Use of the appropriate HAT catalyst was essential to observe productive reactivity. Co(II)based (dmgBF2) and (dmgH2) complexes could be used as catalysts for enal isomerization, although Co(dmgBF2)2(H2O)2 performed better at reduced catalyst loadings (see the SI for details). Other Co-based complexes established for HAT reactivity failed completely, including related Co(III)dmg type catalysts, Cp*Co(II)(bipy)Cl, and Co(III)(salen)Cl complexes, further highlighting the unique challenge of enal isomerization (Fig 2d We were interested in studying the scope of enal isomerization reactions catalyzed by Co(dmgBF2)2(H2O)2/H2 along with further methylenic substrates (Fig ). Norton and co-workers have previously reported Co(dmgBF2)2/H2 catalyzed isomerization reactions with arylalkenes and a,b-unsaturated esters. Enal isomerization of ester and ether containing substrates were successful (OAc, OBn, and OMe; 1, 4, 5), as was a substrate with a free alcohol group (6).