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

Abstract

Silicon(II) fluoride is unstable; therefore, isolation of the stable species is highly challenging and was not successful during the last 45 years. SiF(2) 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 Me(3)SnF. 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 Me(3)SnF 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 SiF(2) about four and a half decades ago.