,
Chem. Commun. (1996) 1009.
[12] R.F. Winter, F.M. Hornung, Organometallics 16 (1997) 4248.
[13] M.I. Bruce, P. Hinterding, P.J. Low, B.W. Skelton, A.H. White,
J. Chem. Soc. Dalton Trans. (1998) 467.
[14] F. Coat, M.-A. Guillevic, L. Toupet, F. Paul, C. Lapinte,
Organometallics 16 (1997) 5988.
[32] F.X. Kohl, P. Jutzi, J. Organomet. Chem. 243 (1983) 119.
.