Ethene-Norbornene Copolymerization with Homogeneous Metallocene and Half-Sandwich Catalysts: Kinetics and Relationships between Catalyst Structure and Polymer Structure. 3. Copolymerization Parameters and Copolymerization Diagrams

The copolymerization parameters of the ethene-norbornene copolymerization using various metallocene and half-sandwich catalysts were determined on the basis of composition data with linear graphical methods: Aside from r1 and r2, values for r11 and r21 could be determined in the case of alternating copolymerizations. In this connection, r21 differs significantly from catalyst to catalyst and reflects the different tendency of each catalyst to produce copolymers with an alternating monomer sequence. The maximum norbornene contents in the copolymer could be achieved by use of sterically less hindered metallocene catalysts. As an exception to this, the half-sandwich catalysts produced copolymers with surprisingly low norbornene contents.

Determination of 113Cd shielding tensor components in cadmium-phosphine complexes from 31P-decoupled 113Cd cross-polarisation/magic angle spinning spectra

Owing to the simultaneous presence of various anisotropic interactions within the isolated M-31P and M(31P)2 fragments in solid transition metal phosphine complexes MX2.PR3 and MX2.2PR3 with, for instance, M = Cd, Hg or Pt, it is not normally possible to unequivocally determine the shielding tensor components of the metal nucleus M from simple 113Cd, 199Hg or 195Pt cross-polarisation/magic angle spinning (CP/MAS) spectra. In this paper it is shown that additional 31P on-resonance high-power decoupling during the acquisition time does allow the determination of the shielding tensor components of M from CP/MAS spectra. Two cadmium(II) complexes, Cd(OAc)2.Pchex3, (chex = cyclohexyl) and Cd(ClO4)2.2Pchex3 were chosen as examples; the 113Cd CP/MAS experiments were carried out at a low external magnetic field strength B0 = 2.35 T.

171Yb cross polarisation/magic-angle spinning of divalent ytterbium complexes

171Yb cross polarisation/magic angle spinning (CP/MAS) is introduced as a new analytical tool for the investigation and structural characterisation of divalent ytterbium complexes. A convenient procedure to optimise the experimental set-up for 171Yb CP/MAS is described.