A process for preparing a reaction product including a halosilane includes: contacting an unsaturated hydrocarbyl halide and a ternary intermetallic compound at a temperature of 300 DEG C to 700 DEG C to form the reaction product. The ternary intermetallic compound includes copper, silicon and a transition metal. The halosilane in the reaction product has formula R1mR2 nHoSiX(4-m-n-o)> where each R1 is independently a saturated monovalent hydrocarbyl group, each R2 is independently an unsaturated monovalent hydrocarbyl group; each X is independently a halogen atom; subscript m is 1, 2, or 3; subscript n is 0, 1, or 2; subscript o is 0, 1, or 2; and a quantity (m + n + o) is 1, 2, or 3. At least a portion of the unsaturated hydrocarbyl groups in the unsaturated hydrocarbyl halide are converted to saturated hydrocarbyl groups (R1) in the halosilane.