Towards rod-shaped molecules based on the twelve-vertex ferratricarbollides

Article abstract of DOI:10.1016/j.jorganchem.2005.01.050

The compounds with a single and double -CH₂C₆H ₄CH₂- spacer, [CpFeC₃B₈H ₁₀-NH-CH₂C₆H₄CH₂-NH- C₃B₈H₁₀FeCp] and [CpFeC₃B ₈H₁₀-N-(CH₂C₆H₄CH ₂)₂-N-C₃B₈H₁₀FeCp], represent the first example of designed shaping by extremely stable cyclopentadienyl-ferratricarbollide (CpFeTCB) cages into rigid molecular constructions approaching linear arrangement.

Full text of DOI:10.1016/j.jorganchem.2005.01.050

Journal of Organometallic Chemistry 690 (2005) 2850–2852
www.elsevier.com/locate/jorganchem
Communication
Towards rod-shaped molecules based on the twelve-vertex
ferratricarbollides q
a,
a
b
a
ˇ
´
*
´
ˇ
´ ˇ
´
Bohumır Gruner , Jaroslav Backovsky´ , Ivana Cısarova , Bohumil Stıbr
¨
a
ˇ
Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, Area of Research Institutes, Husinec-Rezˇ 1001,
ˇ
250 68 Rezˇ, Czech Republic
b
Faculty of Natural Sciences of Charles University, Hlavova 2030, 128 42, Prague 2, Czech Republic
Received 7 September 2004; accepted 26 January 2005
Available online 13 March 2005
Abstract
The compounds with a single and double –CH2C6H4CH2– spacer, [CpFeC3B8H10-NH-CH2C6H4CH2-NH-C3B8H10FeCp] and
[CpFeC3B8H10-N-(CH2C6H4CH2)2-N-C3B8H10FeCp], represent the first example of designed shaping by extremely stable cyclopen-
tadienyl-ferratricarbollide (CpFeTCB) cages into rigid molecular constructions approaching linear arrangement.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Boranes; Carboranes; Linear metallatricarbollide constructions
Tailoring of oligomeric or polymeric materials based
on covalent bonding of boron clusters has attracted
attention during past years [1,2]. This is undoubtedly
due to expected high chemical and thermal stability,
rigidity of the resulting blocks, and a possibility of intro-
ducing functional groups in a space pre-defined array.
However, the spectrum of boron-cluster compounds
usable for designed shaping of covalently bonded mate-
rials has so far been rather limited. The same may apply
to synthetic tools that would allow for building-up such
systems in rational and controlled manners. More
explored seems to be the area of small carboranes and
metallaboranes that allow for easy in situ generation
of {C2B3} and {C3B2} planar rings or pyramidal
{C2B4} subclusters as building blocks for construction
of stable multidecker shapes. Most of them emerged
from the advanced work of GrimesÕ group [3,4]. Also
much extended has been the field of small metallabor-
anes featured by exoskeletal bonding to various organic
substrates in C–C and B–C manners [4,5]. The area of
larger borane clusters is comparatively less explored.
Only few larger multidecker compounds have been re-
ported to date [6] and there are only few compounds
suitable for exo-cluster linkage of boron clusters in para
positions. These have been recently reviewed [2] and
range from p-carboranes 1,12-C2B10H12, 1,10-C2B8H10,
to p-(NH3)2B12H10. Indeed, the first stable rod-like mol-
ecules based on C–C and C–B bonding to p-carborane
cluster units have been reported [7] along with carbor-
anes linked by organic spacer groups [8].
In 1999, we reported [9] on the synthesis of an extre-
mely stable 12-vertex ferratricarbollide, [9-H2N-2-Cp-
closo-2,1,7,9-FeC3B8H10] (1), the H2N-substituent of
which is conveniently attached to one of the cage car-
bons in a p-position with respect to the Fe-centre. This
structural feature constitutes an ideal setting for linear
molecular designs, which we would like to demonstrate
in this initial study. The reaction between 1 and two
equivalents of 1,4-dibromomethylbenzene in 1,2-dimeth-
oxyethane (DME) in the presence of NaH (see Scheme 1,
q
˚
Presented at the EUROBORON 3 meeting, Pruhonice-by-Prague,
the Czech Republic, September 12–16, 2004.
*
Corresponding author. Tel.: +420 2 6617 3120; fax: +420 2 2094
0161.
E-mail address: gruner@iic.cas.cz (B. Gruner).
¨
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.01.050

B. Gru¨ner et al. / Journal of Organometallic Chemistry 690 (2005) 2850–2852
2851
Scheme 1. Synthesis of CpFeTCB rod molecules, (i) NaH, l,4-(BrCH2)2-C6H4, NaH, DME, reflux 120 h.
path i) resulted in the isolation of three products. The
first was identified as orange [9-H3CC6H4CH2NH-2-
Cp-closo-2,l,7,9-FeC3B8H10] (2) (yield 11%), a non-rod
molecule. Other two orange products, [CpFeC3B8H10-
NH-CH2C6H4CH2-NH-C3B8H10FeCp] (3) (yield 24%)
and [CpFeC3B8H10-N-(CH2C6H4CH2)2-N-C3B8H10-
FeCp] (4) (yield 16%), are the desired single- and dou-
ble-spacer dimeric molecules. It must be noted, however,
that the reaction is very slow, most probably due to
combination of both steric shielding of the amino group
by the cage and low nucleophilicity of the H2N-moiety
in 1. Nevertheless, assumed products resulted upon a
prolonged reaction period [10].
As shown in Fig. 1, the structure of 3 was determined
crystallographically [11] and the constitution of com-
pounds 2 and 4 is fully consistent with the NMR data
and the results of mass spectrometry [10].
We can conclude that, single- and double-spacer mol-
ecules with defined linear geometry, based on extremely
stable ferratricarbollide cages, are now, in principle,
available. Therefore, there may also be a good chance
for the synthesis of analogous L-shaped molecules from
˚
Fig. 1. Two different views the molecular structure of 3. ORTEP representation drawn with 50% probability level. Selected interatomic distances (A)
and bond angles (ꢁ): C(1)–Fe(2) 2.030(5), C(7)–Fe(2) 2.044(5), C(1)–B(3) 1.694(6), B(3)–C(7) 1.707(6), C(9)–B(4) 1.725(6), B(6)–B(11) 1.769(6), C(9)–
0
0
˚
N(1) 1.435(6), [C(21)–C(25) centroid]-[C(21 )-C(25 ) centroid] 20.726(17) A; C(9)–N(1)–C(10) 115.8(4), B(11)–Fe(2)–C(1) 86.70(18), C(1)–B(3)–C(7)
106.0(3).

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B. Gru¨ner et al. / Journal of Organometallic Chemistry 690 (2005) 2850–2852
KI (50 mg). The reaction mixture was heated to reflux and stirred
for 48 h. second portion of 1,4-dibromomethyl benzene
the isomeric complex [10-H2N-2-Cp-2,l,7,10-FeC3B8-
H10] [12]. Oligomeric or polymeric linear arrays might
be also obtainable via the full-sandwich closo complexes
of general [Fe(C3B8H10NH2)2] constitution [13,14] that
contain two H2N substituents in positions suitable for
chemical shaping.
A
(490 mg, 1.85 mmol) in DME (20 ml) was then added, followed
by addition of KI (50 mg). The reflux was continued for 4 days,
the overall reaction time being 120 h. After cooling down, the
reaction was quenched by aqueous ethanol (1 ml), the solvent was
evaporated, and the resulting mixture was separated by flash
chromatography on a silica gel column (1.5 · 20 cm), using a 4:1
hexane–benzene mixture to elute the first orange fraction con-
taining 2 (79 mg, 11%). Benzene, followed by CH2Cl2, eluted
compounds 3 and 4 (yields 154 mg, 24% and 119 mg, 16%,
respectively). 2: Rf (C6H6-hexane 1 : 1) 0.42, m.p. 72–75 ꢁC; 11B
NMR (CDC13) d = ꢀ11.4 (1J(B,H) = 150 Hz, B6,11), ꢀ15.3 (162,
B3), ꢀ18.0 (169, B5,12), ꢀ20.8 (154, B10), ꢀ25.1 (173, B4,8).
1H{11B} NMR (CDC13): d = 7.16–7.09 (4H, Ar), 7.09 (br. t, 1H,
NH), 4.58 (5H, Cp), 3.94 (H3); 3.84 (2H, N–CH2); 2.83 (H6,11);
2.34 (CH3), 2.19 (H5,12), 2.11 (2H, cage CH), 2.07 (H4,8), 1.73
(H10); MS: m/z = 375 (59%) [M]+. 3: Rf (C6H6-hexane 1:1) 0.17,
m.p. 246–248 ꢁC (decomp.); 11B NMR (CDC13) d = ꢀ11.4
(1J(B,H) = 150Hz, B6,60,11,110), ꢀ15.3 (162, B3,30), ꢀ17.9 (173,
B5,50,12,120), ꢀ20.9 (154, B10,100), ꢀ24.15 (169, B4,408,80);
1H{11B} NMR (CDCl3) : d = 7.19 (4H, Ar), 7.09 (br. t, 2H,
NH), 4.56 (10H, Cp); 3.91 (H3,30), 3.83 (4H, CH2), 2.8
(H6,60,11,10), 2.16 (H5,50,12 120), 2.09 (4H, cage CH), 2.04
(H4,40,8,80), 1.69 (H10,100); 13C{1H} NMR (CDCl3) d = 138.3,
128.8, 128.5 (4C,Ar), 77.6 (Cp), 68.2 (2C, C9,90), 54.8 (4C, cage
Cl,7,10,70); 53.6 (2C, CH2N); MS: m/z = 644 (25%) [M]+. 4: Rf
(C6H6) 0.06, m.p. 126–129 ꢁC; 11B NMR (CDCl3)
d = ꢀ11.4(1J(B,H) = 150 Hz, B6,60,11,110), ꢀ15.3 (162, B3,30),
ꢀ17.9 (173, B5,5012,120), ꢀ20.9 (154, B10,100), ꢀ24.15 (169,
B4,408,80); 1H{11B} NMR (CDC13): d = 7.33 (4H, Ar), 7.21 (4H,
Ar), 4.6 (10H, Cp), 3.98 (H3,30), 2.94 (8H, N–CH2). 2.88
(H6,60,11,110), 2.24 (H5,50,12,120), 2.14 (4H, cage CH), 2.12
(H4,40,8,80); 1.77 (H10.100); MS: m/z = 746 (30%) [M]+.
Acknowledgements
ˇ
´
´
´
We thank Drs. J. Caslavsky and Z. Plzak for mass
spectra. The work was supported by the Ministry of
Education of the Czech Republic (Project LC523) and
ˇ
by GA CR (Grant No. 203/05/2646).
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