Synthesis and application of pyrrole-based PNP-Ir complexes to catalytic transfer dehydrogenation of cyclooctane

Article abstract of DOI:10.1021/acs.organomet.8b00072

A series of ^tBu- and ⁱPr-substituted PNP-pincer Ir and Rh complexes with pyrrole-based core were synthesized and characterized. The structures of the obtained complexes were varied depending on the size of alkyl substituents and ligands other than PNP ligand. All of them exhibit low activity toward transfer dehydrogenation of cyclooctane.

Full text of DOI:10.1021/acs.organomet.8b00072

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Synthesis and Application of Pyrrole-Based PNP−Ir Complexes to
Catalytic Transfer Dehydrogenation of Cyclooctane
†
‡
,‡
Shin Nakayama, Shogo Morisako, and Makoto Yamashita*
†Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27, Kasuga, Bunkyo-ku, 112-8551
Tokyo, Japan
‡
Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya, Aichi 464-8603, Japan
*
S Supporting Information
t
i
ABSTRACT: A series of Bu- and Pr-substituted PNP−pincer Ir and
Rh complexes with pyrrole-based core were synthesized and
characterized. The structures of the obtained complexes were varied
depending on the size of alkyl substituents and ligands other than PNP
ligand. All of them exhibit low activity toward transfer dehydrogenation
of cyclooctane.
INTRODUCTION
based PNP ligand exhibited no catalytic activity for
dehydrogenation of alkanes (Chart 1), although PNP−Rh
■
Multidentate ligands are widely utilized in organometallic
chemistry and catalysis because of their ability to construct
unique environment around the transition metal atom. Among
them, pincer ligand, a tridentate ligand with meridional
coordination mode, is one of the most promising compounds
for application to catalysis by utilizing the thermal stability of
Chart 1. Examples of Anionic PNP−Pincer Complexes
1
pincer complexes. As one of the most important reactions in
industry, dehydrogenation of alkanes to produce the corre-
sponding alkenes has been widely studied with pincer−Ir
2
complexes after the seminal discovery of homogeneous Ir−
3
phosphine complexes and their improved version with a pincer
4
ligand. To improve catalytic activity for dehydrogenation of
system B with the same ligand exhibited good catalytic
6f,g
alkane, three different modifications of the most active PCP−Ir
catalyst systems have been extensively investigated, i.e., (1)
tuning electronics and sterics of the pincer ligand with a variety
of substituents, (2) using other metals rather than iridium,
and (3) using other coordinating atoms rather than phosphorus
activity. A slightly different anionic PNP ligand system, C,
possessing a pyrrole core has been reported to be used for the
preparation of the corresponding PNP−pincer metal complexes
5
4a,6
12
(Scheme 1). However, there has no report about their
catalytic application toward dehydrogenation of alkane. Herein,
7
and carbon atoms. Among the reported pincer complexes
being active toward dehydrogenation of alkane, a POCSP−Ir
complex possessing a carbon-based PCP ligand with oxygen-
and sulfur-tethered side arms was recently reported to be the
Scheme 1. Previously Reported Synthesis of i-Pr Substituted
PNP−Ir Complexes
5l
most active catalyst system at 200 °C.
Recently, we and others have explored synthesis, structure,
properties, and catalytic activity of late metal complexes
8
possessing a boron-based PBP pincer ligand. Some of these
PBP complexes exhibited a moderate catalytic activity toward
8
i,j,w
dehydrogenation of alkane.
Since the substituent effect of
2
9
10
sp -hybridized boryl ligand as σ-donor and π-acceptor would
not match the thermodynamic requirement for the C(sp )−H
3
1
1
bond cleavage, we turned our attention to the other ligand
system. Considering the anionic nitrogen atom would have
opposite substituent effect, i.e., σ-acceptor and π-donor, anionic
nitrogen-based PNP pincer Ir system would have higher
catalytic activity for dehydrogenation of alkane. However,
recently reported anionic PNP−Ir system A having carbazolide-
Received: February 3, 2018
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00072
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
we report synthesis of pyrrole-based PNP−pincer Ir and Rh
complexes and their catalytic activity toward dehydrogenation
of cyclooctane, which is a landmark reaction to compare
catalytic activity among the different catalyst system.
RESULTS AND DISCUSSION
■
2
i
A solution of previously reported [ Pr-PNP]Ir(cod) complex
1
2a
a-Ir was heated under atmospheric pressure of H to afford
2
3
1
dinuclear Ir(III) complex 4a-Ir (Scheme 2). The P NMR
i
Scheme 2. Synthesis of Dinuclear Pr-Substituted PNP−Ir
Dihydride Complex 4a-Ir and Generation of the
Corresponding Mononuclear Complex 5a-Ir
Figure 1. Molecular structure of 4a-Ir (thermal ellipsoid at 50%
probability; hydrogen atoms except hydride ligand and cocrystallized
hexane molecule omitted for clarity). Selected bond distances (Å) and
angles (deg): Ir1---Ir1* 2.7677(5), Ir1−P1 2.2756(11), Ir1−P2*
2
.2872(10), Ir1−N1 2.117(3), Ir1−H1 1.82(4), Ir1−H1A 1.87(4),
spectra of 4a-Ir exhibited two singlet signals at 2.64 and 51.05
1
3
Ir1−H1B 1.91(4); N1−Ir1−P1 79.42(9), N1−Ir1−P2* 164.73(9),
P1−Ir1−P2* 106.55(4).
ppm, in which the former signal may correspond to the
phosphorus nucleus located trans to hydride, stronger trans-
1
4
1
influencing ligand. The H NMR spectrum of 4a-Ir showed
two inequivalent pyrrole CH signals in the aromatic region and
three characteristic broad hydride signals at −18.85 (broad
multiplet), −12.67 (broad triplet of triplet, J = 65, 21 Hz), and
15
pattern of the remaining signals. The long T (3.95 s) also
supported the conclusion that two hydrogen atoms existed as
hydride ligand. Thus, we tentatively assigned this species as
mononuclear dihydride complex 5a-Ir. All the effort for
recrystallization of 5a-Ir afforded single crystals of 4a-Ir,
probably due to existence of an equilibrium between 4a-Ir and
1
16
−
3.71 (broad multiplet) ppm with integral ratio of 2:1:1. The
1
31
31
H{ P} NMR spectrum (decoupling of P nuclei) exhibited
simplified hydride signals to a broad doublet, a broad singlet,
and a broad triplet. Judging from the integral ratio, two hydride
ligands (−18.85 ppm) are equivalent and coupled with one
hydride ligand. The multiplicity of the signal at −12.67 ppm in
5
a-Ir and the higher crystallinity of 4a-Ir.
Previously reported Bu-substituted PNP ligand 1b
t
12b
was
also treated with iPrMgCl·LiCl and [IrCl(coe) ] to afford
2
2
t
[
Bu-PNP]Ir(coe) complex 2b-Ir (Scheme 3). Subsequent
1
H NMR spectrum indicates that this hydride ligand is coupled
with two P nuclei: one phosphorus atom located at trans
position to the hydride ligand and the other at cis position.
Similarly, the hydride ligand resonating at −3.71 ppm was
coupled with two magnetically equivalent hydride ligands as
Scheme 3. Synthesis of t-Bu Substituted PNP−Ir Complexes
b-Ir and 5b-Ir
2
1
31
confirmed by H{ P} NMR spectrum. The dinuclear structure
of 4a-Ir was confirmed by single-crystal X-ray diffraction
i
analysis (Figure 1). Two phosphorus atoms in the Pr-PNP
ligand coordinated to two different Ir atoms to form the
dinuclear structure. As a result, the pyrrolide nitrogen atom
located in the trans position to the phosphorus atom of the
other ligand. The differential Fourier map indicated the
existence of four hydride ligands. Two of four hydride ligands
bridge two Ir atoms and the remaining two hydride ligands exist
as a terminal hydride. The positions of all four hydride ligands
exposure of 2b-Ir toward H resulted in the formation of
2
t
mononuclear [ Bu-PNP]IrH 5b-Ir as a stable compound in
2
contrast to the case of 5a-Ir probably due to the difference in
steric hindrance around Ir center. The 31P NMR spectrum of
2b-Ir exhibited two distinct doublet signals with almost similar
1
1
31
are consistent with the H and H{ P} NMR spectra. The IR
spectrum of 4a-Ir exhibited characteristic Ir−H vibrations for
chemical shifts (δ 50.7 and 51.8) and an identical coupling
P
−1
terminal Ir−H (at 2127 cm ) and bridging Ir−H−Ir moieties
constants of 342 Hz. Geminal protons at allylic position were
−1
1
(
around 1100 cm ), which were also supported by the
inequivalent in the H NMR spectrum of 2b-Ir probably due to
vibrational analysis with DFT calculations (see SI). To confirm
the potential dissociation of dinuclear structure of 4a-Ir to the
corresponding mononuclear structure, VT NMR experiments
were performed. Heating of 4a-Ir in toluene at 108 °C for 2.5 h
the orthogonal relationship between the coordinating of CC
bond in COE ligand to Ir and the PNP−Ir plane. Single-crystal
X-ray diffraction analysis of 2b-Ir revealed the mononuclear
structure with orthogonally oriented CC bond in the COE
ligand to the PNP−Ir plane (Figure 2). A characteristic CC
vibration (1240 cm ) was observed in the IR spectrum, which
1
led to a quantitative conversion of 4a-Ir. The H NMR
−1
spectrum of the crude product in C D exhibited a character-
6
6
3
1
istic hydride signal at δ −22.62 ppm and C symmetrical
could be assigned by DFT calculations (see SI). The P NMR
H
2v
B
DOI: 10.1021/acs.organomet.8b00072
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 2. Molecular structure of 2b-Ir (thermal ellipsoid at 50%
probability; one of two independent molecules and hydrogen atoms
omitted for clarity). Selected bond distances (Å) and angles (deg)
Figure 3. Molecular structure of 5b-Ir (thermal ellipsoid at 50%
probability; hydrogen atoms except hydride ligand omitted for clarity).
Selected bond distances (Å) and angles (deg): Ir1−P1 2.2947(9),
Ir1−P2 2.3009(9), Ir1−N1 2.011(3), Ir1−H1 1.49(3), Ir1−H1A
1.54(3); P1−Ir1−P2 164.60(3), N1−Ir1−P1 82.27(8), N1−Ir1−P2
82.35(8).
[
2
parameters of second independent molecules are in brackets]: Ir1−P1
.411(2) [Ir2−P4 2.392(3)], Ir1−P2 2.299(2) [Ir2−P3 2.308(2)],
Ir1−N1 2.042(7) [Ir2−N2 2.026(8)], Ir1−C23 2.173(8) [Ir2−C53
2
1
.167(9)], Ir1−C24 2.176(9) [Ir2−C54 2.162(9)], C23−C24
.437(12) [C53−C54 1.417(13)]; P1−Ir1−P2 157.93(8) [P3−Ir2−
P4 158.15(9)], N1−Ir1−P1 78.9(2) [N2−Ir2−P4 78.8(2)], N1−Ir1−
P2 79.6(2) [N2−Ir2−P3 79.7(2)].
Scheme 4. Synthesis of i-Pr Substituted PNP−Rh Complexes
a
6a-Rh and 4a-Rh
spectrum of 5b-Ir exhibited one singlet signal, which is being
1
consistent with mononuclear structure. The simple H NMR
t
spectrum of 5b-Ir showed one Bu signal (36H integral ratio),
one methylene signal (4H), and one CH signal (2H),
indicating that the molecular structure should have C2v
symmetry. The X-ray crystallographic analysis confirmed the
C2v symmetrical structure of 5b-Ir with two hydride ligands
which could be located on the differential Fourier map (Figure
a
LiHMDS: LiN(SiMe ) .
3
2
15
3
). The T1 measurement (398 ms) also supported the
16
hydridic feature of two hydrogen atoms. Two strong Ir−H
−1
17
vibrations at 2147 and 2170 cm , which were assigned by DFT
calculations, also supported the existence of two hydride
ligands.
compound, consisting of Rh(I) and Rh(III) centers or two
18
Rh(II) centers with Rh−Rh bonding. Two hydride signals in
1
the H NMR spectrum separately resonated as quintet of triplet
i
Complexation of Rh with Pr-PNP ligand 1a was also
signals, indicating the following two things: (1) coupling to four
P atoms and two Rh atoms and (2) rapid equilibrium for
migration of terminal hydride ligand between Rh(I)−Rh(III)
structures 4a-Rh and 4a′-Rh (Scheme 5a) or an existence of a
performed by a treatment of 1a with LiHMDS and [RhCl-
i
(
C H ) ] to give a mononuclear [ Pr-PNP]Rh(C H ) complex
2
4 2 2
2
4
6
a-Rh (Scheme 4). Single-crystal X-ray diffraction analysis
revealed C -symmetrical structure of 6a-Rh (Figure 4). The
slightly more stable Rh(II)−Rh(II) structure 4a-Rh
in
sym
2v
3
1
P NMR spectrum of 6a-Rh exhibited one doublet signal
solution (Scheme 5b).
1
t
having a coupling with Rh nucleus and the H NMR spectra of
a-Rh included characteristic 4H signal of coordinating
ethylene ligand, reflecting the C -symmetrical structure of
The Bu-substituted PNP−pincer ligand 1b was also
6
introduced to Rh by a treatment with LiHMDS and
[RhCl(C
H
2
)
4
]
2
to result in a formation of a mononuclear
) complex 6b-Rh (Scheme 6). Exposing a
solution of 6b-Rh toward H afforded the corresponding
mononuclear dihydrogen [ Bu-PNP]Rh(H ) complex 5b-Rh.
2v
2
t
6
4
a-Rh. Reaction of 6a-Rh with H afforded a dinuclear complex
[ Bu-PNP]Rh(C H
2 4
2
a-Rh (Scheme 4), as confirmed by X-ray analysis (Figure 5).
2
3
1
t
In contrast to the case of 6a-Rh, the P NMR spectrum of 4a-
Rh showed two doublet signals at δ 41.3 ( J = 124 Hz) and
2
1
31
Both 6b-Rh and 5b-Rh exhibited one doublet in the P NMR
spectra and C2v symmetrical pattern of the PNP ligand in the
P
RhP
1
13
69.4 ppm ( J
= 169 Hz). Each doublet has different
RhP
1
13
coupling constant to Rh, indicating the environment of two
magnetically inequivalent phosphorus atoms as confirmed by
X-ray analysis. Differential Fourier map in X-ray analysis
indicated the presence of one terminal hydride ligand and one
H and C NMR spectra. Ethylene ligand in 6b-Rh resonated
1
at 3.45 ppm as a doublet of triplet signal in the H NMR
spectrum and at 44.97 ppm as a doublet signal in the C NMR
spectrum. In the case of 5b-Rh, a hydride signal (doublet of
triplet, 2H) was found at −11.5 ppm in the H NMR spectrum.
Single crystal X-ray diffraction analysis revealed the monomeric
1
3
1
1
bridging hydride ligand on Rh. Because the H NMR spectrum
could be observed, 4a-Rh can be considered a diamagnetic
C
DOI: 10.1021/acs.organomet.8b00072
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 5. Potential Equilibrium of 4a-Rh in Solution
Scheme 6. Synthesis of t-Bu Substituted PNP−Rh
Complexes 6b-Rh and 5b-Rh
Figure 4. Molecular structure of 6a-Rh (thermal ellipsoid at 50%
probability; hydrogen atoms and cocrystallized toluene molecule
omitted for clarity). Selected bond distances (Å) and angles (deg):
Rh1−P1 2.3049(15), Rh1−P2 2.3026(16), Rh1−N1 2.011(5), Rh1−
C1 2.135(6), Rh1−C2 2.141(6), C1−C2 1.367(10); P1−Rh1−P2
1
61.83(6), N1−Rh1−P1 81.26(14), N1−Rh1−P2 80.68(14).
Figure 5. Molecular structure of 4a-Rh (thermal ellipsoid at 50%
probability; hydrogen atoms omitted for clarity). Selected bond
distances (Å) and angles (deg): Rh1---Rh2 2.8268(13), Rh1−P1
Figure 6. Molecular structure of 6b-Rh (thermal ellipsoid at 50%
probability; hydrogen atoms omitted for clarity). Selected bond
distances (Å) and angles (deg): Rh1−P1 2.3289(11), Rh1−P2
2.3297(10), Rh1−N1 2.020(3), Rh1−C23 2.143(4), Rh1−C24
2.146(4), C23−C24 1.369(7); P1−Rh1−P2 159.82(4), N1−Rh1−
P1 79.85(10), N1−Rh1−P2 80.16(10).
2.2877(16), Rh1−P4 2.2596(19), Rh2−P2 2.268(2), Rh2−P3
2.2900(15), Rh1−N1 2.080(4), Rh2−N2 2.094(4), Rh1−H69
1.88(5), Rh2−H69 1.78(5), Rh1−H70 1.52(5); P1−Rh1−P4
101.61(4), N1−Rh1−P1 81.22(10), N1−Rh1−P4 164.10(10), P2−
Rh2−P3 101.94(4), N2−Rh2−P3 81.51(9), N2−Rh2−P2 165.64(9).
structures of 6b-Rh and 5b-Rh (Figures 6 and 7). In the solid
state, ethylene ligand in 6b-Rh is in orthogonal relationship
with [PNP]Rh plane. Two peaks in the differential Fourier map
were assigned as dihydrogen ligand [H44−H45 0.97(5) Å] in
Ir complexes exhibited higher activity than those of the
corresponding Rh complexes having the same set of ligand,
which is in contrast to the case of carbazolide-based system.
The highest activity was recorded with 3a-Ir at 220 °C although
the activity was moderate among the reported catalysts. It
should be noted that the most active catalyst, 3a-Ir, could
catalyze dehydrogenation of n-octane with very low TON of 4
at 180−220 °C.
6f,g
5
b-Rh. Existence of two hydrogen atoms as dihydrogen ligand
15,16
was confirmed with its short T (66 ms).
1
All the [PNP] complexes obtained in this study were
subjected to transfer dehydrogenation of cyclooctane as a
catalyst in the presence of tert-butylethylene (Table 1). Except
for 5b-Rh, all the complexes showed no catalytic activity at 140
CONCLUSION
■
2
−7
t
°
C. Similar to the case of previously reported catalysts,
In conclusion, we synthesized and characterized a series of Bu-
i
elevating temperature improved catalytic activity in all cases. All
and Pr-substituted PNP−pincer Ir and Rh complexes having
D
DOI: 10.1021/acs.organomet.8b00072
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
without any purification. H2 gas was purified by passing through
deoxygenating and dehydrating columns (Nikka Seiko). [Ir-
1
9
20
12a
12b
12a
(
coe) Cl] , [Rh(C H ) Cl] , 1a,
1b,
and 2a-Ir
were
2
2
2
4
2
2
synthesized according to the literature procedure. NMR spectra
1
13
were recorded on JEOL ECA (500 MHz for H, 126 MHz for C. 203
MHz for 31P) and JEOL ECA (400 MHz for H) spectrometers.
Chemical shifts are reported in δ (ppm) relative to the residual
protiated solvent for 13C and external H PO for P used as reference.
1
31
3
4
Elemental analysis were performed at the A Rabbit Science Co., Ltd.
IR spectra were obtained on Agilent Cary 630 FTIR (Agilent
Technologies, Inc.) with ATR attachment. Melting points (mp) were
determined with a MPA100 OptiMelt instrument (Tokyo Instru-
ments, Inc.) and are uncorrected. X-ray crystallographic analyses were
performed on a VariMax/Saturn CCD diffractometer. Mass spectra
were measured on a JEOL JMS-700 mass spectrometer.
Synthesis of 4a-Ir. In a 10 mL J. Young tube, a solution of 2a-Ir
778 mg 1.24 mmol, 10.0 mL of benzene) was frozen by cooling with
(
liquid N , and then the headspace of the tube was evacuated. The
2
headspace of the tube was then backfilled with gaseous H . The
2
mixture was allowed to warm to room temperature, then was stirred at
room temperature for 18 h. Volatiles were removed under reduced
pressure to afford black solids. The black solids were recrystallized
from a concentrated toluene solution layered with n-hexane as a
Figure 7. Molecular structure of 5b-Rh (thermal ellipsoid at 50%
probability; hydrogen atoms except hydride ligand omitted for clarity).
Selected bond distances (Å) and angles (deg): Rh1−P1 2.2962(9),
Rh1−P2 2.3009(8), Rh1−N1 2.004(3), Rh1−H44 1.74(3), Rh1−H45
1
dihydride dinuclear complex 5 (286 mg, 44%). H NMR (500 MHz,
1
.70(4); P1−Rh1−P2 162.16(3), N1−Rh1−P1 82.20(7), N1−Rh1−
C D ) δ −18.85 (br m, 2H, hydride, becoming a broad doublet with J
6
6
3
1
P2 81.42(8).
= 7 Hz under P decoupling), −12.67 (br tt, J = 65, 21 Hz, 1H,
31
hydride, becoming a broad singlet under P decoupling), −3.71 (br
dt, J = 7, 7 Hz, 1H, hydride, becoming a broad triplet with J = 9 Hz
Table 1. Catalytic Activity (TON) in the Transfer
Dehydrogenation of Cyclooctane Using Pyrrole-Based
under 31P decoupling), 0.70 (dd, J = 15 Hz, J = 7 Hz, 6H, CH ),
3
3
PH
HH
3
3
3
3
3
a
0
7
(
=
1
1
1
.76 (dd, J = 12 Hz, J 7 Hz, 6H), 0.81 (dd, J = 15 Hz, J
Hz, 6H, CH ), 0.84 (dd, J = 14 Hz, J 7 Hz, 6H, CH ), 0.99
dd, J = 14 Hz, J = 7 Hz, 6H, CH ), 1.02 (dd, J = 11 Hz, J
7 Hz, 7H, CH ), 1.26 (dd, J = 13 Hz, J = 7 Hz, 6H, CH3),
3 PH HH
=
PNP−Ir or PNP−Rh Complexes as Catalyst
PH
HH
PH
HH
3
3
3
PH
HH
3
3
3
3
3
PH HH 3 PH HH
3
3
3
3
.31 (dd, J = 16 Hz, J = 7 Hz, 6H, CH ), 1.48−1.58 (m, 2H),
PH
HH
3
2 2
.65−1.82 (m, 4H), 1.94−2.04 (m, 2H), 2.45 (dd, J = 12 Hz, J
PH
HH=
catalyst
2
5H, C−CH -P), 3.06−3.14 (m, 2H, C−CH −P), 3.62 (d, J = 9
2
2
PH
3
1
Hz, 4H, C−CH −P), 6.31 (s, 2H, pyr-H), 6.36 (s, 2H, pyr-H).
P
temp (°C) 3a-Ir 4a-Ir 2b-Ir 5b-Ir 6a-Rh 4a-Rh 6b-Rh 5b-Rh
2
13
NMR (203 MHz, C D ) δ 2.64 (s), 51.05 (s). C NMR (101 MHz,
6
6
1
1
1
2
2
40
60
80
00
20
0
4
0
6
0
3
4
6
7
0
3
0
0
0
0
5
5
5
0
0
4
5
6
4
3
2
2
CDCl ) δ 16.21 (d, J = 7 Hz, CH ), 16.54 (t, J = 3 Hz, CH3),
7.32 (s, CH ), 17.94 (d, J = 3 Hz, CH ), 18.14 (s, CH ), 19.83 (s,
3
PC
3
PC
2
1
3 PC 3 3
8
9
7
0
5
1
CH ), 20.41 (s, CH ), 20.61 (s, CH ), 21.55 (t, J = 15 Hz, P−CH−
3
3
3
PC
17
28
20
18
9
5
5
1
CH ), 27.38 (d, J = 15 Hz, C−CH −P), 27.38 (s, CH ), 27.60 (s,
3
PC
2
3
1
1
10
11
12
CH ), 29.17 (t, J = 15 Hz, P−CH−CH ), 30.87 (d, J = 40 Hz,
3
PC
3
PC
a
1
P−CH−CH ), 31.87 (d, J = 32 Hz, C−CH −P), 98.45 (dd, J = 4
TONs were estimated by GC with internal standard (n-dodecane).
3
PC
2
Hz, 8 Hz, pyrrole-βC), 105.66 (t, J = 4 Hz, pyrrole-βC), 127.35 (dd, J
=
6, 2 Hz, pyrrole-αC), 136.03 (s, pyrrole-αC); mp 163.5−165.2 °C
−1 +
pyrrole-based backbone. The structures of the obtained
complexes were varied depending on the size of alkyl
substituents and ligands other than PNP ligand to form
mono- or dinuclear complexes. All the newly obtained
complexes were slightly active toward transfer dehydrogenation
of cyclooctane in the presence of tert-butylethylene as a
hydrogen acceptor.
(dec.). IR(ATR) 1114, 1087, 1071, 2127 cm . HRMS(FAB ): Calcd
for C H N P Ir [M]: 1042.3904. Found 1042.3907. See the
36 72
2 4 2
Supporting Information for NMR spectra of the isolated complex.
Generation of 5a-Ir from 4a-Ir. A solution of 4a-Ir (10.0 mg 9.60
μmol, 600 μL of toluene) in a J. Young NMR tube was heated at 108
°
C for 2.5 h. After heating, all the volatiles were removed under
reduced pressure. Then, C D (600 μL) was added to the residue. The
6
6
resulting NMR sample was subjected to NMR measurements to show
nearly quantitative generation of 5a-Ir (see the Supporting
1
EXPERIMENTAL SECTION
Information for NMR spectra). H NMR (400 MHz, toluene-d ) δ
■
8
General Procedures. All the preparations and manipulations
involving air- and moisture-sensitive compounds were carried out
under Argon atmosphere by using Schlenk and glovebox (Miwa MFG,
KIYON) technique. All glassware were dried for 20 min in the 250 °C
−22.62 (t, J = 9 Hz, 1H), 0.85 (dt, J = 7, 7 Hz, 12H), 1.03 (dt, J = 7, 7
3
1
Hz, 12H), 1.69−1.82 (m, 4H), 2.96 (t, J = 4 Hz, 4H), 6.55 (s, 2H);
P
NMR (203 MHz, C D ) δ 70.7 (s).
6 6
Synthesis of 2b-Ir. To a precooled (−35 °C) solution of 1b (86.2
mg, 255 μmol, 3.00 mL of THF) in a 15.0 mL vial, a THF solution of
oven before use. Et O (Kanto Chemical, dehydrated), toluene (Kanto
2
i
Chemical, dehydrated), and n-hexane (Kanto Chemical, dehydrated)
were purified by passing through a solvent purification system (Grass
Contour). Benzene (Kanto Chemical, dehydrated) and dioxane
PrMgCl·LiCl (1.00 M, 224 μL, 224 μmol) was added dropwise at −35
°C. After stirring the resulting solution for 30 min, the solution was
allowed to warm to room temperature. The reaction mixture was
added dropwise to a solution of [Ir(coe) Cl] (100 mg, 112 μmol, 3.00
(
Kanto Chemical, dehydrated) were dried over Na/K alloy with
2
2
stirring and were filtered though a pad of oven-baked alumina before
mL of THF) in a 15.0 mL vial at room temperature. The resulting
solution was stirred at room temperature for 3.5 h. The brown solution
was filtered through a pad of Celite to give a brown filtrate. Removal of
volatiles from the filtrate gave black solids. After dissolution of the
black solid in toluene, 1,4-dioxane (50 μL) was added to the mixture.
use. C D6 was dried by distillation over sodium benzophenone
6
followed by vacuum transfer. Cyclooctane and tert-butylethylene were
used after degassing with freeze−pump−thaw cycles and passing
through a pad of alumina. LiHMDS and n-dodecane were used
E
DOI: 10.1021/acs.organomet.8b00072
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
The resulting suspension was centrifuged, and the supernatant was
collected. Then, the remaining residue was extracted with hexane.
After combining the supernatant and hexane solution, volatiles were
removed under reduced pressure. The residue was recrystallized from
The brown solids were recrystallized by layering toluene solution with
n-hexane at −35 °C to give yellow crystals of 4a-Rh (18.0 mg, 20.9
1
μmol, 38%). H NMR (500 MHz, C D , see the Supporting
6
6
1
1
Information for H NMR spectrum) δ −19.36 (qt, JRhH = 30 Hz,
1
2
1
2
n-hexane to give red solids (53.2 mg, 77.6 μmol, 35%). H NMR (400
JPH = 7 Hz, 1H, hydride), −10.15 (qt, JRhH = 70 Hz, JPH = 20 Hz,
3 3
3
5
MHz, C D ) δ 1.17 (dd, J = 10 Hz, J = 2 Hz, 18H, CH ), 1.23
1H, hydride), 0.74 (dd, J = 14 Hz, J = 7 Hz, 6H, CH ), 0.867
PH HH 3
6
6
PH
PH
3
3
5
3
3
3
3
(
dd, J = 9 Hz, J = 2 Hz, 18H, CH ), 1.43−1.62 (m, 4H, 2CH ),
(dd, J = 15 Hz, J = 7 Hz, 12H), 0.874 (dd, J = 17 Hz, J
7 Hz, 6H), 0.94 (dd, J = 12 Hz, J = 7 Hz, 6H, CH ), 1.21 (dd,
JPH = 10 Hz, J = 7 Hz, 6H, CH ), 1.40 (dd, J = 16 Hz, J = 7
HH 3 PH HH
=
PH
PH
3
2
PH
HH
PH
HH
3
3
1
2
6
6
.70−1.86 (m, 6H, 2CH + 2allylic CHH), 2.54 (ddt, J = 13, 4, 4 Hz,
2
PH HH 3
2
3
3
3
3
H, 2allylic CHH), 2.99 (d, J = 7 Hz, 2H, C−CH −P), 3.19 (d, J =
PH
2
2
3
3
3
Hz, 2H, C−CH −P), 3.45 (dt, J = 7, J Hz, 2H, −CH=CH−),
Hz, 6H, CH ), 1.54 (dd, J = 14 Hz, J = 7 Hz, 6H, CH ), 1.60−
2
PH
HH
3
PH
HH
3
3
3
.41 (d, J = 3 Hz, 1H, pyr-H), 6.46 (d, J = 3 Hz, 1H, pyr-H).
1.71 (m, 2H, P−CH−CH ), 1.77−1.89 (m, 2H, P−CH−CH ), 1.90−
HH
HH
3
3
3
1
2
2
2 2
P NMR (162 MHz,C D ) δ 50.7 (d, J = 342 Hz, 1P), 51.8 (d, J
2.07 (m, 4H, P−CH−CH ), 2.60 (dd, J = 14 Hz, J = 7 Hz, 2H,
6
6
PP
PP
3
PH
HH
342 Hz, 1P). 13C NMR (101 MHz, C D ) δ 27.01 (dd, J = 23, 3 Hz,
2
3
=
C−CH
2
−P), 3.15 (d, JPH = 13 Hz, 2H, C−CH −P), 3.35 (dd, JPH =
2
6
6
3
3
C−CH −P), 27.26 (s, −CH −CH −CH −), 29.69 (dd, J = 19, 3 Hz,
14 Hz, JHH = 7 Hz, 2H, C−CH
CH −P), 6.31 (s, 2H, pyr-H), 6.31 (s, 2H, pyr-H). P NMR (203
MHz, C
2
−P), 3.78 (d, JPH = 13 Hz, 2H, C−
2
2
2
2
31
C−CH −P), 30.23 (s, CH ), 31.31 (s, CH ), 33.24 (s, −CH −CH −
2
2
3
3
2
2
1
1
CH −), 35.37 (dd, J = 6, 3 Hz, P−C−(CH ) ), 36.46 (d, J = 18 Hz,
D ) δ 41.3 (d, JRhP = 124 Hz, 1P), 69.4 ppm (d, JRhP = 169
6 6
2
3 3
13
2
−
−
CH−CH −CH −), 36.48 (dd, J = 6, 3 Hz, P−C−(CH ) ), 44.37 (s,
Hz, 1P). C NMR (101 MHz, C D ) δ 16.91 (d, JPC = 6 Hz), 17.54
(d, JPC = 4 Hz), 19.05 (d, JPC = 5 Hz), 19.56 (d, JPC = 4 Hz), 20.08
(d, JPC = 3 Hz), 20.43 (d, JPC = 6 Hz), 21.55 (d, JPC = 4 Hz), 24.69
6 6
2
2
3 3
2
2
2
CHCH−), 102.75 (d, J = 6 Hz, pyr-βC), 102.99 (d, J = 8 Hz, pyr-
2
2
2
βC), 137.97 (t, J = 3 Hz, pyr-αC), 138.96 (t, J = 4 Hz, pyr-αC). Mp
1
1
1
−1
(
2
d, J = 18 Hz), 27.58 (d, J = 22 Hz), 29.38 (d, J = 22 Hz),
1
64.1−167.8 °C (dec.). IR(ATR) 1240 cm (CC). Anal. Calcd for
PC PC PC
1
1
1
9.83 (d, J = 15 Hz), 30.19 (d, J = 17 Hz), 32.09 (d, J = 23
PC PC PC
C H NP Ir: C, 52.61; H, 8.24; N, 2.04. Found: C, 52.68; H, 8.48; N,
3
0
56
2
Hz), 101.08 (d, JPC = 11 Hz, pyr-βC), 108.91 (t, JPC = 4 Hz, pyr-βC),
2
.08.
Synthesis of 5b-Ir. In a 50 mL J. Young tube, a solution of
1
28.589 (s, pyr-αC), 139.089 (d, J = 5 Hz, pyr-αC). Mp 166.9−
PC
−1
1
69.0 °C (dec.). IR(ATR) 1101 cm (symmetric and antisymmetric
complex 2b-Ir (26.7 mg, 39.0 μmol, 1.50 mL of toluene) was frozen by
Rh−H). Anal. Calcd for C H N P Rh : C, 50.24; H, 8.20; N, 3.25.
cooling with liquid N , and then the headspace of the tube was
36 70
2
4
2
2
Found: C, 50.63; H, 8.34; N, 3.28.
evacuated. The headspace of the tube was then backfilled with gaseous
Synthesis of 6b-Rh. To a solution of 2b (86.2 mg, 255 μmol, 1.55
mL of toluene) in a 15.0 mL vial was added LiHMDS (39.8 mg, 238
μmol) as a solid at room temperature. The reaction mixture was added
dropwise to a solution of [Rh(C H ) Cl] (44.0 mg, 113 μmol, 1.50
H . After thawing the frozen solution, the resulting mixture was
2
allowed to warm to room temperature. The reaction mixture was
stirred at 70 °C for 20 h. Volatiles were removed under reduced
pressure afforded black solids. The black solids were recrystallized by
2
4
2
2
mL of toluene) in a 15.0 mL vial at room temperature. The resulting
solution was stirred at room temperature for 2 h. The brown solution
was filtered through a pad of Celite to give a brown filtrate. Removal of
volatiles from the filtrate gave brown solids. The solids were
recrystallized from toluene to give yellow crystals of 6b-Rh (53.2
layering a concentrated toluene solution with n-hexane to give 5b-Ir
1
(
J
5.2 mg, 9.0 μmol, 23%). H NMR (400 MHz, C D ) δ −22.77 (t,
6
6
3
3
= 9 Hz, 2H, hydride), 1.18 (vt, J = 7 Hz, 36H, CH ), 3.16 (vt,
PH 3
PH
2J = 4 Hz, 4H, C−CH −P), 6.55 (s, 2H, pyr-H). P NMR (162
31
PH
2
13
1
MHz, C D ) δ 89.0 (s). C NMR (101 MHz, C D ) δ 27.57 (t, J =
1
3
6
6
6
6
PC
mg, 77.6 μmol, 35%). H NMR (400 MHz, C D ) δ 1.13 (vt, J = 6
2
1
6
6
PH
1
2 Hz, C−CH −P), 29.98 (t, J = 3 Hz, CH ), 35.11 (t, J = 11
2
2
PC
3
PC
Hz, 36H, CH ), 2.97 (vt, J = 4 Hz, 4H, C−CH −P), 3.45 (d of t,
3
2
3
PH
2
Hz, P−C(CH ) ), 105.05 (t, J = 5 Hz, pyrrole-βC), 144.35 (t, J
2
3
13
3
3
PC
PC
JRhH = 5 Hz, J = 2 Hz, 4H, C H ), 6.41 (s, 2H, pyr−CH).
C
PH
2
4
=
5 Hz, pyrrole-αC). Mp 188.5−190.4 °C (dec.). IR(ATR) 2147 (Ir−
1
−1
NMR (101 MHz, C
6
D
6
) δ 26.75 (t, JPC = 9 Hz, C−CH
2
−P), 30.12
3 3
H), 2170 cm (Ir−H). Anal. Calcd for C H NP Ir: C, 45.81; H,
2
1
22
44
2
(
(
(
7
vt, J = 2.9 Hz, CH ), 35.85 (t, J = 5.3 Hz, P−C(CH ) ), 44.97
PC
3
PC
7
.69; N, 2.43. Found: C, 45.69; H, 7.78; N, 2.38.
1
3
d, J = 12 Hz, C H ), 102.74 (t, J = 5 Hz, pyrrole-βC), 137.79
RhC
2
4
PC
Synthesis of 6a-Rh. To a solution of 1a (300 mg, 0.916 mmol,
.00 mL of toluene) in a 15 mL vial was added LiHMDS (161 mg,
.962 mmol) as a solid at room temperature. After dissolving LiHMDS
2
2
31
td, J = 3, J = 8 Hz, pyrrole-αC). P NMR (162 MHz, C D ) δ
RhC
PC
6
6
4
0
1
−1
0.70 (d, J = 135 Hz). Mp 196.4−199.2 °C. IR(ATR) 1255 cm
RhP
(
CC). Anal. Calcd for C H NP Rh: C, 56.14; H, 9.03; N, 2.73.
24
46
2
with shaking at room temperature, the resulting mixture was added to
a solution of [Rh(C H ) Cl] (178 mg, 0.458 mmol, 3.00 mL of
Found: C, 55.99; H, 9.37; N, 2.89.
2
4
2
2
Synthesis of 5b-Rh. In a 10 mL J. Young tube, a solution of 6b-Rh
10.2 mg, 19.9 μmol, 1.00 mL of toluene) was frozen by cooling with
toluene) in a 15 mL vial. The resulting mixture was stirred at room
temperature for 18 h. After the reaction mixture was filtered through a
pad of Celite, volatiles were removed from the filtrate to afford brown
solids. The residue was recrystallized by layering toluene solution with
n-hexane at −35 °C to give yellow crystals of 6a-Rh (286 mg, 0.625
(
liquid N , and then the headspace of the tube was evacuated. The
2
headspace of the tube was then backfilled with gaseous H . After
2
thawing the frozen solution, the resulting mixture was allowed to warm
to room temperature. The reaction mixture was stirred at 80 °C for 26
h. After filtration of the reaction mixture through a pad of Celite,
volatiles were removed from the filtrate. The residue was recrystallized
by layering toluene solution with n-hexane at −35 °C to give yellow
1
3
mmol, 44%). H NMR (400 MHz, C D ) δ 0.91 (d of vt, J = 7 Hz,
6
6
PH
3
3
3
JHH = 7 Hz, 12H, CH ), 1.01 (d of vt, J = 7 Hz, J = 7 Hz, 12H,
3
PH
HH
2
3
CH ), 1.64−1.75 (sept of vt, J = 2 Hz, J = 7 Hz, 4H, P−
3
PH
HH
2
CHMe ), 2.83 (vt, J = 4 Hz, 4H, C−CH −P), 3.16 (d of t, 3J = 4
1
2
PH
2
PH
crystals of 5b-Rh (3.3 mg, 6.8 μmol, 34%). H NMR (400 MHz,
2
31
1
2
Hz, J
= 2 Hz, 4H, C H ), 6.43 (s, 2H, pyr-H). P NMR (162
RhH
2 4
C D ) δ −11.45 (dt, J
= 21 Hz, J 7 Hz, 2H, hydride), 1.14 (vt,
6
6
RhH
PH
1
13
3
2
MHz, C D ) δ 58.8 (d, J = 135 Hz). C NMR (101 MHz, C D )
δ 17.92 (s, CH ), 18.82 (t, J = 3 Hz, CH ), 24.53 (t, J = 10 Hz,
6
6
RhP
6
6
J
= 7 Hz, 36H, CH ), 3.07 (vt, J = 4 Hz, 4H, C−CH −P), 6.43
(s, 2H aromatic CH). P NMR (203 MHz, C D ) δ 97.68 (d, J
PH
3
31
PH
2
2
1
1
3
PC
3
PC
=
6
6
RhP
1
P−CH(CH ) ), 25.68 (t, J = 10 Hz, C−CH −P), 44.10 (dt, J = 11
13
1
3
3
PC
2
134 Hz). C NMR (101 MHz, C D ) δ 26.08 (t, J = 9 Hz, C−
6
6
PC
3
Hz, 2 Hz, C H ), 103.40 (t, J = 5 Hz, pyr-βC), 137.73 (dt, J = 6 Hz,
2
1
2
4
PC
CH −P), 29.50 (t, J = 4 Hz, CH ), 33.84 (t, J = 8 Hz, P−
2
PC
3
PC
3
Hz, pyr-αC). Mp 115.7−116.4 °C (dec.). Anal. Calcd for
3
2
C(CH ) ), 103.20 (t, J = 5 Hz, pyrrole-βC), 139.35 (d, J = 3 Hz,
3
3
PC
PC
C H NP Rh: C, 52.52; H, 8.37; N, 3.06. Found: C, 52.84; H,
2
0
38
2
pyrrole-αC). Mp 128.2−137.3 °C. IR(ATR) 2112 (Rh−H), 1940
−1
8
.76; N, 3.13.
cm (Rh−H). Anal. Calcd for C H NP Rh: C, 54.21; H, 9.10; N,
22
44
2
Synthesis of 4a-Rh. In a 10 mL J. Young tube, a solution of 6a-Rh
50.2 mg, 110 μmol, 2.00 mL of toluene) was frozen by cooling with
2
.87. Found: C, 53.93; H, 9.19; N, 3.06.
General Procedure for Catalytic Transfer Dehydrogenation
(
liquid N , and then the headspace of the tube was evacuated. The
of Cyclooctane. In a glovebox, catalyst (3.00 μmol) was dissolved in
a solution consisting of cyclooctane (3000 equiv., 9.00 mmol) and H2
acceptor (tert-butylethylene, 600 equiv, 9.00 or 1.80 mmol) in a 10.0
mL J. Young tube. After bringing the tube out from the glovebox, the
tube was heated by using an aluminum-block stirrer. After the
2
headspace of the tube was then backfilled with gaseous H . After
2
thawing the frozen solution, the resulting mixture was allowed to warm
to room temperature. The reaction mixture was stirred at 110 °C for
2
0 h. Volatiles were removed from the filtrate to afford brown solids.
F
DOI: 10.1021/acs.organomet.8b00072
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
indicated time, the tube was cooled down to room temperature. An
internal standard (n-dodecane, 1.00 mmol) was added to the reaction
mixture and then the sample was analyzed by gas chromatography to
estimate yields with a precalculated GC factor toward authentic
samples.
by Ruthenium Pincer Complexes. Chem. Rev. 2014, 114, 12024−
́
12087. (c) Selander, N.; Szabo, K. J. Catalysis by Palladium Pincer
Complexes. Chem. Rev. 2011, 111, 2048−2076. (d) The Chemistry of
Pincer Compounds; Elsevier: Oxford, 2007. (e) Kumar, A.; Bhatti, T.
M.; Goldman, A. S. Dehydrogenation of Alkanes and Aliphatic Groups
by Pincer-Ligated Metal Complexes. Chem. Rev. 2017, 117, 12357−
12384.
(2) (a) Choi, J.; MacArthur, A. H. R.; Brookhart, M.; Goldman, A. S.
Dehydrogenation and Related Reactions Catalyzed by Iridium Pincer
Complexes. Chem. Rev. 2011, 111, 1761−1779. (b) Kumar, A.;
Goldman, A. S. Recent Advances in Alkane Dehydrogenation
Catalyzed by Pincer Complexes. In The Privileged Pincer-Metal
Platform: Coordination Chemistry & Applications; van Koten, G.,
Gossage, R. A., Eds.; Springer International Publishing: Cham, 2016;
pp 307−334;. (c) Haibach, M. C.; Kundu, S.; Brookhart, M.;
Goldman, A. S. Alkane Metathesis by Tandem Alkane-Dehydrogen-
ation−Olefin-Metathesis Catalysis and Related Chemistry. Acc. Chem.
Res. 2012, 45, 947−958. (d) Zhang, Y.; Yao, W.; Fang, H.; Hu, A.;
Huang, Z. Catalytic alkane dehydrogenations. Sci. Bull. 2015, 60,
Details for X-ray Crystallography. Details of the crystal data and
a summary of the intensity data collection parameters for 4a-Ir, 2b-Ir,
5
b-Ir, 6a-Rh, 4a-Rh, 6b-Rh, and 5b-Rh are listed in Table S1. In each
case, a suitable crystal was mounted with a mineral oil to the glass fiber
and transferred to the goniometer of a VariMax Saturn CCD
diffractometer with graphite-monochromated Mo Kα radiation (λ =
0
2
.71075 Å). All the following procedure for analysis, Yadokari-XG
21
009 was used as a graphical interface. The structures were solved by
22
direct method with (SIR-2014 and SIR-97) and refined by full-matrix
2
23
least-squares techniques against F (SHELXL-2014). The intensities
were corrected for Lorentz and polarization effects or NUMABS
program (Rigaku 2005). The non-hydrogen atoms were refined
anisotropically. Hydrogen atoms except hydride ligand were placed
using AFIX instructions. The hydride ligands were refined isotropi-
cally. The molecular structures were drawn by using ORTEP-III
1
316−1331. (e) Tang, X.; Jia, X.; Huang, Z. Challenges and
24
program. Relatively low R value of 6a-Rh would be attributed to the
1
opportunities for alkane functionalisation using molecular catalysts.
low Rint value.
Chem. Sci. 2018, 9, 288−299.
Computational Details. All calculations were performed with
(3) Crabtree, R. H.; Mihelcic, J. M.; Quirk, J. M. Iridium complexes
25
Gaussian 09 (rev. D.01) software package. Both the molecular
in alkane dehydrogenation. J. Am. Chem. Soc. 1979, 101, 7738−7740.
geometries of 9 and 10 were optimized without constraints at the
(4) (a) Gupta, M.; Hagen, C.; Flesher, R. J.; Kaska, W. C.; Jensen, C.
2
6
27
B3LYP level with LanL2DZ/6-31+G* basis sets. The obtained
2
8
M. A highly active alkane dehydrogenation catalyst: stabilization of
dihydrido rhodium and iridium complexes by a P-C-P pincer ligand.
Chem. Commun. 1996, 2083−2084. (b) Gupta, M.; Hagen, C.; Kaska,
W. C.; Cramer, R. E.; Jensen, C. M. Catalytic dehydrogenation of
cycloalkanes to arenes by a dihydrido iridium P-C-P pincer complex. J.
Am. Chem. Soc. 1997, 119, 840−841. (c) Gupta, M.; Kaska, W. C.;
Jensen, C. M. Catalytic dehydrogenation of ethylbenzene and
tetrahydrofuran by a dihydrido iridium P-C-P pincer complex. Chem.
Commun. 1997, 461−462. (d) Xu, W. W.; Rosini, G. P.; Gupta, M.;
Jensen, C. M.; Kaska, W. C.; KroghJespersen, K.; Goldman, A. S.
Thermochemical alkane dehydrogenation catalyzed in solution
without the use of a hydrogen acceptor. Chem. Commun. 1997,
2273−2274. (e) Liu, F. C.; Goldman, A. S. Efficient thermochemical
alkane dehydrogenation and isomerization catalyzed by an iridium
pincer complex. Chem. Commun. 1999, 655−656.
vibrational frequencies were scaled with a factor of 0.9723. The
optimized structures are attached as Supporting Information in “.xyz”
format, which can be viewed with Mercury software.
ASSOCIATED CONTENT
Supporting Information
■
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00072.
Computational details (PDF)
DFT coordinates (XYZ)
Accession Codes
CCDC 1821770−1821776 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(5) (a) Zhu, K.; Achord, P. D.; Zhang, X.; Krogh-Jespersen, K.;
Goldman, A. S. Highly Effective Pincer-Ligated Iridium Catalysts for
Alkane Dehydrogenation. DFT Calculations of Relevant Thermody-
namic, Kinetic, and Spectroscopic Properties. J. Am. Chem. Soc. 2004,
126, 13044−13053. (b) Huang, Z.; Brookhart, M.; Goldman, A. S.;
Kundu, S.; Ray, A.; Scott, S. L.; Vicente, B. C. Highly Active and
Recyclable Heterogeneous Iridium Pincer Catalysts for Transfer
Dehydrogenation of Alkanes. Adv. Synth. Catal. 2009, 351, 188−206.
AUTHOR INFORMATION
Corresponding Author
E-mail: makoto@oec.chembio.nagoya-u.ac.jp.
■
(c) Kuklin, S. A.; Sheloumov, A. M.; Dolgushin, F. M.; Ezernitskaya,
M. G.; Peregudov, A. S.; Petrovskii, P. V.; Koridze, A. A. Highly Active
Iridium Catalysts for Alkane Dehydrogenation. Synthesis and
Properties of Iridium Bis(phosphine) Pincer Complexes Based on
*
ORCID
Ferrocene and Ruthenocene. Organometallics 2006, 25, 5466−5476.
Makoto Yamashita: 0000-0002-3665-5311
Notes
The authors declare no competing financial interest.
3
(
d) Bez
́
ier, D.; Brookhart, M. Applications of PC(sp )P Iridium
Complexes in Transfer Dehydrogenation of Alkanes. ACS Catal. 2014,
, 3411−3420. (e) Kovalenko, O. O.; Wendt, O. F. An electron poor
4
iridium pincer complex for catalytic alkane dehydrogenation. Dalton
Trans. 2016, 45, 15963−15969. (f) Haenel, M. W.; Oevers, S.;
Angermund, K.; Kaska, W. C.; Fan, H.-J.; Hall, M. B. Thermally Stable
Homogeneous Catalysts for Alkane Dehydrogenation. Angew. Chem.,
Int. Ed. 2001, 40, 3596−3600. (g) Gottker-Schnetmann, I.; Brookhart,
̈
M. Mechanistic Studies of the Transfer Dehydrogenation of
ACKNOWLEDGMENTS
■
This research was supported by JST-CREST 14529307 from
JST. We thank Prof. Tamejiro Hiyama (Chuo University) for
providing an access to an X-ray diffractometer. Theoretical
calculations were carried out using resources of the Research
Center for Computational Science, Okazaki, Japan.
Cyclooctane Catalyzed by Iridium Bis(phosphinite) p-XPCP Pincer
̈
Complexes. J. Am. Chem. Soc. 2004, 126, 9330−9338. (h) Gottker-
Schnetmann, I.; White, P.; Brookhart, M. Iridium bis(phosphinite) p-
XPCP pincer complexes: Highly active catalysts for the transfer
dehydrogenation of alkanes. J. Am. Chem. Soc. 2004, 126, 1804−1811.
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DOI: 10.1021/acs.organomet.8b00072
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