Synthesis and Characterization of Rare Earth Siloxide Complexes, M[OSi(O<i>t</i>Bu)₃]₃(L)_x where L is HOSi(O<i>t</i>Bu)₃ and x = 0 or 1

The reaction of lanthanide and group 3 amides, M­[N­(SiMe₃)₃]₃, with 3 equiv of tris­(<i>tert</i>-butoxy)­silanol, (<i>t</i>BuO)₃SiOH, gives M­[OSi­(O<i>t</i>Bu)₃]₃ complexes. Their solid-state structure depends on the size of the lanthanide metal; for M = Sc, Yb, and Lu, the primary coordination sphere is a square-based pyramid in which two siloxides are κ²-coordinated and one is κ¹-coordinated. For La, Nd, and Sm, dimeric structures in which the bridging -OSi­(O<i>t</i>Bu)₃ group is κ³-coordinated are formed. When 4 equiv of silanol is used, the resulting molecules crystallize as 4:1 Si:M adducts, in which a neutral silanol remains coordinated, i.e., M­[(OSi­(O<i>t</i>Bu)₃)₃]­(HOSi­(O<i>t</i>Bu)₃). For M = Sc, Y, Eu, Yb, and Lu, the solid-state structures are based on five-coordinate M, M­(OSi­(O<i>t</i>Bu)₃)₃(κ²-HOSi­(O<i>t</i>Bu)₃). For M = Ce, Nd, and Sm, the coordination number of the metal reaches six in molecules with the general formula M­(OSi­(O<i>t</i>Bu)₃)₂(κ²-OSi­(O<i>t</i>Bu)₃)­(κ²-HOSi­(O<i>t</i>Bu)₃). In solution, the ¹H nuclear magnetic resonance (NMR) spectra are fluxional, resulting in all <i>t</i>Bu groups being chemically equivalent. The solid-state ¹H, ¹³C, and ²⁹Si NMR spectra are consistent with the stereochemistry found in the X-ray crystal structure