Lanthanide Complexes Coordinated by a Dianionic Bis(amidinate) Ligand with a Rigid Naphthalene Linker

The synthetic pathway to a new bis(amidine) ligand with a conformationally rigid naphthalene linker, 1,8-C10H6[NHC-(tBu)=N(2,6-Me-2-C6H3)][N=C(tBu)NH(2,6-Me-2-C6H3)] (3) was elaborated. Deprotonation of this bis(amidine) ligand with two equivalents of nBuLi and subsequent reaction with anhydrous LnCl(3) (Ln = Y, Nd, Sm) allowed the synthesis of the chlorido complexes [1,8-C10H6{NC(tBu)N-2,6-Me2C6H3}(2)]YCl(dme) (4), [1,8-C10H6{NC(tBu)N-2,6-Me(2)C6H(3)}(2)]Nd(dme)(mu-Cl)(2)Li(dme) (5), and [1,8-C10H6{NC(tBu)-N-2,6-Me-2-C6H3}(2)]Sm(thf)(mu-Cl)(2)Li(thf)(2) (6), which are coordinated by the linked dianionic bis(amidinate) ligand. The structures of complexes 4-6 were established by X-ray diffraction studies, which reveal that the new ligand framework can coordinate to the lanthanide atoms in different fashions depending on the central atom ion size. Alkylation of complex 6 with equimolar amounts of LiCH2SiMe3 afforded the unexpected amido-amidinate complex [{1,8-C10H6(NC(tBu)-N-2,6-Me-2-C6H3)(2)}{1,8-C10H6(NC(tBu)N-2,6-Me-2-C6H3)-(NH)}Sm][Li(dme)(3)] (7), which obviously results from the cleavage of one amidinate group during decomposition of the transient alkyl species and ligand redistribution.