Divalent Lanthanide Complexes Supported by the Bridged Bis(amidinates) L [L = Me3SiN(Ph)CN(CH2)3NC(Ph)NSiMe3]: Synthesis, Molecular Structures and One-Electron-Transfer Reactions

Metathesis reactions of YbI2 with Li2L (L = Me3SiN­(Ph)­CN­(CH2)3NC­(Ph)­NSiMe3) in THF at a molar ratio of 1:1 and 1:2 both afforded the Yb­(II) iodide complex [{YbI­(DME)2}22-L)] (1), which was structurally characterized to be a dinuclear Yb­(II) complex with a bridged L ligand. Treatment of EuI2 with Li2L did not afford the analogous [{EuI­(DME)2}22-L)], or another isolable Eu­(II) complex, but the hexanuclear heterobimetallic cluster [{Li­(DME)3}+]2[{(EuI)22-I)23-L)2(Li)4}­(μ6-O)]2– (2) was isolated as a byproduct in a trace yield. The rational synthesis of cluster 2 could be realized by the reaction of EuI2 with Li2L and H2O in a molar ratio of 1:1.5:0.5. The reduction reaction of LLnCl­(THF)2 (Ln = Yb and Eu) with Na/K alloy in THF gave the corresponding Ln­(II) complexes [Yb32-L)3] (3) and [Eu­(μ2-L)­(THF)]2 (4) in good yields. An X-ray crystal structure analysis revealed that each L in complex 3 might adopt a chelating ligand bonding to one Yb atom and each Yb atom coordinates to an additional amidinate group of the other L and acts as a bridging link to assemble a macrocyclic structure. Complex 4 is a dimer in which the two monomers [Eu­(μ2-L)­(THF)] are connected by two μ2-amidinate groups from the two L ligands. Complex 3 reacted with CyNCNCy and diazabutadienes [2,6-iPr2C6H3NCRCRNC6H3iPr2-2,6] (RH, CH3) (DAD) as a one-electron reducing agent to afford the corresponding Yb­(III) derivatives: the complex with an oxalamidinate ligand [LYb­{(NCy)2CC­(NCy)2}­YbL] (5) and the complexes containing a diazabutadiene radical anion [LYb­(iPr2C6H3NCRCRNC6H3iPr2)] (R = H (6), R = CH3 (7)). Complexes 57 were confirmed by an X-ray structure determination.