▁p all ad ium ▁complex ▁with ▁R 1 ▁and ▁R 2 ▁present ▁in ▁a ▁c is ▁relationship . ▁ ▁Another ▁commonly ▁seen ▁mechanism ▁involves ▁the ▁same ▁initial ▁addition ▁of ▁the ▁organ ost ann ane ▁to ▁the ▁trans ▁p all ad ium ▁complex ▁as ▁seen ▁above ; ▁however , ▁in ▁this ▁case , ▁the ▁X ▁group ▁does ▁not ▁coordinate ▁to ▁the ▁tin , ▁producing ▁an ▁open ▁transition ▁state . ▁ ▁After ▁the ▁α - car bon ▁relative ▁to ▁tin ▁attacks ▁the ▁p all ad ium , ▁the ▁tin ▁complex ▁will ▁leave ▁with ▁a ▁net ▁positive ▁charge . ▁ ▁In ▁the ▁scheme ▁below , ▁please ▁note ▁that ▁the ▁double ▁bond ▁coordin ating ▁to ▁tin ▁denotes ▁R 2 , ▁so ▁any ▁al ken yl , ▁al ly l , ▁or ▁ar yl ▁group . ▁ ▁Furthermore , ▁the ▁X ▁group ▁can ▁dis soci ate ▁at ▁any ▁time ▁during ▁the ▁mechanism ▁and ▁bind ▁to ▁the ▁Sn + ▁complex ▁at ▁the ▁end . ▁ ▁D ens ity ▁functional ▁theory ▁calculations ▁predict ▁that ▁an ▁open ▁mechanism ▁will ▁prev ail ▁if ▁the ▁ 2 ▁lig ands ▁remain ▁attached ▁to ▁the ▁p all ad ium ▁and ▁the ▁X ▁group ▁leaves , ▁while ▁the ▁cy clic ▁mechanism ▁is ▁more ▁probable ▁if ▁a ▁lig and ▁dis soci ates ▁prior ▁to ▁the ▁trans met al ation . ▁ ▁Hence , ▁good ▁leaving ▁groups ▁such ▁as ▁trif l ates ▁in ▁polar ▁sol vent s ▁favor ▁the ▁former , ▁while ▁bul ky ▁ph osph ine ▁lig ands ▁will ▁favor ▁the ▁latter . ▁ ▁A ▁less ▁common