1 ,1 -Bis(ethynyl)biferrocene as a linking group for gold, ruthenium, and osmium fragments: synthesis, solid state structures, and electrochemical, UV-Vis, and EPR spectroscopical studies

Article abstract of DOI:10.1021/om8011344

A series of organometallic mono- and disubstituted bis(alkynyl)biferrocenes of type (L_nMC≡C)-(HC≡C)bfc (L_nM = (η⁵-C₅H₅)(Ph₃P)₂RU (8a), (η⁵-C₅H₅)(

Full text of DOI:10.1021/om8011344

1878
Organometallics 2009, 28, 1878–1890
1′,1′′′-Bis(ethynyl)biferrocene as a Linking Group for Gold,
Ruthenium, and Osmium Fragments: Synthesis, Solid State
Structures, and Electrochemical, UV-Vis, and EPR Spectroscopical
Studies
Manja Lohan,† Petra Ecorchard,† Tobias Ru¨ffer,† Fre´de´ric Justaud,‡ Claude Lapinte,*,‡ and
Heinrich Lang*,†
Institut fu¨r Chemie, Lehrstuhl fu¨r Anorganische Chemie, Fakulta¨t fu¨r Naturwissenschaften, Technische
UniVersita¨t Chemnitz, Strasse der Nationen 62, 09111 Chemnitz, Germany, and UMR CNRS 6226 Sciences
Chimiques de Rennes, UniVersite´ de Rennes 1, Campus de Beaulieu, F-35042 Rennes, France
ReceiVed NoVember 27, 2008
A series of organometallic mono- and disubstituted bis(alkynyl)biferrocenes of type (LnMCtC)-
(HCtC)bfc (LnM ) (η5-C5H5)(Ph3P)2Ru (8a), (η5-C5H5)(Ph3P)2Os (8b), (η5-C5H5)(dppf)Ru (8c); bfc )
1′,1′′′-biferrocenyl, ((η5-C5H4)2Fe)2; dppf ) 1,1′-bis(diphenyl)phosphanyl ferrocene, (η5-C5H4PPh2)2Fe)
and (LnMCtC)2bfc (LnM ) (Ph3P)Au (6), (η5-C5H5)(Ph3P)2Ru (9a), (η5-C5H5)(Ph3P)2Os (9b), (η5-
C5H5)(dppf)Ru (9c)) have been synthesized from (HCtC)2bfc (4) with either (Ph3P)AuCl (5) in the
presence of HNEt2/[CuI] (synthesis of 6) or LnMX (LnMX ) (η5-C5H5)(Ph3P)2RuCl (7a); (η5-
C5H5)(Ph3P)2OsBr (7b); (η5-C5H5)(dppf)RuCl (7c)) together with [H4N]PF6 and KOtBu (synthesis of 8
and 9), respectively. The structures of 6, 8b, 9a, 9b, and 9c in the solid state were determined by single-
crystal X-ray structure analysis, showing unsymmetrical (8) or symmetrical geometries (6, 9), with almost
eclipsed conformations or approximately midway positions between the fully eclipsed and the fully
staggered conformation of the bfc cyclopentadienyl rings and with anti geometry of the linear ethynyl
connecting units. UV-vis and NIR 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 temperature.
As organometallic alkynyl ligands, bis(alkynyl)biferrocenes
offer versatile synthetic usability and, due to their structural
rigidity, can be considered as bridging and redox-active units
between transition metal fragments, allowing communication
through the delocalized bonds in the respective array. In contrast
to ferrocenes, 1′,1′′′-functionalized biferrocenyls are less studied
due to the lack of straightforward synthesis methodologies.3
Recently, Dong,4 Long,3a,b Robinson,2a and our group5 reported
on the synthesis, reaction chemistry, and electrochemical
Introduction
Biferrocenes (bfc) in which two ferrocenyl units are connected
by forming a fulvalenide bridge have attracted much attention
because they easily can form mixed-valent Fe(II)-Fe(III)
species by electrochemical or chemical oxidation.1 Molecules
of this type are of interest due to their robustness and electron-
richness. Those with high conjugation can form multiple electro-
active systems joined by a conjugated assembly. Hitherto,
electron transfer rates and charge delocalization of alkynyl- and
mainly alkyl-functionalized biferrocenium salts have been
studied. The structures of these systems in the solid state showed
nonequivalence in the ferrocenyl entities.2
(3) (a) Long, N. J.; Martin, A. J.; Vilar, R.; White, A. J. P.; Williams,
D. J.; Younus, M. Organometallics 1999, 18, 4261. (b) Colbert, M. C. B.;
Hodgson, D.; Lewis, J.; Raithby, P. R.; Long, N. J. Polyhedron 1995, 14,
2759. (c) Schottenberger, H.; Buchmeiser, M.; Polin, J.; Schwarzhans, K.-
E. Z. Naturforsch., B: Chem. Sci. 1993, 48, 1524. (d) Lavastre, O.; Ollivier,
L.; Dixneuf, P. H.; Sibandhit, S. Tetrahedron 1996, 52, 5495. (e) Kahn,
M. S.; Kakkar, A. K.; Long, N. J.; Lewis, J.; Raithby, P. R.; Nguyen, P.;
Marder, T. B.; Wittmann, F.; Friend, R. H. J. Mater. Chem. 1994, 4, 1227.
(f) Touchard, D.; Pirio, N.; Dixneuf, P. H. Organometallics 1995, 14, 4920.
(g) Long, N. J. In Metallocenes: An Introduction to Sandwich Complexes;
Blackwell Science: Oxford, U.K., 1998. (i) Mueller-Westerhoff, U. T.
Angew. Chem. 1986, 98, 700; Angew. Chem., Int. Ed. Engl. 1986, 25, 702.
(j) Yamamoto, T.; Morikata, T.; Marumaya, T.; Kubota, K.; Katada, M.
Macromolecules 1997, 30, 5390. (k) Lai, L.-L.; Dong, T.-Y. J. Chem. Soc.,
Chem. Commun. 1994, 2347.
(4) (a) Dong, T.-Y.; Lin, M.-C.; Chiang, M. Y.-N.; Wu, J.-Y. Organo-
metallics 2004, 23, 3921. (b) Dong, T.-Y.; Shih, H.-W.; Chang, L.-S.
Langmuir 2004, 20, 9340. (c) Dong, T.-Y.; Chen, K.; Lin, M.-C.; Lee, L.
Organometallics 2005, 24, 4198. (d) Dong, T.-Y.; Lin, M.-C.; Chang, S.-
W.; Ho, C.-C.; Lin, S.-F.; Lee, L. J. Organomet. Chem. 2007, 692, 2324.
(e) Dong, T.-Y.; Lin, H.-Y.; Lin, S.-F.; Huang, C.-C.; Wen, Y.-S.; Lee, L.
Organometallics 2008, 27, 555.
* Corresponding authors. (H.L.) Phone: +49-(0)371-531-21210. Fax:
+49-(0)371-531-21219. E-mail: heinrich.lang@chemie.tu-chemnitz.de. (C.L.)
Phone: +33-(0)2-23-23-5963. Fax: +33-(0)2-23-23-6939. E-mail:
claude.lapinte@univ-rennes1.fr.
† Technische Universita¨t Chemnitz.
‡ Universite´ de Rennes 1.
(1) (a) Togni, A.; Hayashi, T., Eds. Ferrocenes: Homogeneous Catalysis-
Organic Synthesis-Materials Science; VCH: Weinheim, Germany, 1995; p
459. (b) Brown, G. M.; Meyer, T. J.; Cowan, D. O.; Le Vanda, C.;
Kaufmann, F. J.; Roling, P. V.; Rausch, M. D. Inorg. Chem. 1975, 14,
506. (c) Cowan, D. O.; Le Vanda, C.; Park, J.; Kaufman, F. J. Acc. Chem.
Res. 1973, 6, 1. (d) Mueller-Westerhoff, U. T. Angew. Chem., Int. Ed. Engl.
1986, 25, 702.
(2) (a) Hore, L.-A.; McAdam, C. J.; Kerr, J. L.; Duffy, N. W.; Robinson,
B. H.; Simpson, J. Organometallics 2000, 19, 5039. (b) Hendrickson, D. N.;
Oh, S. M.; Dong, T.-Y.; Kambara, T.; Cohn, M. J.; Moore, M. F. Comments
Inorg. Chem. 1985, 4, 329. (c) Delville, M.-H.; Robert, F.; Gouzerh, P.;
Linares, J.; Boukheddaden, K.; Varret, F.; Astruc, D. J. Organomet. Chem.
1993, 451, C10.
(5) Ko¨cher, S.; van Klink, G. P. M.; van Koten, G.; Lang, H. J.
Organomet. Chem. 2006, 691, 3319.
10.1021/om8011344 CCC: $40.75
2009 American Chemical Society
Publication on Web 03/02/2009

1′,1′′′-Bis(ethynyl)biferrocene as a Linking Group
Organometallics, Vol. 28, No. 6, 2009 1879
Scheme 1. Modified Synthesis Methodology to Prepare Bis(ethynyl)biferrocene, 4
behavior of alkynyl-containing biferrocenes and polyferrocenes.
It was found that ethynyl(poly)ferrocenyl fragments can act as
organometallic linking units in molecular switches and arrays;
however, the bfc core is incapable of modulating the redox
chemistry of cobalt- and platinum-containing terminal groups.
To gain a better understanding of the electronic behavior of
these molecules, CACAO theoretical studies were carried out
on ((Et3P)2(Ph)PtCtC)2bfc, indicating that the SHOMO is
located at the iron atoms and that there is no appropriate route
for conjugation between platinum and the central bfc unit.2a,3a,6
In contrast, when the end-grafted moieties are manganese-based
organometallic fragments, e.g., Mn(CO)3(η2-Ph2PCH2PPh2), it
is observed that the Mn metal atoms donate electron density
through the acetylene linkage to the biferrocene spacer.3b In
case of the appropriate ruthenium-bfc compounds, for example,
((η2-Ph2PCH2PPh2)(Cl)RuCtC)2bfc, there are different results
reported.3b
After appropriate workup, complex 6 was obtained as a yellow,
fairly stable solid in 55% yield, which dissolves in organic
solvents such as tetrahydrofuran and dichloromethane.
Based on this contrariety we here report a straightforward
method to synthesize gold-, ruthenium-, and osmium-containing
bis(ethynyl)biferrocenes. Electrochemical studies together with
electron paramagnetic resonance measurements of corresponding
radical cations in situ prepared by chemical oxidation and
UV-vis and NIR spectroscopical studies are also reported.
The synthesis of mono- and disubstituted ruthenium- and
osmium-acetylide biferrocenes can be realized as shown in
Scheme 2. Addition of LnMX (LnMX ) (η5-C5H5)(Ph3P)2RuCl
(7a), (η5-C5H5)(Ph3P)2OsBr (7b), (η5-C5H5)(dppf)RuCl (7c);
dppf ) 1,1′-bis(diphenyl)phosphanyl ferrocene, (η5-C5H4P-
Ph2)2Fe) to 4 in a 1:1 molar ratio in the presence of [H4N]PF6
and KOtBu resulted in the formation of orange (LnMCtC)-
(HCtC)bfc (LnM ) (η5-C5H5)(Ph3P)2Ru (8a), (η5-C5H5)(Ph3P)2-
Os (8b), and (η5-C5H5)(dppf)Ru (8c)). Within these reactions
metal vinylidene species are ubiquitously formed as intermedi-
ates.7 Removal of the vinylidene ꢀ-hydrogen atom by tert-
butoxide caused the formation of the neutral ruthenium and
osmium σ-acetylides 8a-8c (Scheme 2, reaction (i)). It was
found that for the synthesis of 8a and 8c a mixture of methanol/
dichloromethane (1:1) was best suited, while under similar
reaction conditions compound 8b was not formed. Changing
to only methanol as solvent, compound 8b was obtained, after
appropriate workup, as an orange solid in moderate yield
(Experimental Section).
Results and Discussion
Synthesis. The preparation of bis(ethynyl)biferrocene (4) was
reported previously by Long and co-workers.3a,b We here
describe a new synthesis methodology to prepare 4 with
improved yields and ease of purification. The synthesis of 4
was accomplished by the palladium-copper-catalyzed Sono-
gashira cross-coupling of 2-methyl-3-butyn-2-ol (2) with di-
iodobiferrocene (1) in refluxing diisopropylamine to produce
(Me2(OH)C-CtC)2bfc (3) (bfc ) 1′,1′′′-biferrocenyl, ((η5-
C5H4)2Fe)2). The deprotection of the propargylic groups with
powdered KOH in toluene gave orange-red (HCtC)2bfc (4)
(Scheme 1). The advantage of this procedure in comparison to
that described earlier3a,b is, in addition to the somewhat higher
yield, the more straightforward purification of intermediate 3
(Experimental Section).
(7) (a) 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. (b) Sato, M.; Shintate, H.;
Kawata, Y.; Sekino, M.; Katada, M.; Kawata, S. Organometallics 1994,
13, 1956. (c) Paul, F.; Ellis, B. G.; Bruce, M. I.; Toupet, L.; Roisnel, T.;
Costuas, K.; Halet, J.-F.; Lapinte, C. Organometallics 2006, 25, 649. (d)
Touchard, D.; Morice, C.; Cadierno, V.; Haquette, P.; Toupet, L.; Dixneuf,
P. H. J. Chem. Soc., Chem. Commun. 1994, 859. (e) Touchard, D.; Haquette,
P.; Guesmi, S.; Le Pichon, L.; Daridor, A.; Touplet, L.; Dixneuf, P. H.
Organometallics 1997, 16, 3640. (f) Humphrey, M. G.; Whittall, I. R.
Organometallics 1996, 15, 1935.
The synthesis of ((Ph3P)AuCtC)2bfc (6) was accomplished
by the [CuI]-catalyzed reaction of 4 with (Ph3P)AuCl (5) in a
1:1 mixture of diethylamine/tetrahydrofuran with concomitant
precipitation of [Et2NH2]Cl at ambient temperature (reaction 1).
(6) (a) Mealli, C.; Proserpio, D. M. CACAO 4.0; Instituto per lo Studio
della Stereochimica ed Energetica dei Composti di Coordinazione: Florence,
Italy, 1994. (b) Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990, 67, 399.

1880 Organometallics, Vol. 28, No. 6, 2009
Scheme 2. Synthesis of Complexes 8 and 9a
Lohan et al.
5
5
5
a
(i) First: LnMX (LnMX ) (η -C5H5)(Ph3P)2RuCl (7a), (η -C5H5)(Ph3P)2OsBr (7b), (η -C5H5)(dppf)RuCl (7c)), 1 equiv, [NH4]PF6, CH2Cl2/
MeOH (1:1), MeOH (in the case of 7b), 25 °C, 16 h; second: KOtBu, CH2Cl2/MeOH (1:1), MeOH (in the case of 7b), 25 °C, 5 h. (ii) first: 7a, 7b,
7c, 2 equiv, [NH4]PF6, CH2Cl2/MeOH (1:1), MeOH (in the case of 7b), 25 °C, 16 h; second: KOtBu, CH2Cl2/MeOH (1:1), MeOH (in the case of
7b), 25 °C, 5 h. (iii) first: 7a, 7b, 7c, 1 equiv, [NH4]PF6, CH2Cl2/MeOH (1:1), MeOH (in the case of 7b), 25 °C, 16 h; second: KOtBu, CH2Cl2/
MeOH (1:1), MeOH (in case of 7b), 25 °C, 5 h.
The synthesis strategy used in the preparation of 8a-8c could
successfully be transferred to the organometallic alkynes
(LnMCtC)2bfc (LnM ) (η5-C5H5)(Ph3P)2Ru (9a), (η5-C5H5)-
(Ph3P)2Os (9b), (η5-C5H5)(dppf)Ru (9c)) in which two ruthe-
nium- and osmium-acetylide building blocks are bonded to bfc
(Scheme 2, reaction (ii)). Reacting 4 with 7a-7c in a 1:2
stoichiometry produced the tetrametallic M2Fe2 complexes
9a-9c (M ) Ru, Os) with yields between 60 and 90%
(Experimental Section). After column chromatography and
crystallization, these compounds could be isolated as orange
solid materials (Experimental Section).
It was also possible to synthesize tetranuclear 9a-9c by
treatment of 8a-8c with 7a-7c in a 1:1 molar ratio (Scheme
2, reaction (iii)).
Compounds 9a-9c rapidly turn dark after exposure to air
and moisture due to oxidation processes, whereby solutions
containing these molecules decompose more easily than solid
materials. Nevertheless, transition metal compounds 8a-8c are
even more reactive than 9a - 9c and, hence, must carefully be
handled under an inert gas atmosphere.
8a-8c is the appearance of two νCtC absorptions at 2100 cm-1
for the HCtC unit and at 2074 cm-1 for the MCtC fragment,
which is attributed to the monosubstitution of these compounds.
A further characteristic vibration is found for 4 at 3302 cm-1
for the H-Ct group.
Also the NMR spectroscopic properties of 6, 8, and 9 correlate
with their formulations as mono- or diacetylide biferrocene
complexes (Vide supra). The cyclopentadienyl protons of the
bfc central unit in the symmetric-arranged systems 6 and 9a-9c
show, as expected, four signals with an AA′XX′ pattern between
3.7 and 4.2 ppm with coupling constants of JHH ) 1.7-1.8 Hz
(for comparison, molecule 4: 4.00, 4.23, 4.26, and 4.40 ppm3a).
For 8a-8c, with an unsymmetrical geometry, a total of eight
signals ranging from 3.8 to 4.4 ppm is typical (Experimental
Section). For the ruthenium- and osmium-bonded cyclopenta-
dienyl groups a singlet is found at ca. 4.3 ppm. Due to the
different chemical environment, the dppf cyclopentadienyl
protons in 8c and 9c appear as four separated signals, whereby
three of them are found between 4.0 and 4.4 ppm and the other
is located at ca. 5.5 ppm.8
Characterization. Complexes 6, 8, and 9 were characterized
by elemental analysis, IR, NMR (1H, 13C{1H}, 31P{1H}),
UV-vis, and EPR spectroscopy. The identities of 6, 8b, and
9a-9c were further confirmed by single-crystal X-ray diffraction
studies. Compounds 6, 8a-8c, and 9a-9c were additionally
investigated by cyclic voltammetric measurements. Additionally,
spectroelectrochemical studies were carried out.
The progress of the complexation of 4 with MLn fragments
could be monitored by IR spectroscopy since a typical shift of
the CtC stretching frequency takes place by changing from 4
(νCtC 2109 cm-1) to 6 (νCtC 2104 cm-1), 8 (νC≡C 2074 cm-1
(MCtC), 2100 cm-1 (HCtC)), and 9 (νCtC 2075 cm-1
(MCtC)), respectively.3a Conspicuous in the IR spectra of
The 13C{1H} NMR spectra of 6, 8, and 9 contain the
corresponding carbon signals for bfc, C5H5, and CtC (Experi-
mental Section). Also the carbon signals of the dppf and phenyl
groups are found in the expected region.8
(8) (a) Packheiser, R.; Ecorchard, P.; Walfort, B.; Lang, H. J. Organomet.
Chem. 2008, 693, 933. (b) Wu, I. Y.; Lin, J. T.; Luo, J.; Sun, S. S.; Li,
C. S.; Lin, K. J.; Tsai, C.; Hsu, C. C.; Lin, J. L. Organometallics 1997, 16,
2038. (c) Gao, L.-B.; Zhang, L.-Y.; Shi, L.-X.; Chen, Z.-N. Organometallics
2005, 24, 1678. (d) Sato, M.; Sekino, M. J. Organomet. Chem. 1993, 444,
185. (e) Lu, X. L.; Vittal, J. J.; Tiekink, E. R. T.; Tan, G. K.; Kuan, S. L.;
Goh, L. Y.; Hor, T. S. A. J. Organomet. Chem. 2004, 689, 1978. (f) Bruce,
M. I.; Butler, I. R.; Cullen, W. R.; Kousantonis, G. A.; Snow, M. R.; Tiekink,
E. R. T. Aust. J. Chem. 1988, 41, 963.

1′,1′′′-Bis(ethynyl)biferrocene as a Linking Group
Organometallics, Vol. 28, No. 6, 2009 1881
Figure 1. ORTEP diagram (50% probability level) of 6 with the atom-numbering scheme (the hydrogen atoms and one disordered CH2Cl2
packing solvent molecule are omitted for clarity). Symmetry transformations used to generate equivalent atoms are labeled with “A”: -x
+ 1/2, -y + 5/2, -z + 1 (center of inversion in between C6 and C6A). Selected bond distances (Å) and angles (deg): C1-C11 1.410(11),
C11-C12 1.184(11), C12-Au1 1.988(7), Au1-P1 2.257(2), C6-C6A 1.456(16), D1-Fe1 1.628(3), D2-Fe1 1.624(3); C1-C11-C12
176.4(9), C11-C12-Au1 173.9(7), C12-Au1-P1 178.5(2), C13-P1-Au1 113.6(3), C19-P1-Au1 111.1 (3) C25-P1-Au1 113.5(3),
D1-Fe1-D2 178.7(1) (D1 ) centroid C1 - C5, D2 ) centroid of C6-C10). The number in parentheses after each calculated value
represents the standard deviation in units of the last significant digits.
The 31P{1H} NMR spectra of all newly synthesized com-
pounds indicate the presence of a single phosphorus environment
with resonance signals for the (Ph3P)Au9 and (η5-C5H5)MLn
(LnM ) (Ph3P)2Ru (8a, 9a), (Ph3P)2Os (8b, 9b), (dppf)Ru (8c,
9c)8,10) building blocks at 41.3 (6), 49.38 (8a), 50.36 (9a), 0.15
(8b), 0.6 (9b), 53.7 (8c), and 53.9 (9c) ppm (Experimental
Section).
Solid State Structures. Single-crystal X-ray structure analysis
was performed for 6, 8b, and 9a-9c. A view of the molecules
is given in Figure 1 (6), Figure 2 (8b), and Figures 3-5 (9a-9c).
Selected bond distances (Å) and angles (deg) are listed in the
legend of Figure 1 (6) and Figure 2 (8b) as well as Table 1
(9a-c). The crystal and structure refinement data for all
compounds are summarized in Tables 6 and 7 (Experimental
Section).
The overall structural features of molecules 6, 8b, and 9a-9c
are similar to those of related structurally characterized
(ethynyl)biferrocene-,2a,3a,b,4,5 phosphine-gold(I) acetylide-,9 and
cyclopentadienyl-phosphine-ruthenium- and cyclopentadienyl-
phosphine-osmium-acetylide-containing molecules.10 They con-
Figure 2. ORTEP diagram (50% probability level) of 8b with the
sist of a biferrocene central entity with linear coordinated
alkynyl-gold(I) units (6) or pseudo-tetrahedral alkynyl-ruthenium
or -osmium moieties bonded to the cyclopentadienyl rings
(Figures 1-5).
The structures of symmetric 6 and 9a-9c show the molecules
to have crystallographic Ci symmetry about the center of the
bis(cyclopentadienyl) connectivity. This imposes a trans-
conformation on the location of the terminal-bonded transition
metal fragments with respect to the inversion center with a step-
atom-numbering scheme (the hydrogen atoms are omitted for
clarity). Selected bond distances (Å) and angles (deg): C43-C44
1.434(5), C42-C43 1.213(5), C42-Os1 2.030(4), Os1-P1 2.2985(9),
Os1-P2 2.2920(9), C49-C54 1.470(5), C59-C64 1.413(6),
C64-C65 1.193(6), D1-Fe1 1.641(1), D2-Fe1 1.640(1), D3-Fe2
1.646(1), D4-Fe2 1.644(1), D5-Os1 1.887(1); C42-C43-C44
177.5(4), C43-C42-Os1 172.3(3), C42-Os1-P1 95.25(10),
C42-Os1-P2 88.50(10), C65-C64-C59 175.8(5), D1-Fe1-D2
178.07(10), D3-Fe2-D4 177.14(9), C12-Os1-D5 122.01(12)
(D1 ) centroid of C1-C5, D2 ) centroid of C6-C10, D3 )
centroid of C13-C17, D4 ) centroid of C18-C22, D5 ) centroid
of C25-C29). The number in parentheses after each calculated
value represents the standard deviation in units of the last significant
digits.
(9) (a) Vicente, J.; Chicote, M. T.; Abrisqueta, M. D.; Jones, P. G.
Organometallics 1997, 16, 5628. (b) Mu¨ller, T. E.; Choi, S. W.-K.; Mingos,
D. M. P.; Murphy, D.; Williams, D. J.; Yam, V. W.-W. J. Organomet.
Chem. 1994, 484, 209. (c) Puddephatt, R. J. ComprehensiVe Coordination
Chemistry; Wilkinson, G. D., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon: Oxford, 1987; Vol. 5, p 861. (d) Grohmann, A.; Schmidbaur,
H. ComprehensiVe Coordination Chemistry II; Abel, E. W., Stone, F. G. A.,
Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol. 3, p 1. (e) Bruce, M. I.;
Horn, E.; Matisons, J. G.; Snow, M. R. Aust. J. Chem. 1984, 37, 1163.
(10) (a) Bruce, M. I.; Jevric, M.; Perkins, G. J.; Skelton, B. W.; White,
A. H. J. Organomet. Chem. 2007, 692, 1757. (b) Powell, C. E.; Cifuentes,
M. P.; McDonagh, A. M.; Hurst, S. K.; Lucas, N. T.; Delfs, C. D.; Stranger,
R.; Humphrey, M. G.; Houbrechts, S.; Asselberghs, I.; Persoons, A.;
Hockless, D. C. R. Inorg. Chim. Acta 2003, 352, 9. (c) Bruce, M. I.;
Hinterding, P.; Tiekink, E. R. T. J. Organomet. Chem. 1993, 450, 209. (d)
Fox, M. A.; Roberts, R. L.; Khairul, W. M.; Hartl, F.; Low, P. J. J.
Organomet. Chem. 2007, 692, 3277. (e) Bruce, M. I.; Hall, B. C.; Kelly,
B. D.; Low, P. J.; Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton
Trans. 1999, 3719.
like conformation of the two ferrocenyl rings (Figures 1-5).11
Both organometallic termini of 6 and 9a-9c point away from
the central biferrocenyl connecting unit. The two C5H4 rings of
this array are coplanar within 0.012 (6), 0.003 (9a), 0.008 (9b),
and 0.003 Å (9c). Similar observations were made for unsym-
metric 8b (0.039 Å) (Figure 2). The cylopentadienyl rings of
individual ferrocenyl building blocks are rotated by 12.92° (6),
0.36° (9a), 0.53° (9b), and 9.47° (9c), which verifies a somewhat
eclipsed arrangement. In 6 the C5H4 rings are approximately
(11) Dong, T.-Y.; Lee, W.-Y.; Su, P.-T.; Chang, L.-S.; Lin, K.-J.
Organometallics 1998, 17, 3323.

1882 Organometallics, Vol. 28, No. 6, 2009
Lohan et al.
Figure 3. ORTEP diagram (50% probability level) of 9a with the atom-numbering scheme (the hydrogen atoms and one disordered CH2Cl2
packing solvent molecule are omitted for clarity). Symmetry transformations used to generate equivalent atoms are labeled with “A”:
-x + 1, -y + 1, -z + 1 (center of inversion in between C6 and C6A). Selected bond distances (Å) and angels (deg) are summarized
in Table 1.
form a cis-conformation (Figure 2). The cylopentadienyl rings
of individual ferrocenyl building blocks are rotated by 14.09°
(Fe1) and 3.41° (Fe2), which verifies an almost eclipsed
conformation and in the case of Fe1 approximately midway
between the fully eclipsed and fully staggered conformation.
The alkynyl ligand and the fulvalenide arrangement are rotated
by 157° (Fe1) with respect to each other, while the free alkyne
ligand is rotated by 70° (Fe2).
Cyclic Voltammetry. Cyclovoltammetric measurements have
been carried out with compounds 4, 8a-8c, and 9a-9c. The
initial scans in the cyclic voltammogram (CV) of these
complexes were run from -0.6 to 1.2 V (vs standard calomel
electrode (SCE)), and the characteristic data are given in Table
2. The cyclic voltammograms are characterized by several
distinct one-electron waves. The bis(alkynyl)biferrocene deriva-
tives 8a-8c, bearing one terminal redox-active building block,
display a reversible wave around 0.0 V. This wave can be
assigned to the [M(II)]/[M(III)] (M ) Ru, Os) redox couples
and is fully reversible for 8a and 8b and partially reversible in
the case of 8c. Clearly, the dppf ligand destabilizes the [Ru(III)]
center. At more positive potentials two other redox events
corresponding to the sequential oxidation of the ferrocene units
are observed. In the case of the osmium complex 8b, these
electron transfers are quasi-reversible at the platinum electrode,
Figure 4. ORTEP diagram (50% probability level) of 9b with the
atom-numbering scheme (the hydrogen atoms and one CHCl3 packing
solvent molecule are omitted for clarity). Symmetry transformations
used to generate equivalent atoms labeled with “A”: -x + 1, -y + 1,
but the presence of the [Ru(III)] group in 8a and 8c strongly
decreases the chemical stability of the oxidized species. These
data suggest that the unpaired electron is probably more
delocalized on the alkynyl ligand in the case of the ruthenium
complexes 8a+ and 8c+.
The cyclic voltammograms of complexes 9a-9c, which
possess a redox-active metal center at both ends of the
bis(alkynyl)biferrocene bridge, show two well-resolved and
quasi-reversible (9a) or weakly reversible (9b and 9c) redox
events close to 0.0 V, corresponding to the stepwise oxidation
of the end groups (Figure 6: 9a, exemplarily). The wave
separation close to 0.2 V in the case of the complexes containing
ruthenium-based termini and slightly smaller in the case of the
bis(osmium) derivative 9b clearly indicates that the electron
transfer at one end is sensed by the metal at the opposite site.
-z + 1 (center of inversion in between C6 and C6A). Selected bond
distances (Å) and angels (deg) are given in Table 1.
midway between the fully eclipsed (0°) and fully staggered (36°)
conformations. The alkynyl ligands and the fulvalenide arrange-
ment are rotated by 157° (6), 71° (9a), 70° (9b), and 80° (9c)
with respect to each other. The Fe-D distances (D ) centroid
of the appropriate bfc cyclopentadienyl ligands) (Figures 1-5)
are characteristic3a,4a and indicate that the iron atoms are almost
equidistant between the cyclopentadienyl and the fulvalenide
ligands, corresponding to those bond distances found for other
ferrocenes.12 The bond lengths and bond angles about the
cyclopentadienyls, fulvalenides, alkynyls, and phosphino sub-
stituents are close to those reported for analogous transition
metal fragments.8,9
Compound 8b does not possess crystallographically imposed
inversion symmetry due to its two different substituents, which
(13) (a) Gritzner, G.; Kuta, J. Pure Appl. Chem. 1984, 56, 461. (b)
Strehlow, H.; Knoche, W.; Schneider, H. Ber. Bunsenges. Phys. Chem. 1973,
77, 760.
(12) Seiler, P.; Dunitz, J. D. Acta Crystallogr., Sect. B 1979, 35, 1068.

1′,1′′′-Bis(ethynyl)biferrocene as a Linking Group
Organometallics, Vol. 28, No. 6, 2009 1883
Figure 5. ORTEP diagram (50% probability level) of 9c with the atom-numbering scheme (the hydrogen atoms and CH2Cl2 packing
solvent molecules are omitted for clarity). Symmetry transformations used to generate equivalent atoms labeled with “A”: -x + 1, -y, -z
+ 1 (center of inversion in between C6 and C6A). Selected bond distances (Å) and angels (deg) are presented in Table 1.
Table 1. Selected Bond Distances (Å) and Angles (deg) for 9a, 9b,
(∆E) between the two redox events and the comproportionation
constant Kc are both representative of the thermodynamic
and 9ca
9a (M ) Ru)
9b (M ) Os)
9c (M ) Ru)
stability of the corresponding mixed-valence state relative to
other redox states. Their magnitude is determined by the sum
of several energetic factors relating to the stability of the reactant
and product complexes, and it is important to keep in mind that
a single redox event is no evidence for the absence of electronic
communication between the redox centers; the presence of two
resolved events establishes that through-bridge electron transfer
with a significant electronic coupling takes place.14,15
M1-P1
2.2911(9)
2.2766(9)
1.8906(16)
2.022(3)
1.209(5)
1.429(5)
1.6491(15)
1.6490(15)
1.456(6)
99.54(3)
122.5(1)
90.09(9)
175.2(3)
173.2(3)
2.2808(13)
2.2915(14)
1.8887(24)
2.025(5)
1.213(8)
1.425(7)
1.6472(24)
1.6487(24)
1.467(11)
99.05(5)
125.4(1)
87.79(14)
174.4(5)
2.2670(12)
2.2635(11)
1.8820(21)
2.025(5)
1.202(6)
1.438(7)
1.6525(21)
1.6477(22)
1.477(10)
96.13(4)
121.8(1)
88.86(13)
174.8(4)
M1-P2
M1-D1b
M1-C12
C11-C12
C1-C11
Fe1-D2c
Fe1-D3d
C6-C6A
Kc
\z
P1-M1-P2
P1-M1-D1
P1-M1-C12
M1-C12-C11
C1-C11-C12
{[Mred]-B-[Mred]}n++{[Mox]-B-[Mox]}(n+2)+ y
2{[Mred]-B-[Mox]}(n+1)+ (1)
172.2(6)
169.9(5)
∆Gc ) ∆E ) E2-E1 ) -(RT/F) log Kc
(2)
a The number in parentheses after each calculated value represents
the standard deviation in units of the best significant digits. b D1 )
centroid of C13-C17. c D2 ) centroid of C1-C5. d D3 ) centroid of
C6-C10.
UV-Vis Spectroscopy. The UV-vis spectra of 4, 8a-8c,
and 9a-9c were recorded in dichloromethane at 293 K, and
characteristic data are collected in Table 3. As shown in Figure
7, all the spectra present the same general aspect with,
nevertheless, a more intense absorption around 270 nm for 8c
and 9c, which can be confidently attributed to the contribution
of the dppf ligand.8 The low-energy bands with maxima below
300 nm can be assigned to π f π intraligand transitions
involving the C5H5 and phosphine ligands as well as the alkynyl
fragments.
At more positive potentials further irreversible oxidations
centered on the biferrocene bridge take place. The presence of
a [M(III)] electron-deficient terminus decreases the reversibility
of the electron transfers on the biferrocene connectivity.
Probably, this behavior is a consequence of a large delocalization
of the electronic vacancy on the biferrocene systems as described
in Scheme 3. A similar behavior was already observed by Sato
and co-workers for related [(η5-C5H5)(PPh3)2RuCtCFc][PF6].7a,b
Comparison of the redox potentials found for 9a with those
recently reported for the related compound [(η5-C5H5)(PPh3)2-
RuCtCFc′CtCRu(PPh3)2(η5-C5H5)]7a (Fc′ ) (η5-C5H4)2Fe)
shows that introduction of a second ferrocenyl group in the
spacer linking the metal termini favors interactions between the
terminal ends. Indeed, for the compound with only one
ferrocenyl unit, the cyclic voltammogram does not discriminate
the redox potentials of the ruthenium termini, while the
potentials of the same termini in 9a are separated by 0.19 V.
No doubt the insertion of an additional ferrocenyl unit between
the terminal redox centers increases the thermodynamic stability
of the mixed-valence species.
With reference to the electronic absorption spectra of fer-
rocene, which shows low-energy absorptions at 326 and 438
nm, and biferrocene, which presents three maxima at 450, 296,
and 269 nm,4a the low-energy absorptions of complex 4
observed at 301 and 450 nm can be assigned to an admixture
of the dπ(Fe) f π*(C′C) metal-to-ligand charge transfer
(MLCT) transition. Comparison of the data indicates that
grafting alkynyl substituents on the biferrocene has only a weak
effect on the HOMO-LUMO gap.
The electronic absorption of (η5-C5H5)(PPh3)2RuCtCFc was
characterized by two bands, at 350 and 435 nm, respectively,
which are very close to the ferrocene d-d bands.7a Complex
9a, which can be regarded as a dimer of this complex, presents
very similar absorptions. Roughly, the data in Table 3 show
that as the number of ferrocenyl and (η5-C5H5)(PPh3)2MCtCFc
The straightforward determination of the two redox potentials
1
2
E0 and E0 for the terminal groups for 9a-9c allowed the
determination of the comproportionation constants for the
equilibrium described by eqs 1 and 2. The potential difference
(14) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877.
(15) Lapinte, C. J. Organomet. Chem. 2008, 693, 793.

1884 Organometallics, Vol. 28, No. 6, 2009
Lohan et al.
Table 2. Electrochemical Data for 4, 8a-8c, and 9a-9ca
[M(II)]/[M(III)]
[Fe2+]/[Fe3+ [Fedppf2+]/[Fedppf
3+
]
]
compd
M
E (∆Ep, Ic/Ia) [V]
E (∆Ep, Ic/Ia) [V]
E (∆Ep, Ic/Ia) [V]
Kc
4
none
0.47 (0.13, ∼1)
0.85 (0.13, ∼1)
0.65 (0.12, <1)
0.89 (0.12, ∼0)
0.60 (0.11, ∼1)
0.82 (0.10, ∼1)
0.57b
8a
8b
8c
9a
9b
9c
Ru
Os
Ru
Ru
Os
Ru
0.09 (0.11, 1)
0.04 (0.11, 1)
0.06 (0.12, <1)
0.70b
0.68b
0.98b
0.03 (0.09, 1)
0.22 (0.10, 1)
-0.03 (0.09, <1)
0.12 (0.05, <1)
0.09 (0.10, <1)
0.30 (0.10, <1)
0.74 (0.12, <1)
1.8 × 103
0.4 × 103
4.0 × 103
0.89b
0.62 (0.10, <1)
0.79 (0.10, <1)
0.64b
0.99b
a Potentials in dichloromethane (0.1 M [nBu4N]PF6; 298 K, platinum electrode, sweep rate 0.100 V s-1) are given in V vs SCE; the
ferrocene-ferrocenium couple [Fc]/[Fc+] (0.460 V vs SCE) was used as an internal calibrant for the potential measurements.13 Redox potentials
determined as (Ea + Ec)/2 for the reversible or partially reversible couples and as Ea for the nonreversible redox systems. b Irreversible.
Table 3. UV-Vis Absorption Spectral Data of Selected Complexes
low temperature and become delocalized as the temperature
increases (electron transfer rate ∼108 s-1).17
in Dichloromethane at 298 K
compd
absorption λ/nm (10-3 ꢀ/dm3 mol-1 cm-1
)
The neutral complexes 4 and 8a-8c were reacted with less
than 1 (ca. 0.8) equiv of ferrocenium in tetrahydrofuran at -60
°C, while compounds 9a-9c were reacted with both 0.8 and
2.0 equiv of ferrocenium. The obtained solutions were trans-
ferred into EPR tubes, and spectra were recorded at 66 K. In
most instances, resolved spectra could be obtained, and the
g-tensor components are summarized in Table 4. All the spectra
display the same pattern characteristic of radicals with axial-
type symmetry. The g| component ranges between 2.28 and 4.28,
and the g tensor varies between 1.86 and 2.09, while the
anisotropy of the ∆g tensor ranges between 0.77 and 2.60.
It is well-established that piano-stool radicals such as [(η5-
C5H5)(PPh3)2Ru(III)CtCR]+ are characterized by a rhombic
signal with three well-separated g-tensor components.7c,18,19 In
this respect, the EPR data obtained for complexes 8a-8c and
9a-9c clearly establish that the unpaired electrons are not
ruthenium or osmium centered, but for all these radicals the
axial symmetry of the EPR spectra suggests that the SOMOs
possess a significant biferrocenium character in line with the
CV data (Vide supra).
4
227 (75), 265 (24), 301 (13), 450 (0,8)
227 (105), 270 (3), 346 (14), 430 (4)
228 (11), 274 (3), 346 (12), 445 (3)
227 (101), 263 (54), 344 (12), 440 (3)
227 (135), 345 (22), 440 (5)
8a
8b
8c
9a
9b
9c
227 (161), 272 (46), 350 (22), 440 (4)
270 (147), 347 (10), 438 (2)
Table 4. EPR Data Determined in Glassy Tetrahydrofuran Solution
compda
g|
g
∆gb
4+
3.24
1.91
1.33
42+
3.46
1.86
1.60
c
8a+
8b+
9a+
9a2+
9b+
9c+
4.283
2.810
2.852
2.885
2.840
2.828
2.005
2.090
1.984
1.986
2.066
2.009
2.278
0.720
0.868
0.899
0.774
0.819
a Measured at 66 K. b ∆g ) g| - g . c Generated using [AgOTf].
(M ) Ru, Os) groups increases, the intensity of the low-energy
bands increases, but the maxima remain around 340 and 440
nm. Therefore, the UV-vis analysis does not reveal significant
interactions between the metal sites on the neutral compounds.
The main feature of the EPR data listed in Table 4 comes
from the large variation of the ∆g values. The ∆g tensor
obtained for 4+ compares well with those obtained for other
1′,1′′′-disubstituted biferrocenium cations with unsaturated
organic moieties.16a The intermediate value found for the tensor
of anisotropy of 4+ suggests that the electron-transfer between
Electron Paramagnetic Resonance. 1′,1′′′-Disubstituted
biferrocenium salts were subjected to several EPR studies.
Important and systematic studies of electron transfer for mixed-
valence disubstituted biferrocenium cations have led to a wealth
of experimental results. Based on EPR and Mo¨ssbauer spec-
troscopies, works reported by Dong and Hendrickson established
a relation between the electron transfer rate in these mixed-
valence compounds and the g-tensor anisotropy of the EPR
spectra. They established that trapped mixed-valence complexes
(electron transfer rate <108 s-1) give EPR spectra with a large
anisotropy (∆g > 1.5), while detrapped mixed-valence com-
pounds (electron transfer rate >108 s-1) have EPR spectra with
a small anisotropy (∆g < 1.1).16,2b Systems with intermediate
tensors of anisotropy (1.1 < ∆g < 1.5) show Mo¨ssbauer behavior
changing with the temperature; they are valence localized at
the two ferrocene units takes place at a rate close to 108 s-1
.
Connecting a single (η5-C5H5)(PPh3)2M building block on one
of the terminal alkynes produces opposite effects on the electron
transfer rate in the monoradicals. Indeed, a very large ∆g value
is obtained for M ) Ru, while small values were found for the
related osmium-containing complex. According to these data,
complex 8a+ should be a trapped mixed-valence complex in
contrast with its parent compound 8b+, for which the unpaired
electron should be delocalized on the two iron centers. In the
case of complex 8c+, it was not possible to obtain resolved EPR
spectra at liquid nitrogen temperature. In the case of the
monoradicals 9a-c[PF6] featuring two redox-active terminal
ends, the axial symmetry of the spectra is maintained, indicating
(16) (a) Dong, T.-Y.; Ho, P.-H.; Lai, X.-Q.; Lin, Z.-W.; Lin, K.-J.
Organometallics 2000, 19, 1096. (b) Dong, T.-Y.; Lee, T.-Y.; Lee, S.-H.;
Lee, G.-H.; Peng, S.-M. J. Am. Chem. Soc. 1985, 107, 7996. (c) Dong,
T.-Y.; Hendrickson, D. N.; Pierponnt, C. G.; Moore, M. F. J. Am. Chem.
Soc. 1986, 108, 963.
(17) Webb, R. J.; Dong, T.-Y.; Pierpont, C. G.; Boone, S. R.; Chadha,
R. K.; Hendrickson, D. N. J. Am. Chem. Soc. 1991, 113, 4806–4812.
(18) Paul, F.; Toupet, L.; The´pot, J.-Y.; Costuas, K.; Halet, J.-F.; Lapinte,
C. Organometallics 2005, 24, 5464.
(19) Rieger, P. H. Coord. Chem. ReV. 1994, 135/136, 203.

1′,1′′′-Bis(ethynyl)biferrocene as a Linking Group
Organometallics, Vol. 28, No. 6, 2009 1885
Table 5. NIR Data for 9a[PF6] and 9a[PF6]2
Vmax (cm-1) ꢀ (M-1 cm-1 (cm-1
(∆V1/2 (∆V1/2
c
theo
e
g
compd
transition
)
)
)
)
(cm-1
)
Hab (cm-1
)
Hab (cm-1
)
exp
9a+
LMCT
IVCT
4500 (6000)a b d
6500 (7200)a
6600 (7500)b
4500 (11 400)a
4400 (4500)b
6200 (10 200)a
6400 (8700)b
820 ( 20
2400 ( 50
2300 ( 50b
800 ( 20
2900
3600
,
,
1098 ( 50
1105 ( 50
3250
3300b
3600b
2900
2900b
3500
3600b
9a2+
LMCT
IVCT
900 ( 20b
2400 ( 50
2400 ( 50b
912 ( 50f
855 ( 50f
3250
3300b
c
a In dichloromethane. b In methane/acetone, 1:3. Calculated using eq 3 for ∆G0 ) -800 cm-1
.
d Masked by a stretching band of the solvent. e Using
eq 4 and assuming a through-space Ru-Fe distance of 6.29 Å as determined in the X-ray crystal structure of 9. f Calculated following eq 5. g Calculated
following eq 6.
Table 6. Crystal and Intensity Collection Data for 6 and 8b
measured for 9a (Vide supra). As the oxidation proceeds, a sharp
absorption band appears in the visible range at 610 nm, while
a very broad absorption increases in the NIR domain with two
apparent maxima at 1540 and 2180 nm. The first one-electron
oxidation proceeds without shift of these three bands. The
molecular extinction coefficients determined for the monocation
9a[PF6] are 15500, 7200, and 6200 dm3 mol-1 cm-1, respec-
tively. As the second oxidation takes place, small red shifts were
observed for the three bands. After completion of the second
oxidation, the spectrum of the dication displays three bands with
apparent maxima at 632, 1606, and 2180 nm and molecular
extinction coefficients of 23 700, 10 200, and 11 400 dm3 mol-1
cm-1, respectively. The two redox events are fully reversible.
Indeed, reduction carried out after the two one-electron oxidation
processes recovered exactly the initial spectrum of the neutral
derivative 9a. One can note that the spectra of the two related
complexes [(η5-C5H5)(PPh3)2RuCtCFc][PF6] and [(η5-C5H5)-
(PPh3)2RuCtCFc′CtCRu(PPh3)2(η5-C5H5)][PF6] are very similar.7a,b
6
8b
1196.91
C60H46Au2Fe2P2 · 0.5CH2Cl2 C65H52Fe2OsP2
fw
1419.47
chemical formula
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
monoclinic
P21/n
30.6325(11)
7.5752(2)
23.4678(8)
110.577(4)
5098.2(3)
1.849
13.2294(2)
20.3860(2)
18.4642(3)
97.5590(10)
4936.42(12)
1.610
ꢀ (deg)
V (Å3)
Fcalc (g cm-3
F(000)
)
2752
2400
cryst dimens (mm)
Z
0.6 × 0.3 × 0.2
0.4 × 0.2 × 0.2
4
4
max. and min. transition 1.00000, 0.46950
1.00000, 0.73240
3.256
absorp coeff (λ, mm-1
scan range (deg)
index ranges
)
6.503
3.01-26.15
2.85-26.06
-37 e h e 37, -9 e k e 9, -16 e h e 16,
-29 e l e 28
-25 e k e 24,
-14 e l e 22
27 526
total reflns
23 395
With reference to previous work on Ru(III) and Fe(III)
acetylide complexes the band close to 600 nm can be safely
attributed to a ligand-to-metal charge transfer (LMCT) band.7c,18
The appearance of two intense absorptions in the NIR range
for both the mixed-valence species 9a+[PF6] and the dication
9a2+[PF6]2 is puzzling. As the bands in the NIR range were
poorly resolved, the deconvolution from the band envelopes was
undertaken for the mixed-valence species 9a+[PF6] and the
dication 9a2+[PF6]2 (Figure 8). Deconvolution in the NIR range
of the experimental spectra recorded in dichloromethane and a
1:3 mixture of dichloromethane/acetone was achieved using
Gaussian functions and assuming two overlapping transitions.
The spectral parameters of the bands obtained for the best fits
have been compiled in Table 5. The two bands are of similar
intensities, but the band at lower energy is much narrower than
the band on the high-energy side of the spectral window.
unique reflns
Rint
5060
0.0284
9705
0.0331
data/restraints/params
5060/0/326
1.334
0.0523, 0.1097
0.0627, 0.1125
1.621, -1.158
9705/0/631
1.020
0.0260, 0.0536
0.0464, 0.0624
1.555, -0.709
goodness-of-fit on F2
a
a
R1 , wR2 [I g 2σ(I)]
a
a
R1 , wR2 (all data)
max. and min. peak
(e Å-3
)
a
R1 ) [∑(|Fo| - |Fc|)/∑|Fo|); wR2 ) [∑(w(Fo - Fc2)2)/∑(wFo )]1/2. S
2
4
) [∑w(Fo - Fc2)2]/(n - p)1/2. n ) number of reflections, p )
parameters used.
2
that the unpaired electrons are not localized on the ruthenium/
osmium termini but on SOMOs with a significant biferrocenium
character. Moreover, the ∆g parameters are small, and therefore
the unpaired electron is expected to be delocalized on the two
ferrocenyl units on the EPR time scale. Consequently, the odd
electron should be delocalized on the whole molecule and
probably exchanges from one redox-active terminus to the other
across the biferrocenyl bridge, which acts as a relay in this long-
distance electron transfer. A resolved EPR spectrum was also
obtained for the dication 9a2+. However, the lack of data in the
literature on EPR spectroscopy of biferrocenium biradicals
makes any further interpretation difficult.
Spectro-electrochemistry of 9a. As the tetranuclear complex
9a presents reversible redox events, the UV-vis-NIR spectra
of 9a[PF6]n (n ) 0, 1, 2) were collected using spectro-
electrochemical methods. The UV-vis-NIR spectra were
obtained with an optically transparent thin-layer electrosynthetic
(OTTLE) cell with a standard design,20 and selected spectra
are shown in Figure 8. Measurements were carried out in
dichloromethane containing 0.1 M [nBu4N]PF6 as supporting
electrolyte. The initial spectrum was identical to the spectrum
According to the Hush model applied to class II unsym-
metrical mixed-valence complexes, the theoretical half-width
(∆V1/2)theo of an IVCT transition is related to ∆G0, the energy
gap between the two potential wells corresponding to the two
diabatic redox states, and to Vmax, the energy on the peak
maximum (eq 3). For complex 9a[PF6] ∆G0 can be estimated
from the difference in the oxidation potentials measured by
cyclic voltammetry under the same conditions for the closely
related model complexes (η5-C5H5)(PPh3)2RuCtCPh10d (E0 )
0.535 V) and compound 4. As these values are rather close,
the ∆G0 gap is expected to be not larger than 0.1 V (i.e., 800
cm-1). Comparison of the theoretical and experimental width at
half-height for the two bands suggests that probably the band
around 4500 cm-1 is too narrow to correspond to an IVCT
transition. More likely this band corresponds to a LMCT, its
intensity being probably too large for a d-d ligand field transition.
Indeed, the intensity of these forbidden transitions are generally
close to 100 M-1 cm-1.7c In contrast, the theoretical width at half-
(20) Duff, C. M.; Heath, G. A. Inorg. Chem. 1991, 30, 2528.

1886 Organometallics, Vol. 28, No. 6, 2009
Lohan et al.
Table 7. Crystal and Intensity Collection Data for 9a, 9b, and 9c
9a 9b
9c
fw
1967.32
2214.46
2026.95
chemical formula
cryst syst
space group
a (Å)
b (Å)
c (Å)
C106H86Fe2P4Ru2 2 CH2Cl2
monoclinic
P21/c
11.8236(7)
16.9641(11)
22.8373(11)
95.319(4)
4560.9(5)
1.433
2012
C106H86Fe2Os2P4 2 CHCl3
monoclinic
P21/c
11.86750(10)
16.88340(10)
22.6922(2)
94.9200(10)
4529.94(6)
1.624
C102H82Fe4P4Ru2 2 CH2Cl2
monoclinic
P21/n
9.98900(10)
24.0564(2)
17.26870(10)
94.5000(10)
4136.87(6)
1.627
ꢀ (deg)
V (Å3)
Fcalc (g cm-3
F(000)
)
2204
2060
cryst dimens (mm)
Z
0.6 × 0.5 × 0.1
0.8 × 0.2 × 0.2
0.2 × 0.1 × 0.1
2
2
2
max. and min. transition
1.02232, 0.98023
0.873
2.94-26.09
-14 e h e 14, -20 e k e 20,
-28 e l e 28
44 399
1.00000, 0.59826
3.408
2.96-26.06
-14 e h e 14, -20 e k e 20,
-28 e l e 28
44 167
1.00000, 0.35330
10.679
3.67-60.62
-11 e h e 10, -27 e k e 27,
-19 e l e 19
32 181
absorp coeff (λ, mm-1
scan range (deg)
index ranges
)
total reflns
unique reflns
Rint
8999
0.0298
8934
0.0225
6185
0.0518
data/restraints/params
8999/75/569
1.088
0.0427, 0.1207
0.0624, 0.1287
1.859, -1.171
8934/33/550
1.134
0.0398, 0.0964
0.0484, 0.1017
2.336, -2.328
6185/0/532
0.971
0.0345, 0.0779
0.0546, 0.0878
1.095, -0.678
goodness-of-fit on F2
a
a
R1 , wR2 [I g 2σ(I)]
a
a
R1 , wR2 (all data)
max. and min. peak (e Å-3
)
a
2
4
2
R1 ) [∑(|Fo| - |Fc|)/∑|Fo|); wR2 ) [∑(w(Fo - Fc2)2)/∑(wFo )]1/2. S ) [∑w(Fo - Fc2)2]/(n - p)1/2. n ) number of reflections, p ) parameters used.
Figure 6. Cyclic voltammogram of 9a (10-3 M solution in dichloromethane at 298 K with [nBu4N]PF6 as supporting electrolyte, scan rate
) 0.100 V s-1. All potentials are referenced to ferrocene/ferrocenium [Fc/Fc+] as an internal reference for potential measurements. E0
values corrected for [Fc/Fc]+ at 0.460 V vs SCE in dichloromethane.13
height of the band with a maximum of absorption near 6500 cm-1
is only slightly larger than the experimental half-width, as expected
for an IVCT corresponding to an electron transfer occurring at a
fast regime on the EPR time scale (Vide supra).21
common polar solvents, the use of such solvents resulted in the
rapid precipitation of the complex. Among the polar solvents
tested only a 1:3 mixture of dichloromethane/acetone proved
to be suitable for a spectro-electrochemical experiment. The data
extracted from these measurements reveal that only the Gaussian
band at higher energy displayed a solvatochromism consistent
with an IVCT transition of a class II mixed-valence complex.21
However, one can note that the solvent effect is relatively small,
indicating that the electronic coupling between the redox-active
centers cannot be regarded as weak.
(∆V1/2)theo ) [2310(Vmax - ∆G0)]1/2
(3)
(4)
Hab ) (2.06 × 10-2/dab)(εmaxVmaxV1/2)1/2
Hab ) (2.06 × 10-2/dab21/2)(εmax
Hab ) (Vmax)/2
ν
max∆ν1/2)1/2
(5)
(6)
On the other hand, the similarity between the spectrum
obtained for the mixed-valence compound and the dication
The influence of the solvent polarity on these bands was also
briefly investigated. However, due to low solubility of 9a in
(21) Astruc, D. Electron Transfer and Radical Processes in Transition-
Metal Chemistry; VCH: New York, 1995; p 630.

1′,1′′′-Bis(ethynyl)biferrocene as a Linking Group
Organometallics, Vol. 28, No. 6, 2009 1887
Scheme 3. Delocalization of Electron Vacancy on
(LnMCtC)2bfc (LnM ) (η5-C5H5)(Ph3P)2Ru (9a), (η5-C5H5)-
(Ph3P)2Os (9b), (η5-C5H5)(dppf)Ru (9c))
between the biferocenyl unit and the two Ru(III) centers and
assuming they behave independently, the effective electronic
coupling can be determined using the modified Hush equation
reported by Bonvoisin and Launay (eq 5) to take into account
the double probability that such an event happens (Table 5).23
Despite the sizable uncertainties associated with the spectro-
scopic measurements and the sensitivity of the compounds, these
values provide support for the proposition that similar electronic
couplings are operative in both complexes.
The solvent has only a minor influence on the IVCT bands,
and consequently, these compounds cannot be considered as
class II mixed-valence complexes in the classification of Robin
and Day.24 Consequently, the electronic coupling is underesti-
mated by Hush treatment (eq 4 or 5) and overestimated by class
III treatment (eq 6, Table 5). They might be close to borderline
class IIA/class IIB according to the subcategorization developed
for symmetric mixed-valence complexes by Brunschwig et al.25
In other words, they can be considered as strongly coupled
mixed-valence complexes with a localized valency in the ground
state.26
Conclusion
A series of bis(ethynyl)biferrocene-based transition metal
complexes of structural type (LnMCtC)(HCtC)bfc (LnM )
(η5-C5H5)(Ph3P)2Ru, (η5-C5H5)(Ph3P)2Os, (η5-C5H5)(dppf)Ru; bfc
) 1′,1′′′-biferrocenyl, ((η5-C5H4)2Fe)2; dppf ) 1,1′-bis(diphenyl)-
phosphanyl ferrocene, (η5-C5H4PPh2)2Fe) and (LnMCtC)2bfc
(LnM ) Ph3PAu, (η5-C5H5)(Ph3P)2Ru, (η5-C5H5)(Ph3P)2Os, (η5-
C5H5)(dppf)Ru) have been synthesized in straightforward con-
secutive synthetic procedures. In these heterobimetallic mol-
ecules a biferrocenyl moiety links different organometallic
termini including Au-, Ru-, and Os-containing building blocks.
The molecule (HCtC)2bfc is fairly stable toward air and
moisture, while the appropriate M2bfc compounds (M ) Au,
Ru, Os) are rapidly oxidized either in solution or in the solid
state. The structures of these molecules in the solid state were
determined by single-crystal X-ray structure analysis. It was
found that symmetric molecules have crystallographic Ci
symmetry and show a trans-conformation. Unsymmetric species
impose cis-conformation. The cyclic voltammetric data estab-
lished that the 1′,1′′′-bis(ethynyl)biferrocene acts as a linking
group for ruthenium and osmium half-sandwich fragments
capable of conveying electronic interaction from one end to the
other more efficiently than the 1,1′-(ethynyl)ferrocene, which
was recognized to behave as an insulator for a model with the
same terminal ends.7a,b The EPR spectroscopy established that
the SHOMOs which contain the odd electrons in 9a-c[PF6]
possess a significant biferrocene character. Interestingly enough,
the small tensors of anisotropy strongly support that the
biferrocenyl bridge acts as a relay in this long-distance electron
transfer. Analysis of the NIR absorption bands also supports
that a direct Ru-Ru electron transfer does not take place in
9a[PF6], the electron exchange occurring through two successive
RuCtCFc electron transfers favored by a fast exchange between
the two ferrocene units. All experimental data support the
conclusion that the strongest interaction may occur between one
indicates that the IVCT cannot be assigned to a direct Ru-Ru
optically induced electron transfer through the bridge. In
contrast, the similarity between the NIR spectra obtained for
9a[PF6] and the complex [(η5-C5H5)(PPh3)2RuCtCFc][PF6]7a,b
is consistent with an IVCT between the biferrocenyl unit and
the Ru(III) termini, in full agreement with the EPR data. During
the reviewing process of our manuscript, a study on biferrocenyl
triiodide based on MIR and NIR spectroscopy and DFT
calculations suggests that the two NIR bands could both be
assigned to IVCT transitions.22 It is also noteworthy that the
spectral parameters obtained for the mixed-valence complex
9a[PF6] and the dication 9a[PF6]2 are very similar, indicating
that the IVCT process occurs through a similar mechanism in
both derivatives with comparable reorganization energies.
However, the magnetic exchange interaction between the odd
electrons through the biferrocene system of the dication remains
unclear. Interestingly, the dication behaves as a symmetric
molecule constituted by two nonsymmetric mixed-valence units
linked by a covalent bond.
Assuming that the Hush theory applies for this IVCT
transition between the biferrocene unit and the Ru(III) termini,
the electronic coupling (Hab) of the mixed-valence complex
9a[PF6] amounts to 1100 ( 50, according to eq 4, when the
Fe-Ru distance is taken as 6.29 Å. In the case of the dication
9a[PF6]2, assuming that two electrons can potentially exchange
(23) Bonvoisin, J.; Launay, J.-P.; V. d.; Auweraer, M.; De Schryver,
F. C. J. Phys. Chem. 1994, 98, 5052.
(24) Robin, M. B.; Day, P. AdV. Inorg. Chem. Radiochem. 1967, 10,
247.
(25) Brunschwig, B. S.; Creutz, C.; Sutin, N. Chem. Soc. ReV. 2002,
31, 168.
(22) Warratz, R.; Aboulfadl, H.; Bally, T.; Tuczek, F. Chem.-Eur. J.
2009, 15, 1604.
(26) Demandis, K. D.; Hartshorn, C. M.; Meyer, T. J. Chem. ReV. 2001,
101, 2655.

1888 Organometallics, Vol. 28, No. 6, 2009
Lohan et al.
Figure 7. UV-vis spectra of complexes 4, 8a-8c, and 9a-9c in dichloromethane at 298 K.
from tetramethylsilane with the solvent as reference signal (1H
NMR: CDCl3 (99.8%), δ 7.26; 13C{1H} NMR: CDCl3 (99.8%), δ
77.16 ppm).27 31P{1H} NMR spectra were recorded at 101.255 MHz
in CDCl3 with P(OMe)3 as an external standard (δ ) 139.0 ppm,
relative to H3PO4 (85%) with δ ) 0.00 ppm). The abbreviation pt
in the 1H NMR spectra corresponds to pseudotriplet. Cyclic
voltammograms were recorded in a dried cell purged with purified
argon. Platinum wires served as working and counter electrodes.
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-
ferrocenium couple [Fc]/[Fc+] (FcH ) (η5-C5H5)2Fe, E0 ) 0.46
V) as reference.13 Electrolyte solutions were prepared from
tetrahydrofuran and [nBu4N]PF6 (Fluka, dried in oil-pump vacuum).
The respective organometallic complexes were added at c ) 1.0
mM. Cyclic voltammograms were recorded in a negative-going
direction at the starting potentials using a Voltalab 3.1 potentiostat
(Radiometer) equipped with a digital DEA 101 electrochemical
analyzer and an IMT 102 electrochemical interface. Melting points
were determined using analytically pure samples, sealed off in
nitrogen-purged capillaries on a Gallenkamp MFB 595 010 M
melting point apparatus. The EPR spectra were recorded in
tetrahydrofuran solutions with a concentration of 1 mmol of the
complex under investigation and ferrocenium as oxidizing agent
with a Bruker EMX-8/2.7 (X-band) spectrometer. UV-visible and
NIR spectra were recorded with a Cary 5000. Microanalyses were
partly performed by the Institute of Organic Chemistry, Chemnitz,
University of Technology.
Figure 8. NIR spectra for 9a+[PF6] (top) and 9a2+[PF6]2 in
dichloromethane and proposed deconvolution.
(η5-C5H5)(PPh3)2M moiety and the biferrocenyl unit through
ethynyl fragments, but while the ferrocene group acts as an
insulator, the biferrocene plays the role of a relay, allowing
electron transfer from one metal terminus to the other one.
Reagents. 1′,1′′′-Bis(ethynyl)biferrocene,3a [(PPh3)AuCl],9e [(PPh3)2-
(η5-C5H5)RuCl],28 [(PPh3)2(η5-C5H5)OsBr],29 and [(dppf)(η5-C5H5)-
RuCl]8f were prepared according to published procedures. All other
chemicals were purchased from commercial suppliers and were used
without further purification.
Experimental Section
Synthesis of 1′,1′′′-(HCtC)2bifc (4).3a,b To 1.0 g (1.608 mmol)
of 1′,1′′′-diiodobiferrocene (1) suspended in 60 mL of degassed
diisopropylamine were added 0.31 mL (3.21 mmol) of 2-methyl-
3-butyn-2-ol followed by 56 mg (5 mol %) of Pd(PPh3)2Cl2 and
32 mg (10 mol%) of Cu(OAc)2. The resulting reaction mixture was
General Data. All reactions were carried out under an atmo-
sphere of nitrogen or argon using standard Schlenk techniques.
Tetrahydrofuran, diethyl ether, and n-hexane were purified by
distillation from sodium/benzophenone ketyl; dichloromethane was
purified by distillation from calcium hydride. Celite (purified and
annealed, Erg. B.6, Riedel de Haen) was used for filtrations.
Instruments. Infrared spectra were recorded with a Perkin-Elmer
FT-IR Spectrum 1000 spectrometer. NMR spectra were recorded
with a Bruker Avance 250 spectrometer (1H NMR at 250.12 MHz
and 13C{1H} NMR at 62.86 MHz) in the Fourier transform mode.
Chemical shifts are reported in δ units (parts per million) downfield
(27) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997,
62, 7512.
(28) Joslin, F. L.; Mague, J. T.; Roundhill, D. M. Organometallics 1991,
10, 521.
(29) Bruce, M. I.; Low, P. J.; Skelton, B. W.; Tiekink, E. R. T.; Werth,
A.; White, A. H. Aust. J. Chem. 1995, 48, 1887.

1′,1′′′-Bis(ethynyl)biferrocene as a Linking Group
Organometallics, Vol. 28, No. 6, 2009 1889
heated to 70 °C and stirred for 12 h. After cooling to 25 °C, the
reaction mixture was filtered through a pad of Celite and all volatiles
were removed under reduced pressure. The remaining material was
subjected to column chromatography on silica gel using a mixture
of toluene/tetrahydrofuran (8:1, v/v). Thus formed 3 was isolated
as a red solid. Yield: 700 mg (1.31 mmol, 81% based on 1).
IR (KBr, cm-1): 2230 (w, νCtC), 3429 (s, νO-H). 1H NMR (250
MHz, CDCl3, δ): 1.56 (s, 12 H, CH3), 2.36 (s, 2 H, OH); 4.03 (pt,
JHH ) 1.8 Hz, 4 H, C5H4), 4.16 (pt, JHH ) 1.8 Hz, 4 H, C5H4),
4.24 (pt, JHH ) 1.8 Hz, 4 H, C5H4), 4.41 (pt, JHH ) 1.8 Hz, 4 H,
C5H4).
KOH (400 mg, 7.12 mmol) was added to 700 mg (1.31 mmol)
of 3, which was dissolved in 50 mL of toluene. The resulting
reaction mixture was heated to 110 °C and stirred 12 h. After
cooling to 25 °C, the resulting mixture was filtered through a pad
of Celite and all volatiles were removed under reduced pressure.
The remaining material was subjected to column chromatography
on silica gel using a mixture of toluene/dichloromethane (1:1, v/v).
After removal of all solvents compound 4 could be isolated as an
orange solid. Yield: 545 mg (1.3 mmol, 99% based on 3).
IR (KBr, cm-1): 2109 (w, νCtC), 3305 (w, νtCH). 1H NMR (250
MHz, CDCl3, δ): 2.66 (s, 1 H, tCH); 4.02 (pt, JHH ) 1.8 Hz, 4 H,
C5H4), 4.23 (pt, JHH ) 1.8 Hz, 4 H, C5H4), 4.25 (pt, JHH ) 1.8 Hz,
4 H, C5H4), 4.4 (pt, JHH ) 1.8 Hz, 4 H, C5H4).
Synthesis of 1′,1′′′-((PPh3)AuCtC)2bifc (6). To 58 mg (0.138
mmol) of 1′,1′′′-bis(ethynyl)biferrocene (4) and 137 mg (0.277
mmol) of (Ph3P)AuCl (5) dissolved in 20 mL of a tetrahydrofuran/
diethylamine mixture of ratio 1:1 was added 5 mg of CuI. The
turbid reaction mixture was stirred for 4 h at room temperature,
and all volatile materials were removed under reduced pressure.
The residue was purified by column chromatography on silica
(column dimension: 30 × 2 cm) using first an n-hexane/dichlo-
romethane mixture (ratio 4:1 v/v) to remove unreacted 4. With
tetrahydrofuran as eluent the title compound 6 was obtained.
Removal of all volatiles in an oil-pump vacuum gave 6 as a yellow
solid. Yield: 100 mg (0.074 mmol, 54% based on 4).
Anal. Calcd for C60H46Au2Fe2P2 (1334.5 g/mol): C, 53.99; H,
3.47. Found: C, 54.01; H 3.52. IR (KBr, cm-1): 2104 (w, νCtCAu).
1H NMR (250 MHz, CDCl3, δ): 3.89 (pt, JHH ) 1.8 Hz, 4 H, C5H4),
4.24 (pt, JHH ) 1.8 Hz, 4 H, C5H4), 4.28 (pt, JHH ) 1.8 Hz, 4 H,
C5H4), 4.44 (pt, JHH ) 1.8 Hz, 4 H, C5H4), 7.4-7.61 ppm (m, 30
H, Ph). 13C{1H} NMR (62.9 MHz, CDCl3, δ): 68.1 (CH/C5H4),
69.9 (CH/C5H4), 70.8 (CH/C5H4), 72.6 (CH/C5H4), 100 (AuCtC),
104.7 (AuCtC), 129.3 (d, JCP ) 11.3 Hz, Cm/C6H5), 129.5 (d, JCP
) 55 Hz, Ci/C6H5), 132 (d, JCP ) 2.4 Hz, Cp/C6H5), 134.4 ppm (d,
JCP ) 14 Hz, Co/C6H5). 31P{1H} NMR (101.25 MHz, CDCl3, δ):
41.39 ppm (s, PPh3).
Synthesis of 1′-[(PPh3)2(η5-C5H5)Ru-CtC]-1′′′-(HCtC)bifc
(8a). To a dark red solution of 100 mg (0.24 mmol) of 4 and 174.2
mg (0.24 mmol) of (η5-C5H5)(PPh3)2RuCl (7a) in 40 mL of a 1:1
dichloromethane/methanol mixture was added 40.7 mg (0.25 mmol)
of [NH4]PF6 in a single portion. The resulting reaction solution
was stirred for 5 h at 25 °C, and then 28 mg (0.25 mmol) of KOtBu
was added in a single portion. The thus obtained reaction mixture
was stirred for a further 5 h at 25 °C. The complete conversion
was monitored by 31P{1H} NMR spectroscopy. Subsequently, all
volatiles were removed under reduced pressure. The residue was
purified by column chromatography on alumina (column dimension:
30 × 2 cm) using diethyl ether/n-hexane (ratio 1:1, v/v) as eluent.
The first band contained unreacted 4 and the second band 8a. By
removing all volatiles in an oil-pump vacuum, complex 8a was
obtained as a pale orange solid. Yield: 186 mg (0.168 mmol, 70%
based on 4).
2 H, C5H4), 3.9 (pt, JHH ) 1.9 Hz, 1.7 Hz, 2 H, C5H4), 4.01 (pt,
JHH ) 1.9 Hz 2 H, C5H4), 4.02 (pt, JHH ) 1.9 Hz 2 H, C5H4), 4.21
(m, 4 H, C5H4), 4.26 (pt, JHH ) 1.9 Hz, 2 H, C5H4), 4.29 (s, 5 H,
C5H5/Cp), 4.4 (pt, JHH ) 1.9 Hz, 2 H, C5H4), 7.09-7.22 (m, 17 H,
Ph),7.48-7.55 ppm (m, 12 H, Ph). 13C{1H} NMR (62.9 MHz,
CDCl3, δ): 64.1 (CtCH), 68.0 (CH/C5H4), 68.2 (CH/C5H4), 68.8
(CH/C5H4), 69.9 (CH/C5H4), 70 (CH/C5H4), 70.3 (CH/C5H4), 70.7
(CH/C5H4), 73.0 (CH/C5H4), 73.7 (Ci/C5H4), 82.1 (Ci/C5H4), 82.9
(CtCH), 85.3 (CH/C5H5), 86.7 (Ci/C5H4), 88 (Ci/C5H4), 107.8
(CtCRu), 109.0 (CtCRu), 127.3 (pt, JCP ) 4.8 Hz, Cm/C6H5),
128.5 (s, Cp/C6H5), 134.1 (pt, JCP ) 4.8 Hz, C°/C6H5), 139.3 ppm
(dd, JCP ) 20 Hz, Ci/C6H5). 31P{1H} NMR (101.25 MHz, CDCl3,
δ): 49.38 ppm (s, PPh3).
Synthesis of 1′,1′′′-((PPh3)2(η5-C5H5)Ru-CtC)2bifc (9a). To
100 mg (0.24 mmol) of 4 and 363 mg (0.5 mmol) of 7a in 50 mL
of a 1:1 dichloromethane/methanol (ratio 1:1, v/v) mixture was
added 81.5 mg (0.5 mmol) of [NH4]PF6 in a single portion. The
reaction mixture was stirred for 5 h at 25 °C, and then 56 mg (0.5
mmol) of KOtBu was added. The resulting reaction mixture was
stirred for 6 h at 25 °C. The complete conversion was monitored
by 31P{1H} NMR spectroscopy. All volatiles were removed under
reduced pressure. The residue was purified by column chroma-
tography on alumina (column dimension: 30 × 2 cm) using a diethyl
ether/n-hexane mixture (ratio 1:1, v/v) as eluent. After removal of
all volatiles in an oil-pump vacuum an orange solid of 9a was
obtained. Yield: 400 mg (0.22 mmol, 92% based on 4).
Anal. Calcd for C106H86Fe2P4Ru2 (1797.54 g/mol): C, 70.84; H,
4.81. Found: C, 70.61; H, 5.08. Mp >154 °C (dec). IR (KBr, cm-1):
1
2075 cm-1 (m, νCtCRu). H NMR (250 MHz, CDCl3, δ): 3.75 (pt,
JHH ) 1.58 Hz, 4 H, C5H4), 3.79 (pt, JHH ) 1.58 Hz, 4 H, C5H4)
3.98 (pt, JHH ) 1.6 Hz, 4 H, C5H4), 4.17 (pt, JHH ) 1.6 Hz, 4 H,
C5H4), 4.2 (s, 10 H, C5H5), 7.01 - 7.16 (m, 39 H, Ph), 7.40-7.47
ppm (m, 21 H, Ph). 13C{1H} NMR (62.9 MHz, CDCl3, δ): 66.8
(Ci/C5H4), 67.0 (CH/C5H4), 68.8 (CH/C5H4), 69.2 (CH/C5H4), 72.2
(CH/C5H4), 85.5 (CH/C5H5), 106.2 (CtCRu), 109.01 (CtCRu),
127.5 (pt, JCP ) 4.8 Hz, Cm/C6H5), 128.7 (d, JCP ) 1 Hz, Cp/C6H5),
134.3 (pt, JCP ) 4.8 Hz, JCP ) 5.2 Hz, C°/C6H5), 139.8 ppm (dd,
JCP ) 20.1 Hz, JCP ) 21.1 Hz, Ci/C6H5). 31P{1H} NMR (101.25
MHz, CDCl3, δ): 50.36 ppm (s, PPh3).
Synthesis of 1′-[(PPh3)2(η5-C5H5)Os-CtC]-1′′′-(HCtC)bifc
(8b). To 114 mg (0.27 mmol) of 4 dissolved in 60 mL of methanol
was added 232 mg (0.27 mmol) of (PPh3)2(η5-C5H5)OsBr (7b)
followed by addition of 49 mg (0.3 mmol) of [NH4]PF6 at 70 °C.
The reaction solution was stirred for 3 h at this temperature until
all of 7b was dissolved. Then the solution was cooled to 25 °C,
and 33.6 mg (0.3 mmol) of KOtBu was added in a single portion.
After 3 h of stirring, all volatiles were removed under reduced
pressure. The residue was purified by column chromatography on
alumina (column dimension: 30 × 3 cm) using a diethyl ether/n-
hexane mixture (ratio 2:1, v/v) as eluent. The first band contained
unreacted 4. From the second band 8b could be isolated as an orange
powder. Yield: 200 mg (0.16 mmol, 62% based on 4).
Anal. Calcd for C65H52Fe2P2Os (1196.98 g/mol): C, 65.22; H,
4.37. Found: C, 65.13; H, 4.42. Mp: 178 °C (dec). IR (KBr, cm-1):
2069 (w, νCtCOs), 2099 (w, νCtCH), 3226 cm-1 (w, νtCH). 1H NMR
(250 MHz, CDCl3, δ): 2.65 (s, 1 H, tCH), 3.79 (pt, JHH ) 1.8 Hz,
2 H, C5H4), 3.87 (pt, JHH ) 1.8 Hz, 2 H, C5H4), 3.98-4.01 (m, JHH
) 1.7 Hz, 4 H, C5H4), 4.19-4.21 (m, JHH ) 1.7 Hz, JHH ) 1.8 Hz,
4 H, C5H4), 4.21 (pt, JHH ) 1.8 Hz, 2 H, C5H4), 4.34 (s, 5 H, C5H5),
4.38 (pt, JHH ) 1.8 Hz, 2 H, C5H4), 7.09-7.22 (m, 18 H, Ph),
7.41-7.47 ppm (m, 12 H, Ph). 13C{1H} NMR (62.9 MHz, CDCl3,
δ): 64.2 (CtCH), 68.0, (CH/C5H4), 68.2 (CH/C5H4), 68.8 (CH/
C5H4), 69.9 (CH/C5H4), 70.1 (CH/C5H4), 70.4 (CH/C5H4), 70.9 (CH/
C5H4), 73.0 (CH/C5H4), 73.7 (Ci/C5H4), 81.4 (CH/C5H5), 82.0 (Ci/
C5H4), 82.9 (CtCH), 87 (Ci/C5H4), 102.7 (CtCOs), 110.1
(CtCOs), 127.4 (pt, JCP ) 4.7 Hz, Cm/C6H5), 128.7 (s, Cp/C6H5),
Anal. Calcd for C65H52Fe2P2Ru (1108.12 g/mol): C, 70.38; H,
4.72. Found: C, 70.11; H, 5.06. Mp >125 °C (dec). IR (KBr, cm-1):
2074 (w, νCtCRu), 2100 (w, νCtCH), 3284 cm-1 (w, νtCH). 1H NMR
(250 MHz, CDCl3, δ): 2.65 (s, 1 H, tCH), 3.79 (pt, JHH ) 1.7 Hz,

1890 Organometallics, Vol. 28, No. 6, 2009
Lohan et al.
134.3 (pt, JCP ) 5.2 Hz, C°/C6H5), 139.5 ppm (dd, JCP ) 49.4 Hz,
JCP ) 54.7 Hz, Ci/C6H5). 31P{1H} NMR (101.25 MHz, CDCl3, δ):
0.15 ppm (s, PPh3).
C5H4/dppf), 73.1 (CH/C5H4/Bfc), 73.8 (CH/C5H4/Bfc), 77.5 (CH/
C5H4/dppf) 82.4 (C′CH), 82.9 (Ci/C5H4), 84.7 (CH/C5H5), 86.6 (Ci/
C5H4), 88.9 (Ci/C5H4), 89.1 (Ci), 105.7 (C′CRu), 110.04 (CtCRu),
125.4 (s, CH/C6H5), 127.3-127.6 (m, CH/C6H5), 128.6 (s, CH/
C6H5), 129.2 (s, CH/C6H5), 134.1 (pt, JCP ) 5.2 Hz, CH/C6H5),
134.5 (pt, JCP ) 4.7 Hz, CH/C6H5), 140.7 (Ci/C6H5) 142.7 ppm
(Ci/C6H5). 31P{1H} NMR (101.25 MHz, CDCl3, δ): 53.7 ppm (s,
PPh2, dppf).
Synthesis of 1′,1′′′-((PPh3)2(η5-C5H5)Os-CtC)2bifc (9b). To
100 mg (0.24 mmol) of 4 dissolved in 60 mL of methanol were
added 413 mg (0.48 mmol) of 7b and then 81.5 mg (0.5 mmol) of
[NH4]PF6 at 70 °C. The reaction solution was heated to reflux for
3 h at this temperature, whereby the orange suspension turned into
a clear red solution. The reaction solution was allowed to cool to
25 °C, and then 56 mg (0.5 mmol) of KOtBu was added in a single
portion, causing the precipitation of a yellow solid. After 3 h of
stirring, all volatiles were removed under reduced pressure. The
residue was subjected to column chromatography on alumina
(column dimension: 30 × 3 cm) using a diethyl ether/n-hexane
mixture (ratio 2:1, v/v) as eluent. After removal of all volatiles
under reduced pressure complex 9b was obtained as an orange solid.
Yield: 300 mg (0.15 mmol, 63% based on 4).
Synthesis of 1′,1′′′-((dppf)(η5-C5H5)Ru-CtC)2bifc (9c). To 100
mg (0.24 mmol) of 4 and 359 mg (0.5 mmol) of 7c in 50 mL of a
1:1 dichloromethane/methanol mixture were simultaneously added
81.5 mg (0.5 mmol) of [NH4]PF6 and 56 mg (0.5 mmol) of KOtBu.
The resulting reaction mixture was stirred for 6 h at room
temperature. The complete conversion was monitored by 31P{1H}
NMR spectroscopy. All volatiles were removed under reduced
pressure. The residue was purified by column chromatography on
alumina (column dimension: 30 × 2 cm) using a diethyl ether/n-
hexane mixture (ratio 1:1, v/v) as eluent. Removal of all volatiles
in an oil-pump vacuum gave 9a as an orange solid. Yield: 420 mg
(0.22 mmol, 94% based on 4).
Anal. Calcd for C106H86Fe2P4Os2 (1975.86 g/mol): C, 64.43; H,
4.38. Found: C, 64.44; H, 4.46. Mp: 185 °C (dec). IR (KBr, cm-1):
2076 (w, νCtCOs). 1H NMR (250 MHz, CDCl3, δ): 3.83 (pt, JHH
)
Anal. Calcd for C102H82Fe4P4Ru2 (1857.16 g/mol): C, 65.96; H,
1.8 Hz, 4 H, C5H4), 3.86 (pt, JHH ) 1.8 Hz, 4 H, C5H4), 4.05 (pt,
JHH ) 1.8 Hz, 4 H, C5H4), 4.24 (pt, JHH ) 1.8 Hz, 4 H, C5H4),
4.35 (s, 10 H, C5H5), 7.08-7.21 (m, 35 H, Ph), 7.42-7.48 ppm
(m, 25 H, Ph). 13C{1H} NMR (62.9 MHz, CDCl3, δ): 68.4 (CH/
C5H4), 69.6 (CH/C5H4), 70.7 (CH/C5H4), 77.5 (CH/C5H4), 87.2 (Ci/
C5H4), 81.4 (CH/C5H5), 109.7 (C′COs), 127.1 (pt, JCP ) 4.7 Hz,
Cm/C6H5), 128.4 (s, Cp/C6H5), 134 (pt, JCP ) 5.2 Hz, C°/C6H5),
139.9 ppm (d, JCP ) 51.8 Hz, Ci/C6H5). 31P{1H} NMR (101.25
MHz, CDCl3, δ): 0.6 ppm (s, PPh3).
4.45. Found: C, 66.03; H, 4.49. Mp: 185 °C (dec). IR (KBr, cm-1):
1
2074 (w, νCtCRu). H NMR (250 MHz, CDCl3, δ): 3.8 (pt, JHH
)
1.8 Hz, 4 H, C5H4), 3.92 (pt, JHH ) 1.8 Hz, 4 H, C5H4), 3.99 (pt,
JHH ) 1.8 Hz, 4 H, C5H4), 4.05 (pt, JHH ) 1.8 Hz, 4 H, C5H4), 4.2
(s, 10 H, C5H5), 4.21-4.25 (m, 12 H, C5H4/dppf), 5.4 (4H, C5H4/
dppf) 7.2-7.36 (m, 25 H, Ph), 7.39-7.46 (m, 10 H, Ph), 7.74-7.82
ppm (m, 5 H, Ph). 13C{1H} NMR (62.9 MHz, CDCl3, δ): 67.9 (CH/
C5H4), 68.44 (CH/C5H4), 69.54 (CH/C5H4), 70.49 (CH/C5H4), 71.32
(CH/C5H4), 73.1 (CH/C5H4), 77.37 (CH/C5H4), 84.74 (CH/C5H5),
88.7 (Ci/C5H4) 89.24 (Ci/C5H4), 109.95 (CtCRu), 125.67 (s,
C/C6H5), 127.3-127.6 (m, CH/C6H5), 128.61 (s, CH/C6H5), 129.28
(s, CH/C6H5), 133.9 (pt, JCP ) 5.2 Hz, CH/C6H5), 134.77 (pt, JCP
) 5.2 Hz, CH/C6H5), 140.01 (Ci/C6H5), 142.6 ppm (Ci/C6H5).
31P{1H} NMR (101.25 MHz, CDCl3, δ): 53.9 ppm (s, PPh2, dppf).
Crystallography. Crystal data for 6, 8b, 9a, 9b, and 9c are
presented in Tables 6 (6, 8b) and 7 (9a, 9b, 9c). All data were
collected on a Oxford Gemini S diffractometer with graphite-
monochromatized Mo KR radiation (λ ) 0.71073 Å) (6, 8b, 9a,
and 9b) and graphite-monochromatized Cu KR radiation (λ )
1.54184 Å) (9c) at 100 K using oil-coated shock-cooled crystals.30
The structures were solved by direct methods using SHELXS-9731
or SIR-9232 and refined by full-matrix least-squares procedures on
F2 using SHELXL-97.33 All non-hydrogen atoms were refined
anisotropically, and a riding model was employed in the refinement
of the hydrogen atom positions.
Synthesis of 1′-[(dppf)(η5-C5H5)Ru-CtC]-1′′′-(HCtC)bifc
(8c). A 100 mg (0.24 mmol) amount of 4 and 173 mg (0.24 mmol)
of (dppf)(η5-C5H5)RuCl (7c) were dissolved in 40 mL of a
dichloromethane/methanol mixture of ratio 1:1 (v/v), and 40.7 mg
(0.25 mmol) of [NH4]PF6 was added in a single portion. The
resulting reaction solution was stirred for 5 h at 25 °C, and then 28
mg (0.25 mmol) of KOtBu was added in a single portion, causing
the precipitation of an orange solid. The resulting reaction mixture
was stirred for a further 3 h at 25 °C. The complete conversion
was monitored by 31P{1H} NMR spectroscopy. Subsequently, all
volatiles were removed under reduced pressure. The residue was
purified by column chromatography on alumina (column dimension:
30 × 2 cm) using a diethyl ether/n-hexane mixture (ratio 1:1, v/v)
as eluent. The first band gave unreacted 4 and the second band 8c.
By removing all solvents in an oil-pump vacuum, complex 8a was
obtained as a pale orange solid. Yield: 210 mg (0.184 mmol, 77%
based on 4).
Anal. Calcd for C63H50Fe3P2Ru (1137.62 g/mol): C, 66.51; H,
4.43. Found: C, 66.52; H, 4.65. Mp: 151 °C (dec). IR (KBr, cm-1):
2065 (w, νCtCRu), 2108 (w, νCtCH), 3290 (w, νtCH). 1H NMR (250
MHz, CDCl3, δ): 2.67 (s, 1 H, tCH), 3.86 (pt, JHH ) 1.7 Hz, 2 H,
C5H4), 3.99-4.02 (m, 2 H, C5H4/dppf), 4.04 (pt, JHH ) 1.7 Hz, 2
H, C5H4), 4.07 (pt, JHH ) 1.7 Hz, 2 H, C5H4), 4.13 (pt, JHH ) 1.7
Hz, 2 H, C5H4), 4.22 (pt, JHH ) 1.7 Hz, 2 H, C5H4), 4.28 (pt, JHH
) 1.7 Hz, 2 H, C5H4), 4.3 (s, 5 H, C5H5), 4.29-4.31 (m, 4 H,
C5H4/dppf) 4.32-4.35 (m, 2 H, C5H4/dppf), 4.44 (pt, JHH ) 1.7
Hz, 2 H, C5H4), 5.5 (pt, JHH ) 1.7 Hz, 2 H, C5H4/dppf), 7.29-7.4
(m, 10 H, Ph), 7.4-7.5 (m, 5 H, Ph), 7.81-7.89 ppm (m, 5 H,
Ph). 13C{1H} NMR (62.9 MHz, CDCl3, δ): 64.2 (CtCH), 67.9
(CH/C5H4/dppf), 68.2 (CH/C5H4/Bfc), 68.3 (CH/C5H4/dppf), 68.7
(CH/C5H4/Bfc), 69.7 (CH/C5H4/Bfc), 69.99 (CH/C5H4/Bfc), 70.4
(CH/C5H4/Bfc), 70.7 (CH/C5H4/Bfc), 71.3 (Ci/C5H4), 73.0 (CH/
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft and to the Fonds der Chemischen
Industrie for generous financial support.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
OM8011344
(30) (a) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1996, 29, 465. (b)
Stalke, D. Chem. Soc. ReV. 1998, 27, 171.
(31) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 467.
(32) Altomare, A.; Cascarano, C.; Giacovazzo, C.; Gualardi, A. J. Appl.
Crystallogr. 1993, 26, 343.
(33) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Go¨ttingen, 1997.