Group 4 metallacarboranes of constrained geometries derived from B(cage)- and cage)-silylamido-substituted carborane ligands: A synthetic and structural investigation

Article abstract of DOI:10.1016/S0022-328X(03)00317-6

The reactions of RNHSi(Me)₂Cl (1, R= t -Bu; 2, R=2,6-(Me₂CH)₂C₆H₃) with the carborane ligands, nido-1-Na(C₄H₈O)-2, 3-(SiMe₃)₂-2,3-C₂B₄ H₅ (3) and Li[ closo-1-R′-1,2-C₂ B₁₀H₁₀] (4), produced two kinds of neutral ligand precursors, nido-5-[Si(Me)₂N(H)R]-2, 3-(SiMe₃)₂-2,3-C₂B₄ H₅, (5, R = t- Bu) and closo-1-R′-2-[Si(Me)₂ N(H)R]-1,2-C₂B₁₀H₁₀ (6, R= t -Bu, R′=Ph; 7, R=2,6-(Me₂CH)₂C₆ H₃, R′=H), in 85, 92, and 95% yields, respectively. Treatment of closo-2-[Si(Me)₂NH(2,6-(Me₂CH) ₂C₆H₃)]-1,2-C₂B ₁₀H₁₁ (7) with three equivalents of freshly cut sodium metal in the presence of naphthalene produced the corresponding cage-opened sodium salt of the carbons apart carborane trianion, [ nido -3-{Si(Me)₂N(2,6-(Me₂CH) ₂C₆H₃)}-1,3-C₂B₁₀ H₁₁]^3- (8) in almost quantitative yield. The reaction of the trianion, 8, with anhydrous MCl₄ (M=Ti and Zr) in 1:1 molar ratio in dry tetrahydrofuran (THF) at -78 °C, resulted in the formation of the corresponding half-sandwich neutral d⁰-metallacarborane, closo-1-M[(Cl)(THF)_n]-2- [1′-η¹σ-N(2,6-(Me₂CH)₂ C₆H₃)(Me)₂Si]-2,4-η⁶ -C₂B₁₀H₁₁ (M=Ti (9), n = 0; M=Zr (10), n = 1) in 47 and 36% yields, respectively. All compounds were characterized by elemental analysis, ¹H-, ¹¹B-, and ¹³C-NMR spectra and IR spectra. The carborane ligand, 7, was also characterized by single crystal X-ray diffraction. Compound 7 crystallizes in the monoclinic space group P 2₁/ c with a = 8.2357(19) A?, b = 28.686(7) A?, c = 9.921(2) A?; β= 93.482(4)°; V = 2339.5(9) A?³, and Z = 4. The final refinements of 7 converged at R = 0.0736; wR= 0.1494; GOF=1.372 for observed reflections.

Full text of DOI:10.1016/S0022-328X(03)00317-6

Journal of Organometallic Chemistry 680 (2003) 173ꢂ181
/
www.elsevier.com/locate/jorganchem
Group 4 metallacarboranes of constrained geometries derived from
B
(cage)- and C(cage)-silylamido-substituted carborane ligands: a
synthetic and structural investigation
Jianhui Wang a,b, Yinghuai Zhu a,b, Shoujian Li a, Chong Zheng a, John A. Maguire b,
Narayan S. Hosmane a,*
a Department of Chemistry and Biochemistry, Northern Illinois University, Normal Road, DeKalb, IL 60115-2862, USA
b Department of Chemistry, Southern Methodist University, Dallas, TX 75275-0314, USA
Received 21 April 2003; received in revised form 21 April 2003; accepted 22 April 2003
Dedicated to Professor M. Frederick Hawthorne on the occasion of his 75th birthday, in recognition of his outstanding contribution to polyhedral
boron chemistry
Abstract
The reactions of RNHSi(Me)2Cl (1, Rꢀ
(SiMe3)2-2,3-C2B4H5 (3) and Li[closo-1-R?-1,2-C2B10H10] (4), produced two kinds of neutral ligand precursors, nido-5-
[Si(Me)2N(H)R]-2,3-(SiMe3)2-2,3-C2B4H5, (5, Rꢀt-Bu) and closo-1-R?-2-[Si(Me)2N(H)R]-1,2-C2B10H10 (6, Rꢀt-Bu, R?ꢀPh; 7,
Rꢀ2,6-(Me2CH)2C6H3, R?ꢀH), in 85, 92, and 95% yields, respectively. Treatment of closo-2-[Si(Me)2NH(2,6-(Me2CH)2C6H3)]-
/
t-Bu; 2, Rꢀ
/
2,6-(Me2CH)2C6H3) with the carborane ligands, nido-1-Na(C4H8O)-2,3-
/
/
/
/
/
1,2-C2B10H11 (7) with three equivalents of freshly cut sodium metal in the presence of naphthalene produced the corresponding cage-
opened sodium salt of the ‘‘carbons apart’’ carborane trianion, [nido-3-{Si(Me)2N(2,6-(Me2CH)2C6H3)}-1,3-C2B10H11]3ꢁ (8) in
almost quantitative yield. The reaction of the trianion, 8, with anhydrous MCl4 (Mꢀ
/
Ti and Zr) in 1:1 molar ratio in dry
78 8C, resulted in the formation of the corresponding half-sandwich neutral d0-metallacarborane, closo-
tetrahydrofuran (THF) at ꢁ
/
1-M[(Cl)(THF)n]-2-[1?-h1s-N(2,6-(Me2CH)2C6H3)(Me)2Si]-2,4-h6-C2B10H11 (Mꢀ
/
Ti (9), nꢀ
/
0; Mꢀ
/
Zr (10), nꢀ1) in 47 and 36%
/
yields, respectively. All compounds were characterized by elemental analysis, 1H-, 11B-, and 13C-NMR spectra and IR spectra. The
carborane ligand, 7, was also characterized by single crystal X-ray diffraction. Compound 7 crystallizes in the monoclinic space
3
˚
˚
˚
˚
group P21/c with aꢀ
refinements of 7 converged at Rꢀ
# 2003 Elsevier Science B.V. All rights reserved.
/
8.2357(19) A, bꢀ
/
28.686(7) A, cꢀ
/
9.921(2) A; bꢀ
/
93.482(4)8; Vꢀ
/
2339.5(9) A , and Zꢀ
/
4. The final
/
0.0736; wRꢀ
/
0.1494; GOFꢀ/1.372 for observed reflections.
Keywords: B(cage)- and C(cage)-silylamido-substituted carboranes; Ligand precursors; Metallacarboranes; Constrained geometry; Crystal structures;
Group 4 carborane; Sigma-bonded ansa ligand
1. Introduction
(Groups 3 and 4) constrained geometry complexes to act
as olefin polymerization catalysts [1,4,5]. The first such
complex
described
was
[{h5-(C5Me4)Me2Si(h1-
Constrained geometry complexes, in which a metal is
associated with an h1-bonding group that is tethered to
an h5-p-bonding ligand, usually a derivative of cyclo-
pentadienide, have received a great deal of attention in
NCMe3)}Sc(PMe3)]2(m-H)2 [4] and, while other h1-base
sites and linking groups have been described [6], the
Si(Me)2(NCMe3) moiety remains one of the most
explored h1-bonding group and has been incorporated
into both single site and binuclear catalytic systems [7].
Another class of p-donor ligands are the dianionic nido-
recent years [1ꢂ
stems from the potential of the early transition metal
/
3]. The major emphasis for these studies
carboranes, especially those in the [(CR)2B10H10]2ꢁ
,
* Corresponding author. Tel.: ꢃ
4802.
E-mail address: nhosmane@niu.edu (N.S. Hosmane).
/
1-815-753-3556; fax: ꢃ1-815-753-
/
[(CR)2B9H9]2ꢁ and [(CR)2B4H4]2ꢁ cage systems [8]. It
was found that the small cage half-sandwich com-
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00317-6

174
J. Wang et al. / Journal of Organometallic Chemistry 680 (2003) 173ꢂ181
/
pounds, [Me2P(CH2)3PMe2]2M?(Et2C2B4H4) (M?ꢀ
/
nipulated in either a dry-box, or an evacuable glove bag,
under an atmosphere of dry nitrogen. All known
compounds among the products were identified by
comparing their IR and H-NMR spectra with those
of authentic samples.
TiMe2 and ZrCl2), when mixed with methylaluminoxane
(MOA) exhibited efficient polymerization catalytic ac-
tivity [9], but studies on the use of the mixed
1
Cp*M[(CR)2B9H9] (Cp*ꢀ
/
C5Me5; Mꢀ/Group 3 or 4
metal) as olefin polymerization catalysts have produced
mixed results [10,11]. On the other hand, the study of
carborane-based constrained geometry ligands has been
much more limited. While complexes with both neutral
[12] and anionic [13] h1-tethered groups have been
reported, the number of such examples is small. Herein,
we report the syntheses of several constrained geometry
silylamido ligands in both the C2B4 and C2B10 cage
systems, along with the results of their metalation
reactions.
2.4. Synthesis of RNHSi(Me)2Cl (1, Rꢀ
2,6-(Me2CH)2C6H3)
/
t-Bu; 2, Rꢀ
/
A 15.6 ml sample of 1.7 M t-BuLi in pentane (26.51
mmol) was slowly added in vacuo to a flask containing
RNH2 (Rꢀ
(Me2CH)2C6H3, 4.70 g, 26.51 mmol) in 20 ml pentane
at ꢁ78 8C. The resulting mixture was slowly warmed to
/
t-Bu, 1.93 g, 26.39 mmol; Rꢀ2,6-
/
/
room temperature, during which time a white precipitate
was produced; stirring was continued over night. The
solvents and volatile t-BuH (2-methylpropane) in the
flask were removed under vacuum to give an off-white
solid of lithium amide. To the flask containing 50 ml
2. Experimental
2.1. Materials
Me2SiCl2 at ꢁ78 8C, the solid lithium amide product
/
was slowly added under nitrogen using a funnel
designed specifically for adding solids. After complete
addition of the solid, the reaction mixture was slowly
warmed to room temperature and stirred further for 6 h.
The reaction mixture was then filtered to collect a clear
filtrate. The unreacted dichlorodimethylsilane from the
filtrate was removed in vacuo to collect an oily liquid
that was distilled under reduced pressure to give color-
Benzene, tetrahydrofuran (THF), toluene, and pen-
tane were dried over Na metal and doubly distilled
before use. Naphthalene was sublimed before use. All
˚
other solvents were dried over 4ꢂ8 A mesh molecular
/
sieves (Aldrich) and were either saturated with dry
argon or degassed before use. The synthesis of 2,3-
bis(trimethylsilyl)-2,3-dicarba-nido-hexaborane (8), and
its subsequent conversion to nido-1-Na(C4H8O)-2,3-
(SiMe3)2-2,3-C2B4H5 (3) followed published procedures
less liquid products [1, Rꢀ/t-Bu, 3.12 g, 18.83 mmol,
71% yield; 2, Rꢀ2,6-(Me2CH)2C6H3, 4.88 g, 18.08
/
[14,15]. Closo-1-R-1,2-C2B10H11 (Rꢀ
/
H, Ph) was ob-
mmol, 68% yield]. Anal. data: Calc. (Found) for
C6H16ClNSi (1): C, 43.48 (43.51); H, 9.73 (9.56); N,
8.45 (8.49)%. C14H24ClNSi (2): C, 62.30 (62.58); H, 8.96
(9.01); N, 5.19 (5.48)%. The IR spectrum of 1 is identical
to that in the literature [16]. NMR data for 1: 1H-NMR
(CDCl3, external Me4Si) d 1.12 [9H, s, C(CH3)3], 0.13
[6H, s, Si(CH3)2], 1.13 [1H, s, NH]; 13C-NMR (CDCl3,
external Me4Si) d 40.31 [C(CH3)3], 33.80 [C(CH3)2],
tained from KATCHEM and used without further
purification. Prior to use, ZrCl4 (Aldrich) was degassed
under vacuum at 120 8C for 24 h. Tert-butyllithium, t-
BuLi (1.7 M solution in pentane, obtained from
Aldrich) was used as received.
2.2. Spectroscopic procedures
1
3.51 [Si(CH3)]; 2: H-NMR (CDCl3, external Me4Si) d
Proton, boron-11, carbon-13 NMR spectra were
recorded on a Bruker Fourier-transform multinuclear
spectrometer at 200, 64.2, 50.3 MHz, respectively.
7.23 [3H, s, Ã
/
C6H3], 3.62 [2H, m, CH(CH3)2 Jꢀ
/
6.91
Hz], 2.51 [1H, s, NH], 1.43 [12H, d, CH(CH3)2 Jꢀ6.91
Hz], 0.84[6H, s, Si(CH3)2]; 13C-NMR (CDCl3, external
/
Infrared spectra were recorded on a Perkinꢂ
/
Elmer
Me4Si) d146: [p-C(Ph)H], 136.7 [NÃ
/
C(Ph)], 125.8 [i-PrÃ
/
Model 1600 FT-IR spectrophotometer and Nicolet
Magna 550 FT-IR spectrophotometer. Elemental ana-
lyses were determined by in-house facility at Northern
C(Ph)], 123.5 [o-C(Ph)], 28.6 [CH(CH3)2], 24.1
[CH(CH3)2], 2.7 [Si(CH3)]; IR (cmꢁ1, KBr) 2: 3371(m,
s), 3063(s, w), 2960(s, s), 2928(s, w), 2867(s, s), 2573(s, s),
1618(m, m), 1596(s, m), 1518(s, m), 1459(s, s), 1439(s, s),
1385(s, m), 1359(s, m), 1326(m, s) 1256(s, m), 1193(s, s),
1078(s, s), 1053(s, s), 1042(s, s), 924(s, s), 882(s, w),
795(s, s) 736(m, m) 672(s, m), 645(s, w), 470(s, s).
Illinois University using a PerkinꢂElmer 2400 CHN
/
elemental analyzer.
2.3. Synthetic procedures
All experiments were carried out in Pyrex glass round-
bottom flasks of 100 ml capacity, equipped with
magnetic stirring bars and high vacuum Teflon valves,
or in a dry-box under an argon atmosphere. After their
initial purifications, non-volatile substances were ma-
2.5. Synthesis of nido-5-t-BuNHSi(Me)2-2,3-(SiMe3)2-
2,3-C2B4H5 (5)
A 20 ml tetrahydrofuran (THF) solution of nido-2,3-
(SiMe3)2-2,3-C2B4H6 (1.10 g, 5.03 mmol) was poured in

J. Wang et al. / Journal of Organometallic Chemistry 680 (2003) 173ꢂ
/181
175
vacuo onto a heterogeneous mixture of NaH (0.25 g,
10.00 mmol) and THF at ꢁ78 8C, and the reaction
mixture was slowly warmed to room temperature. The
flask was occasionally cooled to ꢁ196 8C, to control the
monolithium salt was well dispersed in the flask. This
heterogeneous mixture was cooled to ꢁ788 C and to this
9.63 mmol of RNHSi(Me)2Cl (1, Rꢀt-Bu, 1.60 g; 2,
Rꢀ2,6-(Me2CH)2C6H3, 2.60 g) in 10 ml toluene was
/
/
/
/
/
evolution and buildup of H2 gas. The evolved H2 gas
was pumped out of the flask, and the reaction was
continued until H2 evolution ceased. The mixture was
then filtered in vacuo through a glass frit to collect the
filtrate which was a THF solution nido-1-Na(C4H8O)-
2,3-(SiMe3)2-2,3-C2B4H5 (3) according to the literature
[14]. Then, the clear filtrate was added slowly to a
solution of t-BuNHSi(Me)2Cl (1) (0.83 g, 5.00 mmol) in
slowly added. After complete addition, the mixture was
slowly warmed to room temperature, and stirred for 24
h at this temperature. The resulting heterogeneous
mixture was then filtered in vacuo to remove the solid
LiCl giving a clear yellow filtrate. Solvent from the clear
filtrate was then removed in vacuo to collect a yellow
residue that was identified as 1-R?-2-RNHSi(Me)2-1,2-
C2B10H10 (Rꢀ
/
t-Bu, R?ꢀ/Ph (6), 3.11 g, 8.90 mmol,
dry THF at ꢁ
/
78 8C over a period of 2 h with constant
92% yield; Rꢀ
/
2,6-(Me2CH)2C6H3, R?ꢀ/H (7), 3.48 g,
stirring. After warming to room temperature the mix-
ture was stirred for 24 h and then filtered in vacuo to
give a light yellow filtrate. The solvent from the filtrate
was removed under reduced pressure to produce a pale
yellow residue that was purified by chromatography
using silica gel column under inert atmosphere with
pentane as eluting solvent to collect a yellow oily
product, identified as nido-5-t-BuNHSi(Me)2-2,3-
(SiMe3)2-2,3-C2B4H5 (5) (1.49 g, 4.27 mmol, 85% yield).
Anal. data: Calc. (Found) for C14H39B4NSi3 (5): C,
48.19 (48.43); H, 11.27 (11.16); N, 4.01 (4.23)%. NMR
9.26 mmol, 96% yield). Anal. data: Calc. (Found) for
C14H31B10NSi (6): C, 48.10 (47.86); H, 8.94 (8.72); N,
4.01 (4.22)%. C16H35B10NSi (7): C, 50.89 (51.20); H,
9.34 (8.92); N, 3.71 (3.83)%. NMR data for 6: 1H-NMR
(C6D6, external Me4Si) d 0.07 [6H, s, Si(CH3)2], 0.35
[1H, s, NH], 0.94 [9H, s, C(CH3)3], 6.95ꢂ
C6H5], 13C-NMR (C6D6, external Me4Si) d [SiÃ
33.51 [C(CH3)3], 49.95 [NÃC(CH3)3], 78.59 [SiÃ
83.52 [PhÃC(cage)], 127.16ꢂ
133.27 [C6H5]. 11B-NMR
(C6D6, relative to external BF3×OEt2) d ꢁ8.9 [d, basal
BH, 1J(11BÃ1H)ꢀ
144 Hz], ꢁ3.05 [s, basal BH,
1J(11BÃ1H)ꢀ
144 Hz], 2.29 [d, apical BH,
1J(11BÃ1H)ꢀ
154 Hz], 0.65 [s, apical BH
1J(11BÃ1H)ꢀ123 Hz]; IR data for 6 (cmꢁ1, KBr)
/
7.55 [5H, m,
(CH3)2],
C(cage)],
/
/
/
/
/
/
/
/
/
/
data for 5: 1H-NMR (C6D6, external Me4Si) d 1.21 to ꢁ
0.44 [2H, br, BÃH ÃB], 0.22 [6H, s, BÃSiÃ(CH3)2], 0.43
[18 H, s, 2CÃSiÃ(CH3)3], 0.94 [1H, s, NH], 1.28
[C(CH3)3]; 13C-NMR (C6D6, external Me4Si) d 0.02
[BÃSiÃ(CH3)2], 2.05 [CÃSi(CH3)3], 33.87 [C(CH3)3],
49.31 [NÃ
C(CH3)3], 141 [C(cage)]; 11B-NMR (C6D6,
relative to external BF3×OEt2) d ꢁ50.22 [d, 1 apical
Si]; IR
/
/
/
ꢁ
/
/
/
/
/
/
/
/
/
/
/
3401(s, w), 2966(s, s), 2930(s, s), 2904(s, m), 2868(s,
m), 2582(vs, br), 2274(s, s), 1470(s, s), 1445(s, m), 1404(s,
m), 1383(s, s), 1363(s, s), 1260(s, s), 1219(s, s), 1081(s, s),
1035(s, s), 1020(s, s), 856(s, s), 518(s, s), 492(vs, s), 472(s,
w), 415(s, m). NMR data for 7: 1H-NMR (C6D6,
/
/
/
/
/
/
BH], 0.90 [d, 2 basal BH], 14.74 [br, 1 basal B Ã
/
(cmꢁ1, KBr) 3391(m, s), 2960(s, s), 2925(s, s), 1404(s, s),
1378(s, s), 1358(s, s), 1312(s, s), 1255(s, vs), 1224(s, vs),
1096(s, s), 958(s, m), 938(s, s), 784(s, s), 758(s, s) 688(s,
m), 636(s, m), 625(s, m), 482(s, m).
external Me4Si) d 0.04 [6H, s, Ã
d, Ã 6.88 Hz], 2.21 [1H, NH]
CH(CH3)2, J(1HÃ1H)ꢀ
3.38 [2H, m, Ã 6.88 Hz], 7.10ꢂ
CH(CH3)2, J(1HÃ1H)ꢀ
7.14 [3H, m, Ã
C6H3], 13C-NMR (CDCl3, external
Me4Si) d ꢁ1.43 [SiÃ(CH3)2], 23.48 [CH(CH3)2], 27.85
[CH(CH3)2], 59.88 [SiÃC(cage)], 66.82 [C(cage)], 123.50ꢂ
145.78 [Ã
C6H3]. 11B-NMR (C6D6, relative to external
BF3×OEt2) d ꢁ12.15 [overlapped, basal BH], ꢁ7.06 [d,
basal BH, J(11BÃ1H)ꢀ
152 Hz], ꢁ1.14 [b, apical BH,
1J(11BÃ1H)ꢀ141 Hz]; IR data for 7 (cmꢁ1, KBr)
/Si(CH3)2], 1.17 [12H,
/
/
/
/
/
/
/
/
/
/
2.6. Synthesis of 1-R?-2-N(R)HSi(Me)2-1,2-C2B10H10
/
/
(6, Rꢀ
/
t-Bu, R?ꢀ
/
Ph; 7, Rꢀ
/
2,6-(Me2CH)2C6H3, R?ꢀ
/
/
H)
/
/
/
1
/
/
/
A 5.67 ml solution of 1.7 M t-BuLi in hexane (9.64
mmol) was slowly added to a THF solution of 9.63
/
/
3382(s, w), 3360(s, w), 3070(s, s), 2964(s, s), 2969(s,
m), 2574(s, s), 1617(s, m), 1459(vs, br), 1438(s, s), 1410(s,
w), 1382(s, m), 1322(s, s), 1258(s, s), 1188(s, s), 1098(s,
s), 1072(s, s), 1031(s, s), 914(s, s), 875(s, m), 864(s, w),
834(s, w), 812(s, s), 763(s, w), 724( s, m), 677(s, w), 634(s,
w).
mmol of 1-R-1,2-C2B10H12 (Rꢀ
/
Ph, 2.13 g; Rꢀ/H, 1.39
g) under nitrogen at ꢁ788 C. After complete addition,
/
the reaction mixture was slowly warmed to room
temperature and then stirred for 4 h at this temperature.
The solvent from the reaction mixture was removed
under reduced pressure to give Li[1-R?-1,2-C2B10H10] (4,
R?ꢀ
/
Ph or H) as an off-white solid. The flask containing
2.7. Synthesis of [Naꢃ(THF)n]3[nido-3-
{Si(Me)2N(2,6-(Me2CH)2C6H3)}-1,3-C2B10H11]3ꢁ
(8)
the lithium salt was then attached to a high vacuum line
and pumped at pressures below 5 mTorr to remove any
additional solvating THF. After complete removal of
the solvated THF, if any, 25 ml of anhydrous toluene
was transferred into the flask in vacuo and the resulting
mixture was stirred for 2 h until all of the solid
A 9.26 mmol (3.48 g) sample of [1-(2,6-diisopropany-
lanilinyldimethylsilyl)-1,2-C2B10H11] (7) was reacted
with 28.90 mmol (0.70 g) of freshly cut sodium metal

176
J. Wang et al. / Journal of Organometallic Chemistry 680 (2003) 173ꢂ181
/
and 28.90 mmol (4.00 g) of anhydrous naphthalene in
dry THF (100 ml) at ꢁ78 8C. The reaction mixture was
data for 9: 1H-NMR (C6D6, external Me4Si) d 0.13 [6H,
s, ÃSi(CH3)2], 1.23 [12H, m, Ã
CH(CH3)2, J(1HÃ1H)ꢀ
6.88 Hz], 3.48 [1H, m, Ã 6.88
CH(CH3)2, J(1HÃ1H)ꢀ
Hz], 7.10ꢂ7.14 [3H, m, Ã
C6H3]; 13C-NMR (external
Me4Si) d 1.06 [SiÃ(CH3)2], 25.43 [CH(CH3)3], 29.70
/
/
/
/
/
then allowed to warm to room temperature slowly,
during which time the heterogeneous mixture turned
dark yellow. After stirring the mixture at room tem-
perature over night, the dark yellow solution in the flask
was filtered in vacuo and all of the volatiles, including
naphthalene, were removed from the filtrate at 60 8C.
The yellow residue was dissolved in 60 ml THF and
filtered to remove the excess sodium metal. After
removal of the solvent from the filtrate, a yellow solid,
identified as [Naꢃ(THF)n]3[nido-3-{Si(Me)2N(2,6-
(Me2CH)2C6H3)}-1,3-C2B10H11]3ꢁ [8, 4.08 g, 1.67
/
/
/
/
/
/
[CH(CH3)3], 67.50 [C Ã/Cage], 122.50, 124.50, 129.01,
141.6 [C6H3]; 11B-NMR (C6D6, relative to external
BF3×
7.72 [d, 2BH,], ꢁ
[2BH, ill-defined], ꢁ
14.69 [2BH, d, J(11BÃ
Hz], ꢁ
43.18 [1BH, ill-defined]; IR (cmꢁ1, KBr) 2957(s,
/
OEt2) d ꢁ
/
3.52 [d, 2BH, 1J(11BÃ
/
1H)ꢀ
/
140 Hz],
13.84
1H)ꢀ
112
ꢁ
/
/
12.25 [1BH, ill-defined], ꢁ
/
1
/
/
/
/
s), 2913(s, m), 2862(s, w), 2843(s, w), 2508(br, s), 1398(s,
s), 1259(s, s), 1096(br, s), 1043(s, s), 1015(s, s), 806(s, s).
mmol; m.p.ꢀ
/
265 8C, moderately air-stable, soluble in
polar solvents only], was obtained in 90% yield. Anal.
data: Calc. (Found) for C80H170B50N5Na15Si5×
3(C4H8O) (8): C, 45.20 (45.23); H, 8.00 (8.05); N, 2.86
1
(3.02)%. NMR data for 8: H-NMR (C4D8O, external
/
2.9. Synthesis of closo-1-Zr[(Cl)(THF)]-2-[1?-h1s-
N(2,6-(Me2CH)2C6H3)(Me)2Si]-2,4-h6-C2B10H11
(10)
Me4Si) d ꢁ
CH(CH3)2, J(1HÃ
3.63 [m, THF], 3.87 [1H, m,
J(1HÃ1H)ꢀ
6.87 Hz], 7.10ꢂ7.14 [3H, m, Ã
NMR (C4D8O, external Me4Si) d 0.60 [SiÃ
/
0.08 [6H, Ã
1H)ꢀ
6.87 Hz], 1.77 [m, Ã
CH(CH3)2,
C6H3]; 13C-
(CH3)2],
/
Si(CH3)2], 1.07 [12H, d, Ã
/
/
/
/
THF],
A 0.61 g (0.25 mmol) sample of [Naꢃ(THF)n]3[nido-
3-{Si(Me)2N(2,6-(Me2CH)2C6H3)}-1,3-C2B10H11]3ꢁ (8)
in 20 ml THF was slowly poured onto 0.29 g of ZrCl4
Ã
/
Ã
/
/
/
/
/
/
22.11 [CH(CH3)3], 27.52 [CH(CH3)3], 26.01, 68.02
[C Ã/THF], 66.04 [C Ã/Cage], 122.00, 128.12, 131.60, 141.2
(1.25 mmol) in 10 ml THF at ꢁ78 8C. The reaction
/
mixture was stirred for about an hour at this tempera-
ture and then slowly warmed to room temperature and
stirred for an additional 24 h. The resulting hetero-
geneous brown colored reaction mixture was filtered in
vacuo to collect a clear brown filtrate by removing the
off-white solid, presumably NaCl. The solvent, THF,
was then removed from the filtrate in vacuo, and the
resulting brown solid residue was extracted with three 30
ml aliquots of dry benzene. The combined benzene
extracts were concentrated in vacuo to a total volume of
15 ml, after which 70 ml of dry pentane was added to
[C6H3]; 11B-NMR (C4D8O, relative to external BF3×
/
/
OEt2) d ꢁ
29.10 [2B], ꢁ
/
8.32 [2B], ꢁ
/
19.21 [2B], ꢁ
/
23.86 [2B]; ꢁ
/
38.0[1B], ꢁ
/
42.08 [1B]; IR (cmꢁ1, KBr)
2959(s, s), 2922(s, m), 2863(s, w), 2470(s, s), 1618(s, w),
1458(s, w), 1438(s, s), 1400(s, s), 1358(s, m), 1257(s, s),
1102(br, m), 1041(br, m), 803(s, s).
2.8. Synthesis of closo-1-Ti(Cl)-2-[1?-h1s-N(2,6-
(Me2CH)2C6H3)(Me)2Si]-2,4-h6-C2B10H11 (9)
precipitate
a brown solid, identified as closo-1-
A 0.95 g (0.39 mmol) sample of [Naꢃ(THF)n]3[nido-
3-{Si(Me)2N(2,6-(Me2CH)2C6H3)}-1,3-C2B10H11]3ꢁ (8)
was dissolved in 20 ml THF in vacuo and the resulting
Zr[(Cl)(THF)]-2-[1?-h1s-N(2,6-
(Me2CH)2C6H3)(Me)2Si]-2,4-h6-C2B10H11 (10), in 36%
(0.24 g, 0.43 mmol) yield. Anal. data: Calc. (Found) for
C20H42B10NOSiZrCl (10): C, 41.75 (41.76); H, 7.36
(7.50); N, 2.43 (2.67). NMR data for 10: 1H-NMR
solution was cooled to ꢁ78 8C. To which 0.39 ml (0.39
/
mmol, 1M in toluene) of TiCl4 was added in vacuo and
the resulting mixture was warmed slowly to room
temperature and stirred for 24 h. The dark-brown
colored reaction mixture was then filtered, and the
solvents from the filtrate were removed under reduced
pressure to collect a dark solid residue. This residue was
extracted with 80 ml dry benzene and the benzene
extract was concentrated to a total volume of 10 ml in
vacuo and then mixed with 70 ml of dry pentane to
precipitate a brown solid out of the solution that was
later identified as closo-1-Ti(Cl)-2-[1?-h1s-N(2,6-
(Me2CH)2C6H3)(Me)2Si]-2,4-h6-C2B10H11 (9). After
purification by repeating the above process, 0.42 g
(0.80 mmol, 47% yield) of the product 9 was obtained.
Anal. data: Calc. (Found) for C16H34B10NClSiTi (9): C,
41.78 (41.50); H, 7.45 (7.30); N, 3.05 (3.35)%. NMR
(C6D6, external Me4Si) d 0.12 [6H, s, Ã
[12H, m, Ã 6.90 Hz], 1.95 [4H,
CH(CH3)2, J(1HÃ1H)ꢀ
m, THF], 3.48 [1H, m, CH(CH3)2, J(1HÃ1H)ꢀ
6.90
Hz], 3.88 [4H, m, THF], 7.14ꢂ7.27 [3H, m, Ã
C6H3]; 13C-
NMR (external Me4Si) d 1.02 [SiÃ(CH3)2], 23.90
/Si(CH3)2], 1.29
/
/
/
/
/
/
/
/
[CH(CH3)3], 27.84, 67.33 [C Ã/THF], 28.61 [CH(CH3)3],
70.46 [C Ã/Cage], 123.13, 124.92, 129.05, 141.03 [C6H3];
11B-NMR (C6D6, relative to external BF3×
/
OEt2) d 8.8
154 Hz], ꢁ
5.47 [ill-defined,
33,57 [ill-defined,
[basal 2BH], 2.61 [b, 2BH, J(11BÃ
/
1H)ꢀ
/
/
1
2.61 [b, 2BH, J(11BÃ
/
1H)ꢀ
/
140 Hz], ꢁ
/
1
1BH], ꢁ
/
12.05 [ill-defined, 2BH], ꢁ
/
1BH], IR (cmꢁ1, KBr) 2958(s, s), 2921(s, m), 2860(s, w),
2539(s, s), 1400(s, s), 1260(s, w), 1094(s, s), 1018(s, s),
799(s, s).

J. Wang et al. / Journal of Organometallic Chemistry 680 (2003) 173ꢂ
/181
177
2.10. X-ray structural analysis of closo-2-
[Si(Me)2NH(2,6-(Me2CH)2C6H3)]-1,2-C2B10H11 (7)
and alkyl groups were located, while the H on the
nitrogen was calculated, and all were refined with fixed
isotropic thermal parameters. The final refinements
Crystals of 7 were grown from a hexane/benzene (40/
60, v/v) solution by slow evaporation. The selected
crystal was then mounted on a Bruker SMART CCD
PLATFORM diffractometer, under a low-temperature
stream of nitrogen. The crystallographic data and other
experimental details are summarized in Table 1. Unit
cell parameters and orientation matrix were obtained
from the least-squares refinement of 113 reflections
measured in three different sets of 15 frames each, in
converged at R1ꢀ
/
0.0736, wR2ꢀ
/
0.1494, and GOFꢀ
/
1.372. The atomic coordinates and selected interatomic
distances and angles are listed in the supplementary
materials.
3. Results and discussion
3.1. Synthesis and spectroscopy
range of 4.368B
/
2u B508. At the end of the data
/
The chlorosilylamine precursors, RNHSi(Me)2Cl (1,
collection, the first 50 frames containing 231 reflections,
were re-collected to monitor crystal decay, which was
not observed, so that no time-decay corrections were
Rꢀ
/
t-Bu, 2, Rꢀ2,6-(Me2CH)2C6H3) were prepared in
/
71 and 68% yields, respectively, by the reaction of the
corresponding lithium amide with neat Me2SiCl2. The
excess dichlorodimethylsilane could easily be recycled by
simple distillation after completion of the reaction. The
reaction of nido-1-Na(C4H8O)-2,3-(SiMe3)2-2,3-C2B4H5
(3) with (t-Bu)NHSi(Me)2Cl (1) in a 1:1 mol ratio in
THF, followed by extraction and purification, produced
a new five-substituted small cage carborane, nido-5-(t-
Bu)NHSi(Me)2-2,3-(SiMe3)2-2,3-C2B4H5, (5) in 85%
yield, as shown in Scheme 1. Elemental analysis clearly
shows that a (t-Bu)NHSi(Me)2 moiety has been sub-
stituted for a terminal H in the molecule. The assign-
ment of amine substitution at the five-position is based
on our previous work that showed that the presence of
the bis(trimethylsilyl) groups on the cage carbons leads
exclusively to substitution at the five-position of the
nido-carborane cage for a variety of different alkyl
applied. Of 9670 reflections collected (4.368B
3626 reflections were considered as observed [Iꢀ
and were corrected for Lorentz, polarization and
absorption effects [17]. The structure was solved by
direct methods, and refined by full-matrix least-squares
techniques using SHELXTL [18]. All non-H atoms were
refined anisotropically. The cage H atoms, the phenyl
/
2u B
/
508),
/
2s(I)]
Table 1
Crystallographic data for 7
Empirical formula
Formula weight
Temperature (K)
C16H35B10NSi
377.64
173(2)
˚
Wavelength (A)
0.71073
monoclinic
P21/c
Crystal system
Space group
Unit cell dimensions
groups [19]. The 11B-NMR spectra showed peaks at dꢀ
50.22, 0.90 and 14.74 ppm in a 1:2:1 peak area ratio;
these are quite similar to the 1:2:1 peak area ratio
pattern at dꢀ 49.53, 1.09 and 14.51 ppm reported for
/
˚
a (A)
8.2357(19)
28.686(7)
9.921(2)
93.482(4)8
2339.5(9)
4
ꢁ
/
˚
b (A)
˚
c (A)
b (8)
/
ꢁ
/
3
˚
V (A )
nido-5-i-Bu-2,3-(SiMe3)2-2,3-C2B4H5 whose dimeric
monosodium compound has been structurally charac-
terized [19]. In addition, the 1H-NMR spectrum showed
Z
Density, calculated (Mg mꢁ3
)
1.072
0.103
808
Absorption coefficient (mmꢁ1
F(0 0 0)
)
only a single, broad signal for the BÃ
/
HÃ
/
B bridge
Crystal size (mm3)
0.10ꢄ
2.18ꢂ25.00
95h 59, ꢁ
115l 511
9670
/
0.10ꢄ0.08
/
hydrogen, consistent with Cs cage symmetry.
a
Theta range for data collection (8)
Index ranges
/
Although 5 can be produced in good yield, it is of
limited use as a constrained geometry ligand. Attempts
to deprotonate the ligand with soluble bases, such as
ꢁ
ꢁ/
/
/
/
/185
/
k 534,
/
/
/
Reflections collected
BuLi, and with NaH resulted in the cleavage of the BÃ
/
Si
Independent reflections
3626 [Rint
88.1
ꢀ0.0303]
/
Completeness to thetaꢀ
Absorption correction
/25.008 (%)
bond. Reaction of the neutral ligand with the metalating
agent, Zr(NMe2)4, lead to reaction, with all groups still
attached to the ligand. However, the spectra were quite
complex, indicating a formation of a mixture of
products that could not be separated.
Semi-empirical from equiva-
lents
Max./min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
1.000, 0.660111
Full-matrix least-squares on F2
3626/0/289
1.372
1-R?-2-[Si(Me)2N(H)R]-1,2-C2B10H10 (6, Rꢀ
R?ꢀPh; 7, Rꢀ2,6-(Me2CH)2C6H3, R?ꢀH) was pre-
pared by the reaction of the salt, Li[1-R?-1,2-C2B10H10]
(R?ꢀPh or H) with N(R)HSi(Me)2Cl (1, Rꢀt-Bu; 2,
Rꢀ2,6-(Me2CH)2C6H3), as outlined in Scheme 2. The
yield of this reaction was quite dependent on both the
/t-Bu,
Final R indices [I ꢀ
/
2s(I)]
R1ꢀ
R1ꢀ
0.0010(6)
0.388 and ꢁ0.359
/0.0736, wR2ꢀ
/
0.1494
/
/
/
R indices (all data)
Extinction coefficient
/0.0752, wR2ꢀ
/0.1502
/
/
Largest difference peak and hole
/
3
˚
/
(e A )

178
J. Wang et al. / Journal of Organometallic Chemistry 680 (2003) 173ꢂ181
/
Scheme 1. Synthesis of 5.
solvent and the temperature, in toluene at ꢁ
/
78 8C the
influence of the size of the pendant nitrogen group on
the lability of the other ligands on the capping metal
atom in complexes such as 9 and 10. The carbons apart
yields were 92 and 96% for 6 and 7, respectively. On the
other hand, when the reaction was carried out in THF, a
number of side products were formed that were difficult
to remove, resulting in both lower yields and products of
lower purity. This somewhat complicates the synthetic
procedure in that, although lithiation of the closo-1-R-
1,2-C2B10H11 precursor is carried out in THF, it must be
replaced by toluene for the reaction with
N(R)HSi(Me)2Cl to give 6 and 7. The closo-compound,
[1-(2,6-diisopropanylanilinyldimethylsilyl)-1,2-
structures for 8ꢂ10, shown in Scheme 3, were assigned
/
on the basis of the structural analysis of the nido-
carborane products of the reactions of closo-1,2-
(C6H5CH2)2-1,2-C2B10H10 with a number of Group 1
metals, by Xie and coworkers [20], and on the assump-
tion that metalation would not lead to cage isomeriza-
tion. The NMR spectra, as well as the chemical analyses,
of compounds 8ꢂ10 are consistent with their formula-
/
C2B10H11] (7) was reductively opened with sodium
naphthalide in THF to give the corresponding carbons
tions. For example, the 1H-NMR spectra of these
compounds show resonances for both the silicon-bound
and carbon-bound methyl groups as well as for the i-
propyl and phenyl hydrogens. However, it is significant
apart
trianion,
[nido-3-{Si(Me)2N(2,6-
(Me2CH)2C6H3)}-1,3-C2B10H11]3ꢁ (8) (see Scheme 3),
in 90% yield. The trianion, 8, could be reacted further
that the resonances attributable to N-bound hydrogens
1
with MCl4 (Mꢀ
metallacarboranes, closo-1-M[(Cl)(THF)n]-2-[1?-h1s-
N(2,6-(Me2CH)2C6H3)(Me)2Si]-2,4-h6-C2B10H11 (Mꢀ
Ti, nꢀ0 (9); MꢀZr, nꢀ1 (10)) in 47 and 36% yields,
/
Ti and Zr) in THF to give the
are absent in the H-NMR spectra of 8ꢂ
/
10. While the
11B-NMR spectroscopy proved very useful in elucidat-
ing the structure of 5, it is of limited help as a structural
/
/
/
/
probe for 8ꢂ
10. Consequently, the 11B-NMR spectra of
/
respectively. The lower coordination number of the Ti in
9, compared with that of Zr in 10, is most likely due to
smaller size of the former metal atom. A large group
such as the 2,6-diisopropanylanilinyldimethylsilyl
should increase the lability of the other ligands around
the titanium to the extent that its fourth coordination
site is vacant in 9. Advantage could be taken of the
these compounds consisted of a series of broad, over-
lapping peaks that were difficult to interpret in terms of
specific boron resonances. This same ambiguity was
noted in the 11B-NMR spectra of a number of Group 1
salts of [(C6H5CH2)2C2B10H10]2ꢁ dianion reported by
Xie and coworkers [20]. Further characterization of 8ꢂ
/
Scheme 2. Syntheses of 6 and 7.

J. Wang et al. / Journal of Organometallic Chemistry 680 (2003) 173ꢂ
/181
179
Scheme 3. Cage opening and metalation of 7.
10 must await their X-ray analyses. We are presently
attempting to grow suitable crystals for this purpose.
C(02) to 1148 for NÃ
aspect of this structure is the large C(1)Ã
125.5(2)8. This is most likely due to the repulsion
between the SiÃMe groups and the large diisopropyl-
/
SiÃ
/
C(03/04). The most interesting
/
NÃSi angle of
/
/
3.2. X-ray analysis of 7
phenyl moiety. Such an angle indicates that the lone pair
on nitrogen atom would not be particularly available for
bonding. However, from the formulations of 9 and 10, it
seems that h1-coordination of the N is possible after
removal of its H to form the amido group.
The
closo-2-[Si(Me)2NH(2,6-(Me2CH)2C6H3)]-1,2-
C2B10H11 (7) is a key synthon in the production of the
constrained geometry metallacarboranes, 9 and 10. Of
special concern is the availability of the amine nitrogen
to form additional bonds with the capping metals.
Compounds 8ꢂ10 have not as yet been structurally
/
characterized, however, the crystal structure of 7 could
be obtained and is shown in Fig. 1. Table 1 gives the
pertinent crystallographic information and some se-
lected bond distances and angles are given in the caption
for Fig. 1. A more complete listing of bond distances
and angles, as well as the atomic coordinates are given in
Section 5. The structure of 7 shows that it consists of a
closed C2B10 polyhedron with a distorted icosahedral
cage geometry. The intracage bond distances are quite
similar to those reported for closo-1-(methyl)-2-(phtha-
limidomethyl)-1,2-C2B10H10 [21]. The exo-polyhedral
Si(Me)2NH(2,6-(Me2CH)2C6H3) group in 7 is attached
4. Conclusions
We have prepared and characterized two new con-
strained geometry carborane ligands, nido-5-t-BuNH-
Si(Me)2-2,3-(SiMe3)2-2,3-C2B4H5 (5) and [Naꢃ-
(THF)n]3[nido-3-{Si(Me)2N(2,6-(Me2CH)2C6H3)}-1,3-
C2B10H11]3ꢁ (8). Compound 5 proved of limited use as
a ligand since it could not withstand deprotonation with
a strong base. Reaction of 5 with M(NMe2)4 (MꢀZr
/
and Ti) lead to reaction and possible metalation, but no
characterizable products could be isolated. On the other
hand, [Naꢃ(THF)n]3[nido-3-{Si(Me)2N(2,6-(Me2CH)2-
C6H3)}-1,3-C2B10H11]3ꢁ (8) reacted with MCl4 (Mꢀ
to a cage carbon by a standard 2c2e bond. The SiÃ
/
˚
C(02) bond distance of 1.911(3) A in this compound is
/
˚
C bond distances of 1.869(6) A in
larger than SiÃ
/
Ti, Zr) to give the respective metallacarboranes, closo-
1 - M[(Cl)(THF)n] - 2 - [1? - h1s - N(2,6 - (Me2CH)2C6H3)-
(C5Me4SiMe2N-t-Bu)Ti(prone-2,4-hexadiene) [22], and
in h5:s-Me2Si(C9H6)-h6-(C2B10H10CH2-
1.861(6)
(Me)2Si]-2,4-h6-C2B10H11 (Mꢀ
/
Ti, nꢀ
/
0 (9); MꢀZr,
/
˚
A
NMe)Zr(NC5H5) [23]. The four groups on the silicon
atom are in a distorted tetrahedral arrangement, with
nꢀ/1 (10)), in moderate yields. The metallacarboranes
were characterized by NMR spectra and elemental
analyses.
the XÃ
/
SiÃ
/
Y angles ranging from 103.538 for NÃ
/
SiÃ
/

180
J. Wang et al. / Journal of Organometallic Chemistry 680 (2003) 173ꢂ181
/
Fig. 1. Perspective view of 7 with thermal ellipsoids drawn at the 50% probability level and showing the atomic numbering scheme. Selected bond
˚
lengths (A) and angles (8) are: SiÃ
B(1)ÃC(01) 1.699(5), B(1)ÃC(02) 1.722(5), B(4)Ã
113.73(15), C(04)ÃSiÃC(03) 107.99(18), C(1)ÃNÃ
/
N 1.717(3), SiÃ
C(01) 1.706(5), B(4)Ã
Si 125.5(2).
/
C(02) 1.911(3), NÃ
/
C(1) 1.439(4), SiÃ
/
C(04) 1.848(4), SiÃ
SiÃN, 103.53(14), C(04)Ã
/
C(03) 1.853(3), C(01)Ã
/
C(02) 1.653(4),
N
/
/
/
/
C(02) 1.726(5); C(02)Ã
/
/
/
SiÃN 114.12(16), C(03)Ã
/
/
SiÃ
/
/
/
/
/
[5] P.J. Shapiro, W.D. Cotter, W.P. Schaefer, J.A. Labinger, J.E.
Bercaw, J. Am. Chem. Soc. 116 (1994) 4623.
[6] (a) Y.-X. Chen, P.-F. Fu, C.L. Stern, T.J. Marks, Organometallics
16 (1997) 5958;
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 204610 for compound 7.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 IEZ, UK (Fax: ꢃ44-1223-336033 or e-
mail: deposit@ccdc.cam.ac.uk or web: http://
www.ccdc.cam.ac.uk).
(b) K. Kunz, G. Erker, S. Doring, R. Frohlich, G. Kehr, J. Am.
¨ ¨
Chem. Soc. 123 (2001) 6181.
[7] (a) G.P. Abramo, L. Li, T.J. Marks, J. Am. Chem. Soc. 124 (2002)
13966;
(b) L. Li, M.V. Metz, H. Li, M.-C. Chen, T.J. Marks, L. Liable-
Sands, A.L. Rheingold, J. Am. Chem. Soc. 124 (2002) 12725.
[8] R.N. Grimes, in: E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.),
Comprehenswive Organometallic Chemistry II, vol. 1, Elsevier
/
Science, Oxford, UK, 1995, pp. 373ꢂ
/
430 (Chapter 9)
For reference see
[9] T. Doge, M.A. Curtis, J.M. Russell, M. Sabat, M.G. Finn, R.N.
Grimes, J. Am. Chem. Soc. 122 (2000) 10573.
Acknowledgements
[10] (a) D.J. Crowther, N.C. Baenziger, R.F. Jordan, J. Am. Chem.
Soc. 113 (1991) 1455;
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 JAM) and Northern
Illinois University through a Presidential Research
Professorship. The Forschungspreis der Alexander von
Humboldt-Stiftung and the nominating Professor, Dr.
(b) S. Saccheo, G. Gioia, A. Grassi, D.E. Bowen, R.F. Jordan, J.
Mol. Catal. A 128 (1998) 111.
[11] G.C.’ Bazan, W.P. Schaefer, J.E. Bercaw, Organometallics 12
(1993) 2126.
[12] (a) D.-H. Kim, J.H. Won, S.-J. Kim, J. Ko, S.H. Kim, S. Cho,
S.O. Kang, Organometallics 20 (2001) 4298;
(b) J.-S. Park, D.-H. Kim, S.-J. Kim, J. Ko, S.H. Kim, S. Cho, C.-
H. Lee, S.O. Kang, Organometallics 20 (2001) 4483;
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