Reactivity of the unsaturated hydride [Mo2(η5- C5H5)2(μ-H)(μ-PCy2)(CO) 2] toward P-donor bidentate ligands and unsaturated N-containing organic molecules

Article abstract of DOI:10.1021/om060999k

The reactions of the 30-electron hydride [Mo₂Cp ₂(μ-H)(μ-PCy₂)(CO)₂] with the bidentate P-donor ligands bis(diphenylphosphino)methane (dppm), bis(dimethylphosphino) methane (dmpm), and tetraethylpyrophosphite (tedip) lead to the electron-precise derivatives [Mo₂Cp₂(μ-H)(μ-PCy₂)(CO) ₂(μ-L₂)] (L₂ = dppm, dmpm, tedip), in which the bidentate ligand bridges the dimetal center. In the reaction with dppm, the tricarbonyl derivative [Mo₂Cp₂(μ-H)(μ-PCy ₂)(CO)₃(κ¹-dppm)] is also obtained as a minor byproduct. All of these compounds are obtained as mixtures of isomers, most of them interconverting in solution, and the structure of the major isomer of the tedip derivative was confirmed through an X-ray diffraction study (Mo-Mo = 3.2251(5) A). The title unsaturated hydride reacts readily with isocyanides to give in good yield the insertion products [Mo₂Cp ₂(μ-η.κ:η,κ-HCNR)(μ-PCy₂)(CO) ₂] (R = p-tolyl, ^tBu), having a 5e-donor formimidoyl ligand, as confirmed by an X-ray study of the ^tBu compound. When R = p-tolyl, the addition derivative [Mo₂Cp₂(μ-H)(μ- PCy₂)(CO)₂(CNR)₂] is also obtained as a minor product. Although the title hydride does not react with acetonitrile or simple diazo compounds, it reacts readily with benzyl azide (PhCH₂N ₃) to give two 32-electron derivatives, the azavinylidene complex [Mo₂Cp₂(μ-N=CHPh)-(μ-PCy₂)(CO) ₂] (Mo-Mo = 2.632(1) A) and the amido derivative [Mo ₂Cp₂{μ-NH(CH₂Ph)}(μ-PCy ₂)-(CO)₂], in a 2:1 ratio. The latter product can be obtained almost selectively by reaction of the triply bonded anion [Mo ₂Cp₂(μ-PCy₂)(μ-CO)₂] ^- with benzyl azide in the presence of H₂O as a source of protons. The solution structures of the new complexes are discussed on the basis of the solid-state X-ray studies and the IR and variable-temperature NMR ( ¹H, ³¹P, ¹³C) data, and the reaction pathways responsible for the formation of the new complexes are discussed on the basis of the available information.

Full text of DOI:10.1021/om060999k

Organometallics 2007, 26, 1461-1472
1461
Reactivity of the Unsaturated Hydride
[Mo2(η5-C5H5)2(µ-H)(µ-PCy2)(CO)2] toward P-Donor Bidentate
Ligands and Unsaturated N-Containing Organic Molecules
M. Angeles Alvarez, M. Esther Garc´ıa, Alberto Ramos, and Miguel A. Ruiz*
Departamento de Qu´ımica Orga´nica e Inorga´nica/IUQOEM, UniVersidad de OViedo,
E-33071 OViedo, Spain
ReceiVed October 30, 2006
The reactions of the 30-electron hydride [Mo2Cp2(µ-H)(µ-PCy2)(CO)2] with the bidentate P-donor ligands
bis(diphenylphosphino)methane (dppm), bis(dimethylphosphino)methane (dmpm), and tetraethylpyro-
phosphite (tedip) lead to the electron-precise derivatives [Mo2Cp2(µ-H)(µ-PCy2)(CO)2(µ-L2)] (L2 ) dppm,
dmpm, tedip), in which the bidentate ligand bridges the dimetal center. In the reaction with dppm, the
tricarbonyl derivative [Mo2Cp2(µ-H)(µ-PCy2)(CO)3(κ1-dppm)] is also obtained as a minor byproduct.
All of these compounds are obtained as mixtures of isomers, most of them interconverting in solution,
and the structure of the major isomer of the tedip derivative was confirmed through an X-ray diffraction
study (Mo-Mo ) 3.2251(5) Å). The title unsaturated hydride reacts readily with isocyanides to give in
t
good yield the insertion products [Mo2Cp2(µ-η,κ:η,κ-HCNR)(µ-PCy2)(CO)2] (R ) p-tolyl, Bu), having
a 5e-donor formimidoyl ligand, as confirmed by an X-ray study of the tBu compound. When R ) p-tolyl,
the addition derivative [Mo2Cp2(µ-H)(µ-PCy2)(CO)2(CNR)2] is also obtained as a minor product. Although
the title hydride does not react with acetonitrile or simple diazo compounds, it reacts readily with benzyl
azide (PhCH2N3) to give two 32-electron derivatives, the azavinylidene complex [Mo2Cp2(µ-NdCHPh)-
(µ-PCy2)(CO)2] (Mo-Mo ) 2.632(1) Å) and the amido derivative [Mo2Cp2{µ-NH(CH2Ph)}(µ-PCy2)-
(CO)2], in a 2:1 ratio. The latter product can be obtained almost selectively by reaction of the triply
bonded anion [Mo2Cp2(µ-PCy2)(µ-CO)2]- with benzyl azide in the presence of H2O as a source of protons.
The solution structures of the new complexes are discussed on the basis of the solid-state X-ray studies
and the IR and variable-temperature NMR (1H, 31P, 13C) data, and the reaction pathways responsible for
the formation of the new complexes are discussed on the basis of the available information.
Ph2PCH2PPh2 (dppm), (EtO)2POP(OEt)2 (tedip)),4 [Re2(µ-H)2-
(CO)6(µ-L2)],5 [Re2(µ-H)2(CO)8],6 and [Ru2Cp*2(µ-H)4] (Cp*
) η5-C5Me5)7 or the cations [Ru2(η6-C6Me6)2(µ-H)3]+ 8 and [Ir2-
Introduction
During our preliminary study of the reactivity of the 30-
electron hydride [Mo2Cp2(µ-H)(µ-PCy2)(CO)2] (1), we found
that this complex was quite reactive toward small electron-donor
molecules under mild conditions as a result of its coordinative
and electronic unsaturation.1 For example, two molecules of CO
are rapidly incorporated to the unsaturated dimetal center in 1
to yield the saturated tetracarbonyl [Mo2Cp2(µ-H)(µ-PCy2)-
(CO)4], previously synthesized by us through a more conven-
tional route,2 and rapid reaction also takes place with CNtBu,
now to give the insertion product [Mo2Cp2(µ-HCNtBu)(µ-PCy2)-
(CO)2], having a bridging formimidoyl ligand.1 In these reac-
tions, the hydride complex behaves as a Lewis acid toward the
incoming molecule, which is the electron donor, at least initially.
However, the presence of the bridging hydride ligand allows
for several possible further rearrangements of the incoming
molecule, which may involve its insertion into the Mo-H bond
(as in the above reaction), activation of E-H bonds (E )
p-block element), H2 elimination, etc., as shown by previous
studies on the reactions of small molecules with compounds
having unsaturated M2(µ-H)x centers, such as the neutral
compounds [Os3(µ-H)2(CO)10],3 [Mn2(µ-H)2(CO)6(µ-L2)] (L2 )
Cp*2(µ-dmpm)(µ-H)2]2+ 9
. In all of the above compounds,
(3) (a) Deeming, A. J. AdV. Organomet. Chem. 1986, 26, 1. (b) Burgess,
K. Polyhedron 1984, 3, 1175.
(4) See for example: (a) Garc´ıa-Alonso, F. J.; Garc´ıa-Sanz, M.; Riera,
V.; Anillo-Abril, A.; Tiripicchio, A.; Ugozzoli, F. Organometallics 1992,
11, 801. (b) Garc´ıa-Alonso, F. J.; Riera, V.; Ruiz, M. A.; Tiripicchio, A.;
Tiripicchio-Camellini, M. Organometallics 1992, 11, 370. (c) Garc´ıa-Alonso,
F. J.; Garc´ıa-Sanz, M.; Riera, V. J. Organomet. Chem. 1991, 421, C12. (d)
Carren˜o, R.; Riera, V.; Ruiz, M. A. J. Organomet. Chem. 1991, 419, 163.
(5) (a) Mays, M. J.; Prest, D. W.; Raithby, P. R. J. Chem. Soc., Chem.
Commun. 1980, 171. (b) Prest, D. W.; Mays, M. J.; Raithby, P. R. J. Chem.
Soc., Dalton Trans. 1982, 2021.
(6) (a) Carlucci, L.; Proserpio, D. M.; D’Alfonso, G. Organometallics
1999, 18, 2091. (b) Carlucci, L.; Ciani, G.; von Gudenberg, D. W.;
D’Alfonso, G. J. Organomet. Chem. 1997, 534, 233. (c) Beringhelli, T.;
D’Alfonso, G.; Ciani, G.; Moret, M.; Sironi, A. J. Chem. Soc., Dalton Trans.
1993, 1101.
(7) See for example: (a) Takao, T.; Amako, M.; Suzuki, H. Organo-
metallics 2003, 22, 3855. (b) Suzuki, H. Eur. J. Inorg. Chem. 2002, 1009.
(c) Ohki, Y.; Suzuki, H. Angew. Chem., Int. Ed. 2002, 41, 2994. (d) Takao,
T.; Amako, M.; Suzuki, H. Organometallics 2001, 20, 3406. (e) Ohki, Y.;
Suzuki, H. Angew. Chem., Int. Ed. 2000, 39, 3463. (f) Jones, W. D.; Chin,
R. M.; Hoaglin, C. L. Organometallics 1999, 18, 1786. (g) Takao, T.;
Yoshida, S.; Suzuki, H.; Tanaka, M. Organometallics 1995, 14, 3855. (h)
Tada, K.; Oishi, M.; Suzuki, H. Organometallics 1996, 15, 2422. (i) Suzuki,
H.; Omori, H.; Lee, D. H.; Yoshida, Y.; Fukushima, M.; Tanaka, M.; Moro-
oka, Y. Organometallics 1994, 13, 1129. (j) Suzuki, H.; Kakigano, T.;
Igarashi, M.; Tanaka, M.; Moro-oka, Y. J. Chem. Soc., Chem. Commun.
1991, 5, 283. (k) Omori, H.; Suzuki, H.; Take, Y.; Moro-oka, Y.
Organometallics 1989, 8, 2270. (l) Suzuki, H.; Omori, H.; Moro-oka, Y.
Organometallics 1988, 7, 2579.
* To whom correspondence should be addressed: E-mail:
mara@uniovi.es.
(1) Alvarez, C. M.; Alvarez, M. A.; Garc´ıa, M. E.; Ramos, A.; Ruiz, M.
A.; Lanfranchi, M.; Tiripicchio, A. Organometallics 2005, 24, 7.
(2) Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Rueda, M. T.; Sa´ez, D.
Organometallics 2002, 21, 5515.
10.1021/om060999k CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/06/2007

1462 Organometallics, Vol. 26, No. 6, 2007
AlVarez et al.
Chart 1
Chart 2
however, the number of hydride bridges at least matches the
formal bond order based on the EAN rule, and there is no special
coordinative unsaturation at the metal centers; hence, the
incorporation of any donor molecule must modify the coordina-
tion mode of the bridging hydrides. In contrast, compound 1
displays just one hydride ligand over a formally triple inter-
metallic bond, and the molybdenum atoms are surrounded by
one ligand fewer than usual (coordinative unsaturation). On the
basis of these differences, we might anticipate some distinct
behavior of compound 1 toward small donor molecules, in
comparison to the aforementioned di- and polyhydride species
(for instance, intramolecular dehydrogenation is no longer
possible). In this paper we report the reactions of the unsaturated
hydride 1 toward simple bidentate P-donors such as the
diphosphines R2PCH2PR2 (R ) Ph (dppm), Me (dmpm)) and
the diphosphite (EtO)2POP(OEt)2 (tedip) and the reactions of 1
with small organic molecules containing multiple C-N or N-N
bonds, such as nitriles, isonitriles, diazo compounds, and azides.
These reactions should give a measure of the real degree of
unsaturation of the dimetal center in 1 and its ability for hydride
transfer, respectively. Compound 1 is also quite reactive toward
terminal and internal alkynes, and these results will be reported
separately.
Chart 3
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Compound 2c
Mo(1)-Mo(2)
Mo(1)-C(1)
Mo(2)-C(2)
Mo(1)-H(1)
Mo(2)-H(1)
3.2251(5)
1.909(4)
1.923(5)
1.90(6)
Mo(1)-P(1)
Mo(2)-P(1)
Mo(1)-P(2)
Mo(2)-P(3)
2.467(1)
2.454(1)
2.358(1)
2.397(1)
1.84(6)
O(1)-C(1)-Mo(1)
O(2)-C(2)-Mo(2)
Mo(1)-C(1)-Mo(2)
Mo(1)-P(1)-Mo(2)
C(1)-Mo(1)-Mo(2)
175.3(4)
176.5(4)
67.5(3)
81.7(1)
108.6(1)
C(2)-Mo(2)-Mo(1)
P(3)-Mo(2)-P(1)
P(2)-Mo(1)-P(1)
Mo(1)-H(1)-Mo(2)
85.0(1)
127.0(1)
129.7(1)
119(2)
PCy2)(CO)2(µ-tedip)] (2c) in good yield. The dmpm compound
seems to display a single isomer of type A in solution, although
this was not confirmed by low-temperature NMR data. In
contrast, the tedip compound exhibits three isomers in solution.
Two of these isomers, A and B, are in fast equilibrium in
solution (A/B ) 3 in CD2Cl2 at 183 K) and are analogous to
those found for the diphosphine compounds. The third isomer
(C; Chart 2) does not seem to be in equilibrium with the other
isomers and is obtained in a very low relative amount ((A +
B)/C ) 20).
Structural Characterization of Compounds 2. The structure
of compound 2c (isomer A) was confirmed through a single-
crystal X-ray diffraction study (Table 1 and Figure 1). The
molecule displays two MoCp(CO) fragments in a transoid
arrangement bridged by three ligands: hydride, diphosphite, and
dicyclohexylphosphide. The intermetallic distance, 3.2215(5) Å,
is comparable to those found for the related tri- and tetracarbonyl
species [Mo2Cp2(µ-H)(µ-PRR′)(CO)3L] (L ) CO, PR3),10
ranging from 3.24 to 3.26 Å, thus fully consistent with the
reduction of the intermetallic bond order, from 3 to 1. The tedip
ligand is slightly twisted, so that the phosphorus atoms and the
metal centers are not in the same plane. This could be a steric
effect, since each of the phosphorus atoms is displaced away
from the adjacent Cp ligand. A similar twist is observed in the
Results and Discussion
Reactions of 1 with Bidentate P-Donors. Since the diphos-
phines dppm and dmpm or the diphosphite tedip act usually as
bridging 4e-donor ligands, it is expected that these molecules
would coordinate easily to the unsaturated dimetal center in 1
in a bridging fashion, thus reducing the intermetallic bond order
from 3 to 1. Isomerism, however, can arise if different relative
positions of the ligands are possible, as happens to be the case.
Compound 1 reacts at room temperature with dppm in toluene
to give the addition product [Mo2Cp2(µ-H)(µ-PCy2)(CO)2(µ-
dppm)] (2a) in almost quantitative yield (Chart 1). This
compound is obtained as a mixture of the two isomers A and B
(Chart 2), which in solution are in equilibrium (see below; A/B
) 9 in CD2Cl2 at 183 K). When this reaction is carried out in
dichloromethane, compound 2a is obtained along with small
amounts of the tricarbonyl complex [Mo2Cp2(µ-H)(µ-PCy2)-
(CO)3(κ1-dppm)] (3), which in solution also displays two
isomers, D and E (Chart 3; D/E ) 7 in C6D6 at 293 K). The
reactions of 1 with dmpm and tedip proceed much more rapidly
but give analogously the corresponding addition products [Mo2-
Cp2(µ-H)(µ-PCy2)(CO)2(µ-dmpm)] (2b) and [Mo2Cp2(µ-H)(µ-
(10) (a) Alvarez, C. M.; Alvarez, M. A.; Garc´ıa-Vivo´, D.; Garc´ıa, M.
E.; Ruiz, M. A.; Sa´ez, D.; Falvello, L. R.; Soler, T.; Herson, P. Dalton
Trans. 2004, 4168. (b) Hartung, H.; Walther, B.; Baumeister, U.; Bo¨tcher,
H.-C.; Krug, A.; Rosche, F.; Jones, P. G. Polyhedron 1992, 11, 1563. (c)
Henrick, K.; McPartlin, M.; Horton, A. D.; Mays, M. J. J. Chem. Soc.,
Dalton Trans. 1988, 1083.
(8) Tschan, M. J.-L.; Che´rioux, F.; Karmazin-Brelot, L.; Su¨ss-Fink, G.
Organometallics 2005, 24, 1974.
(9) Fujita, K.; Nakaguma, H.; Hanasaka, F.; Yamaguchi, R. Organome-
tallics 2002, 21, 3749.

ReactiVity of [Mo2(η5-C5H5)2(µ-H)(µ-PCy2)(CO)2]
Organometallics, Vol. 26, No. 6, 2007 1463
Scheme 1. Fluxional Process and Isomerization Equilibrium
Proposed for Compounds 2a and 2ca
Figure 1. ORTEP diagram (30% probability) of compound 2c,
with H atoms, Cy rings, and Et groups omitted, except for the
hydride ligand and the C1 atoms of the Cy rings.
tetracarbonyl derivative [W2Cp2(CO)4(µ-tedip)],11 where the Cp
ligands are also placed in a transoid relative arrangement. In
any case, the phosphide ligand is placed trans to the diphosphite
bridge, in the average Mo2P2 plane. Finally, the centroids of
the cyclopentadienyl rings, the carbonyls, and the hydride ligand
are placed roughly in a plane perpendicular to the above one.
The carbonyls are arranged in mutually transoid but quite
inequivalent positions; one of them is placed cis to the hydride
bridge and thus points away from the intermetallic vector (C(1)-
Mo(1)-Mo(2) ) 108.6(1)°), while the other carbonyl is placed
trans to the hydride ligand and is slightly bent over the
intermetallic bond (C(2)-Mo(2)-Mo(1) ) 85.0(1)°). As a
result, the coordination environment around Mo(2) is of the four-
legged piano-stool type, whereas that around Mo(1) deviates
strongly from that model. This structure can be related to that
of the isoelectronic cation [Mo2Cp2(µ-CH2PPh2)(µ-I)(µ-PPh2)-
(CO)2]+,12 although in that case the presence of a bulky PPh2
group (rather than the small hydride atom) in the plane of the
carbonyls then induces a much more pronounced dissymmetry
in the carbonyl ligands, with C-M-M angles of 120 and 77°,
respectively.
The spectroscopic data collected for compounds 2a-c in
solution show that several isomers are present in solution, at
least for the dppm and tedip compounds (Table 2 and Experi-
mental Section). All of them exhibit C-O stretching bands at
frequencies lower (by 40-70 cm-1) than those of the hydride
1,13 as expected from the substantial increase in the electron
density at the metal centers caused by the coordination of the
bidentate P-donors. The IR spectra of the dppm and dmpm
derivatives exhibit two bands with a pattern (medium and strong,
in order of decreasing frequencies) indicative of the presence
of two carbonyls in a transoid arrangement.14 Indeed, this is
what we would expect for a geometry such as that found in the
solid state for 2c, labeled by us as isomer A, in which the CO
a Substituents on phosphorus are omitted for clarity.
groups define an angle of ca. 160°. In fact, the solid-state IR
spectrum of the crystals of 2c (Nujol emulsion) displays two
C-O stretching bands (1824 (s), 1791 (vs, br) cm-1), consistent
with this transoid arrangement of the CO ligands. However,
the variable-temperature NMR data for 2a (see Experimental
Section) indicate that two interconverting isomers are present
in solution. Thus, the 31P NMR spectrum of 2a at room
temperature shows one set of averaged signals (Table 2) that,
on lowering the temperature, gives the two sets attributed to
isomers A and B.15 The major isomer A presumably corresponds
to the structure found for 2c in the crystal: that is, with the
carbonyls trans and cis, respectively, to the hydride bridge and
the phosphorus ligands arranged mutually trans (Chart 2). This
isomer is fluxional down to 183 K, presumably by displacement
of the hydride ligand between both sides of the average Mo2P3
plane (A and A′ in Scheme 1), then generating a false binary
axis to yield equivalent P, Cp, or CO environments. This
explains, for example, the fact that the hydride resonance at
183 K appears at -9.92 ppm (a position similar to those of
conventional [Mo2Cp2(µ-H)(µ-PRR′)(CO)4] complexes,2,10a,c
)
still as a doublet of triplets, with similar couplings (49 and 43
Hz) to all three P nuclei, in agreement with the cis arrangement
of the hydride with respect to these atoms. The dmpm compound
2b seems to exist in solution only in the form of the fluxional
1
isomer A, since it exhibits sharp H and 31P NMR resonances
at room temperature, the latter revealing a low coupling (JPP
)
10 Hz) between the phosphide and diphosphine P atoms, which
is a characteristic feature of pairs of atoms in a trans arrangement
in these types of cyclopentadienyl complexes.16,17 In contrast,
the minor isomer B in 2a behaves as a rigid asymmetric
molecule at low temperature and is proposed to be derived from
the major isomer by just exchanging the positions of the hydride
Table 2. Selected IRa and 31P{1H} NMRb Data for New Compounds
ν(CO)
1792 (m, sh), 1761 (vs)
compd
δ(µ-P)
δ(µ-P2)
[Mo2Cp2(µ-H)(µ-PCy2)(CO)2(µ-dppm)] (2a)
[Mo2Cp2(µ-H)( µ-PCy2)(CO)2(µ-dmpm)] (2b)
[Mo2Cp2(µ-H)( µ-PCy2)(CO)2(µ-tedip)] (2c)
[Mo2Cp2(µ-H)( µ-PCy2)(CO)3(κ1-dppm)] (3)
[Mo2Cp2{µ-η: κ,η: κ-HCN(p-tol)}(µ-PCy2)(CO)2] (4a)
[Mo2Cp2{µ-η: κ,η: κ-HCNtBu}(µ-PCy2)(CO)2] (4b)
[Mo2Cp2(µ-H)(µ-PCy2){CN(p-tol)}2(CO)2] (5)
[Mo2Cp2(µ-NdCHPh)( µ-PCy2)(CO)2] (6)
[Mo2Cp2(µ-NHCH2Ph)(µ-PCy2)(CO)2] (7)
162
64.3
1793 (m, sh), 1758 (vs)
160.9c
32.4c
1842 (vw, sh), 1832 (w, sh), 1811 (m, sh), 1787 (vs)
1922 (vs), 1830 (s), 1792 (m)
1853 (m, sh), 1836 (vs)
149.5,d 201.8e
180.3,d 187.9e
64.3, -23.8f
196.5f
155.7
1851 (m, sh), 1823 (vs)
155.2
2062 (w),g 2034 (w),g 1925 (s), 1840 (vs)
1874 (m), 1842 (vs)
215.7h
125.4i
1843 (m, sh), 1813 (vs)
111.6i
a Recorded in dichloromethane solution, unless otherwise stated; ν in cm-1 b Recorded in CD2Cl2 solutions at 290 K and 121.50 MHz, unless otherwise
.
stated; δ in ppm relative to external 85% aqueous H3PO4 and J in Hz. µ-P refers to the PCy2 ligand and µ-P2 to the diphosphine or diphosphite ligand.c At
81.04 MHz, JPP ) 10 Hz. d Isomers A and B in C6D6. e Isomer C. f Isomer D in C6D6, JPCP) 25 Hz. g ν(CN). h In CDCl3 at 81.04 MHz. i At 162.01 MHz.

1464 Organometallics, Vol. 26, No. 6, 2007
AlVarez et al.
and phosphide bridges (Chart 2). A similar isomerism has been
previously found by us in the cationic complexes [W2Cp2(µ-
H)(µ-PRR′)(CO)2(µ-dppm)]2+ (R ) R′ ) Ph; R ) H, R′ ) Cy)16
and [M2Cp2(µ-X)(µ-CO)(CO)2(µ-dppm)]+ (M ) Mo, W; X )
SPh, I),17 although these cations display terminal CO ligands
parallel (as opposed to trans) to each other. In agreement with
this proposal, the hydride resonance now exhibits quite different
couplings to the three P atoms (δ -8.78 ppm, JHP ) 35, 48,
and 65 Hz at 183 K). The rigid behavior of this isomer on the
NMR time scale is not surprising, because a displacement of
the bulky dicyclohexylphosphide ligand between both sides of
the average Mo2P3 plane (B and B′ in Scheme 1) could not
possibly take place without severe rearrangements.
The situation in the solutions of the tedip compound 2c is
more complex. The IR spectrum in CH2Cl2 is different from
those of the diphosphine compounds, since it exhibits weak
additional C-O stretching bands at higher frequencies. This is
due to the presence in solution of a third, very minor isomer
(C) in addition to the isomers of type A and B discussed for 2a
(Chart 2), as confirmed by the NMR data.15 Although not all
resonances of isomer C could be identified, due to its low
relative proportion, the data available are informative enough
to conclude that this rigid isomer is not in equilibrium with the
major isomers and most likely has a cis arrangement of its
carbonyl ligands, as persistently found for the aforementioned
cations [W2Cp2(µ-H)(µ-PRR′)(CO)2(µ-dppm)]2+ and [M2Cp2-
(µ-X)(µ-CO)(CO)2(µ-dppm)]+. Evidence for this proposal comes
from the presence of the noted additional C-O stretching bands
at high frequency in the IR spectrum and the strong deshielding
of the dicyclohexylphosphide P nucleus (ca. 50 ppm above the
resonances of isomers A and B). These are the main spectro-
scopic differences found between cis and trans isomers in the
dicarbonyl complexes [M2Cp2(µ-PR2)2(CO)2] (M ) Mo, W).2,18
Spectroscopic Characterization of Compound 3. The side
product formed in the reaction of hydride 1 with dppm was
satisfactorily characterized by IR and NMR spectroscopy, due
to its similarity to the tricarbonyl derivatives [Mo2Cp2(µ-H)-
(µ-PPh2)(CO)3L] (L ) P-donor ligand), previously prepared by
Mays et al. through the photochemical reaction of the tetracar-
bonyl complex [Mo2Cp2(µ-H)(µ-PPh2)(CO)4] with the corre-
sponding ligand.11c
(cis or trans) of L with respect to the bridging hydride.10c
However, the hydride ligands in isomers D and E display similar
couplings to the P nuclei, implying that the relative positions
of the coordinated phosphorus atom of dppm and the hydride
ligand are cis in both isomers (isomer D, δ -12.29 ppm, JPH
)
46, 42 Hz; isomer E, δ -11.95 ppm, JPH ) 49, 39 Hz). This is
only possible by rotating the Mo(CO)2Cp moiety so as to yield
a cis arrangement of both cyclopentadienyl groups. We must
note that the first examples of related cis/trans isomerism in
complexes of the type [Mo2Cp2(µ-H)(µ-PR2)(CO)4] have been
reported only recently,10a although a similar isomerism was
reported previously for isoelectronic thiolate-bridged species.19
The 31P NMR spectrum for the major isomer D in 3 (the
corresponding resonance for the minor isomer E could not be
identified) displays two doublets at 64.3 (κ1 P) and -23.8 ppm
(uncoordinated P atom), both resonances being in the range
expected for a κ1-dppm ligand on a dimolybdenum complex.20
However, the P-P coupling between the free and coordinated
P atoms of the diphosphine is anomalously low (25 Hz) in
comparison to the usual values measured for related molybde-
num complexes (ca. 80 Hz),20 an observation for which we can
give no satisfactory explanation at present. As for the phosphide
ligand, it exhibits no coupling to the diphosphine P atoms
(consistent with their mutual trans disposition) and appears at
a relatively high chemical shift (196.5 ppm), in agreement with
the presence of a single metal-metal bond in the molecule.2
Reactions of 1 with Isocyanides. Compounds having
unsaturated M2(µ-H)x centers are usually reactive toward nitriles
and isocyanides,3,4a,5,7b,9 to give either addition or insertion
derivatives. The insertion processes can lead to new 3e-donor
bridging ligands such as azavinylidene (µ-NdCHR), iminoacyl
(µ-η:κ-HNCR), formimidoyl (µ-η:κ-HCNR), or aminocarbyne
(µ-CNHR). Thus, it is surprising that compound 1 does not react
with neat acetonitrile or benzonitrile, even under refluxing
conditions. In contrast, reaction with 1 equiv of isocyanides CNR
(R ) p-tol, tBu) takes place rapidly at room temperature to give
the formimidoyl complexes [Mo2Cp2(µ-η,κ:η,κ-HCNR)(µ-PCy2)-
t
(CO)2] (R ) p-tol (4a), Bu (4b)), in which the formimidoyl
ligand adopts an unusual 5e-donor coordination mode (µ-η,κ:
η,κ) which renders an electron-precise dimetal center (see
below). In addition, in the reaction with CN(p-tol), a small
amount of the electron-precise diisocyanide derivative [Mo2-
Cp2(µ-H)(µ-PCy2){CN(p-tol)}2(CO)2] (5) is also formed.
Structural Characterization of Compounds 4. The structure
of compound 4b was confirmed through a single-crystal X-ray
diffraction study (Figure 2).1 The molecule displays two MoCp-
(CO) fragments in a transoid arrangement bridged by dicyclo-
hexylphosphide and tert-butylformimidoyl ligands. The latter
ligand is placed perpendicular to the dimetal centers, bonded
through both its C- and N-donor atoms, in a η,κ:η,κ coordination
mode. The arrangement of this ligand is such that the nitrogen
atom is positioned roughly trans to the phosphide bridge (N-
Mo-P ) ca. 100°) and the C atom is placed cis to this group
(C-Mo-P ) ca. 80°), close to the approximate plane where
the carbonyl ligands are placed. The geometry of 4b might thus
be related to that of the dicarbonyl complexes of type [M2Cp2-
(µ-X)(µ-Y)(µ-Z)(CO)2], having three bridging ligands, as
discussed for 2a, in which one of the bridges is close to the
plane of the carbonyls and then renders quite different carbonyl
The IR spectrum of 3 in dichloromethane shows three C-O
stretching bands similar to those reported for these tricarbonyl
1
complexes. The room-temperature H NMR spectrum in C6D6
reveals that compound 3 exhibits the two interconverting isomers
D and E in solution (Chart 3). For the complexes [Mo2Cp2(µ-
H)(µ-PPh2)(CO)3L] two isomers were also found in solution,
with their ratios being dependent on the solvent and ligand L.
These isomers were supposed to differ in the relative position
(11) Alvarez, M. A.; Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.;
Bois, C. Organometallics 1997, 16, 2581.
(12) (a) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; Jeannin, Y. J.
Organomet. Chem. 1989, 375, C23. (b) Riera, V.; Ruiz, M. A.; Villafan˜e,
F.; Bois, C.; Jeannin, Y. Organometallics 1993, 12, 124.
(13) Garc´ıa, M. E.; Melo´n, S.; Ramos, A.; Riera, V.; Ruiz, M. A.; Belletti,
D.; Graiff, C.; Tiripicchio, A. Organometallics 2003, 22, 1983.
(14) Braterman, P. S. Metal Carbonyl Spectra; Academic Press: London,
1975.
(15) A more detailed discussion of the low-temperature spectra of
compounds 2a and 2c, including pictures of the 31P{1H} NMR spectra of
2c, can be found in the Supporting Information.
(16) Alvarez, M. A.; Anaya, Y.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.
Organometallics 2004, 23, 433.
(17) (a) Alvarez, M. A.; Anaya, Y.; Garc´ıa, M. E.; Riera, V.; Ruiz, M.
A.; Vaissermann, J. Organometallics 2003, 22, 456. (b) Alvarez, M. A.;
Anaya, Y.; Garc´ıa, M. E.; Ruiz, M. A. Organometallics 2004, 23, 3950.
(18) Alvarez, M. A.; Garc´ıa, M. E.; Mart´ınez, M. E.; Ramos, A.; Ruiz,
M. A.; Sa´ez, D.; Vaissermann, J. Inorg. Chem. 2006, 45, 6965.
(19) Schollhammer, P.; Pe´tillon, F. Y.; Pichon, R.; Poder-Guillou, S.;
Talarmin, J.; Muir, K. W.; Girwood, S.-E. J. Organomet. Chem. 1995, 486,
183.
(20) (a) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; Jeannin, Y. J.
Organomet. Chem. 1990, 382, 407. (b) Garc´ıa, G.; Garc´ıa, M. E.; Melo´n,
S.; Riera, V.; Ruiz, M. A.; Villafan˜e, F. Organometallics 1997, 16, 624.

ReactiVity of [Mo2(η5-C5H5)2(µ-H)(µ-PCy2)(CO)2]
Organometallics, Vol. 26, No. 6, 2007 1465
Table 3. C-N Distances in Compounds with 5e-Donor
Formimidoyl Ligands
compd
dCN/Å
[Mo2Cp2(µ-η,κ:η,κ-HCNtBu)(µ-PCy2)(CO)2] (4b)
[Cl2(κ2-DTolF)Ta{µ-N(p-tol)}{µ-η,κ:η,κ-HCN(p-tol)}-
Ta(κ2-DTolF)2]
1.388(7)
1.43(1)22
i
[W2(η5-C5H4 Pr)2Cl4(µ-Cl)(µ-η,κ:η,κ-HNCEt)]
1.405(8)23
1.415(1)24
1.346(7)25
1.29(1)26
[Os3(µ-H)(µ3-HCNPh)(CO)9]
[Co3Cp*3(µ-H)(µ3-HCNtBu)]
[Re3(µ-H)3(µ3-HCNCy)(CO)9]-
and related iminoacyl complexes (Table 3). Moreover, this
distance is clearly above the range found for the double CdN
bonds present in 3e-donor formimidoyl ligands (µ-η:κ coordina-
tion mode, 1.21-1.32 Å).24,26-28 In line with this description,
the IR spectrum of a Nujol mull of 4b displays a medium-
intensity band at 1255 cm-1, which we assign to the N-C
stretch of the formimidoyl ligand. Taking into account that the
range of stretching frequencies for single C-N bonds in aliphatic
amines is 1220-1020 cm-1, whereas that for double CdN
Figure 2. ORTEP diagram (30% probability) of compound 4b,1
with H atoms omitted, except the formimidoyl H atom, and Cy
rings and tBu groups omitted, except the corresponding C1 atoms.
Selected bond lengths (Å) and angles (deg): Mo(1)-Mo(2) )
2.883(2), Mo(1)-P ) 2.416(2), Mo(2)-P ) 2.436(2), Mo(1)-
C(1) ) 1.959(6), Mo(1)-C ) 2.101(6), Mo(1)-N ) 2.187(4),
Mo(2)-C(2) ) 1.914(6), Mo(2)-C ) 2.115(6), Mo(2)-N )
2.157(4), C-N ) 1.388(7); C(1)-Mo(1)-Mo(2) ) 80.4(2), C(2)-
Mo(2)-Mo(1) ) 111.5(2), N-Mo(1)-P ) 100.4(1), N-Mo(1)-P
) 79.4(2).
bonds is 1690-1580 cm-1 29
we then come also to the
,
conclusion that the C-N interaction in the formimidoyl ligand
of 4b is close to a single bond.
The above description of the formimidoyl ligand in 4b as a
5e donor is further supported by the C-Mo (ca. 2.11 Å) and
N-Mo (ca. 2.17 Å) distances, which are comparable to the
reference values for single bonds between these atoms. For
example, we find only slightly shorter Mo-N distances in
related dimolybdenum derivatives displaying strongly bound 3e-
donor nitrogen bridges, such as the azavinylidene complexes
[Mo2Cp2(µ-SMe)3{µ-κ:κ-NC(Me)CH2CN}] (ca. 2.10 Å)30 and
[Mo2Cp2(µ-SMe)3(µ-κ:κ-NCHMe)] (ca. 2.08 Å)31 or the keten-
imine complexes of the type [Mo2Cp2(CO)4(µ-κ:κ,η-RNCd
CR′2)] (Mo-N ) ca. 2.06-2.19 Å).32 As for the Mo-C lengths,
these are comparable, for example, to the corresponding lengths
in related complexes having bridging carbonyl ligands over short
intermetallic bonds, such as [Mo2Cp2(µ-PPh2)2(µ-CO)]33 and
[Mo2Cp2(µ-PCy2)(µ-COEt)(µ-CO)]13 (Mo-C distances ca. 2.10
Å).
Spectroscopic data recorded in solution for compounds 4
(Table 2 and Experimental Section) are fully consistent with
the structure of 4b found in the crystal. Thus, the IR spectrum
for these complexes shows two C-O stretching bands with the
typical pattern of trans-dicarbonyls defining angles between CO
groups close to 180°,14 while their 31P NMR spectra exhibit a
resonance at ca. 155 ppm, a position comparable to those of
the phosphide resonances in the trans isomers of the electron-
precise hydrides 2a-c. The 1H NMR spectra for compounds 4
exhibit in each case two cyclopentadienyl resonances, as
expected, while the H atom of the formimidoyl ligand appears
at ca. 4 ppm with a small P-H coupling (ca. 2 Hz). These
chemical shifts are significantly lower than those found previ-
environments, one (cis to that bridge) pointing away from the
metal vector an the other one pointing toward the intermetallic
region (C-Mo-Mo angles for 4b are 80.4(2) and 111.5(2)°,
respectively). The Mo-Mo distance is quite short, 2.883(2) Å,
but it is still consistent with the presence of a single metal-
metal bond by considering that two out of the three single-atom
donors are of small covalent radii (C and N). For instance, the
intermetallic lengths in related dimolybdenum compounds
having three bridging thiolate ligands are even shorter, as found
for the cations [Mo2Cp2(µ-SMe)3(CO)2]+ (2.785 Å) and [Mo2-
Cp*2(µ-SMe)2(µ-SH)(CO)2]+ (2.772(2) Å),21 which are also
electron-precise according to the EAN formalism.
The coordination mode of the formimidoyl ligand in 4b is
very unusual for a dinuclear species. In fact, we are only aware
of one other example of a compound displaying a 5e-donor
formimidoyl ligand across a dimetal center. This is the case of
the tantalum derivative [Cl2(κ2-DTolF)Ta{µ-N(p-tol)}{µ-η,κ:
η,κ-HCN(p-tol)}(κ2-DTolF)2] (DTolF- ) N,N′-di-p-tolylfor-
mamidinate),22 in which the formimidoyl ligand is generated
after a C-N cleavage in a formamidinate group. A similar
coordination mode is also found in the iminoacyl complex [W2-
(η5-C5H4 Pr)2Cl4(µ-H)(µ-HNCEt)], obtained by protonation of
i
a nitrile-bridged precursor.23 In contrast, the coordination of a
formimidoyl ligand as a 5e donor is well documented in some
trinuclear clusters, such as [Os3(µ-H)(µ3-HCNPh)(CO)9],24 [Co3-
Cp*3(µ2-H)(µ3-HCNtBu)],25 and the anion [Re3(µ-H)3(µ3-
HCNCy)(CO)9]-.26 The C-N (formimidoyl) distance in 4b,
1.388(7) Å, is significantly shorter than the average C-N single-
bond distances in organic compounds (ca. 1.47 Å) but falls in
the range found for the aforementioned 5e-donor formimidoyl
(26) Beringhelli, T.; D’Alfonso, G.; Minoja, A.; Ciani, G.; Moret, M.;
Sironi, A. Organometallics 1991, 10, 3131.
(21) Pe´tillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Coord.
Chem. ReV. 1998, 178-180, 203.
(22) Cotton, F. A.; Daniels, L. M.; Murillo, C. A.; Wang, X. Inorg. Chem.
1997, 36, 896.
(27) Beringhelli, T.; D’Alfonso, G.; Freni, M.; Ciani, G.; Moret, M.;
Sironi, A. J. Organomet. Chem. 1990, 399, 291.
(28) Hogarth, G.; Lavender, M. H.; Shukri, K. Organometallics 1995,
14, 2325.
(23) (a) Feng, Q.; Ferrer, M.; Green, M. L. H.; McGowan, P. C.;
Mountford, P.; Mtetwa, V. S. B. J. Chem. Soc., Chem. Commun. 1991,
552. (b) Feng, Q.; Ferrer, M.; Green, M. L. H.; Mountford, P.; Mtetwa, V.
S. B. J. Chem. Soc., Dalton Trans. 1992, 1205.
(24) Adams, R. D.; Golembeski, N. M. J. Am. Chem. Soc. 1979, 101,
2579.
(29) Bellamy, L. J. The Infra-Red Spectra of Complex Molecules, 2nd
ed.; Methuen: London, 1958.
(30) Schollhammer, P.; Pichon, M.; Muir, K. W.; Pe´tillon, F. Y.; Pichon,
R.; Talarmin, J. Eur. J. Inorg. Chem. 1999, 221.
(31) Schollhammer, P.; Cabon, N.; Pe´tillon, F. Y.; Talarmin, J.; Muir,
K. W. Chem. Commun. 2000, 2137.
(25) (a) Casey, C. P.; Widenhoefer, R. A.; Hallenbeck, S. L.; Gavney,
J. A., Jr. J. Chem. Soc., Chem. Commun. 1993, 1692. (b) Casey, C. P.;
Widenhoefer, R. A.; Hallenbeck, S. L.; Hayasi, R. K.; Gavney, J. A., Jr.
Organometallics 1994, 13, 4720.
(32) Curtis, M. D.; Messerle, L.; D’Errico, J. J.; Solis, H. E.; Barcelo, I.
D.; Butler, W. M. J. Am. Chem. Soc. 1987, 109, 3603.
(33) Adatia, T.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby, P.
R. J. Chem. Soc., Dalton Trans. 1989, 1555.

1466 Organometallics, Vol. 26, No. 6, 2007
AlVarez et al.
Chart 4
Scheme 2. Reaction Pathways Proposed for the Formation
of Compounds 4 and 5
ously for compounds having 5e-donor (µ3-η,κ:η,κ or µ2-η,κ:
η,κ)22-26 or even 3e-donor (µ2-η:κ)5b,26,28,34 formimidoyl ligands,
ranging from 7 to 11 ppm. In the aforementioned tantalum
derivative having a µ2-η,κ:η,κ-formimidoyl ligand, the corre-
sponding proton resonance was not unambiguously assigned but
was located in the aromatic region (7-9 ppm).22 We interpret
this spectroscopic feature of compounds 4 as an indication of
strong coordination of the formimidoyl ligand, rendering a
pseudotetrahedral environment (sp3 hybridation) at the bridging
C atom. In agreement with this, the 13C NMR resonance for
the formimidoyl CH atom appears quite shielded (δ ca. 60 ppm),
in comparison to previously reported formimidoyl bridges: for
example, ca. 155 ppm for the tricobalt clusters [Co3Cp*3(µ-H)-
(µ3-HCNCR3)] (R3 ) Me3, Me2Et).25
Spectroscopic Characterization of Compound 5. As men-
tioned above, compound 5 is obtained as a minor product in
the reaction of the hydride 1 with p-tolyl isocyanide. The IR
spectrum of 5 shows two pairs of stretching bands in the 2200-
1600 cm-1 region. The weaker and more energetic bands at
2062 and 2034 cm-1 are due to the C-N stretches of the
isocyanide ligands, whereas the intense bands at 1925 (s) and
1840 (vs) cm-1 clearly correspond mainly to the C-O stretches
of the carbonyl ligands. The large separation (85 cm-1) and
relative intensities of the latter bands suggest that both CO
ligands are bound to the same metal center. Although no suitable
crystals of 5 could be grown to check the full conformational
details, it is likely that the cyclopentadienyl ligands are placed
in a transoid arrangement (Chart 4), as found for most complexes
of the type [M2Cp2(µ-H)(µ-PRR′)(CO)4-nLn] (M ) Mo, W; L
molecule of isocyanide and leading to the insertion products 4.
Although we have detected no intermediates in these reactions,
we can rationalize the experimental results, as depicted in
Scheme 2. The reaction would start with the coordination of a
CNR molecule to one of the metal atoms, this possibly implying
the displacement of a CO ligand into a bridging position, to
yield the unsaturated intermediate A that might reach electronic
saturation in two different ways. The obvious way would be
the incorporation of a second molecule of ligand, to give the
diisocyanide complex 5. However, on the basis of the product
distribution, we conclude that this is a slow process, at least at
low ligand concentrations. Alternatively, intermediate A would
reach electronic saturation by a change in the coordination of
its isocyanide ligand, from the terminal to the σ,π-bonded
bridging mode (B). This type of coordination has been observed
as a result of the addition of isocyanides to the triply bonded
complexes [M2Cp2(CO)2L2] (M ) Mo, W; L2 ) (CO)2,35a
dppm,35b,20b) or to the unsaturated dihydrides [Mn2(µ-H)2(CO)6-
(µ-L2)] (L2 ) dppm, tedip).4a Intermediate B now could
experience more easily the migration of the hydride ligand to
the isocyanide carbon atom (compared to a terminal ligand), to
give the unsaturated intermediate C having a formimidoyl ligand
coordinated in a 3e-donor (µ-η:κ) mode. The unsaturation of
the metal center would now induce the final rearrangement of
this ligand, to adopt the 5e-donor (µ-η,κ:η,κ) coordination mode
that ensures the electronic saturation in the major products 4.
As for the structure of compound 5, it should be noted that the
second isocyanide molecule is incorporated at the metal center
already having a coordinated isocyanide ligand, which is
unexpected on steric grounds. The observed regioselectivity,
then, can be interpreted as a thermodynamic preference that
could be related to the principle of symbiosis.36 We finally note
that a separate experiment proved that 4b does not react with a
second equivalent of isocyanide under mild conditions, this
) 2e-donor ligand).2,10 In agreement with this proposal, the 31
P
NMR spectrum of 5 exhibits a resonance at 215.7 ppm, very
close to the chemical shift measured for the parent tetracarbonyl
[Mo2Cp2(µ-H)(µ-PCy2)(CO)4] (218.8 ppm).2 The 1H spectrum
of 5 displays two resonances for the inequivalent Cp groups,
consistent with the presence of two isocyanide ligands bound
to the same metal center. The hydride resonance appears as a
doublet at -13.32 ppm, with relatively large P-H coupling (JPH
) 35 Hz), these data being similar to the corresponding data
measured for the related complexes [Mo2Cp2(µ-H)(µ-PRR′)-
(CO)3L] (L ) CO, P-donor ligand).2,10 Unexpectedly, the
inequivalent p-tolyl groups display just one methyl resonance,
which could be due to an accidental degeneracy or to the
presence of a fluxional process (not investigated) similar to those
detected for the parent tetracarbonyls [Mo2Cp2(µ-H)(µ-PRR′)-
(CO)4].2,10
Reaction Pathways for the Isocyanide Addition to Com-
pound 1. Compound 5 is the result of a double addition of the
isocyanide ligand to the triply bonded hydride 1, this leading
to the full saturation of the dimetal center, as observed in the
reaction with CO to give [Mo2Cp2(µ-H)(µ-PCy2)(CO)4].1 How-
ever, this obviously must occur in a stepwise manner and in
competition with the main pathway, requiring just a single
(35) (a) Curtis, M. D. Polyhedron 1987, 6, 759 and references therein.
(b) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Falvello, L R.;
Bois, C. Organometallics 1997, 16, 354.
(34) Evans, W. J.; Hanusa, T. P.; Meadows, J. H.; Hunter, W. E.; Atwood,
J. L. Organometallics 1987, 6, 295.
(36) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry, 4th
ed.; Harper and Row: New York, 1993; Chapter 12, p 518.

ReactiVity of [Mo2(η5-C5H5)2(µ-H)(µ-PCy2)(CO)2]
Organometallics, Vol. 26, No. 6, 2007 1467
showing the irreversible character of the insertion process
leading to the formimidoyl complexes 4.
Reaction of 1 toward Diazo Compounds and Organic
Azides. The diazo compounds N2CR2 are well-known to be the
precursors of “CR2” fragments after dinitrogen elimination,
being quite reactive toward unsaturated organic and organo-
metallic compounds. In fact, addition of N2CH2 to unsaturated
complexes having doubly bonded M2(µ-H)2 units has been
shown previously to result in the insertion of a methylene
fragment into a M-H bond to give the corresponding alkyl-
bridged “M2(µ-H)(µ-CH3)” derivatives, often exhibiting C-H-M
agostic interactions.6a,37 Surprisingly, the unsaturated hydride
1 seems to just induce the decomposition of the diazoalkanes
N2CHR (R ) H, SiMe3), since no new organometallic products
were detected in these reactions, even when one of the expected
products, the methyl complex [Mo2Cp2(µ-CH3)(µ-PCy2)(CO)2],
has been previously prepared by us through an independent route
and has a good thermal stability.13
Organic azides (RN3) often undergo reactions with transition-
metal complexes in which dinitrogen can be also extruded, thus
yielding new imido (M-NR) derivatives.38 However, the
reactions with unsaturated hydride complexes can be more
difficult to anticipate. For instance, the reactions of azides with
the unsaturated triosmium cluster [Os3((µ-H)2(CO)10] have been
studied in detail and shown to yield µ3-NR, µ2-NHR, µ2-κ1:κ1-
HNNNR, or even µ2-NdCHR′ derivatives, depending on the
nature of the substituent R and reaction conditions.3 Taking all
these precedents into account, it was of interest to examine the
behavior of the triply bonded hydride 1 toward an organic azide.
In fact, compound 1 reacts smoothly (2.5 h) at room temperature
with an excess of benzyl azide to give a mixture of two distinct
products: the azavinylidene [Mo2Cp2(µ-NdCHPh)(µ-PCy2)-
(CO)2] (6) and the amido derivative [Mo2Cp2{µ-NH(CH2Ph)}-
(µ-PCy2)(CO)2] (7) (6/7 ) 2). During our attempts to find
alternative routes to the above compounds and to better
understand the reaction pathways under operation (see below),
we found out that the above compounds could be also prepared
by reaction of the azide with the unsaturated anion [Mo2Cp2-
(µ-PCy2)(µ-CO)2]-, but now the relative proportions were
dramatically reversed (6/7 ) 0.05). Both products could be
isolated using low-temperature chromatographic techniques, and
a separate experiment indicated that compound 7 in solution
does not transform (by dehydrogenation) into 6 at room
temperature or even in refluxing toluene, in which case only a
generalized decomposition was observed.
Figure 3. ORTEP diagram (30% probability) of compound 6, with
H atoms omitted, except the azavinylidene H atom, and Cy rings
t
and Bu groups omitted, except the corresponding C1 atoms.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
Compound 6
Mo(1)-Mo(2)
Mo(1)-N(1)
Mo(2)-N(1)
N(1)-C(13)
C(13)-H(13)
2.632(1)
2.062(6)
2.084(6)
1.278(9)
0.960(8)
Mo(1)-P(1)
Mo(2)-P(1)
Mo(1)-C(1)
Mo(2)-C(2)
2.380(2)
2.388(2)
1.925(9)
1.949(9)
Mo(1)-N(1)-Mo(2)
Mo(1)-P(1)-Mo(2)
Mo(1)-N(1)-C(13)
Mo(2)-N(1)-C(13)
N(1)-C(13)-C(14)
78.8(2)
67.02(6)
134.6(6)
146.5(6)
125.4(7)
N(1)-C(13)-H(13)
C(14)-C(13)-H(13)
C(1)-Mo(1)-Mo(2)
C(2)-Mo(2)-Mo(1)
121.4(8)
113.0(7)
78.8(3)
94.9(2)
2.084(6) Å, these are similar to those found for other dimolyb-
denum compounds having an azavinylidene bridge, in the range
2.03-2.12 Å.30,31,40 The same applies to the C-N distance
(1.278(9) Å), falling in the range observed for the mentioned
compounds (1.23-1.38 Å) and being indicative of the presence
of a double CdN bond, as expected. In agreement with this,
the angles N(1)-C(13)-H(13) and N(1)-C(13)-C(14), 121.4-
(7) and 125.4(7)°, respectively, are very close to the theoretical
120° expected for an sp2-hybridized C(13) atom, while the
N(19), C(13), H(13), C(14), and Mo atoms are all essentially
in the same plane. This imposes some steric pressure on the
metal center, as the phenyl substituent at the azavinylidene
carbon points toward the cyclopentadienyl ring on the Mo(2)
atom. This is partially relieved by a slight rotation of that MoCp-
(CO) moiety, resulting in distinct CO environments, with the
carbonyl on Mo(2) pointing away from the metal center (Mo-
Mo-C ) 94.9(2)°) and that on Mo(1) pointing toward the
intermetallic region (Mo-Mo-C ) 78.8(3)°).
The spectroscopic data in solution for compound 6 (Table 2
and Experimental Section) are fully consistent with its solid-
state structure. First, the IR spectrum in CH2Cl2 shows two C-O
stretching bands with the characteristic pattern of trans-
dicarbonyls already found in compounds 2 and 4. However, its
31P NMR spectrum now displays a resonance considerably more
shielded than those in the electron-precise complexes 2 and 4.
Actually, its chemical shift (125.4 ppm) falls in the range found
for the related 32-electron compounds trans-[Mo2Cp2(µ-PCy2)-
(µ-X)(CO)2] (X ) 3e-donor ligand),2,13 all of them formally
displaying a ModMo double bond. The 1H and 13C NMR
spectra of 6 confirm the absence of symmetry elements in the
molecule derived from the presence of the rigid and intrinsically
asymmetric azaphenylvinylidene ligand, this explaining the
Structural Characterization of Compounds 6 and 7. A sin-
gle-crystal X-ray diffraction study was performed on compound
6. The molecule displays two MoCp(CO) fragments in a transoid
arrangement and bridging dicyclohexylphosphide and azaben-
zylidene ligands (Figure 3). The intermetallic distance is very
short, 2.632(1) Å (Table 4), and therefore consistent with the
formulation of a ModMo double bond for this complex on the
basis of the EAN rule. That intermetallic separation is even
shorter than those measured in the related 32-electron complexes
trans-[Mo2Cp2(µ-PPh2)2(CO)2] (2.716(1) Å)33 and trans-[Mo2-
Cp2{µ-η2:η2-C2(OMe)2}(µ-PCy2)(CNtBu)2]BF4 (2.6550(5) Å).39
This shortening effect, however, can be attributed to the fact
that nitrogen has a covalent radium smaller than those of carbon
or phosphorus. As for the Mo-N distances, 2.062(6) and
(37) (a) Beringhelli, T.; D’Alfonso, G.; Panigati, M.; Porta, F.; Mercan-
delli, P.; Moret, M.; Sironi, A. J. Am. Chem. Soc. 1999, 121, 2307. (b)
Calvert, R. B.; Shapley, J. R. J. Am. Chem. Soc. 1977, 99, 5225.
(38) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239.
(39) Alvarez, C. M.; Alvarez, M. A.; Garcia, M. E.; Garc´ıa-Vivo´, D.;
Ruiz, M. A. Organometallics 2005, 24, 4122.
(40) (a) Cabon, N.; Pe´tillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir,
K. W. Dalton Trans. 2004, 2708. (b) Herrmann, W. A.; Bell, L. K.; Ziegler,
M. L.; Pfisterer, H.; Pahl, C. J. Organomet. Chem. 1983, 247, 39.

1468 Organometallics, Vol. 26, No. 6, 2007
AlVarez et al.
Chart 5
Scheme 3. Reaction Pathways Operative in the Reactions of
a
1 with PhCH2N3
appearance of independent resonances for the Cp and carbonyl
groups, and the presence of 12 13C cyclohexyl resonances. The
1
azavinylidene ligand gives rise to highly deshielded H (9.83
ppm) and 13C NMR (168.7 ppm) resonances, both of them in
the ranges expected for these sorts of ligands.4a,41
As for compound 7, the spectroscopic data collected in
solution are informative enough to support the proposed
structure (Chart 5), even when no suitable crystals could be
grown for an X-ray diffraction study. In fact, these data are
very similar to those of 6 (Table 2 and Experimental Section)
except for the nitrogenated ligand. Thus, a trans-dicarbonyl
geometry and the presence of a 3e-donor bridge (in addition to
the dicyclohexylphosphide bridge, then yielding a 32-electron
count) is far from doubt. The presence of a benzylamido bridge
is revealed by the appearance in the 1H NMR spectrum of two
resonances (4.95 and 3.64 ppm) corresponding to a pair of
diastereotopic methylenic protons (CH2Ph), and a third one,
somewhat broad, corresponding to the N-bound proton (5.51
ppm). All other spectroscopic data are similar to those of 6 and
then needs no further discussion.
Reaction Pathways in the Formation of Compounds 6 and
7. Although no intermediates were detected in the reactions
leading to complexes 6 and 7, the experimental data available
and the studies previously carried out on the reactions of organic
azides with unsaturated metal complexes allow us to make a
reasonable proposal to explain the observed facts (Scheme 3).
Most likely, the reaction of 1 with the azide starts with the
coordination of the ligand to the dimetal center followed by
rapid insertion in the Mo-H bond, to give an intermediate
species with the bridging triazenido ligand µ-κ1:κ1-HNNNCH2-
Ph (A in Scheme 3). Stable complexes of the latter type have
been prepared by reaction of the unsaturated cluster [Os3(µ-
H)2(CO)10] with alkyl azides.42 At this stage, two distinct
pathways must be proposed to account for the formation of
compounds 6 and 7. In the first place, intermediate A could
spontaneously evolve N2 with a simultaneous 1,3-H atom shift
to give the amide complex 7. This is remarkable, since the
mentioned triazenido osmium complexes require prolonged
heating at 85 °C to experience a similar denitrogenation reaction,
which in that case yields µ3-imido clusters.42 However, in the
case of azides having electron-withdrawing substituents, reac-
tions with [Os3(µ-H)2(CO)10] yielded directly µ2-amido com-
plexes (no triazenido intermediates detected), although pro-
longed heating at 60 °C was still required. It seems therefore
that compound 1 induces denitrogenation processes on the azide
molecules more easily than the triosmium dihydride.
a Mo ≡ MoCp(CO).
through a â-elimination of hydrogen from the benzyl group to
give the dihydride derivative C, which, after an irreversible
reductive elimination of dihydrogen, would give the azavi-
nylidene 6. The unstable nature of the electron-precise imido
intermediate B is unexpected, both because it is an electron-
precise complex and also because organic azides have been often
used in the preparation of organometallic imido complexes. Very
likely, the irreversible elimination of dihydrogen is the ther-
modynamic driving force for this reaction to proceed. The
reaction of the unsaturated hydride 1 with benzyl azide seems
to be the first example of a reaction of an organometallic
compound with an azide to lead directly to an azavinylidene
derivative. The closest precedent to this behavior is found in
the triosmium azavinylidene [Os3(µ-H){µ-NdC(CH3)Ph}-
(CO)10], formed by reaction of [Os3(µ-H)2(CO)10] with N3C-
(dCH2)Ph and further thermolysis of the corresponding triaz-
enido derivative.42 However, the mechanism in that case is
different, since it does not involve the loss of hydrogen. In fact,
the dehydrogenative route leading to 6 represents an unusual
route to azavinylidene ligands, more commonly prepared by
insertion of nitriles into M-H bonds4a,5b,7h,40a,41b or nucleophilic
attack at coordinated nitriles.30,31,40a The chemical behavior of
1 toward organic azides is also different from that found for
the unsaturated dimanganese complexes [Mn2(µ-H)2(CO)6(µ-
L2)], which react with N3SiMe3 to yield the corresponding µ2-
azido derivatives,4c this implying the loss of H and SiMe3
radicals but no denitrogenation.
Alternatively, denitrogenation of the intermediate A might
occur with transfer of the H atom to the metal, to give the
imido-hydride intermediate B. The latter could then evolve
To account for the inverse product distribution found in the
reactions of the anion [Mo2Cp2(µ-PCy2)(µ-CO)2]- with benzyl
azide in the presence of water, we must first note that no
significant reaction takes place under rigorously anhydrous
conditions and that the above anion does not react itself with
water. Thus, we propose that the anion would be in a left-shifted
equilibrium with two addition products, in which the azide
(41) See for example: (a) Do¨nnecke, D.; Halbauer, K.; Imhof, W. J.
Organomet. Chem. 2004, 689, 2707. (b) Zippel, T.; Arndt, P.; Ohff, A.;
Spannenberg, A.; Kempe, R.; Rosenthal, U. Organometallics 1998, 17, 4429.
(c) He, Z.; Neibecker, D.; Lugan, N.; Mathieu, R. Organometallics 1992,
11, 817.
(42) Burgess, K.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R. J. Chem.
Soc., Dalton Trans. 1982, 2085.

ReactiVity of [Mo2(η5-C5H5)2(µ-H)(µ-PCy2)(CO)2]
Organometallics, Vol. 26, No. 6, 2007 1469
Scheme 4. Reaction Pathways Operative in the Reactions of
the Anion [Mo2Cp2(µ-PCy2)(µ-CO)2]- with PhCH2N3 in the
Presence of H2Oa
of an N-bound organic azide is expected to be quite basic. In
fact, in the reactions of the triply bonded [Mo2Cp2(CO)4] with
aryl azides, a second equivalent of azide binds to the dimetal
center, as proposed for E, while its γ-nitrogen attacks the carbon
atom of a CO ligand to finally give the dicarbonyl [Mo2Cp2-
(CO)2(NAr){µ-κ:κ,η-N3(CO)Ar}],46 and a similar behavior was
observed in the reactions of PhN3 with the triosmium clusters
[Os3(CO)10(NCR)2] (R ) Me, Ph).47 In the case of intermediate
E, this basicity must be even more pronounced due to its anionic
nature.
Concluding Remarks. In this paper we have shown that the
unsaturated hydride [Mo2Cp2(µ-H)(µ-PCy2)(CO)2] (1) does
behave as a complex having a triple intermetallic bond, which
is then able to incorporate 2e-donor atoms without compulsory
opening of the hydride bridge, as illustrated by the reactions
with the bidentate P-donors dppm, dmpm, and tedip. Transfer
of the hydride atom to the entering molecule, however, can take
place easily, as revealed by the reactions with isocyanides and
benzyl azide. In the first case, the hydride transfer generates a
formimidoyl ligand which adopts the unusual µ2-κ,η:κ,η coor-
dination mode (5e donor) in order to achieve the electronic
saturation of the dimetal center. The behavior of 1 toward benzyl
azide is different from that reported previously for other
complexes having unsaturated M2(µ-H)x centers toward organic
azides in two aspects. In the first place, loss of N2 takes place
much more easily at our dimolybdenum system, this occurring
at room temperature. Moreover, dehydrogenation between the
hydride and the benzyl substituent can also occur. It is proposed
that loss of N2 can take place in two different ways, one leading
to the amido derivative [Mo2Cp2{µ-NH(CH2Ph)}(µ-PCy2)-
(CO)2] and the other one leading, after dehydrogenation, to the
azavinylidene complex [Mo2Cp2(µ-NdCHPh)(µ-PCy2)(CO)2].
Experimental Section
a Mo ≡ MoCp(CO), except for the starting complex.
General Procedures and Starting Materials. All manipulations
and reactions were carried out under a nitrogen (99.995%)
atmosphere using standard Schlenk techniques. Solvents were
purified according to literature procedures and distilled prior to
use.48 The compounds [Mo2Cp2(µ-PCy2)(µ-CO)2]-, (Li+ salt) and
[Mo2Cp2(µ-H)(µ-PCy2)(CO)2] (1) were prepared as described
previously,13 and all other reagents were obtained from the usual
commercial suppliers and used as received, unless otherwise stated.
Petroleum ether refers to that fraction distilling in the range 65-
70 °C. Chromatographic separations were carried out using jacketed
columns cooled by tap water. Commercial aluminum oxide (activity
I, 150 mesh) was degassed under vacuum prior to use. The latter
was mixed under nitrogen with the appropriate amount of water to
reach the activity desired. IR stretching frequencies of CO ligands
were measured either in solution (using CaF2 windows) or in Nujol
mulls (using NaCl windows) and are referred to as ν(CO). Nuclear
magnetic resonance (NMR) spectra were routinely recorded at
300.13 (1H), 121.50 (31P{1H}), or 75.47 MHz (13C{1H}) at 290 K
in CD2Cl2 solutions unless otherwise stated. Chemical shifts (δ)
are given in ppm, relative to internal tetramethylsilane (1H, 13C) or
external 85% aqueous H3PO4 solutions (31P). Coupling constants
(J) are given in hertz. In the NMR spectra, “fq” stands for “false
quartet” and “Jap” stands for “apparent coupling constant”.
Reaction of Compound 1 with Bis(diphenylphosphino)-
methane (dppm). Compound 1 (0.040 g, 0.068 mmol) and dppm
molecule bridges the dimetal center through either two N atoms
or just one N atom (D and E in Scheme 4). There are some
precedents in support of these intermediates. For example, the
anionic intermediates [Fe2(µ-κ:κ-N3Ar)(µ-SR)(CO)6]- related
to D have been proposed in the reactions of [Fe2(µ-SR)(µ-CO)-
(CO)6]- with ArN3,43 and there are also examples of dinuclear
compounds having an azide ligand bridging the metal centers
by only one N atom, as is the case for the stable complexes
[IrZrCpCp*(µ-NtBu)(µ-N3Ph)]44 and the dipalladium derivative
[Pd2Cl2(dppm)2(µ-κ1-N3SO2Ar)] (Ar ) 2,4,6-C6H2-(iPr)3).45 The
presence of water causes the reaction with our dimolybdenum
anion to proceed rapidly. Thus, the next step would involve
the protonation of intermediates D and E at N atoms. In the
first case, the triazenido intermediate A would likely be obtained,
identical with that formed from the hydride 1. This intermediate,
therefore, would evolve as discussed previously to give a
mixture of compounds 6 and 7 in a 2:1 ratio. Since the
experimental ratio of products in this reaction is 1:20, then this
triazenido route must be of marginal significance. The dominant
route, surely based on more favorable kinetics, would start with
protonation at the γ-nitrogen of intermediate E, to give the
aminodiazenide intermediate F, which, upon denitrogenation,
would finally give the amido complex 7. The γ-nitrogen atom
(43) Wang, Z.-X.; Miao, S.-B.; Zhou, Z.-Y.; Zhou, X.-G. J. Organomet.
Chem. 2000, 601, 87.
(44) Hanna, T. A.; Baranger, A. M.; Bergman, R. G. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 653.
(46) Curtis, M. D.; D’Errico, J. J.; Butler, W. M. Organometallics 1987,
6, 2151.
(47) Burgess, K.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R. J. Chem.
Soc., Dalton Trans. 1982, 2119.
(45) Besenyei, G.; Pa´rka´nyi, L.; Foch, I.; Sima´ndi, L. I. Angew. Chem.,
Int. Ed. 2000, 39, 956.
(48) Armarego, W. L. F.; Chai, C. Purification of Laboratory Chemicals,
5th ed.; Butterworth-Heinemann: Oxford, U.K., 2003.

1470 Organometallics, Vol. 26, No. 6, 2007
AlVarez et al.
(0.029 g, 0.073 mmol) were stirred in CH2Cl2 (10 mL) for 2 h at
room temperature to obtain an orange reddish solution. Solvent was
then removed under vacuum, and the residue was extracted with
dichloromethane-petroleum ether (1:4). The extracts were then
chromatographed on an alumina column. Elution with the latter
mixture gave an orange fraction yielding, after removal of solvents,
the hydride complex [Mo2Cp2(µ-H)(µ-PCy2)(CO)3(κ1-dppm)] (3)
as an orange solid (0.006 g, 9%), shown (by NMR) to be an
equilibrium mixture of the two isomers D and E (D/E ) 7 at 290
K). Elution with dichloromethane-petroleum ether (1:1) gave
another orange fraction, yielding, after removal of solvents,
compound 2a as an orange solid (0.053 g, 81%), also shown (by
NMR) to be an equilibrium mixture of the two isomers A and B
(A/B ) 9 at 183 K). Compound 2a can be also prepared
quantitatively by carrying out the reaction in toluene (10 mL, 2 h)
at room temperature; under these conditions, no traces of 3 were
detected. Anal. Calcd for C49H55Mo2O2P3 (2a): C, 61.26; H, 5.77.
Found: C, 61.21; H, 6.11. Spectroscopic data for 2a are as follows.
31P{1H} NMR: δ 162.0 (s, br, µ-PCy2), 64.3 (s, br, 2P, µ-dppm).
31P{1H} NMR (162.00 MHz, 233 K): δ 161.4 (s, br, µ-PCy2), 64.3
(s, br, 2P, µ-dppm). 1H NMR: δ 7.70-6.90 (m, 20H, Ph), 4.57 (s,
br, 10H, Cp), 3.53 (s, br, 2H, CH2), 2.60-1.10 (m, 22H, Cy), -9.63
(s, br, 1H, µ-H). 13C{1H} NMR (100.63 MHz): δ 246.8 (m, CO),
give compound 2c as an orange solid (0.043 g, 93%), shown (by
NMR) to be an equilibrium mixture of isomers A-C (A/B ) 3 at
183 K, (A + B)/C ) 20 at 290 K). The crystals of isomer A used
in the X-ray study were grown by slow diffusion of a layer of
petroleum ether into a toluene solution of the complex at 253 K.
Anal. Calcd for C32H53O7P3Mo2: C, 46.05; H, 6.40. Found: C,
45.55; H, 5.97. IR ν(CO) (Nujol mull/orange crystals of isomer
A): 1824 (s), 1791 (vs, br) cm-1. Spectroscopic data for isomers
A and B are as follows. 31P{1H} NMR (C6D6, A and B): δ 180.3
(s, 2P, µ-tedip), 149.5 (s, µ-PCy2) ppm. 31P{1H} NMR (290 K, A
and B): δ 178.5 (s, br, 2P, µ-tedip), 149.8 (s, br, µ-PCy2). 31P-
{1H} NMR (183 K, A:B ≈ 3): δ 185.6, 174.8 (2 × d, JPP ≈ 95,
µ-tedip, B), 181.0 (s, 2P, µ-tedip, A), 156.5 (s, µ-PCy2, A), 147.0
1
(s, µ-PCy2, B). H NMR (C6D6, A and B): δ 5.20 (s, 10H, Cp),
4.15-3.70 (m, 4 × 2H, OCH2), 2.60-1.20 (m, 22H, Cy), 1.12 (t,
JPH ) 7, 6H, CH3), 1.04 (t, JPH ) 7, 6H, CH3), -9.85 (dt, JPH
)
1
62, 50, µ-H, 1H) ppm. H NMR (290 K, A and B): δ 5.02 (s, br,
10H, Cp), 4.20-3.80 (m, 4 × 2H, OCH2), 2.60-1.20 (m, 22H,
Cy), 1.33 (t, JPH ) 7, 6H, CH3), 1.24 (t, JPH ) 7, 6H, CH3), -10.25
(s, br, 1H, µ-H). 1H NMR (223 K, A and B): δ 5.02 (s, 10H, Cp),
-10.55 (dt, JPH ) 59, 48, 1H, µ-H). 1H NMR (183 K): δ 5.16, (s,
br, 5H, Cp, B), 4.99 (s, br, 10H, Cp, A), -10.74 (fq, JPH ) 50,
1H, µ-H, A). One cyclopentadienyl and the hydride resonance for
isomer B were obscured by those of the major isomer. 13C{1H}
143.1 (AA′X, |JCP + JCP′| ) 36, C1 Ph), 135.8 (AA′X, |JCP + JCP′
|
) 45, C1 Ph), 134.9, 131.4 (2 × s, C2 Ph), 130.2, 129.1 (2 × s, C4
Ph), 128.4, 128.2 (2 × s, C3 Ph), 88.8 (s, Cp), 52.3 (s, br, C1-Cy),
40.1 (t, JCP ) 23, PCH2), 36.7 (s, C2,6 Cy), 34.9 (d, JCP ) 2.6, C6,2
Cy), 29.4 (d, JCP ) 10, C3,5 Cy), 29.1 (d, JCP ) 9, C5,3-Cy), 27.3
(s, C4 Cy). Low-temperature data for 2a are as follows. Isomer A:
31P{1H} NMR (162.00 MHz, 174 K) δ 162.9 (s, µ-PCy2), 64.8 (s,
br, 2P, µ-dppm); 1H NMR (400.13 MHz, 183 K) δ 8.00-6.50 (m,
Ph, 20H), 4.56 (s, 10H, Cp), 3.47 (s, br, 2H, CH2), 3.00-1.00 (m,
22H, Cy), -9.92 (dt, JPH ) 49, 43, 1H, µ-H). Isomer B: 31P{1H}
NMR (162.00 MHz, 198 K) δ 153.1 (s, br, µ-PCy2), 70.6 (s, br,
1P, µ-dppm), 57.7 (s, br, 1P, µ-dppm); 31P{1H} NMR (162.00 MHz,
183 K) δ 153.1 (s, µ-PCy2), 70.6 (d, JPP ) 93, 1P, µ-dppm), 57.5
(d, JPP ) 93, 1P, µ-dppm); 1H NMR (400.13 MHz, 183 K) δ 4.79
(s, 5Η, Cp), -8.78 (ddd, JPH ) 35, 48, 65, 1H, µ-H) ppm; other
resonances for this isomer were masked by those of the major
isomer. Spectroscopic data for 3 are as follows. Isomer D: 31P-
{1H} NMR (C6D6) δ 196.5 (s, µ-PCy2), 64.3 (d, JPP ) 25, Mo-
NMR (298 K, A and B): δ 245.7 (AA′MX, fq, JCP ) 13, |JCP
+
JCP′| ) 25, CO), 88.0 (s, Cp), 61.8 (AA′X, |JCP + JCP′| ) 10, OCH2),
61.3 (AA′X, |JCP + JCP′| ) 4, OCH2), 50.0 (d, JCP ) 8, C1-Cy),
35.6 (d, JCP ) 4, C2,6-Cy), 34.6 (d, JCP ) 4, C6,2 Cy), 29.1 (d, JCP
) 11, C3,5 Cy), 28.6 (d, JCP ) 10, C5,3 Cy), 27.0 (d, JCP ) 2, C4
Cy), 16.4 (AA′X, |JCP + JCP′| ) 6, CH3), 16.1 (AA′X, |JCP + JCP′
|
) 7, CH3). 13C{1H} NMR (183 K, Cp region): δ 89.6, 86.8 (2 ×
s, Cp, B), 88.0 (s, 2 × Cp, A) ppm. Spectroscopic data for isomer
C are as follows. 1H NMR: δ 4.94, (s, 10H, Cp), -12.58 (td, JPH
) 41, 34, 1H, µ-H); other resonances obscured by those of the
major isomers. 31P{1H} NMR: δ 201.8 (s, µ-PCy2), 186.5 (s, 2P,
µ-tedip). 31P{1H} NMR (243 K): δ 201.9 (s, µ-PCy2), 187.9 (s,
2P, µ-tedip).
Reaction of Compound 1 with p-Tolyl Isocyanide. Compound
1 (0.035 g, 0.061 mmol) was stirred with CN(p-tolyl) (1.5 mL of
a 0.05 M solution in petroleum ether, 0.075 mmol) for 1 min in
dichloromethane (10 mL) to give a yellow-orange solution. Solvent
was then removed under vacuum, the residue extracted with
dichloromethane-petroleum ether (1:4), and the extract chromato-
graphed on an alumina column (activity IV). Elution with the latter
mixture gave two yellow-orange fractions which gave, after removal
of solvents, the compounds [Mo2Cp2{µ-HCN(p-tol)}(µ-PCy2)(CO)2]
(4a, 0.032 g, 75%) and [Mo2Cp2(µ-H)(µ-PCy2){CN(p-tol)}2(CO)2]
(5, 0.004 g, 7%), respectively, both as yellow-orange solids.
1
P-C-P), -23.8 (d, JPP ) 25, Mo-P-C-P); H NMR (C6D6) δ
8.15-6.80 (m, 20H, Ph), 4.60, 4.51 (2 × s, 2 × 5H, 2 × Cp),
3.62, (ABMX, JHH ) 16, JPH ) 3, 3, 1H, CH2), 3.46 (ABMX, JHH
) 16, JPH ) 9, 0, 1H, CH2), 3.10-0.90 (m, 22H, Cy), -12.29 (dd,
JPH ) 42, 46, 1H, µ-H). Isomer E: 1H NMR (C6D6) δ 4.79, 4.71
(2 × s, 2 × 5H, 2 × Cp), -11.95 (dd, JPH) 39, 49, 1H, µ-H)
ppm; other resonances for this isomer were masked by those of
the major isomer.
1
Spectroscopic data for 4a are as follows. H NMR: δ 6.91, 6.74
Preparation of [Mo2Cp2(µ-H)(µ-PCy2)(CO)2(µ-dmpm)] (2b).
Compound 1 (0.030 g, 0.052 mmol) and dmpm (12 µL, 0.074
mmol) were stirred in toluene (10 mL) for 2 min to obtain an orange
solution. Solvent was then removed under vacuum, and the residue
was washed with petroleum ether (2 × 5 mL). Removal of solvents
under vacuum gave compound 2b (0.030 g, 81%) as an orange
microcrystalline powder. Anal. Calcd for C29H47Mo2O2P3: C, 48.89;
H, 6.65. Found: C, 48.81; H, 6.31. 31P{1H} NMR (81.04 MHz):
δ 160.9 (t, JPP ) 10, µ-PCy2), 32.4 (d, JPP ) 10, 2P, µ-dmpm). 1H
NMR (200.13 MHz): δ 4.89 (d, JPH ) 0.5, 10H, Cp), 2.40-1.10
(AB, JHH ) 8, 4H, C6H4), 5.25, 5.06 (2 × s, 2 × 5H, Cp), 3.91 (d,
JPH ) 2, 1H, CHN), 2.80-0.80 (m, Cy, 22H), 2.22 (s, CH3, 3H).
13C{1H} NMR (100.63 MHz): δ 242.8 (d, JCP ) 10, CO), 238.2
(d, JCP ) 8, CO), 153.4 (s, C1 p-tol), 132.7 (s, C4 p-tol), 129.7 (s,
C2 p-tol), 123.4 (s, C3 p-tol), 93.6, 89.1 (2 × s, Cp), 60.9 (d, JCP
) 35, CHN), 49.6 (d, JCP ) 15, C1 Cy), 41.5 (d, JCP ) 8, C1 Cy),
35.9, 35.4 (2 × s, C2,6 Cy), 34.4 (d, JCP ) 4, C2,6 Cy), 32.7 (s, C2,6
Cy), 28.8, 28.1 (2 × d, JCP ) 11, C3,5 Cy), 28.5 (d, JCP ) 14,
C3,5-Cy), 28.4 (d, JCP ) 9, C3,5 Cy), 26.8, 26.7 (2 × s, C4 Cy),
1
20.9 (s, CH3). Spectroscopic data for 5 are as follows. H NMR
(m, 22H, Cy), 2.07 (t, JPH ) 8, 2H, CH2), 1.57 (AA′X3X′3, |JPH
+
(CDCl3, 200.13 MHz): δ 7.17 (d, JHH ) 8, 2H, C6H4), 7.07 (d,
JHH ) 8, 2H, C6H4), 5.33 (s, br, 5H, Cp), 5.24 (s, 5H, Cp), 2.50-
1.00 (m, Cy, 22H), 2.37 (s, 6H, CH3), -13.32 (d, JPH ) 35, 1H,
µ-H).
Preparation of [Mo2Cp2(µ-HCNtBu)(µ-PCy2)(CO)2] (4b). Com-
pound 1 (0.040 g, 0.069 mmol) in dichloromethane (10 mL) was
stirred with CNtBu (1.5 mL of a 0.05 M solution in petroleum ether,
0.075 mmol) for 1 min to give a yellow solution. Solvent was then
JP′H| ) 12, 6H, CH3), 1.42 (AA′X3X′3, |JPH + JP′H| ) 18, 6H, CH3),
-11.49 (dt, JPH ) 57, 41, 1H, µ-H) ppm.
Preparation of [Mo2Cp2(µ-H)(µ-PCy2)(CO)2(µ-tedip)] (2c).
Compound 1 (0.033 g, 0.055 mmol) and tedip (15 µL, 0.061 mmol)
were stirred in toluene (10 mL) for 5 min to obtain an orange
reddish solution. Solvent was then removed under vacuum, and
the residue was washed with petroleum ether (3 mL) at 273 K to

ReactiVity of [Mo2(η5-C5H5)2(µ-H)(µ-PCy2)(CO)2]
Organometallics, Vol. 26, No. 6, 2007 1471
Table 5. Crystal Data for Compounds 2c and 6
removed under vacuum, the residue dissolved in dichloromethane-
petroleum ether (1:4), and this solution chromatographed on an
alumina column (activity IV) at 15 °C. Elution with the same
solvent mixture gave a yellow fraction. Removal of solvents from
the latter fraction yielded compound 4b as a yellow microcrystalline
solid (0.042 g, 92%). The crystals used in the X-ray study were
grown by slow diffusion of a layer of petroleum ether into a diethyl
ether solution of the complex at 253 K. Anal. Calcd for C29H42-
Mo2NO2P: C, 52.81; H, 6.42; N, 2.12. Found: C, 52.24; H, 6.21;
N, 1.90. 1H NMR: δ 5.32, 5.27 (2 × s, 2 × 5H, Cp), 3.72 (d, JHP
) 1.5 Hz, 1H, HCN), 2.30-1.10 (m, 22H, Cy), 0.90 (s, 9H, Me).
2c
6
mol formula
mol wt
cryst syst
space group
radiation (λ, Å)
a, Å
C
32H53Mo2O7P3
C
31H38Mo2NO2P
834.53
triclinic
P1h
679.47
orthorhombic
P212121
0.710 73
9.270(2)
10.598(2)
28.384(5)
90
90
90
2788.3(9)
4
1.619
0.710 73
10.351(2)
10.879(2)
17.308(2)
91.151(2)
98.372(2)
111.963(2)
1782.4(4)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
13C{1H} NMR (C6D6): δ 242.1 (d, JCP ) 9, CO), 238.2 (d, JCP
)
Z
calcd density, g cm-3
abs coeff, mm-1
temp, K
1.555
0.882
120
8, CO), 92.3, 88.2 (2 × s, Cp), 63.6 (d, JCP ) 33, HCN), 54.0 (s,
C1 tBu), 49.3 (d, JCP ) 13, C1- Cy), 44.8 (d, JCP ) 8, C1 Cy), 35.9,
34.4, 33.6 (3 × s, C2,6 Cy), 34.1 (d, JCP ) 4, C2,6 Cy), 31.0 (s, C2
tBu), 28.9-28.1 (4 × d, C3,5 Cy), 26.9, 26.6 (2 × s, C4 Cy).
0.986
100
θ range, deg
2.03-28.33
-13, +13; -14, +14;
-23, +23
43 690
1.43-26.45
-11, +11; 0, 13;
0, 35
index ranges (h, k, l)
Reaction of Compound 1 with Benzyl Azide. Compound 1
(0.045 g, 0.078 mmol) and benzyl azide (60 µL, 0.45 mmol) were
stirred in toluene (10 mL) for 2.5 h to obtain a dark green solution.
Solvent was then removed under vacuum, the residue was extracted
with dichloromethane-petroleum ether (1:9), and the extract was
chromatographed on an alumina column (activity IV) at 233 Κ.
Elution with the latter mixture gave two green fractions. Removal
of solvents from the first fraction yielded [Mo2Cp2(µ-NdCHPh)-
(µ-PCy2)(CO)2] (6) as a green solid (0.032 g, 62%), and removal
of solvents from the second fraction yielded [Mo2Cp2(µ-NHCH2-
Ph)(µ-PCy2)(CO)2] (7), also as a green solid (0.017 g, 32%, see
below). The crystals of compound 6 used in the X-ray study were
grown by slow diffusion of a layer of petroleum ether into a toluene
solution of the complex at 253 Κ. Anal. Calcd for C31H38Mo2-
NO2P: C, 54.80; H, 5.64; N, 2.06. Found: C, 54.46; H, 5.74; N,
1.94. 1H NMR (400.13 MHz): δ 9.83 (s, 1H, CH), 7.60, 7.46, 7.27
(AA′BB′X, 5H, C6H5), 5.40 (s, 5H, Cp), 5.17 (d, JPH ) 0.5, 5H,
Cp), 2.50-1.10 (m, Cy, 22H). 13C{1H} NMR (100.63 MHz): δ
253.1 (d, JPC ) 12, CO), 247.1 (d, JPC ) 14, CO), 168.7 (s, CH),
140.4 (s, C1 Ph), 128.2, 127.3 (2 × s, C2,3 Ph), 127.8 (s, C4 Ph),
no. of rflns collected
23 736
no. of indep rflns (Rint
)
8675 (0.0782)
5937
R1 ) 0.0414,
wR2 ) 0.0694b
R1 ) 0.0871,
wR2 ) 0.0825b
1.109
5754 (0.0972)
4314
R1 ) 0.0560,
wR2 ) 0.1252c
R1 ) 0.0820,
wR2 ) 0.1366c
0.996
no. of rflns with I > 2σ(I)
R indexes (data with
I > 2σ(I))a
R indexes (all data)a
GOF
no. of restraints/params
3/589
0.877, -0.820
0/300
1.090, -1.597
∆F(max, min), e Å-3
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑w(|Fo| - |Fc| )2/∑w|Fo| ]1/2; w
2
2
2
) 1/[σ2(Fo ) + (aP)2 + bP], where P ) (Fo2 + 2Fc )/3. b a ) 0.0000, b )
5.4849. c a ) 0.0786, b ) 0.0000.
2
2
in 3 sets of 30 exposures collected in 3 different ω regions and
eventually refined against all reflections. The software SMART49
was used for collecting frames of data, indexing reflections, and
determining lattice parameters. The collected frames were then
processed for integration by the software SAINT,49 and a multiscan
absorption correction was applied with SADABS.50 Using the
program suite WinGX,51 the structures were solved by Patterson
interpretation and phase expansion and refined with full-matrix
least-squares on F2 with SHELXL97.52 A two-site disorder was
found to be present in one of the ethoxy groups of the bridging
ligand (C27 and C28); the occupancy factors given (0.65 and 0.35)
provided satisfactory refinement. All non-hydrogen atoms were
refined anisotropically, except those involved in the disorder, which
were refined isotropically because they were persistently nonpositive
definites. All hydrogen atoms were located in the Fourier map and
refined, except those of the disordered ethoxy group, which were
geometrically located. All of them were given an overall isotropic
thermal parameter.
92.0, 91.5 (2 × s, Cp), 49.5 (d, JPC ) 20, C1 Cy), 45.2 (d, JPC
)
18, C1 Cy), 35.3 (d, JPC) 2, C2,6 Cy), 35.1 (s, C2,6 Cy), 34.5 (d,
JPC ) 4, C2,6 Cy), 33.1 (s, C2,6 Cy), 28.8-28.3 (4 × d, 4 × C3,5
Cy), 26.7, 26.5 (2 × s, 2 × C4 Cy).
Preparation of [Mo2Cp2(µ-NHCH2Ph)(µ-PCy2)(CO)2] (7).
Distilled water (8 µL, 0.44 mmol) was added to a solution of the
salt Li[Mo2Cp2(µ-PCy2)(µ-CO)2] (ca. 0.05 mmol) and an excess
of benzyl azide (50 µL, 0.37 mmol) in THF (10 mL). The mixture
was stirred for 10 min to give a green brownish solution. Solvent
was then removed under vacuum, the residue was extracted with
dichloromethane-petroleum ether (1:9), and the extract was
chromatographed on an alumina column (activity IV) at 233 Κ.
Elution with the latter mixture gave a tiny pale green band
containing a small amount of 6, and then a green fraction. Removal
of solvents from the latter fraction yielded compound 7 as a green
solid (0.030 g, 88%). Anal. Calcd for C31H40Mo2NO2P: C, 54.63;
X-ray Structure Determination of Compound 6. Collection
of data, structure solution, and refinements were done as described
for 2c, except for the data collection temperature for 6 (100 K).
All non-hydrogen atoms were refined by full-matrix least squares
using anisotropic thermal parameters, except for C(1), O(1), C(3),
and C(7) atoms, as their temperature factors were persistently
nonpositive definites. All hydrogen atoms were fixed at calculated
geometric positions in the last least-squares refinements, except for
H(13), which was located in the Fourier map; however, fixing of
the positional parameters for this atom was also necessary to obtain
a convenient convergence. All hydrogen atoms were given an
overall isotropic thermal parameter. Crystal data for 2c and 6 are
given in Table 5.
1
H, 5.92; N, 2.06. Found: C, 54.31; H, 5.82; N, 1.99. H NMR
(400.13 MHz): δ 7.45-7.30 (m, 5H, C6H5), 5.51 (dd, br, JHH ) 5,
10, 1H, NH), 5.36 (s, 5H, Cp), 4.95 (dd, JHH ) 5, 13, 1H, CH),
4.84 (s, 5H, Cp), 3.64 (dd, JHH ) 10, 13, CH), 2.30-1.10 (m, 22H,
Cy). 13C{1H} NMR (100.63 MHz): δ 254.2 (d, JPC ) 14, CO),
251.7 (d, JPC ) 15, CO), 144.5 (s, C1 Ph), 128.7 (s, C2,3 Ph), 127.2
(s, C4 Ph), 89.9, 89.8 (2 × s, Cp), 73.8 (d, JPC ) 8, CH2), 48.1 (d,
JPC ) 18, C1 Cy), 46.1 (d, JPC ) 17, C1 Cy), 34.7, 34.6 (2 × d, JPC
) 3, 2 × C2,6 Cy), 34.6, 34.2 (2 × s, JPC ) 3, 2 × C2,6 Cy), 28.8-
28.4 (4 × d, 4 × C3,5 Cy), 26.7 (s, 2 × C4 Cy).
(49) SMART & SAINT Software Reference Manuals, Version 5.051
(Windows NT Version); Bruker Analytical X-ray Instruments: Madison,
WI, 1998.
(50) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction; University of Go¨ttingen, Go¨ttingen, Germany, 1996.
(51) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
X-ray Structure Determination of Compound 2c. The X-ray
intensity data for 2c were collected on a Smart-CCD-1000 Bruker
diffractometer using graphite-monochromated Mo KR radiation at
120 K. Cell dimensions and orientation matrixes were initially
determined from least-squares refinements of reflections measured
(52) Sheldrick, G. M. SHELXL97: Program for the Refinement of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany, 1997.

1472 Organometallics, Vol. 26, No. 6, 2007
AlVarez et al.
and text and figures giving a more detailed discussion of the low-
temperature spectra of compounds 2a and 2c, including the 31P-
{1H} NMR spectra of 2c. This material is available free of charge
via the Internet at http://pubs.acs.org.
Acknowledgment. We thank the MEC of Spain for a Ph.D.
grant (to A.R.) and the MCYT for financial support (No.
BQU2003-05471).
Supporting Information Available: CIF files giving crystal-
lographic data for the structural analysis of compounds 2c and 6
OM060999K