Cyclooctene initial dissociation

In ROMP cyclic olefins are polymerized to polyalkenamers. Both 1 and 3 can be used for this reaction, but catalyst 3 was found to be significantly more efficient for the polymerization of cyclooctene derivatives (Eq. 13) [30]. Polymerization commences with initiation of the catalyst through dissociation of a neutral ligand such as a tricyclohexylphosphine for 1 and 3 (see... 

A = 335nm) activates benzene to afford Tp IrH(C6H5) P(OMe)3 (321). Mechanistic studies led the authors to propose initial photolytic dissociation of cyclooctene, with subsequent oxidative addition of benzene to afford the 7-coordinate Ir(V) intermediate Tp IrH3(C6H5). Photolytically induced reductive elimination of H2 then generates a coordinately unsaturated species that is trapped by P(OMe)3 to afford 321. 

Under the conditions of the reaction, c/s-cyclooctene (246) does not react. Evidently, therefore, the biradical that would be formed from (246) prefers to cleave into its components rather than cyclize to (245). The selectivity due to the tendency of the initially formed biradical to collapse immediately to form (244), rather than isomerize to the precursor of (245), is enhanced in the product by extensive (88 %) dissociation of the latter into (246) + F2C=CCl2. 

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