η1-Alkynyl and vinylidene transition metal complexes: 10. Reaction of the metal-acetylide [(η5-C5H5)(CO)(NO)WCCC(CH3)3]Li with 1,2-diiodoethane as electrophile and with various nucleophiles

Treatment of the η1-acetylide complex [(η5-C5H5)(CO)(NO)WCCC(CH3)3]Li (4) with 1,2-diiodoethane in THF at −78 °C, followed by the addition of LiCCR [R=C(CH3)3, C6H5, Si(CH3)3, 6a–6c] or n-C4H9Li and protonation with H2O, afforded the corresponding oxametallacyclopentadienyl complexes (η5-C5H5)W(I)(NO)[η2-OC(CCR)CHCC(CH3)3] (7a–7c), 8c and (η5-C5H5)W(I)(NO)[η2-OC(n-C4H9)CHCC(CH3)3] (9). The formation of these metallafuran derivatives is rationalized by the electrophilic attack of 1,2-diiodoethane onto the metal center of 4 to form first the neutral complex [(η5-C5H5)(I)(CO)(NO)WCCC(CH3)3] (5). Subsequent nucleophilic addition of LiCCR 6a–6c or n-C4H9Li and a reductive elimination step followed by protonation leads to the products 7a–7c and 9. One reaction intermediate could be trapped with CF3SO3CH3 and characterized by a crystal structure analysis. The identity of another intermediate was established by infrared spectroscopic data. The oxametallacyclopentadienyl complex 10 forms in the presence of excess 1,2-diiodoethane through an alternative pathway and crystallizes as a clathrate containing iodine.