Domination of Local Environment Over Pore Confinement Effects on the Catalytic Performances of Single‐Site Cp*Ir^III‐NHC Heterogeneous vs. Homogeneous H/D Exchange Catalysts

Abstract

Three different tailored mesostructured hybrid organic-inorganic materials containing single site Ir-NHC moieties (NHC = N-heterocyclic carbene) were synthesized by a very convenient and attractive methodology: (i) the synthesis of mesostructured materials with different pore-sizes and containing two types of imidazolium units regularly distributed along their channel pores was achieved using a sol-gel process via a templating route; (ii) the in situ transformation of the imidazolium moieties to Ag-NHC units was quantitatively performed; (iii) the transmetallation of Ag-NHC groups with [Cp*IrCl 2 ] 2 was carried out successfully. Each step was controlled fully and evaluated by several analytical techniques (XRD, N 2 adsorption, elemental analysis, and solid state

Mononuclear–Dinuclear Equilibrium of Grafted Copper Complexes Confined in the Nanochannels of MCM‐41 Silica

“…Moreover, the pore size of the silica matrix is another important factor in controlling the copper coordination environment in the confined nanospace, the so-called confinement effect. [77][78][79] When the pore size is expanded, a completely different copper coordination geometry is adopted. As discussed above, when the pore size was about 3.7 nm, EPR revealed two easily distinguished copper tensors: tensor A (g k = 2.195 and A k = 244 cm À1 ) and tensor B (g k = 2.283 and A k = 181 cm À1 ), corresponding to CuN 4 and CuN 2 coordination environments, respectively ( Figure 1 and Table 1).…”

“…[77][78][79] When the pore size is expanded, a completely different copper coordination geometry is adopted. As discussed above, when the pore size was about 3.7 nm, EPR revealed two easily distinguished copper tensors: tensor A (g k = 2.195 and A k = 244 cm…”

Metal–Metal Synergy in Well-Defined Surface Tantalum–Iridium Heterobimetallic Catalysts for H/D Exchange Reactions

“…Tailored hybrid silica matrices containing regularly distributed N-heterocyclic carbenes have been developed in our group and used to access single-site heterogeneous catalysts based on Ru-or Ir-NHC units. [33][34][35][36] Recently, the groups of Delferro and Conley also reported the use of acidic sulfated metal oxides to support iridium sites active in alkanes transformations 37,38 and well-defined Ni and Pd catalysts for olefin polymerization. 39,40 Thus, the type of supports conventionally used for iridium and ruthenium on one hand and tantalum on the other hand are different, and as a result these metals cannot be easily combined using two independent monometallic precursors on a single support.…”

Imidazolium-derived organosilicas for catalytic applications

“…Instead of starting from organotrialkoxysilanes containing an imidazolium or NHC-[ML n ] moiety, some materials have been synthesized from functionalizable organosilicas. Most often, materials containing pending chlorobenzyl fragments were functionalized with mesityl [62][63][64] or methyl imidazole 65,66 to form the corresponding imidazolium salt on the surface of the silica material (Scheme 8). Alternatively, core-shell magnetitesilica nanoparticles were grafted with propylimidazole and subsequently alkylated with 2-picolyl chloride.…”

“…Later on, they reported a more complete study broadening the scope of the reaction of C-H activation to other substrates such as 9-acetylanthracene, benzophenone and diethyl ether. 62 They conclude that the substituents on the NHC ligand have an important influence on the reaction rate in the case of large substrates (M4b better than M4a) and that for heterogeneous systems the nature of the first and second coordination spheres around the metal seems to play a key role (size of the NHC ligand, proximity of the active center to the surface due to the length of the tether and the size of the passivating SiMe 3 groups). In contrast, in the mesoporous range investigated, with pores large enough for easy diffusion of substrates, the rate did not seem to be correlated with the pore size of the material.…”