Electron-Rich Piano-Stool Iron σ-Acetylides Bearing a Functional Aryl Group. Synthesis and Characterization of Iron(II) and Iron(III) Complexes

The synthesis and characterization of a family of para -functionalized complexes 3a − k, [(η 2 -dppe)(η 5 -C 5 Me 5 )Fe(C⋮CC 6 H 4 X)] (dppe = 1,2-(diphenylphosphino)ethane; X = NO 2, CN, CF 3, F, Br, H, Me, t Bu, OMe, NH 2, NMe 2 ), is reported. Most of the complexes were obtained in fair yields from the terminal iron acetylide complex [(η 2 -dppe)(η 5 -C 5 Me 5 )Fe(C⋮CH)] ( 1 ) using a palladium/copper-catalyzed coupling reaction. The complex 3j, with a strongly electron releasing NH 2 group, was synthesized by the more classical vinylidene route. The corresponding thermally stable radical cations could be generated in solution by addition of [(η 5 -C 5 H 5 ) 2 Fe + ][PF 6 - ] from 3a − k and characterized by infrared spectroscopy. Selected examples of these iron(III) salts ( 3a, X = NO 2; 3f, X = H; 3j, X = NH 2 ) were isolated and more completely characterized by Mössbauer spectroscopy. Crystal structures were determined for (η 2 -dppe)(η 5 -C 5 Me 5 )Fe[C⋮C-1,4-(C 6 H 4 )-NO 2 ] ( 3a ), (η 2 -dppe)(η 5 -C 5 Me 5 )Fe(C⋮C-1,4-(C 6 H 4 )-CN] ( 3b ), (η 2 -dppe)(η 5 -C 5 Me 5 )Fe[C⋮C−(C 6 H 5 )] ( 3f ), and [(η 2 -dppe)(η 5 -C 5 Me 5 )Fe{C⋮C-1,4-(C 6 H 4 )NO 2 } + ][PF 6 - ] ( 3a + PF 6 - ).