Syntheses, structures, and coordination of diborylbipyridines and bipyridinediborates

Article abstract of DOI:10.1002/(sici)1099-0682(199903)1999:3<393::aid-ejic393>3.0.co;2-5

6,6'-Bis(diethylboryl)-2,2'-bipyridine (1a) was obtained in low yield by in situ deprotonation of 2,2'-bipyridine in the presence of diethyl(methoxy)borane. 6,6'-Dilithio-2,2'-bipyridine reacts with various alkoxyboranes leading to bipyridinediborates 2 in good yields. The derivatives 2b and 2c allow the formation of the free diborylbipyridines 1b and 1c. The coordination properties of the diboryl-bipyridines as tetra- functional donor-acceptor compounds have been used for the formation of the copper complex 4 and of the adduct 5 which is built from diborylbipyridine and a dihydroxydiboroxan derivative. The composition of the products follows from spectroscopic data and from X-ray structure analyses for 2f, 4, and 5.

Full text of DOI:10.1002/(sici)1099-0682(199903)1999:3<393::aid-ejic393>3.0.co;2-5

FULL PAPER
Syntheses, Structures, and Coordination of Diborylbipyridines and
Bipyridinediborates
Norbert Weis,[a] Hans Pritzkow,[a] and Walter Siebert*[a]
Dedicated to Prof. Dr. Günter Wächtershäuser on the occasion of his 60th birthday
6,6Ј-Bis(diethylboryl)-2,2Ј-bipyridine (1a) was obtained in
functional donor–acceptor compounds have been used for
the formation of the copper complex 4 and of the adduct 5
which is built from diborylbipyridine and a dihydroxydiboro-
xan derivative. The composition of the products follows from
low yield by in situ deprotonation of 2,2Ј-bipyridine in the
presence of diethyl(methoxy)borane. 6,6Ј-Dilithio-2,2Ј-bipy-
ridine reacts with various alkoxyboranes leading to bipyridi-
nediborates 2 in good yields. The derivatives 2b and 2c allow spectroscopic data and from X-ray structure analyses for 2f,
the formation of the free diborylbipyridines 1b and 1c. The
4, and 5.
coordination properties of the diboryl–bipyridines as tetra-
in 6,6Ј-diborylated bipyridines with respect to their donor-
acceptor properties and their potential of forming the mac-
rocycle D.
Introduction
The intramolecular presence of Lewis basic (nitrogen)
and Lewis acidic centers (boron) results in interesting
properties of borylated pyridines and bipyridines. A small
number of borylpyridines has been reported,[1] which were
synthesized as starting compounds for Suzuki coupling re-
actions.[2] 2-(Diethylboryl)pyridine[3] and 3-(diethylboryl)-
pyridine[4] are known for their stability towards moisture
and oxygen. The reason for this is their assembly by inter-
molecular boronϪnitrogen coordination. 2-(Diethylboryl)-
pyridine exists as a dimer (A) in solution and in the solid
state,[5] and 3-(diethylboryl)pyridine as a cyclic tetramer
(B).
Scheme 2
From spectroscopic data the formation of the cyclic ad-
duct E, based on the donorϪacceptor pattern of 2-(diethyl-
boryl)pyridine was postulated.[3] For the tetrafunctional
6,6Ј-diboryl-2,2Ј-bipyridines 1 one may expect a complex
donorϪacceptor behavior due to their geometric require-
ments. In the following the coordination properties of the
donorϪacceptor molecules 1 will be presented. In addition
the formation of bipyridinediborates 2 and their behavior as
N2O2 tetradentate ligands are studied, of which numerous
examples have been reported.[10Ϫ13]
Scheme 1
Results and Discussion
Bipyridines have been the subject of many studies.[6][7]
The π-acceptor properties of this bidentate σ-donor are Synthesis
weak. By introducing electron-withdrawing groups the π*-
Following a general procedure,[14] we synthesized the di-
level is lowered as has been demonstrated with acyl- and
carboxybipyridines (C).[8] The dπǞπ* absorption bands in
L3RuII complexes (L ϭ bipyridines) are shifted toward the
red region of the spectra and this shift increases the quality
of these metal complexes as sensitizers in solar energy con-
verting processes.[9] 6,6Ј-Diboryl-2,2Ј-bipyridines 1 should
also have increased π-acceptor qualities relative to that of
non-substituted bipyridines. We are in particular interested
borylbipyridine 1a by in situ deprotonation of 2,2Ј-bipyri-
dine with lithium diisopropylamide (LDA) in the presence
of an excess of diethyl(methoxy)borane. In this reaction 1a
was obtained in very low yield (1%) besides the monoboryl-
ated product 3a (6%). 1a is a colorless, high-melting solid
of low solubility whereas 3a is a viscous oil. Both sub-
stances are stable toward moisture and air. Their 11B-NMR
spectra (δ ϭ 3) indicate tetracoordinate boron atoms in as
yet unknown assembly, most likely 1a and 3a form donorϪ
acceptor compounds similar to A. In the EI mass spectra
the fragments of the monomeric species with loss of one
[a] Anorganisch-Chemisches Institut der Universität,
Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany
Fax: (internat.) ϩ 49(0)6221/54-5609
E-mail: ci5@ix.urz.uni-heidelberg.de
Eur. J. Inorg. Chem. 1999, 393Ϫ398
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ1948/99/0303Ϫ0393 $ 17.50ϩ.50/0
393

N. Weis, H. Pritzkow, W. Siebert
FULL PAPER
ethyl group appear as highest masses at m/z ϭ 263 [1a Ϫ could be stabilized by thf molecules forming donorϪac-
Et]ϩ and 195 [3a Ϫ Et]ϩ.
ceptor adducts.
Scheme 3
Scheme 5
To improve the yields a stepwise synthesis was carried
out. 6,6Ј-Dilithio-2,2Ј-bipyridine, obtained by a metal/hal-
ogen exchange,[15] was treated with various alkoxyboranes
to give the borate derivatives 2a؊f.
The reaction of the diisobutoxy derivative 2c with chloro-
bis(dimethylamino)borane results in the formation of 6,6Ј-
bis[bis(dimethylamino)boryl]-2,2Ј-bipyridine (1c). It is ob-
tained in 64% yield as a red oil of limited solubility in thf.
In comparison to bis(dimethylamino)organoboranes (δ ϭ
34Ϫ36)[16] the 11B-chemical shift of 1c appears at higher
field (δ ϭ 31). Most likely this is caused by π-interaction
between the pz orbital of the boron atom and the π system
1
of the heterocycle. In the H NMR there is only one signal
for the dimethylamino groups which indicates a free ro-
tation around the BϪN and the BϪC bonds on the NMR
time scale.
In general the reactivity of 2a؊f is high toward HCl/Et2O
and ClSiMe3 (except 2b), resulting in the cleavage of the
boronϪbipyridine bond. Because of their high sensitivity
toward moisture, no satisfactory C,H,N analysis could be
obtained.
Scheme 4
Regardless of the steric and electronic properties of the
substituents, the products 2a؊f are thermally stable and
isolated in 64Ϫ89% yields. All are colorless, crystalline sub-
stances, which, however, are very sensitive toward hydrolysis
to give bipyridine and the corresponding boron com-
pounds. They are characterized by 1H-, 13C-, 11B-NMR
spectroscopy and by an X-ray structure analysis of 2f (see
below). In these molecules the expected leaving groups
LiOR are bound to the diborylbipyridines. There are inter-
actions between the acceptor function (boron) with the al-
koxy group and between the donor function (nitrogen) with
the lithium ion. The formation of this five-membered he-
terocyclic arrangement enhances the stability of the ad-
ducts.
Attempts to synthesize 1a from 2a failed. Reaction of
2b with ClSiMe3 yields the 6,6Ј-bis-di(2-thienyl)boryl]-2,2Ј-
bipyridine (1b) in 36% yield. The combination of steric (iPr)
and electronic effects (thienyl) of the substituents destabi-
lizes the coordination in the dianionic borate 2b and thus
allows the formation of the free diborylbipyridine 1b. Based
on the 11B-NMR spectrum in thf (δ ϭ Ϫ1), its low solu-
bility and high melting point (> 250°C) we propose an ag-
gregation via NϪB donor acceptor interactions to give an
oligomer of unknown structure and number of diborylbipy-
ridine units. The appearence of only one 11B-NMR signal
Scheme 6
Complex Formation
In the borates 2 the bipyridine has an anti conformation
and acts as a tetradentate ligand toward two lithium cat-
ions. Treatment of 2b with one equivalent of (Et4N)2CuCl4
results in the formation of the deep green-blue coordination
compound 4. The copper ion is coordinated by two nitro-
gen and two oxygen atoms of the alkoxy groups. Because
of the paramagnetism of the d9-CuII ion the NMR spectra
of 4 could not be used for characterization. The cyclovol-
tammetry of 4 shows a reversible oxidation at E1/2 ϭ 0.65
V and an irreversible reduction at Ϫ1.1 V.
Scheme 7
An unprecedented coordination mode is observed in the
may indicate a cyclic arrangement. In a chain-like donorϪ adduct 5. It is formed by the interaction of 1a with 1,3-
acceptor compound (1b)n the two terminal BTh2 groups diethyl-1,3-dihydroxydiboroxane. The unknown dihydroxy-
394
Eur. J. Inorg. Chem. 1999, 393Ϫ398

Syntheses, Structures, and Coordination of Diborylbipyridines and Bipyridinediborates
FULL PAPER
diboroxane molecule is stabilized by the intermolecular ag- in CH2Cl2. Figure 2 shows its structure in the crystal. The
gregation. Treatment of 6,6Ј-dilithio-2,2Ј-bipyridine with an copper center has a distorted square-planar coordination
excess of diethyl(methoxy)borane and aqueous workup by two nitrogen and two oxygen atoms. One of the oxygen
leads to 5 in 42% yield. The Lewis donorϪacceptor pattern atoms (O2) deviates strongly from the plane. The geometry
of 1a induces the formation of the matching partner with around O2 differs much from that around O1. The distance
˚
˚
the inverted Lewis functionality. Hydrolysis of the diethyl- Cu1ϪO2 [2.016(3) A] is larger than Cu1ϪO1 [1.962(3) A].
(methoxy)borane yields 1,3-diethyl-1,3-dihydroxydiborox- The oxygen atom O1 shows a planar coordination, while
ane coordinated to the diborylbipyridine 1a. The free di- O2 is pyramidalized. The five-membered cycle of O1 is
hydroxydiboroxane is unstable and is expected to give give planar, that of O2 has an envelope form. The isopropyl
cyclic 1,3,5-boroxine. 5 is characterized by H-, 13C-, 11B- group at O1 lies approximately symmetrical to the plane
1
NMR spectroscopy and an X-ray structure analysis (see be- through the ring, while in the case of O2 it is strongly bent
low). In the 11B-NMR spectrum appears only one broad to one side, and one of the methyl groups reaches a position
signal at δ ϭ 9. Therefore all four boron atoms are quat- above the copper ion. A weak agostic interaction with one
˚
ernized. The Lewis acidic diethylboryl groups act as ac- of its hydrogen atoms to the copper ion [Cu1ϪH 2.48(4) A]
ceptor for the terminal oxygen atoms and the electron pair is observed. The distances between the boron atoms and
˚
of the nitrogen atoms donate to the boron atoms of the the bridging oxygen atoms [1.558(5), 1.575(5) A] are about
˚
dihydroxydiboroxane. The chemical shift of the methylene 0.1 A longer than in regular BϪO bonds of uncoordi-
groups of the diethylboroxane at δ ϭ Ϫ0.2 corresponds nated borates.
with the high electron density at the boron atoms.
Crystal Structures
Single crystals of 2f were grown from a tetrahydrofuran
solution at room temperature. Figure 1 shows a molecule
of 2f, its lithium centers are tetracoordinated. Besides the
bonding to the oxygen atom of the alkoxy group [LiϪO:
˚
1.87(1) A] there is an interaction with the nitrogen atom
˚
[LiϪN: 2.08(1) A] of the bipyridine unit. The coordination
sphere is completed by two thf molecules [LiϪO: 1.97(1)
˚
A]. The five-membered heterocycles are approximately
˚
Figure 2. Structure of 4 in the crystal; selected bond lengths [A]
planar with deviations from the best plane being less than
0.02 A. The bond length B1ϪC1 is 1.64 A. The two pyri-
dine units are twisted by 149.6°.
and angles [°]: B1ϪC1 1.630(6), B1ϪO1 1.558(5), B2ϪO2 1.575(5),
˚
˚
Cu1ϪN1 1.938(3), Cu1ϪN2 1.938(3), Cu1ϪO1 1.962(3), Cu1ϪO2
2.016(3), C5ϪC6 1.483(6), C1ϪB1ϪO1 103.7(3), C10ϪB2ϪO2
104.8(3),
N1ϪCu1ϪN2
80.8(1),
N1ϪCu1ϪO1
83.1(1),
O1ϪCu1ϪO2 114.8(1), O2ϪCu1ϪN2 83.4(1), B1ϪO1ϪC27
116.6(3), C27ϪO1ϪCu1 126.5(3), Cu1ϪO1ϪB1 116.9(2),
N1ϪC5ϪC6ϪN2 7.4, N1ϪC1ϪB1ϪO1 2.1, N2ϪC10ϪB2ϪO2
23.7
Figure 3 shows the molecule structure of 5 in the crystal.
Crystals suitable for X-ray structure analysis were obtained
by slow diffusion of n-hexane in a CH2Cl2 solution of 5.
The molecules of 5 form dimers in the solid state by hydro-
gen bonds. There are two independent dimers (four mol-
ecules) in the cell. They may be described as a donorϪac-
ceptor coordination product of 1a with 1,3-diethyl-1,3-di-
hydroxydiboroxane, with the nitrogen atoms of the bipyri-
dine and the hydroxy groups of the boroxane acting as
donors to the boron atoms. All boron atoms are tetra-
˚
Figure 1. Structure of 2f in the crystal; selected bond lengths [A]
and angles [°]: B1ϪC1 1.642(8), B1ϪO1 1.506(7), B1ϪO2 1.479(7), hedrally coordinated. Three groups of BϪO bonds are
Li1ϪO1 1.87(1), Li1ϪN1 2.08(1), Li1ϪO5 1.97(1), C1ϪB1ϪO1
found, which are clearly distinguished in their distances:
106.4(4),
C1ϪB1ϪO2
112.5(5),
C1ϪB1ϪC11
107.0(4),
One type in the seven-membered ring with the two-coordi-
N1ϪC5ϪC6ϪN2 30.6
˚
nated oxygen atoms varying from 1.415Ϫ1.445 A, two types
The large variety of possible coordination modes of in the five-membered rings with three-coordinated oxygen
CuII[17] are known. Therefore it is of interest to obtain atoms, where they differ in the coordination of the boron
˚
structural information on the copper coordination in 4. Sin- atoms; 1.503Ϫ1.536 A for the boron atoms connected to
˚
gle crystals suitable for an X-ray diffraction study were the nitrogen atoms, and 1.561Ϫ1.620 A for the boron atoms
grown by slow diffusion of n-hexane into the solution of 4 connected to three carbon atoms.
Eur. J. Inorg. Chem. 1999, 393Ϫ398
395

N. Weis, H. Pritzkow, W. Siebert
FULL PAPER
6 h at Ϫ75°C and was allowed to warm up to room temp. over-
night. The red solution was hydrolysed with 100 ml of brine (satu-
rated NaCl solution) and the organic layer was extracted with ethyl
acetate (3 ϫ 100 ml). The combined extracts were dried with anhy-
drous sodium sulfate and the solvent was removed in high vacuo.
The residue was column-chromatographed with silica gel (2 ϫ 30
cm) with a mixture of n-hexane and ethyl acetate (4:1) to give 27
mg (0.09 mmol, 1%) 1a and 97 mg (0.4 mmol, 6%) of 3a. Ϫ 1a: 1H
NMR (200.1 MHz, [D8]thf): δ ϭ 0.55 (t, 12 H, CH2CH3), 0.82 (q,
8 H, CH2CH3), 6.93 (m, 2 H, C10H6N2), 7.63 (m, 2 H, C10H6N2),
8.02 (m, 2 H, C10H6N2). Ϫ 11B NMR (64.2 MHz, CDCl3): δ ϭ
3.2. Ϫ 13C NMR (50.3 MHz, [D8]thf): δ ϭ 8.7 (CH2CH3), 10.5
(CH2CH3), 16 (br., CH2CH3), 123.8, 127.7, 139.0, 147.4 (C10H6N2).
Ϫ MS (70 eV, EI); m/z (%): 263 (26) [M Ϫ Et]ϩ, 235 (8) [M Ϫ Et
Ϫ C2H4]ϩ, 167 (100) [M Ϫ BEt2 Ϫ HCN]ϩ, 78 (16) [C5H4N]ϩ. Ϫ
˚
Figure 3. Structure of 5 in the crystal; selected bond lengths [A]
˚
[mean values and range given (esd. 0.006Ϫ0.009 A)]: BXϪOX 1.440
(1.415Ϫ1.445), BXϪOY 1.525 (1.503Ϫ1.536), BYϪOY 1.595
(1.561Ϫ1.620), BXϪN 1.626 (1.611Ϫ1.650), CAϪCB 1.486
(1.479Ϫ1.494)
1
M. p. > 250°C. Ϫ 3a: H NMR (200.1 MHz, [D8]thf: δ ϭ 0.50 (t,
6 H, CH2CH3), 0.78 (q, 4 H, CH2CH3), 7.24 (m, 1 H, C10H7N2),
7.50 (m, 1 H, C10H7N2), 7.96 (m, 1 H, C10H7N2), 8.06 (m, 1 H,
C10H7N2), 8.40 (m, 2 H, C10H7N2), 8.52 (m, 1 H, C10H7N2). Ϫ 13C
NMR (50.3 MHz, CDCl3): δ ϭ 9.9 (CH2CH3), 13.4 (br., CH2CH3),
118.9, 123.1, 124.5, 136.9, 138.1, 139.8, 141.9, 146.9, 149.2
(C10H7N2). Ϫ 11B NMR (64.2 MHz, CDCl3): δ ϭ 3.4. Ϫ MS (70
eV, EI); m/z (%): 195 (40) [M Ϫ Et]ϩ, 180 (3) [M Ϫ Et Ϫ Me]ϩ,
167 (100) [M Ϫ HCN Ϫ C2H4]ϩ,78 (4) [C5H4Nϩ].
6,6Ј-Bis-di(2-thienyl)boryl]-2,2Ј-bipyridine (1b): 630 mg (0.68 mmol)
of 2b was dissolved in 5 ml of CH2Cl2. 147 mg (1.36 mmol) of
ClSiMe3 in 5 ml of CH2Cl2 was added dropwise at 0°C. The yellow
solution was stirred at room temp. for 15 h. The mixture was fil-
tered and 20 ml of thf was added to the precipitate. The mixture
was again filtered from LiCl. After recrystallisation in thf, 124 mg
Figure 4. Hydrogen-bridged dimer of 5 in the crystal
1
(0.24 mmol, 36%) of 1b was obtained as an amorphus solid. Ϫ H
NMR (200.1 MHz, [D8]thf): δ ϭ 7.39 (dd, 2 H, C4H3S), 7.65 (dd,
1 H, C10H6N2), 7.82Ϫ7.89 (m, 3 H, C10H6N2/C4H3S), 8.05 (dd, 2
H, C4H3S), 8.42 (dd, 1 H, C10H6N2). Ϫ 13C NMR (50.3 MHz,
CDCl3): δ ϭ 120.4, 126.1, 131.0, 133.5, 138.5, 140.1, 141.6
(C10H6N2/C4H3S). Ϫ 11B NMR (64.2 MHz, [D8]thf): δ ϭ 1.0. Ϫ
MS (70 eV, EI): m/z (%): 342 (28) [M Ϫ 2 (C4H3S)]ϩ, 259 (11)
[M Ϫ 3 (C4H3S)]ϩ, 84 (100) [C4H4Sϩ]. Ϫ MS (FAB); m/z (%): 509
[M ϩ 1ϩ]. Ϫ M.p. > 250°C.
Experimental Section
General: Reactions were carried out under dry argon, using stand-
ard Schlenk techniques. Solvents were dried, distilled, and satu-
rated with nitrogen. Glassware was dried with a heat-gun in high
vaccum. Ϫ 1H, 13C, 11B NMR: Bruker AC 200 spectrometer, NMR
references are (CH3)4Si and BF3 · Et2O. Ϫ Mass spectra were ob-
tained with a Finnigan MAT 8200 plus spectrometer using EI tech-
nique. Ϫ Melting points (uncorrected) were obtained with a Büchi
apparatus, using capillaries which were filled under argon and
sealed.
6,6Ј-Bis[bis(dimethyamino)boryl]-2,2Ј-bipyridine (1c): To a solution
of 500 mg (0.79 mmol) of 2c in 5 ml of thf 211 mg (2 mmol) of
ClB(NMe2)2 in 5 ml of Et2O was added dropwise at room. temp.
After some min, a red solid started to precipitate. After stirring at
room temp. overnight, the mixture was filtered. The residue was
destilled in high vacuo (10Ϫ2 mbar, 220°C) yielding 179 mg (0.51
Crystal-Structure Determination: Unique sets of intensity data were
collected at Ϫ70°C with a four-circle diffractometer (Mo-Kα radi-
˚
ation λ ϭ 0.71073 A, graphite monochromator, ω-scan). Empirical
1
mmol, 64%) of 1c as a red oil. Ϫ H NMR (200.1 MHz, [D8]thf):
absorption corrections (ψ-scans) for 2f and 4 were applied. The
structures were solved by direct methods [SHELXS86][18] and re-
fined by least-squares methods based on F2 with all measured re-
flections [SHELXL97].[19] All non-hydrogen atoms were refined an-
isotropically.
δ ϭ 2.52 (s, 12 H, NMe2), 7.60 (d, 2 H, C10H6N2), 7.76 (dd, 2 H,
C10H6N2), 8.38 (d, 2 H, C10H6N2). Ϫ 13C NMR (50.3 MHz,
[D8]thf): δ ϭ 40.4, [N(CH3)2], 120.9, 129.8, 140.8, 142.6 (C10H6N2).
Ϫ
11B NMR (64.2 MHz, [D8]thf): δ ϭ 31.0. Ϫ EI-MS; m/z (%):
253 (25) [M Ϫ B(NMe2)2]ϩ, 226 (46) [M Ϫ B(NMe2)2 Ϫ HCN]ϩ,
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Center: CCDC-102722 (2f), -102723
(4), and -102724 (5). Copies of the data can be obtained free
of charge and by application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: int. code ϩ 44-1223/336-001;
E-mail: deposit@ccdc.cam.ac.uk].
79 (100) [C5H5Nϩ].
2,2Ј-Bipyridine-6,6Ј-diborates 2: 1.57g (5 mmol) of 6,6Ј-dibromo-
2,2Ј-bipyridine, dissolved in 75 ml of thf, was added dropwise
within 20 min to a solution of 10 mmol nBuLi in 50 ml of thf at
Ϫ80°C. After stirring for 45 min, the alkoxyborane, dissolved in
30 ml of Et2O, was added dropwise within 30 min to the red solu-
tion The mixture was allowed to warm up to room temp. overnight.
Half of the solvent was removed in vacuo and 30 ml of n-hexane
was added. After 36 h at 0°C, the mixture was filtered. The borates
were obtained as colorless solids.
6,6Ј-Bis(diethylboryl)-2,2Ј-bipyridine (1a) and 6-Diethylboryl-2,2Ј-
bipyridine (3a): 3.00 g (30 mmol) of Et2BOMe and 900 mg (7.5
mmol) of 2,2Ј-bipyridine were dissolved in 30 ml of Et2O and co-
oled to Ϫ75°C. 15 mmol of LiNiPr2 in 30 ml of Et2O was added 2a: (2.10 g, 3.2 mmol, 64%). Ϫ 1H NMR (200.1 MHz, [D8]thf):
dropwise within 1 h. The resulting yellow solution was stirred for
396
δ ϭ 0.19 (q, 4 H, CH2CH3), 0.71 (t, 6 H, CH2CH3), 3.14 (s, 3 H,
Eur. J. Inorg. Chem. 1999, 393Ϫ398

Syntheses, Structures, and Coordination of Diborylbipyridines and Bipyridinediborates
FULL PAPER
Table 1. Crystal data and structure refinement for 2f, 4, and 5
2f
4
5
Empirical formula
Formula weight
Crystal system
Space group
C46H72B2Li2N2O8S2
880.7
C32H32B2Cu1N2O2S4
690.0
C22H38B4N2O3
421.8
monoclinic
P21
triclinic
triclinic
¯
P1
¯
P1
Unit cell
˚
a [A]
10.418(6)
9.950(5)
13.051(7)
˚
b [A]
14.443(7)
13.434(7)
17.295(9)
˚
c [A]
17.001(8)
13.389(7)
22.120(11)
α [°]
β [°]
γ [°]
90
82.29(4)
89.28(3)
90.66(4)
68.38(3)
79.56(3)
90
76.47(4)
88.84(3)
3
˚
V [A ]
2558(2)
1615(1)
4909(4)
Z
2
2
8
Calcd. density [g/cm3]
Absorp.coeff. [mmϪ1]
F(000)
1.14
1.42
1.14
0.15
0.97
0.07
948
714
1824
Crystal size [mm]
Θmax [°]
Index ranges
No. of reflections
Unique
Observed [I > 2σ(I)]
Transmission
Parameters
0.2 ϫ 0.9 ϫ 1.0
25
0.1 ϫ 0.3 ϫ 0.7
0.4 ϫ 0.4 ϫ 0.7
25
24
Ϫ12/ϩ12, 0/ϩ17, 0/ϩ20
Ϫ10/ϩ11, Ϫ15/ϩ15, 0/ϩ15
Ϫ14/ϩ14, Ϫ19/ϩ19, 0/ϩ25
4711
3129
0.91Ϫ1.00
562
5660
4285
0.82Ϫ1.00
469
15383
8919
Ϫ
1188
Final R indices
R1 [I > 2σ(I)]
wR2
0.052
0.047
0.086
0.140
0.123
0.274
3
˚
Largest diff.peak/hole [e/A ]
0.27/Ϫ0.25
0.56/Ϫ0.42
0.39/Ϫ0.40
OCH3), 7.26Ϫ7.41 (m, 1 H, C10H6N2), 7.80Ϫ7.89 (m, 1 H,
H, ar). Ϫ 13C NMR (50.3 MHz, [D8]thf): δ ϭ 26.3 (CH3), 26.5
C10H6N2), 8.42Ϫ8.46 (m, 1 H, C10H6N2). Ϫ 13C NMR (50.3 MHz, (CH3), 62.8 [CH(CH3)2], 118.9, 124.3, 126.4, 128.6, 130.9, 133.8,
[D8]thf): δ ϭ 9.6 (br., CH2CH3), 11.1(CH2CH3), 49.5 (OCH3), 156.9 (ar). Ϫ 11B NMR (64.2 MHz, [D8]thf): δ ϭ 5.1. Ϫ M. p.
121.0, 124.5, 137.4, 149.9 (C10H6N2). Ϫ 11B NMR (64.2 MHz,
[D8]thf): δ ϭ 8.1. Ϫ M. p. 212Ϫ215°C.
199Ϫ201°C.
{2,2Ј-Bipyridine-6,6Ј-bisdiisopropoxydi(2-thienyl)borato]}-
copper(II) (4): 928 mg (1 mmol) of 2b and 456 mg (1 mmol) of
(Et4N)2CuCl4 were dissolved in 10 ml of CH2Cl2 at room temp.
After stirring for 12 h, the green-blue solution was filtered from
Et4NCl. The solvent was removed in vacuo yielding 650 mg (0.95
mmol, 95%) of 4 as a deep green-blue air-sensitive solid. m. p. >
250°C. Cyclic voltammetry data (EG&G PARC 175 potentiostat):
Pt disc (1 mm) working electrode, CH2Cl2 solution, 0.1  Bu4NPF6
as supporting electrolyte, Pt wire as auxiliar electrode, SCE as refer-
ence electrode. Reversible oxidation at E1/2 ϭ 0.65 V, irreversible
reduction at Ϫ1.1 V.
2b: (4.08 g, 4.4 mmol, 87%). Ϫ 1H NMR (200.1 MHz, [D8]thf):
δ ϭ 0.91 (d, 6 H, CH3), 3.93 [sept, 1 H, CH(CH3)2], 7.04Ϫ7.56 (m,
10 H, CH). Ϫ 13C NMR (50.3 MHz, [D8]thf): δ ϭ 18.9 (CH3), 61.3
[CH(CH3)2], 111.3 (C10H6N2), 118.3 (C4H3S), 120.6 (C4H3S), 122.1
(C10H6N2), 123.4 (C4H3S), 128.0 (C10H6N2), 148.9 (C10H6N2). Ϫ
11B NMR (64.2 MHz, [D8]thf): δ ϭ 0.7. Ϫ M. p. 189Ϫ191°C.
2c: (3.49 g, 3.9 mmol, 78%). Ϫ 1H NMR (200.1 MHz, [D8]thf):
δ ϭ 0.83 (d, 6 H, CH3), 0.90 [d, 6 H, CH2CH(CH3)2], 1.70 [m, 2
H, CH2CH(CH3)2], 3.00Ϫ3.19 [m, 4 H, CH2CH(CH3)2], 6.81Ϫ7.02
(m, 3 H, CH), 7.37Ϫ7.61 (m, 5 H, CH). Ϫ 13C NMR (50.3 MHz,
CDCl3):
δ
ϭ
19.6 (CH3), 32.2 [OCH2CH(CH3)2], 69.8
[OCH2CH(CH3)2], 124.6, 126.7, 133.9, 157.8 (C10H6N2). Ϫ 11B
NMR (64.2 MHz, [D8]thf): δ ϭ 6.6. Ϫ M. p. 242Ϫ244°C.
1,3-Diethyl-1,3-dihydroxydiboroxane Adduct 5 of 1a: 1.57g (5 mmol)
of 6,6Ј-dibromo-2,2Ј-bipyridine, dissolved in 75 ml of thf, was ad-
ded dropwise within 20 min to a solution of 10 mmol of nBuLi in
50 ml of thf at Ϫ80°C. After stirring for 45 min, 2.50 g (25 mmol)
of diethyl(methoxy)borane, dissolved in 30 ml of Et2O, was added
dropwise within 30 min to the red solution. The mixture was al-
lowed to warm up to room temp. overnight. The red solution was
hydrolysed with 100 ml of brine and the organic layer was extracted
with ethyl acetate (3 ϫ 100 ml). The combined extracts were dried
with anhydrous sodium sulfate and the solvent was removed in va-
cuo. The residue was dissolved in 20 ml of thf and 10 ml of n-
hexane was added. After 40 h at 0°C, the mixture was filtered yield-
ing 884 mg (2.1 mmol, 42%) of 5. Ϫ 1H NMR (200.1 MHz,
CD2Cl2): δ ϭ Ϫ0.21 [q, 2 H, OB(OH)CH2CH3], 0.52 [q, 4 H,
OB(CH2CH3)2], 0.64 [t, 3 H, OB(OH)CH2CH3], 0.79 [t, 6 H,
OB(CH2CH3)2], 3.93 (br., 0.8 H, OH), 7.45Ϫ7.67 (m, 2 H,
2d: (2.95 g, 4.1 mmol, 82%). Ϫ 1H NMR (200.1 MHz, [D8]thf):
δ ϭ 3.06 (s, 6 H, CH3), 6.79Ϫ7.00 (m, 3 H, ar), 7.34Ϫ7.52 (m, 5
H, ar). Ϫ 13C NMR (50.3 MHz, [D8]thf): δ ϭ 49.7 (OCH3), 118.8,
124.8, 126.9, 129.3, 133.6, 135.1, 158.3 (ar). Ϫ 11B NMR (64.2
MHz, [D8]thf]): δ ϭ 6.7. Ϫ M. p. > 250°C (dec.).
2e: (3.49 g, 4.5 mmol, 89%). Ϫ 1H NMR (200.1 MHz, [D8]thf):
δ ϭ 0.84 (s, 18 H, CH3), 3.61 (s, 3 H, OCH3), 7.29Ϫ7.45 (m, 2 H,
C10H6N2), 7.65Ϫ7.70 (m, 1 H, C10H6N2). Ϫ 13C NMR (50.3 MHz,
[D8]thf): δ ϭ 34.2 (CH3), 32.8 (CH3), 53.8 [br., BC(CH3)3], 53.9
(OCH3), 117.7 [br., BC(C10H6N2)], 129.2, 130.6, 132.2, 132.7
(C10H6N2). Ϫ 11B NMR (64.2 MHz, [D8]thf): δ ϭ 5.1. Ϫ M. p.
212Ϫ214°C.
2f: (2.91g, 3.3 mmol, 65%). Ϫ 1H NMR (200.1 MHz, [D8]thf): δ ϭ
0.86 (d, 6 H, CH3), 1.07 (d, 6 H, CH3), 3.91 [sept, 2 H, CH(CH3)2], C10H6N2), 7.93 (t, 1 H, C10H6N2). Ϫ 13C NMR (50.3 MHz,
6.80 (m, 2 H, ar), 7.09 (d, 1 H, ar), 7.50 (m, 2 H, ar), 7.76 (dd, 1 CD2Cl2): δ ϭ 7.8 (CH2CH3), 9.6 (CH2CH3), 9.8 (CH2CH3), 15 (br.,
Eur. J. Inorg. Chem. 1999, 393Ϫ398
397

N. Weis, H. Pritzkow, W. Siebert
FULL PAPER
CH2CH3), 123.4, 127.9, 139.6, 146.1 (C10H6N2). Ϫ 11B NMR (64.2
MHz, CD2Cl2): δ ϭ 9.2 (br.). Ϫ M. p. 156Ϫ160°C (dec.).
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