The vacuum pyrolysis of Tl₂R¹R²C₂B₉H₉(R¹=R²=H; R¹=H, R²=CH₃; R¹R²=CH₃) species yielded some interesting thallium-containing heterocarboranes. The major pyrolysis products are thallium metal and TlR¹R²C₂B₉H₁₀. Hydrogen and the corresponding closo-carboranes, R¹R²C₂B₉H₉, were produced as minor products. The reactions of Tl₂R¹R²C₂B₉H₁₀ compounds with weak organic acids yielded the identical Tl₂R¹R²C₂B₉H₁₀ products that were produced by vacuum pyrolysis. The action of strong protic acids on Tl₂R¹R²C₂B₉H₉ produced the nido-carboranes, R¹R²C₂B₉H₉. The mechanism of the pyrolysis reaction and the proposed structures of the Tl₂R¹R²C₂B₉H₁₀ compounds are discussed. The compounds were identified by ¹H and ¹⁹B NMR, IR, mass spectrometry, and elemental analysis. / Master of Science