Synthesis of neutral nickel–methyl complexes with monodentate imines and their sequential insertion of carbon monoxide and imine

Neutral nickel–imine complexes of the form (N^O)Ni(R)(R1NC(H)R2) (N^O = salicylaldiminato; R = CH3, Ph; R1 = alkyl; R2 = aryl) can be prepared by the reaction of (tmeda)Ni(CH3)2, imine and the corresponding salicylaldiminato ligand. The addition of carbon monoxide to these complexes lead to the in situ generation of the corresponding nickel–acyl complexes. With N-methyl or N-benzyl substituted imines, these complexes reductively eliminate the phenolic and acyl ligands to generate esters. However, the less sterically encumbered 3,4-dihydroisoquinoline can couple with the nickel–acyl ligand to form 1,2-diamides in high yield. In situ1H NMR analysis suggests this reaction occurs via insertion of imine into the nickel-acyl bond to form a nickel-bound amide complex.Figure optionsDownload as PowerPoint slide

Neutral nickel–methyl complexes with monodentate imine ligands have been prepared, and found to undergo rapid insertion of carbon monoxide. In the case of 3,4-dihydroisoquinoline, this is followed by coupling of the imine and acyl ligands to form 1,2-diamides. In situ NMR analysis suggests this reaction occurs via insertion of imine into the nickel–acyl bond.Figure optionsDownload as PowerPoint slideResearch highlights
► Neutral nickel–imine complexes are prepared.
► Sequential CO/imine insertion is observed with less sterically encumbered imines.
► Provides a nickel-mediated route to construct 1,2-diamides.