Electron Pair Research Articles

Luminescent Platinum(II) Complexes with Stimuli-Responsive Flexible Lewis Pair Ligands: Spectroscopic and Computational Studies.

A series of new luminescent bimetallic platinum(II) complexes with stimuli-responsive flexible Lewis pair (FlexLP) ligands are described. The FlexLP ligands consist of a dimesitylboron Lewis acid and diphenylphosphine oxide Lewis base which are in equilibrium between the unbound open form and the Lewis adduct, controlled by the hydrogen bond donating strength of the solvent. Spectroscopic techniques and density functional theory (DFT) calculations were used to interpret the photophysics of the platinum(II) complexes. All complexes exhibit tunable absorption in the region of 300-500 nm and green to orange photoluminescence, depending on the ratio of weak (THF) to strong (MeOH) hydrogen bond donating solvent employed. Spectroscopic and computational data shows that phosphine and peripheral acetylide ligands on the platinum(II) centers have limited influence on the emission energy, indicating the emission originates from the FlexLP-dominated fluorescence. Using time-resolved transient absorption spectroscopy it is shown that the complexes undergo intersystem crossing (ISC) to the triplet excited state upon photoexcitation, and the ISC efficiency is affected by the peripheral acetylide ligands. The triplet excited state lifetime can also be manipulated by the state of the FlexLP ligand, with the closed form complexes having longer lifetimes than the open form complexes.

Near-IR Emissive B-N Lewis Pair-Functionalized Anthracenes via Selective LUMO Extension in Conjugated Dimer and Polymer.

Acenes are attractive as building blocks for low gap organic materials with applications, for example, in organic light emitting diodes, solar cells, bioimaging and diagnostics. Previously, we have shown that modification of dipyridylanthracene via B-N Lewis pair fusion (BDPA) strongly redshifts the emission, while facilitating self-sensitized reactivity toward O2 to reversibly generate the corresponding endoperoxides. Herein, we report on the further expansion of the π-system of BDPA to a vinyl-substituted monomer, vinylene-bridged dimer, and a polymer with an average of 20 chromophores. The extension of π-conjugation results in largely reduced band gaps of 1.8 eV for the dimer and 1.7 eV for the polymer, the latter giving rise to NIR emission with a maximum at 731 nm and an appreciable quantum yield of 7 %. Electrochemical and computational studies reveal efficient delocalization of the lowest unoccupied molecular orbital (LUMO) along the pyridyl-anthracene-pyridyl axis, which results in effective electronic communication between BDPA units, selectively lowers the LUMO, and ultimately narrows the band gap. Time-resolved emission and transient absorption (TA) measurements offer insights into the pertinent photophysical processes. Extension of π-conjugation also slows down the self-sensitized formation of endoperoxides, while significantly accelerating the thermal release of singlet oxygen to regenerate the parent acenes.

Bimetallic Fe, Co-Modified TiO2 Derived from NH2-MIL-125(Ti) as an Efficient Photocatalyst for N2 Fixation

The conversion of nitrogen (N2) and water (H2O) into NH3 by photocatalysis under ambient conditions has been considered an environmentally friendly strategy. However, developing effective catalysts for N2 fixation is still challenging. Herein, we report a bimetallic JH Fe, Co/TiO2 derived from NH2-MIL-125(Ti) by the fast Joule heating (FJH) method for visible–light–driven catalytic N2 fixation. It was found that the photocatalytic N2 reduction efficiency of bimetallic FC@TiO2-JH was improved, enabling an NH3 yield rate of 110.14 µmol g−1 h−1 without any sacrificial agents. Furthermore, the rate was higher than those of Fe@TiO2-JH and Co@TiO2-JH, suggesting that the synergistic effect between Fe and Co broke the electronic equilibrium and increased the center of its d-band, enhancing electronic feedback to the antibonding π* orbitals of N2 while weakening the bonding energy of N≡N. Meanwhile, the rate was about 2.75 times higher than that of FC@TiO2-TF, which was calcined in a tube furnace. It is assumed that FJH might lead to the formation of lattice defects, leading to localized charge deficiency, enhanced carrier separation, and transport. Thus, doping of Fe and Co synergistically interacted with the defects produced from FJH, facilitating the photocatalytic reduction process. As detected, it had a greater ability to separate hole–electron pairs and transferred electrons to adsorbed N2 at faster rates. Our work demonstrates a prospective strategy for designing bimetallic catalysts derived from NH2-MIL-125(Ti) for N2 fixation.

From tin(II) to tin(IV): Following solid‐liquid reactions by microscopy

In order to study the formation of complexes independently from stoichiometry we developed a microscale experiment that allows us to monitor the reaction progress by light microscopy In the present study, the complex formation between SnF2 and 1,10‐phenanthroline (phen) with N,N‐dimethylformamide as solvent was investigated over a period of some weeks. By use of this setup, the formation of three different crystals has been observed, whose compositions and structures were determined by single crystal X‐ray diffraction: 3SnF2 · phen, 1, 2SnF2 · SnF4 · phen, 2, SnF4 · phen, 3. While the octahedral fluorine environment of the tin(IV) atoms of 2 and 3 is very regular, the coordinations of the tin(II) atoms in 1 and 2 is irregular. Assuming a non‐bonding 5s electron pair, classical 2c‐2e‐ and symmetrical and asymmetrical, hypervalent 3c‐4e‐bonds ‐ all based on the orthogonal p atomic orbitals of Sn – an approach to analyse and describe these coordinations in a simple comprehensive way is presented.

A Benchmark Study of DFT-Computed p-Block Element Lewis Pair Formation Enthalpies against Experimental Calorimetric Data.

The quantification of Lewis acidity is of fundamental and applied importance in chemistry. While the computed fluoride ion affinity (FIA) is the most widely accepted thermodynamic metric, only sparse experimental values exist. Accordingly, a benchmark of methods for computing Lewis pair formation enthalpies, also with a broader set of Lewis bases against experimental data, is missing. Herein, we evaluate different density functionals against a set of 112 experimentally determined Lewis acid/base binding enthalpies and gauge influences such as solvation correction in structure optimization. From that, we can recommend r2SCAN-3c for robust quantification of this omnipresent interaction.

Crystal structures, NCI-RDG, Hirshfeld surface and energy framework analysis of tetra aryl substitute bispidine and oxaquinuclidine core containing derivatives: A potential COVID-19 drug candidate

Two of the title compounds are crystallized in P21/c and monoclinic face groups. Each crystal unit cell has four molecules. There are two piperidine rings: one in the chair conformation and another one in the boat conformation. The piperidine nitrogen in the boat conformation is joined to the oxygen-containing chair conformation piperidine ring to produce the oxaquinuclidine ring (-N-CH2O-). Furthermore, because of the steric barrier between rings, all aryl groups are oriented in an equatorial position. The crystal network is maintained through several interactions, including C—H⋯O/N/Cl/π. The crystal void and interaction energy studies gave additional evidence of the strength of the crystal packing and intermolecular linkage. Crystal 3b has less cavity than crystal 3c, indicating that it is densely packed. The dispersion energy contribution dominates the stability, according to the analysis of the electrostatic, dispersion, and total energy frameworks. Reduced density gradient (RDG), electron localization function (ELF), and localized orbital locator (LOL) analysis were used to determine the molecular interaction, electron pair density, and maximally localized orbitals overlapping sites, respectively. This approach reveals that oxaquinuclidine ring steric hindrance and the electron densities throughout the molecules. Density function theory (DFT) provides more evidence for the ring's orientation and the molecules' reactivity. A molecular docking investigation of four essential COVID-19 proteins was carried out using these theoretical ideas. This investigation demonstrates that each protein's reactivity varies; certain proteins have more interaction with high electron density molecules (electron-donating substituent), while others have more interaction with low electron density molecules (electron-withdrawing substituent). The ADMET and drug-likeness investigations reveal that methoxy group substituted molecules perfectly correlate with the required pharmacological characteristics. The cytotoxicity of the five compounds was assessed using the HEK293T cell.

Experimental and computational aspects of molecular frustrated Lewis pairs for CO2 hydrogenation: en route for heterogeneous systems?

Catalysis plays a crucial role in advancing sustainability. The unique reactivity of frustrated Lewis pairs (FLPs) is driving an ever-growing interest in the transition metal-free transformation of small molecules like CO2 into valuable products. In this area, there is a recent growing incentive to heterogenize molecular FLPs into porous solids, merging the benefits of homogeneous and heterogeneous catalysis - high activity, selectivity, and recyclability. Despite the progress, challenges remain in preventing deactivation, poisoning, and simplifying catalyst-product separation. This review explores the expanding field of FLPs in catalysis, covering existing molecular FLPs for CO2 hydrogenation and recent efforts to design heterogeneous porous systems from both experimental and theoretical perspectives. Section 2 discusses experimental examples of CO2 hydrogenation by molecular FLPs, starting with stoichiometric reactions and advancing to catalytic ones. It then examines attempts to immobilize FLPs in porous matrices, including siliceous solids, metal-organic frameworks (MOFs), covalent organic frameworks, and disordered polymers, highlighting current limitations and challenges. Section 3 then reviews computational studies on the mechanistic details of CO2 hydrogenation, focusing on H2 splitting and hydride/proton transfer steps, summarizing efforts to establish structure-activity relationships. It also covers the computational aspects on grafting FLPs inside MOFs. Finally, Section 4 summarizes the main design principles established so far, while addressing the complexities of translating computational approaches into the experimental realm, particularly in heterogeneous systems. This section underscores the need to strengthen the dialogue between theoretical and experimental approaches in this field.

Unveiling the Obscure Potential of O-Carborane Based IFLPs for CO2 Sequestration.

Sequestering carbon dioxide (CO2) from the atmosphere is necessary to achieve a sustainable environment. However, the thermodynamic stability of the CO2 molecule poses a significant challenge to its capture, necessitating catalysts that can overcome this stability. The emergence of frustrated Lewis pairs (FLPs) has opened a new dimension in the development of organocatalysts for CO2 capture and utilization. To date, various FLPs have been developed for CO2 sequestration, yet the quest for robust FLPs continues. Based on the intriguing electronic effects of the carborane polyhedral, o-carboranes can be projected as a versatile bridging unit for intramolecular FLPs (IFLPs). In the present work, o-carborane based IFLPs i. e., 1-Al(CH3)2-2-P(CH3)2-1,2-C2B10H10, 1-B(CH3)2-2-P(CH3)2-1,2-C2B10H10, 1-Al(CH3)2-2-N(CH3)2-1,2-C2B10H10, 1-P(CH3)2-2-B(CH3)2-1,2-C2B10H10 abbreviated as AlP, BP, AlN and BN have been proposed for the activation of CO2 molecule. The density functional theory (DFT) based calculations and thorough orbital analysis have been carried out to extensively study the electronic structure of the o-carborane unit. The proposed IFLPs were systematically compared with their corresponding phenyl bridged analogues to assess the effect of o-carborane bridging unit on the reactivity of the acidic and basic sites. The results show that the o-carborane supported IFLPs are more reactive towards CO2 than the phenyl bridged IFLPs. Also, placing the basic site on the B atom at the 4th position of the o-carborane bridge rather than the C atom at the 2nd position results in more reactive IFLPs.

Synthesis and Photochemical Uncaging of Alkene-Protected, Polymer-Bound Vicinal Frustrated Lewis Pairs.

Polymeric materials bearing Frustrated Lewis Pair (FLP) functionality are promising candidates for use as heterogeneous catalysts and adaptive materials, but synthetic access to FLP-functional polymers remains limited due to the incompatibility of FLPs with standard polymerization chemistries. Herein, we describe a synthetic approach that "cages" highly reactive vicinal phosphine-borane FLPs as covalent alkene adducts, which are stable to Ni-mediated vinyl addition polymerization. We discovered that the caged FLP adducts can be photochemically activated to liberate vicinal FLPs, enabling spatiotemporally controlled release of FLPs from polymeric precursors.

Porous Frustrated Lewis Pairs Catalyst Constructed on Defective Zirconium-Based Metal-Organic Frameworks for Hydrogenation Reactions with H2.

A porous metal-organic framework (MOF)-based frustrated Lewis pairs (FLPs) were prepared via a ligand replacement strategy to generate organic linker defects in zirconium-based MOF (MOF-808), thereby exposing Zr sites as Lewis acid. Due to the rigid features of the MOF skeleton, the unsaturated metal cluster and the adjacent lattice oxygen (Lewis bases) are in sterically hindered positions, which formed FLP sites with efficient H2 activation ability. This porous heterogeneous FLP catalyst [MOF-808-OH (15%)] exhibits high performance styrene hydrogenation to ethylbenzene with 99% yield. The high structural stability and reusability enabled the catalyst to maintain an over 98% activity after five cycles. This work provides a defect modulation strategy to prepare MOF-based solid FLP catalysts.

Electronic Force Density Fields: Insights into Partial Bonds, Transition States, and Chemical Structure Evolution.

This paper presents the quantum-topological binding approach, in which the electrostatic and total static force density fields, Fes(r) and , together with the electron density gradient field ∇ρ(r), are simultaneously analyzed to elucidate the chemical structure of transition states and the nature of interatomic interactions for semibroken semiformed partial chemical bonds. The approach attributes the discrepancies between the force fields and Fes(r) to the nonclassical electron-electron interaction effects. The internuclear gap between the zero-flux boundaries of Fes(r) and ∇ρ(r) indicates the interatomic charge transfer phenomenon (ICT) that occurs upon the formation of a system from free atoms. Concomitantly, the mismatch of the zero-flux surfaces defined in and ∇ρ(r) can be interpreted as a phenomenon of the electron-transfer-induced quantum chemical response (QCR), which originates from the electron exchange correlation. Our study permits the assertion of parallels between partial bonds and noncovalent interactions, as both typically exhibit incomplete QCRs, indicating the partial electron sharing of the transferred density. The changes in atomic and pseudoatomic charges are employed to describe the evolution of the chemical structure upon the substitution reaction. It is observed that the acquired difference in the actual atomic electronegativity causes polarization upon the heterolytic breaking of virtually nonpolar bonds. It is further proposed that the proximity of closely related stationary states along the reaction path on a potential energy hypersurface implies their similarity in the manifestation of the ICT and sympathetic QCR. Furthermore, the involvement of an electron pair in a partial bond facilitates its delocalization through the attraction by the static forces and Fes(r) to a neighboring nucleus and through the smearing by the Pauli kinetic force FP(r).

Synergistic effect of Bi and Fe for suppressing hydrogen evolution reaction (HER) and enhancing electrochemical nitrogen reduction reaction (eNRR) performance

The electrochemical nitrogen reduction reaction (eNRR) displays significant potential for the synthesis of ammonia. However, eNRR electrocatalysts with high catalytic activity and selectivity still need to be developed. In this study, a Bi-doped La0.9Bi0.1FeO3-δ (LBiF) perovskite was fabricated as a potential cathode catalyst and incorporated into a protonic ceramic electrolysis cell (PCEC) for eNRR. Electrochemical tests demonstrated that the LBiF cathode reveals higher eNRR catalytic activity and enhanced hydrogen evolution reaction (HER) inhibition compared to undoped LaFeO3 (LF). Characterization of the LBiF cathode following 90 h of NH3 synthesis revealed surface reconstruction of the catalyst during eNRR. Particularly, Bi3+ is partially reduced to Bi2+ and metallic Bi, resulting in A-site defects and an increased concentration of oxygen vacancies (OVs) and Fe4+ in accordance with the charge neutrality principle. Both the OVs and Fe4+ can accept electron pairs provided by N2 due to their unsaturated electronic structures. Furthermore, Bi doping inhibits the HER because Bi preferentially binds to N instead of H. Bi doping creates new Bi3+/Bi2+/Bi0 redox electron pairs, establishing an electron transfer path that improves perovskite conductivity and eNRR electrocatalytic activity. This study sets a foundation for designing eNRR catalysts aimed at suppressing the HER.

Green Preparation of S, N Co-Doped Low-Dimensional C Nanoribbon/C Dot Composites and Their Optoelectronic Response Properties in the Visible and NIR Regions.

The green production of nanocomposites holds great potential for the development of new materials. Graphene is an important class of carbon-based materials. Despite its high carrier mobility, it has low light absorption and is a zero-bandgap material. In order to tune the bandgap and improve the light absorption, S, N co-doped low-dimensional C/C nanocomposites with polymer and graphene oxide nanoribbons (the graphene oxide nanoribbons were prepared by open zipping of carbon nanotubes in a previous study) were synthesized by one-pot carbonization through dimensional-interface and phase-interface tailoring of nanocomposites in this paper. The resulting C/C nanocomposites were coated on untreated A4 printing paper and the optoelectronic properties were investigated. The results showed that the S, N co-doped C/C nanoribbon/carbon dot hybrid exhibited enhanced photocurrent signals of the typical 650, 808, 980, and 1064 nm light sources and rapid interfacial charge transfer compared to the N-doped counterpart. These results can be attributed to the introduction of lone electron pairs of S, N elements, resulting in more transition energy and the defect passivation of carbon materials. In addition, the nanocomposite also exhibited some electrical switching response to the applied strain. The photophysical and doping mechanisms are discussed. This study provides a facile and green chemical approach to prepare hybrid materials with external stimuli response and multifunctionality. It provides some valuable information for the design of C/C functional nanocomposites through dimensional-interface and phase-interface tailoring and the interdisciplinary applications.

Aerobic Fe transformation induced decrease in the adsorption and enhancement in the reduction of Cr(VI) by humic acid-ferric iron coprecipitates

Humic substance (HS)-ferric iron (Fe(III)) coprecipitates are widespread organo-mineral associations in soils and aquifers and have the capacity to immobilize and detoxify Cr(VI). These coprecipitates undergo transformation owing to their thermodynamic instability; however, the effects of this transformation on their environmental behaviors remain unclear, particularly in aerobic environments. In this study, the aerobic transformation of humic acid (HA)-Fe(III) coprecipitates, a representative of HS-Fe(III) coprecipitates, was simulated. The environmental effect was then evaluated after conducting an adsorption–reduction batch experiment toward Cr(VI). The aerobic transformation characteristics, as well as the adsorption/reduction capacity of HA-Fe(III) coprecipitates, were found to depend strongly on their structures. In ferrihydrite (Fh)-like coprecipitates, amorphous Fh is readily transformed into crystalline hematite and goethite at aerobic environments, leading to a much lower specific surface area and adsorption capacity. However, this increasing degree of crystallization enhanced the inductive reduction ability towards Cr(VI) owing to the more significant shift of electron pairs in the FeOC bond toward the HA direction. In HS-like coprecipitates, Fe(III) always serves as a cation bridge connecting HA molecules, but can be reduced to Fe(II) by the associated HA after aerobic transformation. The produced Fe(II), therefore, drove the reduction of the adsorbed Cr(VI). These findings emphasize the pivotal role of aerobic transformation in enhancing the reduction capacity for Cr(VI), which opens a new avenue for the development of in-situ remediation agents for Cr(VI)-contaminated sites.

Dynamic Gas-Bridged Bond: An Opportunity of Fabricating Dynamic Assembled Materials with Gas.

Gas molecules, as a family of unique polyatomic building blocks, have long been considered hard to involve in molecular assembly or construct assembled materials due to their structural simplicity yet paucity of defined interacting sites. To solve this non-trivial challenge, a core idea is to break the limit of current ways of bonding gas molecules, endowing them with new modes of interactions that match the basic requirements of molecular assembly. In recent years, a new concept, named the dynamic gas-bridged bond (DGB), has emerged, which allows for gas molecules to constitute a dynamic bridging structure between other building blocks with the aid of frustrated Lewis pairs. This makes it possible to harness gas in a supramolecular or dynamic manner. Herein, this perspective discusses distinct dynamic natures of DGBs and manifests their particular functions in various fields, including the control of molecular/polymeric self-assembly nanostructures, creation of multidimensional assembled materials, and recyclable catalysts. The future research direction and challenges of dynamic gas-bridged chemistry toward gas-programmed self-assembly and gas-constructed adaptive materials are highlighted.

Synergizing Steric Hindrance and Stacking Interactions To Facilitate the Controlled Assembly of Multiple 41 Metalla‐Knots and Pseudo‐Solomon Links

AbstractIn this work, a noncoplanar terphenyl served as a building block to synthesize a novel 3,3′‐substituted bipyridyl ligand (L1) which further reacted with binuclear half‐sandwich units A/B, giving rise to two aesthetic 41 metalla‐knots in high yields via a coordination‐driven self‐assembly strategy. Furthermore, given the inherent compactness of the 41 metalla‐knots, it creates favorable conditions for the emergence of steric repulsion. We focused on progressively introducing nitrogen atoms featuring a lone pair of electrons (LPEs) into ligand L1 to manipulate the balance of H⋅⋅⋅H/LPEs⋅⋅⋅LPEs steric repulsion during the assembly process, ultimately achieving controlled assembly from 41 metalla‐knots to the pseudo‐Solomon link and then to molecular tweezer‐like assembly facilitated by stacking interactions. All the assemblies were well characterized by solution‐state NMR techniques, ESI‐TOF/MS, and single‐crystal X‐ray diffraction. The evolutionary process of the topological architectures is equivalent to visualizing the synergistic effect of steric hindrance and stacking interactions on structural assembly, providing a new avenue for achieving the controlled synthesis of different topologies.

Synergizing Steric Hindrance and Stacking Interactions To Facilitate the Controlled Assembly of Multiple 41 Metalla-Knots and Pseudo-Solomon Links.

In this work, a noncoplanar terphenyl served as a building block to synthesize a novel 3,3'-substituted bipyridyl ligand (L1) which further reacted with binuclear half-sandwich units A/B, giving rise to two aesthetic 41 metalla-knots in high yields via a coordination-driven self-assembly strategy. Furthermore, given the inherent compactness of the 41 metalla-knots, it creates favorable conditions for the emergence of steric repulsion. We focused on progressively introducing nitrogen atoms featuring a lone pair of electrons (LPEs) into ligand L1 to manipulate the balance of H⋅⋅⋅H/LPEs⋅⋅⋅LPEs steric repulsion during the assembly process, ultimately achieving controlled assembly from 41 metalla-knots to the pseudo-Solomon link and then to molecular tweezer-like assembly facilitated by stacking interactions. All the assemblies were well characterized by solution-state NMR techniques, ESI-TOF/MS, and single-crystal X-ray diffraction. The evolutionary process of the topological architectures is equivalent to visualizing the synergistic effect of steric hindrance and stacking interactions on structural assembly, providing a new avenue for achieving the controlled synthesis of different topologies.

Hydride Shuttle Catalysis: From Conventional to Inverse Mode.

Hydride shuttle catalysis has emerged as a powerful synthetic platform, enabling the selective formation of C-C bonds to yield sp3-rich structures. By virtue of the compelling reactivity of sterically encumbered Lewis acids from the frustrated Lewis pair regime, hydride shuttle catalysis enables the regioselective functionalization of alkyl amines at either the α- or β-position. In contrast to classical Lewis acid reactivity, the increased steric hindrance prevents interaction with the Lewis basic amine itself, instead leading to reversible abstraction of a hydride from the amine α-carbon. The created positive charge facilitates the occurrence of transformations before hydride rebound or a similar capture event happen. In this Perspective, we outline a broad selection of transformations featuring hydride shuttle catalysis, as well as the recently developed approach of inverse hydride shuttle catalysis. Both strategies give rise to a wide array of functionalized amines and offer elegant approaches to otherwise elusive bond formations.

Structural Distortion of g-C3N4 Induced by a Schiff Base Reaction for Efficient Photocatalytic H2 Evolution.

Photocatalytic H2 evolution by water splitting is a promising approach to address the challenges of environmental pollution and energy scarcity. Graphitic carbon nitride (g-C3N4) has emerged as a star photocatalyst because of its numerous advantages. To address the limitations of traditional g-C3N4, namely its inadequate visible light response and rapid recombination of photogenerated carriers, we employed a schiff base reaction to synthesize -C=N- doped g-C3N4. The introduction of -C=N- groups at the bridging nitrogen sites induced structural distortion in g-C3N4, facilitating n-π* electronic transitions from the lone pair electrons of nitrogen atom and extending light absorption up to 600 nm. Moreover, the presence of heterogeneous π-conjugated electron distribution effectively traps photogenerated electrons and enhances charge carrier separation. Benefiting from its expanded spectral response range, unique electronic properties, increased specific surface area, the doped g-C3N4 exhibited outstanding photocatalytic H2 evolution performance of 1050.13 μmol/g/h. The value was 5.9 times greater than the pristine g-C3N4.

Enhancing the electron pair approximation with measurements on trapped-ion quantum computers

The electron pair approximation offers an efficient variational quantum eigensolver (VQE) approach for chemistry simulations on quantum computers. With the number of entangling gates scaling quadratically with system size and a constant measurement overhead, the orbital optimized unitary pair coupled cluster double (oo-upCCD) ansatz strikes a balance between accuracy and efficiency. However, the electron pair approximation prevents the method from achieving quantitative accuracy. To improve it, we explore the theory of second order perturbation (PT2) correction to oo-upCCD. PT2 accounts for the missing broken-pair contributions in oo-upCCD, while retaining its efficiencies. For molecular bond stretching and chemical reactions, the method significantly improves the predicted energy accuracy, reducing oo-upCCD’s error by up to 90%. On IonQ’s quantum computers, we find that the PT2 energy correction is highly noise-resilient. The predicted VQE-PT2 reaction energies are in excellent agreement with noise-free simulators after applying simple error mitigations solely on the VQE energies.