Ethylene polymerization mediated by nickel(II) covalently anchored to silica xerogels

Heterogeneous catalysis is generally widely preferred for industrial applications thanks to the well-known advantages of easier product-catalyst separation and recovery of the catalyst process and, often, to the enhanced stability of the catalyst. But in terms of selectivity, homogeneous catalysis usually provides better results. From this point of view, the grafting of homogeneous catalysts onto a solid support seems the ideal combination in order to achieve the advantages of both heterogeneous and homogeneous catalysis, allowing the developing of more environmentally friendly and economical processes with potential application in the industry. Further, to covalently link a homogeneous onto silica (a support which is thermally, chemically and mechanically resistant, with a well defined structure) is the best way to limit metal leaching and sintering.
Nitrogen-based ligands containing one of several Schiff bases have been reported to form active catalysts with “late-metal” (such as Fe, Pd, Ni,…) for the ethylene polymerization [1]. Moreover, substituted pyrazole-based organometallic complexes gave also promising results in this field.
These facts let us suggest that the pyrazolylpyridine derivatives bearing a tethered trimethoxysilylated group synthesized in a previous work [2] are potentially good candidate to prepare hybrid catalyst (i.e. soluble organometallic complexes covalently bonded onto an insoluble support, in this case silica) with Ni-II, Fe-II or Pd-II for ethylene polymerization.