Silyl group mediated linkage of closo-C2B10-cage to nido-C2B4-carborane

Article abstract of DOI:10.1016/j.inoche.2003.07.002

The reaction of the sodium salt of the monoanion, nido-[2,3-(Si(CH ₃)₃)₂-2,3-C₂B₄H ₅]^-, with (chloromethyl)dimethylchlorosilane in a 1:1 molar ratio produced the B_(cage)-substituted cluster, nido-5-ClCH₂Si(CH₃)₂-2,3-(Si(CH ₂B₄H₅ (1), in 81% yield. This product (1) was reacted further with the lithium salt of [closo-1-R-1,2-C₂B ₁₀H₁₀]^- monoanion (R = Me, Ph) to give the novel linked and mixed C₂B₄/C₂B₁₀ carborane species, 1-Me-2-[5′-SiMe₂CH₂-2′ -3′-C₂B₄H₅]-1,2-C₂B ₁₀H₁₀ (2), 1-Ph-2-[5′SiMe₂CH ₂-2′,3′-(SiMe₃)₂-2′,3′ -C₂B₄H₅]-1,2-C₂B₁₀H ₁₀ (3), in yields of 76% and 81%, respectively.

Full text of DOI:10.1016/j.inoche.2003.07.002

Inorganic Chemistry Communications 6 (2003) 1344–1346
www.elsevier.com/locate/inoche
Silyl group mediated linkage of closo-C2B10-cage to
nido-C2B4-carborane: synthesis of the novel carborane ligand,
1-R-2-[50-(SiMe2CH2)-20,30-(SiMe3)2-20,30-C2B4H5]-1,2-C2B10H10
(R ¼ Me, Ph)
b
a,
*
Yinghuai Zhu a,b,1, John A. Maguire , Narayan S. Hosmane
a
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA
b
Department of Chemistry, Southern Methodist University, Dallas, TX 75275, USA
Received 30 May 2003; accepted 7 July 2003
Published online: 11 September 2003
Abstract
The reaction of the sodium salt of the monoanion, nido-[2,3-(Si(CH3)3)2-2,3-C2B4H5]ꢀ, with (chloromethyl)dimethylchlorosilane
in a 1:1 molar ratio produced the BðcageÞ-substituted cluster, nido-5-ClCH2Si(CH3)2-2,3-(Si(CH3)3)2-2,3-C2B4H5 (1), in 81% yield.
This product (1) was reacted further with the lithium salt of [closo-1-R-1,2-C2B10H10]ꢀ monoanion (R ¼ Me, Ph) to give the novel
linked and mixed C2B4/C2B10 carborane species, 1-Me-2-[50-SiMe2CH2-20,30-(SiMe3)2-20,30-C2B4H5]-1,2-C2B10H10 (2), 1-Ph-2-[50-
SiMe2CH2-20,30-(SiMe3)2-20,30-C2B4H5]-1,2-C2B10H10 (3), in yields of 76% and 81%, respectively.
Ó 2003 Elsevier B.V. All rights reserved.
The study of the coordination chemistry of carborane
clusters derived from the 1-R-2-R0-1,2-C2B10H10 and 2-
R-n-R0-2,n-C2B4H6 (n ¼ 3, 4; R, R0 ¼ H or a CðcageÞ
derivative) cage systems have most often been studied
separately [1–7]. Since each cage system offers its own
attractions, the targeted syntheses of specific linked-
carborane compounds containing both large and small
coordinating cages capable of having charges ranging
from )1 to )4 could lead to a series of ligands having
unique properties. As a first step in the development of
such compounds, we report herein the synthesis and
characterization of the novel linked and mixed C2B4/
C2B10 carborane cages that are envisioned to be the
precursors to the desired ligands for a number of un-
usual metallacarborane complexes.
The reaction of the sodium salt of the [nido-2,3-
(Si(CH3)3)2-2,3-C2B4H5]ꢀ anion [8,9] with (chlorom-
ethyl)dimethylchlorosilane, in a 1:1 molar ratio in
diethyl ether, followed by extraction and purification,
produced a new unique-BðcageÞ-substituted small cage
carborane, nido-5-ClCH2Si(CH3)2-2,3-(Si(CH3)3)2-2,3-
C2B4H5 (1) in 81% yield (Scheme 1) [10]. The reaction of
1 with the lithium salt of the [closo-1-R-1,2-C2B10H10]ꢀ
anion (R ¼ Me, Ph) in 1:1 molar ratio in diethyl ether,
followed by extraction and purification, produced the
novel silyl-bridged, mixed carborane species, 1-R-2-
[50-SiMe2CH2-20; 30-(SiMe3)2-20; 30-C2B4H5]-1,2-C2B10H10
[R ¼ Me (2) and Ph (3)], in yields of 76% and 81%, re-
spectively [11,12]. Unfortunately, compounds 2 and 3
are viscous liquids, so they could not be structurally
characterized by X-ray diffraction. However, their ele-
mental analyses and spectroscopic data are all consistent
with the structures shown for these compounds in
* Corresponding author. Tel.: +1-815-753-3556; fax: +1-815-753-
4802.
1
Scheme 1. The H NMR spectra of all the three com-
pounds show resonances in the d ¼ ꢀ1:82 to )1.20 ppm
range, which are characteristic for the B–H–B bridge
hydrogens of the smaller cage [8,9]. In addition, reso-
nances for the hydrogens in the various alkyl and/or aryl
E-mail addresses: jmaguire@mail.smu.edu (J.A. Maguire), nhos-
mane@niu.edu (N.S. Hosmane).
1
Present address: Institute of Chemical and Engineering Sciences,
Block 28, # 02-08, Ayer Rajah Crescent, Singapore 139959, Singapore.
1387-7003/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2003.07.002

Y. Zhu et al. / Inorganic Chemistry Communications 6 (2003) 1344–1346
1345
Scheme 1.
[2] C.K. Broder, A.E. Goeta, A.K. Howard, A.K. Hughes, A.L.
Johnson, J.M. Malget, K. Wade, J. Chem. Soc., Dalton Trans.
(2000) 3526–3533.
groups (CH3, C6H5, Si–CH3 and CH2) were all found in
1
their expected regions of the H NMR spectra. The 13C
NMR spectra of compounds 2 and 3 confirm the pres-
ence of both the C2B4 and C2B10-cage carbons, as well
as those in the different substituent groups and are all
consistent with the proposed structures. The 11B{H}
NMR spectrum of 1 shows three resonances with a 1:2:1
peak area ratio. The broad singlet at d ¼ 14:87 ppm is
due to the unique boron [B(5) in the usual numbering
system], while the doublets at d ¼ 0:91 and d ¼ ꢀ50:21
ppm are due to the basal and apical BHs, respectively.
This spectrum is quite typical for the nido-5-R-2,3-
(SiMe3)2-2,3-C2B4H5 carboranes [13]. As expected,
these peaks are still retained essentially in their same
positions of the 11B{H} NMR spectra of 2 and 3, in
addition to those observed for the C2B10-cages [14].
The synthesis shown in Scheme 1 is a general one that
could be used to couple different carborane polyhedra to
produce a series of interesting and potentially useful
ansa-ligands. Such work is currently underway in our
laboratories.
[3] R. Uhrhammer, Y.-X. Su, D.C. Swenson, R.F. Jordan, Inorg.
Chem. 33 (1994) 4398–4402.
[4] X. Bei, C. Kreuder, D.C. Swenson, R.F. Jordan, V.G. Young Jr.,
Organometallics 17 (1998) 1085–1091.
[5] Y.-X. Su, C.E. Reck, I.A. Guzei, R.F. Jordan, Organometallics 19
(2000) 4858–4861.
[6] X. Bei, V.G. Young Jr., R.F. Jordan, Organometallics 20 (2001)
355–358.
[7] Z. Xie, Z. Liu, K. Chiu, F. Xue, T.C.W. Mak, Organometallics 16
(1997) 2460–2464.
[8] N.S. Hosmane, N.N. Sirmokadam, M.N. Mollenhauer, J. Orga-
nomet. Chem. 279 (1985) 359–371.
[9] N.S. Hosmane, A.K. Saxena, R.D. Barreto, H. Zhang, J.A.
Maguire, L. Jai, Y. Wang, A.R. Oki, K.V. Grover, S.J. Whitten,
K. Dawson, M.A. Tolle, U. Siriwardane, T. Demisse, J.S. Fagner,
Organometallics 12 (1993) 3001–3014.
[10] All syntheses were performed under an argon atmosphere using a
combination of glove box and high-vacuum techniques. Synthesis
of (1): A solution of 0.75 g (3.41 mmol) of 2,3(Si(CH3)3)2-2,3-
C2B4H6 in 40 ml of dry THF was slowly added over a period of 10
min to a suspension of 0.2 g (7.67 mmol) of NaH in the same solvent
at )78 °C. After addition, the mixture was slowly warmed to room
temperature and held at that temperature for ꢁ1 day. After that
time, the reaction mixture was filtered and the clear filtrate was
added to a solution of 0.5 ml (3.67 mmol) (chloromethyl)dimeth-
ylchlorosilane dissolved in 30 ml of dry THF at )78 °C and kept
at the temperature for 2 h. The system was then warmed to
room temperature and stirred for 2 days. After the reaction, the
solvent was removed under reduced pressure to give a pale yellow
residue. A pure pale yellow oily product, identified as nido-5-
ClCH2Si(CH3)2-2,3-(Si(CH3)3)2-2,3-C2B4H5 (1), was obtained in
81% yield after extraction of the residue with 50 ml of pentane and
drying in a vacuum. Compound 1 was purified by silica gel column
chromatography (eluted with pentane). Elemental Anal. Calcd. for
1: C, 40.49; H, 9.58. Found: C, 40.73; H, 9.77%. The spectroscopic
data for 1: 1H NMR (C6D6, relative to external Me4Si) d )1.40 to
)1.18 [br, 2H, B–H–B], 0.24 [s, 6H, B–Si–(CH3)2], 0.42 [s, 18H, 2 C–
Si–(CH3)3], 2.68 [s, 2H,Cl–CH2]; 11B NMR (C6D6, relative to
external BF3 ꢂ OEt2) d ꢀ50.21 [d, apical BH, 1J(11B–1H) ¼ 175 Hz],
0.91 [d, basal BH, 1J(11B–1H) ¼ 139 Hz], 14.87 [s(br), basal BSi];
13C NMR (C6D6, relative to external Me4Si) d )3.30 [q, Si–(CH3)2,
1J(13C–1H) ¼ 120 Hz], 2.01 [q, Si–(CH3)3, 1J(13C–1H) ¼ 120 Hz],
29.68 [t, Cl–CH2, 1J(13C–1H) ¼ 87 Hz], 141.704 [s (br), cage-C-
substituted]; IR (cmꢀ1, KBr cell) 2955 (s,s), 2894 (s,s), 2864 (s,m)
[m(C–H)], 2571 (s,s) [m(B–H)], 1404 (s,m), 1306 (sh) [d(CH)asym],
1250 (vs,s) [d(CH)sym], 1091 (s,s), 1066 (s,s), 938 (s,s), 840 (vs, br)
[q(CH)], 799 (s,s), 758 (s,s), 687 (m,s), 630 (m,s), 479 (m,s).
Acknowledgements
This work was supported by grants from the National
Science Foundation (CHE-9988045 and CHE-0241319),
the donors of the Petroleum Research Fund, adminis-
tered by the American Chemical Society, The Robert A.
Welch Foundation (N-1322 to J.A.M.) and Northern
Illinois University through a Presidential Research
Professorship. The Forschungspreis der Alexander von
Humboldt-Stiftung and the nominating Professors, Dr.
€
Herbert W. Roesky of Universitat Gottingen and Dr.
Wolfgang Kaim of Universitat Stuttgart, are also hereby
€
€
gratefully acknowledged.
References
[1] A.K. Saxena, J.A. Maguire, N.S. Hosmane, Chem. Rev. 97 (1997)
2421–2462.

1346
Y. Zhu et al. / Inorganic Chemistry Communications 6 (2003) 1344–1346
[11] Synthesis of 2: A 1.50 ml (2.40 mmol) solution of n-BuLi (1.6 M in
hexanes) was added, over a period of 20 min, to a solution of 0.3 g
(1.90 mmol) of 1-Me-1,2 C2B10H11 in 30 ml dry diethyl ether at
)78 °C. After addition, the mixture was allowed to warm to room
temperature and reacted at that temperature for 4 h. The solvent
was then removed under reduced pressure and the residue was
washed with dry pentane to eliminate any unreacted n-BuLi. A 40
ml aliquot of diethyl ether was transferred via high-vacuum line to
1460 (m,s), 1409 (s,s), 1393 (s,s), 1312 (w,s) [d(CH)asym], 1250
(vs,s) [d (CH)sym], 117 (s,s), 1076 (s,s), 1050 (s,s), 1004 (s,s), 927
(s,s), 846 (vs,br) [q(CH)], 758 (s,s), 682 (s,s), 636 (s,s), 502 (s,s),
461 (m,s).
[12] Synthesis of 3: In a procedure identical to that used in the
synthesis and purification of 2 above, except that the lithium salt
of phenyl-ortho-carborane was substituted for its methyl
analogue, 1-Ph-2-[50-SiMe2CH2-20,30-(SiMe3)2-20,30-C2B4H5]-1,2
C2B10H10 (3) was isolated in 81% yield as a sticky pale yellow
substance. Elemental Anal. Calcd. for 3: C, 44.73; H, 9.09. Found:
C, 44.41; H, 8.97%. The spectroscopic data for 3: 1H NMR (C6D6,
relative to external Me4Si) d )1.80 to )1.76 [br, 2H, B–H–B],
)0.07 [s, 6H, B–Si–(CH3)2], 0.43 [s, 18H, 2 C–Si–(CH3)3], 2.40 [s,
a
flask containing the pure lithium salt of 1-methyl-ortho-
carborane to obtain a clear solution that was added over a 30
min interval at )78 °C to a solution of 0.62 (1.90 mmol) 5-
ClCH2Si(CH3)2-2,3-(Si(CH3)3)2-2,3-C2B4H5 (1) in 40 ml diethyl
ether. The reaction mixture was stirred at )78 °C for 2 h and then
was slowly warmed to room temperature. After continued stirring
at room temperature for 2 days, the solvent was removed under
reduced pressure to obtain a slightly yellow, oily residue. This
crude product was extracted with 40 ml of dry pentane, dried in
vacuum and then purified by silica gel column chromatography
(eluted with pentane) to obtain 1-Me-2-[50-SiMe2CH2-20,30-
(SiMe3)2-20,30-C2B4H5]-1,2-C2B10H10 (2) as a pale yellow sticky
oily product in 76% yield. The product could be converted into a
waxy solid when held at 0 °C under an argon atmosphere.
Elemental Anal. Calcd for 2: C, 37.52; H, 9.89. Found: C, 37.75;
2H, C
–CH2–Si], 6.88–7.42 [m, 5H, C6H5]; 11B NMR
ðlarge cageÞ
(C6D6, relative to external BF3 ꢂ OEt2)
d )50.33 [d, apical
BH(small cage), 1J(11B–1H) ¼ 178 Hz], )11.02 [d, apical B–
H(large cage), 1J(11B–1H) ¼ unresolved], )8.53 [sh, basal BH(large
cage), presup1J(11B–1H) ¼ 153 Hz], )3.29 [s, basal BH(large cage),
1J(11B–1H) ¼ 162 Hz], )2.36 [s, basal BH(large cage), 1J(11B–
1H) ¼ 150 Hz], 1.10 [s, overlapping basal BH(large cage) and basal
BH(small cage)], 14.63 [s(br), apical B–Si(small cage)]; 13C NMR
(C6D6, relative to external Me4Si) d )3.65 [q, Si–(CH3)2, 1J(13C–
1
1H) ¼ 152 Hz], 2.02 [q, Si–(CH3)3, J(13C–1H) ¼ 119 Hz], 29.03 [t,
1
H, 9.87%. The spectroscopic data for 2: H NMR (C6D6, relative
to external Me4Si) d )1.82 to )1.58 [br, 2H, B–H–B], 0.22 [s, 6H,
CH2 (large cage), 1J(13C–1H) ¼ 142 Hz], 74.63 [s, large cage-C-
substituted], 83.82 [s, large cage-C-substituted], 127.32–132.98 [m,
C6H5], 143.86 [s (br), small cage-C-substituted]; IR (cmꢀ1, KBr
cell) 2955 (s,br), 2894 (s,s), 2592 (vs,br) [m(B–H)large and small cage],
2274 (m,s), 2264 (s,s), 1947 (m,s), 1537 (m, s), 1501 (m,s), 1454
(m,s), 1408 (s,s), 1393 (s,s), 1322 (s,s) [d(CH)asym], 1250 (vs,s)
[d(CH)sym], 1086 (s,s), 1045 (w,s), 958(m,s), 927 (s,s), 886 (s,s),
835 (vs,br) [q(CH)], 753 (s,s), 692 (s,s), 518 (s,s), 636 (s,s),
497 (s,s).
B–Si–(CH3)2], 0.42 [s, 18H,
2
C–Si–(CH3)3], 1.53 [s, 3H,
–CH2–Si]; 11B NMR (C6D6,
ðlarge cageÞ
C
–CH3], 2.65 [s, 2H,C
ðlarge cageÞ
relative to external BF3 ꢂ OEt2) d )50.39 [d, apical B–H(small
cage), 1J(11B–1H) ¼ 176 Hz], )10.33 [s, apical B–H(large cage),
1J(11B–1H) ¼ 158 Hz], )8.91 [s, basal B–H(large cage), 1J(11B–
1H) ¼ 153 Hz], )5.57 [s, basal B–H(large cage), 1J(11B–1H) ¼ 153
Hz], )4.61 [s, basal B–H(large cage), 1J(11B–1H) ¼ 148 Hz], 0.98 [s,
overlapping basal B–H(large cage) and basal B(small cage)], 14.57
[s(br), basal B-Si(small cage)]; 13C NMR (C6D6, relative to
external Me4Si) d )3.10 [q, Si–(CH3)2, 1J(13C–1H) ¼ 123 Hz],
2.04 [q, Si–(CH3)3, 1J(13C–1H) ¼ 119 Hz], 25.55 [q, CH3(large
cage), 1J(13C–1H) ¼ 132 Hz], 29.23 [t, CH2(large cage), 1J(13C–
1H) ¼ 141 Hz], 69.68 [s, large cage-C-substituted], 75.61 [s, large
cage-C-substituted], 143.98 [s (br), small cage-C-substituted]; IR
(cmꢀ1, KBr cell) 2955 (s,br), 2894 (s,s), 2587 (vs,br) [m(B–
H)large and small cage], 2279 (m,s), 1947 (m,s), 1537 (m,s), 1501 (m,s),
[13] J.A. Maguire, J.-Q. Wang, C. Zheng, C. Li, N.S. Hosmane, Inorg.
Chim. Acta C 334 (2002) 91–104.
[14] (a) Y. Zhu, K. Vyakaranam, J.A. Maguire, W. Quintana, F.
Teixidor, C. Vinas, N.S. Hosmane, Inorg. Chem. Commun. 4
(2001) 486–489;
(b) Y. Zhu, J.A. Maguire, N.S. Hosmane, Inorg. Chem. Commun.
5 (2002) 296–299;
(c) J. Wang, Y. Zhu, S.-J. Li, C. Zheng, J.A. Maguire, N.S.
Hosmane, J. Organomet. Chem. 680 (2003) 172–181.