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 [MLn'](+) group is attached to the cage system in an exopolyhedral manner by one, two, or three agostic B-H-->MLn' 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-(mu-H)(3)-7,8,12-{Cu(PPh3)}-closo-2,1-MoCB10H8], [2,2,2-(CO)(3)-2-PPh3-7,12-(mu-H)(2)-7,12-{Ag(PPh3)}-closo-2,1-MoCB10H9], [2,2,2-(CO)(3)-2-PPh3-7,8,12-(mu-H)(3)-7,8,12-{RuCl(PPh3)(2)}-closo-2,1-MoCB10H8] and [2,2,2-(CO)(3)-2-PPh3-12-(mu-H)-12-{Fe(CO)(2)(eta-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 P-31-{H-1} NMR data have helped elucidate these processes for the isomers observed for this complex. The NMR data (H-1, C-13, B-11, and P-31) for the new compounds are discussed.