1-Bridgehead Substituted Norbornenes in Late Transition Metal Polymerisation Catalyst Studies

Abstract

1-or 4-Substituted norbornene monomers are very attractive because it is a single isomer unlike endo and exo isomers in 5/6 substituted and, syn/anti isomers in 7-substituted norbornene. In this project, the 1-substituted norbornene monomer, norbornene-1-methyl carboxylate monomer, was synthesised from norbornane-2-carboxylic acid in a high yield and in four steps. In each step the product was fully characterized by 1H NMR and 13C NMR spectroscopy. The monomer was subjected to ROMP reactions using 1st , 2nd and modified 2nd generation ruthenium initiators. The polymerisation reaction was monitored by 1H NMR spectroscopy. 1st generation ruthenium initiator showed no evidence for polymerisation, but it indicated the possibility of the formation of a chelating complex as well as an oligomer. When the monomer is inserted at the ruthenium center two different complexes may be formed; a complex via insertion of monomer to the ruthenium center and a complex via chelation of oxygen to the ruthenium center. To isolate the chelated complex, the ROMP reaction of norbornene-1-methyl carboxylate monomer was carried out at the ratio of monomer: 1st generation ruthenium initiator of 1:1. The complex structure could only be identified by 1H NMR spectroscopy and it was not possible to obtain good quality crystals for X-ray crystallography. ROMP reactions using 2nd and modified 2nd generation ruthenium initiators showed that these initiators are efficient for the polymerisation of the norbornene-1-methyl carboxylate monomer. The narrow PDIs indicate reasonably well controlled polymerisation reactions. Addition polymerisation of norbornene-1-methyl carboxylate monomer was carried out using the palladium initiator [Pd(H)(MeCN)(PCy3)2][B(C6F5)4], (Pd 1388). The result of the GPC analysis showed the existence of two peaks with DP of 2 and 16 which suggest the formation of a dimer and an oligomer. Addition polymerisation of norbornene-1-methyl carboxylate monomer using nickel initiator (η6-toluene)Ni(C6F5)2 was carried out. However, based on the result it has been difficult to determine the outcome of the polymerization reaction. The presence of ester group in 1 position most likely leads to coordination or chelation of the norbornene-1-methyl carboxylate monomer to the nickel or palladium metal center.