Preparation and Diels‐Alder Reactivity of Tricarbonyliron Complexes of [2.2.2]Hericene

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Abstract
Treatment of [2.2.2]hericene 10 with Fe2(CO)9 in hexane gave a mixture of monometallic complex 14, two isomeric dimetallic complexes 15 and 16, and a trimetallic complex 19 in which all the three diene moieties of 10, are coordinated. The rate constants of the Diels‐Alder additions of tetracyanoethylene (TCE) and dimethyl acetylenedicarboxylate (DMAD) to the uncomplexed diene moieties of 14–16 have been evaluated and compared with those measured for the uncomplexed 10 and its monoadducts 11A, 11B and bis‐adducts 12A, 12B. The tricarbonyldieneiron function retards the cycloaddition of an homoconjugated, exocyclic s‐cis‐butadiene. The effect is significantly larger for TCE‐ than for DMAD‐additions. The origin of this effect is discussed briefly in terms of the valence‐bond model which is usually assumed to describe the properties of a tricarbonyldieneiron complex, and in terms of the inductive and steric factors of the Fe(CO)3‐group.

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