Synthesis of Phosphino-iminoquinoline-Type Tridentate Ligands with a Tetrahydroacridine Core for Iron-Catalyzed Hydrosilylation

We report the synthesis of a series of phosphino-iminoquinoline (PNN) ligands containing a tricyclic tetrahydroacridine core. The extra ring is hypothesized to create greater rigidity in the iminoquinoline ligand structure, which could impart additional catalyst stability. A series of P-substituted phosphino-iminoacridine ligands is synthesized containing either a mesityl or o-tolyl-substituted imine structure. One example of a phosphino-iminoacridine is metalated with FeCl2, and the resulting complex is characterized by single crystal X-ray analysis and compared to the X-ray structure of the similarly substituted phosphino-iminoquinoline Fe complex. The phosphino-iminoacridine Fe complex is then screened in the hydrosilylation of styrene with phenylsilane. Our phosphino-iminoquinoline catalyst has high reactivity when compared to known phosphino-iminoquinoline and α-diimine iron complexes. All new ligands are also screened in the Fe-catalyzed hydrosilylation of styrene with phenylsilane using an in situ catalyst generation protocol.