Two new ruthenium complexes with chelating-ether benzylidene ligands bearing a furan moiety were synthesized and characterized, including X-ray crystallography. They initiated fast, also at 0 °C, and were found to be highly active in a variety of ring-closing, ene-yne, and cross-metathesis reactions, including an active pharmaceutical ingredient (API) model, which makes them good candidates for the transformation of complex polyfunctional compounds that require mild reaction conditions.
A set of ruthenium complexes bearing a CAAC or uNHC ligand
and
a dithiocatechol fragment have been obtained and characterized spectroscopically.
The activity and Z-selectivity of the newly obtained
catalysts were studied in selected model CM, self-CM, and RCM olefin
metathesis reactions. Intriguingly, and in contrast to structurally
related NHC-bearing catalysts Ru4a and Ru4b, the CAAC and uNHC analogues showed no or only very little activity
in olefin metathesis. Interestingly, despite being not productive
in metathesis reactions conducted in solution, Ru8 enabled
the synthesis of a model 16-membered macrocyclic lactone of valuable
musk smell with excellent chemoselectivity (no C–C double-bond
migration was observed) at a concentration 40 times higher than that
typically used by organic chemists in similar macrocyclizations (200
mM instead of 5 mM) with excellent Z-selectivity.
Unfortunately, also here the conversion was low.
Two new unsymmetrical N-heterocyclic carbene ligand (uNHC)-based ruthenium complexes featuring phenolic OH function were obtained and fully characterised. The more active one was then immobilised on the metal–organic framework (MOF) solid support (Al)MIL-101-NH2. The catalytic activity of such a heterogeneous system was tested, showing that, while the heterogeneous catalyst is less active than the corresponding homogeneous catalyst in solution, it can catalyse selected olefin metathesis reactions, serving as the proof-of-concept for the immobilisation of catalytically active complexes in MOFs using a phenolic tag.
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