A spirocyclic borate and a dihydroborate derived from the 1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion [1,2-(1,2-C 2B10H10)Se2]2-: Structures, NMR spectroscopy, and DFT calculations

Article abstract of DOI:10.1002/ejic.201001324

The reaction of the diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion with BF₃-OEt₂ affords selectively a spirocyclic bis(1,2-dicarba-closo-dodecaborane-1,2-diselena)borate, whereas the analogous reaction with boron trichloride leads mainly to 1,2-bis(ethylseleno)-1,2- dicarba-closo-dodecaborane(12) through ether cleavage. The spirocyclic borate reacts with methanol by cleavage of both Se-B and Se-C bonds. With borane in THF (BH₃/THF) and also with LiBH₄ exchange reactions take place, which afford the 1,2-dicarba-closo-dodecaborane-1,2- diselenadihydroborate. The molecular structures of both borates as tetrabutylammonium salts were determined by X-ray analysis. In solution, the borates were characterized by multinuclear magnetic resonance spectroscopy (¹H, ¹¹B, ¹³C, ⁷⁷Se). The gas-phase geometries of the borate anions were optimized [RB3LYP/6-3111+G(d,p) level of theory], and the NMR spectroscopic parameters (chemical shifts and coupling constants) were calculated.

Full text of DOI:10.1002/ejic.201001324

FULL PAPER
DOI: 10.1002/ejic.201001324
A Spirocyclic Borate and a Dihydroborate Derived from the 1,2-Diselenolato-
1,2-dicarba-closo-dodecaborane(12) Dianion [1,2-(1,2-C2B10H10)Se2]2–:
Structures, NMR Spectroscopy, and DFT Calculations
Bernd Wrackmeyer,*[a] Elena V. Klimkina,[a] and Wolfgang Milius[a]
Keywords: Borates / Carboranes / Selenium / NMR spectroscopy / X-ray diffraction
The reaction of the diselenolato-1,2-dicarba-closo-dodeca-
borane(12) dianion with BF3–OEt2 affords selectively a spi-
rocyclic bis(1,2-dicarba-closo-dodecaborane-1,2-diselena)-
borate, whereas the analogous reaction with boron trichlor-
ide leads mainly to 1,2-bis(ethylseleno)-1,2-dicarba-closo-
dodecaborane(12) through ether cleavage. The spirocyclic
borate reacts with methanol by cleavage of both Se–B and
Se–C bonds. With borane in THF (BH3/THF) and also with
LiBH4 exchange reactions take place, which afford the 1,2-
dicarba-closo-dodecaborane-1,2-diselenadihydroborate. The
molecular structures of both borates as tetrabutylammonium
salts were determined by X-ray analysis. In solution, the bor-
ates were characterized by multinuclear magnetic reso-
nance spectroscopy (1H, 11B, 13C, 77Se). The gas-phase geo-
metries of the borate anions were optimized [RB3LYP/
6-3111+G(d,p) level of theory], and the NMR spectroscopic
parameters (chemical shifts and coupling constants) were
calculated.
Introduction
relying on the seemingly more convenient in situ prepara-
tion of the reagent, since this may give rise to side reactions.
In the present work, we report on the treatment of 3
with boron halides such as Et2O–BF3 and boron trichloride
BCl3, with an aim toward the synthesis of boranes, borane
adducts, or borates. Although the latter are well known in
the chemistry of boron–oxygen compounds,[16,17] well-char-
acterized examples for sulfur[18] or selenium[19] are scarce.
The products observed here were characterized by NMR
spectroscopy, in two cases by X-ray structural analysis, and
gas-phase geometries were optimized by DFT methods,
which also served for the calculation of NMR spectroscopic
parameters (chemical shits and spin–spin coupling con-
stants). So far, solely the dimethyl sulfide borane adduct A
has been isolated and structurally characterized,[10] and one
diborate B derived from the 1,2-diselenolato-1,2-dicarba-
A major part of the rich chemistry of 1,2-dicarba-closo-
dodecaborane(12) 1 (“ortho-carborane”)[1,2] results from
metalation [e.g., dilithiation (2)][1–3] followed by various re-
actions of the reactive metal–carbon bond, among which
the insertion of chalcogens is particularly attractive
(Scheme 1). Indeed, the dianions of type 3 have proved to
be valuable ligands in transition-metal chemistry,[4–7] and
their main-group-element chemistry is also a developing
and promising field.[8–14] The selenium derivative 3 is par-
ticularly attractive, since the 77Se nucleus (natural abun-
dance 7.58%; I = ½) possesses favorable NMR spectro-
scopic properties, and thus 77Se NMR spectroscopy is well
suited to monitor reactions and characterize products, even
in mixtures.[15] We have shown that it is advisable for many
purposes to use 3 after careful isolation[10,12,14] instead of
Scheme 1. Dilithiation of ortho-carborane (1) to give 2, and inser-
tion of selenium into the C–Li bonds.
[a] Laboratorium für Anorganische Chemie II, Universität
Bayreuth,
95440 Bayreuth, Germany
Fax: +49-921-552157
E-mail: b.wrack@uni-bayreuth.de
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A Spirocyclic Borate and a Dihydroborate
closo-dodecaborane(12) dianion in 3 has been reported.[8]
The analogous treatment of the lithium salt 3 (in the
Using the sulfur analogue of 3, [1,2-(1,2-C2B10H10)S2]2–, in presence of ether) with BCl3 gave LiCl accompanied by
reactions with boron halides, the formation of a spiroborate ether cleavage and formation of the seleno ether 5
anion {[1,2-(1,2-C2B10H10)S2]2B}– has been proposed (ca. 80%), the ether adduct of the 2-chloro-4,5-[1,2-di-
mainly on the basis of the 11B NMR spectroscopic signal carba-closo-dodecaborano(12)]-1,3-diselena-2-borolane (ca.
(δ11B = 13.4 ppm) of the central tetracoordinate boron 10%),[10] and some unidentified products. The other con-
atom.[9]
ceivable product, the borate anion 4, was not observed.
Some Aspects of the Reactivity of Tetraselenolatoborate 4
Results and Discussion
Recently it was shown that pyridine reacts with 4,5-[1,2-
dicarba-closo-dodecaborano(12)]-1,3-diselenacyclopentane
7 through cage-opening adduct formation followed by de-
Reaction of 3 with BCl3 and with Et2O–BF3
The results for the reactions of 3 with BCl3 and BF3– boronation.[14] Thus, we have studied the reaction of 4a with
OEt2 are summarized in Scheme 2. Treatment of 3 with pyridine in CD2Cl2. There was no reaction of 4a with
BF3–OEt2 afforded selectively the spirocyclic borate 4, and CD2Cl2. However, when pyridine was added to the CD2Cl2
three-coordinate boron compounds were found to be absent solution, a slow reaction took place (Scheme 3). After 2 d at
in the reaction mixture. The borate 4 is stable in the pres- room temperature, the reaction solution contained a mixture
ence of ether, THF, crown ether, and pyridine (py), and was of borate 4d, 1,3-diselenacyclopentane 7, and nido-anion 8.
analyzed by NMR spectroscopy in solution (Table 1, Fig- Since all relevant NMR spectroscopic data of 7 and 8 are
ure 1). It could be converted into the tetrabutylammonium known,[14] the analysis of this mixture was straightforward.
salt 4e, which could be crystallized for X-ray structural Deboronation of one or both carborane cages in anion 4– to
analysis (vide infra).
give novel di- and trianions was not observed.
Scheme 2. Treatment of the dilithio-1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) 3 with Et2O–BF3 and BCl3.
Table 1. 11B, 13C, and 77Se NMR spectroscopic data[a] of the carborane derivatives 4, 5, and 9.
4a[b]
4b
4c
4d
4e
5
9b
9c
9e
CD2Cl2
CD2Cl2
CD2Cl2
CD2Cl2
CD2Cl2
[D8]toluene
CD2Cl2
CD2Cl2
CD2Cl2
δ13C [C(1,2)]
76.3
76.4
76.4
76.3
76.4
76.0
78.6
78.7
78.7
[9.3] [158.0]
Et2O:
14.8 (CH3),
67.0 (CH2O)
[9.4] [158.2] [157.7]
12-crown-4: py:
[9.9] [158.1]
NBu4:
[163.7]
13.6 [17.6] (CH3),
26.0 [65.2] (CH2)
[158.6]
THF:
25.8, 69.0
[157.5]
12-crown-4:
67.1
Other δ13C
data
THF:
25.9 (CH2),
69.0 (CH2O)
NBu4:
13.7, 20.1,
24.3,
67.8
125.2 (Cβ), 13.7, 20.1,
138.2 (Cγ), 24.3,
149.5 (Cα) 59.4 {2.4}
59.4 {2.6 Hz}
–9.2
392.9,
δ11B (BSe)
δ77Se
6.0 (56.5)
477.2 (57.5)
6.0 (57.8)
478.4 (61.0)
6.2 (60.2)
6.0 (56.5)
6.0 (57.5)
–
–9.3
396.3 (35),
–9.2
392.4,
478.4 (60.4) 477.5 (57.0) 477.5 (58.0)[c] 492.8 [163.7][d],
h
½
= 7 Hz
h
= 110 Hz
h
= 105 Hz
h = 80 Hz
½
½
½
δ77Se (calcd.) 500.7 (–81.8) [–191.5]
460.2 (–47.2) [–192.6]
[a] Coupling constants nJ(77Se,13C) are given in square brackets [Ϯ0.5 Hz]; 1J(77Se,11B) in parentheses (Ϯ0.5 Hz); 1J(14N,13C) in curly
1
brackets; isotope-induced chemical shifts Δ are given in ppb, and the negative sign denotes a shift of the NMR spectroscopic signal of
the heavy isotopomer to lower frequency. [b] δ = 7Li: –0.33 (h = 8 Hz). [c] 1Δ10/11B(77Se): (–280Ϯ20) ppb. [d] 1Δ12/13C(1,2)(77Se):
½
(–305Ϯ5) ppb.
Eur. J. Inorg. Chem. 2011, 2164–2171
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B. Wrackmeyer, E. V. Klimkina, W. Milius
FULL PAPER
Figure 1. Tetrabutylammonium bis(1,2-dicarba-closo-dodecaborane-1,2-diselena)borate 4e: (A) 128.3 MHz 11B NMR spectra. The 77Se
satellites that correspond to 1J(77Se,11B) are marked by arrows. (B) 76.2 MHz 77Se NMR spectrum of 4e (in CD2Cl2, at 23 °C). (C)
n
125.8 MHz 13C{1H} NMR spectrum of 4e (in CD2Cl2, at 23 °C). The 77Se satellites for J(77Se,13C) are marked by asterisks.
Treatment of 4a with methanol (Scheme 4) proceeded ex-
pectedly to give B(OMe)3 along with diselenol 6[10] and the
parent ortho-carborane 1. The formation of 1 indicates that
cleavage of the B–Se bonds leading to 6 is accompanied by
cleavage of the C–Se bonds as well.
Exchange reactions took place (Scheme 4) when 4a re-
acted with borane in THF (BH3/THF). In the reaction
solution, only borate 9b could be identified by its NMR
spectroscopic data (Table 1). To confirm this result, another
route[18a] was followed towards the same borate 9b. Thus,
9b was formed along with 7 (R = D) when a solution of 4a
in CD2Cl2 was treated with LiBH4 in THF. Borate 9b ap-
pears to be surprisingly stable in THF or in CD2Cl2 (only
Scheme 3. Reaction of tetraselenolatoborate 4a with pyridine in
CD2Cl2.
Scheme 4. Some reactions of 4a {4–[Li+(2Et2O)]} with MeOH, BH3/THF, and LiBH4.
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Eur. J. Inorg. Chem. 2011, 2164–2171

A Spirocyclic Borate and a Dihydroborate
Scheme 5. Treatment of the tetrabutylammonium salt 4e with LiBH4 in CD2Cl2/THF followed by 12-crown-4-induced D/H exchange in
7 (R = D) to give 7 (R = H).
after 2 d at room temperature does decomposition become
The analogous NMR spectroscopic study of the dihy-
reveals smaller coupling constant
noticeable). In contrast, lithium dihydrido-1,3,2-benzenethi- droborate
9
a
olatoborate disproportionates in THF/toluene solution to 1J(77Se,11B). The corresponding splitting in the 77Se NMR
give LiBH4, and the spirocyclic lithium bis(benzene-1,2-di- spectrum (Figure 2) is much less well resolved relative to 4.
thiolato)borate.[18a] Treatment of this mixture [9b and 7 (R This can be traced to the smaller magnitude of J(77Se,11B)
1
= D)], which still contained LiBH4 in an excess amount, in 9 and faster 11B nuclear spin relaxation on account of
with crown ether (12-crown-4) caused selective D/H ex- the reduced symmetry around the quadrupolar 11B nucleus.
change[20] to give 7 as the CH2 derivative. Under the experi- The 11B(BH2) NMR spectroscopic signal (δ11B = –9.2 ppm)
mental conditions, the C(H)D derivative was not observed. of 9, hidden underneath of the 11B(carborane) NMR spec-
When the reaction of 4e with LiBH4 was carried out in troscopic signals, was located by selective 1H{11B}, selective
THF together with CD2Cl2 and 12-crown-4 (Scheme 5), 11B{1H}, as well as by observing the J-modulated 11B{1H}
borate 9e was formed along with 7 as the CD2 and CH2 NMR spectrum to make use of the opposite phases of 11BH
derivative, and the tetrabutylammonium salt 9e was isolated and 11BH2 NMR spectroscopic signals.
and characterized by X-ray diffraction (vide infra).
NMR Spectroscopy
Expectedly, the 11B{1H} NMR spectrum of 4– (Fig-
ure 1A) shows four signals for the carborane cage, thereby
indicating fast inversion of both nonplanar five-membered
C2Se2B rings. The assignment is based on relative intensities
1
and selective H{11B} decoupling experiments together with
calculations of chemical shifts (vide infra). In addition, there
is one sharp signal for the tetracoordinate central boron
atom surrounded by four selenium atoms. Indeed, the 77Se
satellites observed here represent the first example of a
nicely resolved splitting due to one-bond 77Se–11B spin–spin
coupling in 11B NMR spectra. This is confirmed by the 77Se
NMR spectrum, which shows a single resonance split into
Figure 2. The 47.7 MHz 77Se{1H} NMR spectrum of 9b (in
CD2Cl2, at 23 °C).
four lines on account of 1J(77Se,11B) (Figure 1, B). The
somewhat distorted shape of the quartet can be traced to
the still rapid nuclear spin relaxation rate of the quadrupolar
DFT Calculations of Molecular Geometries, Chemical
11B nucleus, which causes a shortening of the scalar relax-
Shifts δ11B and δ77Se, and Coupling Constants
ation time T2SC(77Se) (scalar relaxation of the second
kind[21]). This causes the decrease in the intensities of the
The molecular structures of the anions 4 and 9 were opti-
outer lines of the quartet. Another noticeable feature in Fig- mized at the B3LYP/6-311+G(d,p) level of theory. The ex-
ure 1 (B) is a hump underneath of the quartet that is shifted perimental data for 4 and 9 (as the NBu4+ salts) were repro-
to higher frequencies with respect to the center of the quar- duced, shown, for example, by the four different surround-
tet. This hump results from unresolved splitting due to one- ings of the selenium atoms in 4 on account of the nonplanar
bond 77Se–10B spin–spin coupling accompanied by an iso- C2Se2B rings. It appears that the calculated Se–B bond
tope induced chemical shift 1Δ10/11B(77Se) of around lengths are slightly too long when compared with the exper-
–300 ppb. Finally, the 13C{1H} NMR spectrum (Figure 1, imental data. The calculated nuclear shieldings agree satis-
C) shows just one signal for the carborane carbon atoms, factorily with the experimental data (Table 2) for the
accompanied by the 77Se satellites, in addition to the 11B(carborane) nuclei,[22] whereas the calculations under-
13C(Bu) NMR spectroscopic signals of the [NBu4]+ ion.
estimate the shielding of the 11B(borate) nuclei in both 4
Eur. J. Inorg. Chem. 2011, 2164–2171
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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B. Wrackmeyer, E. V. Klimkina, W. Milius
FULL PAPER
and 9 when compared with experimental data. This devia- pared in Table 3. There are no examples of this type of sur-
tion increases with the number of selenium atoms attached roundings of the boron atom in molecular chemistry. Some
to boron. Similarly, the calculated shielding of the 77Se nu- examples with BSe4 structures are known from solid-state
clei in both 4 and 9 is slightly too low (Table 1), although chemistry.[19] The structural data (Table 3) of the carborane
1
the trend is correctly predicted. The calculated J(77Se,11B) moiety and of the C2Se2B rings are similar to those found
coupling constants are numerically larger than the experi- previously for A[10] and they are similar to those reported
mental values. This is the same trend as found for for B, although the standard deviations in the latter are
1
1
1J(77Se,13C).[23] For both J(77Se,11B) and J(77Se,13C), the fairly large.[8] To the best of our knowledge, the borate
calculations predict a negative sign which, in the case of anion 9 is the first example of this type of borate that has
1J(77Se,13C), is in agreement with experimentally deter- been structurally characterized.
mined signs.[15]
Table 2. 11B{1H} NMR spectroscopic data of the carborane deriva-
tives 4e, 4 (calcd.), 9e, and 9 (calcd.).
4e
CD2Cl2
4 (calcd.)
9e
CD2Cl2
9 (calcd.)
B(3,6)
B(4,5,7,11) –9.2
–3.0
–7.0, –1.7, –7.5, –1.6
–9.4, –12.1, –9.2, –11.3, –9.2
–9.1, –11.5, –12.3, –9.2
–9.6, –7.9, –9.9, –7.9
–7.8, –7.5, –7.7, –7.3
33.3
–3.9
–10.4, 0.2
–8.1, –11.8,
–8.1, –11.8
–10.6, –7.9
–9.4, –9.4
–1.8
B(8,10)
B(9,12)
B(13)
–7.3
–6.6
6.0
–7.4
Figure 4. ORTEP plot (50% probabilities; hydrogen atoms, except
for SeBH2, are omitted for clarity) of the molecular structure of
the tetrabutylammonium 1,2-dicarba-closo-dodecaborane-1,2-dis-
elenaborate (9e) (tetrabutylammonium cation is omitted for clar-
ity). For selected distances and angles, see Table 3.
–9.2
X-ray Structural Analyses of the ortho-Carborane
Derivatives 4e and 9e
Table 3. Selected bond lengths [pm] and angles [°] of 4e, 4 (calcd.),
9e, and 9 (calcd.).
To gain structural information on the “free” borate
anions, the tetrabutylammonium salts 4e and 9e were crys-
tallized and studied by X-ray diffraction. The molecular
structure of the borate anions 4 and 9 (Figures 3 and 4)
show the tetrahedral environments of the central boron
atoms. The five-membered C2Se2B rings in the spirocyclic
system 4 as well as in 9 deviate from planarity (Figure 3, B;
Figure 4). This causes different surroundings for the four
selenium atoms in 4 and a slight deviation from ideal tetra-
hedral environments at the boron atom. The experimental
and calculated structural parameters for 4 and 9 are com-
4e
4 (calcd.) 9e
T = 133 K
9 (calcd.)
T = 133 K
C(1)–Se(1)
C(2)–Se(2)
C(3)–Se(3)
C(4)–Se(4)
193.1(5)
193.5(5)
192.5(5)
192.6(5)
195.6
195.8
195.8
195.5
193.6(3)
194.4(3)
195.9
195.9
C(1)–C(2)
C(3)–C(4)
165.2(7)
166.8(7)
165.7
165.4
167.8(4)
168.0
Se(1)–B(13)
Se(2)–B(13)
Se(3)–B(13)
Se(4)–B(13)
205.6(6)
205.9(6)
205.3(6)
207.3(6)
209.4
208.4
208.2
209.5
208.0(4)
208.1(4)
210.9
210.9
Se(1)–B(13)–Se(2)
Se(1)–B(13)–Se(3)
Se(1)–B(13)–Se(4)
Se(2)–B(13)–Se(3)
Se(2)–B(13)–Se(4)
Se(3)–B(13)–Se(4)
107.9(3)
106.4(3)
109.3(3)
109.8(3)
115.9(3)
107.3(3)
107.0
109.0
116.0
107.5
109.7
107.4
103.60(17) 104.8
B(13)–Se(1)–C(1)
B(13)–Se(2)–C(2)
B(13)–Se(3)–C(3)
B(13)–Se(4)–C(4)
97.1(2)
97.4(2)
97.7(2)
97.6(2)
97.5
97.5
97.9
97.8
95.23(15)
95.22(15)
95.5
95.5
Se(1)–C(1)–C(2)
Se(2)–C(2)–C(1)
Se(3)–C(3)–C(4)
Se(4)–C(4)–C(3)
116.1(3)
115.3(3)
115.6(3)
115.3(3)
115.6
115.9
116.1
115.8
114.7(2)
113.8(2)
115.1
115.1
Se(1)–C(1)–C(2)–Se(2)
Se(3)–C(3)–C(4)–Se(4)
0
0
0.9
Distance of B(13) from the plane
Figure 3. ORTEP plot (40% probabilities; hydrogen atoms are
omitted for clarity) of the molecular structure of the tetrabutylam-
monium bis(1,2-dicarba-closo-dodecaborane-1,2-diselena)borate
(4e) (tetrabutylammonium cation and toluene are omitted for clar-
ity). For selected distances and angles, see Table 3.
Se(1)–C(1)–C(2)–Se(2)
Se(3)–C(3)–C(4)–Se(4)
53.5
54.3
87.4
Plane C(1)–C(2)–B(13) to
plane C(3)–C(4)–B(13) [°]
90.2
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A Spirocyclic Borate and a Dihydroborate
Lithium Bis(1,2-dicarba-closo-dodecaborane-1,2-diselena)borate (4)
Conclusion
4[Li(2Et2O)] (4a): Freshly prepared [(1,2-C2B10H10)Se2Li2](Et2O)
(3; 1065 mg, 2.82 mmol) was dissolved in toluene (20 mL). The
solution was cooled to –30 °C, and BF3–OEt2 (0.35 mL;
2.84 mmol) was injected slowly (30 min) through a syringe, then
Et2O (0.5 mL) was added. The reaction mixture was stirred at room
temp. for 20 h. Volatile materials were removed in vacuo, and the
remaining solid was dissolved in toluene (5 mL). The formation of
an oily phase and a white precipitate (LiF) was observed, and the
supernatant liquid was decanted. The remaining oil was separated
from the white solid, washed with toluene (5 mL), and dried in
vacuo to give 563 mg (52%) of 4a as a white powder. Compound
4a: 1H{11B} NMR (399.8 MHz, CD2Cl2, 25 °C): δ = 1.31 [t,
3J(H,H) = 7.1 Hz, 12 H, CH3 from Et2O], 2.06 [br. s, 4 H, HB(9,12)
for δ(11B) = –6.6], 2.19 [br. s, 4 H, HB(8,10) for δ(11B) = –7.3], 2.35
(s, CH3 toluene), 2.44 [br. s, 8 H, HB(4,5,7,11) for δ(11B) = –9.2],
2.74 [br. s, 4 H, HB(3,6) for δ(11B) = –3.0], 3.75 [q, 3J(H,H) =
7.1 Hz, 8 H, OCH2 from Et2O], 7.19 (m, Ar from toluene) ppm.
11B{1H} NMR (160.5 MHz, CD2Cl2; 25 °C): δ = –9.2 [8 B,
B(4,5,7,11)], –7.3 [4 B, B(8,10)], –6.6 [4 B, B(9,12)], –3.0 [4 B,
B(3,6)], 6.0 [1J(77Se,11B) = 56.5 Hz, 1 B, BSe4) ppm. 11B NMR
(160.5 MHz, CD2Cl2; 25 °C): δ = –9.2 [d, J = 160 Hz, 8 B,
B(4,5,7,11)], –7.3 [d, J = 140 Hz, 4 B, B(8,10)], –6.6 [d, 4 B,
B(9,12)], –3.0 [d, J = 160 Hz, 4 B, B(3,6)], 6.0 [s, 1J(77Se,11B) =
56.5 Hz, 1 B, BSe4) ppm.
The spirocyclic bis(1,2-dicarba-closo-dodecaborane-1,2-
diselena)borate 4 is readily accessible from the treatment of
the diselenolato-1,2-dicarba-closo-dodecaborane(12) di-
anion 3 with BF3–OEt2. The borate 4 can be handled as a
solid and is stable in various polar and nonpolar solvents.
It undergoes decomposition with methanol and exchange
reactions with borane in THF (BH3/THF) and also with
LiBH4. These exchange reactions afford the 1,2-dicarba-
closo-dodecaborane-1,2-diselenadihydroborate 9, which ap-
pears to be stable towards disproportionation reactions.
Both borates 4 and 9 were characterized by multinuclear
magnetic resonance methods in solution, thereby establish-
ing 77Se NMR spectroscopy as a useful tool in boron–sele-
nium chemistry, and as tetrabutylammonium salts by X-ray
diffraction in the solid state.
Experimental Section
General: All syntheses and the handling of the samples were carried
out by observing necessary precautions to exclude traces of air and
moisture. Carefully dried solvents and oven-dried glassware were
used throughout. The CD2Cl2 was distilled from CaH2 under an
atmosphere of argon. All other solvents were distilled from Na
metal under an atmosphere of argon. [(1,2-C2B10H10)Se2Li2]-
(Et2O)[12] was prepared according to the published procedure.
Other starting materials were purchased from Aldrich [butyllithium
(1.6 m in hexane), BCl3 (1.0 m in toluene), BF3–OEt2 (purified by
redistillation), pyridine (anhydrous, 99.8%), LiBH4 (Ն95.0%), 12-
crown-4 (98%)], Fluka [selenium metal “gray,” Bu4NCl (Ͼ97%)],
and KatChem. (ortho-carborane 1), and used as received. NMR
spectroscopic measurements were carried out with the following
4[Li(3THF)] (4b) and 4[Li(12-crown-4)] (4c): A solution of 4a
(50 mg, 0.065 mmol) in CD2Cl2 (1.0 mL) was cooled to 0 °C, and
THF (1.0 mmol) or 12-crown-4 (0.08 mmol) was added. The for-
mation of a yellow solution was observed. Volatile materials were
removed in vacuo, the remaining solid was dissolved in [D8]toluene
(1 mL), during which a layer of oil formed at the bottom. The
liquid phase was separated by centrifugation, and the residue at the
bottom was dried in vacuo to leave a yellow oil of 4b (or 4c).
Compound 4b: 1H{11B} NMR (250.1 MHz, CD2Cl2; 25 °C): δ =
1.97 (m, 12 H, CH2 from THF), 2.02 [br. s, 4 H, HB(9,12) for
δ(11B) = –7.3], 2.16 [br. s, 4 H, HB(8,10) for δ(11B) = –7.3], 2.42
[br. s, 8 H, HB(4,5,7,11) for δ(11B) = –9.3], 2.72 [br. s, 4 H, HB(3,6)
for δ(11B) = –2.8], 3.78 (t, 12 H, OCH2 from THF) ppm. 11B{1H}
NMR (80.3 MHz, CD2Cl2; 25 °C): δ = –9.3 [8 B, B(4,5,7,11)], –7.3
[8 B, B(8,10), B(9,12)], –2.8 [4 B, B(3,6)], 6.0 [1J(77Se,11B) =
57.8 Hz, 1B, BSe4] ppm.
1
devices: Bruker DRX 500 and Bruker ARX 250: H, 11B, 13C, and
77Se NMR; Varian INOVA 400: 1H, 11B, 13C, 77Se NMR. Chemical
shifts are given relative to Me4Si [δ1H (CHDCl2)
=
5.33,
53.8,
(C6D5CD2H)
= =
(2.08Ϯ0.01) ppm; δ13C (CD2Cl2)
(C6D5CD3)
=
(20.4Ϯ0.1) ppm]; external BF3–OEt2 [δ11B
=
(0Ϯ0.3) ppm for Ξ(11B) = 32.083971 MHz], neat Me2Se [δ77Se =
(0Ϯ0.1) ppm for Ξ(77Se) = 19.071523 MHz]. Assignments of 1H
and 11B NMR spectroscopic signals are based on selective 1H{11B}
heteronuclear decoupling experiments. IR spectra were determined
with a Perkin–Elmer Spectrum 2000 FTIR. Melting points (uncor-
rected) were determined with a Büchi 510 melting point apparatus.
Elemental analyses [C(H)] of the borates 4 did not give reproduc-
ible results, most likely on account of boron carbide formation and
the slightly varying amount of solvent coordinated to the Li+ cat-
ion.
Compound 4c: 1H{11B} NMR (250.1 MHz, CD2Cl2; 25 °C): δ =
2.16 [br. s, 4 H, HB(9,12) for δ(11B) = –7.1], 2.29 [br. s, 4 H,
HB(8,10) for δ(11B) = –7.1], 2.54 [br. s, 8 H, HB(4,5,7,11) for δ(11B)
= –9.1], 2.85 [br. s, 4 H, HB(3,6) for δ(11B) = –2.9], 3.68 (s, approx.
20 H CH2 from 12-crown-4 in slight excess amount) ppm. 11B{1H}
NMR (80.3 MHz, CD2Cl2; 25 °C): δ = –9.1 [8 B, B(4,5,7,11)], –7.1
[8 B, B(8,10), B(9,12)], –2.9 [4 B, B(3,6)], 6.2 [1J(77Se,11B) =
60.2 Hz, 1 B, BSe4] ppm.
4[Li(npy)] (4d): A solution of 4a (50 mg, 0.065 mmol) in CD2Cl2
(1.0 mL) was cooled to 0 °C and pyridine (1 mL) was added in
excess amount. The formation of a yellow solution was observed.
After 2 d at room temp., volatile materials were removed in vacuo
to leave an orange-red residue that contained 4d (50%), 7 (25%),
and 8 (25%) (1H and 11B NMR spectroscopy). Compound 4d:
1H{11B} NMR (399.8 MHz, CD2Cl2; 25 °C): δ = 2.04 [br. s, 4 H,
All quantum chemical calculations were carried out with the
Gaussian 03 program package (Revision B.02).[24] Optimized gas-
phase geometries at the B3LYP/6-311+g(d,p) level of theory were
found to be minima by the absence of imaginary frequencies. NMR
spectroscopic parameters (nuclear magnetic shielding by the gauge
including atomic orbitals (GIAO) method,[25] and spin–spin cou-
pling constants[26]) were calculated at the same level of theory. Cal-
culated nuclear shieldings σ11B and σ77Se were converted by δ11B
(calcd.) = σ(11B) – σ(11B, B2H6), with σ(11B, B2H6) = +84.1 [δ11B
(B2H6) = 18 and δ11B (BF3–OEt2) = 0], and δ77Se (calcd.) =
σ(77Se) – σ(77Se, SeMe2) with σ(77Se, SeMe2) = +1621.7.
HB(9,12)], 2.17 [br. s,
4 H, HB(8,10)], 2.42 [br. s, 8 H,
HB(4,5,7,11)], 2.73 [br. s, 4 H, HB(3,6)], 7.43 (m, Hβ-py), 7.86 (m,
Hγ-py), 8.49 (m, Hα-py) ppm. 11B{1H} NMR (128.3 MHz, CD2Cl2;
25 °C): δ = –20–0 (overlapping signals for 4d, 7, and 8), 6.0
[1J(77Se,11B) = 56.5 Hz, 1 B, BSe4] ppm.
Eur. J. Inorg. Chem. 2011, 2164–2171
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2169

B. Wrackmeyer, E. V. Klimkina, W. Milius
FULL PAPER
Tetrabutylammonium Bis(1,2-dicarba-closo-dodecaborane-1,2-dis-
the reaction was monitored by 11B NMR spectroscopy. After 24 h
elena)borate (4e): A solution of 4a (100 mg, 0.13 mmol) in CD2Cl2 at room temp., volatile materials were removed in vacuo, the re-
(1.5 mL) was cooled to 0 °C, and degassed Bu4NCl (50 mg,
0.18 mmol) was added. After stirring the reaction mixture for 1 h
at room temp., insoluble materials (LiCl) were separated by centri-
fugation, and the clear liquid was collected. Volatile materials were
removed in vacuo to give a yellow solid. This solid was washed
with [D8]toluene (1 mL) and Et2O (1 mL), and dried in vacuo to
give 4e as a yellow crystalline solid. Single transparent crystals of
maining mixture was dissolved in CD2Cl2 (1 mL), and the liquid
phase was separated by centrifugation. The mixture contained 9b
(80%), 7 (R = D) (20%),[14] and LiBH4. Then 12-crown-4
(0.016 mL, 0.10 mmol) was added to this reaction mixture. Volatile
materials were removed in vacuo, the remaining mixture was dis-
solved in [D8]toluene (1 mL), and the liquid phase was separated
by centrifugation. The remaining oil at the bottom was dried in
vacuo to leave an orange-red residue. After 2 d in CD2Cl2 at room
4e for X-ray analysis were grown from CD2Cl2/[D8]toluene (5:1)
1
solution after 2 d at –30 °C; m.p. 185–190 °C (decomp.). H{11B} temp., the mixture contained 9c (90%), 7 (R = H) (10%),[14] and
3
NMR (399.8 MHz, CD2Cl2; 25 °C): δ = 1.02 [t, J(H,H) = 7.2 Hz, LiBH4.
12 H, CH3 from Bu], 1.43 [sextet, 3J(H,H) = 7.2 Hz, 8 H, CH2
9[Li(nTHF)] (9b): 1H{11B} NMR (399.8 MHz, CD2Cl2; 25 °C): δ
from Bu], 1.61 (m, 8 H, CH2 from Bu), 2.05 [br. s, 4 H, HB(9,12)
= 1.91 (m, CH2 from THF, BH), 2.33 (br. s, 2 H, BH), 2.42 (br. s,
for δ(11B) = –6.6], 2.18 [br. s, 4 H, HB(8,10) for δ(11B) = –7.3], 2.43
4 H, BH), 2.80 (br. s, 2 H, BH), 3.54 (br. s, 2 H, SeBH2), 3.80 (m,
[br. s, 8 H, HB(4,5,7,11) for δ(11B) = –9.2], 2.74 [br. s, 4 H, HB(3,6)
CH2 from THF) ppm. 11B{1H} NMR (128.3 MHz, CD2Cl2;
for δ(11B) = –3.0], 3.18 (m, 8 H, NCH2) ppm. 11B{1H} NMR
25 °C): δ = –9.3 (5B, BSe2), –7.5 [4B, B(8,10), B(9,12)], –3.8 [2B,
(160.5 MHz, CD2Cl2; 25 °C): δ = –9.2 [8 B, B(4,5,7,11)], –7.3 [4 B,
B(3,6)] ppm. 11B NMR (128.3 MHz, CD2Cl2; 25 °C): δ = –9.3 [5B,
B(8,10)], –6.6 [4 B, B(9,12)], –3.0 [4 B, B(3,6)], 6.0 [1J(77Se,11B) =
B(4,5,7,11), BSe2], –7.5 [d, J = 150 Hz, 4B, B(8,10), B(9,12)], –3.8
[d, J = 175 Hz, 2B, B(3,6)] ppm.
9[Li(n12-crown-4)] (9c): 1H{11B} NMR (399.8 MHz, CD2Cl2;
25 °C): δ = 2.03 (br. s, 2 H, BH), 2.07 (br. s, 2 H, BH), 2.43 (br. s,
4 H, BH), 2.81 (br. s, 2 H, BH), 3.56 (br. s, 2 H, SeBH2), 3.78 (s,
CH2 from 12-crown-4) ppm. 11B{1H} NMR (128.3 MHz, CD2Cl2;
57.5 Hz, 1 B, BSe4] ppm. 11B NMR (160.5 MHz, CD2Cl2; 25 °C):
δ = –9.2 [d, J = 170 Hz, 8 B, B(4,5,7,11)], –7.3 [d, J = 145 Hz, 4 B,
B(8,10)], –6.6 [d, 4 B, B(9,12)], –3.0 [d, J = 185 Hz, 4 B, B(3,6)],
1
6.0 [s, J(77Se,11B) = 57.5 Hz, 1 B, BSe4] ppm.
1,2-Bis(ethylseleno)-1,2-dicarba-closo-dodecaborane(12) (5): Freshly
prepared 3 (990 mg, 2.55 mmol) was taken up in toluene (30 mL);
the solution was cooled to –40 °C, and BCl3 (2.55 mL of a 1.0 m
solution in toluene; 2.55 mmol) was injected slowly through a sy-
ringe. After stirring the reaction mixture for 18 h at room temp.,
insoluble materials were separated by centrifugation, and the clear
yellowish liquid was collected. Volatile materials were removed in
vacuo to leave a yellowish oil that contained about 80% of 5 along
with the ether adduct of the 2-chloro-1,2,3-diselenoborolane (10%)
and some unidentified products (1H and 13C NMR spectroscopy).
Compound 5: 1H{11B} NMR (399.8 MHz; [D8]toluene; 25 °C): δ
25 °C): δ = –9.2 (5 B), –7.5 (4 B), –3.9 (2 B) ppm. IR (CD Cl ): ν
˜
2
2
= (B–H) = 2198, 2303 (BH2), 2588 (br) (BH for o-carborane) cm–1.
Treatment of 4e with LiBH4, CD2Cl2, and 12-crown-4: A solution
of 4e (50 mg, 0.059 mmol) in CD2Cl2 (1.5 mL) was cooled to 0 °C
and added to degassed LiBH4 (approx. 2 mg, 0.09 mmol). Then 12-
crown-4 (0.016 mL, 0.10 mmol) was added to this reaction mixture.
The progress of the reaction was monitored by 11B NMR spec-
troscopy. After 12 h at room temp., the mixture contained tetrabu-
tylammonium 1,2-dicarba-closo-dodecaborane-1,2-diselenaborate
(9e) (70%), 7 (R = D, H) (30%), LiBH4, and 12-crown-4. Single
transparent crystals of 9e were grown from CD2Cl2/[D8]toluene
(1:1) solution after 5 d at –30 °C; m.p. 95–100 °C (decomp.). Com-
pound 9e: 1H{11B} NMR (399.8 MHz, CD2Cl2; 25 °C): δ = 1.02
3
= 1.00 [t, J(H,H) = 7.7 Hz, 6 H, 2 CH3 from Et], 2.25 (br. s, 2 H,
3
HB for δ11B = –10.3), 2.56 [q, J(H,H) = 7.7 Hz, 4 H, 2 CH2 from
Et], 2.74 (br. s, 6 H, HB for δ11B = –8.3), 2.89 (br. s, 2 H, HB for
δ11B = –2.4) ppm. 11B{1H} NMR (128.3 MHz; [D8]toluene; 25 °C):
δ = –10.3 (2 B), –8.3 (6 B), –2.4 (2 B) ppm.
Ether Adduct of 2-Chloro-4,5-[1,2-dicarba-closo-dodecaborano(12)]-
1,3-diselena-2-borolane: 77Se NMR (76.2 MHz; [D8]toluene; 25 °C):
δ = 469.0 (br.) ppm. 13C{1H} NMR (125.8 MHz; [D8]toluene;
25 °C): δ = 16.0 (CH3 from Et2O), 70.8 (CH2 from Et2O), 73.4
[C(1,2)] ppm.
Table 4. Crystallographic data of the carborane derivatives 4e and
9e.[a]
4e
9e
Formula
Crystal
C20H56B21NSe4·0.5toluene C18H48B11NSe2
yellowish prism
0.24ϫ0.15ϫ0.16
monoclinic
P21/n
colorless prism
0.24ϫ0.18ϫ0.15
monoclinic
P21/n
Dimensions [mm3]
Crystal system
Space group
a [pm]
Treatment of 4a with MeOH: A solution of 4a (50 mg, 0.065 mmol)
in CD2Cl2 (1.5 mL) was cooled to 0 °C, and MeOH (1 mL) was
added. The progress of the reaction was monitored by 11B NMR
spectroscopy. After 24 h at room temp., the mixture contained 4a
(50%), 6 (30%),[10] 1 (20%), and B(OMe)3. After 2 h at 60 °C, the
mixture contained 6 (20%), 1 (80%), and B(OMe)3 (1H, 11B, 13C
NMR spectroscopy).
1129.6(2)
1904.9(4)
2005.1(4)
97.94(3)
4
1101.8(2)
2157.3(4)
1228.4(3)
100.38(3)
4
b [pm]
c [pm]
β [°]
Z
Treatment of 4a with BH3/THF:
A
solution of 4a (50 mg,
Abs. coeff. μ [mm–1
Measuring range (θ) [°]
Reflections collected
Independent reflections
[IՆ2σ(I)]
]
3.454
1.48–25.77
51076
2.583
1.89–25.66
37953
0.065 mmol) in CD2Cl2 (1.5 mL) was cooled to 0 °C, and BH3–
THF (0.2 mL of a 1.0 m solution in THF, 0.2 mmol) was added.
The progress of the reaction was monitored by 11B NMR spec-
troscopy. After 12 h at room temp., the mixture contained
lithium 1,2-dicarba-closo-dodecaborane-1,2-diselenaborate {9b;
9[Li(nTHF)]} together with B(OBu)3.
6653
4091
Refined parameters
wR2/R1 [IՆ2σ(I)]
435
0.128/0.058
289
0.103/0.040
0.619/–0.730
Max./min. resid. electron 1.185/–0.491
density [epm–3 ϫ10–6
]
Treatment of 4a with LiBH4, CD2Cl2, and 12-crown-4: A solution
of 4a (50 mg, 0.065 mmol) in CD2Cl2 (1.5 mL) was cooled to 0 °C
and added to degassed LiBH4 (approx. 2 mg, 0.09 mmol). Then
THF (0.3 mL) was added to this reaction mixture. The progress of
[a] No absorption corrections were carried out because they did
not improve the parameter set. In both cases, the temperature was
133(2) K.
2170
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2164–2171

A Spirocyclic Borate and a Dihydroborate
3
3
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[t, J(H,H) = 7.2 Hz, 12 H, CH3 from Bu], 1.43 [sextet, J(H,H) =
7.2 Hz, 8 H, CH2 from Bu], 1.61 (m, 8 H, CH2 from Bu), 2.03 (br.
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Crystal Structure Determination of Complexes 4e and 9e: Details
pertinent to the crystal structure determinations are listed in
Table 4. Crystals of appropriate size were sealed under an atmo-
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Received: December 17, 2010
Published Online: March 28, 2011
Eur. J. Inorg. Chem. 2011, 2164–2171
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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