Ferrocenyl-Imidazolylidene Ligand for Redox-Switchable Gold-Based Catalysis. A Detailed Study on the Redox-Switching Abilities of the Ligand

Article abstract of DOI:10.1021/acs.organomet.6b00517

An imidazolium salt with a fused benzoferrocenyl was synthesized. This compound was used as an N-heterocyclic carbene (NHC) precursor, and the related ferrocenyl-imidazolylidene complexes Fc-NHC-ML_n (ML_n = IrCl(COD), IrCl(CO)₂

Full text of DOI:10.1021/acs.organomet.6b00517

Article
pubs.acs.org/Organometallics
Ferrocenyl-Imidazolylidene Ligand for Redox-Switchable Gold-Based
Catalysis. A Detailed Study on the Redox-Switching Abilities of the
Ligand
†
,†
‡
‡
,†
Susana Iban
†
́
̃
ez, Macarena Poyatos,* Louise N. Dawe, Dmitry Gusev, and Eduardo Peris*
Instituto de Materiales Avanzados (INAM), Universitat Jaume I, Avenida Vicente Sos Baynat, 12071 Castellon
Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5, Canada
S Supporting Information
́
, Spain
‡
*
ABSTRACT: An imidazolium salt with a fused benzoferrocenyl was synthesized. This compound was used as an N-heterocyclic
carbene (NHC) precursor, and the related ferrocenyl-imidazolylidene complexes Fc-NHC-ML (ML = IrCl(COD), IrCl(CO) ,
n
n
2
AuCl) were synthesized and fully characterized, including the crystallographic characterization of some of the key structures. The
oxidation of the iridium carbonyl compound Fc-NHC-IrCl(CO) with acetylferrocenium tetrafluoroborate afforded the oxidized
2
ferrocenium-NHC-IrCl(CO) (Fe(III)) species; however the isolated product contained a byproduct resulting from the
2
protonation of the starting Fe(II) complex. The analysis of the electron-donating character of the neutral ligand and the ligand
resulting from the oxidation was carried out by studying the variation of the ν(CO) stretching frequencies of Fc-NHC-IrCl(CO)
2
−1
and its oxidized analogue, revealing that this shift is 2.9 cm , which is consistent with a decrease of the electron-donating
character of the ligand produced by the generation of a positively charged metal complex. DFT calculations were carried out in
order to rationalize these results. The effects of the oxidation of the ligand in homogeneous catalysis were tested by using a
related ferrocenyl-imidazolylidene-gold(I) complex. In the hydroamination of terminal alkynes, the results indicated that the
oxidation of the ligand produced a moderate increase of the activity of the gold catalyst. In the cyclization of alkynes with furans,
the neutral complex was not active, while the product resulting from its oxidation produced moderate to good yields in the
formation of the final products.
INTRODUCTION
In a typical reaction, a redox-switchable catalyst facilitates a
given transformation at a given rate, when the ligand is in the
neutral form. However, upon oxidation (or reduction), the
activity or selectivity of the catalyst changes, or the catalyst can
facilitate a new transformation. Such redox-switchable events
frequently use a metallocene (most often ferrocene) to
influence the ligand’s electron-donating power and, conse-
quently, the catalytic activity of a metal complex may change.
Among the known N-heterocyclic carbene ligands containing
■
In the traditional design of homogeneous catalysts, the choice
of a ligand is based on the notion that the ligand plays a
spectator role. However, some properties of a metal complex
3b
1
may be influenced by essentially ligand-based reactivity. For
example, the introduction of a redox-active functionality within a
ligand framework potentially allows the reactivity and selectivity
of complexed metal centers to be modulated through the
2
electrochemical switching of the redox center. The redox-
active ligand can modify the Lewis acidity/basicity of the metal
or influence the catalytic process by acting as an electron
Received: June 24, 2016
3
reservoir.
©
XXXX American Chemical Society
A
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4
ferrocenyl substituents, few have been used in redox-
switchable catalysts, but they all revealed that the redox event
(yield 95%) by the cyclization of the diaminobenzimidazolium
iodide A with ferrocenecarboxaldehyde, in the presence of
trifluoroacetic acid. Subsequent reaction with methyl iodide in
the presence of potassium carbonate afforded the imidazolium
2, in which the N−H proton of 1 was replaced by a methyl
group (yield 68%). The ferrocenyl-imidazolium salt 2 was used
for the preparation of the NHC-metal complexes by following
the procedures displayed in Scheme 3. In all cases, the NHC
metal complexes were synthesized by the transmetalation from
the in situ prepared NHC-Ag complex 3, which we also isolated
4i−l
has important consequences in their catalytic activities.
Interestingly, most ferrocenyl-containing NHC-based com-
plexes that have been used as redox-switchable catalysts possess
ferrocenyl fragments electronically disconnected from the active
catalytic sites (Scheme 1). Therefore, there is the risk that the
Scheme 1
for its full characterization. The reaction of 2 with Ag O in
2
CH Cl , followed by the addition of [IrCl(COD)] , afforded
2
2
2
the Ir(I) complex 4 in 60% yield. The iridium−carbonyl
compound 5 was obtained by bubbling carbon monoxide over a
CH Cl solution of 4. The gold complex 7 was obtained in 61%
2
2
yield by the reaction of the in situ prepared complex 3 with
[
AuCl(SMe )].
2
All new complexes were characterized by NMR spectroscopy
and electrospray mass spectrometry (ESI-MS) and gave
satisfactory elemental analyses. As a diagnostic of the formation
of the NHC-metal complexes, the C NMR spectra of 3, 4, 5,
and 7, displayed the distinctive signals due to the metalated
carbene carbons at 192.8, 192.0, 182.8, and 178.3 ppm,
respectively.
changes in the chemical properties suffered by the active metal
fragment may not be due to the modification of the electronic
properties of the ligand, but for other reasons, e.g., change in
solubility, decomposition of the catalyst, interaction of the
oxidants with the substrates, etc.
13
We have been recently interested in studying the influence of
additives on the electronic properties of a series of polyaromatic
In order to oxidize the ferrocenyl-imidazolylidene complexes
5
and 7, these were reacted with acetylferrocenium
5
NHC ligands and observed that using additives produced
tetrafluoroborate in dry dichloromethane at room temperature.
The reaction quantitatively produced acetylferrocene, which
was separated by washing the evaporated reaction crude with
dry diethyl ether. As a result of the analysis of the bulk solids
obtained, we concluded that they contained mixtures of the
oxidized ferrocenium complexes 6/8 together with the
protonated Fe(II) species 6-H/ 8-H, respectively. The presence
of the protonated species was confirmed by their mass spectra
important changes in the catalytic activities of the NHC
6
complexes. In this context, we thought that connecting a
ferrocenyl fragment with a polyaromatic backbone of an N-
heterocyclic carbene (NHC) ligand might afford a new family
of NHC ligands whose electronic properties could undergo
subtle electronic changes upon application of redox stimuli and,
therefore, could allow tuning the catalytic activity of the metal
complexes.
On the basis of all these precedents, herein we report the
preparation of an imidazolium salt with a fused ferrocenyl-
benzimidazole, which we used for the preparation of the
corresponding ferrocenyl-NHC metal complexes (Scheme 1,
(
7
ESI-MS), which showed intense peaks assigned to 6-H (m/z =
53.1) and 8-H (m/z = 701.3). In order to determine the
source of the hydrogen atom, we repeated the oxidation of 5 in
deuterated solvents (CD Cl and CD CN). 6-H was again
2
2
3
detected, although with a much lower intensity. When the
reaction was carried out using the same deuterated solvents but
MLn = [IrCl(COD)], [IrCl(CO) ], and [AuCl]). This
2
ferrocenyl monocarbene mimics the topological features of
in the presence of small amounts of D O, the deuterated
7
2
the ubiquitous benzobis(imidazolylidene) ligand, whose
8
species 6-D (m/z = 754.1) was observed. These results suggest
that water might be responsible for the formation of 6-H and 8-
H, although the details about their formation are not clear.
The slow crystallization of the products in a mixture of
dichloromethane/hexane afforded crystals of 6-H and 8-H,
which gave satisfactory elemental analysis and whose structures
were determined by X-ray crystallography (see below for
details). Unfortunately, all our attempts to obtain 6-H and 8-H
by protonation of 5 and 7 with stoichiometric amounts of
HBF or CF COOH were unsuccessful. Similarly, the reaction
electronic properties were extensively studied. Together with
the full characterization of the new metal complexes, we studied
the catalytic properties of the gold complex in the hydro-
amination of alkynes and in the cyclization of 2,5-dimethylfuran
with terminal alkynes. For both processes, the addition of an
oxidant produced an improvement of the activity of the catalyst.
RESULTS AND DISCUSSION
■
a. Synthesis and Characterization of the Compounds.
The reactions displayed in Schemes 2, 3, and 4 summarize all
the synthetic procedures performed in this work. The
ferrocenyl-imidazolium salt 1 was quasi-quantitatively prepared
4
3
of 6-H or 8-H with Cs CO in CH Cl did not afford 5 and 7,
2
3
2
2
therefore suggesting that 6-H and 8-H are not simply
protonated species.
The comparison of the infrared spectra of 5 and 6-H allowed
quantifying the modification of the electron-donating character
of the ferrocenyl-NHC ligand upon protonation. The infrared
spectrum of 6-H showed two CO stretching bands at 2071.2
Scheme 2
−1
and 1989.2 cm . These values may be compared with the two
−1
CO stretching bands shown by 5, at 2068.3 and 1986.3 cm ,
thus indicating that the oxidation of the Fc-NHC ligand affords
an increase of the average stretching frequency Δν (CO) by
av
−1
2
.9 cm , in agreement with the lower electron-donating power
B
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Scheme 3
Scheme 4
decided to introduce a positive charge in the ferrocenyl-NHC
ligand by methylating the unalkylated nitrogen in the
ferrocenyl-imidazolium compound 2. The resulting dicationic
ferrocenyl-imidazolium, 9, allowed us to obtain the cationic
complex [Fc-NHC-IrI(CO) ](BF ), 12, by following the
2
4
procedure described in Scheme 4 (more details about the
synthetic procedure and the characterization of the compounds
may be found in the Experimental Section).
The average of the two CO stretching bands of 12 was only
1
1
.8 cm− higher than the average ν(CO) of the analogue
neutral compound 13 (see Scheme 5), thus indicating that the
introduction of a positive charge in the ferrocenyl-NHC ligand,
by either protonation or methylation, has a small (although not
negligible) influence on the electron-donating character of the
carbene ligand. Complex 12 can be further oxidized in
dichloromethane by addition of acetylferrocenium tetrafluor-
oborate, which is quantitatively transformed into acetylferro-
cene. The IR spectrum of an in situ prepared solution of the
resulting Fe(III) complex 14 showed two CO stretching bands
of the protonated ligand. As a reference for comparing the
magnitude of the modification of the electron-donating
character of the ligand, it may be taken into account that a
similar shift (based on the shift of the Tolman electronic
parameter, TEP) is found between N,N′-dimethylimidazolyli-
dene (IMe) and N,N′-dimethylbenzimidazolylidene (two
NHCs that are considered electronically different). However,
−1
−1
at 2068.0 and 1991.4 cm ; thus the average ν(CO) is 2.4 cm
−1
−1
this shift is much smaller than 9 cm , observed by Bielawski
and co-workers upon the oxidation of their ferrocenyl-NHC
higher than that shown by 12 and 4.2 cm higher than the
average ν(CO) shown by 13 (Scheme 5). Unfortunately, all
attempts to isolate a pure form of 14 were unsuccessful.
The study of the electronic properties of the complexes was
also carried out by means of electrochemical studies. The cyclic
voltammetries were conducted in CH Cl , with [NBu ][PF ] as
4i
ligand (see Scheme 1).
In order to determine if the Δν (CO) value that we
av
obtained upon the protonation of 5 is consistent with the
generation of a positively charged ferrocenyl-NHC ligand, we
2
2
4
6
Scheme 5
C
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the electrolyte. The cyclic voltammograms (CV) of compounds
complexes containing a Fe2+ center, as shown by the isomer
−1
1
and 2 showed a complicated set of bands that could be
shifts at 0.54 and 0.53 mm s and quadrupole splittings of 2.21
2
+
3+
−
−1
tentatively assigned to the successive Fe /Fe and 2I /I2
redox couples and the oxidation of the polyaromatic system
containing the imidazolium ion. It has been previously
and 2.37 mm s , respectively. The spectrum of the bulk solid
resulting from the oxidation of 5 (Figure 2b) reveals two signals
of equal intensity. The outer doublet reflects the presence of a
9
2
+
3+
reported that the presence of iodide (or bromide) counter-
anions in ferrocenylimidazolium salts induces the appearance of
additional peaks due to the increased electroactivity shown by
Fe center, while the inner singlet is consistent with Fe
−1
(singlet, isomer shift at 0.51 mm s ). This result suggests that
3+
2+
this solid contains 6 (Fe ) and 6-H (Fe ) in a 1:1 ratio. The
spectrum of the bulk solid resulting from the oxidation of 7
(Figure 2d) also reveals the presence of two oxidation states for
the iron centers (the Fe center is observed as a doublet at
0.50 mm s , with a quadrupole splitting of 0.67 mm s ). In
this case the relative integrals of the two signals indicate that
10
the imidazolium in close proximity to the iodide. In both
2+
3+
complexes, the band attributed to the oxidation of Fe /Fe
3+
was measured at 0.76 and 0.84 V (versus saturated calomel
electrode, SCE) for 1 and 2, respectively (see Figures S1−S4 in
the Supporting Information). The cyclic voltammograms of
complexes 4, 5, and 7 are displayed in Figure 1. Complex 4,
−1
−1
3+
2+
the bulk solid contains 8 (Fe ) and 8-H (Fe ) in a 1:2 molar
ratio.
The molecular structures of complexes 6-H, 7, 8-H, and 11
were determined by means of X-ray diffraction studies.
The molecular structure of complex 6-H in Figure 3 consists
of a ferrocenyl moiety connected to an iridium chloride
dicarbonyl fragment through a planar benzimidazolium-
imidazolylidene ligand. The cationic nature of the complex is
confirmed by the presence of a tetrafluoroborate counteranion.
The Ir−C
distance is 2.064(9) Å, and the Ir−CO
carbene
distances are 1.916(13) and 1.89(2) Å, for the trans and cis
carbonyl groups, respectively, which are consistent with the
high trans influence of the carbene ligand. The coordination
plane of the Ir(I) fragment is quasi-perpendicular with respect
to the carbene-tricyclic ligand (86.4°). The substituted
cyclopentadienyl fragment of the ferrocenyl group is almost
coplanar with the tricyclic polyaromatic linker, establishing an
angle between them of 4.12°. The distances between the iron
atom and the Cp centroids are 1.677 and 1.640 Å for the
unsubstituted and substituted cyclopentadienyls, in agreement
Figure 1. Cyclic voltammetry (CV) plot of complexes 4, 5, and 7.
Measurements were performed on a 1 mM solution of the analyte in
dry CH Cl with 0.1 M [NBu ][PF ] as the supporting electrolyte,
2
2
4
6
+
+
1
00 mV/s scan rate, Fc/Fc used as standard with E (Fc/Fc ) = 0.46
1/2
12
with the presence of a Fe(II) center. The N−C distances of
the methyl imidazole bound to the ferrocenyl fragment are
similar, 1.342(11) and 1.323(11) Å, indicating a high degree of
delocalization, rather than showing the difference expected for a
single and double bonds, expected for a structure without a
proton at N3. The presence of the N3−H3 proton is also
V vs SCE.
with a ferrocenyl-imidazolylidene ligand bound to [IrCl-
COD)], exhibited two quasireversible redox events at 0.87
(
2
+
3+
+
2+
and 1.18 V, which were attributed to the Fe /Fe and Ir /Ir
redox couples, respectively. Given that the redox potentials for
IrCl(NHC)(COD)] (NHC = unsaturated N-heterocyclic
supported by the close contact with the BF counteranion
4
[
(H3···F3 distance = 1.949 Å), which reflects a hydrogen-
bonding interaction.
The molecular structures of 7 and its protonated analogue 8-
H (vide infra) allow the comparison of the structural changes
produced by the protonation of the ligand.
11
carbene) are known to range between 0.59 and 0.91 V, it
can be concluded that the oxidation of the ferrocenyl fragment
in 4 has a strong influence on the value of the redox potential of
+
2+
the Ir /Ir couple. Complex 5, consisting of a ferrocenylimi-
dazolylidene ligand bound to [IrCl(CO) ], shows two quasi-
The molecular structures of complex 7 and 8-H are displayed
in Figures 4 and 5, respectively. The cationic nature of complex
2
irreversible oxidation processes at 0.88 and 1.17 V, again
attributed to the oxidations occurring at the Fe and Ir centers,
8-H is confirmed by the presence of the BF counteranion. One
4
+
2+
respectively. The value of the redox potential for the Ir /Ir
of the main differences between the two structures is that the
cyclopentadienyl-substituted ring in 7 deviates from the plane
of the tricyclic polyaromatic fragment by 18.64°, while in 8-H
the two planes are almost coplanar (angle 3.11(19)°). The Au−
couple in 4 and 5 is virtually identical, indicating that the
presence of the electron-withdrawing carbonyl ligands has
negligible influence on the redox potential of the iridium center.
Complex 7, in which the ferrocenyl-imidazolylidene is bound
to a Au(I) center, showed one reversible oxidation process at
C
distance in 7 is slightly shorter than in 8-H (1.989 vs
carbene
1.953(6) Å), maybe as a consequence of the lower electron-
donating character of the ligand (in 8-H), which is reflected in a
weaker σ-bond. The metric parameters of the ferrocenyl
fragments of these two structures are almost identical. For
example, the dihedral angles between the cyclopentadienyl
rings are 0.73° and 0.8(3)° for 7 and 8-H, respectively. The
average distances between the Fe atom and the Cp(centroids)
are 1.640 (for 7) and 1.643 Å (for 8-H), which are suggestive of
0
.63 V assigned to the ferrocenyl fragment and an irreversible
reduction event due to the reduction of Au(I) to Au(0).
In order to confirm that complexes 5 and 7 were oxidized to
their Fe(III) analogues in the presence of acetylferrocenium
5
7
̈
tetrafluoroborate, we decided to measure the Fe Mossbauer
spectra of complexes 5 and 7 and of the bulk solids that we
isolated from their reactions with the oxidant. Figure 2 shows
the spectra recorded at 77 K. The spectra of complexes 5 and 7
12
the presence of a Fe(II) center. As in the case of the
(Figure 2a and c, respectively) are fully consistent with the
molecular structure of 6-H, in the case of 8-H, the two N−C
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Figure 2. 57Fe Mo
the oxidation of 7. Open circles are the experimental data, and solid lines are the corresponding spectral fits.
ssbauer spectra (recorded at 77 K) of (a) 5, (b) bulk solid resulting from oxidation of 5, (c) 7, and (d) bulk solid resulting from
̈
Figure 4. Molecular structure of complex 7. Hydrogen atoms and
Figure 3. Molecular diagram of complex 6-H. Ellipsoids are at 50%
probability. Hydrogen atoms (except H3), minor disorder compo-
nents, and solvent are omitted for clarity. Selected bond distances (Å)
and angles (deg): Ir1−C1 2.064(9), Ir1−C31A 1.89(2), Ir1−C30
1.916(13), Ir1−Cl1 2.329(6), C30−O1 1.088(16), C31A−O2A
1.13(3), N3−C17 1.342(11), N4−C17 1.323(11), C17−C18
1.449(12), C1−Ir1−C30 178.1(6), C1−Ir1−Cl1 87.7(3).
solvent (CHCl ) have been omitted for clarity. Ellipsoids are at 50%
3
probability. Selected bond distances (Å) and angles (deg): Au1−C1
1.989(5), Au1−Cl1 2.2823(13), N4−C17 1.382(6), N3−C17
1.326(6), C1−Au1−Cl1 179.58(15).
confirmed by the presence of a tetrafluoroborate counteranion.
The Ir−C
bond distance is 1.9887 Å. The coordination
carbene
plane of the Ir(I) fragment is oriented quasi-perpendicular with
respect to the plane of the tricyclic ligand (87.33°), and the
plane of the substituted Cp ring deviates from the plane of the
tricyclic ligand by 41.29°. The distances between the Fe(II)
center and the centroids of the cyclopentadienyl rings are 1.637
and 1.657 Å for the substituted and unsubstituted Cp rings,
respectively. The two N−C distances of the imidazolyl bound
to the ferrocenyl fragment are quasi-identical (N4−C17 1.350,
N3−C17 1.345), thus indicating a delocalized π-bond between
the three atoms involved.
Complexes 5, 6, and 6-H were studied computationally,
using a local M06L DFT functional and a hybrid ωB97XD
functional with the good-quality def2TZVP basis set (QZVP
for Ir). Both functionals are modern methods suitable for
modeling transition-metal complexes. A search for the lowest
distances of the imidazolyl ring bound to the ferrocenyl
fragment are identical within standard uncertainties (N4−C17
1
.351(7), N3−C17 1.340(7) Å), indicating a high degree of
delocalization, while in the neutral molecule 7 the analogous
distances are more consistent with the presence of a single and
a double bond (N3−C17 1.326, N4−C17 1.462 Å). The
proton bound to the nitrogen of the ligand (H3) is at a distance
of 1.94(2) Å to one of the fluorine atoms of the BF4
counteranion, thus strongly suggesting a hydrogen-bonding
interaction.
Figure 6 shows the molecular structure of complex 11. The
molecule contains a ferrocenyl group connected to an iridium
cyclooctadiene iodide fragment via a benzimidazolium
imidazolylidene ligand. The cationic nature of the molecule is
E
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Figure 5. Molecular structure of complex 8-H. Hydrogen atoms
(
except H3), minor disorder components, and lattice solvent have
been omitted for clarity. Ellipsoids are at 50% probability. Selected
bond distances (Å) and angles (deg): Au1−C1 1.953(6), Au1−Cl1
2
.270(8), N4−C17 1.351(7), N3−C17 1.340(7), C17−C18 1.449(8),
C1−Au1−Cl1 173.0(4).
Figure 7. DFT (M06L)-optimized geometries of complexes 5 (top),
6
-H (center), and 6.
Table 1. Bond Distances (Å) in 5, 6-H, and 6
C1−
C1−
C17−
C17−
Fe−
a
Fe−
a
system
, M06L
Ir
N1
N3
N4
X1
X2
5
5
6
6
6
6
6
2.10
2.09
2.09
2.08
2.10
2.08
2.06
1.35
1.34
1.35
1.35
1.35
1.35
1.37
1.31
1.31
1.32
1.31
1.33
1.32
1.33
1.38
1.38
1.38
1.37
1.36
1.35
1.34
1.62
1.67
1.66
1.68
1.62
1.66
1.64
1.63
1.67
1.67
1.68
1.64
1.67
1.67
, ωB97XD
, M06L
, ωB97XD
-H, M06L
-H, ωB97XD
-H, expt
Figure 6. Molecular structure of complex 11. Hydrogen atoms have
been omitted for clarity. Ellipsoids are at 50% probability. Selected
bond distances (Å) and angles (deg): Ir1−C1 1.9887(7), Ir1−I1
a
2
.6558(6), Ir1−C33 2.101(8), Ir1−C32 2.089(8), Ir1−C36 2.201(8),
X1 and X2 denote the centroids of the C H and C H rings in
5 4 5 5
Figure 7.
Ir1−C29 2.192(8), N4−C17 1.350(8), N3−C17 1.345(9), C7−C18
1.531(12), I1−Ir1−C1 91.4(2).
the singlet 5 placed the two highest occupied molecular orbitals
2
2
energy structures returned the optimized geometries presented
in Figure 7; the selected structural information is collected in
Table 1.
on iron (d and d , HOMO and HOMO−1, at −0.181 06
xy
x −y
and −0.182 15 hartree), while the next two MOs were
2
combinations of the d orbitals of both metals (HOMO−2
z
The data of Table 1 show minor structural changes upon
oxidation or protonation of 5; overall, the three structures of
Figure 7 are similar. Among the salient features are the C17−N
distances that are different by ca. 0.07 Å in 5 and 6 and by ca.
and HOMO−3, at −0.192 00 and −0.192 24 hartree). These
observations qualitatively agree with the CV data of Figure 1,
showing two quasireversible oxidation processes at 0.88 and
1.17 V for 5, attributed to the successive oxidations occurring
first at the iron center and next on iridium.
0.03 Å in 6-H; the latter is in reasonable agreement with the
experiment. Unlike the crystal structures of this work, the
calculated gas-phase structures all exhibit some degree of
rotation of the metal fragments with respect to the NHC ligand
backbone that is obvious when looking at Figure 7. We believe
that these molecules do not benefit by conjugation between the
The final piece of computational data concerns the stretching
vibrations of the carbonyls in the complexes of Figure 7. The
averaged calculated harmonic C−O stretching frequencies of 5
−
1
(M06L: 2087.2, ωB97XD: 2141.2 cm ) and [6-H]BF
4
−1
(M06L: 2091.7, ωB97XD: 2144.8 cm ) are exaggerated
compared to the experimental average ν(CO) = 2027.3 (5)
and 2030.2 (6-H) values, as expected. The changes from 5 to
Cp Fe fragment and the rest of the NHC ligand. The
2
experimental structures of 6-H, 7, and 8-H, where the FeCp2
fragment appears to be in conjugation with the rest of the NHC
ligand, might be influenced by packing.
One question that we wanted to answer with the help of the
calculations was about the location of the unpaired electron in
[6-H]BF upon protonation are small (M06L: 4.5, ωB97XD:
4
−
1
3.6 cm ) and comparable to the experimental value of 2.9
−1
cm in Scheme 5. We noticed a peculiar influence of the
−
counterion, BF , on the calculated frequencies of 6-H. When
4
−
6
. The α-electron density, associated with the unpaired
the cation 6-H was optimized without BF4 using the M06L
−1
electron, was found exclusively on iron in 6 by the ωB97XD
calculation. The M06L calculation found most (0.81) α-spin
density on iron, but suggested some probability (0.26) of
finding the α-spin on iridium as well. The M06L calculation of
functional, the average ν(CO) increased to 2106.6 cm , and
−1
thus the difference versus 5 increased to 19.4 cm . The C−O
−1
stretching frequencies (M06L: 2112.7, ωB97XD: 2155.2 cm )
−
of the radical cation 6, calculated without BF , are also
4
F
DOI: 10.1021/acs.organomet.6b00517
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
significantly shifted versus 5 by 25.5 (M06L) and 14.0 cm−1
oxidant apparently produces a slight increase of the activity.
This increase is more significant for the case of the
hydroamination of phenylacetylene with mesitylamine, for
which 90% and 82% yield of the product is obtained, depending
on whether the oxidant is added or not, respectively (entries 6
and 7).
(
ωB97XD), in disagreement with the small experimental
difference observed upon oxidation of the related complex 12
in Scheme 5. The DFT results suggest that 6 and 6-H might
exist (and should be treated) as tight ion pairs with BF4− in
solution.
b. Catalytic Studies. For the study of the catalytic effects
produced upon the oxidation of the ferrocenyl-imidazolylidene
ligand, we decided to test the Fc-NHC-Au complexes 7 and 8
in two benchmark gold-catalyzed reactions. During the past few
years, gold catalysis has become a hot topic in chemistry,
especially regarding reactions proceeding by activation of
In order to have a more detailed insight into the possible
improvement of the catalytic process by oxidizing the ligand, we
monitored the reaction and studied the time-dependent
reaction profile of the process for the hydroamination of
phenylacetylene using aniline and mesitylamine. As can be
observed from the profiles shown in Figure 8, the addition of
13
unsaturated carbon−carbon bonds. Among homogeneous
Au-based catalysts, those containing NHC ligands are
becoming increasingly visible, probably due to the steric and
electronic stabilization of the complexes imparted by the NHC
1
4e,f
ligands.
Because the activity of the gold-based catalysts has
often been related to the tendency of the Au center to behave
as an electrophile, we thought that the decrease of the electron-
donating character of the NHC ligand produced upon
oxidation (or protonation) of 7 could yield some improvement
of the catalytic efficiency.
We first studied the hydroamination of terminal alkynes, a
process for which several Au-NHC complexes have proved very
1
4
active. For this same reaction, Gabbai and co-workers recently
described that the activity of a Au(III)-based catalyst could be
improved by oxidizing a redox-switchable ligand, which
consequently featured a more Lewis acidic gold center.
Table 2 summarizes the results that we obtained for the
Figure 8. Time-dependent reaction profile of the hydroamination of
phenylacetylene with aniline and mesitylamine. All reactions were
carried out under the same conditions described in Table 2 (Ox. =
oxidant = acetylferrocenium tetrafluoroborate). Lines are only to guide
the eye.
15
Table 2. Activity of Complex 7 (with and without Oxidant)
a
in the Hydroamination of Phenylacetylene with Arylamines
the catalyst not only produces a slightly higher yield of the
product but also accelerates the reaction, hence indicating that
the higher efficiency of the oxidized catalyst is due to inherent
catalytic (kinetic) enhancement, rather than reasons related to
thermodynamic factors (i.e., stability of the catalyst). At this
point it is important that we checked that the reaction is
homogeneously catalyzed, not only because the reaction
mixtures did not show any trace of formation of solid all
along the reaction course but also because the reactions carried
out in the presence of a drop of Hg did not yield any variation
in the reaction yields with respect to those reactions for which
Hg was not added.
A plausible explanation that may justify the small effect
observed in the hydroamination of phenylacetylene is that the
aniline substrate deprotonates 8-H (if formed) and regenerates
the unoxidized catalyst 7. In order to circumvent this, we
decided to test a new catalytic reaction not involving basic
substrates.
b
c
entry
Ar
cat.
additives
yield (%)
1
2
3
4
5
6
7
Ph
Ph
Ph
7
7
AgBF4
89
91
0
AgBF , oxidant
4
oxidant
4-MeC H
7
7
7
7
AgBF4
88
90
82
90
6
4
4
4-MeC H
AgBF , oxidant
6
4
2,4,6-Me C H
AgBF4
3
6
2
2,4,6-Me C H
AgBF , oxidant
3
6
2
4
a
Reaction conditions: 0.5 mmol of phenylacetylene, 0.55 mmol of aryl
amine, 1 mol % of the catalyst 7, 1 mL of CH CN at 90 °C, 3 h. 2
mol % of AgBF and/or 1 mol % of acetylferrocenium tetrafluor-
oborate (oxidant) was added to the reaction mixture. Yields calculated
by GC using anisole (0.5 mmol) as internal standard.
b
3
4
c
We wanted to see if we could provide an example of a
catalytic reaction for which the addition of the oxidant afforded
a more significant improvement. The gold-catalyzed synthesis
of phenols by cyclization of alkynes with furans developed by
Hashmi in 2006 is one of the most important gold-facilitated
hydroamination of phenylacetylene with three different aryl-
amines (aniline, 4-tolylamine, and mesitylamine). The reactions
were carried out at 90 °C in acetonitrile, using a catalyst loading
of 1 mol %. Complex 8 was generated in situ, by addition of
acetylferrocenium tetrafluoroborate to a reaction containing
catalyst 7. With this we intended to minimize the production of
1
6
transformations. Recently, cationic Au-NHC complexes
17
proved to be excellent catalysts for this type of reaction.
8
-H by abstraction of a hydrogen from the solvents used in the
For this reason, we thought that our two Fc-Au complexes 7
and 8 might be good candidates for catalyzing the cyclization of
alkynes with furans. The reactions were carried out following
the method previously described, by reacting the alkyne with
2,5-dimethylfuran in dichloromethane, at room temperature in
the presence of 3 mol % of catalyst and an equal amount of
isolation. The potential activity of the oxidant alone was
discarded by a blank experiment in which the reaction was
carried out in the absence of complex 7 (entry 3). As can be
seen from the results shown, the activity of the catalyst with and
without the oxidant is very similar, although the addition of the
17
G
DOI: 10.1021/acs.organomet.6b00517
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
NaBARF (BARF = tetrakis[3,5-bis(trifluoromethyl)phenyl]-
borate]. As can be seen from the results shown in Table 3,
the isolated species contained the protonated ferrocenyl-
2+
imidazolylidene-iridium complex (6-H, Fe ), together with
3
+
the ferrocenium-imidazolylidene iridium compound (6, Fe )
resulting from the oxidation of the ferrocenyl fragment. These
findings were supported by experimental results, based on the
mass spectrometry of the compounds, X-ray-diffraction studies,
Table 3. Intermolecular Gold(I)-Catalyzed Cyclization of
a
2
,5-Dimethylfuran with Terminal Alkynes
̈
and Mossbauer spectroscopy. Interestingly, DFT calculations
on both the oxidized and protonated species (6 and 6-H,
according to Scheme 3) reveal that large ν(CO) shifts should
be expected for their IR spectra, compared to those calculated
for the neutral parent compound 5, when the calculations are
carried out for the cation alone. However, for the case of the
protonated species 6-H, a much lower ν(CO) shift is obtained
b
entry
R
catalyst
yield (%)
0
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
7
c
8 + 8-H
62
c
7 + oxidant
60
1-butyl
1-butyl
1-hexyl
1-hexyl
m-Tol
7
0
if the molecule is calculated with a BF counteranion, because
4
7 + oxidant
53
0
the ion pair formed by the N−H and one of the fluorine atoms
of the anion is apparently reducing the effect of the positive
charge on the ligand.
7
7 + oxidant
7
66
0
These results are of significant importance because they
reveal that special caution has to be taken when redox-
switchable ligands are used. The modification (or switch) of the
electron-donating nature of the ligand may be wrongly ascribed
to a redox event, while a “protonation” is the real process
happening. In any case, such protonation should be understood
as a consequence of the oxidation of the ligand followed by a
hydrogen abstraction.
The effects of the oxidation of the ligand in homogeneous
catalysis were tested by using the ferrocenyl-imidazolylidene-
gold(I) complex (7, Scheme 3). This compound was tested in
two typical gold-catalyzed reactions. In the hydroamination of
terminal alkynes, the results made us conclude that the
oxidation of the ligand produced a moderate increase of the
activity of the gold catalyst. In the cyclization of alkynes with
furans, the results were more remarkable, because the neutral
complex (7) was not active at all, while the product resulting
from its oxidation (regardless whether this is the oxidized or the
protonated species, 8 or 8-H) produced moderate to good
yields in the formation of the final products. This result
indicates that for this latter reaction the addition of the oxidant
switches the activity of the catalyst on. For both catalytic
reactions, the enhancement of the activity upon oxidation is
interpreted as a consequence of the higher electrophilicity of
the gold center produced by the generation of a cationic ligand
upon its oxidation.
m-Tol
7 + oxidant
75
a
Reaction conditions: 2 mmol of 2,5-dimethylfuran, 1 mmol of alkyne,
.03 mmol of NaBARF, 3 mol % of the catalyst, 2.5 mL of CH Cl at
room temperature, 24 h. Yields of the isolated products.
0
2
2
b
c
Hydroarylated product was also observed.
complex 7 is completely inactive in the reaction, while the
oxidized complex 8 (or 7 + oxidant) produces moderate to
good yields of the final phenols. Interestingly, when we used a
mixture of 8 and 8-H from the precipitation of the bulk material
resulting from the oxidation of 7, we observed that the yield
obtained was the same as that obtained for the in situ
preparation of 8 (compare entries 2 and 3). The results are
particularly interesting because, contrary to what we observed
for the hydroamination of alkynes, in this reaction the oxidation
of the ligand is able to “switch on” the activity of the gold
catalyst.
Under the same reaction conditions, catalyst 7 in the
presence of acetylferrocenium tetrafluoroborate facilitated the
cyclization of 1,4-diethynylbenzene with 2,5-dimethylfuran,
affording the corresponding terphenylene in 45% isolated
yield (Scheme 6). The yield of this reaction is slightly lower
Scheme 6
EXPERIMENTAL SECTION
■
General Considerations. 1,3-Dibutyl-5,6-diaminobenzimidazo-
1
8
5
lium iodide (A) and acetylferrocenium tetrafluoroborate, [Fe(η -
1
9
C H COMe)Cp][BF ], were prepared according to literature
5
4
4
methods. All other reagents were used as received from commercial
suppliers. NMR spectra were recorded on a Varian Innova 300 and
than the best result reported to date with the same substrate
17
(
55% production of the terphenylene), but illustrates the
5
00 MHz or on a Bruker 400 MHz, using CDCl , CD Cl , and
3 2 2
scope of this catalyst in this reaction.
DMSO-d as solvents. Electrospray mass spectra were recorded on a
6
Micromass Quatro LC instrument; nitrogen was employed as drying
and nebulizing gas. Elemental analyses were carried out on a TruSpec
Micro Series. Infrared spectra (FTIR) were performed on a Bruker
EQUINOX 55 spectrometer with a spectral window of 4000−600
CONCLUSIONS
■
In summary, this work describes the preparation of a
ferrocenyl-imidazolylidene ligand, which was coordinated to
iridium(I) and gold(I). The electronic properties of the ligand
were analyzed by means of IR spectroscopy of the
−
1
−1 57
cm . The resolution of the IR experiments is 0.5 cm . Fe
Mossbauer spectra were recorded at the Departament Chemie and
Pharmazie of the University of Erlangen−Nurnberg on a WissEl
Mossbauer spectrometer (MRG-500) at 77 K in constant acceleration
̈
̈
corresponding [IrCl(Fc-NHC)(CO) ] complex 5 and were
2
̈
compared to those shown by its oxidized analogue 6. The
comparison of the IR spectra revealed an unexpected low
modification of the electron-donating power of the ligand upon
oxidation. A more detailed analysis of the nature of the
57
mode. Co/Rh was used as the radiation source. WinNormosfor Igor
Pro software has been used for the quantitative evaluation of the
spectral parameters (least-squares fitting to Lorentzian peaks). The
minimum experimental line widths were 0.20 mm s− . The
temperature of the samples was controlled by an MBBC-HE0106
1
“
oxidized” species revealed that, contrary to our expectations,
H
DOI: 10.1021/acs.organomet.6b00517
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Mo
̈
ssbauer He/N cryostat within an accuracy of ±0.3 K. Isomer shifts
1.44 (m, 4H, NCH CH CH CH ), 0.98 (t, 3JH−H = 20 Hz, 3H,
2
2
2
2
3
3
were determined relative to α-iron at 298 K. Electrochemical studies
were carried out by using an Autolab Potentiostat (model
PGSTAT101) using a three-electrode cell. The cell was equipped
with platinum working and counter electrodes, as well as a silver wire
reference electrode. In all experiments, [NBu ][PF ] (0.1 M in dry
NCH CH CH CH ), 0.95 (t, JH − H
=
20 Hz, 3H,
3
2
2
2
3
1
3
1
NCH CH CH CH ). C{ H} NMR (126 MHz, CDCl ): δ = 192.8
2
2
2
3
(Ag-Ccarbene), 156.3 (NCN), 141.0 (Cq Ph), 135.2 (Cq Ph), 131.2 (Cq Ph),
130.9 (Cq Ph), 100.0 (CH ), 90.3 (CH ), 73.5 (Cq Cp), 70.6 (CHCp),
Ph
Ph
69.9 (CHCp), 69.3 (CHCp), 49.6 (NCH CH CH CH ), 49.5
4
6
2
2
2
3
CH Cl ) was used as the supporting electrolyte with analyte
(NCH CH CH CH ), 32.3 (NCH CH CH CH ), 32.2
2
2
2 2 2 3 2 2 2 3
concentration of approximately 1 mM. Unless otherwise stated,
(NCH CH CH CH ), 32.0 (NCH ), 20.4 (NCH CH CH CH ),
2 2 2 3 3 2 2 2 3
−1
measurements were performed at 100 mV s scan rates. All redox
14.1 (NCH CH CH CH ), 14.0 (NCH CH CH CH ). Electrospray
2 2 2 3 2 2 2 3
+
+
potentials were referenced to the Fc /Fc couple as internal standard
MS (20 V, m/z): 469.3 [M − AgI + H] . Anal. Calcd for
+
with E1/2(Fc/Fc ) versus the SCE = +0.46 V.
C H N AgFeI (703.2): C, 46.12; H, 4.59; N, 7.97. Found: C,
27
32
4
Synthesis and Characterization of the Precursors of the
Ligands and the Metal Complexes. Synthesis of Compound 1.
Ferrocenecarboxaldehyde (337.5 mg, 1.54 mmol) and 6 drops of
trifluoroacetic acid were subsequently added to a solution of
compound A (600 mg, 1.54 mmol) in ethanol (100 mL). The
resulting mixture was heated at reflux for 24 h under aerobic
conditions. After removal of the volatiles, compound 1 was isolated as
46.71; H, 4.86; N, 7.80.
Synthesis of Complex 4. A suspension of the ferrocene-based
imidazolium salt 2 (200 mg, 0.33 mmol) and Ag O (39.25 mg, 0.17
2
mmol) in CH Cl was stirred at room temperature overnight. Then,
2
2
[IrCl(COD)] (112.6 mg, 0.17 mmol) was added. Immediately, the
2
formation of a white precipitate was observed. To complete the
reaction, the suspension was stirred at room temperature for 6 h. The
suspension was filtered through a pad of Celite to remove unreacted
a dark brown solid and was used in the following step without further
1
purification. Yield: 960.8 mg, 95%. H NMR (300 MHz, DMSO-d ): δ
Ag O and other insoluble salts. The solution was concentrated nearly
6
2
=
9.80 (s, 1H, NCHN), 8.13 (s, 2H, CH ), 5.25 (s, 2H, CH ), 4.64
to dryness, and diethyl ether (5 mL) was added to precipitate the
complex, which was collected by filtration and further washed with
diethyl ether. Complex 4 was isolated as a brown solid. Yield: 160 mg,
Ph
Cp
(
s, 2H, CH ), 4.55 (m, 4H, NCH CH CH CH ), 4.16 (s, 5H,
Cp 2 2 2 3
CH ), 1.99−1.90 (m, 4H, NCH CH CH CH ), 1.41−1.31 (m, 4H,
Cp
2
2
2
3
3
3
1
NCH CH CH CH ), 1.04 (t,
NCH CH CH CH ), 0.95 (t, JH − H
J
=
=
15 Hz, 3H,
15 Hz, 3H,
60%. H NMR (500 MHz, CDCl ): δ = 7.60 (s, 1H, CH ), 7.08 (s,
2
2
2
3
H − H
3
Ph
2
2
2
3
1H, CH ), 4.97 (s, 2H, CH ), 4.83−4.60 (m, 6H; 4H,
Ph
Cp
13
1
NCH CH CH CH ). C{ H} NMR (75 MHz, CDCl ): δ = 159.4
NCH CH CH CH ; and 2H, CH ), 4.51 (s, 2H, CH ), 4.22 (s,
2
2
2
3
3
2 2 2 3 cod Cp
(
NCN), 139.4 (NCHN), 138.7 (Cq Ph), 128.0 (Cq Ph), 97.2 (CHPh),
5H, CH ), 4.08 (s, 3H, NCH ), 3.03−3.00 (m, 2H, CH ), 2.33−
Cp
3
cod
7
(
1.8 (CH ), 70.4 (CH ), 69.3 (C ), 68.7 (CH ), 47.8
2.23 (m, 4H, NCH CH CH CH ), 1.65−1.52 (m, 12H; 4H,
Cp
Cp
q Cp
Cp
2
2
2
3
3
NCH CH CH CH ), 30.9 (NCH CH CH CH ), 19.9
NCH CH CH CH ; and 8H, CH ), 1.11 (t, J
= 10 Hz, 6H,
H−H
2
2
2
3
2
2
2
3
2
2
2
3
2 cod
3
(
(
(
NCH CH CH CH ), 13.5 (NCH CH CH CH ). Electrospray MS
NCH CH CH CH ), 1.07 (t, 6H, JH − H
=
10 Hz,
2
2
2
3
2
2
2
3
2
2
2
3
+
13
1
20 V, m/z): 455.3 [M − I] . Anal. Calcd for C H N FeI·4H O
NCH CH CH CH ). C{ H} NMR (126 MHz, CDCl ): δ = 192.0
26
31
4
2
2
2
2
3
3
654.36): C, 47.72; H, 6.01; N, 8.56. Found: C, 47.33; H, 6.19; N,
(Ir-Ccarbene), 155.0 (NCN), 139.7 (Cq Ph), 133.9 (Cq Ph), 132.4 (Cq Ph),
132.1 (Cq Ph), 99.1 (CH ), 89.2 (CH ), 86.1 (CHcod), 74.0 (Cq Cp),
8
.20.
Synthesis of Compound 2. A solution of compound 1 (300 mg,
.51 mmol) and K CO (142.4 mg, 1.03 mmol) in dry acetonitrile (10
Ph
Ph
70.4 (CH ), 69.8 (CH ), 69.2 (CH ), 52.5 (CHcod), 52.2 (CHcod),
Cp
Cp
Cp
0
48.6 (NCH CH CH CH ), 48.5 (NCH CH CH CH ), 33.8
2
3
2
2
2
3
2
2
2
3
mL) was stirred at 90 °C for 1 h. After this time, methyl iodide was
added (33 μL, 0.51 mmol) and the resulting mixture was heated at 90
(CH2 cod), 33.7 (CH2 cod), 31.8 (NCH ), 31.5 (NCH CH CH CH ),
3 2 2 2 3
31.4 (NCH CH CH CH ), 29.7 (CH2 cod), 29.5 (CH2 cod), 20.7
2
2
2
3
°
C overnight. After this time, the solvent was removed under vacuum.
(NCH CH CH CH ), 14.0 (NCH CH CH CH ), 13.9
2 2 2 3 2 2 2 3
The solid residue was dissolved in dichloromethane and filtered
through a pad of Celite to remove insoluble salts. The resulting residue
was taken up in the minimum amount of dichloromethane, diethyl
ether (5 mL) was added, and the precipitated solid was collected by
(NCH CH CH CH ). Electrospray MS (20 V, m/z): 805.2 [M +
2 2 2 3
+
2+
H] and 405.8 [M + H − Cl + CH CN] . Anal. Calcd for
3
C H N ClFeIr (804.27): C, 52.27; H, 5.51; N, 6.97. Found: C,
5
3
44
4
52.36; H, 5.57; N, 7.17.
filtration. Compound 2 was isolated as a light brown solid. Yield: 220.5
Synthesis of Complex 5. CO gas was bubbled through a solution of
1
mg, 68%. H NMR (500 MHz, CDCl ): δ = 10.71 (s, 1H, NCHN),
complex 4 (100 mg, 0.05 mmol) in CH Cl (20 mL) for 1 h at 0 °C.
3
2
2
8
2
2
4
0
.02 (s, 1H, CH ), 7.85 (s, 1H, CH ), 4.99 (s, 2H, CH ), 4.77 (s,
The solution was then concentrated nearly to dryness. The crude solid
was washed three times with hexane to remove the released 1,5-
cylooctadiene. The pure complex 5 was collected by filtration. Yield:
Ph
Ph
Cp
H, NCH CH CH CH ), 4.55 (s, 4H; 2H, NCH CH CH CH ; and
2
2
2
3
2
2
2
3
H, CH ), 4.20 (s, 8H; 5H, CH ; and 3H, NCH ), 2.12−2.01 (m,
Cp
Cp
3
−1
1
H, NCH CH CH CH ), 1.55−1.36 (m, 4H, NCH CH CH CH ),
55.6 mg, 60%. IR (CH Cl ): 2068.3 and 1986.3 cm (νCO). H NMR
2
2
2
3
2
2
2
3
2 2
3
13
1
.97 (t, J
= 20 Hz, 6H, NCH CH CH CH ). C{ H} NMR (126
(300 MHz, CDCl ): δ = 7.72 (s, 1H, CH ), 7.22 (s, 1H, CH ), 4.98
3 Ph Ph
H−H
2
2
2
3
MHz, CDCl ): δ = 159.1 (NCN), 143.3 (Cq Ph), 141.1 (NCHN),
(s, 2H, CH ), 4.87−4.63 (m, 2H, NCH CH CH CH ), 4.53 (s, 4H,
3
Cp
2
2
2
3
1
37.4 (Cq Ph), 128.2 (Cq Ph), 127.9 (Cq Ph), 101.0 (CH ), 93.0 (CH ),
2H, CH and 2H, NCH CH CH CH ), 4.22 (s, 5H, CH ), 4.09 (s,
Ph
Ph
Cp 2 2 2 3 Cp
7
2.4 (Cq Cp), 71.1 (CH ), 70.0 (CH ), 69.7 (CH ), 47.9
3H, NCH ), 2.16−1.87 (m, 4H, NCH CH CH CH ), 1.62−1.39 (m,
Cp
Cp
Cp
3
2
2
2
3
(
3
(
NCH CH CH CH ), 47.7 (NCH CH CH CH ), 32.7 (NCH ),
12H; 4H, NCH CH CH CH ), 1.07−0.99 (m, 6H,
2
2
2
3
2
2
2
3
3
2
2
2
3
13 1
1.4 (NCH CH CH CH ), 31.2 (NCH CH CH CH ), 20.0
NCH CH CH CH ). C{ H} NMR (75 MHz, CDCl ): δ = 182.8
2
2
2
3
2
2
2
3
2 2 2 3 3
NCH CH CH CH ), 13.8 (NCH CH CH CH ), 13.7
(Ir-Ccarbene), 181.6 (Ir-CO), 168.4 (Ir-CO), 156.4 (NCN), 140.9
2
2
2
3
2
2
2
3
(
NCH CH CH CH ). Electrospray MS (20 V, m/z): 469.3 [M −
(Cq Ph), 135.1 (Cq Ph), 131.5 (Cq Ph), 131.2 (Cq Ph), 100.0 (CH ), 90.1
2
2
2
3
Ph
+
2+
I] and 235.2 [M − I + H] . Anal. Calcd for C H N FeI·2H O
(CH ), 73.5 (C ), 70.6 (CH ), 69.8 (CH ), 69.4 (CH ), 49.0
27
33
4
2
Ph
q Cp
Cp
Cp
Cp
(
632.36): C, 51.28; H, 5.90; N, 8.86. Found: C, 51.37; H, 5.67; N,
.72.
Synthesis of Complex 3. A mixture of compound 2 (200 mg, 0.33
mmol) and silver oxide (39.25 mg, 0.17 mmol) in CH Cl (15 mL)
(NCH CH CH CH ), 48.9 (NCH CH CH CH ), 31.9 (NCH ), 31.4
2 2 2 3 2 2 2 3 3
8
(NCH CH CH CH ), 31.3 (NCH CH CH CH ), 20.4
2 2 2 3 2 2 2 3
(NCH CH CH CH ), 14.0 (NCH CH CH CH ), 13.9
2
2
2
3
2
2
2
3
(NCH CH CH CH ). Electrospray MS (20 V, m/z): 753.2 [M +
2
2
2
2
2
3
+
was stirred at room temperature overnight. After this time, the mixture
was filtered through a pad of Celite to remove insoluble salts. The
solvent was removed nearly to dryness, and diethyl ether (5 mL) was
added. The precipitate so formed was collected by filtration and
washed with diethyl ether (5 mL). Complex 3 was isolated as an
orange solid. Yield: 129.5 mg, 55%. H NMR (500 MHz, CDCl ): δ =
H] . Anal. Calcd for C H N ClFeIrO (752.10): C, 46.31; H, 4.29;
29 32 4 2
N, 7.45. Found: C, 46.70; H, 4.62; N, 7.47.
Synthesis of Complex 6. Complex 5 (20 mg, 0.03 mmol) and
acetylferrocenium tetrafluoroborate (8.37 mg, 0.03 mmol) were placed
together in a Schleck tube. The tube was evacuated and filled with
nitrogen three times. The solids were dissolved in dry CH Cl (10
1
3
2
2
7
.70 (s, 1H, CH ), 7.23 (s, 1H, CH ), 4.96 (s, 2H, CH ), 4.55−4.47
mL), and the resulting mixture was stirred at room temperature for 1
h. The solution was then concentrated nearly to dryness, and dry
diethyl ether (5 mL) was added. The brown solid so formed was
Ph
Ph
Cp
(
m, 6H; 4H, NCH CH CH CH ; and 2H, CH ), 4.21 (s, 5H, CH ),
2 2 2 3 Cp Cp
4.06 (s, 3H, NCH ), 2.01−1.89 (m, 4H, NCH CH CH CH ), 1.51−
3
2
2
2
3
I
DOI: 10.1021/acs.organomet.6b00517
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
washed three times with dry diethyl ether in order to remove the
formed acetylferrocene, which is soluble in diethyl ether. Complex 6
was isolated, along with 6-H, as a brown solid. Yield: 20.2 mg, 88%. IR
by filtration. Yield: 49.7 mg, 36%. H NMR (400 MHz, CDCl ): δ =
3
7.79 (s, 2H, CH ), 5.01 (s, 2H, CH ), 4.94 (br s, 4H; 2H, CHcod;
and 2H, CHCp), 4.82 (s, 5H, CHCp), 4.79−4.67 (m, 4H,
NCH CH CH CH ), 4.38 (s, 3H, NCH ), 4.36 (s, 3H, NCH ),
Ph
Cp
−
1
(
CH Cl ): 2071.2 and 1989.2 cm
(νCO). Anal. Calcd for
2
2
2
2
2
3
3
3
C H N ClFeIrO BF (838.9): C, 41.52; H, 3.85; N, 6.68. Found:
3.03 (br s, 2H, CHcod), 1.94−1.81 (m, 4H, NCH CH CH CH ),
29
32
4
2
4
2
2
2
3
C, 41.48; H, 3.80; N, 6.66. Electrospray MS (20 V, m/z): 753.1 [M −
1.66−1.53 (m, 12H; 4H, NCH CH CH CH ; and 8H, CH ), 1.05
2
2
2
3
2 cod
+
−
3
1
3
1
BF + H] . Electrospray MS negative mode (20 V, m/z): 87.3 [BF ] .
(t, J
= 16 Hz, 6H, NCH CH CH CH ). C{ H} NMR (100
H−H 2 2 2 3
4
4
Synthesis of Complex 7. A suspension of the ferrocene-based
MHz, CDCl ): δ = 198.2 (Ir-Ccarbene), 152.5 (NCN Cp), 135.1 (Cq Ph),
3
imidazolium salt 2 (100 mg, 0.17 mmol) and Ag O (19.63 mg, 0.08
128.9 (Cq Ph), 93.6 (CH ), 86.1 (CHcod), 72.8 (Cq Cp), 72.0 (CHCp),
2
Ph
mmol) in CH Cl was stirred at room temperature overnight. Then,
71.2 (CH ), 69.1 (CH ), 56.7 (CH ), 48.8 (NCH CH CH CH ),
2
2
Cp
Cp
cod
2
2
2
3
[
AuCl(SMe )] (50.05 mg, 0.17 mmol) was added. Immediately, the
35.3 (NCH ), 33.1 (CH2 c o d ), 30.8 (CH2 c o d ), 30.3
2
3
formation of a white precipitate was observed. To complete the
reaction, the suspension was stirred at room temperature for 7 h and
then filtered through a pad of Celite. The solution was concentrated
nearly to dryness, and hexane (5 mL) was added to precipitate the
complex, which was collected by filtration and further washed with
(NCH CH CH CH ), 20.6 (NCH CH CH CH ), 14.0
2
2
2
3
2
2
2
3
(NCH CH CH CH ). Electrospray MS (20 V, m/z): 911.1 [M −
2
2
2
3
+
−
I] . Electrospray MS negative mode (20 V, m/z): 126.9 [I] . Anal.
Calcd for C H N I FeIr (1037.66): C, 41.67; H, 4.56; N, 5.40.
36
47 4 2
Found: C, 41.66; H, 4.57; N, 5.44.
hexane. Complex 7 was isolated as an orange solid. Yield: 76.5 mg,
Synthesis of Complex 11. Complex 11 was isolated by anion
1
6
1%. H NMR (500 MHz, CD Cl ): δ = 7.70 (s, 1H, CH ), 7.29 (s,
exchange starting from complex 10 using NaBF . Complex 10 was
2
2
Ph
4
1
H, CH ), 4.96 (s, 2H, CH ), 4.56−4.51 (m, 6H; 4H,
dissolved in CH Cl and introduced in a chromatography column
Ph
Cp
2
2
NCH CH CH CH and 2H, CH ), 4.21 (s, 5H, CH ), 4.08 (s,
packed with silica gel saturated with CH Cl . Elution with 1:1
2
2
2
3
Cp
Cp
2 2
3
4
H, NCH ), 2.03−1.95 (m, 4H, NCH CH CH CH ), 1.53−1.42 (m,
CH Cl /acetone containing NaBF , gave compound 11 as a
2 2 4
3
2
2
2
3
3
1
H, NCH CH CH CH ), 1.00 (t,
J
= 20 Hz, 3H,
tetrafluoroborate salt. Yield: 125.3 mg, 37%. H NMR (400 MHz,
CDCl ): δ = 7.56 (s, 2H, CHPh), 4.95 (s, 4H; 2H, CHCp and 2H,
CHcod), 4.80 (s, 2H, CHCp), 4.77−4.59 (m, 4H, NCH CH CH CH ),
4.29 (s, 8H; 5H, CHCp and 3H, NCH ), 4.25 (s, 3H, NCH ), 3.04 (br
s, 2H, CHcod), 2.26−2.10 (m, 4H, NCH CH CH CH ), 1.94−1.81
(m, 4H, NCH CH CH CH ), 1.66−1.53 (m, 8H, CH2 cod), 1.07 (t,
JH−H = 12 Hz, 6H, NCH CH CH CH ). F NMR (376.5 MHz,
2
2
2
3
H−H
3
NCH CH CH CH ), 0.98 (t, JH − H
NCH CH CH CH ). C{ H} NMR (126 MHz, CD Cl ): δ =
1
=
20 Hz, 3H,
3
2
2
2
3
13
1
2
2
2
3
2
2
2
2
2
3
78.3 (Au-Ccarbene), 156.6 (NCN), 141.6 (Cq Ph), 135.8 (Cq Ph), 130.5
3
3
(
(
(
(
Cq Ph), 130.2 (Cq Ph), 100.2 (CH ), 90.7 (CH ), 70.8 (Cq Cp), 69.9
CH ), 69.5 (CH ), 49.2 (NCH CH CH CH ), 32.1 (NCH ), 32.0
2
2
2
3
Ph
Ph
Cp
Cp
2
2
2
3
3
2
2
2
3
3
19
NCH CH CH CH ), 20.5 (NCH CH CH CH ), 13.9
2
2
2
3
2
2
2
3
2
2
2
3
1
3
1
NCH CH CH CH ). Electrospray MS (20 V, m/z): 701.2 [M +
CDCl ): δ = −152.2. C{ H} NMR (100 MHz, CDCl ): δ = 197.8
(Ir-Ccarbene), 152.6 (NCN), 134.9 (Cq Ph), 128.9 (Cq Ph), 93.1 (CHPh),
85.9 (CHcod), 72.9 (Cq Cp), 71.7 (CH ), 71.0 (CH ), 69.8 (CH ),
2
2
2
3
3
3
+
H] . Anal. Calcd for C H N AuClFe (700.8): C, 46.27; H, 4.60; N,
7
27
32
4
.99. Found: C, 46.25; H, 4.60; N, 7.98.
Synthesis of Complex 8. As described for the oxidation of complex
, complex 7 (150 mg, 0.21 mmol) was reacted with acetylferrocenium
Cp
Cp
Cp
56.5 (CHcod), 48.6 (NCH CH CH CH ), 34.1 (NCH ), 33.1
2 2 2 3 3
5
(CH2 cod), 30.7 (CH2 cod), 30.3 (CH2 cod), 29.4 (NCH CH CH CH ),
2 2 2 3
tetrafluoroborate (67.4 mg, 0.21 mmol) in dry CH Cl (20 mL). The
20.5 (NCH CH CH CH ), 13.9 (NCH CH CH CH ). Electrospray
2
2
2 2 2 3 2 2 2 3
+
resulting mixture was stirred at room temperature for 1 h. Upon
mixing, a color change from orange to red occurred immediately. The
solution was then concentrated nearly to dryness and dry diethyl ether
MS (20 V, m/z): 911.1 [M − BF ] . Electrospray MS negative mode
4
−
(20 V, m/z): 87.1 [BF ] . Anal. Calcd for C H N IFeIrBF
4
36 47
4
4
(997.56): C, 43.34; H, 4.75; N, 5.62. Found: C, 43.39; H, 4.72; N,
(
20 mL) was added. After three subsequent washings with dry diethyl
5.63.
ether, complex 8 was isolated, along with 8-H, as a red solid. Yield:
Synthesis of Complex 12. CO gas was bubbled through a solution
of complex 11 (120 mg, 0.12 mmol) in CH Cl (10 mL) for 2 h at 0
1
30.0 mg, 77%. Anal. Calcd for C H N AuClFeBF (789.6): C,
27 32 4 4
2
2
4
1.17; H, 4.09; N, 7.11. Found: C, 41.09; H, 4.21; N, 7.11.
°C. The solution was then concentrated nearly to dryness. The crude
solid was washed three times with hexane to remove the released 1,5-
cylooctadiene. The pure complex 12 was collected by filtration. Yield:
+
Electrospray MS (20 V, m/z): 701.3 [M − BF ] . Electrospray MS
4
−
negative mode (20 V, m/z): 87.3 [BF ] .
4
−1
1
Synthesis of Compound 9. An excess of methyl iodide (5.62 mL,
94.0 mg, 83%. IR (CH Cl ): 2066.1 and 1988.5 cm (νCO). H NMR
2 2
89.40 mmol) was added to a solution of compound 2 (200 mg, 0.33
(400 MHz, CDCl ): δ = 7.99 (s, 1H, CH ), 4.99 (s, 2H, CH ),
3 Ph Cp
mmol) in dry acetonitrile (10 mL), and the resulting mixture was
heated at 90 °C overnight. After this time, the solvent was removed
nearly to dryness and diethyl ether (5 mL) was added. The brown
precipitate so formed was filtrated and washed with diethyl ether (5
4.91−4.70 (m, 6H; 4H, NCH CH CH CH and 2H, CH ), 4.55 (s,
2
2
2
3
Cp
5H, CH ), 4.35 (s, 6H, NCH ), 2.13−1.83 (m, 4H,
Cp
3
NCH CH CH CH ), 1.60−1.36 (m, 12H; 4H, NCH CH CH CH ),
2
2
2
3
2
2
2
3
19
1.12−0.91 (m, 6H, NCH CH CH CH ). F NMR (376.5 MHz,
2
2
2
3
13
1
mL). Compound 9 was isolated as a dark brown and highly insoluble
CDCl ): δ = −151.5. C{ H} NMR (100 MHz, CDCl ): δ = 186.5
3
3
1
solid. Yield: 200.7 mg, 81%. H NMR (300 MHz, DMSO-d ): δ =
(Ir-Ccarbene), 181.7 (Ir-CO), 167.7 (Ir-CO), 154.2 (NCN), 134.1
6
1
0.05 (s, 1H, NCHN), 8.85 (s, 1H, CH ), 5.33 (s, 2H, CH ), 5.04
(Cq Ph), 129.9 (Cq Ph), 128.8 (Cq Ph), 95.0 (CH ), 73.2 (Cq Cp), 72.0
Ph
Cp
Ph
(
s, 2H, CH ), 4.62−4.57 (m, 4H, NCH CH CH CH ), 4.53 (s, 3H,
(CH ), 71.2 (CH ), 69.0 (CH ), 49.4 (NCH CH CH CH ), 34.9
Cp
2
2
2
3
Cp
Cp
Cp
2
2
2
3
NCH ), 4.29 (s, 3H, NCH ), 4.10 (s, 5H, CH ), 2.02−1.97 (m, 4H,
NCH CH CH CH ), 1.43−1.36 (m, 4H, NCH CH CH CH ), 0.96
(NCH ), 30.8 (NCH CH CH CH ), 20.3 (NCH CH CH CH ), 13.9
3
3
Cp
3 2 2 2 3 2 2 2 3
(NCH CH CH CH ). Electrospray MS (20 V, m/z): 859.2 [M −
+ −
2
2
2
3
2
2
2
3
2
2
2
3
3
13
1
(
t, J
= 15 Hz, 6H, NCH CH CH CH ). C{ H} NMR (75 MHz,
-BF ] . Electrospray MS negative mode (20 V, m/z): 87.2 [BF ] .
H−H
2
2
2
3
4
4
DMSO-d ): δ = 155.2 (NCN), 144.7 (Cq Ph), 137.6 (NCHN), 131.6
Anal. Calcd for C H N O IFeIrBF (945.4): C, 38.11; H, 3.73; N,
30 35 4 2 4
6
(
(
(
1
Cq Ph), 129.7 (Cq Ph), 113.1 (Cq Ph), 104.3 (CH ), 97.6 (CH ), 72.9
5.93. Found: C, 38.24; H, 3.78; N, 5.92.
Synthesis of Complex 15. A mixture of compound 2 (250 mg, 0.43
Ph
Ph
CHCp), 71.9 (CHCp), 70.7 (CHCp), 64.0 (Cq Cp), 47.1
NCH CH CH CH ), 34.5 (NCH ), 30.2 (NCH CH CH CH ),
mmol), K CO (360 mg, 2.60 mmol), [IrCl(COD)] (114 mg, 0.21
2
2
2
3
3
2
2
2
3
2
3
2
9.0 (NCH CH CH CH ), 13.4 (NCH CH CH CH ). Electrospray
mmol), and KI (429 mg, 2.60 mmol) in acetone (40 mL) was stirred
at reflux overnight. After removal of the volatiles, the crude solid was
suspended in CH Cl and filtered through a pad of Celite to remove
2
2
2
3
2
2
2
3
2+
MS (20 V, m/z): 242.3 [M − 2I] . Anal. Calcd for C H N FeI
28
36
4
2
(738.4): C, 45.55; H, 4.91; N, 7.59. Found: C, 45.51; H, 5.00; N, 7.54.
2
2
Synthesis of Complex 10. A mixture of compound 9 (100 mg, 0.13
insoluble salts. The crude solid was purified by column chromatog-
1
mmol), [IrCl(COD)] (45.5 mg, 0.07 mmol), K CO (112.3 mg, 0.81
raphy eluting with CH Cl . Yield: 130 mg, 34%. H NMR (500 MHz,
2
2
3
2
2
mmol), and KI (134.9 mg, 0.81 mmol) in acetone (15 mL) was stirred
at reflux overnight. After removal of the volatiles, the crude solid was
suspended in CH Cl and filtered through a pad of Celite to remove
insoluble salts. The solvent was removed nearly to dryness, and diethyl
ether (5 mL) was added, yielding a brown solid, which was collected
CDCl ): δ = 7.56 (s, 1H, CH ), 7.08 (s, 1H, CH ), 4.93 (s, 2H,
3 Ph Ph
CHCp), 4.87 (br s, 2H, CHcod), 4.73−4.69 (m, 2H,
NCH CH CH CH ), 4.69−4.53 (m, 2H, NCH CH CH CH ), 4.48
2
2
2
2
2
3
2
2
2
3
(s, 2H, CH ), 4.17 (s, 5H, CH ), 4.05 (s, 3H, NCH ), 3.01 (br s,
Cp Cp 3
2H, CHcod), 2.14 (br s, 4H, NCH CH CH CH ), 1.59−1.50 (m, 12H;
2
2
2
3
J
DOI: 10.1021/acs.organomet.6b00517
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
4
6
H, NCH CH CH CH ; and 8H, CH ), 1.07 (t, J
= 15 Hz,
2
2
2
3
2 cod
H−H
ASSOCIATED CONTENT
■
* Supporting Information
3
H, NCH CH CH CH ), 1.03 (t, JH−H = 15 Hz, 6H,
NCH CH CH CH ). C{ H} NMR (126 MHz, CDCl ): δ = 191.9
2
2
2
3
S
1
3
1
2
2
2
3
3
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00517.
(
Ir-Ccarbene), 155.0 (NCN), 139.6 (Cq Ph), 133.8 (Cq Ph), 132.5 (Cq Ph),
1
7
4
32.3 (Cq Ph), 99.1 (CH ), 89.3 (CH ), 84.2 (CHcod), 74.0 (Cq Cp),
Ph Ph
0.4 (CH ), 69.8 (CH ), 69.2 (CH ), 55.8 (CHcod), 55.5 (CHcod),
Cp
Cp
Cp
8.4 (NCH CH CH CH ), 33.2 (CH2 cod), 33.0 (CH2 cod), 31.9
2
2
2
3
NMR spectra of complexes of the new complexes, cyclic
voltammograms of complexes 1, 2, 4, 5, and 7, and
computational details, including atomic coordinates of
optimized structures (PDF)
Crystallographic data for 6-H (CIF)
Crystallographic data for 7 (CIF)
(
NCH ), 31.0 (NCH CH CH CH ), 30.5 (CH2 cod), 30.3 (CH2 cod),
3 2 2 2 3
2
0.7 (NCH CH CH CH ), 14.0 (NCH CH CH CH ). Electrospray
2 2 2 3 2 2 2 3
+
MS (20 V, m/z): 897.2 [M + H] . Anal. Calcd for C H N IFeIr
35
44
4
(
6
895.72): C, 46.92; H, 4.95; N, 6.25. Found: C, 46.90; H, 4.93; N,
.25.
Synthesis of Complex 13. CO gas was bubbled through a solution
of complex 15 (100 mg, 0.05 mmol) in CH Cl (20 mL) for 2 h at 0
2
2
Crystallographic data for 8-H (CIF)
Crystallographic data for 11 (CIF)
°C. The solution was then concentrated nearly to dryness. The crude
solid was washed three times with hexane to remove the released 1,5-
cylooctadiene. The corresponding carbonyl derivative was collected by
filtration as a brown solid. Yield: 58.8 mg, 62%. IR (CH Cl ): 2064.2
and 1986.8 cm (νCO). H NMR (500 MHz, CDCl ): δ = 7.72 (s,
1
2
NCH CH CH CH ), 4.22 (s, 5H, CH ), 4.10 (s, 3H, NCH ), 2.06−
1
NCH CH CH CH ), 1.02 (t,
NCH CH CH CH ), 1.01 (t, JH − H
AUTHOR INFORMATION
Corresponding Authors
E-mail (M. Poyatos): poyatosd@uji.es.
E-mail (E. Peris): eperis@uji.es.
2
2
■
−1
1
3
H, CH ), 7.22 (s, 1H, CH ), 4.99 (s, 2H, CH ), 4.76−4.65 (m,
Ph
Ph
Cp
*
*
H, NCH CH CH CH ), 4.54 (s, 2H, CH ), 4.49−4.42 (m, 2H,
2
2
2
3
Cp
2
2
2
3
Cp
3
.94 (m, 4H, NCH CH CH CH ), 1.56−1.46 (m, 4H,
Notes
2
2
2
3
3
J
=
=
20 Hz, 3H,
20 Hz, 3H,
The authors declare no competing financial interest.
2
2
2
3
H − H
3
2
2
2
3
13
1
NCH CH CH CH ). C{ H} NMR (126 MHz, CDCl ): δ = 182.2
2
2
2
3
3
ACKNOWLEDGMENTS
■
(
(
(
(
(
(
(
Ir-Ccarbene), 180.8 (Ir-CO), 168.0 (Ir-CO), 156.4 (NCN), 140.8
We would like to dedicate this article to the memory of
Cq Ph), 134.9 (Cq Ph), 131.9 (Cq Ph), 128.8 (Cq Ph), 99.9 (CH ), 90.0
CH ), 73.5 (C ), 70.6 (CH ), 69.9 (CH ), 69.4 (CH ), 49.0
NCH CH CH CH ), 48.9 (NCH CH CH CH ), 31.9 (NCH ), 30.8
Ph
Roberto San
́
chez Delgado, a friend, an excellent researcher, and
Ph
q Cp
Cp
Cp
Cp
a reference to all those who knew him. We gratefully
acknowledge financial support from MINECO of Spain
(CTQ2014-51999-P) and the Universitat Jaume I
(P11B2014-02 and P11B2015-24). The authors are grateful
2
2
2
3
2
2
2
3
3
NCH CH CH CH ), 30.7 (NCH CH CH CH ), 20.4
2
2
2
3
2
2
2
3
NCH CH CH CH ), 14.0 (NCH CH CH CH ), 13.9
2
2
2
3
2
2
2
3
NCH CH CH CH ). Electrospray MS (20 V, m/z): 845.1 [M +
2
2
2
3
+
H] . Anal. Calcd for C H N FeIIrO (843.56): C, 41.29; H, 3.82; N,
6
29
32
4
2
to the Serveis Centrals d’Instrumentacio
the Universitat Jaume I for providing spectroscopic and X-ray
facilities. We are also very grateful to Dr. Jorg Sutter
Universitat Erlangen−Nurnberg) for carrying out the
Mossbauer spectroscopy.
́
Cientıfica (SCIC) of
́
.64. Found: C, 41.42; H, 3.84; N, 6.57.
Synthesis of Complex 14. Complex 12 (20 mg, 0.02 mmol) and
̈
acetylferrocenium tetrafluoroborate (6.66 mg, 0.02 mmol) were
dissolved in dry CH Cl (10 mL). The mixture was stirred at room
temperature for 2 h. The solvent was removed nearly to dryness, and
diethyl ether (20 mL) was added. The supernatant ether was removed
with a syringe. This was repeated three times to remove all
acetylferrocene. Yield: 19.0 mg, 87%. IR (CH Cl ): 2068.0 and
(
̈
̈
2
2
̈
REFERENCES
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■
2
2
−
1
1
991.4 cm (νCO). Anal. Calcd for C H N FeIrIO B F (1032.2):
30
35
4
2 2 8
C, 34.91; H, 3.42; N, 5.43. Found: C, 34.89; H, 3.45; N, 5.47.
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negative mode (20 V, m/z): 87.3 [BF ] .
+
4
−
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dichloromethane (2.5 mL) was stirred at room temperature for 24 h.
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dichloromethane to obtain the desired products. The products were
(
d) Hirao, T. Coord. Chem. Rev. 2002, 226, 81−91.
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16,17
identified by comparison to previously reported data.
General Procedure for the Au(I)-Catalyzed Hydroamination
of Phenylacetylene with Aryl Amines. The gold(I) catalyst (1 mol
%
together in a thick-walled Schlenk tube fitted with a Teflon cap. The
tube was then evacuated and filled with nitrogen three times.
Afterward, 1 mL of CH CN was added, and the reaction mixture
was stirred at room temperature for 5 min. After this time, the
corresponding arylamine (0.55 mmol), phenylacetylene (0.5 mmol),
and anisole as internal reference (0.5 mmol) were subsequently added.
The resulting mixture was stirred at 90 °C for the appropriate time.
The evolution of the reactions, yields, and conversions were
determined by GC analysis. The products were identified by
based on metal) and AgBF (2 mol %, 0.01 mmol) were placed
4
3
14f
comparison to previously reported data.
K
DOI: 10.1021/acs.organomet.6b00517
Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.6b00517
Organometallics XXXX, XXX, XXX−XXX