The auracarboranes 1,2-(2) have been synthesized. Both compounds were characterized by NMR and X-ray crystallography. Compound 2 was found to contain an aurophilic interaction between the gold centers. A variable-temperature NMR investigation indicated that the energy barrier separating the gold-gold bonded state and the nonbonded state is 11 ( 1 kcal/mol. Compound 1 crystallized in the monoclinic space group P2 1 /c with a ) 18.3380(9) Å, b ) 14.1037(6) Å, c ) 19.4716(8) Å, ) 112.003(2)°, V ) 4669 Å 3 , and Z ) 4. Data were collected using Mo KR radiation, to a maximum 2θ ) 50°, giving 8865 unique reflections, and the structure was solved by heavy atom methods. The final discrepancy index was R ) 0.047, R w ) 0.055 for 3423 independent reflections with I > 3σ(I). Compound 2 crystallized in the monoclinic space group P2 1 /c with a ) 14.058(6) Å, b ) 18.365(8) Å, c ) 20.387(9) Å, ) 109.22(1)°, V ) 4970 Å 3 , and Z ) 4. Data were collected using Mo KR radiation, to a maximum 2θ ) 45°, giving 5232 unique reflections, and the structure was solved by heavy atom methods. The final discrepancy index was R ) 0.066, R w ) 0.069 for 2536 independent reflections with I > 3σ(I).

The selective placement of substituents on the boron vertices of the three isomeric icosahedral C,B,,H,, carboranes remains as a major target of synthetic strategies."] At the same time, the attachment of functional groups to the carbon vertices and their subsequent conversion is relatively well developed[', since the C H vertices of the parent carboranes may be deprotonated with strong bases and the resulting carbanions employed as nucleophilic reagents. The principal mode of reaction of the BH vertices has been attack by electrophilic reagents leading to halogenation. metalation, or alkylation. ['. '] The nature of the products that result from these electrophilic substitution reactions are very dependent upon the identity of the carborane isomer employed as the substrate.The three isomeric icosahedral C,B,,H,, carboranes are frequently suggested as structural components for molecular scaffoldingL4] and supramolecular constructs.[51 These applications of carboranes might be better served if the BH and C H vertices were converted to their chemically stable and hydrophobically enhanced BCH, and CCH, counterparts. Completely sheathing an icosahedral carborane with methyl groups would provide a form of camouflage for the underlying polyhedral borane framework and produce a molecule whose exterior resembles a hydrocarbon, but whose superstructure is that of a polyhedral borane. Consequently, one might expect the external (CH,), sheath to reduce the reactivity characteristic of the carborane skeleton['* ' I while at the same time presenting opportunities for typical hydrocarbon reactions in an unusual environment. Such compounds would also be expected to exhibit the excellent thermal stability characteristic of carboranes and unsurpassed hydrophobicity. Until now, no successful syntheses have been reported leading to fully alkylated icosahedral carboranes, although a few low-yielding routes are known for the smaller carboranes.[61 and partial substitution of icosahedral carboranes leads to mixtures of isomers which can be difficult or impossible to separate. We here report high-yielding syntheses of 1 ,I 2-dicarba-closo-dodecaborane(I2) derivatives in which all boron vertices are methylated and one or both carbon vertices are either methylated or remain as CH vertices available for lithiation and further reactions.Permethylated 1,12-dicarba-closo-dodecaborane(l2) (1) was obtained in 91 YO isolated yield by reaction of 1,12-dimethyl-1,12-dicarba-closo-dodecaborane( 12)r7a1 with neat methyl trifluoromethanelsulfonate (methyl triflate) and small quantities of trifluoromethanesulfonic acid (triflic acid) acting as a catalyst at reflux for 20 h (Scheme 1). The identity of 1 was clearly indicated by the presence of a single signal in the I'B N M R spectrum with no coupling to hydrogen. The crude reaction products when subjected to GC/MS analysis revealed that the reaction had gone to completion; no species having less than twelve methyl groups was present. Similarly, reaction of 1,12-dicarba-closo-dodecaborane ( 12) BMe ...

The syntheses of macrocyclic species composed of carborane derivatives joined via their carbon vertices by electrophilic mercury atoms are described. The reaction of closo-1,2-Li(2)[C(2)B(10)H(10)(-)(x)()R(x)()] with HgI(2) gives Li(2)[(1,2-C(2)B(10)H(10)(-)(x)()R(x)()Hg)(4)I(2)] [R = Et, x = 2 (5.I(2)Li(2)); R = Me, x = 2 (6.I(2)Li(2)); R = Me, x = 4 (7.I(2)Li(2))]. 6.I(2)(K.[18]dibenzocrown-6)(2) crystallizes in the monoclinic space group C2/m [a = 28.99(2) Å, b = 18.19(1) Å, c = 13.61(1) Å, beta = 113.74(2) degrees, V = 6568 Å(3), Z = 4, R = 0.060, R(w) = 0.070]; 7.I(2)(NBu(4))(2) crystallizes in the monoclinic space group P2(1)/c [a = 12.77(1) Å, b = 21.12(2) Å, c = 20.96(2) Å, beta = 97.87(2) degrees, V = 5600 Å(3), Z = 2, R = 0.072, R(w) = 0.082]. The precursor to 7, closo-8,9,10,12-Me(4)-1,2-C(2)B(10)H(8) (4), is made in a single step by reaction of closo-1,2-C(2)B(10)H(12) with MeI in trifluoromethanesulfonic acid. The free hosts 5, 6, and 7 are obtained by reaction of the iodide complexes with stoichiometric quantities of AgOAc. A (199)Hg NMR study indicates that sequential removal of iodide from 5.I(2)Li(2) and 6.I(2)Li(2) with aliquots of AgOAc solution leads to formation of two intermediate host-guest complexes in solution, presumed to be 5(6)ILi and 5(2)(6)(2).ILi. Crystals grown from a solution of 6.I(2)Li(2) to which 1 equiv of AgOAc solution had been added proved to be an unusual stack structure with the formula 6(3).I(4)Li(4) [tetragonal, I4/m, a = 21.589(2) Å, c = 21.666(2) Å, V = 10098 Å(3), Z = 2, R = 0.058, R(w) = 0.084]. Addition of 2 equiv of NBu(4)Br ion to 5 or 6 gives 5.Br(2)(NBu(4))(2) and 6.Br(2)(NBu(4))(2), respectively, while addition of 1 equiv of KBr to 6 forms 6.BrK. 5.Br(2)(NBu(4))(2) crystallizes in the triclinic space group P&onemacr;, [a = 10.433(1) Å, b = 13.013(1) Å, c = 15.867(2) Å, alpha = 91.638(2) degrees, beta = 97.186(3) degrees, gamma = 114.202(2) degrees, V = 1492 Å(3), Z = 1, R = 0.078, R(w) = 0.104]. The hosts 5 and 6 form 1:1 supramolecular adducts with the polyhedral anions B(10)I(10)(2)(-) and B(12)I(12)(2)(-) in solution.

Reaction of closo-1,12-C2B10H12 (para-carborane) with 2 molar equiv of IC1 in the presence of catalytic quantities of AICI3 affords closo-1,12-C2B;oH 10I2 as a mixture of isomers. The 2,9-(2), 2,3-(3), and 2,7-isomers (4) have been isolated and characterized. Reaction of closo-1,12-C2BioHh-2-I (1) with PhMgBr or 2 with RMgBr (R = Me, Ph) in the presence of PdCl2(PPh3)2 and Cul gives high yields of closo-1,12-C2B10H11 -2-Ph (6) and closo-1,12-C2BioHio-2,9-R2 (7, R = Me; 8, R = Ph), respectively. Reaction of 1 with HC=CPh in the presence of PdCl2(PPh3)2 and pyrrolidine yields closo-1,12-C2B1 oH 11 -2-C=CPh (9). Reaction of 1 or 2 with HC=CSiMe3 under the same conditions affords closo-1,12-C2B1 oH 11 -2-C=CSiMe3 (10) and c/050-1,12-C2B1 oH 11-2,9-(C=CSiMe3)2 ( 12) which react with fluoride ion to give closo-1,12-C2B10H11 -2-C=CH (11) and closo-1,12-C2B10H1 i-2,9-(C=CH)2 ( 13), respectively. The structures of 1, 3, 4, closo-LI2-C2H2B10I10 (5), and 8 have been determined by crystallographic studies. Crystallographic data are as follows: For 1, monoclinic, space group C2/c, a = 10.824(2) k,b = 9.439(1) A, c = 21.414(3) k,0= 102.

Methodology leading to a new class of rodlike p-carborane derivatives is described, involving the palladium-catalyzed coupling of B-iodinated p-carboranes with terminal alkynes. The products of these reactions contain an alkyne substituent at a boron vertex of the p-carborane cage. Reaction of closo-2-I-1,12-C(2)B(10)H(11) (1) with closo-2-(C&tbd1;CH)-1,12-C(2)B(10)H(11) (3) in the presence of pyrrolidine and catalytic quantities of bis(triphenylphosphine)palladium dichloride and cupric iodide yields 1,2-(closo-1',12'-C(2)B(10)H(11)-2'-yl)(2) acetylene (4). Oxidative coupling of 3 in the presence of cupric chloride in piperidine affords 1,4-(closo-1',12'-C(2)B(10)H(11)-2'-yl)(2)-1,3-butadiyne (5). Reaction of 2 molar equiv. of closo-2,9-I(2)-1,12-C(2)B(10)H(10) (6) withcloso-2,9-(C&tbd1;CH)(2)-1,12-C(2)B(10)H(10) (7) in the presence of pyrrolidine and catalytic quantities of bis(triphenylphosphine)palladium dichloride and cupric iodide yields closo-2,9-(closo-2'-I-9'-C&tbd1;C-1',12'-C(2)B(10)H(10))(2)-1,12-C(2)B(10)H(10) (8), a rigid, iodine-terminated carborod trimer in which the p-carborane cages are linked at the 2 and 9 B-vertices by alkyne (C&tbd1;C) bridges. The molecular structures of 5 and the previously described closo-2,9-(C&tbd1;CSiMe(3))(2)-1,12-C(2)B(10)H(10) (9) have been determined by X-ray crystallography. Crystallographic data are as follows: for 5, monoclinic, space group P2/a, a = 12.352(6) Å, b = 14.169 (6) Å, c = 12.384(5) Å, beta = 109.69(2) degrees, V = 2041 Å(3), Z = 4, R = 0.098, R(w)( )()= 0.135; for 9, monoclinic, space group C2/m, a = 22.111(4) Å, b = 7.565(2) Å, c = 6.943(2) Å, beta = 107.871(8) degrees, V = 1105 Å(3), Z = 2, R = 0.059, R(w)( )()= 0.090.