Synthesis and structure of 1,12-diethynyl-para-carborane

Improved syntheses of bis(ethynyl)-para-carboranes, 1,12-(RCC)2-1,12-C2B10H10 and 1,10-(RCC)2-1,10-C2B8H8 (R=H or Me3Si)

“…The protected acetylenes 2 and 6 were likewise obtained from sequential reaction of 8 and 10 with methyllithium and chlorotrimethylsilane. The overall yields of 1, 2, 6 and 7 from para-carboranes 3 and 5 are 69%, 67%, 63% and 48%, respectively, which are superior to reported yields of up to 26% from previous single/two-step syntheses [6][7][8]10]. The convenience of a two-step route is also an obvious advantage in effort and cost over the more elaborate multi-step syntheses, which afford the ethynyl carboranes in comparable yield to those described here [9].…”

“…The reaction of the 12-vertex para-carborane (3) with 1-bromo-2-(trimethylsilyl)ethyne (4) using our usual coppermediated cross-coupling procedure [5] gave 1,12-bis(trimethylsilylethynyl)-para-carborane (2) in low yields; subsequent desilylation of 2 affords the parent species 1, 12-bis(ethynyl)-para-carborane (1) (Scheme 1(a)) [6,7]. A low-yielding synthesis of 2 has been reported by Kaszynski et al [8] while we have also used 1-bromo-3-methyl-1-butyn-3-ol instead of 4 in a two-step synthesis of 1 in low yields [7].…”

Dicarba‐closo‐dodecaboranes with One and Two Ethynyl Groups Bonded to Boron

“…[19] In contrast, a number of dicarba-closo-dodecaboranes with ethynyl groups or other alkynyl substituents bonded to carbon were structurally characterized. [2,[27][28][29][30][31][32] In Figure 1 the diethynyl-substituted clusters 1a and 3a are depicted. The CϵC and B-C bond lengths of 1a and 3a are similar (Table 1) and they are also similar to bond lengths determined for ethynyl groups bonded to boron of different clusters, for example, in the anion [12-HCC-closo-1- [33] ( [34] The differences of the experimentally determined d(CϵC) of the ethynyl-functionalized boron clusters listed in Table 1 are small and not significant (Ͻ3σ).…”

Unsymmetrical p‐Carborane Backbone as a Linker for Donor–Acceptor Dyads

“…[8] Carboranes of the closo form, such as 1,12-dicarbadecaborane (C 2 B 10 H 12 in Scheme 1) are geometrically rigid species with an electronic structure making them optically transparent and redox inactive. [1,9] However, most methods currently available for the synthesis of derivatives of this carborane provide only symmetically disubstituted species, typically those bearing either two alkyne functions, [10] two pyridines, [8] two phosphanes [8] or two 4-iodophenyl [11,12] residues. In the last case, metallation of the para-carborane and transformation to its cuprate at low temperature, and subsequent reaction with 4-(bromoethynyl)iodobenzene provides a homo disubstituted derivative with the functional groups at the vertices of the carborane cluster.…”

“…In the last case, metallation of the para-carborane and transformation to its cuprate at low temperature, and subsequent reaction with 4-(bromoethynyl)iodobenzene provides a homo disubstituted derivative with the functional groups at the vertices of the carborane cluster. [10,12] Although conversion of such a species to an unsymmetrical derivative is possible, this requires statistical cross-coupling reactions that limit the isolated yields, produce disubstituted derivatives that are useless and consume the precious starting material. [12] Note that monosubstituted carboranes are available but heterodisubstituted carboranes are elusive and have not been obtained in a controlled process mostly because of the reactivity of the first functional group towards nucleophiles.…”