Cascade Dehydrogenative Hydroboration for the Synthesis of Azaborabenzofulvenes

Article abstract of DOI:10.1021/acs.orglett.8b00363

Tandem dehydrogenative hydroboration has been established to be highly effective in the synthesis of BN isosteres of benzofulvene and derivatives. The scope of this synthetic method is applicable to a variety of substrates. Spectroscopic and computational studies indicate that the new azaborabenzofulvenes have similar electronic properties as their carbonaceous analogues.

Full text of DOI:10.1021/acs.orglett.8b00363

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Cascade Dehydrogenative Hydroboration for the Synthesis of
Azaborabenzofulvenes
Kang Yuan, Xiang Wang, and Suning Wang*
Department of Chemistry, Queen’s University, Kingston, Ontario K7L 3N6, Canada
S
* Supporting Information
ABSTRACT: Tandem dehydrogenative hydroboration has been
established to be highly effective in the synthesis of BN isosteres
of benzofulvene and derivatives. The scope of this synthetic
method is applicable to a variety of substrates. Spectroscopic and
computational studies indicate that the new azaborabenzofulvenes
have similar electronic properties as their carbonaceous analogues.
olecules or fragments with the same number of atoms
and the same number and same arrangement of
Benzofulvene and derivatives are important scaffolds/
substrates for pharmaceutical reagents and materials.18,19 The
typical preparation of benzofulvenes mainly involves cyclization
of alkenes/alkynes mediated by transition-metal catalysts, Lewis
acid, and organotin compounds,20 which often generate
mixtures of both E and Z isomers.20d,f The synthesis of BN
isosteres of benzofulvenes has not been explored. During our
recent study of internal donor-assisted hydroboration of
alkynes, we discovered that dehydrogenative hydroboration is
a highly effective method for accessing a class of previously
unknown azaborabenzofulvenes shown in Scheme 1. The
details are presented herein.
Dehydrogenative coupling of amine−borane with the aid of a
catalyst has been extensively investigated previously for
generating hydrogen storage materials and hybrid inorganic−
organic polymers.21 Catalyst-free dehydrogenative coupling of
amine−borane is much less explored as it is generally
considered to be a kinetically unfavorable process at room
temperature.21 Recently, Bertrand and we reported facile,
catalyst-free dehydrogenation reactions between primary aryl-
amines and 9-BBN at room temperature.22 Such trans-
formations could serve as a facile approach for constructing a
BN covalent bond. We envisioned that by replacing 9-BBN
with monosubstituted boranes BH2Ar such as BH2(Mes), it
may be possible to generate a B−N and a B−C bond in a one-
pot manner by taking advantage of sequential dehydrogenation
and hydroboration of alkynyl arylamines.
M
electrons are known as isosteres, which play important roles
in drug design, medicinal chemistry, and materials science. The
replacement of a CC unit with a BN unit in aromatic molecules
(BN arenes), for example, has been demonstrated to be a
highly effective approach in creating new molecules or materials
with distinctively different photophysical/chemical properties
from their all carbon analogues.1 One class of BN arenes is
azaborines and derivatives, pioneered by Dewar and co-
workers.2 Rapid advances in azaborine/BN arene chemistry
and applications have been achieved in the past decade.3−10 BN
arene based materials have often been found to perform better
in optoelectronic devices, compared to their carbon analogue-
s.10a Liu et al. demonstrated that isosteric substitution of a C
C unit with a BN unit is a promising strategy for the
development of new pharmaceutical reagents.4
Another class of conjugated BN heterocycles that also
attracts much interest is azaboroles and derivatives, in which a
CC unit in a five-membered ring is replaced by a BN unit.11
Examples of azaboroles include 1,3,2-diazaborole, 1,4,2-
diazaborole, 1,2,4,3-triazaborole, etc. (Scheme 1),12−15 some
Scheme 1. Selected Examples of BN-Containing
Heterocycles along with Their Carbonaceous Counterpart
Based on this consideration, we first examined the reaction 2-
(phenylethynyl)aniline with BH2(Mes) by NMR spectroscopy.
As shown in Figure S2, an amine−borane adduct formed
immediately upon mixing the two reactants (∼0.1 mmol, 1:1, in
1.0 mL of C6D6) at ambient temperature that has a
characteristic four-coordinate boron chemical shift at ∼ −4
ppm in the 11B NMR spectrum. The adduct was gradually
consumed as H2 was produced, as shown by 1H NMR
spectroscopy. A new 11B chemical shift at ∼45 ppm appeared,
of which have been demonstrated to serve as a cyclo-
pentadienyl-like ligands for transition metals.11 In addition,
BN isosteres of indacenes and pentalene have also been
successfully generated.16,17 CC replacement by BN in these
systems have also been found to have a great impact on
electronic properties.
Received: January 31, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b00363
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
which is characteristic of a BN unit.24 The reaction reached
completion with a relatively clean formation of the product 1a
(∼80% yield) after 20 h (Figure S1). The same reaction was
also performed on a synthetic scale using CH2Cl2 as the solvent
at ambient temperature. Chromatography and recrystallization
under air afforded 1a as a yellow solid in 19% yield. The low
isolated yield of 1a was caused by its poor stability on
chromatography. NMR spectroscopic analyses established that
1a is (Z)-3-benzylidene-2-mesityl-2,3-dihydro-1H-benzo[d]-
[1,2]-azaborole, an analogue of benzofulvene, as shown in
Scheme 2. Changing the substrate to p-Br-phenyl- or 1-thienyl-
Scheme 3. Proposed Mechanism for the Dehydrogenative
Hydroboration of Alkynyl Arylamines
that mixing primary anilines with 9-BBN gave a dehydro-
genated product exclusively,22b which is an analogue of B
shown in Scheme 3. Thus, it is possible that in the formation of
BN-benzofulvenes dehydrogenation occurs first. On the other
hand, the internal donor group could act as a directing group to
promote hydroboration under mild conditions.23 To probe the
possibility of amino-directed hydroboration, the reactions of
BH2Ar with secondary 2-alkynylanilines for 8a−10a were
examined. If donor-directed hydroboration occurs first, the
reaction of N-methyl-2-(phenylethynyl)aniline with BH2(Mes)
for 8a should have a comparable rate to that of 2-
(phenylethynyl)aniline for 1a. However, NMR tracking for 8a
showed only the formation of the adduct A after 3 h at ambient
temperature with a small amount of H2 formation, and no
hydroboration was observed (Figures S3 and S4). In contrast,
the reaction for 1a under the same conditions produced the
dehydrogenative hydroboration product 1a in ∼50% yield after
3 h and reached completion after 20 h. For the synthesis of 8a,
the reaction requires several days to complete at ambient
temperature. A similarly slow reaction was also observed for the
second amine substrates used for 9a and 10a at rt. Upon
heating the reaction mixture involving secondary amines to 80
°C, the dehydrogenative hydroboration proceeded smoothly
and generated the desired product within a few hours with
isolated/NMR yields comparable to those of primary
alkynylarylamines (see Scheme 2). On the basis of these
observations, a plausible reaction mechanism is proposed and
shown in Scheme 3. In the dehydrogenative hydroboration
reaction, following adduct A formation, dehydrogenation
occurs first, forming the intermediate B, which presumably
undergoes a rapid cis-hydroboration, forming the final product.
The crystal structures of 2a, 8a, and 10a were examined by
single-crystal X-ray diffraction analyses with those of 8a and
10a shown in Figure 1 (That of 2a is provided in the
Supporting Information). All three molecules have a benzene-
fused B,N heterocycle with an exo CC bond that has a typical
CC bond length, confirming their isosteric relationship with
Scheme 2. Dehydrogenative Hydroboration of Alkynyl
Arylamines Showing Isolated/NMR Yields
substituted alkyne and using the same solvent and reaction
conditions, compounds 2a and 3a were isolated in 13% and
16% yields, respectively. Again, the slow decomposition of the
BN-benzofulvenes on the silica gel column led to the low
isolated yields of these compounds. To enhance the stability of
the product, the Mes group in borane was replaced with a
bulkier 2,4,6-triisopropylphenyl (Tip) group, which did
improve the isolated yield of 4a from the reaction of 2-
(phenylethynyl)aniline with BH2(Tip) to 25%. Nonetheless,
slow decomposition of 4a on column was still observed. Using
BH2(Tip), compound 5a was also prepared and isolated in 24%
yield. Compounds 6a and 7a that contain an electron-donating
carbazolyl and the electron-withdrawing CF3 group, respec-
tively, were also synthesized using the same method, except that
benzene was used as the solvent and heating was necessary to
improve the solubility of the substrates for these two molecules.
NMR data showed that alkyl analogues (R2 = n-Bu, Mes, or
Tip-borane) could also be obtained; however, efforts to purify/
isolate the product failed (see Figure S45a−d). Compounds
1a−7a were fully characterized by NMR and HRMS analyses.
These examples show the applicability of the dehydrogenative
hydroboration to different substrates.
A key mechanistic question concerning the BN-benzofulvene
formation is the sequence of dehydrogenation and hydro-
boration after the formation of the adduct A (Scheme 3). For
compound 1a, no intermediate between A and the final product
was observed in the NMR tracking experiments. Hydroboration
of diarylalkynes normally requires elevated temperatures, while
most of the transformations studied here can readily proceed at
room temperature. Furthermore, previously we have shown
Figure 1. Crystal structures of 8a (left) and 10a (right). Important
bond lengths (Å), 8a/10a: B−N 1.421(4)/1.418(3), B−C1 1.557(4)/
1.564(3), B−C5 1.568(4)/1.573(3), C1−C2 1.476(4) /1.475(3),
C2−C3 1.416(4)/1.412(3), N−C3 1.407(3)/1.422(3), C1−C4
1.351(4)/1.347(3).
B
DOI: 10.1021/acs.orglett.8b00363
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
benzofulvene. The Z configuration of the exo alkene unit is
consistent with cis-hydroboration. In all three structures, the
azaborole ring is planar. The B−N bond lengths in all three
structures are similar (1.40−1.42 Å) and consistent with the
previously reported values of B−N double bonds.4b,24 In the
crystal lattice of 2a, the molecules have an extended 1D
structure facilitated by intermolecular NH···π, π···π stacking,
and Br···π interactions. Like benzofulvenes, which are known to
have a yellow color,20e,f all BN-benzofulvenes reported here
have a yellow or light yellow color in solution and the solid
state as shown in Figure 2.
relative to that of 1b. These data support the notion that 1a and
1b share similar electronic properties. Nonetheless, DFT data
show that the H atom bound to the N atom in 1a possesses a
positive charge character (Figure S10), similar to that in 1,2-
dihydro-1,2-azaborine,4c and the latter was shown to be
important for interactions with proteins via hydrogen bonds.4g
H−D exchange of 1a in CD3OD was examined, and the rate
constant kHD was determined to be 1.7(1) × 10−6 M−1 s−1
(Figure S5). The H−D exchange rate of 1a was about two
times faster than that of 1,2-dihydro-1,2-azaborine.4c
Photolysis of benzene vapor with a mercury resonance lamp
is known to give fulvene as the major product, and fulvene to
benzene photoisomerization was also reported previously.25
Bettinger and Liu showed that 1,2-dihydro-1,2-azaborine
displays a distinct photochemical reactivity.26 These motivated
us to examine the possible photo-conversion of BN-
benzofulvene 6a to benzoazaborine.27 However, only E/Z
isomerization was observed after 30 min irradiation at 360 nm
with a 1:2 E/Z ratio at the photostationary state (Figure S6).
This observation is consistent with the photoreactivity of the
benzofulvene system reported previously.20f
In summary, a facile dehydrogenative hydroboration method
has been established and demonstrated for the synthesis of
various BN-benzofulvenes. The scope of this reaction is general
for a variety of substrates. Computational studies indicate that
the BN-benzofulvenes show electronic properties similar to
those of their all-carbon analogues. The BN unit in BN-
benzofulvenes widens the HOMO−LUMO gap and introduces
a polar N−H bond, which may be useful for applications in
functional materials and pharmaceutical reagents.
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.8b00363.
Experimental details, synthesis, characterization data,
computational results and single-crystal data, and NMR
spectra (PDF)
Figure 2. (Top) Absorption spectra of 1a, 4a, 7a, and 8a in CH2Cl2
(10−5 M) with photographs showing the colors of 1a. (Bottom) TD-
DFT[B3LYP/6-31G(d)]-calculated UV−vis absorption spectra and
HOMO and LUMO energies/diagrams of 1a and its carbon analogue
1b.
Accession Codes
CCDC 1821087−1821089 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing 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.
UV−vis spectra are shown in Figure 2. Compounds 1a, 4a,
and 8a have very similar absorption profiles with a major
absorption band at 320 nm and a weak band at ∼390 nm. DFT
and TD-DFT studies indicate that the first absorption band of
these molecules is mainly from π−π* transitions of the
azaborabenzofulvene core and the styryl fragment. Adding a
carbazolyl to the pendant phenyl group on alkene (7a) leads to
the appearance of a strong absorption band at λmax = ∼350 nm,
which can be attributed to the carbazolyl domination in the
HOMO of 7a, and a great charge transfer character in the S0 →
S1 vertical excitation (HOMO to LUMO), with a very high
oscillator strength (0.350), based on TD-DFT data (Table S7).
To compare the electronic properties of 1a with its carbona-
ceous analogue 1b, DFT and TD-DFT calculations were also
performed for 1b. The HOMO and LUMO orbitals of 1a and
1b are depicted in Figure 2. BN substitution results in a greater
HOMO−LUMO gap by ∼0.2 eV mostly due to destabilization
of the LUMO. TD-DFT-calculated UV−vis spectra for 1a and
1b are similar except that the spectrum of 1a is blue-shifted
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: sw17@queensu.ca.
ORCID
Kang Yuan: 0000-0002-9766-6815
Suning Wang: 0000-0003-0889-251X
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Natural Science and Engineering Research
Council of Canada (RGPIN1193993-2013) for financial
C
DOI: 10.1021/acs.orglett.8b00363
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(17) (a) Wang, X. Y.; Narita, A.; Feng, X.; Mullen, K. J. Am. Chem.
Soc. 2015, 137, 7668. (b) Ma, C.; Zhang, J.; Li, J.; Cui, C. Chem.
Commun. 2015, 51, 5732.
̈
support and The Centre for Advanced Computing at Queen’s
University for computing facilities.
(18) (a) Felts, A. S.; Siegel, B. S.; Young, S. M.; Moth, C. W.;
Lybrand, T. P.; Dannenberg, A. J.; Marnett, L. J.; Subbaramaiah, K. J.
Med. Chem. 2008, 51, 4911. (b) Walters, M. J.; Blobaum, A. L.;
Kingsley, P. J.; Felts, A. S.; Sulikowski, G. A.; Marnett, L. Bioorg. Med.
Chem. Lett. 2009, 19, 3271. (c) Alcalde, E.; Mesquida, N.; Frigola, J.;
REFERENCES
■
(1) (a) Liu, Z.; Marder, T. B. Angew. Chem., Int. Ed. 2008, 47, 242.
(b) Bosdet, M. J. D.; Piers, W. E. Can. J. Chem. 2009, 87, 8.
(c) Campbell, P. G.; Marwitz, A. J. V.; Liu, S.-Y. Angew. Chem., Int. Ed.
2012, 51, 6074. (d) Wang, X.-Y.; Wang, J.-Y.; Pei, J. Chem. - Eur. J.
2015, 21, 3528. (e) Helten, H. Chem. - Eur. J. 2016, 22, 12972.
(f) Belanger-Chabot, G.; Braunschweig, H.; Roy, D. K. Eur. J. Inorg.
́
Chem. 2017, 2017, 4353. (g) Giustra, Z. X.; Liu, S.-Y. J. Am. Chem. Soc.
2018, 140, 1184.
Lop
́
ez-Per
́
ez, S.; Merce,
̀
R. Org. Biomol. Chem. 2008, 6, 3795.
(19) (a) Barbera,
Chem., Int. Ed. 1998, 37, 296. (b) Kosaka, Y.; Kawauchi, S.; Goseki, R.;
Ishizone, T. Macromolecules 2015, 48, 4421.
́
J.; Rakitin, O. A.; Ros, M. B.; Torroba, T. Angew.
(20) (a) Cordier, P.; Aubert, C.; Malacria, M.; Laco
Angew. Chem., Int. Ed. 2009, 48, 8757. (b) Hashmi, A. S. K.; Braun, I.;
Nosel, P.; Schadlich, J.; Wieteck, M.; Rudolph, M.; Rominger, F.
̂
te, E.; Gandon, V.
(2) Dewar, M. J. S.; Kubba, V. P.; Pettit, R. J. Chem. Soc. 1958, 3073.
(3) Ashe, A. J.; Fang, X. Org. Lett. 2000, 2, 2089.
̈
̈
Angew. Chem., Int. Ed. 2012, 51, 4456. (c) Bryan, C. S.; Lautens, M.
Org. Lett. 2010, 12, 2754. (d) Martinelli, C.; Cardone, A.; Pinto, V.;
Mastropasqua Talamo, M.; D'arienzo, M. L.; Mesto, E.; Schingaro, E.;
Scordari, F.; Naso, F.; Musio, R.; Farinola, G. M. Org. Lett. 2014, 16,
3424. (e) Kovalenko, S. V.; Peabody, S.; Manoharan, M.; Clark, R. J.;
Alabugin, I. V. Org. Lett. 2004, 6, 2457. (f) Mohamed, R. K.; Mondal,
S.; Jorner, K.; Delgado, T. F.; Lobodin, V. V.; Ottosson, H.; Alabugin,
I. V. J. Am. Chem. Soc. 2015, 137, 15441.
(21) (a) Staubitz, A.; Robertson, A. P. M.; Manners, I. Chem. Rev.
2010, 110, 4079. (b) Alcaraz, G.; Sabo-Etienne, S. Angew. Chem., Int.
Ed. 2010, 49, 7170. (c) Lorenz, T.; Lik, A.; Plamper, F. A.; Helten, H.
Angew. Chem., Int. Ed. 2016, 55, 7236. (d) Helten, H.; Robertson, A. P.
M.; Staubitz, A.; Vance, J. R.; Haddow, M. F.; Manners, I. Chem. - Eur.
J. 2012, 18, 4665.
(22) (a) Romero, E. A.; Peltier, J. L.; Jazzar, R.; Bertrand, G. Chem.
Commun. 2016, 52, 10563. (b) Yuan, K.; Wang, S. Org. Lett. 2017, 19,
1462.
(23) (a) Yuan, K.; Suzuki, N.; Mellerup, S. K.; Wang, X.; Yamaguchi,
S.; Wang, S. Org. Lett. 2016, 18, 720. (b) Nagai, A.; Murakami, T.;
Nagata, Y.; Kokado, K.; Chujo, Y. Macromolecules 2009, 42, 7217.
(24) Rao, Y. L.; Amarne, H.; Chen, L. D.; Brown, M. L.; Mosey, N. J.;
Wang, S. J. Am. Chem. Soc. 2013, 135, 3407.
(4) (a) Marwitz, A. J. V.; Abbey, E. R.; Jenkins, J. T.; Zakharov, L. N.;
Liu, S.-Y. Org. Lett. 2007, 9, 4905. (b) Abbey, E. R.; Zakharov, L. N.;
Liu, S.-Y. J. Am. Chem. Soc. 2008, 130, 7250. (c) Liu, L.; Marwitz, A. J.
V.; Matthews, B. W.; Liu, S.-Y. Angew. Chem., Int. Ed. 2009, 48, 6817.
(d) Marwitz, A. J. V.; Matus, M. H.; Zakharov, L. N.; Dixon, D. A.; Liu,
S.-Y. Angew. Chem., Int. Ed. 2009, 48, 973. (e) Knack, D. H.; Marshall,
J. L.; Harlow, G. P.; Dudzik, A.; Szaleniec, M. I.; Liu, S.-Y.; Heider, J.
Angew. Chem., Int. Ed. 2013, 52, 2599. (f) Zhao, P.; Nettleton, D. O.;
́
Karki, R. G.; Zecri, F. J.; Liu, S.-Y. ChemMedChem 2017, 12, 358.
(g) Lee, H.; Fischer, M.; Shoichet, B. K.; Liu, S.-Y. J. Am. Chem. Soc.
2016, 138, 12021. (h) Rombouts, F. J. R.; Tovar, F.; Austin, N.;
Tresadern, G.; Trabanco, A. A. J. Med. Chem. 2015, 58, 9287.
(i) Vlasceanu, A.; Jessing, M.; Kilburn, J. P. Bioorg. Med. Chem. 2015,
23, 4453.
(5) (a) Emslie, D. J. H.; Piers, W. E. P.; Parvez, M. Angew. Chem., Int.
Ed. 2003, 42, 1252. (b) Neue, B.; Araneda, J. F.; Piers, W. E.; Parvez,
M. Angew. Chem., Int. Ed. 2013, 52, 9966.
(6) (a) Braunschweig, H.; Geetharani, K.; Jimenez-Halla, J. O. C.;
Schafer, M. Angew. Chem., Int. Ed. 2014, 53, 3500. (b) Braunschweig,
̈
H.; Celik, M. A.; Hupp, F.; Krummenacher, I.; Mailander, L. Angew.
̈
Chem., Int. Ed. 2015, 54, 6347.
(7) (a) Fingerle, M.; Maichle-Mossmer, C.; Schundelmeier, S.;
̈
(25) (a) Kaplan, L.; Wilzbach, K. E. J. Am. Chem. Soc. 1967, 89, 1030.
(b) Ward, H. R.; Wishnok, J. S. J. Am. Chem. Soc. 1968, 90, 5353.
(26) Brough, S. A.; Lamm, A. N.; Liu, S.-Y.; Bettinger, H. F. Angew.
Chem., Int. Ed. 2012, 51, 10880.
Speiser, B.; Bettinger, H. F. Org. Lett. 2017, 19, 4428. (b) Muller, M.;
̈
Maichle-Mossmer, C.; Bettinger, H. F. Angew. Chem., Int. Ed. 2014, 53,
9380. (c) Biswas, S.; Maichle-Mossmer, C.; Bettinger, H. F. Chem.
̈
̈
(27) Scott, L. T.; Schultz, T. H.; Hashemi, M. M.; Wallace, M. B. J.
Commun. 2012, 48, 4564.
Am. Chem. Soc. 1991, 113, 9692.
(8) (a) Wisniewski, S. R.; Guenther, C. L.; Andreea Argintaru, O.;
Molander, G. A. J. Org. Chem. 2014, 79, 365. (b) Jouffroy, M.; Davies,
G. H. M.; Molander, G. A. Org. Lett. 2016, 18, 1606. (c) Liu, X.; Wu,
P.; Li, J.; Cui, C. J. Org. Chem. 2015, 80, 3737.
(9) Taniguchi, T.; Yamaguchi, S. Organometallics 2010, 29, 5732.
(10) (a) Hatakeyama, T.; Hashimoto, S.; Seki, S.; Nakamura, M. J.
Am. Chem. Soc. 2011, 133, 18614. (b) Wang, X.-Y.; Lin, H.-R.; Lei, T.;
Yang, D.-C.; Zhuang, F.-D.; Wang, J.-Y.; Yuan, S.-C.; Pei, J. Angew.
Chem., Int. Ed. 2013, 52, 3117. (c) Zhuang, F.-D.; Han, J.-M.; Tang, S.;
Yang, J.-H.; Chen, Q.-R.; Wang, J.-Y.; Pei, J. Organometallics 2017, 36,
2479. (d) Zhang, W.; Zhang, F.; Tang, R.; Fu, Y.; Wang, X.; Zhuang,
X.; He, G.; Feng, X. Org. Lett. 2016, 18, 3618.
(11) Su, B.; Kinjo, R. Synthesis 2017, 49, 2985.
(12) (a) Weber, L.; Bohling, L. Coord. Chem. Rev. 2015, 284, 236.
̈
(b) Weber, L.; Eickhoff, D.; Marder, T. B.; Fox, M. A.; Low, P. J.;
Dwyer, A. D.; Tozer, D. J.; Schwedler, S.; Brockhinke, A.; Stammler,
H. G.; Neumann, B. Chem. - Eur. J. 2012, 18, 1369.
(13) Su, B.; Li, Y.; Ganguly, R.; Lim, J.; Kinjo, R. J. Am. Chem. Soc.
2015, 137, 11274.
(14) (a) Su, B.; Li, Y.; Ganguly, R.; Lim, J.; Kinjo, R. J. Am. Chem.
Soc. 2015, 137, 11274. (b) Loh, Y. K.; Chong, C. C.; Ganguly, R.; Li,
Y.; Vidovic, D.; Kinjo, R. Chem. Commun. 2014, 50, 8561.
(15) (a) Abbey, E. R.; Zakharov, L. N.; Liu, S. Y. J. Am. Chem. Soc.
2010, 132, 16340. (b) Abbey, E. R.; Zakharov, L. N.; Liu, S. Y. J. Am.
Chem. Soc. 2011, 133, 11508.
(16) Morgan, M. M.; Patrick, E. A.; Rautiainen, J. M.; Tuononen, H.
M.; Piers, W. E.; Spasyuk, D. M. Organometallics 2017, 36, 2541.
D
DOI: 10.1021/acs.orglett.8b00363
Org. Lett. XXXX, XXX, XXX−XXX