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Synthesis and characterisation of the complete series of B-N analogues of triptyceneElectronic supplementary information (ESI) available: Experimental details including assigned NMR data of 3c, 3d, 3e, K[8] (R = p-Me3SiC6H4; p-IC6H4), 14c and 14d. Plots of the 13C{1H} NMR spectra of 3a, 3c, 3d, [4a]Br, [4c]Br, [4e]Br, 14b, 14c and 14d. Decomposition experiments of 3b, [4a]Br and [4b]Br in CD3OD and [4d]Br in CH3OH. X-ray crystal structure analyses of 3c, 3d, 3e, 3f·OEt2 and 12a. CCDC 985503-9855
The reaction between the bisborate Li 2 [ o -C 6 H 4 (BH 3 ) 2 ] and 2 equivalents of an appropriate pyrazole derivative (Hpz R ) in the presence of Me 3 SiCl yields o -phenylene-bridged pyrazaboles HB(μ-pz R ) 2 (μ- o -C 6 H 4 )BH ( 3a-3e ; Hpz R = 4-iodopyrazole ( 3a ), 4-(trimethylsilyl)pyrazole...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Online Access: | Get full text |
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| Summary: | The reaction between the bisborate Li
2
[
o
-C
6
H
4
(BH
3
)
2
] and 2 equivalents of an appropriate pyrazole derivative (Hpz
R
) in the presence of Me
3
SiCl yields
o
-phenylene-bridged pyrazaboles HB(μ-pz
R
)
2
(μ-
o
-C
6
H
4
)BH (
3a-3e
; Hpz
R
= 4-iodopyrazole (
3a
), 4-(trimethylsilyl)pyrazole (
3b
), 3,5-dimethylpyrazole (
3c
), 3,5-di(
tert
-butyl)pyrazole (
3d
), 3,5-bis(trifluoromethyl)pyrazole (
3e
)). The synthesis approach thus provides access to uncharged B-N triptycenes bearing (i) functionalisable groups, (ii) electron-donating or -withdrawing substituents and (iii) pyrazole rings of varying steric demand. Treatment of
p
-R*C
6
H
4
BBr
2
with the potassium tris(pyrazol-1-yl)borates K[HBpz
3
] or K[
p
-R*C
6
H
4
Bpz
3
] yields cationic pyrazolyl-bridged pyrazaboles [
p
-BrC
6
H
4
B(μ-pz)
3
BH]Br ([
4a
]Br) and [
p
-R*C
6
H
4
B(μ-pz)
3
B
p
-C
6
H
4
R*]Br (R* = Br ([
4b
]Br), I ([
4c
]Br), SiMe
3
([
4d
]Br)), which can be regarded as full B-N analogues of triptycene. The B-H bonds of
3b
and [
4a
]Br are unreactive towards
t
BuC&z.tbd;CH even at temperatures of 80 °C, thereby indicating an appreciable thermal stability of the corresponding B-N cage bonds. Most of the cage compounds are sufficiently inert towards water to allow quick aqueous workup. However, NMR spectroscopy in CD
3
OD solution reveals degradation of
3b
or [
4a
]Br to the corresponding pyrazoles and
o
-C
6
H
4
(B(OCD
3
)
2
)
2
or
p
-BrC
6
H
4
B(OCD
3
)
2
/B(OCD
3
)
3
. The diphenylated species [
4b
]Br is significantly more stable under the same measurement conditions; even after 76 d, most of the material degrades only to the stage of the
syn
/
anti
-pyrazaboles
p
-BrC
6
H
4
(CD
3
O)B(μ-pz)
2
B(OCD
3
)
p
-C
6
H
4
Br (
11a
/
11b
). A derivatisation of [
4c
]Br with
n
Bu
3
SnC&z.tbd;C
t
Bu through Stille-type coupling reactions furnishes the alkynyl derivative [
p-t
BuC&z.tbd;CC
6
H
4
B(μ-pz)
3
B
p
-C
6
H
4
C&z.tbd;C
t
Bu]Br ([
4e
]Br). Larger B-N aggregates are also accessible: treatment of the tetrakisborate Li
4
[1,2,4,5-C
6
H
2
(BH
3
)
4
] with 4 equivalents of Hpz
R
in the presence of Me
3
SiCl leads to the corresponding B-N pentiptycenes
14a-14d
(Hpz
R
= 3,5-bis(trifluoromethyl)pyrazole (
14a
), 4-(trimethylsilyl)pyrazole (
14b
), 3,5-dimethylpyrazole (
14c
), 3,5-di(
tert
-butyl)pyrazole (
14d
)).
The B-N/C-C isosterism has been exploited for the facile synthesis of anionic, neutral and cationic B-N analogues of triptycene with variable substituent patterns. |
|---|---|
| ISSN: | 1477-9226 1477-9234 |
| DOI: | 10.1039/c4dt00442f |