Stabilization of Low Valent Silicon Fluorides in the Coordination Sphere of Transition Metals

Silicon­(II) fluoride is unstable; therefore, isolation of the stable species is highly challenging and was not successful during the last 45 years. SiF₂ is generally generated in the gas phase at very high temperatures (∼1100–1200 °C) and low pressures and readily disproportionates or polymerizes. We accomplished the syntheses of stable silicon­(II) fluoride species by coordination of silicon­(II) to transition metal carbonyls. Silicon­(II) fluoride compounds L­(F)­Si·M­(CO)₅ {M = Cr (4), Mo (5), W­(6)} (L = PhC­(NtBu)₂) were prepared by metathesis reaction from the corresponding chloride with Me₃SnF. However, the chloride derivatives L­(Cl)­Si·M­(CO)₅ {M = Cr (1), Mo (2), W­(3)} (L = PhC­(NtBu)₂) were prepared by the treatment of transition metal carbonyls with L­(Cl)­Si. Direct fluorination of L­(Cl)Si with Me₃SnF resulted in oxidative addition products. Compounds 4–6 are stable at ambient temperature under an inert atmosphere of nitrogen. Compounds 4–6 were characterized by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. The molecular structures of 4 and 6 were unambiguously established by single-crystal X-ray diffraction. Compounds 4 and 6 are the first structurally characterized fluorides, after the discovery of SiF₂ about four and a half decades ago.