Sterically Hindered Diazabutadienes (DABs): Competing Reaction Pathways with MeLi

Abstract

Treatment of N,N 0 -bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1,3-butadiene with MeLi results in carbon-carbon bond formation and selective reduction of one of the imine arms to give the N-lithiated salt of the imine/amine, N,N 0 -bis(2,6-diisopropylphenyl)-1,4-diaza-2,3,3-trimethyl-1-butene. This compound crystallizes from Et 2 O as a solvent adduct, exists as a monomer both in solution and the solid state, and features a three-coordinate lithium nucleus that is chelated to oxygen, amido, and imino donors. In contrast, treatment of N,N 0 -bis(2,4,6-trimethylphenyl)-1,4-diaza-2,3-dimethyl-1,3-butadiene with MeLi gives the N-lithiated imine anion N-(2,4,6trimethylphenyl)-1-aza-2-methyl-3-N 0 -(2,4,6-trimethylphenyl)-1,3-butadiene, as the ether adduct, by proton abstraction. With a more hindered base, N,N 0 -bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1,3-butadiene undergoes proton abstraction with lithium diisopropylamide to give the N-lithiated imine anion of the ene/amine, N-(2,6-diisopropylphenyl)-1-aza-2-methyl-3-N 0 -(2,6-diisopropylphenyl)-1,3butadiene, again isolated as the ether adduct. A further equiv of MeLi 3 LiBr added to N-(2,4,6trimethylphenyl)-1-aza-2-methyl-3-N 0 -(2,4,6-trimethylphenyl)-1,3-butadiene gives the doubly N-lithiated salt of the diene/diamide, 2,3-N,N 0 -bis(2,4,6-trimethylphenyl)-1,3-butadiene, in which both nitrogen centers have been reduced, and which adopts a cisoid stereochemistry with respect to the butadiene unit in the solid state.

The Manifold Structural Chemistry of Alkali Metal Enediamide Complexes

“…For Me2 DAD Dipp , deprotonation of the central methyl groups has been observed in some cases. [38,39] Moreover, a number of structurally closely related alkali metal complexes are known, in which the two central carbon atoms of the ligand are part of an additional aromatic system (for instance, derivatives of ortho-phenylenediamine). [40][41][42][43] However, all these com-plexes have been obtained under different conditions and comprise a variety of solvent co-ligands, which makes comparison difficult.…”

Lewis base adducts of diisobutylaluminum azide: synthesis and thermal stability

“…The reaction of diimines with metal alkyls is a convenient route to iminoamine ligands [28,29]. For diimines with unsubstituted backbones, the initial R-M addition across one imine double bond is followed by a hydrogen migration, so that the imine carbon bears the new substituent.…”

Electronic and Geometric Structures of Paramagnetic Diazadiene Complexes of Lithium and Sodium

“…A two‐step phase cycle was used to remove the unwanted echoes. Relaxation‐filtered hyperfine (REFINE) spectroscopy was also applied to obtain at least a qualitative picture of the paramagnetic species present in the sample. For REFINE measurements, a pulse sequence of ( ) together with a four‐step phase cycle were used.…”

“…The so‐far‐reported EPR spectroscopy results on DAD complexes have mostly indicated that the unpaired electron is delocalized over the DAD backbone, and therefore, a dominant ligand‐centered character with small g and A anisotropies is generated. However, there are other cases that report weak or rather strong delocalization into metal centers in addition to the DAD backbone …”