Ligand Influence on Carbonyl Hydroboration Catalysis by Alkali Metal Hydridotriphenylborates [(L)M][HBPh3] (M=Li, Na, K)

Article abstract of DOI:10.1002/chem.201702818

Alkali metal hydridotriphenylborates [(L¹)M][HBPh₃] (L¹=Me₆TREN; M=Li, Na, K) chemoselectively catalyze the hydroboration of carbonyls and CO₂, with lithium being the most active system. A new series

Full text of DOI:10.1002/chem.201702818

A Journal of
Accepted Article
Title: Ligand influence on the carbonyl hydroboration catalysis by alkali
metal hydridotriphenylborates [(L)M][HBPh3] (M = Li, Na, K)
Authors: Jun Okuda, Thomas Spaniol, Hassan Osseili, and Debabrata
Mukherjee
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published online in Early View as soon as possible and may be different
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To be cited as: Chem. Eur. J. 10.1002/chem.201702818
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FULL PAPER
Ligand influence on the carbonyl hydroboration catalysis by
alkali metal hydridotriphenylborates [(L)M][HBPh
3
] (M = Li, Na, K)
†
†
Hassan Osseili, Debabrata Mukherjee, Thomas P. Spaniol, and Jun Okuda*
1
1
[14]
Abstract: Alkali metal hydridotriphenylborates [(L )M][HBPh
Me TREN; M = Li, Na, K) chemoselectively catalyze the hydroboration
of carbonyls and CO
3
] (L
=
reactivity.
2
Here we report the synthesis of complexes
6
[(L )M][HBPh
3
] (M = Li, Na, K) and compare their structures and
1
2
, with lithium being the most active system. A
catalytic hydroboration activity with those of [(L )M][HBPh
3
].
2
new series of complexes [(L )M][HBPh
3
] [M = Li (1), Na (2), K (3)] with
Effects of the coordination of some other N- and O-type
multidentate ligands were also examined. Benzophenone
hydroboration with pinacolborane was chosen as the benchmark
catalytic reaction.
2
the cyclen-derived macrocyclic polyamine Me
4
TACD (L ) were
synthesized in a 'one-pot' fashion and fully characterized including X-
ray crystallography. In the crystal, 1-3 exhibit wide variation in metal
coordination of the [HBPh
structures differ from those in [(L )M][HBPh
3
] anion from lithium to potassium. The
1
3
]. Effects of coordination
of L , L , and other N- and O-donor multidentate ligands on Results and Discussion
Li(HBPh )] were used to rationalize the catalytic activity in carbonyl
1
2
[
3
hydroboration.
1
[
(L )M][HBPh
3
] (M = Li, Na, K) were prepared in high yields by
BPh
tetramethyldisilazides [(L )M{N(SiHMe
also worked well for other metals like magnesium and zinc.
3
-mediated -hydride abstraction from the easily accessible
1
[9]
2 2
) }] in THF. This route
[
15]
[16]
Introduction
The same procedure was applied here and more conveniently in
2
a 'one-pot' fashion. Tetramethyldisilazides [(L )M{N(SiHMe
2
)
2
}]
}] in
readily provided
Molecular s-block metal compounds are historically important
as stoichiometric reagents. Only recently does their use as
catalysts attract increased attention.[1] Lighter alkali metal
hydridoborates [M(H BR4-n)] are routinely used as versatile
n
reducing agents in organic synthesis (M = Li, Na, K; R = H, alkyl,
aryl), offering fine-tuning of chemoselectivity.[2] Hydrido-
2
were first generated in THF by mixing L with [M{N(SiHMe
2
)
2
1
:1 ratio. Treating them subsequently with BPh
3
2
[
(L )M][HBPh
3
] (M = Li (1), Na (2), K (3)] in high yields (Scheme
1
). The same compounds were obtained by mixing L2 with
)] in THF.[9]
[
M(HBPh
3
[
3]
triphenylborates [M(HBPh
3
)] were introduced in the 1950's, but
[
4]
remained mostly unnoticed despite their easy preparation and
significant hydridicity.[5] Only [K(HBPh
)] was employed as a mild
3
and selective reducing agent for carbonyl substrates.[4,
6]

Structural data for [HBPh
well,[7] especially compared to what is known of [BPh
3
] anion remained surprisingly limited as
 [8]
4
] .
Our recent findings have resuscitated [M(HBPh
well-characterized hydridotriphenylborates [(L )M][HBPh
3
)] since the
] (L1
=
1
3
6
Me TREN = tris{2-(dimethylamino)ethyl}amine; M = Li, Na, K)
were recognized as active catalysts in the chemoselective
2
hydroboration of carbonyls and CO using pinacolborane (HBpin),
with lithium showing the highest activity.[9] Stabilization of reactive
organo-alkali metal species in monomeric form by this NNNN-
1
type tripodal polyamine L has already been recognized by
Mulvey et al..[
10]
2
3
Scheme 1. Synthesis of [(L )M][HBPh ] (1-3).
The macrocyclic polyamine 1,4,7,10-tetramethyl-1,4,7,10-
2
tetraazacyclododecane (Me
4
TACD = L ) has also been used as
[11]
an NNNN-type neutral ligand to obtain stable complexes of s-,
Complexes 1-3 were isolated as colorless crystals and fully
[
12]
[13]
d-, and f-block metals. The coordination pattern for open vs.
closed chain multidentate ligands with the same donor set often
exhibits significant difference, leading to different structures and
characterized. They are soluble in THF but insoluble in aromatic
1
and aliphatic hydrocarbons, similar to the L bonded derivatives.
1
13
1
Their H and C{ H} NMR spectra in THF-d
8
display the expected
resonances of a coordinated L2 and the [HBPh
characteristic broad quartet at  3.50-2.94 ppm in the H NMR
]

anion. A
1
3
1
spectrum and a sharp doublet at around  8.8 ppm ( JBH = 76-79
[*]
Hassan Osseili, Dr. Debabrata Mukherjee, Dr. Thomas P. Spaniol,
Prof. Dr. Jun Okuda*
Hz) in the 11B NMR spectrum are attributed to the BH moiety. All
three compounds were authenticated by X-ray crystallography
and the results show a major variation in coordination pattern for
Institute of Inorganic Chemistry, RWTH Aachen University
Landoltweg 1, 52056, Aachen (Germany)
E-mail: jun.okuda@ac.rwth-aachen.de
[
[
HBPh
(L )M][HBPh
3
]. Noticeable structural differences from the structures of
] were also observed.
Complex 1 crystallized as a separate ion-pair with one THF
molecule coordinated to the lithium (Fig. 1). The five-coordinate
[†]
These authors have contributed equally.
1
3
Supporting information for this article is given via a link at the end of the
document.
1
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Chemistry - A European Journal
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2
∠
.854(6); Na1∙∙∙C14 3.075(7); Na1∙∙∙C18 3.448(7). Selected torsion angles (˚):
B1C13C14C15 179.9(6); ∠B1C13C18C17 178.6(7).
cationic lithium center thus adopts a distorted square-pyramidal
geometry with the THF molecule occupying the axial position. In
contrast, the sodium complex 2 is a contact ion pair (CPI) with
+
non-covalent Na ∙∙∙C

interactions ranging from 2.854(6)-3.448(7)

3
Å (Fig. 2). One phenyl ring of the [HBPh ] anion is  -coordinated
3
to the metal via the ipso- and two ortho- carbons. A 3-centered-2-
electron Na∙∙∙HB [Na∙∙∙H: 2.25(7) Å] bonding interaction is also
evident that confers the sodium a formally eight-coordinate
distorted square anti-prismatic geometry. The potassium complex
3
is also a contact ion pair with a 3-center-2-electron K∙∙∙HB
(
K∙∙∙H: 2.73(7) Å] bonding interaction. Interestingly, the anion
] in this case exhibits non-covalent K ∙∙∙C
+
interactions
[
[
HBPh
3

2
3.122(8)-3.280(7) Å] from two phenyl rings, both in  -fashion
involving the ipso and one ortho phenyl carbons (Fig. 3). This
increases the formal coordination number of potassium to nine
with a distorted mono-capped square anti-prismatic geometry.
None of these cation∙∙∙C
phenyl rings in both 2 and 3, which is otherwise often the case.

interactions resulted in distortion of the
[
9,
1
0g, 17]
As expected, the metal-nitrogen distances increase going
down the group, as Li [2.154(11)-2.301(12) Å] < Na [2.444(6)-
.574(6) Å] < K [2.791(7)-2.858(7) Å].
2
Figure 3. Molecular structure of 3. Selected bond distances (Å): K1N1
2.837(7); K1N2 2.858(7); K1N3 2.791(7); K1N4 2.826(6): B1C13
1.642(11); B1C19 1.644(12); B1C25 1.636(11); K1∙∙∙H1 2.73(7); K1∙∙∙C13
3.148(8); K1∙∙∙C14 3.122(8); K1∙∙∙C19 3.280(7); K1∙∙∙C19 3.190(8). Selected
torsion angles (˚): ∠ B1C13C14C15 178.7(7); ∠ B1C13C18C17

179.5(7); ∠B1C19C20C21 179.9(6); ∠B1C19C24C23 179.8(6).
+
Non-covalent M ∙∙∙C

interactions for the alkali metals,
especially for the heavier congeners, are important for
stabilization by coordinative saturation.[18] The Cambridge
Structural Database (CSD) contains more than 300 crystal
+
structures showing K ∙∙∙C

(arene) interactions. Such binding
forces are important in biology for defining protein structures, ion
transportation, molecular recognition, and enzyme catalysis.[
19]
Mulvey, Davidson et al. performed an elaborative study on alkali
1
metal cation∙∙∙C

(arene) interactions using L as the coligand.
1
[10b]
1
[10d]
Complexes like [(L )K][CH Ph],
2
2 6 3 2
[(L )K][CH C H -3,5-Me ],
1
],[10g]
(CH
[
[
(L )K][SiPh
3
and
the
heterobimetallic
Figure 1. Molecular structure 1·THF. Selected bond distances (Å): Li1N1
1
Ph)][10d] are all contact ion pairs in the solid
(L )K][Zn(tBu)
2
2
2.301(12); Li1N2 2.154(11); Li1N3 2.256(11); Li1N4 2.175(11); Li1O1
1
state. Alkali metal cation to anion interaction in [(L )M][A] (M = Li,
1.921(10).
2 2 6 3 2
Ph, CH C H -3,5-Me
] varies systematically.[
10b, 10d]
Na, K; A = CH
While the Li derivatives have LiCH
2
-interactions, the
6
potassium centers are exclusively -arene bonded in  fashion.
The bonding situation for sodium is intermediate; the metal cation
is slightly dislocated towards the -arene while maintaining a
partial NaCH -interaction. Earlier, R. v. Schleyer et al. and
2
Stalke et al. performed similar studies with alkali metal
triphenylmethyl and diphenylpyridylmethyl derivatives using
[
20]
PMDTA (N,N,N',N",N"-pentamethyldiethylenetriamine) ligand.
[
21]
R. v. Schleyer et al. later reviewed this topic comprehensively.
1
In the case of L , both lithium and sodium derivatives
1
crystallized as separate ion pairs [(L )M(thf)][HBPh
3
] (M = Li, Na)
with one coordinated THF molecule.[ Only [(L )K][HBPh
9]
1
] is a
3
+
3
contact ion pair, but the potassium ion is  -bonded [K ∙∙∙C

:
3
.001(4)-3.118(4) Å] to a single phenyl ring and no K∙∙∙HB (K∙∙∙H:
[
9]
3.21 Å) bonding interaction is detected.
1
2
As mentioned earlier, both L and L are NNNN-type Lewis
4
donors that bind to [M(HBPh
3
)] in a  -fashion in the solid state.
Figure 2. Molecular structure of 2. Selected bond distances (Å): Na1N1
But the spatial orientation of their donor sites varies. Nitrogen
arms of the tripodal L1 are
2.574(6); Na1N2 2.483(6); Na1N3 2.552(6); Na1N4 2.444(6); B1C13
.630(9); B1C19 1.630(9); B1C25 1.653(9); Na1∙∙∙H1 2.25(7); Na1∙∙∙C13
atoms of the three CH CH NMe
coplanar forming a trigonal base during metal chelation, while the
2
2
2
1
2
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Chemistry - A European Journal
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FULL PAPER
apical nitrogen binds from the top (Fig. 4).[9] Metal-nitrogen
distances as well as the distance from the trigonal base follow a
trend of Li < Na < K. Whereas, the macrocyclic L2 adopts a
distorted boat-like conformation upon metal coordination with a
square planar arrangement for its nitrogen atoms (Fig. 4). L M
distances also increases with size as Li (0.8368 Å) < Na (1.3362
Time (h)[b]
TOF (103 h1
)
Entry
Catalyst
mol%
0.01
0.1
1
2
3
4
1
1
2
3
18
0.5
12
24
0.56
2
2
0.1
0.08
0.04
Å) < K (1.8440 Å). This coordination diversity together with the N-
0.1
substitution, that is two vs. one methyl groups, might well account
1
for the observed structural differences between [(L )M][HBPh
3
]
[
a]
n(HBpin) = 0.27 mmol, n(substrate) = 0.27 mmol, 0.5 mL of solvent. [b]
Time for complete substrate consumption, detected by NMR spectroscopy.
2
and [(L )M][HBPh
3
].
Effect of ligand coordination was further extended towards
some other neutral multidentate N- and O donors (Table 2). The
3
ancillary ligand-free [Li(HBPh )] itself showed high activity with a
TOF of 13.33•10 h at 0.01 mol% of catalyst loading (entry 1).[9]
3
1
1
Compared to that, L (entry 2 and 3) showed a strong influence
3
1 [9]
by reaching a TOF of above 60•10 h . Open-chain polyamine
tridentate PMDTA (entry 4) and bidentate TMEDA (N,N,N',N'-
tetramethylethylenediamine, entry 5) had almost no to slightly
Figure 4. Binding patterns of L1 and L2 in [(L )M][HBPh
respectively.
1
2
3
3
] and [(L )M][HBPh ],
3
negative effect of coordination since both gave a TOF of 10•10
1
2
h . The closed-chain tetradentate polyamine L (entry 6 and 7)
on the other hand reduced the activity by 25 times, compared to
The smallest and hardest lithium ion resides deepest inside
the pocket of both L1 and L with an additional THF molecule
2
3
the ligand-free [Li(HBPh )]. Likewise, macrocyclic polyether 12-
bonded instead of the [HBPh
3
] anion. The largest and softer
interactions in both cases but to
crown-4 (12-c-4) showed a negative impact with a TOF of
+
potassium ion opts for K ∙∙∙C

3
1
1
.33•10 h (entry 8).
variable degrees. The sodium ion in between has no strong
preference and exhibits both separate as well as contact ion pair
structures. The counter anion can also influence.
Table 2. Ligation effect on [Li(HBPh
3
)] in catalytic hydroboration of
benzophenone.[
a]
[
(L )Na(thf)][BAr ] (BArF
phenyl}borate) has a separate ion pair structure unlike 2.
hydride-encapsulated heterobimetallic "inverse crowns"
Mg (NiPr (-H) (toluene) ] (M = Na, K) have -solvated
2
F
=
tetrakis{3,5-bis(trifluoromethyl)-
[
11a]
The
[
M
2
2
2
)
4
2
2
toluene molecules for both sodium and potassium, but only
weakly bonded in the case of sodium. Toluene can be removed
Entry
L
mol%
0.01
0.01
0.001
0.01
0.01
0.01
0.1
Time (h)[b]
TOF (103 h1
)
under dynamic vacuum.[22]
1
The lithium catalyst [(L )Li][HBPh
3
] showed high activity in
1
2
3
4
5
6
7
8
---
0.75
<0.17
1.5
1
13.3
≥60
66.6
10
3
carbonyl hydroboration of benzophenone with a TOF of ≥ 60•10
L1

1 [9]
h ; the highest number so far among all the catalysts known to
date, including the ones based on transition metals.[1f, 1g, 15, 23]
Further studies have indicated that a dynamic coordination from
L1 in tandem with the THF solvent to the cationic lithium center
was critical for this high activity.[24] Lewis acidity of the metal cation
may contribute significantly.[15, 25] The activities of 1-3 were tested
L1
PMDTA
TMEDA
1
10
in benzophenone hydroboration using HBpin (Table 1). The
L
2
18
0.6
2
1
lithium catalyst 1 was significantly less active than [(L )Li][HBPh
3
]
L2
0.5
0.75
3
and gave TOF values of 0.56•10 h1 and 2•10 h with 0.01 and
3
1
0
.1 mol% of catalyst loading, respectively (entry 1 and 2).
12-c-4
0.1
1.3
3
1
Compared to 1, the sodium catalyst 2 (entry 3, TOF: 0.08•10 h )
and the potassium catalyst 3 (entry 4, TOF: 0.04•10 h ) were 25
and 50 times less active. Activities of [(L )M][HBPh
3
1
[a]
n(HBpin) = 0.27 mmol, n(substrate) = 0.27 mmol, 0.5 mL of solvent. [b] Time
for complete substrate consumption, detected by NMR spectroscopy.
1
3
] followed a
similar trend as Li >> Na ~ K, but the superiority of lithium was
[
9]
1
more pronounced (>300 times). [(L )M][HBPh
3
] (M = Na, K;
3
1
[9]
[(PMDTA)Li][HBPh
3
3
] (4) and [(12-c-4)Li][HBPh ] (5) were
TOF: 0.5•10 h ) were also more active catalysts than 2 and 3.
isolated by mixing the ligands with [Li(HBPh
3
)] in THF and were
fully characterized including an X-ray crystal structure analysis
Table 1. Hydroboration of benzophenone catalyzed by 1-3.[a]
for 5 (Fig. 5). It revealed a THF coordinated separate ion pair
1
structure as 1 and [(L )Li][HBPh
3
]. Crown ether complexes of
alkali metal tetraphenylborates were crystallographically
[
26]
[26]
characterized. 5 is isostructural with [(12-c-4)Li(thf)][BPh
The LiO distances are within the expected range of 2.0187(2)-
.0665(1) Å.
4
].
2
3
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Chemistry - A European Journal
10.1002/chem.201702818
FULL PAPER
Me
6
TREN and Me
4
TACD are both tetradentate but differ in
their coordination topology. Both are suitable as ancillary ligands
for mononuclear group 1 metal complexes. The present work has
shown the differences in the structure and catalytic hydroboration
activity of [(L)M(HBPh )] (M = Li, Na, K). Some other chelating
3
ligands were also studied, showing significant variation in catalytic
activity with the ligand choice for lithium (Fig. 6). While the tripodal
Me
retention of Lewis acidity, the macrocyclic crown ether (12-c-4)
and tetraaza crown (Me TACD) impart more rigidity and
6
TREN offers a unique combination of flexible coordination and
4
decreased Lewis acidity. TMEDA and PMDTA have only marginal
effect compared to the ligand-free catalysis.
Figure 5. Molecular structure of 5·THF. Selected bond distances (Å): Li1O1
2.0665(1); Li1O2 2.0463(2); Li1O3 2.0187(2); Li1O4 2.0428(2); Li1O5
1.9008(1).
1
Thus, L proved to be a better ligand support in carbonyl
hydroboration catalysts based on alkali metals.[ It apparently
clings on to the lithium in solution and prevents oligomerization
while retaining the Lewis acidity at the same time.[9, 27] Dynamic
24]
Figure 6. Influence of the donor
hydroboration of benzophenone by pinacolborane.
3
L in [(L)Li][HBPh ] on the catalytic
[9,
coordination further ensures accessibility of the metal center.
2
4]
PMDTA and TMEDA presumably fail to bind lithium tightly
enough in THF and thus exhibit almost no influence. This is
supported by the fact that a [(TMEDA)Li][HBPh ] complex could
not be isolated by reacting [Li(HBPh )] with TMEDA in THF or
3
Experimental Section
3
even in neat TMEDA. Attempted crystallization from a reaction
mixture at 30 ˚C invariably resulted in the precipitation of
General considerations. All reactions were performed in a dry argon
atmosphere using standard Schlenk techniques or under argon
atmosphere of a glovebox, unless otherwise indicated. Prior to use,
[
Li(HBPh
3
)]. This is intriguing considering the innumerable
[
28]
examples of TMEDA bonded lithium complexes.
However,
glassware was dried overnight at 130 °C and solvents were dried, distilled,
1
and degassed using standard methods. [M(HBPh
=
3
)] and [(L )M][HBPh
3
] (M
that may not reflect the magnitude of the chelate effect or the
overall strength of the TMEDALi interaction. Competition
between TMEDA and THF for the de-aggregation of lithium
Li, Na, K),[4, 9] and [L ] were synthesized according to the literature
2 [33]
procedure. BPh
3
(95% pure) was purchased from abcr and purified by
sublimation. H, C{ H}, 11B, and 29Si{ H} NMR spectra were recorded on
1
13
1
1
reagents can be puzzling.[27, 29] For example, [Li{N(SiMe
independently reacts with 5 equivalents of THF and TMEDA to
give dimeric [[Li{N(SiMe }(thf)] and monomeric
(TMEDA)Li{N(SiMe
}], respectively.[ Thus, TMEDA seems
3 2
) }]
a Bruker DRX400 spectrometer at ambient temperature unless otherwise
1
13
1
mentioned. Chemical shifts ( in ppm) in the H and C{ H} NMR spectra
were referenced to the residual signals of the deuterated solvents.
Abbreviations for NMR spectra: s (singlet), d (doublet), t (triplet), q (quartet),
br (broad). IR spectra were recorded on KBr pellets using an AVATAR 360
FT-IR spectrometer. Elemental analyses were performed on an elementar
vario EL machine. X-ray diffraction data were collected on a Bruker APEX
II diffractometer. Single crystal diffraction data is reported in
crystallographic information files (cif) accompanying this document.
3
)
2
2
27]
[
3 2
)
to coordinate stronger, but an equimolar mixture of THF and
exclusively.[
27]
TMEDA provides [Li{N(SiMe
3
)
2
}(thf)]
2
Likewise,
THF has a substantially greater affinity towards LDA than does
TMEDA.[30] Single crystals for the THF-solvated derivatives
[
M(thf)
n
(HBPh
3
)] (M = Li, Na, K) could not be obtained.
[
31]
1
2-c-4 is known to be an ideal fit for the lithium ion and L2
2
[
(L )Li][HBPh
3
] (1). A solution of Li{N(SiHMe
2
)
2
}] (0.100 g, 0.718 mmol)
[32]
can be considered as the aza-version of 12-c-4.
The
2
and L (0.165 g, 0.722 mmol) in THF (2 mL) were stirred at room
coordinated THF molecules in recrystallized 1·THF and 5·THF
3
temperature. After 10 min, a solution of BPh (0.177 g, 0.730 mmol) in 1
are weakly bonded and can be removed under vacuum as in the
mL of THF was added dropwise and the resulting mixture was stirred for
additional 2 h at room temperature. The solution was concentrated under
reduced pressure. Addition of n-pentane (5 mL) precipitated a white solid,
which was further washed with n-pentane (3 x 2 mL) and dried under
vacuum to give analytically pure 1 (0.315 g, 0.658 mmol, 92% yield) as a
white powder. X-ray diffraction quality single crystals were obtained from
1
[9]
1 [24]
case of [(L )Li(thf)][HBPh
evidence for a labile binding of L and 12-c-4 was found in 1 and
3
]. Unlike L ,
no spectroscopic
2
2
5
in the temperature range between 193 and 298K. L and 12-
+
c-4 thus apparently provide rigid chelations to Li and saturate
its coordination sphere. This may also significantly decrease the
Lewis acidity/electrophilicity of lithium, which is ultimately
manifested in their poorer performance in hydroboration
catalysis.
slow n-pentane diffusion into a concentrated THF solution of 1 at 35 °C.
1
H NMR (400 MHz, THF-d
8
):  7.26 (m, 6 H, o-Ph), 6.83 (m, 6 H, m-Ph),
.66 (m, 3 H, p-Ph), 3.23 (br, q, 1 H, HB), 2.53 (m, 8 H, CH ), 2.21 (s, 20
):  166.1 (ipso-Ph),
), 44.3 (NMe). 11
6
2
and NMe). 13C{ H} NMR (100 MHz, THF-d
1
H, CH
1
2
8
36.7 (o-Ph), 126.1 (m-Ph), 121.7 (p-Ph), 54.5 (CH
2
B
1
7
1
NMR (128 MHz, THF-d
THF-d
Calcd. For C30
.13; N, 11.53.
8
):  10.0 (d, JBH = 76 Hz). Li{ H} NMR (156 MHz,
):  1.8. IR (KBr):  = 2212-1800 cm (multiple bands, BH). Anal.
1
8
44 4
H N BLi: C, 75.31; H, 9.27; N, 11.71. Found: C, 75.02; H,
Conclusion
9
4
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Chemistry - A European Journal
10.1002/chem.201702818
FULL PAPER
2
2
[
(L )Na][HBPh
3
] (2). A solution of L (0.100 g, 0.438 mmol) in 2 mL of THF
)] (0.114 g, 0.428 mmol) in
mL of THF. The resulting mixture was stirred for 0.5 h at room
concentration using a microliter syringe. Reaction progress was monitored
at room temperature using NMR spectroscopy. The products were
characterized by H, 11B, and 13C NMR spectroscopy and compared with
literature data.[9]
was added dropwise to a solution of [Na(HBPh
3
1
1
temperature. All the volatiles were removed under reduced pressure to
give a white solid. The solid was washed with n-pentane (3 x 2 mL) and
dried under vacuum to give analytically pure 2 (0.196 g, 0.396 mmol, 91%
yield) as a white powder. X-ray diffraction quality single crystals were
obtained from slow n-pentane diffusion into a concentrated THF solution
of 2 at 35 °C. H NMR (400 MHz, THF-d
Acknowledgements
1
8
):  7.28 (m, 6 H, o-Ph), 6.91 (m,
),
):  164.0
), 44.7
):  8.4 (d, 1JBH = 76 Hz). IR (KBr): 
BNa: C,
6
2
(
(
=
7
H, m-Ph), 6.76 (m, 3 H, p-Ph), 3.23 (br, q, 1 H, HB), 2.51 (m, 8 H, CH
.17 (s, 20 H, CH
and NMe). 13C{ H} NMR (100 MHz, THF-d
2 8
2
We thank the Deutsche Forschungsgemeinschaft through the
International Research Training Group “Selectivity in Chemo- and
Biocatalysis” for financial support and the Alexander von
Humboldt Foundation for a fellowship to D. M. We also thank
M.Sc. K.-N. Truong and Prof. U. Englert for collecting X-ray data.
1
ipso-Ph), 136.4 (o-Ph), 126.7 (m-Ph), 122.6 (p-Ph), 54.5 (CH
2
NMe). 11B NMR (128 MHz, THF-d
8
2158-1980 cm (multiple bands, BH). Anal. Calcd. for C30
1
H N
44 4
2.87; H, 8.97; N, 11.33. Found: C, 72.14; H, 8.95; N, 11.27.
2
2
Keywords: Alkali metals • Catalysis • Hydroboration • Me
6
TREN
[
(L )K][HBPh
was added dropwise to a solution of [K(HBPh
mL of THF. The resulting mixture was stirred for 0.5 h at room
3
] (3). A solution of L (0.100 g, 0.438 mmol) in 2 mL of THF
3
)] (0.118 g, 0.418 mmol) in
• Aza-crown
1
temperature. All the volatiles were removed under reduced pressure to
give a white solid. The solid was washed with n-pentane (3 x 2 mL) and
dried under vacuum to obtain analytically pure 3 (0.188 g, 0.369 mmol,
[
[
1]
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89% yield) as a white powder. X-ray diffraction quality single crystals were
obtained from slow n-pentane diffusion into a concentrated THF solution
1
of 3 at 35 °C. H NMR (400 MHz, THF-d
8
):  7.30 (m, 6 H, o-Ph), 6.94 (m,
6
H, m-Ph), 6.78 (m, 3 H, p-Ph), 3.20 (br, q, 1 H, HB), 2.25 (m, 28 H, CH
2
2015, 5, 3238-3259.
1
and NMe
2
). 13C{ H} NMR (100 MHz, THF-d
8
):  163.6 (ipso-Ph), 136.3 (o-
a) C. B. Herbert, P. V. Ramachandran, in Reductions in Organic
Synthesis, Vol. 641, American Chemical Society, 1996, pp. 1-30; b) S.
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50.
11
Ph), 126.9 (m-Ph), 122.8 (p-Ph), 54.9 (CH
MHz, THF-d
2
), 44.5 (NMe). B NMR (128
):  7.9 (d, 1JBH = 78 Hz). IR (KBr, cm1):  = 2168-1980 cm
1
8
44 4
(multiple bands, BH). Anal. Calcd. for C30H N BK: C, 70.57; H, 8.69; N,
10.97. Found: C, 70.23; H, 8.54; N, 11.28.
[
2
0
(PMDTA)Li][HBPh
3
] (4). A solution of PMDTA (0.100 g, 0.577 mmol) in
mL of THF was added dropwise to a solution of [Li(HBPh )] (0.143 g,
.571 mmol) in 1 mL of THF. The resulting mixture was stirred for 0.5 h at
3
room temperature. All the volatiles were removed under reduced pressure
to give a white solid. The solid was washed with n-pentane (3 x 2 mL) and
dried under vacuum to afford analytically pure 4 (0.221 g, 0.522 mmol,
9
1% yield) as a white powder. 1H NMR (400 MHz, THF-d
H, o-Ph), 6.83 (m, 6 H, m-Ph), 6.66 (m, 3 H, p-Ph), 3.44 (br, q, 1 H, HB),
8
):  7.23 (m, 6
2
NMe
.42 (m, 4 H, CH
2
), 2.32 (m, 4 H, CH
2
), 2.30 (s, 3 H, NMe), 2.21 (s, 12 H,
):  165.9 (ipso-Ph), 136.7 (o-Ph),
), 57.2 (CH ), 46.3 (NMe ), 43.6
):  8.2 (d, 1JBH = 79 Hz). Li{ H} NMR
):  0.4. IR (KBr):  = 2151-1900 (multiple bands, BH).
BLi: C, 76.60; H, 9.29; N, 9.93. Found: C, 76.12;
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). 13C{ H} NMR (100 MHz, THF-d
1
2
8
1
(
(
26.1 (m-Ph), 121.8 (p-Ph), 59.0 (CH
NMe). 11B NMR (128 MHz, THF-d
156 MHz, THF-d
2
2
2
7
1
8
8
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[
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More than 4000 structures containing [BPh
CSD.
4
] have been deposited in
1
8
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).
):  164.7 (ipso-Ph), 136.7 (o-Ph), 126.3
6
H, m-Ph), 6.69 (m, 3 H, p-Ph), 3.33 (br, q, 1 H, HB), 3.57 (s, 16 H, CH
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C{ H} NMR (100 MHz, THF-d
m-Ph), 122.0 (p-Ph), 70.1 (CH
8
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FULL PAPER
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6
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Chemistry - A European Journal
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FULL PAPER
Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
Comparison of ligands
catalytic carbonyl hydroboration by
(L)M][HBPh ] (M = Li, Na, K) confirms
L
on the
Hassan Osseili, Debabrata Mukherjee,
Thomas P. Spaniol, Jun Okuda*
[
3
the unique combination of Me
and lithium for high activity.
6
TREN
Page No. – Page No.
Ligand influence on the carbonyl
hydroboration catalysis by alkali
metal
(L)M][HBPh
hydridotriphenylborates
3
] (M = Li, Na, K)
[
7
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