Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties Dedicated to our distinguished colleague and friend Professor Bertrand Caro for his scientific achievements in the field of organometallic methylenepyran chemistry.

Article abstract of DOI:10.1016/j.jorganchem.2014.03.029

Wittig reaction between the in situ generated [2,6-diphenyl-4H-pyran-4-yl phosphorane and methyl 4-formylbenzoate afforded the methyl 4-[(2,6-diphenyl-4H- pyran-4-ylidene)methyl]benzoate precursor 2 in 75% yield. The anisyl and ferrocenyl adducts of methylenepyran-containing β-diketones 3 and 4, respectively, were prepared from the base-catalyzed Claisen condensation reaction between precursor 2 and 4-methoxyacetophenone or acetylferrocene, using t-BuO^-K⁺ as basic initiator. Both β-diketones 3 and 4 were isolated as an orange and dark-red crystalline solids in 50% yield, respectively. The acetyl derivative 6, 1-acetyl-1′-methylenepyranyl- ferrocene, was synthesized following a classical Friedel-Crafts acylation reaction of the parent ferrocenylmethylenepyran 5, and isolated in 61% yield as a red microcrystalline powder. The condensation reaction between the electron-rich acetyl complex 6 and acetyl acetate, using lithium diisopropylamide as the active base initiator, provided the ferrocenylmethylenepyran-containing β-diketone, 1-(1,3-dioxobutyl)- 1′-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl] ferrocene 7, isolated in 20% yield as an orange powder. The composition and identity of the new compounds 2-4, 6 and 7 are supported by elemental analysis, FT-IR, one- and two-dimensional ¹H and ¹³C NMR spectral data and mass spectrometry. Additionally, the molecular structures of compounds 2, 4 and 6 were ascertained by single-crystal X-ray diffraction study. FT-IR and NMR spectral data indicate that both β-diketones 3 and 4 do solely exist as their keto-enol tautomeric form in solution and in the solid state, whereas a mixture of keto-enol and β-diketone tautomers in a 73:27 spectroscopic ratio was observed for 7. In the three cases, enolization takes place exclusively away from the anisyl or ferrocenyl group with formation of a six-membered pseudo-aromatic keto-enol ring, confirmed by the crystal structure of 4. Cyclic voltammetric measurements revealed that all the compounds undergo a single one-electron oxidation, localized presumably at the methylenepyran unit. This first oxidation generates a radical cation that undergoes an intermolecular C-C bond coupling to form the corresponding dimer. Anodically shifted to the first oxidation, cyclovoltammogram of 4 exhibits one reversible two-electron oxidation while that of 6 and 7 present two successive reversible one-electron oxidations, attributed in the three cases to the ferrocenyl fragment of the dimer.

Full text of DOI:10.1016/j.jorganchem.2014.03.029

Journal of Organometallic Chemistry 762 (2014) 19e28
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Anisyl and ferrocenyl adducts of methylenepyran-containing
b-diketone: Synthesis, spectral, structural, and redox properties
,
,
a
Néstor Novoa a b, Thierry Roisnel c, Vincent Dorcet c, Jean-René Hamon d , David Carrillo ,
**
*
Carolina Manzur a , Françoise Robin-Le Guen , Nolwenn Cabon
,
b
b,
***
a Laboratorio de Química Inorgánica, Instituto de Química, Pontificia Universidad Católica de Valparaíso, Campus Curauma, Avenida Universidad 330,
Valparaíso, Chile
b UMR 6226 «Institut des Sciences Chimiques de Rennes», CNRS e Université de Rennes 1, IUT Lannion, B.P. 30219, Rue E. Branly, 22302 Lannion, France
c UMR 6226 «Institut des Sciences Chimiques de Rennes», CNRS e Université de Rennes 1, Centre de Diffractométrie X, Campus de Beaulieu,
35042 Rennes Cedex, France
d UMR 6226 «Institut des Sciences Chimiques de Rennes», CNRS e Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Wittig reaction between the in situ generated [2,6-diphenyl-4H-pyran-4-yl phosphorane and methyl 4-
formylbenzoate afforded the methyl 4-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]benzoate precursor 2
Received 21 January 2014
Received in revised form
24 March 2014
in 75% yield. The anisyl and ferrocenyl adducts of methylenepyran-containing
respectively, were prepared from the base-catalyzed Claisen condensation reaction between precursor 2
and 4-methoxyacetophenone or acetylferrocene, using t-BuOꢀKþ as basic initiator. Both
-diketones 3
b-diketones 3 and 4,
Accepted 28 March 2014
b
and 4 were isolated as an orange and dark-red crystalline solids in 50% yield, respectively. The acetyl
derivative 6, 1-acetyl-10-methylenepyranyl-ferrocene, was synthesized following a classical Friedel
eCrafts acylation reaction of the parent ferrocenylmethylenepyran 5, and isolated in 61% yield as a red
microcrystalline powder. The condensation reaction between the electron-rich acetyl complex 6 and
acetyl acetate, using lithium diisopropylamide as the active base initiator, provided the
Dedicated to our distinguished colleague
and friend Professor Bertrand Caro for his
scientific achievements in the field of
organometallic methylenepyran chemistry.
ferrocenylmethylenepyran-containing
b
-diketone, 1-(1,3-dioxobutyl)-10-[(2,6-diphenyl-4H-pyran-4-
Keywords:
Iron
ylidene)methyl] ferrocene 7, isolated in 20% yield as an orange powder. The composition and identity
of the new compounds 2e4, 6 and 7 are supported by elemental analysis, FT-IR, one- and two-
dimensional 1H and 13C NMR spectral data and mass spectrometry. Additionally, the molecular struc-
tures of compounds 2, 4 and 6 were ascertained by single-crystal X-ray diffraction study. FT-IR and NMR
b
-Diketone
Methylenepyran
Structure determination
Ferrocene
spectral data indicate that both
solution and in the solid state, whereas a mixture of ketoeenol and
b
-diketones 3 and 4 do solely exist as their ketoeenol tautomeric form in
-diketone tautomers in a 73:27
b
spectroscopic ratio was observed for 7. In the three cases, enolization takes place exclusively away from
the anisyl or ferrocenyl group with formation of a six-membered pseudo-aromatic ketoeenol ring,
confirmed by the crystal structure of 4. Cyclic voltammetric measurements revealed that all the com-
pounds undergo a single one-electron oxidation, localized presumably at the methylenepyran unit. This
first oxidation generates a radical cation that undergoes an intermolecular CeC bond coupling to form
the corresponding dimer. Anodically shifted to the first oxidation, cyclovoltammogram of 4 exhibits one
reversible two-electron oxidation while that of 6 and 7 present two successive reversible one-electron
oxidations, attributed in the three cases to the ferrocenyl fragment of the dimer.
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
Acetylacetone, also known as pentane-2,4-dione or Hacac, the
quintessential example of the 1,3-dicarbonyl class of compounds
[RC(O)CHR0C(O)R00], was first prepared by Claisen about 125 years
ago, from the base-catalyzed condensation reaction between
* Corresponding author. Tel.: þ33 223 23 59 58.
** Corresponding author. Tel.: þ56 32 227 49 32.
*** Corresponding author. Tel.: þ33 296 46 94 45.
E-mail addresses: jean-rene.hamon@univ-rennes1.fr (J.-R. Hamon), cmanzur@
acetone and ethyl acetate [1]. Since that time, a number of
ucv.cl (C. Manzur), nolwenn.cabon@univ-rennes1.fr (N. Cabon).
http://dx.doi.org/10.1016/j.jorganchem.2014.03.029
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

20
N. Novoa et al. / Journal of Organometallic Chemistry 762 (2014) 19e28
alternative and more efficient synthetic pathways [2e5], including
palladium-catalyzed carbonylative -arylation of acetone [6], have
been developed to produce a broad range of -1,3-dicarbonyl
containing organic substrates, as well as their metallocene-
subsequently reversibly oxidized to ethenediferrocenylbispyrylium
salt [40]. On the other hand, part of us have been interested for
several years in the synthesis of functionalized ferrocenyl-
containing diketones [17,41], as starting materials for the con-
struction of pushepull unsymmetrical Schiff base complexes
exhibiting NLO properties [42]. Thus, we thought that it would be of
interest to design extended electron-rich ferrocenyl-containing
chalcogenomethylenepyrans having a chelating coordination site,
that could, upon electron and proton transfer sequences, become
potential constituents of conjugated polydentate ligands.
a
b
containing
b-diketone counterparts of the type MceC(O)CH2C(O)
R (Mc ¼ (
h
5-C5H5)M(
h
5-C5H4), M ¼ Fe (Fc), Ru (Rc); R ¼ Me, CF3, Ph,
Fc, Rc). Indeed, ferrocene-containing b-diketones were introduced
in the late 1950s [7,8], shortly after the discovery of ferrocene [9],
while its ruthenocene relatives were published only fifty years later
[10]. This constant interest, over the years, of organic, inorganic and
physical chemists to
b
-diketones and related compounds results
In thispiece of work, wereportonthe synthesis, the full analytical
and spectroscopic characterization, and the electrochemical prop-
erties of a series of organic and organometallic complexes containing
the methylenepyran framework bearing phenyl substituent at the
from their valuable intrinsic chemical and physical properties. In
particular, their ketoeenol tautomerism has been extensively
studied in solution by FT-IR and NMR spectroscopy and by elec-
trochemistry and in the solid-state by X-ray single crystal diffrac-
tion analysis [11]. In solution, the 1,3-diketone cores generally exist
as equilibrium mixtures of diketo [RC(O)CHR0C(O)R00] and enolone
[RC(O)CR0]C(OH)R00] tautomers [10e18], whereas in the solid-
state, the ketoeenol isomer is generally the sole form observed
[14e19]. This feature has been rationalized in terms of resonance-
assisted hydrogen bond (RAHB) model based on intercorrelation
between spectroscopic and crystal structure parameters, originally
introduced by Gilli and co-workers [18], for explaining the abnor-
mally strong internal hydrogen bonding within the enolone frag-
2,6 positions of the pyranyl ring, including three new
b-diketones
derivatives, namely, 1-{4-[(2,6-diphenyl-4H-pyran-4-ylidene)
methyl]phenyl}-3-(4-methoxyphenyl)-propane-1,3-dione (3), 1-{4-
[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]phenyl}-3-(ferrocenyl)-
propane-1,3-dione (4), and 1-(1,3-dioxobutyl)-10-[(2,6-diphenyl-
4H-pyran-4-ylidene)methyl]ferrocene (7) (see formulas in Scheme
1). In addition, the crystal and molecular structures of the
ferrocenyl-containing b-diketone 4, its organic precursor 2, and of
the 1-acetyl-10-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl] ferro-
cene derivative 6 were determined by X-ray single crystal diffraction
analysis.
ment. It has long been documented that b-diketones are important
building blocks in organic synthesis [20e22], where in addition to
their established role in the synthesis of various N-containing
heterocyclic derivatives [23,24], they have been widely used for the
Results and discussion
construction of polydentate Schiff base ligands [25]. Likewise,
b
-
Syntheses and spectroscopic characterization
diketone ligands are versatile metal coordinating agents and have
played a significant role in coordination chemistry for a long time
[26]. Due to the presence of two oxygen donor atoms and, as stated
above, facile ketoeenol tautomerism, they easily coordinate with
metal ions after deprotonating the enolic hydrogen atom and
provide stable metal complexes with six-membered chelate rings.
Indeed, the widely used uninegative [OeCReO]ꢀ chelating group is
capable of stabilizing mono- and polynuclear complexes of d- [27]
and f-block [28] metal ions with, for instance, applications in
catalysis [29], and functional materials [30], and has recently
gained increasing attention as constituents of polydentate ligands
in metallo-supramolecular chemistry [31].
Even though less largely utilized, chalcogenomethylenepyran
cores are encountered as building components in various domains
including one-dimensional organic conductors [32], medicinal
technology [33], liquid crystals [34], nonlinear optics (NLO) [35],
and molecular machine [36]. Despite the great potential of this
class of molecules, organometallic chalcogenomethylenepyran
compounds remain scarce. Caro and co-workers first developed
and used benchrotrenyl pyrylium salts as amino acid and protein
labeling reagents [37]. Those authors also opened simple and
efficient routes to NLO active, unsaturated chalcogenomethylene-
pyran Fischer-type chromium and tungsten carbene complexes, as
well as mixed sandwich iron hydrazones using pyrylium salts [38],
or aldehyde functionalized methylenechalcogenopyrans [39].
Precursor 2 is readily obtained following a Wittig-type reaction
of the easily accessible 2,6-diphenyl-4H-pyran-4-yl triphenyl-
phosphonium tetrafluoroborate salt
1 [43] with methyl 4-
formylbenzoate. Treatment of a THF solution of the heterocyclic
phosphorane, generated in situ by reaction of the phosphonium salt
1 with n-butyllithium, with methyl 4-formylbenzoate for 4 h
at ꢀ75 ꢁC, afforded the 4-methylbenzoate methylenepyran 2 in 75%
yield after chromatographic purification and recrystallization from
dichloromethaneen-hexane mixture (Scheme 1). This reaction is,
indeed, similar to that leading to the formation of the known fer-
rocenylmethylenepyran 5 [40]. Compound 2 is an air and thermally
stable yellow crystalline solid with good solubility in THF, diethyl
ether, dichloromethane and chloroform.
The organic and organometallic methylenepyran-containing b-
diketones were prepared from the well-known base-catalyzed
Claisen condensation reaction [1], at ambient temperature using
potassium tert-butoxide as basic initiator [42a]. The stirring of a
THF suspension of the desired salt [ReC(]O)CH2]ꢀKþ (R ¼ 4-MeOe
C6H4 or CpeFe(h
5-C5H4)e, in situ generated by deprotonation of 4-
methoxyacetophenone or acetylferrocene with t-BuOꢀKþ, in the
presence of 2 equivalents of the 4-methylbenzoate methylenepyran
precursor 2 for 15 h at room temperature, yielded the organic
diketone
(3), and the organometallic counterpart CpeFe(
CH]C(OH)(p-C6H4eCH]pyran) (4), both -diketones isolated as
4-MeOeC6H4eC(]O)CH]C(OH)(p-C6H4eCH]pyran)
h
5-C5H4)eC(]O)
Actually,
g-methylenepyrans, which are proaromatic donor, are
b
attracting synthons as electron-donor parts in pushepull struc-
tures as they gain aromaticity upon internal charge transfer
process.
In pursuit of this work, some of us were involved in the prep-
aration of the first ferrocenylmethylenepyran derivative and have
shown that its electro- or chemical oxidative coupling leads to the
reversible formation of ethanediferrocenylbispyrylium salt through
the dimerization of a ferrocenylmethylenepyran radical interme-
diate. Reversible deprotonation of ethanediferrocenylbispyrylium
salt afforded an extended diferrocenylbismethylenepyran that was
orange and dark-red crystalline solids, respectively, in 50% yield
after work up and recrystallization (Scheme 1).
Moreover, in order to design extended electron-rich ferroce-
nylmethylenepyran having a chelating 1,3-dicarbonyl coordination
site, it was necessary to prepare the corresponding acetyl precursor.
Ferrocene is well-known to behave as an aromatic molecule. For
example, it can be easily acetylated with acetyl chloride in the
presence of AlCl3 [44]. Therefore, ferrocenylmethylenepyran 5 was
subjected to such a FriedeleCrafts acylation reaction in dichloro-
methane at 0 ꢁC for 2 h (Scheme 1), yielding the corresponding

N. Novoa et al. / Journal of Organometallic Chemistry 762 (2014) 19e28
21
Scheme 1. Synthesis of the new compounds (2)e(4), (6) and (7).
acetylated derivative, 1-acetyl-10-methylenepyranyl-ferrocene 6,
that was isolated in 61% yield as a red microcrystalline powder.
Under the experimental conditions described above for pre-
paring 3 and 4, the condensation reaction between the electron-
rich acetyl complex 6 and acetyl acetate failed. The increased
electron-donating properties of the ferrocenylmethylenepyran
fragment, with respect to the ferrocenyl one, lowers the acidity of
the methyl hydrogen atoms of acetyl substituent which in turn
necessitates the use of a stronger base. We, therefore, used lithium
diisopropylamide as the active base initiator, a route that has
tautomeric forms [11]. The presence of the enolone isomer is also
indicated by a broad band at 3414, 3446 and 3440 cmꢀ1, respec-
tively, attributed to the asymmetric stretching mode of the OeH
group involved in the [OeH/O] intramolecular hydrogen bond.
Moreover, the spectrum of 7 presents an absorption band at
1729 cmꢀ1 that can be assigned to the
of the keto tautomeric form.
n(C]O) stretching vibration
The formation of the new compounds 2e4, 6 and 7 were readily
noticed in their respective 1H NMR spectrum with in each case a
sharp singlet at d 3.87, 3.91, 2.36, 1.93 and 2.28 ppm assigned to the
proven effective in the synthesis of
ferrocenylmethylenepyran-containing -diketone 7 (Scheme 1),
although 7 was isolated in a modest 20% yield as an orange powder.
Indeed, 1H NMR analysis of the crude product showed that the
the targeted
methyl ester protons of 2, the methoxy protons of 3, and the acetyl
protons of 6, 7-enol and 7-keto, respectively. For 4, the sharp peak
assigned to the protons of the free cyclopentadienyl ring was found
b
b
-
at d 4.23 ppm. Additionally, for 6 and 7, one can note that the two
diketone was formed in 30% spectroscopic yield, with 23% of acetyl
precursor 6, and 47% of unidentified product that could arise from
self condensation of the acetyl starting material [14]. Complex 7
was separated from the reaction mixture by column chromatog-
raphy. Use of N,N-dimethylacetamide instead of ethyl acetate did
not permit to improve the yield of 7.
The new compounds, isolated as microcrystalline powders, are
thermally stable air and moisture insensitive on storage under or-
dinary conditions, exhibiting good solubility in common polar
organic solvents but are less soluble in petroleum ether and n-
hexane and can be crystallized from them. Their composition and
identity are supported by elemental analysis, FT-IR, one- and two-
dimensional NMR spectral data and mass spectrometry. Addition-
ally, the crystal and molecular structures of compounds 2, 4 and 6
were determined by single crystal X-ray diffraction analysis (see
below).
types of hydrogen atoms of the substituted cyclopentadienyl rings
containing either the electron withdrawing acetyl or “acac” group
are deshielded (Dd 0.26 and 0.33 ppm for 6, 0.20 and 0.33 ppm for
7-enol, 0.22 and 0.30 ppm for 7-keto) compared to those attached
to the cyclopentadienyl ring bearing the electron donating meth-
ylenepyran fragment.
Moreover, the 1H NMR spectra of
at 25 ꢁC in CDCl3, exhibited for the 1,3-dione fragment only one set
of two singlets at 6.81 and 6.41 ppm for the vinylic CeH proton,
and at 17.09 and 16.82 ppm for the OeH protons of the enol form,
b-diketones 3 and 4, recorded
d
d
respectively. These downfield positions are in full agreement with
the above discussed FT-IR data and also supported by the crystal
structure of complex 4. The above mentioned solution behavior,
where no keto tautomer can be detected, is similar to that we
recently reported for Cp-Fe(
C5H9O) [17]. By contrast, the 1H NMR spectrum of the
also recorded at 25 ꢁC in CDCl3, showed an enol/keto signal pair,
indicating that (7) does exist as a mixture of ketoeenol and
diketone tautomers in a 73:27 spectroscopic ratio. The vinylic CeH
singlet at 5.65 ppm (1H) for the ketoeenol form gave rise to a
sharp resonance at 3.81 ppm (2H) for the -diketone isomer. The
downfield shifted OeH enol proton was observed at 15.98 ppm. In
h
5-C5H4)eC(O)CH]C(OH)(p-C6H4eOe
-diketone 7,
b
The solid-state FT-IR spectra of all the new compounds exhibi-
ted medium band in the 1650e1400 cmꢀ1 region assigned to the
b
-
n
(C]C) stretching mode of the methylenepyran moiety. In addi-
tion, in the spectra of 2 and 6, the ester and acetyl functionalities
are identified by their intense (C]O) stretching bands at 1715 and
1657 cmꢀ1, respectively. The solid state FT-IR spectra of the
d
n
d
b
b
-
d
diketone derivatives 3, 4 and 7 are quite similar and showed C]O
and C]C medium stretching bands at 1658e1598, 1656e1578 and
the three cases, enolization takes place exclusively away from the
anisyl or ferrocenyl group. This is in agreement with previous ob-
servations [13e18], and with the existence of a resonance driving
1655e1585 cmꢀ1
, respectively, in agreement with ketoeenol

22
N. Novoa et al. / Journal of Organometallic Chemistry 762 (2014) 19e28
force instead of an electronic driving force to explain the domi-
nance of the Cp-Fe(
5-C5H4)eC(O)CH]C(OH)CH3 form toward the
Cp-Fe(
5-C5H4)eC(OH)]CHC(O)CH3 form [14]. Indeed, a linear
relationship has been established between group electronegativity
cR on the Gordy scale and carbonyl stretching frequency (CO) of
h
h
n
methyl esters [14,45]. In the case of complex 2, utilizing the
carbonyl stretching frequency, one can evaluate the electronega-
tivity of the phenylmethylenepyran (R) fragment to be around 2.0.
By extrapolation, since the electronegativity cR of the ferrocenyl
group is lower than that of the phenyl group on the Gordy scale, one
can evaluate the ferrocenylmethylenepyran fragment to have a
lower cR value than the phenylmethylenepyran fragment. Conse-
quently, from an electronic point of view and assuming the value of
2.3 for the methyl group [14,45], the dominant enol isomer should
be ReC(OH)]CHC(O)CH3. Similarly to the ferrocenyl
b-diketone
[14], a resonance driving force may be taken into account to explain
the observed dominant enol form for 7.
Interestingly, on passing from 7-enol to 4 and from 4 to 3, one
can note two successive significant downfield shifts of 0.76/0.40
and 0.84/0.27 ppm for the vinylic and the enol protons, respec-
tively, as a consequence of the participation of the pseudo-aromatic
enol ring in the conjugated system, an effect that can be correlated
with the increasing pyrylium character of the methylenepyran unit
(see below).
Fig. 1. Labeling scheme used for NMR assignments.
2, C-4 and C-6 carbons at
d
153.6, 131.5 and 151.6 ppm, respectively.
The vinylic C-3 and C-5 carbons were seen at
d 102.0 and
108.7 ppm, respectively, and the exocyclic C-7 carbon resonated at
113.2 ppm. Moreover, the phenyl carbons showed up as two sets
of four closely spaced singlets at 124.6/125.0, 128.6/128.7, 129.3/
d
The 1H NMR spectra of compounds 2e4, 6 and 7 displayed also
the three characteristic signal pattern attributed to the H-3, H-5
and H-7 methine protons of the methylenepyran fragment (see
Table 1 and Fig. 1 for atom labeling scheme).
d
129.6 and 133.0/133.4 ppm for the ortho, meta, para and quaternary
carbons, respectively. One can also note that the chemical shift of
the C-7 carbon is sensitive to the electronic nature of its substitu-
The 1H NMR chemical shifts of the H-3/H-5 proton have been
taken as criteria for the degree of the pyrylium character [46]. In
general, the chemical shifts of the hydrogen in the 3/5-position
tend to shift downfield as the contribution of pyrylium resonance
form increases in the ground-state structure of a compound. Thus,
from comparison of the observed H-3/H-5 chemical shift values of
compounds 6 and 7 with those, more deshielded, of compounds 2e
4, it appears that the ferrocenylmethylenepyran derivatives 6 and 7
have a lower pyrylium character. In 2e4 the exocyclic C-7 carbon is
substituted by an electron withdrawing p-C6H4eC(]O)R group
whereas in 6 and 7 it bears the electron releasing ferrocenyl moiety.
The electronic nature of those substituents has also a profound
deshielding effect, up to 0.6 ppm, on the H-7 proton (Table 1).
The 13C NMR spectra of compounds 2e4, 6 and 7, obtained at
25 ꢁC in CDCl3, are fully consistent with the proposed structures
(see Experimental section). For instance, the spectrum of 7 con-
ent, with peaks observed at
d
114.8, 113.2 and 113.0 ppm in 2, 3 and
4, respectively, and at
7-keto, respectively.
d 109.3, 108.9 and 108.8 ppm in 6, 7-enol and
X-ray crystal structures
The molecular structures of compounds 2, 4 and 6 with the atom
labeling scheme are displayed in Figs. 2e4, respectively, with
firms the existence of the ketoeenol/
mixture. The methyne carbon resonates at
enol form, while it shows up at 56.6 ppm for the
rivative. At the same time, the acetyl carbonyl carbon experiences a
downfield shift from 187.1e202.3 ppm, while the ferrocenoyl
b
d
-diketone tautomeric
97.6 ppm for the ketoe
-diketone de-
d
b
d
carbonyl carbon is slightly downfield shifted by 5.6 ppm. In addi-
tion, the 13C NMR of the new compounds exhibited the five reso-
nances expected for the five magnetically non-equivalent carbons
of the methylenepyran core (see Experimental section). For
example, the spectrum of the diketone 3 showed the quaternary C-
Table 1
1H NMR spectral data for the methyne protons of the methylenepyran core.a
Fig. 2. Molecular structure of 2 with the atom numbering scheme; only molecule 2A is
Compd
dH-3 (ppm)
dH-5 (ppm)
dH-7 (ppm)
shown. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at
ꢁ
ꢀ
50% probability. Selected bond distances [A] and angles [ ]: O(1)eC(1) 1.436(8), O(1)e
C(2) 1.348 (9), O(2)eC(2) 1. 197(9), C(9)eC(10) 1.370(10), C(11)eC(12) 1.338(10),
C(13)eC(14) 1.336(9), O(3)eC(12) 1.377(8), O(3)eC(13) 1.376(8); C(1)eO(1)eC(2)
115.1(6), O(1)eC(2)eO(2) 123.8(7), O(2)eC(2)eC(3) 124.4(8), C(6)eC(9)eC(10)
127.8(7), C(9)eC(10)eC(11) 126.8(7), C(9)eC(10)eC(14) 120.1(7), C(10)eC(11)eC(12)
122.7(7), C(10)eC(14)eC(13) 121.7(7), O(3)eC(12)eC(11) 121.4(7), O(3)eC(13)eC(14)
122.9(6), O(3)eC(12)eC(15) 111.9(6), O(3)eC(13)eC(21) 111.2(6), C(12)eO(3)eC(13)
118.0(6).
2
3
4
6
6.64
6.46
6.49
6.34
6.27
6.35
7.06
7.07
7.09
6.80
6.78
6.79
5.96
5.97
5.98
5.46
5.38
5.45
7-Enol
7-Keto
a
Recorded at 25 ꢁC in CDCl3.

N. Novoa et al. / Journal of Organometallic Chemistry 762 (2014) 19e28
23
accordance with previously reported structural data [40]. The
ꢀ
exocyclic CeC bond lengths lie in the range 1.353(10)e1.370(10) A,
thus suggesting a weak pyrylium character [40]. In addition, the
mean planes of the aromatic rings at C-2, C-6 and C-7 (this atom
labeling refers to Fig. 1) are tilted with respect to the mean plane of
the methylenepyran core with dihedral angles of 6.77, 19.37 and
34.65ꢁ for 2A, 6.22, 19.56 and 34.85ꢁ for 2B, 3.75, 14.81 and 18.23ꢁ
for 4, and 17.60, 14.12 and 30.28ꢁ for 6, respectively.
Complexes 4 and 6 contain the 1-ferrocenyl and 1,10-ferrocenyl
moiety, respectively. In compound 4, the iron atom is coordinated to
the free and substituted cyclopentadienyl rings at ring centroid-iron
ꢀ
distances of 1.661 and 1.642 A, respectively, whereas in compound 6
the two ring centroid-iron distances are identical and equal to
ꢀ
1.650 A, although one ring bears a donor methylenepyran substit-
uent and the other an acceptor acetyl one. In each organometallic
fragment, the two carbocyclic ligands are essentially parallel with
ring centroid-iron-ring centroid angles of 177.5ꢁ for 4 and 177.6ꢁ for
6. Those metrical parameters clearly feature a linear sandwich
Fig. 3. Molecular structure of 4 with the atom numbering scheme. Hydrogen atoms
have been omitted for clarity. Thermal ellipsoids are drawn at 50% probability. Selected
ꢁ
ꢀ
bond distances [A] and angles [ ]: C(10)eC(11) 1.461(3), C(11)eO(1) 1.284(3), C(11)e
C(12) 1.419(3), C(12)eC(13) 1.381(3), C(13)eO(2) 1.313(3), C(13)eC(14) 1.466(3),
C(20)eC(21) 1.360(3), C(22)eC(23) 1.334(3), C(23)eO(3) 1.374(3), C(24)eO(3) 1.382(3),
C(24)eC(25) 1.340(3); O(1)eC(11)eC(10) 118.0(2), O(1)eC(11)eC(12) 120.7(2), C(11)e
C(12)eC(13) 120.1(2), O(2)eC(13)eC(12) 120.3(2), O(2)eC(13)eC(14) 115.6(2), C(17)e
C(20)eC(21) 132.8(2), C(20)eC(21)eC(22) 127.7(2), C(20)eC(21)eC(25) 120.0(2),
C(21)eC(22)eC(23) 122.4(2), C(21)eC(25)eC(24) 123.6(2), O(3)eC(23)eC(22)
122.0(2), O(3)eC(24)eC(25) 120.7(2), O(3)eC(23)eC(26) 111.0(2), O(3)eC(24)eC(32)
111.6(2), C(23)eO(3)eC(24) 118.56(19).
structures with typical [h h
5-Fe- 5] coordination mode, and indicate
that there is a Fe(II) oxidation state in each metallocene [47].
On the other hand, within both 4 and 6 the acyl units C(10)e
C(11)eO(1) and C(5)eC(6)eO(8) are almost coplanar with their
corresponding attached cyclopentadienyl rings C(6)/C(10) and
C(1)/C(5) with dihedral angles of 5.42 and 7.66ꢁ, respectively. This
is typical of the conformations observed in acyl ferrocenes Fc-COR
[41,48]. Additionally, in complex 6, the acetyl group exhibits a
classical O(1)eC(6)eC(7) angle of 121.2(2)ꢁ [41,48], and in the two
complexes, the CeC and CeFe bond distances of the ferrocene
sandwiches as well as the C]O bond distance fall all within the
range of standard values [49].
selected bond distances and angles listed in their respective cap-
tions. The three complexes crystallize in the monoclinic centro-
symmetric space group P21/n. Two crystallographically
independent molecules (2A and 2B) are found in the asymmetric
unit cell of 2 while that of 4 and 6 contains each a single molecule.
The single-crystal X-ray diffraction studies confirm both the
monomeric nature and that each compound consists of a [(2,6-
diphenyl-4H-pyran-4-ylidene)methyl] group linked to an aro-
In compound 4, the angles at C(11), C(12) and C(13) of the
[O(1)eC(11)eC(12)eC(13)eO(2)] central core are of 120.7(2),
120.1(2) and 120.3(2)ꢁ, respectively, that are idealized value ex-
pected for a sp2-hybridized carbon atom. The O(1)eC(11), C(11)e
C(12), C(12)eC(13) and C(13)eO(2) bond lengths (see caption of
Fig. 3) observed in this planar skeleton correspond to alternating
double-, single-, double- and single-bonds [49], exhibiting partial
delocalization of the O]CeC]CeO system. Those metrical pa-
rameters are consistent with a ketoeenol tautomeric form for 4,
with an intramolecular O(1)/HeO(2) hydrogen bonding interac-
tion which closes a six-membered pseudo-aromatic ring through
the resonant /O]CeC]CeOH/ fragment [18]. The O/O sepa-
matic C6-ring in the case of the b-diketone 4 and of its precursor 2,
and to an acetylferrocene moiety in the case of 6. Whatever the
substituent at the exocyclic methine carbon atom, the methyl-
enepyran cores remain structurally very similar with alternating
single and double CeC bonds. Table S1 (see Supplementary
material) compares their bond distances and angles, that are in
ꢀ
ration is equal to 2.450 A, in accordance with previously reported
values for ketoeenol tautomers of b-diketone derivatives [13e19].
In addition, the plane of the [OCCCO] framework is almost coplanar
with both the substituted cyclopentadienyl ring and the phenylene
ring, making dihedral angles of 6.22 and 7.02ꢁ, respectively, a sit-
uation that should allow partial conjugation between the two parts
of the molecule. Lastly, the crystal packing of (4) is effected by
intermolecular interactions between an hydrogen atom and the
ꢀ
carbonyl oxygen atom (C(6)eH(6)/O(1)
¼
3.454 A, H(6)/
ꢁ
ꢀ
O(1) ¼ 2.666 A and C(6)eH(6)/O(1) ¼ 140.8 ; symmetry code:
1 ꢀ x, 1 ꢀ y, ꢀz) (Supplementary material, Fig. S1).
Electrochemical studies
The redox behavior of these new organic and organometallic
compounds 2e4, 6 and 7 was investigated by cyclic voltammetry in
dichloromethane containing 0.1 M n-Bu4NþBF4ꢀ as supporting
electrolyte (see Fig. 5, and Figs. S2eS4 of the Supplementary ma-
terial). Their electrochemical data together with those of the
Fig. 4. Molecular structure of 6 with the atom numbering scheme. Hydrogen atoms
have been omitted for clarity. Thermal ellipsoids are drawn at 50% probability. Selected
ꢁ
ꢀ
bond distances [A] and angles [ ]: C(5)eC(6) 1.477(3), C(6)eO(8) 1.219(3), C(6)eC(7)
1.506(4), C(14)eC(15) 1.357(3), C(16)eC(17) 1.335(3), C(19)eC(20) 1.335(3), O(18)e
C(17) 1.389(3), O(18)eC(19) 1.385(3); O(8)eC(6)eC(5) 121.1(2), O(8)eC(6)eC(7)
121.2(2), C(13)eC(14)eC(15) 127.8(2), C(14)eC(15)eC(16) 120.8(2), C(14)eC(15)eC(20)
126.5(2), C(15)eC(16)eC(17) 122.8(2), C(15)eC(20)eC(19) 122.4(2), O(18)eC(17)e
C(16) 121.57(19), O(18)eC(19)eC(20) 122.26(19), O(18)eC(17)eC(21) 111.72(19),
O(18)eC(19)eC27) 111.41(19), C(17)eO(18)eC(19) 118.04(17).
known ferrocenylmethylenepyran
5
[40a], and phenyl-
methylenepyran (PheCH]pyran) 8 [40c], are gathered in Table 2.
For all of the compounds, an irreversible anodic wave, classically
observed for methylenepyran derivatives [40], was observed

24
N. Novoa et al. / Journal of Organometallic Chemistry 762 (2014) 19e28
Fig. 5. Cyclic voltammograms of compounds 4 (a) and 7 (b) at a Pt disk working electrode, in CH2Cl2/0.1 M [n-Bu4N][BF4] at 298 K. Redox potentials are quoted vs. the ferrocene/
ferricenium couple (Cp2Feþ/0).
between ꢀ0.05 and 0.34 V vs. ferrocene/ferricenium (Cp2Feþ/0
)
Finally, for the ferrocenyl-containing compounds, two succes-
sive reversible one-electron oxidation waves for 6 and 7 and one
reversible two-electron oxidation for 4 (based on current ratio)
were observed following the first oxidation process. Cyclic vol-
tammograms of 4 and 7 are displayed in Fig. 5, whereas that of 6 is
presented in Fig. S4 (Supplementary material). Compared to the
precursor compound 5, a positive shift is observed for 6 and 7, due
to the presence of the electron withdrawing substituent. As pre-
viously shown for the ferrocenylmethylenepyran 5, these oxidation
waves may be assigned to the ferrocenyl groups of the dicationic
dimer formed after the first oxidation. In the particular case of 4,
this behavior suggests that there is no electronic communication
between the two ferrocenyl fragments [51].
redox couple (Table 2). For (2)e(4), values of the oxidation potential
(0.23e0.34 V) are comparable to that measured for the parent
phenylmethylenepyran compound 8 (0.23 V) [40c]. For the organ-
ometallic derivatives 6 and 7, only slight variation of the oxidation
potential was observed when compared to that of the parent fer-
rocenylmethylenepyran derivative 5, since the oxidation potential
of this compound was observed at ꢀ0.15 V [40b]. According to the
DFT calculations carried out for 5, which shows that the three
highest occupied MOs have a large metal contribution [40c], the
main difference between 2, 3, 4, 8 and 5, 6, 7 may originate from the
nature of the oxidized site that seems to be the pyran and the
ferrocenyl units, respectively.
Moreover, on the reverse scan of the cyclic voltammogram, a
new irreversible cathodic wave was observed between ꢀ0.69
and ꢀ0.86 V vs. Cp2Feþ/0 that is not observed when the scan is
directly run in reduction (Fig. 5). This electrochemical behavior is
consistent with monoelectronic oxidation followed by rapid
dimerization, as previously demonstrated for ferrocenylmethyle-
nepyran compounds [40a,b]. Indeed, the first oxidation generates a
radical cation which undergoes an intermolecular CeC bond
coupling to form a dimer. The latter is detected on the back scan
with the observation of an irreversible reduction wave. Finally,
when the scan direction was reversed toward more positive po-
tentials, after the appearance of the reduction wave, the voltam-
mogram was identical to the one obtained in the initial scan. This
observation suggests that the product formed upon oxidation is
reduced back to the original compound. This kind of behavior,
already observed by us [40], has also been observed in other mo-
lecular systems [50], and suggests that CeC bond making/breaking
is reversibly induced upon electron transfer.
Conclusions
In this contribution, a new family of electron-rich methyl-
enepyran derivatives has been successfully synthesized and fully
characterized, and their redox properties thoroughly investigated.
All the compounds described in this work contain the 4-[(2,6-
diphenyl-4H-pyran-4-ylidene)methyl] fragment substituted at the
exocyclic CH]C carbon by either p-C6H4CO2CH3 (2), p-CH3OC6H4e
COCH2CO-p-C6H4
(3),
CpFe(C5H4)eCOCH2CO-p-C6H4
(4),
(CH3COC5H4)Fe(C5H4) (6), and (CH3COCH2COC5H4)Fe(C5H4) (7).
Compounds 2, 4 and 6 were also authenticated by single-crystal X-
ray diffraction analysis. FT-IR and 1D and 2D NMR studies clearly
show that both
b-diketones 3 and 4 do exist solelyas theirketoeenol
tautomeric form in solution, whereas a mixture of ketoeenol and
b
-
diketone tautomers was observed for 7 in a 73:27 spectroscopic
ratio. Enolization takes place exclusively away from the anisyl or
ferrocenyl group, suggesting the existence of a resonance driving
force instead of an electronic driving force to explain the dominance
of the ReC(O)CH]C(OH)e form (R ¼ anisyl, Fc). This is supported by
thecrystal structure ofcomplex 4, wherethe six-membered pseudo-
aromatic ketoeenol ring is coplanar with the cyclopentadienyl and
phenylene ring substituents, thus allowing a partial conjugation
between the two redox active parts of the molecule. Owing to their
electron-rich nature, the methylenepyran compounds 2e4, 6 and 7,
studied bycyclic voltammetry are readily oxidized to radical cations.
The oxidation potential values are markedly affected by the position
of the ferrocenyl ring toward the methylenepyrane fragment. The
unstable radical cation evolves by dimerization in bispyrylium sys-
tems that regenerate the starting material upon reduction. These
systems, undergoing reversible CeC bond making/breaking upon
electron transfer, might be interesting in the construction of mo-
lecular switches or memories based on their electrochemical
Table 2
Electrochemical data for compounds 2e8.a
c
Compd
Eox (1)b
Ered
E
½
(2)
E (3)
½
2
3
0.34
0.32
0.23
ꢀ0.15
ꢀ0.02
ꢀ0.05
0.23
ꢀ0.82
ꢀ0.82
ꢀ0.86
ꢀ0.76
ꢀ0.83
ꢀ0.77
ꢀ0.86
4
0.25 (2eꢀ
0.12
0.37
)
5d
6
0.28
0.47
0.44
7
0.33
8d
a
Recorded in CH2Cl2/0.1 M n-Bu4NþBFꢀ4 at 0.1 V sꢀ1, at 298 K; redox potentials
quoted in V vs. the ferrocene/ferricenium couple (Cp2Feþ/0).
b
Irreversible peak.
c
Irreversible peak on the reverse cathodic scan.
Data from Ref. [40].
d

N. Novoa et al. / Journal of Organometallic Chemistry 762 (2014) 19e28
25
response. On the other hand, the new unsymmetrical electron-rich
methylenepyran-containing 1,3-diketones 3, 4 and 7 are also ex-
pected to be strong chelating agents toward transition metal ions,
and may also serve as valuable building blocks in the construction of
polydentate Schiff base ligands, as well as in the synthesis of het-
erocyclic compounds such as pyrazoles which are known to have a
broad spectrum of biological activities.
stirred at ꢀ75 ꢁC for 4 h. Then, the solvent was evaporated under
reduced pressure at room temperature (r.t.). The solid residue was
dissolved in a minimum amount of dichloromethane (DCM) and
absorbed on a column packed with silica gel (grade 60). Elution
with petroleum ethereDCM mixture (1:1) produced the release of
a yellow band that was collected. The solvent was evaporated under
reduced pressure and the product was recrystallized from DCMe
hexane mixture (1:1), affording yellow microcrystals of 2 (1.40 g,
75% yield). A crystal from this crop was used for X-ray structure
determination. M.p. 130e132 ꢁC. C26H20O3$0.05 CH2Cl2
(384.2 g molꢀ1): calcd. C 81.36, H 5.21; found C 81.42, H 5.23. IR
(KBr, cmꢀ1): 1715 (s) (C]O), 1656 (m) (C]C), 1595, 1581, 1493,
Experimental section
General experimental methods
Manipulations of air-sensitive compounds were performed un-
der a dry dinitrogen atmosphere using standard Schlenk tech-
niques. Solvents were dried and distilled under dinitrogen by
standard methods prior to use [52]. Chromatographic purification
1447, (C]C), 1270 (OeC). 1H NMR (400 MHz, CD3COCD3, 25 ꢁC):
4
d
3.75 (s, 3H, CH3), 5.96 (s, 1H, H-7), 6.64 (d, JH,H ¼ 1.75 Hz, 1H,
H-3), 7.06 (d, 4JH,H ¼ 1.75 Hz, 1H, H-5), 7.38 (m, 6H, H-23,24,25 and
3
H-63,64,65), 7.44 (d, JH,H
¼
7.8 Hz, 2H, H-9,13), 7.79 (t,
was performed with Silica gel 60 (0.063e0.200
mm). 2,6-diphenyl-
3JH,H ¼ 6.8 Hz, 4H, H22,26 and H-62,66), 7.85 (d, 3JH,H ¼ 7.8 Hz, 2H,
4H-pyran-4-yl triphenylphosphonium tetrafluoroborate 1 [43],
ferrocenylmethylenepyran 5 [40], and phenylmethylenepyran 8
[53], were synthesized according to published procedures. Methyl
4-formylbenzoate, n-butyllithium (2.5 M in hexanes), acetylferro-
cene, potassium tert-butoxide, 4-methoxyacetophenone, di-
isopropylamine and petroleum ether 40e60 were purchased from
Aldrich and used as received. Solid-state FT-IR spectra were recor-
ded on a Perkin Elmer model 1600 FT-IR or 1000 FT-IR spectro-
photometer using KBr disks, in the range 4000e450 cmꢀ1. 1H and
13C NMR spectra were recorded with either a Bruker Avance III 400
spectrometer at the Universidad Federico Santa María (Valparaíso,
Chile), or a Bruker AV 500 at the Centre Régional de Mesures
Physiques de l’Ouest (CRMPO, Rennes, France) or a Bruker DRX 500
spectrometer at the Service Commun de Recherche de Résonance
Magnétique Nucléaire et de Résonance Paramagnétique Electro-
nique de l’Université de Bretagne Occidentale (Brest, France).
H-10,12). 13C NMR (100 MHz, CD3COCD3, 25 ꢁC):
d 52.5 (CH3), 102.9
(C-3), 109.9 (C-5), 114.8 (C-7), 125.8, 126.3, 127.9, 128.8, 130.0, 130.1,
130.6, 130.9 (CeH arom), 131.0, 132.5, 134.2, 134.3 (Cquat), 144.7
(C-11), 152.5 (C-6), 154.8 (C-2), 167.5 (C]O).
Synthesis of 1-{4-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]
phenyl}-3-(4-methoxyphenyl) propane-1,3-dione (3)
A Schlenk tube was charged with a magnetic stir bar, 4-
methoxyacetophenone (0.220 g, 1.46 mmol), potassium tert-but-
oxide (0.250 g, 2.23 mmol) and 3.0 mL of THF. The reaction mixture
was vigourously stirred for 15 min before a solid sample of com-
pound 2 (1.10 g, 2.89 mmol) was slowly added. After 10 min of
stirring, 2.0 mL of THF were additionally added and the vigorous
stirring was continued for 15 h at r.t. The reaction was quenched
with water and partitioned between water and DCM (3 ꢂ 50 mL).
The combined organic extracts were dried over MgSO4, concen-
trated and adsorbed on a column packed with silica gel. Elution
with petroleum ethereDCM mixture (2:8) produced the release of
an orange band that was collected. The solvent was evaporated
under reduced pressure and the product was recrystallized by slow
diffusion of petroleum ether in a DCM solution of the product,
affording 0.364 g (50% yield) of dark red microcrystals of 3. M.p.
160e163 ꢁC. C34H26O4 (498.57 g molꢀ1): calcd. C 81.91, H 5.26, O
12.84; found C 81.55, H 5.15, O 12.62. IR (KBr, cmꢀ1): 3414 (w) asym
(eOH), 3100 (w) (CeH arom), 2900 (w) (CeH aliph), 1658 (m), 1598
(m) (C]O) and/or (C]C), 760 (m) (CeH). 1H NMR (500 MHz,
Chemical shifts (d) are reported in parts per million (ppm) and
referenced to the residual deuterated solvent peaks. Coupling
constants (J) are reported in Hertz (Hz), and integrations are re-
ported as number of protons. The following abbreviations are used
to describe peak patterns: br ¼ broad, s ¼ singlet, d ¼ doublet,
t ¼ triplet, m ¼ multiplet. 1H and 13C NMR chemical shift assign-
ments are supported by using COSY, HMQC and HMBC NMR tech-
niques, and are given according to the numbering scheme of Fig. 1.
High resolution electro spray ionization mass spectra (ESI-MS)
were obtained at the CRMPO (Rennes) with a WATERS Q-TOF
spectrometer. Elemental analyses were conducted on a Thermo-
FINNIGAN Flash EA 1112 CHNS/O analyzer by the Microanalytical
Service of the CRMPO (Rennes). Cyclic voltammetry experiments
CDCl3, 25 ꢁC):
4JH,H
d 3.91 (s, 3H, CH3), 5.97 (s, 1H, H-7), 6.46 (d,
¼
1.75 Hz, 1H, H-3), 6.81 (s, 1H, CH acac), 6.99 (d,
4
were performed with a
m-AUTOLAB III potentiostat monitored by a
3JH,H ¼ 8.9 Hz, 2H, C6H4eOCH3), 7.07 (d, JH,H ¼ 1.75 Hz, 1H, H-5),
computer. A three-electrode cell was used, equipped with a plat-
inum wire auxiliary electrode, a glassy carbon or a platinum
working electrode, Ag/AgCl non aqueous as reference or silver wire
as a quasi-reference electrode. All the potential are quoted against
the ferrocene-ferricenium redox couple; ferrocene was added as an
internal standard at the end of each experiment [54]. Melting
points were measured in evacuated capillaries on a Kofler Bristoline
melting point apparatus and are uncorrected.
7.47 (t, 3JH,H ¼ 7.5 Hz, 2H, H-24,64), 7.46 (m, 3JH,H ¼ 7.5 and 7.8 Hz,
3
4H, H-23,25 and H-63,65), 7.49 (d, JH,H ¼ 8.5 Hz, 2H, H-9,13), 7.77
(d, 3JH,H ¼ 7.8 Hz, 4H, H-22,26 and H-62,66), 7.97 (d, 3JH,H ¼ 8.5 Hz,
3
2H, H-10,12), 7.99 (d, JH,H ¼ 8.9 Hz, 2H, C6H4eOCH3), 17.09 (s, 1H,
OH). 13C{1H} NMR (125 MHz, CDCl3, 25 ꢁC):
d 55.5 (CH3), 92.0 (CeH
acac), 102.0 (C-3), 108.7 (C-5), 113.2 (C-7), 113.9 (CeH C6H4eOCH3),
124.6 (C-22,26), 125.0 (C-62,66), 127.4 (C-10,12), 127.6 (C-9,13),
128.5 (Cquat C6H4eC]O), 128.7 (C-63,65), 128.7 (C-23,25), 129.2
(CeH C6H4eOCH3), 129.3 (C-64), 129.6 (C-24), 131.5 (C-4), 132.0 (C-
11), 133.0 (C-61), 133.2 (C-21), 143.0 (C-8), 151.6 (C-6), 153,6 (C-2),
163.1 (CeOCH3), 183.6 (CeOH), 185.6 (C]O).
Synthesis of methyl 4-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]
benzoate (2)
To a Schlenk tube containing a stirred solution of 2,6-diphenyl-
Synthesis of 1-(4-((2,6-diphenyl-4H-pyran-4-ylidene)methyl)
4H-pyran-4-yl triphenylphosphonium tetrafluoroborate salt
1
phenyl)-3-(ferrocenyl)propane-1,3-dione (4)
(2.90 g, 4.98 mmol) in THF (40 mL), cooled to ꢀ75 ꢁC, was added
dropwise n-butyllithium (2.30 mL, 5.78 mmol). The solution turned
black. After 15 min of stirring, solid methyl 4-formylbenzoate
(0.818 g, 4.98 mmol) was slowly added. The reaction mixture was
A Schlenk tube was charged with a magnetic stir bar, ace-
tylferrocene (0.32 g, 1.457 mmol), potassium tert-butoxide (0.250 g,
2.23 mmol) and 3.0 mL of THF. After 15 min of stirring, a light

26
N. Novoa et al. / Journal of Organometallic Chemistry 762 (2014) 19e28
brown precipitate formed and the reaction mixture was vigorously
stirred for 2 h before a solid sample of compound 2 (1.1 g,
2.89 mmol) was slowly added. After 10 min of stirring, 2.0 mL of
THF were added and the vigorous stirring was continued for 15 h.
The reaction was quenched with water and partitioned between
water and DCM (3 ꢂ 50 mL). The combined organic extracts were
dried over MgSO4, concentrated and adsorbed on a column packed
with silica gel. Elution with petroleum ethereDCM mixture (4:6)
produced the release of a dark red band that was collected. The
solvent was evaporated under reduced pressure and the product
was recrystallized by slow diffusion of petroleum ether into a DCM
solution of the product, affording 0.420 g (50% yield) of dark red
microcrystals of 4. A crystal from this crop was used for X-ray
structure determination. M.p. 90e93 ꢁC. C37H28O3Fe$0.1CH2Cl2
(584.53 g molꢀ1): calcd. C 76.16, H 4.82; found C 76.56, H 4.86. IR
(KBr, cmꢀ1): 3446 (w) asym (-OH), 3088 (w) (CeH arom), 2965 (w)
(CeH aliph), 1656 (m), 1578 (m) (C]O) and/or (C]C), 764 (m) (Ce
ferrocenylmethylenepyran 5 (0.500 g,1.16 mmol) in freshly distilled
CH2Cl2 (100 mL), under N2 at 0 ꢁC. The reaction mixture was stirred
for 2 h, quenched with water (100 mL), and extracted with DCM.
The organic phase was collected, neutralized with a 0.1 M aqueous
solution of Na2CO3, and dried over MgSO4. The solvent was evap-
orated under reduced pressure to give compound 6 as a red
microcrystalline powder (0.350 g, 61% yield). The product was
recrystallized by slow diffusion of diethyl ether iþnto a DCM solution
of the complex. M.p. 116e118 ꢁC. HRMS-ESI (based on 56Fe)
þ
C30H24O2NaFe [M
Na] m/z calcd: 495.1023; found: 495.1023
(0 ppm). IR (KBr, cmꢀ1): 1657 (s) (C]O), 1601 (w), 1579 (w) (C]C),
1493 (w), 1448 (w) (CeH), 822 (br), 762 (s), 687 (s) (CeH). 1H NMR
(500 MHz, CDCl3, 25 ꢁC):
d
2.36 (s, 3H, CH3), 4.29 (t, 3JH,H ¼ 1.6 Hz,
2H, C5H4), 4.43 (t, 3JH,H ¼ 1.6 Hz, 2H, C5H4), 4.49 (t, 3JH,H ¼ 1.8 Hz, 2H,
C5H4COCH3), 4.76 (t, 3JH,H ¼ 1.8 Hz, 2H, C5H4COCH3), 5.46 (s, 1H, H-
7), 6.34 (s, 1H, H-3), 6.80 (s, 1H, H-5), 7.43e7.45 (m, 6H, H-23,24,25
and H-63,64,65), 7.76e7.69 (m, 4H, H-22,26 and H-62,66). 13C NMR
H). 1H NMR (500 MHz, CDCl3, 25 ꢁC):
d
4.23 (s, 5H, C5H5), 4.59 (br t,
(125 MHz, CDCl3, 25 ꢁC):
d 27.7 (CH3), 69.3, 70.0 (CeH, C5H4), 70.4,
3JH,H ¼ 1.6 Hz, 2H, C5H4), 4.90 (br t, 3JH,H ¼ 1.6 Hz, 2H, C5H4), 5.98 (s,
1H, H-7), 6.41 (s, 1H, CeH acac), 6.49 (s, 1H, H-3), 7.09 (s, 1H, H-5),
7.41e7.51 (m, 8H, H-9,13, H-23,24,25 and H-63,64,65), 7.79 (d,
3JH,H ¼ 7.3 Hz, 4H, H-22,26 and H-62,66), 7.93 (d, 3JH,H ¼ 7.8 Hz, 2H,
H-10,12), 16.82 (s, 1H, OH). 13C{1H} NMR (125 MHz, CDCl3, 25 ꢁC):
73.4 (CeH, C5H4COCH3), 79.9, 86.5 (Cipso C5H4),103.4 (C-3),107.9 (C-
5), 109.3 (C-7), 124.3, 124.7, 128.5, 128.6, 128.8, 129.2 (CeH arom),
132.0 (C-4), 133.3 (C-61), 133.5 (C-21), 149.8 (C-6), 152.0 (C-2), 202.1
(C]O).
Synthesis of 1-(1,3-dioxobutyl)-10-[(2,6-diphenyl-4H-pyran-4-
d
68.6 (C5H4), 70.3 (C5H5), 72.3 (C5H4), 77.3 (Cipso C5H4), 93.2 (]Ce
H acac), 101.8 (C-3), 108.5 (C-5), 113.0 (C-7), 124.5, 124.8, 126.9,
127.5, 128.7, 129.3, 129.6, (CeH arom), 131.2 (C-4), 132.9, 136.6, 137.2
(C-11, C-21, C-61), 142.5 (C-8), 151.2, 153.2 (C-2/C-6), 178.4 (CeOH),
194.8 (C]O).
ylidene)methyl] ferrocene (7)
A
Schlenk tube was charged with
a solution of di-
isopropylamine (576 L, 4.10 mmol) in diethyl ether (4.0 mL) to
m
which was added dropwise n-butyllithium (1.6 mL, 4.0 mmol) at
0 ꢁC. The resulting mixture was stirred for 1 h before solid sample
1-acetyl-10-methylenepyrane-ferrocene 6 (0.500 g, 1.0 mmol) was
slowly added. The reaction mixture was stirred overnight at room
temperature (r.t.). Upon cooling to 0 ꢁC, ethyl acetate (1.0 mL,
10.2 mmol) was added dropwise over a 30 min period, and the
resulting solution was stirred overnight at r.t. The reaction mixture
was hydrolyzed with 1 M aqueous HCl (20 mL) and 50 mL of water,
Synthesis of 1-acétyl-10-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]
ferrocene (6)
A Schlenk tube was charged with a magnetic stir bar, acetyl
chloride (0.26 mL, 3.50 mmol), aluminum trichloride (0.470 g,
3.50 mmol) and DCM (20.0 mL). The resulting mixture was stirred
for
2
h
at rt and added dropwise to
a
solution of
Table 3
Crystallographic data, details of data collection and structure refinement parameters for compounds 2, 4 and 6.
2
4
6
Empirical formula
Formula mass, g molꢀ1
Collection T, K
C52H40O6
760.84
150(2)
C37H28FeO3
576.44
150(2)
C30H24FeO2
472.34
150(2)
Crystal system
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/n
Space group
ꢀ
a (A)
7.0936(14)
30.623(6)
17.892(3)
101.327(6)
3810.9(12)
4
12.5310(8)
5.8917(3)
36.617(2)
98.574(3)
2673.2(3)
4
5.8457(7)
31.725(5)
11.9626(17)
96.648(5)
2203.6(5)
4
ꢀ
b (A)
ꢀ
c (A)
b
(ꢁ)
3
ꢀ
V (A )
Z
Dcalcd (g cmꢀ3
)
1.326
1.432
1.424
Crystal size (mm)
0.32 ꢂ 0.31 ꢂ 0.07
0.6 ꢂ 0.14 ꢂ 0.09
0.6 ꢂ 0.09 ꢂ 0.08
F(000)
1600
1200
984
Abs coeff (mmꢀ1
q
)
0.086
0.603
0.711
Range (ꢁ)
2.93 to 27.48
ꢀ8/9, ꢀ39/39, ꢀ23/23
55,291
3.04 to 27.48
ꢀ16/16, ꢀ5/7, ꢀ47/47
23,189
3.09 to 27.48
ꢀ4/7, ꢀ41/41, ꢀ15/15
17,651
Range h,k,l
No. total refl
No. unique refl
8559
6099
5002
Comp. to qmax (%)
Max/min transmission
Data/restraints/parameters
Final R
97.3
99.3
0.947/0.761
6099/30/387
98.9
0.994/0.833
8559/0/448
R1 ¼ 0.0582
wR2 ¼ 0.1252
R1 ¼ 0.1450
wR2 ¼ 0.1598
1.016
0.945/0.843
5002/0/299
R1 ¼ 0.0416
wR2 ¼ 0.0870
R1 ¼ 0.0660
wR2 ¼ 0.0967
1.058
R1
¼ ¼ 0.0426
[I > 2
s
(I)]
wR2 ¼ 0.0885
R1 ¼ 0.0769
wR2 ¼ 0.1014
1.025
R indices (all data)
Gof/F2
Largest diff. peak/hole (e Åꢀ3
)
0.265/ꢀ0.276
0.307/e0.495
0.377/e0.338

N. Novoa et al. / Journal of Organometallic Chemistry 762 (2014) 19e28
27
and extracted with CH2Cl2. The combined organic extracts were
dried over MgSO4 and the solvent was evaporated to dryness. The
solid residue was dissolved in a minimum amount of DCM and
absorbed on a column packed with silica gel (grade 60). Elution
with petroleum etherediethyl ether (1:4) produced the release of a
red band that was collected. The solvent was evaporated under
reduced pressure, affording 105 mg (20% yield) of 7 as an orange
powder. M.p. 132e134 ꢁC. HRMS-ESIþ (based on 56Fe) C32H26O3Fe
Científico y Tecnológico [FONDECYT (Chile), grant no. 1090310
(C.M. and D.C.)], the Vicerrectoría de Investigación y Estudios
Avanzados, Pontificia Universidad Católica de Valparaíso, Chile
(C.M. and D.C.), the CNRS, the MESR and the Université de Rennes 1
is gratefully acknowledged. N.N. thanks the CONICYT (Chile) for
support of a graduate fellowship and the French Embassy in Chile
for the 2011 scholarship awarded doctoral internship.
ꢃ
[M]þ m/z calcd: 514.1231; found: 514.1228 (1 ppm). IR (KBr, cmꢀ1):
Appendix A. Supplementary material
3440 (br) (OeH), 1729 (m), 1655 (m), 1628 (m), 1602 (m), 1585 (m)
(C]O) and/or (C]C), 1262e1026 (m) (CeO), 800 (m) and 760 (m)
CCDC 949438e949440 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
(CeH). 1H NMR (500 MHz, CDCl3, 25 ꢁC): enol form (73%)
d 1.93 (s,
3H, CH3), 4.28 (t, 3JH,H ¼ 1.4 Hz, 2H, C5H4), 4.43 (t, 3JH,H ¼ 1.4 Hz, 2H,
3
3
C5H4), 4.48 (t, JH,H ¼ 1.5 Hz, 2H, C5H4), 4.76 (t, JH,H ¼ 1.6 Hz, 2H,
C5H4), 5.38 (s, 1H, H-7), 5.65 (s, 1H, CH acac), 6.27 (s, 1H, H-3), 6.78
(s, 1H, H-5), 7.39e7.43 (m, 6H, H-23,24,25 and H-63,64,65), 7.69e
7.76 (m, 4H, H-22,26 and H-62,66), 15.98 (s, 1H, OH); keto form
Appendix A. Supplementary data
(27%) d 2.28 (s, 3H, CH3), 3.81 (s, 2H, CH2), 4.32 (s, 2H, C5H4), 4.46 (s,
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.03.029.
2H, C5H4), 4.54 (s, 2H, C5H4), 4.76 (s, 2H, C5H4), 5.45 (s, 1H, H-7),
6.35 (s, 1H, H-3), 6.79 (s, 1H, H-5), 7.38e7.40 (m, 6H, H-23,24,25 and
H-63,64,65), 7.52e7.54, 7.69e7.71 (2ꢂ m, 2ꢂ 2H, H-22,26 and H-
References
62,66). 13C NMR (125 MHz, CDCl3, 25 ꢁC): enol form (73%)
d 24.0
(CH3) 69.5 (C5H4), 69.6 (C5H4), 70.3 (C5H4), 72.7 (C5H4), 78.3 (Cipso
C5H4), 86.1 (Cipso C5H4), 97.6 (CH3C(OH)]CH), 102.8 (C-3), 108.4
(C-5), 108.9 (C-7), 124.4, 124.8, 128.6, 128.7, 128.8, 128.9 (CeH
arom), 132.5 (C-4), 133.4 (C-61), 133.7 (C-21), 149.6 (C-6), 151.9
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