Ultra-Confined Environments May Restrict the Possible Configurations of Supported Metal Complexes

Area of Science:

• Surface chemistry
• Organometallic chemistry
• Materials science

Background:

• Amido ligand rotation frequencies probe electronic structures in transition metal complexes.
• Silica-supported chromium complexes are used to study ligand donor properties.

Purpose of the Study:

• Investigate amido ligand dynamics in silica-supported chromium complexes.
• Determine the effect of pore confinement on ligand mobility and surface species conformation.

Main Methods:

• Solid-state nuclear magnetic resonance (NMR) spectroscopy to measure rotation frequencies.
• Density functional theory (DFT) calculations to model coordination and conformation.

Main Results:

• Steric hindrance from silica support restricted amido ligand rotation.
• Grafting the complex into 2.2 nm pores enabled rotation of all amido ligands.
• DFT calculations indicated confinement limits coordination sites and surface species configurations.

Conclusions:

• Confinement in nanoporous silica can overcome steric limitations for surface-bound ligands.
• Pore confinement can lead to conformationally homogeneous surface site populations.