Complexes of the Heavier Alkaline Earth Metals Ca, Sr, and Ba with O-Functionalized Phosphanide Ligands

Metathesis reactions between either SrI2 or BaI2 and 2 equiv of the potassium phosphanide [{(Me3Si)2CH}-(C6H4-2-OMe)P]K yield, after recrystallization, the complexes [{([Me3Si]2CH)(C6H4-2-OMe)P}2M(THF)n] [M = Sr,
n = 2 (5); Ba, n = 3 (6)]. Similar metathesis reactions between MI2 and 2 equiv of the more sterically demanding potassium phosphanide [{(Me3Si)2CH}(C6H3-2-OMe-3-Me)P]K yield the chemically isostructural complexes
[{([Me3Si]2CH)(C6H3-2-OMe-3-Me)P}2M(THF)2] [M = Ca (9), Sr (7), Ba (8)]. Compounds 5−9 have been characterized
by multi-element NMR spectroscopy and X-ray crystallography. Complex 9 is thermally unstable and decomposes
at room temperature to give the tertiary phosphane {(Me3Si)2CH}(C6H3-2-OMe-3-Me)P(Me) and an unidentified
Ca-containing product. Compounds 5 and 6 also decompose at elevated temperatures to give the corresponding
tertiary phosphane {(Me3Si)2CH}(C6H4-2-OMe)P(Me) and intractable metal-containing products. The decomposition
of 5, 6, and 9 suggests that these compounds undergo an intramolecular methyl migration from the O atom in one
phosphanide ligand to the P atom of an adjacent phosphanide ligand to give species containing dianionic alkoxo-phosphanide ligands.