Reactions of cobaloxime η 1-allyl complexes with electron deficient alkenes

Abstract

The preparation of several new η 1-allyl (dimethylglyoxime) 2 cobalt complexes ( 7– 12) containing varied axial pyridine ligands is reported. These complexes are synthesized via three different methods: (1) in situ generation and allylation of [L(dmg) 2Co] 2 dimers (where L=various pyridines); (2) generation and allylation of L(dmg) 2Co anions; and (3) an apparent 1,4-hydrocobaltation of 1,3-dienes. Tetracyanoethylene addition to cobaloxime allyl complexes ( 5– 12) yielded cyclized complexes ( 17– 23) and insertion products ( 24– 27). Yields of the cyclized and uncyclized complexes are influenced by the electronics of the axial pyridine ligand with the more electron withdrawing pyridine ligands favoring the formation of more cyclized product. Treatment of cobaloxime allyl complexes ( 8– 10) with benzoquinone yielded rearranged cobaloxime allyl complexes ( 30 and 31) along with para-allyloxysubstituted phenols ( 32– 34). The substituted phenols presumably arise from a Michael addition of the allyl fragment onto benzoquinone followed by a retro Claisen reaction.