Rare-Earth Metal Phosphinidene Complexes: A Trip from Bridging One to Terminal One

Area of Science:

• Organometallic Chemistry
• Rare-Earth Metal Complexes
• Phosphorus Chemistry

Background:

• Phosphinidene complexes are phosphorus analogues of carbene and nitrene complexes, crucial for synthesizing phosphorus-containing molecules.
• While transition metal and actinide phosphinidene complexes are well-studied, rare-earth metal phosphinidene complexes have lagged due to challenging coordination chemistry.
• The inherent hardness of rare-earth metal ions and softness of phosphinidene ligands create a mismatch according to HSAB principles, hindering complex formation.

Purpose of the Study:

• To overcome the synthetic challenges in rare-earth metal phosphinidene complex formation.
• To explore the reactivity of newly synthesized rare-earth metal phosphinidene complexes.
• To advance the understanding and application of rare-earth metal-phosphorus multiple bonding.

Main Methods:

• Synthesis of bridging, mononuclear, and terminal rare-earth metal phosphinidene complexes.
• Utilized specific phosphinidene and supporting ligands to stabilize the complexes.
• Investigated complex reactivity through experimental studies and Density Functional Theory (DFT) calculations.

Main Results:

• Successfully synthesized the first bridging rare-earth metal phosphinidene complex in 2008.
• Achieved the first mononuclear (2018) and terminal (2020) rare-earth metal phosphinidene complexes, overcoming significant stabilization difficulties.
• Demonstrated novel reactivity: bridging complexes act as reductants, and mononuclear complexes catalyze alkene hydrogenation via a 1,2-addition/elimination mechanism.

Conclusions:

• The development represents a significant advancement in rare-earth metal chemistry, moving from bridging to terminal phosphinidene complexes.
• The synthesized complexes display unique catalytic and reductive properties, expanding the known reactivity of rare-earth metals.
• Ligand design strategies may enable future synthesis of related rare-earth metal-arsenic and alkaline-earth metal-phosphorus multiple bonding complexes.