Chiral 2,3-dihydro-1H-1,3,2-diazaboroles

Article abstract of DOI:10.1002/1099-0682(200209)2002:9<2438::AID-EJIC2438>3.0.CO;2-W

A series of differently substituted chiral 2,3-dihydro-1H-1,3,2-diazaboroles has been prepared by various methods. 2-Bromo-1-tert-butyl-3-[(S)-1-phenylethyl]-2,3-dihydro-1H-1,3,2-diazaborole (3a), 2-bromo-1,3-di[(S)-l-phenylethyl]-2,3-dihydro-1H-1,3,2-diazaborole (3b) and 2-bromo-1,3-di[(S)-1-cyclohexylethyl]-2,3-dihydro-1H-1,3,2-diazaborole (3c) were formed from the reaction of the corresponding 1,4-diazabutadienes and boron tribromide and the subsequent reduction of the resulting borolium salts [R¹N^a = CH-CH= N^b(R²)BBr₂] Br(N^a-B) [2a: R¹ = tBu, R² = CH(Me)Ph; 2b: R¹ = R² = CH(Me)Ph; 2c: R¹ = R² = CH(Me)(cC₆H₁₁)] with sodium amalgam. Treatment of (S)-3a with LiAlH₄ or methyllithium afforded 1-tert-butyl-2-hydro-3-[(S)-1-phenylethyl]-2,3-dihydro-1H-1,3,2-diazaborole [(S)-6] and 1-tert-butyl-2-methyl-3-[(S)-1-phenylethyl]-2-3-dihydro-1H-1,3,2-diazaborole [(S)-7], respectively. Aminolysis of the BBr bond of (S)-3a by tertbutylamine or (S)-1-phenylethylamine gave the corresponding 2-tert-butylamino- and 2-[1-phenylethylamino]-2,3-dihydro-1H-1,3,2-diazaboroles (S)-8 and (S,S)-9, respectively. Similarly, (S,S)-3b and (S,S)-3c were reacted with tert-butylamine to furnish the 2-tert-butylamino-2,3-dihydro-1H-1,3,2-diazaborole derivatives (S,S)-11 and (S,S)-12, respectively. The 2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaboroles (S,S)-10 and (S,S)-14 were accessible from 3b or 3c and trimethylstannyllithium. The transformation of achiral 2-bromo-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole into the chiral (S)-2-[1-phenylethylamino] and (S)-2-[1-cyclohexyl-ethylamino] derivatives (S)-15 and (S)-16 was effected by aminolysis with enantiomerically pure (S)-1-phenylethylamine or (S)-1-cyclohexylethylamine. The novel compounds were characterized by ¹H, ¹¹B, ¹³C, and ¹¹⁹Sn NMR spectroscopy as well as mass spectrometry and determination of the optical rotation. The molecular structure of compound 3c was confirmed by X-ray structural analysis. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0682(200209)2002:9<2438::AID-EJIC2438>3.0.CO;2-W

FULL PAPER
Chiral 2,3-Dihydro-1H-1,3,2-diazaboroles
Lothar Weber,*[a] Andreas Rausch,[a] Henning B. Wartig,[a] Hans-Georg Stammler,[a] and
Beate Neumann[a]
Keywords: Boron / Chirality / Diazaboroles / Heterocycles / Crystal structure
A series of differently substituted chiral 2,3-dihydro-1H-
1,3,2-diazaboroles has been prepared by various methods. 2-
Bromo-1-tert-butyl-3-[(S)-1-phenylethyl]-2,3-dihydro-1H-
1,3,2-diazaborole (3a), 2-bromo-1,3-di[(S)-1-phenylethyl]-
2,3-dihydro-1H-1,3,2-diazaborole (3b) and 2-bromo-1,3-
di[(S)-1-cyclohexylethyl]-2,3-dihydro-1H-1,3,2-diazaborole
(3c) were formed from the reaction of the corresponding 1,4-
diazabutadienes and boron tribromide and the subsequent
reduction of the resulting borolium salts [R1Na = CH−CH=
dro-1H-1,3,2-diazaboroles (S)-8 and (S,S)-9, respectively.
Similarly, (S,S)-3b and (S,S)-3c were reacted with tert-bu-
tylamine to furnish the 2-tert-butylamino-2,3-dihydro-1H-
1,3,2-diazaborole derivatives (S,S)-11 and (S,S)-12, respect-
ively. The 2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazabor-
oles (S,S)-10 and (S,S)-14 were accessible from 3b or 3c and
trimethylstannyllithium. The transformation of achiral 2-
bromo-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole
into the chiral (S)-2-[1-phenylethylamino]- and (S)-2-[1-
cyclohexyl-ethylamino] derivatives (S)-15 and (S)-16 was ef-
fected by aminolysis with enantiomerically pure (S)-1-phenyl-
ethylamine or (S)-1-cyclohexylethylamine. The novel com-
Nb(R2)BBr2]Br(Na−B) [2a: R1 = tBu, R2 = CH(Me)Ph; 2b: R1
=
R2 = CH(Me)Ph; 2c: R1 = R2 = CH(Me)(cC6H11)] with sodium
amalgam. Treatment of (S)-3a with LiAlH4 or methyllithium
afforded 1-tert-butyl-2-hydro-3-[(S)-1-phenylethyl]-2,3-dihy- pounds were characterized by 1H, 11B, 13C, and 119Sn NMR
dro-1H-1,3,2-diazaborole [(S)-6] and 1-tert-butyl-2-methyl-3-
[(S)-1-phenylethyl]-2,3-dihydro-1H-1,3,2-diazaborole [(S)-7],
respectively. Aminolysis of the BBr bond of (S)-3a by tert-
butylamine or (S)-1-phenylethylamine gave the correspond-
ing 2-tert-butylamino- and 2-[1-phenylethylamino]-2,3-dihy-
spectroscopy as well as mass spectrometry and determina-
tion of the optical rotation. The molecular structure of com-
pound 3c was confirmed by X-ray structural analysis.
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
The synthesis of the first 2,3-dihydro-1H-1,3,2-diazabor-
oles I dates back to the early 1970s,[1,2] and since then a
series of contributions concerning the synthesis, structure,
and bonding of such heterocycles has been published.[3Ϫ6]
Recently, we started a program investigating the synthesis
of 2-halo-2,3-dihydro-1H-1,3,2-diazaboroles II as starting
materials for further chemical transformations.[7,8] Treat-
ment of II with organolithium compounds,[9] LiSnMe3,[9]
LiAlH4,[9] imidazol-2-ylidenes,[7] amines[10] and silver salts[8]
afforded a series of novel 1,3,2-diazaboroles IIIϪVIII
(Scheme 1).
Scheme 1. Chemical transformations of II
[a]
Fakultät für Chemie der Universität Bielefeld
Terminal as well as internal alkynes are inserted regiose-
lectively into the BϪSn bond of VI in a reaction catalyzed
by low-valent Pd species (Scheme 2).[11]
Universitätsstraße 25, 33615 Bielefeld, Germany
Fax: (internat.) ϩ 49-(0)5201/106-6146
E-mail: lothar.weber@uni-bielefeld.de
2438
 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ1948/02/0909Ϫ2438 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2002, 2438Ϫ2446

Chiral 2,3-Dihydro-1H-1,3,2-diazaboroles
FULL PAPER
an aqueous glyoxal solution and the respective amines in a
molar ratio of 1:2. Compound 1c was isolated as colorless
crystals in 82% yield, whereas 1b was obtained as a color-
less oil as described previously.
Combination of equimolar amounts of 1a and BBr3 in
hexane at 20 °C led to the precipitation of the orange borol-
ium salt 2a. Its moisture sensitivity and low volatility pre-
cluded reliable elemental analyses and useful mass spectra.
The reduction of compound 2a with sodium amalgam in
hexane afforded 1,3,2-diazaborole 3a as a yellow oil in 66%
yield after distillation (Scheme 4).
Scheme 2. Insertion of alkynes into the BϪSn bond of VI
Moreover, it was demonstrated that 1,3,2-diazaboroles
are smoothly converted into 1,3,2-oxazaborolidines IX
upon reaction with an equimolar amount of diphenylket-
ene (Scheme 3).[12]
Scheme 4. Preparation of 1,3,2-diazaboroles 3aϪc (Cy ϭ cyclo-
hexyl)
Scheme 3. Conversion of 2,3-dihydro-1H-diazaboroles into 1,3,2-
oxazaborolidines by treatment with diphenylketene
Here a stereogenic center was created at C(4), and it was
challenging to elaborate conditions that would allow the
stereoselective synthesis of these compounds.
Neat 3a decomposes to a brown oil after 24 h at 20 °C,
therefore it is recommended to store the reaction mixture
and to isolate the compound only prior to use.
The preparation of the yellow borolium salt 2b was
achieved by reaction of diazabutadiene (1b) and boron tri-
bromide under similar conditions. Sodium amalgam reduc-
Results and Discussion
The intention of the work described herein is to provide tion of 2b over a period of two days led to a 32% yield of
efficient syntheses of chiral 2,3-dihydro-1H-1,3,2-diazabor- crude oily 3b. Like 3a, compound 3b should only be isolated
oles as the required precursors for such transformations. immediately before subsequent transformations.
The most obvious way to introduce chirality into 1,3,2-diaz-
In contrast to this, the reduction of analogously prepared
aboroles is the use of chiral substituents at the heteroatoms orange moisture-sensitive 2c with sodium amalgam led to
of the ring. This target may be achieved by the employment the formation of colorless crystalline 3c (60.5%), which sep-
of chiral 1,4-diazabutadienes as starting materials. The lat- arated upon concentrating the hexane reaction solution.
ter are available from the condensation of glyoxal and chiral Further purification of the thermostable product was
primary amines such as (S)-1-phenylethylamine or (S)-1- achieved by sublimation at 80 °C and 5 ϫ 10Ϫ6 bar.
cyclohexylethylamine. The combined condensation of
In the 11B{1H} NMR spectra the 2-bromo-1,3,2-diaza-
glyoxal with tert-butylamine and (S)-phenylethylamine in a boroles 3aϪc show singlets at δ ϭ 17.3 (3a), 19.0 (3b) and
molar ratio of 4:7:1 leads to the formation of a 3:1 mixture 18.2 ppm (3c), which are very similar to the 11B resonance
of 1,4-di-tert-butyl-1,4-diazabutadiene and Ph(Me)CHNϭ in tBuNaCHϭCHNb(tBu)BBr(NaϪB) (δ ϭ 16.2 ppm).[7]
CHϪCHϭNtBu (1a). The former product is easily removed The 1H and 13C NMR resonances of the CHϭCH building
in vacuo at ambient temperature. The residue of crude 1a block (δH ϭ 6.13Ϫ6.41 ppm and δC ϭ 111.9Ϫ114.9 ppm
was purified by distillation to give a light yellow oil (43%
are also very similar to the corresponding data for tBuNa-
yield). This compound is thermolabile and has to be stored CHϭCHNb(tBu)BBr (δH ϭ 6.27 ppm, δC ϭ 113.6 ppm).
at Ϫ30 °C. According to NMR spectroscopic data 1a is a
1:2 mixture of two isomers.
A series of chiral 1,3,2-diazaboroles were derived from 3a
by nucleophilic substitution at the boron center. Reaction
The diazabutadienes (S,S)-Ph(Me)CHNϭCHϪCHϭ of 3a with silver cyanide in acetonitrile for 1 h furnished
NCH(Me)Ph (1b)[13] and (S,S)-c-C6H11(Me)CHNϭ a liquid mixture of 2-isocyano-1,3,2-diazaborole (4) and 2-
CHϪCHϭNϪCH(Me)(c-C6H11) (1c) were prepared from cyano-1,3,2-diazaborole (5) (Scheme 5)
Eur. J. Inorg. Chem. 2002, 2438Ϫ2446
2439

L. Weber, A. Rausch, H. B. Wartig, H.-G. Stammler, B. Neumann
FULL PAPER
Scheme 5. Reaction of (S)-3a with AgCN
1
The presence of both isomers was confirmed by the H,
13C NMR and IR spectra of a freshly prepared sample. Par-
ticularly informative is the IR spectrum where sharp bands
at ν˜ ϭ 2113 and 2206 cmϪ1 are attributed to the ν(CN)
vibrations of the isocyano function in 4 and the cyano
group in 5, respectively. Storing the product mixture at Ϫ30
°C for two weeks or vacuum distillation at 200 °C led to
the complete disappearance of the band at 2113 cmϪ1
.
Scheme 6. Reaction of (S)-3a with LiAlH4, MeLi, tBuNH2 and
(S)-Ph(Me)CHϪNH2
After the rearrangement 4 Ǟ 5 the pure cyano derivative
was obtained as a colorless solid (57% yield). In contrast to
precursor 3a, compound 5 is stable at room temperature. A
similar rearrangement was not observed during the pre-
paration of tBuNaϪCHϭCHϪNb(tBu)BCN(NaϪB) from
the corresponding 2-bromo-1,3,2-diazaborole and AgCN.
To the best of our knowledge stable boryl isocyanides are
still undocumented. The 11B{1H} NMR spectrum of 5 is
The reaction of 2-bromo-1,3,2-diazaborole (S)-3a with
methyllithium in a mixture of hexane and THF (Scheme 6)
cleanly afforded (S)-7 as a colorless oil after distillation at
200 °C and 10Ϫ5 bar (51%). The 11B{1H} NMR spectrum
of (S)-7 shows a singlet at δ ϭ 26.2 ppm, which is identical
with that of tBuNaCHϭCHNb(tBu)BCH3(NaϪB).[3] The
CHϭCH unit appears as two doublets at δ ϭ 6.32 and 6.48
1
characterized by a singlet at δ ϭ 11.6 ppm. In the H and
13C{1H} NMR spectra the HCϭCH unit gives rise to two
doublets at δ ϭ 6.25 and 6.40 ppm (3JH,H ϭ 2.3 Hz) and
two singlets at δ ϭ 114.8 and 116.1 ppm, respectively. In
tBuNaϪCHϭCHϪNb(tBu)BCN(NaϪB) the corresponding
resonances were observed at δB ϭ 12.0 ppm (s), δH ϭ 6.14
ppm (s) and δC ϭ 114.6 ppm (s).
1
ppm (3JH,H ϭ 2.5 Hz) in the H NMR spectrum and two
singlets at δ ϭ 111.1 and 113.5 ppm in the 13C{1H} NMR
spectrum of the compound.
Reduction of (S)-3a with lithium aluminium hydride in a
To increase the steric demand of chiral 1,3,2-diazaboroles
THF/hexane mixture (Scheme 6) afforded the 2-hydro- we introduced bulky amino substituents at the boron atom
1,3,2-diazaborole (S)-6 as a yellow oil (95%). Purification of the ring. Reaction of (S)-3a with an excess of tert-bu-
by vacuum distillation to give (S)-6 as a colorless liquid tylamine in hexane gave (S)-8 (Scheme 6), which was isol-
was accompanied by considerable loss of product (47%). At ated as a yellow oil by vacuum distillation (300 °C, 10Ϫ5
room temperature decomposition of a pure sample to a bar, 74%). Compound (S,S-9) resulted from the treatment
brown oil was complete within 24 h. In the IR spectrum a of (S)-3a with an equimolar amount of (S)-1-phenylethyl-
strong band at ν ϭ 2621 cmϪ1 is due to the 11B-H stretching amine in the presence of triethylamine. The heterocycle was
˜
mode. In the proton-coupled 11B NMR spectrum (CDCl3 isolated as a colorless liquid in 48% yield by vacuum
solution) compound (S)-6 exhibits a doublet at δ ϭ 19.4 distillation. The 11B NMR signals of (S)-8 (δ ϭ 22.3 ppm)
ppm (1JB,H ϭ 146 Hz). These values compare well with the and (S,S)-9 (δ ϭ 21.6 ppm) are similar to those of the
result given for tBuNaCHϭCHϪNb(tBu)BH(NaϪB) [δB ϭ amino-functionalized
1,3,2-diazaboroles
tBuNaCHϭ
1
18.9 ppm (d, JB,H ϭ 149 Hz)].[9] In contrast to the latter CHNb(tBu)BN(H)tBu(NaϪB) (δ ϭ 22.9 ppm) and tBuNa-
compound, where the boron-ligated hydrogen atom appears CHϭCHNb(tBu)BNH(2,6-Me2C6H3)(NaϪB) (δ
ϭ 21.6
1
in the H NMR spectrum as a quadruplet resonance (δ ϭ ppm).[10]
1
4.78 ppm, JB,H ϭ 150 Hz) no such signal was detected in
It was also intended to convert the chiral 1,3,2-diazabor-
ole (S,S)-3b into more stable and sterically more congested
1
the H NMR spectrum of (S)-6.
2440
Eur. J. Inorg. Chem. 2002, 2438Ϫ2446

Chiral 2,3-Dihydro-1H-1,3,2-diazaboroles
FULL PAPER
derivatives. A hexane solution of (S,S)-3b was combined
with a solution of a slight excess of LiSnMe3 in THF at
room temperature, whereupon the stannylated heterocycle
(S,S)-10 was generated. Analytically pure colorless (S,S)-10
was obtained by crystallizing the crude material from tolu-
ene (67% yield). (Scheme 7)
Scheme 8. Synthesis of (S,S)-12, (S,S)-13 and (S,S)-14 from (S,S)-3c
Scheme 7. Conversion of (S,S-3b) into (S,S-10) and (S,S-11)
Compound 10 can be stored at room temperature under
an inert atmosphere without discernible decomposition.
The singlet at δ ϭ 28.2 ppm in the 11B{1H} NMR spectrum
is accompanied by 119Sn satellites (1JSn,B ϭ 994 Hz). Sim-
ilarly, the 119Sn{1H} NMR spectrum of 10 features a quad-
ruplet at δ ϭ 150.0 ppm (1JSn,B ϭ 994 Hz). The 11B{1H}
NMR spectrum of 2,6-Me2C6H3NaCHϭCHNb(2,6-
Me2C6H3)BSnMe3(NaϪB) is characterized by a singlet at
δ ϭ 28.2 ppm with 119Sn satellites (1JSn,B ϭ 960 Hz). The
119Sn{1H} NMR resonance of this molecule appears as a
and (S)-16 [δ ϭ 22.0 (s)] resemble those of 8 and 9 and do
not show any marked influence of the substituent at the
nitrogen atom.
1
quadruplet at δ ϭ 146 ppm with JSn,B ϭ 960 Hz.
The stable amino-functionalized 1,3,2-diazaborole (S,S)-
11 was isolated as a yellow liquid from the reaction of 3b
with a twofold equimolar amount of tert-butylamine in hex-
ane at 20 °C (50%). Similarly, the colorless liquid diazabor-
ole (S,S)-12 was synthesized from (S,S)-3c and tert-bu-
tylamine (58% after distillation at 300 °C, 4 ϫ 10Ϫ6 bar;
Scheme 9. Preparation of (S)-15 and (S)-16
X-ray Structural Analysis of (S,S)-3c
The molecular structure of (S,S)-3c (Figure 1) features a
Scheme 8). Preparation of the 2-butyl-1,3,2-diazaborole planar 1,3,2-diazaborole ring with two nearly orthogonally
(S,S)-13 was accomplished by reaction of 3c with an excess oriented 1-cyclohexylethyl substituents at the nitrogen
of n-butyllithium in a hexane/THF mixture at Ϫ15 to 20 atoms. A C2 axis bisects the molecule along the B(1)ϪBr(1)
˚
°C. Pure colorless oily 13 was obtained by distillation (250 vector. The bond length B(1)ϪBr(1) [1.930(2) A] is close to
°C, 5 ϫ 10Ϫ6 bar, 47%).
the sum of the covalent radii of boron (0.81 A) and bromine
˚
Analogously to the preparation of (S,S)-10 the stannyl- (1.14)[14] and compares well with the BϪBr distances in
[15]
˚
ated diazaborole (S,S)-14 was synthesized as a colorless li- [(2,4,6-Me3C6H2)(Br)B]2 [1.928(4) and 1.932(4) A].
quid from 3c and LiSnMe3 in a THF/hexane mixture BϪBr bond lengths involving sp2-hybridized boron atoms
(58% yield).
range from 1.87(1)
A
in [iPr3PϭNaϪBa(Br)Nb-
˚
A different approach to chiral 1,3,2-diazaboroles was (ϭPiPr3)BbBr2]Br(NaϪBb)[16] or 1.902(5)
A
in 2,6-
˚
based upon the reaction of achiral tBuNaCHϭ Mes2C6H3BBr2 (Mes ϭ 2,4,6-Me3C6H2)[17] to 2.00(1) A in
CHNb(tBu)BBr(NaϪB) with the chiral auxiliaries (S)- the triborane [(Me2N)(Br)B]2BNMe2.[18] Atomic distances
Ph(Me)CHNH2 and (S)-Cy(Me)CHNH2 in the presence of and valence angles within the diazaborole ring are in good
triethylamine (Scheme 9). Heterocycle 15 was isolated as a agreement with the corresponding data for (2,6-
pale yellow oil in 74% yield by distillation (200 °C, 10Ϫ5 Me2C6H3)NaϪCHϭCHϪNb(2,6-Me2C6H3)BI(NaϪB).[18]
˚
˚
bar). The same holds for 16, which was isolated as a color- In (S,S)-3c the BϪN bond length [1.417(1) A] indicates
less oil after distillation (150 °C, 2 ϫ 10Ϫ6 bar, 72%). The multiple bond character. In a series of diazaboroles the
11B{1H} spectra of the 2-amino-1,3,2-diazaboroles (S,S)-11 BϪN bond lengths range from 1.407(5) to 1.450(2) A. The
˚
˚
[δ ϭ 22.5 (s)], (S,S)-12 [δ ϭ 22.1 (s)], (S)-15 [δ ϭ 22.3 (s)] atomic distance C(1)ϪC(1A) [1.350(3) A] and the
Eur. J. Inorg. Chem. 2002, 2438Ϫ2446
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L. Weber, A. Rausch, H. B. Wartig, H.-G. Stammler, B. Neumann
FULL PAPER
2
˚
phases were dried (Na2SO4) and then freed from solvent. The re-
maining yellow oil was kept at 5 ϫ 10Ϫ6 bar and 20 °C to remove
tBuNϭCHϪCHϭNtBu (49.0 g crude 1a). The brown oily residue
(10.0 g) was distilled at (5 ϫ 10Ϫ6 bar, and 70 °C) to give 4.5 g
(43%) of 1a as a light-yellow liquid. This purification step could
not be scaled up because of serious loss of product. IR (film): ν˜ ϭ
3062 cmϪ1 w, 3029 m, 2981 s, 2864 s, 1629 s [ν(CϭN)], 1493 m,
NϪC(sp ) bond length [1.403(2) A] also indicate multiple
bonding. For the N(sp2)ϪC(sp3) single bond N(1)ϪC(2) a
˚
length of 1.471(2) A was determined. The endocyclic
angles in (S)-3c
—
N(1)ϪB(1)ϪN(1A) [107.7(1)°]
B(1)ϪN(1)ϪC(1) [106.6(1)°], and N(1)ϪC(1)ϪC(1A)
[109.5(1)°] — are similar to those in 2,6-Me2C6H3NaCHϭ
CHNb(2,6-Me2C6H3)BI(NaϪB) [106.9(4)°, 107.5(3)°, and
109.1(2)°, respectively].[8] This also applies to the exocyclic
angle N(1)ϪB(1)ϪBr(1) [126.1(1)°] in (S)-3c and the
1
1451 m, 1361 s, 1213 s, 759 s, 699 s. H NMR (CDCl3): δ ϭ 1.21
3
and 1.23 (2s, 9 H, tBu), 1.55 and 1.56 (2d, JH,H ϭ 6.4, 6.8 Hz, 3
3
H, CH3), 4.48 [q, JH,H ϭ 6.8 Hz, 1 H, CHMe], 7.23Ϫ7.33 (m, 5
N(1)ϪB(1)ϪI(1)
angle
[126.6(2)°]
in
2,6- H, HϪPh), 7.92Ϫ8.02 (m, 2 H, NϭCH) ppm. 13C{1H} NMR
(CDCl3): δ ϭ 23.9 (s, CHCH3), 29.27 and 29.34 [2s, C(CH3)], 58.2
and 58.3 [2s, C(CH3)3], 69.66 and 69.71 (2s, CHCH3), 126.6, 126.7,
127.2, 128.5, 128.6, 143.6, 143.7 (7s, CϪPh), 157.0, 157.8, 160.7,
161.5 (4s, HCϭN) ppm. MS/EI: m/z (%) ϭ 216 (6) [Mϩ], 201 (36)
[Mϩ Ϫ CH3], 159 (33) [Mϩ Ϫ tBu], 145 (100) [Mϩ Ϫ CH3 Ϫ CH2ϭ
CMe2]. [α]2D4 ϭ Ϫ97. C14H20N2 (216.33): calcd. C 77.73, H 9.32, N
12.95; found C 77.40, H 9.56, N 12.86.
Me2C6H3NaϪCHϭCHNb(2,6-Me2C6H3)BI(NaϪB).
(S,S)-Cy(Me)CH؊N؍CH؊CH؍N؊CH(Me)Cy (1c): A solution
of (S)-1-cyclohexylethylamine (17.8 g, 140 mmol) in 80 mL of hex-
ane was added during 30 min to a vigorously stirred mixture of
8 mL of aqueous glyoxal (70 mmol) and 50 mL of hexane. Both
phases were separated and the aqueous layer was extracted with
50 mL of hexane. The combined organic phases were dried twice
Figure 1. Molecular structure of (S,S)-3c in the crystal; selected
with Na2SO4. Solvent was removed in vacuo to afford 16.1 g (82%)
˚
bond lengths [A] and bond angles [°]: B(1)ϪBr(1) 1.930(2),
1
of 1c as colorless crystals. H NMR (CDCl3): δ ϭ 0.85 (m, 2 H,
B(1)ϪN(1) 1.417(1), N(1)ϪC(1) 1.403(2), N(1)ϪC(2) 1.471(2),
Cy), 0.93 (m, 2 H, Cy), 1.15 (m, 8 H, Cy), 1.23 (m, 4 H, Cy), 1.42
(m, 2 H, Cy), 1.63 (m, 4 H, Cy), 1.75 (m, 6 H, CH3), 2.97 (q,
3JH,H ϭ 6.6 Hz, 2 H, CHCH3), 7.85 (s, 2 H, NϭCH) ppm. 13C{1H}
NMR (CDCl3): δ ϭ 19.6 (s, CH3), 26.2, 26.3, 26.5, 29.5, 29.8, 43.4
(6s, Cy), 71.6 (s, CHCH3), 160.2 (s, CHϭN) ppm. MS/EI: m/z
(%) ϭ 276 (7) [Mϩ], 193 (100) [Mϩ Ϫ Cy]. [α]2D4 ϭ ϩ34. C18H32N2
(276.47): calcd. C 78.20, H 11.67, N 10.13; found C 77.40, H 11.94,
N 10.30.
C(1)ϪC(1A)
1.350(3);
126.1(1),
131.0(1),
N(1)ϪB(1)ϪN(1A)
B(1)ϪN(1)ϪC(1)
N(1)ϪC(1)ϪC(1A)
107.7(1),
106.6(1),
109.5(1);
Br(1)ϪB(1)ϪN(1)
B(1)ϪN(1)ϪC(2)
B(1)ϪN(1)ϪC(2)ϪC(3) 124.3, B(1)ϪN(1)ϪC(2)ϪC(4) Ϫ110.0
Experimental Section
Preparation of the 2,3-Dihydro-1H-1,3,2-diazaboroles. (S)-tBuNa-
CH؍CHNb {CH(Ph)Me}BBr(Na؊B) (3a): A solution of 1,4-diaza-
butadiene 1a (3.3 g, 15.3 mmol) in 50 mL of hexane and a solution
of boron tribromide (3.85 g, 15.5 mmol) in 50 mL of hexane were
added dropwise and simultaneously at 20 °C to a volume of 100 mL
of hexane. The resulting orange slurry was stirred for another
30 min and filtered. The filter cake was washed with pentane
(50 mL) and dried at 5 ϫ 10Ϫ3 bar. The borolium salt (S)-tBuNaϭ
CHϪCHϭNb{CH(Ph)Me}BBr2]Br(NaϪB) 2a was obtained as an
General: All manipulations were performed under dry argon. Solv-
ents were rigorously dried with an appropriate drying agent and
freshly distilled before use. The following compounds were pre-
pared as described in the literature: (S,S)-Ph(Me)CHNϭ
CHϪCHϭNCH(Me)Ph (1b),[13] tBuNaCHϭCHNb(tBu)BBr-
(NaϪB).[7]
An aqueous glyoxal solution (40%) of tert-butylamine, boron tri-
bromide, silver cyanide, trimethyltin chloride, n-butyllithium,
methyllithium, triethylamine, (S)-1-phenylethylamine and (S)-1-
cyclohexylethylamine were purchased commercially. IR spectra
1
orange powder (6.4 g, 90%). H NMR (CDCl3): δ ϭ 1.75 (s, 9 H,
3
3
tBu), 2.02 (d, JH,H ϭ 6.9 Hz, 3 H, CHCH3), 5.35 (q, JH,H
ϭ
6.9 Hz, 1 H, CHCH3), 7.40 (m, 3 H, Ph), 7.57 (m, 2 H, Ph), 8.40
1
Bruker FTIR Vector 22, Bruker FTIR IFS66. H, 11B, 13C NMR
3
3
(d, JH,H ϭ 7.9 Hz, 1 H, CHϭNϪCH), 8.68 (d, JH,H ϭ 7.9 Hz, 1
H, CHϭNtBu) ppm. 11B{1H} NMR (CDCl3): δ ϭ Ϫ1.2 (s) ppm.
Compound 2a (11.5 g, 24.6 mmol) was added to a mixture of so-
dium amalgam (from 2.5 g, 108 mmol Na and 240 g Hg) and hex-
ane (200 mL) and vigorously stirred for two days. The yellow hex-
ane solution was then decanted and the solvent evaporated. The
remaining brown oil was distilled by means of a hot air gun to
afford 3a as a yellow oil (5.1 g, 66%). As pure diazaborole 3a de-
spectra: Bruker AC 100 (1H, 100.13 MHz, 11B (32.13 MHz); Bruker
Avance DRX 500 (1H, 500.13 MHz, 11B, 160.46 MHz, 13C,
125.75 MHz); references: SiMe4 (1H, 13C), BF3·OEt2 (11B). Mass
spectra EI (70 eV), CI (NH3): Autospec sector-field mass spectro-
meter (Micromass). Optical rotations were measured with a Jasco
DIP-360 in CH2Cl2 solution [c ϭ 0.01 g·mLϪ1, d ϭ 1 dm].
Preparation of the 1,4-Diazabutadienes. (S)-tBuN؍CH؊CH؍
N؊CH(Me)Ph (1a): Solutions of (S)-1-phenylethylamine (28.8 g, composes markedly at ambient temp. within one day, it is recom-
0.24 mol) in hexane (200 mL) and tert-butylamine (121.7 g, 1.90
mol) in hexane (200 mL) were simultaneously added dropwise to a
well-stirred chilled mixture of an aqueous solution of glyoxal 114.3
mL (114.2 mL, 1.0 mol, 0 °C) and 400 mL of hexane. Then stirring
was continued at room temp. for 30 min. The liquid content of the
flask separated into two phases. The aqueous phase was extracted
with hexane (30 mL) and then discarded. The combined hexane
mended to store the compound in the hexane solution over sodium
amalgam and to use the freshly isolated material. IR (film): ν˜ ϭ
3030 cmϪ1 m, 2985 s, 2873 s, 1603 w, 1495 m, 1450 s, 1147 m, 962
1
m, 755 m, 700 s, 610 m. H NMR (CDCl3): δ ϭ 1.51 (s, 9 H, tBu),
3
3
1.66 (d, JH,H ϭ 7.1 Hz, 3 H, CH3), 5.19 (q, JH,H ϭ 7.1 Hz, 1 H,
3
CHCH3), 6.19 (d, JH,H ϭ 2.4 Hz, 1 H, HCϭNCHMe), 6.41 (d,
3JH,H ϭ 2.4 Hz, 1 H, HCϭNtBu), 7.26 (m, 3 H, Ph), 7.3 (m, 2 H,
2442
Eur. J. Inorg. Chem. 2002, 2438Ϫ2446

Chiral 2,3-Dihydro-1H-1,3,2-diazaboroles
FULL PAPER
Ph) ppm. 13C{1H} NMR (CDCl3): δ ϭ 21.4 (s, CHCH3), 31.2 [s, (S)-tBuNaCH؍CHNb[CH(Ph)Me]B؊NC(Na؊B) (4) and (S)-tBu-
C(CH3)3], 52.8 [s, C(CH3)3], 58.3 (s, CHCH3), 111.9 (s, HCϭ solution of 3a
NaCH؍CHNb[CH(Ph)Me]BCN(Na؊B) (5):
NCHMe), 114.9 (s, HCϭNtBu), 126.5, 126.8, 128.3, 144.0 (4s, Ph) (0.65 g, 2.1 mmol) in 5 mL of acetonitrile was added to a slurry of
A
ppm. 11B{1H} NMR (CDCl3): δ ϭ 17.3 s ppm. MS/EI: m/z (%) ϭ
silver cyanide (0.3 g, 2.2 mmol) in hexane (70 mL) and the mixture
308 (6) [Mϩ with 81Br], 306 (7). [Mϩ with 79Br]. [α]2D4 ϭ Ϫ104. was stirred for 1 h. The supernatant yellow solution was decanted,
C14H20BBrN2 (307.04): calcd. C 54.77, H 6.57, N 9.12; found C and the residue was extracted with pentane (2 ϫ 20 mL). The com-
55.40, H 6.89, N 8.62.
bined organic phases were evaporated to dryness to afford a mix-
ture of isocyanide 4 and cyanide 5 as a yellow oil (0.41 g). This
mixture was dissolved in hexane (30 mL) and stored at Ϫ30 °C for
two weeks. The solvent was then removed and the solid brown res-
idue was distilled by means of a hot air gun (200 °C, 5 ϫ 10Ϫ3 bar)
to give 0.3 g (57%) of the 2-cyano derivative 5 as a colorless solid.
IR (KBr): ν˜ ϭ 2976 cmϪ1 (s), 2206 w [ν(CϵN)], 1455 s, 1414 m,
(S,S)-Me(Ph)HCNa؊CH؍CH؊Nb[CH(Ph)Me]BBr(Na؊B) (3b):
A solution of (S,S)ϪMe(Ph)HCϪNϭCHϪCHϭNϪCH(Ph)Me
(1b) (7.04 g, 27.0 mmol) in 50 mL of hexane and a solution of BBr3
(6.67 g, 27.0 mmol) in 50 mL of hexane were added slowly at 20 °C
to 300 mL of hexane, whereupon a yellow precipitate separated.
Stirring was continued for two days. The mixture was then filtered,
the filter cake was washed with hexane (50 mL) and then dried in
vacuo. Yield: 11.2 g (81.4%) [(S,S)ϪMe(Ph)HCϪNaϭCHϪCHϭ
NbϪCH(Ph)MeBBr2]Br(NaϪB) (2b).
1
1372 w, 1336 w, 1259 w, 1228 m, 1156 m, 704 s, 647 m. H NMR
3
(CDCl3): δ ϭ 1.49 (s, 9 H, tBu), 1.74 (d, JH,H ϭ 7.1 Hz, 3 H,
3
3
CH3), 5.19 (q, JH,H ϭ 7.1 Hz, 1 H, CHCH3), 6.25 (d, JH,H
ϭ
3
2.3 Hz, 1 H, ϭCHϪNCH), 6.40 (d, JH,H ϭ 2.3 Hz, 1 H, ϭ
CHNtBu), 7.27 (m, 3 H, Ph), 7.31 (m, 2 H, Ph) ppm. 13C{1H}
NMR (CDCl3): δ ϭ 22.1 (s, CHCH3), 31.6 [s, C(CH3)3], 53.6 [s,
C(CH3)3], 55.1 (s, CHCH3), 114.8 (s, ϭCNCH), 116.1 (s, ϭ
CNtBu), 126.3 (s, CϵN), 126.4, 127.3, 128.5, 143.4 (4s, Ph) ppm.
11B{1H} NMR (CDCl3): δ ϭ 11.6 (s) ppm. MS/EI: m/z (%) ϭ 253
(40) [Mϩ], 252 (10) [Mϩ with 10B]. [α]2D4 ϭ Ϫ140. C15H20BN3
(253.16): calcd. C 71.17, H 7.96, N 16.60; found C 71.16, H 7.93,
N 16.41.
A slurry of 2b (8.0 g, 18.4 mmol) and sodium amalgam (from 230 g
Hg and 2.4 g Na) in 200 mL of hexane was stirred vigorously for
two days. The yellow organic phase was decanted and the solvents
evaporated to dryness to afford 2.1 g (32%) of crude 3b. The
marked thermolability of this compound thwarted reliable ele-
mental analyses. As in the case of 3a it is recommended to store
the reaction mixture and to isolate the required amount of com-
pound prior to use. 1H NMR (C6D6): δ ϭ 1.38 (d, 3JH,H ϭ 7.1 Hz,
3
1
4: IR (KBr): ν˜ ϭ 2113 cmϪ1 w [ν(BϪNϵC)]. H NMR (CDCl3):
6 H, CH3), 5.13 (q, JH,H ϭ 7.1 Hz, 2 H, CHCH3), 6.13 (s, 2 H,
CHϭN), 7.01Ϫ7.17 (m, 10 H, Ph) ppm. 13C{1H} NMR (C6D6):
δ ϭ 21.5 (s, CHCH3), 53.9 (s, CHCH3), 114.6 (s, CHϭN), 126.7,
127.1, 128.5, 144.3 (4s, Ph). 11B{1H} NMR (C6D6): δ ϭ 19.0 (s)
ppm.
3
δ ϭ 1.51 (s, 9 H, tBu), 1.78 (d, JH,H ϭ 7.0 Hz, 3 H, CH3), 5.10
(q, 3JH,H ϭ 7.0 Hz, 1 H, CHCH3), 6.22 (d, 3JH,H ϭ 2.3 Hz, 1 H, ϭ
CHNCH), 6.37 (d, 3JH,H ϭ 2.3 Hz, 1 H, ϭCHNtBu) ppm. 13C{1H}
NMR (CDCl3): δ ϭ 22.5 (s, CH3), 31.6 [s, C(CH3)3], 53.7 [s,
C(CH3)3], 55.7 (s, CHCH3], 114.7 (s, ϭCNtBu), 116.0 (s, ϭ
CNϪCH), 126.3, 127.2, 128.4, 143.3 (4s, Ph).
(S,S)-Me(Cy)HC؊NaCH؍CH؊Nb[CH(Cy)Me]BBr(Na؊B) (3c):
A solution of 1,4-diazabutadiene 1c (8.0 g, 29.0 mmol) in 100 mL
of hexane and a solution of BBr3 (7.52 g, 30.0 mmol) in 100 mL of
hexane were added simultaneously at 0 °C to 100 mL of hexane.
The resulting slurry was allowed to stir for 1 h at 20 °C and was
then filtered. The filter cake was washed with 100 mL of pentane
and dried in vacuo. The borolium salt (S,S)-[Me(Cy)CHϪNaϭ
CHϪCHϭNb{CH(Cy)Me}BBr2]Br(NaϪBr) (2c) was obtained as
an orange solid (14.5 g, 93%). 1H NMR (C6D6): δ ϭ 0.69Ϫ2.00
(S)-tBuNaCH؍CHNb[CH(Ph)Me]BH(Na؊B) (6): At 0 °C a quant-
ity of LiAlH4 (0.05 g, 1.3 mmol) was added to a slurry of 3a (0.4 g,
1.3 mmol) in a mixture of 20 mL of hexane and 5 mL of THF.
After a few minutes of stirring the reaction mixture became clear.
It was then filtered, and the filtrate was evaporated to dryness. The
residue was triturated with pentane (6 mL), and filtered again. Re-
moval of pentane afforded 0.28 g (95%) of crude 6 as a yellow oil.
Distillation with a hot air gun at 150 °C and 2 ϫ 10Ϫ5 bar afforded
pure 6 as a colorless liquid (0.14 g, 47%). This product is temper-
ature-sensitive at room temp.; decomposition to a brown oil was
complete after 24 h (NMR control). IR (film): ν˜ ϭ 3086 m, 3063
m, 3027 m, 2973 s, 2868 s, 2621 s [ν(BH)], 1603 m, 1494 m, 1151
m, 920 m, 753 m, 664 s. 1H NMR (CDCl3): δ ϭ 1.44 (s, 9 H, tBu),
3
(m, 22 H, C6H11), 1.41 (d, JH,H ϭ 6.8 Hz, 6 H, CH3), 3.76 (m, 2
H, CHCH3), 9.12 (s, 2 H, HCϭCH) ppm. 13C{1H} NMR (C6D6):
δ ϭ 18.4 (s, CH3), 26.2, 26.3 (2s, 3,5-CϪCy), 29.0, 31.5 (2s, 2,6-
CϪCy), 42.2 (s, 1-CϪCy), 60.9 (s, CHCH3), 146.7 (s, HCϭCH)
ppm. 11B{1H} NMR (C6D6): δ ϭ 0.6 (s, BBr2), Ϫ23.8 (s, BBr4
)
Ϫ
3
3
ppm.
1.71 (d, JH,H ϭ 7.0 Hz, 3 H, CH3), 4.88 (q, JH,H ϭ 7.0 Hz, 1 H,
3
Solid borolium salt 2c (9.5 g, 18.0 mmol) was combined with so-
dium amalgam [from Na (1.3 g, 55.0 mmol) and 130 g of Hg]. After
the addition of 200 mL of hexane the resulting slurry was stirred
at room temp. for three days. The yellow hexane phase was de-
canted and concentrated to ca 10 mL, whereby crystalline colorless
3c precipitated (4.0 g, 60.5%). The purity of the sample was satis-
factory for most chemical transformations. Analytically pure 3c
was obtained by sublimation at 80 °C and 5 ϫ 10Ϫ6 bar. 1H NMR
(CDCl3): δ ϭ 0.79Ϫ1.81 (m, 22 H, C6H11), 1.25 (d, 3JH,H ϭ 6.8 Hz,
6 H, CH3), 3.46 (m, 2 H, CHCH3), 6.17 (s, 2 H, HCϭCH) ppm.
13C{1H} NMR (CDCl3): δ ϭ 19.6 (s, CH3), 26.15, 26.22 (2s, 3,5-
CϪCy), 26.3 (s, 4-CϪCy), 29.9, 30.3 (2s, 2,6-CϪCy), 44.1 (s, 1-
CHCH3), 6.15 (d, JH,H ϭ 2.0 Hz, 1 H, ϭCHNCH), 6.40 (d,
3JH,H ϭ 2.0 Hz, 1 H, ϭCHNtBu), 7.27 (m, 3 H, Ph), 7.30 (m, 2 H,
Ph) ppm. 13C{1H} NMR (CDCl3): δ ϭ 24.0 (s, CH3), 31.8 [s,
C(CH3)3], 51.5 [s, C(CH3)3], 56.5 (s, CHCH3), 114.4 (s, ϭCNCH),
116.2 (s, ϭCNtBu), 126.1, 126.7, 128.3, 146.1 (4s, Ph) ppm. 11B
1
NMR (CDCl3): δ ϭ 19.4 (d, JB,H ϭ 146 Hz) ppm. MS/EI: m/z
(%) ϭ 228 (7) [Mϩ], 213 (7) [Mϩ Ϫ CH3]. [α]2D4 ϭ ϩ94. C14H21BN2
(228.15): calcd. C 73.70, H 9.28, N 12.28; found C 73.44, H 9.39,
N 12.21.
(S)-tBuNaCH؍CHNb[CH(Ph)Me]BCH3(Na؊B) (7): A sample of
3a (0.57 g, 1.8 mmol) was suspended in a mixture of hexane
CϪCy), 55.6 (s, CHCH3), 113.5 (s, HCϭCH) ppm. 11B{1H} NMR: (40 mL) and THF (2.5 mL). An ethereal solution of methyllithium
δ ϭ 18.2 (s) ppm. MS/CI (toluene): m/z (%) ϭ 367 (9) [MHϩ]. [α] was then added (2 mL, 1.6 ), and the resulting mixture was stirred
24
ϭ Ϫ29. C18H32BBrN2 (367.18): calcd. C 58.88, H 8.78, N 7.63;
at 20 °C for two days. The volatile components were removed in
D
found C 58.44, H 9.17, N 7.48.
vacuo, and the residue was extracted twice with 2.5 mL of hexane.
Eur. J. Inorg. Chem. 2002, 2438Ϫ2446
2443

L. Weber, A. Rausch, H. B. Wartig, H.-G. Stammler, B. Neumann
FULL PAPER
After filtration it was evaporated to dryness to give crude 7 (0.4 g,
(S)-Me(Ph)CH؊Na؊CH؍CH؊Nb[CH(Ph)Me]BSnMe3(Na؊B)
92%) as a red oil. Purification was achieved by hot air distillation (10): Trimethyltin chloride (1.68 g, 8.45 mmol) was added to a
(200 °C, 1.5 ϫ 10Ϫ5 bar) to yield 0.23 g (51%) of 7 as a colorless
slurry of lithium sand (0.13 g, 18.6 mmol) in THF (80 mL) and
liquid. IR (film): ν˜ ϭ 3027 s, 2972 s, 1602 m, 1401 s, 1253 s, 1152 stirred at 20 °C until a green solution was formed (ca. 2 h). A solu-
1
m, 1029 m, 758 m, 700 s, 665 m. H NMR (CDCl3): δ ϭ 0.75 (s, tion of 3b (1.31 g, 5.6 mmol) in hexane (30 mL) was then added
3
3 H, BCH3), 1.56 (s, 9 H, tBu), 1.80 (d, JH,H ϭ 7.1 Hz, 3 H,
dropwise to this mixture and stirring was continued for another
2 h. The volatile components were removed in vacuo and the res-
3
3
CHCH3), 5.12 (q, JH,H ϭ 7.1 Hz, 1 H, CHCH3), 6.32 (d, JH,H ϭ
3
2.5 Hz, 1 H, ϭCHϪNCH), 6.48 (d, JH,H ϭ 2.5 Hz, 1 H, ϭ idue was extracted with pentane (3 ϫ 10 mL). The filtrate was evap-
CHNtBu), 7.34 (m, 3 H, Ph), 7.41 (m, 2 H, Ph) ppm. 13C{1H} orated to dryness. Recrystallization of the residue from toluene
NMR (CDCl3): δ ϭ 22.2 (CHCH3), 31.6 [s, C(CH3)3], 52.4 [s, gave 1.66 g (67%) of 10 as colorless crystals. 1H NMR (C6D6): δ ϭ
2
3
C(CH3)3], 55.7 (s, CHCH3), 111.1 (s, ϭCHNCH), 113.5 (s, ϭ
0.22 (t, JSn,H ϭ 47.3 Hz, 9 H, SnMe3), 1.51 (d, JH,H ϭ 7.1 Hz, 6
CHNtBu), 126.2, 126.3, 128.4, 145.7, (4 s, Ph) ppm. 11B{1H} NMR H, CHCH3), 5.15 (q, JH,H ϭ 7.1 Hz, 2 H, CHCH3), 6.38 (s, 2 H,
3
(CDCl3): δ ϭ 26.2 (s) ppm. MS/EI: m/z (%) ϭ 242 (75) [Mϩ], 241 HCϭCH), 7.01 (t, JH,H ϭ 7.3 Hz, 2 H, p-HϪPh), 7.09 (m, 4 H,
3
(19) [Mϩ with 10B], 227 (54) [Mϩ Ϫ CH3]. [α]2D4 ϭ Ϫ111. C15H23BN
(242.17): calcd. C 73.06, H 10.07, N 12.17; found C 73.28, H 9.85,
N 12.19.
Ph), 7.16 (m, 4 H, Ph) ppm. 13C{1H} NMR (C6D6): δ ϭ Ϫ9.4 [t,
1JSn, C ϭ 298.9 Hz, Sn(CH3)3], 23.0 (s, CHCH3), 55.9 (s, CHCH3),
116.4 (s, HCϭCH), 126.5, 126.7, 128.6, 145.5 (4s, Ph) ppm.
1
11B{1H} NMR (C6D6): δ ϭ 28.2 (t, JSn,B ϭ 994 Hz). 119Sn{1H}
1
NMR (C6D6): δ ϭ Ϫ150.0 (q, JSn,B ϭ 994 Hz) ppm. MS/EI: m/z
(S)-tBuNaCH؍CHNb[CH(Ph)Me]BNHtBu(Na؊B) (8): tert-Bu-
tylamine (1 mL, 0.66 g, 9.0 mmol) was added at room temp. to a
well stirred slurry of 3a (1.3 g, 4.2 mmol) in hexane (10 mL). A
colorless precipitate was formed immediately. After filtration the
filtrate was freed from solvent to yield 1.17 g of a brown oil, which
was subsequently purified by distillation with a hot air gun (300
°C, 10Ϫ5 bar). Compound 8 was obtained as a yellow oil (yield
0.93 g, 74%). IR (film): ν˜ ϭ 3443 cmϪ1 w [ν(NH)], 3061 m, 3027
m, 2986 s, 2865 s, 1602 w, 1494 s, 1135 m, 1028 m, 817 m, 789 m,
753 m, 699 s, 647 m. 1H NMR (CDCl3): δ ϭ 1.28 (s, 9 H, NHtBu),
(%) ϭ 440 (2) [Mϩ]. [α]2D4 ϭ Ϫ119. C21H29BN2Sn (439.00): calcd.
C 56.62, H 6.58, N 6.28; found C 57.46, H 6.66, N 6.38.
(S,S)-Me(Ph)CH؊Na؊CH؍CH؊Nb[CH(Ph)Me]B(NHtBu)-
(Na؊B) (11): A slurry of 3b (1.80 g, 5.0 mmol) in hexane (50 mL)
was treated with tert-butylamine (0.74 g, 1.1 mL, 10 mmol) and
stirred for 5 min at room temperature. The mixture was then fil-
tered. The filtrate was evaporated to dryness to give a red oil
(1.75 g), which was distilled at 200 °C (hot air gun) and 2 ϫ 10Ϫ6
bar to afford 11 as a pale yellow liquid (0.86 g, 50%). IR (film):
ν˜ ϭ 3414 cmϪ1 w [ν(NH)], 3060 m, 3026 m, 2969 s, 2871 m, 1946
w, 1602 m, 1493 s, 1243 m, 1167 m, 1027 m, 757 m, 699 s. 1H NMR
3
1.47 (s, 9 H, ϭCHNϪtBu), 1.69 (d, JH,H ϭ 7.0 Hz, 3 H, CH3),
3
3
5.22 (q, JH,H ϭ 7.0 Hz, 1 H, CHCH3), 5.93 (d, JH,H ϭ 2.8 Hz, 1
H, ϭCHϪNCH), 6.24 (d, 3JH,H ϭ 2.8 Hz, 1 H, ϭCHϪNtBu), 7.21
(m, 1 H, Ph), 7.29 (m, 4 H, Ph) ppm. 13C{1H} NMR (CDCl3): δ ϭ
21.9 (s, CH3), 31.6 [s, NC(CH3)3], 33.6 [s, NHC(CH3)3], 49.2 [s,
NHC(CH3)3], 51.8 [s, ϭCHϪNC(CH3)3], 52.2 (s, CHCH3), 109.6
(s, ϭHCNϪCH), 113.0 (s, ϭCHNtBu), 126.1, 126.4, 128.3, 144.0
3
(CDCl3): δ ϭ 1.15 (s, 9 H, tBu), 1.70 (d, JH,H ϭ 7.0 Hz, 6 H,
3
CH3), 5.04 (q, JH,H ϭ 7.0 Hz, 2 H, CHCH3), 6.12 (s, 2 H, CHϭ
CH), 7.30 (m, 4 H, Ph), 7.34 (m, 6 H, Ph) ppm. 13C{1H} NMR
(CDCl3): δ ϭ 22.4 (s, CH3), 33.2 [s, C(CH3)3], 49.1 [s, C(CH3)3],
111.9 (s, HCϭCH), 126.1, 126.4, 128.2, 145.7, (4s, Ph) ppm.
11B{1H} NMR (CDCl3): δ ϭ 22.5 (s) ppm. [α]2D4 ϭ Ϫ165.
C22H30BN3 (347.31): calcd. C 76.08, H 8.71, N 12.10; found C
75.90, H 8.93, N 11.66.
(4s, Ph) ppm. 11B{1H} NMR (CDCl3): δ ϭ 22.3 (s) ppm. [α]2D4
Ϫ125. C18H30BN3 (299.27): calcd. C 72.24, H 10.10, N 14.04;
ϭ
found C 71.91, H 10.20, N 13.87.
(S,S)-Me(Cy)CHNa؊CH؍CH؊Nb[CH(Cy)Me]BN(H)tBu (12): A
solution of 3c (0.70 g, 1.9 mmol) in hexane (25 mL) was treated at
20 °C with tert-butylamine (0.29 g, 4.0 mmol). After stirring for
10 min this mixture was filtered, and the filtrate was evaporated to
dryness. The residual yellow oil was distilled by means of a hot air
gun (300 °C, 4 ϫ 10Ϫ6 bar) to afford 0.40 g (58%) of 12 as a color-
less oil. IR (film): ν˜ ϭ 3419 cmϪ1 w [ν(NH)], 2923 s, 2843 s, 2658
(S,S)؊tBuNa؊CH؍CHNb؊[CH(Ph)Me]BNH[CH(Ph)Me]-
(Na؊B) (9): Triethylamine (0.12 g, 1.2 mmol) was added to a slurry
of (S)-3a (0.38 g, 1.2 mmol) in hexane (15 mL) at ambient temp.
followed by the addition of (S)-1-phenylethylamine (0.16 g,
1.3 mmol). The reaction mixture spontaneously turned cloudy with
separation of a colorless precipitate. The mixture was stirred for
15 min and then filtered. The filtrate was evaporated to dryness to
yield (S,S)-9 as a red-brown oil (yield 0.38 g, 92%). Distillation of
the product (hot air gun, 150 °C, 2 ϫ 10Ϫ6 bar) gave 0.2 g (48%)
of 9 as a colorless liquid. IR (film): ν˜ ϭ 3463 cmϪ1 w [ν(NH)],
3061 m, 3026 m, 2961 s, 2865 s, 1601 w, 1478 w, 1332 s, 1137 m,
1
w, 1446 s, 1229 s, 890 s, 657 s. H NMR (CDCl3): δ ϭ 0.87Ϫ1.80
3
(m, 22 H, C6H11), 1.20 (d, JH,H ϭ 6.8 Hz, 6 H, CHCH3), 1.21 (s,
9 H, tBu), 3.25 (m, 2 H, CHCH3), 5.95 (s, 2 H, HCϭCH) ppm.
13C{1H} NMR (CDCl3): δ ϭ 22.7 (s, CHCH3), 26.4 (s, 3,5-CϪCy),
26.5 (s, 4-CϪCy), 30.4, 30.8 (2s, 2,6-CϪCy), 31.6 [s, C(CH3)3], 33.6
[s, C(CH3)3], 44.5 (s, 1-CϪCy), 54.4 (s, CHCH3), 110.6 (s, HCϭ
CH) ppm. 11B{1H} NMR (CDCl3): δ ϭ 22.1 (s) ppm. MS/CI
(NH3): m/z (%) ϭ 360 (87) [MHϩ], 359 (100) [MHϩ with 10B and
Mϩ with 11B], 358 (22) [Mϩ, 10B]. [α]2D4 ϭ Ϫ55. C22H42BN3
(359.41): calcd. C 73.52, H 11.78, N 11.69; found C 73.23, H 12.06,
N 11.40.
1
1028 m, 908 w, 758 m, 700 s, 636 m. H NMR (CDCl3): δ ϭ 1.24
3
3
(d, JH,H ϭ 6.9 Hz, 3 H, BNHCCH3), 1.33 (d, JH,H ϭ 6.7 Hz, ϭ
3
HCϪNCHCH3), 1.46 (s, 9 H, tBu), 2.27 (d, JH,H ϭ 8.8 Hz, 1 H,
NH), 4.37 [m, 1 H, N(H)CHCH3], 4.72 (q, JH,H ϭ 7.0 Hz, 1 H,
3
3
CHϭNCHCH3), 5.86 (d, JH,H ϭ 2.6 Hz, 1 H, ϭCHNCH), 6.13
3
(d, JH,H ϭ 2.6 Hz, 1 H, ϭCHNtBu), 7.20 (m, 4 H, Ph), 7.34 (m,
6 H, Ph) ppm. 13C{1H} NMR (CDCl3): δ ϭ 22.1 (s, CNCHCH3),
28.2 (s, HNCHCH3), 31.1 [s, C(CH3)3], 51.5 [s, C(CH3)3], 51.9 (s, (S,S)؊Me(Cy)CHNa؊CH؍CH؊Nb[CH(Cy)Me]B؊nC4H9(Na-B)
CHCH3), 52.0 (s, CHCH3), 109.2 (s, ϭCHNCH), 111.9 (s, ϭ
CHNtBu), 125.3, 125.9, 126.1, 126.15, 128.1, 128.2, 146.5, 148.8
(13): A hexane solution of n-butyllithium (12%, 2.0 g, 3.8 mmol)
was added dropwise at Ϫ15 °C to a solution of 3c (0.76 g,
(8s, Ph) ppm. 11B{1H} NMR (CDCl3): δ ϭ 21.6 (s) ppm. MS/EI: 2.1 mmol) in a mixture of 50 mL of hexane and 10 mL of THF.
m/z (%) ϭ 347 (37) [Mϩ], 346 (9) [Mϩ with 10B]. [α]2D4 ϭ Ϫ99.
C22H30BN3 (347.31): calcd. C 76.08, H 8.71, N 12.10; found C ents were removed in vacuo. The residue was extracted with 30 mL
After stirring for one day at 20 °C the solvent and volatile compon-
76.10, H 8.77, N 11.86.
of pentane. Removal of solvent gave a yellow oil (0.75 g) which was
2444
Eur. J. Inorg. Chem. 2002, 2438Ϫ2446

Chiral 2,3-Dihydro-1H-1,3,2-diazaboroles
FULL PAPER
distilled at 250 °C and 5 ϫ 10Ϫ6 bar to give 0.32 g (47%) of 13 as cuum distillation (150 °C, hot air gun, 2 ϫ 10Ϫ6 bar). IR (film):
1
a colorless oil. H NMR (C6D6): δ ϭ 0.80Ϫ1.70 (m, 31 H, C6H11
ν˜ ϭ 3450 cmϪ1 w [ν(NH)], 2925 s, 2853 m, 1396 s, 1365 s, 1233 s,
3
1
and C4H9), 1.24 (d, JH,H ϭ 6.8 Hz, 6 H, CHCH3), 3.37 (m, 2 H, 1133 m, 821 w, 625 m. H NMR (CDCl3): δ ϭ 0.85Ϫ1.84 (m, 11
CHCH3), 6.19 (s, 2 H, HCϭCH) ppm. 13C{1H} NMR (C6D6): δ ϭ H, C6H11), 1.04 (d, JH,H ϭ 6.6 Hz, 3 H, CHCH3), 1.40 (s, 18 H,
3
14.4 (s, CH2CH3), 20.9 (s, CHCH3), 26.5 (s, CH2CH3), 26.7 (s, 3,5-
tBu), 3.29 (m, 1 H, CHCH3), 6.06 (s, 2 H, HCϭCH) ppm. 13C{1H}
CϪCy), 26.8 (s, 4-CϪCy), 30.3 (s, CH2CH2CH3), 30.7, 30.9 (2s, NMR (CDCl3): δ ϭ 21.5 (s, CHCH3), 26.6, 26.7 (2s, 3,5-CϪCy),
2,6-CϪCy), 44.5 (s, 1-CϪCy), 55.6 (s, CHCH3), 112.4 (s, HCϭCH) 28.6 (s, 4-CϪCy), 30.1 (s, 2,6-CϪCy), 31.4 [s, C(CH3)], 46.5 (s, 1-
ppm. 11B{1H} NMR (C6D6): δ ϭ 26.4 (s) ppm. MS/EI: m/z (%) ϭ
CϪCy), 51.7 [s, C(CH3)3], 110.0 (s, CHϭCH) ppm. 11B{1H} NMR
344 (50) [Mϩ, 11B], 343 (14) [Mϩ, 10B], 262 (20) [Mϩ Ϫ C6H10], (CDCl3): δ ϭ 22.0 (s) ppm. MS/EI: m/z (%) ϭ 305 (62) [Mϩ]. [α]
261 (100) [Mϩ Ϫ C6H11]. [α]2D4 ϭ Ϫ18. C22H41BN2 (344.39): calcd.
ϭ Ϫ6. C18H36BN3 (305.32): calcd. C 70.81, H 11.89, N 13.76;
24
D
C 76.73, H 12.00, N 8.13; found C 76.47, H 12.12, N 7.88.
found C 70.75, H 12.04, N 13.73.
X-ray Structural Analysis of (S,S)-3c: Colorless single crystals were
grown from n-hexane; 0.27 ϫ 0.24 ϫ 0.15 mm, T ϭ 100 K; Nonius
Kappa CCD Mo-Kα (graphite monochromator, λ ϭ 0.71073 A)
(S,S)-Me(Cy)CHNa؊CH؍CH؊Nb[CH(Cy)Me]BSnMe3(Na؊B)
(14): Lithium sand (0.14 g, 20 mmol) was added to a solution of
trimethyltin chloride (0.77 g, 3.9 mmol) in 40 mL of THF and the
slurry was stirred at ambient temp. with sonification. The resulting
˚
empirical formula C18H30BBrN2, tetragonal space group P41212;
˚
unit cell dimensions: a ϭ b ϭ 10.8870(1), c ϭ 16.0510(1) A; V ϭ
mixture was combined with
a solution of (S,S)-3c (1.45 g,
3
1902.47(3) A , dcalcd. ϭ 1.275 g·cmϪ3, Z ϭ 4; µ ϭ 2.16 mmϪ1; range
˚
3.95 mmol) in hexane (20 mL). Stirring was continued for 1 h. The
mixture was then evaporated to dryness, and 30 mL of hexane was
added to the residue. It was filtered, and the filtrate was freed from
solvent to give crude (S,S)-14 as a cloudy yellow oil (1.7 g). Distilla-
tion (250 °C, 1 ϫ 10Ϫ5 bar) gave 1.02 g (58%) of pure (S,S)-14 as
colorless liquid. IR (film): ν˜ ϭ 2979 cmϪ1 m, 2924 s, 2853 s, 2651
w, 2348 w, 1643 s, 1449 s, 1398 s, 1225 m [δ(SnMe3)], 891 w, 764 s,
for data collection: 2.9 Ͻ θ Ͻ 30.0°; index ranges Ϫ15 Ͻ h Ͻ 15,
Ϫ10 Ͻ k Ͻ 10, Ϫ22 Ͻ l Ͻ 22; reflection collected 56253; unique
reflections 2761 (Rint ϭ 0.049); parameters 102; absorption correc-
tion multi-scan, min/max transmission 0.738/0.593: Program used:
SHELXL-97; structure refinement: full-matrix least-squares on F2,
2
wRF ϭ 0.064 (all data) RF ϭ 0.024, wRF ϭ 0.063 based on 2651
unique reflections with I Ͼ 2σ(I), GOOF (F2) ϭ 1.057, maximum
1
2
[(SnMe3)], 513 s. H NMR (C6D6): δ ϭ 0.4 (s, JSn,H ϭ 45.2 Hz, 9
residual electron density 0.561 e AϪ3; hydrogen atoms treated as
˚
3
H, SnMe3), 0.78Ϫ1.74 (m, 22 H, C6H11), 1.22 (d, JH,H ϭ 6.3 Hz,
riding group.
4
6 H, CHCH3), 3.49 (m, 2 H, CHCH3), 6.37 (s, JSn,H ϭ 12.6 Hz, 2
CCDC-180671 [(S,S)-3c] contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Center, 12, Union Road, Cam-
bridge CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
H, CHϭCH) ppm. 13C{1H} NMR (C6D6): δ ϭ Ϫ9.7 (s, JSn,C
ϭ
1
269 Hz, SnCH3), 20.9 (s, CHCH3), 26.6 (s, 4-CϪCy), 26.6, 26.7 (2s,
3,5-CϪCy), 30.68/31.72 (2s, 2,6-CϪCy), 44.7 (s, 1-CϪCy), 58.4 (s,
3
CHCH3), 115.4 (s, JSn,C ϭ 37.9 Hz, HCϭCH) ppm. 11B{1H}
NMR (C6D6): δ ϭ 30.8 (s, 1JSn,B ϭ 986 Hz) ppm. 119Sn{1H} NMR
1
(C6D6): δ ϭ Ϫ149.1 (q, JSn,B ϭ 986 Hz) ppm. MS/CI (NH3):
m/z ϭ 453 (100) [Mϩ ϩ H]. [α]2D4 ϭ Ϫ44. C21H41BN2Sn (451.08):
calcd. C 55.92, H 9.16, N 6.21; found C 56.11, H 9.05, N 6.21.
(S)-tBuNa؊CH؍CH؊Nb(tBu)B؊N(H)CH(Ph)Me(Na؊B)
Equimolar amounts of 1,3,2-diazaborole
tBuNaCHϭ
(15):
Acknowledgments
CHNb(tBu)BBr(NaϪB) (2.33 g, 9.0 mmol) and triethylamine
(1.25 mL, 9.0 mmol) were dissolved in hexane (70 mL). At room
temperature (S)-1-phenylethylamine (1.1 g, 9.0 mmol) was then ad-
ded. After 15 min of stirring the mixture was filtered, and the fil-
trate was freed from solvent and volatile components to afford a
cloudy oil (2.27 g). Pure compound 14 (2.02 g, 74%) was obtained
as a pale yellow oil by distillation (200 °C, hot air gun, 10Ϫ5 bar).
IR (film): ν˜ ϭ 3443 cmϪ1 w [ν(NH)], 2971 s, 2930 m, 2862 m, 1601
This work was generously supported by the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemischen Industrie.
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G. Schmid, J. Schulze, Chem. Ber. 1977, 110, 2744Ϫ2750.
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G. Schmid, J. Schulze, Angew. Chem. 1977, 89, 258Ϫ259;
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CHCH3), 6.19 (s, 2 H, CHϭCH), 7.01 (m, 1 H, p-HϪPh), 7.18 (m,
3
2 H, m-HϪPh), 7.36 (d, JH,H ϭ 7.2 Hz, 2 H, o-HϪPh) ppm.
[5]
[6]
13C{1H} NMR (C6D6): δ ϭ 26.4 (s, CHCH3), 31.8 [s, C(CH3)3],
51.9 [s, C(CH3)3], 54.6 (s, CHCH3), 111.3 (s, HCϭCH), 126.3,
128.6, 148.3 (3s, Ph) ppm. 11B{1H} NMR (C6D6): δ ϭ 22.3 (s)
ppm. MS/CI (NH3): m/z (%) ϭ 300 (100) [MHϩ], 299 (45) [Mϩ].
[α]2D4 ϭ Ϫ29. C18H30BN3 (299.27): calcd. C 72.24, H 10.10, N 10.04;
found C 71.88, H 10.18, N 13.85.
[7]
[8]
[9]
(S)-tBuNa؊CH؍CH؊Nb(tBu)BN(H)CH(Cy)Me(Na؊B)
(16):
Analogously 1.1 g of crude 16 were prepared from tBuNaCHϭ
CHNb(tBu)BBr(NaϪB) (0.93 g, 3.6 mmol), triethylamine (0.37 g,
5.0 mmol) and (S)-1-cyclohexylethylamine (0.46 g, 3.6 mmol). Puri-
fication to afford a colorless oil (0.23 g, 72%) was achieved by va-
[10]
[11]
Eur. J. Inorg. Chem. 2002, 2438Ϫ2446
2445

L. Weber, A. Rausch, H. B. Wartig, H.-G. Stammler, B. Neumann
FULL PAPER
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Received March 5, 2002
[I02114]
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2446
Eur. J. Inorg. Chem. 2002, 2438Ϫ2446