A Rigid Linker for Site-Selective Coordination of Transition Metal Cations: Combining an Acetylacetone with a Caged Phosphine.

The combination of a soft phosphorus and a hard oxygen donor in the new ligand HacacTRIP leads to excellent site selectivity for the coordination of two different metal cations of matching Pearson character. The deprotonation step required for coordinating the acetylacetone oxygen donor further increases the selectivity. In contrast to most phosphines, the use of the caged phosphatriptycene motif enables a rigid and directional orientation of the phosphorus binding site which is required to form stable coordination network structures. In addition to the synthesis of HacacTRIP, we present its selective coordination. The deprotonated acetylacetone was selectively bound to Cu and Fe. The solid state structure of the former displays a rare axial coordination of chloroform molecules. The phosphorus donor was selectively coordinated to the monovalent coinage metal cations Cu, Ag, and Au. The Cu and Ag complexes represent the first examples in which a phosphatriptycene is bound to these metal cations. Heterometallic coordination compounds were characterized with combinations of these two groups. They comprise an oligonuclear Cu/Cu mixed-valence compound in which iodide binds to both Cu and Cu cations and a complex in which acacTRIP bridges Cu and Au. In addition to these discrete aggregates, the ligand has been used to link Fe and Ag into a 2D coordination polymer with unprecedented trigonal planar coordination of three bulky phosphatriptycenes to a cation and resulting honeycomb topology. Its almost regular hexagons underline the desired rigidity of the ditopic acacTRIP ligand.