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(SiMe3)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 [Ph2PNH(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 case.