Studies in solution and the solid state of coordination compounds derived from LiBH4, NaBH4, and bidentate aromatic amines

Article abstract of DOI:10.1002/ejic.200901233

The mixture of 2, 2′-bipyridylamine, 2, 2′'-bipyridine, 1, 10phenanthroline, 1, 2-phenylendiamine, and 1, 4-phenylendiamine each with LiBH₄ and NaBH₄ in a 1:1 molar ratio in THF yields seven new complexes of the type MBH₄-

Full text of DOI:10.1002/ejic.200901233

FULL PAPER
DOI: 10.1002/ejic.200901233
Studies in Solution and the Solid State of Coordination Compounds Derived
from LiBH4, NaBH4, and Bidentate Aromatic Amines
Milagros Aguilar-Martínez,[a] Genaro Félix-Baéz,[b] César Pérez-Martínez,[b]
Heinrich Nöth,[c] Angelina Flores-Parra,[d] Raul Colorado,[d] and
Juan Carlos Galvez-Ruiz*[b]
Keywords: Tetrahydroborates / Alkali metals / N ligands / Structure elucidation
The mixture of 2,2Ј-bipyridylamine, 2,2Ј-bipyridine, 1,10-
phenanthroline, 1,2-phenylendiamine, and 1,4-phenylendi-
amine each with LiBH4 and NaBH4 in a 1:1 molar ratio in
THF yields seven new complexes of the type MBH4·L-THF
and one complex of the type MBH4·L. These compounds
were characterized by IR and NMR spectroscopy and X-ray
single-crystal structure determinations. In the solid state, the
[BH4]– group is bidentate, as deduced from the stretching
patterns observed in IR spectra and confirmed by X-ray sin-
gle-crystal structure analysis. NMR spectroscopy showed
that all amines act as bidentate ligands and are symmetri-
cally coordinated to the metal cation. Complexes LiBH4-2,2Ј-
bipyridine-THF (1), NaBH4-2,2Ј-bipyridine-THF (2), LiBH4-
1,10-phenanthroline-THF (3), and NaBH4-1,10-phen-
anthroline-THF (4) have a discrete molecular structure,
whereas the complexes LiBH4-1,2-phenylendiamine-THF
(5), NaBH4-1,2-phenylendiamine-THF (6), LiBH4-2,2Ј-dipyr-
idilamine (7), and LiBH4-1,4-phenylendiamine-THF (8) have
polymeric structures in the solid state. N-borane-dipyr-
idylamine adduct 9 was isolated from an aged solution of 7.
IR spectroscopy of the new complexes showed that the struc-
tures of complexes 1, 3, 4, and 6 are maintained in the solid
state and in solution. A rotational barrier for the [BH4]– group
of less than 38 KJmol–1 was estimated for some of the new
complexes.
nitrogen and oxygen atoms.[4] A fair number of these com-
plexes have been studied by X-ray diffraction, which shows
that the [BH4]– moiety acts as a mono-, bi-, or tridentate
ligand. The bidentate and tridentate coordination forms of
[BH4]– are the most commonly found in the solid state.[5]
However, the structure in LiBH4·nL compounds are influ-
enced by stereoelectronic effects of both the ligand (L) and
the [BH4]– anion as shown by theoretical results.[6] There-
fore, it is important to understand the circumstances that
cause the [BH4]– group to adopt one of the possible coordi-
nation forms, because this should have an influence on the
chemical behavior of a particular complex.
We are interested in the synthesis and characterization of
novel compounds from neutral amine chelate ligands and
alkali metal tetrahydroborates with specific properties that
can be used in reducing reactions. We have already de-
scribed theoretically theses types of compounds.[6] The
study showed us the importance of carrying out detailed
analysis of the structure of the complexes in solution and
in the solid state because the former is the medium in which
the reduction reactions occur.
Introduction
Alkali metal tetrahydroborates constitute an important
class of reducing reagents with wide applicability in both
organic and inorganic chemistry. They are mainly applied
in reductions of aldehydes and ketones.[1] In addition, alkali
metal tetrahydroborates are used as starting materials for
the synthesis of organometallic derivatives, precursors for
the production of borides and hydrides, as well as other
inorganic materials, and as catalysts for hydrogenation,
isomerization, oligomerization, and polymerization.[2]
Modification of the alkali metal tetrahydroborates has
been performed to augment their chemoselectivity.[3] One of
these modifications includes the use of ligands containing
[a] Departamento de Investigación en Polímeros y Materiales,
Universidad de Sonora,
Blvd. Luis Encinas y Rosales, S/N, 83000, Hermosillo, Sonora,
Mexico
[b] Departamento de Ciencias Químico-Biológicas, Universidad de
Sonora,
Blvd. Luis Encinas y Rosales, S/N, 83000, Hermosillo, Sonora,
Mexico
Fax: +52-662-259-21-64
E-mail: anisolborano@guayacan.uson.mx
[c] Department of Chemistry and Biochemistry, University of
Munich,
Only a few structures of alkali tetrahydroborate com-
plexes with amines have been described.[5,7] Among alkali
metal complexes, lithium compounds have been studied
most comprehensively. Within this context, we studied the
structure of some complexes of LiBH4 and NaBH4 with
Munich, Germany
[d] Departamento de Química, Centro de Investigación y de
Estudios Avanzados,
Mexico D. F.
Eur. J. Inorg. Chem. 2010, 1973–1982
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1973

J. C. Galvez-Ruiz et al.
FULL PAPER
bidentate aromatic amines in solution and in the solid state of the structure of alkali-metal–amine complexes, we re-
to comprehend the influence of solvent and ligand in both corded the IR spectra in THF solution. The results are pre-
structure and chemical behavior.
sented in Table 2.
Results and Discussion
Infrared Spectra in the Solid State and in Solution
Eight new complexes, LiBH4-2,2Ј-bipyridine-THF (1),
NaBH4-2,2Ј-bipyridine-THF
(2),
LiBH4-1,10-phen-
anthroline-THF (3), NaBH4-1,10-phenanthroline-THF (4),
LiBH4-1,2-phenylendiamine-THF (5), NaBH4-1,2-phenyl-
endiamine-THF (6), LiBH4-2,2Ј-dipyridilamine (7), and
LiBH4-1,4-phenylendiamine-THF (8), were obtained from
a LiBH4 solution and a NaBH4 suspension in THF by add-
ing 2,2Ј-bipyridylamine, 2,2Ј-bipyridine, 1,10-phen-
anthroline, 1,2-phenylendiamine, and 1,4-phenylendiamine
in a 1:1 molar ratio. These complexes were stable and easily
handled under anhydrous conditions in the solid state.
To get some information about the structure of the new
compounds, the IR spectra of the solid compounds were
recorded by using KBr pellets. Data for the B–H, N–H,
and aromatic ring stretching vibrations are summarized in
Table 1. These compounds present between two and four
B–H stretching bands, depending of the ligand type and
metal present, which differ from the single and broad band
observed in the IR spectra of solid LiBH4 and NaBH4.[8]
Figure 1. IR patterns for B–H stretching bands in compounds 3
(right) and 7 (left) in KBr.
Table 2. Selected IR stretching bands for complexes 1, 3, and 5–7
in THF solution.[a]
Stretching
1
3
5
6
7
The pattern observed in the B–H stretching bands has
[5c]
been reported in LiBH4(NC5H5)3
(four bands),
bands), and
B–H
2292 (i, br.) 2291 (i, br.) 2292 (m)
2226 (i, br.) 2227 (i, br.) 2225 (m)
2336 (m)
2360 (m)
2392 (m)
2308 (m)
2262 (m)
765 (i)
LiBH4·2[2,4,6-(CH3)3NC5H2][9]
(three
[10]
LiBH4(NC5H4-4-Me)3
(three bands), where the [BH4]–
Aromatic 760 (i)
ring
731 (i)
766 (i)
802 (i)
749 (i)
730 (i)
group acts as a bidentate ligand. The IR data suggest that
the [BH4]– group is present in a dicoordinate interaction
with the metal atom.
From Table 1, two kinds of B–H stretching band patterns
are distinguished; one for compounds 1, 3, 4, and 6 and the
other for the remainder of the compounds (Figure 1). This
means that there are two kinds of bidentate structures de-
pending on the ligand and metal used. Therefore, it would
be helpful to predict the type of structure associated with a
732 (i)
N–H
3387 (i)
3365 (i)
633 (i)
1592 (i)
1502 (i)
1459 (i)
1274 (i)
1249 (i)
3328 (m)
Ligand
422 (br.)
3058 (m)
1417 (i)
1040 (i)
422 (i)
695 (i)
608 (m)
1531 (m)
1234 (m)
990 (i)
2963 (i)
1516 (i)
1423 (m)
1262 (i)
1523 (m)
1459 (i)
1289 (i)
specific ligand. To get some information about the stability [a] (i) intense, (m) medium, (br.) broad, (sh.) shoulder.
Table 1. Important IR stretching bands for the alkali metal bidentate amine complexes in KBr.[a]
Stretching
1
2
3
4
5
6
7
8
B–H
2292 (i, br.)
2226 (i, br.)
2345 (sh.)
2292 (i, br.)
2224 (i, br.)
2368 (sh.)
2291 (i)
2227 (m, br.) 2223 (i, br.)
2378 (sh.)
2292 (i, br.)
2292 (i)
2225 (m)
2350 (m)
2387 (sh.)
750 (i)
2336 (m)
2360 (m)
2392 (m, br.) 2291 (i)
2308 (i)
2225 (i)
2158 (sh.)
2381 (sh.)
736 (i)
769 (m)
856 (i)
2262 (sh.)
Aromatic ring 760 (i)
757 (i)
731 (m)
766 (m)
802 (i)
730 (i)
765 (i)
834 (i)
732 (m)
N–H
3387 (i)
3365 (i)
1592 (i)
1502 (i)
1459 (m)
1274 (i)
3501 (br.)
3328 (m)
3389 (i)
3341 (i)
1256 (i)
1126 (i)
714 (i)
Ligand
3058 (m)
1417 (i)
1040 (i)
3054 (m)
1416 (i)
1040 (i)
2963 (i)
1516 (i)
1423 (m)
1262 (i)
2971 (m)
1508 (i)
1421 (i)
1267 (m)
1495 (i)
1459 (i)
1274 (i)
1531 (m)
1234 (m)
990 (i)
608 (m)
[a] (i) intense, (m) medium, (br.) broad, (sh.) shoulder.
1974
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Coordination Compounds Derived from LiBH4, NaBH4, and Aromatic Amines
Figure 2. IR B–H stretching band pattern of compounds 1 (right) and 5 (left) in KBr and in THF solution.
Comparison of the B–H stretching patterns of the com- Table 3. 11B, 7Li, and 23Na NMR spectroscopic data (δ, ppm; J,
Hz) for compounds 1–8.
pounds in the solid state and in solution reveals a change
in the number of stretching bands. Compounds 1, 3, and 6
conserved the pattern shown in the solid when in solution
(they show an intense doublet; Figure 2), whereas a change
LiBH4
1
3
5
7
8
δ(11B)
–40
81
0.02
–42
81
2.78
–41
81
4.22
–40
81
0.77
–38
82
3.45
–42
82
0.10
1JB,H
(number and intensity of bands) occurred in the other com- 7Li
pounds This is very important, because depending on the
amine used, it is possible to get compounds whose structure
NaBH4
2
4
6
δ(11B)
–40
81
2.85
–43
81
3.34
–42
81
2.25
–43
81
4.0
is the same in the solid state and in solution.
1JB,H
23Na
All new complexes, in the solid state, can be stored in a
vial, under normal conditions, for up to six months and
no degradation was detected by IR or NMR spectroscopy.
However, after a few months in solution, in some com-
plexes, the formation of BH3 adducts are detected (by the
typical 1:3:3:1 quadruplet in the 11B NMR spectra), for ex-
ample, in compound 7.
atoms are equivalent in solution. In compounds 1, 3, and 4
it is possible to see the 10B,1H coupling as a septet signal
1
(1:1:1:1:1:1:1, JB,H ≈ 30 Hz).
To determine the value of ∆G϶ for the rotation of the
[BH4]– group in the new complexes, we lowered the tem-
perature to –90 °C for 1 in [D8]THF and to –60 °C for 3
and 4 in CDCl3, but we did not reach the coalescence tem-
NMR Spectroscopy
The IR data provide some information about the dentic- perature. Nevertheless, those temperatures allowed us to es-
ity of the [BH4]– group, but scarce information about the timate the value of ∆G϶ (by using the Eyring equation)[11]
structure of the complex can be obtained. To determine the as 31.5 KJmol–1 for compound 1 and 36.9 KJmol–1 for 3
coordination mode of the ligand, the coordination sphere and 4. These values are lower than those obtained for tran-
around the metal, and the presence of the [BH4]– anion, we sition metals[2a,2b](V, Nb, and Ta, ionic radii 0.65, 0.70, and
7
carried out multinuclear NMR experiments. The 11B, Li, 0.95 Å, respectively) and indicate that in the compounds
and 23Na NMR spectroscopic data are presented in Table 3. prepared here the [BH4]– group rotates faster than in the
The 11B NMR chemical shift for all compounds is corresponding transition-metal complexes.
1
7
On the other hand, the Li and 23Na chemical shifts are
11B,1H
–40Ϯ3 ppm, which gives a quintuplet with J
in the
range 81–82 Hz. This shows that the geometry of the deshielded by 2–4 ppm with respect to the corresponding
[BH4]– group is similar in all compounds. In general, the alkali metal tetrahydroborate, depending on the amine. This
ligand produces a somewhat better shielding in the 11B is a result of the coordination of the ligand with the alkali
chemical shift of the [BH4]– group, except for compound 7. metal cation. The 7Li chemical shift agrees with a tetracoor-
The deshielding observed in 7 can be the result of a stronger dinate atom.[5c,7a]
1
interaction between the [BH4]– group and the metal cation.
With the use of H and 13C NMR spectroscopy, we de-
1
In the H NMR spectrum, the [BH4]– group shows only termined that each amine uses two nitrogen atoms to coor-
1
one signal as a quartet (1:1:1:1, JB,H ≈ 81 Hz), around dinate in a symmetric form with the alkali metal cation.
0 ppm. This single signal means that the four hydrogen The carbon and hydrogen atoms next to the nitrogen atom
Eur. J. Inorg. Chem. 2010, 1973–1982
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1975

J. C. Galvez-Ruiz et al.
FULL PAPER
are deshielded by 2–6 and 0.2–0.3 ppm, respectively, de- in compounds 5–8, polymeric structures are also possible
pending on the amine. In compounds 5, 6, and 8, the NH2 because of the position of the nitrogen atom and the flexi-
group is also deshielded by 3–4 ppm, indicating that this bility of the ligand (Figure 4).
group is coordinated to the metal cation. However, in com-
pound 7, the 1H chemical shift for the NH proton does not
change, meaning that it is not coordinated. All these facts
evidence the formation of complexes 1–8 and agree with the
Crystal Structures
IR data. In all compounds, except compound 7 (probably
It was possible to grow single crystals from compounds
due to steric effects), a molecule of THF is coordinated to 1–8; unfortunately, not all of them were suitable for X-ray
the metal cation. The amine/THF/MBH4 ratio was 1:1:1 analysis. The solid-state structures of compounds 1, 5, and
for all complexes, except for compound 7 where the amine/ 8 and that of adduct 9 were determined crystallographically.
MBH4 ratio was 1:1.
Selected bond lengths and angles are presented in Table 4.
All these data allow us to propose a discrete molecular
Compound 1 is a 1:1:1 complex formed by 2,2-bipyr-
structure, where the metal cation is surrounded by one idine, LiBH4, and one THF molecule. It crystallizes in the
amine molecule, one THF molecule, and the [BH4]– group orthorhombic space group Pnma with Z = 4. Figure 5 de-
in a tetrahedral geometry (Figure 3). This agrees with our picts the asymmetric unit, which shows a discrete molecule
previous theoretical study suggesting that the discrete struc- with a lithium atom in a distorted tetrahedral geometry [N–
tures were formed by one amine molecule, one THF mole- Li–N 81.1(4)°, N–Li–O 103.1(4)°, N–Li–B 126.1(4)°, O–Li–
cule, and the [BH4]– group are global minimum.[6] However, B 111.8(5)°] surrounded by 2,2-bipyridine, THF, and the
[BH4]– group. The 2,2Ј-bipyridine is planar and coordinates
symmetrically to the lithium atom in a bidentate form with
a N–Li bond length of 2.048(9) Å. The lithium atom lies
almost in the molecular plane of the amine (just bent off
13°). The THF molecule has an envelope conformation
with the oxygen atom out of plane and pointing towards
the lithium atom; two cooperative C–H···π interactions[2c,12]
stabilize the THF approach. The O–Li bond length is
2.01(1) Å. Regarding the [BH4]– group, it has a slightly dis-
torted tetrahedral array with bond angles ranging from
105.0 to 113.0° due to the multiple hydride proton interac-
tions B–H···H–C[13] with the C–H protons of six bipyridine
molecules (Figure 6). This group interacts with the Li atom
[distance B···Li is 2.34(1) Å] by two hydrogen atoms. The
H–Li bond length is 2.010 Å. The terminal B–H bond is
shorter (1.060 Å) than the B–H bridging bond (1.130 Å).
The molecules are packed in the crystal in an alternate
form, with the [BH4]– group laying in the center (Support-
ing Information, Figure S1).
Figure 3. Proposed structures for compounds 1–8.
The crystals of 5 are monoclinic, space group C2/c and
Z = 8. We should mention that there is a residual electron
density due to a disordered toluene molecule (used to crys-
tallize). The crystal structure of compound 5 shares some
characteristics with compound 1. For example, it has a lith-
ium atom in a distorted tetrahedral geometry [N–Li–N
107.9(5)°, N–Li–O 100.8(5)°, and 98.7(5)°, N–Li–B
115.4(5), 114.6(5)°, O–Li–B 117.5(5)°] surrounded by two
molecules of 1,2-phenylendiamine, THF, and the [BH4]–
group (Figure 7). Each amine acts as bidentate ligand and
binds two different lithium atoms, with N1–Li bond lengths
of 2.136(11) and 2.140(10) Å, respectively, which produces
a polymeric array. The THF has an envelope conformation
with the oxygen atom lying in plane; O–Li bond length
1.946(11) Å. The chain is stabilized by two N–H···H–B in-
teractions that have Hδ+···Hδ– bond lengths of 2.362(4) and
2.423(7) Å, respectively (Figure 8).
The chains are joined by Hδ+···Hδ– interactions with N–
H···H–B distances of 2.483(4) and 2.209(4) Å. Also, one C–
H···H–B interaction with a distance of 2.474(5) Å can be
Figure 4. Proposed polymeric structures for compounds 5–7.
1976
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Coordination Compounds Derived from LiBH4, NaBH4, and Aromatic Amines
Table 4. Selected bond lengths [Å] and angles [°] for compounds 1, 5, 8, and 9.
Compound 1
Compound 8
O–Li
N2–Li
N1–Li
B–Li
2.01(1)
2.048(9)
2.048(9)
2.34(1)
2.0100
121.8(3)
103.4(4)
117.9(4)
121.2(4)
106.00
B–H1
B–H2
B–H4
B–H3
1.1300
1.0600
1.0600
1.1300
N1–Li1
N2–Li1
N3–Li1
N1–C1
N2–C4
N3–C7
N1–H2
N1–H1
N2–H1
N2–H2
N1–Li1–N2
2.127(5)
2.146(5)
2.095(4)
1.428(4)
1.418(3)
1.424(3)
0.92(3)
0.86(3)
0.89(3)
0.86(3)
105.5(2)
N3–H1
N3–H2
O10–C11
O10–C14
O10–Li1
B1–H1
B1–H2
B1–H3
B1–H4
0.93(3)
0.87(3)
1.416(3)
1.412(4)
1.924(4)
1.15(3)
1.01(5)
1.10(3)
1. 04(5)
Li–H1
C8–O–Li
C8–O–C8Ј
C1–N2–C3
N2–C1–C6
H1–B–H3
H2–B–H3
H1–B–H2
N2–Li–B1
N2–Li–N3
O–Li–N2
O–Li–B
113.00
126.1(4)
81.1(4)
103.1(4)
111.8(5)
55.00
106.00
H1–Li–H1Ј
H1–N3–H2
C11–O–C14
107(3)
Compound 5
N1–Li1–N3
105.5(2)
109.4(2)
N8–Li
N9–Li
2.136(11)
2.142(10)
1.421(7)
1.434(6)
0.9000
0.9000
0.9000
O10–C14
C1–C6
B–Li
B–H1
B–H2
B–H3
B–H4
Li–H1
Li–H3
1.418(12)
1.3893
N2–Li1–N3
O–Li1–N1
O–Li1–N2
O–Li1–N3
C1–N1–Li1
C4–N2–Li1
C7–N3–Li1
H1–N1–H2
H1–N2–H2
108.9(2)
115.0(2)
108.1(2)
113.4(2)
119.9(2)
106.5(2)
120.9(2)
111(3)
C11–O–Li1
C14–O–Li1
H1–B–H3
H1–B–H4
H1–B–H2
H2–B–H4
H3–B–H4
H2–B–H3
123.6(2)
118.5(2)
115(2)
107(3)
104(3)
111(4)
106(3)
114(3)
N8–C1
N9–C2
N8–H1
N8–H2
N9–H1
N9–H2
O10–Li
2.364(14)
1.23(7)
1.02(8)
0.99(9)
1.07(12)
2.04(6)
2.08(9)
0.9000
1.946(11)
104(3)
O10–C11
1.409(11)
Compound 9
C11–O10–C14 108.6(7)
C11–O10–Li1 120.8(6)
H2–B–H3
H2–B–H4
H3–B–H4
H1–B–H2
O10–Li–N8
O10–Li1–N9
O10–Li–B5
N8–Li–N9
N8–Li–B5
N9–Li–B5
H1–Li–H3
95(7)
112(7)
103(8)
103(5)
100.8(5)
98.7(5)
117.5(5)
107.9(5)
114.6(5)
115.4(5)
51(3)
N2–C1
N2–C3
N2–B
N7–C7
N7–C8
N9–C8
C1–N2–C3
C1–N2–B1
C3–N2–B1
C8–N9–C1
C8–N7–H7
C1–N7–H7
N2–C3–C4
1.361(3)
1.359(3)
1.604(3)
1.367(3)
1.404(3)
1.321(3)
118.3(2)
122.3(2)
119.4(2)
116.2(2)
115.00
N9–C1
N7–H7
B–H1
B–H2
B–H3
1.347(3)
0.8600
1.1400
1.1100
1.0700
H1–N8–H2
H1–N9–H2
C2–C3–C4
C3–C4–C5
Li–B5–H3
Li–B5–H1
Li–B5–H52
H1–B5–H3
H1–B–H4
107.00
107.00
120.02
120.00
61(5)
60(3)
69(4)
N7–C8–N9
N2–B–H1
N2–B–H2
N2–B–H3
H1–B–H2
H1–B–H3
H2–B–H3
119.1(2)
106.00
109.00
106.00
111.00
114.00
111.00
105(5)
132(6)
114.00
123.2(2)
the Li atom [B···Li 2.364(14) Å] through two hydrogen
atoms. The H–Li bond lengths are 2.04(6) and 2.08(9) Å.
The B–H bond length varies from 1.00(9) to 1.23(7) Å.
Compound 8 crystallizes in the same system and space
group as compound 5, that is, monoclinic, space group C2/
c, and Z = 8, but the structure is quite different. Compound
8 shows an ionic, 3D polymeric array with lithium atoms
having a slightly distorted tetrahedral geometry and bond
angles ranging from 105 to 115°. The lithium atom is sur-
rounded by three molecules of 1,4-phenylendiamine and
one THF molecule (Figure 10). Each amine acts as a biden-
tate ligand and binds two different lithium atoms, in a 3D
array, with the same bond lengths but different from other
amines, N1–Li 2.127(5) Å, N2–Li 2.146(5) Å, N3–Li
2.095(4) Å. These amines are arranged almost perpendicu-
lar to each other (Figure 11). The THF shows an envelope
conformation with the oxygen atom lying in the plane; the
O–Li bond length is 1.924(4) Å. Something that distin-
Figure 5. Molecular structure of compound 1.
seen (Figure 9). The four N–H···H–B interactions and the guishes this structure from the previous ones is that the
one C–H···H–B interaction (Supporting Information, Fig- [BH4]– group is not coordinated to the lithium atom. The
ure S2) produce a distorted tetrahedral array with bond [BH4]– group has a lightly distorted tetrahedral geometry
angles ranging from 95 to 132°. This group interacts with (H–B–H bond angles between 104 and 115°) and the B–H
Eur. J. Inorg. Chem. 2010, 1973–1982
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1977

J. C. Galvez-Ruiz et al.
FULL PAPER
Figure 6. B–H···H–C interactions in the crystal of compound 1.
bond lengths span in a range from 1.01 to 1.15 Å. The long-
est B–H bond is involved in a hydride–proton interaction
[Hδ+···Hδ– 2.214(7) Å, angle N–H···Hδ– 171.3°] with a NH2
group. The second longest B–H bond participates in a triple
hydride–proton interaction with three neighboring NH2
groups [Hδ+···Hδ– 2.114(7) Å, angle N–H···Hδ– 166.2°,
Hδ+···Hδ– 2.187(7) Å, angle N–H···Hδ– 146.3°, Hδ+···Hδ–
2.241(7) Å, angle N–H···Hδ– = 145.7°, see Supporting In-
formation].
On the other hand, from an aged THF solution of com-
pound 7 (6 months) we collected nice needles of 9 having
the solid-state structure shown in Figure 12. In this figure
we can see that 2,2-dipyridilamine coordinates with one ni-
trogen atom of the pyridine ring and to one BH3, group,
giving an asymmetric adduct. Formation of compound 9
implies the loss of LiH.[5a]
Figure 7. Asymmetric unit in compound 5, showing a disordered
toluene molecule.
Figure 8. Chain formed in compound 5.
1978
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1973–1982

Coordination Compounds Derived from LiBH4, NaBH4, and Aromatic Amines
Figure 12. Crystalline structure of adduct 9.
The solid-state structure of adduct 9 presents some very
interesting structural features. First, an intermolecular di-
hydrogen bond is observed with a C–H···H–B distance of
2.58 Å with a symmetry-related molecule, resulting in the
formation of a dimer. The C–H···H and B–H···H angles are
142.9 and 80.0°, respectively (Supporting Information, Fig-
ure S3). Second, there is a C–H···π interaction between two
adduct molecules that are located perpendicular to each
other. The C–H···aromatic ring distance and the C–H–aro-
matic ring angle are 2.88 Å and 155°, respectively. Both the
C–H···aromatic ring distance, in the range of the accepted
value (2.6–3.0 Å) for this kind of interaction,[12] and the
angle close to linearity, are consistent with the C–H···π in-
teraction (Supporting Information, Figure S4).
Figure 9. Interactions between chains in compound 5.
All of these unconventional hydrogen bonds are the sup-
ramolecular array scaffolds observed in the adduct derived
from compound 9. This array is shown in Figure 13 and
consists of a chain of dimers kept together by C–H···H–B
and C–H···π hydrogen bonds in a zigzag array.
Figure 10. Molecular structure of compound 8.
Figure 13. Intermolecular array in the lattice of the adduct derived
from compound 7.
It is important to mention that all dihydrogen bonds
where the [BH4]– group is involved can be shorter by
0.10 Å. This shortening comes from the correction that
should be made to the B–H bond lengths obtained by X-
ray diffraction (increment of 0.10 Å)[14a] due to the combi-
nation of both the displacement of the electron cloud on
Figure 11. Crystal packing of compound 8.
Eur. J. Inorg. Chem. 2010, 1973–1982
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1979

J. C. Galvez-Ruiz et al.
FULL PAPER
dipyridylamine, 2,2Ј-bipyridine, 1,10-phenanthroline, and 1,2-
phenylendiamine were purchased from Aldrich and used as re-
ceived. Infrared, in KBr and THF solution, are reported in cm–1.
1H, 13C 11B, 7Li, and 23Na NMR spectra were recorded with a
Bruker Avance 400 spectrometer at 400.1, 100.6, 128.4, 155.4, and
71.5 MHz, respectively; chemical shifts are reported in parts per
million; δ = 1H and 13C were referenced to TMS, 11B to BF3·OEt2,
and 7Li to LiCl·H2O (9.7 ). Elemental analyses were performed
the H atoms (major contributor) and the liberation effect
of the [BH4]– group.[14] Besides, the slightly distorted tetra-
hedral geometry of the [BH4]– group is consistent with the
observed dihydrogen bonds.[12e,14b]
Conclusions
Eight new complexes were prepared from a mixture of with a Flash 1112 Thermo Finnigan analyzer. Melting points were
measured with a Büchi B-540 apparatus. X-ray crystallography
data (Table 5) were measured by using standard procedures with a
Nonius Kappa CCD instrument with CCD area detector by using
graphite-monochromated Mo-Kα radiation at 293 K. Intensities
were measured by using φ + ω scans. The structure was solved
and refined by using SHELX-97.[15] All non-hydrogen atoms were
refined anisotropically. Almost all hydrogen atoms were found in
the difference map (except hydrogen atoms in the [BH4]– group in
compounds 1 and 9 and the NH2 group in compound 5) and al-
lowed to ride on their respective atoms, except for those whose
2,2Ј-bipyridylamine, 2,2Ј-bipyridine, 1,10-phenanthroline,
1,2-phenylendiamine, and 1,4-phenylendiamine with LiBH4
and NaBH4, respectively, in a 1:1 molar ratio in THF. In
all complexes but 8, the [BH4]– group is bidentate in the
solid state, with an estimated rotational energy of less than
38 KJmol–1. All amines act as bidentate ligands and coor-
dinate to metal cations in a symmetric form. Depending
on the amine, we can get discrete molecular or polymeric
complexes. In all studied complexes, the metal cation and
the [BH4]– group show a tetrahedral distorted geometry. coordinates were refined.
The use of bidentate amines augments the stability in the
LiBH4-2,2Ј-bipyridine-THF (1): A THF (15 mL) solution of LiBH4
solid state and in solution (except in 7) under normal condi-
tions of LiBH4 and NaBH4 and also determines the com-
plex–structure type and its prevalence in the solid state and
in solution.
(139 mg, 6.6 mmol) was treated with a THF solution (5 mL) of
2,2Ј-bipyridine (400 mg, 2.6 mmol). This mixture was stirred for
30 min before filtering. The remnant white solid was dried by a
nitrogen stream (577 mg, 90%). M.p. 158–162 °C. Crystals suitable
for X-ray structural determination were obtained by slow evapora-
tion. 1H NMR (CDCl3): δ = 8.26 (d, 3-H, 2,2Ј-bipyridine), 7.31 (t,
4-H, 2,2Ј-bipyridine), 7.82 (t, 5-H, 2,2Ј-bipyridine), 8.67 (d, 6-H,
2,2Ј-bipyridine), 0.08 (q, [BH4]–), 1.83 (t, 2-H,THF), 3.72 (t, 1-H,
THF) ppm. 13C NMR (CDCl3): δ = 155 (C-2), 120 (C-3), 137 (C-
4), 123 (C-5), 149 (C-6), 68.5 (C-2, THF), 25.5 (C-3, THF) ppm.
Experimental Section
General: All manipulations were carried out under a nitrogen atmo-
sphere by using Schlenk techniques. All solvents were dried and
distilled prior to use. Sodium and lithium tetrahydroborate, 2,2Ј-
Table 5. Crystallographic data for the structural analyses of compounds 1, 5, 8, and 9.
1
5
8
9
Formula
Formula weight
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C14H20BLiN2O
250.08
0.25ϫ0.2ϫ0.1
orthorhombic
Pnma
9.7864(7)
11.6589(8)
12.8680(9)
90
C14H20BLiN2O
244.1
0.60ϫ0.25ϫ0.13
monoclinic
C2/c
24.416(1)
12.8108(7)
10.1523(7)
90
C3H4BLiN3O
2048.82
0.10ϫ0.14ϫ0.13
monoclinic
C2/c
23.468(3)
9.308(2)
17.583(6)
90
C10H12BN3
185.04
0.35ϫ0.2ϫ0.15
monoclinic
P21/c
5.1123(2)
15.3366(7)
12.7199(6)
90
β [°]
90
90
1468.2(2)
4
1.131
0.07
536
97.354(2)
90
3149.5(3)
8
1.029
0.06
123.65(2)
90
996.53(8)
8
1.064
0.07
92.265(2)
90
996.53(8)
4
1.233
0.08
γ [°]
V [Å3]
Z
ρcalcd. [Mgm–3]
µ [mm–1]
F(000)
1048
1112
392
Index range
12Յ h Յ 12
–14 Յ k Յ 14
–16 Յ l Յ 16
55.60
–30 Յ h Յ 30
0 Յ k Յ 16
–12 Յ l Յ 12
54.9
–26 Յ h Յ 0
–10 Յ k Յ 0
–16 Յ l Յ 20
47.95
–6 Յ h Յ 6
–19 Յ k Յ 19
–16 Յ l Յ 16
55.2
2θ [°]
T [K]
293
3134
1730
791
0.165
92
1.43
293
6452
3230
1119
0.00
156
1.07
293
2752
2503
1685
0.0094
236
1.06
293
4339
2270
1191
0.069
127
1.10
Refl. collected
Refl. unique
Refl. obs. 2σ
R (int.)
No. variables
GOOF
Final R(2σ)
Final wR2
Larg. res. peak [eÅ–3]
0.086
0.089
0.35
0.149
0.416
0.24
0.0445
0.1339
0.17
0.056
0.061
0.17
1980
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1973–1982

Coordination Compounds Derived from LiBH4, NaBH4, and Aromatic Amines
11B NMR (CDCl3): δ = –40.7 (q, [BH4]–) ppm. 7Li NMR (CDCl3):
NaBH4-1,2-phenylenediamine-THF (6): Following the procedure
δ = 3.98 (s, LiBH ) ppm. IR (KBr or THF): ν = 1591, 2226, 2292
outlined for 1, a THF (15 mL) suspension of NaBH4 (38 mg,
1.0 mmol) was treated with a THF solution (5 mL) of 1,2-phenyl-
enediamine (110 mg, 1.0 mmol). This mixture was stirred for
30 min before filtering. The orange solid was dried by a nitrogen
stream (68 mg, 62%). M.p. 101–105 °C. 1H NMR (CDCl3): δ = 7.5
(d, 3-H, amine), 7.0 (d, 4-H amine), –0.03 (q, [BH4]–), 1.73 (t, 2-H,
THF), 3.75 (t, 1-H, THF) ppm. 13C NMR (CDCl3): δ = 138 (C-
2), 120 (C-3), 110 (C-4), 68.2 (C-2, THF), 25.6 (C-3, THF) ppm.
11B NMR (CDCl3): δ = –43.3 (q, [BH4]–) ppm. IR (KBr or THF):
˜
4
([BH4]–), 760, 3422, 3058, 1417, 1040 (2,2Ј-bipyridine) cm–1.
C14H20BLiN2O (250): calcd. C 67.25, H 8.00, N 11.20; found C
67.45, H 8.14, N 11.55.
NaBH4-2,2Ј-bipyridine-THF (2): Following the procedure outlined
for 1, a suspension of NaBH4 (680 mg, 1.7 mmol) in THF (15 mL)
was treated with a THF solution (5 mL) of 2,2Ј-bipyridine (278 mg,
1.7 mmol). This mixture was stirred for 30 min before filtering. The
remnant white solid was dried by a nitrogen stream (670 mg, 98%).
ν = 1604, 2336.8, 2360.4 (BH ), 730, 3501, 1495, 1459 (amine) cm–1.
˜
4
1
M.p. 100–104 °C. H NMR (CDCl3): δ = 8.42 (d, 3-H, 2,2Ј-bipyr-
C6H16B2N2Na2 (184.13): calcd. C 39.21, H 8.77, N 15.24; found C
39.16, H 5.64, N 14.75.
idine), 7.25 (t, 4-H, 2,2Ј-bipyridine), 7.83 (t, 5-H, 2,2Ј-bipyridine),
8.73 (d, 6-H, 2,2Ј-bipyridine), 0.06 (q, [BH4]–), 1.85 (t, 2-H, THF),
3.75 (t, 1-H, THF) ppm. 13C NMR (CDCl3): δ = 156 (C-2), 123
(C-3), 137 (C-4), 121 (C-5), 149 (C-6), 67.8 (C-2, THF), 25.6 (C-3,
THF) ppm. 11B NMR (CDCl3): δ = –43.3 (q, [BH4]–) ppm. IR
LiBH4-2,2-dipyridylamine (7) and N-BH3-2,2-Dipyridylamine (9):
Following the procedure outlined for 1, a THF (15 mL) solution
of LiBH4 (80 mg, 2.15 mmol) was treated with a THF solution
(5 mL) of 2,2Ј-dipyridylamine (362 mg, 2.11 mmol). This mixture
was stirred for 30 min before filtering. The yellow solid was dried
by a nitrogen stream (307 mg, 83%). M.p. 172–176 °C. 1H NMR
(CDCl3): δ = 8.51 (d, 3-H, amine), 7.44 (t,4-H, amine), 7.95 (d, 5-
H, amine), 8.81 (s, 6-H, amine), 0.31 (q, [BH4]–) ppm. 13C NMR
(CDCl3): δ = 146 (C-2), 113 (C-3), 138 (C-4), 116 (C-5), 153 (C-6)
ppm. 11B NMR (CDCl3): δ = –40.8 (q, [BH4]–) ppm. IR (KBr or
(KBr or THF): ν = 1578, 2224, 2292 (BH ), 757, 3439, 3054, 1416,
˜
4
1040 (2,2Ј-bipyridine) cm–1. C14H20BN2NaO·1/2bipy (345.2): calcd.
C 66.10, H 7.30, N 12.17; found C 65.60, H 6.10, N 12.90.
LiBH4-1,10-phenanthroline-THF (3): Following the procedure out-
lined for 1, a THF (15 mL) solution of LiBH4 (25 mg, 1.1 mmol)
was treated with a THF solution (5 mL) of 1,10-phenanthroline
(207 mg, 1.1 mmol). This mixture was stirred for 30 min before fil-
tering. The remnant yellow solid was dried by a nitrogen stream
(0.20 g, 97%). M.p. 150–154 °C. 1H NMR (CDCl3): δ = 8.99 (d, 2-
H, amine), 7.63 (q, 3-H amine), 8.26 (d, 4-H, amine), 7.82 (s, 5-H
amine), 0.23 (q, [BH4]–), 1.82 (t, 2-H THF), 3.72 (t, 1-H THF)
ppm. 13C NMR (CDCl3): δ = 150 (C-2), 126 (C-3), 136 (C-4), 123
(C-5), 146 (C-11), 128 (–), 68.2 (C-2, THF), 25.8 (C-3, THF) ppm.
11B NMR (CDCl3): δ = –41.5 (q, [BH4]–) ppm. IR (KBr or THF):
THF): ν = 22392, 2308.9, 2262 (BH ), 765, 732, 3328, 608, 153,
˜
4
1234, 990 (amine) cm–1. C20H26B2Li2N6 (385.68): calcd. C 62.27,
H 6.74, N 21.77; found C 63.04, H 7.10, N 21.45. From a THF
solution of 7, left aside for six months, crystals of compound 9
were obtained and analyzed by X-ray diffraction. C10H12BN3·THF
(257.0): calcd. C 65.36, H 7.78, N 16.3; found C 64.06, H 7.29, N
17.14.
LiBH4-1.5(1,4-phenylenediamine)-THF (8): Following the pro-
cedure outlined for 1, to a solution of p-phenylendiamine (310 mg)
in THF (15 mL) was added a solution of LiBH4 (622 mg) in THF
(10 mL). After 30 min, the mixture was filtered and the volume was
reduced to 20 mL. The brown solution was kept at 5 °C and brown
prisms had formed after 1 d (370 mg, 75%). M.p. 185 °C (de-
ν = 2291, 2227 (BH ), 731, 766, 802, 422, 2963, 1516, 1423, 1262
˜
4
(amine) cm–1. C16H20BLiN2O (274.1): calcd. C 70.11, H 7.35, N
10.20; found C 69.45, H 8.10, N 11.25.
NaBH4-1,10-phenanthroline-THF (4): Following the procedure out-
lined for 1, a THF (15 mL) suspension of NaBH4 (36 mg,
0.95 mmol) was treated with a THF solution (5 mL) of 1,10-phen-
anthroline (178 mg, 0.98 mmol). This mixture was stirred for
30 min before filtering. The yellow solid was dried by a nitrogen
stream (182 mg, 99%). M.p. 188–190 °C. 1H NMR (CDCl3): δ =
9.18 (d, 2-H, amine), 7.62 (q, 3-H, amine), 8.25 (d, 4-H, amine),
7.79 (s, 5-H, amine), 0.29 (q, [BH4]–), 1.84 (t, 2-H, THF), 3.73 (t,
1-H, THF) ppm. 13C NMR (CDCl3): δ = 150 (C-2), 126 (C-3), 136
(C-4), 123 (C-5), 146 (C-11), 128 (C-12), 68.1 (C-2, THF), 26.0 (C-
3, THF) ppm. 11B NMR (CDCl3): δ = –42.9 (q, [BH4]–) ppm. IR
1
comp.). H NMR (CDCl3): δ = 7.20 (m, 2-H), 7.00 (m, 3-H), 3.80
(2-H, THF), 1.80 (3-H, THF), –0.3 (q, [BH4]–) ppm. 13C NMR
(CDCl3): δ = 135.7 (C-1), 119.0 (C-2), 111.0 (C-3), 68.0 (C-2,
THF), 26.0 (C-3, THF) ppm. 11B NMR (CDCl3): δ = –41.8 (q,
[BH4]–) ppm. 7Li NMR (CDCl ): δ = 0.10 ppm. IR (KBr): ν =
˜
3
2292, 2225 (BH4), 3421, 3208, 1256, 1126, 834, 714 (amine) cm–1.
C13H24BLiN3O (255.83): calcd. C 60.99, H 9.38, N 16.42; found C
59.40, H 9.30, N 16.46.
CCDC-743489 (for 1), -743490 (for 5), -743491 (for 8), and -743492
(for 9) contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(KBr or THF): ν = 1619, 2293, 2222 (BH ), 736, 769, 804, 2971,
˜
4
1507, 1421, 1267 (amine) cm–1. C12H16B2N2Na2 (256.1): calcd. C
56.33, H 6.30, N 10.95; found C 56.67, H 5.00, N 10.61.
LiBH4-1,2-phenylenediamine-THF (5): Following the procedure
outlined for 1, a THF (15 mL) solution of LiBH4 (68 mg,
1.7 mmol) was treated with a THF solution (5 mL) of 1,2-phenyl-
enediamine (278 mg, 1.7 mmol). This mixture was stirred for
30 min before filtering. The orange solid was dried by a nitrogen
stream (131 mg, 35%). M.p. 178 °C. Crystals suitable for X-ray
structural determination were obtained by slow evaporation of a
Acknowledgments
The authors thank Consejo Nacional de Ciencia y Tecnologia
[CONACYT-Mexico] for financial support and scholarships for
M.A.M., G.F.B., and C.P.M.
1
THF/toluene solution. H NMR (CDCl3): δ = 7.4 (d, 3-H, amine),
7.0 (d, 4-H, amine), –0.03 (q, [BH4]–), 1.75 (t, 2-H, THF), 3.85 (t,
1-H, THF) ppm. 13C NMR (CDCl3): δ = 138 (C-2), 120 (C-3), 110
(C-4), 68.0 (C-2, THF), 26.1 (C-3, THF) ppm. 11B NMR (CDCl3):
[1] a) M. Hudlicky, Reductions in Organic Chemistry, Ellis Hor-
wood Ltd., Chichester, 1984; b) J. Seyden-Penne, Reductions by
the Aluminum and Borohydrides in Organic Synthesis, 2nd ed.,
Wiley-VCH, New York, 1997; c) R. C. Larock, Comprehensive
Organic Transformations: A Guide to Functional Group Prepa-
rations, 2nd ed., Wiley-VCH, New York, 1999; d) B. Zeyniza-
δ = –41 (q, [BH ]–) ppm. IR (KBr or THF): ν = 1616, 2224, 2291
˜
4
(BH4), 633, 1592, 1502, 1459, 1274, 1249 (amine) cm–1.
C10H20BLiN2O (202.18): calcd. C 59.45, H 9.98, N 13.87; found C
58.39, H 8.14, N 12.55.
Eur. J. Inorg. Chem. 2010, 1973–1982
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1981

J. C. Galvez-Ruiz et al.
FULL PAPER
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Received: December 21, 2009
Published Online: March 16, 2010
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