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Photocatalytic Hydrophosphination Using Calcium Precatalysts
Moniruzzaman Moniruzzaman1, Nai-Yuan Jheng1, Rory Waterman1
1Department of Chemistry, University of Vermont, Burlington, VT, 05405, USA.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|April 16, 2025
Summary
Calcium compounds are effective photocatalysts for hydrophosphination reactions under irradiation, expanding s-block catalysis. Nacnac-supported catalysts generate radicals, while unsupported ones react thermally, highlighting ligand importance.
Area of Science:
- Organometallic Chemistry
- Photocatalysis
- Main Group Chemistry
Background:
- Transition-metal compounds are established photocatalysts for hydrophosphination.
- Previous methods were limited to specific substrate types.
- S-block elements offer a new frontier in photocatalysis.
Purpose of the Study:
- To explore the use of calcium compounds as photocatalysts for hydrophosphination.
- To investigate the role of ancillary ligands in calcium-catalyzed hydrophosphination.
- To understand the mechanism of photocatalysis involving s-block elements.
Main Methods:
- Screening of calcium precatalysts and intermediates under photochemical conditions.
- Utilizing various unsaturated substrates like styrenic alkenes, Michael acceptors, and dienes.
- Employing light-emitting diode (LED)-generated blue light for irradiation.
- Characterization using Electron Paramagnetic Resonance (EPR) spectroscopy and radical trapping experiments.
Main Results:
- Calcium compounds, particularly nacnac-supported ones, efficiently catalyze hydrophosphination under blue LED irradiation.
- Nacnac-supported calcium complexes generate radicals, indicating a photoinduced radical pathway.
- Unsupported calcium compounds exhibit EPR silence and proceed via thermal pathways.
- Modest to excellent conversions were achieved for styrenic alkenes, Michael acceptors, and dienes, but not unactivated alkenes.
Conclusions:
- Calcium compounds represent a viable class of s-block photocatalysts for hydrophosphination.
- Photoactivation of π-basic ligands is a broad phenomenon extending beyond transition metals.
- Ancillary ligand choice is crucial for controlling reactivity and avoiding undesired radical pathways, similar to d-block metal catalysis.
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