Heavier alkaline earth metal complexes with phosphinoselenoic amides: Evidence of direct M-Se contact (M = Ca, Sr, Ba)

We report here a series of heavier alkaline earth metal complexes with a phosphinoselenoic amide ligand using two synthetic routes. In the first route, the heavier alkaline earth metal bis(trimethylsilyl)amides [M{N(SiMe 3)2}2(THF)n] (M = Ca, Sr, Ba) were treated with phosphinoselenoic amine [Ph2P(Se)NH(CHPh2)] (3), prepared by the treatment of bulky phosphinamines [Ph 2PNH(CHPh2)] (1) with elemental selenium in THF, and afforded homoleptic alkaline earth metal complexes of composition [M(THF) 2{Ph2P(Se)N(CHPh2)}2] (M = Ca (7), Sr (8), Ba (9)). The metal complexes 7-9 can also be obtained via salt metathesis route where the alkali metal phosphinoselenoic amides of composition [{(THF)2M'Ph2P(Se)N(CHPh2)}2] (M' = Na (5) and K (6)) were reacted with respective metal diiodides in THF at ambient temperature. The solid state structures of the alkali metal complexes 5-6 and alkaline earth metal complexes 7-9 were established by single crystal X-ray diffraction analysis. In the solid state, alkali metal complexes 5 and 6 are dimeric and form a poly-metallacyclic structural motif. In contrast, complexes 7-9 are monomeric and a direct metal-selenium bond is observed in each cas