Supramolecularly Regulated Ligands for Asymmetric Hydroformylations and Hydrogenations

Abstract

Abstract:Herein we report the use of polyether binders as regulation agents (RAs) to enhance the enantioselectivity of rhodium-catalyzed transformations. For reactions of diverse substrates mediated by rhodium complexes of the ,-bisphosphite-polyether ligands 15,ad, the enantiomeric excess (ee) of hydroformylations was increased by up to 82% (substrate: vinyl benzoate, 96% ee), and the ee value of hydrogenations was increased by up to 5% (substrate: N-(1-(naphthalene-1-yl)vinyl)acetamide, 78% ee). The ligand design enabled the regulation of enantioselectivity by generation of an array of catalysts that simultaneously preserve the advantages of a privileged structure in asymmetric catalysis and offer geometrically close catalytic sites. The highest enantioselectivities in the hydroformylation of vinyl acetate with ligand 4b were achieved by using the Rb[B(3,5-(CF3)2C6H3)4 (RbBArF) as the RA. The enantioselective hydrogenation of the substrates 10 required the rhodium catalysts derived from bisphosphites 3a or 4a, either alone or in combination with different RAs (sodium, cesium or (R,R)-bis(1-phenylethyl)ammonium salts). This design approach was supported by results from computational studies.

Kinetic Treatments for Catalyst Activation and Deactivation Processes based on Variable Time Normalization Analysis

“…[5] This analysis allows the removal of the kinetic effect of any component of ar eaction from the temporal concentration profiles.Therefore,ifboth the concentration of active catalyst and the progress of the reaction can be measured simultaneously by any appropriate method, then the intrinsic profile of the main reaction can be obtained ( Figure 1a). [3] As the catalyst formation process is not immediate,t he active catalyst concentration increases over the course of the reaction and the overall reaction profile shows aclear induction period in the formation of the product ( Figure 2a). Thesecond kinetic treatment presented herein uses the reaction progress profile and the orders of reaction to extract the catalyst activation or deactivation profile ( Figure 1b).…”

“…[8] Thecatalyst profile was used to normalize the time scale of the original progress reaction profile using VTNA. [3,9] Thes econd reaction we investigated is the enantioselective aminocatalytic Michael addition of aldehyde to trans-bnitrostyrene ( Figure 3). These observations imply that, under the chosen reaction conditions,the olefin-hydride insertion is the rate-determining step.…”

Supramolecularly fine-regulated enantioselective catalysts

“…6). 27 These studies revealed that ligands with a conformationally labile [1,1'-biaryl]-2,2'-diol motif at the regulation site led to lower conversions in the AHF of the chosen model substrate (i.e. vinyl acetate) and that phosphite groups derived from 3,3'-bis(trimethylsilyl)-[1,1'-binaphthalene]-2,2'-diol provided the highest ees in AHF.…”

Kinetic Treatments for Catalyst Activation and Deactivation Processes based on Variable Time Normalization Analysis

“…Herein, we describe two treatments that facilitate aq uantitative analysis of reactions involving catalyst activation or deactivation processes.O ne or other of these treatments can be used, depending on the available information. We show the feasibility of both methods in the kinetic analysis of real reactions with severe changes of active catalyst concentration during the course of the reaction:ahydroformylation reaction catalyzed by asupramolecular rhodium complex [3] and an aminocatalytic Michael reaction. [4] Thetwo kinetic treatments presented herein are based on the recently described variable time normalization analysis (VTNA).…”

“…Thef irst is an asymmetric hydroformylation catalyzed by asupramolecular rhodium complex, which requires three different units to come together to form an active catalyst:r hodium as active center,a ne nantiopure bisphosphite as ligand, and ar ubidium salt to regulate the geometry of the catalyst (Figure 2). [3] As the catalyst formation process is not immediate,t he active catalyst concentration increases over the course of the reaction and the overall reaction profile shows aclear induction period in the formation of the product (Figure 2a).…”