Binuclear carbyne and ketenyl derivatives of the alkyl-bridged complexes [Mo2(η5-C5H5) 2(μ-CH2R)(μ-PCy2)(CO)2] (R = H, Ph)

Article abstract of DOI:10.1021/om1011819

The 30-electron benzylidyne complex [Mo₂Cp₂(μ-CPh) (μ-PCy₂)(μ-CO)] (Cp = η⁵-C₅H ₅) could be conveniently prepared upon photolysis of the benzyl-bridged complex [Mo₂Cp₂(μ-CH₂Ph) (μ-PCy₂)(CO)₂]. It reacted with CO to give the ketenyl complex [Mo₂Cp₂{μ-C(Ph)CO}(μ-PCy₂)(CO) ₂] (2.6101(2) A), which in turn could be selectively decarbonylated at 353 K to give the 32-electron benzylidyne derivative [Mo ₂Cp₂(μ-CPh)(μ-PCy₂)(CO)₂] (Mo-Mo = 2.666(1) A). Related methylidyne complexes could be obtained from the methyl-bridged complex [Mo₂Cp₂(μ-CH ₃)(μ-PCy₂)(CO)₂] via its trinuclear derivative [Mo₃Cp₂(μ₃-CH)(μ-PCy ₂)(CO)₇]. Thus, the carbonylation of the latter cluster gave the ketenyl complex [Mo₂Cp₂{μ-C(H)CO}(μ- PCy₂)(CO)₂], whereas its reaction with P(OMe)₃ gave the substituted cluster [Mo₃Cp₂(μ₃-CH) (μ-PCy₂)(CO)₆{P(OMe)₃}], which in turn could be thermally degraded to give selectively the 30-electron methylidyne derivative [Mo₂Cp₂(μ-CH)(μ-PCy₂)(μ-CO) ] (Mo-Mo = 2.467(1) A). DFT calculations on the phenylketenyl complex revealed that the metal-ligand interaction is intermediate between the extreme descriptions represented by the acylium (3-electron donor) and ketenyl (1-electron donor) canonical forms of this ligand.

Full text of DOI:10.1021/om1011819

ARTICLE
pubs.acs.org/Organometallics
Binuclear Carbyne and Ketenyl Derivatives of the Alkyl-Bridged
Complexes [Mo2(η5-C5H5)2(μ-CH2R)(μ-PCy2)(CO)2] (R = H, Ph)
M. Angeles Alvarez, M. Esther García, Daniel García-Vivꢀo, M. Eugenia Martínez, and Miguel A. Ruiz*
Departamento de Química Orgꢀanica e Inorgꢀanica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain
S Supporting Information
b
ABSTRACT: The 30-electron benzylidyne complex
[Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (Cp = η5-C5H5) could
be conveniently prepared upon photolysis of the benzyl-bridged
complex [Mo2Cp2(μ-CH2Ph)(μ-PCy2)(CO)2]. It reacted with
CO to give the ketenyl complex [Mo2Cp2{μ-C(Ph)CO}(μ-
PCy2)(CO)2] (2.6101(2) Å), which in turn could be selectively decarbonylated at 353 K to give the 32-electron benzylidyne
derivative [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] (MoꢀMo = 2.666(1) Å). Related methylidyne complexes could be obtained from
the methyl-bridged complex [Mo2Cp2(μ-CH3)(μ-PCy2)(CO)2] via its trinuclear derivative [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)7].
Thus, the carbonylation of the latter cluster gave the ketenyl complex [Mo2Cp2{μ-C(H)CO}(μ-PCy2)(CO)2], whereas its reaction
with P(OMe)3 gave the substituted cluster [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)6{P(OMe)3}], which in turn could be thermally
degraded to give selectively the 30-electron methylidyne derivative [Mo2Cp2(μ-CH)(μ-PCy2)(μ-CO)] (MoꢀMo = 2.467(1) Å).
DFT calculations on the phenylketenyl complex revealed that the metalꢀligand interaction is intermediate between the extreme
descriptions represented by the acylium (3-electron donor) and ketenyl (1-electron donor) canonical forms of this ligand.
’ INTRODUCTION
this Article, we give full details of the preparation and structural
characterization of compound 2 as well as some unsaturated
benzylidyne and phenylketenyl derivatives, including a DFT
analysis of the latter species, aimed to better understand the
metalꢀligand interactions in these electron-deficient molecules.
We also report that related unsaturated methylidyne- and
ketenyl-bridged complexes can be obtained from the methyl-
bridged complex 1b via its trinuclear derivative [Mo3Cp2(μ3-
CH)(μ-PCy2)(CO)7].
Recently, we reported that the photochemical treatment of the
agostic benzyl complex [Mo2Cp2(μ-CH2Ph)(μ-PCy2)(CO)2]
(1a) (Cp = η5-C5H5) promotes its partial decarbonylation and
full dehydrogenation of the alkyl ligand to give with good yield
the benzylidyne-bridged derivative [Mo2Cp2(μ-CPh)(μ-PCy2)-
(μ-CO)] (2), a reactive 30-electron carbyne complex under-
going unusual CꢀC and CꢀP coupling processes under mild
conditions.1 In contrast, the photolysis of the related methyl-
bridged complex [Mo2Cp2(μ-CH3)(μ-PCy2)(CO)2] (1b)
caused the ejection of just a CO molecule to yield a carbonyl
derivative [Mo2Cp2(μ-CH3)(μ-PCy2)(μ-CO)] having a stren-
gthened agostic interaction (Scheme 1). However, the photolysis
of 1b in the presence of several carbonyl complexes gave different
methylidyne-bridged heterometallic clusters, thus revealing the
occurrence of easy dehydrogenation steps after cluster
formation.2 The above dehydrogenation reactions are rare events
for agostic alkyl-bridged complexes. Actually, we can quote only a
couple of precedents of related μ-CH3/μ-CH transformations
involving agostic ligands, those reported to occur at room tem-
perature at Ru2 (through dehydrogenation)3a and Fe3 (through
double oxidative addition of CꢀH bonds) metal centers.3b In
addition, related μ-CH2R/μ-CH/μ-CR transformations (R =
CH2Ph) were described recently to occur at 393 K in a Ru3
cluster.4 Yet this sort of dehydrogenation reaction could provide
a useful synthetic entry to unsaturated binuclear complexes bridged
by arylcarbyne or methylidyne ligands, a type of relatively scarce
molecules that might be considered as the simplest (if crude)
models of related surface species formed in different hetero-
geneously catalyzed reactions, notably the FischerꢀTropsch
(FT) synthesis of hydrocarbons from syngas (CO þ H2).5 In
’ RESULTS AND DISCUSSION
Derivatives of the Benzyl Complex 1a. The photolysis of
toluene solutions of 1a can be carried out easily at 288 K using
visible-UV light to give with good yield the benzylidyne-bridged
derivative [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (2), the trans-
formation being complete in ca. 2 h. Although the formation of 2
is obviously a multistep process involving the eventual elimina-
tion of H2 and a molecule of CO (Scheme 1), no intermediates
could be detected in this reaction through IR and 31P NMR
monitoring of the corresponding solutions. The dehydrogena-
tion step leading to 2 is irreversible, because this product does
not react with H2 even under pressure (60 bar) at room
temperature, but the decarbonylation step is not, as expected
for a 30-electron molecule. Indeed the reaction of 2 with CO (ca.
4 bar) proceeds smoothly at room temperature (ca. 2 d for
completion), to give the ketenyl derivative [Mo2Cp2{μ-C(Ph)-
CO}(μ-PCy2)(CO)2] (3) almost quantitatively (Scheme 2). As
Received: December 18, 2010
Published: March 24, 2011
r
2011 American Chemical Society
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Scheme 1
Scheme 3
Scheme 2
(Scheme 2). On the other hand, the reaction of 4 with CO (ca. 4
bar) to give back the ketenyl complex 3 takes place readily at
room temperature in ca. 4 h, that is, faster than the carbonylation
of 2. Thus, there would be no chance to grow significant amounts
of 4 by direct carbonylation of the starting carbyne complex 2, in
agreement with our experimental results.
It might be questioned whether the carbonylation of 4 to give
the ketenyl complex 3 proceeds by direct attack of CO to the
carbyne ligand, or rather would yield initially an isomeric
tricarbonyl complex [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)3] (as ob-
served in the carbonylation of [Mo2Cp2(μ-COMe)(μ-PCy2)(μ-
CO)] mentioned above), then rearranging into its ketenyl isomer 3.
Indeed, direct attack of Lewis bases on bridging carbyne complexes
is a well-established reaction for electron-precise carbyne-bridged
cations such as [Fe2Cp2(μ-CPh)(μ-CO)(CO)2]þ and [Fe2Cp2-
(μ-CH)(μ-CO)(CO)2]þ.8,9 On the basis of the DFT study of the
isoelectronic complex [Mo2Cp2{μ-C(CO2Me)}(μ-PCy2)(CO)2],6
we could anticipate that both events are likely results of the reaction
of 4 with CO from an orbital point of view. This would be so
because the LUMO in the dicarbonyl complex has a large π*-
(MoꢀMo) character (thus expectedly favoring the formation of
the tricarbonyl derivative) while the LUMOþ1 orbital (0.96 eV
higher in energy) has a large π*(MoꢀC) character (then favoring
the direct attack of CO at the C atom to give 3). However, the
atomic charge at the carbyne atom is 0.2ꢀ0.3e more negative than
those at the Mo atoms (close to 0), and this should disfavor the
direct attack of CO at the carbyne ligand. Thus, we rather trust that
the carbonylation of 4 follows the two-step pathway outlined above.
As for the carbonylation of the carbyne complex 2, this is likely
to follow initially a reaction pathway analogous to that of
the isoelectronic diphosphide-bridged complexes of the type
discussed later, the metalꢀketenyl interaction in this molecule is
intermediate between those expected for 1- and 3-electron
donors, so we have depicted it with an intermetallic bond order
between three and two. The formation of this complex does not
involve just the addition of CO to the unsaturated dimetal center,
but also to the carbyne ligand, and it can be fully reversed by
irradiation of toluene solutions of 3 with visible-UV light at room
temperature. Again, although several steps must be involved both
in the forward and in the back reactions, no intermediates were
detected by IR monitoring of these reactions.
We should note the significant influence that the substituent at
the carbyne ligand has on the overall course of the reactions
under discussion. Thus, we have recently shown that the methox-
ycarbyne complex [Mo2Cp2(μ-COMe)(μ-PCy2)(μ-CO)], a mo-
lecule isoelectronic with 2, reacts with CO to give the electron-
precise tricarbonyl [Mo2Cp2(μ-COMe)(μ-PCy2)(CO)3], rather
than a ketenyl complex.6 Actually, the hypothetical methoxylk-
etenyl complex [Mo2Cp2{μ-C(OMe)CO}(μ-PCy2)(CO)2] was
predicted by DFT calculations to spontaneously undergo a 1,2-shift
of the methoxyl substituent to yield the stable carboxycarbyne
isomer [Mo2Cp2{μ-C(CO2Me)}(μ-PCy2)(CO)2].7
The decarbonylation of the phenylketenyl complex 3 can be
controlled thermally. Actually, it is possible to remove selectively
a CO molecule from this compound by heating its toluene
solutions at 353 K for 2 h, to give the dicarbonyl benzylidyne
complex [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] (4) in good yield.
Further decarbonylation of 4 to give the starting compound 2 is
very slow under these conditions (in fact, only 50% conversion is
reached after 7 h in refluxing toluene), although it can be perfor-
med rapidly (5 min) under visible-UV irradiation, as expected
0
[M2Cp2(μ-PR2)(μ-PR2 )(μ-CO)] previously studied by us
(M = Mo, W).10 Under that scheme, complex 2 might yield
the mentioned species [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)3] step-
wise via a cis isomer of the dicarbonyl 4, with the tricarbonyl
intermediate then finally rearranging into 3 as proposed above.
Derivatives of the Methyl Complex 1b. As stated in the
Introduction, no dehydrogenation could be induced directly on
the methyl ligand of complex 1b, but this took place easily upon
photolysis of the complex in the presence of different metal
carbonyls, to give heterometallic clusters bridged by methylidyne
ligands. Of particular interest was the trimolybdenum cluster
[Mo3Cp2(μ3-CH)(μ-PCy2)(CO)7] (5) (Scheme3), a compound
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Table 1. Selected Bond Lengths and Angles for Compounds 2
and 8
21
8
Mo(1)ꢀMo(2)
Mo(1)ꢀC(1)
Mo(2)ꢀC(1)
Mo(1)ꢀC(2)
Mo(2)ꢀC(2)
Mo(1)ꢀP
2.464(1)
2.09(1)
2.11(1)
1.99(1)
1.97(1)
2.402(2)
2.403(2)
2.467(1)
2.16(2)
2.07(2)
1.92(1)
1.89(2)
2.407(1)
2.407(1)
0.98(2)
Mo(2)ꢀP
Figure 1. ORTEP diagram (30% probability) of compound 8, with Cy
rings (except the C1 atoms) and H atoms (except that at the carbyne
ligand) omitted for clarity.
C(2)ꢀH(2)
Mo(1)ꢀC(1)ꢀMo(2)
Mo(1)ꢀC(2)ꢀMo(2)
Mo(1)ꢀPꢀMo(2)
71.9(3)
77.2(3)
61.7(1)
71.5(6)
80.7(7)
61.7(1)
obtained in good yield upon photolysis of 1b in the presence of
[Mo(CO)6].2 According to an X-ray study, the methylidyne
ligand in this unsaturated cluster bridges the metal atoms quite
asymmetrically, with the HCꢀMo(CO)5 distance of 2.316(3) Å
being substantially longer than the other HCꢀMo lengths (ca.
2.05 Å). Thus, we wondered if compound 5 might be used as a
precursor of binuclear methylidyne complexes related to com-
pounds 2ꢀ4, provided that the Mo(CO)5 fragment could be
removed from the cluster in some convenient way.
Heating a toluene solution of compound 5 at 388 K produced
no significant changes in a few hours. In contrast, this cluster
reacted slowly with CO (ca. 4 atm) at 333 K to cleanly give the
ketenyl complex [Mo2Cp2{μ-C(H)CO}(μ-PCy2)(CO)2] (6)
and [Mo(CO)6] as major products, the latter being identified by
its characteristic CꢀO stretching band. Compound 6 could be
thus isolated in a conventional way and displays the same
structure as compound 3 (see below). However, our attempts
to selectively decarbonylate the ketenyl complex 6, so as to
obtain dicarbonyl or monocarbonyl analogues of the benzylidyne
complexes 2 and 4, were unsuccessful by either thermolytic or
photolytic procedures.
formalism and DFT calculations on the related methoxycarbyne
complex,13 while the MoꢀC(carbyne) lengths of ca. 1.91 Å are
shorter than the MoꢀC(carbonyl) ones (ca. 2.12 Å), as expected
from the different bond orders (1.5 vs 1) of the corresponding
MoꢀC interactions. We note that the MoꢀC lengths in 8 are ca.
0.1 Å shorter than the corresponding distances in 2 or in the
mentioned ethoxycarbyne complex (ca. 1.99 Å), thus pointing to
an especially strong MꢀC bond in this case, perhaps resulting
from the minimum steric requirements of the methylidyne
ligand, as compared to the CPh or COEt groups.
Spectroscopic data in solution for 2 and 8 are comparable to
each other and fully consistent with their solid-state structures
(Table 2). The most characteristic spectroscopic features are the
presence of a band at 1686 cmꢀ1 in the corresponding IR spectra,
due to the CꢀO stretch of the bridging carbonyl, and a strongly
deshielded 13C NMR resonance at ca. 385 ppm corresponding to
the bridgehead carbon atom of the carbyne ligand. The phos-
phide ligand in 2 gives rise to a quite deshielded 31P NMR reso-
nance at 228.5 ppm, a value comparable to those measured for
the alkoxycarbyne complexes [Mo2Cp2(μ-COR)(μ-PCy2)(μ-
CO)].12 In contrast, the methylidyne complex 8 gives rise to a
much more deshielded 31P resonance (288.2 ppm) with no
obvious structural reason for it. We note, however, that the
isoelectronic hydroxycarbyne-bridged cation [Mo2Cp2(μ-COH)-
(μ-PCy2)2]þ gives also a comparably deshielded resonance
(278.3 ppm).14 Another salient spectroscopic feature of the
methylidyne ligand in 8 is the strong deshielding of its H nucleus,
with a chemical shift (δ 16.74 ppm) ca. 5 ppm above that in the
triply bridged methylidyne cluster 5 and the Mo2W and Mo2Cr
analogues (ca. 12 ppm). This can be attributed to the strong
To avoid the formation of the ketenyl ligand upon degradation
of 5 with CO, we also examined some reactions of 5 with simple
P-donors. The best results were obtained with P(OMe)3. This
reaction takes place smoothly at room temperature, but no
cleavage of the cluster occurs. Instead, the substituted cluster
[Mo3Cp2(μ3-CH)(μ-PCy2)(CO)6{P(OMe)3}] (7) is obtained
in good yield. Fortunately, this cluster degrades completely in
refluxing toluene to give the 30-electron methylidyne com-
plex [Mo2Cp2(μ-CH)(μ-PCy2)(μ-CO)] (8) and [Mo(CO)5-
{P(OMe)3}], the latter being identified in the reaction mixture
by the presence in the corresponding IR spectrum of character-
istic CꢀO stretching bands at 2079 (w) and 1950 (vs) cmꢀ1 11
.
Compound 8 could be thus isolated in a conventional way and
was shown to display the same structure as compound 2, as
discussed below.
anisotropy associated with the π
electron density in 8
MoꢀC
(absent in any μ3-CH ligand), this expectedly imposing a
deshielding influence on the CH proton comparable to that of
the double and aromatic CꢀC bonds in hydrocarbons.15
Structural Characterization of the Triply Bonded Carbyne
Complexes 2 and 8. The structure of the methylidyne complex
8 (Figure 1 and Table 1) is very similar to that determined for the
benzylidyne complex 2 in our preliminary report,1 and to that of
the isoelectronic ethoxycarbyne complex [Mo2Cp2(μ-COEt)(μ-
PCy2)(μ-CO)].12 The molecule is built up from two MoCp units
symmetrically bridged by dicyclohexylphosphide, carbonyl and
methylidyne ligands. The intermetallic distance is very short
(2.467(1) Å) and consistent with the triple intermetallic bond
to be proposed for these molecules on the basis of the EAN
Strutural Characterization of the Doubly Bonded Carbyne
Complex 4. The structure of this dicarbonyl complex (Figure 2
and Table 3) is very similar to that of the isoelectronic carbox-
ycarbyne complex [Mo2Cp2{μ-C(CO2Me)}(μ-PCy2)(CO)2]
previously determined by us.7 The molecule displays two sym-
metry-related MoCp(CO) fragments in a transoid arrangement
bridged symmetrically by dicyclohexylphosphide and phenylcar-
byne ligands, with the carbonyl ligands slightly bent over
the intermetallic vector (CꢀMoꢀMo 83.8(4)o). The latter is a
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Table 2. Selected IRa and NMRb Data for New Compounds
compound
ν(CO)a
δ(P)b
δ(μ-C)b
δ(μ-CH)b
[Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (2)
[Mo2Cp2{μ-C(Ph)CO}(μ-PCy2)(CO)2] (3)
[Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] (4)
1686 (s)
228.5
132.6
117.6
133.0
385.2 [15]
15.8 [1]
428.4 [5]
ꢀ13.9
1993 (s), 1895 (s), 1838 (vs)
1913 (w, sh), 1895 (vs)c
1954 (s), 1878 (s), 1838 (vs)d
2006 (m), 1946 (w, sh), 1919 (vs), 1886 (m)
1686 (s)
[Mo2Cp2{μ-C(H)CO}(μ-PCy2)(CO)2] (6)
[Mo3Cp2(μ3-CH)(μ-PCy2)(CO)6{P(OMe)3] (7)
[Mo2Cp2(μ-CH)(μ-PCy2)(μ-CO)] (8)
3.31
163.9 [2], 163.0 (br)
11.42 [6, 6]
288.2
382.7 [14]
16.74
a Recorded in dichloromethane solution, ν in cmꢀ1. b Recorded in CD2Cl2 solutions at 290 K and 400.13 (1H), 162.17 (31P), or 100.63 (13C) MHz, δ in
ppm relative to internal TMS (1H, 13C) or external 85% aqueous H3PO4 (31P). Coupling constants to 31P are shown in square brackets and are given in
Hz. c Recorded in petroleum ether solution. d Recorded in toluene solution.
Figure 2. ORTEP diagram (30% probability) of compound 4, with Cy
Figure 3. ORTEP diagram (30% probability) of compound 7, with Cy
rings (except the C1 atoms) and H atoms (except that at the carbyne
ligand) omitted for clarity.
rings (except the C1 atoms) and H atoms omitted for clarity.
monocarbonyl complex 2 (12 cmꢀ1 higher than its isoelectronic
methoxycarbyne complex). All of this suggests a better electron-
acceptor character of the phenylcarbyne ligand (relative to the
COMe ligand), as far as the metal centers are concerned, and this
is in agreement with the higher electronic charge at the carbyne C
atom computed for the carboxycarbyne complex [Mo2Cp2{μ-
C(CO2Me)}(μ-PCy2)(CO)2] (as compared to its methoxycar-
byne analogue).6 This also suggests that compound 4 might
display a significant donor ability toward different electron
acceptors, a matter under current study.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 4
Mo(1)ꢀMo(1)0
Mo(1)ꢀC(1)
Mo(1)ꢀC(7)
Mo(1)ꢀP
2.666(1)
1.974(7)
1.995(8)
2.408(2)
1.17(1)
Mo(1)ꢀPꢀΜο(1)0
Mo(1)ꢀC(7)ꢀMo(1)0
C(1)ꢀΜο(1)ꢀMo(1)0
C(1)ꢀMo(1)ꢀP
C(1)ꢀMo(1)ꢀC(7)
C(7)ꢀMo(1)ꢀP
67.2(1)
83.8(4)
83.6(2)
87.7(2)
84.6(2)
104.5(2)
C(1)ꢀO(1)
C(7)ꢀC(8)
1.46(2)
characteristic feature of electron-deficient molecules of the
type [Mo2Cp2(μ-PR2)(μ-X)(CO)2] (X = 1ꢀ3-electron donor
group).16,17 The MoꢀMo distance is quite short, 2.666(1) Å,
consistent with the double metalꢀmetal bond to be proposed for
this molecule on the basis of the EAN rule and DFT calculations
on the mentioned carboxycarbyne complex.6 Finally, the MoꢀC-
(carbyne) distances (ca. 1.98 Å) are also quite short, as expected
from the formal bond order of the MoꢀC interactions (1.5); in
fact, these lengths are almost identical to those in the mono-
carbonyl complex 2 (Table 1).
The spectroscopic data in solution for compound 4 (Table 2
and Experimental Section) are fully consistent with its solid-state
structure. Its IR spectrum displays two CꢀO stretching bands
with the typical pattern of trans-dicarbonyl complexes (weak and
strong, in order of decreasing frequency) defining angles be-
tween CO groups close to 180°.11 We note, however, that the
average CꢀO stretching frequency (1904 cmꢀ1) is 26 cmꢀ1
higher than the corresponding figure in the isostructural meth-
oxycarbyne complex [Mo2Cp2(μ-COMe)(μ-PCy2)(CO)2]
(1878 cmꢀ1).2 The same qualitative trend is observed for the
Other spectroscopic features of 4 are as expected and deserve
no detailed comments. For instance, the 31P chemical shift of the
PCy2 group (117.6 ppm) falls in the range found for related 32-
electron compounds of the type trans-[Mo2Cp2(μ-PCy2)(μ-
X)(CO)2] (X = 3e-donor ligand),10,14,16 while the presence of
the bridging carbyne is denoted by the appearance of a strongly
deshielded resonance in the 13C NMR spectrum (428.4 ppm),
with a shift some 25 ppm higher than those of the isoelectronic
methoxycarbyne or carboxycarbyne complexes already men-
tioned (ca. 405 ppm). Note that these chemical shifts are in turn
some 40ꢀ50 ppm higher than those of the corresponding 30-
electron complexes of the type [Mo2Cp2(μ-PCy2)(μ-CX)(μ-
CO)] despite the very similar MoꢀC distances in all of these
complexes, an effect possibly derived from the different interme-
tallic bonding interactions in these two families of compounds.
Solid-State and Solution Structure of the Methylidyne-
Bridged Cluster 7. The structure of the trimolybdenum com-
pound 7 (Figure 3) is very similar to that of its unsubstituted
precursor 5,2 as it can be appreciated from the metric data
collected in the Table 4, and therefore needs not to be discussed
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Table 4. Selected Bond Lengths and Angles for Compounds 5
and 7
52
7
Mo(1)ꢀMo(2)
Mo(1)ꢀMo(3)
Mo(2)ꢀMo(3)
Mo(1)ꢀC(10)
Mo(2)ꢀC(10)
Mo(3)ꢀC(10)
Mo(1)ꢀP(1)
Mo(2)ꢀP(1)
Mo(3)ꢀP(2)
C(10)ꢀH
2.9283(3)
3.0938(3)
3.1245(3)
2.053(3)
2.040(3)
2.316(3)
2.425(1)
2.410(1)
2.927(3)
3.086(3)
3.078(3)
2.02(3)
2.07(3)
2.31(2)
2.422(7)
2.418(6)
2.421(7)
1.10(2)
Figure 4. ORTEP diagram (30% probability) of compound 3, withCyrings
(except the C1 atoms) and H atoms omitted for clarity (taken from ref 1).
0.99(3)
Mo(1)ꢀMo(3)ꢀMo(2)
Mo(1)ꢀMo(2)ꢀC(2)
Mo(2)ꢀMo(1)ꢀC(1)
Mo(2)ꢀPꢀMo(1)
56.2(1)
86.7(1)
87.0(1)
74.5(1)
170.5(2)
170.9(2)
91.4(1)
56.7(1)
Chart 1
89(1)
86(1)
74.4(2)
Mo(1)ꢀC(1)ꢀO(1)
Mo(2)ꢀC(2)ꢀO(2)
Mo(1)ꢀC(10)ꢀMo(2)
Mo(1)ꢀC(10)ꢀH
172(2)
171(2)
91(1)
126(2)
129(2)
78.4(1)
79.0(1)
114(10)
131(10)
79(1)
Mo(2)ꢀC(10)ꢀH
P(1)ꢀMo(1)ꢀC(10)
P(1)ꢀMo(2)ꢀC(10)
P(2)ꢀMo(3)ꢀC(10)
denoted by the distinct bending of the CO ligands over the
intermetallic vector (CꢀMoꢀMo angles ca. 75 and 92°) and the
puckering of the PMoCMo ring (ca. 166°). This geometrical
distortion is not unusual for dicarbonyl complexes of the type
[Mo2Cp2(μ-PCy2)(μ-X)(CO)2],16a,18 and it seems to relieve
the pressure induced by the presence of sterically demanding X
groups (in this case, μ-C(Ph)CO > μ-CPh). The MoꢀMo dis-
tance in 3 (2.6101(2) Å) is intermediate between those mea-
sured for the doubly bonded carbyne complexes 4 or [Mo2Cp2-
{μ-C(CO2Me)}(μ-PCy2)(CO)2] (ca. 2.66 Å), and that for the
almost triply bonded phenyl complex [Mo2Cp2(μ-κ1-Ph)(μ-
PCy2)(CO)2] (2.557(2) Å),16b and therefore would suggest
that the ketenyl ligand in 3 is effectively providing the dimetal
center with more than one electron. This can be rationalized by
assuming the contribution of ketenyl (1-electron donor) and
acylium (3-electron donor) resonant forms to the electronic
structure of the bridging ligand (Chart 1), as proposed previously
for other ketenyl-bridged complexes, such as the neutral com-
plexes [FeWCp{μ-C(SiPh3)CO}(CO)5]19 and [Mn2Cp2{μ-
C(p-C6H4-Me)CO}(CO)4],20 or the cation [Fe2Cp2(μ-C(H)CO}-
(μ-CO)(CO)2]þ.9a Accordingly, the MoꢀC bond distances in 3
(ca. 2.24 Å) are significantly shorter than those measured for the
mentioned phenyl complex (ca. 2.35 Å),16b taken here as an
imperfect model (because of the presence of some additional π
interaction) for a 1-electron C(sp2)-donor ligand. In contrast, the
CꢀCO distance (1.324(2) Å) is only slightly longer than that
expected for a C(sp2)ꢀC(sp) double bond (ca. 1.31 Å),21 this
being somewhat contradictory with the other data. We will
further discuss the bonding within the ketenyl ligand in 3 in
the light of DFT calculations.
79(1)
163(1)
in detail. Although the quality of the diffraction data was very
poor, it is quite apparent that the MoꢀMo, MoꢀP, and MoꢀC-
(carbyne) lengths in these two clusters are very similar to each
other. Noticeably, the phosphite ligand bound to the Mo(3)
atom is positioned trans to the carbyne ligand (PꢀMoꢀC ca.
163°), but this seems to change not much the bonding of the
carbyne ligand to that metal atom, it remaining weaker than the
other two MoꢀC bonds (Mo(3)ꢀC = 2.31(2) Å vs MoꢀC ca.
2.05 Å).
Spectroscopic data for 7 (Table 2 and Experimental Section)
suggest that the solid-state structure is retained in solution. In
particular, the chemical equivalence of the Cp ligands indicates
the retention of the cis arrangement of the MoCp(CO) fragments,
while the relative intensities of the bands above 1900 cmꢀ1 suggest
the presence of a trans-[Mo(CO)4XY] oscillator in the mole-
cule.11 The methylidyne ligand gives rise to a 1H NMR resonance
at 11.47 ppm, a position comparable to that of its precursor 5
(12.26 ppm), with a coupling of 6 Hz to both P atoms. The latter
in turn gives rise to very close and weakly coupled 31P NMR
resonances at 163.9 and 163.0 ppm that could be equally well
assigned to either dicyclohexylphosphide (e.g., 172.8 ppm for 5)
or Mo-bound trimethylphosphite ligands.
Structural Characterization of the Ketenyl Complexes 3
and 6. The structure of the phenylketenyl complex 3 was repor-
ted in our preliminary work (Figure 4)1 and is not very different
from that of the carbyne complex 4. The molecule features two
transoid MoCp(CO) fragments symmetrically bridged by dicy-
clohexylphosphide and phenylketenyl ligands, with the OꢀCꢀ
CꢀC(Ph) chain of the latter essentially contained in the same
plane and positioned roughly perpendicular to the intermetallic
vector. The CO ligands, however, are not longer antiparallel, as
Spectroscopic data in solution for 3 and 6 (Table 2 and
Experimental Section) are similar to each other, thus indicating
that they share the same basic structure, consistent with the solid-
state structure found for 3. For instance, they both give a 31P
NMR resonance at ca. 133 ppm, a chemical shift similar to that of
2 and also comparable to those usually found for other PCy2-
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Organometallics
ARTICLE
bridged dimolybdenum complexes with 32-electron counts,14,16
thus suggesting an important contribution of the acylium form to
the actual bonding in our ketenyl complexes. In the same line, the
bridgehead carbon atom of the ketenyl ligand in compounds 3
and 6 gives rise to quite shielded 13C NMR resonances (15.8
and ꢀ13.9 ppm, respectively), an effect observable also for the
proton resonance of the ketenyl ligand in 6 (3.31 ppm). The
comparison of the latter figures with those of the mentioned
ketenyl complex [Fe2Cp2(μ-C(H)CO}(μ-CO)(CO)2]þ (δC
27.5 ppm, δH 6.94 ppm)9a suggests a still greater contribution
of the acylium form in the case of our compounds.
The IR spectra of compounds 3 and 6 display three CꢀO
stretching bands in each case. The two less energetic bands have
similar frequencies and are thus assigned to the CꢀO stretches of
the carbonyl ligands, as verified by a DFT calculation on 3 (see
below). Therefore, the more energetic band mainly arises from
the CꢀO stretch of the ketenyl ligand in each case, and it is
substantially more energetic for 3 (1993 cmꢀ1) than for 6
(1954 cmꢀ1), with both figures falling in any case within the
range usually observed for bridging ketenyl ligands (1850ꢀ
2100 cmꢀ1).22 This suggests that the exact contributions of the
acylium and ketenyl forms to the bonding in these two complexes
might not be exactly the same. Finally, we must note that the
relative intensities of the two carbonyl bands (strong and very
strong, in order of decreasing frequencies, Table 2) are somewhat
unexpected considering that the angle defined by the CO ligands
in 3 is close to 165°, then leading to the prediction that the
symmetrical CꢀO stretch (the band at ca. 1890 cmꢀ1) should be
rather weak.11 These relative intensities were not modified when
recording the IR spectrum in the solid state, thus excluding a
significant modification of the geometry of the Mo2(CO)2
oscillator upon dissolution of the solid. Instead, the unexpected
intensities of the CꢀO stretches in 3 can be attributed to the
mixing of the carbonyl and ketenyl vibrations, as shown by DFT
calculations to be discussed next.
DFT Calculations on the Phenylketenyl Complex 3. The
electronic structure of the ketenyl cation [Fe2Cp2(μ-C(H)CO}-
(μ-CO)(CO)2]þ was analyzed some years ago using Fens-
keꢀHall MO calculations, and some evidence was then found
for both the acylium and the ketenyl contributions to the metalꢀ
ligand bonding in this compound, although no single orbital
having a large π [CꢀC(O)] bonding character was found.9a We
then judged of interest to analyze the bonding in the phenylk-
etenyl complex 3 using modern Density Functional Theory
(DFT) methods (see the Experimental Section for details).23
Following the methodology previously used by us in the study of
unsaturated carbyne complexes related to compounds 2 and
4,6,13 we have analyzed the electronic structure and bonding in
compound 3 through the properties of the relevant KohnꢀSham
molecular orbitals, and also by inspection of the topological
properties of the electron density, as managed in the Atoms in
Molecules (AIM) theory.24
Figure 5. DFT-optimized structure of compound 3, with H atoms
omitted for clarity.
Table 5. Selected Data for the DFT-Optimized Geometry of
Complex 3a and the Topological Properties of Its Electron
Densityb
2
bond
calc d/R
exp d/R
F
r F
Mo1ꢀMo2
Mo1ꢀP
2.638
2.452
2.440
1.945
1.962
2.259
2.308
1.493
1.399
1.335
1.173
1.167
1.178
76.9
2.6101(2)
2.3984(4)
2.3857(4)
1.939(2)
1.957(2)
2.238(2)
2.255(2)
1.486(2)
1.393(2)
1.324(2)
1.1642
0.487
0.523
0.531
0.946
0.900
0.527
0.459
1.720
2.097
2.158
2.919
2.957
2.910
1.34
3.05
3.10
Mo2ꢀP
Mo1ꢀC1
Mo2ꢀC2
Mo1ꢀC3
Mo2ꢀC3
C3ꢀC5
10.20
10.58
4.63
4.86
ꢀ14.27
ꢀ20.46
ꢀ16.65
22.01
23.84
17.06
CꢀC(Ph)c
C3ꢀC4
C1ꢀO
C2ꢀO
1.157(2)
1.177(2)
75.2(1)
C4ꢀO
C1ꢀMo1ꢀMo2
C2ꢀMo2ꢀMo1
XꢀC3ꢀC4
92.8
92.3(1)
119.4
119.6(2)
a Bond lengths (d, Å) and angles (R, deg) according to the labeling
shown in the figure, with experimental values taken from ref 1. b Values
of the electron density at the bond critical points (F) are given in e Åꢀ3
;
2
values of the laplacian of F at these points (r F) are given in e Åꢀ5; see
the Experimental Section for details of the DFT calculations. c Average
values within the Ph ring.
The most relevant parameters derived from the geometry
optimization of 3 (Figure 5) can be found in Table 5, along with
the corresponding experimental values. The optimized bond
lengths for 3 are in good agreement with the data measured using
X-ray diffraction,1 although the computed values for lengths
involving the metal atoms tend to be slightly longer (less than
0.05 Å) than the corresponding experimental data. This is a
common trend with the functionals currently used in the DFT
computations of transition metal compounds.23a,25 The com-
puted CꢀO stretches were 2109, 1979, and 1944 cmꢀ1, with
relative intensities 94:60:100, corresponding mainly to the ketenyl
and carbonyl (symmetric and asymmetric vibrations) ligands, re-
spectively. These values overestimate the experimental frequencies
(Table 2) by 5ꢀ10%, which seems to be a normal bias for DFT-
derived IR data,6,13,26 while the relative intensities are in reasonable
agreement with those observed in the solution spectra.
The frontier molecular orbitals for 3 (those accounting for the
metalꢀmetal bonding), as well as those involving the most
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ARTICLE
MO145 (and also in MO92) that might be identified with the
interaction expected for the ketenyl form.
The dominant π overlaps within the ketenyl ligand, however,
are located between the C and O atoms and are mostly
concentrated in the orbitals MO110 and MO90 (for the overlap
perpendicular to the intermetallic vector) and in the MO92
(overlap parallel to the MꢀM vector), thus pointing to a
dominant triple-bond picture of the CꢀO interaction. Thus,
we conclude that, from the point of view of the MO analysis, the
electronic structure of the ketenyl ligand in 3 is closer to the
acylium form. However, some πCꢀC overlap can be appreciated
in the ketenyl ligand (orbitals MO145 and MO92).
2
The electron density (F) and its laplacian (r F) at the most
relevant bond critical points (bcp) of compound 3 are also
collected in Table 5. First, we note that the electron density at the
intermetallic bcp (0.487 e Åꢀ3) is somewhat closer to that
computed for the 32-electron carboxycarbyne complex
[Mo2Cp2{μ-C(CO2Me)}(μ-PCy2)(CO)2] (0.444 e Åꢀ3)6 than
to the one computed for the 30-electron hydride [Mo2Cp2(μ-
H)(μ-PCy2)(CO)2] (0.582 e Åꢀ3),16b again in favor of a some-
what higher contribution of the acylium form. However, the
electron density at the MoꢀC (ketenyl) bonds (ca. 0.49 e Åꢀ3) is
much lower than that in the carbyne complex (ca. 0.93 e Åꢀ3),
and indeed lower than the reference values for a single bond (e.g.,
ca. 0.71 e Åꢀ3 for the bridging carbonyls in methoxycarbyne
complex [Mo2Cp2(μ-COMe)(μ-PCy2)(μ-CO)]),13 as expected
if the ketenyl form were to be dominant. Thus, we have to
conclude that both forms should be taken into account to
describe the actual bonding in 3. In fact, the parameters within
the ketenyl CꢀCꢀO chain have values intermediate between
those implied by each of the canonical forms. Thus, the density at
the CꢀCO bond (2.158 e Åꢀ3) is higher than expected for a
single CꢀC bond (e.g., 1.927 e Åꢀ3 in the mentioned carbox-
ycarbyne complex), and comparable to the average density in the
aromatic ring of the complex (2.097 e Åꢀ3), while the values of
F and its laplacian at the CCꢀO bond (2.910 e Åꢀ3 and 17.06 e
Å
ꢀ5) are almost as high as the ones computed for the carbonyl
ligands. Thus, from the point of view of the AIM analysis, it can
be said that both the ketenyl and the acylium forms are of
comparable relevance to describe the metalꢀketenyl bonding in
3, this being in reasonable agreement with the structural data.
Figure 6. Selected molecular orbitals of compound 3, with their
energies (in eV) and main bonding character indicated below.
’ CONCLUDING REMARKS
significant part of the π interactions in the ketenyl ligand, are
shown in Figure 6. The intermetallic bonding for ideal edge-
sharing bioctahedral complexes should follow from the occupa-
tion of one σ, one π, and one δ bonding MO’s, with the
corresponding antibonding orbitals being next in energy.27 We
might therefore expect a configuration of the type σ2π2δ2(δ*)2
for 3, although orbital mixing with the π acceptor ligands usually
modifies this simple picture. Indeed, the frontier orbitals for 3
display considerable mixing. The HOMO is a recognizable
metalꢀmetal δ* orbital (with significant contributions of the
π*CꢀO orbitals of the terminal carbonyls), but the δ and π
bonding orbitals are mixed and distributed among the three
orbitals below, these being followed by the σ component of the
intermetallic bonding (MO144). Noticeably, both the MO146
and the MO145 orbitals have significant σ bonding MꢀC-
(ketenyl) character, with orbital interactions comparable to those
usually found for μ-PR2 ligands, and this points to the 3-electron
donor behavior derived from the acylium form of the ketenyl
ligand (Chart 1). We note, however, a small π(CꢀC) overlap in
The photochemically induced dehydrogenation of the benzyl
complex [Mo2Cp2(μ-CH2Ph)(μ-PCy2)(CO)2], followed by
suitable carbonylation/decarbonylation steps, allows the synthesis
of the unsaturated benzylidyne complexes [Mo2Cp2(μ-CPh)(μ-
PCy2)(μ-CO)] and [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2], and
that of the phenylketenyl complex [Mo2Cp2-{μ-C(Ph)CO}(μ-
PCy2)(CO)2] (3). Related methylidyne complexes can be pre-
pared from the methyl complex [Mo2Cp2(μ-CH3)(μ-PCy2)-
(CO)2] via degradation of its trimolybdenum methylidyne-bridged
derivatives [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)7] and [Mo3Cp2(μ3-
CH)(μ-PCy2)(CO)6{P(OMe)3}]. As compared to their related
methoxycarbyne-bridged complexes, the carbyne compounds
here reported display the following differences: (a) higher
stability of the ketenyl derivatives [Mo2Cp2{μ-C(X)CO}(μ-
PCy2)(CO)2] as compared to the corresponding isomeric and
electron-precise tricarbonyls [Mo2Cp2(μ-CX)(μ-PCy2)(CO)3],
and (b) a stronger π acceptor character, this leading to reduced
electron density at the metal site and increased electron density at
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the bridgehead carbon atom. On the other hand, the bonding in
the phenylketenyl ligand is intermediate between the extreme
descriptions represented by the acylium and the ketenyl canonical
forms, according to the AIM analysis on compound 3, although the
analysis of the orbital interactions in this molecule suggests that the
acylium form would be somewhat more dominant.
90.6, 90.3 (2s, Cp), 50.2 [d, JCP = 22, C1(Cy)], 42.7 [d, JCP = 17,
C1(Cy)], 35.0 [d, JCP = 3, C2(Cy)], 34.1 [d, JCP = 4, C2(Cy)], 33.8 [d,
JCP = 3, C2(Cy)], 32.5 [s, C2(Cy)], 28.5ꢀ28.1 [m, C3(Cy)], 26.6, 26.3
[2s, C4(Cy)], 15.8 (d, JCP = 1, μ-CCO).
Preparation of [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] (4). A to-
luene solution (5 mL) of compound 3 (0.150 g, 0.216 mmol) was
stirred at 353 K for 2 h to give an orange solution. The solvent was then
removed under vacuum, and the residue was chromatographed through
an alumina column (activity IV) at 288 K. Elution with dichlorometha-
neꢀpetroleum ether (1:10) gave a rose fraction yielding, after removal
of the solvents under vacuum, compound 4 as an orange microcrystalline
solid (0.119 g, 83%). The crystals used in the X-ray study were grown by
slow diffusion of petroleum ether into a dichloromethane solution of the
complex at 253 K. Anal. Calcd for C31H37Mo2O2P: C, 56.03; H, 5.61.
’ EXPERIMENTAL SECTION
General Procedures and Starting Materials. All manipula-
tions 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.28 Petroleum
ether refers to that fraction distilling in the range 338ꢀ343 K. The
compounds [Mo2Cp2(μ-CH2Ph)(μ-PCy2)(CO)2] (1a), [Mo2Cp2(μ-
CH3)(μ-PCy2)(CO)2] (1b), and [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)7]
(5) were prepared as described previously.2b,16b All other reagents were
obtained from the usual commercial suppliers and used as received.
Photochemical experiments were performed using jacketed quartz or
Pyrex Schlenk tubes, cooled by tap water (ca. 288 K). A 400 W mercury
lamp placed ca. 1 cm away from the Schlenk tube was used for all the
experiments. Chromatographic separations were carried out using
jacketed columns cooled by tap water. Commercial aluminum oxide
(Aldrich, 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 (ν) were
measured in solution or Nujol mulls and are given in cmꢀ1. Nuclear
magnetic resonance (NMR) spectra were routinely recorded at 400.13
(1H), 162.17 (31P{1H}), or 100.63 MHz (13C{1H}) at 290 K in CD2Cl2
solutions unless otherwise is stated. Chemical shifts (δ) are given in
ppm, relative to internal tetramethylsilane (1H, 13C) or external 85%
aqueous H3PO4 (31P). Coupling constants (J) are given in Hz.
Preparation of [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (2). A to-
luene solution (20 mL) of complex 1b (0.500 g, 0.750 mmol) was
irradiated with visible-UV light in a quartz Schlenk flask at 288 K for 2 h
with a gentle N2 purge to give a red-brown solution. The solvent was
then removed under vacuum, and the residue was extracted with
dichloromethaneꢀpetroleum ether (1:10), and the extracts were chro-
matographed through an alumina column (activity IV) at 288 K. Elution
with dichloromethaneꢀpetroleum ether (1:1) gave a red fraction
yielding, after removal of the solvents under vacuum, compound 2 as
a red solid (0.300 g, 63%). Anal. Calcd for C30H37Mo2OP: C, 56.61; H,
5.86. Found: C, 56.91; H, 5.96. 1H NMR: δ 7.11 [false t, JHH = 8, 2H,
H3(Ph)], 6.98 [t, JHH = 7, 1H, H4(Ph)], 6.58 [false d, JHH = 7, 2H,
H2(Ph)], 5.79 (s, 10H, Cp), 1.82ꢀ0.55 (m, 22H, Cy). 13C{1H} NMR: δ
385.2 (d, JCP = 15, μ-CPh), 300.8 (d, JCP = 9, μ-CO), 163.0 [s, C1(Ph)],
127.7 [s, C3(Ph)], 124.4 [s, C4(Ph)], 121.2 [s, C2(Ph)], 95.6 (s, Cp),
42.6 [d, JCP = 15, C1(Cy)], 42.1 [d, JCP = 13, C1(Cy)], 33.6, 33.5 [2s,
C2(Cy)], 27.6, 27.4 [2d, JCP = 6, C3(Cy)], 26.3, 26.2 [2s, C4(Cy)].
Preparation of [Mo2Cp2{μ-C(Ph)CO}(μ-PCy2)(CO)2] (3). A
toluene solution (10 mL) of compound 2 (0.160 g, 0.252 mmol) was
placed in a bulb equipped with a Young’s valve. The bulb was cooled at
77 K, evacuated under vacuum, and then refilled with CO. The valve was
then closed, and the solution was allowed to reach room temperature
and was further stirred for 40 h to give a green solution. The solvent was
then removed under vacuum, and the residue was chromatographed
through an alumina column (activity IV) at 288 K. Elution with
dichloromethaneꢀpetroleum ether (1:6) gave a green fraction yielding,
after removal of the solvents under vacuum, compound 3 as a green
microcrystalline solid (0.140 g, 80%). Anal. Calcd for C32H37Mo2O3P:
C, 55.50; H, 5.39. Found: C, 55.67; H, 5.13. 1H NMR: δ 7.30ꢀ7.03 (m,
Ph, 5H), 5.30, 5.06 (2s, 2 ꢁ 5H, Cp), 2.38ꢀ1.10 (m, 22H, Cy). 13C{1H}
NMR: δ 249.4 (d, JCP = 13, MoCO), 242.0 (d, JCP = 16, MoCO), 158.7
[s, C1(Ph)], 145.0 (s, μ-CCO), 128.3 [s, C2,3(Ph)], 125.6 [s, C4(Ph)],
1
Found: C, 55.97; H, 5.75. H NMR: δ 7.47 [false t, JHH = 8, 2H,
H3(Ph)], 7.19 [false dd, JHH = 8, 1, 2H, H2(Ph)], 7.12 [tt, JHH = 8, 1, 1H,
H4(Ph)], 5.39 (s, 10H, Cp), 2.50 (m, 2H, Cy), 2.06ꢀ1.11 (m, 20H, Cy).
13C{1H} NMR: δ 428.4 (d, JCP = 5, μ-CPh), 221.5 (d, JCP = 12, MoCO),
167.3 [s, C1(Ph)], 127.7 [s, C3(Ph)], 125.0 [s, C4(Ph)], 119.6 [s,
C2(Ph)], 91.8 (s, Cp), 44.8 [d, JCP = 18, C1(Cy)], 36.5 [s, C2,6(Cy)],
34.4 [s, C6,2(Cy)], 28.5 [d, JCP = 12, C3,5(Cy)], 28.4 [d, JCP = 9,
C
5,3(Cy)], 26.6 [s, C4(Cy)].
Preparation of [Mo2Cp2{μ-C(H)CO}(μ-PCy2)(CO)2] (6). A
toluene solution (5 mL) of compound 5 (0.075 g, 0.091 mmol) was
placed in a bulb equipped with a Young’s valve. The bulb was cooled at
77 K, evacuated under vacuum, and then refilled with CO. The valve was
then closed, and the solution was allowed to reach room temperature
and further stirred at 333 K for 2.5 days to give a yellow-green solution.
The solvent was then removed under vacuum, and the residue was
washed with petroleum ether (4 ꢁ 4 mL) to give compound 6 as a green
microcrystalline solid (0.042 g, 75%). Anal. Calcd for C26H33Mo2O3P:
C, 50.66; H, 5.40; Found: C, 50.57; H, 5.33. 1H NMR: δ 5.28, 5.16 (2s,
2 ꢁ 5H, Cp), 3.31 [s, 1H, μ-C(H)CO], 2.22ꢀ1.22 (m, 22H, Cy).
13C{1H} NMR: δ 247.7 (d, JCP = 14, MoCO), 245.0 (d, JCP = 15,
MoCO), 159.9 [s, μ-C(H)CO], 88.7, 88.3 (2s, Cp), 47.5 [d, JCP = 20,
C1(Cy)], 43.6 [d, JCP = 17, C1(Cy)], 33.8 [d, JCP = 2, C2(Cy)], 32.9 [d,
JCP = 3, C2(Cy)], 32.5, 32.45 [2s, C2(Cy)], 27.3 [d, JCP = 12, 2C2(Cy)],
27.1, 27.0 [2d, JCP = 11, C2(Cy)], 25.4, 25.3 [2s, C4(Cy)], ꢀ13.9 [s, μ-
C(H)CO].
Preparation of [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)6{P(OMe)3}]
(7). Neat P(OMe)3 (12 μL, 0.102 mmol) was added to a toluene
solution (10 mL) of compound 5 (0.056 g, 0.068 mmol), and the
mixture was stirred at room temperature for 1.5 h to give an orange
solution. The solvent was then removed under vacuum, and the residue
was chromatographed through an alumina column (activity IV) at 288
K. Elution with dichloromethaneꢀpetroleum ether (1:4) gave an orange
fraction yielding, after removal of the solvents under vacuum, compound
7 as an orange microcrystalline solid (0.052 g, 84%). The crystals used in
the X-ray study were grown by slow diffusion of petroleum ether into a
toluene solution of the complex at 273 K. Anal. Calcd for C32H42-
1
Mo3O9P2: C, 41.76; H, 4.60. Found: C, 41.87; H, 4.66. H NMR: δ
11.42 (t, JPH = 6, 1H, μ-CH), 5.15 (s, 10H, Cp), 3.70 (d, JPH = 11, 9H,
OMe), 2.08ꢀ1.13 (m, 22H, Cy).
Preparation of [Mo2Cp2(μ-CH)(μ-PCy2)(μ-CO)] (8). A to-
luene solution (10 mL) of compound 7 (0.050 g, 0.054 mmol) was reflu-
xed for 15 min to give a rose solution. The solvent was then removed
under vacuum, and the residue was chromatographed through an
alumina column (activity IV) at 288 K. Elution with dichloromethaneꢀ
petroleum ether (1:3) gave a rose fraction yielding, after removal of
solvents under vacuum, compound 8 as a rose solid (0.022 g, 73%). The
crystals used in the X-ray study were grown by slow diffusion of
petroleum ether into a dichloromethane solution of the complex at
253 K. Anal. Calcd for C24H33Mo2OP: C, 51.44; H, 5.94. Found: C,
1
51.22; H, 5.73. H NMR: δ 16.74 (s, 1H, μ-CH), 5.82 (s, 10H, Cp),
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Table 6. Crystal Data for New Compounds
4
7
8
mol formula
mol wt
C
31H37Mo2O2P
C32H42Mo3O9P2
920.42
C24H33Mo2OP
560.35
664.46
cryst syst
tetragonal
P41212
monoclinic
P21/c
monoclinic
P21/c
space group
radiation (λ, Å)
a, Å
0.71073
9.9779(3)
9.9779(3)
28.4996(6)
90
1.54184
1.54184
8.09170(10)
12.0945(2)
23.2847(2)
90
23.7133(10)
10.2228(3)
31.4145(4)
90
b, Å
c, Å
R, deg
β, deg
90
113.877(3)
90
100.078(2)
90
γ, deg
90
V, Å3
2837.38(13)
4
6963.6(4)
8
2243.60(5)
4
Z
calcd density, g cmꢀ3
absorp coeff, mmꢀ1
temperature, K
θ range (deg)
index ranges (h, k, l)
no. of reflns collected
no. of indep reflns
1.555
1.756
1.659
0.966
10.018
9.906
100(2)
100(2)
100(2)
2.16ꢀ25.22
0, 11; 0, 11; ꢀ34, 34
32 596
2.94ꢀ74.89
ꢀ28, 28; ꢀ7, 11; ꢀ38, 38
36 111
3.86ꢀ73.57
ꢀ8, 9; ꢀ10, 14; ꢀ28, 28
11 425
2554
12 655
4073
(Rint
)
(0.0388)
2426
(0.1065)
8637
(0.0318)
reflns with I > 2σ(I)
3985
R indexes
R1 = 0.048
wR2 = 0.1177b
R1 = 0.0558
wR2 = 0.1302b
1.145
R1 = 0.1342
wR2 = 0.3307c
R1 = 0.1767
wR2 = 0.3499c
1.097
R1 = 0.0432
wR2 = 0.1276d
R1 = 0.0463
wR2 = 0.148d
1.171
[data with I > 2σ(I)]a
R indexes
(all data)a
GOF
no. of restraints/params
ΔF(max, min), e Åꢀ3
0/219
2/731
0/255
1.078, ꢀ0.918
5.148, ꢀ2.14
0.914, ꢀ1.293
a R = ∑||Fo| ꢀ |Fc||/∑|Fo|. wR = [∑w(|Fo|2 ꢀ |Fc|2)2/∑w|Fo|2]1/2. w = 1/[σ2(Fo ) þ (aP)2 þ bP], where P = (Fo þ 2Fc2)/3. b a = 0.0777, b = 0.6356. c a
2
2
= 0.0072, b = 1077.0286. d a = 0.0896, b = 7.1456.
1.81ꢀ0.37 (m, 22H, Cy). 13C{1H} NMR (233 K): δ 382.7 (d, JCP = 14,
μ-CH), 304.9 (d, JCP = 10, μ-CO), 94.4 (s, Cp), 40.3, 38.0 [2d, JCP = 18,
C1(Cy)], 33.4, 33.0 [2s, C2(Cy)], 27.2 [d, JCP = 12, 2C3(Cy)], 26.1, 26.0
[2s, C4(Cy)].
65 mm fixed crystalꢀdetector distance, using the oscillation method,
with 1° oscillation and variable exposure time per image (15ꢀ40 s). Data
collection strategy was calculated with the program CrysAlis Pro CCD.34
Data reduction and cell refinement were performed with the program
CrysAlis Pro RED.34 An empirical absorption correction was applied
using the SCALE3 ABSPACK algorithm as implemented in the program
CrysAlis Pro RED.34 Using the program suite WinGX,32 the structure
was solved by Patterson interpretation and phase expansion and was
refined with full-matrix least-squares on F2 using SHELXL97.33 During
the solution process, two independent molecules of the compound were
found to be present in the asymmetric unit. Most of the non-hydrogen
atoms were refined anisotropically, but due to the poor quality of the
diffraction data a dozen C atoms in each independent molecule had to be
refined isotropically to prevent their temperature factors from becoming
nonpositive definite. Therefore, the final R factors were quite high, all
above 10%. Hydrogen atoms were geometrically placed riding on their
parent atoms, except for H(10B), which was located in the Fourier map
and refined isotropically. The atom H(10) was found in the Fourier map,
but some restraints were necessary to obtain a correct convergence.
Further details of the data collection and refinements are given in
Table 6.
X-ray Structure Determination of Compound 4. Data collec-
tion was performed on a Nonius Kappa CCD single diffractometer,
using graphite-monochromated MoKR radiation. Images were collected
at 45 mm fixed crystal-detector distance, using the oscillation method,
with 1° oscillation and 80 s exposure time per image. Data collection
strategy was calculated with the program Collect.29 Data reduction and
cell refinements were performed with the programs HKL Denzo and
Scalepack.30 Semiempirical absorption corrections were applied using
the program SORTAV.31 Using the program suite WinGX,32 the
structure was solved by Patterson interpretation and phase expansion
and was refined with full-matrix least-squares on F2 with SHELXL97.33
During the solution process, the compound was found to be placed on
the symmetry operation y,x,ꢀz, and displayed a disorder on a cyclohexyl
group, which was modeled introducing 12 instead of 6 carbon atoms
with occupancy factors of 0.5. All non-hydrogen atoms were refined
anisotropically, and all hydrogen atoms were geometrically placed and
refined using a riding model. Further details of the data collection and
refinements are given in Table 6.
X-ray Structure Determination of Compound 8. Data collec-
tion, data reduction, and absorption correction were performed as
described for 7 (5ꢀ20 s exposure time). Using the program suite
WinGX,32 the structure was solved by direct methods and was refined
X-ray Structure Determination of Compound 7. Data collec-
tion was performed on an Oxford Diffraction Xcalibur Nova single
crystal diffractometer, using Cu KR radiation. Images were collected at
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ARTICLE
with full-matrix least-squares on F2 with SHELXL97.33 During the final
stages of the refinement, one of the cyclopentadienyl ligands, the
carbyne, and the bridging carbonyl ligands were found to be disordered
in two positions, which were satisfactorily solved by assigning occupancy
factors of 0.5 in all cases. All of the positional parameters and the
anisotropic temperature factors of all the non-H atoms were refined
anisotropically, except for the atoms involved in the disorder, which were
refined isotropically. All hydrogen atoms were geometrically placed and
refined using a riding model, except for H(2), which was positioned at
fixed coordinates, obtaining satisfactory convergence. Further details of
the data collection and refinements are given in Table 6.
J. Mol. Catal. A 2003, 204ꢀ205, 55. (f) Dry, M. E. Catal. Today 2002,
71, 227.
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Organometallics 2007, 26, 5912.
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27, 543.
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Crocker, M.; Vosejpka, P. C.; Fagan, P. J.; Marder, S. R.; Gohdes, M. A.
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Computational Details. The computations for compound 3 were
carried out using the Gaussian 03 package,35 in which the hybrid method
B3LYP was applied with the Becke three parameters exchange func-
tional36 and the LeeꢀYangꢀParr correlation functional.37 Effective core
potentials (ECP) and their associated double-ζ LANL2DZ basis set
were used for the metal atoms.38 The addition of an f-polarization
function to the basis set of the Mo atoms39 caused no significant
modifications in the computed geometry and electron distribution for
this molecule. The light elements (P, O, C, and H) were described with
the 6-31G* basis.40 Geometry optimizations were performed under no
symmetry restrictions, using initial coordinates derived from X-ray data
of the complex, and frequency analysis was performed to ensure that a
minimum structure with no imaginary frequencies was achieved. Mo-
lecular orbitals and vibrational modes were visualized using the Molekel
program.41 The topological analysis of F was carried out with the Xaim
routine.42
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2002, 21, 5515.
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’ ASSOCIATED CONTENT
(18) Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A. Organo-
metallics 2006, 25, 5734.
(19) Jeffery, J. C.; Ruiz, M. A.; Stone, F. G. A. J. Organomet. Chem.
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S
Supporting Information. CIF file giving the crystallo-
b
graphic data for the structural analysis of compounds 4, 7, and 8.
This material is available free of charge via the Internet at http://
pubs.acs.org.
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’ AUTHOR INFORMATION
Corresponding Author
*E-mail: mara@uniovi.es.
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’ ACKNOWLEDGMENT
We thank the DGI of Spain (Projects CTQ2006-01207 and
CTQ2009-09444) and the Consejería de Educaciꢀon y Ciencia de
Asturias (Project IB09-029) for financial support. We also thank
Sonia Menꢀendez for the scaling-up of the preparation of com-
pound 4.
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