η2-Alkynyl and Vinylidene Transition Metal Complexes. 4.1 Reaction of the Metal−Acetylide [(η5-C5H5)(NO)(CO)WC⋮CR]- with Allyl Halides To Give η3-Allyl Complexes. (η1-Alkynyl-η3-allyl)tungsten Complexes: Preparation and Surface-Catalyzed Isomerization

Treatment of anionic acetylide complexes [(η 5 -C 5 H 5 )(NO)(CO)WC⋮CR] - [R = Si(CH 3 ) 3 ( 3 ), C(CH 3 ) 3 ( 11a ), or C 6 H 5 ( 11b )] with allylic iodides 4b, 14, methallyl iodide, and 3-iodocyclohexene in THF at 0 °C afforded the corresponding η 1 -alkynyl-η 3 -allyl complexes 5 / 6, 12 / 13, and 15 − 19 . The formation of these η 3 -allyl complexes is rationalized by the electrophilic attack on the metal center of acetylide complexes to create a η 1 -allyl complex, which is further stabilized by elimination of a CO ligand. The η 3 -allyl complexes 12a / 13a, 12b / 13b, 18a, and 19a undergo a surface-catalyzed isomerization on silica gel as well as neutral alumina to the (η 2 -allene)tungsten complexes 20 − 23 . The crystal structures of complexes 17b and 20 are reported.