N-(2,4,6-trimethylborazinyl)-substituted boron, aluminum and titanium compounds

Article abstract of DOI:10.1515/znb-2008-0105

The N-lithioborazine LiH₂N₃B₃Me ₃, 1, reacts with organoboron halides not only to the respective borazinyl organylboranes but also by Me/halogen exchange. (Me₂N) ₂B-H₂N₃B₃Me₃ was obtained from 1 and (Me₂N)₂BCl. A new ten-membered B ₆N₄ ring system, 5, results on treatment of Cl(Me ₂N)B-B(NMe₂)Cl with 1. The B-N-borazinyl borazines 6-8 can be prepared from 1 and B-monohalo borazines. The synthesis of 2,4,6-trimethylborazinyl-aluminum and -titanium compounds is achieved only with mononuclear monohalides of Al(III) and Ti(IV). The 2,4,6-trimethylborazinyl- bis(piperidino)alane 9 and the tris(2,6-diisopropylphenoxo)-2,4,6- trimethylborazinyltitanium 10 were characterized by X-ray structure analysis. The distortion of the borazine ring by B and N substitution is discussed. In case of the N-substituted borazines YH₂N₃B ₃Me₃ the B-N bonds of the YNB₂ units are elongated, e. g. for Y = PBr₂ or (RO)₃Ti, while N lithiation leads to a shortening of these B-N bond. These changes of bond lengths are also reflected by changes in the B1-N2 and B3-N3 bond lengths which become shorter in the presence of electron-withdrawing groups, but longer in case of Li substitution. Also, the bond angles B1-N2-B2 and B2-N3-B3 are affected by an increase of up to 128°.

Full text of DOI:10.1515/znb-2008-0105

N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and
Titanium Compounds*
Birgit Gemu¨nd, Berndt Gu¨nther, Jo¨rg Knizek, and Heinrich No¨th
Department Chemie und Biochemie, Universita¨t Mu¨nchen, Butenandtstraße. 5 – 13, 81377 Mu¨nchen,
Germany
Reprint requests to Prof. Dr. H. No¨th. E-mail: H.Noeth@lrz.uni-muenchen.de
Z. Naturforsch. 2008, 63b, 23 – 36; received August 9, 2007
The N-lithioborazine LiH2N3B3Me3, 1, reacts with organoboron halides not only to the re-
spective borazinyl organylboranes but also by Me/halogen exchange. (Me2N)2B-H2N3B3Me3 was
obtained from 1 and (Me2N)2BCl. A new ten-membered B6N4 ring system, 5, results on treat-
ment of Cl(Me2N)B–B(NMe2)Cl with 1. The B-N-borazinyl borazines 6 – 8 can be prepared from 1
and B-monohalo borazines. The synthesis of 2,4,6-trimethylborazinyl-aluminum and -titanium com-
pounds is achieved only with mononuclear monohalides of Al(III) and Ti(IV). The 2,4,6-trimeth-
ylborazinyl-bis(piperidino)alane 9 and the tris(2,6-diisopropylphenoxo)-2,4,6-trimethylborazinyl-
titanium 10 were characterized by X-ray structure analysis.
The distortion of the borazine ring by B and N substitution is discussed. In case of the N-substitut-
ed borazines YH2N3B3Me3 the B–N bonds of the YNB2 units are elongated, e. g. for Y = PBr2 or
(RO)3Ti, while N lithiation leads to a shortening of these B–N bond. These changes of bond lengths
are also reflected by changes in the B1–N2 and B3–N3 bond lengths which become shorter in the
presence of electron-withdrawing groups, but longer in case of Li substitution. Also, the bond angles
B1–N2–B2 and B2–N3–B3 are affected by an increase of up to 128◦.
Key words: Borazine Derivatives, Diborane(4) Compound, Aminoalane, Titanium Phenoxide,
X-Ray Structures
Introduction
ent temperature by substitution at the N atom, even
in the presence of triethylamine or piperidine as HX
scavengers. At reflux temperature Me/X (X = Cl,
Br) exchange can be observed by 11B NMR. How-
ever, it is to be expected that the more strongly basic
diethyl ether complex of N-lithio-2,4,6-trimethylbor-
azine, 1 [1], will react with organoboronhalides to give
borazinyl-substitutedorganoboranesas shown in Eq. 1.
The diethyl ether solvate of N-lithio-2,4,6-trimeth-
ylborazine, 1, [1] is a reagent which can be used
in many ways, as, e. g., for the preparation of tri-
methylborazinyl substituted phosphanes, arsanes or
stibanes [2]. These results suggested that 1 can also
be employed to generate N-(2,4,6-trimethylborazinyl)
derivatives of many more elements, compounds that
are of interest for comparison with the corresponding
mesityl compounds. We report here on first results in-
volving compounds of boron, aluminum and titanium.
A more systematic study is presently conducted.
(1)
Similarly, reaction of 1 with BX3 (X = F, Cl, Br)
may give access to borazinyl-substituted haloboranes
and even tris(trimethylborazinyl)borane provided that
there is no steric hindrance for the third substitu-
tion step. Here we describe only reactions according
to Eq. 1. Although most of the studied organoboron
halides react with 1, one observes also Me/halogen ex-
change. This competing reaction leads to mixtures of
Results
Reactions of Me3B3N3H2Li with organoboron halides
Organoboron halides such as Ph2BBr or PhBCl2
do not react with the borazine Me3B3N3H3 at ambi-
* Contribution to the chemisty of boron, 268. For contribu- products which can be analyzed by 11B NMR or mass
tion 267 see: B. Gemu¨nd, B. Gu¨nther, H. No¨th, ARKIVOC,
2008, 136.
spectrometry, but we have been unable to isolate pure
products either by distillation or by crystallization.
0932–0776 / 08 / 0100–0023 $ 06.00 © 2008 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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24
B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
(2)
Scheme 1.
The 1 : 1 reaction of 1 with Ph2BBr in toluene led possible if the lithium borazine becomes additionally
to Ph2BMe (20 %), (Me3B3N3H2)BPh2 (60 %) and metallated (deprotonated) in the course of the reaction.
Me3−xBrxB3N3H3 (20 %). A 1 : 1 mixture of 1 and Most likely the first step in this reaction is the genera-
PhBCl2 in toluene did not react at r. t., but after heating tion compound 4. Its NH proton should be more acidic
to reflux LiCl was formed and the filtrate showed the than the NH groups in compound 1 due to π-bonding
presence of MePhBCl (15 %), (Me3B3N3H2)B(Cl)Ph with an additional boron atom. And, therefore, one NH
(20%), Me3B3N3H3 (45 %), and Me3−xClxB3N3H3 proton is liable to react with a further molecule of 1 by
(20%). tBu2BCl in hexane did not react with 1 even deprotonation, generating compound4. Two molecules
under reflux conditions. On the other hand, a precipi- of 4 can then react with formation of the ten-membered
tate of LiCl was formed rapidly on mixing 1 in hexane ring 5.
with 9-Cl-9-BBN to give the borazinyl-substituted 9-
BBN derivative, but again Cl/Me exchange was also
noted with the formation of 9-Me-9-BBN.
Compound 1 can also be used to synthesize B,N-
borazinyl-borazines. We used this method to prepare
compounds 6, 7 and 8 according to Scheme 3. Non-
optimized yields are in the range from 45 to 70 %.
Reactions of Me3B3N3H2Li with dimethylamino-
chloroboranes and B-haloborazines
NMR Spectra
Table 1 lists the NMR data of the dimethylamino-
borane derivatives 2 and 5 as well as those of the di-
borazines 6, 7 and 8.
In order to prevent the R/X exchange we stud-
ied some reactions of dimethylamino-chloroboranes
and B-haloborazines with 1 because LiX elimina-
The 11B chemical shift for the B(NMe)2 group
tion is the highly preferred pathway for reactions of of 2 is 31.1 ppm. This is 3.4 ppm at lower field
LiR compounds with aminoboron halides [3]. Indeed, compared with B(NMe2)3 and 1.3 ppm compared
no Me/NMe2 exchange was noted for the 1 : 1 reac- with PhB(NMe2)2 [4]. Although one expects two
tion of 1 with (Me2N)2BCl. The reaction proceeded 11B NMR signals for the B atoms of the borazinyl
smoothly in hexane as shown in Eq. 2 to yield the solid group only a single broad signal with a maximum at
compound 2 in 80 % yield. 2 was characterized only
δ
11B = 36.1 ppm is recorded for 5 at ambient tem-
by NMR and IR spectroscopy and by elemental anal- perature showing a small low field shift in compar-
ysis, because no crystals suitable for X-ray structure ison with 1 (δ11B = 35.4 ppm) [1]. However, two
analysis could be grown. In contrast to this straight- 1H NMR signals are observed for the BMe groups of
forward result we observed an unexpected reaction the ring system. The H atoms of the p-BMe group
when 1 was treated with Cl(Me2N)B–B(NMe2)Cl in are slightly deshielded compared to the H atoms in
a 2 : 1 ratio. We had anticipated that the reaction would o-position. Only a single 1H NMR signal is found
take the course as shown in Scheme 1. However, in- for the B(NMe2)2 group, indicating free rotation about
stead of compound 3, we obtained the ten-membered the respective B–N bonds. This was also observed for
ring compound 5 (Scheme 2). Its formation is only PhB(NMe2)2 [4].
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B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
25
Scheme 2.
Scheme 3.
The ten-membered ring compound 5 must be sym- π-character in contrast to bonds of the Me2N groups of
metrical as there are only two NMR signals for the the diborane(4) unit, because the two 1H NMR signals
B atoms, two for the ring methyl groups and two for these groups are compatible with hindered rotation
for the NMe2 groups. The borazinyl groups are rep- about their BN bonds. This makes the two Me groups
resented by an 11B NMR signal at 35.8 ppm. Its of each NMe2 unit non-equivalent.
B atoms are slightly better shielded than in com-
pound 2 (∆ = 1.5 ppm). In contrast, the B atoms of
the diborane(4) units are significantly deshielded com-
pared with other tetra(amino)diborane(4) compounds
whose 11B NMR signals are observed within the range
from 34 – 38.5 ppm [5]. This indicates that bonds of
the borazinyl nitrogen atoms to the B2 units have little
The pentamethyldiborazine 6 should show four
11B NMR signals. However, only two are observed.
The signals at δ = 30.2 and 34.3 ppm are partially over-
lapping indicating an intensity ratio of 1 : 2. The signal
at 34.3 ppm most likely represents BMe groups with
two NH neighbors, while the better shielded boron
atoms are those with a Me/NH/N environment. There
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26
B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
11B
δ1H p-Me δ1H o-BMe δ1H m-BMe δ1H NMe δ1H NH
Table 1. NMR spectroscopic
data of compounds 2 and 5 to 8
(δ values in ppm).
Compound
2
δ
36.1 Borazine
31.1 B(NMe2)2
35.8 Borazine
41.2 B2(NMe2)2
30.2, 34.3
0.34
0.31
2.51
5
6
0.39
0.15
2.64, 2.80
0.33 3H
0.35 6H
0.20
4.33 (1H)
4.09 (2H)
4.55 (2H)
4.53
7
8
35.8, 38.1
35.8, 38.1
0.31 pme
0.27 (6H)
1.35CMe2
4.06 CH
0.26 (6 H)
0.38, 1.28,
3.94 sept.
4.60
Fig. 2. ORTEP plot of compound 5a: Selected bond
˚
lengths (A) and bond angles (deg) (see also Table 3). B5-N5
1.395(4), B4-N4 1.402(3), N1-B4 1.494(4), N3-B5 1.508(3),
B1–N1 1.439(3), B1–N2 1.426(3), B2–N2 1.424(3),
Fig. 1. Atoms in the asymmetric unit of compound 5 B2–N3 1.441(3), B3–N3 1.444(3), B1–C1 1.575(4), B2-C2
1.572(4), B3-C3 1.590(4), B4–B5A 1.731(4); B3–N1–B4
120.0(2), N1–B4–N4 119.4(2), N1–B4–B5A 114.5(2)
113.6(2), N3–B5–B4A 113.6(2), N4–B4–B5A 125.8(2);
torsion angles: N3–B3–N1–B4 −168.5◦, N1–B1–N2–B5
−149.8◦, N5–B5–B4A–N4A −95.9◦, N1–B4–B5A–N3A
−119.6◦.
(ORTEP).
1
are three H NMR signals for the NH groups in a
2 : 1 : 2 ratio as well as for the protons of the Me groups
(δ1H = 0.20, 0.32, 0.34 in a 2 : 1 : 2 ratio). Although
13C resonances for boron-bonded Me groups can of-
ten not be detected as a consequence of the quadrupole groups in 8. Similar to compound 7, one observes
moment of the boron nuclei, two (instead of three) deshielded BMe protons for the Me2B3N3Me3 unit
broad 13C signals were observed at 1.54 and 2.95 ppm. (δ1H = 0.48 ppm) as compared with the BMe protons
of the Me3B3N3H2 group (δ1H = 0.26 and 0.27 ppm).
The B-pentamethyl-N-triisopropyl-diborazine 7 ex-
hibits also only two 11B NMR signals instead of the ex-
pected four. We attribute the signal at 35.8 ppm to the
Me3B3N3H2 borazine ring, and the signal at 38.1 ppm
to the Me2B3N3(iPr)3 group. The two non-equivalent
Me groups of the Me3B3N3H2 unit are represented
The NH protons are represented by two signals at
δ1H = 2.74 and 2.82 (ratio 2 : 1). This shows that the
NH proton in p-position is deshielded compared with
those in the o-positions.
X-Ray structures of compounds 5 and 6
1
by two H NMR signals at 0.31 and 0.38 ppm (ratio
1 : 2), while the proton resonance for the BMe groups
in the Me2B3N3(iPr)3 unit is observed at 0.76 ppm.
There are two signal pairs for the isopropyl groups
(ratio 2 : 1).
The new ten-membered BN heterocycle 5 crystal-
¯
lizes in the triclinic system, space group P1, Z = 2. The
structure determination revealed two crystallograph-
ically independent molecules, with inversion centers
The close similarity of compounds 7 and 8 is being located in the centroids of the ten-membered
demonstrated by two 11B NMR signals which show the rings. Fig. 1 shows the atoms in the asymmetric
same chemical shifts. There are three types of BMe unit, and Fig. 2 one of the two molecules. Charac-
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B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
27
Fig. 3. The puckered ten-membered B6N4 ring of com-
pound 5a.
Fig. 5. View on the four independent molecules of com-
pound 6.
Fig. 4. Side view on molecule 5a: Interplanar angles (deg):
N1B1B2N3/B1N2B2 8.2◦, N1B1B2N3/B1N1B3N3 4.3◦,
N4B4N1/B5AN5AN2A 120.8◦.
Fig. 6. ORTEP plot of one of the four crystallographically
˚
independent molecules of 6 (6A). B–C bond lengths (A):
teristic is the shape of the ten-membered ring built
from two NBN units of two borazine rings and the
two diborane(4) units (Fig. 3). Due to the inver-
sion center the two borazine units are parallel. The
B–N bond lengths within the borazines span a range
B1-C1 1.571(5), B2-C2 1.571(5), B3-C3 1.575(5), B5-C5
1.566(5), B6–C6 1.573(6) (see also Table 3); interplanar an-
gle N1B1N2B2N3B3/B4N4B5N5B6N6: 69.5◦.
˚
These four bonds span a range from 1.49 to 1.51 A.
They represent single bonds between sp2-type N and
B atoms and can be compared with the exocyclic BN
bond lengths found in B-chloro-Bꢀꢀ,Bꢀꢀꢀbis(-dimethyl-
˚
from 1.426 to 1.444(3) A. These bond lengths agree
nicely with those of other B-triorganoborazines [6].
˚
The B–B bond lengths of 1.731(4) A, are shorter
˚
˚
amino)borazine (dBN = 1.497(3) A) [9].
than in B2(piperidine)4 (dB−B = 1.750(8) A) [7],
Bond angles at atom B1 are rather different. The an-
gle N3–B1–B2A is 114.6(2)◦ while those of N1–B1–
B2A and N3–B1–N1 are 125.7(2)◦ and 119.7(2)◦, re-
spectively. This may be due to the higher BN double
bond contribution of the B1–N1 bond. According to
Gillespie and Nyholm the space required for a double
bond is larger than for a single bond [10].
but longer than in bis(1,3-dimethyl-l,2,3-diazaborol-
˚
idines) (1.693(9) A). [8]. All boron atoms reside in
a planar environment, and all N atoms also. There-
fore, conditions for BN-π-bonding seem to be excel-
lent. However, the B–N bond lengths are not as short
as expected for B–N double bonds as found in mono-
aminoboranes, because all boron atoms have two ni-
trogen neighbors. Therefore, the BN bond order could
Fig. 2 shows that the two adjacent BNMe2 units are
be 1.5 at best. One should, therefore, rather compare twisted against each other by 68◦. Similar interplanar
the BN bond lengths with those of e. g. bis(1,3-dimeth- angles between Me2N groups at adjacent boron atoms
˚
yl)-1,3,2-diazaborolidines (1.414(7) A) [8]. The B–N are also observed in dimethylaminotri- and tetrabor-
bonds from the B2 units to the borazine rings are no- anes [11]. The interplanar angle between the Me2N(4)
ticeably longer than those within the borazine rings. and Me2N(N5A) groups is 63.9◦, and the angle be-
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28
B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
Fig. 7. Stereo view of the unit cell of compound 6
down the crystallographic a axis. Note the hydrogen
bond interaction N–H–N.
tween the planes B2N2B1 and B5N5B4A is even in 6B should be shorter than in 6D due the small in-
closer to 90◦ at 81.2◦.
terplanar angle which may allow some BN π-bonding,
but the B–N bond seems to be only slightly shorter than
in 6D. The smaller interplanar angle in 6B brings the
o-Me groups closer to the NH groups of the neigh-
boring borazine rings than in any of the other three
molecules. This steric effect is most likely the reason
that the B–N distances of 6B and 6D are equal within
standard deviations.
Fig. 4 shows that the borazine rings are not planar
but are present in the boat conformation. This con-
formation of the borazine ring is characterized by the
interplanar angles N3B3N1/B3N3B1N21 = 6.8◦ and
B3N3B1N2/B2N2B1 = 11.6◦.
˚
The B-C bond lengths in compound 5 (1.575(4) A)
correspond with B–C single bonds. Only the B5–C7
bond is longer at 1.590(3)◦. This is the bond to the
methyl group that “looks” into the ten-membered ring.
Although 1,1ꢀ-diborazines, 1,2ꢀ-diborazines and
2,2ꢀ-diborazines have peen prepared by various meth-
ods [12 – 15], as well as some bis(borazinyl)borazines
and tris(borazinyl)-borazines [12], none of them has
yet been fully characterized by NMR spectroscopic
methods and by X-ray crystallography [3]. After hav-
ing obtained single crystals of pentamethyl-1,2ꢀ-dibor-
azinyl, 6, we determined its structure by X-ray crys-
Fig. 7 shows a stereoscopic view on the unit cell
of compound 6. It reveals that the molecules are con-
nected by N–H–N hydrogen bridges.
Bis(tetramethylpiperidino)-N-(2,4,6-trimethylborazin-
yl)alane and tris[2,6-(diisopropylphenoxo)]-N-(2,4,6-
trimethylborazinyl)titanium
1-Lithio-2,4,6-triorganylborazines can be pre-
pared form the respective borazines and alkyl-
lithium compounds [1, 17]. By replacing LiR by
triorganoaluminum compounds, borazinyl-substituted
organoalanes might become available. However,
Me3B3N3H3 did not react with (AlMe3)2 under reflux
conditions in toluene. Moreover, [(Me2N)2AlCl]2 did
also not react with 1 even in refluxing toluene. The
missing reactivity may be due to the dimeric nature
of the amino-chloroalane, making the Al center less
attractive for nucleophilic substitution. Therefore,
we studied the reaction of 1 with the monomeric bis
(tetramethyl-piperidino)chloroalane, tmp2AlCl. In this
case we obtained bis(tetramethylpiperidino)-N-(2,4,6-
trimethylborazinyl)alane, 9, in 85 % yield. It is formed
according to Eq. 3.
¯
tallography. The crystals are triclinic, space group P1.
The unit cell contains 8 molecules of 6, i. e., there are
four independent molecules in the asymmetric unit.
Fig. 5 shows these four molecules and Fig. 6 molecule
6A. The N1–B4 bond which connects the two bor-
azinyl units in 6C is the longest B–N bond within
˚
the molecule with 1.492(3) A. In the molecules 6A,
6B and 6D this B–N bond is shorter: B14–N11 =
˚
˚
1.480(4) A, B24–N21 = 1.485(3) A and B34–N31 =
˚
1.484(3) A. There is a correlation between these B–N
bond lengths and the interplanar angles of the two
borazine units in each diborazine molecule, which
are 69.5◦ for molecule 6A, 60.5◦ for molecule 6B,
86.6◦ for molecule 6C, and 82.3◦ for molecule 6D. The
Reactions of TiCl4 with 1 in various molar ratios
BN π-bonding contribution must be zero in the case from 1 : 1 to 1 : 4 led to yellow and even colorless
of 6C. For similar reasons, the B14–N11 bond length suspensions containing insoluble LiCl. The amount of
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B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
29
(3)
(4)
Table 2. NMR spectroscopic data of compounds 9 and 10
(δ values in ppm).
Compound
δ
11B
35.8, 37.7 0.74
34.0 0.29
δ1H (o-Me) δ1H (p-Me) δ1NH 27Al
δ
9
10
0.29
0.19
4.55
4.38
110.0
–
LiCl formed was in most cases > 90 %. However, at-
tempts to obtain well defined products from toluene so-
lutions at −78 ◦C were unsuccessful. Mass spectromet-
ric analysis showed the presence of the molecular ions
for all members of the series (Me3B3N3H2)nTiCl4−n
(n = 1, 2, 3, 4), but no pure compound could be iso-
lated from the mixture by extraction or crystallization.
Also an attempt to prepare Me2NTi(H2N3B3Me3)3
from Me2NTiCl3 and 1 failed. As we could prepare
the borazinyl-bis-(amino)alane7 by using a monofunc-
tional aluminum species we treated the bulky tris(2,6-
diisopropylphenoxo)titanium chloride with 1. Indeed,
this reaction generated the expected borazinyltitanium
compound 10 as shown in Eq. 4. Compound 10 was
isolated in 80 % yield.
Fig. 8. ORTEP presentation of the molecular structure of
˚
compound 9. Selected bonding parameters (in A or deg;
see also Table 4): Al1-N3 1.821(2), N3-C7 1.496(3), N3-C3
1.499(3), B1-C1 1.577(4), B2-C2 1.581(6); N3–Al1–N3A
124.6(1), N3–Al1–N1 117.69(7), Al1–N3–C3 122.4(2),
Al1–N3–C7 121.8(2), C3–N3–C7 115.8(2).
Spectroscopic characterization
Table 2 lists some relevant NMR spectroscopic data
of compounds 9 and 10.
While compound 9 shows two 11B NMR signals for
the borazinyl substituent, compound 10 exhibits only a
broad signal (h1/2 = 450 Hz). However, in both cases,
1
two H NMR signals for the BMe groups were de-
tected. Because the intensity of the proton signals for
the Me groups in ortho-position is twice that of the
para-position, assignment of the two 1H NMR signals
is unequivocal. From this point of view it is surprising
that the shift difference between the BMe protons for
compound 9 is 0.35 ppm, but only 0.1 ppm for 10. The
27Al resonance at 110 ppm lays in the high field range
for monomeric bis(tetramethylpiperidino)alanes [18].
Fig. 9. ORTEP plot of the titanium compound 10: Se-
lected bond lengths and bond angles (see also Table 4):
B1-C1 1.578(6), B2-C2 1.582(6), B3-C3 1.583(6); O1–C4–
C9 119.7(3), O1–C4–C5 118.5(3), O2–C16–C17 118.5(3),
O2–C16–C21 117.9(4), O3–C28–C29 119.1(3), O3–C28–
C33 118.8(3).
X-Ray structures
lographic twofold axis. The tricoordinated N atoms of
The crystals of the aluminum compound 9 are the tmp ligand are of the sp2 type. They are present in
monoclinic, space group C2/c with Z = 4. There- a distorted trigonal planar environment. This arrange-
fore, the molecule must show crystallographic symme- ment is also found for the Al atom which is surrounded
try. Fig. 8 depicts the structure of the molecule. The by three N atoms which share a plane with the Al atom.
˚
atoms Al1, N1, B2 and C2 are located on a crystal- The Al–N bonds to the tmp substituents (1.821(2) A)
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30
B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
Table 3. Selected bond lengths
5a
5b
6a
6b
6c
6d
˚
(A) and bond angles (deg) of
N1–B1
B1–N2
N2–B2
B2–N3
N3–B3
B3–N1
N1–B4
B4–N4
N4–B5
B5–N5
N5–B6
B6–N6
1.446(3)
1.445(3)
1.442(3)
1.427(4)
1.425(4)
1.440(3)
1.494(4)
1.402(3)
1.448(4)
1.447(4)
1.441(3)
1.427(4)
1.428(4)
1.435(3)
1.507(3)
1.395(4)
1.443(4)
1.432(4)
1.419(4)
1.418(5)
1.431(4)
1.441(4)
1.481(4)
1.409(4)
1.426(4)
1.425(5)
1.427(5)
1.426(4)
1.430(49
1.440(4)
1.427(4)
1.423(4)
1.414(4)
1.423(4)
1.443(4)
1.485(4)
1.419(4)
1.436(4)
1.428(5)
1.428(5)
1.430(5)
1.417(4)
1.439(4)
1.424(4)
1.413(4)
1.427(4)
1.436(4)
1.433(4)
1.492(4)
1.421(4)
1.427(4)
1.417(5)
1.424(5)
1.434(4)
1.409(5)
1.439(4)
1.429(4)
1.428(4)
1.426(4)
1.430(4)
1.437(4)
1.484(4)
1.421(4)
1.438(4)
1.428(5)
1.422(5)
1.439(4)
1.417(4)
compounds 5 and 6.
1.395(4)
1.399(3)
N6–B4
B4–B5A
B1–N1–B3
B2–N3–B3
N2–B2–N3
1.729(4)
119.4(2)
124.2(2)
117.1(2)
1.727(4)
119.7(2)
123.6(2)
117.2(2)
120.6(2)
125.4(3)
114.3(3)
119.6(2)
125.6(3)
1141(3)
120.7(2)
124.1(3)
114.7(3)
120.7(2)
125.3(3)
114.4(3)
are somewhat shorter than the Al–N bond to the bor- are the shortest. This distortion of the ring becomes
˚
azine group (1.844(3) A). This is probably the effect of also apparent by the bond angles. Angle B1–N1–B3
a different twisting of these groups. The interplanar an- is 118.9(3)◦, the N–B–N bond angles on atoms B1
gle between the two C2N units of the tmp substituents and B3 are 117.3(4) and 117.9(3)◦, and at atom B2
is 90.7◦. The borazine plane forms an angle of 125.1◦ even sharper with 113.9(4)◦. In contrast, the B1–N2–
with the N1C3C7 plane. These interplanar angles indi- B2 and the B2–N3–B3 bond angles are 126.1(4)
cate that there is no Al–N π-bonding. The twisting of and 126.5(4)◦.
the tmp groups and the borazine unit is due to steric
The isopropyl groups are bent away from the TiO3
interactions of the methyl groups. Closest H···H con- core, a steric effect to avoid close contacts between
˚
tacts are between 2.3 and 3.1 A.
their Me groups. In line with this is the observation
that the methyl groups Me1 and Me3 of the borazinyl
unit are also bent away from the TiO3 core as shown by
the bond angles N1–B1–C1 and N1–B3–C3 (124.6(4)
and 123.0(3)◦, respectively).
The molecular structure of the titanium com-
pound 10 is shown in Fig. 9. This yellow compound
crystallizes in the monoclinic system, space group
P21/n, Z = 4. Its Ti atom resides in a distorted tetra-
hedral environment of three oxygen atoms and one
nitrogen atom. The O–Ti–O and O–Ti–N bond an-
gles span a range from 104.8(1) to 112.7(1)◦. Its Ti–O
bond lengths are slightly different, the shortest one is
Ti1–O2 (1.760(2)A), the longest Ti1–O1 (1.801(2)A),
while the Ti1–N1 bond is slightly longer (1.941(3) A).
A look at the C–O distances shows that these bonds are
all very short (1.371, 1.372, 1.380(4) A). This can be
Discussion and Outlook
The value of N-lithio-2,4,6-trimethylborazine as a
reagent is limited when competing reactions can take
place as has been demonstrated for its reactions with
organoboron chlorides and bromides. In this case a
Me/X exchange occurs besides the substitution. This
exchange can, however, be suppressed by using amino-
boron chlorides. The formation of compound 2 is
achieved because no Me2N/Me exchange takes place.
However, the substitution reaction may take a course
different as the expected one as shown for the system 1
˚
˚
˚
˚
understood as the C–O–Ti bond angles are quite open:
C4–O1–Ti1 (151.0(2)◦), Ti1–O2–C16 (167.7(2)◦) and
Ti1–O3–C28 (155.4(2)◦), i. e. the O atoms approach sp
hybridization.
The introduction of the (RO)3Ti unit as a sub- and B2Cl2(NMe2)2, where a ten-membered BN ring
stituent at atom N1 of the 2,4,6-trimethylborazine system, 5, is generated. This can only be understood
ring affects the symmetry of the B3N3 ring sig- if the borazinyl unit is doubly metallated. Because we
nificantly. The B–N bonds to atom N1 are rather have so far no evidence that solutions of 1 in ethers
˚
long (1.460(5) A). The neighboring bonds, B1-N2 and or hydrocarbons are unstable with respect to dispro-
˚
N3-B3 (1.427(5) and 1.426(5) A) correspond with portionation into Me3B3N3H3 and Me3B3N3HLi2, the
B–N bond lengths found in many borazine rings, while additional deprotonation of 1 must occur during the re-
the bonds N2-B2 and B2-N3 at 1.419(6) and 1.415(6) action.
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B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
31
˚
Table 4. Selected bond lengths (A) and bond angles (deg) for
strongly electrophilic groups such as CF3, SO3CF3 etc.
or strongly electropositive groups to further substanti-
ate the present view and to compare their structures
with comparable mesityl derivatives.
compounds 9 and 10.
9
10
9
10
126.9(2)
113.6(3)
M–N1 1.844(3) 1.941(3) M–N1–B1 121.0(2)
N1–B1 1.448(3) 1.460(5) M1–N1–B3 121.0(2)
B1–N2 1.441(4) 1.427(5) B1–N1–B3 117.9(3) B3=B1a 118.9(3)
Experimental Section
All experiments were performed by using the Schlenk
techniques with N2 as the protecting gas.
Solvents were made anhydrous by conventional methods.
NMR: Bruker ACP 200 (1H, 11B, 13C), Jeol GSX 270 (1H,
27Al). Standards: C6D6, SiMe4, 1 M aqueous Al(NO3)3 so-
lution, BF3 · OEt2 external. – IR: Nicolet 520 FT; Nujol-
Hostaflon mulls. – Siemens P4 diffractometer with area de-
tector and LT2 low temperature device. – MS: Atlas CH 4
(70 eV).
N2–B2 1.415(3) 1.419(6) N1–B1–N2 119.0(3)
117.3(4)
126.1(4)
B2–N3
N3–B3
B3–N1
1.415(6) B1–N2–B2 124.8(3)
1.426(5) N2–B2–N3 114.4(4) N3=N2a 113.9(4)
1.460(5) B2–N3–B3
N3–B3–N1
125.5(4)
117.9(4)
117.9(4)
N3–B3–N1
1 proved to be a useful reagent for the preparation
of B–N-borazinyl borazines. The introduction of the
borazinyl unit into Al and Ti compounds was, so far,
only successful with mononuclear monochlorides of
Al and Ti.
Reaction of 1 with Ph2BBr
The introduction of substituents, such as lithium,
boron, aluminum, phosphorus, arsenic, antimony or ti-
tanium on the trimethylborazine ring leads to a sig-
nificant distortion of the Me3B3N3H2 unit, and even
the ring planarity may be lost. These distortions can
readily be seen by comparing the B–N bond lengths of
the rings as well as their endocyclic angles [1, 17, 19].
The distance between the metal/non-metal-substituted
N atom to its para B atom (in most cases N1···B2)
may thus be used as a probe for the inductive effect
of the substituents at atoms N1 and/or N4. However,
as the other B–N bond lengths besides those to N1 are
also affected the B2-N1 distance turned out not to be a
good reference. Therefore, we restrict our discussion to
the N1-B1 and N1–B3 bond lengths and the B1–N1–
B3 bond angles. Table 4 lists some of the relevant
data.
To a stirred solution of
1 (570 mg, 2.8 mmol)
in toluene (30 mL) was added a solution of Ph2BBr
(620 mg, 2.80 mmol) in toluene (20 mL). A white pre-
cipitate was formed rapidly. After stirring over night the
solid (LiBr, yield 101 %) was removed by filtration. The
solution showed 11B NMR signals at 75.1 (Ph2BMe,
20 %), 35.3 (Me3B3N3H2BPh2, 60 %) and 31.3 ppm
(Me3−xBrxB3N3H3, 20 %). Attempts to separate the compo-
nents were unsuccessful.
Reaction of 1 with PhBCl2
To a solution of 1 (530 mg, 2.63 mmol) in toluene (30 mL)
was added at ambient temperature a solution of PhBCl2
(0.35 mL, 2.63 mmol) in toluene (20 mL). No reaction
was observed. Therefore, the mixture was kept at reflux for
one day. Then the precipitate (LiCl) was removed by filtra-
tion. The filtrate showed 11B NMR signals at 70.1 (MePh-
BCl, 15 %), 51.6 and 35.6 (PhClB–N3H2B3Me3, 65 %)
and 31.4 ppm (Me3−xClxB3N3H3, 20 %). – MS: m/z =
245 [Me3B3N3H2–BPhCl]+, 224 [Me3B3N3H2–BPhMe]+,
143 [Me2ClB3N3H3]+, 138 [MePhBCl]+.
Table 5 contains preferentially data of unsymmet-
rically substituted borazines, because the ring B–N
bonds in symmetrically substituted borazines differ
only marginally. It shows only data for the boron or ni-
trogen atoms which are unique considering that these
borazines either have a mirror plane or a twofold axis,
or show no symmetry at all. Standard deviations are
Reaction of 1 with tBu2BCl
To a stirred solution of tBu2BCl (520 mg, 2.55 mmol) in
hexane (50 mL) was added at ambient temperature a solution
of 1 (410 mg, 2.53 mmol) in hexane (10 mL). No reaction
was observed at ambient temperature and after keeping the
solution at reflux for 3 d.
˚
usually in the range of 0.003 to 0.005 A. Bond length
˚
differences > 0.01 A represent significant differences
as shown for the substituents Ti(OR)3, SbCl2 or PBr2.
These groups induce a significant bond lengthening,
while N-lithio derivatives show N1-B1/3 distances that
are significantly shorter than the average B–N bond of
Reaction of 1 with 9-chloro-9-borabicyclo [2.2.1]nonane
To a stirred solution of 1 (280 mg, 1.41 mmol) in
toluene/diethyl ether (30/10 mL) was added a solution
of 9-Cl-9-BBN (220 mg, 1.41 mmol) in 10 mL of toluene.
A white precipitate was formed rapidly. After stirring over
night the solid was removed by filtration. The filtrate showed
˚
borazines (1.43 A) (Scheme 4, Table 5). This is due to
the higher electron density at atom N1 which strength-
ens BN-π-bonding. It will be of interest to investigate
unsymmetrically substituted borazines carrying very 11B NMR signals at 35.8 (borazine moiety), 72.3 (B atom
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32
B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
of 9-BBN) and 88.7 (9-Me-9-BBN). After removal of the (s, o-BMe, 6H), 4.54 (s, NH, 1H), 2.64, 2.80 ppm (s, NMe,
solvents a viscous oil remained from which no pure product 12H); δ13C = 36.53 ppm (NMe); δ11B = 35.9, 41.3 ppm
could be isolated by distillation.
(br). – IR (nujol, hostaflon, cm−1): ν = 3440 st, 3000 m,
2955 st, 2922 st, 2872 st, 2856 st, 2793 m, 1474 st, 1408 st,
1346 st, 1325 st, 1298 st, 1273 m, 1183 m, 1145 st, 1112 m,
1093 m, 1075 m, 1063 m, 1046 m, 1016 m, 954 w, 942 w,
891 st, 838 w, 755 w, 709 st, 634 w, 588 w, 580 w, 569 w,
399 w. – C14H44N10B10(460.68): calcd. C 36.50, H 9.63,
N 30.40; found C 36.12, H 9.81, N 29.96.
Reaction of 1 with 2-chloro-1,3-bis(isopropyl)benzo-1,3,2-
diazaborolidine
To a stirred solution of 1 (810 mg, 3.98 mmol) in a mix-
ture of hexane and diethyl ether (30/5 mL) was added a so-
lution of the B-chlorodiazaborolidine (1.12 g, 3.98 mmol)
in hexane (10 mL). The solution turned yellow, but no LiCl
precipitate was formed. Heating to reflux generated a white
precipitate within one h. The mixture was kept boiling for
one day. The solid was then removed from the red solution
by filtration. 11B NMR signals were observed at δ = 22.8
(borolidine unit), 29.1 (1) and 35.4 ppm (trimethylborazine
unit). No crystalline material was formed on attempted crys-
tallization from various solvents.
2,4,6-2ꢀ,4ꢀ-Pentamethyl-B–N-diborazinyl, 6
2,4,6-Trimethylborazine (715 mg, 8.16 mmol) dissolved
in diethyl ether (20 mL) was treated with ◦LiBu (5.5 mL of
a 1.6 M LiBu solution in hexane) at −78 C, and the solu-
tion kept at reflux for 5 h. The turbid solution was dropped
into a solution of 2-bromo-4,6-dimethylborazine (1.17 g,
8.1 mmol) in hexane (50 mL) cooled to −78 ◦C. The mixture
was then kept for 5 h at reflux. After removing the result-
◦
ing solid by filtration the filtrate was stored at −20 C. This
Bis(dimethylamino)-N-(2,4,6-trimethylborazinyl)borane, 2
led to the formation of colorless single crystals of 6. Yield:
◦
835 mg (45 %), m. p. 57 – 58 C. – NMR (in C6D6): δ1H =
A solution of (Me2N)2BCl (530 mg, 3.98 mmol) in hex-
ane (10 mL) was added to a stirred solution of 1 (810 mg,
3.98 mmol) in a mixture of hexane and diethyl ether
(30/5 mL). A fine white precipitate was formed. After the
addition was complete the suspension was stirred for one
day. Then the solid was removed and the volume of the
0.20 (s, BMe, 6H), 0.33 (s, BMe, 3H), 0.35 (s, BMe, 6H),
4.09 (s, NH, 3H), 4.55 ppm (s, NH, 2H); δ13C = 1.54 (Me),
2.95 ppm (Me). – IR (nujol, hostaflon, cm−1): ν = 3442 st,
3422 st, 2950 m, 2908 m, 2866 m, 2397 w, 1806 w, 1670 w,
1647 w, 1586 w, 1482 st, 1459 st, 1300 st, 1208 st, 1198 m,
1183 m, 1670 w, 1647 w, 1586 w, 1483 st, 1459 st, 1333 st,
1314 st, 1300 st, 1208 st, 1198 m, 1183 m, 1156 m, 1127 m,
1120 m, 1080 m, 892 st, 826 w, 806 w, 734 st, 721 st, 703 m,
684 m, 671 m, 578 m, 534 m, 506 m, 460 w, 441 w. – MS: m/z
(%) = 229 (80) [M]+, 214 (100) [M–Me]+, 199 (90) [M–2
Me]+, 184 (15) [M–3 Me]+, 116 (45) [MeB3N3BNH]+,
91 (75) [MeB3N3H]+, 82 (10) [Me2B2N2H2]+, 66 (60)
[Me2B2N2H]+, 41 (30) [MeBNH]+.
1
filtrate r◦educed to /4. Storing the solution for one week
at −25 C generated tiny colorless crystals. Recrystalliza-
tion from toluene, diethyl ether or THF produced no crys-
tals suitable for X-ray structure determination. Yield: 700 mg
(80 %). – NMR data (C6D6): δ1H = 0.31 (s, NMe, 6H), 0.34
(s, BMe, 3H), 2.51 (s, NMe, 12H), 4.62 ppm (s, NH, 2H);
δ11B = 31.1, 36.0 ppm (overlapping signals). – IR (nujol,
hostaflon, cm−1): ν = 3443 m, 3439 m, 2997 m, 2960 st,
2923 st, 2872 st, 2791 m, 1531 wt, 1466 st, 1456 st, 1409 st,
1388 st, 1361 st, 1261 st, 1228 st, 1145 m, 1128 st, 1101 m,
1066 m, 1020 m, 891 m, 845 w, 804 m, 708 m, 660 w, 402 w,
326 w. – C7H23N5B4 (220.51): calcd. C 38.13, H 10.51,
N 31.75; found C 39.17, H 10.44, N 30.77.
2,4,6, 4ꢀ,6ꢀ-Pentamethyl-1ꢀ,3ꢀ,5ꢀ-triisopropyl-B,N-diborazin-
yl, 7
In analogy to 6 a solution of 1 (740 mg, 3.56 mmol)
in hexane/diethyl ether (230/10 mL) was dropped into a
solution of 2-bromo-4,6-dimethyl-2,3,5-triisopropylborazine
(1.14 g, 3.46 mmol) in hexane (10 mL). At r. t. no reac-
tion was observed. After heating for 3 days at reflux, LiBr
1,1ꢀ,3,3ꢀ-Bis(dimethylamino)diboryl-2,4,6-trimethylborazin-
yl-2ꢀ,4ꢀ,6ꢀ-trimethylborazine, 5
To a stirred solution of 1 (1.00 g, 4.93 mmol) in hex- precipitated and was removed by filtration from the sus-
ane (50 mL) was slowly added at −78 ◦C a solution of pension. Crystals separated from the concentrated solution
Cl(Me2N)B–B(NMe2)Cl (450 mg, 2.46 mmol) in hexane (redu◦ced to 1/4 of its original volume) while it was stored
◦
(10 mL). After warming to r. t. and stirring for 2 h a white at 5 C. Yield: 880 mg (70 %), m. p. 173 C. The crystals
precipitate had formed. The suspension was kept at reflux turned out to be twins. Crystallization from CHCl3, CH2Cl2,
over night. Then the solid was removed by filtration. The so- or diethyl ether gave no crystals suitable for X-ray crystal-
lution was concentrated to 1/4 of its original volume in vacuo. lography. – NMR (C6D6): δ1H = 0.31 (s, BMe, 3H), 0.38
◦
The remaining solution was stored at −25 C. Single crys- (s, BMe, 6H), 4.53 (s, NH, 2H), 0.76 (s, BMe, 6H), 1.28
tals separated within a few days. Yield: 510 mg (45 %), m. p. (d, CMe, 12H), 1.35 (d, CMe, 6H), 3.94 (sept., CH, 2H),
142 ◦C. – NMR (in C6D6): δ1H = 0.15 (s, p-BMe, 3H), 0.39 4.06 ppm (sept., CH, 1H); δ13C = 23.5, 23.9 (CMe), 46.4,
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B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
33
Table 5. The influence of sub-
stituents X on the lengths of
A
1.437
1.441
B
C
D
E
F
1.471
1.450
G
H
I
B1–N1
B1–N3
1.449
1.449
117.1
1.557 1.440 1.435
1.423 1.432 1.450
1.444 1.439 1.439
1.451 1.440 1.435
115.9 117.0 119.3
˚
the B–N or N–B bonds (A) and
on the respective NBN or BNB
bond angles (deg). For the num-
bering of the compounds see
Scheme 4.
N1–B1–N3 115.8
103.6 115.6 115.64 116.7
M
1.424 1.439 1.417
1.423 1.437 1.415
K
1.419
1.419
L
1.424
1.423
N
O
P
Q
R
S
N1–B1
N3–B1
1.414
1.420
117.2
1.422 1.411 1.421
1.411 1.413 1.425
118.3 117.1 117.4
N1–B1–N3 117.4
117.65 117.7 124.7 117.4
5
6
9
10
PBr2
SbCl2 PCl
PBr
PH
N1–B1
N1–B3
B1–N1–B3 119.4
1.446
1.440
1.441
1.441
120.6
1.448 1.460 1.482
1.448 1.462 1.482
117.1 118.9 119.8
1.470
1.465
120.9
1.474 1.475 1.452
1.481 1.469 1.464
119.1 120.5 120.4
PHzwit P2
N1–B1
N1–B2
1.462
1.439
1.44
1.49
118.0
B1–N1–B3 121.3
NHSi(NMe2)3
Me
Ph
H
B
H
tBu
Me
Me
B
B
tBu
N
B
N
B
N
N
B
N
B
N
B
B
NHSi(NMe2)3
N
H
(Me2N)3SiHN
NH P(N3P2(NMe2)4
N
F
Me
N
H
F
2
Me
A [19]
Si(SiMe3)3
C [21]
B [20]
SiMe3 SiMe3
N(SiMe2NH)2SiMe2
MeS
B
N
N
SMe
Me
Me
Me
B
Et
N
Et
B
B
N
B
N
N
B
N
B
N
B
N
B
F
N
Me3Si
B
N
B
N
SiMe3
Me
N
F
Me
Et
SiMe3
Me3Si
B
D [22]
F [24]
SMe
E [23]
GePh3
N(SiMe3)2
N(SiMe2NH)2SiMe2
Me
Me
B
N
Et
Et
B
Et
N
Et
B
N
N
B
N
B
N
B
B
B
N
B
Me
Me
N
(Me3Si)2N
)2NH
N
F
N(SiMe2NH)2SiMe2
Me
Et
Et
I [25]
G [24]
H [24]
Me
B
CH2SiCl3
H
H
B
Me
Me
N
B
N
B
N
B
N
B
L [26]
K [6b]
N
H
Cl3SiH2C
CH2SiCl3
N
Me
Me
Me
H
H
Cl
NiPr2
N
N
B
N
N
B
Pr2Ni
B
M [27]
N
B
N H
B
B
H
Cl
H
NiPr2
Scheme 4. Borazines cited in Table 5.
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34
B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
Scheme 4 (continued). Borazines cited in Table 5.
NMe, 6H), 2.82 (s, NMe, 3H), 4.60 ppm (s, br, NH, 2 H);
δ11B = 38.1, 35.8 ppm. – IR (nujol, hostaflon, cm−1): ν =
3455 w, 3434 w, 3004 m, 2965 st, 2895 m, 1566 w, 1471 st,
1439 st, 1417 st, 1371 st, 1346 st, 1336 st, 1319 st, 1302 st,
1254 st, 1242 st, 1203 st, 1184 st, 1162 st, 1135 st, 1115 st,
1025 w, 999 m, 984 m, 886 w, 855 w, 844 w, 808 w, 746 w,
704 w, 675 m, 650 w. – MS: m/z (%) = 271 (75) [M]+, 256
(100) [M–Me]+, 241 (20) [M–2 Me]+, 226 (20) [M–3 Me]+,
48.7 ppm (CMe2); δ11B = 35.8, 38.1 ppm. – IR (nujol,
hostaflon, cm−1): ν = 3475 w, 3437 w, 3026 w, 3004 m,
2961 st, 2875 st, 1561 w, 1470 st, 1440 st, 1419 st, 1360 st,
1334 st, 1319 st, 1302 st, 1254 st, 1242 st, 1205 st, 1184 st,
1161 st, 1135 st, 1120 st, 1025 w, 999 m, 984 m, 962 w,
896 w, 885 m, 855 w, 844 w, 808 w, 764 w. – MS: m/z
(%) = 355 (10) [M]+, 340 (75) [M–Me]+, 325 (25) [M–2
Me]+, 233 (55) [Me2B3N3iPr2]+, 218 (20) [MeB3N3iPr3]+,
203 (15) [B3N3iPr3]+, 190 (12) [Me2B3N3iPr2]+, 147 (15)
[Me2B3N3iPr]+, 122 (55) [Me3B3N3H2]+. – C14H38N6B6
(355.36): calcd. C 47.32, H 10.78, N 23.65; found C 46.12,
H 11.01, N 23.52.
150 (65) [Me2B2N3M3]+, 121 (45) [Me3B3N3H2]+.
2,4,6-Trimethylborazinyl-bis(tetramethylpiperidino)alane, 9
To a stirred solution of 1 (0.876 g, 4.29 mmol) in toluene
(50 mL) were added 23 mL of a 0.2 M solution of tmp2AlCl
(4.6 mmol). A solid separated after about 15 min. The sus-
pension was then heated to reflux over night and the LiCl
precipitate was removed by filtration. The filtrate was re-
duced in volume to about 1/3. Storing the solution at −25 ◦C
◦
provided colorless crystals of 9, m. p. 293 C. Yield: 1.56 g
(85 %). – NMR (in C6D6): δ1H = 0.29 (s, BMe, 3H), 0.74
(s, BMe, 6H), 1.39 (t, β-CH2, 8H), 1.44 (s, Me, 24H), 1.50
(quint, tmp-γ-CH2), 4.55 ppm (s, NH, 2H); δ13C = 18.8
(tmp-γ-CH2), 34.2 (tmp-Me), 39.5 (tmp-β-CH2), 52.5 ppm
(tmp-α-CH2); δ27Al = 110 ppm (h1/2 = 60 Hz). – IR (nu-
2,4,6,2ꢀ,4ꢀ,6ꢀ,3ꢀ,5ꢀ-Octamethyl-N,B-diborazinyl, 8
A solution of BrMe2B3N3Me3 (960 mg, 4.19 mmol) in
hexane (20 mL) was added to a solution of 1 (850 mg,
4.19 mmol), dissolved in hexane/diethyl ether (20/10 mL). jol, hostaflon, cm−1): ν = 3443 m, 3414 m, 2960 st, 2923 st,
No reaction was observed at ambient temperature. After 2857 st, 1473 st, 1404 st, 1378 st, 1362 st, 1345 m, 1333 m,
keeping the mixture at reflux for several hours, a solid had 1306 st, 1299 st, 1235 st, 1201 m, 1177 m, 1131 st, 1065 m,
formed which was removed by filtration. 3/4 of the solvents 1007 w, 884 m, 977 m, 942 m, 926 w, 897 w, 887 w, 865 w,
was removed from the filtrate in vacuo. The soilid that sep- 798 w, 754 w, 715 m, 654 w, 506 w, 528 w, 500 w. – MS:
arated corresponded to a yield of 60 % (680 mg). However, m/z (%) = 429 (25) [M]+, 414 (45) [M–Me]+, 289 (85)
no single crystals could be grown from solutions in CH2Cl2, [M–tmp]+, 274 (100) [M–Me–tmp]+, 166 (30) [tmpAl]+,
diethyl ether or toluene. – NMR (in C6D6): δ1H = 0.26 (s, 122 (15) [Me3B3N3H2]+. – C21H47N5B3Al (429.05): calcd.
BMe, 3H), 0.27 (s, BMe, 6H), 0.49 (s, BMe, 6H), 2.74 (s, C 58.79, H 11.04, N 16.92; found C 56.67, H 10.65, N 16.64.
Unauthenticated
Download Date | 4/12/19 1:52 PM

B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
35
Table 6. Crystallographic data
and data related to structure so-
lution and refinement.
Compound
5
6
9
10
Chem. formula
Form. wght.
Size [mm]
C
14H44B10N10
C10H20B6N6
229.13
C21H48AlB3N5
430.05
C39H62B3N3O3Ti
702.25
460.69
0.15×0.15×0.3 0.1×0.2×0.3 0.10×0.20×0.2 0.30×0.20×0.20
a
−1 = σ2Fo2 +(xP)2 +yP;
Cryst. system
Space group
triclinic
P1
triclinic
P1
monoclinic
C2/c
16.5611(5)
12.9165(4)
12.2131(3)
90
94.49
90
2604.5(1)
4
1.097
monoclinic
P21/n
11.8290(8)
28.392(2)
12.6987(8)
90
97.653(1)
90
4226.8(5)
4
1.102
0.239
1512
−13 ≤ h ≤ 13
−31 ≤ k ≤ 23
−14 ≤ l ≤ 14
46.52
193(2)
18659
5636
3529
0.079
465
0.0879/1.2253
1.012
0.057
0.117
0.24
w
¯
¯
P = (Fo2 +2Fc2)/3.
˚
a, A
7.8592(6)
11.9674(9)
16.255(1)
107.278(2)
92.094(1)
101.607(1)
1422.4(2)
2
1.076
0.063
496
−9 ≤ h ≤ 9
−15 ≤ k ≤ 13
−19 ≤ l ≤ 22
58.12
193(2)
8314
7.929(3)
16.315(4)
22.668(8)
84.12(1)
89.81(1)
78.94(1)
2862(2)
8
˚
b, A
˚
c, A
α, deg
β, deg
γ, deg
3
˚
V, A
Z
ρ(calc), Mg m−3
µ, mm−1
F(000), e
Index range
1.063
0.064
976
0.095
948
−19 ≤ h ≤ 19
−7 ≤ h ≤ 9
−15 ≤ k ≤ 18 −15 ≤ k ≤ 15
−15 ≤ l ≤ 26 −13 ≤ l ≤ 12
2θ, deg
Temp, K
Refl. collect.
Refl. unique
Refl. obs. (4σ)
Rint
49.42
193(2)
6823
6764
5510
0.031
670
49.42
193(2)
6151
1921
1729
0.021
149
0.0948/5.5606
1.050
0.062
0.168
0.92
4490
3147
0.025
307
No. variables
Weighting scheme x/ya 0.0603/0.5746
0.017/2.976
1.307
0.078
0.154
0.35
GOOF
Final R (4σ)
1.124
0.056
0.137
0.29
Final wR2 −3
˚
∆ρmax, e A
Tris(2,6-diisopropyl-phenoxo)-N-(2,4,6-trimethylborazinyl)
titanium, 10
X-Ray structure analysis
Single crystals were placed in precooled perfluoroether
1 (100 mg, 0.49 mmol) was dissolved in diethyl ether oil at −25 ◦C and a specimen selected under the micro-
(5 mL). To this solution was added dropwise and with stirring scope. It was transferred onto a glass fibre mounted on
a solution of (2,6-iPr2C6H3O)3TiCl (300 mg, 0.49 mmol) the goniometer head. The goniometer head was then trans-
dissolved in diethyl ether (10 mL). A white precipitate ferred to the goniometer which was cooled with a stream
formed rapidly. After stirring for additional 2 h the solid of gaseous dinitrogen to −80 ◦C. Five sets of data were
was removed by filtration from the yellow solution. Most collected on 25 frames, each at different settings with ω
of the diethyl ether was then evaporated in vacuo, Yellow changed by 0.4◦. These reflections were used to calcu-
crystals formed within 3 months from the viscous residue. late the dimensions of the unit cell using the program
◦
Yield: 270 mg (80 %); m. p. > 250 C. – NMR: (in C6D6): SMART [28]. Data were collected in the hemisphere mode
δ1H = 0.19 (s, BMe, 3H), 0.29 (s, BMe, 6H), 4.38 (s, NH, and reduced with the program SAINT [29]. The programs
2H), 1.13 (d, CHMe2, 36H), 3.69 (sept., CHMe2, 6H), 6.87 – SHELXTL [30] or SHELXL-97 [31] were used for structure
7.15 ppm (m, H arom, 9H); δ11B = 34.0 ppm. – IR (cm−1): solution and refinement. The molecular structures are de-
ν = 3436 m, 3420 m, 3057 m, 3032 w, 3013 w, 2961 m, picted with displacement ellipsoids at the 25 % probability
2927 st, 2886 m, 2868 st, 1587 w, 1550 w, 1486 st, 1473 st, level.
1434 st, 1361 m, 1324 st, 1305 w, 1295 w, 1281 m, 1254 st,
CCDC 657260 (6), 657261 (9), 657262 (5) and 657263
1194 st, 1168 m, 1145 w, 1139 w, 1102 m, 1072 w, 1058 w, (10) contain the supplementary crystallographic data for
1044 m, 1023 w, 912 st, 880 m, 795 m, 750 m, 721 st, this paper. These data can be obtained free of charge
617 m, 593 w, 574 w, 536 w, 424 m, 388 m, 355 m. – from The Cambridge Crystallographic Data Centre via
C39H62O3N3B3Ti (701.25): calcd. C 66.80, H 8.91, N 5.99; www.ccdc.cam.ac.uk/data request/cif.
found C 66.53, H 8.85, N 5.68.
Unauthenticated
Download Date | 4/12/19 1:52 PM

36
B. Gemu¨nd et al. · N-(2,4,6-Trimethylborazinyl)-substituted Boron, Aluminum and Titanium Compounds
Acknowledgements
We thank Fond der Chemischen Industrie and Chemetall
GmbH, Frankfurt, for the support of our research. Thanks are
also due to Dr. R. Fischer and Mrs. D. Ewald for the mass
spectra.
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[16] We will report on a larger set of boryl-substituted bor-
azines shortly [9].
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