Oligomerisation of isopropenylacetylene in the presence of Fe3(CO)12. Crystal and molecular structure of the open-cluster isomers (see abstract)

Article abstract of DOI:10.1039/b111070p

The reaction of 2-methyl-1-buten-3-yne (isopropenylacetylene, IPA) with triiron dodecacarbonyl in refluxing benzene leads to medium yields of four main derivatives. Two of them are the trinuclear open-cluster isomers Fe₃(CO)₁₀[H

Full text of DOI:10.1039/b111070p

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Oligomerisation of isopropenylacetylene in the presence of
Fe (CO) . Crystal and molecular structure of the open-cluster
3
12
isomers Fe (CO) [H CC(CH )CC(H)C(H)C(CO)C(CH )CH ],
3
10
2
3
3
2
Fe (CO) [HCC(CH )C(H)C(H)C(H)C(CO)C(CH )CH ] and of
3
10
3
3
2
the binuclear complex Fe (CO) [C H (CO)]
2
5
15 18
a
a
a
b
Elisabetta Gatto, Giuliana Gervasio,* Domenica Marabello and Enrico Sappa*
a
Dipartimento di Chimica IFM, Università di Torino, Via P.Giuria 7, I-10125 Torino, Italy.
E-mail: giuliana.gervasio@unito.it
Dipartimento di Scienze e Tecnologie Avanzate, Università del Piemonte Orientale Amedeo
Avogadro, C.so Borsalino 54, I-15100 Alessandria, Italy
b
Received 4th December 2001, Accepted 16th January 2002
First published as an Advance Article on the web 7th March 2002
The reaction of 2-methyl-1-buten-3-yne (isopropenylacetylene, IPA) with triiron dodecacarbonyl in
refluxing benzene leads to medium yields of four main derivatives. Two of them are the trinuclear
open-cluster isomers Fe (CO) [H CC(CH )CC(H)C(H)C(CO)C(CH )CH ] (complex 1a) and
3
10
2
3
3
2
Fe (CO) [HCC(CH )C(H)C(H)C(H)C(CO)C(CH )CH ] (complex 1b) containing an organic ligand formed
3
10
3
3
2
upon tail-to-tail dimerization of the alkyne. In both complexes one isolated iron atom is part of a metallacyclic
five-membered ring formed by three carbon atoms of one alkyne molecule and a carbon belonging to a CO.
The other two iron atoms are linked together; however their bonding to the organic moiety is different in complexes
1
a and 1b. This type of isomerism and the coordination mode of the unique iron atom are unprecedented in
alkyne-cluster chemistry. The other two complexes are binuclear and have been identified, respectively, as
Fe (CO) [C H (CO)] (2) and Fe (CO) L [L = IPA] (3). Complex 2 contains an unprecedented organic ligand
2
5
15 18
2
6
3
formed by three alkyne molecules and one CO; this is different from other L CO (troponic) ligands found in
3
the literature. The structures of complexes 1a, 1b and 2 have been studied by X-ray crystallography. Complex 3 did
not give crystals suitable for X-ray analysis. Reaction pathways leading to new complexes are hypothesized.
Introduction
to explore reaction pathways to obtain iron carbonyl clusters
containing ene-ynes.
Propargyl alcohols, HC᎐CC(OH)RRЈ, react with M (CO)
12
᎐
3
As previously pointed out, triiron clusters of type II are
difficult to obtain. The more simple approach would be the
direct reaction of Fe (CO) with ene-yne ligands. One such
carbonyls (M = Fe, Ru) undergoing dehydration through two
main pathways; one of them (more common when M = Fe)
requires loss of the terminal alkynic hydrogen and of the alco-
holic OH to give the allenylidene clusters Fe (CO) (µ-CO)(µ -
3
12
reaction was attempted using hex-1-en-3-yne (EtC᎐CCH᎐
᎐
᎐
3
9
3
6
CH ). The products, however, were formed upon hydration of
2
2
η -C᎐C᎐CRRЈ) (type I). The second process (more common
when M = Ru, in acidic conditions) occurs through the loss of
the OH and of one hydrogen of an alkylic substituent (eg. RЈ =
Me); it leads to vinyl-acetylide clusters, such as (µ-H)Ru (CO) -
the coordinated alkyne; the splitting of water into its com-
ponents being favoured by the silica used for TLC purifications.
No clusters of type II were observed. A comparable reaction
sequence, starting from Fe (CO) and 1-phenylprop-2-yn-1-ol
3
9
1,2
3
12
[
C᎐CC(᎐CH )R] (type II). The structures of complexes of
᎐ ᎐
2
᎐
[
HC᎐CC(H)(OH)Ph] led to a type I triiron allenyl cluster which
᎐
type I and II are shown in Scheme 1.
underwent reaction with methanol to form an oxygenated
7
metallacycle.
We have now investigated the reaction of Fe (CO) with
3
12
2
-methylbut-1-en-3-yne, HC᎐CC(᎐CH )CH
(isopropenyl-
᎐
᎐
2
3
8
acetylene, IPA). Again, we could not isolate complexes of type
II; however, we could obtain some clusters showing structural
features not reported until now. The structures of the trinuclear
isomers Fe (CO) [H CC(CH )CC(H)C(H)C(CO)C(CH )CH ]
3
10
2
3
3
2
(
1a) and Fe (CO) [HCC(CH )C(H)C(H)C(H)C(CO)C(CH )-
3
1
0
3
3
CH ] (1b) have been deduced from an X-ray diffraction study.
2
The complexes show an unprecedented open cluster structure
and some interesting metal-ligand interaction modes.
Fe (CO) [C H (CO)] (2) was initially hypothesized to belong
Scheme 1
2
5
15 18
to a known class of troponic derivatives; the X-ray analysis
showed instead that it belongs to a new and unprecedented
type of derivative. The oligomerization pathways of IPA in the
presence of Fe (CO) are discussed and compared with those
Free or coordinated ene-yne (or vinyl-acetylene) ligands are
3
important as synthons in metal-mediated organic syntheses,
4
in reaction mechanisms related to anticancer drugs and as
3
12
5
potential NLO materials. The interest in these ligands led us
observed in the presence of Ru (CO) .
3 12
1
448
J. Chem. Soc., Dalton Trans., 2002, 1448–1454
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b111070p

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Experimental
Behaviour of complex 1a on the TLC plates and in solvents
The complex forms a red band during TLC elution, from which
deep red crystals used for the X-ray analysis were obtained. It
gives red solutions when dissolved in benzene, toluene, hexane
and heptane. It immediately turns deep green when dissolved in
CHCl or CH Cl ; from these solutions a deep green solid could
General details, materials, analysis of the products
Triiron dodecacarbonyl (Strem Chemicals, stabilized with
MeOH) and the alkyne (Lancaster Synthesis) were commercial
products and were used as received. Solvents (benzene,
heptane) were dehydrated over sodium. All the reactions were
performed under a dry nitrogen atmosphere in conventional
three necked flasks equipped with gas inlet, cooler, mercury
check valve and magnetic stirring.
3
2
2
be recovered. This green material showed the following spectro-
scopic data. IR (CHCl ): 2109 w, 2071 m–s, 2057 s(sh), 2039
3
vs(b), 2002 s(vb). EI MS: 504 m/z (low intensity, Fe (CO) ),
3
12
4
48 m/z (medium intensity, Fe (CO) ); intense peak at 364
3 10
The reaction mixtures were filtered under N , brought to
2
m/z [Fe (CO) ?, Fe (CO) ?], loss of 7 CO’s (very intense peaks):
3 7 2 9
small volume under reduced pressure and separated on pre-
parative TLC plates (Merck Kieselgel P.F.; eluent mixtures of
light petroleum (bp 40–70 ЊC) and diethyl ether in variable
v/v ratios). The products were crystallized and analyzed by
means of a Bruker Equinox 55 spectrophotometer (KBr cells);
very intense peak at 112 m/z (Fe , Fe(CO) ).
2
2
Behaviour of complexes 1a and 1b under thermal conditions
Complex 1a was dissolved in benzene, under N and heated to
reflux for 10 min. TLC purification showed the presence of
unreacted 1a (ca. 50%), of complex 2 (ca. 30%) of trace
amounts of complex 1b and of 3 together with some other trace
products and decomposition.
Attempts at purifying and crystallizing complex 1b always
resulted in the deposition of crystals of 1b and of 2 together.
The crystals of 1b used for the X-ray analysis were separated by
hand. This behaviour did not allow us to investigate the thermal
reactivity of 1b.
2
1
the H NMR spectra were obtained on a JEOL GX 270/89
9
instrument and electron-impact mass spectra with a Finnigan-
1
0
Mat TSQ-700 quadrupolar mass spectrometer.
1
The H NMR spectrum of IPA, registered for comparison
with those of the complexes, shows signals at: 5.30 m, 5.21 m
(
2H, CH ), 2.81 s (1H, HC᎐), 1.82 t (3H, CH ).
2
3
Reaction of Fe (CO) with IPA
3
12
In a typical reaction, to a suspension of the iron carbonyl
3
3
(
(
ca. 2.0 g, 4 mmol) in benzene (100 cm ) 0.5 cm of liquid IPA
ca. 7 mmol) was added; the mixture was refluxed for 6 min,
X-Ray analyses
then allowed to cool and filtered under N . TLC purification
The crystal data and the refinement parameters of X-ray
analyses are collected in Table 1. The reflection intensities were
collected on a four circle automatic diffractometer Siemens P4.
For complexes 1a, 1b and 2 the Fe, C and O atoms were
anisotropically refined, while the hydrogen atoms were treated
in different ways. In complex 1a all H atoms were localized in
the final Fourier difference maps and refined with fixed Uiso
values. For complex 1b all H atoms were localized on the
Fourier difference maps; for three of them it was necessary to
fix the C–H distance and all were refined with fixed Uiso values.
2
showed the presence of unreacted parent carbonyl (ca. 10%)
and of the following bands: yellow and pink (trace amounts,
not collected), red (1a, ca. 15%), red–brown (1b, ca. 10%), red–
orange (2, ca. 20%) and dark red (3, ca. 20%). The bands
corresponding to 1b and 2 were partly superposed, so that the
complexes could not be collected as pure specimens. Longer
reaction times resulted in lower yields of 1a and 1b and
increased yields of the other complexes, in particular of 2.
In complex 2 the H atoms of CH groups were put in calculated
3
Complex 1a. C 41.8 (41.4), H 2.01 (1.97)% (Calc. values in
positions and refined riding on the corresponding C atoms. The
other H atoms were found on the final maps; for some of them
the coordinates were free during refinement and for others the
C–H distances were fixed. For all H atoms the Uiso value was
fixed during refinement. Any statement regarding the hydrogen
atoms must be considered, obviously, with caution.
CCDC reference numbers 175533–175535.
See http://www.rsc.org/suppdata/dt/b1/b111070p/ for crystal-
lographic data in CIF or other electronic format.
parentheses). IR: 2107 w, 2058 m, 2048 m(sh), 2031 vs, 2020
Ϫ1
1
s(sh), 1992 m, 1985 m, cm . H NMR(C D , Ϫ40 ЊC): 7.05–
6
6
7
1
.03 d (HC᎐, C ), 2.35 d (HC᎐, C , C ), 1.71 s (CH , C or C ),
᎐
10 6 7 3 4 14
ϩ
.25 m (CH ), 0.84 t (CH , C ). EI MS: P = 608 m/z (very low
2
3
5
intensity) and 580 m/z (first very intense peak), loss of 10 CO’s;
very intense peaks at 300 m/z (Fe L ) and 272 m/z (Fe L (CO))
3
2
2
2
(
L = IPA).
Complex 1b. C 41.9, H 2.02% (see 1a). IR: 2054 vs, 2048 s(sh),
1
2
023 s, 1996 vs, 1989 s(sh), 1974 m, 1953 m. H NMR: 6.03 s
(
(
᎐CH, C ), 5.74 dd (᎐CH, C , C ), 5.39 dd (᎐C, C ), 4.83 d
᎐
10 7 8 6
ϩ
Results and discussion
CH ), 1.96 s, 0.89 t (CH ). EI MS: P = 580 m/z, loss of 10
2
3
CO’s (see 1a).
Spectroscopic characterization and reactivity of the new
complexes
Complex 2. C 54.6 (54.4), H 3.4 (3.2)%. IR: 2071 s, 2039 vs,
005 vs, 2001 vs(sh), 1988 m, cm . H NMR: 5.73 d (CH,
The reaction of Fe (CO) with IPA leads to four main organo-
3
12
Ϫ1
1
2
metallic products, all containing oligomeric alkyne ligands.
C ,C ), 5.38 s (CH, C ), 5.09 s (1H), 4.83 s (CH , C or C ), 2.39
1
5
6
8
2
1
15
These were characterized by means of IR and H NMR
d (CH , C or C ), 2.31 d (CH , C ), 2.27 s, 2.23 s (CH ,
2
1
15
2
11
3
spectroscopies and by mass spectrometry. However, in some
instances, in the mass spectra parent ion signals of very low
intensity were obtained; the complexity of the NMR spectra,
also, did not always allow unequivocal attributions. Therefore,
when possible, the structure of the complexes was determined
by X-ray diffraction. Complexes 1a, 1b and 2 gave crystals suit-
able for X-ray analyses; in contrast, 3 did not give good quality
crystals. Thus, for this complex we can only propose a tentative
structure in accordance with the NMR and mass spectrometric
results; on these bases 3 could be a flyover complex (type VI) as
discussed below.
ϩ
C ,C ), 1.57–1.50 m (CH , C ). EI MS: P = 478 m/z, loss of
1
15
3
12
5
CO; intense peak at 304 m/z.
Complex 3. C 52.5 (52.7), H 3.9 (3.76)%. IR: 2051 vs, 2021 vs,
Ϫ1
1
1
(
0
988 m, cm
. H NMR: 6.21 s (1H), 5.41 s (1H), 5.02 d
2H,CH ), 3.83 s (1H), 2.17–2.09 m (4H,CH ), 1.56 s, 1.28 t,
2
2
ϩ
.90 t (9H, CH ). EI MS: P = 478 m/z, loss of 6 CO; very
3
intense peaks at 338 m/z (Fe (CO)L ) (L = IPA), 310 and
2
3
2
72/270 m/z.
The attributions of the NMR spectra are not unequivocal
because of the complex structures of the derivatives and, in
some instances, can be reversed.
The behaviour of 1a on the TLC plates indicates that it is not
sensitive to moisture. In previous work we had observed,
J. Chem. Soc., Dalton Trans., 2002, 1448–1454
1449

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Table 1 Crystal data and refinement parameters for complexes 1a, 1b and 2
Complex
1a
1b
2
Empirical formula
M
T /K
Wavelength/Å
C H Fe O
C H Fe O
607.86
293(2)
0.71073
C H Fe O
6
478.05
293(2)
2
1
12
3
11
21 12
3
11
21 18
2
607.86
293(2)
0.71073
0.71073
Triclinic, P1
¯
Crystal system, space group
Monoclinic, P2 /n
Monoclinic, P2 /c
1
1
a/Å
b/Å
c/Å
α/Њ
β/Њ
γ/Њ
12.9293(15)
14.5344(13)
13.0375(13)
90
105.376(8)
90
2362.3(4)
4, 1.709
14.354(5)
8.028(3)
21.089(8)
90
100.43(2)
90
2390.0(15)
4, 1.689
8.549(5)
14.799(7)
16.467(8)
85.11(3)
85.46(4)
83.57(3)
2057.5(19)
4, 1.543
1.444
3
V/Å
Ϫ3
Z, Calculated density/g cm
µ/mm
Ϫ1
1.876
1.854
F(000)
1216
0.30 × 0.40 × 0.76
1.97 to 27.50
Ϫ16 р h р 1, Ϫ1 р k р 18,
Ϫ16 р l р 16
6545/5389 [R(int) = 0.0330]
99.3
Full-matrix least-squares on F
5389/0/352
1216
0.08 × 0.24 × 0.60
1.96 to 36.08
Ϫ1 р h р 20, Ϫ11 р k р 1,
Ϫ29 р l р 29
8862/6981 [R(int) = 0.0302]
99.8
Full-matrix least-squares on F
6981/3/352
976
Crystal size/mm
θ range data collection/Њ
Limiting indices
0.02 × 0.34 × 0.40
1.24 to 25.00
Ϫ10 р h р 1, Ϫ17 р k р 17,
Ϫ19 р l р 19
8903/7248 [R(int) = 0.0504]
100.0
Full-matrix least-squares on F
7248/17/576
0.942
Refl. collected/unique
Completeness to θ (%)
Refinement method
Data/restraints/parameters
Goodness-of-fit on F
2
2
2
2
1.028
1.010
Final R indices [I > 2σ(I )]
R1 = 0.0449, wR2 = 0.1064
[4021 refl.]
R1 = 0.0476, wR2 = 0.0857
[3673 refl.]
R1 = 0.0605, wR2 = 0.1459
[3712 refl.]
R indices (all data)
Largest diff. peak and hole/e Å
R1 = 0.0663, wR2 = 0.1179
0.520 and Ϫ0.642
R1 = 0.1185, wR2 = 0.1087
0.427 and Ϫ0.599
R1 = 0.1417, wR2 = 0.1855
0.510 and Ϫ0.475
Ϫ3
indeed, that TLC materials may contain traces of water which
is responsible for several surface organometallic reactions
including hydration or dehydration of cluster-bound alkyne
1,2,6,7
ligands.
Hydration of IPA would lead to 2-methyl-3-butyn-
1
-ol [HC᎐C(Me) OH, MBO, see ref. 8]. The reactions of MBO
᎐
2
with Fe (CO) had already been investigated; small yields of a
3
12
type I allenyl complex and higher yields of partially dehydrated
11
(
isomeric) metallacyclic complexes were obtained. None of
these complexes could be detected after the reactions reported
here.
It is worthy to note, also, that 1a is unaffected by the diethyl
ether used in the TLC elution and by hydrocarbon solvents
(
e.g. heptane, benzene, toluene). In contrast, it is very sensitive
to chlorinated solvents; the deep green solutions obtained
Fig. 2 An ORTEP plot of Fe (CO) [HCC(CH )C(H)C(H)C(H)C-
deposited a deep green solid which was identified as Fe (CO) .
3
10
3
3
12
(
CO)C(CH )CH ] 1b, with 30% thermal elliposids.
3
2
We could also observe that upon thermal treatment 1a gives
mainly 2 and that 1b and 2 co-crystallize; this could indicate
that both 1a and (mostly) 1b are precursors of 2. We could
also observe (reactions not reported) that 2 and 3 do not
interconvert. They are presumably formed through different
mechanisms.
moiety Fe
(CO)
connected via an organic ligand formed by a
2
6
tail-to-tail dimerization of two IPA molecules and by one
inserted CO whose origin is discussed below. The mononuclear
moiety (Fe(3)) is identical in the two complexes while in the
binuclear fragments Fe(1) and Fe(2) are enveloped in a different
way by the organic moiety. As discussed below, the isomerism
of the complexes is due to differences in the organic chain and
in its coordination to the metals. Relevant bond distances and
angles are listed in Tables 2 and 3 for complexes 1a and 1b,
respectively.
X-Ray structure of complexes 1a and 1b
The two molecules of complexes 1a and 1b (Fig. 1 and 2) are
formed by a mononuclear moiety Fe(CO) and by a binuclear
4
In the mononuclear fragment Fe(3) has a distorted octahedral
environment. It forms a penta-atomic planar ring (mean devi-
ation from planarity 0.02 and 0.07 Å for 1a and 1b, respectively)
with the organic moiety; the organic moiety behaves as a two-
electron donor, in agreement with the Fe(3)–C(1) and Fe(3)–
C(5) bond distances and with the distances inside the ring.
The C(1)–O(1) distance corresponds to a double bond and in
the ring a double bond is also localized between C(2) and C(3)
(
1.347(4) Å av.). The similarity of the mononuclear fragments
of 1a and 1b includes the C(6)H(6) atoms; the C(2)C(6)
fragment corresponds to one former IPA unit with a triple bond
between C(2) and C(6) and a double bond between C(3) and
C(5).
Fig. 1 An ORTEP plot of Fe (CO) [H CC(CH )CC(H)C(H)C(CO)-
3
10
2
3
C(CH )CH ] 1a, with 30% thermal ellipsoids.
3
2
1
450
J. Chem. Soc., Dalton Trans., 2002, 1448–1454

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Table
2
Some relevant bond distances [Å] and angles [Њ] for
complex 1a
to two iron atoms has not been previously observed, to our
knowledge. The three carbonyl ligands on each iron atom are
staggered.
In complex 1b the binuclear fragment of the molecule is
formed by two iron atoms (Fe(1)–Fe(2) 2.636(1) Å) around
which a five carbon atom chain of the organic moiety (C(10)H–
C(9)Me–C(8)H–C(7)H–C(6)H) is wrapped. Each iron atom is
coordinated to three carbon atoms (Fe(1)–C(10) 2.047(3),
Fe(1)–C(9) 2.086(3), Fe(1)–C(8) 2.072(3); Fe(2)–C(10) 1.970(3),
Fe(2)–C(7) 2.240(3), Fe(2)–C(6) 2.275(3) Å). While in complex
Fe(1)–Fe(2)
Fe(1)–C(8)
Fe(1)–C(9)
Fe(1)–C(10)
Fe(2)–C(8)
Fe(2)–C(7)
Fe(2)–C(6)
Fe(3)–C(1)
Fe(3)–C(5)
C(1)–O(1)
2.7565(6)
1.993(3)
2.105(3)
2.126(4)
1.970(3)
2.102(3)
2.207(3)
2.050(3)
2.069(3)
1.203(4)
C(1)–C(2)
C(2)–C(3)
C(2)–C(6)
C(3)–C(4)
C(3)–C(5)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(9)–C(14)
1.471(4)
1.347(4)
1.487(4)
1.485(4)
1.490(4)
1.402(4)
1.407(4)
1.402(4)
1.412(5)
1.501(6)
1
a the organic moiety begins on Fe(2) with C(6) and ends on
Fe(1) with C(10), in complex 1b the organic ligand begins and
ends on the same atom Fe(2). The carbon–carbon distances are
also different to each other, (C(6)–C(7) 1.383(4), C(7)–C(8)
C(1)–Fe(3)–C(5)
C(2)–C(1)–Fe(3)
C(3)–C(2)–C(1)
C(3)–C(2)–C(6)
C(1)–C(2)–C(6)
C(2)–C(3)–C(4)
C(2)–C(3)–C(5)
81.77(12)
113.4(2)
115.7(3)
122.7(3)
121.6(3)
124.9(3)
118.5(3)
C(3)–C(5)–Fe(3)
C(4)–C(3)–C(5)
C(7)–C(6)–C(2)
C(6)–C(7)–C(8)
C(9)–C(8)–C(7)
C(8)–C(9)–C(10)
C(9)–C(10)–Fe(1)
110.6(2)
116.6(3)
126.2(3)
117.2(3)
140.4(3)
115.7(3)
69.7(2)
1
.466(5), C(8)–C(9) 1.423(5), C(9)–C(10) 1.391(5) Å), and
suggest a greater double bond character of C(6)–C(7) and of
C(9)–C(10); this lower degree of electron delocalization may
suggest the incipient formation of a metallacyclic (ferrole-like)
12
system. Only two pairs of carbonyls are eclipsed (CO(11) and
CO(22), CO(21) and CO(12)).
Table 3 Some relevant bond distances [Å] and angles [Њ] of complex 1b
The carbon chain of 1b is isomeric with that of 1a; in fact, its
formation requires a hydrogen shift from the IPA terminal
C(10) of 1a to the C(8) atom of 1b. The unprecedented open
structures of the clusters and the interactions within the organic
moieties and the metals in 1a and 1b are compared in Scheme 2.
Fe(1)–Fe(2)
Fe(1)–C(10)
Fe(1)–C(8)
Fe(1)–C(9)
Fe(2)–C(10)
Fe(2)–C(7)
Fe(2)–C(6)
Fe(3)–C(1)
Fe(3)–C(5)
C(1)–O(1)
2.636(1)
2.047(3)
2.072(3)
2.086(3)
1.970(3)
2.240(3)
2.275(3)
2.051(3)
2.074(3)
1.206(4)
C(1)–C(2)
C(2)–C(3)
C(2)–C(6)
C(3)–C(5)
C(3)–C(4)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(9)–C(14)
1.474(4)
1.348(4)
1.479(4)
1.485(5)
1.496(5)
1.383(4)
1.466(5)
1.423(5)
1.391(5)
1.508(5)
C(1)–Fe(3)–C(5)
O(1)–C(1)–C(2)
O(1)–C(1)–Fe(3)
C(2)–C(1)–Fe(3)
C(3)–C(2)–C(1)
C(3)–C(2)–C(6)
C(1)–C(2)–C(6)
C(2)–C(3)–C(5)
81.58(13)
124.9(3)
121.9(2)
113.2(2)
114.6(3)
123.4(3)
122.0(3)
119.6(3)
C(2)–C(3)–C(4)
C(5)–C(3)–C(4)
C(3)–C(5)–Fe(3)
C(7)–C(6)–C(2)
C(6)–C(7)–C(8)
C(9)–C(8)–C(7)
C(10)–C(9)–C(8)
C(9)–C(10)–Fe(2)
125.5(3)
114.9(3)
109.8(2)
127.3(3)
121.7(3)
118.3(3)
111.8(3)
116.9(2)
The presence of “isolated” Fe(CO)4 fragments in poly-
metallic derivatives is rare: there are, however, some literature
examples of clusters containing Fe(CO) units linked to tri- and
4
13
bi-nuclear iron fragments through a bridging diphosphine. It
is worthy of note that these clusters undergo degradation to
binuclear fragments; this is helpful when considering the
behaviour of 1a in solution and as a possible precursor of com-
pound 2.
It is difficult to hypothesize the origin of C(1)–O(1); a rea-
sonable hypothesis could be that a Fe(CO) fragment (formed
5
from alkyne-assisted fragmentation of Fe (CO) ) is coordin-
3
12
ated to the three alkynic carbons and that C(1)–O(1) is in
an “agostic” situation between the iron and the carbon atom
chain. This hypothesis would be in accordance with the
observed retro-formation of Fe (CO) [through recombination
Scheme 2
3
12
The Fe(1)–Fe(2) bond is longer in 1a than in 1b, owing to the
different disposition of the organic ligand.
No relevant intermolecular interaction was found from
packing analysis.
of Fe(CO) fragments].
5
In the binuclear fragment of 1a the two iron atoms (Fe(1)–
Fe(2) 2.7565(6) Å) are coordinated to five carbon atoms of the
organic chain (C(10)H –C(9)Me–C(8)–C(7)H–C(6)H) acting as
2
bis π-allylic ligands; each iron atom interacts with three allylic
carbon atoms (Fe(1)–C(10) 2.126(4), Fe(1)–C(9) 2.105(3),
Fe(1)–C(8) 1.993(3); Fe(2)–C(8) 1.970(3), Fe(2)–C(7) 2.102(3),
Fe(2)–C(6) 2.207(3) Å). The Fe(1,2)–C(8) distances are sig-
nificantly shorter than the other ones. The carbon–carbon bond
distances are very similar (1.406(4) Å av.) in agreement with a
delocalization in the C(6)᎐C(10) chain and with a bis-allylic
ligand; therefore, considering the chain as a six-electron-donor,
the 18-electron rule is observed. The C(6)–C(7) and C(9)–C(10)
bonds were originally a triple and a double bond in the
IPA molecules. This coordination mode of five carbon atoms
X-Ray structure of complex 2
The structure of complex 2 is shown in Fig. 3 and significant
bond distances and angles are listed in Table 4; the asymmetric
unit contains two independent molecules (A and B).
In compound 2, two iron atoms (Fe(1)–Fe(2) 2.705(2) Å
mean value between the two molecules of the asymmetric
unit) link three [Fe(1)] and two [Fe(2)] carbonyl ligands and
are coordinated to an alkyne trimer; two IPA alkynes are joined
tail[C(5)]-to-tail[C(6)] from C(1) to C(7) and the third alkyne
moiety is joined head[C(7)]-to-tail[C(8)]. In the middle of the
ؒؒ
J. Chem. Soc., Dalton Trans., 2002, 1448–1454
1451

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Table 4 Bond lengths [Å] and angles [Њ] for complex 2
Molecule A
Molecule B
Fe(1)–Fe(2)
Fe(1)–C(13)
Fe(1)–C(14)
Fe(1)–C(15)
Fe(2)–C(13)
Fe(2)–C(4)
Fe(2)–C(2)
Fe(2)–C(1)
Fe(2)–C(5)
C(1)–C(2)
C(2)–C(4)
C(2)–C(3)
C(4)–C(5)
C(4)–C(9)
C(5)–C(6)
C(6)–C(7)
C(7)–C(10)
C(7)–C(8)
C(8)–C(9)
C(8)–C(13)
C(9)–O(9)
C(10)–C(11)
C(10)–C(12)
C(13)–C(14)
C(14)–C(15)
C(14)–C(16)
2.711(2)
2.033(7)
2.100(7)
2.126(8)
2.039(7)
2.055(7)
2.097(7)
2.151(8)
2.190(7)
1.426(10)
1.431(10)
1.503(10)
1.414(9)
1.507(9)
1.469(10)
1.365(10)
1.464(11)
1.512(10)
1.526(10)
1.559(9)
1.201(8)
1.302(13)
1.508(12)
1.400(9)
1.415(10)
1.519(9)
2.701(2)
2.032(6)
2.097(7)
2.118(9)
2.022(6)
2.044(7)
2.100(8)
2.160(9)
2.218(8)
1.422(11)
1.413(10)
1.507(10)
1.399(10)
1.500(10)
1.448(11)
1.346(10)
1.471(11)
1.518(10)
1.511(10)
1.553(9)
1.201(8)
1.321(14)
1.507(12)
1.419(9)
1.416(11)
1.511(10)
Fig. 3 An ORTEP plot of Fe (CO) [C H (CO)] 2, with 30% thermal
2
5
15 18
ellipsoids.
chain, one CO is bonded to the tail of one unit [C(8)] and to the
head of another [C(4)] thus forming a six-membered carbon
ring. The ring is not planar. Inside the organic chain three types
of C–C bond distance may be found: (i) 1.33(1) Å av., (ii) a
range from 1.40(1) Å to 1.47(1) Å, (iii) 1.52(1) Å av. The first
value corresponds to a double bond character and this value is
associated with the C(6)–C(7) and C(10)–C(11) bonds. The
second range of values (ii) are bonds which display, to a greater
or lesser extent, a delocalized double bond character. These
refer to the double bonds involved in a π-interaction with Fe(1)
C(2)–C(1)–Fe(2)
C(1)–C(2)–C(4)
C(1)–C(2)–C(3)
C(3)–C(2)–C(4)
C(2)–C(4)–C(5)
C(2)–C(4)–C(9)
C(5)–C(4)–C(9)
C(4)–C(5)–C(6)
C(5)–C(6)–C(7)
C(6)–C(7)–C(8)
C(6)–C(7)–C(10)
C(8)–C(7)–C(10)
C(7)–C(8)–C(9)
C(7)–C(8)–C(13)
C(9)–C(8)–C(13)
C(4)–C(9)–C(8)
O(9)–C(9)–C(4)
O(9)–C(9)–C(8)
C(7)–C(10)–C(11)
C(7)–C(10)–C(12)
C(11)–C(10)–C(12)
C(8)–C(13)–C(14)
C(8)–C(13)–Fe(1)
C(8)–C(13)–Fe(2)
Fe(1)–C(13)–Fe(2)
C(13)–C(14)–C(15)
C(13)–C(14)–C(16)
C(15)–C(14)–C(16)
68.3(4)
115.1(7)
121.8(7)
123.0(7)
120.2(7)
121.8(6)
115.8(6)
117.9(7)
121.3(7)
113.6(7)
122.8(8)
123.6(7)
108.1(6)
113.5(6)
102.9(5)
107.5(6)
125.5(6)
127.0(7)
123.0(9)
117.7(9)
119.3(9)
118.5(6)
132.4(5)
111.5(4)
83.5(3)
68.2(4)
114.7(7)
121.5(8)
123.5(7)
122.1(7)
121.9(7)
114.4(7)
118.7(7)
121.7(7)
113.5(7)
124.8(8)
121.7(8)
107.1(6)
111.9(6)
104.1(6)
107.8(6)
123.8(7)
128.4(7)
123.4(9)
116.9(9)
119.8(9)
117.7(6)
131.9(5)
112.1(4)
83.6(2)
(
C(13)–C(14) and C(14)–C(15)) or with Fe(2) (C(1)–C(2), C(2)–
C(4), C(4)–C(5)) or to a delocalization in C(5)–C(6) and C(7)–
C(10) due to two conjugated double bonds. The remaining
bonds (iii) (1.52(1) Å av.) have a more pronounced single bond
character.
The Fe–C bonds linking the organic moiety to the bimetallic
fragment range between the values of 2.022(7) and 2.218(8) Å,
with the shorter values corresponding to the bridge C(13), while
the other values correspond to π-coordination to the iron
atoms.
The organic moiety acts, according to the 18-electron rule, as
an eight-electron donor.
No relevant intermolecular interaction exists.
Oligomerisation pathways of IPA
118.3(7)
123.2(7)
117.6(7)
115.9(7)
123.3(7)
120.5(7)
(
a) Trinuclear complexes. Oligomerisation reactions of IPA
in the presence of Ru (CO) have been reported: this allows
3
12
a comparison with the results of this work. In the presence of
Ru (CO) formation of a type II ene-yne complex occurs as the
first step. This is followed by head-to-tail dimerization and
3
12
1
4
Fe (CO) but that different products are obtained. The “incipi-
3 12
shift of an alkynic hydrogen in the carbon atom chain to form
the closed cluster III (Scheme 3, below). Addition of IPA to
ent” opening of cluster IV (2 M–M bonds) should be compared
with the open structures of 1a and 1b (1 M–M bond only).
This could indicate that: (i) opening of clusters of type II (not
isolated for iron) can be induced by entering IPA molecules and
(ii) that this process can continue, for iron, until separate metal
fragments are obtained.
15
the acetylide complex (µ-H)Ru (CO) [C᎐CC(Me) ] (a type II
3
9
3
structure) results in the formation of a ramified ligand
containing the acetylide in the middle of a seven-carbon
atom chain; two IPA molecules are linked (one head-to-
tail, the other tail-to-tail) to the acetylide α-carbon; again,
hydrogen shift in the carbon chain is observed. Opening of the
cluster and hydride shift to the organic moiety also occur, to
13
(b) Binuclear complexes. In accordance with literature data
and our experimental results, complex 2 and, in far lesser
extent, complex 3 are formed from 1a or 1b. Release of iron,
transfer and shift of C(1)–O(1) to the organic chain, favoured
(or competing) with the entering of a third IPA molecule could
easily explain the formation of 2 and, in lesser extent, that of 3.
A remote possibility is that the binuclear complexes are formed
16
form cluster IV. In IV, however, two M–M bonds are still
present, contrasting with complexes 1. No CO insertion in the
organic moiety was observed in the reactions involving
ruthenium. The structures of clusters III and IV are shown in
Scheme 3.
In this work we provide evidence that oligomerization
and co-oligomerization of IPA also occurs in the presence of
first and that they undergo addition of Fe(CO) (x = 4,5) frag-
ments to form complexes 1.
x
1
452
J. Chem. Soc., Dalton Trans., 2002, 1448–1454

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Scheme 3
Cyclotrimerization of alkynes (and/or CO) on iron com-
plexes is not unknown; flyover derivatives and tropone precur-
sors (see below) are obtained. The mass spectrum of complex
2
showed a parent ion and a fragmentation corresponding
to Fe (CO) [L (CO)]; this led us to think that the structure of 2
2
5
3
could be compared to the not very common troponic complexes
Scheme 4
17
V
shown in Scheme 4. However, the X-ray analysis showed
that 2 belongs to a structural family containing a new organic
moiety.
As previously pointed out, we could not obtain crystals of 3
suitable for an X-ray analysis. On the basis of the analytic,
mass spectrometric and spectroscopic data, this complex could
belong to the family of the Fe (CO) [L(X)L] flyover derivatives
2
6
(
VI) (X = L or CO, Scheme 2). Several iron, cobalt and
ruthenium complexes with X = CO have been reported and
18,19
characterized.
In contrast, only a few complexes where
20
X = alkyne are known. The formation of complexes VI
requires trimerization of the alkynes and shift of the terminal
hydrogen of the “central” alkyne molecule. In our opinion,
complex 3 belongs to this structural type of derivatives. We
cannot exclude, however, that 3 is the result of another cyclo-
trimerization mode found, till now, for only one compound
(
VII, a potential precursor of the troponic VI, also shown in
21
Scheme 4).
A comparison of the organic moieties of complexes 2, V and
VI could be helpful for understanding the cyclo-oligomerization
pattern of alkynes. These are shown in Scheme 5 (the zigzag
lines separate the acetylenic moieties).
In the tropone complexes V, two alkyne molecules are linked
tail-to-tail and the third one head-to-tail. This also occurs in 2.
However, the position and linking of the CO is different in the
two types of structures. In particular, in the troponic complexes
a “linear” carbon chain (with the possibility of forming several
isomers) is present, whereas in 2 the CO is part of a carbon
atom cycle sitting in the middle of the chain. To our knowledge,
this oligomerisation pattern for alkynes (and ene-ynes) has not
been previously evidenced.
Scheme 5
to the acetylide in cluster IV and no CO’s are inserted into the
organic chain. This behaviour is a further example of the great
versatility of alkyne-clusters interactions.
Finally, in the flyover complexes VI (where X = alkyne)
the central alkyne molecule behaves in a comparable way
J. Chem. Soc., Dalton Trans., 2002, 1448–1454
1453

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7
G. Gervasio, D. Marabello and E. Sappa, J. Chem. Soc., Dalton
Trans., 1997, 1851.
Concluding remarks
2
2
Alkyne-cluster chemistry is a quite old research field. Even old
trees, however, can produce flowers and fruits. In this work
we report on new complexes obtained upon oligomerisation
of an ene-yne molecule in the presence of Fe (CO) . New
open-cluster structures have been obtained and new co-
oligomerisation patterns have been evidenced. We also produce
evidence for the formation of metal-carbonyl fragments during
the reactions of trinuclear carbonyls with alkynes; and for the
recondensation of fragments to give retrosynthesis to the
parent carbonyl.
We have also found an unprecedented example of isomerism
in the organic moiety linking open cluster complexes and we
have indirect evidence for the role of these complexes as pre-
cursors of bimetallic compounds. The bonding situation of
C(1)–O(1) in complexes 1a or 1b could also be considered a
model for the transfer of a terminal CO from a metal carbonyl
8 The ligand IPA is closely comparable with the ene-yne ligand
obtained upon coordination-dehydration of 2-methyl-3-butyn-2-ol,
1
HC᎐CC(Me) OH (MBO) on triruthenium clusters. This alcohol is
2
a commercial product which finds uses in organic syntheses. It
was an intermediate of the Reppe process starting from acetylene
and acetone and leading to isoprene in high yields [See for example:
R. J. Tedeschi, Acetylene-based Chemicals from Coal and other
Natural Resources, Marcel Dekker, New York, 1982 ].
3
12
9 Unless otherwise specified, the IR spectra were obtained in heptane
1
solution in the ν(CO) region and the H NMR spectra in CDCl
3
(
except for complex 1 when deuterated benzene was used) at room
temperature with TMS as internal standard.
1
0 Servizio di Spettrometria di Massa, Dipartimento di Scienza e
Tecnologia del Farmaco, Facoltà di Farmacia, Università di Torino.
11 E. Sappa, G. Predieri, A. Tiripicchio and F. Ugozzoli, Gazz. Chim.
Ital., 1995, 125, 51.
2 E. Sappa, J. Organomet. Chem., 1999, 573, 139.
3 R. Hourihane, G. Gray, T. Spalding and T. Deeney, J. Organomet.
Chem., 2000, 595, 191.
4 G. Gervasio, R. Gobetto, P. J. King, D. Marabello and E. Sappa,
Polyhedron, 1998, 17, 2937 and references therein.
15 O. Gambino, E. Sappa, A. M. Manotti Lanfredi and A. Tiripicchio,
1
1
23
fragment to an organic moiety. Complexes 1 could represent
1
“
molecular models” for the interaction between metals and
polymers (IPA and isoprene are closely related) or of corrosion
8
inhibitors. Last but not least, the behaviour of 1a in solution
Inorg. Chim. Acta, 1979, 36, 189.
1
6 E. Sappa, A. M. Manotti Lanfredi and A. Tiripicchio, Inorg. Chim.
Acta, 1978, 36, 197.
led us to think that it can act as an efficient chemical sensor for
chlorinated solvents.
1
7 (a) J. Meunier-Piret, P. Piret and M. van Meerssche, Acta
Crystallogr., 1965, 19, 85; (b) E. Sappa, L. Milone and G. D.
Andreetti, Inorg. Chim. Acta, 1975, 13, 67; (c) E. Sappa, D. Cauzzi,
G. Predieri, A. Tiripicchio and M. Tiripicchio Camellini,
J. Organomet. Chem., 1991, 412, C14; (d ) R. Giordano, E. Sappa,
D. Cauzzi, G. Predieri and A. Tiripicchio, J. Organomet. Chem.,
Acknowledgements
Financial support for this work was obtained, in part, from
MIUR (Rome) under the Cofin 2000 programme and, in part,
from INSTM (Florence).
1
996, 511, 263.
1
8 Carbonyl and cyclopentadienyl complexes of various metals (a)
K. Sunkel, J. Organomet. Chem., 1990, 391, 247; (b) R. J. P. Corriou
and J. J. E. Moreau, J. Chem. Soc., Chem. Commun., 1980, 278;
References and notes
(
c) F. A. Cotton, D. L. Hunter and J. M. Troup, Inorg. Chem., 1976,
1
(a) S. Deabate, P. J. King and E. Sappa, in Metal Clusters in
Chemistry, ed. P. Braunstein, L. A. Oro and P. R. Raithby, Wiley-
VCH, Weinheim, 1999, vol. 2, ch. 8, pp. 796–843; (b) E. Gatto,
G. Gervasio, D. Marabello and E. Sappa, J. Chem. Soc., Dalton
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15, 63; (d ) D. Osella, M. Botta, R. Gobetto, R. Amadelli and
V. Carassiti, J. Chem. Soc., Dalton Trans., 1988, 2519; (e) R. C.
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2
3
J. P. H. Charmant, P. Crawford, P. J. King, R. Quesada-Pato and
E. Sappa, J. Chem. Soc., Dalton Trans, 2000, 4390.
See for example: (a) R. Stragies, M. Schuster and S. Blechert, Chem.
Commun., 1999, 237; (b) J. P. Genet and M. Savignac, J. Organomet.
Chem., 1999, 576, 305.
See for example: (a) K. C. Nicolau, P. Maligres, J. Shin, E. de Leon
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Nicolau, G. Skokotas, S. Furuya, H. Suemune and D. C. Nicolau,
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W.-M. Day, J. Am. Chem. Soc., 1992, 114, 8908.
NLO = Non Linear Optics. See for example: (a) Materials for non-
linear optics: chemical perspectives, ed. S. R. Marder, J. E. Sohn
and G. D. Stucky, ACS Symp. Ser., Washington, DC, 1991, 455;
19 (a) R. S. Dickson and B. C. Greaves, Organometallics, 1993, 12,
3249; (b) J. L. Davidson, M. Green, F. G. A. Stone and A. J. Welch,
J. Chem. Soc., Dalton Trans., 1976, 2044; (c) L. A. Brady, A. F. Dyke,
S. E. Garner, S. A. R. Knox, A. Irving, S. M. Nicholls and A. G.
Orpen, J. Chem. Soc., Dalton Trans., 1993, 487; (d ) G. Gervasio,
E. Sappa and L. Marko, J. Organomet. Chem., 1993, 444, 203.
20 (a) J. Piron, P. Piret, J. Meunier-Piret and M. van Meerssche,
Bull. Soc. Chim. Belg., 1969, 78, 121; (b) P. Piret, J. Meunier-Piret,
M. van Meerssche and G. S. D. King, Acta Crystallogr., 1965, 19, 78;
(c) M. H. Carre and J. J. E. Moreau, Inorg. Chem., 1982, 21, 3099.
21 J. L. Davidson, M. Green, F. G. A. Stone and A. J. Welch, J. Chem.
Soc., Dalton Trans., 1976, 2044.
4
5
22 For example, the review: E. Sappa, A. Tiripicchio and P. Braunstein,
Chem. Rev., 1983, 83, 203 was written in the last century.
(
(
b) D. G. Williams, Angew. Chem., Int. Ed. Engl., 1984, 23, 690;
c) D. M. Burland, Chem. Rev., 1994, 94, 1; (d ) R. S. Marder,
23 See for example: (a) G. Predieri, A. Tiripicchio, M. Tiripicchio
Camellini, M. Costa and E. Sappa, Organometallics, 1990, 9, 1729;
G. Predieri, A. Tiripicchio, M. Tiripicchio Camellini, M. Costa
and E. Sappa, J. Organomet. Chem., 1992, 423, 129; (b) E. Boroni,
M. Costa, G. Predieri, E. Sappa and A. Tiripicchio, J. Chem. Soc.,
Dalton Trans., 1992, 2585; (c) S. Brait, G. Gervasio, D. Marabello
and E. Sappa, J. Chem. Soc., Dalton Trans., 2000, 989.
in Inorganic Materials, ed. D. W. Bruce and D. O’Hare, John
Wiley, Chichester, 1992, p. 136; (e) J. A. Bandy, H. B. Bunting,
M.-H. Garcia, M. L. H. Green, S. R. Marder, M. F. Thompson,
D. Bloor, P. V. Kolinsky, R. J. Jones and J. W. Perry, Polyhedron,
1
992, 11, 1429.
6
G. Gervasio and E. Sappa, J. Organomet. Chem., 1995, 498, 73.
1
454
J. Chem. Soc., Dalton Trans., 2002, 1448–1454