Cationic metal carbonyls ligand substitution reactions

The reactions of nucleophilic reagents with cationic and uncharged metal carbonyl complexes have received much attention in the past, and it is not surprising that these studies have now been extended to isocyanide metal complexes. Different products in these reactions can arise by three general routes these include ligand substitution, reactions involving attack at a ligand, and reduction of the metal complex. All have been observed in reactions with metal isocyanide complexes. 

The reaction of the transition-metal fragments with main group 15 elements directly has proven a very fruitful field for exploration. The methodology has been successful for a wide range of metal complexes. These fall generally into three basic types (1) reactions with cyclopentadienyl metal carbonyls, (2) reactions with homoleptic metal carbonyls and substituted derivatives, and (3) reactions with metal cations in the presence of a multi-dentate chelating ligand. 

Just as with neutral arene or olefin metal carbonyls, the cationic analogs are useful intermediates for the preparation of other substituted cations. This is because the organic moiety is often readily displaced by another ligand and, further, allows carbonyl derivatives to be prepared, which may not be readily accessible by direct reaction (dien = diethylene triamine). 

Cleavage of Metal-metal Bond to Ion Pairs. In polar solvents, heterolytic cleavage to anion/cation complexes is an equilibrium process. This can also be involved in substitution reactions in polar solvents (equations 94 and 95). Substitution at the cation is shown here since, for carbonyl ligands, due to a decrease in back bonding see Back Bonding),... 

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