▁the ▁transition ▁state ▁being ▁highly ▁symmetric . ▁In ▁the ▁example ▁below ▁all ▁add itions ▁are ▁en ant io select ive ▁however ▁the ▁symmetric ▁complex ▁has ▁no ▁reg io control , ▁resulting ▁in ▁a ▁rac em ic ▁product . ▁The ▁asym metric ▁complex ▁is ▁both ▁reg io select ive ▁and ▁en ant io select ive , ▁resulting ▁in ▁a ▁single ▁en anti omer . ▁ ▁The ▁primary ▁application ▁of ▁P HO X ▁lig ands ▁is ▁in ▁p all ad ium ▁catal yst s ▁used ▁for ▁en ant io select ive ▁al ly lic ▁substitution s . ▁They ▁are ▁able ▁to ▁effect ▁a ▁wide ▁range ▁of ▁subst iti u ations ▁including ▁al ly lic ▁alk yl ations ▁( T su ji - T rost ▁reaction ), ▁am in ations ▁and ▁sul fony l ations . ▁ ▁He ck ▁Re action ▁ ▁P all ad ium ▁complex es ▁containing ▁ch iral ▁ph osph ino ox az ol ines ▁have ▁been ▁shown ▁to ▁be ▁efficient ▁catal yst s ▁for ▁the ▁He ck ▁reaction . ▁ ▁High ▁yields ▁and ▁good ▁to ▁excellent ▁en ant io select iv ities ▁have ▁been ▁obtained , ▁with ▁the ▁formation ▁of ▁by - products ▁via ▁C = C ▁bond ▁migration ▁being ▁greatly ▁reduced . ▁P d - P HO X ▁catal yst s ▁have ▁also ▁been ▁used ▁for ▁intr am ole cular ▁He ck ▁re actions ▁and ▁examples ▁exist ▁where ▁they ▁have ▁been ▁shown ▁to ▁be ▁superior ▁to ▁more ▁common ▁lig ands ▁such ▁as ▁B IN AP . ▁ ▁As ym metric ▁H