Coupling Reactions of N‑Propargyl Semi-Salen Compounds Induced by Ruthenium Complex

The coupling reaction of N-propargyl semi-salen compound 1d on [Ru]-Cl ([Ru] = Cp­(PPh3)2Ru) generates the carbene complex 3d containing a substituted 2H-chromene unit in 7 d. The precursor vinylidene complex 2d is isolated from the reaction of the propargyl group of 1d with [Ru]-Cl in 12 h. Addition of an o-cresol moiety to Cα and Cβ of the vinylidene ligand of 2d takes place in a longer reaction time to yield 3d. Reactions of [Ru]-Cl with other analogous compounds 1a, 1b, and 1c, in excess, also afford carbene complexes 3a, 3b, and 3c, respectively, in 48 h via a similar coupling process. Their precursor vinylidene complexes 2a, 2b, and 2c are also observed in 12 h. Structures of 2 and 3 are determined on the basis of spectroscopic data. The solid state structure of the dppe analogue 3a′ is further confirmed by X-ray diffraction analysis. The added o-cresol part comes from compounds 1, instead of aldehyde which is confirmed by the cross-coupling reactions of 2 and 1 using mass spectrometry. For comparison, treatment of [Ru]Cl with the amine analogue 13b retaining the propargyl and phenol moieties yields no coupling product.