▁on ▁the ▁substr ates ▁and ▁conditions . ▁ ▁The ▁most ▁common ▁type ▁of ▁trans met al ation ▁for ▁the ▁St ille ▁coupling ▁involves ▁an ▁associ ative ▁mechanism . ▁ ▁This ▁path way ▁implies ▁that ▁the ▁organ ost ann ane , ▁normally ▁a ▁tin ▁atom ▁bond ed ▁to ▁an ▁al ly l , ▁al ken yl , ▁or ▁ar yl ▁group , ▁can ▁coordinate ▁to ▁the ▁p all ad ium ▁via ▁one ▁of ▁these ▁double ▁b onds . ▁ ▁This ▁produces ▁a ▁fle eting ▁pent aval ent , ▁ 1 8 - elect ron ▁species , ▁which ▁can ▁then ▁under go ▁lig and ▁det achment ▁to ▁form ▁a ▁square ▁plan ar ▁complex ▁again . ▁ ▁Despite ▁the ▁organ ost ann ane ▁being ▁coordin ated ▁to ▁the ▁p all ad ium ▁through ▁the ▁R 2 ▁group , ▁R 2 ▁must ▁be ▁formally ▁transferred ▁to ▁the ▁p all ad ium ▁( the ▁R 2 - S n ▁bond ▁must ▁be ▁broken ), ▁and ▁the ▁X ▁group ▁must ▁leave ▁with ▁the ▁tin , ▁comple ting ▁the ▁trans met al ation . ▁ ▁This ▁is ▁believed ▁to ▁occur ▁through ▁two ▁mechan isms . ▁ ▁First , ▁when ▁the ▁organ ost ann ane ▁initially ▁adds ▁to ▁the ▁trans ▁metal ▁complex , ▁the ▁X ▁group ▁can ▁coordinate ▁to ▁the ▁tin , ▁in ▁addition ▁to ▁the ▁p all ad ium , ▁producing ▁a ▁cy clic ▁transition ▁state . ▁ ▁Break down ▁of ▁this ▁ad duct ▁results ▁in ▁the ▁loss ▁of ▁R 3 S n - X ▁and ▁a ▁tri val ent