Thiocarbene and alkoxycarbene tungsten complexes exhibit typically different reaction paths

The condensation of (butyl)thiocarbene tungsten complex [(OC)5Wdouble bond; length as m-dashC(SEt)Bu] (1a) with an α,β-unsaturated secondary acid amide R2CHdouble bond; length as m-dashCHC(double bond; length as m-dashO)NHR14 in the presence of POCl3/Et3N gives cyclopentadienimines 12, whereas the isostructural alkoxycarbene complex [(OC)5Wdouble bond; length as m-dashC(OEt)Bu] (1c) under similar conditions affords a (N-enamino)ethoxycarbene compound 9. Furthermore, condensation of the (methyl)thiocarbene tungsten complex [(OC)5Wdouble bond; length as m-dashC(SEt)Me] (1b) with an amide 4 yields cyclopentenimines 19 and allenylidene complexes 20, whereas the corresponding ethoxycarbene complex [(OC)5Wdouble bond; length as m-dashC(OEt)CH3] (1d) forms 4-NH-amino-1-tungsta-1,3,5-hexatrienes 16 under similar conditions.