Abstract
The crystal and molecular structures of the three compounds Me 2Si(N tBu) 2(AlPh 2) 2 (I), Me 2Si(N tBu)(N tBuH)AlCl 2 (II) and [Me 2Si(N tBu) 2InMe] 2 (III) have been obtained by X-ray structure determinations. Compound I represents a bicyclic organometallic molecule, in which two four-membered cycles share a common AlN edge (197.5(6) pm). One of the rings consists of a tetravalent silicon atom, a three-valent nitrogen atom, and an aluminum and nitrogen atom with a four-fold coordination, the other ring unites the two latter atoms together with a tetrahedral aluminum and carbon atom. The carbon atom is a member of a phenyl group and is in a special binding position. One of the aluminum atoms in I is thus stabilized by a donor—acceptor bond, the other by a two-electron-three-center-bond (AlC 214.5(8) and 220.7(5) pm). By temperature dependent NMR techniques it can be shown that molecules such as I show fluctional behaviour in non-polar solvents. In molecule II an intramolecular nitrogen—aluminum bond (199.4(2) pm) is responsible for the formation of a cycle, which contains a tetrahedral silicon atom, two nitrogen atoms (four- and three-fold coordination) and an aluminum atom with four ligands. In the crystal of II hydrogen bonds of the type NH ⋯ Cl can be recognized. The indium compound III (point symmetry, C i ( 1 )) may be described as a polycyclic unit built up of three four-membered rings standing orthogonally against each other and sharing common edges. It originates from two SiN 2In cycles which are held together by two Nin donor—acceptor bonds (225.6(4) pm), forming an almost square central N 2In 2 cycle. As a general feature, intramolecular (II), intermolecular donor—acceptor (III) bonds as well as two-electrons-three-center bonds (I), are used to stabilize the electron-deficiency at the aluminum and indium atoms. The synthesis and the properties of the compound Me 2Si(N tBu)(N iProp)(AlMe 2) 2 (IV) are described.
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