Catalytic Main-Group Metal Complexes of Phosphine-Based Pincer Ligands

Pincer ligand complexes, which appeared nearly five decades ago, have provided a valuable platform for the study of fundamental chemical processes and the development of efficient catalysts for many chemical transformations. These complexes have usually contained transition metal atoms or ions, and their respective pincer ligands have often featured phosphine donor groups, which strongly coordinate to the metal center and allow its steric and electronic properties to be fine-tuned. The increasing need to develop cost-effective and sustainable catalytic processes has driven the search for main-group metals as alternatives to commonly-used transition metals. In this review, we show that despite the inherent mismatch between phosphines, which are soft Lewis bases, and main-group metal ions, which are hard Lewis acids, a series of well-defined phosphine-based pincer complexes containing Li(I), Na(I), K(I), Mg(II), Ca(II), Zn(II) and Al(III) have been reported, which have proven to be active catalysts for industrially-relevant transformations.