Decaborane anion tautomerism: Ion pairing and proton transfer control

Article abstract of DOI:10.1039/c8dt00610e

The reaction of 1,8-bis(dimethylamino)naphthalene - which is often referred by the trade name Proton-Sponge (PS) - with decaborane in hexane afforded [HPS][B₁₀H₁₃] (1) salt as a pale-yellow precipitate. Variable-temperature NMR studies allowed the full assignment of ¹H and ¹¹B spectra for this familiar ten-vertex polyhedral anion. In addition, this work reveals that an increase in the temperature leads to the intramolecular exchange of three B-H-B hydrogen atoms around the hexagonal face of the boat-shaped cluster. This previously unrecognised H-tautomerism complements the long-known low-energy proton exchange of only one of the bridging hydrogen atoms. The temperature dependent proton fluxional behaviour controls the molecular environment of the polyhedral cage, averaging the negative charge of the anion. The result is a debilitation of the cation-anion interactions in solution, favouring the transfer of the proton from the organic aromatic cation, [HPS]⁺, to the polyhedral anion, [B₁₀H₁₃]^-. This proton transfer affords Proton-Sponge and decaborane, increasing the entropy of the system and sustaining an equilibrium which at high temperatures shifts toward the neutral reactants and at low temperatures moves toward the ionic products. A single X-ray diffraction analysis of 1 is discussed.

Full text of DOI:10.1039/c8dt00610e

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Decaborane anion tautomerism: ion pairing and
proton transfer control†
Cite this: Dalton Trans., 2018, 47,
5850
Sandra Pérez, Pablo J. Sanz Miguel
and Ramón Macías
*
The reaction of 1,8-bis(dimethylamino)naphthalene—which is often referred by the trade name
Proton-Sponge (PS)—with decaborane in hexane afforded [HPS][B10 13] (1) salt as a pale-yellow
H
1
11
precipitate. Variable-temperature NMR studies allowed the full assignment of H and B spectra for this
familiar ten-vertex polyhedral anion. In addition, this work reveals that an increase in the temperature
leads to the intramolecular exchange of three B–H–B hydrogen atoms around the hexagonal face of the
boat-shaped cluster. This previously unrecognised H-tautomerism complements the long-known low-
energy proton exchange of only one of the bridging hydrogen atoms. The temperature dependent
proton fluxional behaviour controls the molecular environment of the polyhedral cage, averaging the nega-
tive charge of the anion. The result is a debilitation of the cation–anion interactions in solution, favouring
+
−
Received 13th February 2018,
Accepted 16th March 2018
10 13
the transfer of the proton from the organic aromatic cation, [HPS] , to the polyhedral anion, [B H ] . This
proton transfer affords Proton-Sponge and decaborane, increasing the entropy of the system and sustaining
an equilibrium which at high temperatures shifts toward the neutral reactants and at low temperatures
moves toward the ionic products. A single X-ray diffraction analysis of 1 is discussed.
DOI: 10.1039/c8dt00610e
rsc.li/dalton
The capacity of decaborane to accommodate atoms is not
limited to carbon, and this ten-vertex boat-shaped molecule
Introduction
Decaborane plays a central role in polyhedral boron chemistry. can incorporate a large number of elements throughout the
1
0,11
The preparation of this ten-vertex cluster involves the pyrolysis Periodic Table.
For example, reactions with inorganic
of diborane-6 at temperatures near 373 K, a reaction discovered reagents such as NaCN, NaNO , Na SeO , Na (S ) or AsI result
2
2
3
2
x
3
1
by Alfred Stock and co-workers. Decaborane is now commer- in insertion or degradation–insertion of heteroatoms into
cially available, and this versatile molecule can be functiona- the borane skeleton, affording 7-NH -7-CB10 12, 6-NB
These heteroboranes
poration into the framework or by attachment to the cluster can be further functionalized by reactions with Lewis bases,
3
H
9 12
H ,
−
12–15
lized with organic and organometallic groups, either by incor- 7,8-Se B H , 6-SB H or [AsB H ] .
2
9
9
9
11
10 12
1
6,17
surface, affording a completely new realm of possibilities to organic molecules and organometallic fragments.
In fact,
these conventional areas. An example of this rich functional the reactions between decaborane and its heteroboron deriva-
chemistry is the reaction with Lewis bases, L, to give 6,9-(L)2- tives with transition element complexes are general
arachno-B10 12, and the subsequent insertion of acetylenic route for the synthesis of metallaboranes and metalla-
carbon atoms into the cage. This is of considerable impor- heteroboranes.
tance in polyhedral boron chemistry because it affords the for- anes, which, as indicated above, are ubiquitous in polyhedral
2
–5
a
H
1
1,18–23
The latter group includes metallacarbor-
1
2
6–9
mation of dicarbadodecaboranes, namely, 1,2-(R )(R )-closo- boron chemistry.
,2-C B H , which form an extensive family of compounds Decaborane(14) exhibits a dual Lewis/Brønsted nature: (i)
with applications in diverse areas such as medicine, nanoscale with good σ-donor ligands, it forms L-boron ligated adducts
1
2
10 10
6
–9
engineering, catalysis, etc.
(eqn (1)); and (ii) with strong bases, B, it transfers a proton to
give the [nido-B H ] anion (eqn (2)). This ambivalent reac-
−
2,3
1
0
13
tivity is controlled by a balance between the nucleophilic and
basic character of the entering ligand, L; and, in some cases,
both reactions (adduct formation and cluster deprotonation)
can occur in a stepwise manner. For example, in organic-water
mixtures, decaborane behaves as a strong Lewis acid, forming
Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis
Homogénea (ISQCH), Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain.
E-mail: rmacias@unizar.es
†
Electronic supplementary information (ESI) available: Additional NMR data,
including diffusion experiments; Cartesian coordinates for the optimized geo-
metries. CCDC 1583013. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c8dt00610e
a H O-ligated adduct, 6-(H O)-nido-B H , which subsequently
2
2
10 14
dissociates a proton, becoming a Brønsted acid which depend-
5850 | Dalton Trans., 2018, 47, 5850–5859
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ing on the water content can span from moderately strong to of this salt and a full assignment of the NMR data.‡ We com-
2
4,25
very strong acid (eqn (3)).
The dual Lewis/Brønsted acidic plete this research with VT experiments that give further evi-
behaviour of decaborane should play an important role in the dence for the previously reported low-energy proton tautomer-
reactions with inorganic salts (mentioned above) in the ism, together with the discovery of an unknown fluxional
presence of water, triggering adduct formation/deprotonation process. Overall, this work provides a comprehensive charac-
processes that result in insertion/degradation–insertion of terization of the chemical non-rigidity of the decaborane
heteroatoms; whereas the simple deprotonation of decaborane cluster anion. We also discuss that 1 exhibits a protonation/
with various bases has previously utilized to synthesize deprotonation equilibrium.
−
2,3
[
nido-B10H13] .
nido-B10H14 þ 2 L ! 6; 9-ðLÞ -B10H12 þ H2 ðgÞ
ð1Þ
ð2Þ
þ
2
Results and discussion
nido-B10H14 þ B ! ½nido-B10H13ꢀ þ ½HBꢀþ
ꢁ
The addition of Proton-Sponge to decaborane (both reactants
dissolved in hexane) immediately affords a pale-yellow precipi-
tate. This solid is conveniently crystallized from dichloro-
methane/hexane to give yellow needle-like crystals, which were
characterized as the salt [HPS][B H ] (1).
H2O
H2O
ꢁ
ꢁ*
ꢁ*
nido‐B10H14 )ꢁ 6‐ðH2OÞ‐B10H14 )ꢁ ½6‐ðHOÞ‐B10H14ꢀ þ H3O
ð3Þ
1
0
13
−
Similar to its neutral conjugated acid, B10
H
14, the [B10
H
H
13
]
]
In this reaction, Proton-Sponge abstracts a proton from the
−
anion reacts with σ-donor ligands to give [6-(L)-nido-B10
13
10-vertex nido-decaborane, with the subsequent formation of
−
anions that resemble the neutral bis-adducts, 6,9-(L) -arachno- the anion [nido-B H ] (Scheme 1). The resulting yellow
2
10 13
2
B
10
H
12, in which a hydride ion replaces one ligand, L.
crystalline salt, 1, is stable in air at room temperature, and
Interestingly, this 10-vertex polyhedral anion is capable of soluble in chlorinated solvents such as chloroform and
2
6
reacting with alkynes to give ortho-dicarbadodecaboranes,
suggesting that this anionic cluster may also play a role in the
dichloromethane.
classical carbon insertion reactions that take place between X-ray diffraction analysis
bis-decaborane adducts and alkynes. More recently, it has
−
The ten-vertex polyhedral anion [B H ] has been character-
1
0
13
been demonstrated that the decaborane cluster anion can
enhance the ignition delay in hypergolic ionic liquids and it
can also induce hypergolicity to otherwise inactive molecular
ized by X-ray diffraction in the salts [NMe
3
2
(CH Ph)][B10H13] (2)
32,33
and [NEt ][B H ].
Table 1 shows selected distances for
the salts 1 and 2, together with those for decaborane.
Salt 1 crystallized in the space group P ˉ1 (Fig. 1). The dis-
tances and angles are within the ranges found for the pre-
viously reported nido-[B H ] anion in salt 2 and for nido-
It is worth mentioning that in the
neutral decaborane molecule, the B5–B6 and B5–B10 distances
4
10 13
34,35
2
7
solvents.
Clearly, neutral nido-B10
H
14 and anionic [nido-B10H
13]− are
useful, well-known starting materials in polyhedral boron
chemistry. Both clusters have been characterized in the solid
state and solution by means of X-ray diffraction, NMR spec-
troscopy, IR, etc. However, the available NMR data are rather
old, being largely based on low-dispersion spectroscopy with
−
1
0
13
32–35
B
10
H
14 (Table 1).
at 1.789(2) and 1.989(2) Å, respectively, are significantly longer
2
,3,28
little assignment work.
This is particularly evident in
−
the case of the [B H ] anion for which, to the best of our
1
0
13
1
1
1
knowledge, a full assignment of the
B and H NMR
2
9
spectra has not been published yet. Moreover, a fluxional
process involving one of the B–H–B bridging hydrogen
atoms was identified early, but, so far, there have been no
H variable temperature (VT) studies providing experimental
data for the non-rigid behavior of the [nido-B H ]
1
−
1
0
13
2
,3,30
anion.
The formation of the decaborane anion in the salt
HPS][B H ], where PS = Proton-Sponge (1,8-bis(dimethyl-
[
1
0
13
amino)naphthalene), was reported in 1979. The work focused
on the reactivity of PS with different boranes, demonstrating
Scheme 1 Reaction of decaborane with Proton Sponge.
that this strong aromatic base can abstract a proton from nido-
−
B
10
H
14, producing quantitatively [nido-B10
H
13] ; but this paper
‡
Crystal data for 1: [C14
32 10 2
H B N
], triclinic, P ˉ1 , a = 8.1280(5) Å, b = 10.5661(6) Å,
did not offer further experiments dealing with, for example,
c = 13.3633(8) Å, α = 67.7860(10)°, β = 83.6620(10)°, γ = 73.8830(10)°, Z = 2, M
r
=
the assignment of previous NMR data, fluxional behavior or
3
−3
3
1
3
36.51, V = 1020.70(11) Å , Dcalcd = 1.095 g cm , λ(Mo Kα) = 0.71073 Å, T =
3
1
structural studies of the PS salt.
Here we report on the synthesis and characterization of
−1
00 K, µ = 0.056 mm , 15 216 reflections collected, 4858 unique (Rint = 0.0642),
2
o
1 o
215 observed, R (F ) = 0.0568 [I > 2σ(I)], wR
2
(F
) = 0.1659 (all data), GOF =
[
HPS][B H ] (1), including the X-ray crystallographic analysis 1.025. CCDC 1583013.†
10 13
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14
Table 1 Selected B–B interatomic distances (Å) for nido-B10H ,
[
2 2 3
HPS][B10H13] (1) and [NMe (CH Ph )][B10H13] (2) with estimated standard
uncertainties (s.u.) in parentheses. Calculated values for the DFT-opti-
mized energy minimum of salt 1 are enclosed [in brackets]
a
b
nido-B10H
14
1
2
B1–B2
B1–B3
B1–B4
B1–B5
B1–B10
B2–B3
B2–B5
B2–B6
B2–B7
B3–B4
B3–B7
B3–B8
B4–B8
B4–B9
B4–B10
B5–B6
B5–B10
B6–B7
B7–B8
B8–B9
B9–B10
1.787(2)
1.779(3)
1.783(3)
1.749(2)
1.751(2)
1.783(3)
1.792(3)
1.731(2)
1.787(3)
1.787(2)
1.751(2)
1.749(2)
1.792(2)
1.731(2)
1.787(3)
1.790(3)
1.988(2)
1.782(3)
1.988(2)
1.790(2)
1.782(3)
1.763(3) [1.747]
1.789(3) [1.783]
1.794(3) [1.790]
1.744(3) [1.735]
1.785(3) [1.786]
1.766(3) [1.761]
1.787(3) [1.735]
1.752(3) [1.755]
1.760(3) [1.771]
1.774(3) [1.776]
1.765(3) [1.769]
1.734(3) [1.737]
1.777(3) [1.773]
1.715(3) [1.708]
1.745(5)
1.780(5)
1.783(5)
1.731(5)
1.780(4)
1.756(5)
1.785(5)
1.735(5) Fig. 2 View of the B–H⋯H–B contacts along the a axis in the crystal
1.754(5) lattice of 1.
1.765(5)
1.758(5)
1.734(5)
1.767(5) in nature; although, we could also invoke, to some degree,
1.707(5)
1.798(5)
1.657(6)
1.848(4) clusters within the chains. The aromatic cations, [HPS] , are
1.788(5)
2.003(5)
1.768(5)
hydrophophic
interactions
between
the
polyhedral
1.803(3) [1.815]c
−
[nido-B H ] anions as a reason for the close proximity of the
1.688(3) [1.663]
10 13
+
1.870(3) [1.845]
1.793(3) [1.773]
2.021(3) [2.008]
embedded within the cavities of the lattice.
d
1.798(3) [1.774]
1.826(3) [1.784]
1.783(4) NMR spectroscopy: characterization and cluster fluxionality
a
b
c
Data from ref. 35. Data from ref. 32. Shortest B–B distance. In 1959, Lipscomb proposed two possible structures related by
d
Longest B–B distance.
− 37
hydrogen tautomerism for [nido-B10H13] . Twelve years later,
Todd and co-workers reported the characterization of this ten-
vertex polyhedral anion by NMR spectroscopy, providing
experimental data that supported
a fast intramolecular
exchange of one of the three B–H–B bridging hydrogen atoms
2
9
that renders a molecule with a C symmetry in solution. The
s
same fast H-tautomerism was suggested by Heřmánek and
Plešek to take place when decaborane, B10H14, is dissolved in
2
5
water/ethanol (eqn (3)). These spectroscopic results were
further rationalized by computational studies that provided a
1
1
good agreement with the experimentally observed B NMR
3
8
spectrum.
Fig. 1 Crystallographically determined molecular structures of the
1
1
+
−
The above mentioned studies focused on the B NMR spec-
[
13
HPS] cation (left) and of the [nido-B10H ] anion (right) in the salt,
troscopic features of the tridecahydro-decaborate(1−) anion;
[
HPS][B10 13] (1). Ellipsoids are shown at 50% probability levels.
H
1
and, as far as we know, a full H NMR characterization of the
−
anion [B10
H
13] has not been published yet.
Herein we fill this gap; Table 2 shows a complete assign-
1
1
1
than those in the anions of the salts 1 and 2 [1.673(6) and ment of the B and H NMR spectra at 243 K for this paradig-
.859(4) Å, averaged between the two anions]; and that the B5– matic polyhedral anion; and to facilitate the comparison, we
B6–B7 angle of the anionic cluster is ca. 9° smaller than the include NMR data of nido-B H and its pyridine adduct,
1
1
0
14
neutral decaborane cage. These structural changes are the 6,9-(py) -arachno-B H .
2
10 12
1
1
response that the cluster undergoes upon the liberation of a
In CDCl , the B NMR spectrum of 1 at −30 °C exhibits five
3
proton that in neutral decaborane lies along the B5–B6 edge.
The polyhedral ten-vertex nido-anions pack by forming relative intensity four at δ( B) −4.4 ppm corresponds to the
chains along the crystallographic a direction; the shortest resonances of B(5,10) and B(7,8) which in the B spectrum are
interatomic distance within the anionic chains is 2.61(3) Å, accidentally coincident. Selective H–{ B} decoupling experi-
which corresponds to the B2–H2⋯H9–B9 contact (Fig. 2). In ments correlated this boron resonance with the proton signals
addition, two antiparallel chains connect via their B7(H) sites of relative intensity two at +2.43 and +2.91 ppm. Thus, the six
peaks with a 2 : 1 : 4 : 1 : 2 relative intensity ratio. The peak with
1
1
1
1
1
11
(
2.61(4) Å) forming ribbons (Fig. S1, ESI†). These intra- and proton resonances of 2 : 2 : 1 : 1 : 2 : 2 relative intensity in the
1
11
inter-chain distances are significantly longer than the van der positive region of the H–{ B} spectrum at −30 °C are
3
6
Waals radii of two hydrogen atoms (2.4 Å), and we cannot assigned to the B–H terminal hydrogen atoms; whereas the
definitely propose a dihydrogen interaction. Thus, the main two resonances of 1 : 2 relative intensity ratio at −2.70 and
forces that govern the crystal structure of salt 1 should be ionic −3.54 ppm are due to the B–H–B bridging hydrogen atoms on
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1
1
1
Table 2
,9-(py)
calculated B-nuclear shielding values for 1
B and H NMR data of [HPS][B10
H13] (1), nido-B10H14 and
6
2
-arachno-B10 12. In brackets, the corresponding DFT/GIAO-
H
1
1
a,b
11
1
[
13
HPS][B10H ]
δ( B)
δ( H)
B(6,9)
B3
B(5,10)
B(7,8)
B1
B(2,4)
B–H–B
+7.3 [−9.9, +20.7]
+2.9 [−0.1]
+3.46 (2H)
+2.86 (1H)
+2.91 (2H)
+2.43 (2H)
+2.53 (1H)
+0.23 (2H)
−4.4 (4B) [−12.3, −6.1, −0.6,
−8.9]
−5.3 [−7.8]
−35.2 [−44.5, −30.1]
−2.70 (1H), −3.54
(
2H)
c
11
1
B
10
H
14
δ( B)
δ( H)
B(1,3)
B(6,9)
B(5,7,8,10)
B(2,4)
+12.2
+10.3
+0.7
+3.85 (2H)
+3.68 (2H)
+3.12 (4H)
+0.65 (2H)
−2.16 (4H)
−36.0
B–H–B
Fig. 4 Stick diagrams representing the chemical shifts and relative
1
1
intensities in the B NMR spectra of nido-B10
H
14 (lowest trace), nido-
d
11
1
6,9-(py) -B10H
2 12
δ( B)
δ( H)
−
[B
10
H
13
]
(middle) and 6,9-(py) -arachno-B10H12 (top). Hatched lines
2
connect equivalent positions.
B(2,4)
B(6,9)
B(5,7,8,10)
B(1,3)
−3.7
−15.5
−17.7
−39.4
+2.07 (2H)
+0.66 (2H)
+1.64 (4H)
+0.26 (2H)
−4.38 (2H)
10 2 12
B H14, becomes the pyridine adduct, 6,9-(py) -arachno-B10H .
B–H–B
1
1
This B NMR pattern is diagnostic of a nido-to-arachno trans-
formation that implies reorganization of the B–H–B bridging
hydrogen atoms on the hexagonal open face (Fig. 4).
a
b
1
11
Measured at 243 K in CDCl
3
.
Assignments based on H–{ B} selec-
tive experiments, the H-tautomerism that equilibrates B–H positions
1
1
in pairs and DFT/GIAO calculated
B chemical shielding data.
c
d
11
Measured at 298 K in CDCl
3
.
Measured at 298 K in CD Cl
2
2
.
Compared to neutral decaborane, the B NMR spectrum of
the anion exhibits an overall shielding. The largest change corres-
ponds to the B1 resonance that suffers a 17.5 ppm shift toward
low frequency. This boron atom lies trans to the B5–B10 edge,
and the low energy B–H–B bridging hydrogen exchange on the
−
the hexagonal face of boat-shaped ten-vertex [nido-B H ]
1
0
13
(Fig. 3).
11
It is empirically known that boron atoms that lie trans to B6–B5–B10–B9 side has a strong influence on its B chemical
B–H–B bridging hydrogen atoms on the open faces of polyhedral shift. Thus, from the point of view of the empirical “μH rule”, it
11
boron-containing compounds show significantly lower chemi- is clear that the B resonance corresponding to the B1 nucleus
cal shifts than boron vertices in opposite edges that do not should undergo a significant low-frequency shift.
3
9
1
11
have μH bridges. This effect explains the crossing of the
The H–{ B} spectrum at 178 K (Fig. S2, ESI†) demon-
B(1,3) and B(2,4) resonances when the decaborane, nido- strates that the exchange of the bridging hydrogen atom
1
11
Fig. 3 Variable-temperature H–{ B} NMR spectra of [HPS][B10
H13] (1) in CDCl
3
. The peaks marked with blue squares correspond to decaborane,
10
B H14, whereas those marked with red triangles are due to 1.
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between the B5–B6 and B9–B10 edges is still fast on the NMR movement of one bridging hydrogen atom on the B6–B5–B10–
time-scale, implying that the interconversion of the two B9 side of the anion lies about 6.7 kcal mol− above the C
1
1
‡
−1
enantiomeric forms of the anion has a ΔG value lower than static structure, with the C
s
tautomer at 5.4 kcal mol (Fig. 5).
For the full hydrogen rearrangement, we envision that the
1 40
7
kcal mol−
.
This result sets an experimental upper limit on
the differences in energy among the ground state, transition low energy proton exchange along the B6–B5–B10–B9 lateral is
state, and intermediates involved in this H-tautomerism. followed by a proton flip from side to side through a transition
At higher temperatures, the H–{ B} NMR spectra show state of the C symmetry that exhibits an endo-hydrogen atom
that the resonances corresponding to the terminal hydrogen at the BH(6) vertex. This TS is 14.0 kcal mol higher in energy
atoms, H(5,10), H1, H3 and H(7,8) coalesce at 303 K, whereas than the C tautomer, matching the experimentally deter-
1
11
s
−1
1
the signals of the B–H–B bridging hydrogen atoms broaden mined activation energy for this H-tautomerism of 14.2
significantly, and finally coalesce at 315 K (Fig. 3). This spec- kcal mol− (Fig. 6).
1
troscopic behaviour is consistent with
a
second
The combination of these proton shifts (Fig. 5 and 6) pro-
H-tautomerism that involves the exchange of the three brid- vides a rationale for the full exchange of the three B–H–B
−
ging hydrogen atoms on the open face of the nido-anion. The hydrogen atoms on the hexagonal face of [B H ] . The pro-
1
0
13
‡
3
−1
activation energy, ΔG 18, is 14.2 kcal mol , and this value is posed mechanism that combines these low- and high-energy
reproduced in the energy profile calculated for the pathway proton tautomerisms is depicted in Scheme 2.
that leads to the exchange of the three hydrogen atoms
(
vide infra).
Deprotonation/protonation equilibrium
For the low energy H-tautomerism, DFT-calculations give a
transition state (TS), in which the fluxional hydrogen atom
occupies an endo position on either B5 or B10 and which lies
In the previous section, the discussion focuses on the spectro-
scopic NMR characterization of the polyhedral anion in the
hybrid salt 1, and on its fluxional behaviour in solution; but
higher in energy than the C
1
static anion in a range between
(depending on the computational
The exchange of this hydrogen atom can be
−
the VT NMR spectra also reveal that the ions, [B10
[
H
13
]
and
−
1
5
.3 and 7.8 kcal mol
+
HPS] , are present in solution as major products together with
3
0,38
method).
neutral decaborane, B H , and Proton-Sponge as minor com-
1
0
14
regarded to take place (formally) through an intermediate in
which the mobile hydrogen stays along the B5–B10 edge
ponents (see Fig. 3 above and Fig. S3 and S4 in the ESI†).
The existence of well-resolved signals corresponding to the
(
compare the discussion above dealing with the low frequency
chemical shift of B1); this C cluster is a true minimum in the
potential energy surface that lies 4.1 to 6.4 kcal mol above
1
neutral and ionic species in the H NMR spectra implies that
s
the proton transfer is slow in the time-scale of the experiment.
This is clearly demonstrated by the presence of the high fre-
quency signal at δH +19.16 ppm that corresponds to the N–H
proton of the organic cation, together with the fact that this
−
1
3
0,38
1
the parent C static tautomer (Fig. 5).
In this work, we provide new computational data obtained
with the M11L functional and the 6-311++G(d,p) basis set. The
excellent agreement between experimental and computed data
for the geometry of small molecules supports this combination
resonance does not change significantly with the temperature
1
(
see Fig. S3, ESI†). At low temperatures, the intensity of the H
NMR signals that correspond to the neutral molecules, B10
H
14
4
1,42
as a useful predictive tool.
In our DFT calculations, we
included the organic cation in order to account for anion–
cation interactions (vide infra). Thus, in agreement with the
DFT studies mentioned above, together with our low tempera-
1
ture H NMR measurements, the transition state for the fast
Fig. 5 Calculated Gibbs energy profile (in kcal mol− ) in CH
1
Cl
at
Fig. 6 Calculated Gibbs energy profile (in kcal mol−1) in CH
Cl
2
at
2
2
2
2
98.15 K for the fluxional hydrogen rearrangement that interconverts
298.15 K for the side-to-side proton shift on the boat-like hexagonal
+
−
the two enantiomeric forms of the anion in [HPS][B10
H
13] (1). The [HPS]
_a and 1C _a in
Fig. 8) and in the transition states, but this is omitted for clarity.
13
face of [B10H ] in 1. The [HPS] cation was included in the DFT-opti-
cation was included in the DFT-optimized structures (1C
1
s
mized structures (1C
1
_a in Fig. 8) and in the transition state but this is
omitted for clarity.
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+
H
13]− in 1, free deca-
Table 3 Diffusion data of the ions [HPS] and [B10
borane and PS
CD
Cl
2 2
3
CH CN
D
r
H
(Å)
D
H
r (Å)
+
[
[
B
HPS]
1.13
1.05
2.12
1.78
4.9
5.3
2.6
3.1
1.70
1.95
2.18
2.19
3.8
3.3
2.9
2.9
B
10
H
H
13]−
10
14
PS
D × 10−
9
m
2
s−1, 0.07 M solutions at 300 K. Estimated radius in the
+ −
solid state: [HPS] /[B10
13
H ] ion pair in 1, rX-ray = 6.8 Å; decaborane,
r
X-ray = 3.0 Å; PS: rX-ray = 3.9 Å.
Scheme 2 Low- and high-energy hydrogen rearrangements, leading to
the exchange of the three B–H–B bridging hydrogen atoms in [nido-
−
−
+
B
10
H13] .
hedral anion, [nido-B H ] , and the protonated base, [HPS]
10 13
are identical within the experimental error, demonstrating
strong ion pairing and entropy lowering in the system upon
and PS, decreases and eventually the peaks disappear. deprotonation of decaborane by PS.
Conversely, at higher temperatures, the concentration of the
In CD CN, the diffusion coefficients of the polyhedral
3
neutral species increases (see, Fig. 3, S3 and S4 in the ESI†). anion and the organic cation are not identical, indicating that
This behaviour reveals an equilibrium between reactants and the ion pairs are broken in this polar, coordinating solvent. It
products, as illustrated in Scheme 1.
The equilibrium ratio of the anionic versus the neutral are slightly smaller than those found for the free neutral
is interesting to note, however, that the D-values of both ions
1
11
species was measured by H–{ B} NMR at 273, 294, 303, 313 species in the same concentration. This behaviour suggests
and 320 K. As shown in Fig. 7, a straight-line fit to a plot of ln that the ions may interact to a certain level in acetonitrile,
−
1
K
eq versus 1/T is obtained giving ΔH = −13.85 ± 0.25 kcal mol
leading to a weak pairing.
−
1
−1
and ΔS = −36.33 ± 0.25 cal K mol
.
The exothermicity of this equilibrium shows that the N–H Ion pairing and proton transfer
bond in PS is stronger than the B–H–B bond in decaborane.
The negative entropy and the diffusion experiments demon-
The negative value of ΔS was a priori unexpected since the
transfer of a proton between decaborane and PS does not
involve a change in the total number of molecules in the
system. This entropy change demonstrates, therefore, that the
strate that the ions in the hybrid salt 1 form pairs when dis-
solved in CH Cl and CHCl
An approach of the [HPS] cation towards the B6–B5–B10–
2
2
3
.
+
−
B9 side of the [nido-B10H13] anion, from which the proton has
+
protonated base, [HPS] , and the polyhedral anion,
been abstracted, should be, a priori, favoured by electrostatic
forces. In this regard, the values of natural atomic charges
−
[nido-B10
H
13] , form ion pairs in solution. This fact is indepen-
dently supported by diffusion experiments that we describe in
the following paragraphs.
(
NBO) show, as expected, an asymmetric distribution in the C
1
anion versus the C2v neutral decaborane (see Fig. S16, ESI†).
The charge in the anion is polarized on the hexagonal boat-
shaped face of the ten-vertex nido-cluster. The B5 vertex carries
Diffusion experiments
1
the largest negative charge in the static C structure of the
Table 3 shows the diffusion data obtained by NMR spec-
anion, being higher than the charge calculated for the parent
decaborane. Interestingly, the butterfly-like belt, B1–B2–B3–B4,
exhibits a low level of polarization with charge values that
resemble those of the neutral decaborane.
4
3
troscopy. In dichloromethane, the D-values for both the poly-
We also carried out DFT-energy optimizations of several ion
pairs, trying to provide a glimpse of the potential energy
+
−
surface that results from [HPS] -to-[B H ] interactions. The
1
0
13
calculations, as indicated in the Experimental section, were
carried out using a polarizable continuum model in order to
consider the solvent effects. Fig. 8 illustrates four energy-opti-
mized minima, 1C
1
_a, 1C
1
_b, 1C
s s
_a, and 1C _b, together with
the ion pairs, 1C _c and 1C
1
s
_c, that correspond to transition
states (TS’s) involving slight cation/anion rocking. We tried to
find true minima around these two TS’s by changing the coor-
dinates, but the calculations afforded systematically transition
states.
1
Fig. 7 Plot of ln Keq vs. 1/T derived from H NMR intensities signals in
3
CDCl .
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Fig. 8 Calculated Gibbs energy profile (in kcal mol− ) in CH
1
Cl
at 298.15 K for different cation–anion interactions simulating the formation of ion pairs.
2
2
The ion pairs, 1C
1
_a and 1C
1
1
_b, show the same energy, but
In this regard, the hydrogen shift between the enantiomeric
−
−
the 1C _c TS lies 4.0 kcal mol higher in energy. These differ- forms of the [nido-B H ] anion should result in an averaging
1
10 13
ences are in agreement with the above mentioned charge dis- of the negative charge around the B6–B5–B10–B9 side, main-
tribution of the C tautomer in which the butterfly-like B1–B2– taining the polarity of the cage with respect to the plane that
1
B3–B4 belt is much less polarized than the upper hexagonal contains the B6–B9–B2–B4 vertices (see Fig. S16, ESI†). Since
face. Thus, a change of the ion interaction from B1–H1⋯H–PS this low energy H-tautomerism prevails at low temperatures, it
in 1C
1
_a to B3–H3⋯H–PS in 1C _b does not have an energy is reasonable to expect a higher number of N–H⋯H–B inter-
1
cost; whereas the interaction at the B7–H7 upper-belt vertex actions between the ion pairs involving the B1, B5 and B10 ver-
affords an unstable TS, 1C
1
_c.
tices as the temperature decreases.
However, the highest energy penalty as illustrated in Fig. 8
At higher temperatures, the full proton exchange on the
involves the C to C H-tautomerism. The simple shift of the hexagonal face starts to play an important role; and, under the
1
s
B9–H–B10 bridging hydrogen atom in 1C
1
_a to the B5–B6 edge fast regime of the three-proton tautomerism, the charges
−
1
in 1C
s
_a rises 5.4 kcal mol the energy of the system. In con- should average over the cage framework, approaching the situ-
trast to the ion pairs involving the C tautomer, a change of ation found in the C2v decaborane vertices (see Fig. S16†). This
1
the cation–anion interaction from the B1(H) vertex to the scenario should weaken the ion pairs, facilitating the for-
B3(H) vertex has an energy penalty of 1.2 kcal mol−
1
.
mation of the neutral parent reactants, B10
H14 and PS.
−
Moreover, the system becomes more unstable when the
In other words, the H-tautomerism in the [B H ] anion
1
0
13
+
anionic C
B7(H) vertex, affording a TS, 1C
above the lowest energy pairs, 1C _a and 1C _b.
s
tautomer and the [HPS] cation interact around the regulates the charge distribution at the BH vertices, tuning the
_c that lies 10.2 kcal mol−
1
cation–anion interactions in solution. At low temperatures, the
negative charge is polarized favouring ion pairing; but as the
s
1
1
The energy trend found in this small mapping agrees well temperature increases, the negative charge averages around
with cation–anion interactions that depend, to an important the cluster, debilitating the interactions and promoting the
extent, on changes in the charge distribution of the cluster.
proton transfer to give the neutral species. This reverse reac-
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tion is, as discussed above, sustained by an increase in the
entropy of the system.
X-ray analysis of [HPS][B10
tion and refinement parameters were recorded at 100(2) K with
H
13] (1). Crystal data, data collec-
a Bruker APEX DUO diffractometer equipped with an area
detector and graphite monochromated MoK
α
radiation
(
0.71073 Å) using narrow ω rotation (0.3°). Data reduction was
Conclusions
4
4
done with the APEX2 software. The structure was solved by
H13] (1) has been synthesised followed by a direct methods and refined by full-matrix least squares
The salt [HPS][B10
full assignment of the H and B NMR spectra for the classi- methods based on F using the SHELXL-97 and WinGX pro-
1
11
2
−
45,46
cal polyhedral anion [nido-B10
H
13] . Variable-temperature grams.
H–{ B} NMR experiments in the poorly coordinating solvents ence maps.
Hydrogen atoms were located in the Fourier differ-
1
11
+
CD Cl and CDCl3 demonstrated that the ions, [HPS] and
Calculations. All calculations were performed using the
2
2
−
47
10
[B H13] , form pairs that are in equilibrium with the neutral Gaussian 09 package. Structures were initially optimized
reagents, PS and decaborane via a proton transfer between the using standard methods with the STO-3G* basis-sets. The final
polyhedral cage and the organic aromatic base. Additionally, optimizations, including frequency analyses to confirm the
these studies reveal a previously unrecognized H-tautomerism true minima, together with GIAO nuclear-shielding calcu-
48
that involves the exchange of the three B–H–B bridging hydro- lations, were performed using M11L methodology, with the
−
gen atoms around the hexagonal face of the [B H ] anion, 6-311++G(d,p) basis-set. The effect of the solvent employed in
1
0
13
2 2
complementing the long-known low-energy fluxional process experiments (CH Cl , ε = 8.93) was introduced through single-
of a single hydrogen atom. At high temperatures, the fast intra- point calculations at the optimized geometries under vacuum,
molecular rearrangement of the three hydrogen atoms results using the polarizable continuum model that corresponds to
4
9
in a delocalization of the negative charge around the cage; and scrf=(smd,solvent=dichloromethane) at 298.15 K.
GIAO
the polyhedral anions reduce their charge anisotropy, debilitat- nuclear shielding calculations were performed on the final
1
1
ing the cation–anion interactions in solution. This weakening optimized geometries, and computed B shielding values
favors the proton transfer to give the neutral molecules. As a were related to chemical shifts by comparison with the com-
1
1
result, the entropy of the system increases. In other words, a puted value for B
2 6
H , which was taken to be δ( B) +16.6 ppm
variation in temperature changes the H-tautomerism rate con- relative to the BF (OEt ) = 0.0 ppm standard.
3
2
trolling the ion-pair formation/proton transfer equilibrium.
Synthesis of [HPS][nido-B10
H13] (1). 0.9691 g of B10H
14
(
7.928 mmol) was placed in a Schlenk tube under an argon
atmosphere, and dissolved in 25 mL of hexane, which was
injected and the system was then deaerated. In a second
Schlenk tube, 2.0389 g (9.515 mmol) of Proton-Sponge (PS)
was dissolved in 10 mL of hexane, the system was deaerated,
Experimental
General procedures
We carried out the reactions under an argon atmosphere using and, then, the PS solution was added via cannula to the deca-
standard Schlenk-line techniques. Dried solvents were borane solution. Upon addition of the base, a pale-yellow pre-
obtained from a Solvent Purification System from Innovative cipitate was formed. The mixture was stirred for thirty
Technology Inc. Decaborane was sublimed prior to use (45 °C minutes, and the solid was collected by filtration through a
under vacuum). 1,8-Bis(dimethylamino)-naphthalene (referred glass frit in air. Yellow crystals were obtained from dichloro-
throughout the paper by its trade name Proton-Sponge, and methane/pentane. Yield: 2.4 g, 7.132 mmol, 80%. Table 2 lists
1
1
1
abbreviated as PS) was purchased from Sigma-Aldrich and
used as received. The deuterated solvents CDCl , CD Cl and polyhedral anion. In this section, we included additional NMR
CD CN were deaerated, following freeze–pump–thaw methods, data at different temperatures.
B and H NMR data of salt 1 at 243 K, with a focus on the
3
2
2
3
and dried over 3 Å molecular sieves.
Infrared spectra were recorded on a PerkinElmer 100 found: C, 49.36; H, 9.07; N, 8.36. IR (ATR): νmax/cm
spectrometer, using a Universal ATR Sampling Accessory. NMR 2500–2458 s (BH). B–{ H} NMR (160.46 MHz, CDCl , 313 K):
14 32 2
Anal. calcd for B10C H N : C, 49.97; H, 9.58; N, 8.32;
−
1
1
1
1
3
spectra were recorded on Brüker Avance 300 MHz, AV 400 MHz δ +7.10 (2B, s, BH), +2.80 (1B, s, BH), −4.81 (5B, s, BH), −35.23
1
1
11
1
1
11
3
and AV 500 MHz spectrometers, using B, B–{ H}, H, (2B, s, BH). B NMR (160.46 MHz, CDCl , 213 K): δ +7.64 (2B,
1
11
1
11
1
11
1
H–{ B} and H–{ B(selective)} techniques (see Fig. S5–S7†). pseudo-singlet, BH), +2.93 (1B, d, J( B– H) = 114 Hz, BH),
The diffusion experiments were carried out using a standard −4.43 (5B, d, J( B– H) = 112 Hz, BH), −35.20 (2B, d,
pulse sequence for 2D DOSY spectroscopy on a Brüker AV
00 MHz spectrometer; and the data were processed using 298 K): δ +7.16 (2B, d, J( B– H) = 137 Hz, BH), +2.78 (1B, d,
the SimFit (T1/T2 Analysis) of the TopSpin software (see Fig. S7–
S15†). The H NMR chemical shifts were measured relative to BH), −35.25 (2B, d, J( B– H) = 139 Hz, BH). H–{ B} NMR
the partially deuterated solvent peaks but are reported in ppm (500 MHz, CDCl , 243 K): δ +19.36 (1H, s, [H–N–PS] ), +7.97
relative to tetramethylsilane. B chemical shifts are quoted (2H, d, J( H– H) = 8.2 Hz, CH), +7.79 (2H, d, J( H– H) = 7.5
1
11
1
1
11
1
11
3
J( B– H) = 136 Hz, BH). B NMR (160.46 MHz, CDCl ,
4
3
1
11
1
4
1
11
1
1
11
1
J( B– H) = 127 Hz, BH), −4.49 (5B, s, J( B– H) = 118 Hz,
1
1
11
1
1
11
+
3
1
1
2
1
1
2
1
1
2
1
1
3 2
relative to [BF (OEt) ]. Elemental analyses C/H/N were carried Hz, CH), +7.68 (2H, t, J( H– H) = 7.9 Hz, CH), +3.18 (12H, s,
out in a PerkinElmer 2400 CHNS/O analyzer.
1
11
CH). H–{ B} NMR (500 MHz, CDCl , 313 K): δ +18.94 (1H, s,
3
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+
2
1
1
[
H–N–PS] ), +7.97 (2H, d, J( H– H) = 8.2 Hz, CH), +7.78 (2H, 14 P. Paetzold, Eur. J. Inorg. Chem., 1998, 1998, 143–
2
1
1
2
1
1
d, J( H– H) = 7.6 Hz, CH), +7.68 (2H, d, J( H– H) = 7.9 Hz,
CH), +3.44 (2H, s, BH), +3.22 (12H, s, CH), +2.70 (6H, s, BH), 15 J. L. Little, S. S. Pao and K. K. Sugathan, Inorg. Chem., 1974,
0.24 (2H, s, BH), −2.75 (1H, s, BHB), −3.50 (2H, s, BHB). 13, 1752–1756.
H–{ B} NMR (500 MHz, CDCl , 318 K): δ +18.91 (1H, s, [H–N– 16 K. Baše, M. G. H. Wallbridge, X. L. R. Fontaine,
153.
+
1
11
3
+
2
1
1
PS] ), +7.97 (2H, d, J( H– H) = 8.2 Hz, CH), +7.78 (2H, d,
J( H– H) = 7.5 Hz, CH), +7.68 (2H, t, J( H– H) = 7.9 Hz, CH),
N. N. Greenwood, J. H. Jones, J. D. Kennedy and B. Stibr,
Polyhedron, 1989, 8, 2089–2090.
2
1
1
2
1
1
+
3.44 (2H, s, BH), +3.22 (12H, s, CH), +2.70 (6H, s, BH), +0.25 17 B. Stibr, K. Base, J. Plešek, S. Heřmánek, J. Dolansky and
(2H, s, BH), −3.47 (3H, s, BHB).
Z. Janousek, Pure Appl. Chem., 1977, 49, 803–811.
1
8 L. Barton and D. K. Strivastava, in Comprehensive
Organometallic Chemistry II, ed. E. W. Abel, F. G. A. Stone
and G. Wilkinson, Pergamon, New York, 1995, vol. 1, pp.
Conflicts of interest
275–372.
There are no conflicts to declare.
19 J. D. Kennedy, Prog. Inorg. Chem., 1986, 34, 211–434.
2
2
0 A. S. Weller, in Comprehensive Organometallic Chemistry III,
ed. R. H. Crabtree and D. M. P. Mingos, Elsevier, Oxford,
2007, vol. 3, pp. 133–174.
Acknowledgements
1 A. K. Saxena, J. A. Maguire and N. S. Hosmane, Chem. Rev.,
1997, 97, 2421–2462.
We acknowledge the University of Zaragoza (UZ2017-188-43,
UZ2015-CIE-09) for financial support.
22 J. Bould, V. Passarelli, L. A. Oro and R. Macías, Eur. J. Inorg.
Chem., 2017, 2017, 4599–4617.
23 R. Macías, J. Bould, J. Holub, B. Štíbr and J. D. Kennedy,
Dalton Trans., 2008, 4776–4783.
Notes and references
2
4 G. A. Guter and G. W. Schaeffer, J. Am. Chem. Soc., 1956,
78, 3546–3546.
1
A. Stock, Hydrides of Boron and Silicon, Cornell University,
Ithaca, NY, 1933.
25 S. Heřmánek, H. Plotová and J. Plešek, Collect. Czech.
Chem. Commun., 1975, 40, 3593–3601.
2
M. F. Hawthorne, in Adv. Inorg. Chem. Radiochem, ed.
H. J. Emeléus and A. G. Sharpe, Academic Press, 1963, 26 Y. Li, P. J. Carroll and L. G. Sneddon, Inorg. Chem., 2008,
vol. 5, pp. 307–345. 47, 9193–9202.
V. I. Stanko, A. C. Yu, V. A. Brattsev and I. Z. Leonid, 27 P. D. McCrary, P. S. Barber, S. P. Kelley and R. D. Rogers,
Russ. Chem. Rev., 1965, 34, 424. Inorg. Chem., 2014, 53, 4770–4776.
T. Onak, in Comprehensive Organometallic Chemistry, ed. 28 G. M. Bodner and L. G. Sneddon, Inorg. Chem., 1970, 9,
3
4
G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon
Press, Ltd., Oxford, 1982, vol. 1, pp. 411–457.
L. Barton, T. P. Onak, R. J. Remmel and S. G. Shore, in
1421–1423.
29 A. R. Siedle, G. M. Bodner and L. J. Todd, J. Inorg. Nucl.
Chem., 1971, 33, 3671–3676.
5
Gmelin Handbuchder Anorganischen Chemie, Erg-Werk, 30 C. W. Yoon, U. Kusari and L. G. Sneddon, Inorg. Chem.,
979, vol. 54, “Borverbindungen 20”, pp. 122–209. 2008, 47, 9216–9227.
N. S. Hosmane, Boron Science: New Technologies and 31 T. Onak, H. Rosendo, G. Siwapinyoyos, R. Kubo and
Applications, CRC Press, Boca Raton, FL, 2012. L. Liauw, Inorg. Chem., 1979, 18, 2943–2945.
N. S. Hosmane and J. A. Maguire, in Comprehensive 32 A. J. Wynd and A. J. Welch, Acta Crystallogr., Sect. C: Cryst.
1
6
7
Organometallic Chemistry III, ed. D. Michael, P. Mingos and
R. H. Crabtree, Elsevier, Oxford, 2007, pp. 175–264.
R. N. Grimes, Carboranes, Academic Press, Elsevier Inc.,
Amsterdam, 2nd edn, 2011.
Struct. Commun., 1989, 45, 615–617.
33 L. G. Sneddon, J. C. Huffman, R. O. Schaeffer and
W. E. Streib, J. Chem. Soc., Chem. Commun., 1972, 474–
475.
8
9
T. Onak, in Comprehensive Organometallic Chemistry, ed. 34 E. B. Moore Jr., R. E. Dickerson and W. N. Lipscomb,
E. W. Abel, F. G. A. Stone and G. Wilkinson, Elsevier
Science Ltd., Oxford, 1995, vol. 1, pp. 217–255.
0 L. T. Todd, in Comprehensive Organometallic Chemistry, ed.
G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon
Press Ltd., Oxford, 1982, vol. 1, pp. 534–553.
J. Chem. Phys., 1957, 27, 209–211.
35 R. Brill, H. Dietrich and H. Dierks, Acta Crystallogr.,
Sect. B: Struct. Crystallogr. Cryst. Chem., 1971, 27, 2003–
2018.
36 R. S. Rowland and R. Taylor, J. Phys. Chem., 1996, 100,
7384–7391.
1
1
1 L. Wesemann, in Comprehensive Organometallic Chemistry,
ed. D. M. P. Mingos and R. H. Crabtree, Elsevier, Oxford, 37 W. N. Lipscomb, Adv. Inorg. Chem. Radiochem., 1959, 1,
2
007, vol. 3, pp. 113–131.
117–156.
1
1
2 K. Baše, Collect. Czech. Chem. Commun., 1983, 48, 2593.
3 R. W. Rudolph and W. R. Pretzer, Inorg. Synth., 1983, 22,
38 M. Hofmann and P. v. R. Schleyer, Inorg. Chem., 1998, 37,
5557–5565.
2
26–228.
39 S. Hermánek, Chem. Rev., 1992, 92, 325–362.
5858 | Dalton Trans., 2018, 47, 5850–5859
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View Article Online
Dalton Transactions
Paper
4
0 J. D. Kennedy and B. Stíbr, in Current Topics in the
Chemistry of Boron, ed. G. Kabalka, The Royal Society of
Chemistry, Cambridge, 1994, pp. 285–292.
1 A. Vellé, A. Cebollada, S. Ruiz, C. Fonseca Guerra and
P. J. Sanz Miguel, Cryst. Growth Des., 2015, 15, 5873–5878.
2 A. Vellé, A. Cebollada, R. Macías, M. Iglesias, M. Gil-Moles
and P. J. Sanz Miguel, ACS Omega, 2017, 2, 1392–1399.
3 P. S. Pregosin, P. G. A. Kumar and I. Fernández, Chem. Rev.,
J. L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini,
F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson,
D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng,
W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery, Jr.,
J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene,
C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin,
K. Morokuma, O. Farkas, J. B. Foresman and D. J. Fox,
Gaussian 09, Revision A.02, Gaussian, Inc., Wallingford CT,
2016.
4
4
4
2
005, 105, 2977–2998.
4
4
4 APEX2, Bruker-AXS, Madison, Wisconsin, 2011.
5 G. M. Sheldrick, SHELXS-97 AND SHELXL-97, University of
Göttingen, Germany, 1997.
4
4
6 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837–838.
7 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, 48 R. Peverati and D. G. Truhlar, J. Phys. Chem. Lett., 2012, 3,
G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, 117–124.
A. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, 49 A. V. Marenich, C. J. Cramer and D. G. Truhlar, J. Phys.
B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, Chem. B, 2009, 113, 6378–6396.
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Dalton Trans., 2018, 47, 5850–5859 | 5859