Synthesis and Structural Studies on [Mg₃(O₂CC⋮CSiMe₃)₆(HMPA)₄]:  Mechanistic Implications for the Formation of the μ₄-η⁴ Bonding Type in Carbamato-Bridged Mg₆ Cage Compounds

Abstract

The insertion reaction of CO 2 with Mg(C⋮CSiMe 3 ) 2 was characterized by NMR spectroscopic studies to give a cage compound [Mg n (O 2 CC⋮CSiMe 3 ) 2 n ·(THF) m ], 1a, and the addition of HMPA/THF (HMPA = hexamethylphosphoramide) to solutions of 1a produces a trimeric compound, [Mg 3 (O 2 CC⋮CSiMe 3 ) 6 (HMPA) 4 ], 1b . X-ray diffraction studies of this showed 1b to contain a completely centrosymmetric linear array of magnesium atoms linked with μ 2 -η 2 - and μ 2 -η 3 -O 2 CC⋮CSiMe 3 . It was found to be a key compound in the mechanism leading to the formation of μ 4 -η 4 bonding in carbamato-bridged Mg 6 cage compounds.