Contemporary bimetallic molecules: an unusual class of exo-closo metallacarbaboranes having no metal–metal bonds

Abstract

Reactions between cationic metal–ligand fragments and salts of the anionic complexes [2,2,2-(CO)₃-2-PPh₃-closo-2,1-MoCB₁₀H₁₁]⁻ and [2,2-(CO)₂-2-L-closo-2,1-FeCB₁₀H₁₁]⁻ (L = CO or PPh₃) have afforded a range of zwitterionic compounds in which an electrophilic [ML′_n]⁺ group is attached to the cage system in an exopolyhedral manner by one, two, or three agostic B–H⇀ML′_n bonds. The bimetal compounds isolated do not have direct metal–metal bonds, a feature confirmed by X-ray diffraction for [2,2,2-(CO)₃-2-PPh₃-7,8,12-(μ-H)₃-7,8,12-{Cu(PPh₃)}-closo-2,1-MoCB₁₀H₈], [2,2,2-(CO)₃-2-PPh₃-7,12-(μ-H)₂-7,12-{Ag(PPh₃)}-closo-2,1-MoCB₁₀H₉], [2,2,2-(CO)₃-2-PPh₃-7,8,12-(μ-H)₃-7,8,12-{RuCl(PPh₃)₂}-closo-2,1-MoCB₁₀H₈] and [2,2,2-(CO)₃-2-PPh₃-12-(μ-H)-12-{Fe(CO)₂(η-C₅Me₅)}-closo-2,1-MoCB₁₀H₁₀]. The penultimate compound displays in solution complicated dynamic behaviour, in part due to the presence of a number of diastereomeric pairs of enantiomers. Low temperature ³¹P-{¹H} NMR data have helped elucidate these processes for the isomers observed for this complex. The NMR data (¹H, ¹³C, ¹¹B, and ³¹P) for the new compounds are discussed.