Reactions of hypersilyl potassium with rare-earth metal bis(trimethylsilylamides): Addition versus peripheral deprotonation

The scope of hypersilyl potassium, KHyp [Hyp = Si(SiMe3)(3)], as a silylation or deprotonation agent for some rare-earth bis(trimethylsilyl)amides has been explored. Thus, the reaction with Yb{N(SiMe3)(2)}(2) affords the addition product [K][YbHyp{N(SiMe3)(2)}(2)] (2) in high yield, which contains a three-coordinate ytterbium atom, therefore representing the first example of a lanthanide silyl with a coordination number lower than 6. In contrast, deprotonation on the periphery is observed with the tris(amides) Ln {N(SiMe3)(2)}(3) (Ln = Y, Yb) and compounds of the type [K][CH2Si(Me)(2)N(SiMe3)Ln{N(SiMe3)(2)}(2)] (Ln = Y (3), Yb (4)) are isolated. Crystallization of 3 from a mixture of benzene and heptane afforded the bis(benzene) solvate [(C6H6)(2)K][CH2Si(Me)(2)N(SiMe3)Y{N(SiMe3)(2)}(2)] (3a). The reaction between the strong bases (BuLi)-Bu-n/tetramethylenediamine (TMEDA) or (BuLi)-Bu-t with Y{N(SiMe3)(2)}(3) or Yb{N(SiMe3)(2)}(3) yielded the deprotonation product [(tmeda)Li][CH2Si(Me)(2)N(SiMe3)Y{N(SiMe3)(2)}(2)] (6) and the reduction product [LiYb{N(SiMe3)(2)}(3)] (7), respectively. Instead of the expected bimetallic product, the reaction between Ybl(2) and 2 equiv of 3 gave the neutral complex [Y{CH2Si(Me)(2)N(SiMe3)}{N(SiMe3)(2)}(thf)] (8) in good yield. The compounds have been characterized by melting point, elemental analysis, IR spectroscopy, and X-ray crystallography and for selected species by H-1, C-13, Si-29, and Yb-171 NMR spectroscopy. For 3a and 4, the nature of the bonding between the carbanionic centers and the lanthanide and potassium cations was studied by density functional theory calculations.