The first example of a compound containing a mixed-oxidation-state indium sub-halide complex anion, [ln(5)Br(8)(quinuclidine)(4)](-), has been accessed by the controlled decomposition of an indium trihydride adduct, [InH3(quinuclidine)], in the presence of LiBr. An intermediate in this reaction, [InH2Br(quinuclidine)2], has been isolated and suggests that its mechanism involves hydride-bromide exchange, reductive dehydrogenation, and disproportionation process.