Air-stable iron and cobalt catalyst systems for selective hydrosilylation and dehydrogenative silylation of unsaturated substrates

Background

Hydrosilylation, the process of adding silicon hydrides across unsaturated carbon-carbon bonds, is a foundational reaction in the synthesis of silicone-based materials such as adhesives, coatings, and elastomers. The field has historically relied on precious metal catalysts, particularly platinum complexes, due to their high activity and broad substrate compatibility. However, the reliance on platinum presents significant challenges, including high cost, supply chain volatility, and environmental concerns associated with mining and refining. These issues have driven a strong industrial and academic interest in developing alternative catalytic systems based on earth-abundant metals like iron and cobalt, which promise greater sustainability and cost-effectiveness for large-scale applications.

Despite the promise of base metal catalysts, current approaches face substantial hurdles that have limited their adoption. Many iron and cobalt catalysts require rigorous air-free handling due to their sensitivity to oxygen and moisture, necessitating specialized equipment and procedures that are impractical for industrial-scale operations. Additionally, existing base metal catalysts often suffer from poor selectivity, promoting unwanted side reactions such as alkene isomerization or dehydrogenative silylation, which compromise product purity and yield. Functional group tolerance is another limitation, as many catalysts are deactivated by common moieties like amines or ethers, further restricting their utility. These challenges underscore the need for robust, air-stable, and highly selective catalytic systems that can operate efficiently under ambient conditions and with a wide range of substrates.

Technology

This technology introduces a new class of air-stable iron and cobalt precatalysts, supported by pyridine diimine or terpyridine-based pincer ligands with carboxylate X-type ligands, designed for the hydrosilylation and dehydrogenative silylation of unsaturated substrates such as alkenes and alkynes. These precatalysts are uniquely activated in situ by silane substrates, eliminating the need for external reducing agents or air-free handling, and enabling practical, scalable use under ambient conditions. The catalytic system demonstrates high anti-Markovnikov selectivity, effectively suppresses alkene isomerization, and is compatible with a broad range of functional groups, including amines and ethers. This versatility allows for efficient crosslinking of silicone fluids and the production of allylsilanes at low catalyst loadings, making it suitable for applications in the synthesis of specialty silicones, surfactants, and advanced materials.

What differentiates this technology is its combination of air stability, high selectivity, and broad functional group tolerance, which addresses longstanding limitations of both precious metal and previous base metal catalysts. Unlike traditional platinum-based systems that are expensive, sensitive to functional group poisoning, and prone to side reactions, these iron and cobalt catalysts are based on earth-abundant metals and can be handled in air, significantly reducing operational costs and complexity. The in situ activation by silane substrates streamlines the process, while the suppression of isomerization and high anti-Markovnikov selectivity enable the production of purer, more desirable products. Extensive experimental validation and compatibility with industrially relevant substrates further underscore its practical impact, positioning it as a highly attractive and sustainable alternative for the silicone and materials industries.

Benefits

• Air-stable iron and cobalt precatalysts enable easy handling and storage under ambient conditions without special equipment.
• High anti-Markovnikov selectivity with suppression of alkene isomerization improves product purity and yield.
• Eliminates the need for expensive and scarce precious metals like platinum, reducing catalyst cost and supply risks.
• Activated in situ by silane substrates, removing the requirement for external reducing agents or activators.
• Compatible with a wide range of functional groups (e.g., amines, ethers) and industrially relevant silanes, enhancing substrate scope.
• Effective at very low catalyst loadings, supporting cost-efficient and scalable industrial processes.
• Enables synthesis and crosslinking of silicone materials and allylsilanes under mild, ambient conditions.
• Offers a sustainable and practical alternative for silicone industry applications, including coatings, adhesives, and elastomers.

Applications

• Silicone elastomer and gel manufacturing
• Silicone-based adhesive production
• Surfactant and specialty fluid synthesis
• Advanced coatings and tire additives
• Allylsilane pharmaceutical intermediate synthesis

Additional info

These air-stable iron and cobalt complexes utilize pyridine diimine or terpyridine pincer ligands with carboxylate X-type ligands. They facilitate anti-Markovnikov hydrosilylation and dehydrogenative silylation of unsaturated substrates. Activated in situ by silanes, these systems require no external reducing agents. They suppress alkene isomerization, tolerate diverse functional groups, and enable silicone crosslinking at low loadings, providing a sustainable, high-selectivity alternative to platinum catalysis under ambient conditions.