β‐Diketiminate‐Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis, Characterization, Adduct Formation, and Reactivity Studies

The preparation and characterization of a series of magnesium (II) iodide complexes incorporating beta-diketiminate ligands of varying steric bulk and denticity, namely, (ArNCMe) (2) CH (-) (Ar=phenyl, ( (Ph) Nacnac), mesityl ( (Mes) Nacnac), or 2, 6-diisopropylphenyl (Dipp, (Dipp) Nacnac) ), (DippNCtBu) (2) CH (-) ( (tBu) Nacnac), and (DippNCMe) (Me (2) NCH (2) CH (2) NCMe) CH (-) ( (Dmeda) Nacnac) are reported. The complexes ( (Ph) Nacnac) MgI (OEt (2) ), ( (Mes) Nacnac) MgI (OEt (2) ), ( (Dmeda) Nacnac) MgI (OEt (2) ), ( (Mes) Nacnac) MgI (thf), ( (Dipp) Nacnac) MgI (thf), ( (tBu) Nacnac) MgI, and ( (tBu) Nacnac) MgI (DMAP) (DMAP=4-dimethylaminopyridine) were shown to be monomeric by X-ray crystallography. In addition, the related beta-diketiminato beryllium and calcium iodide complexes, ( (Mes) Nacnac) BeI and ( (Dipp) Nacnac) CaI (OEt (2) ) (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, ( (Mes) Nacnac) MgMg ( (Mes) Nacnac) and ( (tBu) Nacnac) MgMg ( (tBu) Nacnac). The reduction of a 1: 1 mixture of ( (Dipp) Nacnac) MgI (OEt (2) ) and ( (Mes) Nacnac) MgI (OEt (2) ) with potassium gave a low yield of the crystallographically characterized complex ( (Dipp) Nacnac) Mg (mu-H) (mu-I) Mg ( (Mes) Nacnac). All attempts to form beryllium (I) or calcium (I) dimers by reductions of ( (Mes) Nacnac) BeI, ( (Dipp) Nacnac) CaI (OEt (2) ) (2), or ( (tBu) Nacnac) CaI (thf) (2) have so far been unsuccessful. The further reactivity of the magnesium (I) complexes ( (Mes) Nacnac) MgMg ( (Mes) Nacnac) and ( (tBu) Nacnac) MgMg ( (tBu) Nacnac) towards a variety of Lewis bases and unsaturated organic substrates was explored. These studies led to the complexes ( (Mes) Nacnac) Mg (L) Mg (L) ( (Mes) Nacnac) (L=THF or DMAP), ( (Mes) Nacnac) Mg (mu-AdN (6) Ad) Mg ( (Mes) Nacnac) (Ad=1-adamantyl), ( (tBu) Nacnac) Mg (mu-AdN (6) Ad) Mg ( (tBu) Nacnac), and ( (Mes) Nacnac) Mg (mu-tBu (2) N (2) C (2) O (2) ) Mg ( (Mes) Nacnac) and revealed that, in general, the reactivity of the magnesium (I) dimers is inversely proportional to their steric bulk. The preparation and characterization of ( (tBu) Nacnac) Mg (mu-H) (2) Mg ( (tBu) Nacnac) has shown the compound to have different structural and physical properties to ( (tBu) Nacnac) MgMg ( (tBu) Nacnac). Treatment of the former with DMAP has given ( (tBu) Nacnac) 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 ( (Mes) Nacnac) Mg (mu-H) (2) Mg ( (Mes) Nacnac) were not successful, a neutron diffraction study of the corresponding magnesium (I) complex, ( (Mes) Nacnac) MgMg ( (Mes) Nacnac) confirmed that the compound is devoid of hydride ligands.