Reaction of B2(o-tol)4 with CO and Isocyanides: Cleavage of the C≡O Triple Bond and Direct C?H Borylations

Article abstract of DOI:10.1002/anie.201800878

The reaction of highly Lewis acidic tetra(o-tolyl)diborane(4) with CO afforded a mixture of boraindane and boroxine by the cleavage of the C≡O triple bond. ¹³C labeling experiments confirmed that the carbon atom in the boraindane stems from CO. Simultaneously, formation of boroxine 3 could be considered as borylene transfer to capture the oxygen atom from CO. The reaction of diborane(4) with ^tBu?NC afforded an azaallene, while the reaction with Xyl?NC furnished cyclic compounds by direct C?H borylations.

Full text of DOI:10.1002/anie.201800878

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Reaction of B₂(o-tol)₄ with CO and Isocyanides: Cleavage of the
CΞO Triple Bond and Direct C-H Borylations
Authors: Yuhei Katsuma, Nana Tsukahara, Linlin Wu, Zhenyang Lin,
and Makoto Yamashita
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201800878
Angew. Chem. 10.1002/ange.201800878
Link to VoR: http://dx.doi.org/10.1002/anie.201800878
http://dx.doi.org/10.1002/ange.201800878

10.1002/anie.201800878
Angewandte Chemie International Edition
COMMUNICATION
Reaction of B2(o-tol)4 with CO and Isocyanides: Cleavage of the
º
C O Triple Bond and Direct C-H Borylations
Yuhei Katsuma,[a] Nana Tsukahara,[a] Linlin Wu,[b] Zhenyang Lin,*[b] Makoto Yamashita*[c]
Abstract: The reaction of highly Lewis-acidic tetra(o-tolyl)diborane(4)
with CO afforded a mixture of boraindane and boroxine via the
cleavage of the CºO triple bond. 13C-labeling experiments confirmed
that the carbon atom in the boraindane stems from CO.
Simultaneously, formation of boroxine 3 could be considered as
"borylene transfer" to capture oxygen atom from CO. The reaction of
diborane(4) with tBu-NC afforded an azaallene, while the reaction with
Xyl-NC furnished cyclic compounds via a direct C-H borylations.
with two 2,4,6-Me3C6H2 (Mes) groups to form the unsymmetric
diborane(4), pinB-BMes2, which exhibits a pinacolato and two
mesityl groups.[8] The absence of heteroatoms at one of the two
boron atoms renders this molecule highly electrophilic. In fact,
pinB-BMes2 reacts with tert-butylisocyanide leading to cleavage
of the NºC triple bond,[8] with CO to provide a CO-coordinated
boraalkene,[8] with alkynes to form diborylalkenes,[9] with 2,6-
dimethylphenylisocyanide to furnish a 1,2-oxaboretane ring,[10]
with pyridine to give C-H functionalized pyridines,[11] and with
electrons to afford the corresponding radical anion.[12] Even
though one can expect that diborane(4)s without the stabilization
from heteroatoms should exhibit higher reactivity than
heteroatom-stabilized diborane(4)s, examples for the reactivity of
such diborane(4)s remain limited.[13] We have recently reported
one such example, i.e., tetra(o-tolyl)diborane(4) (1), which
exhibits high electron affinity and reactivity toward H2 (Scheme
1).[14] Herein, we report that the reaction between 1 and CO
affords 2-boraindane and boroxine leading to concomitant
complete cleavage of the CºO triple bond and a C(sp3)–H bond,
while the reaction with isocyanides furnishes isocyanide-
coordinated boraalkenes or the C(sp2)–H bond cleaved products.
Carbon monoxide (CO) strongly coordinates to low-valent and
electron-rich transition metals to form the corresponding carbonyl
complexes, whereby bonding occurs predominantly via p-
backdonation to CO p*-orbitals.[1] Carbonyl ligands in the
coordination sphere of transition metal complexes exhibit diverse
reactivity, which includes simple or oxidative dissociations,
migratory insertions into covalent metal-ligand bonds, and
electrophilic reactions toward nucleophiles. In comparison, the
reactivity of CO towards main-group elements has been studied
less intensively until recently.[2] However, during the last few
decades a growing number of main-group-element compounds
that react with CO has emerged.[3] Among these, only very few
compounds are able to completely cleave the CºO triple bond in
CO without having to rely on transition metals.[4] Organic
isocyanides are also often used as ligands for transition metals
and as substrates in transition-metal-catalyzed transformations,
given that they are isoelectronic to CO.[5] Similar to CO, organic
isocyanides exhibit a formally divalent character, which renders
them ideal partners for reactions with main-group elements.[3p, 6]
H2
H
H
(1 bar)
B
B
B
B
hexane
RT, 2 h
1
Scheme 1. Reaction of tetra(o-tolyl)diborane(4) (1) with H2
Bis(pinacolato)diborane (B2pin2), which is stabilized by pp-pp
interactions from four adjacent oxygen atoms, has been widely
used for transition-metal-catalyzed borylations of organic
molecules.[7] We have recently reported a modification of B2pin2
Exposure of a benzene solution of 1 to CO (1 bar) resulted in
the formation of 2-boraindane 2 via insertion of the carbon atom
of the CO molecule and cleavage of a C(sp3)–H bond of a methyl
group of an o-tolyl substituent (Scheme 2). The oxygen atom of
CO is incorporated into o-tolylboroxine 3 as evident from NMR
and mass spectra, as well as a comparison with previously
reported spectra.[15] In order to facilitate the characterization, 13CO
was used to generate 13C-labeled 2-13C. The structure of 2 was
unambiguously determined by single-crystal X-ray diffraction
analysis (Figure 1). In the solid state, the boron-containing five-
membered ring is almost planar, whereby the B1 atom is sp2-
hybridized (angle sum around the boron atom: 359.9°). The
captured carbon atom (C8) can be considered as sp3-hybridized,
as the three C–C bonds are non-planar and one hydrogen atom
(H8) was found in the differential Fourier map. The presence of
H8 in 2 was also confirmed by a singlet at dH 4.17 ppm in the 1H
NMR spectrum. In the case of 2-13C, H8 was observed as a
[a]
[b]
Y. Katsuma, N. Tsukahara
Department of Applied Chemistry, Faculty of Science and
Engineering, Chuo University
1-13-27 Kasuga, Bunkyo-ku, 112-8551 Tokyo (Japan)
L. Wu, Prof. Dr. Zhenyang Lin
Department of Chemistry, The Hong Kong University of Science and
Technology
Clear Water Bay, Kowloon, Hong Kong
E-mail: chzlin@ust.hk
Homepage: http://chzlin.people.ust.hk/
Prof. Dr. Makoto Yamashita
[c]
Department of Molecular and Macromolecular Chemistry, Graduate
School of Engineering, Nagoya University
Furo-cho, Chikusa-ku, Nagoya, 464-8603 Aichi (Japan)
E-mail: makoto@oec.chembio.nagoya-u.ac.jp
Homepage: http://oec.chembio.nagoya-u.ac.jp/index-e.html
doublet due to coupling with the introduced 13C nucleus (1JCH
=
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
111 Hz; Figures 2a,b).[16] In the 13C NMR spectrum of 2-13C, three
doublets for aromatic quaternary carbons were found at dC 144.10
This article is protected by copyright. All rights reserved.

10.1002/anie.201800878
Angewandte Chemie International Edition
COMMUNICATION
Figure 2. NMR spectra of 2 and 2-13CO (red solid lines denote coupling with
13C, top: 2; bottom: 2-13C). (a) Schematic summary of the coupling in 2-13C; (b)
the 1H NMR signal for the methine proton; (c) 13C NMR signal for the 13C-bonded
quaternary carbon atom; (d) 13C NMR signal for the methine carbon (the signal
of 2 was increased by one order of magnitude for clarity).
(1JCC = 42 Hz), 144.56 (1JCC = 7 Hz), and 149.16 (1JCC = 39 Hz)
ppm [Figure 2c; cf. 1JCC = 43 Hz for the C(sp2)–C(sp3) linkage in
2
strychnine,[17] and JCC = 3-8 Hz for allylic 13C–C=13C[18]]. In the
aliphatic region, a methine signal was observed at dC 53.34 ppm,
which was strongly enhanced in comparison to that of 2. This
result proves that the methine carbon atom stems from CO via
cleavage of the CºO triple bond in the absence of a transition-
metal complex. Simultaneously, this reaction can be considered
as "borylene transfer" to capture oxygen atom of CO.
A feasible mechanism for the formation of 2 and 3 based on
the DFT calculations is proposed in Scheme 3 (cf. SI for details
and energy profiles). In the first step, a lone pair on the carbon
atom of CO coordinates to one boron atom of 1 to form sp2-sp3
species 4. Based on our previous work on the reaction of
unsymmetric pinB-BMes2 with CO,[8] we considered two possible
pathways, i.e., migration of one o-tolyl group or the boryl group in
4 to afford 5 (red arrows: path A) or 10 (blue arrows: path B). The
cyclization of diboranyl ketone 5 results in the formation of a four-
membered ring in 6. However, DFT calculations suggested a
higher activation energy for the formation of 5 and a very high
activation energy (47.3 kcal/mol) for the subsequent migration of
the o-tolyl group in 6 to furnish 7, which would be able to
dissociate into boraalkene 8 and oxoborane 9.[19] Instead, path B
was calculated as an appropriate mechanism for the formation of
8 and 9. Diborylketone 10 undergoes further migration of a BAr2
group to afford 11 via the formation of a thermally stable B–O
bond. It should be noted that 11 can be considered as a carbene
that is stabilized by a p-donating oxygen atom and a p-accepting
boron atom. This carbene character could induce the subsequent
nucleophilic migration of one o-tolyl group on the negatively
charged boron atom in 11 to furnish 12. Coordination of adjacent
o-tol group to the resulting boraalkene moiety in 12 affords
boraalkene-arene complex 13.[20] The B–Ar bond in 12, which is
more reactive than B–O bond of the similar boraalkene
intermediate in the reaction of pinB-BMes2 with CO,[8] would
induce the rapid intramolecular migration of aryl group. The
coordinating aryl group in 13 migrates to the boraalkene moiety
with an assistance of the lone pair on the oxygen atom to furnish
oxonium borate 14. The subsequent dissociation of 9 from 14
spontaneously takes place to give an allenic betaine 15. To cancel
positive and negative charges in 15, the aryl group on borate
moiety migrates to the carbon atom to furnish boraalkene 8. A
simultaneous intramolecular proton transfer and a cyclization at
the benzylic position finally give boraindane 2. Simultaneously,
oxoborane 9 trimerizes to form boroxine 3.
CO or 13CO
(1 bar)
o-tol
H
o-tol
B
1
3
C
+
O
B
O
1
benzene
rt, 2 h
B
B
o-tol
O
o-tol
o-tol
2: C = 12C (50%) or
2-13C: C = 13C, 11%
3 (37%)
Scheme 2. Reaction of 7 with CO or 13CO (Yield in parentheses estimated by
1H NMR spectroscopy.)
C9
C15
C8
C16
H8
C21
B1
C1
Figure 1. Molecular structure of 2 (thermal ellipsoids set at 50% probability,
hydrogen atoms expect H8 omitted for clarity). Selected bond lengths (Å) and
angles (°): B1–C1 1.558(2), B1–C8 1.613(2), B1–C21 1.582(2), C21–C16
1.507(2), C16–C15 1.395(2), C15–C8 1.524(2); C1–B1–C8 123.65(13), C1–
B1–C21 129.39(13), C8–B1–C21 106.88(12), B1–C8–C15 102.92(11), C8–
C15–C16 112.82(13), C15–C16–C21 112.67(13), B1–C21–C16 104.51(12).
This article is protected by copyright. All rights reserved.

10.1002/anie.201800878
Angewandte Chemie International Edition
COMMUNICATION
path A
of a single diastereoisomer, which is most likely due to the steric
repulsion between two o-tolyl groups.
1
O
C Ar
B
Ar
Ar
Ar Ar
Ar
Ar
C
O
B
Ar
B
Ar
C
O
O
O
B
C
B
O
B
C
+
B
B
Ar
Ar
Ar
8
9
Ar Ar
O
Ar
Ar
B
Ar
C
5
tBu
N
C C N
tBu
Ar
6
7
tBu-NC
(2 equiv.)
B
Ar
Ar2B
Ar
Ar2B
Ar
N
O
Ar
O
Ar
Ar
tBu
tBu
C C N
Ar
1
4
C
B
Ar
C
Ar
10
O
Ar
C
B
benzene
r.t. (71%)
B
B
B
B
B
path B
B
Ar
16
Xyl-NC
16’
Ar
Ar
Ar Ar
Ar
Ar
11
12
Xyl-NC
benzene
benzene
(1 equiv.) r.t. (60%)
(2 equiv.) r.t. (86%)
Ar
C
Ar
Ar
B
B
O
Xyl
B
Ar
13
C
B
Xyl-NC
(1 equiv.)
N
C
–9
C
B
Ar Ar
14
Ar
Ar
B
B
B
Ar
17
B
Ar
18
Ar Ar
Ar
r.t. (98%)
15
C N
C N
H
H
Ar
Xyl
Xyl
H
Ar
Ar
×3
C
B
C
9
3
B
Scheme 4. Reaction of 1 with isocyanides (Ar = o-tol, Xyl = 2,6-Me2C6H3, Yield
estimated by 1H NMR spectroscopy.)
H
Ar
2
8
Ar
Scheme 3. Possible mechanism of for the cleavage of the CºO triple bond
during the reaction between 1 and CO to afford 2 and 3 (Ar = o-tol).
Tetra(o-tolyl)diborane(4) 1 also reacted with isocyanides
(Scheme 4). The reaction of 1 with 2 equiv. of tBu-NC in benzene
afforded 1-azaallene 16. The solid-state structure of 16 was
determined by a single-crystal X-ray diffraction analysis (Figure
3), albeit that the disorder of the structure due to the orientation
C32
B1
C25
t
of the o-tolyl groups and the Bu group on the terminal nitrogen
atom prevented us from estimating accurate structural
parameters. Nevertheless, it is clear that 16 is resulted from a
coupling of two isocyanide molecules at the carbon atom and the
N1
C1
N2
C21
C20
t
separation of the two boron atoms. The N-terminus of the Bu-
B2
N=C moiety is slightly bent [139.4(6)°/133.3(9)°], indicating that
N2 is sp2-hybridized. The 1H NMR spectrum of isolated crystalline
16 indicated the presence of two conformers in solution, probably
due to the restricted rotation around the N1–C1 bond and the
C6
C58
t
relative orientation of the two Bu groups on N1 and N2. The VT
1H NMR spectra of 16 (RT and 70 °C) suggested interconversion
of these isomers on the 1H NMR timescale (cf. SI). The reaction
between 1 and 1 equiv. of Xyl-NC (Xyl = 2,6-Me2C6H3) afforded
17, which contains a benzoannulated six-membered ring. The
structure of 17 was determined by a single-crystal X-ray diffraction
analysis (Figure 4). The annulated benzene ring in 17 is derived
from one of the four o-tolyl groups in 1, whereby the C–H bond at
the 6-position of the annulated o-tolyl group is cleaved. In the solid
state, the six-membered ring in 17 is slightly distorted from
planarity, reflecting the contribution from sp3-hybridized C1 to the
six-membered ring. Given the high number of possible rotamers
of 17, which arises from the orientation of three o-tolyl groups, a
complete characterization of 17 by 1H NMR spectroscopy was not
possible, although the 11B NMR spectrum, the X-ray diffraction
analysis, and the elemental analysis all supported the formation
of 17. The reaction between 1 and 2 equiv. of Xyl-NC led to the
formation of 18, in which Xyl-NC coordinates to 17. Based on the
X-ray crystallographic analysis (Figure 5), coordination of Xyl-NC
to 17 directly affords 18, as confirmed by independent experiment
for the formation of 18 by a reaction of 17 with 1 equiv. of Xyl-NC.
The 1H, 11B, and 13C NMR spectra of 18 suggested the presence
Figure 3. Molecular structure of 16 (thermal ellipsoids set at 50% probability,
minor part of disordered moiety and hydrogen atoms omitted for clarity).
Selected bond lengths (Å) and angles (°): B1–N1 1.407(4), B1–C25 1.584(6),
B1–C32 1.618(10), N1–C1 1.41(2), C1–B2 1.635(15), C1–C20 1.36(2), C20–
N2 1.171(7); B2–C1–C20 1.36(2), C1–C20–N2 1.790(10), C20–N2–C21
139.4(6).
This article is protected by copyright. All rights reserved.

10.1002/anie.201800878
Angewandte Chemie International Edition
COMMUNICATION
could be differentiated from the reactivity of the intermediate 11 in
t
Scheme 3, probably due to higher concentration of Bu-NC in
solution than that of gaseous CO. In the case of using less-
hindered Xyl-NC, the common intermediate 21 engages in a
migration of an o-tolyl group to the carbenic carbon atom, which
generates boraalkene 22.[21] After the rotation of the N-C bond in
22, rotamer 22' would have the appropriate orientation to induce
an electrophilic attack of the boraalkene moiety on the o-tolyl ring.
C2 C7
B2
C1
B1
N1
A
subsequent deprotonation by the negatively charged
boraalkene in 23 would furnish cyclized product 17, followed by
the coordination of Xyl-NC to afford 18.
H44
In summary, we found that the reaction between highly Lewis-
acidic tetra(o-tolyl)diborane(4) 1 and CO afforded a mixture of
boraindane 2 and boroxine 3 via complete cleavage of the CºO
triple bond. The incorporation of the CO carbon atom in
boraindane
2
was confirmed by 13C-labeling experiments.
Simultaneously, formation of boroxine 3 could be considered as
"borylene transfer" to capture oxygen atom from CO. The reaction
between 1 and tBu-NC generated azaallene 13, while the reaction
between 1 and Xyl-NC resulted in the formation of cyclic
compounds 14 and 15 through C-H borylations.
Figure 4. Molecular structure of 17 (thermal ellipsoids set at 50% probability,
hydrogen atoms except H44 omitted for clarity). Selected bond lengths (Å) and
angles (°): C1–N1 1.448(4), N1–B1 1.488(4), B1–C7 1.583(4), C7–C2 1.429(4),
C2–B2 1.543(5); B2–C1–N2 115.0(2), C1–N1–B1 124.7(2), N1–B1–C7
119.9(3), B1–C7–C2 118.5(3), C7–C2–B2 120.7(3), C2–B2–C1 119.8(3).
16
tBu
C N
R
R
N
R
N
R = tBu or Xyl
N
C
B
Ar
Ar
C
Ar
C2
C3
C N R
Ar
Ar
C
B
1
B
B
B
B
Ar
Ar
Ar
Ar
Ar
19
Ar
Ar
B1
20
21
R = Xyl
B2
Ar
Ar
B
C4
N2
B
H
Xyl
Xyl Xyl
BAr2
N1
C1
H1
N
C
N
C
N
C
17
18
B
Ar
B
Ar
B
Ar
C N Xyl
Ar
Ar
Ar
22
TS22-17
Scheme 5. Plausible mechanism for the incorporation of isocyanides in 1 and
the C-H bond cleavage to generate 16-18 (Ar = o-tol, Xyl = 2,6-Me2C6H3)
Figure 5. Molecular structure of 18 (thermal ellipsoids set at 50% probability,
hydrogen atoms except H1 omitted for clarity). Selected bond lengths (Å) and
angles (°): C1–N1 1514(3), N1–B1 1.405(4), B1–C2 1.597(4), C2–C3 1.416(4),
C3–B2 1.620(4), B2–C1 1.648(4), B2–C38 1.604(4), C38–N2 1.155(3); B2–C1–
N1 109.75, C1–N1–B1 124.8 (2), N1–B1–C2119.2(2), B1–C2–C3 117.5(2), C2–
C3–B2 120.0(2), C3–B2–C1 130.0(2), C38–N2–C39 169.3(3)
Acknowledgements
This research was supported by Grant-in-Aid for Scientific
Research (A) (JSPS KAKENHI 17H01191), JST CREST Grant
Number 14529307, and the Research Grants Council of Hong
Kong (HKUST16304017). The authors thank Prof. T. Hiyama
(Chuo University) for providing them with access to an X-ray
diffractometer.
A plausible mechanism for the formation of 16-18 via the
common intermediate 21 is proposed in Scheme 5, based on the
DFT calculations (cf. SI for details and energy profiles). Similar to
the formation of 2 and 3 (Scheme 3), coordination of isocyanide
to the boron atom formed sp2-sp3 species 19. A subsequent B–B
bond cleavage of 19 should generate diborylimine 20 with an
intramolecular coordination of nitrogen atom to the boron atom.
The cleavage of B–C bond to release the ring strain of the BNC
three-membered ring affords boryl-substituted azaboraallene 21.
Because of a carbenic character of 21, similar to 11, a nucleophilic
attack on the central carbon atom of 21 by the second equivalent
of tBu-NC, under simultaneous elimination of the positive charge
on the nitrogen atom would then result in the formation of
azaallene 16. The nucleophilic attack of the second tBu-NC to 21
Keywords: diborane(4) • carbon monoxide • isocyanide • triple
bond • bond cleavage
[1]
[2]
J. F. Hartwig, in Organotransition Metal Chemistry: From Bonding to
Catalysis, University Science Books, Sausalito, CA, 2010.
(a) A. B. Burg, H. I. Schlesinger, J. Am. Chem. Soc. 1937, 59, 780-787;
(b) W. J. J. M. Sprangers, R. Louw, J. Chem. Soc., Parkin Trans. 2 1976,
1895-1901; (c) D. Seyferth, R. M. Weinstein, J. Am. Chem. Soc. 1982,
104, 5534-5535.
[3]
(a) P. Paetzold, B. Redenz-Stormanns, R. Boese, Angew. Chem. Int. Ed.
Engl. 1990, 29, 900-902; (b) S. Luckert, E. Eversheim, M. Müller, B.
This article is protected by copyright. All rights reserved.

10.1002/anie.201800878
Angewandte Chemie International Edition
COMMUNICATION
Redenz-Stormanns, U. Englert, P. Paetzold, Chem. Ber. 1995, 128,
1029-1035; (c) J. Teichmann, H. Stock, H. Pritzkow, W. Siebert, Eur. J.
Inorg. Chem. 1998, 1998, 459-463; (d) M. R. Mason, B. Song, K.
Kirschbaum, J. Am. Chem. Soc. 2004, 126, 11812-11813; (e) N. Nakata,
T. Oikawa, T. Matsumoto, Y. Kabe, A. Sekiguchi, Organometallics 2005,
24, 3368-3370; (f) V. Lavallo, Y. Canac, B. Donnadieu, W. W. Schoeller,
G. Bertrand, Angew. Chem. Int. Ed. 2006, 45, 3488-3491; (g) X. Li, C. Ni,
H. Song, C. Cui, Chem. Commun. 2006, 1763-1765; (h) M. R. Mason, B.
Song, Y. Han, X. Hu, Inorg. Chim. Acta 2008, 361, 3332-3337; (i) X.
Wang, Z. Zhu, Y. Peng, H. Lei, J. C. Fettinger, P. P. Power, J. Am. Chem.
Soc. 2009, 131, 6912-6913; (j) A. Fukazawa, J. L. Dutton, C. Fan, L. G.
Mercier, A. Y. Houghton, Q. Wu, W. E. Piers, M. Parvez, Chem. Sci. 2012,
3, 1814-1818; (k) M. J. Cowley, Y. Ohmori, V. Huch, M. Ichinohe, A.
Sekiguchi, D. Scheschkewitz, Angew. Chem. Int. Ed. 2013, 52, 13247-
13250; (l) H. Braunschweig, T. Dellermann, R. D. Dewhurst, W. C. Ewing,
K. Hammond, J. O. C. Jimenez-Halla, T. Kramer, I. Krummenacher, J.
Mies, A. K. Phukan, A. Vargas, Nat. Chem. 2013, 5, 1025-1028; (m) M.
Sajid, L.-M. Elmer, C. Rosorius, C. G. Daniliuc, S. Grimme, G. Kehr, G.
Erker, Angew. Chem. Int. Ed. 2013, 52, 2243-2246; (n) M. Sajid, A.
Lawzer, W. Dong, C. Rosorius, W. Sander, B. Schirmer, S. Grimme, C.
G. Daniliuc, G. Kehr, G. Erker, J. Am. Chem. Soc. 2013, 135, 18567-
18574; (o) M. Sajid, G. Kehr, C. G. Daniliuc, G. Erker, Angew. Chem. Int.
Ed. 2014, 53, 1118-1121; (p) H. Braunschweig, R. D. Dewhurst, F. Hupp,
M. Nutz, K. Radacki, C. W. Tate, A. Vargas, Q. Ye, Nature 2015, 522,
327-330; (q) W. Lu, H. Hu, Y. Li, R. Ganguly, R. Kinjo, J. Am. Chem. Soc.
2016, 138, 6650-6661; (r) B. Wang, G. Luo, M. Nishiura, Y. Luo, Z. Hou,
J. Am. Chem. Soc. 2017, 139, 16967-16973; (s) X. Shi, C. Hou, C. Zhou,
Y. Song, J. Cheng, Angew. Chem. Int. Ed. 2017, 56, 16650-16653.
(d) H. Y. Chen, S. Schlecht, T. C. Semple, J. F. Hartwig, Science 2000,
287, 1995-1997; (e) T. Ishiyama, J. Takagi, K. Ishida, N. Miyaura, N. R.
Anastasi, J. F. Hartwig, J. Am. Chem. Soc. 2002, 124, 390-391; (f) T.
Ishiyama, N. Miyaura, Chem. Rec. 2004, 3, 271-280; (g) T. Ishiyama, N.
Miyaura, Pure Appl. Chem. 2006, 78, 1369-1375; (h) I. A. I. Mkhalid, J.
H. Barnard, T. B. Marder, J. M. Murphy, J. F. Hartwig, Chem. Rev. 2010,
110, 890-931.
[8]
[9]
H. Asakawa, K.-H. Lee, Z. Lin, M. Yamashita, Nat. Commun. 2014, 5,
4245.
C. Kojima, K.-H. Lee, Z. Lin, M. Yamashita, J. Am. Chem. Soc. 2016,
138, 6662-6669.
[10] Y. Katsuma, H. Asakawa, K.-H. Lee, Z. Lin, M. Yamashita,
Organometallics 2016, 35, 2563-2566.
[11] Y. Katsuma, H. Asakawa, M. Yamashita, Chem. Sci. 2018, 9, in press,
doi: 10.1039/C1037SC04759B.
[12] H. Asakawa, K.-H. Lee, K. Furukawa, Z. Lin, M. Yamashita, Chem.-Eur.
J. 2015, 21, 4267-4271.
[13] (a) T. Wartik, R. Moore, H. I. Schlesinger, J. Am. Chem. Soc. 1949, 71,
3265-3266; (b) G. Urry, J. Kerrigan, T. D. Parsons, H. I. Schlesinger, J.
Am. Chem. Soc. 1954, 76, 5299-5301; (c) G. Urry, T. Wartik, R. E. Moore,
H. I. Schlesinger, J. Am. Chem. Soc. 1954, 76, 5293-5298; (d) A. Finch,
H. I. Schlesinger, J. Am. Chem. Soc. 1958, 80, 3573-3574; (e) P. Ceron,
A. Finch, J. Frey, J. Kerrigan, T. Parsons, G. Urry, H. I. Schlesinger, J.
Am. Chem. Soc. 1959, 81, 6368-6371; (f) A. Höfner, B. Ziegler, R.
Hunold, P. Willershausen, W. Massa, A. Berndt, Angew. Chem. Int. Ed.
Engl. 1991, 30, 594-596; (g) A. Moezzi, M. M. Olmstead, R. A. Bartlett,
P. P. Power, Organometallics 1992, 11, 2383-2388; (h) A. Moezzi, M. M.
Olmstead, P. P. Power, J. Am. Chem. Soc. 1992, 114, 2715-2717; (i) P.
P. Power, Inorg. Chim. Acta 1992, 198–200, 443-447; (j) W. J. Grigsby,
P. Power, Chem.-Eur. J. 1997, 3, 368-375; (k) H. Hommer, H. Noth, J.
Knizek, W. Ponikwar, H. Schwenk-Kircher, Eur. J. Inorg. Chem. 1998,
1519-1527; (l) H. Braunschweig, A. Damme, R. D. Dewhurst, T. Kramer,
T. Kupfer, K. Radacki, E. Siedler, A. Trumpp, K. Wagner, C. Werner, J.
Am. Chem. Soc. 2013, 135, 8702-8707; (m) H. Braunschweig, A.
Damme, T. Kupfer, Chem. Commun. 2013, 49, 2774-2776; (n) N. Arnold,
H. Braunschweig, A. Damme, R. D. Dewhurst, L. Pentecost, K. Radacki,
S. Stellwag-Konertz, T. Thiess, A. Trumpp, A. Vargas, Chem. Commun.
2016, 52, 4898-4901; (o) M. Arrowsmith, J. Bohnke, H. Braunschweig,
Dei, R. D. Dewhurst, W. C. Ewing, C. Horl, J. Mies, J. H. Muessig, Chem.
Commun. 2017, 53, 8265-8267.
[4]
(a) R. Dobrovetsky, D. W. Stephan, J. Am. Chem. Soc. 2013, 135, 4974-
4977; (b) L. D. Curless, E. R. Clark, J. Cid, A. Del Grosso, M. J. Ingleson,
Chem. Commun. 2015, 51, 10903-10906; (c) M. Majumdar, I. Omlor, C.
B. Yildiz, A. Azizoglu, V. Huch, D. Scheschkewitz, Angew. Chem. Int. Ed.
2015, 54, 8746-8750; (d) M. Arrowsmith, J. Böhnke, H. Braunschweig,
M. A. Celik, Angew. Chem. Int. Ed. 2017, 56, 14287-14292; (e) M.
Devillard, B. de Bruin, M. A. Siegler, J. I. van der Vlugt, Chem.-Eur. J.
2017, 23, 13628-13632; (f) C. B. Yildiz, D. Scheschkewitz,
Organometallics 2017, 36, 3035-3042.
[5]
[6]
(a) S. Ozaki, Chem. Rev. 1972, 72, 457-496; (b) A. Dömling, Chem. Rev.
2006, 106, 17-89; (c) G. Qiu, Q. Ding, J. Wu, Chem. Soc. Rev. 2013, 42,
5257-5269; (d) V. P. Boyarskiy, N. A. Bokach, K. V. Luzyanin, V. Y.
Kukushkin, Chem. Rev. 2015, 115, 2698-2779; (e) B. Song, B. Xu, Chem.
Soc. Rev. 2017, 46, 1103-1123.
[14] N. Tsukahara, H. Asakawa, K.-H. Lee, Z. Lin, M. Yamashita, J. Am.
Chem. Soc. 2017, 139, 2593-2596.
(a) F. Bauer, H. Braunschweig, K. Schwab, Organometallics 2010, 29,
934-938; (b) O. Ekkert, G. Kehr, C. G. Daniliuc, R. Fröhlich, B. Wibbeling,
J. L. Petersen, G. Erker, Z. Anorg. Allg. Chem. 2013, 639, 2455-2462;
(c) O. Ekkert, G. G. Miera, T. Wiegand, H. Eckert, B. Schirmer, J. L.
Petersen, C. G. Daniliuc, R. Frohlich, S. Grimme, G. Kehr, G. Erker,
Chem. Sci. 2013, 4, 2657-2664; (d) Z. D. Brown, P. P. Power, Inorg.
Chem. 2013, 52, 6248-6259; (e) N. Kielland, E. Vicente-García, M.
Revés, N. Isambert, M. J. Arévalo, R. Lavilla, Adv. Synth. Cat. 2013, 355,
3273-3284; (f) B. R. Barnett, C. E. Moore, A. L. Rheingold, J. S. Figueroa,
Chem. Commun. 2015, 51, 541-544; (g) A. Jana, V. Huch, H. S. Rzepa,
D. Scheschkewitz, Angew. Chem. Int. Ed. 2015, 54, 289-292; (h) L. Kong,
W. Lu, Y. Li, R. Ganguly, R. Kinjo, Angew. Chem. Int. Ed. 2016, 55,
14718-14722; (i) A. C. McQuilken, Q. M. Dao, A. J. P. Cardenas, J. A.
Bertke, S. Grimme, T. H. Warren, Angew. Chem. Int. Ed. 2016, 55,
14335-14339; (j) J. Li, B. Li, R. Liu, L. Jiang, H. Zhu, H. W. Roesky, S.
Dutta, D. Koley, W. Liu, Q. Ye, Chem.-Eur. J. 2016, 22, 14499-14503; (k)
A. K. Adhikari, M. B. Sárosi, T. Grell, P. Lönnecke, E. Hey-Hawkins,
Chem.-Eur. J. 2016, 22, 15664-15668; (l) L. Kong, W. Lu, Y. Li, R.
Ganguly, R. Kinjo, J. Am. Chem. Soc. 2016, 138, 8623-8629; (m) W. Lu,
Y. Li, R. Ganguly, R. Kinjo, Angew. Chem. Int. Ed. 2017, 56, 9829-9832.
(a) T. Ishiyama, N. Matsuda, N. Miyaura, A. Suzuki, J. Am. Chem. Soc.
1993, 115, 11018-11019; (b) R. T. Baker, P. Nguyen, T. B. Marder, S. A.
Westcott, Angew. Chem. Int. Ed. Engl. 1995, 34, 1336-1338; (c) T.
Ishiyama, M. Yamamoto, N. Miyaura, Chem. Commun. 1997, 689-690;
[15] E. J. Corey, T. Shibata, T. W. Lee, J. Am. Chem. Soc. 2002, 124, 3808-
3809.
[16] The C(sp3)–H coupling constants in cyclic hexose derivatives were
reported to be 1JCH = 130-140 Hz with ideal sp3 hybridized carbon atom
due to six-membered ring. See, T. Klepach, W. Zhang, I. Carmichael, A.
S. Serianni, J. Org. Chem. 2008, 73, 4376-4387. A slightly distorted five-
membered ring in 2 would affect to the hybridization of C8 to possess
smaller bond angle of B1–C8–C15 = 102.92(11)° than that of ideal sp3
carbon. One can expect that this small B–C–C angle would lead to
increase s-character of C–H bond and make coupling constant be
smaller.
[17] R. T. Williamson, A. V. Buevich, G. E. Martin, Org. Lett. 2012, 14, 5098-
5101.
[18] T. D. W. Claridge, High-Resolution NMR Techniques in Organic
Chemistry, Elsevier Science, 2016.
[19] Related Pt-oxoborane species were isolated, characterized, and proven
to be dimerized. See, (a) H. Braunschweig, K. Radacki, A. Schneider,
Science 2010, 328, 345-347. (b) H. Braunschweig, K. Radacki, A.
Schneider, Angew. Chem. Int. Ed. 2010, 49, 5993-5996.
[20] The arene-boraalkene complex 13 could be distinguished from pyridine-
stabilized 7-borabicyclo[4.1.0]hepta-3,5-diene derivatives because of
longer B–C bond in 13. See: (a) Y.-L. Rao, H. Amarne, S.-B. Zhao, T. M.
McCormick, S. Martić, Y. Sun, R.-Y. Wang, S. Wang, J. Am. Chem. Soc.
2008, 130, 12898-12900; (b) H. Amarne, C. Baik, S. K. Murphy, S. Wang,
[7]
This article is protected by copyright. All rights reserved.

10.1002/anie.201800878
Angewandte Chemie International Edition
COMMUNICATION
Chem.-Eur. J. 2010, 16, 4750-4761; (c) H. Amarne, C. Baik, R.-Y. Wang,
S. Wang, Organometallics 2011, 30, 665-668; (d) Y.-L. Rao, H. Amarne,
S. Wang, Coord. Chem. Rev. 2012, 256, 759-770; (e) Y.-L. Rao, L. D.
Chen, N. J. Mosey, S. Wang, J. Am. Chem. Soc. 2012, 134, 11026-
11034; (f) Y.-L. Rao, H. Amarne, L. D. Chen, M. L. Brown, N. J. Mosey,
S. Wang, J. Am. Chem. Soc. 2013, 135, 3407-3410; (g) Y. L. Rao, C.
Hörl, H. Braunschweig, S. Wang, Angew. Chem. Int. Ed. 2014, 53, 9086-
9089; (h) S. K. Mellerup, L. Häfele, A. Lorbach, X. Wang, S. Wang, Org.
Lett. 2017, 19, 3851-3854.
t
[21] The difference in steric factor between Bu and Xyl contributed to alter
the lower-energy pathways from 21 to 16 or 22. See SI for details about
DFT calculations.
…
This article is protected by copyright. All rights reserved.

10.1002/anie.201800878
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
The reaction between highly Lewis-
acidic (o-tol)2B–B(o-tol)2 and CO
afforded a mixture of boraindane and
Yuhei Katsuma, Nana Tsukahara, Linlin
Wu, Zhenyang Lin,* Makoto Yamashita*
CO
(1 bar)
H
o-tol
C
B
B
benzene
rt, 2 h
B
Page No. – Page No.
o-tol
+ boroxine
C≡O cleavage
boroxine via a complete cleavage of
the CºO triple bond. 13C-labeling
experiments demonstrated that the
carbon atom in boraindane stems from
CO. The reaction of diborane(4) with
tBu-NC afforded an azaallene, while
the reaction with Xyl-NC afforded cyclic
compounds via direct C-H borylations.
Reaction of B2(o-tol)4 with CO and
tBu
Isocyanides: Cleavage of the C
Triple Bond and Direct C-H
Borylations
º
O
Ar = o-tol
N
C
Xyl
N
C
Xyl = 2,6-Me2C6H3
Xyl
tBu
N
N
Ar2B
Ar
C
tBu
C
N
B
C
B
Ar
Ar
B
C
N
Ar
Ar
Xyl
H
azaallene
C-H borylation
This article is protected by copyright. All rights reserved.