64
G. Agonigi et al. / Journal of Organometallic Chemistry 731 (2013) 61e66
þ
þ
According to the calculations, compounds [6] and [3] have
similar enthalpy values both in the gas-phase and in CH Cl H is
comprised between 1 and 2 kcal mol ). This fact prompted us to
PerkineElmer Spectrometer equipped with a UATR sampling
accessory (solid samples). NMR measurements were performed at
298 K (unless otherwise stated) on Bruker Avance DRX400 in-
strument equipped with probe BBFO broadband. The chemical
2
2
(D
ꢁ1
þ
þ
find a route for the possible conversion of [3] into its isomer [6]
via hydrogen intramolecular migration. Heating a solution of [3]
BF ] in acetonitrile at reflux temperature resulted in prevalent
decomposition [compound Fe Cp (CO) was recovered in ca. 25%
yield], while analogous treatment in boiling CHCl or (CH Cl) so-
lution was ineffective. The employment of small amounts of a po-
1
13
shifts for H and C NMR spectra were referenced to the non
deuterated aliquot of the solvent; the spectra were fully assigned
[
4
1
13
2
2
4
via DEPT experiments and H, C correlation measured through gs-
HSQC and gs-HMBC experiments [14].
3
2
2
Apparatus and techniques for the electrochemical measure-
tential catalyst such as NHEt
outcomes of these processes.
2
did not influence significantly the
ments were previously described [7]. Electrochemical measure-
n
ments were performed in 0.2 M CH
2
Cl
2
solutions of [N Bu
4
][PF
6
] as
þ
The reaction of 1 with HBF
4
$Et
2
O, affording [3] , is the reverse of
supporting electrolyte and all potential values were referenced to
the ferrocene/ferrocenium couple (ferrocene was added as internal
reference).
Carbon and hydrogen analyses were performed on Carlo Erba
mod. 1106 instrument.
the formation of 1 by deprotonation of [3][BF
4
] [3a]. The synthetic
þ
þ
sequence [3] / 1 / [2] represents a feasible route for the
functionalization of the allenyl ligand, proceeding via CeH activa-
tion and CeC bond formation. The overall result involves the
þ
incorporation of the [CPh
3
]
group with the displacement of the
The computational geometry optimization of the complexes
was carried out using the hybrid DFT EDF2 method [15] without
symmetry constraints, in combination with the LACVP** basis set,
which is a combination of the 6-31G(d,p) basis set with the
LANL2DZ effective core basis set [16].
þ
acidic proton from the methyl group of [3] . With the aim of
obtaining a functionalized allenyl species by one-pot process, we
allowed [3][BF ] to react with NHEt in the presence of PhSSPh.
4 2
Indeed a similar strategy proved to be efficient for the displacement
þ
þ
þ
þ
of one acidic hydrogen with the [SPh] unit in diiron
m
-vinyl-
] with
/PhSSPh failed to give the expected SPh-functionalized
allenyl complex. Instead the previously reported mononuclear
compound [FeCp(CO) SPh] (7) [12] was isolated in good yield.
Further refining was carried out for 1, [3] , 4, [5] and [6] with
iminium complexes [11]. Nevertheless the reaction of [3][BF
NHEt
4
the hybrid DFT M06 functional [17] in combination with a polarized
triple-z quality basis set composed by the 6-311G(d,p) basis set on
2
the light atoms and the LANL2TZ(f) basis set on the metal centre
[18]. The “restricted” formalism was applied to all the complexes.
The stationary points were characterized by IR simulations, from
which the zero-point vibrational energies were computed. In every
cases the Hessian afforded positive eigenvalues. The thermal con-
tributions to enthalpy were calculated on the basis of statistical
mechanics standard formulae (rigid-rotor approximation). Proton
affinity values were calculated from computed quantities as re-
ported in the literature [19]. Implicit solvation was added during
2
The fragmentation reaction leading to 7 suggests that some
mechanism including the formation of radical species could be
operative. It has to be remarked that previous studies on [3] have
outlined that this complex can be easily monoelectronically
reduced to a radical intermediate bearing most of the unpaired
electron density on the iron centres [8b]. The capture of this metal-
based radical by PhSSPh, acting as radical scavenger, may deter-
mine the breaking of the FeeFe bond and the consequent formation
of 7.
þ
þ
þ
the optimization of [3] and [6] by using the C-PCM model for
dichloromethane [20]. The Fukui’s function f (r) for 1 was obtained
e
from the electron density of this compound and from the electron
density of the same compound missing of one electron [10]. DFT
EDF2 calculations were carried out with Spartan 08 [21], while
Gaussian 09 was used for the calculations based on the M06
functional [22]. All the calculations were performed on x86-64
workstation based on Intel Core I7 processor.
3
. Conclusions
The reactions of a diiron propen-2-yl-dimetallacyclopentenone
þ
þ
3
complex with electrophiles (H , CPh
synthesis of -allenyl derivatives. In particular, the protonation
) result in straightforward
m
reaction represents the reverse of the formation of the propen-2-
yl-dimetallacyclopentenone reactant by deprotonation of the
allenyl product.
1:
h
2
-C
])
4.2. Synthesis of [Fe
2
Cp
2
(CO)
2
(
m
-CO){
m
-
h
a
,
b
a b 3
H]C ]C(CH )
(CH E)][BF
2
4
] (E ¼ CPh
3
, [2][BF
4
]; E ¼ H, [3][BF
4
a b g 2
Therefore the allenyl ligand [eC ]C ]C Me ], bridged coor-
dinated to diiron frame, may be viewed as a feasible material for
organic transformation, occurring via CeH bond activation and
successive CeC formation. Otherwise treatment of such allenyl
species with amine, in the presence of a potential radical scavenger
A solution of complex 1 (0.300 g, 0.765 mmol) in CH
2 2
Cl (15 mL)
was treated with [CPh ][BF ] (0.260 g, 0.788 mmol). The mixture
3
4
was stirred at room temperature for 24 h. Hence the volatile ma-
terials were removed in vacuo. The resulting residue was washed
(
PhSSPh), leads to FeeFe cleavage and formation of a SPh-
with Et
Celite pad. Removal of the solvent afforded a dark-red solid corre-
sponding to [2][BF ] (yield 0.497 g, 90%). Red crystals suitable for X-
2
O (2 ꢂ 20 mL), then dissolved in CH
2 2
Cl and filtered on a
containing monoiron complex.
4
4
. Experimental details
ray analysis were collected from a CH
2
Cl
2
solution layered with
ꢀ
Et
2
O and stored at ꢁ30 C. Anal. Calcd. for C37
H
n
31BF
4
Fe
(CO) 2038 (vs), 2013
H); 7.59e7.33
2 3
O : C, 61.54;
4.1. General
H, 4.33. Found: C, 61.37; H, 4.48. IR (CH
2
Cl
2
):
ꢁ
1 1
(m), 1868 (m) cm . H NMR (CD
3
CN)
d
9.83 (s, 1 H, C
a
2
Reactions were carried out under nitrogen atmosphere, using
(15 H, Ph); 5.39, 5.09 (s, 10 H, Cp), 4.26, 3.61 (d, 2 H, JHH ¼ 14 Hz,
13
1
standard Schlenk techniques. Glassware was oven-dried before use.
Solvents were distilled before use under nitrogen from appropriate
drying agents. Chromatography separations were carried out on
columns of Alumina (Fluka, Brockmann Activity I) or Celite (Fluka,
CH
2
); 1.57 (s, 3 H, Me). C{ H} NMR (CD
); 147.6 (ipso-Ph); 145.9 (C
); 92.3, 88.0 (Cp); 58.7 (CPh ); 50.4 (CH
2
3
CN)
d
241.5 (
); 129.7, 128.4,
); 24.4
m-CO); 210.2,
206.0 (CO); 154.2 (C
126.7 (Ph); 123.0 (C
(Me).
b
a
g
3
512 Medium). All reactants were commercial products (Sigmae
4 2
The reaction of 1 (0.450 mmol) with HBF $Et O (0.460 mmol)
Aldrich) of the highest purity available and used as received.
Compound 1 [3a] and ferrocene [13] were prepared according to
the literature. Infrared spectra were recorded at 298 K on FT-IR
was carried out by the same procedure as that described for the
synthesis of [2][BF ]. Thus complex [3][BF ] was recovered in 85%
4 4
yield.
Agonigi, Gabriele
