Computational Design of a Pincer Phosphinito Vanadium ((OPO)V) Propane Monoxygenation Homogeneous Catalyst Based on the Reduction-Coupled Oxo Activation (ROA) Mechanism

Abstract

ABSTRACT:We propose the vanadium bis(2-phenoxyl)phosphinite pincer complex, denoted (OPO)V, as a low temperature water-soluble catalyst for monoxygenation of propane to isopropanol with functionalization and catalyst regeneration using molecular oxygen. We use DFT study to predict that the barrier for (OPO)V to activate the secondary hydrogen of propane is ∆G ‡ = 25.2 kcal/mol at 298K, leading to isopropanol via the new reduction-coupled oxo activation (ROA) mechanism. We then show that reoxidation by dioxygen to complete the cycle is also favorable with ∆G ‡ = 6.2 kcal/mol at 298K. We conclude that (OPO)V represents a promising homogeneous catalyst for the monoxygenation of propane and other alkanes (including ethane), warranting experimental validation.

How High Valence Transition Metal Spreads Its Activity over Nonmetal Oxoes: A Proof-of-Concept Study

“…Previously, Cheng et al proposed that the separation of basic site and the redox site would give some freedom to tune the activity. 27,28 In our case, the V 5+ and PO 31 We expect that the deposition of a small amount vanadium oxide on P 2 O 5 would create an ideal model to test our theoretical proposal.…”

“…Previously, Cheng et al. proposed that the separation of basic site and the redox site would give some freedom to tune the activity. , In our case, the V 5+ and PO are separated by four atoms (−O–P–O–P−), thus providing more room for the rational design.…”

“…Previously, it has been reported that H abstraction by X = O can be viewed as a proton-coupled electron-transfer (PCET) process, in which the transition-metal center serves as the electron acceptor; whereas oxygen serves as the proton acceptor. 25,26 H abstraction by nearby PO has also been named after reduction-coupled oxo activation (ROA) by Goddard et al 9,27,28 Since only one V 5+ is involved in our models, the difference in the activities would be attributed to the basicity of O atoms. Bader charge analysis shows that O atoms on the PO groups carry significant high negative charges of −1.37∼−1.41 a.u., more negative than that on VO (−0.51 a.u.…”

Biomimetic heterobimetallic architecture of Ni(ii) and Fe(ii) for CO2 hydrogenation in aqueous media. A DFT study

“…Second, correction equal to 2.38 kcal mol À1 for 55.4 to 1 molar standard state conversion and À6.32 kcal mol À1 correction for self-solvation were added for water molecules as well. 68 All the above said calculations have been performed using Gaussian 09 soware suite. 65 3 Results and discussions…”

Recent computational studies on transition‐metal carbon–hydrogen bond activation of alkanes

“…By utilizing such species toward n ‐butane, DFT calculations indicate that changing transition metals from first‐ to second‐ to third‐transition row weakens the CH activation power, and overall, vanadium and nickel perform the best for both ligands because the lighter transition metals with high oxidation states are stronger electron acceptors as the higher oxidation states are more stable for heavier metals. A recent study following this protocol predicted facile propane activation by utilizing a vanadium bis(2‐phenoxyl)‐phosphinite pincer complex ((OPO)V) to produce isopropanol . According to the DFT calculations, the overall barrier for (OPO)V V D s (H 2 O) a (resting state in aqueous solution) to activate propane's secondary CH bond is 25.2 kcal/mol at room temperature, and the catalytic circle can be completed by dioxygen reoxidation, making it a capable homogeneous catalyst for the selective oxidation of propane and other alkanes.…”