Reaction of alkoxycarbene complexes of tungsten with 1,2-dihydroquinoline: single vs. double hydride transfers to the carbene–carbon: synthesis, X-ray structure and reactivity of a quinolinium ylide complex of tungsten pentacarbonyl

The more stable dihydropyridine, 1,2-dihydroquinoline (2), reacts with carbene complex of tungsten (CO)5W(OEt)Ph (3) to give the expected quinolinium complex 4, fully characterized by an X-ray structure. By contrast, under the same conditions complex 7 (CO)5W(OEt)Me led to the alkyltungstate 15 as the result of a double hydride transfer to the carbene–carbon. Complex 15 could be trapped by the enamine of morpholine and cyclohexanone and gave the addition product 14. The quinoline in 4 is easily exchangeable by excess pyridine, via a dissociative mechanism, and gives the known pyridinium ylide complex 5.