Sterically encumbered dianionic dicarboranyl pincer ligand (C5H3N)(C2B10H11)2 and its CNC Nickel(II) complex

Article abstract of DOI:10.1016/j.jorganchem.2017.11.004

The novel 2,6-bis(carborane)pyridine (C₅H₃N)(C₂B₁₀H₁₁)₂ ligand precursor containing two icosahedral carborane clusters attached to the pyridine ring was synthesized by the S_NAr reaction between 2,6-difluoropyridine and lithiated ortho-carborane LiC₂B₁₀H_11. Lithiation of the proligand at carbon atoms of carborane cages and the subsequent reaction with Ni(PPh₃)₂Cl₂ afforded the square-planar Ni(II) pincer complex {(C₅H₃N)(C₂B₁₀H₁₀)₂}Ni(CH₃CN). X-ray single crystal diffraction revealed extreme steric hindrance around the metal center in the complex imposed by two carboranyl groups in the rigid pincer-type framework, which was also manifested by the high value of the ligand buried volume %V_bur = 70.6%. The title pincer complex {(C₅H₃N)(C₂B₁₀H₁₀)₂}Ni(CH₃CN) was found to be a competent catalyst for nucleophilic addition of piperidine to acetonitrile.

Full text of DOI:10.1016/j.jorganchem.2017.11.004

Accepted Manuscript
Sterically encumbered dianionic dicarboranyl pincer ligand (C H N)(C B
H
)
5
3
2 10 11 2
and its CNC Nickel(II) complex
Mohammad Jahirul Islam, Mark D. Smith, Dmitry V. Peryshkov
PII:
S0022-328X(17)30636-8
10.1016/j.jorganchem.2017.11.004
JOM 20169
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 10 October 2017
Revised Date: 3 November 2017
Accepted Date: 5 November 2017
Please cite this article as: M.J. Islam, M.D. Smith, D.V. Peryshkov, Sterically encumbered dianionic
dicarboranyl pincer ligand (C H N)(C B ) and its CNC Nickel(II) complex, Journal of
H
2 10 11 2
5
3
Organometallic Chemistry (2017), doi: 10.1016/j.jorganchem.2017.11.004.
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ACCEPTED MANUSCRIPT
Sterically Encumbered Dianionic Dicarboranyl Pincer Ligand
(
C H N)(C B H ) and its CNC Nickel(II) Complex
5
3
2
10 11 2
Mohammad Jahirul Islam, Mark D. Smith, Dmitry V. Peryshkov*
Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter
Street, Columbia, SC 29208, USA
E-mail: peryshkov@sc.edu
Article Type: Special Issue: Beletskaya (Adams)
Keywords: Carboranes, Pincer Complexes, Nickel.
This paper is dedicated to professor Irina P. Beletskaya on the occasion of her 85th
birthday
Highlights:
•
2,6-bis(carborane)pyridine proligand (C H N)(C B H ) was synthesized by the S Ar
5 3 2 10 11 2 N
reaction between 2,6-difluoropyridine and a lithiated ortho-carborane cluster
LiC B H
2
10 11
•
•
Metalation at carbon atoms of the ligand afforded the Ni(II) CNC pincer complex
(C N)(C }Ni(CH CN)
Addition of piperidine to acetonitrile was found to be catalyzed by
(C H N)(C B H ) }Ni(CH CN)
{
5
H
3
2
B
10
H
10
)
2
3
{
5
3
2
10 10 2
3
Abstract: The novel 2,6-bis(carborane)pyridine (C H N)(C B H ) ligand precursor
5
3
2
10 11 2
containing two icosahedral carborane clusters attached to the pyridine ring was
synthesized by the S Ar reaction between 2,6-difluoropyridine and lithiated ortho-
N
carborane LiC B H Lithiation of the proligand at carbon atoms of carborane cages and
2
10 11.
the subsequent reaction with Ni(PPh
3 2 2
) Cl afforded the square-planar Ni(II) pincer
complex {(C H N)(C B H ) }Ni(CH CN). X-ray single crystal diffraction revealed
5
3
2
10 10 2
3
extreme steric hindrance around the metal center in the complex imposed by two
1

ACCEPTED MANUSCRIPT
carboranyl groups in the rigid pincer-type framework, which was also manifested by the
high value of the ligand buried volume %Vbur = 70.6%. The title pincer complex
{
(C H N)(C B H ) }Ni(CH CN) was found to be a competent catalyst for nucleophilic
5 3 2 10 10 2 3
addition of piperidine to acetonitrile.
1
. Introduction
Pincer-type frameworks, which are tridentate ligands that enforce meridional
coordination to a metal center, attracted significant attention in last 20 years.[1] Pincer
complexes of transition metals often exhibit a favorable combination of both stability and
reactivity, which made them invaluable for fundamental studies of reaction mechanisms
and for catalysis. As originally devised by Moulton and Shaw, pincer ligands contain an
anionic carbon center between two pendant phosphine donors “arms”.[2] This
arrangement type has been broadened to include other monoanionic moieties with two
neutral sterically hindered arms and it is the most studied subclass of pincer ligands.[3]
Related dianionic and trianionic pincer-type ligands and their complexes with both early-
and late transition metals have recently attracted increased attention.[4–8]
Icosahedral boron clusters, such as neutral closo- carboranes C B H and their
2
10 12
–
monoanionic counterparts CB H possess an unusual delocalized electronic structure
11
12
as well as an extreme steric hindrance profile that make them interesting building blocks
in ligand design, catalysis, polymer and material chemistry.[9–16] Carboranes have been
used as auxiliary groups attached to phosphines, amines, amides, cyclopentadienyls, and
heterocyclic carbene systems.[17–23]
A number of tridentate complexes containing carboranes has recently emerged.[24–27]
The utilization of the pincer-type geometry with boron cages serving as central
“backbones” allowed, for example, an isolation of an unusual three-membered (BB)>Ru
carboryne metalacycle[28] as well as a development of an efficient, water-tolerant Pd-
based catalyst for Suzuki coupling reactions[26] and an air-tolerant Ru-based catalyst for
alkane transfer dehydrogenation.[29]
2

ACCEPTED MANUSCRIPT
In general, carborane clusters can be exohedrally metalated at carbon or boron vertices.
The C–H bonds of carboranes are relatively acidic (pKa = 22 for ortho-carborane), and
these C atoms can be lithiated and subsequently transmetalated by transition metal salt
metathesis.[30–35] In contrast, unsupported metal-boron bonds of carboranes are
rare.[36–39] However, there are numerous examples of successful metalation of
carborane B–H bonds, primarily by late transition metals, with the use of donor directing
groups attached to the cage. These cyclometalated products are intermediates in direct
selective B-H bond functionalization of boron clusters and often are isolable. [40–46]
In this contribution, we report the synthesis of the novel type of the chelating pincer
ligand precursor containing two sterically hindered icosahedral carborane cages as “arms”
and a pyridine “backbone”. Deprotonation of C-H bonds of both carborane clusters
afforded a dianionic ligand that was successfully metalated to yield a nickel(II) complex.
2
. Results and Discussion
The use of carborane clusters as “arms” of a pincer ligand prompts the use of a neutral
donor as a central “backbone”. The rigidity of the target pincer ligand was an important
consideration, therefore, we chose not to use carborane picolyl derivatives where a boron
cluster is connected to a pyridine ring through the methylene linker.[47–49] Instead, we
elected to use a rigid planar pyridine fragment as its direct functionalization with two
carborane cages in 2- and 6- positions would lead to meridional geometry of the target
ligand. Several synthetic routes to carboranyl pyridines have been reported in literature,
including reactions of decaborane and pyridyl acetylenes and copper-promoted coupling
of 2-bromopyridine and lithiated carborane.[50–52] These synthetic methods, while
successful, have been plagued by relatively low yields. Recently, a simpler alternative
method, involving nucleophilic aromatic substitution of 2-fluoropyridine by lithiated
carborane, has been developed.[53] Notably, all these previously reported synthetic
routes led to pyridine derivatives containing one carborane cage. We surmised that the
N
S Ar reaction of 2,6-difluoropyridine with two equivalents of lithiated carborane would
lead to efficient formation of the dicarboranyl pyridine. Gratifyingly, heating the mixture
of 2,6-difluropyridine with LiC B H in THF at 80 °C under nitrogen atmosphere
2
11 11
3

ACCEPTED MANUSCRIPT
overnight led, after aqueous workup and extraction to dichloromethane, to the target 2,6-
dicarboranyl pyridine (C H N)(C B H ) (1). The product was characterized by the
5
3
2
10 11 2
array of multinuclear NMR spectrometry techniques, mass-spectrometry, and the single
1
1
11
1
crystal X-ray diffraction. The B and B{ H} NMR spectra of 1 exhibited a set partially
1
overlapping signals in the range from -2.6 to -13.1 ppm. The H NMR resonance
corresponding to the remaining C-H bond of the carborane cage was found at 4.49 ppm in
CDCl , which is shifted downfield in comparison with the related signal of the starting
3
C B H cluster at 3.56 ppm.
2
10 12
Scheme 1. Synthesis of 2,6- bis(carborane)pyridine (C H N)(C B H ) (1).
5
3
2
10 11 2
Single crystals of 1 were grown from dichloromethane/hexanes solvent mixture by
slow evaporation on air. The structure determination confirmed the expected geometry of
the proligand with crystallographically-required C and idealized C2v symmetry. The
2
central pyridine fragment is connected to carborane cages through unstrained bonds with
the C2–C3 bond length of 1.496(3) Å, the N1–C3–C2 angle of 116.6(2)º and the C3–C2–
C1 angle of 117.5(2)º. The C1–C2 bond in the carborane cluster is 1.629(2) Å. The
separation between two boron cages is substantial as indicated by the C1···C1A distance
of 4.554(3) Å.
Interestingly, the molecular structure of 1 in the solid state revealed a conformation that
features C–H bonds of carborane clusters pointing inwards the cavity of the ligand, in
other words, towards the nitrogen atom of the pyridine ring. This arrangement is likely
stabilized by the intramolecular C–H···N hydrogen bonding which has been found in the
related 2-carboranylpyridine.[54] Similarly, existence of relatively strong hydrogen
bonds between aryl C–H bonds and nitrogen atoms of pyridines have been
demonstrated.[55]
4

ACCEPTED MANUSCRIPT
Figure 1. Displacement ellipsoid plot (50% probability) of the proligand
(
C H N)(C B H ) (1). (a): a view perpendicular to the (C3–N1–C3A) plane (b): a view
5
3
2 10 11 2
along the (C3–N1–C3A) plane.
The ligand precursor 1 possesses two relatively acidic C-H bonds on two carborane
cages. Deprotonation of the ligand was done using 2.1 equiv n-BuLi in THF at room
temperature. The lithiated ligand was not isolated but used in situ in the reaction with 1.1
equiv of Ni(PPh ) Cl
at 60 ºC for
6
h. The target complex
3
2
2
{
(C H N)(C B H ) }Ni(CH CN) (2) was isolated as a yellow powder.
5
3
2
10 10 2
3
Scheme 2. Synthesis of {(C H N)(C B H ) }Ni(CH CN) (2).
5
3
2
10 10 2
3
5

ACCEPTED MANUSCRIPT
Single crystals of 2·C
6
H
6
were grown from benzene by slow evaporation. The structure
determination revealed the expected square-planar geometry around the nickel center that
is coordinated to two carboranyl arms through carbon atoms, the pyridine ring, and
acetonitrile. The complex adopted crystallographically-required C2v symmetry, however,
elongated displacement ellipsoids of boron atoms suggested mild cluster disorder through
their displacement from the mirror plane. The Ni1–C1 bond length in 2 is 1.929(2) Å.
This value is within the typical range for nickel C-carboranyl compounds (1.880(6)–
2
.01(1) Å).[56] The Ni1–N2(C H ) bond length is 1.882(2) Å and the Ni1–N2(CCH )
6 3 3
bond length is 1.841(2) Å. The C2≡N6 bond length of the coordinated acetonitrile ligand
is 1.134(5) Å. The coordination of the metal center led to the increased strain of the
complex which is indicated by the decreased intraligand angles N1–C3–C2 (113.4(2)º)
and C3–C2–C1 (110.6(2)º). This is also manifested in the decreased separation between
boron cages in 2 with the C1···C1A distance of 3.853(3) Å. The C1–Ni1–C1A bite angle
is close to linearity at 173.7(1)º.
1
13
11
The diamagnetic complex 2 was characterized by H, C, and B NMR, and FTIR
spectroscopies. The FTIR spectrum of the solid sample exhibited characteristic
–
1
–1
11
absorption bands v(B–H) at 2586 cm as well as v(C≡N) at 2332 cm . The B NMR
spectrum contained a set of partially overlapping signals in the range from –3.4 ppm to –
1
1.3 ppm.
6

ACCEPTED MANUSCRIPT
Figure 2. Displacement ellipsoid plot (50% probability) of the
{
(C H N)(C B H ) }Ni(CH CN) complex (2). (a): a view perpendicular to the (C3–
5
3
2
10 10 2
3
N1–Ni1–C3A) plane (b): a general view (c): space-filling diagram of 2 with the
acetonitrile ligand omitted.
Carborane clusters as ligands exert an unusually high degree of steric hindrance due to
their icosahedral shape. For example, each of the metal-carbon bonds in 2 is surrounded
by five neighboring cluster atoms. A space-filling diagram of the complex 2 with
acetonitrile ligand omitted is shown in Figure 2c to highlight steric requirements of 2,6-
bis(carborane)pyridine. Ligand buried volume (%V ) has been recently introduced as a
bur
7

ACCEPTED MANUSCRIPT
quantitative descriptor of steric congestion around the metal center.[57] We found that
the (C H N)(C B H ) ligand in the complex 2 exhibited a high value of %V =
bur
5
3
2
10 10 2
7
0.6%, which indicates a high degree of steric hindrance imposed by the dicarboranyl
pincer ligand. This value can be compared to that for the recently reported complex of
gold featuring two anionic carborane {CB } cages connected to the N-heterocyclic
1
1
carbene backbone.[58] The presence of five-membered ring NHC backbone as well as
two weakly coordinating anionic boron cages in that complex have resulted in the value
of %Vbur of 47.2%. The neutral (C H N)(C B H ) ligand reported herein is pyridine-
5
3
2 10 10 2
2
based, which enforces two neutral {C B10} carborane cages closer to each other leading
to the coordination to the metal center and the increase in %Vbur.
The electron density distribution in the carborane cluster is not uniform and gives rise
to significant differences in the electronic effects of the carborane cage on an exohedral
substituent when attached to either carbon or boron atoms.[59] A carborane cluster is
usually regarded as an electron-withdrawing group when it is bound through its carbon
atom.[60] The high value of the v(CN) in 2 indicates the electron-deficient environment
of the nitrile group which is likely due to coordination to relatively electron-poor C-
carboranyl bound metal center. A significant positive charge on the carbon atom of the
nitrile group would assist a nucleophilic attack, for example, by an amine. Notably, there
have been reports of cationic nickel(II) complexes catalyzing hydroamination of nitriles
via an outer-sphere mechanism.[61,62]
Scheme 3. Addition of piperidine to acetonitrile promoted by 2. The catalyst loading was
1
mol% relative to the amount of piperdine. Acetonitrile served as both the reagent and
the solvent.
We found that the complex 2 efficiently catalyzes the addition of piperidine to
3 5
acetonitrile with the formation of the imine HN=C(CH )NC H10. In a typical reaction, a
8

ACCEPTED MANUSCRIPT
mixture of piperidine and acetonitrile containing 2 (1 mol% relative to the amount of
piperidine) was heated at 80 ºC for 6 h under nitrogen atmosphere (Scheme 3). A
relatively high value of the turnover number (TON = 80) was observed, thus
demonstrating that the complex 2 is a competent catalyst of this reaction.
3
. Conclusions
The novel pincer ligand framework containing two carborane clusters and a central
pyridine backbone was synthesized. The CNC-type pincer complex 2,6-
bis(carboranyl)pyridine nickel(II)(acetonitrile) was prepared in the reaction of the
2 5 3 2 10 10 2 3 2 2
lithiated ligand Li (C H N)(C B H ) and Ni(PPh ) Cl . The molecular structure of the
nickel complex featured high degree of steric hindrance imposed by coordination of two
icosahedral carborane clusters. The title complex was found to be a competent catalyst
for hydroamination of acetonitrile with piperidine.
4
. Experimental Section.
All synthetic manipulations, unless stated otherwise, were carried out either in a nitrogen-
filled VAC drybox or on a dual-manifold Schlenk-style vacuum line.[63] The solvents
were sparged with nitrogen, passed through activated alumina, and stored over activated
4
2 2 3 3 2
Å Linde-type molecular sieves. CD Cl , CDCl , and (CD ) SO were degassed and
stored over activated 4 Å Linde-type molecular sieves. NMR spectra were recorded using
1
13
11
Varian spectrometers at 400 ( H), 100 ( C), 128 ( B) MHz, reported in δ (parts per
1
13
million) and referenced to the residual H/ C signals of the deuterated solvent or an
1
1
external BF (Et O) ( B(δ): 0.0 ppm) standard.
3
2
Synthesis of 2,6-bis(carborane)pyridine (C H N)(C B H ) (1)
5
3
2
10 11 2
A solution of n-butyllithium in hexanes (1.6 M, 3.5 mL, 5.6 mmol) was added to a
solution of ortho-carborane (400 mg, 2.77 mmol) in 10 mL of anhydrous tetrahydrofuran
at room temperature under nitrogen atmosphere. The mixture was stirred at room
temperature for 12 h. 2,6-difluoropyridine (0.13 mL, 1.43 mmol) was added to the
reaction mixture and stirred at 60 °C for 6 h, after which time tetrahydrofuran was
9

ACCEPTED MANUSCRIPT
removed under vacuum. Dichloromethane (50 mL) and water (50 mL) were added, and
products were extracted to the organic layer. The organic portion was passed through a
silica gel column using dichloromethane as an eluent. Volatiles were removed under
vacuum and the unreacted ortho-carborane was sublimed out to obtain pure 2,6-
bis(carborane)pyridine with 28% yield (140 mg, 0.385 mmol).
1
H NMR (CDCl ): δ 7.78 (t, 1H, C H N), 7.63 (d, 2H, C H N), 4.49 (s, 2H, (C-H,
3
5
3
5
3
11
1
C B H ), 3.10–1.50 (overlapping, 20H, B-H, C B H ). B{ H} NMR (CDCl ): δ -2.6,
2
10 11
2
10 11
3
1
3
-
3.4, -8.3, -11.4, -13.1 (br). C NMR (CDCl ): δ 150.5 (C H N), 139.2 (C H N), 122.8
3
5
3
5
3
(C
5
H
3
N), 74.0 (C-C, C
B
2 10
H
11), 56.6 (C-H, C
2
11 9 27
H B10). Calcd for C H B20N: C, 29.57; H,
7
.45; N, 3.83 Found: C, 29.38; H, 7.11, N, 3.61.
Synthesis
of
2,6-bis(carboranyl)pyridine
}Ni(CH CN) (2)
nickel(II)(acetonitrile)
complex
{(C
5
H
3
N)(C
2
B
10
H
10
)
2
3
A solution of n-butyllithium in hexanes (1.6 M, 0.72 mL, 1.16 mmol) was added to a
solution of 2,6-bis(carborane)pyridine (200 mg, 0.55 mmol) in 10 mL of dry
tetrahydrofuran at room temperature under nitrogen. The mixture was stirred at room
temperature for 12 h. Bis(triphenylphosphine)nickel(II) dichloride (395.77 mg, 0.61
mmol) was added and the mixture was stirred at 60 °C for 6 h, after which time volatiles
were removed under vacuum. Hydrochloric acid (3M, 20 mL) and acetonitrile (20 mL)
were added. The mixture was filtered and the resulting precipitate was washed with
hexanes (10 mL) and diethyl ether (10 mL) to obtain 2,6-bis(carboranyl)pyridine
nickel(II)(acetonitrile) complex as a yellow powder (89 mg, 0.19 mmol, 35% yield).
1
2 2 5 3 5 3
H NMR (CD Cl ): δ 7.79 (t, 1H, C H N), 7.22 (d, 2H, C H N), 3.50–1.20 (overlapping,
1
1
1
B-H, C B H ), 2.38 (s, 3H, CH CN). B{ H} NMR (CD Cl ): δ -3.4, -6.7, -7.5, -11.3.
2
10 10
3
2
2
1
3
C NMR ((CD ) SO): δ 159.7 (C H N), 143.1 (C H N), 122.3 (C H N), 118.6
3
2
5
3
5
3
5
3
(
CH
3
CN), 79.7 (C
2
H
11
B10), 71.9 (C
2
H
11
B
10), 1.7 (CH
3
CN). Calcd for C11
26
H B
20
N
2
Ni: C,
2
8.64; H, 5.68; N, 6.07 Found: C, 28.71; H, 5.80, N, 5.72.
Hydroamination of acetonitrile promoted by 2.
10

ACCEPTED MANUSCRIPT
Piperidine (0.1 mL, 1.0 mmol) was added to a solution of 2,6-bis(carboranyl)pyridine
nickel(II)(acetonitrile) complex (2) (4.62 mg, 0.01 mmol) in 5 mL of acetonitrile and the
reaction mixture was stirred at 80 °C for 6 h. A solution of naphthalene (12.82 mg, 1.0
1
mmol) in 10 mL of ether was added to the mixture as an internal H NMR spectroscopy
standard. The volatiles were removed under vacuum at room temperature. The turnover
number (TON = 80) was determined by integration of signals corresponding to the imine
1
product relative to signals of the internal standard (naphthalene) in the H NMR spectrum
of the reaction mixture.
The calculations of the buried volume %Vbur were carried out for the atomic coordinates
from
the
crystal
structure
of
2
using
SambVca2
program
(https://www.molnac.unisa.it/OMtools/sambvca2.0/)[57] with the following (default)
parameters: sphere radius 3.5 Å, distance from the center of the sphere: 2.1 Å, mesh
spacing: 0.05 Å, H atoms not included, and Bondi radii scaled by 1.17.
4
.2 Structure determination details.
X-ray intensity data from a colorless, almond-shaped plate were collected at 100(2) K
using a Bruker D8 QUEST diffractometer equipped with a PHOTON-100 CMOS area
detector and an Incoatec microfocus source (Mo Kα radiation, λ = 0.71073 Å). The raw
area detector data frames were reduced and corrected for absorption effects using the
Bruker APEX3, SAINT+ and SADABS programs.[64–66] Final unit cell parameters
were determined by least-squares refinement of large sets of reflections from the data
sets. The structure was solved with SHELXT.[67,68] Subsequent difference Fourier
2
calculations and full-matrix least-squares refinement against F were performed with
SHELXL-2016 using OLEX2.[69]
4
.2.1. Crystal Structure Determination of (C H N)(C B H ) (1)
5 3 2 10 11 2
The compound crystallized in the tetragonal system. The pattern of systematic absences
in the intensity data was consistent with the space groups I-42d and I4 md. Space group I-
2d (No. 122) was confirmed by structure solution. The asymmetric unit consists of half
1
4
11

ACCEPTED MANUSCRIPT
of one molecule, which is located on a crystallographic two-fold axis of rotation. All non-
hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen
atoms were located in Fourier difference maps and refined freely, resulting in normal
bond distances and displacement parameters. The largest residual electron density peak in
-3
the final difference map is 0.23 e Å , located 0.72 Å from C1. Because of the absence of
heavy atoms in the crystal, the absolute structure could not be determined.
Crystal Data for C H B N (CCDC 1583707): tetragonal, space group I-42d (no. 122),
9
25 20
a = 14.9477(5) Å, c = 19.0491(7) Å, V = 4256.2(3) Å3, Z = 8, T = 100(2) K, µ(MoKα) =
3
0
2
.051 mm-1, M =363.50 g/mol, Dcalc = 1.135 g/cm , 47566 reflections measured (5.45° ≤
Θ ≤ 52.806°), 2188 unique (Rint = 0.0700, Rsigma = 0.0185) which were used in all
calculations. The final R was 0.0401 (I > 2σ(I)) and wR was 0.1047 (all data).
1
2
4
.2.2. Crystal Structure Determination of {(C
5
H
3
2 10 10 2 3 6 6 2
N)(C B H ) }Ni(CH CN)(C H )
(
2·(C H ) )
6 6 2
The compound crystallized in the orthorhombic system. The pattern of systematic
absences in the intensity data was consistent with the space groups Imma and Ima2. The
centrosymmetric group Imma was eventually confirmed as the best description of the
structure. The asymmetric unit consists of ¼ of one Ni complex with crystallographic mm
(
C ) point symmetry, and half of one benzene molecule located on a mirror plane. Atoms
2v
Ni1, N1, C5, N2, C1, C2, B5 and B6 are located in the mirror plane perpendicular to the
crystallographic a axis; Ni1, N1, C5, N2, C6 and C7 are also located in the mirror
perpendicular to the b axis. The carbon and hydrogen atoms of the acetonitrile ligand
(C6 and C7) are disordered across the mirror perpendicular to the a axis and were refined
with half-occupancy. The benzene solvent guest disorder consists of two independent
half-benzene molecules per asymmetric unit, both located on the mirror plane
perpendicular to the b axis. All non-hydrogen atoms were refined with anisotropic
displacement parameters. The anisotropic displacement parameters (adps) of the
disordered benzene carbon atoms were restrained to be approximately spherical using an
ISOR restraint. Some elongated adps for boron atoms in the carborane cage (e.g. U /U =
3
1
1
1.4 for B6) suggest some atoms in the cage part of the structure are displaced away from
12

ACCEPTED MANUSCRIPT
the mirror plane bisecting the cage. A refinement in space group Ima2, which still retains
this mirror plane, also showed strongly prolate boron adps and was unstable. Refinements
in lower space groups without mirror symmetry (e.g. I2 2 2 ) also gave highly prolate
1
1 1
boron ellipsoids and unstable refinements. Disorder modeling in Imma of the carborane
cage part was not successful owing to the small displacements of the B atoms from their
average positions. The best refinement was therefore judged to be in space group Imma
with prolate boron ellipsoids suggesting mild cage disorder. Hydrogen atoms bonded to
carbon were placed in geometrically idealized positions and included as riding atoms
with d(C-H) = 0.95 Å and Uiso(H) = 1.2Ueq(C) for aromatic hydrogen atoms. The
acetonitrile methyl hydrogens were located in a difference map, adjusted to d(C-H) =
0
.98 Å and Uiso(H) = 1.5Ueq(C) included as riding on C7. Hydrogen atoms bonded to
boron atoms were located in difference maps and refined freely. The largest residual
-3
electron density peak in the final difference map is 0.28 e Å , located 0.45 Å from B6.
Crystal Data for C H B N Ni (CCDC 1583707): orthorhombic, space group Imma
2
3
38 20
2
3
(
no. 74), a = 14.4701(8) Å, b = 16.2302(8) Å, c = 14.0240(7) Å, V = 3293.6(3) Å , Z = 4,
-1
3
T = 100(2) K, µ(MoKα) = 0.611 mm , M =617.46 g/mol, D = 1.245 g/cm , 66111
calc
reflections measured (5.02° ≤ 2Θ ≤ 55.472°), 2080 unique (R = 0.0390, Rsigma = 0.0109)
int
which were used in all calculations. The final R was 0.0309 (I > 2σ(I)) and wR was
1
2
0
.0815 (all data).
Acknowledgments.
This material is based in part upon work supported by the National Science Foundation
under Award CHE-1654301.
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