Unexpected C–C bond formation with a ferrocenyl Fischer carbene complex

Abstract

Thermolysis of (OC)5Cr(C(OEt)(Fc)) (1) gives 2,N-diferrocenyl acetamide Fc–CH2–CO–NH–Fc (2) in the presence of amino ferrocene Fc-NH2. In the absence of a nucleophile, 4-ethoxy-2,3,4-triferrocenyl-cyclobut-2-enone (3) forms from 1 under thermal activation. Single crystal X-ray diffraction, NMR spectroscopy and mass spectrometry unambiguously confirm the structure of both unexpected products. Quantum chemical calculations and kinetic experiments by mass spectrometry and IR spectroscopy help to propose conceivable pathways to their formation.