Creating a new class of MOFs

The exceptional porosity and surface area of metal-organic frameworks (MOFs) have driven researchers to use this large class of crystalline materials for gas storage, separations, and other applications, some of which have been commercialized. In the great majority of MOFs, which consist of metal ions or clusters joined by organic linkers, the metals are in the +2, +3, or +4 oxidation states and the linkers are anionic. The unique electronic properties of MOFs with zero-valent or +1 metals could open the door to new applications. But such MOFs have been all but impossible to prepare because of their incompatibility with common anionic ligands such as carboxylates. So R. Eric Sikma and Seth M. Cohen of the University of California San Diego opted for phosphine ligands. The approach worked. The team prepared various types of linkers, including ones with four triphenylphosphine groups coordinated to silicon, and reacted them with several metal precursors. The study resulted in five new MOFs constructed exclusively from metal-phosphine bonds, including some with Pd(0) and Pt(0) metal centers and one Rh(I) compound (Angew. Chem., Int. Ed. 2022, DOI: 10.1002/anie.202115454). The synthesis strategy could lead to new members of this unexplored class of MOFs and provide novel ways of exploiting electron-rich metals, which are known for mediating catalytic transformations.