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 TiIII complex could be replaced with diphenylphosphine to form a catalytically active TiII 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.