Stickstoffverbindungen von elementen der dritten hauptgruppe mit intra- und intermolekularen donor—akzeptor-bindungen: II. Strukturelle untersuchungen

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 AlN 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 (AlC 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 NH ⋯ 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 Nin 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.