Mapping the elimination of water from hydroxyvinylidene complexes of ruthenium(II): Access to allenylidene and vinylvinylidene complexes in a stepwise fashion

Article abstract of DOI:10.1021/om4009247

Reaction of hydroxyvinylidene complexes [Ru(κ¹-OAc) (κ²-OAc)(=C=CHC{OH}R¹R²)(PPh ₃)₂] (R¹ = R² = Ph; R¹ = R² = Me; R¹ = Ph, R² = Me) with [CPh ₃]BF₄ results in the formation of the cationic carbene species [Ru(κ²-OAc)(OC{Me}OCC{H}=CR¹R ²)(PPh₃)₂]BF₄. In these complexes, the κ¹-acetate ligand has changed its binding mode in order to stabilize the resulting cationic species. The carbene complexes may be deprotonated, although the outcome of the reaction depends markedly on the substituent present. In the case in which R¹ = R² = Ph, the hydrogen on the β-carbon of the organic ligand is removed to afford an allenylidene complex [Ru(κ¹-OAc)(κ²-OAc)(=C=C= CPh₂)(PPh₃)₂]. An examination of the structural and spectroscopic parameters for the allenylidene complex indicates that the electronic influence of this ligand is very similar to the corresponding vinylidene and isonitrile analogues. In the cases where R¹ = R ² = Me and R¹ = Me, R² = Ph deprotonation occurs at a methyl group to afford vinylvinylidene complexes [Ru(κ¹-OAc)(κ²-OAc)(=C=C{H}-CR ²=CH₂)(PPh₃)₂] (R² = Me, Ph). No interconversion between vinylvinylidene and allenylidene complexes was observed. The overall process is analogous to a formal E₁-type elimination in which the cationic carbene complex may be viewed as a stabilized carbocation intermediate. A DFT study provided insight into selectivity of the deprotonation step indicating that the greatest relative difference in energy between all the possible isomers of the vinylvinylidene and allenylidene complexes was ca. 20 kJ mol^-1. Interconversion between the two forms of the complex by a [1,3]-hydrogen shift appears to be unlikely due to the higher energy of the corresponding transition state; hence the selectivity in the formation of the vinylvinylidene complexes may be due the site of deprotonation being kinetically controlled. An alternative mechanism for this interconversion between vinylvinylidene and allenylidene complexes in cationic half sandwich metal complexes is proposed, which proceeds via a deprotonation/reprotonation pathway.

Full text of DOI:10.1021/om4009247

Article
pubs.acs.org/Organometallics
Mapping the Elimination of Water from Hydroxyvinylidene
Complexes of Ruthenium(II): Access to Allenylidene and
Vinylvinylidene Complexes in a Stepwise Fashion
Elizabeth J. Smith, David G. Johnson, Robert J. Thatcher, Adrian C. Whitwood, and Jason M. Lynam*
Department of Chemistry, University of York, Heslington, York, YO10 5DD, United Kingdom
S
* Supporting Information
ABSTRACT: Reaction of hydroxyvinylidene complexes [Ru-
(κ1-OAc)(κ2-OAc)(CCHC{OH}R1R2)(PPh3)2] (R1
=
R2 = Ph; R1 = R2 = Me; R1 = Ph, R2 = Me) with [CPh3]-
BF4 results in the formation of the cationic carbene species
[Ru(κ2-OAc)(OC{Me}OCC{H}CR1R2)(PPh3)2]BF4. In
these complexes, the κ1-acetate ligand has changed its bind-
ing mode in order to stabilize the resulting cationic species.
The carbene complexes may be deprotonated, although the
outcome of the reaction depends markedly on the substituent
present. In the case in which R1 = R2 = Ph, the hydrogen on the β-carbon of the organic ligand is removed to afford an
allenylidene complex [Ru(κ1-OAc)(κ2-OAc)(CCCPh2)(PPh3)2]. An examination of the structural and spectroscopic
parameters for the allenylidene complex indicates that the electronic influence of this ligand is very similar to the corresponding
vinylidene and isonitrile analogues. In the cases where R1 = R2 = Me and R1 = Me, R2 = Ph deprotonation occurs at a
methyl group to afford vinylvinylidene complexes [Ru(κ1-OAc)(κ2-OAc)(CC{H}-CR2CH2)(PPh3)2] (R2 = Me, Ph).
No interconversion between vinylvinylidene and allenylidene complexes was observed. The overall process is analogous to a
formal E1-type elimination in which the cationic carbene complex may be viewed as a stabilized carbocation intermediate. A DFT
study provided insight into selectivity of the deprotonation step indicating that the greatest relative difference in energy between
all the possible isomers of the vinylvinylidene and allenylidene complexes was ca. 20 kJ mol−1. Interconversion between the two
forms of the complex by a [1,3]-hydrogen shift appears to be unlikely due to the higher energy of the corresponding transition
state; hence the selectivity in the formation of the vinylvinylidene complexes may be due the site of deprotonation being
kinetically controlled. An alternative mechanism for this interconversion between vinylvinylidene and allenylidene complexes in
cationic half sandwich metal complexes is proposed, which proceeds via a deprotonation/reprotonation pathway.
The simplest manner to generate vinylidene ligands is via the
metal-promoted formal 1,2-hydrogen migration of terminal
alkynes (A → B, Scheme 1),1b,10 although more recently the
INTRODUCTION
■
Transition metal complexes containing unsaturated carbene
ligands, such as vinylidene,1 allenylidene,2 and longer cumu-
lenylidenes2b,3 play an important role in a number of fields. For
example, vinylidene complexes are key intermediates in a range
of catalytic reactions of terminal alkynes which result in carbon−
carbon and carbon−element bond formation in an atom-efficient
manner.1a,4 Moreover, the intermediacy of vinylidene complexes
in these processes may often promote the anti-Markovnikov
addition of substrates to alkynes.4a,5 In a similar fashion, metal
complexes containing allenylidene ligands also play an important
catalytic role. For example, Nishibayashi has demonstrated that
the thiolate-bridged ruthenium dimer [{RuCl(η5-C5Me5)}-
(μ-SR)]2 is an excellent catalyst for a range of propagyl-substitution
reactions: the formation of a ruthenium-bound allenylidene ligand
being a key step in this process.6 Complexes containing allenylidene
ligands have also been shown to be catalysts for alkene metathesis7
and also the decarbonylation of propargyl alcohols.8 In addition to
their uses as intermediates in catalytic reactions, complexes
containing cumulene ligands have been extensively studied for
their interesting electronic and optical properties.2a,9
a
Scheme 1
a
(i) − H2O; (ii) − H2O, R1 = alkyl or aryl, R2 = Me.
formation of disubstituted vinylidene ligands from internal
alkynes has been reported.11 The formation of substituted
Received: September 16, 2013
Published: December 3, 2013
© 2013 American Chemical Society
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vinylidene complexes has also been exploited for the formation of
allenylidene complexes. In a method pioneered by Selegue,12 the
reaction of a terminal propargyl alcohol with an unsaturated
metal complex results in the formation of an intermediate
hydroxy-substituted vinylidene species (Scheme 1, B), which
may then undergo dehydration (either spontaneously or upon
suitable stimulus) to give the desired allenylidene complexes,
C.2b,3c,6l,7f,13 This is generally a robust synthetic method and may
be applied to a range of metal complexes and alkynes bearing
different substituents. Although there is a report of stable unco-
ordinated allenylidenes which may subsequently be coordinated
to suitable metal complexes,13b the vast majority of cumulene
ligands have been assembled within the coordination sphere of a
metal from alkyne precursors.
Although the Selegue method does have a wide applicability,
there are a number of instances in which allenylidene complexes
are not obtained. In the case of propargyl alcohols which have
alkyl substituents, it is possible that an alternative dehydration
pathway may occur to give vinylvinylidene complexes, D,14 and
there are examples of this being a competitive process with both
isomers being in equilibrium. An additional case in which the
Selegue method fails to afford an allenylidene complex, but
has important consequences for catalysis, is the reaction of
[RuCl2(PPh3)4] with HCCCPh2(OH). As shown in
Scheme 2, this reaction affords a ruthenium indenylidene
HCCCPh2(OH) leads to the formation of trans-[Ru(κ1-OAc)-
(κ2-OAc)(CCHC{OH}Ph2)(PPh3)2], 2, which undergoes
a subsequent reaction to give carbonyl complex trans-[Ru(κ1-
OAc)(κ2-OAc)(CO)(PPh3)2] and H2CCPh2: this proved to
be a general reaction for propargyl alcohols of the general form
HCCCR2(OH).19
Access to long-lived hydroxy-substituted vinylidene complexes
offers an opportunity to study the reactivity of such species,
with a view to gaining mechanistic insight into the Selegue
mechanism. In particular, we sought to gain an understanding of
the different elimination pathways. In order to achieve this goal,
we considered that the first step in the process would be the
abstraction of the hydroxy-substituent on the vinylidene with a
suitable Lewis acid, this should give rise to a cationic metal
complex which would be amenable to deprotonation. We now
report how the elimination of water from hydroxy-vinylidene
complexes 2 may be accomplished in a stepwise fashion to
provide initial access to cationic Fischer carbene complexes
stabilized by an acetate ligand. On treatment with a base, these
carbene complexes provided access to allenylidene and vinyl-
vinylidene complexes.
RESULTS AND DISCUSSION
■
Synthesis of Cationic Carbene Complexes. Treatment of
a CH2Cl2 solution of the hydroxy-substituted vinylidene complex
[Ru(κ1-OAc)(κ2-OAc)(CCHC{OH}Ph2)(PPh3)2], 2a
[generated in situ from the reaction of 1 with HCCCPh2-
(OH)], with an equimolar amount of [CPh3]BF4 resulted in
an instantaneous color change from yellow to deep green.
Following concentration of the solution, the carbene complex
a
Scheme 2
[Ru(κ2-OAc)(OC{Me}OCC{H}CPh2)(PPh3)2]BF4,
[3a]BF4, could be isolated by precipitation with pentane
(Scheme 3). The resulting green powder could be crystallized
a
Scheme 3
a
(i) H2O, − 2PPh3, (ii) + PCy3, − H2O, − 2PPh3.
complex, E,15 which has been exploited as an alkene metathesis
catalyst,7f,16 although by the addition of PCy3 it is possible to
prepare allenylidene F.17
a
(i) + [CPh3]BF4, − Ph3COH, CH2Cl2, room temperature, 90 min.
Although the Selegue method is now well established, there
appears to be little mechanistic information on the fundamental
processes which governs the elimination of water. We have
recently demonstrated that the ruthenium acetate complex, cis-
[Ru(κ2-OAc)2(PPh3)2], 1, is a versatile precursor to a range of
complexes containing π-acidic ligands. Reactions of 1 with
CO, [NO]BF4, CNtBu, and terminal alkynes gives rise to com-
plexes trans-[Ru(κ1-OAc)(κ2-OAc)(L)(PPh3)2] (L = CO, NO+,
CNtBu, and CCHR, respectively).18 The presence of the
acetate ligand plays an important role in the formation of the
vinylidene complexes as it lowers the energy to the hydrogen
migration step by a Ligand-Assisted Proton Shuttle (LAPS)
mechanism.10b The reactions of 1 with propargyl alcohols does
not lead to the spontaneous formation of allenylidene complexes.
In this instance, long-lived metastable hydroxyvinylidene com-
plexes were obtained. For example, the reaction of 1 with
by slow diffusion of diethyl ether into a CH2Cl2 solution of the
complex. The H NMR spectrum of [3a]BF4 exhibited two
1
resonances for the methyl groups of the acetate ligands at δ 0.79
and δ 1.31, confirming the different coordination environments.
The 13C{1H} NMR spectrum of the complex also confirmed the
presence of two inequivalent acetate ligands, and importantly, a
triplet resonance was observed at δ 279.8 (2JPC = 9.3 Hz) for the
metal-bound carbon atom. The carbon atoms in the β and γ
positions of the vinyl carbene ligand were observed at δ 127.7 (s)
and δ 146.9 (s), respectively. When the reaction was monitored
by NMR spectroscopy, the formation of [3a]+ was shown to
occur in a quantitative fashion, and the formation of one
equivalent of Ph3COH was observed.
Reaction of either the dimethyl-substituted hydroxyl-
vinylidene complex, 2b, or the related complexes bearing phenyl/
methyl substituents, 2c, with [CPh3]BF4 followed the same
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course (Scheme 3) with purple ([3b]BF4) and green ([3c]BF4)
carbene complexes being obtained, respectively. In the case
of [3c]BF4, only one of the two possible stereoisomers was
obtained. A 2D-NOESY experiment on a CD2Cl2 solution of
[3c]BF4 exhibited NOE cross peaks between the hydrogen atom
of the carbene ligand and the aromatic region which, given that
no NOE peaks were observed for the methyl group, suggests that
the alkene adopts the orientation shown in Scheme 3 with the
hydrogen and phenyl substituents adopting a Z configuration. In
addition, this 2D-NOSEY spectrum exhibited EXSY peaks
between the two acetate resonances, suggesting that they were
undergoing exchange, although this is evidently occurring on a
much slower time scale than complexes containing both κ1- and
κ2-acetate ligands where exchange is typically fast on the NMR
time scale at room temperature.18,19
Obtaining crystals of complexes [3]BF4 which gave high
quality X-ray diffraction data proved to be fraught with difficulty,
despite multiple attempts using a range of conditions. In many
cases, crystals exhibited substantial twinning and disorder, and
only the best data sets obtained are discussed. In the case of
complex [3a]BF4, the resulting structure determination
demonstrates that the connectivity within the complex was as
expected (see Supporting Information); however, the vinyl
group of the carbene was disordered over two sites. It did prove
possible to obtain a higher quality structure of the complex
contain two mutually trans-triphenylphosphine ligands with
the remaining two coordination sites being occupied by a
bidentante ligand, which is probably best viewed as a bidentate
Fischer carbene complex. The ruthenium−carbon bond lengths
(1.843(4)−1.862(3) Å) are shorter than those observed in the
half-sandwich Fischer carbene complexes [Ru(η5-C5H5)(
C{OMe}Et)(PPh3)2]PF6 (1.959(6) Å)20 and [Ru(η5-
C5H5)(C{OMe}CH2Ur)(PPh3)2]X (Ur = uracil; X = PF6,21
1.946(3) Å; X = OTf,22 1.9541(17) Å) but are similar in length to
those observed in octahedral species such as the cyclic carbene
[Ru(κ1-OAc)(κ2-OAc)(COC3H6)(PPh3)2] (1.876(6) Å)18
and [RuCl2(OC{Me}OCCHCPh2)(PPh3)2] (1.862(5) Å).15b
The geometry within the ester tether indicates that the bond-
ing in the cations [3]+ is best described as shown in Scheme 3,
with the CO distance being shorter than C−O. We have
observed this type of metalloenol ester structure previously in a
mechanistic study into the formation of the vinylidene complexes
related to 2; however, in this case it appears that the metalloenol
ester structure B generally lies at higher energy than the cor-
responding vinylidene complexes, A.10b Presumably in the case
of the cations [3]+, the formal generation of a carbocation
on removal of the OH group by [CPh3]+ results in a highly
electrophilic metal-bound carbon, which is stabilized by the
acetate ligand.
[Ru(κ2-O2CPh)(OC{Ph}OCC{H}CPh2)(PPh3)2]BF4,
[3aBz]BF4 (Figure 1), which could be obtained in an identical
In contrast to the reactions involving 2a−2c, treatment of the
unsubstituted hydroxy-vinylidene complex [Ru(κ1-OAc)(κ2-
OAc)(CCHC{OH}H2)(PPh3)2], 2d, with [CPh3]BF4 did
not result in a selective reaction. Addition of [CPh3]BF4 to a
CH2Cl2 solution of 2d at room temperature resulted in an
instantaneous color change from orange to blue. Analysis of the
reaction mixture by NMR spectroscopy demonstrated that
the desired cation [Ru(κ2-OAc)(OC{Me}OCC{H}CH2)-
1
(PPh3)2]BF4, [3d]BF4, was not present. The H and 31P{1H}
NMR spectra indicated that a range of products has been formed
including [Ru(κ1-OAc)(κ2-OAc)(CO)(PPh3)2], [Ph3CPPh3]+,
the phosphonio-ethyl complex [4]+ (identified by X-ray crys-
tallography, see Supporting Information), and, remarkably,
[PEtPh3]+, with the relative amounts of these varying from
reaction to reaction (Scheme 4).
Figure 1. Solid state structure of the cation [3aBz]+; hydrogen atoms,
except for H(16), are omitted for clarity. Thermal ellipsoids, where
shown, are at the 50% probability level.
Further attempts were made to confirm the formation of
[3d]BF4. An equimolar amount of [CPh3]BF4 was added to
a thawing CD2Cl2 solution of 2d, and after warming to
room temperature, the sample was placed directly into a NMR
spectrometer. Under these conditions, a series of resonances for
the cation [3d]+ could be observed. For example, in the 1H NMR
spectrum, resonances for the two geminal hydrogen atoms of the
vinyl group were present at δ 6.32 (d, 3JHH = 11.0 Hz) and δ 6.50
(d, 3JHH = 17.3 Hz): both resonances exhibited a cross peak in a
2D-COSY experiments to an additional proton, which was
obscured by the peaks for the PPh3 ligands. Peaks for the two
acetate groups were observed at δ 0.82 (3H) and 1.86 (3H).
Although [3d]+ was the major product formed under these
conditions, additional as yet unidentified species were also
detected. Complex [3d]+ proved to be unstable and transformed
to a number of number products, the dominant one in all cases
fashion to [3a]BF4, but using [Ru(κ1-O2CPh)(κ2-O2CPh)-
(CCHC{OH}Ph2)(PPh3)2], 2aBz, as the ruthenium-based
precursor. In addition, a structure determination of [3b]BF4 was
obtained from a twinned crystal, and in this case the asymmetric
unit contained two crystallographically independent ruthenium
cations, (see Supporting Information).
A comparison of the structural metrics of the complexes with
general structure [3]+ (Table S2, Supporting Information)
demonstrate that the structures of these compounds are distorted
octahedra with the greatest deviation from an idealized geometry
being imposed by the restricted bite-angle of the κ2-acetate
ligand. As suggested by the NMR spectra, the complexes also
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a
only a single set of resonances of the coordinated acetate ligands,
indicating that these ligands were undergoing rapid κ1/κ2
exchange on the NMR time scale; however the presence of acetate
ligands with both binding modes was confirmed by IR
spectroscopy [1366 cm−1 (κ1-OCOsym), 1435 cm−1 (κ2-OCOsym),
1537 cm−1 (κ2-OCOasym), 1624 cm−1 (κ1-OCOasym), Δν(uni)
258 cm−1, Δν(chelate) 78 cm−1].18,19 The IR spectrum also
exhibited an intense band at 1911 cm−1, again characteristic of the
presence of an allenylidene ligand.23 The corresponding reaction
between [3aBz]BF4 with NaOtBu or [NMe4]OAc both afforded
[Ru(κ1-O2CPh)(κ2-O2CPh)(CCCPh2)(PPh3)2], 5Bz,
which could be identified on the basis of 31P{1H} and 13C{1H}
NMR spectroscopy. However, in the latter case, evidence for
exchange of benzoate and OAc ligands was observed as were
additional side products (see Supporting Information).
Scheme 4
Consistent with these data, the molecular structure of 5, as
determined by single crystal X-ray diffraction, demonstrates that
the ruthenium is coordinated to two mutually trans-phosphine
ligands, κ2- and κ1-bound acetate groups and a diphenylalleny-
lidene ligand (Figure 2). The allenylidene ligand is orientated so
a
(i) + [CPh3]BF4, − Ph3COH, thawing CD2Cl2, warm to room
temperature, (ii) CD2Cl2 room temperature.
appeared to be [PEtPh3]+. Given the apparent instability of
[3d]+, its chemistry was not pursued further.
Reactivity of Cationic Carbene Complexes. Having
developed a straightforward route to the cationic carbene
complexes [3a−3c]+, the next stage of the sequential elimination
of water was to perform a deprotonation. A number of different
bases were screened in each case, and the one affording the most
selective reactions are detailed below. The outcome of the reac-
tion of the cations with a base depended on the nature of the
substituents on the vinyl group. Reaction of [3a]BF4 with
NaOtBu in CH2Cl2 solution resulted in an instantaneous color
change from green to yellow. The solvent was removed and the
residue extracted with diethyl ether; concentration followed by
cooling to −20 °C resulted in the formation of a red solid.
Analysis of this solid (q.v.) indicated that the allenylidene-
containing complex [Ru(κ1-OAc)(κ2-OAc)(CCCPh2)-
(PPh3)2], 5, was the major component of this material (Scheme
5), although small amounts of the 1,2 diphenylvinyl complex
[Ru(κ2-OAc)(CHCPh2)(CO)(PPh3)2], 6, were also present.
Further crystallization from Et2O afforded analytically pure 5,
albeit in a reduced yield. Complex 6 was identified on the basis of
an X-ray diffraction experiment (see Supporting Information)
and has presumably arisen from the formal hydrolysis of the
allenylidene ligand and concomitant loss of AcOH.
Figure 2. Molecular structure of complex 5. Thermal ellipsoids (where
shown) are at the 50% probability level. Hydrogen atoms and an Et2O of
crystallization have been omitted for clarity.
The identification of 5 was secured through a combination of
NMR and IR spectroscopy as well as single crystal X-ray diffrac-
tion. The 13C{1H} NMR spectrum of 5 recorded in CD2Cl2
exhibited characteristic resonances for the three carbons of the
that the phenyl substituents are lying essentially parallel to the
P−Ru−P axis, whereas in the corresponding vinylidene com-
plexes the substituents lie perpendicular to this orientation. This
preference is as expected and demonstrates that both vinylidene
and allenylidene ligands have adopted an orientation so as to
2
allenylidene ligands at δ 305.0 (t, JPC = 17.3 Hz, RuC),
δ 232.8 (t, 3JPC = 5.50 Hz, RuCC), and δ 147.3 (s, RuC
CC).23 Both the 1H and 13C{1H} NMR spectra of 5 exhibited
a
Scheme 5
a
(i) + NaOtBu, − NaBF4, − HOtBu, CH2Cl2, 15 min.
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Table 1. Comparison of Structure and Spectroscopic Metrics from Complexes trans-[Ru(κ1-OAc)(κ2-OAc)(L)(PPh3)2]
L
Ru−P(1)/Å
Ru−P(2)/Å
Ru−O(2)/Å
O(1)−Ru-O(2)
Δν(chelate)/cm−1
NO+
CO
2.4336(8)
2.4060(4)
2.3592(6)
2.3853(7)
2.3844(3)
2.3840(14)
2.4466(8)
2.3873(4)
2.3479(6)
2.3910(7)
2.3787(3)
2.3642(14)
2.0744(19)
2.1897(11)
2.2465(16)
2.2863(18)
2.2914(10)
2.3575(4)
61.55(8)
60.42(2)
59.80(6)
59.08(6)
60.12(7)
56.40(15)
n.d.
54
67
75
78
94
CNtBu
CCHPh
CCCPh2, 5
CC3H6O
maximize π-back-donation from the d orbital, which is shared
with the π-donor acetate ligands.18 The bond lengths within the
ruthenium allenylidene unit (Ru(1)−C5 1.8468(13) Å, C(5)−
C(6) 1.2635(19) Å, C(6)−C(7) 1.3569(19)) are similar to the
related complexes [RuCl2(L)(CCCPh2)(PPh3)] (L =
EtOH, 1.836(4) Å; MeOH 1.833(6) Å, H2O 1.848(9) Å, DMAP,
1.902(4) Å),17 but the metal carbon bond is longer than in
either [RuCl2(CCCPh2)(PCy3)2] (1.794(11) Å) and
[RuCl2(CCCPh2)(PCy3)(IMes)] (1.7932(13) Å),
which may represent the greater basicity of the metal in the
latter examples.17
We have recently proposed that the structural and spectro-
scopic metrics within complexes of the general form trans-
[Ru(κ1-OAc)(κ2-OAc)(L)(PPh3)2] (L = CO, NO+, CNtBu, 
CCHR, CCnH(n+2)O) are diagnostic of the relative σ-donor,
π-acceptor characteristics of the ligands L.18 A comparison of the
data for complex 5 allowed for the effects of the allenylidene
ligand on the electron density at ruthenium to be evaluated. By
comparison with the key parameters shown in Table 1, it is clear
that the electronic effects of the allenylidene ligand are directly
comparable with those for the vinylidene example.
[Ru(κ1-OAc)(κ2-OAc)(CC{H}-CR1CH2)(PPh3)2] (7a
R1 = Me, 7b R1 = Ph). Although we have not been able to obtain
crystals of either complex suitable for study by X-ray diffraction,
the identity of the complexes was determined by NMR spec-
troscopy. In the case of 7a, the 13C{1H} NMR spectrum
2
exhibited resonances at δ 360.4 (t, JPC = 17.0 Hz, Cα), 117.4
(s, Cβ), 137.4 (s, Cγ), and 104.6 (s, Cδ) for the four atoms of the
vinylvinylidene ligand. The 1H NMR spectrum of 7a exhibited a
3
triplet resonance at δ 5.21 (t, JPH = 3.8 Hz) for the proton
attached to the β-carbon of the vinylidene ligand, whereas singlet
resonances were observed at δ 3.75 and 3.48 for the two protons
of the terminal CH2 group. An HSQC experiment demonstrated
that these protons were both connected to the carbon atom
which exhibited a resonance at δ 104.6. Furthermore, a HMBC
experiment demonstrated that the resonances at δ 3.75, the
proton on the β-carbon of the vinylidene ligand, and the methyl
group all showed long-range correlations with the resonance at
δ 137.4, consistent with the proposed assignment.
The reaction between [3c]BF4 and [NMe4]OAc appeared to
1
undertake a similar course, and the H NMR spectrum of the
product, 7b, exhibited a similar series of resonances to 7a. Unfor-
tunately, 7b provided to be unstable in solution, which prohi-
bited the acquisition of a 13C{1H} NMR spectrum, or obtaining a
combustion analysis. However, a mass spectrum obtained using
the LIFDI method did possess a peak at the correct m/z for the
proposed molecular ion. The deprotonation step was shown to
be reversible, as the addition of one equivalent of HBF4·OEt2 to
a sample of 7b resulted in the reformation of [3c]+ as shown by
1H and 31P{1H} NMR spectroscopy.
The reaction of the two methyl-substituted cations [3b]BF4
and [3c]BF4 with a base did not lead to the formation of the
corresponding allenylidene derivatives (Scheme 6). In these
a
Scheme 6
Theoretical Studies and Mechanistic Discussion. The
highly selective deprotonation of the cationic carbene complexes
[3b]+ and [3c]+ to give vinylvinylidene complexes contrasts with
the behavior of water elimination from many half-sandwich
complexes containing hydroxyvinylidene ligands.14a For exam-
ple, allenylidene and vinylidene complexes supported by the
[Ru(η5-C9H7)(PPh3)2]+ group are in equilibrium, and theoreti-
cal studies have shown that they may interconvert via a hydrogen
migration pathway.14a In order to gain insight into apparent lack
of isomerization exhibited by the vinylvinylidene complex 7a to
a
(i) + [NMe4]OAc, − [NMe4]BF4, − HOAc, CH2Cl2, 10 min.
cases, reaction with [NMe4]OAc in CH2Cl2 solution led
to selective deprotonation at the methyl groups of the
vinyl ligand and formation of vinylvinylidene complexes
Figure 3. Potential isomers of 7a examined by DFT.
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a
Scheme 7
a
(i) − H+; (ii) + H+.
v
Figure 4. Potential energy surface for the interconversion between complexes 7av and 7aa via TS7a
-
7a . Energies relative to 7a are given in kJ mol−1 for
v
a
ΔG298 at the bp86/SVP level (top), ΔE at the pbe0/def2-TZVPP level (middle), and ΔG298 at the pbe0/def2-TZVPP level (bottom).
an allenylidene isomer, a theoretical study was undertaken to
determine the relative energy of the vinylvinylidene 7av,
allenylidene 7aa, and metalloenol ester 7am isomers of the com-
plex (Figure 3). Calculations were performed with the Turbomole
program; initial geometry optimizations and frequency calcu-
lations were performed at the BP86/SV(P) level and subsequent
single point energies at pbe0/def2-TZVPP.24
opposite is true at the pbe0/def2-TZVPP level. Indeed, at this
higher level, the isomers of 7am are almost identical to 7av
and may interconvert via a low energy transition state (see
Supporting Information). However, the experimental spectro-
scopic data (most notably the resonance at δ 360.4 in the
13C{1H} NMR spectra of 7a) indicate that the vinylidene form is
the dominant species in solution.
For complex 7av, a total of eight isomers were considered on
the basis of the relative orientation of the κ1-acetate ligand and
the substituent on the vinylvinylidene group (see Supporting
Information). The structure 7av shown in Figure 3 was the lowest
energy conformation and was the global minimum for all struc-
tures investigated at all levels of theory employed. Two isomers
were considered for complex 7aa and four for 7am. It should be
noted that the relative energies of these complexes varied
depending on the computational method employed. At the
BP86/SV(P) level, the calculations indicate that the isomers of
7aa are consistently lower in energy than 7am, whereas the
The potential to interconvert 7av and 7aa via a 1,3-hydrogen
migration pathway in a similar manner to the [Ru(η5-C9H7)-
(PPh3)2]+ system was then investigated.14a In this case, previous
calculations performed on the simplified system [Ru(η5-C5H5)-
(PH3)2]+ indicated that the vinylvinylidene [9av]+ (Scheme 7)
was ca. 9 kJ mol−1 lower in energy than the corresponding allenyl-
idene [9aa]+, and the free energy of the transition state for the
interconversion was 288 kJ mol−1 higher in energy than [9av]+.
In the case of the acetate-substituted complexes, transition state
v
a
v
a
TS7a -7a connects 7a and 7a (as shown by a DRC analysis) with
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a relative free energy at 298 K of +264 kJ mol−1 at the pbe0/
def2-TZVPP level (Figure 4). In order to make an appro-
priate comparison with the literature data, calculations on
[Ru(η5-C5H5)(PH3)2]+ and [Ru(η5-C5H5)(PPh3)2]+-based vi-
nylvinylidene and allenylidene systems were performed using the
computational method used in our studies. In these cases,
transition states for hydrogen migration were found at the pbe0/
def2-TZVPP level with ΔG298 +261 kJ mol−1 and +256 kJ mol−1,
respectively, relative to the vinylvinylidene isomer.
As noted by Gimeno, the magnitude of this barrier is some-
what high for a spontaneous process at 298 K.14a This is further
reinforced by the fact that rapid equilibrium between vinyl-
vinylidene and allenylidene complexes occurs for the [Ru(η5-C9H7)-
(PPh3)2]+ system but not in the case of [Ru(κ1-OAc)(κ2-OAc)-
(PPh3)2], despite the barriers being similar in both cases. With
this in mind, alternative explanations of the difference in behavior
between the two sets of complexes were investigated.
It has been demonstrated that the acidity of vinylidene
β-protons occurs over a wide range. For example, the pKa of the
vinylidene proton in [Fe(η5-C5H5)(CCHMe)(dppe)]+ was
found to be 7.74 0.05 in 2:1 THF-H2O,25 whereas [Ru(η5-
C5H5)(CCHBut)(PMe3)2]+ is much less acidic (pKa 20.2
0.2 in CH3CN).26 In addition, pyridine has been shown to
deprotonate [Ru(η5-C5H5)(CCHPh)(PPh3)2]+,27 whereas
weak bases such as NaHCO3 readily convert [Ru(η5-C5H5)(
CCHSMe)(PMe3)2]+ to [Ru(η5-C5H5)(-CCSMe)-
(PMe3)2].28 With this in mind, an alternative mechanism for
the interconversion of allenylidene and vinylvinylidene com-
plexes was envisaged in which deprotonation of either species
would afford a common alkynyl intermediate: subsequent repro-
tonation could then afford either compound (Scheme 7). Further
support for such a proposal comes from the observation that
treatment of equilibrium mixtures of cationic half sandwich
vinylvinylidene and allenylidene complexes with a base results in
the formation of alkynyl complexes. This process is fully
reversible, regenerating the equilibrium mixture on addition of
acid.14a
In order to determine the feasibility of this process for the two
different systems, the pKa values for the vinylvinylidene and
allenylidene complexes were calculated29 with the alkynyl inter-
mediate being the conjugate base in each case. The resulting data
indicated a marked difference between the cationic half-sandwich
and neutral carboxylate-substituted species. The neutral
compounds 7av and 7aa are predicted to have a far higher pKa
in MeOH (22), and therefore deprotonation/reprotonation via
alkynyl complex [8a]− is predicted to be unfavorable. This is
consistent with the fact that the related compound [RuCl2(
CC{H}-CMeCH2)(PCy3)] does not appear to be
deprotonated in the presence of bases such as NEt3 and
OtBu.14n In contrast, cationic complexes [9]+ are all predicted to
be far more acidic (pKa 5 or 3). Although this analysis does not
give any information about the rate of proton transfer, it
does indicate that the alkynyl intermediates 10 should be
readily thermodynamically accessible in the case of the cationic
complexes. Therefore, this proposed mechanism does provide
effective discrimination between the two systems under
investigation and should be considered as a potential alternative
pathway to the [1,3]-hydrogen migration pathway.
with the initial formation of a cationic intermediate through
formal hydroxide extraction followed by deprotonation, which
may be viewed as being directly analogous to the classical
E1-elimination of water from alcohols to form alkenes. Central to
these observations is the inherent stability of the cationic carbene
complexes. Although the related species [RuCl2(OC{Me}OCC-
{H}CPh2)(PPh3)2] has been prepared from the reaction of
the carbyne complex [RuCl3(CCHCPh2)(PPh3)2] with
acetic acid,15b in the current case the acetate ligand plays a key
role by ensuring that there is no formal coordinative unsaturation
present at any stage during the formation of [3]+. This is a further
example of the chemical noninnocence of carboxylate ligands in
the chemistry of vinylidene and related ligands,10b which com-
plements their role played in C−H functionalization reactions.30
The experimental and theoretical data indicate that the
outcome of the deprotonation of the cationic species, [3]+, is
kinetically controlled and this factor controls the regiochemical
outcome of the dehydration process. The fact that no
rearrangement to the allenylidene isomer is observed either in
the case of 7a or in the related compounds [RuCl2(CCH-
C{Me}CH2)(PCy3)]14n may be explained on the basis of
either the higher energy of the transition state for [1,3]-hydrogen
migration or the high pKa of the vinylvinylidene and allenylidene
complexes.
In summary, we have shown that a Lewis acid may abstract the
OH group from hydroxyvinylidene complexes and that
deprotonation of the subsequently formed cations is a kinetically
controlled process allowing access to allenylidene and vinyl-
vinylidene ligands.
EXPERIMENTAL SECTION
■
All experimental procedures were performed under an atmosphere of
dinitrogen using standard Schlenk line and glove box techniques.
CH2Cl2 and pentane were purified with the aid of an Innovative
Technologies anhydrous solvent engineering system. The Et2O was
distilled over sodium (under argon) before use. The CD2Cl2 used for
NMR experiments was dried over CaH2 and degassed with three
freeze−pump−thaw cycles. The solvent was then vacuum transferred
into NMR tubes fitted with PTFE Young’s taps. NMR spectra were
1
acquired on either a Jeol ECS400 (Operating frequencies; H 399.78
MHz, 13C 100.53 MHz, 19F 376.17 MHz, 11B 128.27 MHz) or a
Bruker AVANCE 500 (Operating Frequencies 1H 500.23 MHz,
31P 202.50 MHz, 13C 125.77 MHz). 31P and 13C spectra were recorded
with proton decoupling. Assignments were completed with the aid of
COSY, DEPT, NOESY, HSQC, HMBC, and 1H−31P HMQC
experiments. Mass spectrometry measurements were performed on a
either a Bruker micrOTOF MS (ESI) or a Waters GCT Premier
Acceleration TOF MS (LIFDI) instrument. IR spectra were acquired on
either a Mattson Research Series or Thermo-Nicolet Avatar 370 FTIR
spectrometer using CsCl solution cells. Elemental analyses were
performed using an Exeter Analytical Inc. CE-440 analyzer. Analysis
of all of the cationic species [3]BF4 is reported. However, all were found
to have a much lower percentage of carbon than expected. These results
were found to be reproducible between batches. Single crystal X-ray
diffraction was carried out on an Oxford Diffraction SuperNova
diffractometer with a molybdenum source. The crystals were kept at
110.0(1) K during data collection. Using Olex2,31 the structures were
solved with either the Superflip32 structure solution program using
Charge Flipping or the XS33 structure solution program using direct
methods or the Patterson method. They were refined with the ShelXL33
refinement package using least squares minimization. After data
collection of [3b]BF4·CH3COCH3, the crystal was found to be non-
merohedrally twinned, which was modeled using CrysAlisPro to obtain
an HKLF 5 formatted data set. This meant that the data coverage for the
minor component and hence overall was low. The crystal of [4]BF4 was
weakly diffracting with complete data only obtained for theta less than
CONCLUSIONS
■
The ready availability of the hydroxyvinylidene complexes 2 has
enabled key intermediates in the Selegue mechanism to be
observed. A two-step dehydration process has been developed
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22.5°. The BF4 anion was modeled as disordered over two positions with
all B−F and F−B−F bond lengths and angles constrained to be
approximately equal. A disordered mixture of DCM and pentane was
observed in the asymmetric unit; however this could not be modeled
satisfactorily. The contribution of the disordered solvent to the hkl file
was removed using the olex2 solvent mask function, which accounted for
a volume of 334 cubic angstroms and 12 electrons.
(s, COOCH3), 186.4 (s, COOCH3), 284.9 (t, 2JPC = 9.2 Hz, RuC).
11B{1H} δB −2.1 (s, BF4). 19F δF −153.3 (s, 10BF4), −153.4 (s, 11BF4). IR
(CH2Cl2): 1096 cm−1 (B−F), 1435 cm−1 (κ2−OCOsym), 1527 cm−1
ν(CC), 1631 cm−1 ν(CO), 1590 cm−1 (κ2−OCOasym), Δν(chelate)
155 cm−1. MS (ESI): m/z 811.1684 (calculated for C45H43102RuP2O4
[M]+ = 811.1687, Δ = 0.3 mDa), [M]+, m/z 549.0772 (calculated for
C27H28102RuPO4 [M]+ −PPh3 = 549.0770, Δ = 0.2 mDa). Anal. for
C45H43 RuP2O4BF4 calcd: C, 60.21; H, 4.83. Found: C, 59.53; H, 5.08.
Full details of the theoretical methods used and the different isomers
of complexes 7av, 7aa, and 7am are presented in the Supporting
Information.
Synthesis of [Ru(κ2-OAc)(OC{Me}OCC{H}CPhMe)(PPh3)2]-
BF4, [3c]BF4. [Ru(κ2-OAc)(OC{Me}OCC{H}CPhMe)(PPh3)2]-
[BF4] (170 mg, 0.177 mmol, 53% yield) was prepared in a similar
manner to [3a]BF4 and was obtained as a dark green powder from cis-
[Ru(κ2-OAc)2(PPh3)2] (250 mg, 0.336 mmol), 2-phenyl-3-butyn-2-ol
(49 mg, 0.336 mmol), and trityl carbenium tetrafluoroborate (111 mg,
0.336 mmol) in CH2Cl2 (20 mL).
cis-[Ru(κ2-OAc)2(PPh3)2]19,34 and cis-[Ru(κ2-O2CPh)2(PPh3)2]35
were synthesized from [RuCl2(PPh3)3],36 as described previously.
HCCC(OH)Ph2, HCCC(OH)MePh, HCCCH2OH, and
[Ph3C]BF4 were obtained from Aldrich Chemicals and HCCC(OH)-
Me2 from Acros Organics; all were used as supplied. [NMe4]OAc and
NaOtBu were obtained from Aldrich Chemicals and dried by heating at
50 °C under reduced pressure for 16 h prior to use.
1
NMR spectra CD2Cl2: H δH 0.86 (s, 3H, COOCH3), 1.82 (s,
3H,CPhCH3), 1.92 (s, 3H, COOCH3), 7.46 (m, 12H, PPh3-H2 or 3),
7.52 (t, 3JHH = 7.6 Hz, 12H, PPh3‑H2 or 3), 7.57 (d, 3JHH = 7.0 Hz, 2H,
Ph-H2 or 3), 7.62 (m, 8H, PPh3-H4 and Ph-H2 or 3), 7.67 (t, 3JHH = 7.0 Hz,
1H, Ph-H4), 8.10 (s, 1H, RuC−CHCPh2). 31P{1H} δP 32.3
Synthesis of [Ru(κ2-OAc)(OC{Me}OCC{H}CPh2)(PPh3)2]BF4,
[3a]BF4. cis-[Ru(κ2-OAc)2(PPh3)2] (250 mg, 0.34 mmol) and 1,1-
diphenylprop-2-yn-1-ol (70 mg, 0.34 mmol) were dissolved in CH2Cl2
(20 mL) and stirred at room temperature for 90 min. Trityl carbenium
tetrafluoroborate (111 mg, 0.34 mmol) was added, and the resulting
solution stirred for 15 min. The CH2Cl2 was then reduced to ca. 3 mL
and the product precipitated by the addition of pentane. After filtration,
the solid product was then redissolved in CH2Cl2 (5 mL), and diethyl
ether (7 mL) was added as a layer. After 2 days, the mother liquor was
removed, and [Ru(κ2-OAc)(OC{Me}OCC{H}CPh2)(PPh3)2]-
[BF4] (245 mg, 0.24 mmol, 71% yield) was obtained as green crystals.
The diphenyl moiety has been assigned as PhA and PhB, though the
relative orientation of the rings is unknown. The peak for the C4 carbon
of PhB could not be located in the 13C NMR spectrum; it is assumed that
the peak is obscured under a resonance from the triphenyl phosphine.
(s, PPh3). 13C{1H} δC 19.6 (s, COOCH3), 22.9 (s, COOCH3), 23.2
(s, CPhCH3), 128.6 (s, RuC-CHCPh2), 129.4 (t, JPC+3JPC
=
1
46.5 Hz, PPh3-C1), 130.6 (t, ΣJ = 10.4 Hz, PPh3-C2 or 3), 130.9 (s, Ph),
131.5 (s, Ph), 132.4 (s, Ph), 133.1 (s, PPh3-C4), 135.4 (t, ΣJ = 12.1 Hz,
PPh3-C2 or 3), 144.0 (s, Ph-C1), 148.7 (s, RuCCHCPhMe), 184.7
(s, COOCH3), 187.7 (s, COOCH3), 284.3 (t, 2JPC = 8.6 Hz, RuC).
11B{1H} δB −2.2 (s, BF4). 19F δF −153.3 (s, 10BF4), −153.4 (s, 11BF4). IR
(CH2Cl2): 1098 cm−1 (B−F), 1433 cm−1 (κ2-OCOsym), 1554 cm−1
ν(CC), 1579 cm−1 (κ2-OCOasym), 1631 cm−1 ν(CO), Δν(chelate)
146 cm−1. MS (ESI): m/z 873.1830 (calculated for C50H45102RuP2O4
[M]+ = 873.1845, Δ = 1.5 mDa), m/z 813.1624 (calculated for
C48H41102RuP2O2 [M − H]+ −AcO = 813.1632, Δ = 1.0 mDa), m/z
611.0912 (calculated for C32H30102RuPO4 [M]+ −PPh3 = 611.0929, Δ =
1.7 mDa), m/z 551.0695 (calculated for C30H26102RuPO2 [M − H]+
−PPh3 −AcO = 551.0717, Δ = 2.2 mDa). Anal. for C50H45RuP2O4BF4
calcd: C, 62.58; H, 4.73; Found: C, 60.27; H, 4.52.
1
NMR spectra CD2Cl2: H δH 0.79 (s, 3H, COOCH3), 1.31 (s, 3H,
COOCH3), 6.58 (m, 2H, PhA-H2), 7.26 (m, 2H, PhB-H2), 7.42 (m, 14H,
PhB-H3, PPh3-H2 or 3), 7.45 (m, 1H, PhA-H4), 7.49 (m, 12H, PPh3-
H2 or 3), 7.60 (m, 6H, PPh3-H4), 7.65 (m, 1H, PhB-H4), 8.37 (s, 1H,
RuC−CHCPh2). 31P{1H} δP 32.4 (s, PPh3). 13C{1H} δC 17.7
(s, COOCH3), 21.9 (s, COOCH3), 127.7 (s, RuC-CHCPh2),
128.3 (s, PhA-C3), 128.4 (t, 1JPC+3JPC = 45.5 Hz, PPh3-C1), 128.8 (s, PhA-
C2), 129.6 (t, ΣJ = 11.5 Hz, PPh3-C2 or 3), 129.7 (s, PhB-C3), 129.9 (s,
PhA-C4), 130.1 (s, PhB-C2), 131.9 (s, PPh3-C4), 134.4 (t, ΣJ = 10.1 Hz,
PPh3-C2 or 3), 140.4 (s, PhA/B-C1), 141.2 (s, PhA/B-C1), 146.9 (s, Ru
CCHCPh2), 183.2 (s, COOCH3), 186.6 (s, COOCH3), 279.8
(t, 2JPC = 9.3 Hz, RuC). 11B{1H} δB −2.1 (s, BF4). 19F δF −153.3 (s,
10BF4), −153.4 (s, 11BF4). IR (CH2Cl2): 1095 cm−1 (B−F), 1434 cm−1
(κ2−OCOsym), 1530 cm−1 (κ2−OCOasym), 1542 cm−1 ν(CC),
1630 cm−1 ν(CO), Δν(chelate) 96 cm−1. MS (ESI): m/z 935.1998
(calculated for C55H47102RuP2O4 [M]+ = 935.2002, Δ = 0.4 mDa),
m/z 673.1079 (calculated for C37H32102RuPO4 [M]+ −PPh3 = 673.1086,
Δ = 0.7 mDa), m/z 613.0861 (calculated for C35H28102RuPO2
[M − H]+ −PPh3 −AcO = 613.0874, Δ = 1.5 mDa; MS/MS showed
that the lower mass species are observed due to fragmentation in the
spectrometer). Anal. for C55H47BF4O4P2Ru, calcd: C, 64.65; H, 4.65.
Found: C, 64.00; H, 4.67.
Synthesis of [Ru(κ2-O2CPh)(OC{Ph}OCC{H}CPh2)(PPh3)2]BF4
[3aBz]BF4. [Ru(κ2-O2CPh)(OC{Ph}OCC{H}CPh2)(PPh3)2][BF4]
(275 mg, 0.27 mmol, 80% yield) was prepared in a similar manner to
[3a]BF4 and was obtained as dark green crystals from cis-[Ru(κ2-
O2CPh)2(PPh3)2] (250 mg, 0.29 mmol),1,1-diphenylprop-2-yn-1-ol
(60 mg, 0.29 mmol), and trityl carbenium tetrafluoroborate (95 mg, 0.29
mmol) in CH2Cl2 (20 mL).
The diphenyl moiety has been assigned as PhA and PhB, though the
relative orientation of the rings is unknown. Some resonances in the 13C
NMR spectrum could not be unequivocally assigned.
NMR spectra CD2Cl2: 1H δH 6.52 (br s, 2H, Ph), 6.74 (m, 2H, PhA-H2),
7.11 (m, 2H, Ph), 7.22 (m, 6H, PhB-H2, COOPh-H2 and Ph), 7.32 (m,
13H, PPh3-H2 or 3, Ph), 7.40 (m, 8H, PPh3-H4 and PhA-H3), 7.45 (m,
15H, PPh3-H2 or 3, Ph), 7.57 (tt, 1H, COOPh-H4), 7.64 (tt, 1H, Ph-H4),
7.69 (tt, 1H, Ph), 8.56 (s, 1H, RuC−CHCPh2). 31P{1H} δP 31.5
(s, PPh3). 13C{1H} δC 123.8 (s, COOPh-C1), 128.9 (s, Ph), 129.5
(t, 1JPC+3JPC = 46.0 Hz, PPh3-C1), 129.5 (s, RuC-CHCPh2), 129.7
(s, COOPh−C2), 130.1 (s, PhA-C3 or 4), 130.3 (s, PhA-C2), 130.4 (s, Ph),
130.5 (t, ΣJ = 9.7 Hz, PPh3-C2 or 3), 130.8 (s, Ph), 130.9 (s, Ph), 131.3
(s, Ph), 132.2 (s, COOPh-C1), 132.2 (s, Ph), 132.7 (s, PPh3-C4), 133.0
(s, Ph), 133.7 (s, Ph), 135.5 (t, ΣJ = 11.6 Hz, PPh3-C2 or 3), 138.1
(s, COOPh-C4), 142.5 (s, Ph-C1), 143.1 (Ph-C1), 147.7 (s, Ru
Synthesis of [Ru(κ2-OAc)(OC{Me}OCC{H}CMe2)(PPh3)2]BF4,
[3b]BF4. [Ru(κ2-OAc)(OC{Me}OCC{H}CMe2)(PPh3)2][BF4]
(174 mg, 0.20 mmol, 58% yield) was prepared in a similar manner to
[3a]BF4 and was obtained as purple crystals from cis-[Ru(κ2-OAc)2-
(PPh3)2] (250 mg, 0.34 mmol), 2-methyl-3-butyn-2-ol (32.5 μL,
0.34 mmol), and trityl carbenium tetrafluoroborate (111 mg, 0.34 mmol) in
CH2Cl2 (20 mL).
CCHCPhMe), 179.7 (s, COOPh), 182.0 (s, COOPh), 281.1 (t, 2JPC
=
9.6 Hz, RuC). 11B δB −2.1 (s, BF4). 19F δF −153.4 (s, 10BF4), −153.5
(s, 11BF4). IR (CH2Cl2): 1095 cm−1 (B−F), 1434 cm−1 (κ2−OCOsym),
1541 cm−1 ν(CC), 1575 cm−1 (κ2−OCOasym), 1602 cm−1 ν(CO),
Δν(chelate) 141 cm−1. MS (ESI): m/z 1059.2280 (calculated for
C65H51102RuP2O4 [M]+ = 1059.2319, Δ = 3.9 mDa), m/z 797.1371
(calculated for C47H36102RuPO4 [M]+ −PPh3 = 797.1402, Δ =
3.1 mDa), m/z 675.1028 (calculated for C40H30102RuPO2 [M − H]+
−PPh3 −AcO = 675.1032, Δ = 0.4 mDa). Anal. for C65H51 RuP2O4BF4
calcd: C, 68.12; H, 4.49. Found: C, 66.70; H, 4.44.
1
NMR spectra CD2Cl2: H δH 0.77 (s, 3H, COOCH3), 1.40 (s, 3H,
COOCH3), 1.74 (s, 3H, CMe2), 1.80 (s, 3H, CMe2), 7.37 (m, 12H,
PPh3-H2 or 3), 7.45 (m, 12H, PPh3 -H2 or 3), 7.54 (m, 6H, PPh3-H4), 7.69
(s, 1H, RuC−CHCMe2). 31P{1H} δP 32.6 (s, PPh3); 13C{1H} δC
18.5 (s, COOCH3), 22.1 (s, COOCH3), 24.1 (s, CMe2), 30.4 (s, CMe2),
128.3 (t, 1JPC+3JPC = 45.7 Hz, PPh3-C1), 129.5 (t, ΣJ = 10.2 Hz, PPh3-
C2 or 3), 130.9 (s, RuC-CHCMe2), 131.9 (s, PPh3-C4), 134.3 (t,
ΣJ = 11.7 Hz, PPh3-C2 or 3), 152.7 (s, RuCCHCMe2), 183.5
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1
Synthesis of [Ru(κ2-OAc)(κ1-OAc)(PPh3)2(CCCPh2)], 5.
NMR spectra CD2Cl2: H δH 0.84 (s, 6H, COOCH3), 4.70 (s, 1H,
RuCC(H)C(Ph)CH2), 4.87 (s, 1H, RuCC(H)C(Ph)CH2),
5.17 (t, 3.6 Hz, 1H, RuCC(H), 6.84−7.57 (39H, Ph). 31P{1H}
NMR δP 34.6 (s, PPh3). IR (CH2Cl2): 1366 cm−1 (κ1-OCOsym),
1436 cm−1 (P-Ph), 1465 cm−1 (κ2-OCOsym), 1534 cm−1 (κ2-OCOasym),
1617 cm−1 (κ1-OCOasym), 1932 cm−1 ν(CC), Δν(uni) 251 cm−1,
Δν(chelate) 69 cm−1. MS(ESI):m/z 873.1848 (calculated for C50H45102RuP2O4
[M + H]+ = 873.1845, Δ = 0.3 mDa), m/z 812.1744 (calculated for
C48H41102RuP2O2 [M − H]+ −AcO = 812.1555, Δ = 18.9 mDa). MS
(LIFDI): m/z 872.20 [M]+, m/z 812.06 [M − H]+ −Ac.
[Ru(κ2-OAc)(OC{Me}OCC{H}CPh2)(PPh3)2]BF4, [3a]BF4 (100 mg,
0.1 mmol), and sodium tert-butoxide (19 mg, 0.15 mmol) were
dissolved in CH2Cl2 and stirred at RT for 15 min. The CH2Cl2 was then
removed and the residue extracted with ether. The resulting solution was
then reduced slightly before being placed in the freezer overnight. This
either produced a red solid of approximately 83% purity by 31P NMR
(20 mg, 0.020 mmol, 22% yield) or analytically pure red needle like
crystals (5 mg, 0.005 mmol, 5% yield).
1
NMR spectra CD2Cl2: H δH 0.91 (s, 6H, COOCH3), 6.93 (at,
Reaction of [Ru(κ2-OAc)(κ1-OAc)(CCH-C(Ph)CH2)-
(PPh3)2], 7b, with HBF4. [Ru(κ2-OAc)(κ1-OAc)(CCH-C-
(Ph)CH2)(PPh3)2], 7b (20 mg, 0.023 mmol), was dissolved in
CD2Cl2 (0.5 mL) to give an orange solution. HBF4·Et2O (3 μL,
0.023 mmol) was added and an immediate color change to dark
green observed. The major product from this reaction was
7.8 Hz, 4H, Ph-H2), 7.15 (ad, 8.2 Hz, 4H, Ph-H3), 7.29 (at, 7.3 Hz, 12H,
PPh3-H2 or 3), 7.33 (ad, 7.0 Hz, 6H, PPh3-H4), 7.36 (m, 6H, Ph-H4),
7.52 (m, 12H, PPh3-H2 or 3). 31P{1H} δP 32.6 (s, PPh3). 13C{1H} δC 23.9
(s, COOCH3), 129.2 (s, Ph-C4), 129.4 (t, ΣJ = 9.6 Hz, PPh3-C2 or 3),
129.9 (s, Ph-C3), 130.0 (s, Ph-C2), 131.4 (s, PPh3-C4), 132.6
1
(t, JPC+3JPC = 41.4 Hz, PPh3-C1), 136.2 (t, ΣJ = 12.1 Hz, PPh3-
[Ru(κ2-OAc)(OC{Me}OCC{H}CPhMe)(PPh3)2]BF4, [3c]BF4, as
shown by comparison of the spectroscopic data with an authentic
sample.
C2 or 3), 147.3 (s, RuCCC), 181.7 (s, COOCH3), 232.8 (t, 3JPC
=
5.50 Hz, RuCC), 305.0 (t, 2JPC = 17.3 Hz, RuC). IR (CH2Cl2):
1366 cm−1 (κ1-OCOsym), 1435 cm−1 (P-Ph), 1459 cm−1 (κ2-OCOsym),
1537 cm−1 (κ2-OCOasym), 1624 cm−1 (κ1-OCOasym), 1911 cm−1 ν(C
CC), Δν(uni) 258 cm−1, Δν(chelate) 78 cm−1. MS (ESI), m/z 957.1781
(calculated for C55H46102RuP2O4Na [M + Na]+ = 957.1822, Δ = 4.1
mDa), m/z 935.1993 (calculated for C55H47102RuP2O4 [M + H]+ =
935.2002, Δ = 0.9 mDa). MS (LIFDI): m/z 934.13 [M]+, m/z 892.14
[M + H]+ −Ac. Anal. for C55H46RuP2O4 calcd: C, 70.73; H, 4.96. Found:
C, 70.33; H, 5.00.
ASSOCIATED CONTENT
* Supporting Information
■
S
Details of theoretical methods used, details of data collection and
structural refinement for X-ray diffraction experiments in
CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org. CCDC 961152 [3a]BF4·
(CH2Cl2)1.5, 961153 [3b]BF4·CH3COCH3, 961154 [3aBz]BF4·
CH2Cl2, 961155 [4]BF4, 961156 [5]·(Et2O)0.5, and 961157 [6]
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif
Spectroscopic Data for [Ru(κ2-OAc)(CHCPh2)(CO)(PPh3)2],
6. Complex 6 was observed as a minor impurity in samples of 5.
In contaminated samples, the following spectroscopic data were
assigned to 6.
NMR CD2Cl2 1H NMR δH 0.47 (s, COOCH3). 31P{1H} δP 38.1
(s, PPh3). MS (ESI) m/z 833.1649 (calculated for C51H41102RuP2O
[M − H]+ −AcO = 833.1684, Δ = 3.5 mDa).
Synthesis of [Ru(κ2-OAc)(κ1-OAc)(PPh3)2(CCH-C(Me)
CH2)], 7a. [Ru(κ2-OAc)(OC{Me}OCC{H}C(Me)2)(PPh3)2]BF4,
[3b]BF4, (100 mg, 0.111 mmol) and tetramethylammonium acetate
(17 mg, 0.125 mmol) were suspended in CH2Cl2 (10 mL). Two minutes
of sonication aided dissolution, and the subsequent reaction was
observed by a color change from dark purple to orange. After 10 min of
stirring at room temperature, the solvent was removed and the residue
extracted with diethyl ether. Removal of the solvent yielded an orange
powder (18 mg, 0.022 mmol, 20% yield).
AUTHOR INFORMATION
Corresponding Author
*E-mail: jason.lynam@york.ac.uk.
■
Notes
The authors declare no competing financial interest.
NMR CD2Cl2 1H δH 0.84 (s, 6H, COOCH3), 1.31 (s, 3H, RuC
C(H)C(CH3)CH2), 3.75 (s, 1H, RuCC(H)C(CH3)CH2), 3.48 (s,
1H, RuCC(H)C(CH3)CH2), 5.21 (t, 3.8 Hz, 1H, RuCCH),
7.40 (t, 7.2 Hz, 12H, PPh3−H2 or 3), 7.44−7.54 (m, 18H, PPh3−H2 or 3
and PPh3−H4). 31P{1H} δP 33.4 (s, PPh3). 13C{1H} δC 23.5 (s,
COOCH3), 23.7 (RuCC(H)C(CH3)CH2), 104.6 (s, RuC
C(H)C(Me)CH2), 117.4 (s, RuCCH), 129.5 (t, ΣJ = 10.1 Hz,
PPh3-C2 or 3), 131.0 (t, 1JPC+3JPC = 43.3 Hz, PPh3-C1), 131.6 (s, PPh3-C4),
136.4 (t, ΣJ = 10.8 Hz, PPh3-C2 or 3), 137.4 (s, RuCC(H)C(CH3)-
ACKNOWLEDGMENTS
■
We are grateful to the EPSRC and University of York for funding
(EPSRC DTA studentship to E.J.S.). This work was supported
in-part by the EPSRC - ‘ENERGY’ grant, ref. no. EP/K031589/1.
Insightful discussions with Professor Odile Eisenstein (Montpellier)
and Dr. John Slattery (York) are gratefully acknowledged. We thank
Miss Natalie Pridmore and Dr. Sam Hart for assistance with X-ray
diffraction experiments.
2
CH2), 181.0 (s, COOCH3), 360.4 (t, JPC = 17.0 Hz, RuC). IR
(CH2Cl2): 1367 cm−1 (κ1−OCOsym), 1434 cm−1 (P-Ph), 1466 cm−1
(κ2-OCOsym), 1552 cm−1 (κ2-OCOasym), 1617 cm−1 (κ1-OCOasym),
1628 cm−1 ν(CC), Δν(uni) 250 cm−1, Δν(chelate) 86 cm−1. MS (ESI):
m/z 811.1637 (calculated for C45H43102RuP2O4 [M + H]+ = 811.1687,
Δ = 5.0 mDa). MS (LIFDI): m/z 810.19 [M]+.
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dx.doi.org/10.1021/om4009247 | Organometallics 2013, 32, 7407−7417