Metal complexes with bifunctional imidazolyl phosphines for catalytic organic transformations : applications in homogeneous and polymer supported alkene isomerization , and hydrogen deuterium exchange

The research covered in this thesis involves studying and understanding the behavior of bifunctional ligands, specifically imidazolylphoshines. The major field of study is reaction of cyclopentadienyl ruthenium complexes with olefins, namely alkene isomerization. In these complexes, the basic nitrogen of the imidazolylphosphine is thought to deprotonate coordinated alkene intermediates reversibly, facilitating isomerization of terminal alkenes to yield internal alkenes selectively. The CpRu alkene isomerization catalyst is capable of moving double bonds as far as 30 positions; further mechanistic studies in presence of deuterium labeling as a tool, has led to development of hydrogen deuterium exchange of olefins at allylic positions. This finding supports the proposed mechanism and provides and outstanding deuteration at positions accessible by isomerization. The alkene isomerization catalyst can be used in a two-phase setting where the catalyst is dissolved in the organic layer and the non-toxic, non-flammable isotopic source (D₂O) is immiscible with the organic layer. Using biphasic settings one can literally wash out reactive protons on the substrate without using organic solvents. In order to control high activity of alkene isomerization catalyst in absence of steric bulk provided by the substrate, bulkier phosphine ligands were synthesized and the activity of their metal complexes toward linear olefins was investigated. As a result, a family of catalysts that is capable of isomerizing unsubstituted linear alkenes to various mixtures have been established, where one can choose a complex to fit the needs of the process at hand. Further investigation with terminal alkenes bearing functional groups can be carried out to investigate whether mono-isomerization will still be the major transformation taking place, which is expected to give access to high-value 2-alkenes. To provide easy product- catalyst separation and potential wider application, the first syntheses of polymer-supported imidazolylphophines were developed, and the alkene isomerization catalyst was thus immobilized on polystyrene-based Merrifield resin. Compared to the homogeneous catalyst, the immobilized catalysts give the same high (E)-selectivity and conversion in isomerizations of terminal olefins to internal olefins with very low metal leaching from the insoluble support. Furthermore, use of organic solvents can be excluded and isomerization can be carried out in neat liquid organic substrate