Hypoelectronic 8–11-vertex irida and rhodaboranes

Abstract

A series of novel isocloso-diiridaboranes [(Cp*Ir)₂B₆H₆], 1, 2; [1,7-(Cp*Ir)₂B₈H₈], 4; [1,4-(Cp*Ir)₂B₈H₈], 5; [(Cp*Ir)₂B₉H₉], 8; isonido-[(Cp*Ir)₂B₇H₇], 3; and 10-vertex cluster [5,7-(Cp*Ir)₂B₈H₁₂], 6 (Cp* = η⁵-C₅Me₅) have been isolated and structurally characterized from the pyrolysis of [Cp*IrCl₂]₂ and BH₃·thf. On the other hand, the corresponding rhodium system afforded 10- and 11-vertices clusters [5-(Cp*Rh)B₉H₁₃)], 7, and [(Cp*Rh)₂B₉H₉], 9, respectively. Clusters 1 and 2 are topological isomers. The geometry of 1 is dodecahedral, similar to that of its parent borane [B₈H₈]^2–, in which two of the [BH] vertices are replaced by two [Cp*Ir] fragments. The geometry of 2 can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. Compounds 4 and 5 are 10-vertex isocloso clusters based on a 10-vertex bicapped square antiprism structure. The only difference between them is the presence of a metal–metal bond in 5. The solid-state structures of 8 and 9 attain an 11-vertex geometry in which a unique six-membered B6H6 moiety is bonded to the metal center. In addition, quantum-chemical calculations have been used to provide further insight into the electronic structure and stability of the clusters. All the compounds have been characterized by IR and ¹H, ¹¹B, and ¹³C NMR spectroscopy in solution, and the solid-state structures were established by X-ray crystallographic analysis.