Photolytic reaction of substituted (ethynyl)benzaldehyde and Fe(CO)5: Formation of indenone and chelated iron complexes

At 0 °C, photolysis of a hexane solution containing Fe(CO)5 and 2-(phenylethynyl)benzaldehyde (1) affords a mixture of mononuclear (tricarbonyliron-2-phenylindenone, (2) and binuclear acetylene coupled iron carbonyl complexes [Fe(CO)3{η4-2,4–(C6H4CHO)2–3,5-(C6H5)2C4}Fe(CO)3], 3, [Fe(CO)3{ η4-2-(η1–C6H4CHO)–4–(C6H4CHO)–3,5-(C6H5)2C4}Fe(CO)2], 4 and [Fe(CO)3{ η4-4-(η1-2–C6H4CHO)–2–(C6H4CHO)–3,5-(C6H5)2 C4}Fe(CO)2], 5. In compounds 4 and 5, the exocyclic iron atom is η4-bonded with the ferracyclopentadiene unit, and it bears two terminal carbonyls. Its 18 electron count is completed by virtue of the aldehydic oxygen atom coordinating to the iron atom. Photolysis of 2-(ferrocenylethynyl)benzaldehyde (6) under similar condition leads to the formation of tricarbonyliron-2-ferrocenylindenone (7) and tetracarbonyl(2-ferrocenyl-3-(2-formylphenyl)maleoyl)iron (8) predominantly.