A long-tethered (P-B-P)-pincer ligand: Synthesis, complexation, and application to catalytic dehydrogenation of alkanes

Article abstract of DOI:10.1039/c6dt02075e

A new long-tethered boron-containing (P-B-P)-pincer ligand 8 has been synthesized. Complexation of 8 with [Ir(coe)₂Cl]₂ (coe = cyclooctene) resulted in (P-B-P)(hydrido)chloroiridium complex (P-B-P)Ir(H)Cl 9. Subsequent reaction with ⁿBuLi led to the formation of dihydride complex (P-B-P)Ir(H)₂10. Both complexes were found to be moderately active for the catalytic dehydrogenation of alkanes.

Full text of DOI:10.1039/c6dt02075e

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: E. H. Kwan, Y. J.
Kawai, S. Kamakura and M. Yamashita, Dalton Trans., 2016, DOI: 10.1039/C6DT02075E.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/dalton

Please do not adjust margins
Dalton Transactions
Page 1 of 12
View Article Online
DOI: 10.1039/C6DT02075E
Journal Name
ARTICLE
A Long-Tethered (P-B-P)-Pincer Ligand: Synthesis, Complexation,
and Application to Catalytic Dehydrogenation of Alkanes
Received 00th January 20xx,
Accepted 00th January 20xx
Enrique Huang Kwan, Yasushi Jack Kawai, Sei Kamakura, Makoto Yamashita*
A new long-tethered boron-containing (P-B-P)-pincer ligand 8 has been synthesized. Complexation of 8 with [Ir(coe)2Cl]2
(coe = cyclooctene) resulted in (P-B-P)(hydrido)chloroiridium complex (P-B-P)Ir(H)Cl 9. Subsequent reaction with nBuLi led
to a formation of dihydride complex (P-B-P)Ir(H)2 10. Both complexes were found to be moderately active for the catalytic
dehydrogenation of alkanes.
DOI: 10.1039/x0xx00000x
www.rsc.org/
related organic transformations initiated by oxidative addition
of C(sp3)-H bond,12 efforts have to be made to further improve
the catalytic activity itself for applications in industrial scale.
Introduction
Alkenes are one of the most important resources for
commodity chemicals. For example, major polymers, such as
polyethylene (PE), polypropylene (PP), polystyrene (PS), and
poly(vinyl chloride) (PVC), are manufactured by polymerization
of alkene monomer.1 The linear n-alcohols used as precursors
of detergents and plasticizers are synthesized through a linear-
selective hydroformylation and subsequent hydrogenation of
alkenes.2 Nowadays, alkenes are synthesized in large scale
mainly by dehydrogenation of alkanes using heterogeneous
metal oxides catalysts. However, the application of
heterogeneous catalysts for dehydrogenation of alkanes is
limited to small alkanes.3-5 An alternative approach could be
the utilization of homogeneous catalysts under a milder
reaction condition.
Recently, we reported the synthesis of hydroboranes 1a
serve as precursors for boron-containing pincer ligands.13 The
B-H bond in 1a is able to engage in oxidative addition with
-c that
-c
transition metals, while the nitrogen atoms bonding to the
boron atom occupy the vacant p-orbital of the boron and thus
prevent π-backdonation from the metal centre to the boron
atom. In these reports, we demonstrated the easy
t
introduction of the precursors to iridium to form the Bu-, Cy-
i
or Pr-substituted (PBP)Ir(H)Cl complexes 2a
-c
(Scheme 1).13 In
the presence of ethylene, pentacoordinate (PBP)Ir complexes
2a were converted into corresponding square planar
(PBP)Ir(C2H4) complexes 3a through a formal elimination of
-c
-c
HCl, induced by a treatment with LiTMP (TMP = 2,2,6,6-
tetramethylpiperidide). PBP-pincer ligand(s) could also be
introduced to Rh,14 Ru,15 Os,15d Pt,16 Co,17 and Ni18 to provide a
wide variety of PBP-pincer complexes. Some of the PBP-pincer
complexes were reported to have catalytic activity for
hydrogenation of aldehyde (Ru),15b hydrosilylation of alkene
(Pt),16a hydrogenation of alkene (Co, Ni),17b and
dehydrogenation of amine-borane (Co).17a Although
tremendous efforts were spent on utilizing (PBP)Ir complexes
as alkane dehydrogenation catalysts, only iPr-substituted
(PBP)Ir(H)Cl 2c and (PBP)Ir(C2H4) 3c exhibited catalytic activity
in the transfer dehydrogenation of COA (Scheme 2).13d
In 1979, Crabtree reported the first example of stoichiometric
dehydrogenation of cyclopentane and cyclooctane (COA) with
tert-butylethylene (TBE) using [(Ph3P)2Ir(H)2(acetone)2]BF4.6
Since then, numerous homogeneous catalysts were developed
for the dehydrogenation of heavier alkanes.7 Among these
complexes, the best catalytic performance was achieved using
the benzene-based PCP-pincer iridium complexes.8 In 2004,
Brookhart modified the PCP-pincer ligand by introducing an
oxygen atom in place of the methylene linkers. A boost in the
catalytic performance with TON up to 2210 was observed
using the resulting POCOP-pincer iridium complexes.9 More
recently, Huang developed the POCSP-pincer iridium
complexes, which show a TON of 5901.10 The similar CCC- and
PCN-pincer systems were also developed.11 Although these
dehydrogenation catalysts have been applied to a variety of
Small P-Ir-P bond angles in our (PBP)Ir system as compared
with the reported (PCP)Ir and (POCSP)Ir systems is postulated
as one of the reasons for the low catalytic activity for transfer
dehydrogenation, by disfavouring the reductive elimination
step from metal(hydrido)alkyl intermediate. To change the
steric environment around the iridium centre, we decided to
elongate
the
methylene
linkers
connecting
the
benzodiazaborole ring and the phosphorous atoms. Herein, we
report the synthesis of a long-tethered P-B-P-pincer ligand
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 2 of 12
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
Journal Name
precursor
8
possessing tBu groups, its complexation with reagent was chosen, which can easily be removed from the
its subsequent product by reprecipitation.
derivatization to iridium dihydride complex (P-B-P)Ir(H)2 10
iridium to form the (P-B-P)Ir(H)Cl
9,
,
Scheme 3. Synthesis of the long-tethered (P-B-P)-pincer ligand precursor
8
and their application as catalysts for dehydrogenation of COA,
ethylbenzene (PhEt) and cyclododecane (CDD).
Scheme 1. PBP-pincer ligand precursors 1a-c previously reported by our group
and their complexation with iridiuma
(a) tBu2PH·BH3, nBuLi; (b) BH3·THF; (c) N-acetylethylenediamine
Complexation with metal
Complexation of thus prepared hydroborane precursor
8
with
(a) HPR2, (CH2O)n; (b) BH3·THF; (c) morpholine; (d) [Ir(L)Cl]2 (L = 1,5-cyclooctadiene for
1a,c, L = C2H4 for 1b); (e) LiTMP, ethylene (TMP = 2,2,6,6-tetramethylpiperidide)
[Ir(coe)2Cl]2 (coe
=
cyclooctene) in benzene at room
(Scheme 4).
temperature led to the isolation of (P-B-P)Ir(H)Cl
9
This hydrido(chloro)iridium complex was characterized by
NMR and IR spectroscopy and high resolution mass
spectrometry (HRMS).
Scheme 2. Catalytic dehydrogenation of cyclooctane by using PBP-pincer iridium
complexes 2a-c with base
Scheme 4. Introduction of long-tethered (P-B-P)-pincer ligand precursor to
iridium atom
PtBu2
Cl
PtBu2
PtBu2
N
N
[Ir(coe)2Cl]2
C6H6
N
N
B
Ir
B
H
H
PtBu2
8
9
The 1H NMR spectrum of
9 showed a characteristic triplet
Results and discussion
signal at δH -20.04 ppm (2JPH = 15 Hz), which is assignable to
the hydride ligand. The chemical shift of the hydride ligand
was lower-field shifted in comparison to those (ca. -40 ppm) of
the previously reported (POCOP)Ir(H)Cl complexes. The
existence of the hydride ligand was also confirmed by an IR
spectrum, possessing a characteristic vibration of Ir–H bond at
2187 cm-1 and is supported by frequency calculations by DFT
methods (see Figure S30 in Supporting Information).
Furthermore, no change in the shape of hydride signal was
detected in the 1H{11B} NMR measurement, implying that
there should be little or no interaction between hydride and
Synthesis of long-tethered (P-B-P)-pincer ligand
Synthesis of the long-tethered (P-B-P)-pincer ligand precursor
8
(Scheme 3) was achieved through
procedure to the preparation of 1a
c 13
phenylenediamine
DMF/dioxane (1:1) gave the tethered bis(amide) derivative
as a white solid. Subsequent reaction of with di(tert-
BH3, and n-butyllithium in THF
afforded phosphinoborane-tethered phenylenediamine
Refluxing with BH3 THF resulted in the formation of , having
benzodiazaborole ring, borane-protected phosphorous
atoms, and propylene side chains. Deprotection of the
phosphine-borane moiety of with N-acetylethylenediamine
led to the hydroborane precursor as colourless oil. Due to
the high solubility of in pentane, the relatively polar amine
a
slight modified
-
.
Reaction of o-
(4) with 3-bromopropionyl chloride in
5
5
t
butyl)phosphinoborane, Bu2PH
⋅
6.
6
⋅
7
a
the boron atom of the (P-B-P)-pincer ligand via a
form. Considering the length of the tethered sidechains,
complex may have twisted structure. According to the
σ-borane
7
9
8
magnetic inequivalency below and above the (P-B-P)Ir plane
and twisted structure, the six sets of methylene protons
8
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 3 of 12
Journal Name
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
between phosphorous and nitrogen atoms became which the benzodiazaborole ring and (PBP)Ir plane are almost
inequivalent to result in eight multiplets (see Figure S24 in coplanar.
Supporting Information). Broadening of the methylene proton
Table 1. Selected bond lengths (Å) and angles (°) of 9 and 10 with those of reference
signals was also observed, suggesting that an equilibrium due
complexes 2a
to flipping of benzodiazaborole plane existed in solution
(Figure 1). The four tert-butyl groups on the phosphorous
atoms were split into one doublet with integral ratio of 18H
and two doublets with integral ratio of 9H each, also
2a
9
10
2.073(7)
2.2761(16)
2.3312(16)
-
B–Ir
Ir–P
Ir–Cl
Ir–H
1.971(6)
2.014(6)
2.3273(12)
2.3357(12)
2.3963(14)
2.3279(14)
2.3288(14)
2.4505(15)
supported this twisting geometry of
9. No change was
observed in the shape and pattern of the tert-butyl and
methylene proton signals when the 1H NMR measurement of
1.63(7)
1.53(8)
1.457(9)
1.452(9)
171.36(6)
91.5(2)
97.0(2)
-
9
1.55(6)
1.47(6)
o
was performed in CDCl3 at 50 C. The two phosphorous atoms
1.429(7)
1.437(7)
1.435(8)
1.463(8)
167.59(5)
91.51(19)
94.05(19)
106.2(2)
9
resonated as one singlet signal at δP 41.6 ppm in the 31P
B–N
in
NMR spectrum and is upfield than our previously reported 2a
(ca. 80 ppm). The boron nucleus in showed a broad singlet
at δB 12.3 ppm, which is more downfield than those reported
-
P–Ir–P
B–Ir–P
B–Ir–Cl
B–Ir–H
158.12(5)
79.14(17)
79.44(17)
157.67(17)
c
9
for 2a
-c
(ca. 30 ppm).
135(2)
54(3)
63(2)
81(2)
N–B–N
105.8(5)
6.27
105.3(5)
45.74
103.6(5)
38.32
PtBu2
N-B-Ir-P
PtBu2
Cl
Ir
Cl
Ir
N
N
N
B
B
N
H
H
PtBu2
PtBu2
9'
9''
Figure 1. Twisting equilibrium of the side-chains of
9 in solution
The structure of
diffraction analysis (Figure 2). Single crystals of
obtained from its benzene solution. The selected bond lengths
(Å) and angles (°) of are summarized in Table 1 with those of
reference complex 2a. In the crystal structure of , the B-Ir
9
was unambiguously determined by X-ray
9
were
9
P2
9
bond length of 2.014(6) Å is slightly longer than those of 2a
N2
[1.971(6) Å], while the Ir-P bond lengths of 2.3279(14) and
Cl1
B1
Ir1
2.3288(14) Å in
those of 2b . The Ir-Cl bond of 2.4505(15) Å in
those of 2a , probably due to the smaller B-Ir-Cl angle (see
below). The B-N bonds of 1.435(8) and 1.463(8) Å in are
slightly longer than those of 2a (ca. 1.431 Å) while the N-B-N
angle [105.3(5)°] in the benzodiazaborole ring in is similar to
those of 2a . The sum of the three angles around the boron
atom is 360°, indicating sp2 hybridization of the boron centre.
The B-Ir-Cl angle [106.2(2)°] in is smaller than those of 2a
9
are similar to those of 2a, but longer than
,
c
9
is longer than
H1
N1
-
c
9
-c
P1
9
-
c
9
-c
(ca. 147°), indicating that the chloride atom is significantly
bent toward the boron atom. This is believed due to the
twisting of the two side-arms, which pushed the two
phosphorous atoms (and therefore the four tert-butyl groups)
toward each other, creating a congested environment around
the iridium centre and the chloride was eventually propelled
Figure 2. ORTEP drawing of 9 (thermal ellipsoid at 50% probability; hydrogen
atoms except hydride ligand and cocrystallized molecules of benzene are
omitted for clarity)
toward boron. It should be noted that the acute angle of P-Ir-P Reaction of 9 with nBuLi
[167.59(5)°], which itself is around 10° larger than those in 2a
, is found in the opposite side of boryl ligand, as confirmed by
two B–Ir–P angles are over 90°. With the B-Ir-H angle of 81(2)°,
the central iridium atom in therefore adopted a distorted
trigonal bipyramidal structure (Y-shaped).19 The N-B-Ir-P
dihedral angle (45.74°) in , which has a twisted geometry, is
-
In the catalytic transfer dehydrogenation of alkanes by using
(PCP)Ir-based catalyst,20 (PCP)Ir(H)2 complexes reacted with
hydrogen acceptor TBE to generate the active T-shaped (PCP)Ir
catalysts, which then underwent oxidative addition of alkanes
to afford the (PCP)Ir(H)(alkyl) intermediates. It then performed
c
9
9
the rate-determining β-hydride elimination of the alkyl chain
to give (PCP)Ir(H)2, releasing alkene as the product. In an effort
significantly larger than those of (PBP)Ir complexes 2a-c, in
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 4 of 12
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
Journal Name
to isolate and study the corresponding (P-B-P)Ir(H)(alkyl) P)Ir(H)(nBu) complex 11 through an alkylation with nBuLi
species, was treated with different alkylating agents. (Scheme 6). We postulated two pathways for the next step.
Reaction of with MeLi and LiCH2SiMe3 led to complex Path A is the direct -H elimination of n-butyl group of (P-B-
mixtures. When a benzene solution of
was mixed with one P)Ir(H)(nBu) 11 to generate (P-B-P)Ir(H)2(1-butene) complex 12
9
9
β
9
,
equivalent of n-butyllithium at room temperature, the colour in which 1-butene may dissociate easily. Path B produces the
of the reaction mixture changed from green to deep brown final product via the following three steps: (i) a B-H bond
and with precipitations. After work-up, dihydride complex (P- reductive elimination to give a low-valent (P-BH-P)Ir(nBu)
B-P)Ir(H)2 10 was isolated as the sole product, where the target species 13, in which (P-BH-P) shows bidentate coordination
(P-B-P)Ir(H)(nBu) was not observed (Scheme 5).
mode, (ii)
BH-P)Ir(H)(1-butene) 14, and (iii) B-H addition to form the (P-B-
P)Ir(H)2(1-butene) complex 12 Considering that more
electron-rich metal centre possessing stronger donor ligand
accelerates -H elimination as observed in Pd(II)-alkyl
β-H elimination of n-butyl ligand on Ir(I) to afford (P-
Scheme 5. Reaction of 9
with nBuLi afforded dihydride complex 10
.
a
β
complex,21 β-H elimination from more electron-rich Ir(I) centre
of 13 may be faster than that from the “electron-deficient”
Ir(III) centre of 11. Although it is still unknown whether path A
or path B is the correct one, the path B may be related to the
observation of B-Ph bond-forming reductive elimination from
(PBP)Ir(Ph)Cl complex and the following loss of benzene
molecule (Scheme 7) by Ozerov et al.22
The resulting complex 10 was fully characterized by NMR and
IR spectroscopy and HRMS. No signal was observed in the
1
typical hydride region (negative chemical shift) in the H NMR
Scheme 6. Possible pathways for the formation of dihydride 10 from complex
9
spectra. However, a triplet signal with a coupling constant of
16 Hz and integral ratio of 2H was observed at δH 0.30 ppm.
Based on the coupling constant and the integral ratio, it is
assignable to two equivalent hydride ligands. The reasons for
PtBu2
Cl
PtBu2
H
nBuLi
N
N
N
N
+
B
H
Ir
B
H
Ir
1-butene
PtBu2
PtBu2
alkene
this low-field hydride signal can be attributed to the strong σ-
9
10
donation from (P-B-P) pincer ligand, as our previously reported
(PBP)Pt(H) exhibited hydride signal at 7.92 ppm.16a The NMR
chemical shift calculations for 10 indicated two hydride signals
resonate at 1.363 (close to the boron atom) and –5.364 ppm
The observed signal at 0.3 ppm in complex 10 is close to the
average (–2.000 ppm) of these calculated signals to indicate
the scrambling of the hydrides at room temperature. The
existence of the hydride ligands was also confirmed by an IR
spectrum, possessing characteristic vibrations at 1859
(antisymmetrical two Ir–H stretch) and 2172 cm-1 (symmetrical
two Ir-H stretch), which are in good match with the vibrations
produced in frequency calculations by DFT methods (see
Figure S31 in Supporting Information). The four tert-butyl
groups on the phosphorous atoms were split into two broad
singlet signals while five sets of broad multiplets were assigned
as the methylene protons of the long tethers. The broadening
of these signals suggests that 10 should also has a similar
nBuLi
dissociation
PtBu2
nBu
Ir
PtBu2
β-H
elim.
H
N
N
B
B
Ir
N
N
H
H
PtBu2
PtBu2
11
12
B-H
ox. add.
B-H
red. elim
PtBu2
PtBu2
β-H
elim.
H
N
N
N
nBu
BH Ir
BH Ir
N
PtBu2
PtBu2
13
14
twisted equilibrium as observed in 9. The two phosphorous
Scheme 7. Recently reported B-Cl elimination from PBP-pincer Ir(III) complex
followed by loss of benzene molecule22
atoms in 10 resonated as one singlet signal at δP 58.8 ppm in
the 31P NMR spectrum and is significantly shifted to lower field
than that of
signal at δB 12.3 ppm, which indicates the existence of B-Ir
bond and is of similar value to
9. The boron nucleus in 10 showed a broad singlet
9.
To get insight into the reaction mechanism for the formation
of 10, the above reaction was repeated and monitored by
1
using H NMR spectroscopy. During the time course, 1-butene
was identified with its vinylic protons at δH 4.95 (d), 5.00 (dd),
and 5.75-5.84 (m) ppm in the 1H NMR spectrum. The initial
step of the reaction should involve the formation of (P-B-
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 5 of 12
Journal Name
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
In an effort to detect the proposed intermediate 11 or 13, the Recrystallization of 10 from pentane gave red crystals which
reaction of 9 and n-butyllithium was also conducted at low were structurally characterized by crystallographic analysis
temperature and was monitored by 1H and 31P NMR (Figure 3). The selected bond lengths (Å) and angles (°) of 10
spectroscopy. Upon mixing, even at –78 °C, the hydride signal are summarized in Table 1. It is noteworthy that 10 is the first
of
0.34 ppm with an integral ratio of 2H and a sharp singlet at δP complex supported by PBP ligand. In the structure of 10, the
58.2 ppm ppm was observed in 1H and 31P NMR spectrum, central iridium atom again formed
distorted trigonal
9 at δH -20.04 ppm disappeared. A new triplet signal at δH example of structurally characterized iridium dihydride
a
respectively. When the reaction mixture was slowly warmed bipyramidal structure (Y-shaped),19 consisting of two apical
up to room temperature, the triplet 1H NMR signal was slightly phosphine ligands and equatorial hydride and boryl ligands.
upper-field shifted to δH 0.30 ppm while the phosphorous The acute P-Ir-P angle in 10 [171.36(6)°], which is on the
atoms resonated at δP 58.8 ppm. These signals should be opposite side of boryl ligand, is slightly larger than that in
assignable to the dihydride complex 10. Thus, we concluded [167.59(5)°]. Other structural features of 10 are similar to
that the energy barrier for -H elimination of n-butyl ligand those of and also possess a twisted geometry.
9
β
9
may be too small to monitor the reaction.
Catalytic transfer dehydrogenation of COA using the long-tethered
(P-B-P)Ir complexes
In the chemistry of (PCP)Ir catalyst, (PCP)Ir(H)2 complexes were
prepared through a two-step reaction: (a) (PCP)Ir(H)Cl reacted
with LiBEt3H in the presence of dihydrogen gas to give The obtained long-tethered (P-B-P)-pincer iridium complexes
9
(PCP)Ir(H)4, and (b) heating (PCP)Ir(H)4 at 130 °C under vacuum was applied as catalysts for the transfer dehydrogenation of
to afford the product (PCP)Ir(H)2. The catalytic activities of cyclooctane (COA). The doubly dehydrogenated product
these (PCP)Ir complexes are known to decrease with trace cyclooctadiene (COD) was not detected in all entries. In the
amount of boron-containing impurities or byproducts.23 Thus, presence of hydrogen acceptor tert-butylethylene (TBE),
it is important to remove carefully all impurities during the heating
9
with tBuOLi at 180 °C in COA furnished singly
work-up and through recrystallization. However, our (P-B- dehydrogenated product cyclooctene (COE) and tert-
P)Ir(H)2 complex 10 formed voluntarily at room temperature butylethane (TBA), with a TON (turnover number) of 17,
by alkylation of
9 with n-butyllithium. The dihydride product estimated by gas chromatography (Table 2, entry 1). When
10 could be obtained in high purity by simple filtration of chloride abstraction was performed with a stronger base
t
inorganic lithium chloride salt and vacuum of 1-butene. This having a larger alkali-metal cation (tBuONa and BuOK), higher
could be considered as a useful method for the preparation of TONs were achieved (Table 2, entries 2 and 3). Increasing the
iridium dihydride complexes as precatalyst for dehydro- reaction temperature to 200 °C slightly improved the TON
genation reactions.
(Table 2, entry 4). When a further stronger base potassium
hexamethyldisilazide (KHMDS) was applied, the TON boosted
up to 102 at 180 °C (Table 2, entry 5). A maximum TON of 113
was observed for 9/KHMDS at 200 °C (Table 2, entry 6). The
catalytic activities of (P-B-P)-pincer iridium dihydride complex
10 toward transfer dehydrogenation of COA was also explored.
Catalysis of the reaction was able to perform even at 140 °C
using TBE as hydrogen acceptor (Table 2, entry 7). Similarly,
the TON improved with higher reaction temperature. The
highest TON was achieved at 160 °C (Table 2, entry 8). Further
elevated temperature resulted in a lower TON, probably due
to the poor thermal stability of 10 and decomposition of the
catalyst (Table 2, entries 9-10).
P1
N1
H1A
Ir1
B1
H1
N2
P2
Figure 3. ORTEP drawing of 10 (thermal ellipsoid at 50% probability; hydrogen
atoms except hydride ligands are omitted for clarity)
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 6 of 12
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
Journal Name
Table 2. Catalytic transfer dehydrogenation of COA by using the long-tethered (P-B-P)Ir
complexes 9a and 10b
100
80
60
40
20
0
(P-B-P)Ir-cat (S/C = 3000)
additive (1.5 equiv. to cat.)
Temp, 15 h
tBu
TBE
tBu
COA
COE
TBA
entry (P-B-P)Ir cat. additive temp (°C) TONc
1
2
9
9
tBuOLi
tBuONa
tBuOK
tBuOK
180
180
180
200
180
200
140
160
180
200
17
18
3
9
52
4
9
58
0
200
400
Time (min)
600
5
9
KHMDS
102
113
48
6
9
KHMDS
Figure 4. Time course of the TON for dehydrogenation of cyclooctane under the
condition of entry 8 in Table2. Each TON was estimated by independent
experiments; the amount of COE was estimated by gas chromatography.
7
10
10
10
10
-
-
-
-
8
126
124
112
9
Scheme 8. Plausible catalytic pathways for the transfer dehydrogenation of
cyclooctane using the long-tethered (P-B-P)Ir complexes 9 and 10
10
a
standard condition: PBP-Ir cat. 9 (3 ꢀmol), additive (4.5 ꢀmol), COA (9 mmol),
b
tert-butylethylene (TBE) (9 mmol), standard condition: PBP-Ir cat. 10 (3 ꢀmol),
COA (9 mmol), tert-butylethylene (TBE) (9 mmol), the amount of COE was
PtBu2
c
N
base
estimated by gas chromatography
B
Ir
PtBu2
9
N
The time course of the reaction progress using 10 was also
studied (Figure 4). An induction period of around five minutes
was observed, probably due to the abstraction of the hydrides
by TBE to generate the catalytically active T-shape (P-B-P)Ir
species. Half of the best TON (entry 8 in Table 2) could be
achieved after around 3 h. It should be noted that the catalytic
transfer dehydrogenation of COA with 10 was completely shut
off when 2-norbornene (NBE) was used as a hydrogen
acceptor. The deactivation of catalyst by NBE may be due to (i)
the formation of highly stable (P-B-P)Ir(nbe) complex, or (ii)
NBE is too bulky to insert into the dihydride 10 for generation
of T-shaped (P-B-P)Ir intermediate. Thus, the present long-
15
P
tBu
tBu
R
B
Ir
P
P
Ir
P
H
R
B
B
Ir
P
H
H
10
16
β-H elim. via Ir(III)
P
dissociation
of B-H bond
addition
of B-H bond
R
P
P
tethered (P-B-P)Ir complexes
9
and 10 could be applied as
R
B
H
Ir
P
H
B
H
Ir
catalysts for the transfer dehydrogenation of COA with a TON
up to 113 and 126, respectively. The latter is the highest TON
ever reported with PBP-pincer iridium complexes. The
robustness of the catalysts is proposed to arise from the steric
protection with tethered side chains or the additional pathway
β-H elim. via Ir(I)
18
17
P
R
for the β-elimination (see below).
A possible mechanism for long-tethered (P-B-P)-pincer iridium
catalysed transfer dehydrogenation of COA is illustrated in
Scheme 8, according to the previously studied PCP-pincer
iridium system. The active species (P-B-P)Ir 15, possessing a T-
shape and 14 electrons, may be generated through the
reaction of
9
with base. C-H oxidative addition of COA to 15
-H
would afford the (hydrido)(cyclooctyl)iridium complex 16
.
β
elimination of cyclooctyl group would result in the formation
of dihydride complex 10, releasing the product COE. To
complete the catalytic cycle and to regenerate the catalytically
active species 15, the last step should involve the abstraction
of the two hydride ligands in 10 with hydrogen acceptor, TBE.
It is also possible to assume an additional pathway, which
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 7 of 12
Journal Name
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
involves the following three steps as we postulate in the the acceptorless dehydrogenation of CDD at 160 °C, giving
n
formation of 10 from
B-H to form Ir(I) alkyl intermediate (P-BH-P)Ir(cyclooctyl) 17
(b) -hydride elimination on Ir(I) metal centre to liberate COE was improved by a higher reaction temperature (Table 3,
9
and BuLi: (a) reductive elimination of cyclododecene as isomer mixture with a TON of 3 after 20 h,
,
estimated by gas chromatography (Table 3, entry 5). The TON
β
and Ir(I) hydride complex (P-BH-P)Ir(H) 18, (c) oxidative entries 6-7). At 230 °C, maximum TON of 7 was achieved
addition of B-H bond to afford Ir(III) dihydride 10, although we (Table 3, entry 8). Hall reported a TON of 126 using a
have no direct evidence at this stage. Theoretical studies will anthraphos-based iridium pincer dihydride complex at 250 °C
be conducted in short future to calculate the energy profile, after 192 h.24 The “anthrapos” ligands confers a thermal
and to determine the rate-determining step of the reaction.
stabilization on the catalysts. Hence the dehydrogenation
reactions can be performed at temperatures over 200 °C that
would normally result in complete decomposition of the pincer
catalysts.
Catalytic transfer dehydrogenation of ethylbenzene and acceptor-
less dehydrogenation of cyclododecane using 10
10 could also catalyse the transfer dehydrogenation of
ethylbenzene (PhEt) at 140 °C in the presence of TBE as
hydrogen acceptor at a reaction time of 15 h, giving styrene as
Conclusions
We designed and synthesized a new (P-B-P)-pincer ligand by
elongating the methylene linkers of the previously reported
the sole product with
a TON of 3, estimated by gas
chromatography (Table 3, entry 1). Higher reaction
temperature improved the TON and the maximum TON of 25
was observed at 180 °C (Table 3, entry 3).
PBP-pincer ligands. Treatment of hydroborane precursor
with [Ir(coe)2Cl]2 generated the coordinatively unsaturated (P-
B-P)Ir(H)Cl complex . The complex was further derived to
8
9
9
n
(P-B-P)Ir(H)2 complex 10 by a reaction with BuLi. This reaction
Table 3. Catalytic dehydrogenation of ethylbenzene and cyclododecane by using the
long-tethered (P-B-P)Ir complex 10a,b
can be considered as a generally applicable method to
synthesize
iridium
dihydride
complexes
aim
for
dehydrogenation reactions. Both
9/base and 10 were
catalytically active for transfer dehydrogenation of COA,
yielding COE. 10 could also catalyse the transfer
dehydrogenation of ethylbenzene and acceptorless
dehydrogenation of cyclododecane. Even there was no direct
information about the reaction mechanism and rate-
determining step, a further mechanistic study with DFT
calculations and improvement of the ligand structure will be
reported in due course.
10 (S/C = 3000)
H2 acceptor
Temp, Time
Ethylbenzene
Styrene
Cyclododecane
Cyclododecene
TONc
alkane
H2 acceptor Time (h)
entry
temp (°C)
PhEt
PhEt
PhEt
PhEt
CDD
CDD
CDD
CDD
TBE
15
15
15
15
20
20
20
20
1
2
3
4
5
6
7
8
140
160
180
200
160
180
200
230
3
10
25
18
3
Experimental
TBE
General procedure. All the preparations and manipulations
involving air and moisture-sensitive compounds were carried
out under an argon atmosphere using standard Schlenk and
glovebox (KIYON) techniques. All glassware were dried for 20
min in the 250 °C oven before use. Ether, CH2Cl2, THF and n-
hexane were purified by passing through a solvent purification
system (Grass Contour). Anhydrous DMF, 1,4-dioxane and n-
pentane were purchased from Wako and used as received. 3-
bromopropionyl chloride was purchased from TCI and used as
received. C6D6 was dried by distillation over sodium-
benzophenone followed by vacuum transfer. NMR spectra
were recorded on JEOL ECA (400MHz or 500 MHz for 1H, 160.5
TBE
TBE
-
-
-
-
4
6
7
a
standard condition: PBP-Ir cat. 10 (3 ꢀmol), ethylbenzene (9 mmol), tert-
b
butylethylene (TBE) (9 mmol), standard condition: PBP-Ir cat. 10 (3 ꢀmol),
cyclododecane (9 mmol), c the amount of alkene (styrene or cyclododecene) was
estimated by gas chromatography
This TON is about half of that reported by Jensen using
(PCP)Ir(H)2.8c Further increased temperature resulted in lower
TONs, probably due to the decomposition of the catalysts.
(Table 3, entry 4).
MHz for 11B, 126 MHz for 13C). Chemical shifts are reported in
δ
ppm relative to the residual protiated solvent for 1H,
deuterated solvent for 13C, and an external BF3·OEt2 for 11B and
85% H3PO4 for 31P used as references. Assignment of all signals
1
in the H and 13C NMR spectra were based on the DEPT135,
Since dehydrogenation reaction without using hydrogen
acceptor has been reported in high temperature condition,8d-e
10 was also applied as catalyst for the acceptorless
dehydrogenation of cyclododecane (CDD). 10 could catalyse
HMQC, and HMBC measurements. IR spectra were obtained
on IRAffinity-1 (Shimadzu). Melting points (mp.) were
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 8 of 12
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
Journal Name
determined with a MPA100 OptiMelt (Tokyo Instruments, Inc.) J = 7.8 Hz, 4°, ipso to N), 168.6 (dd, J = 34.1 Hz, 2.6 Hz, C=O).
and were uncorrected. Mass spectra were measured on a JEOL IR(KBr): 1645 (CO), 3246 (NH).
JMS-700 mass spectrometer. X-ray crystallographic analyses
were performed on VariMax/Saturn CCD diffractometer.
Synthesis of 6. To a THF (20.0 mL) solution of
5 (378 mg, 1.00
mmol) and di(tert-butyl)phosphinoborane complex (640 mg,
n
Details for X-ray crystallographic study. Details of the crystal 4.00 mmol) in a 50.0 mL two-necked flask, BuLi (2.50 M, 1.73
data and summary of the intensity data collection mL, 4.00 mmol) was added dropwise at –78 °C. The yellowish
parameters for and 10 are listed in Table S1. A suitable reaction mixture was then gradually warmed to room
a
9
crystal was mounted with a mineral oil to the glass fiber and temperature and stirred for 16 h. Water (20.0 mL) was added
transferred to the goniometer of Rigaku VariMax Saturn CCD to quench the reaction, followed by the extraction with CH2Cl2
diffractometer with graphite-monochromated Mo K
= 0.71075 Å). All the following procedure for analysis, brine, dried with Na2SO4, and evaporated to give yellow solid.
Yadokari-XG 2009 was used as a graphical interface.25 The The resulting yellow solid was washed with Et2O to afford
structure was solved by direct methods with (SIR-97)26 and white solid of (243 mg, 0.453 mmol, 45 %). 1H NMR (500
refined by full-matrix least-squares techniques against F2 MHz, CDCl3)
0.09 - 0.80 (br m, 6H, P-BH3), 1.27 (d, J = 13.0 Hz,
α radiation (10.0 mL x3). The organic layer was washed with water and
(λ
6
δ
(SHELXL-2014).27 The intensities were corrected with 36H, tBu), 2.10 (dt, J = 11.0 Hz, 7.0 Hz, 4H, -CH2-CH2-P), 2.76
numerical absorption correction by CrystalClear software. The (dt, J = 11.0 Hz, 7.0 Hz, 4H, -CH2-CH2-P), 7.17 (dd, J = 6.0 Hz, 4.0
non-hydrogen atoms were refined anisotropically. Hydrogen Hz, 2H, =CH- ortho to N), 7.49 (dd, J = 6.0 Hz, 4.0 Hz, 2H, =CH-
atoms were placed using AFIX instructions except for hydrogen meta to N), 8.07 (s, 2H, NH). 13C{1H} NMR (126 MHz, CDCl3)
atom of the hydride ligand in and 10, which were found in 12.6 (d, J = 30.7 Hz, -CH2-P), 27.8 (s, C(CH3)3), 32.2 (d, J = 5.5
differential Fourier map as a residual peak and were refined Hz, -CH2-CH2-P), 32.4 (s, C(CH3)3), 125.5 (s, =CH- ortho to N),
isotopically. 126.1 (s, =CH- meta to N), 130.3 (s, 4°, ipso to N), 171.6 (d, J =
9.6 Hz, C=O). 31P{1H} NMR (202 MHz, CDCl3)
45.6 (d, J = 59.9
Details for computation. All calculations were performed with Hz), splitting may come from coupling with 11B (I = 3/2) and 10
Gaussian 09 (rev. D.01) software package.28 Both of the (I = 3) to exhibit broad doublet-like signal. 11B{1H} NMR (160
molecular geometries of and 10 were optimized without MHz, CDCl3) –47.2 (d, J = 45 Hz). IR(KBr): 1655 (CO), 2378 (P-
δ
9
δ
B
9
δ
constraints at the B3LYP level29 with LanL2DZ/6-31G basis BH3), 3246 (NH). HRMS-FAB (m/z): [M]+ calcd for
sets.30,31 Figures S30 and S31 shows the optimised structures C28H56B2N2O2P2, 536.4003; found, 536.3984.
and their calculated displacement vectors, which correspond
to the observed characteristic vibration in IR spectra, of
9 and Synthesis of 7. To a 10.0 mL J-Young tube charged with 6 (258
10. The optimized structures are attached as Supplementary mg, 0.481 mmol), a THF solution of BH3·THF (0.95 M, 2.53 mL,
Information in .xyz format, which can be viewed by Mercury 2.41 mmol) was added at 0 °C. The reaction mixture was
software. The NMR chemical shift calculation of 10 was warmed to 55 °C and was stirred for 21 h to afford a colourless
performed by Gauge-Independent Atomic Orbital (GIAO) solution with white precipitates. Volatiles were removed from
method32 at the B3LYP level with LanL2DZ/6-311++G(2d,p) the reaction mixture under reduced pressure to give white
basis sets. The obtained isotropic shift was compensated with solid. The solid was extracted with THF (10.0 mL) and then
that of SiMe4 which was calculated at the B3LYP/6- filtered through a pad of Celite. Crude product was obtained
311++G(2d,p) level.
after the evaporation of the filtrate. Recrystallization from a
THF solution diffused with pentane resulted in analytically
1
as white solid (99.7 mg, 0.192 mmol, 40 %). H NMR
Synthesis of 5. To a 200 mL two-necked flask was added o- pure
7
phenylenediamine (1.08 g, 9.99 mmol), anhydrous DMF (7.50 (500 MHz, C6D6)
δ
0.03 - 0.63 (br m, 6H, P-BH3), 1.00 (d, J =
mL), and anhydrous 1,4-dioxane (7.50 mL). 3-bromopropionyl 12.1 Hz, 36H, tBu), 1.37 (dt, J = 14.4 Hz, 5.5 Hz, 4H, -CH2-P),
chloride (2.00 mL, 20.0 mmol) was added dropwise to the 2.11 – 2.19 (m, 4H, -CH2-CH2-P), 3.55 (t, J = 6.9 Hz, 4H, N-CH2-),
stirring solution of o-phenylenediamine at 0 °C. The resulting 4.83 (br s, 1H, N-B-H), 7.03 – 7.06 (m, 2H, aromatic CH), 7.08 –
orange solution was stirred at 0 °C for an addition of 30 min, 7.10 (m, 2H, aromatic CH). 13C{1H} NMR (126 MHz, C6D6)
δ 15.7
and then at RT for 16 h. The reaction was quenched by an (d, J = 28.8 Hz, -CH2-P), 26.2 (s, -CH2-CH2P), 27.7 (d, J = 1.2 Hz,
addition of water (28.0 mL) to precipitate the crude product. C(CH3)3), 32.0 (d, J = 26.2 Hz, C(CH3)3), 45.8 (d, J = 12.2 Hz, N-
The resulting precipitate was filtered, washed with water (10.0 CH2-), 109.5 (s, =CH- ortho to N), 119.7 (s, =CH- meta to N),
mL x2) and 5% aqueous HBr (10.0 mL x2). After vacuum drying, 138.0 (s, 4°, ipso to N). 31P{1H} NMR (202 MHz, C6D6)
δ 45.9 (d,
1
5
was obtained as white powder (3.17 g, 8.39 mmol, 84%). H J = 38.1 Hz), splitting may come from coupling with 11B (I = 3/2)
NMR (500 MHz, DMSO-d6) δ
CH2-Br), 2.98 (td, J = 6.5 Hz, 2.6 Hz, 2H, -CH2-Br), 3.74 (t, J = 6.5 (160 MHz, C6D6)
2.85 (td, J = 6.4 Hz, 2.5 Hz, 2H, - and 10B (I = 3) to exhibit broad doublet-like signal. 11B{1H} NMR
–46.4 (dq, J = 184.4 Hz, 50.9 Hz, P-BH3), 21.1
δ
Hz, 2H, -CH2-CH2-Br), 3.88 (t, J = 6.4 Hz, 2H, -CH2-CH2-Br), 7.17 (s, N-B-H). IR(KBr): 1603 (N-B), 2367 (P-BH3), 2577 (N-B-H).
(vt, J = 4.8 Hz, 2H, =CH- ortho to N), 7.55 (quin, 2H, =CH- meta HRMS-FAB (m/z): [M]+ calcd for C28H59B3N2P2, 518.4433; found,
to N), 9.41 (t, J = 6.3 Hz, 2H, NH). 13C{1H} NMR (126 MHz, 518.4407.
DMSO-d6) δ 29.2 (s, -CH2-CH2-Br), 39.0 – 40.0 (m, -CH2-CH2-Br),
125.0 (s, =CH- ortho to N), 125.2 (s, =CH- meta to N), 130.4 (vt,
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 9 of 12
Journal Name
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
n
Synthesis of hydroborane precursor 8. A toluene (5.00 mL) Synthesis of (P-B-P)Ir(H)2 10. A hexane solution of BuLi (2.50
solution of
7
(104 mg, 0.200 mmol) and N- M) was evaporated to give an oily material. An aliquot of the
acetylethylenediamine (513 mg, 5.02 mmol) in a 20.0 mL J- resulting oily material (32.1 mg, 0.502 mmol of nBuLi) in
Young tube was stirred for 19 h at 103 °C. The resulted milky benzene (3.00 mL) was added to a benzene solution (2.00 mL)
suspension was evaporated to dryness and was then extracted of
9 (300 mg, 0.418 mmol) in a 15.0 mL vial at room
with hexane (5.00 mL x2). After filtering off the insoluble temperature. The resulting brown suspension was stirred for 1
material through a pad of Celite, volatiles were removed under h before all the volatiles were removed by vacuo. The brown
reduced pressure to give colourless oil of
1
mmol, 86%). H NMR (500 MHz, C6D6)
8
(84.7 mg, 0.173 solid was dissolved in benzene (2.00 mL) and was then filtered
δ 1.03 (d, J = 10.6 Hz, through a pad of Celite. Pale brown crystals of 10 were
36H, tBu), 1.29 (dt, J = 11.4, 4.0 Hz, 4H, -CH2-P), 1.99 (td, J = obtained from the concentrated filtrate and was subjected to
15.7 Hz, 8.3 Hz, 4H, -CH2-CH2-P), 3.71 (t, J = 7.3 Hz, 4H, N-CH2-), solid state structural characterization (257, mg, 0.376 mmol,
4.84 (br s, 1H, N-B-H), 7.09 (ddt, J = 16.0 Hz, 6.6 Hz, 3.0 Hz, 4H, 90%). 1H NMR (500 MHz, C6D6)
δ
0.30 (t, J = 15.9 Hz, 2H, Ir-H),
aromatic CH). 13C{1H} NMR (126 MHz, C6D6)
δ 18.8 (d, J = 23 1.06 (br s, 18H, tBu), 1.26 (br s, 18H, tBu), 1.70 (br s, 2H, -CH2-
Hz, -CH2-P), 29.9 (d, J = 13.7 Hz, C(CH3)3), 31.3 (d, J = 25.7 Hz, - P), 2.17 (br s, 4H, -CH2-P and -CH2-CH2-P), 2.40 (br s, 2H, -CH2-
CH2-CH2-P), 31.3 (d, J = 22.8 Hz, C(CH3)3), 45.6 (d, J = 14.4 Hz, CH2-P), 3.79 (br s, 2H, N-CH2-), 4.41 (br s, 2H, N-CH2), 6.84 (dd,
N-CH2-), 109.3 (s, =CH- ortho to N), 119.3 (s, =CH- meta to N), J = 5.4 Hz, 3.3 Hz, 2H, aromatic CH), 7.02 (dd, J = 5.4 Hz, 3.3 Hz,
138.2 (s, 4o, ipso to N). 31P{1H} NMR (202 MHz, C6D6)
11B{1H} NMR (160 MHz, C6D6)
20.9 (s). IR(KBr): 1601 (N-B), 12.0 Hz, -CH2-P), 27.2 (s, -CH2-CH2-P), 30.2 (d, J = 275.4 Hz,
2581 (N-B-H). HRMS-FAB (m/z): [M-B+H]+ calcd for C28H54N2P2, C(CH3)3), 35.5 (dt, J = 404.5 Hz, 11.7 Hz, C(CH3)3), 42.4 (s, N-
480.3763; found, 480.3742. CH2-), 105.6 (s, =CH- ortho to N), 117.3 (s, =CH- meta to N),
138.6 (s, 4o ipso to N). 31P{1H} NMR (202 MHz, C6D6)
58.8 (s).
Synthesis of (P-B-P)Ir(H)Cl 9. To a benzene (1.00 mL) solution 11B{1H} NMR (160 MHz, C6D6)
11.5 (br s). IR(KBr): 1600 (N-H)
of [Ir(coe)2Cl]2 (300 mg, 0.335 mmol) in a 15.0 mL vial, a 1859 (Ir-H). HRMS-FAB (m/z): M+ calcd for C28H54BIrN2P2,
benzene solution (3.00 mL) of (328 g, 0.670 mmol) was 684.3485; found, 684.3515.
δ δ 24.7 (t, J =
27.0 (s). 2H, aromatic CH). 13C{1H} NMR (126 MHz, C6D6)
δ
δ
δ
8
added dropwise. The resulting solution was stirred at room
temperature for 1 h. During which, a change in the colour of General procedure for catalytic transfer dehydrogenation of
the reaction mixture from bright orange to greenish yellow COA by using complex 9 with base. In a glovebox, complex
9
was observed. The reaction mixture was then evaporated to (3.00 μmol) and base (1.50 equiv., 4.50 μmol) was dissolved in
dryness, followed by the extraction with hexane (5.00 mL x2). a solution of COA (3000 equiv., 9.00 mmol) and H2 acceptor
After filtration through a pad of Celite, the volatiles were TBE (3000 equiv., 9.00 mmol) in a 10.0 mL J-Young tube. The
removed under reduced pressure to give the crude product. tube was heated in a preheated oil-bath or heating aluminum-
Recrystallization from benzene afforded greenish yellow block stirrer. After indicated time, the tube was cooled down
crystals of 9, which were suitable for X-ray diffraction analysis to room temperature. An internal standard (dodecane, 500
1
(216 mg, 0.301 mmol, 45 %). H NMR (500 MHz, C6D6)
δ
–20.0
ꢀmol) was added to the reaction mixture, then the sample was
(t, J = 14.6 Hz, 1H, Ir-H), 0.82 (t, J = 6.3 Hz, 9H, tBu), 1.24 (t, J = analyzed by gas chromatography to estimate yields with pre-
6.4 Hz, 9H, tBu), 1.34 (td, J = 5.9 Hz, 2.4 Hz, 18H, tBu), 1.62 (td, calculated GC factor with authentic samples.
J = 13.5 Hz, 3.5 Hz, 1H, -CH2-CH2-P), 1.57 – 1.73 (br s, 1H, -CH2-
CH2-P), 1.87 (tt, J = 10.5 Hz, 3.0 Hz, 2H, -CH2-CH2-P), 1.91 (br t, J General procedure for catalytic transfer dehydrogenation of
= 6.5 Hz, 1H, -CH2-CH2-P), 1.99 – 2.15 (br s, 1H, -CH2-CH2-P), COA by using complex 10. In a glovebox, complex 10 (3.00
2.34 (br t, J = 6.5 Hz, 1H, -CH2-CH2-P), 2.90 (td, J = 13.5 Hz, 3.5 μmol) was dissolved in a solution of COA (3000 equiv., 9.00
Hz, 1H, -CH2-CH2-P), 3.57 (dd, J = 14.0 Hz, 7.3 Hz, 1H, N-CH2-), mmol) and H2 acceptor (3000 equiv., 9.00 mmol) in a 10.0 mL
3.77 (dd, J = 14.4 Hz, 6.4 Hz, 2H, N-CH2-), 5.48 (dd, J = 14.6 Hz, J-Young tube. The tube was heated in a preheated oil-bath or
10.3 Hz, 1H, N-CH2-), 6.82 - 6.87 (m, 2H, aromatic CH), 7.00 – heating aluminum-block stirrer. After indicated time, the tube
7.04 (m, 2H, aromatic CH). 13C{1H} NMR (126 MHz, C6D6)
19.0 (t, J = 9.2 Hz, -CH2-P), 26.5 (s, -CH2-CH2-P), 26.9 (s, -CH2- (dodecane, 500
δ
was cooled down to room temperature. An internal standard
mol) was added to the reaction mixture, then
ꢀ
CH2-P), 29.2 (vt, J = 1.1 Hz, C(CH3)3), 31.0 (t, J = 1.6 Hz, C(CH3)3), the sample was analyzed by gas chromatography to estimate
31.3 (t, J = 2.0 Hz, C(CH3)3), 31.5 (t, J = 2.3 Hz, C(CH3)3), 34.3 (t, J yields with pre-calculated GC factor with authentic samples.
= 14.2 Hz, C(CH3)3), 36.5 (t, J = 10.0 Hz, C(CH3)3), 36.7 (t, J = 9.5
Hz, C(CH3)3), 37.6 (t, J = 10.4 Hz, C(CH3)3), 41.5 (s, N-CH2-), 44.2 General procedure for catalytic transfer dehydrogenation of
(s, N-CH2), 106.3 (d, J = 3.6 Hz, =CH- ortho to N), 117.8 (d, J = ethylbenzene by using complex 10. In a glovebox, complex 10
67.4 Hz, =CH- meta to N), 138.6 (d, J = 105.6 Hz, 4o, ipso to N). (3.00 μmol) was dissolved in a solution of ethylbenzene (3000
31P{1H} NMR (202 MHz, C6D6)
C6D6) 12.2 (br s). IR(KBr): 1593 (N-B), 2187 (Ir-H). HRMS-FAB mmol) in a 10.0 mL J-Young tube. The tube was heated in a
(m/z): M+ calcd for C28H53BClIrN2P2, 718.3095; found, preheated oil-bath or heating aluminum-block stirrer. After
δ
41.2 (s). 11B{1H} NMR (160 MHz, equiv., 9.00 mmol) and H2 acceptor TBE (3000 equiv., 9.0
δ
718.3071.
indicated time, the tube was cooled down to room
temperature. An internal standard (dodecane, 500 mol) was
ꢀ
added to the reaction mixture, then the sample was analyzed
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 10 of 12
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
Journal Name
11 (a) A. R. Chianese, A. Mo, N. L. Lampland, R. L. Swartz and P.
T. Bremer, Organometallics, 2010, 29 3019; (b) A. R.
by gas chromatography to estimate yields with pre-calculated
GC factor with authentic samples.
,
Chianese, S. E. Shaner, J. A. Tendler, D. M. Pudalov, D. Y.
Shopov, D. Kim, S. L. Rogers and A. Mo, Organometallics,
2012, 31, 7359; (c) A. R. Chianese, M. J. Drance, K. H. Jensen,
S. P. McCollom, N. Yusufova, S. E. Shaner, D. Y. Shopov and J.
A. Tendler, Organometallics, 2014, 33, 457; (d) X. Jia and Z.
Huang, Science China Chemistry, 2015, 1; (e) X. Jia, L. Zhang,
General
procedure
for
catalytic
acceptorless
dehydrogenation of CDD by using complex 10. In a glovebox,
complex 10 (3.00 μmol) was mixed with CDD (3000 equiv., 9.00
mmol) in a 10.0 mL J-Young tube. The tube was heated in a
preheated oil-bath or heating aluminum-block stirrer. After
indicated time, the tube was cooled down to room
C. Qin, X. Leng and Z. Huang, Chem. Commun., 2014, 50
11056.
,
12 (a) A. S. Goldman, A. H. Roy, Z. Huang, R. Ahuja, W. Schinski
and M. Brookhart, Science, 2006, 312, 257; (b) B. C. Bailey, R.
R. Schrock, S. Kundu, A. S. Goldman, Z. Huang and M.
Brookhart, Organometallics, 2009, 28, 355; (c) M. C. Haibach,
S. Kundu, M. Brookhart and A. S. Goldman, Acc. Chem. Res.,
2012, 45, 947; (d) A. J. Nawara-Hultzsch, J. D. Hackenberg, B.
Punji, C. Suppleet, T. J. Emge, B. C. Bailey, R. R. Schrock, M.
temperature. An internal standard (dodecane, 500 ꢀmol) was
added to the reaction mixture, then the sample was analyzed
by gas chromatography to estimate yields with pre-calculated
GC factor with authentic samples.
Brookhart and A. S. Goldman, ACS Catal., 2013,
R. Ahuja, B. Punji, M. Findlater, C. Supplee, W. Schinski, M.
Brookhart and A. S. Goldman, Nature Chemistry, 2011,
167; (f) A. Thawani, R. Rajeev and R. B. Sunoj, Chem. Eur. J.,
2013, 19, 4069; (g) T. W. Lyons, D. Guironnet, M. Findlater
and M. Brookhart, J. Am. Chem. Soc., 2012, 134, 15708; (h) R.
Yamaguchi and K. Fujita, Ligand Platforms in Homogeneous
Catalytic Reactions with Metals: Practice and Applications for
Green Organic Transformations, John Wiley & Sons, USA,
2015, 109; (i) S. Kundu, T. W. Lyons and M. Brookhart, ACS
3, 2505; (e)
Acknowledgements
3,
This work was supported by a Grant-in-Aid for Scientific
Research on Innovative Areas “Stimuli-responsive Chemical
Species for the Creation of Functional Molecules (No.2408)”
(JSPS KAKENHI Grant Number JP24109012) from JSPS and
CREST area “Establishment of Molecular Technology towards
the Creation of New Functions” (No. 14529307) from JST. We
thank Prof. Tamejiro Hiyama, Chuo University, for providing
Catal., 2013, 3, 1768.
access to an X-ray diffractometer and Prof. Yoshiaki 13 (a) M. Yamashita, Bull. Chem. Soc. Jpn., 2016, 89, 269; (b) Y.
Segawa, M. Yamashita and K. Nozaki, J. Am. Chem. Soc.,
2009, 131, 9201; (c) Y. Segawa, M. Yamashita and K. Nozaki,
Organometallics, 2009, 28, 6234; (d) K. Tanoue and M.
Yamashita, Organometallics, 2015, 34, 4011.
Nishibayashi, The University of Tokyo, for providing access to a
mass spectrometer.
14 (a) M. Hasegawa, Y. Segawa, M. Yamashita and K. Nozaki,
Angew. Chem. Int. Ed., 2012, 51, 6956; (b) Y. Masuda, M.
Hasegawa, M. Yamashita, K. Nozaki, N. Ishida and M.
Murakami, J. Am. Chem. Soc., 2013, 135, 7142.
15 (a) T. Miyada and M. Yamashita, Organometallics, 2013, 32,
5281; (b) T. Miyada, H. E. Kwan and M. Yamashita,
References
1
(a) Ullmann’s Polymers and Plastics, 4 Volume Set: Products
and Processes, Wiley-VCH: Weinheim, Germany, 2016; (b) Y.
Kissin, Alkene Polymerization Reactions with Transition Metal
Catalysts, Elsevier B. V.: Amsterdam, the Netherlands, 2008.
J. Falbe, H. Bahrmann, W. Lipps, D. Mayer and G. D. Frey,
Alcohols, Aliphatic in Ullmann’s Encyclopedia of Industrial
Chemistry, Wiley-VCH: Weinheim, Germany, 2013.
H. Zimmermann and R. Walzl, Ethylene in Ullmann’s
Encyclopedia of Industrial Chemistry, Wiley-VCH: Weinheim,
Germany, 2000.
Organometallics, 2014, 33, 6760; (c) A. F. Hill, S. B. Lee, J.
Park, R. Shang and A. C. Willis, Organometallics, 2010, 29
2
3
,
5661; (d) A. F. Hill and C. M. A. McQueen, Organometallics,
2014, 33, 1977.
16 (a) H. Ogawa and M. Yamashita, Dalton Trans., 2013, 42
625; (b) H. Ogawa and M. Yamashita, Chem. Lett., 2014, 43
664.
,
,
4
5
H. Zimmermann, Propene in Ullmann’s Encyclopedia of
Industrial Chemistry, Wiley-VCH: Weinheim, Germany, 2000.
D. H. James and W. M. Castor, Styrene in Ullmann’s
Encyclopedia of Industrial Chemistry, Wiley-VCH: Weinheim,
Germany, 2000.
17 (a) T.-P. Lin and J. C. Peters, J. Am. Chem. Soc., 2013, 135
,
15310; (b) T.-P. Lin and J. C. Peters, J. Am. Chem. Soc., 2014,
136, 13672.
18 N. Curado, C. Maya, J. Lopez-Serrano and A. Rodriguez,
Chem. Commun., 2014, 50, 15718.
19 J. F. Riehl, Y. Jean, O. Eisenstein and M. Pelissier,
Organometallics, 1992, 11, 729.
20 (a) A. Kumar and A. S. Goldman, Top. Organomet. Chem.,
2016, 54, 307; (b) S. Biswas, Z. Huang, Y. Choliy, D. Y. Wang,
M. Brookhart, K. Krogh-Jespersen and A. S. Goldman, J. Am.
Chem. Soc., 2012, 134, 13276; (c) A. Kumar and A. S.
Goldman, Abstracts of Papers, 245th ACS National Meeting &
Exposition, New Orleans, LA, United States, April 7-11, 2013,
INOR-1202; (d) D. C. Leitch, Y. C. Lam, J. A. Labinger and J. E.
Bercaw, J. Am. Chem. Soc., 2013, 135, 10302; (e) D. C. Leitch,
6
7
8
R. H. Crabtree, J. M. Mihelcic and J. M. Quirk, J. Am. Chem.
Soc., 1979, 101, 7738.
J. Choi, A. H. R. MacArthur, M. Brookhart and A. S. Goldman,
Chem. Rev., 2011, 111, 1761.
(a) M. Gupta, C. Hagen, R. J. Flesher, W. C. Kaska and C. M.
Jensen, Chem. Commun., 1996, 2083; (b) M. Gupta, C.
Hagen, R. J. Flesher, W. C. Kaska, R. E. Cramer and C. M.
Jensen, J. Am. Chem. Soc., 1997, 119, 840; (c) M. Gupta, W.
C. Kaska and C. M. Jensen, Chem. Commun., 1997, 461; (d)
W. W. Xu, G. P. Rosini, M. Gupta, C. M. Jensen, W. C. Kaska,
K. Krogh-Jespersen and A. S. Goldman, Chem. Commun.,
1997, 2273; (e) F. Liu and A. S. Goldman, Chem. Commun.,
1999, 655.
J. A. Labinger and J. E. Bercaw, Organometallics, 2014, 33
,
3353; (f) A. S. Goldman, R. Ahuja and W. Schinski, 2013,
Rutgers, The State University of New Jersey, USA,
US20130123552A; (g) D. F. Brayton, P. R. Beaumont, E. Y.
Fukushima, H. T. Sartain, D. Morales-Morales and C. M.
Jensen, Organometallics, 2014, 33, 5198; (h) D. Morales-
Morales, R. Ro, C. Yung and C. M. Jensen, Inorg. Chim. Acta.,
9
I. Goettker-Schnetmann, P. White and M. Brookhart, J. Am.
Chem. Soc., 2004, 126, 1804.
10 W. Yao, Y. Zhang, X. Jia and Z. Huang, Angew. Chem., Int. Ed.,
2014, 53, 1390.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 11 of 12
Journal Name
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
2004, 357, 2953; (i) W. Yao, Y. Zhang, X. Jia and Z. Huang,
Angew. Chem., 2014, 126, 1414; (j) Y. Shi, T. Suguri, C. Dohi,
H. Yamada, S. Kojima and Y. Yamamoto, Chem. Eur. J., 2013,
19, 10672; (k) G. E. Dobereiner, J. Yuan, R. R. Schrock, A. S.
(a) F. London, J. Phys. Radium, 1937,
8
, 397. (b) R. McWeeny,
Phys. Rev., 1962, 126, 1028. (c) R. Ditchfield, Mol. Phys.,
1974, 27, 789. (d) K. Wolinski, J. F. Hinton and P. Pulay, J. Am.
Chem. Soc., 1990, 112, 8251. (e) J. R. Cheeseman, G. W.
Goldman and J. D. Hackenberg, J. Am. Chem. Soc., 2013, 135
12572; (l) I. Goettker-Schnetmann and M. Brookhart, J. Am.
Chem. Soc., 2004, 126, 9330; (m) D. Bezier and M. Brookhart,
,
Trucks, T. A. Keith and M. J. Frisch, J. Chem. Phys., 1996, 104,
5497.
ACS Catal., 2014,
F. M. Dolgushin, M. G. Ezernitskaya, A. S. Peregudov, P. V.
Petrovskii and A. A. Koridze, Organometallics, 2006, 25
4, 3411; (n) S. A. Kuklin, A. M. Sheloumov,
,
5466; (o) Z. Huang, M. Brookhart, A. S. Goldman, S. Kundu, A.
Ray, S. L. Scott and B. C. Vicente, Adv. Synth. Catal., 2009,
351, 188; (p) K. Zhu, P. D. Achord, X. Zhang, K. Krogh-
Jespersen and A. S. Goldman, J. Am. Chem. Soc., 2004, 126
,
13044; (q) B. Punji, T. J. Emge and A. S. Goldman,
Organometallics, 2010, 29, 2702; (r) F. Liu, E. B. Pak, B. Singh,
C. M. Jensen and A. S. Goldman, J. Am. Chem. Soc., 1999,
121, 4086; (s) M. Findlater, J. Choi, A. S. Goldman and M.
Brookhart, Catal. Met. Complexes, 2012, 38, 113; (t) J. Choi,
A. H. R. MacArthur, M. Brookhart and A. S. Goldman, Chem.
Rev., 2011, 111, 1761; (u) J. Choi and A. S. Goldman, Top.
Organometa. Chem., 2011, 34, 139.
21 (a) D. Tanaka, S. P. Romeril and A. G. Myers, J. Am. Chem.
Soc., 2005, 127, 10323; (b) J. F. Hartwig, Elimination
Reactions in Organotransition Metal Chemistry: From
Bonding to Catalysis, University Science Books, Sausalito, CA.
2010.
22 W.-C. Shih, W. Gu, M. C. Maclnnis, S. D. Timpa, N.
Bhuvanesh, J. Zhou and O. V. Ozerov, J. Am. Chem. Soc.,
2016, 138, 2086.
23 C. M. Jensen, Chem. Commun., 1999, 2443.
24 M. W. Haenel, S. Oevers, K. Angermund, W. C. Kaska, H. J.
Fan and M. B. Hall, Angew. Chem. Int. Ed., 2001, 40, 3596.
25 C. Kabuto, S. Akine, T. Nemoto and E. Kwon, Nippon Kessho
Gakkaishi, 2009, 51, 218.
26 A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R.
Spagna, J. Appl. Crystallogr., 1999, 32, 115-119.
27 G. Sheldrick, Act. Cryst. Sec. A, 2008, 64, 112.
28 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L.
Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H.
Nakai, T. Vreven, J. A. Montgomery Jr, J. E. Peralta, F.
Ogliaro, M. J. Bearpark, J. Heyd, E. N. Brothers, K. N. Kudin,
V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
A. P. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi,
N. Rega, N. J. Millam, M. Klene, J. E. Knox, J. B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P.
Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö.
Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox,
Gaussian09, Revision D.01, Gaussian, Inc.: Wallingford, CT,
USA, 2013.
29 (a) A. D. Becke, Phys. Rev. A, 1988, 38, 3098. (b) C. Lee, W.
Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785. (c) B.
Miehlich, A. Savin, H. Stoll and H. Preuss, Chem. Phys. Lett.,
1989, 157, 200. (d) A. D. Becke, J. Chem. Phys., 1993, 98
5648.
,
30 (a) P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299.
(b) W. R. Wadt and P. J. Hay, J. Chem. Phys., 1985, 82, 284.
(c) P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 270.
31 S. Huzinaga, J. Andzelm, M. Klobukowski, E. Radzio-Andzelm,
Y. Sakai and H. Tatewaki, Gaussian basis sets for molecular
calculations, Elsevier, 1984.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 12 of 12
View Article Online
DOI: 10.1039/C6DT02075E
ARTICLE
Journal Name
Graphical abstract
12 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins