Structure, Electronics and Reactivity of Ce(PNP) Complexes

Area of Science:

• Organometallic Chemistry
• Lanthanide Chemistry
• Coordination Chemistry

Background:

• The coordination chemistry of early lanthanides like cerium(III) is less explored compared to later lanthanides.
• Development of novel ligand frameworks is crucial for stabilizing unusual oxidation states and reactivity.
• The bis[2-(diisopropylphosphino)-4-methylphenyl]amido (PNP) ligand offers unique steric and electronic properties for metal coordination.

Purpose of the Study:

• To develop synthetic methodologies for coordinating the monoanionic PNP ligand framework to cerium(III).
• To characterize the resulting cerium complexes and investigate their structural and electronic properties.
• To explore the reactivity of these cerium complexes, including ligand modification and C-H bond activation.

Main Methods:

• Synthesis and isolation of {(PNP)Ce} and {(PNP)2Ce} type complexes.
• Structural characterization using X-ray diffraction and multinuclear NMR spectroscopy (including 31P NMR).
• Investigation of reactivity through reactions with benzophenone and electrochemical/computational studies.

Main Results:

• Successful coordination of the PNP ligand to cerium(III), forming various complex types.
• Discovery of a novel dianionic PNP ligand (PNP-iPr) with a phosphido-donor functionality, featuring the shortest known molecular Ce-P bond (2.7884(14) Å).
• Observation of C-H bond activation and C-C coupling in a reaction involving a SiMe3 group, yielding a Ce-bound product.
• 31P NMR spectroscopy proved effective for estimating vacant coordination sites and Ce-P bond distances.
• Electrochemical and computational studies indicated that the PNP ligand stabilizes the Ce(III) oxidation state.

Conclusions:

• The developed synthetic routes provide access to a range of novel cerium(III)-PNP complexes.
• The cerium(III) ion can induce significant ligand modification, leading to unique bonding interactions.
• The PNP ligand framework is highly effective in stabilizing the cerium(III) oxidation state and enabling interesting reactivity, such as C-H activation.