Titanium Dinitrogen Complex Catalyzed Hydrophosphination Leveraging the N₂-Unit Electron Reservoir

Metal dinitrogen complexes, a prominent class of compounds in the mimic of Haber-Bosch NH₃ manufacture, have been prevalently adopted for N₂ functionalization to form N-X (X = H, C, Si, etc.) bonds through the stoichiometric reactions with acids and electrophilic reagents. The discovery of alternative application of these complexes beyond aforementioned N₂ functionalization is highly desirable but remains elusive. In this work, we demonstrated that a titanium dinitrogen complex exhibits catalytic potential in the hydrophosphination of alkenes with an outstanding substrate compatibility and a turnover number of 743 was achieved. Mechanistic studies showed that the end-on bridging dinitrogen unit (N₂-unit) of the Ti^III complex could be replaced with diphenylphosphine to form a catalytically active Ti^II species, with the concurrent extrusion of a free N₂ molecule that was probed by ¹⁵N NMR spectroscopy. Thus, each N₂-unit virtually serves as an electron reservoir providing electrons to metal centers to give catalytically active low-valent metal species. This reaction represents a rare example of adopting a metal dinitrogen complex as a precatalyst in organic transformations and the introduction of N₂-unit electron reservoir (NER) concept provides a novel and effective strategy for the invoking of low-valent metal species for catalytic applications.