Synthesis and characterisation of the halogenated azanonaboranes [(iPrNH2)B8H10XNHiPr] (X = Cl, Br, I) and their unexpected hydrolysis to hypho-[B5H10(μ-NHiPr)]

Article abstract of DOI:10.1016/S0020-1693(02)00701-6

Treatment of [(ⁱPrNH₂)B₈H₁₁NHⁱPr] with elemental halogen affords the 8-exo-halogen-substituted derivatives [(ⁱPrNH₂)B₈H₁₀XNHⁱPr] (X=Cl, Br, I). T

Full text of DOI:10.1016/S0020-1693(02)00701-6

Inorganica Chimica Acta 332 (2002) 181–185
www.elsevier.com/locate/ica
Note
Synthesis and characterisation of the halogenated azanonaboranes
i
i
[
( PrNH )B H XNH Pr] (X=Cl, Br, I) and their unexpected
2
8
10
i
hydrolysis to hypho-[B H (m-NH Pr)]
5
10
a
a
b
a,
Claudia Bauer , Detlef Gabel , Thomas D. McGrath , Udo D o¨ rfler *
a
Department of Chemistry, Uni6ersity of Bremen, P.O. Box 330440, 28334 Bremen, Germany
b
Department of Chemistry, Heriot-Watt Uni6ersity, Edinburgh EH14 4AS, UK
Received 9 October 2001; accepted 17 December 2001
Abstract
i
i
Treatment of [( PrNH )B H NH Pr] with elemental halogen affords the 8-exo-halogen-substituted derivatives
2
8
11
i
i
[
( PrNH )B H XNH Pr] (X=Cl, Br, I). The structures of all three compounds are confirmed by NMR spectroscopy and mass
2 8 10
spectrometry, and (for X=Br) by an X-ray diffraction study. The bromoazanonaborane undergoes hydrolytic decomposition to
i
the new five-vertex compound [B H (m-NH Pr)] of hypho-type structure. © 2002 Elsevier Science B.V. All rights reserved.
5
10
Keywords: Azanonaboranes; Halogenation; Hydrolysis; hypho-Clusters; Crystal structures
1. Introduction
2. Results and discussion
The eight-boron atom species [(EtNH )B H NHEt]
1a) was first synthesised in 1962 [1], and was struc-
Chlorine-substituted 2 is formed by gentle passage of
a stream of chlorine through a CH Cl solution of 1b at
2
8
11
(
2
2
turally identified in 1963 [2]. It has a structure based on
an eight-vertex cluster of hypho-type character [3] bear-
ing two amine-derived residues: one amine ligand in an
exo terminal position, and one amino ligand in a bridg-
ing position (Scheme 1).
−78 °C, whilst treatment of the same solution at
It has been shown that members of this hypho-type
i
family [(RNH )B H NHR] [R=Et (1a), Pr (1b)] con-
2
8
11
stitute a good entry into azacarbaborane [4] and aza-
metallaborane chemistry [5]. In order to develop the
chemistry of azametallaboranes containing seven or
eight boron atoms we have become interested in the use
of compounds 1 as starting substrates. Here we report
the syntheses of halogen-substituted derivatives of the
i
i
azanonaborane [( PrNH )B H NH Pr] (1b) [6], which
2
8
11
were obtained in good yield from its reaction with
elemental chlorine, bromine or iodine, and the isolation
of an unexpected hypho-structured pentaborane which
is formed upon hydrolysis of these new haloboranes.
*
Corresponding author. Tel.: +49-421-218 2375; fax: +49-421-
2
0
18 2871.
Scheme 1.
E-mail address: doerfler@chemie.uni-bremen.de (U. D o¨ rfler).
020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(02)00701-6

1
82
C. Bauer et al. / Inorganica Chimica Acta 332 (2002) 181–185
Table 1
Selected NMR parameters for compounds 1b, 2–4
a
Position
1b
2
3
4
l(11B)
l( H)
1
l(11B)
l( H)
1
l(11B)
l( H)
1
l(11B)
l( H)
1
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
+1.6
−55.6
−21.5
−31.8
−11.1
−11.1
−33.6
−31.8
+2.53
−0.63
+1.29
+0.73
+2.53
+2.53
+0.73
−0.63
+2.6
−56.7
−24.3
−31.5
−10.1
−12.7
−33.3
−16.4
+2.69
−0.68
+0.74
+0.74
+2.33
+2.47
+1.02
+1.41 b
+3.4
−55.9
−23.8
−30.7
−10.7
−12.1
−32.1
−21.0
+2.92
−0.67
+0.72
+0.72
+2.46
+2.46
+1.08
+1.37 b
+4.7
−55.5
−24.1
−31.4
−11.1
−11.1
−31.4
−31.4
+3.28
−0.68
+0.70
+1.00
+2.60
+2.45
+1.30
+1.30
b
b
+
0.45
(
(
4,5)
6,7)
−2.09
−2.14
−1.68
−1.85
−2.16
−1.85
+4.24
+3.98
−1.81
−2.09
−1.73
−1.99
−1.74
+4.27
+4.02
c
d
e
f
g
l
N(5,6)
N(3)
−1.08
h
+4.03 i
j
+4.27 k
+3.95
+
4.03
a
In CDCl3 at 20 °C.
endo H atom.
{
b
c
d
e
f
iPrNH} substituent site.
CH at +52.8 (l ), +3.53 (l ); CH at +21.2 and +21.1 (l ), +1.40 (mean) (l ).
C
H
3
C
H
CH at +53.3 (l ), +2.50 (l ); CH at +21.7 (l ), +1.42 (mean) (l ).
C
H
3
C
H
CH at +53.3 (l ), +2.47 (l ); CH at +21.8 (l ), +1.43 (mean) (l ).
C
H
3
C
H
g
h
i
CH at +53.4 (l ), +2.55 (l ); CH at +22.0 (l ), +1.47 (mean) (l ).
C
H
3
C
H
i
{
PrNH } substituent site.
2
CH at +52.2 (l ), +3.43 (l ); CH at +21.2 and +21.1 (l ), +1.05 (mean) (l ).
C
H
3
C
H
j
CH at +51.3 (l ), +3.47 (l ); CH at +21.0 (l ), +1.04 (mean) (l ).
C
H
3
C
H
k
l
CH at +51.4 (l ), +3.44 (l ); CH at +21.1 (l ), +1.03 (mean) (l ).
C
H
3
C
H
CH at +51.5 (l ), +3.48 (l ); CH at +21.2 (l ), +1.06 (mean) (l ).
C
H
3
C
H
−
78 °C with 1 equiv. of bromine or iodine results in
There are no other significant patterns of changes in
chemical shift for the other boron atoms in 2–4 relative
to the starting material. Similar halogen-dependent
the formation of 3 and 4, respectively.
i
i
[
( PrNH )B H NH Pr]+X
2 8 11 2
11
changes in B chemical shift have been observed in
i
i
“
[( PrNH )B H XNH Pr]+HX (X=Cl, Br, I)
other boranes (for example, B H [7]). It was not
2
8
10
10 14
possible to determine by NMR spectroscopy whether
the exo or the endo hydrogen atom at B(8) had been
replaced by halogen. It is known that these H atoms
All three halogen-substituted azanonaboranes are ob-
tained as colourless solids. Reaction of 1b with an
excess of bromine yields a mixture of several com-
pounds including monosubstituted 3 (as observed by
NMR spectroscopy). Separation of the mono- and ap-
parently disubstituted products by various methods was
unsuccessful.
1
resonate at l( H)= +0.45 (exo) and −0.63 (endo) in
1
b. In compounds 2–4 the chemical shifts of the re-
1
maining H atom at B(8) are l( H)= +1.41 (2), +1.37
3) and +1.30 (4). These values are also highly affected
(
1
1
1
by the presence of the halogen atom itself and hence the
position (exo or endo) could not be established by
NMR spectroscopy alone. Accordingly, a structural
study of the brominated derivative 3 was performed.
The structure obtained by X-ray diffraction crystallo-
graphy is shown in Fig. 1 and selected geometric
parameters are listed in Table 2.
The B and H NMR data for halogen-substituted
compounds 2–4 are summarised in Table 1, along with
the corresponding parameters for the starting material
1
b [6]. These data for compounds 2–4 were readily
assigned by one- and two-dimensional homo- and
hetero-nuclear correlation techniques and were consis-
tent with the molecular structure of 3 determined in the
X-ray work (see below). The influence of the halogen
atom on the basic shielding patterns of compounds 2–4
appears to be relatively localised. Compared to the
unsubstituted parent 1b there is a downfield shift of
5.4 ppm for the chlorine-substituted boron atom B(8)
in 2. Bromo- and iodo-substitution likewise produce
downfield shifts of 10.8 and 0.4 ppm, respectively.
Compound 3 is seen to retain the overall parent
hypho-type [(RNH )B H NHR] architecture, with one
2
8
11
H atom replaced by bromine. This bromine substituent
is confirmed to be bonded to B(8) and is found in an
exo position. The boron–bromine distance B(8)ꢀBr(1)
1
in 3 is 2.043(8) A
distance in, for example, [MeNB H Br] (1.949(9) A
,
, significantly longer than the BꢀBr
,
)
11
11

C. Bauer et al. / Inorganica Chimica Acta 332 (2002) 181–185
183
[
8] and [(PMe Ph) B H Br] (1.986(4) A
,
) [9], but falls
,
results in cluster decomposition to form mainly boric
acid. Additionally we found a further product in small
yield, which could be identified by NMR spectroscopy
and mass spectrometry (see Section 3) as [B H (m-
2
2 10 11
within the expected ranges (ca. 1.88–2.06 A) [10], albeit
towards the longer end of this range. Interboron dis-
tances in compounds 1b [6] and 3 are essentially identi-
cal within experimental error, and the additional bromo
substituent does not significantly influence the gross
structure.
5
10
i
NH Pr)] (5a, Fig. 2). At first sight this product might be
regarded as a derivative of arachno-B H [11], with the
5
11
m-H atom bridging the B(3)ꢀB(4) connectivity (arachno-
i
Although the halogen-substituted derivatives 2–4 are
air-stable, treatment with water-contaminated solvents
B numbering) replaced by a {m-NH Pr} residue. How-
5
ever, the NHR group is not isoelectronic with an
electron-deficient bridging hydrogen but is instead an
electron-precise moiety which is formally attached to
two skeletal boron atoms via one normal covalent bond
and one dative bond allowing the NHR unit to provide
three electrons to the cage. Electron-counting consider-
ations then indicate 5a to be of hypho structure, derived
from hypothetical hypho-B H .
5
13
Two species related to 5a have been reported by
Gaines and co-workers [12]. The compounds [B H (m-
5
10
t
NHR)] (R= Bu, 5b; R=SiMe , 5c) were obtained
3
from the reaction of 2-Br-B H with the corresponding
5
8
RSiMe3 reagents in CH Cl . Although 5c was only
2
2
identified as a trace impurity, 5b was fully character-
ised, including an X-ray diffraction study.
1
1
1
The B and H NMR parameters for 5a were inde-
Fig. 1. An ORTEP drawing of the crystallographically determined
molecular structure of 3 with displacement ellipsoids shown at 50%
probability. For clarity hydrogen atoms are drawn as circles with an
arbitrary small radius.
pendently assigned fully by one- and two-dimensional
NMR experiments and its B NMR data correspond
closely with those reported [12] for 5b. It is of interest
to compare the B chemical shifts for 5a (and 5b) with
11
1
1
Table 2
−
the equivalent data for the hypho-[B H ] anion [13].
5
12
Selected interatomic distances (A) and interbond angles (°) for
,
i
i
The boron atoms of the latter resonate at l −57.6 (B1)
and −15.9 (B2–5), whereas for compounds 5 the peak
positions are around l −58 (B1), −16 (B2,3) and −9
[
( PrNH )B H BrNH Pr] (3) in 3·CHCl
2 8 10
3
Bond distances
Br(1)ꢀB(8)
B(3)ꢀB(4)
B(3)ꢀB(8)
B(5)ꢀB(6)
2.043(8)
B(7)ꢀB(8)
B(3)ꢀN(3)
B(5)ꢀN(56)
B(6)ꢀN(56)
1.879(11)
1.578(8)
1.561(10)
1.553(10)
(
B4,5). Thus it appears that it is those basal boron
1.879(10)
1.912(10)
1.943(12)
atoms B(4,5), distant from the m-NHR group in com-
pounds 5, which are most affected by the presence of
the amino moiety. This may indicate some more subtle
electronic interaction of the m-NHR unit with the clus-
ter than simple considerations would suggest.
Yields of 5a are low, and could not be improved even
by controlled hydrolysis of 3, thus rendering this route
not yet useful to species of this type. Preliminary studies
suggest that halogenated derivatives of other azanonab-
oranes 1 may also undergo similar degradation. How-
ever, as these findings show, the area of intermediate-
size azanonaboranes continues to reveal novel chem-
istry. We are further exploring this potential.
Bond angles
B(3)ꢀB(8)ꢀBr(1)
B(1)ꢀB(8)ꢀBr(1)
B(7)ꢀB(8)ꢀBr(1)
B(3)ꢀB(1)ꢀB(8)
B(8)ꢀB(1)ꢀB(7)
115.6(4)
111.7(5)
117.1(5)
68.5(5)
N(3)ꢀB(3)ꢀB(1)
N(3)ꢀB(3)ꢀB(4)
N(3)ꢀB(3)ꢀB(8)
B(1)ꢀB(3)ꢀB(8)
B(5)ꢀN(56)ꢀB(6)
112.4(5)
117.4(5)
115.3(5)
55.7(4)
66.1(4)
77.2(5)
3
. Experimental
3.1. General
Reactions were carried out in dry solvents under dry
oxygen-free dinitrogen. Chlorine, bromine and iodine
i
i
were obtained commercially and [( PrNH )B H NH Pr]
2
8
11
Fig. 2. Structure of hypho-[B H10(m-NHR)] species (5).
(1b) [6] was prepared by literature methods. NMR
5

1
84
C. Bauer et al. / Inorganica Chimica Acta 332 (2002) 181–185
spectroscopy was performed in Bruker DPX200 and
AM400 instruments operating at approximately 4.7 and
[+2.25], BH (4,5) −8.7 (t, J=122 Hz) [+1.41, +
2
1
13
2.55]; additionally, l( H) [( C)]: m(2,5) and m(3,4): −
9
]
.4 T. Chemical shifts l are given in ppm relative to
0.60 [–]; CH: +2.95 [54.9]; CH : +1.30 [20.9]; NH:
3
1
−
=100 MHz for l( H) (nominally SiMe ), ]=32.083
+0.62 [–]. DCI MS (negative); m/z: 121 (M −1,
4
1
1
972 MHz for l( B) (nominally [F B·OEt ] in CDCl )
80%).
3
2
3
13
and ]=25.145 004 MHz for l( C) (nominally SiMe ).
4
]
is as defined in Ref. [14]. Electron impact (70 eV,
00 °C) and direct chemical ionisation (reactant gas
NH ) mass spectra were recorded in a Finnigan MAT
3
.3. X-ray diffraction study of 3·CHCl3
2
3
3
6
.3.1. Crystal data
8
3
3
200.
C H B BrN ·CHCl , M =413.05, triclinic, P1
(
, a=
6
27
8
2
3
r
.623(5), b=9.705(3), c=16.831(5) A
,
, h=102.087(14),
.2. Synthesis
3
i=95.77(3), k=98.55(3)°, V=1036.4(8) A
colourless block, 0.3×0.4×0.6 mm, D =1.324
Mg m , v=2.359 mm , F(000)=420, T=173(2)
,
, Z=2,
calc
i
i
−3
−1
.2.1. [( PrNH )B H ClNH Pr] (2)
2
8
10
A sample of 1b (100 mg, 0.47 mmol) was dissolved in
CH Cl (10 ml) and cooled to −78 °C. A gentle
K. A total of 5363 reflections was measured (Siemens
,
P4 diffractometer, Mo Ka X-radiation, u=0.71073 A)
for 2.755q522.50° (−75h56, −105k510, −
2
2
stream of chlorine was passed through the solution for
0 s. After stirring for 1 h at room temperature (r.t.) the
2
185l518), of which 2698 were unique (R =0.0462).
int
more volatile components were removed, and the solid
An empirical absorption correction („ scans) was ap-
plied (Tmax=0.6176, Tmin=0.4850).
residue redissolved in CHCl (5 ml). Cooling to −
3
2
0 °C afforded 2 as a colourless solid [80 mg, 69%,
+
m.p. 115–118 °C]. EI MS; m/z: 249 (M , 40%), 213
3.3.2. Structure solution and refinement
+
i
+
(
M −Cl, 6%), 43 ( Pr , 100%).
The structure was solved by direct methods, devel-
oped by Fourier synthesis and refined anisotropically
(full-matrix least-squares on F ) using the SHELXTL/PC
suite of programs [15]. One molecule of chloroform
solvate was found to co-crystallise per molecule of 3. A
i
i
2
3
.2.2. [( PrNH )B H BrNH Pr] (3)
2
8
10
A sample of 1b (100 mg, 0.47 mmol) was dissolved in
CH Cl (10 ml) and cooled to −78 °C, and then a
solution of Br (75 mg, 24 ml, 0.47 mmol) in CH Cl (5
ml) was added. After stirring for 1 h at r.t. the more
volatile components were removed, and the solid
residue redissolved in CHCl (5 ml). At −20 °C 3 was
obtained as colourless crystals [89 mg, 65%, m.p. 122–
24 °C]. EI MS; m/z: 293 (M , 13%), 213 (M −Br,
3%), 43 ( Pr , 100%).
2
2
2
2
2
total of 240 parameters was refined to final R =0.0558,
1
wR =0.1295 for 2087 data with I\2|(I) and R =
2
1
0
.0799, wR =0.1417 for all 2698 data, and with a
2
2
3
goodness-of-fit on F =1.059. Maximum and minimum
residual electron density were 1.017 and −0.733
e A , respectively, both near Br(1).
+
+
−
3
1
1
,
i
+
i
i
3
.2.3. [( PrNH )B H INH Pr] (4)
2
8
10
4. Supplementary material
Similar to the procedure for compound 3, 1b (100
mg, 0.47 mmol) and I (118 mg, 0.47 mmol) gave 4 as
2
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 174693 for compound
a colourless solid [124 mg, 78%, m.p. (dec.) 115–
+
+
1
5
18 °C ]. EI MS; m/z: 341 (M , 8%), 213 (M −I,
7%), 43 ( Pr , 100%).
i
+
3
·CHCl . Copies of this information may be obtained
3
free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336-
033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
i
3
.2.4. [B H (v-NH Pr)] (5a)
5
10
A sample of 3 (89 mg, 0.30 mmol) was dissolved in
CH Cl (10 ml) and cooled to 0 °C, and then a solution
2
2
of H O (60 mg, 3.3 mmol) in THF (5 ml) was added.
2
After stirring for 0.5 h at r.t. the more volatile compo-
nents were removed. The resulting solid residue was
Acknowledgements
extracted with CHCl (5 ml), filtered to remove boric
3
acid, and the filtrate purified by repeated preparative
We thank the Deutsche Forschungsgemeinschaft, the
Fonds der chemischen Industrie and Heriot-Watt Uni-
versity for support, and acknowledge use of the Chem-
ical Database Service, Daresbury, UK. We are also
grateful to Dr. G.M. Rosair, Heriot-Watt University,
for her helpful assistance.
TLC. Development with hexane/CH Cl (3:7) gave 5a
2
2
as a colourless oil (4 mg, 0.033 mmol, 11%, R 0.77).
F
11
1
NMR (CDCl , 20 °C) l( B) [l( H) for terminal H]:
3
BH (1) −57.8 (dd, J =140 Hz, J =49 Hz) [+1.25,
2
1
2
−
1.07], BH(2,3) −15.5 (dd, J =141 Hz, J =44 Hz)
1 2

C. Bauer et al. / Inorganica Chimica Acta 332 (2002) 181–185
185
[
[
8] P. Lomme, M. Roth, U. Englert, P. Paetzold, Chem. Ber. 129
1996) 1227.
9] U. D o¨ rfler, T.D. McGrath, P.A. Cooke, J.D. Kennedy, M.
References
(
[
[
[
[
[
1] B.M. Graybill, A.R. Pitochelli, M.F. Hawthorne, Inorg. Chem. 1
1962) 626.
2] R. Lewin, P.G. Simpson, W.N. Lipscomb, J. Chem. Phys. 39
1963) 1532.
3] P. MacKinnon, X.L.R. Fontaine, J.D. Kennedy, P.A Salter,
Collect. Czech. Chem. Commun. 61 (1996) 1773.
4] U. D o¨ rfler, D.L. Ormsby, R. Greatrex, J.D. Kennedy, Inorg.
Chim. Acta 304 (2000) 268.
5] (a) U. D o¨ rfler, J.D. Kennedy, L. Barton, C.M. Collins, N.P.
Rath, J. Chem. Soc., Dalton Trans. (1997) 707;
Thornton-Pett, J. Chem. Soc., Dalton Trans. (1997) 4739.
(
[
[
10] The United Kingdom Chemical Database Service, D.A. Fletcher,
R.F. McMeeking, D.J. Parkin, J. Chem. Inf. Comput. Sci. 36
(
(
1996) 746.
11] (a) R.E. Williams, F.J. Gerhart, E. Pier, Inorg. Chem. 4 (1965)
239;
b) R.R. Rietz, R. Schaeffer, L.G. Sneddon, J. Am. Chem. Soc.
2 (1970) 3514;
c) J.B. Leach, T. Onak, J. Spielman, R.R. Rietz, R. Schaeffer,
1
(
9
(
L.G. Sneddon, Inorg. Chem. 9 (1970) 2170.
12] D.F. Gaines, R.W. McGaff, D.R. Powell, Inorg. Chem. 32
(1993) 2612.
(
b) U. D o¨ rfler, P.A. Salter, X.L.R. Fontaine, N.N. Greenwood,
[
J.D. Kennedy, M. Thornton-Pett, Collect. Czech. Chem. Com-
mun. 64 (1999) 947;
(
c) U. D o¨ rfler, N.P. Rath, M. Thornton-Pett, L. Barton, J.D.
[13] R.J. Remmel, H.D. Johnson II, I.S. Jaworiwski, S.G. Shore, J.
Kennedy, in preparation.
Am. Chem. Soc. 97 (1975) 5395.
[
[
6] U. D o¨ rfler, M. Thornton-Pett, J.D. Kennedy, J. Chem. Soc.,
Dalton Trans. (1997) 2547.
7] R.F. Sprecher, B.E. Aufderheide, G.W. Luther III, J.C. Carter,
J. Am. Chem. Soc. 96 (1974) 4404.
[14] W. McFarlane, Proc. R. Soc. London, Ser. A 306 (1968)
185.
[15] G.M. Sheldrick, SHELXTL/PC, BrukerAXS Inc., Madison, WI,
USA, 1999.