Bis(azido)palladium(II) Complexes Bearing an (R or S)-(BINAP) Ligand: Synthesis, Structures, and Catalytic Application to Suzuki–Miyaura C─C Coupling Reactions

Full text of DOI:10.1002/bkcs.11934

Note
DOI: 10.1002/bkcs.11934
BULLETIN OF THE
S. M. Choi et al.
KOREAN CHEMICAL SOCIETY
Bis(azido)palladium(II) Complexes Bearing an (R or S)-(BINAP)
Ligand: Synthesis, Structures, and Catalytic Application
to Suzuki–Miyaura C─C Coupling Reactions
‡
‡
Sun Myeong Choi,† Sera Lee,† Yong-Joo Kim,†,¶, Ji Hun Lee, Soon W. Lee, and
*
Jun-Chul Choi§,¶,
*
†Department of Chemistry, Kangnung-Wonju National University, Gangneung 210-702, South Korea.
*E-mail: yjkim@kangnung.ac.kr
‡Department of Chemistry, Sungkyunkwan University, Natural Science Campus, Suwon, South Korea
§National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
*E-mail: junchul.choi@aist.go.jp
¶These authors contributed equally to this work.
Received September 17, 2019, Accepted November 25, 2019
Keywords: BINAP, Palladium, Azido, Suzuki-Miyaura C─C coupling
Chiral ligand 2,20-bis(diphenylphosphino)-1,10-binaphthyl
(BINAP) is widely utilized as an ancillary ligand for late-
transition-metal complexes, especially for Ru and Rh
metals, in asymmetric organic catalysis.1,2 BINAP–Pd
palladium(II) (5). The ORTEP drawings clearly show the
(R)- or (S)-form of the complex. The naphthalene rings on
the BINAP ligand are perpendicular to each other, inducing
the C2 symmetry required for the complexes to be chiral. To
the best of our knowledge, these are the first examples in
which the structures of both the (R)- and (S)-forms of the
chiral (BINAP)Pd(II) azido complexes have been deter-
mined. The Pd─N3 bond lengths (2.07 Å) agree well with
those of known Pd azido complexes. 9,10
(II) complexes in particular have been intensively investi-
3,4
gated as catalysts for reactions such as amination
and
C─C coupling.5–7 However, it is worth noting that BINAP–
Pd(II) complexes containing a pseudohalogen ligand have
not been reported to exhibit C─C coupling activity, proba-
bly because of their poor solubility or low catalytic activity.
Our research group has continually investigated the syn-
thesis and catalytic properties of group 10 metal-
pseudohalogen complexes.8 As an extension of our investi-
gations into the scope of these complexes, we decided to
prepare BINAP–Pd(II) complexes containing an azido
ligand as a pseudohalogen group, expecting to find catalytic
activity in Suzuki–Miyaura C─C coupling reactions. We
report herein the synthesis, structures, and catalytic activity
of these complexes.
We examined the dipolar cycloaddition of the azido ligands
in complexes 4 and 6 with organic isothiocyanates [R–NCS;
R = Ph, (S)-(+)-CH(CH3)Ph, Me3Si], with the expectation of
affording five-membered heterocyclic rings in the products.
Consistent with our expectation, these complexes undergo
dipolar addition to phenyl or 1-phenyl ethyl iosthiocyanates to
afford bis(S-coordinated tetrazole–thiolato) Pd(II) complexes
8 and 9 (Eq. 1 in Scheme 3). Heating was required for the
reaction to proceed, which agrees well with previous reports,
in which the preparation of Pd(II) azido complexes containing
chelating ligands demands more vigorous conditions for small
molecule insertion than that of bis(tertiary phosphine)–Pd
(II) azido complexes.11 In contrast, room-temperature reactions
with trimethylsilyl isothiocyanate (TMS–NCS) proceeded
slowly to give the ligand-substituted bis(isothiocyanato)
Pd(II) complexes 10 (Eq. 2 in Scheme 3). The progress of the
above reactions can be readily monitored by the disappearance
of the IR absorption band of the starting compounds (6 and 7)
at ca. 2028 cm−1, indicating the formation of the S-coordinated
tetrazole–thiolato products (8 and 9). In addition, the appear-
ance of characteristic symmetric and asymmetric NCS bands
at 2107–2108 and 2078–2080 cm−1, respectively, can be used
to confirm the formation of isothiocyanato complexes, [(S)-
(Tol-BINAP)Pd(NCS)2] (10) (Eq. 2 in Scheme 3). The inde-
pendent reaction of complex 6 with an aqueous KSCN also
Our target complexes, chiral (BINAP)–Pd–bis(azido)
complexes, could be prepared in two steps. First, the
BINAP–Pd(II) chloro complexes, [(R)-(BINAP)PdCl2] (1),
[(S)-(BINAP)PdCl2] (2), and [(R)-(Tolyl-BINAP)PdCl2]
(3), were prepared in quantitative yields by substitution of
the acetonitrile ligands of [(CH3CN)2PdCl2] with BINAP,
as shown in Scheme 1.
In the second step, complexes 1–3 were treated with aque-
ous NaN3 to afford the corresponding Pd(II) azido com-
plexes in high yields (4–7 in Scheme 2). Isolated products
were characterized by spectroscopy (IR and NMR) and X-
ray diffraction. The IR spectra of complexes 4–7 exhibit
characteristic azide bands at 2028–2036 cm−1. These azido
complexes are readily solvated in CH2Cl2 or THF. Figures 1
and 2 show the molecular structures of cis-{(R)-BINAP)}bis
(azido)palladium(II) (4) and cis-{(S)-BINAP)}bis(azido)
Bull. Korean Chem. Soc. 2019
© 2019 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Wiley Online Library
1

Note
BULLETIN OF THE
ISSN (Print) 0253-2964 | (Online) 1229-5949
KOREAN CHEMICAL SOCIETY
Scheme 1. Ligand exchange with BINAP.
afforded complex 10 in high yield without the formation any
linkage isomers.
Figure 3 shows the molecular structure of complex 9. Two
tetrazole moieties lie above and below the molecular plane,
defined by phosphorus and two sulfur atoms. As expected,
the chirality of the BINAP ligand in complexes 4 and 9 is the
same (Figures 1 and 3).
Many (BINAP)Pd complexes are widely employed as
catalysts for asymmetric organic reactions. However, the
utility of neutral (BINAP)Pd-catalyzed C─C coupling reac-
tions as compared with that of ionic (BINAP)Pd complexes
has not been reported. In this context, we examined the
applicability of the (BINAP)Pd-pseudohalogen complexes
prepared in this study for catalyzing Suzuki–Miyaura C─C
coupling reactions.
To optimize the reaction, the coupling was performed
under various conditions in the presence of Pd catalyst (com-
plex 4, 1 or 0.5 mol %) as shown in Table 1. Entry 6 shows
the highest isolated yield of the biaryl product with a small
quantity of the (BINAP)Pd catalyst and a short reaction time.
Therefore, we applied this optimized condition to various
combinations of aryl bromides and phenyl boronic acid (entry
1–9) as well as aryl boronic acids (entry 10–13) as seen in
Scheme 4 and Table 2.
Figure 1. Molecular structure of compound 4ꢀ2(CH2Cl2). Atoms
labeled with “a” are related to the corresponding numbered atoms
by a two-fold rotation. Two co-crystallized dichloromethane mole-
cules are omitted for clarity. Selected bond lengths (Å) and bond
angles (ꢁ): Pd1–N1 2.070(5), Pd1–P1 2.267(1), N1–N2 1.185(8),
N2–N3 1.157(10); N1#1–Pd1–N1 89.4(3), N1#1–Pd1–P1 167.8
(2), N1–Pd1–P1 90.0(1), P1–Pd1–P1#1 93.17(6), N2–N1–Pd1
117.7(4), N3–N2–N1 176.5(8). Symmetry transformations used to
generate equivalent atoms: A = −x + 2, y, −z + 3/2.
was not afforded, maybe because the electron-rich 4-pyridyl
group hinders transmetallation necessary for the C─C cross-
coupling by reductive elimination. Therefore, we believe that
Table 2 shows relatively high yields when our (BINAP)Pd
complex was used for aryl bromides containing either acti-
vated or deactivated aryl groups, with the exception of entry
13, which afforded the homo coupled product. In the case of
entry 13, the expected product of the C─C cross-coupling
Figure 2. Molecular structure of compound 5ꢀ2(CH2Cl2). Atoms
labeled with “a” are related to corresponding numbered atoms by
a two-fold rotation. Selected bond lengths (Å) and bond angles
(ꢁ): Pd1–N1 2.071(6), Pd1–P1 2.268(1), N1–N2 1.194(9), N2–N3
1.169(10); N1A–Pd1–N1 90.7(3), N1A–Pd1–P1 89.15(17), N1–
Pd1–P1 168.3(2), P1–Pd1–P1A 93.32(7), N2–N1–Pd1 117.0(5),
N3–N2–N1 176.2(9). Symmetry transformations used to generate
equivalent atoms: A = −x + 1, y, −z + 1/2.
Scheme 2. Synthesis of (BINAP)Pd(II) azides.
Bull. Korean Chem. Soc. 2019
© 2019 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
2

BULLETIN OF THE
Note
KOREAN CHEMICAL SOCIETY
Scheme 3. Reactions of (R-BINAP)Pd(II) azide with R-NCS.
instead of C─C cross-coupling, homo coupling to give 4,40-
diacetylbiphenyl occurs under present conditions.
These results suggest that neutral (BINAP)Pd(II) azide
can be employed as efficient catalysts for Suzuki–Miyaura
C─C coupling reactions.
In summary, new chiral Pd(II) azido complexes having an
(R)- or (S)-(BINAP) ligand were synthesized and particularly
in the case of the (R)- and (S)-forms of the chiral (BINAP)Pd
(II) azido complexes were structurally characterized by spec-
troscopy and X-ray diffraction. The reactivity of these azido
complexes towards organic isothiocyanates depended on the
reaction conditions. These complexes were effective for cata-
lyzing Suzuki–Miyaura C─C coupling reactions. We also
reported the first example of Pd(II) pseudo-halogen complexes
containing chiral BINAP ligands, a potential precursor for
new types of heterocyclic tetrazole compounds, which can be
useful in other palladium-catalyzed organic transformation.
Figure 3. Molecular structure of compound 9ꢀ2(CH2Cl2). Selected
bond lengths (Å) and bond angles (ꢁ): Pd1–P2 2.273(1), Pd1–P1
2.296(1), Pd1–S2 2.387(1), S1–C45 1.720(5), S2–C54 1.714(4),
N1–N2 1.345(5), N1–C45 1.356(6), N2–N3 1.284(6), N3–N4 1.359
(5), N4–C45 1.339(5), N5–C54 1.339(6), N5–N6 1.352(5), N6–N7
1.293(6), N7–N8 1.355(5), N8–C54 1.365(5); P2–Pd1–P1 92.70(4),
P2–Pd1–S2 88.09(4), P1–Pd1–S2 165.09(4), S2–Pd1–S1 91.02(4).
Recrystallization from THF-diethyl ether or CH2Cl2-hexane
gave orange solids of [(R)-(BINAP)Pd(N3)2] (4, 0.310 g,
97%). Single crystals for X-ray crystallography were grown
from CH2Cl2-hexane at −35ꢁC.
Complexes [(S)-(BINAP)Pd(N3)2] (5, 95%), and [(R)-
(Tol-BINAP)Pd(N3)2] (6, 90%) were prepared analogously.
Reactions of Complexes 4 and 6 with R–NCS {(R = Ph),
(S)-(+)-1-Phenylethyl, Trimethylsilyl}. To a Schlenk flask
containing complex 4 (0.150 g, 0.18 mmol) THF (4 mL)
and
(S)-(+)-1-Phenylethyl
isothiocyanate
(48 μL,
Experimental
0.41 mmol) were added in that order. After stirring for 18 h
at 50ꢁC, volatiles in the reaction mixture were evaporated
under vacuum, and the resulting residues were washed with
All manipulations of air-sensitive compounds were per-
formed under N2 or Ar using standard Schlenk-line tech-
niques. The analytical laboratory at Kangwon National
University at Samcheok carried out elemental analyses with
Flash EA 1112 analyzers (Thermofisher Scientific, Bremen,
Germany). X-ray reflection data were obtained at the Korea
Basic Science Institute (Seoul, Korea). The (CH3CN)2PdCl2
was prepared by a modified literature method.13 Complexes
[(R)-(BINAP)PdCl2] (1), [(S)-(BINAP)PdCl2] (2), and [(R)-
(Tol-BINAP)PdCl2] (3) were analogously prepared from the
general ligand substitution using [Pd(CH3CN)2Cl2]13 with an
equivalent of the corresponding BINAP ligands.14
Table 1. Optimization reactions for the Suzuki–Miyaura cross-
coupling reactions of 4-bromo (or chloro) acetophenone with
phenyl boronic acid.
Isolated
yield (%)
Entry
Solvent
Base
R (ꢁC)
t (h)
1
2
3a
4
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
K2CO3
Cs2CO3
K2CO3
K2CO3
Na2CO3
K2CO3
K2CO3
K2CO3
50
50
50
50
50
50
50
50
2.0
2.0
1.0
1.0
1.0
1.0
1.0
1.0
99
64
31
93
85
99
65
86
5
6b
7c
8d
Preparation of [(R)-(BINAP)Pd(N3)2] (4), [(S)-(BINAP)
Pd(N3)2] (5), and [(R)-(Tol-BINAP)Pd(N3)2] (6). To a
Schlenk flask containing 1 (0.315 g, 0.39 mmol) CH2Cl2
(3 mL) and a NaN3 solution (0.077 g, 1.18 mmol) dis-
solved in H2O (3 mL) were added in that order. After stir-
ring for 18 h at room temperature, the solvent was
evaporated to give a pale orange solid, which was extracted
with CH2Cl2 and evaporated again to afford crude solids.
All 1 mol% unless stated.
a Under air.
b Cat. 0.5 mol %.
c 4-chloroacetophenone.
d Cat. is (BINAP)PdCl2.
Bull. Korean Chem. Soc. 2019
© 2019 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
3

BULLETIN OF THE
Note
KOREAN CHEMICAL SOCIETY
General Procedure for Suzuki–Miyaura Cross-Coupling
Reactions. For synthetic details and spectral data, see the
Appendix S1 (Supporting Information).
X-Ray Structure Determination. Details on X-ray structure
are described in Appendix S1.
Acknowledgments. This work was supported by Basic Sci-
ence Research Program through the National Research Foun-
dation of Korea (NRF) funded by the Ministry of Education,
Science and Technology (NRF-2016R1D1A3B03932228).
Scheme 4. Suzuki-Miyaura Cross-Coupling reactions.
Table 2. C─C coupling reactions of aryl bromide and aryl
boronic acid.
Supporting Information. Additional supporting informa-
tion may be found online in the Supporting Information
section at the end of the article.
Isolated
yield [%]
Entry
1
Aryl bromide
Product
99
References
2
3
68
93
1. S. Akutagawa, Appl. Cat. A. 2019, 21, 1737.
2. T. Ohkuma, N. Kurono, In Privileged Chiral Ligands and
Catalysts, Q.-L. Zhou Ed., Wiley-VCH, Verlag GmbH,
Weinheim, 2011, p. 1.
3. (a) J. F. Hartwig, Pure Appl. Chem. 2004, 76, 507.
(b) M. Kawatsura, J. F. Hartwig, J. Am. Chem. Soc. 2000,
122, 9546. (c) L. M. Alcazar-Roman, J. F. Hartwig,
A. L. Rheingold, L. M. Liable-Sands, I. A. Guzei, J. Am.
Chem. Soc. 2000, 122, 4618.
4
5
86
71
6
7
99
91
4. J. W. Faller, J. C. Wilt, Org. Lett. 2005, 7, 633.
5. M. Shibaski, M. Sodeoka, J. Synth, Org. Chem., Jpn. 1994,
52, 956.
6. A. Lei, X. Zhang, Org. Lett. 2002, 4, 2285.
7. M. Ogasawara, H. Ngo, T. Sakamoto, T. Takahashi, W. Lin,
Org. Lett. 2005, 7, 2881.
8
9
66
81
8. (a) K.-E. Lee, H.-T. Jeon, S.-Y. Han, J. Ham, Y.-J. Kim,
S. W. Lee, Dalton Trans. 2009, 6578. (b) Y.-J. Kim, J.-H. Lee,
T. Kim, J. Ham, Z. N. Zheng, S. W. Lee, Eur. J. Inorg. Chem.
2012, 6011. (c) H.-K. Kim, J.-H. Lee, Y.-J. Kim, Z. N. Zheng,
S. W. Lee, Eur. J. Inorg. Chem. 2013, 4958. (d) K.-W. Kim, Y.-
J. Kim, H. J. Lim, S. W. Lee, Bull. Kor. Chem. Soc. 2015, 36,
2952. (e) J.-H. Choi, K.-Y. Choi, Y.-J. Kim, H. J. Im, S. W. Lee,
Bull. Kor. Chem. Soc. 2017, 38, 812.
9. B. Bendiksen, W. C. Riley, M. W. Babich, J. H. Nelson,
R. A. Jacobson, Inorg. Chim. Acta 1982, 57, 29.
10. W. P. Fehlhammer, L. F. Dahl, J. Am. Chem. Soc. 1972,
94, 3377.
10
11
12
94
91
99
11. (a) Y.-J. Kim, Y.-S. Kwak, Y.-S. Joo, S. W. Lee, J. Chem.
Soc. Dalton Trans. 2002, 144. (b) Y.-J. Kim, J.-T. Han,
S. Kang, W. S. Han, S. W. Lee, Dalton Trans. 2003, 3357.
(c) Y.-J. Kim, X. Chang, J.-T. Han, M. S. Lim, S. W. Lee,
Dalton Trans. 2004, 3699.
12. Y. K. Kang, D. Y. Kim, Bull. Kor. Chem. Soc. 2008,
29, 2093.
13. R. Doyle, P. E. Slade, H. B. Jonassen, Inorg. Synth. 1960,
6, 218.
13a
50
a Homo coupling product, CH3C(O)-C6H4-C6H4-C(O)CH3.
hexane and diethyl ether. Recrystallization from CH2Cl2/
(diethyl ether) gave orange crystals of [(R)-(BINAP)Pd
{(SCN4(R)}2] (R = Ph) (8, 0.174 g, 86%).
Complexes, [(R)-(BINAP)Pd{(SCN4(R)}2] (R = CH(Me)
Ph) (9, 89%), and [(R)-(Tol-BINAP)Pd(NCS)2] (10, 68%)
were analogously prepared.
14. A. C. Véron, M. Felber, O. Blacque, B. Spingler, Polyhedron
2013, 52, 102.
Bull. Korean Chem. Soc. 2019
© 2019 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
4