N–N Bond Formation by a Small-Ring Phosphine Catalyst via the P^III/P^V Cycle: Mechanistic Study and Guidelines to Obtain a Good Catalyst

Abstract

The mechanism of the N–N cross-coupling of nitroarene and aniline catalyzed by 1,2,2,3,4,4-hexamethylphosphetane oxide (1PO) as well as the prediction of a better catalyst was theoretically investigated using DFT and DLPNO-CCSD­(T) calculations. An active species 1P is generated through deoxygenation of 1PO by diphenylsilane. Then, 1P extracts one oxygen atom from nitroarene to produce nitrosoarene. In this deoxygenation step, the [3 + 1] cheletropic addition is a rate-determining step with the ΔG 0≠ and ΔG 0 values of 28.8 and −7.3 kcal/mol, respectively. Next, nitrosoarene exclusively undergoes a dehydrative condensation reaction with aniline to form an azo-cation intermediate, which is the origin of the high selectivity in this cross-coupling reaction. In this step, 2,4,6-trimethylbenzoic acid plays an essential role to significantly reduce the ΔG 0≠ value from 41.1 to 14.8 kcal/mol. Subsequently, 1P reacts with the azo cation to form a stable hydrazinylphosphonium species through the nucleophilic attack of the phosphorus atom to the cationic nitrogen atom. The phosphonium center preferably accepts a hydroxyl group from water to ensure the formation of hydrazine in the subsequent step. In the [3 + 1] cheletropic addition step, the highest occupied molecular orbital (HOMO) of 1P plays an important role. The small-ring scaffold of 1P raises the HOMO energy compared to acyclic phosphorus compounds to achieve high activity of 1P. Substitution of a dimethylamino group for the methyl group in 1P was theoretically predicted to improve the activity by further increasing the HOMO energy.

Hydroboration Reduction of CO2 Catalyzed by a Doubly Reduced Arylborane: DFT Insight into Double Active-Site and CO2 Self-Promoting Single Active-Site Mechanisms and Counterion Effects

“…The average entropy error ( S err ) of the bimolecular adduction process for the present boron-based systems ( S err = 23.9 cal/mol/K) is similar to that of the transition-metal systems studied by Sakaki et al ( S err = 23.0 cal/mol/K) . The SMD and PCM solvent models have no significant impact on the Whitesides’ method (see Tables S2 and S4), and this method has been extensively applied to other reaction systems. − On the other hand, Martin’s method involves using high pressure ((PCM, P = 1354 atm) M06/TZVP//BP86/SVP) to simulate the condensed-phase situation, and the entropy error varies from 17.7 to 32.7 cal/mol/K, as shown in Table S5, distinguishing it from the Whitesides’ method. The average value of S err evaluated by using Martin’s method is 25.7 cal/mol/K, slightly larger than the Whitesides’ correction in reducing the overestimated entropy.…”

Acetone Serving as a Solvent and Interaction Partner Promotes the Direct Olefination of N-Tosylhydrazones under Visible Light

“…To give a better understanding of the reaction mechanism, we performed DFT calculations at the M06-2 X /6–311++g­(d,p)-SMD­(acetone)//M06-2X/def2-SVP level of theory. All the calculations were carried with Gaussion 16 program and the entropy effect was corrected with the method developed by Whitesides et al like in the previous studies. − As shown in 3 TS1 , three C–H···O interactions (b1 = 2.745 Å, b2 = 2.651 Å, b3 = 2.254 Å), three C–H···N interactions (b4 = 2.462 Å, b6 = 2.730 Å, b9 = 2.782 Å), one C–H··· π interaction (b8 = 2.412 Å) and one π–π interaction (b5 = 3.575 Å) are observed, which could be visualized from the noncovalent interaction (NCI) plots (see details in Figure S7). Following the nitrogen release via 3 TS2 , carbene intermediate 3 INT5 in the triplet state is produced with a reaction barrier of 11.9 kcal mol –1 .…”

Recent Advances in Catalytic Nitrogen–Nitrogen Bond Formation Reactions

“…Moreover, the synthesis of an investigational TPRV1 receptor antagonist 80 was demonstrated via a one-pot intermolecular N–N reductive coupling and intramolecular cyclization. This phosphine oxide-catalyzed N–N cross-coupling reaction was theoretically investigated later by Sakaki and Zeng using DFT and DLPNO-CCSD­(T) calculations …”