Design and synthesis of ruthenium indenylidene-based catalysts for olefin metathesis

Ruthenium catalysts--Synthesis;Metathesis (Chemistry);Alkenes

Urbina-Blanco, César A. ; Nolan, Steven P. ; Nolan, Steven P.

University:University of St Andrews

Department:Chemistry (School of)

关键词: Ruthenium catalysts--Synthesis;    Metathesis (Chemistry);    Alkenes;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/3737/C%c3%a9sarAUrbina-BlancoPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

As part of a European wide effort to develop metathesis catalysts for use infine chemical and pharmaceutical compound synthesis, this study focuses on thedesign and synthesis of ruthenium based catalysts for olefin metathesis.The aim, of this work was simple: to develop new, more active, more stable,easy to synthesise and commercially viable Ruthenium based catalysts, as welltrying to rationalize the effect of structural changes on reactivity.Two different approaches were explored in order to develop more activecatalysts bearing N-heterocyclic carbene (NHC) ligands: changing the leavinggroup and the effect of the NHC moiety in indenylidene type complexes. Over 12new catalysts were developed and their activity compared to that of commerciallyavailable catalysts. Overall, the new complexes exhibited superior reactivitycompared to previously reported catalysts in several benchmark transformations.However, olefin metathesis is a very substrate specific reaction, and rather thanfinding one catalyst that is superior to all, a catalogue of catalysts suitable forspecific transformations was developed.In addition, the effect of structural changes on substrate activity wasinvestigated in the ring closing metathesis of 1,8-nonadienes. The reactionprofiling showcased the presence of a gem-difluoro group as an accelerating groupin this incarnation of the olefin metathesis reaction and leads to ring formationover polymerization.In order to rationalize the effect of structural changes on catalyst activity,kinetic studies dealing with the initiation mechanism of ruthenium-indenylidenecomplexes were examined and compared with that of benzylidene counterparts. Itwas discovered that not all indenylidene complexes followed the same mechanism,highlighting the importance of steric and electronic properties of so-calledspectator ligands, and that there is no single mechanism for the ruthenium-basedolefin metathesis reaction. These results highlight the importance of systematicdevelopment of catalysts and that as scientists we should not take for granted.