Hemilabile N-Xylyl-N ′-methylperimidine carbene iridium complexes as catalysts for C-H activation and dehydrogenative silylation: Dual role of N-xylyl moiety for ortho-C-H bond activation and reductive bond cleavage

Article abstract of DOI:10.1021/ja406519u

Direct dehydrogenative silylation of pyridyl and iminyl substrates with triethylsilane was achieved using (L)Ir(cod)(X) (1) (L = a perimidine-based carbene ligand, X = OAc and OCOPh) complexes as catalysts under toluene refluxing conditions in the presence of norbornene as a hydrogen scavenger, and the silylated products were obtained in good yields. The isolated bis(cyclometalated)iridium complexes, (C^aC:)(C ^aN)IrOAc (2) (C^aC: = a cyclometalated perimidine-carbene ligand and C^aN = a cyclometalated pyridyl- and iminyl-ligated aromatic substrate), were key intermediates, where cyclometalated five-membered metallacycles of substrates such as phenylpyridine were selectively formed before yielding mono-ortho-silylation products. The bis(cyclometalated)iridium complex ( ^XyC^aC:)(C^aN)IrOAc (2d) (^XyC^aC: = a cyclometalated N-xylyl-N′-methylperimidine-carbene ligand and C^aN = a 2-pyridylphenyl ligand), reacted with 2 equiv of Et₃SiH to give an iridium hydride complex, (L⁴)(C^aN)Ir(H) (SiEt₃) (8d) (L⁴ = N-CH₃, N-3,5-(CH ₃)₂C₆H₃ perimidine), via demetalation of a N-3,5-xylyl ring of the carbene ligand of 2d. The formation of 8d was confirmed by isolating the corresponding chloro complex (L ⁴)(C^aN)Ir(Cl)(SiEt₃) (8d-Cl) by treatment with CCl₄. The N-methyl moiety of the carbene ligand coordinated to 8d was cyclometalated in the presence of norbornene at room temperature to afford (^MeC^aC:)(C ^aN)Ir(SiEt₃) (10d) (^MeC ^aC: = a cyclometalated N-xylyl-N′-methylperimidine- carbene), while at high temperature 8d reacted with norbornene and Et ₃SiH to afford the silylated product, 2-(2-triethylsilyl) phenylpyridine (3a) and norbornane. A deuterium labeling experiment using 2d and Et₃SiD (excess) revealed the incorporation of deuterium atoms at two ortho-positions of the N-xylyl group (>90%) and at the 3-position of 2-pyridylphenyl ligand (ca. 40%) within 3 h at room temperature, indicating that the cyclometalation/demetalation of the N-xylylperimidine carbene and 2-phenylpyridine ligands were reversible processes. Isolation of these cyclometalated iridium complexes under controlled conditions and D-labeling experiments thus revealed a dual function of the N-aryl group bound to the perimidine-carbene ligand, which acted as both a neutral carbene ligand and a monoanionic ortho-metalated aryl-carbene ligand through reversible C-H bond activation and Ir-C bond cleavage of the N-aryl group during the catalytic cycle.

Full text of DOI:10.1021/ja406519u

Article
pubs.acs.org/JACS
Hemilabile N‑Xylyl‑N′‑methylperimidine Carbene Iridium Complexes
as Catalysts for C−H Activation and Dehydrogenative Silylation: Dual
Role of N‑Xylyl Moiety for ortho-C−H Bond Activation and Reductive
Bond Cleavage
Gyeongshin Choi, Hayato Tsurugi, and Kazushi Mashima*
Department of Chemistry, Graduate School of Engineering Science, Osaka University, and CRST, JST, Toyonaka, Osaka 560-8531,
Japan
S
* Supporting Information
ABSTRACT: Direct dehydrogenative silylation of pyridyl and
iminyl substrates with triethylsilane was achieved using
(L)Ir(cod)(X) (1) (L = a perimidine-based carbene ligand,
X = OAc and OCOPh) complexes as catalysts under toluene
refluxing conditions in the presence of norbornene as a
hydrogen scavenger, and the silylated products were obtained
in good yields. The isolated bis(cyclometalated)iridium
complexes, (C∧C:)(C∧N)IrOAc (2) (C∧C: = a cyclometalated
perimidine-carbene ligand and C∧N = a cyclometalated pyridyl- and iminyl-ligated aromatic substrate), were key intermediates,
where cyclometalated five-membered metallacycles of substrates such as phenylpyridine were selectively formed before yielding
mono-ortho-silylation products. The bis(cyclometalated)iridium complex (XyC∧C:)(C∧N)IrOAc (2d) (XyC∧C: = a cyclo-
metalated N-xylyl-N′-methylperimidine-carbene ligand and C∧N = a 2-pyridylphenyl ligand), reacted with 2 equiv of Et3SiH to
give an iridium hydride complex, (L4)(C∧N)Ir(H)(SiEt3) (8d) (L4 = N-CH3, N-3,5-(CH3)2C6H3 perimidine), via demetalation
of a N-3,5-xylyl ring of the carbene ligand of 2d. The formation of 8d was confirmed by isolating the corresponding chloro
complex (L4)(C∧N)Ir(Cl)(SiEt3) (8d-Cl) by treatment with CCl4. The N-methyl moiety of the carbene ligand coordinated to
8d was cyclometalated in the presence of norbornene at room temperature to afford (MeC∧C:)(C∧N)Ir(SiEt3) (10d) (MeC∧C: =
a cyclometalated N-xylyl-N′-methylperimidine-carbene), while at high temperature 8d reacted with norbornene and Et3SiH to
afford the silylated product, 2-(2-triethylsilyl)phenylpyridine (3a) and norbornane. A deuterium labeling experiment using 2d
and Et3SiD (excess) revealed the incorporation of deuterium atoms at two ortho-positions of the N-xylyl group (>90%) and at
the 3-position of 2-pyridylphenyl ligand (ca. 40%) within 3 h at room temperature, indicating that the cyclometalation/
demetalation of the N-xylylperimidine carbene and 2-phenylpyridine ligands were reversible processes. Isolation of these
cyclometalated iridium complexes under controlled conditions and D-labeling experiments thus revealed a dual function of the
N-aryl group bound to the perimidine-carbene ligand, which acted as both a neutral carbene ligand and a monoanionic ortho-
metalated aryl-carbene ligand through reversible C−H bond activation and Ir−C bond cleavage of the N-aryl group during the
catalytic cycle.
The advantages of N-heterocyclic carbene (NHC) ligands
are their strong coordination ability and their easily sterically
and electronically tunable nature.3,4 Some hemilabile ligands of
NHCs connected with a N or O donor atom have been reported.5
The recent development of NHCs and their hemilabile ligand
system prompted us to design and prepare a new type of
hemilabile ligand comprising NHCs and carbanions as a more
labile site in which the M−C bond formation is kinetically labile
due to facile C−H bond activation and reversible C−H bond
formation of the N-aromatic unit of the carbene ligands by
late transition metals (Chart 1b). The hemilabile nature of the
N-arylated heterocyclic carbene ligand of Cp*Ir(NHC) is a
notable example reported by Peris et al.,6 in which the carbene
INTRODUCTION
■
Transition metals supported by chelating ligands are versatile
scaffolds for mediating various catalytic organic transformations.
Among the chelating ligands, hemilabile ligands in which two or
more different heteroatoms coordinate to a metal center1 have
attracted increased attention due to their ability to change their
coordination mode from a rigid multidentate chelation to a
coordinatively unsaturated monodentate ligation for approach-
ing substrates, as well as to occupy the coordinatively unsaturated
sites by chelation to stabilize the unstable intermediate species. In
such a context, suitable selection of heteroatoms and the rational
design of hemilabile ligands lead to high activity and selectivity
of their transition metal complexes in various catalytic reactions.
A large number of hemilabile ligands with a phosphine atom
combined with N, O, or S donor atom(s) have been developed
(Chart 1a).2
Received: June 27, 2013
© XXXX American Chemical Society
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ligand through the formation and cleavage of an Ir−C bond,
which directly controls the catalytic reaction, as the first example
of a carbanion site acting as a labile coordination site of hemilabile
ligation during the catalytic cycle.
Chart 1. Hemilabile Ligation to Transition Metal Centers
RESULTS AND DISCUSSION
■
Direct Dehydrogenative Silylation Reaction. We began
a direct dehydrogenative silylation of 2-phenylpyridine with
triethylsilane by screening for the best iridium catalyst precursor
among 1a and its derivatives (L)Ir(cod)(X) (1bf) with dif-
ferent N-substituted perimidine-based carbene ligands (L) and
monoanionic ligands (X). A toluene solution of 1af (5 mol%)
and 2-phenylpyridine was heated at refluxing temperature for 3 h
prior to the addition of triethylsilane (3 equiv), and the results
of the catalytic dehydrogenative silylation are summarized in
Table 1.14 Iridium complexes 1a and 1b, having an acetate and a
Table 1. Screening of Ligands and Additive Effect19
ligand showed hemilability via metalation/demetalation of a
phenyl group attached to one N atom of the carbene ligand
(Chart 2), although many heterometallacycles are very stable and
can act as a supporting ligand under catalytic conditions.7−9
b
entry [Ir]a
R
X
additive
yield (%)
1
1a
1b
1c
1d
1e
1f
H
OAc
OCOPh
Cl
22
21
c
2
H
3
H
d
Chart 2. Reversible Metalation/Demetalation Behavior of a
Carbene-Based Hemilabile Ligand
4
Me
OMe
tBu
Me
Me
Me
Me
Me
OAc
OAc
OAc
OAc
OAc
OAc
OAc
OAc
68
5
18
c
6
7
1d
1d
1d
1d
1d
1,5-cyclooctadiene
norbornadiene
cyclooctene
74
43
57
99
46
8
9
10
11
2-norbornene
3,3-dimethylbutene
We10 and Richeson’s group11 reported the synthesis of rhodium
and iridium complexes having a series of six-membered perimidine
carbene ligands with different functional groups on two nitrogen
atoms. Recently, we found that the N-phenyl group of perimidine
ligands bound to the iridium atom of (L1)Ir(cod)(OAc) (L1 =
N-CH3, N-C6H5 perimidine carbene ligand) (1a) in the presence
of 2-phenylpyridine underwent smooth C−H bond activation of
not only the N-phenyl group of the ligand but also the phenyl
group of the coordinating 2-phenylpyridine to give a distinctive
bis(cyclometalated)iridium complex 2a (eq 1). In association with
b
Determined by GC analysis by using dodecane as an internal
c
d
standard. Trace. Isolated yield.
benzoate ligand attached to the metal center, showed almost the
same reactivity, giving 2-(2-(triethylsilyl)phenyl)pyridine (3a) in
22% and 21% yield, respectively (entries 1 and 2 in Table 1),
while a chloride derivative 1c did not give any silylated product
(entry 3), indicating that carboxylate ligands were necessary to
activate C−H bonds of 2-phenylpyridine and the N-phenyl group
of the carbene ligand.10,15,16 Substituents at the 3,5-positions of
the phenyl group attached to the nitrogen atom of the perimidine-
based carbene ligand sensitively affected the catalytic activity;
complex 1d with a 3,5-xylyl group produced 3a in 68% yield
(entry 4), whereas both 1e with a 3,5-dimethoxyphenyl group
and 1f with a 3,5-di-tert-butylphenyl group were inferior catalyst
precursors (entries 5 and 6), suggesting that bulkiness on the
carbene ligands was a critical predetermining factor.17 Thus, we
presumed that the N-3,5-xylyl group was more effective for the
the unique double C−H bond activation at the iridium center,
we report here that iridium complexes with an N-arylperimidine
carbene ligand are catalysts for the C−H activation/dehydrogenative
silylation reaction of pyridyl- and iminyl substrates.12,13 Mechanistic
studies, including the isolation of key intermediates, revealed that
the N-aryl group of perimidine carbene ligands act as a hemilabile
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product elimination step compared with N-Ph and N-3,5-
dimethoxyphenyl groups (vide infra).
and 3c: 82% yield). In sharp contrast, substituents at the phenyl
ring of 2-phenylpyridiene sensitively affected the yield of the
silylated products: a monomethyl substituent at the para and meta
positions of the phenyl ring afforded excellent yields, quantitative
for 3d and 88% for 3e, whereas ortho-monomethyl and 3,5-
dimethyl derivatives of the phenyl ring suppressed the silylation
reaction, 5% for 3f and trace for 3g. 2-(4′-Anisyl)pyridine afforded
the product 3h in 90% yield, which was comparable to that of 3d
(98%), while a withdrawing substituent, a trifluoromethyl group,
at the para-position resulted in a low yield of 3i (59%). These
observations clearly indicated that steric congestion at the phenyl
ring of the substrates was an important factor. Benzo[h]quinoline
and N-phenylpyrazole were silylated under the same conditions
(3l: 49% yield and 3m: 64% yield, respectively). The low yields of
3l and 3m might be due to the formation of relatively stable five-
membered iridacycles compared with that of 2-phenylpyridine.
Using the best catalyst precursor 1d, we examined the additive
effects of olefins and cyclic dienes, because the cyclooctadiene
ligand of 1d was liberated in the reaction course to give 1,3-
cyclooctadiene and cyclooctene (vide infra).10 The combination
of 1d with cyclooctadiene afforded 3a in a slightly increased
yield (74%, entry 7), while the addition of norbornadiene,
another chelating diene, suppressed the yield of 3a (43%, entry 8),
indicating that cyclic dienes have somewhat negative additive effects
due to the strong affinity to the coordinatively unsaturated metal
center. On the other hand, to our surprise, the addition
of 2-norbornene improved the catalytic activity to afford 3a in
quantitative yield (entry 10) because of the high reactivity ascribed to
the ring strain, although the addition of cyclooctene (3 equiv) and
3,3-dimethylbutene gave 3a in 57% (entry 9) and 46% yield (entry
11), respectively.18 GC-MS analysis of the reaction mixture in entry
10 revealed the formation of more than 1 equiv of norbornane,
clearly indicating that norbornene acted as a hydrogen scavenger for
the coupling reaction. Such alkene additive effects have been noted
for the C−H functionalization/silylation of arenes with hydrosilanes
catalyzed by ruthenium and iridium complexes.13,18
t
Furthermore, several aromatic imines bearing a Ph, Bu, Cy, or
Me substituent at the nitrogen atom were examined for direct
dehydrogenative silylation. The reaction of N-benzylideneaniline
with Et3SiH under the optimized reaction conditions gave the
ortho silylation product 3j in 87% yield without any CN
bond reduction of the imine moiety of the substrates.20
N-Benzylidenemethylamine and N-benzylidenecyclohexylamine
smoothly reacted with Et3SiH to give the corresponding silylated
products in moderately high yields; however, these compounds
were moisture-sensitive and readily hydrolyzed upon purification
through silica gel chromatography to give the same aldehyde,
2-(triethylsilyl)benzaldehyde (3n) (eq 2). In contrast, a bulky
Substrate Scope Using Pyridyl and Iminyl as Directing
Groups. Under the best catalyst conditions of 1d and norbornene
(3 equiv), we explored the scope of direct silylation of some
N-functionalized substrates such as pyridyl- and iminyl-arenes, and
the results are summarized in Table 2. The methyl substituent at
the para and ortho positions of the pyridine ring of phenylpyridine
afforded the corresponding products in good yields (3b: 83% yield
a
Table 2. DirectDehydrogenativeortho-C−H Silylation of Arenes
substrate such as N-benzylidene-tert-butylamine, which could not
form a bis(cyclometalated)iridium complex via C−H bond activa-
tion due to steric hindrance around the nitrogen atom of the sub-
strate (vide infra), resulted in a trace amount of a silylated product.
Isolation and Characterization of Bis(cyclometalated)
iridium Complex 2d. Pretreatment to heat the reaction
mixture of 1d and 2-phenylpyridine in refluxing toluene for 3 h
before the addition of triethylsilane was essential; otherwise the
yield of the desired silylated product was significantly decreased.
These observations prompted us to conduct the reaction by
heating the toluene solution of 1d in the presence of 1 equiv of
2-phenylpyridene to afford a bis(cyclometalated)iridium com-
plex 2d, in which the carbene ligand and 2-phenylpyridine
were cyclometalated to give a spiro-type skeleton of two five-
membered iridacycles (eq 3).11 The H NMR spectrum of 2d
1
a
Reaction conditions: substrate (1.0 mmol), nbe (norbornene, 3 equiv),
and 5 mol% of 1d in 5 mL of toluene. Reactions were run at 115 °C
(oil-bath temperature) and Et3SiH (3 equiv) was added to the reaction
mixture after 3 h. Products were isolated by silica gel chromatogaraphy.
showed one set of the perimidine-based carbene ligand,
cyclometalated 2-phenylpyridine, and the acetate group, whereas
b
1
Determined by H NMR using ferrocene as an internal standard.
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the resonances due to cyclooctadiene of 1d were not observed.
The most notable resonance in the 13C{1H} NMR spectra of 2d
was that of the Ccarbenes, which appeared at δC 193.7. We tested
the catalytic activity of the isolated complex 2d under the
optimized reaction conditions heated at 115 °C with 3 equiv of
norbornene, the silylation reaction of 2-phenylpyridine with
Et3SiH using 5 mol% of 2d without any preheating treatment
gave the corresponding silylated product 3a in quantitative yield,
consistent with the catalytic activity observed when using 1d as
the catalyst precursor under the preheating conditions.21
Scheme 1. Preparation of Bis(cyclometalated)iridium
Complexes
The cyclometalated structure of 2d was determined by X-ray
crystallographic analysis (Figure 1), and selected bond distances
by spectroscopic methods and combustion analyses, together
with crystallographic studies for 4d, 5d, 6d, and 7d.24 Thus, such
experimental results suggested that pyridyl and iminyl moieties
worked as directing groups for C−H bond activation, and stability
of the resulting metallacycle played a key role in the catalytic
silylation reaction (vide supra).
Figure 1. ORTEP drawings of the molecular structure of 2d. All
hydrogen atoms are omitted for clarity. Selected bond distances (Å) and
angles (deg): Ir−C(1), 1.986(8); Ir−C(14), 2.202(6); Ir−C(19),
2.003(8); Ir−N(3), 2.116(6); Ir−O(1), 2.222(5); Ir−O(2), 2.249(4);
C(1)−Ir−C(14), 80.1(3); C(19)−Ir−N(3), 80.3(3); C(14)−Ir−N(3),
101.7(3); O(1)−Ir−O(2), 58.84(19); C(14)−Ir−C(19), 90.2(3).
Mechanistic Study for Dehydrogenative Silylation.
NMR Measurements of the Controlled Reaction Mixture. To
investigate catalytically active species for the dehydrogenative
silylation reaction, we conducted controlled experiments using
the isolated complex 2d. At first, the reaction mixture of complex
2d and Et3SiH (3 equiv) in C6D6 at room temperature was
monitored by NMR spectroscopy, and several resonances in the
region of metal hydride were detected, but not all of them could
be assigned (Figure 2a).25 In this reaction, the formation of
and angles were compared with its analog 2a.10 The coordination
environments around the iridium metal are essentially the
same: each iridium atom possesses both the cyclometalated
2-phenylpyridine and the cyclometalated perimidine ligand.
An acetate coordinates to the iridium atom in a κ2-coordination
mode. The C(1)−Ir distances for 2a and 2d are 1.979(8) and
1.987(7) Å, respectively. The distance of Ir−C(14) for 2d is
2.021(6) Å, noticeably longer than that of 2a (1.979(7) Å). The
bond angles of C(14)−Ir−N(3) and C(14)−Ir−C(27) for 2d
are 101.8(3)° and 90.3(3)°, slightly larger than those of 2a
(98.5(2)° and 87.8(3)°) due to the steric congestion around the
metal center of 2d, which accelerated the C−Si bond formation
in the catalytic cycle.
1
triethylsilyl acetate, Et3SiOAc, was confirmed by its H NMR
spectrum along with GC-MS. In sharp contrast to the formation
Isolation and Characterization of Cyclometalated
Iridium Complexes bearing Cyclometalated Perimidine-
based Carbene Ligand. As outlined in Scheme 1, reactions of
1d with benzo[h]quinoline and N-benzylidenemethylamine,
respectively, afforded the bis(cyclometalated)iridium complexes
4d and 5d via activation of the aromatic C(sp2)−H bond,
corresponding to the catalytic silylation of benzo[h]quinoline
and N-benzylidenemethylamine.16d,e,22 Similarly, reactions of 1d
with 2-vinylpyridine and N-(3-phenylallylidene)aniline yielded
the corresponding complexes 6d and 7d by the activation of
olefinic C(sp2)−H bonds.23 These complexes were characterized
Figure 2. The 1H NMR spectra in the region of Ir-hydride for
reactions of 2d with (a) Et3SiH (3 equiv), (b) Et3SiH (3 equiv) and
2-phenylpyridine (1.5 equiv), (c) Et3SiH (3 equiv), 2-phenylpyridine
(1.5 equiv), and norbornene (3 equiv) at room temperature.
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of several complicated species without 2-phenylpyridine, the
reaction of 2d and Et3SiH (3 equiv) in the presence of 1.5 equiv
of 2-phenylpyridine afforded only two singlet peaks assignable to
Ir−H at δH −5.55 (major product) and −15.28 (minor product)
in a 7:1 ratio (Figure 2b). The major product was determined
spectroscopically to be a hydride complex 8d, while the minor
product was assigned to be the other hydride complex 9d,
which was a cyclometalated product of the Et3Si moiety (eq 4)
8d-Cl were superimposed on those of 8d except for the absence
of a hydride signal and one singlet for one of two ortho-N-xylyl
moieties: two singlet resonances assignable to ortho-hydrogen
atoms of the N-xylyl moiety were observed at δH 8.13 and 6.23,
and one signal was shifted to a lower magnetic field due to the
interaction between the iridium metal center and the N-xylyl
moiety. The overall molecular structure was determined by X-ray
analysis.
Figure 3 shows the molecular structure of the iridium com-
plex 8d-Cl. The iridium atom possessed a square pyramidal
(vide infra). Such cyclometalation reaction of the Ir−SiR3 (R = alkyl,
aryl) moiety to form iridasilacycle structures was independently
reported by Milstein26 and Tilley et al.27 Upon heating of this
reaction mixture at 100 °C, no silylated product 3a was obtained,
but these complexes decomposed to give unidentified species.
We already confirmed the additive effects of norbornene in
the catalytic reaction. Thus, 3 equiv of norbornene was added
to the C6D6 solution containing 2d, Et3SiH (3 equiv), and
2-phenylpyridine (1.5 equiv) at room temperature to induce a
decrease in the intensity of the major Ir−H resonance at δH
−5.55, suggesting that norbornene inserted into Ir−H presum-
ably gives a norbornyliridium species, though this could not be
detected. Meanwhile, the signal of the minor Ir−H species
appearing at δH −15.28 remained intact (Figure 2c), suggesting
that the minor product 9d was a decomposed product outside of
the catalytic cycle. At room temperature, no silylated product 3a
was obtained; however, heating the reaction mixture at 100 °C for
6 h produced 3a (quant.) and norbornane (3 equiv), in good
accordance with the catalytic reaction.
Figure 3. ORTEP drawing of the molecular structure of 8d-Cl. All
hydrogen atoms are omitted for clarity. Selected bond distances (Å) and
angles (deg): Ir−Cl, 2.461(3); Ir−C(1), 1.988(12); Ir−Si, 2.356(4);
Ir−C(19), 2.014(11); Ir−N(3), 2.100(10); Ir−Ccent, 2.664 (Ccent
=
midpoint of C(13)−C(14)); Cl−Ir−C(1), 89.9(3); Si−Ir−N(3),
89.9(3); C(1)−Ir−C(19), 94.8(5); C(19)−Ir−N(3), 82.1(4).
penta-coordinated structure supported by C and N atoms of
cyclometalated 2-phenylpyridine, a carbene carbon of the neutral
perimidine-based carbene ligand, a Si atom of the triethylsilyl
group, and a chloride atom. A phenyl ring on a nitrogen atom of
the perimidine-based carbene ligand interacts with an iridium
atom trans to the Ir−SiEt3 moiety to form an octahedral structure,
and the distance of Ir−Ccent (Ccent = midpoint of C(13)−C(14))
is 2.664 Å, which is consistent with the lower-field shift of one
Major Product 8d and its Decomposed Product 10d. We
first focused on isolating and characterizing the major hydride
species 8d. Although isolation of 8d was difficult due to facial
decomposition during the purification process, we could
1
characterize the complex 8d by H NMR measurement even
when minor species were contained in the reaction mixture. The
1H NMR spectrum displays two ortho C−H bonds and two CH3
resonances of the N-xylyl moiety at δH 7.28, 6.88, 2.16, and 1.22
inequivalently, indicating the difficulty of the N-xylyl ring to
freely rotate at ambient temperature.28 According to the general
method of converting Ir−H to Ir−Cl species by CCl4, we added
CCl4 to in situ-generated 8d in toluene at room temperature,
followed by silica-gel column chromatography, thus isolating the
corresponding Ir complex 8d-Cl (eq 5). The spectral features of
1
of two ortho-C−H singlet signals in the H NMR spectrum.
A silyl group coordinates to the metal center at the cis-position to
2-phenylpyridine and a perimidine-based carbene ligand. The
Ir−Si distance is 2.356(4) Å, consistent with typical M−Si (M = Ir
and Rh) bonds.29,30 The distance of Ir−C(1) in 8d-Cl is
1.989(12) Å, indicating a typical M−Ccarbene bond but it is
noticeably shorter than the Ir−Ccarbene distance in [(PhC∧C:)2Ir-
(μ-Cl)]2 (PhC∧C: = cyclometalated N-methyl-N-phenylperimi-
dine carbene) (2.042(3) Å).10
Figure 2c clearly shows that the addition of norbornene
induced a decrease in the hydride signal due to 8d at room
temperature. Upon prolonged standing of the reaction mixture
for 4 days at room temperature, we obtained a new complex,
bis(cyclometalated)Ir(SiEt3) complex (10d), as sparingly
soluble dark red crystals in 54% yield (eq 6). Complex 10d
was fully characterized by spectroscopic measurements along
with X-ray diffraction studies, which revealed that complex 10d
has a cyclometalated N-methyl group of the perimidine-carbene
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Minor Product 9d and Its Related Complexes. For minor
product 9d, we could not isolate 9d even by treatment with CCl4
followed by a separation trial. Thus, we conducted the reaction of
2d with the other silane, BnMe2SiH.33 The 1H NMR spectrum of
the reaction mixture of 2d with BnMe2SiH (3 equiv) at room
temperature displayed two signals at δH −4.92 (11d) and −15.28
(12d), corresponding to the previous observation of the reaction of
2d with Et3SiH (3 equiv). At room temperature, the hydride signal
due to 11d gradually disappeared and only the hydride signal
assignable to 12d was observed (Scheme 2, Figure 5).25c,26,34
ligand, to form a four-membered ring as a consequence of unique
C(sp3)−H bond activation.31 Notable spectral data were that
two hydrogen atoms on a cyclometalated methylene group of the
carbene ligand, forming a four-membered metallacycle, sepa-
rately appeared at δH 3.45 and 3.39 as doublet signals, and the
resonance for Ccarbene was observed at δC 169.9, which was shifted
to lower field than that in 2d.
Scheme 2. Reaction of 2d with Me2BnSiH
Figure 4 clearly shows that the coordination environment
around the iridium center of 10d adopts a unique square
Figure 4. ORTEP drawing of the molecular structure of 10d. All
hydrogen atoms and solvent molecules are omitted for clarity. Selected
bond distances (Å) and angles (deg): Ir−C(1), 2.086(5); Ir−C(2),
2.083(5); Ir−C(19), 2.042(5); Ir−Si, 2.3106(15); Ir−N(3), 2.141(5);
C(1)−Ir−C(2), 65.35(19); C(1)−Ir−C(19), 164.3(2); C(1)−Ir−
N(3), 114.93(18); C(1)−Ir−Si, 92.00(15); C(19)−Ir−N(3),
78.57(19).
1
Figure 5. The H NMR hydride resonances for 11d and 12d: (a) 2d
with Me2BnSiH (3 equiv) at room temperature, (b) 6 h, and (c) 10 h.
pyramidal geometry where an iridium atom is surrounded by two
cyclometalated fragments of 2-phenylpyridine and the peri-
midine-based carbene ligand at the basal position in addition to
a triethylsilyl group occupying an apex position.30 The distances
of Ir−C(1) and Ir−C(2) for 10d are 2.086(5) and 2.082(5) Å,
respectively, indicating elongation of an Ir−C(1) bond com-
pared with an Ir−Ccarbene bond of 2d (1.987(7) Å) and a shorter
Ir−C(2) bond distance compared with a normal Ir−Cmethyl bond
distance due to formation of the four-membered metallacycle
via C(sp3)−H bond activation of a N-methyl group of the
perimidine-based carbene ligand. The Ir−Si distance of
2.3108(16) Å is normal and comparable to that found in the
pentacoordinated complexes Ir(acac)H(SiPh3)(PCy3)
(2.307(1) Å)30 and IrHCl(SiiPr2OH)(PEt3)2 (2.313.(6) Å).32
The angles of C(1)−Ir−C(2) and N(3)−Ir−C(27) are
65.29(19)° and 78.56(19)°, respectively, and such environments
thus enforce the complex to adopt an unusual, distorted square
pyramidal geometry.
Although complex 11d and its chlorination product 11d-Cl were
characterized in the similar manner as 8d and 8d-Cl, complex
12d was characterized spectroscopically to be a five-membered
iridasilacycle, in which C(sp2)−H activation was rather favored
over C(sp3)−H activation of the four-membered iridasilacycle of
the Ir−SiEt3 moiety.35 The resonances of 12d for two methyl
groups bound to the silicon atom were separately observed at δH
0.00 and 0.22 in the 1H NMR spectrum and at δC 4.9 and 5.5 in the
13C NMR spectrum. The six signals for aromatic carbons of the
benzyl group were inequivalently observed as well due to the rigid
iridasilacycle structure. The signal for the metalated carbon
appeared at δC 144.5 with correlations to resonances of methylene
bound to the silicon atom in 2D 1H−13C HMQC and 2D 1H−13C
HMBC measurement, clearly supporting the formation of
iridasilacycle (see Supporting Information). Milstein et al. reported
F
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Scheme 3. Proposed Mechanism for Iridium-Catalyzed Dehydrogenative Silylation
species A, B, and 8d were in equilibrium, and such reversible
cyclometalation and decyclometalation reactions for the iridium
species were confirmed by a deuterium labeling experiment
using Et3SiD (vide infra). The second step was the insertion of
2-norbornene into the Ir−H bond of 8d, forming norbornyliri-
dium species C, which was thermally unstable even at room
temperature and C(sp3)−H activation of the N-methyl group of
the carbene ligand slowly proceeded to give 10d, presumably due
to the difficulty for the free rotation of the N-aryl ring to approach
the ortho-C(sp2)−H bond at the iridium metal center. Heating
the reaction mixture induced rotation of the N-3,5-xylyl ring of
the carbene ligand, and subsequent ortho-C(sp2)−H bond
activation of the N-aryl ring of the carbene ligand afforded the
five-coordinated Ir−SiEt3 intermediates D along with a release
of norbornane. In this step, C−H bond activation of the carbene
ligand was expected to proceed through either an oxidative
addition of the C−H bond to form an Ir(V) intermediate37,38 or a
σ-bond metathesis pathway between Ir-norbornyl and the ortho-
C−H bond, suggested by Bergman39 and Periana,40 respectively.
In the next step, from D to F via E, the σ-bond of Et3Si−H
coordinated to the five-coordinated iridium metal center of D to
form the σ-bond coordinated species E. The silicon atom of the
that an iridasilacycle, (PMe3)3(H)Ir(o-C6H4SiPh2), proceeded via
ortho-metalation of the silyl ligand attached to the transient
Ir(I) species in situ generated by the elimination of CH4 from
(PMe3)3Ir(SiPh3)(Me)(H).36 Similarly, it was likely assumed that
complex 12d was formed via an intramolecular C(sp2)−H
activation of SiBnMe2 by Ir(I) species generated by reductive
elimination of 2-phenylpyridine from 11d. Thus, though this was
not direct evidence, we assumed that 9d was a four-membered
iridasilacycle, as depicted in eq 4, via an intramolecular C(sp3)−H
activation. Similar C(sp3)−H activation of alkyl groups on the silicon
atom was observed for (Me3P)3(H)IrSiMe2SiMe(SiMe3)SiMe2CH2
from (PMe3)3IrSi(SiMe3)3.27
Proposed Mechanism. Scheme 3 shows a plausible catalytic
cycle for the dehydrogenative silylation of 2-phenylpyridine.
At the beginning, the catalyst precursor 2d reacted with 1 equiv
of Et3SiH to give a five-coordinated Ir−H species A along with
the formation of Et3SiOAc. The addition of 1 equiv of Et3SiH to
A induced the demetalation of the N-3,5-xylyl ring of the carbene
ligand or the phenyl ring of the substrate via concerted Ir−Si and
C−H bond formations after coordination of the Si−H σ-bond to
the iridium atom to give B and complex 8d, respectively, the
latter of which was thermally unstable to afford 9d. The iridium
G
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coordinating Et3Si−H began to interact with the carbanion of the
2-pyridylphenyl moiety to form a σ-complex-assisted metathesis
(σ-CAM) intermediate, and both Ir−H and C−Si bond
formations proceeded together with cleavage of the Si−H
bond to give an ortho-silylated 2-phenylpyridine-coordinated
iridium species F. The σ-CAM pathway is often proposed for late
transition metal catalyzed reactions involving H−E bond
cleavage (E = H, B, Si, C) proposed by Sabo-Etienne and co-
workers, and bond formation and cleavage reactions proceed
without changing the oxidation state of the metal center.41 Due
to the presence of the bulky SiEt3 group attached to the iridium
center and the N-3,5-xylyl group of the carbene ligand, C−Si
bond formation of the substrate proceeded selectively. At the
final stage, exchange of the ortho-silylated 2-phenylpyridine to
2-phenylpyridine regenerated the catalytically active species B.
Deuterium labeling of 2d with excess Et3SiD (15 equiv) in the
presence of 2-phenylpyridine (1.5 equiv) at room temperature
demonstrated the reversibility of cyclometalation/decyclometa-
lation steps for iridium species A, B, and 8d in Scheme 3. Three
deuterium atoms were incorporated at the two ortho-positions of
the N-3,5-xylyl ring of the carbene ligand and one ortho-position
of the phenyl ring of 2-phenylpyridine, and after 3 h, we added
CCl4 to give 8d-Cl-d3 in 69% yield (eq 7). The D-content of the
EXPERIMENTAL SECTION
■
General Procedures. All manipulations involving air- and moisture-
sensitive organometallic compounds were carried out under argon using
the standard Schlenk technique or an argon-filled glovebox. All iridium
complexes and perimidine-based carbene ligands were prepared according
to the literature, including (L)Ir(cod)(X) (L = perimidine-based
carbene, X = OAc, OCOPh, and Cl) complexes.10 2-Phenylpyridine,
1-phenylpyrazol, N-benzylidenemethylamine, N-benzylidene-tert-butyl-
amine, dimethylphenylsilane, and benzyldimethylsilane were purchased
from Sigma-Aldrich and purified by distillation over CaH2. 2-Methyl-6-
phenylpyridine and triethylsilane were purchased from TCI and dried
over CaH2, degassed by afreeze−pump−thaw cycle (3 times), and vacuum-
transferred from CaH2. N-Benzylideneaniline was purchased from
Sigma-Aldrich and used as received. Benzo[h]quinoline was purchased
from TCI and used as received. 2-(4-Methoxyphenyl)pyridine, 2-(4-
trifluoromethylphenyl)pyridine, 4-methyl-2-phenylpyridine, (3-(pyridin-
2-yl)phenyl)methylium, (3-methyl-5-(pyridin-2-yl)phenyl)methylium,
and N-benzylidenecyclohexanamine were prepared according to
previously published procedures.43,44 2-Phenylpyridine-d9 was prepared
according to a previously reported procedures.45 Toluene, THF, CH2Cl2,
and hexane were dried and deoxygenated by passing through a Grubbs
column(Glass CounterSolventDispendingSystem, NikkoHansen& Co,
Ltd.). Benzene-d6 was dried over CaH2 and degassed by a freeze−pump−
thaw cycle (3 times) and vacuum-transferred from CaH2. CD2Cl2 and
DMSO-d6 were degassed and stored under Ar. 1H NMR (400 MHz), 2H
NMR (61 MHz), 13C NMR (100 MHz), and 19F NMR (376 MHz)
spectra were measured on BRUKER AVANCEIII−400 spectrometer. 29Si
NMR (85 MHz) spectra were referenced relative to a tetramethylsilane
1
standard. Assignments for H and 13C NMR peaks for some of the
complexes were aided by 2D 1H−1H COSY, 2D 1H−13C HMQC, and 2D
1H−13C HMBC spectra. GC−MS measurement performed out using
a DB-1 capillary column (0.25 mm × 30 m) on a Shimadzu GCMS−
QP2010Plus. Massspectra were recorded onBruker DaltonicsMicroTOF
II-HB and JEOL JMS−700. IR spectra were recorded on a JASCO FT/
IR−230 spectrometer. The elemental analyses were recorded by a Perkin-
Elmer 2400 at the Faculty of Engineering Science, Osaka University. All
melting points were recorded on Yanaco micro melting point apparatus.
Flash column chromatography was performed using silica gel 60 (0.040−
0.0663 nm, 230−400 mesh ASTM).
3,5-xylyl ring and phenyl ring of the substrate was estimated to be
90% and 40%, respectively.42 The high deuterium content sug-
gests the rapid equilibrium among 8d, A, and B in the proposed
cycle, and each step in the equilibrium involves reversible
Ir−Si/C−H bond formation and cleavage through the σ-CAM
pathway without a change in the oxidation state of the metal
center.25a−c
Preparation of (L4)Ir(cod)(OAc) (1d) (L4 = N-CH3, N-3,5-
(CH3)2C6H3 Perimidine Carbene). THF (30 mL) was added to a
Schlenk containing LiN(SiMe3)2 (167 mg, 9.98 ×10−1 mmol), [IrCl(cod)]2
(336 mg, 4.99 × 10−1 mmol), N-methyl-N-3,5-dimethylphenylperimi-
dium iodide (L4)[I] (414 mg, 1.00 mmol), and AgOAc (1.67 g, 10 mmol)
at room temperature, and then the resulting reaction mixture was stirred
for 6 h at room temperature. After all volatiles were removed under
reduced pressure, the resulting solids were extracted with CH2Cl2, which
was concentrated to give the title product 1d (551 mg, 8.52 × 10−1
CONCLUSIONS
■
1
mmol) as yellow powder. Yield: 85%. Mp 224 °C (dec). H NMR
We developed an Ir(carbene)-catalyzed direct dehydrogenative
silylation of pyridyl- and iminyl-ligated arenes with triethylsilane
via C−H bond functionalization, which selectively afforded
a mono-ortho-silylation product in good to excellent yield.
A variety of aromatic compounds containing a nitrogen atom as a
directing group can be used for the dehydrogenative silylation.
Noteworthy was that the intramolecular C−H bond activation of
an N-xylyl ring of the perimidine-based carbene ligand, leading
to cyclometalated iridium species, efficiently enhanced the
dehydrogenative silylation reaction. During the catalytic cycle,
the perimidine-based carbene ligand changed its electronic
and structural properties via a cyclometalation/decyclometala-
tion reaction. In this context, cyclometalated monoanionic
carbene increased the steric crowding around the iridium metal
center and acted as a hydride acceptor returning back to neutral
carbene, demonstrating the utility of the carbanion as a labile
coordination site of hemilabile ligation, which is, to the best of
our knowledge, the first example of the hemilabile nature of
carbene ligands bearing a labile carbanion site.
(400 MHz, C6D6, 30 °C): δ 7.59 (s, 1H, CH of NAr), 7.09 (d, 3JH−H
=
8.0 Hz, 1H, perimidine ring), 7.00−7.05 (m, 2H, perimidine ring), 6.91
3
3
(s, 1H, CH of NAr), 6.83 (dd, JH−H = 8.0 Hz, JH−H = 7.9 Hz, 1H,
perimidine ring), 6.73 (s, 1H, CH of NAr), 6.26 (d, 3JH−H = 7.8 Hz, 1H,
perimidine ring), 6.14 (d, 3JH−H = 7.8 Hz, 1H, perimidine ring), 4.45−
4.51 (m, 2H, =CH of cod), 4.12 (s, 3H, NCH3), 2.91 (t, 3JH−H = 6.6 Hz,
1H, =CH of cod), 2.31−2.40 (m, 2H, CH2 of cod and =CH of cod), 2.25
(s, 3H, CH3 of NAr), 2.23 (s, 3H, CH3COO), 2.15 (s, 3H, CH3 of NAr),
1.92−1.97 (m, 2H, CH2 of cod), 1.54−1.63 (m, 3H, CH2 of cod), 1.21−
1.25 (m, 2H, CH2 of cod). 13C NMR (100 MHz, C6D6, 30 °C) δ 207.2
(IrC), 176.1 (CO), 142.2, 140.8, 140.5, 138.5, 138.4, 137.1, 135.3,
130.2 (CH), 130.0 (CH), 127.9 (CH, perimidine ring), 125.8 (CH),
125.6 (CH), 121.1 (CH), 120.7 (CH), 120.3 (CH), 107.0 (CH,
perimidine ring), 105.2 (CH of NAr), 86.1 (=CH of cod), 81.2 (=CH
of cod), 53.9 (=CH of cod), 49.0 (=CH of cod), 43.8 (NCH3), 36.7
(CH2 of cod), 30.9 (CH2 of cod), 30.4 (CH2 of cod), 27.3 (CH2 of cod),
24.1 (two CH3 of NAr), 21.6 (OCCH3). IR (KBr tablet, cm−1): 3448,
2916, 1635, 1583, 1420, 1380, 1341, 1307, 813, 760. Anal. Calcd for
C30H33IrN2O2: C, 55.79; H, 5.15; N, 4.34. Found: C, 55.48; H, 5.18; N,
4.52.
H
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Preparation of (L5)Ir(cod)(OAc) (1e) (L5 = N-CH3, N-3,5-
(OCH3)2C6H3 Perimidine Carbene). The synthesis of 1e was identical
to that of 1d except that N-methyl-N-3,5,-dimethoxylphenylperimidium
iodide, (L5)[I], was used as a carbene precursor. Yield: 83%. Yellow
powder, mp 198 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 7.45
(dd, 4JH−H = 2.3 Hz, 4JH−H = 1.7 Hz, 1H, CH of NAr), 7.09−6.99 (m,
3H, perimidine ring), 6.86−6.81 (m, 1H, perimidine ring (1H) and CH
of NAr (1H)), 6.48 (dd, JH−H = 2.3 Hz, JH−H = 1.7 Hz, 1H, CH of
NAr), 6.30 (dd, 3JH−H = 7.7 Hz, 4JH−H = 0.9 Hz, 1H, perimidine ring),
6.24 (dd, 3JH−H = 7.6 Hz, 4JH−H = 1.0 Hz, 1H, perimidine ring), 4.60−
4.50 (m, 2H, =CH of cod), 4.10 (s, 3H, NCH3), 3.62 (s, 3H, OCH3),
3.32 (s, 3H, OCH3), 2.97 (t, 3JH−H = 6.4 Hz, 1H, =CH of cod), 2.50 (td,
3J = 7.9 Hz, 3JH−H = 4.1 Hz, 1H, =CH of cod), 2.41−2.31 (m, 1H, CH2 of
cod), 2.15 (s, 3H, CH3COO), 1.98−1.90 (m, 2H, CH2 of cod), 1.87−
1.77 (m, 1H, CH2 of cod), 1.74−1.61 (m, 2H, CH2 of cod), 1.21−1.11
(m, 2H, CH2 of cod). 13C NMR (100 MHz, C6D6, 30 °C): δ 206.3 (Ir
C), 175.7 (CO), 162.7, 161.5, 142.2, 137.7, 136.6, 134.9, 128.0 (CH),
127.7 (CH), 120.9 (CH), 120.5 (CH), 120.0, 108.3 (CH of NAr), 106.9
(CH of NAr), 106.7 (CH of perimidine ring), 104.9 (CH of perimidine
ring), 102.3 (CH of perimidine ring), 85.4 (=CH of cod), 81.3 (=CH of
cod), 55.5 (OCH3), 55.3 (OCH3), 54.0 (=CH of cod), 49.1 (=CH of
cod), 43.3 (NCH3), 36.5 (CH2 of cod), 30.6 (CH2 of cod), 30.4 (CH2 of
cod), 26.9 (CH2 of cod), 23.8 (OCCH3). IR (KBr tablet, cm−1) v =
3438, 3002, 2957, 2877, 2834, 1631, 1609, 1582, 1469, 1425, 1379,
1348, 1330, 1307, 1234, 1205, 1193, 1154, 1081, 1056, 816, 764, 670.
Anal. Calcd for C30H33IrN2O4: C, 53.16; H, 4.91; N, 4.13. Found: C,
53.12; H, 5.06; N, 4.31.
7.34 (d, 3JH−H = 8.3 Hz, 1H, perimidine ring), 7.10 (t, 3JH−H = 8.0 Hz,
2H, Ar), 7.02−6.91 (m, 5H, Ar), 6.77 (td, 3JH−H = 7.4, 4JH−H = 1.4 Hz,
3
4
1H, perimidine ring), 6.56 (ddd, JH−H = 7.1, 5.6 Hz, JH−H
=
1.3 Hz, 1H, py), 6.39 (s, 1H, CH of NAr), 6.18 (d, 3JH−H = 7.6 Hz, 1H,
perimidine ring), 3.70 (s, 3H, NCH3), 2.22 (s, 3H, CH3 of NAr), 1.76 (s,
3H, CH3COO), 1.67 (s, 3H, CH3 of NAr). 13C NMR (100 MHz, C6D6,
30 °C): δ 193.7 (IrC), 186.6 (CO), 166.0, 153.4, 147.5 (HCN
of 2-Phpy), 145.4, 144.6, 139.5 (CH), 137.6, 135.4, 134.9, 130.5, 130.0
(CH of perimidine ring), 128.9, 128.6, 127.4 (CH), 127.3 (CH of NAr),
127.1 (CH), 124.2 (CH), 122.0, 121.7, 121.6, 121.4 (CH of perimidine
ring), 120.7 (CH of perimidine ring), 120.0, 118.6 (CH of perimidine
ring), 110.9 (CH), 110.8 (CH), 106.0 (CH of perimidine), 42.4
(NCH3), 25.8 (OCCH3), 23.4 (CH3 of NAr), 21.2 (CH3 of NAr).
IR (KBr tablet, cm−1) v = 3446, 2923, 1610, 1584, 1542, 1457, 1423,
1384, 1345, 1325, 1091, 1049, 1019, 817, 749, 736, 677. Anal. Calcd
for C33H29IrN3O2: C, 57.29; H, 4.23; N, 6.07. Found: C, 56.81; H, 4.38;
N, 6.15.
4
4
Synthesis of (XyC∧C:)(C∧N)Ir(OAc) (XyC∧C: = Cyclometalated
Perimidine-Based Carbene, C∧N = Cyclometalated Benzo[h]-
quinoline) (4d). The synthesis of 4d was identical to that of 2d except
that benzo[h]quinoline was used as a substrate (83% yield). Yellow
powder, mp > 270 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 8.98
(d, 3JH−H = 4.8 Hz, 1H, HCN of benzo[h]quinoline), 7.57 (d, 3JH−H
=
4.4 Hz, 1H, Ar), 7.55 (d, 3JH−H = 6.0 Hz, 1H, Ar), 7.51 (dd, 3JH−H = 7.9,
4JH−H = 1.0 Hz, 1H, CH of benzo[h]quinoline), 7.36 (d, J = 7.7 Hz, 1H,
Ar), 7.21 (d, 3JH−H = 7.2 Hz, 1H, Ar), 7.18 (s, 1H, CH of NAr), 7.14−
3
7.12 (m, 2H, Ar), 7.11 (d, JH−H = 4.0 Hz, 1H, Ar), 6.96−7.04 (m,
Preparation of (L6)Ir(cod)(OAc) (1f) (L6 = N-CH3, N-3,5-
(tBu)2C6H3 Perimidine Carbene). The synthesis of 1f was identical
to that of 1d except that N-methyl-N-3,5-di-tert-butylphenylperimidium
iodide (L6)[I] was used as a carbene precursor. Yield: 87%. Yellow
powder, mp 252 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 8.05
(t, 4JH−H = 1.9 Hz, 1H, CH of NAr), 7.66 (t, 4JH−H = 1.9 Hz, 1H, CH
of NAr), 7.09−6.99 (m, 4H, perimidine ring and CH of NAr), 6.77
(t, 3JH−H = 8.1 Hz, 1H, perimidine ring), 6.27 (d, 3JH−H = 7.3 Hz, 1H,
perimidine ring), 6.12 (d, 3JH−H = 7.8 Hz, 1H, perimidine ring), 4.57 (q,
3JH−H = 7.7 Hz, 1H, =CH of cod), 4.46 (t, 3JH−H = 6.5 Hz, 1H, =CH of
3
4
3H, Ar), 6.91 (dd, JH−H = 8.0 Hz, JH−H = 5.2 Hz, 1H, CH of
benzo[h]quinoline), 6.27 (s, 1H, CH of NAr), 6.21 (d, J = 7.7 Hz, 1H,
perimidine ring), 3.72 (s, 3H, NCH3), 2.19 (s, 3H, CH3 of NAr), 1.82 (s,
3H, CH3COO), 1.31 (s, 3H, CH3 of NAr). 13C NMR (100 MHz, C6D6,
30 °C): δ 192.4 (IrC), 186.7 (CO), 153.3, 146.5 (HCN of
benzo[h]quinoline), 145.2, 141.7, 140.5, 136.5 (CH), 136.3 (CH),
135.6, 134.9, 134.2, 133.1, 130.5, 129.8, 129.7, 129.3, 128.7, 128.6, 127.4,
127.3, 127.1 (CH of NAr), 126.8, 123.4, 121.8 (CH), 121.0 (CH), 120.8
(CH), 119.8, 111.0 (CH), 110.8 (CH), 106.1 (CH of perimidine ring),
42.7 (NCH3), 25.9 (OCCH3), 22.7 (CH3 of NAr), 21.1 (CH3 of NAr).
IR (KBr tablet, cm−1) v = 3431, 2918, 1631, 1583, 1525, 1479, 1453,
1427, 1383, 1346, 1327, 1230, 1190, 1139, 1085, 1037, 929, 834, 816,
764, 719, 677. Anal. Calcd for C35H29IrN3O2: C, 58.72; H, 4.08; N, 5.87.
Found: C, 59.21; H, 3.89; N, 5.48.
cod), 4.17 (s, 3H, NCH3), 2.96 (t, 3J = 6.6 Hz, 1H, =CH of cod), 2.50−
2.46 (m, 1H, =CH of cod), 2.40−2.32 (m, 1H, CH2 of cod), 2.28 (s, 3H,
CH3COO), 2.04−1.87 (m, 2H, CH2 of cod), 1.69−1.58 (m, 1H, CH2 of
cod), 1.57−1.44 (m, 2H, CH2 of cod), 1.43 (s, 9H, tBu), 1.30 (s, 9H,
tBu), 1.16−1.05 (m, 2H, CH2 of cod). 13C NMR (100 MHz, C6D6,
Preparation of (XyC∧C:)(C∧N) Ir(OAc) (XyC∧C: = Cyclometalated
Perimidine-Based Carbene, C∧N = Cyclometalated N-Benzyli-
denemethylamine) (5d). The synthesis of 5d was identical to that of
5a except that 1d was used as a precursor (93% yield). Orange powder,
mp > 270 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 7.77 (s, 1H,
MeN=CHPh), 7.49 (s, 1H, CH of NAr), 7.48 (d, 3JH−H = 6.9 Hz, 1H,
Ar), 7.20 (d, 3JH−H = 7.6 Hz, 1H, perimidine ring), 7.09 (t, 3JH−H = 8.5
Hz, 2H, Ar), 6.99 (d, 3JH−H = 8.0 Hz, 1H, perimidine ring), 6.95 (d, 3J =
30 °C): δ 206.3 (IrC), 175.6 (CO), 153.5, 151.5, 140.5, 138.4,
136.8, 134.9, 127.6 (CH of NAr), 126.7 (CH of NAr), 122.5 (CH of
NAr), 122.1 (CH of a perimidine ring), 120.7 (CH of perimidine ring),
120.4 (CH of perimidine ring), 120.2, 106.6 (CH of perimidine ring),
104.8 (CH of perimidine ring), 84.7 (=CH of cod), 81.5 (=CH of cod),
53.6 (=CH of cod), 48.8 (=CH of cod), 43.2 (NCH3), 36.1 (CH2 of
cod), 35.5 (N-3,5-{C(CH3)3}2C6H3), 35.1 (N-3,5-{C(CH3)3}2C6H3),
31.6 (CH3 of N-3,5-{C(CH3)3}2C6H3), 31.5 (CH3 of N-3,5-{C-
(CH3)3}2C6H3), 30.7 (CH2 of cod), 30.0 (CH2 of cod), 27.3 (CH2 of
cod), 23.9 (OCCH3). One carbon resonance is overlapped with C6D6
signals. IR (KBr tablet, cm−1) v = 3421, 2961, 2877, 2831, 1634, 1583,
1527, 1475, 1428, 1381, 1361, 1340, 1297, 1136, 1079, 816, 765, 713,
670. Anal. Calcd for C36H45IrN2O2: C, 59.23; H, 6.21; N, 3.84. Found:
C, 59.66; H, 5.93; N, 4.29.
7.9 Hz, 1H, perimidine ring), 6.87−6.81 (m, 2H, Ar), 6.67 (td, 3JH−H
=
7.5 Hz, 4JH−H = 1.6 Hz, 1H, perimidine ring), 6.46 (s, 1H, CH of NAr),
3
6.15 (d, JH−H = 7.8 Hz, 1H, perimidine ring), 3.64 (s, 3H, NCH3 of
perimidine ring), 3.35 (s, 3H, NCH3 of N-benzylidenemethylamine),
2.24 (s, 3H, CH3 of NAr), 2.07 (s, 3H, CH3 of NAr), 1.78 (s, 3H,
CH3COO). 13C NMR (100 MHz, C6D6, 30 °C): δ 193.0 (IrC), 186.2
(CO), 175.4 (MeN=CHPh), 153.1, 148.4, 146.3, 145.7, 138.5 (CH),
135.4, 134.9, 132.9, 130.9 (CH), 130.6, 129.3, 128.7, 128.6, 128.6, 127.4,
127.2 (CH), 126.9 (CH of NAr), 121.7, 121.4, 121.0 (CH), 120.8 (CH),
110.9 (CH of perimidine ring), 110.7 (CH of NAr), 106.0 (CH of
perimidine ring), 44.5 (NCH3 of N-benzylidenemethylamine), 42.3
(NCH3 of perimidine ring), 25.2 (OCCH3), 23.5 (CH3 of NAr), 21.2
(CH3 of NAr). IR (KBr tablet, cm−1) v = 3446, 3056, 2919, 1631, 1607,
1583, 1526, 1457, 1428, 1382, 1345, 1325, 1228, 1141, 1089, 1049,
1034, 1019, 815, 760, 749, 736, 679. Anal. Calcd for C30H29IrN3O2: C,
54.94; H, 4.46; N, 6.41. Found: C, 55.25; H, 4.32; N, 6.17.
Preparation of (XyC∧C:)(C∧N) Ir(OAc) (XyC∧C: = Cyclometalated
Perimidine-Based Carbene, C∧N = Cyclometalated 2-Phenyl-
pyridine) (2d). Toluene was added to a Schlenk containing a
corresponding (L4)Ir(cod)OAc (L4 = perimidine-based carbene) 1d
(170 mg, 2.63 × 10−1 mmol) and 2-phenylpyridine (50.0 mg, 3.22 ×
10−1 mmol) at room temperature. The reaction mixture was stirred
under toluene refluxing conditions for 48 h under an argon atmosphere.
The mixture was cooled to ambient temperature, and the solvent was
evaporated under vacuum. The resulting solid was washed by hexane
(3 times) to give a corresponding bis(cyclometalated)iridium complex
2d in 93% yield (169 mg, 2.45 × 10−1 mmol). Yellow powder, mp >
Preparation of (XyC∧C:)(C∧N) Ir(OAc) (XyC∧C: = Cyclometalated
Perimidine-Based Carbene, C∧N = Cyclometalated 2-Vinyl-
pyridine) (6d). The synthesis of 6d was identical to that of 6a except
that 1d was used as a precursor (92% yield). Yellow powder, mp > 270 °C
(dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 9.05 (d, 3JH−H = 7.5 Hz,
270 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 8.75 (dd, 3JH−H
=
5.4 Hz, 4JH−H = 1.7 Hz, 1H, py), 7.542 (d, 3JH−H = 7.6 Hz, 1H, Ar), 7.541
(s, 1H, CH of NAr), 7.49 (dd, 3JH−H = 7.8 Hz, 4JH−H = 1.4 Hz, 1H, Ar),
I
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Journal of the American Chemical Society
Article
1H, py), 8.58 (d, 3JH−H = 5.6 Hz, 1H, py), 7.50 (s, 1H, CH of NAr), 7.48
(d, 3JH−H = 7.6 Hz, 1H, perimidine ring), 7.11−7.05 (m, 3H, Ar), 7.01−
6.93 (m, 3H, Ar), 6.87 (d, 3JH−H = 8.0 Hz, 1H, perimidine ring), 6.56 (dd,
3JH−H = 7.2 Hz, 4JH−H = 1.4 Hz, 1H, py), 6.51 (s, 1H, CH of NAr), 6.15 (d,
6.83 (t, 3JH−H = 8.2 Hz, 1H, Ar), 6.78 (d, 3JH−H = 7.0 Hz, 1H, Ar), 6.66 (t,
3JH−H = 7.3 Hz, 1H, Ar), 6.43 (t, 3JH−H = 6.5 Hz, 1H, CH of 2-Phpy), 6.33
(t, 3JH−H = 7.7 Hz, 2H, Ar), 6.23 (s, 1H, ortho CH of NAr), 6.15 (s, 1H,
para CH of NAr), 4.15 (s, 3H, NCH3), 1.76 (s, 3H, CH3 of NAr), 1.62
(s, 3H, CH3 of NAr), 1.07 (t, 3JH−H = 7.8 Hz, 9H, Si(CH2CH3)3), 0.88
J = 7.6 Hz, 1H, perimidine ring), 3.62 (s, 3H, NCH3), 2.23 (s, 3H, CH3 of
NAr), 1.93 (s, 3H, CH3 of NAr), 1.75 (s, 3H, CH3COO). 13C NMR
(100 MHz, C6D6, 30 °C): δ 192.0 (IrC), 186.4 (CO), 167.3, 157.2,
153.4, 147.5, 145.8, 137.7 (CH), 135.4, 134.8, 132.9, 132.4 (CH), 130.8,
127.3 (CH), 127.2 (CH), 127.0 (CH of NAr), 121.6, 121.4, 120.8 (CH),
119.7 (CH), 118.6 (CH of perimidine ring), 113.5, 110.8 (CH of
perimidine ring), 110.7, 105.9 (CH of perimidine ring), 41.7 (NCH3),
25.7 (OCCH3), 23.1 (CH3 of NAr), 21.2 (CH3 of NAr). IR (KBr tablet,
cm−1) v = 3448, 3058, 2959, 1632, 1604, 1595, 1584, 1526, 1469, 1441,
1426, 1383, 1325, 1222, 1139, 1087, 1037, 816, 798, 763, 677. Anal.
Calcd for C29H27IrN3O2: C, 54.27; H, 4.24; N, 6.55. Found: C, 54.53;
H, 4.12; N, 6.80.
3
(q, JH−H = 6.5 Hz, 6H, Si(CH2CH3)3). 13C NMR (100 MHz, C6D6,
30 °C): δ 183.8 (IrC), 167.0, 153.7, 150.9, 145.1, 145.0 (HCN of
2-Phpy), 142.6, 142.5, 140.3, 140.2, 140.0, 137.5, 136.8 (CH), 136.6
(CH), 136.2, 135.0, 129.9 (CH), 129.7 (CH), 128.5, 127.5, 121.1 (CH),
120.9, 120.6, 120.5, 119.6, 117.5 (CH), 106.2, 105.0 (CH), 44.3
(NCH3), 21.2 (CH3 of NAr), 20.3 (CH3 of NAr), 9.7 (Si(CH2CH3)3),
8.4 (Si(CH2CH3)3). Some carbon resonances are overlapped with C6D6
signals. 29Si NMR (85 MHz, C6D6, 35 °C): δ 6.33. IR (KBr tablet, cm−1)
v = 3447, 2944, 2869, 1634, 1603, 1585, 1477, 1422, 1380, 1345, 1316,
1089, 1004, 815, 762, 729, 661. Anal. Calcd for C37H41ClIrN3Si: C,
56.72; H, 5.27; N, 5.36. Found: C, 56.41; H, 4.90; N, 5.33.
Preparation of (XyC∧C:)(C∧N) Ir(OAc) (XyC∧C: = Cyclometalated
Perimidine-Based Carbene, C∧N = Cyclometalated N-(3-
Phenylallylidene)aniline) (7d). The synthesis of 7d was identical to
that of 7a except 1d was used as a precursor (94% yield). Bright pink
powder, mp > 270 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 8.27
(d, 3JH−H = 2.4 Hz, 1H, NCH), 7.71 (s, 1H, CH of NAr), 7.60−7.55
(m, 3H, Ar), 7.14−7.10 (m, 4H, Ar), 7.05−6.93 (m, 5H, Ar), 6.84−6.75
Reaction of 2d with Et3SiD. Triethylsilane-d1 (170 mg, 1.45 mmol)
was added to benzene solution of 2d (100 mg, 1.45 × 10−1 mmol) in the
presence of 2-phenylpyridine (33.8 mg, 2.18 × 10−1 mmol) in a J-Young
tube. 2H NMR (61 MHz, C6D6, 30 °C): δ 8.06 (s, D of 8d), 7.31 (br s),
7.15 (br s), 7.08(s, D of 8d), 6.09 (br s, D of 9d), −5.68 (s, Ir−D of 8d),
−15.35 (s, Ir−D of 9d). The reaction mixture was stirred at room
temperature for 30 min, and then, CCl4 (112 mg, 7.25 × 10−1 mmol)
was added to the reaction mixture. The reaction mixture was stirred
for 20 h at ambient temperature, and all volatiles were removed under
vacuum. The bright orange powder was obtained by washing with
hexane (5 mL × 3 times) (see Figure S4, 1H NMR spectra of 8d-Cl and
8d-Cl-d3 in Supporting Information).
3
(m, 4H, Ar), 6.68 (s, 1H, CH of NAr), 5.86 (d, JH−H = 7.6 Hz, 1H,
perimidine ring), 3.18 (s, 3H, NCH3), 2.61 (s, 3H, CH3 of NAr), 2.31 (s,
3H, CH3 of NAr), 1.22 (s, 3H, CH3COO). 13C NMR (100 MHz, C6D6,
30 °C): δ 195.3 (IrC), 193.0, 186.8, 169.6 (NCH), 153.4, 152.2,
148.8, 148.4, 134.7, 134.6, 132.7, 132.1, 130.1, 129.0 (CH), 127.4, 127.3
(CH), 127.2, 126.6, 125.9 (CH), 124.0 (CH), 121.7 (CH), 121.6, 121.1
(CH), 116.2, 111.2 (CH), 110.9 (CH), 105.8 (CH of perimidine), 41.5
(NCH3), 24.5 (OCCH3), 23.1 (CH3 of NAr), 21.4 (CH3 of NAr). IR
(KBr tablet, cm−1) v = 3445, 2916, 1633, 1583, 1526, 1483, 1474, 1459,
1441, 1381, 1365, 1361, 1355, 1342, 1334, 1327, 1316, 1306, 1201,
1086, 816, 760, 697, 687, 682. Anal. Calcd for C37H33IrN3O2: C, 59.74;
H, 4.47; N, 5.65. Found: C, 59.60; H, 4.21; N, 5.49. Some carbon
resonances are overlapped with C6D6 signals.
Preparation of [(MeC∧C:)(C∧N)Ir(SiEt3)] (MeC∧C: = Cyclometa-
lated Perimidine-Based Carbene, C∧N = Cyclometalated 2-
Phenylpyridine) (10d). Triethylsilane (50.3 mg, 4.33 × 10−1 mmol)
was added to 2d (100 mg, 1.45 × 10−1 mmol) in the presence of
2-phenylpyridine (33.6 mg, 2.17 × 10−1 mmol) in 5 mL of toluene.
2-Norbornene (40.7 mg, 4.32 × 10−1 mmol) was added to the reaction
mixture sequentially. The reaction mixture was kept at room
temperature for 4 days, and all volatiles were removed under reduced
pressure. Dark red crystals were obtained in 38% yield (41 mg, 5.49 ×
10−2 mmol) by recrystallization with toluene/hexane. mp > 270 °C
(dec). 1H NMR (400 MHz, CD2Cl2, 30 °C): δ 7.66 (d, 3JH−H = 7.4 Hz,
1H, py), 7.59−7.53 (m, 3H, Ar), 7.39 (t, 3JH−H = 7.8 Hz, 2H, Ar), 7.33
(d, J = 6.8 Hz, 2H, Ar), 7.26−7.20 (m, 3H, Ar), 7.11 (t, 3JH−H = 7.9 Hz,
1H, perimidine ring), 7.07−7.02 (m, 2H, Ar), 6.95 (d, 3JH−H = 7.0 Hz,
1H, Ar), 6.67 (d, 3JH−H = 7.4 Hz, 1H, perimidine ring), 6.37 (s, 1H, CH
Characterization of [(C∧N)Ir(L)(SiEt3 )H] (C∧N = Cyclometa-
lated 2-Phenylpyridine, L = N-CH3, N-3,5-(CH3)2C6H3 Perimi-
dine-Based Carbene) (8d). Triethylsilane (5.05 mg, 4.35 × 10−2
mmol) was added to benzene solution of 2d (10.0 mg, 1.45 × 10−2
mmol) in the presence of 2-phenylpyridine-d9 (2.38 mg, 1.45 × 10−2
mmol) in a J-Young tube. 1H NMR (400 MHz, C6D6, 30 °C): δ 8.29 (d,
3
3JH−H = 5.6 Hz, 1H, py), 8.03 (d, JH−H = 7.3 Hz, 1H, Ar), 7.66 (d,
3JH−H = 7.7 Hz, 1H, perimidine ring), 7.33 (td, 3JH−H = 7.2 Hz, 4JH−H
=
of NAr), 6.00 (d, 3JH−H = 7.7 Hz, 1H, perimidine ring), 3.45 (d, 2JH−H
=
8.5 Hz, 1H, NCH2Ir), 3.39 (d, 2JH−H = 8.5 Hz, 1H, NCH2Ir), 2.50 (s,
3H, CH3 of NAr), 2.32 (s, 3H, CH3 of NAr), 0.57 (t, 3JH−H = 7.7 Hz, 9H,
Si(CH2CH3)3), 0.40 (q, 3JH−H = 7.8 Hz, 6H, Si(CH2CH3)3). 13C NMR
(100 MHz, CD2Cl2, 30 °C): δ 189.0, 172.4, 169.3, 155.8, 151.1, 143.3,
142.5, 141.9, 141.2, 138.9, 138.9, 136.8, 135.5, 131.1, 128.9, 128.8, 128.0,
127.6, 127.5, 123.0, 122.9, 121.7, 120.9, 120.5, 119.7, 119.2, 118.0, 106.5,
101.4, 21.6, 21.5, 8.9, 7.9, 7.3. 29Si NMR (85 MHz, C6D6, 30 °C): δ 7.02.
IR (KBr tablet, cm−1) v = 3451, 3047, 2925, 2868, 1630, 1583, 1526,
1471, 1421, 1380, 1340, 1313, 1216, 1162, 1000, 815, 765, 750, 732.
Anal. Calcd for C37H40IrN3Si: C, 59.49; H, 5.40; N, 5.62. Found: C,
59.53; H, 5.41; N, 5.79.
1.3 Hz, 1H, perimidine ring), 7.28 (s, 1H, ortho CH of NAr), 7.25 (d, J =
8.9 Hz, 1H, Ar), 7.20−7.15 (m, 2H, Ar), 7.15−7.09 (m, 2H, Ar), 7.01−
6.96 (m, 1H, Ar), 6.90 (m, 1H, Ar, overlapped with CH of NAr), 6.88 (s,
1H, ortho CH of NAr), 6.51 (s, 1H, para CH of NAr), 6.42 (d, 3JH−H
=
7.5 Hz, 1H, perimidine ring), 6.26 (dd, 3JH−H = 7.3 Hz, 4JH−H = 1.3 Hz,
3
1H, py), 6.18 (d, JH−H = 8.0 Hz, 1H, perimidine ring), 3.99 (s, 3H,
NCH3), 2.16 (s, 3H, CH3 of NAr), 1.22 (s, 3H, CH3 of NAr), 0.99−0.95
(m, 9H, Si(CH2CH3)3, overlapped with free HSiEt3) 0.79−0.73 (m, 6H,
Si(CH2CH3)3, overlapped with free Et3SiOAc), −5.55 (s, 1H, Ir−H).
29Si NMR (85 MHz, C6D6, 30 °C): δ 5.35.
Preparation of [(C∧N)Ir(L)(SiEt3 )Cl] (C∧N = Cyclometalated 2-
Phenylpyridine, L = N-CH3, N-3,5-(CH3)2C6H3 Perimidine-Based
Carbene) (8d-Cl). Triethylsilane (50.3 mg, 4.33 × 10−1 mmol) was
added to 2d (100 mg, 1.45 × 10−1 mmol) in the presence of
2-phenylpyridine (33.6 mg, 2.17 × 10−1 mmol) in 8 mL of toluene. The
reaction mixture was stirred at room temperature for 30 min, and then,
CCl4 (111 mg, 7.22 × 10−1 mmol) was added to the reaction mixture.
The reaction mixture was stirred for 20 h at ambient temperature, and all
volatiles were removed under vacuum. The orange powder was washed
by hexane (5 mL × 3 times) and was dried under vacuum. Bright orange
powder was obtained in 69% yield (78.3 mg, 1.00 × 10−1 mmol). mp >
Preparation of [(C∧N)Ir(L)(SiMe2 Bn)Cl] (C∧N = Cyclometa-
lated 2-Phenylpyridine, L = N-CH3, N-3,5-3,5-(CH3)2C6H3
Perimidine-Based Carbene) (11d-Cl). A similar procedure to that
for 8d-Cl was employed without excess of 2-phenylpyridine. The
mixture was purified by silica-column chromatography (46% yield). Red
powder, mp > 270 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 9.11
(d, 3JH−H = 7.4 Hz, 1H, py), 7.98 (d, 3JH−H = 5.6 Hz, 1H, Bn), 7.91 (s,
1H, CH of NAr), 7.35 (t, 3JH−H = 7.4 Hz, 1H, Ar), 7.14−1.11 (m, 3H,
Ar), 7.09−7.07 (m, 3H, Ar), 7.05−7.03 (m, 3H, Ar), 6.97 (t, 3JH−H = 7.1
Hz, 1H, Ar), 6.85 (t, 3JH−H = 8.0 Hz, 1H, Ar), 6.78 (d, 3JH−H = 8.1 Hz,
1H, Ar), 6.67 (t, 3JH−H = 7.7 Hz, 1H, Bn), 6.34 (d, 3JH−H = 7.5 Hz, 1H,
Ar), 6.24 (d, 3JH−H = 7.8 Hz, 1H, perimidine ring), 6.16 (s, 1H, CH of
NAr), 6.11 (s, 1H, CH of NAr), 5.89 (t, 3JH−H = 6.2 Hz, 1H, Bn), 4.09
270 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 10.08 (d, 3JH−H
=
5.7 Hz, 1H, HCN of 2-Phpy), 8.13 (s, 1H, ortho CH of NAr), 7.22 (d,
3JH−H = 7.7 Hz, 1H, perimidine ring), 7.17−7.13 (m, 1H, Ar, overlapped
3
2
with C6D6), 7.08 (d, JH−H = 8.3 Hz, 1H, Ar), 7.04 (m, 2H, Ar), 6.94
(s, 3H, NCH3), 2.74 (d, JH−H = 13.7 Hz, 1H, Si(CH2Ph)Me2), 2.57
2
(d, 3JH−H = 8.3 Hz, 1H, CH of 2-Phpy), 6.88 (t, 3JH−H = 7.3 Hz, 1H, Ar),
(d, JH−H = 13.7 Hz, 1H, Si(CH2Ph)Me2), 1.68 (s, 3H, CH3 of NAr),
J
dx.doi.org/10.1021/ja406519u | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
1.43 (s, 3H, CH3 of NAr), 0.18 (s, 3H, IrSi(CH3)2Bn), −0.26 (s, 3H,
IrSi(CH3)2Bn). 13C NMR (100 MHz, C6D6, 30 °C): δ 205.5 (IrC),
170.9, 166.8, 154.7 (CN of 2-Phpy), 146.3, 145.5, 142.9, 139.6, 137.4,
137.0, 136.6 (CH), 136.1, 135.0 (CH), 130.5 (CH of NAr), 129.9, 129.1
(CH), 128.5, 127.6, 123.8 (CH), 123.6, 122.2 (CH of NAr), 122.03 (CH
of NAr), 122.0 (CH of perimidine ring), 121.43 (CH), 121.41 (CH),
121.0, 120.4, 117.5 (CH of perimidine ring), 106.5 (CH of perimidine
ring), 105.7 (CH of perimidine ring), 44.2 (NCH3), 29.3 (Si(CHPh)-
Me2), 21.0 (CH3 of NAr), 20.5 (CH3 of NAr), 1.5 (SiBn(CH3)2), 1.0
(SiBn(CH3)2). Some carbon resonances are overlapped with C6D6
signals. 29Si NMR (85 MHz, C6D6, 35 °C): δ −4.01. IR (KBr tablet,
cm−1) v = 3450, 3056, 2949, 1634, 1603, 1491, 1474, 1424, 1380, 1347,
1317, 1231, 1147, 1080, 855, 815, 759, 734, 701. Anal. Calcd for
C40H39ClIrN3Si: C, 58.77; H, 4.81; N, 5.14. Found: C, 58.89; H, 4.39;
N, 5.54.
11d-Cl. These materials are available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
mashima@chem.es.osaka-u.ac.jp
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
G.C. thanks the Japan Society for the Promotion of Science for a
fellowship. H.T. acknowledges the financial support by Adaptable
and Seamless Technology transfer Program through target-driven
R&D (A-STEP) of the Japan Science and Technology Agency
(JST), Japan. This work was supported by Grant-in-Aid for
Scientific Research on Innovative Areas, “Molecular Activation
Directed toward Straightforward Synthesis”, MEXT, Japan.
Preparation of [(2-Phpy)Ir(L)(SiMe2Bn)H] (2-Phpy = Coordi-
nated 2-Phenylpyridine, L = N-CH3, N-3,5-(CH3)2C6H3 Perimi-
dine-Based Carbene) (12d). Benzyldimethylsilane (217 mg, 1.44
mmol) was added to 2d (200 mg, 2.89 × 10−1 mmol) in 8 mL of toluene.
The reaction mixture was stirred at room temperature for 10 h. All
volatiles were removed under reduced pressure. The residue that formed
was washed with cold pentane (8 mL × 2 times) and dried under vacuum.
The orange powder was obtained in 61% yield (145 mg, 1.77 × 10−1
mmol). mp 194 °C (dec). 1H NMR (400 MHz, C6D6, 30 °C): δ 8.35 (d,
3JH−H = 5.5 Hz, 1H, CH of 2-Phpy), 7.97 (d, 3JH−H = 7.3 Hz, 1H, CH of
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2
(s, 3H, NCH3), 2.45 (d, JH−H = 12.9 Hz, 1H, Si(CH2Ph)Me2), 2.35
(d, 2JH−H = 12.9 Hz, 1H, Si(CH2Ph)Me2), 1.85 (s, 3H, CH3 of NAr),
1.31 (s, 3H, CH3 of NAr), 0.22 (s, 3H, SiBn(CH3)2), 0.00 (s, 3H,
SiBn(CH3)2), −15.28 (s, 1H, Ir−H). 13C NMR (100 MHz, C6D6,
30 °C): δ 203.5 (IrC), 172.9, 169.3, 152.4 (CH of 2-Phpy), 146.3,
145.0 (CH of 2-Phpy), 144.5 (Ir−C of SiCH2Ph), 142.7, 141.1, 137.9,
136.3, 136.3, 135.6, 135.1, 131.1, 130.8 (CH of NAr), 130.0, 129.2,
129.0, 128.9 (ortho CH of SiCH2Ph), 128.5, 124.0, 123.1, 122.0, 121.3
(CH of perimidine ring), 120.7, 120.0, 119.9, 119.3, 118.5 (CH of NAr),
118.2, 116.4, 105.7 (CH of perimidine ring), 103.7 (CH of perimidine
ring), 43.9 (NCH3), 33.6 (Si(CH2Ph)Me2), 21.3 (CH3 of NAr), 20.7
(CH3 of NAr), 5.5 (SiBn(CH3)2), 4.9 (SiBz(CH3)2). 29Si NMR (85
MHz, C6D6, 30 °C): δ −9.98. Anal. Calcd for C40H40IrN3Si: C, 61.35; H,
5.15; N, 5.37. Found: C, 61.30; H, 5.25; N, 5.15.
X-ray Crystallographic Analysis. All crystals were handled similarly.
The crystals were mounted on the CryoLoop (Hampton ReseArCh Corp.)
with a layer of mineral oil and placed in a nitrogen stream. Measurements
were made on Rigaku R-AXIS RAPID imaging plate area detector or
Rigaku AFC7R/Mercury CCD detector with graphite-monochromated
Mo Kα radiation (λ = 0.71075). Crystal data and structure refinement
parameters were listed in Supporting Information (Table S7).
The structure was solved by direct methods on SIR97 or SHELXS97,46
after being refined on F2 by full-matrix least-squares methods using
SHELXL-97.47 Measured nonequivalent reflections with I > 2.0σ(I) were
used for the structure determination. The hydrogen atoms were included in
the refinement on calculated positions riding on their carrier atoms. The
(5) N-Heterocyclic carbene with N, O and S donors: (a) Jimenez, M.
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2
function minimized was [∑w(Fo2 − Fc2)] (w = 1/[σ2(Fo ) + (aP)2 + bP]),
2
2
where P = (max(Fo ,0) + 2Fc2)/3 with σ2(Fo ) from counting statistics. The
functions R1 and wR2 were (∑||Fo| − |Fc||)/∑|Fo| and [∑w(Fo2 − Fc2)2/
4
∑(wFo )]1/2, respectively. The ORTEP-3 program was used to draw
molecules.48
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental and characterization details, tables for optimizing
the catalytic conditions, and molecular structures of metal
complexes 1d−1i, 4d, 5d, 6d, 7d, and 11d-Cl (PDF) and a CIF
file for complexes 1d−1i, 2d, 4d, 5d, 6d, 7d, 8d-Cl, 10d, and
Mas-Marza,
́
E.; Mata, J. A.; Peris, E. Chem.Eur. J. 2011, 17, 10453−
10461. (l) Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner, P.
K
dx.doi.org/10.1021/ja406519u | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
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