Chemical reduction and dimerization of 1-chloro-2,3,4,5-tetraphenylborole

Article abstract of DOI:10.1002/chem.201001556

As neutral isoelectronic analogues of the elusive cyclopentadienyl cation, boroles have been of interest for their prospective applications as strong Lewis acids, chromophores, and electron acceptors. Recently our group discovered a π-nucleophilic boryl anion based on the borole system. In an effort to extend borole chemistry, we now report the molecular structure of 1-chloro-2,3,4,5- tetraphenylborole (1) and its corresponding borole dianion resulting from the two-electron reduction of 1 with KC₈. The thermally induced dimerization of 1 yields an unprecedented boracyclohexadiene/borolene spiro-bicyclic compound and the resulting dimer was fully characterized including a single-crystal X-ray analysis. As an extension of borole chemistry, the reduction of 1-chloro-2,3,4,5-tetraphenylborole (1) leads to the corresponding dianionic derivative. Dimerization of 1 under thermal conditions results in the formation of a spiro-bicyclic compound that features a bora-cyclohexadiene and a borolene ring (see picture). Solid-state molecular structures of all three compounds are also reported.

Full text of DOI:10.1002/chem.201001556

FULL PAPER
DOI: 10.1002/chem.201001556
Chemical Reduction and Dimerization of 1-Chloro-2,3,4,5-tetraphenylborole
Holger Braunschweig,* Ching-Wen Chiu, Johannes Wahler, Krzysztof Radacki, and
Thomas Kupfer[a]
Abstract: As neutral isoelectronic ana-
logues of the elusive cyclopentadienyl
cation, boroles have been of interest
for their prospective applications as
strong Lewis acids, chromophores, and
electron acceptors. Recently our group
discovered a p-nucleophilic boryl anion
based on the borole system. In an
effort to extend borole chemistry, we
now report the molecular structure of
1-chloro-2,3,4,5-tetraphenylborole (1)
and its corresponding borole dianion
resulting from the two-electron reduc-
tion of 1 with KC8. The thermally in-
duced dimerization of 1 yields an un-
precedented boracyclohexadiene/boro-
lene spiro-bicyclic compound and the
resulting dimer was fully characterized
including a single-crystal X-ray analy-
sis.
Keywords: antiaromaticity
·
bor-
oles · boron · reduction · spiro com-
pounds
Introduction
tionalization at the boron atom practical.[7c,8] The presence
of the electron-deficient boron center renders borole deriva-
tives strong Lewis acids with potential applications in cataly-
sis, anion sensing, and optoelectronics.[5a,b,e] The increasing
research focus on boroles is reflected by the considerable
number of reports published in the past two years alone.[7–9]
To date, the substituents successfully installed at the boron
atom range from aryl groups, halogens, and amino groups,
to ferrocenyl and platinum complex fragments.
Two-electron reduction of a borole results in a 6p aromat-
ic Hꢀckel system, isoelectronic to the well-studied cyclopen-
tadienyl anion. Accordingly, the coordination chemistry of
the borole dianion as a ligand for transition metals has been
a motivation for researchers in the field.[6b,10] However, in
spite of the aromatic nature of this boracycle, very few
borole dianions have been isolated and structurally charac-
terized; their boron substituents are limited to aryl and
amino groups.[7b,11] We recently disclosed the reaction of a
carbene-stabilized borole monoanion with methyl iodide,
and suggested that this anion may serve as a useful p-boryl
anion and boron nucleophile.[12] To broaden our understand-
ing of borole anions, we now report the solid-state structure
of 1-chloro-2,3,4,5-tetraphenylborole (1), its reduction to the
chloroborole dianion, and an unusual dimerization reaction
of the chloroborole.
Functionalized boron-containing p-conjugated systems have
attracted considerable attention due to their promising ap-
plications in optoelectronics that can be ascribed to the
presence of the low-lying empty p orbital at boron.[1] Studies
on boracycles have illustrated that the incorporation of
boron into a cyclic p-conjugated system has a more pro-
nounced effect on the electronic state of the molecule than
for its acyclic analogue.[2] In addition to aromatic boracycles,
that is, borirenes[3] and borepines,[4] recent focus has shifted
to their counterparts to induce stronger perturbation of the
p-system.[5] As the smallest neutral antiaromatic boracycle,
borole is extremely electron deficient and requires steric
protection of the C4B core for the isolation of monomeric,
non-annulated derivatives.[6] Even though the synthesis of
pentaarylboroles was reported in the 1980s, the structural
characterization of these compounds was only accomplished
very recently.[7] However, the study of boroles was to some
extent limited to pentaarylboroles until the recent isolation
of 1-chloro- and 1-bromoboroles, which make direct func-
[a] Prof. Dr. H. Braunschweig, Dr. C.-W. Chiu, J. Wahler,
Dr. K. Radacki, Dr. T. Kupfer
Institut fꢀr Anorganische Chemie
Julius-Maximilians-Universitꢁt Wꢀrzburg
Am Hubland, 97074 Wꢀrzburg (Germany)
Fax : (+49)931-31-84623
E-mail: h.braunschweig@mail.uni-wuerzburg.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001556.
Chem. Eur. J. 2010, 16, 12229 – 12233
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
12229

Results and Discussion
By steric protection of the C4B core with phenyl groups, the
electron-deficient chloroborole 1 can be readily isolated by
the boron–tin exchange reaction of BCl3 with 1,1-dimethyl-
2,3,4,5-tetraphenylstannole, as previously described.[8] Single
crystals of 1 suitable for X-ray diffraction analysis were ob-
tained as dark green needles from a concentrated CH2Cl2
solution at À608C.
The results of the X-ray diffraction analysis (Figure 1)
confirm the presence of a tricoordinate, planar boron atom
in the solid state as indicated by the sum of the angles
Scheme 1. Reduction and dimerization of 1.
Supporting Information). Within each molecular unit, the
borole ring is essentially planar with two potassium atoms
located above and below the C4B plane in a h5 manner
(Figure 2). The propeller arrangement of the phenyl groups
Figure 1. Molecular structure of 1 in the solid state with hydrogen atoms
and solvent molecules omitted for clarity. Thermal ellipsoids are set at
50% probability. Selected bond lengths [ꢃ] and angles [8]: B1–Cl1
1.7433(14), B1–C1 1.5636(18), B1–C4 1.5663(18), C1–C2 1.3619(16), C2–
C3 1.5196(17), C3–C4 1.3547(16); C1-B1-C4 107.72(10), B1-C1-C2
104.35(10), C1-C2-C3 111.60(10), C2-C3-C4 111.96(10), C3-C4-B1
104.36(10), C1-B1-Cl1 126.34(9), C4-B1-Cl1 125.94(10).
Figure 2. Molecular structure of the K2[1] fragment in K2ACHTNUTRGNENUG(THF)2[1] in the
solid state with hydrogen atoms and solvent molecules omitted for clarity.
Thermal ellipsoids are set at 50% probability. Selected bond lengths [ꢃ]
and angles [8]: B1–Cl1 1.839(4), B1–C1 1.517(6), B1–C4 1.505(6), C1–C2
1.456(5), C2–C3 1.418(5), C3–C4 1.451(5), B1–K1 3.178(4), B1–K2
3.102(4); C1-B1-C4 107.7(3), B1-C1-C2 105.2(3), C1-C2-C3 110.6(3), C2-
C3-C4 110.6(3), C3-C4-B1 105.8(3), C1-B1-Cl1 127.4(3), C4-B1-Cl1
124.9(3).
around B1 of 360.08. As in pentaarylboroles, a propeller-like
arrangement of the phenyl groups with respect to the central
C4B ring is observed.[7] However, no close contacts between
B1 and phenyl groups were identified, suggesting the pres-
À
ence of an isolated borole system. The pronounced C C
bond length alternation is consistent with the optimized sin-
glet ground state geometry of antiaromatic pentaarylbor-
oles.[7a,b] The B1 Cl1 distance of 1.7433(14) ꢃ is in the ex-
with an average tilting angle of 42.168 is typical. The boron
atom features a trigonal-planar geometry with the sum of
À
2
À
pected range for an sp B Cl bond, such as in (C6F5)2BCl
(1.746(5) ꢃ),[13] (C6H3F2)2BCl (1.755(2) ꢃ),[14] and Cp*2BCl
(1.790(3) ꢃ).[15]
À
the angles around the boron atom of 360.08. The B C and
À
C C bond lengths within the borole ring are comparable to
Chemical reduction of 1 with excess KC8 in THF affords
those measured for K
[C4Ph4BPh], indicative of the 6p-elec-
À
the corresponding borole dianion K
G
tron aromaticity. The B1 Cl1 bond length of 1.839(4) ꢃ is
noticeably elongated compared to that observed in 1 as a
result of the electronic repulsion between the p electrons of
the borole ring and the lone pairs on the chlorine atom.
In addition to chemical reduction, a thermal stability
study of 1 was performed. Heating a solution of 1 in di-
chloromethane at 408C leads to the formation of a new
compound (2) after two days (Scheme 1). The 1H NMR
spectrum of 2 contains a complicated splitting pattern be-
tween d=5.80 to 7.27 ppm. Additionally the 11B NMR reso-
nances of 2, detected as two broad signals at d=59.0 and
74.4 ppm, suggest that compound 1 dimerizes into an asym-
metric molecule with two chemically nonequivalent tricoor-
dinate boron centers. Solid-state structural determination of
yield (Scheme 1). K2A(THF)2[1] is stable in the solid state
CTHUNGTRENNUNG
under inert atmosphere but extremely sensitive towards air
and moisture. As expected, the 11B NMR resonance of K2-
ACHTUNGTRENNUNG
CHTUNGTRENNUNG
CHTUNGTRENNUNG
G
are bridged by a potassium–chlorine interaction to form an
extended structure in the solid state (see Figure S1 in the
12230
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 12229 – 12233

Reactions of 1-Chloro-2,3,4,5-tetraphenylborole
FULL PAPER
2 was achieved by single-crystal X-ray analysis. Compound 2
crystallizes from a THF/hexane (1:1) solution at ambient
temperature as yellow block crystals. As indicated in
Figure 3, compound 2 is a chiral spiro compound that fea-
Scheme 2. Proposed dimerization mechanism of 1.
culations on the system. Geometry optimization of 1 and its
hypothetical carbene isomer (1’) was carried out by DFT
methods (B3LYP, 6-31g**). Single-point energy calculations
of these two molecules reveal an energy difference of
68 kcalmolÀ1 between 1 and 1’, which is too high to be over-
come under mild heating conditions. Therefore, the carbene
insertion reaction pathway is unlikely to occur during the di-
merization process of 1.
Figure 3. Molecular structure of 2 in the solid state with hydrogen atoms
omitted for clarity. Thermal ellipsoids are set at 50% probability. Select-
ed bond lengths [ꢃ] and angles [8]: B1–Cl1 1.7527(18), B2–Cl2
1.7741(18), B1–C1 1.594(2), B1–C4 1.591(2), C1–C2 1.542(2), C2–C3
1.346(2), C3–C4 1.540(2), B2–C4 1.586(2), B2–C8 1.525(2), C4–C5
1.511(2), C5–C6 1.354(2), C6–C7 1.477(2), C7–C8 1.373(2); C1-B1-C4
111.46(13), C1-B1-Cl1 124.69(12), C4-B1-Cl1 123.69(12), C4-B2-C8
120.32(14), C4-B2-Cl2 119.48(12), C8-B2-Cl2 120.15(12).
Another proposed reaction pathway is the initial forma-
tion of the [2.2.1]bicyclo dimer, in which the addition reac-
À
À
tures one five-membered and one six-membered B-chloro-
tion occurs over the B1 C1 bond instead of the C1 C2
bond. Owing to the strong electron deficiency of the boron
atom in boroles there is considerable contribution of the
charge-separated zwitterionic formulas 1b and 1c, both fea-
turing a B=C double bond and a carbenium center. It is as-
sumed that the cycloaddition took place at the less hindered
part of the molecule, that is, the borataalkene moiety, rather
than the sterically encumbered C=C double bond. This bicy-
clic derivative quickly undergoes subsequent phenyl migra-
À
À
À
boracycle. Since the C2 C3, C5 C6, and C7 C8 bond
lengths are typical for a C=C bond, the six-membered ring
can be described as a boracyclohexadiene,[17] while the five-
membered ring is a borolene.[11b] Both boron atoms adopt a
trigonal-planar geometry as indicated by the sum of angles
around the boron atom of 359.88 and 360.08, respectively.
À
Notably, the B2 C8 bond is significantly shorter than the
À
À
other B C bonds. The B2 C8 bond length of 1.525(2) ꢃ is
also shorter than that observed in the 9-dimesitylboryl acri-
dinyl radical (1.559(5) ꢃ), which features a formal one-elec-
À
tion and B C bond rearrangement to form the spiro-bicyclic
compound.
tron B=C double bond, implying the presence of significant
[18]
À
p-bonding character of the B2 C8 bond. Accordingly, the
À
À
B2 Cl2 bond is slightly longer than the B1 Cl1 bond as a
consequence of increased electron density at B2 from the p-
electron delocalization of the butadiene backbone.
Conclusion
In summary, chemical reduction of 1-chloro-2,3,4,5-tetraphe-
nylborole was carried out, and the resulting 1-chloroborole
dianion was isolated and structurally characterized. The bor-
acyclohexadiene/borolene spirobicyclic compound 2 was
synthesized by thermally induced dimerization of 1. The de-
tailed dimerization mechanism of 1 is currently under inves-
tigation with computational methods in our laboratory.
The thermally induced rearrangement/dimerization of 1 is
a unique process when compared to other pentaarylborole
derivatives, which generally possess good thermal stability
even in hot toluene solution.[7b,c] The formation of the spiro
compound is also distinct from the [2.2.1]bicycloborole
dimers commonly formed by sterically less demanding bor-
oles via a Diels–Alder reaction.[19] Two possible reaction
pathways are depicted in Scheme 2. The first one involves a
[1,5]-sigmatropic migration of the phenyl group to generate
a transient a-borylated carbene species, which subsequently
Experimental Section
À
inserts into the B C bond of the other chloroborole. How-
ever, this reaction pathway was ruled out by theoretical cal-
General considerations: All syntheses were carried out under an argon
atmosphere with standard Schlenk and glovebox techniques. C4Ph4BCl
Chem. Eur. J. 2010, 16, 12229 – 12233
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
12231

H. Braunschweig et al.
was prepared according to published procedures.[8] Hexane, THF, and
CH2Cl2 were dried by distillation over Na/K alloy (hexane, THF) or
phosphorus pentoxide (CH2Cl2) under argon and stored over molecular
sieves. CD2Cl2 was degassed with three freeze–pump–thaw cycles and
stored over molecular sieves. [D8]THF was degassed and dried by passing
through activated alumina. Elemental analyses were obtained on a Ele-
mentar Vario MICRO cube instrument. NMR spectra were recorded on
a Bruker Avance 500 NMR spectrometer (500 MHz for 1H, 160 MHz for
11B, 126 MHz for 13C{1H}) and a Bruker Avance 400 NMR spectrometer
(400 MHz for 1H, 128 MHz for 11B, 100.5 MHz for 13C{1H}). Chemical
shifts are given in ppm, and are referenced against external Me4Si (1H,
13C), and BF3·Et2O (11B).
CCDC-779266 (1), CCDC-778763 (K2ACTHUNGTRENNU(G THF)2[1]), and CCDC-778764 (2)
contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallograph-
ic Data Centre via www.ccdc.cam.ac.uk/data_request/cif
Acknowledgements
This work is supported by the DFG. C.-W. C. is grateful for a postdoctor-
al fellowship from the Alexander von Humboldt Foundation.
Synthesis of K2ACHTUNGTRENNUNG(THF)2[1]: THF (1 mL) was added to a mixture of
C4Ph4BCl (50.0 mg, 124 mmol) and KC8 (50.0 mg, 370 mmol) at room tem-
perature to give a dark red solution. The mixture was stirred for 10 min
and then filtered. Hexane (2 mL) was diffused into the solution over a
[1] a) N. Matsumi, K. Naka, Y. Chujo, J. Am. Chem. Soc. 1998, 120,
5112–5113; b) T. Noda, Y. S. Ogawa, Y. Shirota, Adv. Mater. 1999,
11, 283–285; c) S. Yamaguchi, T. Shirasaka, K. Tamao, Org. Lett.
2000, 2, 4129–4132; d) S. Yamaguchi, S. Akiyama, K. Tamao, J. Am.
Chem. Soc. 2000, 122, 6335–6336; e) Y. Shirota, T. Kinoshita, K.
Noda, T. O. Okumoto, J. Am. Chem. Soc. 2000, 122, 11021–11022;
f) S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem. Soc. 2001,
123, 11372–11375; g) C. D. Entwistle, T. B. Marder, Angew. Chem.
2002, 114, 3051–3056; Angew. Chem. Int. Ed. 2002, 41, 2927–2931,
and references therein; h) C. D. Entwistle, T. B. Marder, Chem.
Mater. 2004, 16, 4574–4585; i) Y. Qin, G. Cheng, O. Achara, K.
Parab, F. Jꢁkle, Macromolecules 2004, 37, 7123–7131; j) K. Parab, Y.
Quin, F. Jꢁkle, Poly. Mater. Sci. Eng. Prepr. 2005, 93, 422; k) C.-H.
Zhao, A. Wakamiya, Y. Inukai, S. Yamaguchi, J. Am. Chem. Soc.
2006, 128, 15934–15935; l) F. Jꢁkle, Coord. Chem. Rev. 2006, 250,
1107–1121; m) H. Li, A. Sundararaman, K. Venkatasubbaiah, F.
Jꢁkle, J. Am. Chem. Soc. 2007, 129, 5792–5793; n) A. Wakamiya, K.
Mori, S. Yamaguchi, Angew. Chem. 2007, 119, 4351–4354; Angew.
Chem. Int. Ed. 2007, 46, 4273–4276; o) M. Haussler, B. Tang, Z.
Adv. Polym. Sci. 2007, 209, 1–58; p) M. Elbing, G. C. Bazan, Angew.
Chem. 2008, 120, 846–850; Angew. Chem. Int. Ed. 2008, 47, 834–
838.
[2] a) R. Boese, N. Finke, J. Henkelmann, G. Maier, P. Paetzold, H. P.
Reisenauer, G. Schmid, Chem. Ber. 1985, 118, 1644–1654; b) S.
Qiao, D. A. Hoic, G. C. Fu, J. Am. Chem. Soc. 1996, 118, 6329–
6330; c) D. A. Hoic, J. R. Wolf, W. M. Davis, G. C. Fu, Organometal-
lics 1996, 15, 1315–1318; d) S. Qiao, D. A. Hoic, G. C. Fu, Organo-
metallics 1997, 16, 1501–1502; e) G. E. Herberich, U. Englert, B.
Ganter, M. Pons, R. Wang, Organometallics 1999, 18, 3406–3413;
f) X. Zheng, G. E. Herberich, Organometallics 2000, 19, 3751–3753;
g) D. J. H. Emslie, W. E. Piers, M. Parvez, Angew. Chem. 2003, 115,
1290–1293; Angew. Chem. Int. Ed. 2003, 42, 1252–1255; h) T. K.
Wood, W. E. Piers, B. A. Keay, M. Parvez, Angew. Chem. 2009, 121,
4069–4072; Angew. Chem. Int. Ed. 2009, 48, 4009–4012; i) A. Waka-
miya, K. Mori, T. Araki, S. Yamaguchi, J. Am. Chem. Soc. 2009, 131,
10850–10851.
period of 5 h to give K2ACHTUNGTRENNUNG(THF)2[1] as a bright red solid, which was washed
with cold diethyl ether (0.5 mL) and dried (19.1 mg, 30.6 mmol, 25%).
Single crystals that were suitable for X-ray crystallography were obtained
by the same method. 1H NMR (400 MHz, [D8]THF): d=6.26–6.30 (m,
2H), 6.59–6.64 (m, 2H), 6.66–6.71 (m, 4H), 6.76–6.81 (m, 8H), 6.97–
7.00 ppm (m, 4H); 11B NMR (128 MHz, [D8]THF): d=26.6 ppm (br);
13C{1H} NMR (100.5 MHz, [D8]THF): d=116.4, 120.6, 121.8, 126.7, 127.0,
129.3, 132.3, 146.0, 149.2 ppm; elemental analysis calcd (%) for
C36H36BClK2O2: C 69.17; H 5.80; found: C 68.15; H 5.61.
Synthesis of 2: C4Ph4BCl (47.0 mg, 117 mmol) was dissolved in CH2Cl2
(1.5 mL) and heated to 408C for 42 h to give a brown solution. The sol-
vent was removed under reduced pressure, hexane (1 mL) was added to
the brown residue and stirred for 3 h. The resulting precipitate was fil-
tered, washed with hexane (3ꢄ1 mL), and dried under vacuum to give
Cl2B2C8Ph8 (2) (25.0 mg, 31.0 mmol, 52%) as a yellow solid. Analytically
pure crystals suitable for X-ray crystallography were obtained by recrys-
tallization from THF/hexane (1:1). 1H NMR (500 MHz, CD2Cl2): d=
5.80–5.82 (m, 1H), 6.04–6.05 (m, 1H), 6.40–6.43 (m, 1H), 6.49–6.51 (m,
1H), 6.62–6.73 (m, 6H), 6.84–6.87 (m, 3H), 6.91–7.06 (m, 15H), 7.09–
7.14 (m, 5H), 7.18–7.27 ppm (m, 7H); 11B NMR (160 MHz, CD2Cl2): d=
59.0 (br), 74.4 ppm (br); 13C{1H} NMR (126 MHz, CD2Cl2): d=69.9, 83.7,
125.3, 125.7, 126.1, 126.3, 126.4, 126.5, 126.7, 127.0, 127.2, 127.5, 127.6,
127.7, 128.0, 128.3, 129.6, 129.9, 130.0, 130.4, 130.9, 131.2, 131.6, 132.4,
138.4, 139.6, 140.3, 140.7, 141.1, 141.2, 142.0, 143.3, 145.6, 145.9, 153.4,
165.1 ppm; elemental analysis calcd (%) for C56H40B2Cl2: C 83.51; H
5.01; found: C 83.20; H 5.20.
Crystal structure determination: The crystal data of 1, K2ACTHNUGTRNE(UNG THF)2[1], and
2 were collected on a Bruker X8APEX diffractometer with a CCD area
detector and multilayer mirror monochromated MoKa radiation. The
structure was solved by using direct methods, refined with the Shelx soft-
ware package,[20] and expanded by using Fourier techniques. All non-hy-
drogen atoms were refined anisotropically. Hydrogen atoms were as-
signed to idealized positions and were included in structure factors calcu-
lations.
[3] a) C. Habben, A. Meller, Chem. Ber. 1984, 117, 2531–2537; b) C.
Pues, A. Berndt, Angew. Chem. 1984, 96, 306–307; Angew. Chem.
Int. Ed. Engl. 1984, 23, 313–314; c) J. J. Eisch, B. Shafii, J. D. Odom,
A. L. Rheingold, J. Am. Chem. Soc. 1990, 112, 1847–1853; d) H.
Braunschweig, T. Herbst, D. Rais, F. Seeler, Angew. Chem. 2005,
117, 7627–7629; Angew. Chem. Int. Ed. 2005, 44, 7461–7463; e) H.
Braunschweig, I. Fernꢅndez, G. Frenking, K. Radacki, F. Seeler,
Angew. Chem. 2007, 119, 5307–5310; Angew. Chem. Int. Ed. 2007,
46, 5215–5218; f) H. Braunschweig, T. Herbst, D. Rais, S. Ghosh, T.
Kupfer, K. Radacki, A. Crawford, R. Ward, T. Marder, I. Fernꢅndez,
G. Frenking, J. Am. Chem. Soc. 2009, 131, 8989–8999; g) H.
Braunschweig, T. Herbst, K. Radacki, G. Frenking, M. A. Celik,
Chem. Eur. J. 2009, 15, 12099–12106; h) H. Braunschweig, Q. Ye, K.
Radacki, Chem. Commun. 2009, 6979–6981.
Crystal data for 1ACHTUNGTRENNUNG(CH2Cl2)2: C30H24BCl5, Mr =572.55, green needle, 0.32ꢄ
0.13ꢄ0.10 mm3, monoclinic space group P21/c, a=13.268(5), b=
25.573(8), c=8.225(3) ꢃ, b=103.277(16)8, V=2716.4(16) ꢃ3, Z=4,
1calcd =1.400 gcmÀ3
, , FACHTGUNTREN(UNNG 000)=1176, T=100(2) K, R1 =
m=0.553 mmÀ1
0.0344, wR2 =0.0889, 6517 independent reflections [2q ꢀ 56.88] and 325
parameters.
Crystal data for K2ACHTUNGTRENNUNG(THF)2[1]: C72H72B2Cl2K4O4, Mr =1250.22, orange
3
¯
plate, 0.20ꢄ0.09ꢄ0.02 mm , triclinic space group P1, a=10.8311(14), b=
10.8933(14), c=14.5463(18) ꢃ, a=68.684(2), b=77.066(3), g=
84.902(3)8, V=1558.2(3) ꢃ3, Z=1, 1calcd =1.332 gcmÀ3, m=0.422 mmÀ1, F-
ACHTUNGTRENNUNG
(000)=656, T=103(2) K, R1 =0.0982, wR2 =0.2213, 6134 independent re-
flections [2q ꢀ 52.848] and 386 parameters.
Crystal data for 2: C56H40B2Cl2, Mr =805.40, yellow plate, 0.20ꢄ0.13ꢄ
0.04 mm3, orthorhombic space group Pbca, a=17.9229(16), b=
[4] a) J. J. Eisch, J. E. Galle, B. Shafii, A. L. Rheingold, Organometallics
1990, 9, 2342–2349; b) A. J. Ashe III, J. W. Kampf, W. Klein, R.
Rousseau, Angew. Chem. 1993, 105, 1112–1113; Angew. Chem. Int.
Ed. Engl. 1993, 32, 1065–1066.
19.9110(18), c=23.771(2) ꢃ, V=8483.1(14) ꢃ3, Z=8, 1calcd =1.261 gcmÀ3
,
m=0.192 mmÀ1
, FACHTUNGTRENNUNG
(000)=3360, T=100(2) K, R1 =0.0546, wR2 =0.0903,
8706 independent reflections [2q ꢀ 52.888] and 541 parameters.
12232
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 12229 – 12233

Reactions of 1-Chloro-2,3,4,5-tetraphenylborole
FULL PAPER
[5] a) P. A. Chase, W. E. Piers, B. O. Patrick, J. Am. Chem. Soc. 2000,
122, 12911–12912; b) S. Yamaguchi, T. Shirasaka, S. Akiyama, K.
Tamao, J. Am. Chem. Soc. 2002, 124, 8816–8817; c) P. A. Chase,
P. E. Romero, W. E. Piers, M. Parvez, B. O. Patrick, Can. J. Chem.
2005, 83, 2098–2105; d) K. S. Thanthiriwatte, S. R. Gwaltney, J.
Phys. Chem. A 2006, 110, 2434–2439; e) A. Wakamiya, K. Mishima,
K. Ekawa, S. Yamaguchi, Chem. Commun. 2008, 579–581.
[6] a) J. J. Eisch, N. K. Hota, S. Kozima, J. Am. Chem. Soc. 1969, 91,
4575–4577; b) G. E. Herberich, B. Buller, B. Hessner, W. Oschmann,
J. Organomet. Chem. 1980, 195, 253–259; c) J. J. Eisch, J. E. Galle,
S. Kozima, J. Am. Chem. Soc. 1986, 108, 379–385.
[11] a) G. E. Herberich, M. Hostalek, R. Laven, R. Boese, Angew. Chem.
1990, 102, 330–331; Angew. Chem. Int. Ed. Engl. 1990, 29, 317–318;
b) G. E. Herberich, T. Wagner, H.-W. Marx, J. Organomet. Chem.
1995, 502, 67–74; c) R. J. Wehmschulte, M. A. Khan, B. Twamley, B.
Schiemenz, Organometallics 2001, 20, 844–849; d) P. E. Romero,
W. E. Piers, S. A. Decker, D. Chau, T. K. Woo, M. Parvez, Organo-
metallics 2003, 22, 1266–1274.
[12] H. Braunschweig, C.-W. Chiu, K. Radacki, T. Kupfer, Angew. Chem.
2010, 122, 2085–2088; Angew. Chem. Int. Ed. 2010, 49, 2041–2044.
[13] W. E. Piers, R. E. von H. Spence, L. R. MacGillivray, M. J. Zaworot-
ko, Acta Crystallogr. Sect. C 1995, 51, 1688–1689.
[7] a) H. Braunschweig, I. Fernꢅndez, G. Frenking, T. Kupfer, Angew.
Chem. 2008, 120, 1977–1980; Angew. Chem. Int. Ed. 2008, 47, 1951–
1954; b) C.-W. So, D. Watanabe, A. Wakamiya, S. Yamaguchi, Orga-
nometallics 2008, 27, 3496–3501; c) C. Fan, W. E. Piers, M. Parvez,
Angew. Chem. 2009, 121, 2999–3002; Angew. Chem. Int. Ed. 2009,
48, 2955–2958; d) J. Kçhler, S. Lindenmaier, I. Fischer, H.
Braunschweig, T. Kupfer, D. Gamon, C.-W. Chiu, J. Raman Spec-
trosc. 2010, 41, 636–641.
[14] W. Fraenk, T. M. Klapçtke, B. Krumm, P. Mayer, H. Nçth, H. Pio-
trowski, M. Suter, J. Fluorine Chem. 2001, 112, 73–81.
[15] C. L. B. Macdonald, J. D. Gorden, A. Voigt, S. Filipponi, A. H.
Cowley, Dalton Trans. 2008, 1161–1176.
[16] G. E. Herberich, B. Buller, B. Hessner, W. Oschmann, J. Organomet.
Chem. 1980, 195, 253–259.
[17] a) G. E. Herberich, J. Rosenplanter, B. Schmidt, U. Englert, Organo-
metallics 1997, 16, 926–931; b) I. Ghesner, W. E. Piers, M. Parvez,
R. McDonald, Chem. Commun. 2005, 2480–2482.
[8] H. Braunschweig, T. Kupfer, Chem. Commun. 2008, 4487–4489.
[9] H. Braunschweig, C.-W. Chiu, K. Radacki, P. Brenner, Chem.
Commun. 2010, 46, 916–918.
[18] C.-W. Chiu, F. P. Gabbaꢆ, Angew. Chem. 2007; 119, 1753–1755;
Angew. Chem. Int. Ed. 2007, 46, 1723–1725.
[10] a) G. E. Herberich, J. Hengesbach, U. Kçlle, W. Oschmann, Angew.
Chem. 1977, 89, 43–44; Angew. Chem. Int. Ed. Engl. 1977, 16, 42–
43; b) G. E. Herberich, B. Hessner, W. Boveleth, H. Luethe, R.
Saive, L. Zelenka, Angew. Chem. 1983, 95, 1024; Angew. Chem. Int.
Ed. Engl. 1983, 22, 996; c) G. E. Herberich, H. Ohst, Chem. Ber.
1985, 118, 4303–4313; d) G. E. Herberich, W. Boveleth, B. Hessner,
M. Hostalek, D. P. J. Kçffer, M. Negele, J. Organomet. Chem. 1987,
319, 311–326.
[19] P. J. Fagan, E. G. Burns, J. C. Calabrese, J. Am. Chem. Soc. 1988,
110, 2979–2981.
[20] G. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112–122.
Received: June 3, 2010
Published online: September 13, 2010
Chem. Eur. J. 2010, 16, 12229 – 12233
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
12233