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.

Graphical abstractPhotolysis of a hexane solution of 2-(phenylethynyl)benzaldehyde and Fe(CO)5 at 0 °C results in a mixture of mononuclear (tricarbonyliron-2-phenylindenone) and binuclear ironcarbonyl complexes. Interestingly, in some of the binuclear complexes one of the aldehydic oxygen atoms is coordinated to the exocyclic iron.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of phenyl and ferrocenyl substituted tricarbonylironindenone complexes. ► Formation of chelated ironcarbonyl complexes. ► Conversion of tricarbonylironindenone complexes to respective indenones. ► Phenyl substituted reactant prefer intermolecular coupling.