Adducts of the heavier group 13 element halides with aminoiminoboranes [1]

Article abstract of DOI:10.1515/znb-2004-0608

2,2,6,6-Tetramethylpiperidino-tert-butylimino borane, 1a, and 2,2,6,6-tetramethyl-piperidino-2,6-diisopropylphenylimino borane (1b), react with the trichlorides of Al, Ga and In or with AlBr₃ to 1:1 to give the addition products tmp=B=N(ECl₃)tBu (E = Ga (2a), In (2b) and tmp = B = N(EHal₃)(C₆H₃,2,6-iPr₂), (E = Al, Hal = Cl, (2c), E = Al, Hal = Br (2d)). E = Ga, Hal = Cl (2e). All these compounds have an allene type structure with short BN bonds as shown by the determination of the crystal structures of 2a, b. NMR data are in accord with this structure. No isomerization to tmp-BHal-NR-EHal₂ has been observed at temperatures up to their melting points.

Full text of DOI:10.1515/znb-2004-0608

Adducts of the Heavier Group 13 Element Halides with
Aminoiminoboranes [1]
Barbara Bo¨ck, Ulrike Braun, Tassilo Habereder, Peter Mayer, and Heinrich No¨th
Department of Chemistry, University of Munich, Butenandtstr. 5 – 13, D-81 377 Mu¨nchen, Germany
Reprint requests to Prof. Dr. H. No¨th. Tel. (49) 89 2180 77454. Fax: (49) 89 2180 77455.
E-mail: H.Noeth@lrz.uni-muenchen.de
Z. Naturforsch. 59b, 681 – 684 (2004); received January 26, 2004
2,2,6,6-Tetramethylpiperidino-tert-butylimino borane, 1a, and 2,2,6,6-tetramethyl-piperidino-2,6-
diisopropylphenylimino borane (1b), react with the trichlorides of Al, Ga and In or with
AlBr3 to 1:1 to give the addition products tmp=B=N(ECl3)tBu (E = Ga (2a), In (2b) and
tmp = B = N(EHal3)(C6H3,2,6-iPr2), (E = Al, Hal = Cl, (2c), E = Al, Hal = Br (2d)). E = Ga,
Hal = Cl (2e). All these compounds have an allene type structure with short BN bonds as shown
by the determination of the crystal structures of 2a, b. NMR data are in accord with this structure. No
isomerization to tmp-BHal-NR-EHal2 has been observed at temperatures up to their melting points.
Key words: ECl3 Adducts, Aminoiminoborane, NMR Spectra, X-Ray Diffraction
Introduction
The reactions of iminoboranes with covalent main
group element halides and hydrides follow an addition-
insertion mechanism as shown in eqs. (1) and (2)
[2, 3]. In most cases, the first step cannot be ob-
served as found for the chlorides of boron, silicon,
germanium, tin, and phosphorus [2 – 6]. However, in
case of AlCl3, AlBr3, and GaCl3 [7] as well as of
AsI3, SbBr3, SbI3, and BiCl3 [8] adducts of type
2 were isolated for 2,2,6,6-tetramethylpiperidino-tert-
butyliminoborane (1a), and characterized by NMR
spectroscopy and for the group 15 element halides also
by X-ray structure analysis [8]. Also, adducts of this
aminoiminoborane were obtained with metal carbonyl
fragments [9] or PdCl2 [10]. These complexes have
also been characterized by X-ray methods. However,
no molecular structures could so far be determined for
the adducts of any of the trihalides of group 13 ele-
ments. Therefore, we investigated the reactions of a
more bulky aminoiminoborane 1b with trihalides of Al
and Ga, as well as of 1a with GaCl3 and InCl3, ex-
pecting more stable compounds and, particularly, with
hope to be able to grow single crystals.
by reacting the metals in a stream of purified chlorine. NMR:
Bruker ACP-200 and Jeol GSX 270; IR: Nicolet TF-IR spec-
trometer; X-ray structure analysis: Siemens P4 diffractome-
ter equipped with a CCD detector and LT2 low tempera-
ture device (2a) or IPDS, Stoe diffractometer (2b). Mo-Kα -
radiation, graphite monochromator.
2,2,6,6-Tetramethylpiperidino-tert-butyliminoborane gal-
lium trichloride (2a): GaCl3 (0.76 g, 4.3 mmol) was dis-
solved in diethyl ether (20 ml). The solution was cooled to
◦
−78 C and a solution of 1a in hexane (36.3 ml, 0.119 M,
4.3 mmol) was added with stirring. A precipitate occurred
immediately. After allowing the suspension to attain room
temperature most of the solvents were removed from the
solid by a cannula. The solid was dried in vacuo, and was
then dissolved in toluene (20 ml). The resulting solution was
layered with hexane (10 ml). After some days colorless crys-
◦
tals of 2a were isolated. Yield: 1.52 g (92%), m. p. 95 C
Experimental Section
(dec.). IR (Nujol/Hostaflon): ν(NBN) = 1812 st (cm−1).
MS (EI, 80 ◦C, 70 eV): 398 (7%, M.+), 207 (80%, M+-Me),
126 (70%, tmp-Me+). C13H27N2BCl3Ga (398.25): calcd.
C 39.17, H 6.78, N 7.03; found C 38.42, H 6.96, N 6.58.
Experiments were conducted under anhydrous conditions
using Schlenck techniques. 1a was prepared as cited in [4],
and 1b as described in [11]. GaCl3 and InCl3 were obtained
c
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682
B. Bo¨ck et al. · Adducts of the Heavier Group 13 Element Halides with Aminoiminoboranes
Table 1. Chemical shifts for the 1H, 11B, 13C and 27Al resonances (in ppm) and line widths (in Hz), given in parenthesis for
compounds 2a – e. Data recorded in deuterated toluene.
δ
11B
δ
27Al
δ1H
H2,3,4
H6/7
H11-13
1.33 s
1.38
H16-18
H20a
H21,22
2a
2b
2c
2d
2e
33.7 (448)
33.3 (470)
31.3 (550)
33.6 (955)
30.6 (305)
1.09 – 1.38 m
1.15 – 1.37 m
1.1 – 1.40 m
1.14 – 1.44 m
1.03 – 1.60 m
0.96 s, 1.22 s
1.08 s, 1.29 s
1.41 s, 1.72 s
1.35 s
103.6 (75)
93.4 (50)
7.07 – 7.12 m
6.98 – 7.07 m
7.09 – 7.13 m
3.53b
3 – 34c
3.61d
1.23 d, 1.29 d
1.18 d, 1.51 d
1.26 d, 1.33 d
1.41 s, 1.74 s
δ
13C
C1/5
55.3
51.2
59.5
57.6
57.1
C2/4
36.4
38.8
35.8
37.5
37.3
C3
C6/7
C10
55.8
56.4
C11/13
32.7
33.2
C15/19
C17
C16/18
C20
C21/22
C14
2a
2b
2c
2d
2e
a
16.4
17.8
16.0
16.3
16.3
29.7,
29.5,
28.2,
31.1
31.1
31.1
32.4
32.5
129.3
128.9
128.2
124.2
125.6
125.2
136.8
134.1
133br
29.1
28.6
28.6
24.1, 25.3
25.39, 25.4
25.2, 25.4
142.8
144.4
145.2
septets, b 1J(H,H) = 6.35 Hz, c 1J(H,H) = 6.60 Hz, d broad.
2,2,6,6-Tetramethylpiperidino-tert-butyl-iminoborane in-
dium trichloride (2b): As described for 2a, a suspension of
InCl3 (0◦.442 g, 2.0 mmol) in diethyl ether (25 ml) was cooled
to −78 C and was allowed to react with a hexane solution
of 1a (30 ml, 0.07 M, 3.0 mmol). The mixture was stirred for
30 h at ambient temperature. No 11B NMR signal could then
be detected in the solution. The product was isolated by fil-
tration, dissolved in toluene (20 ml) and the solution layered
with hexane (20 ml). Colorless crystals of 2b formed dur◦ing
standing for one night. Yield: 0.56 g, (63%), m. p. 105 C.
IR (Nujol/Hostaflon): 1808 st (cm−1). – C13H27N2BCl3In
(443.35): calcd. C 35.19, H 6.09, N 6.23; found C 34.78,
H 6.16, N 6.32.
Scheme. Labels of the C- and H-atoms in Table 1.
◦
Yield: 0.77 g (80%), m. p. 117 – 120 C (dec.). IR (Nujol):
1837 m, 1777 st (νBN2), 388, 360 (νs, νas AlBr3) (cm−1). –
C21H35N2BCl3Ga (502.42): calcd. C 50.20, H 7.02, N 5.85;
found C 48.85, H 7.49, N 5.89.
X-ray structure determination. Single crystals were se-
lected and fixed on a glass fiber. Cell constants were calcu-
lated from the reflections on a set of 60 frames using the
program SMART [12]. Data collection was performed at
−80 ◦C in the hemisphere mode. For data reduction the pro-
gram SAINT [12] was used. The structures were solved and
refined by applying the program SHELX97 [13]. Crystal-
lographic data are deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication no. CCD
229830 and 229831. Copies of the data can be obtained free
of charge, on application to CCDC, 12 Union Road, Cam-
bridge CB2 1 EZ, UK. (fax: +44 1223-336033 or e-mail:
deposit@ccdc.ca.ac.uk.
2,6-Diisopropylphenylimino-2,2,6,6-tetramethylpiperidi-
noborane aluminum trichloride (2c): A suspension of AlCl3
(0.65 g, 4.6 mmol) in pentane (15 ml) was cooled to −60 ◦C.
Then a solution of 1b (1.53 g, 4.5 mmol) in pentane (20 ml)
was added while stirring. Stirring was continued at am-
bient temperature over night, the insoluble 2c isolated by
filtration and dried in vacuo. Yield: 1.22 g (58%), m. p.
◦
118 – 120 C (dec). IR (nujol): 1768 st, 1830 m (cm−1). –
C21H35N2AlBCl3 (459.65): calcd. C 54.87, H 7.76, N 6.09,
Cl 23.12; found C 52.48, H 7.77, N 5.62, Cl 22.0.
2,6-Diisopropylphenylimino-2,2,6,6-tetramethylpiperidi-
noborane aluminum tribromide (2d): To a suspension of
AlBr3 (◦0.68 g, 2.5 mmol) in hexane (10 ml) was added
at −50 C with vigorous stirring a solution of 1b (0.98 g,
3.0 mmol) in hexane (15 ml). The suspension was allowed
to slowly attain room temperature. The yield of isolated
2d was 1.126 g (75%), m. p. 145 ◦C (dec.). IR (Nujol):
1815 st. 1760 vst, (νBN2), 461, 410 (νs, νas AlBr3) (cm−1). –
C21H35N2AlBBr3 (593.03): calcd. C 42.43, H 5.59, N 4.72;
found C 39.84, H 5.90, N 4.35.
Results and Discussion
GaCl3 and InCl3 were found to react with the
aminoiminoborane 1a to give the adducts 2a, b. These
are the first adducts of group 13 element trihalides of
1a of which single crystals for X-ray structure analy-
sis could be obtained. The aminoiminoborane 1b was
shown to add AlCl3, AlBr3 and GaCl3 quite readily to
produce adducts 2c, d, e, which proved to be sparingly
2,6-Diisopropylphenylimino-2,2,6,6-tetramethylpiperidi-
noborane gallium trichloride (2e): As described for 2d from
GaCl3 (0.34 g, 1.9 mmol) an 1b (0.64 g, 1.9 mmol) in a total
of 25 ml of hexane. 2e was obtained as a slightly pink solid. soluble in hexane or diethyl ether.
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B. Bo¨ck et al. · Adducts of the Heavier Group 13 Element Halides with Aminoiminoboranes
Table 2. Selected bonding para◦meters of 2a, b. Bond lengths
683
˚
are given in A, bond angles in , e.s.d’s in parenthesis.
B1-N2
2a 1.317(4)
2b 1.312(2)
B1-N1
1.343(4)
1.345(2)
N2-E
1.937(1)
2.139(1)
av. E-Cl
2.173(1)
2.348(1)
N1-B1-N2 C10-N2-E B1-N2-E τC10N2E1/C1N2C5
2a 178.9(2)
2b 177.9(2)
Sum of bond angles at N1, N2 and B1 in all cases 360 .
123.2(2)
120.9(1)
116.3(2)
115.8(1)
97.0
97.3
◦
Table 3. Crystallographic data for 2a, b and data related to
data collection and structure refinement.
Compound
2a
2b
Chem. formula
Form. wght.
C13 H27 B Cl3 Ga N2 C13 H27 B Cl3 In N2
398.25
443.35
Cryst. size [mm]
Cryst. system
Space group
0.10×0.20×0.30
Orthorhombic
Pbca
14.9850(1)
13.4330(1)
19.2096(1)
90
0.15×0.20×0.42
Orthorhombic
Pbca
14.8128(8)
13.7001(9)
19.454(1)
90
90
90
3947.9(4)
8
1.492
1.596
1792
−19 ≤ h ≤ 15
−18 ≤ k ≤ 18
−25 ≤ l ≤ 23
55.84
200(2)
24355
4688
3601
Fig. 1. Molecular structure of compound 2a in ORTEP de-
scription. Thermal ellipsoids are represented with 25% prob-
˚
ability. Selected bond lengths (in A): Ga1-Cl1 2.1616(9),
˚
a, [A]
Ga1-Cl2 2.1860(8), Ga1-Cl3 2.1718(8), N1-C1 1.514(3),
N1-C5 1.511(4), N2-C10 1.528(3). – Selected bond an-
gles (in ◦): C1-N1-B1 120.2(2), B1-N2-Ga1 116.3(2), B1-
N1-C5 118.9(2), B1-N2-C10 120.5(2), C1-N1-C5 120.8(2),
N2-Ga1-Cl1 112.79(7), N2-Ga1-Cl2 104.25(6), N2-Ga1-Cl3
109.41(7). Analogous data for 2b: In1-Cl1 2.3391(6), In1-
Cl2 2.3609(5), In1-Cl3 2.3496(6), N1-C1 1.509(3), N1-
C5 1.509(3), N2-C10 1.511(2). – Selected bond angles
(◦): C1-N1-B1 119.81.2(1), B1-N2-In1 115.8(1), B1-N1-
C5 118.9(2), B1-N2-C10 123.2(1), C1-N1-C5 121.3(1),
N2-In1-Cl1 112.90(5), N2-In1-Cl2 102.69(4), N2-In1-Cl3
108.62(5).
˚
b, [A]
˚
c, [A]
α, [◦]
β, [◦]
γ, [◦]
90
90
3
˚
V, [A ]
3866.77(4)
8
Z
ρ (calcd.) [Mg/m3] 1.368
µ [mm−1
F(000)
]
1.830
1648
−16 ≤ h ≤ 15
−15 ≤ k ≤ 15
−22 ≤ l ≤ 22
49.40
193(2)
17265
3101
Index range
son with δ27Al for AlCl3 NMe3 [108.9 ppm (h1/2
=
·
2θ[◦]
Temp. [K]
Refl. collected
Refl. unique
Refl. observed (4σ) 2403
R (int.)
·
77 Hz)] and AlBr3 NMe3 (103.8, (h1/2 = 94 Hz) [14].
That the shielding at the Al Atoms is somewhat less
than in the trimethylamine adducts is most likely due
to the steric effect of the tert-butyl group.
0.0487
188
0.0373
188
0.02330/0
1
No. variables
Except for 2d there are two H resonances for the
Weighting schemea 0.0289/3.0125
CMe2 groups of the tetramethylpiperidino units in the
1H spectra but, and only one for 2d, e in the 13C NMR
spectra. This is in accord with the allene type structure
of t◦hese compounds. On cooling solutions of 2d below
20 C one observes two signals: the coalescence tem-
x/y
GOOF
Final R(4σ)
Final wR2
1.038
0.944
0.0311
0.0671
0.284
0.0231
0.0507
0.533
Larg. res. peak
3
˚
[e/A ]
◦
perature is 25 C, and with ∆ν = 13.2 Hz one arrives
a
w
−1 = σ2Fo2 +(xP)2 +yP; P = (Fo2 +2F2)/3.
c
at ∆G# = 62+/ −3 kJmol−1, indicating a low barrier
to rotation about the BN bonds.
Typically for the formation of the adducts is the low
field shift of the 11B resonance with a concomitant de-
crease in the line widths (except for 2d). The difference
in shielding is larger for compounds 1a, b (29.5 and
28.1 ppm, respectively) than for 2c, d, e (19.2, 21.5
and 18.5 ppm). The line widths are still rather broad,
ranging from 385 to 925 Hz, respectively (see Table 1
for NMR data). The aluminum atom in 2c, d is present
In line with the structure of compounds 2 is the
strong IR band of the antisymmetric BN2 vibration
at 1812 and 1808 cm−1 for 2a, b and between 1760
and 1777 cm−1 for 2c, d, e. In each case also a
10BN2 band in the range of 1815 to 1837 cm−1 was
observed.
Compounds 2a, b are isotypic, crystallizing in the
in a tetracoordinated state as is shown by a compari- orthorhombic system in space group Pbca. Relevant
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684
B. Bo¨ck et al. · Adducts of the Heavier Group 13 Element Halides with Aminoiminoboranes
crystallographic data are summarized in Table 3. Be-
cause the molecular structures of the two compounds
are rather similar (of course not for the E-N and E-Cl
bonds) only one is presented in Fig. 1. Typical bonding
parameters are presented in Table 2.
The NBN bond angle of both compounds is close
to 180◦ and the planes EN2C10/C1N2C5 are twisted
by 97.0 and 97.3◦, respectively. The tricoordinated N
and B atoms reside in a planar environment. In spite of
the planar N1 atoms the tetramethylpiperidinorings are
present in a chair conformation. The two BN bonds dif-
The Ga-N bond in 2a is on the short side for
Ga-N bonds. Values for comparison are 1.981 and
˚
1.977 A for the eight membered ring [Me2Ga-NPh-
CPh-O]2 [15]. Also, the In-N bond in 2b is signifi-
cantly shorter than those found in Me3In·NHCy2, and
˚
[Me3In-MeHN-(CH2)]2 (2.38 A) [16], and the dis-
˚
tances of 2.188– 2.239(3) A for ClIn(cyN-CtBu-Ncy)2
with a pentacoordinated In atom [17]. The In-N single
˚
bond is generally assumed to be 2.28 A [18, 19]. The
short GaN and InN bonds observed for 2a, b can be
associated with the inductive effect of the ECl3 group.
The new adducts are perfectly stable under anhy-
fer significantly in lengths. In both cases the BN bond drous conditions, and the formation of compounds of
type 3 have not been observed under relatively mild
conditions up to the melting points of the compounds.
to the EX3 bearing nitrogen atom N2 is shorter than to
N1 of the tetramethylpiperidino group but the differ-
ences in bond lengths are less pronounced than in the
complexes with PdCl2 [10] and M(CO)5 [9]. The N-E-
Cl bond angles vary from 104.3 to 112.8◦ for 2a and
Acknowledgements
We thank Prof. P. Klu¨fers for allowing us to use a IPDS
from 102.7◦ to 112.9◦ for 2b, while the Cl-E-Cl bond Stoe diffractometer, and Chemetall GmbH for supporting this
study.
angles are close to the tetrahedral angle.
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Version 5.1, Massachusetts.
[13] SHELX97, G. W. Sheldrick, University of Go¨ttingen
(1997).
[14] P. Wolfgardt, Ph. D. thesis, University of Munich
(1975).
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