Inorganic Chemistry, Vol.39, No.9, 1901-1906, 2000
The synthesis and characterization of bis-substituted derivatives of the [a(2)-B20H18](4-) anion and the interconversion of isomers
The apical-apical (a(2)) isomer of [Et4N](4)[B20H18] reacts with oxalyl chloride in dichloromethane to produce a protonated his-substituted carbonyl species, [Et4N][a(2)-B20H17(CO)(2)] ([Et4N][H1]), in 60% yield. Removal of the bridging hydrogen of the[H1](-) anion in aprotic media results in rearrangement to form the equatorial-equatorial [e(2)-B20H16(CO)(2)](2-) anion ([e(2)-1](2-)). The reaction of [Et4N][H1] with sodium azide in acetonitrile produces [Et4N](3)-[a(2)-B20H17(NCO)(2)] ([Et4N](3)[H-2]) in 53% yield, which subsequently reacts with isopropylamine in acetonitrile to provide the urea derivative [a(2)-B20H16(NH2C(O)NH(i-Pr))(2)](2-) ([Et4N](2)[4]) in 89% yield. The [H1](-) ion is hydrolyzed in aqueous acetonitrile to give a protonated [a(2)-B20H17(CO2H)(2)](3-) ion ([H3](3-)) in 61% yield. The a(2) isomers of the bis-substituted species [B20H16(CO2H)(2)](4-) ([3](4-)), [B20H16(NCO)(2)](4-) ([2](4-)), and [B20H16(NH2C-(O)NH(i-Pr))(2)](2-) ([4](2-)), formed by the removal of the bridging proton from their protonated precursors, rearrange to form a mixture of ae isomers in solution.