Reactions of sulfido-bridged molybdenum dimers with diynes as a route to multinuclear dithiolene complexes

Article abstract of DOI:10.1021/om050317d

The bridgin sulfido ligands in dunuclear molybdenum complexes of the formula (Me_nCpMoμ-S)₂S₂CH₂, where n = 0 or 1, react with alkynes to form alkenedithiolate complexes. These reactions have been extended to a series of diynes, including 2,4-hexadiyne, 1,4-diphenyl-l,3-butadiyne, 1,3-diethynylbenzene, and 1,4- bis(trimethylsilylethynyl)benzene, to form bis(alkenedithiolate) complexes. The corresponding mono-adducts have also been synthesized by the reaction of the molybdenum dimer with the diyne in a 1:1 molar ratio. The new alkyne adducts have been characterized by spectroscopic techniques and cyclic voltammetry, and both the 1:1 and 2:1 adducts of 1,4-diphenyl-1,3-butadiyne have been identified by X-ray structural determinations. Synthetic routes to a hexanuclear complex and higher molecular weight oligomers linked by alkenedithiolate ligands are also described. Tetranuclear complexes linked by the 1,3-dialkynes show two closely spaced oxidation waves in the cyclic voltammogram, suggesting a small degree of electronic communication between the dimers.

Full text of DOI:10.1021/om050317d

4406
Organometallics 2005, 24, 4406-4415
Reactions of Sulfido-Bridged Molybdenum Dimers with
Diynes as a Route to Multinuclear Dithiolene Complexes
Rachel Newell, Claire Ohman, and M. Rakowski DuBois*
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309
Received April 21, 2005
The bridging sulfido ligands in dunuclear molybdenum complexes of the formula
(MenCpMoµ-S)2S2CH2, where n ) 0 or 1, react with alkynes to form alkenedithiolate com-
plexes. These reactions have been extended to a series of diynes, including 2,4-hexadiyne,
1,4-diphenyl-1,3-butadiyne, 1,3-diethynylbenzene, and 1,4-bis(trimethylsilylethynyl)benzene,
to form bis(alkenedithiolate) complexes. The corresponding mono-adducts have also been
synthesized by the reaction of the molybdenum dimer with the diyne in a 1:1 molar ratio.
The new alkyne adducts have been characterized by spectroscopic techniques and cyclic
voltammetry, and both the 1:1 and 2:1 adducts of 1,4-diphenyl-1,3-butadiyne have been
identified by X-ray structural determinations. Synthetic routes to a hexanuclear complex
and higher molecular weight oligomers linked by alkenedithiolate ligands are also described.
Tetranuclear complexes linked by the 1,3-dialkynes show two closely spaced oxidation waves
in the cyclic voltammogram, suggesting a small degree of electronic communication between
the dimers.
Introduction
alkenedithiolate ligands undergo an unusual range of
reactions. For example, we reported that complexes of
the formula (CpMo)2(S2CH2)(SCRdCRS), 1, react with
protic acids to form an isomeric mixture of cationic
derivatives, as shown in eq 1.12 Studies of the protonated
Recent work in the area of metal dithiolene chemistry
has been extensively reviewed.1 Mononuclear metal
complexes with alkenedithiolate ligands have been
studied for many years because of the charge-delocal-
izing properties of the ligands and the various applica-
tions that extend from this property.2-8 In addition, the
pterin molecule containing the enedithiolate unit is
known to occur in the molybdenum oxotransferase and
hydroxylase enzymes,8,9 and mononuclear enedithiolate
complexes of molybdenum and tungsten have been the
subject of renewed interest as potential models for the
enzymes.10,11 In this paper we explore the syntheses of
new polynuclear alkenedithiolate complexes of molyb-
denum. In our early studies of dinuclear molybdenum
complexes, we found that complexes containing µ-η2-
phenylacetylene adduct established that the addition of
base, such as triethylamine, regenerated the original
alkenedithiolate complex. In addition the isomeric cat-
ion mixture reacted with molecular hydrogen to give the
1,1-dithiolate-bridged complex and with nonbasic nu-
cleophiles to give R- or â-substituted styrenes, e.g.,
Scheme 1.
(1) Stiefel, E. I., Ed. Dithiolene Chemistry, Syntheses, Properties, and
Applications. In Progress in Inorganic Chemistry; Karlin, K. D., Ed.;
2004; Vol. 52.
The fact that these alkenedithiolate complexes are
prepared from the reactions of unactivated alkynes with
the Cp2Mo2S4 core provides an exceptionally flexible
synthetic route to more complex multimetallic struc-
tures that may show a similar range of unusual reac-
tivities. Very few metal complexes that are connected
by linked alkenedithiolate ligands as shown in Scheme
2 have been reported previously. The reaction of 1,4-
diphenyl-1,3-butadiyne with [ReS4]- and ethanedithiol
resulted in the dinuclear rhenium complex I in Scheme
2.13 Electrophilic attack of the C-H bond in CpCo-
(1-Ph-ethenedithiolate) resulted in the linked structure
II,14 but this product was formed in very low (2%) yield.
The homonuclear Pt2 and mixed metal Ni-Pt deriva-
(2) Cummings, S. D.; Eisenberg, R. In Dithiolene Chemistry, Syn-
theseis, Properties, and Applications, Stiefel, E. I., Ed. In Progress in
Inorganic Chemistry; Karlin, K. D., Ed.; 2004; Vol. 52, p 315.
(3) Hissler, M.; McGarrah, J. E.; Connick, W. B.; Geiger, D. K.;
Cummings, D. S.; Eisenberg, R. Coord. Chem. Rev. 2000, 208, 115.
(4) Paw, W.; Cummings, S. D.; Mansour, M. A.; Connick, W. B.;
Geiger, D. K.; Eisenberg, R. Coord. Chem. Rev. 1998, 171, 125.
(5) (a) Van Houten, K. A.; Heath, D. C.; Pilato, R. S. J. Am. Chem.
Soc. 1998, 120, 12359. (b) Van Houten, K. A.; Heath, D. C.; Barringer,
C. A.; Rheingold, A. L.; Pilato, R. S. Inorg. Chem. 1998, 37, 4647.
(6) Sato, A.; Ojima, E.; Akutsu, H.; Naakazaawa, Y.; Kobayashi, H.;
Tanaka, H.; Kobayashi, A.; Cassoux, P. Phys. Rev. B 2000, 61, 111.
(7) Cassoux, P. Coord. Chem. Rev. 1999, 186, 213.
(8) Kirk, M. L.; McNaughton, R. L.; Helton, M. E. In Dithiolene
Chemistry, Syntheseis, Properties, and Applications; Stiefel, E. I., Ed.
In Progress in Inorganic Chemistry; Karlin, K. D., Ed.; 2004; Vol. 52.
(9) Nieter Burgmayer, S. J. In Dithiolene Chemistry, Synthesis,
Properties, and Applications; Stiefel, E. I., Ed. In Progress in Inorganic
Chemistry; Karlin, K. D., Ed.; 2004; Vol. 52.
(10) Pilato, R. S.; Stiefel, E. I. In Bioinorganic Catalysis; Reedijk,
J., Bouwman, E., Eds.; Marcel Dekker: New York, 1999; p 81.
(11) McMaster, J.; Tunney, J. M.; Garner, C. D. In Dithiolene
Chemistry, Synthesis, Properties, and Applications; Stiefel, E. I., Ed.
In Progress in Inorganic Chemistry; Karlin, K. D., Ed.; 2004; Vol. 52.
(12) Laurie, J. C. V.; Duncan, L.; Haltiwanger, R. C.; Weberg, R.
T.; Rakowski DuBois, M. J. Am. Chem. Soc. 1986, 108, 6234.
(13) Dopke, J. A.; Wilson, S. R.; Rauchfuss, T. B. Inorg. Chem. 2000,
39, 5014.
10.1021/om050317d CCC: $30.25 © 2005 American Chemical Society
Publication on Web 07/26/2005

Multinuclear Dithiolene Complexes
Organometallics, Vol. 24, No. 18, 2005 4407
Scheme 1
Scheme 2
spectroscopy, electrospray mass spectral data, and
elemental analyses. The NMR spectra were consistent
with a structure with equivalent dimers, and a parent
ion for each expected product was observed in the ESI
mass spectra. Mono-adducts of the same dialkyne
ligands were also prepared for comparative purposes,
eq 3. These products, 4 and 5, were also isolated and
characterized by elemental analyses, mass spectra, and
NMR data, as described in the Experimental Section.
X-ray Diffraction Studies. The 1:1 and 2:1 adducts
of the molybdenum dimers with 1,4 diphenyl-1,3-
butadiyne were further compared by X-ray diffraction
studies. A perspective drawing of the 1:1 adduct, 5, is
shown in Figure 1a, and selected bond distances and
angles are given in Table 1. The structure of 5 is very
similar to those observed for other alkyne adducts of
the Cp2Mo2S4 unit,16 and the structural parameters of
the molybdenum-sulfur bonds and angles as well as
those of the bridging dithiolene ligand are within
expected ranges. The dithiolene C-C distance (C7-C8)
is 1.34(1) Å, while the distance for C9-C10 of the free
alkyne is 1.20(1) Å. The uncoordinated alkyne has a
near linear C9-C10-C(phenyl) angle of 177.0°, but the
angle of the alkyne with the dithiolate ligand, C10-
C9-C8, is distorted slightly, with a value of 167.6 (11)°.
The structure of the 2:1 adduct, 3, confirms that each
of the alkynes has formed an adduct with the sulfido
bridges of a molybdenum dimer. A perspective drawing
is shown in Figure 1b, and selected bond distances and
angles are given in Table 2. The 1,3-diene portion of the
bridging ligand is in an s-trans configuration with the
C(7)-C(8)-C(9) and C(8)-C(9)-C(10) angles of the
diene equal to 131.1(5)° and 127.8(4)°, respectively. The
C(7)-C(8)-C(9)-C(10) torsion angle is 121.2 (6)°. The
tives of structure III have been synthesized by metal
ion addition to 1,2,3,4-butadienetetrathiolate generated
in situ.15 None of the products in Scheme 2 has been
structurally characterized, and electrochemical studies
that explore the electronic linking properties of the bis-
alkenedithiolate ligand have not been reported. In this
paper we report our initial synthetic investigations of
the use of diynes to form multimetallic complexes that
result from linked alkenedithiolate complexes of di-
nuclear molybdenum derivatives.
Results and Discussion
Syntheses of Tetranuclear Alkenedithiolate Com-
plexes. The reactions of 2 equiv of (MeCpMoµ-S)2-
S2CH2 with the conjugated dialkynes shown in eq 2 (Cp′
) MeCp) were carried out. The reactions led to the
(14) Kajitani, M.; Hagino, G.; Tamada, M.; Fujita, T.; Sakurada, M.;
Akiyama, T.; Sugimori, A. J. Am. Chem. Soc. 1996, 118, 489.
(15) Keefer, C. E.; Purrington, S. T.; Bereman, R. D.; Boyle, P. D.
Inorg. Chem. 1999, 38, 5437.
(16) (a) McKenna, M.; Wright, L. L.; Miller, D. J.; Tanner, L.;
Haltiwanger, R. C.; Rakowski DuBois, M. J. Am. Chem. Soc. 1983,
105, 5329. (b) Miller, W. K.; Haltiwanger, R. C.; Van Derveer, M. C.;
Rakowski DuBois, M. Inorg. Chem. 1983, 22, 2973.
formation of bis-adducts 2 and 3, which were isolated
and characterized by spectroscopic techniques. The
formulations of the products were confirmed by 1H NMR

4408 Organometallics, Vol. 24, No. 18, 2005
Newell et al.
been carried out to introduce different linkers between
the dinuclear units. For example, the reaction of 2 equiv
of the molybdenum reagent with 1,3-diethynylbenzene
led to the formation of the bis-adduct 6, and the bis-
adduct of 1,4-bis(trimethylsilylethynyl)benzene, 7, was
also prepared, as shown in eq 4.
The formulations of the products were confirmed by
electrospray mass spectral data and by elemental
analyses. As expected the 1H NMR data for these com-
plexes were consistent with equivalent alkenedithiolate-
bridged dimers within the structures. In each case one
singlet was observed for the four Cp ligands and
resonances for the linking unit were consistent with a
symmetrical structure. The mono-adducts of the dialky-
nylbenzene ligands were also prepared for comparative
purposes, eq 5. These products, 8 and 9, were also
Figure 1. Perspective drawing and numbering scheme for
(a) mono-adduct of (MeCpMoµ-S)2S2CH2 and 1,4-diphenyl-
butadiyne (5) and (b) bis-adduct of (MeCpMo)2(µ-S)2S2CH2
and 1,4-diphenylbutadiyne (3). Thermal ellipsoids are
shown at the 50% probability level.
Table 1. Bond Distances and Selected Bond
Angles for 1:1 Adduct, 5
Bond Distances (Å)
Mo(1)-S(1)
Mo(1)-S(2)
Mo(1)-S(3)
Mo(1)-S(4)
Mo(2)-S(1)
Mo(2)-S(2)
Mo(2)-S(3)
Mo(2)-S(4)
S(1)-C(7)
2.435(3)
2.450(3)
2.453(3)
2.443(3)
2.442(3)
2.462(3)
2.431(2)
2.440(3)
1.808(9)
S(3)-C(8)
1.809(10)
1.811(11)
1.814(10)
1.484(14)
1.342(12)
1.428(13)
1.200(12)
1.437(12)
2.6009(12)
S(2)-C(29)
S(4)-C(29)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(10)-C(11)
Mo(1)-Mo(2)
isolated and characterized by elemental analyses, mass
spectra, and NMR data. For example in the NMR
spectrum of the mono-adduct of 1,3-diethynylbenzene,
8, a singlet for the proton of the free alkyne is observed
at 3 ppm, while the proton of the coordinated alkene-
dithiolate ligand occurs downfield at 6.2 ppm. Four
multiplets are observed for inequivalent phenyl protons.
Electrochemical Studies. The cyclic voltammo-
grams for a series of dinuclear alkenedithiolate com-
plexes (MenCpMo)2(S2CH2)(S(R)CdC(R)S) have been
studied previously.16a,17 The CVs for selected examples
of these complexes have now been obtained using a
glassy carbon electrode in benzonitrile/0.3 M Bu4NBF4
solutions relative to the internal standard ferrocene so
that direct comparisons can be made with the new
complexes reported here. The complexes typically show
Bond Angles (deg)
Mo(1)-S(1)-Mo(2)
Mo(1)-S(3)-Mo(2)
Mo(1)-S(2)-Mo(2)
Mo(1)-S(4)-Mo(2)
S(2)-C(29)-S(4)
C(6)-C(7)-C(8)
64.45(7) S(1)-C(7)-C(8)
64.36(6) S(3)-C(8)-C(7)
63.93(7) S(1)-C(7)-C(6)
64.36(7) S(3)-C(8)-C(9)
115.8(8)
116.8(7)
115.1(7)
112.9(7)
130.3(10)
96.6(5)
129.1(9)
C(7)-C(8)-C(9)
C(8)-C(9)-C(10) 167.6(11)
bond distances and angles of the dithiolate ligands are
similar to those of previous structures of alkenedithio-
late-bridged molybdenum dimers. The carbon-carbon
linkage between the two dimers, C(8)-C(9), has a bond
distance of 1.465 Å, characteristic of a single bond, while
the CdC distances of the dithiolene linkages are almost
identical, with a distance of 1.34 Å.
Other Alkenedithiolate Linking Ligands. The
reactions of (CpMoµ-S)2(S2CH2) with other diynes have
(17) Casewit, C. J.; Haltiwanger, R. C.; Noordik, J.; Rakowski
DuBois, M. Organometallics 1985, 4, 119.

Multinuclear Dithiolene Complexes
Organometallics, Vol. 24, No. 18, 2005 4409
Table 2. Bond Distances, Selected Bond Angles,
and Selected Torsion Angles for 2:1 Adduct, 3
oxidation waves; for example, the CV data for 3 together
with the differential pulse voltammogram for the two
reversible waves are shown in Figure 2. The first and
Bond Distances (Å)
Mo(1)-S(1)
Mo(1)-S(2)
Mo(1)-S(3)
Mo(1)-S(4)
Mo(2)-S(1)
Mo(2)-S(2)
Mo(2)-S(3)
Mo(2)-S(4)
S(1)-C(8)
2.4466(12)
2.4640(14)
2.4495(13)
2.4425(13)
2.4450(12)
2.4610(13)
2.4407(14)
2.4521(13)
1.816(5)
S(3)-C(7)
1.828(5)
1.817(5)
1.848(6)
1.469(7)
1.338(7)
1.465(6)
1.345(7)
1.486(6)
2.6044(6)
second oxidation waves for 2 are observed at E1/2
)
S(2)-C(17)
S(4)-C(17)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(10)-C(11)
Mo(1)-Mo(2)
-0.321 (∆EP ) 63 mV) and -0.185 V (∆EP ) 61 mV) vs
Fc and for 3 at -0.261 (∆EP ) 83 mV) and -0.112 V
(∆Ep ) 80 mV) vs Fc. These waves are assigned to the
following couples in the tetranuclear species:
Mo3+-Mo3+/Mo3+-Mo3+ to Mo3+-Mo4+/Mo3+-Mo3+ and
Mo3+-Mo4+/Mo3+-Mo3+ to Mo3+-Mo4+/Mo3+-Mo4+. The
second pair of oxidation waves for 3 is irreversible, and
the anodic peak potentials are given in Table 3. The
splitting of the Mo(III)/(IV) oxidation waves indicates
that there is electronic communication between the two
dimers in 2 and 3. Although the relatively small
splitting of the waves, 130 mV for 2 and 150 mV for 3,
shows that the coupling is quite weak, to our knowledge,
this is the first example of such communication associ-
ated with a bis-dithiolene ligand.
Selected Bond Angles (deg)
Mo(1)-S(1)-Mo(2)
Mo(1)-S(3)-Mo(2)
Mo(1)-S(2)-Mo(2)
Mo(1)-S(4)-Mo(2)
S(2)-C(17)-S(4)
C(6)-C(7)-C(8)
64.34(3)
64.36(3)
63.85(3)
64.30(3)
96.1(3)
S(1)-C(8)-C(7)
117.4(4)
115.1(4)
111.2(3)
116.8(3)
131.1(5)
127.8(4)
S(3)-C(7)-C(8)
S(1)-C(8)-C(9)
S(3)-C(7)-C(6)
C(7)-C(8)-C(9)
C(8)-C(9)-C(10)
128.2(4)
126.0(4)
C(9)-C(10)-C(11)
Selected Torsion Angles (deg)
S(3)-C(7)-C(8)-C(9)
169.3(4) C(7)-C(8)-C(9)-C(10) 121.2(6)
S(5)-C(10)-C(9)-C(8) 165.9(4)
A number of dinuclear complexes have been linked
by unsaturated ligands in previous studies. For exam-
ple, extensive studies of quadruply bonded Mo and W
dimers linked through the backbone of bridging dicar-
boxylate and diamidate ligands have been reported.19-22
These dimers have also been linked by metal alkoxide
units.23 The degree of electronic communcation has been
shown to vary from completely localized to completely
delocalized, depending on the nature and geometry of
the bridging ligand. Studies of singly bonded ruthenium
dimers linked by polyalkynes coordinated in axial
positions trans to the M-M bond have also been
reported.24 The splitting of the oxidation waves is
generally significantly larger for these systems than the
differences in E1/2 values observed here.
The coupling between the dimers in 2 and 3 may occur
through space as a result of electrostatic interactions,
and/or the coupling may result from electron delocal-
ization mediated by the unsaturated bis-dithiolene
ligand. We attempted to prepare an analogue of 3
containing a saturated bis-alkanedithiolate ligand so
that the electrochemical properties of the dithiolene and
dithiolate derivatives could be compared. Although the
sulfido ligands of (MeCpMoµ-S)2(S2CH2) react reversibly
with mono-alkenes to form alkanedithiolate ligands, no
reactions were observed when this dimer was reacted
with conjugated dienes, such as trans,trans-1,4-diphen-
yl-1,3-butadiene or trans-trans-2,4-hexadien-1-ol, in sto-
ichiometric or excess ratios. Steric hindrance that would
a quasi-reversible one-electron oxidation wave attrib-
uted to the MoIII-IIIfMoIII-IV couple near -0.2 to
-0.3 V, as shown in Table 3. One or two irreversible
oxidations are observed at more positive potentials. The
potentials show a small variation that correlates with
the electron-donating abilities of the alkyne and Cp
substituents. Although the mixed valence Mo(III)/IV
alkenedithiolate adducts have not been isolated, closely
related mixed valence cations with 1,2-alkanedithiolate
ligands, e.g., [(CpMoSC3H6S)2]+, have been prepared
and characterized as class III (completely delocalized)
structures.18
The cyclic voltammograms of the new 1:1 diyne
adducts, 4, 5, 8, and 9, were recorded in benzonitrile
under the conditions reported above, and potentials are
included in Table 3. Each of the complexes shows a
quasi-reversible oxidation wave near -0.2 to -0.3 V vs
ferrocene for the MoIII-IIIfMoIII-IV couple, and in
most cases an irreversible wave near +0.4 V is observed.
The potentials are consistent with the nature of the
substituents on the alkeneditiolate ligands; for example,
the hexadiyne adduct is more readily oxidized than the
diphenylbutadiyne adduct by ca. 80 mV, as expected for
the more electron-donating substituents provided by the
former ligand.
The cyclic voltammograms of the tetranuclear com-
plexes linked by the dialkynylbenzene ligands, 6 and
7, were almost identical to those observed for the
corresponding mono-adducts. For example, for the ad-
ducts of 1,4-bis(trimethylsilylethynyl)benzene, the mono-
adduct, 9, showed an oxidation at -0.23 V vs Fc with a
∆EP ) 96 mV and ia/ic ) 1, while the CV of the bis-
adduct, 7, displayed an oxidation at -0.23 V, ∆Ep ) 87
mV and ia/ic ) 1. The data indicate that in the oxidized,
monocationic bis-adducts 6 and 7, no electronic com-
munication through the phenyl-bridged alkenedithiolate
ligands is evident, and each dinuclear molybdenum unit
is independent of the other.
(19) (a) Cotton, F. A.; Donahue, J. P.; Murillo C. A. J. Am. Chem
Soc. 2003, 125, 5436. (b) Cotton, F. A.; Donahue, J. P.; Murillo, C. A.;
Perez, L. M. J. Am. Chem. Soc. 2003, 125, 5486.
(20) Bursten, B. E.; Chisholm, M. H.; Clark, R. J. H.; Firth, S.;
Hadad, C. M.; MacIntosh, A. M.; Wilson, P. J.; Woodward, P. M.;
Zaleski, J. M. J. Am. Chem. Soc. 2002, 124, 3050.
(21) (a) Cotton, F. A.; Liu, C. Y.; Murillo, C. A.; Villagran, D.; Wang,
X. J. Am. Chem. Soc. 2004, 126, 14822. (b) Cotton, F. A.; Liu, C. Y.;
Murillo, C. A.; Villagran, D.; Wang, X. J. Am. Chem. Soc. 2003, 125,
13564. (c) Cotton, F. A.; Daniels, L. M.; Donahue, J. p.; Liu, C. Y.;
Murillo, C. A. Inorg. Chem. 2002, 41, 1354.
(22) Chisholm, M. H.; Clark, R. J. H.; Gallucci, J.; Hadad, C M.;
Patmore, N. J. J. Am. Chem. Soc. 2004, 126, 8303.
(23) Cotton, F. A.; Dalal, N. S.; Liu, C. Y.; Murillo, C. A.; North, J.
M.; Wang, X. J. Am. Chem. Soc. 2003, 125, 12945. Cotton, F. A.; Liu,
C. Y.; Murillo, C. A.; Wang, X. Inorg. Chem. 2003, 42, 4619.
(24) Shi, Y.; Yee, G. T.; Wang, G.; Ren, T. J. Am. Chem. Soc. 2004,
126, 10552. (b) Xu, G. L.; DeRosa, M. C.; Crutchley, R. J.; Ren, T. J.
Am. Chem. Soc. 2004, 126, 3728. (c) Xu, G. L.; Zou, G.; Ni, Y. H.;
DeRosa, M. C.; Crutchley, R. J.; Ren, T. J. Am. Chem. Soc. 2003, 125,
10057.
However, the cyclic voltammograms and differential
pulse voltammograms of the 2:1 adducts of the 1,3- and
2,4-diynes, 2 and 3, show sets of two closely spaced
(18) Casewit, C. J.; Rakowski DuBois, M. Inorg. Chem. 1986, 25,
74.

4410 Organometallics, Vol. 24, No. 18, 2005
Table 3. Electrochemical Data for Alkyne Adductsa
Newell et al.
E1/2, V vs Fc,
MoIIIfMoIV (∆Ep, mV)
E1/2 or Ep,
other oxidations
complex
(CpMo)2(S2CH2)(SC(Et)dC(Et)S)
(CpMo)2(S2CH2)(SC(H)dC(CO2Et)S)
(MeCpMo)2(S2CH2)(SC(Ph)dC(Ph)S)
(MeCpMo)2(S2CH2)(SC(CO2Me)dC(CO2Me)S)
4 (1:1 add, 2,4-hexadiyne)
5 (1:1 add, 1,4-Ph2-1,3-butadiyne)
8 (1:1 add. 1,3-diethynylbenzene)b
9 (1:1 add, 1,4-dialkynylbenzene)b
6 (2:1 add, 1,3-diethynylbenzene)b
7 (2:1 add, 1,4-dialkynylbenzene)b
2 (2:1 add, 2,4-hexadiyne)
-0.299 (130)
-0.186 (133)
-0.246 (91)
-0.092 (185)
-0.278 (129)
-0.196 (75)
-0.205 (124)
-0.228 (94)
-0.227 (75)
-0.234 (87)
-0.321 (63)
-0.185 (61)
-0.261 (83)
-0.112 (80)
0.134 (274)
0.315 (irr), 0.819 (irr)
0.400 (182)
0.724 (irr)
0.296 (irr), 0.691 (irr)
0.380 (irr), 0.732 (irr)
0.41 (irr)
not det.
∼0.42 (irr)
∼0.42 (irr)
0.403 (irr), 0.715 (irr)
3 (2:1 add, 1,4-Ph2-1,3-butadiyne)
0.622 (irr), 0.771 (irr)
a Recorded in benzonitrile/0.3 M n-Bu4NBF4 at a glassy carbon electrode. Scan rates are 200 mV/s unless otherwise indicated. b Scan
rate ) 50 mV/s.
near-IR region at 990 nm (ꢀ ) 1500 M-1 cm-1). The
latter band is associated with transitions in the indi-
vidual delocalized dimers in [3]2+. The band occurs at
wavelengths similar to those observed for previously
studied mixed valence dimolybdenum complexes with
dithiolate ligands.18 Although we were unable to iso-
late the monocation of 3, the electronic spectrum of
[3]+ was obtained by mixing equimolar solutions of 3
in THF and [3]2+ in CH3CN. A very broad, unresolved
absorption was observed in the visible region (see
Experimental Section), and an intervalence transfer
band between dimers was not resolved or identified.
Such a band may not be observed because of the
small difference in potentials observed between the [3]+
Figure 2. Cyclic voltammogram and differential pulse
and [3]2+ waves and the assignment of weak coupling
voltammogram of
3 recorded in benzonitrile/0.3 M
Bu4NBF4 at a scan rate of 200 mV/s.
and largely localized electron density between the
dimers.
occur at the sp3-hybridized carbons of the resulting
alkanedithiolate ligands may account for the lack of
reactivity in these cases.
The reactions of protic acid were also studied with
the analogue of 3 with unsubstituted Cp ligands, as
these derivatives were expected to be slightly less prone
to oxidation. However once again the NMR spectra
indicated that a paramagnetic product had formed,
suggesting an irreversible oxidation had occurred.
X-ray Diffraction Study of [3]2+. A single crystal
of the oxidized tetranuclear complex derived from ad-
duct formation with 1,4-diphenyl-1,3-butadiyne was
isolated, and an X-ray diffraction study was carried
out.25 A perspective drawing of the dication is shown in
Figure 3, and selected distances and angles are given
in Table 4. Almost all the bond distances in the
structure of the dication are very similar to those of the
neutral analogue discussed above, but a small, but
significant change in bond distances is observed for the
Mo-Mo bonds. The average value of the two M-M
bonds decreases from 2.6047(6) Å in the neutral complex
to 2.5896(10) Å in the dication. The molecular orbital
descriptions of a simplified neutral MoIII-III dimer
[CpMo(SH)2]2 indicated that the HOMO of the com-
plex includes a δ bonding overlap of two metal d orbitals
and an antibonding contribution from the sulfur p
orbitals.26 In the tetranuclear dication, an electron has
been removed from the HOMO of each dimer. The
Reactions of the Tetranuclear Complex 3 with
Acid. The reaction of 3 with protic acid was studied. If
the reaction proceeded in a manner analogous to the
dinuclear protonation (see eq 1), this proton addition
would provide a means of reversibly changing the
nature of the bridging ligand beween the dimers.
However the addition of 2 equiv of HBF4 or HSO3CF3
to 3 did not result in a reversible protonation; instead,
we observed the oxidation of the complex and the
formation of hydrogen, which was detected in the NMR
spectrum when the protonation was carried out in a
sealed NMR tube. The dicationic oxidized product, [3]2+
was paramagnetic and did not give a sharp NMR
spectrum. The complex was characterized by mass
spectroscopy and cyclic voltammetry. The envelope
observed at m/z 1336 in the mass spectrum is consistent
with an intact tetranuclear dication with a single triflate
anion (P - OTf). The CV of the oxidized product shows
waves at the same potentials as observed for 3. The
product is proposed to contain two mixed valence
MoIII/IV dithiolene-bridged dimers linked by the buta-
diene fragment.
The electronic spectrum of the 1,4-diphenyl-1,3-
buatadiene adduct [3]2+ has been compared with that
of the neutral starting complex 3. A band in the vis-
(25) Structural comparisons of three redox states of complexes
showing strong electronic coupling between dimolybdenum units have
been reported.21a
(26) DuBois, D. L.; Miller, W. K.; Rakowski DuBois, M. J. Am. Chem.
Soc. 1981, 103, 3429. (b) Bursten, B. C.; Cayton, R. H. Inorg. Chem.
1989, 28, 2846.
ible region shifts from 610 nm for 3 to 700 nm for [3]2+
,
and a new absorption is observed for the dication in the

Multinuclear Dithiolene Complexes
Organometallics, Vol. 24, No. 18, 2005 4411
Figure 3. Two perspective views and numbering scheme for the dication [3]2+. The view on the left shows the orientation
of the linking 1,4-diphenylbis(ethenedithiolate) ligand. The view on the right better shows the relative orientations of the
two molybdenum dimers. Phenyl rings are omitted from this ORTEP for clarity.
Table 4. Bond Distances, Selected Bond Angles,
observed M-M bond shortening upon oxidation of 3 to
and Selected Torsion Angles for Oxidized 2:1
[3]2+ suggests that the antibonding contribution to the
Adduct, [3]2+
orbital has been diminished and that the sulfur anti-
Bond Distances (Å)
bonding interaction is a more important contributor
than the metal-metal interaction in the HOMO of this
system.
Mo(1)-S(3)
Mo(1)-S(4)
Mo(1)-S(1)
Mo(1)-S(2)
Mo(2)-S(3)
Mo(2)-S(4)
Mo(2)-S(1)
Mo(2)-S(2)
S(3)-C(8)
2.458(2)
2.455(2)
2.458(3)
2.458(3)
2.441(2)
2.429(3)
2.451(3)
2.454(2)
1.815(8)
S(4)-C(7)
1.793(8)
S(1)-C(17)
S(2)-C(17)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(10)-C(11)
Mo(1)-Mo(2)
1.826(10)
1.824(11)
1.455(12)
1.354(11)
1.477(10)
1.351(10)
1.479(12)
2.5958(11)
A comparison of Figures 1b and 3 shows that the
relative orientations of the two molybdenum dimers are
significantly different for 3 and [3]2+. This arises from
the much larger C7-C8-C9-C10 torsion angle for [3]2+
(146°) compared to that of 3 (121°).
Syntheses of Complexes of Higher Nuclearity.
In our early work, the hydrosulfido-bridged dimer
[CpMo(µ-S)(µ-SH)]2 was found to react with alkynes to
form the bis-alkyne adduct with the elimination of H2.27
A similar type of reaction of the hydrosulfido complex
can be carried out with 2 equiv of 5 to form the
hexanuclear complex, 10, eq 6. The reaction proceeds
Selected Bond Angles (deg)
Mo(1)-S(3)-Mo(2)
Mo(1)-S(4)-Mo(2)
Mo(1)-S(1)-Mo(2)
Mo(1)-S(2)-Mo(2)
S(1)-C(17)-S(2)
C(6)-C(7)-C(8)
63.99(6)
64.21(7)
63.84(7)
64.80(6)
96.3(5)
S(3)-C(8)-C(7)
118.3(6)
116.5(7)
115.6(6)
115.9(6)
125.8(8)
127.1(7)
S(4)-C(7)-C(8)
S(3)-C(8)-C(9)
S(4)-C(7)-C(6)
C(7)-C(8)-C(9)
C(8)-C(9)-C(10)
127.5(7)
126.5(7)
C(9)-C(10)-C(11)
Selected Torsion Angles (deg)
S(4)-C(7)-C(8)-C(9)
170.9(6) C(7)-C(8)-C(9)-C(10) 146.4(8)
S(7)-C(10)-C(9)-C(8) 169.9(6)
are observed as two singlets of unequal intensity with
a total integration value of four protons. Multiplets for
the MeCp protons are observed between 5.4 and 5.8
ppm, while two sets of phenyl multiplets are observed
at 7.2 and 6.65 ppm. The integration ratio of the MeCp
to total phenyl protons agrees with the expected value
of 24:20. The differential pulse voltammogram for the
trimer, 10, shows two reversible oxidation waves at
-0.23 and 0.018 V vs Fc in a ratio of approximately 2:1.
These are assigned to the MoIII-III to MoIII-IV
couples in the methanedithiolate-bridged dimers and
the central bis-dithiolene complex, respectively. The as-
signment is consistent with the relative current ampli-
tudes and also with the relative oxidation potentials of
dinuclear complexes (CpMo)2(S2CH2)(SC(R)dC(R)S) and
[CpMo(SC(R)dC(R)S)]2. For similar R groups, the former
methanedithiolate-bridged derivatives generally are
oxidized more easily than the bis(dithiolene) com-
plexes.17
In the reaction described above, the methanedithio-
late complex, which has only one set of reactive sulfido
bridges, serves as a capping reagent. The reaction of
[MeCpMo(S)(SH)]2 with 1,4-diphenyl-1,3-butadiyne was
carried out in a 1:1 ratio in THF at room temperature
overnight to determine whether soluble polymeric or
oligomeric products could be formed, as shown in eq 7.
A coordination polymer that incorporates repeating
at room temperature overnight to form a brown product,
which was purified by column chromatography. The
mass spectrum of the product shows a parent ion peak
at 1868, consistent with the proposed trimer of dimers.
1
The H NMR spectrum of the product suggests that a
mixture of isomers is present. Isomers are likely to
result from syn or anti orientations of the two meth-
anedithiolate complexes about the central dimer. (Only
the anti isomer is shown in eq 6.) For example, NMR
resonances assigned to the methanedithiolate protons
(27) Rakowski DuBois, M.; VanDerveer, M. C.; DuBois, D. L.;
Haltiwanger, R. C.; Miller, W. K. J. Am. Chem. Soc. 1980, 102, 7456.

4412 Organometallics, Vol. 24, No. 18, 2005
Newell et al.
units of a dinuclear Cp-molybdenum complex has been
reported previously.28
dithiolene formation has been observed after formation
of the first dithiolene adduct. Products containing from
one to three dinuclear units have been synthesized by
appropriate synthetic routes, and isolated and charac-
terized, and preliminary work indicates that larger
molecular weight products can also be synthesized. The
electrochemical properties of the products have been
studied by cyclic voltammetry. The bis-adducts of the
molybdenum dimers with the 1,3- and 2,4-diynes show
evidence for weak electronic communication between
discrete dimer units, whereas the bis-adducts of 1,3- and
1,4-dialkynylarenes do not. The new dinuclear, tetra-
nuclear, and hexanuclear complexes reported here
provide the framework for interesting further synthetic
elaborations, and they will be the subject of further
studies. In addition, these studies suggest that reactions
of the molybdenum dimers with polyynes may give rise
to new materials.
The reaction produced a red soluble material that was
isolated in ca. 50% yield after filtration through alu-
mina. The NMR spectrum of the product shows broad-
ened, poorly resolved resonances with chemical shifts
very similar to the sharper multiplets observed for the
hexanuclear complex discussed above. The ESI+ mass
spectrum of the material shows envelopes at m/z ) 680,
1360, 2040, 2720, 3400, and 4080 in decreasing intensi-
ties. The observed m/z values represent multiples of 680,
corresponding to [(MeCpMo)2S4 + PhCdC-CdCPh]n,
and can be assigned to dimolybdenum-alkenedithiolate
chains containing from 2 to 12 molybdenum ions (n )
1-6). For the more intense envelopes, the complex
isotope patterns for the multiple molybdenum ions have
been calculated and found to agree with the observed
spectra. Several other m/z envelopes are also observed
in the spectrum, and some of these are assigned in the
Experimental Section. The cyclic voltammogram for this
material was recorded in dichloromethane. Two closely
spaced quasi-reversible oxidations of equal current
amplitude are observed at -0.17 (110) and 0.048 (87)
V vs Fc, suggesting a communication between dimers
similar to that observed for the tetranuclear complexes.
Similar observations of two oxidation waves have been
reported for ferrocene-containing polymers.29 Further
work will be necessary to determine the extent of
oligomerization/polymerization in this product.
Although our syntheses of polynuclear products have
focused primarily on derivatives of 1,4-diphenyl-1,3-
butadiyne, we have obtained evidence that the reactions
are quite general and similar products are formed with
the other diynes. For example, the reaction of the mono-
adduct 4 (2 equiv) with [MeCpMo(S)(SH)]2 forms a
hexanuclear product analogous to 10, and the reaction
of [MeCpMo(S)(SH)]2 with 1 equiv of 1,4-bis(trimethyl-
silylethynyl)benzene forms a coordination polymer simi-
lar to that shown in eq 7. NMR and mass spectroscopic
data for these products are included in the Experimental
Section.
Experimental Section
All reactions were performed under a nitrogen atmosphere
using standard Schlenk techniques. Tetrahydrofuran was
distilled from sodium/benzophenone and degassed with nitro-
gen prior to use. All other solvents were obtained from Fisher
or Aldrich and used without further purification. 1,4-Diphe-
nylbutadiyne, 2,4-hexadiyne, 1,4-bis(trimethylsilylethynyl)-
benzene, and trifluoromethanesulfonic acid were obtained from
Aldrich and used without further purification. 1,3-Diethynyl-
benzene was purchased from Lancaster. (MenCpMoµ-S)2S2CH2
and [MenCpMo(S)(SH)]2 (where n ) 0 or 1) were prepared
according to literature methods.30
1
Instrumentation. H NMR spectra were acquired with a
Varian Inova 400- or 500-MHz instrument. Chemical shifts
(δ) are reported relative to tetramethylsilane. Electrospray
ionization (ESI) mass spectra were collected using an HP
59987A electrospray with an HP 5989B mass spectrometer.
Electronic spectra were collected on an Agilent 8453 UV-
visible spectrometer. Cyclic voltammograms and square wave
voltammograms were obtained using a Cypress systems model
CS-1200 computer-aided electrolysis system using a glassy
carbon working electrode. The voltammograms were recorded
under a nitrogen atmosphere on 0.3 M Bu4NBF4 benzonitrile
solutions. The ferrocene/ferrocenium couple was used as an
internal reference. Permethylferrocene/permethylferrocenium
or cobaltocene/cobaltocenium were used as secondary refer-
ences when the ferrocene couple was obscured. All potentials
are reported with respect to the ferrocene/ferrocenium couple.
Elemental analyses were carried out by Desert Analytics
Laboratory, Tucson, AZ.
Synthesis of Bis-adduct of (MeCpMoµ-S)2S2CH2 with
2,4-Hexadiyne, 2. (MeCpMoµ-S)2S2CH2 (0.200 g, 0.406 mmol)
and 2,4-hexadiyne (0.0158 g, 0.203 mmol) were stirred for 2 h
in tetrahydrofuran. As the reaction proceeded, the color of the
solution changed from blue to green. The solvent was removed
in vacuo, and the solid was recrystallized by layering hexane
onto a methylene chloride solution to give green microcrystals.
Yield: 0.143 g, 66%. 1H NMR (CDCl3, 500 MHz): 1.19 (s, 6 H,
Me), 2.02 (s, 6 H, CpCH3), 5.65 (m, 16 H, CH3Cp), 6.25 (br s,
4 H, CH2). 13C NMR (CDCl3, 400 MHz): δ 16.63 (CH3Cp), 20.43
(S-C-CH3) 89.46 (dC), 90.66 (dC), 93.50 (Cp), 94.62 (Cp),
95.81 (Cp), 112.379 (CH2) Anal. Calcd for C32H38Mo4S8: C,
36.16; H, 3.60. Found: C, 35.84; H 3.53. MS, m/z (ESI positive
ion): 1063 (P+). Cyclic voltammetry, E1/2, V (∆EP, mV): -0.321
(63) (Mo3+Mo3+/Mo3+Mo3+f Mo3+Mo3+/Mo3+Mo4+); -0.185 V
(61) (Mo3+Mo3+/Mo3+Mo4+f Mo3+Mo4+/Mo3+Mo4+); Epa, 0.403
(irrev); and Epa, 0.715 V (irrev).
Summary. The cyclopentadienyl molybdenum dimers
containing bridging sulfido ligands react readily with
diynes to form polynuclear alkenedithiolate complexes.
Reactions proceed with conjugated 1,3- and 2,4-diynes
as well as with dialkynylarenes. No evidence for deac-
tivation of the second alkyne of the diyne toward
(28) Allshouse, J.; Haltiwanger R. C.; Allured, V.; Rakowski DuBois,
M. Inorg. Chem. 1994, 33, 2505.
(29) (a) Foucher, D. A.; Tang, B. Z.; Manners, I. J. Am. Chem. Soc.
1992, 114, 6246. (b) Brandt, P. F.; Rauchfuss, T. B. J. Am. Chem. Soc.
1992, 114, 1926.
(30) Cowans, B. A.; Rakowski DuBois, M. In Organometallic Syn-
thesis; King, R. B., Eisch, J., Eds.; 1986; Vol. III, p 262.

Multinuclear Dithiolene Complexes
Organometallics, Vol. 24, No. 18, 2005 4413
Synthesis of Bis-adduct of (MeCpMoµ-S)2S2CH2 with
1,4-Diphenylbutadiyne, 3. (MeCpMoµ-S)2S2CH2 (0.128 g,
0.26 mmol) and 1,4-diphenylbutadiyne (0.026 g, 0.13 mmol)
were stirred in 40 mL of tetrahydrofuran for 1 h. The solvent
was removed in vacuo, and the solid was recrystallized by slow
diffusion of diethyl ether into a methylene chloride solu-
tion. Yield: 0.100 g, 65%. 1H NMR (CD2Cl2, 500 MHz): δ 2.05
(s, ∼11 H, CH3Cp), 5.67 (m, 16 H, CH3Cp), 6.35 (br s, 4 H,
CH2), 6.73 (m, 4 H, Ph), 7.24 (2 m, 6 H, Ph). Anal. Calcd for
C42H42Mo4S8: C, 42.50; H, 3.56. Found: C, 42.12; H 3.69. MS,
m/z (ESI positive ion): 1187 (P+); 694 (P - 1,4 diphenylbuta-
diyne+). Cyclic voltammetry, E1/2, V (∆EP, mV): -0.261 (83)
(Mo3+Mo3+/Mo3+Mo3+f Mo3+Mo3+/Mo3+Mo4+); -0.112 (80)
(Mo3+Mo3+/Mo3+Mo4+f Mo3+Mo4+/Mo3+Mo4+); Epa, 0.622
(irrev); and Epa, 0.771 (irrev). Visible spectrum in tetrahy-
drofuran, nm (M-1 cm-1), 427 (4.41 × 103), 610 (6.30 × 102),
700 (sh).
(0.165 g, 0.138 mmol). The solvent from the green filtrate was
removed, and the residue was redissolved in approximately
2-3 mL of CH2Cl2 and hexanes were added. The mixture was
placed in the freezer, and after 24 h another crop of the
product (0.017 g, 0.014 mmol) was collected by filtration.
Yield: 0.182 g (69.2%). MS (MALDI+): m/z 1200 (P+); 737 (P+
- ((CpMoµ-S)2S2CH2)). 1H NMR (500 MHz, CDCl3): δ 6.64 (s,
4 H, Ph bridge), 6.22 (s, 4 H, S2CH2), 5.84 (s, 20 H, Cp), -0.28
(s, 18 H, SiMe3). CV, E1/2 V vs Fc (∆Ep mV): -0.234 (87). Anal.
Calcd for C38H46Mo4S8Si2: C, 38.06; H, 3.84. Found: C, 38.51;
H, 3.67.
Synthesis of Mono-adduct of (CpMoµ-S)2S2CH2 with
1,3-Diethynyl)benzene, 8. (CpMoµ-S)2S2CH2 (0.101 g, 0.217
mmol) was dissolved in 5 mL of THF. 1,3-Diethynylbenzene
(27 µL, 0.214 mmol) was syringed into the solution and the
solution immediately turned green. The mixture was allowed
to stir for 18 h, after which the solvent was removed in vacuo.
The resulting green residue was washed with cold (-78 °C)
petroleum ether and then chromatographed on a short
CH2Cl2/neutral alumina column. One green band was eluted
with 100% CH2Cl2, which contained the product. Yield: 0.054
g (42.1%). MS (ESI+): m/z 591 (P+). 1H NMR (500 MHz,
CDCl3): δ 7.36, 7.25, 7.18, 7.12 (m, 4 H, Ph), 6.77 (s, 1 H,
dCH), 6.28 (s, 2 H, S2CH2), 5.89 (s, 10 H, Cp), 2.99 (s, 1 H,
CtCH). CV, E1/2 V vs Fc (∆Ep, mV): -0.205 (129). Anal. Calcd
for C21H18Mo2S4: C, 42.70; H, 3.05. Found: C, 42.48; H, 3.01.
Synthesis of Mono-adduct of (CpMoµ-S)2S2CH2 with
1,4-Bis(trimethylsilylethynyl)benzene, 9. (CpMoµ-S)2-
S2CH2 (0.077 g, 0.166 mmol) was dissolved in 10 mL of THF.
1,4-Bis[(trimethylsilyl)ethynyl]benzene (0.045 g, 0.166 mmol)
was added to the solution slowly, under a flow of nitrogen.
The solution immediately turned green, and the mixture was
allowed to stir at room temperature for 3 h. The solvent was
removed in vacuo, and the green residue was washed with cold
(-78 °C) petroleum ether. The residue was then eluted through
a short neutral alumina column. One green band was eluted
with 100% CH2Cl2, and it contained the product. Yield: 0.035
g (28.7%). MS (MALDI+): m/z 735 (P+). 1H NMR (500
MHz, CDCl3): δ 7.12 (s, 2 H, Ph), 6.63, 6.60 (2s, 2 H, Ph), 6.08
(s, 2 H, S2CH2), 5.80 (s, 10 H, Cp), -0.26 (s, 18 H, SiMe3).
CV, E1/2 V vs Fc (∆Ep, mV): -0.228 (94). Anal. Calcd for
C27H34Mo2S4Si2: C, 44.13; H, 4.63. Found: C, 44.53; H, 4.61.
Synthesis of Hexanuclear Complex 10. Complex 5 (0.116
g, 0.168 mmol) and [MeCpMo(µ-S)(µ-SH]2 (0.040 g, 0.083
mmol) were stirred in THF under N2 for 3 days. The solution
was filtered in air, and the solvent was removed by rotary
evaporation. The resulting solid was chromatographed on an
alumina column with chloroform, and the main brown band
was collected. The solvent was removed by rotary evaporation,
and ether was layered on the resultant brown oil. After 1 h a
brown powder formed that could be removed by filtration.
Yield: 0.061 g, 39%. 1H NMR (CD2Cl2, 500 MHz): δ 1.77 (2 s,
∼5 H, CH3Cp), 1.98 (s, ∼5 H, CH3Cp), 2.04 (s, ∼5 H, CH3Cp),
5.64 (m, 24 H, CH3Cp), 6.22, 6.18 (2 s, 4 H, CH2), 6.74 (3 m, 8
H, Ph), 7.22 (m, 13 H, Ph). MS, m/z (ESI positive ion): 1868
(P+); 1173, (P - 694); 694 (MeCpMoµ-S)2S2CH2 + diyne). Cyclic
voltammetry, E1/2, V (∆EP, mV): -0.225 V (86); 0.023 V (70);
Epa, 0.302 (irrev); and Epa, 0.681 (irrev). Differential pulse
voltammetry, Ep (|i|), -0.229 V (10.8 uA), 0.018 V (7.5 uA).
Vis spectrum in THF (nm, (M-1 cm-1)): 432 (9.3 × 103); ∼500
(sh); 624 (1.3 × 103); 700 (sh); ∼800 (weak sh).
Synthesis of Mono-adduct of (MeCpMoµ-S)2S2CH2 with
2,4-Hexadiyne, 4. A solution of 2,4-hexadiyne (0.951 g, 12.2
mmol) in 15 mL of tetrahydrofuran was added to a solution of
(MeCpMoµ-S)2S2CH2 (0.300 g, 0.609 mmol) in 40 mL of
tetrahydrofuran. The solution was stirred for 30 min, and the
solvent was removed in vacuo. The green solid was recrystal-
lized by adding 10 mL of acetonitrile to a solution in 3 mL of
diethyl ether. Yield: 0.091 g, 26%. 1H NMR (CDCl3, 500
MHz): δ 1.58 (s, 3 H, tC-CH3), 1.97 (s, 3 H, S-C-CH3), 2.08
(s, 6 H, CH3Cp), 5.75 (2 m, 8 H CH3Cp), 6.25 (s, 2 H, CH2).
MS, m/z (ESI positive ion): 570 (P+). Cyclic voltammetry, E1/2
,
V (∆EP, mV): -0.278 (129) (Mo3+Mo3+ f Mo3+Mo4+); Epa, 0.296
(irrev); and Epa, 0.691 (irrev).
Synthesis of Mono-adduct of (MeCpMoµ-S)2S2CH2 with
1,4-Diphenylbutadiyne, 5. (MeCpMoµ-S)2S2CH2 (0.133 g,
0.27 mmol) and 1,4-diphenylbutadiyne (0.970 g, 4.06 mmol)
were stirred in 50 mL of tetrahydrofuran for 30 min. The
solvent was removed in vacuo, and the solid was placed on an
alumina column and washed with 200 mL of hexane to remove
excess 1,4-diphenylbutadiyne. The product was removed from
the column with acetone, and water was layered on the acetone
solution to yield green crystals. Yield: 0.016 g, 8.5%. 1H NMR
(CD2Cl2, 500 MHz): δ 2.11 (s, 6 H, CH3Cp), 5.80 (2 m, 8 H,
CH3Cp), 6.33 (s, 2 H, CH2), 7.25 (m, ∼9 H, Ph), 7.57 (m, 2 H,
Ph). Anal. Calcd for C29H26Mo2S4: C, 50.14; H, 3.77. Found:
C, 50.26; H 3.60. MS, m/z (ESI positive ion): 694 (P+); 492 (P
- 1,4 diphenylbutadiyne+). Cyclic voltammetry, E1/2, V (∆EP,
mV): -0.196 V (75) (Mo3+Mo3+ f Mo3+Mo4+); Epa, 0.380 (irrev);
and Epa, 0.732 (irrev).
Synthesis of Bis-adduct of (CpMoµ-S)2S2CH2 with 1,3-
Diethynylbenzene, 6. (CpMoµ-S)2S2CH2 (0.157 g, 0.338
mmol) was dissolved in 20 mL of THF. 1,3-Diethynylbenzene
(21 µL, 0.169 mmol) was syringed into the solution over the
course of 5 min. The solution immediately turned green, and
a green precipitate formed. The mixture was allowed to stir
for 5 h, after which it was filtered and the green solid was
collected (0.062 g, 0.059 mmol). The solvent from the green
filtrate was removed, and the residue was redissolved in
CH2Cl2 and then layered with hexanes and placed in the
freezer overnight. A second crop of product (0.072 g, 0.068
mmol) was collected by filtration. Yield: 0.134 g, (75.1%). MS
1
(MALDI+): m/z 986 (P+). H NMR (500 MHz, CDCl3): δ 7.05
(s, 1 H, Ph), 7.047 (s, 2 H, Ph), 6.95 (t, 1 H, Ph), 6.62 (s, 2 H,
dCH), 6.27 (s, 4 H, S2CH2), 5.86 (s, 20 H, Cp). CV, E1/2 V vs
Fc (∆Ep mV): -0.227 (75). Anal. Calcd for C32H30Mo4S8: C,
36.44; H, 2.80. Found: C, 36.29; H, 3.08.
A similar procedure was followed with 4 to form an
1
analogous hexanuclear complex. H NMR (CDCl3, 500 MHz):
δ 1.09 (overlapping singlets, 12 H, Me); 2.05, 1.99, 1.87 (3 s,
18 H, CH3Cp), 5.52 (m, 16 H, CH3Cp), 5.48, 5.43 (2 m, 8 H,
CH3Cp), 6.17 (overlapping singlets, 4 H, CH2). MS, m/z (ESI
positive ion): 1618 (P+); 1128, (P - (MeCpMoµ-S)2S2CH2)); 634
(P - 2(MeCpMoµ-S)2S2CH2).
Reaction of [MeCpMo(µ-S)(µ-SH)]2 with 1,4-Diphenyl-
1,3-butadiyne. 1,4-Diphenylbutadiyne (0.262 g, 1.29 mmol)
and [MeCpMo(S)SH]2 (0.622 g, 1.29 mmol) were stirred at
Synthesis of Bis-adduct of (CpMoµ-S)2S2CH2 with 1,4-
Bis(trimehylsilylethynyl)benzene, 7. (CpMoµ-S)2S2CH2
(0.204 g, 0.439 mmol) was dissolved in 20 mL of THF. 1,4-
Bis[(trimethylsilyl)ethynyl]benzene (0.065 g, 0.240 mmol) was
added to the solution slowly, under a flow of nitrogen. The
solution immediately turned green, and a green precipitate
formed. The mixture was allowed to stir at room temperature
for 4 h, it was then filtered, and the green solid was collected

4414 Organometallics, Vol. 24, No. 18, 2005
Newell et al.
Table 5. Crystal Data and Collection Parameters for the Bis-adduct of (MeCpMo)2(µ-S)2S2CH2and
1,4-Diphenylbutadiyne (3), the Mono-adduct of (MeCpMo)2(µ-S)2S2CH2 and 1,4-Diphenylbutadiyne (5), and
the Product of Reaction of 3 with Trifluoromethanesulfonic Acid [3]2+
3
5
32+
formula
C42H42Mo4S8
1187.00
monoclinic
14.8754(6)
16.9565(7)
16.4576(6)
90
C29H26Mo2S4
694.62
orthorhombic
17.5179(13)
11.9804(9)
25.3939(19)
90
(C42H42Mo4S8)(CF3SO3)2(C3H6O)0.9
1535.46
fw (amu)
cryst syst
a (Å)
triclinic
10.4965(5)
15.1664(6)
18.0759(8)
76.5010(10)
78.3560(10)
80.0590(10)
2716.6(2)
b (Å)
c (Å)
R (deg)
â (deg)
92.8870(10)
90
90
90
γ (deg)
volume (Å3)
space group
Z
4145.9(3)
P2(1)/n (#14)
4
5329.5(7)
Pbca (#61)
8
P1h (#2)
2
density, calc (g/cm3)
λ(Mo KR)
temp (K)
1.902
1.731
1.877
0.71073
0.71073
0.71073
138
158
155
scan type, deg
θ range (deg)
no. of indep reflns
no. of reflns obsd
ω scans, 0.3
1.80 to 27.48
9474 [R(int) ) 0.0817]
31 624
ω scans, 0.3
1.98 to 27.48
6112 [R(int) ) 0.2828]
40 162
ω scans, 0.3
2.00 to 27.48
12 454 [R(int) ) 0.0893]
21 662
absorp coeff (mm-1
R1 (for Fo > 4σFo)a
R1, wR2 (all data)b
GOFc
)
1.618
1.273
1.356
0.0484 for 6826 data
0.0780, 0.130
0.997
0.0802 for 2840 data
0.1884, 0.1920
0.951
0.0736 for 6227 data
0.1603, 0.1934
0.950
largest peak, hole (e-/Å-3
)
1.51, -1.63
1.740, -1.063
1.408, -0.0866
2
2
a R ) R1 ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑[w(Fo2 - Fc )2]/∑[w(Fo2)2]]1/2
.
c GOF ) S ) [∑[w(Fo2 - Fc )2]/(M - N)]1/2 where M is the number
of reflections and N is the number of parameters refined.
room temperature in 200 mL of THF under N2 for 1-3 days.
The solution was filtered in air (to remove a small amount of
solid that NMR showed to be impure product), and solvent
was removed from the filtrate by rotary evaporation. The
resulting solid was filtered through alumina with chloroform,
and the red-brown filtrate was collected. Layering ether on
this solution resulted in precipitation of a red-brown pow-
for 3. Visible absorption spectrum in acetonitrile, nm (M-1
cm-1): shoulder at ∼433 (4.25 × 103), 699 (2.63 × 103), 989
(1.51 × 103).
Visible Absorption Spectrum of [3]+. Complex 3 was
dissolved in tetrahydrofuran, and [3]2+ was dissolved in
acetonitrile to make 0.45 mM solutions. Both of these solutions
were degassed with nitrogen, then 1 mL of each solution was
syringed into a 1 cm quartz cell that had been evacuated and
filled with nitrogen. The visible absorption spectrum was
obtained immediately after mixing. A very broad absorption
band extending from ∼500 to 1000 nm was observed with λmax
at 691 nm (1.71 × 103).
1
der. Yield: 0.464 g, 52%. H NMR (CD2Cl2): δ 1.81 (br, 6 H,
CH3Cp), 5.32 (br, 8 H, CH3Cp), 6.72 (br, 4 H, Ph), 7.22 (br, ∼7
H, Ph). MS (ESI positive ion), m/z, intensity, 1 unit )
([MeCpMoS2]2 + 1,4 diphenylbutadiyne): 680 (17) [(1 unit)]+;
882 (48) [(1 unit) + 1,4 diphenylbutadiyne]+; 1360 (32) [2
units]+; 1562 (15) [(2 units) + 1,4 diphenylbutadiyne]+; 2040
(26) [3 units]+; 2242 (2.3) [(3 units) + 1,4 diphenylbutadiyne]+;
2720 (5) [4 units]+; 2922 (2.7) [(4 units) + 1,4 diphenyl-
butadiyne]+; 3400 (3.2) [5 units]+; 3602 (2.3) [(5 units) + 1,4
diphenylbutadiyne]+; 4080 (2.2) [6 units]+. Cyclic voltammetry
in CH2Cl2, E1/2, V (∆EP, mV): -0.169 (110); 0.048 V (87); Epa,
0.966 (irrev). Visible spectrum in tetrahydrofuran, (nm, M-1
cm-1 per unit), 481 (3.34 × 103), ∼580 (sh); 677 (3.87 × 102),
809 (sh, ∼1.43 × 102).
X-ray Crystallography. A crystal of appropriate size was
mounted on a glass fiber using Paratone-N oil, transferred to
a Siemens SMART diffractometer/CCD area detector, centered
in the beam (Mo KR; λ ) 0.71073 Å; graphite monochromator),
and cooled to -135 to -115 °C by a nitrogen low-temperature
apparatus that had been previous calibrated by a thermocouple
placed at the same position as the crystal. Preliminary
orientation matrix and cell constants were determined by
collection of 60 10-s frames, followed by spot integration and
least-squares refinement. A minimum of a hemisphere of data
was collected using 0.3° $ scans at 30 s per frame. The raw
data were integrated and the unit cell parameters refined
using SAINT. Data analysis was performed using XPREP.
Absorption correction was applied using SADABS. The data
were corrected for Lorentz and polarization effects, but no
correction for crystal decay was applied. Structure solutions
and refinements were performed (SHELXTL-Plus V5.0) on F2.
Crystal data and collection parameters are given in Table 5.
Bis-adduct of (MeCpMoµ-S)2S2CH2 with 1,4-Diphenyl-1,3-
butadiyne (3). Crystals suitable for X-ray diffraction studies
were grown by letting ether diffuse into a solution of the
compound in dichloromethane at room temperature. Prelimi-
nary data indicated a monoclinic cell with the P(21)/n space
group. All non-H atoms were refined anisotropically. All
H-atoms were placed in idealized positions and were included
in structure factor calculations but were not refined.
A similar procedure was followed with 1,4-bis(trimethylsi-
lylethynyl)benzene to form a polymeric product. 1H NMR
(CDCl3): δ -0.29 (18 H, Me3Si), 2.0 (overlapping singlets, 6
H, CH3Cp), 5.60 (m, 8 H, CH3Cp), 6.65, 6.76 (2m, 4 H, Ph).
MS (ESI positive ion), m/z, 1 unit ) ([MeCpMoS2]2 + 1,4-bis-
(trimethylsilylethynyl)benzene): 748 [(1 unit)]+; 1498 [2 units]+;
1768 [(2 units) + diyne]+; 2244 [3 units]+; 2518 [(3 units) +
diyne]+; 2996 [4 units]+; 3265 [(4 units) + diyne]+; 3744 [5
units]+; 4017 [(5 units) + diyne]+; 4764 [(6 units) + diyne]+.
Synthesis of [3]2+ Complex 3 (0.068 g, 0.0572 mmol) and
trifluoromethanesulfonic acid (10.1 uL, 0.144 mmol) were
stirred in 40 mL of methylene chloride under nitrogen for 3
days. The solution was filtered to obtain 0.050 g of a green
solid. This solid could be recrystallized by dissolving in
acetonitrile and letting diethyl ether slowly diffuse into the
solution. Yield: 33%. No resonances for the product were
observed by NMR, but when the reaction was performed in
an NMR tube, a sharp resonance assigned to H2 was observed
at 4.63 ppm. MS, m/z (ESI positive ion): 1336 (P - CF3SO3)+;
1186 (P - 2CF3SO3)+; 694 ((MeCpMoµ-S)2(S2CH2) + diyne).
Cyclic voltammetry: potentials are identical to those reported
Mono-adduct of (MeCpMoµ-S)2S2CH2 and 1,4-Diphen-
yl-1,3-butadiyne (5). Crystals suitable for X-ray diffraction
studies were grown by letting ether diffuse into a solution of

Multinuclear Dithiolene Complexes
Organometallics, Vol. 24, No. 18, 2005 4415
the compound in dichloromethane at room temperature.
Preliminary data indicated a monoclinic cell with the Pbca
space group. All non-H atoms were refined anisotropically. All
H atoms were placed in idealized positions and were included
in structure factor calculations but were not refined.
placed in idealized positions and were included in structure
factor calculations but were not refined.
Acknowledgment. Support for parts of this work
by the National Science Foundation and by the Division
of Chemical Sciences, Office of Basic Energy Sciences,
Office of Energy Research, U.S. Department of Energy,
is gratefully acknowledged.
[3](OTf)2. Crystals suitable for X-ray diffraction studies
were grown by letting ether diffuse into a solution of the
compound in acetone at room temperature. Preliminary data
indicated a triclinic cell with the P1h space group. A molecule
of acetone cocrystallized and was found to be present 90% of
the time. The disorder in one of the two triflate counterions
was modeled by letting one of the sulfurs and one of the
oxygens refine to two equivalent positions. The methylcyclo-
pentadienyl ligands attached to Mo3 and Mo4 were also
disordered, and the disorder was modeled by letting the methyl
groups refine to two equivalent positions. All atoms other than
hydrogen, the disordered sulfur and oxygen, and the disordered
methyl groups were refined anisotropically. All H atoms were
Supporting Information Available: Tables of crystal
and refinement data, positional and equivalent isotropic
thermal parameters, bond distances and angles, and torsional
angles for 3, [3]2+, and 5; ESI mass spectra for polymeric
formulation. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM050317D