Synthesis and Characterization of a New Alkenyldecaborane and Alkenyl Monocarbon Carboranes

Article abstract of DOI:10.1021/ic951138z

Decaborane(14) reacts with 1-(CH₃)₃SiC≡CC₄H₉ in the presence of dimethyl sulfide to give the new alkenyl-decaborane 5-(S(CH₃)₂)-6-[(CH₃)₃Si(C ₄H₉)C=CH]B₁₀H₁₁, (I). Crystal data for 5-(S(CH₃)₂)-6-[(CH₃)₃Si(C ₄H₉)C=CH]B₁₀H₁₁ : space group P2₁/n, monoclinic, a = 9.471(1) ?, b = 13.947(3) ?, c = 17.678(3) ?, β= 100.32(1)°. A total of 3366 unique reflections were collected over the range 2.0° ≤ 26 ≤ 56.0°, of which 1763 reflections had F_o² ≥ 3σ(F_o²) and were used in the final refinement. R_F = 0.083; R_wF = 0.094. The single-crystal X-ray structure of 5-(S(CH₃)₂)-6-[((CH₃)₃Si) ₂C=CH]B₁₀H₁₁ (A) is also reported. Crystal data for 5-(S(CH₃)₂)-6-[((CH₃)₃Si) ₂C==CH]B₁₀H₁₁ space group, P2₁2₁2₁, orthorhombic, a = 9.059 (3) ?, b = 12.193(4) ?, c = 21.431(3) ?. A total of 4836 unique reflections were collected over the range 6° ≤ 26 ≤ 140°, of which 3705 reflections had F_o² ≥ 3σ(F_o²) and were used in the final refinement. R_F = 0.052; R_wf = 0.059. The reactions of 5-(S(CH₃)₂)6-[(CH₃)₃Si(C ₄H₉)C=CH]B₁₀H₁₁, and 5-(S(CH₃)₂)6-[((CH₃)₃Si) ₂C=CH]B₁₀H₁₁ with a variety of alkyl isocyanides were investigated. All of the alkenyl monocarbon carboranes reported are the result of incorporation of the carbon atom from the isocyanide into the alkenyldecaborane framework and reduction of N≡C bond to a N-C single bond. The characterization of these compounds is based on ¹H and ¹¹B NMR data, IR spectroscopy, and mass spectrometry.

Full text of DOI:10.1021/ic951138z

2568
Inorg. Chem. 1996, 35, 2568-2575
Synthesis and Characterization of a New Alkenyldecaborane and Alkenyl Monocarbon
Carboranes
Glamarie Burgos-Adorno,† Patrick J. Carroll,‡ and William Quintana*,§
Department of Chemistry and Biochemistry, New Mexico State University, Box 30001, Department 3C,
Las Cruces, New Mexico 88003-8001, Department of Chemistry and Laboratory for Research on the
Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, and
Department of Chemistry, University of Puerto Rico, Cayey Campus, Cayey, Puerto Rico 00640
ReceiVed August 29, 1995X
Decaborane(14) reacts with 1-(CH3)3SiCtCC4H9 in the presence of dimethyl sulfide to give the new alkenyl-
decaborane 5-(S(CH3)2)-6-[(CH3)3Si(C4H9)CdCH]B10H11 (I). Crystal data for 5-(S(CH3)2)-6-[(CH3)3Si-
(C4H9)CdCH]B10H11: space group P21/n, monoclinic, a ) 9.471(1) Å, b ) 13.947(3) Å, c ) 17.678(3) Å, â )
100.32(1)°. A total of 3366 unique reflections were collected over the range 2.0° e 2θ e 56.0°, of which 1763
2
2
reflections had Fo g 3σ(Fo ) and were used in the final refinement. RF ) 0.083; RwF ) 0.094. The single-
crystal X-ray structure of 5-(S(CH3)2)-6-[((CH3)3Si)2CdCH]B10H11 (A) is also reported. Crystal data for
5-(S(CH3)2)-6-[((CH3)3Si)2CdCH]B10H11: space group, P212121, orthorhombic, a ) 9.059 (3) Å, b ) 12.193(4)
Å, c ) 21.431(3) Å. A total of 4836 unique reflections were collected over the range 6° e 2θ e 140°, of which
2
2
3705 reflections had Fo g 3σ(Fo ) and were used in the final refinement. RF ) 0.052; RwF ) 0.059. The
reactions of 5-(S(CH3)2)6-[(CH3)3Si(C4H9)CdCH]B10H11 and 5-(S(CH3)2)6-[((CH3)3Si)2CdCH]B10H11 with a
variety of alkyl isocyanides were investigated. All of the alkenyl monocarbon carboranes reported are the result
of incorporation of the carbon atom from the isocyanide into the alkenyldecaborane framework and reduction of
NtC bond to a N-C single bond. The characterization of these compounds is based on 1H and 11B NMR data,
IR spectroscopy, and mass spectrometry.
Introduction
In each of these reactions the alkyl isocyanide is acting as a
nucleophile, while the boron hydride molecule is acting as an
electrophile. The result is an attack on the negatively charged
carbon atom of the isocyanide molecule, resulting in carbon
incorporation into the boron-containing cage and reduction of
the NtC bond to a N-C single bond.
The reactivity of decaborane(14) with a number of alkyl
isocyanides or the cyanide ion was first investigated by Knoth
and Todd in the late 1960s, who showed that the product
obtained consisted of a one-carbon-insertion monocarbon
carborane and that the NtC bond was reduced to a NH2-C
bond.1-6
We have continued to investigate the reactivity of substituted
boron hydrides toward isocyanides by performing experiments
that involve the substituted alkenylboranes 5-(S(CH3)2)-6-
[(CH3)3Si(C4H9)CdCH]B10H11 and 5-(S(CH3)2)-6-[((CH3)3-
Si)2CdCH]B10H11, with different isocyanides.
Boron hydrides and carboranes having pendant alkenyl groups
are relatively few. The formation of these alkenyl monocarbon
carboranes gives an unique opportunity to investigate the
reactivity not only of the carborane cage but also of the ancillary
alkenyl group associated with the cage. One possibility that
could be explored is the possible polymerization of the alkenyl
group, producing boron-containing polymers which could be
used as precursors to other materials. Another possible ap-
plication for these types of materials is their subsequent
conversion into molecules which could be used in boron neutron
capture therapy studies.
1
RNtC + B10H14 f nido-7-(RNH2)-7-CB10H12
CtN- + B10H14 f nido-6-(NC)B10H12 f
(1)
5
nido-7-(NH3)-7-CB10H12 (2)
Another borane and a thiaborane, 5-(S(CH3)2)-9-(C6H13)-
B10H11 and SB9H11, were found to react also with (CH3)3NtC,
resulting in the incorporation of the carbon atom of the
isocyanide and reduction of the NtC bond.2,4
(CH3)3CNtC + 5-(S(CH3)2)-6-(C6H11)B10H11 f
4
nido-3-(S(CH3)2)-7-((CH3)3CNH)-11-(C6H11)B10H10 (3)
The results presented in this communication confirm that this
type of chemistry is general for boron hydrides based on the
decaborane(14) framework, due to the intrinsic electrophilic
character of these molecules. Their facile conversion into
alkenyl monocarbon carboranes could open new synthetic
pathways for the production of new and interesting compounds,
which could have a variety of applications, depending on the
(CH3)3CNtC + SB9H11 f
2
nido-8-((CH3)3CNH2)-7-CSB9H9 (4)
† University of Puerto Rico.
‡ University of Pennsylvania.
§ New Mexico State University.
X Abstract published in AdVance ACS Abstracts, April 1, 1996.
(1) Hyatt, D. E.; Owen, D. A.; Todd, L. J. Inorg. Chem. 1966, 5, 1749-
1751.
(4) Hernandez, D. M.; Huffman, J. C.; Todd, L. J. Inorg. Chem. 1987,
26, 213-215.
(2) Arafat, A.; Friesen, G. D.; Todd, L. J. Inorg. Chem. 1983, 22, 3721-
(5) Knoth, W. H.; Little, J. L.; Lawrence, J. R.; Scholer, F. R.; Todd, L.
J. Inorg. Synth. 1968, 11, 33-41.
3724.
(3) Sneath, R. L.; Todd, L. J. Inorg. Chem. 1973, 12, 44-48.
(6) Knoth, W. H. J. Am. Chem. Soc. 1967, 89, 1274.
0020-1669/96/1335-2568$12.00/0 © 1996 American Chemical Society

Alkenyl Monocarbon Carboranes
Inorganic Chemistry, Vol. 35, No. 9, 1996 2569
Table 1. 11B Nuclear Magnetic Resonance Chemical Shiftsa
compound
δ, ppm (J, Hz)
rel intens
5-(S(CH3)2)-6-[(CH3)3Si(C4H9)CdCH]B10H11 (I)b
29.84c (s), 2.89 (128), -2.13,d
-4.41 (146), -6.76,c -11.47,d
-24.15 (142), -41.74 (149)
-2.62,c -3.48,c -10.64,d -12.61,d
-20.11,d -21.82,d -27.38 (145),
-30.59 (144), -32.75(144)
-4.31,c -10.39,c -21.84,d
-27.96 (172), -31.10 (124),
-32.44c
1:2:1:1:1:1:2:1
2-(S(CH3)2)-7-(C6H5CH2NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (II)b
2-(S(CH3)2)-7-((CH3)3CNH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (III)b
2-(S(CH3)2)-7-(C4H9NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (IV)b
2-(S(CH3)2)-7-(C4H9NH)-11-[(CH3)3Si(C4H9)CdCH]-7-CB10H10 (V)b
1:2:1:1:1:1:1:1:1
3:2:2:1:1:1
-4.45,c,d -12.15,c -13.36,d
-21.60,d -22.31,d -28.32 (134),
-31.59 (142), -33.69 (148)
-4.46,c,d -11.57,c -22.69,d
-24.26 (138), -28.40 (130),
-31.78 (143), -33.88 (135)
3:1:1:1:1:1:1:1
3:2:1:1:1:1:1
a 128.4 Hz. b C6D6 solvent. c Singlet. d Coupling constants could not be reliably calculated due to overlapping peaks. e (CD3)2CdO solvent.
Table 2. 1H Nuclear Magnetic Resonance Chemical Shifts
compound
δ, ppm
5-(S(CH3)2)-6-[(CH3)3Si (C4H9)CdCH]B10H11 (I)a,b
-2.352 (2, b, BHB), 0.034 (9, s, (CH3)3Si), 1.038 (3, t, CH3),
1.454 (4, m, CH2CH2), 1.609 (3, s, SCH3), 1.719 (3, s, SCH3),
2.039 (2, m, CdCCH2), 7.043 (1, s, CdCH)
2-(S(CH3)2)-7-(C6H5CH2NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (II)d,e -3.36 (2, b, BHB), 0.07 and 0.22 (18, s, (CH3)3Si), 1.88 (1, b, NH),
2.70 (6, s, S(CH3)2), 3.74 and 4.03 (2, d, CH2), 5.30 (1, s, CdCH),
7.08 (1, m, C6H5), 7.23 (2, m, C6H5), 7.26 (2, m, C6H5)
2-(S(CH3)2)-7-((CH3)3CNH)-11-[((CH3)3Si)2CdCH]7-CB10H10 (III)b,e -2.547 (2, b, BHB), 0.22 and 0.45 (18, s, (CH3)3Si), 1.16 (9, s, (CH3)3C),
1.45 (3, s, SCH3), 1.49 (3, s, SCH3), 1.85 (1, b, NH), 7.42 (1, s, CdCH)
2-(S(CH3)2)-7-(C4H9NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (IV)b,c
-2.851 (2, b, BHB), 0.333 and 0.346 (18, s, (CH3)3Si), 0.871 (3, t, CH3),
1.261 and 1.418 (4, m,CH2CH2) 1.569 (3, s, SCH3), 1.638 (3, s, SCH3),
2.287 (1, b, NH), 3.003 and 2.594 (2, m, NHCH2), 6.275 (1, s, CdCH)
2-(S(CH3)2)-7-(C4H9NH)-11-[(CH3)3Si(C4H9)CdCH]-7-CB10H10 (V)b,c -2.132 (2, b, BHB), 0.374 (9, s, (CH3)3Si), 1.051(6, m, CH3 from C4H9
on NHCH2CH2CH2CH3 and CdCCH2CH2CH2CH3), 1.413 (8, m, CH2
from NHCH2CH2CH2CH3 and CdCCH2CH2CH2CH3), 1.593 (1, m,
NH), 1.752 (3, s, SCH3), 1.817 (3, s, SCH3), 2.134 (2, m, CdCCH2),
3.104 and 2.657 (2, d of d, NHCH2), 6.453 (1, s, CdCH)
a 400.0 MHz. b C6D6 solvent. c 200.0 MHz. d CD2Cl2 solvent. e 250 MHz. f (CD3)2CdO solvent.
resolution mass spectra were obtained on a VG 7070-H mass
spectrometer, except that of I. The high-resolution mass spectral data
for I were obtained from the Nebraska Center for Mass Spectrometry
of the University of Nebraska.
kind of pendant organic groups attached to the boron hydride
framework.
Experimental Section
X-ray diffraction data were obtained on an Enraf-Nonius four-circle
CAD-4 and an AFC7R diffractometer employing Cu KR radiation from
a highly oriented monochromator.
Tables 1-3 summarize relevant 11B NMR, 1H NMR, and IR
information for the compounds discussed on this paper.
All manipulations were carried out using standard high-vacuum or
inert-atmosphere techniques, when warranted, as described by Shriver.7
Materials.The compound nido-5-(S(CH3)2)6-[((CH3)3Si)2CdCH]-
B10H11 was prepared according to the reported literature procedure.8
Decaborane(14) was purchased from Callery Chemical and recrystal-
lized from boiling heptane prior to use. Anhydrous dimethyl sulfide,
1-(trimethylsilyl)-1-hexyne, and the isocyanides used in this study,
n-C4H9NtC, (CH3)3CNtC, and C6H5CH2NtC were purchased from
Aldrich Chemical and used as received. Benzene and hexane were
obtained from Fisher Scientific and dried according to literature
procedures prior to use. C6D6, DMSO-d6, acetone-d6, and TMS were
purchased from Isotech and used as received.
Physical Measurements. The 128.4 MHz boron-11 and 400.0 MHz
proton NMR spectra were obtained on a Varian Unity-400 Fourier
transform spectrometer. All boron-11 chemical shifts were referenced
to BF3‚O(C2H5)2 ) 0.0 ppm, with a negative sign indicating an upfield
shift. Proton NMR spectra at 200 MHz were obtained on a Varian
Gemini-200 Fourier transform spectrometer. Proton chemical shifts
were referenced to TMS ) 0.00 ppm, with positive values indicating
downfield shifts.
All melting points are uncorrected.
Crystallographic Structure Determinations of 5-(S(CH3)2)-6-
[((CH3)3Si)2CdCH]B10H11 (A) and 5-(S(CH3)2)6-[(CH3)3Si-
(C4H9)CdCH]B10H11 (I). Single-crystals of A and I were grown
overnight by slow evaporation in air of a methylene chloride/heptane
solution. See Table 4 for crystal data. The cell constants for both
compounds were determined from a least-squares fit of the setting
angles for 25 accurately centered reflections. X-ray intensity data were
collected on an Enraf Nonius four-circle CAD-4 diffractometer
controlled by a PDP 8/A computer for A and on an AFC7R
diffractometer for I. Both diffractometers employed graphite-mono-
chromated Cu KR radiation (λ ) 1.541 84 ×81Å) and used the ω -2θ
scanning technique. X-ray data were processed, and the structures were
solved and refined by using either the Molecular Structure Corp. teXsan
package9 on a Silicon Graphics Indigo R4000 computer for compound
I or a VAX 750 minicomputer which had the Enraf-Nonius structure
package10 for compound A. For compound A , a total of 4836
reflections were measured over the ranges 6° e 2θ e 140° and -11
Infrared spectra were recorded on a Perkin-Elmer 337 grating infrared
spectrophotometer and on Perkin Elmer 1720 Fourier transform
spectrophotometer. Low-resolution CI mass spectra and all high-
(7) Shriver, D. F.; Drezdzon, M. A. Manipulation of Air SensitiVe
Compounds; 2nd ed.; Wiley: New York, 1986.
(8) Ernest, R. L.; Quintana, W.; Rosen, R.; Carroll, P. J.; Sneddon, L. G.
Organometallics 1987, 6, 80-88.
(9) teXsan: Crystal Structure Analysis Package, Molecular Structure Corp.
(1985, 1992).
(10) B. A. Frenz and Associates Inc., College Station, TX 77840, and Enraf-
Nonius, Delft, Holland.

2570 Inorganic Chemistry, Vol. 35, No. 9, 1996
Burgos-Adorno et al.
Table 3. Infrared Spectral Data
compound
ν, cm-1
5-(S(CH3)2)-6-[(CH3)3Si(C4H9)CdCH]B10H11 (I)
2935 (m), 2927 (m), 2895 (w), 2870 (m), 2862 (m), 2582 (w), 2565 (s),
2552 (s), 2542 (sh), 2530 (sh), 2520 (s), 1554 (m), 1471 (m),
1427 (m), 1330 (w), 1261 (m), 1245 (s), 1115 (m), 1039 (s),
991 (m), 937 (w), 905 (w), 852 (m), 832 (s), 806 (m), 758 (m),
716 (w), 686 (w), 624 (w
2-(S(CH3)2)-7-(C6H5CH2NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (II)
2-(S(CH3)2)-7-((CH3)3CNH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (III)
2-(S(CH3)2)-7-(C4H9NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (IV)
2-(S(CH3)2)-7-C4H9NH-11-[S(CH3)2i(C4H9)CdCH]-7-CB10H10 (V)
3325 (m), 3020 (m), 2970 (m), 2880 (sh), 2440 (s), 1630 (m), 1480 (s),
1400 (w), 1280 (w), 1250 (s), 1160 (w), 950 (m), 880 (sh), 860 (sh),
840 (m), 760 (m), 680 (m), 650 (m), 620 (w)
3310 (m), 3010 (m), 2960 (m), 2900 (sh), 2800 (sh), 2540 (s), 1610 (w),
1400 (br, m), 1050 (sh), 1000 (m), 980 (sh), 900 (m), 860 (sh),
840 (m), 750 (w), 740 (w), 690 (m), 650 (w)
3285 (m), 3015 (m), 2950 (m), 2910 (sh), 2470 (s), 1615 (m), 1465 (s),
1390 (w), 1245 (sh), 1140 (w), 1000 (m), 980 (sh), 965 (m),
875 (sh), 845 (m), 740 (w), 645 (m)
3325 (m), 3005 (m), 2975 (m), 2870 (sh), 2490 (s), 1620 (m), 1470 (s),
1370 (w), 1020 (sh), 990 (m), 960 (sh), 945 (m), 835 (m), 700 (w),
620 (w)
Table 4. Data Collection and Structure Refinement Information for
5-(S(CH3)2)-6-[((CH3)3Si)2CdCH]B10H11 (A) and
5-(S(CH3)2-6-[(CH3)3Si(C4H9)CdCH]B10H11 (I)
Table 5. Atomic Positional Parameters and Their Estimated
Standard Deviations for 5-(S(CH3)2)-6-[((CH3)3Si)2CdCH]B10H11
(A)
A
I
atom
x
y
z
Beq, Å2
formula
fw
space group
Z
crystal class
a, Å
b, Å
C10H36B10SSi2
352.74
P212121
C11H36B10SSi
336.67
P21
Si1
Si2
S
0.2698(2)
0.5612(2)
0.5925(1)
0.2878(7)
0.3192(6)
0.1377(6)
0.1056(7)
0.3874(6)
0.3383(3)
0.1657(7)
0.0190(5)
0.0744(7)
0.2584(7)
0.4353(5)
0.4257(5)
0.3052(8)
0.0960(7)
0.2485(7)
0.4603(9)
0.6583(7)
0.7068(7)
0.6231(6)
0.6285(6)
0.4707(1)
0.3329(1)
0.3649(1)
0.2776(5)
0.2145(5)
0.2178(5)
0.3330(5)
0.3468(4)
0.3186(4)
0.2475(5)
0.3197(5)
0.4493(5)
0.4425(5)
0.3185(3)
0.3713(4)
0.5616(5)
0.3922(5)
0.5632(4)
0.2258(6)
0.4503(5)
0.2415(5)
0.4988(5)
0.3874(5)
0.14510(6)
0.09698(6)
0.35822(6)
0.4036(3)
0.3309(3)
0.3625(3)
0.4133(3)
0.3474(2)
0.2744(2)
0.2816(3)
0.3379(3)
0.3686(3)
0.3954(3)
0.2148(2)
0.1592(2)
0.0773(2)
0.1305(3)
0.2139(2)
0.0365(2)
0.0595(3)
0.1294(3)
0.3274(3)
0.4389(3)
4.95(3)
5.06(3)
4.86(2)
4.7(1)
4.3(1)
5.3(1)
5.4(1)
3.9(1)
4.0(1)
4.9(1)
5.5.(1)
5.5.(1)
4.8(1)
3.99(9)
4.15(9)
8.1(2)
8.1(2)
6.1(1)
9.3(2)
7.7(2)
7.4(1)
7.0(2)
7.1(2)
4
4
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
C1
C2
CA
CB
CC
CD
CE
CF
CG
CH
orthorhombic
9.059(1)
12.193(3)
21.431(3)
monoclinic
9.471(1)
13.947(3)
17.678(3)
100.32(1)
2297.2(6)
16.15
c, Å
â, deg
V, Å3
2367.4(4)
20.73
µ, cm-1
crystal size, mm
0.30 × 0.45 × 0.20
0.38 × 0.27 × 0.20
D
calc, g/cm3
0.990
0.939
radiation (λ, Å)
scan range, deg
h,k,l collected
Cu KR (1.541 84)
6 e 2θ e 140
(11,(14,(26
4836
Cu KR (1.541 84)
2 e 2θ e 56
+10,+15,(19
3366
no. of reflns measd
no. of reflns for
3705
1763
2
Fo2 > 3σ(Fo )
no. of variables
244
0.052
0.059
253
0.083
0.094
RF
RwF
8
a Beq ) /3[U11(aa*)2 + U22(bb*)2 + U33(cc*) + 2U12(aa*bb*) cos
e h e 11, -14 e k e 14, -26 e l e 26. For compound I, 3366
reflections were collected over the ranges 2° e 2θ e 56° and 0 e h e
10, 0 e k e 15, -19 e l e 19. For both compounds three standard
reflections were measured every 3500 s of X-ray exposure. Compound
A showed a decay of 9.5% and compound I showed a decay of 12.5%
over the course of data collection. A linear decay correction was
applied for both compounds.
The intensity data were corrected for Lorentz and polarization effects
but not for absorption. For compound A, 3705 reflections were unique,
and for I, 1763 were unique, having F2 > 3σ(F2), and they were used
in the subsequent structure refinement.
γ) + 2U13(aa*cc* cos â) + 2U23(bb*cc* cos R)].
were placed 3.13 g (25.6 mmol) of decaborane(14), 3.75 mL (51.2
mmol) of dimethyl sulfide, and 150 mL of dry benzene. The flask
was sealed and degassed three times under vacuum. The resulting
solution was heated to reflux for 12 h, with periodic degassing to ensure
removal of hydrogen gas produced during the course of the reaction.
After evolution of hydrogen gas had ceased, the flask was opened and
3.96 g (5.2 mL, 25.6 mmol) of 1-(trimethylsilyl)-1-hexyne was syringed
into the yellow solution. The flask was then resealed and degassed
three times. The solution was heated to reflux for an additional 48 h,
at which time, the solution had turned red. The benzene solvent was
removed under vacuum, along with free dimethyl sulfide, which is a
byproduct of the reaction. An oily solid remained inside the flask after
most of the solvent had been removed. To this solid was added
dropwise 25 mL of methanol, by using an addition funnel, which
resulted in the dissolution of the solid and evolution of hydrogen gas.
The flask was then placed inside a refrigerator for 5 h, after which a
small amount of a yellow solid had precipitated from the solution. This
solid was filtered off through a medium-porosity frit, and the resulting
filtrate was placed in a 400 mL beaker.
Both structures were solved by direct methods. Refinement was
full-matrix least-squares techniques based on F to minimize the quantity
Σw(|Fo| - |Fc|)2 with w ) 1/σ2(F).
Non-hydrogen atoms were refined anisotropically; cage hydrogens
were refined isotropically; all other hydrogens were included as constant
contributions to the structure factors and were not refined. For A,
refinement converged to RF ) 0.052 and RwF ) 0.059; for I, RF, )
0.083 and RwF ) 0.094. Tables containing relevant information such
as data collection and structure refinement details, positional parameters
of selected atoms, and selected interatomic distances for both com-
pounds are presented in Tables 4-7. Tables containing positional
parameters of hydrogen atoms, anisotropic thermal parameters, and bond
angles are available as Supporting Information.
The beaker containing the methanol solution was cooled at -50 °C,
and water was added very slowly via an addition funnel. The addition
of water resulted in the precipitation of more of the yellow solid. The
methanol/water solution was filtered through a medium-porosity frit,
Reaction of Decaborane(14) with 1-(Trimethylsilyl)-1-hexyne. In
a 250 mL round-bottom flask equipped with a high-vacuum stopcock

Alkenyl Monocarbon Carboranes
Inorganic Chemistry, Vol. 35, No. 9, 1996 2571
Table 6. Atomic Positional Parameters and Their Estimated
Standard Deviations for
5-(S(CH3)2)-6-[(CH3)3Si(C4H9)CdCH]B10H11 (I)
at room temperature for 6 h. Noncondensables were removed at 1 h
intervals. Once the solution turned yellow, it was heated at reflux for
an additional 18 h. The benzene was removed in Vacuo, the resulting
oily solid was dissolved in 20 mL of methanol, and the mixture was
stirred at room temperature for 1 h, resulting in the evolution of
hydrogen gas. The resulting solution was then cooled at -5 °C in a
water-ice bath, resulting in the formation of a yellow precipitate with
was filtered off and dissolved in 5 mL of methylene chloride. The
mother liquor was added to 30 mL of methylene chloride, and the
mixture was left until two phases were clearly visible. Then, 5.0 g of
sodium bisulfite was added to the solution, and the aqueous layer was
separated from the organic layer with the aid of a separatory funnel.
The methylene chloride solutions were combined and evaporated under
reduced pressure, resulting in the isolation of 2-(S(CH3)2)-7-(C6H5CH2-
NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (II) [brown solid; 0.40 g (0.84
mmol), 60% yield; Rf ) 0.45; mp 254-6 °C]. Mass measurements
atom
x
y
z
Beq,a Å2
Si
S
0.7656(2)
0.2177(2)
0.226(1)
0.240(1)
0.161(1)
0.225(1)
0.2774(9)
0.399(1)
0.381(1)
0.383(1)
0.412(1)
0.293(1)
0.4744(9)
0.6144(8)
0.6485(8)
0.6635(9)
0.720(1)
0.717(1)
0.738(1)
0.785(1)
0.9387(9)
0.364(1)
0.079(1)
-0.6173(2)
-0.4580(2)
-0.7565(8)
-0.6913(8)
-0.6397(7)
-0.6824(7)
-0.5703(6)
-0.6334(7)
-0.7532(8)
-0.7666(9)
-0.655(1)
-0.5745(7)
-0.6039(6)
-0.5948(5)
-0.5628(6)
-0.4533(7)
-0.4222(8)
-0.3162(8)
-0.5590(9)
-0.7493(7)
-0.5700(9)
-0.3798(6)
-0.4036(6)
0.2696(2)
0.1903(1)
0.0945(7)
0.0099(7)
0.0843(7)
0.1749(7)
0.1458(6)
0.2063(6)
0.1703(6)
0.0563(7)
0.0111(7)
0.0447(6)
0.2983(5)
0.3215(4)
0.4034(5)
0.4135(5)
0.4952(6)
0.5066(7)
0.1748(6)
0.2580(7)
0.3276(6)
0.1874(6)
0.1211(6)
7.4(1)
6.8(1)
7.8(6)
7.9(6)
7.1(6)
6.9(5)
6.3(5)
6.6.(5)
7.1(5)
8.0(6)
7.7(6)
6.9(5)
6.8(4)
5.8(4)
7.1(5)
7.9(5)
9.9(6)
12.5(8)
11.0(7)
10.9(7)
11.9(7)
9.4(6)
9.6(6)
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
1H43 14N32S28Si2, 471.3585; found, 471.3528.
12
11
calculated for
C B
18 10
(B) The procedure followed was the same as for the reaction of
benzyl isocyanide, the amounts used were the following: 0.25 g (0.71
mmol) of 5-(S(CH3)2)6-[((CH3)3Si)2CdCH]B10H11, 0.10 mL of tert-
butyl isocyanide, and 25 mL of dry benzene. The reaction was worked
up in the same manner, resulting in the formation of 0.15 g (0.34
mmol) of 2-(S(CH3)2)-7-((CH3)3CNH)-11-[((CH3)3Si)2CdCH]-7-CB10H10
(III), corresponding to a 48% yield of monocarbon carborane based
on starting material. Mass measurement: calculated for
12
11
C
15
1H45 14N32S28Si2, 437.3742; found, 437.3762. Mp: 247-8 °C.
B
10
(C) In a 100 mL round-bottom flask equipped with a stirring bar
8
a Beq ) /3[U11(aa*)2 + U22(bb*)2 + U33(cc*) + 2U12(aa*bb*) cos
and a high-vacuum stopcock were placed 0.73 g (2.16 mmol) of
5-(S(CH3)2)6-[((CH3)3Si)2CdCH]B10H11, 0.25 mL of n-butyl isocyanide,
and 50 mL of a 60:40 benzene/hexane solution. The contents of the
flask were degassed three times, and the reaction mixture was heated
to reflux for a period of 12 h. After the solution was cooled to room
temperature a yellow precipitate containing 2-(S(CH3)2)-(7-C4H9NH)-
11-[((CH3)3Si)2CdCH]-7-CB10H10 (IV) was observed and was removed
by filtration through a medium-porosity frit. The filtrate was reduced
in Vacuo to 10 mL, resulting in the formation of additional 2-(S(CH3)2)-
7-(C4H9NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 precipitate, which was
also removed by filtration. The combined weight of crude 2-(S(CH3)2)-
7-(C4H9NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10 (IV) obtained was 0.59
g (67.3% based on starting material). Recrystallization from methanol/
water produced 0.35 g (40.2%) of the off-white carborane 2-(S(CH3)2)-
7-(C4H9NH)-11-[((CH3)3Si)2CdCH]-7-CB10H10, mp 251-3 °C. The
11B NMR spectrum of IV was similar to those obtained for II and III.
On the basis of on this information, it seems reasonable that IV has a
similar structure.
Reaction of 5-(S(CH3)2)-6-[(CH3)3Si(C4H9)CdCH]B10H11 with
n-Butyl Isocyanide. In a 100 mL round-bottom flask, equipped with
a high-vacuum stopcock, were placed 0.50 g (1.49 mmol) of
5-(S(CH3)2)6-[(CH3)3Si(C4H9)CdCH]B10H11 and 0.20 mL of n-butyl
isocyanide. The flask was then attached to a high-vacuum line, and
its contents were degassed. Benzene (25 mL) was directly condensed
onto the reactants, and the resulting solution was stirred at reflux for
12 h. Noncondensables were removed periodically from the reaction
mixture. The benzene was then stripped off, by using the high-vacuum
line, and the resulting solid was digested in methanol (20 mL) for 6 h.
The methanol solution was cooled at -5 °C in a water-ice-rock salt
bath until a slightly yellow precipitate was formed. The precipitate
was then filtered off and dried overnight in a desiccator.
γ) + 2U13(aa*cc* cos â) + 2U23(bb*cc* cos R)].
Table 7. Selected Interatomic Distances (Å) for
5-(S(CH3)2)-[((CH3)3Si)2CdCH]B10H11 (A)
5-(S(CH3)2)-[(CH3)3Si(C4H9)CdCH]B10H11 (I)
bond
A
I
bond
A
B
B1-B2 1.759(8) 1.718(15) B9-B10
B1-B3 1.777(8) 1.741(14) C1-C2
B1-B4 1.792(9) 1.781(15) C1-B6
B1-B5 1.726(8) 1.706(14) Si1-C2
B1-B10 1.796(8) 1.792(13) Si2-C2
1.793(8) 1.768(15)
1.358(6) 1.351(9)
1.550(7) 1.569(13)
1.886(5) 1.860(7)
1.873(4)
B2-B3 1.778(3) 1.759(15) Si1-CA (C7)a 1.856(6) 1.838(10)
B2-B5 1.763(8) 1.745(12) Si1-CB (C8)a 1.869(6) 1.866(10)
B2-B6 1.763(8) 1.771(13) Si1-CC (C9)a 1.866(5) 1.890(9)
B2-B7 1.792(8) 1.786(14) Si2-CD
B3-B4 1.777(9) 1.776(16) Si2-CE
B3-B7 1.788(9) 1.799(14) Si2-CF
B4-B8 1.766(8) 1.789(15) C2-C3
B4-B9 1.712(9) 1.702(15) C3-C4
B4-B10 1.795(9) 1.782(15) C4-C4
B5-B6 1.661(7) 1.673(13) C5-C6
B5-B10 1.810(8) 1.821(14) S-B5
1.845(7)
1.862(6)
1.862(6)
1.495(10)
1.541(11)
1.512(12)
1.493(14)
1.885(5) 1.885(9)
B6-B7 1.795(8) 1.785(13) S-CG (C10)a 1.784(6) 1.771(8)
B7-B8 2.000(8) 2.028(15) S-CH (C11)a 1.780(5) 1.798(8)
B8-B9 1.784(9) 1.793(17)
a Notation in parentheses refers to the numbering sequence used for
compound I.
and 2.50 g of 5-(S(CH3)2)-6-[(CH3)3Si(C4H9)CdCH]B10H11 (I) was
isolated. [7.45 mmol, 29.1% yield based on decaborane(14)]. Anal.
Calcd: C, 39.24; H, 10.78. Found, C, 38.98; H, 9.84.11 Mp: 98-
1
11
100 °C. Exact mass measurement: calculated for 12C11 H36
B
10
32S28Si,
The identity of the compound was established as 2-(S(CH3)2)-7-
((CH3)3CNH)-11-[(CH3)3Si(C4H9)CdCH]B10H10 (V) [yellowish solid;
0.36 g (0.91 mmol), 61% yield; mp 262-3 °C]. On the basis of the
similarity of the 11B NMR spectrum of V to those of the other
compounds discussed, the structure of V is assumed to be similar to
those of II-IV.
338.3238; found, 338.3280.
Reaction of 5-(S(CH3)2)-6-[((CH3)3Si)2CdCH]B10H11 with Alkyl
Isocyanides. Caution! Addition and transferal of alkyl isocyanides
must be performed inside a well-ventilated hood. Some of these
compounds are highly toxic, and even small amounts leave a pungent
odor behind that lasts in the area for around 3-4 h.
(A) In a Kjedahl 100 mL flask equipped with a high-vacuum
stopcock were placed 0.50 g (1.42 mmol) of 5-(S(CH3)2)6-[((CH3)3-
Si)2CdCH]B10H11 and 0.17 mL (1.40 mmol) of benzyl isocyanide.
Benzene (25 mL) was then condensed in, the mixture was and stirred
Results and Discussion
The reaction of decaborane(14) with 1-(trimethylsilyl)-1-
hexyne in the presence of dimethyl sulfide resulted in the
formation of 5-(S(CH3)2)-6-[(CH3)Si(C4H9)CdCH]B10H11. The
formation of this compound is not surprising, since under similar
circumstances, reaction of B10H14 with (CH3)3SiCtCSi(CH3)3
(11) When loss of molecular hydrogen is taken into consideration, the
analysis is as follows: C, 39.48; H, 10.24.

2572 Inorganic Chemistry, Vol. 35, No. 9, 1996
Burgos-Adorno et al.
Figure 2. ORTEP drawing of the molecular structure of 5-(S(CH3)2)-
6-[((CH3)3Si)2CdCH]B10H11 (A).
12
reported for 5-(S(CH3)2)-9-C6H11-B10H11 and 5-(S(CH3)2)-6-
Figure 1. ORTEP Drawing of the molecular structure of 5-(S(CH3)2)-
6-[(CH3)3Si(C4H9)CdCH]B10H11 (I).
[(CH3)3Si(CH3)CdCH]B10H11.8
The structures of these compounds are very similar to those
-
found for the isoelectronic B10H13 anion.13 In B10H13-, the
and CH3CtCSi(CH3)3 in the presence of dimethyl sulfide also
results in the formation of compounds analogous to I.
B5-B6 distance is rather short, 1.65 Å,13 whereas in B10H14
the same bond has an intramolecular distance of 1.790(3) Å.14
This shortening could be due to the increased two-center, two-
electron character of this bond. In compound I this distance
was found to be 1.673(13) Å, in agreement with the reported
distances for 5-(S(CH3)2)9-C6H11-B10H11 (1.64(1) Å)12 and
5-(S(CH3)2)6-[(CH3)3Si(CH3)CdCH]B10H11 (1.657(1) Å).8 In
contrast, the boron-boron distance between B7 and B8 in this
compound is rather long (2.028(15) Å).
A similar situation arises for 5-(S(CH3)2)-6-[((CH3)3Si)2CdCH]-
B10H11. The B5-B6 intermolecular distance was found to be
1.661(7) Å, while the B7-B8 distance was determined to be
2.000(8) Å. The other boron-boron, boron-carbon, and
carbon-carbon distances in both compounds fall within ex-
pected ranges for molecules of this type. The presence of long
boron-boron and short boron-boron bonds in both I and A
should activate these molecules for reaction toward nucleophiles,
such as isocyanides.
The exopolyhedral organosilyl group of I is bound to the
6-position of the borane, and this group is of the type
RR′CdCH, suggesting that, following hydroboration of silylated
acetylene, this fragment rearranged via a trimethylsilyl migration
from the R-carbon to the â-carbon of the olefinic unit. This
type of migration has been observed previously with other
organoboron compounds.8,15 As observed with bis(trimethyl-
silyl)acetylene and (trimethylsilyl)propyne, the reaction of
B10H12(S(CH3)2)2 with 1-(trimethylsilyl)-1-hexyne involves
initial hydroboration of the acetylene, followed by trimethylsilyl
migration, dissociation of one dimethyl sulfide molecule, and
migration of the second dimethyl sulfide molecule from an
apical position in the initial borane to a basal position in the
final product. The trimethylsilyl migration in this compound
could be explained in terms of steric repulsions between the
silyl group and the decaborane cage. By migrating, the
B10H12(S(CH3)2)2 + (CH3)3SiCtCR f
5-(S(CH3)2)-6-[(CH3)3Si(R)CdCH]B10H11 (5)
R ) (CH3)3Si, CH3, C4H9
The reaction of isocyanides with boron hydrides has been
previously studied by Todd and coworkers.1-6 It was found to
yield the first monocarbon carborane derived from deca-
borane(14). Among the analogous systems which have also
been found to react with isocyanides in a similar fashion are
SB9H11,2 SeB9H11,2 and 5-S(CH3)2-9-C6H11-B10H11.4 All of
-
these compounds have a B10H14 or, like either A or I, a B10H13
type structure.
Synthesis and Structural Studies of Alkenyldecaboranes.
The identity of I was established by 11B and 1H NMR spectra,
as well as single-crystal X-ray diffraction techniques. Mass
spectrometric measurements were also consistent with the
structure of I. In addition, the single-crystal X-ray structure
for 5-S(CH3)2-6-[((CH3)3Si)2CdCH]B10H11 (A) is being re-
ported. The synthesis of this compound was first reported by
Sneddon and co-workers,8 although the data presented suggested
that indeed the structure of this compound was very similar to
that of 5-S(CH3)2-6-[(CH3)3Si(CH3)CdCH]B10H11, which was
reported in a previous Communication.8 No structural confir-
mation was presented. The discussion regarding the charac-
terization of this compound has been previously reported.8
Figures 1 and 2 show ORTEP drawings for compounds I and
A.
The 11B NMR spectrum of I consisted of eight resonances
in the ratio 1:2:1:1:1:2:1, with singlets at 29.84 and -6.76 ppm,
which corresponds to substitution at two boron atoms by (CH3)3-
Si(C4H9)CdCH and S(CH3)2 groups. The 11B NMR spectrum
of I is indeed very similar to those reported for 5-S(CH3)2-6-
[(CH3)3Si(CH3)CdCH]B10H11 and 5-S(CH3)2-6-[((CH3)3Si)2-
(12) (a) Tolpin, E. I.; Misuzawa, E.; Becker, D. S.; Venzel, J. Inorg. Chem.
1980, 19, 1182-1187. (b) Misuzawa, E.; Rudnick, S. E.; Eriks, K.
Inorg. Chem. 1980, 19, 1188-1191.
(13) Sneddon, L. G.; Huffman, J. C.; Schaeffer, R.; Streib, W. E. J. Chem.
Soc., Chem. Commun. 1972, 474-475.
1
CdCH]B10H11.8 The H NMR spectrum showed resonances
(14) Brill, V. R.; Dietrich, H.; Dierks, H. Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem. 1971, B27, 2003-2018.
characteristic of (CH3)3Si, C4H9, S(CH3)2, and CdCH groups,
as well as the presence of bridge hydrogens in the borane
molecule. The single-crystal X-ray diffraction structure obtained
for I showed intramolecular distances very similar to those
(15) (a) Wehrmann, R.; Pues, C.; Klusik, H.; Berdnt, A. Angew. Chem.,
Int. Ed. Engl. 1984, 23, 372-373. (b) Wrackmeyer, B.; Bihlmayer,
C.; Schilling, M. Chem. Ber. 1983, 116, 3182-3191.

Alkenyl Monocarbon Carboranes
Inorganic Chemistry, Vol. 35, No. 9, 1996 2573
Figure 4. Cage skeletal structure of 2-(S(CH3)2)-7-RNH-11-[(CH3)3-
Si(R′)CdCH]B10H10 (II, R ) C6H5CH2, R′ ) (CH3)3Si; III, R )
(CH3)3C, R′ ) (CH3)3Si; IV, R ) C4H9, R′ ) (CH3)3Si; V, R ) C4H9,
R′ ) C4H9).
relative areas of 3:2:1:1:1:1; for compound III, the 11B NMR
spectrum consists of eight resonances with relative areas of 3:1:
1:1:1:1:1; for compound IV, the 11B NMR spectrum is
somewhat simplified, with relative areas of 3:2:2:1:1:1. Finally,
for compound V, the 11B NMR spectrum shows resonances of
relative intensities 1:2:1:1:1:1:1:1:1. Coincidental overlap of
signals will tend to simplify the observed 11B NMR. This is
1
clearly the case for compounds II-IV. The H NMR spectra
Figure 3. Proposed reaction scheme leading to the formation of
alkenyldecaboranes.
of these compounds show lack of mirror symmetry. With the
exception of the spectrum of V, they showed split peaks for
the dimethyl sulfide groups attached to the boron cage.
Likewise, for II-V, there are two distinct peaks for each of
the trimethylsilyl groups, indicating the lack of a mirror plane
that will make these groups magnetically equivalent during the
NMR experiment. 1H NMR data for these compounds are
summarized in Table 3.
trimethylsilyl group increases its distance from the decaborane
cage, hence minimizing possible steric interactions with the cage.
The proposed reaction scheme for the formation of I is shown
in Figure 3. Initial attack on the alkyne results in the formation
of an intermediate having both dimethyl sulfide groups still
bonded to the boron cage, while the trimethylsilyl group starts
its migration from the R-carbon to the â-carbon. In the second
step, the dimethyl sulfide bonded to the boron which has the
alkenyl group migrates while hydrogen and dimethyl sulfide
are liberated from the intermediate; finally migration of
hydrogens results in the formation of the observed product. This
reaction scheme is important, since it does not lead to the
formation of monocarbon carboranes, which is the case when
bis(trimethylsilyl)acetylene is used. Clearly, the formation of
the alkenyldecaboranes must follow a different reaction pathway.
The mass spectrum of compound I shows the expected
fragmentation pattern. For I, the cutoff at m/e 338 corresponds
The presence of N-H stretch bands in the IR spectra of these
compounds suggested that their structures might be analogous
to that of the previously reported carborane 3-S(CH3)2-7-(t-C4H9-
NH)-8-(C6H11)-7-CB10H10, which was reported by Todd and
coworkers.4 The structure of this monocarbon carborane was
confirmed by single-crystal X-ray diffraction. It is important
to point out that insertion of the isocyanide carbon into the
decaborane frame of 5-(S(CH3)2)-9-C6H11-B10H11 did not disturb
the relative positions of the of the dimethyl sulfide and
cyclohexyl groups. Another distinguishing feature of this
compound is that, instead of reduction of the NtC bond to an
NH2R group, the reduction was to an amino group (NHR). This
behavior is clearly different from that of B10H14, which, when
reacted with isocyanides, results in the formation of monocarbon
carboranes having NH2R groups.
12
11
to the assigned empirical formula
C B
1H36 32S28Si+. In
11 10
addition, the fragments found at m/e 276, 219, and 146 are
consistent with the stepwise loss of S(CH3)2, C4H9, and (CH3)3-
Si groups, respectively.
The normal type of reaction that takes place between
decaborane(14) and alkynes results in the formation of substi-
tuted o-carboranes.16 Clearly, when trimethylsilyl groups are
part of the alkyne, this is not the case. Sneddon and coworkers
confirmed the fact that when bis(trimethylsilyl)acetylene reacts
with decaborane(14), two products are formed, a monocarbon
carborane, 9-S(CH3)2-7-[((CH3)3Si)2CH]-7-CB10H11, and an
alkenyldecaborane similar to I. When (trimethylsilyl)propyne
Synthesis and Characterization of Alkenyl Monocarbon
Carboranes. The reactions of 5-(S(CH3)2)-6-[((CH3)3Si)2CdCH]-
B10H11 and 5-(S(CH3)2)-6-[(CH3)Si(C4H9)-CdCH]B10H11 with
isocyanides were found to produce monocarbon carboranes via
insertion of the carbon atom of the isocyanide unit, accompanied
by the protonation of the nitrogen atom. The product geometry
is based on an icosahedron missing one vertex, yielding an 11-
vertex nido monocarbon carborane, the basic structure of which
is shown in Figure 4.
(16) (a) Kutal, C. R.; Owen, D. A.; Todd, L. J. Inorg. Synth. 1968, 11,
19-23. (b) Heying, T. L.; Ager, J. W., Jr.; Clark, S. L.; Mangold, D.
L.; Goldstein, H. L.; Hillman, M.; Pollack, R. J.; Szymanski, J. W.
Inorg. Chem. 1963, 2, 1089-1092. (c) Fein, M. M.; Grafstein, D.;
Paustian, J. E.; Bobinski, J.; Liechstein, B. M.; Mayes, N.; Schwartz,
N. N.; Cohen, M. S. Inorg. Chem. 1963, 2, 1115-1119. (d) Zakharkin,
L. I.; Stanko, V. I.; Brattsev, V. A.; Chapovskii, Yu. A.; Klimova, A.
I.; Oxlobystin, O. Yu.; Ponomarenko, A. A. Dokl. Akad. Nauk SSSR
1964, 155, 1119-1112. (e) Dupont, J. A.; Hawthorne, M. F. J. Am.
Chem. Soc. 1964, 86, 1643. (f) Paxson, T. E.; Callahan, K. P.;
Hawthorne, M. F. Inorg. Chem. 1973, 12, 708-709. (g) Fein, M. M.;
Bobinski, J.; Mayes, N.; Schwartz, N.; Cohen, M. S. Inorg. Chem.
1963, 2, 1111-1115.
The 11B NMR spectra of these compounds are consistent with
the proposed structures. For the related compound 3-(S(CH3)2)-
7-((CH3)3CNH)-11-(C6H11)B10H10, a single-crystal X-ray struc-
ture has been reported.4 The 11B NMR spectra for these
monocarbon carboranes show the lack of mirror symmetry
imposed on the molecule due to the presence of three exopoly-
hedral groups. All the compounds show clearly the two singlets,
which is consistent with two boron atoms containing organic
groups directly attached to them, rather than a hydrogen. For
compound II, 11B NMR spectrum shows seven resonances with

2574 Inorganic Chemistry, Vol. 35, No. 9, 1996
Burgos-Adorno et al.
Figure 5. Possible icosahedral positions for the incorporation of the
carbon atom of the isocyanide into a 10-vertex polyhedral alkenyl-
borane.
is the alkyne used, only the alkenyldecaborane product is
obtained. It was found that, for the case of bis(trimethylsilyl)-
acetylene, conversion of the alkenyldecaborane into the mono-
carbon carborane was not possible under any circumstances.8
This result suggests that these alkenyldecaboranes might be
related to the “unreactive” isomer of B10H12(S(CH3)2), which
has been found not to undergo reactions with acetylenes to
produce carboranes.17
A previous study conducted by Todd and coworkers has
shown that the cyclohexyl-substituted borane derivative
5-(S(CH3)2)9-C6H11-B10H11, which might be related to the
“unreactive” isomer of B10H12(S(CH3)2), undergoes reaction with
tert-butyl isocyanide, resulting in carbon insertion into the
borane framework and reduction of the NtC triple bond.4 Thus,
the compound is activated for attack by a nucleophile, such as
an isocyanide.
Huckel calculations (giving Mulliken atomic charges) per-
formed on 5-(S(CH3)2)-9-C6H11-B10H11 indicated that the boron
carrying the cyclohexyl group had the higher relative positive
atomic charge in the cluster.12 This observation is in agreement
with the results obtained by Tolpin and coworkers, who showed
that pyridine attacked at the B9 position of the borane cluster.12
It is significant to note that, even the presence of a bulky
substituent, such as cyclohexyl, did not prevent attack by
pyridine at this position.
Figure 6. Possible reaction sequence leading to the formation of
2-(S(CH3)2)-7-(RNH)-11-[(CH3)3Si(R)CdCH]B10H10 (II, R ) C4H9, R′
) C4H9; III, R ) C4H9, R′ ) (CH3)3Si; IV, R ) (CH3)3C, R′ ) (CH3)3-
Si; V, R ) CH2C6H5, R′ ) (CH3)3Si) and the second unobserved isomer
of the reaction.
formation of the observed product. The second possible
configuration will include B6, B7, B8, B9, and the incoming
carbon atom. If the attack occurs on that side of the molecule,
the resulting product will have a carbon atom on the second
possible icosahedral position. This will force the dimethyl
sulfide associated with the cage to be placed on the open face
of the monocarbon carborane and not in the position in which
is found, namely, the lower belt of boron atoms in the structure.
A plausible reaction sequence illustrating the products obtained
on the basis of the point of attack of the isocyanide is shown in
Figure 6.
Undoubtedly, a similar type of reaction sequence can occur
upon reaction of isocyanides with the alkenylboranes reported
in this communication. The attack will probably be initiated
at B6, followed by formation of carbon-boron bonding interac-
tions, resulting in the incorporation of the isocyanide carbon
into the borane framework.
Todd observed that the yields obtained from the reaction of
5-(S(CH3)2)-9-C6H11-B10H11 with tert-butyl isocyanide were
moderate and had argued that this could a consequence of the
existence of a second isomer that cannot be isolated under the
reaction conditions.4 We have observed the same pattern in
The fact that the incorporation of the isocyanide molecule
occurred without disturbing the relative positions of the sub-
stituents already present on the parent alkenylboranes supports
the theory that attack of the isocyanide occurred on the side of
the molecule having the highest electrophilic character, which
is the open face formed by B5, B6, B9, and B10 atoms. It is
interesting to note that although it should be expected that this
side of the molecule is more sterically crowded, due to the
presence of the substituent groups on the borane, electronic
factors seem to be more important, since the second predicted
product is not observed at all. This reactivity is in agreement
with the previously reported reaction of tert-butyl isocyanide
with 5-(S(CH3)2)9-C6H11-B10H11. In that molecule the iso-
cyanide carbon attacked selectively at B9, the boron with the
most electrophilic character on the cage, even though it had a
bulky cyclohexyl group already attached at that position.4
Another example supporting the idea that electronic factors seem
to be of more importance than steric factors is that pyridine
the reactivity of these alkenylboranes with isocyanides.
A
possible explanation to this observation is the fact that these
alkenylboranes do not have mirror symmetry, as demonstrated
by the 11B NMR data. This lack of mirror symmetry will lead
to the creation of two nonequivalent icosahedral positions, as
shown in Figure 5, in which the carbon atom could be
incorporated into the borane framework. The first configuration
would be formed by B5, B6, B9, B10, and the incoming carbon
atom. Attack on that side of the molecule will result in the
(17) (a) Hill, W. E.; Johnson, F. A.; Novak, R. W. Inorg. Chem. 1975, 14,
1244-1249. (b) Knoth, W. H.; Muetterties, E. L. J. Inorg. Nucl. Chem.
1961, 20, 66-72. (c) Stibr, B.; Plesek, S.; Hermanek, S. Collect. Czech.
Chem. Commun. 1972, 37, 2696-2700.

Alkenyl Monocarbon Carboranes
Inorganic Chemistry, Vol. 35, No. 9, 1996 2575
reacts with 5-(S(CH3)2)-9-C6H11-B10H11 resulting in the forma-
tion of 6-(C6H11)-6,9-(py)2B10H11 in good yield.12
Acknowledgment. G.B.A. acknowledges the MBRS pro-
gram for summer support. We thank the National Science
Foundation (Grant CHE-9502406) for support of this research
and Mr. Monte Mauldin for assistance with the collection of
1H and 11B NMR data.
In summary, the alkenyldecaboranes 5-(S(CH3)2)6-[(CH3)3-
Si(C4H9)CdCH]B10H11 and 5-(S(CH3)2)6-[((CH3)3Si)2CdCH]-
B10H11 have been shown to produce monocarbon carboranes in
moderate yields. The presence of a pendant alkenyl group in
these monocarbon carboranes presents an interesting possibility
in expanding the chemistry of these compounds to involve the
attached organic groups. It is our intention to continue research
dealing with these compounds by taking advantage of this fact.
Supporting Information Available: Tables of bond angles, aniso-
tropic temperature factors, and hydrogen atom coordinates for com-
pounds I and A (10 pages). Ordering information is given on any
current masthead page.
IC951138Z