On the chemistry of gallium .8. Synthesis and structure of [tris(trimethylsilyl)silyl]-substituted gallanes and gallates

Reaction of lithium tris(trimethylsilyl)silanide . 3THF with R(2)GaCl (R = 2,2,6,6-tetramethylpiperidino, Me, Cl) yields tmp(2)GaSi(SiMe(3))(3) (3) and R(2)Ga(THF)Si(SiMe(3))(3) (R = Me, Cl) (7, 9). Both gallium nitrogen bonds in 3 are cleaved by protic reagents. Depending on the acidity of these agents, either oligomeric gallanes [(RO)(2)GaSi(SiMe(3))(3)](n) (R = Et, H, n = 2, 3) (11, 12) or tetramethylpiperidinium gallates [X(3)GaSi(SiMe(3))(3)](-)(X = OPh, Cl) (13, 14) are formed. Hydroxide 11 adds lithium hydroxide to afford the mixed lithium gallium hydroxide 15. Single-crystal X-ray diffraction studies confirm the suggested constitutions. The gallium-silicon bond can adopt values between 236 and 247 pm. Here electronic influences of the substituents on the gallium center are of great importance as well as their steric demand. This is underlined by quantum chemical calculations on the ab initio (SCF) level.