Transfer semihydrogenation of alkynes catalyzed by imidazo[1,5-a]pyrid-3-ylidenepd complexes: Positive effects of electronic and steric features on N-heterocyclic carbene ligands

Article abstract of DOI:10.1246/BCSJ.20190333

To investigate the catalytic utility of the imidazo[1,5-a]pyrid-3-ylidene (IPC) ligand, Pd-catalyzed transfer semihydrogenation of alkynes with formic acid as a hydrogen source was conducted. The steric bulkiness of the substituent on N2 affected the configuration of the π-allyl moiety of the precatalyst of IPC-Pd-π-allyl complexes and the robustness of the catalytic process. The catalytic activities of IPC-Pd complexes were clearly higher than those of conventional NHC-Pd complexes.

Full text of DOI:10.1246/BCSJ.20190333

Document type: Article
Transfer Semihydrogenation of Alkynes Catalyzed
by Imidazo[1,5-a]pyrid-3-ylidene­Pd Complexes: Positive Effects
of Electronic and Steric Features on N-Heterocyclic Carbene Ligands
Fumitoshi Shibahara,* Takahiro Mizuno, Yoshifuru Shibata, and Toshiaki Murai*
Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University,
Yanagido, Gifu 501-1193, Japan
E-mail: fshiba@gifu-u.ac.jp
Received: November 13, 2019; Accepted: December 19, 2019; Web Released: December 26, 2019
Fumitoshi Shibahara
Dr. Fumitoshi Shibahara received a B.S. degree from Doshisha University in 1997. He obtained his Ph.D. in
organic chemistry from Kyoto University in 2003 under the guidance of Professor Kyoko Nozaki and the
supervision of Professor Hiyama. During this period, he worked as a research fellow in Professor Nozaki’s
group attached to Japan Science and Technology Agency (JST) for two and a half years from October 2000.
In April 2003, he was appointed an assistant professor at Gifu University. He visited Professor Michael J.
Krische’s group at University of Texas at Austin as a Donald D. Harrington Faculty Fellow from September
2
007 to August 2008. Currently, he is an associate professor at Gifu University.
R
Abstract
To investigate the catalytic utility of the imidazo[1,5-a]pyrid-
-ylidene (IPC) ligand, Pd-catalyzed transfer semihydrogena-
N
N
3
P
tion of alkynes with formic acid as a hydrogen source was con-
ducted. The steric bulkiness of the substituent on N2 affected
the configuration of the π-allyl moiety of the precatalyst of IPC-
Pd-π-allyl complexes and the robustness of the catalytic proc-
ess. The catalytic activities of IPC-Pd complexes were clearly
higher than those of conventional NHC-Pd complexes.
Figure 1. Similarity of Buchwald-type phosphine ligands
and 5-aryl IPCs.
Keywords: Imidazo[1,5-a]pyrid-3-ylidene ligand
j
acter; theoretical and spectral studies of IPCs actually confirmed
1
3
Semihydrogenation j Transfer hydrogenation
such π-accepting character. Alcarazo and Fürstner also report-
ed a π-accepting character as well as a σ-donating character of
the related IPC derivatives, though the discussion was based on
the orbital interaction of an additional paracyclophane struc-
Introduction
5
,14
Since the first example of imidazo[1,5-a]pyridine-based N-
heterocyclic carbenes (NHCs), namely imidazo[1,5-a]pyridyli-
dene (imidazopyridine carbenes: IPCs), was reported, they have
attracted much attention as a new class of stabilized carbenes.
Recently, there has been a growing interest in not only their
ture.
Consequently, their transition metal (TM) complexes
showed different reactivities than conventional NHC­TM com-
1
2­34
plexes.
In this regard, several groups have examined IPCs
1
­4
as alternatives to conventional NHC ligands in, for example,
1
5­19
cross-coupling-type reactions,
only a few productive examples.
but these efforts resulted in
5
­11
17­19
structural features, but also their electronic properties.
This
In addition, some reports
research has gradually revealed that the carbenes have non-
negligible π-accepting character that is mostly canceled by the
internal stabilization of vacant orbitals by the resonance effect
of the lone-pairs on adjacent nitrogen atoms in most conven-
on the use of IPC-TM complexes as π-acidic catalysts usually
gave productive results, which is one of the weaker areas of
catalysis with conventional NHC ligands due to their sole σ-
1
5,20­30
donating character.
Those observations encouraged us to
1
2,13
tional NHCs, while maintaining high σ-donating character.
further explore the use of IPC-TM complexes as π-acidic cata-
lysts. The steric environment is also an important feature of
IPCs, and 5-aryl-substituted compounds can be expected to
exert similar or even greater steric hindrance than a series of
In fact, we recently investigated the putative interaction of the
π*-orbital of the fused pyridine moiety and the vacant p-orbital
of carbene carbon in IPCs since they should overlap and make a
new accepting orbital that may show good π-accepting char-
1
9
Buchwald-type phosphine ligands (Figure 1), which may also
332 | Bull. Chem. Soc. Jpn. 2020, 93, 332–337 | doi:10.1246/bcsj.20190333
© 2020 The Chemical Society of Japan

meaningfully affect the catalytic activities. Herein we report the
synthesis and structural investigation of IPC­Pd π-allyl com-
plexes and their catalytic applications. The IPC-Pd complexes
catalyzed the transfer semihydrogenation of alkynes with for-
mic acid as a hydrogen donor, and the catalytic system showed
significantly higher activity than the related Pd complex of
conventional NHC reported by Elsevier.34
venient method for selectively obtaining Z-olefins, and the
reactions passed through ¢-hydride elimination of alkoxylate
or formate complexes to give hydride complex, migratory
insertion of alkyne into H-metal bond followed by alkene
Results and Discussion
Synthesis of Pd­Imidazo[1,5-a]pyrid-3-ylidene­π-allyl
Complexes. To investigate the fundamental electronic and
steric effects, 5-phenyl-N-Me or -N-Mes IPC 1a and 1b as well
as 5-unsubstituted 1c were selected to minimize the effects of
the auxiliary functional groups. The IPC precursors 1a­c were
N
N
2
.96 - 3.25 Å
Cl
2
,12,13
Pd
prepared according to previously reported procedures.
With these IPC precursors in hand, we obtained the correspond-
ing IPC­Pd­π-allyl complexes 3 by a conventional method,
complexation with Ag O followed by transmetallation to
2
[
Pd(π-allyl)Cl] , as shown in Scheme 1. The syntheses of 3a
2
and 3b from 5-arylated IPC precursors 1a and 1b were com-
pleted, and the corresponding IPC­Pd­π-allyl complexes were
obtained in high yields via two steps. We performed X-ray
structure analyses of these complexes (Figure 2). Both com-
plexes showed less than the sum of van der Waals radii of Pd
and C atoms distance between the C5 aryl group of IPC and Pd
3
a
3
5
center (<3.33 ¡), thus existence of the intramolecular inter-
action of Pd and the aryl group is implied. These interactions
are very similar to those in the case of Pd-Buchwald phosphine
N
3
6
ligand complexes. The coordination plane of Pd and the
imidazopyridine plane were almost orthogonal. In addition, the
substituents on N2 in the imidazopyridine ring significantly
influenced the conformation of the π-allyl group on the Pd
center, and, in complex 3a, which has a less sterically hindered
methyl group at the N2 position of IPC, the π-allyl moiety was
highly disordered, though such disorder was scarcely observed
N
3
.05 - 3.32 Å
Pd
9
Cl
in complex 3b. On the other hand, the complexation of ster-
ically less-hindered IPC precursor 1c failed, and gave a com-
plex mixture. Analysis of the crude mixture of the reaction by
ESI-MS mainly indicated two IPC coordinated complexes
along with the reductive elimination product, N-methyl-3-allyl-
imidazopyridinium (Figure 3).
Transfer Semihydrogenation of Internal Alkynes Cata-
lyzed by IPC-Pd Complexes. Pd-catalyzed transfer semi-
hydrogenation of alkynes with a hydrogen donor is a con-
3b
Figure 2. ORTEP drawings of 3a and 3b with thermal
ellipsoids at 50% probability. One of the disordered π-allyl
groups on 3a is omitted for clarity. The full structure of 3a
is shown in the Supporting Information.
N
Me
N
Pd
+
N
Me
Me
N
N
N
X
R
Ag
CH
rt, 3.5 h
O (0.90 equiv)
N
R
2
N
N
N
2
Cl , dark,
2
AgI
Ar
Ar
N
Me Exact Mass: 370.0404
Exact Mass:
73.1079
N
1
1
1
1
a R = Me Ar = Ph
2a quant
2b 91%
Pd
b
c
Mes
Me
Ph
H
N
Me
N
2c
52%
Exact Mass: 279.0108
Pd
Me
N
N
[
Pd( allyl)Cl]
2
N R
N
(0.50 equiv)
Pd
Exact Mass: 411.0796
CH
2
Cl
2
, dark, rt, 3.5 h
Ar
Cl
3
3
3
a
b
c
80%
89%
complex mixture
Figure 3. ESI-MS spectrum (not calibrated) for the crude
mixture in the synthesis of Pd-IPC complex 3c.
Scheme 1. Synthesis of IPC­Pd­π-allyl complexes 3a­c.
Bull. Chem. Soc. Jpn. 2020, 93, 332–337 | doi:10.1246/bcsj.20190333
© 2020 The Chemical Society of Japan | 333

+
CO2
HCOO–
L’
L’
L’
O
R1
L Pd
L Pd H
Pd
O
R1
-
elimination
L
R2
H
R2
R1
R2
H
R1
L’
L’
H
protonolysis
H
H
Pd
Pd
migratory
insertion
R2
L
L
R1
R1
R1
H
H+
R2
R2
R2
Scheme 2. Generally Accepted Catalytic Cycle for the Pd-
catalyzed Transfer Semihydrogenation of Internal Alkynes.
N
N
HCOOH (5.5 equiv)
Pd
Figure 4. Reaction profiles of the semihydrogenation of 4
with different amounts of water. The reactions were con-
ducted in CH3CN (16 mL) on a 2.7 mmol scale. The yields
were determined by GC-FID analysis with mesitylene as
an internal standard.
N(C H ) (5.5 equiv)
2
5 3
Pd-cat. (1 mol %)
PPh3 (2 mol %)
Cl
H
H
3b: 61%
Ph
Me
CH CN, 70 °C, 100 min
3
Ph
Me
4
5
N
N
Pd
Cl
IMes: 43%34
Scheme 3. Very initial screening of the reaction: stock
distilled AN was used. The AN had been distilled more
than a year ago.
elimination via protonolysis or σ-bond metathesis with hydro-
gen donors (alcohol or formic acid) (Scheme 2). These respec-
tive processes, in particular ¢-hydride elimination and migra-
tory insertion, would be accelerated by a π-acidic catalyst.
Therefore, we choose this reaction to test the potential of the
IPC­Pd complexes as π-acidic catalysts.
Initially, we conducted the reactions of phenylprop-1-yne (4)
(
2.7 mmol) with IPC­Pd complex 3b (1 mol %), and PPh (2
3
Figure 5. Reaction profiles of the semihydrogenation of 4
with IPCs 3. The result with IMes-Pd complex was taken
from ref. 34.
mol %), triethylamine (5.5 equiv), and formic acid (5.5 equiv)
in acetonitrile (AN) (16 mL) according to the previous Elsevier
system (Scheme 3).34 The reaction likely proceeded faster than
that with the previous conventional NHC­Pd complex. Mean-
while, in the initial rough investigations, we realized that the
reaction behavior sensitively changed with the conditions of
the AN used in our system, and in particular with the content of
water, though the actual reason is still unclear. For example, the
isomerization and overreduction of generated alkene proceeded
under rigorously anhydrous conditions rather than unpurified
conditions. To check this behavior, we added a small and con-
stant amount of water to freshly opened commercially available
dehydrated AN (Kanto Chemical), and plotted the respective
reaction profiles (Figure 4). The reaction proceeded rapidly in
AN and reached almost 100% yield of Z-phenylprop-1-ene (5)
after 100 min, but, after the reaction was complete, the amount
of generated 5 immediately and rapidly decreased due to
isomerization to thermodynamically stable E-olefin and over-
reduction to phenylpropane (yields were not determined). On
the other hand, the addition of 20 ¯L of water (to 16 mL of AN)
suppressed such undesired side reactions. Although the reac-
tivities significantly dropped in the presence of too much water
reached completion. The purities of formic acid and triethyl-
amine did not influence the reaction behavior under our system.
Therefore, to gain satisfactory reproducibility, we carried out
all reactions with a constant amount of water-added dry AN.
With the reaction conditions in hand, we then screened the
catalysts by using the reaction of phenylprop-1-yne (4)
(Figure 5). To compare the results to those with the previous
IMes­Pd system, the figure also shows data taken from the
3
4
Elsevier study. The in situ-generated complex 3c showed the
fastest initial reaction rate, but after the reaction was complete,
the yield of 5 significantly dropped and E-olefin and over-
reduction product were mainly obtained. On the other hand, the
reaction with both complexes 3a and 3b gave product 5 with
good efficiency, and bulkier 3b showed a slightly faster initial
reaction rate. The initial rates of the reactions of all complexes
3 were faster than those in the previously reported IMes­Pd
system. To check the effect of water addition in the IMes-Pd
system, the reaction with that under our conditions was also
conducted whereas the situation did not significantly change,
and showed rather decreased efficiency (100 min, 33% yield).
(
i.e., 1000 ¯L to 16 mL of AN), the reaction still proceeded
and chemoselectivity was maintained even when the reaction
334 | Bull. Chem. Soc. Jpn. 2020, 93, 332–337 | doi:10.1246/bcsj.20190333
© 2020 The Chemical Society of Japan

HCOOH (5.5 equiv)
NEt3 (5.5 equiv)
Table 1. Transfer Semihydrogenation of Alkynes Catalyzed
by 3ba
3b (1 mol%)
H
H
HCOOH (5.5 equiv)
NEt3 (5.5 equiv)
PPh (2 mol%)
3
C H
C H
3 7
3
7
MeCN, 70 °C, 14 h
87%(NMR yield)
C H
3
C H
3
N Mes
Pd
7
7
3b (1 mol%)
H
H
N
Z-only
PPh3 (2 mol%)
Ph
R
MeCN, 70 °C, time
Ph
R
Scheme 4. Reaction of 4-octyne.
Cl
3b
catalytic activity with most of the alkynes than the conven-
tional NHC­Pd system. An aliphatic internal alkyne, 4-octyne
also underwent the semihydrogenation to give Z-4-octene
without loss of efficiency though the reaction time was not
optimized (Scheme 4). In this case, isomerization of the olefin
and over reduction were not observed at all even after elon-
gated reaction time. Overall, the reaction system likely indicat-
ed better Z-selectivity than the previous IMes system, whereas
as in Figure 4, the isomerization and overreduction processes
were obviously inhibited by addition of water. Therefore, the
water probably affected inhibition of re-coordination of gener-
ated Z-alkenes to result in better selectivities as like the effect
Time
Z-yield
(%)
Z-selectivity
(%)
Entry
R
(h)
1
2
3
4
5
6
7
8
Me
Et
Ph
9(24)
1.5
5(24)
1
2(48)
1(2)
2(3)
4
98(92)
89
99(99)
97
99(99)
®
99(75)
b
H
ND
COOH
CH2OH
COOMe
COMe
68(45)
89(92)
79(85)
99
95(71)
97(92)
95(93)
99(E)
aReaction conditions: CH3CN (5.8 mL), HCOOH (0.21 mL,
.5 mmol), NEt3 (0.76 mL, 5.5 mmol), H2O (8 ¯L), alkyne
1 mmol), 3b (1 mol %), PPh3 (2 mol %) and mesitylene
internal standard for GC) at 70 °C under an Ar atmosphere.
5
(
(
of addition of PPh in the previous system.
3
Conclusion
The solution was bubbled with Ar for 5 min to degas. The
reactions were monitored by GC-FID and GC-MS, and the
yields were determined by GC-FID calibrated with mesitylene
as an internal standard. The reaction times shown were those
required to reach maximum yield at the time of sampling. The
numbers in parentheses are those for the reaction with the
In conclusion, imidazo[1,5-a]pyridine-derived carbene
ligands were shown to be effective in the Pd-catalyzed semi-
hydrogenation of alkynes. Probably due to the π-accepting
character of the ligand, the corresponding IPC­Pd complexes
showed significantly higher activity than the conventional
IMes-Pd complex. The steric bulkiness of the IPC likely affect-
ed the robustness of the complex as well as its catalytic activity.
These results strongly suggest a new direction for the use of
IPC in TM catalyses. Further explorations of catalyses with
IPC as a ligand are underway in our laboratory.
34
IMes-Pd system taken from the previous Elsevier report.
b
Polymerization mainly took place.
Next, by using complex 3b, which showed the most balanced
reactivity among the present catalysts, we treated several
alkynes under this catalytic system (Table 1). The yield of the
reaction of 4 reached 98% after only 9 h, and the Z-selectivity
was almost perfect, while the reaction with IMes­Pd catalyst
reached full conversion after 24 h with similar selectivity
Experimental
General Remarks. All reagents were purchased from com-
mercial sources and used without further purification. Solvents
were distilled over appropriate drying reagents and degassed
via bubbling of Ar gas for 30 min. Dehydrated acetonitrile
was purchased from Kanto Chemical and used as received.
Conversions and yields of the semihydrogenation of alkynes
(
Entry 1). The reaction of phenylbut-1-yne also gave the prod-
uct in high yield (Entry 2). Diphenyl acetylene is known to be a
difficult substrate in this reaction, but the reaction took place
quantitatively in our system, and the yield of the product
reached 99% after only 5 h (Entry 3). This result was in sharp
contrast to the results of the reaction with the IMes­Pd system.
On the other hand, the reaction of phenylacetylene reached
full conversion after 1 h, but no desired styrene was obtained;
instead, only a polymeric material was generated (Entry 4).
Although the use of phenylpropiolic acid as a substrate signifi-
cantly reduced the efficiency and selectivity under the previous
IMes-Pd system, the corresponding Z-phenylpropenoic acid
was obtained in good yield with high Z-selectivity under the
present 3b system (Entry 5). With phenylpropynol and methyl
1
were checked by GC-FID analysis as well as H NMR of crude
mixtures. The retention times in the GC analysis of substrates
and products were checked via the coexistence of commercial
authentic samples as well as GC-MS analysis under identical
conditions. The supplementary crystallographic data for this
paper can be obtained free of charge from The Cambridge
Crystallographic Data Centre at CCDC 1957782 (3a) and
CCDC 1957781 (3b).
General Procedure for the Synthesis of NHC-Pd(π-allyl)-
Cl Complexes. To a solution of imidazo[1,5-a]pyridinium salt
in anhydrous CH Cl (0.1 M) was added Ag O (1.0 equiv) at
2
2
2
3
-phenylpropiolate, the time to full conversion was shorter than
room temperature under an argon atmosphere and the mixture
was stirred under light-shielding conditions at room temper-
ature for 14­17 h (overnight). The reaction mixture was then
filtered and the filtrate was concentrated in vacuo. The residue
which mainly contained IPC-Ag complex was used for the next
reaction without further purification. The yields shown in
Scheme 1 are based on the quantity of unpurified material. To a
that in the previous IMes system, but the yields were slightly
reduced though the selectivities were maintained (Entries 6
and 7). Finally, methyl(phenylethynyl)ketone also gave semi-
hydrogenated product, but spontaneous isomerization to E-
olefin took place to give the olefin in almost quantitative yield
(Entry 8). Overall, the present system clearly showed higher
Bull. Chem. Soc. Jpn. 2020, 93, 332–337 | doi:10.1246/bcsj.20190333
© 2020 The Chemical Society of Japan | 335

solution of the residue in anhydrous CH Cl2 (0.25 M) was
61, 6207.
2
added [Pd(π-allyl)Cl] (0.5 equiv) at room temperature under
3
4
S. Würtz, F. Glorius, Acc. Chem. Res. 2008, 41, 1523.
J. Iglesias-Sigüenza, C. Izquierdo, E. Díez, R. Fernández,
2
an argon atmosphere and the mixture was stirred under light-
shielding conditions at that temperature for 14­17 h (over-
night). The reaction mixture was filtered through a Celite plug
and the filtrate was evaporated in vacuo to give the correspond-
ing IPC-Pd(π-allyl)Cl complexes.
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6
Chloro(π-allyl)(2-methyl-5-phenylimidazo[1,5-a]pyridine-
2
3
-ylidene)palladium(II) (3a).
0.3 mmol scale, 80% yield
7
(
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3
1
1
5
132, 3098, 3043, 2941, 1896, 1772, 1651, 1574, 1540, 1507,
488, 1453, 1441, 1368, 1315, 1291, 1272, 1157, 1122, 1078,
020, 1000, 953, 928, 877, 784, 765, 717, 707, 651, 643, 617,
8
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9
R. Lyapchev, P. Petrov, M. Dangalov, N. G. Vassilev,
¹
1 1
60 499, 481 cm ; H NMR (CDCl ) (mixture of conformers
3
J. Organomet. Chem. 2017, 851, 194.
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H), 2.06 (d, 11.7 Hz, 0.4H), 2.14 (d, J = 13.5 Hz, 1H), 2.72
br, 0.4H), 2.95 (d, J = 13.5 Hz, 0.4H), 3.02 (d, J = 5.8 Hz,
1
0
K. Azouzi, C. Duhayon, I. Benaissa, N. Lugan, Y. Canac, S.
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(
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1
1
H), 3.66 (brm, 0.4H), 3.77 (br, 0.4H), 3.96 (d, J = 7.2 Hz,
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Hz, 1H), 6.36 (br, 0.4H), 6.45 (d, J = 6.3 Hz, 1H), 6.81­6.84
(
8
m, 1.4H), 7.26­7.42 (m, 7.4H), 7.61 (brs, 0.4H), 8.11 (s, 1H),
.54 (s, 1H); C NMR (CDCl ) (mixture of conformers regard-
3
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3
1
4
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ing direction of π-allyl group) δ 40.3, 49.5, 50.1, 69.4, 71.8,
12.4, 113.1, 114.1, 114.4, 114.8, 116.7, 121.8, 127.8, 128.4,
28.8, 129.4, 130.0, 130.6, 133.0, 135.3, 139.8, 171.7; MS
1
1
1
5
+
¹ +
(ESI): m/z exact mass calcd for C H N Pd ([M ¹ Cl ] )
17 17 2
1
6
3
55.0421; found: 355.0425.
Chloro(π-allyl)(2-mesithyl-5-phenylimidazo[1,5-a]pyridine-
-ylidene)palladium(II) (3b). 0.3 mmol scale, 81% yield
1
7
3
(
3
1
9
5
from 1b) as a yellow solid. mp 113.4 °C (dec.); IR (KBr) 3434,
1
8
117, 3072, 3019, 2915, 1763, 1651, 1607, 1540, 1490, 1441,
365, 1337, 1308, 1274, 1264, 1199, 1166, 1072, 1032, 992,
37, 918, 893, 853, 782, 760, 733, 709, 700, 679, 634, 620,
1
9
2
019, 9, 8110.
¹
1 1
92, 567, 527, 499 cm ; H NMR (CDCl ) (mixture of con-
3
20 A. Schmidt, N. Grover, T. K. Zimmermann, L. Graser, M.
formers regarding direction of π-allyl group) δ 1.13 (br, 1H),
.8­2.0 (m, 4.8H), 2.10­2.40 (m, 11.2H), 3.01 (m, 1.6H), 3.65
m, 1.6H), 4.04 (br, 0.6H), 4.68 (br, 1H), 6.51 (br, 1.6H), 6.86­
Cokoja, A. Pöthig, F. E. Kühn, J. Catal. 2014, 319, 119.
T. K. Meister, J. W. Kück, K. Riener, A. Pöthig, W. A.
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22 D.-A. Park, J. Y. Ryu, J. Lee, S. Hong, RSC Adv. 2017, 7,
52496.
1
(
2
1
6
.93 (m, 5.2H), 7.31­7.52 (m, 10.2H), 8.44 (br, 0.6H);
C NMR (CDCl3) (mixture of conformers regarding direction
13
of π-allyl group) δ 17.4, 18.8, 21.1, 49.4, 51.2, 71.1, 111.9,
13.5, 115.2, 115.4, 116.9, 122.4, 128.1, 128.7, 129.5, 133.4,
35.2, 136.4, 136.8, 138.9, 140.6, 174.2; MS (ESI): m/z exact
23 C. B. Schwamb, K. P. Fitzpatrick, A. C. Brueckner, H. C.
Richardson, P. H.-Y. Cheong, K. A. Scheidt, J. Am. Chem. Soc.
2018, 140, 10644.
24 Y. Tang, I. Benaissa, M. Huynh, L. Vendier, N. Lugan, S.
Bastin, P. Belmont, V. César, V. Michelet, Angew. Chem., Int. Ed.
1
1
+
¹ +
mass calcd for C H N Pd ([M ¹ Cl ] ) 459.1047; found:
2
5
25
2
4
59.1048.
2
019, 58, 7977.
A. P. Prakasham, M. K. Gangwar, P. Ghosh, Eur. J. Inorg.
Chem. 2019, 295.
2
5
We are grateful for financial support from JSPS KAKENHI
grant 18H04245 in the context of ‘Precisely Designed Catalysts
with Customized Scaffolding.’
2
6
R. Nakano, K. Nozaki, J. Am. Chem. Soc. 2015, 137,
1
0934.
2
7
W. Tao, S. Akita, R. Nakano, S. Ito, Y. Hoshimoto, S.
Supporting Information
Ogoshi, K. Nozaki, Chem. Commun. 2017, 53, 2630.
S. Akita, R. Nakano, S. Ito, K. Nozaki, Organometallics
018, 37, 2286.
H. Yasuda, R. Nakano, S. Ito, K. Nozaki, J. Am. Chem. Soc.
018, 140, 1876.
W. Tao, X. Wang, S. Ito, K. Nozaki, J. Polym. Sci., Part A:
Full details of X-ray diffraction analysis data of 3a and 3b.
Spectral data for 1a and 1b. Copies of H NMR and C NMR
for 1a, 3a, and 3b. This material is available on https://doi.org/
2
8
1
13
2
2
2
9
1
0.1246/bcsj.20190333.
3
0
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