▁cycle ▁involves ▁an ▁ox id ative ▁addition ▁of ▁a ▁hal ide ▁or ▁pseud oh al ide ▁( 2 ) ▁to ▁a ▁p all ad ium ▁catal yst ▁( 1 ), ▁trans met al ation ▁of ▁ 3 ▁with ▁an ▁organ ot in ▁re agent ▁( 4 ), ▁and ▁re duct ive ▁elim ination ▁of ▁ 5 ▁to ▁yield ▁the ▁couple d ▁product ▁( 7 ) ▁and ▁the ▁reg ener ated ▁p all ad ium ▁catal yst ▁( 1 ). ▁ ▁However , ▁the ▁detailed ▁mechanism ▁of ▁the ▁St ille ▁coupling ▁is ▁extremely ▁complex ▁and ▁can ▁occur ▁via ▁numerous ▁reaction ▁path ways . ▁ ▁Like ▁other ▁p all ad ium - catal yz ed ▁coupling ▁re actions , ▁the ▁active ▁p all ad ium ▁catal yst ▁is ▁believed ▁to ▁be ▁a ▁ 1 4 - elect ron ▁P d ( 0 ) ▁complex , ▁which ▁can ▁be ▁generated ▁in ▁a ▁variety ▁of ▁ways . ▁ ▁Use ▁of ▁an ▁ 1 8 - ▁or ▁ 1 6 - ▁electron ▁P d ( 0 ) ▁source ▁P d ( P Ph 3 ) 4 , ▁P d ( d ba ) 2 ▁can ▁under go ▁lig and ▁dis soci ation ▁to ▁form ▁the ▁active ▁species . ▁ ▁Second , ▁ph osph ines ▁can ▁be ▁added ▁to ▁lig and less ▁p all ad ium ( 0 ). ▁ ▁Finally , ▁as ▁p ict ured , ▁reduction ▁of ▁a ▁P d ( II ) ▁source ▁( 8 ) ▁( P d ( O Ac ) 2 , ▁P