We
disclose the direct synthesis of methylmethoxysilanes from pentacopper
silicide, Cu5Si, and dimethyl carbonate, DMC, affording
high levels of dimethylsilyl products without the use of halide
catalysts. When Cu5Si powder (99.5%) was reacted
with DMC at 350 °C, Me2Si(OMe)2 was the
major silane product at >70% selectivity. In contrast, when a high
purity Cu5Si (99.99%) was used, the reaction afforded mainly
permethoxylated silanes. ICP-OES identified several impurity elements
in the low purity Cu5Si. By synthesizing materials that
contained the individual impurity elements and reacting them with
DMC, tin was revealed as being a crucial promoter. XPS revealed that
tin segregates to the surface under reaction conditions, and elevated
tin levels have a significant impact on DMC reactivity with the surface.
XPS also suggests that tin is in the zero oxidation state at the surface,
which provides some insight to its role in the direct synthesis of
methylmethoxysilanes.