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. SiF2 is generally generated in the gas phase at very high temperatures (similar to 1100-1200 degrees 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(COSi. Direct fluorination of L(Cl)Si with Me3SnF resulted in oxidative additi n1 products. Compounds 4-6 are stable at ambient 'temperature under an inert atmosphere of nitrogen. Compounds 4-6 were characterized by NMR spectroscopy, El-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.