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)2N(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)2K][CH2Si(Me)2N(SiMe3)Y{N(SiMe3)2}2] (3a). The
reaction between the strong bases nBuLi/tetramethylenediamine (TMEDA) or tBuLi with Y{N(SiMe3)2}3 or
Yb{N(SiMe3)2}3 yielded the deprotonation product [(tmeda)Li][CH2Si(Me)2N(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 YbI2
and 2 equiv of 3 gave the neutral complex [Y{CH2Si(Me)2N(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 1H, 13C, 29Si, and 171Yb 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.