Hexagonal Planar [B6H6] within a [B6H12] Borate Complex: Structure and Bonding of [(Cp*Ti)2(μ-η6 : η6-B6H6)(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)(mu-eta(6) : eta(6)-B6H6)(mu-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.

Automated summary

This study reports the synthesis of a triple-decker sandwich complex of titanium with a nearly planar six-membered [B6H6] ring. The achievement of the planar structure is attributed to the specific structural pattern and the larger ring size. However, the bond strength is reduced due to significant electron delocalization.