Conference Publication Details
Mandatory Fields
Amir-Ebrahimi, V;Hamilton, JG;Nelson, J;Rooney, JJ;Rooney, AD;Harding, CJ
RING OPENING METATHESIS POLYMERISATION AND RELATED CHEMISTRY
Free radical forming activity of the Grubbs catalyst and related organometallics.
2002
January
Published
1
3 ()
Optional Fields
OPENING METATHESIS POLYMERIZATION OLEFIN METATHESIS CARBENE
217
226
When (PCy)(2)RuCl2CHPh, RuCl2(PPh3)(3), or RhCl(PPh3)(3) is added in CH2Cl2 solution to p-benzoquinone strong persistent concentrations of the quinone radical-anion are found. The epr spectra show that in each case only one species is formed, and the very well resolved hyperfine splittings are accurately simulated on the basis that the four hydrogen atoms are inequivalent because of close engagement with the metal donor complexes, thereby removing the two orthogonal symmetry axes present in the free radical anions. The results are therefore not only of great theoretical interest but they also demonstrate a sensitive means of estimating the basicities of the metal complexes.During ring-opening metathesis polymerization (ROMP) of norbornadiene (NBD) with the Grubbs catalyst a free radical is also observed as a I : 2 : I triplet, which is also formed, but to a much weaker extent, with norbornene (NBE), cyclopentene and 1,7-octadiene. The identity of this triplet, and that of a transient doublet observed together with the triplet in the case of benzonorbornadiene, are discussed as well as the possible role of radicals in initiation of ROMP, crosslinking of ROMP products, and polymerization of alpha-methylstyrene.Methyl aluminoxane (MAO) is also found to catalyse ROMP of NBE and addition polymerization of alpha-methylstyrene. The obvious intermediates responsible for initiation here are either a metalla-carbenium ion, e.g. RCH[Al](-), formed via an agostic precursor, or a metalla-radical RCH[Al]. These possibilities are discussed in the light of the free radical activity of the Grubbs catalyst.
Grant Details