A series of bis- and tris(oxobenzimidazolyl)hydroborato compounds, namely, [Bo]Na and [To]-Na (R = Me, Bu, Ad), which feature uncommon sterically demanding LX [O] and LX [O] donor ligands, have been obtained via the reactions of NaBH with 1-R-1,3-dihydro-2H-benzimidazol-2-ones. Evidence that the alkyl substituents are suitably located to have a significant impact on the coordination environment is provided by the observation that the methyl derivative [To]Na(κ-diglyme) exhibits κ-coordination of the diglyme, whereas the t-butyl and adamantyl derivatives, [To]Na(κ-diglyme) and [To]Na(κ-diglyme), exhibit κ-coordination. The [Bo] and [To] ligands also allow for isolation of discrete mononuclear thallium compounds, [Bo]Tl and [To]Tl, for which the steric demands of the ligands have been quantified in terms of both cone angle and buried volume concepts.