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

The steric bulk of the well-known (BDI)-B-DIPP ligand (CH[C(CH3)N-DIPP](2), DIPP=2,6-diisopropylphenyl) was increased by replacing isopropyl for isopentyl groups. This very bulky (BDI)-B-DIPeP ligand could not stabilize the radical species ((BDI)-B-DIPeP)Mg-.: reduction of ((BDI)-B-DIPeP)MgI with Na gave ((BDI)-B-DIPeP)(2)Mg-2 with a rather long Mg-Mg bond of 3.0513(8) angstrom. Addition of TMEDA prior to reduction gave complex ((BDI)-B-DIPeP)(2)Mg-2(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 ((BDI)-B-DIPeP)(2)Mg-2(C6H6), which formally contains the anti-aromatic anion C6H62-, reacted with tBuOH as a Bronsted base to 1,3- and 1,4-cyclohexadiene and with H-2 as a two electron donor to ((BDI)-B-DIPeP)(2)Mg2H2 and C6H6. It also reductively cleaved the C-F bond in fluorobenzene and gave ((BDI)-B-DIPeP)MgPh, ((BDI)-B-DIPeP)MgF, and C6H6.