Reaction of Tungsten Vinylcarbene Complexes with Enamines

In this paper we describe the reaction of vinylcarbene complexes 4 and 7 with enamines
5 and 9 to form the η1-acyl complexes 6, 8, and 10. From a mechanistic point of view, the
reaction starts with the nucleophilic addition of the β-carbon atom of the enamine to the
α-carbon atom of the vinylcarbene complex, generating the zwitterionic structure 12. Instead
of the expected ring closure to a metallacyclobutane derivative and concomitant metathesis,
intermediate 12 undergoes nucleophilic addition of a carbonyl carbon atom to the iminium
carbon atom and rearrangement to the observed η1-acyl complexes. Furthermore the reaction
of the η1-vinylidene complex [(CO)(NO)(Cp)WCCH2)] (1) with the enamines 5 and 9 is
described. While enamine 5 preferably reacts as a nucleophile and produces finally the alkene
complex 11, the reaction of enamine 9 with 1 begins by a proton transfer step and ends
with the η1-acyl complex 10. Single-crystal X-ray diffraction data of 6 and 11 are reported.