Electronic communication in dinuclear C4-bridged tungsten complexes

Article abstract of DOI:10.1021/ja909764x

The dinuclear tungsten carbyne [X(CO)₂(dppe)WC ₄W(dppe)(CO)₂X] (dppe = 1,2-bis(diphenylphosphino)ethane; X = I (3), Cl (7)) complexes were prepared from the bisacetylide precursor Li₂[(CO)₃(dppe)WC₄W(CO)₃(dppe)] (2) via oxidative replacement of one CO group at each tungsten center with a halide substituent. The iodide ligand In 3 could be substituted with Isothiocyanate or triflate resulting In [X(CO)₂(dppe)WC₄W(dppe)(CO) ₂X] complexes (X = NCS (8), OTf (9)). Substitution of two and all four CO ligands In 3 was achieved via subsequent photolytic or thermal activation with dppe. The half-substituted complex [I(CO) ₂(dppe)WC₄W(dppe)₂I] (11) allows reversible one-electron oxidation which results In the monocatlonlc species [I(CO) ₂(dppe)WC₄W(dppe)₂I][PF₆] (11[PFe]). The all-dppe substituted complex [I(dppe)₂WC ₄W(dppe)₂I] (10) possesses two reversible redox states leading to the stable monocationic [I(dppe)₂WC₄W(dppe) ₂I][PF₆] (10[PF₆]) and the dicationic [I(dppe)₂WC₄W(dppe)₂I][PF₆] ₂ (10[PF₆]₂) compounds. The complexes 2, 3, [W(CO)₃(dppe)(C=CPh)(I)] (4), [X(CO)2(dppe)W=C-C(Me)=C(Me)C=W(dppe) (CO)₂X] (X = I (5), Cl (6)), 7, 8, 10, 11 and 11[PF₆] were characterized by single crystal X-ray diffraction. The electronic properties of complexes 10,10[PF₆], 10[PF₆]₂, as well as of compounds 11 and 11[PF₆], were Investigated using cyclic voltammetry (CV), EPR, IR, near-IR spectroscopy, and magnetization measurements. These studies showed that the [W]≡C-C≡C-C≡[W] canonical form of the bridged system with strong tungsten-carbon Interaction contributes significantly to the electronic coupling In the mixedvalent species 10[PF₆] (comproportionation constant K_c = 7.5 × 10⁴) and to the strong antiferromagnetic coupling In the dicationic complex 10[PF ₆]₂ (exchange Integral J = -167 cm^-1). In addition, the rate for electron transfer between the tungsten centers In 10[PF₆] was evaluated by near-IR and IR studies.

Full text of DOI:10.1021/ja909764x

Published on Web 02/10/2010
Electronic Communication in Dinuclear C4-Bridged Tungsten
Complexes
Sergey N. Semenov, Olivier Blacque, Thomas Fox, Koushik Venkatesan, and
Heinz Berke*
Department of Inorganic Chemistry, UniVersity of Zu¨rich, Winterthurerstrasse 190,
8057 Zu¨rich, Switzerland
Received November 17, 2009; E-mail: hberke@aci.uzh.ch
Abstract: The dinuclear tungsten carbyne [X(CO)2(dppe)WC4W(dppe)(CO)2X] (dppe ) 1,2-bis(diphe-
nylphosphino)ethane; X ) I (3), Cl (7)) complexes were prepared from the bisacetylide precursor
Li2[(CO)3(dppe)WC4W(CO)3(dppe)] (2) via oxidative replacement of one CO group at each tungsten center
with a halide substituent. The iodide ligand in 3 could be substituted with isothiocyanate or triflate resulting
in [X(CO)2(dppe)WC4W(dppe)(CO)2X] complexes (X ) NCS (8), OTf (9)). Substitution of two and all four
CO ligands in 3 was achieved via subsequent photolytic or thermal activation with dppe. The “half-substituted”
complex [I(CO)2(dppe)WC4W(dppe)2I] (11) allows reversible one-electron oxidation which results in the
monocationic species [I(CO)2(dppe)WC4W(dppe)2I][PF6] (11[PF6]). The “all-dppe substituted” complex
[I(dppe)2WC4W(dppe)2I] (10) possesses two reversible redox states leading to the stable monocationic
[I(dppe)2WC4W(dppe)2I][PF6] (10[PF6]) and the dicationic [I(dppe)2WC4W(dppe)2I][PF6]2 (10[PF6]2) com-
pounds. The complexes 2, 3, [W(CO)3(dppe)(CtCPh)(I)] (4), [X(CO)2(dppe)WtC-C(Me)dC(Me)-
CtW(dppe)(CO)2X] (X ) I (5), Cl (6)), 7, 8, 10, 11 and 11[PF6] were characterized by single crystal X-ray
diffraction. The electronic properties of complexes 10, 10[PF6], 10[PF6]2, as well as of compounds 11 and
11[PF6], were investigated using cyclic voltammetry (CV), EPR, IR, near-IR spectroscopy, and magnetization
measurements. These studies showed that the [W]tC-CtC-Ct[W] canonical form of the bridged system
with strong tungsten-carbon interaction contributes significantly to the electronic coupling in the mixed-
valent species 10[PF6] (comproportionation constant Kc ) 7.5 × 104) and to the strong antiferromagnetic
coupling in the dicationic complex 10[PF6]2 (exchange integral J ) -167 cm-1). In addition, the rate for
electron transfer between the tungsten centers in 10[PF6] was evaluated by near-IR and IR studies.
Scheme 1. Canonical Forms of a C4 Unit in [M]C4[M] Structures
Introduction
Organometallic dinuclear metal complexes of the type [Ln-
MCxMLn] (M ) metal; L ) ligand) are thought to have great
potential for their application as devices in molecular electronics.
Among other aspects these abilities are based on their basic
function of “single-electron” conductance across the linear,
unsaturated carbon bridge and on their redox-active end groups
lending electrons for through-bridge travel. Such type of
compounds in particular can potentially function as a molecular
wire. Molecular wires constitute the basis for the construction
of field-effect transistors and diodes. In addition to this their
mixed valent states are exceptional models for electron transfer
studies.1-5 The complexes with n ) 4 are the most ubiquitous
of these series of complexes and have been reported for Mn,6
Fe,7,8 Re,9 Ru,10,11 Pt,12 W and Mo centers.13,14 The electronics
and structures of the C4 chain correspond for most complexes
to the acetylenic butadiynediyl canonical form, but for rarer other
cases they correspond to the cumulenic butatrienebisylidene
form (Scheme 1).
propensity for polarization.8 These complexes therefore often
show high degrees of electron delocalization resulting in efficient
stabilization of mixed-valence species. Various such complexes
possess low thermal and air stability, which would limit their
application in molecular electronics and hinder also attempts
for further buildup of oligonuclears based on such systems.
The most common and well-documented end groups are the
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There are only two examples of a carbyne-type butynebis-
(triyl) bridge reported for related W and Mo complexes.13 The
C4 chain has been demonstrated as one of the most efficient
bridges for electronic communication between metal centers due
to the presence of two transmitting π-systems and their
9
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J. AM. CHEM. SOC. 2010, 132, 3115–3127 3115

A R T I C L E S
Semenov et al.
[Re(NO)(Cp)(PPh3)] and [Fe(dppe)(Cp*)] moieties.15 These
units, however, represent stopper functions that provide no
functionality for a hook-up to electrodes or for further extension
of these systems to form oligonuclears. The acetylenic or
cumulenic chemistry of platinum has been extensively re-
ported;16,17 however, Pt compounds do not normally provide
suitable redox properties for single-electron conductance. Moreover,
in π-delocalized Pt(II) systems, delocalization is often interrupted
at the metal center, which may hinder the electron travel in single-
molecule junctions.18 Ruthenium complexes with fragments
[Ru(P2)2], P2 ) dppe and dppm (dppm ) 1,2-bis(diphenylphos-
phino)methane) seem to offer the right balance between electronic
delocalization and redox properties, and stability required for
applications.19 Such complexes were therefore used in single-layer
capacity studies and recently also in single-electron conductance
measurements.20 However, the absence of new metal end groups
with an appropriate combination of properties seems to currently
impede further progress in the field.
Bridged complexes with emphasis on the carbyne canonical
forms [LnM]C4[MLn] are expected to possess higher stability
and the possibility for facile synthetic modifications.21-25
Carbyne-type canonical forms promise strong involvement of
metal orbitals in the π-conjugated systems with the possibility
for a tuning of spectroscopic, in particular NLO (nonlinear
optical), properties.25-29 Organometallic polymers based on such
type of building blocks connected by bisacetylides have great
implications, since these compounds retain conjugation along
the backbone.25,27 Mononuclear tungsten Fischer-type carbyne
complexes are relatively common species, and several prepara-
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However, dinuclear C4-bridged complexes with emphasis on
the carbyne structure are rare except for [W]C4[W] and
[Mo]C4[Mo] systems.13 These compounds were synthesized
using relatively complex procedures starting from mononuclear
precursors utilizing the oxidative coupling of C2 units to build
the C4 bridges. Physical characterization of these complexes
have been limited to CV studies.33 Moreover, these complexes
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Electronics of Dinuclear C4-Bridged Tungsten Complexes
A R T I C L E S
Scheme 2
Scheme 3
Scheme 4
tionalization. In this paper we demonstrate facile synthetic access
to tungsten complexes with delocalized, preferably carbyne-
type [W]C4[W] structures where [W] is [(X)W(dppe)(CO)2],
[(X)W(dppe)2], and replaceable X groups. A thorough study is
sought to unravel the physical properties of these complexes
for proper pre-evaluation prior to measurements of single-
electron conductance.
Scheme 5
Results and Discussion
Synthesis and Characterization of Complexes. Substitution
reactions of fac-W(CO)3(dppe)(L) (L ) acetone, THF) com-
plexes with lithium acetylides were explored earlier as routes
to access the corresponding tungsten acetylide species.32,34 In
these studies the fac-W(CO)3(dppe)(acetone) intermediate could
not be used, since it was necessary to avoid acetone in the
reaction mixture; instead the fac-W(CO)3(dppe)(THF) complex
(1) turned out to be more feasible because the released THF
does not have any impact on the reaction. It was isolated in
55% yield after two steps starting from W(CO)6 and could be
stored at -30 °C over long periods of time.35 As depicted in
Scheme 2, subsequent reaction of 1 with solid [Li2C4(THF)n]36
gave the key compound Li2[(CO)3(dppe)W(CtCCtC)
W(dppe)(CO)3] (2) in 51% yield upon precipitation with
benzene. Attempts to use in situ generated lithium salt, Li2C4,
obtained from Me3SiCtCCtCSiMe3 and MeLi ·LiBr produced
side reactions and thus gave lower yields in comparison with
the utilization of solid [Li2C4(THF)n]. The 13C NMR spectrum
of 2 showed two resonances for the C4 chain at 106.2 (CR) and
106.9 (Cꢀ) ppm. In the IR spectra typical ν(CtO) bands were
observed at 1892, 1814, and 1727 cm-1. The band positions
were similar to those of the previously reported
M[W(dppe)(CO)3(CtCR)] (M ) Li, Na; R ) Ph, Me, H)
series.32
The CR resonances were shifted high field in comparison with
many of the reported mononuclear tungsten carbyne complexes,
indicating changes in the electronic structure.24,25,32 The 31P
NMR spectrum showed a superimposed singlet (W nucleus not
magnetically active) and doublet at 29.3 ppm with 1J(31P,183W)
) 228 Hz. The oxidative transformation to 3 is unprecedented.
A related type of transformation was put forward for
[RuC4Ru]0-4+ systems, but was never clearly confirmed.11 In
order to trace the intermediates of the conversion of 2 to 3, a
“model” reaction between Li[W(CO)3(dppe)(CtCPh)] and one
equivalent of I2 was carried out, which was found to proceed
via a seven-coordinated [W(CO)3(dppe)(CtCPh)(I)] complex
(4) (Scheme 3). On the basis of these observations the formation
of [(CO)3(dppe)(I)WC4W(I)(dppe)(CO)3] is invoked as a pri-
mary intermediate in the formation of 3.
According to Scheme 4, compound 2 was reacted with
electrophiles. Treatment of 2 with Me3OBF4 in the presence of
NBu4X (X ) Cl, I) with subsequent oxidation by I2 or
[FeCp2][PF6] gave the neutral complexes 5 and 6. This reaction
is thought to involve the intermediate [X(CO)2(dppe)WtC-
C(Me)dC(Me)-CtW(dppe)(CO)2X][NBu4]2 presumably re-
sulting from a sequence of electrophilic attacks by Me3O+
followed by rearrangement of the bridge to the carbyne form
and subsequent substitution of CO activated by the trans effect
of carbyne as was found in mononuclear complexes.32,37
A chloride derivative [Cl(CO)2(dppe)WC4W(dppe)(CO)2Cl]
(7) analogous to 3 was obtained in 15% yield upon treatment
of 2 with chloroform or in 51% yield applying chlorination with
C2Cl6 (Scheme 5).
Conversion of 2 into the [I(CO)2(dppe)WC4W(dppe)(CO)2I]
complex 3 as indicated in Scheme 2 was effected by oxidation
with 2 equiv of I2. The reaction from 2 to 3 was anticipated to
involve single-electron oxidation steps, loss of CO, and coor-
dination of iodide or I+ transfer at each tungsten center. 3 was
obtained as air-stable violet crystals in 80% yield and was fully
characterized by NMR, IR spectroscopy, and elemental analysis.
A carbyne-type structure was presumed. The CR and Cꢀ
resonances appear as triplets at 225.2 and 87.5 ppm with
We then sought to utilize 3 and 7 for variation of the axial
groups by substitution with labile anionic ligands. The best
results were achieved using silver salts due to concomitant
enforcement of the halogen abstraction (Scheme 6). Since
N-bound isothiocyanate ligands could principally be used for
the anchoring of such molecules via sulfur coordination to
gold surfaces as required for measurements of single-electron-
3
2J(13C,31P) ) 11.1 Hz and J(13C,31P) ) 3.7 Hz, respectively.
(34) Roth, G.; Fischer, H. Organometallics 1996, 15, 1139–1145.
(35) Birdwhistell, K. R.; Dema, A. C.; Li, X.; Lukehart, C. M.; Owen,
M. D. Inorg. Synth. 1992, 29, 141–146.
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A R T I C L E S
Semenov et al.
Scheme 6
Scheme 7
conductivities,38 the heterogeneous reaction of a THF solution
of 3 with AgSCN was carried out, which indeed afforded
the isothiocyanate derivative [SCN(CO)2(dppe)WC4W(dppe)-
(CO)2NCS] (8). The N-coordination was assigned on the basis
of υ (NCS) observed at 2034 cm-1. Bands lower than 2100
cm-1 are more typical for isothiocyanates (N-coordination)
derivatives,39 and the structure was further confirmed by
X-ray analysis. The reaction with silver triflate gave the
corresponding substituted product [(OTf)(CO)2(dppe)WC4W-
(dppe)(CO)2(OTf)] (9) in 83% yield.
of the CO ligands becoming labile in higher oxidation states of
the tungsten centers. Indeed, CO-containing carbyne compounds
of the type [W(CR)(CO)nL4-2nX] typically showed electro-
chemically irreversible behavior.24 However, mononuclear “all-
phosphine”-substituted complexes of the type [W(CR)(PP)2X]
possess reversible redox processes.41
In order to fine-tune the electrochemical properties of such
types of compounds to the requirements of the redox wires, the
substitution of the CO ligands of 3 with dppe was attempted
by thermal and photolytic activation (Scheme 7). UV irradiation
of 3 produced the unsymmetrically substituted complex
[I(CO)2(dppe)WC4W(dppe)2I] (11), which showed four different
13C NMR signals for the carbon chain at 230.3, 212.3, 93.9,
and 83.0 ppm. However, approaching exhaustive CO substitu-
tion of 3 by extended UV irradiation led to degradation of 11.
Substitution of all four CO molecules could eventually be
effected by heating compound 3 to 140 °C in diglyme with
intermittent removal of the evolved CO applying vacuum. The
desired product [I(dppe)2WC4W(dppe)2I] (10) precipitated dur-
ing the course of the reaction as large dark-green crystals in
85-90% yield. In contrast to the previously discussed com-
plexes, 10 furnished a broad 31P NMR signal at around 45 ppm.
The 13C NMR spectrum revealed sharp signals for the CR and
Cꢀ nuclei, but broad lines for ipso-C6H5 carbon atoms. The
broadening was attributed to ligand dynamics confirmed by
variable-temperature 31P NMR studies as shown in Figure 1.
The initially broad 31P NMR signal splits upon lowering the
temperature into four doublets, two of which overlap. Phos-
phorus nuclei in trans positions are known to couple more
strongly than the nuclei in cis positions. Hence, the coupling
constants of 2JP-P ≈ 120 Hz can be attributed to the phosphorus
nuclei in the trans position. We assume an arrangement of four
inequivalent “in-plane” phosphorus nuclei due to the tilting
distortion of the square pyramid formed by the four phosphorus
nuclei and the CR. This could be attributed from the crystal
structure, where the P4 plane is not fully perpendicular to the
The spectroscopic properties of 7-9 overall resemble those
of 3. For instance the 31P NMR shifts are similar to those of
1
mononuclear tungsten carbynes, and the JW-P coupling con-
stants were only slightly affected by the new substituent in the
axial positions.25,27,32 The Cꢀ resonances of the symmetrical
molecules 3 and 7-9 shift monotonically downfield with a
decreasing size of the ligand trans to the C4 chain. This behavior
is consistent with an increase of the WCR bond lengths from 3
to 8 and might be related to an increase in the π-acceptor
property on going from I- to NCS-. A similar behavior was
observed in the [XW(PMe3)4(CH)] series.40 The Cꢀ resonances
of 3 and 7-9 shift monotonically highfield from I- to OTf-.
The IR spectra exhibit two characteristic absorptions for the
CtO vibrations in the range of 2000-1925 cm-1. These
ν(CtO) are shifted to lower energies with respect to the
comparable mononuclear compounds [(X)(CO)2(dppe)WC-
R],23,29,31 which might be due to a increase in electron density
on the metal center and a concomitant weaker tungsten-to-carbon
bond in 3 and 7-9. The ν(CtO) bands of 3 show a slight high
energy shift upon substitution of the iodine ligands by chlorides
and by about 15 cm-1 upon substitution with the OTf.
CV studies on the complexes 3 and 7-9 revealed irreversible
oxidation behavior, which was thought to be due to the presence
(38) Han, W. H.; Durantini, E. N.; Moore, T. A.; Moore, A. L.; Gust, D.;
Rez, P.; Leatherman, G.; Seely, G. R.; Tao, N. J.; Lindsay, S. M. J.
Phys. Chem. B 1997, 101, 10719–10725.
(39) Sabatini, A.; Bertini, I. Inorg. Chem. 1965, 4, 1665–1667.
(40) Holmes, S. J.; Schrock, R. R.; Churchill, M. R.; Wasserman, H. J.
Organometallics 1984, 3, 476–484.
(41) van der Eide, E. F.; Piers, W. E.; Parvez, M.; McDonald, R. Inorg.
Chem. 2007, 46, 14–21.
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Electronics of Dinuclear C4-Bridged Tungsten Complexes
A R T I C L E S
Figure 1. Temperature-dependent 31P NMR shifts of 10 in a toluene-d8/
CD2Cl2 (4:1) mixture.
WtC bond vector (for more details see crystal structure
discussion below), making all four phosphorus atoms inequiva-
lent. At higher temperatures upcoming dynamic processes
average the phosphorus positions within the NMR time scale,
giving rise to the observed broad signal.
In contrast to 3, complexes 10 and 11 could be oxidized in
facile reactions with [FeCp2][PF6], leading to the corresponding
monocationic products 10[PF6] and 11[PF6] (Scheme 7). 10
could be oxidized further to the dicationic species 10[PF6]2 upon
reaction with [Ph3C][PF6]. It is important to mention at this point
that 11 failed the oxidation to a dicationic form, which is in
constrast to 10, where both mono- and dicationic derivatives
were isolated. This confirms that only CO-free units of the type
[W(CR)(PP)2X] can undergo reversible oxidation. The third
diphosphine substitution forming 11 had only little effect on
the ν(CtO) position in comparison to 3. In contrast to this, the
oxidation of 11 to 11[PF6] induced a larger shift of the ν(CtO)
bands of about 15 cm-1 to higher energies.
Complex 10 is stable in air in solid state and only slowly
decomposes in solution. It was also found that the complex is
stable toward strong bases and acids such as HBF4 and MeLi.
10 reacts with thallium triflate showing iodine substitution with
the formation of thallium iodide precipitate. This reaction is
currently being investigated to exploit for substitution of iodine
to acetylenes.
Figure 2. ORTEP-like drawing of 2 (top) and 3 (bottom) (50% probability
level of thermal ellipsoids). Hydrogen atoms and solvent molecules are
omitted for clarity. Coordinated THF molecules are shown in wire style.
and 8. This indeed is the first example of related complexes to
clearly document a redox-induced structural switch from an
acetylene to a carbyne form of bridge. The axial ligands lead
to tightening of the WtC carbyne bonds via π donation with
increasing influence from NCS to I. A related structural trend
was observed in mononuclear species.42 The π-donor effect also
affects the CR-Cꢀ bond distances, which get longer, and the
central Cꢀ-Cꢀ′ bonds, which shorten upon going from I to NCS.
The bond length alternation in the bridge (CR-Cꢀ vs Cꢀ-Cγ)
of 3, 7, 8 resembles qualitatively that of a metal-capped C6
system.43
All of the [W]C4[W] structures display distortions from
linearity. Complexes 3, 7, 8, and 10 show S-shape distortion
(transoid), compounds 2 and 11 have bow-shaped distortion
(cisoid). For complexes containing [trans-W(CO)2(dppe)X], the
(WCRCꢀ) and (CRCꢀCꢀ′) angles contribute approximately equally
to the deviation from linearity. However, for 10 and 11
constructed from [trans-W(dppe)2X] centers, the (WCRCꢀ)
angles of ∼172° contribute a large portion to the total deviation
more than the (CRCꢀCꢀ′) angles (∼176o). Gladysz et al. have
shown by DFT calculations for platinum-capped polyynes that
the energetic barrier for bow-shaped distortions in [M]Cn[M]
systems is quite small (about 2 kcal/mol), which is indeed in
Structural Studies of Complexes 2-8, 10, 11, 11[PF6]. All
compounds except 9, 10[PF6], and 10[PF6]2 were structurally
characterized. The ORTEP plots of 2, 3, 10, 11 are presented
in Figures 2 and 3. The plots for structures of 4-8 and 11[PF6]
are presented in the Supporting Information. Selected bond
distances are summarized in Table 1.
The structure of 2 revealed a dianionic complex along with
two lithium cations, which are in tetrahedral environment
coordinating two THF molecules and one acetylenic bond of
the C4 bridge. The anionic part comprises two octahedral
tungsten fragments, and the structure of the C4 bridge is close
to a butadiynyl form. Structures 3, 7, and 8 consist of a C4 chain
with pseudo-square pyramidal [trans-W(CO)2(dppe)X] end
groups (X ) I (3), Cl (7), NCS (8)). The W-CR bond lengths
are close to the size of a triple bond.23 The CR-Cꢀ bonds are
longer than the central Cꢀ-Cꢀ′, clearly indicating that the
oxidation of 2 causes the structure of the C4 bridge to transform
from an acetylenic to a biscarbynic canonical form. The C4
bridge acts as a flexible electron reservoir, which switches upon
oxidation of the tungsten centers from one-electron donation
(acetylenic) at each side in 2 to three-electron donation in 3, 7,
(42) (a) Carriedo, G. A.; Riera, V.; Gonzalez, J. M. R.; Sanchez, M. G.
Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1990, 46, 581–
584. (b) Zhang, L.; Gamasa, M. P.; Gimeno, J.; da Silva, M. F.; C,
G.; Pombeiro, A. J. L.; Graiff, C.; Lanfranchi, M.; Tiripicchio, A.
Eur. J. Inorg. Chem. 2000, 1707–1715.
(43) Dewhurst, R. D.; Hill, A. F.; Willis, A. C. Organometallics 2005, 24,
3043–3046.
9
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A R T I C L E S
Semenov et al.
3 than in 11. The oxidized [trans-W(dppe)2I] center of 11[PF6]
shows elongated W-P bonds and a contraction of the W-I
bond in comparison with the corresponding bond lengths of 11.
In general, changes of the bond lengths upon oxidation were
found to be less prominent. The structural changes upon
oxidation are the basis of the application of the Franck-Condon
model, which would reflect the barrier for the electron transfer
between the tungsten centers of dinuclear complex.
Structure 10 consists of two symmetrically arranged [trans-
W(dppe)2X] fragments bridged by a C4 system resembling a
carbynic structure [W]tC-CtC-Ct[W]. As previously men-
tioned, a comparison of 10 and 3 reveals that the W-P bonds
contract upon CO substitution, and the C4 chain shows a more
pronounced [W]tC-CtC-Ct[W] alternation. Two important
points to note for further discussion of the through-bridge
metal· · · · metal interaction for 10: there is distortion of the
[W]C4[W] from linearity and distortion of the [trans-
CtW(dppe)2I] fragment from C4V symmetry. The S-shape of
10 is reflected by the deviation of the angle between the mean
plane (P1, P2, P3, P4) and the W · · · · W axis, which is equal to
15°. In this view the otherwise symmetrized structure of 10
would be closer to C2h than to C4h or D4d. The coordination
environment of the tungsten center is also distorted with an angle
between the perpendicular of the mean plane (P1, P2, P3, P4)
and the W-C axis of about 10°. Furthermore the W-P distances
in 10 are significantly different, W-P3 and W-P4 (both about
2.44 Å) are shorter than the W-P1 and W-P2 distances, which
are about 2.51 Å. The structural parameters of the inner
coordination sphere of the tungsten centers in 5 and 6 are almost
identical to those in 3 and 7 except for separations in the bridge.
The WtC bond distances reflect typical triple bond lengths. A
tungsten dinuclear complex with an analogous C4(CH3)2 bridge
was structurally characterized by Templeton and co-workers.13
Spectroscopic Studies with Emphasis on the Characteriza-
tion of the C4 Bridges. Raman and UV-Vis Studies. Selected
Raman, NMR, and UV-vis spectroscopic data are listed in
Table 2. They will be discussed for the sake of a structural and
electronic characterization mainly of the [W]C4[W] unit and
for the characterization of the through-bridge [W] · · · · [W]
interactions.
Figure 3. ORTEP-like drawing of 10 (top) and 11 (bottom) (50%
probability level of thermal ellipsoids). Hydrogen atoms and solvent
molecules are omitted for clarity.
Table 1. Selected Average Bond Lengths of Compounds 2, 3,
5-8, 10, 11, and 11[PF6]; Assignment of the Bond Lengths in the
C4 Bridge According to the Following Notation: [W]CRCꢀCꢀ′CR′[W]
W-CR
W-CR′
CR-Cꢀ
CR′-Cꢀ′
bond
W-P
W-X
W-CO
Cꢀ-Cꢀ′
2
3
5
6
7
8
2.500(2)
1.987(7) 2.189(5) 1.228(8) 1.40(1)
The Raman spectra of 3, 6-11, 10[PF6], 10[PF6]2, 11[PF6]
showed strong bands around 1150 and 1930 cm-1 that can be
attributed to the ν(WC) and symmetrical ν(C4) vibrations,
respectively (Table 2). Related carbynic structures of the
complexes with substantial MtC triple bond character were
found to possess in their ν(MC) vibrations strong dependence
on the nature of the carbyne substituents and only little variation
with respect to the type of trans-carbyne ligand.29,45 The ν(WC)
vibrations of complexes 2, 3, 7-11, 10[PF6], 10[PF6]2, 11[PF6]
appear at significantly lower wavenumbers than those of
mononuclear complexes of the type [(X)(CO)2(dppe)WtC-R]
(∼1300 cm-1) indicating electronic delocalization presumably
with contribution from the carbenic form of the bridge.
Similarly, ν(CC) bands of these compounds were observed
around 1930 cm-1 at significantly lower energies than ν(CtC)
vibrations of related mononuclear tungsten carbyne complexes
in conjugation with CtC bonds.31 Those modes were observed
in the range of 2050-2100 cm-1. For the dinuclear [{Cp*(PPh3)-
(NO)Re}2(µ-C4)] complex, the ν(C4) vibration was located at
2056 cm-1. The strong shifts of the ν(C4) Raman bands of
complexes 2, 3, 7-11, 10[PF6], 10[PF6]2, 11[PF6] also indicate
2.5382(9) 2.8610(3) 2.025(4) 1.844(3) 1.320(5) 1.299(7)
2.514(2) 2.9121(7) 2.028(1) 1.850(9) 1.420(2) 1.38(2)
2.527(2) 2.519(2)
2.026
1.816(6) 1.48(2)
1.36(3)
2.5349(8) 2.5037(7) 2.024(3) 1.849(3) 1.346(4) 1.242(6)
2.533(1) 2.181(4)
2.4741(6) 2.8618(2)
2.492(2), 2.8776(6),
2.533(2) 2.8573(7)
2.569(2), 2.8291(5),
2.525(2) 2.8500(5)
2.026(5) 1.857(5) 1.352(7) 1.231(7)
1.847(2) 1.370(3) 1.244(4)
1.849(8), 1.34(1),
10
11
2.03(1)
1.27(1)
1.840(8) 1.36(1)
1.827(6), 1.359(9),
1.838(6) 1.345(9)
11[PF6]
2.034(9)
1.255(9)
the range of crystal packing effects.17,44 In accord with this
observation and with the fact that 10 and 11 with bulky [trans-
W(dppe)2X] fragments are more distorted than complexes with
[trans-W(CO)2(dppe)X] units, we attribute the deviation from
linearity to steric and crystal packing effects.
A comparison of 3 with 11 revealed that the “asymmetric”
diphosphine substitution has only little effect on the CO bond
distances of both sides. The average W-P distance at the [trans-
W(dppe)2I] center is shorter than in the [trans-W(CO)2(dppe)X].
Also the bond alternation of the bridge is more pronounced in
(44) Szafert, S.; Gladysz, J. A. Chem. ReV. 2003, 103, 4175–4206.
(45) Dao, N. Q. J. Organomet. Chem. 2003, 684, 82–90.
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Electronics of Dinuclear C4-Bridged Tungsten Complexes
A R T I C L E S
Table 2. Raman, NMR and UV-Vis Data of Complexes 2, 3, 5-11, 10[PF6], 10[PF6]2 and 11[PF6]
Raman [cm-1
]
NMR [ppm]
13C
absorption [nm]
31P{1H}
(1JW-P (d, satellite) [Hz])
13C
(Cꢀ (Cꢀ′))
λ1 (ε/1000
λ2a (ε/1000
ν(C4)
ν(WC)
(CR (CR′))
[M-1 cm-1])
[M-1 cm-1])
2b
2080
1947
1474
34.4 (202)
29.3 (228)
28.0 (225)
38.2 (230)
37.5 (226)
39.9 (234)
44.8 (236)
45
106.2
225.2
106.9
87.5
274 (45)
407 (340)
462 (39)
450 (30)
382 (190)
412 (330)
367 (400)
412 (290)
410 (300)
460 (3.2)
533 (5.6)
3
1149, 1109
1067
5b,c
6b,c
7
8
9
10
1936
1923
1964
1892
1894
1149, 1113
1114, 1082
1173, 1127
1084
228.4
232.1
85.8
82.1
82.1
86.5
517 (3)
543 (4.7)
524 (2.5)
668 (2.3)
702 (1.8),
470 (6)
213.1
10[PF6]
1082
10[PF6]2
11d
1895
1916
1936
1078
413 (160)
416 (300)
406 (280)
520 (7.8),
660 (1.7)
780 (1),
480 (4.5)
503 (7),
1141, 1100
1143, 1096
38.7 (230),
(32.3) (268)
230.3 (212.3)
93.9 (83.0)
11[PF6]
620 (2.7)
a For the unsymmetrical complexes two absorptions of lower intensity are present. b 2, 5, 6 have an electronic structure deviating from those of the
other compounds; therefore, the classification of the UV-vis absorption bands differs from those of the other complexes. c In the first column ν(CdC).
d The NMR chemical shifts in brackets belong to the [(I)(dppe)2WtC-] fragment.
from 3 to 10 did not influence λ1 but strongly shifted λ2 from
533 to 668 nm. The decreasing energy of λ2 is in agreement
with a decrease in the π-acceptor properties of the dppe relative
to the CO ligand resulting in an energetic increase of dxy. The
spectra of the unsymmetrical complexes 11, 11[PF6], 10[PF6]
show one strong and two weak absorptions.
Electronic Communication between the Tungsten Centers.
The interaction between the metal centers in the [W]C4[W]
systems was evaluated on the basis of the stabilization energy
of the mixed-valence complex, electronic delocalization, electron-
transfer capability, and ordering in the spin system.3-5,46-48
CV Evidence for Stabilization of Mixed-Valence Complexes.
As expected, the unsymmetrical complex 11 has only one
reversible redox step with an E1/2 value of -435 mV Vs Fc0/+
(Figure 5). This is explained on the basis that only the pure
phosphine-substituted tungsten center has reversible redox
properties. The unpaired electron is therefore expected to be
localized in the dxy orbital of the [(I)(dppe)2WC-] unit.49-51
The given E1/2 value is, however, found at significantly higher
potential than those of the mononuclear carbyne complexes
([ClW(dmpe)2(CH)] -880 mV and [ClW(PMe3)4(CH)] -910
mV), indicating direct influence of the P4 framework in-plane
with the HOMO of such systems (Figure 4). This lower
reduction potential is assumed to be due to lower σ-donating
and higher π-accepting properties of the dppe ligand. For the
symmetric complex 10 two oxidation waves were found at -543
mV and -253 mV revealing that both tungsten centers are
involved in the redox process. But a relatively small peak
separation of 10 was observed witnessing only moderate
electronic coupling of the tungsten centers.
Figure 4. Qualitative molecular orbital diagram for a tungsten carbyne
complex of the type discussed.
reduced bond orders in agreement with contribution from the
biscarbenic form of [W]C4[W] π-system.
It should be mentioned at this point that differences of the
ancillary ligand sphere of complexes 3 and 7-12 also influence
the ν(C4) Raman bands. For instance, the triflate derivative 9
shows a high-energy shift of the ν(C4) vibration by about 30
cm-1, the dppe-substituted complex 10 shows significant shifts
(30-100 cm-1) of both ν(C4) and ν(WC) to lower energies with
respect to the corresponding band of 3.
The UV-vis spectra of the symmetrical complexes 3, 7-10
show two main absorptions λ1 and λ2. The best approximation
for the electronic description of the [W]C4[W] systems is a
formulation with the bridge in the carbynic form (Figure 4).28
Indeed for the complexes described in this paper, two
electronic transitions were found with one quite intense absorp-
tion at about 400 nm assigned to a π f π* (λ1) transition, while
the weaker absorption is anticipated to be associated with a dxy
f π* (λ2) transition. Figure 4 comprises a qualitative MO
scheme showing that the position of λ1 should be in a first-
order approximation affected only by the axial ligands, while
λ2 is mainly influenced by the equatorial ligands due to changes
in the energy of the dxy orbital being of δ-type with ideally no
or only little orbital interaction with the bridge π-orbitals. The
experiments confirmed the qualitative picture of Figure 4. The
position of the π f π* (λ1) transition is indeed changing with
the axial ligand X, as observed for complexes 3, 7-9. However,
significant changes in the equatorial ligand patterns on going
Under rigorous symmetry conditions, i.e. molecular distor-
tions or pseudo-symmetries excluded, the HOMO is of δ-type
(46) Astruc, D. Acc. Chem. Res. 1997, 30, 383–391.
(47) McCleverty, J. A.; Ward, M. D. Acc. Chem. Res. 1998, 31, 842–851.
(48) Barlow, S.; O’Hare, D. Chem. ReV. 1997, 97, 637–669.
(49) Salaymeh, F.; Berhane, S.; Yusof, R.; de la Rosa, R.; Fung, E. Y.;
Matamoros, R.; Lau, K. W.; Zheng, Q.; Kober, E. M.; Curtis, J. C.
Inorg. Chem. 1993, 32, 3895–3908.
(50) Richardson, D. E.; Taube, H. Coord. Chem. ReV. 1984, 60, 107–129.
(51) (a) Gagne, R. R.; Spiro, C. L.; Smith, T. J.; Hamann, C. A.; Thies,
W. R.; Shiemke, A. D. J. Am. Chem. Soc. 1981, 103, 4073–4081. (b)
Moore, K. J.; Lee, L.; Mabbott, G. A.; Petersen, J. D. Inorg. Chem.
1983, 22, 1108–1112.
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A R T I C L E S
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Figure 6. EPR spectra of (a) 11[PF6] at 298 K in CH2Cl2 solution; (b)
11[PF6] at 20 K in CH2Cl2 glass; (c) 10[BArf4] at 160 K in toluene solution;
(d) 10[PF6] at 20 K in CH2Cl2/toluene glass.
EPR Study for Through-Bridge Electron Transfer in the
Dinuclear Complexes. Localization or delocalization of an
electron becomes evident through signal averaging at metal
centers using different methods, such as EPR and IR.3,5
Therefore, EPR measurements were carried out for 11[PF6],
10[PF6], 10[BArf4], and 10[PF6]2 (Figure 6). 10[BArf4] (BArf4-
tetrakis[(3,5-trifluoromethyl)phenyl]borate) was used instead of
10[PF6] due to its solubility in toluene, which was required as
a solvent to obtain a good signal-to-noise ratio in 100-200 K
temperature interval. Compound 10[BArf4] was prepared in situ
by anion exchange between Na[BArf4] and 10[PF6]. The EPR
spectra of 10[PF6] and 10[BArf4] in frozen CH2Cl2 at 20 K are
completely identical. No clear signal was detected for 10[PF6]2,
apparently due to strong antiferromagnetic interactions.
Compound 11[PF6] showed one signal with g ) 2 at room
temperature and in frozen toluene solution, confirming electron
localization on the [trans-W(dppe)2I] center. The signal is fully
symmetrical at room temperature and revealed only slight
asymmetry in glass, which reflects only small spin-orbit
coupling as expected from the molecular orbital diagram with
the unpaired electron localized in the energetically rather isolated
dxy orbital (see Figure 4). A hyperfine coupling is detected due
to coupling with the four phosphorus nuclei. Thus, the solution
spectra of 11[PF6] could be modeled with a hyperfine 31P
coupling constant of 31 G and a line broadness of 20 G. The
EPR spectrum of the mixed-valence complex 10[PF6] did not
show any signal at room temperature. A signal of reasonable
intensity was observed only below 160 K. The line broadness
was then almost twice that of the signal of 11[PF6] which
prevented observation of hyperfine coupling. The spectrum in
frozen toluene solution at 20 K showed stronger anisotropy than
in the case of 11[PF6].
Figure 5. Cyclic voltammogram for 11[PF6] (top) and 10 (bottom) in
CH2Cl2 with 0.1 M [nBu4N][PF6]; Au electrode; E vs Fc0/+; scan rate )
100 mV/s; 20 °C.
(Figure 4) not allowing interactions with the halogens or the
bridge system, which possess σ- or π-type orbitals. Due to this,
orbital overlap between the HOMO or SOMO and the bridge
can not occur. In a C4h or D4d structure this would prevent
π-orbital influence of the axial ligands on the redox properties
of such species.41 Nevertheless a through-bridge electronic
coupling was observed, which is thought to originate from
symmetry lowering allowing with just “approximate” orthogo-
nality of the π-type orbitals of the bridge and the axial ligands
with the HOMO or SOMO of δ-type symmetry. As we have
seen, a symmetry lowering to C2h in the solid-state structure of
10 is evident. It is also prevailing in solution as confirmed by
31P NMR. Symmetry lowering induces mixing of the δ-orbital
with the dxz and dyz orbitals and consequently electronic
communication depending on the extent of the mixing. A
spin-orbital coupling may be another important factor for
tungsten contributing mixing between orbitals of different
symmetry.
The ∆E value for 10 of 290 mV (Kc ) 7.5 × 104) is similar
to that reported for another related C4-bridged system with low-
symmetry end groups (250 mV).33 It is indicative of a borderline
class II-/III-type system according to the Robin-Day classifica-
tion.52 The peak separation is also solvent dependent, since in
THF a ∆E value of 250 mV was found (see Supporting
Information). Another explanation for this small but significant
peak splitting was reported in the literature.49 In accordance
with this, the oxidation of the [M]C4[M] system would lead to
enhancement of the π-acceptor properties of the C4 chain to
stabilize the system and consequently to increase the second
oxidation potential.
The broadness of the signal of 10[PF6] is interpreted in terms
of electron dynamics with intramolecular transfer between the
remote metal ends or with a stronger spin-orbit coupling.
IR Investigation of Through-Bridge Electron Transfer in
the Dinuclear Complexes. IR can usually be utilized as a probe
to measure the extent of the electron delocalization via the extent
of averaging of the characteristic absorptions strongly affected
by the oxidation state of the metal center. Furthermore, in
symmetry-lowered systems with electron exchanges between
the metal centers slow on the IR time scale (10-13 s), one can
often identify new absorptions forbidden to appear in a
(52) Robin, M. B.; Day, P. AdV. Inorg. Chem. Radiochem. 1967, 10, 247–
422.
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Electronics of Dinuclear C4-Bridged Tungsten Complexes
A R T I C L E S
Figure 8. Schematic energy diagram explaining the origin of the charge
transfer bands in the near-IR range.
Figure 7. ν(C4) absorptions in the IR spectra of 10, 10[PF6], and 10[PF6]2
(CH2Cl2, room temperature, 5 × 10-3 M).
symmetrical system.3,53 In the spectra of the mixed-valence
complex we did not find shifts for any absorption that might
originate from oxidation of the metal center; however, our
system seemed to be well suited for the latter approach, because
of the highly symmetric C4 bridge and the IR forbidden central
ν(CC) vibration. The appearance of an intense ν(CC) band in
the IR spectrum of 10[PF6] indicates that this vibration is no
longer forbidden, because on the IR time scale the centered
symmetry of the molecule is apparently broken by tungsten
centers of different electron counts. The IR spectra of the
complexes 10, 10[PF6] and 10[PF6]2 are presented in Figure 7.
The IR spectra of the symmetrical complexes 10 and 10[PF6]2
are presented for comparison in Figure 7 demonstrating the
presence of only weak ν(C4) bands. In contrast to 10 and
10[PF6]2, 10[PF6] possesses an intense band at 1981 cm-1
corresponding to a symmetric ν(C4) vibration. As mentioned
previously, the presence of strong symmetrical ν(CC) vibration
is an indicator of localization in the IR time scale. It should be
mentioned that delocalization in such a short time regime would
be characteristic of full delocalization and typically observed
only for strongly interacting systems.48
Figure 9. NIR spectra for 10[PF6] (black), 11[PF6] (blue), and 10[PF6]2
(red) in CH2Cl2. Regions with high noise due to solvent absorptions were
linearly approximated. The bottom spectrum shows the NIR absorption of
10[PF6] in CDCl3, where the solvent background is less than that in CH2Cl2.
where ε is the absorption coefficient in M-1 cm-1, ∆ν1/2 the
width of the absorption band at half-height in cm-1, EIT the
energy of the band maximum in cm-1, and d the electron transfer
distance in Å. The spectra for 11[PF6], 10[PF6], and 10[PF6]
are presented in Figure 9.
All spectra are of relatively low intensity and broad especially
that of 10[PF6]. The bands of 11[PF6] and 10[PF6]2 are centered
at significantly higher energies than those of 10[PF6]. The fact
that 11[PF6] and 10[PF6]2 have a similar absorption in the NIR
supports the idea that this absorption is a result of a π f dxy
transition (see Figure 4). The spectrum of 10[PF6] can be
explained as a superposition of a π f dxy transition and a charge-
transfer transition, Figure 9. Calculations with overlapping bands
NIR Evidence for Through-Bridge Electron Transfer in
the Dinuclear Complexes. The electron transfer between the
metal centers is sketched in the schematic energy diagram in
Figure 8.2
Near-IR spectroscopy allows direct measurement of the
reorganization parameter λ and approximation of the electronic
coupling energy Hab via the following equations:3
Hab(cm-1) ) [(4.2 × 10-4)ε∆ν¯1/2EIT]1/2/d; λ ) EIT
9
J. AM. CHEM. SOC. VOL. 132, NO. 9, 2010 3123

A R T I C L E S
Semenov et al.
2NAg2ꢀ2
1
ꢁ )
·
(3 + eJ/kT
)
kT
with g and J as parameters. The minimized value for the g-factor
is close to a free electron value of 2. The derived J indicates a
singlet-triplet gap equal to 167 cm-1, which is significantly
more than 26 cm-1 observed for related bis-carbyne complex
and than J for dinuclear W and Mo complexes in low spin d5
and d1 configurations.47,56,57 Comparable values of exchange
energies were obtained for dinuclear ruthenium complexes.58
The antiferromagnetic nature of the spin interactions could be
explained by a spin-polarization mechanism involving eight
p-orbitals of the bridge.57 The presence of strong antiferromag-
netic coupling provides additional evidence for the interaction
of metal orbitals with the π-orbitals of the bridge required for
the mediation of magnetic ordering over long distance. The
original data showed also presence of small paramagnetic
impurities. The amount of these impurities was estimated using
a fitting procedure of the sum of the antiferromagnetic and
paramagnetic contributions on the level of 2% (see Supporting
Information for details). This paramagnetic contribution was
subtracted from the presented curve.
Figure 10. Temperature dependence of ꢁ vs T for 10[PF6]2. The data are
corrected for core diamagnetism, van Vleck paramagnetism, and other
temperature-independent contributions. Contribution from a small (on the
level of 2%) paramagnetic impurity has been compensated. The uncorrected
data are presented in the Supporting Information.
must possess tentative character. We estimated by using the right
edge of the plateau of the given band as the center of the charge
transfer band in the calculations. An estimate of the reorganiza-
tion parameter λ for 10[PF6] from this absorption band amounts
to 2000 nm (5000 cm-1). This value is significantly smaller in
energy than those of the majority of published systems detected
in the range of 1000 to 1500 nm.3,48,50,54 The low value would
indicate a small reorganization energy, which is in agreement
with the derived structural data, where only small changes in
bond distances were detected upon oxidation. Approximation
of Hab leads to an energy of about 250 cm-1. Within the
nonadiabatic limit, the rate constant for electron transfer is given
by the following equation:2,55
Conclusion
A versatile synthetic route to C4-bridged tungsten complexes
of the type [W]C4[W] ([W] ) [(X)W(dppe)(CO)2] and [(X)W(d-
ppe)2]) was developed. The structures of the W(0) complexes
were found to be close to a diacetylenic canonical form
[W(0)]-CtC-CtC-[W(0)], while the structures with W(II)
centers could be ascribed with biscarbynic bridge structures
[W(II)]tC-CtC-Ct[W(II)]. The termini could be function-
alized with reactive triflate substituents to eventually enable
expansion of these dinuclear systems to polynuclear complexes.
The mixed-valent complex 10[PF6] was found to reflect a class
II system of the Robin-Day classification52 possessing medium
M· · · · M “electronic communication” with barrier between the
remote metal termini. The rate of electron transfer in this system
was found to be in the same range as the EPR time scale, but
appeared localized on the IR time scale. The remarkable
stability, along with the ease of functionalization of the metal
termini makes these complexes suitable candidates for “with
barrier” organometallic wires to build complex single-electron
devices.
k ) (2H2ab/p)(π3/λkbT)1/2exp(-λ(1 - 2Hab/λ)2/4kbT)
From this equation we calculated a value of 1.5 × 1011 s-1
for our system, which is consistent with electron localization
on the IR time scale and with a borderline case between
localized behavior and an averaging situation for the EPR
exchange.
Magnetic Measurements to Characterize Through-Bridge
Electronic Interaction in the Dinuclear Complexes. The mag-
netic properties of 11[PF6], 10[PF6], and 10[PF6]2 were
established by variable-temperature magnetization measure-
ments. The magnetic susceptibilities of 11[PF6] and 10[PF6]
showed a typical paramagnetic behavior, as could be expected
from the presence of one unpaired electron in these molecules
(Figures 8S and 9S in the Supporting Information). The
magnetic susceptibility of 10[PF6]2 shows a maximum at 150
K (Neel temperature) and drops considerably on going to higher
temperatures (Figure 10).
Experimental Section
General Procedures. All the manipulations were carried out
under a nitrogen atmosphere using Schlenk techniques or a drybox.
Reagent grade benzene, toluene, hexane, pentane, diethyl ether, and
tetrahydrofuran were dried and distilled from sodium benzophenone
ketyl prior to use. Dichloromethane and acetonitrile were distilled
from CaH2, and chloroform was dried by P2O5. The modified
literature procedures were used to prepare the following compounds:
W(CO)3(dppe)(THF),35 Li2C4(THF)x,36 see Supporting Information
Thus, the magnetic behavior of 10[PF6]2 is typical of a
strongly antiferromagnetically coupled spin dimer. To obtain
an estimate of the exchange coupling, we fitted the experimental
data with the equation for a spin-1/2 dimer model (spin
Hamiltonian: H ) -JS1 ·S2):
(56) (a) Hu, J. S.; Sun, J. B.; Hopkins, M. D.; Rosenbaum, T. F. J. Phys.:
Condens. Matter 2006, 18, 10837–10841. (b) Thompson, A. M. W. C.;
Gatteschi, D.; McCleverty, J. A.; Navas, J. A.; Rentschler, E.; Ward,
M. D. Inorg. Chem. 1996, 35, 2701–2703. (c) Stobie, K. M.; Bell,
Z. R.; Munhoven, T. W.; Maher, P. J.; McCleverty, J. A.; Ward, M. D.;
McInnes, E. J. L.; Totti, F.; Gatteschi, D. Dalton Trans. 2003, 36–45.
(57) Ung, V. A.; Thompson, A. M. W. C.; Bardwell, D. A.; Gatteschi, D.;
Jeffery, J. C.; McCleverty, J. A.; Totti, F.; Ward, M. D. Inorg. Chem.
1997, 36, 3447–3454.
(53) Demadis, K. D.; El-Samanody, E. S.; Coia, G. M.; Meyer, T. J. J. Am.
Chem. Soc. 1999, 121, 535–544.
(54) Ward, M. D. Chem. Soc. ReV. 1995, 121–134.
(55) Sutin, N. Prog. Inorg. Chem. 1983, 30, 441–498.
(58) Aquino, M. A. S.; Lee, F. L.; Gabe, E. J.; Bensimon, C.; Greedan,
J. E.; Crutchley, R. J. J. Am. Chem. Soc. 1992, 114, 5130–5140.
9
3124 J. AM. CHEM. SOC. VOL. 132, NO. 9, 2010

Electronics of Dinuclear C4-Bridged Tungsten Complexes
A R T I C L E S
for details. All other chemicals were used as obtained from
commercial suppliers. IR spectra were obtained on a Bio-Rad FTS-
45 instrument and Bio-Rad Excalibur FTS-3500. NMR spectra were
W(CO)3(dppe)(THF) (1 g, 1.35 mmol) in 80 mL of THF. This
mixture was stirred during 18 h at 55 °C. The resulting brown
suspension was filtered and concentrated to 20 mL in Vacuo.
Complex 2 was obtained as a powder after addition of benzene
(60 mL) to the THF solution. The product was recrystallized from
a glyme/ether mixture. Yield: 610 mg (0.346 mmol, 51%). Single
crystals suitable for X-ray diffraction were grown by addition of
ether to the THF solution of 2. Anal. Calcd for C86H84Li2O9P4W2:
C, 58.45; H, 4.79. Found: C, 58.24; H, 4.69. IR (cm-1): 2050
1
measured on a Varian Mercury spectrometer at 200 MHz for H
and 81 MHz for 31P{1H}, Varian Gemini-2000 spectrometer at 300
1
MHz for H and 75 MHz for 13C{1H} and on a Bruker-DRX-500
spectrometer at 500 MHz for 1H, 125.8 MHz for 13C{1H} and 202.5
MHz for 31P{1H}. Chemical shifts for 1H and 13C are given in ppm
relative to TMS and those for 31P relative to phosphoric acid. The
UV-vis and near-IR spectra were recorded on a Varian CARY 50
Scan UV-visible and on a Varian CARY 500 Scan UV-visible-
near-IR spectrometers. CHN elemental analyses were performed
with a LECO CHN-932 microanalyzer. Raman spectra were
recorded on a Renishaw Ramanscope spectrometer (633 nm). Cyclic
voltammograms were obtained with BAS 100W voltammetric
analyzer equipped with the low volume cell. The cell was equipped
with an Au working and a Pt counter electrode, and a non-aqueous
reference electrode. All sample solutions (CH2Cl2) were ap-
proximately 5 × 10-3 M in substrate and 0.1 M in Bu4NPF6, and
were prepared under nitrogen. Ferrocene was subsequently added
and the calibration of voltammograms recorded. BAS 100W
program was employed for data analysis. X-band EPR spectra were
obtained using Bruker EMX Electron Spin Resonance system. To
measure spectrum of 10+ at different temperatures toluene solution
was required. Due to insolubility of 10[PF6] in toluene, the [PF6]-
counter-ion was exchanged to [BArf4]- by treatment of 10[PF6]
with Na[BArf4] in CH2Cl2. The spectra of 10[PF6] and 10[BArf4]
in frozen solution at 20 K are fully identical. A solution spectrum
of 11[PF6] was modeled with help of Bruker WIN EPR Simfonia
software. Magnetization measurements were carried out on a
Quantum Design SQUID magnetometer, molar magnetic suscep-
tibility was calculated according to the equation ꢁ ) (M·Mw)/(m·H),
where M ) experimental magnetization, Mw ) molecular weight,
m ) sample weight, H ) magnetic field.
1
(CtC), 1892 (CO), 1814 (CO), 1726 (CO). H NMR (200 MHz,
THF-d8) δ ) 7.99-7.71 (m, 15H, C6H5), 7.38-7.22 (m, 25H,
C6H5), 2.83 (m, 4H, CH2), 2.35 (m 4H, CH2). 31P NMR (81 MHz,
1
THF-d8) δ ) 34.40 (s, JW-P (d, satellite) ) 202 Hz). 13C NMR
2
2
(125 MHz, THF-d8) δ ) 218.5 (dd, JC-P(cis) ) 7.3 Hz, JC-P(trans)
) 34.5 Hz, CO (equatorial)), 213.5 (s, CO (axial)), 140.7 (d, 1JC-P
1
) 37.5 Hz, ipso-C6H5), 140.0 (d, JC-P ) 37.5 Hz, ipso-C6H5),
129.2 (s, C6H5), 128.7 (s, C6H5), 128.1 (m, C6H5), 106.9 (s, Cꢀ),
106.2 (t, 2JC-P ) 12.5 Hz, CR), 32.3 (dd, 1JC-P ) 18.5 Hz, 2JC-P
)
18.0 Hz, CH2).
[I(CO)2(dppe)WC4W(CO)2(dppe)I] (3). Ten milliliters of a
THF solution of iodine (121 mg, 0.47 mmol) was added dropwise
to a solution of 2 (400 mg, 0.23 mmol) in glyme/THF (10/15 mL)
at -60 °C. After stirring the reaction mixture for 20 min, the cooling
bath was removed, and the mixture was additionally stirred for 6 h
at room temperature. The resulting brown-violet solution was
evaporated to dryness in Vacuo. Addition of acetonitrile (5 mL)
resulted in the formation of violet crystals of 3 (300 mg, 0.19 mmol)
which were filtered and washed with acetonitrile (10 mL). A second
crystallization from the filtrate afforded an additional 30 mg (0.019
mmol) of the desired product 3. Yield: 330 mg (0.21 mmol, 91%).
Single crystals suitable for X-ray diffraction were grown by cooling
a dichloromethane solution of 3. Anal. Calcd for C60H48I2O4P4W2:
C, 45.66; H, 3.07. Found: C, 45.76; H, 3.20. IR (cm-1): 1990 (CO),
1929 (CO). 1H NMR (500 MHz, CD2Cl2) δ ) 7.68-7.58 (m, 16H,
C6H5), 7.46-7.42 (m, 8H, C6H5) 7.41-7.37 (m, 4H, C6H5),
7.27-7.23 (m, 4H, C6H5), 7.18-7.13 (m, 8H, C6H5), 3.1 (m, 4H,
CH2), 2.6 (m, 4H, CH2). 31P NMR (81 MHz, CD2Cl2) δ ) 29.32
(s, 1JW-P (d, satellite) ) 228 Hz). 13C NMR (125 MHz, CD2Cl2) δ
X-ray Diffraction Studies on 2-8, 10, 11, 11[PF6]. Data
collection for crystals of 2 and 6, were carried out on Stoe IPDS
diffractometer (Imaging Plate Detector System with graphite-
monochromated Mo KR radiation, λ ) 0.71073 Å)59 and for others
on Oxford Diffraction Xcalibur R diffractometer (4-circle kappa
platform, Ruby CCD detector and a single wavelength Enhance
X-ray source with Mo KR radiation, λ ) 0.71073 Å) at 183(2) K
using a cold N2-gas stream from an Oxford Cryogenic System. Pre-
experiment, data collection, and data reduction (unit cell determi-
nation, intensity data integration, and empirical absorption correc-
tion) for for 3-8, 10, 11, 11[PF6]: were carried out with the Oxford
CrysAlisPro software.60 The structures were solved with the unique
data sets using the Patterson method of the program SHELXS-97.
The structure refinement was performed with the program SHELXL-
97.61 Non-hydrogen atoms were refined anisotropically by full-
matrix least-squares techniques based on F2. The hydrogen atoms
of the organic groups were placed in calculated positions and refined
with a riding model with a fixed temperature factor. The program
PLATON62 was used to check the result of the X-ray analysis.
The disorders observed for one THF molecule in 1, for the positions
of the -CH2-CH2- units of the dppe ligand and for the C4 bridge
between the transition metals in 7 and 8, were treated with the
EADP and PART instructions of SHELXL-97 and anisotropically
refined. Further details on all structures are provided in Tables 1Sa
and 1Sb, and in the form of cif files available as part of the
Supporting Information or from the CCDC under deposition
numbers 754637-754645 and 755094.
2
2
) 225.2 (t, JC-P ) 11.1 Hz, CR), 211.2 (dd, JC-P(cis) ) 6.9 Hz,
2JC-P(trans) ) 43,0 Hz, CO), 134.7 (d, 1JC-P ) 25.1 Hz, ipso-C6H5),
134.3 (d, 1JC-P ) 25.2 Hz, ipso-C6H5), 133.3 (d, 2JC-P ) 11.9 Hz,
ortho-C6H5), 132.5 (d, 2JC-P ) 9.8 Hz, ortho-C6H5), 130.7 (d, 4JC-P
3
) 62.5 Hz, para-C6H5), 128.7 (t, JC-P ) 10.5 Hz, meta-C6H5),
3
1
2
87.5 (t, JC-P ) 3.7 Hz, Cꢀ) 38.4 (dd, JC-P ) 28.1 Hz, JC-P
)
11.9 Hz, CH2).
[IW(CO)3(dppe)(CCPh)] (4). A solution of lithium pheny-
lacetylide (7.5 mg, 0.068 mmol) in THF (2 mL) was slowly
added to a solution of W(CO)3(dppe)(THF) (60 mg, 0.068 mmol)
in 5 mL of THF. This mixture was stirred during 20 min at
room temperature. To the resulting yellow solution of
Li[W(CO)3(dppe)(CCPh)] was added dropwise a THF solution
of iodine (17 mg, 0.068 mmol) at -20 °C. The resulting brown-
yellow solution was evaporated to dryness in Vacuo. Addition
of acetonitrile (2 mL) to the remaining solid led to the formation
of orange crystals of 4, which were filtered and washed with
acetonitrile (5 mL). Single crystals suitable for X-ray diffraction
were grown by layering a CH2Cl2 solution with acetonitrile.
Yield: 38 mg (0.043 mmol, 63%). Anal. Calcd for
C37H29IO3P2W: C, 49.58; H, 3.49. Found: C, 49.50; H, 3.41. IR
(cm-1): 2024 (CO), 1955 (CO), 1896 (CO). 1H NMR (200 MHz,
CD2Cl2) δ ) 7.67 (br, 15H, PC6H5), 7.46 (m, 25H, PC6H5), 7.04
(m, 3H, CCC6H5), 6.55 (m, 2H, CCC6H5), 2.85-2.65 (m, 4H,
CH2). 31P NMR (81 MHz, CD2Cl2) δ ) 28-22 br. 13C NMR
(125 MHz, CD2Cl2) δ ) 133.1 (s, C6H5), 130.7 (s, C6H5), 130.1
(s, C6H5), 128.5 (s, C6H5), 127.6 (s, C6H5), 126.7 (s, C6H5), 126.0
(s, C6H5), 26.6 (br, CH2).
Li2[(CO)3(dppe)WC4W(CO)3(dppe)] (THF)3(C6H6)2 (2).
Solid Li2C4(THF)x (150 mg) was added to a solution of
(59) Stoe IPDS Software, Version 2.87 5/1998 ed.; Stoe & Cie: Darmstadt,
Germany, 1998.
(60) CrysAlisPro, Version 1.171.32.5 ed.; Oxford Diffraction Ltd.: Ab-
ingdon, Oxfordshire, England, 2007.
(61) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(62) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.
[X(CO)2(dppe)WCC(Me)C(Me)CW(CO)2(dppe)X] (5 (X )
I), 6 (X ) Cl)). Solid [Me3O]BF4 (7 mg, 0.046 mmol) was slowly
added to the solution of 2 (40 mg, 0.023 mmol) and NBu4I or
9
J. AM. CHEM. SOC. VOL. 132, NO. 9, 2010 3125

A R T I C L E S
Semenov et al.
NBu4Cl (25 or 19 mg, 0.069 mmol) in glyme (2 mL) at -20 °C.
Stirring of this mixture for 6 h led to the formation of a pale-orange
precipitate (15 mg for I and 5 mg for Cl), which was filtered and
dispersed in CH2Cl2 (8 mL). To this solution was added iodine (3
mg, 0.012 mmol) or [FeCp2]PF6 (2.6 mg, 0.008 mmol) in 2 mL of
CH2Cl2. After stirring the reaction mixture for 1 h, the solvent was
removed in Vacuo, and the red-brown product obtained was
crystallized from CH2Cl2/acetonitrile to give 5 and 6 as red crystals,
respectively. Single crystals of 5 and 6 suitable for X-ray diffraction
were grown by slow evaporation of CH2Cl2 from CH2Cl2/acetoni-
trile mixture. For 5: Yield: 7 mg (0.0044 mmol, 20%). Anal. Calcd
for C62H54I2O4P4W2: C, 46.30; H, 3.38. Found: C, 46.28; H, 3.60.
C6D5Cl)63 δ ) 232.1 (s, CR), 210.8 (dd, 2JC-P(cis) ) 7.1 Hz, 2JC-P(trans)
) 50.0 Hz, CO), 143.8 (s, NCS), 134.0 (d, 1JC-P ) 49.5 Hz, ipso-
N
N
C6H5), 133.1 (d, JC-P ) 18.5 Hz, C6H5), 132.6 (d, JC-P ) 18.4
Hz, C6H5), 131.2 (s, C6H5), 130.9 (s, C6H5), 129.5 (d, NJC-P ) 16.5
N
Hz, C6H5), 128.9 (d, JC-P ) 16.6 Hz, C6H5), 82.1 (s, Cꢀ) 24.9
1
2
(dd, JC-P ) 36 Hz, JC-P ) 16.5 Hz, CH2).
[(TfO)(CO)2(dppe)WC4W(CO)2(dppe)(OTf)] (9). A solution
of silver triflate (17 mg, 0.064 mmol) in THF (3 mL) was added
dropwise to a solution of 3 (50 mg, 0.032 mmol) in THF (3 mL)
at room temperature. After stirring the reaction mixture for 20 min,
the solution was filtered and cooled to -30 °C to give 9 as pale-
violet needles. Yield: 43 mg (0.026 mmol, 83%). Anal. Calcd for
C62H48F6O10P4S2W2: C, 45.89; H, 2.98; N. Found: C, 45.81; H, 3.07;
1
IR (cm-1): 1976 (CO), 1918 (CO). H NMR (200 MHz, CD2Cl2)
1
IR (cm-1): 2000 (CO), 1945 (CO). H NMR (200 MHz, THF-d8)
δ ) 7.85-7.57 (m, 15H, C6H5), 7.44-7.34 (m, 25H, C6H5), 3.15
(m, 4H, CH2), 2.75 (m, 4H, CH2), 0.56 (s, 6H, CH3). 31P NMR (81
MHz, CD2Cl2) δ ) 28.04. 13C NMR (125 MHz, CD2Cl2) δ ) 133.0
(s, C6H5), 132.3 (s, C6H5), 129.0 (m, C6H5), 128.5 (m, C6H5), 30.0
(m, CH2), 10.7 (s, CH3). For 6: Yield: 1 mg (0.0007 mmol, 3%).
Anal. Calcd for C62H54Cl2O4P4W2: C, 52.24; H, 3.82. Found: C,
δ ) 7.68-7.59 (m, 15H, C6H5), 7.42-7.34 (m, 25H, C6H5),
2.96-2.85 (m, 8H, CH2). 31P NMR (81 MHz, THF-d8) δ ) 44.82
(s, 1JW-P ) (d, satellite) 236 Hz). 19F NMR (188 MHz, THF-d8) δ
) -79.31 (s, SO3CF3). 13C NMR (125 MHz, CD2Cl2) 215.7 (dd,
2
1
2JC-P(cis) ) 7 Hz, JC-P(trans) ) 50.5 Hz, CO), 135.6 (d, JC-P
)
N
45.6 Hz, ipso-C6H5), 133.8 (d, JC-P ) 11.7 Hz, C6H5), 133.4 (d,
1
52.47; H, 3.97. IR (cm-1): 1983 (CO), 1921 (CO). H NMR (200
NJC-P ) 11.5 Hz, C6H5), 131.6 (d, JC-P ) 40.6 Hz, ipso-C6H5),
1
131.7 (s, C6H5), 129.9 (d, NJC-P ) 10.2 Hz, C6H5), 129.6 (d, NJC-P
MHz, CD2Cl2) δ ) 7.82-7.57 (m, 15H, C6H5), 7.45-7.32 (m, 25H,
) 10.5 Hz, C6H5), 82.1 (s, Cꢀ) 28.2 (dd, 1JC-P ) 29.0 Hz, 2JC-P
)
C6H5), 2.97 (m, 4H, CH2), 2.70 (m, 4H, CH2), 0.53 (s, 6H, CH3).
1
31P NMR (81 MHz, CD2Cl2) δ ) 38.19 (s, JW-P (d, satellite) )
11.2 Hz, CH2).
230 Hz). 13C NMR (125 MHz, CD2Cl2) δ ) 132.7 (m, C6H5), 130.7
(s, C6H5), 130.0 (m, C6H5), 128.6 (m, C6H5), 26.3 (m, CH2), 16.7
(s, CH3).
[I(dppe)2WC4W(dppe)2I] (10). 3 (300 mg, 0.192 mmol) and
diphenylphosphinoethane (dppe) (450 mg, 1.13 mmol) in diglyme
(21 mL) were placed into a Young-Schlenk tube. The mixture
was heated at 140 °C for 7 days. The tube was evacuated three
times during this time. Large dark-green crystals of 10 separated
as the solution became more transparent. Single crystals suitable
for X-ray diffraction were grown by layering a CH2Cl2 solution
with pentane. Yield: 395 mg (0.174 mmol, 91%). Anal. Calcd for
[Cl(CO)2(dppe)WC4W(CO)2(dppe)Cl] (7). Method 1: Chloro-
form (1 mL) was added to the solution of 2 (40 mg, 0.023 mmol)
in diglyme (2 mL). The reaction mixture was kept at room
temperature until a color change to dark violet was observed. After
that the solvent was removed in Vacuo. The reaction mixture was
adsorbed onto silica gel and subjected to column chromatography
using benzene as eluent to isolate a red band to give 6 mg (0.0034
mmol, 15%) of 7. A pink powder was isolated after removal of the
solvent and subsequent washing with acetonitrile and drying in
Vacuo. Method 2: A solution of C2Cl6 (12.15 mg, 0.053 mmol) in
THF (1 mL) was added dropwise to a solution of 2 (40 mg, 0.023
mmol) in glyme (1 mL) at room temperature. After stirring the
reaction mixture for 6 h, the solvent was removed in Vacuo, and
the red-brown product obtained was washed three times with 1 mL
of acetonitrile and dried in Vacuo. Single crystals suitable for X-
ray diffraction were grown by layering a benzene solution with
pentane. Yield: 17 mg (0.012 mmol, 51%). Anal. Calcd for
C60H48Cl2O4P4W2: C, 51.64; H, 3.47. Found: C, 51.81; H, 3.71. IR
C
108H96I2P8W2: C, 57.32; H, 4.28. Found: C, 57.12; H, 4.14. IR
(cm-1): 1900 (CtC). 1H NMR (200 MHz, CD2Cl2): δ ) 7.85 (br,
15H, C6H5), 7.26-6.76 (m, 65H, C6H5), 2.81 (m, 8H, CH2), 1.82
(m, 8H, CH2). 31P NMR (81 MHz, C6D6): δ ) 45 br. 13C NMR
(125 MHz, CD2Cl2) δ ) 213.1 (m, CR), 141.7 (br, ipso-C6H5), 139.9
(br, ipso-C6H5), 135.5 (s, C6H5), 134.0 (s, C6H5), 129.4 (s, C6H5),
126.8 (s, C6H5), 86.5 (s, Cꢀ) 36.0 (m, CH2).
[I(dppe)2WC4W(dppe)2I][PF6] (10[PF6]). To a solution of 10
(40 mg, 0.0177 mmol) in 8 mL of dichloromethane was added
dropwise a solution of [FeCp2][PF6] (5.9 mg, 0.0177 mmol). The
reaction mixture was stirred for 1 h, and the solvent was removed
in Vacuo. The resulting solid was washed with benzene to remove
ferrocene and recrystallized by layering the CH2Cl2 solution with
ether to give 10[PF6]. Yield: 25.5 mg (0.0106 mmol, 60%). Anal.
Calcd for C108H96I2F6P9W2: C, 53.86; H, 4.02. Found: C, 53.97; H,
4.21. IR (cm-1): 1891 (CtC). 1H NMR (200 MHz, CD2Cl2): δ )
8.54-7.03 (m, C6H5), 1.26 (br), 0.2 (br), -2.6 (br), -3.4 (br), -4.8
(br).
[I(dppe)2WC4W(dppe)2I][PF6]2 (10[PF6]2). A solution of
[Ph3C][PF6] (14.3 mg, 0.0354 mmol) was added dropwise at -20
°C to a solution of 10 (40 mg, 0.0177 mmol) in 8 mL of
dichloromethane. The reaction mixture was stirred for 10 min at
room temperature, and the solvent was removed in Vacuo. The
resulting solid was washed with benzene and recrystallized by
layering a CH2Cl2 solution with ether to give 10[PF6]2. Yield: 24
mg (0.0094 mmol, 53%). Anal. Calcd for C108H96I2F12P10W2: C,
50.81; H, 3.79. Found: C, 50.69; H, 3.86. IR (cm-1): 1892 (CtC).
1H NMR (200 MHz, CD2Cl2): δ ) 9.12-7.2 (m, C6H5), 1.35 (br),
-0.64 (br), -5.82 (br), -6.82 (br).
1
(cm-1): 1992 (CO), 1934 (CO). H NMR (200 MHz, C6D6) δ )
7.75-7.54 (m, 15H, C6H5), 7.06-6.89 (m, 25H, C6H5), 2.55 (m,
4H, CH2), 2.15 (m, 4H, CH2); 31P NMR (81 MHz, C6D6) δ ) 37.46
(s, 1JW-P (d, satellite) ) 226 Hz); 13C NMR (125 MHz, C6D6) δ )
228.4 (s, CR), 215.0 (dd, 2JC-P(cis) ) 7.2 Hz, 2JC-P(trans) ) 48.0 Hz,
1
CO), 135.3-135.0 (d, JC-P ) 42.5 Hz, ipso-C6H5), 133.5-133.2
3
(m, C6H5), 130.7-130.4 (d, JC-P ) 40.4 Hz, para-C6H5),
128.7-128.6 (m, C6H5), 85.8 (s, Cꢀ) 27.8 (dd, 1JC-P ) 26 Hz, 2JC-P
) 12.5 Hz, CH2).
[(SCN)(CO)2(dppe)WC4W(CO)2(dppe)(NCS)] (8). An excess
of the AgSCN (50 mg, 0.16 mmol) was added to a THF solution
(5 mL) of 3 (50 mg, 0.032 mmol). The reaction mixture was stirred
for 18 h at 50 °C. The resulting brown suspension was filtered,
and solvent was removed in Vacuo. Complex 8 formed as violet
needles after crystallization from CH2Cl2/pentane. Single crystals
suitable for X-ray diffraction were grown by layering benzene
solution with pentane. Yield: 24 mg (0.017 mmol, 52%). Anal.
Calcd for C62H48N2O4P4S2W2: C, 51.69; H, 3.36; N, 1.94. Found:
C, 51.75; H, 3.46; N, 1.96. IR (cm-1): 2034 (NCS), 1988 (CO),
1931 (CO). 1H NMR (500 MHz, CD2Cl2) δ ) 7.62-7.52 (m, 15H,
C6H5), 7.49 (m, 10H, C6H5), 7.35-7.15 (m, 15H, C6H5), 2.88 (m,
4H, CH2), 2.62 (m, 4H, CH2). 31P NMR (81 MHz, C6D5Cl) δ )
[I(dppe)2WC4W(dppe)(CO)2I] (11). 3 (50 mg, 0.032 mmol) and
diphenylphosphinoethane (dppe) (40 mg, 0.1 mmol) were placed
into Young-Schlenk tube and dissolved in a mixture of 3 mL of
THF with 0.3 mL of CH3CN. This tube was irradiated by a 125 W
(63) The NMR 13C signals of the phenyl groups of dppe were determined
separately in CD2Cl2 solution. N ) 2 for ortho carbons, 3 for meta
carbons, 4 for para carbons. Unfortunately, reliable assignment is
difficult in this case.
1
39.88 (s, JW-P ) (d, satellite) 234 Hz). 13C NMR (125 MHz,
9
3126 J. AM. CHEM. SOC. VOL. 132, NO. 9, 2010

Electronics of Dinuclear C4-Bridged Tungsten Complexes
A R T I C L E S
medium pressure UV lamp (six intervals, 10 min each). The reaction
was monitored by 31P NMR and stopped when the signal of 3 had
disappeared. The reaction mixture was evaporated, washed with
pentane, and subsequently subjected to flash chromatography (silica
gel, benzene) to give 23 mg of 11. It was recrystallized from
benzene. Single crystals suitable for X-ray diffraction were grown
by layering a benzene solution with pentane. Yield: 23 mg (0.012
mmol, 38%). Anal. Calcd for C84H72I2O2P6W2: C, 52.52; H, 3.78.
solution of 11 (25 mg, 0.013 mmol) in 5 mL of dichloromethane.
The reaction mixture was stirred for 1 h, and the solvent was
removed in Vacuo. The resulting solid was washed with benzene
to remove ferrocene and redissolved in 1 mL of THF. The solution
was placed at -30 °C. Brown crystals of 11[PF6] appeared after
one day. Yield: 20 mg (0.0097 mmol, 74%). Anal. Calcd for
C84H72I2F6O2P7W2: C, 48.84; H, 3.51. Found: C, 49.01; H, 3.65.
1
IR (cm-1): 2000 (CO), 1938 (CO). H NMR (200 MHz, CD2Cl2):
1
Found: C, 52.37; H, 3.92. IR (cm-1): 1987 (CO), 1922 (CO). H
δ ) 9.1-6.75 (br, C6H5), 2.81 (br, CH2), 2.29 (br, CH2).
NMR (200 MHz, C6D6): δ ) 7.72-7.58 (m, 16H, C6H5), 7.27 (m,
8H, C6H5), 7.08 (m, 17H, C6H5), 6.95 (m, 15H, C6H5), 6.78 (m,
4H, C6H5), 2.91 (m, 6H, CH2), 2.36 (m, 6H, CH2). 31P NMR (81
MHz, C6D6): δ ) 31.74 (s, 2P, 1JW-P (d, satellite) ) 230 Hz), 32.33
(s, 4P, 1JW-P ) (d, satellite) 268 Hz). 13C NMR (125 MHz, CD2Cl2)
Acknowledgment. We thank S. Weyeneth, F. Muranyi, and A.
Tsirlin for help with the magnetic measurements. Funding from
the Swiss National Science Foundation (SNSF) and from the
University of Zu¨rich are gratefully acknowledged.
2
δ ) 230.3 (s, CR W(dppe)(CO)2), 212.8 (dd, JC-P(cis) ) 6.7 Hz,
2JC-P(trans) ) 42.0 Hz, CO), 212.3 (s, CR W(dppe)2) 140.9-139.6
(m, ipso-C6H5), 136.1-134.9 (m, C6H5), 134.2 (s, C6H5), 133.8 (d,
Supporting Information Available: Details of X-ray experi-
ments, crystallographic information files, ORTEP-like plots of
4-8, 11[PF6], CV of 10 in THF, temperature dependence of ꢁ
vs T for 10[PF6], 11[PF6], and 10[PF6]2. This material is
available free of charge via the Internet at http://pubs.acs.org.
N
JC-P ) 12 Hz, C6H5), 132.7 (d, JC-P ) 10 Hz, C6H5), 130.1 (s,
C6H5), 129.7 (s, C6H5), 128.9-128.7 (m, C6H5), 127.5 (s, C6H5),
93.9 (s, Cꢀ1), 83.0 (s, Cꢀ2), 36.0 (m, CH2 W(dppe)2), 28.6 (dd, 1JC-P
2
) 27.7 Hz, JC-P ) 11.9 Hz, CH2 W(dppe)(CO)2).
[I(dppe)2WC4W(dppe)(CO)2I][PF6] (11[PF6]). A solution of
[FeCp2][PF6] (4.3 mg, 0.013 mmol) was added dropwise to a
JA909764X
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J. AM. CHEM. SOC. VOL. 132, NO. 9, 2010 3127