Cossee

P. Cossee, Proceedings of the International Congress on Coordination Chemisty, 1961, p. 241. 

The conclusion may be drawn that the data obtained of comparative studies of olefin polymerization by the one-component catalyst (TiCl2) and two-component systems (TiCl2 + AlEtxCl ) confirm the concept of monometallic active centers on the surface of titanium chlorides developed by Cossee and Arlman (170-173). 

The theoretical problems of the coordination mechanism of the propagation reaction were considered by Cossee et al. 170,186, 187). 

Figure 9.21. The Cossee-Arlman mechanism of chain growth in ethylene polymerization involves the insertion of ethylene in the...

Another possibility is that carbene species are generated via the dissociative adsorption of ethylene onto two adjacent chromium sites [71]. A second ethylene molecule then forms an alkyl chain bridge between the two chromium sites this can subsequently propagate via either the Cossee or the Green-Rooney mechanism. 

Frataxin Mitochondrial iron frataxin-mice (Cossee Friedreich s ataxia (Harding,... 

The Cr5+ ion has only one unpaired electron hence, no zero-field splitting is expected. Indeed, a well-resolved spectrum has been observed for the ion on alumina 147, 148), silica gel 149-151), silica-alumina 152-154), and magnesium oxide 155). The line may be resolved into parallel and perpendicular g values. As van Reijen and Cossee (151) have shown, the values of g range from 1.970 to 1.975 whereas, the values of g range from 1.898 to 2.002, depending on the treatment of a Cr/SiCh sample. These authors have suggested that Cr5+ in two different symmetries is present one has a long relaxation time and can be observed at room temperature, but the other has a very short relaxation time and can be observed only at very low temperatures (—253°). 

Studies of V4+, which is also a 3d1 ion, have been carried out by several investigators (151, 162, 163). The spectra are often complex due to a nuclear spin of i however, good resolution has been achieved for the ion in a particular symmetry. After a vacuum treatment of vanadium on silica gel at 500° van Reijen and Cossee (151) observed the spectra shown in Fig. 33. Both spectra were obtained with the sample at 20°K. The authors attributed the first spectrum to the (V04)4" ion and the second to the... 

Here we discuss more details of the Cossee mechanism using recent evidence obtained by modern organometallic chemistry, together with relevant results of theoretical calculations. 

The Cossee mechanism has been demonstrated by direct observation of organometallic complexes where a C = C bond inserts itself into an M-C bond as shown in Eq. (7)-(9). A labeling experiment on a cationic platinum complex 111 indicated the reversible insertion of the coordinated alkene into the Pt-C bond as shown in Eq. (7) [142]. 

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