Conformationally constrained N-heterocyclic phosphine-diimine with dual functionality

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Supramolecular Chemistry

Background:

• The synthesis and coordination behavior of novel heterocyclic ligands are crucial for developing new catalytic systems and materials.
• Ambidentate ligands, capable of binding through multiple donor atoms, offer unique opportunities for complex structural diversity and reactivity.
• Understanding the factors governing selective coordination in multidentate ligands is essential for controlling complex formation.

Purpose of the Study:

• To synthesize and characterize a novel tricyclic 1,3,2-diazaphospholidine-4,5-diimine ligand (4a).
• To investigate the coordination chemistry of ligand 4a with various transition metal complexes and pnictogen halides.
• To elucidate the binding modes and structural features of the resulting metal complexes using X-ray diffraction and DFT studies.

Main Methods:

• Synthesis of the 1,3,2-diazaphospholidine-4,5-diimine ligand (4a) via condensation.
• Coordination reactions with metal carbonyls (W(CO)5, CpCo(CO)) and pnictogen halides (PCl3, AsCl3, SbCl3).
• Single-crystal X-ray diffraction analysis and Density Functional Theory (DFT) calculations.

Main Results:

• Ligand 4a was successfully synthesized and exhibited selective coordination behavior.
• Complexes with W(CO)5 and CpCo(CO) showed phosphorus lone-pair coordination.
• Complexes with AsCl3 and SbCl3 involved binding to the diimine moiety, forming dimers through chloride bridges.

Conclusions:

• Ligand 4a demonstrates selective binding, coordinating to transition metals via phosphorus and to Lewis acidic electrophiles via the diimine unit.
• The formation of dinuclear complexes is inhibited due to the deactivation of the second binding site after the initial coordination.
• The observed selectivity provides insights into the design of ligands for specific metal-ligand interactions and catalytic applications.