The present invention relates to a method for the preparation of tertiary-hydrocarbylsilyl compounds through a Grignard reaction. A Grignard reagent of formula RMgX, in which R is a tertiary-hydrocarbyl group and X is a halogen atom, is reacted with a silicon compound of formula R.sup.1.sub.a SiX.sub.4-a ; where R.sup.1 is a substituted or unsubstituted monovalent hydrocarbon group and a is an integer with a value of zero to three. The process is ran in the presence of a catalytic quantity of a cyano compound or a thiocyanate compound.