Sustainable Catalysis E-Book
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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Highlighting sustainable catalytic processes in synthetic organic chemistry and industry, this useful guide places special emphasis on catalytic reactions carried out at room temperature.
It describes the fundamentals, summarizes key advances, and covers applications in industrial processes in the field of energy generation from renewables, food science, and pollution control. Throughout, the latest research from various disciplines is combined, such as homogeneous and heterogeneous catalysis, biocatalysis, and photocatalysis. The book concludes with a chapter on future trends and energy challenges for the latter half of the 21st century.
With its multidisciplinary approach this is an essential reference for academic and industrial researchers in catalysis science aiming to design more sustainable and energy-efficient processes.
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Veröffentlichungsjahr: 2017
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Table of Contents
Cover
Title Page
Copyright
Chapter 1: Introduction to Room-Temperature Catalysis
1.1 Introduction
1.2 Room-Temperature Homogeneous Catalysts
1.3 Room-Temperature Heterogeneous Catalysts
1.4 Conclusions and Perspectives
References
Chapter 2: Functionalized Ionic Liquid-based Catalytic Systems with Diversified Performance Enhancements
2.1 Introduction
2.2 Functionalized ILs for Enhancing Catalytic Activity
2.3 Functionalized ILs for Improving Reaction Selectivity
2.4 Functionalized ILs for Facilitating Catalyst Recycling and Product Isolation
2.5 Functionalized ILs for Making Relay Catalysis
2.6 Cation and Anion Synergistic Catalysis in Ionic Liquids
2.7 Functionalized ILs for Aqueous Catalysis
2.8 Catalysis by Porous Poly-ILs
2.9 Functionalized IL-Based Carbon Material for Catalysis
2.10 Summary and Conclusions
References
Chapter 3: Heterogeneous Room Temperature Catalysis – Nanomaterials
3.1 Introduction
3.2 Solid-Acid-Based Nanomaterials
3.3 Grafted-Metal-Ions-Based Nanomaterial
3.4 Metal NPs-Based Nanomaterial
3.5 Metal Oxide NPs-Based Nanomaterial
3.6 Summary and Conclusions
References
Chapter 4: Biocatalysis at Room Temperature
4.1 Introduction
4.2 Transaminases
4.3 Hydrolases
4.4 Laccases
4.5 Enzymes in Ionic Liquids
References
Chapter 5: Room Temperature Catalysis Enabled by Light
5.1 Introduction
5.2 UV Photochemistry
5.3 Visible Light Photoredox Catalysis
5.4 Room Temperature Cross-Coupling Enabled by Light
5.5 Photochemistry and Microreactor Technology – A Perfect Match?
5.6 The Use of Photochemistry in Material Science
5.7 Solar Fuels
5.8 Conclusion
References
Chapter 6: Mechanochemically Enhanced Organic Transformations
6.1 Introduction
6.2 Mechanochemical Techniques and Mechanisms: Neat versus Liquid-Assisted Grinding (LAG)
6.3 Oxidation and Reduction Using Mechanochemistry
6.4 Electrocyclic Reactions: Equilibrium and Templating in Mechanochemistry
6.5 Recent Advances in Metal-Catalyzed Mechanochemical Reactions
6.6 New Frontiers in Organic Synthesis Enabled by Mechanochemistry
6.7 Conclusion and Outlook
Acknowledgments
References
Chapter 7: Palladium-Catalyzed Cross-Coupling in Continuous Flow at Room and Mild Temperature
7.1 Introduction
7.2 Suzuki Cross-Coupling in Continuous Flow
7.3 Heck Cross-Coupling in Continuous Flow
7.4 Murahashi Cross-Coupling in Continuous Flow
7.5 Concluding Remarks
References
Chapter 8: Catalysis for Environmental Applications
8.1 Introduction
8.2 Ferrate (FeO
4
2−
) for Water Treatment
8.3 Magnetically Separable Ferrite for Water Treatment
8.4 UV, Solar, and Visible Light-Activated TiO
2
Photocatalysts for Environmental Application
8.5 Catalysis for Remediation of Contaminated Groundwater and Soils
8.6 Novel Catalysis for Environmental Applications
8.7 Summary and Conclusions
Acknowledgments
Disclaimer
References
Chapter 9: Future Development in Room-Temperature Catalysis and Challenges in the Twenty-first Century
Case Study 1: Magnetic Pd Catalysts for Benzyl Alcohol Oxidation to Benzaldehyde
1.1 Introduction
1.2 Pd/MagSBA Magnetic Catalyst for Selective Benzyl Alcohol Oxidation to Benzaldehyde
1.3 Summary and Conclusions
References
Case Study 2: Development of Hydrothermally Stable Functional Materials for Sustainable Conversion of Biomass to Furan Compounds
2.1 Introduction
2.2 Metal–Organic-Framework as a Potential Catalyst for Biomass Valorization
2.3 Xylose Dehydration to Furfural Using Metal–Organic-Framework, MIL-101(Cr)
2.4 Conclusion
References
Index
End User License Agreement
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Guide
Cover
Table of Contents
Begin Reading
List of Illustrations
Chapter 1: Introduction to Room-Temperature Catalysis
Figure 1.1 Brønsted acidic ionic liquids (BAILs) used as catalyst in the synthesis of α-aminophosphonates in a one-pot, three-component reaction.
Figure 1.2 Multiple-acidic ionic liquids in the synthesis of bis-indolylmethanes.
Scheme 1.1 Synthetic procedure for [Ni(P
R
2
N
R′
2
)
2
(CH
3
CN)]
2+
complexes.
Figure 1.3 WERSA isolation procedure from rice straw.
Scheme 1.2 Synthesis of carboranes with homogeneous silver catalysts.
Scheme 1.3 Plausible mechanism for the gold-catalyzed oxidative homocoupling of terminal alkynes.
Figure 1.4 (a) Overview of the PdCNT catalyst assembly; (b) structure of DANTA; (c) structure of PDADMAC.
Scheme 1.4 Preparation of Silica-3p-TPP.
Figure 1.5 Encapsulation of PVP and Pd in the 3D interconnected pore channels of KIT-5.
Scheme 1.5 Schematic representation of the synthesis of SiO
2
/Pd–NP/porous-SiO
2
core–shell–shell nanospheres.
Figure 1.6 TEM images of (a) SiO
2
/Pd–NP core–shell nanospheres with 20 nm Pd–NP chemisorbed on aminopropyl-modified silica nanospheres and the corresponding (b) SiO
2
/Pd–NP/SiO
2
core–shell–shell nanospheres, and (c) SiO
2
/Pd–NP/porous-SiO
2
core–shell–shell nanospheres etched for 120 min.
Scheme 1.6 A schematic illustration of the formation and shape evolution of the Pd/Fe
3
O
4
spheres in the whole synthetic process.
Scheme 1.7 General reaction pathways for the oxidation of GLY and PG.
Scheme 1.8 Proposed reaction mechanism for polyols oxidation catalyzed by PtAu–starch/HT. (Tongsakul
et al
. 2013 [67]. Reproduced with permission of American Chemical Society.)
Figure 1.7 Structure of monoliths 1−10.
Scheme 1.9 Huisgen [3+2] cycloaddition.
Scheme 1.10 Synthesis of silica-functionalized Cu(I) iodide [SiO
2
–CuI].
Scheme 1.11 Suggested mechanism for the Cu/AlO(OH)–H
5
IO
6
catalytic system.
Figure 1.8 The pictures of (a) CuNPs@SCF dispersed in the reaction solution, (b) the reaction solution at the end of the reaction after the application of lab magnet.
Scheme 1.12 Grafting of phthalocyanine on crystalline nanocellulose: (i) EPTMAC, NaOH; (ii) Cu–tetrasulfonate phthalocyanine. Inset: Digital photos of NCC–PC (solid) and NCC–PC (aqueous suspension).
Figure 1.9 TEM photographs describing the morphology of the catalyst: (a) silica nanoparticles used as a support, (b) Au seeds, and (c) Au nanoparticles decorating the surface of the silica after amino–silane coupling. (d) Histogram (
N
= 220) showing the particle-size distribution of the Au nanoparticles.
Chapter 2: Functionalized Ionic Liquid-based Catalytic Systems with Diversified Performance Enhancements
Figure 2.1 Schematic illustration of acid catalysis with Brønsted acid ILs. (BAIL: brønsted acid ionic liquid; SFBAIL: sulfonyl functionalized brønsted acid ionic liquid).
Scheme 2.1 Nucleophilic substitution of benzhydrol and phenylacetylene over different acidic ILs.
Figure 2.2 Phase behavior of IL catalyst in the abovementioned reaction (a) IL
1a
; (b) Forbes' IL; (c) congener of
1a
without sulfonyl group, the photos were taken at 100 °C.
Scheme 2.2 Reductive alkylation of indole with cyclic ketones by using IL
1a
as catalyst.
Figure 2.3 Color change due to the condensation reaction at interface between CH
2
Cl
2
and Brønsted acid IL.
Scheme 2.3 Biphasic synthesis of porphyrin.
Figure 2.4 Esterification of citric acid with
n
-butanol over Brønsted acid IL contains heteropolyacid anion; (a) catalyst (solid at
bottom
), citric acid (white solid in the
middle
), and alcohol (liquid in the
upper phase
) before mixing; (b) homogeneous mixture during the reaction; (c) heterogeneous mixture near completion of the reaction; (d) at the end of the reaction, the catalyst precipitated out.
Figure 2.5 Polyoxometalate-based ILs remain in the bottom of vessel. Esterification illustrated by the catalyst: (a) before reaction; (b) during the reaction; (c) at the end of the reaction.
Scheme 2.4 Conversion of fructose into 5-alkoxymethylfurfural ethers in heterogeneous system.
Figure 2.6 General principle of thermo-regulated phase separable catalysis (TPSC)-based AGET ATRP. (r.t: roomtemperature).
Figure 2.7 Hydrogenation of aromatic ketone in a choline–betainium IL with the aid of palladium catalyst.
Scheme 2.5 Hydrogenation of phenol to cyclohexane catalyzed by Rh nanoparticles in Brønsted acid IL.
Figure 2.8 Conversion of tetrahydrofurfurylacetone via combination of Ru and Brønsted acid IL in a one-pot two-step system. (FF: furfural; FFA: furfuralacetone; THFA: 4-(2-tetrahydrofuryl)-2-butanol).
Scheme 2.6 Cooperative nucleophilic–electrophilic organocatalysis by IL.
Scheme 2.7 Conversions of hemicelluloses to furfural by Brønsted acid IL in aqueous system.
Scheme 2.8 Pinacol rearrangements of triphenylethylene glycol in IL and water using microwave.
Figure 2.9 Schematic illustration of MPIL-based heterogeneous catalysts.
Figure 2.10 Schematic structure of the magnetic nanoparticles supported multilayered cross-linked poly(ionic liquid). (AIBN: 2,2′-Azobis(2-methylpropionitrile).
Figure 2.11 Synthesis of metal/metal oxide-supported carbon catalysts from ILs using hard-templating method.
Figure 2.12 Ionic liquid precursors used to synthesize the N-doped carbon materials.
Figure 2.13 One-pot synthesis of metal-supported N-doped carbon catalytic materials from metal-containing IL precursors.
Chapter 3: Heterogeneous Room Temperature Catalysis – Nanomaterials
Scheme 3.1 Cyanosilylation of aromatic aldehydes/ketones catalyzed by catalyst
1
.
Scheme 3.2 GO catalyzed Michael-type Friedel–Crafts addition of indoles.
Scheme 3.3 G-SO
3
H catalyzed hydration of propylene oxide.
Scheme 3.4 Nanoferrite–Ni catalyzed hydrogenation reactions.
Scheme 3.5 Asymmetric allylation of 4-nitrobenzaldehyde with allyltributyltin catalyzed by nano-Fe
3
O
4
–Pd–NHC complex.
Scheme 3.6 Sonogashira coupling of benzoyl chloride with phenylacetylene catalyzed by Pd(OAc)
2
@dendrimer.
Scheme 3.7 (a) Hydrogenation of olefins and (b) reduction of nitrobenzene by Pd(II) grafted on MONT, (c) schematic representation of the NHC-based ligand.
Scheme 3.8 Suzuki–Miyaura coupling reactions catalyzed by the chiral Pd NPs.
Scheme 3.9 PVP-stabilized Au/Pd alloy NPs-catalyzed Ullmann coupling of 4-Chlorotoluene.
Scheme 3.10 Polymer
1
(
x
/
y
/
z
28 : 34 : 38).
Scheme 3.11 Oxidation of (±)-1-phenylethanol using the PI Au NCs.
Scheme 3.12 Stille reaction catalyzed by dendrimer-encapsulated Pd NPs.
Scheme 3.13 Chemoselective reduction of aromatic nitroarenes catalyzed by NAP-Mg–Au(0). Conversion/selectivity valves and reaction time are listed below each product.
Scheme 3.14 The imination of nitroarenes using aldehydes and carbon monoxide by Au/TiO
2
.
Scheme 3.15 Reduction of nitroarenes to anilines catalyzed by Pd@NAC-800.
Scheme 3.16 rGO-Co
30
Pd
70
-catalyzed tandem reduction of various aromatic nitro or nitriles or carbonyl compounds.
Scheme 3.17 AuCNT-catalyzed oxidation of various silanes.
Scheme 3.18 AuCNT-catalyzed N-formylation of secondary/primary amines.
Scheme 3.19 Laser-driven amide formation between benzaldehyde and morpholine (a) and tandem oxidation/amidation reaction between benzyl alcohol and morpholine to 4-benzoylmorpholine (b) catalyzed by Au/SiO
2
at room temperature.
Scheme 3.20 Pd-MAGSNC catalyzed Suzuki–Miyaura coupling of aryl bromides and phenylboronic acid.
Scheme 3.21 Selective examples of aerobic oxidation of alcohols using Au@PMO catalytic system.
Scheme 3.22 The reduction of 4-nitrophenol by Ni/SNTs.
Scheme 3.23 The oxidation of 1-phenylethanol by Au/MIL-101 (CD/PVP).
Scheme 3.24 The oxidation of cinnamyl alcohol by Pd/MIL-101.
Scheme 3.25 The oxidation of alcohol catalyzed by Pt@MOF-177 under solvent- and base-free condition at room temperature.
Scheme 3.26 Hydrogenation of hydroxy-aromatic derivatives with 5 wt% Pd/MIL-101.
Scheme 3.27 Encapsulation of Pd NPs in UiO-67 via preincorporation of metal precursor method.
Scheme 3.28 Hydrogenation of (a) tetraphenylethylene, (b) styrene, and (c) nitrobenzene.
Scheme 3.29 Encapsulation of PdNi NPs in UiO-67 via the in situ metal precursor incorporation method.
Scheme 3.30 Room temperature reduction of nitrobenzene for aniline formation by PdNi-in-UiO-67.
Scheme 3.31 Knoevenagel condensation of 4-nitrobenzaldehyde and malononitrile and subsequent selective hydrogenation catalyzed by Pd@IRMOF-3 core–shell nanocomposites.
Scheme 3.32 Reaction pathways in the hydrogenation of cinnamaldehyde.
Scheme 3.33 Chemoselective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde.
Scheme 3.34 Deoxygenation of styrene oxide on TiO
2
particles under photoirradiation.
Chapter 4: Biocatalysis at Room Temperature
Figure 4.1 Reaction for the synthesis of l-phenylalanine catalyzed by the enzyme AAT.
Figure 4.2 Enantiomerically pure (
S
)-amines using ω-transaminases. (Adapted from Ref. [21].)
Figure 4.3 Complementary approaches for the preparation of enantio-enriched achiral primary amines corresponding to the reaction run forward and reverse, respectively. (a) Kinetic resolution starting with racemic (
rac
) amines is limited by 50% maximum yield. Nevertheless, employing pyruvate as amine acceptor shifts the reaction to the product side. (b) Theoretically, a 100% yield is possible in asymmetric synthesis from prochiral ketones if the equilibrium can be shifted appropriately. (Koszelewski
et al
. 2010 [22]. Reproduced with permission of Elsevier.)
Figure 4.4 Kinetic resolution of
rac
-
1a–d
using sol–gel entrapped ω-transaminase.
Figure 4.5 (
R
)-Valinol.
Figure 4.6 Lipase-catalyzed hydrolysis reaction [48].
Figure 4.7 Carbon–carbon bond formation through aldol addition, according to [74]).
Figure 4.8 Asymmetric aldol reaction between acetone and different aromatic aldehydes using porcine pancreatic lipase (PPL), according to [75].
Figure 4.9 Aldol addition between a tricyclic ketone and
in situ
-generated acetaldehyde (produced in the reaction media due to hydrolysis of vinyl acetate), according to [76].
Figure 4.10 Michael addition of 1,3-dicarbonyl compounds and an α/β-unsaturated aldehyde or ketone according to [74].
Figure 4.11 One-pot Mannich reaction between acetone, aniline, and aromatic aldehydes under aqueous conditions, according to [75].
Figure 4.12 Michael addition between different secondary amines (such as pyrrolidine, piperidine, and diethylamine) and acrylonitrile, according to [79].
Figure 4.13 Lipase-catalyzed perhydrolysis reaction according to [80].
Figure 4.14 Lipase-catalyzed epoxidation of α/β-unsaturated compounds, according to Svedendahl
et al
. [81].
Figure 4.15 Kinetic resolution of
p
-chlorostyrene oxide, according to [84].
Figure 4.16 Lipase-catalyzed enantioselective transesterification of 1-bromo-3-(4-(2-methoxy-ethyl)phenoxy)-propan-2-ol, according to [86].
Figure 4.17 Kinetic resolution according to [88].
Figure 4.18 Structure of malathion.
Figure 4.19 General structure and details of the active site of laccase (
Trametes trogii
laccase, PDB ID: 2HRG). The three cupredoxin-like domains (D1, D2 and D3) are shown in green, cyan, and magenta, respectively. Purple blue spheres represent copper ions and red spheres depict coordinating water molecules. The residues of the internal transfer pathway from T1 Cu to the T2/T3 trinuclear cluster are colored in yellow. Residues involved in the first coordination sphere of the catalytic coppers and their interactions (as black dashes) are also represented.
Figure 4.20 A simplified reaction mechanism of laccase oxidation of suitable substrate, using coniferyl alcohol as an example.
Figure 4.21 Kinetically controlled synthesis of phenylethyl acetate from 2-phenylethanol and vinyl acetate catalyzed by
Pseudomonas cepaceae
lipase.
Figure 4.22 Resolution of (±)-1 using pancreatin lipase in [C
8
mim][PF
6
] at room temperature [211].
Figure 4.23 Soybean peroxidase (SBP)-catalyzed polymerization of
p
-cresol.
Figure 4.24 A new route for enzymatic
in situ
saccharification in water–ionic liquid mixture.
Figure 4.25 Schematic illustration of the asymmetric whole-cell biotransformation of 2-octanone to (
R
)-2-octanol in a biphasic system with ionic liquids (LB-ADH:
Lactobacillus brevis
alcohol dehydrogenase; CB-FDH:
Candida boidinii
formate dehydrogenase).
Figure 4.26 The asymmetric reduction of 4′-bromo-2,2,2-trifluoroacetophenone to (
R
)-4′-bromo-2,2,2-trifluoroacetophenyl alcohol by alcohol dehydrogenase isolated from
Rhodococcus erythropolis
(ADH RE) and co-factor recycling by the glucose dehydrogenase 103 (GDH 103)-mediated oxidation of glucose.
Figure 4.27 Whole cell reaction in ionic liquid: asymmetric reduction of 4′-methoxyacetophenone.
Figure 4.28 Synthesis of chiral epichlorohydrin by CPO-catalyzed epoxidation of 3-chloropropene. (Adapted from Ref. [191].)
Figure 4.29 Esterification reaction of esculin and rutin.
Figure 4.30 Esterification of − EC with gallic acid to epicatechingallate using tannase.
Chapter 5: Room Temperature Catalysis Enabled by Light
Scheme 5.1 UV-induced photocyclizations at room temperature.
Scheme 5.2 Norrish reactions in organic synthetic photochemistry.
Scheme 5.3 Intermolecular [2+2] photocycloadditions.
Scheme 5.4 Ruthenium polypyridyl complexes as versatile visible light photoredox catalysts and their photocatalytic cycle with reductive and oxidative quenching pathways.
Scheme 5.5 Visible light photoredox catalysis for the direct coupling of
N
-methylmorpholine with an unfunctionalized pyridazine.
Scheme 5.6 Merging photoredox catalysis with organocatalysis to enable asymmetric organic transformations.
Scheme 5.7 Photocatalytic C−H arylation of heteroarenes with Eosin Y.
Scheme 5.8 Photoinduced copper-catalyzed Ullmann C−N coupling at room temperature.
Scheme 5.9 Room temperature C−H arylation by merging palladium and photoredox catalysis.
Scheme 5.10 Room temperature C
sp2
−C
sp3
coupling by merging nickel and photoredox catalysis.
Scheme 5.11 Room temperature oxyarylation of alkenes by merging gold and photoredox catalysis.
Scheme 5.12 Intramolecular [5+2] photocycloaddition to prepare the key pyrrolo[1,2-
a
]azepine core required for the total synthesis of (±)-neostenine.
Scheme 5.13 Photocatalytic Stadler–Ziegler synthesis of arylsulfides in a visible light photomicroreactor.
Scheme 5.14 Continuous flow photocatalytic aerobic oxidation to produce oxytocin.
Scheme 5.15 Continuous flow singlet oxygen oxidation en route to artemisinin.
Scheme 5.16 (a) Controlled living radical polymerization of methacrylates. (b) Patterning of surfaces by using a photomask. (c) Gradient structures by using a neutral density filter.
Scheme 5.17 End group modification of maleimide functionalized poly(butyl acrylate) via a [2+2] cycloaddition reaction in batch and flow.
Scheme 5.18 (a) Schematic representation of the microfluidic flow-focusing device to prepare Janus particles. (b) Image of the setup.
Scheme 5.19 Norrish type I α-cleavage to prepare radicals that can reduce Ag
+
to prepare Ag nanoparticles.
Scheme 5.20 Artificial photosynthesis using solar energy to split water into hydrogen and oxygen.
Chapter 6: Mechanochemically Enhanced Organic Transformations
Figure 6.1 Examples of two aldimine condensation reactions taking place by different mechanisms of mass transfer. (a) Mixing of 4-aminotoluene with 2-hydroxy-3-methoxybenzaldehyde produces an orange eutectic melt in which the reaction takes place. (b) Upon mixing with a glass rod for 2 min, the entire reaction mixture is molten. (c) The melt is of sufficiently low viscosity to be handled with a pipette. (d) The condensation of 4-methylaniline and 4-hydroxybenzaldehyde is an example of a reaction that does not take place via an intermediate liquid phase. (e) Powder X-ray diffraction (PXRD) analysis of the solid reaction mixture reveals partial formation of the product imine.
Figure 6.2 Mechanochemical synthesis of zwitterionic
m
-aminobenzoquinones, reported by Fang
et al
. [38]: (a) general reaction scheme and (b) dependence of the reaction mixture temperature on the amount of milling media, expressed as “bead height.”
Scheme 6.1 Substances involved in the oxidation of anilines to nitrobenzenes.
Scheme 6.2 Mechanochemical transformation of thioethers and thiophenes into sulfones using Oxone [48].
Scheme 6.3 Mechanochemical reduction of aldehydes and ketones by milling with NaBH
4
, as described by Naimi-Jamal
et al.
[59].
Scheme 6.4 Ball milling reduction of methyl benzoate esters through LiBH
4
formed by
in situ
metathesis of NaBH
4
and LiCl [58].
Figure 6.3 (a) Mechanochemical Diels–Alder reaction of fullerene C
60
and anthracene; (b) the evolution of the reaction mixture during 60 min milling of C
60
and anthracene in a 1.2 : 1 stoichiometric ratio and (c) the evolution of the reaction mixture during 60 min milling of the previously prepared 1 : 1 Diels–Alder adduct of anthracene and C
60
[65].
Figure 6.4 (a) Mechanochemical Diels–Alder reaction of fullerene C
60
with pentacene; (b, c) steric considerations for the formation of Diels–Alder adducts based on a 2 : 1 ratio of C
60
and pentacene.
Figure 6.5 The mechanochemical and photochemical [2+2] dimerization of olefins directed by a resorcinol as a catalytic, hydrogen-bonding template, developed by the MacGillivray group [67, 69].
Scheme 6.5 Examples of mechanochemically conducted copper-catalyzed azide–alkyne Huisgen “click” reactions achieved by using (a) external copper(II) acetate as the catalyst and (b) copper milling equipment as the catalyst source [86, 87].
Scheme 6.6 Mechanochemical ruthenium-catalyzed olefin metathesis in a ball mill [91].
Scheme 6.7 (a) Mechanochemical synthesis of [Cp*RhCl
2
]
2
, the organometallic catalyst used for (b) the mechanochemical C−H activation and halogenation of
o
-phenylpyridine conducted in the planetary mill [98].
Scheme 6.8 Mechanochemical ball milling cyclopropanation of alkenes with diazoacetates using a silver metal foil as the source of silver catalyst [100].
Scheme 6.9 Mechanochemical synthesis of the natural product Leu-enkephalin through a seven-step sequence of solvent-free mechanochemical coupling and thermochemical deprotection steps, developed by the Lamaty group [105].
Scheme 6.10 Mechanochemical synthesis of antidiabetic sulfonyl-urea drugs reported by Tan
et al.
[107].
Scheme 6.11 The mechanochemically enabled synthesis of dumbbell C
120
molecule from C
60
using KCN, discovered by Wang
et al.
[110].
Scheme 6.12 Mechanochemically enabled synthesis of sulfonyl guanidines by copper-catalyzed coupling of carbodiimides and aryl sulfonamides, reported by Tan
et al.
[111].
Figure 6.6 Isolation of elusive aryl
N
-thiocarbamoylbenzotriazoles as bench-stable solids using mechanochemistry, reported by Štrukil
et al.
(a) the comparison of solution-based and mechanochemical milling reactivity and (b) fragment of the crystal structure of a mechanochemically prepared aryl
N
-thiocarbamoylbenzotriazole, identified by structure determination from X-ray powder diffraction data.
Chapter 7: Palladium-Catalyzed Cross-Coupling in Continuous Flow at Room and Mild Temperature
Scheme 7.1 Mechanism for the Suzuki–Miyaura reaction.
Scheme 7.2 Lithiation/borylation/Suzuki–Miyaura cross-coupling sequence for the synthesis of biaryl derivatives.
Scheme 7.3 Lithiation/borylation/Suzuki–Miyaura cross-coupling sequence for the synthesis of biaryl derivatives in a microflow system.
Figure 7.1 Substrate scope of continuous flow lithiation/borylation/Suzuki–Miyaura cross-coupling sequence starting from aryl bromides.
[a]
The Suzuki–Miyaura cross-coupling reaction was finished in 4 min.
Scheme 7.4 Lithiation/borylation/Suzuki–Miyaura cross-coupling sequence of heteroarenes with aryl halides in a flow system.
Scheme 7.5 Substrate scope of continuous flow lithiation/borylation/Suzuki–Miyaura cross-coupling sequence starting from furan derivatives.
[a]
0.44 M NaF aqueous solution was used instead of KOH.
[b]
0.87 M KF aqueous solution was used instead of KOH.
Scheme 7.6 Total synthesis of diflunisal via lithiation/borylation/Suzuki–Miyaura cross-coupling in a microflow system.
Scheme 7.7 Continuous flow Suzuki–Miyaura cross-coupling sequence using SiliaCat DPP-Pd as supported catalyst.
Scheme 7.8 Substrate scope of continuous flow Suzuki–Miyaura cross-coupling sequence with different aryl bromides and 4-methoxyphenylboronic acid.
Scheme 7.9 Substrate scope of continuous flow Suzuki–Miyaura cross-coupling reaction with different aryl bromides/triflate and phenylboronic acid derivatives.
Scheme 7.10 Continuous flow Suzuki–Miyaura cross-coupling on a gram scale of substrate.
Scheme 7.11 Continuous flow Suzuki–Miyaura cross-coupling reaction of phenyl boronic acid with aryl halides using SS-Pd as heterogeneous catalyst.
Scheme 7.12 A schematic diagram of the Suzuki–Miyaura cross-coupling reaction of phenyl boronic acid with aryl halides using SS-Pd as heterogeneous catalyst.
Scheme 7.13 Mechanism of the Heck–Mizoroki reaction.
Scheme 7.14 Mechanism of the Heck–Matsuda reaction.
Scheme 7.15 Diazotization/palladium-catalyzed Heck–Matsuda coupling sequence.
Scheme 7.16 Continuous flow diazotization/homogeneous Heck–Matsuda cross-coupling sequence of aryl amines with methyl acrylate using a three-stream flow device.
Figure 7.2 Substrate scope of continuous flow diazotization/homogeneous Heck–Matsuda cross-coupling sequence starting from aniline derivatives.
[a]
Residence time for the diazotization in reactor 1.
Scheme 7.17 Continuous flow diazotization/heterogeneous Heck–Matsuda cross-coupling sequence of aryl amines with methyl acrylate using a three-stream flow device.
Figure 7.3 Substrate scope of continuous flow diazotization/heterogeneous Heck–Matsuda cross-coupling sequence starting from aniline derivatives.
[a]
Total residence time including reactors 1 and 2.
Scheme 7.18 Oxidative Heck coupling reaction between 4-methoxyphenyl boronic acid and ethyl acrylate.
Scheme 7.19 Continuous flow oxidative Heck cross-coupling sequence of aryl boronic acid with ethyl acrylate using a dual-channel microreactor.
Scheme 7.20 Substrate scope of continuous flow oxidative Heck cross-coupling reaction starting from aryl boronic acids.
Scheme 7.21 Mechanism for the Murahashi reaction.
Scheme 7.22 Lithiation/Murahashi cross-coupling sequence for the synthesis of biaryl derivatives in continuous flow.
Scheme 7.23 Continuous flow lithiation/Murahashi cross-coupling sequence of aryl bromides using a two-stream flow device.
Scheme 7.24 Substrate scope of continuous flow lithiation/Murahashi cross-coupling reaction starting from aryl boronic acids.
[a]
CPME was used as solvent in the presence of TMEDA (3 equiv.) for the Murahashi cross-coupling reaction.
Scheme 7.25 Continuous flow lithiation/Murahashi cross-coupling sequence starting from thiophene.
Chapter 8: Catalysis for Environmental Applications
Figure 8.1 Effect of Pd loading to ZVI immobilized onto activated carbon on 2-chlorobiphenyl (PCB) dechlorination kinetics.
Figure 8.2 (a) Graphene/TiO
2
and (b) graphene/ZnO nanohybrid films displaying the charge transfer mechanisms occurring during the photocatalytic process.
Figure 8.3 (a) Structure of a hybrid organolead halide perovskite. (Cai
et al
. 2013 [84]. Reproduced with permission of Royal Society of Chemistry.) (b) Image of flexible perovskite solar cell on PET/ITO substrate and (c) performance of flexible solar cell pre- and post-bending.
Figure 8.4 Scheme displaying the photocatalytic mechanism occurring within the Ag
3
PO
4
/g-C
3
N
4
composite.
Case Study 1: Magnetic Pd Catalysts for Benzyl Alcohol Oxidation to Benzaldehyde
Figure 1 TEM images of (a) 1.0Pd/MagSBA, (b) 2.0Pd/MagSBA, (c) 3.0Pd/MagSBA, and (d) 4.0Pd/MagSBA, respectively.
Figure 2 XRD patterns of Pd/MagSBA.
Figure 3 Catalytic performance of 3.0Pd/MagSBA: (a) 80 °C, (b) 85 °C, and (c) 90 °C.
Figure 4 Catalytic performance of 2.0Pd/MagSBA: (a) 80 °C, (b) 85 °C, and (c) 90 °C.
Figure 5 Catalytic performance at 85 °C: (a) 4.0Pd/MagSBA, (b) 3.0Pd/MagSBA, (c) 2.0Pd/MagSBA, and (d) 1.0Pd/MagSBA.
Figure 6 Recycling ability of 3.0Pd/MagSBA.
Case Study 2: Development of Hydrothermally Stable Functional Materials for Sustainable Conversion of Biomass to Furan Compounds
Figure 1 Role of Lewis and Brønsted acids in mechanism of xylose dehydration [28].
Figure 2 Yield of furfural using various standard catalyst.
Figure 3 XRD patterns of (a) MIL-101(Cr) and (b) MIL-OTS.
Figure 4 FTIR spectra of MIL-101(Cr) and MIL-OTS.
Figure 5 TEM images of (a) MIL-101(Cr), (b) MIL-OTS-0.5, (c) STEM image of MIL-OTS-0.5, and (d–e) EDS Mapping of MIL-OTS-0.5.
Figure 6 XRD pattern of (a) raw fly ash and (b) AFA.
Figure 7 FTIR spectra of raw fly ash and AFA.
Figure 8 TEM-EDX of AFA showing uniform distribution of Si, Al, O, and S.
Figure 9 XRD patterns of (a) AFA, (b) MIL-101(Cr), and (c) MIL-AFA.
Figure 10 TEM image and EDS of MIL-AFA.
Figure 11 FTIR spectra of MIL-SnP-composite, mesoporous SnP and MIL-101(Cr).
Figure 12
31
P MAS NMR spectra of SnP and MIL-SnP.
Figure 13 TEM-EDS of MIL-SnP composite.
Figure 14 N
2
adsorption-desorption isotherms of catalysts developed.
Figure 15 FTIR-Pyridine spectra of catalysts developed.
Figure 16 TGA profile of catalysts developed.
List of Tables
Chapter 1: Introduction to Room-Temperature Catalysis
Table 1.1 Properties of crude and upgraded oil
Table 1.2 Reusability of the SiliaCat Pd(0) hydrogel in the selective catalytic hydrogenation of
trans
-cinnamic acid under mild conditions
Table 1.3 Comparison of the results obtained from Au NP@SIL-
g
-G with other supported Au catalysts for the oxidation of benzyl alcohol
Chapter 3: Heterogeneous Room Temperature Catalysis – Nanomaterials
Table 3.1 A list of nanomaterials for the room temperature catalytic reactions
Chapter 4: Biocatalysis at Room Temperature
Table 4.1 Examples of α-chiral amines and transaminases sources
Table 4.2 Subdivisions of hydrolases, according to http://www.enzyme-database.org
Table 4.3 Some applications of enzymes and ionic liquids for biocatalysis at room temperature
Table 4.4 Products and conversions (by HPLC) obtained from the transesterification reaction of soybean oil by
Pseudomonas cepacia
lipase (PS-Amano) with alcohols in BMI · NTf
2
at room temperature [209]
Sustainable Catalysis
Energy-Efficient Reactions and Applications
Edited by Rafael Luque and Frank Leung-Yuk Lam
The Editors
Prof. Rafael Luque
Universidad de Córdoba
Departamento de Química Orgánica
Carretera Nacional IV
A, Km. 396
Edificio C-3
14014 Córdoba
Spain
Prof. Frank Leung-Yuk Lam
The Hong Kong University of Science & Technology
Chemical and Biomolecular Engineering
Clear Water Bay
Kowloon
Hong Kong
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Cover Design Formgeber
Chapter 1Introduction to Room-Temperature Catalysis
Eduardo J. Garcia-Suarez1,2,3 and Anders Riisager1
1Technical University of Denmark, Centre for Catalysis and Sustainable Chemistry, Department of Chemistry, Kemitorvet, Building 207, 2800 Kgs. Lyngby, Denmark
2Tecnalia, Energy and Environment Division, Parque Tecnológico de Álava, Leonardo Da Vinci, 11, 01510 Miñano, Spain
3IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao, Spain
1.1 Introduction
The world's energy demand is expected to increase significantly in the coming years as a result of the exponential economic growth of emerging countries, BRIC (Brazil, Russia, India, and China). Such an increased energy request is closely associated with environmental concerns and deficiency in water supply. These key challenges should be addressed by creating and maintaining conditions that allow humans and nature to exist in productive harmony. Only such a sustainable direction will permit fulfilling the social, environmental, and economic requirements of present and future generations and avoid the world passing the point of no return [1].
Chemistry has always played a pivotal role in development of societies by improving the quality of life, the lifespan, and so on. However, despite its many important progresses, chemistry is often recognized more as a problem than as the solution to our daily needs. Indeed, the task of changing the persisting vision that society and governments uphold about chemistry is one of the biggest challenges of chemists for the 21st century; this challenge should start from the design and development of benign and efficient manufacture protocols. To improve chemical production efficiency and fulfill international legislation, a multidisciplinary approach aimed at reducing by-products/waste, optimizing energy utilization, controlling emissions (climatic change), and using renewable materials to avoid hazardous or toxic substances is mandatory. In this connection, the “Green Chemistry” concept, being a list of 12 principles, is one of the most exciting, innovative, and realistic approaches that has emerged in order to minimize the drawbacks of chemical processing and contribute to the protection of the environment [2]. “Green Chemistry” advocates increasing research on new renewable feedstocks, environmentally benign solvents (preferably water), catalysis, and greener technologies, processes, and products. Among the “Green Chemistry” principles, the ninth, focused on catalysis, plays a key role in certifying the world's sustainability by improving processes in the chemical industry, making them more efficient and benign. The development of greener catalytic protocols through the rational design of new catalysts, both homogeneous and heterogeneous, as well as solvent choice is important as it will increase valuation and understanding at the government level and in society.
A “catalyst” is a substance that increases the rate at which a chemical reaction proceeds without itself becoming permanently involved. There are many fundamental parameters in a chemical reaction that can be controlled by selecting the appropriate catalyst, including, for example, energy consumption, selectivity, productivity, and atom economy. Accordingly, the development of new catalysts or catalytic systems can be considered as an important step toward establishing a more green and sustainable chemical industry. In this regard, the design of more effective catalysts and catalytic protocols that allow a chemical process to be carried out at room temperature is a highly beneficial way to minimize both the energy demand and the risk (minimizing safety issues) for employees of a chemical plant. Furthermore, by decreasing the reaction temperature, the selectivity toward the desired product normally increases, thereby minimizing undesired side reactions and by-products. On the other hand, the reaction kinetics can be significantly hampered at room temperature and the catalyst should therefore be selected carefully to provide a system having a sufficiently low activation energy that allows the reaction to proceed at an acceptable rate without auxiliary energy input. Such selected catalysts for room-temperature reaction protocols can be both homogeneous (e.g., organometallic complexes, ionic liquids) and heterogeneous (e.g., metal nanoparticles, supported nanoparticles). Recently, excellent reviews by Lam and Luque have covered this topic in detail [3].
The aim of this chapter is to provide an overview and point out some of the most relevant catalytic systems that allow carrying out catalytic reactions at room temperature. The catalytic systems will be divided in two main groups depending on the nature of the catalyst involved, namely, (i) ionic liquids and (ii) homogeneous and heterogeneous catalyst-containing transition metals from groups 9 to 11 of the periodic table.
1.2 Room-Temperature Homogeneous Catalysts
Homogeneous catalysts are often superior to heterogeneous ones in terms of activity and, in particular, selectivity. In addition, the reaction conditions (temperature, pressure, etc.) are usually milder. However, homogeneous catalysis is hampered by other important issues from an industrial or applicability point of view, such as catalyst recovery and recyclability.
1.2.1 Ionic-Liquid-Based Catalytic Systems at Room Temperature
Ionic liquids are defined as salts only composed of ions, which melt without being decomposed. A special group of ionic liquids are the so-called room-temperature ionic liquids, which are liquid below 100 °C. The first known ionic liquid (ethanolammonium nitrate) was reported in 1888 by Gabriel and Weiner [4]. Later in 1914, Walden reported the synthesis of other ionic liquids such as, for example, ethylammonium nitrate [5], but it was only in 1943 that the term “ionic liquid” was coined by Barrer [6]. In the 1970s to the 1990s, novel ionic liquids were developed and studied by US military researchers to be applied mainly as electrolytes in batteries [7]. In the past 15 years, ionic liquids have become of great importance for scientists due to their unique properties, mainly their low vapor pressure, solubility, easy functionalization (task-specific ionic liquids), and their successful applications in catalysis, nanoparticle stabilization, electrochemistry, medicine, analytical methods, benign reaction media, and so on. One main advantage of ionic liquids is the huge pool available. In principle, this allows the possibility of selecting just the right ionic liquid for a specific application. In catalysis, the selection of the ionic liquid is determined mainly by solubility characteristics (providing often biphasic systems that allow the recovery of the employed catalyst), intrinsic catalytic properties, as well as their thermal and chemical stability. Here, we overview some reactions that are conducted at room temperature in the presence of ionic liquids as catalyst and/or reaction media.
An important subgroup of ionic liquids are the so-called acidic ionic liquids, where a Brønsted or Lewis acid functionality is part of the ionic liquid ions. They have been used to replace traditional mineral acids (MeSO3H, H2SO4, HF) or traditional Lewis acids (AlCl3, FeCl3) successfully and, often, with superior performance. In organic synthesis, the acidic ionic liquids have been extensively used and numerous reports have come out in the past years concerning their use as solvents or catalysts at room temperature. Since it is not possible to survey all these applications, representative examples will be pointed out to show the potential of the acidic ionic liquids in organic synthesis.
α-Aminophosphonates are compounds of great interest due to their biological and chemical applications (antibacterial, antitumor, antiviral, enzyme inhibitors). The synthesis of these compounds is normally carried out through the so-called Kabachnik–Fields reaction in the presence of a dehydrating agent and a Lewis acid. In 2009, Akbari and Heydari used a Brønsted acidic ionic liquid (BAIL) (Figure 1.1a) as catalyst instead of the Lewis acid for the synthesis of α-aminophosphonates through a one-pot, three-component (phosphite, aldehyde or ketone, and amine) reaction [9]. They got excellent results in terms of yield (up to 98%) in short reaction times at room temperature. Furthermore, the employed BAIL catalyst could be recovered and reused up to six times without any deactivation. In 2010, Fang et al. prepared a series of “halogen-free” BAILs to be tested as catalysts in the same reaction and obtained good results at room temperature in aqueous media [10]. In 2014, Peng et al. prepared a different BAIL based on the choline cation (Figure 1.1b), also to be used as catalyst in the same one-pot, three-component reaction. They claimed that their synthesized choline-based BAIL was cheaper and less toxic than the one previously reported by Akbari and Heydari [9]. Excellent results were obtained under solvent-free conditions at room temperature in short time reactions with isolated yields up to 95%. The recyclability of the catalyst was also tested up to six times without any decrease in activity or degradation of the BAIL [8].
Figure 1.1 Brønsted acidic ionic liquids (BAILs) used as catalyst in the synthesis of α-aminophosphonates in a one-pot, three-component reaction.
(Adapted with permission from Ref. [8]. Copyright (2014) Wiley.)
In a recent work, Ying et al. [11] showed the effectiveness in terms of activity and recyclability of using multiple-acidic ionic liquids as catalysts for the synthesis of α-aminophosphonates at room temperature under solvent-free conditions. The same authors used the multiple-acidic ionic liquids in the synthesis of bis-indolylmethanes (Figure 1.2), compounds with biological activity and of great interest in the medical chemistry, under solvent-free conditions and at room temperature. Among the applied multiple-acidic ionic liquids, [TEOA][HSO4] (triethanolammonium hydrogensulfate) showed the best performance, giving the products in excellent yield (up to 90%) after a few minutes of reaction. In addition, the catalytic system was reused up to five times without showing any sign of deactivation [12].
Figure 1.2 Multiple-acidic ionic liquids in the synthesis of bis-indolylmethanes.
(Adapted with permission from Ref. [12]. Copyright (2014) Elsevier.)
The protection of hydroxyl groups is an essential task in organic synthesis to avoid unwanted reactions where, for example, Grignard or alkyllithium reagents are involved. In this connection, acidic ionic liquids have shown to be alternatives to commonly used volatile organic solvents in the protection of alcohols at room temperature with excellent yields in less than 5 min reaction, making the overall process safer and greener [13]. The esterification of carboxylic acids with alcohols is a reaction of great interest because it yields esters that are valuable intermediates in the chemical industry. Chloroaluminate-based acidic ionic liquids, as substitutes of inorganic acids, were first tested in the esterification reaction by Deng et al. [14]. The authors highlight two main advantages of using chloroaluminate-based acidic ionic liquids instead of, for example, sulfuric acid: (i) The insolubility of the produced esters facilitate easy separation from the reaction media and (ii) the recovery and reuse of the employed ionic liquid after removing the water formed during the reaction. Despite these advantages, the well-known high sensitivity of this kind of acidic ionic liquids to moisture or organic acids make them nonideal candidates for the esterification reaction since one of the by-products is water. Esterification of alcohols with acetic acid anhydride was probed to proceed in the presence of BAILs at room temperature, achieving good conversion without detecting any side reactions. Furthermore, due to the insolubility of most of the esters into the ionic liquids, the catalytic system allowed to be recycled and reused up to five times with only a small decrease in activity due to the loss of ionic liquid during the recycling procedure [15]. Upgrading of bio-oil in order to extend the range of its application could be achieved through a Fischer esterification with alcohols in the presence of dicationic ionic liquids with Brønsted acidity at room temperature, overcoming moisture and acidity problems related to bio-oil (Table 1.1) [16].
Table 1.1 Properties of crude and upgraded oil
Properties
Crude oil
Upgraded oil
Moisture (wt%)
32.8
8.2
pH
2.9
5.1
Kinematic viscosity (mm
2
s
−1
)
13.03
4.90
High heating value (MJ kg
−1
)
17.3
24.6
C (%)
41.82
50.64
H (%)
8.75
10.77
O (%)
48.73
38.03
N (%)
0.64
0.39
Source: Xiong et al. 2009 [16]. Adapted with permission of American Chemical Society.
The Diels–Alder reaction is an important organic reaction for the synthesis of natural products and physiologically active molecules, and any improvement in the reaction rate and/or the selectivity is of special interest. In 1999, chloroaluminate-based ionic liquids were tested in the room-temperature Diels–Alder reaction between cyclopentadiene and methylacrylate as a test reaction. The employed ionic liquid showed to be superior to the traditional organic solvents employed so far, yielding high conversion and higher endo/exo selectivity [17]. In the Diels–Alder reaction between cyclopentene and methylacrylate, the selectivity toward the endo product was attributed by Welton and coworkers to the ability of the employed ionic liquid to form H-bonds with the dienophile. The use of ionic liquids offers the potential to be used as solvents for Diels–Alder reactions, substituting even the traditional Lewis acids and extending the application to other reagents that can be sensitive to moisture, oxygen, or to strong Lewis acids [18]. Chiral ionic liquids are an interesting kind of ionic liquids that theoretically could transfer their chirality to the final product when applied as solvent, making them highly attractive for asymmetric synthesis. In this sense, the asymmetric aza-Diels–Alder reaction between asymmetric amines and the Danishefsky's diene was carried out successfully with moderate to high diasteroselectivity at room temperature using a chiral ionic liquid catalyst/reaction media without the presence of Lewis acids or organic solvents [19]. Many other ionic liquids – with or without special modifications – have also been used successfully at room temperature in other organic asymmetric and nonasymmetric reactions, such as Knovenagel condensation [20–22], asymmetric aldol condensation [23], and so on. In general, the use of ionic liquids has demonstrated their potential to make chemical reactions safer, greener, and energetically more efficient; and, in many cases, the use of the ionic liquids allows the formation of biphasic systems that make product separation and reutilization of the catalysts easy. However, their application at the industrial level is still hampered by their relatively high viscosity and price level compared to common reaction media, which give rise to concerns about mass transfer limitations and process economy due to the large amounts required. Hence, to overcome these problems, development of improved ionic liquids and associated technology is needed in the future.
1.2.2 Transition Metal Homogeneous Catalysts
Transition metals, and mainly their organometallic complexes, represent a benchmark in homogeneous catalysis. The complexes are special because their electronic and steric properties – which normally rule the catalytic reaction – can be modified and fine-tuned by choosing the appropriate metal and rational design of the ligand. Transition-metal-based homogeneous catalysts are well known to catalyze many reactions of industrial interest, such as polymerization, carbonylation, hydrogenation, oxidation, cross-coupling, epoxidation, and so on, and have historically contributed to develop systems that work under mild conditions. However, the use of such homogeneous catalysts is hampered by their recovery and separation from the reaction media, which normally is energy intensive. Only a limited number of examples of transition-metal-based catalysts operating at room temperature are reported. Here, a few late transition catalysts – mainly with metals from the groups 9 to 11 – and their performance in reactions at room temperature are discussed.
1.2.2.1 Group 9-Based Homogeneous Catalysts (Co, Rh, Ir)
Homogeneous hydrogenation of arenes at room temperature was performed in 1977 by Muetterties and coworkers with a cobalt complex catalyst, η3-C3H5Co[P(OCH3)3]3 [24]. Such reactions were earlier dominated by heterogeneous metallic systems based mainly on Ni, Pd, Pt and Rh, but these systems were hampered by lack of stereo- and chemoselectivity. The use of homogeneous catalysts enabled the possibility of getting systems where good stereoselectivity as well as chemoselectivity could be achieved.
A rhodium-based catalyst, RhCl(CO)(PMe3)2, was tested in the homogeneous carbonylation of liquefied propane at room temperature yielding butanal with high selectivity [25]. This catalytic system was shown to be a promising alternative for the selective functionalization of gaseous alkanes. A series of water-soluble rhodium complexes obtained by reaction of rhodium precursors with 1,3,5-triaza-7-phosphaadamantane (PTA) were used as catalysts in the isomerization and condensation of allylic alcohol at room temperature in aqueous media, showing advantages over commercial methods [26]. The selectivity of the reaction was easily controlled by the amount of base added, obtaining one of the products in quantitative yield. In addition, these water-soluble catalysts allowed also catalyst recovery and reutilization, making the overall process greener and energetically efficient. Another water-soluble Rh(I)-complex, RhCl(CO)(TPPTS)2 (TPPTS = m-P(C6H4SO3Na)3), was used successfully in the polymerization of terminal alkynes at room temperature under mild reaction conditions. The reactions were carried out under biphasic conditions, which allowed the recovery and reutilization of the catalytic system [27]. The polymerization of these alkynes yielded conjugated systems that are interesting due to their photosensitivity and optical nonlinear susceptibility. The first polymerization of terminal alkynes was performed by Natta using Ziegler catalysts in 1958 [28]. The homogeneous hydrogenation of olefins and acetylenes was carried out efficiently at room temperature and atmospheric pressure of hydrogen with an iridium-based catalyst, [Ir(σ-carb)(CO)(PhCN)(PPh3)] (σ-carb = 7-C6H5-1,2-C2B10H10) [29].
1.2.2.2 Group 10-Based Homogeneous Catalysts (Ni, Pd, Pt)
Among group 10 metals, Ni is more attractive and preferable as catalyst since it is cheaper than Pd and Pt. Ni(NO3)2·6H2O was used as a homogeneous catalyst at room temperature for the production of 2-((1H-benzo[d]imidazol-2-ylamino)(aryl)methylthio)acetates in a multicomponent reaction (MCR) [30].
[Ni(PR2NR′2)2(CH3CN)]2+ complexes (Scheme 1.1) are the first example of homogeneous catalysts employed successfully in the electrocatalytic oxidation of formate to be used in fuel cells [31]. Mechanistic studies showed that the pendant amine plays the main role in the rate-determining step that involves the transfer of a proton from the formate to the amine. The turnover frequencies (TOFs) for the catalyst employed were comparable to any other reported formate/formic acid oxidation catalysts. Asymmetric α-arylation of ketones with chloro- and bromoarenes has been catalyzed by a homogeneous Ni(0)-complex, [(R)-BINAP]Ni(η2-NC-Ph) ((R)-BINAP = (R)-(+)-(1,1′-Binaphthalene-2,2′-diyl)bis(diphenylphosphine)), in toluene at room temperature at high reaction rates with excellent yield (up to 91% and above 98% of enantiomeric excess, ee) [32]. The advantage of running the reaction at room temperature is the attenuation of the decomposition of the Ni(0) complex to form the less active Ni(I) species.
Scheme 1.1 Synthetic procedure for [Ni(PR2NR′2)2(CH3CN)]2+ complexes.
(Galan et al. 2012 [31]. Reproduced with permission of American Chemical Society.)
Water extract of rice straw ash (WERSA) was employed as reaction media together with Pd(OAc)2 without the presence of any ligand, base, or promoter in the Suzuki–Miyaura cross-coupling reaction at room temperature of different bromoaryl compounds and arylboronic acids, yielding good to excellent conversions [33]. WERSA was prepared by burning the rice straw to ashes that were further suspended in water and filtered off (Figure 1.3). Since WERSA is composed of different cations and anions and due to its basic nature (Na+, K+, Mg2+, Ca2+ and OH−), the addition of a base – essential for the Suzuki reaction – was not needed. WERSA is an aqueous-based reaction medium where the palladium can be immobilized and after extraction of the reaction products with a nonpolar organic solvent, such as diethylether, the WERSA-Pd system can be recovered and reused. In this manner, the system could be reused up to six times without significant loss of activity after the fourth run, probably due to metal leaching into the organic phase.
Figure 1.3 WERSA isolation procedure from rice straw.
(Boruah et al. 2015 [33]. Reproduced with permission of Royal Society of Chemistry.)
Catalytic oxidation of secondary alcohols to ketones have been carried out efficiently at room temperature or slightly higher temperature (38 °C) in 1977 with a catalytic system formed by PdCl–NaOAc using molecular oxygen as oxidant [34]. This catalytic system substituted the previous PdCl–Cu(II)-salt catalytic system, where higher temperatures (70–120 °C) were required. A series of five-membered P,C-orthopalladate complexes with different monodentante ligands were synthesized and tested in the Suzuki–Miyaura cross-coupling at room temperature [35]. The palladium-based catalyst, [Pd(PPh3)(Cl){P(OPh)2(OC6H4)}], showed good to excellent activity for all the substrates tested including the cheaper, more available, less reactive, and challenging arylchlorides.
A homogeneous diplatinum complex, [Pt2(μ-dppm)] (dppm = Ph2PCH2PPh2) showed to be effective in the catalytic synthesis of dimethylformamide through the hydrogenation of CO2 at room temperature under mild reaction conditions. This catalyst substituted previous ones where the required reaction conditions were more harsh [36].
1.2.2.3 Group 11-Based Homogeneous Catalysts (Ag, Au)
A homogeneous silver catalyst was used for the synthesis of carboranes in temperatures ranging from room temperature to 40 °C [37]. Carbonanes are boron clusters with unique structural and electronic properties with potential use in creating new diagnostics, therapeutics, and electronically tunable materials. The preparation of these compounds usually required high temperatures (80–120 °C) [38–40], but the tested homogeneous silver catalysts (Scheme 1.2) facilitated preparation of functionalized carboranes in good to excellent yield at reduced reaction temperatures in the range from room temperature to 40 °C. The lower reaction temperature opens up the possibility of preparing carboranes from thermally sensitive alkynes that otherwise undergo degradation or side reactions at higher temperatures. McNulty
