Hydroboration of alkyne-functionalized 1,3,2-benzodiazaboroles

Article abstract of DOI:10.1002/ejic.201201489

Reactions of equimolar amounts of dicyclohexylborane (DCB) with a series of 2-alkynyl-1,3-diethyl-1,3,2-benzodiazaboroles R-C≡C-B(NEt) ₂C₆H₄ (1: R = nBu, 2: R = tBu, 3: R = Ph, 4: R = p-Me₂NC₆H₄, 5: R = p-MeOC₆H ₄) regioselectively afforded the 1,1-diborylalkenes (Z)-R(H)C=C{(B{NEt}₂C₆H₄)B(c-C ₆H₁₁)₂} (7a-11a) as the result of a cis-addition of the BH bond of the borane to the C≡C triple bond in compounds 1 to 5. In contrast to this, reaction of Me₃Si-C≡C- B(NEt)₂C₆H₄ (6) with HB(c-C₆H ₁₁)₂ yielded a 2.5:1 mixture of the 1,2-diborylated alkene (Z)-Me₃Si{(c-C₆H₁₁)₂B}C=CHB(NEt) ₂C₆H₄ (12b) and the 1,1-regioisomer (Z)-Me ₃Si(H)C=C{B(NEt)₂C₆H₄}{B(c-C ₆H₁₁)₂} (12a). These results were rationalized by the differing π-acceptor qualities of the benzodiazaborolyl and trimethylsilyl substituents at the C≡C triple bond in compounds 1 to 6. The novel products 7-12 were characterized by elemental analysis, mass spectrometry and NMR spectroscopy (¹H, ¹¹B, and ¹³C NMR). The molecular structures of 9b and 12b were substantiated by single-crystal X-ray diffraction analysis. Copyright

Full text of DOI:10.1002/ejic.201201489

FULL PAPER
DOI:10.1002/ejic.201201489
Hydroboration of Alkyne-Functionalized 1,3,2-
Benzodiazaboroles
Lothar Weber,*[a] Daniel Eickhoff,[a] Johannes Halama,[a]
Stefanie Werner,[a] Jan Kahlert,[a] Hans-Georg Stammler,[a] and
Beate Neumann[a]
Keywords: Hydroboration / Alkynes / Boron heterocycles
Reactions of equimolar amounts of dicyclohexylborane
(DCB) with a series of 2-alkynyl-1,3-diethyl-1,3,2-benzodi-
azaboroles R–CϵC–B(NEt)2C6H4 (1: R = nBu, 2: R = tBu, 3: R
B}C=CHB(NEt)2C6H4 (12b) and the 1,1-regioisomer (Z)-
Me3Si(H)C=C{B(NEt)2C6H4}{B(c-C6H11)2} (12a). These re-
sults were rationalized by the differing π-acceptor qualities
= Ph, 4: R = p-Me2NC6H4, 5: R = p-MeOC6H4) regioselec- of the benzodiazaborolyl and trimethylsilyl substituents at
tively afforded the 1,1-diborylalkenes (Z)-R(H)C=C-
{(B{NEt}2C6H4)B(c-C6H11)2} (7a–11a) as the result of a cis-ad-
dition of the BH bond of the borane to the CϵC triple bond
in compounds 1 to 5. In contrast to this, reaction of Me3Si–
the CϵC triple bond in compounds 1 to 6. The novel products
7–12 were characterized by elemental analysis, mass spec-
trometry and NMR spectroscopy (1H, 11B, and 13C NMR). The
molecular structures of 9b and 12b were substantiated by
single-crystal X-ray diffraction analysis.
CϵC–B(NEt)2C6H4 (6) with HB(c-C6H11 2 yielded a 2.5:1
)
mixture of the 1,2-diborylated alkene (Z)-Me3Si{(c-C6H11)2-
Introduction
A few years ago we launched a program on the synthesis
and investigation of the photophysical properties of 1,3,2-
benzodiazaboroles III,[1] which are functionalized at the
boron center by organic groups with extended conjugated
π-electron systems, such as phenyl-, biphenyl-, thienyl-, di-
thienyl-, or aryl(heteroaryl)-ethynyl units. Generally these
compounds exhibit intense blue to green fluorescence upon
UV irradiation.[2]
Compounds III are either generated by base-assisted cy-
clo-condensation of o-phenylenediamine (I) with organodi-
bromoboranes II or by treatment of 2-bromo-1,3,2-benzo-
diazaborole (IV)[3] with organolithium compounds V. Care-
ful inspection of the type III species disclose the complete
absence of 2-alkenyl-1,3,2-benzodiazaboroles that contain
additional functionalities at the organic backbone. The pro-
tocols devised in Scheme 1 suffer from the fact that alkenyl-
dihaloborane functionalities may not be tolerated by the
strongly Lewis-acidic boryl center. Alternatively the intro-
duction of an alkenyl group by reaction of IV with an ap-
propriate lithium derivative or Grignard reagent is impeded
by the pronounced reactivity of the latter towards most
functional groups.
Scheme 1. Synthetic routes to 2-organo-1,3,2-benzodiazaboroles.
Recently protocols for the regio- and stereoselective hy-
droboration of alkynylboranes by means of dicyclohex-
ylborane (DCB), which afforded geminal diborylalkenes,
were published.[4,5] Motivated by this, we present an ac-
count on the hydroboration of 2-alkynyl-1,3,2-benzodiaza-
boroles[6] with equimolar amounts of DCB in this paper.[7]
Results and Discussions
2-Alkynyl-1,3,2-benzodiazaboroles 2 to 5 have recently
been obtained by reacting 2-bromo-1,3,2-benzodiazaborole
(IV)[3] with an equimolar amount of the freshly prepared
lithium acetylides[6] (Scheme 2).
[a] Fakultät für Chemie, Universität Bielefeld,
P.O.B. 100131, 33501 Bielefeld, Germany
Fax: +49-521-106-6146
E-mail: lothar.weber@uni-bielefeld.de
Homepage: www.uni-bielefeld.de
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In the 11B{1H} NMR spectra of 7 to 11 the resonances
of the boron atoms of the heterocycle were observed at δ =
29.7–30.4 ppm, whereas the 11B nuclei of the DCB unit gave
rise to singlets at δ = 77.1–81.8 ppm. In the precursors 1 to
6 the 11B NMR signals were registered at a much higher
field (δ = 20.3–21.2 ppm).[6]
In a series of 1,3,2-diazaboroles with phenyl substituents
at the boron atom broad singlets were also located in the
range of δ = 28.6–29.3 ppm.[2c,8] The B-atoms of the dicy-
clohexylboryl (BCy2) groups in the boryl alkenes 13[4] and
14[9] appeared as singlets at δ = 80 and 82 ppm in the 11B
Scheme 2. Synthesis of compounds 1 to 6.
Derivatives 1 and 6 were synthesized analogously from NMR spectra (Figure 1).
IV and lithium 1-hexynide or lithium trimethylsilylethynide
in 84 or 71% yield, respectively.
Reaction of DCB with equimolar amounts of alkynes 1
to 5 in diethyl ether at ambient temperature led to the re-
gioselective formation of 1,1-diborylalkenes 7a to 11a ac-
companied by only minor amounts of the isomeric trans-
1,2-diborylalkenes 7b to 11b [yields from 0% (8b) to 9%
Figure 1. Compounds 13 and 14.
(9b, 11b)]. The reaction of the silylethynyl derivative 6 with
DCB afforded a 29:71 mixture of 1,1-diborylalkene 12a and
In the 11B NMR spectrum of the isomeric mixture 12a,b
one broad singlet at δ = 28.6 ppm for the benzodiazaborole
part was registered, whereas two singlets at δ = 79.6 and
76.3 ppm were assigned to the BCy2 units.
trans-1,2-diborylalkene 12b (Scheme 3). In all of the cases
the hydroboration of the carbon–carbon triple bond was
virtually quantitative.
The vinylic hydrogen atoms in 8a and 12a gave rise to
singlets at δ = 6.65 and 6.70 ppm, whereas the correspond-
ing proton in 7a was observed as a triplet at δ = 6.76 ppm
(3JH,H = 6.9 Hz). The presence of aryl rings in 9a to 11a
led to a significant deshielding of the vinyl protons to δ =
7.55–7.94 ppm. In the 1,2-diborylated regioisomer 12b the
signal for the vinylic hydrogen was observed at a much
higher field (δ = 6.39 ppm) than in 12a.
In the spectra of 7 and 9 to 11 singlets of low intensity
at δ = 5.64, 5.62, 5.51, and 5.63 ppm are assigned to the
minor trans-1,2-diborylated isomers. These assignments are
based upon NOESY-NMR spectroscopic experiments.
In the 13C{1H} NMR spectra of the 1,1-diborylalkenes
the resonances of the β-C-atom of the C=C double bond
range from 147.1 ppm in 9a to 160.6 ppm in 8a. Broad sing-
lets in the spectrum of 12b at δ = 137.3 and 174.7 ppm were
attributed to the β- and α-C-atoms of the C=C unit. The
intense luminescence displayed by thf solutions of benzodi-
Scheme 3. Hydroboration of 1–6 with DCB.
azaborolylalkynes 4 (λmax,em = 355 nm) and 5 (λmax,em
=
410 nm)[6c] is completely quenched by the hydroboration to
The change from diethyl ether to n-hexane as a solvent
for the hydroboration of the representatives 1 and 5 had no
significant influence on the isomeric ratio of the products
7a,b or 11a,b. As evident from the arylated species 9, 10,
and 11 the isomeric ratio also seems to be independent of
the nature of the substituents in the para-positions of the
aryl rings.
10a and 11a.
X-ray Structural Analyses of 9b and 12b
Single crystals of 9b suitable for an X-ray structural
Due to the poor solubility of DCB in n-hexane the hy- study (Table 1) were obtained from a solution of the iso-
droboration of 1 and 5 took 16 h, whereas in ether the reac- meric mixture in n-hexane at –20 °C. The molecular struc-
tions were complete after 2 to 4 h. Products 7 to 12 were ture of 9b (Figure 2) displays a planar 1,3,2-benzodiazabor-
isolated as colorless, viscous, moisture-, and air-sensitive ole unit, which is attached to a (2-phenyl-2-dicyclohexylbo-
oils. Colorless crystals can be grown from solutions of crude ryl)-ethenyl group by means of a B–C single bond of
9 and 12 in n-hexane. Purification of the obtained oils by 1.561(4) Å. Both of the boryl substituents at the C=C
distillation or sublimation was thwarted by decomposition. double bond [1.357(4) Å] are located in a trans position.
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Table 1. Experimental details for the hydroboration of acetylene derivatives 1–6.
BDB–ϵ–R
R
HBCy2
g [mmol]
Solvent
[mL]
Reaction
time [h]
Total yields
g [%]
Product
ratio a/b
g [mmol]
1
1
2
3
4
5
5
6
nBu
nBu
tBu
Ph
Ph-NMe2
Ph-OMe
Ph-OMe
SiMe3
0.66 (2.6)
0.27 (1.1)
0.42 (1.7)
0.77 (2.8)
0.55 (1.7)
1.14 (3.7)
0.25 (0.8)
0.54 (2.0)
0.51 (2.9)
0.21 (1.2)
0.32 (1.8)
0.50 (2.8)
0.31 (1.7)
0.67 (3.7)
0.16 (0.9)
0.40 (2.2)
Et2O (5)
4
16
4
4
4
2
16
6
1.08 (96)
0.47 (99)
0.72 (98)
1.20 (95)
0.86 (100)
1.78 (99)
0.35 (91)
0.85 (94)
96:4
94:6
100:0
91:9
93.5:6.5
91:9
n-C6H14 (4)
Et2O (20)
Et2O (5)
Et2O (6)
Et2O (8)
n-C6H14 (5)
Et2O (5)
91:9
29:71
The B–C single bonds to the heterocycle [B(1)–C(11)
1.560(2) Å] and to the BCy2 unit [B(2)–C(12) 1.557(2) Å]
are similar to those found in 9b. The B(1)–C(11)–C(12)–
B(2) arrangement is slightly more bent out of a plane as
evident from the torsion angle of 172.8°. The plane defined
by the atoms B(1), C(11), and C(12) is roughly orthogonal
to the plane of the diazaborole ring with torsion angles
N(1)–B(1)–C(11)–C(12) of –95.4° and N(2)–B(1)–C(11)–
C(12) of 92.6°. The Si atom is nearly located within the
plane defined by B(1), C(11), and C(12) [torsion angle
Si(1)–C(12)–C(11)–B(1) = –3.3°]. The bonding parameters
within the benzodiazaborole part are as expected.
Figure 2. Molecular structure of 9b in the crystal. H-atoms and the
disordered unit of minor occupation are omitted for clarity. Se-
lected bond lengths [Å] and angles [°]: B(1)–N(1) 1.434(4), B(1)–
N(2) 1.438(4), N(1)–C(1) 1.390(4), N(2)–C(2) 1.394(4), N(1)–C(7)
1.462(4), N(2)–C(9) 1.462(4), C(1)–C(2) 1.410(4), B(1)–C(11)
1.561(4), C(11)–C(12) 1.357(4), C(12)–C(13) 1.500(4), C(12)–B(2)
1.579(4), B(2)–C(19) 1.579(4), N(1)–B(1)–N(2) 106.2(3), B(1)–
N(1)–C(1) 108.3(2), B(1)–N(2)–C(2) 108.4(2), N(1)–C(1)–C(2)
108.8(2), N(2)–C(2)–C(1) 108.2(2), N(1)–B(1)–C(11) 125.2(3),
N(2)–B(1)–C(11) 128.6(3), B(1)–C(11)–C(12) 127.7(3), C(11)–
C(12)–C(13) 122.6(3), C(11)–C(12)–B(2) 121.7(3), C(13)–C(12)–
B(2) 115.5(2), C(12)–B(2)–C(19) 117.9(3), N(1)–B(1)–C(11)–C(12)
–114.8, N(2)–B(1)–C(11)–C(12) 67.2, B(1)–C(11)–C(12)–B(2)
175.7, C(18)–C(13)–C(12)–B(2) –132.4, C(18)–C(13)–C(12)–C(11)
43.2.
Figure 3. Molecular structure of 12b in the crystal. Selected bond
lengths [Å] and angles[°]: B(1)–N(1) 1.434(2), B(1)–N(2) 1.429(2),
N(1)–C(1) 1.393(2), N(2)–C(2) 1.397(2), N(1)–C(7) 1.456(2), N(2)–
C(9) 1.455(2), C(1)–C(2) 1.406(2), B(1)–C(11) 1.560(2), C(11)–
C(12) 1.351(2), C(12)–Si(1) 1.892(1), C(12)–B(2) 1.557(2), B(2)–
C(19) 1.583(2), N(1)–B(1)–N(2) 105.9(1), B(1)–N(1)–C(1) 108.6(1),
B(1)–N(2)–C(2) 108.8(1), N(1)–C(1)–C(2) 108.5(1), N(2)–C(2)–
C(1) 108.2(1), N(1)–B(1)–C(11) 125.7(1), N(2)–B(1)–C(11)
128.0(1), B(1)–C(11)–C(12) 131.0(1), C(11)–C(12)–Si(1) 122.7(1),
C(11)–C(12)–B(2) 122.5(1), Si(1)–C(12)–B(2) 114.7(1), C(12)–B(2)–
C(19) 121.6(1), N(1)–B(1)–C(11)–C(12) –95.4, N(2)–B(1)–C(11)–
C(12) 92.6, B(1)–C(11)–C(12)–B(2) 172.8, Si(1)–C(12)–B(2)–C(19)
–90.0, Si(1)–C(12)–C(11)–B(1) –3.3.
The B(1)–C(11)–C(12)–B(2) arrangement is not com-
pletely planar featuring a torsion angle of 175.7°. The plane
defined by the atoms B(1), C(11), and C(12) is significantly
twisted out of the plane of the B/N heterocycle as evident
by torsion angles N(1)–B(1)–C(11)–C(12) of –114.8° and
N(2)–B(1)–C(11)–C(12) of 67.2°. The phenyl ring also devi-
ates from the plane defined by the atoms B(2), C(11), and
C(12) as given by the dihedral angle of 44.8°. The dicyclo-
hexylboryl group is linked to the C=C bond by means of a
B–C single bond of 1.579(4) Å. One of the cyclohexyl rings
[C(25)–C(30)] is disordered. The bonding parameters within
the benzodiazaborole fragment are as expected from numer-
ous structures and are not further considered here. The X-
ray analytical study is clearly performed from the minor
isomer of the hydroboration process of 3 with DCB.
The regiochemistry of the hydroboration of 1 to 5 with
DCB resembles that observed in the reactions of a series of
Single crystals of 12b were grown from the crude iso- alkynyl pinacolato boranes R–CϵC–Bpin with DCB. The
meric mixture in n-hexane at –20 °C. As given in 9b, the products obtained were subsequently protodeboronated by
analysis of 12b displays the picture of a trans-configured treatment with acetic acid.[5] Additionally, Siebert et al. re-
1,2-diborylalkene [C(11)–C(12) = 1.351(2) Å] (Figure 3). ported on the preparation of 1,1-diborylethene 16 by hydro-
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boration of catecholatoborylethyne (15) with catecholato- ported by Matteson by aldehyde and ketone condensation
borane in 86% yield with only traces of the isomeric trans- with tris(boryl)methanides.[11] 1,1-Diborylalkenes also re-
1,2-diborylethene.[10] (Scheme 4).
sulted from the treatment of silylated alkynes (with the ex-
ception of HCϵC–SiMe3) with chlorinated diboranes.[12,13]
Electronically activated and bulky terminal alkenes undergo
1,1-diborylation when reacted with an excess of bis(pinacol-
ato)diborane in the presence of Pd-catalyst and AlEt3.[14]
Moreover Shimizu et al. devised a highly efficient stereo-
selective route to 1,1-diboryl-1-alkenes by reacting alkylid-
ene type lithium carbenoids with bis(pinacolato)dibor-
ane.[15]
Synthesis of 1,2-diborylated alkenes date back to the
year 1959 when Schlesinger et al. reported on the 1,2-cis-
addition of B2Cl4 to alkynes, a general protocol which was
frequently employed thereafter.[12,13,16]
Scheme 4. Reaction of 15 with catecholatoborane.
Diboranes with oxygen- or nitrogen-based substituents
are usually less reactive. Nevertheless their addition to
alkynes was smoothly achieved under the catalysis of low
valent complexes, whereby bis(boryl) metal complexes oc-
curred as catalytically active species.[17–20]
In the absence of severe steric hindrance these results
would agree with a charge controlled B–H cis-addition to
the CϵC triple bond, whereby the boryl substituent at the
acetylene skeleton serves as a π-acceptor directing the posi-
tively polarized BCy2 moiety to the already borylated ter-
minus (Scheme 5).
Conclusions
A regioselective synthesis of 1,3,2-benzodiazaboroles
containing alkenyl substituents at the boron center was ef-
fected by hydroboration of 2-alkyl- and 2-aryl-ethynyl-
1,3,2-benzodiazaboroles with dicyclohexylborane. The dicy-
clohexylboryl unit was thereby added preferentially to the
α-carbon atom of the triple bond to give 1,1-diborylated
alkenes. In the case of the silylethynyl-1,3,2-benzodiazabor-
ole 6 the situation changed and the hydroboration led favor-
ably to the trans-1,2-diborylated alkene 12b. This observa-
tion was rationalized by a different charge distribution of
the π-electrons of the CϵC bond in 2-alkylethynyl-1,3,2-
benzodiazaborole, such as 8 (or 17), and 2-trimethylsilyl-
ethynyl-1,3,2-benzodiazaborole 12 (or 18).
Scheme 5. Charge controlled B–H addition to the triple bond in
boryl acetylenes.
In the trimethylsilyl acetylene a similar regiochemistry
for hydroboration with DCB was encountered thereby
opening a mild synthetic route to cis-silylalkenes by a hy-
droboration/protodeboronation sequence.[9]
The hydroboration of 2-trimethylsilylethynyl-1,3,2-
benzodiazaborole with DCB leads to a 71:29 mixture of the
regioisomers 12b and 12a, with clear preference for an in-
verse direction of the B–H addition. Obviously the benzodi-
azaborolyl and the Me3Si group are competing for the π-
electrons of the triple bond, whereby the silyl group is
slightly favored.
The charge distributions at the triple bond in the model
1,3,2-benzodiazaborolyl alkynes 17 and 18, estimated by
Mulliken population analysis, support this idea (Figure 4).
A change in the polarity of the CϵC unit of 17 occurs by
the exchange of the tert-butyl group with the Me3Si moiety
in 18.
Experimental Section
General: All of the operations were performed under dry, oxygen-
free argon by using the standard Schlenk techniques. The solvents
were dried with appropriate drying agents and freshly distilled un-
der argon before use. The following compounds were prepared ac-
cording to literature procedures: 2-bromo-1,3-diethyl-1,3,2-benzo-
diazaborole (IV),[3] 2-tert-butylethynyl-1,3-diethyl-1,3,2-benzodiaz-
aborole (2),[6a] 2-phenylethynyl-1,3-diethyl-1,3,2-benzodiazaborole
(3),[6a] 4Ј-dimethylaminophenylethynyl-1,3-diethyl-1,3,2-benzodi-
azaborole (4),[6b] 4-methoxyphenylethynyl-1,3-diethyl-1,3,2-benzo-
diazaborole (5),[6b] and dicyclohexylborane.[7] Trimethylsilyl acetyl-
ene was purchased commercially. The NMR spectra were recorded
at ambient temperature with a Bruker AM Avance DRX 500 in-
strument. External standards: SiMe4 (1H, 13C) and BF3·Et2O (11B).
The mass spectra were recorded with a VG Autospec sector field
mass spectrometer (Micromass). Due to incomplete combustion of
organoboron compounds, elemental analyses, particularly C-val-
ues, may not be satisfactory. The Mulliken charges of the model
geometries 17 and 18 were calculated on the MP2/6-31G*//B3LYP/
6-31G*[21] level of theory with the Gaussian 03[22] program pack-
Figure 4. Mulliken charges of the triple bond in 17 and 18.
The families of 1,1- and 1,2-diborylalkenes are not new.
The first representatives of 1,1-diborylethenes were re- age.
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2-(1Ј-Hexynyl)-1,3-diethyl-1,3,2-benzodiazaborole (1): A solution of
Table 2. X-ray crystallography.
1-hexyne (0.48 g, 5.84 mmol) in n-hexane (60 mL) was treated at
20 °C with a 1.6 m solution of n-butyllithium (3.65 mL, 5.84 mmol).
After 10 min a sample of 2-bromo-1,3-diethyl-1,3,2-benzodiazabor-
ole (1.47 g, 5.84 mmol) was added and the mixture was stirred for
another 16 h. After filtration the solvent and volatile components
were removed in vacuo and the residual oil was purified by short-
path distillation (130 °C, 10–6 bar). Compound 1 (1.24 g, 84%) was
9b
12b
Empirical formula
M [gmol–1
Measurment device
C30H42B2N2
452.28
Nonius Kap-
paCCD
0.71073
100(2)
C27H46B2N2Si
448.37
Bruker KAPPA
APEX II
0.71073
]
Wavelength [Å3]
Temperature [K]
100(2)
1
3
obtained as a colorless oil. H NMR (C6D6): δ = 0.81 (t, JHH
=
Crystal dimension [mm] 0.30ϫ0.30ϫ0.14 0.25ϫ0.21ϫ0.16
3
7.2 Hz, 3 H, CH2CH2CH2CH3), 1.21 (t, JHH = 7.2 Hz, 6 H,
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
P21/c
15.893(3)
16.9983(4)
10.5218(19)
90
108.877(16)
90
2689.6(7)
4
1.117
0.063
984
3.0–27.5
44993
triclinic
CH2CH3), 1.38 (m, 4 H, CH2CH2CH2CH3), 2.19 (t, 3JHH = 6.9 Hz,
¯
P1
3
2 H, CH2CH2CH2CH3), 3.76 (q, JHH = 7.2 Hz, 4 H, CH2CH3),
10.0251(4)
10.3532(4)
14.2454(6)
84.147(2)
70.166(2)
80.618(2)
1370.51(10)
2
1.087
0.102
492
2.45–27.50
60426
6253
0.0309
5297
294
1.040
0.0367
0.0975
0.375/–0.201
912884
6.94 (m, 2 H, CH=CH–CH=CH), 7.11 (m, 2 H, CH=CH–
CH=CH) ppm. 13C{1H} NMR (C6D6):
δ
=
13.5 (s,
α [°]
β [°]
γ [°]
CH2CH2CH2CH3), 16.1 (s, CH2CH3), 19.9 (s, CH2CH2CH2CH3),
21.9 (s, CH2CH2CH2CH3), 30.8 (s, CH2CH2CH2CH3), 38.1 (s,
CH2CH3), 108.8 (s, B-CϵC), 108.9 (s, CH=CH–CH=CH), 119.1 (s,
CH=CH–CH=CH), 137.0 (s, C2N2) ppm. 11B{1H} NMR (C6D6): δ
= 21.1 (s) ppm. MS/EI: m/z (%) = 254.2 (100) [M+], 239.2 (95) [M –
Me+]. C16H23BN2 (254.18): calcd. C 75.60, H 9.24, N 10.77; found
C 75.34, H 9.24, N 10.77.
V [Å3]
Z
ρcalcd. [gcm–1
]
μ [mm–1
F(000)
Θ [°]
]
2-(Trimethylethynyl)-1,3-diethyl-1,3,2-benzodiazaborole (2): A solu-
tion of trimethylsilylacetylene (0.25 g, 2.55 mmol) in n-hexane
(30 mL) was treated at 20 °C with a 1.6 m solution of n-butyllithium
(1.59 mL, 2.55 mmol). After 15 min a sample of 2-bromo-1,3-di-
ethyl-1,3,2-benzodiazaborole (0.64 g, 2.55 mmol) was added and
the mixture was stirred for another 16 h. After filtration the filtrate
was liberated from the solvent and volatiles in vacuo. The solid
residual was recrystallized from n-hexane to give a colorless solid
Collected reflections
Unique reflections
R(int)
Reflections [IϾ2σ(I)]
Refined parameters
GOF
6149
0.0740
4817
336
1.050
Rf [I Ͼ 2σ(I)]
0.0649
0.1816
0.331/–0.330
912883
pseudomerohedral twin, domain ratio
32:68; the cyclohexyring C(25) to C(30)
is disordered in ratio (78:22)
wRF2(all data)
Δρmax/min [eÅ–3
CCDC number
Remarks
]
1
2 (0.49 g, 71%). H NMR (C6D6): δ = 0.24 (s, 9 H, SiMe3), 1.17
3
3
(t, JHH = 7.2 Hz, 6 H, CH2CH3), 3.72 (q, JHH = 7.2 Hz, 4 H,
CH2CH3), 6.89 (m, 2 H, CH=CH–CH=CH), 7.07 (m, 2 H,
CH=CH–CH=CH) ppm. 13C{1H} NMR (C6D6): δ = –0.21 [s,
Si(CH3)3], 15.9 (s, CH2CH3), 38.1 (s, CH2CH3), 109.1 (s, CH=CH–
CH=CH), 115.0 (s, B-CϵC), 119.4 (s, CH=CH–CH=CH), 136.8
(s, C2N2) ppm. 11B{1H} NMR (C6D6): δ = 20.3 (s) ppm. MS/EI:
m/z (%) = 270.2 (89) [M+], 255.2 (100) [M – Me+]. C15H23BN2Si
(270.25): calcd. C 66.66, H 8.58, N 10.37; found C 66.07, H 8.68,
N 10.19.
hexyl), 38.0 (s, CH2CH3), 108.8 (s, CH=CH–CH=CH), 118.6 (s,
CH=CH–CH=CH), 137.7 (s, C2N2), 153.5 (s, B2C=CH) ppm.
11B{1H} NMR (C6D6): δ = 29.8 (s, BN2), 78.2 (s, BCy2) ppm. MS/
EI: m/z (%) = 432.3 (100) [M+], 287.2 (35), 267.2 (58). HRMS (EI):
calcd. for C28H46B2N2 432.38416; found 432.38520.
General Procedure for the Hydroboration of the 2-Alkynyl-1,3,2-
benzodiazaboroles 1–6: The acetylene derivative and a slight excess
of dicyclohexylborane were combined in a given volume of diethyl
ether or n-hexane. The resulting mixture was stirred at 20 °C until
the components were completely dissolved. The solvent was re-
moved in vacuo and the residue was dissolved in n-hexane. After
filtration the hexane was evaporated under reduced pressure to
yield the respective products as colorless very viscous oils. Crystalli-
zation of the oily mixtures of 9a,b and 12a,b in n-hexane afforded
colorless crystals of 9b and 12b (Table 2). Due to the pronounced
sensitivity of the products, in most cases no reliable elemental
analyses were obtained. More details are compiled in Table 1.
8a: 1H NMR (C6D6): δ = 0.99 (s, 9 H, tBu), 1.24 (t, 3JHH = 7.2 Hz,
6 H, CH2CH3), 1.27–1.47 (m, 12 H, c-C6H11), 1.67–1.77 (m, 10 H,
c-C6H11), 3.57 (q, JHH = 7.2 Hz, 2 H, CH2CH3), 3.67 (q, JHH
7.2 Hz, 2 H, CH2CH3), 6.65 (s, 1 H, B2C=CH), 7.00 (m, 2 H,
CH=CH–CH=CH), 7.08 (m, H, CH=CH–CH=CH) ppm.
3
3
=
2
13C{1H} NMR (C6D6): δ = 15.2 (s, CH2CH3), 27.2, 28.0, 28.2 (3s,
CH2-cyclohexyl), 29.5 [s, C(CH3)3], 34.9 [s, C(CH3)3], 37.1 (s, CH-
cyclohexyl), 38.2 (s, CH2CH3), 108.9 (s, CH=CH–CH=CH), 118.6
(s, CH=CH–CH=CH), 137.7 (s, C2N2), 160.6 (s, B2C=CH) ppm.
11B{1H} NMR (C6D6): δ = 29.9 (s, BN2), 77.3 (s, BCy2) ppm. MS/
EI: m/z (%) = 432.3 (100) [M+], 349.1 (45) [M+ – Cy].
Spectroscopic Data of the Products 7–11a, 12a, and 12b
1
3
9a: H NMR (C6D6): δ = 1.03 (t, JHH = 7.2 Hz, 6 H, CH2CH3),
1.29 (m, 8 H, c-C6H11), 1.40 (m, 4 H, c-C6H11), 1.72 (m, 2 H, c-
3
7a: 1H NMR (C6D6):
δ
=
0.80 (t, JHH
=
7.6 Hz,
3
H,
3
3
CH2CH2CH2CH3), 1.20 (t, JHH = 7.2 Hz, 6 H, CH2CH3), 1.19–
C6H11), 1.78 (m, 8 H, c-C6H11), 3.49 (q, JHH = 7.2 Hz, 4 H,
1.38 (m, 12 H, c-C6H11, 4 H, CH2CH2CH2CH3), 1.69–1.77 (m, CH2CH3), 6.87 (m, 3 H, H-phenyl), 6.98 (m, 2 H, CH=CH–
3
3
10 H, c-C6H11), 2.08 (dt, JHH = 6.9, JHH = 7.4 Hz, 2 H, CH–
CH2CH2CH2CH3), 3.60 (q, 3JHH = 7.2 Hz, 4 H, CH2CH3), 6.76 (t, phenyl), 7.55 (s, 1 H, B2C=CH) ppm. 13C{1H} NMR (C6D6): δ =
3JHH = 6.9 Hz, 1 H, B2C=CH), 7.01 (m, 2 H, CH=CH–CH=CH),
16.1 (s, CH2CH3), 27.2, 28.0, 28.2 (s, CH2-cyclohexyl), 37.5 (s, CH-
7.09 (m, 2 H, CH=CH–CH=CH) ppm. 13C{1H} NMR (C6D6): δ cyclohexyl), 38.2 (s, CH2CH3), 109.0 (s, CH=CH–CH=CH), 118.1
14.0 (s, CH2CH2CH2CH3), 15.5 (s, CH2CH3), 22.6 (s, (s, CH=CH–CH=CH), 127.8 (s, p-C-phenyl), 128.3 (s, o-C-phenyl),
CH=CH), 7.06 (m, 2 H, CH=CH–CH=CH), 7.18 (m, 2 H, H-
=
CH2CH2CH2CH3), 27.2, 28.0, 28.2 (3s, CH2-cyclohexyl), 31.8 (s,
CH2CH2CH2CH3), 35.9 (s, CH2CH2CH2CH3), 37.1 (s, CH-cyclo-
128.7 (s, m-C-phenyl), 137.7 (s, C2N2), 140.0 (s, i-C-phenyl), 147.1
(s, B2C=CH) ppm. 11B{1H} NMR (C6D6): δ = 30.0 (s, BN2), 81.8
Eur. J. Inorg. Chem. 2013, 2608–2614
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FULL PAPER
(s, BCy2) ppm. MS/EI: m/z (%) = 452.3 (100) [M+], 286.2 (47)
[M+ – BCy2], 260.1 (63) [M+ – BCy2 – CH3]. HRMS (EI): calcd.
for C30H42B2N2 452.35286; found 452.35384. C30H42B2N2 (452.29):
calcd. C 79.67, H 9.36, N 6.19; found C 78.40, H 9.23, N 5.99.
C. Schmidt, T. Braun, H.-G. Stammler, B. Neumann, Dalton
Trans. 2006, 2127–2132; c) L. Weber, V. Werner, M. A. Fox,
T. B. Marder, S. Schwedler, A. Brockhinke, H.-G. Stammler, B.
Neumann, Dalton Trans. 2009, 1339–1351.
L. Weber, H.-B. Wartig, H.-G. Stammler, B. Neumann, Z.
Anorg. Allg. Chem. 2001, 627, 2663–2668.
[3]
[4]
1
3
10a: H NMR (C6D6): δ = 1.15 (t, JHH = 7.2 Hz, 6 H, CH2CH3),
1.31 (m, 8 H, c-C6H11), 1.48 (m, 4 H, c-C6H11), 1.73 (m, 2 H, c-
C6H11), 1.80 (m, 8 H, c-C6H11), 2.32 [s, 6 H, N(CH3)2], 3.60 (q,
J. A. Soderquist, A. M. Rane, K. Matos, J. Ramos, Tetrahedron
Lett. 1995, 36, 6847–6850.
3JHH = 7.2 Hz, 4 H, CH2CH3), 6.22 (d, JHH = 9.4 Hz, 2 H, o-H-
3
[5]
[6]
G. Molander, N. M. Ellis, J. Org. Chem. 2008, 73, 6841–6844.
a) L. Weber, A. Penner, I. Domke, H.-G. Stammler, B. Neum-
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V. Werner, M. A. Fox, T. B. Marder, S. Schwedler, A. Brockh-
inke, H.-G. Stammler, B. Neumann, Dalton Trans. 2009, 2823–
2831; c) A. Chrostowska, M. Maciejczyk, A. Dargelos, P. Bay-
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5116.
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379.
D. S. Matteson, Synthesis 1975, 147–158.
phenyl), 7.05 (m, 2 H, CH=CH–CH=CH), 7.09 (m, 2 H, CH=CH–
3
CH=CH), 7.25 (d, JHH = 8.5 Hz, 2 H, m-H-phenyl), 7.94 (s, 1 H,
B2C=CH) ppm. 13C{1H} NMR (C6D6): δ = 15.3 (s, CH2CH3),
27.3, 28.1, 28.5 (3s, CH2-cyclohexyl), 37.4 (s, CH-cyclohexyl), 38.1
(s, CH2CH3), 39.4 [s, N(CH3)2], 108.8 (s, CH=CH–CH=CH), 111.7
(s, C-phenyl), 118.6 (s, CH=CH–CH=CH), 128.4 (s, i-C-phenyl),
130.9 (s, C-phenyl), 137.9 (s, C2N2), 150.4 [s, C-N(CH3)2], 152.2 (s,
B2C=CH) ppm. 11B{1H} NMR (C6D6): δ = 30.4 (s, BN2), 79.0 (s,
[7]
[8]
BCy2) ppm. MS/EI: m/z (%) = 482.5 (45) [M+], 319.2 (100) [M+
–
BCy2].
[9]
1
3
11a: H NMR (C6D6): δ = 1.09 (t, JHH = 7.2 Hz, 6 H, CH2CH3),
1.30 (m, 8 H, c-C6H11), 1.45 (m, 4 H, c-C6H11), 1.74 (m, 2 H, c-
[10]
3
C6H11), 1.78 (m, 8 H, c-C6H11), 3.15 (s, 3 H, OCH3), 3.53 (q, JHH
= 7.2 Hz, 4 H, CH2CH3), 6.46 (d, 3JHH = 8.5 Hz, 2 H, CH-phenyl),
7.02 (m, 2 H, CH=CH–CH=CH), 7.08 (m, 2 H, CH=CH–
[11]
[12]
W. Siebert, M. Hildenbrand, P. Hornbach, G. Karger, H. Pritz-
kow, Z. Naturforsch. B 1989, 44, 1179–1186.
3
CH=CH), 7.15 (d, JHH = 8.5 Hz, 2 H, CH-phenyl), 7.67 (s, 1 H,
B2C=CH) ppm. 13C{1H} NMR (C6D6): δ = 15.2 (s, CH2CH3),
27.2, 28.0, 28.3 (3s, CH2-cyclohexyl), 37.5 (s, CH-cyclohexyl), 38.0
(s, CH2CH3), 54.4 (s, O-CH3), 108.9 (s, CH=CH–CH=CH), 113.8
(s, C-phenyl), 118.8 (s, CH=CH–CH=CH), 130.5 (s, C-phenyl),
132.5 (s, i-C-phenyl), 137.8 (s, C2N2), 148.9 (s, B2C=CH), 159.9 (s,
C-OCH3) ppm. 11B{1H} NMR (C6D6): δ = 29.7 (s, BN2), 77.1 (s,
BCy2) ppm.
[13]
[14]
[15]
H. Klusik, C. Pues, A. Berndt, Z. Naturforsch. B 1984, 39b,
1042–1045.
J. Takaya, N. Kirai, N. Iwasawa, J. Am. Chem. Soc. 2011, 133,
12980–12983.
a) T. Hata, H. Kitagawa, H. Masai, T. Kurahashi, M. Shimizu,
T. Hiyama, Angew. Chem. 2001, 113, 812–814; Angew. Chem.
Int. Ed. 2001, 40, 790–792; b) T. Kurahashi, T. Hata, H. Masai,
H. Kitagawa, M. Shimizu, T. Hiyama, Tetrahedron 2002, 58,
6381–6995.
1
3
12a: H NMR (C6D6): δ = –0.04 (s, 9 H, SiMe3), 1.24 (t, JHH
=
[16]
a) P. Ceron, A. Finch, J. Frey, J. Kerrigan, T. Parsons, G. Urry,
H. I. Schlesinger, J. Am. Chem. Soc. 1959, 81, 6368–6371; b)
R. W. Rudolph, J. Am. Chem. Soc. 1967, 89, 4216–4217; c) M.
Zeldin, A. R. Gatti, T. Wartik, J. Am. Chem. Soc. 1967, 89,
4217–4218; d) W. Haubold, A. Gemmler, Chem. Ber. 1980, 113,
3352–3356; e) M. Hildenbrand, H. Pritzkow, U. Zenneck, W.
Siebert, Angew. Chem. 1984, 96, 371–372; Angew. Chem. Int.
Ed. Engl. 1984, 23, 371–372.
a) T. Ishiyama, N. Matsuda, N. Miyaura, A. Suzuki, J. Am.
Chem. Soc. 1993, 115, 11018–11019; b) T. Ishiyama, N. Mat-
suda, M. Murata, F. Ozawa, A. Suzuki, N. Miyaura, Organo-
metallics 1996, 15, 713–720.
a) C. N. Iverson, M. R. Smith III, J. Am. Chem. Soc. 1995, 117,
4403–4404; b) C. N. Iverson, M. R. Smith III, Organometallics
1996, 15, 5155–5165.
G. Lesley, P. Nguyen, N. J. Taylor, T. B. Marder, A. J. Scott, W.
Clegg, N. C. Norman, Organometallics 1996, 15, 5137–5154.
K. M. Anderson, M. J. Lesley, N. C. Norman, A. G. Orpen, J.
Starbuck, New J. Chem. 1999, 23, 1053–1055.
a) C. Møller, M. S. Plesset, Phys. Rev. 1934, 46, 618–622; b)
J. A. Pople, R. Seeger, R. Krishnan, Int. J. Quantum Chem.
1977, 12, 149–163; c) R. J. Bartlett, Annu. Rev. Phys. Chem.
1981, 32, 359–401; d) A. D. Becke, J. Chem. Phys. 1993, 98,
5648–5652; e) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988,
37, 785–789; f) G. A. Petersson, M. A. Al-Laham, J. Chem.
Phys. 1991, 94, 6081–6090; g) G. A. Petersson, A. Bennett,
T. G. Tensfeldt, M. A. Al-Laham, W. A. Shirley, J. Mantzaris,
J. Chem. Phys. 1988, 89, 2193–2218.
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr, T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tom-
asi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
7.2 Hz, 6 H, CH2CH3), 1.27–1.47 (m, 12 H, c-C6H11), 1.71–1.85
(m, 10 H, c-C6H11), 3.68 (q, JHH = 7.2 Hz, 2 H, CH2CH3), 6.70
3
(s, 1 H, B2C=CH), 6.99 (m, 2 H, CH=CH–CH=CH), 7.08 (m, 2
H, CH=CH–CH=CH) ppm. 13C{1H} NMR (C6D6): δ = –1.1 [s,
Si(CH3)3], 15.6 (s, CH2CH3), 27.1, 27.8, 27.9 (3s, CH2-cyclohexyl),
36.5 (s, CH-cyclohexyl), 38.1 (s, CH2CH3), 109.0 (s, CH=CH–
CH=CH), 118.9 (s, CH=CH–CH=CH), 137.4 (s, C2N2), 148.3 (s,
B2C=CH) ppm. 11B{1H} NMR (C6D6): δ = 28.6 (s, BN2), 79.6 (s,
BCy2) ppm.
[17]
[18]
3
12b: 1H NMR (C6D6): δ = 0.05 (s, 9 H, SiMe3), 1.16 (t, JHH
=
7.2 Hz, 6 H, CH2CH3), 1.27–1.47 (m, 12 H, c-C6H11), 1.71–1.85
3
(m, 10 H, c-C6H11), 3.68 (q, JHH = 7.2 Hz, 2 H, CH2CH3), 6.39
(s, 1 H, B-CH), 6.98 (m, 2 H, CH=CH–CH=CH), 7.09 (m, 2 H,
CH=CH–CH=CH) ppm. 13C{1H} NMR (C6D6): δ = 0.2 [s,
Si(CH3)3], 15.6 (s, CH2CH3), 27.3, 28.3, 28.6 (s, CH2-cyclohexyl),
36.4 (s, CH-cyclohexyl), 38.0 (s, CH2CH3), 108.8 (s, CH=CH–
CH=CH), 118.8 (s, CH=CH–CH=CH), 133.8 (br., N2B-CH), 137.3
(s, C2N2), 174.7 (s, C=C-BCy2) ppm. 11B{1H} NMR (C6D6): δ =
28.6 (s, BN2), 76.3s (BCy2) ppm. MS/EI: m/z (%) = 448.5 (14) [M+],
[19]
[20]
[21]
366.4 (16) [M+ – Cy], 270.2 (65) [M+ – HBCy2], 255.2 (53) [M+
–
HBCy2 –CH3], 174.2 (100) [BDB – H]. HRMS (EI): calcd. for
C27H46B2N2Si 448.36109; found 448.36270.
[1] For reviews on 1,3,2-diazaboroles, see: a) L. Weber, Coord.
Chem. Rev. 2001, 215, 39–77; b) L. Weber, Coord. Chem. Rev.
2008, 252, 1–31; c) M. Yamashita, K. Nozaki, Pure Appl.
Chem. 2008, 80, 1187–1194; d) M. Yamashita, K. Nozaki, Bull.
Chem. Soc. Jpn. 2008, 81, 1377–1392; e) L. Weber, Eur. J. Inorg.
Chem. 2012, 5595–5609.
[22]
[2] a) L. Weber, V. Werner, I. Domke, H.-G. Stammler, B. Neum-
ann, Dalton Trans. 2006, 3777–3784; b) L. Weber, I. Domke,
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FULL PAPER
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratch-
ian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gom-
perts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dap-
prich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q.
Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayak-
kara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03, rev. E.01,
Gaussian, Inc., Wallingford CT, 2004.
Received: December 10, 2012
Published Online: March 20, 2013
Eur. J. Inorg. Chem. 2013, 2608–2614
2614
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim