Cyclopentadienyl rings, methyl substitution

A number of alkylated and ring-annelated derivatives of cyclopentadienyl-thallium(I) have been reported. All were prepared by the same procedure used for the parent compound, and relevant experimental data are listed in Table I. None of these compounds is as stable as cyclopentadienylthallium-(I) the methyl-substituted derivative, for example, undergoes essentially spontaneous oxidation on exposure to the atmosphere (25), and, qualitatively, the order of stability has been assessed (105) as... 

Metallocenes with substituted cyclopentadienyl rings. Metallocenes with methylated rings were among the first heavy alkaline earth metallocenes to be structurally characterized, but many other substituents have been incorporated into bis(cyclopentadienyl) complexes. Under this classification are included compounds with indenyl ligands, which in... 

Studies have shown that unsymmetrical [Ijferrocenophanes in which only one of the cyclopentadienyl rings is methyl-substituted yield regioregular PFSs via transition metal-catalyzed ROP, whereas thermal ROP of the same monomers yields regioirregular materials. 

Small structural changes in the catalysts can produce even more remarkable results. Substitution of a methyl group in the cyclopentadienyl ring of iPr(CpHu)ZrCl2 led to the produetion of hemiisotactic polypropylene. In this structure, every second stereogeruc carbon has an isotactic configuration, and the centers in between have atactic placements. Thus, there is order and disorder along the chain in a well-defined manner. 

When neat 18a is heated in an evacuated sealed tube at 130°C for 1 hour 19a is obtained quantitatively. The polymer 19a is soluble in THF and the sample purified from THF-hexane is a yellow fibrous material with A/vv = 5.2 X 10 and A/n = 3.4 x 10, and readily forms amber, free-standing films by casting from toluene solution. By this ROP method, symmetrically and unsymmetrically substituted poly(ferrocenylsi-poly(ferrocenylsilanes) (19) [71,72] and polysilane-poly(ferrocenylsilane) copolymers, (20) [73] have been prepared. The ROP of [l]ferrocenophane with unsymmetrically methylated cyclopentadienyl rings (21) to investigate the C—Si bond cleavage mechanism in the thermal ROP gives a polymer (22) in which three types of silicon environment exist, showing that... 

To overcome this problem Bashkin and Kinlen [33, 34] have shown that sufficient methyl substitution of the cyclopentadienyl rings can render ferrocenium stable to O2, and ring-methylated Fc" analogues may be used to fabricate stable reference electrodes. 

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