Hydride abstraction from [MCpBz(CO)3H] (M = Mo, W; CpBz = C5(CH2Ph)5): New cationic complexes stabilized by η5:η2-C5H 4:C6H5 bonding of the pentabenzylcyclopentadienyl ligand

Article abstract of DOI:10.1021/om300070m

Hydride abstraction from [MCp^Bz(CO)₃H] (M = Mo, W; Cp^Bz = C₅(CH₂Ph)₅) using trityl cations led to [M{η⁵:η²-C₅Bz ₄CH₂Ph}(CO)₃]BAr_F (BAr_F = B(3,5-C₆H₃(CF₃)₂)₄; M = Mo (3), W (4)) or [MCp^Bz(CO)₃(FBF₃)] (M = Mo (5), W (6)) depending on the trityl counterions. The stabilization of the acidic metal centers in 3 and 4 is made through the coordination of a C=C bond of one phenyl ring, generating ansa-bridged cyclopentadienyl-phenyl carbonyl complexes. 5 and 6 are zwitterionic compounds stabilized by the coordination of the BF₄ anion. An exchange process between coordinated and noncoordinated phenyl rings occurs in dichloromethane solutions of 3. VT NMR experiments gave the exchange rate at various temperatures and ΔG^? ₂₉₈ = 10.1 ± 0.2 kcal mol^-1. In 4 the phenyl bonding is static at room temperature, on the NMR time scale. Reactions of 3 and 4 with CO and H₂O led to [MCp^Bz(CO)₄]BAr _F (M = Mo (7), W (8)) and [MCp^Bz(CO)₃(OH ₂)]BAr_F (M = Mo (11), W (12)). In CH₂Cl ₂ solutions 3 and 4 convert slowly to 7 and 8, respectively. DFT calculations attest to the stability of 3 to H₂O bonding and also show that the replacement of phenyl coordination by CO is a favorable process (ΔH = -13.8 kcal mol^-1).

Full text of DOI:10.1021/om300070m

Article
pubs.acs.org/Organometallics
Hydride Abstraction from [MCpBz(CO)3H] (M = Mo, W; CpBz =
C5(CH2Ph)5): New Cationic Complexes Stabilized by η5:η2-C5H4:C6H5
Bonding of the Pentabenzylcyclopentadienyl Ligand
M. Augusta Antunes, Luis G. Alves, Sonia Namorado, Jose R. Ascenso, Luis F. Veiros,
́
́
and Ana M. Martins*
́ ́
Centro de Química Estrutural, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa,
Portugal
S
* Supporting Information
ABSTRACT: Hydride abstraction from [MCpBz(CO)3H] (M = Mo, W; CpBz
=
C5(CH2Ph)5) using trityl cations led to [M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (BArF =
B(3,5-C6H3(CF3)2)4; M = Mo (3), W (4)) or [MCpBz(CO)3(FBF3)] (M = Mo (5), W
(6)) depending on the trityl counterions. The stabilization of the acidic metal centers in
3 and 4 is made through the coordination of a CC bond of one phenyl ring,
generating ansa-bridged cyclopentadienyl−phenyl carbonyl complexes. 5 and 6 are
zwitterionic compounds stabilized by the coordination of the BF4 anion. An exchange
process between coordinated and noncoordinated phenyl rings occurs in dichloro-
methane solutions of 3. VT NMR experiments gave the exchange rate at various
temperatures and ΔG⧧ = 10.1 0.2 kcal mol−1. In 4 the phenyl bonding is static at
298
room temperature, on the NMR time scale. Reactions of 3 and 4 with CO and H2O led
to [MCpBz(CO)4]BArF (M = Mo (7), W (8)) and [MCpBz(CO)3(OH2)]BArF (M =
Mo (11), W (12)). In CH2Cl2 solutions 3 and 4 convert slowly to 7 and 8, respectively.
DFT calculations attest to the stability of 3 to H2O bonding and also show that the
replacement of phenyl coordination by CO is a favorable process (ΔH = −13.8 kcal mol−1).
arene dearomatization and further functionalization,7 the
INTRODUCTION
■
reverse situation, that is, acidic metal centers stabilized by
intramolecular η2-arene bonding, is restricted. Relevant
examples of these types of compounds are (i) Cp(CO)W[μ-
C(p-tolyl)(R)](μ-CO)Pd(Cl), which presents a bridging
alkylidene ligand where the p-tolyl group binds to the
tungsten,8 (ii) [CpMo(PPh3)(CO)2]+, which displays a η2-Ph
interaction of one phenyl ring of the triphenylphosphine ligand
with the metal,9 and (iii) [(η5:ηn-Cp(bridge)Ph)M(R)2]+,
where M = Ti, Zr and the bridge is a Me2C fragment.5 Related
examples, where arene coordination compensates for the
electronic deficiency of an acidic metal center, are the reactions
of [CpReH(NO)(CO)] with tropylium or trityl cations that
lead to the formation of [CpRe(NO)(CO)(η2-arene)] (η2-
arene = η2-C7H8, η2-PhCHPh2). The arene ligands in these
reactions are formed in situ by reactions of the cations with the
hydride ligand.10
Hemilabile ligands display important roles in the stabilization
and reactivity of metal complexes with significant implications
in catalysis. Classic examples for this behavior are allylic η3/η1
and indenyl η5/η3 shifts,1,2 but the array of ligands displaying
hemilabile behavior and their participation in a increasing
number of catalytic processes have grown extraordinarily with
the emergence of chelating polyfunctional ligands that may
readily tune and support complex reactivity by changing their
bonding modes.3 The good kinetic and thermodynamic
properties provided by the cyclopentadienyl ring to organo-
metallic complexes encouraged its use as a basic frame for the
building of chelating polyfunctional ligands in combination with
soft or hard donors.4 However, the connection of cyclo-
pentadienyl and phenyl moieties through carbon- or silicon-
based bridges is currently limited to group 4 metal complexes
that display phenyl coordination in 16e cations of the general
formula [(η5:ηn-C5H4(bridge)Ph)M(R)2]+.5
Following our interest in molybdenum and tungsten
compounds supported by the bulky pentabenzylcyclopenta-
dienyl ligand,6 we report now new cationic complexes of this
family and demonstrate the ability of the pentabenzylcyclo-
pentadienyl to behave as a chelating ligand through the
additional η2-Ph bonding of one benzyl group. While electron-
rich metal complexes stabilize η2-arene coordination through
metal to arene back-bonding to give C−H oxidative addition or
The results reported here are closely connected to the
catalytic activity displayed by [MCpBz(CO)3]+ in the ionic
hydrogenation of ketones and further attest to the determining
role of intramolecular interactions and fluxional processes
offered by hemilabile ligands in catalysis. Among other factors
previously discussed, the high activity displayed by
Received: January 27, 2012
Published: May 16, 2012
© 2012 American Chemical Society
4387
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
[MCpBz(CO)3]+ in comparison to that of [MCp(CO)3]+ and
[MCp(CO)2(PMe3)]+ is likely due to the ability of the
pentabenzylcyclopentadienyl ligand to stabilize the unsaturated
16e molybdenum cation responsible for H2 activation.6d,11
4 as ionic compounds was also confirmed by the 19F and 11B
NMR spectra, which show the characteristic resonances of
BArF. The IR spectra show typical stretching bands for the
carbonyl ligands at 2057 and 1978 cm−1 for 3 and at 2050 and
1963 cm−1 for 4. A comparison of the νCO bands in 3 and 4
with those of the parent compounds6c is consistent with the
formation of cationic metal centers.
The magnetic equivalence of the ortho and meta protons of
the bonded phenyl ring hints at a fluxional process
corresponding to the equilibrium presented in Scheme 2.
RESULTS AND DISCUSSION
■
Synthesis and Reactivity. The stoichiometric addition of
Ph3CBArF (BArF = B(3,5-C6H3(CF3)2)4) to the hydrides
[MCpBz(CO)3H] (M = Mo (1), W (2); CpBz = pentabenzyl-
cyclopentadienyl) in dichloromethane results in hydride
transfer to the trityl cation and formation of the cationic
complexes [M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (M = Mo (3),
W (4)), which are obtained in high yields (75% for 3 and 90%
for 4) as dark purple and purple solids, respectively (Scheme
1).
Scheme 2
Scheme 1
1
Low-temperature H NMR studies performed in a dichloro-
methane-d2 solution of 3 showed that this process could not be
stopped until −80 °C, as the only observed effect was the
broadening of all resonances. This result is in accordance with a
low activation energy barrier for the process, as confirmed by
DFT calculations presented below.
The NOESY spectrum of complex 3 reveals cross-peaks
between all ortho protons (see Figure 1). This result is
The proton and carbon NMR spectra of 3 and 4 provide the
evidence for their molecular structures. The spectra are
diagnostic of Cs symmetry with a plane containing the
methylene and the ipso carbons of the bridging benzyl group
and crossing the C−C bond of the cyclopentadienyl ring that is
opposite to the metal-coordinated phenyl ring. Thus, in the 1H
NMR spectra of both compounds, the methylenic protons of
the five benzyl groups give rise to one singlet and to two AB
systems, integrating for four protons each. The chemical shifts
of the ortho protons of the bridging benzyl constitute further
evidence for the coordination of the phenyl ring,5a as they are
displaced upfield (δ 6.51 ppm for 3 and δ 6.54 ppm for 4) in
comparison to those for other pentabenzylcyclopentadienyl
tricarbonyl complexes.6a,c−e The 13C NMR spectra of 3 and 4
also support the coordination of the phenyl group to the
metals, as evidenced by the broadening and upfield shift of the
ortho carbon resonances (δ 102.1 ppm for 3 and δ 98 ppm for
4)9 and by the downfield shift of the meta carbon signals (δ
142.2 ppm for 3 and δ 144.3 ppm for 4) in comparison with
other η5-CpBz cationic carbonyl compounds.6a,c−e Additionally,
the carbon NMR spectra show two resonances above 200 ppm
that are due to the carbonyl ligands (δ 232.5 and 227.4 ppm for
3 and δ 220.6 and 220.2 ppm for 4). The identification of 3 and
Figure 1. Aromatic region of the NOESY spectrum of 3 at 293 K,
showing the cross-peaks between the ortho resonances of all benzyl
groups for 3 (500 MHz, CD2Cl2, mixing time 500 ms).
consistent with another fluxional process that can be attributed
to an equilibrium exchange process in which each of the five
phenyl groups are, in turn, coordinating to the metal. The
exchange rate constants associated with this process were
calculated from the intensities of 2D-EXSY peaks of the ortho
protons at six different temperatures. As expected, the
mechanism of the intramolecular exchange process is simple
and the relaxation matrix contains only one exchange rate
constant value. Variable-temperature studies yielded the rate
constants reported in Table 1, and the activation parameters
ΔH⧧ = 14.9 0.4 kcal mol−1, ΔS⧧ = 16 1 kcal mol−1, and
ΔG⧧298 = 10.1 0.2 kcal mol−1 were obtained using the Eyring
equation (see Figure 1S in the Supporting Information). The
4388
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
Table 1. Exchange Rate Constants k for 3 at Different
Temperatures
Scheme 3
a
T (K)
k (s−1
)
T (K)
k (s−1
)
290
293
296
0.18
0.25
0.32
301
306
312
0.53
0.82
1.19
a
Errors in rate constants range from 5 to 10%.
moderately high value of ΔG⧧ is in agreement with the
298
formation of a labile Mo−η2-Ph bond in 3. The same dynamic
process was not observed for the tungsten analogue 4, and the
NOESY spectrum of a dichloromethane-d2 solution of this
compound at room temperature is compatible with a static
coordination of one phenyl group as a consequence of a
stronger metal−carbon bond.
Treatment of 1 and 2 with Ph3CBF4 in dichloromethane-d2
results in the formation of the zwitterionic species
[MCpBz(CO)3(FBF3)] (M = Mo (5), W (6)), displayed in
Scheme 1. This behavior, which is similar to that for other
cyclopentadienyl analogues,12 shows that when the counterion
is a small coordinating anion the formation of the zwitterionic
complexes is preferred over η2-phenyl coordination. It is
formation of 7 and 8 in CD2Cl2 solutions, and the 11B and 19
F
NMR spectra also did not show any signals other than those
assignable to BArF. This result may suggest that the fragment
resulting from CO release decomposes through radical
processes to paramagnetic species that are not detected by
NMR. The formation of a few crystals of [MoCpBz(CO)3]2
after a few months in the NMR tube attests to the reduction of
molybdenum and supports the occurrence of redox processes.
This observation raised the question of the origin of CO. It is
known that thermal decarbonylation of [MCpBz(CO)3]2 is a
source of CO with formation of [MoCpBz(CO)2]2.6c Therefore,
reactions of [Mo{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (3) with
[MoCpBz(CO)3]2 in 2:1 and 1:1 ratios were carried out with
the aim of assessing if the latter complex could be the origin of
CO to form [MoCpBz(CO)4]BArF. The results of these
reactions were ambiguous because though the NMR spectra
reveal the formation of 7 and also a residual amount of
[MoCpBz(CO)2]2, the reactions led to other minor species that
could not be identified. The ratio between 7 and
[MoCpBz(CO)2]2 excludes [MoCpBz(CO)3]2 as being the
only CO source for the formation of 7. It is clear that addition
of [MCpBz(CO)3]2 to dichloromethane-d2 solutions of [M-
{η5:η2-C5Bz4CH2Ph}(CO)3]+ in a sealed tube accelerates the
formation of [MCpBz(CO)4]+ and gives rise to the formation of
small amounts of [MCpBz(CO)2]2, but the integration of the
NMR spectra did not clarify the matter.
−
significant that in the presence of BF4 the stabilization of the
16e cationic center through intramolecular coordination of one
phenyl ring is not observed, while the coordination of the
phenyl ring is favored when the bulky Ph3CBArF is used as
hydride abstractor. The influence of counterions in the course
of reactions is well documented as a determining factor in
catalytic reactions;13 however, the formation of η2-arene species
in hydride abstraction reactions has been observed only
rarely9,12 and the compensation for the electronic unsaturation
of metal centers is usually provided by the coordination of
counterions or solvent molecules.12 The situation reported here
reflects the noncoordinating behavior of BArF, which is likely a
consequence of steric factors. The bulkiness of the cyclo-
pentadienyl ring and BArF forces this anion to stay away from
the metal and compels the ansa-bridged coordination of the
CpBz ring to balance the electron deficiency of the metal center.
−
The coordination of BF4 in 5 and 6 is supported by the 19F
NMR data. At room temperature an exchange between the four
fluorides of the BF4− ion justifies the equivalence of all fluorine
resonances in 5; this process is stopped at −80 °C, leading to
the splitting of each signal in three nonequivalent resonances.14
The exchange process is slower in the tungsten complex; two
resonances corresponding to the bridging and to the terminal
fluorides are observed at room temperature. A limit spectrum
identical with that obtained for 5 is attained on cooling.
The 1H NMR spectra of 7 and 8 display one set of
resonances corresponding to the CpBz ligand, and the 13C NMR
spectra show only one resonance for the CO ligands, as
expected for a four-legged piano-stool geometry. The IR
spectra in KBr pellets show four strong νCO bands between
2110 and 1977 cm−1 and between 2108 and 1957 cm−1 for 7
and 8, respectively; however, in CH2Cl2 solutions each
compound gives rise to only two bands (νCO 2109, 2034
cm−1 for 7 and 2107, 2024 cm−1 for 8). The observation of two
bands in solution is in agreement with the free rotation of the
CpBz ligand and the C4v symmetry displayed by the complexes
in solution and suggests that the high number of carbonyl
bands in the solid state may be due to symmetry reduction
associated with crystal packing. A comparison between the IR
spectra of 7 and 8 with those of 3 and 4, respectively, also
points out the stabilization conferred by the phenyl
[M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (M= Mo (3), W (4))
complexes are stable in the solid state at room temperature
under an atmosphere of dry nitrogen. However, in CD2Cl2
solution the 1H spectra start to display new resonances
corresponding to about 1% decomposition after 1 day for 3 and
4 days for 4, which gradually increase with time. The NMR data
for the new species are consistent with the occurrence of a
carbonyl exchange reaction leading to the formation of
[MCpBz(CO)4]BArF (M = Mo (7), W (8)), which were
identified by comparison of the NMR spectra with those of
authentic samples obtained by reactions of 3 and 4 with CO
(Scheme 3). In the absence of CO the formation of the
tetracarbonyls is very slow, but it is immediate and quantitative
when CO is added to dichloromethane solutions of 3 or 4. No
other species are observed by NMR concomitantly with the
4389
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
coordination in the η5:η2-pentabenzylcyclopentadienyl com-
pounds and the highly acidic nature of the metal centers in the
cationic tetracarbonyl complexes. Indeed, the CO stretching
bands in 7 and 8 do not deviate notably from the value
observed for free CO and are in accordance with the short
carbon−oxygen distances revealed by the X-ray structures of
[MCpBz(CO)4]BF4 discussed below.
X-ray Diffraction. Complexes 9 and 10 are isomorphous
and crystallize in the P1 space group with a cocrystallized
̅
dichloromethane molecule. The molecular structure of 10
(Figure 2) illustrates the structures of both complexes, and
relevant bond distances and angles for 9 and 10 are presented
in Table 2.
The extreme solubility of 7 and 8 in ordinary solvents such as
dichloromethane, toluene, and diethyl ether gives rise to very
viscous solutions that hamper the formation of crystals suitable
for X-ray characterization. However, crystals of [MCpBz(CO)4]-
BF4 (M = Mo (9), W (10)) suitable for X-ray diffraction (see
below) were grown in the NMR tubes from CD2Cl2 solutions
of [MCpBz(CO)3(FBF3)] after some months. These results
confirm that, in the absence of additional good donors,
tetracarbonyl cationic species are decomposition products of
cationic Mo and W pentabenzylcyclopentadienyl tricarbonyl
complexes.
The stability of [M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (3 and
1
4) in air was tested. The H NMR spectrum of 4 reveals no
signals of decomposition when the complex is left in the solid
state in air for several weeks. However a dichloromethane
solution of 4 in open air shows 40% conversion to
[WCpBz(CO)3(OH2)]BArF (12) within 2 h. The molybdenum
analogue 3 is, as expected, more sensitive; even in the solid
state the conversion to [MoCpBz(CO)3(OH2)]BArF (11)
reaches about 50% after 3 h in air. Complexes 11 and 12
were independently prepared by reactions of 3 and 4 with water
(Scheme 3). A color change from purple to orange is observed
upon addition of an excess of degassed distilled water to
dichloromethane solutions of 3 and 4. Evaporation of the
solvent under vacuum gave initially red-orange oils that convert
Figure 2. Molecular structure of 10 showing thermal ellipsoids at the
50% probability level. Hydrogen atoms, BF4 , and CH2Cl2 are omitted
for clarity.
−
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 9
and 10
9
10
Distances (Å)
1.9904(11)
2.052(3)
M−CpBz
M−C(6)
M−C(7)
M−C(8)
1.9936(10)
2.035(3)
2.032(3)
2.051(2)
2.030(3)
1.132(3)
1.138(3)
1.120(3)
1.138(3)
CT
1
to purple solids on further exposure to vacuum. The H NMR
2.043(3)
spectrum of the red-orange samples reveal the presence of
variable amounts of the aqua complexes [MCpBz(CO)3(OH2)]-
BArF and [M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF. The formula-
tion of 11 and 12 as the aqua adducts was mainly supported by
2.047(3)
M−C(9)
2.051(3)
C(6)−O(1)
C(7)−O(2)
C(8)−O(3)
C(9)−O(4)
1.123(3)
1.127(3)
1
the H NMR and IR spectra. The proton NMR spectra in
1.123(3)
CD2Cl2 show broad resonances, at δ 4.99 ppm for 11 and δ
5.12 ppm for 12, accounting for the two protons of coordinated
water, together with a broad peak at about δ 2 ppm associated
with free water. The NOESY spectra display EXSY cross-peaks
between free and coordinated water that are symptomatic of a
slow exchange in solution. The chemical shifts observed for the
water protons in 11 and 12 are shifted strongly downfield in
relation to the values reported for the closely related complex
1.127(3)
Angles (deg)
117.50(8)
116.69(8)
118.81(8)
124.26(9)
177.8(2)
CpBzCT−M−C(6)
CpBzCT−M−C(7)
CpBzCT−M−C(8)
CpBzCT−M−C(9)
M−C(6)−O(1)
M−C(7)−O(2)
M−C(8)−O(3)
M−C(9)−O(4)
C(6)−M−C(7)
C(7)−M−C(8)
C(8)−M−C(9)
C(9)−M−C(6)
118.86(8)
124.55(8)
117.60(7)
116.94(8)
177.4(2)
176.7(2)
177.6(2)
175.8(2)
75.65(10)
73.89(10)
77.44(10)
77.10(10)
176.0(2)
177.8(2)
[MoCp(CO)2(PPh3)(OH2)]BArF (2.87 < δH O < 3.31 ppm),
2
176.2(2)
described by Bullock and co-workers.15 Despite the fact that the
proton chemical shifts of coordinated water habitually suffer
large displacements, mainly related to fluxional processes that
depend on the solvents and free water content, the difference
noted above reflects the highly acidic nature of the metal
centers in 11 and 12 due to the presence of one extra carbonyl
instead of a phosphine ligand.
77.74(10)
77.25(11)
76.07(11)
73.60(10)
In both compounds the cationic fragments have the typical
four-legged piano-stool geometry with distances between the
metals and the ring centroids (M−CpBzCT) of 1.9904(11) and
1.9936(10) Å in 9 and 10, respectively. As is usually observed
in pentabenzylcyclopentadienyl complexes four benzyl sub-
stituents are directed above the Cp ring planes and one points
down toward the metals. The metal−carbonyl bond lengths are
slightly elongated and the C−O distances are shortened in
The reversibility of the hydration reactions was confirmed by
NMR, as the only species observed after exposure of the
mixtures to prolonged vacuum were the starting compounds
[M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF. The lability of water
contrasts with the static behavior of 7 and 8, for which no
displacement of CO was registered even after many hours
under vacuum.
4390
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
comparison to those in [MCpBz(CO)3H].6c The C−O bond
lengths (ranging from 1.123(3) to 1.127(3) Å for 9 and from
1.120(3) to 1.138(3) Å for 10) are very close to the value
reported for free carbon monoxide (1.128 Å), thus correspond-
ing to CO bonds. These features reflect the competition of
four CO ligands to the metal to ligand back-bonding, which is
restricted in consequence of the cationic charge of the
compounds. In general the structural parameters obtained for
9 and 10 agree with those for other half-sandwich molybdenum
and tungsten carbonyl complexes.6,16,17
DFT Calculations. The experimental results described
above were further complemented by computational studies
obtained by means of DFT calculations (see Computational
Details).18 Thus, complex 3+, [Mo{η5:η2-C5Bz4CH2Ph}-
(CO)3]+, was the subject of a geometry optimization in order
to clarify the nature of the interaction between the metal and
the coordinated benzyl group of the CpBz ligand. In the
calculated structure (see Figure 3) the coordination of the
value excludes this intermediate from the mechanism of
exchange between the five phenyl groups discussed above,
since the experimental activation enthalpy measured by NMR
for this process (ΔH⧧ = 14.9 kcal mol−1, see Figure S1 in the
Supporting Information) is considerably lower than the
enthalpy splitting between 3+ and A. Thus, the exchange
mechanism is probably concerted, with every new phenyl
coordination causing the cleavage of the previous one and
avoiding, in this way, an unstable intermediate such as A.
In summary, the calculations confirm that the electron
deficiency on the metal, created by the loss of the hydride in the
original complex, is compensated by the coordination of one
benzyl substituent of the CpBz ligand. In this way, the cation
[Mo{η5:η2-C5Bz4CH2Ph}(CO)3]+ (3+) is able to maintain a
formal electron count of 18.
The mechanism of the fluxional process involving the
coordinated benzyl group was also investigated. That process
was observed by NMR (see Scheme 2) and makes both sides of
the coordinated phenyl ring equivalent. The corresponding
enthalpy profile is represented in Figure 3, along with the
optimized structures for the relevant species.
The fluxional process occurs in a single step, going over a
transition state (TS) in which coordination of the phenyl group
is totally symmetric, as shown by two equal Mo−Cortho
distances of 3.21 Å. These correspond to weak interactions
(WI = 0.05), indicating that one Mo−Cortho bond is practically
broken before the other one starts to form along the fluxional
process. In the transition state (TS) the electron loss in the
metal center due to the weakening of the Mo−Cortho bond is
partially balanced by a strengthening of the interaction between
the metal and the ipso C atom (dMo−C = 2.77 Å, WI = 0.12).
This reinforcement of the Cipso coordination, in TS, is made
possible by the release of steric constraint in the metallacycle,
being a consequence of the elongation of the Mo−Cortho
distance. Most importantly, the barrier calculated (ΔH⧧ = 8.8
kcal mol−1) corroborates a facile process that could not be
stopped in the temperature range employed in the NMR
studies (see above), being considerably smaller than the
experimental value obtained for the exchange of a coordinated
phenyl group.
The mechanism of fluxionality of the coordinating phenyl
group was also calculated for the tungsten complex 4+. The
enthalpy barrier obtained, ΔH⧧ = 9.4 kcal mol−1, is higher than
that calculated for 3+, as expected on going from a Mo to a W
complex, but is also small enough to justify that the process
cannot be stopped in the temperature range employed in the
NMR experiments, in agreement with the experimental
observations.
Figure 3. Enthalpy profile (PBE0, kcal mol−1) calculated for the
fluxional process involving the coordinated phenyl group in 3+. The
optimized geometries are represented with the coordinated benzyl
group and the Mo(CO)3 fragment highlighted. The relevant Mo−C
distances (Å) are indicated.
benzyl group via the ortho C atom is evident. The
corresponding Mo−Cortho distance of 2.57 Å is indicative of
an attractive interaction, as is further corroborated by a Wiberg
index (WI)19 of 0.21. The geometry constraints imposed by the
The stabilization of the 16-electron fragment
[MCpBz(CO)3]+, which results from hydride loss in the original
complexes [MCpBz(CO)3H] (1 and 2), can also be achieved
through coordination of one extra ligand, as shown by the
experimental results discussed above. Neutral 2-electron donors
(L) yielded cations, [MCpBz(CO)3L]+, such as the aqua
complexes (L = H2O, 11+ and 12+), or the tetracarbonyl
five-membered metallacycle in 3+ (Mo−CCp−C −Cipso
−
CH2
C
ortho) push the ipso C atom away from the metal (dMo−C
=
2.95 Å), weakening the corresponding Mo−C bond (WI =
0.06) and resulting in what may be viewed as a very distorted
coordination of a double bond (CipsoCortho).
−
species [MCpBz(CO)4]+ (7+−10+). The BF4 counterion also
The stabilization achieved by coordination of the phenyl
group in 3+ was evaluated by a comparison between 3+ and a
putative intermediate with none of the phenyl groups
coordinating the metal, [Mo(η5-C5Bz5)(CO)3]+ (A; see Figure
S2 in the Supporting Information). Cation 3+ is more stable
than this intermediate by ΔH = 24.3 kcal mol−1, providing a
clear indication of the stability gained by the complex through
the coordination of the phenyl group. In addition, that enthalpy
coordinates to the metal, forming the zwitterionic complexes 5
and 6. The corresponding reactions of addition of one extra
ligand to [Mo{η5:η2-C5Bz4CH2Ph}(CO)3]+ (3+) were studied
by DFT, and the enthalpy balances obtained are summarized in
Figure 4.
The most favorable reaction among all addressed in Figure 4
is CO addition with formation of the tetracarbonyl complex
4391
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
CONCLUDING REMARKS
■
The work described reveals new facets of half-sandwich
molybdenum and tungsten carbonyls. The intramolecular
coordination of one phenyl ring of the pentabenzylcyclopenta-
dienyl ligand follows hydride abstraction from
[MCpBz(CO)3H] (M = Mo, W) when a trityl salt of a bulky
noncoordinating anion is used. The coordination of the ansa-
bridging benzyl group to Mo is fluxional, involving an exchange
between the five benzyl groups for metal binding, but its
bonding in the W analogue is static at room temperature, on
the NMR time scale. The rate constants and the activation
parameters for the exchange process have been determined
from the intensities of 2D-EXSY peaks of the ortho protons.
The use of Ph3CBF4 as a hydride abstractor results in borate
coordination and formation of zwitterionic complexes. The
results reported here point out that the cationic species formed
upon hydride abstraction depend on the balance between the
steric properties of the starting complex and the counterion.
The stabilization achieved by the intramolecular coordination
of the phenyl ring in the absence of other donors may be
responsible for the different activities of [MoCp′(CO)3]+
systems (Cp′ = C5Bz5, C5H5) in the ionic hydrogenation of
ketones.6d,11 Among other aspects related to fine electronic
differences between the two systems,6d the much higher activity
of the pentabenzylcyclopentadienyl system is likely related to
the η2-Ph bonding that may support the regeneration of the
catalyst [MoCp′(CO)3(H)2]+ upon reaction of the tricarbonyl
cations with H2.
Figure 4. Enthalpy balance calculated (PBE0, kcal mol−1) for the
addition of one extra ligand to 3+.
[W{η5:η2-C5Bz4CH2Ph}(CO)3]BArF is stable in air in the
solid state. In solution [M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (M
= Mo, W) reacts readily with H2O, which displaces the metal-
coordinated phenyl group to give the corresponding aqua
adducts. The hydration reaction may be quantitatively reverted
under vacuum. [M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF and
[MCpBz(CO)3(FBF3)] convert slowly to [MCpBz(CO)4]BX4
(X = ArF, F) in dicloromethane solutions. The simultaneous
formation of [MCpBz(CO)3]2, observed by NMR, suggests a
disproportionation process. The tetracarbonyl cations
[MCpBz(CO)4]BX4 (M = Mo, W; X = ArF, F) display a four-
legged piano-stool geometry and are very stable toward CO
loss.
[MoCpBz(CO)4]+ (7+/9+). The calculated energy balance (ΔH
= −13.8 kcal mol−1) indicates a stable product, in excellent
agreement with the experimental results discussed above. In
fact, CO addition to the tricarbonyl species is a nonreversible
reaction and, in addition, the tetracarbonyl complexes 7+−10+
are the final decomposition products observed for the
tricarbonyl species.
Another interesting result is the rather small absolute value
calculated for the enthalpy balance of the hydration reaction
(ΔH = −1.3 kcal mol−1). This result agrees well with the
reversible character experimentally observed for this reaction
and with the establishment of an equilibrium between the two
complexes [Mo{η5 :η2 -C5 Bz4 CH2 Ph}(CO)3 ]+ and
[MoCpBz(CO)3(OH2)]+. Thus, binding of the water molecule
replaces the benzyl group in the metal coordination sphere but
no significant stabilization is achieved with this process.
An enthalpy balance of ΔH = −12.6 kcal mol−1, obtained for
t h e f o r m a t i o n o f t h e z w i t t e r i o n i c s p e c i e s
[MoCpBz(CO)3(FBF3)] (5), corroborates its formation as
experimentally identified. In fact, the small size and hard donor
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were carried out
under dry nitrogen by using standard Schlenk and high vacuum line
techniques or in a nitrogen-filled glovebox. Dichloromethane and n-
hexane were predried using 4 Å molecular sieves and freshly distilled
from CaH2 under a nitrogen atmosphere. Dichloromethane-d2 was
dried with activated 4 Å molecular sieves, degassed by freeze−pump−
thaw cycles, and stored under an atmosphere of nitrogen. The
compounds [MCpBz(CO)3H] (M = Mo (1), W (2))6c and
Ph3CBArF20 were prepared according to published procedures. Carbon
monoxide (purity 99.997% CO-N47) was purchased from Air Liquide
Portugal. NMR spectra were recorded on Bruker AVANCE 300, 400,
and 500 MHz MHz spectrometers at 296 K, unless stated otherwise.
1H NMR spectra were referenced internally to the residual proton
solvent resonances relative to tetramethylsilane (dichloromethane-d2, δ
5.32 ppm), 13C{1H} NMR spectra were referenced internally to the
residual solvent resonances (dichloromethane-d2, δ 54.0 ppm), 19F
NMR spectra were referenced externally to CF3COOH (δ −76.55
ppm), and 11B NMR spectra were referenced externally to BF3·Et2O
(δ 0 ppm); proton and carbon assignments were made using HSQC,
COSY, NOESY, and HMBC 2-D NMR experiments. Infrared spectra
were recorded on a Jasco FI/IR-4100 spectrophotometer. Elemental
−
properties of the BF4 anion allows its coordination to the
metals and stabilization of the resulting tricarbonyl species
through formation of [MoCpBz(CO)3(FBF3)] (M = Mo (5), W
(6)). On the other hand, if the anion is the bulkier and
−
noncoordinative BAr4 , the corresponding adduct is not
formed and the previous process does not occur. Metal
stabilization has to be attained through benzyl coordination,
following the necessary rearrangement on the CpBz ligand
conformation.
4392
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
purple solid (0.390 g, 75% yield). 1H NMR (CD2Cl2, 500.1 MHz, 296
Table 3. Crystallographic Data for 9 and 10
3
K): δ (ppm) 7.96 (t, 2H, JHH = 7.4 Hz, m-PhA), 7.80 (t, 8H, o-Ph of
BArF), 7.61 (s, 4H, p-Ph of BArF), 7.47 (t, 1H, 3JHH = 7.8 Hz, p-PhA),
7.37−7.31 (overlapping, 6H total, 4H, m-PhB, 2H, p-PhB), 7.12 (t, 2H,
p-PhC), 7.07−7.04 (overlapping, 8H total, 4H, m-PhC, 4H, o-PhB),
6.75 (m, 4H, o-PhC), 6.51 (d, 2H, 3JHH = 6.4 Hz, o-PhA), 3.96 (d, 2H,
9
10
empirical formula
formula wt
temp (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
C45H37BCl2F4MoO4
895.40
C45H37BCl2F4O4W
983.31
150
150
2JHH = 17 Hz, CH2B/B′PhB), 3.86 (d, 2H, JHH = 17 Hz, CH2 ′ PhB),
2
B /B
0.710 73
0.710 73
triclinic
3.78 (d, 2H, JHH = 16 Hz, CH2C/C′PhC), 3.58 (d, 2H, JHH = 16 Hz,
2
2
triclinic
C /C
A
CH2 ′ PhC), 3.58 (s, 2H, CH2 PhA). 13C{1H} NMR (CD2Cl2, 75.5
P1
̅
P1
̅
4
MHz, 296 K): δ (ppm) 232.5 (CO), 227.4 (CO), 162.2 (q, JCB = 50
Hz, i-Ph of BArF), 142.2 (m-PhA), 136.4 (i-PhB or i-PhC), 136.3 (i-PhB
or i-PhC), 135.2 (s, o-Ph of BArF), 131.0 (i-PhA), 129.5 (qm, 2JCF = 30
Hz, m-Ph of BArF), 129.9 (m-PhB), 129.4 (o-PhB), 128.8 (o-PhC),
128.7 (m-PhC), 128.5 (p-PhA), 128.4 (p-PhB), 128.2 (p-PhC), 125.0 (q,
9.8453(4)
10.2772(4)
19.8022(8)
97.231(2)
91.260(2)
95.104(2)
1978.69(14)
2
9.8487(3)
10.2715(3)
19.8080(6)
97.230(2)
91.264(2)
95.034(2)
1979.08(10)
2
b (Å)
c (Å)
3
1JCF = 272 Hz, CF3 of BArF), 117.9 (m, JCF = 4 Hz, p-Ph of BArF),
α (deg)
114.6 (CpC), 111.6 (CpB), 106.1 (CpA), 102.1 (o-PhA), 32.9
(CCH2Ph), 30.4 (CBH2Ph), 29.6 (CAH2Ph). 19F{1H} NMR (CD2Cl2,
282.4 MHz, 296 K): δ (ppm) −62.8 (s, CF3). 11B NMR (CD2Cl2, 96.3
MHz, 296 K): δ (ppm) −6.6 (m). IR (CH2Cl2): νCO 2057, 1978 cm−1.
Anal. Calcd for C75H47BF24MoO3: C, 57.68; H, 3.04. Found: C, 57.90;
H, 2.96.
β (deg)
γ (deg)
V (Å3)
Z
calcd density
1.503
1.650
(Mg m−3
)
[W{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (4). The compound was
prepared from [WCpBz(CO)3H] (2; 0.341 g, 0.43 mmol) following
the procedure described above for 3. Compound 4 was obtained as a
abs coeff (mm−1
)
0.530
912
3.117
976
F(000)
cryst size (mm)
θ range for data
collection (deg)
0.02 × 0.10 × 0.25
2.35−25.40
0.10 × 0.10 × 0.10
2.75−30.12
1
purple solid in 90% yield (0.640 g). H NMR (CD2Cl2, 500.1 MHz,
296 K): δ (ppm) 8.05 (t, 2H, 3JHH = 7.3 Hz, m-PhA), 7.75 (t, 8H, o-Ph
of BArF), 7.58 (s, 4H, p-Ph of BArF), 7.39−7.29 (overlapping, 7H
total, 1H, p-PhA 4H, m-PhB, 2H, p-PhB), 7.11 (t, 2H, p-PhC), 7.05−
7.02 (overlapping, 8H total, 4H, m-PhC, 4H, o-PhB), 6.72 (m, 4H, o-
limiting indices
−11 ≤ h ≤ 11, −12 ≤ k ≤ −13 ≤ h ≤ 13, −14 ≤ k ≤
11, −19 ≤ l ≤ 23
14, −27 ≤ l ≤ 27
no. of collected/
unique rflns [Rint]
26 950/7220 [0.0457]
57 051/11 533 [0.0416]
3
2
PhC), 6.54 (d, 2H, JHH = 6.4 Hz, o-PhA), 3.95 (d, 2H, JHH = 17 Hz,
CH2B/BPhB), 3.88 (d, 2H, JHH = 17 Hz, CH2 ′ PhB), 3.87 (d, 2H,
2
B /B
completeness to θ
(%)
98.9 (θ = 25.40)
98.9 (θ = 30.12)
2JHH = 16 Hz, CH2C/C′PhC), 3.66 (d, 2H, JHH = 16 Hz, CH2 ′ PhC),
2
C /C
A
3.61 (s, 2H, CH2 PhA). 13C{1H} NMR (CD2Cl2, 125.8 MHz, 296 K):
refinement method full-matrix least squares on full-matrix least squares on
F2
F2
4
δ (ppm) 220.6 (CO), 220.2 (CO), 162.2 (q, JCB = 50 Hz, i-Ph of
BArF), 144.3 (m-PhA), 136.9 (i-PhB or i-PhC), 136.8 (i-PhB or i-PhC),
135.6 (i-PhA), 135.4 (s, o-Ph of BArF), 130.0 (m-PhB), 129.5 (qm, 2JCF
= 30 Hz, m-Ph of BArF), 129.5 (m-PhC), 128.9 (o-PhC), 128.5 (p-PhB),
128.4 (p-PhA), 128.3 (p-PhC), 127.8 (o-PhB), 125.2 (q, 1JCF = 272 Hz,
no. of data/
restraints/params
7220/0/514
11 533/0/514
goodness of fit on
1.036
1.040
F2
final R indices (I >
R1 = 0.0361, wR2 =
0.0780
R1 = 0.0263, wR2 =
0.0592
CF3 of BArF), 118.1 (m, JCF = 4 Hz, p-Ph of BArF), 111.2 (CpC),
3
a
2σ(I))
110.0 (CpB), 103.7 (CpA), 98 (vb, o-PhA), 33.3 (CCH2Ph), 31.0
(CBH2Ph), 29.8 (CAH2Ph). 19F{1H} NMR (CD2Cl2, 282.4 MHz, 296
K): δ (ppm) −62.8 (s, CF3). 11B NMR (CD2Cl2, 96.3 MHz, 296 K): δ
(ppm) −6.6 (m). IR (CH2Cl2): νCO 2050, 1963 cm−1. Anal. Calcd for
C75H47BF24WO3: C, 54.70; H, 2.88. Found: C, 54.61; H, 2.81.
[MoCpBz(CO)3(FBF3)] (5). A dichloromethane solution of Ph3CBF4
(0.37 g, 1.10 mmol) was slowly added to a solution of
[MoCpBz(CO)3H] (1; 0.78 g, 1.10 mmol) in the same solvent. A
color change from yellow to reddish was observed immediately. The
mixture was allowed to react for about 1 h, and the solvent was
removed to dryness. The residue was washed with hexane to remove
Ph3CH and dissolved again in CH2Cl2 and filtered. The solvent was
evaporated almost completely under vacuum, leading to the formation
of a red solid. Hexane (3 mL) was added dropwise, and the solution
was filtered off. The solid was dried under vacuum. Yield: 79% (0.68
g). The reaction was also performed in a J. Young valve NMR tube in
dichloromethane-d2 using Ph3CBF4 (0.020 g, 0.061 mmol) and
[MoCpBz(CO)3H] (1; 0.042 g, 0.061 mmol). For this reaction, the
NMR spectra revealed that 5 and Ph3CH were the unique species in
solution. 1H NMR (CD2Cl2, 500.1 MHz, 296 K): δ (ppm) 7.16−7.10
(overlapping, 15H total, 10H, m-Ph, 5H, p-Ph), 6.84 (m, 10H, o-Ph),
3.73 (s, 10H, CH2Ph). 13C{1H} NMR (CD2Cl2, 125.6 MHz, 296 K): δ
(ppm) 244.9 (CO), 226.6 (CO), 137.8 (i-Ph), 129.0 (o-Ph), 128.9 (m-
Ph), 127.4 (p-Ph), 118.0 (C5Bz5), 32.2 (CH2Ph). 19F{1H} NMR
a
R indices (all data)
R1 = 0.0514, wR2 =
0.0819
R1 = 0.0320, wR2 =
0.0606
abs cor
multiscan
multiscan
largest diff peak/
0.647 and −0.627
1.503 and −0.819
hole (e Å−3
)
a
2
R1 = ∑||Fo| − |Fc||/∑|Fo|; wR2 = {∑[w(Fo − Fc2)2]/
2
∑[w(Fo )2]}1/2
.
analyses were performed by Laborator
Portugal.
́ ́
io de Analises of IST, Lisbon,
[Mo{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (3). To a dichloromethane
solution of [MoCpBz(CO)3H] (1; 0.360 g, 0.52 mmol) at 0 °C was
added dropwise a solution of Ph3CBArF (0.571 g, 0.52 mmol) in the
same solvent. The solution changed immediately from pale yellow to
dark red-brown. The reaction mixture was stirred at 0 °C for 2 h and
then at room temperature for a further 3 h. The solvent was removed
under vacuum, leading to a dark red-brown oil that became a solid
after a while under vacuum. The solid was washed several times with n-
hexane to remove Ph3CH and dried under vacuum to give 3 as a dark
2
(CD2Cl2, 282.4 MHz, 193 K): δ (ppm) −152.97 (d, JFF = 93.7 Hz,
(μ-F)10BF3), −153.04 (d, 2JFF = 93.7 Hz, (μ-F)11BF3), −338.24 (q, 2JFF
= 92.1 Hz, (μ-F)BF3). 11B NMR (CD2Cl2, 96.3 MHz, 296 K): δ
(ppm) −0.72 (s, FBF3). IR (CH2Cl2), νCO 2064, 1991, 1932 cm−1;
νB−F 1126, 848, 713 cm−1. Anal. Calcd for C43H35BF4MoO3: C, 66.00;
H, 4.51. Found: C, 65.78; H, 4.38.
4393
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
[WCpBz(CO)3(FBF3)] (6). Compound 6 was prepared by the same
procedures described for 5. With Ph3CBF4 (1.10 g, 2.13 mmol) and
[WCpBz(CO)3H] (1; 1.85 g, 2.13 mmol) as starting materials, 6 was
isolated in 89% yield (1.64 g). 1H NMR (CD2Cl2, 300.1 MHz, 296 K):
δ (ppm) 7.10−7.06 (overlapping, 15H total, 10H, m-Ph, 5H, p-Ph),
6.79 (m, 10H, o-Ph), 3.85 (s, 10H, CH2Ph). 13C{1H} NMR (CD2Cl2,
75.5 MHz, 296 K): δ (ppm) 231.8 (CO), 222.1 (CO), 138.0 (i-Ph),
129.0 (o-Ph), 128.9 (m-Ph), 127.4 (p-Ph), 115.1 (C5Bz5), 32.3
(CH2Ph). 19F{1H} NMR (CD2Cl2, 282.4 MHz, 296 K): δ (ppm)
−151.3 (br, (μ-F)BF3), −365.7 (br,(μ-F)BF3). 11B NMR (CD2Cl2,
96.3 MHz, 296 K): δ (ppm) 0.74 (br, FBF3). IR (CH2Cl2), νCO 2074,
2009, 1947 cm−1; νB−F 1101, 874, 713 cm−1. Anal. Calcd for
C43H35BF4WO3: C, 59.34; H, 4.05. Found: C, 59.69; H, 4.32.
solution of [W{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (4; 0.104 g, 0.063
mmol) at room temperature, with vigorous stirring. After 5 min the
violet solution had changed to red-orange. The mixture was stirred for
1/2 h, followed by evaporation of the solvent under vacuum to give 12
1
as a red-orange oil in 45% yield. H NMR (CD2Cl2, 400.1 MHz, 296
K): δ (ppm) 7.74 (t, 8H, o-Ph of BArF), 7.57 (s, 4H, p-Ph of BArF),
7.18−7.14 (overlapping, 15H total, 10H, m-Ph, 5H, p-Ph), 6.85 (m,
10H, o-Ph), 5.12 (br, 2H, W−OH2), 3.78 (s, 10H, CH2Ph), 2.41 (br,
free H2O). 13C{1H} NMR (CD2Cl2, 100.6 MHz, 296 K): δ (ppm)
227.7 (CO), 221.7 (CO), 162.3 (q, 4JCB = 50 Hz, i-Ph of BArF), 137.3
2
(i-Ph), 135.4 (s, o-Ph of BArF), 129.6 (m-Ph), 129.5 (qm, JCF = 30
1
Hz, m-Ph of BArF), 128.9 (o-Ph), 128.2 (p-Ph), 125.2 (q, JCF = 272
3
Hz, CF3 of BArF), 118.1 (m, JCF = 4 Hz, p-Ph of BArF), 115.3
[MoCpBz(CO)4]BArF (7). A dichloromethane-d2 solution of [Mo-
{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (3; 0.046 g, 0.030 mmol) was
transferred to a J. Young valve NMR tube. The solution was then
frozen in liquid nitrogen, evacuated on a vacuum line, and sparged
with carbon monoxide. Upon warming to room temperature the
solution turned yellow within 5 min. Evaporation of the solvent under
(C5Bz5), 32.6 (CH2Ph). 19F{1H} NMR (CD2Cl2, 282.4 MHz, 296 K):
δ (ppm) −62.8 (s, CF3). 11B NMR (CD2Cl2, 96.3 MHz, 296 K): δ
(ppm) −6.6 (m). IR (KBr pellet): νOH 3677 and 3613 cm−1 (w, br).
Solution NMR Studies. In order to obtain the relaxation
matrixes21 for the exchange of phenyl rings in compound 3, two-
dimensional exchange spectra, 2D-EXSY, were acquired using the
NOESY pulse sequence of the Bruker library over a reduced spectral
width of 1500 Hz centered on the aromatic proton region. The mixing
time was optimized to 500 ms, long enough to get good signal to noise
but short enough to avoid relaxation effects. All 2D spectra were
acquired as a 1k × 64 data array with 8 scans per increment. After zero
filling to get the same digital resolution on both dimensions, the
spectra were processed with a shifted square sine bell in both t1 and t2
domains. The exchange rate constants at 15, 17.5, 20, 25, and 30 °C
were then calculated with the EXSYCALC program (Mestrelab
Research, Santiago de Compostela, Spain) for a three-site exchange
process. The volumes of diagonal and cross peaks of 2D-EXSY spectra
needed for the calculations were measured using the SPARKY software
(T. D. Goddard and S. G. Kneller, University of California at San
Francisco). At each temperature the equilibrium magnetization of each
site was also determined by integration of the diagonal peaks of a 2D-
EXSY spectrum ran with a very short mixing time of 2 ms.
1
vacuum gave 7 as a dark golden solid in quantitative yield. H NMR
(CD2Cl2, 300.1 MHz, 296 K): δ (ppm) 7.77 (t, 8H, o-Ph of BArF),
7.59 (s, 4H, p-Ph of BArF), 7.22−7.16 (overlapping, 15H total, 10H,
m-Ph, 5H, p-Ph), 6.85 (m, 10H, o-Ph), 3.98 (s, 10H, CH2Ph). 13C{1H}
NMR (CD2Cl2, 75.5 MHz, 296 K): δ (ppm) 216.4 (CO), 162.4 (q,
4JCB = 50 Hz, i-Ph of BArF), 137.3 (i-Ph), 135.4 (s, o-Ph of BArF),
129.9 (m-Ph), 129.5 (qm, 2JCF = 30 Hz, m-Ph of BArF), 128.7 (p-Ph),
1
128.7 (o-Ph), 125.2 (q, JCF = 272 Hz, CF3 of BArF), 118.6 (C5Bz5),
3
118.1 (m, JCF = 4 Hz, p-Ph of BArF), 32.5 (CH2Ph). 19F{1H} NMR
(CD2Cl2, 282.4 MHz, 296 K): δ (ppm) −62.7 (s, CF3). 11B NMR
(CD2Cl2, 96.3 MHz, 296 K): δ (ppm) −6.6 (m). IR: KBr pellet, νCO
2110, 2058, 2036, 1977 cm−1; CH2Cl2, 2109, 2034 cm−1. Anal. Calcd
for C76H47BF24MoO4: C, 57.52; H, 2.98. Found: C, 57.24; H, 2.69.
[WCpBz(CO)4]BArF (8). The compound was prepared from
[W{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (4; 0.045 g, 0.027 mmol)
following the procedure described above for 7. An orange solution
was obtained after 1 h at room temperature. Evaporation of the solvent
1
under vacuum gave 8 as a dark orange solid in quantitative yield. H
Computational Details. All calculations were performed using the
Gaussian 03 software package,22 and the PBE0 functional, without
symmetry constraints. That functional uses a hybrid generalized
gradient approximation (GGA), including a 25% mixture of Hartree−
Fock23 exchange with DFT exchange correlation, given by the Perdew,
Burke, and Ernzerhof functional (PBE).24 The optimized geometries
were obtained with a LanL2DZ basis set25 augmented with an f-
polarization function26 for Mo and W and a standard 6-31G(d,p)27 for
the remaining elements (basis b1). Transition state optimizations were
performed with the Synchronous Transit-Guided Quasi-Newton
Method (STQN) developed by Schlegel et al.,28 following extensive
searches of the potential energy surface. Frequency calculations were
performed to confirm the nature of the stationary points, yielding one
imaginary frequency for the transition state and none for the minima.
The transition state was further confirmed by following its vibrational
mode downhill on both sides and obtaining the minima presented on
the energy profile. A natural population analysis (NPA)29 and the
resulting Wiberg indices19 were used to study the electronic structure
and bonding of the optimized species. The electronic energies (Eb1)
obtained were converted to standard enthalpies at 298.15 K (Hb1) by
using zero point energy and thermal energy corrections based on
structural and vibration frequency data calculated at the PBE0/b1 level
of theory.
Single point energy calculations were performed using a improved
basis set (basis b2) and the geometries optimized at the PBE0/b1
level. Basis b2 consisted of a 3-21G basis set30 with an added f
polarization function26 for Mo and standard 6-311++G(d,p)31 for the
remaining elements (basis b1 was used for W). Solvent effects
(CH2Cl2) were considered in the PBE0/b2//PBE0/b1 energy
calculations using the polarizable continuum model (PCM) initially
devised by Tomasi and co-workers32 as implemented in Gaussian 03.33
The molecular cavity was based on the united atom topological model
applied on UAHF radii, optimized for the HF/6-31G(d) level.
NMR (CD2Cl2, 400.1 MHz, 296 K): δ (ppm) 7.77 (t, 8H, o-Ph of
BArF), 7.60 (s, 4H, p-Ph of BArF), 7.24−7.16 (overlapping, 15H total,
10H, m-Ph, 5H, p-Ph), 6.84 (m, 10H, o-Ph), 4.04 (s, 10H, CH2Ph).
13C{1H} NMR (CD2Cl2, 100.6 MHz, 296 K): δ (ppm) 203.9 (CO),
4
162.4 (q, JCB = 50 Hz, i-Ph of BArF), 137.3 (i-Ph), 135.4 (s, o-Ph of
2
BArF), 129.9 (m-Ph), 129.5 (qm, JCF = 30 Hz, m-Ph of BArF), 128.7
(p-Ph), 128.7 (o-Ph), 125.2 (q, 1JCF = 272 Hz, CF3 of BArF), 118.1 (m,
3JCF = 4 Hz, p-Ph of BArF), 116.6 (C5Bz5), 32.6 (CH2Ph). 19F{1H}
NMR (CD2Cl2, 282.4 MHz, 296 K): δ (ppm) −62.7 (s, CF3). 11B
NMR (CD2Cl2, 96.3 MHz, 296 K): δ (ppm) −6.6 (m). IR: KBr pellet,
νCO 2108, 2049, 2026, 1957 cm−1; CH2Cl2, 2107, 2024 cm−1. Anal.
Calcd for C76H47BF24WO4: C, 54.50; H, 2.83. Found: C, 54.43; H,
2.45.
[MoCpBz(CO)3(H2O)]BArF (11). A dichloromethane-d2 solution of
[Mo{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (3; 0.040 g, 0.026 mmol) was
transferred to a J. Young valve NMR tube, and an excess of previously
degassed distilled water (5 μL, 0.28 mmol) was added at room
temperature. Immediately a dark orange solution was obtained. NMR
1
characterization revealed the formation of 11 in 70% yield. H NMR
(CD2Cl2, 400.1 MHz, 296 K): δ (ppm) 7.75 (t, 8H, o-Ph of BArF),
7.59 (s, 4H, p-Ph of BArF), 7.20−7.13 (overlapping, 15H total, 10H,
m-Ph, 5H, p-Ph), 6.86 (m, 10H, o-Ph), 4.99 (br, 2H, Mo−OH2), 3.74
(s, 10H, CH2Ph), 2.47 (br, free H2O). 13C{1H} NMR (CD2Cl2, 100.6
4
MHz, 296 K): δ (ppm) 238.6 (CO), 226.3 (CO), 162.4 (q, JCB = 50
Hz, i-Ph of BArF), 137.5 (i-Ph), 135.4 (s, o-Ph of BArF), 129.5 (m-Ph),
2
129.5 (qm, JCF = 30 Hz, m-Ph of BArF), 129.0 (o-Ph), 128.1 (p-Ph),
125.2 (q, 1JCF = 272 Hz, CF3 of BArF), 118.1 (m, 3JCF = 4 Hz, p-Ph of
BArF), 117.7 (C5Bz5), 32.5 (CH2Ph). 19F{1H} NMR (CD2Cl2, 282.4
MHz, 296 K): δ (ppm) −62.8 (s, CF3). 11B NMR (CD2Cl2, 96.3 MHz,
296 K): δ (ppm) −6.6 (m). IR (KBr pellet): νOH 3677 and 3619 cm−1
(w, br).
[WCpBz(CO)3(H2O)]BArF (12). An excess of previously degassed
distilled water (16 μL, 0.89 mmol) was added to a dichloromethane
4394
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
The enthalpy values presented along the text (Hb2soln) were derived
from the electronic energy values obtained at the PBE0/b2//PBE0/b1
level, including solvent effects (Eb2soln), according to the expression
Coleman, K. S.; Cowley, A. R.; Green, M. L. H. Organometallics 2010,
29, 4858−4870.
(2) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 2nd ed.; Wiley: New York, 1994; p 91. (b) O’Connor, J. M.;
Casey, C. P. Chem. Rev. 1987, 87, 307. (c) Calhorda, M. J.; Veiros, L.
soln
soln
Hb2 = Eb2 + Hb1 − Eb1
F. Coord. Chem. Rev. 1999, 185−186, 37. (c) Calhorda, M .J.; Romao,
̃
X-ray Data Collection, Structure Solution, and Refinement.
Suitable crystals of compounds 9 and 10 were selected and coated in
FOMBLIN oil and mounted on a Bruker AXS-KAPPA APEX II
diffractometer using graphite-monochromated Mo Kα radiation (λ =
0.710 73 Å). A full sphere of data was collected at 150(2) K using ω
scans of 0.5° per frame. Cell parameters were retrieved using Bruker
APEX2 software and refined using Bruker SAINT on all observed
reflections. Absorption corrections were applied using SADABS.34
Structure solution and refinement were performed using direct
methods with the programs SIR9735 and SHELXS-97,36 both included
in the package of programs WINGX-Version 1.80.05.37 Non-hydrogen
atoms were refined anisotropically. All hydrogens were inserted in
idealized positions and refined riding on the parent carbon atom.
Torsion angles, mean square planes, and other geometrical parameters
were calculated using SHELX.38 Illustrations of the molecular
structures were made with ORTEP3.39 Details of the data collection
and refinement are given in Table 3. Data for complexes 9 and 10 were
deposited at the Cambridge Crystallographic Data Centre with
references CCDC 837442 and 837443, respectively.
C. C.; Veiros, L. F. Chem. Eur. J. 2002, 8, 868. (d) Stoll, M. E.;
Belanzoni, P.; Calhorda, M. J.; Drew, M. G. B.; Fel
́
ix, V.; Geiger, W. E.;
Gamelas, C. A.; Goncalves, I. S.; Romao, C. C.; Veiros, L. F. J. Am.
̧
̃
Chem. Soc. 2001, 123, 10595−10606.
(3) (a) Deckers, P. J. W.; Hessen, B.; Teuben, J. H. Angew. Chem., Int.
Ed. 2001, 40, 2516−2519. (b) Munha,
T.; Fryzuk, M. D.; Martins, A. M. Dalton Trans. 2009, 7494−7508.
(c) Antunes, M. A.; Munha, R. F.; Alves, L. G.; Schafer, L. L.; Martins,
́
R. F.; Veiros, L. F.; Duarte, M.
́
A. M. J. Organomet. Chem. 2011, 696, 2−6.
(4) (a) Kimmich, B. F. M.; Fagan, P. J.; Hauptman, E.; Marshall, W.
J.; Bullock, R. M. Organometallics 2005, 24, 6220−6229. (b) Gomes, P.
T.; Green, M. L. H.; Martins, A. M. J. Organomet. Chem. 1998, 551,
133−138. (c) Kandepi, V. V. K. M.; Cardoso, J. M. S.; Peris, E.; Royo,
B. Organometallics 2010, 29, 2777−2782. (d) Zhang, L.; Gao, W.; Tao,
X.; Wu, Q.; Mu, Y.; Ye, L. Organometallics 2011, 30, 433−440. (e) Li,
J.; Gao, W.; Wu, Q.; Li, H.; Mu, Y. J. Organomet. Chem. 2011, 696,
2499−2506. (f) Siemeling, U. Chem. Rev. 2000, 100, 1495−1526.
(g) Muller, C.; Vos, D.; Jutzi, P. J. Organomet. Chem. 2000, 600, 127−
̈
143. (h) Jutzi, P.; Siemeling, U. J. Organomet. Chem. 1995, 500, 175−
185. (i) Jutzi, P.; Redeker, T. Eur. J. Inorg. Chem. 1998, 663−674.
ASSOCIATED CONTENT
* Supporting Information
■
(j) Butenschon, H. Chem. Rev. 2000, 100, 1527−1564.
̈
S
(5) (a) Flores, J. C.; Wood, J. S.; Chien, J. C. W..; Rausch, M. D.
Organometallics 1996, 15, 4944−4950. (b) Saßmannshausen, J.;
Powell, A. K.; Anson, C. E.; Wocadlo, S.; Bochmann, M. J. Organomet.
Chem. 1999, 592, 84−94. (c) Deckers, P. J. W.; Hessen, B.
Organometallics 2002, 21, 5564−557. (d) Longo, P.; Amendola, A.
G.; Fortunato, E.; Boccia, A. C.; Zambelli, A. Macromol. Rapid
Commun. 2001, 22, 339−344.
Figure S1, giving the Eyring plot for benzyl exchange in 3,
Figure S2, giving a representation of the optimized structure of
intermediate A, tables giving atomic coordinates for all
optimized species, and CIF files giving crystallographic data
for complexes 9 and 10. This material is available free of charge
via the Internet at http://pubs.acs.org.
(6) (a) Martins, A. M.; Branquinho, R.; Cui, J.; Dias, A.; Duarte, M.
T.; Fernandes, J.; Rodrigues, S. J. Organomet. Chem. 2004, 689, 2368−
AUTHOR INFORMATION
Corresponding Author
*E-mail: ana.martins@ist.utl.pt.
■
2376. (b) Martins, A. M.; Romao, C. C.; Abrantes, M.; Azevedo, M.
̃
C.; Cui, J.; Dias, A. R.; Duarte, M. T.; Lemos, M. A.; Lourenco̧ , T.;
Poli, R. Organometallics 2005, 24, 2582−2589. (c) Namorado, S.; Cui,
J.; de Azevedo, C. G.; Lemos, M. A.; Duarte, M. T.; Ascenso, J. R.;
Dias, A. R.; Martins, A. M. Eur. J. Inorg. Chem. 2007, 1103−1113.
(d) Namorado, S.; Antunes, M. A.; Veiros, L. F.; Ascenso, J. R.;
Duarte, M. T.; Martins, A. M. Organometallics 2008, 27, 4589−4599.
(e) Antunes, M. A.; Namorado, S.; de Azevedo, C. G.; Lemos, M. A.;
Duarte, M. T.; Ascenso, J. R.; Martins, A. M. J. Organomet. Chem.
2010, 695, 1328−1336.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the Fundaca
̧
o para a Cien
̂
cia e a Tecnologia,
̃
Portugal, for funding (PTDC/QUI/66187/2006, PEst-OE/
QUI/UI0100/2011, SFRH/BD/13374/2003, SFRH/BPD/
26745/2006, SFRH/BD/44295/2008) and to the Portuguese
NMR Network (IST-UTL Centre) for providing access to the
NMR facility. L.F.V. acknowledges UTL/Santander for
financial support.
(7) (a) Keane, J. M.; Harman, W. D. Organometallics 2005, 24,
1786−1798. (b) Chin, R. M.; Dong, L.; Duckett, S. B.; Jones, W. D.
Organometallics 1992, 11, 871−876. (c) Harman, W. D. Chem. Rev.
1997, 97, 1953−1978. (d) Norris, C. M.; Reinartz, S.; White, P. S.;
Templeton, J. L. Organometallics 2002, 21, 5649−5656.
(8) Macchioni, A.; Pregosin, P. S.; Engel, P. F.; Mecking, S.; Pfeffer,
M.; Daran, J. C.; Vaissermann, J. Organometallics 1995, 14, 1637−
1645.
REFERENCES
■
(1) (a) Pregosin, P. S.; Salzmann, R. Coord. Chem. Rev. 1996, 155,
35−68. (b) Herrmann, J.; Pregosin, P. S.; Salzmann, R.; Albinati, A.
Organometallics 1995, 14, 3311−3318. (c) Breutel, C.; Pregosin, P. S.;
Salzmann, R.; Togni, A. J. Am. Chem. Soc. 1994, 116, 4067−4068.
(d) Pregosin, P. S.; Salzmann, R.; Togni, A. Organometallics 1995, 14,
842−847. (e) Wassenaar, J.; van Zutphen, S.; Mora, G.; Le Floch, P.;
Siegler, M. A.; Spek, A. L.; Reek, J. N. H. Organometallics 2009, 28,
2724−2734. (f) Moreno, A.; Pregosin, P. S.; Fuentes, B.; Veiros, L. F.;
Albinati, A.; Rizzato, S. Organometallics 2009, 28, 6489−6506.
(g) Deng, W.; You, S.; Hou, X.; Dai, L.; Xia, W.; Sun, J. J. Am.
Chem. Soc. 2001, 123, 6508−6519. (h) Faller, J. W.; Wilt, J. C.
Organometallics 2005, 24, 5076−5083. (i) Mandal, S. K.; Gowda, G. A.
N.; Krishnamurthy, S. S.; Nethaji, M. Dalton Trans. 2003, 1016−1027.
(j) Camus, J. M.; Andrieu, J.; Richard, P.; Poli, R. Eur. J. Inorg. Chem.
2004, 1081−1091. (k) Filipuzzi, S.; Pregosin, P. S.; Albinati, A.;
Rizzato, S. Organometallics 2006, 25, 5955−964. (l) Dastgir, S.;
(9) Cheng, T. Y.; Szalda, D. J.; Bullock, R. M. Chem. Commun. 1999,
1629−1630.
(10) Sweet, J. R.; Graham, W. A. G. Organometallics 1983, 2, 135−
140.
(11) (a) Song, J.-S.; Szalda, D. J.; Bullock, R. M.; Lawrie, J. C.;
Rodkin, M. A.; Northon, J. R. Angew. Chem., Int. Ed. Engl. 1992, 31,
1233−1235. (b) Bullock, R. M. Chem. Eur. J. 2004, 10, 2366−2374.
(12) Beck, W.; Sunkel, K. Chem. Rev. 1988, 88, 1405−1421 and
̈
references cited therein..
́
(13) (a) Lanza, G.; Fragala, I. L.; Marks, T. J. Organometallics 2002,
21, 5594−5612. (b) Rocchigiani, L.; Zuccaccia, C.; Zuccaccia, D.;
Macchioni, A. Chem. Eur. J. 2008, 14, 6589−6592. (c) Zuccaccia, C.;
Stahl, N. G.; Macchioni, A.; Chen, M. C.; Roberts, J. A.; Marks, T. J. J.
Am. Chem. Soc. 2004, 126, 1448−1464. (d) Chen, M. C.; Roberts, J. A.
S.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 4605−4625. (e) Chen, M.
4395
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396

Organometallics
Article
C.; Marks, T. J. J. Am. Chem. Soc. 2001, 123, 11803−11804.
(f) Macchioni, A. Chem. Rev. 2005, 105, 2039−2073. (g) Martins,
A. M.; Ascenso, J. R.; Costa, S. M. B.; Dias, A. R.; Ferreira, H.; Ferreira,
J. A. B. Inorg. Chem. 2005, 44, 9017−9022. (h) Alves, L. G.; Dazinger,
G.; Veiros, L. F.; Kirchner, K. Eur. J. Inorg. Chem. 2010, 3160−3166.
Chem. Phys. 1985, 83, 735. (g) Reed, A. E.; Curtiss, L. A.; Weinhold, F.
Chem. Rev. 1988, 88, 899. (h) Weinhold, F.; Carpenter, J. E. The
Structure of Small Molecules and Ions; Plenum: New York, 1988; p 227.
(30) (a) Binkley, J. S.; Pople, J. A.; Hehre, W. J. J. Am. Chem. Soc.
1980, 102, 939. (b) Gordon, M. S.; Binkley, J. S.; Pople, J. A.; Pietro,
W. J.; Hehre, W. J. J. Am. Chem. Soc. 1982, 10, 2797. (c) Pietro, W. J.;
Francl, M. M.; Hehre, W. J.; Defrees, D. J.; Pople, J. A.; Binkley, J. S. J.
Am. Chem. Soc. 1982, 104, 5039. (d) Dobbs, K. D.; Hehre, W. J. J.
Comput. Chem. 1987, 8, 861. (e) Dobbs, K. D.; Hehre, W. J. J. Comput.
Chem. 1987, 8, 880. (f) Dobbs, K. D.; Hehre, W. J. J. Comput. Chem.
1986, 7, 359.
(31) (a) McClean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72,
5639. (b) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem.
Phys. 1980, 72, 650. (c) Wachters, A. J. H. J. Chem. Phys. 1970, 52,
1033. (d) Hay, P. J. J. Chem. Phys. 1977, 66, 4377. (e) Raghavachari,
K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062. (f) Binning, R. C., Jr.;
Curtiss, L. A. J. Comput. Chem. 1990, 11, 1206. (g) McGrath, M. P.;
Radom, L. J. Chem. Phys. 1991, 94, 511. (h) Clark, T.; Chandrasekhar,
J.; Spitznagel, G. W.; Schleyer, P. v. R. J. Comput. Chem. 1983, 4, 294.
(i) Frisch, M. J.; Pople, J. A.; Binkley, J. S. J. Chem. Phys. 1984, 80,
3265.
́
(i) Munha, R. F.; Antunes, M. A.; Alves, L. G.; Veiros, L. F.; Fryzuk,
M. D.; Martins, A. M. Organometallics 2010, 29, 3753−3764.
(14) (a) Sunkel, K.; Urban, G.; Beck, W. J. Organomet. Chem. 1983,
̈
252, 187−194. (b) Appel, M.; Beck, W. J. Organomet. Chem. 1987,
319, C1−C4.
(15) Cheng, T.-Y.; Szalda, D. J.; Hanson, J. C.; Muckerman, J. T.;
Bullock, R. M. Organometallics 2008, 27, 3785−3795.
(16) Leoni, P.; Grilli, E.; Pasquali, M.; Tomassini, M. Dalton Trans.
1986, 1041−1043.
(17) Brammer, L.; Zhao, D.; Bullock, R. M.; McMullan, R. K. Inorg.
Chem. 1993, 32, 4819−4824.
(18) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: New York, 1989.
(19) (a) Wiberg, K. B. Tetrahedron 1968, 24, 1083. (b) Wiberg
indices are electronic parameters related to the electron density
between atoms. They can be obtained from a natural population
analysis and provide an indication of the bond strength.
(20) Bahr, S. R.; Boudjouk, P. J. Org. Chem. 1992, 57, 5545−5547.
(21) Perrin, C. L.; Gipe, R. K. J. Am. Chem. Soc. 1984, 106, 4036−
4038.
̀
(32) (a) Cances, M. T.; Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997,
107, 3032. (b) Cossi, M.; Barone, V.; Mennucci, B.; Tomasi, J. Chem.
Phys. Lett. 1998, 286, 253. (c) Mennucci, B.; Tomasi, J. J. Chem. Phys.
1997, 106, 5151.
(33) (a) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999. (b) Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. J. Chem. Phys.
2002, 117, 43.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision
C.02; Gaussian, Inc., Wallingford, CT, 2004.
(34) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction; University of Gottingen, Gottingen, Germany, 1996.
̈
̈
(35) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. J. Appl. Crystallogr. 1999, 32, 115.
(36) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Gottingen, Gottingen, Germany, 1997.
̈
̈
(37) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(38) Sheldrick, G. Acta Crystallogr. 2008, A64, 112.
(39) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(23) Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab Initio
Molecular Orbital Theory; Wiley: New York, 1986.
(24) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997,
78, 1396. (b) Perdew, J. P. Phys. Rev. B 1986, 33, 8822.
(25) (a) Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical
Chemistry; Schaefer, H. F., III, Ed.; Plenum: New York, 1976; Vol. 3, p
1. (b) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (c) Wadt,
W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (d) Hay, P. J.; Wadt, W.
R. J. Chem. Phys. 1985, 82, 2299.
(26) Ehlers, A. W.; Bohme, M.; Dapprich, S.; Gobbi, A.; Hollwarth,
̈
̈
A.; Jonas, V.; Kohler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
̈
Chem. Phys. Lett. 1993, 208, 111.
(27) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971,
54, 724. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys.
1972, 56, 2257. (c) Hariharan, P. C.; Pople, J. A. Mol. Phys. 1974, 27,
209. (d) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163. (e) Hariharan,
P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(28) (a) Peng, C.; Ayala, P. Y.; Schlegel, H. B.; Frisch, M. J. J.
Comput. Chem. 1996, 17, 49. (b) Peng, C.; Schlegel, H. B. Israel J.
Chem. 1994, 33, 449.
(29) (a) Carpenter, J. E.; Weinhold, F. J. Mol. Struct. (THEOCHEM)
1988, 169, 41. (b) Carpenter, J. E. Ph.D. thesis, University of
Wisconsin, Madison, WI, 1987. (c) Foster, J. P.; Weinhold, F. J. Am.
Chem. Soc. 1980, 102, 7211. (d) Reed, A. E.; Weinhold, F. J. Chem.
Phys. 1983, 78, 4066. (e) Reed, A. E.; Weinhold, F. J. Chem. Phys.
1983, 78, 1736. (f) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J.
4396
dx.doi.org/10.1021/om300070m | Organometallics 2012, 31, 4387−4396