Alkaline Earth Complexes of Silylated Aminopyridinato Ligands: Homoleptic Compounds and Heterobimetallic Coordination Polymers

The synthesis and characterization of magnesium and calcium complexes of sterically demanding aminopyridinato ligands is reported. The reaction of the 2-Me₃SiNH-6-MeC₅H₃N (<b>L</b>^<b>1</b>H), 2-MePh₂SiNH-6-MeC₅H₃N (<b>L²</b>H), and 2-Me₃SiNH-6-PhC₅H₃N (<b>L</b>^<b>3</b>H) with KH in tetrahydrofuran (THF) yielded potassium salts <b>L</b>^<b>1</b>K­(thf)_0.5 (<b>1</b>), <b>L</b>^<b>2</b>K (<b>2</b>), and <b>L</b>^<b>3</b>K­(thf)_0.5 (<b>3</b>), which, through subsequent reaction with MgI₂ and CaI₂, afforded the homoleptic complexes (L)₂Ae­(thf)_<i>n</i> [L = <b>L</b>^<b>1</b>, Ae = Mg, <i>n</i> = 1 (<b>4</b>); L = <b>L</b>^<b>2</b>, Ae = Mg, <i>n</i> = 0 (<b>5</b>); L = <b>L</b>^<b>3</b>, Ae = Mg, <i>n</i> = 0 (<b>6</b>); L = <b>L</b>^<b>2</b>, Ae = Ca, <i>n</i> = 2 (<b>7</b>)] and heterobimetallic calciates {[(L)₃Ca]­K}_∞ [L = <b>L</b>^<b>1</b> (<b>8</b>); L = <b>L</b>^<b>2</b> (<b>9</b>)]. The solid state structure of <b>8</b> reveals a polymeric arrangement in which the calciate units are interlocked by bridging potassium ions. Metalation reactions between <b>L</b>^<b>1</b>H or <b>L</b>^<b>2</b>H and (^<i>n</i>Bu)₂Mg lead to the solvent-free compounds (L)₂Mg [L = <b>L</b>^<b>1</b> (<b>10</b>); L = <b>L</b>^<b>2</b> (<b>5</b>)]. The bridged butyl mixed-metal complex [(<b>L</b>^<b>1</b>)­Li­(μ₂-^<i>n</i>Bu)­Mg­(<b>L</b>^<b>1</b>)]_∞ (<b>11</b>) was also obtained via a cocomplexation reaction with ^<i>n</i>BuLi and (^<i>n</i>Bu)₂Mg. <b>11</b>, which adopts a monodimensional polymeric array in the solid state, is a rare example of an alkyl-bridged Li/Mg complex and the first complex to feature an unsupported bridging butyl interaction between two metals. Changing the cocomplexation reaction conditions, the order of reagents added to the reactions mixture, and with the use of a coordinating solvent (tetrahydrofuran) formed the magnesiate complex (<b>L</b>^<b>1</b>)₃MgLi­(thf) (<b>12</b>)