COMMUNICATIONS [ I ] 0. Kahn. J. Krober. C. Jay. Adi.. M N / c 1992. ~ . 4. 718.  0:s. Jung, C. C;. Pierpont. .I A m . Cilni;. Stir-. 1994. 116. 1127.  J A. Real. E. Andrhs, M. C. Mu~ioz.M. Julve, T. Granier. A. Bousseksou. F Varret. Scicwr-c 1995. 268. 265.  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.  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. .  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. F. Sapiiia. E. Coronado. D. Beltrin. R. Burriel. J A i i i . C/icm. Sor-. 1991. 11.1. 7940. and rcferences therein.  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 / . 447 [ I l l T. Mallah. S. Thihb,iut. M. Verdaguer. P. Veillet. Suoice 1993. 262. 1554.  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 unpublished.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. a). I I - C ' 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 mail.smu.edu [**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 structures.[2.9l 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. COMMUNICATIONS 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. 1 nneda I I c 1 2 140-16S’C J = 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.  K. Wade. Elecrron Dcficienr Compon17cl.s.Nelson, London. 1971.  J. D. Kennedy, Progress 117 Inorganic Che~nisrr:~.. Vol. 34. Wiley. New York, 1986. [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.  B. M Gimarc, D. S. Warren, J. J. Ott. C. Brown, / ~ I O I . X C/1011. 1991. 30. 1598. COMMUNICATIONS 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 3802. 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. 3933. T D. Getman. C. 8. Knobler. M. F. Hawthorne. J. Anr. Chem So<..1990. If?. 4593. 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 Aromatic** 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 significantly. & 1995. 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. 3a 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 nPrBr ____) b=-l.l (q. 1 J ( C . H ) = 1 1 9 . 5 H z . SiMe,), -33.32 (s. Ph cage-C); IR (C,H,). i.= 2581 (s). 2541 ( m ) c r n - ' (B-H): Ge M S : m :(%):435(rMt. 100).73(Me,Si.60).3. ' H N M R 2Li+ n L 'nPr (200 MHI. C,D,. 295 K. TMS ext.): d = 0.20- 4 0 (hr.. 3b L 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 Ph (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 z(%). (C,H,,).? = 25XD(s),2539(m)cm-'(B-H),MS.r7i Ph--l(\ >Ph 435 ( M + . 100). 73 (Me&. 58). r.* Crystal data for 2 (C,,H,,B,Si,. M , = 435.4): monoclinic. ?7Bu Y2, n , ~ = 9 . 6 2 8 ( 2 ) h=7.332(2). , ~ = 1 9 9 2 4 ( 5 ) 8 , .p = 3c 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 Li(C&Oz)z \~(C~H&)Z Li(thf), 1841 reflections) and corrected for Lorentz and polarizaph* - - - - - --Li(thT)3 tion effects. The structure was solved by direct methods ph+Ge p h + G : and subsequent difference Fourier synthesis using Ph Ph j Ph Ph 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 2a 2b 4 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. dichloro-2,3.4.5-tetraphenylgermole (Scheme 1 ) . The dilithium 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 chem.wisc.edu 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 \ XPh Y l ~ ~ Technion-Israel Institute of Technology 32000 Haifa (Israel) [**I 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.