Reactivity of stabilized Li/Cl carbenoids towards lewis base adducts of BH3: B-H bond activation versus carbene dimerization

Article abstract of DOI:10.1002/chem.201302612

B-H bond activation: Depending on the stability of the borane adduct, Li/Cl carbenoids react with BH₃×LB either under B-H bond activation at the carbenic carbon center or under carbene dimerization. The B-H bond activation proceeds in a stepwise fashion with the nucleophilic attack of the Li/Cl carbenoid at BH₃×LB as the crucial step determining the course of the reaction. Copyright

Full text of DOI:10.1002/chem.201302612

DOI: 10.1002/chem.201302612
Reactivity of Stabilized Li/Cl Carbenoids towards Lewis Base Adducts of
À
BH3: B H Bond Activation versus Carbene Dimerization
Sebastian Molitor and Viktoria H. Gessner*[a]
For many years the activation of small molecules had
been a research field limited to transition-metal complexes.
However, the past few decades have revealed several exam-
ples of non-metallic systems also applicable in bond activa-
tion reactions.[1] Without doubt, one of the most prominent
examples are singlet carbenes, which have been shown to ac-
tivate a variety of small molecules amongst others dihydro-
gen, CO, P4, and even ammonia.[2] Thereby, in some cases
substituent effects at the carbene carbon atom have been
shown to be crucial for the activity of a particular carbene.
Another—not less impressive—non-metal system establish-
ed in small molecule activation chemistry is that of the so-
À
Figure 1. Compounds formed by B H bond activation and selected reac-
tivities towards boranes.
called frustrated Lewis pairs (FLPs).[3] Comparable to car-
benes, this class of compounds has proven to be applicable
in a variety of activation reactions. In recent years, the acti-
À
vation of B H bonds has received special attention due to
the versatile utility of boranes in many organic transforma-
al reaction pathways are feasible: i) the formation of a
simple carbene borane adduct such as A after elimination of
lithium chloride, ii) formation of borate B analogous to or-
À
tions. B H activation or splitting had been reported with
the aid of transition metals as early as the 1980s.[4] However,
non-metallic systems have long been reluctant in this reac-
tion. For example, N-heterocyclic carbenes (NHCs) general-
ly react with the parent BH3 and its Lewis base adducts
under simple formation of the corresponding NHC·BH3
adduct (such as A Figure 1). No hydroboration of the car-
bene center is usually observed. The hitherto only example
ganolithium compounds, or iii) B H bond activation. In re-
À
lated work that appeared during the final stages of prepara-
tion of this Communication, So, Mꢀzailles and co-workers
À
reported on the B H bond activation using a carbenoid
stable at room temperature, which resulted in the formation
of a dimeric borane adduct.[8] Herein however, we show that
with more reactive carbenoids different reactivities are ob-
served depending on the borane source. Whereas with
À
of B H bond activation of a carbene species was reported
by Bertrand and co-workers using
À
a
cyclic (alkyl)-
borane–THF and thioether adducts B H bond activation
(amino)carbene (CAAC) in combination with the more hy-
and subsequent formation of a borate species is observed,
the carbenoids were shown to be unreactive towards trial-
kylamine adducts, leading to the dimerization of the corre-
sponding carbene.
dridic pinacolborane to selectively form 1.[5] Earlier the
group of Stephan had shown that FLPs are also applicable
in the B H bond splitting reaction by formation of salt 2.
[6]
À
An analogous salt formation was reported by Alcarazo and
co-workers with carbodiphosphorane as Lewis base even al-
lowing an activation of the less hydridic parent borane,
BH3.[7]
In the course of our investigations on the general reactivi-
ty patterns of electronically stabilized Li/Cl carbenoids we
became interested in their reactivity towards boranes. Sever-
The a-chlorinated carbenoid precursor 2 was obtained by
straightforward lithiation of the silyl-substituted phosphane
sulfide 1 and subsequent chlorination with hexachloroethane
(Scheme 1, see also the Supporting Information). As report-
ed earlier, compound 2 is selectively deprotonated at low
temperatures by using methyllithium as deprotonation re-
agent. The thus formed Li/Cl carbenoid 3 is stable at tem-
peratures up to À308C and can be used for in situ transfor-
mations.[9] To examine the reactivity of carbenoid 3 towards
[a] S. Molitor, Dr. V. H. Gessner
À
B H bonds we first studied the reactivity towards catechol-
Institut fꢁr Anorganische Chemie
borane and pinacolborane. However, the addition of both
boranes resulted in the formation of a complex mixture of
compounds, with 1 and 2 being the main products. This ob-
servation indicated that—amongst other pathways—hydride
transfer (to form 1) occurs during the reaction process.
Julius-Maximilians-Universitꢂt Wꢁrzburg
Am Hubland, 97074 Wꢁrzburg (Germany)
E-mail: vgessner@uni-wuerzburg.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201302612.
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Chem. Eur. J. 2013, 19, 11858 – 11862

COMMUNICATION
Scheme 1. Reactivity of carbenoid 3 towards different boranes; formation
of borate 4.
Thus, we turned our attention towards the less hydridic
parent borane BH3.
Warming of a solution of 3 in THF with an excess of
BH3·THF adduct from À788C to room temperature led to a
complete decoloration of the yellowish carbenoid solution.
NMR spectroscopic studies of the crude product showed the
selective formation of a single new species featuring a signal
at d=58.3 ppm (C6D6) in the 31P{1H} NMR spectrum (2: d=
46.3 ppm). Work-up delivered a colorless, moisture-sensitive
solid in 83% yield, which was characterized by multinuclear
NMR spectroscopy, as well as elemental and single-crystal
X-ray diffraction analysis. All methods confirmed the unex-
pected formation of lithium borate 4 formed by additional
protonation of the former carbenic carbon atom (Scheme 1).
The proton is clearly evident as a broad doublet at d=
Figure 2. Molecular structures of lithium borate 4 (top) and (S,S)-4-
À
SiMePh2 (bottom). Selected bond lengths [ꢄ] and angles [8]: 4: S P
À
À
À
À
1.9622(6), P C13 1.7926(15), Si C13 1.8930(16), B C13 1.660(2), B Li
2.259(3); B-C13-P 111.2(1), B-C13-Si 109.3(1), P-C13-Si 117.25(8), C13-
2.66 ppm in the 1H NMR spectrum. The 11B NMR resonance
À
À
À
B-Li 173.76(14). 4-SiMePh2: S1 P1 1.990(2), S2 P2 1.984(2), S3 P3
À
À
À
À
1.9858(19), S4 P4 1.981(2), S1 Li1 2.548(8), S2 Li1 2.491(8), S3 Li4
1
of 4 (d=À28.6 ppm; J
(1H,11B)=81.4 Hz) further confirms
ACHTUNGTRENNUNG
À
À
À
À
2.431(8), S4 Li4 2.489(9), P1 C1 1.794(4), P2 C2 1.777(3), P3 C3
1.773(4), P4 C4 1.790(4), Si1 C1 1.913(5), Si2 C2 1.879(4), Si3 C3
1.882(4), Si4 C4 1.864(5), C1 B1 1.654(6), C2 B2 1.670(6), C3 B3
1.674(6), C4 B4 1.658(6); B1-C1-P1 107.5(3), B1-C1-Si1 110.7(3), P1-C1-
Si1 117.7(2), B2-C2-P2 108.2(3), B2-C2-Si2 108.6(3), P2-C2-Si2 119.1(2),
B3-C3-P3 107.4(3), B3-C3-Si3 108.4(3), P3-C3-Si 121.4(2), P4-C4-Si4
117.8(2) (toluene solvent omitted for clarity).
the four-coordinate boron atom involved in coupling to the
À
À
À
À
7
adjacent hydrides. The Li and 29Si NMR signals appear at
À
À
À
À
À
d=0.47 and d=À9.9 ppm, respectively. Borate 4 is highly
moisture sensitive and hydrolyzes quantitatively in the pres-
ence of water under formation of starting compound 1. The
formation of borate 4 is quite remarkable as lithium carbe-
noids usually react under elimination of lithium chloride.[10]
À
Also the B H bond activation product previously reported
molecules, one of which is depicted in Figure 2. Both dimers
differ from each other in the configuration at the stereogen-
ic carbon atom. In the crystal, only the homochiral dimers,
(R,R)- and (S,S)-4-SiMePh2, were found. Both structures
clearly confirm the presence of the borate unit as well as the
hydrogen atom at the central carbon atom. These hydrogen
atoms were all found in the difference Fourier map and re-
is formed by LiCl elimination.[8]
The selective formation of lithium borate 4 was also ob-
served with BH3·SMe2 and (BH3)2·tBuSCH2CH2StBu as
borane sources, all leading to the THF-coordinated product.
The same holds true for changing the silyl moiety in the car-
benoid to SiMePh2. In the resulting borate 4-SiMePh2, the
phenyl substituents at both the silicon and phosphorus cen-
ters, become diastereotopic and appear as separate multip-
À
fined independently. The B C distances (4: 1.660(2) ꢄ; 4-
SiMePh2 (av) 1.664(6) ꢄ) are in the range of known alkyl-
borates.[11] The P-C-Si backbone shows only marginal differ-
ences compared with the PCH2Si derivative 1 (see the Sup-
porting Information). In both structures the lithium atoms
show interactions with the hydridic hydrogen atoms at the
boron atoms. Such stabilizing metal hydrogen interactions
are typical for metal hydrides and have—in the case of lithi-
um—first been introduced by Wade and co-workers.[12,13] In
4, the coordination sphere of lithium is completed by coordi-
1
lets in the H NMR spectrum. Due to the synthetic method,
the lithium borates 4 and 4-SiMePh2 are formed as racemic
mixtures.
The molecular structure of lithium borate 4 and its deriva-
tive 4-SiMePh2 are depicted in Figure 2. Compound 4 crys-
tallizes as a monomer in the monoclinic space group P21/n,
4-SiMePh2 as a pseudo-C2 symmetric dimer in the triclinic
¯
space group P1. The unit cell of 4-SiMePh2 contains two
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11859

V. H. Gessner and S. Molitor
nation of three THF molecules, whereas in 4-SiMePh2 addi-
tional coordination of the thiophosphinoyl moieties is ob-
served.
The observed reactivity of the lithium carbenoids to form
the corresponding borates 4 under simultaneous reduction
is—to the best of our knowledge—unprecedented. The ob-
served hydration reaction with the more hydridic catechol
and pinacol borane suggests
ment. Indeed, borate formation was found to possess the
lowest reaction barrier of only 11.5 kcalmolÀ1. The alterna-
tive carbene formation as well as hydride chloride exchange
turned out to be much higher in energy with barriers of 34.3
and 50.4 kcalmolÀ1, respectively (for details on alternative
mechanisms and computational methods, see the Supporting
Information). Scheme 2 depicts the whole reaction pathway
that the hydrogen chloride ex-
change proceeds via an intra-
molecular borane/borate spe-
À
cies and thus via an overall B
H
bond activation reaction.
However, to exclude the in-
volvement of the solvent in the
course of the reaction, we per-
formed additional deuteration
experiments. In the past, pro-
tonation reactions in the pres-
ence of alkaline-earth metals
have often been referenced to
hydrogen abstraction from
ethereal solvents.[14] Thus we
repeated the reaction of 3, pre-
pared from solid methyllithi-
um,
with
in
(BH3)2·tBuSCH2CH2StBu
Scheme 2. Calculated mechanism for the formation of 4.
deuterated [D8]THF. No incor-
poration of deuterium could
2
be identified in the H NMR spectrum, but exclusive forma-
for the formation of 4, Figure 3 the energy profile of the re-
action. The borate formation via TS1 was found to be the
crucial reaction step determining the course of the reaction.
The formed intermediate borate Int1 next reacts—mediated
by a second borane molecule (TS2) under hydride chloride
exchange—to form the alkylborane species Int2, thus com-
pleting the hydroboration at the carbenic carbon atom.
Elimination of BH2Cl finally furnishes the product.
1
tion of the protonated compound 4, as evidenced by H and
11B NMR spectroscopy. This strongly suggests that replace-
ment of the chloride should occur via reduction by a
borane/borate species.[10] We envisioned that in our case re-
duction would be facilitated by a second borane molecule,
which would finally lead to 4 and the formation of a chloro-
borane species. Indeed, it was found that a slight excess of
borane source is necessary for quantitative formation of
4.[15] Repeating the reaction with BD3·THF (freshly prepared
À
Overall the mechanism can be described as a stepwise B
H bond splitting reaction through a nucleophilic attack of
the carbenoid at the borane (borate formation) followed by
hydride–chloride exchange. Surprisingly, despite the highly
À
from NaBD4 and BF3·OEt2) finally confirmed the B H split-
ting. No signal for the methylene proton was observed any-
more in the 1H NMR spectrum and only a singlet in the
11B NMR spectrum at d=À29.1 ppm (see the Supporting In-
formation).
To gain further insight into the reaction mechanism, DFT
calculations [B3LYP/6-311+gACTHNUGRTNEUNG(d,p)] on a monomeric model
system of 3 (Ph substituents and THF replaced by Me and
Me2O, respectively) were performed. Three reaction path-
ways were studied: i) formation of the corresponding lithium
borate followed by chloride hydride exchange (Path A); ii)
chloride hydride exchange followed by borate formation
(Path B), and iii) formation of the corresponding free car-
bene after LiCl elimination and subsequent hydroboration
À
via B H bond activation (Path C). Due to the high nucleo-
philicity of carbenoid 3, Path A was expected to be prefer-
red over Path B. Furthermore, Path C can be ruled out, as
no lithium chloride formation was observed in the experi-
Figure 3. Energy profile of the calculated mechanism for the formation of
4 (=Pro); free energies are given in kcalmolÀ1
.
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À
B H Bond Activation
COMMUNICATION
exergonic nature of this reaction (DG° =À67.2 kcalmolÀ1) a
different reactivity was observed when BH3·NMe3 (or
BH3·NEt3) was used as borane source. In this case no borate
formation was observed, but dimerization of the intermedi-
ate formed carbene. Interestingly, dimerization (CI/MS: m/z
976) did not lead to olefin formation as known for carbenes
(such as in the Wanzlick equilibrium) and other carbe-
noids.[16,17] Instead the dimerization was found to occur via
sulfur transfer to selectively form bis-ylide 5 (Scheme 3).
carbenoids might also furnish the B H bond activation with
the less reactive BH3·NMe3.
À
In conclusion, we have reported on the reactivity of elec-
tronically stabilized Li/Cl carbenoids towards different
Lewis base adducts of parent BH3. This reactivity strongly
differs from the reactivity usually observed with simple or-
ganolithium compounds and NHCs. Depending on the sta-
À
bility of the borane adduct either B H bond activation at
the carbenic carbon center or dimerization of the carbene is
À
observed. DFT calculations showed that the B H bond acti-
vation proceeds in a stepwise fashion during which the nu-
cleophilic attack of the Li/Cl carbenoid at BH3·LB is the
crucial reaction step. In the case of more stable borane ad-
ducts, borate formation competes with carbene formation
and therefore further reaction pathways. These findings sug-
gest that also other—less stable carbenoids—should be ap-
Scheme 3. Dimerization of carbenoid 3.
À
plicable in B H bond activation reactions and that the
choice of the borane source might be crucial for selective
transformations.
Ylide 5 was isolated as an orange air-stable solid in 48%. It
is characterized by a single signal at d=37.8 ppm in the
31P NMR spectrum. In the 1H NMR spectrum ([D8]THF)
only broadened resonances in the aromatic region were ob-
served, which sharpened upon cooling of the sample to
À808C (see Supporting Information for VT-NMR spectro-
scopy). X-ray diffraction analysis confirmed the constitution
of 5. The central structural motif consists of an S-P-C-S-C-P
six-membered ring featuring saddle conformation, which ex-
Acknowledgements
We thank the DFG (Emmy Noether program), the FCI and the AvH
Foundation for financial support. We also thank Rockwood Lithium
GmbH for the supply of chemicals and Prof. H. Braunschweig for gener-
ous support and helpful discussions.
1
plains the complex splitting in the H NMR spectrum (axial
and equatorial positions of the phenyl substituents at phos-
phorus). The carbon atom in 5 features a planar environ-
ment (sum of angles: 360.0(4)8 and 159.1(4)8) with short-
Keywords: bond activation · boranes · carbenoids · density
functional calculations · lithium
À
ened P C bond lengths due to electrostatic interactions (see
Supporting Information).[18]
[1] P. P. Power, Nature 2010, 463, 171–177.
The formation of 5 is also observed without addition of
any borane source. This is contrary to the methylsilyl-substi-
tuted derivatives of 3, which solely furnished complex prod-
uct mixtures upon warming, thus underlining the stabiliza-
tion by the phenyl substituents.[9] Chivers and co-workers
have recently reported on the formation of a dimeric species
analogous to 5 as a by-product of a two-electron oxidation
of a dilithio methandiide.[19,20] They suggested a carbene spe-
cies as intermediate, which undergoes electrophilic attack at
[2] For examples see: a) G. D. Frey, V. Lavallo, B. Donnadieu, W. W.
Schoeller, G. Bertrand, Science 2007, 316, 439–441; b) O. Back, G.
Kuchenbeiser, B. Donnadieu, G. Bertrand, Angew. Chem. 2009, 121,
5638–5641; Angew. Chem. Int. Ed. 2009, 48, 5530–5533; c) T. W.
Hudnall, J. P. Moerdyk, C. W. Bielawski, Chem. Commun. 2010, 46,
4288–4290; d) F. Lavigne, E. Maerten, G. Alcaraz, V. Branchadell,
N. Saffon-Merceron, A. Baceiredo, Angew. Chem. 2012, 124, 2539–
2541; Angew. Chem. Int. Ed. 2012, 51, 2489–2491; e) A. G. Tskhov-
rebov, E. Solari, M. D. Wodrich, R. Scopelliti, K. Severin, J. Am.
Chem. Soc. 2012, 134, 1471–1473.
[3] For reviews, see: a) D. W. Stephan, G. Erker, Angew. Chem. 2010,
122, 50–81; Angew. Chem. Int. Ed. 2010, 49, 46–76; b) D. W. Ste-
phan, Dalton Trans. 2009, 3129–3136; c) D. W. Stephan, Org.
Biomol. Chem. 2008, 6, 1535–1539.
[4] For the first examples in this field, see: a) R. Wilczynski, L. G. Sned-
don, J. Am. Chem. Soc. 1980, 102, 2857–2858; b) R. Wilczynski,
L. G. Sneddon, Inorg. Chem. 1981, 20, 3955–3962; c) T. Davan,
E. W. Corcoran, L. G. Sneddon, Organometallics 1983, 2, 1693–
1694; d) J. D. Hewes, C. W. Kreimendahl, T. B. Marder, M. F. Haw-
thorne, J. Am. Chem. Soc. 1984, 106, 5757–5759; e) D. Mꢂnnig, H.
Nçth, Angew. Chem. 1985, 97, 854–855; Angew. Chem. Int. Ed.
Engl. 1985, 24, 878–879.
À
the sulfur of the P S bond. An analogous mechanism might
also be applicable for carbenoid 3. Indeed computational
studies confirm that borate formation possesses a much
higher reaction barrier for the amine adduct, BH3·NMe3,
compared to the ether and thioether adducts. In fact, when
using a phenyl-substituted model system the carbene forma-
tion (DG° =24.0 kcalmolÀ1) was revealed to be slightly fa-
vored over the nucleophilic attack of the carbenoid at the
borane (DG° =30.2 kcalmolÀ1). These findings demonstrate
À
that borate formation is the crucial step for the B H bond
[5] G. D. Frey, J. D. Masuda, B. Donnadieu, G. Bertrand, Angew. Chem.
2010, 122, 9634–9637; Angew. Chem. Int. Ed. 2010, 49, 9444–9447.
[6] M. A. Dureen, A. Lough, T. M. Gilbert, D. W. Stephan, Chem.
Commun. 2008, 4303–4305.
[7] B. Inꢀs, M. Patil, J. Carreras, R. Goddard, W. Thiel, M. Alcarazo,
Angew. Chem. 2011, 123, 8550–8553; Angew. Chem. Int. Ed. 2011,
50, 8400–8403.
activation of carbenoid species. This depends on the stability
of the borane (as demonstrated above) but also on the nu-
cleophilicity of the carbenoid itself. The formation of 5 ac-
counts for the great electronic stabilization of the carbenoid
by the thiophosphinoyl and silyl moiety. More nucleophilic
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V. H. Gessner and S. Molitor
[8] H. Heuclin, S. Y.-F. Ho, X. F. Le Goff, C.-W. So, N. Mꢀzailles, J. Am.
Chem. Soc. 2013, 135, 8774–8777.
[9] a) V. H. Gessner, Organometallics 2011, 30, 4228–4231; b) T. Cantat,
X. Jacques, L. Ricard, X. F. Le Goff, N. Mꢀzailles, P. Le Floch,
Angew. Chem. 2007, 119, 6051–6054; Angew. Chem. Int. Ed. 2007,
46, 5947–5950.
40 ppm, which we reference to the chloroborane species. For com-
plete conversion a minimum of 1.4 equiv BH3 is necessary.
[16] For dimerization of carbenes, see: a) H. W. Wanzlick, Angew. Chem.
1962, 74, 129–134; Angew. Chem. Int. Ed. Engl. 1962, 1, 75–80;
b) R. W. Alder, M. E. Blake, L. Chaker, J. N. Harvey, F. Paolini, Jan
Schꢁtz, Angew. Chem. 2004, 116, 6020–6036; Angew. Chem. Int. Ed.
2004, 43, 5896–5911; c) V. W. P. Bçhm, W. A. Herrmann, Angew.
Chem. 2000, 112, 4200–4202; Angew. Chem. Int. Ed. 2000, 39, 4036–
4038.
[17] For dimerization of carbenoids, see: a) G. Kçbrich, H. R. Merkle,
Chem. Ber. 1966, 99, 1782; b) P. A. Morken, P. C. Bachand, D. C.
Swenson, D. J. Burton, J. Am. Chem. Soc. 1993, 115, 5430–5439;
c) T. Rꢁffer, C. Bruhn, A. H. Maulitz, D. Strçhl, D. Steinborn, Orga-
nometallics 2000, 19, 2829–2831; d) G. Kçbrich, R. H. Fischer, Tetra-
hedron 1968, 24, 4343–4346; e) U. Burger, R. Huisgen, Tetrahedron
Lett. 1970, 11, 3057–3060.
[10] G. Kçbrich, H. R. Merkle, Angew. Chem. 1967, 79, 50–51; Angew.
Chem. Int. Ed. Engl. 1967, 6, 74.
[11] a) C. Eaborn, M. N. A. El-Kheli, P. B. Hitchcock, J. D. Smith, J.
Chem. Soc. Chem. Commun. 1984, 1673–1674; b) J. Knizek, H.
Nçth, J. Organomet. Chem. 2000, 614, 168–187; c) D. Franz, M.
Bolte, H.-W. Lerner, M. Wagner, Dalton Trans. 2011, 40, 2433–
2440; d) W. Petz, F. ꢅxler, B. Neumꢁller, R. Tonner, G. Frenking,
Eur. J. Inorg. Chem. 2009, 4507–4517; e) S. Marks, R. Koppe, T. K.
Panda, P. W. Roesky, Chem. Eur. J. 2010, 16, 7096–7100.
[12] D. R. Armstrong, W. Clegg, H. M. Colquhoun, J. A. Daniels, R. E.
Mulvey, I. R. Stephenson, K. Wade, J. Chem. Soc. Chem. Commun.
1987, 630–632.
[18] Due to the low quality of the crystals no detailed structure discus-
sion is possible.
[19] J. Konu, T. Chivers, Chem. Commun. 2008, 4995–4997.
[20] For examples of dilithio methandiides, see: a) A. Kasani, R. P. K.
Babu, R. McDonald, R. G. Cavell, Angew. Chem. 1999, 111, 1580–
1582; Angew. Chem. Int. Ed. 1999, 38, 1483–1484; b) T. Cantat, L.
Ricard, P. Le Floch, N. Mꢀzailles, Organometallics 2006, 25, 4965–
4976; c) L. Orzechowski, G. Jansen, S. Harder, Angew. Chem. 2009,
121, 3883–3887; Angew. Chem. Int. Ed. 2009, 48, 3825–3829; d) J.
Vollhardt, H.-J. Gais, K. L. Lukas, Angew. Chem. 1985, 97, 607–609;
Angew. Chem. Int. Ed. Engl. 1985, 24, 610–611; e) G. Linti, A.
Rodig, H. Pritzkow, Angew. Chem. 2002, 114, 4685–4687; Angew.
Chem. Int. Ed. 2002, 41, 4503–4506; f) P. Schrçter, V. H. Gessner,
Chem. Eur. J. 2012, 18, 11223–11227.
[13] For further reports about Li-H-B interactions, see: a) A. Heiner, D.
Stalke, J. Organomet. Chem. 1997, 542, 25–28; b) K. Izod, LJ.
Bowman, C. Wills, W. Clegg, R. W. Harrington, Dalton Trans. 2009,
3340–3347; c) K. Izod, W. McFarlane, B. V. Tyson, W. Clegg, R. W.
Harrington, Chem. Commun. 2004, 570–571; d) K. Izod, C. Wills,
W. Clegg, R. W. Harrington, Organometallics 2006, 25, 38–40.
[14] a) Y. Wang, B. Quillian, P. Wei, C. S. Wannere, Y. Xie, R. B. King,
H. F. Schaefer, III, P. v. R. Schleyer, G. H. Robinson, J. Am. Chem.
Soc. 2007, 129, 12412–12413; b) V. Malatesta, K. U. Ingold, J. Am.
Chem. Soc. 1981, 103, 609–614; c) T. C. Cheng, L. Headley, A. F.
Halasa, J. Am. Chem. Soc. 1971, 93, 1502–1503; d) J. F. Garst, Acc.
Chem. Res. 1971, 4, 400–406.
Received: June 16, 2013
Revised: July 5, 2013
Published online: July 29, 2013
[15] In the 11B NMR spectrum of the reaction mixture, several trace
amounts of boron species could be detected between d=0 and
11862
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