Cycloaddition Reactions of Dicarbonyl(η⁵-cyclopentadienyl)(η¹-indenyl)iron

[3 + 2]-Cycloaddition reactions of the title compound with maleic anhydride and tetracyanoethylene form benzonorbornene derivatives. Dimethyl fumarate, dimethyl acetylenedicarboxylate, and diethyl azodicarboxylate do not react analogously. The reduced reactivity of indenyl-Fp compared to cyclopentadienyl-Fp supports the proposal that the Latter reacts with electron-deficient alkenes by [4 + 2]-cycloaddition rather than [3 + 2]-cycloaddition.