Low Valent Magnesium Chemistry with a Super Bulky β-Diketiminate Ligand

The steric bulk of the well-known ^DIPP BDI ligand (CH[C(CH₃ )N-DIPP]₂ , DIPP=2,6-diisopropylphenyl) was increased by replacing isopropyl for isopentyl groups. This very bulky ^DIPeP BDI ligand could not stabilize the radical species (^DIPeP BDI)Mg^. : reduction of (^DIPeP BDI)MgI with Na gave (^DIPeP BDI)₂ Mg₂ with a rather long Mg-Mg bond of 3.0513(8) Å. Addition of TMEDA prior to reduction gave complex (^DIPeP BDI)₂ Mg₂ (C₆ H₆ ), which could also be obtained as its THF adduct. It is speculated that combination of a bulky spectator ligand and TMEDA prevents dimerization of the intermediate Mg^I radical, which then reacts with the benzene solvent. Complex (^DIPeP BDI)₂ Mg₂ (C₆ H₆ ), which formally contains the anti-aromatic anion C₆ H₆ ^2- , reacted with tBuOH as a Brønsted base to 1,3- and 1,4-cyclohexadiene and with H₂ as a two electron donor to (^DIPeP BDI)₂ Mg₂ H₂ and C₆ H₆ . It also reductively cleaved the C-F bond in fluorobenzene and gave (^DIPeP BDI)MgPh, (^DIPeP BDI)MgF, and C₆ H₆ .