Synthesis and structures of bis(silylene)iron complexes containing new six-membered chelate rings

Reaction of Cp′Fe(CO)2SiMe2SiMe2Cl (1a: Cp′=η5-C5H5 (Cp), 1b: Cp′=η5-C5Me5 (Cp*)) with acetic acid in the presence of base (pyridine or Et3N) afforded Cp′Fe(CO)2SiMe2SiMe2OCOMe (2a: Cp′=Cp, 77%; 2b: Cp′=Cp*, 87%). Similarly, the reaction of 1b with 2-pyridone in the presence of Et3N gave Cp*Fe(CO)2SiMe2SiMe2O(2-C5H4N) (3, 43%). Photolysis of 2a, 2b, and 3 produced Cp′(CO)Fe{SiMe2⋯OC(Me)O⋯SiMe2} (4a: Cp′=Cp, 4b: Cp′=Cp*) and Cp*(CO)Fe{SiMe2⋯O(2-C5H4N)⋯SiMe2} (5) quantitatively, in which an acetoxy or 2-pyridyloxy group bridges two silylene ligands to form a six-membered chelate ring. 4a and 5 were structurally characterized by single-crystal X-ray diffraction experiments. All the FeSi bonds are significantly shorter than normal FeSi single bonds and are consistent with their unsaturated bond character. The six-membered chelate ring consists of two entirely different and delocalized unsaturated bond systems.