Electrophilic Impact of High-Oxidation State Main-Group Metal and Ligands on Alkane C–H Activation and Functionalization Reactions

Abstract

High-oxidation state main-group metal complexes are potential alternatives to transition metals for electrophilic alkane C−H functionalization reactions. However, there is little known about how selection of the p-block, main-group metal and ligand impact alkane C−H activation and functionalization thermodynamics and reactivity. This work reports density functional theory calculations used to determine qualitative and quantitative features of C−H activation and metal-methyl functionalization energy landscapes for reaction between high-oxidation state d 10 s 0 In III , Tl III , Sn IV , and Pb IV carboxylate complexes with methane. While the main-group metal influences the C−H activation barrier height in a periodic manner, the carboxylate ligand has a much larger quantitative impact on C−H activation with stabilized carboxylate anions inducing the lowest barriers. For metal-methyl reductive functionalization reactions, the main-group metal dramatically influences the barrier heights, which are correlated to reaction thermodynamics and bond heterolysis energies as a model for two-electron reduction energies. Overall, this work begins to outline which main-group metals and carboxylate ligands could be useful for alkane functionalization systems that utilize electrophilic C−H activation and metal-alkyl functionalization reactions.

Direct Partial Oxidation of Methane Catalyzed by an In Situ Generated Active Au(III) Complex at Low Temperature in Ionic Liquids

“…The transition state (TS D ‡ ) bearing a C−H activated CH 4 was obtained by the QST3 method and found to have a sixmembered ring consisting of an activated CH 4 , the Au III center, and two oxygen atoms in the CF 3 SO 3 − ligand. This transition state has a free energy barrier of 26.7 kcal/mol from structure B. Six-membered metal cycle with activated Csp3-H structures have also been reported on metal atoms such as Pt, 79 Ir, 18 and Ti 21,80 H-bonding effect is considered to be minor without affecting the relative energies of the species in the reaction profiles. In addition to the five-coordinated structure, as described in Figure 3, monovalent cation structures in the C−H activation process were all calculated by DFT calculation.…”

“…5−14 A large number of works on selective CH 4 oxidation have been focused on metal complexes, including precious metals such as Pt II , 15 Pd II , 16 Au III/I , 17 and Ir III18 and main-group metals such as Hg II , 19 Sb V , 20 In III , Sn IV , Ti II , and Pb IV in strongly acidic media. 21 A landmark work by Periana et al 14 showed the conversion of CH 4 to methyl bisulfate, (CH 3 )HSO 4 , as a primary product that was subsequently worked up by hydrolysis to produce CH 3 OH.…”

“…The partial oxidation of CH 4 in homogeneous systems has attracted considerable interest since Shilov et al reported the direct conversion of CH 4 to CH 3 OH using Pt II as the C–H activation catalyst and Pt IV as the oxidant at 120 °C . Mechanistic studies and numerous efforts have been made to improve the efficiency of this “Shilov Chemistry”. − A large number of works on selective CH 4 oxidation have been focused on metal complexes, including precious metals such as Pt II , Pd II , Au III/I , and Ir III and main-group metals such as Hg II , Sb V , In III , Sn IV , Ti II , and Pb IV in strongly acidic media . A landmark work by Periana et al showed the conversion of CH 4 to methyl bisulfate, (CH 3 )­HSO 4 , as a primary product that was subsequently worked up by hydrolysis to produce CH 3 OH.…”

Supramolecular Organization and Evaporation of Polymeric Tin Trifluoroacetates

“…Our results reflected that of a recent publication on the mechanism of methane activation by main group trifluoroacetates, and readers are directed there for a more in-depth discussion of the electronic structure of 2 with respect to its reactivity. 49 During our early attempts to structurally characterize 1 F and 2 F , we obtained crystals of other compounds that hinted at the rich structural diversity available to tin trifluoroacetates. The cagelike cluster hexakis[tin(II) bis(trifluoroacetate) trimethylphosphine]…”

Supramolecular Organization and Evaporation of Polymeric Tin Trifluoroacetates

“…Our results reflected that of a recent publication on the mechanism of methane activation by main group trifluoroacetates, and readers are directed there for a more in-depth discussion of the electronic structure of 2 with respect to its reactivity. 49 During our early attempts to structurally characterize 1 F and 2 F , we obtained crystals of other compounds that hinted at the rich structural diversity available to tin trifluoroacetates. The cagelike cluster hexakis[tin(II) bis(trifluoroacetate) trimethylphosphine] [(1 ←PMe ) ] was obtained by slow cooling of a toluene solution of 1 F and a slight excess of PMe 3 .…”