Zinc compounds metallated ring systems

A comparison of these compounds with the corresponding zinc derivatives should clarify the influence of the empty d orbitals involved in the bonding situation of the alkaline earth metal bis(phosphanides). Whereas zinc bis[bis(trimethylsilyl)amide] is monomeric due to the steric demand of the bulky amide ligand [6], the trimethylsilyl substituted phosphanide leads to oligomers such as dimers or trimers [7], The influence of the pnicogen atom is small, thus the phosphorus and arsenic derivatives (Fig. 5.) look very similar [8] or even crystallize isotypically. In contrast to the d metals calcium, strontium and barium, zinc derivatives solely build up monocyclic ring systems. 

In the quinoline ring system, the heterocyclic ring is more easily reduced than the benzene ring, forming tetrahydro-compounds or even decahydroquinoline derivatives under hydrogenation conditions. Quinolines have also been reduced to 1,2,3,4-tetrahydroquinolines by zinc borohydride and dimethylaniline under sonication conditions or with indium metal in... 

The mechanisms of the electrophilic substitutions in the isoxazole nucleus have not yet been studied. They should not differ fundamentally from those usually accepted for the substitution of aromatic systems but the structural specificity of the isoxazole ring might give rise to some peculiarities, as recently specially discussed.One important point is that isoxazole shows a clearcut tendency to form coordination compounds. Just as pyridine and other azoles, isoxazoles coordinate with halogens and the salts of heavy metals, for example of cadmium,mercury,zinc. Such coordination... 

The coordination polymerisation of cyclic carbonates with a six-membered ring in the molecule, such as trimethylene carbonate (l,3-dioxan-2-one) and 2,2-dimethyltrimethylene carbonate (5,5-dimethyl-l,3-dioxan-2-one) [148-150], carried out in the presence of metal carboxylates e.g. zinc stearate, tin-based catalysts such as the di(w-butyl)stannic diiodide-triphenylphosphine system [151] or porphinatoaluminium compounds such as (tpp)AlOR [149] is not accompanied with decarboxylation and yields the respective polycarbonates (Table 9.2). The ring cleavage during the polymerisation of trimethylene carbonate and 2,2-dimethyltrimethylene carbonate in the presence of the above catalysts has been found [148,149,151] to occur at the C(0)-0 bond, resulting... 

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