Synthesis, characterization and reactivity of heteroleptic rare earth metal bis(phenolate) complexes

The synthesis, characterization and reactivity of heteroleptic rare earth metal complexes supported by the carbon-bridged bis(phenolate) ligand 2,2′-methylene-bis(6-tert-butyl-4-methyl-phenoxo) (MBMP2−) are described. Reaction of (C5H5)3Ln(THF) with MBMPH2 in a 1 : 1.5 molar ratio in THF at 50 °C produced the heteroleptic rare earth metal bis(phenolate) complexes (C5H5)Ln(MBMP)(THF)n (Ln = La, n = 3 (1); Ln = Yb (2), Y (3), n = 2) in nearly quantitative yields. The residual C5H5−groups in complexes 1 to 3 can be substituted by the bridged bis(phenolate) ligands at elevated temperature to give the neutral rare earth metal bis(phenolate) complexes, and the ionic radii have a profound effect on the structures of the final products. Complex 1 reacted with MBMPH2 in a 1 : 0.5 molar ratio in toluene at 80 °C to produce a dinuclear complex (MBMP)La(THF)(μ-MBMP)2La(THF)2 (4) in good isolated yield; whereas complexes 2 and 3 reacted with MBMPH2 under the same conditions to give (MBMP)Ln(MBMPH)(THF)2 (Ln = Yb (5), Y (6)) as the final products, in which one hydroxyl group of the phenol is coordinated to the rare earth metal in a neutral fashion. The reactivity of complexes 5 and 6 with some metal alkyls was explored. Reaction of complex 5 with 1 equiv. of AlEt3 in toluene at room temperature afforded unexpected ligand redistributed products, and a discrete ion pair ytterbium complex [(MBMP)Yb(THF)2(DME)][(MBMP)2Yb(THF)2] (7) was isolated in moderate yield. Furthermore, reaction of complex 5 with 1 equiv. of ZnEt2 in toluene gave a ligand redistributed complex [(μ-MBMP)Zn(THF)]2 (8) in reasonable isolated yield. Similar reaction of complex 6 with ZnEt2 also afforded complex 8; whereas the reaction of complex 5 with 1 equiv. of n-BuLi in THF afforded the heterodimetallic complex [(THF)Yb(MBMP)2Li(THF)2] (9). All of these complexes were well characterized by elemental analyses, IR spectra, and single-crystal structure determination, in the cases of complexes 1, 2 and 4–9.