Methyl camouflage in the ten-vertex closo-dicarbaborane(10) series. Isolation of closo-1,6-R₂C₂B₈Me₈ (R = H and Me) and their monosubstituted analogues

Abstract

Reported are procedures leading to the first types of methyl camouflaged dicarbadecaboranes with fewer than eleven vertices. The compounds contain the closo-1,6-C2B8 scaffolding inside the egg-shaped hepta - decamethyl sheath, which imparts unusually high air and solvolytic stability to all of these compounds.

Thiaboranes on Both Sides of the Icosahedral Barrier: Retaining and Breaking the Barrier with Carbon Functionalities

“…Consequently, the methylated borons in the 11 B NMR spectrum of 7,8,9,10,11,12‐Me 6 ‐ closo ‐1‐SB 11 H 5 are significantly paramagnetically deshielded to high frequencies (i. e. downfield‐shifted) with respect to the parent compound (−5.6 ppm for B(7–11), 18.2 ppm for B(12)). This quantitatively agrees with the trend observed for methylated carbaboranes . In contrast, the borons of the pentagonal belt directly adjacent to sulfur are more shielded (i. e. upfield shifted) than in the parent compound (−5.2 ppm for B(2–6)) …”

“…This quantitatively agrees with the trend observed for methylated carbaboranes. [30,31,32] In contrast, the borons of the pentagonal belt directly adjacent to sulfur are more shielded (i. e. upfield shifted) than in the parent compound (À 5.2 ppm for B (2)(3)(4)(5)(6)). [26] Nido Thiaborane Clusters…”

“…After column chromatography on silica gel using hexane as an eluent, 0.210 g (85 % yield based on the starting 1-SB 11 H 11 ) of 7,8,9,10,11,12-Me 6closo-1-SB 11 H 5 were obtained as a white powder, as unambiguously verified by the ab initio/GIAO/NMR structural tool (see Table 3 and refs. [5,14,[30][31][32] as other examples of this structural methodology). Its purity > 98 % was assessed by GC MS. Figure 5.…”

Quantitative syntheses of permethylated closo-1,10-R2C2B8Me8 (R = H, Me) carboranes. Egg-shaped hydrocarbons on the Frontier between inorganic and organic chemistry

“…Another straightforward route leading to quantitative formation of permethylated dicarbaboranes 2 consists in thermal isomerisation of closo -1,6-R 2 C 2 B 8 Me 8 (3) carboranes (R = H 3a or Me 3b) 10 by heating at 400–500 °C in a sealed tube for 2 h. A similar thermal isomerisation principle could be also applied to the substituted derivatives, for example to closo -1,6-H 2 C 2 B 8 Me 7 -8-OTf (4a), 10 which underwent cage rearrangement to afford 97% of the closo -1,10-H 2 C 2 B 8 Me 7 -2-OTf (5a) upon a similar heating, as shown in Scheme 2 .…”

“…2 ) and those leading to a series of halo derivatives 1,10-H 2 C 2 B 8 H 7 -2-X. 6 The successful B-methylation experiments in the 12-vertex carborane series, 7–9 together with those achieved by our group in the B-methylation of closo -1,6-C 2 B 8 H 10 , 10 arachno -6,9-C 2 B 8 H 14 , 11 prompted us to extend boron-methylation strategy to the most stable members of the 10-vertex closo series, closo -1,10-R 2 C 2 B 8 H 10 (1) (where R = H or Me), which have been now relatively easily available. 12 In this article we would like to present electrophilic reactions with methylation agents leading to quantitative permethylation of B-vertexes under the formation of rigid, hydrocarbon–boron structures of egg shape that exhibit outstandingly high stability.…”