Cyclopentadienyl rings, methyl

Photolysis of Cp2TiAr2 in benzene solution yields titanocene and a variety of aryl products derived both intra- and intermolecularly (293—297). Dimethyl titan ocene photolyzed in hydrocarbons yields methane, but the hydrogen is derived from the other methyl group and from the cyclopentadienyl rings, as demonstrated by deuteration. Photolysis in the presence of diphenylacetylene yields the dimeric titanocycle (28) and a titanomethylation product [65090-11-1]. 

Interaction of the iron metal atoms with thiophenes (thiophene, 2-methyl-, and 2,5-dimethylthiophene) in the vapor phase at 77 K with subsequent heating in a carbon monoxide atmosphere also leads to the formation of ferrole 83 [76JOM(l 18)37, 77CJC3509]. The iron cyclopentadienyl ring is planar and all the bonds have multiple character. 

The IR spectra of the polymer (P) contained two sharp absorptions near 1000 and 1100 cm-- -, indicative of the presence of unsubstituted cyclopentadienyl rings in the products. The 250-MHz - -H-NMR spectrum, shown in Figure 3, contained the expected peaks for the methyl, methylene, and cyclopentadienyl protons, respectively, at 61.52, 1.57 and 4.04 ppm. No olefinic proton resonances were present, and all of the samples of the polymer in Table II exhibited the same - -H-NMR spectrum. 

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... 

From IR data it appears that in the solid state the magnesium atoms are associated via methyl bridge bonds and that the cyclopentadienyl rings are approximately pentahapto bonded as indicated in structure XXIVb. When dissolved in benzene, the methyl bridge bonds are retained. 

The X-ray crystal structure of LXXa confirms the presence of isolated cations and anions in the solid state. In the cation, the pentamethylcyclo-pentadienyl n system is symmetrically pentahapto bonded to the tin atom (see LXX in Fig. 14). The tin-ring centroid distance is considerably shorter than in decamethylstannocene. The methyl groups are bent away from the plane of the cyclopentadienyl ring. 

Modifications of Cs-symmetric metallocenes may lead to Ci-symmetric metallocenes (Fig. 8). If a methyl group is introduced at position 3 of the cyclopentadienyl ring, stereospecificity is disturbed at one of the reaction sites so that every second insertion is random a hemiisotactic polymer is produced (276, 277). If steric hindrance is greater (e.g., if a /-butyl group replaces the methyl group), stereoselectivity is inverted, and the metallocene catalyzes the production of isotactic polymers (178-180). 

---