New features of ROMP by heterogenization of molybdenum carbene complexes

Abstract

An inorganic carrier based on alumina covered with methylaluminoxane (MAO) which had been crosslinked by various diols was used to immobilize molybdenum carbene complexes of the type Mo(CH- t-Bu)(NAr)(OC(CH 3) 2CF 3) 2 (1) and Mo(CH- t-Bu)(NAr)(OTf) 2(dme) (2) (Ar2,6-C 6H 3- i-Pr 2). Employment of fluorinated diols heavily increased the activity in ring-opening metathesis polymerization (ROMP) of different substituted norbornenes, 2-azanorbornene, cyclooctene, cyclooctadiene and metathesis reaction of acyclic alkenes. Investigations were made on differences in stereochemistry of polymers obtained by these new supported complexes compared with homogeneous polymerization initiated by (1). The immobilized initiators produced polymers with a higher content of trans vinylene, particularly when monomers were substituted with bulky groups. Terminal alkenes like 1-hexene worked as chain transfer agents. Thus regulation of molecular weight was possible. In addition these supported carbene complexes showed a surprisingly high stability of the alkylidene species in suspension—even after 30 days of polymerization the activity was still about 15% of the initial value.