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The First Carborane with a Distorted Cuboctahedral Structure.

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[ I ] 0. Kahn. J. Krober. C. Jay. Adi.. M N / c 1992.
~ . 4. 718.
[2] 0:s. Jung, C. C;. Pierpont. .I A m . Cilni;. Stir-. 1994. 116. 1127.
[3] J A. Real. E. Andrhs, M. C. Mu~ioz.M. Julve, T. Granier. A. Bousseksou. F
Varret. Scicwr-c 1995. 268. 265.
[4] C. P Laiidre. M . Melvillc. J. S. Miller in M ~ i , q i ( v iM
( ~o I e ~ ~ ~ i M
/ i im
r q x d v (Eds.
D. Gattcschi. 0. Kahn. J. S. Miller. I; Palacio). Kluwer. Dordrecht, 1991.
p. 395.
[5] A. Gleizes. M Verdaguer. J. A m C%eri~.
So(. 1984. 106. 3727.
161 0. Kahn. Y. Pei. M. Verdaguer. J. P Renard. J. Sletten. J. , 4 1 1 1 . C ' h r t i r .So<,. 1988.
110. 7x2.
[7] 0 Guillou. R. L. Oushoorn. 0 . Kahn, K.Boubekeur. P Batail. A ~ i p i C/imi.
1992, l(J4, 658: Aiigew. C h i . [ ! I [ . E d . Dig/. 1992, 31. 626.
[8]F. Sapiiia. E. Coronado. D. Beltrin. R. Burriel. J A i i i . C/icm. Sor-. 1991. 11.1.
7940. and rcferences therein.
[9] M. Ohba. N. Maruono, H. Okawa. T. Enoki. JLM. Latour. J. Am. C/i~ii;.So..
1994. 116. 11566.
[lo] H. 0 Stumpf: L. 0uah;ib. Y. Pei. D. Grandjem. 0 Kahn. Srirtrcc. 1993. 2 6 / .
[ I l l T. Mallah. S. Thihb,iut. M. Verdaguer. P. Veillet. Suoice 1993. 262. 1554.
[12] W. R. Entley. G. S. Girolami. S m r r c ~ r1995. 26#. 397
[131 S Dccurtins. H. W. Schnialle. P. Schneuwley. J. Ensling. P. Ghtllch. .I Am.
C/WIJISoc. 1994. 116. 9521
I141 R. Clement. P G . Lacroix. D. O'Hare. J. Evans. Ad,. M a t w . 1994. 6. 794.
[I51 J. Kim. J. M Lim. H. Yoon. H. Kany. Y Do. unpublished.
[ 161 K. Nakamoto. /iifr[ired ui;d R m w i i Spi,r-/rci of Inorgoiii~.rind Coiirdiiiorifju
C'ompoimIc. 3rd ed.. Wiley, New York. 1978, p. 232.
[I 71 Crystal data for I : M = 631.06.crystal size 0.3 x 0.3 x 0.1 mm, 297 K. triclinic,
space group PI. (I =7.228(1), / I =7.338(2). ( ' =11.392(1) A. x =102.70(1).
= 1.77 g ~ m - ~ ,
[j = 91 . I 7( I ) . 7 = 93 37 ( I ) , V = 592.1 ( 2 ) A'. Z = I , pL,,,L4
F(000) = 322. p = I 84 mm-I. Enraf-Nonius CAD4 diffmctometer. Mo,, radiation. ( i = 0.71073
20,,, = 50 . 2003 unique reflections. 1894 observed
with 6,> 40(F0).Lorenzian polarizstion and absorption corrections were carried out. Thc structure was solved by heavy atom methods (SHELXS-86).
anisotropic least-squares refinement (SHELXL-93) for non-H atoms. all H
atoms included in located positions; 196 parameters, R , = 0.0214 (based o n
F),x R , = 0.0593 (based on F') with
= n'(F:) + (0.0371 P)'+0.321 P.
where P = (F,:+2F:),3: 5=1.026: residual electron density: max = 0.31.
min = - 0.46 c k 3 . Crystallographic data (excluding structure factors) for
the structure(s) reported in this paper have been deposited with the Cambridge
Crysta\lographic Data Centre as supplementary puclication no. CCDC-17915. Copies of thc data can he obtained free of charge on application to The
Director. CCDC, 12 Union Road. Cambridge CB2 IEZ. UK (fax int code
+(1223) 336-033; e-mail: teched(a chemcrys.cain,ac uk).
[I81 A. Bondi. J. P l i n . CIie~ii.1964. 68. 441.
The First Carborane with a Distorted
Cuboctahedral Structure **
Narayan S. Hosmane,* Hongming Zhang,
John A. Maguire, Ying Wang, Colacot J. T h o m a s ,
and Thomas G. Gray
Dedicated fo Professor William N . Lipscomb
Nearly 35 years ago, Lipscomb suggested the classical diamond -square-diamond (DSD) mechanism to explain the rearrangement of BH and CH vertices in polyhedral closoboranes and -carboranes.['l He proposed that conversion of the
"carbons adjacent" 1.2-carborane (closo-I ,2-C,B,,H I 2 ) involves six simultaneous DSD processes that give rise to a cuboctahedron, which can then collapse to give the "carbons apart"
1,7 isomer (closo-I ,7-C,Bt,H 2). Diamond-square-diamond
[*] Prof. Dr. N. S. Hosmane. Dr H. Zhang. Prof. Dr. J A. Maguirc, Dr. Y. Wang.
Dr. C. J. Thomas. T. G Gray
Department of Chemistry. Southern Methodist University
Dallas. TX 75275 (USA)
Fax. Int. code +(214)768-4089
e-mail nhosmane(o
[**I This "ark was supported by grants from the National Sclence Foundatlon
(CHE-9400672). thc Robert A. Welch Foundation (N-1016). and thedonors of
the Petroleum Research Fund, administered by the American Chemical society N . S H. is a Camille and Henry Dreyfus Scholar.
processes. or processes that are related to it, have been used in
rationalizing a number of isomerizations found in boranes, carboranes, metallaboranes, and metalla~arboranes.[~ Despite
the general acceptance of the DSD process, there is not agreement on the mechanism of the isomerization of the icosahedral
carbordnes or on the viability of the cuboctahedron as an intermediate.'" '. s] Irrespective of its specific nature, any DSD process will lead to a structure that is more open than the original,
and an increase in cage electron density should stabilize such
The two-electron reductions of c/oso-1.2-C,Bi,Hi, and doso1,2-(CR),B,H, are known to yield the corresponding "carbons
apart" nido-carborane dianions, in which the cage carbons are
on the open carborane faces and are separated by a boron
atom."'. ' I In contrast, the two-electron reduction of the "carbons adjacent" biscarborane (1 .2-C2B,,H, produces a much
less open structure in which two of the triangular f x e s open to
produce four-membered rings, similar to what would arise from
a single DSD process.["] This raises the question as to whether
a more open, cuboctahedron-like structure could be stabilized
enough for characterization if two more electrons were to be
added to the 1.2-carborane precursor by replacing two two-electron BH vertices with two three-electron CR groups, thus giving
a total of 28 valence electrons.
The pioneering work of Grimes et al. on Fe and C o metal-mediated oxidative ligand fusion indicates that such substitutions
are possible.[131However, none of the synthesized (CR),B,H,
cages (R is a less bulky Me or Et moiety) showed a cuboctahedron-like structure.[I31 Thus, it is clear that in order to produce
this type of carborane a different synthetic strategy is warranted. We report herein the synthesis and characterization of the
first "carbons apart" tetracarbaborane, (CSiMe,),B,H,. whose
solid-state structure resembles a cuboctahedron.
The reinvestigation of the reaction of anhydrous NiCI,
with the dilithiacarborane closo-exo-4,5-[(~c-H),Li(tmeda)I-lLi(tmeda)-2,3-(SiMe,),-2,3-C2B4H41i41
in 1 : 1 stoichiometry afforded a mixture of two products, the previously reported closocarborane I , i 1 4 . 1 s 1which was isolated as a colorless liquid by a
vacuum distillation at 25 "C, and a white crystalline solid, which
was found to be a 1 :1 mixture of 2 and 3 (Scheme 1). Fractional
crystallization of the solid from a solution of benzene and hexane (1 : 1) allowed the separation of the two isomers. A neat
sample of 2 was found to undergo thermal isomerization at
140- 165"C to yield 3 exclusively. The isomerization reaction
showed no indication of reversibility, indicating that 3 is the
more stable isomer. This conclusion is supported by ab initio
molecular orbital calculations on the model compounds
C,B,H,, with D,, and C,, symmetries, in which the SiMe,
groups are replaced by hydrogen atoms. These calculations
show that at the 6-31G*//3-21G* level of theory the C,B, cage
with C, symmetry is more stable than that with D,,symmetry
by 124.2 k J m 0 1 - ' . [ ' ~ As
~ expected, the mass ~pectra,~"]I R
spectra,["] and elemental analyses (see Experimental Procedure) of 2 and 3 are identical; however, the I'B and I3C N M R
spectra["l are quite different. Isomer 2 exhibits a single peak in
the I'B N M R spectrum at 6 = - 30.18, along with a single
cage-carbon resonance in its I3C N M R spectrum at 6 =
- 33.32; isomer 3 shows these resonances at 6 = - 5.57 and
6 = - 11.41, respectively. It is evident in the X-ray crystal structure of 2 (Fig. 1 ) and in a preliminary X-ray analysis of the more
stable isomer 3 that while the cage-carbons might be equivalent
(2)or nearly equivalent (3), there are two sets of borons in both
isomers. Therefore, the appearances of single resonances in the
'B N M R spectra of both compounds indicate that the C,B,
cages of both 2 and 3 are fluxional on an NMR time scale.
Nevertheless, the solid-state structure of 2 (Fig. l)[l8] is that
of a distorted cuboctahedron with a D,,-symmetric cage)’”’
reminiscent of Lipscomb’s proposed intermediate structure.(’]
Owing to the heteronuclear nature of the faces, the CzBzrectangular faces are not planar and the B-B distances are not all
equal. There are two sets of boron atoms: one of them consists
of B(3), B(4), B(3a), and B(4a), and the other of B(2), B(5).
B(2a), and B(5a). These could be interchanged by a dual DSD
process that produces an intermediate of D,, symmetry.[20i
The data available for 2 and 3 show that their structures are
quite different from those of the “carbons adjacent” (CR),B,H,
isomers reported by Grimes et al., in which the cage-carbons are
located on the same side of the cage.r131It is of interest to note
that neither 2 nor 3 could be converted to the “carbons adjacent” isomers. Moreover, the use of Grimes’s methodology for
the oxidative ligand fusion, involving the reaction of FeCI, with
the monosodium salt of nido-2,3-(Sih4e,),-2.3-C2B4H6
failed to
produce the “carbons adjacent’’ (CSiMe,),B,H
isomers. The
* ‘B N M R spectra of the product were the same as those of 3,
thus exemplifying the role of the C (cage)-bound bulky SiMe,
substituents positioned e.xo on the carborane polyhedron in deWhile the
termining the course of the cage fusion reactioi~.~”’]
mechanism for the formation of the (CSiMe,),B,H, isomers is
not known. the isolation and structural characterization of 2
demonstrate that the cuboctahedron geometry in carbordnes
can be stabilized by increasing the total number of valence electrons in a 12-vertex cage to 28 and by introducing steric bulk on
the bonding C,B, Faces.
= H; tineda = (Me,NCH&
Scheme I . Synthesi\ 0 1 tetracarbaborane 2 with a distorted cuboctahedral structure.
E.uperirnenta1 Procedure
A 20.5 mmol sample of /usr~-e.~v-4,5-[(~c-H),Li(tmeda)~-l-Li(tineda)-2.3-(SiMe,),
2.3-C,B,H, [I41 was allowed to react with 20.8 mmol of anhydrous NU, (2.7 p) in
dry benzene (20 mL) at 0 C for 12h. during which the color o f t h e solution turned
dark brown and some black solid started to precipitate. The heterogeneous mixture
was then filtered through a frit in vacuo. the residue was washed with warm benzene
( 3 x 10 mL). and the washings were collected along with a filtrate. The volatile
components of this pale-yellow filtrate were fractionated through a series of traps
maintained at 0. -45. -78, and -196°C. over 2 d While solvent and tmeda
condensed in the t r a p a t -78 C, c/oso-1.2~(SiMe,),-l.2-C,B,H, (1) remained in the
-45 C trap (1.2 g. 5.50 mmol, 2 7 % yield) The pale-brow recidue that remained
in the flask usas sublimed at 110--120 C in vacuo to give a uhite crystalline solid
( I .O g, 22% yield) at 0 C Solution N M R spectra of this substance indicated the
presence of isomers 2 and 3 in equal amounts. Subsequent slow recrystallization of
this solid from benzene and hexane (111) gave colorless plates of 2:0.45 p,
1.03 mmol, 10% yield; stable in air; soluble in both polar and nonpolar organic
found (calculated): C 44.16
solvents; m.p. 94-.95 C , Anal for C,,H,,B,Si,:
(44 15). H 1043 (10.19), 5 19.60 (19.85). The mother liquor contained predominantly isomer 3. as identified by its ‘H, “B, and 13CN M R spectra. The mother
liquor was concentrated to dryness, the white residue was sublimed a t 140- 165 C
in vdcuo over 4 h. and the resulting solid was dissolved in C,D, for characterization.
The NMR spectra of this solution unambiguously indicated the presence of 3 only
Vacuum resublimation of this solid at 140- 165 C yielded colorless rectangular
(pnsmaticfcrystals o f 3 : 049g. 1.13 mmol. 11 %yield: stable i n air: solublein both
polar and nonpolar organic solvents; m.p. 68 C ; Anal for C’,,H,,B,Si,- found
(calculated): C44.13 (44.15). H 10.23 (l0.19), B19.71 (19.8S)j.
Received: November 17. 1995 [Z 8560 IE]
German version: Angrn.. Chwr. 1996. f08,1093-1095
Keywords: boron compounds . carboranes . rearrangements
Fig. I . Crystal structure ot‘ 2. The H atoms of the SiMe, groups are omitted for
clarity. Selected distances [A] and angles [ 1. C(l)-B(2) 1672(3), C(l)-B(5)
1.685(3). C ( l ) - B ( 3 a ) I 604(3). C(l)-B(4a) 1.596(3). B(2)-B(3) 1.879(3). B(2jC ( 6 ) 1682(3). B(Z)-B(4a) 1.904(3),B(3)-5(4)1.798(3).B(3)-C(6)1.601(3),
B(3)C ( l a) 1.604(3). B ( 3 ) - B ( i a ) I .877(3). B (4)-B(5) 1.893 ( 3 ) , B(4)-C(6) 1.585(3),
B(4)-C(l ii) I .590(3). B(4)-B (2a) 1.904(3). B(5)-C(6) 1.670(3), B(S)-B(3a)
1.877(3). B(2) - B ( 5 ) 2.192. B ( S ) - . - B ( Z a ) 2.161. B ( 4 ) . . - B ( 3 a ) 3.072.
C ( 1 ) . C(6) 2 504. B(S)-B(4)-B(Za) 69.4(1). B(3)-B(4)-B(5) 95.6(1). B(2)-B(3)B(4) 96.4(1). B(3)-C(6)-B(5) 113.4(1). B(4)-C(6j-B(5) 71.1(1). B(2)-C(6)-B(5)
\\I\I\.B\>\-C\h\-0(3) 69.8\11.B\3)-C(6)-814\ 68.7\1).
[I] W. N. Lipscomb. D. Britton, J Cl7em. P/7>x 1960. 33. 275: W. N. Lipscomb.
Science 1966, 153. 373.
[2] K. Wade. Elecrron Dcficienr Compon17cl.s.Nelson, London. 1971.
[3] J. D. Kennedy, Progress 117 Inorganic Che~nisrr:~..
Vol. 34. Wiley. New York,
[41 D. M. P. Mingos, D. J. Wales in Eleclmn Defwienr Boron wid C‘odmi Clturera.
(Eds.: G. A Oiah. K. Wade, R . E. Williams). Wiley. Neu York. 1991. Chapter
5. and references therein.
[5] B. M Gimarc, D. S. Warren, J. J. Ott. C. Brown, / ~ I O I . X C/1011. 1991. 30.
M L. McKee, J. ,4117. Chrni. Six 1995. 117, 8001.
G. M. Edvenson. D. F. GdineS, /no,x. C/ietii. 1990. 2Y. 1210.
Y V. Roberts. B. F. G. Johnson. J. C'/7em. Sot.. D o / m i ? h i s . 1994. 759
. i x 1973. 95,
R. Mason. K. Thomas, D. M. P. Mingos. J. An?. C h ~ m S
F. Y. Lo. C. E. Strouse, K. P Callahan. C. B. Knohler. M. F. Hawthorne,
J. Am. Cl~en?.
Soc. 1975, 97. 428. and references therein.
N S. Hosmane, L. Jia. H Zhang. J. W. Bausch. G. K. S. Prakash, R. E.
Williams. T. P. Onak. If7or-g.C / i m . 1991. 30. 3793: H. Zhang. Y Wang. A. K .
Saxena. A. R. Oki. J. A. Maguire. N. S. Hosmane. Organiit~~e~u//ic.~
1993. 12.
T D. Getman. C. 8. Knobler. M. F. Hawthorne. J. Anr. Chem So<..1990. If?.
W. M. Maxwcll, V. R. Miller, R N. Grimes. 1nor.g. Chrrii. 1976, IS. 1343:
J An?. C/ziwi. Soc. 1976. 98. 4818. R. B. Maynard. R. N. Grimes. ihirl. 1982,
104. 5983. ftiorg. Sw7th. 1983, 22, 215. R. N. Grimes. A d , . /nurg. C/ien~.
Rudiocherii. 1983, 26, 55.
N. S. Hosmane. A. K. Saxena. R. D. Barreto. H Zhang. J. A. Maguire. L. Jia.
Y.Wang. A. R. Oki. K. V. Grover. S. J. Whitten. K . Dawson. M . A. Tolle.
U Siriwaidane. T Demissie. J. S. Fagner. Orgunonirtu//ic\
1993. f.?. 3001.
N. S. Hosmane. R. D. Barreto. M. A. Tolle. J. J. Alexaiider. W. Quintana. U. Siriwdrdane. S. G. Shore. R. E.
Williams, / n n r ~ .C/imi. 1990. 29. 2698.
SPARTAN. Version 4.0. Wavefunction Inc.. Irvine, CA.
The Dianion of Tetraphenylgermole is
Robert West,* Honglae Sohn, Douglas R. Powell,
Thomas Miiller, and Yitzhak Apeloig
The anions of siloles and germoles have stimulated a great
deal of interest lately.[*- 51 Tetraphenylgermole dianions have
been studied in T H F by Hong and Boudjouk,L61who proposed
a delocalized structure on the basis of the I3C N M R spectrum.
On the other hand, Tilley and co-workers have recently reported
the X-ray structure of the germole anion, [(MeC),GeSi(SiMeJJ, as its lithium salt l."]The structure is highly localized; the C-C bond lengths within the five-membered ring vary
2: ' H N M R (200MHz. C,D,. 295 K. T M S e x t ) .
d = 0.20-4.0 (hr., 8 H, basal and apical BH), 0.17 (hr s.
3 6 H . SiMe,); "B N M R (64.2 MHz. C,D,, 295 K.
BF, OEt, ext.): 6 = - 30.18 (d. ' J ( 5 . H ) = 162.1 HL.
cage-BH): I3CNMR(50.3 MHz.C6D,,.295 K.TMSext.):
4 Li, THF
(q. 1 J ( C . H ) = 1 1 9 . 5 H z . SiMe,), -33.32 (s.
cage-C); IR (C,H,). i.=
2581 (s). 2541 ( m ) c r n - ' (B-H):
M S : m :(%):435(rMt. 100).73(Me,Si.60).3. ' H N M R
n L 'nPr
(200 MHI. C,D,. 295 K. TMS ext.): d = 0.20- 4 0 (hr..
8 H. basal and apical BH). 0.16 (br. s. 36 H. SiMe,): "B
N M R (64.2 MHL. C,D,. 295 K. BF, . OEt? ext.):
6 = - 5 57 (d. ' J ( 9 . H ) =146.5 Hz. cage-BH): "C N M R
(SO 3 M H r , C,D,, 295 K, T M S ext.). d = -1.4 (q.
' J ( C , H ) = 1 2 0 . 3 H z . SiMe,). -11.41 (s. cage C ) . IR
(C,H,,).? = 25XD(s),2539(m)cm-'(B-H),MS.r7i
435 ( M + . 100). 73 (Me&. 58).
Crystal data for 2 (C,,H,,B,Si,. M , = 435.4): monoclinic.
Y2, n , ~ = 9 . 6 2 8 ( 2 ) h=7.332(2).
~ = 1 9 9 2 4 ( 5 ) 8 , .p =
93.36(2) . V = 1404.0(6) A'. Z = 2. prdlid= 1.030 Mgrn-'.
11 = 0.214 rnm
: Data were collected on a Siemens R3m
V diffrdctoineter at -43 C (Mu,,: 2 8 =3.5-44.0 and
1841 reflections) and corrected for Lorentz and polarizaph*
- - - - - --Li(thT)3
tion effects. The structure was solved by direct methods
p h + G :
and subsequent difference Fourier synthesis using
Ph \Li(C4H80&
SHELXTL-Plus (G. M Sheldrick. Strrrccurr Dererri71nuL1(CeHeO2fz
tin17 Sofmurc, Priigrurn Pui,kup. Siemens Analytical X-ray
Instruments Inc.. Madison. W1 (USA) 1990). 2 has acenter
of symmetry at the geometric center of the cage and was
refined o n F with all non-H atoms anisotropically and H
Scheme 1. Synthesis of 2 and 3a c.
atoms isotropically. The final refinement convei-ged at
R = 0.029. IT-R= 0.040 and GOF = 1.12 for 1431 observed
reflections Further details of the crystal structure investication may he obtained from the Fachinformationszentrum Karlsruhe.
We now reoort on the structure of the dilithium salt of the
D-76344 Eggenstein-Leopoldshafen (Germany), on quoting the depository
fro,,, 1 ,I tetraphenylgermole dianion (21, which was
number CSD-59274.
In Fieure 1 the interatomic connectlvities are drawn such that atomS seDarated
hy less than 2.00 8, are connected, while atoms at distances greater than 2.15 A
are considered not to iiiteritct and are not connected.
[*I Prof. R. West. H. Sohn. Dr. D. R. Powell
According to M O calculatmns. this isomer is an interinediate 40.0 kJ mo1-I
Department of Chemistry. University of Wisconsin
higher in energy than 2.
Madison. WI 53706 (USA)
J. Yang. K.-J. Lu. J. A. Maguire. N. S. Hosmane. unpublished results
Fax: Int code +(608)262-6143
e-mail . wcstw
Dr. T. Muller
Fachinstitut fur Allgemeine und Anorgdnische Chemie der
Humholdt Universitit
Hessische Strasse 1-2. D-10115 Berlin (Germany)
Prof. Y. Apeloig
Department of Chemistry
Technion-Israel Institute of Technology
32000 Haifa (Israel)
This research was supported by grants from the National Science Founda.
tion and the Israe"JS Binational Science Foundation. We thank youngshang
Pak for valuable assistance. T. M. thanks Prof. Dr. N. Auner for his
and support of this work.
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structure, first, carborane, distorted, cuboctahedral
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