Ligand bridged dimers

The pyrazine-bridged dimer (330) is prepared as shown in Scheme 67. Detailed cyclic vol-tammetric studies on this and related N-heterocyclic ligand bridged dimers indicate a weak cluster-cluster interaction across the bridge at anodic potentials but significant interactions at cathodic potentials as the electron content of the clusters increases. Electronic spectral measurements support... 

Phosphorus and Nitrogen Ligand-bridged Dimers 4.11 Hydrocarbon-bridged Metal-metal Bonded Dimers... 

Molybdenocene, jt-bound Organic Ligand-bridged Dimers... 

Reactions of acetylenes with M2Xg(THT)3 yield monomeric, ligand-bridged dimeric and metal-metal-bound dimeric complexes depending on the alkyne substituents. An alkyne-bridged dimer, Ta2Cl6(RC=CR)(THF)2, with a Ta-Ta distance of 268 pm, results for R = CMes . 

In principle, any of the steps in Scheme 2 can be rate limiting from the diffusion controlled formation of the association complex to the substitutional breakup of the successor complex. Because of the multiplicity of steps, a detailed interpretation of an experimentally observed rate constant can be extremely difficult. However, in some cases it has been possible to obtain direct or indirect information about the electron transfer step in an inner-sphere reaction using chemically prepared, ligand-bridged dimeric complexes. For example, reduction of the Co -Ru precursor to the product shown in equation (7) by Ru(NH3)6 + or Eu + occurs selectively at the Ru " site. The initial reduction to give Ru is followed by intramolecular electron transfer from Ru to Co which is irreversible since the Co site is rapidly lost by aquation. ... 

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