Slow reactions of isomeric metallacarboranes of general formulae [(NMe₂)₃TaC₂B₉H₁₁] (3 isomers) and [(NMe₂)₃TaC₂B₉H₁₀Me] (3 isomers) with CD₂Cl₂ afford quantitative yields of monochloro complexes [Cl(NMe₂)₂TaC₂B₉H₁₁] and [Cl(NMe₂)₂TaC₂B₉H₁₀Me]. Exposure to CD₂Cl₂ for months leads to solutions containing about 70% of the dichlorides in three cases. More prolonged exposure of these and the other monochlorides leads to a mixture of boron-substituted complexes. Hydrolysis of [3,3,3-(NMe₂)₃-3,1,2-TaC₂B₉H₁₁] by moist toluene results in the formation of the oxo-bridged complex 3,3'-[3,3-(NMe₂)₂-3,1,2-TaC₂B₉H₁₁]₂(μ-O), characterised by single-crystal X-ray crystallography. The limited solubility of the latter complex in CD₂Cl₂ eliminates the presence of this compound in the reaction of [3,3,3-(NMe₂)₃-3,1,2-TaC₂B₉H₁₁] with CD₂Cl₂. The reaction of [2,2,2-(NMe₂)₃-2,1,12-TaC₂B₉H₁₁] with CH₂Br₂ in C₆D₆ quantitatively yields the monobromide [2-Br-2,2-(NMe₂)₂-2,1,12-TaC₂B₉H₁₁]. Prolonged reaction with CH₂Br₂ leads directly to isomeric boron-substituted complexes with no evidence for dibromides. The influence on ¹¹B, ¹³C and ¹H NMR chemical shifts of replacing an amide group in [(NMe₂)₃TaC₂B₉H₁₁] with chloride to give [Cl(NMe₂)₂TaC₂B₉H₁₁] is also discussed.