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

The steric bulk of the well‐known ^DIPPBDI ligand (CH[C(CH₃)N‐DIPP]₂, DIPP=2,6‐diisopropylphenyl) was increased by replacing isopropyl for isopentyl groups. This very bulky ^DIPePBDI ligand could not stabilize the radical species (^DIPePBDI)Mg^.: reduction of (^DIPePBDI)MgI with Na gave (^DIPePBDI)₂Mg₂ with a rather long Mg‐Mg bond of 3.0513(8) Å. Addition of TMEDA prior to reduction gave complex (^DIPePBDI)₂Mg₂(C₆H₆), 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 (^DIPePBDI)₂Mg₂(C₆H₆), which formally contains the anti‐aromatic anion C₆H₆^2?, reacted with tBuOH as a Brønsted base to 1,3‐ and 1,4‐cyclohexadiene and with H₂ as a two electron donor to (^DIPePBDI)₂Mg₂H₂ and C₆H₆. It also reductively cleaved the C?F bond in fluorobenzene and gave (^DIPePBDI)MgPh, (^DIPePBDI)MgF, and C₆H₆.