Synthesis and Structures of Dimethyldihydropyrene Iron Carbonyl Complexes

Abstract

Reaction of the Diels−Alder adduct 10 (derived from the aryne 11 of dimethyldihydropyrene (DHP) and furan)7 with Fe2(CO)9 at room temperature gave the deoxygenated benzannelated DHP 9 and iron tetracarbonyl complex 6. However, the same reaction at elevated temperature produced 9 as well as the mono-iron tricarbonyl complex 7, the bis-iron tricarbonyl complex 8 (12%), and a very small amount of 6. On heating, complex 6 converts to DHP 9 and complex 7, but does not form 8. Likewise DHP 9 does not form from either complex 7 or 8, and so the latter is formed directly from 10. The structures of 7 and 8 were determined by X-ray crystallography. The main feature of these molecules is the bending of the DHP rings upon coordination of the iron tricarbonyl groups. These molecules are crowded, with strong interactions found between the carbonyl groups and the internal methyl groups and the tert-butyl groups. The π-electron delocalization in the normally aromatic DHP ring has been greatly reduced by the complexation.