Construction of a Functionalized Selenophene-Allylidene Ligand via Alkyne Double Action at a Diiron Complex

Article abstract of DOI:10.1002/ejic.202000371

The diiron μ-vinyliminium compounds [Fe₂Cp₂(CO)(μ-CO){μ-η¹:η³-C³HC²HC¹NMe(R)}]CF₃SO₃ (R = Me, 2a; R = Xyl = 2,6-C₆H₃Me₂, 2b; Cp = η⁵-C₅H₅) reacted with grey selenium, in the presence of sodium methoxide, to give the corresponding Se-functionalized derivatives [Fe₂Cp₂(CO)(μ-CO){μ-η¹:η³-C³HC²(Se)C¹NMe(R)}], 3a–b, in ca. 50 % yields. The monoiron zwitterionic complex [FeCp(CO){SeC¹(NMe₂)C²HC³H}], 4, was obtained as a side-product (31 %) of the reaction leading to 3a. The treatment of 3b with S₈/NaOMe afforded the 2-ferra-thiophene [FeCp(CO){SC³HC²HC¹NMe(Xyl)}], 5, in 49 % yield. The straightforward reactions of 3a with a two-fold excess of dialkylacetylenedicarboxylates led to functionalized 3-amino-selenophenes appended to the diiron frame through a bridging allylidene ligand, [Fe₂Cp₂(CO)(μ-CO){μ-η¹:η³-C⁷(CO₂R)C⁶(CO₂R)C³HC²SeC⁵(CO₂R)C⁴(CO₂R)C¹(NMe₂)}] (R = Me, 6a; R = Et, 6b; R = tBu, 6c), in approximately 50 % yields. The synthesis of 6a–c is the result of two distinct modes of reactivity exhibited by the alkyne reactant in one pot, i.e. 1,3-dipolar cycloaddition to C and Se atoms and insertion into Fe-μ-alkylidene. All the products were characterized by means of elemental analysis, IR and multinuclear NMR spectroscopy, and the molecular structure of 6a was elucidated by a single-crystal X-ray diffraction study.

Full text of DOI:10.1002/ejic.202000371

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Diiron Alkyne Complexes
Construction of a Functionalized Selenophene-Allylidene Ligand
via Alkyne Double Action at a Diiron Complex
Alice De Palo,[a] Stefano Zacchini,[b] Guido Pampaloni,[a] and Fabio Marchetti*[a]
Abstract: The
diiron
μ-vinyliminium
compounds selenophenes appended to the diiron frame through a bridging
ligand,
[Fe2Cp2(CO)(μ-CO){μ-η1:η3-C7(CO2R)-
[Fe2Cp2(CO)(μ-CO){μ-η1:η3-C3HC2HC1NMe(R)}]CF3SO3 (R = Me, allylidene
2a; R = Xyl = 2,6-C6H3Me2, 2b; Cp = η5-C5H5) reacted with grey C6(CO2R)C3HC2SeC5(CO2R)C4(CO2R)C1(NMe2)}] (R = Me, 6a; R =
selenium, in the presence of sodium methoxide, to give the Et, 6b; R = tBu, 6c), in approximately 50 % yields. The synthesis
corresponding Se-functionalized derivatives [Fe2Cp2(CO)(μ- of 6a–c is the result of two distinct modes of reactivity exhib-
CO){μ-η1:η3-C3HC2(Se)C1NMe(R)}], 3a–b, in ca. 50 % yields. The ited by the alkyne reactant in one pot, i.e. 1,3-dipolar cycloaddi-
monoiron zwitterionic complex [FeCp(CO){SeC1(NMe2)C2HC3H}], tion to C and Se atoms and insertion into Fe-μ-alkylidene. All
4, was obtained as a side-product (31 %) of the reaction leading the products were characterized by means of elemental analy-
to 3a. The treatment of 3b with S8/NaOMe afforded the 2-ferra- sis, IR and multinuclear NMR spectroscopy, and the molecular
thiophene [FeCp(CO){SC3HC2HC1NMe(Xyl)}], 5, in 49 % yield. structure of 6a was elucidated by a single-crystal X-ray diffrac-
The straightforward reactions of 3a with a two-fold excess of tion study.
dialkylacetylenedicarboxylates led to functionalized 3-amino-
Introduction
The insertion of (electron-poor) alkynes into metal-μ-alkyl-
idene bonds aroused attention due to its relevance to the C–C
chain growth in the Fischer–Tropsch process,[17] and has been
documented with complexes based on the [M2Cp2(CO)2] skele-
ton (M = Fe, Ru),[18] and Rh–Ru,[19] Rh–Os[20] and Ir–Os sys-
tems.[21] In general, a vacant metal site is necessary to allow
alkyne entrance through preliminary η2-coordination; both
chemical and photolytic methods may be employed to this pur-
pose,[19,20] except in the rare case that cleavage of the metal–
metal linkage is feasible.[21]
Alkynes are versatile reagents in a multitude of valuable organic
transformations,[1] some of them being established even on an
industrial scale, such as the Dötz reaction,[2] the alkyne meta-
thesis[3] and the alkyne cyclotrimerization.[4] Alkynes are prone
to cyclization reactions, and in particular 1,3-dipolar cycloaddi-
tions to various substrates provide straightforward access to a
range of heterocyclic structures with possible pharmaceutical
applications.[5] The insertion of an alkyne molecule into a metal-
carbon bond represents the key step of useful metal-catalysed
syntheses,[6] and is a viable procedure to grow organometallic
fragments. This kind of reaction has been described with refer-
ence to a variety of monometal species and ligands, including
alkyls,[7] aryls,[8] vinyls,[9] and alkylidenes.[10] Two adjacent metal
centres are able to provide cooperative effects in reactivity, thus
favouring the insertion of alkynes into the bond between one
metal and a suitable bridging ligand;[11] in this regard, a wide
number of reactions have been reported involving, inter alia,
bridging carbonyl,[12] thiocarbonyl,[13] isocyanide,[14] carbyne,[15]
and carbido units.[16]
The interest of some of us in the construction of functional-
ized organometallic structures, since almost 20 years ago, has
been focused on diiron complexes,[11c,22] which constitute a
matter of growing interest for several reasons. First, the dinu-
clear system offers the opportunity for reactivity patterns which
are not available to similar monoiron species, as also mentioned
above. In addition, iron as element is substantially nontoxic and
earth abundant, and thus an appealing candidate to develop
new sustainable metal-directed synthetic routes and metal
complexes for medicinal applications.[23]
In the course of our research, we previously described the
sequential assembly of small molecular units to afford diiron
complexes with a bridging-coordinated Se-functionalized li-
gand (A); this latter is firmly anchored to the [Fe–Fe] frame
through a C3 chain featured by an extensive charge delocaliza-
tion and described by means of three main resonance forms
(see Scheme 1).[24] However, the C3 carbon clearly manifests
alkylidene character, according to X-ray (equidistance between
[a] Dr. A. De Palo, Prof. Dr. G. Pampaloni, Prof. Dr. F. Marchetti
Dipartimento di Chimica e Chimica Industriale, Università di Pisa,
Via G. Moruzzi 13, 56124 Pisa, Italy
E-mail: fabio.marchetti1974@unipi.it
http://people.unipi.it/fabio_marchetti1974/
[b] Prof. Dr. S. Zacchini
Dipartimento di Chimica Industriale “Toso Montanari”,
Università di Bologna,
Viale Risorgimento 4, 40136 Bologna, Italy
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.202000371.
the two iron atoms, as determined for R = Xyl, R′ = Me) and 13
C
NMR (typical low-field resonance in the range 180–200 ppm)
data. Compounds of type A exhibit a rich chemistry which is
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Scheme 1. Resonance forms representing a bridging Se-derivatized C3 ligand (A-I: allylidene; A-II: vinyliminium; A-III: bis-alkylidene), and alkyne cycloaddition
to form a μ-alkylidene-selenophene derivative (BMe).[26] R = Me or Xyl = 2,6-C6H3Me2; R′ = alkyl, aryl or CO2Me.
essentially related to the zwitterionic nature of the bridging analysis, IR and 1H NMR spectroscopy only. The IR spectra of
ligand.[24b,25] In particular, a peculiar combination of substitu- 3a–b in dichloromethane exhibit two bands due to the carb-
ents enables 1,3-dipolar cycloaddition by dimethylacetylenedi- onyl ligands at ca. 1970 and 1790 cm–1, and an additional ab-
carboxylate, leading to the selenophene-substituted μ-alkyl-
idene species BMe (Scheme 1);[26] note that the use of a large
excess (up to 10 equiv.) of alkyne does not modify this out-
come. In the framework of our recent interest in the develop-
ment of diiron complexes with bridging C3 ligands as potential
anticancer drugs[27] and on account of the relevance of the se-
lenophene moiety in medicinal chemistry,[28] we came inter-
ested in preparing some new simple selenophene derivatives
analogous to BMe for biological studies. Surprisingly, we ob-
served that the Me/H replacement (R′) resulted in a dramatic
change of the reactivity of compounds A with dialkylacetylene-
dicarboxylates, activating at the same time two distinct reactiv-
ity pathways and thus providing access to a novel class of
highly functionalized hydrocarbyl ligands.
sorption accounting for the substantial double bond nature of
C1–N (e.g. at 1603 cm–1 in the case of 3b). The NMR spectra of
3a–b (in CDCl3) display diagnostic low field resonances due to
the alkylidene {C3H} unit [e.g. in the case of 3b: δ(1H) =
1
12.42 ppm, δ(13C) = 186.7 ppm]. The H NMR characterization
of 3a was complicated by the instability of this compound, and
broad signals were recognized in this case. Of the two possible
isomeric forms expected for 3b (E and Z, with reference to the
possible orientations of the two different N-substituents), only
the Z isomer exists in CDCl3 solution.[24b,25] The selenium centre
in 3b manifests itself with a 77Se signal falling at 241.8 ppm.
The reaction leading to 3a is not selective, since a small amount
of the monoiron complex 4 was produced, which was recov-
ered in 31 % yield after work-up. Complex 4, maintaining the
C2–H unit, might be viewed as the result of selenium incorpora-
tion along a fragmentation process initiated by electron transfer
to 2a.[30] Compound 4 was identified on the basis of a compari-
son of its IR and NMR features with those of the strictly analo-
gous species [FeCp(CO){SeC1(NMe2)C2HC3(Me)}], crystallograph-
ically characterized and recently published.[24b] In 4, the imin-
ium character of the C1=N bond is evidenced by the inequiva-
Results and Discussion
The previously reported diiron vinyliminium compounds 2a–b
were prepared from the respective μ-aminocarbyne precursors,
1a–b, via removal of one carbonyl ligand and subsequent acet-
ylene insertion into iron–carbyne bond, using an optimized pro-
cedure (see Scheme 2 and Experimental for details). The reac-
tion of 2a–b with an excess of sodium methoxide, in tetra-
hydrofuran in the presence of grey selenium, proceeded with
dehydrogenative selanylation affording the new selenium-func-
tionalized complexes 3a–b,[24b,25] in approximately 50 % yields
(Scheme 2). The methoxide presumably plays the role of a re-
ducing agent towards 2a–b, thus generating neutral radical de-
rivatives undergoing H/Se exchange.[29]
1
lence of the methyl substituents in the H NMR spectrum (3.64
and 3.33 ppm, CDCl3 solution). The C3 carbon exhibits some
alkylidene nature [δ(13C) = 174.1 ppm], while the {C2H} unit is
substantially alkenic [δ(1H) = 7.43 ppm, δ(13C) = 137.5 ppm].
The selenium atom resonates at 210.1 ppm. Although the struc-
ture of 4 may be well described as a zwitterionic 2-ferra-5-imin-
ium-selenophene (Scheme 2) in analogy to the crystallographic
data of [FeCp(CO){SeC1(NMe2)C2HC3(Me)}], some delocalization
is present within the five-membered cycle and contributions
from alternative resonance forms should be envisaged.
Compound 3b was isolated after alumina chromatography
as a stable solid under N2 atmosphere, and fully characterized;
conversely, 3a revealed rather unstable especially in solution for
Reactions analogous to those yielding 3a–b but employing
prolonged times, hence its characterization relied on elemental elemental sulfur did not afford diiron derivatives
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Scheme 2. Synthesis of di- and monoiron complexes via reactions of diiron vinyliminium compounds, 2a–b, with elemental chalcogens and sodium methoxide
(R = Me or Xyl = 2,6-C6H3Me2).
(Scheme 2).[24a] More precisely, a complicated mixture of prod-
ucts was recovered from 3a, while the reaction involving 2b
resulted in the prevalent formation of 5. Compound 5, belong-
ing to a family of strictly similar compounds which was de-
scribed previously,[24a,31] was isolated in 49 % yield and unam-
biguously identified by means of a comparative analysis of
spectroscopic data. The IR spectrum in CH2Cl2 consists of an
intense band at 1935 cm–1. The NMR spectra show a single set
of resonances, ascribable to the E configuration of substituents
at the iminium moiety. The C1 carbon resonates at 253.0 ppm,
thus revealing its aminocarbene identity.[32] Typical low field
resonances feature also the C2 and C3 carbons (132.8 and
182.6 ppm, respectively).[24a]
Similarly to what discussed for 4 and based on the X-ray
characterization of [FeCp(CO){SC3(Me)C2HC1NMe(Xyl)}], the
Scheme 3. Synthesis of functionalized selenophene-allylidene diiron com-
plexes, via alkyne 1,3-dipolar annulation (i) and alkyne insertion into Fe-μ-
alkylidene bond (ii).
most representative structure of 5 is a 2-ferra-3-amino-thio-
phene (Scheme 2), although contributions from other reso-
nance forms are not totally negligible.[24a]
The treatment of a CH2Cl2 solution of 3a with a two-fold
molar excess of dialkylacetylenedicarboxylates led to the forma-
tion of complexes 6a–c, containing an unprecedented bridging
selenophene-modified allylidene ligand (Scheme 3). Com-
pounds 6a–c were isolated in ca. 50 % yields after purification
by alumina chromatography.
The structure of 6a was ascertained by single-crystal X-ray
diffraction (Figure 1, Table 1). It consists of a cis-[Fe2Cp2(CO)(μ-
CO)] core, to which is (μ-η1:η3)-coordinated an allylidene ligand
functionalized with a very rare example of multi-substituted 3-
amino-selenophene.[33,34]
It should be noted that allylidene ligands bridging two metal
centres in a μ-η1:η3 fashion are not uncommon in organometal-
lic chemistry,[35] being previously described also in analogous
complexes based on the [M2Cp2(CO)(μ-CO)] scaffold (M = Fe[36]
Figure 1. Molecular structure of 6a. Displacement ellipsoids are at the 30 %
probability level. H-atoms, except H(3), have been omitted for clarity.
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Table 1. Selected bond lengths [Å] and angles [°] for 6a.
The synthesis of 6a–c might be viewed as the result of a two-
step sequence, presumably comprising fast 1,3-dipolar alkyne
cycloaddition to the Se and C1 atoms of 3a, affording the inter-
mediate selenophene-alkylidene species BH, followed by slower
alkyne insertion into the Fe-μ-alkylidene bond (Scheme 3, steps
i and ii). As a matter of fact, the cycloaddition of C2(CO2Me)2 to
A affording BMe (compare Scheme 1 and Scheme 3) and analo-
gous reactions are almost instantaneous.[26] In contrast to the
literature, the alkyne insertion step does not require any chemi-
cal/photolytic process to generate a vacant site at one metal
centre; instead, the hemilabile nature of the bridging ligand in
BH is presumably responsible for the initial η2-coordination of
the alkyne moiety, which is expected to precede the inser-
tion.[15c] Consistently, it was found that the iron coordination of
the amino pendant group in BMe can be easily replaced by an
isocyanide molecule under mild conditions.[26]
Fe(1)–Fe(2)
2.5302(10)
1.981(5)
1.948(5)
2.035(5)
1.154(6)
1.438(7)
1.448(6)
1.434(6)
1.878(5)
1.419(6)
175.4(4)
80.58(17)
119.2(4)
122.2(4)
114.3(4)
111.2(4)
127.1(3)
Fe(1)–C(11)
Fe(2)–C(12)
Fe(2)–C(7)
Fe(2)–C(3)
C(12)–O(2)
C(6)–C(3)
1.750(6)
1.902(5)
1.965(5)
2.061(5)
1.171(6)
1.438(6)
1.385(6)
1.358(7)
1.864(4)
Fe(1)–C(12)
Fe(1)–C(7)
Fe(2)–C(6)
C(11)–O(1)
C(7)–C(6)
C(3)–C(2)
C(2)–C(1)
C(1)–C(4)
C(4)–C(5)
Se(1)–C(2)
Se(1)–C(5)
C(1)–N(1)
Fe(1)–C(11)–O(1)
Fe(1)–C(7)–Fe(2)
C(7)–C(6)–C(3)
C(3)–C(2)–C(1)
C(2)–C(1)–C(4)
C(4)–C(5)–Se(1)
C(3)–C(2)–Se(1)
Fe(1)–C(12)–Fe(2)
Fe(1)–C(7)–C(6)
C(6)–C(3)–C(2)
Se(1)–C(2)–C(1)
C(1)–C(4)–C(5)
C(2)–Se(1)–C(5)
Sum at N(1)
81.31(19)
124.5(3)
127.7(4)
110.5(3)
115.9(4)
88.0(2)
346.5(7)
Note that the outcomes of the reactions shown in Scheme 1
and Scheme 3 are strictly related to the bulkiness at the C3 and
N atoms. More precisely, the alkyne insertion is feasible with
the {C3H} alkylidene unit (Scheme 3), but precluded in the pres-
ence of a R′ substituent (Scheme 1, R′ = Me, CO2Me, aryl).[24a]
Similarly, the alkyne annulation forming the selenophene ring
is not possible when nitrogen is substituted with the xylyl moi-
ety, as previously demonstrated.[24a] Accordingly, 3b was almost
unreactive towards dimethylacetylenedicarboxylate in CH2Cl2
solution, and only minor decomposition was detected after 18
hours by IR spectroscopy; also, this evidence corroborates the
idea that the alkyne insertion must follow the formation of an
intermediate selenophene-alkylidene ligand (structure BH in
Scheme 3).
or Ru[37]). However, such ligands typically consist of a hydro-
carbyl C3 chain, bearing only a limited degree of functionaliza-
tion in some cases.[36] In 6a, Fe(1) is σ-coordinated to C(7)
[Fe(1)–C(7) 1.948(5) Å], whereas Fe(2) is coordinated to all three
carbon atoms constituting the η3-allylidene unit, i.e. C(3), C(6)
and C(7). In agreement with this, C(6)–C(7) [1.438(7) Å] and
C(6)–C(3) [1.438(6) Å] distances are almost identical and mani-
fest some π-character. Nonetheless, Fe(2)–C(7) [1.965(5) Å] is
slightly shorter than Fe(2)–C(6) [2.035(5) Å] and Fe(2)–C(3)
[2.061(5) Å], suggesting also a vinylalkylidene character of the
C3–C6–C7 moiety. The μ-CO ligand shows a considerable asym-
metry [Fe(1)–C(12) 1.981(5) Å, Fe(2)–C(12) 1.902(5) Å], as a con-
sequence of the more π-acidic terminal CO ligand on Fe(1) with
respect to the η3-allylidene ligand on Fe(2). The selenophene
ring is perfectly planar [mean deviation from the Se(1)–C(2)–
C(1)–C(4)–C(5) least-squares plane 0.0159 Å] and the bonding
parameters are comparable to those available for analogous
hetero-cyclic systems.[26,34] The C(1)–N(1) distance [1.419(6) Å]
is typical for a C(sp2)–N single bond,[38] as also suggested by
the sum of the angles at N(1) [346.5(7)°], which indicates a sp3
rather than sp2 hybridization of nitrogen.
Conclusions
The versatile {Fe2Cp2(CO)2} skeleton is a convenient tool to as-
semble small organic/inorganic fragments up to the building
of unusual molecular architectures, possibly not available from
monometal species or conventional organic synthesis.[11c,41]
Herein, we have described that the reaction of a pre-
The IR spectra of 6a–c, in dichloromethane, share a common constructed bridging hydrocarbyl ligand derivatized with a
pattern consisting of five absorptions, accounting for the termi- selenido function undergoes addition of two alkyne molecules
nal and bridging carbonyls, the carboxylato groups and an producing an expansion of the carbonic chain from C3 to C7.
alkenic function (e.g. for 6a at 1966, 1799, 1730, 1707 and The resulting selenophene-functionalized μ-allylidene species is
1
1584 cm–1, respectively). The H and 13C NMR spectra of 6a–c unprecedented in organometallic chemistry and might be alter-
(in CDCl3) are in perfect accordance with the X-ray structure of natively viewed as a rare example of multi-functionalized 3-
6a. They display a single resonance for the amino-group, indi- amino-selenophene ring, which is also connected to the diiron
1
cating free rotation around the C1–N bond. The H resonance core. Two key features should be remarked, being quite uncom-
of the C3-bound hydrogen is upfield shifted (e.g. at 0.53 ppm mon in the landscape of organometallic chemistry: 1) the alk-
in the case of 6a), in agreement with what previously recog- yne reactant plays two distinct roles at two different, non-con-
nized for (μ-η1:η3)-allylidene/vinylalkylidene ligands in analo- tiguous sites of the starting molecule, assisted by the coopera-
gous diiron and diruthenium complexes.[18d,39] The alkylidene tive effects provided by the bimetallic system; 2) the alkyne
nature of the C7 carbon is reflected by a diagnostic low field insertion into the Fe-μ-alkylidene bond occurs smoothly due to
resonance (e.g. at 173.8 ppm for 6a), while the carbon atoms the hemilabile character of the reacting ligand, weakly binding
belonging to the selenophene ring give raise to four signals one iron centre through a pendant amino group. Conversely,
in the 127–156 ppm range. The 77Se NMR spectra contains a alkyne insertion reactions into metal-bridging alkylidenes in
resonance at ca. 560 ppm; for sake of comparison, the selenium poly-metal systems are generally triggered by a photochemical/
atom in unsubstituted selenophene occurs at 613 ppm (CDCl3 chemical stimulus, generating a vacant metal site which is re-
solution).[40]
quired for alkyne entrance.
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(μ-CO); 226.8 (C1); 210.2 (CO); 184.8 (C3); 89.9, 87.1 (Cp); 52.4 (C2);
50.9, 44.8 (NMe2).
Experimental Section
[Fe2Cp2(CO)(μ-CO){μ-η1:η3-C3HC2HC1NMe(Xyl)}]CF3SO3, 2b (Fig-
1. Synthesis and Characterization of Compounds
ure 3)[48]
General Details: Unless otherwise specified, operations were car-
ried out under N2 atmosphere using standard Schlenk techniques,
and isolated products were stored under N2. Solvents were pur-
chased from Merck and distilled before use under N2 from appropri-
ate drying agents. Organic reactants (TCI Europe or Merck) were
commercial products of the highest purity available. Compounds
1a–b were prepared according to a published procedure.[42] Chro-
matographic separations were carried out on columns of deacti-
vated alumina (Merck, 4 % w/w water). Infrared spectra of solutions
were recorded on a Perkin Elmer Spectrum 100 FT-IR spectrometer
with a CaF2 liquid transmission cell (2300–1500 cm–1 range), and
then processed with Spectragryph software.[43] NMR spectra were
recorded at 298 K on a Bruker Avance II DRX400 instrument
equipped with a BBFO broadband probe. Chemical shifts (expressed
in parts per million) are referenced to the residual solvent peaks
Figure 3. Structure of the cation of 2b.
The title compound was prepared by using a procedure analogous
to that described for 2a, from 1b (2.00 g, 3.22 mmol) and acetylene,
and stored in air. Brown solid, yield 0.997 g (50 %). Anal. calcd. for
1
(1H, 13C),[44] or to external standard (77Se, SeMe2). H and 13C NMR
C
25H24F3Fe2NO5S: C, 48.49; H, 3.91; N, 2.26; S, 5.18; found C, 48.22;
H, 3.97; N, 2.33; S, 5.09. IR (CH2Cl2): ν /cm–1 = 2005vs. (CO), 1820s
1
spectra were assigned with the assistance of H-13C (gs-HSQC and
˜
(μ-CO), 1628m (C2C1N). H NMR (CDCl3): δ/ppm = 12.73, 12.57 (d, 1
1
gs-HMBC) correlation experiments.[45] NMR signals due to a second
isomeric form (where it has been possible to detect them) are itali-
cized. Elemental analyses were performed on a Vario MICRO cube
instrument (Elementar).
H, JHH = 7.1 Hz, C3H); 7.44–6.92 (m, 3 H, C6H3); 5.49, 4.59 (d, 1 H,
3
3JHH = 7.1 Hz, C2H); 5.43, 5.36, 4.74, 5.16 (s, 10 H, Cp); 4.15, 3.50
(NMe); 2.51, 2.28, 1.71, 1.93 (C6H3Me2). E/Z ratio = 1.2. 13C{1H} NMR
(CDCl3): δ/ppm = 253.3, 253.2 (μ-CO); 233.9, 232.1 (C1); 209.7, 208.9
(CO); 189.1, 188.0 (C3); 144.7, 141.2 (ipso-C6H3); 133.6–129.0 (C6H3);
90.1, 89.9, 87.0, 86.5 (Cp); 53.2, 52.2 (C2); 52.1, 46.1 (NMe); 17.9, 17.7,
17.5, 16.9 (C6H3Me2).
[Fe2Cp2(CO)(μ-CO){μ-η1:η3-C3HC2HC1NMe2}]CF3SO3, 2a (Fig-
ure 2)[46]
Synthesis of [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C3HC2(Se)C1NMe2}], 3a
(Figure 4)
Figure 2. Structure of the cation of 2a.
Compound 1a (2.00 g, 3.77 mmol) was dissolved into acetonitrile
(30 mL) and treated with Me3NO (365 mg, 4.86 mmol) in air. The
resulting mixture was stirred for 2 hours, and progressive darkening
of the solution was observed. The complete conversion of the start-
ing material into the acetonitrile adduct [Fe2Cp2(CO)(μ-CO)-
(NCMe){μ-CNMe2}]CF3SO3 was checked by IR spectroscopy.[47] The
volatiles were eliminated under reduced pressure, hence the dark
brown residue was dissolved into dichloromethane (ca. 40 mL). A
large excess of acetylene, separately produced by dropwise and
careful water addition to calcium carbide, was bubbled into the
solution for two minutes. The resulting mixture was stirred at room
temperature for 72 hours. The final solution was charged on an
alumina column. Elution with CH2Cl2/THF (1:1 v/v) allowed to sepa-
rate impurities, then a green-brown fraction was collected using
MeOH as eluent. The solvent was evaporated under reduced pres-
sure, then the residue was dissolved in CH2Cl2 and this dichloro-
methane solution was filtered through Celite to remove some NaCl
(alumina contaminant). The title product was precipitated upon ad-
dition of petroleum ether (ca. 50 mL) to the filtered solution (ca.
20 mL), dried under vacuum and finally stored in air. Yield 1.60 g,
80 %. Anal. calcd. for C18H18F3Fe2NO5S: C, 40.86; H, 3.43; N, 2.65; S,
Figure 4. Structure of 3a.
A stirred mixture of 2a (200 mg, 0.378 mmol) and grey Se (300 mg,
3.80 mmol) in THF (15 mL) was treated with sodium methoxide
(40 mg, 0.74 mmol). The resulting mixture was stirred for 2 hours,
until IR analysis evidenced the complete consumption of 2a. The
final mixture was filtered through a celite pad using dichloro-
methane as eluent. The solvent was removed under reduced pres-
sure from the filtered solution, the residue was repeatedly washed
with diethyl ether (4 × 30 mL) and then dried under vacuum. Green
solid, yield 92 mg, 53 %. Anal. calcd. for C17H17Fe2NO2Se: C, 44.58;
H, 3.74; N, 3.06; found C, 44.45; H, 3.82; N, 3.12. IR (CH2Cl2):
ν /cm–1 = 1969vs. (CO), 1790s (μ-CO), 1618m (C1N). 1H NMR (CDCl3):
˜
δ/ppm = 12.12 (s, 1 H, C3H); 4.95, 4.66 (s, 10 H, Cp); 3.75, 3.39 (s, 6
H, NMe2).
[Fe2Cp2(CO)(μ-CO){μ-η1:η3-C3HC2(Se)C1N(Me)(Xyl)}], 3b (Fig-
ure 5)
A stirred mixture of 2b (100 mg, 0.161 mmol) and grey Se (128 mg,
1.61 mmol) in THF (15 mL) was treated with sodium methoxide
(26 mg, 0.48 mmol). The resulting mixture was stirred for 1 hour,
6.06; found C, 40.78; H, 3.51; N, 2.62; S, 6.16. IR (CH Cl ): ν /cm–1
=
˜
2
2
1994vs. (CO), 1816s (μ-CO), 1676w (C2C1N). 1H NMR ([D6]acetone): until IR analysis evidenced the complete consumption of 2b. The
δ/ppm = 12.38 (br, 1 H, C3H); 5.52, 5.19 (s, 10 H, Cp); 5.03 (br, 1 H,
C2H); 3.92, 3.33 (NMe2). 13C{1H} NMR ([D6]acetone): δ/ppm = 256.0
final mixture was filtered through a celite pad using THF as eluent.
The solvent was removed from the filtered solution under reduced
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(26 mg, 0.484 mmol). The resulting mixture was stirred for 30 min-
utes, until IR analysis evidenced the complete consumption of 2b
and the appearance of an intense band at 1937 cm–1 (THF solution).
This mixture was filtered through a short alumina pad using THF as
eluent, then the volatiles were removed under vacuum from the
filtered solution. Subsequent alumina chromatography of the resi-
due led to isolate a red fraction, corresponding to 5, using heptane/
diethyl ether (2:1 v/v) as eluent. Compound 5 was isolated as an
air-stable, red solid upon removal of the solvent under vacuum.
Yield 28 mg (49 %). Anal. calcd. for C18H19FeNOS: C, 61.20; H, 5.42;
Figure 5. Structure of 3b.
pressure, the residue was dissolved in CH2Cl2 and this solution
charged on an alumina column. Elution with CH2Cl2 allowed to sep-
arate impurities, then a green fraction was collected using THF as
eluent. A green solid was isolated upon evaporation of the solvent
under vacuum. Yield 48 mg (54 %). Anal. calcd. for C24H23Fe2NO2Se:
C, 52.59; H, 4.23; N, 2.56; found C, 52.38; H, 4.18; N, 2.67. IR (CH2Cl2):
N, 3.96: S, 9.08; found C, 61.09; H, 5.51; N, 3.92; S, 9.23. IR (CH2Cl2):
3
ν /cm–1 = 1935vs. (CO). 1H NMR (CDCl3): δ/ppm = 8.11 (d, JHH
=
˜
5.6 Hz, 1 H, C3H); 7.18–7.09 (m, 3 H, C6H3); 6.03 (d, JHH = 5.6 Hz, 1
H, C2H); 4.72 (s, 5 H, Cp); 3.68 (s, 3 H, NMe); 2.25, 2.02 (s, 6 H,
C6H3Me2). 13C{1H} NMR (CDCl3): δ/ppm = 253.0 (C1); 217.9 (CO);
182.6 (C3); 132.8 (C2); 145.6, 133.4, 133.1, 129.3, 128.9; 127.9 (C6H3);
83.1 (Cp); 47.9 (NMe); 17.8, 17.8 (C6H3Me2).
3
ν /cm–1 = 1970vs. (CO), 1796s (μ-CO), 1603 (C1N), 1584w (arom C=
˜
1
C). H NMR (CDCl3): δ/ppm = 12.42 (s, 1 H, C3H); 7.29, 6.97 (m, 3 H,
Synthesis of [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C7(CO2Me)C6(CO2Me)-
C3HC2SeC5(CO2Me)C4(CO2Me)C1(NMe2)}], 6a (Figure 8)
C6H3); 5.03, 4.36 (s, 10 H, Cp); 3.59 (s, 3 H, NMe); 2.65, 2.03 (s, 6 H,
C6H3Me2). 13C{1H} NMR (CDCl3): δ/ppm = 262.3 (μ-CO); 234.5 (C1);
211.2 (CO); 186.7 (C3); 142.2 (ipso-C6H3); 135.5, 134.3, 129.3, 129.1,
128.9 (C6H3); 89.9, 88.5 (Cp); 89.7 (C2); 47.2 (NMe); 18.1 (C6H3Me2).
77Se NMR (CDCl3): δ/ppm = 241.8.
Synthesis and isolation of [FeCp(CO){SeC1(NMe2)C2HC3H}], 4
(Figure 6)
Figure 8. Structure of 6a.
Addition of dimethylacetylenedicarboxylate (0.12 mL, 0.98 mmol)
to a solution of 3a (150 mg, 0.328 mmol) in THF (15 mL) resulted
in fast colour change from green to red, and the resulting solution
was stirred for further 8 hours. Afterwards, the volatiles were elimi-
nated under reduced pressure, the residue was dissolved in diethyl
ether and this solution charged on an alumina column. The fraction
containing the title product was isolated using dichloromethane/
diethyl ether (1:1 v/v) as eluent. Removal of the solvent under vac-
uum afforded a red solid. Yield 150 mg (62 %). Anal. calcd. for
Figure 6. Structure of 4.
The title compound was obtained as a by-product of the reaction
leading to 3a. The diethyl ether solution collected from the wash-
ings (see above) was filtered through an alumina column (diethyl
ether as eluent). Thus, a red fraction was obtained, corresponding
to 4. Compound 4 was isolated as an air-stable, red solid upon
removal of the solvent under vacuum. Yield 64 mg (31 %). Anal.
calcd. for C11H13FeNOSe: C, 42.61; H, 4.23; N, 4.52; found C, 42.52;
C
29H29Fe2NO10Se: C, 46.93; H, 3.94; N, 1.89; found C, 46.83; H, 4.00;
N, 1.92. IR (CH Cl ): ν /cm–1 = 1966vs. (CO), 1799s (μ-CO), 1730vs.
˜
2
2
1
(OC=O), 1707vs-sh (OC=O), 1584w (C=C). H NMR (CDCl3): δ/ppm =
4.80, 4.62 (s, 10 H, Cp); 4.05, 3.95, 3.82, 3.81 (s, 12 H, CO2Me); 2.62
(s, 6 H, NMe2); 0.53 (s, 1 H, C3H). 13C{1H} NMR (CDCl3): δ/ppm =
262.8 (μ-CO); 213.5 (CO); 179.4, 171.0 (C6-CO + C7-CO); 173.8 (C7);
167.8, 162.6 (C4-CO + C5-CO); 155.8 (C2); 149.2 (C1); 140.7, 127.4 (C4
+ C5); 90.5 (C6); 88.3, 87.0 (Cp); 53.1, 52.8, 52.4, 52.2 (CO2Me); 51.0
(C3); 43.7 (NMe2). 77Se NMR (CDCl3): δ/ppm = 557.4.
H, 4.30; N, 4.44. IR (CH2Cl2): ν /cm–1 = 1930vs. (CO), 1535w (C3=C2).
˜
1H NMR (CDCl3): δ/ppm = 8.96 (d, 1 H, JHH = 6.3 Hz, C3H); 7.43 (d,
3
3
1 H, JHH = 6.3 Hz, C2H); 4.58 (s, 5 H, Cp); 3.64, 3.33 (s, 6 H, NMe2).
13C{1H} NMR (CDCl3): δ/ppm = 227.5 (CO); 218.8 (C1); 174.1 (C3);
137.5 (C2); 82.8 (Cp); 43.2 (NMe2). 77Se NMR (CDCl3): δ/ppm = 210.1.
Synthesis and isolation of [FeCp(CO){SC3HC2HC1NMe(Xyl)}], 5
(Figure 7)
[Fe2Cp2(CO)(μ-CO){μ-η1:η3-C7(CO2Et)C6(CO2Et)C3HC2SeC5-
(CO2Et)C4(CO2Et)C1(NMe2)}], 6b (Figure 9)
Figure 9. Structure of 6b.
Figure 7. Structure of 5.
The title compound was prepared by using the same procedure
A stirred mixture of 2b (100 mg, 0.161 mmol) and S8 (60 mg, described for the synthesis of 6a, from 3a (130 mg, 0.284 mmol)
0.23 mmol) in THF (15 mL) was treated with sodium methoxide and diethylacetylenedicarboxylate (0.14 mL, 0.85 mmol). Eluent for
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European Journal of Inorganic Chemistry
chromatography: diethyl ether. Brown solid, yield 127 mg (56 %).
Anal. calcd. for C33H37Fe2NO10Se: C, 49.65; H, 4.67; N, 1.75; found C,
(CMe3); 52.6 (C3); 43.5 (NMe2); 29.1, 28.3, 28.2 (CMe3). 77Se NMR
(CDCl3): δ/ppm = 555.7.
49.60; H, 4.74; N, 1.84. IR (CH2Cl2): ν /cm–1 = 1964vs. (CO), 1798s (μ-
˜
CO), 1726vs. (OC=O), 1711vs. (OC=O), 1582w (C=C). 1H NMR (CDCl3):
δ/ppm = 4.77, 4.60 (s, 10 H, Cp); 4.42–4.18 (m, 8 H, CH2CH3); 2.61
(s, 6 H, NMe2); 1.57–1.15 (m, 12 H, CH2CH3); 0.50 (s, 1 H, C3H). 13C{1H}
NMR (CDCl3): δ/ppm = 263.4 (μ-CO); 213.9 (CO); 179.3, 170.5 (C6-CO
+ C7-CO); 175.0 (C7); 167.3, 162.3 (C4-CO + C5-CO); 156.1 (C2); 149.1
(C1); 141.2, 128.0 (C4 + C5); 91.3 (C6); 88.7, 87.1 (Cp); 63.3, 62.0, 61.5,
61.1 (CH2CH3); 51.3 (C3); 43.5 (NMe2); 14.9, 14.4, 14.1 (CH2CH3). 77Se
NMR (CDCl3): δ/ppm = 557.4.
2. X-ray Crystallography
Crystal data and collection details for 6a are reported in Table 2.
Data were recorded on a Bruker APEX II diffractometer equipped
with a PHOTON2 detector using Mo-Kα radiation. The structure was
solved by direct methods and refined by full-matrix least-squares
based on all data using F2.[49] Hydrogen atoms were fixed at calcu-
lated positions and refined using a riding model, except H(3) which
was located in the Fourier map and refined isotropically using the
1.2-fold Uiso of the parent C(3) atom. All non-hydrogen atoms were
refined with anisotropic displacement parameters.
[Fe2 Cp2 (CO)(μ -CO){μ -η1 :η3 - C7 (CO2 tBu)C6 (CO2 tBu)-
C3HC2SeC5(CO2tBu)C4(CO2tBu)C1(NMe2)}], 6c (Figure 10)
Deposition Number 1996466 (for 6a) contains the supplementary
crystallographic data for this paper. These data are provided free of
charge by the joint Cambridge Crystallographic Data Centre and
Fachinformationszentrum Karlsruhe Access Structures service
www.ccdc.cam.ac.uk/structures.
Supporting Information (see footnote on the first page of this
article): NMR spectra of products.
Figure 10. Structure of 6c.
The title compound was prepared by using the same procedure
described for the synthesis of 6a, from 3a (104 mg, 0.227 mmol)
and di-tert-butyl acetylenedicarboxylate (154 mg, 0.681 mmol). Elu-
ent for chromatography: diethyl ether. Brown solid, yield 106 mg
(49 %). Anal. calcd. for C44H53Fe2NO10Se: C, 55.83; H, 5.64; N, 1.48;
Acknowledgments
We gratefully thank the University of Pisa (Fondi di Ateneo 2019)
for financial support.
found C, 55.91; H, 5.55; N, 1.41. IR (CH2Cl2): ν /cm–1 = 1961vs. (CO),
˜
Keywords: Iron · Alkyne insertion · Cycloaddition ·
Bridging ligands · Selenophenes
1793s (μ-CO), 1703vs. (OC=O), 1682vs. (OC=O), 1532w (C=C). 1H
NMR (CDCl3): δ/ppm = 4.79, 4.64 (s, 10 H, Cp); 2.56 (s, 6 H, NMe2);
1.76, 1.57, 1.48, 1.42 (s, 36 H, CMe3); 0.21 (s, 1 H, C3H). 13C{1H} NMR
(CDCl3): δ/ppm = 265.7 (μ-CO); 214.3 (CO); 179.0, 169.9 (C6-CO + C7-
CO); 176.0 (C7); 166.2, 161.5 (C4-CO + C5-CO); 154.9 (C2); 149.8 (C1);
142.2, 129.4 (C4 + C5); 92.2 (C6); 88.2, 86.7 (Cp); 83.5, 82.8, 81.8, 81.3
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C29H29Fe2NO10Se
742.19
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