Reaction cycle coupling rules

Another interesting alternative combines catalysis and electrochemistry [35]. In the reductive coupling cycle of two bromobenzene molecules to biphenyl, the Pd catalyst provides just two electrons. This reaction can be performed in an electrochemical cell, where the electrons are supplied from an outside source [36]. We thus see that catalysis gives us a variety of green alternatives to the classic stoichiometric process. There are no hard and fast rules as to which route to choose - it all depends on the reaction conditions, and on the chemicals available. 

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