Bridging ligands double

It is hard to envisage a ligand, which generally requires a double equivalent transformation, being reduced in preference to the central atom. Even if Lr is formed as intermediate by direct interaction with Y, it is likely to act as a reductant, and the equilibrium M+a + L = M+a 1 + L will be shifted to the right. This is in fact the mechanism of ligand-bridged redox reactions as demonstrated in the case of Co(III)L-Cr(II) reactions (86). 

In the course of probing the range of reactivity accessible to decamethyl-samarocene, substrates containing C=N double bonds as part of 6-membered heterocycles have been tested. In the reaction with pyridazine reductive carbon-carbon bond formation occurred (compare Sect. 3.2) [99], The coupled ligand bridges two Sm(III) centers via the four nitrogen positions. In the phenazine reaction one phenazine ligand is placed between the Sm(III) centers (Fig. 20 Table 16) [203]. 

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