Ethynylferrocene insertion into Fe-C bond in bridging aminocarbyne diiron complexes: New triiron vinyliminium complexes

Article abstract of DOI:10.1016/j.jorganchem.2010.07.027

The μ-aminocarbyne complexes [Fe₂{μ-CN(Me)(R)}(μ-CO) (CO)(NCMe)(Cp)₂][SO₃CF₃] (R = Me, 1a; Xyl, 1b; Xyl = 2,6-Me₂C₆H₃) react with ethynylferrocene to give the corresponding bridg

Full text of DOI:10.1016/j.jorganchem.2010.07.027

Journal of Organometallic Chemistry 695 (2010) 2519e2525
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ethynylferrocene insertion into FeeC bond in bridging aminocarbyne diiron
complexes: New triiron vinyliminium complexes
*
Luigi Busetto, Rita Mazzoni, Mauro Salmi, Stefano Zacchini, Valerio Zanotti
Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
The
Xyl ¼ 2,6-Me2C6H3) react with ethynylferrocene to give the corresponding bridging vinyliminium
complexes [Fe2{
h1 3-C]N(Me)(R)CHC(Fc)}(
tion of the ethynylferrocene in the metalecarbyne bond is regiospecific, and leads to the formation of
only one isomer.
m
-aminocarbyne complexes [Fe2{
m
-CN(Me)(R)}(
m
-CO)(CO)(NCMe)(Cp)2][SO3CF3] (R ¼ Me, 1a; Xyl, 1b;
Received 28 June 2010
Received in revised form
27 July 2010
Accepted 29 July 2010
Available online 6 August 2010
m
-
:h
m
-CO)(CO)(Cp)2][SO3CF3] (R ¼ Me, 2a; R ¼ Xyl, 2b). Inser-
Complexes 2a and 2b undergo hydride addition (by NaBH4) affording the enaminoalkylidene complex
[Fe2{
m
-
h1
:h
3-C(H)(N(Me)2)CHC(Fc)}(
m
-CO)(CO)(Cp)2] (3a) and the bis-alkylidene [Fe2{
m- :h
h1 2-C(N(Me)
Keywords:
(Xyl))CH2C(Fc)}(
m
-CO)(CO)(Cp)2] (3b), respectively. Upon treatment with NaH, compounds 2a and 2b
Vinyliminium
Aminocarbyne
Alkyne insertion
Ferrocene
Metallacycle
Diiron complexes
undergo fragmentation, affording the 1-metalla-2-aminocyclopenta-1,3-dien-5-one complexes [Fe(CO)
(Cp){C(N(Me)(R))}CHC(Fc)C(O)}] (R ¼ Me, 4a; R ¼ Xyl, 4b).
The molecular structures of 2b, 3b and 4b have been determined by X-ray diffraction studies.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
coordination, vinyliminium ligands display a unique and distinct
reactivity compared to the corresponding non coordinated conju-
Metal-assisted CeC and Ceheteroatom bond formation has
a major role in the construction of highly complex molecular archi-
tectures [1]. Synthetic strategies also include the use of dinuclear
(polynuclear) transition metal complexes, which take advantage of
specific activation modes associated to multisite coordination, to
promote the assembly of small and simple molecular units [2]. As an
example, the assembly of bridging C1 ligands (such as alkylidynes or
alkylidenes) with alkenes or alkynes (C2 units), provides an effective
entry to the synthesis of bridging C3 species [2a,3]. Within this field,
gated species [7]. A further significant aspect is that the observed
CeC bond formation is assisted by iron, which is a cheap and envi-
ronmental sustainable transition metal. This is of great interest in
view of the growing demand for processes based on safe transition
metal in the place of toxic and less abundant transition metals [8].
Based on these considerations, we decided to extend our studies
to the insertion of ethynylferrocene in the metal alkylidyne carbon
bond of 1. The primary aim was to generate a bridging vinyliminium
ligand connected to a further iron atom, in the form of ferrocenyl
(Fc). Indeed, addition of ethynylferrocene to compounds and
molecular arrays, including transition metal complexes [9], might
significantly alter their nature and reactivity, due to the redox
properties associated with the Fc group. The present work is
intended to support these proposals.
we have shown that the diiron
m-aminoalkylidyne complexes I
undergo insertion of alkynes into a metalecarbyne bond to form
bridging vinyliminium complexes II (Scheme 1) [4].
The transformation shown in Scheme 1 is interesting for several
reasons. First, insertion of a primary alkyne into the metal carbon
bond is regiospecific: CeC bond formation occurs exclusively
between the bridging alkylidyne carbon and the primary carbon of
the alkyne. A second point is that the resulting bridging C3 ligand is
2. Results and discussion
a a,b unsaturated iminium coordinated in a m-
h1h3 mode. Conju-
2.1. Insertion of ethynylferrocene into the ironecarbon bond of
aminocarbyne complexes
gated iminiums are essential intermediates in iminiumeenamine
catalysis [5], and have a major role in the development of the orga-
nocascade catalysis [6]. However, as consequence of the bridging
The bridging aminocarbyne complexes [Fe2{m-CN(Me)(R)}(m-CO)
(CO)(NCMe)(Cp)2][SO3CF3] (R ¼ Me, 1a; Xyl, 1b; Xyl ¼ 2,6-Me2C6H3)
react with ethynylferrocene, in refluxing CH2Cl2, to give the corre-
* Corresponding author. Tel.: þ39 (0)512093695.
E-mail address: valerio.zanotti@unibo.it (V. Zanotti).
sponding m-vinyliminium complexes [Fe2{m- :h
h1 3-C]N(Me)(R)CHC
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.07.027

2520
L. Busetto et al. / Journal of Organometallic Chemistry 695 (2010) 2519e2525
R
H
Me
R
N
C
N
C
R'
CO
Fe
Me
HC CR'
C
OC
C
NCMe
Fe
Fe
Fe
C
O
C
O
R = Me, Xyl
R'= H, alkyl, aryl, SiMe3, CO2Me
II
I
Scheme 1.
(Fc)}(
yields (Scheme 2).
m
-CO)(CO)(Cp)2][SO3CF3] (R ¼ Me, 2a; R ¼ Xyl, 2b) in ca. 80%
In Scheme 2 the carbon atoms of the bridging chain have been
labeled to make clearer the discussion and the considerations
presented hereafter.
The reaction parallels those of 1 with simple organic alkynes
(Scheme 1), with insertion into the metal carbon bond leading to
the regiospecific formation of a vinyliminium ligand in which the Fc
group is bound to the C3 carbon of the bridging carbon chain.
Compounds 2a,b were purified by chromatography on alumina
and characterized by IR, NMR spectroscopy, and elemental analysis.
Moreover, the molecular structure of 2b has been determined by
X-ray diffraction. The ORTEP diagram is shown in Fig. 1, and the
main bond lengths and angles are reported in Table 1. The cation is
Fig. 1. Molecular structure of 2b with key atoms labeled (all H-atoms, except H(14),
have been omitted for clarity). Thermal ellipsoids are at the 30% probability level.
composed by a cis-[Fe2(
m-CO)(CO)(Cp)2] to which is coordinated
C1, C2 and C3, in the range typical for vinyliminium ligands (e.g. for
2b, at 231.7, 55.3 and 205.2 ppm, respectively). The IR spectra of
a bridging
m
-
h1 3-C]N(Me)(Xyl)CHC(Fc) ferrocene-substituted
:h
vinyliminium ligand. All bonding parameters are as expected for
this class of complexes [4], and the substituents at the iminium
group display the usual E-conformation.
2a,b (in CH2Cl2) show the expected n(CO) band pattern consisting of
one absorption for the terminal carbonyl (e.g. at 2001 cmꢀ1 for 2b)
and one for the bridging carbonyl (e.g. at 1817 cmꢀ1 for 2b).
These results, together with previous results present clear
evidence that the incorporation of alkynes into bridging
The NMR spectra of 2a,b confirm that the reaction is regiospe-
cific and leads to the formation of only one of the two possible
isomers that insertion of a non-symmetric alkyne into the metal
carbon bond might produce. Indeed, the CH portion of the inserted
HC^CFc generates a 1H NMR resonance at 4.70 ppm which is in the
range expected for C2eH [4], and is consistent with the geometry
observed in the solid. The alternative isomer would have presented
a C3eH proton with a low field resonance, at about 11 ppm.
Moreover, the NMR spectra (in CDCl3) of 2b show the presence of
a significant NOE effect between the N-methyl and one Cp ring,
demonstrating that 2b, in solution, adopts the same E-configura-
tion, with respect to the C1]N double bond, that is observed in the
solid. Finally, the resonances attributable to the ferrocenyl group
are observed in the typical range at about 4e5 ppm. Relevant
features in the 13C NMR spectra include the resonances due to the
Table 1
ꢁ
ꢀ
Selected bond lengths (A) and angles ( ) for 2b and 3b.
2b
3b
Fe(1)eFe(2)
Fe(2)eC(11)
Fe(1)eC(12)
Fe(2)eC(12)
Fe(1)eC(13)
Fe(2)eC(13)
Fe(1)eC(14)
Fe(1)eC(15)
C(11)eO(11)
C(12)eO(12)
C(13)eC(14)
C(14)eC(15)
C(13)eC(25)
C(15)eN(1)
N(1)eC(16)
N(1)eC(17)
Fe(3)eCt(1)a
Fe(3)eCt(2)b
2.5552(10)
1.757(7)
1.975(6)
1.875(6)
2.048(5)
1.962(5)
2.076(5)
1.842(5)
1.137(7)
1.171(7)
1.412(6)
1.427(7)
1.484(7)
1.301(6)
1.479(7)
1.458(6)
1.645(2)
1.664(2)
2.5270(4)
1.733(2)
1.841(2)
1.972(2)
1.9788(18)
2.0159(19)
2.587(2)
1.8830(19)
1.148(3)
1.186(3)
1.537(3)
1.492(3)
1.480(3)
1.316(2)
1.468(3)
1.453(3)
1.654(2)
1.657(2)
SO3CF3
SO3CF3
Fe
R
Me
R
H
N
C
C2
N
C1
C3
Me
OC
NCMe
C(14)eC(13)eFe(2)
C(13)eC(14)eC(15)
C(14)eC(15)eFe(1)
C(14)eC(15)eN(1)
N(1)eC(15)eFe(1)
C(15)eN(1)eC(16)
C(15)eN(1)eC(17)
C(17)eN(1)eC(16)
Fe(2)eC(13)eC(25)
C(14)eC(13)eC(25)
122.4(4)
118.4(4)
77.7(3)
132.2(4)
147.3(4)
121.1(4)
122.4(4)
116.4(4)
119.6(3)
116.3(4)
114.57(13)
95.34(14
CO
Fe
Fe
Fe
Fe
HC CFc
-NCMe
99.44(12)
121.88(17)
138.68(15)
121.68(17)
122.14(16)
116.17(16)
117.00(13)
114.68(16)
C
O
C
O
R
Me
Xyl
1a
1b
2a
2b
a
Ct(1) is the centroid of the substituted Cp-ring bonded to Fe(3).
Ct(2) is the centroid of the unsubstituted Cp-ring bonded to Fe(3).
b
Scheme 2.

L. Busetto et al. / Journal of Organometallic Chemistry 695 (2010) 2519e2525
2521
aminoalkylidyne units is general, and the presence of a ferrocenyl
group, as alkyne substituent, modifies neither the reaction
outcome, nor its regioselective character.
2.2. Reactions of the vinyliminium complexes with NaBH4
One of the most distinctive aspects of bridging vinyliminium
complexes is the fact that they undergo nucleophilic addition at the
iminium carbon (C1) or at the adjacent position (C2), in the place of
a
conjugated addition (addition at
b position), which is typically
observed in unsaturated iminiums (non coordinated). A repre-
a,b
sentative example is provided by hydride addition (from NaBH4)
[10]. Interestingly, the regiochemistry of the reaction is governed by
the nature of the N substituent, in that the sterically demanding Xyl
groupgenerallyacts as protecting groupwith respect tothe iminium
carbon, and directs hydride addition to the adjacent
a position.
In theory, the presence of a Fc substituent might alter this
reaction pattern, as a consequence of steric and electronic effects. In
reality, we found that complexes 2a and 2b react with NaBH4,
leading to the formation of the complexes 3a and 3b, respectively
(Scheme 3), in full agreement with the usual behavior of vinyl-
iminium diiron complexes [10].
Compounds 3a,b were purified by chromatography on alumina
and characterized by spectroscopy, and elemental analysis. The
molecular structure of 3b was determined by X-ray diffraction. The
ORTEP diagram is shown in Fig. 2, while the main bond lengths and
angles are reported in Table 1. The geometry and bonding param-
eters of 3b are in perfect agreement with those previously found for
Fig. 2. Molecular structure of 3b with key atoms labeled (all H-atoms, except H(14)
and H(15), have been omitted for clarity). Thermal ellipsoids are at the 30% probability
level.
the closely related
m-vinylalkylidene complex [Fe2{
m- :h
h1 2-C(N
sterically demanding Xyl group (as in 2b) Hꢀ addition is selectively
directedtotheC2, with formationof thebis-alkylidene complexes 3b.
NMR data are consistent with the above picture; in particular,
both 1H and 13C NMR resonances of 3a are very similar to that of
analogous complexes previously reported, which simply contain
a different group (e.g. Tol, SiMe3, Me or CH2OH) in the place of Fc
[10a]. Most relevant features include the resonances of the C1H and
C2H protons, that appear as doublets. Their coupling constant (of
about 10 Hz) indicates that they are mutually trans, which corre-
spond to an E configuration of the vinyl group. Therefore, the
addition is both regio- and stereo-selective.
(Me)(Xyl))CH2C(COOMe)}(
m-CO)(CO)(Cp)2] [10a]. As a consequence
of hydride addition, C(14) is transformed into a saturated tetra-
ꢀ
coordinated carbon and the Fe(1)/C(14) contact [2.587(2) A]
becomes completely non-bonding. This breaks off the
p-bond
connection between the bridging alkylidene C(13) and the terminal
ꢀ
ꢀ
alkylidene C(15) [C(13)eC(14) 1.537(3) A; C(14)eC(15) 1.492(3) A].
The terminal alkylidene function is stabilized by significant -bond
p
ꢀ
delocalization involving the nitrogen atom [C(15)eN(1) 1.301(6) A;
ꢀ
C(15)eFe(1) 1.8830(19) A].
The selective transformation of 2a into 3a is consistent with
hydride addition occurring preferentially at the iminium carbon,
with consequent transformation of the bridging vinyliminium into
The NMR data of 3b are similar to those of previously reported
bis-alkylidene complexes of the type [Fe2{
(Xyl)}( -CO)(CO)(Cp)2], containing the R group in the place of Fc
m- :h
h1 2-C(R)CH2CN(Me)
a stable
m-vinylalkylidene. Conversely, in the presence of the
m
(R ¼ Tol, SiMe3, Me, CH2OH, COOMe, Bun, H) [10a]. The only
remarkable difference between 3b and the corresponding species
that do not contain Fc, consists in the fact that these latter species
are generally isomeric mixtures, with the E configuration predom-
inant, but not exclusive (Scheme 4). Conversely, 3b adopts exclu-
sively the E configuration, as revealed by the presence of NOE effect
between the N-methyl and one Cp ring. The isomeric forms are due
to the orientation assumed by the different N substituents (Me and
Xyl), as a consequence of the double bond character of the C1eN
interaction, and are in agreement with the aminocarbene nature of
the ligand.
Me
H
H
Me
C2
Fc
N
C2
Fc
N
C1
C3
Me
C3
Me
C1
CO
CO
NaBH4
Fe
Fe
H
Fe
Fe
C
C
O
O
2a
3a
Xyl
H
As for the alkyne insertion reaction (Scheme 2), the presence of
Fc substituents does not change significantly the reaction profile
concerning hydride addition, neither the geometry of the addition
products.
C2
H
Fc
CO
N
H
Xyl
Fc
C1
C3
Fe
C2
Me
C3
N
C1
NaBH4
Fe
Me
CO
Fe
Fe
C
O
2.3. Reactions of the vinyliminium complexes with NaH
C
O
2b
A further peculiar aspect of the bridging vinyliminium ligand,
3b
which is unusual for non coordinated
species, is the proton abstraction from the
a
,
b
unsaturated iminium
position. The CeH
Scheme 3.
a
a

2522
L. Busetto et al. / Journal of Organometallic Chemistry 695 (2010) 2519e2525
R
H
H
H
R
H
H
Xyl
Me
R
Me
OC
C
H
R
Fc
N
N
C
C2
C1
C
C3
N
Me
C1 C2
N
C
C
CO
Fe
C
NaH
THF
Me
CO
CO
Xyl
C3
Fe
Fe
Fe
Fe
Fe
Fe
Fe
C
C
O
C
O
O
C
O
E
Z
R
Me
Xyl
2a
2b
4a
4b
Scheme 4.
deprotonation leads to the formation of reactive intermediate
species [11], which can be combined with a variety of reagents (e.g.
elemental sulfur or selenium [12], diazoacetates [13], arylisocya-
Scheme 6.
ꢀ
aminocarbene C(7)eN(1) interaction [1.329(3) A] shows a partial
double bond character. The CeC interactions present an alternating
nides [7b], and phenyldisulphides [14]), resulting in
a CeH
replacement with a range of functional groups ( -functionaliza-
a
ꢀ
behavior; thus, C(8)eC(9) [1.346(3) A] is an almost pure double bond,
tion). Some of these functionalization reactions are shown in
Scheme 5, as example.
ꢀ
ꢀ
whereas C(7)eC(8) [1.456(3) A] and C(9)eC(10) [1.519(3) A] are
essentially single bonds. Finally, the aminocarbene nitrogen substit-
uents adopt an E arrangement, as previously found for analogous
complexes.
In this case, the presence of a Fc substituent shows a relevant
influence on the reaction outcome: we have found that complexes
2a,b, upon treatment with NaH in the presence of elemental sulfur
or N2CH(CO2Et) do not react to form products analogous to III or IV
(Scheme 5). Conversely, 2a,b undergo fragmentation of the diiron
unit, leading to the formation of metallacycle products 4a,b
(Scheme 6). The observed rearrangement is simply the conse-
quence of the treatment with NaH, and does not involve reagents
such as S or N2CHCO2Et, normally used to trap the deprotonated
intermediate. Therefore, the products 4a,b can be formed by
reacting 2a,b with NaH only (Scheme 6).
The spectroscopic data of 4a,b are consistent with the structure
found in the solid. In particular, the 13C NMR spectra of 4a,b (in
CDCl3), show the typical low-field resonances for the acyl carbon
(e.g. at 268.7 ppm for 4b) and for the aminocarbene carbon C1 (e.g.
at 262.2 ppm for 4b). In agreement with the aminocarbene nature
of the ligand, there is absence of free rotation around the C1eN
interaction due to the partial double bond character of the inter-
action. As a consequence, the two N-methyls in 4a are non-equiv-
alent, in the NMR time-scale, and give rise to distinct resonances.
Likewise, NOE investigations indicate that the nitrogen substitu-
ents of 4b adopt the E configuration, with respect to the C1eN
interaction, that is the same configuration observed in the solid.
Formation of the metallacyclic complexes 4a,b is not unprece-
dented. In a restricted number of cases the treatment of vinyl-
iminium complexes with NaH, in the absence of trapping reagents,
leads to the formation of analogous cyclometallated products. In
particular, complexes analogous to 4b (containing Me, CO2Me,
CMe2OH in place of Fc) and a metallacycle compound similar to 4a
Compounds 4a,b were obtained in about 70e75% yield after
purification by column chromatography on alumina, and were char-
acterized by IR and NMR spectroscopy, and elemental analysis. In
addition, the molecular structure of 4b has been determined by X-ray
diffraction:theORTEPdiagramisshowninFig. 3, whilethemainbond
lengths and angles are reported in Table 2. The structure of 4b is
closely related to that previously reported for the 1-metalla-2-ami-
nocyclopenta-1,3-dien-5-one complex [Fe(CO)(Cp){C(N(Me)(Xyl))
CHC(Me)C(O)}] displaying very similar bonding parameters [11].
Thus, the five atoms constituting the metallacycle ring are almost
coplanar (mean deviation from the Fe(1)eC(7)eC(8)eC(9)eC(10)
ꢀ
ꢀ
least-squaresplane0.0480 A). TheFe(1)eC(7)[1.908(2) A]andFe(1)e
ꢀ
C(10) [1.935(2) A] interactions are typical for a metaleaminocarbene
and a metaleacyl; the former shows a strong
whereas the latter is mainly a interaction. Accordingly, the C(10)eO
(2)interaction[1.216(3) A]isanalmostpuredoublebond,andalsothe
p back-bonding,
s
ꢀ
Me
N
S
C
R''
Fe
Base
C
C
R
Me
H α
C
CO
Fe
β
N
R''
CO
S
III
R
C
C
-H+
Fe
Fe
EtOOC
H
C
C
O
N2C(H)CO2Et
-H+
N
II
Me
N
N
C
R = Me, Xyl
R''
Fe
R'' = H, alkyl, aryl
Base = NaH
R
C
C
CO
Fe
IV
Fig. 3. Molecular structure of 4b with key atoms labeled (all H-atoms, except H(8),
Scheme 5.
have been omitted for clarity). Thermal ellipsoids are at the 30% probability level.

L. Busetto et al. / Journal of Organometallic Chemistry 695 (2010) 2519e2525
2523
Table 2
Selected bond lengths (A) and angles ( ) 4b.
All the reactions proceed in high yields and are almost
completely selective.
ꢁ
ꢀ
Fe(1)eC(6)
Fe(1)eC(10)
C(7)eC(8)
C(9)eC(10)
C(9)eC(11)
N(1)eC(21)
Fe(2)eCt(1)a
1.727(3)
1.935(2)
1.456(3)
1.519(3)
1.455(3)
1.465(3)
1.639(2)
Fe(1)eC(7)
C(6)eO(1)
C(8)eC(9)
C(10)eO(2)
C(7)eN(1)
N(1)eC(22)
Fe(2)eCt(2)b
1.908(2)
1.155(3)
1.346(3)
1.216(3)
1.329(3)
1.450(3)
1.652(2)
4. Experimental details
4.1. General
All reactions were routinely carried out under a nitrogen atmo-
sphere, using standard Schlenk techniques. Solvents were distilled
immediately before use under nitrogen from appropriate drying
agents. Chromatography separations were carried out on columns of
deactivated alumina (4% w/w water). Glassware was oven-dried
before use. Infrared spectra were recorded at 298 K on a Per-
kineElmer Spectrum 2000 FT-IR spectrophotometer and elemental
analyses were performed on a ThermoQuest Flash 1112 Series EA
Instrument. All NMR measurements were performed at 298 K on
Mercury Plus 400 instrument. The chemical shifts for 1H and 13C were
referenced to internal TMS. The spectra were fully assigned via DEPT
experiments and 1H,13C correlation through gs-HSQC and gs-HMBC
experiments [18]. NOE measurements were recorded using the
DPFGSE-NOE sequence [19]. All the reagents were commercial
products (Aldrich) of the highest purity available and used as
received. [Fe2(CO)4(Cp)2] was purchased from Strem and used as
received. Compounds 1a,bwere prepared by published methods [20].
Fe(1)eC(7)eC(8)
C(8)eC(9)eC(10)
C(10)eFe(1)eC(7)
Fe(1)eC(10)eO(2)
C(11)eC(9)eC(10)
C(8)eC(7)eN(1)
C(7)eN(1)eC(22)
114.99(15)
112.07(19)
83.05(9)
126.73(18)
123.42(18)
116.65(18)
123.97(17)
C(7)eC(8)eC(9)
C(9)eC(10)eFe(1)
C(9)eC(10)eO(2)
C(8)eC(9)eC(11)
Fe(1)eC(7)eN(1)
C(7)eN(1)eC(21)
C(22)eN(1)eC(21)
115.62(19)
113.32(15)
119.9(2)
124.51(19)
128.33(16)
122.45(19)
113.55(17)
a
Ct(1) is the centroid of the substituted Cp-ring bonded to Fe(2).
Ct(2) is the centroid of the unsubstituted Cp-ring bonded to Fe(2).
b
(containing a Bun group in place of Fc) have been previously
reported [11].
The metallacycle products clearly result from the assembly of
the bridging vinyliminium ligand with a CO ligand, and do not
require deprotonation. The reaction likely proceeds through
a mechanism alternative to
a CeH deprotonation, in which NaH
does not remove the CeH proton, but rather acts as reducing
a
4.2. Synthesis of [Fe2{
(Cp)2][SO3CF3] (R ¼ Me, 2a; R ¼ Xyl, 2b)
m- :h m-CO)(CO)
h1 3-C]N(Me)(R)CHC(Fc)}(
agent, favoring fragmentation of the dinuclear precursor and
cyclization. The observed cyclization implies loss of a Fe containing
fragment, formally corresponding to [CpFe]þ. We do not know the
fate of the Fe fragment, that likely generates unidentified decom-
position products, except for traces of [Fe2(CO)4Cp2], detected after
chromatographic separation. The behavior of 2a,b is peculiar, in
that most of the vinyliminium complexes preferentially undergo
deprotonation, upon treatment with NaH. The different behavior is
presumably related to the presence of the ferrocenyl substituent:
the redox properties of the Fc group might indeed favor reduction
over deprotonation, thus affecting the reaction outcome. Unfortu-
nately, the major consequence is the absence of reaction path
A solution of 1a (544 mg, 1.0 mmol) in CH2Cl2 (30 mL) was
treated with ethynylferrocene (315 mg, 1.5 mmol). The reaction
mixture was heated at reflux temperature for 4 h, then was allowed
to cool to room temperature. Removal of the solvent and chroma-
tography of the residue on an alumina column, with CH3OH as
eluent, afforded a green/brown solid, corresponding to 2a. Yield:
585 mg; 82%. Anal. Calcd. for C28H26F3Fe3NO5S: C, 47.16; H, 3.67; N,
1.96. Found: C, 47.32; H, 3.54; N, 1.95%. IR (CH2Cl2)
1807 (s); 5.15 (s, 5H, Cp); 5.11
(CN) 1686 (w) cmꢀ1.1H NMR (CDCl3)
(s, 1H, C2H); 4.81, 4.27 (s, 10H, Cp); 4.57, 4.50, 4.40, 4.30 (br m, 4H,
n(CO) 1989 (vs),
n
d
leading to
a CH replacement. On the other hand, complexes 4a,b
C3eC5H4); 3.80, 3.25 (s, 6H, NMe). 13C{1H} NMR (CDCl3)
d 257.4 (m-
consist of a ferrocenyl unit having an unusual substituent: a met-
allacyclopentadienone. Indeed the design of new ferrocene-based
molecular architectures [15] requires access to ferrocene complexes
with unusual substituents on the cyclopentadienyl ring, which is
mostly challenging, by a synthetic point of view [16].
CO); 225.1 (C1); 210.3 (CO); 201.2 (C3); 91.4, 87.5 (Cp); 69.9 (CpFc);
108.2, 72.4, 69.4, 68.1, 67.3 (C3C5H4); 54.2 (C2); 51.7, 44.7 (NMe) ppm.
Compound 2b was prepared with the same procedure described
for 2a, by reacting 1b with ethynylferrocene.
Crystals suitable for X-ray analysis were obtained by
a dichloromethane solution, layered with diethyl ether, at ꢀ20 ꢁC.
Compound 2b (yield: 85%). Anal. Calcd. for C35H32F3Fe3NO5S: C,
52.34; H, 4.02; N, 1.74. Found: C, 52.22; H, 4.14; N, 1.80%. IR (CH2Cl2)
Finally, since complexes 2a,b, 3a,b, and 4a,b contain a ferrocenyl
group, they have been also investigated by electrochemical
methods. Electrochemical data were obtained from 10ꢀ3 M solu-
tions in CH2Cl2 with [Bu4N][PF6] 0.1 M. Cyclic voltammograms show
reversible anodic peaks due to the ferrocenyl moiety. The potential
values (E1/2 in mV, referenced to the SCE, at a scan speed
n
(CO) 2001 (vs), 1817 (s);
7.45e6.96 (m, 3H, Me2C6H3); 5.37, 5.08 (s, 10H, Cp); 4.77 (s, 1H,
C2H); 4.72, 4.64, 4.40, 4.16 (m, 4H, C3eC5H4); 4.26 (s, 3H, NMe); 4.12
n .
(CN) 1628 (w) cmꢀ1 1H NMR (CDCl3)
d
y
¼ 100 mV sꢀ1) are reported in the experimental part. Values are in
(s, 5H, Cp); 2.38, 1.79 (s, 6H, Me2C6H3). 13C{1H} NMR (CDCl3)
d 254.2
a good agreement with the data reported for ethynylferrocenes [17].
(CO); 231.7 (C1); 210.2 (CO); 205.2 (C3); 145.4, 131.5, 129.8, 129.4
(Me2C6H3); 92.2, 87.9 (Cp); 108.3, 72.2, 70.1, 68.7, 67.9 (C3eC5H4);
69.6 (CpFc); 55.3 (C2); 46.1 (NMe2); 18.1, 17.4 (Me2C6H3) ppm.
3. Conclusions
Alkyne insertion into the metal carbon bond of bridging ami-
nocarbyne ligands in diiron complexes has been successfully
extended to ethynylferrocene. The resulting bridging vinyliminium
4.3. Synthesis of [Fe2{
m
-
h1
:
h
3-C(H)(NMe2)CHC(Fc)}(
2-C(N(Me)(Xyl))CH2C(Fc)}(
m
m
-CO)(CO)
-CO)(CO)
(Cp)2] (3a) and [Fe2{
(Cp)2] (3b)
m
-
h1
:
h
fragment contains a ferrocenyl substituent in the
b position. The
reactivity of the vinyliminium complexes containing three iron
centres closely resembles that of vinyliminium complexes obtained
from purely organic alkynes, except for an higher tendency to
undergo fragmentation and cyclization. New and unprecedented
metallacycle complexes are consequently formed: they contain the
Fc group as substituent on a five-member metallacycle.
A solution of 2a (355 mg, 0.5 mmol) in THF (20 mL) was treated
with NaBH4 (93 mg, 2.5 mmol). The resulting mixture was stirred at
room temperature for 60 min. Then, the solvent was removed
under reduced pressure. The solid was re-dissolved in the minimal
amount of CH2Cl2, then it was chromatographed through an
alumina column, with CH2Cl2 as eluent, affording 3a. Yield:

2524
L. Busetto et al. / Journal of Organometallic Chemistry 695 (2010) 2519e2525
Table 3
254 mg; 90%. Anal. Calcd. for C27H27Fe3NO2: C, 57.39; H, 4.82; N,
2.48. Found: C, 57.32; H, 4.62; N, 2.55%. IR (CH2Cl2) (CO) 1927
4.74 (br s, 5H, Cp); 4.70 (d, 1H,
Crystal data and experimental details for 2b, 3b$CH2Cl2 and 4b.
n
(vs), 1750 (s) cmꢀ1. 1H NMR (CDCl3)
d
Complex
Formula
Fw
2b
3b$CH2Cl2
C35H35Cl2Fe3NO2
740.09
4b
C2H, 3JHH ¼ 10.0 Hz); 4.74, 4.52, 4.38, 4.33 (br s, C3eC5H4); 4.34 (br s,
C35H32F3Fe3NO5S
803.23
296(2)
0.71073
Triclinic
P1
10.4304(16)
11.5864(18)
14.537(2)
97.155(2)
102.884(2)
99.454(2)
1665.5(4)
2
C29H27Fe2NO2
533.22
296(2)
0.71073
Triclinic
P1
7.3663(11)
10.7966(15)
16.091(2)
89.201(2)
78.213(2)
77.453(2)
1222.2(3)
2
10H, Cp þ CpFc); 2.48 (s, 6H, NMe2); 1.72 (d,1H, C1H, 3JHH ¼ 10.0 Hz).
T, K
295(2)
13C{1H} NMR (CDCl3)
d 278.8 (m
-CO); 218.1 (CO); 177.2 (C3); 104.8
ꢀ
l
, A
0.71073
Triclinic
P1
(C1); 87.9, 80.8 (Cp); 68.9 (CpFc); 111.5, 72.2, 68.1, 67.5, 67.2
Crystal system
Space group
(C3C5H4); 66.9 (C2); 41.2 (NMe2) ppm.
ꢀ
a, A
10.4823(8)
11.8523(9)
14.0455(11)
98.2600(10)
93.9670(10)
110.8180(10)
1600.5(2)
2
Compound 3b was prepared with the same procedure described
for 3a, by reacting 2b with NaBH4. Crystals suitable for X-Ray
diffraction were obtained by a CH2Cl2 solution, layered with
hexane, at ꢀ20 ꢁC.
ꢀ
b, A
ꢀ
c, A
ꢁ
ꢁ
ꢁ
a
,
b
,
g
,
Compound 3b (yield: 91%). Anal. Calcd. for C34H33Fe3NO2: C,
3
ꢀ
Cell volume, A
Z
62.33; H, 5.08; N, 2.14. Found: C, 62.21; H, 5.14; N, 2.03%. IR (CH2Cl2)
n
(CO) 1919 (vs), 1738 (s) cmꢀ1. 1H NMR (CDCl3)
d
7.32e6.92 (m, 3H,
Dc, g cmꢀ3
1.602
1.412
820
1.536
1.541
760
1.449
1.213
552
, mmꢀ1
Me2C6H3); 4.81, 4.36, 4.23 (s, 15H, Cp); 4.43e4.26, 4.07 (m, 4H,
m
2
C3C5H4); 4.30 (d, 1H, C2H, JHH ¼ 20.0 Hz); 3.72 (s, 3H, NMe); 3.35
F(000)
Crystal size, mm
(d,1H, C2H, 2JHH ¼ 20.0 Hz); 2.20,1.92 (s, 6H, Me2C6H3). 13C{1H} NMR
0.21 ꢂ 0.16 ꢂ 0.14 0.21 ꢂ 0.15 ꢂ 0.11 0.22 ꢂ 0.14 ꢂ 0.12
ꢁ
q
limits,
1.46e26.00
16,416
1.48e27.00
17,889
1.26e26.99
13,704
(CDCl3) d 284.5(m
-CO); 271.7 (C1); 219.7 (CO); 161.4 (C3); 142.8,129.2,
Reflections
collected
128.4, 128.3 (Me2C6H3); 88.3, 85.3 (Cp); 74.3 (C2); 69.0 (CpFc); 115.8,
69.1, 66.8, 66.5, 65.5 (C3C5H4); 45.9 (NMe); 17.9,17.5 (Me2C6H3) ppm.
Independent
reflections
Data/restraints/
parameters
Goodness on fit
on F2
6504
6937
5293
[Rint ¼ 0.0302]
[Rint ¼ 0.0195]
[Rint ¼ 0.0279]
6504/242/436
6937/0/397
5293/1/313
4.4. Synthesis of [Fe(CO)(Cp){C(N(Me)(R))CHC(Fc)C(O)}] (R ¼ Me,
4a; R ¼ Xyl, 4b)
1.061
1.030
1.002
A solution of 2a (355 mg, 0.5 mmol) in THF (20 mL) was treated
with NaH (60 mg, 2.5 mmol). The resulting mixture was stirred at
room temperature for 1 h. Then, it was filtered on an alumina pad.
The solvent was then removed under reduced pressure. The solid
was re-dissolved in the minimal amount of CH2Cl2, and passed
through an alumina column, with CH2Cl2 as eluent, affording 4a.
Yield: 166 mg; 75%. Anal. Calcd. for C22H21Fe2NO2: C, 59.63; H, 4.78;
R1 (I > 2
wR2 (all data)
s
(I))
0.0575
0.1800
0.0319
0.0870
0.745/ꢀ0.550
0.0325
0.0823
0.293/ꢀ0.272
Largest diff. peak 0.747/ꢀ0.662
ꢀꢀ3
and hole, e A
(empirical absorption correction SADABS) [21]. Structures were
solved by direct methods and refined by full-matrix least-squares
based on all data using F2 [22]. All hydrogen atoms were fixed at
calculated positions and refined by a riding model, except H(14) in
2b, H(14) and H(15) in 3b$CH2Cl2, and H(8) in 4b which were located
in the Fourier map and refined isotropically using the 1.2 fold Uiso
value of the parent C-atoms. All non-hydrogen atoms were refined
with anisotropic displacement parameters. Similar Urestraints were
applied to the C-atoms (s.u. 0.005) in 2b.
N, 3.16. Found: C, 59.55; H, 4.69; N, 3.25%. IR (CH2Cl2)
(vs); (CN) 1616 (m);
(COacyl) 1593 (m) cmꢀ1. 1H NMR (CDCl3)
(s, 1H, C2H); 5.00, 4.73, 4.43, 4.40 (m, 4H, C3C5H4); 4.53, 4.10 (s, 10H,
Cp); 3.65, 3.47 (s, 6H, NMe). 13C{1H} NMR (CDCl3)
270.1 (COacyl);
n
(CO) 1910
n
n
d
7.50
d
258.9 (C1); 222.7 (CO); 172.9 (C3); 141.4 (C2); 85.4 (Cp); 75.0, 71.5,
71.0, 70.7, 68.9 (C3C5H4); 70.2 (CpFc); 51.7, 43.0 (NMe) ppm.
Compound 4b was prepared with the same procedure described
for 4a, by reacting 2b with NaH. Crystals suitable for X-ray
diffraction were obtained from a CH2Cl2 solution, layered with
hexane, at ꢀ20 ꢁC.
Acknowledgement
Compound 4b (yield: 72%). Anal. Calcd. for C29H27Fe2NO2: C,
65.32; H, 5.10; N, 2.63. Found: C, 65.38; H, 5.14; N, 2.63%. IR (CH2Cl2)
We thank the Ministero dell’Università e della Ricerca Scientifica
e Tecnologica (M.I.U.R.) (project: ‘New strategies for the control of
reactions: interactions of molecular fragments with metallic sites in
unconventional species’) and the University of Bologna for financial
support.
n
(CO) 1914 (vs);
(CDCl3)
7.29e7.16 (m, 3H, Me2C6H3); 6.74 (s, 1H, C2H); 4.95, 4.40,
4.36, 4.30 (m, 4H, C3C5H4); 4.67, 4.02 (s, 10H, Cp); 3.77 (s, 3H, NMe);
n(CN) 1625 (m); n
(COacyl) 1596 (m) cmꢀ1. 1H NMR
d
2.21, 2.17 (s, 6H, Me2C6H3). 13C{1H} NMR (CDCl3)
d 268.7 (COacyl);
262.2 (C1); 222.1 (CO); 173.0 (C3); 143.1 (C2); 145.7, 132.9, 132.7
129.4, 129.1, 128.8 (Me2C6H3); 85.3 (Cp); 74.6, 71.6, 71.0, 70.9, 68.7
(C3C5H4); 70.2 (CpFc); 48.7 (NMe); 17.9, 17.7 (Me2C6H3).
Appendix. Supplementary material
CCDC 782189, 782188 and 782190 for contain the supplemen-
tary crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
4.5. Electrochemical measurements
Electrochemical data for 2a,b, 3a,b and 4a,b were obtained from
10ꢀ3 M solutions in CH2Cl2 with [Bu4N][PF6] 0.1 M (E1/2 in mV,
References
referenced to the SCE, at a scan speed
553; 3a, 529; 3b, 534, 4a, 511; 4b, 507 mV.
y
¼ 100 mV sꢀ1): 2a, 560; 2b,
[1] (a) E. Negishi, Bull. Chem. Soc. Jpn. 80 (2007) 233e257;
(b) K. Tamao, Top. Curr. Chem. 219 (2002) 1e9;
(c) A. de Meijere, F. Diederich (Eds.), Metal-Catalyzed Cross Coupling Reac-
tions, second ed. Wiley-VCH, Weinheim, Germany, 2004;
(d) A. de Meijere, H. Hopf, Chem. Rev. 106 (2006) 4785e4786.
[2] (a) V. Ritleng, M.J. Chetcuti, Chem. Rev. 107 (2007) 797e858;
(b) M. Cowie, Can. J. Chem. 83 (2005) 1043e1055;
4.6. X-ray crystallography for 2b, 3b$CH2Cl2 and 4b
Crystal data and collection details for are reported in Table 3. The
diffraction experiments were carried out on a Bruker APEX II
diffractometerequipped with a CCD detector using Mo-K
(c) S.A.R. Knox, J. Organomet. Chem. 400 (1990) 255e272;
(d) P. Braunstein, J. Rosè, in: P. Braunstein, L.A. Oro, P.R. Raithby (Eds.), Metal
Cluster in Chemistry, Wiley-VCH, Weinheim, 1999;
a radiation.
Data were corrected for Lorentz polarization and absorption effects

L. Busetto et al. / Journal of Organometallic Chemistry 695 (2010) 2519e2525
2525
R.A. Adams, F.A. Cotton (Eds.), Catalysis by Di- and Polynuclear Metal Cluster
Complexes, Wiley-VCH, New York, 1998.
[10] (a) V.G. Albano, L. Busetto, F. Marchetti, M. Monari, S. Zacchini, V. Zanotti,
Organometallics 23 (2004) 3348e3354;
[3] L. Busetto, P. Maitlis, V. Zanotti, Coord. Chem. Rev. 254 (2010) 470e486 and
references therein.
(b) V.G. Albano, L. Busetto, F. Marchetti, M. Monari, S. Zacchini, V. Zanotti,
J. Organomet. Chem. 690 (2005) 837e846.
[4] V.G. Albano, L. Busetto, F. Marchetti, M. Monari, S. Zacchini, V. Zanotti,
Organometallics 22 (2003) 1326e1331.
[11] L. Busetto, F. Marchetti, S. Zacchini, V. Zanotti, Organometallics 24 (2005)
2297e2306.
[5] (a) A. Erkkilä, I. Majander, P.M. Pihko, Chem. Rev. 107 (2007) 5416e5470;
(b) S. Mukherjee, J.W. Yang, S. Hoffmann, B. List, Chem. Rev. 107 (2007)
5471e5569;
[12] L. Busetto, F. Marchetti, S. Zacchini, V. Zanotti, Organometallics 25 (2006)
4808e4816.
[13] L. Busetto, F. Marchetti, S. Zacchini, V. Zanotti, Organometallics 26 (2007)
3577e3584.
(c) B. List, Acc. Chem. Res. 37 (2004) 548e557;
(d) B. List, R.A. Lerner, C.F. Barbas III, J. Am. Chem. Soc. 122 (2000) 2395e2396.
[6] Selected reviews include: (a) B. Simmons, A.M. Walji, D.W.C. MacMillan,
Angew. Chem., Int. Ed. 48 (2009) 4349e4353;
[14] L. Busetto, F. Marchetti, R. Mazzoni, M. Salmi, S. Zacchini, V. Zanotti, J. Orga-
nomet. Chem. 693 (2008) 3191e3196.
[15] For a comprehensive overview of ferrocene see: (a) A. Togni, T. Hayashi (Eds.),
Ferrocenes: Homogeneous Catalysis e Organic Synthesis e Materials Science,
Wiley-VCH, Weinheim, 1995;
(b) D. Enders, C. Grondal, M.R.M. Hüttl, Angew. Chem., Int. Ed. 46 (2007)
1570e1581;
(c) P. Melchiorre, M. Marigo, A. Carlone, G. Bartoli, Angew. Chem., Int. Ed.
47 (2008) 6138e6171;
(d) B. List, Chem. Commun. 8 (2006) 819e824.
(b) A. Togni, R.L. Halterman (Eds.), Metallocenes, Wiley-VCH, Weinheim, 1998;
(c) P. Stepnicka (Ed.), Ferrocenes; Ligands Materials and Biomolecules, John
Wiley & Sons, West Sussex, 2008.
ꢁ
ꢁ
ꢁ
[7] See for example: (a) L. Busetto, F. Marchetti, S. Zacchini, V. Zanotti, Eur. J.
Inorg. Chem. (2007) 1799e1807;
(b) L. Busetto, F. Marchetti, S. Zacchini, V. Zanotti, Organometallics 27 (2008)
5058e5066.
[8] (a) B. Plietker (Ed.), Iron Catalysis in Organic Chemistry, Wiley-VCH, Weinheim,
2008;
[16] (a) A.H. Stoll, P. Mayer, P. Knochel, Organometallics 26 (2007) 6694e6697;
(b) Y. Wang, W. Weissensteiner, F. Spindler, V.B. Arion, K. Mereiter,
Organometallics 26 (2007) 3530e3540;
(c) P. Christophe, B. Odell, J.M. Brown, Chem. Commun. (2004) 598e599;
(d) M. Steurer, K. Tiedl, Y. Wang, W. Weissensteiner, Chem. Commun. (2005)
4929e4931;
(b) S. Enthaler, K. Junge, M. Beller, Angew. Chem., Int. Ed. 47 (2008) 3317e3321;
(c) A. Correa, O.G. Mancheño, C. Bolm, Chem. Soc. Rev. 37 (2008) 1108e1117;
(d) B.D. Sherry, A. Fürstner, Acc. Chem. Res. 41 (2008) 1500e1511;
(e) R.M. Bullock, Angew. Chem., Int. Ed. 46 (2007) 7360e7363.
[9] See for example: (a) D.-H. Wu, C.-H. Wu, Y.-Z. Li, D.-D. Guo, X.-M. Wang,
H. Yan, Dalton Trans. (2009) 285e290;
(e) D.C.D. Butler, C.J. Richards, Organometallics 21 (2002) 5433e5436;
(f) D. van Leusen, B. Hessen, Organometallics 20 (2001) 224e226;
(g) C. Metallinos, J. Zaifman, L. Dodge, Org. Lett. 10 (2008) 3527e3530.
[17] H. Fink, N.J. Long, A.J. Martin, G. Opromolla, A.J.P. White, D.J. Williams,
P. Zanello, Organometallics 16 (1997) 2646e2650.
[18] W. Wilker, D. Leibfritz, R. Kerssebaum, W. Beimel, Magn. Reson. Chem. 31
(1993) 287e292.
[19] K. Stott, J. Stonehouse, J. Keeler, T.L. Hwang, A.J. Shaka, J. Am. Chem. Soc. 117
(1995) 4199e4200.
[20] G. Cox, C. Dowling, A.R. Manning, P. McArdle, D. Cunningham, J. Organomet.
Chem. 438 (1992) 143e158.
[21] G.M. Sheldrick, Sadabs, Program for Empirical Absorption Correction.
University of Göttingen, Germany, 1996.
(b) A. Albinati, F. Fabrizi de Biani, P. Leoni, L. Marchetti, M. Pasquali, S. Rizzato,
P. Zanello, Angew. Chem., Int. Ed. 44 (2005) 5701e5705;
(c) W.-Y. Wong, K.-Y. Ho, K.-H. Choi, J. Organomet. Chem. 670 (2003) 17e26;
(d) U. Siemeling, J. Vorder BrKggen, U. Vorfeld, B. Neumann, A. Stammler,
H.-G. Stammler, A. Brockhinke, R. Plessow, P. Zanello, F. Laschi, F. Fabrizi de
Biani, M. Fontani, S. Steenken, M. Stapper, G. Gurzadyan, Chem.dEur. J 9
(2003) 2819e2833;
(e) C. Lebreton, D. Touchard, L. Le Pichon, A. Daridor, L. Toupet, P.H. Dixneuf,
Inorg. Chim. Acta 272 (1998) 188e196.
[22] G.M. Sheldrick, SHELX97, Program for Crystal Structure Determination.
University of Göttingen, Germany, 1997.