A Coupling reaction in organic chemistry is a general term for a variety of reactions where two fragments are joined together with the aid of a Metal Catalyst. In one important reaction type, a main group Organometallic Compound of the type R-M (R = organic fragment, M = main group center) reacts with an Organic Halide of the type R'-X with formation of a new Carbon-Carbon bond in the product R-R'. The most common type of Coupling reaction is the Cross Coupling reaction.