Bis(η6-cycloborane)chromium [Cr(η6-B6H12)2] as a Boron Analog of Bis(η6-benzene)chromium

Inspired by the newly discovered sandwich D5d [Os(η5-B5H10)2] as a carbon-free analog of ferrocene [Fe(η5-C5H5)2] and based on extensive global searches and first-principles theory calculations, we present herein the viable possibility of a staggered sandwich bis(η6-cycloborane)chromium D6d [Cr(η6-B6H12)2] (1) with two equivalent η6-B6H12 ligands isovalent with benzene as the boron analog of the eclipsed bis(η6-benzene)chromium D6h [Cr(η6-C6H6)2] (2). Detailed coordination bonding pattern, energy decomposition, and magnetically induced ring current analyses indicate that D6d 1 matches the 18-electron rule (1S21P61D10) and exhibits similar aromaticity to D6h 2, rendering high stability to the system. The metal–ring coordination bonding in D6d 1 is dominated by effective Cr → (η6-B6H12)2 δ-back-donations which appear to be significantly stronger than the corresponding Cr → (η6-C6H6)2 δ-back-donations in D6h 2, leading to an unusually short ring–ring distance of 2.70 Å and a large HOMO-LUMO gap of 7.06 eV in 1. D6d 1 and D6h 2 can also be used as building blocks to form their sandwich tetramers D2h [Cr4B48H76] (3) and D2h [Cr4C48H28] (4) and sandwich two-dimensional nanosheets [Cr(η6-B6H6)2] (5) and [Cr(η6-C6)2] (6) via partial or complete dehydrogenations, respectively.