Heterotrimetallic M-M′-M″ transition metal complexes based on 1,3,5-triethynylbenzene: Synthesis, solid state structure, and electrochemical and UV-vis characterization. EPR analysis of the in Situ generated associated radical cations

Article abstract of DOI:10.1021/om800206k

The synthesis of a series of complexes with different organometallic building blocks unsymmetrically arranged around the periphery of a 1,3,5-triethynylbenzene core is discussed. They are accessible by diverse consecutive reaction sequences, which allow the introduction of transition metal units such as Fc, [(^tBu₂bpy)(CO)₃Re], [(η₅-C₅H₅)(Ph₃P)₂Ru], [(η₅-C₅H₅)(Ph₃P) ₂Os], and trans-[(Ph₃P)₂(Cl)Pt] (Fc = (η₅-C₅H₅)(η₅-C ₅H₄)Fe; ^tBu₂bpy = 4,4′-di-tert-butyl-2,2′-bipyridyl). The solid state structures of five complexes have been determined. The electrochemical behavior of the newly synthesized mono-, heterobi-, and heterotrimetallic assemblies have been studied, showing that there is no significant electronic interaction between the respective metal atoms. UV-vis spectroscopic measurements suggest a weak interaction between the appropriate metal atoms. The associated radical cations were in situ generated by stepwise chemical oxidation and characterized by continuous wave electron paramagnetic resonance (EPR) investigations in X-band performed at low temperatures.

Full text of DOI:10.1021/om800206k

3444
Organometallics 2008, 27, 3444–3457
Heterotrimetallic M-M′-M′′ Transition Metal Complexes Based on
1,3,5-Triethynylbenzene: Synthesis, Solid State Structure, and
Electrochemical and UV-Vis Characterization. EPR Analysis of the
in Situ Generated Associated Radical Cations
Rico Packheiser,§ Petra Ecorchard,§ Tobias Ru¨ffer,§ Manja Lohan,§ Bjo¨rn Bra¨uer,§
Fre´de´ric Justaud,§ Claude Lapinte,*,† and Heinrich Lang*,†
Lehrstuhl fu¨r Anorganische Chemie, Institut fu¨r Chemie, Fakulta¨t fu¨r Naturwissenschaften, Technische
UniVersita¨t Chemnitz, Strasse der Nationen 62, 09111 Chemnitz, Germany, and Sciences Chimiques de
Rennes, UniVersite´ de Rennes-1-CNRS (UMR 6226), Campus de Beaulieu, 35042 Rennes Cedex, France
ReceiVed March 5, 2008
The synthesis of a series of complexes with different organometallic building blocks unsymmetrically
arranged around the periphery of a 1,3,5-triethynylbenzene core is discussed. They are accessible by
diverse consecutive reaction sequences, which allow the introduction of transition metal units such as
Fc, [(tBu2bpy)(CO)3Re], [(η5-C5H5)(Ph3P)2Ru], [(η5-C5H5)(Ph3P)2Os], and trans-[(Ph3P)2(Cl)Pt] (Fc )
t
(η5-C5H5)(η5-C5H4)Fe; Bu2bpy ) 4,4′-di-tert-butyl-2,2′-bipyridyl). The solid state structures of five
complexes have been determined. The electrochemical behavior of the newly synthesized mono-, heterobi-,
and heterotrimetallic assemblies have been studied, showing that there is no significant electronic interaction
between the respective metal atoms. UV-vis spectroscopic measurements suggest a weak interaction
between the appropriate metal atoms. The associated radical cations were in situ generated by stepwise
chemical oxidation and characterized by continuous wave electron paramagnetic resonance (EPR)
investigations in X-band performed at low temperatures.
ated carbon ligands such as alkynyls,2,3 (poly)phenylenesethynyl-
Introduction
enes,4–6 arylethenyls,7 or cumulenes8 were used as connecting
The chemistry of carbon-rich, π-conjugated, and rigid-
structured organometallic molecules is of fundamental interest
and has captured much attention, due to the manifold attractive
properties associated with some of these compounds.1 In recent
years many homo- and heterobimetallic complexes with organic
and/or inorganic connecting units have been designed and
synthesized, and their chemical and physical properties were
intensively studied.1 However, less is known about transition
metal complexes in which more than two different metal atoms
are linked through a common bridging ligand. So far, unsatur-
units to span diverse metal atoms. One example is 1,3,5-
triethynylbenzene, which can act as a core in organometallic
chemistry to prepare symmetrical and unsymmetrical transition
metal complexes.9,10 Due to its geometry and active coordination
sites, this molecule allows extension of the core in three
directions by using, for example, dehydrohalogenation or C-C
coupling reactions. Symmetric homosubstitution around the
benzene core by iron-, iridium-, chromium-, gold-, and platinum-
containing metal building blocks has been achieved,9 and
heterometallic complexes of triethynylbenzene featuring, for
example, trans-[(dppm)2(Cl)Ru], trans-[(dppm)2(Cl)Os], [(η5-
C5H5)(PPh3)2Ru] (dppm ) bis(diphenylphosphino)methane),
* To whom correspondence should be addressed. E-mail: heinrich.lang@
chemie.tu-chemnitz.de (H.L.); claude.lapinte@univ-rennes1.fr (C.L).
§ Technische Universita¨t Chemnitz.
(2) Homobimetallic systems with all-carbon bridges:(a) Bruce, M. I.;
Low, P. J. AdV. Organomet. Chem. 2004, 50, 179. (b) Szafert, S.; Gladysz,
J. A. Chem. ReV. 2006, 106, PR1–PR33. (c) Bruce, M. I.; Jevric, M.; Skelton,
B. W.; Smith, M. E.; White, A. H.; Zaitseva, N. N. J. Organomet. Chem.
2006, 691, 361. (d) Maurer, J.; Winter, R. F.; Sarkar, B.; Zalis, S. J. Solid
State Electrochem. 2005, 9, 738. (e) Coat, F.; Paul, F.; Lapinte, C.; Toupet,
L.; Costuas, K.; Halet, J.-F. J. Organomet. Chem. 2003, 683, 368. (f) Meyer,
W. E.; Amoroso, A. J.; Horn, C. R.; Jaeger, M.; Gladysz, J. A. Organo-
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J. A. J. Am. Chem. Soc. 2000, 122, 810.
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Costuas, K.; Davin, T.; Ellis, B. G.; Halet, J. F.; Lapinte, C.; Low, P. J.;
Smith, M. E.; Skelton, B. W.; Toupet, L.; White, A. H. Organometallics
2005, 24, 3864. (b) Bruce, M. I.; Humphrey, P. A.; Jevric, M.; Skelton,
B. W.; White, A. H. J. Organomet. Chem. 2007, 692, 2564. (c) Bruce,
M. I.; Cole, M. L.; Gaudio, M.; Skelton, B. W.; White, A. H. J. Organomet.
Chem. 2006, 691, 4601. (d) Bruce, M. I.; Ellis, B. G.; Skelton, B. W.; White,
A. H. J. Organomet. Chem. 2000, 607, 137. (e) Bruce, M. I.; Hall, B. C.;
Low, P. J.; Smith, M. E.; Skelton, B. W.; White, A. H. Inorg. Chim. Acta
2000, 300, 302–633. (f) Jiao, H.; Costuas, K.; Gladysz, J. A.; Halet, J.-F.;
Guillemot, M.; Toupet, L.; Paul, F.; Lapinte, C. J. Am. Chem. Soc. 2003,
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† Universite´ de Rennes-1–CNRS.
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10.1021/om800206k CCC: $40.75
2008 American Chemical Society
Publication on Web 06/27/2008

Transition Metal Complexes Based on 1,3,5-Triethynylbenzene
Scheme 1. Synthesis of 8
Organometallics, Vol. 27, No. 14, 2008 3445
and ferrocenyl end-grafted moieties are also known.10 Such
organometallic molecules are of great interest, due to their
extended π-system, which can provide reversible redox chem-
istry,4a,b,5c,d,6e,9a,10c,d luminescence properties,1a,b,5a,b,10b photo-
induced electron or energy transfer processes,5f,11 or even liq-
uid crystalline behavior.1a,12 Also applications in the field
of metallo-dendrimers,1s,9f–9j,10e,13 nonlinear optical materi-
als,1a,e,s,4d,h,6d,7a,9g,i,14 and molecular electronics1r,15 are possible.
However, only one example is known in which three different
transition metal fragments are unsymmetrically arranged around
the periphery of a 1,3,5-triethynylbenzene core.10c
As an extension of our previous work on the synthesis and
characterization of heteromultimetallic complexes in which
different early and late transition metals are connected by
carbon-rich organic π-conjugated bridging units, we here
describe straightforward methods for the synthesis of diverse
unsymmetrical organometallic complexes based on 1,3,5-
triethynyl benzene. In addition, electrochemical and UV-vis
spectroscopical studies together with electron paramagnetic
resonance (EPR) measurements of the corresponding radical
cations prepared in situ by chemical oxidation were carried out.
For the synthesis of heterobimetallic 1-(FcCtC)-3-
[(tBu2bpy)(CO)3ReCtC]-5-(HCtC)C6H3 (8) (tBu2bpy ) 4,4′-
(4) Homometallic systems with aryldiethynyl bridges:(a) Chawdhury,
N.; Long, N. J.; Mahon, M. F.; Ooi, L.; Raithby, P. R.; Rooke, S.; White,
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840. (b) de Montigny, F.; Argouarch, G.; Costuas, K.; Halet, J. F.; Roisnel,
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Gaspar, B.; Laubender, M.; Werner, H. J. Organomet. Chem. 2003, 684,
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2005, 24, 4298. (b) Wong, K. M. C.; Lam, S. C. F.; Ko, C. C.; Zhu, N.;
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Results and Discussion
As suitable starting material for the preparation of trinuclear
σ-alkynyl complexes based on the 1,3,5-ethynylbenzene core,
1-(FcCtC)-3,5-(HCtC)2C6H3 (6) (Fc ) (η5-C5H5)(η5-C5H4)Fe)
was selected, because alkynyl ferrocenes are known to be very
robust to further reactions, are electron-rich, and show a
reversible redox chemistry.9a,16 Complex 6 is known in literature,
but its synthesis and characterization has not been reported so
far.10c For this reason, a straightforward high-yield synthesis
procedure for 6 was developed (Scheme 1).
To increase the selectivity of the Sonogashira carbon-carbon
cross-coupling reaction, we used 1-iodo-3,5-dibromobenzene (1)
instead of 1,3,5-tribromobenzene.9a This versatile single-step
reaction was performed by treatment of 1 with ethynylferrocene
(2) in the stoichiometric ratio of 1:1 at ambient temperature
(Scheme 1), whereby mononuclear 1-(FcCtC)-3,5-Br2C6H3 (3)
could be isolated in 85% yield. The introduction of the alkynyl
substituents in 3 was accomplished by a two-step synthesis
methodology by reacting 3 with trimethylsilylacetylene (4) to
give 1-(FcCtC)-3,5-(Me3SiCtC)2C6H3 (5), which after desi-
lylation with [nBu4N]F produced 6 (Scheme 1).
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Dixneuf, P. H. Coord. Chem. ReV. 1998, 178-180, 409.

3446 Organometallics, Vol. 27, No. 14, 2008
Packheiser et al.
di-tert-butyl-2,2′-bipyridyl) we used in the beginning of our
studies the standard literature procedures for the preparation of
[(tBu2bpy)(CO)3Re] acetylides, i.e., the reaction of monolithiated
6 with [(tBu2bpy)(CO)3ReCl] (7).17 However, no reaction took
place when diethyl ether, tetrahydrofuran, or mixtures of these
solvents were used. Complex 8 was also not formed in the
reaction of 6 with 7 in presence of NEt3 and [AgOTf] (OTf )
triflate, OSO2CF3) in refluxing tetrahydrofuran.10b,17a,b Thus, we
developed a new synthesis method to prepare 8 by monolithia-
tion of 6 with LiN(SiMe3)2 in toluene at 0 °C and refluxing the
reaction mixture after addition of 7 (Scheme 1). Heterobimetallic
8 was isolated as an orange solid after column chromatography
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Figure 1. Molecular structure (ORTEP, 30% probability level) of
6. Only one of the two independent molecules of 6 is presented
with the atom-numbering scheme. Hydrogen atoms are omitted for
clarity. Selected bond distances (Å) and bond angles (deg):
C11-C12, 1.192(3); C19-C20, 1.158(4); C21-C22, 1.154(3); Fe1-
D1,1.652(2);Fe1-D2,1.647(2);C1-C11-C12,176.1(2);C11-C12-C13,
176.0(2); C15-C19-C20, 179.7(3); C17-C21-C22, 179.6(3) (D1
) centroid of C1-C5, D2 ) centroid of C6-C10).
on silica gel in 65% yield (Experimental Section). The only
byproduct in this reaction could be identified as 1-(FcCtC)-
3,5-[(tBu2bpy)(CO)3ReCtC]2C6H3 (9), which could be isolated
in low yield (Experimental Section).
Complex 8 gave a satisfactory elemental analysis and was
characterized by 1H, 13C{1H}, and IR spectroscopy. The
structure of 8 in the solid state was determined by single-crystal
X-ray diffraction. The identity of 9 was evidenced by IR and
1H NMR spectroscopy as well as mass spectrometry.
Most characteristic in the IR spectra of 8 and 9 is the
appearance of two νC≡C absorptions at 2217 and 2093 cm-1
(8) or at 2213 and 2089 cm-1 (9), which can be assigned to the
FcCtC and ReCtC units, respectively. However, for the
noncoordinated HCtC entity in 8 only the respective ν
≡C-H
vibration is observed at 3291 cm-1, while the CtC stretching
frequency is concealed by the strong carbonyl vibrations (1884,
1901, 2003 cm-1).
1
The H NMR spectrum of 8 reveals a singlet at 2.93 ppm,
corresponding to the acetylenic proton. Due to the unsym-
metrical substitution, the aryl protons on the 2,4,6-positions of
the central phenylene ring in 8 were found to show three
separated pseudotriplets with JHH ) 1.6 Hz, while for complex
9 these protons evince a doublet and a triplet. The protons of
the ferrocene and bipyridyl units give typical resonances with
the anticipated chemical shifts and coupling patterns (Experi-
mental Section).
Single crystals of 6 and 8 suitable for X-ray diffraction studies
could be grown from a diethyl ether/n-hexane solution (2:1) of
6 or by slow vapor diffusion of n-hexane into a dichloromethane
solution containing 8. Figures 1 and 2 show the perspective
drawings of 6 and 8 together with the atom-numbering scheme.
j
Molecule 6 crystallizes in the triclinic space group P1 with
two independent molecules in the asymmetric unit. The differ-
ence between these two molecules is the orientation of the
ferrocene moiety relative to the central phenylene ring. The
interplanar angles between the substituted cyclopentadienyl ring
and the C6H3 entity are found to be 86.32(0.08)° and 3.64(0.16)°.
The ferrocene unit shows an eclipsed conformation (3.94(6)°)
with characteristic Fe1-D1 and Fe1-D2 (D1 ) centroid of
C1-C5, D2 ) centroid of C6-C10) separations.9a,16 The
acetylide unit is, with angles of 176.1(2)° (C1-C11-C12) and

Transition Metal Complexes Based on 1,3,5-Triethynylbenzene
Organometallics, Vol. 27, No. 14, 2008 3447
acidic alkynes.18 Nevertheless, attempts to obtain 1-(FcCtC)-
3 - [ ( t B u 2 b p y ) ( C O ) 3 R e C t C ] - 5 - [ { [ T i ] ( µ - σ , π -
CtCSiMe3)2}CuCtC]C6H3 by reacting 8 with [{[Ti](µ-σ,π-
CtCSiMe3)2}CuCH3] in tetrahydrofuran at room temperature
failed, presumably due to the steric bulkiness of the bis(alky-
nyl)titanocene and the [(tBu2bpy)(CO)3Re] fragments.
In contrast, the preferred synthetic method for the preparation
of heterotrimetallic compounds was accomplished by the
addition of [(η5-C5H5)(Ph3P)2RuCl] (10) to 8 in a 1:1 methanol/
dichloromethane mixture at 25 °C in the presence of [NH4]PF6
and KOtBu, respectively (Scheme 2). The Ru-CtCR bond
formation is generally done in two separate steps, giving first
the vinylidene complex, which after deprotonation affords the
appropriate ruthenium acetylide. In case of the reaction of 10
with 8 we found that the simultaneous addition of [NH4]PF6
and the base KOtBu gave significantly better yields of 12. The
isostructural osmium(II) complex 13 could be prepared by the
reaction of 8 with [(η5-C5H5)(Ph3P)2OsBr] (11) in refluxing
methanol in the presence of [NH4]PF6 followed by deprotonation
of the vinylidene intermediate by addition of sodium metal. After
appropriate workup, 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-
[(η5-C5H5)(Ph3P)2MCtC]C6H3 (12, M ) Ru; 13, M ) Os)
could be isolated as orange solids in 63% (12) or 67% (13)
yield (Experimental Section).
A possibility to introduce a platinum building block in 8 exists
in the reaction of this compound with cis-[(PPh3)2PtCl2] (14)
in refluxing chloroform in the presence of diethyl amine.19 To
avoid the formation of the corresponding platinum bis(acetylide)
complex, an excess of 14 was used. 1-(FcCtC)-3-[(tBu2bpy)-
(CO)3ReCtC]-5-[trans-Cl(Ph3P)2PtCtC]C6H3 (15) could be
isolated as a yellow solid in good yield after purification by
column chromatography on silica gel.
Figure 2. Molecular structure (ORTEP, 30% probability level) of
8 with the atom-numbering scheme. Hydrogen atoms are omitted
for clarity. Selected bond distances (Å) and bond angles (deg):
Fe1-D1, 1.638(5); Fe1-D2, 1.633(5); C11-C12, 1.179(15);
C42-C43, 1.197(12); C19-C20, 1.179(7); Re1-C20, 2.151(6);
Re1-C39, 1.952(7); Re1-C40, 1.917(6); Re1-C41, 1.889(7);
C39-O1, 1.165(6); C40-O2, 1.161(6); C41-O3, 1.189(6); Re1-N1,
2.173(4);Re1-N2,2.177(4);C1-C11-C12,176.3(13);C11-C12-C13,
175.9(15); C17-C42-C43, 176.6(16); C15-C19-C20, 173.8(5);
C19-C20-Re1, 176.2(4); N1-Re1-N2, 73.59(15) (D1 ) centroid
of C1-C5, D2 ) centroid of C6-C10).
Pendant nitrogen-containing ligands should be capable of
coordinating to different transition metal fragments and conse-
quently should be suitable for the preparation of transition metal
assemblies of higher nuclearity. Thus, we have been interested
in introducing an NCN-pincer unit (NCN ) [C6H3(CH2NMe2)2-
2,6]-) as chelating ligand in 8. Therefore, complex 8 was reacted
with equimolar amounts of I-1-C6H2(CH2NMe2)2-3,5-Br-4 (16)
under typical Sonogashira cross-coupling conditions (Scheme
2 and Experimental Section).20 The respective heterobimetallic
NCN-pincer molecule 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-
5-[Br-4-C6H2(CH2NMe2)2-3,5-CtC-1]C6H3 (17) was formed in
good yield along with traces of acetylide-coupled 18 (Scheme
2). In 18 two 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]C6H3 frag-
ments are connected via a linear butadiyne unit. A practical
method to extend the conjugation of ethynylphenyl systems is
given by the oxidative homocoupling of the appropriate terminal
acetylene by the Eglinton-Glaser reaction.21 Thus, complex 18
could directly be prepared in good yield by the oxidative
176.0(2)° (C11-C12-C13), linear with a typical CtC bond
distance of 1.179(15) Å.
Complex 8 crystallizes in the monoclinic space group P21/n.
The FcCtC and HCtC units and a part of one tert-butyl group
are disordered and have been refined to split occupancies of
0.61/0.39 (Fe1, C1-C11), 0.64/0.36 (C42, C43), and 0.70/0.30
(C32, C34). The structure of 8 shows a somewhat distorted
octahedral geometry around Re1 with three carbonyl ligands
arranged in a facial fashion and Fe1 as part of a sandwich
structure. The N1-Re1-N2 angle, at 73.59(15)°, is significantly
less than 90°, as required by the bite distance exerted by the
steric demand of the chelating bipyridyl (Figure 2). Similar
observations were found in, for example, 1-[(bpy′)(CO)3ReCtC]-
3,5-(HCtC)2C6H3 (bpy′ ) 4,4′-dimethyl-2,2′-bipyridyl).10b The
bond distances of the three alkynyl units are 1.179(15)
(C11-C12), 1.179(7) (C19-C20), and 1.197(12) Å (C42-C43)
(Figure 2), which are comparable to those found for other
triethynylbenzene metal-containing molecules.9,10 The Re1-C20-
C19-C15 unit is almost linear (Re1-C20-C19, 176.2(4)°;
C15-C19-C20, 173.8(5)°), as found in related rhenium(I)
acetylides.10b,17
(18) (a) Frosch, W.; Back, S.; Rheinwald, G.; Ko¨hler, K.; Pritzkow,
H.; Lang, H. Organometallics 2000, 19, 4016. (b) Frosch, W.; Back, S.;
Lang, H. Organometallics 1999, 18, 5725. (c) Frosch, W.; Back, S.;
Rheinwald, G.; Koehler, K.; Zsolnai, L.; Huttner, G.; Lang, H. Organo-
metallics 2000, 19, 5769.
(19) (a) Furlani, A.; Licoccia, S.; Russo, M. V.; Chiesi Villa, A.;
Guastini, C. J. Chem. Soc., Dalton Trans. 1984, 2197. (b) D’Amato, R.;
Furlani, A.; Colapietro, M.; Portalone, G.; Casalboni, M.; Falconieri, M.;
Russo, M. V. J. Organomet. Chem. 2001, 627, 13. (c) D’Amato, R.;
Fratoddi, I.; Cappotto, A.; Altamura, P.; Delfini, M.; Bianchetti, C.; Bolasco,
A.; Polzonetti, G.; Russo, M. V. Organometallics 2004, 23, 2860.
(20) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975,
50, 4467.
Complex 8 possesses a free ethynyl moiety that provides a
further reactive site and therefore should have a great potential
to introduce a third transition metal building block. Thus, the
reaction behavior of the disubstituted iron-rhenium assembly
8 toward diverse transition metal complexes was studied.
However, it was found that treatment of 8 with [(Ph3P)AuCl]
resulted in a ligand exchange to afford [(tBu2bpy)(CO)3ReCl]
along with so far undefined species.
(21) (a) Eglinton, G.; McCrae, W. AdV. Org. Chem. 1963, 4, 225. (b)
Stang, P. J.; Diederich, F. Modern Acetylene Chemistry; VCH: Weinheim,
1995. (c) Glaser, G. Chem. Ber. 1869, 2, 422. (d) Glaser, G. Liebigs Ann.
Chem. 1870, 159.
The synthesis of organometallic π-tweezer-based copper
(I) acetylides is possible by the reaction of [{[Ti](µ-σ,π-
CtCSiMe3)2}CuCH3] ([Ti] ) (η5-C5H4SiMe3)2Ti) with CH-

3448 Organometallics, Vol. 27, No. 14, 2008
Scheme 2. Reaction Chemistry of 8: Synthesis of Heterometallic 12, 13, 15, 17, and 18a
Packheiser et al.
5
t
5
a
(i) [(η -C5H5)(PPh3)2RuCl] (10), [NH4]PF6, KO Bu, CH2Cl2/MeOH, 25 °C; (ii) 1. [(η -C5H5)(PPh3)2OsBr] (11), [NH4]PF6, MeOH, reflux, 2.
Na, MeOH, 25 °C; (iii) cis-[(PPh3)2PtCl2] (14), CHCl3/HNEt2, reflux; (iv) 1-I-NCN-4-Br (16), [(PPh3)2PdCl2]/[CuI], HNiPr2, 35 °C; (v) [CuCl], O2,
pyridine, 40 °C.
dimerization of 8 catalyzed by cuprous(I) chloride in pyridine
under an oxygen atmosphere (Scheme 2).
intensity band at 2064 (12), 2065 (13), and 2116 (15),
respectively, corresponding to the νCtC absorptions of the Ru,
Os, and Pt metal alkynyls, which are diagnostic and represent
a useful monitoring tool.19,24,25 The additionally expected CtC
stretching vibrations in 17 and 18 could not be located, since
they are obviously concealed by the strong carbonyl bands.
Nevertheless, the formation of both species could be followed
to completion by disappearance of the CtC-H band (3291
cm-1).
The 1H NMR spectroscopic properties of 12, 13, 15, 17, and
18 correlate with their formulations as heterobi- or heterotri-
metallic complexes (Experimental Section). Characteristic of
all complexes is the singlet for the tBu groups at 1.45 ppm, the
typical ferrocene resonance signals between 4.15 and 4.45 ppm,
the bipyridine protons with the respective coupling pattern, and
a complicated series of multiplets for the aromatic protons of
the phenyl groups present. The cyclopentadienyl ring at
ruthenium and osmium gives a singlet at 4.26 (12) or 4.34 ppm
(13). The aryl protons of the central phenylene ring were found
as three separated pseudotriplets showing an upfield shift upon
The standard procedure involving lithiation-transmetalation
for the synthesis of palladium- and platinum-NCN-pincers,22
however, could not be applied for the preparation of 1-(FcCtC)-
3-[(tBu2bpy)(CO)3ReCtC]-5-(XM-4-C6H2(CH2NMe2)2-3,5-
CtC-1)C6H3 (M ) Pd, Pt; X ) Cl, Br), since lithiation of 17
appeared not to be possible. Another possibility to introduce
transition metals in NCN-pincer chemistry is given by the
oxidative addition of carbon-halide bonds to low-valent transi-
tion metals, i.e., [Pd2(dba)3×CHCl3] (dba ) dibenzylidene
acetone).23 For the preparation of isostructural platinum NCN-
pincer complexes the platinum source [Pt(tol)2(SEt2)]2 (tol )
4-tolyl) can be used.23 Thus, we reacted 17 with [Pd2(dba)3×
CHCl3] and [Pt(tol-4)2(SEt2)]2, respectively, in benzene or
toluene solutions at different temperatures. It was found that
the addition of the Pd and Pt starting materials to 17 did not
lead to the formation of the desired compounds, which was
evidenced by NMR spectroscopic measurements, e.g., the
introduction of platinum into the NCN-pincer unit leads to the
appearance of typical platinum satellites for the resonance
signals of the CH2NMe2 arms, which, however, could not be
observed.
(24) (a) Paul, F.; Ellis, B. G.; Bruce, M. I.; Toupet, L.; Roisnel, T.;
Costuas, K.; Halet, J.-F.; Lapinte, C. Organometallics 2006, 25, 649. (b)
Bruce, M. I.; Low, P. J.; Hartl, F.; Humphrey, P. A.; de Montigny, F.;
Jevric, M.; Lapinte, C.; Perkins, G. J.; Roberts, R. L.; Skelton, B. W.; White,
A. H. Organometallics 2005, 24, 5241. (c) Sato, M.; Kawata, Y.; Shintate,
H.; Habata, Y.; Akabori, S.; Unoura, K. Organometallics 1997, 16, 1693.
(d) Bruce, M. I.; Skelton, B. W.; White, A. H.; Zaitseva, N. N. J. Organomet.
Chem. 2002, 650, 141. (e) Powell, C. E.; Cifuentes, M. P.; McDonagh, A.;
Hurst, S. K.; Lucas, N. T.; Delfs, C. A.; Stranger, R.; Humphrey, M. G.;
Houbrechts, S.; Asselberghs, I.; Persoons, A.; Hockless, D. C. Inorg. Chim.
Acta 2003, 352, 9.
The IR spectra of 12, 13, and 15 exhibit next to the weak
FcCtC and ReCtC and intense CO vibrations a medium-
(22) (a) Grove, D. M.; van Koten, G.; Louwen, J. N.; Noltes, J. G.;
Spek, A. L.; Ubbels, H. J. C. J. Am. Chem. Soc. 1982, 104, 6609. (b)
Lagunas, M. C.; Gossage, R. A.; Spek, A. L.; van Koten, G. Organometallics
1998, 17, 731. (c) Back, S.; Lutz, M.; Spek, A. L.; Lang, H.; van Koten,
G. J. Organomet. Chem. 2001, 620, 227.
(23) Rodr´ıguez, G.; Albrecht, M.; Schoenmaker, J.; Ford, A.; Lutz, M.;
Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 2002, 124, 5127.
(25) Xia, H. P.; Ng, W. S.; Ye, J. S.; Li, X. Y.; Wong, W. T.; Lin, Z.;
Yang, C.; Jia, G. Organometallics 1999, 18, 4552.

Transition Metal Complexes Based on 1,3,5-Triethynylbenzene
Organometallics, Vol. 27, No. 14, 2008 3449
Figure 3. Molecular structure (ORTEP, 30% probability level) of 12. Only one of the two independent molecules of 12 is presented with
the atom-numbering scheme. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and bond angles (deg): Fe1-D1, 1.667(7);
Fe1-D2, 1.671(8); C30-C31, 1.193(17); Re1-N1, 2.169(12); Re1-N2, 2.184(10); Re1-C8, 2.096(14); C7-C8, 1.234(17); Re1-C9,
1.922(15); Re1-C10, 1.874(19); Re1-C11, 1.939(15); C9-O1, 1.132(16); C10-O2, 1.175(19); C11-O3, 1.178(16); Ru1-D3, 1.878(6);
Ru1-P1, 2.289(4); Ru1-P2, 2.276(3); Ru1-C43, 1.995(12); C42-C43, 1.223(16); C5-C30-C31, 178.1(16); C30-C31-C32, 178.4(16);
N1-Re1-N2, 74.5(4); Re1-C8-C7, 174.3(11); C1-C7-C8, 176.3(13); P1-Ru1-P2, 100.46(11); Ru1-C43-C42, 173.8(10);
C3-C42-C43, 169.2(12) (D1 ) centroid of C32-C36, D2 ) centroid of C37-C41, D3 ) centroid of C44-C48).
the coordination of the alkynyl unit to Ru(II), Os(II), or Pt(II),
which is most distinctive in 15, where the protons next to the
[(PPh3)2(Cl)PtCtC] group appear at 5.77 and 5.80 ppm. Such
an upfield shift in the C6H3 signals in 12, 13, and 15 compared
to 8 may be suggestive of the electron-richness of the appropriate
transition metal moieties leading to a reduced electron donation
from the alkynyl unit.
together with the atomic numbering scheme and selected bond
distances (Å) and angles (deg). The crystallographic data are
summarized in Table 5 (Experimental Section).
Complexes 12 and 13 are quite similar and both crystallize
in the monoclinic space group P2/c with two independent
molecules and three solvent molecules of CHCl3 in the
asymmetric unit. Figures 3 and 4 represent only one of the two
molecules. In both crystal structures the second molecule shows
a disorder of a part of the CtC-Fc unit, which has been refined
to split occupancies of 0.60/0.40 (12) and 0.59/0.41 (13). In
addition, the disorder of one tert-butyl group in 13 has been
refined to split occupancies of 0.66/0.34 (C15-C18). For
complex 12 this disorder could not successfully be refined.
In contrast, complex 15 crystallizes in the monoclinic space
group P21/n together with one molecule of CHCl3. Thereby the
tert-butyl groups and the chloroform show a disorder that has
been refined to split occupancies of 0.65/0.35 (C8-C10), 0.50/
0.50 (C16-C19), and 0.62/0.38 (C80,Cl2-Cl4).
As typical of other ferrocene complexes the Fe-D1 and
Fe-D2 separations in 12, 13, and 15 are found between 1.640(3)
and 1.699(8) Å.9a,16 The two cyclopentadienyl ligands are
thereby rotated by 2.18(0.60)° (12), 4.04(0.56)° (13), and
3.43(0.46)° (15) with respect to each other, which verifies an
almost eclipsed conformation. The Fc-CtC-CPh units are, as
expected, essentially linear with typical CtC separations.
The structures of 12, 13, and 15 show a slightly distorted
octahedral geometry around Re1 with three carbonyl ligands
in a facial fashion. The N1-Re1-N2 bond angles are, at
74.5(4)°, 74.4(4)°, and 74.29(16)°, significantly less than 90°,
as required by the bite distance exerted by the steric demand of
the chelating bipyridyl ligand. The Re-CtC-CPh units confirm,
with bond angles of 170.6(10)-177.3(6)°, an almost linear
arrangement. Furthermore, the CtC distances are typical for
rhenium metal acetylides. Compared to the Re-CCO separations
the Re-CCtC distances are somewhat longer, which is indicative
for little or no significant π-back-bonding to the acetylide unit.
The 31P{1H} NMR spectra of 12 and 13 show a singlet
indicative of equivalent phosphine environments. The spectrum
of the platinum complex 15 presents the expected signal, which
consists of three lines in the ratio of 17:66:17 because of the
coupling with 195Pt. The magnitude of 1J
Pt is known to act
31P195
as a useful probe of the geometry of any present isomer in d8-
electron-configured square-planar Pt(II) complexes.26 The
1J
31P195
Pt value of 15 is, at 2657 Hz, in agreement with the values
found in other square-planar platinum complexes with trans-
geometry.19,27
For complexes 12, 13, 15, 17, and 18 electrospray ionization
mass spectrometric investigations indicated the presence of the
appropriate molecular ion [M + H]+ with characteristic isotope
distribution patterns. Characteristic for these compounds is the
formation of fragments, such as [(tBu2bpy)(CO)3Re]+ (539.1),
[(C5H5)(PPh3)2Ru(CO)]+ (719.0), and [(C5H5)(PPh3)2Os(CO)]+
(809.1).28
Single crystals of heterotrimetallic 12, 13, and 15 suitable
for X-ray structure analysis could be obtained by layering
chloroform solutions of 12, 13, or 15 with n-pentane. Figures
3–5 depict the perspective drawings of the respective complexes
(26) Pregosin, P. S. Kunz, R. W. Eds. 31P- and 13C-NMR of Transition
Metal Phosphine Complexes; Springer Verlag” Berlin, 1976.
(27) (a) Cross, R. J.; Davidson, M. F. J. Chem. Soc., Dalton Trans.
1986, 1987. (b) Bhattacharyya, P.; Sheppard, R. N.; Slawin, A. M. Z.;
Williams, D. J.; Woollins, J. D. J. Chem. Soc., Dalton Trans. 1993, 2393.
(28) (a) Xia, H. P.; Wu, W. F.; Ng, W. S.; Williams, I. D.; Jia, G.
Organometallics 1997, 16, 2940. (b) Bianchini, C.; Casares, J. A.; Peruzzini,
M.; Romerosa, A.; Zanobini, F. J. Am. Chem. Soc. 1996, 118, 4585, and
references therein.

3450 Organometallics, Vol. 27, No. 14, 2008
Packheiser et al.
Figure 4. Molecular structure (ORTEP, 30% probability level) of 13. Only one of the two independent molecules of 13 is presented with
the atom-numbering scheme. Hydrogen atoms and three molecule of CHCl3 are omitted for clarity. Selected bond distances (Å) and bond
angles (deg): Fe1-D1, 1.697(7); Fe1-D2, 1.699(8); C30-C31, 1.178(16); Re1-N1, 2.179(10); Re1-N2, 2.175(9); Re1-C8, 2.105(11);
C7-C8, 1.240(15); Re1-C9, 1.913(15); Re1-C10, 1.917(15); Re1-C11, 1.958(12); C9-O1, 1.160(15); C10-O2, 1.161(16); C11-O3,
1.127(15); Os1-D3, 1.886(5); Os1-P1, 2.285(3); Os1-P2, 2.279(3); Os1-C43, 2.020(11); C42-C43, 1.208(15); C5-C30-C31, 178.8(14);
C30-C31-C32, 179.1(16); N1-Re1-N2, 74.4(4); Re1-C8-C7, 170.6(10); C1-C7-C8, 174.1(12); P1-Os1-P2, 99.92(10); Os1-C43-C42,
176.3(9); C3-C42-C43, 170.8(11) (D1 ) centroid of C32-C36, D2 ) centroid of C37-C41, D3 ) centroid of C44-C48).
Figure 5. Molecular structure (ORTEP, 50% probability level) of 15 with the atom-numbering scheme. Hydrogen atoms and one CHCl3
solvent molecule are omitted for clarity. Selected bond distances (Å) and bond angles (deg): Fe1-D1, 1.640(3); Fe1-D2, 1.651(3); C30-C31,
1.199(8); Re1-N1, 2.178(4); Re1-N2, 2.177(5); Re1-C22, 2.114(5); C22-C23, 1.214(7); Re1-C1, 1.963(6); Re1-C2, 1.920(7); Re1-C3,
1.918(6); C1-O1, 1.144(7); C2-O2, 1.145(7); C3-O3, 1.153(7); Pt1-Cl1, 2.3553(13); Pt1-P1, 2.3124(13); Pt1-P2, 2.3154(13); Pt1-C43,
1.959(5); C42-C43, 1.197(7); C28-C30-C31, 174.1(6); C30-C31-C32, 173.3(6); N1-Re1-N2, 74.29(16); Re1-C22-C23, 177.2(5);
C22-C23-C24, 177.3(6); P1-Pt1-P2, 173.09(5); Cl1-Pt1-C43, 179.29(16); Pt1-C43-C42, 173.2(5); C26-C42-C43, 178.9(6) (D1
) centroid of C32-C36, D2 ) centroid of C37-C41).

Transition Metal Complexes Based on 1,3,5-Triethynylbenzene
Organometallics, Vol. 27, No. 14, 2008 3451
Table 1. Electrochemical Data for 6, 8, 12, 13, 15, and 18a
compd
bpy/bpy•- E0 (∆Ep)
[Fe(II)]/[Fe(III)] E0 (∆Ep)
[Re(I)]/[Re(II)] Ep,ox
[M(II)]/[M(III)] Ep,ox
Ep,ox/E0 (∆Ep)
6
8
18
12
13
15
0.15 (0.12)
0.13 (0.105)
0.13 (0.085)
0.13 (0.085)
0.14 (0.105)
0.11 (0.09)
-2.07 (0.14)
-2.05 (0.115)
-2.08 (0.13)
-2.09 (0.13)
-2.07 (0.125)
0.64
0.64
0.67
0.64
0.61
1.37
0.05
-0.10
1.09/1.33
0.86 (0.19)/1.44
1.19/1.39
a Cyclic voltammograms from 10-3 M solutions in dichloromethane at 25 °C with [n-Bu4N]PF6 (0.1 M) as supporting electrolyte, scan rate ) 0.10 V
s-1. All potentials are given in V and are referenced to the FcH/FcH+ redox couple (FcH ) (η5-C5H5)2Fe) with E0 ) 0.00 V (∆Ep ) 0.10 V)).32,33
Detailed experimental conditions are listed in the Experimental Section.
The geometries of the isostructural [(η5-C5H5)(PPh3)2M] (M
) Ru, Os) building blocks in 12 and 13 are similar to those of
many previously reported examples.24,25,29 Both complexes have
pseudotetrahedral environments about the metal centers with
P1-M-P2 angles of 100.46(11)° (12) and 99.92(10)° (13). The
M-P distances range between 2.276(3) and 2.289(4) Å, and
the average M-Cp distances amount to 1.878(6) (12) and
1.886(5) Å (13). The alkynyl moieties are, as expected, linear
with angles between 169.2(12)° and 176.3(9)° and typical CtC
separations.24,25,29
As typical of metals with d8 electron configuration, the
platinum(II) possesses a slightly distorted square-planar coor-
Figure 6. Cyclic voltammogram of 13 (10-3 M solution in
dichloromethane at 25 °C with [n-Bu4N]PF6 (0.1 M) as supporting
electrolyte, scan rate ) 0.10 V s-1. All potentials are referenced
to the FcH/FcH+ redox couple (FcH ) (η5-C5H5)2Fe) with E0 )
0.00 V (∆Ep ) 0.10 V)).32,33
dination geometry (rms deviation 0.0721 Å), as can be seen
from the angles around Pt1 (e.g., P1-Pt1-P2, 173.09(5)°) with
a linear trans-oriented CPh-CtC-Pt-Cl arrangement (C26-
C42-C43, 178.9(6)°; Pt1-C43-C42, 173.2(5)°; Cl1-Pt1-C43,
179.29(16)°, Figure 5). The deviation from an ideal square-
planar arrangement can be explained by steric interactions
between the bulky groups around Pt1. A similar behavior was
also observed for, e.g., trans-[(PEt2Ph)2(Cl)Pt(CtCPh)].30c The
CtC separation of the alkynyl moiety is, at 1.197(7) Å,
representative for platinum σ-alkynyl complexes.30
Electrochemical Properties. Complexes 6, 8, 12, 13, 15, and
18 were studied by cyclic voltammetry (Table 1). By comparison
of the complexes it is conspicuous that there is no significant
electronic interaction between the respective metal centers. This
observation is based on the substitution pattern of the central
phenylene ring in 1,3- and 5-position, which is unfavorable for
a communication between the metal atoms.
In all complexes the [Fe(II)]/[Fe(III)] oxidation is found to
be reversible between 0.11 and 0.15 V, whereby compared to
6, this oxidation process is facilitated due to addition of further
electron-releasing transition metal entities. The [(tBu2bpy)-
(CO)3Re] building block gives rise to at least two redox
processes.10b In the cathodic region a quasi-reversible reduction
couple is found at ca. -2.07 V, which was tentatively assigned
as a bipyridyl ligand-centered reduction,5a,17c,31 as it occurred
Table 2. UV-Vis Absorption Spectral Data of Selected Complexes
in CH2Cl2 at 298 K
compd
absorption λ/nm (10-3 ꢀ/dm3 mol-1 cm-1
)
6
7
8
12
13
15
18
303 (19), 349 (4), 442 (2)
292 (50), 378 (21), 430 (12, sh)
292 (70), 350 (15, sh), 419 (8)
293 (72), 350 (26, sh), 419 (6)
292 (62), 340 (24), 430 (4)
292 (60), 350 (13, sh), 420 (3)
298 (80), 316 (62, sh), 338 (40), 420 (4)
at almost identical potential for complexes 8, 12, 13, 15, and
18. With regard to related rhenium(I) diimine complexes the
oxidation of [Re(I)] to [Re(II)] occurs at ca. 0.64 V, which
means a less positive potential than in the chloro precursor
7.5a,17c,31 Notable is that the introduction of the trans-
[(PPh3)2(Cl)Pt] fragment in 15 renders the oxidation of both
the iron and the rhenium site slightly more favorable.
For the bivalent group 8 transition metals ruthenium and
osmium quasi-reversible oxidation processes are observed (Table
1). The [Ru(II)]/[Ru(III)] oxidation in 12 is found at Ep,ox
)
0.05 V, whereas the oxidation of [Os(II)] to [Os(III)] in 13
occurs at a more negative potential (Table 1, Figure 6). This
observation is in agreement with previous findings on related
systems in which the [Os(II)]/[Os(III)] redox change is easier
than the [Ru(II)]/[Ru(III)] one.24b Another oxidation wave found
in the cyclic voltammogram of 13 at E0 ) 0.86 V can be
assigned to a further oxidation of the [(η5-C5H5)(PPh3)2Os]
fragment ([Os(III)]/[Os(IV)], see Figure 6).
(29) (a) Matsuzaka, H.; Okimura, H.; Sato, Y.; Ishii, T.; Yamashita,
M.; Kondo, M.; Kitagawa, S.; Shiro, M.; Yamasaki, M. J. Organomet.
Chem. 2001, 625, 133. (b) Whittall, I. R.; Humphrey, M. G.; Hockless,
D. C. R.; Skelton, B. W.; White, A. H. Organometallics 1995, 14, 3970.
(c) Wu, I. Y.; Lin, J. T.; Luo, J.; Li, C. S.; Tsai, C.; Wen, Y. S.; Hsu,
C. C.; Yeh, F. F.; Liou, S. Organometallics 1998, 17, 2188. (d) Cordiner,
R. L.; Albesa-Jove´, D.; Roberts, R. L.; Farmer, J. D.; Puschmann, H.;
Corcoran, D.; Goeta, A. E.; Howard, J. A. K.; Low, P. J. J. Organomet.
Chem. 2005, 690, 4908.
(30) (a) Yam, V. W. W.; Tao, C. H.; Zhang, L.; Wong, K. M. C.;
Cheung, K. K. Organometallics 2001, 20, 453. (b) Onitsuka, K.; Fujimoto,
M.; Kitajima, H.; Ohshiro, N.; Takei, F.; Takahashi, S. Chem.-Eur. J. 2004,
10, 6433. (c) Cardin, C. J.; Cardin, D. J.; Lappert, M. F.; Muir, K. W.
J. Chem. Soc., Dalton Trans. 1978, 46. (d) Zheng, Q.; Hampel, F.; Gladysz,
J. A. Organometallics 2004, 23, 5896.
By going to a more positive potential, the cyclic voltammo-
grams of complexes 8, 12, 13, and 15 show additional
(33) A conversion of given electrode potentials to the standard normal
hydrogen electrode is possible: Strehlow, H.; Knoche, W.; Schneider, H.
Ber. Bunsenges. Phys. Chem. 1973, 77, 760.
(34) (a) Breikss, A. I.; Abruna, H. D. J. Electroanal. Chem. 1986,
201, 347. (b) Lau, V. C. Y. Ph.D. Thesis, The University of Hong Kong,
1997.
(31) (a) Yam, V. W. W.; Chong, S. H. F.; Ko, C. C.; Cheung, K. K.
Organometallics 2000, 19, 5092. (b) Yam, V. W. W.; Lau, V. C. Y.;
Cheung, K. K. Organometallics 1996, 15, 1740.
(32) Ferrocene/ferrocenium redox couple:Gritzner, G.; Kuta, J. Pure
Appl. Chem. 1984, 56, 461.

3452 Organometallics, Vol. 27, No. 14, 2008
Packheiser et al.
Table 3. g Values for the Cation [8]+
b
T (K)
g|
g
∆ga
giso
77
40
20
10
silent
4.366
4.348
4.330
1.925
1.925
1.925
2.44
2.42
2.41
2.74
2.73
2.73
b
a ∆g ) g| - g . giso ) (g| + 2g )/3.
NMR active at liquid nitrogen temperature. The origin of this
behavior was attributed to a fast spin-lattice relaxation (T1)
and a small splitting of the Kramers doublets.37–39 At 20 K, T1
becomes long enough to permit the observation of the EPR
signal characteristic of ferrocinium (g| ) 4.36, g ) 1.30 at 20
K). The EPR spectrum of a glassy solution displays two g values
characteristic of a radical with an axial symmetry because gx -
gy is too small to split the x,y EPR peak. It is noteworthy that
the line width and the anisotropy of the g tensor are very large.
Introduction of phenyl substituents on the C5 rings reduces both
the anisotropy of the signal and the line width, allowing the
detection of the radicals at 77 K. It has been shown that the
EPR signal is very sensitive to the perturbation of the radical
associated with the introduction of aromatic substituents on the
cyclopentadienyl ligands. For example, a single phenyl on one
cyclopentadienyl ligand significantly modifies the values of the
g tensors (g| ) 3.98, g ) 1.62).39 This observation was for us
a source of motivation for using EPR spectroscopy to study
radical species in situ generated from 8, 12, 13, 15, and 18, in
order to detect magnetic interaction between the metal centers
connected through the 1,3,5-triethynylbenzene core.
Treatment of 8 with 1 equiv of [AgOTf] in tetrahydrofuran
at -60 °C provided a yellow solution, which was transferred
into an EPR tube and cooled at 77 K. The EPR spectrum run at
this temperature did not present any signal (Supporting Informa-
tion). However, upon further cooling, a signal characteristic of
a radical with an axial symmetry progressively appeared. The
g| and g tensor components obtained for [8]+ are close enough
to the values already reported for ferrocinium to conclude that
the oxidation of 8 takes place on the (η5-C5H5)(η5-C5H4R)Fe
moiety (Table 3).
The perturbation induced by the 1,3,5-triethynylbenzene core
and the rhenium center is without any detectable effect on g|,
but contributes to a large increase of the g tensor. However,
the large line width and the weak difference between gx and gy
do not allow the splitting of the x,y EPR peak. The thermal
stability of [8]+ was established by recording an identical
spectrum of the same sample after storing it for approximately
1 h at 20 °C.
Complex 8 was then reacted with 2 equiv of [AgOTf] at -60
°C in tetrahydrofuran. The obtained yellow solution was
transferred into an EPR tube and a spectrum was recorded at
77 K (Figure 8). The two tensor components corresponding to
the ferrocinium center are now clearly visible in the spectrum,
suggesting that the presence of a second unpaired electron
narrows the line shape. The spectrum also displays a well-
resolved signal with an axial symmetry. This signal consists of
a sextet in the parallel tensor and a relatively sharp singlet for
the orthogonal tensor. The sextet, which results from the
hyperfine coupling of the unpaired electron with the nuclear
spin of rhenium (I, 185,187Re ) 5/2), probes the contribution of
the rhenium center on the resulting radical. The large anisotropic
Figure 7. UV-vis spectra of selected complexes in dichlo-
romethane at 298 K.
irreversible oxidations, which cannot indisputably be assigned
to specific redox processes. By reference to complexes contain-
ing the [(η5-C5H5)(PPh3)2Ru] redox termini the further oxidation
at 1.09 V of 12 may originate from oxidation at the ruthenium
center.4j,35 The irreversible oxidation at Ep,ox ) 1.19 V (15)
most likely arises from an oxidation at the platinum(II) center
([Pt(II)]/[Pt(III)]).36 However, the possible involvement of a
1,3,5-triethynylbenzene ligand-centered oxidation cannot com-
pletely be excluded.10b
UV-Visible Absorption Spectroscopy. The electronic ab-
sorption spectrum of the mononuclear complex 6 shows a high-
energy band at 303 nm and two low-energy bands at 349 and
442 nm in dichloromethane solution at room temperature (Table
2 and Figure 7). The high-energy band can be assigned to an
intraligand (IL) πfπ* transition of 1,3,5-triethynylbenzene
since the free ligand also absorbs strongly at similar energies.
With reference to the electronic absorption of ferrocene, which
shows low-energy absorptions at 326 and 438 nm, the low-
energy absorption bands of 6 at 349 and 442 nm are assigned
as admixtures of dπ(Fe)fπ*(CtC) metal-to-ligand charge
transfer (MLCT) transitions.
The UV-vis spectrum of the Fe/Re complex 8 displays a
similar pattern. The low-energy bands are blue-shifted and can
be tentatively assigned as an admixture of dπ(Fe)fπ*(CtC)
and dπ(Re)fπ*(CtC) MLCT transitions. Note that the related
1-[(bpy)(CO)3ReCtC]-4-(HCtC)C6H4 also presents an absorp-
tion band centered at 420 nm.5b The addition of a third metal
center onto the connecting ligand does not induce significant
change on the low-energy absorption band, suggesting that
neither the ruthenium, osmium, nor platinum units have a
significant contribution to the HOMO-LUMO gap. In the case
of the tetranuclear complex 18, the high-energy bands assigned
to IL πfπ* transitions are slightly more intense and the
shoulders around 316 and 338 nm are almost resolved, in
agreement with the extension of the organic π-system. Es-
sentially, the UV-vis spectra of the polynuclear metal com-
plexes consist of the sum of the absorptions of the individual
building blocks, suggesting that only negligible interactions take
place between the metal centers.
EPR Spectroscopy. The ferrocinium cation constitutes a very
specific EPR probe. The ferrocinium cation is EPR silent and
(35) (a) Gao, L.-B.; Zhang, L.-Y.; Shi, L.-X.; Chen, Z.-N. Organome-
tallics 2005, 24, 1678. (b) Bruce, M. I.; Low, P. J.; Costuas, K.; Halet,
J.-F.; Best, S. P.; Heath, G. A. J. Am. Chem. Soc. 2000, 122, 1949. (c)
Bruce, M. I.; Ellis, B. G.; Low, P. J.; Skelton, B. W.; White, A. H.
Organometallics 2003, 22, 3184.
(36) Wong, W.-Y.; Lu, G.-L.; Choi, K.-H. J. Organomet. Chem. 2002,
659, 107.
(37) Fritz, H. P.; Keller, H. J.; Schwarzhans, K. E. J. Organomet. Chem.
1966, 6, 652–659.
(38) Prins, R. Mol. Phys. 1970, 19, 603–620.
(39) Prins, R.; Reinders, F. J. J. Am. Chem. Soc. 1969, 91, 4929–4931.

Transition Metal Complexes Based on 1,3,5-Triethynylbenzene
Organometallics, Vol. 27, No. 14, 2008 3453
Figure 8. EPR spectrum of 8 reacted with 1 (a, 10 K) and 2 (b, 77
K) equiv of [AgOTf] in tetrahydrofuran.
Figure 9. Experimental (black) and simulated (gray) EPR spectra
(77 K) of 12 reacted with 2 equiv of [AgOTf] in tetrahydrofuran
(the low-field component at g ) 4.28 has been omitted for clarity).
(∆g) and isotropic (giso) tensors indicate that the dπ(Re) orbital
contribution to the g values is large and suggest that the SOMO
and the doubly occupied orbitals of [8]+ are close in energy.
in the addition of the signal of a radical with an axial symmetry
and a radical with a rhombic geometry, attributed to the
ferrocinium and the ruthenium units, respectively (Figure 9).
The sample stability was good in the solvent glass, but the
intensity of the signal decreases after warming of the solution
for a few minutes. The three features corresponding to the three
components of the g tensor of the rhombic radical are well
resolved. The low-field g tensor was split into a sextet by
hyperfine coupling with the rhenium nucleus. Moreover, the two
high-field features are partially split into 1:2:1 triplets by
hyperfine coupling with the two equivalent 31P nuclei. The g
tensors and the 185,187Re and 31P coupling were extracted by
simulation (Figure 9, Table 4). The g tensors are typical of a
piano-stool-centered radical40 and are qualitatively similar to
those reported for the isostructural ruthenium(III)/iron(III)
complexes [(η5-C5Me5)(dppe)RuCtC-1,4-(C6H4)X]+ and [(η5-
C5Me5)(dppm)FeCtC-1,4-(C6H4)X]+.24a,41 The observation of
the hyperfine coupling of the unpaired electron with both one
rhenium and two phosphorus atoms definitely establishes that
some electronic interaction between the rhenium and ruthenium
The diradical that results from the double oxidation of 8 is
thermally stable in tetrahydrofuran at 20 °C for at least 1 h, as
established by monitoring the intensity of the EPR signal. In
accord with the EPR observation, the doubly oxidized species
could be regarded as a biradical with one electron centered on
the ferrocinium moiety, while the second electron is located on
the rhenium building block. The product resulting from the one-
electron oxidation of [8]+ possesses an EPR spectrum charac-
teristic of a biradical involving both the ferrocinium and rhenium
centers; it cannot be regarded as [8]2+. Indeed, it has been
demonstrated by cyclic voltammetry (Vide supra) that the second
one-electron oxidation of 8 is not chemically reversible.
Therefore, as soon as [8]2+ is generated in solution from the
one-electron oxidation of [8]+, it should be transformed into a
new compound (i.e., [8′]2+) through a chemical reaction. One
can assume that the oxidation of the rhenium building block
should probably be followed by the decoordination of a carbonyl
group. Other chemical reactions can also be envisaged, such as
the Re-Csp bond cleavage, but such a process will not be
consistent with the observed EPR spectrum.
The respectively yellow-orange and yellow tetrahydrofuran
solutions of radical [15]+ and [18]2+ obtained by treatment of
15 and 18 with 1 equiv of [AgOTf] were subjected to EPR
experiments. The signal characteristic of the ferrocinium cation
could not be observed in these two cases. Treatment of these
solutions with a second equivalent of [AgOTf] allowed the
observation of both signals corresponding to the iron and
rhenium building blocks in the case of 15, while for compound
18, the signature of the ferrocinium center was not observed.
For the doubly oxidized compounds 8, 15, and 18, the g tensors
corresponding to the rhenium-centered radicals are very similar,
indicating that the structure of the rhenium center is not
perturbed by the introduction of platinum or the duplication of
the structure.
building blocks takes place in [12]2+
.
In contrast with the other complexes, the first oxidation takes
place on the osmium moiety in the case of complex 13. Indeed,
treatment of trimetallic 13 with 1 equiv of [AgOTf] under the
same experimental conditions provides a spectrum correspond-
ing to a metal-centered radical with a rhombic symmetry. The
presence of additional signals in the spectrum suggests that the
decomposition of the native radical cannot be completely
stopped by working at low temperature. A subsequent oxidation
allowed the observation of the ferrocinium signature, but the
presence of too many paramagnetic impurities prevented the
determination of the tensor components.
The ∆ms ) 2 transitions characteristic of the triplet states of
the biradicals could not be detected for any of the five doubly
oxidized compounds studied. In contrast with the bi- and
trinuclear iron(III) complexes [1,3-{(η5-C5Me5)(dppe)FeCtC}2-
(C6H4)][PF6]2 and [1,3-{(η5-C5Me5)(dppe)Fe-CtC}3(C6H3)]-
[PF6]3, for which through-bridge ferromagnetic metal-metal
exchange interactions were observed,9b the spin carriers are not
apparently magnetically coupled in the complexes here consid-
ered. When observed, the g tensors of the ferrocinium moiety
are only weakly altered by the presence of a second radical
centered on rhenium or ruthenium. However, a small decrease
Treatment of compound 12 with 1 equiv of the silver salt
[AgOTf], as described above, provided an EPR-active solution.
The EPR spectrum displayed a very broad signal centered at g
) 2.05, while the low-field component of the spectrum of the
ferrocenyl radical was not detected. It is assumed that the odd
electron could exchange at a fast regime with respect to the
EPR time scale between the iron and ruthenium centers, in
accord with the relatively close potentials of these redox centers
(Vide supra). Note that the electron transfer can take place either
through the bonding or through space and does not establish
the existence of electronic interactions between the metal
centers. Treatment of [12]+ with a second oxidizing reagent
allowed the observation of a spectrum that essentially consists
(40) Rieger, P. H. Coord. Chem. ReV. 1994, 135/136, 203–286.
(41) Connelly, N. G.; Gamasa, M. P.; Gimeno, J.; Lapinte, C.; Lastra,
E.; Maher, J. P.; Narvor, N. L.; Rieger, A. L.; Rieger, P. H. J. Chem. Soc.,
Dalton Trans. 1993, 2575–2578.

3454 Organometallics, Vol. 27, No. 14, 2008
Packheiser et al.
Table 4. EPR Spectroscopic Data for Compounds 8, 12, 13, 15, and 18 Reacted with 1 and 2 equiv of Oxidanta
1 equiv of [AgOTf]
2 equiv of [AgOTf]
cmpd
g1
g2
g3
∆g
g1
g2
g3
∆g
8
silent
2.32 (122 G)
4.262
2.32
2.084
1.913
2.07 (32 G)
1.92
0.23
2.35
0.31
2.36
12
g ) 2.054, ∆Hpp ) 700 G
(120 G)
(122 G)
2.01 (14 G)
2.082
4.28
b
13
15
2.12
1.985
silent
1.895
0.22
2.312
0.23
0.23
c
1.925
2.084
18
2.084, ∆Hpp ) 250 G
2.311 (122 G)
a At 77 K in tetrahydrofuran glass. b Due to partial decomposition, the g tensors could not be extracted. c Not determined.
Table 5. Crystal and Intensity Collection Data for 6, 8, 12, 13, and 15
6
8
12×3 CHCl3
3481.08
171H145Cl9Fe2
13×3 CHCl3
3655.31
171H141Cl9Fe2
15×CHCl3
1745.24
C80H67Cl4FeN2
O3P2PtRe
fw
334.18
871.80
chemical formula
C22H14Fe
C43H37FeN2O3Re
C
C
N4O6P4
N4O6Os2
Re2Ru2
P4Re2
cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
P1
monoclinic
P21/n
16.0242(9)
12.0532(9)
19.8283(16)
90
101.457(5)
90
3753.4(5)
1.543
monoclinic
P2/c
25.5669(5)
11.3780(3)
53.1036(11)
90
91.512(2)
90
15442.5(6)
1.497
monoclinic
P2/c
25.7473(14)
11.4332(6)
53.214(3)
90
91.527(5)
90
15659.1(15)
1.550
monoclinic
P21/n
23.2869(10)
12.9871(5)
24.1528(9)
90
93.857(3)
90
7288.0(5)
1.591
j
11.814(9)
12.369(9)
12.749(10)
71.211(13)
78.614(13)
64.992(12)
1594(2)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Fcalc (g cm-3
F(000)
)
1.392
688
1736
7000
7240
3448
cryst dimens (mm3)
Z
0.4 × 0.3 × 0.3
0.4 × 0.1 × 0.1
0.7 × 0.6 × 0.2
0.4 × 0.1 × 0.02
0.3 × 0.05 × 0.05
4
4
4
4
4
max., min. transmn
absorp coeff (µ, mm-1
scan range (deg)
index ranges
0.99999, 0.89342
0.941
1.00000, 0.71715
3.649
1.00000, 0.77206
2.190
1.00000, 0.09099
9.606
1.00000, 0.42374
4.008
)
1.69 to 26.37
-14 e h e 14
-14 e k e 15
0 e l e 15
18 264
2.80 to 26.00
-19 e h e 19
-14 e k e 14
-24 e l e 24
34 504
2.83 to 26.00
-30 e h e 31
-12 e k e 14
-65 ′ l e 53
86 133
3.43 to 60.64
-29 e h e 28
-12 e k e 12
-59 e l e 60
91 818
2.97 to 26.12
-28 e h e 28
-16 e k e 16
-29 e l e 29
68 767
total no. of reflns
no. of unique reflns
R(int)
6516
0.0285
7356
0.0695
30 035
0.0745
23 192
0.0765
14 362
0.0331
no. of data/restraints/params
6513/0/415
1.042
0.0326, 0.0848
0.0419, 0.0913
0.284, -0.353
7356/684/607
0.966
0.0343, 0.0625
0.0797, 0.0776
1.055, -0.754
30 035/535/1907
1.122
0.1036, 0.2156
0.1543, 0.2347
5.840, -2.381
23 192/334/1938
1.032
0.0695, 0.1729
0.1007, 0.1950
5.724, -1.373
14 362/153/949
1.108
0.0323, 0.0759
0.0546, 0.0948
2.390, -1.722
goodness-of-fit on F2
R1,a wR2a [I g 2σ(I)]
R1,a wR2a (all data)
max., min. peak in final Fourier map (e Å-3
)
a R1 ) [∑(||Fo| - |Fc||)/∑|Fo|); wR2 ) [∑(w(Fo - Fc ) )/∑(wFo4)]1/2. S ) [∑w(Fo - Fc ) ]/(n - p)1/2. n ) number of reflections, p ) parameters
2
2 2
2
2 2
used.
of the ∆g tensor suggesting a small increase of the π-ligand
5-(CtC)C6H3]2, respectively (Fc ) (η5-C5H5)(η5-C5H4)Fe;
tBu2bpy)4,4′-di-tert-butyl-2,2′-bipyridyl;NCN)C6H2(CH2NMe2)2-
3,5), the appropriate transition metals are connected by a
π-conjugated triethynylbenzene backbone. The X-ray crystal
structures of five complexes have also been determined.
Electrochemical, electron paramagnetic resonance, and UV-vis
spectroscopic investigations of the heterometallic complexes
show only very weak interactions between the respective metal
atoms. Taken as a whole, our results indicate that the 1,3,5-
triethynylbenzene is a suitable connector both to link different
metal centers together and to keep their individual behavior.
character in the description of the SOMO was observed.
Similarly the presence of the ferrocinium center is apparently
not sensed by the platinum and ruthenium building blocks.
Nevertheless, the presence of a second radical modifies the
relaxation process of the ferrocenyl cation, allowing its observa-
tion at liquid nitrogen temperature in 8, 12, 13, and 15. In
contrast, in the tetranuclear compound 18, the signature of the
ferrocinium unit could not be detected at 77 K.
Conclusion
A novel series of mono-, heterobi-, and heterotrimetallic
complexes based on the 1,3,5-triethynylbenzene core have
successfully been synthesized using different consecutive
synthesis methods. In the thus formed organometallic molecules
1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-(HCtC)C6H3,1-(FcCtC)-
3-[(tBu2bpy)(CO)3ReCtC]-5-[(η5-C5H5)(Ph3P)2MCtC]C6H3 (M
) Ru, Os), 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-[trans-
(Ph3P)2(Cl)PtCtC]C6H3, 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-
Experimental Section
General Data. All reactions were carried out under an atmo-
sphere of nitrogen using standard Schlenk techniques. Tetrahydro-
furan, diethyl ether, n-hexane, n-pentane, and petroleum ether were
purified by distillation from sodium/benzophenone ketyl; dichlo-
romethane and chloroform were purified by distillation from calcium
hydride. Celite (purified and annealed, Erg. B.6, Riedel de Haen)
was used for filtrations.
t
5-(1-Br-NCN-4-CtC)C6H3,and[1-(FcCtC)-3-[(Bu2bpy)(CO)3ReCtC]-

Transition Metal Complexes Based on 1,3,5-Triethynylbenzene
Organometallics, Vol. 27, No. 14, 2008 3455
Instruments. Infrared spectra were recorded with a Perkin-Elmer
FT-IR spectrometer Spectrum 1000. 1H NMR spectra were recorded
with a Bruker Avance 250 spectrometer operating at 250.130 MHz
in the Fourier transform mode; 13C{1H} NMR spectra were
recorded at 62.860 MHz. Chemical shifts are reported in δ units
(parts per million) downfield from tetramethylsilane with the solvent
as reference signal (1H NMR: CDCl3, δ ) 7.26; 13C{1H} NMR:
CDCl3, δ ) 77.16).42 31P{1H} NMR spectra were recorded at
101.255 MHz in CDCl3 with P(OMe)3 as external standard (δ )
139.0, rel to H3PO4 (85%) with δ ) 0.00 ppm). ESI-TOF mass
spectra were recorded using a Mariner biospectrometry workstation
4.0 (Applied Biosystems). Cyclic voltammograms were recorded
in a dried cell purged with purified argon. Platinum wires served
as the working electrode and the counter electrode. A saturated
calomel electrode in a separated compartment served as reference
electrode. For ease of comparison, all electrode potentials are
converted using the redox potential of the ferrocene/ferrocinium
couple FcH/FcH+ (FcH ) (η5-C5H5)2Fe, E0 ) 0.00 V) as
reference.32,33 Electrolyte solutions were prepared from tetrahy-
drofuran or dichloromethane and [nBu4N]PF6 (Fluka, dried in oil-
pump vacuum). The appropriate organometallic complexes were
added at c ) 1.0 mM. Cyclic voltammograms were recorded on a
Voltalab PGZ 100 instrument (Radiometer). UV-vis spectra were
obtained on a Cary 5 spectrometer. The EPR spectra were recorded
with a Bruker EMX-8/2.7 (X-band) spectrometer. Tetrahydrofuran
solutions of the diamagnetic neutral complexes were reacted with
[AgOTf] at -60 °C. After 15 min of stirring the solutions were
transferred at this temperature in quartz EPR tubes and were
immediately frozen with liquid nitrogen, and EPR spectra were run
at 77 K. Microanalyses were performed with a FLASHEA 1112
Series CHN analyzer (Thermo).
1-iodo-3,5-dibromobenzene). The analytical data correspond to
values reported in ref 9a.
Preparation of 1-(FcCtC)-3,5-(Me3SiCtC)2C6H3 (5). To a
degassed diisopropylamine solution (50 mL) containing 500 mg
(1.13 mmol) of 1-(FcCtC)-3,5-Br2C6H3 (3) were added 400 mg
(4.08 mmol) of trimethylsilylacetylene, [(PPh3)2PdCl2] (50 mg), and
[CuI] (25 mg). The resulting suspension was stirred for 1 h at room
temperature, followed by 15 h at 40 °C. After cooling it to room
temperature the reaction mixture was filtered through a pad of
Celite, and subsequently all volatiles were removed under reduced
pressure. The residue was purified by column chromatography on
silica gel using petroleum ether/dichloromethane (4:1, v/v) as eluent.
After evaporation of the solvents in an oil-pump vacuum, 5 was
obtained as an orange solid. Yield: 405 mg (0.85 mmol, 76% based
on 3).
Anal. Calcd for C28H30FeSi2 (478.56): C, 70.27; H, 6.32. Found:
C, 69.89; H, 6.38. Mp: 148 °C. IR (KBr, cm-1): 2159 (m, νCtCSi),
2216 (m, νCtCFc). 1H NMR (δ, CDCl3): 0.29 (s, 18 H, SiMe3), 4.26
(s, 5 H, C5H5), 4.27 (pt, JHH ) 1.8 Hz, 2 H, Hꢀ/C5H4), 4.52 (pt,
JHH ) 1.8 Hz, 2 H, HR/C5H4), 7.54 (t, JHH ) 1.4 Hz, 1 H, C6H3),
7.56 (d, JHH ) 1.4 Hz, 2 H, C6H3). 13C{1H} NMR (δ, CDCl3): 0.1
(SiMe3), 64.7 (Ci/C5H4), 69.3 (CH/C5H4), 70.2 (C5H5), 71.7 (CH/
C5H4), 84.3 (CtCFc), 90.2 (CtCFc), 95.7 (CtCSi), 103.6
(CtCSi), 123.9 (Ci/C6H3), 124.7 (Ci/C6H3), 134.3 (CH/C6H3), 134.5
(CH/C6H3).
Preparation of 1-(FcCtC)-3,5-(HCtC)2C6H3 (6). 1-(FcCtC)-
3,5-(Me3SiCtC)2C6H3 (5) (400 mg, 0.84 mmol) was dissolved in
tetrahydrofuran (30 mL) and treated with 1.8 mL (1.80 mmol) of
[nBu4N]F (1.0 M in tetrahydrofuran) at 0 °C. After 30 min of stirring
the cooling bath was removed and stirring was continued for 1 h.
Afterward all volatiles were evaporated under reduced pressure,
and the obtained residue was purified by column chromatography
on silica gel using a mixture of petroleum ether/dichloromethane
(3:1, v/v) as eluent. After evaporation of all volatiles the title
compound was obtained as an orange solid. Yield: 260 mg (0.78
mmol, 93%).
Reagents. 1-Iodo-3,5-dibromobenzene,43 ethynylferrocene,44 tri-
methylsilylacetylene,45 [(tBu2bpy)(CO)3ReCl],46 [(η5-C5H5)(PPh3)2-
RuCl],47 [(η5-C5H5)(PPh3)2OsCl],48 cis-[(PPh3)2PtCl2],49 and I-1-
C6H2(CH2NMe2)2-3,5-Br-450 were prepared according to published
procedures. All other chemicals were purchased from commercial
suppliers and were used as received.
Anal. Calcd for C22H14Fe (334.2): C, 79.07; H, 4.22. Found: C,
78.48; H, 4.47. Mp: 154 °C. IR (KBr, cm-1): 2208 (m, νCtCFc),
Modified Preparation of 1-(FcCtC)-3,5-Br2C6H3 (3). To 500
mg (1.38 mmol) of 1-iodo-3,5-dibromobenzene (1) and 300 mg
(1.43 mmol) of ethynylferrocene (2) dissolved in 50 mL of degassed
diisopropylamine were added [(PPh3)2PdCl2] (40 mg) and [CuI]
(20 mg) at 0 °C. The resulting reaction mixture was stirred for 2 h
at this temperature, followed by stirring overnight at 25 °C.
Afterward the suspension was filtered through a pad of Celite, and
the filtrate was evaporated to dryness under reduced pressure. The
residual material was purified by column chromatography on
alumina using a 4:1 mixture of petroleum ether and dichloromethane
as eluent. The title complex was obtained from the first orange
band as a red solid. Yield: 520 mg (1.17 mmol, 85% based on
1
3284 (s, νtC-H). H NMR (δ, CDCl3): 3.12 (s, 2 H, tCH), 4.25
(s, 5 H, C5H5), 4.27 (pt, JHH ) 1.8 Hz, 2 H, Hꢀ/C5H4), 4.51 (pt,
JHH ) 1.8 Hz, 2 H, HR/C5H4), 7.54 (t, JHH ) 1.4 Hz, 1H, C6H3),
7.59 (d, JHH ) 1.4 Hz, 2H, C6H3). 13C{1H} NMR (δ, CDCl3): 64.5
(Ci/C5H4), 69.2 (CH/C5H4), 70.2 (C5H5), 71.7 (CH/C5H4), 78.5
(CtCH), 82.1 (CtCH), 84.0 (CtCFc), 90.5 (CtCFc), 122.9 (Ci/
C6H3), 124.9 (Ci/C6H3), 134.5 (CH/C6H3), 135.0 (CH/C6H3).
Preparation of 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-
(HCtC)C6H3 (8) and 1-(FcCtC)-3,5-[(tBu2bpy)(CO)3ReCtC]2-
C6H3 (9). To 350 mg (1.05 mmol) of 1-(FcCtC)-3,5-(HCtC)2-
C6H3 (6) dissolved in 60 mL of toluene was added LiN(SiMe3)2
(170 mg, 1.02 mmol) in a single portion at 0 °C. After 2 h of stirring
at this temperature the cooling bath was removed and stirring was
continued for 1 h. Then 200 mg (0.35 mmol) of [(tBu2bpy)-
(CO)3ReCl] (7) was added, and the reaction mixture was heated to
100-110 °C for 5 h, while the progress of the reaction was
monitored by TLC. After cooling to room temperature a few drops
of ethanol were added to destroy the unreacted lithium acetylide
and all volatiles were removed under reduced pressure. The residue
was purified by column chromatography on silica gel using a diethyl
ether/petroleum ether mixture of ratio 2:1 as the eluent. After
removal of the first band, which contained unreacted 1-(FcCtC)-
3,5-(HCtC)2C6H3 (6), the second band was collected. After
evaporation of the solvents under reduced pressure an orange solid
identified as 8 was obtained. Additionally, from a third yellow band
a small amount of complex 9 was isolated. Yield: 8, 195 mg (0.22
mmol, 65% based on 7); 9, 20 mg (0.114 mmol, 8% based on 7).
(42) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997,
62, 7512.
(43) (a) Baxter, P. N. W. Chem.-Eur. J. 2003, 9, 5011. (b) Lustenberger,
P.; Diederich, F. HelV. Chim. Acta 2000, 83, 2865.
(44) Polin, J.; Schottenberger, H. Org. Synth. 1996, 13, 262.
(45) Brandsma, L. PreparatiVe Acetylenic Chemistry; Elsevier-Verlag:
Amsterdam, 1988; p 114.
(46) (a) Wrighton, M. S.; Morse, D. L. J. Am. Chem. Soc. 1974, 96,
998. (b) Wrighton, M. S.; Morse, D. L.; Pdungsap, L. J. Am. Chem. Soc.
1975, 97, 2073.
(47) (a) Joslin, F. L.; Mague, J. T.; Roundhill, D. M. Organometallics
1991, 10, 521. (b) Bruce, M. I.; Windsor, N. J. Aust. J. Chem. 1977, 30,
1601.
(48) (a) Wanandi, P. W.; Tilley, T. D. Organometallics 1997, 16, 4299.
(b) Bruce, M. I.; Windsor, N. J. Aust. J. Chem. 1977, 30, 1601. (c) Bruce,
M. I.; Low, P. J.; Skelton, B. W.; Tiekink, E. R. T.; Werth, A.; White,
A. H. Aust. J. Chem. 1995, 48, 1887.
(49) Jensen, K. A. Z. Anorg. Allg. Chem. 1936, 229, 265.
(50) Rodr´ıguez, G.; Albrecht, M.; Schoenmaker, J.; Ford, A.; Lutz, M.;
Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 2002, 124, 5127.
8: Anal. Calcd for C43H37FeN2O3Re (871.83): C, 59.24; H, 4.28;
N, 3.21. Found: C, 58.99; H, 4.46; N, 3.06. Mp: >196 °C (dec).

3456 Organometallics, Vol. 27, No. 14, 2008
Packheiser et al.
IR (KBr, cm-1): 1884, 1901, 2003 (s, νCO), 2093 (w, νCtCRe), 2217
(w, νCtCFc), 3291 (m, νtC-H). 1H NMR (δ, CDCl3): 1.47 (s, 18H,
tBu), 2.93 (s, 1 H, tCH), 4.18 (s, 5 H, C5H5), 4.21 (pt, JHH ) 1.8
Hz, 2 H, Hꢀ/C5H4), 4.41 (pt, JHH ) 1.8 Hz, 2 H, HR/C5H4), 6.96
(pt, JHH ) 1.6 Hz, 1 H, C6H3), 7.06 (pt, JHH ) 1.6 Hz, 1 H, C6H3),
after removal of all volatiles, the title complex 13. Yield: 90 mg
(0.055 mmol, 67% based on 11).
Anal. Calcd for C84H71FeN2O3OsP2Re (1650.73): C, 61.12; H,
4.34; N, 1.70. Found: C, 61.42; H, 4.47; N, 1.75. Mp: >178 °C
(dec). IR (KBr, cm-1): 1893, 2003 (s, νCO), 2065 (m, νCtCOs), 2212
3
1
t
7.16 (pt, JHH ) 1.6 Hz, 1 H, C6H3), 7.46 (dd, JH5H6 ) 5.8 Hz,
(w, νCtCFc). H NMR (δ, CDCl3): 1.45 (s, 18 H, Bu), 4.19 (pt,
4JH5H3 ) 1.9 Hz, 2 H, H5/tBu2bpy), 8.09 (d, JH3H5 ) 1.9 Hz, 2 H,
H3/tBu2bpy), 8.97 (d, JH6H5 ) 5.8 Hz, 2 H, H6/tBu2bpy). 13C{1H}
NMR (δ, CDCl3): 30.5 (CH3), 35.7 (C(CH3)3), 65.1 (Ci/C5H4), 68.9
(CH/C5H4), 70.1 (C5H5), 71.5 (CH/C5H4), 76.9 (CtCH), 83.1
(CtCH), 84.9 (CtCFc), 88.5 (CtCFc), 104.1 (CtCRe), 119.4
(CH/tBu2bpy), 121.6 (Ci/C6H3), 123.6 (Ci/C6H3), 124.2 (CH/
tBu2bpy), 128.4 (Ci/C6H3), 131.0 (CH/C6H3), 134.5 (CH/C6H3),
134.8 (CH/C6H3), 152.9 (CH/tBu2bpy), 155.8 (Ci/tBu2bpy), 162.9
(Ci/tBu2bpy), 193.0 (CO), 198.3 (CO).
JHH ) 1.8 Hz, 2 H, Hꢀ/C5H4), 4.21 (s, 5 H, C5H5/Fc), 4.34 (s, 5 H,
C5H5/Os), 4.42 (pt, JHH ) 1.8 Hz, 2 H, HR/C5H4), 6.54 (pt, JHH
)
1.6 Hz, 1 H, C6H3), 6.80 (pt, JHH ) 1.6 Hz, 1 H, C6H3), 6.93 (pt,
JHH ) 1.6 Hz, 1 H, C6H3), 7.03-7.23 (m, 18 H, C6H5), 7.39-7.48
3
4
(m, 12 H, C6H5), 7.45 (dd, JH5H6 ) 5.8 Hz, JH5H3 ) 2 Hz, 2 H,
H5/tBu2bpy), 8.08 (d, JH3H5 ) 2 Hz, 2 H, H3/tBu2bpy), 9.01 (d,
4
3JH6H5 ) 5.8 Hz, 2 H, H6/tBu2bpy). 31P{1H} NMR (δ, CDCl3):
0.6 (s, OsPPh3). MS (ESI-TOF, m/z): 1651.2 [M + H]+, 539.1
[(tBu2bpy)(CO)3Re]+, 809.1 [(PPh3)2(C5H5)Os(CO)]+.
Preparation of 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-
[trans-(PPh3)2(Cl)PtCtC]C6H3 (15). To 100 mg (0.115 mmol)
of 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-(HCtC)C6H3 (8) and
135 mg (0.171 mmol) of cis-[(PPh3)2PtCl2] (14) dissolved in 15
mL of chloroform was added 0.5 mL of diethylamine. The resulting
reaction mixture was stirred for 5 h at reflux. After cooling to room
temperature all volatiles were removed in an oil-pump vacuum,
and the residue was purified by column chromatography on silica
gel using a mixture of dichloromethane/toluene (2:1, v/v) as eluent.
Complex 15 was obtained as an orange powder. Yield: 110 mg
(0.068 mmol, 59% based on 8).
9: Anal. Calcd for C64H60FeN4O6Re2×1/2C7H8 (1455.51): C,
55.70; H, 4.43; N, 3.85. Found: C, 56.03; H, 4.31; N, 3.61. Mp:
>215 °C (dec). IR (KBr, cm-1): 1898, 2004 (s, νCO), 2089 (w,
ν
CtCRe), 2213 (w, νCtCFc). 1H NMR (δ, CDCl3): 1.46 (s, 36 H,
tBu), 4.13 (s, 5 H, C5H5), 4.15 (pt, JHH ) 1.9 Hz, 2 H, Hꢀ/C5H4),
4.32 (pt, JHH ) 1.9 Hz, 2 H, HR/C5H4), 6.41 (t, JHH ) 1.6 Hz, 1 H,
C6H3), 6.58 (d, JHH ) 1.6 Hz, 2 H, C6H3), 7.42 (dd, JH5H6 ) 6.0
Hz, JH5H3 ) 1.9 Hz, 4 H, H3/tBu2bpy), 8.07 (d, JH3H5 ) 1.9 Hz, 4
H, H3/tBu2bpy), 8.90 (d, JH6H5 ) 6.0 Hz, 4 H, H6/tBu2bpy). MS
(ESI-TOF, m/z): 1409.7 [M + H]+, 539.3 [(tBu2bpy)(CO)3Re]+.
Preparation of 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-[(η5-
C5H5)(Ph3P)2RuCtC]C6H3 (12). To 85 mg (0.098 mmol) of
1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-(HCtC)C6H3 (8) and 65
mg (0.090 mmol) of [(η5-C5H5)(PPh3)2RuCl] (10) dissolved in a
mixture of dichloromethane/methanol (40 mL, ratio 1:1) were
simultaneously added 18 mg (0.110 mmol) of [NH4]PF6 and 14
mg (0.125 mmol) of KOtBu. The resulting reaction mixture was
stirred for 5 h at 25 °C. The complete conversion of [(η5-
C5H5)(PPh3)2RuCl] (10) was monitored by 31P{1H} NMR spec-
troscopy. Subsequently, all volatiles were removed in an oil-pump
vacuum, and the residue was purified by column chromatography
on silica gel. The excess of 8 was eluted as an orange band using
toluene/dichloromethane (5:1, v/v) as eluent. The title compound
was eluted with a mixture of toluene/tetrahydrofuran (10:1, v/v),
giving after removal of the solvents in vacuum an orange-red solid.
Yield: 88 mg (0.056 mmol, 63% based on 8).
Anal. Calcd for C79H66ClFeN2O3P2PtRe (1625.93): C, 58.36; H,
4.09; N, 1.72. Found: C, 58.31; H, 4.02; N, 1.25. Mp: >178 °C
(dec). IR (KBr, cm-1): 1898, 2004 (s, νCO), 2090 (m, νCtCRe), 2116
(w, νCtCPt), 2211 (w, νCtCFc). 1H NMR (δ, CDCl3): 1.43 (s, 18 H,
tBu), 4.17 (s, 5 H, C5H5), 4.18 (pt, JHH ) 1.9 Hz, 2 H, Hꢀ/C5H4),
4.36 (pt, JHH ) 1.9 Hz, 2 H, HR/C5H4), 5.77 (pt, JHH ) 1.6 Hz, 1
H, C6H3), 5.80 (pt, JHH ) 1.6 Hz, 1 H, C6H3), 6.49 (pt, JHH ) 1.6
Hz, 1 H, C6H3), 7.31-7.46 (m, 20 H (C6H5) + 2 H (H5/tBu2bpy)),
4
7.67-7.80 (m, 10 H, C6H5), 8.05 (d, JH3H5 ) 1.7 Hz, 2 H, H3/
3
tBu2bpy), 8.96 (d, JH6H5 ) 5.8 Hz, 2 H, H6/tBu2bpy). 31P{1H}
NMR (δ, CDCl3): 20.5 (1J31P195Pt ) 2656.7 Hz, PtPPh3). MS (ESI-
TOF, m/z): 1626.8 [M + H]+, 539.3 [(tBu2bpy)(CO)3Re]+.
Preparation of 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReC’C]-5-(Br-
4-C6H2(CH2NMe2)2-3,5-CtC-1)C6H3 (17). To a mixture of 150
mg (0.172 mmol) of 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-
(HCtC)C6H3(8)and65mg(0.165mmol)ofBr-1-I-4-C6H2(CH2NMe2)2-
2,6 (16) in 10 mL of tetrahydrofuran and 15 mL of diisopropylamine
were added [(PPh3)2PdCl2] (55 mg) and [CuI] (25 mg). The reaction
mixture was stirred for 2 h at 35 °C. Afterward, all volatiles were
removed under reduced pressure and the remaining residue was
purified by column chromatography on silica gel using a mixture
of petroleum ether/tetrahydrofuran (10:1, v/v) as eluent. Compound
17 was further purified by precipitation from a concentrated
dichloromethane solution (2 mL) with n-hexane (20 mL) and
washed twice with 10 mL portions of n-hexane. After drying in an
oil-pump vacuum compound 17 was obtained as an orange solid.
Yield: 135 mg (0.118 mmol, 68% based on 16).
Anal. Calcd for C84H71FeN2O3P2ReRu (1561.57): C, 64.61; H,
4.58; N, 1.79. Found: C, 65.09; H, 5.03; N, 1.62. Mp: >175 °C
(dec). IR (KBr, cm-1): 1901, 2003 (s, νCO), 2064 (m, νCtCRu), 2096
(w, νCtCRe), 2220 (w, νCtCFc). 1H NMR (δ, CDCl3): 1.45 (s, 18 H,
tBu), 4.19 (pt, JHH ) 1.9 Hz, 2 H, Hꢀ/C5H4), 4.21 (s, 5 H, C5H5/
Fc), 4.26 (s, 5 H, C5H5/Ru), 4.42 (pt, JHH ) 1.9 Hz, 2 H, HR/
C5H4), 6.57 (pt, JHH ) 1.6 Hz, 1 H, C6H3), 6.82 (pt, JHH ) 1.6 Hz,
1 H, C6H3), 6.97 (pt, JHH ) 1.6 Hz, 1 H, C6H3), 7.03-7.23 (m, 18
H, C6H5), 7.39-7.48 (m, 12 H (C6H5) + 2 H (H5/tBu2bpy)), 8.09
4
3
(d, JH3H5 ) 1.7 Hz, 2 H, H3/tBu2bpy), 9.01 (d, JH6H5 ) 5.8 Hz,
2 H, H6/tBu2bpy). 31P{1H} NMR (δ, CDCl3): 49.4 (s, RuPPh3.
MS (ESI-TOF, m/z): 1563.1 [M + H]+, 719.0 [(PPh3)2(C5H5)-
Ru(CO)]+.
Anal. Calcd for C55H54BrFeN4O3Re×1/2CH2Cl2 (1183.46): C,
56.33; H, 4.68; N, 4.73. Found: C, 56.52; H, 4.85; N, 4.65. Mp:
>172 °C (dec). IR (KBr, cm-1): 1901, 2004 (s, νCO), 2090 (w,
Preparation of 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-[(η5-
C5H5)(Ph3P)2OsCtC]C6H3 (13). A mixture of 70 mg (0.081
mmol) of [(η5-C5H5)(PPh3)2OsBr] (11), 80 mg (0.092 mmol) of
1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-(HCtC)C6H3 (8), and 15
mg (0.092 mmol) of [NH4]PF6 was stirred in methanol (50 mL)
for 3 h at reflux, whereby the orange suspension turned into a clear
red solution. The reaction mixture was allowed to cool to room
temperature, and then sodium metal (5 mg) was added with stirring,
causing the precipitation of a yellow solid. All volatile materials
were removed under reduced pressure, and the residue was subjected
to column chromatography on silica gel. By using first toluene/
dichloromethane (5:1, v/v) as eluent, the excess of 8 was removed.
Changing the eluent to toluene/tetrahydrofuran (10:1, v/v) afforded,
ν
CtCRe), 2215 (w, νCtCFc). 1H NMR (δ, CDCl3): 1.47 (s, 18 H,
tBu), 2.32 (s, 12 H, NMe2), 3.52 (s, 4 H, CH2), 4.20 (s, 5 H, C5H5),
4.21 (pt, JHH ) 1.9 Hz, 2 H, Hꢀ/C5H4), 4.42 (pt, JHH ) 1.9 Hz, 2
H, HR/C5H4), 7.00 (pt, JHH ) 1.6 Hz, 1 H, C6H3), 7.05 (pt, JHH
)
1.6 Hz, 1 H, C6H3), 7.24 (pt, JHH ) 1.6 Hz, 1 H, C6H3), 7.43 (s, 2
3
4
H, C6H2), 7.48 (dd, JH5H6 ) 5.8 Hz, JH5H3 ) 1.9 Hz, 2 H, H5/
tBu2bpy), 8.10 (d, JH3H5 ) 1.9 Hz, 2 H, H3/tBu2bpy), 8.99 (d,
4
3JH6H5 ) 5.8 Hz, 2 H, H6/tBu2bpy). MS (ESI-TOF, m/z): 1141.4
[M + H]+, 539.2 [(tBu2bpy)(CO)3Re]+.
Preparation of {1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-
(CtC)C6H3}2 (18). To a pyridine solution (10 mL) containing

Transition Metal Complexes Based on 1,3,5-Triethynylbenzene
Organometallics, Vol. 27, No. 14, 2008 3457
[CuCl] (3 mg, 0.031 mmol) was added a solution of 100 mg (0.115
mmol) of 1-(FcCtC)-3-[(tBu2bpy)(CO)3ReCtC]-5-(HCtC)C6H3
(8) in dry pyridine (10 mL), and the mixture was stirred for 1 h
under an oxygen atmosphere at 40 °C. Afterward all volatiles were
removed under reduced pressure, giving a residual solid that was
subjected to column chromatography on silica gel using diethyl
ether/n-hexane (3:1, v/v) as eluent. The product was further purified
by precipitation from a concentrated dichloromethane solution (2
mL) with n-hexane (20 mL) and washed twice with 10 mL portions
of n-hexane. After drying in an oil-pump vacuum compound 18
was obtained as an orange solid. Yield: 90 mg (0.052 mmol, 90%).
matized Mo KR radiation (λ ) 0.71073 Å) at 293(2) K using oil-
coated shock-cooled crystals.51 The structures were solved by direct
methods using SHELXS-9752 or SIR-9253 and refined by full-matrix
least-squares procedures on F2 using SHELXL-97.54 All non-
hydrogen atoms were refined anisotropically, and a riding model
was employed in the refinement of the hydrogen atom positions.
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
Industrie for generous financial support. B.B. thanks the
Fonds der Chemischen Industrie for a fellowship.
Anal. Calcd for C86H72Fe2N4O6Re2×1/2CH2Cl2 (1784.09): C,
58.23; H, 4.12; N, 3.14. Found: C, 58.15; H, 4.01; N, 2.92. Mp:
>190 °C (dec). IR (KBr, cm-1): 1901, 2005 (s, νCO), 2088 (w,
Supporting Information Available: Tables of atomic coordi-
nates, bond lengths, angles, torsion angles, and anisotropic displace-
ment parameters for 6, 8, 12, 13, and 15. This material is available
free of charge via the Internet at http://pubs.acs.org.
ν
CtCRe), 2213 (w, νCtCFc). 1H NMR (δ, CDCl3): 1.48 (s, 36 H,
tBu), 4.20 (s, 10 H, C5H5), 4.22 (pt, JHH ) 1.9 Hz, 4 H, Hꢀ/C5H4),
4.43 (pt, JHH ) 1.9 Hz, 4 H, HR/C5H4), 6.93 (pt, JHH ) 1.6 Hz, 2
H, C6H3), 7.11 (pt, JHH ) 1.6 Hz, 2 H, C6H3), 7.21 (pt, JHH ) 1.6
OM800206K
3
4
Hz, 2 H, C6H3), 7.49 (dd, JH5H6 ) 5.8 Hz, JH5H3 ) 2 Hz, 4 H,
(51) (a) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615. (b)
Kottke, T.; Lagow, R. J.; Stalke, D. J. Appl. Crystallogr. 1996, 29, 465. (c)
Stalke, D. Chem. Soc. ReV. 1998, 27, 171.
(52) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(53) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Gualardi, A. J. Appl.
Crystallogr. 1993, 26, 343.
H5/tBu2bpy), 8.10 (d, JH3H5 ) 2 Hz, 4 H, H3/tBu2bpy), 8,98 (d,
4
3JH5H6 ) 5.8 Hz, 4 H, H6/tBu2bpy).
Crystal Structure Determinations. Crystal data for 6, 8, 12,
13, and 15 are presented in Table 5. The data for 6 were collected
on a Bruker Smart CCD 1k diffractometer and for 8, 12, 13, and
15 on a Oxford Gemini S diffractometer with graphite-monochro-
(54) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Go¨ttingen, 1997.