Iridium(III) Cp* complexes for the efficient hydroamination of internal alkynes

Article abstract of DOI:10.1021/om300550k

A series of iridium(III) and rhodium(III) 1,2,3,4,5- pentamethylcyclopentadienyl (Cp*) complexes of the type [M(Cp*)(LL)Cl]BPh₄ were synthesized, where LL is a chelating diimine or mixed pyrazolyl-phosphine or pyrazolyl-N-heterocyclic carbene donor ligand. The majority of these complexes were characterized by X-ray crystallography, allowing for a detailed comparison of their structural properties. These complexes were shown to yield active hydroamination catalysts upon in situ abstraction of the chloride coligand using AgBF₄. The activity of these catalysts for the intramolecular hydroamination of alkyne-amines to yield indolyl and pyrolyl heterocycles was investigated. It was found that chelating ligand groups containing a strongly coordinating N-heterocyclic carbene donor led to the most effective catalysis and that an increase in the steric bulk of the ligand was detrimental to the catalyst efficiency.

Full text of DOI:10.1021/om300550k

Article
pubs.acs.org/Organometallics
Iridium(III) Cp* Complexes for the Efficient Hydroamination of
Internal Alkynes
Katherine Gray,† Michael J. Page,† Jorg Wagler,‡ and Barbara A. Messerle*,†
̈
†School of Chemistry, University of New South Wales, Sydney NSW 2052, Australia
‡Research School of Chemistry, The Australian National University, Canberra ACT 0200, Australia, and Institut fur Anorganische
̈
Chemie, Technische Universitat Bergakademie Freiberg, 09596 Freiberg, Germany
̈
S
* Supporting Information
ABSTRACT: A series of iridium(III) and rhodium(III) 1,2,3,4,5-pentamethylcy-
clopentadienyl (Cp*) complexes of the type [M(Cp*)(LL)Cl]BPh4 were
synthesized, where LL is a chelating diimine or mixed pyrazolyl-phosphine or
pyrazolyl-N-heterocyclic carbene donor ligand. The majority of these complexes
were characterized by X-ray crystallography, allowing for a detailed comparison of
their structural properties. These complexes were shown to yield active
hydroamination catalysts upon in situ abstraction of the chloride coligand using
AgBF4. The activity of these catalysts for the intramolecular hydroamination of
alkyne-amines to yield indolyl and pyrolyl heterocycles was investigated. It was
found that chelating ligand groups containing a strongly coordinating N-
heterocyclic carbene donor led to the most effective catalysis and that an increase
in the steric bulk of the ligand was detrimental to the catalyst efficiency.
Scheme 1. (a) Important Indolyl-Containing Natural
Products; (b) Synthesis of Indoles via Catalyzed
Hydroamination of ortho-Alkynylanilines
INTRODUCTION
■
The transition metal catalyzed hydroamination reaction, which
involves the addition of N−H bonds across carbon−carbon
double or triple bonds, offers an atom-efficient pathway to
producing amines and imines.1 When applied in an intra-
molecular fashion, the hydroamination reaction provides a
useful route to the synthesis of nitrogen heterocycles, an
important class of compounds found in numerous biologically
active natural products. One particularly important type of
nitrogen heterocycle is the indole moiety, which binds with
high affinity to many biological receptors and is prevalent in
such a wide range of pharmaceutical agents it is often said to
have a “privileged” structure.2 Prominent examples of bio-
logically active indole-containing products include 5-hydroxy-
tryptamine (serotonin), D-lysergic acid diethylamide (LSD),
and the anti-inflammatory drugs indomethacin and etodolac
(Scheme 1a).2 Typically the synthesis of suitably modified
indoles requires the application of challenging multistep
procedures often relying on the introduction of bulky
protecting and/or directing groups that can impair the ultimate
functionality of the molecule.2,3 However, in recent years the
transition metal catalyzed intramolecular hydroamination of
ortho-alkynylanilines has proven to be a particularly successful
strategy for the synthesis of a wide range of indole motifs
(Scheme 1b).4
terminal alkynes to yield alkynylaniline intermediates, which
underwent subsequent cyclization to give the indole
product.5d,e More recently a range of simple Au complexes
(e.g., NaAuCl4,9a,b AuOTf3,9c PPh3AuOTf9d,e) have emerged as
able catalysts for the cyclization of alkynylanilines. While
displaying moderate activity, these systems have received
particular attention due to the ability of the gold catalyst to
also functionalize the C3 position of the product indole in a
tandem one-pot procedure.9f A number of reports have also
demonstrated the utility of group 9 metal complexes as catalysts
for the hydroamination reaction. For example Trost et al.
A number of late transition metal complexes, especially those
containing Pd,5 Cu,6 Rh,7 Ru,8 and Au,9 have demonstrated a
high catalytic activity as well as functional group tolerance for
the hydroamination of alkynylanilines. Early interest in Pd/Cu-
mediated hydroamination catalysis emerged from the use of
these systems in the C−C coupling of o-haloanilines with
Received: June 18, 2012
Published: August 10, 2012
© 2012 American Chemical Society
6270
dx.doi.org/10.1021/om300550k | Organometallics 2012, 31, 6270−6277

Organometallics
Article
Chart 1. Iridium(III) and Rhodium(III) Cp* Complexes Used for the Catalyzed Hydroamination of Alkynyl-Amines and
a
-Anilines
a
Complexes containing ligands 1 and 2 were reported previously.
Scheme 2
employed a rhodium(I)/phosphine system to catalyze the
cyclization of alkynylanilines containing a terminal alkyne
bond.7a Interestingly, internal alkynes were entirely inactive
under these conditions. On the other hand, an iridium(III)-
hydride catalyst reported by Crabtree and co-workers that gave
excellent conversions, under very mild reaction conditions, for
the cyclization of internal alkynylanilines, was entirely inactive
toward terminal alkynes.10
In previous studies we have reported a number of highly
efficient Rh(I) and Ir(I) catalysts for the hydroamination of
both alkynylanilines11 and aliphatic alkynylamines.12 A large
impact on catalyst activity was observed in these systems by
simply varying the nature of a chelating ligand group, for
example from simple bidentate bis-imine and bis-pyrazolyl
nitrogen donor ligands to heteroditopic nitrogen-phosphine
and nitrogen-N-heterocyclic carbene donor ligands. One
limitation of these systems is their low catalytic activity toward
substrates containing nonterminal alkyne groups. Following a
combinatorial screening of different metal−ligand combinations
we recently identified a series of in situ generated Ir(III)
complexes of the type [IrCp*(NN)Cl]+ (where Cp* =
1,2,3,4,5-pentamethylcyclopentadienyl and NN = a bidentate
N-donor ligand) that were active catalysts for the hydro-
amination of nonterminal alkyne substrates such as 2-(2-
phenylethynyl)aniline (8).13
Here we report the synthesis of a series of Ir(III) and Rh(III)
Cp* complexes containing bidentate ligand groups, including
the diimine ligands ClPh-BIAN (3) and Mes-DAD (4), and the
heteroditopic pyrazolyl-phosphine ligand PzP (5) and
pyrazolyl-carbene ligands PzIMes (6) and PzIMe (7) (Chart
1). Where catalysts of this type have not previously been
considered as hydroamination catalysts, we have investigated
6271
dx.doi.org/10.1021/om300550k | Organometallics 2012, 31, 6270−6277

Organometallics
Article
the activity of these complexes as catalysts for the intra-
molecular hydroamination of both 2-(2-phenylethynyl)aniline
(8) and 4-phenyl-3-butyne-1-amine (9) to yield 2-phenylindole
(10) and 2-phenyl-1-pyrroline (11), respectively (Chart 1).
sphere of all complexes are summarized in Table 1. Included for
comparison is the metric data for the previously reported
complex [Ir(Cp*)(Mes-BIAN)Cl]BF4 (17a) containing the
Mes-BIAN (2) ligand.14
Comparing the structure of complexes 12a and 17a, we can
see that the Ir−N bond lengths are only slightly longer for the
complex containing the mesityl-substituted ligand Mes-BIAN
(2) compared to complexes with the p-chlorophenyl-
substituted ligand ClPh-BIAN (3). In these compounds the
flat side of the aryl groups is exposed to the Ir-coordination
sphere, so there is no pronounced repulsion between IrClCp*
and the mesityl Me groups. Therefore the steric forces between
the mesityl or p-chlorophenyl groups and the IrClCp* fragment
are similar. In contrast, the Ir−N bond lengths for complex 13a,
which contains the N-mesityl-substituted Mes-DAD (4) ligand,
are significantly shorter than those of complex 17a, containing
the similar N-mesityl-substituted Mes-BIAN (2) ligand.
Considering the similar steric demands of these two ligands,
the shorter Ir−N bond length observed with Mes-DAD (4)
suggests a greater σ-donation capacity of the Mes-DAD ligand
than that of the Mes-BIAN (2) ligand. The shorter Ir−N bond
length of complex 13a results in a notably longer Ir−Cp*
distance compared to both complexes 12a and 17a.
RESULTS AND DISCUSSION
■
Synthesis of Iridium and Rhodium Cp* Complexes.
The iridium (12a and 13a) and rhodium (12b and 13b) Cp*
complexes containing the bidentate diimine ligands ClPh-BIAN
(3) and Mes-DAD (4), respectively, were synthesized following
the general methods reported by Kennedy (Scheme 2a).14
A
toluene or acetone solution of the ligand and metal precursor
[M(Cp*)Cl2]2 (M = Rh or Ir) was stirred for 30 min followed
by addition of a methanol solution of sodium tetraphenylbo-
rate, and the solid product was isolated. Similarly, the iridium
complex 14a was synthesized by direct reaction of the
pyrazolyl-phosphine ligand PzP (5) with the iridium precursor
[Ir(Cp*)Cl2]2 and sodium tetraphenylborate in methanol.15
Synthesis of Ir (15a and 16a) and Rh (15b and 16b)
complexes containing the N-heterocyclic carbene (NHC)
ligands PzIMes (6) and PzIMe (7) was achieved via
transmetalation of the carbene from an in situ generated silver
complex. An acetone solution of the imidazolium tetraphe-
nylborate salt (5·HBPh4 or 6·HBPh4) was treated with silver
oxide for 1 h followed by addition of the Ir or Rh metal
precursor [M(Cp*)Cl2]2 (Scheme 2b). All the complexes (12−
16) were found to be air stable in the solid state and in
solutions of acetone, apart from complex 14a, which contains
an oxygen-sensitive phosphine group and decomposes in
aerated solutions.
For the carbene-containing complexes 15a and 16a the
longer Ir−C and Ir−Cp* bond lengths in complex 15a indicate
a greater interaction between IrClCp* and the PzIMes (6)
ligand than was observed between the IrClCp* and the PzIMe
(7) ligand of 16a. This result is probably a reflection not only of
the greater steric bulk of mesityl versus methyl but also of the
more flexible ethyl bridge in PzIMe (7), allowing this ligand to
adopt a more sterically favorable conformation. It is also worth
noting how the structures of the two ligands, PzIMes (6) and
PzIMe (7), significantly impact the C−Ir−N bite angle of the
chelate in complexes 15a (82.76(6)°) and 16a (91.30(14)°),
respectively. Unsurprisingly the bulky PPh2 donor of the PzP
(5) ligand in complex 14a results in the longest Ir−ligand and
Ir−Cp* bonds of the series.
The solid-state structures of complexes 12a, 13a, 13b, 14a,
15a, 15b, 16a, and 16b were all characterized using X-ray
crystallography. ORTEP diagrams of the cationic Ir complexes
of compounds 12a, 13a, 14a, 15a, and 16a are shown in Figure
1. Similar structures were observed for the analogous Rh
complexes 13b, 15b, and 16b; see the Supporting Information.
Selected bond lengths and angles of the inner coordination
1
There is evidence of steric congestion in the H and 13C
NMR spectra of the rhodium and iridium complexes. In the 1H
NMR spectra of complexes 13a, 13b, 15a, and 15b inequivalent
ortho-methyl proton resonances for the mesityl groups of Mes-
DAD (4) and PzIMes (6) were observed, indicating restricted
rotation about the N−CAr bond on the NMR time scale.
Similarly, inequivalent ortho and meta 13C NMR signals were
observed for the p-chlorophenyl substituents in complexes 12a
and 12b containing the ClPh-BIAN (3) ligand.
Catalysis. To achieve an active catalyst using the
coordinatively saturated Rh(III) and Ir(III) chloro complexes
12−16, abstraction of the chloride coligand is required to
generate a vacant coordination site on the metal through which
the substrate may bind.13 The active catalysts were therefore
synthesized in situ via reaction of the chloro complexes 12−16
with two molar equivalents of AgBF4, resulting in precipitation
of the insoluble AgCl and AgBPh4 salts.
Hydroamination of 2-(2-Phenylethynyl)aniline (8).
The hydroamination of 2-(2-phenylethynyl)aniline (8) to give
2-phenylindole (10) was initially investigated using the Ir(III)
complexes 12a, 13a, 14a, 15a, and 16a as catalysts. Also
included in this study was the previously reported complex
[Ir(Cp*)(Mes-BIAN)Cl]BF4 (17a) containing the Mes-BIAN
ligand 2. The reactions were carried out using 5 mol % of Ir
complex and 10 mol % of AgBF4 in acetone-d6 at 50 °C and
Figure 1. ORTEP diagrams of the cations in the crystal structures of
compounds 12a·CH2Cl2, 13a, 14a·0.8(n-hexane), 15a, and 16a.
Thermal displacement ellipsoids are drawn at the 50% probability
level, and hydrogen atoms have been omitted for clarity. Selected
atoms are labeled.
1
were monitored using H NMR spectroscopy (Figure 2). The
6272
dx.doi.org/10.1021/om300550k | Organometallics 2012, 31, 6270−6277

Organometallics
Article
Table 1. Selected Bond Lengths (Å) and Angles (deg) for the Ir(III) Complexes 12a−17a and Rh(III) Complexes 13b, 15b, and
16b
a
complex
17a14
LL
M−N
M−X (P, C)
M−Cp*
L−M−L
Mes-BIAN
2.122(5)
1.806(1)
76.5(3)
2.122(5)
12a
13a
ClPh-BIAN
Mes-DAD
2.0996(14)
2.1087(15)
2.0743(18)
2.0765(17)
2.0898(17)
2.1018(16)
2.111(3)
1.803(1)
1.819(1)
76.27(6)
76.22(7)
14a
15a
16a
13b
PzP
2.3093(5)
2.067(2)
2.026(4)
1.831(1)
1.820(1)
1.816(1)
1.805(1)
90.06(5)
82.76(6)
91.30(14)
76.56(9)
PzIMes
PzIMe
Mes-DAD
2.107(2)
2.112(2)
15b
16b
PzIMes
PzIMe
2.107(4)
2.072(5)
2.029(4)
1.865(1)
1.815(1)
83.18(16)
90.97(15)
2.107(4)
a
Distance between the metal atom and the least-squares plane of the five carbon atoms of the Cp* ring.
Figure 2. Hydroamination of 2-(2-phenylethynyl)aniline (8) to 2-phenylindole (10) using complexes 12a−17a as catalyst precursors with the
variable ligand group identified in parentheses.
most efficient of these catalysts was found to be the complex
16a, bearing the pyrazolyl-NHC ligand PzIMe (7), which
achieved 90% conversion of 8 to 10 after 90 min. The pyrazole-
phosphine-containing complex 14a also showed a superior
catalytic activity to the diimine-containing catalysts 12a, 13a,
and 17a. For the Mes-DAD (4)-containing complex (13a) the
poor result was attributed to decomposition of the catalyst after
20 min.16 The exceptionally high catalytic activity of complex
16a may be a result of the smaller steric bulk of the PzIMe (7)
ligand, with the larger N-mesityl and PPh2 substituents present
in complexes 15a and 14a (respectively) inhibiting coordina-
tion of the substrate to the metal center.
The catalytic activity of the most effective iridium complex
(16a) was compared to its rhodium analogue 16b. It was found
that the rhodium complex was only half as active as its iridium
congener under the same reaction conditions, with complex
16b achieving only 46% conversion after 90 min relative to 90%
for 16a.
The efficiency of the most active catalyst of the series, 16a,
for the hydroamination of 2-(2-phenylethynyl)aniline compares
favorably with other late transition metal catalysts. Several
analogous Ir(III) and Rh(III) complexes of the formula
[M(Cp*)Cl2(NHC)] were reported recently by Ogata et al.,
where the active catalysts were also synthesized by addition of a
Ag salt to abstract one of the chloride ligands.17 These
complexes were moderately active for the hydroamination of 2-
(2-phenylethynyl)aniline, achieving less than 73% conversion of
the substrate after 24 h in refluxing acetonitrile with 10 mol %
metal loading, where the best catalyst we report here (16a)
achieves 90% conversion in 1.5 h, with 5% loading. Consistent
with our results, a higher catalyst activity was observed by
Ogata et al. for their Ir compounds compared to their Rh
compounds, with the highest activity obtained for the catalyst
containing the least sterically bulky NHC ligand. Conversely, a
highly efficient Ir(III) hydroamination catalyst developed by
Crabtree and co-workers achieved 92% conversion for the
6273
dx.doi.org/10.1021/om300550k | Organometallics 2012, 31, 6270−6277

Organometallics
Article
Figure 3. Hydroamination of 4-phenyl-3-butyne-1-amine (9) to 2-phenyl-1-pyrroline (11) using complexes 12a−17a as catalyst precursors with the
variable ligand group identified in parentheses.
cyclization of 2-(2-phenylethynyl)aniline within 1 h at 35 °C
and 1 mol % catalyst loading.10
the iridium complex [Ir(bpm)(CO)2]BPh4 is a far less active
catalyst than its rhodium congener for this transformation.
Reaction Mechanism. A proposed mechanism for the
hydroamination of alkyne-amines using the Ir(III) catalysts
under investigation here is shown in Scheme 3. The active
Hydroamination of 4-Phenyl-3-butyne-1-amine (9).
Optimization of reaction conditions for the hydroamination of
4-phenyl-3-butyne-1-amine (9) to yield 2-phenyl-1-pyrroline
(11) indicated that the catalysis was most successful in THF-d8
solutions at 60 °C. Only 3 mol % of the Ir complex (12a−17a)
was used and 6 mol % AgBF4, and the reaction progress was
Scheme 3. Proposed Mechanism for the Cyclization of 8
Catalyzed by the Ir(III) Complexes 12a−17a
1
monitored using H NMR spectroscopy (Figure 3).
A similar and much more pronounced trend in reaction rates
was observed here than reported above for the hydroamination
of 2-(2-phenylethynyl)aniline (8). Namely, complexes 14a,
15a, and 16a, containing the mixed donor pyrazole-phosphine/
carbene ligands, are far superior catalyst precursors for the
hydroamination of 9 compared to the diimine-containing
complexes 12a, 13a, and 17a. In fact, catalysts containing the
diimine ligands appear to be almost entirely inactive for the
conversion of this substrate. The reactivity of NHC containing
complexes 15a and 16a is very similar, presumably the smaller
steric bulk of the substrate 4-phenyl-3-butyne-1-amine (9)
compared to 2-(2-phenylethynyl)aniline (8) minimizes the
influence that steric crowding about the metal center has on the
reaction rate. The poor activity of the phosphine-containing
complex 14a appears to be due to a steady deactivation of the
catalyst, as evident from its reaction profile in Figure 3, with a
maximum conversion of 40% achieved after 3 h.
Comparison of the iridium complex 16a (95% conversion
after 3 h) with its rhodium analogue 16b (15% conversion after
3 h) leads to the conclusion that rhodium(III) is an ineffective
metal center for hydroamination catalysts of this type.
Both carbene-containing complexes 15a and 16a show
excellent catalytic activity and are comparable to some of the
best catalysts reported in the literature for this reaction.4−12 In
particular, the efficiency of catalysts 15a and 16a is nearly
equivalent to that of [Rh(bpm)(CO)2]BPh4 (bpm = bis(1-
pyrazolyl)methane, 1), which we previously reported as one of
the most active hydroamination catalysts for this reaction.11a It
is curious to note that in contrast to the results reported here
catalyst is the coordinatively unsaturated intermediate A formed
on chloride abstraction from the catalyst precursor 12a−17a.
The intermediate A first coordinates to the substrate (8) to give
the alkyne complex B. The electrophilic metal center activates
the CC bond toward nucleophilic attack from the pendant
amine group, yielding intermediate C. Protonolysis of the Ir−C
bond then completes the cycle regenerating A and eliminating
the cyclized product (10). It is likely that the catalyst resting
state involves the reversible coordination of the substrate
through its amine substituent to yield D. This process is
6274
dx.doi.org/10.1021/om300550k | Organometallics 2012, 31, 6270−6277

Organometallics
Article
procedures, as were the catalysis substrates 2-(2-phenylethynyl)aniline
(8)5b and 4-phenyl-3-butyn-1-amine (9).12c All manipulations of metal
complexes and air-sensitive reagents were performed using standard
Schlenk techniques or in a nitrogen-filled glovebox. Solvents were
dried by conventional methods and distilled immediately prior to use.
Deuterated solvents were purchased from Cambridge Isotopes and
Aldrich Chemical Co. Inc., dried with suitable drying agents, and
vacuum transferred prior to use.
consistent with a recent mechanistic investigation we reported,
supported by DFT calculations, for N-vinylindole formation via
tandem imine formation and cycloisomerization of 8 catalyzed
by [Ir(Cp*)Cl2]2.18 A similar mechanism was also proposed for
the hydroamination of alkynylanilines using other late
transition metal catalysts.5c,9a,12
The mechanism is consistent with our observation that
complexes 14a, 15a, and 16a, containing heteroditopic
pyrazolyl-carbene or pyrazolyl-phosphine ligands, are much
more active catalysts than the diimine-containing complexes
12a, 13a, and 17a. The N-heterocyclic carbene and phosphine
ligands are very strong σ-donors; therefore complexes
containing these ligand groups will have less attraction for
the amine σ-donor of the substrate and more affinity for
coordinating the π-accepting CC bond, thereby facilitating
formation of the catalytically relevant intermediate B.
Conversely, the relatively weak σ-donating diimine ligands
would yield complexes with a stronger preference for
coordinating the substrate amine, thus stabilizing the catalyti-
cally inactive intermediate D. This reasoning would also explain
the significant decrease in reaction rate observed when the aryl
substituents on the BIAN ligands are changed from mesityl
(complex 17a) to electron-withdrawing para-chlorophenyl
(complex 12a). It should also be noted that the stronger
metal−ligand bonds formed by carbene and phosphine donor
groups may prevent complete dissociation of the ligand during
catalysis and so inhibit decomposition of the complex.
1H, 13C, and 31P NMR spectra were recorded on Bruker DPX 300
and DMX 500 spectrometers at 298 K unless otherwise stated. 1H and
13C chemical shifts (δ) are referenced to residual solvent resonances
and are quoted in ppm. The following abbreviations are used to
identify NMR resonances: Np (naphthyl), Ph (phenyl), Pz
(pyrazolyl), Im (imidazolyl), and In (indolyl). Melting points were
recorded using a Reichert apparatus and are uncorrected. Electrospray
mass spectra (ESI-MS) were performed by the Biological Mass
Spectrometry Facility (BMSF), University of New South Wales.
Microanalyses were performed by the Campbell Microanalytical
Laboratory, University of Otago, New Zealand. Single-crystal X-ray
structure analyses were performed on a Nonius Kappa CCD
diffractometer (at the Research School of Chemistry, The Australian
National University) and on a Bruker AXS X8 APEX2 CCD
diffractometer (at the Technische Universitat Bergakademie Freiberg).
̈
The structures were solved by direct methods (SHELXS) and refined
with full-matrix least-squares on F2 (SHELXL) in WinGX.23 All non-
hydrogen atoms were refined anisotropically. H atoms were refined
isotropically in idealized positions (riding model). Crystallographic
data for the structures have been deposited with the Cambridge
Crystallographic Data Centre, CCDC-876339 (12a·CH2Cl2), CCDC-
876335 (13a),CCDC-876340 (13b), CCDC-876337 (14a·0.8-
(C6H14)), CCDC-876338 (15a), CCDC-876342 (15b), CCDC-
876336 (16a), and CCDC-876341 (16b). Copies of the data can be
obtained free of charge online via www.ccdc.cam.ac.uk/data_request/
cif. Thermal ellipsoid diagrams of the molecules were generated using
ORTEP-324 and POV-Ray 3.62.25
CONCLUSION
■
We have successfully synthesized a range of Ir(III) and Rh(III)
complexes of the type [M(Cp*)(LL)Cl]BPh4, containing the
diimine ligands ClPh-BIAN (3) and Mes-DAD (4) and the
heteroditopic pyrazolyl-phosphine and pyrazolyl-carbene li-
gands PzP (5), PzIMes (6), and PzIMe (7). The majority of
these compounds were characterized by X-ray crystallography,
allowing a detailed comparison of their structural properties in
the solid state. These complexes yield active hydroamination
catalysts upon abstraction of the chloride coligand with AgBF4.
The hydroamination of the nonterminal alkyne-amines 2-(2-
phenylethynyl)aniline (8) and 4-phenyl-3-butyne-1-amine (9)
was investigated. It was found that the Ir(III) complexes were
far superior catalysts compared to the Rh(III) complexes for
the hydroamination of both aliphatic amines and anilines. The
most active catalysts are formed from iridium complexes with
ligands containing the strongly coordinating NHC or
phosphine donors PzIMes (6) and PzIMe (7). Steric shielding
of the metal center by the inclusion of large substituents on the
ligand scaffold was shown to have a detrimental impact on
catalyst activity, with the complex containing the sterically least
bulky ligand PzIMe (7) affording a catalyst of superior activity.
The most active catalysts reported here have an activity
comparable to that of some of the best catalysts reported in the
literature for this reaction. Further work on expanding the
substrate scope of these catalysts is ongoing.
Synthesis of Ir(III) and Rh(III) Complexes. [M(Cp*)(ClPh-
BIAN)Cl]BPh4 (M = Ir, 12a; M = Rh, 12b). A suspension of the
iridium or rhodium precursor [M(Cp*)Cl2]2 (0.100 mmol) and ligand
ClPh-BIAN (3) (47 mg, 0.118 mmol) in toluene (20 mL) was stirred
for 30 min prior to addition of a methanol (1 mL) solution of NaBPh4
(50 mg, 0.146 mmol). The resulting dark brown solution was stirred
overnight at room temperature to give a dark brown precipitate. The
precipitate was filtered and recrystallized from dichloromethane and
hexane to yield the product.
Iridium complex 12a: dark brown needles (89%). MS (ESI,
CH2Cl2) m/z: 763.10 [M − BPh4]+ (100%). Anal. Found (calcd) for
C58H49BCl3IrN2·0.5CH2Cl2: C, 61.93 (62.41); H, 4.67 (4.48); N, 2.38
1
3
(2.49). H NMR (300 MHz, acetone-d6): δ 8.40 (d, 2H, J = 8.4 Hz,
3
NpH), 7.95−7.78 (m, 8H, PhH), 7.74 (t, 2H, J = 15.7 Hz, NpH),
7.34 (d, 2H, 3J = 7.4 Hz, NpH), 7.33 (m, 8H, o-BPh4), 6.90 (t, 8H, 3J =
3
14.6 Hz, m-BPh4), 6.75 (t, 4H, J = 7.5 Hz, p-BPh4), 1.39 (s, 15H,
CH3). 13C{1H} NMR (75 MHz, acetone-d6): δ 175.0 (NC), 163.9
1
(q, JB−C = 49.2 Hz, ipso-BPh4), 146.1 (NpC) 145.2 (NC), 136.1 (q,
2JB−C = 1.3 Hz, o-BPh4), 134.9 (CCl), 132.6 (NpCH), 131.5 (NpC),
131.0 (PhC), 129.7 (PhC), 129.2 (NpCH), 125.4 (NpC) 125.2
3
(NpCH), 125.0 (q, JB−C = 2.6 Hz, m-BPh4), 123.6 (PhC), 123.2
(PhC), 121.2 (p-BPh4), 92.1 (CCH3), 7.6 (CH3).
Rhodium complex 12b: red-brown needles (50%). Anal. Found
(calcd) for C58H49BCl3RhN2·0.5CH2Cl2: C, 67.96 (67.78); H, 5.09
1
(4.86); N, 2.66 (2.70). H NMR (300 MHz, acetone-d6): δ 8.34 (d,
3
3
2H, J = 8.4 Hz, NpH), 7.96−7.76 (m, 8H, PhH), 7.71 (t, 2H, J =
15.7 Hz, NpH), 7.33 (m, 8H, o-BPh4), 7.26 (d, 2H, 3J = 7.4 Hz, NpH),
6.90 (t, 8H, 3J = 14.7 Hz, m-BPh4), 6.75 (t, 4H, 3J = 7.5 Hz, p-BPh4),
1.39 (s, 15H, CH3). 13C{1H} NMR (75 MHz, acetone-d6): δ 172.4
EXPERIMENTAL SECTION
■
General Procedures. Iridium(III) chloride hydrate was obtained
from Precious Metals Online P/L and used without further
purification. All other reagents were purchased from Aldrich,
Lancaster, and Ajax Fine Chemicals. The ligands ClPh-BIAN (3),19
Mes-DAD (4),20 PzP (5),12b PzIMe·HBPh4 (6·HBPh4),21 and
1
(NC), 164.3 (q, JB−C = 49.9 Hz, ipso-BPh4), 145.5 (NpC) 145.4
(NC), 136.1 (d, 2JB−C = 1.4 Hz, o-BPh4), 134.5 (CCl), 132.7 (NpCH),
131.4 (NpC), 131.1 (PhC), 129.7 (PhC), 129.0 (NpCH), 125.6
3
(NpCH) 125.3 (NpC), 125.0 (q, JB−C = 2.9 Hz, m-BPh4), 123.2
PzIMes·HBPh4 (7·HBPh4)21 and metal precursors [Ir(Cp*)Cl2]2
(PhC), 123.0 (PhC), 121.2 (p-BPh4), 98.3 (d, 1JRh−C = 8.0 Hz, CCH3),
7.9 (CH3).
22
22
and [Rh(Cp*)Cl2]2 were synthesized according to published
6275
dx.doi.org/10.1021/om300550k | Organometallics 2012, 31, 6270−6277

Organometallics
Article
[M(Cp*)(Mes-DAD)Cl]BPh4 (M = Ir, 13a; M = Rh, 13b). An acetone
(15 mL) solution of the iridium or rhodium precursor [M(Cp*)Cl2]2
(0.130 mmol) and ligand Mes-DAD (4) (77.1 mg, 0.264 mmol) was
stirred overnight at room temperature to give a dark solution and a
black-brown precipitate. A methanol (1 mL) solution of NaBPh4 (95.0
mg, 0.278 mmol) was added, and the dark suspension stirred for 40
min at room temperature. The solvent was removed in vacuo to give a
black-brown solid, which was recrystallized from dichloromethane and
hexane to yield the product.
C50H53BClIrN4: C, 63.36 (63.32); H, 5.77 (5.63); N, 6.05 (5.91).
3
1H NMR (300 MHz, acetone-d6): δ 8.24 (d, 1H, J = 2.6 Hz, PzH),
3
3
7.87 (d, 1H, J = 2.3 Hz, PzH), 7.86 (d, 1H, J = 2.3 Hz, ImH), 7.33
3
(m, 8H, o-BPh4), 7.29 (d, 1H, J = 2.3 Hz, ImH), 7.03 (s, 1H, ArH),
2
3
6.98 (d, 2H, J = 14.0 Hz, CH2), 6.91 (t, 8H, J = 7.2 Hz, m-BPh4),
6.90 (s, 1H, ArH), 6.76 (t, 4H, 3J = 7.2, p-BPh4), 6.68 (t, 1H, 3J = 5.1
2
Hz, PzH), 6.00 (d, 1H, J = 14.0, CH2), 2.31 (s, 6H, p-CH3), 2.15 (s,
6H, o-CH3), 1.97 (s, 6H, o-CH3), 1.57 (s, 15H, CH3). 13C{1H} NMR
1
(75 MHz, acetone-d6): δ 164.0 (q, JB−C = 49.1 Hz, ipso-BPh4), 155.4
(NCN), 144.1 (PzC), 139.0 (p-C), 138.1 (NC), 136.1 (q, JB−C = 1.5
2
Iridium complex 13a: very dark brown-black powder (77%). MS
(ESI, CH2Cl2) m/z: 655.2 [M − BPh4]+ (100%). Anal. Found (calcd)
for C54H59BClIrN2·1.5CH2Cl2: C, 60.39 (60.49); H, 5.76 (5.67); N,
Hz, o-BPh4), 134.8 (o-C), 134.7 (o-C), 134.1 (PzC), 129.1 (m-CH),
127.7 (m-CH), 125.5 (ImC), 125.0 (q, 3JB−C = 2.6 Hz, m-BPh4), 122.5
(ImC), 121.2 (p-BPh4), 108.3 (PzC), 91.3 (CCH3), 63.5 (CH2), 20.1
(p-CH3), 19.3 (o-CH3), 18.3 (o-CH3), 8.5 (CH3).
1
2.69 (2.54). H NMR (300 MHz, acetone-d6): δ 9.29 (s, 2H, N
3
CH), 7.33 (m, 8H, o-BPh4), 7.13 (s, 4H, ArH), 6.91 (t, 8H, J = 14.7
3
Hz, m-BPh4), 6.76 (t, 4H, J = 7.2 Hz, p-BPh4), 2.40 (s, 6H, o-CH3),
Rhodium complex 15b: orange powder (43%). MS (ESI, CH2Cl2)
m/z: 539.1 [M − BPh4]+ (100%). 1H NMR (300 MHz, acetone-d6): δ
8.17 (d, 1H, 3J = 2.8 Hz, PzH), 7.89 (d, 1H, 3J = 2.0 Hz, PzH), 7.83 (d,
1H, 3J = 2.0 Hz, ImH), 7.33 (m, 8H, o-BPh4), 7.28 (d, 1H, 3J = 2.0 Hz,
ImH), 7.12 (s, 1H, ArH), 7.03 (s, 1H, ArH), 6.91 (t, 8H, 3J = 14.7 Hz,
m-BPh4), 6.88 (d, 1H, 2J = 14.1 Hz, CH2), 6.76 (t, 4H, 3J = 7.2 Hz, p-
BPh4), 6.59 (t, 1H, 3 = 2.8 Hz, PzH), 6.10 (d, 1H, 2J = 14.1 Hz, CH2),
2.18 (s, 6H, p-CH3), 2.00 (s, 6H, o-CH3), 1.93 (s, 6H, o-CH3), 1.54 (s,
2.37 (s, 6H, p-CH3), 2.15 (s, 6H, o-CH3), 1.24 (s, 15H, CH3). 13C{1H}
NMR (75 MHz, acetone-d6): δ 174.1 (NC), 164.0 (q, 1JB−C = 49.6
Hz, ipso-BPh4), 145.0 (NC), 138.6 (p-C), 136.0 (q, 2JB−C = 1.5 Hz, o-
3
BPh4), 130.8 (o-C), 130.2 (m-CH), 128.9 (o-C), 125.0 (q, JB−C = 2.8
Hz, m-BPh4), 121.2 (p-BPh4), 94.8 (CCH3), 19.7 (p-CH3), 19.5 (o-
CH3), 18.1 (o-CH3), 7.2 (CH3).
Rhodium complex 13b: red powder (44%). MS (ESI, CH2Cl2) m/z:
565.1 [M − BPh4]+ (100%). Anal. Found (calcd) for C54H59BClRhN2:
C, 72.80 (73.27); H, 6.86 (6.72); N, 3.17 (3.16). 1H NMR (300 MHz,
acetone-d6): δ 8.78 (d, 2H, 3JH−Rh = 2.9 Hz, NCH), 7.33 (m, 8H, o-
BPh4), 7.16 (s, 2H, ArH), 7.14 (s, 2H, ArH), 6.91 (t, 8H, 3J = 17.7 Hz,
m-BPh4), 6.76 (t, 4H, 3J = 7.2 Hz, p-BPh4), 2.44 (s, 6H, o-CH3), 2.35
(s, 6H, p-CH3), 2.23 (s, 6H, o-CH3), 1.25 (s, 15H, CH3). 13C{1H}
NMR (75 MHz, acetone-d6): δ 171.2 (NC), 164.5 (q, 1JB−C = 49.1
Hz, ipso-BPh4), 144.7 (NC), 138.1 (p-C), 136.0 (q, 2JB−C = 1.5 Hz, o-
BPh4), 130.3 (o-C), 130.1 (m-CH), 129.5 (o-C), 129.0 (m-CH), 125.0
(q, 3JB−C = 2.8 Hz, m-BPh4), 121.2 (p-BPh4), 99.8 (d, 2JC−Rh = 8.0 Hz,
CCH3), 19.8 (p-CH3), 19.7 (o-CH3), 18.5 (o-CH3), 7.6 (CH3).
[Ir(Cp*)(PzP)Cl]BPh4 (14a). The iridium precursor [Ir(Cp*)Cl2]2
(95 mg, 0.120 mmol), NaBPh4 (48 mg, 0.140 mmol), and the ligand
PzP (5) (55 mg, 0.196 mmol) were weighed into a Schlenk flask, and
methanol (15 mL) was added. A yellow precipitate formed
immediately, and the mixture was filtered to give an orange solid.
The solid was washed with toluene (to remove unreacted [Ir(Cp*)-
Cl2]2), and the resulting bright yellow solid recrystallized from acetone
and methanol and then recrystallized from dichloromethane and
hexane to give complex 14a as bright yellow crystals (136 mg, 72%).
MS (ESI, CH2Cl2) m/z: 643.1 [M − BPh4]+ (100%). Anal. Found
(calcd) for C51H52BClIrN2P·0.5C6H14: C, 64.41 (64.50); H, 5.78
1
15H, CH3). 13C{1H} NMR (75 MHz, acetone-d6): δ 171.9 (d, JRh−C
= 55.2 Hz, NCN), 164.0 (q, 1JB−C = 49.1 Hz, ipso-BPh4), 145.2 (PzC),
139.0 (p-C), 138.1 (NC), 136.0 (q, 2JB−C = 1.5 Hz, o-BPh4), 135.0 (o-
C), 134.6 (o-C), 134.5 (PzC), 129.4 (m-CH), 127.7 (m-CH), 126.0
3
(ImC), 125.0 (q, JB−C = 2.7 Hz, m-BPh4), 123.3 (ImC), 121.3 (p-
1
BPh4), 108.3 (PzC), 98.4 (d, JRh−C = 7.0 Hz, CCH3), 63.1 (CH2),
20.0 (p-CH3), 19.3 (o-CH3), 18.2 (o-CH3), 8.7 (CH3).
Iridium complex 16a: yellow crystals (60%). MS (ESI, CH2Cl2) m/
z: 539.1 [M − BPh4]+ (100%). Anal. Found (calcd) for
C43H47BClIrN4: C, 60.12 (60.17); H, 5.39 (5.52); N, 6.78 (6.53).
3
1H NMR (300 MHz, acetone-d6): δ 8.03 (d, 1H, J = 2.6 Hz, PzH),
3
3
7.92 (d, 1H, J = 2.3 Hz, PzH), 7.45 (d, 1H, J = 2.0 Hz, ImH), 7.33
(m, 8H, o-BPh4), 7.35 (d, 1H, 3J = 2.0 Hz, ImH), 6.91 (t, 8H, 3J = 14.8
3
3
Hz, m-BPh4), 6.76 (t, 4H, J = 7.2 Hz, p-BPh4), 6.57 (t, 1H, J = 5.1
Hz, PzH), 5.13 (m, 1H, CH2), 4.91 (m, 1H, CH2), 4.78 (m, 1H, CH2),
4.54 (m, 1H, CH2), 3.94 (s, 3H, NCH3), 1.62 (s, 15H, CH3). 13C{1H}
NMR (75 MHz, acetone-d6): δ 164.0 (q, 1JB−C = 49.6 Hz, ipso-BPh4),
2
150.0 (NCN), 146.0 (PzC), 136.0 (q, JB−C = 1.5 Hz, o-BPh4), 135.9
(PzC), 125.0 (q, 3JB−C = 2.8 Hz, m-BPh4), 124.4 (ImC), 124.2 (ImC),
121.3 (p-BPh4), 108.4 (PzC), 91.0 (CCH3), 49.9 (CH2), 49.3 (CH2),
38.2 (NCH3), 8.0 (CH3).
Rhodium complex 16b: orange needles (63%). MS (ESI, CH2Cl2)
m/z: 449.1 [M − BPh4]+ (100%). Anal. Found (calcd) for
C43H47BClRhN4: C, 66.60 (67.16); H, 6.31 (6.16); N, 7.31 (7.29).
1
(5.91); N, 2.85 (2.79). H NMR (300 MHz, acetone-d6): δ 8.04 (d,
3
3
1H, J = 2.4 Hz, PzH), 7.82 (d, 1H, J = 2.3, PzH), 7.65−7.29 (m,
3
18H, PPh2 and o-BPh4), 6.91 (t, 8H, J = 14.7 Hz, m-BPh4), 6.76 (t,
3
1H NMR (300 MHz, acetone-d6): δ 8.04 (d, 1H, J = 2.4 Hz, PzH),
4H, 3J = 7.2 Hz, p-BPh4), 6.58 (t, 1H, 3J = 5.1 Hz, PzH), 5.20 (m, 1H,
NCH), 4.59 (m, 1H, NCH), 3.47 (m, 1H, PCH), 2.71 (m, 1H, PCH),
3
3
7.95 (d, 1H, J = 2.2 Hz, PzH), 7.51 (d, 1H, J = 1.8, ImH), 7.48 (d,
1H, 3J = 2.0, ImH), 7.33 (m, 8H, o-BPh4), 6.91 (t, 8H, 3J = 14.7 Hz, m-
BPh4), 6.76 (t, 4H, J = 7.3 Hz, p-BPh4), 6.56 (t, 1H, J = 4.9 Hz,
PzH), 5.01 (m, 1H, CH2), 4.94 (m, 1H, CH2), 4.68 (m, 1H, CH2),
4.60 (m, 1H, CH2), 3.99 (s, 3H, NCH3), 1.64 (s, 15H, CH3). 13C{1H}
NMR (75 MHz, acetone-d6): δ 164.8 (d, JRh−C = 49.6 Hz, NCN),
164.0 (q, JB−C = 49.5 Hz, ipso-BPh4), 146.0 (PzC), 136.0 (q, JB−C
1.5 Hz, o-BPh4), 135.4 (PzC), 125.0 (q, JB−C = 2.6 Hz, m-BPh4),
124.4 (ImC), 124.2 (ImC), 121.2 (p-BPh4), 108.4 (PzC), 90.9 (d,
1JRh−C = 7.1 Hz, CCH3), 49.8 (CH2), 49.3 (CH2), 38.2 (NCH3), 8.0
(CH3).
1.53 (d, 15H, JH−P = 2.2 Hz, CH3). 13C{1H} NMR (75 MHz,
3
3
3
1
acetone-d6): δ 164.0 (q, JB−C = 49.5 Hz, ipso-BPh4), 146.3 (PzC)
2
136.0 (br, PzC and o-BPh4), 133.3 (d, JP−C = 9.4 Hz, o-PPh), 132.5
(d, 2JP−C = 9.8 Hz, o-PPh), 131.7 (d, 4JP−C = 2.6 Hz, p-PPh), 131.4 (m,
1
4
3
ipso-PPh2), 131.0 (d, JP−C = 2.6 Hz, p-PPh), 128.9 (d, JP−C = 11.0
Hz, m-PPh) 128.1 (d, JP−C =11.0 Hz, m-PPh), 125.0 (q, JB−C = 2.9
Hz, m-BPh4), 121.2 (p-BPh4), 108.3 (PzC), 95.1 (d, JP−C = 2.9 Hz,
1
2
3
3
=
3
2
1
CCH3), 48.5 (NCH2), 25.1 (d, JP−C = 35.7 Hz, PCH2), 8.0 (CH3).
31P{1H} NMR (121 MHz, acetone-d6): δ −2.0.
[M(Cp*)(PzIR)Cl]BPh4 (R = Mes, M = Ir, 15a, or M = Rh, 15b; R =
Me, M = Ir, 16a, or M = Rh, 16b). Ag2O (59 mg, 0.254 mmol) was
added to an acetone (25 mL) solution of the ligand precursor
PzIMes·HBPh4 (6·HBPh4) or PzIMe·HBPh4 (7·HBPh4) (0.310
mmol), and the mixture was stirred at room temperature for 2 h.
The rhodium or iridium precursor [M(Cp*)Cl2]2 (0.150 mmol) was
added, and the mixture was stirred overnight at room temperature.
The mixture was filtered over Celite, and the filtrate reduced to
dryness. Recrystallization of the residue from dichloromethane and
hexane afforded the pure product.
Catalyzed Hydroamination of Aminoalkynes. Metal-catalyzed
reactions were performed on a small scale in NMR tubes fitted with a
concentric Teflon valve Young’s top. Reagents were weighed out in a
nitrogen-filled glovebox, and the solvent was distilled directly into the
NMR tubes under vacuum. The time zero was taken when the tube
was placed into an NMR spectrometer preset at an elevated
1
temperature. The reaction progress was monitored by acquiring H
NMR spectra at regular intervals, and the percentage conversions were
obtained by integration of product resonances versus starting material.
Typical procedures for the hydroamination of 2-(2-phenylethynyl)-
aniline (8) and 4-phenyl-3-butyn-1-amine (9) are given below. Note:
Iridium complex 15a: yellow crystals (56%). MS (ESI, CH2Cl2) m/
z: 629.1 [M − BPh4]+ (100%). Anal. Found (calcd) for
6276
dx.doi.org/10.1021/om300550k | Organometallics 2012, 31, 6270−6277

Organometallics
Article
Soluble Ag(I) salts are also known to be effective hydroamination
catalysts,26 and an excess of AgBF4 reagent has the potential to yield
misleading catalysis data. To affect a more reproducible outcome and
ensure there was no excess Ag(I) salt present, the relatively small
quantity of AgBF4 was measured directly into the NMR tube first and
the other reagents adjusted to fit the desired stoichiometry.
2-(2-Phenylethynyl)aniline (8). Acetone-d6 (0.6 mL) was added
to an NMR tube containing complex 16a (4.2 mg, 5.0 μmol), 2-(2-
phenylethynyl)aniline (8) (19.3 mg, 100 μmol), and AgBF4 (2.0 mg,
10 μmol). The tube was shaken vigorously, resulting in a white
precipitate of AgCl and AgBPh4. The mixture was then heated at 50
°C.
(8) (a) Nair, R. N.; Lee, P. J.; Rheingold, A. L.; Grotjahn, D. B.
Chem.Eur. J. 2010, 16, 7992. (b) Varela-Fernandez, A.; Varela, J. A.;
Saa, C. Adv. Synth. Catal. 2011, 353, 1933.
(9) (a) Arcadi, A.; Bianchi, G.; Marinelli, F. Synthesis 2004, 4, 610.
(b) Alfonsi, M.; Arcadi, A.; Aschi, M.; Bianchi, G.; Marinelli, F. J. Org.
Chem. 2005, 70, 2265. (c) Zhang, Y.; Donahue, J. P.; Li, C.-J. Org. Lett.
2007, 9, 627. (d) Patil, N. T.; Singh, V.; Konala, A.; Mutyala, A. K.
Tetrahedron Lett. 2010, 51, 1493. (e) Hirano, K.; Inaba, Y.; Takahashi,
N.; Shimano, M.; Oishi, S.; Fujii, N.; Ohno, H. J. Org. Chem. 2011, 76,
1212. (f) Arcadi, A. Chem. Rev. 2008, 108, 3266.
(10) Li, X.; Chianese, A. R.; Vogel, T.; Crabtree, R. H. Org. Lett.
2005, 7, 5437.
4-Phenyl-3-butyn-1-amine (9). Tetrahydrofuran-d8 (0.6 mL)
was added to an NMR tube containing complex 16a (4.2 mg, 5.0
μmol) and AgBF4 (2.0 mg, 10 μmol). The tube was shaken vigorously
to give a white precipitate of AgCl and AgBPh4. 4-Phenyl-3-butyn-1-
amine (9) (24.5 mg, 169 μmol) was injected into the NMR tube, and
the mixture heated at 60 °C.
(11) (a) Burling, S.; Field, L. D.; Messerle, B. A. Organometallics
2000, 19, 87. (b) Dabb, S. L.; Ho, J. H. H.; Hodgson, R.; Messerle, B.
A.; Wagler, J. Dalton Trans. 2009, 634.
(12) (a) Field, L. D.; Messerle, B. A.; Wren, S. L. Organometallics
2003, 22, 4393. (b) Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner,
P. Organometallics 2005, 24, 4241. (c) Burling, S.; Field, L. D.;
Messerle, B. A.; Rumble, S. L. Organometallics 2007, 26, 4335.
(d) Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner, P.; Failes, T.
Organometallics 2007, 26, 2058.
ASSOCIATED CONTENT
■
S
* Supporting Information
(13) Kennedy, D. F.; Messerle, B. A.; Rumble, S. L. New J. Chem.
2009, 33, 818.
(14) Kennedy, D. F.; Messerle, B. A.; Smith, M. K. Eur. J. Inorg.
X-ray crystallographic data are available in electronic format as
CIF files. This material is available free of charge via the
Internet at http://pubs.acs.org.
Chem. 2007, 80.
(15) The Rh congener of 14a was not synthesised due to concurrent
catalytic investigations indicating a far superior performance of the Ir
complexes for this series.
(16) It has previously been reported that ligands of this type are
susceptible to hydrolysis and rupture of the central C−C bond:
Gasperini, M.; Ragaini, F.; Gazzola, E.; Caselli, A.; Macchi, P. Dalton
Trans. 2004, 3376.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: +61 2 96621697. Ph: +61 2 93854683. E-mail: b.
messerle@unsw.edu.au.
Notes
(17) Ogata, K.; Nagaya, T.; Fukuzawa, S. J. Organomet. Chem. 2010,
695, 1675.
The authors declare no competing financial interest.
(18) Kennedy, D. F.; Nova, A.; Willis, A. C.; Eisenstein, O.; Messerle,
B. A. Dalton Trans. 2009, 10296.
(19) Gasperini, M.; Ragaini, F.; Cenini, S. Organometallics 2002, 21,
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support from the
University of New South Wales, the Australian National
University, and the Australian Research Council.
2950.
(20) Kliegman, J. M.; Barnes, R. K. J. Org. Chem. 1970, 35, 3140.
(21) Page, M. J.; Wagler, J.; Messerle, B. A. Dalton Trans. 2009, 35,
7029.
(22) White, C.; Yates, A.; Maitlis, P. M. Inorg. Synth. 1992, 29, 228.
(23) (a) Sheldrick, G. M. SHELXS-97, Program for the Solution of
Crystal Structures, Version WinGX(C), Release 97-2; 1986−1997.
(b) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement, Version WinGX(C), Release 97-2; 1993−1997. Sheldrick,
G. M. Acta Crystallogr. A 2008, 64, 112−122 : WinGX, Release 2003.
(24) ORTEP-3: Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(25) POVRay 3.62, Persistence of Vision Raytracer; Persistence of
Vision Pty. Ltd.: Williamstown, Victoria, Australia, 2004; http://www.
povray.org/.
REFERENCES
■
(1) (a) Muller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675 , and
̈
references therein. (b) Brunet, J. J.; Neibecker, D. In Catalytic
Heterofunctionalization; Togni, A.; Grutzmacher, H., Eds.; VCH:
̈
Weinheim, 2001; p 91. (c) Pohlki, F.; Doye, S. Chem. Soc. Rev.
2003, 32, 104. (d) Severin, R.; Doye, S. Chem. Soc. Rev. 2007, 36,
1407.
(2) Horton, D. A.; Bourne, G. T.; Smythe, M. L. Chem. Rev. 2003,
103, 893.
(3) Humphrey, G. R.; Kuethe, J. T. Chem. Rev. 2006, 106, 2875.
(4) (a) Pohlki, F.; Doye, S. Chem. Soc. Rev. 2003, 32, 104. (b) Patil,
N. T.; Singh, V. J. Organomet. Chem. 2011, 696, 419.
(26) Beeren, S. R.; Dabb, S. L.; Messerle, B. A. J. Organomet. Chem.
2009, 694, 309.
(5) (a) Iritani, K.; Matsubara, S.; Utimoto, K. Tetrahedron Lett. 1988,
29, 1799. (b) Arcadi, A.; Cacchi, S.; Marinelli, F. Tetrahedron Lett.
1989, 30, 2581. (c) Cacchi, S.; Carnicelli, V.; Marinelli, F. J.
Organomet. Chem. 1994, 475, 289. (d) Zeni, G.; Larock, R. C. Chem.
Rev. 2004, 104, 2285. (e) Cacchi, S.; Fabrizi, G. Chem. Rev. 2005, 105,
2873. Terrasson, V.; Michaux, J.; Gaucher, A.; Wehbe, J.; Marque, S.;
Prim, D.; Campagne, J.-M. Eur. J. Org. Chem. 2007, 5332.
(f) Majumdar, K. C.; De, N.; Roy, B. Synthesis 2010, 24, 4207.
(6) (a) Ezquerra, J.; Pedregal, C.; Lamas, C. J. Org. Chem. 1996, 61,
5804. (b) Hiroya, K.; Itoh, S.; Ozawa, M.; Kanamori, Y.; Sakamoto, T.
Tetrahedron Lett. 2002, 43, 1277. (c) Cacchi, S.; Fabrizi, G.; Parisi, L.
M. Org. Lett. 2003, 5, 3843. (d) Hiroya, K.; Itoh, S.; Sakamoto, T. J.
Org. Chem. 2004, 69, 1126. (e) Ohno, H.; Ohta, Y.; Oishi, S.; Fujii, N.
Angew. Chem., Int. Ed. 2007, 46, 2295.
(7) (a) Trost, B. M.; McClory, A. Angew. Chem., Int. Ed. 2007, 46,
2074. (b) Isono, N.; Lautens, M. Org. Lett. 2009, 11, 1329.
6277
dx.doi.org/10.1021/om300550k | Organometallics 2012, 31, 6270−6277