Thermal and photochemical reactions of η⁵- cyclopentadienyl(naphthoyl)-(dicarbonyl)iron complexes with alkynes: Formation of benzindenones and dihydropentalenones

?⁵-Cyclopentadienyl(1- and 2-naphthoyl)(dicarbonyl)iron complexes (6a) and (6b) have been synthesised from the appropriate acid chlorides and sodium ?⁵-cyclopentadienyl(dicarbonyl)iron-(1-). UV irradiation of (6a) and (6b) separately with diphenylacetylene in benzene gives 1,2-diphenyl-3H-benz[e]inden-3-one (8), and 2,3-diphenyl-1H-benz[e]inden-1-one (7) respectively, together with smaller quantities of bis(?⁵- cyclopentadienyl)(tetracarbonyl)di-iron. The benz[e]indenones (7) and (8) are also formed in low yield from diphenylacetylene and ?⁵- cyclopentadienyl(1- and 2-naphthoyl)(dicarbonyl)iron complexes respectively, in hot decalin. A second product from the thermal reaction is c-4,c-6a-dihydro-4- (1- or 2-naphthyl)-2,3-diphenylpentalen-1(r-3aH)-one (9a) or (9b), respectively, incorporating a cyclopentadienyl group. A compound of the last type (9c) is also formed in a thermal reaction of ?⁵-cyclopentadienyl(1- naphthoyl)(dicarbonyl)iron with 1-phenylpropyne. The molecular structures of (7) and (9a) were elucidated by X-ray crystallography.