Dynamic ligand reactivity in a rhodium pincer complex

Area of Science:

• Organometallic chemistry
• Catalysis
• Coordination chemistry

Background:

• Ligand cooperativity enhances reactivity in metal complexes.
• Typically, ligands act as Brønsted bases and metals as Lewis acids.
• New cooperative ligand designs are needed for novel catalytic applications.

Purpose of the Study:

• To synthesize and characterize a new phosphane-pyridine-amide ligand (PNN(H2)) with Rh(I).
• To explore the stepwise activation and cooperative reactivity of the PNN(H2) ligand.
• To demonstrate the catalytic application of the activated ligand in substrate mono-alkylation.

Main Methods:

• Synthesis of the PNN(H2) ligand and its rhodium complexes.
• Stepwise activation via proton and hydride loss, and deprotonation.
• Structural characterization of key complexes (1, 3, 4, and 5).
• Catalytic testing for sulfonamide mono-alkylation.

Main Results:

• The PNN(H2) ligand undergoes stepwise activation to form amine, amido, and dearomatized species.
• The dearomatized PNN' ligand exhibits dual cooperative modes: basic methine and electrophilic imine.
• The system successfully catalyzes the mono-alkylation of o-toluenesulfonamide with iodomethane.
• The first structurally characterized rhodium aminal complex (5) was formed.

Conclusions:

• The novel PNN(H2) ligand enables unique cooperative reactivity through stepwise activation.
• The dearomatized PNN' ligand acts as a bifunctional catalyst component.
• This work expands the scope of cooperative ligand design for catalytic transformations.