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Abstract

Reaction of HCHO with B₁₀H₁₄ under aqueous alkaline conditions yields the arachno 10-vertex [6-CB₉H₁₄]^- anion 2 (60%) which upon solid-state thermolysis as its Cs⁺ salt yields the closo 9-vertex [4-CB₈H₉]^- anion 1 (45%). MeCHO reacts similarly to give the C-methylated arachno [6-Me-6-CB₉H₁₃]^- anion 4 (37%) which upon thermolysis gives the closo [4-Me-4-CB₈H₈]^- anion 3 (72%). PhCHO with B₁₀H₁₄ under alkaline conditions gives the nido 10-vertex [6-Ph-6-CB₉H₁₁]^- anion 6 (85%) which upon thermolysis of its [NEt₄]⁺ salt gives the closo [4-Ph-4-CB₈H₈]^- anion 5 (73%). In a preliminary iodination investigation, unsubstituted closo anion 1 with elemental I₂ in CH₂Cl₂ gives approximately equimolar closo [4-CB₈H₈-3-I]^- 12 and closo [4-CB₈H₈-5-I]^- 13 (ca 60%) and smaller amounts of closo [4-CB₈H₇-5,6-I₂]^- 14 (12%). The [NEt₄]⁺ salts of 1, 3 and 5 are characterised crystallographically, as is the [PMePh₃]⁺ salt of 12.

Keywords: Boranes; Carboranes; Monocarbaboranes; Thermolyses; Iodination; [4-CB₈H₉]^-.

References: 50 live references.