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)MgtBu, 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-OtBu)]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.