Hypoelectronic isomeric diiridaboranes [(Cp*Ir)₂B₆H₆]: the “Rule-Breakers”(Cp* = η⁵-C₅Me₅)

Abstract

In an effort to synthesize supraicosahedral iridaboranes, pyrolysis of [Cp*IrCl2]2 with excess [BH3·] was carried out, and this synthesis afforded the isomeric iridaborane [(Cp*Ir)2B6H6] clusters 1 and 2. The geometry of 1 was determined to be dodecahedral, i.e., similar to that of [B8H8](2-), whereas 2 was found to exhibit a cluster shape that can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. The calculation of a large HOMO-LUMO gap further rationalized the isocloso structures for these isomers.

Hypoelectronicity and Chirality in Dimetallaboranes of Group 9 Metals

“…Structure B6Ir2–1 is closely related to the experimentally observed red Cp* 2 Ir 2 B 6 H 6 isomer. , The experimental Ir–Ir distance of 2.762 Å for this isomer, determined by X-ray crystallography, is very close to the predicted Ir–Ir distance in B6Ir2–1* of 2.780 Å. However, the central Ir 2 B 6 polyhedron in the predicted structures B6Ir2–1 and its permethylated analogue B6Ir2–1 * is a bisdisphenoid, whereas the central Ir 2 B 6 polyhedron in the experimental red Cp* 2 Ir 2 B 6 H 6 isomer is a bicapped trigonal prism.…”

“…The 8- and 9-vertex Cp 2 M 2 B n –2 H n –2 ( n = 8, 9; M = Co, Rh, Ir) structures (Table ) are discussed first in view of the interesting permethylated diiridaboranes Cp* 2 Ir 2 B n –2 H n –2 ( n = 8, 9) recently reported by Ghosh and co-workers (Figure ). , The two lowest energy Cp 2 M 2 B 6 H 6 (M = Co, Rh, Ir) structures are the two possible structures with a central M 2 B 6 bisdisphenoid having both metal atoms at degree 5 vertices (Table ). For the experimentally observed Cp* 2 Ir 2 B 6 H 6 system, these two structures are essentially energetically degenerate within 0.5 kcal/mol.…”

“…Experimental work on the Cp 2 M 2 B n –2 H n –2 (M = Co, Rh, Ir) dimetallaboranes with 2 n skeletal electrons was rather limited until the recent serendipitous syntheses of the diiridaboranes Cp* 2 Ir 2 B n –2 H n –2 (Cp* = η 5 -Me 5 C 5 ; n = 8, 9, 10) by Ghosh and co-workers (Figure ). , Two isomers of the 8-vertex Cp* 2 Ir 2 B 6 H 6 system were synthesized. The yellow isomer was found to have a bisdisphenoidal structure corresponding to the 8-vertex closo deltahedron.…”

“…Cp* 2 Ir 2 B n –2 H n –2 ( n = 8, 9, 10) diiridaboranes synthesized by Ghosh and co-workers , shown as diamond-square-diamond processes for the interconversion of the C 2 enantiomers in the 8- and 9-vertex systems. Unlabeled vertices are boron atoms.…”

“…In view of these interesting diiridaborane structures recently synthesized by Ghosh and co-workers, , we undertook a comprehensive density functional theory study of the complete series of dimetallaboranes Cp 2 M 2 B n –2 H n –2 of the group 9 metals (M = Co, Rh, Ir). As was previously found for the isoelectronic Cp 2 Fe 2 C 2 B n –4 H n –2 systems, only the 10-vertex Cp 2 M 2 B 8 H 8 systems favored isocloso structures.…”