Synthesis and Reactivity of Bis(silylene)-Coordinated Calcium and Divalent Lanthanide Complexes

Divalent lanthanide complexes of Eu (1) and Yb (2) coordinated by a chelating pyridine-based bis(silylene) ligand were isolated and fully characterized. Compared to the Eu^II complex 1, the Yb^II complex 2 presents a lower thermal stability, resulting in the activation of one Si^II -N bond and formation of an Yb^III complex (3), which features a unique silylene-pyridyl-amido ligand. The different thermal stability of 1 and 2 points towards reduction-induced cleavage of one Si^II -N bond of the bis(silylene) ligand. Successful isolation of the corresponding redox-inert bis(silylene) Ca^II complex (5) was achieved at low temperature and thermal decomposition into a Ca^II complex (4) bearing the same silylene-pyridyl-amido ligand was identified. In this case, the thermolysis reaction proceeds through another, non-redox induced, mechanism. An alternative higher yielding route to 4 was developed through an in situ generated silylene-pyridyl-amine proligand.