Pd-Mediated Activation of Molecular Oxygen in a Nonpolar Medium

Abstract

The mechanism for direct insertion of O2 in a toluene-solvated palladium−hydride bond (avoiding palladium zero) has been elucidated using quantum mechanics (B3LYP/LACVP** with the PBF polarizable continuum solvent model) for PdII((−)-sparteine)(Cl)(H) and the model compound PdII(bipyridine)(Cl)(H). We find that the process involves (1) the abstraction of the hydrogen atom by triplet oxygen, (2) the formation of a stable L2XPdIOOH triplet species, (3) a spin transition resulting in a stable L2XPdIIOOH singlet species, and (4) the loss of H2O2 and completion of the catalytic cycle upon the addition of HX. The limitations involved in the spin transition, the formation of the triplet PdI−OOH species and the stability of that triplet species are all dependent on the presence of an H-bond acceptor cis to the hydride and the electronic characteristics of the other ligands which may or may not stabilize the PdI species. Without this cis H-bond acceptor and/or electron-withdrawing ligands that can stabilize PdI, the reaction will not proceed via the palladium hydride insertion mechanism in a nonpolar environment.

ReaxFF Reactive Force Field for Molecular Dynamics Simulations of Hydrocarbon Oxidation

“…[38][39][40][41][42][43][44] This functional also provides a good description of the PES of transition metal-containing molecules. [45][46][47][48][49][50][51][52][53][54][55] It is important to have a consistent QM method for building a training set, so we have chosen to use the B3LYP functional to build and expand the force field to describe systems such as hydrocarbons, metals, and metal oxides.…”

Oxygen Reduction Mechanism of Monometallic Rhodium Hydride Complexes

“…In the case of 2c/d, the ORR yields a small amount (ca. 10%) of a third product with 31 P{ 1 H} and 1 H NMR spectral features consistent with a complex of the form fac-Rh III Cl 3 (CNAd)(P(4-X-C 6 H 4 ) 3 ) 2 (6c/ d). The spectral features of 6c/d are also observed upon the addition of PhICl 2 to 1c/d in the synthesis of 3c/d.…”

“…The hydride species 2 was generated in situ by the addition of five molar equivalents of HCl using 4.2 M HCl in 1,4-dioxane. 31 P{ 1 H} NMR revealed that 2 formed rapidly and quantitatively. Each UV−vis sample was prepared as follows: (1) In the glovebox, 3.50 mL of THF and an appropriate amount of 4.2 M HCl in 1,4-dioxane were added to a quartz cuvette sealed with a septum cap; (2) approximately 500 μL of the stock CH 2 Cl 2 solution of 2 were added to a small vial sealed with a septum cap; (3) on the benchtop, a measured amount of O 2 was injected into the quartz cuvette using a gastight syringe, and the cuvette was vigorously shaken to ensure complete mixing and equilibration of O 2 .…”

“…1 H NMR (500 MHz, C 6 D 6 ) δ/ ppm: 0.97 (br, d, 6H), 1.13 (br, m, 6H), 1.51 (br, m, 3H), 6.79 (m, 12H), 7.79 (m, 12H). 31 Preparation of cis,trans-Rh III Cl 2 H(CNAd)(P(4-X-C 6 H 4 ) 3 ) 2 (2) (X = F (2a), Cl (2b), Me (2c), OMe (2d)). Complex 1a (100 mg, 0.107 mmol) and a magnetic stirbar were added to a 20 mL scintillation vial.…”

The Role of NHC Ligands in Oxidation Catalysis

“…A similar system was used in the cyclization reaction of suitable phenols to dihydrobenzofuranes [92]. The mechanism of the aerobic alcohol oxidation with palladium catalyst systems was also studied theoretically [93][94][95][96].…”