An Alternative Synthesis of the Oligoalumosiloxane [Ph 2 SiO] 8 [Al(O)OH] 4 and its Alcohol Adducts

The oligoalumosiloxanes {[Ph 2 SiO] 8 [Al(O)OH] 4 ·2,5Et 2 O·HO t Bu} ( 6 ) and {[Ph 2 SiO] 8 [Al(O)OH] 4 ·2Et 2 O·2HO i Pr} ( 7 ) have been obtained from the reaction of diphenylsilanediol with aluminium‐ tri ‐ tert ‐butoxide and aluminium‐ tri ‐ iso ‐propoxide in ethyl ether with reasonable yields. In a 1:1 molar mixture of toluene and the respective alcohol ( iso ‐propanol or tert ‐butanol), the ethyl ether molecules in {[Ph 2 SiO] 8 [Al(O)OH] 4 ·4Et 2 O}, in 6 or 7 can be completely displaced forming the compounds [Ph 2 SiO] 8 [Al(O)OH] 4 ·4HO i Pr ( 8 ) and [Ph 2 SiO] 8 [Al(O)OH] 4 · n HO t Bu ( 9 ). Whereas 6 , 7 and 8 are crystalline, 9 is obtained as a viscous liquid. An X‐ray structure determination on {[Ph 2 SiO] 8 [Al(O)OH] 4 ·3Et 2 O·HO t Bu} reveals different bonding modes of the diethyl ether molecules to the oligoalumosiloxane compared to the tert ‐butanol, which forms two hydrogen bonds (one to the OH‐group of the inner Al 4 (OH) 4 cycle and one through the alcohol OH‐group to a Si–O–Al moiety. The alcohol adducts have been characterized in solution through 1 H‐, 13 C‐ and 29 Si‐NMR and show dynamic equilibria between the oligoalumosiloxane [Ph 2 SiO] 8 [Al(O)OH] 4 and the alcohol molecules.