Chemistry of C-trimethylsilyl-substituted heterocarboranes. 22. Synthetic, spectroscopic, structural, and bonding studies on half- and full-sandwich gallacarboranes of 2,3- and 2,4-C2B4 carborane ligand systems

Article abstract of DOI:10.1021/om970555b

The reaction of the TMEDA-solvated group 1 salts of the carborane dianions [2,n-(SiMe₃)₂-2,n-C₂B₄H ₄]^2- (n = 3, 4) with GaC1₃ in a 2:1 carborane-to-GaCl₃ molar ratio gave the corresponding full-sandwich gallacarboranes [2,2′,n,n′-(SiMe₃) ₄-1,1′-commo-Ga(1,2,n-GaC₂B₄H ₄)₂]^- (n = 3 (I), 4 (II)) in 36% and 38% yields, respectively. Lowering the carboraneto-GaCl₃ molar ratio to 1:1 produced the half-sandwich chlorogallacarboranes 1-(TMEDA)-1-Cl-2,n-(SiMe₃)₂-1,2,n-GaC₂B ₄H₄ (n = 3 (III), 4 (IV)) in 51% and 41% yields, respectively. Compounds I-IV were characterized on the basis of¹H, ¹¹B, and ¹³C NMR spectra, IR spectra, and single-crystal X-ray analyses. The structures of the gallacarboranes show that the gallium atoms are not equally bonded to the atoms in the C₂B₃ faces of the carboranes but are slipped toward the more boron rich sides of the faces. Slippages in I and II are such that maximum differences in the Ga-C₂B₃ distances were 0.34 ? in I and 0.45 ? in II. The distortions were much larger in III and IV such that the carboranes are better described as being η³- and η²-bonded, respectively.

Full text of DOI:10.1021/om970555b

Organometallics 1997, 16, 5163-5170
5163
Ch em istr y of C-Tr im eth ylsilyl-Su bstitu ted
Heter oca r bor a n es. 22. Syn th etic, Sp ectr oscop ic,
Str u ctu r a l, a n d Bon d in g Stu d ies on Ha lf- a n d
F u ll-Sa n d w ich Ga lla ca r bor a n es of 2,3- a n d 2,4-C B
2
4
Ca r bor a n e Liga n d System s
,
†
Narayan S. Hosmane,* Kai-J uan Lu, Hongming Zhang, and J ohn A. Maguire
Department of Chemistry, Southern Methodist University, Dallas, Texas 75275
Received J uly 1, 1997X
3 2
The reaction of the TMEDA-solvated group 1 salts of the carborane dianions [2,n-(SiMe ) -
2
-
2
,n-C
2
B
4
H
4
]
(n ) 3, 4) with GaCl
3
in a 2:1 carborane-to-GaCl
3
molar ratio gave the
-1,1′-commo-Ga(1,2,n-
corresponding full-sandwich gallacarboranes [2,2′,n,n′-(SiMe
3
)
4
-
GaC
to-GaCl
-Cl-2,n-(SiMe
2
B
4
H
4
)
2
] (n ) 3 (I), 4 (II)) in 36% and 38% yields, respectively. Lowering the carborane-
molar ratio to 1:1 produced the half-sandwich chlorogallacarboranes 1-(TMEDA)-
-1,2,n-GaC
3
1
3
)
2
2 4 4
B H (n ) 3 (III), 4 (IV)) in 51% and 41% yields, respectively.
1
11
13
Compounds I-IV were characterized on the basis of H, B, and C NMR spectra, IR spectra,
and single-crystal X-ray analyses. The structures of the gallacarboranes show that the
gallium atoms are not equally bonded to the atoms in the C
are slipped toward the more boron rich sides of the faces. Slippages in I and II are such
that maximum differences in the Ga-C distances were 0.34 Å in I and 0.45 Å in II. The
distortions were much larger in III and IV such that the carboranes are better described as
2 3
B faces of the carboranes but
2
B
3
3
2
being η - and η -bonded, respectively.
In tr od u ction
occupy the apical positions above the C2B3 pentagonal
faces of the carboranes but are slightly slipped toward
the boron atoms of these faces. Each gallium is also
bound to an alkyl group that is oriented over the
adjacent cage carbons of the carborane. The metal
atoms have been found to act as Lewis acid sites, and a
number of complexes have been reported between the
half-sandwich gallacarboranes and bidentate bases such
Although the metallacarborane complexes of gallium
in both the C2B9 and C2B4 cage systems have been the
subject of a number of investigations,1 thus far, the
results have been quite uneven. The only report of an
icosahedral gallacarborane is that from Hawthorne and
co-workers on the synthesis and structure of the full-
sandwich gallacarborane Tl[commo-3,3′-Ga(3,2,1-
GaC2B9H11)2].2 No half-sandwich complexes in this
ligand system are known. J ust the opposite is true in
as 2,2′-bipyridine and 2,2′-bipyrimidine, as well as the
4-7
tridentate base 2,2′:6′,2′′-terpyridine.
Similar ad-
ducts have been found between these same Lewis bases
the smaller, C2B4 cage system, where only half-
and the gallium atom in the isomeric carbons-apart
sandwich complexes have been reported.3
-7
The struc-
gallacarborane 1-(t-C4H9)-2,4-(SiMe3)2-1,2,4-GaC2B4H4.7
tures of the carbons-adjacent complexes 1-Me-1,2,3-
GaC2B4H6 and 1-(t-C4H9)-2,3-(SiMe3)2-1,2,3-GaC2B4H4
show that the gallium atoms, in formal +3 states,
In all cases, the gallium-alkyl bond seems quite stable
and there was no hint of the formation of either the full-
sandwich gallacarborane or half-sandwich complexes in
which the alkyl group had been substituted. However,
our report on the synthesis of the novel digallane
complex closo-1-Ga[σ-closo-1-Ga-2,4-(SiMe3)2-2,4-C2B4H4]-
3
4
†
Camille and Henry Dreyfus Scholar.
Abstract published in Advance ACS Abstracts, November 1, 1997.
1) (a) Hosmane, N. S. Pure Appl. Chem. 1991, 63, 375. (b) Saxena,
X
(
8
A. K.; Maguire, J . A.; Banewicz, J . J .; Hosmane, N. S. Main Group
Chem. News 1993, 1, 14. (c) Hosmane, N. S.; Maguire, J . A. Adv.
Organomet. Chem. 1990, 30, 99. (d) Hosmane, N. S.; Maguire, J . A. J .
Cluster Sci. 1993, 4, 297. (e) Hosmane, N. S. In Main Group Elements
and Their Compounds; Kumar Das, V. G., Ed.; Narosa/Springer-
Verlag: New Delhi, India, 1996, p 299. (f) Saxena, A. K.; Maguire, J .
A.; Hosmane, N. S. Chem. Rev. 1997, 97, 2421.
2) (a) Schubert, D. M.; Bandman, M. A.; Rees, W. S., J r.; Knobler,
C. B.; Lu, P.; Nam, W.; Hawthorne, M. F. Organometallics 1990, 9,
046. (b) Bandman, M. A.; Knobler, C. B.; Hawthorne, M. F. Inorg.
Chem. 1989, 28, 1204.
3) Grimes, R. N.; Rademaker, W. J .; Denniston, M. L.; Bryan, R.
F.; Greene, P. T. J . Am. Chem. Soc. 1972, 94, 1865.
4) Hosmane, N. S.; Lu, K.-J .; Zhang, H.; J ia, L.; Cowley, A. H.;
Mardones, M. A. Organometallics 1991, 10, 963.
5) Hosmane, N. S.; Zhang, H.; Lu, K.-J .; Maguire, J . A.; Cowley, A.
H.; Mardones, M. A. Struct. Chem. 1992, 3, 183.
6) Maguire, J . A.; Hosmane, N. S.; Saxena, A. K.; Zhang, H.; Gray,
T. G. Phosphorus, Sulfur and Silicon Relat. Elem. 1994, 87, 129.
7) Hosmane, N. S.; Saxena, A. K.; Lu, K. -J .; Maguire, J . A.; Zhang,
2,4-(SiMe3)2-2,4-C2B4H4 raised the question as to
whether it would be possible to develop synthetic
methods to further react the half-sandwich gallacarbo-
ranes and prepare, in reasonable yields, either full-
sandwich compounds or metal-metal-bonded half-
sandwich gallacarboranes. One possible approach is to
prepare compounds having better leaving groups, such
as halogens, bound to the apical gallium atoms. It was
this possibility that led us to investigate the reactions
(
2
(
2-
of the [2,n-(SiMe3)2-2,n-C2B4H4] ligands with GaCl3,
(
under various conditions, to produce a series of hitherto
unknown half-sandwich chlorogallacarborane complexes
as well as the full-sandwich gallacarboranes. A later
report will detail the reactivities of the chlorogallacar-
boranes.
(
(
(
H.; Wang, Y.; Thomas, C. J .; Zhu, D.; Grover, B. R.; Gray, T. G.;
Eintracht, J . F.; Isom, H.; Cowley, A. H. Organometallics 1995, 14,
(8) Saxena, A. K.; Zhang, H.; Maguire, J . A.; Hosmane, N. S.; Cowley,
A. H. Angew. Chem., Int. Ed. Engl. 1995, 34, 332.
5
104.
S0276-7333(97)00555-4 CCC: $14.00 © 1997 American Chemical Society

5
164 Organometallics, Vol. 16, No. 24, 1997
Ta ble 1. F T NMR Sp ectr a l Da ta for Ga lla ca r bor a n es I-IVa
Hosmane et al.
δ, splitting, assignt ( J ( B- H) or 1J (13C- H), Hz)
1
11
1
1
rel area
compd
00.13 MHz H NMR Datab
1
2
I
II
III
IV
2.20, br overlapping, TMEDA; 2.05, br overlapping, TMEDA; 0.54, s, SiMe3
2.37, s, TMEDA; 2.23, s, TMEDA; 0.09, s, SiMe3
2.35, br, TMEDA; 2.02, br, TMEDA; 0.66, s, SiMe3
2:6:9
2:6:9
2:6:9
2:6:9
2.21, v br, TMEDA; 2.05, v br, TMEDA; 0.52, s, br, SiMe3
6
4.21 MHz 11B NMR Datac
I
II
III
IV
14.25, v br, basal BH (unresolved); -1.90, v br, basal BH (unresolved); -46.24 , v br, apical BH (unresolved)
22.5, v br, basal BH (unresolved); 4.55, v br, basal BH (unresolved); -47.46, d, apical BH (188.7)
14.29, v br, basal BH (unresolved); -2.26, v br, basal BH (unresolved); -47.67, d, apical BH (145)
24.02, v br, basal BH (unresolved); 6.01, v br, basal BH (unresolved); -46.27, d, br, apical BH (134.3)
2:1:1
1:2:1
2:1:1
1:2:1
5
0.32 MHz 13C NMR Datab,d
I
II
III
IV
117.77, s, cage C (SiCB); 56.85, t, CH2 (133.2); 46.05, q, Me (134.6); 3.02, q, SiMe3 (118.9)
99.92, s(br), cage C (SiCB); 56.72, t, CH2 (130.45); 45.80, q, Me (133.8); 1.61, q, SiMe3 (117.2)
118.32, s, cage C (SiCB); 57.07, t, br, CH2 (123.3); 45.97, q, Me (130.2); 3.02, q, v br, SiMe3 (118.2)
101.8, s(br), cage C (SiCB); 56.17, t, br, CH2 (132.3); 48.23, q, br, Me (130); 1.79, q, br, SiMe3 (119)
1:1:2:3
1:1:2:3
1:1:2:3
1:1:2:3
a
1
C6D6 was used as solvent and an internal standard at δ 7.15 ppm (in the H NMR spectra) with a positive sign indicating a downfield
shift. Legend: s ) singlet, d ) doublet, t ) triplet, q ) quartet, v ) very, br ) broad. Shifts relative to external Me4Si. c Shifts relative
b
d
to external BF3‚OEt2. Since relaxation of a quaternary carbon is much slower than that of a CH unit, the relative areas of the substituted
carbons of the cage could not be measured accurately.
described elsewhere,11 a 2.624 g (11.94 mmol) sample of nido-
,3-(SiMe -2,3-C was first reacted in vacuo with an
excess quantity (0.417 g, 17.38 mmol) of NaH in a 1:1 mixture
20 mL) of TMEDA and benzene at room temperature for 6 h,
to produce the corresponding TMEDA-solvated dimeric mono-
sodium compound [1-Na(TMEDA)-2,3-(SiMe -2,3-C
After purification, the monosodium compound was dissolved
in a 1:1 mixture (20 mL) of anhydrous TMEDA and benzene
and was further reacted with a pentane solution of t-BuLi (7.03
mL of a 1.7 M solution, 11.95 mmol) in vacuo at 0 °C and then
warmed to room temperature to obtain a pale orange solution
of the mixed Na/Li compound exo-Li(TMEDA)-1-Na(TMEDA)-
Exp er im en ta l Section
2
3
)
2
2 4 6
B H
Ma ter ia ls. 2,3-Bis(trimethylsilyl)-2,3-dicarba-nido-hexabo-
rane(8) and 1,2-bis(trimethylsilyl)-1,2-dicarba-closo-hexabo-
(
rane(6) were prepared using the literature methods.9
-11
The
closo-carborane was subsequently converted to the correspond-
ing N,N,N′,N′-tetramethylethylenediamine (TMEDA)-solvated
carbons-apart dinatracarborane closo-exo-5,6-[(µ-H)
3
)
2
2 4 5 2
B H ] .
2
Na-
by reduc-
Prior to use,
(
TMEDA)]-1-Na(TMEDA)-2,4-(SiMe
3
)
2
-2,4-C
2
1
B
4
H
4
2
tion with Na/C10
H
8
as outlined previously.
TMEDA (Aldrich) was distilled in vacuo and stored over
sodium metal and its purity was checked by IR and NMR
spectra and boiling point measurements. Before use, naph-
thalene (Aldrich) was sublimed in vacuo, Na metal (Aldrich)
2
,3-(SiMe
3
)
2
-2,3-C
2
B
4
H
4
. This solution was then poured, in
(1.051 g, 5.97
vacuo, into a benzene (5 mL) solution of GaCl
3
3
was freshly cut in a drybox, and anhydrous GaCl (Strem
mmol) at 0 °C. The resulting heterogeneous mixture was
stirred constantly at room temperature overnight, during
which time it turned gray to off-white. The mixture was
filtered in vacuo, and the residue on the frit was washed
several times with benzene to collect a clear filtrate. The solid
residue, identified by qualitative analyses as a mixture of
NaCl, LiCl, and elemental Ga (not measured), was discarded.
After removal of all the solvents from the filtrate, a slightly
colored semisolid residue remained in the flask. Anhydrous
dry benzene (20 mL) was then condensed into this flask, and
the resulting mixture was stirred constantly for 2 h. At this
point, the stirring was stopped; the mixture was allowed to
stand overnight and then filtered in vacuo to collect a clear
filtrate. Upon slow removal of benzene from the filtrate, in
Chemicals) was heated at 120 °C in vacuo overnight to remove
any last traces of moisture in the sample. Benzene, THF, and
n-hexane were dried over LiAlH and doubly distilled; all other
4
solvents were dried over 4-8 mesh molecular sieves (Aldrich)
and either saturated with dry argon or degassed before use.
Sp ectr oscop ic a n d An a lytica l P r oced u r es. Proton,
boron-11, and carbon-13 pulse Fourier transform NMR spectra,
at 200, 64.2, and 50.3 MHz, respectively, were recorded on an
IBM-WP200 SY multinuclear NMR spectrometer. Infrared
spectra were recorded on a Nicolet Magna 550 FT-IR spectro-
photometer. Elemental analyses were obtained from E+R
Microanalytical Laboratory, Inc., Corona, NY.
Syn th etic P r oced u r es. All experiments were carried out
in Pyrex glass round-bottom flasks of 100-250 mL capacities,
containing magnetic stirring bars and fitted with high-vacuum
Teflon valves. Nonvolatile substances were manipulated in
either a drybox or an evacuable glovebag under an atmosphere
of dry nitrogen. All known compounds among the products
were identified by comparing their IR and NMR spectra with
those of authentic samples.
vacuo, colorless crystals identified as [Li(TMEDA)
2
][2,2′,3,3′-
(
SiMe -1,1′-commo-Ga(1,2,3-GaC ] (I) (1.591 g, 2.137
3
)
4
2 4 4 2
B H )
mmol, 36% yield) were obtained. The anionic full-sandwich
carbons-adjacent gallacarborane I (mp 248 °C) is soluble in
both polar and nonpolar organic solvents. Anal. Calcd for
C
4
28
H
76
B
8
Si
5.11; H, 10.26; N, 7.46. The NMR and IR spectral data for I
are given in Tables 1 and 2, respectively.
Syn th esis of [Na(TMEDA) ][2,2′,4,4′-(SiMe
Ga (1,2,4-Ga C ] (II). A sample of the TMEDA-solvated
dinatracarborane closo-exo-5,6-[(µ-H) Na(TMEDA)]-1-Na(T-
MEDA)-2,4-(SiMe -2,4-C was prepared from the reac-
tion of 1.16 g (5.33 mmol) of closo-1,2-(SiMe -1,2-C with
4 4
N GaLi: C, 45.18; H, 10.28; N, 7.53. Found: C,
Syn th esis of [Li(TMEDA)
2 3 4
][2,2′,3,3′-(SiMe ) -1,1′-commo-
Ga (1,2,3-Ga C ] (I). In a procedure identical with that
2
4 4 2
B H )
2
3 4
) -1,1′-commo-
(9) (a) Hosmane, N. S.; Sirmokadam, N. N.; Mollenhauer, M. N. J .
2 4 4 2
B H )
Organomet. Chem. 1985, 279, 359. (b) Hosmane, N. S.; Mollenhauer,
M. N.; Cowley, A. H.; Norman, N. C. Organometallics 1985, 4, 1194.
2
3
)
2
2 4 4
B H
(
c) Barreto, R. D.; Hosmane, N. S. Inorg. Synth. 1992, 29, 89.
3
)
2
2 4 4
B H
(10) Hosmane, N. S.; Barreto, R. D.; Tolle, M. A.; Alexander, J . J .;
Quintana, W.; Siriwardane, U.; Shore, S. G.; Williams, R. E. Inorg.
Chem. 1990, 29, 2698.
0.25 g (10.87 mmol) of freshly cut Na metal and 0.683 g (5.33
mmol) of naphthalene in a 1:1 solvent mixture (20 mL) of
(11) Hosmane, N. S.; Saxena, A. K.; Barreto, R. D.; Zhang, H.;
12
TMEDA and benzene at 25 °C as described elsewhere. After
Maguire, J . A.; J ia, L.; Wang, Y.; Oki, A. R.; Grover, K. V.; Whitten, S.
J .; Dawson, K.; Tolle, M. A.; Siriwardane, U.; Demissie, T.; Fagner, J .
S. Organometallics 1993, 12, 3001.
it was separated from naphthalene, the TMEDA-solvated
dinatracarborane (2.64 g, 5.32 mmol), isolated as a brown solid,
was transferred to a reaction flask containing a magnetic
(12) (a) Hosmane, N. S.; J ia, L.; Zhang, H.; Bausch, J . W.; Prakash,
G. K. S.; Williams, R. E.; Onak, T. P. Inorg. Chem. 1991, 30, 3793. (b)
J ia, L. M.S. Thesis, Southern Methodist University, Dallas, Texas,
stirring bar. A benzene (20 mL) solution of GaCl
.66 mmol) was slowly poured, in vacuo, onto the solid
dinatracarborane at 0 °C, and the resulting heterogeneous
3
(0.469 g,
2
1
992. (c) Zhang, H.; Wang, Y.; Saxena, A. K.; Oki, A. R.; Maguire, J .
A.; Hosmane, N. S. Organometallics 1993, 12, 3933.

C-Trimethylsilyl-Substituted Heterocarboranes
Organometallics, Vol. 16, No. 24, 1997 5165
elsewhere and above in the synthesis of II,12 a 5.00 mmol (1.09
g) sample of closo-1,2-(SiMe ) -1,2-C B H was reacted over-
3 2 2 4 4
night at 25 °C with 0.23 g (10.0 mmol) of freshly cut Na metal
and 0.641 g (5.00 mmol) of freshly sublimed naphthalene in a
Ta ble 2. In fr a r ed Absor p tion s for Ga lla ca r bor a n es
-
1
a
I-IV (cm ; C
absorption
3101 (vs), 3077 (vs), 3041 (vs) [ν(C-H)], 2543 (br, m),
6
D
6
vs C
6
D
6
)
compd
I
1
:3 mixture of dry TMEDA and dry benzene, to produce the
corresponding carbons-apart disodium compound closo-exo-5,6-
(µ-H) Na(TMEDA)]-1-Na(TMEDA)-2,4-(SiMe -2,4-C . Af-
2
1
1
4
494 (w) [ν(B-H)], 1821 (ms), 1648 (w), 1518 (w),
481 (vs), 1335 (br, m), 1252 (w), 1135 (m), 1036 (vs),
011 (m), 943 (m), 838 (m), 764 (w), 671 (vs),
86 (br, m)
[
2
3
)
2
2 4 4
B H
ter removal of all the solvents and naphthalene, the TMEDA-
solvated disodium compound was isolated as a brown crystalline
solid in near-quantitative yield (2.45 g, 4.94 mmol). This solid
was then transferred to a reaction flask containing a magnetic
II
2957 (vs), 2898 (vs), 2866 (ms), 2774 (ms) [ν(C-H)],
2
2
1
9
531 (vs) [ν(B-H)], 2354 (ms), 2262 (ms),
125 (m, br), 1886 (ms), 1561 (ms), 1508 (ms),
462 (vs), 1364 (ms), 1252 (vs), 1200 (ms), 1108 (ms),
84 (w), 839 (vs), 754 (ms), 636 (w), 551 (w, br)
stirring bar. At this point, a benzene (25 mL) solution of GaCl
0.881 g, 5.00 mmol) was slowly poured, in vacuo, onto the
3
(
III
IV
2957 (vs), 2898 (vs), 2859 (ms), 2762 (ms) [ν(C-H)],
disodium compound in the flask at 0 °C and the resulting
heterogeneous mixture was stirred at room temperature
overnight, during which time the mixture turned from brown
to a gray off-white. The mixture was filtered in vacuo to collect
a clear filtrate. The solid residue that remained on the frit
after several washings with anhydrous benzene, identified by
qualitative analyses as a mixture of NaCl and elemental Ga
2
1
1
5
556 (vs), 2551 (vs) [ν(B-H)], 1639 (ms), 1548 (ms),
515 (vs), 1456 (vs), 1284 (vs), 1253 (vs), 1102 (vs),
046 (ms), 921 (ms), 839 (ms), 786 (ms), 620 (ms),
84 (br, m)
2959 (vs), 2894 (ms) [ν(C-H)], 2534 (vs), 2501 (vs)
[ν(B-H)], 2357 (w), 1912 (br, m), 1546 (ms), 1506 (vs),
1
1
7
460 (vs), 1425 (vs), 1290 (ms), 1244 (vs), 1192 (ms),
107 (ms), 1074 (ms), 993 (ms), 924 (w), 839 (vs),
47 (ms), 623 (w), 577 (br, m)
(not measured), was discarded. The clear filtrate was con-
centrated in vacuo and then allowed to stand for several days
at room temperature; this resulted in the formation of trans-
parent crystals (0.898 g, 2.04 mmol, 41% yield), identified as
a
Legend: v ) very, s ) strong or sharp, m ) medium, w )
weak, sh ) shoulder, br ) broad.
1
-Cl-1-(TMEDA)-2,4-(SiMe
half-sandwich carbons-apart chlorogallacarborane IV (mp 142
C) is soluble in both polar and nonpolar organic solvents.
Anal. Calcd for C14 Si GaCl: C, 38.29; H, 8.74; N, 6.38.
3 2 2 4 4
) -closo-1,2,4-GaC B H (IV). The
mixture was stirred at room temperature overnight, during
which time it turned gray to off-white. At this point, the
mixture was filtered in vacuo to collect a clear filtrate. The
solid residue that remained on the frit after several washings
with anhydrous benzene was later identified by qualitative
analyses as a mixture of NaCl and elemental Ga (not mea-
sured) and was discarded. The clear filtrate was then con-
centrated in vacuo and allowed to stand for several days at
room temperature; this resulted in the formation of colorless
crystals (0.761 g, 1.00 mmol, 38% yield) that were identified
°
H
38
B
4
2 2
N
Found: C, 38.51; H, 8.58; N, 6.17. The NMR and IR spectral
data for IV are given in Tables 1 and 2, respectively.
X-r a y An a lyses of Ga lla ca r bor a n es I-IV. Colorless
transparent X-ray-quality crystals of the gallacarboranes I-IV
were grown very slowly from their respective benzene solu-
tions. These crystals were transferred to a drybox and placed
in a covered dish containing paraffin. After protection with
paraffin, the crystals were removed from the drybox, coated
with an epoxy resin in air, and then sequentially mounted on
a Siemens R3m/V diffractometer under a low-temperature
nitrogen stream. The pertinent crystallographic data and
conditions for data collection are summarized in Table 3. Final
unit cell parameters were obtained by a least-squares fit of
the angles of 24-30 accurately centered reflections in the 2θ
range from 16 to 32.0°. Intensity data were collected at 220
K using graphite-monochromated Mo KR radiation. Three
standard reflections were monitored during the data collection
and did not show any significant changes in intensities. The
data were corrected for Lorentz and polarization effects, and
absorption corrections were also applied. The structures were
as [Na(TMEDA)
GaC ] (II). The anionic full-sandwich carbons-apart
gallacarborane II (mp 197 °C) is soluble in both polar and
nonpolar organic solvents. Anal. Calcd for C28 Si
GaNa: C, 44.22; H, 10.07; N, 7.37. Found: C, 43.97; H,
0.04; N, 7.23. The NMR and IR spectral data for II are given
2 3 4
][2,2′,4,4′-(SiMe ) -1,1′-commo-Ga(1,2,4-
2
4 4 2
B H )
H
76
B
8
4
-
N
4
1
in Tables 1 and 2, respectively.
Syn t h esis of 1-Cl-1-(TME DA)-2,3-(SiMe ) -closo-1,2,3-
3 2
Ga C
elsewhere, a 1.464 g (6.66 mmol) sample of nido-2,3-(SiMe
,3-C was reacted in vacuo with 7.84 mL of a 1.7 M
2 4 4
B H (III). In a procedure identical with that described
1
1
3 2
) -
2
2 4 6
B H
pentane solution of t-BuLi (13.33 mmol) in a 1:1 mixture (20
mL) of TMEDA and benzene at 0 °C for 2 h, and then at room
temperature for 4 h, to produce the corresponding TMEDA-
1
3
solved by direct methods using the SHELXTL-Plus package
and subsequent Fourier syntheses. Full-matrix least-squares
refinements were performed for all four structures. Scattering
factors, as well as anomalous dispersion corrections for the
heavy atoms, were taken from ref 14. While the anionic
sandwich gallacarborane unit in I possesses a center of
symmetry, the TMEDA-solvated Li cation has a 2-fold sym-
metric axis which is parallel to the crystallographic b axis.
The structure of II is similar to that of I, with the exception
solvated dilithium compound closo-exo-4,5-[(µ-H)
2
Li(TMEDA)]-
1
-Li(TMEDA)-2,3-(SiMe -2,3-C , in essentially quanti-
3
)
2
2 4 4
B H
tative yield (3.08 g, 6.64 mmol). All of the dilithium compound
was redissolved in dry benzene (20 mL) and poured, in vacuo,
onto anhydrous GaCl (1.173 g, 6.66 mmol) in a reaction flask
3
at 0 °C. The resulting heterogeneous mixture was stirred
constantly at room temperature overnight, during which time
the mixture turned gray to off-white. The mixture was filtered
in vacuo, and the residue on the frit was washed with benzene
several times to collect a clear filtrate. The solid residue on
the frit, identified by qualitative analyses as a mixture of LiCl
and elemental Ga (not measured), was discarded. The clear
filtrate was concentrated in vacuo and then allowed to stand
for several days at room temperature to produce transparent
that the Li(TMEDA)
2 2
cation is replaced by a Na(TMEDA)
cationic unit. In I the TMEDA nitrogens surround the Li in
an approximately tetrahedral fashion, while in II the Na(T-
2
MEDA) unit is sufficiently distorted such that the Na and
the four nitrogens are almost coplanar. There are also 1.5
benzene molecules per gallacarborane sandwich molecule of
II found in the crystal lattice. On the other hand, the crystal
lattice of the half-sandwich chlorogallacarborane III contains
two solvated benzene molecules and has a mirror plane of
symmetry, with Ga, Cl, B(14), and B(16) residing on the mirror
crystals, identified as 1-Cl-1-(TMEDA)-2,3-(SiMe
GaC (III; 1.496 g, 3.41 mmol, 51% yield). The half-
sandwich carbons-adjacent chlorogallacarborane III (mp 186
C) is soluble in both polar and nonpolar organic solvents.
Anal. Calcd. for C14 Si GaCl: C, 38.29; H, 8.74; N, 6.38.
3 2
) -closo-1,2,3-
2
4 4
B H
°
plane. The methyl groups of the SiMe
3
moieties in III were
H
38
B
4
2 2
N
Found: C, 38.13; H, 8.80; N, 6.12. The NMR and IR spectral
data for III are given in Tables 1 and 2, respectively.
(
13) Sheldrick, G. M. Structure Determination Software Programs;
Siemens X-ray Analytical Instrument Corp., Madison, WI, 1991.
14) International Tables For X-ray Crystallography; Kynoch
Press: Birmingham, U.K., 1974, Vol. IV.
Syn t h esis of 1-Cl-1-(TME DA)-2,4-(SiMe
3 2
) -closo-1,2,4-
(
Ga C (IV). In a procedure identical with that described
2
4 4
B H

5
166 Organometallics, Vol. 16, No. 24, 1997
Ta ble 3. Cr ysta llogr a p h ic Da ta a for Ga lla ca r bor a n es I-IV
II III
Hosmane et al.
I
IV
formula
fw
C28H76N4B8Si4LiGa [C28H76N4B8Si4NaGa]‚1.5C6H6 [C14H38N2B4Si2ClGa]‚2C6H6 [C14H38N2B4Si2ClGa]‚C6H6
744.4
877.6
595.3
517.2
space group
a, Å
b, Å
C2/c
P21/c
Cm
P212121
12.085(1)
12.702(1)
19.280(2)
90
2959.4(5)
4
1.161
20.924(9)
11.927(5)
19.349(9)
90.87(3)
4821(3)
4
13.512(4)
18.048(8)
22.433(9)
92.23(2)
5710(4)
4
9.927(5)
18.621(9)
9.768(5)
103.99(3)
1752(2)
2
c, Å
â, deg
3
V, Å
Z
-
3
Dcalcd, g cm
1.026
0.692
1.021
0.600
1.128
0.947
-
1
abs coeff, mm
1.111
crystal dmns, mm
scan type
scan sp in ω: min, max 6.51, 29.30
ω0 . /12 5θ × 0.35 × 0.30 ω0 . /22 0θ × 0.30 × 0.10
ω0 . /32 0θ × 0.35 × 0.10
6.0, 30.0
3.5-44.0
220
θ0 /. 23 θ5 × 0.25 × 0.10
3.5, 35.0
3.5-46.0
230
5.0, 30.0
3.0-42.0
230
2
T, K
θ range, deg
3.5-44.0
230
decay, %
0
0
0
0
no. of data collected
no. of obsd rflns,
F > 6.0σ(F)
3063
1289
5736
1391
1160
923
2336
2060
no. of params refined
210
251
167
287
GOF
1.56
0.40, -0.26
0.061
1.37
0.36, -0.32
0.067
1.88
0.68, -0.64
0.065
1.28
0.38, -0.50
0.036
3
∆
R
Fb max,min, e/Å
c
Rw
0.073
0.075
0.081
0.052
a
Graphite-monochromatized Mo KR radiation, λ ) 0.710 73 Å. b R ) ∑||Fo| - |Fc||/∑|Fo|, Rw ) [∑w(Fo - Fc) /∑w(Fo) ]1/ 2. c w ) 1/[σ (Fo)
2
2
2
2
+
0.001(Fo) ].
disordered with occupancy factors of 55% for C(21), C(22), and
Resu lts a n d Discu ssion
C(23) and 45% for C(211), C(221), and C(231). There was one
solvated benzene molecule per half-sandwich chlorogallacar-
borane in the unit cell of IV. The positions of the methyl,
methylene, and benzene H atoms in all four structures were
calculated using a riding model. All cage H atoms were located
in difference Fourier maps and, with the exception of IV, were
not refined. The hydrogen atoms of the carborane cage in IV
were refined with their isotropical thermal parameters as a
Syn th esis. The half- and full-sandwich gallacarbo-
ranes were synthesized in basically the same manner,
that is, from the reaction of the appropriate [2,n-
2
-
(SiMe ) -2,n-C B H ] (n ) 3, 4) dianionic ligand with
3
2
2
4
4
GaCl3 (see Scheme 1). The nature of the product was
independent of the isomeric form of the carborane and
the nature of the group 1 counterions but did depend
on the beginning stoichiometry of the reaction. The
yields for both carborane isomers were comparable, with
the half-sandwich compounds being obtained in 51%
and 41% yields for n ) 3, 4, respectively, while those of
the full-sandwich complexes were slightly less (36%
and 38% for n ) 3, 4, respectively). It is of interest that,
even though only about half the maximum amounts of
the half-sandwich gallacarboranes were obtained, there
was no evidence of the “excess” carborane reagents
reacting further with the chlorogallacarboranes. How-
ever, an initial 2:1 carborane-to-GaCl3 molar ratio gave
exclusively the full-sandwich compounds. This indicates
w
common variable. The final values of R and weighted R are
listed in Table 3, while the selected interatomic distances and
angles are given in Table 4. The atomic coordinates, a full
list of bond distances and angles, anisotropic thermal param-
eters, and the positions of the H atoms are given in the
Supporting Information.
Ca lcu la tion s. The 11B NMR spectra of compounds I-IV
were verified by GIAO (gauge independent atomic orbital)15
ab initio molecular orbital calculations at the HF/6-311G**
level on the model compounds 1-(NH
3
)
2
-1-Cl-1,2,n-GaC
2 4 6
B H
]- (n
3 (VII), 4 (VIII)). The structures were optimized by
(n ) 3 (V), 4 (VI)) and [commo-1,1′-Ga(1,2,n-GaC B H )
2 4 4 2
)
approximate density function theory (DFT) hybrid methods
1
6
using Becke’s three-parameter method and the correlation
that the initial reaction of GaCl with carborane must
3
1
7
functional of Lee, Yang, and Parr with the 3-21G* basis set
be essentially quantitative; if an excess of carborane was
1
8
(
B3LYP/3-21G*). All calculations were carried out on a Dec-
not originally present, the reaction would cease at the
half-sandwich compound. The less than quantitative
yields in the syntheses of III and IV are more likely
due to the high solubility of the chlorogallacarboranes
in the benzene solvent, rather than to a lack of reactivity
between the carboranes and GaCl3. It should be noted
that the yields reported in the Experimental Section
were of the crystallized products and were not opti-
mized; once the conditions are optimized, the controlled
direct reaction of the carborane dianions with GaCl3
should prove to be a very efficient synthetic route to both
the full-sandwich gallacarboranes and the half-sand-
wich chlorogallacarboranes.
RA or a Silicon Graphics Indigo2 RS10000 workstation using
1
9
the Gausian 94 series of programs. The chemical shifts,
listed in Table 5, are given relative to BF ‚OEt as a standard.
3
2
The standard was subjected to the same optimization/GIAO
cycle as were the compounds.
(
15) Wolinski, K.; Hilton, J . F.; Pulay, P. J . Am. Chem. Soc. 1990,
1
12, 8251.
(
(
(
16) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
17) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev., B 1988, 37, 785.
18) For a discussion of DFT methods, see: Ziegler, T. Chem. Rev.
1
991, 91, 651 and references therein.
19) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
(
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T.; Peterson, G.
A.; Montgomery, J . A.; Raghavachari, K.;. Al-Laham, M. A.; Zakrze-
wski, V. G.; Ortiz, J . V.; Foresman, J . B.; Peng, C. Y.; Ayala, P. Y.;
Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . P.; Head-Gordon, M.; Gonzalez, C.; Pople, J . A. Gaussian
X-r a y Cr ysta l Str u ctu r es. The solid-state struc-
tures of I-IV were determined by single-crystal X-ray
diffraction. Figures 1 and 2 show the structures of the
full-sandwich [2,2′,n,n′-(SiMe3)4-1,1′-commo-Ga(1,2,n-
9
4, Revision B.3; Gaussian, Inc., Pittsburgh, PA, 1995.

C-Trimethylsilyl-Substituted Heterocarboranes
Organometallics, Vol. 16, No. 24, 1997 5167
Ta ble 4. Selected Bon d Len gth s (Å) a n d Bon d An gles (d eg) for Ga lla ca r bor a n es I-IV
Bond Lengths (Å)
Compound I
Ga-Cnt(1)
Ga-C(11)
Ga-C(12)
Ga-B(13)
Ga-B(14)
Ga-B(15)
1.878
Li-N(31)
2.095 (17)
C(12)-B(16)
B(13)-B(14)
B(13)-B(16)
B(14)-B(15)
B(14)-B(16)
B(15)-B(16)
1.724 (17)
1.670 (20)
1.761 (19)
1.674 (20)
1.797 (19)
1.776 (19)
2.489 (11)
2.468 (11)
2.243 (14)
2.141 (13)
2.249 (13)
Li-N(32)
2.086 (17)
1.527 (16)
1.584 (19)
1.728 (18)
1.573 (16)
C(11)-C(12)
C(11)-B(15)
C(11)-B(16)
C(12)-B(13)
Compound II
Ga-Cnt(21)
Ga-Cnt(22)
Ga-C(11)
Ga-B(12)
Ga-C(13)
Ga-B(14)
Ga-B(15)
Ga-C(21)
Ga-B(22)
Ga-C(23)
Ga-B(24)
Ga-B(25)
1.920
1.929
Na-N(51)
2.488 (25)
2.522 (25)
2.432 (29)
2.491 (25)
1.521 (32)
1.638 (36)
1.663 (34)
1.563 (32)
1.785 (36)
1.578 (35)
1.693 (34)
1.707 (42)
B(14)-B(16)
B(15)-B(16)
C(21)-B(22)
C(21)-B(25)
C(21)-B(26)
B(22)-C(23)
B(22)-B(26)
C(23)-B(24)
C(23)-B(26)
B(24)-B(25)
B(24)-B(26)
B(25)-B(26)
1.713 (39)
1.767 (40)
1.587 (38)
1.604 (34)
1.698 (36)
1.500 (37)
1.774 (39)
1.545 (32)
1.712 (34)
1.705 (37)
1.755 (38)
1.777 (38)
Na-N(52)
2.431 (21)
2.605 (25)
2.390 (21)
2.119 (30)
2.190 (30)
2.483 (23)
2.544 (31)
2.418 (20)
2.159 (27)
2.141 (26)
Na-N(61)
Na-N(62)
C(11)-B(12)
C(11)-B(15)
C(11)-B(16)
B(12)-C(13)
B(12)-B(16)
C(13)-B(14)
C(13)-B(16)
B(14)-B(15)
Compound III
Ga-Cnt(3)
Ga-Cl
Ga-C(11)
Ga-B(13)
2.126
Ga-B(14)
2.073 (18)
2.121 (15)
1.522 (26)
1.674 (25)
C(11)-C(11A)
B(13)-B(14)
B(13)-B(16)
B(14)-B(16)
1.425 (33)
1.635 (25)
1.708 (26)
1.655 (35)
2.237 (5)
2.833 (17)
2.334 (20)
Ga-N(31)
C(11)-B(13)
C(11)-B(16)
Compound IV
Ga-Cnt(4)
Ga-Cl
Ga-C(11)
Ga-B(12)
Ga-C(13)
Ga-B(14)
Ga-B(15)
2.273
Ga-N(31)
2.166 (5)
2.099 (5)
1.528 (10)
1.594 (10)
1.688 (10)
1.520 (10)
B(12)-B(16)
C(13)-B(14)
C(13)-B(16)
B(14)-B(15)
B(14)-B(16)
B(15)-B(16)
1.793 (11)
1.560 (10)
1.702 (10)
1.758 (11)
1.761 (11)
1.721 (11)
2.193 (2)
2.747 (6)
3.078 (7)
2.877 (6)
2.248 (7)
2.157 (8)
Ga-N(32)
C(11)-B(12)
C(11)-B(15)
C(11)-B(16)
B(12)-C(13)
Bond Angles (deg)
Compound I
Cnt(1)-Ga-Cnt(1A) 180
Si(2)-C(12)-B(13)
119.2(9) B(13)-B(14)-B(15)
110.7(10) B(13)-B(14)-B(16)
136.5(8) B(15)-B(14)-B(16)
63.9(7) C(11)-B(15)-B(14)
64.4(8) C(11)-B(15)-B(16)
108.2(11) B(14)-B(15)-B(16)
62.0(8) C(11)-B(16)-C(12)
63.1(8) C(11)-B(16)-B(13)
103.0(10) C(12)-B(16)-B(13)
60.9(7) C(11)-B(16)-B(14)
61.4(8) C(12)-B(16)-B(14)
108.2(10) B(13)-B(16)-B(14)
61.6(8) C(11)-B(16)-B(15)
62.7(8) C(12)-B(16)-B(15)
52.5(7) B(13)-B(16)-B(15)
93.9(9) B(14)-B(16)-B(15)
53.6(7)
97.0(8)
96.6(9)
56.0(8)
53.7(7)
93.3(9)
95.5(9)
55.9(8)
N(31)-Li-N(32)
88.5(5) C(11)-C(12)-B(13)
118.7(13) Si(2)-C(12)-B(16)
121.6(5) C(11)-C(12)-B(16)
121.5(13) B(13)-C(12)-B(16)
109.8(10) C(12)-B(13)-B(14)
63.6(7) C(12)-B(13)-B(16)
64.7(8) B(14)-B(13)-B(16)
129.9(8)
N(31)-Li-N(31A)
N(31)-Li-N(32A)
N(32)-Li-N(32A)
C(12)-C(11)-B(15)
C(12)-C(11)-B(16)
B(15)-C(11)-B(16)
Si(2)-C(12)-C(11)
Compound II
Cnt(21)-Ga-Cnt(22) 178.2
B(14)-C(13)-B(16)
63.0(15) B(12)-B(16)-B(15)
106.9(20) C(13)-B(16)-B(15)
61.8(15) B(14)-B(16)-B(15)
62.2(16) B(22)-C(21)-B(25)
99.6(19) B(22)-C(21)-B(26)
58.4(15) B(25)-C(21)-B(26)
59.0(16) C(21)-B(22)-C(23)
52.2(13) C(21)-B(22)-B(26)
93.3(17) C(23)-B(22)-B(26)
53.3(13) B(22)-C(23)-B(24)
98.3(18) B(22)-C(23)-B(26)
96.7(18) B(24)-C(23)-B(26)
55.2(15) C(23)-B(24)-B(25)
56.9(15) C(23)-B(24)-B(26)
98.1(18) B(25)-B(24)-B(26)
99.4(18) C(21)-B(25)-B(24)
58.7(16) C(21)-B(25)-B(26)
108.4(20) B(24)-B(25)-B(26)
65.3(17) C(21)-B(26)-B(22)
65.0(16) C(21)-B(26)-C(23)
108.5(21) B(22)-B(26)-C(23)
60.4(16) C(21)-B(26)-B(24)
62.4(16) B(22)-B(26)-B(24)
112.9(19) C(23)-B(26)-B(24)
66.7(17) C(21)-B(26)-B(25)
65.0(15) B(22)-B(26)-B(25)
105.1(19) C(23)-B(26)-B(25)
62.1(15) B(24)-B(26)-B(25)
61.8(15)
104.3(19)
60.1(15)
60.5(15)
54.3(15)
94.6(17)
50.9(14)
98.3(18)
92.0(18)
52.9(13)
54.9(14)
93.6(18)
95.5(17)
57.7(15)
N(51)-Na-N(52)
N(51)-Na-N(61)
N(52)-Na-N(61)
N(52)-Na-N(62)
N(51)-Na-N(62)
N(61)-Na-N(62)
B(12)-C(11)-B(15)
B(12)-C(11)-B(16)
B(15)-C(11)-B(16)
C(11)-B(12)-C(13)
C(11)-B(12)-B(16)
C(13)-B(12)-B(16)
B(12)-C(13)-B(14)
B(12)-C(13)-B(16)
78.8(8) C(13)-B(14)-B(15)
171.4(11) C(13)-B(14)-B(16)
100.2(9) B(15)-B(14)-B(16)
171.5(10) C(11)-B(15)-B(14)
100.8(8) C(11)-B(15)-B(16)
81.5(9) B(14)-B(15)-B(16)
116.2(19) C(11)-B(16)-B(12)
68.0(15) C(11)-B(16)-C(13)
64.7(16) B(12)-B(16)-C(13)
104.6(18) C(11)-B(16)-B(14)
59.8(15) B(12)-B(16)-B(14)
60.3(14) C(13)-B(16)-B(14)
112.7(19) C(11)-B(16)-B(15)
66.4(15)
Compound III
Cnt(3)-Ga-Cl
102.7
134.6
B(13)-C(11)-C(11A) 111.5(10) B(13)-B(14)-B(16)
62.5(11) B(13)-B(16)-B(14)
58.1(11)
Cnt(3)-Ga-N(31)
Cl-Ga-N(31)
B(16)-C(11)-C(11A) 64.8(6) B(13)-B(14)-B(13A) 102.0(18) C(11)-B(16)-C(11A) 50.4(13)
96.7(4) C(11)-B(13)-B(14)
82.1(8) C(11)-B(13)-B(16)
64.4(12) B(14)-B(13)-B(16)
107.1(15) B(16)-B(14)-B(13A) 62.5(11) B(13)-B(16)-C(11A) 92.2(13)
62.1(13) C(11)-B(16)-B(13)
59.3(13) C(11)-B(16)-B(14)
N(31)-Ga-N(31A)
B(13)-C(11)-B(16)
53.5(10) B(13)-B(16)-B(13A) 96.1(18)
99.5(14)
Compound IV
Cnt(4)-Ga-Cl
98.9
130.7
136.7
B(12)-C(11)-B(16)
B(15)-C(11)-B(16)
C(11)-B(12)-C(13)
67.5(5) C(13)-B(14)-B(15)
63.2(4) C(13)-B(14)-B(16)
108.1(6) B(15)-B(14)-B(16)
60.5(5) C(11)-B(15)-B(14)
61.2(4) C(11)-B(15)-B(16)
113.3(6) B(14)-B(15)-B(16)
67.3(5) C(11)-B(16)-C(13)
65.2(4) C(11)-B(16)-B(12)
103.3(5) B(12)-B(16)-C(13)
61.3(4) C(11)-B(16)-B(14)
58.5(4) B(12)-B(16)-B(14)
102.7(5) C(13)-B(16)-B(14)
61.1(4) C(11)-B(16)-B(15)
60.8(4) B(12)-B(16)-B(15)
93.4(5) C(13)-B(16)-B(15)
52.0(4) B(14)-B(16)-B(15)
51.5(4)
98.8(5)
92.8(5)
53.5(4)
55.7(4)
95.0(5)
99.1(5)
60.6(4)
Cnt(4)-Ga-N(31)
Cnt(4)-Ga-N(32)
Cl-Ga-N(31)
99.1(2) C(11)-B(12)-B(16)
99.9(2) C(13)-B(12)-B(16)
83.9(2) B(12)-C(13)-B(14)
112.1(5) B(12)-C(13)-B(16)
125.5(4) B(14)-C(13)-B(16)
Cl-Ga-N(32)
N(31)-Ga-N(32)
B(12)-C(11)-B(15)
Si(1)-C(11)-B(16)
a
Cnt ) centroid of the C2B3 bonding face.

5
168 Organometallics, Vol. 16, No. 24, 1997
Hosmane et al.
Ta ble 5. Ca lcu la ted 11B NMR Ch em ica l Sh ifts of
a
Mod el F u ll- a n d Ha lf-Sa n d w ich Ga lla ca r bor a n es
δb
compd
basalc uniqued
apicale
-
-
[
[
1
1
commo-1,1′-Ga(1,2,3-GaC
commo-1,1′-Ga(1,2,4-GaC
2
2
B
B
4
4
H
H
6
6
]
]
(V) 13.37(2) -4.56(1) -46.47(1)
(VI) 5.01(2) 19.36(1) -47.14(1)
,1-(NH
,1-(NH
3
)
)
2
-1-Cl-1,2,3-GaC
-1-Cl-1,2,4-GaC
2
B
B
4
H
H
6
(VII)
9.67(2) -2.37(1) -46.73(1)
3
2
2
4
6
(VIII) 7.71(2) 20.12(1) -44.17(1)
a
Geometries optimized at the B3LYP/3-21G* level. b GIAO
calculated chemical shifts at the HF/6-311G** level, relative to
BF3‚OEt2 calculated at the same level. Relative areas are given
c
in parentheses. Equivalent to B(13,15) in Figure 1, B(14,15,24,25)
d
in Figure 2, B(13) in Figure 3, or B(14,15) in Figure 4. Equivalent
to B(14) in Figure 1, B(12,22) in Figure 2, B(14) in Figure 3, or
e
B(12) in Figure 4. Equivalent to B(16) in Figures 1, 3, and 4 or
B(16,26) in Figure 2.
-
GaC2B4H4] complexes for n ) 3 (I), 4 (II), respectively.
The structures of the half-sandwich 1-Cl-1-(TMEDA)-
2
,n-(SiMe3)2-2,n-C2B4H4 (n ) 3 (III), 4 (IV)) are given
in Figures 3 and 4, respectively. Table 4 lists some
important bond distances and bond angles. In both of
the full-sandwich complexes the galliums are located
between the two C2B3 pentagonal faces of the carborane
ligands. Gallacarborane I is the more symmetric of the
two complexes, with the gallium atom being a center of
symmetry for the complex, while in the less symmetric
II the dihedral angle between the two C2B3 faces is
F igu r e 1. Perspective view of the carbons adjacent gal-
lacarborane sandwich [Li(TMEDA)
commo-Ga(1,2,3-GaC ] (I), showing the atom-num-
bering scheme. The thermal ellipsoids are drawn at the
0% probability level. For clarity, the cationic Li(TMEDA)
2 3 4
][2,2′,3,3′-(SiMe ) -1,1′-
2
4 4 2
B H )
4
2
unit and all H’s except those of the carborane cage in the
anionic unit are removed.
4
.68°. In addition, the C2B4 cages in II are slightly
In both compounds the galliums are not symmetrically
bound to the C2B3 facial atoms but are dislocated or
slipped away from the centroidal positions above the
faces. The bond distances listed in Table 4 show that
in the carbons-adjacent complex I the slippage is toward
the unique boron (B(14) in Figure 1), while in the
carbons-apart complex II, the slippage is in the opposite
direction, that is, away from the unique borons (B(12)
twisted with respect to one another such that the B(12)-
B(16)-B(26)-B(22) dihedral angle is 171.97° (see Figure
2
graphically unique, an inspection of the interatomic
distances given in Table 4 reveals that the differences
in equivalent bond distances in the two cages are almost
within their combined experimental indeterminations.
). While the two carborane cages in II are crystallo-
2 4
Sch em e 1. Syn th eses of Ha lf- a n d F u ll-Sa n d w ich Ga lla ca r bor a n es of th e C B Ca ge System s

C-Trimethylsilyl-Substituted Heterocarboranes
Organometallics, Vol. 16, No. 24, 1997 5169
F igu r e 2. Perspective view of the carbons apart galla-
F igu r e 4. Perspective view of the carbons apart half-
carborane sandwich [Na(TMEDA)
2 3 4
][2,2′,4,4′-(SiMe ) -1,1′-
sandwich gallacarborane 1-Cl-1-(TMEDA)-2,4-(SiMe
3 2
) -
commo-Ga(1,2,4-GaC ] (II), showing the atom-
2
4 4 2
B H )
closo-1,2,4-GaC (IV), showing the atom-numbering
2
4 4
B H
numbering scheme. The thermal ellipsoids are drawn at
the 40% probability level. For clarity, the cationic Na(T-
MEDA) unit and all H’s except those of the carborane cage
2
scheme. The thermal ellipsoids are drawn at the 40%
probability level. For clarity, all H’s except those of the
carborane cage are removed.
in the anionic unit are removed.
in both compounds the galliums are severely slip-
distorted. As was the case in the commo complexes, the
gallium is slipped toward the unique boron (B(14) in
Figure 3) in the carbons-adjacent complex III and in
the opposite direction in IV. The extent of the slip
3
distortion in III is such that the carborane is η -bonded
to the metal (the relevant distances are Ga-B(14) )
2
.073 Å, Ga-B(13) ) 2.334 Å, and Ga-C(11) ) 2.833
Å). Similar slippages were found in the compounds 1-L-
1
2
-t-C4H9-2,3-(SiMe3)2-1,2,3-GaC2B4H4 (L ) 2,2′-C10H8N2,
5
,7
,2′-C8H6N4), which show the same general geometry
as given in Figure 3 on the replacement of the Cl by a
tert-butyl group and the TMEDA by the heterocyclic
base. It turns out that the Ga-C2B4 distances in the
complex where L ) 2,2′-C8H6N4 are almost identical
with those found for III listed in Table 4 (the equivalent
distances in the bipyrimidine complex are Ga-B(14) )
2
.077 Å, Ga-B(13) ) 2.379 Å, and Ga-C(11) ) 2.883
5
F igu r e 3. Perspective view of the carbons adjacent half-
Å). Such a similarity is found when the structure of
sandwich gallacarborane 1-Cl-1-(TMEDA)-2,3-(SiMe
3
)
2
-
IV is compared to that of the carbons-apart tert-butyl-
closo-1,2,3-GaC (III), showing the atom-numbering
2
4 4
B H
substituted species 1-(2,2′-C8H6N4)-1-t-C4H9-2,4-(SiMe3)2-
scheme. The thermal ellipsoids are drawn at the 40%
probability level. For clarity, all H’s except those of the
carborane cage are removed.
7
1
,2,4-GaC2B4H4; the distances equivalent to those in
IV for the bipyrimidine complex are Ga-B(12) ) 3.018
Å, Ga-B(14,15) ) 2.193 Å, and Ga-C(11,13) ) 2.826
Å. In both IV and its tert-butyl analogue metal slippage
is severe enough so that the carboranes are best
and B(22) in Figure 2). In both compounds the extent
of slippage is sufficient so as to produce a disparity
between the Ga-C(11,12) and the Ga-B(14) distances
of 0.34 Å in I and a 0.45 Å difference between the Ga-
B(13,14) and the Ga-B(12) distances in II (see Table
2
described as being η -bonded to the galliums. However,
the metal causes distortions in the carborane cage such
that the unique boron, B(12) in Figure 4, is lifted above
the C(11)-C(13)-B(14)-B(15) plane, indicating that
4
). A similar slip distortion was observed by Hawthorne
there is some interaction between the gallium and the
and co-workers in the carbons-adjacent [commo-3,3′-
7,20
more remote facial atoms.
The structures of the
-
2
Ga(3,2,1-GaC2B9H11)2] , where a disparity of 0.44 Å
was found between the gallium and the C2B3 facial
atoms, which are equivalent to C(11,12) and B(14) in
Figure 1.2
bipyridine complexes 1-(2,2′-C10H8N2)-1-t-C4H9-2,n-
(
SiMe3)2-1,2,n-C2B4H4 (n ) 3, 4) show geometries similar
to those of III and IV and the bipyrimidine complexes,
with the exception that the former seem to be a bit more
7
The structures of the half-sandwich chlorogallacar-
boranes, given in Figures 3 and 4, show each complex
to be a very distorted pentagonal bipyramid in which a
slip-distorted.
NMR a n d IR Sp ectr a . The H, 11B and 13C NMR
1
spectra of the compounds I-IV are listed in Table 1.
(TMEDA)ClGa moiety occupies the apical position above
the C2B3 pentagonal face of the carborane. However,
(20) For details, see ref 6.

5
170 Organometallics, Vol. 16, No. 24, 1997
Hosmane et al.
All spectra show the expected resonances for the car-
borane cages and TMEDA molecules and are consistent
with the formulations and structures of the compounds
neutral and anionic closo- and nido-carboranes.23 The
model compounds differ from I-IV in that hydrogen
atoms replace SiMe3 groups on the cage carbons and
two NH3 molecules are substituted for the TMEDA
molecules. It has been shown that the former simpli-
fication does not materially effect the GIAO calculated
1
1
shown in Figures 1-4. The B NMR spectra of all the
gallacarboranes show the same general pattern exhib-
ited by the C2B4 metallacarboranes, that is, an upfield
resonance (δ -46 to -47 ppm) due to the apical boron,
with the peaks for the less shielded C2B3 facial boron
atoms being shifted downfield by some 40-70 ppm. In
the carbons-adjacent complexes I and III the basal
borons are the least shielded and a 2:1:1 peak area ratio
pattern is found, while in the carbons-apart isomers (II
and IV) the relative shielding of the basal and unique
borons is reversed and a 1:2:1 peak area ratio pattern
results. These same patterns are found in the other
1
1
23
B chemical shifts; the replacement of TMEDA by two
NH3’s, while a more severe simplification, does at least
3
provide for coordination of the gallium with two sp -
1
1
hybridized nitrogens. The calculated B NMR chemical
shifts of these model compounds are listed in Table 5.
A comparison of these results with those found for
compounds I-IV, given in Table 1, shows that the
chemical shifts calculated for the model compounds
agree well with the experimental values of the analo-
gous trimethylsilyl-substituted gallacarboranes. The
calculated chemical shifts of the model compounds show
very little change in chemical shifts on replacing the
ammonia/Cl groups with a carborane ligand. Therefore,
group 13-C2B4 metallacarboranes, as well as in the
precursor group 1 compounds.5
,7,11,12
The changes in the
chemical shifts of the cage borons on complexation of
the ligand with different metal groups have been
interpreted in terms of changing metal-carborane
bonding interactions,5 with the apical boron resonance
being especially affected.21 Thus, the most striking
aspect of the data in Table 1 is the apparent insensitiv-
1
1
the nearly equivalent B NMR spectra found experi-
mentally for the half- and full-sandwich gallacarboranes
should not raise concerns about possible decomposition
in solution.
,7
1
1
ity of the B NMR spectra to the nature of the capping
groups. In both the carbons-adjacent and carbons-apart
isomers, the NMR spectra of the full- and half-sandwich
gallacarboranes are almost identical. This could indi-
cate that a dianionic carborane ligand would, fortu-
itously, perturb the electron density in another metal-
bound C2B4 cage to about the same extent as does a
TMEDA molecule and a chloride ion, so that any
The IR absorptions of compounds I-IV are given in
Table 2. Other than providing confirmation for the
absences of bridging hydrogens in the compounds, the
spectra contain no unusual features and are listed for
the purposes of qualitative analysis.
Con clu sion s. The direct reaction of the dianions of
the carbons-adjacent and carbons-apart carboranes in
the C2B4 cage system with GaCl3 in a 1:1 molar ratio
was found to produce the half-sandwich chlorogalla-
carboranes 1-Cl-2,n-(SiMe3)2-1,2,n-GaC2B4H4 (n ) 3, 4),
which could be isolated as their TMEDA adducts. The
gallium-bound chloride was found to be reactive and
could be replaced by other groups, as demonstrated by
the formation of the corresponding full-sandwich gal-
lacarboranes [2,2′,n,n′-(SiMe3)4-1,1′-commo-Ga(1,2,n-
1
1
differences in the B NMR spectra of the half- and full-
sandwich species would be masked by experimental
3
indetermination. Because of interactions with the /2
2
2
11
spin of gallium, the B NMR spectra of the gallacar-
boranes are quite broad, and small chemical shift
changes may not be detected. On the other hand, the
spectral similarity could indicate that equilibria are set
up such that the dominant forms in solution are not
those shown in Figures 1-4. In an effort to gain some
-
GaC2B4H4)2] . The reactivity of the chlorogallacarbo-
ranes toward other functional groups is currently under
investigation and will be the subject of a future report.
1
1
insight into the effects of ligand substitution on the
B
NMR spectra of the gallacarboranes, 11B NMR chemical
Ack n ow led gm en t. This work was supported by
grants from the Robert A. Welch Foundation (Grant
Nos. N-1016 and N-1322), the donors of the Petroleum
Research Fund, administered by the American Chemi-
cal Society, and the National Science Foundation.
shifts for the model compounds [commo-1,1′-Ga(1,2,n-
-
C2B4H6)2] (n ) 3 (V), 4 (VI)) and 1,1′-(NH3)2-1-Cl-1,2,n-
GaC2B4H6 (n ) 3 (VII), 4 (VIII)) were carried out using
GIAO methods at the HF/6-311G** level. This level of
theory was found to give good results for a number of
Su p p or tin g In for m a tion Ava ila ble: Atomic coordinates
(Table S-1), all bond lengths and bond angles (Table S-2),
anisotropic displacement parameters (Table S-3), and H-atom
coordinates and isotropic displacement coefficients (Table S-4)
for I-IV (24 pages). Ordering information is given on any
current masthead page.
(
21) (a) Herm a´ nek, S.; Hnyk, D.; Havlas, Z. J . Chem. Soc., Chem.
Commun. 1989, 1859. (b) B u¨ hl, M.; Schleyer, P. v. R.; Havlas, Z.; Hnyk,
D.; Herm a´ nek, S. Inorg. Chem. 1991, 30, 3107. (c) Fehlner, T. P.; Czech,
P. T.; Fenske, R. F. Inorg. Chem. 1990, 29, 3103.
(
22) Brevard, C.; Granger, P. Handbook of High Resolution Multi-
nuclear NMR; Wiley: New York, 1981.
23) Ezhova, M. B.; Zhang, H.; Maguire, J . A.; Hosmane, N. S. J .
Organomet. Chem., in press.
(
OM970555B