The discovery of sandwich complexes with ferrocene (I) highlighted the fundamental role of cyclopentadienyl (Cp) ligands in sandwich complexes. The tunability of Cp ligands has inspired chemists to explore isoelectronic planar main-group rings (P5, As5, Sb5, Bi5, Si5, B5) as alternative ligand frameworks aiming to achieve greater electronic versatility. Notably, in 2002, the isolation of the fully inorganic metallocene, [Ti(P5)2] 2- (II), marked the first 16e carbon-free sandwich complex. In contrast, boron rings remained largely unexplored for decades due to the intrinsic electron deficiency of boron and its preference for polyhedral cluster geometries. This perception was overturned by transition-metal templation strategies. Grimes reported the first pentaborane ring complex [(CpFe)B5H10], which was later extended to Ru and Ir analogues by Fehlner. Recently, we have synthesized the Os analogue (III) using a Cp-based metal precursor. Encouraged by these results, we attempted to synthesize carbon-free sandwich complexes using various metal precursors, for example, [M2(μ-Cl)2(COD)2] (M = Ir, Rh), [M(PPh3)3Cl2] (M = Ru, Os), [Cp*Fe(dppe)Cl] and [Fe(dppe)Cl2]n; however, these efforts were unsuccessful. Interestingly, using [Os(PPh3)3Cl2] and [Cp*OsBr2]2 as precursors, we have isolated a tetraborane [B4H8] 2- (IV) and a hexaborane [B6H11] - (V) rings, stabilized by the monometallic Os-templates. These results will be discussed in detail.