Synthesis and Characterization of Rare Earth Siloxide Complexes, M[OSi(OtBu)3]3(L)x where L is HOSi(OtBu)3 and x = 0 or 1

The reaction of lanthanide and group 3 amides, M­[N­(SiMe3)3]3, with 3 equiv of tris­(tert-butoxy)­silanol, (tBuO)3SiOH, gives M­[OSi­(OtBu)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(OtBu)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(OtBu)3)3]­(HOSi­(OtBu)3). For M = Sc, Y, Eu, Yb, and Lu, the solid-state structures are based on five-coordinate M, M­(OSi­(OtBu)3)3(κ2-HOSi­(OtBu)3). For M = Ce, Nd, and Sm, the coordination number of the metal reaches six in molecules with the general formula M­(OSi­(OtBu)3)2(κ2-OSi­(OtBu)3)­(κ2-HOSi­(OtBu)3). In solution, the 1H nuclear magnetic resonance (NMR) spectra are fluxional, resulting in all tBu 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.