New synthetic and structural studies on nitroso-ortho-carboranes RCB10H10CNO and bis(ortho-carboranyl)amines (RCB10H10C)2NH (R = Ph or Me)

Article abstract of DOI:10.1016/j.poly.2008.12.014

Improved procedures are reported for the preparation of nitroso-carboranes RCb°NO (Cb° = 1,2-C₂B₁₀H₁₀; R = Ph, Me at cage carbon C2) in 44-77% yield, and of dicarboranylamines (RCb°)₂NH in 55-65% yield by reacti

Full text of DOI:10.1016/j.poly.2008.12.014

Polyhedron 28 (2009) 789–795
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
New synthetic and structural studies on nitroso-ortho-carboranes RCB10H10CNO
and bis(ortho-carboranyl)amines (RCB10H10C)2NH (R = Ph or Me)
a
a
b
b,1
Mark A. Fox a, , J.A. Hugh MacBride , Richard J. Peace , William Clegg , Mark R.J. Elsegood
,
*
Kenneth Wade a,
*
a Chemistry Department, Durham University Science Laboratories, South Road, Durham DH1 3LE, UK
b School of Chemistry, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Improved procedures are reported for the preparation of nitroso-carboranes RCb°NO (Cb° = 1,2-C2B10H10
;
Received 9 October 2008
Accepted 5 December 2008
Available online 23 January 2009
R = Ph, Me at cage carbon C2) in 44–77% yield, and of dicarboranylamines (RCb°)2NH in 55–65% yield by
reactions between the lithio-carboranes, RCb°Li and nitrosyl chloride, NOCl, in cold mixtures of diethyl
ether and either pentane (for RCb°NO) or dimethoxyethane (for (RCb°)2NH). Deprotonation of the amines
by KOtBu in toluene in the presence of 18-crown-6, (CH2CH2O)6, affords the salts [K(18-crown-
6)]+[(RCb°)2N]ꢀ. X-ray crystal structures of PhCb°NO, (PhCb°)2NH, (MeCb°)2NH and [K(18-crown-
6)]+[(PhCb°)2N]ꢀ are described, and the bonding implications of their cage C. . .C distances (1.68, 1.80,
1.75 and 1.99 Å, respectively) are discussed. These species provide further striking examples of the
Keywords:
ortho-Carborane
p-Bond
Amine group
Nitroso group
Crystal structure
Clusters
remarkable capacity of the ortho-carborane cage to act as a sensitive indicator of the p-donor character-
istics of ligands attached to its cage carbon atoms.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
of X, from 1.66 Å in PhCb°H to 1.77 Å in PhCb°NH2; significantly
longer C1–C2 distances were found in anionic systems such as
PhCb°Oꢀ (2.00 Å) or PhCb°NHꢀ (2.30 Å) with recognisably stronger
This paper reports a new study of reactions between lithio-car-
boranes, RCb°Li (Cb° = 1,2-C2B10H10, ortho-carboranyl; R = Ph, Me
at cage carbon C2), and nitrosyl chloride, NOCl, carried out to opti-
mise the syntheses and determine the structures of two important
categories of ortho-carborane derivatives containing exo-C–N
bonds, viz nitroso-carboranes RCb°NO and dicarboranylamines,
(RCb°)2NH (Scheme 1). Earlier studies [1–3] had already shown
such products to be accessible by RCb°Li/NOCl reactions, but had
left unclear what preparative procedures (temperature, solvent,
etc.) were best suited to each product, and had given no structural
information on either type of product. Our interest in them, and in
salts of amide anions [(RCb°)2N]ꢀ preparable by deprotonation of
the amines (RCb°)2NH, concerned their use to explore further the
remarkable sensitivity of the ortho-carborane cage, notably its C–
p-donors (Fig. 1). These findings have been supplemented by com-
putational studies on XCb°X systems by Oliva et al. [10]. Related
studies by Teixidor and Viñas on thiolato and phosphino deriva-
tives of ortho-carboranes also showed similar C1–C2 distance
lengthening attributed to exo-C–S or C–P
ric effects [11]. The cage C–C bond lengthening caused by
is readily intelligible if the p-AO involved in exo-C@X -bonding is
-bonding
p
-bonding as well as ste-
p-donors
p
that which is also primarily responsible for cage C1–C2
r
(AO = atomic orbital, Fig. 1).
Because amides NR0R00 are expected to feature as
p-donors, we
considered that experimental evidence of the structures of species
RCb°NO, (RCb°)2NH and (RCb°)2Nꢀ, in particular their C1–C2 and
C1–N distances and C1–N@O or C1–N–C10 angles, would reveal
whether the NO, NHCb°R and NCb°Rꢀ ligands employed available
C bond length, to the p-donor characteristics of C-attached ligands
X in derivatives RCb°X or XCb°X [4–9].
Our experimental and computational studies [9] on compounds
PhCb°X (X = H, F, OH or NH2) had shown the cage C1–C2 bond
‘lone pair’ electrons for dative p-bonding, and shed further useful
light on the sensitivity of the ortho-carborane cage to
p-donor
substituents.
lengths to increase (in that sequence) with the
p-donor capacity
Although first reported over 40 years ago, carboranes with
C–nitrogen substituents have received only sporadic or highly
selective attention. Isocyanates RCbNCO (Cb = 1,2-, 1,7- or 1,12-
C2B10H10), obtainable from acid chlorides RCbCOCl and lithium
azide LiN3 [12], have been quite widely exploited as intermediates
from which to prepare various organo-nitrogen carboranes as suit-
able candidates for use in Boron Neutron Capture Therapy (BNCT)
* Corresponding authors.
E-mail addresses: m.a.fox@durham.ac.uk (M.A. Fox), kenneth.wade@durham.
ac.uk (K. Wade).
1
Current address: Chemistry Department, Loughborough University, Loughbor-
ough, Leicestershire, LE11 3TU, UK.
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.12.014

790
M.A. Fox et al. / Polyhedron 28 (2009) 789–795
that their CNO units are bent at nitrogen [15], with the nitrosyl
R
C
C
groups acting as one-electron ligands to the carborane cages. The
colourless secondary amines (RCb°)2NH were recovered after treat-
ment of the unsublimed material with methanol (for details, see
Section 4).
We infer that the nitroso-carboranes are formed in the first
stage of the reaction (Eq. (1)) and that the secondary amines result
from the reaction of the nitroso-carborane with a second mole of
lithio-carborane, despite competition from excess nitrosyl chloride
(Eq. (2));
Li
C
NO
C
H
N
C
NOCl
Et2O
R
R
C
C
R
C
+
(RCbo)2NH
RCboNO
RCboLi
R = Me
RCbꢁLi þ NOCl ! RCbꢁNO þ LiCl
ð1Þ
ð2Þ
Pentane
-40oC
69%
77%
0%
11%
22%
63%
55%
Pentane -117oC
RCbꢁNO þ RCbꢁLi ! ðRCbꢁÞ2NOLi
DME
DME
-40oC
-78oC
It is not clear, however, how the lithio-hydroxylamine (RCb°)2NOLi
is then reduced to the amine, (RCb°)2NH. It may be significant that
the bidentate coordinating solvent, 1,2-dimethoxyethane, MeOCH2-
CH2OMe, favours reaction (2). There are parallels here with aro-
matic ring chemistry, in that both aryl nitroso compounds ArNO
and diarylamines Ar2NH are accessible from ArLi or ArMgX and
NOCl [16].
10%
-40oC
-117oC
-40oC
61%
42%
0%
Pentane
Pentane
DME
10%
0%
55%
56%
R = Ph
-78oC
5%
DME
Our early preparations of anionic species [RCb°X]ꢀ from neutral
parent species used proton sponge, PS, C10H6(NMe2)2, to deproto-
nate the hydroxycarborane PhCb°OH and the thiol PhCb°SH [6,7].
We therefore attempted to deprotonate the amine (PhCb°)2NH in
toluene by proton sponge. This failed; the amine crystallised un-
changed from these solutions. However, addition of a solution of
potassium t-butoxide and an equimolar proportion of 18-crown-
6 deposited pale yellow crystals, with 77% yield of the salt [K(18-
crown-6)]+[(PhCb°)2N]ꢀ. This pale yellow salt is, surprisingly, sta-
ble to air and moisture, though the parent amine, (PhCb°)2NH is
regenerated by ethanoic acid. In previous studies we were unable
to obtain the amide PhCb°NHꢀ by deprotonation of the amine
PhCb°NH2; cage degradation occurred instead [9]. Although the
yellow salt appears to crystallise well from 1,2-dichlorobenzene,
single crystals suitable for X-ray diffraction were grown from a
solution in diethyleneglycol dimethyl ether, (MeOC2H4)2O, into
which cyclohexane diffused slowly from an upper layer. The col-
ourless salt [K(18-crown-6)]+[(MeCb°)2N]ꢀ was similarly formed
in 86% yield from a solution of potassium t-butoxide and an equi-
molar proportion of 18-crown-6 with amine (MeCb°)2NH. The con-
trast in the formation and stability between the anions PhCb°NHꢀ
and (RCb°)2Nꢀ suggests that the PhCb°NHꢀ anion is capable of a
nucleophilic attack on a second carborane molecule leading to cage
degradation, whereas the two bulky cages in the anion (RCb°)2Nꢀ
inhibit the capacity of this amide to attack a second carborane
molecule.
Scheme 1.
[13], and di-isocyanates OCNCbmNCO (Cbm = 1,7-C2B10H10) have
been converted into diamines H2NCbmNH2 for use in polymers
[14]. The nitrosyl chloride–lithio-carborane reaction by contrast
appears to have been studied by only two research groups, and
not at all during the past thirty years, despite the range of C–N car-
borane derivatives in principle accessible via nitroso-carboranes
[1,3]. Unfortunately the early reports by Kauffman et al . and
Zakharkin et al. gave conflicting yields of nitroso derivatives (25–
80%) and limited experimental details.
2. Results and discussion
2.1. Synthetic aspects
In our studies of low-temperature reactions between the lithio-
carboranes, MeCb°Li or PhCb°Li, and nitrosyl chloride in equivalent
amounts (Scheme 1), we used 1:1 mixtures of diethyl ether and
pentane, or of diethyl ether and dimethoxyethane (DME), as sol-
vent. The products obtained were broadly in line with those re-
ported by Zakharkin et al. [2,3]. In diethyl ether and pentane, the
nitroso-carboranes RCb°NO were the main product (42–77%),
though some dicarboranylamine (RCb°)2NH could normally also
be isolated (0–22%). However, when diethyl ether and DME were
used as a solvent mix, the secondary amines (RCb°)2NH were the
main products (55–63%), yields of nitroso-carboranes being 10%
or less. Although overall yields varied with the temperature at
which the reaction was carried out, the product balance did not.
Our work-up procedure involved treatment with aqueous potas-
sium hydrogen carbonate followed by sublimation to obtain the
blue nitroso compounds RCb°NO. The strong NO stretching absorp-
tions at ca. 1565 cmꢀ1 in the IR spectra of these compounds show
2.2. Structural aspects
In crystalline PhCb°NO (Fig. 2), the N@O bond (length
1.182(2) Å) lies roughly in the C(2)–C(1)–N(1) plane. The phenyl
ring is perpendicular to this plane. The C(1)–N(1) bond length of
1.490(2) Å is consistent with negligible exo-C–N
p-bonding, as is
the C(1)–C(2) cluster bond length of 1.677(2) Å, virtually identical
to that in the computed geometry of PhCb°F (1.674 Å), and slightly
different from that in the computed geometry of PhCb°H (1.659 Å)
with a similarly orientated phenyl group [9]. Reported X-ray-de-
rived geometries of PhCb°H with the orientation of the phenyl
group roughly coplanar with the H(1)–C(1)–C(2) plane reveal
shorter C(1)–C(2) bond distances of 1.643(2) and 1.649(2) Å
[5,17–19]. The C(1)–N@O bond angle of 113.0(2)° is midway be-
tween typical trigonal planar and tetrahedral bond angles. As a
comparison nitrosobenzene, PhNO, has N@O and C–N bond lengths
of 1.241(7) and 1.421(7) Å, respectively, and its C–N@O bond angle
is 114.8(5)° [20]. All of these features imply that the NO substitu-
X
X = pi-donor
atom
C1
C2Ph
Fig. 1. Orbitals involved in the lengthening of the C1–C2 distance of PhCb°X.

M.A. Fox et al. / Polyhedron 28 (2009) 789–795
791
Table 1
Selected bond lengths (Å) and angles (°) for (MeCb°)2NH, (PhCb°)2NH and
[(PhCb°)2N]ꢀ (averages for equivalent bonds).
(MeCb°)2NH (2)
(PhCb°)2NH (3)
(PhCb°)2Nꢀ (4)
C(1)–N(1)
C(1)–C(2)
C(2)–C(13)
C(1)–N(1)–C(10)
N(14)–C(1)–C(2)
C(13)–C(2)–C(1)
1.410(4)
1.750(4)
1.512(4)
131.1(2)
117.2(2)
117.0(2)
1.405(2)
1.798(3)
1.504(3)
132.0(2)
117.09(14)
117.94(14)
1.350(4)
1.987(3)
1.491(4)
127.0(2)
118.8(2)
116.7(2)
The molecular structures of the secondary amines, (MeCb°)2NH
and (PhCb°)2NH, and of the anion (PhCb°)2Nꢀ of the salt [K(18-
crown-6)]+[(PhCb°)2N]ꢀ ꢂ 0.5(MeOC2H4)2O, are shown in Fig. 3. Se-
lected bond distances and angles are given in Table 1. There are
small differences between the lengths of corresponding bonds in
the two cages in each compound that are not regarded as signifi-
cant; average values for equivalent bonds are used in the discus-
sion where appropriate. The conformations of the two amines
and amide anion in their respective crystal structures are very sim-
ilar, and the trigonal nitrogen atoms of the two amines have a pla-
nar configuration. Fig. 4 shows the environment surrounding the
amide anion in the salt, including the cation and diglyme molecule.
Fig. 2. Molecular structure of PhCb°NO (1). Selected bond lengths (Å) and angles (°),
N(1)–O(1) 1.182(2), C(2)–C(13) 1.510(2), C(2)–C(1)–N(1) 112.1(2), C(13)–C(2)–C(1)
120.3(2). Displacement ellipsoids are drawn at the 50% probability level.
ent is acting as a one-electron ligand to the cage even though its
orientation aligns the nitrogen lone pair sp2 AO in the same plane
as (though divergent from) the C1 p–AO involved in C1–C2
r-
bonding.
a
b
c
Fig. 3. Molecular structures of the dicarboranyl amines, (a) (MeCb°)2NH (2) and (b) (PhCb°)2NH (3), and (c) the (PhCb°)2Nꢀ anion of the salt [K(18-crown-
6)][(PhCb°)2N] ꢂ 0.5(MeOC2H4)2O (4).

792
M.A. Fox et al. / Polyhedron 28 (2009) 789–795
Fig. 4. Crystal structure of the salt [K(18-crown-6)][(PhCb°)2N]ꢂ0.5(MeOC2H4)2O (4) showing interactions between the cation and anion and between cation and solvent.
Selected distances in Å, B(8). . ..K 3.53, B(7). . ..K 3.85, B(12). . .K 3.74, O(1). . .K 2.756(4). Both disorder components are shown for the solvent molecule. H atoms have been
omitted except for those involved in the cation-anion interactions.
The potassium cation effectively caps a triangular face of one of the
two cages (a face remote from the two cage carbon atoms) in a
manner common in potassium-18-crown-6 salts of carborane an-
ions [21]. The diglyme molecule, with its central oxygen atom
O(2) disordered over two sites in the crystal structure, is coordi-
nated through its outer oxygen atoms to two cations.
The structures of the amines and amide anion differ from that of
the nitroso derivative PhCb°NO in showing clear evidence, in their
conformations, bond distances and angles, of significant exo-N@C
Involvement of the tangentially orientated p-AO at C1 in the X–
C1–C2 plane as the acceptor orbital for dative exo- -bonding from
nitrogen reduces the C1–C2 -bonding contribution to the cage
p
r
bonding orbital, and so lengthens the cage C–C bond (Fig. 1). The
effect is most marked in the amide anion (PhCb°)2Nꢀ, which has
C–C bonds of length 1.980(3) and 1.995(3) Å, effectively the same
length as in the anion [PhCb°O]ꢀ (2.001(3) and 2.065(7) Å) [6,9],
even though one nitrogen lone pair is shared between two cages.
In the amines (RCb°)2NH, the cage C–C bonds, 1.748(4) and
1.752(4) Å when R = Me and 1.794(3) and 1.799(3) Å when
R = Ph, are understandably shorter than those in the amide. The
difference of 0.05 Å between the two amines can be attributed to
dative
p-bonding from one nitrogen p-AO to both cages, which
show concomitant distortion (C(1)–C(2) bond lengthening). The
features that lead us to this conclusion are as follows (see Table 1).
The CNC angle in the phenyl amine (PhCb°)2NH is 132° and falls
to 127° in the amide anion [(PhCb°)2N]ꢀ, showing that the nitrogen
atom remains sp2 hybridised on deprotonation, the ‘lone pair’ hav-
ing greater repulsive effect than the NH bond which it replaces. The
CNC angles are perhaps slightly affected by the repulsion between
the two cages since the closest HꢂꢂꢂH separation between the cages
is ca. 2.47 Å, longer than corresponding distances of 2.27 and 2.25
found in the related biscarboranyl sulfide, (PhCb°)2S, and sulfoxide,
(PhCb°)2SO, respectively [8]. The CNC angle in diphenylamine
Ph2NH is 129° and falls to 121° in the Ph2Nꢀ anion [22,23].
In all three compounds the radial planes of the C–C bonds of
both cages, i.e. their CCN planes, are roughly perpendicular to the
trigonal nitrogen CNC plane so that the nitrogen p-orbital contain-
ing an electron pair is aligned with the cage C–C bonds. The closely
similar conformation of the three compounds effectively precludes
the possibility that this conformation is the fortuitous result of
crystal packing forces, since these are unlikely to have the same ef-
fect in the crystal structures of the amines, still less in that of the
ionic amide with large counter-ions.
a p-bonding contribution from the phenyl group [5].
3. Conclusions
This paper reports improved low-temperature procedures by
which reactions between lithio-carboranes and nitrosyl chloride
can be used as preparative routes to two important categories of
carborane derivatives, viz. nitroso derivatives RCb°NO, and dicarb-
oranylamines (RCb°)2NH, the former using mixtures of diethyl
ether and pentane as solvent and the latter using 1,2-dimethoxy-
ethane instead of pentane in the solvent mix. Deprotonation of
the amines (RCb°)2NH in toluene by potassium t-butoxide in the
presence of the macrocyclic ether 18-crown-6 afforded the air-
and moisture-stable salts [K(18-crown-6)]+ [(RCb°)2N]ꢀ.
The crystal structures of PhCb°NO, (PhCb°)2NH, (MeCb°)2NH
and [K(18-crown-6)]+[(PhCb°)2N]ꢀ ꢂ 0.5(MeOC2H4)2O have been
determined, and shown to shed further useful light on the capacity
of the ortho-carborane cage to function as a sensitive probe of the
p
-donor characteristics of cage C-attached ligands. The cage C1–C2
and the exo-C–N bond lengths and the ligand orientations in these
compounds reinforce the generalisation that -donor ligands at-
tached to an ortho-carborane carbon atom adopt an orientation
that involves in exo- -bonding the p-orbital on carbon that other-
We conclude that both carborane cages in each amine
(RCb°)2NH, and in the anion (PhCb°)2Nꢀ, are oriented to allow da-
p
tive
plane into the p-orbital on C1 that is aligned for cage C1–C2
bonding (Fig. 1). Evidence for that exo-C@N -bonding is provided
p-bonding from the p-orbital perpendicular to the C–N–C
r
-
p
p
wise participates in cage C1–C2
r-bonding.
by the C–N distances in these systems (Table 1), which at 1.404(2)–
1.410(4) Å in the amines (RCb°)2NH and 1.354(4)–1.355(4) Å in the
amide (PhCb°)2Nꢀ are far shorter than would be appropriate for
single C–N bonds between three- or even two-coordinate nitrogen
and six-coordinate carbon atoms. The shorter C@N bond in the
amide (PhCb°)2Nꢀ is intelligible in that deprotonation of the amine
4. Experimental
All air-sensitive manipulations were carried out under dry, oxy-
gen-free N2. Stirring refers to use of a magnetic stirrer. Pentane was
distilled over sodium. 1,2-Dimethoxyethane was dried by reflux
and distillation over potassium; ether refers to diethyl ether dried,
where appropriate, over sodium. Ether solutions were dried over
magnesium sulfate and evaporated near room temperature. 1-
(PhCb°)2NH increases the
p-donor capacity of the nitrogen atom.
The average C–N distances in diphenylamine Ph2NH and in the
diphenylamide Ph2Nꢀ anion are 1.400(4) and 1.370(5) Å, respec-
tively [22,23].

M.A. Fox et al. / Polyhedron 28 (2009) 789–795
793
Methyl-ortho-carborane [24] and 1-phenyl-ortho-carborane [25]
were prepared by literature methods and dried by sublimation at
0.01 mm Hg. Commercial nitrosyl chloride (BDH Chemicals Ltd.)
was used as received.
Melting points were measured in capillary tubes with an Elec-
trothermal 9200 heating block. Infrared spectra were recorded
from KBr discs on Perkin–Elmer 1600 series FTIR or Perkin–Elmer
1720ꢃ FTIR spectrometers and ultraviolet spectra with a Shimadzu
UV 1201. Elemental carbon, hydrogen and nitrogen analyses were
performed using Exeter Analytical CE-440 or Carlo Erba Strument-
azione EA Model 1106 instruments. Mass spectra (MS) were re-
2H, H7, 11), 2.50 (s, 1H, H12), 2.41 (s, 2H, H3,6), 2.19 (s, 3H,
H8,9,10), 1.88 (s, 2H, H4,5); 11B{1H} NMR (CDCl3) d: ꢀ2.4 (s, 1B,
B12), ꢀ6.6 (s, 1B, B9), ꢀ10.2 (s, 4B, B7,8,10,11), ꢀ11.0 (s, 2B,
B3,6), ꢀ12.6 (s, 2B, B4,5); 13C{1H} NMR (CDCl3) d: 111.4 (s, carbo-
rane C1), 73.3 (s, carborane C2), 23.0 (s, CH3).
1-Phenyl-2-nitroso-ortho-carborane (1) (crystals for X-ray dif-
fraction were obtained by slow vacuum sublimation 40°C/
0.01 mm Hg): Found: C, 38.9; H, 6.0; N, 5.2; C8H15B10NO requires:
C, 38.5; H, 6.1; N, 5.6%; MS (EI+, m/z) [M]+ 245–253; 249 (100); IR
(KBr disc, cmꢀ1) 3098, 3072 (Ar CH); 2577br (BH); 1560s (NO),
1493m, 1446m; 1340w; 1270w, 1059s; 897; 867m; 753s; 724w
(carborane skeleton), 688.8s; 1H{11B} NMR (CDCl3) d: 7.83 (d,
corded on
a VG Micromass 7070E instrument under E.I
conditions (EI) at 70 eV. Values of M show the isotope range 10Bn
to 11Bn including a 13C contribution if observed. NMR spectra were
measured using Varian Unity-300 (1H, 11B, 13C), Bruker AM250 (1H,
13C), Bruker Avance 400 (1H, 11B, 13C) and/or Varian Inova 500 (1H,
11B) instruments. All chemical shifts are reported in d (ppm) and
coupling constants in Hz. 1H NMR spectra were referenced to resid-
ual protio impurity in the solvent (CDCl3, 7.26 ppm; CD3CN,
1.85 ppm). 13C NMR spectra were referenced to the solvent reso-
nance (CDCl3, 77.0 ppm; CD3CN, 118.3 ppm). 11B NMR spectra
were referenced externally to Et2O ꢂ BF3, d = 0.0 ppm. Peak assign-
ments of cage boron and hydrogen atoms were determined where
possible with the aid of 2D 11B{1H}–11B{1H} COSY, selective 1H{11B}
and 1H{11B}–11B{1H} correlation spectra.
3JHH 8 Hz, 2H, ortho-phenyl), 7.49 (t, JHH 7.4 Hz, 1H, para-phenyl),
3
7.42 (t, 3JHH 7.8 Hz, 2H, meta-phenyl), 2.99 (s, 2H, H4,5), 2.67 (s, 3H,
H7,11,12), 2.33 (s, 3H, H8,9,10), 2.09 (s, 2H, H3,6). 11B{1H} NMR
(CDCl3) d: ꢀ2.0 (s, 1B, B12), ꢀ4.4 (s, 1B, B9), ꢀ9.8 (s, 2B, B7, 11),
ꢀ10.4 (s, 2B, B8, 10), ꢀ12.6 (s, 2B, B3, 4, 5, 6); 13C NMR (CDCl3)
1
2
d: 131.1 (d of t, JCH 159 Hz, JCH 7 Hz, m-C phenyl), 130.1 (d of t,
2
1
1JCH 161 Hz, JCH 7 Hz, m-C phenyl), 128.9 (d of d, JCH 162 Hz,
2JCH 8 Hz, o-C phenyl), 114.1 (carborane C1), 81.3 (carborane C2).
Bis(2-methyl-1-ortho-carboranyl)amine (2) gave colourless
crystals from hexane, m.p. 205.5–207 °C. Found: C, 21.4; H, 8.3;
N, 4.0. C6H27B20N requires: C, 21.9; H, 8.2; N, 4.3. MS (EI+, m/z)
[M]+ 245–253; 249(100); IR mmax (KBr) [cmꢀ1]: 3389 (NH); 2963,
2943 (methyl CH); 2680w, 2670w, 2606, 2573, 2541 (BH); 1496;
1443, 1383 (methyl CH); 1297 (CN); 1261; 1084; 1029; 800; 727
(carborane skeleton); 475; 416; 1H{11B} NMR (CDCl3), d: 4.84
(br.s, 1H, NH), 2.51 (s, 4H, H4,5), 2.41 (s, 4H, H3,6), 2.30 (s, 4H,
H7,11), 2.28 (s, 2H, H9), 2.22 (s, 2H, H12), 2.10 (s, 6H, CH3), 2.09
(s, 4H, H8,10); 11B{1H} NMR (CDCl3), d: ꢀ5.2 (2B, B9), ꢀ6.4 (2B,
B12), ꢀ10.3 (12B), ꢀ11.7 (4B, B8,10); 13C{1H} NMR (CDCl3), d:
90.9 (C1), 81.8 (C2), 22.1 (CH3). 1H{11B} NMR (CD3CN), d: 6.76
(br.s, 1H, NH), 2.58 (s, 4H, BH), 2.38 (s, 4H, BH), 2.35 (s, 6H, CH3),
2.29 (s, 4H, BH), 2.16 (s, 4H), 2.02 (s, 4H); 11B{1H} NMR (CD3CN),
d: ꢀ6.1, ꢀ7.0 (4B, B9,12), ꢀ10.8 (12B), ꢀ12.3 (4B); 13C{1H} NMR
(CD3CN), d: 93.3 (C1), 83.7 (C2), 22.2 (CH3).
5. Reaction of 1-methyl- and 1-phenyl-ortho-carboranes with
nitrosyl chloride
Nitrosyl chloride (5 ml) was condensed into a calibrated tube
cooled to ca. ꢀ25 °C, transferred under reduced pressure into the
co-solvent, ether or pentane (20 ml), at ca. ꢀ40 °C and the flask
was brought to atmospheric pressure with dinitrogen. A solution
of the lithio-carborane, prepared by slowly adding butyllithium
(6.6 ml, 1.6 M in hexane; 10.5 mmol) to the substituted ortho-car-
borane (10.0 mmol) in 1,2-dimethoxyethane or pentane, (20 ml),
was added dropwise with stirring at ꢀ40 °C (acetone/CO2),
ꢀ78 °C (acetone/CO2) or ꢀ117 °C (ethanol/N2) during ca. 35 min
and the mixture was allowed to warm to room temperature during
ca. 3 h. The solution was added in small portions to potassium
hydrogen carbonate (40 g) in water (110 ml), the organic layer
was diluted with ether, washed with water, dried and evaporated.
The blue nitroso-compounds were separated from the resulting
semi-solid by sublimation at ca. 70 °C/0.01 mm Hg and the residue
was triturated with methanol (12 ml; the nitroso-carboranes are
unstable to this solvent) to give the amines as white crystalline
powders. The yields of nitroso-compounds and amines obtained
using various bath temperatures and co-solvents are summarised
in Scheme 1.
1-Methyl-2-nitroso-ortho-carborane formed volatile blue crys-
tals identical with a sample prepared under the literature condi-
tions; attempts to measure the melting point of this compound
in open capillary tubes caused evaporation of the sample, leaving
a colourless residue which melted sharply at the temperature,
208–210 °C, given in the literature [3] for the nitroso-derivative.
A DSC scan showed a broad exotherm at 230 °C and the residue
was shown by IR to consist of boric acid and closo-carborane prod-
ucts. 1-Phenyl-2-nitroso-ortho-carborane gave blue crystals m.p.
43–44 °C (literature [2] 54–55 °C).
Bis(2-phenyl-1-ortho-carboranyl) amine (3) formed colourless
rhombic crystals from xylene m.p. 242–244.5 °C, literature [2]
239–241 °C. Found: C, 41.8; H, 7.0; N, 2.9; C16H31B20N requires:
C, 42.4; H, 6.9; N, 3.1%. MS (EI+, m/z) 440–458; 454(100), IR (KBr
disc, cmꢀ1) : 3391 (NH); 3062w, 2989w (Aryl CH); 2654, 2633,
2602s, 2584 (BH); 1508 (NH); 1495, 1447 (Ar. skeleton); 1306s
(CN); 1069; 1039; 1004; 798; 755, 689 (C6H5); 729 (carborane
skeleton). 1H{11B} NMR (CDCl3), d: 7.57 (d, 4H, ortho phenyl CH),
7.52 (t, 2H, para phenyl CH), 7.52 (t, 4H, meta phenyl CH); 4.46
(m, 1H, NH); 2.71 (s, 4H, H3,6), 2.30 (s, 4H, H4,5), 2.28 (s, 2H,
H12), 2.21 (s, 2H, H9), 2.03 (s, 8H, H7,8,10,11); 11B{1H} NMR
(CDCl3), d: ꢀ3.6 (s, 2B, B9), ꢀ5.8 (s, 2B, B12), ꢀ10.4 (8B, B3,4,5,6),
ꢀ12.2 (8B, B7,8,10,11); 13C NMR (CDCl3), d: 131.3 (C6H5 para),
129.6 (C6H5 ipso); 131.7, 128.9 (C6H5 ortho and meta), 94.4 (C2 or
C1), 90.3 (C1 or C2). 1H{11B} NMR (CD3CN), d: 7.73 (d, 4H, ortho
phenyl CH), 7.59 (t, 2H, para phenyl CH), 7.47 (t, 4H, meta phenyl
CH); 6.55 (m, 1H, NH); 3.00 (s, 4H, H3,6), 2.20 (s, 8H, BH), 1.90
(s, 4H, BH), 1.77 (s, 4H, BH); 11B{1H} NMR (CD3CN), d: ꢀ4.2 (s,
2B, B9), ꢀ6.7 (s, 2B, B12), ꢀ10.7 (8B), ꢀ12.1 (4B), ꢀ13.1 (4B).
6. Potassium-18-crown-6 salt of bis(2-phenyl-1-ortho-
carboranyl)amide
1-Methyl-2-nitroso-ortho-carborane: Found: C, 19.2, H, 8.0, N,
7.0 C3H15B10NO requires C, 19.2, H, 8.0, N, 7.4; MS (EI+, m/z)[M]+
186–190; 188 (100); IR (KBr disc, cmꢀ1) 3106w, 3063w, 2948w
(methyl CH); 2599s, br (BH); 1567s (NO); 1445; 1389; 1111;
1046; 1022; 948; 921; 892; 721m (carborane skeleton); 697w,
640w, 540w; 1H{11B} NMR (CDCl3) d: 2.74 (s, 3H, CH3), d: 2.53 (s,
Bis(2-phenyl-1-ortho-carboranyl)amine (255 mg, 5.6 mmol) in
warm (ca. 55 °C) toluene (10 ml) was added under nitrogen to a
solution of potassium t-butoxide (160 mg, 13.4 mmol) and 18-
crown-6 (390 mg, 14.5 mmol) in toluene (5 ml). The mixture was
heated briefly (ca. 90 °C, 1 min) and the blue–green oil which sep-
arated initially formed a pale yellow granular solid within a few

794
M.A. Fox et al. / Polyhedron 28 (2009) 789–795
seconds. After standing overnight at room temperature the solid
was washed with toluene to give the amide salt as a pale yellow
powder (325 mg, 77%). Found: C, 44.2; H, 7.3; N, 1.7.
C28H54B20KO6N requires: C, 44.5; H, 7.2; N, 1.9%. Recrystallisation
from 1,2-dichlorobenzene furnished yellow rectangular prisms,
m.p. 254–257 °C, whose colour deepens reversibly on warming
and which gave the same analysis as before. The crystalline amide
is unchanged by exposure to air or contact with water but rapidly
forms the parent amine in contact with ethanoic acid. Single crys-
tals of the hemisolvate (4) suitable for X-ray diffraction were
grown from a solution in diethyleneglycol dimethyl ether into
which cyclohexane was diffused slowly from an upper layer.
M.p. 254–257 °C; MS (EI+, m/z) 440–457; 453(100, M+), MS (CI+,
NH3, m/z) 282 (18-C-6+NH4+); IR (KBr disc, cmꢀ1): 3062w (Ar. CH);
2899, 1472, 1351, 1108s, 966, 838 (18-crown-6); 2575s, 2555s
(BH); 1495, 1447 (Ar. skeleton); 1395s, br (CN); 1284; 1248;
1072; 1039, 1004w; 775, 883w, 806w, 775w; 745, 691 (C6H5
o.o.p.); 732w (carborane skeleton); 643w; 570w; 525. 1H{11B}
NMR (CD3CN), d: 7.36 (d, 4H, ortho phenyl CH), 7.23 (t, 2H, para
phenyl CH), 7.17 (t, 4H, meta phenyl CH); 3.47 (s, 24H, 18-C-6);
2.68 (s, 4H, H4,5), 2.13 (s, 10H, H3,6,7,9,11), 1.72 (s, 2H, H12),
1.58 (s, 4H, H8,10). 11B{1H} NMR (CD3CN), d: ꢀ4.4 (1B, B9), ꢀ8.3
(2B, B3,6); ꢀ10.5 (2B, B7,11); ꢀ12.6 (3B, B4,5,12); ꢀ16.3 (2B,
B8,10). 13C{1H} NMR (CD3CN), d: 137.7 (C6H5 ipso); 129.3 (C6H5
para); 131.1, 128.8 (C6H5 ortho and meta); 129.5 (C1), 89.8 (C2);
13C{1H} NMR (CD3CN), d: 120.0 (C1), 87.0 (C2), 70.9 (18-C-6),
22.2 (CH3).
8. Crystal structure determinations
Crystals of the compounds 1–4 were examined on Bruker SMART
(1, 2) and Stoe STADI4 (3, 4) diffractometers with Mo K
a radiation
(k = 0.71069 Å; Cu K with k = 1.54184 Å for 3) at 160 K (180 K
a
for 4). Crystal data and other information are given in Table 2. Stan-
dard methods and software were employed, including refinement
on all F2 values [26]; no absorption corrections were applied, and
no structural disorder was found.
Acknowledgements
We thank EPSRC for funding (WC, MAF, JAHM, RJP).
Appendix A. Supplementary data
CCDC 690385, 690386, 690387 and 690388 contain the supple-
mentary crystallographic data for 1, 2, 3 and 4. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk.
70.9 (18-C-6). kmax (THF, 20 °C): 317 nm (loge, 3.92).
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2008.12.014.
7. Potassium-18-crown-6 salt of bis(2-methyl-1-ortho-
carboranyl)amide
References
By a similar procedure as above with bis(2-methyl-1-ortho-
carboranyl)amine as the starting carborane, colourless crystals of
the desired salt (86% yield) were obtained from toluene solution.
M.p. 209–210 °C; Found: C, 34.3; H, 8.1; N, 1.8. C18H50B20KO6 N re-
quires: C, 34.2; H, 8.0; N, 2.2%. MS (ESꢀ, m/z) 323–332; 328 (100,
Mꢀ), MS (ES+, m/z) 303 (K18-C-6+); IR (KBr disc, cmꢀ1): 2914,
1471, 1350, 1110s, 967, 839 (18-crown-6); 2560s (BH); 1413s, br
(CN); 1369; 1283; 1246; 1072; 1034, 730w (carborane skeleton);
695w; 419. 1H{11B} NMR (CD3CN), d: 3.47 (s, 24H, 18-C-6); 2.30
(s, 4H, H4,5), 2.15 (s, 4H, H3,6), 1.98 (s, 4H, H7,11), 1.85 (s, 6H,
CH3), 1.82 (s, 2H, H9), 1.59 (s, 4H, H8,10), 1.53 (s, 1H, H12).
11B{1H} NMR (CD3CN), d: ꢀ7.5 (1B, B9), ꢀ8.8 (2B, B3,6); ꢀ11.3
(2B, B7,11); ꢀ12.3 (2B, B4,5); ꢀ13.7 (1B, B12), ꢀ15.4 (2B, B8,10).
[1] J.M. Kauffman, J. Green, M.S. Cohen, M.M. Fein, E.L. Cottrill, J. Am. Chem. Soc. 86
(1964) 4210;
L.I. Zakharkin, V.N. Kalinin, G.G. Zhigareva, Izv. Akad. Nauk. SSSR Ser. Khim.
(1970) 912.
[2] L.I. Zakharkin, V.N. Kalinin, Doklady Akad. Nauk. SSSR 164 (1965) 577.
[3] L.I. Zakharkin, G.G. Zhigareva, Zh. Obshch. Khim. 45 (1975) 1293.
[4] W. Clegg, H.M. Colquhoun, R. Coult, M.A. Fox, W.R. Gill, P.L. Herbertson, J.A.H.
MacBride, K. Wade, Spec. Publ. R. Soc. Chem. 143 (1994) 232;
K. Wade, M.G. Davidson, M.A. Fox, W.R. Gill, T.G. Hibbert, J.A.H. MacBride,
Phosphorus, Sulfur and Silicon 125 (1997) 73;
L.A. Boyd, H.M. Colquhoun, M.G. Davidson, M.A. Fox, W.R. Gill, P.L. Herbertson,
T.G. Hibbert, J.A.H. MacBride, R.J. Peace, G.P. Rivers, K. Wade, Spec. Publ. R. Soc.
Chem. 201 (1997) 289;
M.A. Fox, R.J. Peace, J.A.H. MacBride, K. Wade, J. Chem. Soc., Dalton Trans.
(1998) 401;
W. Clegg, R. Coult, M.A. Fox, W.R. Gill, J.A.H. MacBride, K. Wade, Polyhedron 12
(1993) 2711.
[5] E.S. Alekseyeva, M.A. Fox, J.A.K. Howard, J.A.H. MacBride, K. Wade, Appl.
Organomet. Chem. 17 (2003) 499.
[6] D.A. Brown, W. Clegg, H.M. Colquhoun, J.A. Daniels, I.R. Stephenson, K. Wade, J.
Chem. Soc., Chem. Commun. (1987) 889.
Table 2
Crystal data and refinement information for compounds 1–4.
[7] R. Coult, M.A. Fox, W.R. Gill, K. Wade, W. Clegg, Polyhedron 11 (1992) 2717.
[8] A.S. Batsanov, W. Clegg, R.C.B. Copley, M.A. Fox, W.R. Gill, R.S. Grimditch, T.G.
Hibbert, J.A.K. Howard, J.A.H. MacBride, K. Wade, Polyhedron 25 (2006) 300.
[9] L.A. Boyd, W. Clegg, R.C.B. Copley, M.G. Davidson, M.A. Fox, T.G. Hibbert, J.A.K.
Howard, A. Mackinnon, R.J. Peace, K. Wade, Dalton Trans. (2004) 2786.
[10] J.M. Oliva, N.L. Allan, P.v.R. Schleyer, C. Viñas, F. Teixidor, J. Am. Chem. Soc. 127
(2005) 13547.
Compound
1
2
3
4
Formula
M
Crystal system
Space group
a (Å)
C8H15B10NO C6H27B20
249.3
N
C16H31B20
453.6
N
C31H61B20KNO7.5
823.1
329.5
monoclinic
P21/c
10.942(2)
8.4999(12)
15.068(2)
monoclinic monoclinic triclinic
P21/n
11.302(6)
12.705(7)
14.167(7)
P21/n
P1
[11] R. Kivekäs, R. Sillanpää, F. Teixidor, C. Viñas, R. Nuñez, Acta Crystallogr., Sect. C
50 (1994) 2027;
10.560(3)
13.135(4)
18.695(6)
10.370(3)
14.629(4)
15.790(4)
101.80(3)
92.53(2)
102.81(2)
b (Å)
c (Å)
R. Kivekäs, R. Sillanpää, F. Teixidor, C. Viñas, R. Nuñez, Acta Crystallogr., Sect. C
51 (1995) 1864;
R. Kivekäs, F. Teixidor, C. Viñas, R. Nuñez, Acta Crystallogr., Sect. C 51 (1995)
1868;
J.M. Oliva, C. Viñas, J. Mol. Struct. 55 (2000) 33;
J. Llop, C. Viñas, J.M. Oliva, F. Teixidor, M.A. Flores, R. Kivekäs, R. Sillanpää, J.
Organomet. Chem. 657 (2002) 232.
a
(°)
b (°)
102.986(4)
107.03(2)
97.48(3)
c
(°)
V (Å3)
1365.6(3)
4
6842
2392
0.038
182
0.049
0.143
0.25, ꢀ0.23
1945(2)
4
7511
2784
0.055
251
0.076
0.168
0.22,
ꢀ0.20
2571.0(14) 2276.3(11)
4
Z
2
Data collected
Unique data
Rint
4420
4356
0.030
339
0.059
0.165
5825
5825
[12] T.L. Heying, J.W. Ager Jr., S.L. Clark, R.P. Alexander, S. Papetti, J.A. Reid, S.I. Trotz,
Inorg. Chem. 2 (1963) 1097;
L.I. Zakharkin, V.N. Kalinin, Zh. Obshch. Khim. 35 (1965) 1882.
[13] S.B. Kahl, R.A. Kasar, J. Am. Chem. Soc. 118 (1996) 1223;
Y. Endo, T. Iijima, Y. Yamakoshi, M. Yamaguchi, H. Fukasawa, K. Shudo, J. Med.
Chem. 42 (1999) 1501;
Refined parameters
551
0.063
0.196
R (on F, F2 > 2
r
)
Rw (on F2, all data)
R.A. Kasar, G.M. Knudsen, S.B. Kahl, Inorg. Chem. 38 (1999) 2936;
M. Scobie, M.D. Threadgill, J. Chem. Soc., Perkin Trans. I (1994) 2059;
T. Totani, K. Aono, K. Yamamoto, K. Tawara, J. Med. Chem. 24 (1981) 1492.
Min., max. electron
0.30, ꢀ0.28 0.76, ꢀ0.35
density (e Åꢀ3
)

M.A. Fox et al. / Polyhedron 28 (2009) 789–795
795
[14] V.V. Korshak, N.I. Bekasova, N.G. Komarova, L.G. Komarova, V.V. Vagin, Acta
[21] K. Chui, H.-W. Li, Z. Xie, Organometallics 19 (2000) 5447;
G. Zi, H.-W. Li, Z. Xie, Organometallics 21 (2002) 5415;
Polym. 40 (1989) 439;
A. Rusanov, L. Komarova, G. Kats, M. Prigozhina, Int. J. Polym. Mater. 25 (1994)
117.
T. Marx, B. Mosel, I. Pantenburg, S. Hagen, H. Schulze, L. Wesemann, Chem. Eur.
J. 9 (2003) 4472;
[15] C.E. Housecroft, A.G. Sharpe, Inorganic Chemistry, 3rd Ed. Pearson, 2008, p.
653–654.
M.A. Fox, A.E. Goeta, A.K. Hughes, A.L. Johnson, J. Chem. Soc., Dalton Trans.
(2002) 2132;
[16] W.L. Waters, P.G. Marsh, J. Org. Chem. 40 (1975) 3344;
P. Buck, G. Kobrich, Tetrahedron Lett. (1967) 1563;
H. Gilman, J. Am. Chem. Soc. 49 (1927) 1052;
E. Muller, H. Metzer, Chem. Ber. 89 (1956) 396;
W.L. Waters, P.G. Marsh, J. Org. Chem. 40 (1975) 3349.
[17] R.L. Thomas, G.M. Rosair, A.J. Welch, Acta Crystallogr., Sect. C 52 (1996) 1024.
[18] I.V. Glukhov, K.A. Lyssenko, A.A. Korlyukov, M.Y. Antipin, Russ. Chem. Bull. 54
(2005) 547.
R. Littger, U. Englich, J.T. Spencer, Inorg. Chem. 36 (1997) 6434;
M.-S. Cheung, H.-S. Chen, Z. Xie, Organometallics 23 (2004) 517.
[22] M.A. Rodriguez, S.D. Bunge, Acta Crystallogr., Sect. E 59 (2003) o1123.
[23] M.G. Davidson, S. Lamb, Polyhedron 16 (1997) 4393;
P.B. Hitchcock, A.V. Khvostov, M.F. Lappert, A.V. Protchenko, J. Organomet.
Chem. 647 (2002) 198.
[24] M.F. Hawthorne, T.D. Andrews, P.M. Garrett, E.P. Olsen, M. Reintjes, F.N. Tebbe,
L.F. Warren, P.A. Wegner, D.C. Young, Inorg. Synth. 10 (1967) 91.
[25] P.T. Brain, J. Cowie, D.J. Donohoe, D. Hnyk, D.W.H. Rankin, D. Reed, B.D. Reid,
H.E. Robertson, A.J. Welch, M. Hofmann, P.v.R. Schleyer, Inorg. Chem. 35 (1996)
1701.
[19] M. Tsuji, J. Org. Chem. 69 (2004) 4063;
I.V. Glukhov, K.A. Lyssenko, A.A. Korlyukov, M.Y. Antipin, Faraday Discuss. 135
(2007) 203;
I.V. Glukhov, M.Y. Antipin, K.A. Lyssenko, Eur. J. Inorg. Chem. 7 (2004) 1379.
[20] M. Gdaniec, T. Bytner, M. Szyrszyng, T. Połonski, J. Inclusion Phenom.
Macrocyclic Chem. 40 (2001) 243.
[26] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.