Why is the Ir(III)-Mediated Amido Transfer Much Faster Than the Rh(III)-Mediated Reaction? A Combined Experimental and Computational Study

Abstract

The mechanism of the Ir(III) and Rh(III)-mediated C-N coupling reaction, which is the key step of catalytic C-H amidation, was investigated in an integrated experimental and computational study. Novel amidating agents containing a 1,4,2-dioxazole moiety allowed for designing a stoichiometric version of the catalytic C-N coupling reaction and giving access to reaction intermediates that reveal details about each step of the reaction. Both DFT and kinetic studies strongly point to a mechanism where the M(III) complex engages the amidating agent via oxidative coupling to form a M(V)-imido intermediate, which then undergoes migratory insertion to afford the final C-N coupled product. For the first time, the stoichiometric versions of the Ir and Rh-mediated amidation reaction were compared systematically to each other. Iridium reacts much faster than rhodium (~ 1100 times at 6.7 °C) with the oxidative coupling being so fast that the activation of the initial Ir(III)-complex becomes rate-limiting. In the case of Rh, the Rh-imido formation step is rate-limiting. These qualitative difference stems from a unique bonding feature of the dioxazole moiety and the relativistic contraction of the Ir(V), which affords much more favorable energetics for the reaction. For the first time, a full molecular orbital analysis is presented to rationalize and explain the electronic features that govern this behavior.

Redox Control of Aluminum Ring-Opening Polymerization: A Combined Experimental and DFT Investigation

“…Detailed explanations will be given in the DFT calculation section. [86][87][88][89][90][91][92][93][94] and predictive studies. [95][96][97][98][99][100][101][102][103][104] To gain a better understanding of the polymerization processes discussed above, detailed theoretical studies were essential.…”

Comparison of the Reactivities and Selectivities of Group 9 [Cp*MIII] Catalysts in C−H Functionalization Reactions

“…[40] Metalation of 2-phenylpyridine throughC ÀHa ctivation generated rhodacycle I (M = Rh),w hich could coordinate to the 2-phenylpyridine substrate to afford an off-cyclic species( II). [40] Metalation of 2-phenylpyridine throughC ÀHa ctivation generated rhodacycle I (M = Rh),w hich could coordinate to the 2-phenylpyridine substrate to afford an off-cyclic species( II).…”

“…Subsequently,d etailed experimental and computational studies on the CÀNc oupling reactions with Rh III and Ir III were reported( Scheme 30 a). [40] Metalation of 2-phenylpyridine throughC ÀHa ctivation generated rhodacycle I (M = Rh),w hich could coordinate to the 2-phenylpyridine substrate to afford an off-cyclic species( II). Reversible ligand exchange with an aminatinga gent,f ollowed by CÀNi nsertioni nto the RhÀC bond with the extrusion of CO 2 ,w ould lead to another rhodacyclic species(IV).…”

Intermolekulare, verzweigt‐selektive und redoxneutrale Cp*IrIII‐katalysierte allylische C‐H‐Amidierung

“…[5] In komplementärer Weise berichteten Blakey et al über die allylische Aminierung von b-substituierten Styrolen unter Verwendung von Cp*Rh III als Katalysator (Schema 1A (ii)). [8,9] Aufgrund unserer Erfahrung mit Cp*Rh III -katalysierten allylischen C-H-Funktionalisierungen haben wir angenommen, dass ein Rh III -Allyl-Intermediat ambiphile Eigenschaften haben kçnnte. [7] Chang et al führten Dioxazolone als stabile Nitrenvorläufer fürdie redoxneutrale ortho-dirigierte C-H-Amidierung von Arenen ein, wobei Curtius-artige Umlagerungen vermieden werden konnten, die in der Metallnitren-Chemie als problematisch gelten.…”

“…[7] Chang et al führten Dioxazolone als stabile Nitrenvorläufer fürdie redoxneutrale ortho-dirigierte C-H-Amidierung von Arenen ein, wobei Curtius-artige Umlagerungen vermieden werden konnten, die in der Metallnitren-Chemie als problematisch gelten. [8,9] Aufgrund unserer Erfahrung mit Cp*Rh III -katalysierten allylischen C-H-Funktionalisierungen haben wir angenommen, dass ein Rh III -Allyl-Intermediat ambiphile Eigenschaften haben kçnnte. [10] Während in mehreren Berichten die elektrophile Natur von Cp*Rh III -Allyl-Intermediaten beschrieben wird, die durch nukleophile Kupplungsreagenzien abgefangen werden kçnnen, wurde die Reaktion der Rh-Allyl-Einheit mit einem Elektrophil noch nicht beschrieben.…”