Reactivity of the unsaturated dimolybdenum anion [Mo2(η5-C5H5)2(μ-PCy2)(μ-CO)2]- towards electrophiles based on p- and d-block elements

Article abstract of DOI:10.1016/j.jorganchem.2009.09.023

The 30-electron binuclear anion [Mo₂Cp₂(μ-PCy₂)(μ-CO)₂]^- reacts with the chlorophosphite ClP(OEt)₂ or the organotin chlorides Cl₂SnPh₂ or ClSnPh₃ to give compounds of the formula trans-[Mo₂Cp₂(μ-E)(μ-PCy₂)(CO)₂], (E = P(OEt)₂, SnPh₃, SnPh₂Cl). In contrast, this anion reacts with the organosilicon chlorides ClSiR₃ (R = Ph, Me) to give unstable silyloxycarbyne-bridged complexes [Mo₂Cp₂(μ-PCy₂)(μ-COSiR₃)(μ-CO)], which rapidly hydrolyze to give the known hydride [Mo₂Cp₂(μ-H)(μ-PCy₂)(CO)₂]. Two main types of products were also observed in the reactions of the title anion with different chlorocomplexes of the transition and post-transition metals. Thus, the reactions with [MCl₂Cp₂] (M = Ti, Zr) give moisture-sensitive isocarbonyl-bridged complexes of the type [Mo₂Cp₂(μ-COMClCp₂)(μ-PCy₂)(μ-CO)]. In contrast, softer metallic electrophiles such as [AuCl(PR₃)] (R = ⁱPr, ptol) react with the anion at the dimolybdenum site to form new trimetallic clusters of the formula [AuMo₂Cp₂(μ-PCy₂)(CO)₂(PR₃)], also retaining a Mo-Mo triple bond. Subsequent reactions of the latter products with the solvate complexes [Au(PR₃)(THF)][PF₆] give the tetranuclear clusters [Au₂Mo₂Cp₂(μ-PCy₂)(CO)₂(PR₃)₂][PF₆] (Mo-Mo = 2.5674(3) A? and Au-Au = 2.7832(2) A? when R = ⁱPr). Finally, the reaction of the title anion with HgI₂ gives the pentanuclear cluster [Hg{Mo₂Cp₂(μ-PCy₂)(CO)₂}₂] or the trinuclear cluster [Mo₂Cp₂(μ-HgI)(μ-PCy₂)(CO)₂] depending on the stoichiometry being actually used for the reaction. The trinuclear species is only stable in tetrahydrofuran (THF), and decomposes to give a mixture of the dimeric species [Mo₂Cp₂(μ-HgI)(μ-PCy₂)(CO)₂]₂ along with variable amounts of the known iodide-bridged complex [Mo₂Cp₂(μ-I)(μ-PCy₂)(CO)₂].

Full text of DOI:10.1016/j.jorganchem.2009.09.023

Journal of Organometallic Chemistry 695 (2010) 36–44
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactivity of the unsaturated dimolybdenum anion
[Mo2(
g
5-C5H5)2(
l-PCy2)(
l
-CO)2]ꢀ towards electrophiles based on p- and d-block
elements
*
M. Angeles Alvarez, M. Esther García, Alberto Ramos, Miguel A. Ruiz
Departamento de Química Orgánica e Inorgánica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain
a r t i c l e i n f o
a b s t r a c t
The 30-electron binuclear anion [Mo2Cp2(l-PCy2)(l
-CO)2]ꢀ reacts with the chlorophosphite ClP(OEt)2
Article history:
Received 9 August 2009
Received in revised form 16 September
2009
Accepted 18 September 2009
Available online 27 September 2009
or the organotin chlorides Cl2SnPh2 or ClSnPh3 to give compounds of the formula trans-[Mo2Cp2-
-E)( -PCy2)(CO)2], (E = P(OEt)2, SnPh3, SnPh2Cl). In contrast, this anion reacts with the organosilicon
chlorides ClSiR3 (R = Ph, Me) to give unstable silyloxycarbyne-bridged complexes [Mo2Cp2( -PCy2)-
-COSiR3)( -CO)], which rapidly hydrolyze to give the known hydride [Mo2Cp2( -H)( -PCy2)(CO)2].
(
l
l
l
(
l
l
l
l
Two main types of products were also observed in the reactions of the title anion with different
chlorocomplexes of the transition and post-transition metals. Thus, the reactions with [MCl2Cp2]
Keywords:
Molybdenum
Gold
Metal–metal interactions
Heterometallic clusters
Carbonyl ligands
Metal carbonyl anions
(M = Ti, Zr) give moisture-sensitive isocarbonyl-bridged complexes of the type [Mo2Cp2(
ClCp2)( -PCy2)(
-CO)]. In contrast, softer metallic electrophiles such as [AuCl(PR3)] (R = iPr, ptol) react
with the anion at the dimolybdenum site to form new trimetallic clusters of the formula [AuMo2Cp2-
-PCy2)(CO)2(PR3)], also retaining a MoꢀMo triple bond. Subsequent reactions of the latter products
l-COM-
l
l
(
l
with the solvate complexes [Au(PR3)(THF)][PF6] give the tetranuclear clusters [Au2Mo2Cp2(l-PCy2)
(CO)2(PR3)2][PF6] (MoꢀMo = 2.5674(3) Å and AuꢀAu = 2.7832(2) Å when R = iPr). Finally, the reaction
of the title anion with HgI2 gives the pentanuclear cluster [Hg{Mo2Cp2(l-PCy2)(CO)2}2] or the trinuclear
cluster [Mo2Cp2(
tion. The trinuclear species is only stable in tetrahydrofuran (THF), and decomposes to give a mixture of
the dimeric species [Mo2Cp2( -HgI)( -PCy2)(CO)2]2 along with variable amounts of the known iodide-
bridged complex [Mo2Cp2( -I)( -PCy2)(CO)2].
l-HgI)(l-PCy2)(CO)2] depending on the stoichiometry being actually used for the reac-
l
l
l
l
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
posed of one
involving
r
and two d components, with the latter ones also
p
-backbonding to the bridging carbonyls [4]. In our early
Metal carbonyl anions are very useful reagents in organometal-
lic synthesis mainly due to their high nucleophilicity, which allows
them to react with a great variety of electrophiles to form new
MꢀE bonds (E = H, C, p- or d-block element) [1]. However, although
the chemistry of mono- and polynuclear metal carbonyls has been
widely explored, that of the binuclear anions having a me-
talꢀmetal bond is comparatively less developed. This is specially
so in the case of binuclear anions having multiple metalꢀmetal
bonds, of which only a few examples have been reported in the lit-
erature [2]. A few years ago we reported an efficient synthetic
report we found that this anion was reactive towards many differ-
ent electrophiles, both based in p-block and in d-block elements,
thus opening a new synthetic path to novel unsaturated deriva-
tives that might be difficult or impossible to prepare from conven-
tional (electron-precise) precursors [3]. Recently we have reported
a detailed study of the reactivity of anion 1 towards C-based elec-
trophiles RX revealing that, depending on the particular reagent
being used, three different types of products can be formed: (a) al-
kyl-bridged complexes [Mo2Cp2(
byne-bridged complexes [Mo2Cp2( -COR)(
halide-bridged complexes [Mo2Cp2(l-PCy2)(
l-PCy2)(l-R)(CO)2], (b) alkoxycar-
l
l-PCy2)(
l-CO)], and (c)
route to the dicyclohexylphosphide-bridged anion [Mo2Cp2(
l
-
l-X)(CO)2] (X = Cl, Br, I).
PCy2)(
l
-CO)2]ꢀ (1), for which a MoꢀMo triple bond must be for-
These results suggest that there are three main pathways under
operation in these reactions: (1) nucleophilic attack of the anion
through its dimetal centre, (2) nucleophilic attack through the O
atoms of the bridging carbonyls, and (3) electron transfer to the
added reagent [2].
mulated under the Effective Atomic Number (EAN) formalism
(Chart 1) [3]. Subsequent DFT calculations on this anion allowed
us to describe more precisely this multiple bond as being com-
In this paper we complete our general study of the reactivity
of the anion 1 by examining its reactions with electrophilic
* Corresponding author. Fax: +34 985103446.
E-mail address: mara@uniovi.es (M.A. Ruiz).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.09.023

M.A. Alvarez et al. / Journal of Organometallic Chemistry 695 (2010) 36–44
37
of the PCy2 group is consistent with the formulation of a double
MoꢀMo bond for 2, and is comparable to those found for other
isoelectronic compounds bearing bridging PCy2 ligands [5],
whereas the shielding of the P(OEt)2 group is comparable to that
measured for the isoelectronic complex [Mo2Cp2{
l-OP(OEt)2}-
{l
-P(OEt)2}(CO)2] [6]. It should be kept in mind, however, that
the 31P chemical shifts of diethoxyphosphide ligands are rather
insensitive to the coordination environment and metalꢀmetal
bond order in this type of binuclear carbonyl complexes [2]. Be-
sides this, the P–P coupling in 2 is quite low (19 Hz) as usually
found for unsaturated phosphide complexes displaying almost
flat M2P2 central rings, in contrast with the strong couplings
(ca. 100 Hz) found for tetracarbonyl compounds of formula
Chart 1.
molecules based on elements different from carbon, either p-block
elements (S, P, Si, Sn) or d-block ones (Ti, Zr, Au, Hg). As it will
be shown below, the multisite reactivity exhibited by 1 towards
C-based electrophiles is also found when faced to these new
electrophiles, these being incorporated either to the dimetal site,
to give heterometallic clusters with Mo2M (M = Sn, Au, Hg),
Mo2Au2 and Mo4Hg cores, or to the oxygen atom of the bridging
carbonyl ligands, this leading to rather unstable silyloxycarbyne
[Mo2Cp2(l-PR2)(l
-PR02)(CO)4], these having puckered M2P2 cen-
tral rings with no metalꢀmetal bonds [7]. The 1H NMR spectrum
of 2 exhibits a single resonance for both Cp ligands at 5.40 ppm,
but two different multiplets for the methylenic protons of the OEt
groups, as expected for a trans-dicarbonyl structure, this implying
that the metal centres are related by a C2 operation, but not by a
symmetry plane.
The synthetic route giving complex 2 can be also used to pre-
pare other mixed-phosphide derivatives of the group 6 elements,
by using the pertinent chlorophosphine (ClPCy2, ClPPh2, etc.),
and it can be considered as a synthetic alternative to methods
previously described for this sort of mixed-phosphide complexes.
The main synthetic procedure previously developed to obtain
these species is based on the photochemical treatment of the
and isocarbonyl-bridged Mo2(l3-C:C:O–CO)M complexes (M = Ti,
Zr). Some of these results were reported in our preliminary work
on the reactivity of 1 [3].
2. Results and discussion
2.1. Reactions of the anion 1 with chlorophosphines
The anionic complex 1 (Li+ salt) reacts with ClP(OEt)2 to give the
tetracarbonyl hydrides [Mo2Cp2(l-H)(l-PR2)(CO)4] with the per-
tinent primary or secondary phosphines HPR0R00 (A in Scheme
mixed-phosphide derivative trans-[Mo2Cp2(l-PCy2){l-P(OEt)2}-(CO)2]
1) [5]. An alternative route to these species is the reaction of
an electron-precise tetracarbonyl anion of the type [Mo2Cp2(l-
(2) in moderate yield (Chart 2). This compound can be
synthesized also by reacting 1 with the pyrophosphite (EtO)2PO-
P(OEt)2, and also by the reaction of the anionic complex
PR2)(CO)4]ꢀ with the pertinent chlorophosphine, followed by
decarbonylation (B in Scheme 1) [7]. A major drawback of the
latter route is the decarbonylation step of the tetracarbonyl
intermediate, only efficient in some of the cases. Our route is
to be especially useful actually in those cases where decarbony-
lation is not possible (route B) or when the corresponding
HPR0R00 reagent is not accessible (route A). Compound 2 is a good
example of the limitations derived from latter circumstance,
since the corresponding phosphonite HP(OEt)2 is not a stable
molecule.
[Mo2Cp2{l-P(OEt)2}(l
-CO)2]ꢀ [1,2] with ClPCy2, although the
yields in the latter case are lower, due to the instability of the
diethoxyphosphide-bridged anion.
Compound 2 was fully characterized by IR and NMR spectros-
copy in solution. Its IR spectrum exhibits two CꢀO stretching
bands at 1876 (m, sh) and 1848 (vs) cmꢀ1, with the pattern char-
acteristic of trans-dicarbonyl complexes and with frequencies
somewhat higher than those of the related complexes
[Mo2Cp2(l-PCy2)(l
-PRR02)(CO)2] (R = R0 = Ph, Cy; R = H, R0 = Cy)
[5], as expected from the lower basicity of the diethoxyphosphide
ligand, when compared to diaryl or dialkylphosphide ligands. The
31P NMR spectrum exhibits two doubles at very different chemi-
cal shifts, 119.5 (PCy2) and 352.1 [P(OEt)2] ppm. The 31P shielding
Scheme 1. Synthetic routes to unsaturated mixed-phosphide bridged complexes of
Chart 2.
the group 6 elements.

38
M.A. Alvarez et al. / Journal of Organometallic Chemistry 695 (2010) 36–44
2.2. Reactions of the anion 1 with organochlorides of the group 14
elements
ones (harder electrophiles) either attack the O(carbonyl) atom of
the anion (Si) or experience fast electron-transfer reactions giving
eventually the corresponding halide-bridged complexes (C and
Ge). From our previous work on the reactions of 1 with C-based
electrophiles, however, we concluded that not only the nature of
the electrophilic fragment to be added, but also that of the leaving
group (halide) might be critical for directing the reaction of the an-
ion 1 through one or another of the three main reaction pathways
under operation [2].
The lithium salt of the anionic complex 1 reacts with the silicon
chlorides ClSiR3 (R = Ph, Me) to give solutions containing the new
silyloxycarbyne-bridged complexes [Mo2Cp2(l-COSiR3)(l-PCy2)(l-CO)]
[R = Ph (3a), Me (3b)] as the major products (Chart 2). These
compounds turned out to be extremely sensitive to air and
moisture, and all attempts to isolate them as pure materials led
to their progressive decomposition. In spite of this, the available
IR and 31P NMR data are very similar to those previously
2.3. Reactions of the anion 1 with group 4 metallocene dichlorides
measured for the alkoxycarbyne complexes [Mo2Cp2(
(l-PCy2)(l-CO)] [R = Me, Et, Pr, Cy, C(O)Ph] [2,3], then indicating
l
-COR)-
i
We have also examined the reactions of the anion 1 with several
transition metal-based electrophiles. When faced to several
carbonyl halide complexes (i.e. reactions with [FeCp(CO)2Cl],
[ReBr(CO)5], [MoClCp(CO)3] or [IrCl(CO)(PPh3)2]) the anion 1 gives
a strong structural similarity. Thus, the IR spectra of compounds
3 exhibit a band in THF solution at ca. 1700 cmꢀ1, a typical fre-
quency for the CꢀO stretch of the bridging carbonyl ligand in the
mentioned carbyne complexes, whereas the chemical shifts for
the P atoms in the 31P NMR spectra, 230.8 (3a) and 220.7
(3b) ppm, compare well with the values of 223–229 ppm mea-
sured for these carbyne complexes. We should mention that, when
recording the IR spectra of compounds 3a,b in solution, a strong
band at 1837 cmꢀ1 is always observed, due to the formation of
the corresponding halide-bridged derivative [Mo2Cp2(l-X)(l-
PCy2)(CO)2], this being indicative of the occurrence of dominant
electron-transfer processes. In contrast, the reactions with the
harder and oxophilic metallocene dichlorides [MCl2Cp2] (M = Ti,
Zr) proceed very fast to give the heterometallic derivatives
[Mo2Cp2(
3). These compounds were easily hydrolyzed upon manipulation to
give the unsaturated hydride [Mo2Cp2( -H)( -PCy2)(CO)2], and
l-COMClCp2)(l-PCy2)(l-CO)] [M = Ti (5a), Zr (5b)] (Chart
the hydride derivative [Mo2Cp2(l-H)(l-PCy2)(CO)2] [2,8,9], pre-
sumably by fast hydrolysis of the silyloxycarbyne complexes with-
l
l
in the IR plates.
they could not be isolated as pure materials. However, the avail-
able IR and 31P NMR data provide strong support for the proposed
structure, strongly related to those of the silyloxy- or alkoxycar-
byne compounds discussed above. Again, a characteristic single
CꢀO stretching band at ca. 1690 cmꢀ1 in THF denotes the presence
of a single CO ligand in a bridging position. When compared to
those of compounds 3, the CꢀO stretches for compounds 5 are
ca. 10 cmꢀ1 less energetic. This difference must be taken as
significant, since the frequencies of the bridging carbonyls in this
sort of molecules are relatively insensitive to changes in the metal
environment. It seems then that the metallic fragments MCp2Cl
have an electron-withdrawing influence on the dimolybdenum
centre significantly weaker than the hard non-metal based
electrophiles (C, Si). Finally, we note that the chemical shifts for
the bridging P atoms in compounds 5 (ca. 220 ppm), are comparable
to those in compounds 3 (Table 1) or to those in the alkoxycarbyne
complexes mentioned above [2,3].
In contrast to the reactions of 1 with silicon organochlorides,
those with the tin organochlorides ClSnPh3 and Cl2SnPh2 give the
bridging stannyl complexes [Mo2Cp2(l-PCy2)(l-SnPh2X)(CO)2]
[X = Ph (4a), Cl (4b)] after 20 h and 5 min, respectively (Chart 2).
Compound 4a was obtained only in moderate yield, since signifi-
cant amounts of other by-products were also present in the crude
reaction mixture, although they could not be properly character-
ized. We also note that this complex had been previously synthe-
sized by us through the reaction of the unsaturated hydride
[Mo2Cp2(l-H)(l-PCy2)(CO)2] with HSnPh3 [8,10]. As for compound
4b, it turned out to be much more unstable than 4a, surely due to
the presence of a reactive SnꢀCl bond left in the molecule, and it
decomposes progressively upon workup, so it could not be isolated
as a pure material. The available spectroscopic data for this com-
plex, however, are very similar to those of the triphenylstannyl
compound 4a (previously characterized by X-ray diffraction meth-
ods [8,10]), and thus indicative of their structural analogy. The
spectroscopic data in solution for 4a have been discussed in detail
previously, and therefore no further analysis of the data for com-
pound 4b is needed. We should note, however, that the coordina-
tion position of the SnR3 groups in complexes 4, bridging two
metal atoms, is very unusual for triorganostannyl groups, which
usually are found terminally-bound to transition metals. To our
knowledge, there are only two other examples in the literature
with the same coordination mode for a SnR3 group, these being
Complexes 5 have a (l-C,C,O–CO) ligand connecting the three
metal atoms, which is an unusual coordination mode for a carbonyl
ligand. There are only
a
few examples in the literature of
the tin-manganese complexes [Mn2{
l-Sn:Sn,P-SnR2OP(OEt)2}{l-
P(OEt)2}(CO)6L] (R = Bu, Ph; L = CO, tertiary phosphine) [11], and
the tin–germanium compound [K(2,2,2-crypt)][Ge9(
l2-SnPh3)]
[12].
The anion 1 reacts with BrGePh3 to give the bromide-bridged
complex [Mo2Cp2( -Br)( -PCy2)(CO)2] [2] as the main product,
l
l
thus implying the operation of an effective electron-transfer mech-
anism in this case. We recall here that a similar result (formation of
the halide complex) was obtained in the reaction of 1 with ClCPh3
[2]. In contrast, the reaction of 1 with ClPbPh3 is thought to give
first a Mo2Pb compound analogous to compounds 4, then extrud-
ing ‘‘PbPh2” to give the phenyl-bridged complex [Mo2Cp2(
l-
Ph)( -PCy2)(CO)2] [9]. In summary, in the reactions with XEPh3
l
electrophiles (E = group 14 element) we observe that the heavier
elements of the group (Sn and Pb), which are softer electrophiles,
tend to bind to the dimetal center of the anion, whereas the lighter
Chart 3.

M.A. Alvarez et al. / Journal of Organometallic Chemistry 695 (2010) 36–44
39
Table 1
Selected IRa and 31P{1H} NMRb data for new compounds.
Compound
m
(CO)
dP, [J]
[Mo2Cp2(
[Mo2Cp2(
[Mo2Cp2(
[Mo2Cp2(
[Mo2Cp2(
[Mo2Cp2(
[Mo2Cp2(
[AuMo2Cp2(
[AuMo2Cp2(
[Au2Mo2Cp2(
[Au2Mo2Cp2(
l
l
l
l
l
l
l
-PCy2){
-COSiPh3)(
-COSiMe3)(
l
-P(OEt)2}(CO)2] (2)
-PCy2)( -CO)] (3a)
-PCy2)( -CO)] (3b)
1876 (m, sh), 1848 (vs)
1699d
352.1 [19]c 119.5 [19]c
230.8e,f
l
l
l
l
1700d
220.7e
-PCy2)(
-PCy2)(
l
-SnPh3)(CO)2] (4a)
1865 (m), 1809 (vs)
1887 (m, sh), 1837 (vs)d
1666
248.5 [85]g
l-SnClPh2)(CO)2] (4b)
235.7 [101]g,h
221.0h
-COTiClCp2)(
l
-PCy2)(
-PCy2)(
-PCy2)(CO)2{P(ptol)3}] (6a)
-PCy2)(CO)2(PiPr3)] (6b)
l-CO)] (5a)
-COZrClCp2)(
l
l
l
l-CO)] (5b)
1667
219.0f,h
1803 (m, sh), 1784 (vs)d
1801 (m, sh), 1780 (vs)d
1859 (m, sh), 1839 (vs)
1859 (m, sh), 1833 (vs)
1782
213.2,i 64.0i
209.4 [10].c,j,k 90.4 [10]c,j,k
244.5 [5],c 60.0 [5],c-144.2 [712]l
l
l
-PCy2)(CO)2{P(ptol)3}2][PF6] (7a)
-PCy2)(CO)2(PiPr3)2][PF6] (7b)
239.2 [4],c,m 90.7 [4],
234.9m
,
c m-144.4 [712]l,m
[HgMo4Cp4(l-PCy2)2(CO)4] (8)
[Mo2Cp2(
[Mo2Cp2(
l
l
-HgI)(l-PCy2)(CO)2] (9)
1831 (m, sh), 1798 (vs)d
1869 (m, sh), 1830 (vs)d
223.5 [268]h,n
251.4 [198]h,n
-HgI)(l-PCy2)(CO)2]2 (10)
m .
in cmꢀ1
a
b
c
Recorded in dichloromethane solution, unless otherwise stated,
Recorded in CD2Cl2 solutions at 290 K and 121.50 MHz, unless otherwise stated, d in ppm relative to external 85% aqueous H3PO4, J in Hz.
J(31P–31P).
d
e
f
In tetrahydrofuran.
In CH2Cl2/D2O.
At 81.04 MHz.
J(31P–117Sn) ꢁ J(31P–119Sn).
In tetrahydrofuran/D2O.
In C6D6.
In toluene-d8.
At 162.04 MHz.
J(31P–19F).
g
h
i
j
k
l
m
n
In CDCl3.
J(31P–199Hg).
compounds displaying this type of coordination for carbon monox-
and Tl[PF6], to give the tetranuclear clusters [Au2Mo2Cp2(l-PCy2)-
ide. In the unsaturated complex [Mo2Ti2Cp2Cp*2(
l
-C,C,O–CO)2(CO)2]
(CO)2(PR3)2][PF6] (7a,b) (Chart 3), which were much more stable
than their neutral precursors and could be fully characterized even
through X-ray diffraction methods.
[13], the MoꢀMo separation of 2.647(1) Å suggests the presence
of a double, rather than a triple intermetallic MoꢀMo bond, so
that the Ti-bound carbonyl groups seem to be behaving (as
concerning the dimolybdenum centre) as 3-electron donor
bridging carbyne ligands, rather than 2-electron donor bridging
2.5. Solution structure of compounds 6a,b
carbonyls. Other related examples are the cobalt clusters [Co3(l-
These unsaturated clusters turned out to be rather unstable,
decomposing progressively upon the usual workup, so we could
not isolate them as pure materials. Their IR spectra in THF solution
exhibit CꢀO stretching bands at ca. 1800 (m, sh) and 1780 (vs)
cmꢀ1, with the characteristic pattern of trans-dicarbonyl com-
COMClCp2)(CO)9] (M = Ti [14], Zr [15]), for which we can assume
the presence of a 3-electron donor carbyne according to the EAN
formalism. In this context, we trust that the best way to view the
Ti-bound CO ligands in compounds 5, as concerning the dimolyb-
denum centres, is as 3-electron donor bridging carbynes, which
is in good agreement with the corresponding spectroscopic data,
closely related to those of the alkoxycarbyne compounds
pounds of the type [M2Cp2(l-X)(l-Y)(CO)2]. These frequencies,
however, are some 50 cmꢀ1 lower than those of the related hydride
complex, this being consistent with the lower electronegativity of
the gold–phosphine fragment compared to the hydrogen atom. The
chemical shifts for the bridging P atoms of the PCy2 ligands (ca.
210 ppm) are lower than that in the related hydride (232.3 ppm)
and comparable to the chemical shift in the anion 1 (208.5 ppm)
[2], therefore consistent with the formulation of a MoꢀMo triple
bond for these trinuclear clusters. As for the gold-bound phos-
phine, it gives rise to a resonance at 64.0 ppm (6a) and 90.4 ppm
(6b), these being values comparable to those found in the literature
for clusters with [AuP(ptol)3] [18] or [AuPiPr3] [19] groups bridging
dimetal centres. The P–P coupling constant is negligible for 6a and
very low (10 Hz) for 6b, as expected for a coupling through three
bonds in this type of clusters [18,19]. The proton NMR spectra
are essentially consistent with the structure proposed for 6a,b,
since they both exhibit a single resonance for the Cp ligands, re-
lated through a C2 symmetry axis in the proposed structure. The
absence of any symmetry plane relating both metal centres in this
structure, however, should render inequivalent (diastereotopic)
methyl groups for the isopropyl phosphine ligand in 6b, but actu-
ally only a single resonance is observed for these groups in the
room temperature 1H NMR spectra. Either an accidental degener-
acy or a concerted exchange of the carbonyl ligands, as proposed
to occur for the related hydride complex [9], would account for this
[Mo2Cp2(l-COR)(l-PCy2)(l-CO)] [2].
2.4. Reactions of the anion 1 with gold–phosphine complexes
The isolobal relationship between the [AuPR3]+ cations and the
proton [16] gives support to the experimental finding that in many
cases the reactions of organometallic complexes with gold cations
proceed in a way similar to the corresponding protonation reac-
tions. This principle has been exploited as a general procedure
for the synthesis of heterometallic clusters of the transition metals
containing group 11 fragments [17]. Thus we might anticipate that
the anion 1 might react with the chlorocomplexes [AuCl(PR3)]
i
(R = ptol, Pr) to give unsaturated Mo2Au analogues of the hydride
complex [Mo2Cp2(l-H)(l-PCy2)(CO)2]. Indeed this reaction takes
place rapidly to give green-brownish solutions of the new hetero-
i
metallic clusters [AuMo2Cp2(l-PCy2)(CO)2(PR3)] [R = ptol (6a), Pr
(6b)] (Chart 3). Since the above unsaturated hydride still retains
some electron-donor ability for binding to other metal fragments
[8] we also examined whether the isoelectronic complexes 6 could
add further gold cations. Indeed, these trimetallic clusters react
with tetrahydrofuran solutions of [Au(PR3)(THF)][PF6] (R = ptol,
iPr), prepared ‘‘in situ” from the corresponding chloride complexes

40
M.A. Alvarez et al. / Journal of Organometallic Chemistry 695 (2010) 36–44
spectroscopic observation, although we have not studied this mat-
ter in detail.
both cases. This cationic cluster can also be viewed as two
MoCp(CO) fragments bridged by a dicyclohexylphosphide and
two Au(PiPr3) cations eventually coupled to each other. In any case,
this structure strongly resembles that of the alkyne-bridged cation
2.6. Structural characterization of compounds 7a,b
[Mo2Cp2{l- :g l
g2 2-C2(OMe)2}( -PCy2)(CNtBu)2]BF4 [20], although
the number of electrons available for intermetallic bonding is dif-
ferent. Incidentally, we note that the latter cation is also formed
by the eventual coupling of two bridging (methoxycarbyne)
ligands.
According to the EAN rule, a MoꢀMo triple bond can be
formulated for 7b, which is consistent with the experimental inter-
metallic distance of 2.5673(3) Å, a figure comparable to the values
of 2.528(2) and 2.574(1) Å measured, respectively for the neutral
Compound 7b was characterized in the solid state through an
X-ray diffraction analysis (Table 2 and Fig. 1). The cationic cluster
exhibits an almost regular tetrahedral Mo2Au2 core. The coordina-
tion sphere around both Mo atoms is completed with one Cp and
one CO ligand at each metal centre, placed in a transoid arrange-
ment, and with a PCy2 group symmetrically bridging both metals.
The P and Mo atoms are almost in the same plane as the centroid of
the AuꢀAu bond, which in turn is almost perpendicular to MoꢀMo
bond. Finally, each of the gold atoms bear a phosphine ligand, with
the P atom almost placed in the corresponding Mo2Au plane in
30-electron dimolybdenum compounds [Mo2Cp2(l-H)(l-PCy2)-(CO)2]
and [Mo2Cp2( -SnPh3)( -PCy2)(CO)2] [8]. Thus it can be concluded
l
l
that the intermetallic separations in all these electron-deficient
molecules are largely determined by the orbital interactions, with
only a modest influence of the size of the bridging atoms (H, Sn,
Au). Moreover, we note that the MoꢀMo distance in 7b is still ca.
0.1 Å shorter than that measured in the structurally related alkyne
complex mentioned above (2.6550(5) Å), this being a 32-electron
complex with a formal MoꢀMo double bond. As for the MoꢀAu
lengths we note that, because of the slight tilting of the AuꢀAu axis
away from the perpendicular to the MoꢀMo axis, there are two dif-
ferent MoꢀAu distances: Mo(1)ꢀAu(1)ꢁMo(2)ꢀAu(2)ꢁ2.83 Å, and
Mo(1)ꢀAu(2)ꢁMo(2)ꢀAu(1)ꢁ2.91 Å. These intermetallic lengths
are comparable to the average value found for the related elec-
Table 2
Selected bond lengths (Å) and angles (°) for compound 7b.
Mo(1)–Mo(2)
Mo(1)–Au(1)
Mo(1)–Au(2)
Mo(2)–Au(1)
Mo(2)–Au(2)
Au(1)–Au(2)
Mo(1)–P(3)
Mo(2)–P(3)
Au(1)–P(1)
Au(2)–P(2)
Mo(1)–C(1)
Mo(2)–C(2)
Au(1)–C(1)
2.5673(3)
2.8216(2)
2.9111(2)
2.9142(2)
2.8327(2)
2.7832(2)
2.403(1)
2.389(1)
2.311(1)
2.324(1)
1.941(3)
1.958(3)
2.584(3)
2.563(3)
61.89(1)
65.27(1)
53.15(1)
53.08(1)
64.79(2)
79.9(1)
tron-precise trinuclear cluster [AuMo2Cp2(l-PPh2)(CO)4(PPh3)],
although the asymmetry of the bridging AuPPh3 moiety in that
molecule is much higher, with the MoꢀAu lengths differing by
ca. 0.2 Å [21]. Finally, we note that the AuꢀAu distance of
2.7832(2) Å in 7b falls in the short side of the range usually found
in heterometallic clusters containing gold(I)ꢀgold(I) bonding
interactions (2.70–3.10 Å) [17]. This trend of gold atoms for bind-
ing to other gold atoms is known as ‘‘aurophilicity” and is a rele-
vant element determining the structure and physical properties
of many homo and heterometallic gold(I) compounds [22,23]. In
the case of compound 7b, by virtue of the isolobal relationship be-
tween H and the Au(PR3) fragments, we could consider this cation
as a model of a dimolybdenum cation having a bridging dihydro-
gen ligand, a coordination mode yet to be experimentally deter-
mined for the hydrogen molecule.
Au(2)–C(2)
Mo(2)–Mo(1)–Au(2)
Mo(2)–Mo(1)–Au(1)
Mo(2)–Au(1)–Mo(1)
Mo(2)–Au(2)–Mo(1)
Mo(1)–P(3)–Mo(2)
C(1)–Mo(1)–Mo(2)
C(2)–Mo(2)–Mo(1)
Mo(1)–C(1)–O(1)
Mo(2)–C(2)–O(2)
88.9(1)
169.9(2)
170.7(2)
A final feature to be noted in the structure of 7b concerns the
carbonyl ligands, which are slightly bent towards the MoꢀMo
bond as usually found for related 30-electron dimolybdenum com-
plexes [8–10], but also seem to be involved in weak semi-bridging
interactions with the gold atoms, as denoted by the relatively short
values of 2.584(3) and 2.563(3) Å for the C(1)ꢀAu(1) and
C(2)ꢀAu(2) separations, respectively, and by the moderate devia-
tion of the respective MoꢀCꢀO angles (ca. 170o) from linearity.
This feature is relatively common in heterometallic carbonyl clus-
ters containing gold–phosphine moieties [17], although it is not
clear if such interactions are of a truly bonding nature in all cases.
For instance, even stronger Cꢂ ꢂ ꢂAu interactions have been found in
the heterometallic clusters [AuMo2Cp2(l-PPh2)(CO)4(PPh3)]
[2.405(5) Å] [21], and [Au3Mn2{ -P(OEt)2}(CO)6(PPh3)3] [2.51(2)
l
and 2.56(2) Å] [24]. In the case of compound 7b, however, we trust
that these Auꢂ ꢂ ꢂC contacts are genuinely bonding in origin, since
the AuꢀAu bond is rotated by ca. 4° towards the carbonyl ligands.
In contrast, the tilting of the CꢀC bond in the structurally related
cation [Mo2Cp2{l- :g l
g2 2-C2(OMe)2}( -PCy2)(CNtBu)2]+ is ca. 12°
away from the terminal isocyanide ligands.
The IR and NMR spectra for compounds 7a,b are also in good
agreement with the solid-state structure just discussed for 7b.
Thus, the retention of the transoid arrangement of the CO ligands
is denoted by the IR spectra, both showing two CꢀO stretching
Fig. 1. ORTEP diagram (30% probability) of the cation in compound 7b, with H
i
atoms, Cy rings (except C1 atoms) and Pr groups omitted for clarity.

M.A. Alvarez et al. / Journal of Organometallic Chemistry 695 (2010) 36–44
41
bands with the characteristic pattern (of medium and strong inten-
sities, in order of decreasing frequency) of such spatial arrange-
ment. The 31P NMR spectra exhibit in each case
single
a
resonance for the gold-bound phosphine ligands, denoting the
chemical equivalence of the AuPR3 groups, while the resonance
of the phosphide ligand appears as a strongly deshielded triplet
(dP ca. 240 ppm), as invariably found for our 30-electron com-
plexes. The P–P couplings in these compounds are relatively low
(ca. 5 Hz) and comparable to those measured in the trinuclear clus-
ters 6. Finally, the 1H NMR spectra exhibits in each case a single
resonance for the Cp ligands, and for 7b displays two distinct mul-
tiplets for the diastereotopic Me groups of the isopropyl substitu-
ents, as expected for the static structure of the cation.
As suggested above, the formation of the digold cations 7 from
the neutral Mo2Au clusters 6 might be considered as a model for
the protonation of the isolobal hydride [Mo2Cp2(l-H)(l-PCy2)-
(CO)2]. Actually, the reaction of the latter hydride with HBF4 in
dichloromethane takes place very rapidly at 233 K to give a mix-
ture of several species containing hydride ligands. Unfortunately,
all of them are thermally unstable and evolve at room temperature
to give products containing no hydride ligands which could not be
fully characterized, presumably arising from the elimination of
dihydrogen in the low temperature intermediates. The formation
of compounds 7, in fact, can be rationalized by assuming for the
neutral precursors 6 an electronic structure similar to that of the
Chart 4.
diffraction methods, and that proposed for [Hg{Mn2(l-
PPh2)(CO)8}2] [27], a cluster found to be also very insoluble in or-
ganic solvents. In all these compounds, the metal atoms around
the Hg atom define a pseudotetrahedral geometry, although the an-
gles formed by the two ‘‘M2Hg” triangles can be quite different from
90°, depending on quite subtle factors. For instance, the Os6Hg clus-
isoelectronic hydride [Mo2Cp2(
determined using DFT methods [9]. According to the latter, com-
pounds 6 should have an intermetallic -bonding frontier orbital
l-H)(l-PCy2)(CO)2], previously
p
(HOMO-2 for the hydride complex) with the right shape and en-
ergy to bind an electrophile like the [Au(PR3)]+ cation approaching
the dimetal centre from the normal to the Mo2P plane (Scheme 2).
A minimum rearrangement, no doubt driven by the aurophilic
interaction thus established, would yield the final tetranuclear
clusters 7.
ters (l4-Hg)[Os3(l-PR2)(l-CO)(CO)9]2 have been found to display
quite different degrees of distortion from the ideal geometries
depending on the substituents at the (remote to Hg) phosphide li-
gands, with the angle between Os2Hg planes being 46.29(4)° when
R = Ph, and 84.93(3)° when R = iBu [28].
The IR spectrum of 8 in dichloromethane solution displays a
single band at 1782 cmꢀ1, this suggesting that both trans-dicar-
bonyl fragments of the cluster have similar metal environments.
The 1H NMR spectrum exhibits a single resonance for all the cyclo-
pentadienyl ligands of the molecule, indicative of the presence of a
symmetry element relating both dimolybdenum fragments. Unfor-
tunately, a 13C NMR spectrum could not be obtained for compound
8 due to its low solubility. Finally, its 31P NMR spectrum exhibits a
strongly deshielded resonance (234.9 ppm), as observed for all
other molecules having 30-electron dimolybdenum centres re-
ported in this work (Table 1). Because of its high electron defi-
ciency, compound 8 would be a unique example among the
2.7. Reactions of the anion 1 with ½ equivalent of HgI2
The anion 1 reacts with half an equivalent of HgI2 in THF to give
brown solutions of the pentanuclear compound [HgMo4Cp4(l-
PCy2)2(CO)4] (8) (Chart 4). This compound, quite insoluble in most
of the organic solvents, could be only characterized spectroscopi-
cally, since crystals suitable for an X-ray analysis could not be
grown. The structure proposed for 8 is based on those of previously
reported clusters having M4Hg skeletons, such as [Fe2{
(CH2OCH3)}( -CNCH3)(CNCH3)4-
-StBu)(CO)6]2Hg [25] and [{Ni2(
-dppm)}2Hg][NiCl4] [26], both of them characterized by X-ray
l-C@CH-
l
l
(l
reported clusters having a M4(l4-Hg) central core, and it could
be viewed as an Hg atom coordinated by two MoꢀMo triple bonds.
2.8. Stoichiometric reactions of the anion 1 with HgI2
When using one equivalent (instead of 0.5) of HgI2, the anion 1
reacts in THF to give the trinuclear cluster [Mo2Cp2(l-HgI)(l-
PCy2)(CO)2] (9) which, upon removal of the solvent and addition
of toluene, gives solutions containing variable amounts of the
iodide-bridged complex [Mo2Cp2(
compound formulated as the hexanuclear complex [Mo2Cp2(
HgI)( -PCy2)(CO)2]2 (10), the latter being usually obtained in min-
l-I)(l-PCy2)(CO)2] [2] and a new
l
-
l
or amounts. The characterization of compounds 9 and 10 was quite
unsatisfactory, since none of them could be obtained as pure mate-
rials, and the structures proposed for these substances are some-
what speculative (Chart 4). In the first place, since compound 9
rapidly decomposes upon removal of the solvent (THF) we cannot
rule out the possibility that 9 is actually forming an adduct with
the solvent, perhaps by coordination of a THF molecule to the Hg
atom, thus reducing the coordinative unsaturation of that metal
Scheme 2. View along the MoꢀMo axis of the interaction of the [AuPR3]+ cations
i
(R = ptol, Pr) with compounds 6 to give 7 (terminal ligands omitted for clarity).

42
M.A. Alvarez et al. / Journal of Organometallic Chemistry 695 (2010) 36–44
centre. In any case, the IR spectra for both compounds exhibit CꢀO
stretching bands with the characteristic pattern of trans-dicarbonyl
compounds. The 31P NMR spectra of these compounds (Table 1) ex-
hibit quite deshielded phosphide resonances (as invariably found
for our triply-bonded dimolybdenum complexes) displaying
199Hg couplings of 268 Hz (9) and 198 Hz (10), thus confirming
the presence of Hg atoms bound to the dimolybdenum centres.
For instance, the P–Hg coupling in the related (if electron-precise)
were measured in solution using CaF2 windows and are referred
to as (CO). Nuclear Magnetic Resonance (NMR) spectra were rou-
tinely recorded at 300.13 (1H), 121.50 (31P{1H}) or 75.47 MHz
13C{1H}), at 290 K in CD2Cl2 solutions unless otherwise stated.
m
(
For some of the most sensitive products, 31P NMR spectra were re-
corded directly using the crude reaction mixtures in non-deuter-
ated solvents. In those cases, a coaxial tube containing D2O was
immersed into the solution and the data are then given as recorded
in solvent/D2O. Chemical shifts (d) are given in ppm, relative to
internal tetramethylsilane (1H, 13C) or external 85% aqueous
H3PO4 solutions (31P). Coupling constants (J) are given in Hertz.
heterometallic cluster [Mn2(l-HgCl)(l-PPh2)(CO)8] was found to
be 258 Hz [27].
The dimerization of compound 9 to give 10 might just involve
the formation of iodide bridges, thus achieving a pseudotetrahe-
dral environment around the Hg atom. Precedents for this can be
4.1. Preparation of [Mo2Cp2(l-PCy2){l-P(OEt)2}(CO)2] (2)
found in the structures of the clusters [Os3(CO)9(l3-C2Ph)(l2-
Cl)(HgCl)]2 [29] and [Ru3(CO)9(C6H9)(HgBr)]2 [30]. However, other
Neat ClP(OEt)2 (30 L, 0.28 mmol) was added to a solution con-
l
alternative structures are possible.
taining ca. 0.07 mmol of the lithium salt of the anion 1 in tetrahydro-
furan (10 mL), and the mixture was stirred for 2 h to yield a brown
solution. After removal of the solvents under vacuum, the residue
was chromatographed through alumina (activity IV). A green frac-
tion was eluted with dichloromethane–petroleum ether (1:4) which
gave, after removal of solvents under vacuum, compound 2 as a
green microcrystalline solid (25 mg, 46%). Anal. Calc. for
C29H44Cl2Mo2O3P (2 ꢂ CH2Cl2): C, 44.58; H, 5.68. Found: C, 44.84;
H, 5.39%. 1H NMR d 5.40 (d, JPH = 0.5, Cp, 10H), 4.28, 3.98 (2 ꢃ m,
OCH2, 2 ꢃ 2H), 2.50–1.10 (m, Cy, 22H), 1.37 (t, JHH = 7, CH3, 6H).
The anion 1 also reacts easily with other binary metal halides
such as CuCl, SnCl2, and ZnCl2, to yield in most cases solutions
thought to contain the corresponding compounds of type
[Mo2Cp2(l-M)(l-PCy2)(CO)2] (M = Cu, SnCl, ZnCl) as major species,
according to the available spectroscopic data. Unfortunately, these
products also decomposed upon removal of the solvent (THF), to
give the chloride-bridged complex [Mo2Cp2(l-Cl)(l-PCy2)(CO)2]
[2] as the major organometallic species in solution.
3. Concluding remarks
4.2. Preparation of solutions of [Mo2Cp2(l-COSiPh3)(l-PCy2)(l-CO)]
(3a)
In the preceding sections we have shown that the reactions of
the unsaturated dimolybdenum anion 1 with electrophiles based
on elements different from carbon follow analogous paths to those
observed in the reactions of 1 with hydrocarbon halides, that
is, binding of the electrophile at the dimetal site, binding at the
O(carbonyl) atoms, and electron-transfer. Reactions with electrophiles
based on soft metallic elements (Sn, Au, Hg) tend to incorporate
the incoming fragment to the intermetallic region, whereas those
reactions with electrophiles based on harder or more oxophilic ele-
ments (Si, Ti, Zr) lead to the incorporation of the electrophile at the
O site of the bridging carbonyl ligands. At present, the factors
favouring the electron-transfer processes responsible for the for-
Neat ClSiPh3 (0.060 g, 0.20 mmol) was added to a solution of the
lithium salt of the anion 1 (ca. 0.06 mmol) in tetrahydrofuran
(10 mL), and the mixture was stirred for 24 h to give a red-brown
solution containing compound 3a as the major species. This com-
pound turned out to be very air- and moisture-sensitive, and it
could not be isolated nor further purified.
4.3. Preparation of solutions of [Mo2Cp2(l-COSiMe3)(l-PCy2)(l-CO)]
(3b)
Neat ClSiMe3 (20 lL, 0.20 mmol) was added to a solution of the
mation of the halide-bridged complexes [Mo2Cp2(l-X)(l-PCy2)
lithium salt of the anion 1 (ca. 0.05 mmol) in tetrahydrofuran
(10 mL), and the mixture was stirred for 5 min to give a red-brown
solution containing compound 3b as the major species. This com-
pound also turned out to be very air- and moisture-sensitive, and it
could not be isolated nor further purified.
(CO)2], a dominant process in the reactions of 1 with several Mo,
Re, Fe and Ir carbonyl halide complexes, are not clearly understood.
Finally, the fact that the anion 1 reacts with chlorophosphines to
give mixed-phosphide derivatives apparently does not fit into the
above scheme, since this would lead us to rather predict for the
phosphorus-based electrophiles a chemical behaviour comparable
to that of the silicon halides.
4.4. Preparation of [Mo2Cp2(l-SnPh3)(l-PCy2)(CO)2] (4a)
Solid ClSnPh3 (0.025 g, 0.07 mmol) was added to a solution of
the lithium salt of the anion 1 (ca. 0.05 mmol) in tetrahydrofuran
(10 mL), and the mixture was stirred for 20 h at room temperature
to give a brown solution containing compound 4a as the major
species. After removal of the solvent under vacuum, the residue
was chromatographed on an alumina column (activity IV) at
258 K. A brown-greenish fraction was eluted with dichlorometh-
ane–petroleum ether (1:8), this yielding, after removal of solvents
under vacuum, compound 4a as a brown-greenish solid (0.022 g,
46%). Spectroscopic data for this product were identical to those re-
ported for the same species in the Ref. [10].
4. Experimental
All manipulations and reactions were carried out under a nitro-
gen (99.995%) atmosphere using standard Schlenk techniques. Sol-
vents were purified according to literature procedures, and
distilled prior to use [31]. Tetrahydrofuran solutions of the Li+ salt
of the anion [Mo2Cp2(l-PCy2)(l
-CO)2]ꢀ (1) were prepared in situ
as described previously [2,3], 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 at ca. 288 K or
by a closed 2-propanol circuit, kept at the desired temperature
with a cryostat. Commercial aluminium 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
4.5. Preparation of solutions of [Mo2Cp2(l-SnClPh2)(l-PCy2)(CO)2]
(4b)
Solid Cl2SnPh2 (0.035 g, 0.10 mmol) was added to a solution of
the lithium salt of the anion 1 (ca. 0.05 mmol) in tetrahydrofuran
(10 mL) to give instantaneously a brown solution containing

M.A. Alvarez et al. / Journal of Organometallic Chemistry 695 (2010) 36–44
43
compound 4b as the major species. This compound turned out to
be very unstable, and it decomposed rapidly upon the usual work-
up (filtration, crystallization, etc.) so it could not be obtained as a
pure material.
uum and the green residue was washed with petroleum ether
(3 ꢃ 8 mL), and extracted with THF–dichloromethane (1:10). The
extracts were then filtered through alumina (activity IV) and the
solvents were removed from the filtrate to give compound 7a as
a green solid (0.043 g, 50%). Anal. Calc. for C66H74Au2F6Mo2O2P4
(7a): C, 46.01; H, 4.33. Found: C, 45.83; H, 4.17%. 1H NMR (CDCl3)
d 7.28 (dd, JPH = 12, JHH = 7, H2-Ph, 12H), 7.15 (d, JHH = 7, H3-Ph,
12H), 4.86 (s, Cp, 10H), 2.80–1.20 (m, Cy, 22H), 2.39 (s, CH3, 18H).
4.6. Preparation of solutions of [Mo2Cp2(l-COTiClCp2)(l-PCy2)(l-CO)]
(5a)
Solid [TiCl2Cp2] (0.015 g, 0.06 mmol) was added to a solution of
the lithium salt of the anion 1 (ca. 0.05 mmol) in tetrahydrofuran
(10 mL) and the mixture was stirred to give instantaneously a
black solution containing compound 5a as the major species. This
compound turned out to be highly moisture-sensitive, rapidly
4.11. Preparation of [Au2Mo2Cp2(l
-PCy2)(CO)2(PiPr3)2][PF6] (7b)
The procedure is identical to that described above for 7a but
using [AuCl(PiPr3)] (0.027 g, 0.06 mmol) instead, along with TlPF6
(0.023 g, 0.07 mmol) and a solution of 6b (ca. 0.06 mmol). In that
way, compound 7b was obtained as a green solid (0.057 g, 66%).
Anal. Calc. for C42H74Au2F6Mo2O2P4: C, 35.16; H, 5.20. Found: C,
35.03; H, 5.29%. 1H NMR d 4.94 (s, Cp, 10H), 2.75–1.25 (m, Cy,
22H), 2.53 (m, CH, 6H), 1.38, 1.37 (2 ꢃ dd, JPH = 16, JHH = 7, CH3,
2 ꢃ 18H).
reacting with trace amounts of water to give [Mo2Cp2(
PCy2)(CO)2] as the main decomposition product, so it could not
be isolated as a pure material.
(CO) (THF): 1688 cmꢀ1
l-H)(l-
m
.
4.7. Preparation of solutions of [Mo2Cp2(l-COZrClCp2)(l-PCy2)(l-
CO)] (5b)
Solid [ZrCl2Cp2] (0.040 g, 0.14 mmol) was added to a solution of
the lithium salt of the anion 1 (ca. 0.05 mmol) in tetrahydrofuran
(10 mL), and the mixture was stirred for 20 min to give a red-
brown solution containing compound 5b as the major species,
along with variable amounts of [Mo2Cp2(l-H)(l-PCy2)(CO)2], the
latter being formed by the hydrolysis of the former. This compound
4.12. Preparation of [HgMo4Cp4(l-PCy2)2(CO)4] (8)
Solid HgI2 (0.011 g, 0.024 mmol) was added to a solution
(10 mL) of the lithium salt of the anion 1 (ca. 0.05 mmol) in tetra-
hydrofuran (10 mL) to give instantaneously a brown suspension.
After removal of the solvent under vacuum, the brown residue
was extracted with dichloromethane–petroleum ether (1:1) and
the extracts were filtered through alumina (activity IV). Removal
of solvents from the filtrate gave compound 8 as a brown micro-
crystalline solid (0.030 g, 85%). Anal. Calc. for C48H64HgMo4O4P2:
C, 42.66; H, 4.77. Found: C, 42.95; H, 5.12%. 1H NMR (CDCl3) d
5.18 (s, Cp, 20H), 2.50–1.00 (m, Cy, 44H).
also is highly moisture-sensitive, so it could not be isolated as a
pure material.
m
(CO) (THF): 1692 cmꢀ1
.
4.8. Preparation of [AuMo2Cp2(
l-PCy2)(CO)2{P(ptol)3}] (6a)
Solid [AuCl{P(ptol)3}] (0.027 g, 0.05 mmol) was added to a solu-
tion of the lithium salt of the anion 1 (ca. 0.05 mmol) in tetrahydro-
furan (10 mL) to give instantaneously a brown solution. After
removal of the solvent under vacuum, the residue was extracted
with toluene–petroleum ether (1:1) and the extract was filtered
using a cannula. The solvents were then removed under vacuum
to give a brown-greenish solid containing 6a as the major product.
All attempts to further purify this material resulted in its progres-
sive decomposition. 1H NMR (C6D6) d 7.60 (dd, JPH = 11, JHH = 8, H2-
Ph, 6H), 6.91 (d, JHH = 8, H3-Ph, 6H), 5.09 (s, Cp, 10H), 2.65–1.20 (m,
Cy, 22H), 1.97 (s, CH3, 9H).
4.13. Stoichiometric reaction of 1 with HgI2
Solid HgI2 (0.022 g, 0.048 mmol) was added to a solution of the
lithium salt of the anion 1 (ca. 0.05 mmol) in tetrahydrofuran
(10 mL) to give instantaneously a brown solution of the unstable
cluster [Mo2Cp2(l-HgI)(l-PCy2)(CO)2] (9). After removal of the sol-
vent under vacuum, the brown residue was extracted with toluene
(2 ꢃ 10 mL) and filtered through diatomaceous earth to give a
green solution containing variable amounts of [Mo2Cp2(l-I)-
(l-PCy2)(CO)2] [2] and [Mo2Cp2(l-HgI)(l-PCy2)(CO)2]2 (10). All
4.9. Preparation of [AuMo2Cp2(
l
-PCy2)(CO)2(PiPr3)] (6b)
attempts to isolate compound 10 as a pure material were unsuc-
cessful. Data for compound 10: 1H NMR d 5.04 (s, Cp, 20H); the
resonances corresponding to the Cy groups were overlapped with
Solid [AuCl(PiPr3)] (0.024 g, 0.06 mmol) was added to a solution
of the lithium salt of the anion 1 (ca. 0.06 mmol) in tetrahydrofuran
(10 mL) to give instantaneously a brown solution. After removal of
the solvent under vacuum, the residue was washed with petro-
leum ether (2 ꢃ 10 mL) and extracted with toluene (2 ꢃ 7 mL).
The extracts were filtered using a cannula and the solvent was then
removed from the filtrate to give a brown solid containing com-
pound 6b as the major product. All attempts to further purify this
material resulted in its progressive decomposition. 1H NMR
(400.13 MHz, tol-d8) d 4.99 (s, Cp, 10H), 2.60–1.20 (m, Cy, 22H),
1.78 (m, CH, 3H), 0.98 (dd, JPH = 15, JHH = 7, CH3, 18H).
those of [Mo2Cp2(
d 255.6 (s,
-PCy2).31P{1H} NMR (THF/D2O) d 251.4 (s, JP–199Hg
198, -PCy2).
l-I)(l
-PCy2)(CO)2]. 31P{1H} NMR (121.52 MHz):
l
=
l
4.14. X-ray structure determination of compound 7b
Crystals suitable for X-ray diffraction analysis were obtained by
the slow diffusion of a layer of petroleum ether into a saturated
solution of the compound in dichloromethane at room tempera-
ture. The X-ray intensity data were collected on a Kappa-Appex-II
Bruker diffractometer using graphite-monochromated Mo
Ka
4.10. Preparation of [Au2Mo2Cp2(
l
-PCy2)(CO)2{P(ptol)3}2][PF6] (7a)
radiation. The software APEX [32] was used for collecting frames
with the omega/phi scans measurement method. The collected
frames were then processed for integration by the software SAINT
[33], and a multi-scan absorption correction was applied with
SADABS [34]. Using the program suite WINGX [35] the structure was
solved by Patterson interpretation and phase expansion, and
refined with full-matrix least squares on F2 with SHELXL97 [36].
The cation of the compound was found to have all isopropyl groups
attached to P(1) and the cyclopentadienyl ligand bound to Mo(2)
A solution of [Au{P(ptol)3}(THF)][PF6] was prepared in situ by
stirring a mixture of TlPF6 (0.017 g, 0.05 mmol) and [AuCl{P(ptol)3}]
(0.027 g, 0.05 mmol) in tetrahydrofuran (5 mL) for 10 min. The
solution was filtered using a cannula and added to a crude
solution of 6a (ca. 0.05 mmol, prepared as described above) in tet-
rahydrofuran (5 mL), and the mixture was then stirred for 5 min to
give a green solution. The solvent was then removed under vac-

44
M.A. Alvarez et al. / Journal of Organometallic Chemistry 695 (2010) 36–44
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Tiripicchio, Organometallics 22 (2003) 1983.
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(2007) 4930.
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(2007) 6197.
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5374.
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3527.
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Comprehensive Organometallic Chemistry, vol. 6, Pergamon, Oxford, UK, 1982
(Chapter 40);
Crystal data for compound 7b.
Molecular formula
Molecular weight
Crystal system
Space group
Radiation (k, Å)
a (Å)
C42H74Au2F6Mo2O2P4
1434.71
Triclinic
ꢀ
P1
0.71073
9.8068(2)
14.5526(2)
17.6160(3)
88.869(1)
77.136(1)
83.474(1)
2435.04(7)
2
1.957
b, (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc, g cmꢀ3
Absorption coefficient (mmꢀ1
Temperature (K)
h Range (°)
)
6.697
120
1.19–28.32
ꢀ12, 13; ꢀ19, 19; 0, 23
66464
Index ranges (h, k, l)
Reflections collected
Independent reflections
12065 [Rint = 0.0410]
10610
Reflection with I > 2
R indexes (I > 2
(I))a
R indexes (all data)a
r(I)
r
R1 = 0.0219, wR2 = 0.0438b
R1 = 0.0276, wR2 = 0.0453b
1.063
(b) I.D. Salter, Adv. Organomet. Chem. 29 (1989) 249;
(c) D.M.P. Mingos, M.J. Watson, Adv. Inorg. Chem. 39 (1992) 327;
(d) I.D. Salter, in: E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.), Comprehensive
Organometallic Chemistry, second ed., vol. 10, Pergamon, Oxford, UK, 1995
(Chapter 5).
Goodness-of-fit (GOF)
Restraints/parameters
0/528
1.063, ꢀ1.186
D
q
(maximum, minimum), e Åꢀ3
a
R1
=
R
||Fo|ꢀ|Fc||/
R
|Fo|, wR2 = [
R
w(|Fo|2ꢀ|Fc|2)2/
R r +
w|Fo|2]1/2; w = 1/[ 2(Fo2) + (aP)2
[18] (a) X.-Y. Liu, V. Riera, M.A. Ruiz, M. Lanfranchi, A. Tiripicchio, Organometallics
22 (2003) 4500;
bP] where P = (Fo2 + 2Fc2)/3.
b
a = 0.0161, b = 1.1672.
(b) X.-Y. Liu, V. Riera, M.A. Ruiz, Organometallics 13 (1994) 2925;
(c) R. Carreño, V. Riera, M.A. Ruiz, A. Tiripicchio, M. Tiripicchio-Camellini,
Organometallics 13 (1994) 993.
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(2004) 4750;
(b) E. Delgado, B. Donnadieu, M.E. García, S. García, M.A. Ruiz, F. Zamora,
Organometallics 21 (1992) 780.
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Organometallics 24 (2005) 4122;
(b) M.E. García, D. García-Vivó, M.A. Ruiz, Organometallics 27 (2008) 543.
[21] H. Hartung, B. Walter, U. Baumeister, H.-C. Bötcher, A. Krug, F. Rosche, P.G.
Jones, Polyhedron 11 (1992) 1563.
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Chem., Int. Ed. Engl. 27 (1988) 1544.
disordered in two positions. Occupancy factors of 0.5/0.5 and
0.65/0.35 gave a reasonable fit. All non-hydrogen atoms were
refined anisotropically, except the disordered carbon atoms, which
were refined isotropically. Hydrogen atoms were fixed at calculated
positions and were given an overall isotropic thermal parameter.
Crystallographic data and structure refinement details for 7b are
collected in Table 3.
[23] (a) H. Schmidbaur, Gold Bull. 33 (2000) 3;
Acknowledgements
(b) P. Pyykkö, Angew. Chem., Int. Ed. 43 (2004) 4412;
(c) P. Pyykkö, Inorg. Chim. Acta 358 (2005) 4413.
[24] X.-Y. Liu, V. Riera, M.A. Ruiz, A. Tiripicchio, M. Tiripicchio-Camellini,
Organometallics 15 (1996) 974.
[25] D. Seyferth, D.P. Ruschke, W.M. Davis, M. Cowie, A.D. Hunter, Organometallics
13 (1994) 3834.
We thank the MEC of Spain for a grant (to A.R.) and financial
support (projects BQU2003-05471 and CTQ2006-01207/BQU).
Appendix A. Supplementary data
[26] J. Gong, J. Huang, P.E. Fanwick, C.P. Kubiak, Angew. Chem., Int. Ed. Engl. 29
(1990) 396.
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[31] W.L.F. Armarego, C. Chai, Purification of Laboratory Chemicals, fifth ed.,
Butterworth-Heinemann, Oxford, UK, 2003.
[32] APEX 2, version 2.0-1; Bruker AXS Inc., Madison, Wisconsin, USA, 2005.
CCDC 743404 contains the supplementary crystallographic data
for compound 7b. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.jorganchem.2009.09.023.
[33] SMART
& SAINT Software Reference Manuals, Version 5.051 (Windows NT
Version), Bruker Analytical X-ray Instruments, Madison WI, 1998.
[34] G.M. Sheldrick, SADABS, Program for Empirical Absorption Correction, University
of Göttingen, Göttingen, Germany, 1996.
References
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