Synthesis and applications of tricarbonyliron complexes of dendralenes

[3]Dendralene and [4]dendralene are converted smoothly into tricarbonyliron complexes. The structures of four complexes analyzed by DFT and single-crystal X-ray analysis show that, in contrast to free hydrocarbons, complexed dendralenes prefer a roughly in-plane conformation. The complexes are stable towards Fe(CO)₃ group migration up to 150 °C. The synthetic value of Fe(CO)₃ complexation in the dendralene series is demonstrated through a variety of selective synthetic manipulations (Diels-Alder reaction, dipolar cycloaddition, Simmons-Smith cyclopropanation, dihydroxylation, olefin cross metathesis) that are not achievable by direct transformation of the free hydrocarbons. Application to the synthesis of a previously unreported, highly reactive linear/cross-conjugated hydrocarbon is also described. Simplicity through complexation: Tricarbonyliron complexes of dendralenes are readily prepared and stable. They allow the formation of products that cannot be accessed directly from dendralenes, including unprecedented structures (see scheme).