A synthetic, structural and reactivity study of [(η4-C4R4)Co(η5-C5H4X)] complexes, R=Me or Et; X=CHO, CHCHFc, CHCH(η5-C5H4)Co(η4-C4Ph4), CHC(CN)2: Unexpected formation of [(η5-cyclopentadienyl)(η4-3,4,5,6-tetraethyl-α-pyrone)cobalt]

The tetraethyl- and tetramethyl-cyclobutadiene complexes [(η4-C4R4)Co(η5-C5H4CHO)] R=Et, 5, R=Me, 7, and [(η4-C4R4)Co(η5-C5H4CO2Me)] R=Et, 6, R=Me, 8, are conveniently prepared by photolysis of the corresponding isocobaltocenium cations [(η4-C4R4)Co(η6-C6H5Me)]+ in acetonitrile, and subsequent treatment with Na[C5H4CHO] or Na[C5H4CO2Me]. The aldehydes 5 and 7 undergo Wittig and Knoevenagel reactions with [FcCH2PPh3]I and CH2(CN)2, to form …