N-alkylation of ammine-undecahydro-closo-dodecaborate(1-)

The reactions of the ammine-undecahydro-close-dodecaborate(1-) anion with alkyl halides have been studied in detail. The degree of alkylation of the nitrogen was found to be dependent upon the steric demands of the alkyl groups. The derivatives were characterized by NMR and infrared spectroscopy. Four compounds were crystallized for single crystal X-ray diffraction studies. The tetrahedral coordination of the nitrogen atom of the bis-alkylated derivatives was found to deviate towards planarity with increasing steric hindrance of the substituents. - The syntheses, crystal structures, and spectral properties of four N-alkyl derivatives of [H3N-B12H11](-), ammine-undecahydro-closo-dodecaborate(1-) (3), are reported. Alkylation of 3 with ethyl iodide was achieved in dimethyl sulfoxide using potassium hydroxide as a base. This led to orthorhombic crystals of [N(n-C4H9)(4)][(CH3CH2)(3)N-B12H11] (4). The reaction of 3 with benzyl chloride resulted in the bisbenzylated product, isolated as triclinic crystals of [PPN][(C6H5CH2)(2)NH-B12H11] (5). The alkylation of 3 with 2-bromopropane gave a mixture of the mono- and bisalkylated products. The monoalkylated derivative [PPN][(CH3)(2)CH)NH2-H-12(11)] (6, crystallized in the triclinic space group (P) over bar 1) and the bisalkylated product [PPN]([(CH3)(2)CH](2)NH-B12H11] (7, monoclinic, P2(1)/c) were separated on the basis of their different water solubilities. The solid-state structures of the compounds 4-7 revealed a slight distortion of the Bla icosahedron. The length of the B(1)-N(1) bond was found to be dependent on the steric requirements of the attached amine, e.g. primary amine < secondary amine < tertiary amine. This is demonstrated by the variation in the B-N bond lengths; from 157.8(2) pm for 6, 158.5(5) pm for 5, 160.0(3) pm for 7, to 163.7(6) pm for 4.