Modeling of Ru and Fe based olefin metathesis
Michael T. Feldmann, Richard P. Muller, and William A. Goddard,
Materials and Process Simulation Center, Caltech
Olefin metathesis is an important reaction for many
chemical processes including polymerization. It has been shown that
the Grubbs ruthenium-based catalyst is very efficient at olefin metathesis
with high functional group tolerance. It has been so successful that
we would quickly deplete the world of its supply of ruthenium if
we were to use it for all its applications. Looking at related elements
that have a higher natural abundance leads to iron. Iron should have
similar electronic behavior which could lead to a successful iron based
olefin metathesis catalyst.
The mechanism of the ruthenium-based Grubbs catalyst
of the formula L2X2Ru=CHR has been examined. Experimentally it has
been shown that L=PCy3,PiPr3, X=Cl, and R=CHPh2 produce an effective catalyst.
When X=Cl and R=H in our theoretical study, L was varied from a simple
phosphine to a carbene and an sp2 nitrogen donating ligand. Understanding
gained from this mechanism has allowed for possible performance enhancement
of the ruthenium-based catalyst. In addition, the iron-based analog
is showing promise as the ligand effects are being understood and tuned
to the needs of the iron-based reaction pathway.
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