Chemistry of compounds with the 1-carba-closo-dodecaborane(12) framework

Abstract

Synthesis of various compounds containing the l-carba-c1oso-dodecaborane cage is reported. The isolated derivatives include zwitterionic I-L-I-CBlt Htl (L = H3N and (CH3hS) and 12-L-I-CB tt Htl (L = (CH3)2S and CH 3 SCH 2 SCH 3 ) compounds along with C-substituted derivatives of the general formula [I-X-CBII HI tl-(X = HOOC, HO, CH 3 0, HS and CH 3 S).Direct halogenation of [1-CB II H I2 1-produces [7,8,9,1O,12-CI s -I-CB II H 7 1-, [7,8,9,10,11,12--X6-I-CBIIH61-(X = CI, Br), [12-1-CB II H I tl-and [7,12-I 2 +CB II H I0 1-substituted species. Constitution of all produ(ts was established by t H, liB, IR and mass spectrometry and is supported by some chemical reactions of the compounds.The [1-CBl.lH12]-anion (I) was first isolated in 1967 by Knoth!, who later 2 improved the synthesis and made initial attempts at substitution, impure samples of B-bromo and 1-(CH 3 hSi-derivatives being the only products. We have recently found a more convenient route 3 .4 to the parent anion I and to some of its uncharged l-L-I-CBllHll (II) (L = CH3NH 2, (CH3)2NH and (CH3hN) congeners. We wish to report in this paper some other possibilities of synthetizing a series of new substituted derivatives in this area of borane chemistry.Several new derivatives of the anion I and its zwitterionic analogues II can be obtained either from the relevant 7-substituted 7-carba-nido-undecaboranes, 7-L-7--CBlOHI2 (III), by inserting the missing boron vertex or by modifying the present exoskeletal functional group in the compounds of the type II.If 7-H3N-7-CBlOHI2 (IlIa) is treated with sodium tetrahydroborate followed by prolonged heating with triethylamine borane at 200°C and the intermediate product is then hydrolyzed with hydrochloric acid, l-amine-l-carba-closo-dodecaborane(ll), I-H3N-I-CBuHu (lIa), can be obtained in good yield as the parent compound of the loN-substituted species. Its N-monomethylderivative lIb is available from the N,N-dimethyl derivative 3 lIe by a curious demethylation with iodine 4 and the N,N,N-trimethyl derivative lId results from successive methylation of any of compounds 11 a-e. Derivatives II a -e behave as weak N-acids with pK" values 6'0, 6'5, and 5'7, respectively (50% ethanol), giving rise to anions [1-H 2N-I-CB IIH II] -(Ia). [1-CH3NH-I-CB1.1HII]-(Ib)4 and [1-(CH3)2N-I-CBtIHu]-(Ie)3.

Carborane acids. New “strong yet gentle” acids for organic and inorganic chemistry

“…The IR spectrum shows very little perturbation of the CB 11 cluster bands relative to the silylium starting material so protonation of the anion must occur on the halogen substituents (red atoms X in Fig. 1) at the same positions (7)(8)(9)(10)(11)(12) …”

“…The prospects are good that tailoring the substituents on the CB 11 cluster, such as the introduction of fluoro 48 or trifluoromethyl 49 groups, will lower the basicity of the anion without sacrificing chemical stability, and lead to even stronger acids than H(CHB 11 Cl 11 ).…”

“…1). 11 Upon reading that anions of this type had an ''…oral toxicity to rats roughly comparable to sodium chloride…'' 12 we began to comprehend their extraordinary inertness and their potential as weakly coordinating anions.…”

“…Carborane acids are exceptionally strong acids because their anions are exceptionally weak bases. This arises from the large size of the anions, the delocalized nature of the negative charge in the CB 11 cluster, and the shield of halide substituents. However, there is an equally important consideration for attaining high acidity.…”

Four Decades of Organic Chemistry of closo-Boranes: A Synthetic Toolbox for Constructing Liquid Crystal Materials. A Review

“…Carborane and monocarbaborate-derived anions are highly nucleophilic and react with a wide range of C-electrophiles providing a convenient route to C-C bonds. The C-lithium reagents are particularly useful in the alkylation with primary iodides and bromides and carboxylation reactions described for carboranes including para-carboranes 6 (refs 20,82,83 ) and 10 (refs 58,84,85 ), and also for monocarbaborates 2 (refs 67,86 ) and 8 (ref. 61 ).…”