Reaction cascade: Ortho-C–H activation and C–C coupling of benzophenone leading to tetranuclear organoiron and mononuclear organocobalt complexes

•Reaction cascade of benzophenone includes C–H activation and C–C coupling steps.•Subsequent insertion/addition sequence with low valent Fe(PMe3)4 and Co(PMe3)4.•Dimerization constitutes a four membered Fe2O2 core structure.•Single electron transfer reaction afforded cyclometalated mononuclear cobalt complex.•Formation mechanisms of both complexes explain the key steps of the proposed sequence.

The novel tetranuclear mixed valent iron(II)/iron(0) complex (1) was prepared by ortho-metalation of benzophenone with zerovalent Fe(PMe3)4 (d8) followed by a subsequent insertion of an additional equivalent of benzophenone under ring expansion (seven-membered metallacycle). Dimerization and spontaneous dihydrogen loss, constitutes a four membered Fe2O2 core structure in which both incorporated chelating phenylrings are additionally attached by low-valent Fe(PMe3)3-fragments in η4-mode. In a single electron transfer reaction, by C–C-coupling of two molecules benzophenone with zerovalent Co(PMe3)4 (d9), cyclometalated mononuclear five-membered cobalt(II) alcoholate complex (2) is obtained. The crystal structures of 1 and 2 were determined and supported by gas phase DFT calculations and the formation mechanisms of both complexes are discussed.

Graphical abstractReaction cascade: Ortho-metalation of benzophenone with zerovalent iron and cobalt is observed followed by a subsequent addition/insertion of an additional equivalent benzophenone.Figure optionsDownload full-size imageDownload as PowerPoint slide