Monoanionic Quasi-Imido Ligands Based on 1‑Methyl-4-iminopyridine and Complexes with the Main Group Elements Mg, Al, and Zn

The syntheses of monoanionic quasi-imido (MQI) nitrogen donor ligands based on (1-methylpyridin-4­(1H)-ylidene)­amide, and their chemistry with main group elements, are reported. The electronic structure of the ligand allows delocalization of a positive charge onto the N-heterocycle, which is accompanied by aromatization. The unsubstituted MQI ligand was found to form insoluble intractable products on reaction with nontransition-metal alkyls; thus, substituents were introduced to increase solubility and stability of those complexes and enable their study. The precursors 3,5-bis­(3,5-dimethylphenyl)-1-methylpyridin-4­(1H)-imine [MQI^Me]H and 3,5-bis­(3,5-di-tert-butylphenyl)-1-methylpyridin-4­(1H)-imine [MQI^tBu]H both gave isolable complexes. The species {[MQI^tBu]­MgCl­(THF)}₂, {[MQI^tBu]­MgMe}₂, {[MQI^tBu]­AlMe₂}₂, {[MQI^tBu]­ZnMe}₂, and {[MQI^Me]­MgCl­(THF)}₂ were prepared. As well, [MQI]H precursors were coordinated with Lewis acidic boron- and aluminum-derived Lewis acids. Charge delocalization onto pyridine was examined by crystallography and NMR spectroscopy.