Enantiopure Calcium Iminophosphonamide Complexes: Synthesis, Photoluminescence, and Catalysis.

The synthesis of calcium complexes ligated by three different chiral iminophosphonamide ligands, L-H (L=[Ph2 P{N(R)CH(CH3 )Ph}2 ]), L'-H (L'=[Ph2 P{NDipp}{N(R)CH(CH3 )Ph}]), (Dipp=2,6-i Pr2 C6 H3 ), and L''-H (L''=[Ph2 P{N(R)CH(CH3 )naph}2 ]), (naph=naphthyl) is presented. The resulting structures [L2 Ca], [L'2 Ca], and [L''2 Ca] represent the first examples of enantiopure homoleptic calcium complexes based on this type of ligands. The calcium complexes show blue-green photoluminescence (PL) in the solid state, which is especially bright at low temperatures. Whereas the emission of [L''2 Ca] is assigned to the fluorescence of naphthyl groups, the PL of [L2 Ca] and [L'2 Ca] is contributed by long-lived phosphorescence and thermally activated delayed fluorescence (TADF), with a strong variation of the PL lifetimes over the temperature range of 5-295 K. Furthermore, an excellent catalytic activity was found for these complexes in hydroboration of ketones at room temperature, although no enantioselectivity was achieved.