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

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.