In Situ Kinetic Studies of Rh(II)-Catalyzed Asymmetric Cyclopropanation with Low Catalyst Loadings

Abstract

Dirhodium tetracarboxylates are versatile catalysts for the reactions of donor/acceptor carbenes. They catalyze a variety of transformations, including enantioselective intermolecular cyclopropanations. This study is focused on understanding the kinetics of the rhodium-catalyzed cyclopropanation, and this information was used to develop conditions for conducting the reactions with very low catalyst loadings. The enantioselective cyclopropanation of styrenes can be conducted with a catalyst loading of 0.001 mol % and still maintain high levels of enantioselectivity (86−99% ee). A triarylcyclopropanecarboxylate (TPCP) catalyst, Rh 2 (p-Ph-TPCP) 4 , was the optimum catalyst for maintaining high enantioselectivity with very low catalyst loading. The reaction also benefited from using dimethyl carbonate as the solvent, an environmentally benign and nontoxic material.

A New Ligand Design Based on London Dispersion Empowers Chiral Bismuth–Rhodium Paddlewheel Catalysts

“…Indeed, no drop in productivity or optical purity was noticed—without any further optimization of the conditions—when the reaction was performed with only 0.005 mol % of 3b on a mmol scale ( Table 1 , entry 10). 78 The robustness of these conditions was confirmed by the additional example shown in Table 2 (entry 6, 1.3 g scale). 79…”

Optimized Immobilization Strategy for Dirhodium(II) Carboxylate Catalysts for C−H Functionalization and Their Implementation in a Packed Bed Flow Reactor

“…While the well‐defined nature of the support material and uniform pore size and structure allow the synthesis of well‐defined supported catalysts, the presence of long straight mesopores surrounding the active rhodium sites can lead to substrate or product transport limitations, depending on the reaction conditions and the diameter and length of the mesopores. Given that the dirhodium catalyzed C−H functionalization reactions are generally quite fast, we postulated that transport through the channels could have a non‐negligible effect on the overall reaction rate. Moreover, the decomposition of diazo compounds generates nitrogen gas, which may result in significant transport limitations in the porous support structure of our heterogeneous system.…”

“…Immobilization of the catalyst within aquasi-2D, platelet SBA-15 support mitigates some diffusionall imitations of reactant and product to and from the dirhodium active site, increasing catalyst TOF. [18] Development of Rh 2 (S-2-Cl-5-CF 3 TPCP) 4 Catalyst After optimizing the catalyst immobilization position and silica support material, we sought to employ the optimal catalyst in the Rh 2 (S-o-ClTPCP) 4 series in apacked bed flow reactor for CÀHinsertion of C2 CÀHbonds.The Rh 2 (S-2-Cl-5-BrTPCP) 4 catalyst (16)c onsistently gives enantio-and regioselectivities that outperform those of the Rh 2 (S-o-ClTPCP) 4 catalyst. [13e] However,t he installation of the ethynyl group,which is necessary for immobilization, requires aS onogashira coupling with an aryl bromide leaving group.…”

Optimized Immobilization Strategy for Dirhodium(II) Carboxylate Catalysts for C−H Functionalization and Their Implementation in a Packed Bed Flow Reactor

“…SBA-15 is am odel, ordered mesoporous silica support material containing one dimensional cylindrical mesopores. [15] While the well-defined nature of the support material and uniform pore size and structure allow the synthesis of welldefined supported catalysts,t he presence of long straight mesopores surrounding the active rhodium sites can lead to substrate or product transport limitations,d epending on the reaction conditions and the diameter and length of the mesopores.G iven that the dirhodium catalyzed CÀHf unctionalization reactions are generally quite fast, [16] we postulated that transport through the channels could have an onnegligible effect on the overall reaction rate.M oreover,t he decomposition of diazo compounds generates nitrogen gas, which may result in significant transport limitations in the porous support structure of our heterogeneous system. Thus, we hypothesized that shortening the pore length of the SBA-15 silica support would result in af aster diffusion of the reactants and products to and from the catalyst immobilized within the SBA-15 mesopores,w hile allowing the evolved nitrogen gas to more rapidly escape from the catalyst.…”

“…Immobilization of the catalyst within aquasi-2D, platelet SBA-15 support mitigates some diffusionall imitations of reactant and product to and from the dirhodium active site, increasing catalyst TOF. [18] Angewandte Chemie Forschungsartikel Development of Rh 2 (S-2-Cl-5-CF 3 TPCP) 4 Catalyst After optimizing the catalyst immobilization position and silica support material, we sought to employ the optimal catalyst in the Rh 2 (S-o-ClTPCP) 4 series in apacked bed flow reactor for CÀHinsertion of C2 CÀHbonds.The Rh 2 (S-2-Cl-5-BrTPCP) 4 catalyst (16)c onsistently gives enantio-and regioselectivities that outperform those of the Rh 2 (S-o-ClTPCP) 4 catalyst. [13e] However,t he installation of the ethynyl group,which is necessary for immobilization, requires aS onogashira coupling with an aryl bromide leaving group.…”