REACTIONS BETWEEN IRON(0) ALKYNYLCARBENE COMPLEXES AND CYCLOPENTADIENE - FORMATION OF IRON(0) ETA(1)-VINYLCARBENE COMPLEXES AND THEIR FACILE THERMAL TRANSFORMATION INTO THE CORRESPONDING (ETA(3)-ETA(1)-ALLYLACYL)IRON(II) COMPLEXES

[(3-tert-Butylnorbornadienyl)ethoxymethylene]Fe(CO)4, the iron(0) eta(1)-vinylcarbene complex 2, is obtained from the reaction of [(3,3-dimethylbutynyl)ethoxymethylene]Fe(CO)4 (1a) with cyclopentadiene at 25-degrees-C. Complex 2 transforms into the eta(3):eta(1)-allylacyl complex 4a via a CO insertion reaction at the original carbene carbon by heating at 50-degrees-C for 1 h. However, direct formation of eta(3):eta(1)-allylacyl complexes is observed in reactions of cyclopentadiene with other alkynylcarbene complexes, 1b (R = SiMe3), 1c (R = cyclohexyl), 1d (R = n-propyl), and 1e (R = phenyl), at 25-degrees-C.