Transition Metal as Template: Reversing the Synthesis Logic in the Preparation of Pincer Complexes

The conventional synthetic approach to transition metal pincer complexes calls for the preparation of the tridentate pincer (pro)ligand first, with subsequent introduction of the transition metal center as the last step. This work demonstrates that the alternative synthetic logic, where the central main group element is introduced last, can be applicable to a number of PEP pincer complexes (E=B, Al, Si, P) derived from phosphinophenols and phosphinopyrroles. This approach obviates the need to isolate well-behaved propincer precursors, and instead relies on the formation of phosphine-metal adducts first, whose nature determines the stoichiometry of the needed main group reagent to complete the synthesis.