NEW POLYCYCLIC ALUMINOPOLYSILOXANES

When diphenyldihydroxysilane, Ph2Si(OH)(2), is allowed to react with t he aluminiumalkoxydihydride (tBu-O)AlH2, the polycyclic compound [(Ph2 Si)(2)O-3](4)Al-4(OH)(4), 1, is formed. The compound is made up of fiv e eight membered cycles, the central one originating from formal donor -acceptor bonds between OH groups and Al atoms. The structure of 1 can be modified by reacting it with Lewis bases like Et3N, Et2O or C5H5N; in each case the basic structure of the polycycle is conserved, howev er serious changes are observed in the central Al4O4 ring depending up on the basicity (the hydrogen withdrawing properties) of the oxygen or nitrogen atom. It is intriguing that the pseudo host-guest behaviour of 1 is not the same for different bases and the 'shell' or 'basket' f ormed by the multiple phenyl groups and the shape of the Al-O-Si-skele ton is functioning as a selective trap such that the four OH groups ac comodate two, three and four molecules of Et3N (2), Et2O (3) and C5H5N (4), respectively The spatial consideration of the central part of th e molecular unit for the incoming base i.e. an opening or closing effe ct is subjected to the steric requirements of the base employed. The r eplacement of hydrogen atoms in 1 by lithium atoms results in further cyclisation of the molecule to yield a higher polycyclic compound, [(P h2Si)(2)O-3](4)O4Al4Li4, which can be isolated as a tetrakis(diethylet her) adduct (5) or as a tris(diethylether) bis(ammonia) adduct (6). Ne vertheless the connection of the atoms in 1 is retained in compounds 5 and 6. If the organic bases attacking 1 are replaced by the smaller a nd more acidic water molecule the new compound 7, [(Ph2Si)(2)O-3](6)Al -6(OH)(3)Al(OH)(6)3OEt(2), is formed, the structure of which is compl etely different from 1, 2, 3 or 4. In this case the starting molecule has been rearranged by the influence of water.