Coordination Chemistry of Small Molecule Activation, Generation, and Transfer

Researchers in the authorʼs laboratory have investigated small-molecule activation reactions using low-coordinate early transition-metal complexes supported by sterically demanding N-hydrocarbyl anilide ligands. Such complexes are potent one, two, or three-electron reducing agents, and early on the focus was on small molecules including N2, NO, and N2O with metalligand multiply bonded systems formed as products of the bond activation reactions. Reactions with P4 (white phosphorus) and As4 led respectively to complexes with metal-phosphorus or metal-arsenic triple bonds. This led to the notion of element or molecule activation using transition metals, to be followed by atom or group transfer to organic molecules. Phosphorus transfer was achieved in a novel phosphaalkyne synthesis method involving transfer of a P4-derived phosphorus atom using a niobium complex. Next, diphosphorus transfer was achieved using first a niobium and then an anthracene-based platform, the latter culminating in a synthesis of diphosphatriazolate, P2N3 −. Triphosphorus group transfer was harnessed in a synthesis of AsP3. This was echoed by the synthesis of HCP3. Anthracene emerged as a privileged two-electron platform for the construction of molecular precursors to reactive intermediates including HCP, P2, and phosphorus mononitride, PN. This account thus describes an arc from the activation of kinetically inert small molecules to the synthesis, transfer, or transient generation of reactive ones.