Organoboranes Oxidation and Lewis Base Borane Complexes Preparation Using Oxygen Adsorbed Carbon Materials

Abstract

Readily accessible oxygen adsorbed carbon materials like activated carbon (AC) and carbon black (CB) are useful for the oxidation of alkyl and alkenyl boranes, prepared by generating diborane using the NaBH4/I2 reagent system, to obtain the corresponding alcohols, ketones or aldehydes in 53–99 % in the presence of aq. NaOH. A mechanism involving the formation of HOO− Na+ intermediate in situ upon reaction of oxygen adsorbed carbon materials or formation of borate complexes with the negative end of the adsorbed oxygen is considered. Whereas, electron deficiency created in the carbon skeleton upon adsorption of oxygen leads to reaction with NaBH4 and PPh3 or pyridine to give the corresponding Ph3P:BH3 complex in 21–77 % and pyridine:BH3 complex in 40–52 % yields. The carbon materials could be recovered and reused after heating at 200 °C and re-adsorption of molecular oxygen at 25 °C.