Unexpected Latency of -Stereoretentive Ruthenium Olefin Metathesis Catalysts Bearing Unsymmetrical N-heterocyclic Carbene or Cyclic(alkyl)(amino)carbene Ligands.

A set of ruthenium complexes bearing a CAAC or uNHC ligand and a dithiocatechol fragment have been obtained and characterized spectroscopically. The activity and -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 and , 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, 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 -selectivity. Unfortunately, also here the conversion was low.