Monocarbaborane anion chemistry. {COOH}, {CH2OH} and {CHO} units as functional groups on ten-vertex monocarbaborane anionic compounds

Abstract

B₁₀H₁₄ reacts with para-C₆H₄(CHO)(COOH) in aqueous KOH solution to give the [nido-6-CB₉H₁₁-6-(C₆H₄-para-COOH)]⁻ anion 1, which undergoes cage closure with iodine in alkaline solution to give the [closo-2-CB₉H₉-2-(C₆H₄-para-COOH)]⁻ anion 2. Upon heating, anion 2 rearranges to form the [closo-1-CB₉H₉-1-(C₆H₄-para-COOH)]⁻ anion 3. Similarly, B₁₀H₁₄ with glyoxylic acid OHCCOOH in aqueous KOH gives the [arachno-6-CB₉H₁₃-6-(COOH)]⁻ anion 4, which undergoes cage closure with iodine in alkaline solution to give the [closo-2-CB₉H₉-2-(COOH)]⁻ anion 5. Upon heating, anion 5 rearranges to give the [closo-1-CB₉H₉-1-(COOH)]⁻ anion 6. Reduction of the {COOH} anions 3 and 6 with diisobutylaluminium hydride gives the {CH₂OH} hydroxy anions [closo-1-CB₉H₉-1-(C₆H₄-para-CH₂OH)]⁻7 and [closo-1-CB₉H₉-1-(CH₂OH)]⁻8 respectively. The [closo-1-CB₉H₉-1-(C₆H₄-para-CH₂OH)]⁻ anion 7 can also be made via isomerisation of the [closo-2-CB₉H₉-2-(C₆H₄-para-CH₂OH)]⁻ anion 9, in turn obtained from the [nido-6-CB₉H₁₁-6-(C₆H₄-para-CH₂OH)]⁻ anion 10, which is obtained from the reaction of B₁₀H₁₄ with terephthaldicarboxaldehyde, C₆H₄-para-(CHO)₂, in aqueous KOH solution. Oxidation of the hydroxy anions 7 and 8 with pyridinium dichromate gives the aldehydic [closo-1-CB₉H₉-1-(C₆H₄-para-CHO)]⁻ anion 11 and the aldehydic [closo-1-CB₉H₉-1-(CHO)]⁻ anion 12 respectively, characterised as their 2,4-dinitrophenylhydrazone derivatives, the [closo-1-CB₉H₉-1-C₆H₄-para-CHN–NHC₆H₃(NO₂)₂]⁻ anion 13 and the [closo-1-CB₉H₉-1-CHN–NHC₆H₃(NO₂)₂]⁻ anion 14 respectively.