Propene/ethene-[1-13C] copolymerization as a tool for investigating catalyst regioselectivity, 1 - Theory and calibration

In a previous letter, we proposed the synthesis and C-13 NMR characterization of propene/ethene-[1-C-13] copolymers at low ethene-[1-C-13] content as a convenient tool for measuring the regioselectivity of coordinated propene polyinsertion, in case 13C NMR fails to detect the regiomistakes in propene homopolymers. In the present article, we introduce the foundations of the approach in more detail, and illustrate how its scope can be extended to the evaluation of catalyst "dormancy" due to regiochemical monomer inversion. The method was calibrated for two well-known C-2-symmetric ansa-metallocene catalysts (namely, rac-Me2Si(1-indenyl)(2)ZrCl2 and rac-Me2Si(2-Me-4-phenyl-1-indenyl)(2)ZrCl2), by means of a cross-check with results of a C-13 NMR characterization of samples of poly(propene-[3-C-13]) prepared under corresponding experimental conditions. In particular, it was proved that the fraction of consecutive 2,1 insertions in propene homopolymerization promoted by the quoted catalysts, although nonzero, is low enough not to invalidate the propene/ethene-[1-C-13] copolymerization approach.