Catalytic Oxidative Dehydrogenative Coupling of Cage B-H/B-H Bonds for Synthesis of Bis(o-carborane)s

Article abstract of DOI:10.1021/acs.orglett.9b02129

An efficient and succinct protocol for synthesis of bis(o-carborane) connected by a B-B bond via palladium catalyzed oxidative dehydrogenative coupling of cage B-H/B-H bonds was developed for the first time. A series of bis(o-carborane)s connected by B(4)

Full text of DOI:10.1021/acs.orglett.9b02129

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Catalytic Oxidative Dehydrogenative Coupling of Cage B−H/B−H
Bonds for Synthesis of Bis(o‑carborane)s
Ji Wu,† Ke Cao,*,† Cai-Yan Zhang,† Tao-Tao Xu,† Li-Fang Ding,† Bo Li,‡ and Junxiao Yang†
†State Key Laboratory of Environment-Friendly Energy Materials and School of Material Science and Engineering, Southwest
University of Science and Technology, 59 Qinglong Road, Mianyang, Sichuan 621010, P. R. China
‡Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang, Sichuan 621900, P. R. China
S
* Supporting Information
ABSTRACT: An efficient and succinct protocol for synthesis of bis(o-carborane) connected by a B−B bond via palladium
catalyzed oxidative dehydrogenative coupling of cage B−H/B−H bonds was developed for the first time. A series of bis(o-
carborane)s connected by B(4)−B(4)′ and B(4)−B(5)′ bonds was synthesized with moderate to good yields. This work opens
the door for miscellaneous applications of bis(o-carborane) in related disciplines and has important value in design and
synthesis of different kinds of biscarboranes.
arboranes are a class of carbon−boron molecular clusters
a general and environmentally friendly protocol for synthesis of
bis(o-carborane) connected by a B−B bond (BBC), which
keeps the property evaluation and potential applications of
BBC in its infancy.
C
with three-dimensional (3D) aromaticity analogues to
benzene, which have extensive applications in pharmaceuticals
for boron neutron capture therapy (BNCT),1 building blocks
in functional materials,2 and ligands in organometallic as well
as coordination chemistry.3 Correspondingly, biscarboranes
can be viewed as 3D analogues to biphenyl and have also
found important applications as unique bidentate ligands,4
structural units for the construction of rigid rod molecules,5
metallacarboranes,6 and supraicosahedral bis(heteroborane)s.7
Additionally, they might also have potential application in
asymmetric catalysis by design and synthesis of ligand
analogues to BINAP.
For bis(o-carborane), 1,1′-bis(o-carborane) connected by a
cage C−C bond is the most well-known and first synthesized
from the reaction of B10H12(CH3CN)2 with diacetylene by
Hawthorne half a century ago.8 After then, the CuCl mediated
coupling of 1,2-Li2C2B10H10 is the dominating route for the
synthesis of 1,1′-bis(o-carborane).9 For biscarborane con-
nected by a B−B bond, there were some controversies on the
reproducibility in its early stage.10 Until 1983, the 9,9′-bis(1,2-
Me2-o-carborane) was precisely synthesized in the presence of
a catalytic amount of Pd(OAc)2 and stoichiometric Tl-
(OCOCF3)2 by Usyatinskii and coworkers11 (Scheme 1b).
Then, the 9,9′-bis(m-carborane) was further synthesized from
9,9′-bis(m-carboranyl) mercury12 (Scheme 1c). However, the
4,4′-bis(o-carborane) is only a proposed byproduct in the
reaction of dinido-carborane with diborane.13 We can see that
the high toxicity thallium and mercury salts are indispensable
for synthesis of biscarboranes connected by B−B bonds in the
traditional methods. To the best of our knowledge, there is not
Transition metal catalyzed C−H activation/cross dehydro-
genative coupling for direct functionalization of carbon-based
molecules has emerged as a powerful strategy over the past
decades, which represents the most succinct and atom-
economical synthetic route for construction of carbon−carbon
and carbon−heteroatom bonds. Due to the three-dimensional
aromaticity of o-carborane analogues to benzene, utilization of
the transition metal catalyzed cage B−H activation for
regioselective boron functionalization of o-carbrane has
resulted in many advancements in recent years.14−17 Syntheti-
cally, transition metal catalyzed cage B−H activation and
following cross dehydrogenative coupling of B−H/B−H bonds
is the most efficient strategy for construction of BBC.
However, the 10 B−H bonds of o-carborane are not fully
equal, and the electrophilic reactivity is reduced in the
following order: B(9, 12) > B(8, 10) > B(4, 5, 7, 11) > B(3,
6).18 Therefore, the method to control the selectivity of the
formation of B−B bonds via specific B−H/B−H coupling is
the key problem to be considered. Recently, Xie’s group and
ours accomplished the regioselective construction of B−C and
B−O bonds via cross dehydrogenative coupling of the cage B−
H bond with C−H and O−H bonds,14j,16e respectively. These
works indicated that the direct selective functionalization of
Received: June 20, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b02129
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 1. Strategies for Synthesis of Biscarboranes
Table 1. Optimized Conditions for the Selective Oxidative
Dehydrogenative Coupling of B(4)−H Bond of 9-
a
Benzamide-o-carborane
b
entry
catalyst (10%)
oxidant
solvent
2a/3a (%)
1
2
3
4
5
6
7
8
9
10
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
Pd(MeCN)4(BF4)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
2 equiv AgF
2 equiv AgF
2 equiv AgF
2 equiv AgF
2 equiv AgF
2 equiv AgF
2 equiv AgBF4
2 equiv AgOTf
2 equiv AgOAc
0.5 equiv AgF
2 equiv AgOAc
0.5 equiv AgF
3 equiv AgOAc
0.5 equiv AgF
3 equiv AgOAc
0.5 equiv AgF
2 equiv AgOAc
toluene
DCE
MeCN
THF
toluene
toluene
toluene
toluene
toluene
toluene
31/8
23/8
23/4
6/0
4/4
4/8
8/0
12/17
38/21
11
12
13
Pd(OAc)2
toluene
toluene
toluene
43/20
57/23
c
Pd(OAc)2/NiCl2
c
NiCl2
the B−H bond via dehydrogenative coupling is a potential
strategy for construction of BBC. However, as the B−H bonds
of o-carborane are much less polar than the cage C−H bonds,
the direct dehydrogenative coupling of cage B−H/B−H bonds
for construction of BBC with good selectivity is still an
intricate project.
Recently, we found that when the benzamide was introduced
on B(9), the charge distribution of 9-benzamide-o-carborane
has a great change, and B(4, 5, 8, 10, 12) were much more
negative than those in o-carborane. More importantly, the
B(4)−H and B(5)−H bonds were more polarized when
comparing the relative charge change of other B−H bonds.
Additionally, the B(4)−H bond is slightly more polarized than
the B(5)−H bond. On the basis of this characteristic, we
developed a selective arylation of 9-amide-o-carborane on B(4)
with arylboronic acid; meanwhile, the electrophilic reaction on
B(8, 10, 12) was inhibited completely.16f Inspired by this
result, we envisioned a general method for the synthesis of
BBC via intermolecular oxidative dehydrogenative coupling of
B(4)−H bonds with good selectivity.
To initiate our research, 9-benzamide-o-carborane was
selected as the model substrate to screen conditions, and the
results are summarized in Table 1. After many efforts, we
found such an oxidative dehydrogenative coupling of B(4)−H
bond could be accomplished in the presence of Pd(OAc)2 and
AgF in toluene at 60 °C for 24 h, which gave the desired bis(o-
carborane) connected by a B(4)−B(4)′ bond (2a) in 31%
yield. Meanwhile, the isomer 3a connected by a B(4)−B(5)′
bond was also formed in 8% yield (entry 1), which might
ascribed to the slight difference in reactivity of B(4)−H and
B(5)−H bonds. Importantly, 2a and 3a could be easily
separated by column chromatography. Further studies
indicated that Pd(OAc)2 was more favorable for this
transformation in toluene (entries 2−6). Subsequently, the
silver salts were also examined, and the results demonstrated
that the coupling proceeded smoothly in the presence of 0.5
a
All reactions were carried out using 0.2 mmol 1a, 10 mol % catalyst,
and 2 mL of solvent at 60 °C for 24 h under an argon atmosphere.
b
c
Isolated yields. 10 mol % NiCl2.
equiv of AgF and 3 equiv of AgOAc and gave the combined
yield of 2a and 3a in 63% yield (entry 11). Furthermore, we
found that when 10 mol % of NiCl2 was added, the combined
yield was further improved to 80% (entry 12). A control
experiment demonstrated that NiCl2 could not catalyze this
dehydrogenative coupling in the absence of Pd(OAc)2 (entry
13). This result implies that the nickel might not be the
catalytic active center.
Under the optimized conditions (Table 1, entry 12), the
scope of 9-amide-o-carboranes was then examined. As can be
seen from Scheme 2, for 9-(4-R-benzamide)-o-carboranes
(1a−1f), the benzamides substituted with electron-donating
or electron-withdrawing groups were all compatible with this
transformation and gave the corresponding bis(o-carborane)s
connected by B(4)−B(4)′ and B(4)−B(5)′ bonds in moderate
to good yields (2a−2f). Additionally, the exact structures of 2d
and 3d were unambiguously confirmed by X-ray crystallo-
graphic analysis (Figure 1).19 For 9-(3-R-benzamide)-o-
carboranes (1g−1i), the electron-donating group was more
favorable for the coupling, and the expected products were
generated in moderate to good yields (2g−2i). The electronic
and steric effect of substituents has a distinct influence on the
coupling of 9-(2-R-benzamide)-o-carboranes (1j−1n), 1o and
1p, and the desired products were afforded in moderate yields
(2j−2p). Interestingly, 9-alkylamide-o-carboranes were also
compatible with this coupling (1q−1r), and only the bis(o-
carborane)s connected by a B(4)−B(4)′ bond were formed
but with a lower conversion ratio (2q−2r). These above
synthesized BBCs are potential synthons for synthesis of
diazonium salts of BBC via removal of the acyl group and a
diazotization reaction, which would be a universal intermediate
B
DOI: 10.1021/acs.orglett.9b02129
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 2. Synthesis of Bis(o-carborane)s via Selective
Oxidative Dehydrogenative Coupling of 9-Amide-o-
carboranes
Scheme 3. Proposed Mechanism for Synthesis of Bis(o-
carborane)s via Oxidative Dehydrogenative Coupling of
Cage B−H/B−H Bonds
a,b
B(5)−H bond by PdIV. Additionally, the NiCl2 might be a
Lewis acid, which activates the carbonyl of 9-amide-o-
carborane and facilitates the formation of PdIV intermediate.
In conclusion, we developed a palladium catalyzed selective
oxidative dehydrogenative coupling of cage B−H/B−H bonds
for the synthesis of bis(o-carborane) connected by a B−B bond
for the first time. A series of bis(o-carborane)s connected by
B(4)−B(4)′ and B(4)−B(5)′ bonds was synthesized with
moderate to good yields. A plausible mechanism involving one
B−H activation at PdII and another B−H activation at PdIV
was proposed for the formation of B(4)−B(4)′ and B(4)−
B(5)′ bonded bis(o-carborane)s. This work represents the first
efficient and general strategy for synthesis of bis(o-carborane)
connected by a B−B bond via oxidative dehydrogenative
coupling of cage B−H/B−H bonds, which would be useful for
design and synthesis of many kinds of biscarboranes and opens
the door for evaluating the properties and miscellaneous
applications of BBCs in related disciplines.
a
All reactions were carried out on a 0.2 mmol scale in 2 mL of toluene
b
at 60 °C for 24 h under an argon atmosphere. Isolated yields; the
ratios of isomers 2 and 3 were calculated based on the isolated yields
and are given in parentheses. Isolated yields were calculated based on
the consumed 9-amide-o-carboranes, and the conversion ratios of 9-
c
amide-o-carboranes are given in parentheses.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b02129.
Detailed experimental procedures, complete character-
1
ization data, and copies of H, 13C, 11B{H}, and 11B
Figure 1. Crystal structure of 2d (left) and 3d (right).
NMR spectra (PDF)
for the synthesis of many kinds of BBC derivatives20 and would
have important value in promoting the applications of BBCs in
related disciplines.
Accession Codes
CCDC 1904327 and 1904329 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
To elucidate the possible mechanism, two control experi-
ments for 1a by addition of radical scavenger (1,4-
benzoquinone and TEMPO) were carried out under the
standard conditions, and the desired products were obtained in
69 and 61% yields, respectively. This result indicates the
selective B−H/B−H coupling would not be a radical
mechanism. Based on the experimental results and our
previous work on selective arylation of B(4)−H of 9-amide-
o-carboranes, we considered the cyclopalladium intermediate A
should form first by amide guided selective B(4)−H
activation.14k,16f The bis(o-carborane) connected by a B(4)−
B(5)′ bond is generated along with the B(4)−B(4)′ one;
therefore, the highly electrophilic PdIV intermediate B should
form in the presence of silver salts and had less selectivity
following activation of B(4)′−H and B(5)′−H bonds of
another 9-amide-o-carborane via intermediates C and D,
respectively21 (Scheme 3). In view of the ratio of regioisomers,
we consider these results to be reasonable as the slightly more
polarized B(4)−H bond should be activated prior to the
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: caoke@swust.edu.cn.
ORCID
Ke Cao: 0000-0003-0348-2386
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (Grant 21602182), the Longshan
academic talent research supporting program of SWUST
C
DOI: 10.1021/acs.orglett.9b02129
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(10) (a) Stanko, V. I.; Gol’tyanin, Yu. V.; Brattsev, V. A. Zh. Obshch.
Khim. 1967, 37, 2360−2361. (b) Zakharkin, L. N.; Kalinin, V. N.
Izvestiya Akad. Nauk SSSR 1971, 2310−2312.
(Grants 17LZX324, 18LZX305, and 18LZXT02), and the
Project of State Key Laboratory of Environment-Friendly
Energy Materials, SWUST (Grants 17fksy0102 and
18fksy0206).
(11) Usyatinskii, A. Y.; Ryabov, A. D.; Shcherbina, T. M.; Bregadze,
V. I.; Godovikov, N. N. Bull. Acad. Sci. USSR, Div. Chem. Sci. 1983, 32,
1485−1487.
REFERENCES
(12) Zakharkin, L. I.; Krainova, N. Yu.; Pisareva, I. V.; Antonovich,
V. A. Synth. React. Inorg. Met.-Org. Chem. 1985, 15, 655−661.
■
(1) (a) Hawthorne, M. F. Angew. Chem., Int. Ed. Engl. 1993, 32,
950−984. (b) Soloway, A. H.; Tjarks, W.; Barnum, B. A.; Rong, F. G.;
Barth, R. F.; Codogni, I. M.; Wilson, J. G. Chem. Rev. 1998, 98, 1515−
1562. (c) Valliant, J. F.; Guenther, K. J.; King, A. S.; Morel, P.;
Schaffer, P.; Sogbein, O. O.; Stephenson, K. A. Coord. Chem. Rev.
2002, 232, 173−230. (d) Armstrong, A. F.; Valliant, J. F. Dalton Trans
2007, 4240−4251. (e) Issa, F.; Kassiou, M.; Rendina, L. M. Chem.
̌
́
̌
̌
̀
̌
(13) Janousek, Z.; Hermanek, S.; Plesek, J.; Stlbr, B. Collect. Czech.
Chem. Commun. 1974, 39, 2363−2373.
(14) (a) Qiu, Z.; Quan, Y.; Xie, Z. J. Am. Chem. Soc. 2013, 135,
12192−12195. (b) Quan, Y.; Xie, Z. J. Am. Chem. Soc. 2014, 136,
15513−15516. (c) Lyu, H.; Quan, Y.; Xie, Z. Angew. Chem., Int. Ed.
2015, 54, 10623−10626. (d) Quan, Y.; Xie, Z. Angew. Chem., Int. Ed.
2016, 55, 1295−1298. (e) Lyu, H.; Quan, Y.; Xie, Z. Angew. Chem.,
Int. Ed. 2016, 55, 11840−11844. (f) Lyu, H.; Quan, Y.; Xie, Z. J. Am.
Chem. Soc. 2016, 138, 12727−12730. (g) Quan, Y.; Tang, C.; Xie, Z.
Chem. Sci. 2016, 7, 5838−5845. (h) Lyu, H.; Quan, Y.; Xie, Z. Chem. -
Eur. J. 2017, 23, 14866−14871. (i) Cheng, R.; Qiu, Z.; Xie, Z. Nat.
Commun. 2017, 8, 14827. (j) Quan, Y.; Lyu, H.; Xie, Z. Chem.
Commun. 2017, 53, 4818−4821. (k) Lyu, H.; Zhang, J.; Yang, J.;
Quan, Y.; Xie, Z. J. Am. Chem. Soc. 2019, 141, 4219−4224. (l) Cheng,
R.; Li, B.; Wu, J.; Zhang, J.; Qiu, Z.; Tang, W.; You, S.-L.; Tang, Y.;
Xie, Z. J. Am. Chem. Soc. 2018, 140, 4508−4511.
Rev. 2011, 111, 5701−5722. (f) Ay, A. N.; Akar, H.; Zaulet, A.; Vinas,
̃
C.; Teixidor, F.; Zumreoglu-Karan, B. Dalton Trans 2017, 46, 3303−
3310. (g) Kuthala, N.; Vankayala, R.; Li, Y.-N.; Chiang, C. S.; Hwang,
K. C. Adv. Mater. 2017, 29, 1700850. (h) Calabrese, G.; Daou, A.;
Barbu, E.; Tsibouklis, J. Drug Discovery Today 2018, 23, 63−75.
(2) (a) Hosmane, N. S. Boron Science: New Technologies and
Applications; Taylor & Francis Group, 2012. (b) Prokhorov, A. M.;
Hofbeck, T.; Czerwieniec, R.; Suleymanova, A. F.; Kozhevnikov, D.
N.; Yersin, H. J. Am. Chem. Soc. 2014, 136, 9637−9642. (c) Kirlikovali,
K. O.; Axtell, J. C.; Gonzalez, A.; Phung, A. C.; Khan, S. I.; Spokoyny,
A. M. Chem. Sci. 2016, 7, 5132−5138. (d) Mukherjee, S.; Thilagar, P.
Chem. Commun. 2016, 52, 1070−1093. (e) Wu, X.; Guo, J.; Cao, Y.;
Zhao, J.; Jia, W.; Chen, Y.; Jia, D. Chem. Sci. 2018, 9, 5270−5277.
(3) (a) Xie, Z. Acc. Chem. Res. 2003, 36, 1−9. (b) Deng, L.; Xie, Z.
Coord. Chem. Rev. 2007, 251, 2452−2476. (c) Spokoyny, A. M.;
Reuter, M. G.; Stern, C. L.; Ratner, M. A.; Seideman, T.; Mirkin, C. A.
J. Am. Chem. Soc. 2009, 131, 9482−9483. (d) Spokoyny, A. M.;
Machan, C. W.; Clingerman, D. J.; Rosen, M. S.; Wiester, M. J.;
Kennedy, R. D.; Stern, C. L.; Sarjeant, A. A.; Mirkin, C. A. Nat. Chem.
2011, 3, 590−596. (e) Yao, Z.-J.; Jin, G.-X. Coord. Chem. Rev. 2013,
257, 2522−2535. (f) Spokoyny, A. M. Pure Appl. Chem. 2013, 85,
903−919. (g) Zhang, Y.; Zhang, Z.-X.; Wang, Y.; Li, H.; Bai, F.-Q.;
Zhang, H.-X. Inorg. Chem. Front. 2018, 5, 1016−1025. (h) Hosmane,
N. S.; Maguire, J. A. Comprehensive Organometallic Chemistry III, Vol.
3, Elsevier: Oxford, 2007, Chapter 5.
(15) (a) Zhang, X.; Zheng, H.; Li, J.; Xu, F.; Zhao, J.; Yan, H. J. Am.
Chem. Soc. 2017, 139, 14511−14517. (b) Zhang, X.; Yan, H. Chem.
Sci. 2018, 9, 3964−3969.
(16) (a) Cao, K.; Huang, Y.; Yang, J.; Wu, J. Chem. Commun. 2015,
51, 7257−7260. (b) Wu, J.; Cao, K.; Xu, T.-T.; Zhang, X.-J.; Jiang, L.;
Yang, J.; Huang, Y. RSC Adv. 2015, 5, 91683−91685. (c) Cao, K.; Xu,
T.-T.; Wu, J.; Jiang, L.; Yang, J. Chem. Commun. 2016, 52, 11446−
11449. (d) Xu, T.-T.; Zhang, C.-Y.; Cao, K.; Wu, J.; Jiang, L.; Li, J.;
Li, B.; Yang, J. ChemistrySelect 2017, 2, 3396−3399. (e) Xu, T.-T.;
Cao, K.; Wu, J.; Zhang, C.-Y.; Yang, J. Inorg. Chem. 2018, 57, 2925−
2932. (f) Xu, T.-T.; Cao, K.; Zhang, C.-Y.; Wu, J.; Jiang, L.; Yang, J.
Chem. Commun. 2018, 54, 13603−13606. (g) Zhang, C.-Y.; Cao, K.;
Xu, T.-T.; Wu, J.; Jiang, L.; Yang, J. Chem. Commun. 2019, 55, 830−
833.
(17) Selected examples for functionalization of other boron clusters
via B−H activation: (a) Zhang, Y.; Sun, Y.; Lin, F.; Liu, J.; Duttwyler,
S. Angew. Chem., Int. Ed. 2016, 55, 15609−15614. (b) Lin, F.; Yu, J.-
L.; Shen, Y.; Zhang, S.-Q.; Spingler, B.; Liu, J.; Hong, X.; Duttwyler, S.
J. Am. Chem. Soc. 2018, 140, 13798−13807.
(18) Potenza, J. A.; Lipscomb, W. N.; Vickers, G. D.; Schroeder, H.
A. J. Am. Chem. Soc. 1966, 88, 628−629.
(19) CCDC numbers for 2d and 3d are 1904327 and 1904329,
respectively.
(4) (a) Kirlikovali, K. O.; Axtell, J. C.; Anderson, K.; Djurovich, P. I.;
Rheingold, A. L.; Spokoyny, A. M. Organometallics 2018, 37, 3122−
3131. (b) Axtell, J. C.; Kirlikovali, K. O.; Dziedzic, R. M.; Gembicky,
M.; Rheingold, A. L.; Spokoyny, A. M. Eur. J. Inorg. Chem. 2017,
2017, 4411−4416.
(5) (a) Yang, X.; Jiang, W.; Knobler, C. B.; Mortimer, M. D.;
Hawthorne, M. F. Inorg. Chim. Acta 1995, 240, 371−378. (b) Yang,
X.; Jiang, W.; Knobler, C. B.; Hawthorne, M. F. J. Am. Chem. Soc.
(20) Zhao, D.; Xie, Z. Chem. Sci. 2016, 7, 5635−5639.
(21) Hull, K. L.; Lanni, E. L.; Sanford, M. S. J. Am. Chem. Soc. 2006,
128, 14047−14049.
̌
1992, 114, 9719−9721. (c) Muller, J.; Base, K.; Magnera, T. F.;
̈
Michl, J. J. Am. Chem. Soc. 1992, 114, 9721−9722.
(6) (a) Chan, A. P. Y.; Rosair, G. M.; Welch, A. J. Inorg. Chem. 2018,
57, 8002−8011. (b) Yruegas, S.; Axtell, J. C.; Kirlikovali, K. O.;
Spokoyny, A. M.; Martin, C. D. Chem. Commun. 2019, 55, 2892−
2895. (c) Ellis, D.; McKay, D.; Macgregor, S. A.; Rosair, G. M.;
Welch, A. J. Angew. Chem., Int. Ed. 2010, 49, 4943−4945. (d) Man,
W. Y.; Ellis, D.; Rosair, G. M.; Welch, A. J. Angew. Chem., Int. Ed.
2016, 55, 4596−4599. (e) Zhao, D.; Zhang, J.; Lin, Z.; Xie, Z. Chem.
Commun. 2016, 52, 9992−9995. (f) Wong, Y. O.; Smith, M. D.;
Peryshkov, D. V. Chem. - Eur. J. 2016, 22, 6764−6767.
(g) Thiripuranathar, G.; Man, W. Y.; Palmero, C.; Chan, A. P. Y.;
Leube, B. T.; Ellis, D.; McKay, D.; Macgregor, S. A.; Jourdan, L.;
Rosair, G. M.; Welch, A. J. Dalton Trans 2015, 44, 5628−5637.
(h) Thiripuranathar, G.; Chan, A. P. Y.; Mandal, D.; Man, W. Y.;
Argentari, M.; Rosair, G. M.; Welch, A. J. Dalton Trans. 2017, 46,
1811−1821.
(7) Ellis, D.; Rosair, G. M.; Welch, A. J. Chem. Commun. 2010, 46,
7394−7396.
(8) Dupont, J. A.; Hawthorne, M. F. J. Am. Chem. Soc. 1964, 86,
1643−1643.
(9) Ren, S.; Xie, Z. Organometallics 2008, 27, 5167−5168.
D
DOI: 10.1021/acs.orglett.9b02129
Org. Lett. XXXX, XXX, XXX−XXX