The Pauson-Khand reaction: A gas-phase and solution-phase examination using electrospray ionization mass spectrometry

Article abstract of DOI:10.1021/om200717r

A series of dicobalt hexacarbonyl complexes with charged alkyne ligands were prepared to enable the study of the Pauson-Khand reaction using ESI-MS. The hexacarbonyl complexes can be activated in the gas phase through removal of a CO ligand. The resulting pentacarbonyl ions react readily with alkenes, and no discrimination between alkenes was found for this step, indicating that alkene association is not rate determining in the intermolecular reaction. Solution-phase ESI-MS studies on a system set up for intramolecular reactivity revealed only the hexacarbonyl complex as a detectable intermediate, and the reaction was shown to have a large enthalpy and entropy of activation, consistent with ligand dissociation being rate limiting in the reaction.

Full text of DOI:10.1021/om200717r

ARTICLE
pubs.acs.org/Organometallics
The Pauson-Khand Reaction: A Gas-Phase and Solution-Phase
Examination Using Electrospray Ionization Mass Spectrometry
Matthew A. Henderson,† Jingwei Luo,† Allen Oliver,‡ and J. Scott McIndoe*,†
†Department of Chemistry, University of Victoria, P.O. Box 3065, Victoria, British Columbia V8W 3V6, Canada
‡Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame,
Indiana 46556-5670, United States
S Supporting Information
b
ABSTRACT: A series of dicobalt hexacarbonyl complexes with charged alkyne ligands
were prepared to enable the study of the PausonÀKhand reaction using ESI-MS. The
hexacarbonyl complexes can be activated in the gas phase through removal of a CO
ligand. The resulting pentacarbonyl ions react readily with alkenes, and no discrimina-
tion between alkenes was found for this step, indicating that alkene association is not
rate determining in the intermolecular reaction. Solution-phase ESI-MS studies on a
system set up for intramolecular reactivity revealed only the hexacarbonyl complex as a
detectable intermediate, and the reaction was shown to have a large enthalpy and
entropy of activation, consistent with ligand dissociation being rate limiting in the
reaction.
’ INTRODUCTION
rapidly.24 Efforts have been expended to trap or detect later
intermediates.25 Evans and co-workers were able to crystallize a
pentacarbonyldicobalt enyne complex with an (intramolecular)
alkene filling the sixth coordination site,26 but the subsequent
insertion reaction failed. Another study employed a chiral
cyclopropene complex in an intermolecular reaction with a
Co2(CO)6(alkyne) complex and trapped an inserted byproduct
in which the cyclopropene ring had opened.27 It seems when the
alkene binds with a favorable orientation, alkene insertion follows
along with CO insertion and subsequent reductive elimination of
the product.28 When the alkene binds in an unfavorable geome-
try, alkene insertion follows because this reaction is not depen-
dent on the stereochemistry of the alkene, but subsequent CO
insertion is prevented, indicating that stereospecificity is dictated
by this reaction. In order to satisfy the valencies of both cobalt
atoms, the cyclopropene ring opens for anionic coordination of
the third carbon atom. Another study with evidence of penta-
carbonyl complexes employed alkynes with donor atoms such as
sulfur, which displace one CO ligand and trap the coordination
site.29,30
The Pauson-Khand reaction was discovered in 1971 during
investigations of the reaction of Co2(CO)8 with various simple
compounds.1,2 Under a high pressure of CO, an alkene, an alkyne,
and CO were observed to combine in a [2 + 2 + 1] cycloaddition
reaction to generate a cyclopentenone ring (eq 1).3 The reaction
has since found applications in natural product synthesis, thanks to
high stereoselective control and good yields.4,5
The reaction was initially stoichiometric, yields were generally
low, and high pressures of CO and extended reaction times were
required.6,7 Activators that allow less forcing conditions have since
been introduced, including amine oxides, cyclohexylamine,8 sulfides,9
phosphine oxides,10 and even water.11 Catalytic and intramolecular
variants are known,12 and other complexes have shown reac-
tivity, including Ru3(CO)12,13 several Rh-containing complexes,14,15
MoCp2(CO)4,16 W(CO)5(THF),17 ZrCp2Cl2,18 and Fe(CO)5.19,20
The reaction has been performed in ionic liquids, enabling the
recycling of the catalyst.21
Although the PausonÀKhand reaction has been around for
several decades, there is just one detailed kinetic study, employ-
ing (trimethylsilyl)ethyne and norbornadiene (NBD).31 The
authors used reaction progress kinetic analysis32 to determine
the rate (=k[Co2(CO)8]1.3[NBD]0.3À1.2/[CO]1.9), and two
important points are immediately apparent. First of all, the
alkyne does not appear in the rate equation at all. This means
Magnus and co-workers proposed a stoichiometric mechan-
ism based on their observations of the unique stereospecificity
characteristic of the cyclization.22 The related catalytic mechan-
ism (Scheme 1) was proposed in 1990.23
Calculations on the reaction profile show a large energy barrier
for the formation of C, with subsequent reactions occurring
Received: August 2, 2011
Published: September 25, 2011
r
2011 American Chemical Society
5471
dx.doi.org/10.1021/om200717r Organometallics 2011, 30, 5471–5479
|

Organometallics
ARTICLE
Scheme 1. Proposed Catalytic Cycle for the Intermolecular
PausonÀKhand Reaction
Scheme 2. From Secondary Amine, through Dicobalt
Hexacarbonyl Complex, to Cyclopentenone product
Figure 2. Single-crystal X-ray structure of the cationic part of
[Co2(CO)6(1)][BPh4]. The tetraphenylborate anion is not shown for the
sake of clarity. Key bond lengths (Å): Co1ÀCo2, 2.461; C7ÀC8, 1.334;
C8ÀC9, 1.488; 1.311 ( 0.01 Å; CoÀC, 1.96 ( 0.01; CÀO, 1.13 ( 0.01;
CoÀCO, 1.81 ( 0.02; CÀN, 1.52 ( 0.02. Key bond angles (deg):
C6ÀC7ÀC8, 146.2; CoÀCoÀC, 51 ( 1; CoÀCÀCo, 77.5 ( 0.3.
Figure 1. Functionalized pyrrolidinium and piperidinium salts. XÀ
=
BrÀ, PF6À, BPh4À, Tf2NÀ.
that the alkyne is not involved in the rate-determining step, and
higher concentrations of alkyne have no effect on the rate of
the reaction. Second, added carbon monoxide decreases the
reaction rate.
one CO ligand. In this paper, we used approach f and prepared
pyrrolidinium and piperidinium salts with an alkyne and/or
alkene functionality (Figure 1).44
We, and numerous other research groups, are interested in
exploiting the unusual speed and sensitivity of ESI-MS to analyze
catalytic reactions,33 but the technique can analyze only ions
preformed in solution. With many catalysts being neutral metal
complexes,34 one of the following is required: (a) loss (or gain) of
an anionic ligand such as XÀ;35 (b) oxidation of electron-rich
metals;36 (c) association with a charged species such as H+,37
Na+,38 or Ag+;39 (d) deprotonation of an acidiccompound;40 (e) a
charged ancillary ligand, most often a phosphine;41 (f) a charged
substrate that imparts its charge to the metal to which it is bound.42
The PausonÀKhand reaction has been studied previously by
ESI-MS, using the bis(diphenylphosphino)methane (dppm)
ligand and phenylacetylene to make Co2(CO)4(DPPM)(μ2-
HC2C6H5).43 The methylene of dppm is sufficiently acidic under
ESI conditions that it deprotonates to provide an [M À H]À
anionic complex that could be characterized in the negative-ion
mode; therefore, this study was an example of approach d.38 The
[Co2(CO)4(DPPM)(μ2-HC2C6H5) À H]À ion was subjected
to collisional activation with norbornene gas in the collision cell,
and coordination of one alkene moiety was observed after loss of
These salts were prepared in good yield starting from secondary
or tertiary amines, and all reacted readily with Co2(CO)8 in
dichloromethane at room temperature to form the corresponding
Co2(CO)6(μ-alkyne) complex. The synthetic strategy is exempli-
fied in Scheme 2 for the preparation of [Co2(CO)6(2)][PF6] and,
ultimately, the cyclopentenone product [2 + CO][PF6].
The reactivities of 1À4 were examined in different ways and
will be dealt with separately.
’ RESULTS AND DISCUSSION
Charged Alkyne Complexes. 1+ has a single alkyne functional
group. As the hexafluorophosphate or tetraphenylborate salt, it
reacted smoothly with Co2(CO)8 to form [Co2(CO)6(1)][X] -
(X = PF6, BPh4), and a single-crystal X-ray structure was obtained
for [Co2(CO)6(1)][BPh4] (Figure 2).
Having no additional alkene or alkyne functionality,
[Co2(CO)6(1)]+ can undergo the PausonÀKhand reaction
intermolecularly only. We first examined its gas-phase behavior by
5472
dx.doi.org/10.1021/om200717r |Organometallics 2011, 30, 5471–5479

Organometallics
ARTICLE
Figure 3. Gas-phase reactions of [Co2(CO)6(1)]+ with three different alkenes at a cone voltage of 20 V. In each case, one CO ligand is removed and the
alkene adds to [Co2(CO)5(1)]+. The alkene does not add to the fully saturated ion.
EDESI-MS45 (see the Supporting Information) to obtain a baseline
sense of its reactivity: i.e. how it fragmented under collision-induced
dissociation (CID) and what ligands were removed most easily. Loss
of six carbon monoxide ligands starts at a relatively low energy (10 V),
and all six ligands are gone at approximately 35 V. Free 1+ also begins
to appear as a fragment at relatively low voltages, below 25 V. The
complexity observed at high energy is the result of a multitude of
different fragmentation processes: the CoÀCo bond can break to
make a [Co(CO)x(1)]+ complex; NÀC bonds can also break to give
the methyl pyrrolidinium ion or [Cox(CO)yC3H3]+ ions; CÀH
activation of the pyrrolidinium ring is also apparent. However, the
high-energy regime is less interesting than what happens at low
energies, as the solution reactivity is most likely to mimic the latter.
The facile and selective removal of a single CO ligand allowed gas-
phase reactions46 to be conducted, by introducing a volatile alkene
(1-hexene, 2,5-dihydrofuran, and cyclopentene) into the source while
energizing the ions.
Figure 4. Single-crystal X-ray structure of [Co2(CO)6(3)][PF6]. Key
bond lengths (Å): Co1ÀCo2, 2.473; C6ÀC7, 1.487; C7ÀC8, 1.336;
C10ÀC11, 1.311; CoÀC, 1.96 ( 0.01; CÀO, 1.14 ( 0.01; CoÀCO,
1.82 ( 0.01; CÀN, 1.52 ( 0.01; PÀF, 1.60 ( 0.02. Key bond angles
(deg): C6ÀC7ÀC8, 145.14; C1ÀN1ÀC5, 109.74; C9ÀC10ÀC11,
121.05; CoÀCÀCo, 78.2 ( 0.2; CoÀCoÀC, 50.8 ( 0.2.
Strained alkenes (such as cyclopentene) are known to react
preferentially in the PausonÀKhand reaction, and this has been
attributed to a lower energy LUMO.25 Back-donation from the
metal d orbitals into the alkene LUMO is a critical aspect of
metallacycle formation (which is also the alkene insertion
reaction). Those alkenes with more accessible LUMOs were
more reactive. Estimates of reactivity can be made by considering
the CdCÀC bond angles. Cyclohexene, with an angle of 128°, is
sluggish to react, but both norbornene (107°) and cyclopentene
(112°) are more reactive.16c Alkenes activated by electron-with-
drawing groups also show good reactivity.47
A qualitative comparison of the reactivity of the cyclopentene
system with both 1-hexene (an unstrained alkene) and 2,5-
dihydrofuran (a strained and electronically activated alkene) was
performed. [Co2(CO)6(1)]+ was sprayed into the source con-
ventionally, while the alkene was entrained into the nitrogen
desolvation gas. Raising the cone voltage (a means of collisionally
activating ions in the source) to 20 V caused loss of one CO ligand,
and gas-phase alkene coordination was observed to take place
(Figure 3). No dramatic differences in alkene reactivity were
observed, even taking into account the different gas-phase con-
centrations of alkene (which depend on the boiling points; see the
Supporting Information). We might expect the reactivities of these
alkenes to be similar, given that alkene coordination is indepen-
dent of the subsequent insertion reaction. As soon as a CO ligand
dissociates, alkene coordination is likely to occur quickly, regard-
less of strain or electronic effects. It is the subsequent insertion
reaction that depends on strain or electronic activation.
The product of the gas phase reaction, [Co2(CO)5(1)(alkene)]+,
is set up for the PausonÀKhand reaction, having alkyne, alkene, and
CO all precoordinated to cobalt. However, MS/MS studies on
[Co2(CO)5(1)(alkene)]+ invariably regenerated [Co2(CO)5(1)]+
(i.e., loss of alkene) as the first fragment (see the Supporting
Information). Given that alkenes bind more weakly than CO to
low-oxidation-state metals and the insertion is trapped with additional
CO, the fact that we were unable to see a complete gas-phase
PausonÀKhand transformation is unsurprising.
However, this experimental gas-phase result differs from
Gimbert’s calculations on the equivalent ion (C in Scheme 2),43
which predicted that it had already undergone the insertion
reaction to form D. We see no evidence of the insertion reaction
having happened, because the first fragmentation of the pre-
cursor ion [Co2(CO)5(1)(alkene)]+ was alkene loss. Had the
insertion step already occurred, CID would have caused simple
CO dissociation instead, because the insertion step is effectively
irreversible.24 Therefore, while gas-phase studies show excellent
evidence for the identity of intermediate C, experimental evi-
dence for intermediate D is still lacking.
Charged Enyne Complexes. Constructing a charged sub-
strate with both alkene and alkyne functionality was achieved
according to Scheme 2. 3 PF6 reacted smoothly with Co2(CO)8
3
5473
dx.doi.org/10.1021/om200717r |Organometallics 2011, 30, 5471–5479

Organometallics
ARTICLE
(PEEK chromatography tubing of nominal inner diameter 127 μm),
and online dilution can be used to improve spray quality and/or
quench the reaction. Overpressures of 1À5 psi are typically used to
achieve the desired flow rate (about 10 μL minÀ1), and dense data
may be obtained on the abundance of all charged species in solution,
including low-abundance intermediates.49 For this experiment, we
used CO as the pressurizing gas. Because the reaction produces
Co4(CO)12 as a byproduct, and this cluster is rather insoluble, we
found crystallization of this compound caused the ion current to drop
steadily over the course of the reaction and eventually the PEEK
tubing would block completely. Spectra were normalized to the total
ion current (TIC) to correct for these spray irregularities.
Co2(CO)8 was added to a chlorobenzene solution of [3][Tf2N]
under a CO atmosphere and the reaction monitored for 75 min
using ESI-MS (Figure 5). The appearance of only one inter-
mediate was observed, the anticipated [Co2(CO)6(3)]+.
It in turn was consumed, with the appearance of the product,
[3 + CO]+. No intermediates were observed in the reaction
(i.e., species with more or less than six CO ligands), again consistent
with the ligand dissociation step being rate determining.
Figure 5. Abundance vs time data for [3]+ (starting material),
[Co2(CO)6(3)]+ (intermediate), and [3 + CO]+ (product). Data were
collected using positive ion ESI-MS in chlorobenzene, pressurized (with
CO gas) sample infusion with online dilution with acetone, and a
Schlenk flask saturated with CO before data collection began. Data have
been normalized to the total ion current. The scan time was 10 s per
spectrum. Approximately 20% of the total ion current at the end of the
reaction consisted of numerous low-abundance byproducts, none of
which exceeded 5% of the total.
The reaction was repeated at different temperatures, this time
starting with the preprepared complex [Co2(CO)6(3)][Tf2N],
which was injected directly into a hot, CO-saturated solution.
The reaction was conducted at 65, 70, and 75 °C. Speciation was
complicated due to the appearance of aggregates and solvent
adducts, but these signals could be combined in a rational way
(see Supporting Information) to obtain traces of reaction pro-
gress (Figure 6). The rate increases with temperature; the first
20% of the reaction is slow but after that point each trace follows
(pseudo) first-order kinetics. Plotting the natural log of the
concentration of [Co2(CO)6(3)]+ vs time for each experiment
produced a plot which was initially curved but that had a straight-
line region in the middle (covering conversions from 25% to at
least 80%; reactions were stopped when the total ion current
dropped too low to obtain good data), with kobs = 0.050, 0.099,
and 0.245 sÀ1 at 65, 70, and 75 °C, respectively.
to form [Co2(CO)6(3)][PF6] (analogous reactivity was ob-
served for 2 PF6), and the X-ray crystal structure is shown in
3
Figure 4. Bond lengths and angles are very similar to those of
[Co2(CO)6(1)][BPh4]. The CdC double bond at 1.311 Å is
slightly shorter than the bound alkyne at 1.336 Å, indicating the
degree to which the CtC triple bond is weakened by coordina-
tion to the two cobalt centers. The double bond is oriented well
away from the metals, consistent with the fact that they are
coordinatively saturated. It is not, however, difficult to imagine a
conformation in which the alkene is capable of bonding directly
to cobalt, provided a coordination site is made available through
dissociation of a CO ligand.
The enthalpy and entropy of activation were determined using
an Eyring plot (inset, Figure 6), which provided the activation
parameters: ΔHq = 150 kJ molÀ1 and ΔSq= 110 J molÀ1 KÀ1
.
These relatively large values are consistent with the rate-determin-
ing step being ligand dissociation. They compare with values for
ΔHq = 123.6 ( 11.0 kJ molÀ1 and ΔSq = 72.4 ( 37.3 J molÀ1 KÀ1
for the rate of reaction of Rh4(CO)12 with an alkyne, another
reaction thought to be limited by dissociation of a CO ligand.50
Bis-Alkynes. The reactivity of bis-alkyne compounds is less
explored than that for enynes;51,52 some reports of bis-alkyne
complexes employing Co2(CO)8 are in the bis-cyclopentenone
reaction within the same organic moiety (i.e., both alkynes
undergo separate intermolecular PausonÀKhand reactions with-
out any intramolecular interference from the other alkyne).53,54
In this system, however, the alkyne groups are positioned such
that they may react with each other as an alkene and alkyne, as
two alkenes, or as two alkynes.
Gas-phase reactions of [Co2(CO)6(2)]+ and [Co2(CO)6(3)]+
were investigated, and as expected, the complexes readily lost CO
under CID conditions, analogous to the casefor [Co2(CO)6(1)]+.
Evidence that intramolecular alkene coordination occurred was
obtained indirectly, because this transformation does not involve a
change in m/z value and is hence invisible to mass spectrometric
methods. Cyclopentene was introduced into the source and did
not react at all with [Co2(CO)5(2)]+ or [Co2(CO)5(3)]+, imply-
ing that the vacant coordination site generated by loss of CO was
occupied by the alkene (see the Supporting Information). CID of
the cations in the gas phase did not produce any product ions
representing the desired product, [L + CO]+.
However, because all the components of the PausonÀKhand
reaction (CO, alkyne, alkene) are present on [Co2(CO)6(3)]+,
the opportunity existed for a simple solution-phase analysis of the
Unlike the case for compounds [Co2(CO)6(L)][PF6]
(L = 1À3), it was not possible to isolate the hexacarbonyl
complex [Co2(CO)6(4)][PF6] in pure form, because even at
room temperature the second alkyne moiety was sufficiently
reactive to displace a third CO ligand to form a pentacarbo-
nyl complex (Figure 7).
The occurrence of the pentacarbonyl complex [Co2(CO)5-
(4)][PF6] in abundance was encouraging, as it represented the
possible isolation of an intermediate complex whereby a cyclic
production of [3 CO]+ from [3]+. We have recently developed
3
tools for the constant monitoring of reactions under “real”
conditions using ESI-MS: namely, pressurized sample infusion
(PSI).48 This approach to reaction monitoring essentially in-
volves a cannula transfer from a solution in a Schlenk flask
into the mass spectrometer via narrow-diameter tubing
5474
dx.doi.org/10.1021/om200717r |Organometallics 2011, 30, 5471–5479

Organometallics
ARTICLE
Figure 6. Intensity vs time data for [Co2(CO)6(3)]+ (starting material) and [3 + CO]+ (product), collected at three different temperatures. Inset:
Eyring plot for the three different temperatures.
Figure 7. ESI-MS of the reaction between [4][PF6] and Co2(CO)8 in
refluxing dichloromethane. After 4 h, [Co2(CO)6(4)]+ had almost
completely disappeared, to be replaced by [Co2(CO)5(4)]+.
Figure 8. Single-crystal X-ray structure of the cationic part of
[(Co2(CO)6)2(4)][PF6]. The hexafluorophosphate anion is not shown
product could be reductively eliminated with the same regiochem-
for the sake of clarity. Key bond lengths (Å): Co1ÀCo2, 2.456; Co3ÀCo4,
2.463; C7ÀC8, 1.328; C10ÀC11, 1.336; C9ÀC10, 1.488; C6ÀC7, 1.480;
1.311 ( 0.01 Å; CoÀC, 1.96 ( 0.01; CÀO, 1.13 ( 0.01; CoÀCO, 1.81 (
0.02; CÀN, 1.52 ( 0.02. Key bond angles (deg): C9ÀC10ÀC11, 146.1;
C6ÀC7ÀC8, 147.0; CoÀCoÀC, 51 ( 1; CoÀCÀCo, 77.5 ( 0.3.
istry of an intramolecular enyne system.55 Unfortunately, attempts
to crystallize [Co2(CO)5(4)][PF6] produced only crystals of bis-
(hexacarbonyldicobalt) bis(propargyl)piperidinium hexafluoropho-
sphate, [{Co2(CO)6}2(4)][PF6] (X-ray structure in Figure 8), a
minor product observed in the ESI-MS and a possible decomposi-
tion product of [Co2(CO)5(4)][PF6]. Along with these crystals, a
brown powder formed at the bottom of each tube, consistent with
an accompanying decomposition product.
indicative of a bridging carbonyl ligand37 and the 2105 cmÀ1 band was
shifted to 2099 cmÀ1
.
The UVÀvis spectra of complexes [Co2(CO)6(L)][PF6]
(L = 1+À3+) are quite similar (Table 2 and Figure 9).
[Co2(CO)5(4)][PF6] was subtly different, having a blue shift
of the peak in the visible region and lacking a peak in the region of
360 nm, supporting the notion that the coordination sphere of
this complex is distinctly different from those of the other three
complexes.
As was the case for [Co2(CO)6(L)][PF6] (L = 2, 3), CID in
the gas phase did not lead to production of [4 + CO]+ from
[Co2(CO)6(4)]+ (see the Supporting Information).
Analogous neutral compounds of bis-alkynyl amines have
been reported.56 Bond lengths and angles in this compound
are very similar to those observed in the other two structures and
are between the two cobalt clusters in this one.
In the absence of crystallographic evidence, we examined the
pentacarbonyl complex [Co2(CO)5(L)][PF6] in solution using
other spectroscopic techniques and compared the data to those for
the other complexes. The IR spectra of the metal complexes (Table 1)
correlated well with literature data.37 For complexes [Co2(CO)6(L)]
[PF6] (L = 1+À3+) four bands were visible in the terminal bonding
region. As reported for neutral enyne complexes,57 the alkene group
does not displace a CO ligand and occupy a coordination site on the
metal complex. The spectrum of [Co2(CO)5(4)][PF6] was slightly
different, as it had an additional broad absorption at 1983 cmÀ1
’ CONCLUSIONS
Our investigations support the notion that the rate-determin-
ing step of the intramolecular PausonÀKhand reaction is CO
5475
dx.doi.org/10.1021/om200717r |Organometallics 2011, 30, 5471–5479

Organometallics
ARTICLE
Table 1. IR Frequencies (cmÀ1 a
)
complex
terminal CO
bridging CO
[Co2(CO)6(1)][PF6]
2105 (st), 2067 (vs), 2045 (vs), 2027 (sh)
2105(st), 2067 (vs), 2045 (vs), 2034 (sh)
2105 (st), 2066 (vs), 2045 (vs), 2033 (sh)
2099 (st), 2066 (m), 2044 (vs), 2027 (sh)
[Co2(CO)6(2)][PF6]
[Co2(CO)6(3)][PF6]
[Co2(CO)5(4)][PF6]
a All spectra were run in dichloromethane.
1983 (st, broad)
Table 2. UVÀVis Peaks for Cobalt Complexes
complex
peak, nm
[Co2(CO)6(1)][PF6]
[Co2(CO)6(2)][PF6]
[Co2(CO)6(3)][PF6]
[Co2(CO)5(4)][PF6]
356, 364, 421
356, 365, 421
356, 364, 421
405
dissociation. Gas-phase studies on the early steps in the reaction
scheme showed that CO dissociation and alkene coordination
can both be readily achieved and that the coordination of alkene
is insensitive to the nature of the alkene, suggesting that the effect
of the nature of the alkene operates on some later step in the
reaction. Gas-phase investigation of an complex set up for
intramolecular reactivity showed circumstantial evidence for
alkene coordination, in that complexes activated by CO dissocia-
tion were unreactive toward intermolecular alkene association.
The reaction could not be driven to completion in the gas phase,
probably due to the absence of CO required to trap the inserted
intermediates and hence promote further steps. Turning to the
solution phase, the intramolecular reaction could be monitored
using PSI-ESI-MS and no intermediates apart from the dicobalt
hexacarbonyl ion were observed, suggesting that the later steps in
the reaction are relatively fast. Positive values of ΔHq and ΔSq
suggest that the rate-determining step is ligand dissociation,
consistent with early loss of CO that allows the alkene to
coordinate and the rest of the reaction to proceed.
Figure 9. UV/vis spectra of [Co2(CO)6(L)][PF6] (L = 1À3) and
[Co2(CO)5(4)][PF6] (from top to bottom).
0.5 V; source temperature, 80 °C; desolvation temperature, 150 °C;
cone gas flow, 100 L/h; desolvation gas flow, 100 L/h; collision voltage,
2 V (for MS experiments); collision voltage, 2À40 V (for MS/MS
experiments); low and high mass resolution, 10.0; MCP voltage, 2700 V.
Gas-phase ionÀmolecule reactions were carried out by a published
method.46
1 Br. Methylpyrrolidine (3.84 g, 45.1 mmol) and diethyl ether (30 mL)
3
were cooled to 0 °C in a 100 mL round-bottom flask. Propargyl bromide
(5 mL of an 80% solution in toluene, 6.90 g, 57.5 mmol) in ether (25 mL)
was added dropwise. The mixture was subsequently warmed to room
temperature and stirred overnight. The solvent was then evaporated and the
white product dried under vacuum for 24 h (8.97 g, 44.0 mmol, 97%). Mp:
62À68 °C. 1H NMR (CD3OD): δ (ppm) 4.50 (d, 2H, CH2-d); 3.75 (m,
4H, CH2-b); 3.52 (t, 1H, CH-f); 3.29 (s, 3H, CH3-a); 2.31 (m, 4H, CH2-c).
13C NMR (CD3OD): δ (ppm) 81.96 (e); 73.33 (f); 65.25 (b); 54.50 (d);
50.44 (a); 23.20 (c).
’ EXPERIMENTAL SECTION
All solvents were dispensed from an MBRAUN solvent purification
system and used within minutes. Inert-atmosphere techniques were used
for all syntheses involving Co2(CO)8. Reagents were purchased from
Aldrich and used without subsequent purification. UVÀvis spectra were
collected on an Agilent 8453 UVÀvis spectrometer, and IR spectra were
collected on a Perkin-Elmer FT-IR spectrum 1000 instrument.
For the X-ray diffraction studies, arbitrary spheres of data were
collected for the samples on a Bruker APEX-II diffractometer using a
combination of ω and j scans of 0.5°.58 Data were corrected for
absorption and polarization effects and analyzed for space group
determination.59 The structures were solved by direct methods and
expanded routinely.60 The models were refined by full-matrix least-
squares analysis of F2 against all reflections. All non-hydrogen atoms
were refined with anisotropic thermal displacement parameters. Unless
otherwise noted, hydrogen atoms were included in calculated positions.
Thermal parameters for the hydrogens were tied to the isotropic thermal
parameter of the atom to which they are bonded (1.5Â for methyl, 1.2Â
for all others). Crystal structure depictions were created using Ortep-361
and Povray.62
1 PF6. An aqueous solution (20 mL of H2O) of 1 Br (1.413 g, 6.96
3
3
mmol) and sodium hexafluorophosphate (1.19 g, 7.08 mmol) was
prepared. The mixture was heated to facilitate dissolution and then
cooled to room temperature. The white crystals were filtered with a cold
water wash and dried overnight under vacuum (0.62 g, 2.30 mmol, 33%).
Mp: 146À147 °C. 1H NMR (CD3OD): δ (ppm) 4.33 (d, 2H, CH2-d);
3.67 (m, 4H, CH2-b); 3.45 (t, 1H, CH-f); 3.22 (s, 3H, CH3-a); 2.28 (m,
4H, CH2-c). 13C NMR (CD3OD): δ (ppm) 81.78 (e); 73.05 (f); 65.15
(b); 54.27 (d); 50.24 (a); 23.08 (c). 31P NMR (CD3OD): δ (ppm)
À143.22 (septet for PF6À).
1 BPh4. A 5 mL aqueous solution of 1 Br (0.102 g, 0.502 mmol)
3
3
was added to a 5 mL aqueous solution of sodium tetraphenylborate
(0.161 g, 0.470 mmol) and stirred for 15 min. A white product formed
immediately. An extra 5 mL of water was added to enhance stirring. The
product (0.183 g, 0.413 mmol, 87.8%) was collected by vacuum filtration
with a wash of water. Dec pt: >200 °C. 1H NMR (CD3CN): δ (ppm)
7.31 (m, 8H, CH-i); 7.05 (t, 8H, CH-h); 6.87 (t, 4H, CH-j); 4.11 (d, 2H,
CH2-d); 3.53 (m, 4H, CH2-b); 3.14 (t, 1H, CH-f); 3.14 (s, 3H, CH3-a);
2.14 (m, 4H, CH2-c). 13C NMR (CD3CN): δ (ppm) 165.79 (g), 136.74
All mass spectra were collected by using a Micromass Q-ToF micro
mass spectrometer in positive ion mode using pneumatically assisted
electrospray ionization: capillary voltage, 2900 V; extraction voltage,
5476
dx.doi.org/10.1021/om200717r |Organometallics 2011, 30, 5471–5479

Organometallics
ARTICLE
(i), 126.60 (h), 122.77 (j), 81.47 (f), 72.63 (e), 65.09 (b), 54.29 (d),
50.58 (a), 22.77 (c).
Propargyl Piperidine. Piperidine (7.5 mL, 6.5 g, 75.9 mmol) in
tetrahydrofuran (50 mL) was added to a slurry of sodium hydride (2.05 g,
85.5 mmol) in tetrahydrofuran (75 mL) over 1 h. The mixture was
stirred at room temperature for another 1 h. A mixture of propargyl
bromide (9.93 g of an 80% toluene solution, 66.2 mmol) in tetrahy-
drofuran was then added dropwise over 1 h, and the mixture was stirred
overnight. The mixture was quenched with a sodium chloride solution
(1 mol LÀ1) and the organic phase separated. The aqueous phase was
then extracted with ethyl acetate (3 Â 50 mL) followed by tetrahy-
drofuran (2 Â 50 mL) and combined with the original organic fraction.
After drying with anhydrous magnesium sulfate and filtering with a THF
wash, the solvent was removed on a rotary evaporator and the orange
product distilled to give a light yellow liquid (5.41 g, 43.9 mmol, 66%).
1H NMR (CDCl3): δ (ppm) 4.24 (t, 1H); 3.16 (d, 2H); 2.39 (m, 4H);
1.51 (m, 4H); 1.34 (m, 2H). 13C NMR (CDCl3): δ (ppm) 72.80, 68.36,
52.98, 47.43, 25.73, 23.74.
Allyl Pyrrolidine.63. Allyl bromide (6 mL, 8.4 g, 69.4 mmol) in
diethyl ether (20 mL) was added dropwise to pyrrolidine (5.1 g, 71.7
mmol) in ether (20 mL) at 0 °C over 30 min. The solution was then
warmed to room temperature and stirred overnight, followed by a
potassium hydroxide extraction (3 Â 25 mL of a 3 M solution). The
subsequent aqueous phase was then extracted with dichloromethane and
all organic portions were combined, dried with anhydrous magnesium
sulfate, and filtered. The solvent was removed on the rotary evaporator,
and the orange liquid was distilled (the fraction that boiled at 120 °C was
retained) to give a colorless product (3.5 g, 31.5 mmol, 45%). 1H NMR
(CDCl3): δ (ppm) 5.88 (m, 1H); 5.21 (m, 2H); 3.02 (d, 2H); 2.43 (m,
4H); 1.71 (m, 4H). 13C NMR (CDCl3): δ (ppm) 136.23, 116.53, 59.22,
53.96, 23.40.
2 Br. Allyl pyrrolidine (0.667 g, 6.00 mmol) and propargyl bromide
3
4 Br. Propargyl piperidine (1.00 g, 8.1 mmol) was added to
(0.80 mL, 1.07 g, 7.19 mmol) were stirred in ether (30 mL) overnight.
The white product was filtered and collected (0.453 g, 1.86 mmol, 31%).
Mp: 140À146 °C. 1H NMR (CD3OD): δ (ppm) 6.11 (m, 1H, CH-b);
5.76 (m, 2H, CH2-a); 4.30 (s, 2H, CH2-f); 4.16 (d, 2H, CH2-c); 3.68 (m,
4H, CH2-d); 3.49 (t, 1H, CH-h); 2.28 (m, 4H, CH2-e). 13C NMR
(CD3OD): δ (ppm) 129.40 (a); 126.55 (b); 82.03 (h); 73.04 (g); 64.55
(c); 63.10 (d); 51.25 (f); 23.22 (e).
3
propargyl bromide (1.38 g of an 80% toluene solution, 9.2 mmol) along
with toluene (30 mL), and the mixture was stirred at room temperature
for 24 h. The solution was then refluxed for 1 h, and the brown product
was vacuum filtered with a toluene wash and dried under vacuum
overnight (0.839 g, 3.5 mmol, 43%). Mp: 200 °C dec. 1H NMR
(CD3OD): δ (ppm) 2.73 (d, 4H, CH2-c); 1.91 (t, 4H, CH2-d); 1.57
(t, 2H, CH-a); 0.23 (m, 4H, CH2-e); 0.02 (m, 2H, CH2-f). 13C NMR
(CD3CN): δ (ppm) 83.00 (c); 71.09 (a); 59.45 (d); 51.01 (b); 21.19
(f); 20.29 (e).
2 PF6. An aqueous solution of 2 Br (0.265 g, 1.16 mmol, 20 mL of
3
3
H2O) was added to an aqueous solution of sodium hexafluorophosphate
(0.208 g, 1.24 mmol, 10 mL of H2O). The mixture was reduced to a
volume of 10 mL and left overnight in the refrigerator at 5 °C. The white
crystals were filtered with a water wash, and the filtrate was then reduced
again to a smaller volume and transferred back into the refrigerator for
further crystallization. The combined yield of both aliquots was 0.092 g,
0.312 mmol, 27%. Mp: 78À80 °C. 1H NMR (CD3OD): δ (ppm) 5.96
(m, 1H, CH-b); 5.70 (m, 2H, CH2-a); 4.15 (d, 2H, CH2-f); 4.01 (d, 2H,
CH2-c); 3.55 (m, 4H, CH2-d); 3.36 (t, 1H, CH-h); 2.16 (m, 4H,
CH2-e). 13C NMR (CD3OD): δ (ppm) 129.37 (a); 126.43 (b);
81.96 (h); 72.95 (g); 64.53 (c); 63.03 (d); 51.10 (f); 23.13 (e). 31P NMR
(CD3OD): δ (ppm) À143.23 (septet).
4 PF6. This complex was prepared as for 1 PF6 with the following
3
3
amounts of reagents and solvents: 4 Br (0.166 g, 0.689 mmol), sodium
3
hexafluorophosphate (0.18 g, 1.07 mmol), water (30 mL). Isolated
product: 0.0799 g, 0.26 mmol, 38%. Mp: 160À161 °C. 1H NMR
(CD3OD): δ (ppm) 4.46 (s, 4H, CH2-c); 3.62 (t, 4H, CH2-d); 3.53
(t, 2H, CH-a); 1.97 (m, 4H, CH2-e); 1.74 (m, 2H, CH2-f). 13C NMR
(CD3OD): δ (ppm) 83.39 (c); 71.33 (a); 59.90 (d); 51.05 (b); 21.81
(f); 20.68 (e). 31P NMR (CD3OD): δ (ppm) À143.24 (septet).
4 BPh4. A 20 mL aqueous solution of 4 Br (0.37 g, 1.53 mmol) was
3
3
added to a 20 mL aqueous solution of sodium tetraphenylborate (0.60 g,
1.75 mmol) and the mixture stirred for 20 min. The white product
(0.578 g, 1.20 mmol, 78%) was vacuum filtered with a water wash. X-ray-
quality crystals were grown by the slow evaporation of an acetone
solution. Mp: 134À136 °C. 1H NMR (CD3CN): δ (ppm) 7.19 (m, 8H,
CH-i); 6.91 (t, 8H, CH-h); 6.76 (t, 4 h, CH-j); 4.15 (d, 4H, CH2-c); 3.36
(t, 4H, CH2-d); 3.11 (t, 2H, CH-a); 1.86 (m, 4H, CH2-e); 1.76 (m, 2H,
CH2-f). 13C NMR (CD3CN): δ (ppm) 163.8 (g), 135.42 (i), 125.26
(h), 121.46 (j), 81.83 (a), 69.57 (b), 58.47 (d), 49.81 (c), 19.89 (f),
18.96 (e).
Allyl Piperidine. Allyl bromide (15.6 g, 128.9 mmol), piperidine
(10.5 g, 123.3 mmol), and sodium hydride (3.3 g, 145.9 mmol) were
combined as described in the literature to yield allyl piperidine (11.9 g,
95.0 mmol, 77%) after a partial dynamic vacuum distillation. 1H NMR
(CDCl3): δ (ppm) 5.82 (m, 1H); 5.05 (m, 2H); 2.89 (d, 2H); 2.30
(s, 4H); 1.52 (m, 4H); 1.37 (m, 2H). 13C NMR (CDCl3): δ (ppm)
135.5, 117.33, 62.56, 54.37, 25.86, 24.26.
3 Br. Propargyl bromide (2.42 g of an 80% solution in toluene, 16.2
3
mmol) in toluene (20 mL) was added to allyl piperidine (1.94 g, 15.5
mmol) in toluene (20 mL). The mixture was stirred at room tempera-
ture for 48 h, and the resulting white product was vacuum filtered,
followed by vacuum drying overnight. (2.47 g, 10.1 mmol, 67%). Mp:
154À156 °C. 1H NMR (CD3CN): δ (ppm) 5.99À5.70 (m, 3H, CH-a,
b); 4.43 (d, 2H, CH2-g); 4.15 (d, 2H, CH2-c); 3.53 (m, 4H, CH2-d);
3.27 (t, 1H, CH-i); 1.91 (m, 4H, CH2-e); 1.69 (m, 2H, CH2-f). 13C
NMR (CD3CN): δ (ppm) 129.88 (a); 125.01 (b); 82.68 (c); 71.77 (g);
62.33 (h); 59.23 (d); 50.38 (i); 21.39 (f); 20.31 (e).
[Co2(CO)6(1)][PF6]. Dicobalt octacarbonyl (0.207 g, 0.604 mmol)
and 1b (0.122 g, 0.45 mmol) were mixed as solids in a Schlenk flask. Dry
dichloromethane was then added (10 mL), and the mixture was stirred
at room temperature for 4 h under N2. The solvent was evacuated, and
the mixture was washed with ether (4 Â 8 mL). The red solid was then
dried under vacuum for 2 h and collected (0.068 g, 0.122 mmol, 27%).
Mp: 120 °C dec. 1H NMR (CD2Cl2): δ (ppm) 6.32 (s, 1H); 4.77, (s,
2H); 3.59 (m, 4H); 3.13 (s, 3H); 2.25 (s, 4H). 13C NMR (CD2Cl2): δ
(ppm) 75.09, 67.67, 65.03, 49.50, 22.16. 31P NMR (CD2Cl2): δ (ppm)
À143.79 (septet). IR (cmÀ1, CH2Cl2): 2105 (st), 2067 (vs), 2045 (vs),
1605 (m, broad). UVÀvis (nm): 356, 364, 421.
3 PF6. To 30 mL of water was added 3 Br (0.45 g, 1.85 mmol) and
3
3
sodium hexafluorophosphate (0.37 g, 2.20 mmol). The mixture was
stirred for 15 min, and the white product was filtered (0.216 g). The
filtrate was boiled to reduce the volume down to 15 mL and transferred to
the freezer (À10 °C) for 4 h. These crystals were then filtered (0.171 g) to
give a combined yield of 0.387 g, 1.25 mmol, 68%. Mp: 85À86 °C. 1H
NMR (CD2Cl2): δ (ppm) 5.76 (m, 3H, CH-a,b); 3.99 (d, 2H, CH2-g);
3.95 (d, 2H, CH2-c); 3.36 (m, 4H, CH2-d); 2.85 (t, 1H, CH-i); 1.86 (m,
4H, CH2-e); 1.70 (q, CH2-f). 13C NMR (CD2Cl2): δ (ppm) 131.46 (a);
122.74 (b); 82.22 (c); 70.17 (g); 62.73 (h); 59.22 (d); 49.45 (i); 20.90
(f); 20.15 (e). 31P NMR (CD2Cl2): δ (ppm) À143.82 (septet).
[Co2(CO)6(1)][BPh4]. Dicobalt octacarbonyl (1.06 g, 3.10 mmol)
was weighed out in a Schlenk flask in the glovebox and transferred to the
Schlenk line. 1. Ph4 (1.01 g, 2.26 mmol) was then added as a solid,
3
followed by dichloromethane (40 mL). The reaction mixture was stirred
at room temperature and tracked by ESI-MS. After about 4 h, the
reaction was stopped. Solvent was evaporated under vacuum, and the
remaining solid was washed successively with 10 mL portions of dry
diethyl ether until the washings were colorless. The dark product was
5477
dx.doi.org/10.1021/om200717r |Organometallics 2011, 30, 5471–5479

Organometallics
ARTICLE
dried under vacuum overnight and then collected in air (0.996 g, 1.36
mmol, 60%). X-ray-quality crystals were grown by solvent diffusion of
dichloromethane and diethyl ether at À10 °C; a thin layer of 1-butanol
was put between the two solvents to slow diffusion. This product
decomposed quickly in the solid state and was only characterized by
X-ray crystallography.
’ ASSOCIATED CONTENT
S
Supporting Information. Figures giving MS data and
b
tables and CIF files giving data for the crystal structure determi-
nations. This material is available free of charge via the Internet at
http://pubs.acs.org.
[Co2(CO)6(2)][PF6]. Dicobalt octacarbonyl (0.0917 g, 0.268 mmol)
was weighed out in a Schlenk flask in a glovebox and then transferred to
the Schlenk line, to which 2b (0.0435 g, 0.147 mmol) was added as a solid.
Dry dichloromethanewas thenadded against a stream of nitrogen, and the
mixture was stirred at room temperature for 2 h. The solvent was then
evacuated and the remaining solid was washed with dry diethyl ether
(4 Â 6 mL). The remainingsolid was thendried under vacuumfor 2 h and
collected (0.0595 g, 0.102 mmol, 69%). Mp: 80 °C dec. 1H NMR
(CD2Cl2): δ (ppm) 6.36 (s, 1H); 5.79 (m, 3H); 4.67 (s, 2H); 3.96
(d, 2H); 3.56 (m, 4H); 2.21 (m, 4H). 13C NMR (CD2Cl2): δ (ppm)
130.42, 124.09, 63.87, 62.56, 62.14, 22.35. 31P NMR (CD2Cl2): δ (ppm)
À143.83 (septet). IR (cmÀ1, CH2Cl2): 2105 (st), 2067 (vs), 2045 (vs),
2034 (shoulder). UVÀvis (nm): 356, 365, 421.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: mcindoe@uvic.ca.
’ REFERENCES
(1) Khand, I. U.; Knox, G. R.; Pauson, P. L.; Watts, W. E. Chem.
Commun. 1971, 36.
(2) Khand, I. U.; Knox, G. R.; Pauson, P. L.; Watts, W. E. J. Chem.
Soc., Perkin Trans. 1 1973, 975–977.
(3) Pauson, P. L. Tetrahedron 1985, 41, 5855–5860.
(4) Magnus, P.; Principe, L. M.; Slater, M. J. J. Org. Chem. 1987, 52,
1483–1486.
[Co2(CO)6(3)][PF6]. Dicobalt octacarbonyl (0.15 g, 0.439 mmol)
and 3b (0.087 g, 0.281 mmol) were added to a Schlenk flask as solids
against a dry nitrogen atmosphere. Dry dichloromethane (10 mL) was
then added, and the mixture was allowed to react for 2 h. The solvent was
then evaporated, and the red solid was washed with ether (3 Â 8 mL)
and then dried under vacuum for 2 h. The dark red product (0.131 g,
0.220 mmol, 78%) was collected, and X-ray-quality crystals were grown
by dichloromethane and ether solvent diffusion in the freezer, with a
small layer of 1-butanol between them. Mp: 90 °C dec. 1H NMR
(CD2Cl2): δ (ppm) 6.38 (s, 1H); 5.74 (m, 3H); 4.70 (s, 2H); 4.00 (d,
2H); 3.42 (m, 4H); 1.88 (m, 4H); 1.72 (m, 2H). 13C NMR (CD2Cl2): δ
(ppm) 130.91, 122.91, 75.25, 74.03, 62.69, 62.10, 58.86, 20.96, 20.32.
31P NMR (CD2Cl2) δ (ppm) À143.79 (septet). IR (cmÀ1, CH2Cl2):
2105 (st), 2066 (vs), 2045 (vs). UVÀvis (nm): 356, 364, 421 nm.
[Co2(CO)6(4)][PF6]. Dicobalt octacarbonyl (0.0405 g, 0.118 mmol)
and4b(0.0391 g, 0.127 mmol) were mixedassolids in a Schlenk flask. Dry
dichloromethane (8 mL) was added at 0 °C, and the mixture was stirred
for 1 hatthis temperature before beingwarmedtoroom temperature. The
solution was stirred overnight at room temperature and then refluxed for 1
h. The solvent was then evacuated, and the solid was washed once with
hexane (8 mL) and then ether (2 Â 8 mL) followed by drying under
vacuum. The red product was then collected in air (0.0523 g, 0.0926
mmol, 79%). Mp: 130°Cdec. 1H NMR (CD2Cl2): δ(ppm) 7.20 (s, 2H);
4.40 (m, 4H); 4.05 (m, 2H); 3.58 (m, 2H); 1.85 (m, 4H); 1.70 (m, 2H).
13C NMR (CD2Cl2): δ (ppm) 140.92, 129.13, 64.53, 64.23, 63.68, 28.93,
20.79, 20.24, 19.72, À0.01. 31P NMR (CD2Cl2): δ (ppm) À143.75
(septet). IR (cmÀ1, CH2Cl2): 2099 (st), 2066 (m), 2044 (vs), 2027 (s),
1983 (m, broad). UVÀvis (nm): 405.
(5) (a) Blanco-Urgoiti, J.; Anorbe, L.; Perez-Serrano, L.; Domin-
guez, G.; Perez-Castells, J. Chem. Soc. Rev. 2004, 33, 32–42. (b) Fletcher,
A. J; Christie, S. D. R. J. Chem. Soc., Perkin Trans. 1 2000, 1657–1668. (c)
Gibson, S. E.; Mainolfi, N. Angew. Chem., Int. Ed. Engl. 2005,
44, 3022–3037. (d) Green, J. R. Curr. Org. Chem. 2001, 5, 809–826.
(6) Khand, I. U.; Knox, G. R.; Pauson, P. L.; Watts, W. E.; Foreman,
M. I. J. Chem. Soc. Perkin Trans. 1 1973, 977–981.
(7) Geis, O.; Schmalz, H. G. Angew. Chem., Int. Ed. Engl. 1998, 37
(7), 911–914.
(8) Sugihara, T.; Yamada, M.; Ban, H.; Yamaguchi, M.; Kaneko, C.
Angew. Chem., Int. Ed. Engl. 1997, 36, 2801–2804.
(9) Sugihara, T.; Yamada., M.; Yamaguchi, M.; Nishizawa, M. Synlett
1999, 771–773.
(10) Billington, D. C.; Helps, I. M.; Pauson, P. L.; Thomson, W.;
Willison, D. J. Organomet. Chem. 1988, 354, 233–242.
(11) Sugihara, T.; Yamaguchi, M. Synlett 1998, 1384–1386.
(12) (a) Hanson, B. E. Comments Inorg. Chem. 2002, 23, 289–318.
(b) Wang, H.; Sawyer, J. R.; Evans, P. A.; Baik, M-.J. Angew. Chem., Int.
Ed. Engl. 2008, 47, 342–345. (c) Pagenkopf, B. L.; Livinghouse, T. J. Am.
Chem. Soc. 1996, 118, 2285–2286.
(13) Morimoto, T.; Chatani, N.; Fukumoto, Y.; Murai, S. J. Org.
Chem. 1997, 62, 3762–3765.
(14) Kobayashi, T.; Koga, Y.; Narasaka, K. J. Organomet. Chem. 2001,
624, 73–87.
(15) Jeong, N.; Ki Sung, B.; Sung Kim, J.; Bong Park, S.; Deok Seo,
S.; Young Shin, J.; Yeol In, K.; KyungChoi, Y. Pure Appl. Chem. 2002,
74, 85–91.
(16) Mukai, C.; Uchiyama, M.; Hanaoka, M. J. Chem. Soc., Chem.
Commun. 1992, 1014–1015.
(17) Hoye, T. R.; Suriano, J. A. J. Am. Chem. Soc. 1993, 115 (3),
1154–1156.
(18) Negishi, E.;Holmes, S.J.;Tour, J. M.;Miller,J.A.;Cederbaum,F. E.;
Swanson, D. R.; Takahashi, T. J. Am. Chem. Soc. 1989, 111, 3336–3346.
(19) Pearson, A. J.; Dubbert, R. A. J. Chem. Soc., Chem. Commun.
1991, 202–203.
(20) Pearson, A. J.; Dubbert, R. A. Organometallics 1994, 13, 1656–1661.
(21) Mastrorilli, P.; Nobile, C. F.; Paolillo, R.; Suranna, G. P. J. Mol.
Catal. A: Chem. 2004, 214, 103–106.
(22) Magnus, P.; Exon, C.; Albaugh-Robertson, P. Tetrahedron
1985, 41 (24), 5861–5869.
(23) Rautenstrauch, V.; Megard, P.; Conesa, J.; Kuster, W. Angew.
Chem., Int. Ed. Engl. 1990, 29, 1413–1416.
(24) Yamanaka, M.; Nakamura, E. J. Am. Chem. Soc. 2001, 123,
1703–1708.
(25) Gordon, C. M.; Kiszka, M.; Dunkin, I. R.; Kerr, W. J.; Scott, J. S.;
Gebicki, J. J. Organomet. Chem. 1998, 554, 147–154.
ESI-MS Reaction Monitoring Using Pressurized Sample
Infusion. A flask with a built-in condenser topped with a J. Young tap
and a side arm fitted with a septum was used for these experiments, as
described in ref 49. A solution of [3][Tf2N] (0.224 g, 0.50 mM in
chlorobenzene) was monitored using this PSI-ESI-MS setup. To this
solution was added Co2(CO)8 (0.228 g, 0.68 mM in chlorobenzene) by
syringe through the septum to initiate the reaction. Alternatively,
preprepared [Co2(CO)6(3)][Tf2N] (0.010 g, 0.014 mM) was mon-
itored by ESI-MS at temperatures of 65, 70, and 75 °C. Overpressure in
the flask was held at 5 psi throughout all reactions, and the temperature
was monitored by a temperature probe inserted into the pressurized
flask (thus, the temperature is the real solution temperature). The
reaction mixture was diluted online en route to the MS with acetone at
1 mL/h. The solution end of the PEEK tubing was protected with a
standard cannula filter system to avoid the tube being blocked by
insoluble byproduct. Data were processed by normalizing the abundance
of each species to the total ion count of all species in the spectrum.
5478
dx.doi.org/10.1021/om200717r |Organometallics 2011, 30, 5471–5479

Organometallics
ARTICLE
(26) Banide, E. V.; Muller-Bunz, H.; Manning, A. R.; Evans, P.;
McGlinchey, M. J. Angew. Chem., Int. Ed. 2007, 46, 2907–2910.
(27) Pallerla, M. K.; Yap, G. P. A.; Fox, J. M. J. Org. Chem. 2008,
73, 6137–6141.
(56) Battaglia, L .P.; Delledonne, D.; Nardelli, M.; Predieri, G.;
Chiusoli, G. P.; Costa, M.; Pelizzi, C. J. Organomet. Chem. 1989,
363, 209–222.
(57) Krafft, M. E.; Bo~naga, L. V. R.; Hirosawa, C. J. Org. Chem. 2001,
(28) de Bruin, T. J. M.; Milet, A.; Greene, A. E.; Gimbert, Y. J. Org.
66, 3004–3020.
Chem. 2004, 69, 1075–1080.
(58) APEX-II v 2008-1, Bruker AXS, Madison, WI.
(59) Sheldrick, G. M. SADABS; University of G€ottingen, G€ottingen,
Germany, 2008. Sheldrick, G. M. XPREP; University of G€ottingen,
G€ottingen, Germany, 2008.
(60) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(61) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(62) http://www.povray.org/
(29) Krafft, M. E.; Scott, I. L.; Romero, R. H.; Feibelmann, S.; Van
Pelt, C. E. J. Am. Chem. Soc. 1993, 115, 7199–7207.
(30) Verdaguer, X.; Vazquez, J.; Fuster, G.; Bernardes-Genisson, V.;
Greene, A. E.; Moyano, A.; Pericas, M. A.; Riera, A. J. Org. Chem. 1998,
63, 7037–7052.
(31) Cabot, R.; Lledo, A.; Reves, M.; Riera, A.; Verdaguer, X.
Organometallics 2007, 26, 1134–1142.
(63) De Vynck, V.; Goethals, E. J. Macromol. Rapid Commun. 1997,
18, 149–156.
(32) Blackmond, D. G. Angew. Chem., Int. Ed. 2005, 44, 4302–4320.
(33) (a) Jackson, S. M.; Chisholm, D. M.; McIndoe, J. S.; Rosenberg,
L. Eur. J. Inorg. Chem. 2011, 327–330. (b) Santos, L. S., Ed. Reactive
Intermediates: MS Investigations in Solution; Wiley-VCH: Weinheim,
Germany, 2010.
(34) (a) Rylander, P. N., Organic Syntheses with Noble Metal Cata-
lysts; Academic Press: New York, 1973. (b) Brandsma, L.; Vasilevsky,
S. F.; Verkruijsse, H. D., Application of Transition Metal Catalysts in
Organic Synthesis; Springer: New York, 1999. (c) Jones, W. H., Ed.
Catalysis in Organic Synthesis; Academic Press: Toronto, 1980. (d)
Heaton, B., Ed. Mechanisms in Homogeneous Catalysis; Wiley-VCH:
Weinheim, Germany, 2005.
(35) Henderson, W.;Evans, C. Inorg. Chim. Acta 1999, 294, 183–192.
(36) Santos, L. S.; Rosso, G. B.; Pilli, R. A.; Eberlin, M. N. J. Org.
Chem. 2007, 72, 5809–5812.
(37) (a) Decker, C.; Henderson, W.; Nicholson, B. K. J. Chem. Soc.,
Dalton Trans. 1999, 3507–3513. (b) Farrer, N. J.; McDonald, R.;
McIndoe, J. S. Dalton Trans. 2006, 4570–4579.
(38) Farrer, N. J.; McDonald, R.; Piga, T.; McIndoe, J. S. Polyhedron
2010, 29, 254–261.
(39) Henderson, W.; Nicholson, B. K. J. Chem. Soc., Chem. Commun.
1995, 2531–2532.
(40) Henderson, W.; McIndoe, J. S.; Nicholson, B. K.; Dyson, P. J.
J. Chem. Soc., Dalton Trans. 1998, 519–525.
(41) (a) Hinderling, C.; Adlhart, C.; Chen, P. Angew. Chem., Int. Ed.
1998, 37, 2685–2689. (b) Chisholm, D. M.; Oliver, A. G.; McIndoe, J. S.
Dalton Trans. 2010, 39, 364–373.
(42) (a) Adlhart, C.; Chen, P. Helv. Chim. Acta 2000, 83, 2192–2196.
(b) Crawford, E.; Lohr, T.; Leitao, E. M.; Kwok, S.; McIndoe, J. S. Dalton
Trans. 2009, 9110–9112.
(43) Gimbert, Y.; Lesage, D.; Milet, A.; Fournier, F.; Greene, A. E.;
Tabet, J. C. Org. Lett. 2003, 5, 4073–4075.
(44) Fei, Z.; Zhao, D.; Scopelliti, R.; Dyson, P. J. Organometallics
2004, 23, 1622–1628.
(45) (a) Butcher, C. P. G.; Dyson, P. J.; Johnson, B. F. G.; Khimyak, T.;
McIndoe, J. S. Chem. Eur. J.2003, 9, 944–950. (b) Crawford, E.; Dyson, P. J.;
Forest, O.; Kwok, S.; McIndoe, J. S. J. Cluster Sci. 2006, 17, 47–63.
(46) Henderson, M. A.; Kwok, S.; McIndoe, J. S. J. Am. Soc. Mass
Spectrom. 2009, 20, 658–666.
(47) Billington, D. C.; Helps, M. I.; Pauson, P. L.; Thomson, W.;
Willison, D. J. Organomet. Chem. 1998, 354, 233–242.
(48) Vikse, K. L.; Woods, M. P.; McIndoe, J. S. Organometallics
2010, 29, 6615–6618.
(49) Vikse, K. L.; Ahmadi, Z.; Manning, C. C.; Harrington, D. A.;
McIndoe, J. S. Angew. Chem., Int. Ed. 2011, 50, 8304–8306.
(50) Allian, A. D.; Tjahjono, M.; Garland, M. Organometallics 2006,
25, 2182–2188.
(51) Pearson, A. J.; Shively, R. J., Jr.; Dubbert, R. A. Organometallics
1992, 11, 4096–4104.
(52) Maryanoff, B. E.; Zhang, H. C. Arkivoc 2007, 7, 7–35.
(53) Rausch, B. J.; Gleiter, R.; Rominger, F. Dalton Trans. 2002,
2219–2226.
(54) Roy, S. K.; Basak, A. Chem. Commun. 2006, 1646–1648.
(55) Pearson, A. J.; Shively, R. J., Jr. Organometallics 1994, 13,
578–584.
5479
dx.doi.org/10.1021/om200717r |Organometallics 2011, 30, 5471–5479