Zn(II) Robson macrocycles as templates for chelating diphosphines

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Catalysis

Background:

• Robson macrocycles (RMCs) are versatile platforms for constructing complex molecular architectures.
• Dinuclear zinc(II) complexes of RMCs (Zn-RMCs) serve as effective templates for supramolecular assembly.
• Monophosphines with Lewis base functionalities can interact with metal centers, enabling templated synthesis.

Purpose of the Study:

• To construct novel chelating diphosphines using Zn-RMCs as templates.
• To investigate the structural and stability factors of the templated diphosphines.
• To evaluate the performance of the synthesized diphosphines in homogeneous catalysis, specifically rhodium-catalyzed hydroformylation.

Main Methods:

• Template-directed synthesis utilizing dinuclear Zn(II) complexes of Robson macrocycles.
• Coordination of Lewis base-functionalized monophosphines to Zn(II) centers.
• Structural characterization using X-ray diffraction.
• Spectroscopic identification of platinum complexes using Nuclear Magnetic Resonance (NMR).
• Evaluation of catalytic activity in rhodium-catalyzed hydroformylation of 1-octene.

Main Results:

• Successful construction of chelating diphosphines templated by Zn-RMCs.
• Stability of the diphosphines is influenced by functional group affinity and RMC structure.
• X-ray diffraction confirmed ditopic phosphine coordination on opposite faces of the RMC.
• Pre-organization via transition metal coordination led to same-face coordination.
• NMR identified cis-PtCl(2) complexes for several templated diphosphines.
• In situ assembled diphosphines exhibited a chelating effect in hydroformylation.
• The combination of Zn-RMC 3 and phosphine A yielded the highest linear-to-branched (l/b) ratio of 13 in acetonitrile.

Conclusions:

• Dinuclear Zn(II) Robson macrocycles are effective templates for synthesizing chelating diphosphines.
• The templated diphosphines demonstrate utility as ligands in rhodium-catalyzed hydroformylation, enhancing selectivity.
• Structural control over phosphine coordination is achievable through templating and pre-organization strategies.