Alkane dehydrogenation catalyzed by a PN³P pincer iridium hydride complex

Abstract

The use of an iridium-based pincer complex, specifically the PN³P pincer ligand backbone, for an efficient alkane dehydrogenation reaction is explored. Herein, we investigate the catalytic performance of a PN³P pincer iridium dihydride complex (Ir2) in the dehydrogenation reaction of cyclooctane to cyclooctene. With 0.1 mol% of Ir2, cyclooctane with tert-butylethylene (TBE) as a hydrogen acceptor and NaO^tBu as a base, we achieved conversion up to 55% of tert-butylethylene (TBE) with a TON up to 546. These results highlight the potential of PN³P pincer iridium dihydride complexes as robust catalysts for selective alkane dehydrogenation under mild reaction conditions. Furthermore, DFT calculations strongly support our proposed mechanism.

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Alkane dehydrogenation (AD) is one of the most important reactions in the petrochemical industry as it uses abundant alkane to produce valuable olefins that are chemically versatile and can act as intermediates in higher value alkane synthesis through olefin coupling.^1,2 This reaction can also serve as an alternative pathway for high-temperature steam cracking of alkanes, which is energy-consuming and produces several undesirable side-products.³ In the case of alkane dehydrogenation, molecular hydrogen (H₂) is produced as the primary by-product along with olefins. H₂ is one of the rising energy carriers owing to its high energy density and environmentally benign nature.⁴ While significant efforts have been devoted to hydrogen production, such as via water splitting,^5a methane pyrolysis^5b and biomass gasification,^5c AD could eventually also serve as an attractive alternative pathway for H₂ generation. Despite the attractive advantages of the dehydrogenation of alkanes to alkenes and H₂, it is a highly endothermic process,⁶ and this characteristic is a serious hindrance to the wide implementation of this reaction.

There are some examples of metal complexes developed over the past few decades for the dehydrogenation of alkanes, including those used with hydrogen acceptors, UV and irradiation.^7,8 However, those complexes that contain a PCP pincer-type ligand utilized with a hydrogen acceptor have emerged at the top, outperforming the others in terms of stability, TON and selectivity.^2,9 Pincer ligands incorporating iridium are often used in catalytic dehydrogenation systems given their outstanding catalytic activity and stability.^7,10–15 Over the past decade, the high-valent oxidation state of iridium has been extensively explored for the catalytic dehydrogenation of alkanes.^16–23

Early work by Jensen and Kaska in 1996 demonstrated the potential of such systems.^16a They first synthesized complex 2 from 1 in the presence of H₂ and LiBEt₃H (Scheme 1), where the iridium dihydride complex 2 showed greater stability with no observable decomposition over a week; whereas the hydrochloride precursor 1 showed significant decomposition after 24 h. These foundational studies have established the basis of pincer–iridium catalysts, enabling further detailed mechanistic investigations on this catalytic system.

Scheme 1 Iridium dihydride complex developed by Jensen and Kaska for the dehydrogenation of alkanes.

In 2021, Goldmann and co-worker reported alkane dehydrogenation catalysed by a (^tBu₄POCOP)Ir complex that proceeded through a proton-coupled electron-transfer (PCET) pathway using oxidants and bases as a proton and electron acceptor.²⁴ In a subsequent study, they investigated the intramolecular C(sp³)–H activation during alkane dehydrogenation using (p-pyridyl-^tBuPCP)–IrCl⁺ cation (p-pyridyl-^tBuPCP = 3,5-bis(di-tertbutylphosphinomethyl)-2,6-dimethylpyridin-4-yl) complexes.²⁵ In 2022, the same group further expanded this chemistry by reporting a bis(2-di-tert-butyl-phosphinophenyl)phosphine (^tBuP^HPP) iridium complex for the dehydrogenation of alkanes and demonstrated that the C–H activation using a more crowded Ir(III) complex ((^tBu₄PCP)IrCl⁺ (^RPCP = 2,6-C₆H₃(CH₂PR₂) occurred intramolecularly, whereas the less crowded (ⁱPr₄PCP)IrCl⁺ undergoes intermolecular C–H activation.^9,19

Metal–ligand cooperativity (MLC) plays an important role in C–H bond activation by enabling reversible ligand participation during catalysis.^26–33 In the case of a pyridine-based pincer complex, the MLC involved in the aromatization–dearomatization of the pyridine ring results in more efficient activation of various bonds.^29,34–51 PN³P pincer complexes have previously demonstrated great performance in various chemical reactions, particularly in CO₂ hydrogenation⁵² and formic acid dehydrogenation.⁵³ Herein, we report the catalytic activity of a PN³P–pincer iridium complex towards the dehydrogenation of alkanes (Fig. 1) and the evaluation of PN³P–pincer iridium complexes Ir1, Ir2 and Ir3 for alkane dehydrogenation (Table 1).

Fig. 1 This work: alkane dehydrogenation catalysed by a PN³PIrH₂ complex.

Table 1 Optimization of the reaction conditions towards cyclooctane dehydrogenation^a

Entry	Ir cat.	Base	Oxidant	Conv.^b (%)	TON^b
a For the reaction, alkane (3.0 mmol), TBE (3.0 mmol), Ir cat (3.0 µmol, 0.1 mol%), base (15.0 µmol, 0.5 mol%), and oxidant (15.0 µmol, 0.5 mol%) were heated in an autoclave.b Determined by GC using mesitylene as an internal standard. TONs were calculated based on conversion of TBE determined by GC.
1	Ir1	NaO^tBu	—	10	99
2	Ir2	NaO^tBu	—	55	546
3	Ir3	NaO^tBu	—	40	403
4	Ir1	NaO^tBu	[Fe]^+[BF4]^−	16	157
5	Ir2	NaO^tBu	[Fe]^+[BF4]^−	56	558
6	Ir3	NaO^tBu	[Fe]^+[BF4]^−	42	415
7	Ir2	KO^tBu	—	48	481
8	Ir2	KO^tBu	[Fe]^+[BF4]^−	50	502

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To continue the study of these PN³P–pincer iridium complexes, we synthesized Ir1, Ir2 and Ir3 according to a previously reported method.⁵⁴ To test the performance of these catalysts for dehydrogenation reactions, we investigated the dehydrogenation reaction of cyclooctane (COA) as a model substrate and tert-butylethylene (TBE) as a sacrificial hydrogen acceptor. We conducted the reaction of cyclooctane (3.0 mmol) and TBE (3.0 mmol) with sodium tert-butoxide (NaO^tBu) as a base and an Ir1 catalyst (3.0 µmol, 0.1 mol%). The reaction mixture was heated at 150 °C in a closed reaction tube. The reaction was monitored by GC-MS as well as ¹H-NMR, and we observed after 24 h the formation of cyclooctene (COE) as well as a trace amount of the 1,3-cyclooctadiene (1,3-COD) product with an overall conversion of 10%, and a TON up to 99 was achieved (Table 1, entry 1). Next, we studied the performance of the dearomatized PN³P pincer dihydride iridium complex, Ir2. Surprisingly, the Ir2 catalyst under similar reaction conditions gave 55% conversion with a TON up to 546 (Table 1, entry 2). When the Ir3 catalyst was tested under similar reaction conditions, it gave a conversion of 40% with a TON up to 403 (Table 1, entry 3). Next, we studied the effect of oxidants to tune the oxidation potential, for example ferrocenium salts, [Fe]⁺[BF₄]⁻, for alkane dehydrogenation reactions.²⁴ We observed that the addition of [Fe]⁺[BF₄]⁻ salt (Fe = Ferrocenium) to the reaction mixture enhanced the conversion for all Ir catalysts by 2–6% (Table 1, entries 4–6). Next, we examined the effect of another base, namely potassium tert-butoxide (KO^tBu), with and without adding [Fe]⁺[BF₄]⁻, which gives a slightly lower conversion as compared to NaO^tBu (Table 1, entries 7 and 8).

The concentration of TBE also plays a crucial role in driving the dehydrogenation reaction of COA forward. We studied different ratios of Ir2:TBE:COA as shown in Table 2. When the reaction was carried out with a ratio of 1 : 100 : 1000 of Ir2:TBE:COA, it resulted in 5% conversion with a TON up to 3 (Table 2, entry 1). The conversion for the dehydrogenation of COA was increased to 24% when the ratio of TBE was increased to 1 : 500 : 1000, giving a TON up to 118 (Table 2, entry 2). On further increase of the ratio to 1 : 1000 : 1000, the conversion enhanced to 55% with a higher TON of up to 546 (Table 2, entry 3). This observation highlights the importance of maintaining a sufficiently high molar ratio of TBE to COA to effectively scavenge hydrogen and shift the reaction equilibrium towards dehydrogenation.

Table 2 Optimization of the reaction conditions towards cyclooctane dehydrogenation^a

Entry	[Ir]:COA	[Ir]:TBE	Temp.	Conv.^b (%)	TON^b
a For the reaction, alkane (3.0 mmol), TBE (0.3–3.0 mmol), Ir2 cat (0.1 mol%), and NaO^tBu (15.0 µmol, 0.5 mol%) were heated in an autoclave.b Determined by GC using mesitylene as an internal standard. TON was calculated based on the conversion of TBE determined by GC.
1	1000	100	150	5	3
2	1000	500	150	24	118
3	1000	1000	150	55	546

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Further, we explored the dehydrogenation process with KO^tBu and NaO^tBu as a base at different time intervals. In the case of KO^tBu, the reaction was carried out initially for 4 h, and GC analysis of the reaction mixture showed a TBE conversion of 45% with a TON of up to 447 (Table 3, entry 1). Extending the reaction time to 16 h and 24 h further increased the TBE conversion to 47% and 48%, respectively, with a corresponding TON up to 466 and 481 (Table 3, entries 2 and 3). Whereas, in the case of NaO^tBu as a base, 4 h, 16 h and 24 h time intervals gave 49%, 50% and 55% TBE conversion with a TON up to 499, 501 and 546, respectively (Table 3, entries 4–6). This observation suggested that extending the reaction time for the dehydrogenation reaction does not substantially improve the catalytic activity of Ir2.

Table 3 Time-dependent study for cyclooctane dehydrogenation^a

Entry	Time (h)	Base	Conv. of TBE^b (%)	TON^b
a For the reaction, alkane (3.0 mmol), TBE (3.0 mmol), Ir2 cat (0.1 mol %), and base (15.0 µmol, 0.5 mol%) were heated in an autoclave.b Determined by GC using mesitylene as an internal standard. TON was calculated based on conversion of TBE determined by GC.
1	4	KO^tBu	45	447
2	16	KO^tBu	47	466
3	24	KO^tBu	48	481
4	4	NaO^tBu	49	499
5	16	NaO^tBu	50	501
6	24	NaO^tBu	55	546

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Next, we studied the substrate scope using both linear and cyclic alkanes. The dehydrogenation of linear alkanes is particularly challenging because of the higher energy required for C–H activation compared to cyclic alkanes.⁵⁵ We initially explored n-octane as a substrate. The reaction was carried out using n-octane, Ir2, and NaO^tBu in the presence of TBE at 150 °C. After 15 h reaction time, the reaction was analyzed by GC, which gave 15% TBE conversion. Along with 1-octene as the dehydrogenated product, we also observed a trace amount of isomerized 2-octene and 1,2-dimethylcyclohexane (Table 4, entry 1). These results suggest that the linear alkane shows lower reactivity towards the dehydrogenation reaction. In contrast, a cyclic alkane, namely cyclohexane, is effectively converted to cyclohexene with a yield of 10% (Table 4, entry 2). However, complete dehydrogenation of the product to form benzene was not observed. Next, we evaluated 1,2,3,4-tetrahydronaphthalene as a bicyclic substrate. After the reaction, we observed fully dehydrogenated naphthalene as a product with 25% total conversion along with 5% of the partially dehydrogenated product, 1,4-dihydronapthalene (Table 4, entry 3).

Table 4 Substrate scope study^a

Entry	Alkane	Product	Conv.^b (%)
a For the reaction, alkane (3.0 mmol), TBE (3.0 mmol), Ir2 cat (0.1 mol %), and NaO^tBu (15.0 µmol, 0.5 mol%) were heated in an autoclave.b Determined by GC using mesitylene as an internal standard.
1	n-octane		15
2			10
3			25

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To shed light on the reaction mechanism, density functional theory (DFT) calculations were performed using the Gaussian 16 suite⁵⁶ (for more details, see the supplementary information (SI)). As shown in Fig. 2, the reaction cycle begins with the formation of catalytically active species IN1, resulting from the reaction of Ir2 with the base NaO^tBu along with the loss of ^tBuOH. The active species IN1 then forms a loosely bound adduct with TBE to form IN2, which is uphill by 5.7 kcal mol⁻¹. Next, the first hydrogen abstraction occurs at IN2 to give IN3 via three membered transition state TS1, with a free energy barrier of 29.7 kcal mol⁻¹. Subsequently, IN3 undergoes the second hydrogen abstraction to generate the Ir-catalyst (IN4) in its lowest oxidation state along with the alkane, having a transition state (TS2) barrier of 6.5 kcal mol⁻¹. Then, the complex IN4 binds with the cyclooctane via σ-complex IN5, which is slightly exergonic by 3.9 kcal mol⁻¹. Next, IN5 undergoes 1,2-addition of the C–H bond across the Ir catalyst to give cyclooctane intermediate IN6, traversing transition state TS3 with a barrier of 10.2 kcal mol⁻¹. Finally, the β-hydride abstraction from the cyclooctyl group in IN7 leads to the formation of the cyclooctene product (COE) along with the regeneration of active catalyst IN1. These four membered transition states (TS4) required a transition state barrier of 11.8 kcal mol⁻¹. Overall, these calculations indicate that the alkene insertion is the rate determining step of the reaction with the highest transition energy barrier of 29.7 kcal mol⁻¹.

Fig. 2 Free energy profile of the dehydrogenation of cyclooctane using an Ir2 catalyst. Free energy values are at the M06/SDD(Ir)/def2-TZVP(C,H,O,N,P,Na)//BP86/SDD(Ir)/def2-SVP(C,H,O,N,P,Na) level of theory. Non-essential hydrogen atoms have been omitted for the sake of clarity.

After the detailed DFT study, the possible reaction mechanism is illustrated as shown in Fig. 3.⁵⁷ The first step is the insertion of TBE into the 16-electron iridium dihydride (Ir2) complex to produce alkyl hydride complex B, which undergoes reductive elimination to form the 14-electron C species. This complex activates the C–H bond of cyclooctane to give species D, followed by β-hydride elimination to yield cyclooctene and regenerate the Ir2.

Fig. 3 Possible reaction mechanism of COA with TBE using Ir2.

Conclusion

PN³P iridium complexes Ir1, Ir2 and Ir3 with 2,6-diamino phosphine ligands have been studied towards the dehydrogenation of alkanes. The PN³P pincer iridium dihydride complex (Ir2) shows good catalytic performance in the dehydrogenation reaction of cyclooctane to cyclooctene. We achieved conversion up to 55% of tert-butylethylene (TBE) with a TON up to 546. These results highlight the potential of the PN³P pincer iridium dihydride complex as a robust catalyst for selective alkane dehydrogenation under mild reaction conditions. DFT calculations show that once the active species I formed after the treatment of NaO^tBu, it forms a loosely bound adduct with TBE to form intermediate II, which is uphill by 5.7 kcal mol⁻¹. Given that TBE is a mono substituted olefin and highly selective for hydrogenation, the dehydrogenation is turnover-limiting and alkene (TBE and COE) complexes are the resting states. When the concentration of TBE is low, the hydrogenation is turnover-limiting and the resting state is Ir2, while at high [TBE], COA dehydrogenation is turnover-limiting, and the resting state is the vinyl hydride.

Conflicts of interest

The authors declare no competing financial interest.

Data availability

The authors confirm that the data supporting the findings of this study are available within the article and its supplementary information. Raw data that support the findings of the study are available from the corresponding author, upon reasonable request. Supplementary information is available. See DOI: https://doi.org/10.1039/d6nj01950a.

Acknowledgements

This work was supported by the Agency for Science, Technology and Research's (A*STAR) Council Strategic Fund C230415018 and the HTCO Seed Fund (C231218002). M. V. M. is thankful for the financial support from the ANRF (ANRF/ECRG/2024/002337/CS) and CNMS, Jain University, Bangalore, India. H. K. W. acknowledge King Abdullah University of Science and Technology (KAUST).

References

1. J. A. Labinger, D. C. Leitch, J. E. Bercaw, M. A. Deimund and M. E. Davis, Top. Catal., 2015, 58, 494–501.
2. K. I. Goldberg and A. S. Goldman, Acc. Chem. Res., 2017, 50, 620–626.
3. (a) S. J. F. Sadrameli, Acc. Chem. Res., 2015, 140, 102–115; (b) T. Ren, M. Patel and K. Blok, Energy, 2006, 31, 425–451; (c) M. Tuomaala, M. Hurme and A. M. Leino, Appl. Therm. Eng., 2010, 30, 45–52.
4. K. Mazloomi and C. Gomes, Renewable Sustainable Energy Rev., 2012, 16, 3024–3033.
5. (a) G. Chen and T. Zhang, cMat, 2025, 2, e12287; (b) S. R. Patlolla, K. Katsu, A. Sharafian, K. Wei, O. E. Herrera and W. Mérida, Renewable Sustainable Energy Rev., 2023, 181, 113323; (c) A. C. Chang, H. F. Chang, F. J. Lin, K. H. Lin and C. H. Chen, Int. J. Hydrogen Energy, 2011, 36, 14252–14260.
6. H. Afeefy, NIST Chemistry Webook 2005.
7. (a) A. Kumar, T. M. Bhatti and A. S. Goldman, Chem. Soc. Rev., 2017, 117, 12357–12384; (b) J. J. Sattler, J. Ruiz-Martinez, E. Santillan-Jimenez and B. M. Weckhuysen, Chem. Rev., 2014, 114, 10613–10653; (c) Z. Nawaz, Rev. Chem. Eng., 2015, 31, 413–436.
8. (a) M. J. Burk and R. H. Crabtree, J. Am. Chem. Soc., 1987, 109, 8025–8032; (b) D. Shee and A. Sayari, Appl. Catal., A, 2010, 389, 155–164.
9. B. M. Gordon, N. Lease, T. J. Emge, F. Hasanayn and A. S. Goldman, J. Am. Chem. Soc., 2022, 144, 4133–4146.
10. (a) X. Jia and Z. Huang, Nat. Chem., 2016, 8, 157–161; (b) F. Yu, R. Tao, Y. Su, G. Liu and Z. Huang, Org. Lett., 2022, 24, 4563–4568.
11. R. H. Crabtree, M. F. Mellea, J. M. Mihelcic and J. M. Quirk, J. Am. Chem. Soc., 1982, 104, 107–113.
12. M. J. Burk, R. H. Crabtree, C. P. Parnell and R. J. Uriarte, Organometallics, 1984, 3, 816–817.
13. M. Findlater, J. Choi, A. S. Goldman and M. Brookhart, Catal. Met. Complexes, Springer, 2012, pp. 113–141.
14. J. Choi, A. H. R. MacArthur, M. Brookhart and A. S. Goldman, Chem. Rev., 2011, 111, 1761–1779.
15. M. C. Haibach, S. Kundu, M. Brookhart and A. S. Goldman, Acc. Chem. Res., 2012, 45, 947–958.
16. (a) M. Gupta, C. Hagen, R. J. Flesher, W. C. Kaska and C. M. Jensen, Chem. Commun., 1996, 2083–2084; (b) M. Gupta, C. Hagen, R. J. Flesher, W. C. Kaska and C. M. Jensen, Chem. Commun., 1996, 2083–2084; (c) J. Belli and C. M. Jensen, Organometallics, 1996, 1532–1534; (d) M. Gupta, C. Hagen, W. C. Kaska, R. E. Cramer and C. M. Jensen, J. Am. Chem. Soc., 1997, 119, 840–841; (e) D. W. Lee, W. C. Kaska and C. M. Jensen, Organometallics, 1998, 17, 1–3; (f) C. M. Jensen, Chem. Commun., 1999, 2443–2449; (g) D. Morales-Morales, D. W. Lee, Z. Wang and C. M. Jensen, Organometallics, 2001, 20, 1144–1147; (h) D. Morales-Morales, R. Redón, C. Yung and C. M. Jensen, Inorg. Chim. Acta, 2004, 357, 2953–2956.
17. (a) K. B. Renkema, Y. V. Kissin and A. S. Goldman, J. Am. Chem. Soc., 2003, 125, 7770–7771; (b) K. E. Allen, D. M. Heinekey, A. S. Goldman and K. I. Goldberg, Organometallics, 2013, 32, 1579–1582.
18. (a) X. Zhou, S. Malakar, T. Dugan, K. Wang, A. Sattler, D. O. Marler, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman, ACS Catal., 2021, 11, 14194–14209; (b) A. Parihar, T. J. Emge, F. Hasanayn and A. S. Goldman, J. Am. Chem. Soc., 2025, 147, 10279–10297.
19. S. Kundu, Y. Choliy, G. Zhuo, R. Ahuja, T. J. Emge, R. Warmuth, M. Brookhart, K. Krogh-Jespersen and A. S. Goldman, Organometallics, 2009, 28, 5432–5444.
20. A. Kumar, T. Zhou, T. J. Emge, O. Mironov, R. J. Saxton, K. Krogh-Jespersen and A. S. Goldman, ACS Catal., 2015, 137, 9894–9911.
21. R. Ahuja, B. Punji, M. Findlater, C. Supplee, W. Schinski, M. Brookhart and A. S. Goldman, Nat. Chem., 2011, 3, 167–171.
22. B. Punji, T. J. Emge and A. S. Goldman, Organometallics, 2010, 29, 2702–2709.
23. A. Paul and C. B. Musgrave, Angew. Chem., Int. Ed., 2007, 46, 8153.
24. A. D. R. Shada, A. J. Miller, T. J. Emge and A. S. Goldman, ACS Catal., 2021, 11, 3009–3016.
25. T. M. Bhatti, A. Kumar, A. Parihar, H. K. Moncy, T. J. Emge, K. M. Waldie, F. Hasanayn and A. S. Goldman, J. Am. Chem. Soc., 2023, 145, 18296–18306.
26. D. Milstein, Philos. Trans. R. Soc., A, 2015, 373, 20140189.
27. M. Rauch, S. Kar, A. Kumar, L. Avram, L. J. Shimon and D. Milstein, J. Am. Chem. Soc., 2020, 142, 14513–14521.
28. J. R. Khusnutdinova and D. Milstein, Angew. Chem., Int. Ed., 2015, 54, 12236–12273.
29. T.-F. Ramspoth, J. Kootstra and S. R. Harutyunyan, Chem. Soc. Rev., 2024, 53, 3216–3223.
30. N. E. Smith, W. H. Bernskoetter and N. Hazari, J. Am. Chem. Soc., 2019, 141, 17350–17360.
31. M. R. Elsby and R. T. Baker, Chem. Soc. Rev., 2020, 49, 8933–8987.
32. E. Ben-Ari, G. Leitus, L. J. Shimon and D. Milstein, J. Am. Chem. Soc., 2006, 128, 15390–15391.
33. (a) E. Fogler, J. A. Garg, P. Hu, G. Leitus, L. J. Shimon and D. Milstein, Chem. – Eur. J., 2014, 20, 15727–15731; (b) Q.-Q. Zhou, Y.-Q. Zou, S. Kar, Y. Diskin-Posner, Y. Ben-David and D. Milstein, ACS Catal., 2021, 11, 10239–10245.
34. C. Gunanathan and D. Milstein, Acc. Chem. Res., 2011, 44, 588–602.
35. H. Li, B. Zheng and K.-W. Huang, Coord. Chem. Rev., 2015, 293, 116–138.
36. T. Shimbayashi and K. I. Fujita, Catalysts, 2020, 10, 635.
37. T. Zell and D. Milstein, Acc. Chem. Res., 2015, 48, 1979–1994.
38. T. P. Gonçalves, I. Dutta and K.-W. Huang, Chem. Commun., 2021, 57, 3070–3082.
39. Y. Pan, C. L. Pan, Y. Zhang, H. Li, S. Min, X. Guo, B. Zheng, H. Chen, A. Anders and Z. Lai, Chem. – Asian J., 2016, 11, 1357–1360.
40. M. H. Huang, J. Hu and K.-W. Huang, J. Chin. Chem. Soc., 2018, 65, 60–64.
41. H. Li, Y. Wang, Z. Lai and K.-W. Huang, ACS Catal., 2017, 7, 4446–4450.
42. T. Chen, H. Li, S. Qu, B. Zheng, L. He, Z. Lai, Z.-X. Wang and K.-W. Huang, Organometallics, 2014, 33, 4152–4155.
43. S. S. Gholap, A. Al Dakhil, P. Chakraborty, H. Li, I. Dutta, P. K. Das and K.-W. Huang, Chem. Commun., 2021, 57, 11815–11818.
44. S. B. Dawood, P. Chakraborty, L. Yang and K.-W. Huang, Tetrahydron Lett., 2025, 167, 155664.
45. Y. Pan, C. L. Pan, Y. Zhang, H. Li, S. Min, X. Guo, B. Zheng, H. Chen, A. Anders and Z. Lai, Chem. – Asian J., 2016, 11, 1294.
46. M. J. Ajitha and K.-W. Huang, Organometallics, 2025, 44, 2099–2106.
47. S. Qu, Y. Dang, C. Song, M. Wen, K.-W. Huang and Z.-X. Wang, J. Am. Chem. Soc., 2014, 136, 4974–4991.
48. H. Li, T. P. Gonçalves, D. Lupp and K.-W. Huang, ACS Catal., 2019, 9, 1619–1629.
49. T. P. Gonçalves and K.-W. Huang, J. Am. Chem. Soc., 2017, 139, 13442–13449.
50. C. Guan, Y. Pan, E. P. L. Ang, J. Hu, C. Yao, M.-H. Huang, H. Li, Z. Lai and K.-W. Huang, Green Chem., 2018, 20, 4201–4205.
51. L.-P. He, T. Chen, D.-X. Xue, M. Eddaoudi and K.-W. Huang, J. Organomet. Chem., 2012, 700, 202–206.
52. Y. Pan, C. Guan, H. Li, P. Chakraborty, C. Zhou and K.-W. Huang, Dalton Trans., 2019, 48, 12812–12816.
53. L. Alrais, S. S. Gholap, I. Dutta, E. Abou-Hamad, B. W. J. Chen, J. Zhang, M. N. Hedhili, J.-M. Basset and K.-W. Huang, Appl. Catal., B, 2024, 342, 123439.
54. Y. Pan, C. Guan, H. Li, P. Chakraborty, C. Zhou and K.-W. Huang, Dalton Trans., 2019, 48, 12812–12816.
55. X. Tang, X. Jia and Z. Huang, Chem. Sci., 2018, 9, 288–299.
56. M. Frisch, et al.,. Gaussian 16, Revision C.02, Gaussian, Inc., Wallingford CT, 2019.
57. D. Bézier, C. Guan, K. Krogh-Jespersen, A. S. Goldman and M. J. Brookhart, Chem. Sci., 2016, 7, 2579–2586.

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