Electronic structure and reactivity of the carbyne-bridged dimolybdenum radical [Mo2(η5-C5H5) 2(μ-CPh)(μ-PCy2)(μ-CO)]+

Article abstract of DOI:10.1021/om300989j

The unsaturated compound [Mo₂Cp₂(μ-CPh)(μ- PCy₂)(μ-CO)] (1, Cp = η⁵-C₅H ₅) reacts with trace amounts of water in the presence of [FeCp ₂]BF₄ to give a mixture of the hydroxycarbyne complex [Mo₂Cp₂(μ-COH)(μ-CPh)(μ-PCy₂)]BF ₄ (minor) and the hydroxo complex [Mo₂Cp ₂(μ-CPh)(OH)(μ-PCy₂)(CO)]BF₄ (major product), with the latter rapidly rearranging to give the carbene isomer cis-[Mo₂Cp₂(μ-η¹:η³-CHPh) (O)(μ-PCy₂)(CO)]BF₄ (Mo-Mo = 2.9435(3) A). An analogous reaction takes place with phenol, to give selectively the related phenoxo complex [Mo₂Cp₂(μ-CPh)(OPh)(μ-PCy ₂)(CO)]BF₄. In contrast, the reactions of 1 with H ₂SiPh₂ or H₃BNH₂^tBu in the presence of [FeCp₂]BF₄ result in the selective H transfer to the O atom of the carbonyl ligand, to give the mentioned hydroxycarbyne complex. All the above reactions can be rationalized by assuming the initial formation of the radical cation [Mo₂Cp ₂(μ-CPh)(μ-PCy₂)(μ-CO)]⁺ (2), a molecule displaying a somewhat weakened intermetallic bonding (Mo-Mo = 2.537 A vs 2.493 A in 1) and a linear semibridging carbonyl, with both the LUMO and most of the unpaired electron density being located at a single molybdenum atom, with a much smaller distribution over the oxygen atom of the carbonyl ligand, according to density functional theory calculations. As expected, the radical 2 adds rapidly a molecule of nitric oxide to give a diamagnetic product, but spontaneous decarbonylation also takes place to eventually give the 30-electron nitrosyl complex [Mo₂Cp ₂(μ-CPh)(μ-PCy₂)(μ-NO)]BF₄. Deprotonation of cis-[Mo₂Cp₂(μ-η¹: η³-CHPh)(O)(μ-PCy₂)(CO)]BF₄ gives the neutral carbyne complex cis-[Mo₂Cp₂(μ-CPh)(O)(μ- PCy₂)(CO)] (Mo-Mo = 2.8024(5) A), which upon protonation reverts to its carbene precursor, via the corresponding hydroxo complex. Related trans isomers can be prepared through protonation reactions of trans-[Mo ₂Cp₂(μ-CPh)(O)(μ-PCy₂)(CO)] (Mo-Mo = 2.8206(6) A), a complex easily prepared by reacting the dicarbonyl [Mo₂Cp₂(μ-CPh)(μ-PCy₂)(CO)₂] with air.

Full text of DOI:10.1021/om300989j

Article
pubs.acs.org/Organometallics
Electronic Structure and Reactivity of the Carbyne-Bridged
Dimolybdenum Radical [Mo2(η5‑C5H5)2(μ-CPh)(μ-PCy2)(μ-CO)]+
M. Angeles Alvarez, M. Esther García, Daniel García-Vivo, Sonia Menendez, and Miguel A. Ruiz*
́
́
́ ́
Departamento de Química Organica e Inorganica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain
S
* Supporting Information
ABSTRACT: The unsaturated compound [Mo2Cp2(μ-CPh)-
(μ-PCy2)(μ-CO)] (1, Cp = η5-C5H5) reacts with trace amounts
of water in the presence of [FeCp2]BF4 to give a mixture of the
hydroxycarbyne complex [Mo2Cp2(μ-COH)(μ-CPh)(μ-
PCy2)]BF4 (minor) and the hydroxo complex [Mo2Cp2(μ-
CPh)(OH)(μ-PCy2)(CO)]BF4 (major product), with the latter
rapidly rearranging to give the carbene isomer cis-[Mo2Cp2(μ-
η1:η3-CHPh)(O)(μ-PCy2)(CO)]BF4 (Mo−Mo = 2.9435(3)
Å). An analogous reaction takes place with phenol, to give
selectively the related phenoxo complex [Mo2Cp2(μ-CPh)-
t
(OPh)(μ-PCy2)(CO)]BF4. In contrast, the reactions of 1 with H2SiPh2 or H3BNH2 Bu in the presence of [FeCp2]BF4 result in
the selective H transfer to the O atom of the carbonyl ligand, to give the mentioned hydroxycarbyne complex. All the above
reactions can be rationalized by assuming the initial formation of the radical cation [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)]+ (2), a
molecule displaying a somewhat weakened intermetallic bonding (Mo−Mo = 2.537 Å vs 2.493 Å in 1) and a linear semibridging
carbonyl, with both the LUMO and most of the unpaired electron density being located at a single molybdenum atom, with a
much smaller distribution over the oxygen atom of the carbonyl ligand, according to density functional theory calculations. As
expected, the radical 2 adds rapidly a molecule of nitric oxide to give a diamagnetic product, but spontaneous decarbonylation
also takes place to eventually give the 30-electron nitrosyl complex [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-NO)]BF4. Deprotonation of
cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-PCy2)(CO)]BF4 gives the neutral carbyne complex cis-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)-
(CO)] (Mo−Mo = 2.8024(5) Å), which upon protonation reverts to its carbene precursor, via the corresponding hydroxo
complex. Related trans isomers can be prepared through protonation reactions of trans-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)(CO)]
(Mo−Mo = 2.8206(6) Å), a complex easily prepared by reacting the dicarbonyl [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] with air.
Scheme 1
INTRODUCTION
■
We have shown previously that binuclear cyclopentadienyl
complexes with metal−metal multiple bonds are useful
substrates to induce unusual bond formation and cleavage
processes involving the ligands surrounding the coordinatively
and electronically unsaturated dimetal center present in these
molecules. The 30-electron benzylidyne complex [Mo2Cp2(μ-
CPh)(μ-PCy2)(μ-CO)] (1)1 is one of these species (Cp = η5-
C5H5). For instance, it can be alkylated to give a cationic bis-
carbyne complex, [Mo2Cp2(μ-COMe)(μ-CPh)(μ-PCy2)]-
(CF3SO3), the latter undergoing C−C coupling between its
carbyne ligands upon addition of simple donor molecules (L),
to give alkyne-bridged complexes of the type [Mo2Cp2{μ-η2:η2-
C(OMe)CPh}(μ-PCy2)L2](CF3SO3) in a reversible way.2
Interestingly, compound 1 undergoes a related redox-induced
P−C coupling involving the carbyne and phosphide ligands.
Thus, although 1 does not react itself with the secondary
phosphine HPEt2, it reacts instantaneously in the presence of
stoichiometric amounts of the ferrocenium salt [FeCp2]BF4, to
give the phosphinocarbene derivative [Mo2Cp2(μ-η1:η1,κ1-
CPhPEt2)(μ-PEt2)(CO)(PHEt2)]BF4 in high yield (Scheme
1).2 More recently we have shown that 1 reacts with
diphenyldisulfide (and also with HSPh) in the presence of
[FeCp2]BF4 to give a thiolate derivative undergoing related P−
C coupling upon carbonylation, now in a reversible way
(Scheme 1).3 The above reactions are themselves of interest
Received: October 22, 2012
© XXXX American Chemical Society
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since the coupling between PR2 and CR ligands at di- or
polynuclear complexes to give bridging phosphinocarbene
ligands has been observed only in a few instances,4,5 and little
is known about the reversibility of such processes.
Scheme 2
Since compound 1 does not react itself with either PHEt2 or
S2Ph2, the reactions depicted in the Scheme 1 are likely to be
initiated by the removal of one electron from 1 to give an
extremely reactive 29-electron radical complex, [Mo2Cp2(μ-
CPh)(μ-PCy2)(μ-CO)]BF4 (2), which would afterward react
with the phosphine or disulfide reagents, respectively. It was
thus of interest to examine in more detail the formation,
structure, and chemical behavior of this putative paramagnetic
species, in order to be able to further exploit its full synthetic
potential. Organometallic radicals are quite elusive species, even
if they are involved in many fundamental reactions such as
ligand substitution, isomerization, atom transfer, electron
transfer, and metal−metal bond formation, but most of work
in this area has been devoted to the study of mononuclear
species.6,7 In contrast, the chemistry of binuclear radicals,
particularly those having metal−metal bonds and electron
counts below 34, has been comparatively little explored.8−10
Among the latter compounds, the 33-electron diiron and
diruthenium complexes [Fe2Cp2(μ-CSMe)(μ-CO)(CO)2] and
[M2Cp2(μ-CMe)(μ-CO)(CO)2] (M = Fe, Ru) are the only
ones bearing carbyne ligands that appear to have been studied
so far,9 this adding more interest to the study of the reactivity of
the dimolybdenum radical 2. Further interest in the chemistry
of binuclear radicals stems from their use as synthetic analogues
and models of the active centers of several naturally occurring
enzymes such as the [FeFe]- and [NiFe]-hydrogenases.11 We
have shown previously that unsaturated binuclear radicals can
be somewhat stabilized by using bridging P-donor ligands, thus
allowing for a more controlled study of its chemical behavior.
Such an approach is exemplified by the chemistry developed
around the phosphide-bridged complex [Mo2Cp2(μ-PPh2)-
(CO)4 ]1 2 and the diphosphine-bridged cations
[M2Cp2(CO)x(μ-R2PCH2PR2)]+ (M = Mo, W; R = Me, Ph;
x = 2−4),13 all of them displaying a metal-centered reactivity. In
the case of compound 2, however, the presence of the bridging
carbyne ligand might be the origin of some carbyne-centered
reactivity, as it might be guessed from the behavior of the
mentioned diiron complexes and also by that of some 17-
electron mononuclear carbyne complexes.7b In this paper we
analyze the likely geometry and electronic structure of this
paramagnetic complex in the light of density functional theory
(DFT) calculations carried out on both the cation of 2 and its
neutral precursor 1. This in turn will be useful to rationalize the
reactivity of 2 toward simple molecules such as water, silanes,
alcohols, or nitric oxide, among others. Moreover, complex 2
has been found to be very reactive toward a variety of bidentate
ligands having E−H bonds (E = O, S, P), and the results of the
latter reactions will be reported separately.
these compounds was found to be strongly dependent upon the
precise experimental conditions, particularly the amount of
water available (always present in trace amounts in the solvent,
therefore proportional to the amount of solvent used) and the
reaction time. Under the most anhydrous conditions used by us
(reaction carried out in a CD2Cl2 solution within an NMR
tube), monitoring of the reaction mixture revealed that, just
after the mixing of reagents, the ratio 3:4:cis-5 was around
3:10:1, but afterward the amounts of 3 and 4 gradually
decreased, while that of cis-5 increased, so that the latter
compound was the only species present in the solution after ca.
20 min. The presence of water greatly speeded these
transformations: thus, the addition of a drop of water to the
NMR tube just after mixing of reagents caused an immediate
transformation to give cis-5 as the unique product detectable by
31P NMR spectroscopy. The monitoring of this reaction when
carried out in a Schlenk tube in dichloromethane solution (ca. 5
mL) gave similar results, except for the fact that, due to the
greater amount of water available, the carbene cis-5 was the
major species present even after the initial mixing of reagents.
Of course, on-purpose addition of water causes the immediate
full conversion into the carbene complex, which can be thus
isolated in a conventional way (see the Experimental Section).
The unstable complexes 3 and 4 could be selectively
generated through specific reactions (see later), and this
allowed us to carry out some independent experiments to
establish the role of water in the oxidation of 1 (Scheme 2).
First we could observe that CD2Cl2 solutions of the hydroxo
complex 4 would slowly isomerize at room temperature to give
cis-5, with this transformation being complete in ca. 20 min.
However, when a drop of water was added to the NMR tube
upon dissolution of 4, the transformation into the carbene
complex was immediate, as determined by 31P NMR spectros-
copy. This suggests that the isomerization 4/cis-5 likely is an
intermolecular process mediated by external reagents such as
water or even the solvent. The external anion can be excluded
as a possible proton vehicle since the oxidation of 1 with a
ferrocenium salt having a less coordinating anion such as
[FeCp2](BAr′4) [Ar′ = 3,5-C6H3(CF3)2] gave rapidly cis-5′
(BAr′4− salt) without detectable amounts of the corresponding
hydroxo complex. In any case, we note how different the above
transformation is from that of the structurally related hydroxo
complexes [M2Cp2(OH)(μ-PPh2)2(CO)]BF4 (M = Mo, W),
which at room temperature transform into the corresponding
RESULTS AND DISCUSSION
■
Oxidation Reactions of the Carbyne Complex 1. When
no external reagents are added to a dichloromethane solution of
the unsaturated compound 1, the addition of [FeCp2]BF4 to
this solution promotes a immediate reaction to give a mixture
of up to three new species: the hydroxycarbyne complex
[Mo2Cp2(μ-COH)(μ-CPh)(μ-PCy2)]BF4 (3), the hydroxo
complex [Mo2Cp2(μ-CPh)(OH)(μ-PCy2)(CO)]BF4 (4), and
the carbene complex cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-
PCy2)(CO)]BF4 (cis-5) (Scheme 2). The relative ratio of
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for the DFT-Computed Structures of 1 and the Cation in 2
a
1
1
2
1
2
Mo1−Mo2
Mo1−P3
Mo2−P3
Mo1−C26
Mo2−C26
Mo1−C5
Mo2−C5
C26−C31
C5−O4
2.464(1)
2.402(3)
2.403(2)
1.99(1)
1.97(1)
2.09(1)
2.11(1)
1.46(2)
1.18(1)
2.493
2.450
2.450
1.993
1.999
2.122
2.118
1.455
1.193
2.537
2.473
2.450
1.973
2.033
2.472
2.014
1.448
1.169
Mo1−P3−Mo2
Mo1−C26−Mo2
Mo1−Mo2−C5
Mo1−Mo2−C26
P3−Mo2−C5
P3−Mo2−C26
P3−Mo1−C5
P3−Mo1−C26
Mo2−C5−O4
Mo1−C5−O4
61.2
77.3
54.1
51.2
88.6
89.9
88.5
90.1
144.1
143.8
62.0
78.6
64.6
49.7
92.5
91.4
81.8
92.1
166.9
124.7
a
Experimental values determined by X-ray diffraction (see ref 2).
oxo hydride isomers [M2Cp2(μ-H)(O)(μ-PPh2)2(CO)]BF4.14
It is sensible to assume that the relatively high electron density
at the bridgehead carbon of the carbyne ligand (see later)
provides a driving force for the formation of the carbene (rather
than hydride) isomer of the hydroxo complex 4.
This is a common trend with the functionals currently used in
the DFT computations of transition metal compounds.16a,19
We should stress that this neutral molecule displays essentially
symmetrical bridging groups. It might have been expected that
the removal of one electron from 1 would cause a generalized
reduction in all interatomic distances, particularly those
involving the metal atoms. Actually this was the observed
effect upon removal of one electron from the singly bonded
complex [Mo2Cp2(CO)4(μ-Ph2PCH2PPh2)] (from ca. 3.27 to
2.99 Å)13b and more recently on the isolectronic complex
[W2Cp2(CO)4(PMe3)2] (from ca. 3.23 to 3.03 Å).10 In
contrast, the intermetallic length in 2 increases by some 0.05
Å, while the average Mo−CPh and Mo−P lengths remain
almost unperturbed. The most dramatic change, however, takes
place at the carbonyl ligand, which rearranges into a type II
linear semibridging mode,20 it being strongly bound to Mo2
(Mo−C = 2.014 Å) and only weakly bound to Mo1 (Mo···C =
2.472 Å), while the Mo−C−O angle (166.9°) approaches
linearity. The latter geometrical parameters are comparable to
the experimental values measured for the semibridging
carbonyls in the 30-electron complex [W2Cp2(CO)2(μ-
Ph2PCH2PPh2)] (average values W−C = 1.97 Å, W···C =
2.44 Å, W−C−O = 167°)21 or in the isoelectronic dimers
[M2L2(CO)4] (M = Mo, W; L = Cp or related ligand).22 Linear
semibridging carbonyls of this type are favored for substrates
with high intermetallic bond orders,23 and this should be the
case for the cation in 2. In all, however, the geometrical
parameters suggest that the intermetallic bond order is
somewhat reduced when going from 1 to 2, which is against
simple predictions based on the effective atomic number
(EAN) formalism, but consistent with the MO and AIM
analysis to be discussed below.
The frontier MOs for 1 are comparable to those computed
for the methoxycarbyne complex [Mo2Cp2(μ-COMe)(μ-
PCy2)(μ-CO)],15 except that the δ component of the
intermetallic bond having π-bonding character with respect to
the metal−carbyne bond (MO 129) is much more stabilized in
the benzylidyne complex. Apart from this, its triple M−M bond
can be similarly described as having one σ (MO 131) and two δ
components, with the latter having some (MO 133) and
significant (MO 129) bonding character to the bridging CO
and CR ligands, respectively. Notably, the HOMO of the
molecule is a bonding orbital having σ Mo−CO bonding
character. Therefore, we can understand that the removal of
one electron from this molecule might cause a significant
weakening in the Mo−CO bond, which is consistent with the
rearrangement (from bridging to linear semibridging) com-
puted for the carbonyl ligand in 2.
The hydroxycarbyne complex 3 is analogous to the
methoxycarbyne complex [Mo2Cp2(μ-COH)(μ-COMe)(μ-
PCy2)]BF4, a thermally unstable species rearranging at room
temperature into the corresponding hydride isomer
[Mo2Cp2(μ-COMe)(H)(μ-PCy2)(CO)]BF4, before full de-
composition takes place.15 In contrast, the dichloromethane
solutions of 3 are stable for a few hours at room temperature,
although they eventually decompose, with no hydride isomer
being detected during the process. An independent experiment
revealed that compound 3 is rapidly deprotonated by water in
dichloromethane solution, to cleanly regenerate the carbonyl
complex 1. This is not unexpected after considering that
hydroxycarbyne complexes have been previously generated
through protonation reactions of carbonyl-bridged precursor-
s.14a,15 Not surprisingly either, the addition of 1 equiv of
[FeCp2]BF4 and a drop of water to a dichloromethane solution
of 1 caused its immediate transformation into cis-5.
In all, the above data suggest that the radical complex 2
formed after removal, by the ferrocenium cation, of one
electron from 1 would rapidly cleave the O−H bond of water
molecules in two possible ways: either by capturing the OH
group at the metal site (dominant path) or by abstracting an H
atom at the oxygen of the bridging carbonyl (minor pathway).
This is consistent with the observation of an irreversible
+
oxidation wave at −0.14 V (vs the FeCp2 /FeCp2 couple) in
the CV diagram of 1, when recorded in dichloromethane
solution. In order to better understand this dual behavior of
radical 2, we carried out some calculations and additional
reactivity studies, to be discussed next.
Geometric and Electronic Structure of the Para-
magnetic Complex 2. We have carried out DFT16
calculations on both 1 and 2. Following the methodology
previously used by us in the study of unsaturated carbyne
complexes,15,17 we have analyzed the electronic structure and
bonding in these complexes through the properties of the
relevant Kohn−Sham molecular orbitals (MO) and also by
inspection of the topological properties of the electron density,
as managed in the atoms in molecules (AIM) theory.18
The optimized bond lengths for the neutral substrate are in
good agreement with the data measured through X-ray
diffraction (Table 1),2 although the computed values for
lengths involving the metal atoms tend to be slightly longer (by
less than 0.05 Å) than the corresponding experimental data.
C
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The structural rearrangement occurring upon formation of 2
also modifies the intermetallic interactions in the cation, but in
a less obvious way. Although the single-occupation MOs
computed for 2 display considerable mixing, we can still
identify pairs of α- and β-spin orbitals accounting for the σ
(MO 131β and MO 129α) and one δ component (MO 134α
and MO 133β) of the intermetallic bond. We notice that the
latter component has considerable π-bonding character to the
linear semibridging carbonyl, thus nicely reproducing the earlier
interpretations that explain the prevalence of this type of
carbonyl in complexes with multiple metal−metal bonds as
derived from the stabilizing influence of these π-bonding
interactions.20,22 Steric effects have been proposed alternatively
to explain the appearance of this sort of bridging ligand,23 but
obviously this is not the case for compound 2, which has the
same steric constraints as those in its neutral precursor 1.
Besides this, the second δ component of the intermetallic bond
present in 1 (the one involving π bonding to the carbyne
ligand) can be clearly recognized in only a single orbital of the
cation in 2 (MO 128β). Thus, it appears that just three
electrons would be clearly involved in δ(Mo−Mo) bonding
interactions, which is consistent with the moderate increase of
the intermetallic distance (compared to 1) computed for 2.
On the other hand we note the presence, among the frontier
orbitals, of one with a nonbonding character (MO 132α),
which therefore represents unpaired electron density largely
located at the Mo1 atom, with a smaller contribution from the
oxygen atom of the semibridging carbonyl. This is fully
consistent with the distribution of the total spin density in the
cation (Figure 3), which indeed is essentially located at the
site), while the hydroxycarbyne complex 3 (following from the
capture of a H radical by the oxygen site) is the minor product.
We do not expect any primary reaction to take place at the
carbyne C atom, in contrast to the chemical behavior observed
for the paramagnetic Fe2 and Ru2 carbyne complexes
mentioned in the Introduction.
The preceding orbital analysis does not give a full picture of
the changes occurring at the carbyne and carbonyl ligands.
These can be further analyzed by inspection of the topological
properties of the electron density (Table 2). First we note that
the electron density (ρ) at the intermetallic bond critical point
(bcp) in 1 (0.624 e Å−3) is slightly higher than the one
computed for its methoxycarbyne analogue [Mo2Cp2(μ-
COMe)(μ-PCy2)(μ-CO)] (0.609 e Å−3),15 but in any case
consistent with the triple intermetallic bond present in these
molecules. Upon oxidation, that density is somewhat reduced
to 0.553 e Å−3, a value still much higher than the values
computed for related species having double metal−metal bonds
(e.g., 0.444 e Å−3 for the 32-electron carboxycarbyne complex
[Mo2Cp2{μ-C(CO2Me)}(μ-PCy2)(CO)2])17 and actually com-
parable to the density computed for the 30-electron hydride
[Mo2Cp2(μ-H)(μ-PCy2)(CO)2] (0.582 e Å−3), a molecule with
a triple intermetallic bond having one tricentric (Mo2H) and
two bicentric (Mo−Mo) components.24 Thus we conclude that
the intermetallic bond in 1 is only moderately weakened upon
oxidation, perhaps in part because of a larger delocalization of
δ-bonding electron density on the semibridging CO. As for the
carbyne ligand, the average value of ρ at the Mo−C bcp (0.90 e
Å−3) remains almost unchanged upon oxidation. In contrast,
significant changes are computed for the carbonyl ligand. Thus,
upon oxidation of 1, the density at the Mo2−C5 bond is
increased from 0.72 to 0.80 e Å−3, consistent with the
appearance of a significant π-bonding contribution to that
bond already noted, while no bcp could be located between the
carbonyl and the Mo1 atom. At the same time, the density at
the C−O bond is increased (from to 2.81 to 2.95 e Å−3), then
approaching the values computed for terminal carbonyls.
Oxidatively Induced Reactions of 1 with Alcohols,
Silanes, and Borane Adducts. To better understand the
factors driving the reactions of the radical 2 to take place at the
metal or oxygen sites, we investigated the oxidatively induced
reactions of 1 with other reagents having E−H bonds, with E
being a p-block element. We have noted above that the reaction
with molecules having P−H and S−H bonds (reactions with
PHEt2 and HSPh) occur preferentially at the metal site to form
the corresponding Mo−P and Mo−S bonds, respectively.2,3 We
have now examined some reactions with molecules having O−
H, N−H, C−H, Si−H, and B−H bonds. Unfortunately, these
reactions are seriously limited by kinetics, for if the added
reagent reacts with 2 too slowly, then the reaction with water
occurs preferentially to eventually give only cis-5.
Figure 1. DFT-optimized structure of the cation in compound 2, with
H atoms omitted for clarity.
Mo1 atom, with some participation of the oxygen atom and
even smaller contributions from the Mo2 and C(carbyne)
atoms. Moreover, the LUMO in the cation also is largely
located at the Mo1 atom (MO134β, see the Supporting
Information). Thus, from this orbital analysis we can conclude
that the radical 2 should react preferentially at the Mo1 site,
because of both the large concentration of unpaired electron
density and the availability of an empty MO of low energy
centered at this position, while the second site of attachment
for an external radical should be the oxygen atom of the
carbonyl. These conclusions are consistent with the outcome of
reaction of 2 with water, which gives as the major product the
hydroxo complex 4 (capture of an OH radical by the metal
No reaction other than the formation of cis-5 was observed
when adding [FeCp2]BF4 to dichloromethane solutions of 1
containing an excess of NH2(p-tol) or different 1-alkynes
(HCCR, with R = p-tol, CO2Me). However, in the presence
t
of the silane SiH2Ph2 or the borane adduct H3B·NH2 Bu
(molecules which are themselves unreactive toward 1), a fast
reaction takes place to give the hydroxycarbyne complex 3, a
result of the selective abstraction, by the oxygen site in the
radical 2, of a hydrogen atom from the corresponding Si−H
and B−H bonds (Scheme 3). In contrast, when the reaction
was carried out in the presence of phenol, then the phenoxo
complex [Mo2Cp2(μ-CPh)(OPh)(μ-PCy2)(CO)]BF4 (6) was
D
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Figure 2. Selected molecular orbitals computed for 1 and the radical cation in 2, with their energies (in eV) and main bonding character indicated
below.
formed selectively, this following from the selective abstraction
of a phenoxyl group by the metal site in 2. Complex 6 is
structurally related to the hydroxo complex 4 (see below) and
also is rather unstable; it slowly undergoes hydrolysis upon
manipulation, to eventually give cis-5 via compound 4.
From the above data we conclude that the outcome of the
reactions of radical 2 are strongly influenced by the donor
properties of the incoming molecule and obviously also by the
strength of the E−H bond to be cleaved. We should recall here
that the Mo1 atom not only bears most of the unpaired spin
density but also is the greater contributor to the LUMO of the
cation in 2. Therefore, H−ERn reagents with a significant donor
ability of the E atom would tend to bind first the metal site,
then evolving through dehydrogenation (easier for the weaker
E−H bonds), thus accounting for the formation of a new Mo−
ERn bond. The silanes and borane adducts lack any lone
electron pair and are therefore very poor donors, this
precluding their efficient coordination at the metal site. Yet,
the corresponding E−H bonds are relatively weak, with this
now facilitating the H abstraction by the O atom of the
carbonyl ligand, to generate a new and strong O−H bond.
Under this view, the failure of 2 to react rapidly with amines
and 1-alkynes would follow from a combination of two adverse
E
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a
b
Table 3. Selected IR and 31P{1H} and 13C{1H} NMR Data
for New Compounds
compound
ν(XO)
δ (P)
δ (μ-C) [JPC]
[Mo Cp2(μ-CPh)(μ-PCy2)(μ-CO)]
1686
(s)
228.5
385.2 [15]
2c
(1)
e
e
[Mo2Cp2(μ-COH)(μ-CPh)(μ-PCy2)]
BF4 (3)
1304
(w)
254.8
401.4 [14]
357.8 [14]
d
d
d
[Mo2Cp2(μ-CPh)(OH)(μ-PCy2)(CO)] 1965
302.4
236.4
238.5
242.5
277.3
195.8
187.4
267.9
181.0
413.1
BF4 (4)
(s)
cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-
PCy2)(CO)]BF4 (cis-5)
1944
(s)
cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-
PCy2)(CO)]BAr′4 (cis-5′)
1952
(s)
177.0
trans-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-
PCy2)(CO)]BF4 (trans-5)
1930
(s)
Figure 3. Total spin density for the radical cation in 2.
[Mo2Cp2(μ-CPh)(OPh)(μ-PCy2)
(CO)]BF4 (6)
1962
(s)
Table 2. Topological Properties of the Electron Density in
a
Complexes 1 and 2
cis-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)
(CO)] (cis-7)
1915
(s)
360.0 [7]
1
2
trans-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)
(CO)] (trans-7)
1895
(s)
bond
ρ
∇2ρ
1.85
ρ
∇2ρ
1.62
[Mo2Cp2(μ-CPh)(μ-PCy2)(μ-NO)]BF4 1511
(8) (s)
404.5 [14]
132.3[4]
Mo1−Mo2
Mo1−P3
Mo2−P3
Mo1−C(5)
Mo(2)−C(5)
Mo(1)−C(26)
Mo(2)−C(26)
C(5)−O(4)
C(26)−C(31)
0.624
0.502
0.500
0.715
0.720
0.909
0.895
2.807
1.954
0.553
0.484
0.500
not found
0.800
0.946
0.829
2.952
1.979
3.31
3.33
2.87
3.33
[Mo2Cp2(μ-CHPh)(O)(μ-PCy2)(NO)] 1610
BF4 (9) (s)
a
6.04
Recorded in dichloromethane solution, with X−O (X = C, N)
b
stretching bands (ν(XO)) in cm−1. Recorded in CD2Cl2 solutions at
290 K and 162.00 MHz (31P) or 100.62 MHz (13C) unless otherwise
stated; δ in ppm relative to external 85% aqueous H3PO4 or internal
TMS, respectively; JPC in Hz. Data from ref 1. Recorded in Nujol
mull. Recorded at 233 K.
6.10
9.45
9.37
9.50
9.44
8.92
c
d
23.83
−16.07
28.64
−16.44
e
a
Values of the electron density at the bond critical points (ρ) are given
in e Å−3, and values of the Laplacian of ρ at these points (∇2ρ) are
given in e Å−5, with the labeling according to Figure 1; see the
Experimental Section for details of the DFT calculations.
the bridgehead COR atoms at ca. 370 ppm. In the case of 3, the
13C NMR spectrum displays a second strongly deshielded
resonance, which is therefore safely assigned to the benzylidyne
ligand (401.4 ppm). We note that both carbyne resonances
display a P−C coupling of 14 Hz, comparable to that measured
in the starting complex 1, in agreement with the similar P−
Mo−C angles involving the carbyne ligands in all these
molecules.25 We also note that the Cp ligands give rise to single
13C or 1H NMR resonances, thus indicating that the
hydroxycarbyne group undergoes fast rotation around its C−
O bond, as previously observed for other hydroxycarbyne-
bridged complexes.14a,15,26 Unfortunately we could not identify
the resonance of the OH group in the 1H NMR spectrum of 3,
but its presence is supported by the appearance of a broad band
at ca. 3400 cm−1 in its solid-state IR spectrum, corresponding
to the O−H stretch of this group.
Scheme 3
The spectroscopic data for compounds 4 and 6 are similar to
each other, suggesting that these asymmetric species share the
same basic structural features. They display a high-frequency
C−O stretch at ca. 1965 cm−1, indicative of the presence of a
terminal carbonyl in a cationic complex.27 Unexpectedly, both
complexes display strongly deshielded 31P NMR resonances at
302.4 and 277.3 ppm, respectively. This is a feature
characteristic of Mo2(μ-PCy2) complexes having triple
intermetallic bonds. Actually, such high values have been
previously observed only for hydride complexes of the type
[Mo2Cp2(H)(μ-X)(μ-PCy2)(CO)]BF4 (X = COMe,
PCy2),15,28 which however display a transoid arrangement of
their terminal hydride and semibridging carbonyls. We have
recently shown that the related ditungsten complexes cis-
[W2Cp2(X)(μ-PPh2)2(CO)]BF4 display terminal hydroxo and
thiolate ligands, which rather behave as three-electron donors
due to strong π bonding to the metal atoms.29 In contrast, the
circumstances: a relatively poor donor ability of these molecules
and the relatively high strength of their N−H and C−H bonds.
Spectroscopic Characterization of Hydroxo, Alkoxo,
and Hydroxycarbyne Complexes. The spectroscopic data
available for the hydroxycarbyne complex 3 (Table 3 and
Experimental Section) are similar to those of the isoelectronic
hydroxy- and methoxycarbyne cations [Mo2Cp2(μ-X)(μ-
COMe)(μ-PCy2)]BF4 (X = COH, CPh)15,2 and, therefore,
need no detailed analysis. We just note that all these 30-
electron cations are characterized by strongly deshielded 31P
NMR resonances at ca. 260 ppm and 13C NMR resonances for
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dimolybdenum thiolate complex [Mo2Cp2(CPh)(μ-PCy2)(μ-
SPh)(CO)]BF4 seems to prefer a geometry with bridging
thiolate (again a three-electron donor group) and essentially
terminal benzylidyne ligands, according to DFT calculations.3
In all these previous cases, however, the corresponding cations
are 32-electron complexes for which a double metal−metal
bond can be formulated according to the EAN formalism. In
line with this, the PR2 ligands in all these species give rise to
relatively shielded 31P NMR resonances (around 110 ppm).
This does not appear to be the case for compounds 4 and 6,
which display strongly deshielded 31P resonances characteristic
of 30-electron complexes while keeping a bridging benzylidyne
ligand (δC 413.1 ppm for 4). From all these considerations we
conclude that the Mo−OR binding in compounds 4 and 6
must be described as an essentially single bond, this leading us
to propose a formal triple intermetallic bond for these
molecules.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for cis-
5′
Mo1−Mo2
Mo1−P1
Mo2−P1
Mo2−C2
Mo1−C2
Mo1−C3
Mo1−C4
Mo1−C1
Mo2−O2
C2−C3
2.9435(3)
2.3958(8)
2.4316(7)
2.083(3)
2.191(3)
2.393(3)
2.675(3)
1.998(3)
1.689(2)
1.446(4)
1.421(4)
1.416(4)
1.361(4)
C6−C7
C7−C8
C8−C3
1.417(5)
1.358(4)
1.436(4)
75.14(2)
87.0(1)
109.5(1)
106.4(1)
82.8(1)
97.9(1)
98.9(1)
99.8(1)
115(2)
Mo1−P1−Mo2
Mo1−C2−Mo2
Mo2−Mo1−C1
Mo1−Mo2−O2
P1−Mo1−C1
P1−Mo1−C2
P1−Mo2−O2
P1−Mo2−C2
C3−C2−H2
C3−C4
C4−C5
C5−C6
Structure of the Carbene Complex cis-5′. The structure
considerable multiplicity in that bond. Actually, the oxo ligand
in cis-5′ must be better considered as a four-electron donor,
this leading to the electronic saturation of the dimetal center.
As a result, a single metal−metal bond might be formulated for
this 34-electron complex under the EAN formalism, which is in
agreement with the relatively high intermetallic length of
2.9435(3) Å. For comparison, the intermetallic distance in the
32-electron carbyne complex [Mo2Cp2(μ-CPh)(μ-PCy2)-
(CO)2] is only 2.666(1) Å.1
−
of complex cis-5 was determined on a crystal of its BAr′4 salt
cis-5′. The cation is built up from CpMo(CO) and CpMo(O)
units placed in a cisoid arrangement and bridged by
dicyclohexylphosphide and benzylidene ligands (Figure 4).
The spectroscopic data in solution for the salts cis-5 and cis-
5′ are comparable to each other, this revealing the presence of
−
only moderate cation−anion interactions for the BF4 ion.
Moreover they are fully consistent with the structure found in
the crystal. Of particular interest concerning the description of
the Mo−O and Mo−Mo bonds is the observation of a relatively
deshielded 31P NMR resonance at ca. 240 ppm, more than 100
ppm above the usual shifts observed for 32-electron complexes
of the type [Mo2Cp2(μ-X)(μ-PCy2)(CO)2] (X = three-electron
donor group; e.g., δP 117.6 ppm when X = CPh), thus
supporting the formulation of this cation as a 34-electron
complex with a single Mo−Mo bond. For comparison, the
electron-precise tricarbonyls [Mo2Cp2(μ-X)(μ-PCy2)(CO)3]
(X = COMe, CHCH(p-tol), CHCH2) display similarly
deshielded 31P NMR resonances in the range 220−250
ppm.17,33
Figure 4. ORTEP diagram (30% probability) of the cation in
compound cis-5′, with H atoms (except H2) and Cy groups (except
their C1 atoms) omitted for clarity.
The coordination of the carbene ligand is strongly asymmetric,
it being strongly bound to the O-bearing metal atom (Mo−C =
2.083(3) Å) and more loosely to the CO-bearing metal
(2.191(3) Å); additionally, the ipso carbon of the phenyl ring is
clearly within bonding distance of the Mo1 atom (2.393(3) Å),
while one of the ortho carbons might be viewed as weakly
interacting with that metal atom (2.675(3) Å). Therefore, the
carbene ligand can be formally viewed as a four-electron donor,
bound to the metal center through the carbene atom and a
double C−C bond of its aryl ring (μ-η1:η3 coordination mode).
This coordination mode of arylcarbene ligands has been
previously characterized crystallographically in a few instan-
ces,30,31 including the dimolybdenum complex [Mo2Cp2{μ-
η1:η3-C(p-tol)2}(μ-CO)(CO)3]. The coordination of the aryl
ring in all these complexes seems to induce some localization
effect on the ring (alternating long and short C−C bonds
lengths) and some shortening in the carbene-aryl C−C bond,
with these structural features also being observed in cis-5′
(Table 4).
The carbene ligand in cis-5 retains in solution the μ-η1:η3
coordination mode found in the solid state. Thus, the 13C
NMR spectrum of the complex displays, in addition to a
resonance at 177.0 ppm consistent with the presence of a
bridging carbene ligand,34 six distinct resonances for the aryl
ring, with the ipso (102.0 ppm) and one of the ortho resonances
(101.2 ppm) being considerably shifted upfield (by some 60
and 30 ppm, respectively), thus denoting their coordination to
1
a metal atom in solution. In line with this, the H NMR
spectrum of this complex reveals an unusual shielding for one
of the ortho aryl resonances (δH ca. 4.6 ppm), while the carbene
C−H resonance appears strongly deshielded (δH ca. 10 ppm).
These spectroscopic features are common to previous binuclear
complexes having μ-η1:η3 arylcarbene ligands.30c,35
Neutral Derivatives and trans Isomers of Compounds
4 and 5. The addition of a strong base such as 1,8-
diazabicycloundec-7-ene to dichloromethane solutions of either
the hydroxo complex 4 or its carbene isomer cis-5 causes their
immediate deprotonation to give the neutral oxo carbyne
complex cis-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)(CO)] (cis-7),
which retains the cisoid arrangement of the MoCp fragments
The Mo−O length in this cation is very short (1.689(2) Å),
as usually found in organometallic complexes having terminal
oxo ligands,32 a feature indicative of the presence of
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found in its cationic carbene precursor, as confirmed crystallo-
graphically (Scheme 4 and Figure 5). This neutral complex
Scheme 5
Scheme 4
corresponding hydroxo complex is just too unstable and
rapidly rearranges into its more stable isomer trans-5.
The spectroscopic data available for trans-5 (Table 3 and
Experimental Section) are comparable to those of its cis isomer
and therefore deserve no detailed analysis. We just note that
this isomer displays a C−O stretching band some 15 cm−1
lower than that of its cis isomer, a difference also observed for
the cis and trans isomers of the neutral oxo complexes 7. As for
1
the carbene ligand, it gives rise to H NMR resonances similar
to those of cis-5, that is, a very deshielded C−H resonance (δH
ca. 11 ppm) and five inequivalent aryl resonances, one of them
quite shielded (δH ca. 4.6 ppm), thus indicating the μ-η1:η3
coordination of the arylcarbene ligand in this isomer.
Structural Characterization of the Oxo Complexes 7.
The structures of the cis and trans isomers of the oxo carbyne
complex 7 were determined through X-ray analysis (Figures 5
and 6 and Table 5). Both molecules are built up from
Figure 5. ORTEP diagram (30% probability) of cis-7, with H atoms
and Cy groups (except their C1 atoms) omitted for clarity.
could be easily reprotonated upon reaction with HBF4·OEt2, a
process taking place selectively at the oxo ligand as expected,14
to give the hydroxo complex 4, thus completing a loop
connecting hydroxo carbyne, oxo carbene, and oxo carbyne
complexes.
Taking into account the retention of stereochemistry
observed in the above reactions, it could be anticipated that a
whole set of trans isomers of compounds 4, 5, and 7 might be
prepared, should a trans isomer of any of these compounds be
available. Mays et al. have shown previously that the reaction of
the dicarbonyl complex trans-[Mo2Cp2(μ-PPh2)2(CO)2] with
air gives the oxo derivative trans-[Mo2Cp2(O)(μ-PPh2)2(CO)]
as the major product, whereas the same reaction with the
carbonyl complex [Mo2Cp2(μ-PPh2)2(μ-CO)] instead leads
preferentially to the cis isomer.36 Similar selectivity was
observed in the reactions of the methoxycarbyne complexes
[Mo2Cp2(μ-COMe)(μ-PCy2)(CO)x] with air (x = 1, 2).37
Thus, it was not surprising that we could prepare selectively the
trans isomer of complex 7 by reacting the dicarbonyl
[Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] with air (Scheme 5). The
neutral complex trans-7 thus obtained then reacts readily with
HBF4·OEt2, but we could not detect a hydroxo complex in the
reaction mixture; instead, the trans isomer of the carbene
complex 5 was the only product present in the solution, a
compound that reverts to its neutral precursor trans-7 upon
reaction with a strong base. No doubt the protonation of trans-
7 is initiated at the oxo ligand, but apparently the
Figure 6. ORTEP diagram (30% probability) of trans-7, with H atoms
and Cy groups (except their C1 atoms) omitted for clarity.
CpMo(CO) and CpMo(O) units bridged by dicyclohexyl-
phosphide and benzylidyne ligands in a similar way, except for
the relative conformation of the terminal ligands. In the trans
isomer the central Mo2PC rhombus is nearly flat (dihedral P1−
Mo1−Mo2−C2 angle 179.8°) and the terminal carbonyl is
nearly normal to the intermetallic axis, while the oxo ligand
points away from the intermetallic region (Mo−Mo−O ca.
110°). In the cis isomer, however, the central Mo2PC rhombus
is significantly puckered (dihedral P1−Mo1−Mo2−C2 angle
155.6°), and the CO and O ligands are placed almost parallel to
each other (Figure 5). The conformation of the trans isomer
has been previous determined crystallographically in the related
H
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Table 5. Selected Bond Lengths (Å) and Angles (deg) for the cis and trans Isomers of Compound 7
cis-7
trans-7
cis-7
trans-7
Mo1−Mo2
Mo1−P1
Mo2−P1
Mo1−C1
Mo1−C2
Mo2−C2
Mo2−O2
C2−C3
2.8024(5)
2.363(1)
2.467(2)
1.962(6)
1.928(6)
2.089(5)
1.720(4)
1.465(8)
1.146(6)
2.8206(6)
2.354(1)
2.437(1)
1.970(5)
1.920(5)
2.096(5)
1.704(4)
1.465(7)
1.154(6)
Mo1−P1−Mo2
Mo1−C2−Mo2
Mo1−Mo2−O2
Mo2−Mo1−C1
P1−Mo1−C1
P1−Mo1−C2
P1−Mo2−O2
P1−Mo2−C2
Mo1−C1−O1
70.89(4)
88.4(2)
72.11(4)
89.1(2)
103.6(1)
78.6(2)
109.6(1)
87.7(2)
91.7(1)
88.4(2)
101.2(2)
105.5(1)
93.5(2)
103.3(2)
102.1(1)
95.5(2)
C1−O1
174.0(4)
176.4(5)
oxo complexes trans-[M2Cp2(μ-X)(O)(μ-PPh2)(CO)] (M =
Mo, X = PPh2,36 CHCHPh;38 M = W, X = CH2PPh2).21 On
the other hand, the conformation of the cis isomer can be
related to those recently determined for several diphenylphos-
phide-bridged Mo2 and W2 complexes of the type [M2Cp2(μ-
PPh2)2(X)(CO)]n+ (n = 1, 0), with X being a terminal
monodentate or chelate anionic ligand.14a,29,39
The above conformational differences, however, have little
influence on the interatomic distances, which are comparable in
both isomers of compound 7 but still deserve some analysis.
The Mo−O lengths of ca. 1.71 Å are almost as short as that in
cis-5, but the intermetallic lengths of ca. 2.81 Å are significantly
longer, actually midway between the reference value for a
double bond (cf. 2.666(1) Å in [Mo2Cp2(μ-CPh)(μ-PCy2)-
(CO)2])1 and the value of 2.9435(3) Å measured for the
“single” Mo−Mo bond in cis-5. We have previously interpreted
this sort of intermediate situation as resulting from a
diminished π(Mo−O) bonding interaction that can be
visualized by using a mixture of canonical forms involving the
oxo ligand acting as a two- or a four-electron donor,
respectively.40 This can be represented in the case of 7 through
the forms I and II depicted in Chart 1, with the latter implying
closely than anticipated for a situation intermediate between
the extreme descriptions represented by the forms I and II (cf.
1.94(2) Å for the WC bond in the carbene complex [W{κ3-
(NC4HMe2)3BH}(CMePh)(CO)2]BF4).41
The spectroscopic data in solution for the cis and trans
isomers of complex 7 are consistent with the structural data just
discussed. First we note that both isomers give rise to 31P NMR
resonances at ca. 190 ppm, a chemical shift much higher than
the values expected for 32-electron complexes with double
Mo−Mo bonds (cf. 117.6 ppm for [Mo2Cp2(μ-CPh)(μ-
PCy2)(CO)2]), but still lower than the value of ca. 236 ppm
recorded for the 34-electron complex cis-5. This again suggests
a situation intermediate between those represented by the
canonical forms I and II of Chart 1. In line with this, the 13C
NMR resonance of the bridgehead atom of the carbyne ligand
in cis-7 (δC 360.0 ppm) appears significantly more shielded
than the corresponding resonances in related dimolybdenum
complexes having symmetrically bridging CPh ligands, with
chemical shifts in the range 385−435 ppm.1,3 We finally note
that the cis isomer displays a C−O stretching frequency some
20 cm−1 higher than its trans isomer, as noted already for the
isomers of 5. A similar trend was found for the cis and trans
isomers of the diphenylphosphide-bridged oxo complex
[Mo2Cp2(O)(μ-PPh2)2(CO)].36 It is tempting to attribute
this effect to the slightly stronger Mo−O interaction apparent
for the trans isomer, because that would increase the π back-
donation of the metal center to the carbonyl, therefore reducing
the stretching frequency of the latter ligand.
Chart 1
Nitrosyl Derivatives of Complex 1. Nitrogen monoxide is
a stable radical expected to react readily with organometallic
radicals to afford more stable diamagnetic products,12,13b and
indeed this is the case of compound 2. Thus, although the triply
bonded complex 1 does not react rapidly with diluted NO
(2000 ppm in N2), it does it instantaneously in the presence of
[FeCp2]BF4 to give the nitrosyl-bridged complex [Mo2Cp2(μ-
CPh)(μ-PCy2)(μ-NO)]BF4 (8) in good yield. This reaction is
presumably initiated by NO coordination to the radical 2, to
give an intermediate A having CO and NO ligands that would
rapidly release CO to give 8 (Scheme 6). However, we have not
identified such an intermediate upon monitoring of the above
reaction.
the asymmetric coordination of the bridging ligands, closer to
the CO-bearing metal atom. Thus, although a form of type II
would be dominant in the cation of cis-5 (and presumably also
in the case of the mentioned complexes trans-[M2Cp2(μ-
X)(O)(μ-PPh2)(CO)], because of their large intermetallic
lengths, in the range 2.89−2.95 Å), both canonical forms would
contribute significantly to the bonding in compound 7.
Incidentally we note that the trans isomer displays a slightly
shorter Mo−O length of 1.704(4) Å, which correlates with a
slightly longer Mo−Mo length of 2.8206(6) Å (greater
contribution of the form II). In any case, the donor efficiency
of the oxo ligand in 7 is much superior to that of the terminal
CO, as concluded from the significant elongation of the Mo−P
and Mo−C(carbyne) bonds involving the O-bearing metal
atom (ca. 0.09 and 0.12 Å, respectively). This effect is so
pronounced that the actual Mo−C lengths for the carbyne
ligand of 1.92 and 2.09 Å approach the reference values for
double and single bonds involving an sp2 C atom even more
Unsaturated binuclear complexes bridged by nitrosyl ligands
are rather uncommon species,42 but they can be involved in
interesting reactions, particularly the cleavage of the N−O bond
of the nitrosyl ligand, as observed for 32-electron complexes of
the type [M2Cp2R2(μ-NO)2] (M = Mo, W).43 Interestingly, no
complex with a nitrosyl ligand bridging a triple intermetallic
bond appears to have been previously described in the
literature. Unfortunately our attempts to grow X-ray quality
−
crystals of 8 or its BAr′4 salt were unsuccessful. Attempts to
I
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interaction with the metal atoms. From all the above data,
however, we cannot establish the exact conformation of the
molecule, although it likely corresponds to the cis isomer having
the Ph group pointing away from the puckered central Mo2PC
ring of the molecule, expectedly more favored on steric
grounds.
Scheme 6
CONCLUDING REMARKS
■
One-electron oxidation by [FeCp2]BF4 greatly increases the
reactivity of the relatively inert 30-electron complex
[Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (1), thus enabling it to
rapidly react with many different molecules under mild
conditions. According to DFT calculations, the radical species
[Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)]+ (2) formed after removal
of one electron from 1 displays a somewhat weakened
intermetallic bonding and a linear semibridging carbonyl,
while both the LUMO and most of the unpaired electron
density are located at a single molybdenum atom, with a much
smaller distribution over the oxygen atom of the carbonyl
ligand. As a result, the reactions of 2 with simple H−ERn
reagents (thiols, phosphines, alcohols, etc.) are expected to be
initiated by the coordination of these donor molecules at the
Mo site, followed by the cleavage of one H−E bond to
eventually yield a new Mo−ERn bond. Molecules lacking a
reasonable donor ability, but having relatively weak H−E
bonds, instead might be involved in H transfer to the O atom of
the carbonyl ligand of 2 to give the hydroxycarbyne complex
[Mo2Cp2(μ-COH)(μ-CPh)(μ-PCy2)]+, as observed in the
reactions with silanes and borane adducts. Finally, molecules
with poor donor properties and strong H−E bonds would fail
to react with 2 fast enough to avoid the interaction of this
reactive radical with trace water molecules. The latter reaction
takes place at both the Mo and O sites, with the former being
dominant and leading to the unstable hydroxo complex
[Mo2Cp2(μ-CPh)(OH)(μ-PCy2)(CO)]+ rapidly rearranging
into its carbene isomer cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-
PCy2)(CO)]+, which in turn is reversibly deprotonated to give
the corresponding oxo carbyne derivative cis-[Mo2Cp2(μ-
CPh)(O)(μ-PCy2)(CO)]. The stereochemistry of these
products is preserved along the pertinent transformations, a
circumstance allowing the preparation of the corresponding
trans isomers by starting from trans-[Mo2Cp2(μ-CPh)(O)(μ-
PCy2)(CO)]. As expected, the radical 2 adds rapidly a molecule
of nitric oxide to give a diamagnetic product, but spontaneous
decarbonylation also takes place to eventually give the 30-
electron nitrosyl complex [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-
NO)]+, a cation that seems to have a strongly electrophilic
character.
purify the latter salts through column chromatography on
alumina promoted instead a clean transformation on 8, to give
the neutral carbene complex [Mo2Cp2(μ-CHPh)(O)(μ-PCy2)-
(NO)]BF4 (9) in good yield (Scheme 6). Presumably, the
formation of 9 involves the nucleophilic attack of surface
hydroxide groups on the cation of 8, followed by a H migration
from the coordinated OH to the carbyne ligand in the resulting
intermediate B, a process analogous to the isomerization 4/cis-
5 discussed above (Scheme 2). In agreement with this, a
separate experiment confirmed that 9 can be obtained by
stirring a dichloromethane solution of 8 with solid KOH.
Actually, the latter reaction also gives a small amount of a
second species (not isolated) that displays a 31P NMR
resonance at 180.8 ppm, quite close to that of 9 (181.0
ppm), therefore being proposed as a geometric isomer of the
main product. In any case, the above transformation reveals
that the unsaturated nitrosyl complex 8 is a highly electrophilic
substrate, and further studies on the reactivity of this electron-
deficient cation are now under way in our laboratory.
The structural characterization of 8 is straightforward on the
basis of the available spectroscopic data. The presence of a
symmetrically bridging carbyne ligand is denoted by the
appearance of a strongly deshielded resonance at 405 ppm in
its 13C NMR spectrum, while the presence of the bridging
nitrosyl is confirmed by the observation of a low-frequency N−
O stretch at 1511 cm−1 in its solid-state spectrum.42 As a result,
the cation in 8 is a 30-electron complex for which a triple
intermetallic bond is to be formulated under the EAN
formalism, which is in agreement with the strong deshielding
of its 31P nucleus (δP ca. 270 ppm). In contrast, compound 9
gives rise to a 31P NMR resonance comparable to those of the
oxo complexes 7, while its solid-state IR spectrum establish
unambiguously the presence of terminal nitrosyl (νNO 1606
cm−1) and oxo (νMoO 933 cm−1) ligands.32,42 At the same time,
its 13C NMR spectrum shows the absence of any deshielded
carbyne resonance, which has been instead replaced by a much
more shielded CH resonance at 132.3 ppm, consistent with the
presence of a bridging carbene ligand (δH 8.70 ppm),34 while
the resonances of the phenyl ring are normal, indicating no
EXPERIMENTAL SECTION
■
General Procedures and Starting Materials. All manipulations
and reactions were carried out under a nitrogen atmosphere
(99.999%) using standard Schlenk techniques. Solvents were purified
according to literature procedures and distilled prior to use.44
Petroleum ether refers to that fraction distilling in the range 338−
343 K. Compounds [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (1),1
[Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2],1 [FeCp2]BF4,45 Na[B{3,5-
C6H3(CF3)2}4] (NaBAr′4),46 and [FeCp2](BAr′4)47 were prepared
as described previously. All other reagents were obtained from the
usual commercial suppliers and used as received. Chromatographic
separations were carried out using jacketed columns cooled by tap
water (ca. 288 K) or by a closed 2-propanol circuit, kept at the desired
temperature with a cryostat. Commercial aluminum oxide (activity I,
150 mesh) was degassed under vacuum prior to use. The latter was
J
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mixed under nitrogen with the appropriate amount of water to reach
the activity desired. Filtrations were performed using diatomaceous
earth unless otherwise stated. IR C−O stretching frequencies were
measured in solution, are referred to as νCO (solvent), and are given in
wavenumber units (cm−1). Nuclear magnetic resonance (NMR)
spectra were routinely recorded at 400.13 (1H), 162.00 (31P{1H}), or
100.62 MHz (13C{1H}) at 290 K in CD2Cl2 solutions unless otherwise
stated. Chemical shifts (δ) are given in ppm, relative to internal
tetramethylsilane (1H, 13C) or external 85% aqueous H3PO4 solution
(31P). Coupling constants (J) are given in hertz. Cyclic voltammetry
(CV) experiments were performed in an airtight custom-made
electrolytic cell using a Pt working electrode, an Ag wire reference
electrode, and a Pt wire auxiliary electrode. [NBu4][PF6] was used as
the supporting electrolyte (0.1 M solutions), and the analyte
concentration was typically ca. 10−3 M in dichloromethane. All the
potentials were referenced versus the ferrocene/ferrocenium couple,
used as internal reference in all the experiments.
Preparation of cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-PCy2)(CO)]-
BAr′4 (cis-5′′). Solid [FeCp2](BAr′4) (0.082 g, 0.078 mmol) and a
droplet of water (4 μL, 0.22 mmol) were added to a dichloromethane
solution (5 mL) of compound 1 (0.050 g, 0.078 mmol) to give a red
solution immediately, and the mixture was stirred for 5 min. The
solvent was then removed under vacuum, and the residue was
dissolved in a minimum amount of dichloromethane/petroleum ether
(1:2) and chromatographed on alumina (activity IV) at 253 K. Elution
with the same solvent mixture gave a brown fraction yielding, after
removal of solvents, compound cis-5′ as a red-brown microcrystalline
solid (0.050 g, 80%). The crystals used in the X-ray diffraction study
were grown by the slow diffusion of a layer of toluene into a
dichloromethane solution of the complex at 253 K. Anal. Calcd for
C62H50BF24Mo2O2P: C, 49.10; H, 3.32. Found: C, 49.27; H, 3.43. IR
1
(Nujol): 1942 (vs, νCO), 944 (s, νMoO). H NMR: δ 9.80 (s, 1H, μ-
CH), 7.72 [s, 8H, H2(Ar′)], 7.56 [s, 4H, H4(Ar′)], 7.75, 7.64, 7.41,
7.36 (4m, 4 × 1H, Ph), 6.08, 4.63 (2s, 2 × 5H, Cp), 4.67 [d, JHH = 7,
1H, H2(Ph)], 2.6−1.2 (m, 22H, Cy). 13C{1H} NMR: δ 234.2 (d, JPC
=
Preparation of [Mo2Cp2(μ-COH)(μ-CPh)(μ-PCy2)]BF4 (3). Di-
phenylsilane (0.025 μL, 0.135 mmol) was added to a solution of
compound 1 (0.030 g, 0.047 mmol) in dichloromethane (3 mL), and
the mixture was stirred at room temperature for 3 min. Solid
[FeCp2]BF4 (0.013 g, 0.047 mmol) was then added to the solution,
and the mixture was stirred for 2 min to give a yellow solution, which
was filtered. Petroleum ether (10 mL) was then added to the filtrate,
and the solvents were removed under vacuum. The resulting residue
was then washed with petroleum ether (3 × 5 mL) and dried under
vacuum to give compound 3 as a reasonably pure yellow solid (0.028
g, 82%). Attempts to further purify this solid through crystallization
resulted in its progressive decomposition. This reaction also can be
performed directly in CD2Cl2 (0.5 mL) within an NMR tube and also
by using tert-butylamine-borane adduct (0.030 g, 0.345 mmol) instead
of diphenylsilane. IR (Nujol): 3400 (br, νOH), 1635 (br, δOH), 1304
(w, νCO). 1H NMR (233 K): δ 7.30 [false t, JHH = 7, 2H, H3(Ph)], 7.19
[t, JHH = 7, 1H, H4(Ph)], 6.71 [false d, JHH = 7, 2H, H2(Ph)], 6.12 (s,
10H, Cp), 2.0−0.5 (m, 22H, Cy); the OH resonance could not be
16, CO), 177.0 (s, μ-CH), 162.1 [m, JCB = 50, C1(Ar′)], 135.2 [s,
C2(Ar′)], 137.3, 133.6, 131.7, 130.5 (4s, Ph), 129.3 [q, JCF = 32,
C3(Ar′)], 125.0 [q, JCF = 273, CF3], 103.3, 91.3 (2s, Cp), 102.0 [s,
C1(Ph)], 101.2 [s, C2(Ph)], 57.3 [d, JCP = 18, C1(Cy)], 55.2 [d, JCP
=
9, C1(Cy)], 36.4, 35.0 [2d, JCP = 6, C2(Cy)], 34.8, 33.4 [2d, JCP = 4,
C2(Cy)], 28.7 [d, JCP = 11, C3(Cy)], 28.6 [d, JCP = 10, C3(Cy)], 28.3,
28.1 [2d, JCP = 12, C3(Cy)], 26.6, 26.5 [2s, C4(Cy)].
Preparation of trans-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-PCy2)(CO)]-
BF4 (trans-5). Neat HBF4·OEt2 (12 μL, 0.087 mmol) was added to a
dichloromethane solution (5 mL) of compound trans-7 (0.050 g,
0.076 mmol) at room temperature, and the mixture was stirred for 3
min to give a red solution. Workup as described for 3 gave compound
trans-5 as a red solid (0.046 g, 82%). Anal. Calcd for
1
C30H38BF4Mo2O2P: C, 48.67; H, 5.17. Found: C, 48.30; H, 4.88. H
NMR: δ 11.00 (s, 1H, μ-CH), 7.82, 7.73, 7.63, 7.35 (4m, 4 × 1H, Ph),
5.49, 4.55 (2s, 2 × 5H, Cp), 4.62 [d, JHH = 7, 1H, H2(Ph)], 3.0−1.2
(m, 22H, Cy).
Preparation of [Mo2Cp2(μ-CPh)(OPh)(μ-PCy2)(CO)]BF4 (6).
Phenol (ca. 0.050 g, 0.53 mmol) was added to a solution of
compound 1 (0.050 g, 0.078 mmol) in dichloromethane (3 mL), and
the mixture was stirred at room temperature for 3 min. Solid
[FeCp2]BF4 (0.022g, 0.078 mmol) was then added to the solution,
and the mixture was stirred for 5 min to give a green solution, which
was filtered. Petroleum ether (10 mL) was then added to the filtrate,
and the solvents were removed under vacuum. The resulting residue
was then washed with petroleum ether (3 × 5 mL) and dried under
vacuum to give a green solid containing compound 6 as a major
species, along with variable amounts of cis-5 (0.055 g, 85%). Attempts
to further purify this solid through crystallization resulted in its
progressive transformation into the mentioned complex (see Results
and Discussion section). 1H NMR: δ 7.55, 7.34 [2 false t, JHH = 7, 2 ×
2H, H3(Ph)], 7.13, 6.90 [2t, JHH = 7, 2 × 1H, H4(Ph)], 6.83, 6.66 [2
false d, JHH = 7, 2H, H2(Ph)], 5.90, 5.70 (2s, 2 × 5H, Cp), 2.96−0.40
(m, 22H, Cy).
Preparation of cis-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)(CO)] (cis-7).
Neat 1,8-diazabicycloundec-7-ene (12 μL, 0.08 mmol) was added to
a dichloromethane solution (5 mL) of compound cis-5 (0.050 g, 0.067
mmol) at room temperature, and the mixture was stirred for 1 min to
give a yellow solution. After removal of solvents under vacuum, the
residue was chromatographed on alumina (activity IV) at 288 K.
Elution with dichloromethane/petroleum ether (1:4) gave a yellow
fraction yielding, after removal of solvents, compound cis-7 as a yellow
solid (0.037 g, 88%). The crystals used in the X-ray diffraction study
were grown by the slow diffusion of a layer of petroleum ether into a
dichloromethane solution of the complex at 253 K. Anal. Calcd for
C30H37Mo2O2P: C, 55.22; H, 5.72. Found: C, 54.95; H, 5.53. 1H NMR
(300.13 MHz): δ 7.34 [false t, JHH = 7, 2H, H3(Ph)], 7.05 [t, JHH = 7,
1H, H4(Ph)], 6.81 [false d, JHH = 7, 2H, H2(Ph)], 5.47, 5.33 (2s, 2 ×
5H, Cp), 2.5−0.7 (m, 22H, Cy). 13C{1H} NMR: δ 360.0 (d, JPC = 7,
μ-C), 238.5 (d, JPC = 10, CO), 168.9 [s, C1(Ph)], 127.8 [s, C3(Ph)],
123.7 [s, C4(Ph)], 119.8 [s, C2(Ph)], 101.0, 92.4 (2s, Cp), 47.6 [d, JCP
= 12, C1(Cy)], 44.1 [d, JCP = 18, C1(Cy)], 36.3, 33.8, 32.5 [3s,
identified in this spectrum. 13C{1H} NMR (233 K): δ 401.4 (d, JPC
=
14, μ-CPh), 357.8 (d, JPC = 14, μ-COH), 160.1 [s, C1(Ph)], 128.0 [s,
C4(Ph)], 127.4 [s, C3(Ph)], 122.3 [s, C2(Ph)], 98.4 (s, Cp), 41.7 [d,
JCP = 18, C1(Cy)], 40.9 [d, JCP = 17, C1(Cy)], 33.0, 32.7 [2s, C2(Cy)],
26.9, 26.7 [2d, JCP = 12, C3(Cy)], 25.8, 25.7 [2s, C4(Cy)].
Preparation of cis-[Mo2Cp2(μ-CPh)(OH)(μ-PCy2)(CO)]BF4 (4).
Neat HBF4·OEt2 (12 μL, 0.087 mmol) was added to a dichloro-
methane solution (5 mL) of compound cis-7 (0.050 g, 0.076 mmol) at
233 K, and the mixture was stirred for 3 min at this temperature to
give a green solution. Workup as described for 3 gave a green solid
shown by NMR to contain compound 4 as the major species (0.048 g,
85%). All attempts to further purify this solid through crystallization
resulted in its progressive transformation into its isomer cis-5 (see
text). IR (Nujol): 3500 (vbr, νOH), 1954 (s, νCO). 1H NMR (253 K): δ
7.51 [false t, JHH = 7, 2H, H3(Ph)], 7.23 [t, JHH = 7, 1H, H4(Ph)], 6.63
[false d, JHH = 7, 2H, H2(Ph)], 5.96, 5.94 (2s, 2 × 5H, Cp), 2.4−1.2
(m, 22H, Cy). 13C{1H} NMR (253 K): δ 413.1 (s, μ-C), 233.1 (d, JPC
= 8, CO), 165.4 [s, C1(Ph)], 128.8 [s, C4(Ph)], 128.4 [s, C3(Ph) and
C2(Ph)], 105.2, 96.9 (2s, Cp), 47.8 [d, JCP = 12, C1(Cy)], 46.4 [d, JCP
= 15, C1(Cy)], 33.2, 32.3, 30.8, 29.0 [4s, C2(Cy)], 26.6, 26.5, 26.5,
26.4 [4d, JCP = 12, C3(Cy)], 25.9, 25.8 [2s, C4(Cy)].
Preparation of cis-[Mo2Cp2(μ-η1:η3-CHPh)(O)(μ-PCy2)(CO)]BF4
(cis-5). Solid [FeCp2]BF4 (0.022g, 0.078 mmol) was added to a
dichloromethane solution (5 mL) of compound 1 (0.050 g, 0.078
mmol) to give a green solution immediately. Then water (4 μL, 0.22
mmol) was added, whereupon the solution turned dark red, and the
mixture was further stirred for 5 min. After removal of the solvent
under vacuum, the residue was washed with petroleum ether (3 × 5
mL) and dried under vacuum to give compound cis-5 as a brown solid
(0.048 g, 83%). Anal. Calcd for C30H38BF4Mo2O2P: C, 48.67; H, 5.17.
Found: C, 48.35; H, 4.92. IR (Nujol): 1935 (vs, νCO), 930 (s, νMoO).
1H NMR: δ 10.34 (s, 1H, μ-CH), 8.05, 7.64, 7.40, 7.33 (4m, 4 × 1H,
Ph), 6.17, 4.78 (2s, 2 × 5H, Cp), 4.60 [d, JHH = 7, 1H, H2(Ph)], 2.2−
1.2 (m, 22H, Cy).
K
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Organometallics
Article
C2(Cy)], 33.4 [d, JCP = 3, C2(Cy)], 28.6, 28.3, 27.8 [3d, JCP = 12,
C3(Cy)], 28.4 [d, JCP = 8, C3(Cy)], 26.8, 26.7 [2s, C4(Cy)].
refined anisotropically, except the carbon atoms involved in the
disorder. All hydrogen atoms were geometrically placed and refined
using a riding mode.
Preparation of trans-[Mo2Cp2(μ-CPh)(O)(μ-PCy2)(CO)] (trans-
7). A dichloromethane solution (5 mL) of [Mo2Cp2(μ-CPh)(μ-
PCy2)(CO)2] (0.050 g, 0.075 mmol) was stirred in the open air for 5
min. The Schlenk tube was then closed, and the mixture was further
stirred at room temperature for 8 h to give a yellow solution. Workup
as described for cis-7 gave compound trans-7 as a yellow solid (0.035
g, 72%). The crystals used in the X-ray diffraction study were grown by
the slow diffusion of a layer of petroleum ether into a dichloromethane
solution of the complex at 253 K. Anal. Calcd for C30H37Mo2O2P: C,
X-ray Structure Determination of Compound trans-7. The X-
ray intensity data were collected on a Kappa-Appex-II Bruker
diffractometer using graphite-monochromated Mo Kα radiation at
100 K. The software APEX was used for collecting frames with the ω/
ϕ scans measurement method.55 The Bruker SAINT software was
used for the data reduction,56 and a multiscan absorption correction
was applied with SADABS.57 Structure solution and refinements were
performed as described above, with all hydrogen atoms being
geometrically placed and refined using a riding model. All non-H
atoms were freely refined anisotropically except for C(12) and C(17),
which were refined anisotropically in combination with the
instructions DELU and SIMU. Moreover a highly disordered molecule
of hexane placed on a symmetry element was found to be present in
the asymmetric unit; therefore the SQUEEZE procedure, as described
above, was used.
Computational Details. The computations for compounds 1 and
2 were carried out using the GAUSSIAN03 package,58 in which the
hybrid methods B3LYP (1) and UB3LYP (2) were applied with the
Becke three-parameter exchange functional59 and the Lee−Yang−Parr
correlation functional.60 Effective core potentials and their associated
double-ζ LANL2DZ basis set were used for the metal atoms.61 The
light elements (P, O, C, and H) were described with the 6-31G*
basis.62 Geometry optimizations were performed under no symmetry
restrictions, using initial coordinates derived from the X-ray data of 1,
and frequency analyses were performed to ensure that a minimum
structure with no imaginary frequencies was achieved in each case.
Molecular orbitals and vibrational modes were visualized using the
MOLEKEL program.63 The topological analysis of the electron density
was carried out with the Xaim routine.64
1
55.22; H, 5.72. Found: C, 54.90; H, 5.48. H NMR (300.13 MHz): δ
7.55 [false d, JHH = 7, 2H, H2(Ph)], 7.45 [false t, JHH = 7, 2H, H3(Ph)],
7.25 [t, JHH = 7, 1H, H4(Ph)], 5.42, 5.40 (2s, 2 × 5H, Cp), 2.2−0.8
(m, 22H, Cy).
Preparation of [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-NO)]BF4 (8). Nitric
oxide (0.2% solution in N2) was bubbled through a solution of
compound 1 (0.050 g, 0.078 mmol) in dichloromethane (10 mL) for 5
min. Solid [FeCp2]BF4 (0.022 g, 0.078 mmol) was then added to the
solution, and the mixture was stirred for 10 min while keeping the NO
bubbling, to give an orange solution, which was filtered. Workup as
described for 3 gave compound 8 as an orange solid (0.052, 91%).
Anal. Calcd for C29H37BF4Mo2NOP: C, 48.03; H, 5.14; N, 1.93.
1
Found: C, 47.70; H, 4.95; N, 1.75. H NMR: δ 7.43 [false t, JHH = 7,
2H, H3(Ph)], 7.33 [t, JHH = 7, 1H, H4(Ph)], 6.82 [false d, JHH = 7, 2H,
H2(Ph)], 6.41 (s, 10H, Cp), 2.6−1.2 (m, 18H, Cy), 0.72−0.50 (m,
4H, Cy). 13C{1H} NMR: δ 404.5 (d, JPC = 14, μ-CPh), 159.1 [s,
C1(Ph)], 130.9 [s, C4(Ph)], 128.8 [s, C3(Ph)], 123.6 [s, C2(Ph)],
103.6 (s, Cp), 43.9 [d, JCP = 15, C1(Cy)], 41.7 [d, JCP = 16, C1(Cy)],
33.7, 33.1 [2s, C2(Cy)], 27.0 [d, JCP = 15, C3(Cy)], 26.8 [d, JCP = 16,
C3(Cy)], 25.7, 25.6 [2s, C4(Cy)].
Preparation of [Mo2Cp2(μ-CHPh)(O)(μ-PCy2)(NO)] (9). Com-
pound 8 (0.030 g, 0.041 mmol) was dissolved in a minimum amount
of dichloromethane/petroleum ether (1:1) and chromatographed on
alumina (activity IV) at 253 K. Elution with the same solvent mixture
gave a green fraction yielding, after removal of solvents, compound 9
as a green microcrystalline solid (0.022 g, 81%). Anal. Calcd for
C29H38Mo2NO2P: C, 53.14; H, 5.84; N, 2.14. Found: C, 52.80; H,
ASSOCIATED CONTENT
* Supporting Information
■
S
A CIF file with full crystallographic data of compounds cis-5′,
cis-7, and trans-7. A PDF file containing data (complete ref 59,
figures, selected bond distances and angles, selected molecular
orbitals, atomic charges and topological properties of the
electron density) for the DFT-optimized structures of 1 and 2,
and a table with crystal data of compounds cis-5′ and 7. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
5.61; N, 1.95. IR (Nujol): 1606 (vs, νNO), 933 (s, νMoO). H NMR: δ
8.70 (s, 1H, μ-CH), 7.11 [false t, JHH = 7, 2H, H3(Ph)], 6.85 [t, JHH
=
7, 1H, H4(Ph)], 6.33 [false d, JHH = 7, 2H, H2(Ph)], 5.48, 5.44 (2s, 2 ×
5H, Cp), 2.7−0.6 (m, 22H, Cy). 13C{1H} NMR: δ 163.0 [s, C1(Ph)],
132.3 (d, JPC = 4, μ-CH), 128.1 [s, C4(Ph)], 127.6 [s, C3(Ph)], 122.3
[s, C2(Ph)], 101.2, 96.2 (2s, Cp), 46.0 [d, JCP = 15, C1(Cy)], 42.1 [d,
JCP = 13, C1(Cy)], 35.2, 33.7 [2d, JCP = 2, C2(Cy)], 32.3 [d, JCP = 1,
C2(Cy)], 32.0 [d, JCP = 3, C2(Cy)], 28.5, 28.1, 27.8 [3d, JCP = 12,
C3(Cy)], 28.4 [d, JCP = 10, C3(Cy)], 26.7, 26.6 [2s, C4(Cy)].
AUTHOR INFORMATION
Corresponding Author
*E-mail: mara@uniovi.es.
■
X-ray Structure Determination of Compounds cis-5′ and cis-
7. The X-ray intensity data were collected at 100 K on a Nonius
KappaCCD single-crystal diffractometer, using graphite-monochro-
mated Mo Kα radiation. Images were collected at a 40 mm (cis-5′) or
35 mm (cis-7) fixed crystal−detector distance, using the oscillation
method, with 1° oscillation and 40 and 100 s exposure times per
image, respectively. Data collection strategy was calculated with the
program Collect,48 and data reduction and cell refinements were
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the DGI of Spain for financial support (Project
CTQ2009-09444) and the Consejeria de Educacion
for grants (to S.M. and D.G.-V.). We also thank the
Universidad de Santiago de Compostela (Unidad de Rayos
X) for the collection of the diffraction data.
■
performed with the programs HKL Denzo and Scalepack.49
A
́
́
of Asturias
semiempirical absorption correction was applied using the program
SORTAV.50 Using the program suite WinGX,51 the structure was
solved by Patterson interpretation and phase expansion using
SHELXL97 and refined with full-matrix least-squares on F2 using
SHELXL97.52 For compound cis-5′ all non-hydrogen atoms were
refined anisotropically, and all hydrogen atoms were geometrically
placed and refined using a riding model, except for H(2), which was
located on the Fourier map and refined isotropically. A molecule of an
unidentified solvent was found to be present in the asymmetric unit;
therefore the SQUEEZE procedure,53 as implemented in PLATON,54
was used. Compound cis-7 was found to crystallize with a molecule of
dichloromethane. Moreover one of the cyclopentadienyl ligands was
found to be disordered over two positions, which were satisfactorily
refined with 0.58/0.42 occupancies. All non-hydrogen atoms were
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