Synthesis and reactivity of monoborylacetylene derivatives

Article abstract of DOI:10.1002/1099-0682(200102)2001:2<373::AID-EJIC373>3.0.CO;2-6

The catechol-substituted monoborylacetylenes 1a-d are obtained from the reaction of bis(diisopropylamino)borylacetylene with catechol derivatives and 2,2′-biphenol. The catalytic trimerization of 1a-d with [(η⁵-C₅H₅)Co(CO)₂] yields isomeric mixtures of the triborylbenzene derivatives 2a,2a′, 2b,2b′, and 2c,2c′. The reaction of 2a,2a′ with mesityllithium provides the hexamesityl-substituted 1,3,5-triborylbenzene 2e. Hydroboration of 1a with catecholborane affords a mixture of 1,1-bis(1,3,2-benzodioxaborol-2-yl)ethene (3a) and trans-1,2-bis(1,3,2-benzodioxaborol-2-yl)ethene (4a). Hydroboration of 1a and 3a with one or two mol of HBCl₂ and subsequent substitution of the chlorine atoms of the product with catechol leads in each case to the 1,1,1-trisborylmethane derivative 5a in 83 and 78% yield, respectively, which forms the tris(THF) adduct 5a(thf)_3-. Treatment of 5a with tBuLi yields 1,1,1-tris[di(tert-butyl)boryl]ethane 6a. [Co₂(CO)₈] reacts with 1a to give 3-(1,3,2-benzodioxaborol-2-yl)-l,2-bis(tricarbonylcobalta)tetrahe drane (9a). The new compounds have been characterized by NMR spectroscopy and mass spectrometry as well as by X-ray structure analyses for 1a, 3a, 5a, 5a(thf)₃, and 9a.

Full text of DOI:10.1002/1099-0682(200102)2001:2<373::AID-EJIC373>3.0.CO;2-6

FULL PAPER
Synthesis and Reactivity of Monoborylacetylene Derivatives
Yiqun Gu,[a] Hans Pritzkow,[a] and Walter Siebert*[a]
Dedicated to Prof. Ulrich Müller on the occasion of his 60th birthday
Keywords: Alkynes / Boranes / Boron / Hydroboration / Phenols
The catechol-substituted monoborylacetylenes 1a−d are ob-
sequent substitution of the chlorine atoms of the product with
tained from the reaction of bis(diisopropylamino)borylace- catechol leads in each case to the 1,1,1-trisborylmethane de-
tylene with catechol derivatives and 2,2Ј-biphenol. The cata- rivative 5a in 83 and 78% yield, respectively, which forms the
lytic trimerization of 1a−d with [(η5-C5H5)Co(CO)2] yields
isomeric mixtures of the triborylbenzene derivatives 2a,2aЈ,
2b,2bЈ, and 2c,2cЈ. The reaction of 2a,2aЈ with mesityllithium
provides the hexamesityl-substituted 1,3,5-triborylbenzene
2e. Hydroboration of 1a with catecholborane affords a mix-
ture of 1,1-bis(1,3,2-benzodioxaborol-2-yl)ethene (3a) and
tris(THF) adduct 5a(thf)3. Treatment of 5a with tBuLi yields
1,1,1-tris[di(tert-butyl)boryl]ethane 6a. [Co2(CO)8] reacts
with 1a to give 3-(1,3,2-benzodioxaborol-2-yl)-1,2-bis(tricar-
bonylcobalta)tetrahedrane (9a). The new compounds have
been characterized by NMR spectroscopy and mass spectro-
metry as well as by X-ray structure analyses for 1a, 3a, 5a,
trans-1,2-bis(1,3,2-benzodioxaborol-2-yl)ethene (4a). Hydro- 5a(thf)3, and 9a.
boration of 1a and 3a with one or two mol of HBCl2 and sub-
Introduction
115 °C (1d). Compounds 1a؊c are soluble in common or-
ganic solvents whereas 1d dissolves only in toluene and
Alkynylboranes are interesting synthons for a variety of THF and forms a stable THF adduct.
compounds. Köster et al.[1] prepared monoborylacetylenes
by reacting amine-stabilized dialkylchloroboranes with
metal acetylides. The addition of diethyl ether-trifluorobor-
ane to the formed adducts leads to donor-free borylacetyl-
enes. Thermally stable monoborylacetylenes[2,3] are ob-
tained with electron-donating groups such as dialkylamino
or alkoxy, which reduce the Lewis acidity at the boron
center. Dialkoxyborylacetylenes[4,5] may be formed from the
corresponding aminoacetylenes. In the reaction of metal
acetylides with dialkoxyhaloboranes the halogen atom as
well as the alkoxy substituents are replaced. In contrast, the
reaction of diaminohaloboranes with metal acetylides leads
to the expected compounds in good yields. Here we report
Scheme 1
1
The H NMR spectra of 1a؊d exhibit a singlet for the
on the synthesis and properties of the catechol-substituted acetylenic proton between δ ϭ 2.77 (1a) and 2.37 (1d). In
monoborylacetylene derivatives 1a؊c.
the 13C NMR spectra the signals of the α carbon atoms
(bound to boron) were not observed; the signals for the β
carbon atoms (δ ϭ 94Ϫ86) are shifted to lower field relative
to alkylacetylenes (δ ϭ 70Ϫ80),[7] which may indicate an
interaction of the empty orbital at boron with the π system
of the triple bond. Also, the oxygen atoms in 1a؊c may
compete for the empty orbital at boron. In 1d the boron
atom is in bonding contact with the oxygen atom of one
THF molecule. The 11B NMR signal for 1d is shifted to
higher field (δ ϭ 15.9) relative to the values for 1a (δ ϭ
24.1), 1b, and 1c (both δ ϭ 24.3). The X-ray structure ana-
lysis of 1a (Figure 1) reveals an almost linear BϪCϪCϪH
moiety. The boron atom is trigonal coordinated, and the
heterocycle is almost planar. Compound 1a has approxi-
Results and Discussion
Synthesis and Properties of Monoborylacetylenes (1)
For the preparation of catechol-substituted monoboryl-
acetylenes bis(diisopropylamino)borylacetylene[6] is reacted
in THF with two equivalents of HCl and one equivalent of
catechol or biphenol, leading to the monoborylacetylenes
1a؊d in 46 to 68% yield (Scheme 1). The colorless solids
may be sublimed in vacuo (1a؊c) or recrystallized (1d); the
melting points of the products are between 45 °C (1c) and
˚
mately C2v symmetry, the CϵC distance [1.195(3) A] is
[a]
Anorganisch-Chemisches Institut der Universität Heidelberg,
slightly widened relative to other RϪCϵCϪR com-
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: (internat.) ϩ 49-6221/545-609
pounds[8] (1.183 A) and the BϪC bond [1.520(4) A] is short
˚ ˚
Eur. J. Inorg. Chem. 2001, 373Ϫ379
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0202Ϫ0373 $ 17.50ϩ.50/0
373

Y. Gu, H. Pritzkow, W. Siebert
FULL PAPER
for a BϪC single bond. This is in agreement with structural carbon atoms of the central aromatic ring of the symmet-
data for oxygen-substituted diborylacetylenes.[6,9]
rical isomer 2a. Resonances at δ ϭ 141.6, 137.9, and 134.7
are due to the central aromatic carbon atoms (CH) of the
unsymmetrical derivative 2aЈ. The 1H NMR spectra of
2b,2bЈ and 2c,2cЈ indicate that the unsymmetrical derivat-
ives are the main products. In the aromatic region, these
compounds exhibit multiplets for the substituted catechol
groups at δ ϭ 6.44Ϫ6.66 for 2b,2bЈ (in [D4]MeOH) and δ ϭ
7.17Ϫ7.43 for 2c,2cЈ (in CD2Cl2). A second multiplet at δ ϭ
7.50Ϫ7.77 in the spectrum of 2b,bЈ is generated by the three
unsymmetrical protons of the central arene ring. The cor-
responding signals for 2cЈ can be fully assigned: the two
adjacent protons give rise to two doublets of doublets at
Figure 1. Molecular structure of 1a in the crystal; selected bond
˚
length [A] and angles [°]: B1ϪO1 1.387(3), B1ϪO2 1.372(3),
4
δ ϭ 8.31 (3JHH ϭ 7.5 Hz, JHH ϭ 1.3 Hz) and δ ϭ 8.14
B1ϪC1 1.520(4), C1ϪC2 1.195(3), C2ϪH2 1.00(3); O1ϪB1ϪO2
112.3(2), O1ϪB1ϪC1 123.2(2), O2ϪB1ϪC1 124.4(2), B1ϪC1ϪC2
178.7(2), C1ϪC2ϪH2 176(1)
5
(3JHH ϭ 7.5 Hz, JHH ϭ 0.8 Hz), the resonance for the re-
maining proton appears as a pseudo triplet at δ ϭ 8.74
(averaged JHH ഠ 1 Hz). In addition, the nine methyl groups
of the three tert-butyl substituents of 2cЈ result in two sig-
nals at δ ϭ 1.37 and 1.35, integrating for nine and eighteen
protons respectively, which belong to the groups in the 2-
and 1,4-positions. The 13C NMR spectra also indicate the
predominant formation of the unsymmetrical structures 2bЈ
and 2cЈ. In the aromatic region of the 13C NMR spectra of
2c,2cЈ 19 of the expected 21 signals for the nonboron-bound
carbon atoms can be distinguished. A signal for the central
C(H) carbon atoms in the symmetrical structure is not
found, which means either that 2c is not present or that its
concentration is very low. In the spectra of the products
2a,2aЈ and 2b,2bЈ, however, the presence of small amounts
of the isomers 2a and 2b is clearly seen. Beside the aromatic
13C resonances for 2aЈ/2bЈ, signals at δ ϭ 131.6 and 130.7
are assigned to the central C(H) atoms in 2a and 2b, re-
spectively.
Trimerization of 1 to Triborylbenzene Derivatives (2)
Only a few triborylbenzene derivatives are known;[10,11]
these have been prepared in low yields by Grignard reac-
tions. The synthesis of substituted arenes by cobalt-cata-
lyzed trimerization of alkynes is well established and has
led to a broad application in organic synthesis.[12] Very re-
cently we obtained hexaborylbenzene derivatives by cyclo-
trimerization of diborylacetylenes in the presence of cata-
lytic amounts of (η5-cyclopentadienyl)dicarbonylcob-
alt.[13,14] Analogously, in refluxing toluene the monoboryl-
acetylenes 1a؊c form isomeric mixtures of the triboryl-
benzene derivatives 2a,2aЈ, 2b,2bЈ, and 2c,2cЈ in good yields
(Ͼ50%; Scheme 2). The 1,3,5- and 1,2,4-isomers could not
be separated.
The reaction of 2a,2aЈ with mesityllithium provides the
hexamesityl-substituted triborylbenzene derivative 2e in
49% yield (Scheme 3). Its spectroscopic data and the X-ray
structure analysis confirm that the symmetric isomer 1,3,5-
tris(dimesitylboryl)benzene (2e) has been formed. This
compound was first prepared in 2% yield from 1,3,5-tribro-
mobenzene Grignard reagent and fluorodimesitylborane.[11]
Scheme 2
The mixtures of 2a؊c,2aЈ؊cЈ are light brown, air-stable
solids. The product 2a,2aЈ is not soluble in most organic
solvents; it partially dissolves in methanol, however, with
slow decomposition and formation of catBOMe (δ11B ϭ
18). In contrast, 2b,2bЈ and 2c,2cЈ easily dissolve in THF
and CH2Cl2.
Scheme 3
The 11B NMR spectra exhibit broad signals at δ ϭ 30.1
for 2a,2aЈ (in [D4]MeOH), δ ϭ 29.6 for 2b,2bЈ, and δ ϭ
Hydroboration of 1a to Yield 1,1-Bis(1,3,2-benzodioxa-
borol-2-yl)ethene (3a), trans-1,2-Bis(1,3,2-benzodioxa-borol-
2-yl)ethene (4a), and 1,1,1-Tris(1,3,2-benzodioxaborol-2-
yl)ethane (5a)
1
33.9 for 2c,2cЈ (in CD2Cl2). In the H NMR spectrum of
2a,2aЈ several signals appear in the arene region. The pat-
tern for ortho substitution of the catechol group is found
between δ ϭ 6.60 and 6.76. A multiplet between δ ϭ 8.1
Alkynes and alkenes are hydroborated regioselectively by
and 7.5 is assigned to the central rings of 2a,aЈ. In the 13C 1,3,2-benzodioxaborole (catecholborane).[15] The reaction
NMR spectrum, three signals at δ ϭ 146.2, 120.9, and 116.3 of the monoborylacetylene 1a with catecholborane at 80 °C
are found for the carbon atoms of the catechol groups. A leads to a mixture of 1,1-bis(1,3,2-benzodioxa-borol-2-yl)e-
signal at δ ϭ 131.6 is assigned to the hydrogen-substituted thene (3a) and a small amount of trans-1,2-bis(1,3,2-benzo-
374
Eur. J. Inorg. Chem. 2001, 373Ϫ379

Synthesis and Reactivity of Monoborylacetylene Derivatives
FULL PAPER
Scheme 5
78% yield (Scheme 5). It is a colorless solid, which is soluble
in toluene, THF, and dichloromethane. The spectroscopic
data of 5a are discussed below.
Scheme 4
The hydroboration of 1a with [HBCl2] and subsequent
substitution of the chlorine atoms by catechol groups leads
to 1,1,1-triborylethane (5a) in 83% yield (Scheme 6). The
solid is recrystallized from THF to yield the THF adduct
5a(thf)3; in toluene it loses THF and forms crystalline 5a.
Both compounds have been studied by X-ray structure ana-
lyses (see below). The related compound [(MeO)2B]3CCH3
has been reported previously.[18]
dioxaborol-2-yl)ethene (4a) in 86% yield (Scheme 4).[16] The
cis-addition of catecholborane proceeds regioselectively fav-
oring the formation of the 1,1-isomer 3a. Only a minor
amount of the 1,2-isomer 4a is obtained. Related 1,2-deriv-
atives with a cis-arrangement have been reported by Marder
and Norman,[17] and isomeric 1,1-diborylethene derivatives
have been synthesized by Matteson.[18] Colorless 3a melts
at 105 °C with decomposition, it is soluble in toluene, ben-
zene, and THF.
In the NMR spectra only signals for 3a were found, in-
dicating that the amount of the 1,2-derivative 4a is rather
small. However, its formation was unambiguously proven
by X-ray structure analysis (see below). The 1H NMR spec-
trum of 3a exhibits a multiplet signal between δ ϭ
6.60Ϫ6.93 for the aromatic protons and for the alkene hy-
drogen atoms. In the 13C NMR spectrum one finds three
signals at δ ϭ 148.8, 123.1, and 112.9 for the aromatic car-
bon atoms. One sharp signal for the CH2 carbon atom of
the ethene unit at δ ϭ 154.9 proves the presence of the 1,1-
isomer, its chemical shift is similar to that of comparable
compounds.[19,20] In the 11B NMR spectrum one signal ap-
pears at δ ϭ 32.2.
Scheme 6
1
The H NMR spectrum of 5a indicates a C3 symmetry
with three boryl substituents bonded to one carbon atom.
The ortho substitution pattern for the aromatic region is
observed between δ ϭ 6.67Ϫ6.97, and a singlet appears at
δ ϭ 2.04 for the methyl group. The 13C NMR spectroscopic
data confirm the assignments from the 1H NMR spectrum.
The 11B NMR spectrum shows one broad signal at δ ϭ 35.
The X-ray diffraction study reveals that 5a(thf)3 has ap-
proximately C3v symmetry (Figure 3 and 4). The hetero-
cycles are almost planar. The boron-bound carbon atom is
˚
almost tetrahedral, and the C1ϪC2 bond is 1.556(5) A. All
BϪC and BϪO bond lengths in 5a(thf)3 are normal. The
distances from the boron to the oxygen atoms of the THF
˚
molecules (2.72Ϫ2.91 A) are relatively short. This, and the
geometrical arrangement of the THF molecules, suggests a
very weak interaction between these atoms. A similar ar-
rangement was found in 1,1,2,2-tetrakis(1,3,2-benzodiox-
aborol-2-yl)ethane·2THF.[9] The THF-free solid-state struc-
ture of 5a is almost identical to that of 5a(thf)3. No signifi-
cant changes in bond lengths and angles are observed,
which means that the influence of the THF molecules in
5a(thf)3 on its structural parameters is negligible.
Figure 2. Molecular structure of 4a in the crystal; selected bond
˚
lengths [A] and angles [°]: C1ϪC1a 1.348(10), C1ϪB1 1.554(8),
B1ϪO1 1.386(7), B1ϪO2 1.386(7), C1ϪH1 1.12(5); C1aϪC1ϪB1
122.3(6),
C1ϪB1ϪO1
125.8(5),
C1ϪB1ϪO2
122.8(5),
O1ϪB1ϪO2 111.4(5)
In the solid state the molecule 4a (Figure 2) has a crystal-
lographic inversion center at the midpoint of the CϭC
1,1,1-Tris[di(tert-butyl)boryl]ethane (6a)
˚
double bond and is almost planar (max. dev. 0.04 A) re-
sulting in C2h symmetry. Both the B and C atoms of the
Treatment of 5a with tBuLi results in the formation of
ethene unit are planar coordinated. The heterocycles are al- 1,1,1-tris[di(tert-butyl)boryl]ethane (6a) in 12% yield
most planar and they are in a coplanar arrangement (dihed- (Scheme 7). Compound 6a is a colorless, thermally stable
ral angle: 0°). The length of the C1ϪC1a bond [1.348(10) liquid, which does not form any closo-C2B3 carborane by
˚
A] is that of a double bond and the BϪC bonds [1.554(8) elimination of trisorganoboranes. In the mass spectrum of
6a the molecular ion Mϩ is absent; however, Mϩ patterns
˚
A] are a bit shorter than single bonds.
As indicated above, the hydroboration of 1a with catech- for the C2B3 carborane derivative 7a (m/z ϭ 258) and for
olborane stops after the first cis-addition. However, 3a re- the C2B4 carborane derivative 8a [m/z ϭ 325, (M Ϫ H)ϩ]
acts with HBCl2,[21,22] and subsequent substitution of the appear. These carboranes are most likely formed in the
Cl atoms by catechol leads to 1,1,1-triborylethane (5a) in mass spectrometer. The 11B NMR spectrum does not show
Eur. J. Inorg. Chem. 2001, 373Ϫ379
375

Y. Gu, H. Pritzkow, W. Siebert
FULL PAPER
Scheme 7
3-(1,3,2-Benzodioxaborol-2-yl)-1,2-bis(tricarbonylcobalta)-
tetrahedrane (9a)
Dicobaltahexacarbonyl-η2-alkyne complexes are ob-
tained by reacting alkynes with Co2(CO)8.[23] Analogously,
the monoborylacetylene 1a reacts with [Co2(CO)8] in hex-
ane with elimination of CO to give complex 9a (Scheme 8).
Figure 3. Molecular structure of 5a(thf)3 in the crystal; selected
˚
bond lengths [A] and angles [°]: C1ϪC2 1.556(5), C1ϪB1 1.544(6),
C1ϪB2 1.564(6), C1ϪB3 1.569(6), B1ϪO1 1.407(5), B1ϪO2
1.395(5), B2ϪO3 1.397(5), B2ϪO4 1.385(5), B3ϪO5 1.387(6),
B3ϪO6 1.395(6); B1ϪC1ϪC2 110.8(3), B1ϪC1ϪB2 110.2(3),
B1ϪC1ϪB3 105.9(3), B2ϪC1ϪB3 108.5(3), C2ϪC1ϪB2 110.5(3),
˚
C2ϪC1ϪB3 110.9(3). Selected bond lengths [A] and angles [°] for
Scheme 8
5a: CϪC 1.556 [1.554Ϫ1.557(3)], CϪB 1.568 [1.560Ϫ1.581(3)],
BϪO 1.385 [1.380Ϫ1.398(3)], BϪCϪC 110.4Ϫ113.1(2), BϪCϪB
103.3Ϫ113.1(2)
Chromatographic workup of the dark brown solution
and crystallization from toluene gives dark crystals of 9a in
42 % yield. It is soluble in hexane, toluene, THF, or
CH2Cl2, although it decomposes when exposed to light or
1
heat. In the H NMR spectrum the aromatic protons ap-
pear as an ortho pattern between δ ϭ 6.70Ϫ6.94, the ali-
phatic proton gives a singlet at δ ϭ 5.83 and is thus shifted
downfield by more than 3 ppm relative to 1a (δ ϭ 2.77).
This has been explained in related compounds by the elec-
tronegativity of the Co2C2 unit and the anisotropy effect of
the CϵO groups. In the 13C NMR spectrum three signals
appear at δ ϭ 149.0, 123.2, and 112.8 for the aromatic car-
bon atoms. The signal for CO at δ ϭ 200 is broadened by
intramolecular CO exchange. A broad signal at δ ϭ 71 is
found for the boron-bonded carbon, whereas the signal for
the other carbon atoms appears at δ ϭ 81.9. The 11B NMR
signal at δ ϭ 32.6 is shifted downfield by 8 ppm with re-
spect to that of 1a (δ ϭ 24.1).
The X-ray diffraction study confirms the structure of 9a
as that of a tetrahedrane (Figure 5). The almost linear
BϪCϪCϪH moiety in 1a has been altered by the com-
plexation, the angles are decreased to 151.0(2)°
(B1ϪC2ϪC1) and 141(1)° (C2ϪC1ϪH1). The atoms
C1ϪC2ϪCo1ϪCo2 form a distorted tetrahedrane, the di-
Figure 4. Molecular structure of 5a(thf)3 as viewed along the
C1ϪC2 vector
any signal for the carboranes, it contains only the signal for hedral angle O1ϪB1ϪC2ϪC1 is 11.9°. The CoϪCo bond
[24]
6a at δ ϭ 83.4. The 1H NMR spectrum exhibits two singlets length of 2.48 A is comparable with other data,
the dis-
˚
at δ ϭ 1.92 and 1.11 in the ratio 1:18, the 13C NMR spec- tance between the carbon atoms of the tetrahedrane
˚
˚
trum shows two signals at δ ϭ 14.1 and 30.3, the carbon [1.334(3) A] is 0.14 A longer than the CϪC bond in 1a, and
atoms adjacent to boron are not detected.
is of the same magnitude as a double bond.[24b,24c]
376
Eur. J. Inorg. Chem. 2001, 373Ϫ379

Synthesis and Reactivity of Monoborylacetylene Derivatives
FULL PAPER
Ϫ
13C NMR (50 MHz, CDCl3): δ ϭ 21.3 (CH3), 93 (br., CϵCH),
112.0, 113.3, 123.8, 133.4, 145.4, 147.6 (C6H3), BC not observed.
Ϫ
11B NMR (64 MHz, CDCl3): δ ϭ 24.3. Ϫ EI-MS: m/z (%) ϭ
158 (100) [Mϩ]. Ϫ C9H7BO2 (158.0): calcd. C 68.43, H 4.47; found
C 67.24, H 4.64.
1c: 1.915 g (68%), m.p. 45 °C. Ϫ 1H NMR (200 MHz, CDCl3): δ ϭ
1.31 (s, 9 H, CH3), 2.75 (s, 1 H, CϵCH), 7.28Ϫ7.14 (m, 3 H, C6H3).
Ϫ
13C NMR (50 MHz, CDCl3): δ ϭ 31.7 (CH3), 34.9 [C(CH3)3],
93 (br., CϵCH), 110.0, 111.7, 120.1, 144.3, 145.2, 147.4 (Car), BC
not observed. Ϫ 11B NMR (64 MHz, CDCl3): δ ϭ 24.3. Ϫ EI-MS:
m/z (%) ϭ 200 (24.6) [Mϩ], 185 (100) [Mϩ Ϫ CH3]. Ϫ C12H13BO2
(200.0): calcd. C 72.05, H 6.55; found C 71.38, H 6.51.
1d·THF: 2.715 g (66%), m.p. 115 °C (dec.). Ϫ 1H NMR (200 MHz,
CDCl3): δ ϭ 1.94 (quint, 4 H, THF), 2.37 (s, 1 H, CϵCH), 4.00
(t, 4 H, THF), 7.45Ϫ7.02 (m, 8 H, Har). Ϫ 13C NMR (50 MHz,
CDCl3): δ ϭ 25.3 (THF), 69.5, 86 (br., CϵCH), 121.3, 124.1, 128.7,
129.2, 129.7, 153.1 (Car), BC not observed. Ϫ 11B NMR (64 MHz,
Figure 5. Molecular structure of 9a in the crystal; selected bond
CDCl3): δ ϭ 15.9. Ϫ EI-MS: m/z (%) ϭ 220 (100) [Mϩ]. Ϫ HR-
˚
lengths [A] and angles [°]: C1ϪC2 1.334(3), C1ϪCo1 1.956(2),
12
EIMS: m/z ϭ 220.0698 [Mϩ], calcd. for
(∆ ϭ 0.2 mmu).
C
14
1H911B16O2: 220.0696
C1ϪCo2 1.957(2), C2ϪCo1 1.991(2), C2ϪCo2 1.976(2), Co1ϪCo2
2.480(1), C2ϪB1 1.528(3); H1ϪC1ϪC2 141(1), C1ϪC2ϪB1
151.0(2), Co1ϪC1ϪCo2 78.67(7), Co1ϪC2ϪCo2 77.41(7),
C1ϪC2ϪCo1 68.9(1), C1ϪC2ϪCo2 69.4(1), C2ϪC1ϪCo1 71.7(1),
C2ϪC1ϪCo2 70.9(1), C1ϪCo1ϪC2 39.51(8), C1ϪCo2ϪC2
39.66(8), C1ϪCo1ϪCo2 50.68(6), C2ϪCo1ϪCo2 51.03(5)
Tris(1,3,2-benzodioxaborol-2-yl)benzene
Isomers
(2a,2aЈ),
Tris[1,3,2-(5-methylbenzo)dioxaborol-2-yl]benzene Isomers (2b,2bЈ),
and Tris[1,3,2-(5-tert-butylbenzo)dioxaborol-2-yl]benzene Isomers
(2c,2cЈ): Monoborylacetylene (1a: 0.865 g; 1b: 0.956 g; 1c: 1.209 g;
6.0 mmol) and (η5-cyclopentadienyl)dicarbonylcobalt (0.055 g,
0.3 mmol, 5 mol-%) were heated in 15 mL of toluene for 24 h under
reflux. The solid was separated and washed several times with small
amounts of solvent (2a,2aЈ: THF and CH2Cl2; 2b,2bЈ: toluene and
CH2Cl2; 2c,2cЈ: hexane) and dried in vacuum.
Experimental Section
General: All reactions were carried out under a purified nitrogen
atmosphere. The solvents were dried according to published pro-
cedures. Ϫ NMR: Bruker AC 200 or DRX 200 and Jeol FX-90 Q
(11B, external standard, BF3·OEt2; 1H, 13C, standards were the sig-
nals of the residual protons in the deuterated solvents, calculated
relative to TMS). Ϫ MS: Finnigan MAT 8230, ZAB-2F VG-Micro-
mass and Jeol MS station JMS 700. Ϫ The following compounds
were prepared according to literature procedures: bis(diisopropyl-
amino)borylacetylene,[6] catecholborane.[15] * Boron carbide forma-
tion often reduces the found values.
2a,2aЈ: 1.345 g (52%), m.p. 237 °C. Ϫ 1H NMR (200 MHz,
[D4]MeOH): δ ϭ 6.76Ϫ6.60 (m, 12 H, C6H4), 8.10Ϫ7.50 (m, 3 H,
C6H3). Ϫ 13C NMR (50 MHz, [D4]MeOH): δ ϭ 116.3, 120.9
(C6H4), 131.6 (C6H3, central, symm.), 134.7, 137.9, 141.7 (C6H3,
central, unsymm.), 146.2 (C6H4).
Ϫ
11B NMR (64 MHz,
[D4]MeOH): δ ϭ 30.1. Ϫ EI-MS: m/z (%) ϭ 432 (100) [Mϩ]. Ϫ
HR-EIMS: m/z ϭ 432.1183 [Mϩ], calcd. for
C
24
1H1511B316O6:
12
432.1148 (∆ ϭ 3.6 mmu). Ϫ C24H15B3O6 (431.8): calcd. C 66.76,
H 3.50; found C 65.28*, H 3.72.
1,3,2-Benzodioxaborol-2-yl-acetylene (1a), 1,3,2-(5-Methylbenzo)-
dioxaborol-2-yl-acetylene (1b), 1,3,2-(5-tert-Butyl-benzo)dioxaborol-
2b,2bЈ: 1.550 g (55%), m.p. 220 °C. Ϫ 1H NMR (200 MHz,
[D4]MeOH): δ ϭ 2.18 (s, 9 H, CH3), 6.66Ϫ6.44 (m, 9 H, C6H3,
terminal), 7.64Ϫ7.50, 7.77 (each br., 3 H, C6H3, central). Ϫ 13C
NMR (50 MHz, [D4]MeOH): δ ϭ 21.0 (CH3), 116.5, 117.4, 121.4
(C6H3, terminal), 130.7 (C6H3, central, symm.), 132.1 (C6H3, cent-
ral, unsymm.), 134.5 (C6H3, terminal), 137.9, 141.1 (C6H3, central,
unsymm.), 144.1, 146.3 (C6H3, terminal). Ϫ 11B NMR (64 MHz,
2-yl-acetylene
(1c),
and
2-Ethinyldibenzo[d.f]-1,3,2-dioxa-
borepine·THF (1d·thf): To a stirred solution of bis(diisopropyl-
amino)borylacetylene (3.307 g, 14.0 mmol) in 50 mL of THF at
Ϫ78 °C was added HCl·OEt2 (3.12 ; 10 mL, 31.2 mmol) within
30 min. Stirring was continued for 30 min., and NH2iPr2Cl formed
as a white solid. Then, 14.0 mmol of the corresponding aromatic
diol (1a: 1.540 g of catechol; 1b: 1.744 g of 4-methylcatechol; 1c:
2.330 g of 4-tert-butylcatechol; 1d: 2.644 g of 2,2Ј-biphenol) dis-
solved in 10 mL of THF was added and the reaction mixture was
allowed to warm overnight to room temperature. After filtration of
the solid the solution was reduced almost to dryness. The products
1a, 1b, and 1c were sublimed, 1d was crystallized from THF.
[D4]MeOH): δ ϭ 29.6. Ϫ EI-MS: m/z (%) ϭ 474 (100) [Mϩ]. Ϫ
12
HR-EIMS: m/z ϭ 474.1643 [Mϩ], calcd. for
C
27
1H2111B316O6:
474.1617 (∆ ϭ 2.6 mmu). Ϫ C27H21B3O6 (473.9): calcd. C 68.43,
H 4.47; found C 67.39, H 4.71.
1
2cЈ: 1.858 g (52%), m.p. 190 °C. Ϫ H NMR (200 MHz, CD2Cl2):
δ ϭ 1.35 (s, 18 H, CH3), 1.37 (s, 9 H, CH3), 7.43Ϫ7.17 (m, 9 H,
1a: 1.227 g (61%), m.p. 53 °C. Ϫ 1H NMR (200 MHz, CDCl3): δ ϭ
2.77 (s, 1 H, CϵCH), 7.24Ϫ7.14 (m, 4 H, C6H4). Ϫ 13C NMR
(50 MHz, CDCl3): δ ϭ 93.7 (br., CϵCH), 113.7, 124.3, 148.5
(C6H4), BC not observed. Ϫ 11B NMR (64 MHz, CDCl3): δ ϭ
24.1. Ϫ EI-MS: m/z (%) ϭ 144 (100) [Mϩ]. Ϫ HR-EIMS: m/z ϭ
3
5
C6H3, terminal), 8.14 (dd, 3 H, JHH ϭ 7.5 Hz, JHH ϭ 0.8 Hz),
8.31 (dd, 3 H, 3JHH ϭ 7.5 Hz, 4JHH ϭ 1.3 Hz, H adj.), 8.74 (pseudo
triplet, 3 H, averaged JHH ഠ 1 Hz). Ϫ 13C NMR (50 MHz,
CD2Cl2): δ ϭ 31.9 (CH3), 35.2 [C(CH3)3], 110.32, 110.36, 110.40,
111.87, 111.93, 111.95 [C(H) catechol, adj. to C(O)] 120.06, 120.13,
120.21 [C(H) catechol, adj. to C(CH3)3], 146.58, 146.62 [C(CH3)3],
147.25, 147.33, 147.42, 148.80, 148.84 [C(O)], BC not observed. Ϫ
11B NMR (64 MHz, CD2Cl2): δ ϭ 33.9. Ϫ EI-MS: m/z (%) ϭ 600
144.0382 [Mϩ], calcd. for 12C8 H511B16O2: 144.0383 (∆ ϭ 0.1
1
mmu).
1b: 1.009 g (46%), m.p. 48 °C. Ϫ 1H NMR (200 MHz, CDCl3): δ ϭ
2.36 (s, 3 H, CH3), 2.75 (s, 1 H, CϵCH), 7.12Ϫ6.88 (m, 3 H, C6H3). (90) [Mϩ], 585 (100) [Mϩ Ϫ CH3]. Ϫ HR-EIMS: m/z ϭ 600.2994
Eur. J. Inorg. Chem. 2001, 373Ϫ379
377

Y. Gu, H. Pritzkow, W. Siebert
FULL PAPER
12
[Mϩ], calcd. for
C
36
1H3911B316O6: 600.3026 (∆ ϭ 3.2 mmu). Ϫ
added within 40 min. After 18 h of stirring at room temperature
the solid was isolated by filtration, washed several times with hex-
ane and dried in vacuum. Recrystallization from toluene yielded 5a
(4.282 g, 83%).
C36H39B3O6 (600.1): calcd. C 72.05, H 6.55; found C 70.44*, H
6.53.
1,3,5-Tris(dimesitylboryl)benzene (2e): To a suspension of 2a,2aЈ
(0.210 g, 0.44 mmol) in toluene (30 mL) was added a solution of
MesLi·OEt2 (1.191 g) in Et2O (10 mL) at Ϫ20 °C. The mixture was
then heated for 3 h under reflux. After removal of the solvents the
reaction mixture was worked-up by column chromatography (SiO2/
THF). Recrystallization from toluene yielded 0.330 g of 2e (49%),
Procedure B: To a suspension of 3a (1.543 g, 5.8 mmol) in 30 mL
of pentane was added BCl3 (2 mL, 23.0 mmol) at Ϫ20 °C. Then,
triethylsilane (0.900 g, 7.7 mmol) in 20 mL of pentane was very
slowly added. After 2 h of stirring at room temperature the solution
was cooled to Ϫ20 °C and catechol (0.644 g, 5.8 mmol) in 5 mL of
THF was added within 30 min. The reaction mixture was stirred
for 18 h at Ϫ20 °C. Thereafter the solid was separated, washed
several times with hexane, and dried in vacuum. Recrystallization
from toluene yielded 5a (1.731 g, 78%), m.p. 155 °C (dec.) Ϫ 1H
NMR (200 MHz, C6D6): δ ϭ 2.04 (s, 3 H, CH3), 6.97Ϫ6.67 (m, 12
H, C6H4). Ϫ 13C NMR (50 MHz, C6D6): δ ϭ 12.2 (CH3), 112.8,
122.9, 149.0 (C6H4). Ϫ 11B NMR (64 MHz, C6D6): δ ϭ 35.4. Ϫ
1
m.p. 235 °C. Ϫ H NMR (200 MHz, CDCl3): δ ϭ 1.88 (s, 36 H,
o-CH3), 2.23 (s, 18 H, p-CH3), 6.70 (s, 12 H, C6H2), 7.50 (s, 3 H,
C6H3). Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ 21.2 (CH3), 23.4, 128.0,
138.4, 140.5 (C6H2), 145.1 (C6H3), BC not observed. Ϫ 11B NMR
(29 MHz, [D8]toluene): δ ϭ 88. Ϫ EI-MS: m/z (%) ϭ 822 (2) [Mϩ
Ϫ H], 703 (6) [Mϩ Ϫ Mes Ϫ H], 574 (12) [Mϩ Ϫ BMes2], 324 (54)
[Mϩ Ϫ 2BMes2 Ϫ H], 249 (91) [BMes2]ϩ, 120 (100) [MesH]ϩ, 105
(75) [MesHϩ Ϫ Me].
EI-MS: m/z (%) ϭ 384 (100) [Mϩ]. Ϫ HR-EIMS: m/z ϭ 384.1169
12
[Mϩ], calcd. for
C
20
1H1511B316O6: 384.1147 (∆ ϭ 2.1 mmu). Ϫ
C20H15B3O6 (383.8): calcd. C 62.59, H 3.94; found C 61.01*, H
4.27.
Bis(1,3,2-benzodioxaborol-2-yl)ethenes (3a and 4a): A solution of
1a (0.800 g, 5.6 mmol) and CatBH·THF (1.067 g, 5.6 mmol) in
20 mL of THF was heated at 80 °C under reflux for 4 h. Then the
solvent was partially removed in vacuum and a white solid (1.267 g,
86%, m.p. 105 °C dec.) separated. It contained 3a and a small
amount of 4a, which was not detected by NMR spectroscopy but
obtained by crystallization from toluene.
1,1,1-Tris[di(tert-butyl)boryl]ethane (6a):
A suspension of 5a
(1.00 g, 2.6 mmol) in 70 mL of hexane was reacted at Ϫ70 °C with
9 mL of tBuLi. After stirring at Ϫ20 °C the mixture was heated for
5 h under reflux. Separation of the solid resulted in a yellow solu-
tion, which was slowly concentrated under reduced pressure
(50 Torr). The yellow, oily residue was distilled at 80 °C/0.4 Torr to
3a: 1H NMR (200 MHz, C6D6): δ ϭ 6.93Ϫ6.60 (m, 8 H, C6H4),
6.99 (s, 2 H, BCH). Ϫ 13C NMR (50 MHz, C6D6): δ ϭ 112.8, 123.0,
148.8 (C6H4), 154.9 (CH2). Ϫ 11B NMR (64 MHz, C6D6): δ ϭ 32.2.
Ϫ EI-MS: m/z (%) ϭ 264 (30) [Mϩ]. Ϫ C14H10B2O4 (263.8): calcd.
C 63.73, H 3.82; found C 63.18, H 4.13.
1
yield 6a (0.122 g, 12%). Ϫ H NMR (200 MHz, CDCl3): δ ϭ 1.11
[s, 54 H, C(CH3)3], 1.92 (s, 3 H, CH3). Ϫ 13C NMR (50 MHz,
CDCl3): δ ϭ 14.1 (CH3), 30.3 [C(CH3)3], BC not observed. Ϫ 11B
NMR (29 MHz, CDCl3): δ ϭ 83.4. Ϫ EI-MS: m/z (%) ϭ 325 (0.8)
[Mϩ(8a) Ϫ H], 258 (1.2) [Mϩ(7a)], 243 (1.9) [Mϩ(7a) Ϫ Me], 41
(100).
1,1,1-Tris(1,3,2-benzodioxaborol-2-yl)ethane (5a): Procedure A: To
a solution of 1a (1.941 g, 13.5 mmol) in 50 mL of pentane was ad-
ded BCl3 (6 mL, 69.1 mmol) at Ϫ20 °C. Then triethylsilane (4.00 g,
34.4 mmol) in 10 mL of pentane was added very slowly at Ϫ20 °C. 3-(1,3,2-Benzodioxaborol-2-yl-1,2-bis(tricarbonylcobalta)tetra-
After 2 h of stirring at room temperature the solution was cooled
to Ϫ20 °C and catechol (3.053 g, 27.7 mmol) in 10 mL of THF was
hedrane (9a): To a solution of Co2(CO)8 (2.034 g, 5.9 mmol) in
30 mL of hexane at Ϫ20 °C was slowly added 1a (0.856 g,
Table 1. Data for the crystal structure analyses
1a
4a
5a(thf)3
5a
9a
Empirical formula
Formula weight
Crystal system
Space group
C8H5BO2
143.93
tetragonal
I41/a
16.96(3)
16.96(3)
10.43(2)
90
90
90
2999(9)
16
1.275
0.089
1184
C14H10B2O4
263.84
monoclinic
P21/n
C20H15B3O6·3C4H8O C20H15B3O6
Co2C14H5BO8
429.85
600.06
monoclinic
P21/n
383.50
orthorhombic
Pbca
triclinic
¯
P1
˚
Unit cell a [A]
5.870(3)
6.002(3)
17.693(9)
90
11.883(9)
11.959(10)
22.725(16)
90
11.996(2)
30.683(4)
39.120(5)
90
6.7766(1)
7.6633(1)
15.5942(3)
100.385(1)
94.252(1)
102.229(1)
773.15(2)
2
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
96.95(4)
90
91.09(6)
90
90
90
3
˚
Volume [A ]
Z
618.8(5)
2
3229(4)
4
14399(3)
32
Density [g/cm3]
1.416
1.234
1.416
1.846
µ [mmϪ1
F(000)
]
0.100
0.087
0.101
2.186
272
1272
3168
424
Crystal size [mm]
θ-range[°]
0.80 ϫ 0.50 ϫ 0.20 0.35 ϫ 0.35 ϫ 0.30 0.90 ϫ 0.60 ϫ 0.35
0.38 ϫ 0.21 ϫ 0.13 0.46 ϫ 0.17 ϫ 0.03
24.94
0/20, 0/20, 0/12
1325
949
120
0.0384
0.0917
203(2)
23.96
22.50
26.36
28.28
Index ranges (h, k, l)
No. of reflections
observed [I Ͼ 2σI]
Parameters
Ϫ6/6, 0/6, 0/20
876
Ϫ12/11, 0/12, 0/24
4183
0/14, 0/38, 0/48
14670
Ϫ9/8, Ϫ10/9, 0/20
3750
590
111
2307
9532
3087
403
1285
246
R1 [I Ͼ 2σI]
wR2
T (K)
0.0598
0.2013
203(2)
0.30/Ϫ0.33
0.0588
0.0444
0.0279
0.1544
0.1162
0.0697
203(2)
173(2)
173(2)
Max. residual electron 0.13/Ϫ0.15
0.22/Ϫ0.19
0.29/Ϫ0.25
0.67/Ϫ0.36
3
˚
density [e/A ]
378
Eur. J. Inorg. Chem. 2001, 373Ϫ379

Synthesis and Reactivity of Monoborylacetylene Derivatives
FULL PAPER
[2]
[3]
[4]
´
J. Soulie, P. Cadiot, Bull. Soc. Chim. Fr. 1966, 3846.
B. Wrackmeyer, H. Nöth, Z. Naturforsch. 1974, 29b, 564.
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Brotherton, A. L. McCloskey, J. L. Boone, H. M. Manasevit,
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C. Blanchard, E. Framery, M. Vaultier, Synthesis 1996, 46.
H. Schulz, G. Gabbert, H. Pritzkow, W. Siebert, Chem. Ber.
1993, 126, 1593.
5.9 mmol) in 20 mL of hexane. After stirring for 3 days at 20 °C
the solvent was removed and the reaction mixture separated by
column chromatography (florisil): with n-hexane red-brown
Co2(CO)8, and with toluene brown 9a was eluted (1.082 g, 42%),
1
[5]
[6]
m.p. 125 °C (dec.). Ϫ H NMR (200 MHz, C6D6): δ ϭ 5.83 (s, 1
H, CH), 6.94Ϫ6.70 (m, 4 H, Har),. Ϫ 13C NMR (50 MHz, C6D6):
δ ϭ 71 (br., CB), 81.9 (CH), 112.8, 123.2, 149.0 (Car), 200 (br.,
CO). Ϫ 11B NMR (64 MHz, C6D6): δ ϭ 32.6. Ϫ EI-MS: m/z (%) ϭ
430 (12) [Mϩ], 402 (39) [Mϩ Ϫ CO], 374 (6) [Mϩ Ϫ 2CO], 346 (16)
[Mϩ Ϫ 3CO], 318 (36) [Mϩ Ϫ 4CO], 290 (91) [Mϩ Ϫ 5CO], 262
[7]
[8]
M. Hesse, H. Meier, B. Zeeh, Spektroskopische Methoden in der
Organischen Chemie, 4. Aufl., Thieme Verlag, Stuttgart, 1991.
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Siebert, Eur. J. Inorg. Chem. 1999, 1693.
(46) [Mϩ Ϫ 6CO], 118 (100) [Bcat Ϫ H]ϩ. Ϫ HR-EIMS: m/z ϭ
[9]
12
429.8763 [Mϩ], calcd. for
2.2 mmu).
C
14
1H511B16O859Co2: 429.8741 (∆ ϭ
[10]
[11]
[12]
[13]
[14]
D. R. Stern, R. M. Washburn, U. S. Pat. 3092652, C. A.
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X-ray Crystal Structure Analyses of 1a, 4a, 5a, 5a(thf)3 and 9a:
Table 1 contains details of the structures. The intensities for 1a, 4a,
and 5a(thf)3 were measured with a four-circle diffractometer, and
for 9a and 5a with a CCD area detector (Mo-Kα radiation, λ ϭ
Int. Ed. Engl. 1984, 23, 539.
A. Maderna, H. Pritzkow, W. Siebert, Angew. Chem. 1996, 108,
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C. Ester, A. Maderna, H. Pritzkow, W. Siebert, Eur. J. Inorg.
Chem. 2000, 1177.
˚
0.71073 A, graphite monochromator, ω-scans). The structures were
solved by direct methods (SHELXS-86)[25] and refined by least-
square methods based on F2 with all measured reflections
(SHELXL-97)[26]. For 1a, 4a, 5a and 9a the hydrogen atoms were
located by difference Fourier synthesis and refined isotropically; for
5a(thf)3 the hydrogen atoms were inserted in calculated positions.
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publication
nos. CCDC-148514 (1a), -148515 (4a), -148516 [5a(thf)3], -150265
(5a), and -148517 (9a). Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [Fax: (internat.) ϩ44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
[15]
[16]
[17]
[18]
[19]
[20]
G. W. Kabalka, Org. Prep. Proced. Int. 1977, 9, 133.
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D. S. Matteson, Synthesis 1975, 147.
F. Lhermitte, B. Carboni, Synlett 1996, 377.
M. Hildenbrand, H. Pritzkow, U. Zenneck, W. Siebert, Angew.
Chem. 1984, 96, 371; Angew. Chem. Int. Ed. Engl. 1984, 23, 371.
H. C. Brown, N. Ravindran, J. Am. Chem. Soc. 1973, 95, 2396.
R. Soundararajan, D. S. Matteson, J. Org. Chem. 1990, 55,
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[21]
[22]
[23] [23a] P. Galow, A. Sebald, B. Wrackmeyer, J. Organomet. Chem.
[23b]
1983, 259, 253. Ϫ
ganomet. Chem. 1974, 12, 323. Ϫ
R. S. Dickson, P. J. Fraser, Adv. Or-
[23c]
H. Greenfield, H. W.
Sternberg, R. A. Friedel, J. H. Wotiz, R. Markby, I. Wender,
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Chem. Ber. 1961, 94, 2829.
[24] [24a]
Acknowledgments
Support of this work by the Deutsche Forschungsgemeinschaft
(SFB 247), the Fonds der Chemischen Industrie, and the BASF
AG is gratefully acknowledged. We thank Dr. Peter Greiwe for
helpful discussions.
C. Elschenbroich, A. Salzer, Organometallchemie, Verlag
[24b]
Teubner, Stuttgart, 1993. Ϫ
W. G. S ly, J. Am. Chem. Soc.
[24c]
1959, 81, 18. Ϫ
F. A. Cotton, J. D. Jamerson, B. R. Stults,
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[25]
[26]
G. M. Sheldrick, SHELXS86, University of Göttingen, 1986.
G. M. Sheldrick, SHELXL97, University of Göttingen, 1997.
Received May 10, 2000
[1]
R. Köster, H. J. Horstschäfer, P. Binger, Liebigs Ann. Chem.
1968, 717, 1.
[I00189]
Eur. J. Inorg. Chem. 2001, 373Ϫ379
379