Asymmetric Ethynes. Syntheses of Ethynylferrocene Paradigms

Article abstract of DOI:10.1515/znb-1996-1204

Synthetic methods to bifunctional ethynes have been examined. Direct ethynylation, the Stephens-Castro reaction, the Pd-catalysed Hagihara coupling, transmetalation reactions and nucleophilic additions have been evaluated in the preparation of substituted

Full text of DOI:10.1515/znb-1996-1204

Asymmetrie Ethynes. Syntheses of Ethynylferrocene Paradigms
Johann Polin2, Herwig Schottenbergerb, Karl Eberhard Schwarzhansb *
a Dipartimento di Chimica "G. Ciamician", Universitä degli Studi di Bologna,
Via Selmi 2, 1-40126 Bologna, Italy
b Institut für Allgemeine, Anorganische und Theoretische Chemie, Universität Innsbruck,
Innrain 52a, A-6020 Innsbruck, Austria
Dedicated to Prof. Dr. H. P. Fritz
Z. Naturforsch. 51 b, 1683-1690 (1996); received June 10, 1996
Ethynylferrocene, Donor-Acceptor Systems, Coupling Reactions
Synthetic methods to bifunctional ethynes have been examined. Direct ethynylation, the
Stephens-Castro reaction, the Pd-catalysed Hagihara coupling, transmetalation reactions and
nucleophilic additions have been evaluated in the preparation of substituted ferrocenylethynes
with intended use of these materials in electrochemical and nonlinear optical investigations.
Asymmetric ferrocenylethynes are promising candidates for applications in contemporary ma-
terials science. Synthetically, 1,4-bis(ferrocenylethynylene)benzene (1), l,3,5-tris(ferrocenyl-
ethynylene)benzene (2), and 9,10-bis(ferrocenylethynylene)anthracene (3) are obtained in high
yields, whereas 4-ferrocenylethynylene-2,3,5,6-tetrafluorostyrene (4) and potassium (ferro-
cenylethynylene)triphenyl borate (5) are accessible in only moderate yields. Further extension
of this chemistry to additional heteronuclear bimetallic coordination compounds has been at-
tempted, but without success due to severe difficulties in both preparation and characterization
of these materials.
Introduction
this structural element, on the other hand, is getting
important in advanced molecular architectures. For
instance, organic networks mimicing diamondoide
or zeolithic arrays are accessible by self-assembling
of acetylene based templates [101. Consequently,
organic solid state chemistry significantly benefits
from the electronic and structural particularities of
this molecular constituent.
The C = C carbon-carbon triple bond established
itself as a versatile organic building-block that en-
ables well-defined molecular structures particularly
when combined with aryl substituents. The syn-
thetic potential of ethynes and ethynylarenes offers
a vast variability ranging from direct ethynylation
and metal-mediated coupling reactions to cyclo- and
polymerization [1]. Acetylene based systems find
wide utilization in LCs [2], polymer LEDs [3], high
performance thermosets and carbon-carbon com -
posites [4], Suitable functionalization leads to struc-
tures with applications in electro- [5] and magneto-
chemical [6] devices, to NLO-phores with \ (2) and
X(3) response [7], to supramolecular components for
photonics [8] as well as to chemicals with signif-
icant bioactivity [9], comprising derivatives such
as HIV reverse transcriptase inhibitors [9e]. Most
of the aforementioned utilizations profit from the
sp-conjugation of acetylenic spacers which allows
intramolecular interactions like charge averaging or
energy and electron transfer. The enforced rigidy of
This paper reports on the synthesis of bifunc-
tional ethynes with emphasis on ethynylferrocenes,
applying various organometallic substitution reac-
tions. The target materials are designed for basic
electrochemical and hyperpolarizability studies.
Diarylacetylenes in Nonlinear Optics and Molecu-
lar Electronics
For the application-oriented construction of tar-
get compounds with acetylenic bridging ligands
three obvious candidates can be envisaged. First,
the title compound ethynylferrocene itself, second,
ferrocenyl-4,4'-disubstituted tolane derivatives, and
third, ferrocenyl-ethynyl-2,2'-bipyridyl metal com-
plexes with the respective potential for uses in the
fields of nonlinear optics and molecular electronics.
* Reprint requests to Prof. Dr. K. E. Schwarzhans.
0939-5075/96/1200-1683 $ 06.00
©
1996 Verlag der Zeitschrift für Naturforschung. All rights reserved.
K
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J. Polin et al. ■Asymmetrie Ethynes. Syntheses of Ethynylferrocene Paradigms
Tolane based donor-acceptor molecules have ex-
ferrocene [18] which represents an economic and
versatile module. Alternative synthetic methods
are more tedious and generally more expensive.
Ferrocenylacetylenes have soon been recognized
as potential starting materials to more complex
organometallics and macromolecular systems ow-
ing to the terminal ethyne which enables a variety
cessively been discussed as materials for nonlin-
ear optics because of their structural and elec-
tronic features [11J. Systematic theoretical stud-
ies, SHG, EFISH and THG measurements of 4,4'-
disubstituted tolanes with numerous different sub-
stituents give evidence that both suszeptibilities and
hyperpolarizabilities are at best moderate. Con- of distinct coupling reactions. Diferrocenylacety-
sequently, the significant enhancement of nonlin-
ear optical responses necessitates new concepts.
Synthetical approaches which take this demand
into account comprise the integration of novel
substituents such as inductive and cationic ac-
ceptors, replacing diphenylacetylenes by (phenyl-
ethynylene)pyridinium links, (and use in LB films
lene, [2.2]ferrocenophane-l,13-diyne (both being
widely used in intervalence transfer studies [lb]),
(ferrocenylethynylene)benzene and ferrocenyl-1-
naphthylacetylene are well-known derivatives [5a,
18a, 19]. Subsequent preparation of heteronuclear
(ferrocenylethynylene)cobaltocenium salts [20] and
further electrochemical investigations complement
[12] or superlattice environments [13], respec- the range of acetylene-bridged bimetallocenes. As
tively), as well as the preparation of oligo(ethynyl-
enephenylene) spacers [7b,e, 14] and polymers
with pendent NLO-phores [15], Since ferrocene
derivatives represent the most versatile class of
organometallic systems in the field of nonlinear
optics, the investigation of (ferrocenylethynylene)-
phenylenes instead of diphenylacetylenes appears
inviting. The donor-acceptor compound 4 for in-
stance has been designed as monomer precursor to
branched polyvinyls.
2,2'-Bipyridyl derivatives with ethynyl sub-
stituents at their 4,4'- or 5,5'-positions rather than
6,6' (for sterical reasons in coordination com -
pounds) and, to some extent, cognate terpyridines
with less favorable chelating characteristics as
well as rigid 1,10-phenanthrolines find continued
interests in molecular electronics. Corresponding
mono-, di- and polynuclear Ru(II) and Os(II) com-
plexes allow photoinduced energy and electron
transfer processes [16], Properly designed systems
permit the manufacture of homo- and heteronuclear
coordination complexes with tunable redox and lu-
minescence properties.
mentioned above, the proposed bis- and tris(ferro-
cenylethynylene)arenes 1,2 and 3 are of comparable
interest with regard to intervalence transfer studies.
Organometallic chromophores are quite interest-
ing for nonlinear optics because they may exhibit
(a) M LCT and LMCT interactions, (b) redox re-
versibility which makes the metal center an ex-
tremely strong acceptor or donor, and (c) gen-
erally low-energy excited states with dipole mo-
ments significantly different from their ground-
state dipole moments. These properties give rise
to large optical nonlinearities. Ionic species of-
fer additional important features such as counte-
rion metathesis to obtain higher nonlinear opti-
cal responses and non-centrosymmetric structures,
the basic requirement for second-order NLO ma-
terials, as well as favorable solubility and proces-
sibility characteristics. The intense color of cer-
tain systems, however, causes transparency prob-
lems and nonlinear optical investigation of salts
and mixed-valency metal complexes in solution is
restricted to the Hyper-Rayleigh Scattering tech-
nique (HSR), which is the only method avail-
able for determining the ß values of such com-
pounds [21]. Consequently, acceptor substituted
ferrocenylethynes like 4-(ferrocenylethynylene)-
cyanobenzene [7a, 22], 4-(ferrocenylethynylene)-
acetylbenzene [23], 4-(ferrocenylethynylene)nitro-
benzene [22, 23], (ferrocenylethynylene)dimesityl-
borane [7c] and l,8-bis(ferrocenyl)octatetrayne
[7d] can be found among recently discussed NLO-
phores. However, 4-ferrocenylethynylene-2,3,5,6-
Bi- and termetallocenes such as compounds
1,
2 and 3 are likely suited for basic elec-
trochemical investigations. Furthermore, 1,3,5-
tris(phenylethynylene)benzene and l,3,5-tris(ferro-
cenylvinylene)benzene analogues of compound 2
have recently been reported as potential NLO-
phores [17].
Ethynylferrocene derivatives
The Vilsmeier reaction has been recognized to be
a highly efficient synthetic route towards ethynyl- tetrafluorostyrene
4
and potassium (ferrocenyl-
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J. Polin et aL ■Asymmetrie Ethynes. Syntheses of Ethynylferrocene Paradigms
1685
naphthylacetylene [18a, 19, 24]. We tried the cou-
pling of cuprous ferrocenylacetylide with 1,4-di-
bromobenzene and 9,10-dibromoanthracene which
kFe
Fe
Fe
Fe
[20]
yielded l,4-bis(ferrocenylethynylene)benzene
1
and 9 ,10-bis(ferrocenylethynylene)anthracene 3.
However, purification and separation from 1,4-
diferrocenyl-l,3-butadiyne, the byproduct which
results from undesired dimerization, turned out
to be difficult and the yields were not satis-
factory. The Hagihara coupling, i.e. the Pd/Cu-
catalysed reaction of terminal ethynes with
haloarenes in amine solvents, has already been re-
ported to be favorable in the preparation of di-
ferrocenylacetylene, 1,3,5-tris(phenylethynylene)-
benzene and 9,10-diethynylanthracene derivatives,
respectively [8a,d, 17a, 25]. Even the synthe-
sis of (ferrocenylethynylene)benzene and (ferro-
cenylvinylene)benzene derivatives has been re-
ported to profit from Pd-catalysed reaction condi-
tions according to Hagihara and Heck, respectively
[5b, 17b, 26]. Accordingly, the Pd/Cu-mediated
preparation of 1 and 2 from commercially avail-
able bromobenzene precursors proceeded smooth
with yields up to 95 %. However, considerable
amounts of monosubstituted (9-bromo-10-ferro-
cenylethynylene)anthracene were obtained in the
synthesis of 3 under quite mild conditions, which
indicates the necessity of elevated temperatures and
elongated reaction times in this case of twofold sub-
JJl,
<ggs
Fe
[32]
[24]
Fe
-< 3 5 3
Co
pf;
Fe
f?S>
[20]
Fe
<g^L-
JL
[19a]
[5b]
Fe
Table I. Chart of selected ethynylferrocene derivatives.
stitution.
Furthermore, it was among the aims to enrich the
ethynylene)triphenyl borate 5 have been prepared
to meet several of the more important requirements
for x (2) materials. Synthesis and characterization
spectrum of heterobimetallic acetylenes by addi-
tional coordination complexes. However, the syn-
thesis of novel systems, namely //6-(ferrocenyl-
of (ferrocenylethynylene)benzene chromium tricar- ethynylene)benzene chromium tricarbonyl, rf-
bonyl and pentamethylcyclopentadienyl ruthenium
complexes, on the other hand, failed. These findings
stress the necessity of convenient accessibility as
an additional demand for purposive materials. Syn-
thetic approaches towards the aforementioned novel
ferrocenylethynyl derivatives 1-5 will therefore be
discussed in the following section with emphasis on
the most efficient routes.
(ferrocenylethynylene)-/?-chlorobenzene chromium
tricarbonyl and (/75-pentamethylcyclopentadienyl)-
ruthenium[/76-(ferrocenylethynylene)benzene] tri-
flate under Hagihara conditions from appropriate
precursors failed. Insufficient coupling and/or am-
bigous characterization of the target compounds
prohibited access to these asymmetric ethynes,
although the large-scale preparation of respec-
tive starting materials (r/6-4-bromochlorobenzene
chromium tricarbonyl, (/;5-pentamethylcyclopenta-
dienyl)ruthenium(//6-iodobenzene) triflate) proved
possible.
Results and Discussion
An early approach to (ferrocenylethynylene)-
arenes by Stephens and Castro, i. e. coupling
of cuproacetylides with haloarenes in pyridine,
yielded materials such as diferrocenylacetylene,
[2.2]ferrocenophane-l,13-diyne and ferrocenyl-1-
The synthesis of 9, lO-bis(ferrocenylethynylene)-
anthracene gave evidence that the nucleophilic
addition method that utilizes anthraquinone and
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J. Polin et al. ■Asymmetrie Ethynes. Syntheses of Ethynylferrocene Paradigms
Fe
Fig. 1. Coupling reactions of ethynylferrocene to target compounds 1-5:. a) 1,4-diiodobenzene; (Ph3P)2PdCl2/Cu(I)I/
('Pr)iNH, 18 h, r.t.; b) 1,3,5-tribromobenzene; (Ph3P)2PdCl2/Cu(I)I/('Pr)2NH, 6 d. RF; c) anthraquinone; 1. n-
BuLi/THF, -78°C, 2. TMEDA/l,4-dioxane, 18 h, RF, 3. ZnCl2 • 2 H20/HOAc/l,4-dioxane, 60 min, r.t.; d) 2,3,4,5,6-
pentafluorostyrene; »-BuLi/THF, -78°C, 2 h, r.t.; e) triphenylborane; 1. n-BuLi/THF, -78°C, 18 h, r.t., 2. KC1, H20;
f) (7;5-pentamethylcyclopentadienyl)ruthenium(776-iodobenzene); (Ph3P)2PdCl2/Cu(I)I/('Pr)2NH, 14 h, RF; g) 77 -4-
bromochlorobenzene chromium tricarbonyl; (Ph^PhPdCF/ Cu(I)I/('Pr)2NH, 4 d, r.t.
lithium acetylides as reaction partners is quite ef-
ficient and competes well with the palladium catal-
ysed approach. The addition-elimination reaction
generally proceeds without problems and yielded
compound 3 with 77%. The lanthanide mediated
version of the carbonyl alkynylation [27] has not
been tested but could certainly be advantageous.
phosphate and related systems [7b, 20], as well as
in the preparation of ethynylpentafluorobenzenes
[28], Further substitution in monosubstituted per-
fluorobenzenes predominantly occurs in para posi-
tion [28]. Thus, it was of interest to study the reac-
tion of ethynylferrocene with 2,3,4,5,6-pentafluoro-
styrene, which is commercially available and guar-
antees convenient access to 4-ferrocenylethynylene-
2,3,5,6-tetrafluorostyrene 4. The styrene unit en-
ables polymerization which is particularly interest-
ing as the favorable inductive effect of fluoro sub-
stituents in perfluoroarenes and the acetylene bridge
promise remarkable nonlinear optical activity.
One of the most straightforward preparation
methods to diarylethynes is the reaction of mono-
substituted ethynes with susceptible arenes via
in situ generation of lithium acetylides. This
strategy proved successful in the synthesis of
(ferrocenylethynylene)cobaltocenium hexafluoro-
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J. Polin et al. ■Asymmetrie Ethynes. Syntheses of Ethynylferrocene Paradigms
1687
Even ethynyltriphenyl borates and phosphino-
boratoacetylenes have been prepared by direct
ethynylation [29]. Both materials, the zwitter-
ionic (diphenylmethylphosphino)triphenylborato-
acetylene [29b, 30], and (ferrocenylethynylene)di-
mesitylborane [7c], have been proposed as NLO-
phores besides transparent ammonium/borate zwit-
terions [31]. On the other hand, combination
of ethynylferrocene with triphenylborane yielded
potassium (ferrocenylethynylene)triphenyl borate
5, an additional boron containing compound
with distinct advantages for second order nonlin-
ear optics. Following the synthetic concepts, the
most desirable material would be (cobaltocenium-
ethynylene)triphenyl borate. However, we were yet
not able to prepare this zwitterionic D/A complex.
The preparation of lithium ferrocenylacetylide
and subsequent transmetallation finally has been
reported as method of choice in the Pd-
catalysed coupling to squaric acid derivatives such
as 3-ferrocenyl-4-(ferrocenylethynylene)cyclobut-
3-en-l,2-dione and 3,4-bis(ferrocenylethynylene)-
cyclobut-3-en-l,2-dione [32], which represent an
additional class of ethyne bridged D/A-systems and
contribute to the more classical donor-acceptor sys-
tems as 4-(ferrocenylethynylene)nitrobenzene, 4-
(ferrocenylethynylene)cyanobenzene and 4-(ferro-
cenylethynylene)acetylbenzene [22, 23].
mg, 0.4 mmol) were added, and the system, which soon
darkens, was stirred at room temperature for 18 h.
The reaction mixture was filtered by suction through
a sintered glass frit (G3) and successively washed
with small amounts of diisopropylamine, hexane and
diethylether. The residue was taken up in THF, fil-
tered again and the solvent evaporated under reduced
pressure. The product was dried in vacuo. Pure 1,4-
bis(ferrocenylethynylene)benzene (0.93 g, 1.9 mmol,
94%) was obtained. MS: m/z = 493 (100%).
Substanz: FiPhiF
Formel: C30H22Fe2
Experimental Section
All experiments were carried out under an inert atmo-
sphere using standard Schlenk technique unless otherwise
indicated. THF was distilled under argon from sodium
benzophenone and reagent grade dichloromethane from
calcium hydride. Starting materials were used as pur-
chased without further purification or prepared according
to literature procedures and checked for purity. Silica for
column chromatography was purchased from Fluka. The
analytical equipment for spectroscopic characterization
comprises: Bruker AM 300 and AM 200 ('H NMR, l3C
NMR; b [ppm] vs. TMS); Nicolet 510M FT-IR (IR; v
[cm-1]); CH-7 MAT (El, 70 eV) and Finnigan MAT 90
(MS); Hitachi U 2000 (UV-VIS; Amax [nm]).
Fig. 2. MS l,4-Bis(ferrocenylethynylene)benzene.
l,3,5-Tris(ferrocenylethynylene)benzene (2)
1,3,5-Tribromobenzene (31.5 mg, 1.0 mmol) was
dissolved in diisopropylamine (5 ml). Bis(triphenyl-
phosphine)palladium(II) chloride (3.5 mg, 0.05 mmol)
and copper(I) iodide (19 mg, 0.1 mmol) were added, and
the system was stirred at room temperature. Ethynylfer-
rocene (0.693 g, 3.3 mmol) was dissolved in diisopropyl-
amine (15 ml) and slowly added to the reaction mixture
by means of a dropping funnel. The solution darkens im-
mediately. The dropping funnel was then replaced by a
reflux condenser and the system stirred under reflux. The
color of the reaction mixture turned brown after 3 h when
1,4-Bis(ferrocenylethynylenejbenzene (1)
Ethynylferrocene (0.84 g, 4.0 mmol) and 1,4-diiodo- TLC showed 3 spots; after 2 d only two TLC-spots re-
benzene (0.66 g, 2.0 mmol) were suspended in diiso-
propylamine (15 ml) under argon. The system was stirred
for a few minutes, bis(triphenylphosphine)palladium(II)
chloride (140 mg, 0.2 mmol) and copper(I) iodide (76.0
mained visible. The reaction was terminated after 6 d,
when coupling was completed.
The reaction mixture was filtered through a sintered
glass frit and carefully washed with diisopropylamine.
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J. Polin et al. ■Asymmetrie Ethynes. Syntheses of Ethynylferrocene Paradigms
The residue was taken up in THF and combined with small
amounts of product that could be isolated from the mother
liquor. The solvent was removed under reduced pres-
sure and 1,3,5-tris(ferrocenylethynylene)benzene (0.66 g,
94%) was obtained.
4-Ferrocenylethynylene-2,3.5,6-tetrafluorostyrene (4)
Ethynylferrocene (0.5 g, 2.4 mmol) was dissolved in
THF (20 ml) and the system cooled to -78°C. /?-Butyl-
lithium (2.0 M solution in /7-pentane, 1.2 ml, 2.4 mmol)
was added and the solution stirred for 1h while rising the
temperature to r.t..
IR (KBr): 3100 w, 2970 s, 2850 m, 2725 w, 2220 m
u(C=C), 1760 m, b. 1560 m. b, 1480 w, 1420 w, 1400
w, 1120 s, 1045 w, 1030 m, 1003 s, 970 s, 878 s, 820 s,
b, 758 w, 682 w. - 'H NMR (CC14): 7.53 s, 3H, 4.40, m,
6H, 4.18 m, 21H. - 13C NMR (CC14) 174.4, 132.5, 71.0,
69.7, 68.4. - MS: m/z = 702 (M+ ). - UV/Vis (CC14, 10“6
mol/ml): 238, 262, 306, 448.
2,3,4,5,6-Pentafluorostyrene (0.36 ml, 2.6 mmol) was
slowly added and the system stirred for 2 h at room
temperature. The color of the reaction mixture changed
into an intense red. The solution was concentrated to
remove solvent and unreacted pentafluorostyrene. The
brownish-red residue was taken up in dry /7-hexane and
stirred overnight. The solution was concentrated and
the product purified by column chromatography (Sil-
ica G-60741, 220-440 mesh, 3x60 cm, /7-hexane/diethyl
ether 70:30). An orange band and 120 mg of a red oil
were isolated. The degree of purity of fraction 1 could
be increased by a second chromatographic separation
(Silica G-60741, 220-440 mesh, 5x60 cm, /7-hexan/di-
ethyl ether 50:50) which yielded 4-ferrocenylethynylene-
2,3,5,6-tetrafluorostyrene (0.55 g, 59%). Fraction 2 con-
tained low-molecular weight oligomers with MS-peaks at
441,556 and 614.
9,10-Bis-(ferrocenylethynylene)anthracene (3)
Ethynylferrocene (1.05 g, 5.0 mmol) was dissolved in
dry THF (25 ml). The solution was cooled to -78°C and
/7-butyllithium (2.4 M solution in /7-hexane, 2.1 ml) was
slowly added. The mixture was warmed to room temper-
ature and stirred for 60 min. After removal of solvents
the remaining orange residue was dissolved in dry 1,4-
dioxane (30 ml). Anthraquinone (0.52 g, 2.5 mmol) and
TMEDA (5 ml) were added to the solution and the system
was refluxed for 18 h. The color of the reaction mixture
changed from red to olive brown.
IR (KBr): 3099 m, 3035 w, 2934 m, 2856 m, 2234 m,
1648 m, 1476 s, 1418 m, 1300 m, 1273 w, 1161 m. 1043
w, 955 s, 878 w, 822 s, 772 w, 484 s. - 1H NMR (CDC13):
6.61 dxd, 1H, 5.05 d, 1H (J = 17.7 Hz), 5.64 d, 1H (J
= 11.6 Hz), 4.48 "t", 2H, 4.22 "t", 2H, 4.17 s, 5H. - l3C
NMR (CDCI3): 123.9, 122.2, 71.7, 70.0, 69.4. - MS: m/z
= 383 M+' (100%).
Precipitation of the orange intermediate glycol iso-
mer was achieved by adding 100 ml of water. The crude
product was filtered (G3) and remaining residues in the
flask were extracted with dichloro methane. The com-
bined crops were purified by column chromatography
(Silica G-60741, 5x15 cm, 1. /7-hexane, 2. diethylether).
The hexane fraction was discarded whereas the ether frac-
tion yielded the pure intermediate almost quantitatively
after removing the solvent and drying.
Potassium (ferrocenylethynylene)triphenyl borate (5)
A flask was charged under inert atmosphere with tin(II)
chloride dihydrate (68 mg, 0.4 mmol) and acetic acid
(50 %, 30 ml). The intermediate glycols (251 mg, 0.4
mmol) were dissolved in dry 1,4-dioxane (30 ml) and
slowly added to the tin chloride solution by means of
a dropping funnel. The color of the solution turned red
with formation of a precipitate. The reaction was termi-
nated after 60 min, the system filtered and the residue
was washed with water and dried. The product was taken
up in small amounts of dichloro methane and purified
by column chromatography (Silica G-60742, 4x40 cm,
77-pentane/diethylether 50:50). The eluent was removed
and the product dried. 9,10-Bis(ferrocenylethynylene)-
anthracene (0.183 g, 77%) was obtained as a deep purple
powder.
Triphenylborane [33]: Sodium tetraphenyl borate (20,0
g, 58,4 mmol) was dissolved in hot water (300 ml) and
cooled to room temperature with stirring. A second solu-
tion was prepared from aqueous trimethylamine solution
(15 %, 26.7 ml) and concentrated HC1 (21.4 ml, 257
mmol). The solutions were combined with spontaneous
formation of white trimethylammonium tetraphenyl bo-
rate [NH(CH3)3]+[B(C6H5)4]- . The system was vigor-
ously stirred for 5 min and the precipitate filtered and
dried. The white ammonium salt was pyrolized by slowly
rising the temperature to 160°C to remove trimethyl-
amine and benzene before collecting the pure product.
Triphenylborane was obtained in 80% yield as white crys-
tals and stored under argon at 4°C.
IR (KBr): 3091 w, 2964 w, 2198 m, 1775 w, 1725 w,
Potassium (ferrocenylethynylene)triphenyl borate (in
1652 w, 1621 w. 1436 w, 1410 w, 1370 m. 1170 w. 1106 analogy to the protocol of [29a]): Ethynylferrocene (1.05
g, 5.0 mmol) was dissolved in dry THF (25 ml) under
argon. The system was cooled to -78°C and treated with
s, 1064 m, 1003 s, 818 s, 753 s, 642 s, 529 w, 496 s. - MS:
m/z = 594.
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J. Polin et al. ■Asymmetrie Ethynes. Syntheses of Ethynylferrocene Paradigms
H-butyllithium (2.4 M solution in n-hexane, 2.1 ml, 5.0
mmol). After stirring for 90 min the solution was com-
bined with triphenylborane (1.16 g, 4.8 mmol) in THF
(50 ml). The cooling-bath was removed after 30 min and
stirring was continued for further 18 h at room tempera-
ture.
Conclusion
The synthesis of asymmetric acetylenes and ferrocenyl
acetylenic donor/acceptor systems with perfluorinated
arenes or aryl borates as the acceptor components is re-
ported, using the easily accessible ethynylferrocene as key
starting material. Bi- and termetallocenes are prepared
by means of the well-established Hagihara coupling,
whereas the fluoroarene and phenyl borate acceptor con-
taining systems are accessible by nucleophilic substitu-
tion and nucleophilic addition, respectively. The latter ma-
terials introduce both inductive acceptor and covalently
bonded anionic terminal functionalities with distinct ad-
vantages in ferrocene based NLO-phores, and contribute
to the prevailingly studied classical organic functional
groups as generally discussed in many tolane based struc-
tures. Further conceptual development towards molecular
composites from these representatives gives rise to inno-
vative and quite efficient materials with application in the
fields of molecular electronics and photonics.
The solvent was removed and the residue taken up in
water. The mixture was extracted with n-hexane until the
organic phase remained almost colorless. The aqueous
phase was combined with a solution of potassium chlo-
ride (1.17 g, 15.7 mmol) in water (50 ml) to precipitate
potassium borate. The flaky product was isolated by suc-
tion through a sintered glass frit, washed with water and
dried. Potassium (ferrocenylethynylene)triphenyl borate
(0.68 g, 28%) was obtained as yellow-orange powder.
IR (KBr): 3060 w, 2155 w, 1592 w, 1580 w, 1480 m,
1430 m, 1262 w, 1154 m, 1106 s, 1026 m, 1001 m, 945
m, 818 s, 764 m, 751 s, 739 s, 616 m, 596 m, 538 m, 486
s, 452 m. - 'H NMR (CD3CN): 7.36 d, 6H (J = 8 Hz),
7.00 t, 6H (J = 8 Hz), 6.87 t, 3H ( 7 = 8 Hz), 4.24 "t",
2H (J = 4 Hz), 4.16 s, 5H, 4.04 "t", 2H (J = 4 Hz). - 13C
NMR (CD3CN): 135.9, 131.4, 126.7, 89.1 (C=C), 71.2,
70.8, 70.2, 67.8. - MS: m/z = 451 (C3„H24BFe, 100%). -
UV/Vis (CC14, 10“6 mol/ml): 284, 444.
Acknowledgements
This research was supported by the Fonds zur
Förderung der wissenschaftlichen Forschung, Vienna,
Austria (Project 10182 MOB).
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