Stabilization of Low Valent
Silicon Fluorides in the
Coordination Sphere of Transition Metals
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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<sub>2</sub> 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)<sub>5</sub> {M = Cr (<b>4</b>),
Mo (<b>5</b>), W(<b>6</b>)} (L = PhC(N<i>t</i>Bu)<sub>2</sub>) were prepared by metathesis reaction from the corresponding
chloride with Me<sub>3</sub>SnF. However, the chloride derivatives
L(Cl)Si·M(CO)<sub>5</sub> {M = Cr (<b>1</b>), Mo (<b>2</b>), W(<b>3</b>)} (L = PhC(N<i>t</i>Bu)<sub>2</sub>) were prepared by the treatment of transition metal carbonyls
with L(Cl)Si. Direct fluorination of L(Cl)Si with Me<sub>3</sub>SnF
resulted in oxidative addition products. Compounds <b>4</b>–<b>6</b> are stable at ambient temperature under an inert atmosphere
of nitrogen. Compounds <b>4</b>–<b>6</b> were characterized
by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. The
molecular structures of <b>4</b> and <b>6</b> were unambiguously
established by single-crystal X-ray diffraction. Compounds <b>4</b> and <b>6</b> are the first structurally characterized fluorides,
after the discovery of SiF<sub>2</sub> about four and a half decades
ago
