Synthesis and reactivity of the triply bonded binuclear anion [W 2(η5-C5H5)2μ- PCy2] (μ-CO)2-: Tungsten makes a difference

Article abstract of DOI:10.1021/om9010005

The title anion can be conveniently prepared from the cation [W ₂Cp₂(μ-PCy₂)(CO)₄+] ⁺ via the iodo complex [W₂Cp₂(μ-I)(μ-PCy ₂)(CO)₂], which is easily reduced with Na-amalgam. This anion reacts with different electrophiles both at the W and O sites to give unusual unsaturated molecules such as the hydride [W₂Cp ₂(H)(μ-PCy₂(CO)₂], methoxycarbyne [W ₂Cp₂(μ-COMe)(μ-PCy₂)(μ-CO)], triphenyltin [W₂Cp₂(μ-SnPh₃)(μ-PCy ₂)(CO)₂], and phosphinoxycarbyne [W₂Cp ₂(μ-COP¹Bu₂)(μ-PCy₂)(μ-CO)] derivatives, all of them exhibiting novel structural features or unparalleled compositions.

Full text of DOI:10.1021/om9010005

512 Organometallics 2010, 29, 512–515
DOI: 10.1021/om9010005
Synthesis and Reactivity of the Triply Bonded Binuclear Anion
[W2(η5-C5H5)2( μ-PCy2)( μ-CO)2]-: Tungsten Makes a Difference
ꢀ
M. Angeles Alvarez, M. Esther Garcıa, Daniel Garcıa-Vivo, Miguel A. Ruiz,* and
M. Fernanda Vega
´
ꢀ
Departamento de Quımica Organica e Inorganica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain
ꢀ
Received November 16, 2009
Summary: The title anion can be conveniently prepared from
the cation [W2Cp2(μ-PCy2)(CO)4]þ via the iodo complex
[W2Cp2(μ-I)(μ-PCy2)(CO)2], which is easily reduced with
Na-amalgam. This anion reacts with different electrophiles
both at the W and O sites to give unusual unsaturated
molecules such as the hydride [W2Cp2(H)(μ-PCy2)(CO)2],
methoxycarbyne [W2Cp2(μ-COMe)(μ-PCy2)(μ-CO)], triphe-
nyltin [W2Cp2(μ-SnPh3)(μ-PCy2)(CO)2], and phosphinoxy-
carbyne [W2Cp2(μ-COPtBu2)(μ-PCy2)(μ-CO)] derivatives,
all of them exhibiting novel structural features or unparalleled
compositions.
molecule exhibiting two distinct nucleophilic sites located
at the Mo and O atoms, thus enabling the preparation of a
great variety of novel unsaturated derivatives.8 Some of these
derivatives in turn display a remarkable reactivity and
synthetic potential, as in the case of the hydride [Mo2Cp2-
(μ-H)(μ-PCy2)(CO)2],9 the methoxycarbyne [Mo2Cp2-
(μ-COMe)(μ-PCy2)(μ-CO)],10 and the agostic alkyl deriva-
tives [Mo2Cp2(μ-CH2R)(μ-PCy2)(CO)2] (R = H, Ph).11 We
should also note the ability of the diphenylphosphide-
bridged anion [Mo2Cp2(μ-PPh2)(μ-CO)2]- to cleave N-O
bonds of cationic nitrosyl complexes at low temperatures.12
Thus, we can safely state that 30-electron anions of the type
[Mo2Cp2(μ-PA2)(μ-CO)2]- are indeed the key synthetic
entry to a whole chemistry being developed around unsatu-
rated dimolybdenum carbonyl complexes having very dif-
ferent functionalities. It was therefore a natural extension of
this work attempting to prepare related ditungsten species so
as to examine the effect of the metal (tungsten vs
molybdenum) on the structure and chemical behavior of all
the above unsaturated species. In this paper we report the
preparation of the 30-electron ditungsten anion [W2Cp2-
(μ-PCy2)(μ-CO)2]- (3) (Naþ salt) and a preliminary study
of its chemical behavior. As shown below, the presence of
tungsten instead of molybdenum causes notorious modifica-
tions not only in the reactivity of this sort of unsaturated
anion but also in the structure and stability of the products,
thus significantly expanding their synthetic potential.
A few years ago we discovered an efficient synthetic route
leading to the 30-electron dimolybdenum anions of general
formula [Mo2Cp2(μ-PA2)(μ-CO)2]-, (A = Cy, Ph, OEt) via
the corresponding chloro complexes [Mo2Cp2(μ-Cl)(μ-PA2)-
(CO)2].1 These compounds were almost the first carbonyl
anions having metal-metal triple bonds to be reported.
Actually, to our knowledge the only other 30-electron bi-
nuclear anion previously described appears to be [Re2(μ-
H)3(CO)6]-, a species prepared a long time ago but never
studied in detail.2 Moreover, only a few other unsaturated
carbonyl anions have been reported so far, these including
the 33-electron paramagnetic complex [Fe2(μ-PtBu2)2-
(CO)5]- 3 and a few 32-electron anions such as the dihydrides
[M2(μ-H)2(CO)8]2- (M = Cr, Mo, W)4 and [Mn2(μ-PPh2)-
(μ-H)2(CO)6]-,5 the diiron complex [Fe2(μ-PPh2)(CO)6]-,6
and the dimanganese species [Mn2(CO)6(μ-Ph2PCH2-
PPh2)]2-.7 Thus, we had a unique opportunity to explore
the chemistry of a binuclear anion under conditions of high
unsaturation at the metal centers. Our subsequent work has
confirmed that the dicyclohexylphosphide-bridged anion
[Mo2Cp2(μ-PCy2)(μ-CO)2]- is indeed a highly reactive
The anion 3 can be prepared in a three-step reaction
starting from the hydride [W2Cp2(μ-H)(μ-PCy2)(CO)4],
which is first protonated (and dehydrogenated) with HBF4
þ3
OEt2 to give the unsaturated cation [W2Cp2(μ-PCy2)(CO)4]
(9) (a) Alvarez, C. M.; Alvarez, M. A.; Garcıa, M. E.; Ramos, A.;
Ruiz, M. A.; Lanfranchi, M.; Tiripicchio, A. Organometallics 2005, 24,
7. (b) Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A. Organo-
metallics 2006, 25, 5374. (c) Alvarez, C. M.; Alvarez, M. A.; García, M. E.;
Ramos, A.; Ruiz, M. A.; Graiff, C.; Tiripicchio, A. Organometallics 2007,
26, 321. (d) Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A.
Organometallics 2007, 26, 1461. (e) Alvarez, M. A.; García, M. E.; Ramos,
A.; Ruiz, M. A.; Lanfranchi, M.; Tiripicchio, A. Organometallics 2007, 26,
5454. (f) García, M. E.; Ramos, A.; Ruiz, M. A.; Lanfranchi, M.; Marchio, L.
Organometallics 2007, 26, 6197.
*To whom correspondence should be addressed. E-mail: mara@
uniovi.es.
ꢀ
(1) Garcıa, M. E.; Melon, S.; Ramos, A.; Riera, V.; Ruiz, M. A.;
Belletti, D.; Graiff, C.; Tiripicchio, A. Organometallics 2003, 22, 1983.
(2) Ginsberg, A. P.; Hawkes, M. J. J. Am. Chem. Soc. 1968, 90, 5930.
(b) Hawkes, M. J.; Ginsberg, A. P. Inorg. Chem. 1969, 8, 2189.
(3) Van der Linden, J. G. M.; Heck, J.; Walter, B.; Bottcher, H.-C.
Inorg. Chim. Acta 1995, 217, 29.
(4) Lin, J. T.; Hagen, G. P.; Ellis, J. E. J. Am. Chem. Soc. 1983, 105,
2296 and references therein.
(5) Henrick, K.; Iggo, J. A.; Mays, M. J.; Raithby, P. R. J. Chem.
ꢀ
(10) (a) Garcıa, M. E.; Garcıa-Vivo, D.; Ruiz, M. A.; Alvarez, S.;
ꢀ
ꢀ
Aullon, G. Organometallics 2007, 26, 4930. (b) García, M. E.; García-Vivo,
ꢀ
D.; Ruiz, M. A.; Alvarez, S.; Aullon, G. Organometallics 2007, 26, 5912. (c)
ꢀ
Soc., Chem. Commun. 1984, 209.
García, M. E.; García-Vivo, D.; Ruiz, M. A. Organometallics 2008, 27, 169.
ꢀ
(6) Seyferth, D.; Brewer, K. S.; Wood, T. G.; Cowie, M.; Hilts, R. W.
Organometallics 1992, 11, 2570.
(7) Liu, X. Y.; Riera, V.; Ruiz, M. A.; Lanfranchi, M; Tiripicchio, A.
(d) García, M. E.; García-Vivo, D.; Ruiz, M. A. Organometallics 2009, 28,
4385.
ꢀ
(11) (a) Alvarez, M. A.; Garcıa-Vivo, D.; Garcıa, M. E.; Martınez,
Organometallics 2003, 22, 4500 and references therein.
(8) (a) Garcıa, M. E.; Melon, S.; Ramos, A.; Ruiz, M. A. Dalton
Trans. 2009, 8171. (b) Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A.
J. Organomet. Chem. 2009, 694, 3864. (c) Alvarez, M. A.; García, M. E.;
Ramos, A.; Ruiz, M. A. J. Organomet. Chem. 2009, 695, 36.
M. E.; Ramos, A.; Ruiz, M. A. Organometallics 2008, 27, 1973. (b)
Alvarez, M. A.; García, M. E.; Martínez, M. E.; Ramos, A.; Ruiz, M. A.
Organometallics 2009, 28, 6293.
(12) Garcıa, M. E.; Garcıa-Vivo, D.; Melon, S.; Ruiz, M. A.; Graiff,
C.; Tiripicchio, A. Inorg. Chem. 2009, 48, 9282.
ꢀ
ꢀ
ꢀ
r
pubs.acs.org/Organometallics
Published on Web 01/08/2010
2010 American Chemical Society

Communication
Organometallics, Vol. 29, No. 3, 2010 513
Scheme 1
Scheme 2
(1; BF4- salt)13 and then reacted with NaI in refluxing 1,2-
dichloroethane to give the iodo derivative [W2Cp2(μ-I)(μ-
PCy2)(CO)2] (2),14 which is finally reduced with Na-amal-
gam in tetrahydrofuran to yield cleanly the Naþ salt of the
anion 3 (Scheme 1).15 The formation of 1 is analogous to that
previously implemented by us for different dimolybdenum
cations of the type [Mo2Cp2(μ-PHR)(CO)4]þ,16a and the
spectroscopic data are comparable to those of the PPh2-
bridged complex [W2Cp2(μ-PPh2)(CO)4]þ;16b therefore, a
similar structure is assumed for this fluxional cation. As
for the iodo complex 2, the corresponding spectroscopic data
in turn indicate a strong structural relationship with the
dimolybdenum complexes [Mo2Cp2(μ-X)(μ-PCy2)(CO)2]
(X = Cl, Br, I), recently reported by us using different
synthetic methods.8a
the corresponding hydride [W2Cp2(H)(μ-PCy2)(CO)2] (4).17
However, unlike its dimolybdenum analogue, which displays
solely an H-bridged structure,9a,f compound 4 exists in
solution as a mixture of two isomers in equilibrium: the
expected one with a bridging hydride ligand (B, major
isomer) and a second one having a terminal hydride and a
bridging or semibridging carbonyl (T, minor isomer). The
latter is deduced from the presence of a relatively low
frequency C-O stretching band at 1739 cm-1 in the IR
spectrum and of a quite deshielded resonance at 272.7 ppm in
the low-temperature 13C NMR spectra (when exchange
becomes slow on the NMR time scale). The terminal
coordination of the hydride ligand in isomer T is suggested
by its relatively low hydride shielding (δH -0.71 ppm) and
the quite different values of the P-W couplings in the 31P
resonance (239 and 379 Hz), reflecting a great difference in
the coordination numbers of both metal centers. The above
proposals are supported by DFT calculations, indicating
that the structure with the bridging hydride (B) is some 15 kJ
mol-1 below a structure with a terminal hydride and a
semibridging carbonyl (T) (Figure 1).18 A third isomer with
a semibridging hydride and a bridging carbonyl was found to
be much higher in energy (see the Supporting Information).
Isomers B and T both display very short intermetallic lengths
The Naþ salt of the anion 3 is only poorly soluble in
tetrahydrofuran, and a suspension of this salt is obtained when
using ordinary amounts of solvent. These suspensions, how-
ever, can be used for further reactivity studies without pro-
blems. The available spectroscopic data for this highly air-
sensitive anion suggest a structure very similar to that of its
molybdenum analogue,8a with two carbonyl ligands and a
dicyclohexylphosphide group symmetrically bridging the un-
saturated ditungsten center. The unique C-O stretching band
of 3 appears at a very low frequency (1546 cm-1), which is
34 cm-1 below the corresponding band in the dimolybdenum
analogue, thus suggesting a stronger interaction of the oxygen
atoms with the alkaline cations and a higher electrostatic
charge at those O atoms, in line with the reactivity discussed
below. We finally note the progressive increase of the P-W
couplings in the sequence 1 (222 Hz) < 2 (292 Hz) < 3 (378
Hz), this reflecting with fidelity the corresponding decrease in
the number of terminal ligands around the metal atoms.
The chemical behavior and synthetic potential of 3 are
illustrated through the reactions shown in Scheme 2. As
expected, this anion is easily protonated by (NH4)PF6 to give
˚
of ca. 2.54 A and high electron densities at the intermetallic
bond critical points (ca. 0.64 e A-3, see the Supporting Infor-
˚
mation), in agreement with the triple metal-metal bond to
be proposed for these molecules under the EAN formalism.
For comparison, the corresponding values computed for the
(13) Selected data for 1: ν(CO) (CH2Cl2) 2002 (m), 1958 (vs), 1931 (s)
cm-1 31P{1H} NMR (121.52 MHz, CD2Cl2) δ 138.7 (s, JPW = 222 Hz).
;
˚
hydride-bridged [Mo2Cp2(μ-H)(μ-PCy2)(CO)2] were 2.535 A
(14) Selected data for 2: ν(CO) (C2H4Cl2) 1863 (w, sh), 1826 (vs)
cm-1 31P{1H} NMR (121.52 MHz, CD2Cl2) δ 89.3 (s, JPW = 292 Hz).
(15) Selected data for 3: ν(CO) (THF) 1546 (s) cm-1 31P{1H} NMR
(121.52 MHz, Me2CO-d6/D2O) δ 152.7 (s, JPW = 378 Hz).
and 0.582 e A-3, respectively.9f Interestingly, the presence of
˚
;
the isomer T in the solutions of 4 might imply a significant
modification in the reactivity of this ditungsten complex, in
comparison to that observed for [Mo2Cp2(μ-H)(μ-PCy2)-
(CO)2].9 Preliminary experiments, currently under way,
indicate that this is the case.
;
ꢀ
(16) (a) Alvarez, C. M.; Alvarez, M. A.; Garcıa-Vivo, D.; Garcıa, M.
ꢀ
E.; Ruiz, M. A.; Saez, D.; Falvello, L. R.; Soler, T.; Herson, P. Dalton
Trans. 2004, 4168. (b) Alvarez, C. M.; García, M. E.; Rueda, M. T.; Ruiz,
ꢀ
M. A.; Saez, D.; Connelly, N. G. Organometallics 2005, 24, 650.
(17) Selected data for 4: ν(CO) (CH2Cl2) 1864 (w, sh), 1822 (vs), 1739
(w) cm-1; 1H NMR (400.13 MHz, CD2Cl2, 193 K) δ -0.71 (d, JPH = 31,
JHW = 99 Hz, 1H, W-H, isomer T), -6.77 (s, JHW = 121 Hz, 1H, μ-H,
isomer B), B/T ratio 3; 31P{1H} NMR (162.00 MHz, CD2Cl2, 213 K) δ
193.6 (s, JPW = 240, 379 Hz, T), 167.2 (s, JPW = 318 Hz, B); 13C{1H}
NMR (100.63 MHz, CD2Cl2, 193K) δ 272.7 (s, br, μ-CO, T), 244.2 (s, br,
CO, T), 233.5 (s, br, 2CO, B).
(18) Density functional theory calculations were performed with the
GAUSSIAN03 program package using the hybrid method B3LYP,
together with a standard 6-31G* basis on all atoms except W, for which
a valence double-ζ quality basis set and LANL2DZ effective core
potentials were used. See the Supporting Information for further details.

514 Organometallics, Vol. 29, No. 3, 2010
Alvarez et al.
Figure 1. DFT optimized structures of the isomers of com-
pound 4 having bridging (left, B) or terminal (right, T) hydride
˚
ligands. Selected bond lengths for B (A): W1-W2 = 2.545,
W1-P = 2.429, W2-P = 2.439, W1-H = 1.870, W2-H =
1.867, W1-C1=1.956, W2-C2=1.946. Selected bond lengths
˚
for T (A): W1-W2=2.536, W1-H6=1.707, W1-P=2.467,
W2-P=2.400, W1-C7=1.978, W2-C7=2.438, W2-C5=
1.945, W1-C5=2.795.
Figure 2. ORTEP drawing (30% probability) of compound 6,
with H atoms and phenyl and cyclohexyl rings (except the C1
˚
atoms) omitted for clarity. Selected bond lengths (A) and angles
(deg): W1-W2=2.5794(3), W1-Sn1=2.8843(4), W2-Sn1=
2.9451(4), W1-P1 = 2.387(1), W2-P1 = 2.379(1), W1-C1 =
1.920(5), W2-C2=1.958(6); C1-W1-W2=72.0(2), C2-W2-
W1=91.3(2).
The enhanced nucleophilicity at the O atoms of the
bridging carbonyls in the anion 3 (in comparison to its
molybdenum analogue) is evidenced by its reaction with
MeI, this giving the methoxycarbyne complex [W2Cp2-
(μ-COMe)(μ-PCy2)(μ-CO)] (5) as the major product,19
along with a minor species yet not isolated but tentatively
identified as the corresponding methyl-bridged complex
[W2Cp2(μ-Me)(μ-PCy2)(CO)2] on the basis of spectro-
scopic analogies (δH -1.18 ppm, JHP = 2 Hz) with the
analogous dimolybdenum species.9f For comparison, the
dimolybdenum anion reacts with MeI to give exclusively
the methyl-bridged derivative,8a,9f and it only gives the
corresponding methoxycarbyne complex when using
stronger methylating agents such as (Me3O)BF4 and Me2-
SO4.1,8a Compound 5 displays a quite low C-O stretching
frequency of 1625 cm-1, some 50 cm-1 below those in the
corresponding Mo2 complex.8a Therefore, a much higher
electron-donor ability of this unsaturated molecule
(compared to the Mo2 analogue) can be foreseen, to be
investigated in the near future.
mentioned isomers and in any case consistent with the triple
metal-metal bond to be proposed for 6 under the EAN
formalism.
The ditungsten anion 3 can even allow the formation of
compounds that cannot be obtained at all using the Mo2
anion [Mo2Cp2(μ-PCy2)(μ-CO)2]- or any other reagent. For
instance, we have shown previously that the latter anion
reacts with chlorophosphines ClPR2 to give the correspond-
ing mixed-phosphide derivatives of type [Mo2Cp2(μ-PR2)(μ-
PCy2)(CO)2].8c In contrast, the anion 3 reacts with chlor-
ophosphines through the oxygen atom of the carbonyl
ligands, to give initially the corresponding phosphinoxycar-
byne derivatives of type [W2Cp2(μ-COPR2)(μ-PCy2)(μ-
CO)]. These are rather unstable and air-sensitive species that
cannot be isolated as solid materials, but we have been able
to properly characterize the most stable member of this series
t
The anion 3 also reacts with several electrophiles based on
metallic elements to give unsaturated heterometallic deriva-
tives difficult to obtain otherwise. For example, its reaction
with ClSnPh3 gives with high yield the rare stannyl-bridged
derivative [W2Cp2(μ-SnPh3)(μ-PCy2)(CO)2] (6).20 The struc-
ture of this molecule (Figure 2)21 is similar to that of its
dimolybdenum analogue,9a,b but there is one relevant differ-
ence: while the Mo2 complex exhibits a symmetrically brid-
(R = Bu (7)), which displays spectroscopic properties for
the bridging carbyne (δC 342.7 ppm), carbonyl (νCO 1660
cm-1, δC 291.6 ppm), and phosphide ligands (δP 165.7 ppm,
JPW = 362 Hz) comparable to those of the methoxycarbyne
complex 5. We note that, to our knowledge, no other
complex having a carbyne ligand of the type C-O-PR2
seems to have been ever reported in the literature. More
interestingly, because of the presence of the lone electron pair
on phosphorus, the phosphinoxycarbyne ligand might be
considered as a bifunctional group, and further studies are
now in progress to analyze the chemical behavior of this
unusual ligand.
In summary, we have shown that the replacement of
molybdenum with tungsten in the 30-electron anions
[M2Cp2(μ-PCy2)(μ-CO)2]- has significant effects not
only on the reactivity but also on the structure and nature
of the corresponding derivatives. The ditungsten anion 3
exhibits enhanced nucleophilicity at the O sites, while
allowing the terminal binding of the incoming electrophile
at the metal site. The first property allows the formation of
unprecedented phosphinoxycarbyne (COPR2) complexes.
Further studies are now in progress to fully explore the
synthetic potential of this triply bonded ditungsten
anion.
˚
ging stannyl group (Mo-Sn = 2.9139(7) and 2.9244(7) A),
˚
compound 6 displays W-Sn distances differing by ca. 0.06 A
from each other, a structural distortion that, by recalling the
H/SnPh3 analogy, might be related to the geometrical path
connecting the extreme isomers of types B and T in the
hydride 4. We also note the short intermetallic length of
˚
2.5794(3) A in 6, close to the values computed for the
(19) Selected data for 5: ν(CO) (CH2Cl2) 1625 (s) cm-1 31P{1H}
;
NMR (121.52 MHz, CD2Cl2) δ 173.5 (s, JPW = 358 Hz); 13C{1H} NMR
(75.48 MHz, CD2Cl2) δ 342.9 (d, JCP = 9 Hz, μ-COMe), 302.3 (s, μ-CO).
(20) Selected data for 6: ν(CO) (CH2Cl2) 1879 (m), 1821 (vs) cm-1
;
31P{1H} NMR (162.17 MHz, CD2Cl2) δ 178.5 (s, JPW = 305 Hz, JP119
Sn
≈ JP117Sn = 67 Hz).
(21) X-ray data for 6: red-brown crystals, triclinic (P1), a =
˚
˚
˚
10.1693(1) A, b = 11.5192(1) A, c = 19.3320(2) A, R = 77.199(1)°,
o
3
˚
β = 85.446(1)°, γ = 68.037(1) , V = 2048.03(4) A , T = 100 K, Z = 2,
R = 0.0212 (observed data with I > 2σ(I)), GOF = 1.276.

Communication
Organometallics, Vol. 29, No. 3, 2010 515
Acknowledgment. We thank the DGI of Spain (Project
CTQ2006-01207 and a grant to M.F.V.) and the COST
action CM0802 ‘‘PhoSciNet’’ for supporting this work.
ꢀ
We also thank Dr. David Saez for the preparation of
compound 1.
Supporting Information Available: Text, tables, and figures
giving experimental procedures and spectroscopic data for new
compounds and details of DFT calculations on compound 4, and a
CIF file giving crystallographic data for compound 6. This material
is available free of charge via the Internet at http://pubs.acs.org.