Open access peer-reviewed chapter

Late Transition Metal (LTM)-NHC Catalyzed Transformations of Renewable Chemicals to Fine Chemicals, Fuels, and Intermediates

Written By

Kurra Mohan, Bollikolla Hari Babu, Khandapu Bala Murali Krishna, Kotra Vijay and Varala Ravi

Submitted: September 13th, 2021 Reviewed: October 11th, 2021 Published: November 11th, 2021

DOI: 10.5772/intechopen.101164

From the Edited Volume

Carbene

Edited by Satyen Saha and Arunava Manna

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Abstract

This title of the book chapter deals with the late transition metal-NHC (N-heterocyclic carbene) catalyzed transformations of renewable chemicals, i.e., bio-mass resources (carbohydrates/vegetable oils/natural products) into useful chemicals via oxidation, hydrogenation, dehydration, polymerization, hydrolysis, etc. along with brief introductory notes on late transition metals, carbenes, and renewable chemicals for better understanding to the reader.

Keywords

  • late transition metals
  • NHC
  • renewable chemicals
  • fine chemicals
  • fuels
  • intermediates

1. Introduction

Organocatalysis plays a pivotal role in the field of synthetic organic chemistry as well as the pharmaceutical industry through diversifying activation strategies owing to meeting the principles of green chemistry [1, 2, 3, 4] in terms of cost-effectiveness, longevity, and less toxic compared to conventional transition metal catalysis [5, 6, 7, 8]. In this regard, N-heterocyclic carbene (NHC) plays a major role in diversified organic transformations [9, 10, 11].

1.1 Renewable chemicals

Renewable chemicals or “bio-based chemicals” are chemicals obtained from renewable sources, such as agricultural feedstock, agricultural waste, organic waste products, biomass, and microorganisms [12]. In general, in chemical industries, processes include the utilization of fossil resources. As the need for energy consumption and population increasing, limited availability of fossil resources has become a risky task in the low or underdeveloped nations to perform trade. Henceforth, alternative renewable resources such as lignin, hemicellulose, cellulose, starch, and protein have become more focus of utility.

1.2 Carbene

The term “Carbene” refers to the presence of neutral bivalent carbon with six valence electrons in N-heterocyclic compounds (Figure 1). The first reported carbene (I) was by Bartrand et al. in 1988 [13], as resonance stabilized ylide form. After a few years, the first stable NHC was reported by Arduengo et al. as an imidazolium ring [14]. In NHC, the singlet state of carbene is more thermodynamically favorable than triplet carbene. Because nitrogen is present near to carbon of carbene, it lowers the energy of the highest occupied molecular orbital (HOMO) while it increases the energy of the lowest unoccupied molecular orbital’s. The nucleophilicity of carbene also increases (A) not only above energy character but also presence of inductive effect, mesomeric and lone pair to vacant p-orbital favors singlet carbene. Most NHCs are based on imidazolium, triazolium, or thiazolium ring-containing molecules. NHCs dimerize reversible in the form of the Wanzlick equilibrium (B) [15, 16].

Figure 1.

The structure and stabilization of the first persistent carbene and NHC’s.

Since the discovery of metal carbenes in 1964 by Fisher et al. [17], fascinating applications in both catalysis and synthesis are being observed [18].

1.3 Late transition metals

Late transition metals are on the right side of the d-block, from group 8 to 11 (and 12 if it is counted as transition metals) as shown in Figure 2.

Figure 2.

Late transition metals.

1.4 Free carbine route

The general synthesis of carbene complexes involves the utilization of strong bases and harsh reaction conditions which involves high cost and more time.

1.5 Transmetalation route

It involves the transfer of the carbine fragment from a suitable metal center [generally Ag(I) or Cu(I)] to a precursor of the metal center of interest [19, 20, 21, 22] as shown in Figure 3.

Figure 3.

Transmetalation route for the synthesis of carbenes.

Even though, transmetalation method has operational simplicity but lacks atom economy. Hence, it is applied, in general, in scalable industrial processes.

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2. Applications of late transition metal NHC’s

2.1 CO2 as building blocks

The exploitation of carbon dioxide as a renewable green source of carbon in organic synthesis is of continued interest. In this regard, late transition metal NHCs play a major role for the specified purpose.

2.1.1 Formylation of amines

The use of CO2 for procuring C1-containing molecules is an evolved methodology exploiting N-heterocyclic carbenes (NHCs) as efficient catalysts [23, 24]. NHCs promoted the formylation of a wide scope of N-H bonds, with CO2 and hydrosilanes (Figure 4) [25].

Figure 4.

Formylation of amines with CO2 and hydrosilanes.

2.1.2 Carboxylation of terminal alkynes

Yu and Zhang [26] developed a Cu-NHC catalyzed conversion of CO2 to carboxylic acids in good to excellent yields under ambient conditions with wide substrate/functional group tolerance (Figure 5).

Figure 5.

Mechanistic approach for carboxylation of terminal alkynes.

2.1.3 Methylation of amines

Olivier et al. have designed using CO2 as a C1 building block for the catalytic methylation of amines using simple zinc salts and ligands (Figure 6) [27].

Figure 6.

N-methylation of amines.

2.1.4 Insertion of CO2 into terminal alkynes viacopper bis-NHC

Silver bis-NHC has exhibited better performance than Copper bis-NHC towards the carboxylation of terminal alkynes using Cs2CO3 as an additive (Figure 7) [28].

Figure 7.

Carboxylation of terminal alkynes.

2.1.5 Carboxylative cyclization of propargylamine

Tahani et al. synthesized dinuclear gold (I) complexes and investigated the carboxylative cyclization of propargylamine (PPA) (Figure 8) [29].

Figure 8.

Carboxylative cyclization of propargylamine.

2.2 Oxidation

2.2.1 Dehydrogenative oxidation of alcohols

Ir-NHC complexes were synthesized in aqueous media for the oxidation of secondary alcohols to ketones. In addition, primary alcohols were transformed to carboxylic acids in the absence of a base [30].

2.2.2 Oxidation of bio-polyols to lactic acid

Lactic acid has prominent applications in bio-plastics manufacturing. A recyclable NHC-iridium coordination polymer with a porous structure can oxidize a wide range of bio-polyols such as sorbitol to prepare lactic acid with superior selectivity and reactivity [31].

2.2.3 Dehydrogenative catalysis using alcohols

Huang et al. reported LTM-NHCs for the conversion of alcohols into aldehydes or ketones through acceptors alcohol dehydrogenation (AAD). In addition, they successfully demonstrated oxidative coupling of alcohols to form C-O, C-C, and C-N/C=N bond formations (Figure 9) [32].

Figure 9.

Dehydrogenative catalysis using alcohols.

2.2.4 Dehydrogenation of sugar alcohols

Manas and Campos et al. [33] reported Ir-NHC catalyzed oxidative protocol for the selective conversion of sorbitol, xylitol, and other polyols into lactic acid (Figure 10).

Figure 10.

Oxidation of sugar alcohols to lactic acid.

2.3 Dehydration

2.3.1 Cp*IrCl2(NHC) in hydrogen transfer initiated dehydration (HTID)

A recyclable Cp*IrCl2(NHC) (Cp* = pentamethylcyclopentadienyl) complex in ionic liquid could covert glycerol into 1,3-propanediol and subsequently to propionaldehyde by hydrogen transfer initiated dehydration (HTID) in excellent yields in the presence of air (Figure 11) [34, 35].

Figure 11.

Cp*IrCl2(NHC) in hydrogen transfer initiated dehydration (HTID).

2.3.2 Fructose to 5-hydroxymethylfurfural (HMF)

A new heterogeneous and recyclable Fe-NHCs immobilized on mesoporous expanded starch and Starbon™ 350 could be utilized successfully for the effective dehydration of fructose to HMF [36].

2.4 Reduction/hydrogenation

2.4.1 Hydrogenolysis of aryl ethers using Ni-NHC

Ni-NHC complex in the presence of a suitable base (NaOtBu) could effectively convert C-O bonds in lignin to various useful scaffolds useful in biomass conversion [37]. Hartwig et al. mechanically investigated the reduction of diaryl ethers to corresponding phenols (Figure 12) [38].

Figure 12.

Hydrogenolysis of diaryl ethers.

2.4.2 Transfer hydrogenation using Ir-NHC

Using water soluble Ir-NHCs proved that glycerol can be exploited as a hydrogen donor to convert a biomass-derived phytochemical, levulinic acid, to selectively produce γ-hydroxyvaleric acid (GHV) and lactic acid (LA) [39].

2.4.3 Iridium-based hydride transfer catalysts

Lu et al. reported homogeneous Ir-NHC catalysts, which can be utilized for the storage of H2 and fine chemicals through hydride transfer catalysis [40] (Figure 13).

Figure 13.

Iridium-based hydride transfer catalysts.

2.5 Miscellaneous organic transformations

2.5.1 Sugars to heterocycles

Zhang and Yong developed a synthetic protocol employing Cr-NHC along with ionic liquid for the selective production of 5-hydroxymethylfurfural from glucose and fructose (Figure 14) [41].

Figure 14.

Conversion of sugars into heterocycles.

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3. Conclusion

In this book chapter, authors tried to emphasize the applications of “Late Transition Metal” (LTM)-NHC catalyzed organic transformations as given in a nutshell below:

Oxidation of carbohydrates:To develop carbohydrate oxidation products as a useful alternative to those derived from petrochemical sources.

Hydrogenation of carbohydrates/fatty acids:This objective concerns the development of LTM-NHC catalysts for the hydrogenation of carbohydrates and unsaturated vegetable oils.

Dehydration/hydrolysis of carbohydrates/fatty acids:Development of dehydration/hydrolysis of carbohydrates/fatty acids with LTM-NHC catalysts to obtain fine chemicals and fuel intermediates.

Polymerization with renewable resources:This objective deals with the application of LTM-NHC catalysts in the polymerization of natural monomers of renewable chemicals or monomers derived from renewable resources to synthetic polymers (polymerization of lactic acid, glucose, glycerol, terpenes, etc.).

The present research is directed towards the conversion of methanol to H2 and CO2 using LTM-NHC catalysis.

CH3OHg+H2OLTMNHCCatalyst3H2g+CO2gE1

We do hope this compilation on very important LTM-NHC applications would help wide readers among synthetic organic chemists.

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Acknowledgments

Dr. RV is thankful to Dr. Ch.V. Rajasekhar, Scrips Pharma, and Dr. P.G. Kiran, Swastha BioSciences for their continued support.

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Conflict of interest

The authors declare no conflict of interest.

References

  1. 1. Dalko PI. Enantioselective Organocatalysis. KGaA, Weinheim: WILEY-VCH Verlag Gmbh & Co.; 2007
  2. 2. Berkessel A, Groger H. Asymmetric Organocatalysis—From Biomimetic Concepts to Applications in Asymmetric Synthesis. KGaA, Wienheim: WILEY-VCH Verlag GmbH & Co.; 2006
  3. 3. Aleman J, Cabrera S. Applications of asymmetric organocatalysis in medicinal chemistry. Chemical Society Reviews. 2013;42:774-793. DOI: 10.1039/C2CS35380F
  4. 4. Busacca CA, Fandrick DR, Song JJ, Senanayake CH. The growing impact of catalysis in the pharmaceutical industry. Advanced Synthesis and Catalysis. 2011;353:1825-1864. DOI: 10.1002/adsc.201100488
  5. 5. Parmar D, Sugiono E, Raja S, Rueping M. Complete field guide to asymmetric BINOL-phosphate derived brønsted acid and metal catalysis: History and classification by mode of activation; Brønsted acidity, hydrogen bonding, ion pairing, and metal phosphates. Chemical Reviews. 2014;114:9047-9153. DOI: 10.1021/cr5001496
  6. 6. Ishikawa T. Superbases for Organic Synthesis: Guanidines, Amidines, Phosphazenes and Related Organocatalysts. New York: Wiley; 2009
  7. 7. Zhang Z, Schreiner PR. (Thio)urea organocatalysis—What can be learnt from anion recognition? Chemical Society Reviews. 2009;38:1187-1198. DOI: 10.1039/B801793J
  8. 8. Hashimoto T, Maruoka K. Recent development and application of chiral phase-transfer catalysts. Chemical Reviews. 2007;107:5656-5682. DOI: 10.1021/cr068368n
  9. 9. Federsel H-J. Asymmetry on large scale: The roadmap to stereoselective processes. Nature Reviews. Drug Discovery. 2005;4:685-697. DOI: 10.1038/nrd1798
  10. 10. Breuer M, Ditrich K, Habicher T, Hauer B, Keseler M, Sturmer R, et al. Industrial methods for the production of optically active intermediates. Angewandte Chemie International Edition. 2004;43:788-824. DOI: 10.1002/anie.200300599
  11. 11. Fiorani G, Guo W, Kleij AW. Sustainable conversion of carbon dioxide: The advent of organocatalysis. Green Chemistry. 2015;17:1375-1389. DOI: 10.1039/C4GC01959H
  12. 12. Chandel AK, Garlapati VK, Kumar SPJ, Hans M, Singh AK, Kumar S. The role of renewable chemicals and biofuels in building a bioeconomy. Biofuels, Bioproducts and Biorefining. 2020;14(4):830-844. DOI: 10.1002/bbb.2104
  13. 13. Igau A, Grutzmacher H, Baceiredo A, Bertrand G. Analogous alpha, alpha.’-bis-carbenoid, triply bonded species: Synthesis of a stable lambda.3-phosphino carbene-.lambda.5-phosphaacetylene. Journal of the American Chemical Society. 1988;110:6463-6466. DOI: 10.1021/ja00227a028
  14. 14. Arduengo AJ, Harlow RL, Kline M. A stable crystalline carbene. Journal of the American Chemical Society. 1991;113:361-363. DOI: 10.1021/ja00001a054
  15. 15. Herrmann WA, Kocher C. N-heterocyclic carbenes. Angewandte Chemie International Edition. 1997;36:2162-2187. DOI: 10.1002/anie.199721621
  16. 16. Hopkinson MN, Richter C, Schedler M, Glorius F. An overview of N-heterocyclic carbenes. Nature. 2014;510:485-496. DOI: 10.1038/nature13384
  17. 17. Fischer EO, Maasbol A. On the existence of a tungsten carbonyl carbene complex. Angewandte Chemie. 1964;76:645. DOI: 10.1002/anie.196405801
  18. 18. Fischer EO, Maasbol A. Übergangsmetall-Carben-Komplexe, II. Phenylmethoxycarben- und Methylmethoxycarben-pentacarbonyl-chrom, -molybdän, -wolfram und -cyclopentadienyl-dicarbonyl-mangan. Chemistry. 1967;100(2445). DOI: 10.1002/cber.19671000744
  19. 19. Wang HMJ, Lin IJB. Facile synthesis of silver (I)-carbene complexes. Useful carbene transfer agents. Organometallics. 1998;17:972-975. DOI: 10.1021/om9709704
  20. 20. Furst MRL, Cazin CSJ. Copper N-heterocyclic carbene (NHC) complexes as carbene transfer reagents. Chemical Communications. 2010;46:6924-6925. DOI: 10.1039/C0CC02308F
  21. 21. Díez-González S. N-Heterocyclic Carbenes. From Laboratory Curiosities to Efficient Synthetic Tools. 2nd ed. London: Royal Society of Chemistry; 2017
  22. 22. Scattolin T, Nolan SP. Synthetic routes to late transition metal—NHC complexes. Trends in Chemistry. 2020;2(8). DOI: 10.1016/j.trechm.2020.06.001
  23. 23. Anis T, Blondiaux E, Xavier F, Thibault C. Reductive functionalization of CO2 with amines: An entry to formamide, formamidine and methylamine derivatives. Green Chemistry. 2015;17:157-168. DOI: 10.1039/C4GC01614A
  24. 24. Riduan SN, Zhang Y, Ying JY. Conversion of carbon dioxide into methanol with silanes over N-heterocyclic carbene catalysts. Angewandte Chemie International Edition. 2009;48:3322. DOI: 10.1002/anie.200806058
  25. 25. Jacquet O, Gomes CDN, Ephritikhine M, Cantat T. Recycling of carbon and silicon wastes: Room temperature formylation of N-H bonds using carbon dioxide and polymethylhydrosiloxane. Journal of the American Chemical Society. 2012;134:2934. DOI: 10.1021/ja211527q
  26. 26. Yu D, Zhang Y. Copper, and copper-N-heterocyclic carbene-catalyzed C-H activating carboxylation of terminal alkynes with CO2 at ambient conditions. Proceedings of the National Academy of Sciences of the United States of America. 2010;107(47):20184-20189. DOI: 10.1073/pnas.1010962107
  27. 27. Jacquet O, Xavier F, Christophe DNG, Thibault C. CO2 as a C1 building block for the catalytic methylation of amines. Chemical Science. 2013;4:2127. DOI: 10.1039/c3sc22240c
  28. 28. Velázquez HD, Wu Z-X, Vandichel M, Verpoort F. Inserting CO2 into terminal alkynes via bis-(NHC)-metal complexes. Catalysis Letters. 2017;47(2):463-471. DOI: 10.1007/s10562-016-1920-5
  29. 29. Bayrakdar TACA, Nahra F, Davis JV, Mohan MG, Captain B, Temprado M, et al. Dinuclear Gold(I) complexes bearing alkyl-bridged bis(Nheterocyclic carbene) ligands as catalysts for carboxylative cyclization of propargylamine: Synthesis, structure, and kinetic and mechanistic comparison to the mononuclear complex [Au(IPr)Cl]. Organometallics. 2020;39(15):2907-2916. DOI: 10.1021/acs.organomet.0c00404
  30. 30. Fujita K, Tamura R, Yuhi T, Yoshida M, Onoda M, Yamaguchi R. Dehydrogenative oxidation of alcohols in aqueous media catalyzed by a water-soluble dicationic iridium complex bearing a functional N-heterocyclic carbene ligand without using base. ACS Catalysis. 2018;7(10):7226-7230. DOI: 10.1021/acscatal.7b02560
  31. 31. Wu J, Shen L, Duan S, Chen Z-N, Zheng Q, Liu Y, et al. Selective Catalytic dehydrogenative oxidation of bio-polyols to lactic acid. Angewandte Chemie International Edition. 2020;59(33):13871-13878. DOI: 10.1002/anie.202004174
  32. 32. Huang M, Liu J, Li Y, Lan X-B, Su P, Zhao C, et al. Recent advances on N-heterocyclic carbene transition metal complexes for dehydrogenative catalysis using alcohols. Catalysis Today. 2020;370:114-141. DOI: 10.1016/j.cattod.2020.10.022
  33. 33. Manas MG, Campos J, Sharninghausen LS, Lin E, Crabtree RH. Selective catalytic oxidation of sugar alcohols to lactic acid. Green Chemistry. 2015;17:594-600. DOI: 10.1039/C4GC01694G
  34. 34. Wang Y-M, Lorenzini F, Rebros M, Saunders GC, Marr AC. Combining bio- and chemo-catalysis for the conversion of bio-renewable alcohols: Homogeneous iridium catalysed hydrogen transfer initiated dehydration of 1,3-propanediol to aldehydes. Green Chemistry. 2016;18(6):1751-1761. DOI: 10.1039/c5gc02157j
  35. 35. Ma Y, Wang Y-M, Morgan PJ, Jackson RE, Liu X, Saunders GC, et al. Designing effective homogeneous catalysis for glycerol valorisation: Selective synthesis of a value-added aldehyde from 1,3-propanediol via hydrogen transfer catalysed by a highly recyclable, fluorinated Cp*Ir(NHC) catalyst. Catalysis Today. 2018;307:248-259. DOI: 10.1016/j.cattod.2017.09.036
  36. 36. Matharu AS, Ahmed S, Almonthery B, Macquarrie DJ, Lee Y-S, Kim Y. Novel Starbon™/HACS-supported N-heterocyclic carbene-iron (III) catalyst for efficient conversion of fructose to HMF. ChemSusChem. 2017;11(4):716-725. DOI: 10.1002/cssc.201702207
  37. 37. Xu L, Chung LW, Wu Y-D. Mechanism of Ni-NHC catalyzed hydrogenolysis of aryl ethers: Roles of the excess base. ACS Catalysis. 2016;6:483-493. DOI: 10.1021/acscatal.5b02089
  38. 38. Saper NI, Hartwig JF. Mechanistic investigations of the hydrogenolysis of diaryl ethers catalyzed by nickel complexes of N-heterocyclic carbene ligands. Journal of the American Chemical Society. 2017;139:17667-17676. DOI: 10.1021/jacs.7b10537
  39. 39. Wang K, Heltzel J, Evan S, Culley K, Gabriel L, Adelina V. Transfer hydrogenation of levulinic acid from glycerol and ethanol using water-soluble iridium N-heterocyclic carbene complexes. Journal of Organometallic Chemistry. 2020;919:121310. DOI: 10.1016/j.jorganchem.2020.121310
  40. 40. Lu Z, Cherepakhin V, Demianets I, Lauridsen PJ, Williams TJ. Iridium-based hydride transfer catalysts: From hydrogen storage to fine chemicals. Chemical Communications. 2018;54:7711. DOI: 10.1039/c8cc03412e
  41. 41. Yong G, Zhang Y, Ying JY. Efficient catalytic system for the selective production of 5-hydroxymethylfurfural from glucose and fructose. Angewandte Chemie International Edition. 2008;47:9345-9348. DOI: 10.1002/anie.200803207

Written By

Kurra Mohan, Bollikolla Hari Babu, Khandapu Bala Murali Krishna, Kotra Vijay and Varala Ravi

Submitted: September 13th, 2021 Reviewed: October 11th, 2021 Published: November 11th, 2021