Addition of terminal alkynes to aromatic nitriles catalyzed by divalent lanthanide amides supported by amidates: Synthesis of ynones

Article abstract of DOI:10.1055/s-0033-1338446

An efficient protocol has been established for the synthesis of conjugated ynones via addition of terminal alkynes to aromatic nitriles, which is catalyzed by novel divalent lanthanide amide complexes. All the reactions gave the products in good to excell

Full text of DOI:10.1055/s-0033-1338446

LETTER
▌1269
lAettder dition of Terminal Alkynes to Aromatic Nitriles Catalyzed by Divalent
Lanthanide Amides Supported by Amidates: Synthesis of Ynones
Synthesis of Ynones
Hao Ding, Chengrong Lu, Xiaolin Hu, Bei Zhao,* Bing Wu, Yingming Yao*
College of Chemistry, Chemical Engineering and Materials Science, Dushu Lake Campus, Soochow University, Suzhou 215123, P. R. of China
Fax +86(512)65880305; E-mail: zhaobei@suda.edu.cn
Received: 20.02.2013; Accepted after revision: 04.04.2013
show broaden applications in catalytic transformations,
Abstract: An efficient protocol has been established for the synthe-
such as hydroamination,9 amidation,10 and polymeriza-
sis of conjugated ynones via addition of terminal alkynes to aromat-
tion.11 Meanwhile, the divalent lanthanide chemistry has
received considerable attention in recent years, as they are
ic nitriles, which is catalyzed by novel divalent lanthanide amide
complexes. All the reactions gave the products in good to excellent
yields at room temperature under solvent-free conditions without found to have wide applications in various homogeneous
reactions.12 However, the amidate ligand system has not
been introduced in divalent lanthanide chemistry to date.
any additives. The novel lanthanide amide catalysts were also syn-
thesized and structurally characterized for the first time.
Key words: terminal alkyne, aromatic nitrile, divalent lanthanide
Herein, we successfully synthesized and characterized the
complex, amidate, ynone
divalent ytterbium and europium amide complexes stabi-
lized by amidate ligands for the first time. As expected,
these divalent lanthanide amides were found to be effi-
Conjugated ynones are versatile building blocks in organ-
cient single-component catalysts for the preparation of
ic synthesis1 and widely present in natural products and
ynones by the addition reaction of terminal alkynes with
synthetic materials.2 Recently, some researchers have
aromatic nitriles, and the europium complexes showed
paid much attention to prepare ynones through metal-cat-
higher catalytic activity, which represents the rare example
alyzed cross-coupling reactions. Beller and co-workers
that divalent europium complex exhibited high catalytic
have reported the Pd-catalyzed carbonylative Sonogashira
activity in catalytic organic reactions.12i
coupling of aryl derivatives, such as aryl bromides, aryl
The protonolysis reaction of the appropriate amide pro-
ligands with Ln[N(TMS)2]2 (Ln = Eu, Yb) gave the four
divalent amidate lanthanide amides, {LLn[N(TMS)2](THF)}2
[L1 = 2,6-i-Pr2C6H3NC(O)Ph, Ln = Eu (1), Yb (2);
amines, and aryl triflates,3 while several groups have also
reported the similar reactions by using aryl iodides as the
substrates.4 In 2011, Lee and co-workers found the palla-
dium-catalyzed carbonylative reactions of aryl iodides
and alkynyl carboxylic acids via decarboxylative cou-
pling.5 In addition, some researchers synthesized ynones
by palladium-catalyzed coupling of terminal alkynes with
acid chlorides.6 Among the published methods, corrosive
acyl chlorides or strictly prepared carbon monoxide, as
well as indispensable stoichiometric amounts of bases are
usually required. In 2012, Cheng and co-workers found
that the iron-catalyzed synthesis of ynones from silylated
alkynes with acid chlorides could smoothly undergo with-
out any bases.7 But this reaction should be carried out in
toxic MeNO2 at low temperature (–15 °C). To the best of
our knowledge, there is only one paper available reporting
the direct addition of aromatic nitriles to terminal alkynes
to afford conjugated ynones catalyzed by Ln[N(TMS)2]3.8
However, in Zhou’s method, an appropriate acidity of pri-
mary amines is still required, and the yields are moderate
to good. Thus, the search for new catalysts for a more ef-
ficient and convenient strategy for the preparation of con-
jugated ynones is of great interest and importance.
L2 = 2,6-Me2C6H3NC(O)Ph,
Ln = Yb
(3)],
and
{L2 Eu2[N(TMS)2]2(THF)3} (4) in good yields (Scheme
2
1), and crystals suitable for X-ray diffraction were ob-
tained from mixed hexane–THF solvent at room tempera-
ture.
The crystal structure of complex 1 is given in Figure 1 (a).
Complex 1 has a dinuclear centrosymmetric structure.
The Eu center in complex 1 is five-coordinated by one ox-
ygen atom and one nitrogen atom from an amidate ligand
(L1), one nitrogen atom from the N(TMS)2 group, and two
oxygen atoms from another amidate ligand and the sol-
vated THF molecule, respectively. The coordination ge-
ometry around each central metal can be described as a
tetrahedron, when the chelating amidate ligand is consid-
ered to occupy a single coordination vertex. Complexes 2
and 3 are isostructural with complex 1. Complex 4 has
also a dinuclear structure (Figure 1, b), but the coordina-
tion environment around the two europium atoms is in-
equivalent. The Eu1 is six-coordinated by two oxygen
atoms and two nitrogen atoms from two amidate ligands
(L2), one nitrogen atom from a N(TMS)2 group, and one
oxygen atom from a THF molecule. The coordination ge-
ometry around the Eu1 center can also be described as a
tetrahedron in view of single vertex for each amidate.
However, the Eu2 center is five-coordinated by two oxy-
gen atoms from two amidate ligands, one nitrogen atom
As steric and electronic properties of the amidate ligand
can be easily tunable, the trivalent rare-earth-metal com-
plexes bearing amidate ligands have been reported to
SYNLETT 2013, 24, 1269–1274
Advanced online publication: 29.04.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1338446; Art ID: ST-2013-W0161-L
© Georg Thieme Verlag Stuttgart · New York

1270
H. Ding et al.
LETTER
Ar
O
N
O
N(SiMe3)2
1 Ln = Eu Ar = 2,6-disopropylphenyl
Ln
2 Ln = Yb Ar = 2,6-disopropylphenyl
3 Ln = Yb Ar = 2,6-dimethylphenyl
O
Ln
O
N
(Me3Si)2N
O
Ar
Ar
N
THF
Ln[N(SiMe3)2]2
+
H
60 °C, 4 h
N(TMS)2
O
N
O
N
4
Eu
O
Eu
N(TMS)2
O
O
Scheme 1 Preparation of divalent lanthanide amides supported by amidates
from a N(TMS)2 group, and two oxygen atoms from two with 2,6-diisopropylphenyl is more efficient (Table 1, en-
coordinated THF molecules. The coordination geometry try 11 vs. entry 17). The effects of the reaction conditions
around the Eu2 center can be described as a distorted on the yield were further examined using complex 1, since
quadrangular pyramid, where the four oxygen atoms are it showed the highest activity for this reaction. As expect-
almost coplanar, with the sum of the bond angles nearly ed, the reaction was sensitive to temperature, where room
360°, and the nitrogen atom N4 locates at the axial vertex.
temperature proved to be the optimum choice (Table 1,
entries 1 and 4–6). The yield increased with the increase
of the molar ratio of alkyne to nitrile, and the maximum
yield was obtained at the ratio of 3:1 (Table 1, entries 1, 7,
and 8). The excess amount of acetylene used was recov-
ered almost quantitatively. Moreover, the yield can reach
up to 95% under solvent-free conditions for 12 hours
(Table 1, entry 11).
The substrate scope and limitation of this methodology
were subsequently investigated, and the results are sum-
marized in Table 2. It can be seen that most of the alkynes
and nitriles proceeded smoothly to produce conjugated
ynones in good to excellent isolated yields, varied from
82–96%. However, the location of the substituent on the
phenyl ring of nitrile had significant effect on this reac-
tion. For example, the reaction of phenylacetylene with o-
tolunitrile proceeded sluggishly, only trace of product was
isolated (Table 2, entry 5), whereas the reactions under-
went smoothly for other aromatic nitriles, including het-
eroaromatic nitrile (Table 2, entry 9). However, efforts
toward realization of the addition of phenylacetylene to
aliphatic nitriles failed (Table 2, entry 10). As for the ste-
ric or electronic properties of aromatic alkynes, there were
scarcely any effects on the yields of ynones (Table 2, en-
tries 11–20). Aliphatic alkynes underwent the addition re-
action to produce the desired products, but the yields
decreased apparently (Table 2, entries 21 and 22). It may
be attributed to the slower activation speed in comparison
with that of aromatic alkynes, which can be considered as
one of the key steps included in the catalytic cycle.13 It
was unexpected that heteroaromatic alkyne hardly gave
the target product under the given conditions (Table 2,
entry 23).
Figure 1 ORTEP diagrams of complexes 1 and 4 with the probabil-
ity ellipsoids drawn at the 20% level, and hydrogen atoms are omitted
for clarity, respectively.
With the easily prepared complexes in hand, the catalytic
behaviors of the divalent amidate lanthanide amides were
explored. The addition reaction of phenylacetylene 5a
with cyanophenyl 6a was first examined as a model reac-
tion catalyzed by these divalent lanthanide amides, and
the preliminary results are summarized in Table 1. It can
be seen that all of these complexes can successfully cata-
lyze this addition reaction to give conjugated ynones at
room temperature and the optimum choice of the catalyst
loading can be reduced to 2.5 mol%. The activity greatly
depends on the central metals, with the activity trend of
Yb < Eu (Table 1, entries 11 and 15–17). The bulkiness of
the substituents on the aryl ring of the amidate ligand also
affects the activity. The complex stabilized by the ligand
Synlett 2013, 24, 1269–1274
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of Ynones
1271
Table 1 Optimization of the Reaction Conditions
O
1) catalyst
Ph
Ph
Ph CN
+
2) hydrolysis
Ph
5a
6a
7aa
Entry
Catalyst
Catalyst loading (mol%) Time (h)
Temp
5a/6a
Solvent
Yield (%)a
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
3
4
2.5
1
24
24
24
24
24
24
24
24
3
r.t.
1:1
1:1
1:1
1:1
1:1
1:1
2:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
78
50
66
65
26
31
87
96
74
88
95
57
70
78
29
18
53
r.t.
3
5
r.t.
4
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
40 °C
60 °C
0 °C
r.t.
5
6
7
8
r.t.
9
r.t.
10
11
12
13
14
15
16
17
6
r.t.
12
12
12
12
12
12
12
r.t.
r.t.
THF
r.t.
toluene
hexane
r.t.
r.t.
r.t.
r.t.
a Isolated yield based on nitrile.
Table 2 The Addition of Terminal Alkynes with Aromatic Nitriles Catalyzed by Complex 1a
O
1) cat. 1 (2.5 mol%), r.t.
12 h, solvent-free
R2
R1
R2 CN
+
2) hydrolysis
R1
5
6
7
Entry
Alkyne
R1
Nitrile
R2
Ynone
Yield (%)b
1
2
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
6a
6b
6c
6d
6e
6f
Ph
7aa
7ab
7ac
7ad
7ae
7af
7ag
7ah
7ai
95
4-MeC6H4
3-MeC6H4
4-F3CC6H4
2-MeC6H4
4-MeOC6H4
4-ClC6H4
4-BrC6H4
2-thienyl
Me
96
3
91
4
92
5
trace
72
6
7
6g
6h
6i
82
8
77
9
47
10
6j
7aj
messy
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1269–1274

1272
H. Ding et al.
LETTER
Table 2 The Addition of Terminal Alkynes with Aromatic Nitriles Catalyzed by Complex 1a (continued)
O
1) cat. 1 (2.5 mol%), r.t.
12 h, solvent-free
R2
R1
R2 CN
+
2) hydrolysis
R1
5
6
7
Entry
Alkyne
R1
Nitrile
R2
Ynone
Yield (%)b
11
12
13
14
15
16
17
18
19
20
21
22
23
5b
5b
5b
5b
5c
5c
5c
5c
5d
5e
5f
4-FC6H4
4-FC6H4
4-FC6H4
4-FC6H4
6a
6b
6c
6d
6a
6b
6c
6d
6a
6a
6a
6a
6a
Ph
7ba
7bb
7bc
7bd
7ca
7cb
7cc
7cd
7da
7ea
7fa
93
92
91
93
90
94
92
91
90
85
61
28
trace
4-MeC6H4
3-MeC6H4
4-F3CC6H4
Ph
4-MeC6H4
4-MeC6H4
4-MeC6H4
4-MeC6H4
3-MeC6H4
2-FC6H4
n-Bu
4-MeC6H4
3-MeC6H4
4-F3CC6H4
Ph
Ph
Ph
5g
5h
TMS
Ph
7ga
7fa
2-thienyl
Ph
a All reactions were conducted with 2.5 mol% of complex 1 at r.t. for 12 h without solvent. And the molar ratio of terminal alkynes to aromatic
nitriles is 3:1.
b Isolated yield based on nitrile.
Based on the mechanism raised by Z. Hou,13e a possible a nitrile to A could afford an imino lanthanide intermedi-
catalytic cycle for the present monoaddition reaction is ate B. Then, B regenerates A by receiving a proton from
proposed in Scheme 2. The acid–base reaction of divalent another molecule of the alkyne, while the addition product
lanthanide amide with a terminal alkyne should yield an C is taken off. Hydrolysis of C gives the corresponding
alkynide species A, which is the key intermediate of the ynone.
catalytic cycle. Coordination and subsequent insertion of
[Ln] N(SiMe3)2
R
R
R1
O
[Ln] =
N
O
5
Ln
HN(SiMe3)2
R1
NH
R2
O
hydrolysis
[Ln]
R2
N
R2
A
C
R1
R1
6
7
R1
5
THF
[Ln]
N
R2
R1
B
Scheme 2 A possible mechanism for the catalytic addition of terminal alkynes to nitriles
Synlett 2013, 24, 1269–1274
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of Ynones
1273
In summary, we have developed an efficient protocol to
construct conjugated ynone frameworks via the economi-
cal reactions of terminal alkynes with aromatic nitriles
catalyzed by divalent amidate lanthanide amides under
solvent-free conditions in good to excellent yields. The
structures of the novel catalysts are well characterized by
the X-ray diffraction analyses. The reactivity depends ap-
parently on both the central metals of the catalysts, and the
properties of the amidate ligands. It is noteworthy that the
divalent europium complex 1 showed the highest activity
on the reaction, which represents the rare example that di-
valent europium complex exhibited high catalytic activity
in homogeneous catalysis. However, the reaction with al-
iphatic nitriles or heteroaromatic alkyne has not been suc-
cessful yet. Efforts in this direction are ongoing in our
laboratory.
Acknowledgment
We gratefully acknowledge financial supports from the National
Natural Science Foundation of China (Grants 21172165 and
21132002), the Priority Academic Program Development of Jiang-
su Higher Education Institutions, and the Natural Science Founda-
tion of the Jiangsu Higher Education Institutions (Project
10KJD150005).
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
r
t
iornat
Primary Data for this article are available online at ht-
tp://www.thieme-connect.com/ejournals/toc/synlett and can be ci-
ted using the following DOI: 10.4125/pd0044th. mPiDrayrmaPitDrayra410t.25p/d00Pm4hrit.DyraZtaheln1
0
1Cheymrst
i
References
General Procedure for the Preparation of Divalent Amidate
Lanthanide Amide Complexes
(1) (a) Moteki, S. A.; Han, J. W.; Arimitsu, S.; Akakura, M.;
Nakayama, K.; Maruoka, K. Angew. Chem. Int. Ed. 2012,
51, 1187. (b) Ramachary, D. B.; Venkaiah, C.; Krishna, P.
M. Chem. Commun. 2012, 48, 2252. (c) Shi, S.-L.; Kanai,
M.; Shibasaki, M. Angew. Chem. Int. Ed. 2012, 51, 3932.
(d) Yamamoto, A.; Ueda, A.; Brémond, P.; Tiseni, P. S.;
Kishi, Y. J. Am. Chem. Soc. 2012, 134, 893. (e) Jiang, H. F.;
Pan, X. Y.; Huang, L. B.; Zhao, J.; Shi, D. B. Chem.
Commun. 2012, 48, 4698.
(2) (a) Sawada, Y.; Furumi, S.; Takai, A.; Takeuchi, M.;
Noguchi, K.; Tanaka, K. J. Am. Chem. Soc. 2012, 134, 4080.
(b) McLeod, M. C.; Wilson, Z. E.; Brimble, M. A. J. Org.
Chem. 2012, 77, 400. (c) Plażuk, D.; Zakrzewski, J.;
Nakatani, K.; Makal, A.; Woźniak, K.; Domagała, S. RSC
Adv. 2012, 2, 3512. (d) Tsvetkov, N. P.; Bayir, A.;
Schneider, S.; Brewer, M. Org. Lett. 2012, 14, 264.
(3) (a) Wu, X.-F.; Neumann, H.; Beller, M. Chem. Eur. J. 2010,
16, 12104. (b) Wu, X.-F.; Neumann, H.; Beller, M. Angew.
Chem. Int. Ed. 2011, 50, 11142. (c) Wu, X.-F.; Sundararaju,
B.; Neumann, H.; Dixneuf, P. H.; Beller, M. Chem. Eur. J.
2011, 17, 106.
(4) (a) Delude, L.; Masdeu, A. M.; Alper, H. Synthesis 1994,
1149. (b) Ahmed, M. S. M.; Mori, A. Org. Lett. 2003, 5,
3057. (c) Rahman, M. T.; Fukuyama, T.; Kamata, N.; Sato,
M.; Ryu, I. Chem. Commun. 2006, 2236. (d) Liu, J. M.;
Peng, X. G.; Sun, W.; Zhao, Y. W.; Xia, C. G. Org. Lett.
2008, 10, 3933. (e) Wang, Y.; Liu, J. H.; Xia, C. G.
Tetrahedron Lett. 2011, 52, 1587.
(5) Park, A.; Park, K.; Kim, Y.; Lee, S. Org. Lett. 2011, 13, 944.
(6) (a) Chen, L.; Li, C.-J. Org. Lett. 2004, 6, 3151. (b) Alonso,
D. A.; Nájera, C.; Pacheco, M. C. J. Org. Chem. 2004, 69,
1615. (c) Cox, R. J.; Ritson, D. J.; Dane, T. A.; Berge, J.;
Charmant, J. P. H.; Kantacha, A. Chem. Commun. 2005,
1037. (d) Baxendale, I. R.; Schou, S. C.; Sedelmeier, J.; Ley,
S. V. Chem. Eur. J. 2010, 16, 89. (e) Santra, S.; Dhara, K.;
Ranjan, P.; Bera, P.; Dash, J.; Mandal, S. K. Green Chem.
2011, 13, 3238. (f) Bakherad, M.; Keivanloo, A.;
Bahramian, B.; Jajarmi, S. Synlett 2011, 311.
Synthesis of {L1Eu[N(TMS)2](THF)}2 (1)
To a stirred THF solution of Eu[N(TMS)2]2(THF)2 (10 mL, 1.23 g,
2.00 mmol), a THF solution of L1 (20 mL, 0.56 g, 2.00 mmol) was
added dropwise. The mixture was stirred for 4 h at 60 °C and then
concentrated under reduced pressure to give a pale yellow solid.
The product was recrystallized by dissolving in a minimum amount
of hexanes, with a few drops of THF. Yellow crystals were obtained
at r.t. in several days (1.04 g, 78%). Anal. Calcd for
(C29H48N2O2Si2Eu)2: C, 52.39; H, 7.28; N, 4.21. Found: C, 52.45;
H, 7.61; N, 4.13.
Synthesis of {L1Yb[N(SiMe3)2](THF)}2 (2)
The synthesis of complex 2 was carried out in the same way as that
described for complex 1, but Yb[N(TMS)2]2(THF)2 (1.27 g, 2.00
mmol) was used instead of Eu[N(TMS)2]2(THF)2. Black crystals
were obtained at r.t. in several days (1.12 g, 82%). Anal. Calcd for
(C29H48N2O2Si2Yb)2: C, 50.78; H, 7.05; N, 4.08. Found: C, 50.85;
H, 7.21; N, 3.95.
Synthesis of {L2Yb[N(TMS)2](THF)}2 (3)
The synthesis of complex 3 was carried out in the same way as that
described for complex 2, but L2 (0.45 g, 2.00 mmol) was used in-
stead of L1. Black crystals were obtained at r.t. in several days (0.88
g, 70%). Anal. Calcd for (C25H40N2O2Si2Yb)2: C, 47.67; H, 6.40; N,
4.45. Found: C, 47.70; H, 6.55; N, 4.23.
Synthesis of {L2 Eu2[N(TMS)2]2(THF)3} (4)
The synthesis of 2complex 4 was carried out in the same way as that
described for complex 1, but L2 (0.45 g, 2.00 mmol) was used in-
stead of L1. Yellow crystals were obtained at r.t. in several days
(0.71 g, 55%). Anal. Calcd for C54H88N4O5Si4Eu2: C, 50.29; H,
6.88; N, 4.34. Found: C, 50.31; H, 6.95; N, 4.27.
General Experimental Procedure for the Direct Synthesis of
Conjugated Ynones Catalyzed by Complex 1
A 10 mL Schlenk tube under dried argon was charged with the com-
plex 1 (33 mg, 0.025 mmol). Alkyne (3 mmol) was added, after stir-
ring for 3 min, nitrile (1 mmol) was then added. The mixture was
stirred at r.t. for 12 h and then was quenched with 0.5 M H2SO4. The
mixture was extracted with Et2O. The organic layer was separated,
dried over anhyd MgSO4, concentrated under reduced pressure, and
purified by flash column chromatography to afford desired product.
Flash column chromatography was performed over silica gel (300–
400 mesh) using the mixture of PE and EtOAc (50:1 or 25:1) as
eluent.
(7) Gandeepan, P.; Parthasarathy, K.; Su, T.-H.; Cheng, C.-H.
Adv. Synth. Catal. 2012, 354, 457.
(8) Shen, Q. S.; Huang, W.; Wang, J. L.; Zhou, X. G.
Organometallics 2008, 27, 301.
(9) Stanlake, L. J. E.; Schafer, L. L. Organometallics 2009, 28,
3990.
(10) Thomson, J. A.; Schafer, L. L. Dalton Trans. 2012, 41, 7897.
(11) (a) Stanlake, L. J. E.; Beard, J. D.; Schafer, L. L. Inorg.
Chem. 2008, 47, 8062. (b) Wang, Q. W.; Zhang, F. R.; Song,
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1269–1274

1274
H. Ding et al.
LETTER
Shen, Q. Chem. Commun. 2012, 48, 9780. (i) Garcia, J.;
H. B.; Zi, G. F. J. Organomet. Chem. 2011, 696, 2186.
(c) Zhang, F. R.; Zhang, J. X.; Song, H. B.; Zi, G. F. Inorg.
Chem. Commun. 2011, 14, 72.
Allen, M. J. Eur. J. Inorg. Chem. 2012, 4550.
(13) (a) Frantz, D. E.; Fässler, R.; Tomooka, C. S.; Carreira, E.
M. Acc. Chem. Res. 2000, 33, 373. (b) Nishiura, M.; Hou, Z.;
Wakatsuki, Y.; Yamaki, T.; Miyamoto, T. J. Am. Chem. Soc.
2003, 125, 1184. (c) Wei, C.; Mague, J. T.; Li, C.-J. Proc.
Natl. Acad. Sci. U.S.A. 2004, 101, 5749. (d) Nishiura, M.;
Hou, Z. J. Mol. Catal. A: Chem. 2004, 213, 101. (e) Zhang,
W.-X.; Nishiura, M.; Hou, Z. J. Am. Chem. Soc. 2005, 127,
16788. (f) Zhang, W.-X.; Nishiura, M.; Hou, Z. Angew.
Chem. Int. Ed. 2008, 47, 9700. (g) Wang, Z.; Wang, Y.;
Zhang, W.-X.; Hou, Z.; Xi, Z. J. Am. Chem. Soc. 2009, 131,
15108. (h) Wang, Y.; Zhang, W.-X.; Wang, Z.; Xi, Z.
Angew. Chem. Int. Ed. 2011, 50, 8122.
(12) (a) Panda, T. K.; Zulys, A.; Gamer, M. T.; Roesky, P. W. J.
Organomet. Chem. 2005, 690, 5078. (b) Takaki, K.;
Komeyama, K.; Kobayashi, D.; Kawabata, T.; Takehira, K.
J. Alloys Compd. 2006, 408–412, 432. (c) Delbridge, E. E.;
Dugah, D. T.; Nelson, C. R.; Skelton, B. W.; White, A. H.
Dalton Trans. 2007, 143. (d) Zhou, H.; Guo, H. D.; Yao, Y.
M.; Zhou, L. Y.; Sun, H. M.; Sheng, H. T.; Zhang, Y.; Shen,
Q. Inorg. Chem. 2007, 46, 958. (e) Datta, S.; Gamer, M. T.;
Roesky, P. W. Organometallics 2008, 27, 1207. (f) Du, Z.;
Li, W. B.; Zhu, X. H.; Xu, F.; Shen, Q. J. Org. Chem. 2008,
73, 8966. (g) Dugah, D. T.; Skelton, B. W.; Delbridge, E. E.
Dalton Trans. 2009, 1436. (h) Yang, S.; Du, Z.; Zhang, Y.;
Synlett 2013, 24, 1269–1274
© Georg Thieme Verlag Stuttgart · New York