Synthesis and Structure of Siloxy-Substituted ZnO Aggregates Having (ZnO)n (n = 2, 4) and Zn3O4 Cores

Abstract

Convenient syntheses and X-ray crystallographic characterizations of the first bis(trimethylsilyl)amido-, methyl-, and iodozinc triorganosiloxide aggregates 1−5 are described. They are accessible by the simple reaction of ZnR′2 [R = Me, N(SiMe3)2] with the respective silanols R3SiOH (R = Me, Et, iPr), which affords the dimeric [(Me3Si)2NZnOSiR3]2 (1a: R = iPr; 1b: R = Et), trinuclear [(MeZn)2Zn(OSiiPr3)4] (2a), {[(Me3Si)2NZn]2Zn(OSiR3)4} (2b: R = Et; 2c: R = Me), and tetranuclear heterocubanes [MeZnOSiR3]4 (3a: R = Me; 3b: R = Et), respectively. The latter were oxidized with four equivalents of elemental iodine to form the tetraiodo derivatives [IZnOSiR3]4 (4a: R = Me; 4b: R = Et) in 82 and 88% yield, respectively. Due to the higher polarity of the Zn−I vs. Zn−C σ-bond, the Zn−O distances of the almost regular Zn4O4 core in 4a are 2−6 pm shorter than those observed in the less Lewis-acidic cluster 3b. However, the Zn−O distances in 3b and 4a are ca. 10−15 pm longer than those in 1a, 2a, and 2c, due to different coordination numbers at Zn and the effects of ring strain. Remarkably, the iodo derivatives 4a,b undergo dissociation in THF to give the respective dimeric THF solvates [IZn(THF)OSiR3]2 (5a: R = Me; 5b: R = Et), whereas the Zn4O4 cores in 3a and 3b are retained even in aprotic polar solvents.