The leaving group X in the organic partner is usually a halide, although triflate, tosylate and other pseudohalide have been used. Chloride is an ideal group due to the low cost of organochlorine compounds.  Frequently, however, C–Cl bonds are too inert, and bromide or iodide leaving groups are required for acceptable rates.  The main group metal in the organometallic partner usually is an electropositive element such as tin, zinc, silicon, or boron.