Synthesis, molecular structure, and electrochemistry of 1-ferrocenyl-1,2-dicarba-closo-dodecaboranes

Article abstract of DOI:10.1002/ejic.201300110

Bis(dimethylsulfido)decaborane, 6,9-(Me₂S)₂-arachno- B₁₀H₁₂, reacts smoothly with ferrocenyl alkynes FcC≡CR [1a-h; Fc = ferrocenyl, R = H (1a), CH₃ (1b), Ph (1c), 4-MeO₂CC₆H₄ (1d), Fc (1e), C≡CFc (1f), C(O)CH₃ (1g), and CO₂CH₂CH₃ (1h)] to afford the corresponding 1-ferrocenyl-1,2-dicarba-closo-dodecaboranes 2a-h in good yields. Ester 2h was further reduced to the respective hydroxymethyl derivative, 1-Fc-2-CH₂OH-1,2-closo-C₂B₁₀H ₁₀ (3). The reaction of 6,9-(Me₂S)₂-B ₁₀H₁₂ with FcC≡CSiMe₃ proceeded in a different manner to produce (among other products) an SMe₂ adduct of an opened decaborane substituted with a 2-ferrocenyl-2-(trimethylsilyl)ethen-1- yl group (4). This compound probably results through hydroboration of the starting alkyne and migration of the SiMe₃ group. All prepared compounds were characterized by spectroscopic methods (¹H, ¹³C, and ¹¹B NMR spectroscopy, IR spectroscopy, and mass spectrometry), and their molecular structures were determined by single-crystal X-ray diffraction analysis. In addition, the compounds were studied by cyclic and differential pulse voltammetry on a platinum disc electrode to reveal simple ferrocenyl-centered oxidations for the singly ferrocenylated carboranes and two consecutive oxidation waves for compounds 2e and 2f, which possess two ferrocenyl substituents. Copyright

Full text of DOI:10.1002/ejic.201300110

FULL PAPER
DOI:10.1002/ejic.201300110
Synthesis, Molecular Structure, and Electrochemistry of
1-Ferrocenyl-1,2-dicarba-closo-dodecaboranes
[a]
[a]
[b]
ˇ
ˇ
ˇ
ˇ
ˇ
ˇ
Ales Korotvicka, Ivan Snajdr, Petr Stepnicka,*
[b]
[c]
[a]
ˇ
ˇ
ˇ
Ivana Císarová, Zbynek Janousek, and Martin Kotora*
Keywords: Carboranes / Metallocenes / Structure elucidation / Electrochemistry / Addition
Bis(dimethylsulfido)decaborane,
6,9-(Me2S)2-arachno-
probably results through hydroboration of the starting alkyne
and migration of the SiMe3 group. All prepared compounds
were characterized by spectroscopic methods (1H, 13C, and
11B NMR spectroscopy, IR spectroscopy, and mass spectrome-
try), and their molecular structures were determined by sin-
B10H12, reacts smoothly with ferrocenyl alkynes FcCϵCR
[1a–h; Fc = ferrocenyl, R = H (1a), CH3 (1b), Ph (1c), 4-Me-
O2CC6H4 (1d), Fc (1e), CϵCFc (1f), C(O)CH3 (1g), and
CO2CH2CH3 (1h)] to afford the corresponding 1-ferrocenyl-
1,2-dicarba-closo-dodecaboranes 2a–h in good yields. Ester gle-crystal X-ray diffraction analysis. In addition, the com-
2h was further reduced to the respective hydroxymethyl de-
rivative, 1-Fc-2-CH2OH-1,2-closo-C2B10H10 (3). The reaction
of 6,9-(Me2S)2-B10H12 with FcCϵCSiMe3 proceeded in a dif-
ferent manner to produce (among other products) an SMe2
adduct of an opened decaborane substituted with a 2-ferro-
cenyl-2-(trimethylsilyl)ethen-1-yl group (4). This compound
pounds were studied by cyclic and differential pulse voltam-
metry on a platinum disc electrode to reveal simple ferro-
cenyl-centered oxidations for the singly ferrocenylated
carboranes and two consecutive oxidation waves for com-
pounds 2e and 2f, which possess two ferrocenyl substituents.
cenyl group in the vicinity of the triple bond exerts steric
hindrance that could in turn affect the reactivity of the
triple bond. So far, monoferrocenylalkynes have been em-
ployed in transition-metal-catalyzed[4] or -mediated[5]
[2+2+2] cycloadditions to provide the corresponding ferro-
cenylbenzenes, in reactions with reduced metallocenes to
form the corresponding ferrocene-substituted metallacyclo-
pentadienes or η2-alkyne complexes,[6] in [4+2] cycload-
ditions with tetraalkylcyclobutadiene complexes to give rise
to Dewar benzenes,[7] and as reaction partners in the C–C
cleavage reaction of phenylenes.[8] The bulky diferrocenyl-
ethyne has been studied much less in this regard, very likely
owing to a relatively difficult means of access to this com-
pound.[9]
Given our interest in the synthesis of ferrocene-substi-
tuted compounds[5,7,8] and variously substituted carbor-
anes,[10] it was rather surprising to find that there has not
yet been undertaken any systematic study into the addition
reactions of decaborane or its adducts (L2-arachno-B10H12)
and ferrocenylalkynes. In fact, there appear to be just two
reports that concern the synthesis of (mono)ferrocenyl-
carborane by the reaction of decaborane with ferrocenyl-
ethyne in the presence of MeCN.[11] Likewise, studies into
other ferrocenyl-substituted boranes and metallaboranes re-
main still scarce.[12] This provided a strong impetus for us
to assess the scope of the reaction of decaborane derivative
6,9-(Me2S)2-arachno-B10H12 with variously substituted
ferrocenylalkynes and to characterize in detail thus-access-
ible ferrocenylated closo-1,2-dicarbadodecaboranes.
Introduction
The reaction between decaborane adducts of type L2-
arachno-B10H12 (L = MeCN, Et2S, Me2S, and so on) and
alkynes is one of the key procedures for the synthesis of
mono- and disubstituted 1,2-closo-carboranes. This process
is general with respect to the substituents attached to car-
bon atoms of the triple bond and usually proceeds well to
afford the respective substituted carboranes in good
yields.[1,2]
Ferrocenylalkynes constitute an attractive subclass
among alkynes, mostly because their utilization in various
addition and cycloaddition reactions provides direct access
to compounds functionalized with the redox-active, metal-
containing ferrocene moiety.[3] In addition, the bulky ferro-
[a] Department of Organic Chemistry, Faculty of Science, Charles
University,
Hlavova 8, 12843 Praha 2, Czech Republic
Fax: +420-221-951-326
E-mail: kotora@natur.cuni.cz
Homepage: http://orgchem.cz/kotora
[b] Department of Inorganic Chemistry, Faculty of Science,
Charles University,
Hlavova 8, 12843 Praha 2, Czech Republic
Fax: +420-221-951-253
E-mail: stepnic@natur.cuni.cz
Homepage: http://web.natur.cuni.cz/~stepnic/
[c] Institute of Organic Chemistry and Biochemistry, AS CR, v.v.i.,
Flemingovo nám. 2, 16610 Praha 6, Czech Republic
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300110.
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Table 1. Prepraration of ferrocenylcarboranes 2a–2h.
Results and Discussion
Synthesis and Spectra
The starting alkynes were all obtained from ferrocenyl-
ethyne 1a by using the previously developed procedures.
Thus, 1-ferrocenylpropyne 1b was prepared by lithiation of
1a with nBuLi followed by treatment with methyl iodide. A
similar method (i.e., electrophilic quench of metalated 1a)
was used to prepare compounds 1g and 1h.[13] Phenyl- and
(4-methoxycarbonyl)phenyl derivatives 1c and 1d were ob-
tained by Sonogashira reaction of 1a with the respective
aryl halides, whereas diferrocenylethyne 1e was synthesized
by homo-alkyne metathesis of 1b.[14] Diyne 1f was obtained
by the Glaser coupling.[15]
The reactions of ferrocenylalkynes 1 with 6,9-(Me2S)2-
arachno-B10H12 were carried out under the usual conditions
(i.e., the alkyne was heated with the decaborane adduct un-
der reflux conditions in toluene for 16 h; Scheme 1).
Scheme 1. Reaction of 6,9-(Me2S)2-B10H12 with ferrocenylalkynes.
In all cases but one the reactions proceeded uneventfully
to afford the expected 1-ferrocenyl-1,2-dicarba-closo-do-
decaboranes (Table 1). The reactions with methyl-, phenyl-,
and 4-MeO2CC6H4-substituted ferrocenylalkynes 1b–1d
yielded the corresponding closo-carboranes 2b–2d in good
isolated yields of 21, 61, and 60%, respectively. The reaction
with the sterically hindered diferrocenylethyne 1e also pro-
ceeded surprisingly well, which provided 1,2-diferrocenyl-
1,2-dicarba-closo-dodecaborane 2e in 58% yield. Likewise,
the reaction with 1,4-diferrocenylbutadiyne 1f gave 2f in
52% isolated yield. The presence of two triple bonds in 1f
could in principle enable a twofold reaction, thereby giving
rise to the corresponding bridged bis-carborane.[16] How-
ever, we did not isolate any such compound from the reac-
tion mixture.
The general procedure also proved feasible for electron-
deficient ferrocenyl alkynes 1g and 1h, which bear the reac-
tive acetyl and carboxymethyl groups. The corresponding
[a] Isolated yields.
carboranes 2g–2h were isolated in reasonable 29 and 55% acetylferrocene was isolated after the standard workup
1
yields, respectively.
(33% isolated yield; H NMR spectroscopic data were in
For a comparison, the reaction with ferrocenylethyne 1a agreement with the published ones[19]). The presence of car-
was also performed as reported previously,[11] and com- borane 2a in the reaction mixture was not confirmed. It is
pound 2a was isolated in 26% yield (isolated yields in the assumed that acetylferrocene was formed by hydroboration
original reports were not given). Compound 2b was recently of the triple bond and subsequent hydrolysis. The reaction
obtained by a different route.[17] Furthermore, we attempted with 1-ferrocenylpropyne 1b yielded the expected carborane
to carry out the direct reaction of decaborane B10H14 with 2b in 28% isolated yield, whereas the reaction with diferro-
representative alkynes 1a, 1b, and 1e in ionic liquid (bmim)- cenylethyne 1e did not proceed at all, and the starting alk-
Cl (bmim = 1-butyl-3-methylimidazolium) as was described yne was recovered unchanged. Although the direct reaction
earlier for simple alkynes.[18] In the case of ethynylferrocene of decaborane with alkynes might represent a simpler and
1a, a complex reaction mixture resulted, from which only more straightforward approach to substituted carboranes,
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its scope seems to be limited compared to reactions with
adducts L2-arachno-B10H12. Safety issues with handling and
manipulation of hazardous decaborane also disfavor the di-
rect route.
The prepared 1,2-dicarbadodecaboranes 2a–2h were
characterized by a combination of multinuclear NMR spec-
troscopy (1H, 13C, and 11B), IR spectroscopy, mass spec-
trometry, and elemental analysis. In addition to these con-
ventional methods, all isolated compounds were charac-
terized by single-crystal X-ray diffraction analysis, which
unequivocally confirmed their formulation (see below). The
11B NMR spectra of 2a–2h display a pattern typical for
symmetrically (2e) and unsymmetrically (2a–2d, 2f–2h) sub-
stituted 1,2-dicarbadodecaboranes. The spectra of the sym-
metrically substituted 1,2-dicarba-closo-dodecaborane show
the signals in the order δB: B(12,9) Ͼ B(8,10) Ͼ
B(5,4,7,11) Ͼ B(3,6). The patterns seen for the unsymmet-
rically substituted 1,2-dicarba-closo-dodecaboranes depend
on the electronic nature of the substituents.[20]
Scheme 3. Reaction of 6,9-(Me2S)2-B10H12 with 1h to furnish com-
pound 4.
To extend the scope of accessible “ortho-carborane” de-
rivatives, the ester derivative 2h was converted into the cor-
responding alcohol 3 by reduction with diisobutylalumin-
ium hydride (DIBAL-H) in dichloromethane (Scheme 2).
The reduction proceeded cleanly and furnished the alcohol
in a 96% isolated yield. The compound was characterized
by spectroscopic methods and its structure was determined
by X-ray diffraction analysis.
Figure 1. PLATON plot of the structure of 4 showing the atom-
labeling scheme and displacement ellipsoids at the 30% probability
level. Selected distances and angles (in Å and °): S1–B5 1.890(4),
S1–C16 1.796(4), S1–C17 1.795(4), B5–B6 1.670(5), B6–C1
1.561(5), C1–C2 1.350(4), C2–C3 1.487(4), C2–Si1 1.903(3); C1–
C2–C3 117.4(2), C16–S1–C17 100.9(2), C1–C2–Si1 118.9(2), B6–
C1–C2–Si1 –0.1(5), B–B (range) 1.670(5)–2.032(6); ferrocenyl moi-
ety: Fe–C 2.028(3)–2.061(3) Å, tilt 1.7(2)°.
Scheme 2. Reduction of ester 2h to alcohol 3.
Finally, we attempted to treat 6,9-(Me2S)2-arachno-
B10H12 with 1-trimethylsilyl-2-ferrocenylethyne (1i)[6]
(Scheme 3). According to TLC analysis, which was used to
monitor the course of the reaction, the starting alkyne dis-
appeared completely under the standard reaction condi-
tions to afford a complex reaction mixture. A tedious col-
umn chromatography provided several fractions, but none
of them contained the expected product (as could be judged
from the 1H and 11B NMR spectra). However, crystalli-
zation of one of the fractions provided crystalline nido-bor-
ane derivative (4; ca. 5% yield), which was fully charac-
terized by NMR spectroscopy and elemental analysis. In
addition, the compound afforded crystals suitable for a sin-
gle-crystal X-ray analysis, which revealed a rather unusual
structure (Figure 1).
lecule, which comes from the starting decaborane adduct,
and is bonded to one of the boron atoms at the opened ten-
vertex borane cage. From a mechanistic viewpoint, the nido-
borane 4 appears to be the product of hydroboration of the
triple bond followed by 1,2-migration of the trimethylsilyl
group. A similar rearrangement was previously observed
only in the case of reactions of bis(trimethylsilyl)ethyne
and (trimethylsilyl)propyne with 6,9-(Me2S)2-arachno-
B10H12.[17]
Description of Molecular Structures of 2a–h and 3
The molecular structures of 2a–h and 3 were determined
by single-crystal X-ray diffraction analysis. Compounds
First, the C–C triple bond was transformed into the 2a[11] and 2b[21] have been structurally characterized already
double bond, and its trimethylsilyl substituent migrated before, but for the sake of consistency, we have redeter-
from the terminal carbon atom of the original triple bond mined their crystal structures under the same conditions.
to the internal carbon atom of the newly formed double The structures of 2c, 2f–h, and 3 are depicted in Figures 2,
bond. Second, the product contains a dimethyl sulfide mo- 3, 4, 5, 6, and 7, whereas those of 2a, 2b, and 2d are pre-
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sented in the Supporting Information (Figures S1–S3). Se-
lected geometric data for all compounds are summarized in
Table 2.
Figure 4. PLATON plot of 2f (molecule 1) showing the atom-label-
ing scheme and displacement ellipsoids at the 30% probability level
(see note in the caption to Figure 3).
Figure 2. PLATON plot of 2c showing the atom-labeling scheme
and displacement ellipsoids at the 30% probability level. Only one
orientation of the disordered cyclopentadienyl ring C(9–12) is
shown for clarity.
Figure 5. PLATON plot of 2g showing the atom-labeling scheme
and displacement ellipsoids at the 30% probability level.
Figure 3. PLATON plot of 2e (molecule 1) showing the atom-label-
ing scheme and displacement ellipsoids at the 30% probability
level. Note: Atomic labels in the second independent molecule are
of the C2B10 cages in the structurally characterized com-
pounds are rather uniform and do not depart from the us-
obtained by changing the first digit of the respective atomic labels ual ranges (B–B 1.757–1.799 Å, B–C 1.690–1.745 Å for all
to 2.
structurally characterized compounds). The planes that bi-
sect the carborane cage, namely, {C1,C2,B9,B12} and
The structures of 2a–h are essentially molecular[22] with {B3,B6,B8,B10}, are mutually perpendicular (dihedral
the exception of alcohol 3, which forms cyclic centrosym- angles 89.6–90.0°), which reflects the rigidity of the com-
metric arrays through O–H···O hydrogen bonds (Figure 8). pact closo-carborane cage. Compound 2a, which bears the
Often, the compounds crystallize with two molecules per smallest substituent (hydrogen atom) at C2, exhibits the
asymmetric unit (2a, 2e, 2g, and 3). However, the indepen- shortest C1–C2 distance, and its ferrocenyl substituent is
dent molecules typically show only marginal differences.
oriented above the C1–C2 bond and tilted with respect to
Generally, the structural data for 2a–h and 3 compare the {C1,C2,B9,B12} plane, which bisects the carborane
well with those reported earlier for fc(2-Me-1,2-C2B10H10)2 cage (see parameter δ in Table 2). All other structurally
(fc = ferrocene-1,1Ј-diyl)[11b] and ferrocenylated carboranes characterized ferrocenylated closo-carboranes assume a dif-
reported recently by Xie and co-workers.[21] The geometry ferent conformation. The ferrocenyl substituents in their
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Figure 7. PLATON plot of 3 (molecule 1) showing the atom-label-
ing scheme and displacement ellipsoids at the 30% probability level
(see note in the caption to Figure 3).
Figure 6. PLATON plot of 2h showing the atom-labeling scheme
and displacement ellipsoids at the 30% probability level.
Table 2. Selected geometric data for compounds 2a–h and 3 (in Å and °).[a,b]
2a[c]
2b
2c[b]
2d[d]
2e[e]
2f[f]
2g[g]
2h[h]
3[i]
C1–C2
1.653(2)
[1.653(3)]
1.490(2)
[1.490(2)]
120.6(1)
[120.5(2)]
n.a.
1.691(3)
[1.701(3)]
1.485(3)
[1.484(3)]
115.7(2)
[116.1(1)]
1.546(4)
[1.538(3)]
117.0(2)
[117.2(2)]
–1.0(3) [–
5.5(2)]
1.712(2)
[1.713(2)]
1.489(2)
[1.488(2)]
117.3(1)
[117.7(1)]
1.531(2)
[1.525(2)]
116.5(1)
[117.6(1)]
1.701(2)
1.491(2)
116.5(1)
1.515(2)
117.6(1)
0.4(2)
1.733(2)
1.484(2)
115.5(1)
1.503(2)
118.0(1)
2.6(2)
1.718(4) 1.764(2) [1.757(2)]
1.481(4) 1.483(2) [1.485(2)]
114.3(2) 116.7(1) [115.7(1)]
1.498(4) 1.479(3) [1.488(2)]
118.4(2) 117.2(1) [116.5(1)]
1.714(4)
1.486(3)
114.9(2)
1.448(4)
114.1(2)
–2.2(3)
1.697(2)
1.487(2)
116.01(9)
1.528(2)
115.28(9)
–2.6(1)
C1–C3
C2–C1–C3
C2–C13
C1–C2–C13
n.a.
C3–C1–C2–C13 n.a.
2.8(3)
0.4(2) [0.5(2)]
2.8(2) [1.5(2)]
φ
44.22(6)
[42.58(8)]
23.00(7) (Fe11)/23.69(6)
(Fe12) [20.64(7) (Fe21)/
22.96(7) (Fe22)]
82.7(1) (Fe11)/88.9(1)
(Fe12) [88.3(1) (Fe21)/
89.4(1) (Fe22)]
19.47(8)
[21.0(1)]
22.42(5)
[23.66(5)]
21.61(5)
89.04(9)
20.72(6)c
89.3(1)
26.3(1)
17.3(1)
89.5(2)
1.639(1)
1.651(2)
4.0(2)
22.08(5)
83.97(8)
1.6460(6)
1.6536(7)
3.66(8)
δ
71.1(1)
[71.7(1)]
84.3(2)
[78.9(1)]
81.73(8)
[89.44(9)]
69.3(2)
Fe–Cg1
Fe–Cg2
τ
1.6447(8)
[1.6438(9)]
1.6433(9) (Fe11)/1.6480(9)
1.636(1)
[1.639(1)]
1.6492(7)
[1.6473(7)]
1.6449(7) 1.6405(9)
1.644(1) (Fe12) [1.6419(9) (Fe21)/
1.6554(9) (Fe22)]
1.653(1) (Fe11)/1.6559(9)
1.653(2) (Fe12) [1.6489(9) (Fe21)/
1.662(1) (Fe22)]
1.6537(9)
[1.657(1)]
1.6696(6)/
1.6522(7)
1.644(1)
[1.651(1)]
1.6548(7)
[1.6542(7)]
1.6323(6)d
6.2(1) [4.8(1)]
4.3(1) (Fe11)/4.6(1) (Fe12)
[5.0(1) (Fe21)/3.7(1)
(Fe22)]
3.5(1)
[4.1(2)]
4.08(9)
[4.26(9)]
3.05(9)
3.2(1)c
2.3(2)
[a] Definitions: Cp1 and Cp2 are planes of the cyclopentadienyl rings C3–C7 and C8–C12, respectively. Cg1 and Cg2 denote their
respective centroids. φ = angle subtended by the vectors Cg···Cg2 and C1–C2; δ = the dihedral angle subtended by the plane
{C1,C2,B9,B12} and the plane of the substituted cyclopentadienyl ring (Cp1). τ denotes the dihedral angle of the cyclopentadienyl planes
Cp1 and Cp2 (i.e., the tilt angle). Values in square brackets correspond to the second structurally independent molecule in the crystal
structure. The labeling schemes in molecules 1 and 2 are strictly analogous, with the respective atomic labels having 1 or 2 added as the
first digit. [b] Further data for 2c: The dihedral angle of the phenyl ring and the {C1,C2,B9,B12} plane is 71.3(1)°. [c] Value for the more
populated orientation of the unsubstituted Cp ring. [d] Further data for 2d: C19–O1 1.206(4)°, C19–O2 1.326(4)°, O1–C19–O2 124.1(3)°;
dihedral angle of the phenyl ring and the {C1,C2,B9,B12} plane is 79.4(2)°; dihedral angle of the {C19, O1, O2} plane and the phenyl
ring is 12.3(4)°. [e] For clarity, the labels of the iron atoms are specified for values relating to the two independent ferrocenyl substituents.
[f] Further data for 2f: C13–C14 1.158(5)°, C14–C15 1.426(5)°, C2–C13–C14 165.5(3)°, C13–C14–C15 166.6(4)°. Compound 2e: Fe–Cg1/
Cg2 distances for the FcCϵC group are 1.642(1)/1.648(1), the tilt angle is 2.0(2)°. [g] Further data for 2g: C=O 1.203(3) [1.190(3)], C(O)–
CH3 1.468(4) [1.456(4)], O=C–CH3 123.0(3) [122.5(3)]. [h] Further data for 2h: C13–O1 1.193(2), C13–O2 1.323(2), O2–C14 1.467(2).
[i] Further data for 3: CH2–O 1.408(2) [1.410(2)].
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Table 3. Summary of the redox potentials for carboranes 2a–h and
3.[a]
R
E°Ј [V versus FcH/FcH+]
2a
2b
2c
2d
2e
2f
2g
2h
3
H
Me
Ph
0.265
0.275
0.250
0.270
4-C6H4CO2CH3
Fc
CϵCFc
Ac
CO2CH2CH3
CH2OH
0.200, 0.345
Epa = 0.330, Epc = 0.175
0.270
0.280
0.275
[a] E°Ј = 1/2(Epa +Epc), in which Epa (Epc) are anodic (cathodic)
peak potentials in cyclic voltammetry. Conditions: Pt disc elec-
trode, 1,2-dichloroethane solutions containing 0.1 m Bu4N[PF6] as
the supporting electrolyte scan rate: 200 mVs–1.
Figure 8. View of the cyclic hydrogen-bonded array in the crystal
structure of alcohol 3. The hydrogen-bond parameters are as fol-
lows: O1–H1···O2, O1···O2 2.747(2) Å, angle at H1 169(2)°; O2–
H2···O1, O2···O1 2.836(2) Å; angle at H2 169(2)°.
These redox processes were controlled by diffusion
[ipa [vprop ] (ν1/2); ipa is anodic peak current and ν the scan
rate], were electrochemically reversible, and corresponded
to a one-electron redox transition. The associated redox po-
tentials were found in a rather narrow range (ΔE°Ј ≈ 30 mV;
see Table 3), which indicates a limited electronic influence
of the second substituent (2-R) attached to the 1-Fc-1,2-
C2B10H10 cage on the redox properties of the ferrocenyl
group.
molecules are rotated above the adjacent trigonal CB2 face
(C1, B4, B5), presumably to avoid spatial contacts with the
substituent at C2. As a result, the ferrocenyl groups are near
to perpendicular to the central {C1,C2,B9,B12} plane and
show δ angles in the range of approximately 69–90°. It is
also noteworthy that variation in the C1–C2 bond lengths
(1.69–1.73 Å) in 2a–h and 3 does not seem to follow any
obvious trend (e.g., with electronic and/or properties of the
substituents at C2).
Ferrocene moieties in 2a–h and 3 are regular and show
tilt angles below approximately 6° [maximum: 6.2(1)° for
2a, molecule 1]. In all cases, the distance of the iron atom
from the centroid of the substituted cyclopentadienyl ring
(Fe–Cp1) is slightly shorter than that between the iron atom
and the centroid of the unsubstituted cyclopentadienyl ring.
Such a difference in the Fe–Cp distances very likely reflects
the electron-withdrawing nature of the electron-deficient
carborane cage, thereby resulting in a transfer of electron
density from the ferrocenyl group to the C2B10 skeleton and
strengthening the Fe–C5H4 bonding relative to Fe–C5H5.[23]
Figure 9. Cyclic voltammogram of 2a as recorded on a Pt disc elec-
trode in 1,2-dichloroethane (scan rate 0.2 Vs–1).
Electrochemistry
The electrochemical behavior of carboranes 2 and 3 was
Introduction of a second ferrocenyl group such as in 2e
studied by cyclic and square-wave voltammetry on a plati- was reflected by an appearance of a second redox wave
num disc electrode by using approximately 0.5 mm solutions (Figure 10). Thus, compound 2e was oxidized in two dis-
in 1,2-dichloroethane that contained 0.1 m Bu4N[PF6] as tinct one-electron redox steps, thus suggesting some elec-
the supporting electrolyte. The pertinent data are presented tronic communication between the chemically equivalent
in Table 3.
ferrocenyl groups. The separation of the redox waves (ca.
Compounds that contain one ferrocenyl substituent (2a– 145 mV) suggests this compound to be a weakly coupled
d, 2g, 2h, and 3) expectedly displayed a single redox change redox system, at the borderline between class I and II sys-
within the accessible potential window, which can be attrib- tems according to the Robin–Day classification.[24] The eth-
uted to the ferrocene/ferrocenium couple (FeII/III; Figure 9). ynyl spacer present in 2f makes the two ferrocenyl groups
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more distant and further lowers their interaction. Conse-
quently, the individual waves become closer than in 2e and
Conclusion
Our systematic study demonstrates that reactions of 6,9-
(Me2S)2-arachno-B10H12 with ferrocenyl alkynes FcCϵCR
bearing simple and functional (organic) substituents pro-
vide a viable route to the corresponding 1-ferrocenyl-2-R-
1,2-dicarba-closo-dodecaboranes. An analogous reaction
with FcCϵCSiMe3 surprisingly takes a different course,
thereby producing a complicated product mixture from
which an unusual opened borane–dimethyl sulfide adduct
bearing the 2-ferrocenyl-2-(trimethylsilyl)-ethen-1-yl group
was isolated in tiny amounts. The 1,2-dicarba-closo-dodeca-
boranes possess similar compact icosahedral structures dec-
orated with the substituents (Fc and R) at the outer side.
No clear trends were detected among the structural param-
eters, thereby reflecting a possible influence of the attached
substituent (R). Similarly, the influence of the R moiety on
the redox response of the monoferrocenylated carboranes,
which all undergo reversible one-electron oxidation that is
attributable to the ferrocene/ferrocenium couple, is also
very limited. Introduction of a second ferrrocenyl moiety
is reflected by another more or less separated wave, which
indicates some electronic communication between the re-
dox-active ferrocenyl pendants.
appear convoluted (Figure 11).
Experimental Section
Figure 10. Cyclic (CV) and square-wave (SQW) voltammograms of
2e (conditions: Pt disc electrode, 1,2-dichloroethane). Modulation
amplitude is given for the SQW voltammograms. For clarity, the
cyclic voltammogram (scan rate 0.2 Vs–1) is shifted by +25 μA.
Materials and Methods: Ethynylferrocene (1a) was obtained from
Acros. Alkynylferrocenes 1b–1h[6,13–15] and 6,9-(Me2S)2-arachno-
[25]
B10H12 were synthesized according to the literature procedures.
Toluene was distilled from Na/benzophenone ketyl prior to use.
All reactions were carried out in flame-dried glassware under an
atmosphere of dry N2 or Ar.
NMR spectra were recorded on spectrometers with different op-
erating frequencies (1H: 600 or 400 MHz; 13C: 150 or 101 MHz,
11B: 128 MHz). Boron signals were assigned with the aid of 11B,11B
COSY and 1H[11B(selective)] NMR spectroscopic experiments. The
samples were dissolved in [D6]benzene and the spectra were refer-
enced to the residual solvent signal (C6D6: δH = 7.16 ppm, δC
=
128.0 ppm), tetramethylsilane (internal standard, δH = δC = 0 ppm)
or BF3·OEt2 (internal standard for 11B NMR spectroscopy). TLC
analyses were performed on silica gel 60 F254 aluminum sheets,
column chromatography was carried out on silica gel 60 or Brock-
mann II alumina.
Electrochemical measurements were carried out with a computer-
controlled polarograph μAUTOLAB III (Eco Chemie, The Nether-
lands) at room temperature (ca. 22 °C) using a three-electrode cell
equipped with a platinum disc working electrode (2 mm diameter),
a platinum sheet auxiliary electrode, and a double-junction Ag/
AgCl (3 m KCl) reference electrode. The compounds were dissolved
in anhydrous 1,2-dichloroethane (Sigma–Aldrich) to give a solution
that contained approximately 0.5 mm of the analyzed compound
and 0.1 m Bu4N[PF6] (Fluka, p.a. for electrochemistry). The solu-
tions were deaerated by bubbling with argon and then kept under
an argon blanket. The redox potentials were calculated as E°Ј =
1/2(Epa + Epc), in which Epa and Epc are the anodic and cathodic
peak potentials in cyclic voltammetry, and are given relative to in-
ternal ferrocene/ferrocenium reference. The values were reproduc-
ible within approximately 5 mV.
Figure 11. Cyclic (CV) and square-wave (SQW) voltammograms of
2f (conditions: Pt disc electrode, 1,2-dichloroethane). Modulation
amplitude is specified for the SQW voltammograms. The cyclic vol-
tammogram (scan rate 0.2 Vs–1) is shifted by +25 μA to avoid over-
laps.
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General Procedure for the Preparation of Carboranes 2: 6,9-
(Me2S)2-B10H12 (147 mg, 0.6 mmol) and the corresponding alkyne
(0.4 mmol) were placed into a round-bottomed flask equipped with
a condenser and an argon inlet. Toluene (4 mL) was added, and
the reaction mixture was heated in an oil bath at 120 °C under
argon for 16 h. After cooling, methanol (2 mL) was added to the
reaction mixture, and the volatiles were removed under reduced
pressure. The residue was purified by column chromatography on
silica gel to afford the product by using chloroform or dichloro-
methane/hexane mixtures as the eluent. Particular synthetic details
and characterization data are given below.
1-Ferrocenyl-2-[4-(methoxycarbonyl)phenyl]-1,2-dicarba-closo-dode-
caborane (2d): {[4-(Methoxycarbonyl)phenyl]ethynyl}ferrocene
(69 mg, 0.2 mmol), 6,9-(Me2S)2-B10H12 (64 mg, 0.26 mmol). Col-
umn chromatography (2:1 hexane/CHCl3) yielded 56 mg (61%) of
the title compound as an orange solid, m.p. 162–164 °C (CHCl3).
1H{11B} NMR (400 MHz, C6D6): δ = 7.66 (d, J = 8.5 Hz, 2 H, H–
Ar), 7.22 (d, J = 8.6 Hz, 2 H, Ar–H), 3.91 (s, 5 H, Fc), 3.89–3.86
(m, 2 H, Fc), 3.52–3.47 (m, 2 H, Fc), 3.33 (s, 4 H, CH3 and 12-H),
3.16 (br. s, 1 H, B9–H), 3.06 [br. s, 2 H, B(3,6)–H], 2.96 [br. s, 2
H, B(8,10)–H], 2.86 [br. s, 2 H, B (7,11)–H], 2.72 [br. s, 2 H, B(4,5)–
H] ppm. 13C NMR (151 MHz, C6D6): δ = 165.79 (C=O), 135.79
(C–Ar), 132.36 (C–Ar), 131.58 (C–Ar), 129.74 (C–Ar), 128.68 (C–
Ar), 86.16 (C–carborane), 85.01 (C–carborane), 83.37 (Fc), 71.72
(Fc), 71.09 (Fc), 69.23 (Fc), 52.06 (CH3) ppm. 11B NMR
(128 MHz, C6D6, BF3·OEt2): δ = –0.54 (d, JB,H = 152 Hz, 1 B,
B12), –1.83 (d, JB,H = 131 Hz, 1 B, B9), –7.91 [d, JB,H = 130 Hz, 4
B, B(8,10; 7,11)], –9.84 [d, JB,H = 115 Hz, 4 B, B(3,6; 4,5)] ppm.
HRMS (EI) calcd. for C20H2610B211B8O2Fe: 462.2285; found
462.2286. MS (EI): m/z (%) = 462.2 (100) [M+], 279.2 (10), 216.1
(20), 121.0 (20). C20H26B10FeO2 (464.22): calcd. C 51.95, H 5.67,
1-Ferrocenyl-1,2-dicarba-closo-dodecaborane (2a): Ethynylferrocene
(105 mg, 0.50 mmol), 6,9-(Me2S)2-B10H12 (183 mg, 0.75 mmol).
Column chromatography (6:1 hexane/CH2Cl2) yielded 43 mg
(26%) of 2a as an orange solid. Spectral characteristics were in
agreement with the published data,[11b] m.p. 121–123 °C (CHCl3).
1H NMR (600 MHz, C6D6): δ = 3.92 (apt, J = 2.0 Hz, 2 H, Fc),
3.87 (s, 5 H, Fc), 3.70 (apt, J = 2.0 Hz, 2 H, Fc), 2.86 (s, 1 H, CH)
ppm. 13C NMR (150 MHz, C6D6): δ = 65.3 (C–carborane), 69.0
(Fc), 70.5 (Fc), 70.6 (Fc), 76.5 (Fc), 86.4 (C–carborane) ppm.
Fe 12.08; found C 51.68, H 5.69, Fe 11.39. IR (KBr): ν = 2591,
˜
1-Ferrocenyl-2-methyl-1,2-dicarba-closo-dodecaborane (2b): (Pro-
pyn-1-yl)ferrocene, (90 mg, 0.40 mmol), 6,9-(Me2S)2-B10H12
(146 mg, 0.60 mmol). Column chromatography (10:1 hexane/
CH2Cl2) yielded 29 mg (21%) of the title compound as an orange
solid. Spectral characteristics were in agreement with the published
2573, 2552, 1724, 1434, 1287, 1123, 836 cm–1. Rf (2:1 hexane/
CHCl3) = 0.5.
1,2-Diferrocenyl-1,2-closo-dicarbadodecaborane (2e): Diferrocenyl-
ethyne (39 mg, 0.1 mmol), 6,9-(Me2S)2-B10H12 (37 mg, 0.15 mmol).
Column chromatography (4:1 hexane/CHCl3) yielded 30 mg (58%)
of the title compound as a red solid, m.p. 259–261 °C (CHCl3).
1H{11B} NMR (400 MHz, C6D6): δ = 3.97–3.90 (m, 14 H, Fc),
3.64–3.58 (m, 4 H, Fc), 3.36 [br. s, 2 H, B(9,12)–H], 3.13 [br. s, 4
H, B(3,6; 4,5)–H], 2.89 [br. s, 4 H, B(7,11; 8,10)–H] ppm. 13C
NMR (151 MHz, C6D6): δ = 86.04 (C–carborane), 83.64 (Fc),
72.08 (Fc), 71.02 (Fc), 68.88 (Fc) ppm. 11B NMR (128 MHz, C6D6,
BF3·OEt2): δ = –1.81 [d, J = 114 Hz, 2 B, B(9,12)], –7.95 [d, J =
106 Hz, 6 B, B(3,6; 4,5; 7,11)], –11.11 [d, J = 125 Hz, 2 B, B(8,10)]
ppm. HRMS (EI) calcd. for C22H2810B211B8Fe2: 512.1893; found
512.1887. MS (EI): m/z (%) = 512.2 (100) [M+], 447.2 (10), 256.1
(20), 121.2 (80). C22H28B10Fe2 (514.18): calcd. C 51.58, H 5.51;
1
data,[21] m.p. 127 °C (CHCl3). H{11B} NMR (400 MHz, C6D6): δ
= 4.02 [apt, JH,H = 2.0 Hz, 2 H, Fc], 3.98 (s, 5 H, Fc), 3.76 (apt,
JH,H = 2.0 Hz, 2 H, Fc), 3.11 (br. s, 1 H, B12–H), 3.00 (br. s, 1 H,
B9–H), 2.93 [br. s, 2 H, B(8,10)–H], 2.73 [br. s, 2 H, B(3,6)–H],
2.50 [s, 2 H, B(5,4)-H], 2.36 [s, 2 H, B(7,11)–H], 1.04 (s, 3 H, CH3)
ppm. 13C NMR (75 MHz, C6D6): δ = 84.3 (C–carborane), 82.1 (C–
carborane), 78.0 (Fc), 72.0 (Fc), 71.6 (Fc), 69.7 (Fc), 23.0 (CH3)
ppm. 11B NMR (128 MHz, C6D6, BF3·OEt2): δ = –4.80 [d, JB,H
=
155 Hz, 2 B, B(9,12)], –9.97 [d, JB,H = 165 Hz, 6 B, B(4,5; 7,11;
8,10)], –11.85 [d, JB,H = 152 Hz, 2 B, B(3,6)] ppm. HRMS calcd.
for C13H2210B211B8Fe: 342.2069; found 342.2069. MS (ESI): m/z
(%) = 342 (100) [M+], 256 (7), 228 (27). C13H22B10Fe (344.20):
calcd. C 45.62, H 6.48, Fe 16.32; found C 45.68, H 6.27, Fe 16.03.
found C 51.45, H 5.29. IR (KBr): ν = 2663, 2603, 2576, 1443, 1269,
˜
1108, 821 cm–1. Rf (4:1 hexane/CHCl3) = 0.6.
IR (KBr): ν = 2624, 2596, 2575, 2563, 1106, 1135, 829 cm–1. R
˜
f
(10:1 hexane/CH2Cl2) = 0.3.
1-Ferrocenyl-2-(ferrocenylethyn-1-yl)-1,2-dicarba-closo-dodecabor-
ane (2f): 1,4-Diferrocenyl-1,3-butadiyne (84 mg, 0.2 mmol), 6,9-
(Me2S)2-B10H12 (59 mg, 0.24 mmol). Column chromatography (5:1
hexane/CH2Cl2) yielded 56 mg (52%) of the title compound as an
orange solid, m.p. 211 °C (benzene/chloroform). 1H {11B} NMR
(400 MHz; C6D6): δ = 4.44 (apt, JH,H = 2.0 Hz, 2 H, Fc), 4.08 (apt,
JH,H = 2.0 Hz, 2 H, Fc), 4.00 (s, 5 H, Fc), 3.92 (s, 5 H, Fc), 3.88
(apt, JH,H = 2.0 Hz, 2 H, Fc), 3.76 (apt, JH,H = 2.0 Hz, 2 H, Fc),
3.20 (br. s, 1 H, B12–H), 3.03 (br. s, 1 H, B9–H), 3.01 [br. s, 6 H,
B(4,5; 7,11; 8,10)–H], 2.83 [br. s, 2 H, B(3,6)–H] ppm. 13C NMR
(75 MHz, C6D6): δ = 86.8 (C–carborane), 84.8 (C–carborane), 84.1
(Fc), 80.1 (Fc), 72.8 (Fc), 72.7 (Fc), 72.5 (C–alkyne), 71.5 (Fc),
71.0 (Fc), 70.3 (Fc), 69.8 (Fc), 62.4 (C–alkyne) ppm. 11B NMR
(128 MHz, C6D6, BF3·OEt2): δ = –1.71 (d, JB,H = 151 Hz, 1 B,
B12), –4.11 (d, JB,H = 151 Hz, 1 B, B9), –9.13 [d, JB,H = 143 Hz, 6
B, B(4,5; 8, 0; 7,11)], –10.28 [d, JB,H = 150 Hz, 2 B, B(3,6)] ppm.
HRMS calcd. for C24H2810B211B8Fe2: 536.1893; found 536.1894.
MS (EI): m/z (%) = 536 (47) [M+], 268 (8), 186 (21), 121 (44), 84
(100). C24H28B10Fe2 (538.18): calcd. C 53.75, H 5.26, Fe 20.83;
1-Ferrocenyl-2-phenyl-1,2-dicarba-closo-dodecaborane (2c): (2-Phen-
ylethynyl)ferrocene (100 mg, 0.35 mmol), 6,9-(Me2S)2-B10H12
(128 mg, 0.53 mmol). Column chromatography (2:1 hexane/CHCl3)
yielded 85 mg (60%) of the title compound as an orange solid, m.p.
171–174 °C (CHCl3). 1H{11B} NMR (400 MHz, C6D6): δ = 7.23
(d, JH,H = 7.7 Hz, 2 H, Ar–H), 6.77 (t, JH,H = 7.4 Hz, 1 H, Ar–
H), 6.70 (t, JH,H = 7.8 Hz, 2 H, Ar–H), 3.93 (s, 5 H, Fc), 3.91 (t,
JH,H = 1.9 Hz, 2 H, Fc), 3.51 (t, JH,H = 1.8 Hz, 2 H, Fc), 3.42 (br.
s, 1 H, B12–H), 3.28 (br. s, 1 H, B9–H), 3.17 [br. s, 2 H, B(3,6)–
H], 3.13 [br. s, 2 H, B(8,10)–H], 2.97 [br. s, 2 H, B(7,11)–H], 2.89
[br. s, 2 H, B(4,5)–H] ppm. 13C NMR (151 MHz, C6D6): δ = 131.73
(C–Ar), 131.49 (C–Ar), 130.34 (C–Ar), 128.68 (C–Ar), 86.29 (C–
carborane), 85.98 (C–carborane), 83.65 (Fc), 71.77 (Fc), 71.04 (Fc),
69.02 (Fc) ppm. 11B NMR (128 MHz, C6D6, BF3·OEt2): δ = –0.97
(d, JB,H = 110 Hz, 1 B, B12), –1.78 (d, JB,H = 114 Hz, 1 B, B9),
–7.86 [d, JB,H = 142 Hz, 4 B, B(8,10; 7,11)], –9.29 [d, JB,H
=
110 Hz, B(3,6)], –10.02 [d, JB,H = 110 Hz, 2 B, B(4,5)] ppm.
HRMS (EI) calcd. for C18H2410B211B8Fe: 404.2231; found
404.2227. MS (EI): m/z (%) = 404.2 (100) [M+], 278.2 (5), 200.1
(10), 121.2 (20). C18H24B10Fe (406.22): calcd. C 53.48, H 5.98, Fe
found C 53.83, H 5.07, Fe 20.14. IR (KBr): ν = 2636, 2600, 2583,
˜
2572, 2234, 1106, 1046, 1022, 829, 821, 506, 486 cm–1. Rf (5:1 hex-
ane/CH2Cl2) = 0.3.
13.81; found C 53.63, H 5.81, Fe 13.56. IR (KBr): ν = 2642, 2600,
˜
2582, 2561, 1416, 1281, 1045, 1003, 830 cm–1. Rf (2:1 hexane/
1-Ferrocenyl-2-acetyl-1,2-dicarba-closo-dodecaborane (2g): 4-Ferro-
CHCl3) = 0.4.
cenylbut-3-yn-2-one (108 mg, 0.4 mmol), 6,9-(Me2S)2-B10H12
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(147 mg, 0.6 mmol). Column chromatography (3:1 hexane/CH2Cl2)
yielded 43 mg (29%) of the title compound as an orange solid, m.p.
Reaction of 6,9-(Me2S)2-B10H12 with [(Trimethylsilyl)ethynyl]ferro-
cene: Isolation of 4: [(Trimethylsilyl)ethynyl]ferrocene (171 mg,
0.6 mmol), B10H12·(Me2S)2 (222 mg, 0.9 mmol). Column
chromatography (3:1 hexane/CHCl3) yielded 62 mg (35%) of a
crude compound as an orange solid. This solid was extracted with
1
107 °C (hexane). H {11B} NMR (400 MHz; C6D6): δ = 4.09 (apt,
JH,H = 2.0 Hz, 2 H, Fc), 3.91 (s, 5 H, Fc), 3.70 (apt, JH,H = 2.0 Hz,
2 H, Fc), 3.25 (br. s, 1 H, B12–H), 3.10 [br. s, 2 H, B(3,6)–H] 2.94
(br. s, 1 H, B9–H), 2.92 [br. s, 2 H, B(8,10)–H], 2.87 [s, 4 H, B(4,5; hexane/CH2Cl2 (3 mL), and the extract was filtered through a short
7,11)–H], 1.51 (s, 3 H, CH3) ppm. 13C NMR (75 MHz, C6D6): δ =
pad of silica gel (1:1 hexane/CH2Cl2) to afford 12 mg (5%) of ana-
1
85.1 (C–carborane), 83.9 (C–carborane), 83.6 (Fc), 72.3 (Fc), 71.5
lytically pure 4 as an orange solid, m.p. (hexane) 152 °C. H{11B}
(Fc), 69.9 (Fc), 28.8 (CH3) ppm. 11B NMR (128 MHz, C6D6, NMR (400 MHz, C6D6): δ = 7.73 (s, 1 H, CH), 4.32 (dt, JH,H
=
BF3·OEt2): δ = 0.53 [d, JB,H = 148 Hz, 1 B, B(12)], –2.90 (d, JB,H
= 150 Hz, 1 B, B9), –7.62 [d, JB,H = 165 Hz, 2 B, B(8,10)], –9.52
[d, JB,H = 163 Hz, 6 B, B(3,6; 4,5; 7,11)] ppm. HRMS calcd. for
C14H2210B211B8OFe: 370.2023; found 370.2018. MS (EI): m/z (%)
= 370 (100) [M+], 326 (8), 121 (17), 75 (21). C14H22B10FeO
(372.20): calcd. C 45.41, H 5.99, Fe 15.08; found C 45.27, H 5.74,
2.5, 1.3 Hz, 1 H, Fc), 4.24 (dt, JH,H = 2.5, 1.3 Hz, 1 H, Fc), 4.11
(s, 5 H, Fc), 4.15 (dt, JH,H = 2.4, 1.3 Hz, 1 H, Fc), 4.07 (dt, JH,H
= 2.4, 1.3 Hz, 1 H, Fc), 3.96 [br. s, 1 H, B(1 or 3)–H], 3.55 [br. s,
2 H, B(8,10)–H], 3.37 [br. s, 1 H, B(1 or 3)–H], 3.32 (br. s, 1 H,
B7–H), 2.32 (br. s, 1 H, B9–H), 1.68 (br. s, 1 H, B2–H), 1.54 (s, 3
H, CH3), 1.40 (s, 3 H, CH3), 1.36 (br. s, 1 H, B4–H), 0.01 (s, 9 H,
Fe 14.87. IR (KBr): ν = 2585, 2559, 1728, 1356, 1264, 1107, 1036, SiMe3), –2.22 (br. s, 1 H, μ-H), –2.48 (br. s, 1 H, μ-H), –2.68 (br.
˜
825, 501 cm–1. Rf (3:1 hexane/CH2Cl2) = 0.3.
s, 1 H, μ-H) ppm. 13C NMR (150 MHz, C6D6): δ = 147.9 (CH),
143.8 (C) 93.8 (C), 69.3 (Fc), 68.0 (Fc), 67.8 (Fc), 67.4 (Fc), 25.7
(CH3), 22.1 (CH3), 0.9 (SiMe3) ppm. 11B NMR (128 MHz, C6D6,
BF3·OEt2): δ = 29.22 (br. s, 1 B, B6), 2.40 [d, J = 133 Hz, 2 B,
B(1,3)], –2.91 (s, 1 B, B5), –4.95 (d, J = 148 Hz, 1 B, B10), –7.43
[d, J = 212 Hz, 2 B, B(7,8)], –12.35 (d, J = 101 Hz, 1 B, B9), –24.5
(d, J = 146 Hz, 1 B, B2), –42.05 (d, J = 151 Hz, 1 B, B4) ppm.
HRMS calcd. for C17H3610B211B8FeSSi: 464.2660; found 464.2658.
MS (ES+): m/z (%) = 464 (25) [M+], 309 (8), 301 (100), 279 (16).
C17H36B10FeSSi (466.26): calcd. C 43.95, H 7.81, S 6.90, Fe 12.02;
1-Ferrocenyl-2-(ethoxycarbonyl)-1,2-dicarba-closo-dodecaborane
(2h): Ethyl 3-ferrocenylpropynoate (113 mg, 0.4 mmol), 6,9-
(Me2S)2-B10H12 (147 mg, 0.6 mmol). Column chromatography (3:1
hexane/CH2Cl2) yielded 88 mg (55%) of the title compound as an
orange solid, m.p. 129 °C (hexane). 1H{11B} NMR (400 MHz,
C6D6): δ = 4.19 (apt, JH,H = 2.0 Hz, 2 H, Fc), 3.94 (s, 5 H, Fc),
3.74 (apt, JH,H = 2.0 Hz, 2 H, Fc), 3.46 (q, JH,H = 6.9 Hz, 2 H,
CH2), 3.28 (br. s, 1 H, B12–H), 3.10 [br. s, 2 H, B(3,6)–H], 3.00
(br. s, 2 H, B9–H), 2.96 [br. s, 2 H, B(8,10)–H], 2.87 [br. s, 2 H,
B(3,4)–H], 2.82 [br. s, 2 H, B(7,11)–H], 0.54 (t, JH,H = 7.3 Hz, 3
H, CH3) ppm. 13C NMR (75 MHz, C6D6): δ = 159.0 (CO), 84.5
(C–carborane), 83.9 (C–carborane), 78.6 (Fc), 72.5 (Fc), 71.5 (Fc),
69.7 (Fc), 64.6 (CH2), 14.0 (CH3) ppm. 11B NMR (128 MHz, C6D6,
BF3·OEt2): δ = –0.16 (d, JB,H = 151 Hz, 1 B, B12), –3.62 (d, JB,H
= 150 Hz, 1 B, B9), –8.91 [d, JB,H = 189 Hz, 2 B, B(8,10)], –10.25
[d, JB,H = 154 Hz, 6 B, B(3,6; 4,5; 7,11)] ppm. HRMS calcd. for
C15H2410B211B8O2Fe: 400.2129; found 400.2132. MS (EI+): m/z (%)
= 400 (100) [M+], 372 (37) [M+ – Et], 327 (14) [M+ – COOEt], 121
(49). C15H24B10FeO2 (402.21): calcd. C 45.01, H 6.04, Fe 13.95;
found C 44.18, H 7.77, S 6.89, Fe 12.42. IR (KBr): ν = 2588, 2567,
˜
2552, 2528, 1425, 1248, 1105, 1036, 991, 860, 824. Rf (3:1 hexane/
CHCl3) = 0.4.
X-ray Crystallography: Full-set diffraction data (ϮhϮkϮl; θmax
=
26–27.5°, data completeness: 99.1–100.0%) were collected with an
Apex2 diffractometer equipped with a Cryostream Cooler (Oxford
Cryosystems) using graphite-monochromated Mo-Kα radiation (λ
= 0.71073 Å) and were corrected for absorption by using the meth-
ods incorporated in the diffractometer software. The measurements
were usually carried out at 150(2) K. In the cases, when extensive
cooling caused disintegration of the available crystals, the lowest
applicable temperature was roughly estimated and then used for
the measurement (see Table S1 in the Supporting Information).
found C 44.92, H 5.76, Fe 13.70. IR (KBr): ν = 2600, 2581, 1744,
˜
1257, 1108, 1025, 822, 493 cm–1. Rf (3:1 hexane/CH2Cl2) = 0.35.
Preparation of 1-Ferrocenyl-2-(hydroxymethyl)-1,2-dicarba-closo-
dodecaborane (3): Compound 2h (72 mg, 0.18 mmol) was dissolved
in anhydrous CH2Cl2 (1 mL) and the solution was cooled to 0 °C.
The structures were solved by direct methods (SHELXS-87[26]) and
refined by full-matrix least-squares cycles on the basis of F2
(SHELXL-97[26]). The non-hydrogen atoms were refined with an-
isotropic displacement parameters. Hydrogen atoms on the boron
cage were always clearly detectable on the difference Fourier maps
but were included in their idealized positions. Nonetheless, good-
quality diffraction data obtained for 2b, 2e, 2h, and 3 allowed us
to refine these hydrogen atoms with unconstrained positional pa-
rameters while Uiso(H) was kept fixed to 1.2 Ueq(B). CH hydrogen
atoms were included in their calculated positions and refined as
riding atoms with Uiso(H) assigned to a multiple of Ueq(C) of their
bonding carbon atom. Crystals of 2d and 2h are chiral. Whereas
the former compound proved to be a racemic twin, the crystal of
2h was found to be enantiomerically pure.
Then
a solution of diisobutylaluminium hydride (0.45 mL,
0.45 mmol, 1 m solution in CH2Cl2) was added dropwise. After stir-
ring for 30 min, the reaction was quenched with addition of diato-
mite (0.5 g), ethanol (5 drops) and water (one drop). After 30 min
anhydrous MgSO4 was added, and the reaction mixture was fil-
tered. The solid phase was washed by CHCl3 (3ϫ1.5 mL). Volatiles
were removed under reduced pressure to obtain pure alcohol 3
(62 mg, 96% yield) as an orange solid, m.p. 111–112 °C (hexane).
1H{11B} NMR (400 MHz, C6D6): δ = 4.06 (apt, JH,H = 2.0 Hz, 2
H, Fc), 3.96 (s, 5 H, Fc), 3.77 (apt, JH,H = 2.0 Hz, 2 H, Fc), 3.21
(s, 1 H, B12–H), 3.11 (s, 2 H, CH2), 2.99 (s, 1 H, B9–H), 2.90 [s, 2
H, B(8,10)–H], 2.74 [s, 2 H, B(3,6)–H], 2.46 [s, 4 H, B(5,10; 7,11)–
H], 1.12 (br. s, 1 H, OH) ppm. 13C NMR (75 MHz, C6D6): δ =
83.6 (C-carborane), 83.6 (C-carborane), 83.0 (Fc), 72.1 (Fc), 71.6
(Fc), 70.0 (Fc), 63.5 (CH2) ppm. 11B NMR (128 MHz, C6D6,
BF3·OEt2): δ = –2.20 (d, JB,H = 157 Hz, 1 B, B12), –3.60 (d, JB,H
= 177 Hz, 1 B, B9), –9.05 [d, JB,H = 176 Hz, 2 B, B(8,10)], –10.80
[d, J = 149 Hz, 6 B, B(3,6; 4,5; 7,11)] ppm. HRMS calcd. for
C13H2210B211B8OFe: 358.2023; found 358.2022. MS (EI): m/z (%)
Relevant crystallographic data and structure refinement parameters
are available as Supporting Information (Table S1). Geometric data
and structural drawings were obtained with a recent version of the
PLATON program.[27] All numerical values were rounded with re-
spect to their estimated standard deviations (ESDs) given in one
decimal. Parameters that relate to atoms in constrained positions
(hydrogen atoms) are given without ESDs.
= 358 (100) [M+], 326 (12), 121 (72), 87 (47). IR (KBr): ν = 3324,
˜
2410, 2592, 1262, 1070, 1024, 837, 823, 501 cm–1. Rf (1:1 hexane/
CCDC-893330 (for 2a), -893331 (for 2b), -893332 (for 2c), -893333
(for 2d), -893334 (for 2e), -893335 (for 2f), -893336 (for 2g) -893337
CH2Cl2) = 0.23.
Eur. J. Inorg. Chem. 2013, 2789–2798
2797
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[8] A. Korotvicˇka, I. Císarˇová, J. Roithová, M. Kotora, Chem. Eur.
J. 2012, 18, 4200–4207.
(for 2h), -893338 (for 3), and -893339 (for 4) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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This work was financially supported by the Ministry of Education,
Youth and Sports of the Czech Republic (project number
MSM0021620857), by the Institute of Organic Chemistry and Bio-
chemistry, Academy of Science of the Czech Republic (project
number RVO 61388963), and by the Czech Science Foundation
(grant numbers 207/11/0338 and P207/11/0705). The authors also
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Published Online: April 9, 2013
Eur. J. Inorg. Chem. 2013, 2789–2798
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim