Metal-Only Lewis Pairs with Transition Metal Lewis Bases

The Lewis plasticity of transition metals is discussed to better understand a good transition metal Lewis base. Bergman and Anderson presented an example of the iridium complex in which the two magnesium fragments adopt a bridging position between two Lewis-basic metal fragments. Here, the contribution of the orbital and electrostatic components to the overall stability of the complexes were found to be relatively similar. A recent use of XANES techniques by Gabbai and co-workers, has shown that there are few experimental diagnostic tools for determining whether a metal-metal bond is covalent, dative, or a mixture of the two. The unusual adduct was prepared by Del Paggio and co-workers, resulting in the exchange of one CO with one phosphine ligand between the two metals. During the course of their studies on metal-metal dative bonding, Pomeroy and co-workers uncovered two highly unusual trinuclear complexes, which they described as having two M-M dative bonds in tandem.