Synthesis and reactivity of η4-diene-Fe(CO)3 complexes from exo-2-oxazolidinone dienes. A facile generation of stable conjugated enol-enamido species

Article abstract of DOI:10.1021/om900772z

A synthesis of new η⁴ -diene-Fe(CO)₃ complexes derived from the novel exo-2-oxazolidinone dienes is described. These complexes were prepared by thermal complexation of the substituted dienes with diiron nonacarbonyl to afford the corresponding complexes as crystal solids. The X-ray single-crystal structure analysis revealed characteristic structural properties for diene-iron complexes, showing that in the conformation of the distorted trigonal-pyramidal geometry two of the carbonyl groups point out from the metal toward the vertex C4 and C5 atoms of the heterocycle. Unsuccessful functionalization of the diene moiety by acylation or alkylation of the allylic position indicated the strong stability of these dienes. This stability facilitated the generation of stable and unprecedented conjugated enamine-enol ester- and enamido-enol-Fe(CO)₃ complexes, by either kinetic or themodynamic control of the reaction conditions.

Full text of DOI:10.1021/om900772z

Organometallics 2010, 29, 149–159 149
DOI: 10.1021/om900772z
Synthesis and Reactivity of η4-Diene-Fe(CO)3 Complexes
from exo-2-Oxazolidinone Dienes. A Facile Generation of
Stable Conjugated Enol-Enamido Species
Fernando Ortega-Jimenez,†,§ Adriana Benavides,† Francisco Delgado,*,†
ꢀ
Hugo A. Jimenez-Vazquez, and Joaquı
†
´
n Tamariz*,†
ꢀ
ꢀ
†
´
ꢀ
ꢀ
Departamento de Quımica Organica, Escuela Nacional de Ciencias Biologicas-IPN, Prol. Carpio y Plan de
Ayala, 11340 Mexico, D. F., Mexico and Departamento de Ciencias Quımicas, Facultad de Estudios
§
ꢀ
´
Superiores Cuautitlaꢀn-UNAM, Campo 1, Cuautitlaꢀn Izcalli, Estado de Meꢀxico, 54740, Mexico
Received September 4, 2009
A synthesis of new η4-diene-Fe(CO)3 complexes derived from the novel exo-2-oxazolidinone dienes
is described. These complexes were prepared by thermal complexation of the substituted dienes with
diiron nonacarbonyl to afford the corresponding complexes as crystal solids. The X-ray single-crystal
structure analysis revealed characteristic structural properties for diene-iron complexes, showing that
in the conformation of the distorted trigonal-pyramidal geometry two of the carbonyl groups point
out from the metal toward the vertex C4 and C5 atoms of the heterocycle. Unsuccessful functiona-
lization of the diene moiety by acylation or alkylation of the allylic position indicated the strong
stability of these dienes. This stability facilitated the generation of stable and unprecedented
conjugated enamine-enol ester- and enamido-enol-Fe(CO)3 complexes, by either kinetic or themo-
dynamic control of the reaction conditions.
Introduction
tions,2 reductions,3 alkylations,4 and cycloadditions,4c,5
among others (Scheme 1).6 The Fe(CO)3 group can also
promote the stabilization of unstable dienes or dienic tauto-
mers.7 Moreover, the complex can be directly involved in the
functionalization of the diene through diverse reactions; for
instance, acylation,8 cyclocarbonylation,7a,9 formylation,10
alkylation,11 and isomerization (Scheme 1).12 The fact that
the deprotection of the η4-diene-Fe(CO)3 complexes is
an easy, practical, and efficient reaction converts these
complexes into a very attractive protecting group and syn-
thons in organic synthesis.13
The Fe(CO)3 group has been traditionally used as a
protecting group for conjugated dienes, as (η4-1,3-diene)-
Fe(CO)3 complexes.1 These complexes are stable enough to
allow the interconversion of functional groups (FGI) into the
same molecule with a variety of reactions such as oxida-
*Corresponding authors. Fax: (þ52)55-5729-6300/46211. E-mail:
jtamariz@woodward.encb.ipn.mx; fdelgado@woodward.encb.ipn.mx.
(1) (a) Donaldson, W. A. Transition Metal Alkene, Diene, and
Dienyl Complexes: Complexation of Dienes for Protection. In Compre-
hensive Organometallic Chemistry; Abel, E. W., Stone, F. G. A., Wilkinson,
G., Eds.; Pergamon Press: Oxford, UK, 1995; Vol. 12, pp 623-635. (b)
Davies, S. G. Organotransition Metal Chemistry: Application to Organic
Synthesis; Pergamon Press: Oxford, UK, 1982; pp 83-115. (c) Bates, R. W.
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r
2009 American Chemical Society
Published on Web 12/10/2009
pubs.acs.org/Organometallics

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Ortega-Jimenez et al.
150 Organometallics, Vol. 29, No. 1, 2010
Scheme 1. Diene Protecting and Activating Fe(CO)3 Group
in Transformation of Vicinal Functional Groups, as Well as
Acylation and Deprotonation/Electrophilation Reactions
Scheme 2. Synthesis of Dienes 3-5 from 1 and 2 and Their
Conversion to Natural Carbazoles
We have developed a tandem methodology to prepare the
novel N-substituted exo-2-oxazolidinone dienes 3-5,14
which involves a base-assisted condensation of R-diketones
2 and isocyanates 1 in the presence of a dehydrating agent
(Scheme 2). The use of the unsymmetrical R-diketones 2b
and 2c under similar reaction conditions furnished dienes 4
and 5 as a single regio- and stereoisomer.14b,c This metho-
dology has been successfully applied to the synthesis of 1,
4-dimethyl-substituted dienes15 and also of those analogues
containing the dienic moiety in a six-membered ring.16
Dienes 3 and 4 have proved to be useful synthons in the
preparation of carbazoles,17 leading to the total synthesis of
a series of naturally occurring carbazoles.18 Moreover, they
have been converted into new polycyclic oxazol-2-one deri-
vatives by a tandem [4þ2] cycloaddition/cyclopentannula-
tion/1,5-sigmatropic rearrangement process with Fischer
(arylalkynyl)(alkoxy)carbenes19 and have turned out to be
efficient substrates for the synthesis of η4:π2-diene-iridium(I)
complexes, whose reactivity with alkynylphosphines and
aldehydes was also studied.20
stability of dienes 3-5 was gathered from the Diels-Alder
addition to activated alkenes with electron-withdrawing
groups, such as methyl vinyl ketone14 and alkyl acrylates,18a
at high temperatures to afford the corresponding cycloadducts
in modest to good yields. Hence, by treatment of the dienes
with diiron nonacarbonyl in benzene at reflux, the series of
Fe(CO)3 complexes 6a-e, 7a-e, and 8a-e were obtained in
moderate to good yields (Table 1). It is noteworthy that the
novelty of these compounds resides, among other features, in
the fact that, to best of our acknowledge, there are few reports
of Fe(CO)3 complexes of exocyclic dienes substituted by two
heteroatoms.21
Actually, the general procedure was established by opti-
mizing the preparation of complex 6a (Table 1, entries 1-3),
in which the best molar ratio for the mixture diene/Fe2(CO)9
was 1:3, and the reaction temperature was set to that of the
refluxing solvent. Under these conditions, the reaction time
was shortened to 3 h, providing the best yield. However, the
efficiency of the procedure for the other analogues was not
the same, even changing some parameters of the reaction.
Although the yields were moderate for most of the cases, the
best ones were observed only for diene complexes 6a and 7a.
No correlation was found between yields and the kind or
position of the substituent in the benzene ring (Table 1). For
instance, the presence of a methyl group at the ortho position,
which can be expected to be more hindered, did not sig-
nificantly deplete the yield. In general, the reaction was clean
and almost no side products were detected, recovering the
unreacted starting dienes. A longer reaction time or further
addition of Fe2(CO)9 did not improve the conversion rate.
It should be noted that ortho-substituted N-aryl complexes
6b, 7b, and 8b were obtained as an inseparable mixture of
atropoisomers in about a 64:36 ratio. Structural analysis by
spectroscopy did not provide evidence about the relative
configuration of the major rotamer. However, it is expected
that the latter corresponds to the less hindered anti isomer
(the methyl group with respect to the Fe(CO)3 group).
Electronic Absorption, Infrared, and NMR Spectra of
Complexes 6-8. Ultraviolet (UV) spectra of dienes 3a, 4a,
and 5a and of complexes 6a, 7a, and 8a were measured in
acetonitrile as the solvent. The spectra of the dienes are
With the aim of evaluating the stability and versatility of
exo-2-oxazolidinone dienes 3-5, herein we describe the
synthesis, structural characterization, and spectral proper-
ties of the new (η4-1,3-diene)-Fe(CO)3 complexes 6-8, as
well as the study of their reactivity toward acylation and
alkyllithium addition reactions.
Results and Discussion
Preparation of (η4-exo-4-Methylene-5-alkylidene-2-oxazoli-
dinone)-Fe(CO)3 Complexes 6-8. Evidence of the thermal
ꢀ
ꢀ
ꢀ
(14) (a) Hernandez, R.; Sanchez, J. M.; Gomez, A.; Trujillo, G.;
Aboytes, R.; Zepeda, G.; Bates, R. W.; Tamariz, J. Heterocycles 1993,
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36, 1951–1956. (b) Mandal, A. B.; Gomez, A.; Trujillo, G.; Mendez, F.;
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Jimenez, H. A.; Rosales, M. J.; Martínez, R.; Delgado, F.; Tamariz, J. J. Org.
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Chem. 1997, 62, 4105–4115. (c) Fuentes, A.; Martínez-Palou, R.; Jimenez-
ꢀ
Vazquez, H. A.; Delgado, F.; Reyes, A.; Tamariz, J. Monatsh. Chem. 2005,
136, 177–192.
(15) Martı
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nez, R.; Jimenez-Vazquez, H. A.; Reyes, A.; Tamariz, J.
Helv. Chim. Acta 2002, 85, 464–482.
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(16) Martınez, R.; Jimenez-Vazquez, H. A.; Delgado, F.; Tamariz, J.
Tetrahedron 2003, 59, 481–492.
(17) Mandal, A. B.; Delgado, F.; Tamariz, J. Synlett 1998, 87–89.
(18) (a) Zempoalteca, A.; Tamariz, J. Heterocycles 2002, 57, 259–267.
(b) Benavides, A.; Peralta, J.; Delgado, F.; Tamariz, J. Synthesis 2004, 2499–
2504. (c) Bernal, P.; Benavides, A.; Bautista, R.; Tamariz, J. Synthesis 2007,
1943–1948. (d) Bernal, P.; Tamariz, J. Helv. Chim. Acta 2007, 90, 1449–
1454.
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(19) Reyes, L.; Mendoza, H.; Vazquez, M. A.; Ortega-Jimenez, F.;
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Fuentes-Benıtes, A.; Jimenez-Vazquez, H.; Flores-Conde, M. I.; Miranda,
R.; Tamariz, J.; Delgado, F. Organometallics 2008, 27, 4334–4345.
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Mendez-Rojas, M. A.; Tamariz, J.; Benavides, A. Organometallics 2006,
25, 172–176.
(21) Filippou, A. C.; Rosenauer, T. Angew. Chem., Int. Ed. 2002, 41,
2393–2395.

Article
Organometallics, Vol. 29, No. 1, 2010 151
Table 1. Preparation of η4-Diene Fe(CO)3 Complexes 6a-e,
Table 2. 1H NMR Selected Data of the Dienes 3a, 4a, and 5a and
7a-e, and 8a-ea
η4-Diene-Fe(CO)3 Complexes 6a-e, 7a-e, and 8a-ea
Mp
(°C)
yield
(%)b
δ (ppm)
entry diene
Ar
C6H5
C6H5
C6H5
C6H4-2-
Me
C6H4-4-
Me
C6H4-3-Cl
C6H4-4-Cl
C6H5
C6H4-2-
Me
C6H4-4-
Me
C6H4-3-Cl
C6H4-4-Cl
C6H5
C6H4-2-
Me
T (°C) t (h) complex
diene
H-7ab
4.35
H-7bb
H-6bc
Rd
4.93
1.86
2.33
2.59
2.59
2.58
2.60
2.60
1.83
1.84
1.83
1.83
1.83
2.24-2.34
2.01-2.19
2.22-2.42
2.02-2.13
2.24-2.35
2.02-2.14
2.24-2.32
2.03-2.13
2.24-2.33
1
2
3
4
3a
3a
3a
3b
40
60
80
80
12 6a
119-120
119-120
119-120
158-160
60
65
75
42
3ae
4ae
5af
6a
6b
6c
6d
6e
7a
7b
7c
4.76
4.58
4.59
0.33
0.30
0.30
0.34
0.32
0.20
0.19
0.19
0.22
0.21
0.20
0.19
4.98
5.42
5.38
0.51
0.50
0.50
0.52
0.51
1.27
1.27
1.27
1.29
1.29
1.17
1.14-1.23
8
3
3
6a
6a
6b
4.18
4.19
2.17
1.90
2.13
2.17
2.13
2.05
1.78
2.02
2.07
2.02
2.06
1.80
5
3c
80
3
6c
123-124
53
6
7
8
9
3d
3e
4a
4b
80
80
80
80
3
3
3
3
6d
6e
7a
7b
110-111
107-108
163-164
158-160
38
40
86
43
10
4c
80
3
7c
102-103
63
7d
7e
8a
8b
11
12
13
14
4d
4e
5a
5b
80
80
80
80
3
3
3
3
7d
7e
8a
8b
161-163
105-106
126-127
113-115
48
36
58
48
8c
8d
8e
2.03
0.18
0.22
0.19
1.15
1.18
1.18
2.02-2.14g
2.03
15
5c
C6H4-4-
Me
C6H4-3-Cl
C6H4-4-Cl
80
3
8c
113-114
52
16
17
5d
5e
80
80
3
3
8d
8e
121-122
127-128
59
48
a Conditions: Fe2(CO)9 (3.0 mol equiv), benzene, reflux, N2 atm.
a Measured in CDCl3, with TMS as internal standard. b As a doublet,
ca. J = 3.0 Hz, for dienes; ca. J = 5.2 Hz for complexes. c As a doublet,
J = 3.5 Hz, for diene 3a; as a quartet, J = 7.3 Hz, for diene 4a, and as
triplet, J = 7.7 Hz, for diene 5a; as a doublet, ca. J = 5.3 Hz for
complexes 6a-e; as a quartet, ca. J = 6.4 Hz for complexes 7a-e; as a
triplet, ca. J = 7.7 Hz for complexes 8a-e. d As a doublet, ca. J = 5.3 Hz,
for complexes 6a-e; as a doublet, ca. J = 6.4 Hz for complexes 7a-e; as
a multiplet for the methylene group of complexes 8a-e. e ref 14b. f Ref 28.
g Signal overlapped by the multiplet of the methylene group.
b Calculated after recrystallization.
similar between them, showing three separate high-intensity
bands in the range 204-209, 227-233, and 257-264 nm,
where the first and the latter are attributed to the aromatic
πfπ* transitions, and the central one is due to the diene
πfπ* transition (the calculated wavelength is about
229 nm).22 In the case of the spectra of complexes, the
carbonyl nfπ* transitions of the Fe(CO)3 group appear as
a low-intensity long-wavelength band at about 309-314 nm
as a tail of the high-intensity band.23 The latter is a broad
band showing a maximum and two additional absorptions as
well-defined shoulders, which are due to the overlapping of
aromatic and diene πfπ* transitions.24
The infrared (IR) spectra of the Fe(CO)3 complexes are
also similar between them. Strong bands appear in the
spectrum between 2100 and 1900 cm-1, which correspond
to the characteristic stretching frequencies of the carbonyl
groups of the Fe(CO)3 moiety.25 In addition, in the region of
1790-1750 cm-1, the spectra show a strong absorption due
to the CdO stretching mode of the carbamate heterocycle.
1H NMR spectra of the series of complexes 6-8 show
chemical shifts for all the vinylic protons that are largely
shielded with respect to those of the precursor dienes
(Table 2).26 Protons H-6b and H-7b (the in protons) are
more affected by the shielding effect of the tricarbonyliron
complex than protons H-6a and H-7a (the out protons). This
is due to the fact that the former are closer than the latter to
the coordination sphere of the metal.26,27 The larger upfield
shielding effect on the protons H-7a and H-7b with respect to
protons H-6 is a consequence of the larger delocalization of
the nitrogen atom lone-pair with respect to the oxygen atom
through the double bond, as also observed for the free-
complex dienes 3-5.14,28 The signals of the vinylic protons
were assigned by NOE experiments: For instance, for com-
plex 6a, irradiation of H-7a produced an enhancement of the
(22) Woodward, R. B. J. Am. Chem. Soc. 1942, 64, 72–75.
(23) Lundquts, T. T.; Cais, M. J. Org. Chem. 1962, 27, 1167–1172.
(24) For the full UV absorptions of dienes 3a, 4a, and 5a and of
complexes 6a, 7a, and 8a, see Table 1 in Supporting Information.
(25) (a) Pettit, R.; Emerson, G. F. Adv. Organomet. Chem. 1964, 1, 1–
46. (b) Emme, I.; Labahn, T.; de Meijere, A. Eur. J. Org. Chem. 2006, 399–
404. (c) Docherty, G. F.; Knox, G. R.; Pauson, P. L. J. Organomet. Chem.
1998, 568, 287–290. (d) Reboul, V.; Guillou, C.; Tha, C. Tetrahedron Lett.
1999, 40, 8355–8358. (e) Christie, S. D. R.; Cummins, J.; Elsegood, M. R. J.;
Dawson, G. Synlett 2009, 257–259.
(26) Danks, T. N.; Howells, M. E.; Ackland, M. J. J. Organomet.
Chem. 1999, 579, 53–58.
(27) (a) Chaudhury, S.; Donaldson, W. A.; Bennett, D. W.; Haworth,
D. T.; Siddiquee, T. A.; Kloss, J. M. J. Organomet. Chem. 2004, 689,
1437–1443. (b) Ackland, M. J.; Danks, T. N.; Howells, M. E. J. Chem. Soc.,
Perkin Trans. 1 1998, 813–817.
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(28) Benavides, A.; Martınez, R.; Jimenez-Vazquez, H. A.; Delgado,
F.; Tamariz, J. Heterocycles 2001, 55, 469–485.

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Ortega-Jimenez et al.
152 Organometallics, Vol. 29, No. 1, 2010
Figure 2. Molecular structure of 7a (ellipsoids at 30% prob-
ability level). Select bond lengths (A) and angles (deg): C(4)-Fe-
(1) 2.083(3), C(5)-Fe(1) 2.078(3), C(6)-Fe(1) 2.151(3),
C(7)-Fe(1) 2.109(3); C(5)-C(4)-N(3) 105.9(3), C(7)-C-
(4)-N(3) 132.7(3), N(3)-C(4)-Fe(1) 124.3(2), O(1)-C(5)-Fe-
(1) 124.1(2), C(4)-C(5)-O(1) 108.9(3).
Figure 1. Molecular structure of 6c (ellipsoids at 50% prob-
ability level). Select bond lengths (A) and angles (deg): C(5)-C-
(6) 1.399(7), C(4)-C(7) 1.412(6), C(4)-C(5) 1.386(7), C(4)-
Fe(1) 2.098(4), C(5)-Fe(1) 2.068(4), C(6)-Fe(1) 2.117(4),
C(7)-Fe(1) 2.122(5); C(5)-C(4)-C(7) 120.0(4), C(4)-C(5)-
C(6) 123.2(4), C(5)-C(4)-Fe(1) 69.4(3), C(7)-C(4)-Fe(1)
71.4(3), C(6)-C(5)-Fe(1) 72.4(3).
Table 3. X-ray Selected Data of the Structures of Diene 4d and
η4-Diene-Fe(CO)3 Complex 7a
signals of proton H-7b (20%) and aryl protons (1.8%), while
the irradiation of proton H-7b induced an enhancement of
the signals of H-7a (24%) and H-6b (12%).
A strong shielding effect on the 13C NMR chemical shifts
of the diene moiety is also observed due to the tricarbonylir-
on coordination, with respect to the noncomplexed dienes.
This effect is much larger for the terminal carbons C-6 and
C-7 of the diene (ca. 62 ppm) than that for the inner carbons
C-4 and C-5 (ca. 27 ppm). This has been associated with a
larger extent of hybridization change (π to sp3) of the
terminal carbon atoms with respect to the inners of the
diene-Fe(CO)3 complex.29
4d
7a
X-ray Diffraction of η4-Diene-Fe(CO)3 Complexes 6-8.
The structures of complexes 6-8 were unambiguously estab-
lished by X-ray diffraction analysis, and interesting structur-
al features can be extracted from them. The structure of
complex 6c shows a conformational preference for the
coordination of fragment Fe(CO)3 to the diene ligand, in
which the iron atom lies over the plane of the butadiene
ligand in a distorted trigonal square-pyramidal structure
and is equidistant from each of the four carbon atoms
(2.1 ( 0.05 A) (Figure 1).30 As expected,7b,25a,31 two carbonyl
ligands are pointing out from the metal to the C4 and C5
vertices, respectively, of the coordinated diene, and the third
one is oriented to the center and at the opposite side of the
diene moiety.
Comparison between the data of the X-ray structures of
complex 7a (Figure 2) and the analogue free diene 4d14b
provides the following features (Table 3): (a) Selected bond
distances of the diene moiety indicate that, unlike free diene
4d, where the inner C4-C5 bond is longer than the exocyclic
double bonds (C4-C7 and C5-C6), in complex 7a almost
Bond Distances (A)
C4-C5
C4-C7
C5-C6
1.44(1)
1.34(1)
1.28(1)
1.389(4)
1.410(4)
1.402(5)
Bond Angles (deg)
C4-C5-C6
C5-C4-C7
C5-C6-Me
132.0(7)
128.7(8)
126.5(7)
123.5(3)
121.0(3)
121.5(3)
Dihedral Angles (deg)
C4-C5-C6-Me
C7-C4-N3-C9
C7-C4-N3-C2
C6-C5-O-C2
179.2
-4.0
178.7
177.1
170.8
9.4
-171.7
174.4
equalized C-C bond lengths within the coordinated diene
ligand are observed (note: the inner C4-C5 bond is shorter
than the exocyclic double bonds);32 (b) selected bond angles
of the dienic frame of 7a show that there is a reduction of
these angles with respect to the free diene 4d (Table 3), which
can be associated with the π-back-bonding effect of the metal
that produces the hybridization at the carbon atoms of the
vinylic double bonds to approach sp3; (c) the dihedral angle
values in complex 7a support the previous observation, since
the sp3-like hybridization of the carbon dienic frame should
cause the substituents (methyl group and vinylic protons) to
bend back from the metal (note: the value (170.8°) for the
dihedral angle C4-C5-C6-Me indicates a nonplanarity of
the methyl group with respect to the plane of the heterocycle,
and the coordination generates a distortion of the coplanarity
(29) Retcofsky, H. L.; Frankel, E. N.; Gutowsky, H. S. J. Am. Chem.
Soc. 1966, 88, 2710–2712.
(30) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1–S83.
ꢀ
(31) Coquerel, Y.; Depres, J. P.; Greene, A. E.; Philouze, C.
J. Organomet. Chem. 2002, 659, 176–185.
(32) (a) Young, V. G. Jr.; Dasgupta, B.; Donaldson, W. A. J. Chem.
Cryst. 1996, 26, 569–571. (b) Howell, J. A. S.; Bell, A. G.; O'Leary, P. J.;
McArdle, P.; Dunningham, D.; Stephenson, G. R.; Hastings, M. Organo-
metallics 1994, 13, 1806–1812. (c) Wang, J.-L.; Ueng, C.-H.; Cheng, S.-J.;
Yeh, M.-C. P. Organometallics 1994, 13, 4453–4461. (d) Nakanishi, S.;
Yamamoto, H.; Otsuji, Y.; Nakazumi, H. Tetrahedron: Asymmetry 1993, 4,
1969–1972.

Article
Organometallics, Vol. 29, No. 1, 2010 153
Scheme 3. Reactivity of Diene Fe(CO)3 Complexes 6-8 with
t-BuLi
Figure 3. Molecular structure of 8d (ellipsoids at 30% prob-
ability level). Select bond lengths (A) and angles (deg): C(4)-Fe-
(1) 2.068(8), C(5)-Fe(1) 2.083(8), C(6)-Fe(1) 2.151(9),
C(7)-Fe(1) 2.096(9); C(5)-C(4)-Fe(1) 70.9(6), C(7)-C-
(4)-Fe(1) 71.6(5), C(6)-C(5)-Fe(1) 73.2(5), C(4)-C(5)-Fe(1)
69.7(6), C(4)-C(7)-Fe(1) 69.4(5), C(5)-C(6)-Fe(1) 68.0(5),
C(8)-C(6)-Fe(1) 125.4(6).
between the diene and the heterocycle, as suggested by the
dihedral angles C7-C4-N3-C9 (9.4°) and C7-C4-N3-
C2 (-171.7°)); (d) although in both cases, diene 4d and
complex 7a, the aromatic ring is almost orthogonal with
respect to the heterocycle plane; in 7a the aromatic ring is also
bending back from the side of the Fe(CO)3 coordination.
Similar structural features are observed for the ethyl-
substituted diene 8d, whose X-ray structure is shown in
Figure 3.
Reactivity of Complexes 6-8. Preparation of Enamine-
Enol Ester Fe(CO)3 Complexes 9a-9d and Enamido-Enol
Fe(CO)3 Complexes 10-11. Although the tricarbonyliron
group has been useful as a stabilizing group for dienes and
related unsaturated systems,1a,33 the Fe(CO)3 group can
assist the functionalization of the diene in the η4-coordina-
tion complex through a variety of reactions with a high regio-
and stereoselectivity.8-12,34 Therefore, we decided to explore
the reactivity and selectivity of complexes 6-8 in such
reactions. Thus, following the acylation protocol described
by Franck-Newmann for the synthesis of optically active
alcohols,35 diene 7a was submitted to similar Friedel-Crafts
conditions (AcCl, AlCl3, CH2Cl2, 0-20 °C).36 However, the
reaction gave rise to the full recovery of the starting material,
Table 4. Preparation of η4-Diene Fe(CO)3 Complexes 9a-d,
10a-c, and 11a-f
diene
entry complex nucleophile methoda product
mp
(°C)
yield
(%)b
1
2
3
4
5
6
7
8
6a
7a
7e
8a
7b
7e
8a
6a
6a
6a
6a
7a
7a
7a
7a
7a
7a
7a
7a
t-BuLi
t-BuLi
t-BuLi
t-BuLi
t-BuLi
t-BuLi
t-BuLi
MeLi
n-BuLi
MeLi
n-BuLi
MeLi
EtLi
n-BuLi
s-BuLi
MeLi
EtLi
n-BuLi
s-BuLi
A
A
A
A
B
B
B
A
A
B
B
A
A
A
A
B
B
B
B
9a
9b
9c
9d
oil
35
45
40
20
35
35
40
20
40
5
30
25
25
60
40
5
69-70
59-60
99-100
89-90
109-110
110-111
97-98
oil
97-98
oil
115-116
oil
oil
10a
10b
10c
11a
11b
11a
11b
11c
11d
11e
11f
11c
11d
11e
11f
9
10
11
12
13
14
15
16
17
18
19
oil
115-116
oil
oil
5
40
30
oil
a Method A: Alkyllithium (1.0 mol equiv), THF, N2 atm, -70 °C to rt
(3 h), then stirring for 12 h. Method B: Alkyllithium (1.0 mol equiv),
THF, N2 atm, -70 °C to -10 °C, then stirring for 3 h. b Calculated after
column chromatography.
even if the acylation agent (Ac2O) and the catalyst (BF3 Et2O)
were changed. Upon increasing the reaction temperature,
decomposition of the complex was also observed.
3
Following the known protocol of deprotonation and
electrophilation of diene Fe(CO)3 complexes,11b compound
7a was treated with LDA at low temperature (-78 °C) and
methyl iodide or p-nitrobenzaldehyde was added to trap the
likely preformed carbanion. However, starting material was
recovered. The inductive electron donor effect of the diene
Fe(CO)3 scaffold may be the cause of the low acidity of the
protons of the methyl group grafted to the diene.25a
The origin of this stability of the complex may also be due
to the electron-releasing effect of the heteroatoms of the
fused heterocycle toward the diene Fe(CO)3 coordination.
Therefore, this effect would inhibit the electron delocaliza-
tion of the heteroatom lone-pairs toward the carbonyl group
of the oxazolidinone ring of complexes 6-8. To gain
more insight about this hypothesis, the reactivity of strong
hard nucleophiles, such as tert-butyllithium, was evaluated.
Indeed, complex 7a underwent the attack of the nucleophilic
species to provide the enamine-enol ester complex 9b as
the major product (Scheme 3), and nonreacted starting
material was recovered (Table 4). The reaction was extended
to complexes 6a, 7e, and 8a, observing similar results
(Scheme 3). Thus, when they were submitted to similar
reaction conditions, complexes 9a, 9c, and 9d, were isolated,
respectively, in low to moderate yields (Table 4, entries 1-4).
(33) (a) Pearson, A. J. Acc. Chem. Res. 1980, 13, 463–469. (b) Birch, A.
J.; Kelly, L. F. J. Organomet. Chem. 1985, 285, 267–280.
(34) (a) Fatiadi, A. J. J. Res. Natl. Inst. Stand. Technol. 1991, 96, 1–
113. (b) Iwata, C.; Takamato, Y. Chem. Commun. 1996, 2497–2504.
(35) (a) Franck-Newmann, M.; Chemla, P.; Martina, D. Synlett
1990, 641–642. (b) Wasicak, J. T.; Craig, R. A.; Henry, R.; Dasgupta, B.;
Li, H.; Donaldson, W. A. Tetrahedron 1997, 53, 4185–4198.
(36) Tagliaferri, E.; Campiche, P.; Roulet, R.; Gabioud, R.; Vogel,
P.; Chapuis, G. Helv. Chim. Acta 1985, 68, 126–134.

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Ortega-Jimenez et al.
154 Organometallics, Vol. 29, No. 1, 2010
The structure of these complexes was established by
spectroscopy. For example, the IR spectrum of 9b shows a
band at 3388 cm-1, which corresponds to the stretching
vibration of the N-H bond, as well as the strong bands
between 2046 and 1944 cm-1 corresponding to the stretching
frequencies of the carbonyl groups of the Fe(CO)3 moiety,
and at 1748 cm-1 a strong-intensity band appears due to the
CdO stretching mode of the ester group. In comparison with
the chemical shifts of the corresponding protons of complex
7a (Table 2), in the 1H NMR spectrum of complex 9b, besides
the presence of the signal of the tert-butyl group as a singlet
at 1.38 ppm, the signals due to the gem-vinyl protons H-1a
(2.21 ppm) and H-1b (0.29 ppm) are shifted slightly to low
field, and proton H-4 is shifted to high field (1.09 ppm). In
the 13C NMR spectrum of complex 9b, the signal of the
carbon atom of the carbonyl group is largely deshielded to
176.6 ppm, with respect to the chemical shift of the carbonyl
group of the cyclic carbamate (154.6 ppm) of 7a, which
indicates that the latter was converted to an ester group.
The assignments of the 1H and 13C NMR spectra were
supported by 2D (HMQC, HMBC) and NOE experiments.
Interestingly, in contrast with the previous protocol
(method A), in which the reaction mixture was slowly
warmed (about 3 h) to room temperature and then stirred
for 12 h, a different product was furnished when the reaction
with 7b was carried out by adding the lithium reagent at
-78 °C, followed by rapidly increasing the temperature to
-10 °C, stirring for 3 h, and quenching the reaction mixture
by water addition (method B). This product corresponded to
enamido-enol Fe(CO)3 10a, and it was obtained as a single
product (Scheme 3). Similar behavior was observed by
reacting substrates 7e and 8a, giving conjugated enamido-
enols 10b and 10c, respectively (Table 4, entries 5-7).
These results suggest that in the formation of complexes
10a-c the least stable product was captured, whereas in the
formation of 9b by warming to room temperature and
maintaining the reaction for 12 h, the most stable product,
9, was isolated.
The structure of these complexes was also established by
spectroscopy. For example, the IR spectrum of 10a shows a
broad band at 3440 cm-1, which corresponds to the stretch-
ing vibration of the O-H bond. At 1617 and 1591 cm-1 two
medium-intensity bands appear due to the CdO stretching
mode of the amide group, and the strong bands correspond-
ing to the stretching frequencies of the carbonyl groups of the
Fe(CO)3 moiety are also found. In the 1H NMR spectrum of
this complex, the singlet of the tert-butyl group is shielded to
1.07 ppm, as well as the signals due to the gem-vinyl protons
H-1a (1.40 ppm), H-1b (-0.52 ppm), and H-4 (0.90 ppm)
with respect to the chemical shifts of the corresponding
protons of complex 9b (vide supra). In the 13C NMR spec-
trum of complex 10a, the signal of the carbon atom of the
amide group is more deshielded (183.4 ppm) than the
chemical shift of the carbonyl group of the ester group
(176.6 ppm) of 9b, which suggests that the lone-pair of the
nitrogen atom is not coplanar to the π orbital of the carbonyl
group of the amide in the former complex. Interestingly, a
similar but strong downfield shift (129.5 ppm) is observed for
the carbon atom C-2, the base of the nitrogen atom of the
enamido moiety. In contrast, the carbon atom C-3, the base
of the oxygen atom of the enol moiety, is shifted to high field
(97.5 ppm) with respect to the same carbon atoms of the
enamine (114.1 ppm) and the ester (111.3 ppm) moieties of
complex 9b. This spectroscopic analysis of the structure of
Figure 4. Molecular structure of 10b (ellipsoids with 30% prob-
ability level). Select bond lengths (A) and angles (deg): C(2)-
Fe(1) 2.123(4), C(3)-Fe(1) 2.118(3), C(4)-Fe(1) 2.049(3), C(5)-
Fe(1) 2.059(4), C(4)-N(4) 1.452(5); C(3)-C(2)-Fe(1) 70.3(2),
C(1)-C(2)-Fe(1) 124.6(3), O(3)-C(3)-C(4) 122.4(3), O(3)-
C(3)-Fe(1) 126.6(3), C(4)-C(3)-Fe(1) 67.5(2), C(2)-C(3)-
Fe(1) C(5)-C(4)-N(4) 118.9(3), N(4)-C(4)-Fe(1) 129.3(3).
Scheme 4. Reactivity of Diene Fe(CO)3 Complexes 6a and 7a
with Alkyl Lithium Reagents
10b was supported by the measurement of its X-ray diffrac-
tion structure (Figure 4). The latter reveals that Fe(CO)3
binds to the η4-diene ligand, in which the conformation of
the carbonyl group of the amide is oriented to the hydroxyl
group, being stabilized by an intramolecular hydrogen bond-
ing. The crystal lattice exhibited static disorder due to the
random presence of the two possible conformers of the tert-
butyl group among different unit cells.
Compounds 9a-d and 10a-c represent a novel example of
stabilization of highly reactive and unstable conjugated enamine-
enol esters and enamido-enols by coordination to Fe(CO)3.
Actually, conjugated enols stabilized by complexing to the Fe-
(CO)3 group have been previously reported in the literature.37
However, to the best of our knowledge, this is the first time that
a stabilized enol conjugated to an enamido group is described.
With the aim of further evaluating the regioselectivity in
the opening of the oxazolidin-2-one ring by alkyllithium
additions, methyllithium, ethyllithium, n-butyllithium, or
sec-butyllithium was added to 6a and 7a (Scheme 4). Table 4
summarizes the results of these additions under both reac-
tion conditions. Unexpectedly, the addition of methyl-
lithium to 6a under both methods provided a single
product, which corresponded to the enamido-enol complex
11a (Table 4, entries 8 and 10). Analogous results were
(37) DePuy, C. H.; Jablonski, C. R. Tetrahedron Lett. 1969, 3989–
3991.

Article
Organometallics, Vol. 29, No. 1, 2010 155
Scheme 5. Selectivity in Carbamate Ring-Opening of Diene Fe-
(CO)3 Complexes 6-8 by Additions of Alkyllithium Reagent
Experimental Section
General Procedures and Instrumentation. Melting points
(uncorrected) were determined with a Fisher-Johns capillary
melting point apparatus. IR spectra were recorded on a Perkin-
Elmer 2000 spectrophotometer. 1H and 13C NMR spectra were
recorded on Varian Mercury (300 MHz) and Varian VNMR
System (500 MHz) NMR instruments, with CDCl3 as the
solvent and TMS as internal standard. High-resolution mass
spectra (HRMS) were obtained, in electron impact (EI) (70 eV)
mode, on a Jeol JSM-GCMate II spectrometer. X-ray crystallo-
graphic structures were obtained on Siemens P4 and Oxford
XcaliburS diffractometers. UV spectral data were recorded on a
Bausch & Lomb Spectronic 2000. Microanalyses were per-
formed by M-H-W Laboratories (Phoenix, AZ). Analytical
TLC was carried out using E. Merck silica gel 60 F254 coated
0.25 plates, visualized by a long- and short-wavelength UV
lamp. Flash column chromatography was performed over
Natland International Co. silica gel (230-400 mesh). All
air- and moisture-sensitive reactions were carried out under
nitrogen using oven-dried glassware. Benzene and THF were
freshly distilled over sodium, and methylene chloride and ethyl
acetate over calcium hydride, prior to use. All other reagents
were used without further purification. Dienes 3a-e, 4a-e, and
5a-e were prepared as reported.14b,c,28
observed with the addition of n-butyllithium, to yield only
complex 11b (Table 4, entries 9 and 11). Similarly, when the
series of alkyllithium reagents were reacted with complex 7a,
the additions turned out to give only the enamido-enol
complexes 11c-f (Table 4, entries 12-19). In all cases,
method A was more efficient than method B for the conver-
sion, giving higher yields.
General Method for the Preparation of Complexes 6a-e,
7a-e, and 8a-e. A mixture of Fe2(CO)9 (8.02 mmol, 3 equiv),
the corresponding diene, 3a-e, 4a-e, or 5a-e (2.67 mmol,
1 equiv), and freshly dried benzene (5 mL) were placed in a 25
mL two-necked, round-bottomed flask (equipped with a reflux
condenser and a rubber septum), and the mixture was stirred
and heated at reflux for 3 h under nitrogen atmosphere. Upon
cooling, the reaction mixture was filtered over Celite, and the
solvent was removed under vacuum. The crude product was
purified by column chromatography over silica gel impregnated
with triethylamine (10%) in hexane (hexane/EtOAc, 9:1), to give
complexes 6a-e, 7a-e, or 8a-e.
These results suggest that the enamido-enol complexes
11a-f are both the kinetic and the most stable opened-ring
products. This can be explained by the fact that, after
addition of the alkyllithium to the carbonyl group of the
cyclic carbamate, the opening pathway (a) of the ring in
species I leads to the lithium enamide II, which is a stronger
base (less stable) than enolate III. This is in turn formed by
the opening pathway (b) of the ring in species I (Scheme 5).
Hence, in the case of the addition of these alkyllithium
reagents, the unstable intermediate II cannot be reached.
All attempts to isolate the enamine-enol ester products,
such as 9, from the addition of the alkyllithium reagents
were unsuccessful, since increasing the reaction temperatures
above room temperature showed the same enamido-
enol complexes or decomposition of the starting material.
In contrast, it is likely that in the case of the addition of
tert-butyllithium, intermediates II and III have similar
stabilities.
Tricarbonyl-η4-[4,5-dimethylene-3-phenyl-1,3-oxazolidin-2-one]-
iron(0) (6a). Following the general method, with 0.50 g of 3a
and 2.92 g of Fe2(CO)9, 0.655 g (75%) of 6a was obtained as a
yellow-greenish solid: mp 119-120 °C; FT-IR νmax (KBr) 2052,
1
1980, 1962 [Fe(CO)3], 1764 (CdO) cm-1; H NMR (300 MHz,
CDCl3) δ 0.33 (d, J = 5.2 Hz, 1H, H-7b), 0.51 (d, J = 5.4 Hz, 1H,
H-6b), 2.17 (d, J = 5.2 Hz, 1H, H-7a), 2.59 (d, J = 5.4 Hz, 1H, H-
6a), 7.41-7.57 (m, 5H, Ph-H); 13C NMR (75.4 MHz, CDCl3)
δ 19.6 (C-7), 21.8 (C-6), 111.0 (C-4), 122.3 (C-5), 125.0 (C-9), 128.3
(C-11), 129.5 (C-10), 132.5 (C-8), 154.2 (C-2), 206-209 [Fe(CO)3];
MS (70 eV) m/z 327 (Mþ, 2), 299 (6), 271 (30), 243 (100), 189 (13),
172 (14), 91 (18), 77 (16), 56 (50), 51 (15). Anal. Calcd for
C14H9NO5Fe: C, 51.41; H, 2.77; N, 4.28. Found: C, 51.50; H,
2.82; N, 4.23.
Conclusions
We have synthesized a series of new η4-diene-Fe(CO)3
complexes 6a-e, 7a-e, and 8a-e derived from the novel
exo-2-oxazolidinone dienes. The complexation of the latter
was carried out by thermal treatment with diiron nonacar-
bonyl to afford the corresponding complexes as crystal
solids. The X-ray diffraction analysis of complexes 6c, 7a,
and 8d did not reveal any unusual structural features, in
agreement with the structures of common diene-iron com-
plexes. Evaluation of the reactivity of these complexes under
acylation or base-promoted electrophilation conditions pro-
vided evidence of the high stability of these complexes.
Because of this stability, the carbonyl group of the cyclic
carbamate resulted in the reactive electrophilic center of the
molecule, to the extent that it underwent the addition of
alkyllithium reagents. The outcome of the latter allowed for
the isolation of either stable and unprecedented conjugated
enamine-enol ester Fe(CO)3 complexes 9a-d, which proved
to be the thermodynamic products, or the less stable enam-
ido-enol Fe(CO)3 complexes 10a-c and 11a-f.
Tricarbonyl-η4-[4,5-dimethylene-3-(2-methylphenyl)-1,3-oxa-
zolidin-2-one]iron(0) (6b). Following the general method, with
0.537 g of 3b and 2.92 g of Fe2(CO)9, 0.382 g (42%) of 6b as a
mixture of atropoisomers (66:34) was obtained as yellow crys-
tals: mp 158-160 °C; FT-IR νmax (film) 2039, 1963 [Fe(CO)3],
1780 (CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ 0.30 (d, J =
5.0 Hz, 1H, H-7b), 0.50 (d, J = 5.1 Hz, 1H, H-6b), 1.90 (d, J =
5.0 Hz, 1H, H-7a), 2.38 (s, 3H, CH3-Ar), 2.59 (d, J = 5.1 Hz,
1H, H-6a), 7.23-7.54 (m, 4H, H-10, H-11, H-12, H-13); 13C
NMR (75.4 MHz, CDCl3) δ 17.1 (CH3-Ar), 19.4 (C-7), 22.1
(C-6), 111.7 (C-4), 123.0 (C-5), 127.5, 127.6, 130.1, 131.0 (C-8),
131.7, 135.7 (C-9), 155.0 (C-2), 206-208 [Fe(CO)3]. Signals
attributed to the minor isomer: 1H NMR (300 MHz, CDCl3) δ
0.35 (d, J = 5.0 Hz, 1H, H-7b), 1.94 (d, J = 5.0 Hz, 1H, H-7a),
2.25 (s, 3H, CH3-Ar); 13C NMR (75.4 MHz, CDCl3) δ 18.3
(CH3-Ar), 20.2 (C-7), 21.9 (C-6), 111.8 (C-4), 123.9 (C-5),
126.8, 127.1, 129.4, 132.1, 136.3, 153.7 (C-2). Anal. Calcd for
C15H11NO5Fe: C, 52.82; H, 3.25; N, 4.11. Found: C, 52.91; H,
3.43; N, 4.06.

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Ortega-Jimenez et al.
156 Organometallics, Vol. 29, No. 1, 2010
Tricarbonyl-η4-[4,5-dimethylene-3-(4-methylphenyl)-1,3-oxa-
zolidin-2-one]iron(0) (6c). Following the general method, with
0.537 g of 3c and 2.92 g of Fe2(CO)9, 0.482 g (53%) of 6c was
obtained as a yellow-greenish solid: mp 123-124 °C; FT-IR
NMR (300 MHz, CDCl3) δ 0.23 (d, J = 5.2 Hz, 1H, H-7b), 1.28 (q,
J = 6.4 Hz, 1H, H-6), 1.82 (d, J = 5.2 Hz, 1H, H-7a), 1.83 (d, J =
6.4 Hz, 3H, CH3), 2.25 (s, 3H, CH3-Ar). Anal. Calcd for
C16H13NO5Fe: C, 54.11; H, 3.69; N, 3.94. Found: C, 54.11; H,
3.71; N, 4.02.
ν
max (KBr) 2054, 1980, 1964 [Fe(CO)3], 1783 (CdO) cm-1; 1H
NMR (300 MHz, CDCl3) δ 0.30 (d, J = 5.2 Hz, 1H, H-7b), 0.50
(d, J = 5.4 Hz, 1H, H-6b), 2.13 (d, J = 5.2 Hz, 1H, H-7a), 2.41
(s, 3H, CH3-Ar), 2.58 (d, J = 5.4 Hz, 1H, H-6a), 7.29-7.39 (m,
4H, H-9, H-10); 13C NMR (75.4 MHz, CDCl3) δ 20.2 (C-7),
21.2 (CH3-Ar), 22.2 (C-6), 111.6 (C-4), 122.7 (C-5), 125.3 (C-9),
130.1 (C-8), 130.5 (C-10), 139.0 (C-11), 154.9 (C-2), 206-209
[Fe(CO)3]; MS (70 eV) m/z 341 (Mþ, 1), 283 (2), 267 (14), 237
(1), 193 (3), 161 (33), 146 (35), 146 (35), 133 (10), 132(100), 91
(77), 65 (33), 38 (13). Anal. Calcd for C15H11NO5Fe: C, 52.82;
H, 3.25; N, 4.11. Found: C, 52.97; H, 3.16; N, 4.19.
Tricarbonyl-η4-[(Z)-5-ethylidene-4-methylene-3-(4-methylphenyl)-
1,3-oxazolidin-2-one]iron(0) (7c). Following the general method,
with 0.574 g of 4c and 2.92 g of Fe2(CO)9, 0.597 g (63%) of 7c
was obtained as a yellow solid: mp 102-103 °C; FT-IRνmax (KBr)
1
2042, 1980, 1960 [Fe(CO)3], 1770 (CdO) cm-1; H NMR (300
MHz, CDCl3) δ0.19 (d, J = 5.2 Hz, 1H, H-7b), 1.27 (q, J = 6.5 Hz,
1H, H-6), 1.83 (d, J=6.5Hz,3H,CH3),2.02(d,J= 5.2, 1H, H-7a),
2.41(s, 3H, CH3-Ar), 7.25-7.39 (m, 4H, H-9, H-10); 13CNMR(75.4
MHz, CDCl3) δ 13.8 (CH3), 18.6 (C-7), 21.1 (CH3-Ar), 38.7 (C-6),
108.1 (C-4), 123.2 (C-5), 125.3 (C-9), 130.1 (C-8), 130.5 (C-10), 138.9
(C-11), 154.8 (C-2), 206-209 [Fe(CO)3]; MS (70 eV) m/z 355 (Mþ,
2), 327 (3), 299 (26), 271 (100), 227 (1), 215 (4), 174 (16), 91 (11), 84
(5), 56 (15). Anal. Calcd for C16H13NO5Fe: C, 54.11; H, 3.69; N,
3.94. Found C, 54.23; H, 3.83; N, 3.96.
Tricarbonyl-η4-[3-(3-chlorophenyl)-4,5-dimethylene-1,3-oxa-
zolidin-2-one]iron(0) (6d). Following the general method, with
0.591 g of 3d and 2.92 g of Fe2(CO)9, 0.366 g (38%) of 6d was
obtained as a yellow solid: mp 110-111 °C; FT-IR νmax (film)
2049, 1976 [Fe(CO)3], 1782 (CdO) cm-1; 1H NMR (300 MHz,
CDCl3) δ 0.34 (d, J = 3.0 Hz, 1H, H-7b), 0.52 (d, J = 3.4 Hz,
1H, H-6b), 2.17 (d, J = 3.0 Hz, 1H, H-7a), 2.60 (d, J = 3.4 Hz,
1H, H-6a), 7.36-7.83 (m, 4H, H-9, H-11, H-12, H-13); 13C
NMR (75.4 MHz, CDCl3) δ 20.0 (C-7) 22.4 (C-6), 110.7 (C-4),
122.8 (C-5), 123.4 (C-13), 125.5 (C-9), 129.0 (C-11), 139.0 (C-
12), 133.9 (C-8), 135.5 (C-10), 154.2 (C-2), 206-209 [Fe(CO)3];
MS (70 eV) m/z 361 (Mþ, 2), 333 (7), 305 (55), 277 (100), 241
(38), 197 (40), 167 (17), 142 (28), 91 (19), 84 (41). Anal. Calcd
for C14H8ClNO5Fe: C, 46.51; H, 2.23; N, 3.87. Found: C,
46.75; H, 2.19; N, 3.70.
Tricarbonyl-η4-[(Z)-3-(3-chlorophenyl)-5-ethylidene-4-methy-
lene-1,3-oxazolidin-2-one]iron(0) (7d). Following the general
method, with 0.629 g of 4d and 2.92 g of Fe2(CO)9, 0.481 g
(48%) of 7d was obtained as yellow crystals: mp 161-162 °C;
FT-IR νmax (film) 2036, 1968 [Fe(CO)3], 1782 (CdO) cm-1; 1H
NMR (300 MHz, CDCl3) δ 0.22 (d, J = 5.3 Hz, 1H, H-7b), 1.29
(q, J = 6.5 Hz, 1H, H-6), 1.83 (d, J = 6.5 Hz, 3H, CH3), 2.07 (d,
J = 5.3 Hz, 1H, H-7a), 7.35-7.66 (m, 4H, H-9, H-11, H-12,
H-13); 13C NMR (75.4 MHz, CDCl3) δ 13.8 (CH3), 18.7 (C-7),
39.0 (C-6), 107.3 (C-4), 123.3 (C-5), 123.4 (C-13), 125.5 (C-9),
128.9 (C-11), 130.9 (C-12), 134.0 (C-8), 135.9 (C-10), 154.2
(C-2), 206-209 [Fe(CO)3]; MS (70 eV) m/z 375 (Mþ, 2), 347
(5), 319 (49), 291 (100), 255 (27), 211 (20), 155 (15), 111 (10), 84
(15). Anal. Calcd for C15H10ClNO5Fe: C, 47.97; H, 2.68; N,
3.73. Found: C, 47.77; H, 2.74; N, 3.76.
Tricarbonyl-η4-[3-(4-chlorophenyl)-4,5-dimethylene-1,3-oxazo-
lidin-2-one]iron(0) (6e). Following the general method, with 0.591
g of 3e and 2.92 g of Fe2(CO)9, 0.386 g (40%) of 6e was obtained
as a yellow solid: mp 107-109 °C; FT-IR νmax (KBr) 2054, 1976
Tricarbonyl-η4-[(Z)-3-(4-chlorophenyl)-5-ethylidene-4-methy-
lene-1,3-oxazolidin-2-one]iron(0) (7e). Following the general
method, with 0.629 g of 4e and 2.92 g of Fe2(CO)9, 0.36 g
(36%) of 7e was obtained as yellow crystals: mp 105-106 °C;
FT-IR νmax (KBr) 2050, 1972 [Fe(CO)3], 1780 (CdO) cm-1; 1H
NMR (300 MHz, CDCl3) δ 0.21 (d, J = 5.3 Hz, 1H, H-7b), 1.29
(q, J = 6.4 Hz, 1H, H-6), 1.83 (d, J = 6.4 Hz, 3H, CH3), 2.02 (d,
J = 5.3 Hz, 1H, H-7a), 7.43-7.50 (m, 4H, H-9, H-10); 13C NMR
(75.4 MHz, CDCl3) δ 13.8 (CH3), 18.5 (C-7), 39.0 (C-6), 107.4
(C-4), 123.3 (C-5), 126.6 (C-9), 130.1 (C-10), 131.4 (C-8), 134.5
(C-11), 154.3 (C-2), 206-209 [Fe(CO)3]; MS (70 eV) m/z 375
(Mþ, 2), 347 (4), 319 (30), 291 (100), 255 (3), 211 (4), 207 (11), 155
(6), 111 (9), 91 (10), 84 (18), 56 (34). Anal. Calcd for
C15H10ClNO5Fe: C, 47.97; H, 2.68; N, 3.73. Found: C, 48.09;
H, 2.88; N, 3.72.
1
[Fe(CO)3], 1786 (CdO) cm-1; H NMR (300 MHz, CDCl3) δ
0.32 (d, J = 5.3 Hz, 1H, H-7b), 0.51 (d, J = 5.4 Hz, 1H, H-6b),
2.13 (d, J = 5.3 Hz, 1H, H-7a), 2.60 (d, J = 5.4 Hz, 1H, H-6a),
7.41-7.52 (m, 4H, H-9, H-10); 13C NMR (75.4 MHz, CDCl3) δ
19.9 (C-7), 22.4 (C-6), 110.8 (C-4), 122.8 (C-5), 126.6 (C-9), 130.2
(C-10), 131.3 (C-8), 134.6 (C-11), 154.4 (C-2), 206-209
[Fe(CO)3]; MS (70 eV) m/z 361 (Mþ, 2), 333 (5), 305 (35), 277
(100), 241 (6), 197 (11), 167 (11), 142 (11), 91 (12), 84 (27), 56 (41).
Anal. Calcd for C14H8ClNO5Fe: C, 46.51; H, 2.23; N, 3.87.
Found: C, 46.34; H, 2.12; N, 3.86.
Tricarbonyl-η4-[(Z)-5-ethylidene-4-methylene-3-phenyl-1,3-oxa-
zolidin-2-one]iron(0) (7a). Following the general method, with
0.537 g of 4a and 2.92 g of Fe2(CO)9, 0.783 g (86%) of 7a was
obtained as yellow crystals: mp 163-164 °C; FT-IR νmax (KBr)
1
2050, 1970, 1964 [Fe(CO)3], 1782 (CdO) cm-1; H NMR (300
Tricarbonyl-η4-[(Z)-4-methylene-3-phenyl-5-propylidene-1,
3-oxazolidin-2-one]iron(0) (8a). Following the general meth-
od, with 0.574 g of 5a and 2.92 g of Fe2(CO)9, 0.549 g (58%) of
8a was obtained as a yellow solid: mp 126-127 °C; FT-IR
MHz, CDCl3) δ 0.20 (d, J = 5.2 Hz, 1H, H-7b), 1.27 (q, J = 6.4
Hz, 1H, H-6), 1.83 (d, J = 6.4 Hz, 3H, CH3), 2.05 (d, J = 5.2 Hz,
1H, H-7a), 7.39-7.57 (m, 5H, H-9, H-10, H-11); 13C NMR (75.4
MHz, CDCl3) δ 13.9 (CH3), 18.7 (C-7), 38.8 (C-6), 107.9 (C-4),
123.3 (C-5), 125.4 (C-9), 128.7 (C-11), 129.9 (C-10), 132.9 (C-8),
154.6 (C-2), 206-209 [Fe(CO)3]; MS (70 eV) m/z 201 (Mþ, 100),
186 (1), 156 (21), 142 (3), 118 (93), 104 (15), 77 (73), 65 (6). Anal.
Calcd for C15H11NO5Fe: C, 52.82; H, 3.25; N, 4.11. Found: C,
52.65; H, 3.05; N, 4.03.
ν
max (KBr) 2044, 1980, 1956 [Fe(CO)3], 1756 (CdO) cm-1; 1H
NMR (500 MHz, CDCl3) δ 0.20 (d, J = 5.2 Hz, 1H, H-7b),
1.17 (dd, J = 7.6, 6.8 Hz, 1H, H-6), 1.26 (t, J = 7.4 Hz, 3H,
CH3CH2), 2.06 (d, J = 5.2 Hz, 1H, H-7a), 2.03-2.13 (m, 1H,
CH3CH2), 2.24-3.34 (m, 1H, CH3CH2), 7.38-7.59 (m, 5H,
H-9, H-10, H-11); 13C NMR (125 MHz, CDCl3) δ 15.9
(CH3CH2), 18.8 (C-7), 22.5 (CH3CH2), 47.6 (C-6), 107.9 (C-
4), 122.5 (C-5), 125.4 (C-9), 128.7 (C-11), 129.9 (C-10), 132.9
(C-8), 154.7 (C-2), 207-209 [Fe(CO)3]; MS (70 eV) m/z 215
(Mþ, 65), 170 (5), 156 (4), 129 (4), 118 (100), 77 (48), 51 (20).
Anal. Calcd for C16H13NO5Fe: C, 54.11; H, 3.69; N, 3.94.
Found: C, 53.90; H, 4.00; N, 3.85.
Tricarbonyl-η4-[(Z)-5-ethylidene-4-methylene-3-(2-methylphenyl)-
1,3-oxazolidin-2-one]iron(0) (7b). Following the general method,
with 0.574 g of 4b and 2.92 g of Fe2(CO)9, 0.407 g (43%) of 7b as
a mixture of atropoisomers (63:37) was obtained as a yellow solid:
mp 158-160 °C; FT-IR νmax (KBr) 2049, 1973 [Fe(CO)3], 1766
(CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ 0.19 (d, J = 5.1 Hz,
1H, H-7b), 1.27 (q, J = 6.4 Hz, 1H, H-6), 1.78 (d, J = 5.1 Hz, 1H,
H-7a), 1.84 (d, J = 6.4 Hz, 3H, CH3), 2.37 (s, 3H, CH3-Ar),
7.26-7.43 (m, 4H, H-10, H-11, H-12, H-13); 13C NMR (75.4 MHz,
CDCl3) δ 13.8 (CH3), 18.7 (C-7), 38.7 (C-6), 107.9 (C-4), 123.3
(C-5), 124.3, 128.3, 128.7, 129.8, 131.1 (C-8), 132.8 (C-9), 154.6 (C-
2), 208-209 [Fe(CO)3]. Signals attributed to the minor isomer: 1H
Tricarbonyl-η4-[(Z)-4-methylene-3-(2-methylphenyl)-5-propy-
lidene-1,3-oxazolidin-2-one]iron(0) (8b). Following the general
method, with 0.611 g of 5b and 2.92 g of Fe2(CO)9, 0.472 g (48%)
of 8b as a mixture of atropoisomers (62:38) was obtained
as yellow crystals: mp 113-115 °C; FT-IR νmax (film) 2047,

Article
Organometallics, Vol. 29, No. 1, 2010 157
1970 [Fe(CO)3], 1782 (CdO) cm-1
;
1H NMR (300 MHz,
was removed and the dark brown residue was dissolved in
EtOAc (10 mL) and filtered over alumina. The solvent was
removed under vacuum, and the crude product was purified by
column chromatography over silica gel (hexane/EtOAc, 9:1), to
afford complexes 9a-d.
Method B. To a solution of the corresponding complex 7a, 7e,
or 8a (0.6 mmol) in 5 mL of dry THF at -70 °C was slowly added
t-BuLi (0.6 mmol, 1.7 M) under nitrogen atmosphere. The
mixture was allowed to reach -10 °C (∼3 h). At this point,
the solvent was removed and the dark brown residue was
dissolved in EtOAc (10 mL) and filtered over alumina. The
solvent was removed under vacuum and the crude product was
purified by column chromatography over silica gel (hexane/
EtOAc, 9:1), to afford complexes 10a-c.
CDCl3) δ 0.19 (d, J = 5.1 Hz, 1H, H-7b), 1.14-1.23 (m, 1H,
H-6), 1.27 (t, J = 7.3 Hz, 3H, CH3CH2), 1.80 (d, J = 5.1 Hz, 1H,
H-7a), 2.01-2.19 (m, 1H, CH3CH2), 2.22-2.42 (m, 1H,
CH3CH2), 2.38 (s, 3H, CH3-Ar), 7.26-7.43 (m, 4H, H-10,
H-11, H-12, H-13); 13C NMR (75.4 MHz, CDCl3) δ 15.9
(CH3CH2), 18.0 (CH3-Ar), 18.1 (C-7), 22.6 (CH3CH2), 47.5
(C-6), 108.3 (C-4), 122.9 (C-5), 127.5, 127.9, 130.1, 131.1 (C-8),
131.6, 135.8 (C-9), 154.7 (C-2), 207-209 [Fe(CO)5]. Signals
1
attributed to the minor isomer: H NMR (300 MHz, CDCl3)
δ 0.23 (d, J = 5.1 Hz, 1H, H-7b), 1.84 (d, J = 5.1 Hz, 1H, H-7a),
2.25 (s, 3H, CH3-Ar); 13C NMR (75.4 MHz, CDCl3) δ 18.9 (C-
7), 22.6 (CH3CH2), 47.3 (C-6), 126.9, 127.1, 129.4, 131.0 (C-8),
132.1 (C-9). Anal. Calcd for C17H5NO5Fe: C, 55.31; H, 4.10; N,
3.79. Found: C, 55.46; H, 4.22; N, 3.76.
Tricarbonyl-η4-[3-(phenylamino)-2-(pivaloyloxy)buta-1,3-diene]-
iron(0) (9a). Following method A with 6a, complex 9a (35%) was
obtained as a brown oil: FT-IR νmax (KBr) 3420 (NH), 2046, 1967,
[Fe(CO)3], 1750 (CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ 0.26
(d, J = 4.8 Hz, 1H, H-4b), 0.45 (d, J = 4.8 Hz, 1H, H-1a), 1.35 (s,
9H, H-11), 1.94 (d, J = 4.8 Hz 3H, H-4a), 2.28 (d, J = 4.8 Hz, 1H,
H-1b), 5.51 (s, 1H, NH), 7.03 (t, J = 7.8 Hz, 1H, H-8), 7.11 (d, J =
7.8 Hz, 2H, H-6), 7.29 (d, J = 7.8 Hz, 2H, H-7); 13C NMR (75.4
MHz, CDCl3) δ 27.0 (C-11), 31.1 (C-4), 32.2 (C-1), 39.4 (C-10),
110.8 (C-3), 117.8 (C-2), 120.5 (C-6), 123.4 (C-8), 129.3 (C-7),
140.6 (C-5), 177.4 (CO); HRMS (EI) calcd for C18H19FeNO5 [M]þ
385.0616, found 385.0615.
Tricarbonyl-η4-[(Z)-4-methylene-3-(4-methylphenyl)-5-propy-
lidene-1,3-oxazolidin-2-one]iron(0) (8c). Following the general
method, with 0.611 g of 5c and 2.92 g of Fe2(CO)9, 0.512 g (52%)
of 8c was obtained as a yellow crystalline solid: mp 113-114 °C;
FT-IR νmax (film) 2042, 1981, 1951 [Fe(CO)3], 1778 (CdO)
cm-1; 1H NMR (500 MHz, CDCl3) δ 0.18 (d, J = 5.2 Hz, 1H, H-
7b), 1.15 (dd, J = 7.9, 6.5 Hz, 1H, H-6), 1.25 (t, J = 7.4 Hz, 3H,
CH3CH2), 2.03 (d, J = 5.2 Hz, 1H, H-7a), 2.02-2.13 (m, 1H,
CH3CH2), 2.24-2.35 (m, 1H, CH3CH2), 2.41 (s, 3H, CH3-Ar),
7.28-7.37 (m, 4H, H-9, H-10); 13C NMR (125 MHz, CDCl3) δ
15.9 (CH3CH2), 18.7 (C-7), 21.2 (CH3-Ar), 22.5 (CH3CH2), 47.5
(C-6), 108.2 (C-4), 122.5 (C-5), 125.4 (C-9), 130.1 (C-8), 130.5
(C-10), 138.9 (C-11), 154.9 (C-2), 207-209 [Fe(CO)3]; MS (70
eV): m/z 369 (Mþ, 1), 341 (3), 313 (24), 285 (100), 229 (5), 132 (9),
91 (10), 56 (12). Anal. Calcd for C17H15NO5Fe: C, 55.31; H,
4.10; N, 3.79. Found: C, 55.40; H, 4.16; N, 3.74.
Tricarbonyl-η4-[(Z)-2-(phenylamino)-3-(pivaloyloxy)penta-1,
3-diene]iron(0) (9b). Following method A with 7a, complex 9b
(45%) was obtained as a brown solid: mp 69-70 °C; FT-IR
ν
max (KBr) 3388 (NH), 2046, 2033, 1969, 1944 [Fe(CO)3], 1748
(CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ 0.29 (d, J = 4.5
Hz, 1H, H-1b), 1.09 (q, J = 6.0 Hz, 1H, H-4), 1.38 (s, 9H, H-11),
1.47 (d, J = 6.0 Hz, 3H, CH3), 2.21 (d, J = 4.5 Hz, 1H, H-1a),
5.34 (s, 1H, NH), 6.97-7.08 (m, 3H, H-6, H-8), 7.26-7.30 (m,
2H, H-7); 13C NMR (75.4 MHz, CDCl3) δ 14.8 (CH3), 27.1 (C-
11), 30.4 (C-1), 39.3 (C-10), 46.9 (C-4), 111.3 (C-3), 114.1 (C-2),
120.0 (C-6), 122.7 (C-8), 129.3 (C-7), 141.1 (C-5), 176.6 (CO);
HRMS (EI) calcd for C18H21NO4Fe [M - 28]þ 371.0820, found
371.0814.
Tricarbonyl-η4-[(Z)-3-(3-chlorophenyl)-4-methylene-5-pro-
pylidene-1,3-oxazolidin-2-one]iron(0) (8d). Following the gen-
eral method, with 0.666 g of 5d and 2.92 g of Fe2(CO)9, 0.613 g
(59%) of 8d was obtained as a pale yellow solid: mp 121-
122 °C; FT-IR νmax (KBr) 2044, 1972, 1956 [Fe(CO)3], 1770
(CdO) cm-1; 1H NMR (500 MHz, CDCl3) δ 0.22 (d, J = 5.2
Hz, 1H, H-7b), 1.18 (dd, J = 7.9, 6.5 Hz, 1H, H-6), 1.26 (t,
J = 7.3 Hz, 3H, CH3CH2), 2.02-2.14 (m, 2H, H-7a and
CH3CH2), 2.24-2.32 (m, 1H, CH3CH2), 7.38-7.43 (m, 2H,
H-11 and H-13), 7.45-7.48 (m, 1H, H-12), 7.52-7.53 (m, 1H,
H-9); 13C NMR (125 MHz, CDCl3) δ 15.9 (CH3CH2), 18.8 (C-
7), 22.5 (CH3CH2), 47.7 (C-6), 107.3 (C-4), 122.6 (C-5), 123.4
(C-13), 125.5 (C-9), 128.9 (C-11), 130.9 (C-12), 134.0 (C-8),
135.5 (C-10), 154.2 (C-2), 207-209 [Fe(CO)3]; MS (70 eV) m/z
389 (Mþ, 1), 361 (4), 333 (42), 305 (100), 269 (29), 223 (13),
Tricarbonyl-η4-[(Z)-2-(4-chlorophenylamino)-3-(pivaloyloxy)-
penta-1,3-diene]iron(0) (9c). Following method A with 7e, com-
plex 9c (30%) was obtained as a brown solid: mp 59-60 °C;
FT-IR νmax (KBr) 3415 (NH), 2043, 1979, 1958, [Fe(CO)3], 1755
(CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ 0.27 (d, J = 4.5 Hz,
1H, H-1b), 0.88 (q, J = 6.3 Hz, 1H, H-4),1.38 (s, 9H, H-11), 1.46
(d, J = 6.3 Hz 3H, CH3), 2.13 (d, J = 4.5 Hz, 1H, H-1a), 5.32 (s,
1H, NH), 6.90 (d, J = 8.4 Hz, 2H, H-6), 7.24 (d, J = 8.4 Hz, 2H,
H-7); 13C NMR (75.4 MHz, CDCl3) δ 14.8 (CH3), 27.1 (C-11),
31.5 (C-1), 39.3 (C-10), 47.0 (C-4), 112.9 (C-3), 113.6 (C-2), 121.0
(C-6), 127.5 (C-8), 129.3 (C-7), 140.0 (C-5), 176.6 (CO); HRMS
(EI) calcd for C19H20ClNO5Fe [M]þ 433.0379, found 433.0374.
Tricarbonyl-η4-[(Z)-2-(phenylamino)-3-(pivaloyloxy)hexa-
1,3-diene]iron(0) (9d). Following method A with 8a, complex 9d
(40%) was obtained as a brown solid: mp 99-100 °C; FT-IR νmax
(KBr) 3396 (NH), 2037, 1959, [Fe(CO)3], 1748 (CdO) cm-1; 1H
NMR (300 MHz, CDCl3) δ 0.29 (d, J = 4.5 Hz, 1H, H-1b), 0.87
(t, J = 6.9 Hz, 3H, CH2CH3), 0.90-0.96 (m, 2H, CH2CH3), 1.09
(t, J = 7.3 Hz, 1H, H-4), 1.38 (s, 9H, H-11), 2.23 (d, J = 4.5 Hz,
1H, H-1a), 5.34 (s, 1H, NH), 6.97-7.08 (m, 3H, H-6, H-8),
7.24-7.29 (m, 2H, H-7); 13C NMR (75.4 MHz, CDCl3) δ 15.7
(C-4), 23.0 (CH2CH3), 27.1 (C-11), 30.7 (C-1), 39.3 (C-10), 55.9
(CH2CH3), 112.2 (C-3), 114.2 (C-2), 120.0 (C-6), 122.6 (C-8),
129.3 (C-7), 141.2 (C-5), 176.6 (CO); HRMS (EI) calcd for
C20H23NO5Fe [M]þ 413.0926, found 413.0928.
167 (16), 111 (9), 84 (19), 56 (17). Anal. Calcd for C16H12
ClNO5Fe: C, 49.32; H, 3.10; N, 3.59. Found: C, 49.11; H,
3.22; N, 3.60.
-
Tricarbonyl-η4-[(Z)-3-(4-chlorophenyl)-4-methylene-5-propylidene-
1,3-oxazolidin-2-one]iron(0) (8e). Following the general method,
with 0.629 g of 5e and 2.92 g of Fe2(CO)9, 0.449 g (48%) of 8e was
obtained as a pale yellow solid: mp 127-128 °C; FT-IR νmax
(KBr) 2046, 1984, 1960 [Fe(CO)3], 1766 (CdO) cm-1; 1H NMR
(500 MHz, CDCl3) δ 0.19 (d, J = 5.2 Hz, 1H, H-7b), 1.18 (dd,
J = 7.8, 6.6 Hz, 1H, H-6), 1.30 (t, J = 7.3 Hz, 3H, CH3CH2), 2.03
(d, J = 5.2 Hz, 1H, H-7a), 2.03-2.13 (m, 1H, CH3CH2),
2.24-2.33 (m, 1H, CH3CH2), 7.42-7.47 (m, 2H, H-9),
7.40-7.52 (m, 2H, H-10); 13C NMR (125 MHz, CDCl3) δ 15.9
(CH3CH2), 18.6 (C-7), 22.5 (CH3CH2), 47.7 (C-6), 107.5 (C-4),
122.6 (C-5), 126.6 (C-9), 130.2 (C-10), 131.4 (C-8), 134.6 (C-11),
154.8 (C-2), 207-209 [Fe(CO)3]. Anal. Calcd for C16H12-
ClNO5Fe: C, 49.33; H, 3.10; N, 3.59. Found: C, 49.45; H, 3.03;
N, 3.60.
General Methods for the Reaction of Complexes 6a, 7a, 7e, and
8a with t-BuLi. Method A. To a solution of the corresponding
complexes 6a, 7a, 7e, or 8a (0.6 mmol) in 5 mL of dry THF at
-70 °C was slowly added t-BuLi (0.6 mmol, 1.7 M) under
nitrogen atmosphere. The mixture was allowed to reach room
temperature (∼3 h) and stirred for 12 h. At this point, the solvent
Tricarbonyl-η4-[(Z)-3-hydroxy-2-(N-phenylpivalamido)penta-
1,3-diene]iron(0) (10a). Following method B with 7a, complex
10a (35%) was obtained as a brown solid: mp 89-99 °C; FT-IR
ν
max (KBr) 3448 (OH), 2040, 1979, 1951 [Fe(CO)3], 1617, 1591
(CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ -0.52 (d, J = 4.2
Hz, 1H, H-1b), 0.90 (q, J = 6.0 Hz, 1H, H-4), 1.07 (s, 9H, H-11),

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Ortega-Jimenez et al.
158 Organometallics, Vol. 29, No. 1, 2010
1.40 (d, J = 4.2 Hz 3H, H-1a), 1.59 (d, J = 6.0 Hz, 3H, CH3),
7.34 -7.40 (m, 5H, H-6, H-7, H-8), 8.20 (s, 1H, OH); 13C NMR
(75.4 MHz, CDCl3) δ 14.3 (CH3), 29.4 (C-11), 31.9 (C-1), 42.6
(C-10), 52.5 (C-4), 97.5 (C-3), 129.5 (C-2, C-6), 129.4 (C-8),
130.4 (C-7), 144.0 (C-5), 183.4 (CO); HRMS (EI) calcd for
C18H21NO4Fe [M - 28]þ 371.0820, found 371.0815.
J = 4.2 Hz, 1H, H-4b), 0.82 (t, J = 6.0 Hz, 3H, CH3(CH2)3CO),
0.88-0.92 (m, 3H, H-1a, CH3(CH2)3CO), 1.58-1.64 (m, 2H,
CH3(CH2)3CO), 2.14-2.20 (m, 1H, CH3(CH2)2CH2CO), 2.24
(d, J = 4.2 Hz, 1H, H-4a), 2.31-2.36 (m, 1H, CH3(CH2)2-
CH2CO), 7.27-7.49 (m, 5H, H-6, H-7, H-8), 8.53 (s, 1H, OH);
13C NMR (75.4 MHz, CDCl3) δ 13.6 (C-13), 22.1 (C-11), 27.4
(C-12), 33.8(C-1), 36.0 (C-4), 36.3 (C-10), 97.2 (C-3), 128.4 (C-
6), 128.9 (C-2), 129.0 (C-8), 130.0 (C-7), 143.3 (C-5), 177.7 (CO).
Tricarbonyl-η4-[(Z)-3-hydroxy-2-(N-phenylethanamido)]-
penta-1,3-diene]iron(0) (11c). Starting with 7a, complex 11c
was obtained at 25% by following method A and at 5% by
following method B, both as a brown solid: mp 115-116 °C;
FT-IR νmax (KBr) 3449 (OH), 2045, 1957 [Fe(CO)3], 1636
(CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ -0.52 (d, J =
4.2 Hz, 1H, H-1b), 0.90 (q, J = 6.0 Hz, 1H, H-4), 1.33 (d,
J = 4.2 Hz, 1H, H-1a), 1.59 (d, J = 6.0 Hz, 3H, CH3), 2.08
(s, 3H, CH3CO), 7.25-7.27 (m, 3H, H-6, H-8), 7.45-7.47
(m, 2H, H-7), 8.51 (s, 1H, OH); 13C NMR (75.4 MHz,
CDCl3) δ 14.5 (CH3), 25.1 (CH3CO), 31.8 (C-1), 52.1 (C-4),
94.7 (C-3), 128.2 (C-2, C-6), 128.9 (C-8), 130.0 (C-7), 143.8
(C-5), 174.9 (CO); HRMS (EI) calcd for C14H15NO3Fe [M -
56]þ 301.0401; found 301.0381.
Tricarbonyl-η4-[(Z)-3-hydroxy-2-(N-phenylpivalamido)hexa-
1,3-diene]iron(0) (10b). Following method B with 7e, complex
10b (35%) was obtained as a brown solid: mp 110-111 °C;
FT-IR νmax (KBr) 3448 (OH), 2043, 1964, [Fe(CO)3], 1630, 1593
(CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ -0.53 (d, J = 4.5
Hz, 1H, H-1b), 0.78-0.87 (m, 3H, H-4, CH2CH3), 1.07 (s, 9H,
H-11), 1.12 (t, J = 7.3 Hz, 3H, CH2CH3), 1.41 (d, J = 4.5 Hz,
1H, H-1a), 7.34-7.43 (m, 5H, H-6, H-7, H-8), 8.20 (s, 1H, OH);
13C NMR (75.4 MHz, CDCl3) δ 15.8 (CH2CH3), 22.8 (C-4),
29.4 (C-11), 32.0 (C-1), 42.6 (C-10), 61.4 (CH2CH3), 97.4 (C-3),
128.5 (C-6), 128.9 (C-2), 129.0 (C-8), 130.1 (C-7), 143.7 (C-5),
183.1 (CO); HRMS (EI) calcd for C18H23NO3Fe [M - 56]þ
357.1027, found 357.1015.
Tricarbonyl-η4-[(Z)-2-(N-4-chlorophenylpivalamido)-3-hydro-
xyhexa-1,3-diene]iron(0) (10c). Following method B with 8a,
complex 10c (35%) was obtained as a brown solid: mp 109-110
°C; FT-IR νmax (KBr) 3448 (OH), 2044, 1972, 1958, [Fe(CO)3],
1620, 1595 (CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ -0.52
(d, J = 4.2 Hz, 1H, H-1b), 0.90 (q, J = 6.0 Hz, 1H, H-4),1.09 (s,
9H, H-11), 1.33 (d, J = 4.2 Hz 1H, H-1a), 1.59 (d, J = 6.0 Hz,
3H, CH3), 7.31 (d, J = 8.4 Hz, 2H, H-6), 7.42 (d, J = 8.4 Hz, 2H,
H-7), 8.17 (s, 1H, OH); 13C NMR (75.4 MHz, CDCl3) δ 14.5
(CH3), 29.7 (C-11), 31.9 (C-1), 42.8 (C-10), 52.9 (C-4), 97.6
(C-3), 105.0 (C-2), 129.7 (C-6), 131.8 (C-7), 135.5 (C-8), 142.5
(C-5), 183.4 (CO).
General Methods for the Reaction of Complexes 6a and 7a with
Alkyl Lithium Reagents. Method A. To a solution of the
corresponding complex 6a or 7a (0.6 mmol) in 5 mL of dry
THF at -70 °C was slowly added RLi (R = Me, Et, n-Bu, or
s-Bu) (0.6 mmol) under nitrogen atmosphere. The mixture was
allowed to reach room temperature (∼3 h) and stirred for 12 h.
At this point, the solvent was removed and the dark brown
residue was dissolved in EtOAc (10 mL) and filtered over
alumina. The solvent was removed under vacuum, and the crude
product was purified by column chromatography over silica gel
(hexane/EtOAc, 99:1), to afford complexes 11a-f.
Tricarbonyl-η4-[(Z)-3-hydroxy-2-(N-phenylpropanamido)-
penta-1,3-diene]iron(0) (11d). Starting with 7a, complex 11d was
obtained at 25% by following method A and at 5% by following
method B, both as a brown oil: FT-IR νmax (KBr) 2043, 1965
[Fe(CO)3], 1714, 1668 (CdO) cm-1; 1H NMR (300 MHz, CDCl3)
δ -0.50 (d, J = 4.5 Hz, 1H, H-1b), 0.78 (q, J = 6.3 Hz, 1H, H-4),
1.12-1.17 (m, 4H, H-1a, CH3CH2CO), 1.54 (d, J = 6.3 Hz, 3H,
CH3), 4.09-4.15 (m, 1H, CH3CH2CO), 4.22-4.30 (m, 1H,
CH3CH2CO), 7.14-7.34 (m, 5H, H-6, H-7, H-8), 8.31 (s, 1H,
OH); 13C NMR (75.4 MHz, CDCl3) δ 14.2 (C-11), 14.4 (CH3),
31.5 (C-1), 33.5 (C-10), 51.5 (C-4), 96.2 (C-3), 127.5 (C-2), 127.7
(C-8), 129.0 (C-6), 129.1 (C-7), 142.9 (C-5), 176.9 (CO).
Tricarbonyl-η4-[(Z)-3-hydroxy-2-(N-phenylpentanamido)penta-
1,3-diene]iron(0) (11e). Starting with 7a, complex 11e was obtained
at 60% by following method A and at 40% by following method
B, both as a brown oil: FT-IR νmax (KBr) 2048, 1964 [Fe(CO)3],
1636, 1591 (CdO) cm-1; 1H NMR (300 MHz, CDCl3) δ -0.50 (d,
J = 4.5 Hz, 1H, H-1b), 0.79-0.88 (m, 4H, H-1, CH3(CH2)3CO),
1.22-1.25 (m, 3H, H-1a, CH3(CH2)3CO), 1.59-1.67 (m, 5H,
CH3, CH3(CH2)3CO), 2.15-2.23 (m, 1H, CH3(CH2)2CH2CO),
2.30-2.35 (m, 1H, CH3(CH2)2CH2CO), 7.27-7.48 (m, 5H, H-6,
H-7, H-8), 8.54 (s, 1H, OH); 13C NMR (75.4 MHz, CDCl3) δ 13.6
(C-13), 14.9 (CH3), 22.0 (C-11), 27.5 (C-12), 31.8 (C-1), 36.3
(C-10), 52.1 (C-4), 94.9 (C-3), 128.4 (C-6), 128.7 (C-2), 128.8
(C-8), 129.9 (C-7), 143.4 (C-5), 177.6 (CO); HRMS (EI) calcd for
C19H21NO5Fe [M]þ 399.0769, found 399.0755.
Method B. To a solution of complex 7a (0.6 mmol) in 5 mL of
dry THF at -70 °C was slowly added RLi (R = Me, Et, n-Bu, or
s-Bu) (0.6 mmol) under nitrogen atmosphere. The mixture was
allowed to reach -10 °C (∼3 h). At this point, the solvent was
removed and the dark brown residue was dissolved in EtOAc
(10 mL) and filtered over alumina. The solvent was removed
under vacuum, and the crude product was purified by column
chromatography over silica gel (hexane/EtOAc, 99:1), to afford
complexes 11a-f.
Tricarbonyl-η4-[(Z)-3-hydroxy-2-(2-methyl-N-phenylbutanamido)-
penta-1,3-diene]iron(0) (11f). Starting with 7a, complex 11f was
obtained at 40% by following method A and at 30% by following
method B, both as a brown oil: FT-IR νmax (KBr) 2044, 1966
Tricarbonyl-η4-[(Z)-3-hydroxy-2-(N-phenylethanamido)buta-
1,3-diene]iron(0) (11a). Starting with 6a, complex 11a was
obtained at 20% by following method A and at 5% by following
method B, both as a brown solid: mp 97-98 °C; FT-IR
νmax (KBr) 3449 (OH), 2048, 1968 [Fe(CO)3], 1635 (CdO),
[Fe(CO)3], 1726 (CdO) cm-1 1H NMR (300 MHz, CDCl3)
;
δ -0.51 (d, J = 4.2 Hz, 1H, H-1b), 0.85-0.94 (m, 4H, H-4,
CH3CH2CH(CH3)CO), 1.05 (d, J = 6.3 Hz, 3H, CH3CH2CH-
(CH3)CO), 1.25 (d, J = 4.2 Hz, 1H, H-1a), 1.32-1.43 (m, 1H,
CH3CH2CH(CH3)CO), 1.61 (d, J = 6.3 Hz, 3H, CH3),
2.41-2.48 (m, 2H, CH3CH2CH(CH3)CO), 7.21-7.47 (m, 5H,
H-6, H-7, H-8), 8.50 (s, 1H, OH); 13C NMR (75.4MHz, CDCl3) δ
9.3 (C-13), 14.3 (CH3), 19.2 (C-12), 28.1 (C-11), 31.8 (C-1), 40.8
(C-10), 52.2 (C-4), 94.9 (C-3), 128.1 (C-2), 128.3 (C-6), 128.8 (C-
8), 129.0 (C-7), 143.5 (C-5), 181.4 (CO); HRMS (EI) calcd for
C18H21NO4Fe [M - 28]þ 371.0820, found 371.0820.
Single-Crystal X-ray Crystallography. A single crystal of
compound 6c was obtained by recrystallization from hexane/
MeOH, 2:1, compound 7a from hexane/C6H6, 2:1, compound
8d from hexane/CH2Cl2, 9:1, and 10b from CH2Cl2/hexane, 1:6,
as yellow crystals. These were mounted on glass fibers. Crystal-
lographic measurements were performed using Mo KR radia-
tion (graphite crystal monochromator, λ = 71073 A) at room
1
cm-1; H NMR (300 MHz, CDCl3) δ -0.51 (d, J = 4.2 Hz,
1H, H-1b), 0.13 (d, J = 4.2 Hz, 1H, H-4b), 1.31 (d, J = 4.2 Hz,
3H, H-1a), 2.08 (s, 3H, CH3CO), 2.24 (d, J = 4.2 Hz, 1H, H-4a),
7.26-7.48 (m, 5H, H-6, H-7, H-8), 8.50 (s, 1H, OH); 13C NMR
(75.4 MHz, CDCl3) δ 25.1 (C-10), 33.4 (C-1), 36.0 (C-4), 97.0 (C-
3), 128.2 (C-6), 129.0 (C-8), 129.1 (C-2), 130.0 (C-7), 143.7 (C-5),
174.8 (CO); HRMS (EI) calcd for C14H13NO4Fe [M - 28]þ
315.0194, found 315.0194.
Tricarbonyl-η4-[3-hydroxy-2-(N-phenylpentanamido)buta-
1,3-diene]iron(0) (11b). Starting with 6a, complex 11b was
obtained at 40% by following method A and at 30% by
following method B, both as a brown oil: FT-IR νmax (KBr)
3451 (OH), 2048, 1964 [Fe(CO)3], 1634 (CdO) cm-1; 1H NMR
(300 MHz, CDCl3) δ -0.53 (d, J = 4.5 Hz, 1H, H-1b), 0.13 (d,

Article
Organometallics, Vol. 29, No. 1, 2010 159
temperature. Three standard reflections, which were monitored
periodically, showed no change during data collection. Unit cell
parameters were obtained from least-squares refinement of 26
reflections in the range 2° < 2θ < 20°. Intensities were corrected
for Lorentz and polarization effects. No absorption correction
was applied. Anisotropic temperature factors were introduced
for all non-hydrogen atoms. Hydrogen atoms were placed in
idealized positions and their atomic coordinates refined. Unit
weights were used in the refinement. Details of data collection
and refinement for these crystals are listed in Table 12
(Supporting Information) and CIF files, which include bond
distances and angles, atomic coordinates, and anisotropic ther-
mal parameters. Structures were solved using the SHELXTL,38
SHELX97,39 or SIR9240 programs as implemented in the WinGX
suite41 and refined using SHELXTL or SHELX97 within
WinGX, on a personal computer. Inallcases ORTEP and packing
diagrams were made with PLATON and ORTEP-3.42
Acknowledgment. We thank Bruce Allan Larsen for
revising the English of the manuscript. J.T. acknowledges
SIP-IPN (Grants 20070339, 20080527, and 20090519)
and CONACYT (Grants 43508-Q and 83446), and F.D.
SIP-IPN (Grants 20070617, 20080331, and 20090936) and
CONACYT (Grant 44038) for financial support. F.O.
thanks DGAPA-UNAM for a postdoctoral fellowship.
A.B. thanks CONACYT for a graduate scholarship awar-
ded. A.B. thanks CGPI/IPN (PIFI) and Ludwig K. Hellweg
Foundation for scholarship complements. F.D. and J.T. are
fellows of the EDI-IPN and COFAA-IPN programs.
Supporting Information Available: Tables summarizing UV
spectral data, melting points, 1H and 13C NMR data of the
complexes 6a-e, 7a-e, 8a-e, 9a-d, 10a-c, and 11a-f, includ-
ing images of IR, 1H and 13C NMR (HMQC, HMBC, and NOE
experiments), and mass spectra for most of the complexes.
Crystallographic information for 6c, 7a, 8d, and 10b in cif
format, including X-ray diffraction data, atomic coordinates,
thermal parameters, and complete bond distances and angles.
This material is available free of charge via the Internet at http://
pubs.acs.org and from the Cambridge Crystallographic Data
Centre (fax: þ44-1223-336-003; e-mail: deposit@ccdc.cam.
ac.uk; or http//www.ccdc.cam.ac.uk) as supplementary publi-
cation nos. CCDC 756198 (6c), CCDC 756199 (7a), CCDC
756200 (8d), and CCDC 756201 (10b).
(38) (a) SHELXTL, v. 5.10; Bruker AXS, Inc.: Madison, WI, 1998. (b)
Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(39) SHELX97, Programs for Crystal Structure Analysis, Release
€
€
97-2; Instit€ut f€ur Anorganische Chemie der Universitat: D-3400 Gottingen,
Germany.
(40) SIR92. Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi,
A. J. Appl. Crystallogr. 1993, 26, 343-350.
(41) WinGX. Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
(42) (a) PLATON. Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7-13.
(b) ORTEP-3. Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.