[9-{2-(Dimethylamino)ethyl}fluorenyl] as a Ligand on Magnesium Leads to a THF Ring-Opening by the Fluorenyl Moiety

[9-{2-(dimethylamino)ethyl}fluorenyl] (L2)− is explored as a simple yet effective ancillary ligand for heteroleptic Mg chemistry. The proligand L2H reacts with [Mg(nBu)2(thf)x] to give [(L2)Mg(nBu)(thf)] (1), whose THF can be replaced by DMAP (4-dimethylaminopyridine) to give [(L2)Mg(nBu)(dmap)] (2). 1 catalyzes the hydroamination/cyclization of a few benchmark primary aminoalkenes to prove the effectiveness of (L2)−. But a heteroleptic [(L2)MgH], another signature test for a ligand on Mg, is inaccessible either by β-H elimination from [(L2)Mg(NHiPr·BH3)(L)] (L = THF (3); DMAP (4)) or by ligand exchange between [(L2)K] (6) or [(L2)2Ca] (7) and MgBr2. More interestingly, reacting 1 with PhSiH3 gives a THF ring-opened complex [(L2)Mg{(μ-O-(CH2)4-FLL2}]2 (52), where the fluorenyl of a (L2)− acts as the nucleophile. The homoleptic [(L2)2Mg], though not isolated, is likely an intermediate toward the ring-opening, and a plausible mechanism is postulated by the help of density functional theory calculations. In addition, 7 readily gives the solvent-separated ion pair [Ca(thf)6][L2]2 (8) in THF to suggest the limitation of (L2)− with the heavier alkaline earths. In this regard, (L2)− is closely compared to an analogous [(Flu)-(CH2)2-NHCDipp]−((L1)−; NHC = N-heterocyclic carbene, Dipp = 2,6-iPr2–C6H3) that has a bulky NHC in the place of NMe2 in the chelating side arm.