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.

Reaction 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 as PowerPoint slide