Low coordinate magnesium chemistry supported by a bulky β-diketiminate ligand

Abstract

A series of magnesium(II) alkyl, alkoxide, carboxylate, amide and halide complexes stabilised by the bulky β-diketiminate ligand, HC(C(Me)N-2,6-ⁱPr₂C₆H₃)₂ (BDI), have been synthesised and structurally characterised. (BDI)H reacts with MgMe₂ in Et₂O to give the four-coordinate complex (BDI)MgCH₃(Et₂O), 1, and in toluene to afford [(BDI)Mg(μ-CH₃)]₂, 2. Three coordinate complexes may be accessed by increasing the size of the alkyl ligand; hence, the reaction of (BDI)H with ^tBu₂Mg yields (BDI)Mg^tBu, 3, while Li(BDI) reacts with ⁱPrMgCl to afford (BDI)MgⁱPr, 4; a similar reaction with PhMgCl affords the diethyl ether adduct (BDI)MgPh(Et₂O), 5. The etherates 1 and 5 may be converted into the base-free complexes, 2 and (BDI)MgPh, 6, respectively, upon heating in vacuo. The direct reaction of (BDI)H with RMgX (X = Cl or Br) results in relatively inert halide-bridged dimers of formula [(BDI)Mg(μ-X)]₂, (X = Cl, 7; X = Br, 8). The alkylmagnesium derivatives react readily with alcohols, amines or carboxylic acids to yield alkoxide, amide and carboxylate complexes, respectively. For example, 4 reacts with ⁱPrOH (or O₂) to form [(BDI)Mg(μ-OⁱPr)]₂, 9. Convenient one-pot synthetic procedures have been developed using commercially available Bu₂Mg. Treatment of Bu₂Mg with (BDI)H, followed by its reaction with MeOH, ^tBuOH, ⁱPr₂NH, (Me₃Si)₂NH, MeCO₂H or PhCO₂H affords [(BDI)Mg(μ-OMe)]₂, 10, [(BDI)Mg(μ-O^tBu)]₂, 11, (BDI)Mg(NⁱPr₂), 12, (BDI)Mg(NTMS₂), 13, [(BDI)Mg(μ-O₂CMe])]₂, 14, and [(BDI)Mg(μ-O₂CPh)]₂, 15, respectively. The molecular structures of complexes 4–8 and 12–15 are reported.