Mesoionic Pyrrolium Complexes and Dihydropyrroles by Cycloaddition of (Non-enolizable) Imines to an [(1-Alkynyl)carbene]tungsten Complex

Reaction of the [(1-alkynyl)carbene]tungsten complex (CO)5W=C(OEt)C≡CPh (1a) with non-enolizable imines, e.g. 9-fluorenone imines 2 [NR = N(iPr), N(c-C6H11)], affords novel mesoionic pyrrolium carbonyltungstates 3 (by [3+2] cycloaddition) together with dihydropyrroles 4 (by dichotomy of the C=N bond and subsequent insertion of the carbene carbon atom into an NC–H bond). Cross-conjugated azametallatrienes 6 and pentacarbonyltungsten complexes 7 of the dihydropyrroles 4 have been identified to be precursors to compound 4. Compounds 3b, 4a, and 6a have been characterized by X-ray crystal structure analyses.