Synthesis and structural characterization of hydroxyethyl- and alkoxyethyl-o-carboranes and their alkali and rare earth metal complexes

Article abstract of DOI:10.1021/om034081u

Facile and practical syntheses of 1,2-(HOCH₂CH₂)₂-1,2-C₂B₁₀ H₁₀ (1), its derivatives 1,2-(ROCH₂CH₂)₂-1,2-C₂B₁₀ H₁₀ (R = CH₃ (2), CH₂Ph (4)), and 1-(CH₃OCH₂CH₂)-1,2-C₂B₁₀ H₁₁ (3) were reported. Treatment of 1 with excess K metal in THF gave, after fractional crystallization from acetone containing 18-crown-6 ether, two complexes, [{nido-(HOCH₂-CH₂)(OCH₂CH₂) C₂B₁₀H₁₀}{K(18-crown-6)}]_n (5) and [{nido-(HOCH₂CH₂)₂C₂B₉ H₁₀}{K(18-crown-6)}]_n (6) in a molar ratio of 1:2. Reaction of 2 with MeOK in methanol afforded, after treatment with Me₃NHCl, [Me₃NH][nido-(CH₃OCH₂ CH₂)₂C₂B₉ H₁₀] (7). 2 reacted with excess Na metal in THF to yield [{η⁶-[(CH₃OCH₂CH₂)₂ C₂B₁₀H₁₀] Na}{Na(THF)}]_n (8). Interactions of 2 with LnCl₃ in the presence of excess Li or Na metal gave, after recrystallization from a mixture of different solvents, half-sandwich 13-vertex closo-metallacarboranes [{η⁷-[(CH₃-OCH₂CH₂)₂ C₂B₁₀H₁₀]Er} {Na(CH₃CN)₂}]₂ (9) and [{η⁷-[(CH₃OCH₂CH₂)₂ C₂B₁₀H₁₀]Y} {Li-(THF)₃}]₂ (10). Complexes [[{[η⁷-(CH₃OCH₂CH₂)C₂ B₁₀H₁₁]Er(THF)} {Na(CH₃CN)(THF)}]₂]_n (11) and [{[η⁷-(CH₃OCH₂CH₂)C₂ B₁₀H₁₁]Y(THF)} {Na(THF)₃}]₂ (12) were prepared in a similar manner from the monosubstituted o-carborane 3, LnCl₃, and excess Na in THF. These complexes were characterized by various spectroscopic data, elemental analyses, and X-ray diffraction studies. Structural studies show that the Lewis base-functionalized sidearms have some effects on the coordination environments of the central metal atom through intramolecular interactions between the donor atoms of the sidearms and Lewis acidic metal ions, but do not change the gross structures of the 13-vertex lanthanacarboranes.

Full text of DOI:10.1021/om034081u

Organometallics 2004, 23, 517-526
517
Syn th esis a n d Str u ctu r a l Ch a r a cter iza tion of
Hyd r oxyeth yl- a n d Alk oxyeth yl-o-Ca r bor a n es a n d Th eir
Alk a li a n d Ra r e Ea r th Meta l Com p lexes
Mak-Shuen Cheung, Hoi-Shan Chan, and Zuowei Xie*
Department of Chemistry, The Chinese University of Hong Kong, Shatin,
New Territories, Hong Kong, China
Received August 1, 2003
Facile and practical syntheses of 1,2-(HOCH2CH2)2-1,2-C2B10H10 (1), its derivatives 1,2-
(ROCH2CH2)2-1,2-C2B10H10 (R ) CH3 (2), CH2Ph (4)), and 1-(CH3OCH2CH2)-1,2-C2B10H11
(3) were reported. Treatment of 1 with excess K metal in THF gave, after fractional
crystallization from acetone containing 18-crown-6 ether, two complexes, [{nido-(HOCH2-
CH2)(OCH2CH2)C2B10H10}{K(18-crown-6)}]n (5) and [{nido-(HOCH2CH2)2C2B9H10}{K(18-
crown-6)}]n (6) in a molar ratio of 1:2. Reaction of 2 with MeOK in methanol afforded, after
treatment with Me3NHCl, [Me3NH][nido-(CH3OCH2CH2)2C2B9H10] (7). 2 reacted with excess
Na metal in THF to yield [{η6-[(CH3OCH2CH2)2C2B10H10]Na}{Na(THF)}]n (8). Interactions
of 2 with LnCl3 in the presence of excess Li or Na metal gave, after recrystallization from
a mixture of different solvents, half-sandwich 13-vertex closo-metallacarboranes [{η7-[(CH3-
OCH2CH2)2C2B10H10]Er}{Na(CH3CN)2}]2 (9) and [{η7-[(CH3OCH2CH2)2C2B10H10]Y}{Li-
(THF)3}]2 (10). Complexes [[{[η7-(CH3OCH2CH2)C2B10H11]Er(THF)}{Na(CH3CN)(THF)}]2]n
(11) and [{[η7-(CH3OCH2CH2)C2B10H11]Y(THF)}{Na(THF)3}]2 (12) were prepared in a similar
manner from the monosubstituted o-carborane 3, LnCl3, and excess Na in THF. These
complexes were characterized by various spectroscopic data, elemental analyses, and X-ray
diffraction studies. Structural studies show that the Lewis base-functionalized sidearms have
some effects on the coordination environments of the central metal atom through intramo-
lecular interactions between the donor atoms of the sidearms and Lewis acidic metal ions,
but do not change the gross structures of the 13-vertex lanthanacarboranes.
In tr od u ction
pended ether moieties is largely unexplored4 due partially
to the difficulties in the synthesis of ligands.5
Carboranes containing organic functional groups are
useful as multifunctional molecules for material science1
and as boron carriers for boron neutron capture therapy.2
Those with Lewis base functionalities tethered to the
cage carbon atoms can be the precursors to interesting
ligands for both d- and f-block metal atoms, particularly
with regard to the possibility of either simultaneous or
competitive σ-(substituent) and π-(carborane) ligation.
Furthermore, the functionalized side chain could tem-
porarily and reversibly coordinate to a metal ion, while
stabilizing highly reactive, electronically and sterically
unsaturated complexes. In fact, a number of metalla-
carboranes containing alkylamido pendent groups have
been reported.3 These complexes show interesting struc-
tural features and reactivity patterns.3 In sharp con-
trast, the chemistry of metallacarboranes with ap-
As a part of our ongoing research on structure/
reactivity relationships of lanthanacarboranes,6 we are
interested in substituent effects, particularly those with
Lewis base functionalities. With this in mind, we have
developed a method of high-yield synthesis of alkoxy-
ethyl-o-carboranes. In this contribution, we report on
the synthesis and structural characterization of hy-
droxyethyl- and alkoxyethyl-o-carboranes and their
alkali and rare earth metal complexes.
Exp er im en ta l Section
Gen er a l P r oced u r es. All experiments were preformed
under an atmosphere of dry dinitrogen with the rigid exclusion
(3) (a) Lee, J .-D.; Baek, C.-K.; Ko, J .; Park, K.; Cho, S.; Min, S.-K.;
Kang, S. O. Organometallics 1999, 18, 2189. (b) Zhu, Y.; Vyakaranam,
K.; Maguire, J . A.; Quintana, W.; Teixidor, F.; Vin˜as, C.; Hosmane, N.
S. Inorg. Chem. Comm. 2001, 4, 486. (c) Kim, D.-H.; Won, J . H.; Kim,
S.-J .; Ko, J .; Kim, S. H.; Cho, S.; Kang, S. O. Organometallics 2001,
20, 4298. (d) Park, J .-S.; Kim, D.-H.; Kim, S.-J .; Ko, J .; Kim, S. H.;
Cho, S.; Lee, C.-H.; Kang, S. O. Organometallics 2001, 20, 4483. (e)
Park, J .-S.; Kim, D.-H.; Ko, J .; Kim, S. H.; Cho, S.; Lee, C.-H.; Kang,
S. O. Organometallics 2001, 20, 4632. (f) Lee, J .-D.; Lee, Y.-J .; J eong,
H.-J .; Lee, J . S.; Lee, C.-H.; Ko, J .; Kang, S. O. Organometallics 2003,
22, 445. (g) Lee, Y.-J .; Lee, J .-D.; Ko, J .; Kim, S.-H.; Kang, S. O. Chem.
Commun. 2003, 1364.
* Corresponding author. Fax: (852)26035057. Tel: (852)26096269.
E-mail: zxie@cuhk.edu.hk.
(1) (a) Yang, X.; J iang, W.; Knobler, C. B.; Hawthorne, M. F. J . Am.
Chem. Soc. 1992, 114, 9719. (b) Mu¨ller, J .; Base, K.; Magnera, T. F.;
Michl, J . J . Am. Chem. Soc. 1992, 114, 9721. (c) Chizhevsky, I. T.;
J ohnson, S. E.; Knobler, C. B.; Gomez, F. A.; Hawthorne, M. F. J . Am.
Chem. Soc. 1993, 115, 6981. (d) Zinn, A. A.; Zheng, Z.; Knobler, C. B.;
Hawthorne, M. F. J . Am. Chem. Soc. 1996, 118, 70.
(2) (a) Soloway, A. H.; Fairchild, R. G. Cancer Res. 1990, 50, 1061.
(b) Yamamoto, Y. Pure Appl. Chem. 1991, 63, 423. (c) Hawthorne, M.
F. Angew. Chem., Int. Ed. Engl. 1993, 32, 950. (d) Soloway, A. H.;
Tjarks, W.; Barnum, B. A.; Rong, F.-G.; Barth, R. F.; Codogni, I. M.;
Wilson, J . G. Chem. Rev. 1998, 98, 1515.
(4) Shaw, K. F.; Reid, B. D.; Welch, A. J . J . Organomet. Chem. 1994,
482, 207.
(5) Shaw, K. F.; Welch, A. J . Polyhedron 1992, 11, 157.
(6) Xie, Z. Acc. Chem. Res. 2003, 36, 1.
10.1021/om034081u CCC: $27.50 © 2004 American Chemical Society
Publication on Web 12/31/2003

518 Organometallics, Vol. 23, No. 3, 2004
Cheung et al.
of air and moisture using standard Schlenk or cannula
techniques, or in a glovebox. All organic solvents (except CH3-
CN) were refluxed over sodium benzophenone ketyl for several
days and freshly distilled prior to use. CH3CN was refluxed
over CaH2 for several days and distilled immediately prior to
use. All chemicals were purchased from either Aldrich or Acros
Chemical Co. and used as received unless otherwise noted.
Infrared spectra were obtained from KBr pellets prepared in
(2:1, 10 mL) was slowly added with stirring. The reaction
mixture was refluxed overnight and then quenched with 30
mL of water. The organic layer was separated, and the aqueous
solution was extracted with Et2O (20 mL × 2). Removal of the
solvents gave the yellow oil. Column chromatographic (SiO2,
230-300 mesh) separation using n-hexane/ethyl acetate (25:
3) as eluant gave 2 (1.26 g, 4.8 mmol, 52%), 3 (0.42 g, 2.1 mmol,
23%), and o-C2B10H12 (0.12 g, 0.8 mmol), respectively. For 3:
1H NMR (CDCl3): δ 3.92 (s, 1H, cage CH), 3.46 (t, J ) 6.0 Hz,
2H, CH2CH2OCH3), 3.31 (s, 3H, CH2CH2OCH3), 2.49 (t, J )
6.0 Hz, 2H, CH2CH2OCH3). 13C NMR (CDCl3): δ 70.0 (CH2-
CH2OCH3), 60.1 (cage C), 58.6 (CH2CH2OCH3), 37.4 (CH2CH2-
OCH3). 11B NMR (CDCl3): δ -2.4 (1B), -5.9 (1B), -10.1 (2B),
-11.2 (2B), -12.5 (2B), -13.2 (2B). IR (KBr, cm-1): ν 2961
(w), 2573 (vs), 1399 (m), 1257 (vs), 1082 (vs), 979 (vs), 819 (vs),
502 (m). MS (FAB): 202 with correct isotope distribution.
P r ep a r a tion of 1,2-(C6H5CH2OCH2CH2)2-1,2-C2B10H10
(4). This compound was prepared as a white solid (at -4 °C)
from 1,2-(HOCH2CH2)2-1,2-C2B10H10 (1; 2.32 g, 10.0 mmol),
n-BuLi in n-hexane (1.60 M, 12.5 mL, 20.0 mmol), and benzyl
bromide (4.27 g, 25.0 mmol) in toluene/Et2O using the same
procedures reported for 2: yield 1.77 g (43%). 1H NMR
(CDCl3): δ 7.38 (m, 10H, C6H5CH2), 4.50 (br s, 4H, C6H5CH2),
3.83 (t, J ) 6.9 Hz, 4H, CH2CH2O), 2.51 (t, J ) 6.9 Hz, 4H,
CH2CH2O). 13C NMR (CDCl3): δ 137.4, 129.0, 128.7, 127.8,
73.1 (C6H5CH2), 68.4 (CH2CH2O), 34.9 (CH2CH2O), the cage
carbon atoms were not observed. 11B NMR (CDCl3): δ -5.1
(2B), -11.5 (8B). IR (KBr, cm-1): ν 3050 (w), 2942 (m), 2894
(m), 2582 (vs), 1422 (m), 1346 (m), 1053 (s), 917 (w), 734 (m),
514 (w). MS (FAB): 412 with correct isotope distribution.
P r epar ation of [{n ido-(HOCH2CH2)(OCH2CH2)C2B10H10}-
{K(18-cr ow n -6)}]n (5) a n d [{n id o-(HOCH2CH2)2C2B9H10}-
{K(18-cr ow n -6)}]n (6). Finely cut K metal (390 mg, 10.0
mmol) was added to a THF (25 mL) solution of 1,2-(HOCH2-
CH2)2-1,2-C2B10H10 (1; 232 mg, 1.0 mmol), and the mixture was
stirred at room temperature for a week. After removal of excess
K and solvent, a THF solution (20 mL) of 18-crown-6 (254 mg,
1.0 mmol) was added and stirred for 10 min. Removal of THF
and fractional crystallization from acetone in air afforded 5
(172 mg, 0.3 mmol, 30%) and 6 (330 mg, 0.6 mmol, 60%) as
colorless crystals, respectively. For 5: 1H NMR (acetone-d6):
δ 4.24 (t, J ) 5.0 Hz, 1H, CH2CH2OH), 4.06 (dt, J ) 5.0 and
5.7 Hz, 2H, CH2CH2OH), 3.65 (s, 24H, C12H24O6), 3.26 (t, J )
5.7 Hz, 2H, CH2CH2O), 2.34 (m, 4H, CH2CH2O). 13C NMR
(acetone-d6): δ 71.3 (C12H24O6), 68.1 (CH2CH2OH), 65.3
(CH2CH2O), 40.5 (CH2CH2O); the cage carbon atoms were not
observed. 11B NMR (acetone-d6): δ 32.0 (1B), 11.7 (1B), 3.1
(2B), -3.1 (1B), -14.9 (1B), -20.0 (1B), -25.7 (1B), -28.6 (1B),
-34.0 (1B). IR (KBr, cm-1): ν 3488 (s), 2903 (vs), 2520 (vs),
1465 (m), 1391 (m), 1349 (m), 1105 (vs), 956 (m) 835 (m). Anal.
Calcd for C18H43B10KO8: C, 40.43; H, 8.11. Found: C, 40.14;
H, 7.88. For 6: 1H NMR (acetone-d6): δ 4.03 (t, J ) 5.4 Hz,
2H, CH2CH2OH), 3.74 (dt, J ) 5.4 and 6.9 Hz, 4H, CH2CH2-
OH), 3.66 (s, 24H, C12H24O6), 2.58 (t, J ) 6.9 Hz, 4H, CH2-
CH2OH). 13C NMR (acetone-d6): δ 71.0 (C12H24O), 63.8 (CH2CH2-
OH), 38.9 (CH2CH2OH); the cage carbon atoms were not
observed. 11B NMR (acetone-d6): δ -9.9 (2B), -11.6 (1B),
-17.3 (2B), -18.4 (2B), -33.6 (1B), -36.6 (1B). IR (KBr, cm-1):
ν 3549 (s), 2899 (vs), 2519 (vs), 1466 (m), 1351 (m), 1246 (m),
1108 (vs), 959 (m) 838 (m). Anal. Calcd for C18H44B9KO8: C,
41.19; H, 8.45. Found: C, 41.25; H, 8.71.
the glovebox on
a Perkin-Elmer 1600 Fourier transform
spectrometer. 1H and 13C NMR spectra were recorded on a
Bruker DPX 300 spectrometer at 300.13 and 75.47 MHz,
respectively. 11B NMR spectra were recorded on a Varian Inova
400 spectrometer at 128.32 MHz. All chemical shifts are
reported in δ units with references to the residual protons of
the deuterated solvents for proton and carbon chemical shifts
and to external BF3‚OEt2 (0.00 ppm) for boron chemical shifts.
Elemental analyses were performed by MEDAC Ltd., Brunel
University, Middlesex, U.K.
P r ep a r a tion of 1,2-(HOCH2CH2)2-1,2-C2B10H10 (1). A 1.60
M solution of n-BuLi in n-hexane (12.5 mL, 20.0 mmol) was
added dropwise to a solution of o-C2B10H12 (1.44 g, 10.0 mmol)
in a dry toluene/Et2O mixture (2:1, 30 mL) with stirring at 0
°C. The mixture was allowed to warm to room temperature
and stirred for 30 min. The solution was then cooled to 0 °C,
and a solution of ethylene oxide (0.88 g, 20.0 mmol) in toluene/
Et2O (2:1, 10 mL) was added with stirring. The reaction
mixture was stirred at room temperature overnight and then
quenched with 50 mL of water. The organic layer was
separated, and the aqueous layer was extracted with Et2O (30
mL × 2). The combined organic portions were dried over
anhydrous Na2SO4. Removal of the solvents gave a white solid
that was washed with n-hexane (10 mL × 2) and dried under
vacuum to afford 1 as a white powder (2.14 g, 92%). Recrys-
tallization from dichloromethane yielded colorless crystals. 1H
NMR (acetone-d6): δ 4.05 (t, J ) 5.0 Hz, 2H, CH2CH2OH),
3.72 (dt, J ) 5.0 and 6.9 Hz, 4H, CH2CH2OH), 2.57 (t, J ) 6.9
Hz, 4H, CH2CH2OH). 13C NMR (acetone-d6): δ 79.7 (cage C),
61.5 (CH2CH2OH), 38.4 (CH2CH2OH). 11B NMR (acetone-d6):
δ -4.7 (2B), -10.4 (8B). IR (KBr, cm-1): ν 3236 (vs), 2950 (w),
2585 (vs), 1455 (m), 1416 (m), 1352 (m), 1064 (vs), 731 (m).
Anal. Calcd for C6H20B10O2: C, 31.02; H, 8.68. Found: C, 31.02;
H, 8.91.
P r ep a r a tion of 1,2-(CH3OCH2CH2)2-1,2-C2B10H10 (2). A
1.60 M solution of n-BuLi in n-hexane (12.5 mL, 20.0 mmol)
was added dropwise to a solution of 1,2-(HOCH2CH2)2-1,2-
C2B10H10 (1; 2.32 g, 10.0 mmol) in a dry toluene/Et2O mixture
(2:1, 30 mL) at 0 °C. The mixture was allowed to warm to room
temperature and stirred for 30 min. The solution was then
cooled to 0 °C, and a solution of iodomethane (3.55 g, 25.0
mmol) in toluene/Et2O (2:1, 10 mL) was slowly added with
stirring. The reaction mixture was stirred overnight and then
quenched with 30 mL of water. The organic layer was
separated, and the aqueous layer was extracted with ether (30
mL × 2). The combined organic portions were dried over
anhydrous Na2SO4. Removal of the solvents gave a colorless
1
oil that became a white solid at -4 °C (2.16 g, 83%). H NMR
(CDCl3): δ 3.49 (t, J ) 6.9 Hz, 4H, CH2CH2OCH3), 3.32 (s,
6H, CH2CH2OCH3), 2.50 (t, J ) 6.9 Hz, 4H, CH2CH2OCH3).13C
NMR (CDCl3): δ 70.7 (CH2CH2OCH3), 58.6 (CH2CH2OCH3),
34.9 (CH2CH2OCH3); the cage carbon atoms were not observed.
11B NMR (CDCl3): δ -4.2 (2B), -10.2 (8B). IR (KBr, cm-1): ν
2931 (m), 2879 (m), 2578 (vs), 1454 (m), 1352 (m), 1120 (vs).
MS (FAB): 260 with correct isotope distribution.
3
P r ep a r a tion of [Me NH][n id o-(CH3OCH2CH2)2C2B9H10
]
(7). Distilled CH3OH (15 mL) was added to a mixture of 1,2-
(CH3OCH2CH2)2-1,2-C2B10H10 (2; 260 mg, 1.0 mmol) and KOH
(224 mg, 4.0 mmol) with stirring at 0 °C. The reaction mixture
was warmed to room temperature and then refluxed overnight.
After removal of the solvent, water (10 mL) was added. The
aqueous solution was neutralized with diluted HCl. Addition
of aqueous Me3NHCl solution gave a white precipitate. The
product was filtered off, washed with water (3 × 5 mL), and
dried in a vacuum to give 7 as a white solid (266 mg, 86%). 1H
P r ep a r a tion of 1,2-(CH3OCH2CH2)2-1,2-C2B10H10 (2) a n d
1-(CH3OCH2CH2)-1,2-C2B10H11 (3). A 1.60 M solution of
n-BuLi in n-hexane (12.5 mL, 20.0 mmol) was added dropwise
to a solution of o-C2B10H12 (1.44 g, 10.0 mmol) in a dry toluene/
Et2O mixture (2:1, 30 mL) with stirring at 0 °C. The mixture
was allowed to warm to room temperature and stirred for 30
min. The solution was then cooled to 0 °C, and a solution of
chloroethyl methyl ether (2.36 g, 25.0 mmol) in toluene/Et2O

Hydroxyethyl- and Alkoxyethyl-o-Carboranes
Organometallics, Vol. 23, No. 3, 2004 519
NMR (acetone-d6): δ 3.65 (t, J ) 6.5 Hz, 4H, CH2CH2OCH3),
3.51 (s, 6H, CH2CH2OCH3), 3.09 (s, 9H, (CH3)3NH), 2.55 (t, J
) 6.5 Hz, 4H, CH2CH2OCH3). 13C NMR (acetone-d6): δ 74.1
(cage C), 64.3 (CH2CH2OCH3), 62.0 (CH2CH2OCH3), 42.3
(s), 1420 (m), 1256 (w), 1023 (m), 800 (m), 531 (m). Anal. Calcd
for C30H74B20Er2N2Na2O6: C, 31.18; H, 6.45; N, 2.42. Found:
C, 31.24; H, 6.33; N, 2.27.
P r ep a r a tion of [{[η7-(CH3OCH2CH2)C2B10H11]Y(THF )}-
{Na (THF )3}]2 (12). This complex was prepared from 3 (202
mg, 1.0 mol), finely cut Na metal (230 mg, 10.0 mmol), and
YCl3 (195 mg, 1.0 mmol) in THF using the identical procedure
reported for 9. Recrystallization from THF/toluene (1:1, 20 mL)
((CH3)3NH), 38.2 (CH2CH2OCH3). 11B NMR (acetone-d6):
δ
-9.2 (2B), -10.3 (1B), -17.0 (2B), -18.0 (2B), -33.3 (1B),
-36.1 (1B). IR (KBr, cm-1): ν 3615 (br m), 2912 (s), 2535 (s),
1362 (m), 1250 (m), 1112 (s), 960 (m), 851 (m). Anal. Calcd for
1
C
11H34B9NO2: C, 42.66; H, 11.07. Found: C, 42.35; H, 11.15.
P r ep a r a tion of [{η6-[(CH3OCH2CH2)2C2B10H10]Na }{Na -
gave 12 as yellow crystals (225 mg, 37%). H NMR (pyridine-
d5): δ 3.63 (m, 16H, THF), 3.30 (br s, 2H, CH2CH2OCH3), 3.16
(br s, 3H, CH2CH2OCH3), 2.20 (br s, 2H, CH2CH2OCH3), 1.64
(m, 16H, THF). 13C NMR (pyridine-d5): δ 75.3 (CH2CH2OCH3),
67.1 (THF), 57.1 (CH2CH2OCH3), 43.0 (CH2CH2OCH3), 25.0
(THF); the cage carbon atoms were not observed. 11B NMR
(pyridine-d5): δ -8.1 (3B), -12.6 (3B), -19.4 (2B), -20.8 (2B).
IR (KBr, cm-1): ν 2957 (s), 2879 (s), 2436 (vs), 1611 (s), 1452
(THF )}]n (8). Finely cut Na metal (230 mg, 10.0 mmol) was
added to a THF (25 mL) solution of 1,2-(CH3OCH2CH2)2-1,2-
C2B10H10 (2; 260 mg, 1.0 mmol), and the mixture was stirred
at room temperature for a week. After removal of excess Na,
the clear pale yellow solution was concentrated to about 10
mL, and toluene (about 10 mL) was added. 8 was isolated as
colorless crystals after this solution stood at room temperature
(s), 1257 (s), 1042 (vs), 801 (s). Anal. Calcd for C30H74B20
-
1
Na2O7Y2 (12-3THF): C, 36.51; H, 7.56. Found: C, 36.26; H,
7.69.
X-r a y Str u ctu r e Deter m in a tion . All single crystals were
for 3 days (196 mg, 52%). H NMR (pyridine-d5): δ 3.91 (br s,
4H, CH2CH2OCH3), 3.64 (m, 4H, THF), 3.27 (s, 6H, CH2CH2-
OCH3), 3.10 (br s, 4H, CH2CH2OCH3), 1.58 (m, 4H, THF). 13C
NMR (pyridine-d5): δ 75.4 (CH2CH2OCH3), 67.2 (THF), 57.1
(CH2CH2OCH3), 43.2 (CH2CH2OCH3), 25.1 (THF); the cage
carbon atoms were not observed. 11B NMR (pyridine-d5): δ
-2.4 (3B), -5.2 (3B), -11.1 (2B), -23.7 (2B). IR (KBr, cm-1):
ν 2929 (vs), 2882 (vs), 2577 (vs), 2504 (vs), 2426 (vs), 1453 (s),
1112 (vs), 1058 (vs), 906 (m), 734 (w). Anal. Calcd for C12H32B10-
Na2O3: C, 38.08; H, 8.52. Found: C, 38.43; H, 8.29.
P r ep a r a tion of [{η7-[(CH3OCH2CH2)2C2B10H10]Er }{Na -
(CH3CN)2}]2 (9). Finely cut Na metal (230 mg, 10.0 mmol)
was added to a THF (10 mL) solution of 2 (260 mg, 1.0 mmol),
and the mixture was stirred at room temperature for 2 days.
ErCl3 (274 mg, 1.0 mmol) was then added, and the reaction
mixture was stirred at room temperature for 4 days. The
precipitate and excess Na metal were filtered off and washed
with THF (5 mL × 3). Removal of the solvent gave a pink solid
that was extracted with CH3CN (10 mL × 2). The resulting
solutions were combined and concentrated to about 10 mL,
and toluene (about 7 mL) was added. 9 was isolated as pink
crystals after this solution stood at room temperature over-
night (186 mg, 35%). 1H NMR (pyridine-d5): δ 1.82 (s, CH3-
CN), and other broad, unresolved peaks. 13C NMR (pyridine-
d5): δ 116.8 (CH3CN), 30.9, 22.0, 13.4 (CH2CH2OCH3), 0.3
(CH3CN). 11B NMR (pyridine-d5): many broad, unresolved
resonances. IR (KBr, cm-1): ν 2909 (s), 2828 (s), 2484 (vs), 2434
(vs), 2355 (s), 1460 (m), 1208 (m), 1039 (s), 798 (m). Anal. Calcd
for C24H60B20Er2N4Na2O4: C, 27.05; H, 5.68; N, 5.26. Found:
C, 27.01; H, 5.56; N, 5.05.
immersed in Paraton-N oil and sealed under N
2 in thin-walled
glass capillaries. Data were collected at 293 K on a Bruker
SMART 1000 CCD diffractometer using Mo KR radiation. An
empirical absorption correction was applied using the SADABS
program.7 All structures were solved by direct methods and
subsequent Fourier difference techniques and refined aniso-
tropically for all non-hydrogen atoms by full-matrix least-
squares calculations on F2 using the SHELXTL program
package.8 For noncentrosymmetric structures 1 and 8, the
values of the Flack’s parameter x are 1.0(2) and 0.0(7),
respectively.9 Most of the carborane hydrogen atoms were
located from difference Fourier syntheses. All other hydrogen
atoms were geometrically fixed using the riding model. Crystal
data and details of data collection and structure refinements
are given in Tables 1 and 2. Selected bond distances are
compiled in Table 3. Further details are included in the
Supporting Information.
Resu lts a n d Discu ssion
Hyd r oxyeth yl-o-ca r bor a n e a n d Its Der iva tives.
The synthesis of ether-o-carboranes 1-R1-2-R2-1,2-
C2B10H10 (R1 ) (CH2)nOCH3, R2 ) H, n ) 1-3; R1 ) R2
) CH2OCH3) was achieved by the addition of the
appropriate substituted alkynes to activated borane
B10H12(SMe2)2.5 This method is not practical for those
with more than one methylene unit separating the cage
carbon and oxygen atoms since the isolation yields were
<5% for n ) 2 or 3.5 A new methodology is desired. We
then thought about the reactions of (LiOCH2CH2)2-
C2B10H10 with RX or Li2C2B10H10 with MeOCH2CH2Cl,
which would directly give ether-o-carboranes.
P r ep a r a tion of [{η7-[(CH3OCH2CH2)2C2B10H10]Y}{Li-
(THF )3}]2 (10). This complex was prepared from 2 (260 mg,
1.0 mmol), finely cut Li metal (69 mg, 10.0 mmol), and YCl3
(195 mg, 1.0 mmol) in THF using the identical procedure
reported for 9. Recrystallization from THF/toluene (1:1, 20 mL)
1
gave 10 as yellow crystals (258 mg, 45%). H NMR (pyridine-
d5): δ 3.84 (br s, 4H, CH2CH2OCH3), 3.59 (m, 24H, THF), 3.20
(s, 6H, CH2CH2OCH3), 2.96 (br s, 4H, CH2CH2OCH3), 1.58 (m,
24H, THF). 13C NMR (pyridine-d5): δ 74.8 (CH2CH2OCH3),
66.7 (THF), 57.1 (CH2CH2OCH3), 42.9 (CH2CH2OCH3), 24.6
(THF); the cage carbon atoms were not observed. 11B NMR
(pyridine-d5): δ 0.26 (3B), -6.6 (4B), -14.1 (1B), -22.3 (2B).
IR (KBr, cm-1): ν 2957 (s), 2881 (s), 2490 (vs), 2460 (s), 2400
(s), 1668 (s), 1452 (s), 1260 (s), 1042 (vs), 802 (s). Anal. Calcd
for C20H56B20Li2O5Y2 (9-5THF): C, 30.62; H, 7.19. Found: C,
30.88; H, 7.39.
P r epar ation of [[{[η7-(CH3OCH2CH2)C2B10H11]Er (THF)}-
{Na (CH3CN)(THF )}]2]n (11). This complex was prepared
from 3 (202 mg, 1.0 mmol), finely cut Na metal (230 mg, 10.0
mmol), and ErCl3 (274 mg, 1.0 mmol) in THF using the
identical procedure reported for 9. Recrystallization from CH3-
CN/THF (1:1, 20 mL) gave 11 as orange crystals (225 mg, 39%).
1H, 13C, and 11B NMR (pyridine-d5): many broad, unresolved
resonances. IR (KBr, cm-1): ν 2919 (s), 2519 (vs), 2171 (s), 1597
It has been reported that primary o-carboranyl alco-
hols can be prepared by transesterification,10 hydrolysis
of o-carboranyl ester,11 and reaction of lithio-o-carborane
with epoxides.11,12 Among these, the reaction of Li2C2B10-
H10 with ethylene oxide drew our attention, although
(7) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
1996.
(8) Sheldrick, G. M. SHELXTL, 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems,
Inc.: Madison, WI, 1997.
(9) Flack, H. D. Acta Crystallogr. 1983, A39, 876.
(10) Fein, M. M.; Grafstein, D.; Paustian, J . E.; Bobinski, J .;
Lichstein, B. M.; Mayes, N.; Schwartz, N. N.; Cohen, M. S. Inorg. Chem.
1963, 2, 1115.
(11) (a) Heying, T. L.; Ager, J . W.; Clark, S. L.; Alexander, R. P.;
Papetti, S.; Reid, J . A.; Trotz, S. I. Inorg. Chem. 1963, 2, 1097. (b)
Grafstein, D.; Bobinski, J .; Dvorak, J .; Smith, H.; Schwartz, N.; Cohen,
M. S. Fein, M. M. Inorg. Chem. 1963, 2, 1120.

520 Organometallics, Vol. 23, No. 3, 2004
Cheung et al.
Ta ble 1. Cr ysta l Da ta a n d Su m m a r y of Da ta Collection a n d Refin em en t Deta ils for 1 a n d 5-8
1
5
6
7
8
formula
cryst size (mm)
fw
C6H20B10O2
0.28 × 0.25 × 0.20
232.3
C18H43B10KO8
0.38 × 0.34 × 0.15
534.7
C18H44B9KO8
0.60 × 0.55 × 0.45
524.9
C11H34B9NO2
0.60 × 0.50 × 0.38
309.7
C12H32B10Na2O3
0.55 × 0.36 × 0.35
378.5
cryst syst
space group
a, Å
orthorhombic
P212121
6.912(1)
13.768(1)
14.182(1)
90.00
triclinic
P1h
triclinic
P1h
triclinic
P1h
monoclinic
P21
9.529(2)
10.063(2)
11.451(2)
90.00
98.01(1)
90.00
1087.3(3)
2
1.156
8.961(1)
9.252(1)
18.935(2)
98.24(1)
99.49(1)
106.29(1)
1456.1(2)
2
11.458(1)
12.083(1)
12.281(1)
73.12(1)
65.37(1)
77.75(1)
1470.8(2)
2
8.204(1)
11.400(2)
11.586(2)
95.30(1)
109.76(1)
98.60(1)
996.3(2)
2
b, Å
c, Å
R, deg
â, deg
90.00
γ, deg
90.00
V, Å3
1349.6(2)
4
Z
Dcalcd, Mg/m3
radiation (λ), Å
2θ range, deg
µ, mm-1
F(000)
1.143
1.220
1.185
1.032
Mo KR (0.71073)
4.12 to 50.00
0.063
Mo KR (0.71073)
2.22 to 50.00
0.221
Mo KR (0.71073)
3.54 to 50.00
0.218
Mo KR (0.71073)
3.66 to 50.00
0.059
Mo KR (0.71073)
3.60 to 50.00
0.102
488
568
560
336
400
no. of obsd reflns
no. of params refnd
goodness of fit
R1
2382
3797
5147
3511
2579
163
389
340
222
277
1.011
1.153
1.037
1.041
1.022
0.055
0.075
0.056
0.060
0.079
wR2
0.141
0.188
0.160
0.182
0.196
Ta ble 2. Cr ysta l Da ta a n d Su m m a r y of Da ta Collection a n d Refin em en t Deta ils for 9-12
9
10
11
12
formula
cryst size (mm)
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C
24H60B20Er2N4Na2O4
C40H96B20Li2O10Y2
0.80 × 0.65 × 0.29
1145.1
triclinic
P1h
C30H74B20Er2N2Na2O6
0.38 × 0.22 × 0.12
1155.6
monoclinic
P21/n
12.162(1)
9.608(1)
22.639(1)
90.00
103.18(1)
90.00
C42H100B20Na2O10Y2
0.48 × 0.47 × 0.21
1205.2
triclinic
P1h
0.44 × 0.30 × 0.22
1065.5
triclinic
P1h
9.546(1)
9.707(1)
14.008(1)
96.98(1)
107.18(1)
111.57(1)
1113.8(1)
1
9.974(1)
13.581(2)
14.813(2)
114.74(1)
95.64(1)
99.05(1)
1769.4(4)
1
10.503(1)
12.002(1)
14.249(1)
104.54(1)
94.20(1)
111.65(1)
1588.3(2)
1
2575.5(2)
2
1.490
Z
D
calcd, Mg/m3
1.588
1.075
1.260
radiation (λ), Å
2θ range, deg
µ, mm-1
Mo KR (0.71073)
3.16 to 56.04
3.797
Mo KR (0.71073)
4.74 to 50.00
1.672
Mo KR (0.71073)
3.58 to 56.08
3.292
Mo KR (0.71073)
3.00 to 56.02
1.878
F(000)
522
600
1148
632
no. of obsd reflns
no. of params refnd
goodness of fit
R1
5272
317
4271
337
6226
299
7543
358
0.951
1.046
1.086
0.918
0.029
0.084
0.048
0.060
wR2
0.070
0.205
0.118
0.145
hydroxyl protons. The 13C NMR spectrum is consistent
with the results derived from the 1H NMR data. The
11B NMR spectrum exhibits a 2:8 splitting pattern,
which is commonly observed in disubstituted o-carbo-
ranes. The IR spectrum displays characteristic O-H
Ta ble 3. Selected Bon d Len gth s for Ra r e Ea r th
Com p lexesa
9 (Er)
10 (Y)
11 (Er)
12 (Y)
Ln-C(2)
Ln-C(5)
Ln-B(3)
Ln-B(4)
Ln-B(6)
Ln-B(7)
Ln-B(8)
Ln‚‚‚B
2.351(4)
2.352(4)
2.675(4)
2.667(4)
2.710(4)
2.745(5)
2.705(4)
2.700(4)
2.924(4)
2.20(4)
2.344(8)
2.382(8)
2.674(9)
2.714(9)
2.726(10)
2.764(9)
2.738(10)
2.746(9)
2.983(10)
2.04(9)
2.364(5)
2.352(6)
2.635(7)
2.649(7)
2.699(6)
2.784(6)
2.719(6)
2.748(6)
2.851(6)
2.32(6)
2.392(4)
2.378(4)
2.640(5)
2.668(5)
2.742(5)
2.803(5)
2.761(5)
2.755(4)
2.918(5)
2.23(4)
and B-H absorptions at ca. 3236 and 2585 cm-1
,
respectively. The solid-state structure of 1 is confirmed
by single-crystal X-ray analyses (Figure 1). The bond
distances and angles are normal and comparable to
other o-carborane derivatives.13,14 Like other hydroxy-
o-carboranes,14 the hydroxyl groups in 1 are involved
in hydrogen bonds to form linear polymeric chains
(Figure 2). The O‚‚‚O(H) distances are 2.681(4) and
Ln-H
2.63(4)
2.76(9)
2.42(6)
2.52(4)
Ln-O(1)
Ln-O(2)
2.562(3)
2.424(3)
2.415(5)
2.486(6)
2.494(5)
2.498(3)
2.436(5)b
2.440(3)b
(12) (a) Grafstein, D.; Bobinski, J .; Dvorak, J .; Paustian, J . E.; Smith,
H. F.; Karlan, S.; Vogel, C.; Fein, M. M. Inorg. Chem. 1963, 2, 1125.
(b) Zakharkin, L. I. Tetrahedron Lett. 1964, 33, 2255. (c) Gomez, F.
A.; Hawthorne, M. F. J . Org. Chem. 1992, 57, 1384.
(13) Zi, G.; Li, H.-W.; Xie, Z. Organometallics 2002, 21, 5415.
(14) (a) Herzog, A.; Knobler, C. B.; Hawthorne, M. F. Angew. Chem.,
Int. Ed. 1998, 37, 1552. (b) Peymann, T.; Knobler, C. B.; Khan, S. I.;
Hawthorne, M. F. J . Am. Chem. Soc. 2001, 123, 2182. (c) Maderna,
A.; Herzog, A.; Knobler, C. B.; Hawthorne, M. F. J . Am. Chem. Soc.
2001, 123, 10423. (d) Herzog, A.; Knobler, C. B.; Hawthorne, M. F. J .
Am. Chem. Soc. 2001, 123, 12791. (e) Maderna, A.; Huertas, R.;
Hawthorne, M. F.; Luguya, R.; Vicente, M. G. H. Chem. Commun.
2002, 1784.
a
b
All in Å. Ln-O(THF) distances.
no characterization data were reported.11b We decided
to examine this reaction. Reaction of Li2C2B10H10 with
excess ethylene oxide in toluene/Et2O at 0 °C afforded
1,2-(HOCH2CH2)2-1,2-C2B10H10 (1) in 92% yield (Scheme
1
1). This reaction was very fast and clean. The H NMR
spectrum clearly exhibits two sets of methylene protons
and a triplet at δ ) 4.05 ppm attributable to the

Hydroxyethyl- and Alkoxyethyl-o-Carboranes
Organometallics, Vol. 23, No. 3, 2004 521
Sch em e 1
F igu r e 1. Molecular structure of 1,2-(HOCH2CH2)2-1,2-
C2B10H10 (1). Selected bond distances (Å): C(1)-C(2) )
1.684(3), C(1)-C(3) ) 1.521(3), C(3)-C(4) ) 1.518(4), C(4)-
O(1) ) 1.422(4), C(2)-C(6) ) 1.525(4), C(6)-C(7) ) 1.502-
(4), C(7)-O(2) ) 1.417(4).
F igu r e 2. Intermolecular O‚‚‚H-O interactions in 1.
to the lithium atom, which probably blocks the second
step of the reaction to some extent, leading to the
formation of both mono- and disubstituted carboranes.
A similar result was achieved if MeOCH2CH2Cl was
2.706(4) Å, respectively, which are at the long end of
2.4-2.7 Å normally observed in hydrated proton ions.15
Since hydroxyl can be converted into many other
functional groups,16 it is expected that 1 would be a very
useful synthon. Reaction of 1 with 2 equiv of n-BuLi
followed by treatment with excess iodomethane or
benzyl bromide afforded 1,2-(CH3OCH2CH2)2-1,2-C2-
B10H10 (2) or 1,2-(C6H5CH2OCH2CH2)2-1,2-C2B10H10 (4)
in 83 or 43% yield, respectively (Scheme 1). The 1H NMR
spectra of 2 and 4 exhibit two triplets in the range 2.5-
3.9 ppm attributable to -CH2-CH2- protons. The
OCH3 and OCH2Ph resonances are also observed. The
1
replaced by MeOCH2CH2OTs. The H NMR spectrum
of 3 shows two triplets and one singlet corresponding
to the CH2CH2OCH3 unit and a broad singlet at 3.92
ppm assignable to the cage CH proton.5 Its 11B NMR
spectrum exhibits a 1:1:2:2:2:2 splitting pattern, which
is significantly different from that of 2.
Alk a li Meta l Com p lexes. Treatment of 1 with
excess K metal in THF gave, after recrystallization from
an acetone solution of 18-crown-6, a mixture of products
on the basis of 11B NMR analyses. The products were
separated by fractional crystallization after hydrolysis,
affording [{nido-(HOCH2CH2)(OCH2CH2)C2B10H10}{K(18-
crown-6)}]n (5) and [{nido-(HOCH2CH2)2C2B9H10}{K(18-
crown-6)}]n (6) in a molar ratio of 1:2. It is assumed that
1 reacts with K metal to produce the intermediate
K4[(OCH2CH2)2C2B10H10], in which one of the ethoxide
groups attacks the more electron-deficient boron bonded
to two cage carbon atoms in the C2B4 bonding face to
give the deprotonated form of 5 in an intramolecular
manner. On the other hand, the potassium ethoxide can
serve as a deboronating reagent17 to attack the boron
atom of the icosahedral cage in an intermolecular way
to generate the deprotonated form of 6. A derivative of
6, [Me3NH][nido-(CH3OCH2CH2)2C2B9H10] (7), was pre-
pared from the reaction of 2 with KOMe in MeOH,
followed by treatment with Me3NHCl. These transfor-
mations are summarized in Scheme 2.
1
13C NMR spectra are in line with their H NMR data.
Their 11B NMR spectra exhibit a typical 2:8 splitting
pattern for disubstituted o-carboranes. The IR spectra
display a characteristic B-H absorption at about 2580
cm-1
.
Reaction of Li2C2B10H10 with excess MeOCH2CH2Cl
in toluene/Et2O at reflux temperature gave, after col-
umn chromatographic separation, 2 and monosubsti-
tuted o-carborane 1-(CH3OCH2CH2)-1,2-C2B10H11 (3) in
a molar ratio of 7:3 (Scheme 1). This reaction was closely
monitored by 11B NMR spectroscopy, which indicated
that the molar ratio of 2:3:o-C2B10H12 was about 6:3:1
in the reaction mixture. This ratio stayed almost
unchanged even when a large excess of MeOCH2CH2Cl
was used. The 11B NMR also showed that this is a
stepwise substitution reaction. The oxygen atom of the
sidearm in the monosubstituted species may coordinate
Complexes 5-7 were characterized by various spec-
troscopic data and X-ray diffraction studies. The 11B
(15) J oesten, M. D.; Schaad, L. J . Hydrogen Bonding; Marcel
Dekker: New York, 1974.
(16) Morrison, R. T.; Boyd, R. N. Organic Chemistry, 6th ed.;
Prentice Hall: NJ , 1992; p 692.
(17) Wiesboeck, R. A.; Hawthorne, M. F. J . Am. Chem. Soc. 1964,
86, 1642.

522 Organometallics, Vol. 23, No. 3, 2004
Cheung et al.
Sch em e 2
Sch em e 3
NMR spectra exhibit a 1:1:2:1:1:1:1:1:1 splitting pattern
for 5 and a 2:1:2:2:1:1 splitting pattern for both 6 and
7, respectively. In addition, the proton-coupled 11B NMR
spectrum of 5 shows that the peak at 32.0 ppm does
not split, indicating boron bonding to the oxygen atom.
Treatment of 2 with excess finely cut Na metal in
THF gave, after recrystallization from THF/toluene,
[{η6-[(CH3OCH2CH2)2C2B10H10]Na}{Na(THF)]n (8) in
52% yield (Scheme 3). It is highly air- and moisture-
sensitive, but remains stable for months at room tem-
perature under an inert atmosphere. The 1H NMR
spectrum supports the ratio of one THF molecule per
carboranyl ligand. The 13C NMR spectrum is consistent
B(2)-C(3) bond. The K atom is disordered over two sets
of positions with 0.5:0.5 occupancies (named as K(1) and
K(2), respectively), and both sit at the inversion centers.
As shown in Figure 3, K(2) is located at the center of
18-crown-6 and coordinates to two additional oxygen
atoms from the two sidearms, while K(1) bonds to two
additional B-H bonds from two cages, resulting in the
formation of polymeric chains. The B(2)-O(7) distance
of 1.398(8) Å is comparable to the value of 1.413(2) Å
found in Co[(C2B9H10OR)(C2B9H11)]-.21 The K(2)-O(8)
distance of 2.831(5) Å compares to the K-O(THF)
1
with the result derived from the H NMR data. Its 11B
NMR spectrum exhibits a 3:3:2:2 splitting pattern. The
solid-state IR spectrum displays a very strong B-H
absorption at 2577 cm-1 and a strong peak at 2426 cm-1
,
implying B-H-M interactions.18,19
distance of 2.840(5) Å in [(THF)2K(18-crown-6)][nido-
Single-crystal X-ray analyses reveal that 5 is a kinetic
isomer generated from the hydrolysis of the potassium
salt of the corresponding carborane dianion.13,20 Six- and
five-membered rings share one common edge of the
22
(C6H5CH2)2C2B10H11
]
and the K-O(H2O) distance of
2.769(1) Å in [{µ-1,2-[o-C6H4(CH2)2]-1,2-C2B10H11}K(18-
crown-6)]2(µ-OH2).13 The K(1)‚‚‚H(10)-B(10) distance of
3.01(2) Å is very close to the K‚‚‚H-C distance of 3.00-
(2) Å observed in {K(18-crown-6)}{[(C6H5CH2)2C2B10-
(18) (a) Xie, Z.; Wang, S.; Zhou, Z.-Y.; Xue, F,; Mak, T. C. W.
Organometallics 1998, 17, 489. (b) Xie, Z.; Wang, S.; Zhou, Z.-Y.; Mak,
T. C. W. Organometallics 1998, 17, 1907. (c) Xie, Z.; Wang, S.; Zhou,
Z.-Y.; Mak, T. C. W. Organometallics 1999, 18, 1641. (d) Xie, Z.; Wang,
S.; Yang, Q.; Mak, T. C. W. Organometallics 1999, 18, 2420. (e) Wang,
S.; Yang, Q.; Mak, T. C. W.; Xie, Z. Organometallics 1999, 18, 4478.
(f) Wang, S.; Yang, Q.; Mak, T. C. W.; Xie, Z. Organometallics 1999,
18, 1578.
H
10]K(18-crown-6)}.22 The average K-O(18-crown-6)
distances of 2.819(3) and 2.800(3) Å are comparable to
those normally observed in the complexes containing the
[K(18-crown-6)] moiety.13,22
Like 5, the K atom in 6 is also disordered over two
sets of positions with 0.5:0.5 occupancies, and both of
them sit at the inversion centers. Each K atom in the
(19) (a) Khattar, R.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem.
1990, 29, 2191. (b) Khattar, R.; Knobler, C. B.; Hawthorne, M. F. J .
Am. Chem. Soc. 1990, 112, 4962.
(20) (a) Churchill, M. R.; DeBoer, B. G. Inorg. Chem. 1973, 12, 2674.
(b) Dunks, G. B.; Wiersema, R. J .; Hawthorne, M. F. J . Am. Chem.
Soc. 1973, 95, 3174. (c) Getman, T. G.; Knobler, C. B.; Hawthorne, M.
F. Inorg. Chem. 1990, 29, 158.
(21) Sivaev, I. B.; Starikova, Z. A.; Sjo¨berg, S.; Bregadze, V. I. J .
Organomet. Chem. 2002, 649, 1.
(22) Chui, K.; Li, H.-W.; Xie, Z. Organometallics 2000, 19, 5447.

Hydroxyethyl- and Alkoxyethyl-o-Carboranes
Organometallics, Vol. 23, No. 3, 2004 523
F igu r e 3. Molecular structure of [{nido-(HOCH2CH2)-
(OCH2CH2)C2B10H10}{K(18-crown-6)}]n (5), showing a por-
tion of the infinite polymeric chain. Selected bond distances
(Å): C(1)-B(2) ) 1.551(7), C(3)-B(2) ) 1.581(6), C(1)-C(6)
) 1.494(8), O(8)-K(2) ) 2.831(8), C(3)-C(4) ) 1.510(7),
C(4)-C(5) ) 1.493(7), C(5)-O(7) ) 1.456(7), O(7)-B(2) )
1.398(8), C(1)-B(6) ) 1.557(7), B(6)-B(5) ) 1.838(13),
B(5)-B(4) ) 1.869(12), C(3)-B(4) ) 1.620(7).
F igu r e 5. Molecular structure of [Me3NH][nido-(CH3-
OCH2CH2)2C2B9H10] (7). Selected bond distances (Å): C(7)-
C(8) ) 1.574(3), C(7)-C(11) ) 1.534(3), C(11)-C(12) )
1.477(3), C(12)-O(1) ) 1.433(3), O(1)-C(13) ) 1.420(3),
C(8)-C(21) ) 1.527(3), C(21)-C(22) ) 1.508(3), C(22)-O(2)
) 1.407(3), O(2)-C(23) ) 1.420(3), C(7)-B(11) ) 1.616(3),
B(11)-B(10) ) 1.839(5), B(10)-B(9) ) 1.815(5), B(9)-C(8)
) 1.611(3).
F igu r e 4. Molecular structure of [{nido-(HOCH2CH2)2-
C2B9H10}{K(18-crown-6)}]n (6), showing a portion of the
infinite polymeric chain. Selected bond distances (Å): C(7)-
C(8) ) 1.585(3), O(1)-K(1) ) 2.785(2), O(2)-K(2) ) 2.791-
(2), C(7)-B(11) ) 1.624(3), B(10)-B(11) ) 1.824(4), B(9)-
B(10) ) 1.841(4), C(8)-B(9) ) 1.620(4).
F igu r e 6. Molecular structure of [{η6-[(CH3OCH2CH2)2-
C2B10H10]Na}{Na(THF)}]n (8), showing one asymmetric
unit of the infinite polymeric chain. Selected bond distances
(Å): Na(1)-C(1) ) 2.661(5), Na(1)-B(2) ) 2.802(6), Na-
(1)-C(3) ) 2.944(5), Na(1)-B(4) ) 2.763(6), Na(1)-B(5) )
2.964(6), Na(1)-B(6) ) 2.955(7), Na(1)-O(1) ) 2.546(4),
Na(1)-O(2) ) 2.379(5), Na(2)-O(3) ) 2.282(5), Na(2)-B(4)
) 2.880(7), Na(2)-B(5) ) 2.797(6).
complex cation K(18-crown-6)+ coordinates, in addition
to the six oxygen atoms of the crown ether, to two
oxygen atoms of the hydroxyethyl groups from different
cages, leading to the formation of infinite polymeric
chains, shown in Figure 4. The average K-O(crown)
distances of 2.780(2) and 2.810(2) Å and the K-O(OH)
distances of 2.785(2) and 2.791(2) Å are all shorter than
the corresponding values found in 5.
The solid-state structure of 7 is shown in Figure 5. It
consists of a nido-C2B9 cage and an associated cation
+
HNMe3 via a N(1)-H‚‚‚O(1) hydrogen bond with a
distance of 2.762(3) Å.15 The geometry of the C2B9 cage
is similar to that in 6 and other C2B9 derivatives.23
Single-crystal X-ray analyses confirm that 8 contains
only one THF molecule (Figure 6), which compares
to the highly solvated analogue {[η6-(C6H5CH2)2C2-
B10H10]Na(THF)}{Na(THF)3}.22 One of the Na atoms
is η6-bound to the hexagonal C2B4 face and η3-bound
to the B3 face of the neighboring nido-carborane cage
and is coordinated to two oxygen atoms of the side-
F igu r e 7. Intermolecular Na‚‚‚H-B interactions in 8.
arms. The other Na atom is η2-bound to each of two
cages and is coordinated to two oxygen atoms from one
THF molecule and one sidearm, respectively. Thus, a
coordination polymeric structure of 8 is generated, as
shown in Figure 7. The Na(1)-cage atom distances
range from 2.661(5) to 2.964(6) Å with an average value
of 2.848(6) Å, indicating a highly asymmetrical η6-
(23) (a) Saxena, A. K.; Hosmane, N. S. Chem. Rev. 1993, 93, 1081.
(b) Grimes, R. N. In Comprehensive Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: New York, 1995;
Vol. 1, p 373. (c) Xie, Z. Coord. Chem. Rev. 2002, 23, 231.

524 Organometallics, Vol. 23, No. 3, 2004
Cheung et al.
Sch em e 4
F igu r e 8. Molecular structure of the {η7-[(CH3OCH2-
2-
CH2)2C2B10H10]Er}2 ion in 9.
ployed in the reactions. Reactions of 5-7 with excess
NaH in THF, followed by treatment with 1 or 0.5 equiv
of LnCl3, were also attempted. No pure products,
however, were isolated.
Complexes 9-12 are extremely air- and moisture-
sensitive, but remain stable for months at room tem-
perature under an inert atmosphere. They are quite
soluble in polar organic solvents such as THF, CH3CN,
and pyridine, sparely soluble in toluene, and insoluble
in n-hexane.
The NMR spectra of 9 and 11 are not informative
because of the strong paramagnetism of Er3+. The
diamagnetic yttrium complexes 10 and 12 are, however,
1
found to provide the interpretable NMR data. The H
NMR spectrum of 10 shows that two sidearms have the
same chemical environment in solution and supports
the ratio of three THF molecules per carborane cage.
Its 11B NMR spectrum exhibits a 3:4:1:2 splitting
pattern with the chemical shifts ranging from 0.3 to
bonding. This measured value is much larger than the
2.776(2) Å found in {η6-(C6H5CH2)2C2B10H10}Na(THF)}-
{Na(THF)3},22 in which the Na atom is bonded to the
open C2B4 face in a symmetrical η6-fashion. Such a slip
distortion may result from the relatively stronger
interactions between the Na(1) and two oxygen atoms
of the sidearms (2.379(5) and 2.564(4) Å). This type of
intramolecular interaction also reduces the level of
solvation. Other structural parameters in 8 are similar
to those reported in the literature.22
Ra r e Ea r th Meta l Com p lexes. Treatment of 2 with
excess finely cut Li or Na metal in THF, followed by
reaction with 1 equiv of LnCl3 in the presence of excess
alkali metal, gave, after recrystallization from CH3CN/
toluene, [{η7-[(CH3OCH2CH2)2C2B10H10]Er}{Na(CH3-
CN)2}]2 (9) or [{η7-[(CH3OCH2CH2)2C2B10H10]Y}{Li-
(THF)3}]2 (10) if recrystallizing from THF/toluene. 9 was
also prepared from the reaction of 8 with ErCl3 in the
presence of excess Na, followed by recrystallization from
CH3CN/toluene (Scheme 3). [[{[η7-(CH3OCH2CH2)-
C2B10H11]Er(THF)}{Na(CH3CN)(THF)}]2]n (11) and [{[η7-
(CH3OCH2CH2)C2B10H11]Y(THF)}{Na(THF)3}]2 (12) were
prepared from 3, finely cut Na metal, and LnCl3 in THF
using the same procedure reported for 9, followed by
recrystallization from CH3CN/THF or THF/toluene,
respectively (Scheme 4). It is noteworthy that only half-
sandwich lanthanacarboranes were isolated even if 2
equiv of carborane (carborane:LnCl3 ) 2:1) was em-
1
-22.3 ppm. The H NMR spectrum of 12 indicates the
presence of MeOCH2CH2 and cage CH protons and
supports the ratio of four THF molecules per carborane
cage. A 3:3:2:2 splitting pattern is observed in the 11B
NMR spectrum of 12 with the chemical shifts spanning
from -8.1 to -20.8 ppm. The IR spectra of 9-12 display
a very strong peak at about 2490 cm-1 and a medium
strong peak at about 2355 cm-1, implying B-H-Ln
interactions.18,19
The molecular structures of 9 and 10 are confirmed
by single-crystal X-ray diffraction studies. They are very
similar except for the associated complex cations, Na-
(CH3CN)2+ in 9 and Li(THF)3+ in 10, respectively. Both
9 and 10 are centrosymmetrical dimers. Each rare earth
metal is η7-bound to the arachno-carborane ligand and
σ-bound to two B-H bonds from the neighboring
arachno-carborane and coordinated to two oxygen atoms
of the pendant ether substituents in a four-lagged piano
stool arrangement (Figures 8 and 9). The complex
cations or the solvation environments of the Na+ or Li+
ions seem to have very little effect on the geometry of
the metallacarboranes. In comparison with [{η7-[(C6H5-
CH2)2C2B10H10]Ln(THF)}{Na(THF)3}]2,24 the intramo-
(24) Chui, K.; Yang, Q.; Mak, T. C. W.; Lam, W. H.; Lin, Z.; Xie, Z.
J . Am. Chem. Soc. 2000, 122, 5758.

Hydroxyethyl- and Alkoxyethyl-o-Carboranes
Organometallics, Vol. 23, No. 3, 2004 525
F igu r e 9. Closer view of the coordination environment of
Y in 10.
F igu r e 11. Molecular structure of the {[η7-(CH3OCH2-
2-
CH2)C2B10H11]Er}2 ion in 11.
F igu r e 10. Intermolecular Na‚‚‚H-B interactions in 11.
lecular interactions between the central metal atoms
and the oxygen atoms of the sidearms in 9 and 10 make
the rare earth metal unsolvated and pull the metal
atoms toward the B(3,4) side of the C2B5 bonding face.
The average Ln-C(cage) distances of 2.352(4) Å in 9
and 2.363(8) Å in 10 are shorter than the corresponding
values of 2.366(2) and 2.392(3) Å found in [{η7-[(C6H5-
CH2)2C2B10H10]Ln(THF)}{Na(THF)3}]2 (Ln ) Er, Y),24
respectively (Table 3). The average Ln-B(cage) dis-
tances of 2.700(4) Å in 9 and 2.723(10) Å in 10 are longer
than the corresponding values of 2.665(2) and 2.685(3)
Å observed in [{η7-[(C6H5CH2)2C2B10H10]Ln(THF)}{Na-
(THF)3}]2 (Ln ) Er, Y),24 respectively. The average
Ln-O distances of 2.493(3) Å in 9 and 2.451(6) Å in 10
are significantly longer than the values of 2.341(1) and
2.352(2) Å found in [{η7-[(C6H5CH2)2C2B10H10]Ln(THF)}-
{Na(THF)3}]2 (Ln ) Er, Y),24 respectively. These data
indicate that the substituents on the cage carbon atoms
have some effects on the structural parameters and
coordination environments of the central metal atoms.
Single-crystal X-ray analyses reveal that 11 adopts a
polymeric structure with less solvated Na atoms as
linkers (Figure 10), whereas that for 12 is a centrosym-
metrical dimer. However, the coordination environ-
ments of the central metal atoms in 11 and 12 are
identical and similar to those observed in 9 and 10
except for one THF molecule replacing one methoxy-
ethyl moiety, as shown in Figure 11. Figure 12 shows
the closer view of the fragment {[η7-(CH3OCH2CH2)-
C2B10H11]Y(THF)}- in 12.
F igu r e 12. Closer view of the coordination environment
of Y in 12.
corresponding values of 2.363(8) and 2.723(10) Å in 10.
The Ln-O(sidearm) distances are 2.494(5) Å in 11 and
2.498(3) Å in 12, which compare to the values of 2.493-
(3) Å in 9 and 2.451(6) Å in 10. These data indicate that
the bond distances in yttrium complexes are much more
sensitive than lanthanides to the coordination environ-
ments, suggesting there may be different bonding
interactions between ligands and metal. The yttrium’s
d-orbitals can participate in π bonding, while only ionic
interactions are present between lanthanides and ligands
since f-orbitals do not involve in π bonding.
Con clu sion
Facile and practical syntheses of hydroxyethyl- and
alkoxyethyl-o-carboranes were reported. These com-
plexes are useful precursors to nido-R2C2B9H92-, nido-
R2C2B10H102-, and arachno-R2C2B10H104- types of ligands.
They may find many applications in organometallic
chemistry23 and carborane-based materials.1
Several half-sandwich 13-vertex lanthanacarboranes
incorporating arachno-carborane ligands were prepared
and structurally characterized. They did not react with
another equivalent of carboranyl ligand to form full-
sandwich species. Structural studies show that the
Lewis base-functionalized sidearms have some effects
on the coordination environments of the central metal
The average Er-C(cage) distance of 2.358(6) Å and
Er-B(cage) distance of 2.697(7) Å in 11 are almost
identical with the values of 2.352(4) and 2.700(4) in 9.
The average Y-C(cage) distance of 2.385(4) Å and
Y-B(cage) distance of 2.723(8) Å in 12 compare to the

526 Organometallics, Vol. 23, No. 3, 2004
Cheung et al.
atom through intramolecular interactions between the
donor atoms of the sidearms and Lewis acidic metal
ions, but do not change the gross structures of the 13-
vertex lanthanacarboranes.
Ack n ow led gm en t. The work described in this ar-
ticle was supported by a grant from the Research Grants
Council of the Hong Kong Special Administration
Region (Project No. CUHK4254/01P). We thank Dr.
Guofu Zi for assistance in the preparation of complex
10. Z.X. acknowledges the Croucher Foundation (Hong
Kong) for a Senior Research Fellowship Award.
The structural parameters of yttrium complexes are
more sensitive to the changes in coordination environ-
ments than those of f-block analogues probably because
of the differences in the bonding nature between the
metal atoms and arachno-carborane ligands: more
covalent interactions in d-block complexes versus pure
ionic interactions in f-block ones. For example, obvious
differences in Y-cage atom distances are observed
among 10, 12, and [{η7-[(C6H5CH2)2C2B10H10]Y(THF)}-
{Na(THF)3}]2,24 whereas those for Er complexes are
almost identical.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data collection details, atomic coordinates, bond
distances and angles, anisotropic thermal parameters, and
hydrogen atom coordinates for complexes 1 and 5-12. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM034081U