Terminal and Super-Basic Parent Imides of Hafnium

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Materials Science

Background:

• Hafnium complexes are crucial in catalysis and materials science.
• The synthesis and characterization of novel hafnium-nitrogen bonds are of significant interest.
• Understanding the electronic structure and reactivity of these complexes provides insights into chemical bonding and reaction mechanisms.

Purpose of the Study:

• To synthesize and characterize a novel dinuclear hafnium complex with a parent imido ligand.
• To investigate the electronic structure and super-basic character of a key nitrido intermediate.
• To explore the reactivity of the hafnium-nitrogen triple bond with electrophiles.

Main Methods:

• Reduction of a hafnium bisazide precursor using KC8.
• Encapsulation of the potassium counterion with crown-ether or cryptand.
• Density Functional Theory (DFT) calculations for electronic structure and pKa determination.
• Spectroscopic characterization of the synthesized complexes.

Main Results:

• Successful synthesis of the dinuclear hafnium complex [(PN)(PNC)Hf=NH{μ2-K}]2 (2).
• Formation of discrete salts [K(encap)][(PN)(PNC)Hf≡NH] (3, 4) with a terminal parent imide and short Hf-N bonds.
• Identification of a super-basic monomeric nitrido intermediate [(PN)2Hf≡N]− (A) with a computed pKBH+ of ~57.
• Demonstration of the reactivity of the Hf≡NH bond with various electrophiles.

Conclusions:

• The study presents the first discrete salts featuring a terminal parent imide ligand with exceptionally short Hf-N bonds.
• A highly basic nitrido intermediate with a covalent Hf≡N triple bond was identified and characterized.
• The novel hafnium complexes exhibit interesting reactivity, opening avenues for new synthetic methodologies.