One-pot synthesis of 1,6-diiodo-2,3,4,5-tetracarba-nido-hexaboranes(6) and mechanistic studies on the reaction system alkynes/BI3/NaK 2.8

Article abstract of DOI:10.1002/ejic.200300704

Attempts to prepare the tetracarba-nido-octaborane(8) derivative (EtC) ₄(BI)₄ (4) by treatment of 3-hexyne with BI₃ (2 equiv.) and NaK_2.8 led to 2,3,4,5-tetraethyl-1,6-diiodo-2,3,4,5- tetracarba-nido-hexaborane(6) (2a) as the predominant product with trace quantities of 4 as well as 2,3-diethyl-1,4,5,6,7-pentaiodo-2,3-dicarba-closo- heptaborane(7) (5). Starting at -78 °C, reactions of 3-hexyne, 2-butyne or diphenylacetylene, respectively, with BI₃ (1 equiv.) and NaK _2.8 afforded the corresponding 1,6-diiodo-2,3,4,5-tetracarbanido- hexaboranes(6) 2a-c as the single carborane products. In the cases of 3-hexyne and diphenylacetylene, the formation of hexaorganylbenzene derivatives was also detected. To confirm the formation of 4 and 5, the independent dehalogenation of cis-3,4-bis(diiodoboryl)-3-hexene (3) with NaK_2.8 has been studied, which indeed affords 4 and 5, with the former being the predominant product. A mechanism for the formation of 2a has been proposed, which involves iodoboration of the alkyne to give the borylalkene 1a. This is followed by deiodination, presumably yielding the iodoborirene derivative 7, which easily dimerizes to form the 1,4-diboracyclo-2,5-hexadiene derivative 8. Subsequent rearrangement leads to the final C₄B₂-nido-carborane 2a. To determine the stereochemistry of 1a, its pyridine adduct 9 (and the isomer 9′) and catechol derivative 10 (and the isomer 10′), and the diisopropylamino derivative 11 have also been prepared. The new compounds have been characterized by MS and NMR spectroscopy, and the structures of 2a, 3, 9 and 9′ were confirmed by single-crystal X-ray analyses. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300704

FULL PAPER
One-Pot Synthesis of 1,6-Diiodo-2,3,4,5-tetracarba-nido-hexaboranes(6) and
Mechanistic Studies on the Reaction System Alkynes/BI3/NaK2.8
Yong Nie,[a] Stefan Schwiegk,[a] Hans Pritzkow,[a] and Walter Siebert*[a]
´
Dedicated to Professor Jose Vicente on the occasion of his 60th birthday
Keywords: Boron / Boranes / Carboranes / Heterocycles / Iodine bridges
Attempts to prepare the tetracarba-nido-octaborane(8) deriv- former being the predominant product. A mechanism for the
ative (EtC)4(BI)4 (4) by treatment of 3-hexyne with BI3 (2
equiv.) and NaK2.8 led to 2,3,4,5-tetraethyl-1,6-diiodo-
formation of 2a has been proposed, which involves iodobor-
ation of the alkyne to give the borylalkene 1a. This is fol-
2,3,4,5-tetracarba-nido-hexaborane(6) (2a) as the predomi- lowed by deiodination, presumably yielding the iodoborir-
nant product with trace quantities of 4 as well as 2,3-diethyl-
1,4,5,6,7-pentaiodo-2,3-dicarba-closo-heptaborane(7) (5).
ene derivative 7, which easily dimerizes to form the 1,4-di-
boracyclo-2,5-hexadiene derivative 8. Subsequent re-
arrangement leads to the final C4B2-nido-carborane 2a. To
determine the stereochemistry of 1a, its pyridine adduct 9
(and the isomer 9Ј) and catechol derivative 10 (and the iso-
mer 10Ј), and the diisopropylamino derivative 11 have also
been prepared. The new compounds have been character-
ized by MS and NMR spectroscopy, and the structures of 2a,
3, 9 and 9Ј were confirmed by single-crystal X-ray analyses.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Starting at −78 °C, reactions of 3-hexyne, 2-butyne or di-
phenylacetylene, respectively, with BI3 (1 equiv.) and NaK2.8
afforded the corresponding 1,6-diiodo-2,3,4,5-tetracarba-
nido-hexaboranes(6) 2a−c as the single carborane products.
In the cases of 3-hexyne and diphenylacetylene, the forma-
tion of hexaorganylbenzene derivatives was also detected.
To confirm the formation of 4 and 5, the independent dehalo-
genation of cis-3,4-bis(diiodoboryl)-3-hexene (3) with NaK2.8
has been studied, which indeed affords 4 and 5, with the
Introduction
The (HC)4(BR)2 organoborane/carborane system (A, B)
has attracted considerable interest because the structures
observed depend on the substituents (R) which attached to
the boron atoms. Apart from the classical 1,4-diboracyclo-
2,5-hexadienes A,[1] and non-classical 2,3,4,5-tetracarba-
nido-hexaboranes(6) B,[2] the compounds C,[3a] D,[3b] [3c] in
E
between these two limits have also been reported. Peralkyl-
ated 2,3,4,5-tetracarba-nido-hexaboranes(6), known since
the mid-1960s, are more stable than the parent compound
[4]
C4B2H6
but their reactivities have only recently been
studied.[5,6]
In order to investigate substitution reactions of B, func-
tional groups (R) other than alkyl groups are needed at the
boron atom(s). In 1994 we reported the formation of a 1,6-
dichloro-2,3,4,5-tetracarba-nido-hexaborane(6)[7] derivative
by photochemical transformation of 1,4-dichloro-2,3,5,6-
tetrakis(isopropylidene)-1,4-diboracyclohexane. The low
yield of the (alkylC)4(BCl)2 carborane did not allow further
reactivity studies to be carried out. Wrackmeyer et al. were
able to obtain 1,6-dibromo-2,3,4,5-tetracarba-nido-hexa-
boranes(6)[5a] in high yield by treating 1,4,6,9-tetraalkyl-3,8-
diethyl-2,7-bis(diethylboryl)-5-stannaspiro[4.4]nona-1,3,6,8-
tetraenes with BBr3. They also studied the reactions be-
tween the peralkylated 2,3,4,5-tetracarba-nido-hexabor-
anes(6) and an excess of BBr3 (and BI3), whereby the corre-
sponding B6-halo substituted carboranes were formed.[5b]
Nucleophilic substitution reactions of such B-halo carbor-
anes were found to replace the basal B6-halogen atom to
give the corresponding carboranes with organyl,[5c] stan-
[a]
Anorganisch-Chemisches Institut der Universität Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: (internat.) ϩ49-(0)6221-545-609
E-mail: walter.siebert@urz.uni-heidelberg.de
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DOI: 10.1002/ejic.200300704
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One-Pot Synthesis of 1,6-Diiodo-2,3,4,5-tetracarba-nido-hexaboranes
FULL PAPER
nyl[5d] and diphenylphosphanyl[5e] groups as well as, in the reactions on a small scale for NMR spectroscopic studies.
1,6-dibromo case, an N-bonded [Fe2(CO)6(µ-SN)] substitu- On standing at room temperature, yellow crystals of 2a
ent in the 6-position.[5f] Currently there is no easy pathway (vide infra) were obtained whereas the bromo compounds
to such B-functionalized C4B2-nido-carboranes.
are oils.[5a,5b]
In our efforts to prepare the iodo analog of the tetra-
[8]
carba-nido-octaborane(8) (EtC)4(BCl)4
we have devel-
oped a one-pot route to 1,6-diiodo-2,3,4,5-tetracarba-nido-
hexaboranes(6) involving alkynes, BI3 and NaK2.8 alloy. In
this paper we report the synthesis and characterization of
the resultant C4B2-nido-carboranes, and a possible mecha-
nism for their formation is proposed.
Scheme 2
Results and Discussion
The analogous reaction with 2-butyne proceeded
smoothly but the yellowish nido-(MeC)4(BI)2 (2b) was ob-
tained only in low yield. The 11B NMR spectrum exhibits
Synthesis of 1,6-Diiodo-2,3,4,5-tetracarba-nido-
hexaboranes(6)
1
two signals at δ ϭ 5.7, Ϫ48.6 ppm and the H NMR spec-
The reaction between 3-hexyne, BI3 (2 equiv.) and NaK2.8
alloy at room temperature, in a one-pot manner (Scheme 1),
gave a mixture of products. Its 11B NMR spectrum shows
two dominant signals at δ ϭ 5.5 and Ϫ52.7 ppm in a 1:1
ratio, typical of C4B2-nido-carboranes[2] (type B). The EI-
MS spectrum exhibits the molecular ion pattern with the
correct isotopic distribution for the formula (EtC)4(BI)2
(2a). The other peaks can be assigned to nido-(EtC)4(BI)4
(4) and the novel species closo-(EtC)2(BI)5 (5), respectively,
both exhibiting the expected isotopic patterns. Compounds
4 and 5 were formed only in trace amounts.
trum shows two singlets for the two different methyl groups.
The 13C NMR spectrum gives the corresponding signals for
the methyl and the skeletal carbon atoms non-adjacent to
the basal boron, while the signal for the other two skeletal
carbon atoms was not observed. In the mass spectrum the
molecular ion peak with the expected isotopic pattern was
found.
Whereas calculations[10] suggest that such nido-carbor-
anes bearing halogen substituents at the boron atom(s)
would prefer a classical type A structure, we have found
that 2a and 2b are perfectly stable like the bromo ana-
logs.[5a,5b] The reaction of diphenylacetylene with BI3/NaK2.8
also proceeds but the orange-yellow nido-(PhC)4(BI)2 (2c)
was also obtained in low yield. It was characterized by 11B
NMR spectroscopy (δ ϭ 7.9, Ϫ50.1 ppm), and the high-
resolution mass spectrum exhibits the molecular ion peak
having the correct isotopic distribution. Unfortunately, the
formation of a significant amount of hexaphenylbenzene
hampered the successful isolation and the recording of sat-
isfactory NMR spectra. Moreover, it was found to be un-
stable at room temperature even when stored under nitro-
gen, as indicated by its color which turned from orange-
yellow to pale yellow. This instability is different from the
cases of 2a and 2b, and reminiscent of the instability of the
Scheme 1
Starting at low temperature (Ϫ78 °C) the same reaction iodoboration product of diphenylacetylene with BI3, which
gave 2a as the single product in 51% yield as a yellow, sensi- leads to a 9,10-dihydro-9-boraanthracene derivative.[9]
tive and viscous oil. The yield can be increased to 66% when
In order to verify the formation of compounds 4 and
a 1:1 ratio of 3-hexyne and BI3 was used (Scheme 2). In the 5, the independent dehalogenation of 3[11a] (Scheme 3) was
latter case a very small amount of hexaethylbenzene could carried out. Attempts to obtain 3 through a redox reaction
also be detected. The 11B NMR spectrum of 2a exhibits of 3-hexyne and two equivalents of BI3 were not success-
1
two signals at δ ϭ 5.5 and Ϫ52.5 ppm. The H NMR spec- ful.[11b] However, the halogen exchange reaction of 6[12]
trum shows an ABX3 spin pattern for the methylene pro- with BI3 led to 3, a yellow crystalline solid, which is ex-
tons of the ethyl groups, and the 13C NMR spectrum exhib- tremely sensitive to air and moisture. In solution it exhib-
its the corresponding four signals for the two different ethyl ited a 11B NMR signal at δ ϭ 11.8 ppm. No change in the
groups. The signals responsible for the skeletal carbon chemical shift was observed upon cooling the sample to
atoms non-adjacent to the basal boron were observed, while Ϫ30 °C but only broadening of the signal. The significant
the signals for the other two skeletal carbon atoms (ex- shift to high field compared with that of 6 (δ ϭ 53.9 ppm)
pected at ca. 105 ppm[5a]) were not observed. It should be indicates some additional intra- or intermolecular interac-
noted that the formation of 2a was first reported by Wrack- tion. An X-ray structural determination revealed that 3
meyer et al.,[5a] (see Introduction) when they carried out forms an intramolecular BϪIϪB bridge to yield 3Ј. In solu-
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Y. Nie, S. Schwiegk, H. Pritzkow, W. Siebert
FULL PAPER
tion a fast equilibrium is present as shown in Scheme 4, PhBBr2/K system by Lappert et al.,[13] in which they
which explains the single 11B NMR signal.
claimed to have obtained a perphenylated 1,4-diboracy-
clohexadiene derivative or an unknown carborane species.
These results, however, could not be reproduced by Eisch
et al.[14] The other system involves the alkynes/MeBBr2/C8K
reaction reported by van der Kerk et al.,[15] who claimed to
have obtained stable peralkylated 1,4-diboracyclohexadiene
derivatives as the main products through a borylene mecha-
nism, while Wrackmeyer et al.[16] (in the cases of 3-hexyne
and 5-decyne) obtained the corresponding C4B2-nido-car-
boranes. No 1,4-diboracyclohexadiene derivatives could be
detected.
In order to get an insight into the formation of 2, we
selected 2a as our target compound. A possible pathway to
2a is shown in Scheme 5. Iodoboration of 3-hexyne with
BI3 afforded 1a, its dehalogenation presumably yielded the
iodoborirene intermediate 7, which might dimerize[1d,17] to
give 1,4-diboracyclohexadiene 8 or the bicyclic analog of
type C (see Introduction) with iodine at boron and ethyl at
carbon atoms as intermediates to rearrange to the carbor-
ane 2a.
Scheme 3
Scheme 4
The dehalogenation of 3 starting at Ϫ65 °C gave com-
pound 4 in 29% yield. When the same reaction was carried
out at room temperature, the yield was lower. Compound 4
exhibits two 11B NMR signals at δ ϭ Ϫ10.5 and
Ϫ13.4 ppm, which are shifted to lower frequencies in com-
[8]
parison with nido-(EtC)4(BCl)4
(δ ϭ Ϫ1.5 and Ϫ5.5
ppm). In the mass spectrum, the molecular ion at m/z ϭ
716 is the base peak and has the correct isotopic distri-
bution, while the formation of 5 was only detected by a
cutoff peak at m/z ϭ 771 [Mϩ] of very low intensity.
To further study the scope and limitations of this ap-
proach, a series of other alkynes has been studied using the
same or similar procedures. In the cases of 5-decyne, di-tert-
butylacetylene, bis(trimethylsilyl)acetylene, and di-p-tolyl-
acetylene, all the reactions led to decomposition products.
Scheme 5
The first step is the iodoboration of 3-hexyne to yield 1a.
In a study involving this step for the preparation of the
2,5-dihydro-1,2,5-thiadiborol,[9,18] the iodoboration product
was reported to be a cis/trans mixture (ca. 2:3 cis/trans ra-
tio) based on acetolysis which is an established method[19]
for determining the stereochemistry of haloboration prod-
ucts (we repeated the acetolysis reaction and a ratio of 1:1
was obtained). The problem is that at room temperature the
1H NMR spectrum shows two sets of ethyl signals and the
13C NMR spectrum exhibits only six signals, whereas a cis/
trans mixture should give more signals. Moreover, the 11B
NMR spectrum exhibits only one signal at δ ϭ 40 ppm.
As a result of this[20] some reactions were carried out with
[Fe2(CO)9] and Me2S but unfortunately neither com-
plexation nor adduct formation was observed. Later, the
very similar reaction of 3-hexyne and BBr3 was studied by
Wrackmeyer.[21] Their results revealed that it is a stereose-
lective cis-addition, while the fast cisϪtrans isomerization
led to a mixture. This allowed the assignment of both iso-
mers by NMR spectroscopic methods. We tried to deter-
The debromination reaction of 3-hexyne and BBr3 (1
[5a]
equiv.) afforded the known nido-(EtC)4(BBr)2
in 49%
yield, together with a small amount of hexaethylbenzene,
while the analogous reaction using BCl3 gave a mixture of
unidentified boron-containing species, and a significant
amount of hexaethylbenzene. Surprisingly, the reaction sys-
tem of diphenylacetylene-/BBr3/NaK2.8 led only to de-
composition irrespective of whether the one-step or step-
wise procedures were used. Efforts to produce the corre-
sponding nido-C4B2 carboranes with CH cluster atoms,
starting from ethyne or phenylacetylene, and BI3 (or BBr3),
respectively, were not successful.
Mechanistic Considerations
There have been two similar dehalogenation reactions re- mine the stereochemistry of the present iodoboration prod-
ported. One is the early study of the diphenylacetylene/ ucts using a method more direct than acetolysis. It turned
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One-Pot Synthesis of 1,6-Diiodo-2,3,4,5-tetracarba-nido-hexaboranes
FULL PAPER
out, in agreement with Wrackmeyer’s findings, that the re-
action of 3-hexyne and BI3 gave the cis isomer 1a
(Scheme 6), which underwent a slow isomerization to the
thermodynamically more stable trans isomer 1aЈ, thus al-
lowing the characterization and even separation of both iso-
mers. The pyridine adduct 9 and the catechol derivative 10
showed much faster cisϪtrans isomerizations than the par-
ent 1a, while the amino derivative 11 did not isomerize at
room temperature even over a timescale of weeks. The X-
ray structural analyses of 9 (cis) and 9Ј (trans) unequivo-
cally confirmed the stereochemical assignments.
Scheme 7
methyl derivative (MeC)4(BMe)2,[25] and by microwave
spectroscopy[26] of the parent derivative (HC)4(BH)2.[4] The
structures were confirmed by X-ray diffraction analy-
ses.[3c,5f] In 1992, Berndt et al.,[3c] reported the structure of
a benzo-annelated derivative, and in 1996 Herberhold,
Wrackmeyer et al.[5f] published the structure of the first ex-
ample of an ‘‘undisturbed’’ pentamethyl-nido-C4B2 carbor-
ane with an N-bonded [Fe2(CO)6(µ-NS)] complex fragment
in the 6-position. Derivatives of a benzo compound[3c] with
transition metal complex fragments coordinated to the ben-
zene ring have also been synthesized.[6b]
Scheme 6
The second step in the formation of 2a is the dehalogen-
ation of 1a. Apart form the one-pot reactions, the stepwise
reaction (see Exp. Sect.) also afforded 2a in a somewhat
lower yield (43%). Although we do not have direct evidence
for the formation of the borirene intermediate 7, we found
11B NMR signals for the reaction mixtures which may be
assigned to the corresponding 1,4-diboracyclohexadiene 8
(broad signals at ca. 68 and 67 ppm in the formation of 2a
and 2b, respectively), near to the expected region for 1,4-
diboracyclohexadienes (55Ϫ65 ppm).[22]
The molecular structure of 2a is shown in Figure 1. Its
C4B2 skeleton adopts the expected nido structure (Cs sym-
metry) with an apical six-coordinate boron atom. The BϪB
˚
bond length of 1.821 A is similar to, but slightly shorter
The redox reaction of 3 with 3-hexyne shown in Scheme 7
(analogous to the preparation of the corresponding 1,3-di-
iodo-2,3-dihydro-1,3-diborol derivatives[23] and the 1,4-di-
iodo-1,4-diboracyclohexene compounds[24]) indeed afforded
the expected carborane 2a. The reaction mixture showed a
broad 11B NMR signal at δ ϭ 66 ppm. As suggested by
Schleyer et al.[17] the straightforward intramolecular re-
arrangement of 1,4-diboracyclohexa-2,5-dienes into carbor-
anes is forbidden by symmetry and our attempts to separate
8 by distillation led gradually to 2a, as evidenced by 11B
NMR spectroscopy and EI-MS (see Exp. Sect.). Although
this redox reaction (Scheme 7) represents a new route to the
corresponding
1,4-diboracyclohexadienes/C4B2-nido-car-
Figure 1. Molecular structure of 2a, hydrogen atoms omitted for
boranes, the difficult access to the cis-1,2-diborylalkene 3
prevents its practical application.
clarity, thermal ellipsoids are shown at the 40% probability level;
˚
selected bond lengths [A] and angles [°]: I1ϪB1 2.155(3), I2ϪB2
2.126(3), C1ϪC2 1.457(4), C2ϪC3 1.437(4), C3ϪC4 1.459(3),
C1ϪB1 1.522(3), C4ϪB1 1.526(4), C1ϪB2 1.705(4), C2ϪB2
1.713(4), C3ϪB2 1.713(4), C4ϪB2 1.708(4), B1ϪB2 1.821(4);
C2ϪC1ϪB1 108.3(2), C1ϪB1ϪC4 104.1(2), B1ϪC4ϪC3 107.9(2),
C4ϪC3Ϫ C2 109.6(2), C3ϪC2ϪC1 109.2(2), B2ϪB1ϪI1 130.0(2),
X-ray Structural Analyses of 2a, 3, 9 and 9Ј
The structures of the C4B2-nido-carboranes were pre-
viously examined by electron diffraction studies of the hexa- B1ϪB2ϪI2 140.1(2)
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Y. Nie, S. Schwiegk, H. Pritzkow, W. Siebert
FULL PAPER
than, the corresponding distances in the above-mentioned
(MeC)4(BMe)[B(µ-NS)Fe2(CO)6][5f] (1.836 A), in the benzo-
˚
annelated structure[3c] (1.870 A) and in the parent derivative
˚
[26]
˚
(HC)4(BH)2
(1.886 A). The B2ϪC distances vary within
˚
a narrow range (1.705Ϫ1.713 A), and are also slightly
shorter than the values in the examples mentioned[5f,3c]
˚
(1.720Ϫ1.743 and 1.673Ϫ1.865 A, respectively), which can
be attributed to the different steric environments around the
skeleton. The skeletal CϪC distances were found to be al-
˚
most identical (av. 1.451 A), and are also similar to the aver-
˚
age of 1.438 A in (MeC)4(BMe)[B(µ-SN)Fe2(CO)6. The
four skeletal carbon atoms are in one plane, and the four
exo-polyhedral carbon atoms C5, C7, C9, C11 are bent out
˚
of the C4 plane towards B2 by an average of 0.24 A. The
five-membered C4B open face is not planar, with B1 lying
˚
ca. 0.15 A below the C4 plane. The dihedral angle between
the C4 plane and the C2B1 plane is ca. 9o. The BϪI bond
˚
lengths are 2.126 and 2.155 A, respectively, and are similar
Figure 2. Molecular structure of 3, thermal ellipsoids are shown at
to the reported values in some other B-iodinated polyhedral
˚
the 40% probability level; selected bond lengths [A] and angles [°]:
˚
borane and carborane clusters, for example 2.133 A (av.) in
I1ϪB2 2.160(4), I1ϪB1 2.383(4), I2ϪB1 2.231(4), I3ϪB1 2.201(4),
I4ϪB2 2.107(4), B1ϪC2 1.571(6), B2ϪC1 1.510(5), C1ϪC2
1.371(5), B2ϪI1ϪB1 81.1(2), C2ϪB1ϪI3 117.0(3), C2ϪB1ϪI2
111.0(3), I3ϪB1ϪI2 112.25(18), C2ϪB1ϪI1 102.8(2), I3ϪB1ϪI1
HNB11Cl5I6,[27a] 2.09Ϫ2.17 A in polyiodinated p-carbor-
˚
anes,[27b] and also similar to that of 2.10(4) A in BI3.
[28]
˚
The molecular structure of 3 is shown in Figure 2. The 105.9(2), I2ϪB1ϪI1 106.8(2), C1ϪB2ϪI4 127.7(3), C1ϪB2ϪI1
two BI2 groups are in a cis arrangement, and the I1 atom
is intramolecularly coordinated to B1, forming a unique
113.8(3), I4ϪB2ϪI1 118.5(2), C2ϪC1ϪB2 118.5(3), C1ϪC2ϪB1
123.5(3)
BϪIϪB bridge. The boron atom B2 is tri-coordinate and
2
˚
the B2ϪI4 bond length of 2.107 A is typical of an IϪB(sp )
distance. B1 is four-coordinate, however, and the B1ϪI2
˚
and B1ϪI3 distances are 2.231 and 2.201 A, respectively,
and are very similar to the reported values for IϪB(sp3)
[29a]
˚
˚
bonds, e.g. 2.21(1) A (av.) in [Ph2PBI2]2
and 2.229 A
[29b]
(av.) in (vi3P)BI3
(where vi is vinyl). The BϪI bond
lengths involving the bridging I1 atom are 2.160 and 2.383
˚
A, respectively, and the latter is longer than the sum of the
covalent radii of the two atoms, indicating that the interac-
tion between B1 and I1 is weak.
Figure 3 (a and b) show the structures of 9 (cis) and 9Ј
(trans), respectively. In both structures the boron atom is
four-coordinate, adopting a slightly distorted tetrahedral
geometry. The bond lengths and angles in both structures
are very similar. The BϪI bond lengths are 2.269 and 2.306
˚
˚
A in 9, and 2.275(3) and 2.294(3) A in 9Ј, respectively, simi-
lar to the corresponding values in compound 3. The corre-
˚
˚
sponding BϪN distances of 1.587 A in 9 and 1.596 A in 9Ј,
respectively, are similar to, but slightly shorter than, those
found in other pyridine adducts.[30]
Conclusion
Figure 3. a) (left) Molecular structure of 9, hydrogen atoms omitted
for clarity, thermal ellipsoids are shown at the 40% probability le-
˚
vel; selected bond lengths [A] and angles [°]: I1ϪB1 2.269(3),
We have developed a one-pot synthesis of 1,6-diiodo-
2,3,4,5-tetracarba-nido-hexaborane(6) derivatives involving
disubstituted alkynes, BI3 and NaK2.8. Considering the re-
ady availability of the starting materials and the product 2a,
it has been convenient to study the reactivities of such BϪI
functionalized carboranes and dehalogenation is a practical
method for the preparation of carboranes. The formation
I2ϪB1 2.306(3), I3ϪC2 2.141(3), N1ϪB1 1.587(4), B1ϪC1
1.600(4), C1ϪC2 1.343(4), N1ϪB1ϪC1 114.4(2), N1ϪB1ϪI1
111.8(2), C1ϪB1ϪI1 109.2(2), N1ϪB1ϪI2 101.4(2), C1ϪB1ϪI2
113.6(2), I1ϪB1ϪI2 106.1(1). b) (right) Molecular structure of 9Ј,
hydrogen atoms omitted for clarity, thermal ellipsoids are shown at
˚
the 40% probability level; selected bond lengths [A] and angles [°]:
I1ϪB1 2.275(3), I2ϪB1 2.294(3), I3ϪC2 2.160(3), N1ϪB1
1.596(4), B1ϪC1 1.607(4), C1ϪC2 1.342(4), N1ϪB1ϪC1 114.8(2),
N1ϪB1ϪI1 111.3(2), C1ϪB1ϪI1 109.7(2), N1ϪB1ϪI2 100.8(2),
of 4 from the dehalogenation of 3 confirms that bis(boryl- C1ϪB1ϪI2 114.0(2), I1ϪB1ϪI2 105.7(1).
1634  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2004, 1630Ϫ1638

One-Pot Synthesis of 1,6-Diiodo-2,3,4,5-tetracarba-nido-hexaboranes
FULL PAPER
NaK2.8 (0.9 mL) at room temp. The reaction mixture became gray
in ca. 20 min, and was stirred for 1 day, then filtered (G4 frit). The
residue was washed with hexane (2 ϫ 15 mL), and the slightly pink
filtrate was dried in vacuo, leaving a red-brown oil (238 mg), which
was a mixture of 2a, 4 and 5. EI-MS: m/z (%) ϭ 440 (100) (2a),
alkenes) are the precusors of nido-C4B4 carboranes. Such
dehalogenation reactions at room temperature are more
complex and give lower yields than at lower temperatures.
A possible mechanism of the formation of C4B2-nido-hexa-
boranes(6) has been proposed and studied using 2a as a
representative example. The stereochemistry of the iodo-
boration product of the alkyne has been clarified as cis,
using a more direct method than acetolysis, and the cis-
trans isomerization exists in the addition product 1a and
some of the derivatives.
716 (3.35) (4), and 771 (44.83) (5). HR-MS (EI): m/z ϭ 439.9847
12
(2a); calcd. for
C
12
1H2011B2127I2 439.9840 (∆m ϭ 0.6 mmu),
12
m/z ϭ 715.8150 (4); calcd. for
C
12
1H2011B4127I4 715.8116 (∆m ϭ
3.4 mmu), m/z ϭ 715.6464 (5); calcd. for 12C6 H1011B5127I5
1
715.6472 (∆m ϭ Ϫ0.8 mmu).
b): To a solution of BI3 (3.126 g, 7.98 mmol) in hexane (30 mL) at
Ϫ78 °C was added 3-hexyne (332 mg, 4.04 mmol) dropwise. The
mixture immediately became yellow-brown, and NaK2.8 (2 mL) was
then added with a syringe. The reaction mixture was stirred at Ϫ78
°C for ca. 10 min, the cooling bath was removed, and the mixture
was warmed to ambient temperature and stirred for 1 day. The
mixture was then filtered (G4 frit), and the residue washed with
hexane (2 ϫ 15 mL). The yellow filtrate was dried in vacuo, leaving
a yellow viscous oil, which was distilled to give 2a (455 mg, 51%)
as the single carborane product. In this case, no hexaethylbenzene
was detected.
Experimental Section
All reactions and manipulations were performed in dry glassware
under argon or nitrogen using standard Schlenk techniques. Sol-
vents were dried, distilled, and saturated with nitrogen. NMR:
Bruker DRX 200 spectrometer; Et2O·BF3 was used as the external
standard for 11B NMR spectroscopy; as internal references for H
1
and 13C NMR spectroscopy, the signals of the deuterated solvent
(CDCl3) were used and calculated relative to TMS. MS: ZAB-2F
VH Micromass CTD spectrometer, and a JEOL MS Station JMS
700 spectrometer both using the EI ionization technique. Melting
points (uncorrected) were measured with a Büchi apparatus, using
capillaries which were filled under nitrogen and sealed.
Formation of 2a from the Redox Reaction of 3-Hexyne and 3: 3-
Hexyne (196 mg, 2.3 mmol) was added dropwise to a solution of 3
(1.357 g, 2.22 mmol) in hexane (25 mL) at Ϫ60 °C. The mixture
was warmed to ambient temperature during which time it became
deep brown indicating the formation of I2. The 11B NMR spectrum
showed a signal at δ ϭ 66 ppm. All the volatiles were removed in
vacuo and the resultant red oil was distilled at 71 °C/ 8 ϫ 10Ϫ2
Torr to give a yellowish oil (533 mg, 55%), which gradually became
deep red. The 11B NMR (C6D6, 64 MHz) data of the original distil-
late: δ ϭ 57.6 (s), 45.7, 5.9, Ϫ9.0 (BI3), Ϫ52.4 ppm; after three days,
the corresponding signals were: δ ϭ 57 (s), 32, 5.9, Ϫ52.4 ppm;
after three weeks, there were only two 11B NMR signals: δ ϭ 5.9,
Ϫ52.4 ppm (2a). The EI-MS spectrum was identical to that of
authentic 2a.
2,3,4,5-Tetraethyl-1,6-diiodo-2,3,4,5-tetracarba-nido-hexaborane(6)
(2a). Formation from 3-Hexyne, BI3 (1 equiv.) and NaK2.8
a) One-Pot Procedure: To a solution of BI3 (872 mg, 2.23 mmol) in
hexane (40 mL) at Ϫ78 °C was added 3-hexyne (190 mg, 2.3 mmol)
dropwise, and NaK2.8 (0.9 mL, excess) was then added with a syr-
inge. The mixture was stirred for ca. 15 min, and the cooling bath
was then removed. The reaction mixture was warmed to ambient
temperature, stirred overnight, and then filtered (G4 frit) and the
residue washed with hexane (2 ϫ 15 mL). The solvent of the yellow
filtrate was removed in vacuo, leaving a yellow viscous oil. Distil-
lation at 80 °C/ 2 ϫ 10Ϫ3 Torr gave 2a (326 mg, 66%) as a yellow,
air-sensitive oil, which slowly solidified. For reactions with up to
28 mmol of BI3, longer reaction times (1 week) were needed (av.
1,6-Diiodo-2,3,4,5-tetramethyl-2,3,4,5-tetracarba-nido-hexa-
borane(6) (2b): Same procedures as described for 2a. 2-Butyne
(426 mg, 7.9 mmol), BI3 (3.09 g, 7.9 mmol), NaK2.8 (2 mL). The
final yellow viscous oil was distilled at 95 °C/ 3 ϫ 10Ϫ2 Torr to give
2b (225 mg, 15%) as a yellowish solid; m.p. 92Ϫ94 °C. 1H NMR
(CDCl3, 200 MHz): δ ϭ 1.72 (s, 6 H, CH3), 1.87 (s, 6 H, CH3)
ppm. 11B NMR (CDCl3, 64 MHz): δ ϭ 5.7 (s, Bbasal), Ϫ48.6 (s,
1
yield Ͼ 60%, m.p. 52 °C). H NMR (CDCl3, 200 MHz): δ ϭ 1.20
3
3
(t, JH,H ϭ 7.6 Hz, 6 H, CH3), 1.26 (t, JH,H ϭ 7.6 Hz, 6 H, CH3),
1.87Ϫ 2.04 (m), 2.11Ϫ 2.38 (m, 8 H, CH2) ppm. 11B NMR (CDCl3,
64 MHz): δ ϭ 5.5 (s, Bbasal, 1 B), Ϫ52.5 (s, Bapical, 1 B) ppm. 11B
NMR (C6D6, 64 MHz): δ ϭ 5.9 (s, Bbasal, 1 B), Ϫ52.4 (s, Bapical, 1
B) ppm. 13C NMR (CDCl3, 50 MHz): δ ϭ 13.5, 14.2 (CH3), 18.9,
20.4 (CH2), 114.2 ppm (skeletal carbon atoms non-adjacent to the
basal boron), the signals for the other basal carbon atoms not ob-
B
apical) ppm. 13C NMR (CDCl3, 50 MHz): δ ϭ 11.29, 12.55 (CH3),
110.7 ppm (skeletal carbon atoms non-adjacent to basal boron),
the signals for the other basal carbon atoms not observed. EI-MS:
m/z (%) ϭ 384 (94) [Mϩ], 257 (100) [Mϩ Ϫ I]. HR-MS (EI):
1
m/z ϭ 383.9218 [Mϩ]; calcd. for 12C8 H1211B2127I2 383.9215 (∆m ϭ
served. EI-MS: m/z (%) ϭ 440 (100) [Mϩ], 313 (20.3) [Mϩ Ϫ I].
0.3 mmu).
HR-MS (EI): m/z ϭ 439.9842 [Mϩ]. Calcd. For
439.9840 (∆m ϭ 0.2 mmu).
C
12
1H2011B2127I2
12
1,6-Diiodo-2,3,4,5-tetraphenyl-2,3,4,5-tetracarba-nido-hexa-
borane(6) (2c): Same procedures as described for 2a. Diphenyl-
acetylene (1.38 g, 7.7 mmol), BI3 (3.03 g, 7.7 mmol), NaK2.8
(1.6 mL). The yellow filtrate was cooled, and some yellow solid
(mainly hexaphenylbenzene) was filtered, and the yellow filtrate
was dried in vacuo to give 2c (147 mg, ca. 5%) and a small amount
of hexaphenylbenzene as an orange yellow solid. 11B NMR
(CD2Cl2, 64 MHz): δ ϭ 7.9 (s, Bbasal), Ϫ50.1 (s, Bapical), (δ ϭ 8.2
and Ϫ49.6 ppm in CDCl3) ppm. EI-MS: m/z (%) ϭ 632 (100) [Mϩ],
b) Stepwise Procedure: To a solution of BI3 (2.165 g, 5.53 mmol) in
hexane (50 mL) was added dropwise 3-hexyne (470 mg, 5.7 mmol)
at Ϫ50 °C, and the resultant solution was warmed to ambient tem-
perature. The resultant red solution (11B NMR: δ ϭ 40.5 ppm) was
cooled to Ϫ60 °C again and NaK2.8 (2 mL) was added with a syr-
inge. The workup procedure which followed was similar to that of
the one-pot procedure and yielded 2a (520 mg, 43%).
505 (69.6) [Mϩ Ϫ I]. HR-MS (EI): m/z ϭ 631.9855 [Mϩ]; calcd.
Reactions of 3-Hexyne with BI3 (2 equiv.) and NaK2.8 at Different
Temperatures
12
for
C
28
1H2011B2127I2 631.9841 (∆m ϭ 1.4 mmu).
a): A solution of BI3 (858 mg, 2.19 mmol) in hexane (35 mL) was
added dropwise to a mixture of 3-hexyne (90 mg, 1.1 mmol) and
cis-3,4-Bis(diiodoboryl)-3-hexene (3):[11a] A portion of 3,4-bis(di-
chloroboryl)-3-hexene (6) (2.13 g, 8.7 mmol) was added to BI3
Eur. J. Inorg. Chem. 2004, 1630Ϫ1638
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1635

Y. Nie, S. Schwiegk, H. Pritzkow, W. Siebert
FULL PAPER
3
3
(4.653 g, 11.9 mmol) at room temperature. The resultant dark
brown solution was stirred at room temperature for ca. 2.5 h. The
reaction flask was connected to a condensation apparatus, the trap
cooled to Ϫ78 °C, and the system was kept at ca. 60 mbar over-
night. All volatiles were then removed under high vacuum, and
the resultant dark brown residue was recrystallized five times from
hexane (ca. 20 mL), four times at Ϫ84 °C, and the last time at Ϫ28
°C. Compound 3 (2.53 g, 47.5%) was obtained as a yellow crystal-
line solid, which can be kept at Ϫ28 °C for a long period of time,
2.77 (q, JH,H ϭ 7.4 Hz, 2 H, CH2), 2.86 (q, JH,H ϭ 7.4 Hz, 2 H,
CH2), 7.70 (m), 8.19(m), 9.39 (m) (py-H) ppm. 11B NMR (CDCl3,
64 MHz): δ ϭ Ϫ13.9 ppm. 13C NMR (CDCl3, 50 MHz): δ ϭ 14.4,
14.9 (CH3), 32.4, 39.5 (CH2), 115.2 (ϭCϪI), 126.6, 142.4, 147.6
ppm (py-C), the signal of the boron-bound carbon was not ob-
served.
trans-3-Diiodoboryl-4-iodo-3-hexene؊Pyridine Adduct (9Ј): Slow
isomerization of 9 (cis) at room temperature afforded 9Ј within one
week as yellow crystals from a CH2Cl2 solution. M.p. 108Ϫ110 °C,
1
3
m.p. 70Ϫ72 °C. H NMR (C6D6, 200 MHz): δ ϭ 1.02 (t, JH,H
ϭ
1
3
dec. H NMR (CDCl3, 200 MHz): δ ϭ 0.74 (t, JH,H ϭ 7.4 Hz, 3
7.5 Hz, 6 H, CH3), 2.29 (q, JH,H ϭ 7.5 Hz, 4 H, CH2) ppm. 11B
NMR (C6D6, 64 MHz): δ ϭ 11.8 ppm. 13C NMR (C6D6, 50 MHz):
δ ϭ 14.8 (CH3), 26.2 (CH2), 178.4 (CϭC) ppm. EI-MS: m/z (%) ϭ
3
3
3
H, CH3), 1.25 (t, JH,H ϭ 7.4 Hz, 3 H, CH3), 1.94 (q, JH,H
ϭ
3
7.2 Hz, 2 H, CH2), 2.98 (q, JH,H ϭ 7.4 Hz, 2 H, CH2), 7.76 (m),
8.26(m), 9.47 (m) (py-H) ppm. 11B NMR (CDCl3, 64 MHz): δ ϭ
Ϫ20.8 ppm. 13C{11B} NMR (CDCl3, 50 MHz): δ ϭ 12.9, 13.7
(CH3), 38.8, 45.3 (CH2), 120.0 (ϭCϪI), 126.4, 142.9, 146.9 (py-C),
147.9 (CϭCϪB) ppm. The EI-MS failed to give definite infor-
mation.
485 (100) [Mϩ Ϫ I]. HR-MS (EI): m/z ϭ 484.8128 [Mϩ Ϫ I]; calcd.
1
For
12C6 H1011B2127I3
484.8103
(∆m
ϭ
2.5
mmu).
C6H10B2I4(611.4): calcd. C 11.79, H 1.65; found C 12.23, H 1.61.
Tetraethyltetraiodotetracarba-nido-octaborane(8) (4): To a solution
of 3 (2.3 g, 3.76 mmol) in hexane (40 mL) at Ϫ65 °C was added
NaK2.8 (1.5 mL, excess) dropwise with a syringe. After ca. 1 h the
cooling bath was removed, and the reaction mixture was warmed
to room temperature and stirred for 3 days. The reaction mixture
was filtered (G4 frit) and the residue washed with hexane (2 ϫ
15 mL), the light yellow filtrate dried in vacuo, leaving a yellow
viscous oil which slowly solidified, containing 4 (385 mg, 28.6%)
and a trace amount of 5. 11B NMR (CDCl3, 64 MHz): δ ϭ Ϫ10.5
(s, 2 B), Ϫ13.4 (s, 2 B) ppm. EI-MS: m/z (%) ϭ 716 (100) [Mϩ] (4),
589 (91.7) [M1ϩϪ I]. 771(4.3) [Mϩ] (5). HR-MS (EI): m/z ϭ
cis-3-(1,3,2-Benzodioxaborol-2-yl)-4-iodo-3-hexene (10): A solution
of 1a (730 mg, 1.54 mmol) in CH2Cl2 (10 mL) was added dropwise
to a solution of catechol (169 mg, 1.54 mmol) in CH2Cl2 (15 mL)
at Ϫ45 °C. The reaction mixture was warmed to ambient tempera-
ture and the solvent removed in vacuo to give 455 mg (90%) of 10
as a deep red liquid. 1H NMR (CDCl3, 200 MHz): δ ϭ 1.10 (t,
3
3JH,H ϭ 7.6 Hz, 3 H, CH3), 1.17 (t, JH,H ϭ 7.4 Hz, 3 H, CH3),
3
3
2.43 (q, JH,H ϭ 7.6 Hz, 2 H, CH2), 2.73 (q, JH,H ϭ 7.4 Hz, 2 H,
CH2), 7.10- 7.33 (m, 4 H, C6H4) ppm. 11B NMR (CDCl3, 64 MHz):
δ ϭ 31.1 ppm. 13C NMR (CDCl3, 50 MHz): δ ϭ 12.9, 14.4 (CH3),
26.7, 35.7 (CH2), 110.1 (ϭCϪI), 112.7, 122.8, 147.9 ppm (C6H4),
the boron-bound carbon n.o ppm. EI-MS: m/z (%) ϭ 328 (50.6)
715.8112 [M1ϩ]; calcd. For 12C12 H2011B4127I4 715.8117 (∆m ϭ Ϫ0.5
1
771.6440 [M2ϩ]; Calcd. For 12C6 H1011B5127I5
1
mmu). m/z
ϭ
[Mϩ], 246 (100) [Mϩ Ϫ C6H10], 201 (99.8) [Mϩ Ϫ I]. HR-MS (EI):
771.6471 (∆m ϭ Ϫ3.1 mmu).
m/z ϭ 328.0116 [Mϩ]; calcd. For
(∆m ϭ Ϫ1.5 mmu).
C
12
1H1411B127I16O2 328.0131
12
cis-3-Diiodoboryl-4-iodo-3-hexene (1a):[9,18] The procedure in the lit-
erature was slightly modified. To a solution of BI3 (3.245 g,
8.3 mmol) in pentane (50 mL) was added 3-hexyne (681 mg,
8.3 mmol) dropwise at Ϫ25 °C. The red mixture was warmed to
ambient temperature and the deep pink solution was transferred to
another flask, leaving a little black solid on the wall of the original
flask. The solution was dried in vacuo to give analytically pure
1a almost quantitatively as a deep red liquid. 1H NMR (CDCl3,
200 MHz): δ ϭ 1.08 (t, 3JH,H ϭ 7.4 Hz, 3 H, CH3), 1.22 (t, 3JH,H ϭ
trans-3-(1,3,2-Benzodioxaborol-2-yl)-4-iodo-3-hexene (10Ј): The iso-
merization of 10 (cis) at room temperature afforded 10Ј within ca.
3 weeks (as indicated by NMR in a CDCl3 solution). 1H NMR
3
(CDCl3, 200 MHz): δ ϭ 1.12 (t, JH,H ϭ 7.6 Hz, 3 H, CH3), 1.27
(t, 3JH,H ϭ 7.4 Hz, 3 H, CH3), 2.60 (q, 3JH,H ϭ 7.4 Hz, 2 H, CH2),
3.22 (q, 3JH,H ϭ 7.6 Hz, 2 H, CH2), 7.12- 7.33 (m, 4 H, C6H4) ppm.
11B NMR (CDCl3, 64 MHz): δ ϭ 29.1 ppm. 13C NMR (CDCl3,
50 MHz): δ ϭ 13.3, 15.6 (CH3), 36.6, 39.9 (CH2), 112.2 (ϭCϪI),
112.6, 122.9, 147.9 ppm (C6H4), the boron-bound carbon n.o.
3
7.6 Hz, 3 H, CH3), 2.15 (q, JH,H ϭ 7.6 Hz, 2 H, CH2), 2.62 (q,
3JH,H ϭ 7.4 Hz, 2 H, CH2) ppm. 11B NMR (CDCl3, 64 MHz): δ ϭ
40.0 ppm. 13C NMR (CDCl3, 50 MHz): δ ϭ 14.2, 15.0 (CH3), 24.7,
33.3 (CH2), 106.4 (ϭC-I), 157.6 (br., ϭCϪB) ppm.
cis-3-(Diisopropylamino)iodoboryl-4-iodo-3-hexene (11): Diisopro-
pylamine (1.07 g, 10.6 mmol) was added dropwise to a solution of
1a (2.45 g, 5.2 mmol) in hexane (50 mL) at Ϫ40 °C. The mixture
was warmed to ambient temperature and filtered, the light yellow
filtrate was dried in vacuo to give a red oil, which was distilled at
82 °C/ 5.9 ϫ 10Ϫ2 Torr to give yellow 11 (1.8 g, 76%). 1H NMR
trans-3-Diiodoboryl-4-iodo-3-hexene (1aЈ): Slow isomerization of 1a
(cis) at room temperature afforded 1aЈ (not complete within 5
weeks as indicated by NMR in a CDCl3 solution, with partial de-
compostion). 1H NMR (CDCl3, 200 MHz): δ ϭ 1.08 (t, JH,H
ϭ
3
3
(CDCl3, 200 MHz): δ ϭ 1.04 (t, JH,H ϭ 7.3 Hz, 3 H, Et CH3),
3
7.2 Hz, 3 H, CH3), 1.15 (t, JH,H ϭ 6.7 Hz, 3 H, CH3), 2.2 (q,
3
3
1.14 (t, JH,H ϭ 7.6 Hz, 3 H, Et CH3), 1. 24 (d, JH,H ϭ 6.7 Hz, 3
3JH,H ϭ 7.2 Hz, 2 H, CH2), 2.61 (q, JH,H ϭ 6.7 Hz, 2 H, CH2)
3
3
H, iPr CH3), 1.30 (d, JH,H ϭ 6.7 Hz, 3 H, iPr CH3), 1.49 (d,
ppm. 11B NMR (CDCl3, 64 MHz): δ ϭ 43.5 ppm. 13C NMR
(CDCl3, 50 MHz): δ ϭ 12.8, 14.0 (CH3), 33.6, 39.1 (CH2), 114.6
(ϭCϪI), 158.1 (br., ϭCϪB) ppm.
3
3JH,H ϭ 7.2 Hz, 3 H, iPr CH3), 1.54 (d, JH,H ϭ 7.2 Hz, 3 H, iPr
CH3), 2.10 (m, 1 H, Et CH2), 2.31 (m, 1 H, Et CH2), 2.53 (q,
3JH,H ϭ 7.4 Hz, 2 H, Et CH2), 3.53 (sept, 1 H, iPr CH), 3.95 (sept,
1 H, iPr CH) ppm. 11B NMR (CDCl3, 64 MHz): δ ϭ 28.1 ppm.
13C NMR (CDCl3, 50 MHz): δ ϭ 14.2, 14.3, (Et CH3), 21.0, 22.1,
23.0, 24.0 (iPr CH3), 25.5, 34.2 (Et CH2), 47.8, 53.9 (iPr CH), 110.1
ppm (ϭCϪI), the boron-bound carbon n.o. EI-MS: m/z (%) ϭ 447
cis-3-Diiodoboryl-4-iodo-3-hexene؊Pyridine Adduct (9): Pyridine
(223 mg, 2.8 mmol) was added dropwise to a solution of 1a (1.33 g,
2.8 mmol) in hexane (25 mL) at Ϫ25 °C. The color immediately
turned to deep red and a yellow precipitate then appeared. The
mixture was warmed to room temperature, the solvent removed in
vacuo, and an orange-yellow powder 9 was obtained quantitatively.
The X-ray quality crystals were grown from a toluene solution at
(2.4) [Mϩ], 320 (100) [Mϩ Ϫ I], 238 (39.8) [Mϩ Ϫ I Ϫ2C3H5].
12
HR-MS (EI): m/z ϭ 447.0079 [Mϩ]; calcd. for
447.0091 (∆m ϭ Ϫ1.2 mmu).
C
12
1H24N11B127I2
Ϫ28 °C. M.p. 30 °C. 1H NMR (CDCl3, 200 MHz): δ ϭ 1.05 (t,
X-ray Structural Determinations: Crystal data and details of the
3JH,H ϭ 7.4 Hz, 3 H, CH3), 1.29 (t, JH,H ϭ 7.4 Hz, 3 H, CH3), structural determinations are listed in Table 1. The intensity data
3
1636
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 1630Ϫ1638

One-Pot Synthesis of 1,6-Diiodo-2,3,4,5-tetracarba-nido-hexaboranes
Table 1. Crystal data and structure refinement for 2a, 3, 9 and 9Ј
FULL PAPER
2a
3
9
9Ј
Empirical formula
Molecular weight
Crystal system
Space group
C12H20B2I2
439.70
orthorhombic
Pna21
12.1078(7)
14.3226(8)
9.2587(5)
90
90
90
1605.6(2)
4
1.819
C6H10B2I4
611.36
monoclinic
P21/n
11.9871(7)
7.7401(4)
14.8450(9)
90
102.841(1)
90
1342.9(2)
4
3.024
9.236
1072
C11H15BI3N
552.75
monoclinic
P21/n
11.0923(9)
12.0214(10)
11.8779(10)
90
92.848(2)
90
1581.9(2)
4
2.321
5.905
1008
C11H15BI3N
552.75
orthorhombic
Pbca
8.6602(4)
14.2028(7)
24.8358(13)
90
90
90
3054.8(3)
8
2.404
˚
a (A)
˚
b (A)
˚
c (A)
α [°]
β [°]
γ [°]
3
˚
V (A )
Z
dcalcd. [g cmϪ3
]
µ (Mo-Kα) [mmϪ1
F(000)
]
3.89
832
6.116
2016
Crystal size [mm]
Θmax. [°]
Index ranges h, k, l
Reflections collected
Independent (Rint)
No. of parameters
GooF
0.45 ϫ 0.15 ϫ 0.08
32.0
0/17, 0/21, Ϫ13/13
14404
5198 (0.0274)
226
1.050
0.37 ϫ 0.25 ϫ 0.16
32.0
Ϫ17/17, 0/11, 0/21
412363
4559(0.0279)
145
1.106
0.45 ϫ 0.36 ϫ 0.25
32.0
Ϫ16/16, 0/17, 0/17
14891
5345(0.0270)
205
1.117
0.25 ϫ 0.15 ϫ 0.12
32.0
0/12, 0/21, 0/36
29275
5281(0.0374)
205
1.095
R1(I Ͼ 2σI)
wR2 (all reflections)
Resid. electron density [e·A
0.0219
0.0526
1.240/ Ϫ0.518
0.0289
0.0734
2.265/Ϫ2.149
0.0273
0.0714
1.476/ Ϫ2.388
0.0245
0.0592
1.695/Ϫ0.694
Ϫ3
˚
]
[3b]
975Ϫ980; Angew. Chem. Int. Ed. Engl. 1984, 23, 969.
M.
for 2a, 3, 9, 9Ј were collected with a Bruker AXS Smart CCD
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diffractometer at 103(2) K (graphite-monochromated Mo-Kα radi-
[3c]
˚
ation, λ ϭ 0.71073 A, , ω-scans). Data were corrected for Lorenz
H. Michel, D. Steiner, S. Wocadlo, J. Allwohn, N. Stamatis, W.
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reflections (SHELXL-97).[32] All non-hydrogen atoms were refined
anisotropically. CCDC-219079 (for 2a), -219080 (for 3), -219081
(for 9) and -219082 (for 9Ј) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Center, 12 Union Road, Cam-
bridge CB2 1EZ, UK; Fax: (internat.) ϩ 44-1223-336-033; E-mail:
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Early View Article
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1638
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