Highly energetic tetraazidoborate anion and boron triazide adducts

Article abstract of DOI:10.1021/ic001119b

The first crystal structures of the highly energetic tetraazidoborate anion and boron triazide adducts with quinoline and pyrazine as well as of tetramethylpiperidinium azide have been determined. Synthesis procedures and thorough characterization by spectroscopic methods of these hazardous materials are given. Quantum chemical calculations were carried out for B(N₃)₄^-, B(N₃)₃, C₅H₅N·B(N₃)₃, (N₃)₃B·NC₄H₄N· B(N₃)₃, and the hypothetical C₃H₃N₃· [B(N₃)₃]₃ at HF, MP2, and B3-LYP levels of theory. The structure of tetraazidoborate was optimized to S₄ symmetry and confirmed the results obtained from the X-ray diffraction analysis. The dissociation enthalpies for the pyridine (model for quinoline) as well as for the pyrazine adduct were calculated. For pyridine-boron triazide a value of 10.0 kcal mol^-1 (for pyrazine-bis(boron triazide) an average of 2.35 kcal mol^-1 per BN unit) was obtained.

Full text of DOI:10.1021/ic001119b

1334
Inorg. Chem. 2001, 40, 1334-1340
Highly Energetic Tetraazidoborate Anion and Boron Triazide Adducts†
Wolfgang Fraenk, Tassilo Habereder, Anton Hammerl, Thomas M. Klapo1tke,*
Burkhard Krumm, Peter Mayer, Heinrich No1th, and Marcus Warchhold
Department of Chemistry, University of Munich, Butenandtstrasse 5-13 (D), D-81377 Munich, Germany
ReceiVed October 10, 2000
The first crystal structures of the highly energetic tetraazidoborate anion and boron triazide adducts with quinoline
and pyrazine as well as of tetramethylpiperidinium azide have been determined. Synthesis procedures and thorough
characterization by spectroscopic methods of these hazardous materials are given. Quantum chemical calculations
were carried out for B(N3)4-, B(N3)3, C5H5N‚B(N3)3, (N3)3B‚NC4H4N‚B(N3)3, and the hypothetical C3H3N3‚
[B(N3)3]3 at HF, MP2, and B3-LYP levels of theory. The structure of tetraazidoborate was optimized to S4 symmetry
and confirmed the results obtained from the X-ray diffraction analysis. The dissociation enthalpies for the pyridine
(model for quinoline) as well as for the pyrazine adduct were calculated. For pyridine-boron triazide a value of
10.0 kcal mol-1 (for pyrazine-bis(boron triazide) an average of 2.35 kcal mol-1 per BN unit) was obtained.
Introduction
of these materials were mentioned on the basis of qualitative
observations. Detailed investigations of this field on related
boron azides are reported.4,5,13
The chemistry of boron azides, first reported by E. Wiberg
et al. in 1954,1 was further investigated by P. I. Paetzold,2-4
and the field has been reviewed.5,6 Although the tetraazidoborate
anion is known for more than 40 years, no spectroscopic data
exist.1 Structural and spectroscopic data for boron dichloride
azide (trimeric)7,8 and dimethylboron azide have, however, been
reported in the literature.9 Quite recently, additional boron azides
have been reported and structurally characterized.10-12 Calcu-
lated structures and gas-phase syntheses of boron triazide, boron
chloride diazide, and boron dichloride azide are known;
however, B(N3)3 has not been characterized in the condensed
phase.13-15 An isoelectronic analogue of boron triazide, the
triazidocarbenium cation, has lately been reexamined with
experimental and theoretical studies.16
Results and Discussion
Syntheses and Properties of Boron Azides. The highly
explosive lithium tetraazidoborate (1) was prepared according
to a slightly modified procedure (cf. ref 1) by the reaction of
lithium tetrahydridoborate with etheral hydrazoic acid. Hydra-
zoic acid was conveniently prepared by treatment of sodium
azide with etheral tetrafluoroboric acid.
Compound 1 can be isolated as a solid but detonates when
exposed to heat, electrostatic discharge, and/or mechanical
shock. According to ref 1, lithium tetraazidoborate is also
friction-sensitive. Traces of moisture immediately result in
formation of hydrazoic acid, identified in the IR and 14N NMR
spectra.
In this work we present synthetic, spectroscopic, structural,
and computational aspects of new sensitive boron triazide
adducts and tetraazidoborate anion. The explosive properties
Three coordinated boron azides (R2BN3) and diazides [RB-
(N3)2] are well-known; however, structural data previously
reported are limited. Our interest in boron azides11,12 prompted
us to examine the reactivity of boron halides containing bulky
substituents toward azides. Such a bulky, electron-donating
substituent is the 2,2,6,6-tetramethylpiperidino (tmp) group.
Attempts to convert bis(2,2,6,6-tetramethylpiperidino)boron
fluoride into the corresponding azide failed, which is in contrast
to the reported synthesis of bis(2,6-dimethylpiperidino)boron
azide containing a less bulky substituent.17 This is likely due to
the fact that two tmp groups attached to boron prevent further
nucleophilic attack. Prolonging the reaction time in addition to
refluxing in dichloromethane led to the isolation of crystals
suitable for X-ray crystallography. It was shown that hydrolysis
(formation of HN3) under BN bond cleavage took place and
that 2,2,6,6-tetramethylpiperidinium azide (2) was formed. This
observation was applied in the following reaction for the
† Dedicated to Professor P. I. Paetzold on the occasion of his 65th
birthday.
* To whom correspondence should be addressed. E-mail: tmk@cup.uni-
muenchen.de.
(1) Wiberg, E.; Michaud, H. Z. Naturforsch. 1954, 96, 497, 499.
(2) Paetzold, P. I. Z. Anorg. Allg. Chem. 1963, 326, 47.
(3) Paetzold, P. I.; Hansen, H. J. Z. Anorg. Allg. Chem. 1966, 345, 79.
(4) Paetzold, P. I. Fortschr. Chem. Forsch. 1967, 8, 437.
(5) Paetzold, P. I. AdV. Inorg. Chem. 1987, 31, 123.
(6) Mu¨ller, J.; Paetzold, P. I. Heteroat. Chem. 1990, 1, 461.
(7) Mu¨ller, U. Z. Anorg. Allg. Chem. 1971, 382, 110.
(8) Wiberg, N.; Joo, W. C.; Schmid, K. H. Z. Anorg. Allg. Chem. 1972,
394, 197.
(9) Hausser-Wallis, R.; Oberhammer, H.; Einholz, W.; Paetzold, P. I.
Inorg. Chem. 1990, 29, 3286.
(10) Paine, R. T.; Koestle, W.; Borek, T. T.; Duesler, E. N.; Hiskey, M.
A. Inorg. Chem. 1999, 38, 3738.
(11) Fraenk, W.; Habereder, T.; Klapo¨tke, T. M.; No¨th, H.; Polborn, K. J.
Chem. Soc., Dalton Trans. 1999, 4283.
(12) Fraenk, W.; Klapo¨tke, T. M.; Krumm, B.; Mayer, P. J. Chem. Soc.,
Chem. Commun. 2000, 667.
synthesis of an ammonium tetraazidoborate, displaying an
(13) Mulinax, R. L.; Okin, G. S.; Coombe, R. D. J. Phys. Chem. 1995, 99,
6294.
-
alternative route for creating B(N3)4
.
The reaction of tmpBCl2 with trimethylsilyl azide has been
reported to result in the formation of 2,2,6,6-tetramethylpiperi-
dinoboron diazide (3).18 Compound 3 is stable at ambient
(14) Johnson, L. A.; Sturgis, S. A.; Al-Jihad, I. A.; Liu, B.; Gilbert, J. V.
J. Phys. Chem. A 1999, 103, 686.
(15) Travers, M. J.; Eldenburg, E. L.; Gilbert, J. V. J. Phys. Chem. A 1999,
103, 9961.
(16) Petrie, M. A.; Sheehy, J. A.; Boatz, J. A.; Rasul, G.; Surya Prakash,
G. K.; Olah, G. A.; Christe, K. O. J. Am. Chem. Soc. 1997, 119, 8802.
(17) Pieper, W.; Schmitz, D.; Paetzold, P. I. Chem. Ber. 1981, 114, 3801.
10.1021/ic001119b CCC: $20.00 © 2001 American Chemical Society
Published on Web 02/10/2001

Tetraazidoborate and Boron Triazide Adducts
Inorganic Chemistry, Vol. 40, No. 6, 2001 1335
Table 1. NMR Data of 1-6 (δ in ppm, ∆ν1/2 in Hz)
LiB(N3)4,a 1,
THF-d8
[tmpH2]N3,b 2,
tmpB(N3)2, 3,
[tmpH2][B(N3)4], 4,
qui‚B(N3)3,c 5,
pyr‚[B(N3)3]I2,d 6,
CDCl3
C6D6
CD2Cl2
CDCl3
CDCl3
CHN
NH2
CH2
CH3
13C{1H}
CN
C-2,6
C-3,5
C-4
9.37 (m, 1H)e
148.0/145.0f
2.0
9.01 (s)
142.6
14.6
8.7 (br)
1.72-1.61 (m)
1.45
6.5 (br)
1.39-1.25 (m)
1.81-1.69 (m)
1.20 (s)
1.50 (s)
55.9
35.2
16.4
27.4
54.4
36.6
15.0
31.9
23.0
59.0
35.6
16.3
28.0
0.5
CH3
11B
-0.2
14N (∆ν1/2
NR
)
-312(400)
-141(40)
-206(35)
-303(300)
-133(100)
-303(300)
-276(350)
-298(700)
-149(70)
-183(130)
-261(680)
-308(870)
-141(110)
-200(150)
-296(120)
-311(660)
-144(70)
-199(140)
-154(290)
-307(800)
-147(70)
-186(130)
-70(∼1500)
Nâ
Nγ
NC
a 7Li NMR, δ ) -0.9. b tmp ) 2,2,6,6-tetramethylpiperidino. c qui ) quinoline. d pyr ) pyrazine. e Additional 1H NMR resonances: δ 8.71 (m,
2H), 8.08 (m, 1H), 7.84 (m, 1H), 7.76 (m, 2H). f Additional 13C NMR resonances: δ 141.1, 133.4, 130.1, 129.5, 129.0, 124.1, 120.7.
temperature and reacts readily with HN3 via BN bond cleavage
to the tetramethylpiperidinium salt of tetraazidoborate (4):
2192-2102 cm-1 (Raman). The symmetric stretching vibration
(νN-N) is not as useful for characterizing boron azides because
it occurs in the same frequency range as νBN
.
NMR Spectroscopy. The multinuclear NMR data of com-
pounds 1-6 are listed in Table 1. A solvent effect on the line
shape of the azide resonances in the 14N NMR spectrum is
observed for 1. Changing from diethyl ether to THF-d8 causes
a decrease of the line width of all three resonances, the largest
observed for Nγ (∆ν1/2 ) 250 Hz, Et2O). This is presumably
due to the better coordination ability of THF to lithium, causing
a tetraazidoborate with smaller interactions with the cation,
therefore leading to sharper resonances in the 14N NMR
spectrum.20 The 11B NMR shifts of B(N3)4- in 1 (δ -0.2) and
4 (δ 0.5) are comparable to that of BF4- (δ -1.4) and are low-
field-shifted compared to other tetrapseudohalogen borates (δ
B(NCO)4-, -11.5; B(NCS)4-, -16.7; B(CN)4-, -38.6).21
Keeping in mind the typical range of amine-borane adducts
in the region around zero,22 the resonance of 6 (11B NMR, δ
14.6) is exceptionally low-field-shifted. Compared with the
expected value of the quinoline adduct in 5 (11B NMR, δ 2.0),
this shift indicates a weaker interaction between boron and donor
nitrogen in 6 and suggests more a dissociated form of boron
Both the lithium (1) and tetramethylpiperidinium salts (4) are
highly moisture-sensitive (HN3 formation); however, 4 is less
explosive than 1.
From earlier reports,1 it was shown that it is extremely
difficult to obtain the free boron triazide in the solid state. The
adduct with pyridine, C5H5N‚B(N3)3, is a distillable liquid but
explodes violently above certain temperatures or when traces
of HN3 are present (hydrolysis).4 To obtain information with
regard to the solid-state structure of a boron triazide adduct,
we selected quinoline as a promising pyridine analogue. The
quinoline and also the pyrazine adduct of boron triazide were
synthesized according to
1
triazide in the presence of pyrazine. The H resonances of the
hydrogen atoms in R-position to the nitrogen of the donor base
in 5 and 6 are deshielded by 0.55 ppm relative to that of the
free base because of the electron-withdrawing borane. The 14
N
resonances of quinoline and pyrazine in 5 (δ -154) and 6 (δ
-70) are high-field shifted, displaying quinolinium and pyrazin-
ium character, respectively, relative to the shifts of the free bases
(14N NMR, δ -73 for quinoline and δ -50 for pyrazine in
CDCl3).
modified to ref 4, by addition of trimethylsilyl azide to a mixture
consisting of the Lewis base and boron trichloride. Both adducts,
in particular the diadduct pyrazine-bis(boron triazide) (6), are
explosive crystalline solids, which detonate violently on impact,
rapid heating, and/or electrostatic discharge.
Description of the Crystal Structures. Tetramethylpiperi-
dinium azide (2) crystallizes in the space group Cmc21 with
four formula units in the unit cell. The cation takes up a chair
conformation as shown in Figure 1. The N-N-N angle of the
azide group is close to linearity (178.8(2)°), as expected, and
the N-N distances are 1.174(3) Å for N(1)-N(2) and
1.177(2) Å for N(2)-N(3), typical for ionic azides. The cation
and anion are linked by NH2‚‚‚N3 hydrogen bridges as displayed
The reaction of trimethylsilyl azide with a 3:1 mixture
consisting of boron trichloride and 1,3,5-triazine resulted in a
violent explosion during the workup procedures. Therefore,
studies on this system were not further pursued. It remains
unclear whether the triazine-tris(boron triazide) adduct and/or
partially substituted boron azides had been formed. All com-
2,19
pounds are expected, and (BCl2N3)3
extremely explosive.
was proved to be
All of the boron azides discussed here show in the vibrational
spectra (IR, Raman) the characteristic antisymmetric stretching
vibrations (νNdN) in the regions 2183-2113 cm-1 (IR) and
(20) Witanowski, M.; Stefaniak, L.; Webb, G. A. Annu. Rep. NMR
Spectrosc. 1986, 18, 486.
(21) Bernhardt, E.; Henkel, G.; Willner, H. Z. Anorg. Allg. Chem. 2000,
626, 560 and references therein.
(18) Mennekes, T.; Paetzold, P. I. Z. Anorg. Allg. Chem. 1995, 621, 1175.
(19) Paetzold, P. I.; Gayoso, M.; Dehnicke, K. Chem. Ber. 1965, 98, 1173.
(22) No¨th, H.; Wrackmeyer, B. Nuclear Magnetic Resonance, Spectroscopy
of Boron Compounds; Springer-Verlag: Berlin, 1978; Vol. 14.

1336 Inorganic Chemistry, Vol. 40, No. 6, 2001
Fraenk et al.
Figure 3. ORTEP plot of the molecular structure of the two 2,2,6,6-
tetramethylpiperidinium tetraazidoborate (4) units with thermal el-
lipsoids drawn at the 25% probability level. Selected bond lengths (Å)
and angles (deg) are the following: B(1)-N(1) 1.549(6), N(1)-N(2)
1.219(5), N(2)-N(3) 1.135(5), N(1)-N(2)-N(3) 176.8(5), B(1)-
N(1)-N(2) 117.6(4), N(1)-B(1)-N(4) 113.2(4), N(1)-B(1)-N(10)
113.7(5), N(7)-B(1)-N(10) 114.6(4), N(4)-B(1)-N(7) 113.6(5),
N(4)-B(1)-N(10) 101.5(4), N(7)-B(1)-N(1) 100.9(3).
Figure 1. ORTEP plot of the molecular structure of 2,2,6,6-
tetramethylpiperidinium azide (2) with thermal ellipsoids drawn at the
25% probability level. Hydrogen atoms bound to carbon are omitted
for clarity. Selected bond lengths (Å) and angles (deg) are the
following: N(1)-N(2) 1.174(3), N(2)-N(3) 1.177(2), N-C(1)
1.527(2), N-H(1) 0.89(2), N-H(2) 0.87(3), N(1)-N(2)-N(3)
178.8(2), C(1)-N-C(1A) 120.2(2).
Figure 4. View of the unit cell of 4 showing N-H‚‚‚N interactions.
Bond lengths (Å) and angles (deg) are the following: N(25)-H(25A)‚
‚‚N(19) 3.047(6), 169.7; N(25)-H(25B)‚‚‚N(10) 3.116(5), 172.3;
N(26)-H(26A)‚‚‚N(1) 3.076(5), 175.4; N(26)-H(26B)‚‚‚N(15)
3.209(6), 167.6.
Scheme 1
Figure 2. View of the unit cell of 2 showing N-H‚‚‚N interactions.
Bond lengths (Å) and angles (deg) are the following: N-H(1)‚‚‚N(3)
2.864(2), 176(2); N-H(2)‚‚‚N(1) 2.945(2), 173(2).
-
γ-nitrogen atom of two adjacent B(N3)4 groups; e.g., all NH
hydrogens are involved in hydrogen bridges.
In the two B(N3)4- units the B-N bond lengths ranges from
1.529(7) to 1.549(6) Å and from 1.509(8) to 1.535(8) Å. The
shorter bonds are those in which the γ-nitrogen atom is involved
in N-H‚‚‚N bonding. The NR-Nâ bond lengths are on average
equal for both B(N3)4- anions (1.22/1.24 Å), while the terminal
Nâ-Nγ bonds are significantly shorter, the ranges spanning
values of 1.046(6)-1.142(7) Å. Thus, the bonding contribution
of A dominates over B (Scheme 1). These data agree very well
with calculated values as do the bond angles. Here for B(1) the
B(1)-N-N bond angles range from 116.8(4)° to 120.6(4)°,
while they are much more uniform for B(2) (119.0(6)-
120.3(5)°).
in Figure 2. The N‚‚‚N(3) and the N‚‚‚N(1) contacts are
2.864(2) and 2.945(2) Å, and the N-H(1)‚‚‚N(3) and the
N-H(2)‚‚‚N(1) angles are almost linear (176(2)° and 173(2)°).
The tetraazidoborate 4 crystallizes in the space group P21/n
with Z ) 8. Therefore, there are two independent [tmpH2]-
[B(N3)4] units in the asymmetric unit (Figure 3). This is due to
the fact that one tmpH2 cation is present in a chair conformation
while the second cation is disordered. The fact that there are
two independent units results from the different arrangement
of N-H‚‚‚N bridges between the tmpH2 cations and the azido
groups of the borate (Figure 4). One type of tmpH2+ coordinates
via two single NH hydrogen atoms adjacent to R-nitrogen atoms
-
+
of the two different B(N3)4 units, while the second tmpH2
makes single N-H‚‚‚N bridges to one R-nitrogen and one
The reverse is found for the N-N-N bond angles, which
are 175.0(6)-176.8(5)° for B(1) and 162.8(6)-174.8(6)° for

Tetraazidoborate and Boron Triazide Adducts
Inorganic Chemistry, Vol. 40, No. 6, 2001 1337
Figure 6. ORTEP plot of the molecular structure of pyrazine-bis-
(boron triazide) (6) with thermal ellipsoids drawn at the 25% probability
level. Hydrogen atoms are omitted for clarity. Selected bond lengths
(Å) and angles (deg) are the following: B(1)-N(1) 1.511(3), N(1)-
N(2) 1.225(2), N(2)-N(3) 1.132(2), B(1)-N(10) 1.657(2), N(1)-
N(2)-N(3) 175.4(2), B(1)-N(1)-N(2) 118.6(2), N(1)-B(1)-N(4)
111.2(1), N(1)-B(1)-N(10) 106.4(1), N(7)-B(1)-N(10) 103.7(1),
N(4)-B(1)-N(7) 115.2(2), N(4)-B(1)-N(10) 105.5(1), N(7)-B(1)-
N(1) 113.9(2).
Figure 5. ORTEP plot of the molecular structure of quinoline-boron
triazide (5) with thermal ellipsoids drawn at the 25% probability level.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
angles (deg) are the following: B(1)-N(1) 1.527(3), N(1)-N(2) 1.226-
(2), N(2)-N(3) 1.137(2), B(1)-N(10) 1.619(2), N(1)-N(2)-N(3)
175.2(2), B(1)-N(1)-N(2) 118.8(2), N(1)-B(1)-N(4) 114.0(1), N(1)-
B(1)-N(10) 109.9(1), N(7)-B(1)-N(10) 110.9(1), N(4)-B(1)-N(7)
113.6(2), N(4)-B(1)-N(10) 104.6(1), N(7)-B(1)-N(1) 104.0(1).
correlated MP2 and B3-LYP levels of theory,27,28 using a
polarized 6-31+G(d,p) double-ú basis set with a diffuse function
added.29
The structures and frequencies of B(N3)3 and the adducts
C5H5N‚B(N3)3 (as a model for C9H7N‚B(N3)3 (5)) and C4H4N2‚
[B(N3)3]2 (6) were computed at SCF (HF) and density functional
levels of theory (B3-LYP).28
Whereas the CCSD(T) method has generally been shown to
be reliable for covalently bound nonmetal compounds,30,31 often
the less expensive MP2 and B3-LYP methods in combination
with a double-ú basis set give very good structural results and
vibrational frequencies.30,31
-
B(2). In any case, B(2)(N3)4 is much less symmetric than
-
B(1)(N3)4-. Therefore, the ideal S4 symmetry for the B(1)(N3)4
-
anion is almost realized while the B(2)(N3)4 anion is less
symmetric. Obviously, N-H‚‚‚N bonding and packing effects
play a role.
Quinoline-boron triazide (5) crystallizes in the space group
P1h with two formula units in the unit cell. The boron atom is
surrounded by the three azide groups and the quinoline in a
tetrahedral fashion (Figure 5). The B-NR distance is 1.523-
(3)-1.527(3) Å, which is comparable with the distance found
for 4. While the NR-Nâ bond lengths range from 1.216(2) to
1.226(2) Å, the Nâ-Nγ bond distances range from 1.129(2) to
1.137(2) Å, showing considerable NtN triple bond charac-
ter.23,24 The B-Nqui distance is as for a coordinative bond, 1.619-
(2) Å, longer than the B-NR bond lengths. The three azide
groups are, as for a typical covalently bound azide group,
slightly bent (N-N-N, 173.7(2)-175.2(2)°); the B-N-N
angles range from 118.8(2)° to 119.4(2)°.
The 1:2 adduct pyrazine-bis(boron triazide) (6) crystallizes
in the space group P1h with one molecule in the unit cell (Figure
6). The B-NR (1.511(3)-1.520(3) Å), NR-Nâ (1.217(2)-
1.225(2) Å), and the Nâ-Nγ (1.128(2)-1.133(2) Å) distances
are almost identical with those found for 5. A significant
difference is found for the B-Npyr bond length. The latter is
1.657(2) Å, significantly longer than the corresponding distance
found for 5, assuming only a weak B-Npyr interaction. However,
a boron atom on the way to planarity in 6 is not unambiguously
observed. The N-N-N (175.4(2)-175.4(2)°) and the B-N-N
(118.6(2)-121.1(2)°) angles are similar to the corresponding
values found for 5.
(26) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R.
L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.;
Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian 98, revision A.3; Gaussian, Inc.:
Pittsburgh, PA, 1998.
(27) (a) Møller, C.; Plesset, M. S. Phys. ReV. 1934, 46, 618. (b) Bartlett,
R. J.; Silver, D. M. J. Chem. Phys. 1975, 62, 3258. (c) Pople, J. A.;
Binkley, J. S.; Seeger, R. Int. J. Quantum Chem., Quantum Chem.
Symp. 1976, 10, 1. (d) Pople, J. A.; Seeger, R.; Krishnan, R. Int. J.
Quantum Chem., Quantum Chem. Symp. 1977, 11, 1. (e) Saebo, S.;
Almlof, J. Chem. Phys. Lett. 1989, 154, 83. (f) Head-Gordon, M.;
Pople, J. A.; Frisch, M. J. Chem. Phys. Lett. 1988, 153, 503. (g) Frisch,
M. J.; Head-Gordon, M.; Pople, J. A. Chem. Phys. Lett. 1990, 166,
275, 281. (h) Head-Gordon, M.; Head-Gordon, T. Chem. Phys. Lett.
1994, 220, 122.
Recently, the crystal structures of group13 tetraazido anions
of the heavier homologues (Al, Ga, In) as well as amine adducts
of gallium/indium triazides have been reported.25
Quantum Chemical Calculations. The calculations were
performed with the program package Gaussian 98.26 The
structure of B(N3)4-, its total energy (E) and zero-point energy
(zpe), and the vibrational data were calculated at the electron-
(28) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. 1988, B37, 785. (b)
Becke, A. D. Phys. ReV. 1988, A38, 3098. (c) Miehlich, B.; Savin,
A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200. (d) Becke,
A. D. J. Chem. Phys. 1993, 98, 5648.
(29) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54,
724. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
56, 2257. (c) Hariharan, P. C.; Pople, J. A. Mol. Phys. 1974, 27, 209.
(d) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163. (e) Hariharan, P.
C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(30) Dixon, D. A.; Feller, D. Computational Thermochemistry of Fluori-
nated Compounds; 14th ACS Winter Fluorine Conference, St.
Petersburg, FL, January 17-22, 1999; Abstract 29.
(31) Klapo¨tke, T. M.; Schulz, A.; Harcourt, R. D. Quantum Chemical
Methods in Main-Group Chemistry; Wiley: Chichester, New York,
1998; p 89.
(23) Klapo¨tke, T. M. Chem. Ber. 1997, 130, 443 and references therein.
(24) Tornieporth-Oetting, I. C.; Klapo¨tke, T. M. Angew. Chem., Int. Ed.
Engl. 1995, 34, 511.
(25) Sussek, H.; Stowasser, F.; Pritzkow, H.; Fischer, R. A. Eur. J. Inorg.
Chem. 2000, 455 and references therein.

1338 Inorganic Chemistry, Vol. 40, No. 6, 2001
Fraenk et al.
Table 2. Crystal Data and Structure Refinements for 2 and 4-6
2
4
5
6
empirical formula
fw
temp [K]
cryst size [mm]
cryst syst
space group
a [Å]
C9H20N4
184.28
200(3)
C9H20BN13
321.15
200(3)
0.36 × 0.10 × 0.07
monoclinic
P21/n
7.7179(3)
14.8750(8)
29.553(2)
C9H7BN10
266.06
193(2)
C4H4B2N20
353.86
193(2)
0.30 × 0.05 × 0.03
0.40 × 0.30 × 0.30
0.20 × 0.10 × 0.10
orthorhombic
triclinic
triclinic
a
Cmc21
P1h
P1h
9.581(1)
11.325(1)
9.945(1)
7.2035(7)
8.2093(8)
11.642(1)
104.729(2)
96.014(2)
112.423(1)
599.6(1)
6.7658(7)
7.1468(8)
8.2400(9)
66.586(2)
83.475(2)
84.455(2)
362.68(7)
1
b [Å]
c [Å]
R [deg]
â [deg]
95.438(6)
γ [deg]
V [Å3]
1079.0(2)
4
1.134
0.072
408
3377.5(3)
8
1.263
0.089
1360
Z
D
2
calcd [g/cm3]
1.474
0.104
272
1.620
0.125
178
abs coeff [mm-1
F(000)
]
θ range [deg]
2.78-27.98
-12 e h e 12
-14 e k e 14
-12 e l e 11
4361
1.95-24.03
-8 e h e 8
-17 ek e 17
-33 e l e 25
10 762
3.72-57.74
-9 e h e 9
-10 ek e 10
-14 e l e 14
3530
5.40-58.46
-7 e h e 8
-8 e k e 9
-10 e l e 10
2120
index range
reflns collected
independent reflns
obsd reflns
max, min transm
data/restraints/params
goodness-of-fit F2
R1, wR2 [I > 4σ(I)]
R1, wR2 (all data)
largest diff peak/hole [e/Å3]
1305 (Rint ) 0.0416)
4970 (Rint ) 0.0464)
1854 (Rint ) 0.0176)
1107 (Rint ) 0.0213)
1047
2334
1492
972
0.9956, 0.9915
4970/5/411
0.867
1.000, 0.706
1854/0/181
1.054
0.0400, 0.1085
0.0520, 0.1176
0.233/-0.177
1.000, 0.5810
1107/0/126
1.062
0.0391, 0.1092
0.0439, 0.1131
0.185/-0.197
1305/1/111
0.954
0.0295, 0.0585b
0.0446, 0.0622
0.168/-0.185
0.0684, 0.1690b
0.1366, 0.1968
0.619/-0.293
a Flack parameter 0(2). b [I > 2σ(I)].
-
Table 3. Computed Structural Parameters and Energies for B(N3)4
HF/6-31+G(d,p)
B3-LYP/6-31+G(d,p)
MP2(FC)/6-31+G(d,p)
MP2(FULL)/6-31+G(d,p)
symmetry
S4
S4
S4
S4
-E/au
677.964 094
0
39.6
1.552
1.206
1.109
107.9
118.0
175.9
681.873 491
0
36.2
1.552
1.217
1.149
108.1
121.1
174.8
680.129 841
680.182 260
NIMAG
zpe/kcal mol-1
d(B-N1)/Å
1.544
1.229
1.177
107.7
120.2
173.9
1.542
1.227
1.176
107.8
120.2
174.0
d(N1-N2)/Å
d(N2-N3)/Å
×c1 (N1′-B-N1)/deg
(B-N1-N2)/deg
(N1-N2-N3)/deg
Tetraazidoborate Anion, B(N3)4-. At the HF/6-31+G(d,p)
lengths of 3.63 Å. However, when electron correlation was taken
into account at the hybride B3-LYP level of theory both
experimentally observed adducts, C5H5N‚B(N3)3 and C4H4N2‚
[B(N3)3]2 (6) were found to represent true minima (NIMAG )
0) with very good agreement between the observed and
computed structural parameters. It is important to stress that
for the 1:1 adduct the computed B‚‚‚N (C5H5N‚B(N3)3) bond
length of 1.663 Å is considerably shorter than the computed
B‚‚‚N bond length of 1.735 Å for the 1:2 adduct C4H4N2‚
[B(N3)3]2 (6). This trend is in good agreement with the
experimental values of 1.619(2) Å for C9H7N‚B(N3)3 (5) and
1.657(2) Å for C4H4N2‚[B(N3)3]2 (6).
-
level of theory the structure of the B(N3)4 anion was fully
optimized in C1 symmetry, resulting in an S4 structure with no
imaginary frequencies (NIMAG ) 0). Consequently, the MP2
and B3-LYP computations were performed within S4 symmetry
(Table 3). The computed B3-LYP frequencies (Table 4) are in
excellent accord with the experimental IR and Raman data.
Table 4 shows a comparison of the experimentally observed
and computed frequencies, which have been scaled with
appropriate scaling factors (HF, 0.89; B3-LYP, 0.96).32
Compounds B(N3)3, C5H5N‚B(N3)3 (As a Model for C9H7N‚
B(N3)3 (5)), C4H4N2‚[B(N3)3]2 (6), and C3H3N3‚[B(N3)3]3. The
structures, energies and vibrational data of B(N3)3, C5H5N‚
B(N3)3, and C4H4N2‚[B(N3)3]2 (6) were computed at HF/6-31G-
(d) and B3-LYP/6-31G(d) levels of theory. Whereas at the
noncorrelated HF level the 1:1 adduct C5H5N‚B(N3)3 was found
to represent a true minimum; the 1:2 adduct C4H4N2‚[B(N3)3]2
(6) was found not to be stable but to dissociate and form a very
weakly bound van der Waals type complex with B‚‚‚N bond
The dissociation energies according to
C5H5N‚B(N3)3 f B(N3)3 + C5H5N
(3)
and
C4H4N2‚[B(N3)3]2 (6) f 2B(N3)3 + C4H4N2
(4)
can be used to obtain an appreciation for the B‚‚‚N bond
strengths in both adducts. The calculated total energies (Table
5) can be used to predict theoretically the reaction enthalpy
(32) Foresman, J. B.; Frisch, A. Exploring Chemistry with Electronic
Structure Methods, 2nd ed.; Gaussian, Inc.: Pittsburgh, PA, 1993; p
64.

Tetraazidoborate and Boron Triazide Adducts
Inorganic Chemistry, Vol. 40, No. 6, 2001 1339
-
Table 4. Computed and Vibrational Results for B(N3)4
the average BDE; the elimination of the first B(N3)3 unit from
6 is thermodynamically even more feasible than the value of
2.35 kcal mol-1 suggests.
The adduct of 1,3,5-triazine, C3H3N3, and B(N3)3, i.e., the
compound C3H3N3‚[B(N3)3]3, was found to be unstable at both
HF and B3-LYP levels of theory. At the density functional B3-
LYP/6-31G(d) level this species was found to represent a very
weakly bound van der Waals type adduct with B‚‚‚N distances
of 3.5 Å (E ) -1 833.001 393 au, NIMAG ) 0, zpe ) 127.9
kcal mol-1).
HF/6-31+
G(d,p),a,b
F ) 0.89
B3-LYP/6-31
+G(d,p),a IR (intens) Raman (intens)
F ) 0.96
(1)
(1)
ν1 (A) 2200 (0/154)
2175 (0)
2192 (2)
2172 (1)
2140 (2)
1373 (4)
1352 (6)
1319 (3)
917 (1)
ν2 (B) 2178 (1387/112) 2158 (955)
2183 (s)
ν3 (E) 2160 (2167/85) 2143 (1399) 2131 (vs)
ν4 (A) 1317 (0/47)
ν5 (B) 1289 (561/2)
ν6 (E) 1284 (724/2)
1344 (0)
1332 (259)
1331 (266)
875 (443)
845 (480)
708 (0)
663 (63)
623 (48)
583 (26)
580 (0)
576 (4)
483 (0)
396 (8)
380 (3)
1361 (s)
1326 (s)
885 (s)
ν7 (E)
ν8 (B)
ν9 (A)
900 (540/6)
846 (529/7)
743 (0/1)
826 (m)
Conclusion
ν
ν
ν
ν
ν
ν
ν
ν
ν
ν
ν
ν
ν
ν
ν
ν
10 (B) 700 (135/8)
701 (m)
645 (m)
584 (m)
The highly explosive lithium tetraazidoborate, in agreement
with its first report by E. Wiberg, was shown to be LiBN12, is
the third highest nitrogen-containing solid material (90.45%)
following hydrazinium azide and ammonium azide (93.29%).
As the last member in the series of the group13 tetraazido
anions, tetraazidoborate is finally structurally and spectroscopi-
cally characterized. Moreover, in addition to this, structurally
characterized explosive adducts of boron triazide are reported.
NMR shifts and quantum chemical calculations have been used
to predict and/or confirm the BN3 bonding situation obtained
from the results of X-ray crystallography.
11 (E) 649 (72/3)
12 (B) 629 (43/0)
13 (A) 626 (0/0.1)
14 (E) 622 (5/0.2)
15 (A) 490 (0/6)
16 (B) 402 (13/10)
17 (E) 385 (3/1)
18 (A) 291 (0/6)
19 (B) 285 (2/2)
20 (A) 160 (0/5)
21 (E) 130 (2/1)
507 (4)
424 (w)
288 (0)
281 (3)
154 (0)
122 (2)
303 (6)
180 (8)
108 (10)
22 (B)
23 (E)
24 (B)
25 (A)
81 (0/9)
73 (0)
45 (0.2/7)
36 (0.2/9)
30 (0/10)
41 (0.3)
36 (0.1)
29 (0)
Experimental Section
CAUTION. All of the materials described here are explosive and
toxic, in particular hydrazoic acid, 1, and 6. They may violently explode
under various conditions and should be handled only in small amounts
with extreme caution. The use of safety equipment like leather gloves,
leather coat, and face shield is strongly advised.
a IR intensities in km mol-1 b Raman intensities in Å4 amu-1
. .
Table 5. Computed Structural Parameters and Energies for B(N3)3,
C5H5N‚B(N3)3, and C4H4N2‚[B(N3)3]2 (6)
-E,
au
zpe,
d(B‚‚‚N),
General. All manipulations of air- and moisture-sensitive materials
were performed under an inert atmosphere of dry nitrogen using
standard Schlenk techniques. Solvents were dried and degassed by
standard methods. Raman spectra were recorded on a Perkin-Elmer
2000 NIR FT-Raman spectrometer fitted with a Nd:YAG laser (1064
nm), and infrared spectra were recorded on a Nicolet 520 FT-IR
spectrometer between KBr plates or as a pellet as described. The
elemental analyses were performed with a C, H, N Analysator
Elementar Vario EL. NMR spectra were recorded on a JEOL EX400
instrument. Chemical shifts are recorded with respect to (CH3)4Si (1H,
13C), BF3‚OEt2 (11B), CH3NO2 (14N), and LiCl (7Li). For the determi-
nation of the melting points, samples were heated in capillaries in a
Bu¨chi B540 instrument. Bis(2,2,6,6-tetramethylpiperidino)boron fluoride
and 2,2,6,6-tetramethylpiperidinoboron dichloride were prepared ac-
cording to refs 34 and 35. Other chemicals were used as received
(Aldrich, Fluka).
compound
kcal mol-1 NIMAG
Å
HF/6-31G(d)
514.615732
761.310530
B(N3)3
C5H5N‚B(N3)3
31.1
92.7
0
0
0
0
0
1.679
3.630
C4H4N2‚[B(N3)3]2 (6) 1291.920907
114.9
59.9
C5H5N
C4H4N2
246.695820
262.683005
52.1
B3LYP/6-31G(d)
B(N3)3
C5H5N‚B(N3)3
517.542046
765.841636
28.6
0
0
0
0
0
86.0
107.6
55.9
1.663
1.735
C4H4N2‚[B(N3)3]2 (6) 1299.404581
C5H5N
C4H4N2
248.284973
264.317234
48.4
values for reactions 3 and 4. The dissociation energies of
reactions 3 and 4 were calculated, which, after correction31 for
zero-point energies (Table 5), differences in rotational (∆U(1)rot
) (3/2)RT; ∆U(2)rot ) 3RT) and translational (∆U(1)tr ) (3/2)-
RT; ∆U(2)tr ) 3RT) degrees of freedom, and the work term
(p∆V(1) ) 1RT; p∆V(2) ) 2RT), were converted into the gas-
phase dissociation enthalpies at room temperature:
Recordings of mass spectra and NMR spectra of the triazine reaction
were not done because of possible damage to the instruments. Elemental
analyses were performed for all compounds except for 1 and 6, but
only useful results are reported.
Crystallography. The data for 2 and 4 (Table 2) were collected on
a STOE IPDS area detector. The structures were solved and refined
by direct methods using the SHELX-97 package. The data for 5 and 6
(Table 2) were collected on a SIEMENS SMART area detector. The
structures were solved by direct methods (SHELXS-97) and refined
by means of full-matrix least-squares procedures using SHELXL-97.
For 4, all non-hydrogen atoms were refined anisotropically except
for the disordered carbon atoms of one of the tmp cations. Their
refinement leads to SOF values of 0.48 and 0.52. All hydrogen atoms
were put in calculated positions.
Syntheses and Characterization of Compounds. Improved Prepa-
ration of Etheral Hydrazoic Acid. A solution of HBF4 in diethyl ether
(2 M) was added dropwise to a suspension of NaN3 in diethyl ether at
-78 °C. The mixture was warmed slowly and stirred for an additional
12 h at ambient temperature. The volatile components of this mixture
∆H°298 ) +10.0 kcal mol-1
∆H°298 ) +4.7 kcal mol-1
for reaction 3
for reaction 4
Therefore, the bond dissociation enthalpy value (BDE) for the
1:1 adduct (dissociation into B(N3)3 and C5H5N) is 10.0 kcal
mol-1 and corresponds to a “normal” Lewis acid-Lewis base
B‚‚‚N bond strength.31,33 However, for the 1:2 adduct the
average BDE is only 2.35 kcal mol-1, which accounts for a
very weak and only loosely bound adduct (cf. 11B NMR
chemical shifts in solution). This value, however, reflects only
(33) Klapo¨tke, T. M.; Tornieporth-Oetting, I. C. Nichtmetallchemie;
(34) No¨th, H.; Weber, S. Z. Naturforsch. 1983, 38b, 1460.
(35) No¨th, H.; Rasthofer, B.; Weber, S. Z. Naturforsch. 1984, 39b, 1058.
VCH: Weinheim, 1994.

1340 Inorganic Chemistry, Vol. 40, No. 6, 2001
Fraenk et al.
were condensed under reduced pressure into a glass vessel containing
dry ether to give a solution of HN3 in diethyl ether.
to warm slowly. After it was additionally stirred for 12 h at 25 °C the
solvent and all volatile compounds were removed by vacuum evapora-
tion, leaving a colorless solid. The crude product was purified by
recrystallization from a cooled concentrated solution in dichloro-
methane, resulting in 0.22 g (70%) of pure 4; mp, 81-84 °C (dec). IR
(Nujol): 3407 (m) (ν(NH)), 3019/2982/2857 (m-s) (ν(CH)), 2146/
2113 (vs) (νas(N3)), 1607 (s), 1592 (s), 1474 (vs), 1458 (vs), 1440 (vs),
1369 (vs), 1303 (vs), 1275 (vs), 1178 (s), 1154 (s), 1116 (m), 1040
Lithium Tetraazidoborate (1). A solution of 1.3 M HN3 in diethyl
ether (5.2 mmol, 4 mL) was added to a solution of LiBH4 (1.0 mmol)
in diethyl ether (10 mL) at -78 °C. A colorless solid immediately
precipitated. The suspension was allowed to warm slowly, and the
formation of hydrogen was observed. After the solution was additionally
stirred (12 h) at ambient temperature, all volatile products were removed
in vacuo and the remaining oil was extracted twice with diethyl ether.
After vacuum evaporation of the ether, the remaining solid was washed
with hexane and dried again in vacuo. 1 was isolated as a colorless
solid; yield, 0.11 g; mp, 75-78 °C (dec). IR (Nujol, selected
absorptions): 2183/2131 (s-vs) (νas(N3)), 1361 (s), 1326 (s), 1263 (vs),
1146 (m), 1099 (m), 1043 (s), 885 (s), 826 (m), 701 (m), 645 (m), 584
(m), 424 (w) cm-1. Raman (50 mW): 2192/2172/2140 (1-2) (νas(N3)),
1373 (4), 1352 (6), 1319 (3), 1033 (1), 917 (1), 599 (1), 583 (1), 507
(m), 975 (vs), 879 (vs), 863 (vs), 797 (m), 588 (w), 466 (w) cm-1
.
Raman (100 mW): 3022/2988/2962/2934/(3-9) (ν(CH)), 2152/2113/
2103 (2-3) (νas(N3)), 1475 (2), 1459 (2), 1437 (2), 1398 (1), 1334 (4),
1319 (4), 1267 (1), 1229 (2), 1059 (1), 883 (1), 707 (4), 571 (2), 352
(4), 287 (4), 164 (6), 95 (10) cm-1
.
Quinoline-Boron Triazide (5). Trimethylsilyl azide (0.35 g, 3.0
mmol) was added to a mixture of quinoline (0.13 g, 1.0 mmol) and
boron trichloride (1.0 mmol, 1 M in hexane) in dichloromethane (5
mL) at -78 °C. After it was additionally stirred for 4 h at ambient
temperature all volatile materials were removed in vacuo, leaving a
colorless solid. The product was recrystallized from dichloromethane,
resulting in colorless crystals of 5; yield, 0.24 g (90%); mp, 100-105
°C (dec). Anal. Calcd for C9H7BN10: C, 40.63; H, 2.65; N, 52.65. Found
C, 40.58; H, 2.98; N, 51.22. IR (Nujol, selected values): 3125/3111/
3053 (m) (ν(CH)), 2162/2155/2122 (m-vs) (νas(N3)), 1593 (vs), 1518
(vs), 1404 (s), 1373 (vs), 1236 (vs), 1149 (vs), 981 (vs), 922 (vs), 878
(vs), 776 (vs), 643 (vs), 586 (vs), 479 (s) cm-1. Raman (50 mW): 3102/
3067/2987 (2-4) (ν(CH)), 2154/2115 (1) (νas(N3)), 1623 (2), 1595 (4),
1446 (1), 1375 (10), 1331 (3), 1311 (3), 1151 (1), 1085 (2), 1030 (1),
834 (2), 807 (1), 704 (3), 536 (4), 298 (4), 287 (3), 250 (2), 218 (3),
(4), 303 (6), 180 (8), 108 (10) cm-1
.
Reaction of Bis(2,2,6,6-tetramethylpiperidino)boron Fluoride
with Trimethylsilyl Azide. A solution of tmp2BF (0.31 g, 1.0 mmol)
in dichloromethane (5 mL) was treated with trimethylsilyl azide (0.23
g, 2.0 mmol) at -78 °C. The solution was allowed to warm slowly
and was stirred for 2 weeks at ambient temperature. Monitoring of
this mixture by 11B NMR spectroscopy showed no change of the starting
material. After it was additionally refluxed for 48 h, crystals were slowly
obtained. By use of X-ray analyses, these crystals were found to be
2,2,6,6-tetramethylpiperidinium azide (2). The remaining solution gave
no evidence of the formation of a boron azide and was discarded. Data
for 2: mp 143-146 °C. IR (pellet, selected absorptions): 3443 (s, br)
(νNH), 3011/2952/2857/2821/2770 (m) (ν(CH)), 2037/2024/2010 (vs)
(νas(N3)), 1634 (m), 1579 (m), 1474 (w), 1387 (m), 1335 (vw) (νs-
188 (3), 127 (9) cm-1
.
Pyrazine-Bis(boron triazide) (6). 6 was prepared from trimeth-
ylsilyl azide (0.17 g, 1.5 mmol), pyrazine (0.02 g, 0.25 mmol), and
boron trichloride (0.25 mmol) in dichloromethane solution (5 mL)
following the method described for 5. Yield, 0.07 g (75%); mp, 85-
88 °C (explosion). IR (Nujol, selected values): 3125/3102 (m) (ν(CH)),
2151/2131 (vs) (νas(N3)), 1489 (s), 1434 (vs), 1382 (vs), 1190 (s), 1124
(s), 1099 (vs), 991 (vs), 972 (vs), 959 (vs), 831 (vs), 746 (vs), 667
(vs), 634 (vs) 578 (s), 541 (s), 488 (s) cm-1. Raman (50 mW): 3114/
3105 (2-3) (ν(CH)), 2167/2139/2124 (1-3) (νas(N3)), 1643 (6), 1541
(1), 1348 (3), 1340 (2), 1328 (2), 1305 (2), 1088 (1), 1054 (5), 1003
(1), 957 (1), 785 (1), 696 (1), 634 (1), 486 (2), 420 (2), 321 (4), 189
(N3)), 1231 (m), 1119 (m), 980 (w), 910 (w), 710 (w), 641 (m) cm-1
.
Raman (200 mW): 3024/2978/2963/2934/2917 (6-9) (ν(CH)), 1747
(1), 1452 (2), 1335 (10) (νs(N3)), 1270 (2), 1228 (2), 1055 (2), 915
(2), 886 (2), 788 (2), 574 (4), 473 (6), 325 (5), 178 (6), 119 (7) cm-1
.
2,2,6,6-Tetramethylpiperidinoboron Diazide (3). A solution of
2,2,6,6-tetramethylpiperidinoboron dichloride (0.44 g, 2.0 mmol) in
toluene (10 mL) was treated with trimethylsilyl azide (0.23 g, 2.0 mmol)
at -78 °C. The solution was allowed to warm slowly and was stirred
for 12 h at ambient temperature. The solvent and all volatile products
were removed by vacuum evaporation at 25 °C, leaving a liquid. The
product was distilled under reduced pressure to give 0.38 g of colorless
liquid 3 (80%); bp, 70-72 °C/0.01 Torr. Anal. Calcd for C9H18BN7:
C, 45.98; H, 7.71; N, 41.70. Found C, 45.68; H, 7.70; N, 40.07. IR
(neat): 3018/2945/2865 (m-s) (ν(CH)), 2157/2114 (m-vs) (νas(N3)),
1458 (m), 1384 (vs), 1354 (vs), 1318 (s), 1286 (s), 1173 (m), 1131
(m), 1064 (m), 975 (w), 876 (w), 707 (w), 649 (w), 574 (w), 476 (w)
cm-1. Raman (50 mW): 3022 (2), 2988 (4), 2962 (6), 2934 (7), 2152/
2133/2113/2102 (1-2) (νas(N3)), 1476 (3), 1441 (3), 1404 (3), 1356
(2), 1321 (2), 1115 (1), 974 (1), 883 (1), 786 (1), 549 (3), 304 (2), 121
(4), 170 (5), 128 (10), 106 (8), 90 (9) cm-1
.
Acknowledgment. Financial support of this work by the
University of Munich and the Fonds der Chemischen Industrie
is gratefully acknowledged.
Supporting Information Available: Tables of crystal data, struc-
ture solutions and refinement, atomic coordinates, bond lengths and
angles, and anisotropic thermal parameters for 2 and 4-6 in CIF
format. This material is available free of charge via the Internet at
http://pubs.acs.org.
(10) cm-1
.
2,2,6,6-Tetramethylpiperidinium Tetraazidoborate (4). A solution
of HN3 in diethyl ether (1.0 mL, 1.3 mmol) was added to a solution of
3 (0.12 g, 0.5 mmol) in diethyl ether (5 mL) at -20 °C and was allowed
IC001119B