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