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Article

Mechanistic Studies of Oxygen-Atom Transfer (OAT) in the Homogeneous Conversion of N2O by Ru Pincer Complexes

by
Guangchao Liang
1,*,
Min Zhang
2 and
Charles Edwin Webster
3,*
1
Academy of Advanced Interdisciplinary Research, Xidian University, Xi’an 710071, China
2
Department of Pharmacy, Medical School, Xi’an International University, Xi’an 710077, China
3
Department of Chemistry, Mississippi State University, Starkville, Mississippi State, MS 39762, USA
*
Authors to whom correspondence should be addressed.
Inorganics 2022, 10(6), 69; https://doi.org/10.3390/inorganics10060069
Submission received: 24 April 2022 / Revised: 12 May 2022 / Accepted: 23 May 2022 / Published: 25 May 2022
(This article belongs to the Special Issue Computational Catalysis: Methods and Applications)
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Abstract

:
As the overall turnover-limiting step (TOLS) in the homogeneous conversion of N2O, the oxygen-atom transfer (OAT) from an N2O to an Ru-H complex to generate an N2 and Ru-OH complex has been comprehensively investigated by density functional theory (DFT) computations. Theoretical results show that the proton transfer from Ru-H to the terminal N of endo N2O is most favorable pathway, and the generation of N2 via OAT is accomplished by a three-step mechanism [N2O-insertion into the Ru-H bond (TS-1-2, 24.1 kcal mol−1), change of geometry of the formed (Z)-O-bound oxyldiazene intermediate (TS-2-3, 5.5 kcal mol−1), and generation of N2 from the proton transfer (TS-3-4, 26.6 kcal mol−1)]. The Gibbs free energy of activation (ΔG‡) of 29.0 kcal mol−1 for the overall turnover-limiting step (TOLS) is determined. With the participation of potentially existing traces of water in the THF solvent serving as a proton shuttle, the Gibbs free energy of activation in the generation of N2 (TS-3-4-OH2) decreases to 15.1 kcal mol−1 from 26.6 kcal mol−1 (TS-3-4). To explore the structure–activity relationship in the conversion of N2O to N2, the catalytic activities of a series of Ru-H complexes (C1–C10) are investigated. The excellent linear relationships (R2 > 0.91) between the computed hydricities (ΔGH−) and ΔG‡ of TS-3-4, between the computed hydricities (ΔGH−) and the ΔG‡ of TOLS, were obtained. The utilization of hydricity as a potential parameter to predict the activity is consistent with other reports, and the current results suggest a more electron-donating ligand could lead to a more active Ru-H catalyst.

Graphical Abstract

1. Introduction

As a dominant ozone-depleting emission [1,2,3] and a greenhouse gas with about 300 times the global warming potential than that of CO2 (based on the 100-year timescale) [4,5,6], nitrous oxide (N2O) has been brought to the frontier of climate and environmental protection [7,8,9]. Efforts that aim to terminate environmentally detrimental N2O have been examined in the last few decades [10,11]. Beyond the commonly studied decomposition of N2O catalyzed by metal oxides (MOs) [12,13,14,15], a variety of possible conversions of N2O have also been investigated, including O-atom insertion into metal-H and metal-C bonds [16,17,18,19,20,21], cleavage of N-O and N-N bonds [22,23,24,25], and reactions with organic substrates [11,26,27,28]. Among the reactions, the exothermic/exergonic conversion of N2O mediated by CO generating N2 and less harmful CO2 (N2O + CO → N2 + CO2, Δ G r x n ° = −86.3 kcal mol−1) [29,30] is considered as a practicable and cost-effective method to simultaneously address the environmental dilemma created by the emission of N2O and CO [30,31,32,33].
Milstein and co-workers showed that a dicarbonyl PNN-Ru-H pincer complex (I, Scheme 1, PNN = 6-((di-tert-butylphosphino)methylene)-6H-[2,2′-bipyridin]-1-ide) could serve as an efficient catalyst in the homogeneous conversion of N2O and CO [31]. The dicarbonyl PNN-Ru-H complex (I, Scheme 1) catalyzed the conversion of N2O and CO to generate N2 and CO2 with a turnover number (TON) of up to 579 referenced to N2 and 561 referenced to CO2 after heating for 22 h at 70 °C.
The overall mechanism of the conversion of N2O and CO by the Ru-H species includes: (1) the generation of N2 and a dicarbonyl Ru-OH complex (II, Scheme 1) via oxygen-atom transfer (OAT), (2) the formation of a dicarbonyl Ru-COOH complex (III, Scheme 1) via the intramolecular nucleophilic attack of OH on the nearby CO group, (3) the release of CO2 and the formation of a monocarbonyl Ru-H complex (IV, Scheme 1) via decarboxylation, and (4) the regeneration of the dicarbonyl PNN-Ru-H active species (I, Scheme 1) via the nucleophilic attack of a free CO. The generation of N2 via oxygen-atom transfer was proposed as the turnover-limiting step (TOLS), which was supported by the observation of a relatively fast formation of CO2 via an intramolecular reaction between the Ru-OH species and CO [31]. This experimentally established turnover-limiting step is also verified by computational studies [34,35,36].
It has come to our attention that the oxygen-atom transfer (OAT) between N2O and the Ru-H complex has not been fully investigated yet. Three categories of reactions between the N2O and Ru-H complex that need to be considered are: (1) the proton transfer from Ru-H to the terminal N of N2O (I, Chart 1), (2) the proton transfer from Ru-H to the terminal O of N2O (II, Chart 1), and (3) the hydride transfer from Ru-H to the central N of N2O (III, Chart 1). The generation of N2 via proton transfer and hydride transfer from Ru-H to N2O must be thoroughly evaluated and compared. Various transition states of proton transfer from Ru-H to N2O could be proposed, as induced by different geometries of N2O adduct (endo vs. exo isomer). The effect of the geometries of N2O (endo vs. exo isomer) in the oxygen-atom transfer (OAT) from N2O to Ru-H to generate N2 and Ru-OH must also be appropriately addressed.
In this contribution, the detailed reaction mechanism for the oxygen-atom transfer (OAT) from N2O to Ru-H in the conversion of N2O has been comprehensively investigated using density functional theory (DFT) computations. With the detailed reaction mechanism for the conversion of N2O to N2 in hand (Figure 1), the turnover-limiting step for the conversion of N2O and CO by a series of Ru-H complexes (Chart 2) with different electron-donating and electron-withdrawing groups have been investigated to explore the structure–activity relationship, and the results provided here are the continuous efforts for the homogeneous conversion of N2O by the transition metal complex.

2. Computational Methods

Full gas-phase geometry optimizations were performed using the method of B3LYP [37,38,39,40] with Grimme’s D3 [41] dispersion with Becke–Johnson damping [D(3BJ)] [42] and basis set 1 (BS1) (B3LYP-D3(BJ)/BS1) through Gaussian 16 [43]. To account for the solvent effect of tetrahydrofuran (THF), B3LYP-D3(BJ)/BS2 single-point computations using the SMD [44] solvation model with parameters consistent with tetrahydrofuran (THF) as the solvent were performed on the B3LYP-D3(BJ)/BS1 optimized geometries [SMD(THF)-B3LYP-D3(BJ)/BS2//B3LYP-D3(BJ)/BS1]. For comparison, optimizations using B3LYP-D3(BJ)/BS2 with the SMD [44] solvation model in THF were also performed [SMD(THF)-B3LYP-D3(BJ)/BS2, see SI]. In basis set 1 (BS1), the modified LANL2DZ [45,46] basis set and LANL2DZ effective core potentials (ECP) were used for Ru, the LANL2DZ(d,p) [45,47] basis set and LANL2DZ ECP were used for P, and the 6-31G(d’) [48,49,50] basis sets were used for all other atoms (C, N, O, and H). In basis set 2 (BS2), the Ahlrichs Def2-TZVP [51,52] basis sets and related ECP were used for Ru, and TZVP [53] basis sets were used for all other atoms (C, N, O, P, F, and H). The Gaussian 16 default ultrafine integration grid, 2-electron integral accuracy of 10−12, and SCF convergence criterion of 10−8 were used for all computations, and vibrational frequency computations were performed to verify the nature of all stationary points. All located transition states were obtained with only one imaginary frequency, and minima without any imaginary frequencies were obtained. The default rigid-rotor-harmonic-oscillator (RRHO) approximation was used to calculate the vibrational contribution to entropy. The intrinsic reaction coordinate (IRC) computations from the located transition states were performed, and both directions of the reaction path following the transition state were computed (see SI for the IRC plots) [54,55]. Gibbs free energies of activation (ΔG‡) and free energies of reaction (ΔG°) were determined with standard conditions of 1 atm and 298.15 K, which are relative to the Ru-H complex (in kcal mol−1). The Gibbs free energies from the SMD(THF)-B3LYP-D3(BJ)/BS2//B3LYP-D3(BJ)/BS1 computations are presented in the main text. The Gibbs free energies from the SMD(THF)-B3LYP-D3(BJ)/BS2 computations are presented in the supporting information. Gibbs free energies for the overall turnover-limiting steps (TOLS) were determined based on the energetic span/transition state theory. The accuracy and reliability of the computational method [SMD(THF)-B3LYP-D3(BJ)/BS2//B3LYP-D3(BJ)/BS1] was verified. Good agreement between the SMD(THF)-B3LYP-D3(BJ)/BS2//B3LYP-D3(BJ)/BS1 computations and the SMD(THF)-B3LYP-D3(BJ)/BS2 computations was obtained, and the mean absolute deviation (MAD) was 0.5 (Table S1) and the coefficient linear regression (R2) was 0.9967 (Figure S1) [56,57,58].

3. Results and Discussion

To fully understand the oxygen-atom transfer (OAT) from N2O to an Ru-H complex (Scheme 1), the proposed pathway for the proton transfer from Ru-H to the terminal N of endo N2O is presented in the following Section 3.1 (Figure 1), and other higher energetic pathways including: (1) the proton transfer from Ru-H to the terminal O of N2O (Scheme S2) and (2) hydride transfer from Ru-H to the central N of N2O (Figures S6 and S7) are presented in the supporting information.

3.1. Proton Transfer from Ru-H to the Terminal N of Endo N2O

The release of N2 from an oxygen-atom transfer from N2O via the pathway of the proton transfer from Ru-H to the terminal N of endo N2O involves two important (Z)-O-bound oxyldiazene intermediates (structures 2 and 3, Figure 1). Structure 2, which has an intramolecular hydrogen bond between the oxyldiazene substrate and the anionic pyridinyl unit, is generated by the insertion of N2O into the Ru-H bond of the Ru-H complex (structure 1) via TS-1-2 at 24.1 kcal mol−1 (Figure 1). It should be noted that the bent geometry of the O atom in the six-membered ring caused by the intramolecular hydrogen bond in (Z)-O-bound oxyldiazene intermediate 2 prevents the direct proton transfer from the terminal N-H to the O atom. Intermediate 2 must go through a necessary change of geometry to form its structural isomer 3 in order to accomplish the proton transfer. There is a facile geometry isomerization from intermediate (Z)-O-bound oxyldiazene intermediate 2 to 3 via TS-2-3 (5.5 kcal mol−1, Figure 1). The O-bound oxyldiazene intermediate 3 is 6.4 kcal mol−1 lower in energy than 2 (–2.4 vs. 3.8 kcal mol−1), which is partially due to the breaking of the six-membered ring formed from the intramolecular hydrogen bond. In structure 2, the orientation of the lone pair of electrons is unfavorable for the proton transfer to the oxygen from the terminal N-H. However, from structure 3, the proton transfer from the terminal N-H to the O may occur. The geometry of (Z)-O-bound oxyldiazene intermediate 3 is consistent with reported Ru/Rh intermediates [59,60,61], but is dissimilar to the recent results of Xie and co-workers [34]. From the O-bound diazene intermediate 3, the cyclic four-membered ring transition state for the proton transfer (TS-3-4, 26.6 kcal mol−1, Figure 1) forms the Ru-OH complex (structure 4, Figure 1) and molecular N2. The generation of N2 from the proton transfer (TS-3-4) is the TOLS for the conversion of N2O to N2. The Gibbs free energy of activation for the overall turnover-limiting steps (TOLS) based on the energetic span/transition state theory is determined as 29.0 kcal mol−1 (3 to TS-3-4, Figure 1) [62,63]. The generation of separated N2 and the Ru-OH complex (structure 4) from the Ru-H complex and N2O is favorable by –65.1 kcal mol−1 (Figure 1). The effect of potentially existing traces of water in the THF solvent in the homogeneous conversion of N2O was also considered. Anticipated lower Gibbs free energy of activation in the generation of N2 (15.1 kcal mol−1, TS-3-4-OH2, Figure 1) with the participation of potentially existing H2O serving as a proton shuttle compared to the non-assisted generation of N2 (26.6 kcal mol−1, TS-3-4, Figure 1) was obtained. No such assistance of solvent THF was found (34.2 kcal mol−1, TS-3-4-THF, Figure 1). The result of the H2O-assisted generation of N2 is consistent with Poater’s results on the hydrogenation of N2O by the PNP-Ru-dihydride pincer complex [35,36].
Another structural isomer that created a pathway for the N2 generation from the N2O oxygen-atom transfer involves an intermediate without an intramolecular hydrogen bond, and is presented in Figure S6. Structures 2b, 3b, and 4b in Figure S6 are the structural isomers of structures 2, 3, and 4 in Figure 1 with a different orientation of diazene substrate and the OH group. For this alternative pathway, slightly higher ΔG‡ are found (26.5 kcal mol−1 for TS-1b-2b vs. 24.1 kcal mol−1 for TS-1-2, 27.5 kcal mol−1 for TS-3b-4b vs. 26.6 kcal mol−1 for TS-3-4). The effect on the ΔG‡ for the generation of N2 from the anionic pyridinyl is relatively small. The possible proton transfer from Ru-H to the terminal O of N2O was also investigated (Scheme S2), and significantly higher ΔG‡ were obtained (40.6 kcal mol−1 for TS-1-2d and 38.6 kcal mol−1 for TS-1b-2c). Compared to the formation of the Ru-O bond in Figure 1, the relatively small electronegativity of terminal N of N2O made it difficult to form Ru-N bonds (2c and 2d in Scheme S2), which caused the higher ΔG‡. Even higher ΔG‡ were also obtained for the hydride transfer from Ru-H to the central N of N2O (42.7 kcal mol−1 for TS-1-5 and 45.2 kcal mol−1 for TS-1b-5b, Figures S6 and S7).
The above discussed mechanistic studies of the homogeneous oxygen-atom transfer (OAT) from N2O to the Ru-H complex to generate an N2 and Ru-OH complex clearly showed that the pathway of the proton transfer from Ru-H to the terminal N of endo N2O is most favorable (Figure 1). It is accomplished by three asynchronous steps including N2O insertion into the Ru-H bond (TS-1-2), change of geometry of the formed O-bound diazene intermediate (TS-2-3), and the generation of N2 from the proton transfer (TS-3-4). The last step (TS-3-4) forming the molecular N2 and Ru-OH complex is the overall turnover-limiting step (TOLS) in the proposed three-step mechanism.

3.2. Hydricity as A Parameter to Predict the Activity

The concept of hydricity has been previously utilized to interpret the structure–activity relationships in transition-metal hydride species involved homogeneous catalysis [64,65,66,67,68,69,70]. The hydrogenation of CO2 to formate catalyzed by molecular Co-H complexes presented an excellent linear relationship between the logarithm of the catalytic turnover frequency and the hydricity of Co-H complexes (R2 = 0.9956), and significantly improved activity for Co-H complexes with relatively stronger hydride-donating ability were observed [66]. The model using the relationship between hydricities and the one-electron reduction potential of the transition-metal complexes is also used to study the reactivity of transition-metal hydride complexes in the CO2 reduction [68]. The hydricity (ΔGH−) of each Ru-H complex was calculated using the equation presented in Scheme 2 [64,65].
To explore the structure–activity relationship in the conversion of N2O to N2, the catalytic pathways of a series of Ru-H complexes (C1–C7, Chart 2) were investigated. The parent PNN-Ru-H complex was modified by the introduced electron-donating (CH3) and electron-withdrawing groups (CF3) on the para positions of these two pyridinyl fragments. For comparison, the structural isomers of the Ru-H complex with the PNC ligand [PNC = 6′-((di-tert-butylphosphino)methyl)-(2,2′-bipyridin)-3-ide] were also modeled (C8–C10, Chart 2). It is noted that the Ru-H complex with the PNC ligand [PNC = 6′-((di-tert-butylphosphino)methyl)-(2,2′-bipyridin)-3-ide] was significantly less active than the PNN-Ru-H complex in the homogeneous conversion of N2O and CO [31].
The most favorable intramolecular hydrogen-bond-involved pathway (Figure 1) for the conversion of N2O to N2 catalyzed by Ru-H complexes (C1–C10, Chart 2) is studied. The ΔG‡ for TS-1-2 (formation of O-bound diazene intermediate from insertion of N2O into the Ru-H bond) and TS-3-4 (generation of N2 from proton transfer) are summarized in Table 1. Catalysts with an electron-withdrawing group (CF3) generally produce higher ΔG‡ for TS-1-2 and TS-3-4 compared to catalysts with an electron-donating group (CH3). The ΔG‡ of TS-1-2 for C1 [(PCF3NCF3N)-Ru-H], C4 [(PNN)-Ru-H], and C7 [(PCH3NCH3N)-Ru-H] are 24.9, 24.1, and 23.6 kcal mol−1, respectively (Table 1). The ΔG‡ of TS-3-4 for C1 [(PCF3NCF3N)-Ru-H], C4 [(PNN)-Ru-H], and C7 [(PCH3NCH3N)-Ru-H] are 27.3, 26.6, and 26.0 kcal mol−1, respectively (Table 1). It is noted the C8 [(PNC)-Ru-H] has a higher ΔG‡ for the turnover-limiting step (TOLS, TS-3-4) compared to C4 [(PNN)-Ru-H] (28.4 vs. 26.6 kcal mol−1), which is consistent with the experimental reports [31].
Computed Ru-H harmonic stretching frequencies (νRu-H, gas-phase B3LYP-GD3BJ/BS1 computations) and computed hydricities (SMD(THF)-B3LYP-GD3BJ/BS2//B3LYP-GD3BJ/BS1) are also summarized in Table 1. Computational results show that introducing the CF3 electron-withdrawing group strengthens the Ru-H bond (higher Ru-H stretching frequencies) compared to the CH3 electron-donating group (1950.9 cm−1 for C1 [(PCF3NCF3N)-Ru-H], 1943.3 for C4 [(PNN)-Ru-H], and 1941.9 for C7 [(PCH3NCH3N)-Ru-H]. These results are consistent with the computed hydricities, and a stronger Ru-H bond has a poorer hydride-donating ability (the more positive hydricity value). The computed hydricities are 54.7 kcal mol−1 for C1 [(PCF3NCF3N)-Ru-H], 50.9 for C4 [(PNN)-Ru-H], and 49.1 for C7 [(PCH3NCH3N)-Ru-H] (Table 1). The computed hydricities, together with the Ru-H stretching frequencies, demonstrate that the hydride-donating ability for the Ru-H complexes with the CF3 electron-withdrawing group is poorer compared to the complexes with the CH3 electron-donating group.
In order to quantitatively explore the structure–activity relationship in the conversion of N2O to N2, the relationship between the computed ΔG‡ and Ru-H stretching frequencies (Figure 2), and the relationship between the computed ΔG‡ and computed hydricities (Figure 3) were fitted. Good linear relationships between computed ΔG‡ and Ru-H stretching frequencies (R2 = 0.9658 for C1–C7, and R2 = 0.8578 for C8–C10, Figure 2) were obtained, and excellent correlations exist between ΔG‡ of TS-3-4 and the computed hydricities (R2 = 0.9158 for C1–C7, and R2 = 0.9765 for C8–C10, Figure 3). Excellent linear fittings between the ΔG‡ of TOLS and the computed hydricities (R2 = 0.9381 for C1–C7, and R2 = 0.9272 for C8–C10, Figure 4) were also obtained. The structure–activity relationship using hydricity to predict the activity is consistent with the results from studies on the molecular transition-metal hydride involved CO2 hydrogenation, CO2 reduction, and H2 evolution [66,67,68,71,72]. This result suggests that a more active Ru-H catalyst with a higher turnover frequency for the conversion of N2O to N2 would come from introducing a more electron-donating ligand.

4. Conclusions

A comprehensive theoretical investigation of the reaction between N2O to an Ru-H complex using DFT computations was performed. The proton transfer from Ru-H to the terminal N of endo N2O (Figure 1) was shown as the most favorable pathway, which includes N2O insertion into the Ru-H bond (TS-1-2, 24.1 kcal mol−1), change of geometry of the formed (Z)-O-bound oxyldiazene intermediate (TS-2-3, 5.5 kcal mol−1), and the formation of an Ru-OH complex and generation of N2 from a proton transfer step (TS-3-4, 26.6 kcal mol−1). Significantly low Gibbs free energy of activation in the generation of N2 (15.1 kcal mol−1, TS-3-4-OH2) with the participation of potentially existing traces of H2O in the THF solvent serving as a proton shuttle was observed. The excellent linear relationships between the computed hydricities (ΔGH−) and the Gibbs free energies of activation (ΔG‡) of TS-3-4, between the computed hydricities (ΔGH−) and the Gibbs free energy of activation (ΔG‡) of TOLS (R2 > 0.91), suggest that hydricity could be utilized as a potential parameter to predict the catalytic activities, and the design of more active Ru-H catalysts could benefit from ligand modification with more electron-donating groups.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics10060069/s1, Table S1. Comparisons of the Gibbs free energies; Figure S1. Linear relationship; Scheme S1. Computed APT charges of N2O; Figure S2. IRC plots; Figure S3. IRC plots; Figure S4. IRC plots; Figure S5. IRC plots; Figure S6. Free energy diagram for an alternative higher-energy pathway; Scheme S2. Free energy diagram for proton transfer; Figure S7. Free energy diagram for N2 generation from hydride transfer; Figure S8. Free energy diagram for a higher-energy hydride transfer; Figure S9. Linear fitting; Table S2. DFT computed energies; Table S3. SMD(THF)-B3LYP-GD3BJ/BS2 computed energies; Table S4. Cartesian coordinates.

Author Contributions

G.L.: conceptualization, investigation, formal analysis, methodology, writing—reviewing and editing, and funding acquisition; M.Z.: investigation and formal analysis; C.E.W.: conceptualization, formal analysis, writing—reviewing and editing, and funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the start-up funds from Xidian University (1018/10251210050), and also partially supported by the Mississippi State University Office of Research and Economic Development and the United States National Science Foundation (OIA-1539035).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

We thank the high-performance computing platform of Xidian University (XDHCPP) and the Mississippi Center for Supercomputing Research (MCSR) for computing support. We are grateful for the financial support from the Academy of Advanced Interdisciplinary Research and the start-up funds from Xidian University (1018/10251210050). This study was also partially supported by the Mississippi State University Office of Research and Economic Development and the United States National Science Foundation (OIA-1539035).

Conflicts of Interest

The authors declare no conflict of interest.

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Inorganics 10 00069 sch001 550
Scheme 1. Proposed pathway for the conversion of N2O and CO by PNN-Ru-H complex.
Scheme 1. Proposed pathway for the conversion of N2O and CO by PNN-Ru-H complex.
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Inorganics 10 00069 ch001 550
Chart 1. Proton transfer (I and II) and hydride transfer (III) between Ru-H and N2O.
Chart 1. Proton transfer (I and II) and hydride transfer (III) between Ru-H and N2O.
Inorganics 10 00069 ch001
Inorganics 10 00069 g001 550
Figure 1. Free energy diagram for N2 generation from proton transfer to the terminal N of endo N2O. Selected atom distances are given in Å, selected bond angles are given in degrees, and ΔG°/ΔG‡ are in kcal mol−1.
Figure 1. Free energy diagram for N2 generation from proton transfer to the terminal N of endo N2O. Selected atom distances are given in Å, selected bond angles are given in degrees, and ΔG°/ΔG‡ are in kcal mol−1.
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Inorganics 10 00069 ch002 550
Chart 2. Studied Ru-H complexes for the conversion of N2O to N2.
Chart 2. Studied Ru-H complexes for the conversion of N2O to N2.
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Inorganics 10 00069 sch002 550
Scheme 2. Equation used to calculate the hydricity (ΔGH−) of Ru-H complex.
Scheme 2. Equation used to calculate the hydricity (ΔGH−) of Ru-H complex.
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Inorganics 10 00069 g002 550
Figure 2. Linear fitting between the computed hydricities (ΔGH−) and Ru-H stretching frequencies.
Figure 2. Linear fitting between the computed hydricities (ΔGH−) and Ru-H stretching frequencies.
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Inorganics 10 00069 g003 550
Figure 3. Linear fitting between the Gibbs free energies of activation (ΔG‡) of TS-3-4 and the computed hydricities (ΔGH−).
Figure 3. Linear fitting between the Gibbs free energies of activation (ΔG‡) of TS-3-4 and the computed hydricities (ΔGH−).
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Inorganics 10 00069 g004 550
Figure 4. Linear fitting between the computed hydricities (ΔGH−) and the Gibbs free energy of activation (ΔG‡) of TOLS.
Figure 4. Linear fitting between the computed hydricities (ΔGH−) and the Gibbs free energy of activation (ΔG‡) of TOLS.
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Table
Table 1. Computed hydricities, Ru-H stretching frequencies, and Gibbs free energies of activation, ΔG‡.
Table 1. Computed hydricities, Ru-H stretching frequencies, and Gibbs free energies of activation, ΔG‡.
CatalystHydricity, ΔGH–
(kcal mol−1)		Ru-H
(cm−1)		TS-1-2
(kcal mol−1)		TS-3-4
(kcal mol−1)		TOLS
(kcal mol−1)
C1, (PCF3NCF3N)-Ru-H54.71950.924.927.330.6
C2, (PCF3NN)-Ru-H53.01947.124.426.729.5
C3, (PNCF3N)-Ru-H51.61946.124.226.929.6
C4, (PNN)-Ru-H50.91943.324.126.629.0
C5, (PCH3NN)-Ru-H49.41941.324.126.428.0
C6, (PNCH3N)-Ru-H49.81942.423.726.128.4
C7, (PCH3NCH3N)-Ru-H49.11941.923.626.027.5
C8, (PNC)-Ru-H52.21910.724.028.430.9
C9, (PCH3NCH3C)-Ru-H50.81906.523.927.930.3
C10, (PCF3NCF3C)-Ru-H57.31914.024.629.331.6
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Liang, G.; Zhang, M.; Webster, C.E. Mechanistic Studies of Oxygen-Atom Transfer (OAT) in the Homogeneous Conversion of N2O by Ru Pincer Complexes. Inorganics 2022, 10, 69. https://doi.org/10.3390/inorganics10060069

AMA Style

Liang G, Zhang M, Webster CE. Mechanistic Studies of Oxygen-Atom Transfer (OAT) in the Homogeneous Conversion of N2O by Ru Pincer Complexes. Inorganics. 2022; 10(6):69. https://doi.org/10.3390/inorganics10060069

Chicago/Turabian Style

Liang, Guangchao, Min Zhang, and Charles Edwin Webster. 2022. "Mechanistic Studies of Oxygen-Atom Transfer (OAT) in the Homogeneous Conversion of N2O by Ru Pincer Complexes" Inorganics 10, no. 6: 69. https://doi.org/10.3390/inorganics10060069

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