Photochemical Synthesis and Stereodynamic Behavior of Alkoxy-Bridged (Silylene) (germylene)iron Complexes

Mixed (silylene) (germylene)iron complexes have been synthesized for the first time and are internally stabilized by a donor bridging alkoxy group: [Cp′(CO)Fe{GeMe₂--O(R)--SiMe₂|] (Cp′= C₅Me₅; R = Me, Bu^t). Two-dimensional and variable-temperature ¹H NMR spectroscopies establish germylene-methyl group exchange. Computer simulation of the spectra and calculation using the Eyring equation yield values for ΔG^‡298 for the process of 62 kJ mol⁻¹ (R = Me) and 61 kJ mol⁻¹ (R = Bu^t). A mechanism involving cleavage of the Ge--O partial bond, followed by rotation of the resulting coordinated germylene moiety about the Fe=Ge double bond, is proposed for this exchange. The (silylene) (germylene)iron complexes are weighted toward the (methoxysilyl) (germylene) form, indicating that germylene ligands are more stable than their silicon analogues.