Kinetically Directed Reactivity of Magnesium Dihydropyridides with Organoisocyanates

Although reactions between β-diketiminato magnesium species containing monocyclic 1,4-dihydropyridide ligands and the representative ketone benzophenone are observed to provide reduction by formal hydride transfer to yield magnesium diphenylphenoxide, similar reactions with organic isocyanates display only a very limited propensity toward hydride transfer and reduction to amidate species. In these latter systems, reaction primarily takes place with Mg–N insertion to afford O-bound ureide complexes. Further reactions of a magnesium dihydro-isoquinolide complex, which is constrained to hydride dearomatization at the 2-position only, display more variable behavior. Although similar Mg–N insertion and ureide formation is observed for reactions with isocyanates bearing less sterically demanding N-substitution, more bulky isocyanates provide unusual enamide C–C coupling reactivity.