Tris(pentamethylcyclopentadienyl) Complexes of Late Lanthanides Tb, Dy, Ho, and Er: Solution and Mechanochemical Syntheses and Structural Comparisons

The tris(pentamethylcyclopentadienyl) complexes, (C5Me5)3Ln (Ln = Tb, Dy, Ho, and Er), have been synthesized to determine if structural trends observed with the larger rare-earth metals, La–Gd, extend to the smaller metals and to determine the level of steric crowding associated with C–H bond activation of benzene and toluene as found for the (C5Me5)3Y complex of the smaller rare-earth metal, yttrium. Three different synthetic methods were used. (C5Me5)3Tb was synthesized in benzene from (C5Me5)2Tb(μ-Ph)2BPh2 and KC5Me5, which established that it does not activate benzene. In contrast, complexes of Dy, Ho, and Er were not isolable in benzene or toluene. (C5Me5)3Dy was synthesized in pentane from [(C5Me5)2DyH]2 and 1,2,3,4-tetramethylfulvene. Solvent-free mechanochemistry was utilized to synthesize the Ho and Er complexes by ball-milling (C5Me5)2Ln(μ-Ph)2BPh2 and KC5Me5 as solids. This route also provided the Tb, Dy, and Y complexes. Crystallographic analysis of these complexes of the smaller metals has al...