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 (L1H), 2-MePh2SiNH-6-MeC5H3N (L2H), and 2-Me3SiNH-6-PhC5H3N (L3H) with KH in tetrahydrofuran (THF) yielded potassium
salts L1K­(thf)0.5 (1), L2K (2), and L3K­(thf)0.5 (3), which, through subsequent reaction with MgI2 and CaI2, afforded the homoleptic complexes (L)2Ae­(thf)n [L = L1, Ae = Mg, n = 1 (4); L = L2, Ae = Mg, n = 0 (5); L = L3, Ae = Mg, n = 0 (6); L = L2, Ae = Ca, n =
2 (7)] and heterobimetallic calciates {[(L)3Ca]­K}∞ [L = L1 (8); L = L2 (9)]. The solid state structure of 8 reveals a
polymeric arrangement in which the calciate units are interlocked
by bridging potassium ions. Metalation reactions between L1H or L2H and (nBu)2Mg lead to the
solvent-free compounds (L)2Mg [L = L1 (10); L = L2 (5)]. The bridged butyl mixed-metal complex [(L1)­Li­(μ2-nBu)­Mg­(L1)]∞ (11) was also obtained via a cocomplexation
reaction with nBuLi and (nBu)2Mg. 11, 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 (L1)3MgLi­(thf) (12).