Six-Ring Ligands

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]. 

The structure resembles the corresponding anthracene complex [203]. The ligand is bonded in an allylic fashion with Sm-N bonds in the range of Ln-N (r-bonds and Ln-C bonds at the long range end of allylic interactions (2.866(3), 2.877(2) A). In contrast the reaction of SmCpf with acridine again yielded a coupled product, which contains a similar allylic bonding pattern (Sm-C, 2.944(5), 2.970(5) A) [203]. 

Fused heterocyclic dianionic ligands are also accessible to lanthanide(III) complexes which has been shown for quinoxaline and phenazine [204] (Table 16). The existence and availability of the alkali metal precursors allows the usual metathesis reaction. 

Reaction of Cp LuH with pyridine yielded the orthometallated (C,N- /2) pyridine complexes under release of hydrogen [205]. The scandium complexes CpfScR (R = H, CH3, C6H5, CH2C6H5) show a similar reaction [206]. 

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