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

Abstract

The steric bulk of the well-known DIPP BDI ligand (CH[C(CH 3 )N-DIPP] 2 ,D IPP = 2,6-diisopropylphenyl) was increased by replacing isopropyl for isopentyl groups.T his very bulky DIPeP BDI ligand could not stabilizet he radical species ( DIPeP BDI)MgC:r eduction of ( DIPeP BDI)MgI with Na gave ( DIPeP BDI) 2 Mg 2 with ar ather long Mg-Mg bond of 3.0513(8) .A ddition of TMEDAp rior to reduction gave complex ( DIPeP BDI) 2 Mg 2 (C 6 H 6 ), which could also be obtained as its THF adduct. It is speculated that combination of abulky spectator ligand and TMEDAp revents dimerization of the intermediate Mg I radical, which then reacts with the benzene solvent. Complex ( DIPeP BDI) 2 Mg 2 (C 6 H 6 ), which formally contains the anti-aromatic anion C 6 H 6 2À ,r eacted with tBuOH as aBrønsted base to 1,3-and 1,4-cyclohexadiene and with H 2 as at wo electron donor to ( DIPeP BDI) 2 Mg 2 H 2 and C 6 H 6 .I ta lso reductively cleaved the C À Fb ond in fluorobenzene and gave ( DIPeP BDI)MgPh, ( DIPeP BDI)MgF,and C 6 H 6 .

Evidence of AlIIRadical Addition to Benzene

“…In confirmation of the 1 H NMR data, the 13 C NMR spectrum shows two new signals at chemical shifts of 124.6 and 29.9 ppm. These NMR spectroscopic data compare favorably with the reported quinoid type benzene moiety suggesting a Birch‐type reduction product of benzene [14a, 19, 20] …”

“…The group of Harder has shown that the combination of the nucleophilic Al I compound ( II ) with the highly Lewis acidic (NacNac)Ca + analogue reduces benzene [18] . Notably, the isolobal Mg compound can also undergo a Birch‐type benzene reduction, when the dimerization of the intermediate Mg I radical is prevented by a super bulky spectator ligand ((HC{C(Me)N[2,6‐(3‐pentyl)‐phenyl]} 2 )) and a coordinating species, TMEDA (N,N,N′,N′‐tetramethylethylenediamine) [19] . In the course of the development of this work, the group of Braunschweig reported a similar outcome, in which the aluminum center is coordinated to an N ‐heterocyclic carbene (NHC) and stabilized by a redox‐active ferrocenyl substituent [20] .…”

Heteroleptic Heavier Alkaline Earth Metal Amide Complexes Stabilized by a Superbulky β-Diketiminate Ligand

“…10 We recently introduced the superbulky β-diketiminate ligand DIPeP BDI (CH[C(Me)N-DIPeP] 2 , DIPeP = 2,6-di-iso-pentylphenyl) in low-valent Mg(I) chemistry. 21 It was shown that this bulkier version of the DIPP BDI ligand, in which the isopropyl groups have been replaced for iso-pentyl moieties, gave a ( DIPeP BDI)Mg-Mg( DIPeP BDI) complex with a considerably stretched Mg−Mg bond. Subsequently, we demonstrated that this ligand allows for the isolation of heteroleptic [( DIPeP BDI)SrH] 2 and [( DIPeP BDI)SrEt] 2 complexes, which are up to 70 °C stable toward ligand exchange reactions.…”

Grignard reagent formation via C–F bond activation: a centenary perspective

“…This effect was explored by Harder and coworkers, who used an exceptionally bulky β-diketiminate to prepare a magnesium complex with an Mg–(benzene)–Mg core. 81 This complex was capable of cleaving the C–F bond in PhF, in close analogy to the Crimmin's reaction, although the reaction time was much longer in this case (5 days at 100 °C required).…”