Stepwise construction of a 4-hydroxyphenyl functionalized O,N,N-tridentate ferrocene-containing enaminone: Spectral, analytical and structural studies

Article abstract of DOI:10.1016/j.ica.2012.04.028

Tetrahydropyranylation of methyl-4-hydroxybenzoate proceeds with formation of its corresponding THP aromatic ether THP-O-p-C₆H ₄CO₂CH₃ (1; THP = tetrahydropyranyl, C ₅H₉O). Reaction with in

Full text of DOI:10.1016/j.ica.2012.04.028

Inorganica Chimica Acta 390 (2012) 184–189
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Inorganica Chimica Acta
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Stepwise construction of a 4-hydroxyphenyl functionalized O,N,N-tridentate
ferrocene-containing enaminone: Spectral, analytical and structural studies
a
Salvador Celedon a, Mauricio Fuentealba b, Thierry Roisnel c, Jean-René Hamon c, , David Carrillo ,
⇑
Carolina Manzur a,
⇑
a Laboratorio de Química Inorgánica, Instituto de Química, Pontificia Universidad Católica de Valparaíso, Campus Curauma, Avenida Universidad 330, Valparaíso, Chile
b Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK
c UMR 6226 ‘‘Sciences Chimiques de Rennes’’, CNRS-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:
Tetrahydropyranylation of methyl-4-hydroxybenzoate proceeds with formation of its corresponding THP
aromatic ether THP–O–p-C6H4CO2CH3 (1; THP = tetrahydropyranyl, C5H9O). Reaction with in situ gener-
ated carbanion of acetylferrocene gave the protected organometallic complex Fc–C(@O)CH@C(OH)
Received 15 February 2012
Received in revised form 19 April 2012
Accepted 20 April 2012
(p-C6H4–O–THP) (2, Fc@(g g
5–C5H5)Fe( 5–C5H4)) featuring keto-enol functionality; subsequent acidic
Available online 28 April 2012
treatment of 2 afforded the 4-hydroxyphenyl substituted counterpart Fc–C(@O)CH@C(OH)(p-C6H4OH)
(3) that exists as a 73/27 mixture of keto-enol/b-diketone tautomers in DMSO solution. The functional-
ized tridentate metalloligand Fc–C(@O)CH@C(p-C6H4OH)N(H)CH2CH2NH2 (4) incorporating O,N,
N-donors is readily obtained upon Schiff base condensation of 3 with 1,2-diaminoethane. Complex 4
exists exclusively as its ferrocenyl-enaminone tautomer in solution and in the solid state. Compounds
1–4 were characterized by NMR (1H, 13C) and IR spectroscopy as well as by elemental analysis and
single-crystal X-ray diffraction.
This article is dedicated to the memory of
our friend and colleague Dr. Andrés Goeta.
Keywords:
Ferrocene
Enaminone
Metalloligand
Tridentate ligand
O,N,N ligand
X-ray structure
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
benzyldithiocarbazate, 2-aminoethanol or hydroxyanilines, and 2-
(aminomethyl)pyridine, respectively. Both organic and organome-
In the beginning of the 1980’s, Costes and co-workers reported
on the monocondensation reaction of 2,4-pentanedione with 1,2-
diaminoethane leading to the formation and the first isolation of
the stable and easily handled O,N,N-tridentate unsymmetrical
Schiff base 7-amino-4-methyl-5-aza-3-hepten-2-one, CH3C(@O)
CH@C(CH3)N(H)CH2CH2NH2 [1]. Its organometallic counterpart
containing the ubiquitous ferrocenyl subunit Fc–C(@O)
tallic singly condensed compounds are referred as ‘‘half units’’ or
‘‘hemi-ligands’’ [1,8], and in solution they can exist as a tautomeric
mixture of keto-amine (enaminone) and keto-imine (iminone)
forms [9]. The anionic deprotonated forms of the above mentioned
tridentate enaminones can be viewed as potentially pseudo-iso-
electronic with the cyclopentadienyl anion bearing a pendant do-
nor arm. They could, therefore, serve as good chelating ligands
for transition metals, lanthanides and main group elements with
for instance, potential applications in catalysis [10,11]. On the
other hand, replacement of the terminal methyl group of the par-
ent enaminone by the electronically related three-dimensional
ferrocenyl fragment brought about not only an expansion of the
important structural organic moiety into the third dimension
[12], but also the very useful redox properties [13], and the extre-
mely rich chemistry of ferrocene [14]. Accordingly, our interest in
the development of half unit metalloligands stemmed from their
potential as building blocks for the preparation, upon condensation
with salicylaldehydes, of a new class of unsymmetrical tetraden-
tate salen-type ligands and their metal-centered complexes substi-
tuted with donor and acceptor organometallic moieties [15],
exhibiting second-order nonlinear optical (NLO) responses [16].
H@C(CH3)N(H)CH2CH2NH2 (Fc@(g g
5–C5H5)Fe( 5–C5H4)) was pre-
pared during the same decade [2], and structurally characterized
by us almost twenty years later [3]. At the same time, we also re-
ported on the synthesis and X-ray crystal structure of its relative
O,N,N-tridentate metalloligand formed from monocondensation
of ferrocenoylacetone and 1,2-phenylenediamine [4]. In the middle
of the 2000’s, Shi et al. also disclosed related tridentate metalloli-
gand exhibiting O,N,S [5], O,N,O [6], and O,N,N-donor sets [7]; they
were obtained by monocondensation of ferrocenoylacetone with S-
⇑
Corresponding authors. Fax: +33 223 23 56 37 (J.-R. Hamon), +56 32 227 49 39
(C. Manzur).
E-mail addresses: jean-rene.hamon@univ-rennes1.fr (J.-R. Hamon), cmanzur@
ucv.cl (C. Manzur).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.04.028

S. Celedon et al. / Inorganica Chimica Acta 390 (2012) 184–189
185
Thus, in pursuit of this work, we have focused on the design of a
novel metalloligand functionalized with a phenolic group at the
three-position of the hex-2-en-4-azo chain thus, leaving the
O,N,N-donor set of the enaminone core available for further reactiv-
ity. The potential anchoring group might then be covalently bound
to an organic or inorganic substrate through a single point of
attachment, in order to immobilize catalysts [17] or to obtain ori-
ented non-centrosymmetric materials showing NLO activity [18].
Herein, we report on the stepwise synthetic approach of the 4-
hydroxyphenyl functionalized organometallic enaminone, Fc–
C(@O)CH@C(p-C6H4OH)N(H)CH2CH2NH2 (4), as well as of its three
precursors isolated along its four-step construction, using only
commercially available reagents. The first step consists in the pro-
tection of hydroxyl group of methyl-4-hydroxybenzoate via a tetra-
hydropyranylation reaction [19], to produce the corresponding THP
aromatic ether derivative 1 (THP = tetrahydropyranyl). Its reaction
with the in situ generated carbanion of acetylferrocene gave the
protected organometallic b-diketone 2, of which the THP protecting
group is subsequently removed by acidic treatment to afford the 4-
hydroxyphenyl substituted b-diketone 3. Finally, the unprece-
dented functionalized tridentate metalloligand 4 incorporating
O,N,N-donors is obtained upon Schiff base condensation of 3 with
1,2-diaminoethane. The formation of 1–4 (see formulae in Schemes
1 and 2) was proven by FT-IR and NMR spectroscopy, and unambig-
uously established by single-crystal X-ray structural analyses.
Scheme 2. Synthesis of the protected and deprotected organometallic diketones 2
and 3, and of the O,N,N-tridentate metalloligand 4.
aqueous solution of NaCl (30 mL) to remove PPTS. The obtained
emulsion was treated with diethyl ether (50 mL) giving two
phases. The saline aqueous phase containing PPTS was discarded.
This procedure was repeated three times. Finally, the organic phase
was dried over MgSO4, filtered, evaporated and chromatographed
through silica gel 70–230 mesh, using a mixture of hexane/ethyl
acetate (4:1) as eluent. The solvents were removed under vacuum
and evaporated to dryness, and the residue recrystallised from
diethyl ether/hexane (1:1) to give the pure colorless crystalline so-
lid of 1. Yield: 1.01 g, 65%. A suitable crystal of this crop was used
for a X-ray crystal structure determination. Mp: 62 °C. Anal. Calc.
for C13H16O4 (236.27 g molꢀ1): C, 66.09; H, 6.83. Found: C, 66.26;
2. Experimental
2.1. General experimental methods
H, 6.79%. IR (KBr pellet, cmꢀ1): 3066 (vw), 3017 (w)
2985 (w), 2969 (w), 2950 (m), 2892 (w), 2846 (w)
m
m
m
(CH arom),
(CH aliph),
Reactions were performed under a nitrogen atmosphere using
standard Schlenk techniques. Solvents were dried and distilled un-
der dinitrogen by standard methods prior to use. All chemicals
were purchased from Aldrich and used without further purifica-
tion. IR spectra of solid samples of complexes 1–4 were recorded
on a Perkin Elmer model 1600 FT-IR spectrophotometer, in the
range 4000–450 cmꢀ1. NMR spectra were obtained at 298 K on a
Bruker Avance III 400 spectrometer (1H NMR at 400.13 MHz and
13C NMR at 100.6 MHz). The chemical shifts are referenced to the
residual deuterated solvent peaks. Chemical shifts (d) and coupling
constants (J) are expressed in parts per million (ppm) and hertz
(Hz), respectively. Microanalyses were conducted on a Thermo-
FINNIGAN Flash EA 1112 CHNS/O analyzer by the Microanalytical
Service of the CRMPO at the University of Rennes 1, France. Melting
points were measured in evacuated capillaries on a Kofler Bristo-
line melting point apparatus.
1713 (vs)
m
(C@O), 1286 (vs), 1243 (vs), 1172 (vs)
(C–O). 1H
NMR (CDCl3): 1.63 (m, 2H, CH2 THP), 1.82 (m, 2H, CH2 THP), 1.94
(m, 2H, CH2 THP), 3.58 (m, 1H, CH2–O), 3.79 (m, 1H, CH2–O), 3.83
3
(s, 3H, CH3), 5.55 (t, JH,H = 3.2 Hz, 1H, O–CH–O), 7.11 (d,
3
3JH,H = 8.8 Hz, 2H, C6H4), 7.94 (d, JH,H = 8.8 Hz, 2H, C6H4).
2.2.2. Synthesis of 2
To a solution of acetylferrocene (0.81 g, 3.56 mmol) in THF
(15 mL) was added potassium tert-butoxide (0.48 g, 4.27 mmol)
and the reaction mixture was stirred at room temperature (rt) for
45 min. Then, a solid sample of 1 (1.00 g, 4.27 mmol) was added
to the reaction medium which was allowed to stir for 5 h before
addition of a 0.5 M aqueous hydrochloric acid solution (20 mL).
The obtained emulsion was treated with diethyl ether (3 ꢁ 50 mL)
according to the method described in Section 2.2.1. The resulting
concentrated organic phase was absorbed on silica gel (70–230
mesh) and eluted with a mixture of hexane/diethyl ether (1:4).
Slow evaporation of this eluate deposited orange-red, rod-shaped
crystals of 2 suitable for X-ray single crystal analysis. Yield:
0.93 g, 51%. Mp: 178 °C. Anal. Calc. for C24H24FeO4 (432.30 g molꢀ1):
C, 66.68; H, 5.60. Found: C, 66.69; H, 5.68%. IR (KBr pellet, cmꢀ1):
2.2. Syntheses and characterization
2.2.1. Synthesis of 1
To a solution of methyl-4-hydroxybenzoate (1.00 g, 6.57 mmol)
and of pyridinium-p-toluensulfonate (PPTS) (0.35 g, 1.4 mmol) in
methylene chloride (50 mL), was added 3,4-dihydro-2H-pyran
(DHP) (0.72 mL, 7.89 mmol). The reaction mixture was stirred for
5.0 h at room temperature (rt), and then washed with a saturated
3437 (w)
2875 (vw), 2850 (vw)
(C@C), 1237 (vs), 1174 (vs)
m
(OH), 3098 (vw), 3086 (vw)
(CH aliph), 1603 (vs)
(C–O). 1H NMR (CDCl3): 1.61(m, 2H,
m
(CH arom), 2940 (w),
m
m(C@O), 1556 (s)
m
m
CH2 THP), 1.70 (m, 2H, CH2 THP), 1.89 (m, 2H, CH2 THP), 3.63 (m,
1H, CH2–O), 3.87 (m, 1H, CH2–O), 4.22 (s, 5 H, C5H5), 4.54(s, 2H,
3
Hb C5H4), 4.88 (s, 2H, H C5H4), 5.53 (t, JH,H = 2.5 Hz, 1H, O–CH–
a
3
O), 6.33 (s, 1H, CH@C), 7.13 (d, JH,H = 8.8 Hz, 2H, C6H4), 7.90 (d,
3JH,H = 8.8 Hz, 2H, C6H4), 16.67 (s, 1H, OH).
2.2.3. Synthesis of 3
To a solution of 2 (0.90 g, 2.08 mmol) in THF (20 mL) was added
a 2.0 M aqueous hydrochloric acid solution (20 mL). The reaction
Scheme 1. Synthesis of the protected tetrahydropyranyl aromatic ether 1.

186
S. Celedon et al. / Inorganica Chimica Acta 390 (2012) 184–189
mixture was stirred for 30 min at rt before being treated with
diethyl ether (3 ꢁ 30 mL) according to the method described in
Section 2.2.1. The organic phase was evaporated to dryness and
the obtained solid was chromatographed on silica gel and eluted
with pentane/diethyl ether (7:3). The eluate was then allowed to
stand at –3 °C for 7 d, which results in the separation of red crystals
of 3, of which a clear dark red one was selected for a X-ray single
crystal analysis. Yield: 0.58 g, 81%. Mp: 125 °C. Anal. Calc. for
culated positions. Details about the data collection and refinement
for the X-ray structures of compounds 1–4 are documented in
Table 1, and additional crystallographic details are in the CIF files.
3. Results and discussion
In 1957, Hauser and Lindsay first reported the preparation of
the parent–diketone derivative 1-ferrocenyl-3-phenylpropane-
1,3-dione resulting from condensation of acetylferrocene with
methyl benzoate, by using potassium amide as the active base
additive in liquid ammonia [24]. Fifty years later, we disclosed that
the deprotonation of acetylferrocene can be effected under more
practical conditions by using potassium tert-butoxide as the active
base initiator in tetrahydrofuran (THF) at room temperature [15a].
In order to introduce a functional 4-hydroxyphenyl group onto the
ferrocenyl b-diketone framework under basic conditions the hy-
droxyl group must first be protected. This was achieved using the
tetrahydropyranylation reaction that has been recognized as an
useful and representative method for the protection of alcohols un-
der mild conditions [19].
C
19H16FeO3 (348.18 g molꢀ1): C, 65.54; H, 4.63. Found: C, 65.67;
H, 4.67%. IR (KBr pellet, cmꢀ1): 3445 (vw)
(OH), 3121 (m), 3094
(m) (CH arom), 2952 (w), 2736 (w), 2674 (w), 2601 (w) (CH
aliph), 1607 (vs) (C@O), 1577 (s)
(C@C). 1H NMR ((CD3)2SO):
Keto-enol tautomer, 4.21 (s, 5 H, C5H5), 4.62 (br s, 2H, Hb C5H4),
m
m
m
m
m
3
5.05 (br s, 2H, H C5H4), 6.68 (s, 1H, CH@C), 6.90 (d, JH,H@8.3 Hz,
a
3
2H, C6H4), 7.96 (d, JH,H = 8.3 Hz, 2H, C6H4), 10.30 (br s, 1H,
C6H4OH); b-diketone tautomer, 4.26 (s, 5 H, C5H5), 4.41 (s, 2H,
CH2), 4.62 (br s, 2H, Hb C5H4), 4.83 (br s, 2H, H C5H4), 6.86 (d,
a
3
3JH,H = 8.5 Hz, 2H, C6H4), 7.92 (d, JH,H = 8.5 Hz, 2H, C6H4), 10.40
(br s, 1H, C6H4OH). 13C{1H} NMR ((CD3)2SO): Keto-enol tautomer,
68.55 (C C5H4), 69.99 (C5H5), 71.99 (Cb C5H4), 77.94 (Cipso C5H4),
a
92.29 (CH@C), 115.42 (C6H4), 125.25 (Cipso C6H4), 129.09 (C6H4),
161.40 (C–OH), 180.23 (CH@C), 192.03 (C@O); b-diketone tauto-
3.1. Synthesis, characterization and X-ray diffraction study of the
protected tetrahydropyranyl aromatic ether 1
mer, 50.17 (CH2), 69.53 (C C5H4), 69.70 (C5H5), 72.50 (Cb C5H4),
a
79.12 (Cipso C5H4), 115.23 (C6H4), 128.28 (Cipso C6H4), 131.24
(C6H4), 162.34 (C–OH), 192.88 (C(@O)–C6H4), 198.00 (C(@O)–
C5H4).
Treatment of methyl-4-hydroxybenzoate solution in dichloro-
methane with a slight excess of 3,4-dihydro-2H-pyran in the pres-
ence of pyridinium-p-toluensulfonate (PPTS) as catalyst [19], at
ambient temperature for 5 h, led to the tetrahydropyranylation
product with composition (C5H9O)–p-OC6H4CO2CH3 (1), in 65%
yield (Scheme 1, see Section 2.2.1 for experimental details). Com-
pound 1 is a colorless crystalline solid with good solubility in
THF, diethyl ether and acetone.
The formation of the THP ether species 1 was readily noticed in
the 1H NMR spectrum. Beside the sharp singlet at d = 3.83 ppm for
the methyl ester group, 1 exhibited a series of five multiplets rang-
ing between d = 1.63 and 3.79 ppm, and a triplet at d = 5.55 ppm for
the THP ring protons in CDCl3. In the solid state IR spectrum, the
2.2.4. Synthesis of 4
To a solution of 3 (0.50 g, 1.44 mmol) in ethanol (10 mL) in a
Schlenk flask equipped with a condenser were added a solution
of ethylenediamine (0.30 mL, 4.32 mmol) in ethanol (5 mL) and
two drops of glacial acetic acid. The reaction mixture was refluxed
for 3 h. The red solid formed was filtered off and washed with cold
ethanol (3 ꢁ 5 mL) and then with diethyl ether (3 ꢁ 5 mL). Recrys-
tallization from hot methanol gave the orange-red crystalline solid
4. Yield: 0.25 g, 45%. A clear light orange crystal from this crop was
selected for X-ray crystallography. Mp: 186 °C (dec). Anal. Calc. for
C
21H22FeN2O2 (390.27 g molꢀ1): C, 64.63; H, 5.68; N, 7.18. Found:
C, 64.09; H, 5.71; N, 6.91%. IR (KBr pellet, cmꢀ1): 3437 (w)
(OH),
3366 (m) sym(NH2), 3280 (w) (NH), 3100 (vw), 3080 (vw)
(CH arom), 2976 (vw), 2962 (vw), 2921 (vw), 2876 (vw) (CH
aliph), 1610 (m) (C@O), 1582 (vs)
(C@C), 1545 (m) d(NH2). 1H
ester functionality is identified by an intense m(C@O) stretching
m
band at 1713 cmꢀ1. In addition, the structure of compound 1 was
unambiguously established by low-temperature single-crystal X-
ray structure analysis.
m
m
m
m
m
m
3
The molecular structure of 1 is displayed in Fig. 1, with selected
bond distances and angles given in the caption. It showed the
effective tetrahydropyranylation of the phenol group, with THP
ring adopting a rigid chair conformation (Fig. 1). A structural fea-
ture of this THP ring to be noted is the two different oxygen-carbon
bond lengths, O(4)–C(9) and O(4)–C(13) of 1.4178(16) and
1.4411(15) Å, respectively. That could be attributed to the moder-
ate electron withdrawing effect of the p–O–C6H4CO2CH3 group at
the C(9) atom. The C–C distances in the phenylene ring fall be-
tween 1.3820(18) and 1.3936(19) Å (avg = 1.3898(18) Å) whereas
those of the pyranyl group are found between 1.5120(18) and
1.5303(19) Å (avg = 1.5222(18) Å).
NMR ((CD3)2SO): 2.63 (t, JH,H = 6.0 Hz, 2H, CH2NH2), 3.14 (q,
3JH,H = 5.5 and 6.0 Hz, 2H, N(H)CH2), 4.13 (s, 5H, C5H5), 4.38 (t,
3JH,H = 1.8 Hz, 2H, Hb C5H4), 4.72 (t, JH,H = 1.8 Hz, 2H, H C5H4),
3
a
3
5.36 (s, 1H, CH@C), 6.82 (d, JH,H = 8.4 Hz, 2H, C6H4), 7.22 (d,
3JH,H = 8.4 Hz, 2H, C6H4), 10.83 (t, JH,H = 5.5 Hz, 1H, NH). 13C{1H}
3
NMR ((CD3)2SO): 42.10 (CH2NH2), 47.32 (N(H)CH2), 68.05 (C
a
C5H4), 69.36 (C5H5), 70.29 (Cb C5H4), 82.98 (Cipso C5H4), 93.66
(CH@C), 115.20 (C6H4), 125.98 (Cipso C6H4), 129.37 (C6H4), 158.57
(C–OH), 164.16 (CH@C), 190.44 (C@O).
2.3. Crystal structure determinations
Diffraction data were collected at 120 K on a Oxford Diffraction
Gemini CCD diffractometer and processed using the Oxford Diffrac-
tion CrysAlisPRO software for 1, 3 and 4, and at 150 K on an APEX II
Bruker-AXS diffractometer for 2, using in both cases graphite-
3.2. Synthesis and characterization of protected and deprotected
ferrocenyl b-diketones 2 and 3
monochromated Mo-K
a
radiation (k = 0.71073 Å). Using OLEX2
The stirring of a THF suspension of [Fc–C(@O)CH2]K, in situ gen-
erated by deprotonation of acetylferrocene with tBuOK, with a
slight excess of the organic species 1 for 5 h at room temperature
yielded the THP-protected organometallic precursor Fc–
C(@O)CH@C(OH){p-C6H4(2–O–C5H9O)} (2), isolated as orange-red
crystalline solid in 51% yield (Scheme 2). Subsequent acid hydroly-
sis (2.0 M aq. HCl) of a THF solution of 2 afforded the deprotected
organometallic b-diketone Fc–C(@O)CH@C(OH)(p-C6H4OH) (3,
[20], the structures of 1, 3 and 4 were solved with the SHELXS struc-
ture solution program [21], using direct methods, while the struc-
ture of 2 was solved by direct methods using SIR97 [22]. They were
refined with the SHELXL refinement package [21], using full-matrix
least squares techniques based on F2 with aid of WINGX program
[23]. All non-hydrogen atoms were refined with anisotropic dis-
placement parameters. H atoms were finally included in their cal-

S. Celedon et al. / Inorganica Chimica Acta 390 (2012) 184–189
187
Table 1
Crystallographic data, details of data collection and structure refinement parameters for compounds 1–4.
Compound
1
2
3
4
Empirical formula
C
13H16O4
C24H24FeO4
432.28
C19H16FeO3
348.17
C21H22FeN2O2
390.26
Formula weight, (g molꢀ1
)
236.26
Collection T (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
120(2)
monoclinic
C2/c
19.1563(10)
7.5570(4)
17.1881(9)
110.869(3)
2325.0(2)
8
150(2)
monoclinic
P21/a
10.1967(7)
11.9793(9)
16.1904(11)
90.853(3)
1977.4(2)
4
120(0)
orthorhombic
Pbca
9.7943(6)
17.2850(16)
17.4952(5)
90.00
2961.8(3)
8
120(2)
monoclinic
P21/c
9.1849(2)
9.72339(18)
20.6783(4)
101.185(2)
1811.68(7)
4
b (°)
V (Å3)
Z
Dcalc (g cmꢀ3
)
1.350
1.452
1.562
1.431
Crystal size (mm)
0.25 ꢁ 0.3 ꢁ 0.5
0.4 ꢁ 0.1 ꢁ 0.06
0.27 ꢁ 0.1 ꢁ 0.04
0.28 ꢁ 0.1 ꢁ 0.09
F(000)
1008
904
1440
816
Absorption coefficient (mmꢀ1
h Range(°)
)
1.031
0.791
0.100
0.850
5.44–58.38
5.21–58.53
ꢀ23/23, ꢀ9/9, ꢀ21/21
11677
2294
99.9
3.40–27.48
ꢀ13/10, ꢀ15/15, ꢀ19/21
29524
4499
99.1
2.28–52.04
ꢀ13/12, ꢀ23/23, ꢀ23/23
37603
3744
92.1
Range h, k, l
ꢀ12/12, ꢀ13/13, ꢀ28/26
Total reflections
Unique reflections
Comp. to hmax (%)
63872
4717
95.8
Maximum/minimum transmission
Data/restraints/parameters
Final R indices [I > 2(I)]
0.954/0.735
4499/0/262
R1 = 0.0771, wR2 = 0.2294
R1 = 0.0952, wR2 = 0.2425
1.153
1.000/0.848
3744/0/210
R1 = 0.0312, wR2 = 0.0679
R1 = 0.0411, wR2 = 0.0724
1.052
1.000/0.868
4717/4/246
R1 = 0.0389, wR2 = 0.0758
R1 = 0.0645, wR2 = 0.0856
1.035
0.401/ꢀ0.412
2294/0/155
R1 = 0.0396, wR2 = 0.1066
R1 = 0.0501, wR2 = 0.1129
1.045
0.283/ꢀ0.224
R indices (all data)
Goodness of fit (GOF) on F2
Largest difference in peak and hole (e Åꢀ3
)
1.247/ꢀ0.626
0.382/ꢀ0.349
is presumably due to the high solubility of 2 in chloroform allow-
ing the preparation of saturated NMR solutions. It is known that
high concentrations drive the keto-enol equilibrium towards the
enol side [25]. By contrast, the 1H NMR1H NMR spectrum of the
much less soluble compound 3, recorded at 25 °C in DMSO-d6,
showed that it does exist as a mixture of keto-enol and b-diketone
tautomers in a 73:27 ratio. The vinylic C–H singlet at 6.68 ppm
(1H) for the keto-enol form gave rise to a sharp resonance at
4.41 ppm (2H) for the b-diketone isomer. The broad downfield
shifted O–H enol proton was not observed but has been located
at 17.15 ppm in acetone-d6, in which solvent a complete enoliza-
tion is achieved (see Supplementary information). The phenolic
proton resonates at 10.30 and 10.40 ppm, respectively and vanish
upon addition of D2O. The 13C NMR spectrum of 3 in DMSO-d6 con-
firms the existence of the keto-enol/b-diketone tautomeric mix-
ture. The methyne carbon (C(12), see Fig. 2 for the labeling
scheme) resonates at 92.29 ppm for the keto-enol form, while it
shows up at 50.17 ppm for the b-diketone derivative. At the same
Fig. 1. Molecular structure of 1 with the atom numbering scheme. Hydrogen atoms
have been omitted for clarity. Thermal ellipsoids are drawn at 50% probability.
Selected bond distances (Å) and angles (°): O(1)–C(1) 1.4488(15), O(1)–C(2)
1.3453(16), O(2)–C(2) 1.2074(16), O(3)–C(6) 1.3744(15), O(3)–C(9) 1.4123(15),
O(4)–C(9) 1.4178(16), O(4)–C(13) 1.4411(15), C–C(Ph) avg = 1.3898(18), C–C(pyr-
anyl) avg = 1.5222(18); C(1)–O(1)–C(2) 114.92(10), O(1)–C(2)–O(2) 123.21(12),
C(6)–O(3)–C(9) 118.73(10), O(3)–C(9)–O(4) 106.83(10), C(9)–O(4)–C(13)
110.65(10).
time, C(13) experiences
192.88 ppm.
a downfield shift from 180.23 to
81%) as dark red crystals upon work up (Scheme 2). Both 2 and 3
are soluble in THF, diethyl ether and methylene chloride. The
two air and thermally stable complexes were characterized by
spectroscopic, elemental and X-ray diffraction analyses (see
Section 3.4).
3.3. Synthesis and characterization of the O,N,N-tridentate
The solid state IR spectra of 2 and 3 showed C@O and C@C in-
tense stretching bands at 1603/1556 and 1607/1577 cmꢀ1, respec-
tively, in agreement with keto-enol tautomeric forms. The 1H
NMR1H NMR spectra of 2 and 3 showed common similar reso-
nances consistent with the [Fc–C(@O)CH@C(p-C6H4–)] framework;
those are a singlet and two triplets or broad singlets for the ferr-
ocenyl fragment, a singlet for the methine proton and two doublets
for the p-phenylene group (see Section 2 for details). Additionally,
the spectrum of 2 recorded at 25 °C in CDCl3 exhibited the same
signal pattern for the THP group as that observed for 1, and only
one set of two singlets at 6.33 and 16.67 ppm for the C–H and
O–H protons of the enol form, respectively. This solution behavior
is similar to that reported for the parent derivative Fc-C(O)CH@
C(Ph)OH, for which the percentage of keto-enol tautomeric form
was determined under the same conditions to be 95% [25]. This
metalloligand 4
The phenol substituted ferrocenyl keto-amine complex 4 (‘‘half
unit’’) with composition Fc–C(@O)CH@C(p-C6H4OH)N(H)CH2CH2
NH2 was successfully prepared by the monocondensation reaction
between ethylenediamine and precursor 3 (3:1) in refluxing etha-
nol for 3 h (Scheme 2). The tridentate metalloligand 4 incorporat-
ing O and N donors was isolated as an orange-red crystalline
solid in 45% reasonable yield. This air and thermally stable com-
pound exhibits a good solubility in DMSO and MeOH but is insol-
uble in non-polar solvents. FT-IR and multinuclear and 2D NMR
spectroscopies, single-crystal X-ray diffraction, and elemental
analysis served to confirm its structure. In addition, high resolution
ESI-MS of 4 gave an exact mass of m/z = 413.0928 for [M+Na]+ that
matched the calculated value of 413.09284 (Relative error: 0 ppm),

188
S. Celedon et al. / Inorganica Chimica Acta 390 (2012) 184–189
Table 2
Selected bond distances (Å) and angles (°) for compounds 2, 3, and 4.
2
3
4
Bond distances
C(6)–C(11)
O(1)–C(11)
C(11)–C(12)
C(12)–C(13)
C(13)–Xa
1.465(7)
1.253(6)
1.453(7)
1.356(8)
1.346(6)
1.481(7)
1.370(7)
1.390(8)
2.043(5)
2.040(5)
1.461(2)
1.2740(18)
1.422(2)
1.375(2)
1.3283(18)
1.464(2)
1.3507(19)
1.390(2)
2.0463(17)
2.0440(16)
1.480(2)
1.265(2)
1.423(3)
1.386(2)
1.348(2)
1.486(3)
1.357(2)
1.388(3)
2.044(2)
2.0434(18)
C(13)–C(14)
C(17)–Xb
C–C(Ph)c avg
Fe(1)–C(Cp)c avg
Fe–C(Cp0)c avg
Angles (°)
O(1)–C(11)–C(12)
C(11)–C(12)–C(13)
C(12)–C(13)–Xa
121.0(5)
121.2(5)
120.9(5)
120.41(14)
121.25(14)
120.73(14)
122.76(16)
123.81(17)
121.74(17)
a
X = O(2) for 2 and 3; X = N(1) for 4.
X = O(3) for 2 and 3; X = O(2) for 4.
Abbreviations: Cp = C5H5, Cp0 = C5H4, Ph = C6H4.
b
c
C@O group. The downfield position of this signal that disappeared
on deuteration with D2O, is in full agreement with the above dis-
cussed IR data and also supported by the crystal structure of
enaminone 4 (vide infra). Such observations are similar to that re-
ported for the monocondensation product obtained by reaction of
ferrocenoylacetone with ethylenediamine [2,3], 2-aminoethanol
[6], alkylanilines and o-anisidine [7,26]. In addition, the spectrum
of 4 contained a upfield shifted sharp vinylic C–H resonance at
5.36 ppm, compared to the 6.33 and 6.68 ppm chemical shifts ob-
served for 2 and 3, respectively. The methylene triplet and quadru-
plet resonances at 2.63 (2H) and 3.14 (2H) ppm, respectively,
reflect the asymmetry of the ligand. The terminal NH2 and phenolic
protons were not observed. The unsymmetrical nature of 4 is con-
firmed by the 13 lines observed in its decoupled 13C NMR spec-
trum. Specifically, the two methylene carbons resonate at 42.10
and 47.32 ppm, and the three carbons of the enaminone core show
up at 93.66 ppm for the C(12)-methyne, 164.16 ppm for the C(13)-
ene and 190.44 ppm for the C(11)-carbonyl carbon nuclei, respec-
tively (see Fig. 2 for the numbering scheme).
3.4. Molecular structures
Perspective views of the two organometallic keto-enol tautom-
ers 2 and 3, and of the O,N,N-tridentate enaminone 4 are shown in
Fig. 2, with selected bond distances and angles listed in Table 2.
The single-crystal X-ray diffraction studies confirm both the mono-
meric nature and that each compound exists as the Z–s–Z confor-
mational form.1 Complexes 2–4 contain a ferrocenyl unit with an
iron atom coordinated to the free and substituted cyclopentadienyl
rings at a ring centroid-iron distances of 1.652/1.642, 1.652/1.645
and 1.647/1.645 Å, with ring centroid-iron-ring centroid angle of
178.8°, 178.6° and 177.9°, respectively, indicating that there is a
Fe(II) oxidation state in each metallocene [27].
In the [O(1)–C(11)–C(12)–C(13)–X] central cores (X@O(2) for 2
and 3, N(1) for 4), the angles at C(11), C(12) and C(13) lie between
120.41(14)° and 123.81(17)° (Table 2) and that at N(1) (C(13)–
N(1)–C(20)) is of 125.73(16)°. Those values are very close to the
idealized value of 120° expected for a sp2-hybridized atom. The
O(1)–C(11, C(11)–C(12), C(12)–C(13) and C(13)–X bond lengths
Fig. 2. Molecular structures of 2 (top), 3 (middle), and 4 (bottom) with the atom
numbering schemes. Hydrogen atoms have been omitted for clarity. Thermal
ellipsoids are drawn at 50% probability.
and the expected isotopic distribution for the molecular ion peak
(Supplementary information, Fig. B1).
Like for precursors 2 and 3, the solid state IR spectrum of 4
showed C@O and C@C intense stretching bands at 1610/
1582 cmꢀ1, in accordance with a keto-enamine tautomeric form.
In addition, spectrum of 4 exhibited both symmetric and deforma-
tion stretching modes of the terminal NH2 group at 3366 and
1545 cmꢀ1, respectively, and a weak band at 3280 cmꢀ1 attributed
to the stretching vibration of the enamine N–H group. This band is
shifted to a lower energy as a consequence of the N–Hꢂ ꢂ ꢂO intra-
molecular hydrogen bond [9].
The metalloligands 4 was obtained as Z isomer, as deter-
mined by 1H NMR1H NMR spectroscopy carried out in DMSO-d6
at 25 °C, which showed a deshielded triplet of the amino proton
at 10.83 ppm due to hydrogen bonding between N–H and the
1
Such Fc–C(@O)CH@C–(R)XH derivatives may have the following four isomers: E–
s–E, E–s–Z, Z–s–E, and Z–s–Z in which E and Z refer to two possible geometric
conformations for the carbon–carbon double bond and s–E and s–Z to both isomerism
about the carbon–carbon single bond between the carbon–carbon and carbon–
oxygen double bonds; see Ref. [9].

S. Celedon et al. / Inorganica Chimica Acta 390 (2012) 184–189
189
observed in this planar skeleton correspond to alternating double-,
single-, double- and single-bonds (Table 2) [28], thus exhibiting
partial delocalization of the O@C–C@C–X system. Those metrical
parameters are consistent with a keto-enol tautomeric form for 2
and 3 and a keto-enamine form for 4, with an intramolecular
O(1)ꢂ ꢂ ꢂH–X which closes a six-membered pseudo-aromatic ring
through the resonant ꢂ ꢂ ꢂO@C–C@C–XHꢂ ꢂ ꢂ fragment [29]. The
Oꢂ ꢂ ꢂX separations are equal to 2.521(5), 2.4937(16) and
2.674(2) Å, respectively, in accordance with previously reported
structural data for ferrocene containing keto-enol or enaminone
derivatives [2,3,6,7,26,30]. In 2–4, the plane of the [OCCCX] frame-
work makes dihedral angles with the substituted cyclopentadienyl
ring of 25.3°, 16.5° and 7.3°, respectively, whereas the phenylene
ring is oriented out of this plane with dihedral angles of 19.5°,
23.1° and 53.1°, respectively. Clearly, for 4, the substituted cyclo-
pentadienyl ring may in part conjugate with the enaminonic skel-
eton whereas the phenylene ring is not involved in the conjugation
of this skeleton. In addition, the structure of complex 2 shows that
the tetrahydropyranyl protecting group adopts the same chair
conformation as already seen in its precursor 1 with two distinct
intracyclic C–O distances of 1.397(8) and 1.425(9) Å and C–C
bond lengths falling between 1.497(10) and 1.542(10) Å
(avg = 1.506(10) Å). In complex 4, the C–N distances in the ethyl-
ene diamine arm are identical (1.461(2) and 1.468(2) Å) and longer
by ꢃ0.12 Å than the C(13)–N(1) (1.348(2) Å) which is part of a
delocalized enaminonic system.
a postdoctoral fellowship. S.C. thank the CONICYT (Chile) for sup-
port of a graduate fellowship.
Appendix A. Supplementary material
CCDC-844554 (for 1), 844937 (for 2), 844555 (for 3) and 844556
(for 4); contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2012.04.028.
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nyl containing enaminone functionalized with a 4-hydroxyphenyl
group at the three-position of the hex-2-en-4-azo chain, Fc–
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The authors thank Drs S. Sinbandhit and P. Jehan (CRMPO, Re-
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spectrum of 4, respectively. This research has been performed as
part of the Chilean-French International Associated Laboratory
for ‘’Inorganic Functional Materials’’ (LIAMIF-CNRS N°836). Finan-
cial support from the Fondo Nacional de Desarrollo Científico y
Tecnológico [FONDECYT (Chile), Grant No. 1090310 (C.M., D.C.
and M.F.)], the Vicerrectoría de Investigación y Estudios Avanzados,
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