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 MgI 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 .