β‐Diketiminate‐Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis,Characterization, Adduct Formation,and Reactivity Studies |
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| Authors: | Simon?J Bonyhady Cameron Jones Prof Sharanappa Nembenna Dr Andreas Stasch Dr Alison?J Edwards Dr Garry?J McIntyre Dr |
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| Institution: | 1. School of Chemistry, Monash University, PO Box 23, Melbourne, VIC, 3800 (Australia), Fax: (+61)?3‐9905‐4597;2. Bragg Institute, Australian Nuclear Science and Technology Organisation, PMB1, Menai, N.S.W. 2234 (Australia);3. Institut Laue‐Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9 (France) |
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| Abstract: | The preparation and characterization of a series of magnesium(II) iodide complexes incorporating β‐diketiminate ligands of varying steric bulk and denticity, namely, (ArNCMe)2CH]? (Ar=phenyl, (PhNacnac), mesityl (MesNacnac), or 2,6‐diisopropylphenyl (Dipp, DippNacnac)), (DippNCtBu)2CH]? (tBuNacnac), and (DippNCMe)(Me2NCH2CH2NCMe)CH]? (DmedaNacnac) are reported. The complexes (PhNacnac)MgI(OEt2)], (MesNacnac)MgI(OEt2)], (DmedaNacnac)MgI(OEt2)], (MesNacnac)MgI(thf)], (DippNacnac)MgI(thf)], (tBuNacnac)MgI], and (tBuNacnac)MgI(DMAP)] (DMAP=4‐dimethylaminopyridine) were shown to be monomeric by X‐ray crystallography. In addition, the related β‐diketiminato beryllium and calcium iodide complexes, (MesNacnac)BeI] and {(DippNacnac)CaI(OEt2)}2] were prepared and crystallographically characterized. The reductions of all metal(II) iodide complexes by using various reagents were attempted. In two cases these reactions led to the magnesium(I) dimers, (MesNacnac)MgMg(MesNacnac)] and (tBuNacnac)MgMg(tBuNacnac)]. The reduction of a 1:1 mixture of (DippNacnac)MgI(OEt2)] and (MesNacnac)MgI(OEt2)] with potassium gave a low yield of the crystallographically characterized complex (DippNacnac)Mg(μ‐H)(μ‐I)Mg(MesNacnac)]. All attempts to form beryllium(I) or calcium(I) dimers by reductions of (MesNacnac)BeI], {(DippNacnac)CaI(OEt2)}2], or {(tBuNacnac)CaI(thf)}2] have so far been unsuccessful. The further reactivity of the magnesium(I) complexes (MesNacnac)MgMg(MesNacnac)] and (tBuNacnac)MgMg(tBuNacnac)] towards a variety of Lewis bases and unsaturated organic substrates was explored. These studies led to the complexes (MesNacnac)Mg(L)Mg(L)(MesNacnac)] (L=THF or DMAP), (MesNacnac)Mg(μ‐AdN6Ad)Mg(MesNacnac)] (Ad=1‐adamantyl), (tBuNacnac)Mg(μ‐AdN6Ad)Mg(tBuNacnac)], and (MesNacnac)Mg(μ‐tBu2N2C2O2)Mg(MesNacnac)] and revealed that, in general, the reactivity of the magnesium(I) dimers is inversely proportional to their steric bulk. The preparation and characterization of (tBuNacnac)Mg(μ‐H)2Mg(tBuNacnac)] has shown the compound to have different structural and physical properties to (tBuNacnac)MgMg(tBuNacnac)]. Treatment of the former with DMAP has given (tBuNacnac)Mg(H)(DMAP)], the X‐ray crystal structure of which disclosed it to be the first structurally authenticated terminal magnesium hydride complex. Although attempts to prepare (MesNacnac)Mg(μ‐H)2Mg(MesNacnac)] were not successful, a neutron diffraction study of the corresponding magnesium(I) complex, (MesNacnac)MgMg(MesNacnac)] confirmed that the compound is devoid of hydride ligands. |
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| Keywords: | low oxidation state magnesium hydrides magnesium metal– metal interactions X‐ray diffraction |
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