A silica-supported, switchable, and recyclable hydroformylation-hydrogenation catalyst.

Area of Science:

• Heterogeneous catalysis
• Organometallic chemistry
• Materials science

Background:

• Homogeneous hydroformylation catalysts offer high selectivity but suffer from separation difficulties.
• Immobilization of transition metal complexes onto solid supports is a key strategy to combine homogeneous catalyst advantages with heterogeneous system benefits.
• Developing robust and recyclable catalytic systems is crucial for sustainable chemical synthesis.

Purpose of the Study:

• To covalently tether a homogeneous hydroformylation catalyst to a polysilicate support for enhanced recyclability and selectivity.
• To investigate the catalytic performance of the immobilized rhodium complex in hydroformylation and hydrogenation reactions.
• To explore the possibility of switching the catalytic system between different reaction modes (hydroformylation, hydrogenation, tandem) by adjusting reaction conditions.

Main Methods:

• Preparation of the immobilized catalyst via sol-gel process and covalent anchoring of a rhodium-phenoxazine complex to silica.
• Characterization of the immobilized catalyst using solid-state NMR (31P, 29Si MAS NMR), FT-IR, and X-ray photoelectron spectroscopy.
• Evaluation of catalytic activity and selectivity in hydroformylation and hydrogenation of 1-octene under various conditions (CO/H2, H2 alone, presence of propanol).

Main Results:

• The immobilized rhodium catalyst demonstrated high selectivity for linear aldehydes (94.6%) with a linear-to-branched ratio of 65.
• An unexpected hydrogenation of the aldehyde to 1-nonanol occurred as a secondary product.
• The system exhibited tunable behavior, acting as a selective hydroformylation catalyst (X), a hydrogenation catalyst (Y), or a tandem hydroformylation/hydrogenation catalyst (Z), with reversible switching and retained performance.

Conclusions:

• Covalent immobilization of the rhodium complex onto a polysilicate support yields a highly selective and recyclable hydroformylation catalyst.
• The immobilized system offers unprecedented control, allowing reversible switching between distinct catalytic modes (hydroformylation, hydrogenation, tandem) by simple manipulation of reaction conditions.
• This versatile catalytic system provides a sustainable approach for the selective synthesis of aldehydes and alcohols from alkenes.