A Macrocyclic Gold(I)–Biphenylene Complex: Triangular Molecular Structure with Twisted Au2(diphosphine) Corners and Reductive Elimination of [6]Cycloparaphenylene

Article abstract of DOI:10.1002/ange.202005482

The digold(I) complex [Au₂Cl₂(Cy₂PCH₂PCy₂)] reacts with 4,4′-diphenylene diboronic acid to form a triangular macrocyclic complex with twisted Au-P-C-P-Au groups at the three corners. The synthesis of

Full text of DOI:10.1002/ange.202005482

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Titel: Macrocyclic Gold(I)-biphenylene Complex: Triangular Molecular
Structure with Twisted Au2(diphosphine) Corners and Reductive
Elimination of [6]Cycloparaphenylene
Autoren: Yoshitaka Tsuchido, Ryota Abe, Tomohito Ide, and Kohtaro
Osakada
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Zitierweise: Angew. Chem. Int. Ed. 10.1002/anie.202005482
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10.1002/ange.202005482
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Macrocyclic Gold(I)-biphenylene Complex: Triangular Molecular
Structure with Twisted Au2(diphosphine) Corners and Reductive
Elimination of [6]Cycloparaphenylene
Yoshitaka Tsuchido*,[a] [b] Ryota Abe,[a] Tomohito Ide,[c] and Kohtaro Osakada*[a]
Abstract: The digold(I) complex [Au2Cl2(Cy2PCH2PCy2)] reacts
with 4,4'-diphenylene diboronic acid to form triangular
A dinuclear arylgold(I) complex with a diphosphine ligand
[Au2(C6H4-F-4)2(dppm)] (dppm bis(diphenylphosphino)
a
=
macrocyclic complex with twisted Au-P-C-P-Au groups at the
three corners. The synthesis of the complex and its chemical
oxidation produced [6]cycloparaphenylene ([6]CPP) in 59%
overall yield.
methane) was recently reported to cause reductive elimination of
4,4’-difluorobiphenyl upon oxidation with PhICl2.[7] The reaction
involves the oxidative chlorination of two Au(I) centers, the
intramolecular migration of an aryl ligand, forming
a
chloro(diaryl)gold(III) center, and 1,1-reductive elimination of
biaryl (Scheme 1). This new kind of C(sp2)–C(sp2) bond-forming
reaction can be extensively applied to synthesis of conjugated
oligo- aromatic compounds. [8]
Organogold complexes have attracted attention because of both
their characteristic structures and properties potentially useful in
catalysis, liquid crystals, devices, bioimaging, and therapies.[1]
Gold(III) complexes have common square-planar structures, but
they attracted much less attention than complexes of Pt(II), the
other 5d8 metal.[2] Gold(I) prefers linear two-coordinated structure,
and forms dinuclear complexes with diphosphine ligands such as
α,ω-bis(diphenylphosphino)alkanes, which are normally used as
chelating ligand.[3,4] Aurophilicity between two Au(I) centers
stabilizes the molecular structure and conformation with close
Au(I) positions (Au–Au distance of about 3.0 Å).[5] Multinuclear
organogold(I) complexes with such components are expected to
Cl
Cl
Ph
Ar
Ph
Ph2
P
Ph
Ar
Ar
Ph
Ph
AuI
AuIII Ar
AuII
P
PhICl2
P
Ar Ar
AuI
AuII
P
Ar
AuI
P
P
Ar
Ph
Ph2
Ph
Cl
Ph
Cl
Scheme 1. C-C bond formation from Au2 complex, reported in ref 7.
Over this past decade, the successful synthesis of
[n]cycloparaphenylenes ([n]CPP where n is number of phenylene
group) and related macrocyclic p-conjugated compounds have
been reported from the less-strained macrocyclic precursors,
which are formed by using an efficient C(sp2)–C(sp2) bond
formation as summarized in Scheme 2. Jasti[9a] (Scheme 2a) and
Itami[9b] (Scheme 2b) independently reported successful
synthesis of CPP. They employed Pd-catalyzed Suzuki coupling
reaction of acyclic precursors and aromatization of the resulted
have unique structures. Figure
1 summarizes macrocyclic
complexes having more than two Au(I)–C bonds.[6]
macrocyclic
organic
molecules
with
1,4-
dimethoxycyclohexadiene or 1,4-bis(alkoxy)-2,5-cyclohexadiene
groups. Yamago isolated square-shaped tetraplatinum
complexes having four biphenylene-4,4’-diyl ligands, [Pt(C6H4-
C6H4)(dppf)]4 (dppf = 1,1’-bis(diphenylphosphino)ferrocene) and
obtained [8]CPP from oxidation of the complex (Scheme 2c).[10]
The reaction was developed to less-strained macrocyclic
diplatinum precursors with aromatizable units in the ligand and its
transformation into the cyclic polyaromatic compounds.[11] Owing
to the square planar coordination geometry of platinum center,
these Pt(II) complexes were formed via 4+4 self-assembly, and
functioned as the precursors of [4n]cycloparaphenylene
derivatives. Isobe applied the reaction for the synthesis of the
narrow sidewall segments of chiral carbon nanotubes.[12] Although
these are few examples of 3+3 self-assembled system have also
been reported by using an organic linker with a bent structure,[13]
a direct synthetic way for non-substituted cycloparaphenylene
composed of less than seven phenylene groups has not been
developed.
Figure 1. Macrocyclic complexes composed of Au(I)-C bonds.
[a]
[b]
Dr. Y. Tsuchido, R. Abe, Prof. Dr. K. Osakada
Laboratory for Chemistry and Life Science, Institute of Innovative
Research, Tokyo Institute of Technology
4259-R1-3 Nagatsuta, Midori-ku, Yokohama, 226-8503 (Japan)
Dr. Y. Tsuchido
Department of Chemistry, Faculty of Science, Tokyo University of
Science
Kagurazaka 1-3, Shinjuku-ku, Tokyo, 162-8601 (Japan)
E-mail: tsuchido@rs.tus.ac.jp
[c]
Dr. T. Ide
Department of Chemical Science and Engineering, National Institute
of Technology, Tokyo College
1220-2 Kunugida-machi, Hachioji-shi, Tokyo, 193-0997 (Japan)
Supporting information for this article is given via a link at the end of
the document
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10.1002/ange.202005482
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(a) Bertozzi & Jasti
Cy
Cy
Cy
Cy
MeO
OMe
P
P
I
+
I
B(pin)
Pd
MeO
MeO
MeO
MeO
Na
C10H8
Au Au
n
B(OH)2
B(OH)2
cat.
Cy
Cy
Cy
Cl
P
Au
Cs2CO3
OMe
MeO
+
(1)
n
P
Au Cl
Tol/EtOH/H2O
50 oC, 20 h
B(pin)
OH
OMe
[9]CPP (n = 1) 43%
[12]CPP (n = 2) 52%
[18]CPP (n = 4) 36%
Cy
MeO
Cy
P
Cy
P
Au
Au
Au
Au
1
Cy
Cy
2% (n = 1),10% (n = 2),
10% (n = 4)
(b) Itami
P
OH
P
(pin)B
2 (77%)
Cy
Cy
Cy
Cy
OH
RO
+
OH
RO
I
RO
C1
B(pin)
I
Pd
cat.
(b)
(a)
RO
pTsOH
P1’ P1
Au1’
C3’
Au1
C3
OR
P1
C1
2
Au1
OR
OR
HO
C3
[12]CPP
62%
OR
HO
HO
P1’
Au2
51%
HO
Au1’
C4
C5
P2
C2
P3
Au3’
(R = MOM)
P3’
C2’
P2’
C4
C4’
Au2
P3
P2
Au2’
Au3
(c) Yamago
Au2’
C5
C5’
P3’
P2’
Pt
Pt
C2
SnMe3
C2’
Au3
Au3’
1) dppf
91%
Cl
Pt
+
Cl
2) Br2
SnMe3
Pt
Pt
[8]CPP
49%
Figure 2. ORTEP drawing of complex 2 (30% level of probability): (a) top
view, (b) side view. Hydrogen atoms are omitted for clarity. Selected atom
distances and angles: Au1-Au1' 3.1799(11) Å, Au2-Au3 3.0696(8) Å, C3-
Au1-P1 177.9(4)o, C4-Au2-P2 169.5(5)o, C5-Au3-P3 178.1(5)o, Au1-P1-
C1 113.1(5)o, Au2-P2-C2 108.7(4)o, Au3-P3-C3 111.9(5)o, P1-C1-P1'
110.5(11)o, P2-C1-P3 115.1(7)o.
57%
Cy
Cy
Cy
Cy
(d) This work
P
P
Au Au
B(OH)2
Cy
Cy
Cy
Cs2CO3
PhICl2
Cl
P
Au
+
P
Au Cl
Cy
Cy
P
Cy
Cy
Cy
P
Au
Au
Au
B(OH)2
The triangle-shaped molecule is composed of three
biphenylene ligands as the sides and three Au2(dcpm) units at the
corners with torsion angles between Au–C bonds of 58.5o (C4-
Au2 and Au3-C5) and 48.7o (C3-Au1 and Au1'-C3'). Pairs of Au(I)
centers bonded by a dcpm ligand are close to each other with
distances of 3.1799(11) (Au1-Au1’) and 3.0696(8) Å (Au2-Au3).
The molecule maintains the above structure in C2H2Cl4 solution,
as indicated by an absorption peak at 300 nm and fluorescence
at 376 nm with φF = 0.05,[15] which are assigned to ligand-to-
metal-metal charge transfer (LMMCT) between a phenylene
group and the neighboring Au(I)2 unit.[16] The reaction in Eq 1
afforded the complex with the macrocyclic structure rather than
an acyclic one. The aurophilicity between two Au(I) centers
stabilizes its triangular-shaped molecular structure. The dihedral
angle between two Au–P bond of organogold complex with dcpm
ligand is regulated as around 60o by strong auric interaction,
which provides the selective formation of the triangular
hexagold(I) complex (2).
Au
[6]CPP
76%
P
P
77%
Cy
Cy
Cy
Cy
✓ Direct synthesis of small cycloparaphenylene (e.g. [6]CPP) ✓ High overall yield
✓ Short reaction steps ✓ Recovery of starting digold complex
Scheme 2. Synthetic methods of [n]cycloparaphenylenes ([n]CPPs). (a)
Bertozzi/Jasti method,[9a] (b) Itami method,[9b] (c) Yamago method,[10] (d)
This work.
A macrocyclic trinuclear transition metal complex with linear
oligophenylene-4,4’-diyl ligands should have a strained molecular
structure, but it would undergo reductive elimination of
cycloparaphenylenes whose number of phenylene groups is a
multiple of three. In this paper, we report the synthesis of a
triangular macrocyclic gold(I) complex composed of three
biphenyelene-4,4’-diyl ligands and three Au2-diphosphine units
and its oxidation to yield [6]CPP in high efficiency (Scheme 2d).
The reaction of 4,4'-diphenylene diboronic acid with
[Au2Cl2(dcpm)] (dcpm = bis(dicyclohexylphosphino)methane) (1)
in the presence of Cs2CO3 (1.0:1.0:6.0 molar ratio) in
toluene/ethanol/water at 50 oC produced the triangular
hexagold(I) complex, [Au2(C6H4-C6H4)(dcpm)]3 (2), as shown in
Eq. 1. The product was isolated in 77% yield by separation of the
solid formed in the reaction mixture by filtration.[14] Figure 2 shows
the molecular structure of complex 2 determined by X-ray
crystallography.
Complex 2 has three chirality axes formed by the twisted
Au2P2C five-membered ring in each corner of the triangle. X-ray
crystallography revealed the structure with one M and two P
chirality axes, 2(MPP) (Figure 2, space group P21212). Figure 3
summarizes the structures of 2(MPP) and its enantiomeric isomer
(2(MPP)), and two possible structures with D3-symmetry, 2(PPP)
and 2(MMM). DFT calculation revealed that the MPP and MMP
isomers with C2-symmetry are more stable than the D3-symmetric
isomers (2(PPP) and 2(MMM)) by ΔG = 1.53 kcal mol-1. Reaction
in Eq 1 probably results in the formation of all four isomers with
similar stabilities. The 31P{1H} NMR spectrum of the reaction
product shows a single signal at 47.7 ppm (C2D2Cl4, r.t.). The 1H
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10.1002/ange.202005482
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Cy
Cy
Cy
and 31P{1H} NMR spectra of complex 2 in C2D2Cl4 do not change
Cl
P
Au
PhICl2
o
over the temperature range from -40 to +20 C. The NMR data
+
2
(2)
P
Au Cl
DMF
-60 oC, 0.5 h
then 25 oC, 25 h
suggest that the diastereomeric isomers reach equilibrium in the
solution with faster than the NMR time scale. The low solubility of
the complex prevented measurements at temperature lower than
-40 oC and detailed studies of 13C{1H} NMR spectroscopy.
Cy
1 (62%)
[6]CPP (76%)
1
The progress of the reaction in Eq 2 was monitored by H
NMR spectroscopy (Figure 4). The spectra of aliquots from the
reaction mixture from 0 to 20 h contained a set of signals, a singlet
(6.68 ppm) and two doublets (6.84, 6.99 ppm) with a 1:1:1
integrated ratio. The signals were assigned to a meta-stable
Organic triangular macrocycles with linear sides and twisted
corners have also been reported.[17] Hartley synthesized a
molecule with three helical o-phenylene units at the corners of
triangle. Temperature-dependent NMR spectroscopy revealed
occurrence of the stereochemical inversion of the molecule with
an activation energy in the range of 17-18 kcal mol-1. Similar
molecules having binaphthyl and helicene as groups with axial
chirality do not exhibit the conformational change on the NMR
time scale.
1
intermediate, and the pattern of H NMR signals implies the
existence of the terphenylene-4,4’-diyl ligand bridging two Au
atoms. After 25 h, these signals disappeared completely and a
new singlet signal was observed at 7.64 ppm, which matches the
reported chemical shift of [6]CPP.[19]
C2-symmetric isomers
solv.
Cy
Cy
Cy
Cy
Cy
Cy
Cy
Cy
0 h
P
P
P P
a
b
c
Au Au
Au Au
M
P
5 h
20 h
25 h
Cy
P
Cy
P
P
P
M
M
Cy
P
Cy
P
Au
Au
Au
Au
Au
Au
Au
Au
Cy
Cy
Cy
Cy
P
P
P
P
2(MMP)
Cy
Cy
Cy
Cy
Cy
2(MPP)
X-ray in Figure 2
Cy
Cy
Cy
[6]CPP
D3-symmetric isomers
Cy
Cy
Cy
Cy
Cy
Cy
Cy
Cy
P
P
P P
δ /ppm
Au Au
Au Au
M
P
Figure 4. Changes in 1H NMR during oxidative chlorination of Au complex
2 caused by addition of PhICl2 (500 MHz, CDCl3, r.t.). See Scheme 3 for
the assignment of the signals a-c.
Cy
P
P
Cy
P
M
Cy
P
M
Cy
P
Au
Au
Au
Au
Au
Au
Cy
Cy
Cy
Cy
P
Au
Au
P
P
P
P
Cy
Cy
2(MMM)
2(PPP)
Cy
Cy
Cy
Cy
Cy
Cy
Cy
Cy
Cy
Cy
Cy
Cy
Cy
P
P
P
AuI
Cl
P
Cy
Cl AuII AuII Cl
AuIII
Cl
Figure 3. Structural isomers of Au complex 2
The oxidative chlorination[7] of complex 2 occurs upon the
PhICl2
addition of a threefold molar amount of PhICl2 in DMF[18] at 25 oC.
Silica gel column chromatography (CH2Cl2 as eluent) of the
reaction mixture after 25 h gave both [6]cycloparaphenylene
([6]CPP, 76% yield) and [Au2Cl2(dcpm)] (1) (62% yield) in pure
forms. [6]CPP[19] is the smallest among the cycloparaphenylenes
having an even number of phenylene groups. Jasti and Yamago
independently reported its preparation. Pd-catalyzed cross
coupling cyclization and subsequent dealkoxylation gave [6]CPP
in 0.7% overall yield (eight steps). The six sequential reactions
2
Cl
Cl
AuII
AuII
AuII
AuII
Cy
Cy
P
Cl AuIII
AuIII
Cy
Cy
Cl
P
Cy
P
P
Cy
P
P
Cy
Cy
Cl
Cl
II
Cy
Cy
Cy
I
Cy
P
P
Cy
Cy
Cy
AuI
AuI
Cy
Cl
Cl
Cy
P
Cy
AuI
Cy
P
Cy
Cy
AuI
Cy
P
Cl
Cy
Cl
P
AuIII
AuIII
Cy
Cl
c
Cl
b
involving the synthesis of
a
macrocyclic tetraplatinum
—(1)2
a
—1
intermediate and its careful oxidation afforded the product in 9%
yield. The synthesis of [6]CPP on the order of grams (1.3 g) was
achieved by using macrocyclic diplatinum complex having
aromatizable 1,4-dimethoxycyclohexadiene groups in the ligand
as the intermediate (23% in 7 steps). The reactions in Eqs 1 and
2 of this study afforded [6]CPP in 59% overall yield and recovered
starting digold complex 1 in 48% yield.
[6]CPP
Cl
AuIII
Cy
P
AuIII
Cl
Cy
AuI
Cl
Cy
P
P
AuI
Cy
Cy
Cl
P
III
Cy
IV
Cy
Cy
Meta-stable intermediate
Scheme 3. Plausible reaction mechanism of [6]CPP formation by oxidative
chlorination of Au complex 2.
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10.1002/ange.202005482
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COMMUNICATION
Scheme 3 shows the plausible reaction mechanism. The
oxidative chlorination of complex 2 forms intermediate I with six
Au(II) centers. The subsequent migration of an aryl ligand to its
causes eliminates [6]CPP, followed by recovery of the starting Au-
diphosphine complex. The formation of the complex and its
oxidation results highly strained organic compounds with high
efficiency under mild conditions.
adjacent
Au
center
forms
intermediate
II
with
chloro(diaryl)gold(III) and chlorogold(I) groups bridged by the
diphosphine ligand. Formation of a C-C bond from intermediate II
gives intermediate III, which undergoes rapid rearrangement into
sterically more favorable intermediate IV with two 4,4’-
terphenylene-4,4’-diyl ligands between the two Au(I) centers. The
NMR spectra of the reaction mixture (Figure 4) are consistent with
the structure of IV. The exchange between the phosphine and
chloride ligands at the gold center occurs rapidly, which gave the
averaged 1H NMR signals. The C-Au-C bond angle of
intermediate IV is estimated to be 80.9o by theoretical calculations.
Conversion of intermediate III into IV may occur via reductive
elimination of a macrocyclic monogold(I) intermediate, resulting in
the slippage of the gold center while maintaining coordination of
the phenylene group to the Au (I) center. A similar of migration of
Ni and Pd centers was found in a study of catalyst transfer
coordination polymerization and its model reaction.[20]
Acknowledgements
This work was financially supported by JSPS KAKENHI
(Grant No. JP18K19095/JP19K15533) and the ‘Dynamic Alliance
for Open Innovation Bridging’ from the Ministry of Education,
Culture, Sports, Science and Technology of Japan (MEXT),
Grant-in-Aid for 2018 Kanto Chemical Award in Synthetic Organic
Chemistry, Japan. The authors thank their colleagues in the
Center for Advanced Materials Analysis, Technical Department,
Tokyo Institute of Technology for carrying out NMR and X-ray
diffraction analyses.
Conflict of interest
The authors declare no competing financial interest.
A dinuclear Pt(II) complex with two terphenylene-4,4’-diyl
ligands was obtained by the procedure shown in Scheme 4.[21]
The pattern of1H NMR signals of the Pt(II) complex is similar with
the intermediate IV in Scheme 3. Thus, [6]CPP and its Pt complex
with a highly strained structure causes both oxidative addition of
a C–C bond to a Pt(0) center and C–C coupling accompanied by
reductive elimination.
Keywords: Au(I) complex, Metallomacrocycle,
Cycloparaphenylene, Reductive Elimination.
References and Notes
[1] (a) H. Schmidbaur, A. Schier, Gold Organometallics, in Comprehensive
Organometallic Chemistry III. From Fundamentals to Applications, Vol. 2, Eds.
By D. M. P. Mingos, R. H. Crabtree, Pergamon Press, pp 251-307 (2007). (b)
C.-Y. Wu, T. Horibe, C. B. Jacobsen, F. D. Toste, Nature, 2015, 517, 449-
454. (c) T. Kaharu, R. Ishii, T. Adachi, T. Yoshida, S. Takahashi, J. Mater.
Chem., 1995, 5, 687-692. (d) K. Fujisawa, F. Mitsuhashi, P. Anukul, K. Taneki,
O. Younis, O. Tsutsumi, Polym. J., 2018, 50, 761-769. (e) E. Y.-H. Hong, C.-
T. Poon, V. W.-W. Yam, J. Am. Chem. Soc., 2016, 138, 6368-6371. (f) E. R.
T. Tiekink, Crit. Rev. Oncol. Hemat., 2002, 42, 225-248. (g) E. E. Langdon-
Jones, S. J. A. Pope, Chem. Commun., 2014, 50, 10343-10354.
Ph3P
PPh3
PtII
PPh3
Ph3P
PtII
[Pt0(PPh3)4]
(2.2 eq.)
[6]CPP
C6H6
100 oC, 65 h
PtII
Ph3P
98%
PPh3
[2] K. Osakada, Platinum-Carbon s-Bonded Complexes, in Comprehensive
Organometallic Chemistry III. From Fundamentals to Applications, Vol. 8, Eds.
By D.M. P. Mingos, R. H. Crabtree, Pergamon Press, pp 445-609 (2007).
[3] (a) J. Vicente, J. Gil-Rubio, N. Barquero, P. G. Jones, D. Bautista,
Organometallics, 2008, 27, 646-659. (b) P. Teo, J. Wang, L. L. Koh, T. S. A.
Hor, Dalton Trans., 2009, 5009-5014. (c) E. M. Barreiro, E. V. Boltukhina, A.
J. P. White, K. K. Hii, Chem. Eur. J., 2015, 21, 2686-2690.
Scheme 4. Formation of dinuclear Pt(II) complex with two p-
terphenylenediyl units via oxidative addition of [6]CPP to [Pt(PPh3)4] [21]
.
The rate-determining step among all the reactions in
Scheme 2 should be the reductive elimination of the product from
intermediate IV. The bulky cyclohexyl (Cy) groups at the
phosphine ligand (dcpm) help accelerate the reductive elimination.
The DMF solvent is considered to enhance the dissociation of a
Cl ligand from intermediate IV, giving three coordinated
intermediate.[18] Hoffman reported the reductive elimination of
alkanes from a tri-coordinated gold(III) complex, which occurs via
a Y-shaped intermediate.[22]
[4] For chelating coordination of diphosphine to Au(I) center, See: Y. Wang, M.
Liu, R. Cao, W. Zhang, M. Yin, X. Xiao, Q. Liu, N. Huang, J. Med. Chem.,
2013, 56, 1455-1466.
[5] (a) H. Schmidbaur, Gold Bull., 2000, 33, 3-10. (b) H. Schmidbaur A. Schier,
Chem. Soc. Rev., 2012, 41, 370-412. (c) H. Schmidbaur, A. Schier, Chem.
Soc. Rev., 2008, 37, 1931-1951. (d) M. J. Katz, K. Sakai, D. B. Leznoff, Chem.
Soc. Rev., 2008, 37, 1884-1895.
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Chem. Commun., 1983, 1304-1306. (b) H. Scmidbaur, R. Franke, Chem. Ber.,
1975, 108, 1321-1328. (c) J. D. Basil, H. H. Murray, J. P. Fackler, Jr., J.
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Delord, D. Marler, J. Am. Chem Soc., 1985, 107, 6908-6915. (d) J. P. Fackler,
Jr., Inorg. Chem., 2002, 41, 6959-6972. (e) J. C. Vickery, A. L. Balch, Inorg.
Chem., 1997, 36, 5978-5983. (f) M. J. Irwin, L. M. Rendina, J. J. Vittal, R. J.
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In summary, the 3+3 self-assembly of an aromatic ligand
precursor and a digold-diphosphine complex proceeds smoothly
to afford the hexagold(I) complex with
a triangle-shaped
molecular structure. Stereoisomers originating from chiral axes at
the corners are easily converted via exchange of the two Au-P
bonds of the Au2(diphosphine) unit. Oxidation of the complex
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10.1002/ange.202005482
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Entry for the Table of Contents
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The
digold(I)
complex
Author(s), Corresponding Author(s)*
[Au2Cl2(Cy2PCH2PCy2)] reacts with
4,4'-diphenylene diboronic acid to form
a triangular macrocyclic complex with
twisted Au-P-C-P-Au groups at the
three corners. The synthesis of the
complex and its chemical oxidation
Page No. – Page No.
Title
produced
[6]cycloparaphenylene
([6]CPP) in 59% overall yield.
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