Exploration of Light-Driven, Zirconium Catalyzed Hydrophosphination and Progress Towards Asymmetric Hydrophosphination

Direct irradiation of UV or visible light on zirconium catalyzed hydrophosphination reactions have shown to improve relative reaction rate and unlock new reactivity in contrast to reactions run in ambient light or the exclusion of light. The fist compound observed to receive this benefit was a triamidoamine-supported zirconium complex abbreviated (N3N)Zr that has been extensively studied by our group. UV-vis spectroscopy and TD-DFT calculations of early experiments revealed the nature of this improved reactivity being the population of an excited state that exhibits significant Zr–P σ* character in the active catalyst upon photon absorbance. This nd charge transfer elongates the Zr–P bond, allowing for facile substrate insertion. It was hypothesized that this behavior was not exclusive to the geometry or donor ligand set of (N3N)Zr, and various other zirconium catalysts of distinguished ligand types were examined. Known zirconium hydrophosphination catalysts present in the literature had their relative rates of catalysis improved through photolysis. Other zirconium compounds that were previously inactive as hydrophosphination catalysts can now achieve this reactivity through irradiation. Varying the wavelength of light also plays an important role in these reactions, and UV-vis spectroscopy can be used to identify the exact transition wavelengths. These results are leveraged to make progress towards zirconium catalyzed asymmetric hydrophosphination to produce chiral phosphines, which are important auxiliaries in other enantiospecific transformation. The value of this work is further highlighted by the vast majority of asymmetric hydrophosphination catalysts being of platinum or palladium, where a relatively abundant and inexpensive metal could be used as substitute. Our results have also led to the implementation of these methods on other formally d0 transition-metal catalysts with similar results