Lowering the Barrier to C–H Activation at Ir^III through Pincer Ligand Design

Abstract

Selective C–H activation of benzene and n-octane under mild conditions by a pincer IrIII carboxylate complex, (CCCMesityl)­Ir­(OAc)2(OH2) (1a), is described. A kinetic study of benzene activation was undertaken, and the resulting Eyring analysis informed the design of a tButylCCCMethyl-ligated IrIII carboxylate, which exhibited a ΔG ⧧ value for the reaction lower than that observed for 1a. Elimination of the aquo ligand was found to further lower the ΔG ⧧ value of benzene activation, enabling C–H activation by IrIII at temperatures as low as 30 °C.

3D vs. turbostratic: controlling metal–organic framework dimensionality via N-heterocyclic carbene chemistry

“…Such a reaction would lead to the formation of cyclometalated Ir(III) complexes, as indicated in the literature for the solution chemistry performed under similar conditions, namely THF at reux temperature. [40][41][42][43][44] In such complexes, Ir is coordinated not only to the C 2 position of the NHC, but also the C1 found on the neighboring aromatic ring, effectively forming a chelate complex that is generally attached to two or three NHC ligands due to its octahedral coordination and the chelation effect (Table S3, † entries 3 and 4). The tris-cyclometalated-Ir(III) complex (Table S3, † entry 3), does not well describe the data, as it has only two types of C atoms at distances of 2.03 Å and 2.08 Å; however, a biscyclometalated iridium(III) complex (Table S3, † entry 4) produced the best t that easily converged (Fig.…”

Metal–Ligand–Anion Cooperation in C–H Bond Formation at Platinum(II)

“…Through studies of model transition metal systems, several distinct mechanisms have been established for this bond cleavage step that generates a metal–alkyl. Mechanisms that require a change in oxidation state, e.g., oxidative addition (OA, Chart a), are often contrasted with those that maintain the metal oxidation state, e.g., concerted metalation deprotonation (CMD, Chart b). ,− Metal–ligand cooperative (MLC, Chart c) mechanisms have been recently invoked. − The heterolytic H 2 activation step in Noyori’s hydrogenation reactions is a classic example of MLC bond activation . In C–H activation via MLC, a basic site on the ligand formally accepts the proton, with the anionic carbon fragment binding to the Lewis acidic metal.…”