Facile decarboxylation of propiolic acid on a ruthenium center and related chemistry

Article abstract of DOI:10.1021/om300157w

Spontaneous decarboxylation of RC≡CCO₂H (R = H, Ph) occurs in reactions with RuCl(PP)Cp (PP = (PPh₃)₂, dppe) to give [Ru(=C=CHR)(PP)Cp]⁺. Computational studies (DFT) of possible decarboxylation mechanisms suggest that the reaction that leads to extrusion of CO₂ and formation of [Ru(=C=CH₂)(dppe)Cp]⁺ most likely occurs by initial interaction of the anion HC≡CCO₂ ^- with RuCl(dppe)Cp by coordination of carboxylate to Ru, followed by formation of an η²-alkyne intermediate which rearranges to the η¹-ethynyl species with loss of CO₂. Protonation of the ethynyl group affords the parent vinylidene. In contrast, reactions of HC≡CCO₂R (R = Me, Et) with RuCl(PP)Cp and [NH ₄]PF₆ in MeOH have given [Ru{=C(OMe)CH₂(CO ₂R)}(PP)Cp]⁺, formed by attack of MeOH at C _α of the intermediate vinylidenes [Ru{=C=CH(CO ₂R)}(PP)Cp]⁺. Deprotonation of the carbenes affords Ru{C(OMe)=CH(CO₂R)}(PP)Cp as mixtures of cis and trans isomers. The vinylidenes, which are obtained directly from RuCl(PP)Cp and HC≡CCO ₂R in the presence of [NH₄]PF₆ in Bu ^tOH, can be deprotonated (Na/PrⁱOH) to the corresponding alkynyls. Attempted deprotonation of [Ru(=C=CH₂)(dppe)Cp]⁺ with LiBu gave the binuclear cyclobutenylidinium complex [{Ru(dppe)Cp} ₂(μ-C₄H₃)]⁺. The X-ray diffraction molecular structures of [{Ru(dppe)Cp}₂(μ-C ₄H₃)]PF₆ (11), [Ru{=C(OMe)CH ₂(CO₂Me)}(dppe)Cp]PF₆ (13), Ru{C(OMe)=CH(CO₂R)}(dppe)Cp (R = Me (15), Et (16)) and Ru(C≡CCO₂R)(dppe)Cp (R = Me (21), Et (22)) are described.

Full text of DOI:10.1021/om300157w

Article
pubs.acs.org/Organometallics
Facile Decarboxylation of Propiolic Acid on a Ruthenium Center and
Related Chemistry
John H. Bowie,† Michael I. Bruce,*,† Mark A. Buntine,†,‡ Alexander S. Gentleman,† David C. Graham,†
Paul J. Low,§ Gregory F. Metha,† Cassandra Mitchell,† Christian R. Parker,† Brian W. Skelton,∥,⊥
and Allan H. White⊥
†Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC), School of Chemistry & Physics, University of
Adelaide, Adelaide, South Australia 5005, Australia
‡Department of Chemistry, Curtin University, P.O. Box U1978, Perth, Western Australia 6845, Australia
§Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, England
∥CMCA, University of Western Australia, Crawley, Western Australia 6009, Australia
⊥Chemistry M313, University of Western Australia, Crawley, Western Australia 6009, Australia
S
* Supporting Information
ABSTRACT: Spontaneous decarboxylation of RCCCO2H (R = H, Ph) occurs in
reactions with RuCl(PP)Cp (PP = (PPh3)2, dppe) to give [Ru(CCHR)(PP)-
Cp]+. Computational studies (DFT) of possible decarboxylation mechanisms suggest
that the reaction that leads to extrusion of CO2 and formation of [Ru(C
CH2)(dppe)Cp]+ most likely occurs by initial interaction of the anion HCCCO2
−
with RuCl(dppe)Cp by coordination of carboxylate to Ru, followed by formation of an
η2-alkyne intermediate which rearranges to the η1-ethynyl species with loss of CO2. Protonation of the ethynyl group affords the
parent vinylidene. In contrast, reactions of HCCCO2R (R = Me, Et) with RuCl(PP)Cp and [NH4]PF6 in MeOH have given
[Ru{C(OMe)CH2(CO2R)}(PP)Cp]+, formed by attack of MeOH at Cα of the intermediate vinylidenes [Ru{C
CH(CO2R)}(PP)Cp]+. Deprotonation of the carbenes affords Ru{C(OMe)CH(CO2R)}(PP)Cp as mixtures of cis and trans
isomers. The vinylidenes, which are obtained directly from RuCl(PP)Cp and HCCCO2R in the presence of [NH4]PF6 in
ButOH, can be deprotonated (Na/PriOH) to the corresponding alkynyls. Attempted deprotonation of [Ru(C
CH2)(dppe)Cp]+ with LiBu gave the binuclear cyclobutenylidinium complex [{Ru(dppe)Cp}2(μ-C4H3)]+. The X-ray diffraction
molecular structures of [{Ru(dppe)Cp}2(μ-C4H3)]PF6 (11), [Ru{C(OMe)CH2(CO2Me)}(dppe)Cp]PF6 (13), Ru{C-
(OMe)CH(CO2R)}(dppe)Cp (R  Me (15), Et (16)) and Ru(CCCO2R)(dppe)Cp (R = Me (21), Et (22)) are
described.
Relatively few examples of decarboxylations at lower
temperatures are known. While decarboxylation of a variety
of organic substrates in the presence of transition-metal
compounds, particularly those of copper, is a well-established
transformation,9 such reactions generally require heating or
free-radical initiation. Under the mild conditions described
above, such reactions are rare and appear to be confined to
polyfluorinated systems. Thus, the reaction between RhCl-
(CO)(PPh3)2 and TlO2CC6F5 affords Rh(C6F5)(CO)(PPh3)2
directly,12 while similar reactions with PtCl2(dppx)2 (x = e, p,
b) in the presence of pyridine proceed at room temperature to
give PtCln(C6F5)2−n(dppx) (n = 0, 1).13 Optimum yields in the
second reaction are obtained in refluxing pyridine, however. A
similar preparation of AgCH(CF3)2 from (CF3)2CHCO2Ag in
pyridine is known,14 while the reactions between Hg(OAc)2
and ArCO2H (Ar = (MeO)nC6H5−n(OMe)n, n = 2 (2,6), 3
(2,3,4; 2,4,6)) in aqueous MeOH are reported to give HgAr2
via Hg(OAc)Ar.15 The proposed mechanism for the latter
INTRODUCTION
■
Fixation of CO2 by organic molecules to give carboxylates is a
useful synthetic method, since CO2 is a readily available starting
material that is nontoxic and is a C1 moiety.1 In the context of
alkyne chemistry, carboxylation is usually carried out with
metalated (Li, Mg) terminal alkynes reacting with CO2
directly.2 Also known is the Cu-catalyzed coupling of alkynes
with CO2, especially in the presence of alkyl bromides.3
Initially, this reaction was reported to require elevated
temperatures (100 °C) in polar solvents, although later studies
used more reactive Cu/diamine,4 Cu/NHC,5 or Cu/
phosphine6 or, in one case, ligand-free Ag7 systems.
The reverse reaction, decarboxylation of metal carboxylates,
has long been used as a route to organometallic compounds.
Originally described in 1901, the Pesci reaction uses thermal
decarboxylation of the metal carboxylate formed from a metal
salt and the carboxylic acid, often involving copper.8 Many
examples of its use both in the condensed phase9 and, more
recently, in the gas phase, have been reported.10 It is of use in
organic synthesis, potentially in metal-catalyzed syntheses.11
Received: February 26, 2012
Published: August 1, 2012
© 2012 American Chemical Society
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Article
reaction resembles that of electrophilic aromatic substitution.
Decarboxylation of TlO2CC6F5 to give C6F5H has also been
described.13,16
Scheme 1. Reaction of HCCCO2H with RuCl(dppe)Cp
The closest example to the present work is the reaction of
Hg(OAc)2 with phenylpropiolic acid to give Hg(CCPh)2,
which occurs between 0 °C and room temperature.17 Several
mechanisms have been invoked to explain the decarboxylation
reactions, most involving the formation of carbanions or free
radicals.9
Elegant studies by O’Hair and his co-workers have extended
the decarboxylation to the gas phase, studying particularly the
formation of a variety of organocuprate species by multistage
mass spectrometry experiments.18 The minima and transition
states relevant to fragmentation of ions [Cu(O2CR)2]− (R =
Me, Et, CF3) have been examined by DFT methods.19
Recently, we have been interested in examining the reactions
of alkynecarboxylic acids and their esters with ruthenium
complexes Ru(PP)Cp (PP = (PPh3)2, dppe). As previously
described, the esters afford vinylidene and derived vinyl
complexes;20,21 we take this opportunity here to record
relevant X-ray structural and spectroscopic data. The reactions
with propiolic acids were originally carried out as a possible
route, in the event unsuccessful, to 3-oxopropadienylidene
(C3O) derivatives, by analogy with the well-established route to
allenylidenes:22
Treatment of RuCl(PP)Cp′ with potassium propiolate in
methanol also resulted in spontaneous elimination of CO2
(most efficiently achieved by using refluxing MeOH) with
formation of the neutral alkynyls Ru(CCH)(PP)Cp*
((PP)Cp′ = (PPh3)2Cp (6), (dppe)Cp* (7)) in good to high
yields (Scheme 2). In the presence of [NH4]PF6, the vinylidene
Scheme 2. Formation of a Cyclobutenylidinium−Ruthenium
Complex
RuCl(PP)Cp′ + HC CCR2(OH)
→ [Ru{CCCHC(OH)R2}(PP)Cp′]+
→ [Ru(CCCR2)(PP)Cp′]+
RuCl(PP)Cp′ + HC CC(OH)O
→ [Ru{CCHC(OH)O}(PP)Cp′]+
→ [Ru(CCCO)(PP)Cp′]+
[Ru(CCH2)(PPh3)2Cp]PF6 (8) was obtained from the
former precursor. With PhCCCO2K, RuCl(PPh3)2Cp gave
Ru(CCPh)(PPh3)2Cp (9). Attempted formation of a
binuclear μ-C2 complex by using C2(CO2K)2 was thwarted,
only RuH(PP)Cp′ being isolated. A similar reaction of
RuCl(PPh3)2Cp, (HO2C)CC(CO2K), and [NH4]PF6 in
refluxing MeOH gave the carbene complex [Ru{CMe-
(OMe)}(PPh3)2Cp]PF6 (10), probably formed by a double
decarboxylation and protonation of 6 so formed by [NH4]+,
followed by addition of MeOH to the resulting vinylidene 8.
Formation of a Cyclobutenylidinium Complex. In
studies of the deprotonation of the parent vinylidene [Ru(
CCH2)(dppe)Cp]PF6 with LiBu, we found that the reaction
was accompanied by the formation of an orange material, which
was successfully isolated and characterized by mass spectrom-
etry and an X-ray structural determination as the binuclear
cyclobutenylidinium complex [{Ru(dppe)Cp}2(μ-C4H3)]PF6
(11) (Scheme 2). Once its identity had been established, a
logical synthesis by reaction of equivalent amounts of [Ru(
CCH2)(dppe)Cp]PF6 with Ru(CCH)(dppe)Cp at room
temperature for 2 h was carried out. Workup by filtration of a
dichloromethane extract of the dried reaction mixture into
diethyl ether afforded pure 11 as a yellow-brown solid in 86%
yield.
Only one substantiated example of a 3-oxopropadienylidene
complex is known, namely Cr(CCCO)(CO)5,
obtained from a reaction between [Cr(I)(CO)5]− and AgC
CCH(CO2Na).23
Instead, the reaction resulted in facile decarboxylation
reactions to give the parent vinylidenes, which can be
deprotonated to the ethynyl−ruthenium complexes. This
paper describes this chemistry and attempts to delineate
possible mechanisms for this reaction.
RESULTS
■
Reactions of Propiolic Acids or Their Salts. Attempted
preparations of [Ru{CCH(CO2H)}(dppe)Cp]PF6 (1)
from propiolic acid and RuCl(dppe)Cp under conditions
similar to those used for preparation of the esters [Ru{C
CH(CO2R)}(dppe)Cp]PF6 (R = Me (2), Et (3)) afforded
instead the light yellow parent vinylidene [Ru(CCH2)-
(dppe)Cp]PF6 (4) (Scheme 1), identical with the material
prepared in the conventional manner from RuCl(dppe)Cp and
HCCSiMe3 in ButOH.24 The same complex was isolated
from a reaction between RuCl(dppe)Cp and Ag[PF6] (to
generate [Ru(thf)(dppe)Cp]PF6 in situ), followed by addition
of propiolic acid. Finally, an attempt to intercept the propiolic
vinylidene by carrying out the reaction in MeOH gave only
[Ru{CMe(OMe)}(dppe)Cp]PF6 (5) as an off-white solid.
This complex is a known product from the reaction of MeOH
with vinylidene 4.20
Complex 11 was characterized by microanalysis, spectrosco-
py, and a single-crystal X-ray structure determination. In
addition to signals from the Ru(PPh3)2Cp group, a
cumulenylidene ν(CC) band was found at 1980 cm−1. In the
1H NMR spectrum, triplets at δ 2.83 (CH2) and 5.3 (CH) in a
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2/1 ratio were assigned to the C4H3 protons. The 13C NMR
spectrum contains resonances at δ 54.9 (CH2), 174.1 (CH),
and 262.1 (t, Ru−C), assigned to three of the four carbons of
the bridging C4 ligand. In the ES-MS, the molecular cation is at
m/z 1181, with related ions at m/z 565 ([Ru(dppe)Cp]+) and
606 ([Ru(NCMe)(dppe)Cp]+; from solutions containing
MeCN).
1.402, 1.403(4) Å), suggesting that the positive charge is
delocalized over atoms C(1,4,3) as well as the two Ru atoms,
which are attached to C(1,3) by short Ru−C multiple bonds
(1.971, 1.968(3) Å), as indicated in the structural diagram of
the cation. The C4 group is planar (χ2 = 32), Ru(1,2) deviations
being 0.125(7) and 0.053(7) Å (to the same side). There are
pronounced asymmetries in the C(1,3)−Ru−P angles at each
metal.
Following this synthesis, we attempted to obtain the mixed
complex [{Cp(dppe)Ru}(μ-C4H3){Ru(dppe)Cp*}]PF6 (12)
from reactions between equimolar amounts of Ru(C
CH)(dppe)Cp and [Ru(CCH2)(dppe)Cp*]PF6, or from
the reverse addition of [Ru(CCH2)(dppe)Cp]PF6 to
Ru(CCH)(dppe)Cp*, both in thf at room temperature.
However, the only complex that could be isolated from either
reaction was 11. Neither the mixed analogue nor [{Ru(dppe)-
Cp*}2(μ-C4H3)]+ was formed.
Figure 1 shows the binuclear cation in [{Ru(dppe)Cp}2(μ-
C4H3)]PF6 (11). Two Ru(dppe)Cp groups, with Ru−P =
Reactions between equimolar amounts of (i) Ru(C
CH)(dppe)Cp and [Ru(CCH2)(dppe)Cp]PF6, (ii)
Ru(CCH)(dppe)Cp* and [Ru(CCH2)(dppe)Cp*]-
PF6, (iii) Ru(CCH)(dppe)Cp and [Ru(CCH2)(dppe)-
Cp*]PF6, and (iv) Ru(CCH)(dppe)Cp* and [Ru(C
CH2)(dppe)Cp]PF6 dissolved in d6-acetone were monitored by
31P NMR. For reaction i, the C4H3 complex [{Ru(dppe)-
Cp}2(μ-C4H3)]PF6 (11) forms in less than 25 min, the color of
the solution changing from yellow to orange. No reaction
occurred between the two Cp* complexes in reaction ii. In
reactions iii and iv, equilibria between all four possible
components were set up, with proton transfer from the
vinylidene to the more basic Cp* derivative being favored.
Consequently, the only cyclobutenylidinium complex detected
is the symmetrical complex [{Ru(dppe)Cp}2(μ-C4H3)]PF6
(11), accompanied by an equimolar amount of [Ru(C
CH2)(dppe)Cp]PF6 (4). These reactions are summarized in
Scheme 3. The specificity found here is likely to be a
consequence of the steric protection of Cα and Cβ by the bulky
Cp* ligands together with the dppe Ph groups. This reaction
proceeds by attack of the electron-rich Cβ upon the electron-
Figure 1. Plot of the cation in [{Ru(dppe)Cp}2(μ-C4H3)]PF6 (11).
2.2449−2.2696(9) Å and Ru−C(cp) = 2.26 Å (average), are
attached at the 1,3-positions of a four-membered ring. Three
hydrogen atoms were located on the C4 ring, one on C(2) and
two on C(4). The bridging ligand is thus the parent
cyclobutenylidinium group, substituted examples of which
have earlier been crystallographically substantiated in (OC)5Cr-
{μ-C4H2(CO2Me)}Fe(CO)2Cp25 and [{Ru(dppe)Cp*}2{μ-
CCC4H2(SiMe3)CC}]PF6.26 In agreement with this
assignment, there are two long (C(1,3)−C(2) = 1.542,
1.547(5) Å) and two short C−C distances (C(1,3)−C(4) =
a
Scheme 3. Reactions between Ethynyl−Ruthenium and Vinylidene−Ruthenium Complexes
a
[Ru] = Ru(dppe)Cp, [Ru*] = Ru(dppe)Cp*.
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Scheme 4. Reactions of Ruthenium Complexes with Propiolic Acid and Esters
poor Cα of both reagents, resulting in a formal [2 + 2]
cycloaddition reaction.
dppe ligand by two PPh3 groups. As previously noted, for
steric reasons it is likely that the major isomer is trans, although
the NMR spectra are not a reliable guide to the stereo-
chemistry.27
Reactions of HCCCO2R (R = Me, Et). Reactions
between RuCl(dppe)Cp and HCCCO2R (R = Me, Et)
were carried out in refluxing methanol in the presence of
[NH4]PF6.21 Conventional workup afforded pale yellow solids,
which were characterized as the carbene complexes [Ru{
C(OMe)CH2(CO2R)}(dppe)Cp]PF6 (R = Me (13), Et (14);
Scheme 4) by elemental microanalyses (as for all complexes
described herein) and spectroscopic methods, detailed in the
Experimental Section. Only data relevant to the organic group
will be discussed below. Thus, the IR spectra contained ester
In these reactions, the carbene cations 10, 13, 14, 17, and 18
result from attack by MeOH on Cα of the initially formed
vinylidene complexes [Ru{CCH(CO2R)}(PP)Cp]+.28
However, if tert-butyl alcohol is used as solvent for the initial
reaction between RuCl(dppe)Cp and HCCCO2R (R = Me,
Et), the orange vinylidenes [Ru{CCH(CO2R)}(dppe)-
Cp]PF6 (R = Me (2), Et (3)) are obtained, ButOH being too
bulky to attack at the Cα atoms, which are sterically protected
by the Ph groups of the tertiary phosphine ligands. These two
compounds were characterized particularly by the downfield
triplet resonances of Cα at δC 198.8 and 200.5, respectively
(J(CP) = 17 Hz for both). Other resonances could be assigned
to the groups present, including OMe at δH 3.1 and δC 51.6, the
CH at δH 4.1 (for both complexes, with J(CP) = 1 Hz), and the
ester CO at δC 163.2 and 162.8. Both IR spectra contained
ν(CO) at 1697 cm−1 and ν(CC) at 1619 cm−1. Molecular
cations at m/z 649 and 663 were found in the ES-MS of 2 and
3, respectively. Some sensitivity to oxidation (by adventitious
air) and solvent used for the ES sample (MeCN) was evident
from accompanying ions at m/z 593 ([Ru(CO)(dppe)Cp]+)
and 606 ([Ru(NCMe)(dppe)Cp]+).
1
ν(CO) absorptions at ca. 1740 and 1250 cm−1. The H NMR
spectra contained singlets at δ 2.9 (OMe, 13 and 14) and 3.7
(for 13, CO2Me), or multiplets at δ 1.2, 3.8, and 4.1 (CO2Et,
for 14). The 13C NMR spectrum similarly contained
resonances at δ 163.5 (ester CO) and 293.2 (RuC), with
the Me/Et resonances at δ 14.0. The electrospray mass spectra
(ES-MS) contained parent molecular cations at m/z 680 (13)
and 694 (14), together with fragment ions at m/z 593
[Ru(CO)(dppe)Cp]+ and 565 [Ru(dppe)Cp]+.
Deprotonation of both 13 and 14 with metallic sodium or
KOBut in MeOH solution resulted in the separation of pale
yellow powders, which were characterized as the neutral vinyl
complexes Ru{C(OMe)CH(CO2R)}(dppe)Cp (R = Me
(15), Et (16), respectively). Their IR spectra contained strong
ν(CO) absorptions at 1667, 1141, and 1048 cm−1, together
with a weaker ν(CC) band at 1493 cm−1. The NMR spectra
of these complexes indicated that cis and trans isomers, each in
the ratio 4/1, were present. Thus, characteristic Cp resonances
were found for 15 at δH 4.6 (major)/4.5 (minor) and δC 85.1/
86.2. Similarly, the OMe groups resonated at δH 2.2/2.7 and δC
49.5/49.2, the CO2Me groups at δH 3.5/3.4 and δC 53.9/62.1,
and the CH groups at δH 4.9/5.3 and δC 100.6/103.0. The ester
CO carbons were found at δC 170.5/160.4, while the RuC
signals overlapped at δC 224.9. Similar resonances were found
for the ethyl ester complex 16. The 31P resonances for the dppe
ligands are at δP 93.0/96.5 and 92.7/96.1, respectively. In the
ES-MS M+ ions were found at m/z 680 and 695, respectively.
The analogous carbenes [Ru{C(OMe)CH2(CO2R)}-
(PPh3)2Cp]PF6 (R = Me (17), Et (18)) and the vinyl
compounds cis- and trans-Ru{C(OMe)CH(CO2R)}-
(PPh3)2Cp (R = Me (19), Et (20)) were similarly prepared
from RuCl(PPh3)2Cp.27 As detailed in the Experimental
Section, their spectroscopic properties were very similar to
those of complexes 13−16, with the exception of the
anticipated differences resulting from replacement of the
Deprotonation of vinylidenes 2 and 3 with sodium in PriOH
readily afforded the corresponding neutral alkynyls Ru(C
CCO2R)(dppe)Cp (R = Me (21), Et (22)) as light yellow
solids. In their IR spectra, v(CC) bands were found at 2039
and 2050 cm−1, respectively, together with ν(CO) bands at
1658 and 1655 cm−1. The ES-MS contained [M + H]+ ions at
m/z 649 and 663, respectively; again, the operating conditions
resulted in the presence of the carbonyl and acetonitrile cations
found in the spectra of precursors 2 and 3, no doubt as a result
of ready protonation occurring in solution.
Molecular structures. The structures of complexes 13, 15,
16, 21, and 22 have been confirmed by single-crystal X-ray
diffraction studies. The cation of 13 and single molecules of 15
and 21 are portrayed in Figures 2−4; the similar molecules of
16 and 22 are shown in Figures S1 and S2 (Supporting
Information), while selected bond parameters of all molecules
are collected in Table S1 (Supporting Information). All
complexes contain the ruthenium atoms pseudo-octahedrally
coordinated by the Cp, two P atoms, and the carbon atom of
the unsaturated ligand, with P(1)−Ru−P(2) and P(1,2)−Ru−
C(1) angles in the ranges 83.31(3)−84.82(2) and 80.65(4)−
93.17(9)°, respectively. For the neutral complexes, the Ru−P
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Figure 4. Plot of a molecule of Ru(CCCO2Me)(dppe)Cp (21).
Figure 2. Plot of the cation in [Ru{C(OMe)CH2(CO2Me)}-
(dppe)Cp]PF6 (13). Only one component of the disordered carbene
ligand is shown.
C(1) in 13 and at C(1) and C(2) in 15 and 16 indicate the sp2
hybridization of this atom, whereas the angles at C(1) and C(2)
in alkynyls 21 and 22 (177.8(2), 177.80(14)°) are close to
linear, as expected for C(sp) atoms. Within the ester groups,
parameters associated with the various C−O bonds are within
the usual ranges.
DISCUSSION
■
The syntheses of complexes described above parallel the well-
known alkyne-to-vinylidene conversion by means of a 1,2-H
shift, followed by characteristic reactions involving nucleophilic
addition of MeOH to Cα of the resulting vinylidenes to give the
corresponding alkoxycarbene complexes. Deprotonation of the
vinylidenes or carbenes gives neutral alkynyls and alkoxyvinyls,
respectively.27,28
The unusual decarboxylation of propiolic acids RC
CCO2H or their potassium salts under mild conditions in the
presence of complexes containing the Ru(PP)Cp′ moieties may
proceed via initial formation of the expected vinylidene [Ru{
CCR(CO2H)}(PP)Cp′]+, but this could not be intercepted
before decarboxylation occurred. Instead, this reaction provides
a useful synthetic approach to the parent vinylidenes which
does not use either ethyne or ethynyltrimethylsilane.
To gain more insight into the low-temperature decarbox-
ylation reaction that results in the formation of the parent
vinylidene [Ru(CCH2)(dppe)Cp]+ (4), DFT calculations
were used to explore various reaction pathways and to provide
information about the intermediate and transition state
structures involved. Currently accepted mechanisms for the
formation of vinylidene complexes from 1-alkynes include an
approach of the metal center to the terminal carbon (Cα) with
Figure 3. Plot of a molecule of Ru{C(OMe)CH(CO2Me)}(dppe)-
Cp (15).
distances range between 2.2450(4) and 2.2709(6) Å, while the
Ru−C(cp) separations average 2.239−2.267 Å. These param-
eters do not differ significantly from those found in many other
analogous complexes with similar structures. The longer Ru−P
distances (2.2890, 2.3043(10) Å) and increased Ru−C(cp)
separations (2.267(11) Å (average)) in the cation of 13 reflect
the reduced back-bonding into the Ru−P MOs.
The most interesting features relate to the unsaturated
ligands derived from the alkynes. In carbene 13, the Ru−C(1)
distance of 1.933(4) Å is consistent with a degree of multiple
bonding expected for the RuC interaction and may be
compared with the longer values of 1.989(2), 2.008(2) Å
(alkynyl; Ru−C(sp)) and 2.070(2), 2.083(3) Å (vinyl; Ru−
C(sp2)) found in the neutral complexes. Similarly, the C(1)−
C(2) distances in 15 and 16 (1.365(4), 1.372(3) Å) and in 21
and 22 (1.221(3), 1.184(2) Å) are consistent with the presence
of CC double and CC triple bonds, respectively. Angles at
concomitant 1,2-migration of the proton over the alkyne to
29−31
Cβ
or formation of the η2-alkyne complex, followed by
oxidative addition of the C−H bond to the metal center and a
concerted 1,3-shift of H to Cβ.32 The latter route has been
demonstrated experimentally for Rh complexes32 and, rarely,
for Ru.33 The latter mechanism appears to be more difficult for
a d6 → d4 change (RuII → RuIV) than for a d8 → d6 change (RhI
→ RhIII).
In performing the present calculations, two scenarios were
considered: one looking at the interaction of HCCCO2H
with RuCl(dmpe)Cp and the other similarly involving the
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Figure 5. Calculated decomposition route of Ru−propiolic acid complex I. [Ru] = Ru(dmpe)Cp. In this and the following figures, energies are given
in kJ mol−1.
propiolate ion [HCCCO2]−. For the former, three reaction
pathways were determined overall, with the starting point for all
of them involving the initial formation of an η2-alkyne
intermediate. For the latter scenario, only one reaction pathway
was computed, commencing with the formation of an
intermediate containing a coordinated carboxylate group.34,35
Figure 5 presents one of the three reaction pathways
determined for the decarboxylation reaction occurring after the
interaction of HCCCO2H with RuCl(dmpe)Cp. As shown,
the first step of this pathway results in formation of the initial
η2-alkyne−Ru intermediate I, which is followed by intra-
molecular attack on the Ru center by the C−H bond of HC
CCO2H. This gives reaction intermediate II by formation of
Ru−C and Ru−H bonds. Transition state TSI‑II is determined
to be 76.2 kJ mol−1 higher in energy than structure I (80.2 kJ
mol−1 when ButOH solvation is taken into account). This is the
lowest energetic barrier determined for all reaction pathways
involving the interaction of HCCCO2H with RuCl(dmpe)-
Cp (two alternative pathways involving this interaction but with
higher energies are given in the Supporting Information). After
the formation of II, the proton bridging the Ru and Cβ migrates
to Cα via transition state TSII‑III, leading to the formation of the
carboxyvinylidene intermediate III, which is the global
minimum on the potential energy surface of the [Cp(dmpe)-
Ru]+−HCCCO2H interaction. Formation of III is then
followed by proton transfer from the CO2H group to Cα with
concomitant extrusion of CO2 and formation of a [Ru(C2H2)-
(dmpe)Cp]+ isomer (IV). This isomer would be expected to
rearrange to the parent vinylidene [Ru(CCH2)(dmpe)-
Cp]+ (V), as shown earlier by studies of the alkyne to
vinylidene isomerizations occurring in [Ru(HCCR)-
(PMe3)2Cp]+ (R = H, Me)31 and [Ru(HCCCO2Me)-
(dippe)Cp*]+.33 Despite the low initial energetic barrier
associated with this reaction pathway, the barrier related to
the proton transfer from the CO2H group to Cα is 179.5 kJ
mol−1 (157.4 kJ mol−1 with the ButOH solvation correction)
relative to structure III. We regard this as being too large for
the decarboxylation reaction to proceed via this mechanism
under mild conditions. Hence, as all three reaction pathways
possess large energetic barriers associated with the CO2H
proton transfer process, it would appear that likely mechanisms
for the decarboxylation reaction which involve an initial Ru−
(η2-HCCCO2H) intermediate are not viable.
A reaction sequence involving oxidative addition of HC
CCO2H to the Ru center to give a hydrido−Ru(IV)
intermediate is detailed in the Supporting Information (Figure
S5 and discussion therein). Although the initial step has a
satisfyingly low energy barrier, subsequent processes involve
much higher energies and we conclude that this route is
improbable.
We then considered an alternative approach involving
interaction of the propiolate anion with the Ru center (Figure
6). Initial formation of the coordinated carboxylate inter-
mediate VI leads to the formation of the η2-alkynecarboxylate
intermediate VII via transition state TSVI‑VII. This is followed
by concomitant shortening of the Ru−Cα bond, lengthening of
−
the Ru−Cβ bond, and cleavage of the C−CO2 bond to yield
Figure 6. Calculated pathway for decomposition of Ru−propiolate
complex VI. [Ru] = Ru(dmpe)Cp.
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the parent ethynyl Ru(CCH)(dmpe)Cp VIII with sponta-
neous emission of CO2. Finally, protonation of VIII at the Cβ
atom and rearrangement occurs to give [Ru(CCH2)-
(dmpe)Cp]+ (V). Closer inspection of transition state TSVI‑VII
shows that it is 98.9 kJ mol−1 higher in energy than VI (64.8 kJ
mol−1 with the ButOH solvation correction). Furthermore,
transition state TSVII‑VIII is 37.1 kJ mol−1 higher in energy than
VII (80.4 kJ mol−1 with the ButOH solvation correction).
Despite the initially encountered barrier being of energy similar
to that calculated in the reaction pathway shown in Figure 5,
the subsequent energetic barrier for the liberation of CO2 is
significantly lower in energy than any of the barriers
encountered in the three reaction pathways which start from
propiolic acid itself (relative to gas-phase energetics). Hence,
we suggest that the facile decarboxylation reaction that leads to
[Ru(CCH2)(dmpe)Cp]+ with extrusion of CO2 most
likely occurs via initial coordination of HCCCO2− to the Ru
center obtained from the precursor RuCl(dmpe)Cp. This
conclusion is also supported by the same decarboxylation
reaction occurring with the salt HCCCO2K.
energy pathway derives from an initial structure involving η2
coordination of O2CCC− to the Ru center. Addition of
ethynyl−ruthenium to cationic vinylidene−ruthenium moieties
afforded a further example of a binuclear cyclobutenylidinium
complex by (Cα + Cβ) coupling. The formation of several
alkynyl, vinylidene, and carbene complexes from HCCCO2R
(R = H, Me, Et) and RuCl(PP)Cp (PP = (PPh3)2, dppe) is also
described, together with single-crystal XRD structure determi-
nations of some of the complexes, these studies supplementing
earlier reports.20,21
EXPERIMENTAL SECTION
■
General Considerations. All reactions were carried out under dry
nitrogen, although normally no special precautions to exclude air were
taken during subsequent workup. Common solvents were dried,
distilled under nitrogen, and degassed before use. Separations were
carried out by preparative thin-layer chromatography on glass plates
(20 × 20 cm2) coated with silica gel (Merck, 0.5 mm thick).
Instruments. IR spectra were obtained on a Bruker IFS28 FT-IR
spectrometer. Spectra in CH2Cl2 were obtained using a 0.5 mm path
length solution cell with NaCl windows. Nujol mull spectra were
obtained from samples mounted between NaCl disks. NMR spectra
were recorded on a Varian 2000 instrument (1H at 300.13 MHz, 13C at
75.47 MHz, 31P at 121.503 MHz). Unless otherwise stated, samples
were dissolved in CDCl3 contained in 5 mm sample tubes. Chemical
shifts are given in ppm relative to internal tetramethylsilane for 1H and
13C NMR spectra and external H3PO4 for 31P NMR spectra.
Coupling of Ethynyl and Vinylidene To Form Cyclo-
butenylidinium. Deprotonation of vinylidene to alkynyl is a
well-established reaction, and its reverse is often the reaction of
choice for the preparation of vinylidene complexes.28 However,
in the case of the present complexes, while deprotonation of
the ester derivatives affords the expected alkynyl or alkoxyvinyl
derivatives, when applied to the parent vinylidene, rapid
coupling of the ethynyl complex with remaining vinylidene
occurred to give the binuclear cyclobutenylidinium complex 11.
Formation of this type of complex has been described on
several occasions. The first mentioned treatment of FpCCPh
(Fp = Fe(CO)2Cp) with HBF4·OMe2 or FSO3Me to give
[Fp2(μ-C4RPh2)]+ (R = H, Me).36−38 Thermolysis of [Ru(
CCHMe)(PMe3)2Cp][M(CO)3Cp] (M = Cr, Mo, W) in
MeCN afforded a mixture of [Ru(NCMe)(PMe3)2Cp]+ and
[{Ru(PMe3)2Cp}2(μ-C4HMe2)]+.39 More recently, Fischer and
co-workers have described the addition of FpCCR (R = Me,
Bu, Ph, C6H4NO2-4, CO2Me) to Cr(CCMe2)(CO)5 to
give the neutral heterobimetallic analogues {(OC)5Cr}(μ-
C4Me2R){Fp}; several related complexes were also prepared,
with extensions to butadiynyl complexes such as FpCCC
CR (R = SiMe3, Bu, Ph) affording {(OC)5Cr}{μ-C4(C
CR)Me2}{Fp} and hence some trimetallic derivatives.25 Similar
chemistry of Ru(CCCCSiMe3)(dppe)Cp* afforded {Ru-
(dppe)Cp*}2{μ-CCC4H2(SiMe3)CC} as one product.26
With the HOMO of alkynyl−metal complexes being localized
on Cβ,40,41 electrophilic attack by the vinylidene thereupon
readily leads to the bimetallic C4R3 compounds (Scheme 2).
Formation of Complexes from HCCCO2R (R = Me,
Et). The syntheses of complexes described above parallel the
well-known alkyne-to-vinylidene conversion by means of a 1,2-
H shift,29,30 followed by characteristic reactions involving
nucleophilic addition of MeOH to Cα of the resulting
vinylidenes to give the corresponding alkoxycarbene complexes.
Deprotonation of the vinylidenes or carbenes gives neutral
alkynyls and alkoxyvinyls, respectively.27,28,42
Electrospray mass spectra (ES-MS, positive ion mode) were obtained
from samples dissolved in MeOH unless otherwise indicated; if
necessary, NaOMe was added as an aid to ionization.43 Solutions were
injected into a Fisons VG Platform II spectrometer via a 10 mL
injection loop. Nitrogen was used as the drying and nebulizing gas.
Ions listed are the most intense in the respective ion clusters.
Elemental analyses were carried out by CMAS, Belmont, Victoria,
Australia.
Reagents. The complexes RuCl(PP)Cp (PP = (PPh3)2,44 dppe45),
Ru(CCH)(PP)Cp,20,46 and [Ru(CCH2)(PP)Cp]PF620,46 were
obtained as previously described. HCCCO2H, HCCCO2K,
PhCCCO2K, and (HO2C)CC(CO2K) were purchased from
Aldrich and used as received; methyl and ethyl propiolates were
prepared from HCCCO2H.
Decarboxylation of Propiolic Acids. Reactions of Propiolic
Acid. Propiolic acid (77 mg, 1.10 mmol) was added to a suspension of
RuCl(dppe)Cp (302 mg, 0.502 mmol) and [NH4]PF6 (82 mg, 0.499
mmol) in dry degassed t-BuOH (5 mL). The mixture was refluxed for
2 h to give a light yellow precipitate. Hot solvent was removed by
cannula, and the light yellow precipitate was washed with Et2O (2 × 4
mL) to remove traces of t-BuOH and dried under vacuum to give
[Ru(CCH2)(dppe)Cp]PF6 (4).
Ag[PF6] (42 mg, 0.166 mmol) was added to a solution of
RuCl(dppe)Cp (100 mg, 0.166 mmol) in degassed thf (15 mL) and
stirred at room temperature for 15 min. The solution immediately
changed to red-orange with the precipitation of AgCl. After filtration,
propiolic acid (23 mg, 0.333 mmol) was added to the filtrate and the
mixture stirred at room temperature for 2 h to give a yellow-orange
solution. Solvent was removed under vacuum, the residue was
extracted with CH2Cl2 (3 mL), and the solution was filtered into
rapidly stirred Et2O (30 mL) to give a light brown precipitate.
Filtration, washing with Et2O (3 mL), and drying under vacuum gave
[Ru(CO)(dppe)Cp]PF6.
Propiolic acid (48 mg, 0.68 mmol) was added to a suspension of
RuCl(dppe)Cp (203 mg, 0.338 mmol) and [NH4]PF6 (55 mg, 0.338
mmol) in degassed MeOH (10 mL). The reaction mixture was stirred
at the reflux point for 2 h to give an off-white precipitate. This was
isolated by filtration, washed with MeOH (2 mL), and dried under
high vacuum to give [Ru{CMe(OMe)}(dppe)Cp]PF6 (5; 49 mg,
19%).
CONCLUSIONS
■
Spontaneous decarboxylation of propiolic acids or their
potassium salts in similar reactions is attributed to the stability
of the parent vinylidene complex, which theoretical studies have
already shown to resist the insertion of CO2. Computational
studies of possible reaction mechanisms suggest that the lowest
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Reactions of KO2CCCR (R = H, Ph). In general, reactions
between powdered RuCl(PP)Cp′ ((PP)Cp′ = (PPh3)2Cp, (dppe)-
Cp*) and KO2CCCR (R = H, Ph) were carried out in refluxing
MeOH for several hours, although they proceeded slowly at room
temperature. Qualitatively, the reaction of RuCl(PPh3)2Cp was faster
than that of RuCl(dppe)Cp*.
washing with Et2O (5 mL) gave 11, which was dried under vacuum.
Anal. Calcd for C66H57F6P5Ru2: C, 60.00; H, 4.35; M (cation), 1321.
Found: C, 60.01; H, 4.42. IR (Nujol, cm−1): 1980 s ν(CCC), 839 vs
ν(PF). 1H NMR (d6-acetone): δ 7.6−7.2 (m, 40H, Ph), 5.3 (1H, CH),
4.9 (10H, Cp), 2.87 (8H, PCH2), 2.83 (t, 2H, CH2). 13C NMR (d6-
acetone): δ 262.1 (m, Ru−C), 174.1 (CH), 141.2−129.0 (m, Ph), 87.6
(Cp), 54.9 (s, CH2), 27.3 (t, PCH2). 31P NMR (d6-acetone): δ 86.1
(dppe), −142.7 (sep, J(PF) = 708 Hz, PF6). ES-MS (MeOH−MeCN,
m/z): 565, [Ru(dppe)Cp]+; 606, [Ru(MeCN)(dppe)Cp]+; 1180,
[{Ru(dppe)Cp}2(C4H3)]+.
Attempts To Prepare [{Ru(dppe)Cp}(μ-C4H3){Ru(dppe)Cp*}]PF6
(12). A solution of [Ru(CCH2)(dppe)Cp*]PF6 (49 mg, 0.061
mmol) and Ru(CCH)(dppe)Cp (36 mg, 0.061 mmol) in degassed
thf (20 mL) was stirred at room temperature for 2 h. The yellow
solution changed to yellow-brown. After removal of solvent, the
residue was extracted with CH2Cl2 and filtered into Et2O (30 mL),
precipitating yellow-brown [{Ru(dppe)Cp}2(μ-C4H3)]PF6 (11). This
was isolated by filtration, washed with Et2O (5 mL), and dried under
vacuum.
A mixture of RuCl(PPh3)2Cp (100 mg, 0.138 mmol) and HC
CCO2K (22 mg, 0.207 mmol) in MeOH (5 mL) was heated at the
reflux point for 3 h, after which time a yellow precipitate had separated.
After cooling, the solid was collected and washed with MeOH (2 × 3
mL) and hexanes (4 mL) to give Ru(CCH)(PPh3)2Cp (6; 66 mg,
1
67%). H NMR: δ 2.02 (t, J(HP) = 3 Hz, 1H, CH), 4.28 (s, 5H,
Cp), 7.09−7.51 (m, 30H, Ph). 31P NMR: δ 51.0 (s, PPh3). The
reaction between RuCl(PPh3)2Cp and HCCCO2K, carried out in
the presence of [NH4]PF6, gave [Ru(CCH2)(PPh3)2Cp]PF6.
The product from RuCl(dppe)Cp* (150 mg, 0.223 mmol) and HC
CCO2K (36 mg, 0.336 mmol) was yellow Ru(CCH)(dppe)Cp* 7
(97 mg, 66%). 1H NMR (C6D6): δ 1.69 (s, 15H, Cp*), 2.06 (t, J(HP)
= 3 Hz, 1H, HC), 2.00, 2.83 (2m, 2 × CH2, CH2P), 7.03−8.04 (m,
20H, Ph). 31P NMR: δ 82.3 (s, dppe).
A solution containing [Ru(CCH2)(dppe)Cp]PF6 (93 mg, 0.127
mmol) and Ru(CCH)(dppe)Cp*] (84 mg, 0.127 mmol) in
degassed thf (20 mL) similarly gave yellow-brown 11.
Similarly, RuCl(PPh3)2Cp (100 mg, 0.138 mmol) and KO2CCCPh
(32 mg, 0.152 mmol) in MeOH (5 mL) gave, after refluxing for 90
min, a yellow precipitate of Ru(CCPh)(PPh3)2Cp (9; 95 mg, 87%).
1H NMR: δ 4.33 (s, 5H, Cp), 7.07−7.53 (m, 35H, Ph). 31P NMR: δ
51.5 (s, PPh3).
Reactions of Propiolic Esters with Chloro−Ruthenium
Complexes. [Ru{C(OMe)CH2(CO2R)}(dppe)Cp]PF6 (R = Me (13),
Et (14)). HCCCO2R (61 mg for 13 (R = Me), 71 mg for 14 (R =
Et); 0.722 mmol) was added to a suspension of RuCl(dppe)Cp (203
mg, 0.337 mmol) and [NH4]PF6 (55 mg, 0.338 mmol) in degassed
MeOH (20 mL). The reaction mixture was stirred at the reflux point
for 1 h. After removal of solvent, the residue was extracted with
CH2Cl2 and the extract filtered into Et2O (30 mL), precipitating a light
yellow solid. This was isolated by filtration, washed with Et2O (2 mL),
and dried under vacuum. The precipitate was recrystallized from
CH2Cl2/MeOH under nitrogen.
Reactions of KO2CCCCO2R (R = H, K). A mixture containing
RuCl(PPh3)2Cp (191 mg, 0.263 mmol), (HO2C)CC(CO2K) (20
mg, 0.132 mmol), and [NH4]PF6 (23 mg, 0.138 mmol) in MeOH (8
mL) was heated at the reflux point for 6 h. After this time, unreacted
RuCl(PPh3)2Cp (81 mg, 42%) was removed by filtration. The filtrate
was layered with Et2O and kept at −10 °C for 24 h to give yellow
1
[Ru{CMe(OMe)}(PPh3)2Cp]PF6 (10; 62 mg, 53%). H NMR: δ
2.96 (s, 3H, Me), 3.21 (s, 3H, OMe), 4.69 (s, 5H, Cp), 6.89−7.38 (m,
30H, Ph). 13C NMR δ 46.78 (Me), 61.00 (OMe), 91.58 (Cp),
128.28−136.28 (Ph), 308.78 (t, J(CP) = 13 Hz, RuC). 31P NMR: δ
48.3 (PPh3), −142.3 (sept, J(PF) = 708 Hz, PF6). ES-MS (MeOH, m/
z): 429, [Ru(PPh3)Cp]+.
1
R = Me (13; 223 mg, 0.270 mmol, 80%). H NMR: δ 7.6−7.1 (m,
20H, Ph), 5.1 (5H, Cp), 3.8 (2H, CH2), 3.7 (3H, OMe), 3.0 (m, 2H,
PCH2), 2.9 (3H, Me), 2.7 (m, 2H, PCH2). 13C NMR: δ 293.4 (t,
J(CP) = 13 Hz, RuC), 163.7 (CO2), 133.3−128.7 (Ph), 90.8 (Cp),
61.3, 60.1, 52.9, 28.2 (t, CH2CH2). 31P NMR: δ 89.5 (dppe), −142.8
(sep, J(PF) = 708 Hz, PF6). ES-MS (m/z): 564, [Ru(dppe)Cp]+; 592,
[Ru(CO)(dppe)Cp]+; 680, [Ru{C(OMe)CH2(CO2Me)}(dppe)Cp]+.
IR (KBr, cm−1): 1737 s ν(ester CO), 1247 s ν(CO), 839 vs ν(PF).
Anal. Calcd for C36H37F6O3P3Ru: C, 52.37; H, 4.52; M (cation), 825.
Found: C, 52.28; H, 4.54.
Addition of RuCl(PPh3)2Cp (191 mg, 0.263 mg) to a mixture of
(HO2C)CC(CO2K) (20 mg, 0.132 mmol) and K2CO3 (18 mg,
0.132 mmol) in MeOH (8 mL) and heating at the reflux point for 2.5
h afforded a yellow precipitate of RuH(PPh3)2Cp (119 mg, 65%).47 1H
NMR (C6D6): δ −11.09 (t, J(PH) = 34 Hz, 1H, RuH), 4.49 (s, 5H,
Cp), 6.89−7.56 (m, 30H, Ph). 13C NMR (C6D6): δ 82.39 (Cp),
127.59−142.43 (Ph). 31P NMR (C6D6): δ 69.2 (PPh3). ES-MS
(MeOH, m/z): 690, [M − H]+; 429 [Ru(PPh3)Cp]+.
Similarly, RuCl(dppe)Cp* (176 mg, 0.263 mmol), (HO2C)C
C(CO2K) (20 mg, 0.132 mmol), and K2CO3 (18 mg, 0.32 mmol) in
refluxing MeOH (8 mL) after 18 h afforded RuH(dppe)Cp* (92 mg,
55%).48 1H NMR (C6D6): δ −13.50 (t, J(PH) = 34 Hz, 1H, RuH),
1.76 (s, 15H, Cp*), 1.89, 1.94 (2s (br), 2 × 2H, dppe), 7.10−7.82 (m,
20H, Ph). 31P NMR (C6D6): δ 69.2 (PPh2). ES-MS (MeOH, m/z):
635, [M − H]+.
Cyclobutenylidinium Complex. Synthesis of [{Ru(dppe)Cp}2(μ-
C4H3)]PF6 (11). n-BuLi (0.16 mL, 1.74 M, 0.28 mmol) was added to a
solution of [Ru(CCH2)(dppe)Cp]PF6 (103 mg, 0.139 mmol) in
dry degassed thf (20 mL) at −78 °C. The reaction mixture was stirred
at −78 °C for 15 min before being warmed to room temperature for
15 min, at which time the color had changed to orange-yellow. After
the mixture was cooled to −78 °C, SiClMe3 (0.026 mL, 0.208 mmol)
was added to remove excess n-BuLi and the mixture was stirred for 30
min. After a further 30 min at room temperature, solvent was removed
under vacuum to give a yellow-brown solid, which was recrystallized
from acetone/hexane to give brown needles of [{Ru(dppe)Cp}2(μ-
C4H3)]PF6 (11; 118 mg, 86%).
1
R = Et (14; 192 mg, 0.229 mmol, 68%). H NMR: δ 7.6−7.1 (m,
20H, Ph), 5.1 (5H, Cp), 4.1 (q, 2H, CH2), 3.8 (2H, CH2), 3.0 (m, 2H,
PCH2), 2.9 (3H, OMe), 2.7 (m, 2H, PCH2), 1.2 (t, 3H, Me). 13C
NMR: δ 293.1 (t, J(CP) = 13 Hz, RuC), 163.3 (CO2), 139.0−128.7
(Ph), 90.8 (Cp), 61.9, 61.1, 60.3, 28.0 (t, CH2CH2), 14.0 (Me). 31P
NMR: δ 89.6 (dppe), −142.8 (sep, J(PF) = 708 Hz, PF6). ES-MS (m/
z): 565, [Ru(dppe)Cp]+; 595, [Ru(CO)(dppe)Cp]+; 695, [Ru{C-
(OMe)CH2(CO2Et)}(dppe)Cp]+. IR (KBr, cm−1): 1725 s ν(ester
CO), 1275 s ν(CO), 839 vs ν(PF). Anal. Calcd for C37H39F6O3P3Ru:
C, 52.92; H, 4.68; M (cation), 840. Found: C, 52.95; H, 3.49.
Ru{C(OMe)CH(CO2R)}(dppe)Cp (R = Me (15), Et (16)). Sodium
(4.17 mg, 0.181 mmol) was added to a solution of [Ru{
C(OMe)CH2(CO2R)}(dppe)Cp]PF6 (150 mg for 15 (R = Me),
153 mg for 16 (R = Et); 0.181 mmol) in MeOH (20 mL). As sodium
slowly dissolved in solution, a light yellow precipitate separated. The
reaction mixture was stirred at room temperature for 15 min. The
precipitate was isolated by filtration, washed with MeOH (2 mL),
dried under vacuum, and recrystallized from CH2Cl2/hexane.
R = Me (15; 71 mg, 0.104 mmol, 58%). This complex is obtained as
1
a 4/1 isomeric mixture. H NMR: major isomer, δ 4.9 (1H, CH), 4.6
(5H, Cp), 3.5 (3H, CO2Me), 2.2 (3H, OMe); minor isomer, δ 5.3
(1H, CH), 4.5 (5H, Cp), 3.4 (3H, CO2Me), 2.7 (3H, OMe); common
A solution containing [Ru(CCH2)(dppe)Cp]PF6 (75.8 mg,
0.103 mmol) and [Ru(CCH)(dppe)Cp] (60.8 mg, 0.103 mmol)
in degassed thf (25 mL) was stirred at room temperature for 2 h, after
which time the yellow solution had changed to yellow-brown. After
removal of solvent, a CH2Cl2 extract of the residue was filtered into
Et2O (30 mL), precipitating a yellow-brown solid. Filtration and
resonances, δ 7.8−7.1 (m, 20H, Ph), 2.7, 2.6 (2m, 2 × 2H, PCH2). 13
C
NMR: major isomer, δ 170.5 (CO2), 100.6 (CH), 85.1 (Cp), 53.9,
49.5, 29.7 (t, CH2CH2); minor isomer, δ 160.4 (CO2), 103.0 (CH),
86.2 (Cp), 62.1, 49.2, 29.2 (t, CH2CH2); common resonances, δ 224.9
(t, J(CP) = 15 Hz, Ru−C), 144.8−127.2 (m, Ph). 31P NMR: δ 96.5
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Article
(minor isomer), 93.0 (major isomer). ES-MS (m/z): 681, [Ru(C-
(OMe)CHCO2Me)(dppe)Cp]+. IR (KBr, cm−1): 1667 m ν(CO),
1493 s ν(CC), 1141 s ν(CO), 1048 s ν(CO). Anal. Calcd for
C36H36O3P2Ru: C, 63.62; H, 5.34; M, 680 Found: C, 63.60; H, 5.27.
R = Et (16; 89 mg, 0.104 mmol, 77%). This complex is obtained as
(CDCl3): δ 51.9 (major), 51.0 (minor). ES-MS (m/z): 806,
[Ru{C(OMe)CH(CO2Me)}(PPh3)2Cp]+. IR (KBr, cm−1): 1686 m
ν(CO), 1493 s ν(CC), 1149 s ν(CO), 1046 s ν(CO). Anal. Calcd
for C46H42O3P2Ru: C, 68.56; H, 5.25; M, 806. Found: C, 68.58; H,
5.23.
1
a 4/1 isomeric mixture. H NMR: major isomer, δ 4.9 (1H, CH), 4.6
R = Et (20; 89 mg, 0.108 mmol, 60%). This complex was obtained
as a 65/35 isomeric mixture. 1H NMR: major isomer, δ 5.4 (1H, CH),
4.4 (5H, Cp), 4.2 (2H, CH2), 2.5 (3H, OMe), 1.3 (3H, Me); minor
isomer, δ 5.8 (1H, CH), 4.3 (5H, Cp), 4.0 (2H, CH2), 3.1 (3H, OMe),
1.2 (3H, Me); common resonances, δ 7.4−7.2 (m, 30H, Ph). 13C
NMR: major isomer, δ 170.5 (CO2), 102.6 (CH), 85.8 (Cp), 57.8,
58.1, 14.9; minor isomer, δ 160.5 (CO2), 104.4 (CH), 87.2 (Cp), 62.6,
57.6, 14.3; common resonances, δ 222.1 (t, J(CP) = 16 Hz, Ru−C),
140.2−127.0 (Ph). 31P NMR: δ 51.9 (major), 51.0 (minor). ES-MS
(m/z): 820, [Ru{C(OMe)CH(CO2Et)}(PPh3)2Cp]+. IR (KBr, cm−1):
1681 m ν(CO), 1493 s ν(CC), 1144 s ν(CO), 1048 s ν(CO). Anal.
Calcd for C47H44O3P2Ru: C, 68.85; H, 5.41; M, 820. Found: C, 68.73;
H, 5.29.
(5H, Cp), 4.0 (q, 2H, CH2), 2.2 (3H, OMe), 1.2 (t, CH3); minor
isomer, δ 5.3 (1H, CH), 4.6 (5H, Cp), 3.8 (q, 2H, CH2), 2.6 (3H,
OMe), 1.1 (t, Me); common resonances, δ 7.8−7.1 (m, 20H, Ph), 2.7
(m, 2H, PCH2), 2.5 (m, 2H, PCH2). 13C NMR: major isomer, δ 224.3
(t, J(CP) = 15 Hz, Ru−C), 170.4 (CO2, major), 101.3 (CH), 85.4
(Cp), 57.5, 54.1, 29.8 (t, CH2CH2), 15.1 (Me); minor isomer, δ 229.2
(t, J(CP) = 15 Hz, Ru−C), 160.2 (CO2), 104.1 (CH), 86.3 (Cp), 62.3,
53.9, 29.3 (t, CH2CH2), 15.0 (Me); common resonances, δ 144.8−
127.4 (m, Ph). 31P NMR: δ: 96.1 (minor isomer), 92.7 (major
isomer). ES-MS (m/z): 565, [Ru(dppe)Cp]+; 593, [Ru(CO)(dppe)-
Cp]+; 695, [Ru{C(OMe)CH(CO2Et)}(dppe)Cp]+. IR (KBr, cm−1):
1667 m ν(CO), 1493 s ν(CC), 1141 s ν(CO), 1046 s ν(CO). Anal.
Calcd for C37H38O3P2Ru: C, 64.06; H, 5.52; M, 694. Found: C, 63.96;
H, 5.64.
[Ru{CCH(CO2R)}(dppe)Cp]PF6 (R = Me (2), Et (3)). HC
CCO2R (62 mg for 2 (R = Me), 73 mg for 3 (R = Et); 0.741 mmol)
was added to a suspension of RuCl(dppe)Cp (204 mg, 0.339 mmol)
and [NH4]PF6 (55 mg, 0.338 mmol) in degassed t-BuOH (5 mL).
The reaction mixture was stirred at the reflux point for 2 h, generating
an orange precipitate. After removal of the hot solvent by cannula
filtration, the orange precipitate was washed with Et2O (2 × 4 mL) to
remove traces of t-BuOH and dried under vacuum.
[Ru{C(OMe)CH2(CO2R)}(PPh3)2Cp]PF6 (R = Me (17), Et (18)).
HCCCO2R (61 mg for 17 (R = Me), 71 mg for 18 (R = Et); 0.722
mmol) was added to a suspension of RuCl(PPh3)2Cp (245 mg, 0.337
mmol) and [NH4]PF6 (55 mg, 0.338 mmol) in degassed MeOH (20
mL). The reaction mixture was stirred at reflux for 1 h. After removal
of solvents, the residue was extracted with CH2Cl2 and filtered into
Et2O (30 mL), precipitating a light orange solid. This was isolated by
filtration, washed with Et2O (2 mL), dried under vacuum, and
recrystallized from CH2Cl2/MeOH under nitrogen.
1
R = Me (2; 213 mg, 0.268 mmol, 79%). H NMR: δ 7.9−7.1 (m,
20H, Ph), 5.5 (5H, Cp), 4.1 (t, 1H, CH), 3.1 (3H, Me), 3.0 (m, 4H,
PCH2). 13C NMR: δ 198.8 (t, J(CP) = 16 Hz, RuC), 163.2 (CO2),
135.8−129.0 (Ph), 110.2 (CH), 88.1 (Cp), 51.6 (Me), 29.0 (t, PCH2).
31P NMR: δ 76.1 (dppe), −142.8 (sept, J(PF) = 709 Hz, PF6). ES-MS
(m/z): 565, [Ru(dppe)Cp]+; 593, [Ru(CO)(dppe)Cp]+; 606, [Ru-
(MeCN)(dppe)Cp]+; 649, [Ru(CCHCO2Me)(dppe)Cp]+. IR (KBr,
cm−1): 1697 s ν(CO), 1619 s ν(CC), 839 vs ν(PF). Anal. Calcd for
C35H33F6O2P3Ru: C, 52.97; H, 4.19; M (cation), 749. Found: C,
52.85; H, 4.18.
1
R = Me (17; 263 mg, 0.276 mmol, 82%). H NMR: δ 7.7−6.9 (m,
30H, Ph), 4.8 (5H, Cp), 4.5 (2H, CH2), 3.8 (3H, OMe), 3.4 (3H,
CO2Me). 13C NMR: δ 297.9 (m, RuC), 164.9 (CO2), 135.5−128.2
(Ph), 91.9 (Cp), 90.6, 61.9, 52.2. 31P NMR: δ 46.2 (PPh3), −142.8
(sep, J(PF) = 708 Hz, PF6). ES-MS (m/z): 719, [Ru(CO)-
(PPh3)2Cp]+; 807, [Ru{C(OMe)CH2(CO2Me)}(PPh3)2Cp]+. IR
(KBr, cm−1): 1731 s ν(ester CO), 1264 s ν(CO), 839 vs ν(PF).
Anal. Calcd for C46H43F6O3P3Ru: C, 58.05; H, 4.55; M (cation), 952.
Found: C, 57.94; H, 4.54.
1
R = Et (3; 208 mg, 0.257 mmol, 76%). H NMR: δ 7.6−7.2 (m,
20H, Ph), 5.5 (5H, Cp), 4.1 (t, 1H, CH), 3.68 (q, 2H, CH2), 3.0 (m,
4H, PCH2), 0.9 (t, 3H, Me). 13C NMR: δ 200.5 (t, J(CP)17 Hz,
RuC), 162.8 (CO2), 134.8−127.9 (Ph), 110.5 (CH), 88.1 (Cp),
60.5 (CH2), 27.7 (t, PCH2), 14.1 (Me). 31P NMR: δ 75.9 (dppe),
−142.7 (sept, J(PF) = 708 Hz, PF6). ES-MS (m/z): 565,
[Ru(dppe)Cp]+; 593, [Ru(CO)(dppe)Cp]+; 606, [Ru(MeCN)-
(dppe)Cp]+; 663, [Ru(CCHCO2Et)(dppe)Cp]+. IR (KBr, cm−1):
1689 s ν(CO), 1613 s ν(CC), 833 vs ν(PF). Anal. Calcd for
C36H35F6O2P3Ru: C, 53.54; H, 4.37; M (cation), 808. Found: C,
53.57; H, 4.25.
1
R = Et (18; 234 mg, 0.242 mmol, 72%). H NMR: δ 7.7−6.9 (m,
30H, Ph), 4.8 (5H, Cp), 4.5 (2H, CH2), 4.2 (q, 2H, CH2), 3.4 (3H,
OMe), 1.3 (t, 3H, CH3). 13C NMR: δ 298.4 (t, J(CP) = 13 Hz, Ru
C), 164.5 (CO2), 135.6−128.2 (Ph), 91.9 (Cp), 90.7, 65.8, 62.2, 13.9.
31P NMR: δ 46.1 (PPh3), −142.8 (sep, J(PF) = 708 Hz, PF6). ES-MS
(m/z): 719, [Ru(CO)(PPh3)2Cp]+; 821, [Ru{C(OMe)-
CH2(CO2Et)}(PPh3)2Cp]+. IR (KBr, cm−1): 1725 s ν(ester C−O),
1264 s ν(CO), 839 vs ν(PF). Anal. Calcd for C47H45F6O3P3Ru: C,
58.45; H, 4.70; M (cation), 966. Found: C, 58.33; H, 4.76.
Ru{C(OMe)CH(CO2R)}(PPh3)2Cp (R = Me (19), Et (20)). Sodium
(4 mg, 0.18 mmol) was added to a solution of [Ru{C(OMe)-
CH2(CO2R)}(PPh3)2Cp]PF6 (172 mg for 19 (R = Me), 175 mg for
20 (R = Et); 0.181 mmol) in MeOH (20 mL). As the sodium slowly
dissolved, a light yellow precipitate formed. The reaction mixture was
stirred at room temperature for 15 min. The precipitate was isolated
by filtration, washed with MeOH (2 mL), dried under vacuum, and
recrystallized from CHCl2/hexane.
Ru(CCCO2R)(dppe)Cp (R = Me (21), Et (22)). Sodium (18 mg,
0.80 mmol) was added to a solution of [Ru{CCH(CO2R)}-
(dppe)Cp]PF6 (159 mg for 21 (R = Me), 162 mg for 22 (R = Et);
0.20 mmol) in PriOH (10 mL). The reaction mixture was stirred at
room temperature for 2 days, giving a light yellow precipitate. Solvent
was removed by cannula filtration, and the residue was dried under
vacuum.
1
R = Me (21; 65 mg, 0.100 mmol, 50%). H NMR: δ 7.8−7.2 (m,
t-BuOK (37 mg, 0.332 mmol) was added to a solution of [Ru{
C(OMe)CH2(CO2Me)}(PPh3)2Cp]PF6 (105 mg, 0.110 mmol) in dry
thf (30 mL). The reaction mixture immediately changed color from
light orange to red-orange. After the mixture was stirred at room
temperature for 15 min, solvent was removed under vacuum and the
residue was recrystallized from benzene/hexane, yielding yellow
crystals.
20H, Ph), 4.8 (5H, Cp), 3.4 (3H, Me), 2.8 (m, 2H, PCH2), 2.3 (m,
2H, PCH2). 13C NMR: δ 152.8 (CO2), 141.2−127.6 (m, Ph), 104.8
(Ru−C), 88.0 (C), 83.4 (Cp), 51.0 (Me), 27.9 (t, PCH2). 31P NMR: δ
85.6 (dppe). ES-MS (m/z): 565, [Ru(dppe)Cp]+; 593, [Ru(CO)-
(dppe)Cp]+; 606, [Ru(MeCN)(dppe)Cp]+; 649, [Ru(C2CO2Me)-
(dppe)CpH]+. IR (KBr, cm−1): 2039 s ν(CC), 1658 s ν(CO). Anal.
Calcd for C35H32O2P2Ru: C, 64.91; H, 4.98; M, 648. Found: C, 64.92;
H, 4.90.
R = Me (19; 95 mg, 0.117 mmol, 65%). The product was obtained
1
1
as a 7/3 isomeric mixture. H NMR: major isomer, δ 5.4 (1H, CH),
R = Et (22; 71 mg, 0.108 mmol, 54%). H NMR: δ 7.8−7.2 (m,
4.4 (5H, Cp), 3.7 (3H, CO2Me), 2.5 (3H, OMe); minor isomer, δ 5.8
(1H, CH), 4.3 (5H, Cp), 3.5 (3H, CO2Me), 3.1 (3H, OMe); common
resonances, δ 7.3−7.1 (m, 30H, Ph). 13C NMR: major isomer, δ 170.9
(CO2), 102.1 (CH), 85.8 (Cp), 58.2, 49.8; minor isomer, δ 160.8
(CO2), 103.9 (CH), 87.3 (Cp) 62.6, 52.0; common resonances, δ
222.9 (t, J(CP) = 16 Hz, Ru−C), 140.1−127.2 (Ph). 31P NMR
20H, Ph), 4.8 (5H, Cp), 3.8 (q, 2H, CH2), 2.8 (m, 2H, PCH2), 2.3 (m,
2H, PCH2), 1.1 (t, 3H, Me). 13C NMR: δ 152.7 (CO2), 141.5−127.6
(m, Ph), 105.3 (Ru−C), 83.3 (Cp), 79.6 (C), 59.7 (CH2), 27.9 (t,
PCH2), 14.5 (Me). 31P NMR: δ 85.9. ES-MS (m/z): 565,
[Ru(dppe)Cp]+; 606, [Ru(MeCN)(dppe)Cp]+; 663, [Ru(C2CO2Et)-
(dppe)Cp]+. IR (KBr, cm−1): 2050 s ν(CC), 1655 s ν(CO) cm−1.
5270
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Organometallics
Article
Table 1. Crystal Data and Refinement Details
11
13
15
16
21
22
formula
MW
C66H61F6P4Ru2·F6P.2C3H6O
1441.29
C36H37O3P2Ru·F6P C36H36O3P2Ru
C37H38O3P2Ru
693.68
C35H32O2P2Ru·CH2Cl2 C36H34O2P2Ru
825.64
679.66
732.54
661.64
cryst syst
space group
a/Å
monoclinic
C2/c
monoclinic
P21/n
orthorhombic
Pna21
orthorhombic
Pna21
triclinic
monoclinic
P21/c
P1
̅
46.357(3)
16.548(2)
11.4212(14)
18.348(2)
17.869(2)
10.5412(10)
16.1841(15)
18.276(2)
10.6795(10)
16.1890(15)
8.8398(14)
12.126(2)
16.502(3)
80.644(3)
80.180(3)
73.254(3)
1657
9.4256(7)
16.0155(11)
20.5021(14)
b/Å
11.9083(8)
24.695(2)
c/Å
α/deg
β/deg
γ/deg
V/Å3
ρc/g cm−3
107.864(1)
95.738(2)
101.760(1)
12975
1.476
8
3450
1.589
4
3049
1.481
4
3160
1.458
4
3030
1.450
4
1.468
Z
2
2θmax/deg
60
58
58
58
60
67
μ(Mo Kα)/
0.65
0.66
0.66
0.63
0.76
0.66
mm−1
Tmin/max
0.85
0.80
0.88
0.92
0.79
0.86
cryst dimens/
mm3
0.50 × 0.23 × 0.15
0.32 × 0.28 × 0.16 0.45 × 0.20 ×
0.55 × 0.40 ×
0.23
0.55 × 0.24 × 0.10
0.48 × 0.40 × 0.32
0.16
Ntot
91 596
10 650
27 906
28 867
22 965
43 203
N (Rint)
No
18 060 (0.061)
12254
8678 (0.056)
6843
7567 (0.024)
7233
7801 (0.015)
7705
9545 (0.046)
8324
11 526 (0.020)
9598
R1
0.048
0.059
0.029
0.020
0.037
0.031
wR2 (a, b)
0.14 (0.071, 13.7)
0.116 (0.098, 3.1)
0.065 (0.030, 23) 0.051 (0.026,
1.37)
0.111 (0.082, 0.18)
0.080 (0.035, 2.1)
Anal. Calcd for C36H34O2P2Ru: C, 65.35; H, 5.18; M, 662. Found: C,
65.30; H, 5.07.
performed with dmpe (1,2-bis(dimethylphosphino)ethane) in place of
dppe (1,2-bis(diphenylphosphino)ethane) used experimentally. Ex-
cellent agreement between the real and simplified systems has been
found in previous studies.60
Structure Determinations. Full spheres of diffraction data were
measured at ca. 153 K using a Bruker AXS CCD area-detector
instrument. Ntot reflections were merged to Nunique (Rint cited) after
“empirical”/multiscan absorption correction (proprietary software), all
reflections being used in the full-matrix least-squares refinements on
F2; No values with F > 4σ(F) were considered “observed”. All data
were measured using monochromatic Mo Kα radiation (λ = 0.710 73
Å). Anisotropic displacement parameter forms were refined for the
non-hydrogen atoms; hydrogen atoms were treated with a riding
Upon attaining all optimized structures, harmonic vibrational
frequency calculations at the same level of theory were subsequently
performed to ascertain whether they were local minima (zero
imaginary frequencies) or local transition state maxima (one imaginary
frequency). Wave function stability tests (Stable=Opt) were also
performed in order to ensure that there were no instabilities in the
optimized electronic wave functions. Once the characteristics of all
individual stationary points was determined and their wave function
stabilities verified, various reaction pathways (Figures 5 and 6 and
Figures S3−S5 (Supporting Information)) were explored by visually
linking specific transition-state structures to minimum structures and
confirmed using intrinsic reaction coordinate (IRC) calculations.
In order to account for the effects of solvation upon the energetics
of the reaction pathways, single-point energy corrections were
calculated by means of a polarizable continuum model (IEP-
PCM)61−63 using radii based on the united atom topological model
(RADII = UAHF). To simulate experimental conditions in ButOH,
the values for the static dielectric constant (ε = EPS), dynamic
dielectric constant (εinf = EPSINF), solvent density (ρ = DENSITY),
and solvent radius (r = RSOLV) were set to 12.47, 1.92, 0.0063
particles/Å3, and 2.70 Å, respectively. The EPS and DENSITY values
were generated from readily available data,64 while the remaining
values were not readily available and were calculated using the square
of the refractive index of ButOH for the EPSINF value65 and the
Stearn−Eyring equation for the RSOLV value.66
2
2
model. Reflection weights were (σ2(Fo ) + (aP)2 + bP)−1 (P = (Fo
+
2Fc2)/3). Neutral atom complex scattering factors were used;
computation used the SHELXL-97 program.49 Pertinent results are
given in the figures (which show non-hydrogen atoms with 50%
probability amplitude displacement ellipsoids) and in Table 1 and
Table S1 (Supporting Information).
Variata. 11·C3H6O: the two independent PF6 groups are disposed
about a crystallographic 2 axis and an inversion center, respectively.
The central C4H3 group was assigned as such from refinement
behavior and difference map evidence.
13: the ligand string was modeled as disordered over two sets of
sites from C(2) onward, site occupancies being set at 0.5 after trial
refinement. The PF6 was also modeled as disordered about the F(1)−
P−F(2) axis, component occupancies refining to 0.867(10) and
complement (minor component adp form isotropic).
15 and 16: these complexes are isomorphous, the specimens chosen
being of opposite chiralities (xabs = −0.04(2), −0.015(15),
respectively).
21: the solvent molecule was modeled with the Cl atoms disordered
over two sets of sites, occupancies refining to 0.808(8) and
complement.
Computational Methods. All calculations were carried out using
the Gaussian03 suite of programs.50 All geometry optimizations were
performed using the B3LYP51−53 density functional and the
LANL2DZ/6-31+G(d,p) compound basis set (LANL2DZ54,55 on
the ruthenium atom and the 6-31+G(d,p)56−59 basis set on the
remaining atoms), with pure d functions (5D) used throughout. In
order to minimize computational resources, all calculations were
In each of the reaction pathways presented, the relative gas-phase
Gibbs free energies of all minima and transition states are represented
by solid lines. The relative ButOH solvation-corrected Gibbs free
energies are represented by dashed lines. All relative energy values
discussed and displayed throughout the computational section of this
paper are in kJ mol−1 and were calculated at 298 K unless otherwise
specified.
5271
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Organometallics
Article
(13) Deacon, G. B.; Elliott, P. W.; Erven, A. P.; Meyer, G. Z. Anorg.
Allg. Chem. 2005, 631, 843.
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J. Organomet. Chem. 1982, 233, C1.
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Allg. Chem. 2005, 631, 843.
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Mass Spectrom. 2006, 255−256, 45. (c) O’Hair, R. A. J.; Waters, T.;
Cao, B. Angew. Chem., Int. Ed. 2007, 46, 7048.
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(21) Cifuentes, M. P.; Roxburgh, F. M.; Humphrey, M. G. J. Chem.
Educ. 1999, 76, 401.
ASSOCIATED CONTENT
* Supporting Information
■
S
Figures S1 and S2 (plots of Ru{C(OMe)CH(CO2Et)}-
(dppe)Cp (16) and Ru(CCCO2Et)(dppe)Cp (22), tables
giving selected bond parameters for 11, 13, 15, 16, 21, and 22,
text giving full details and Figures S3−S5 relating to
computational studies of three alternative pathways for the
decarboxylation reaction of propiolic acid on the Ru(dppe)Cp
center, text giving the full citation for ref 50, and CIF files
giving crystallographic data for the compounds studied by X-ray
diffraction. This material is available free of charge via the
Internet at http://pubs.acs.org. Full details of the structure
determinations (except structure factors) have also been
deposited with the Cambridge Crystallographic Data Centre
as CCDC 662444−662449. Copies of this information may be
obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K. (fax, + 44 1223 336 033; e-
mail, deposit@ccdc.cam.ac.uk; web, http://www.ccdc.cam.ac.
uk).
(22) (a) Selegue, J. P. Organometallics 1982, 1, 217. (b) Winter, R. F.;
́ ̌
Zalis, S. Coord. Chem. Rev. 2004, 248, 1543. (c) Rigaut, S.; Touchard,
D.; Dixneuf, P. H. Coord. Chem. Rev. 2004, 248, 1585.
(23) Berke, H. Angew. Chem. 1980, 92, 224; Angew. Chem., Int. Ed.
1980, 19, 225.
AUTHOR INFORMATION
Corresponding Author
*Fax: + 61 8 8303 4358. E-mail: michael.bruce@adelaide.edu.
■
(24) Perkins, G. J. Unpublished results.
(25) (a) Fischer, H.; Leroux, F.; Roth, G.; Stumpf, R. Organometallics
1996, 15, 3723. (b) Leroux, F.; Stumpf, R.; Fischer, H. Eur. J. Inorg.
Chem. 1998, 1225.
(26) Bruce, M. I.; Ellis, B. G.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 2005, 690, 1772.
au.
Notes
The authors declare no competing financial interest.
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(b) Bruce, M. I.; Swincer, A. G. Aust. J. Chem. 1980, 33, 1471.
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Organomet. Chem. 1985, 282, 383.
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Chem. Soc. 1994, 116, 8105. (b) Wakatsuki, Y. J. Organomet. Chem.
2004, 689, 4092.
ACKNOWLEDGMENTS
■
We thank Professor Brian Nicholson (University of Waikato,
Hamilton, New Zealand) for providing the mass spectra. We
acknowledge support of this work by the ARC and a generous
loan of RuCl3·nH2O from Johnson Matthey plc, Reading, U.K.
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