1,2-Dihydro[1,3,2]diazaborolo[1,5-a]pyridines: A novel class of heterocycles

Article abstract of DOI:10.1039/b009156l

Reaction of a pyridine carbaldimine 2-^tBuN=CHC₅H₄N 1a with a molar equivalent of boron tribromide afforded a bicyclic 1,3,2-diazaborolium bromide 2a as an orange solid, whereas 1a and the corresponding 2-(2,6-Me₂C₆H₃)N= CHC₅H₄N 1b with two equivalents of boron trifluoride gave non-ionic yellow adducts 3a and 3b. The reduction of compounds 2a, 3a and 3b with an excess of sodium amalgam in a hexane slurry led to the formation of 1-X-2-R-1,2-dihydro[1,3,2]diazaborolo[1,5-a]pyridines 4 (X = Br; R = ^tBu), 5a (F; ^tBu) and 5b (F; 2,6-Me₂C₆H₃) as yellow oils (4a, 5a) or a yellow wax (5b), respectively. Treatment of 4 with an excess of chlorotrimethylsilane caused a Br/Cl exchange to afford chloro derivative 6. The addition of a methyl group to the boron atom was effected by reaction of heterocycle 4 with methyllithium. The BCN derivative 8 resulted from treatment of 4 with silver cyanide. Reduction of 4 with lithium aluminium hydride gave the 1-hydro-derivative 9, whereas the BS^tBu compound was obtained from the reaction of 4 with KS^tBu. Compound 8 was subjected to an X-ray diffraction analysis.

Full text of DOI:10.1039/b009156l

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1,2-Dihydro[1,3,2]diazaborolo[1,5-a]pyridines: a novel class of
heterocycles
Lothar Weber,*a Markus Schnieder,a Roland Boeseb and Dieter Bläserb
a Fakultät für Chemie der Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld,
Germany. E-mail: lothar.weber@uni-bielefeld.de
b Institut für Anorganische Chemie der Universität Essen, Universitätsstr. 5–7, 45117 Essen,
Germany. E-mail: roland.boese@uni-bielefeld.de
Received 15th November 2000, Accepted 5th January 2001
First published as an Advance Article on the web 30th January 2001
Reaction of a pyridine carbaldimine 2-tBuN᎐CHC H N 1a with a molar equivalent of boron tribromide afforded a
᎐
5
4
bicyclic 1,3,2-diazaborolium bromide 2a as an orange solid, whereas 1a and the corresponding 2-(2,6-Me C H )N᎐
᎐
2
6
3
CHC5H4N 1b with two equivalents of boron trifluoride gave non-ionic yellow adducts 3a and 3b. The reduction of
compounds 2a, 3a and 3b with an excess of sodium amalgam in a hexane slurry led to the formation of 1-X-2-R-1,2-
dihydro[1,3,2]diazaborolo[1,5-a]pyridines 4 (X = Br; R = tBu), 5a (F; tBu) and 5b (F; 2,6-Me2C6H3) as yellow oils
(4a, 5a) or a yellow wax (5b), respectively. Treatment of 4 with an excess of chlorotrimethylsilane caused a Br/Cl
exchange to afford chloro derivative 6. The addition of a methyl group to the boron atom was effected by reaction of
heterocycle 4 with methyllithium. The BCN derivative 8 resulted from treatment of 4 with silver cyanide. Reduction
of 4 with lithium aluminium hydride gave the 1-hydro-derivative 9, whereas the BStBu compound was obtained from
the reaction of 4 with KStBu. Compound 8 was subjected to an X-ray diffraction analysis.
for the preparation of the 2-bromo derivative 4 and the 2-fluoro
derivatives 5a,5b as well (Scheme 1). Thus combination of
Introduction
The recent development of high-yield syntheses of boron-
functionalized 2,3-dihydro-1H-1,3,2-diazaboroles (A)1 has
made a new impact upon the chemistry of such heterocycles.2
Chemical reactions with 2-halogeno-2,3-dihydro-1H-1,3,2-
diazaboroles either occur with retention of the ring skeleton or
with a transformation thereof. Processes of the first type usually
involve nucleophilic displacements at boron, where hydrogen,3
carbon,1–3 tin,3 nitrogen,4 oxygen,1 sulfur5 or halogen atoms5
serve as donor functions. The conversion of 2,3-dihydro-1H-
1,3,2-diazaboroles into 1,3,2-oxazaborolidines was achieved by
treatment with ketenes.6
Searching for novel boron–nitrogen systems, our interest has
been focused on molecules with fused 1,3,2-diazaborole rings.
From a formal point of view molecules A are derived from
Scheme 1
pyrrole by replacement of a C᎐C double bond by the iso-
᎐
electronic B=N group. Consistently, the bicyclic system B is a
BN analogue of indole, and compounds such as C may be
envisaged as BN derivatives of indolizine. In contrast to a series
of benzo-1,3,2-diazaboroles B,7 molecules of type C are
unknown to date.
In this paper we give an account on the synthesis, structure
and reactivity of the first 1,2-dihydro[1,3,2]diazaborolo[1,5-a]-
pyridines C.
equimolar amounts of the pyridine carbaldimine 1a and boron
tribromide in n-hexane at ambient temperature afforded the
borolium salt 2 as an orange precipitate in 85% yield. The solid
usually was contaminated with small amounts (<10%) of the
corresponding tetrabromoborate, which however has no influ-
ence on the designed reaction sequence. Reduction of a slurry
of 2 in n-hexane with an excess of sodium amalgam to com-
pound 4 was achieved in 79% yield. The product was isolated as
an air- and moisture-sensitive yellow oil, which is thermally
sufficiently stable to be distilled at 10Ϫ3 mbar by heating with
a hot air gun (150–200 ЊC). In contrast to the formation of
borolium salt 2, the reaction of n-hexane solutions of the
pyridine carbaldimine 1a (R = tBu) or 1b (R = 2,6-Me2C6H3)
Results and discussion
The protocol which previously has been devised for the syn-
thesis of 2-halogeno-1,3,2-diazaboroles1 proved to be suitable
378
J. Chem. Soc., Dalton Trans., 2001, 378–382
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b009156l

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Table 1 Selected bond lengths (Å) and angles (Њ) for compound 8
with two molar equivalents of BF3ؒOEt2 dissolved in diethyl
ether led to precipitation of the yellow adduct 3a or 3b (78–81%
yield). Stirring slurries of the adduct 3a or 3b in n-hexane with
an excess of sodium amalgam during 48 h at room temperature
cleanly afforded the heterocycle 5a as a yellow oil (67% yield) or
5b as a yellow wax in 63% yield. Both compounds were purified
by short path vacuum distillation.
N(1)–C(9)
N(1)–B(2)
B(2)–C(10)
N(3)–C(12)
C(5)–C(6)
C(7)–C(8)
C(10)–C(11)
1.386(2)
1.429(2)
1.538(3)
1.4934(19)
1.424(2)
1.425(3)
1.148(2)
N(1)–C(5)
B(2)–N(3)
N(3)–C(4)
C(4)–C(5)
C(6)–C(7)
C(8)–C(9)
1.416(2)
1.420(2)
1.395(2)
1.362(2)
1.353(2)
1.339(2)
Compound 4 turned out to be an excellent starting material
for further chemical transformations (Scheme 2). Treatment
C(9)–N(1)–C(5)
C(5)–N(1)–B(2)
N(3)–B(2)–C(10)
C(4)–N(3)–B(2)
B(2)–N(3)–C(12)
C(4)–C(5)–N(1)
N(1)–C(5)–C(6)
C(6)–C(7)–C(8)
C(8)–C(9)–C(1)
120.26(14)
107.58(13)
128.95(15)
107.63(14)
128.03(14)
108.11(13)
118.27(14)
120.58(16)
120.77(16)
C(9)–N(1)–B(2)
N(3)–B(2)–N(1)
N(1)–B(2)–C(10)
C(4)–N(3)–C(12)
C(5)–C(4)–N(3)
C(4)–C(5)–C(6)
C(7)–C(6)–C(5)
C(9)–C(8)–C(7)
N(11)–C(10)–B(2)
132.16(15)
106.53(15)
124.51(15)
124.34(14)
110.14(14)
133.62(15)
119.82(16)
120.30(16)
178.86(17)
Scheme 2
Fig. 1 Crystal structure of compound 8.
of it with a slight excess of chlorotrimethylsilane at 20 ЊC in n-
hexane solution led to a clean Br/Cl exchange. Chloro deriva-
tive 6 was isolated by vacuum distillation as a yellow oil in 95%
yield. Generally this synthetic approach to 2-chloro-1,3,2-
of π electron density in the bicyclic systems is accompanied by
a high-field shift of the 11B NMR signals ∆δ = 1.0–3.1 ppm, when
compared with the corresponding monocyclic systems. In the
1
monocyclic systems the H NMR resonances for the ring pro-
diazaboroles RNCH᎐CHN(R)BCl (R = tBu or 2,6-Me C H )
᎐
2
6
3
tons of the HC᎐CH unit were observed in the narrow range
᎐
is more convenient than the previously described route via
2-dichloroborolium chlorides, because it circumvents the use of
free boron trichloride and guarantees a clean work-up (the only
by-product is volatile Me3SiBr!) with high yields. Methyllithium
and 4 underwent reaction in an n-hexane–diethyl ether solution
in the temperature range between 0 and 20 ЊC to generate the
methylated heterocycle 7 as a yellow oil (58% yield). Cyano
derivative 8 resulted from the metathesis reaction between 4 and
silver cyanide in acetonitrile at ambient temperature in the
absence of daylight. It was isolated by vacuum distillation as
light yellow crystals in 73% yield. The synthesis of the light
yellow oily borohydride 9 was achieved in 79% yield by com-
bination of equimolar amounts of 4 and lithium aluminium
hydride in a tetrahydrofuran–n-hexane mixture. The ligation of
a sulfur-containing substituent onto the boron atom of the
bicyclic skeleton was accomplished by reaction of 4 with solid
KStBu in n-hexane. Compound 10 was isolated as a light yellow
oil after distillation (10Ϫ3 mbar, 300 ЊC, hot air gun).
of δ 5.99 (X = F) to 6.43 (X = StBu). In the BN-perturbed
indolizines the remaining CH protons of the five-membered
ring give rise to absorptions at nearly the same positions.
In the 13C-{1H} NMR spectra the 13C nuclei of the CH᎐CH
᎐
unit in BuNCH᎐CHN(tBu)BX give rise to a singlet at δ 109.9
t
᎐
(X = F)–114.8 (X = StBu). In the fused systems generally a
high-field shift of this resonance is obvious ranging from
δ 99.74 for 5a (X = F) to 106.1 for 8 (X = CN) and 10
(X = StBu). The adjacent quaternary carbon atom of the C᎐CH
᎐
unit was observed in the range from δ 125.3 for 5a to 128.0 for 8.
In the 1H NMR spectrum of compound 9 a quartet at
δ 4.75 (1JBH = 154 Hz) is attributed to the hydrogen atom ligated
to the boron atom. Consistently the non-1H-decoupled 11B
NMR spectrum displays a doublet with JB,H = 155 Hz. In
tBuNCH᎐CHN(tBu)BH the BH unit gives rise to a quartet at
᎐
δ 4.78 (JBH = 150 Hz) in 1H NMR spectrum.
Inspection of the 11B-{1H} NMR spectra of the novel 1,2-
dihydro[1,3,2]diazaborolo[1,5-a]pyridines 4, 5a, 6–9 showed
an increased shielding as follows: 7 (δ 23.9) > 10 (19.9) > 5a
(18.0) ≈ 6 (17.9) ≈ 9 (17.9) > 4 (14.7) > 8 (8.9). A similar
trend was observed for the monocyclic 1,2-dihydro-1,3,2-diaza-
X-Ray structural analysis of compound 8
For a full characterization of the novel ring systems an X-ray
structural analysis of compound 8 was performed. Single crys-
tals (light yellow blocks) were grown from n-hexane at Ϫ20 ЊC.
Selected bonding parameters are compiled in Table 1. The
structure (Fig. 1) features a planar molecule which may be con-
sidered as a 2,3-dihydro-1H-1,3,2-diazaborole connected to a
1,3-butadiene unit via the two adjacent carbon and nitrogen
boroles tBuNCH᎐CHN(tBu)BX: X = CH3 (δ 26.2) > StBu
᎐
(21.9) > F (20.3) ≈ Cl (20.2) > H (18.9) > Br (16.2) > CN
(12.0). It is obvious, however, that the increased delocalization
J. Chem. Soc., Dalton Trans., 2001, 378–382
379

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Ϫ
atoms. Alternatively, the compound may be derived from an
indolizine in which the CC double bond of the five membered
ring adjacent to the nitrogen atom is replaced by the isoelec-
tronic and isosteric BN unit. In contrast to a series of sym-
metrically substituted 2,3-dihydro-1H-1,3,2-diazaboroles the
bonding parameters within the borole part of 8 differ signifi-
cantly. The B–N distances [1.420(2), 1.429(2) Å] indicate
multiple bond character. In diazaboroles the B–N bond lengths
range from 1.395(4) to 1.450(2) Å.1–4 The bond length C(4)–
C(5) in 8 [1.362(2) Å] compares well with the corresponding CC
also contains about 10% of BBr4 as an anion. 1H NMR
(CDCl3): δ 1.93 (s, 9H, tBu), 8.21 (t, 3JH,H = 6.9, 1H, CH), 8.77
3
(t, JH,H = 7.5, 1H, CH), 8.95 (s, 1H, tBuNCH), 9.37 (d,
3
3JH,H = 8.2, CH) and 11.36 (d, JH,H = 8.2 Hz, NCH). 13C-{1H}
NMR (CDCl3): δ 30.66 [s, C(CH3)3], 67.17 [s, C(CH3)3], 130.46
t
(s, CH), 130.52 (s, CH), 143.02 (s, BuNCH), 143.56 (s, CH),
146.97 (s, CH) and 161.83 (s, CHN). 11B-{1H} NMR (CDCl3):
δ Ϫ2.2 (s).
C H N(BF )[CH᎐N(tBu)BF ]-2 3a. A solution of Et OؒBF
᎐
5
4
3
3
2
3
(8.11 g, 57.2 mmol) in 40 ml of diethyl ether was added drop-
wise at 20 ЊC to a stirred solution of 6.01 g (28.6 mmol) of
compound 1a in 100 ml of n-hexane. After the addition was
complete stirring was continued for 1 h. The precipitate was fil-
tered off and washed with n-hexane (3 × 20 ml). Drying of the
filter-cake at 10Ϫ3 mbar afforded adduct 3a, yield 8.04 g (81%)
as a yellow solid (Found: C, 41.41; H, 4.53; N, 9.32. C5H7BF3N
requires C, 40.33; H, 4.74; N, 9.41%). 1H NMR (CDCl3): δ 1.69
multiple bond in (2,6-Me C H )NCH᎐CHN(2,6-Me C H )BI
᎐
2
6
3
2
6
3
[1.362(8) Å],1b and thus appears at the upper end of the
range 1.315(11)–1.362(8) Å encountered for such bonds in
diazaboroles. The endocyclic bonds N(3)–C(4) [1.395(2) Å]
and N(1)–C(5) [1.416(2) Å] differ significantly in length. In
tBuNCH᎐CHN(tBu)BCN→Cr(CO) the CN separations are
᎐
5
1.373(6) and 1.389(7) Å and were regarded as having mul-
tiple bond character.3 The calculated value for a Csp –Nsp
2
2
t
(s, 9H, Bu), 8.21 (m, 1H, CH), 8.69–8.73 (m, 2H, CH), 8.91
single bond is 1.45 Å.8 In 8 this is only valid for N(3)–C(4). The
3
t
(d, JH,H = 8.2 Hz, N᎐CH) and 9.66 (s, 1H, BuN᎐CH). 13C-
᎐
᎐
CN bond which is common to both rings is elongated and com-
{1H} NMR [(CD3)2SO]: δ 27.9 [s, C(CH3)3], 61.9 [s, C(CH3)3],
127.5 (s, CH), 131.2 (s, CH), 144.0 (s, CH), 148.2 (s, CH), 150.3
(s, CH᎐C) and 165.1 (s, HC᎐NtBu). 11B-{1H} NMR (CDCl3):
2
2
pares with one of the exocyclic single bonds Nsp –Csp meas-
ured in 2,6-Me C H NCH᎐CHN(2,6-Me C H )BH [1.421(3)
᎐
2
6
3
2
6
3
᎐
᎐
Å].3 The carbon–carbon distances in the six-membered ring of
8 alternate. Double bonds are C(8)–C(9) [1.339(2) Å] and
C(6)–C(7) [1.353(2) Å], whereas the longer bonds C(5)–C(6)
[1.424(2) Å] and C(7)–C(8) [1.425(3) Å] may be considered as
single bonds. The boron atom is linked to a cyano group via a
B–Csp single bond of 1.538(3) Å. The C(10)–N(11) bond length
of 1.148(2) Å resembles that in cyanogen (1.15 Å).9 The endo-
cyclic angles N(1)–B(2)–N(3) [106.53(15)], B(2)–N(3)–C(4)
[107.63(14)], N(3)–C(4)–C(5) [110.14(14)], C(4)–C(5)–N(1)
[108.11(13)], and B(2)–N(1)–C(5) [107.58(13)Њ] correspond to
δ Ϫ1.35 (s). 19F-{1H} NMR [(CD3)2SO]: δ Ϫ148.6.
C H N(BF )[CH᎐N(2,6-Me C H )(BF )]-2 3b. Analogously
᎐
5
4
3
2
6
3
3
6.54 g (31.1 mmol) of compound 1b and 8.81 g (62.2 mmol) of
BF3ؒOEt2 were combined to yield 8.4 g (78%) of adduct 3b as
a light yellow powder (Found: C, 48.57; H, 4.18; N, 8.09.
1
C7H7BF3N requires C, 48.61; H, 4.08; N, 8.10%). H NMR
3
[(CD3)2SO]: δ 2.08 (s, 6H, o-CH3), 6.96 (t, JH,H = 7.5, 1H, p-H
3
of aryl), 7.08 (d, JH,H = 7.5, 2H, m-H of aryl), 7.63–7.65
3
5
(m, 1H, CH), 8.08 (dt, JH,H = 7.5, JH,F = 1.3, 1H, CH), 8.25
3
those in (2,6-Me C H )NCH᎐CHN(2,6-Me C H )BH.3 Owing
(d, JH,H = 8.2, CH), 8.34 (s, 1H, aryl N᎐CH) and 8.75
᎐
᎐
2
6
3
2
6
3
(d, 3JH,H = 4.4 Hz, CH). 13C-{1H} NMR [(CD3)2SO]: δ 17.91 (s,
o-CH3), 121.92 (s, CH), 124.12 (s, CH aryl), 126.31 (s, CH),
128.07 (s, CH aryl), 129.03 (s, o-C aryl), 138.61 (s, i-C
aryl), 148.82 (s, CH), 149.76 (s, CH), 152.44 (s, NCCHN) and
to the unsymmetrical substitution pattern, the exocyclic bonds
at boron atom B(2) [124.51(15); 128.95(15)Њ] and at the nitrogen
atoms N(1) [132.16(15)Њ] and N(3) [124.34(14); 128.03(14)Њ] are
significantly different.
162.7 (s, CH᎐N aryl). 11B-{1H} NMR [(CD3)2SO]: δ Ϫ1.1 (s).
᎐
19F-{1H} NMR [(CD3)2SO]: δ Ϫ146.58 (s).
Experimental
General procedures
tBuNCH᎐CCH᎐CHCH᎐CHNBBr 4. A sample of 6.4 g (15.5
᎐
᎐
᎐
All manipulations were performed under an atmosphere of dry
dinitrogen using standard Schlenk techniques. All solvents were
dried by common methods and freshly distilled prior to use.
mmol) of salt 2 and 180 ml of n-hexane were added at 20 ЊC to
an alloy made of 2.0 g (87.0 mmol) of sodium metal and 200 g
of mercury. The slurry was vigorously stirred for 48 h. Storing
overnight led to clean separation of two liquid phases. The
yellow hexane phase was carefully decanted and liberated from
solvent and volatile components at ca. 10Ϫ2 mbar (20 ЊC) to
afford spectroscopically pure product 4 as a yellow viscous oil.
Purification was achieved by short path distillation (column:
5 × 1 cm) with a hot air gun (10Ϫ3 mbar, 150–200 ЊC), yield 3.1 g
(79%) (Found: C, 47.30; H, 5.44; N, 11.17. C10H14BBrN2
requires C, 47.48; H, 5.58; N, 11.07%). 1H NMR (C6D6): δ 1.34
The compounds 2-tBuN᎐CHC H N 1a10 and 2-(2,6-Me2C6-
᎐
5
4
H )N᎐CHC H N 1b11 were prepared according to liter-
᎐
3
5
4
ature methods. Boron tribromide, boron trifluoride–diethyl
ether, chlorotrimethylsilane, methyllithium, silver cyanide,
t
lithium aluminium hydride and BuSH were purchased com-
mercially. NMR spectra were recorded on a Bruker AM Avance
DRX 500 spectrometer (1H, 11B, 13C, 19F, 29Si) using SiMe4,
BF3ؒOEt2 and CFCl3 as external standards. The IR spectra
were recorded on Bruker FT-IR Vector 22 instruments.
Mass spectra: VG Autospec sector field mass spectrometer
(Micromass).
t
3
(s, 9H, Bu), 5.61 (t, JH,H = 6.1, 1H, CH), 5.99–6.05 (m, 1H,
CH), 6.31 (s, 1H, tBuNCH᎐), 6.60 (d, 3JH,H = 9.5, 1H, CH) and
᎐
7.35 (d, 3JH,H = 7.9 Hz, 1H, CNCH). 1H NMR (CDCl3): δ 1.64
t
3
(s, 9H, Bu), 5.91 (t, JH,H = 6.3, 1H, CH), 6.24–6.28 (m, 1H,
Preparations
CH), 6.65 (s, 1H, tBuNCH᎐), 6.82 (d, 3JH,H = 9.4, 1H, CH) and
᎐
7.40 (d, JH,H = 6.9 Hz, 1H, CNCH). 13C-{1H} NMR (C6D6):
3
[tBuN᎐CHCCH᎐CHCH᎐CHNBBr ]Br 2a. A three-necked
᎐
᎐
᎐
2
t
δ 31.31 [s, C(CH3)3], 54.29 [s, C(CH3)3], 104.85 (s, BuNCH),
107.83 (s, CH), 118.52 (s, CH) and 118.63 (s, CH). 13C-{1H}
NMR (CDCl3): δ 31.41 [s, C(CH3)3], 54.41 [s, C(CH3)3], 104.47
(s, tBuNCH), 107.35 (s, CH), 118.10 (s, CH), 126.66 (s, CH) and
127.66 (s, CH). 11B-{1H} NMR (C6D6): δ 14.8. 11B-{1H} NMR
(CDCl3): δ 14.7. MS/EI (70 eV): m/z = 252 (Mϩ, 22) and 196
flask, equipped with two dropping funnels and a stirrer, was
filled with 400 ml of n-hexane. Simultaneously, solutions of the
pyridine carbaldimine 1a (4.99 g, 30.7 mmol) in 100 ml of
n-hexane and boron tribromide (7.70 g, 30.7 mmol) in 100 ml
of n-hexane were added dropwise at 20 ЊC. After the addition
stirring was continued for 2 h. The orange precipitate was fil-
tered off and washed with n-hexane (3 × 50 ml). The filter cake
was dried at 10Ϫ3 mbar to afford salt 2a as an orange powder,
yield 10.78 g (85%) (Found: C, 27.46; H, 3.32; N, 6.02.
C10H14BBr3N2 requires C, 29.10; H, 3.42; N, 6.79%). The salt
[Mϩ Ϫ (CH ) C᎐CH , 100%].
᎐
3
2
2
tBuNCH᎐CCH᎐CHCH᎐CHNBF 5a. A 303 g quantity of
᎐
᎐
᎐
1% sodium amalgam (130.5 mmol Na) was combined at room
380
J. Chem. Soc., Dalton Trans., 2001, 378–382

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temperature with 5.1 g (17.1 mmol) of adduct 3a and 180 ml of
n-hexane. It was stirred for 48 h and worked up analogously to
the preparation of 4. Solvent was removed at 20 ЊC and 40
mbar, and the brown viscous residue subjected to distillation
(10Ϫ3 Torr, 150 ЊC, hot air gun) to give 2.2 g (67% yield) of
product 5a as a yellow oil (Found: C, 62.41; H, 7.44; N, 14.52.
13C-{1H} NMR: δ 31.83 [s, C(CH3)3], 53.41 [s, C(CH3)3], 103.50
(s, tBuNCH), 105.57 (s, CH), 117.37 (s, CH), 118.21 (s, CH) and
t
126.05 (s, BuNCH᎐C). 11B-{1H} NMR (CDCl3): δ 23.9 (s).
᎐
MS/EI: m/z = 188 (Mϩ, 40) and 132 [Mϩ Ϫ (CH ) C᎐CH ,
᎐
3
2
2
100%].
1
tBuNCH᎐CCH᎐CHCH᎐CHNBCN 8. Silver cyanide (0.32 g,
C10H14BFN2 requires C, 62.54; H, 7.35; N, 14.59%). H NMR
᎐
᎐
᎐
(CDCl3): δ 1.43 (d, 5JH,F = 1.2, 9H, tBu), 5.63 (t, 3JH,H = 6.3, 1H,
2.4 mmol) and compound 4 (0.56 g, 2.2 mmol) were mixed in
acetonitrile (50 ml) at ambient temperature and in the absence
of light. After 30 min of stirring volatiles were removed in vacuo
to afford a brown oil, which was subjected to short path distil-
lation (10Ϫ3 mbar, 300 ЊC, hot air gun), yield 0.32 g (73%) of
light yellow crystalline 8 (Found: C, 66.30; H, 7.05; N, 20.91.
t
CH), 6.01–6.04 (m, 1H, CH), 6.14 (s, 1H, BuNCH), 6.58 (dd,
3JH,H = 9.4, 5JH,F = 1.3, 1H, CH) and 7.04 (d, 3JH,H = 6.9 Hz, 1H,
CH). 13C-{1H} NMR (CDCl3): δ 30.93 [s, C(CH3)3], 52.45 [s,
t
C(CH3)3], 99.74 (s, BuNCH), 105.75 (s, CH), 117.76 (s, CH),
t
118.14 (s, CH), 125.32 (s, BuNCH᎐C) and 126.66 (s, CH);
᎐
11B-{1H} NMR (CDCl3): δ 18.0 (s). 19F-{1H} NMR (CDCl3):
1
C11H14BN3 requires C, 66.37; H, 7.09; N, 21.11%). H NMR
δ Ϫ162.86 (s). MS/EI: m/z = 192 (Mϩ, 42) and 136 [Mϩ Ϫ
t
3
(C6D6): δ 1.20 (s, 9H, Bu), 5.59 (t, JH,H = 6.1, CH), 5.99–6.05
(CH ) C᎐CH , 100%].
t
3
᎐
3
2
2
(m, 1H, CH), 6.12 (s, 1H, BuNCH), 6.58 (d, JH,H = 9.5) and
3
1
7.37 (d, JH,H = 7.0 Hz, CH). H NMR (CDCl3): δ 1.58 (s, 9H,
tBu), 6.05 (t, 3JH,H = 6.9, 1H, CH), 6.35–6.38 (m, 1H, CH), 6.63
2,6-Me C H NCH᎐CCH᎐CHCH᎐CHNBF 5b. Analogously,
᎐
᎐
᎐
2
6
3
t
3
4.4 g (12.7 mmol) of adduct 3b were reduced with 303 g of 1%
sodium amalgam (130.5 mmol Na) to afford 1.92 g (63%) of
yellow waxy compound 5b after short path distillation (10Ϫ3
mbar, 250 ЊC, hot air gun) (Found: C, 70.42; H, 6.67; N, 11.34.
(s, 1H, BuNCH), 6.90 (d, JH,H = 9.4, 1H, CH) and 7.60 (d,
3JH,H = 6.9 Hz, 1H, CH). 13C-{1H} NMR (CDCl3): δ 31.85 [s,
t
C(CH3)3], 54.67 [s, C(CH3)3], 106.10 (s, BuNCH), 109.14 (s,
CH), 118.34 (s, CH), 119.61 (s, CH), 128.02 (s, tBuNCH᎐C) and
᎐
1
128.39 (s, CH). 11B-{1H} NMR (CDCl3): δ 8.9 (s). IR (KBr,
C14H14BFN2 requires C, 70.04; H, 5.88; N, 11.67%). H NMR
3
cmϪ1): ν (C᎐N) 2200w. MS/EI: m/z = 199 (M , 20) and 143
ϩ
᎐
(CDCl3): δ 2.12 (s, 6H, o-CH3), 5.75 (t, JH,H = 6.3, 1H, CH),
᎐
[Mϩ Ϫ (CH ) C᎐CH , 100%].
5.96 (s, 1H, aryl NCH), 6.13–6.16 (m, 1H, CH), 6.67 (d,
3JH,H = 9.4, CH), 7.10–7.12 (m, 3H, CH aryl) and 7.17 (d,
3JH,H = 7.5 Hz, CH). 13C-{1H} NMR (CDCl3): δ 18.13 (s,
o-CH3), 103.09 (s, aryl NCH), 106.24 (s, CH), 118.34 (s, CH),
᎐
3
2
2
tBuNCH᎐CCH᎐CHCH᎐CHNBH 9. A solution of com-
᎐
᎐
᎐
pound 4 (1.77 g, 7.0 mmol) in 60 ml of n-hexane was added to a
slurry of 0.27 g (7.0 mmol) of LiAlH4 in 10 ml of THF and
stirred for 30 min at room temperature. It was filtered and the
filtrate evaporated to dryness. The residue was extracted with
50 ml of n-hexane. It was filtered and the filtrate liberated from
volatile components to afford a yellow oil. Distillation with a
short path at 10Ϫ3 mbar and a hot air gun (100 ЊC) afforded 0.96
g (79%) of pure 9 as a light yellow oil (Found: C, 68.39; H, 8.74;
N, 15.92. C10H15BN2 requires C, 69.01; H, 8.69; N, 16.10%). 1H
NMR (C6D6): δ 1.27 (s, 9H, tBu), 5.60 (t, 3JH,H = 6.3, 1H, CH),
6.07–6.10 (m, 1H, CH), 6.34 (s, 1H, tBuNCH), 6.73 (d,
118.50 (s, CH), 124.75 (s, NCH᎐C), 126.79 (s, C aryl), 127.00 (s,
᎐
C aryl), 128.08 (s, C aryl) and 135.16 (s, i-C aryl). 11B-{1H}
NMR (CDCl3): δ 17.9 (s). 19F-{1H} NMR (CDCl3): δ Ϫ168.15
(s). MS/EI: m/z = 240 (Mϩ).
tBuNCH᎐CCH᎐CHCH᎐CHNBCl 6. A solution of 1.0 g (9.2
᎐
᎐
᎐
mmol) of chlorotrimethylsilane in 20 ml of n-hexane was
added dropwise at 20 ЊC to a solution of compound 4 (1.8 g, 7.1
mmol) in 30 ml of n-hexane, and stirring continued for 2 h. All
volatile components were removed in vacuo (10Ϫ3 mbar) at
40 ЊC to afford product 6 as a yellow oil, yield 1.36 g (95%)
(Found: C, 57.62; H, 7.03; N, 13.40. C10H14BClN2 requires C,
3
1
3JH,H = 9.4, 1H, CH) and 7.25 (d, JH,H = 7.5 Hz, 1H, CH). H
t
1
NMR (CDCl3): δ 1.44 (s, 9H, Bu), 4.75 (q, JB,H = 154, 1H,
BH), 5.73 (t, JH,H = 6.9, 1H, CH), 6.13–6.16 (m, 1H, CH),
1
3
57.61, H, 6.77; N, 13.44%). H NMR (C6D6): δ 1.30 (s, 9H,
tBu), 5.59 (t, 3JH,H = 5.7, 1H, CH), 6.00–6.03 (m, 1H, CH), 6.21
t
3
6.51 (s, 1H, BuNCH), 6.76 (d, JH,H = 9.4, 1H, CH) and 7.37
t
3
(d, 3JH,H = 6.9 Hz, 1H, CH). 13C-{1H} NMR (C6D6): δ 31.81 [s,
(s, 1H, BuNCH), 6.59 (d, JH,H = 9.4, 1H, CH) and 7.23 (d,
3JH,H = 6.9 Hz, 1H, CH). 1H NMR (CDCl3): δ 1.52 (s, 9H, tBu),
t
C(CH3)3], 52.23 [s, C(CH3)3], 104.51 (s, BuNCH), 106.80 (s,
3
CH), 118.35 (s, CH), 118.72 (s, CH), 128.87 (s, tBuNCH᎐C) and
5.79 (t, JH,H = 6.3, 1H, CH), 6.14–6.17 (m, 1H, CH), 6.46
᎐
t
3
130.74 (s, CH). 13C-{1H} NMR (CDCl3): δ 31.88 [s, C(CH3)3],
(s, 1H, BuNCH), 6.71 (d, JH,H = 9.4, 1H, CH) and 7.24 (d,
3JH,H = 6.9 Hz, 1H, CH). 13C-{1H} NMR (C6D6): δ 31.06
[s, C(CH3)3], 53.92 [s, C(CH3)3], 103.65 (s, tBuNCH), 107.44 (s,
52.37 [s, C(CH3)3], 104.02 (s, tBuNCH), 106.30 (s, CH), 118.07
t
(s, CH), 118.13 (s, CH), 127.90 (s, BuNCH᎐C) and 130.52
᎐
CH), 118.45 (s, CH), 118.51 (s, CH), 125.25 (s, tBuNCH᎐C) and
1
᎐
(s, CH). 11B NMR (C6D6): δ 18.0 (d, JB,H = 155). 11B-{1H}
127.31 (s, CH). 13C-{1H} NMR (CDCl3): δ 31.11 [s, C(CH3)3],
NMR (CDCl3): δ 17.9 (s). MS/EI: m/z = 174 (Mϩ, 32) and 118
53.98 [s, C(CH3)3], 103.19 (s, tBuNCH), 106.88 (s, CH), 118.03
[Mϩ Ϫ (CH ) C᎐CH , 100%].
᎐
3
2
2
t
(s, CH), 118.10 (s, CH), 125.26 (s, BuNCH᎐C) and 127.05 (s,
᎐
CH). 11B-{1H} NMR (C6D6): δ 18.0 (s). 11B-{1H} NMR (CDCl3):
tBuNCH᎐CCH᎐CHCH᎐CHNBStBu 10.
A quantity of
᎐
᎐
᎐
δ 17.9 (s). MS/EI: m/z = 208 (Mϩ, 22) and 152 [Mϩ Ϫ
KStBu (0.77 g, 6.0 mmol) was added to a solution of compound
4 (1.48 g, 5.8 mmol) in 80 ml of n-hexane and vigorously stirred
at room temperature for 24 h. It was filtered and the filtrate
freed from volatiles. The yellow oily residue was distilled at 10Ϫ3
mbar with a hot air gun (300 ЊC) to afford 0.96 g (63%) of
product 10 as a light yellow oil (Found: C, 62.47; H, 8.94; N,
(CH ) C᎐CH , 100%].
᎐
3
2
2
tBuNCH᎐CCH᎐CHCH᎐CHNBCH 7. A 1.6 M solution of
᎐
᎐
᎐
3
methyllithium (2.7 ml, 4.3 mmol) in diethyl ether was added
dropwise at 0 ЊC to a solution of compound 4 (1.10 g, 4.3
mmol) in 50 ml of n-hexane. After warming to ambient tem-
perature the mixture was stirred for 2 h. Volatile components
were removed in vacuo. The residue was extracted with 50 ml of
n-hexane, and LiBr removed by filtration. The filtrate was freed
from solvent to afford pure product 7 as a yellow oil, yield
0.47 g (58%) (Found: C, 70.26; H, 9.14; N, 15.03. C11H17BN2
requires C, 70.25; H, 9.11; N, 14.89%). 1H NMR (CDCl3):
1
10.85. C14H23BN2S requires C, 64.13; H, 8.84; N, 10.68%). H
NMR (CDCl3): δ 1.40 (s, 9H, StBu), 1.63 (s, 9H, NtBu), 5.86
3
(t, JH,H = 6.9, 1H, CH), 6.22–6.25 (m, 1H, CH), 6.67 (s, 1H,
tBuNCH), 6.79 (d, 3JH,H = 9.4, 1H, CH) and 7.76 (d, 3JH,H = 6.9
Hz, 1H, CH). 13C-{1H} NMR (CDCl3): δ 32.71 [s, NC(CH3)3],
34.93 [s, SC(CH3)3], 47.39 [s, SC(CH3)3], 55.13 [s, NC(CH3)3],
t
106.07 (s, BuNCH), 106.83 (s, CH), 118.13 (s, CH), 118.54 (s,
δ 0.78 (s, 3H, CH3), 1.47 (s, 9H, Bu), 5.68 (t, JH,H = 6.3, 1H,
CH), 127.41 (s, BuNCH᎐C) and 129.60 (s, CH). 11B-{1H}
t
3
t
᎐
CH), 6.06–6.09 (m, 1H, CH), 6.45 (s, 1H, BuNCH), 6.70
(d, JH,H = 9.4, 1H, CH) and 7.20 (d, JH,H = 8.2 Hz, 1H, CH).
NMR (CDCl3): δ 19.9 (s). MS/EI: m/z 262 (Mϩ, 32) and 206
t
[Mϩ Ϫ (CH ) C᎐CH , 100%].
3
3
᎐
3
2
2
J. Chem. Soc., Dalton Trans., 2001, 378–382
381

View Article Online
Table 2 Crystallographic data for compound 8
Forschungsgemeinschaft, Bonn, and by the Fonds der
Chemischen Industrie, Frankfurt/Main, which is gratefully
acknowledged.
Empirical formula
Mr
C11H14BN3
199.06
T/K
Space group
Crystal system
203
Pnma
Orthorhombic
References
1 (a) L. Weber, E. Dobbert, H.-G. Stammler, B. Neumann, R. Boese
and D. Bläser, Chem. Ber., 1997, 130, 705; (b) L. Weber, E. Dobbert,
R. Boese, M. T. Kirchner and D. Bläser, Eur. J. Inorg. Chem., 1998,
1145.
2 For earlier work on 1,3,2-diazaboroles see G. Schmid, J. Lehr,
M. Polk and R. Boese, Angew. Chem., 1991, 103, 1029; G. Schmid,
J. Lehr, M. Polk and R. Boese, Angew. Chem., Int. Ed. Engl., 1991,
30, 1015; G. Schmid, M. Polk and R. Boese, Inorg. Chem., 1990, 29,
4421 and cited literature.
3 L. Weber, E. Dobbert, H.-G. Stammler, B. Neumann, R. Boese and
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4 L. Weber, E. Dobbert, A. Rausch, H.-G. Stammler and B.
Neumann, Z. Naturforsch., Teil B, 1999, 54, 363.
5 L. Weber and M. Schnieder, unpublished work.
6 L. Weber, M. Schnieder, T. C. Maciel, H. B. Wartig, M. Schimmel,
R. Boese and D. Bläser, Organometallics, 2000, 19, 5791.
7 D. Ulmenschneider and J. Goubeau, Chem. Ber., 1957, 90, 2733;
H. Berger, K. Niedenzu and J. W. Dawson, J. Org. Chem., 1962, 27,
4701; J. Goubeau and H. Schneider, Liebigs Ann. Chem., 1964, 675,
1; J. Schulze, Ph.D. Thesis, University of Essen, 1980.
8 A. N. Chernega, A. V. Ruban, V. D. Romanenko, L. N. Markovskii,
A. A. Korkin, M. Y. Antipin and Y. T. Struchkov, Heteroatom.
Chem., 1991, 2, 229.
a/Å
b/Å
13.1155(5)
6.8622(3)
11.8952(4)
1070.58(7)
4
0.075
13046
1441 (R(int) = 0.034)
1039/88
0.0565, 0.1315
0.0750, 0.1429
c/Å
V/Å3
Z
µ(Mo-Kα)/mmϪ1
Reflections collected
Independent reflections
Reflections with I > 2σ(I)/parameters
Final R1, wR2 (I > 2σ(I))
(all data)
Crystal structure determination of compound 8
The data were collected with a Siemens SMART100 Detector
System on
a three axis platform using graphite-mono-
chromatized Mo-Kα radiation. Software for structure solution/
refinement: Bruker AXS SHELXTL Version 5.10 DOS/
WIN95/NT. Hydrogen atoms treated as riding groups in ideal-
ized positions. All other data are summarized in Table 2.
CCDC reference number 153165.
9 Holleman-Wiberg, Lehrbuch der Anorganischen Chemie, 101st edn.,
Walter de Gruyter, Berlin, 1995, p. 873.
10 A. J. Clark, D. J. Duncalf, R. P. Filik, D. W. Haddleton, G. H.
Thomas and H. Wongtap, Tetrahedron Lett., 1999, 40, 3807.
11 G. Schmauss and P. Barth, Z. Naturforsch., Teil B, 1970, 25, 789.
Acknowledgements
This work was financially supported by the Deutsche
382
J. Chem. Soc., Dalton Trans., 2001, 378–382