Substituent effects. Synthesis and structural characterization of group 4 metallacarboranes containing (C6H5CH2) 2C2B9H92- and [o-C 6H4(CH2)2]C2B 9H92- ligands

Article abstract of DOI:10.1021/om049629r

Substituants on the carborane cage carbons affect not only bonding interactions between the group 4 metal ion and the carboranyl of the C ₂B₉ system but also the reactivity pattern of the resulting metal complexes. Treatment of MCI₄(THF)₂ with 1 equiv of [(C₆H₅CH₂)₂C ₂B₉H₉]Na₂(THF),_x in THF at room temperature gave the bis(carboranyl) complexes {n⁴:n ²-[(C₆H₅CH₂)₂C ₂B₉H₉]₂MCI(THF)}{Na(THF) ₃} (M = Zr (1), Hf (2)). Under the same reaction conditions, interaction of TiCl₄(THF)₂ with 1 equiv of [(C ₆H₅CH₂)₂C₂B ₉H₉]Na₂(THF)_x led to the isolation of a small amount of TiCl₃(THF)₃ and B-substituted zwitterionic compound (C₆H₅CH₂) ₂C₂B₉H₉(THF) (4). Reaction of 1 with 1 equiv of Li[N(SiMe₃)₂] resulted in the replacement of a Na⁺ by a Li⁺, giving the ionic complex [n ³:n²-{(C₆H₅CH₂) ₂C₂B₉H₉}₂ZrCl-(THF)] [Li(THF)₄] (3). ClZr[N(SiMe₃)₂]₃ was isolated from the reaction of 1 with excess Li-[N(SiMe₃) ₂]. An equimolar reaction between M(NEt₂)₄ and (C₆H₅CH₂)₂B₉H ₁₁ afforded the monocarboranyl complexes [n²-(C ₆H₅CH₂)₂C₂B ₉H₉]M(NEt₂)₂(NHEt₂) (M = Ti (5), Zr (6)). It is believed that the additional N(p _π)→M(d_π) interactions stabilize this type of complex. Treatment of MCl₄(THF)₂ with 1 equiv of less bulky yet rigid [{o-C₆H₄(CH₂) ₂}C₂B₉H₉]Na₂-(THF) _x generated a bent-metallocene type of complex, [{o-C ₆H₄(CH₂)₂}C₂B ₉H₉]₂M(THF)₂ (M = Zr (7), Hf (8)). These metallacarboranes were all fully characterized by various spectroscopic techniques and elemental analyses. Molecular structures of 1 and 3-5 were confirmed by single-crystal X-ray analyses.

Full text of DOI:10.1021/om049629r

Organometallics 2004, 23, 4301-4307
4301
Su bstitu en t Effects. Syn th esis a n d Str u ctu r a l
Ch a r a cter iza tion of Gr ou p 4 Meta lla ca r bor a n es
2-
Con ta in in g (C6H5CH2)2C2B9H9 a n d
2-
[o-C6H4(CH2)2]C2B9H9 Liga n d s
Wai-Chuen Kwong,† Hoi-Shan Chan,† Yong Tang,‡ and Zuowei Xie*,†
Department of Chemistry, The Chinese University of Hong Kong, Shatin,
New Territories, Hong Kong, and State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road,
Shanghai 200032, People’s Republic of China
Received May 25, 2004
Substituents on the carborane cage carbons affect not only bonding interactions between
the group 4 metal ion and the carboranyl of the C2B9 system but also the reactivity pattern
of the resulting metal complexes. Treatment of MCl4(THF)2 with 1 equiv of [(C6H5-
CH2)2C2B9H9]Na2(THF)x in THF at room temperature gave the bis(carboranyl) complexes
{η4:η2-[(C6H5CH2)2C2B9H9]2MCl(THF)}{Na(THF)3} (M ) Zr (1), Hf (2)). Under the same
reaction conditions, interaction of TiCl4(THF)2 with 1 equiv of [(C6H5CH2)2C2B9H9]Na2(THF)x
led to the isolation of a small amount of TiCl3(THF)3 and B-substituted zwitterionic compound
(C6H5CH2)2C2B9H9(THF) (4). Reaction of 1 with 1 equiv of Li[N(SiMe3)2] resulted in the
replacement of a Na+ by a Li+, giving the ionic complex [η3:η2-{(C6H5CH2)2C2B9H9}2ZrCl-
(THF)][Li(THF)4] (3). ClZr[N(SiMe3)2]3 was isolated from the reaction of 1 with excess Li-
[N(SiMe3)2]. An equimolar reaction between M(NEt2)4 and (C6H5CH2)2C2B9H11 afforded the
monocarboranyl complexes [η2-(C6H5CH2)2C2B9H9]M(NEt2)2(NHEt2) (M ) Ti (5), Zr (6)). It
is believed that the additional N(pπ)fM(dπ) interactions stabilize this type of complex.
Treatment of MCl4(THF)2 with 1 equiv of less bulky yet rigid [{o-C6H4(CH2)2}C2B9H9]Na2-
(THF)x generated a bent-metallocene type of complex, [{o-C6H4(CH2)2}C2B9H9]2M(THF)2 (M
) Zr (7), Hf (8)). These metallacarboranes were all fully characterized by various spectroscopic
techniques and elemental analyses. Molecular structures of 1 and 3-5 were confirmed by
single-crystal X-ray analyses.
In tr od u ction
however, very limited, probably because of steric hin-
drance of the carboranyl ligands and/or low stability of
Group 4 metallacarboranes have been extensively
studied.1 A series of full- and half-sandwich metalla-
carboranes of the C2B4 systems have been prepared and
structurally characterized, in which group 4 metals are
always η5-bound to the open C2B3 five-membered ring.2
The reaction chemistry of these metallacarboranes is,
their alkyl derivatives.2a,c,d,f
Many group 4 metallacarboranes of the C2B9 systems
are also known.3 In contrast to the C2B4 system, their
alkyl derivatives are isolable and show a rich reaction
chemistry. For example, [Cp*(C2B9H11)]MCH3 (Cp* )
C5Me5) exhibits a variety of ligand exchange, insertion
(alkenes, alkynes, etc.), and ligand C-H activation
reactions characteristic of electrophilic metal alkyls.3b,d-f,h
It is noted that the solid-state structures and reactivity
patterns of these complexes are dependent upon the size
* Corresponding author. Fax: (852)26035057. Tel: (852)26096269.
E-mail: zxie@cuhk.edu.hk.
† The Chinese University of Hong Kong.
‡ Shanghai Institute of Organic Chemistry.
(1) For reviews, see: (a) Grimes, R. N. In Comprehensive Organo-
metallic Chemistry II; Abel, E. W., Stone, F. A. G., Wilkinson, G., Eds.;
Pergamon: Oxford, 1995; Vol. 1, p 371. (b) Saxena, A. K.; Hosmane,
N. S. Chem. Rev. 1993, 93, 1081.
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2872. (b) Crowther, D. J .; Baenziger, N. C.; J ordan, R. F. J . Am. Chem.
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F. J . Am. Chem. Soc. 1995, 117, 10403. (d) Yoshida, M.; J ordan, R. F.
Organometallics 1997, 16, 4508. (e) Yoshida, M.; Crowther, D. J .;
J ordan, R. F. Organometallics 1997, 16, 1349. (f) Kreuder, C.; J ordan,
R. F.; Zhang, H. Organometallics 1995, 14, 2993. (g) Bei, X.; Young,
V. G.; J ordan, R. F. Organometallics 2001, 20, 355. (h) Bei, X.; Kreuder,
C.; Swenson, D. C.; J ordan, R. F.; Young, V. G. Organometallics 1998,
17, 1085. (i) J ohnson, S. E.; Knobler, C. B.; Hawthorne, M. F. J . Am.
Chem. Soc. 1992, 114, 3996. (j) Bowen, D. E.; J ordan, R. F.; Rogers, R.
D. Organometallics 1995, 14, 3630. (k) Kim, D. H.; Won, J . H.; Kim,
S. J .; Ko, J .; Kim, S. H.; Cho, S.; Kang, S. O. Organometallics 2001,
20, 4298. (l) Zhu, Y.; Vyakaranam, K.; Maguire, J . A.; Quintana, W.;
Teixidor, F.; Vinas, C.; Hosmane, N. S. Inorg. Chem. Commun. 2001,
4, 486. (m) Lee, Y.-J .; Lee, J .-D.; Ko, J .; Kim, S.-H.; Kang, S. O. Chem.
Commun. 2003, 1364.
(2) (a) Thomas, C. J .; J ia, L.; Zhang, H.; Siriwardance, U.; Maguire,
J . A.; Wang, Y.; Brooks, K. A.; Weiss, V. P.; Hosmane, N. S.Organo-
metallics 1995, 14, 1365. (b) Siriwardance, U.; Zhang, H.; Hosmane,
N. S. J . Am. Chem. Soc. 1990, 112, 9637. (c) Mao, S. S. H.; Tilley, T.
D.; Rheingold, A. L.; Hosmane, N. S. J . Organomet Chem. 1997, 533,
257. (d) Hosmane, N. S.; Zhang, H.; J ia, L.; Colacot, T. J .; Maguire, J .
A.; Wang, X.; Hosmane, S. N.; Brooks, K. A. Organometallics 1999,
18, 516. (e) Zhang, H.; J ia, L.; Hosmane, N. S. Acta Crystallogr. 1993,
C49, 453. (f) Hosmane, N. S.; Wang, Y.; Zhang, H.; Lu, K. J .; Maguire,
J . A.; Gray, T. G.; Brooks, K. A.; Waldho¨r, E.; Kaim, W.; Kremer, R.
K. Organometallics 1997, 16, 1365. (g) Hosmane, N. S.; Zheng, C. Acta
Crystallogr. 2000, C56, 525. (h) Stockman, K. E.; Houseknecht, K. L.;
Boring, E. A.; Sabat, M.; Finn, M. G.; Grimes, R. N. Organometallics
1995, 14, 3014. (i) Swisher, R. G.; Sinn, E.; Grimes, R. N. Organome-
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M.; Finn, M. G.; Grimes, R. N. J . Am. Chem. Soc. 2000, 122, 10573.
10.1021/om049629r CCC: $27.50 © 2004 American Chemical Society
Publication on Web 08/07/2004

4302 Organometallics, Vol. 23, No. 18, 2004
Kwong et al.
Cl2): δ 7.35-7.16 (m, 20H) (aryl H), 3.63 (d, J ) 15 Hz, 4H)
(C6H5CH2), 3.54 (d, J ) 15 Hz, 4H) (C6H5CH2), 3.66 (m, 16H)
(THF), 1.85 (m, 16H) (THF). 13C NMR (CD2Cl2): δ 138.09,
129.31, 127.93, 126.52 (aryl C), 68.05 (THF), 41.34 (C6H5CH2),
25.25 (THF), the cage carbons were not observed. 11B NMR
(CD2Cl2): δ -2.48 (2), -15.97 (4), -19.73 (4), -25.57 (4),
-34.26 (4). IR (KBr, cm-1): νBH 2532 (s), 2321 (w). Anal. Calcd
for C44H70B18ClNaO3Zr (1 - THF): C, 53.31; H, 7.12. Found:
C, 53.60; H, 7.35.
Ch a r t 1
P r ep a r a tion of {η4:η2-[(C6H5CH2)2C2B9H9]2HfCl(THF )}-
{Na (THF )3} (2). This complex was prepared as yellow crystals
from HfCl4(THF)2 (0.46 g, 1.00 mmol) and [(C6H5CH2)2C2B9H9]-
Na2(THF)x (1.00 mmol) in THF (35 mL) using the procedure
of the group 4 metals. One of the Hf complexes, shown
in Chart 1, draws our attention, in which the bridging
C2B9H11 ligand bonds to two metals in η2- and η3-
2-
fashion, respectively.3c Interestingly, it resembles “[Cp*-
(C2B9H11)]HfCH3” species in reactivity.
1
identical to that reported for 1: yield 0.35 g (61%). H NMR
(CD2Cl2): δ 7.38-7.12 (m, 20H) (aryl H), 3.81 (d, J ) 15 Hz,
4H) (C6H5CH2), 3.64 (d, J ) 15 Hz, 4H) (C6H5CH2), 3.55 (m,
16H) (THF), 1.77 (m, 16H) (THF). 13C NMR (CD2Cl2): δ 142.25,
131.35, 129.27, 127.76 (aryl C), 68.66 (THF), 40.15 (C6H5CH2),
25.46 (THF), the cage carbons were not observed. 11B NMR
(CD2Cl2): δ -2.18 (2), -15.70 (4), -19.62 (4), -25.32 (4),
-33.86 (4). IR (KBr, cm-1): νBH 2556 (s), 2355 (w). Anal. Calcd
for C48H78B18ClNaO4Hf: C, 50.10; H, 6.83. Found: C, 50.50;
H, 7.15.
P r ep a r a tion of [η3:η2-{(C6H5CH2)2C2B9H9}2Zr Cl(THF )]-
[Li(THF )4] (3). To a toluene (20 mL) solution of 1 (0.38 g, 0.36
mmol) was slowly added a toluene (15 mL) solution of LiN-
(SiMe3)2 (0.061 g, 0.36 mmol) at room temperature, and the
reaction mixture was stirred for 2 days. After removal of the
solvent, the residue was extracted with THF/toluene (1:5, 3 ×
10 mL). The clear solutions were combined and concentrated
to about 15 mL. 3 was isolated as orange crystals after this
solution stood at room temperature for 5 days (0.25 g, 62%).
1H NMR (CD2Cl2): δ 7.33-7.10 (m, 20H) (aryl H), 3.77 (br s,
20H) (THF), 3.19 (d, J ) 15.0 Hz, 4H) (C6H5CH2), 3.03 (d, J )
15 Hz, 4H) (C6H5CH2), 1.91 (br s, 20H) (THF). 13C NMR (CD2-
Cl2): δ 141.80, 129.39, 127.24, 125.09 (aryl C), 68.24 (THF),
40.81 (C6H5CH2), 25.11 (THF), the cage carbons were not
observed. 11B NMR (CD2Cl2): δ -8.37 (2), -11.88 (4), -19.49
(6), -26.60 (2), -37.10 (4). IR (KBr, cm-1): νBH 2529 (s), 2318
(w). Anal. Calcd for C44H70B18ClLiO3Zr (3 - 2THF): C, 54.19;
H, 7.24. Found: C, 54.28; H, 7.41.
Rea ction of 1 w ith Excess LiN(SiMe3)2. Isola tion of
ClZr [N(SiMe3)2]3. To a toluene (20 mL) solution of 1 (0.38 g,
0.36 mmol) was slowly added a toluene (20 mL) solution of
LiN(SiMe3)2 (0.24 g, 1.44 mmol) at room temperature, and the
reaction mixture was stirred for 2 days. After removal of the
solvent, the residue was extracted with toluene (3 × 10 mL).
The clear solutions were combined and concentrated to about
10 mL. ClZr[N(SiMe3)2]3 was isolated as colorless crystals after
this solution stood at room temperature for 4 days (0.12 g,
55%). 1H NMR (CD2Cl2): δ 0.22 (s). Its solid-state structure
was confirmed by a single-crystal X-ray analysis.
Rea ction of TiCl4(THF )2 w ith [(C6H5CH2)2C2B9H9]Na 2-
(THF )x. Isola tion of TiCl3(THF )3 a n d (C6H5CH2)2C2B9H9-
(THF )‚2(C6H5CH3) (4‚2(C6H5CH3)). To a THF (20 mL)
solution of TiCl4(THF)2 (0.33 g, 1.00 mmol) was slowly added
a THF (15 mL) solution of [(C6H5CH2)2C2B9H9]Na2(THF)x
(prepared in situ from [Me3NH][(C6H5CH2)2C2B9H10] (0.37 g,
1.00 mmol) and NaH (0.12 g, 5.00 mmol)4) at room tempera-
ture, and the mixture was stirred overnight. The color of the
solution turned gradually to dark green. After removal of the
solvent, the solid was extracted with THF/toluene (1:5, 2 ×
15 mL). The clear solutions were combined and concentrated
to about 15 mL. A small amount of dark green crystals and a
few pale yellow ones were obtained after this solution stood
at room temperature for 3 days. The dark green crystals were
identified as TiCl3(THF)3, and the pale yellow ones were
characterized to be 4‚2(C6H5CH3) by single-crystal X-ray
analyses, respectively. It was not possible to take the spec-
troscopic data for 4‚2(C6H5CH3) due to an insufficient amount
of crystals obtained.
We are interested in the bonding interactions between
2-
group 4 metal ions and R2C2B9H9 ligands and the
effects of such bonding on reactivity. Our previous work
shows that introduction of two benzyl groups into the
cage carbon atoms of the C2B9 system can force the
lanthanide ion to move away from the top of the C2B3
five-membered ring to the side of the cage, resulting in
the formation of exo-nido-lanthanacarboranes.4 With
2-
this in mind, we introduced (C6H5CH2)2C2B9H9 and
2-
[o-C6H4(CH2)2]C2B9H9
ligands into group 4 metal
chemistry to study the effects of cage carbon substitu-
ents on bonding interactions between the carboranyl
and metal ion and on reactivity of the resulting metal-
lacarboranes. These results are reported in this article.
Exp er im en ta l Section
Gen er a l P r oced u r es. All experiments were performed
under an atmosphere of dry dinitrogen with the rigid exclusion
of air and moisture using standard Schlenk or cannula
techniques, or in a glovebox. All organic solvents were freshly
distilled from sodium benzophenone ketyl immediately prior
5
to use. [Me3NH][(C6H5CH2)2C2B9H10],4 [o-C6H4(CH2)2]C2B10H10
,
M(NEt2)4 (M ) Ti, Zr),6 and MCl4(THF)2 (M ) Ti, Zr, Hf)6 were
prepared according to literature methods. All other chemicals
were purchased from Aldrich Chemical Co. and used as
received unless otherwise noted. Infrared spectra were ob-
tained from KBr pellets prepared in 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 and 75 MHz, respectively. 11B NMR spectra were recorded
on a Varian Inova 400 spectrometer at 128 MHz. All chemical
shifts are reported in δ units with reference 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 ME-
DAC Ltd., U.K.
P r ep a r a tion of {η4:η2-[(C6H5CH2)2C2B9H9]2Zr Cl(THF )}-
{Na (THF )3} (1). To a THF (20 mL) solution of ZrCl4(THF)2
(0.37 g, 0.98 mmol) was slowly added a THF (15 mL) solution
of [(C6H5CH2)2C2B9H9]Na2(THF)x (prepared in situ from [Me3-
NH][(C6H5CH2)2C2B9H10] (0.37 g, 1.00 mmol) and NaH (0.12
g, 5.00 mmol)4) at room temperature, and the mixture was
stirred overnight. After removal of the solvent, the sticky
residue was extracted with toluene (2 × 15 mL). The toluene
solutions were combined and concentrated to about 15 mL, to
which was added n-hexane (2 mL). 1 was isolated as orange
crystals after this solution stood at room temperature for a
week (0.38 g, 72% based on carboranyl salt). 1H NMR (CD2-
(4) (a) Xie, Z.; Liu, Z.; Chiu, K.-y.; Xue, F.; Mak, T. C. W. Organo-
metallics 1997, 16, 2460. (b) Xie, Z.; Liu, Z.; Yang, Q.; Mak, T. C. W.
Organometallics 1999, 18, 3603.
(5) Zi, G.; Li, H.-W.; Xie, Z. Organometallics 2002, 21, 5415.
(6) Wang, H.; Wang, Y.; Li, H.-W.; Xie, Z. Organometallics 2001,
20, 5110.

Substituent Effects
Organometallics, Vol. 23, No. 18, 2004 4303
P r ep a r a tion of (C6H5CH2)2C2B9H11. To a suspension of
[(C6H5CH2)2C2B9H9]Na2(THF)x (prepared from [Me3NH][(C6H5-
CH2)2C2B9H10] (1.25 g, 3.35 mmol) and NaH (0.36 g, 15.00
mmol)4) in toluene (25 mL) was added 85% H3PO4 (10.20 g,
88.5 mmol). The resulting two-phase mixture was vigorously
stirred at room temperature overnight. The toluene layer was
decanted, and the H3PO4 layer was extracted with toluene (2
× 15 mL). The toluene solutions were combined and dried over
MgSO4. After removal of toluene under vacuum, the pale
yellow solid was recrystallized from toluene/n-hexane to give
(C6H5CH2)2C2B9H11 as a white solid (0.76 g, 72%). 1H NMR
(CD2Cl2): δ 7.35-7.16 (m, 10H) (aryl H), 3.64 (d, J ) 15 Hz,
2H) (C6H5CH2), 3.54 (d, J ) 15 Hz, 2H) (C6H5CH2). 13C NMR
(CD2Cl2): δ 137.94, 129.29, 128.04, 126.60 (aryl C), 86.91 (cage
C), 41.34 (C6H5CH2). 11B NMR (CD2Cl2): δ 3.50 (2), -9.79 (2),
-13.72 (1), -19.37 (1), -28.33 (3). IR (KBr, cm-1): νBH 2552
(s). Anal. Calcd for C16H25B9: C, 61.07; H, 8.01. Found: C,
61.25; H, 7.96.
P r epar ation of [η2-(C6H5CH2)2C2B9H9]Ti(NEt2)2(NHEt2)‚
CH2Cl2 (5‚CH2Cl2). A toluene (15 mL) solution of (C6H5-
CH2)2C2B9H11 (0.79 g, 2.51 mmol) was added dropwise to a
toluene (10 mL) solution of Ti(NEt2)4 (0.84 g, 2.50 mmol) with
vigorous stirring at room temperature, and the reaction
mixture was stirred overnight. After removal of the solvent,
the red solid was recrystallized from a CH2Cl2 solution,
affording 5‚CH2Cl2 as red crystals (1.37 g, 83%). 1H NMR (CD2-
Cl2): δ 7.20 (m, 10H) (aryl H), 5.31 (s, 2H) (CH2Cl2), 3.18 (d,
J ) 15 Hz, 2H) (C6H5CH2), 3.03 (d, J ) 15 Hz, 2H) (C6H5CH2),
2.72 (q, J ) 7.2 Hz, 12H) (NCH2CH3), 1.13 (t, J ) 7.2 Hz, 18H)
(NCH2CH3). 13C NMR (CD2Cl2): δ 141.85, 129.47, 127.27,
125.14 (aryl C), 42.85 (NCH2CH3), 40.87 (C6H5CH2), 13.08
(NCH2CH3), the cage carbons were not observed. 11B NMR
(CD2Cl2): δ 1.15 (3), -7.03 (4), -23.08 (1), -25.67 (1). IR (KBr,
cm-1): νBH 2524 (s), 2393 (m). Anal. Calcd for C28H54B9N3Ti
(5): C, 58.20; H, 9.42; N, 7.27. Found: C, 58.56; H, 9.32; N,
6.97.
slowly added a THF solution (10 mL) of [Me3NH][{o-C6H4-
(CH2)2}C2B9H10] (0.22 g, 0.74 mmol) at room temperature, and
the mixture was refluxed overnight. After removal of excess
NaH and a half amount of THF, the resulting [{o-C6H4(CH2)2}-
C2B9H9]Na2(THF)x was slowly added to a THF solution (10 mL)
of ZrCl4(THF)2 (0.28 g, 0.74 mmol) at room temperature. The
reaction mixture was then stirred overnight. After removal of
the precipitate and the solvent, the residue was extracted with
hot toluene (3 × 10 mL). The toluene solutions were combined
and concentrated to about 15 mL, to which was added
n-hexane (2 mL). 7 was isolated as a white crystalline solid
after this solution stood at room temperature for 2 days (0.17
g, 65%, based on carboranyl salt). 1H NMR (pyridine-d5): δ
6.95 (m, 8H) (aryl H), 3.63 (m, 8H) (THF), 3.40 (d, J ) 15 Hz,
4H) (C6H4(CH2)2), 3.29 (d, J ) 15 Hz, 4H) (C6H4(CH2)2), 1.59
(m, 8H, THF). 13C NMR (pyridine-d5): δ 139.30, 128.0, 126.95
(aryl C), 67.14 (THF), 39.71 (C6H4(CH2)2), 25.13 (THF), cage
carbon atoms were not observed. 11B NMR (pyridine-d5): δ
-5.86 (6), -9.50 (8), -12.06 (2), -32.51 (2). IR (KBr, cm-1):
νBH 2526 (s). Anal. Calcd for C28H50B18O2Zr: C, 47.73; H, 7.15.
Found: C, 47.36; H, 7.35.
P r ep a r a tion of [{o-C6H4(CH2)2}C2B9H9]2Hf(THF )2 (8).
This complex was prepared as a yellow solid from HfCl4(THF)2
(0.34 g, 0.73 mmol) and [{o-C6H4(CH2)2}C2B9H9]Na2(THF)x
(prepared in situ from [Me3NH][{o-C6H4(CH2)2}C2B9H10] (0.22
g, 0.74 mmol) and NaH (0.08 g, 3.33 mmol) in THF) in THF
(30 mL) using the procedure identical to that reported for 7:
yield 0.18 g (61% based on the carboranyl salt). 1H NMR
(pyridine-d5): δ 6.97 (m, 8H) (aryl H), 3.63 (m, 8H, THF), 3.42
(d, J ) 15 Hz, 4H) (C6H4(CH2)2), 3.27 (d, J ) 15 Hz, 4H) (C6H4-
(CH2)2), 1.59 (m, 8H, THF). 13C NMR (pyridine-d5): δ 139.79,
127.61, 125.50 (aryl C), 70.75 (cage C), 67.84 (THF), 40.38
(C6H4(CH2)2), 25.81 (THF). 11B NMR (pyridine-d5): δ -5.71
(6), -9.43 (8), -12.00 (2), -32.23 (2). IR (KBr, cm-1): νBH 2551
(s). Anal. Calcd for C28H50B18O2Hf: C, 42.47; H, 6.37. Found:
C, 42.36; H, 5.99.
P r ep a r a tion of [η2-(C6H5CH2)2C2B9H9]Zr (NEt2)2(NHEt2)
(6). This complex was prepared as yellow crystals from (C6H5-
CH2)2C2B9H11 (0.31 g, 1.00 mmol) and Zr(NEt2)4 (0.38 g, 1.00
mmol) in toluene (30 mL) using the procedure identical to that
X-r a y Str u ctu r e Deter m in a tion . All single crystals were
immersed in Paraton-N oil and sealed under N2 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 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 Table 1. Selected bond lengths are compiled in Table
2. Further details are included in the Supporting Information.
1
reported for 5: yield 0.49 g (78%). H NMR (CD2Cl2): δ 7.21
(m, 10H) (aryl H), 3.19 (d, J ) 15 Hz, 2H) (C6H5CH2), 3.01 (d,
J ) 15 Hz, 2H) (C6H5CH2), 2.70 (q, J ) 7.2 Hz, 12H) (NCH2-
CH3), 1.15 (t, J ) 7.2 Hz, 18H) (NCH2CH3). 13C NMR (CD2-
Cl2): δ 141.91, 130.75, 127.18, 125.01 (aryl C), 44.62 (NCH2-
CH3), 40.79 (CH2C6H5), 13.54 (NCH2CH3), the cage carbons
were not observed. 11B NMR (CD2Cl2): δ 0.24 (3), -8.41 (4),
-24.56 (1), -27.14 (1). IR (KBr, cm-1): νBH 2518 (s), 2354 (w).
Anal. Calcd for C28H54B9N3Zr: C, 54.13; H, 8.76; N, 6.76.
Found: C, 54.34; H, 8.75; N, 6.55.
P r ep a r a tion of [Me3NH][{o-C6H4(CH2)2}C2B9H10]. To a
mixture of 1,2-[o-C6H4(CH2)2]-1,2-C2B10H10 (0.62 g, 2.52 mmol)
and KOH (0.56 g, 10.7 mmol) was added freshly distilled CH3-
OH (40 mL) with stirring at 0 °C. The reaction mixture was
allowed to warm to room temperature within 30 min and was
refluxed for 2 days. After removal of the solvent, water (15
mL) was added. The aqueous solution was neutralized with
diluted HCl. Addition of aqueous Me3NHCl solution gave a
white precipitate. The product was collected by filtration,
washed with water (3 × 10 mL), and dried in a vacuum to
give a white powder (0.53 g, 71%). 1H NMR (acetone-d6): δ
7.01 (m, 4H) (aryl H), 3.20 (s, 9H) (HN(CH3)3), 3.08 (d, J ) 15
Hz, 2H) (C6H4(CH2)2), 2.86 (d, J ) 15 Hz, 2H) (C6H4(CH2)2).
13C NMR (acetone-d6): δ 144.28, 132.17, 130.83 (aryl C), 50.68
(HN(CH3)3), 44.90 (C6H4(CH2)2), the cage carbons were not
observed. 11B NMR (acetone-d6): δ -11.19 (2), -12.43 (1),
-20.87 (2), -21.79 (2), -35.88 (1), -38.16 (1). IR (KBr, cm-1):
νBH 2576 (s). Anal. Calcd for C13H28B9N: C, 52.81; H, 9.55; N,
4.74. Found: C, 52.59; H, 9.69; N, 4.50.
Resu lts a n d Discu ssion
Rea ction of MCl4(THF )2 w ith [(C6H5CH2)2C2B9H9]-
Na 2. Treatment of MCl4(THF)2 with 1 equiv of [(C6H5-
CH2)2C2B9H9]Na2(THF)x in THF at room temperature
gave, after recrystallization from a toluene/n-hexane
solution, the bis(carboranyl) complexes {η4:η2-[(C6H5-
CH2)2C2B9H9]2MCl(THF)}{Na(THF)3} (M ) Zr (1), Hf
(2)) in good yields (Scheme 1). Expected half-sandwich
complexes were not isolated, but they might serve as
intermediates which reacted further with another equiva-
lent of carboranyl salt to give the thermodynamically
stable products. This result differs significantly from
(7) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
1996.
(8) SHELXTL V 5.03 Program Package; Siemens Analytical X-ray
Instruments, Inc.: Madison, WI, 1995.
P r ep a r a tion of [{o-C6H4(CH2)2}C2B9H9]2Zr (THF )2 (7). To
a suspension of NaH (0.08 g, 3.33 mmol) in THF (10 mL) was

4304 Organometallics, Vol. 23, No. 18, 2004
Kwong 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 for 1 a n d 3-5
1
3
4‚2(C6H5CH3)
5‚CH2Cl2
formula
cryst size (mm)
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C
48H78B18ClNaO4Zr
C52H86B18ClLiO5Zr
0.60 × 0.45 × 0.25
1119.4
triclinic
P1h
C34H47B9O
0.50 × 0.25 × 0.20
569.0
monoclinic
P21/c
10.616(2)
10.968(2)
28.299(5)
90
100.48(1)
90
C29H56B9Cl2N3Ti
0.60 × 0.50 × 0.30
662.9
triclinic
P1h
0.35 × 0.35 × 0.25
1063.3
triclinic
P1h
14.287(7)
15.103(7)
15.133(8)
63.36(1)
86.49(1)
83.52(1)
2900(2)
2
11.572(1)
13.575(1)
19.779(1)
87.14(1)
85.83(1)
86.25(1)
3088.9(4)
2
10.249(1)
11.374(1)
17.818(2)
85.43(1)
88.30(1)
65.13(1)
1878.6(4)
2
3240.2(9)
4
1.166
Z
D
calcd, Mg/m3
1.218
1.204
1.172
radiation (λ), Å
2θ range, deg
µ, mm-1
Mo KR (0.71073)
3.0 to 50.0
0.284
Mo KR (0.71073)
3.5 to 50.0
0.264
Mo KR (0.71073)
3.9 to 50.0
0.063
Mo KR (0.71073)
4.0 to 52.0
0.394
F(000)
1112
1176
1216
704
no. of obsd reflns
no. of params refnd
goodness of fit
R1
7567
719
10809
4247
379
4890
436
703
0.960
1.007
0.998
1.092
0.078
0.056
0.095
0.059
wR2
0.176
0.143
0.265
0.177
Ta ble 2. Selected Bon d Len gth s (Å) for 1 a n d 3
Sch em e 2
1
3
Zr-C1
Zr-C2
Zr-B3
Zr-B4
Zr-B5
Zr-B23
Zr-B24
Zr-Cl1
Zr-O5
2.774(4)
2.918(4)
2.637(5)
2.408(5)
2.451(5)
2.643(6)
2.329(6)
2.395(2)
2.185(4)
3.054(4)
3.017(4)
2.528(4)
2.310(4)
2.575(3)
2.482(4)
2.353(4)
2.388(1)
2.226(2)
Sch em e 1
of a small amount of dark green crystals and a few
colorless ones (Scheme 2). The 11B NMR of the mother
liquor was very complicated. The dark green crystals
did not contain any boron atom, as indicated by the 11B
NMR, and were identified as the known trivalent Ti-
(III) chloride complex TiCl3(THF)3 by a single-crystal
X-ray analysis.9 The spectroscopic data of the colorless
crystals were unable to be taken due to an insufficient
amount of materials, but its structure was confirmed
by a single-crystal X-ray analysis to be a B-substituted
zwitterionic compound, (C6H5CH2)2C2B9H9(THF)‚2(C6H5-
CH3) (4‚2(C6H5CH3)), as shown in Figure 1. The forma-
tion of 4 may be mediated by titanium chloride.10 Dark
green color also appeared if the above reaction was
carried out in dry toluene, indicating the presence of
trivalent Ti(III) species generated in the reaction. It is
noteworthy that reaction of Cp2TiCl2 with [(Me3-
Si)2C2B4H4]Li2 in dry benzene gave a trivalent complex,
[Cp{(Me3Si)2C2B4H4}Ti]2.11 No pure product was iso-
lated from the reaction of TiCl3(THF)3 with 1 equiv of
[(C6H5CH2)2C2B9H9]Na2(THF)x in THF.
Substitution of the chloro group in 1 was attempted.
Treatment of 1 with 1 equiv of Li[N(SiMe3)2] in toluene
(9) The molecular structure of TiCl3(THF)3 was reported, see:
Handlovicˇ, M.; Miklosˇ, D.; Zikmund, M. Acta Crystallogr. 1981, B37,
811.
(10) Lewis acid-promoted substitution reactions of the cage B-H
bond were reported, see: Kang, H. C.; Lee, S. S.; Knobler, C. B.;
Hawthorne, M. F. Inorg. Chem. 1991, 30, 2024, and references therein.
(11) Hosmane, N. S.; Wang, Y.; Zhang, H.; Maguire, J . A.; Waldho¨r,
E.; Kaim, W.; Binder, H.; Kremer, R. K.Organometallics 1994, 13, 4156.
that of the C2B4 system, in which half-sandwich me-
tallacarboranes were isolable.2d,j
Under the same reaction conditions, interaction of
TiCl4(THF)2 with 1 equiv of [(C6H5CH2)2C2B9H9]Na2-
(THF)x in THF at room temperature led to the isolation

Substituent Effects
Organometallics, Vol. 23, No. 18, 2004 4305
F igu r e 1. Molecular structure of (C6H5CH2)2C2B9H9(THF)
(4) (the two solvated toluene molecules are not shown).
Selected bond distances (Å): C1-C3 ) 1.537(5), C1-C2 )
1.583(5), C1-B5 ) 1.602(5), C2-B3 ) 1.613(5), C2-C16
) 1.543(5), B3-B4 ) 1.853(6), B4-B5 ) 1.767(6), B4-O1
) 1.499(5).
F igu r e 2. Molecular structure of the anion [η4:η2-{(C6H5-
CH2)2C2B9H9}2ZrCl(THF)]- in 1 (the coordinated Na-
(THF)3 complex cation is removed for clarity).
+
resulted in the replacement of a Na+ by a Li+, giving
the ionic complex [η3:η2-{(C6H5CH2)2C2B9H9}2ZrCl(THF)]-
[Li(THF)4] (3) in 62% yield. The major alteration is that
a group 1 ion complex no longer coordinates to the cage
in 3. Reaction of 1 with excess Li[N(SiMe3)2] led to the
isolation of ClZr[N(SiMe3)2]3 in 55% yield. Its solid-state
structure was confirmed by single-crystal X-ray analyses
and is the same as the reported one.12 Surprisingly, the
carboranyl ligands rather than the chloro group were
replaced by the amido moieties.13 There were no reac-
tions between 1 and Me3SiCH2MgCl or CpNa since 1
was recovered and no changes were observed in the 11B
NMR. On the other hand, 1 did react with MeLi or LiCt
CPh, leading to brown solutions with complicated 11B
NMR spectra, suggesting that the resulting metal alkyl
complexes may be unstable. No pure products were
isolated from these reactions. These results also indicate
that the coordinated chloro group in 1 is probably
protected by the surrounding ligands to some extent,
which inhibits the attacks by large nucleophiles. This
reactivity pattern resembles that exhibited by full-
sandwich zirconacarborane chloride complexes of the
C2B4 system.2a,c,d
F igu r e 3. Molecular structure of the anion [η3:η2-{(C6H5-
CH2)2C2B9H9}2ZrCl(THF)]- in 3 (the separated [Li(THF)4]+
complex cation is removed for clarity).
doublet centered around 2530 cm-1 and a shoulder at
about 2330 cm-1 attributable to a M-H-B stretching
mode.14
Complexes 1-3 were characterized by various spec-
1
troscopic techniques. The H NMR spectra showed that
Molecular structures of 1 and 3 derived from single-
crystal X-ray analyses are shown in Figures 2 and 3,
respectively. The Na(THF)3+ complex cation binds to the
Zr atom via three sets of B-H-Na interactions in 1,
while 3 consists of well-separated, alternating layers of
discrete tetrahedral cations [Li(THF)4]+ and anions. The
coordination environments of the Zr atom in both 1 and
3 are similar, but the coordination details and the
orientations of four benzyl moieties are different in both
complexes. Table 2 lists some bond distances around the
Zr atom for comparison. The Zr-Cl and Zr-O distances
are all shorter than the corresponding values of 2.467-
(2) and 2.273(5) Å observed in [{η5-(Me3Si)RC2B4H4}2-
ZrCl(THF)]- (R ) H, Me, Me3Si).2a Steric effects im-
the methylene protons of the benzyl groups in all three
complexes are nonequivalent with the coupling constant
J ) 15 Hz and indicated the molar ratio of two THF
molecules per cage in 1 and 2 and two and a half THF
molecules per cage in 3, respectively. Their 13C NMR
spectra exhibited four aromatic carbon signals in the
range 142-125 ppm, one methylene carbon resonance
at about 40 ppm, and two peaks attributable to THF.
The cage carbons were not observed in the 13C NMR
spectra. The 11B NMR spectra of 1 and 2 were very
similar, displaying a 1:2:2:2:2 splitting pattern, whereas
that of 3 showed a 1:2:3:1:2 splitting pattern. The solid-
state IR spectra of 1-3 displayed a characteristic
(12) Airoldi, C.; Bradley, D. C.; Chudzynska, H.; Hursthouse, M. B.;
Malik, K. M. A.; Raithby, P. R. J . Chem. Soc., Dalton Trans. 1980,
2010.
(13) It was reported that ClZr[N(SiMe3)2]3 did not react with excess
Li[N(SiMe3)2]; see ref 12.
(14) (a) Xie, Z.; Yan, C.; Yang, Q.; Mak, T. C. M. Angew. Chem., Int.
Ed. 1999, 38, 1761. (b) Chui, K.; Yang, Q.; Mak, T. C. W.; Lam, W.-H.;
Lin, Z.; Xie, Z. J . Am. Chem. Soc. 2000, 122, 5758. (c) Wang, S.; Li,
H.-W.; Xie, Z. Organometallics 2001, 20, 3842.

4306 Organometallics, Vol. 23, No. 18, 2004
Kwong et al.
Sch em e 3
posed by the benzyl groups lead to much longer Zr-
C(cage) distances, with the shortest one being 2.774(4)
Å. If the reported longest Zr-cage atom distance of
2.789(6) Å found in [η5:η6:σ-Me2Si(C9H6)(C2B10H10CH2-
NMe)]Zr(NC5H5)15 is taken as a cutoff point, the Zr atom
is then bound to one of the (C6H5CH2)2C2B9H92- lignads
in η4- and η3-fashion in 1 and 3, respectively. The large
variations in bond lengths within the complex are
perhaps due to the steric effects generated by the
substituents. The differences in bond lengths between
1 and 3 may result from packing forces.16
F igu r e 4. Molecular structure of [η2-(C6H5CH2)2C2B9H9]-
Ti(NEt2)2(NHEt2) (5) (the solvated dichloromethane mol-
ecule is not shown). Selected bond distances (Å): Ti1-B3
) 2.379(3), Ti1-B4 ) 2.283(3), Ti1-N1 ) 2.225(2), Ti1-
N2 ) 1.879(2), Ti1-N3 ) 1.867(2).
2 equiv of Et3NHCl and Me3SiCl to give a mixture of
complexes as suggested by very complicated 11B NMR
spectra.
The above results show that substituent effects are
very obvious, which cause slip distortion of the Zr atom
from the center of the C2B3 bonding face of the carbo-
ranyl ligand. As a result, mono(carboranyl) species are
unstable, which would react further with another
equivalent of carborane dianion to produce the thermo-
dynamically more stable bis(carboranyl) complexes.
The 11B NMR spectra of both 5 and 6 showed a 3:4:
1:1 splitting pattern which differs significantly from that
1
of (C6H5CH2)2C2B9H11. Their H NMR spectra exhibited
one multiplet of aromatic protons, two doublets of benzyl
methylene protons, and only one set of Et protons,
suggesting there are possible exchanges of the N-H
proton between M-NEt2 groups.
Rea ction of M(NEt2)4 w ith (C6H5CH2)2C2B9H11. To
stabilize the half-sandwich species, it is necessary to
fulfill either steric or electronic requirements of the
central metal ions. The amido group can donate lone-
pair electrons to a d0 metal ion in addition to a normal
σ bond to meet the electronic requirements, which may
lead to the isolation of half-sandwich complexes.3j,17
An equimolar reaction between M(NEt2)4 and (C6H5-
CH2)2C2B9H11 in toluene at room temperature gave,
after recrystallization from CH2Cl2, the monocarboranyl
complexes [η2-(C6H5CH2)2C2B9H9]M(NEt2)2(NHEt2) (M
) Ti (5), Zr (6)) in good yields (Scheme 3). (C6H5-
CH2)2C2B9H11 was prepared in 72% yield by treatment
of [(C6H5CH2)2C2B9H9]Na2 with 85% H3PO4 in toluene
Figure 4 shows the molecular structure of 5. Its
crystal lattice contains one CH2Cl2 of solvation. Unlike
(η5-C2B9H11)Zr(NEt2)2(NHEt2)3j and (η5-C2B9H11)Ti-
(NMe2)2(NHMe2),17 the Ti atom in 5 is bound to
(C6H5CH2)2C2B9H92- in η2-fashion via B-H-Ti interac-
tions. Again, this example illustrates the importance of
the cage carbon substituents in bonding interactions
between the dicarbollide and a group 4 metal ion. The
Ti-B distances are 2.379(3) and 2.283(3) Å, with an
average value of 2.331(3) Å. This measured value is well
comparable to the average Ti-cage atom distance of
2.375(6) Å in (η5-Et2C2B4H4)TiCl2(PMe3)2,2j but signifi-
cantly shorter than the average Ti-cage atom distances
of 2.423(2) Å in (η5-C2B9H11)Ti(NMe2)2(NHMe2),17 2.463-
(3) Å in [(η5-C5Me5)(η5-C2B9H11)TiMe]n,3g and 2.407(6)
Å in [(η5-C5H5){η5-(Me3Si)2C2B4H4}TiCl(THF),2f pre-
sumably due to the differences in coordination number
of the Ti(IV) ion.18 The short Ti-N(2) and Ti-N(3) bond
distances (1.879(2) and 1.867(2) Å) and the planar
geometry around the N(2) and N(3) nitrogen atoms
indicate that both nitrogen atoms with sp2 hybridization
are engaged in N(pπ)fTi(dπ) interactions. The Ti-N(1)-
(amine) distance of 2.225(2) Å is much longer than the
Ti-N(amido) ones, and the N(1) adopts a pyramidal
geometry. These distances are comparable to the cor-
responding values observed in (η5-C2B9H11)Ti(NMe2)2-
(NHMe2).17
at room temperature according to the literature method
3j
for the preparation of C2B9H13
.
This reaction was
closely monitored by 11B NMR since [(C6H5CH2)2C2B9H9]-
Na2 and (C6H5CH2)2C2B9H11 showed different splitting
patterns in the 11B NMR spectra. Alkane elimination
reactions were also examined. To our surprise, there
were no reactions at all between (C6H5CH2)2C2B9H11
and M(CH2Ph)4 (M ) Ti, Zr) or Zr(CH2SiMe3)4 in toluene
at 0-50 °C. As the temperature was increased to >50
°C, the color of the mixture changed from pale yellow
to dark blue with complicated 11B NMR spectra, sug-
gesting that decomposition reactions proceeded at tem-
peratures > 50 °C. These results imply that the acidity/
basicity is not the sole factor to control these elimination
reactions; steric factors must also be taken into account.
The isolation of 5 and 6 implies that the additional
N(pπ)fTi(dπ) interactions can make compensation for
the losses of electrons from the carboranyl ligand, thus
stabilizing the half-sandwich complexes.
Ligand substitution and protonolysis reactions were
attempted. 5 did not react with THF. It did react with
(15) Wang, Y.; Wang, H.; Li, H.-W.; Xie, Z. Organometallics 2002,
21, 3311.
(16) Getman, T. D.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem.
1992, 31, 101.
Rea ction of MCl4(THF )2 w ith [{o-C6H4(CH2)2}-
C2B9H9]Na 2. The above examples clearly demonstrate
(17) Zi, G.; Li, H.-W.; Xie, Z. Organometallics 2002, 21, 3850.
(18) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.

Substituent Effects
Organometallics, Vol. 23, No. 18, 2004 4307
Sch em e 4
7 and 8 may be best described as a full-sandwich type
of structure, in which the metal ion is η5-bound to each
of the two carboranyl ligands and coordinated to two
THF molecules.
Con clu sion
Unlike the unsubstituted C2B9H112-, which is usually
η5-bound to group 4 metal ions,3 the dibenzyl-sub-
stituted one, (C6H5CH2)2C2B9H92-, is a more versa-
tile ligand and can bond to the metal ions in η2-, η3-, or
η4-fashion, resulting in the formation of the ‘slipped’ or
exo-nido metallacarboranes. The less bulky yet rigid
o-xylylene-substituted carboranyl ligand, {o-C6H4(CH2)2}-
C2B9H92-, prefers to be η5-bound to group 4 metal ions.
Effects of substituents on the bonding interactions
between the group 4 metal ion and the carboranyl of
the C2B9 system are very obvious.
Only bis(carboranyl) group 4 metal complexes were
isolated from 1:1 stoichiometric reactions of MCl4(THF)2
with the sodium salts of carborane dianions. Mono-
(carboranyl) group 4 metal complexes were prepared
via amine elimination reactions of M(NEt2)4 and neu-
tral carborane acids, presumably the additional
N(pπ)fM(dπ) interactions stabilizing this type of com-
plexes. Ligand substitution reactions of the above
complexes were attempted but not very successful. For
example, the chloro group in 1 was found to be inert in
the presence of (Me3Si)2NLi, Me3SiCH2MgCl, or CpNa,
most likely due to the very crowded environments
around the Cl atom.
that benzyl substituents on the open C2B3 five-mem-
bered ring of the C2B9 system can change the bonding
modes between the cage and group 4 metal ion, leading
to the formation of exo-nido-metallacarboranes. If the
two benzyl groups are replaced by a less bulky yet rigid
moiety of o-xylylene, what would be the bonding mode
between the carboranyl ligand and group 4 metal ion?
Using the conventional method for the synthesis of
dicarbollide,19 [{o-C6H4(CH2)2}C2B9H9]Na2 was easily
prepared from µ-1,2-[o-C6H4(CH2)2]-1,2-C2B10H10. Treat-
ment of MCl4(THF)2 with 1 equiv of [{o-C6H4(CH2)2}-
C2B9H9]Na2(THF)x in THF at room temperature af-
forded, after recrystallization from a toluene solution,
[{o-C6H4(CH2)2}C2B9H9]2M(THF)2 (M ) Zr (7), Hf (8))
in good yields (Scheme 4). Many attempts were made
to grow X-ray-quality crystals, but all failed.
The 1H NMR spectra of both 7 and 8 showed one
multiplet of aromatic protons, two doublets of o-xylylene
methylene protons, and two multiplets of THF protons
and supported the molar ratio of one THF molecule per
cage. Such a low THF-to-cage molar ratio suggests that
complexes 7 and 8 may not contain any complex cation
Na(THF)x. Their 13C NMR spectra exhibited three
aromatic carbon signals in the range 139-126 ppm, one
methylene carbon resonance at about 40 ppm, and two
peaks attributable to THF. The 11B NMR spectra of 7
and 8 were very similar, displaying a 3:4:1:1 splitting
pattern. Their solid-state IR spectra displayed a char-
Ack n ow led gm en t. This work was supported by
grants from the Research Grants Council of the Hong
Kong Special Administration Region (Project No. 403103)
and National Natural Science Foundation of China
through the Outstanding Young Investigator Award
Fund (Project No. 20129002). Z.X. acknowledges the
Croucher Foundation for a Senior Research Fellowship
Award.
acteristic terminal B-H absorption around 2530 cm-1
,
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data and data collection details, atomic coordinates, bond
distances and angles, anisotropic thermal parameters, and
hydrogen atom coordinates for complexes 1, 3, 4‚2(C6H5CH3),
and 5‚CH2Cl2 as CIF files. This material is available free of
charge via the Internet at http://pubs.acs.org.
indicating there are no B-H-M interactions.14 Elemen-
tal analyses are consistent with the formula of [{o-C6H4-
(CH2)2}C2B9H9]2M(THF)2. On the basis of these results,
(19) Wiesbock, R. A.; Hawthorne, M. F. J . Am. Chem. Soc. 1964,
86, 1642.
OM049629R