Hexagonal Planar [B ₆ H ₆ ] within a [B ₆ H ₁₂ ] Borate Complex: Structure and Bonding of [(Cp*Ti) ₂ (μ‐ɳ ⁶ : ɳ ⁶ ‐B ₆ H ₆ )(μ‐H) ₆ ]

Isolation of planar [B6H6] is a long-awaited goal in boron chemistry. Several attempts in the past to stabilize [B6H6] were unsuccessful due to the domination of polyhedral geometries. Herein, we report the synthesis of a triple-decker sandwich complex of titanium [(Cp*Ti)2(μ-η6 : η6-B6H6)(μ-H)6] (1), which features the first-ever experimentally achieved nearly planar six-membered [B6H6] ring, albeit within a [B6H12] borate. The small deviation from planarity is a direct consequence of the predicted structural pattern of the middle ring in 24 Valence Electron Count (VEC) triple-decker complexes. The large ring size of [B6H6] in 1 brings the metal–metal distance into the bonding range. However, significant electron delocalization from the M−M bonding orbital to the bridging hydrogen and B−B skeleton in the middle decreases its bond strength.