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Abstract
N-Heterocyclic carbenes have become common ligand in organometallic chemistry, however a
general and effective design method for chiral NHC complexes has yet to be introduced. Efforts
in ligand design for chiral NHC ligands have mostly been directed towards the introduction of
chiral substituents into monodentate imidazolylidene NHC’s. The dynamic nature of these
systems, however, prevents a sufficient definition of chiral space required for asymmetric
induction (Figure 1). Bidentate ligands generally create more rigid metal complexes, which may
help to overcome this problem. The target ligand for this thesis will combine the atropisomeric
binaphtyl backbone with the less explored but readily obtainable 1,2,3-triazolylidenes (Figure
1): 1,2,3-triazolylidenes can be synthesized using ‘click’-chemistry, a [3+2]-dipolar
cycloaddition reaction between an azide and an alkyne.
Figure 1: Dynamic effects within mono-dentate NHC’s; Target complexes for this thesis (α)
The target ligand was efficiently synthesized in a three step synthesis with an overall yield of
91% starting from commercially available starting materials. Silver, palladium, rhodium and
iridium complexes were synthesized through direct deprotonation of the ligand in the presence
of the appropriate metal source. The strong electron donating properties of the NHC ligand are
illustrated by the rhodium(I) dicarbonyl complex, for which a very low νavg(CO) was observed.
Rhodium(I) complex α was tested in the catalytic asymmetric hydrosilylation of ketones,
allowing for good conversion, also at low catalyst loadings of 0.2 mol%, and promising levels of
enantioselectivity (up to 51% ee).