Synthesis and derivatization of the 2-amino-closo-decaborate anion [2-B10H9NH3]−

A novel high-yield method of synthesis of the [2-B10H9NH3]− anion was elaborated. The method proposed includes reaction of the closo-decaborate anion with acetonitrile in the presence of acid, followed by hydrolysis of the formed nitrilium derivative [2-B10H9NCMe]− first to the acetamide derivative [2-B10H9NH2COMe]− and then to the amine. The crystal molecular structure of (Bu4N)[2-B10H9NHC(OH)Me] was determined by single crystal X-ray diffraction method. In the solid state, the acetamide derivative exists in the O-protonated tautomeric form and has a Z-configuration where the NH proton and the OH group are trans around the CN bond. The reaction of the [2-B10H9NH3]− anion with aromatic aldehydes in methanol in the presence of catalytic amounts of alkali gives N-protonated Schiff bases [2-B10H9NHCHR]− (R=C6H5, C6H4-2-OMe, C6H4-4-NHCOMe). Reduction of the Schiff bases with NaBH4 in aqueous methanol gives the corresponding monoalkylamino derivatives [2-B10H9NH2CH2R]− (R=C6H5, C6H4-2-OMe, C6H4-4-NHCOMe). The approach developed can be used in the synthesis of functional derivatives of the closo-decaborate anion for applications in nuclear medicine.