Molecular geometries, synthesis

It is clear from the preceding section that the field of tethered arene-metal complexes is dominated by ruthenium and by arene-phosphines as ligands. In part, this situation has arisen because of the current surge of interest in the catalytic properties of ruthenium complexes in organic synthesis.85,86 Moreover, the tethered arene complexes are usually air-stable, crystalline solids with a well-defined, half-sandwich molecular geometry that, in principle, can lock the configuration at the metal centre. These compounds should, therefore, be ideal both for the study of the stereospecificity of reactions at the metal centre and for stereospecific catalysis. 

The theory of atoms in molecules192 recovers all the fundamental concepts of chemistry, of atoms and functional groups with characteristic properties, of bonds, of molecular structure and structural stability, and of electron pairs and their role in molecular geometry and reactivity. The atomic principle of stationary action extends the predictions of quantum mechanics to the atomic constituents of all matter, the proper open systems of quantum mechanics. All facets of the theory are predictive and, as a consequence, the theory can be employed in many fields of research at the atomic level, from the design and synthesis of new drugs and catalysts, to the understanding and prediction of the properties of alloys. 

As was mentioned before, isomerisation of the substituted indoles does not occur under the conditions used in this study. The selectivity of the catalytic reaction should therefore only depend on the relative rates of formation of the enehydrazines 2 and 3 in the conformation which aliows their [3,3]-sigmatropic rearrangement to occur (which is the conformation drawn in Scheme 1). The sorption data and molecular geometries indicate that the formation of both enehydrazines 2 and 3 inside the channels of zeolite beta should be possible, but 2 is probably severely hindered in adopting the conformation required for indolization, given the fact that this conformation is even bulkier than the indole isomer 4 which is formed from it. The selective Fischer synthesis of 2-benzyl-3-methylindole 5 catalyzed by zeolite beta is therefore a true example of transition state selectivity. 

The synthesis of pyranoid sugar derivatives having an episulfide group fused to the ring involves requirements of molecular geometry more critical than for episulfides on an acyclic chain. Conversion of an epoxide in a locked-ring system to an episulfide by the action of thiourea or thiocyanate ion is diflicult, because reactions of this type involve a trans-fused, cyclic intermediate (91), formation of which requires a [Pg.179]

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