Controllable Factors of Supported Ir Complex Catalysis for Aromatic C–H Borylation

Rhodium-Iodide Complex on a Catalytically Active SiO2 Surface for One-Pot Hydrosilylation-CO2 Cycloaddition

In this study, a novel Rh-iodide complex was synthesized through a surface reaction between an immobilized Rh cyclooctadiene complex and alkylammonium iodide (N⁺ I^- ) on SiO₂ . In the presence of ammonium cations, the SiO₂ -supported Rh-iodide complex could be effectively used for the one-pot synthesis of various silylcarbonate derivatives starting from epoxy olefins, hydrosilanes, and CO₂ . The maximum turnover numbers (TONs) for the hydrosilylation reaction and the CO₂ cycloaddition were 7600 (Rh) and 130 (N⁺ I^- ), respectively. The catalyst exhibited much higher performance for hydrosilylation than solely the Rh complex on SiO₂ . The mechanism of the Rh-catalyzed hydrosilylation reaction and the local structure of Rh, which is affected by the co-immobilized N⁺ I^- , were investigated by using Rh and I K-edge XAFS and XPS. Analysis of the XAFS profiles indicated the presence of a Rh-I bond. The Rh unit was in its electron-rich state. Curve-fitting analysis of the Rh K-edge EXAFS profiles suggests dissociation of the cycloocta-1,5-diene (COD) ligand from the Rh center. Results from spectroscopic and kinetic analyses revealed that the high activity of the catalyst (during hydrosilylation) could be attributed to a decrease in steric hindrance and the electron-rich state of the Rh. The decrease in the steric hindrance could be attributed to the absence of COD, and the electron-rich state promoted the oxidative addition of Si-H. To the best of our knowledge, this is the first example of a one-pot silylcarbonate synthesis as well as a determination of a novel surface Rh-iodide complex and its catalysis.

Recent Advances in Heterogeneous Ir Complex Catalysts for Aromatic C–H Borylation

Aromatic C–H borylation catalyzed by an Ir complex is among the most powerful methods for activating inert bonds. The products, i.e., arylboronic acids and their esters, are usable chemicals for the Suzuki–Miyaura cross-coupling reaction, and significant effort has been directed toward the development of homogeneous catalysis chemistry. In this short review, we present a recent overview of current heterogeneous Ir-complex catalyst developments for aromatic C–H borylation. Not only have Ir complexes been immobilized on support surfaces with phosphine and bipyridine ligands, but Ir complexes incorporated within solid materials have also been developed as highly active and reusable heterogeneous Ir catalysts. Their catalytic activities and stabilities strongly depend on their surface structures, including linker length and ligand structure.

1 Introduction and Homogeneous Ir Catalysis

2 Heterogeneous Ir Complex Catalysts for C–H Borylation Reactions

3 Other Heterogeneous Metal Complex Catalysts for C–H Borylation Reactions

4 Summary and Outlook