Mo-catalyzed cross-metathesis reaction of propynylferrocene

Article abstract of DOI:10.1002/ejic.200800128

Catalysts formed in situ from [Mo(CO)₆] and halophenols in dichloromethane efficiently promote cross metathesis reactions of (prop-1-yn-1-yl)ferrocene with various functionalized alkynes to give the corresponding alkynylferrocenes with good selectivity and yields. Optimization of the reaction conditions by changing the phenol component has been carried out, revealing a critical influence of the phenol structure on the reaction yield. The structures of selected compounds were determined by single-crystal X-ray diffraction, and the results (particularly the crystal packing) were correlated with DFT calculations. In addition, the series of alkynes 4-XC ₆H₄C≡CFc (Fc = ferrocenyl) differing by the substituent X was studied by electrochemical methods, manifesting a good correlation between the redox potential of the ferrocene/ ferrocenium couple and the Hammett σ_p constants of the remote substituents X. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800128

FULL PAPER
DOI: 10.1002/ejic.200800128
Mo-Catalyzed Cross-Metathesis Reaction of Propynylferrocene
[a]
[a][‡]
[a]
[b]
[b]
ˇ
ˇ
Petr Novák, Róbert Gyepes, Ivana Císarová,
Tomás Bobula, Jason Hudlický,
[b]
[a,c]
ˇ
ˇ
ˇ
Petr Stepnicka,* and Martin Kotora*
Keywords: Alkynes / Metallocenes / Metathesis / Electrochemistry / X-ray diffraction
Catalysts formed in situ from [Mo(CO)6] and halophenols in
dichloromethane efficiently promote cross metathesis reac-
tions of (prop-1-yn-1-yl)ferrocene with various functionalized
alkynes to give the corresponding alkynylferrocenes with
good selectivity and yields. Optimization of the reaction con-
ditions by changing the phenol component has been carried
out, revealing a critical influence of the phenol structure on
the reaction yield. The structures of selected compounds
were determined by single-crystal X-ray diffraction, and the
results (particularly the crystal packing) were correlated with
DFT calculations. In addition, the series of alkynes 4-
XC6H4CϵCFc (Fc = ferrocenyl) differing by the substituent X
was studied by electrochemical methods, manifesting a good
correlation between the redox potential of the ferrocene/
ferrocenium couple and the Hammett σp constants of the re-
mote substituents X.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
ral product synthesis,[3] polymer and macromolecular chem-
istry,[4] and in organometallic chemistry.[5]
Introduction
In the last ten years, the scientific community has wit-
nessed an enormous surge in the application of alkene me-
tathesis toward many different areas of chemistry, including
the synthesis of natural compounds and related substances,
polymer chemistry, as well as organometallic synthesis. This
development apparently reflects the ready availability of the
metathesis catalysts, versatility of the reaction, and its toler-
ance to a wide range of functional groups.[1] By contrast,
the analogous reaction involving alkynes (i.e., alkyne me-
tathesis) has been developed much less, mostly because its
application faces several problems, such as catalyst per-
formance, unfavorable reaction conditions, limited compati-
bility with functional groups, etc. Nonetheless, as these ob-
stacles are slowly but steadily eliminated, alkyne metathesis
gains importance as a useful synthetic method. Thus, al-
kyne metathesis[2] has become an indispensable tool in natu-
The catalytic systems used in alkyne metathesis can be
classified into two groups: (i) structurally undefined cata-
lysts formed “in situ” from of Mo[6] or W[7] carbonyls and
phenols, and (ii) catalysts based on defined molybdenum[8]
and tungsten[9] carbyne or molybdenum amide com-
plexes.[10] Although the former catalytic systems are gen-
erally less reactive, they attract attention because of their
simplicity. On the other hand, the unknown nature of the
catalytically active species makes their use rather unpredict-
able, which, in turn, initiated attempts at refinement of the
reaction conditions. It has been found that the reactivity
of the metal carbonyl/phenol system can be improved by
substituting resorcinol, used in the original Mortreux sys-
tem,[6] by phenols bearing electron-withdrawing groups.
Among them, the best results were achieved with halophen-
ols such as 4-chlorophenol,[11,12] 4-(trifluoromethyl)phe-
nol,[12] and 2-fluorophenol.[13] Other additives such as si-
lanes[14] or ethers[15] were studied as well.
[a] Department of Organic and Nuclear Chemistry and Centre for
New Antivirals and Antineoplastics, Faculty of Science, Charles
University,
Although it has been clearly demonstrated that the scope
of alkyne metathesis is very wide, its use in the synthesis of
alkynes bearing organometallic fragments, namely metall-
ocenyl groups, remains rather unexplored. So far, only three
Hlavova 8, 128 43 Praha 2, Czech Republic
Fax: +420-221-951-326
E-mail: kotora@natur.cuni.cz
[b] Department of Inorganic Chemistry, Faculty of Science, papers dealing with the homometathesis of metallocene al-
Charles University,
kynes have been published. The first two deal with the syn-
Hlavova 8, 128 43 Praha 2, Czech Republic
thesis of bis(ruthenocenyl)ethynes,[16] while the last one re-
E-mail: stepnic@natur.cuni.cz
ports the preparation of diferrocenylethyne.[17] In view of
[c] Institute of Organic Chemistry and Biochemistry, v.v.i., Acad-
emy of Sciences of the Czech Republic,
Flemingovo nám. 2, 166 10 Praha 6, Czech Republic
the foregoing discussion, it is rather surprising that alkyne
cross-metathesis has not yet been studied with metallocenyl-
alkynes, because it could potentially open a practical route
to new metallocene derivatives, complementary to cross-
coupling reactions.
[‡] Summer research participant. Current address: Ridley College,
P. O. Box 3013, 2 Ridley Rd., St. Catharines ON L2R 7C3,
Canada
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2008, 3911–3920
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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P. S teˇpnicˇka, M. Kotora et al.
FULL PAPER
Results and Discussion
Metathesis Reactions
Since it was shown that the [Mo(CO)6]/2-fluorophenol
system belongs to the most active “instant” catalysts,[13] we
decided to use it as a standard catalyst for the cross-alkyne
metathesis reaction of (prop-1-yn-1-yl)ferrocene (1). As the
second alkyne component, we chose a range of arylalkynes
bearing electron-donating and -withdrawing groups as well
as some alkyl-substituted derivatives. The metathesis of 1
with various alkynes 2 was carried out in the presence
[Mo(CO)6] (20 mol-%) and 2-fluorophenol (100 mol-%) in
toluene at 120–125 °C (Scheme 1) under argon in a closed
vial until complete consumption of the starting material
was achieved (usually 1–3 h). Despite the rather harsh reac-
tion conditions, the metathesis reaction proceeded well in
Scheme 1. Metathesis of 1-ferrocenylprop-1-yne (1) with alkynes 2
to give ferrocenylalkynes 3.
ynylferrocenes 3c and 3d in 63 and 59% yield, respectively.
Alkyne 2e bearing a COOMe group afforded 3e in 54%
yield, while somewhat lower yields (32 and 33%) were at-
tained with ferrocenylalkynes 3f and 3g bearing stronger
electron-withdrawing groups (CF3, CN).
all cases, affording the expected alkynylferrocenes
3
(Table 1) in good yields along with minor amounts of di-
ferrocenylethyne (4) and disubstituted ethynes as the self-
metathesis products (isolated in yields of 5–20%).
The reaction with electron-rich arylalkynes 2a and 2b
furnished the corresponding products 3a and 3b in good
isolated yields of 62 and 42%, respectively. Likewise, the Table 2. Influence of various phenols on the reaction of 1 with
alkynes 2e.
metathesis with propynylbenzene (2c) and 4-(prop-1-yn-1-
yl)-1,1Ј-biphenyl (2d) proceeded satisfactorily, giving alk-
Table 1. Metathesis of ferrocenylpropyne 1 with alkynes 2.
[a] For aqueous solutions. [b] Calculated values (ref.[13]), n.a.: not
available. [c] Isolated yields. [d] Ref.[18a] [e] Ref.[18b] [f] Ref.[18c] [g]
[a] Isolated yields.
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Ref.[18d]
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Eur. J. Inorg. Chem. 2008, 3911–3920

Mo-Catalyzed Cross-Metathesis Reaction of Propynylferrocene
The reaction with 2-octyne (2h) proceeded smoothly, giv-
In view of these results, we conclude that the ability of
ing rise to 3h in 64% yield. By contrast, the metathesis with the [Mo(CO)6]/phenol system to promote the metathesis re-
acetoxyalkyne 2i gave the corresponding product 3i in a action is compromised only partly with the acidity of the
rather low yield of 27%. Similar reactions with 2-(prop-1- phenol component. An alternative explanation of the dif-
yn-1-yl)pyridine and 2-(prop-1-yn-1-yl)thiophene were also ferent reactivities could be sought in other properties of the
checked, but the reaction did not take place. It is likely that 2- and 4-nitrophenols. For instance, it is known that 2- and
the high Lewis acidity of the heteroatoms either did not 4-nitrophenols can exist in tautomeric forms[19] and may
allow the formation of the catalytically active species or led thus form a catalytically inactive species upon the reaction
to its deactivation (e.g., by complexation of the Mo species). with [Mo(CO)6]. This, however, does not account for the
Recently, we[17] and Grela et al.[13] showed that a combi- inability of the 3-nitrophenol-based catalyst to promote the
nation of [Mo(CO)6] with other halogenated phenols could reaction.
promote the formation of the catalytically active species.
Additionally, it was suggested[13] that only phenols within a
Crystallography
certain acidity (pKa) range promote the formation of the
catalytically active species. To verify whether this assump-
To study the influence of the benzene-ring substituents
tion is applicable also in this instance, we determined the on the solid-state structure, we conducted single-crystal X-
catalytic activity of species resulting from a combination of ray diffraction analysis for all compounds that yielded crys-
[Mo(CO)6] and various phenols, using metathesis between tals of suitable quality. Although the structure of 3g has
1 and 2e as the model reaction (Table 2).
already been reported,[20] we repeated its structural analysis
It is worth mentioning that the reaction proceeded to to create a coherent data set with a minimal systematic bias
give the expected product 3e in good yields in all cases when due to dissimilar experimental conditions (e.g., tempera-
halogenated phenols were used (Table 2, Entries 1–3,5,6,9– ture). The molecular structures of 3b, 3e, 3f, and 3g are
11). Surprisingly, 4-fluorophenol (Entry 1), 2-chlorophenol shown in Figure 1, and geometric data are given in Table 3.
(Entry 5), 2,4,5-trichlorophenol (Entry 9), and pentafluoro-
The molecular geometries of 3b, 3e, 3f, and 3g compare
phenol (Entry 10) furnished better yields of 3e (63, 62, 60, favorably with those reported for other structurally charac-
and 80%) than that of the standard procedure[13] (Entry 3). terized alkynes FcCϵCAr, where Ar is an aryl group.[20,21]
Since the metathesis reaction took place even in the pres- An inspection of the data listed in Table 1 reveals only neg-
ence of more acidic phenols (Entries 9–11), it follows that ligible influence of the substituent at the aryl moiety on the
the assumption concerning the influence of phenol acid- geometric parameters. The minor differences observed are
ity[13] does not apply in this case. Catalytic systems based usually of no statistical significance and can be attributed
on 2- and 4-nitrophenol (Entries 7 and 8) did not promote to crystal packing effects. In all cases, the bonds connecting
the reaction, which is in agreement with the previous re- the alkyne moiety to the ferrocenyl and phenylene groups
ports.[13] Neither did the metathesis proceed with 3-ni- are noticeably shorter than the ordinary single bond be-
trophenol (Entry 4).
cause of extensive conjugation between the π systems.
Figure 1. PLATON plots of (a) 3b (molecule 1), (b) 3e, (c) 3g, and (d) 3f showing displacement ellipsoids at the 30% probability level.
The ring carbon atoms are labeled consecutively, and hence, only the labels for the pivotal atoms and the atoms adjacent to them are
shown to avoid complicating the figures. Atomic labels in molecule 2 of 3b are obtained by adding 20 to the respective atom labels in
molecule 1 [except for Fe(2)]. For 3g, only half of the molecule is structurally independent because of the imposed crystallographic
symmetry (mirror plane).
Eur. J. Inorg. Chem. 2008, 3911–3920
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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P. S teˇpnicˇka, M. Kotora et al.
FULL PAPER
Table 3. Selected geometric data for 3b, 3e, 3f, and 3g (in Å dividual molecules. The most important feature – common
and °).[a]
to all of the four compounds – is the generation of a long-
Parameter
3b
3b
3e[c]
3f[d]
3g[e]
range interaction between the substituted cyclopentadienyl
and phenylene rings. Should these two rings be (nearly) par-
allel, one of the acetylenic π systems is utilized as a media-
tor between the aromatic systems (Figure 2). Owing to this
conjugation, the σ-bonds adjacent to the triple bond gain
some surplus π character.
(mol. 1) (mol. 2)
Fe–Cg(1)
Fe–Cg(2)
ЄCp(1),Cp(2)
FcC–Cϵ
CϵC
C–CC6H4
FcC–CϵC
CϵC–C6H4
ЄCp1,Ph
1.647(2) 1.652(2) 1.644(1) 1.6424(8) 1.6419(8)
[b]
[b]
[b]
[b]
–
–
–
–
1.646(1) 1.6513(9) 1.645(1)
2.1(1) 0.2(1) 2.7(1)
1.432(4) 1.424(4) 1.427(3) 1.431(3) 1.435(2)
1.200(4) 1.204(4) 1.198(3) 1.197(3) 1.193(3)
1.436(4) 1.438(4) 1.436(3) 1.436(3) 1.437(3)
178.4(2) 177.2(3) 177.7(3) 179.3(2) 178.4(2)
176.7(2) 175.8(3) 177.2(2) 180.0(2) 176.7(2)
1.0(2)
7.3(2)
2.9(1)
90
69.6(1)
[a] The ring planes are defined as follows: Cp(1) = C(1–5), Cp(2)
= C(6–10), Ph = C(13–18). Cg(1) and Cg(2) are the centroids of
the cyclopentadienyl rings Cp(1) and Cp(2), respectively. [b] Not
reliable because of disorder of the unsubstituted cyclopentadienyl
ring (see Experimental Section). [c] Further data: C(19)–O(1)
1.208(3), C(19)–O(2) 1.338(3), C(20)–O(2) 1.445(3), O(1)–C(19)–
O(2) 123.4(2). [d] Further data: C(15)–F(1) 1.336(2), C(15)–F(2)
1.291(4), F(1)–C(15)–F(2) 107.6(2), F(1)–C(15)–F(1#) 102.5(2), #
= x, 3/2 – y, z. [e] Further data: C(19)–N 1.147(3), C(16)–C(19)–N
179.3(2).
Figure 2. Orbital 77 of 3e shown at the 5% probability level.
The conjugation depicted above involves the partially
antibonding (though still occupied) orbitals on the con-
nected aromatic rings. Although the fully bonding π orbit-
als of both rings are also properly shaped to generate an
analogous interaction, no significant mixing with the al-
kyne orbitals occurs because of the large energy separation
between them (Figure 3).
A notable difference can be seen in the mutual orienta-
tion of the phenylene and ferrocene moieties. Whereas the
benzene rings in 3b and 3e deviate only slightly from the
plane of their parent Cp(1) ring, those in 3g and 3f are
mutually rotated by as much as 69.6(1)° and 90°, respec-
tively. This, however, may reflect the presence of two mutu-
ally perpendicular π systems at the triple bond that are
available for conjugation and would ideally give rise to two
extreme, fully conjugated conformations having the aro-
matic rings either parallel with the Cp ring or rotated by
90°.
Figure 3. Orbital 64 of 3e (5% probability) represents the practi-
cally unchanged (originally a1) orbital of the ferrocene unit.
Compound 3b crystallizes with the triclinic space group
P1 and has two molecules in the asymmetric unit. The re-
Since orbital 77 is generated by an attractive interaction
in the C5H4CϵCC6H4 system, two corresponding partially
bonding/antibonding orbitals and one fully antibonding
(virtual) orbital are also formed (Figure 4).
¯
maining alkynes crystallize in monoclinic space groups,
though with different symmetry. Whereas 3g and 3e form
centrosymmetric crystal lattices, compound 3f is chiral
(space group P21). The molecule of 3f resides on the crystal-
lographic mirror plane so that the plane accommodates the
benzene ring and the triple bond, and bisects the ferrocene
and CF3 units. A striking feature of the crystal assemblies
is that the polar moieties (where present) do not exert any
significant intermolecular contacts. The individual mole-
cules of 3b and 3e associate predominantly through π···π
stacking interactions[22] of their benzene rings with
centroid···centroid distances close to the interplanar separa-
tion in α-graphite[23] and, additionally, through C–H···π in-
teractions. On the other hand, 3e and 3g seem to form es-
sentially molecular crystals, though with appropriately as-
sembled molecular dipoles. In order to gain more insight
into the role of the terminal substituents in the crystal as-
semblies, we have studied the electronic structure of the al-
kynes by computational methods.
Figure 4. Orbitals 79 (top left), 86 (top right) and 90 (bottom) of
3e (all at the 2% probability level). The two partially bonding/anti-
bonding 79 and 86 and the completely antibonding 90 are partners
to orbital 77; orbital 90 is the LUMO.
The stabilization in the solid state was examined for the
molecular pair 3e···3e at positions obtained from X-ray dif-
fraction analysis. Since the electrostatic potential did not
Theoretical Calculations
The differences in the solid state arrangements can be justify a dominant role of electrostatic interactions for
explained already by examining the bonding relations in in- 3e···3e (see below), an alternative model based on covalent
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Eur. J. Inorg. Chem. 2008, 3911–3920

Mo-Catalyzed Cross-Metathesis Reaction of Propynylferrocene
stabilization was adopted. The only significant attractive nificant electrostatic minima. Likewise, the most negative
intermolecular interaction was found in orbital 161 of the values of the electrostatic potential for 3e are found on the
dimer (Figure 5).
carboxylic oxygen atoms (lone pairs).
Electrochemistry
Having the series of (arylethynyl)ferrocenes 3a–3g in
hand, we decided to study their electrochemical behavior by
cyclic and differential pulse voltammetry at a platinum disc
electrode in dichloromethane. A representative cyclic vol-
tammogram is shown in Figure 8, and the potentials are
given in Table 4.
Figure 5. Orbital 161 of the 3e···3e dimer (2% probability level).
As it is evident from the orbital shape, the intermolecular
π···π interaction is affected by the second (originally degen-
erate) benzene orbital. Although the best overlap of such
orbitals would occur without any shift, the encountered lat-
eral displacement is a compromise between π···π attractive
and repulsive interactions of several π-like molecular orbit-
als, in accordance with the dipolar model proposed by
Hunter and Sanders.[24]
The rotation of the phenylene ring by 90° must clearly
pick a different mechanism for the conjugation to be
achieved. Alternatively, the perpendicular arrangement (ob-
served for 3f and 3g) makes use of the conjugation via both
acetylenic π systems, as demonstrated by orbitals 80 and 81
for 3f (Figure 6). The partially antibonding counterparts of
these orbitals are depicted in Figure 7.
Figure 8. Cyclic voltammogram of 3d as recorded in CH2Cl2 solu-
tion at a Pt-disc electrode and 0.1 Vs–1 scan rate. The potential
scale is referenced to the ferrocene/ferrocenium couple.
Table 4. Summary of the electrochemical data.[a]
Figure 6. Orbitals 80 (left) and 81 (right) for 3f (5% probability
level) responsible for conjugation of the perpendicular aromatic
rings.
Ferrocene 3
R
E°Ј [V]
σp(R)[b]
3a
3b
3c
3d
3e
3f
OMe
Me
H
+0.090
+0.100
+0.115
+0.115
+0.145
+0.150
+0.160
–0.28
–0.14
0
+0.02
+0.44
+0.53
+0.71
Ph
COOMe
CF3
CN
3g
[a] Recorded in CH2Cl2 at a Pt disc electrode. The potentials are
given relative to the ferrocene/ferrocenium reference. E°Ј was calcu-
lated as the mean of the anodic and cathodic peak potentials in
cyclic voltammetry: E°Ј = ½ (Epa + Epc). [b] The σp-constants were
taken from ref.[25]
Figure 7. Orbitals 86 (left) and 87 (right; both at 5% probability
level) for 3f.
In contrast to the parallel arrangement, the perpendicu-
lar setting offers some additional stabilization, since the in-
The redox properties of the alkynes are very similar, and
teraction between the phenylene ring and the CϵC bridge the voltammograms show single reversible oxidation attrib-
lacks any substantial antibonding interaction with the fer- utable to the ferrocene/ferrocenium couple. In all cases, the
rocene unit (cf. orbitals 79 and 86 in Figure 4). Conse- redox wave occurs at a more positive value than that for
quently, the originally e1g benzene orbitals decrease in en- unsubstituted ferrocene, which corresponds with the elec-
ergy and are less prone to enter intermolecular interactions. tron-withdrawing nature of the phenylethynyl group (σp =
Lacking any significant π···π stacking interactions, the 0.16).[25] However, the exact position of the wave changes
crystal assemblies of 3f and 3g are governed predominantly with the substituent at the phenyl ring. As evidenced by
by dipolar interactions. The electrostatic potential, which is the data in Table 2, the electron-donating groups make the
most negative at the terminal electron-withdrawing groups, oxidation easier, while the electron-withdrawing groups in-
supports this assumption. By contrast, the molecule of 3b crease the redox potential. This trend can be better illus-
forming π···π stacked aggregates does not exhibit any sig- trated by the linear free-energy correlation between the po-
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P. S teˇpnicˇka, M. Kotora et al.
FULL PAPER
wave vials and Schlenk techniques. Catalysts, phenols, toluene, and
the other reagents used were obtained from commercial suppliers
(Aldrich or Fluka) and were used without further purification.
Dichloromethane and chloroform were dried with CaH2 and dis-
tilled under argon before use. NMR spectra were recorded with a
Varian UNITY 300 INOVA or Varian UNITY 400 INOVA instru-
ment at 300 or 400 MHz (1H) and 75 or 100 MHz (13C) as solutions
in C6D6 and are referenced to the residual solvent signal. Infrared
spectra were recorded with a Bruker IFS 55 instrument with the
ATR technique. HR mass spectra were recorded with a ZAB-SEQ
(VG Analytical) spectrometer by using EI. Melting points (uncor-
rected) were determined with a Kofler apparatus. TLC was per-
formed on silica gel 60 F254-coated aluminum sheets (Merck). Col-
umn chromatography was performed on a preparative silica gel
(63–200 µm) column. Electrochemical measurements were carried
out with a computer-controlled multipurpose polarograph µAU-
TOLAB III (Eco Chemie, Netherlands) at room temperature by
using a standard three-electrode cell with a rotating platinum disc
electrode (AUTOLAB RDE, 3 mm diameter) as the working elec-
trode, a platinum sheet auxiliary electrode, and a Ag/AgCl (3 
KCl) reference electrode. The compounds were dissolved in dichlo-
romethane (Fluka, absolute, declared H2O content Ͻ0.005%) to
give a solution containing 1 m of the analyte and 0.1  Bu4NPF6
(Fluka, purissimum for electrochemistry). The solutions were de-
aerated with argon prior to the measurement and then kept under
an argon blanket. The redox potentials are given relative to the
ferrocene/ferrocenium reference, which was recorded before and af-
ter each measurement.
tential of the ferrocene/ferrocenium oxidation and Ham-
mett σp constants of the substituents (Figure 9). Although
the absolute difference of the redox potentials is only
70 mV, their good correlation with σp indicates that the
phenylethynyl moiety efficiently conveys the electronic in-
fluence of the remote modifying group, which corresponds
with the observations made in the series of phenyl-[26,27] and
(2-phenylethenyl)-substituted[27,28] ferrocenes.
Figure 9. Linear free-energy relationship (LFER) between the re-
dox potential of the ferrocene/ferrocene oxidation of 3a–3g and the
Starting Materials: The synthesis of 1-ferrocenylprop-1-yne (1) and
diferrocenylethyne (4) were performed according to the previously
reported methods, and their spectral characteristics were in agree-
ment with previously reported data.[17] 1-Methoxy-4-(1-propyn-1-
yl)benzene (2a), 1-methyl-4-(1-propyn-1-yl)benzene (2b), methyl 4-
(1-propyn-1-yl) benzoate (2e), 1-(1-propyn-1-yl)-4-(trifluorometh-
yl)benzene (2f), 4-(1-propyn-1-yl)benzonitrile (2g), 2-(prop-1-yn-1-
yl)pyridine (2j), 2-(prop-1-yn-1-yl)thiophene (2k), and 3-(prop-1-
yn-1-yl)furan (2l) were prepared by Sonogashira coupling of the
corresponding aryl halides with propyne.[29] 4-(Prop-1-yn-1-yl)bi-
phenyl (2d) was prepared by lithiation of commercial 4-(ethynyl)-
biphenyl with nBuLi followed by reaction with MeI in analogy to
the synthesis of 1. Pent-3-yn-1-yl acetate (2i) was prepared by reac-
tion of pent-3-en-1-ol with acetyl chloride and Et3N in dichloro-
methane.
Hammett σp constants. Parameters of the fit: E°Ј = 0.071(3) σp
+
0.112(1), R2 = 0.993.
Conclusions
We have demonstrated that the cross metathesis of (prop-
1-yn-1-yl)ferrocene with alkynes in the presence of a simple
catalytic system comprising [Mo(CO)6] and halophenols
(modified Mortreux system) offers an alternative synthetic
approach to substituted alkynylferrocenes. The reaction
proceeds well with both aryl- and alkylpropynes to give the
corresponding products in good yields and in reasonable
selectivities, tolerating many functional substituents. In ad-
dition, the study showed that the metathesis reaction takes
place with a wide array of halophenols with pKA values in
the range 4.9–9.9, which clearly indicates that the course of
the reaction does not depend strictly on the acidity of the
phenol OH group.
Structural data collected for the representative arylferro-
cenylalkynes, in conjunction with the results of DFT calcu-
lations, suggest extensive conjugation of the present π sys-
tems. This observation is in line with electrochemical data
for 4-XC6H4CϵCFc, indicating a good electronic com-
munication between the ferrocene unit and the remote mod-
ifying group R.
General Procedure for Mo-Catalyzed Metathesis of 1-Ferrocenyl-
prop-1-yne: Reactions were performed under an argon atmosphere
in dried microwave vials. To a solution of 1-ferrocenylprop-1-yne
(1) (112 mg, 0.5 mmol) in dry toluene (3 mL) was added [Mo(CO)
6] (13.2 mg, 0.05 mmol), 2-fluorophenol (56 mg, 45 µL, 1 mmol),
and the appropriate propynyl derivative (1 mmol). The reaction
mixture was heated to 120–130 °C until no further progress of the
reaction was observed (2–24 h). The course of the reaction was
monitored by TLC. The reaction mixture was then quenched with
NaOH (1 ), and washed with dichloromethane (3ϫ50 mL). The
combined organic fractions were washed with water (50 mL), brine
(50 mL), and dried with MgSO4. The volatiles were removed under
reduced pressure and column chromatography of the residue on
silica gel (hexane/chloroform) afforded the products.
[(4-Methoxyphenyl)ethynyl]ferrocene (3a): 1-Methoxy-4-(1-propyn-
1-yl)benzene (2a) (146 mg, 1 mmol); reaction time 5 h. Column
chromatography (5:1 hexane/CHCl3) afforded 98 mg (62%) of the
title compound as an orange solid: m.p. 124–125 °C (EtOH). 1H
NMR (400 MHz, C6D6): δ = 3.18 (s, 3 H), 3.93–3.96 (m, 2 H), 4.11
Experimental Section
General Comments: Mo-catalyzed reactions were performed under
an atmosphere of dry argon by using vacuum-line, standard micro-
3916
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3911–3920

Mo-Catalyzed Cross-Metathesis Reaction of Propynylferrocene
(s, 5 H), 4.48–4.51 (m, 2 H), 6.57–6.62 (m, 2 H), 7.47–7.52 (m, 2 126.1 (2 C), 126.3 (2 C), 132.4 ppm. IR (neat): ν = 3097, 3076,
˜
H) ppm. 13C NMR (100 MHz, C6D6): δ = 55.4, 67.3, 69.7 (2 C),
71.0 (5 C), 72.4 (2 C), 87.2, 88.1, 115.1 (2 C), 117.4 133.8 (2 C),
2956, 2920, 2851, 2226, 1933, 1733, 1616, 1464, 1401, 1323, 1171,
1108, 1072, 1012, 848, 824, 743 cm–1. HRMS (m/z): calcd. for
C19H13F3Fe 354.03188; found 354.03101. Rf (25:1 hexane/CHCl3)
160.4 ppm. IR (neat): ν = 3097, 2992, 2959, 2923, 2830, 1901, 1607,
˜
1515, 1258, 1105, 1027, 830 cm–1. UV/Vis (hexane): λmax (ε, = 0.54.

–1 cm–1) = 446 (2926) nm. HRMS (m/z): calcd. for C19H16FeO
[(4-Cyanophenyl)ethynyl]ferrocene (3g): 4-(1-Propyn-1-yl)benzoni-
trile (2g) (141 mg, 1 mmol); reaction time 4 h. Column chromatog-
raphy (5:1 hexane/CHCl3) afforded 52 mg (33%) of the title com-
pound as orange needles; m.p.: 171–172 °C (EtOH). 1H NMR
(400 MHz, C6D6): δ = 3.92–3.99 (m, 2 H), 4.05 (s, 5 H), 4.40–4.48
(m, 2 H), 6.78 (d, J = 8.0 Hz, 2 H), 7.03–7.07 (m, 2 H) ppm. 13C
NMR (100 MHz, C6D6): δ = 65.1, 70.4 (2 C), 71.1 (5 C), 72.7 (2
C), 85.9, 94.7, 112.0, 119.2, 129.2, 132.3 (2 C), 132.7 (2 C) ppm.
316.05506; found 316.05482. C19H16OFe (316.17): calcd. C 72.17,
H 5.10; found C 72.04, H 5.20. Rf (5:1 hexane/CHCl3) = 0.28.
[(4-Methylphenyl)ethynyl]ferrocene (3b): 1-Methyl-4-(1-propyn-1-
yl)benzene (2b) (130 mg, 1 mmol); reaction time 3 h. Column
chromatography (5:1 hexane/CHCl3) afforded 63 mg (42%) of the
1
title compound as a red needles: m.p. 95–97 °C (EtOH). H NMR
(300 MHz, C6D6): δ = 1.98 (s, 3 H), 3.92–3.96 (m, 2 H), 4.09 (s, 5
H), 4.46–4.50 (m, 2 H), 6.80–6.85 (m, 2 H), 7.46–7.52 (m, 2 H)
ppm. 13C NMR (75 MHz, C6D6): δ = 21.9, 66.7, 69.8 (2 C), 70.9
(5 C), 72.5 (2 C), 89.0, 122.4, 130.1 (2 C), 132.4 (2 C), 138.4 ppm.
IR (neat): ν = 3097, 2953, 2923, 2851, 2220, 2199, 1936, 1598, 1502,
˜
1407, 1270, 1159, 1102, 1003, 845 cm–1. UV/Vis (hexane): λmax (ε,

–1 cm–1) = 450 (2695) nm. HRMS (m/z): calcd. for C19H13FeN
IR (neat): ν = 2956, 2920, 2848, 1515, 1461, 1410, 1374, 1260, 1186,
˜
311.03974; found 311.04053. C19H13FeN (311.17): calcd. C 73.33,
H 4.21, N 4.50; found C 72.68, H 4.36, N 4.03. Rf (5:1 hexane/
CHCl3) = 0.22.
1105, 1024, 923, 815, 680 cm–1. UV/Vis (hexane): λmax (ε, –1 cm–1)
= 450 (1143) nm. HRMS (m/z): calcd. for C19H16Fe 300.06014;
found 300.06050. C19H16Fe (300.18): calcd. C 76.05, H 5.35; found
C 76.28, H 5.51. Rf (5:1 hexane/CHCl3) = 0.18.
(2-Heptyn-1-yl)ferrocene (3h): Oct-2-yne (2h) (110 mg, 1 mmol), re-
action time 5 h. Column chromatography (6:1 hexane/CHCl3) af-
forded 94 mg (64%) of the title compound as a dark brown oil. 1H
NMR (400 MHz, C6D6): δ = 0.81 (t, J = 7.2 Hz, 3 H), 1.17 (q, J
= 7.2 Hz, 2 H), 1.26–1.38 (m, 2 H), 1.43 (kv, J = 6.6 Hz, 2 H), 2.18
(t, J = 6.9 Hz, 2 H), 3.88–3.91 (m, 2 H), 4.10 (s, 5 H), 4.40–4.42
(m, 2 H) ppm. 13C NMR (100 MHz, C6D6): δ = 14.8, 20.6, 23.2,
(Phenylethynyl)ferrocene (3c): (1-Propyn-1-yl)benzene (2c) (116 mg,
1 mmol), reaction time 5 h. Column chromatography (5:1 hexane/
CHCl3) afforded 90 mg (63%) of the title compound as a red solid.
UV/Vis (hexane): λmax (ε, –1 cm–1) = 464 (3737) nm. The spectro-
scopic data were in agreement with the previously reported ones.[30]
[(1,1Ј-Biphenyl-4-yl)ethynyl]ferrocene (3d): 4-(Prop-1-yn-1-yl)-1,1Ј- 29.7, 32.1, 68.2, 69.2 (2 C), 70.8 (5 C), 72.3 (2 C), 79.7, 87.3 ppm.
biphenyl (2d) (192 mg, 1 mmol), reaction time 4 h. Column
IR (neat): ν = 3097, 2956, 2926, 2857, 1712, 1464, 1258, 1204, 1108,
˜
chromatography (9:1 hexane/CHCl3) afforded 107 mg (59%) of the
1057, 1024, 1000, 821, 728 cm–1. HRMS: m/z calcd. for C17H20Fe
title compound as an orange solid: m.p. 143–144 °C (EtOH). 1H 280.09144; found 280.09175. Rf (6:1 hexane/CHCl3) = 0.24.
NMR (400 MHz, C6D6): δ = 3.94–3.98 (m, 2 H), 4.11 (s, 5 H),
4-(Ferrocenyl)but-3-yn-1-yl Acetate (3i): Pent-3-yn-1-yl acetate (2i)
4.50–4.54 (m, 2 H), 7.10–7.22 (m, 4 H), 7.28–7.39 (m, J = Hz, 4
(126 mg, 1 mmol), reaction time 10 h. Column chromatography
H) 7.57–7.64 (m, 1 H) ppm. 13C NMR (100 MHz, C6D6): δ = 66.7,
(5:1 hexane/CHCl3) afforded 40 mg (27%) of the title compound
69.9 (2 C), 71.0 (5 C), 72.5 (2 C), 87.2, 90.6, 124.2, 128.0 (2 C),
as a dark red oil. 1H NMR (400 MHz, C6D6): δ = 1.65 (s, 3 H),
128.1, 128.2 (2 C), 129.7 (2 C), 132.8 (2 C), 133.1, 141.44 ppm. IR
2.35 (t, J = 5.1 Hz, 2 H), 3.87–3.90 (m, 2 H), 4.03–4.08 (m, 2 H)
(neat): ν = 3097, 3025, 2956, 2923, 2851, 2223, 1909, 1488, 1446,
˜
(overlapping with the OCH2 signal), 4.07 (s, 5 H), 4.35–4.39 (m, 2
1407, 1105, 1006, 842, 767, 704 cm–1. UV/Vis (hexane): λmax (ε,
H) ppm. 13C NMR (100 MHz, C6D6): δ = 21.0, 68.1, 69.3 (2 C),

–1 cm–1) = 450 (4143) nm. HRMS (m/z): calcd. for C24H18Fe
70.9 (5 C), 72.4 (2 C), 81.1, 82.1, 170.5 ppm. IR (neat): ν = 3096,
˜
362.07579; found 362.07510. C24H18Fe (362.24): calcd. C 79.60, H
4.98; found C 79.24, H 5.20. Rf (9:1 hexane/CHCl3) = 0.28.
2961, 2924, 2851, 2233, 1741, 1727, 1459, 1383, 1363, 1239, 1039,
1003, 817 cm–1. HRMS (m/z): calcd. for C16H16FeO2 296.04997;
found 296.05010. Rf (5:1 hexane/CHCl3) = 0.20.
Methyl 4-[(Ferrocenyl)ethynyl] Benzoate (3e): Methyl 4-(1-propyn-
1-yl) benzoate (2e) (174 mg, 1 mmol), reaction time 5 h. Column
chromatography (5:1 hexane/CHCl3) afforded 93 mg (54%) of the
title compound as an orange solid: m.p. 154–155 °C (EtOH). 1H
NMR (400 MHz, C6D6): δ = 3.45 (s, 3 H), 3.93–3.97 (m, 2 H), 4.07
(s, 5 H), 4.45–4.48 (m, 2 H), 7.39–7.45 (m, 2 H), 7.94–7.99 (m, 2
H) ppm. 13C NMR (100 MHz, C6D6): δ = 52.3, 65.8, 70.2 (2 C),
71.0 (5 C), 72.6 (2 C), 86.7, 93.3, 129.7, 130.3 (2 C), 132.2 (2 C),
General Procedure for Cross-Metathesis of 1 with 2e in the Presence
of Various Phenols: To a solution of 1 (56 mg, 0.25 mmol) in dry
toluene (3 mL) was added [Mo(CO)6] (6.6 mg, 0.025 mmol), phenol
(0.25 mmol), and 2e (87 mg, 0.5 mmol). The reaction mixture was
heated to 130 °C for 8 h and then quenched with NaOH (2 ) and
washed with dichloromethane (2ϫ20 mL). The combined organic
fractions were washed with H2O (50 mL), brine (50 mL), and dried
with MgSO4. The volatiles were removed under reduced pressure
and column chromatography of the residue on silica gel (4:1 hex-
ane/chloroform) afforded 3e.
166.8 ppm. IR (neat): ν = 3085, 3016, 2950, 2206, 1936, 1724, 1604,
˜
1431, 1404, 1273, 1108, 962, 926, 830, 767, 695 cm–1. UV/Vis (hex-
ane): λmax (ε, –1 cm–1) = 450 (2868) nm. HRMS (m/z): calcd. for
C20H16FeO2 344.04997; found 344.04951. C20H16O2Fe (344.18)
calcd. C 69.79, H 4.69, found C 69.31, H 4.49. Rf (5:1 hexane/
CHCl3) = 0.50.
1. Reaction in the Presence of 4-Fluorophenol: 4-Fluorophenol
(28 mg, 0.25 mmol). Chromatography afforded 54 mg (63%) of 3e,
5 mg (6%) of 1, and 7 mg (7%) of 2.
{[4-(Trifluoromethyl)phenyl]ethynyl}ferrocene (3f): 1-(1-Propyn-1-
yl)-4-(trifluoromethyl)benzene (2f) (184 mg, 1 mmol); reaction time
7 h. Column chromatography (25:1 hexane/CHCl3) afforded 57 mg
(32%) of the title compound as an orange solid: m.p. 127–128 °C
2. Reaction in the Presence of 4-Chlorophenol: 4-Chlorophenol
(32 mg, 0.25 mmol). Chromatography afforded 42 mg (49%) of 3e
and 4 mg (5%) of 2.
1
(EtOH). H NMR (300 MHz, C6D6): δ = 3.93–3.97 (m, 2 H), 4.07
(s, 5 H), 4.44–4.48 (m, 2 H), 7.11–7.18 (m, 2 H) overlapping with
the C6D6 signal, 7.24–7.31 (m, 2 H) ppm. 13C NMR (75 MHz,
C6D6): δ = 30.9, 65.5, 70.3 (2 C), 71.1 (5 C), 72.7 (2 C), 85.9, 92.8,
3. Reaction in the Presence of 2-Fluorophenol: 2-Fluorophenol
(28 mg, 45 µL, 0.25 mmol). Chromatography afforded 47 mg (54%)
of 3e, 3 mg (3%) of 1, and 6 mg (6%) of 2.
Eur. J. Inorg. Chem. 2008, 3911–3920
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3917

ˇ
P. S teˇpnicˇka, M. Kotora et al.
FULL PAPER
4. Reaction in the Presence of 3-Nitrophenol: 3-Nitrophenol (35 mg,
0.25 mmol). Formation of 3e and 2 was not observed. The starting
material remained unchanged.
analyzed with the HKL program package.[31] The data for 3e and
3g were corrected for absorption. The ranges of the transmission
factors are given in Table 5.
The structures were solved by direct methods (SIR97[32]) and re-
fined by the full-matrix least-squares procedure on F2
(SHELXL97[33]). The unsubstituted cyclopentadienyl in both struc-
turally independent molecules of 3b are disordered and were mod-
eled as if contributed by two orientations. The components were
refined independently with isotropic displacement parameters,
which led to fractional occupancies of ca. 28:72. All other non-
hydrogen atoms were refined with anisotropic displacement param-
eters. The hydrogen atoms were included in the calculated positions
and refined as riding atoms. Relevant crystallographic data are
given in Table 5. Geometric parameters and structural drawings
were obtained by using a recent version of the Platon program.[34]
5. Reaction in the Presence of 2-Chlorophenol: 2-Chlorophenol
(32 mg, 26 µL, 0.25 mmol). Chromatography afforded 53 mg (62%)
of 3e, 3 mg (4%) of 1, and 6 mg (8%) of 2.
6. Reaction in the Presence of 2,4-Dichlorophenol: 2,4-Dichlorophe-
nol (40 mg, 0.25 mmol). Chromatography afforded 42 mg (48%) of
3e and 5 mg (6%) of 1.
7. Reaction in the Presence of 2-Nitrophenol: 2-Nitrophenol (35 mg,
0.25 mmol). Formation of 3e and 2 was not observed. The starting
material remained unchanged.
8. Reaction in the Presence of 4-Nitrophenol: 4-Nitrophenol (35 mg,
0.25 mmol). Formation of 3e and 2 was not observed. The starting
material remained unchanged.
CCDC-667781 (3b), -667782 (3e), -667783 (3g), and -667784 (3f)
contain the supplementary 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_requ-
est/cif.
9. Reaction in the Presence of 2,4,5-Trichlorophenol: 2,4,5-Tri-
chlorophenol (52 mg, 0.25 mmol). Chromatography afforded 42 mg
(48%) of 3e and 3 mg (3%) of 2.
10. Reaction in the Presence of 2,3,4,5,6-Pentafluorophenol:
2,3,4,5,6-Pentafluorophenol (46 mg, 0.25 mmol). Chromatography
afforded 69 mg (80%) of 3e and 5 mg (6%) of 2.
Computational Details: Computational studies have been per-
formed on the Bohr Cluster located at the J. Heyrovský Institute
of Physical Chemistry, Academy of Sciences of the Czech Republic,
by using Gaussian 03, Revision C.02.[35] DFT results were obtained
by carrying out spin-restricted calculations by utilizing Becke’s
1988 exchange functional[36] and the Perdew-Wang 91 gradient-cor-
11. Reaction in the Presence of 2,3,4,5,6-Pentachlorophenol:
2,3,4,5,6-Pentachlorophenol (66 mg, 0.25 mmol). Chromatography
afforded 39 mg (45%) of 3e and 9 mg (3%) of 2.
X-ray Crystallography: All crystals used for single-crystal X-ray rected correlation functional[37] (BPW91). The numerical integra-
diffraction analysis were grown from ethanol (3b: orange plate,
0.05ϫ0.16ϫ0.30 mm3, 3e: red plate, 0.04ϫ0.50ϫ0.58 mm3, 3g:
orange needle, 0.12ϫ0.12ϫ0.50 mm3, 3f: orange block,
0.35ϫ0.45ϫ0.60 mm3). Full-set diffraction data (ϮhϮkϮl, 2θ Յ
tion grid consisted of a pruned grid with 99 radial shells each with
590 angular points. Calculations utilized the Douglas–Kroll–Hess
2nd order scalar relativistic Hamiltonian[38] and the 6-311++G(d,p)
basis set employed for all atoms. All input geometries were those
54–55°) were collected with a Nonius KappaCCD diffractometer obtained from the diffraction experiments; their computational op-
equipped with a Cryostream Cooler (Oxford Cryosystems) using
graphite monochromatized Mo-Kα radiation (λ = 0.71073 Å) and
timization was not attempted. Orbital numberings are given ac-
cording to their increasing energy. Natural Bonding Analysis
Table 5. Crystallographic and collection data and structure refinement parameters for 3b, 3e, 3g, and 3f.[a]
Compound
3b
3e
3g
3f
Formula
C19H16Fe
300.17
C20H16FeO2
344.18
C19H13FeN
311.15
C19H13F3Fe
354.14
M [gmol–1]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
triclinic
P1 (no. 2)
monoclinic
P21/c (no. 14)
7.4731(2)
18.5749(4)
11.4966(3)
monoclinic
P21 (no. 4)[g]
9.6748(4)
7.3107(2)
10.1676(4)
monoclinic
P21/m (no. 11)
7.6412(2)
8.7141(2)
11.5452(3)
¯
7.5552(2)
10.8247(4)
17.7486(5)
80.192(2)
79.539(2)
89.744(2)
1406.02(8)
4
1.418
1.058
22106
6180/4693
2.18
108.077(1)
98.704(2)
97.432(2)
γ [°]
V [Å3]
1517.10(7)
4
710.87(4)
2
762.29(3)
2
1.543
1.016
11780
3472/3315
2.6
3.10
3.21, 8.05
0.66, –0.52
Z
Dcalcd. [gmL–1]
µ(Mo-Kα) [mm–1]
Diffractions total
Unique/obsd.[b] diffractions
Rint [%][c]
1.507
1.454
1.001[f]
21754
1.051[h]
11825
3339/2893
4.62
3.64
3262/3066
4.25
2.34
2.73, 5.26
0.22, –0.31
[b,d]
R (observed data) [%]
5.15
R, wR (all data) [%][d]
7.08, 13.7
4.42, 9.59
∆ρ [eÅ–3]
1.80,[e] –0.50
1.67,[e] –0.33
2
[a] Common details: T = 150(2) K. [b] Diffractions with Io Ͼ 2σ(Io). [c] Rint = Σ|Fo – Fo2(mean)|/ΣFo2, where Fo2(mean) is the average
2
2 2
intensity of symmetry-equivalent diffractions. [d] R = Σ||Fo| – |Fc||/Σ|Fo|, wR = [Σ{w(Fo – Fc ) }/Σ w(Fo2)2]1/2. [e] The residual electron
density probably reflects the crystal shape (thin plates) and possible defects due to layered structure. [f] The range of transmission
coefficients: 0.787–0.970. [g] Flack’s parameter = 0.03(1). [h] The range of transmission coefficients: 0.682–0.899.
3918
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3911–3920

Mo-Catalyzed Cross-Metathesis Reaction of Propynylferrocene
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Natural Bond Analysis[39] program integrated in Gaussian. Con-
tour diagrams of the molecular orbitals were obtained with
Molden.[40]
Supporting Information (see footnote on the first page of this arti-
cle): Calculated orbital energies and orbital diagrams for 3b and
3e–g and spectroscopic data for all prepared compounds.
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Received: February 1, 2008
Published Online: April 11, 2008
3920
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3911–3920