Pavan Kumar Kanchrala for their valuable suggestions, encouragement and evaluations throughout my research period. I am very thankful to the academic department, student affairs and research and development department of IIT Guwahati for their help whenever I needed.
Indian Institute of Technology Guwahati
Department of Chemistry
Declaration
Indian Institute of Technology Guwahati
CERTIFICATE
Hydrofunctionalization reactions
Organometallic systems have been reported to efficiently catalyze (de)hydrofunctionalization reactions such as (de)hydrogenation, 18-19 hydroamination, 20 hydroetherification, 21-23 hydrosilylation, 24 hydroboration, 25 hydroformylation26 and hydrocarboxylation.27 Ideally, the catalytic conversion systems involving organometallic systems. . Kanu Das, Ph.D Thesis, IIT Guwahati 4 often mitigates the stoichiometric amount of waste generation leading to a nuclear-economy transformation involving a minimum number of steps.
Representative functionalization reaction
In both cases, the insertion mode determines the regioselectivity in the final products, leading to the Markovnikov (branched) or the anti-Markovnikov (linear) products.
Plausible catalytic cycle involved in hydrofunctionalization reaction
- Hydrogenation and dehydrogenation
Equilibrium between hydrogenation and dehydrogenation
Kanu Das, Ph.D Thesis, IIT Guwahati 5 via two possible routes; olefin/alkyne insertion into either the M−H bond (Path A) or the M−X bond (Path B). Kanu Das, Ph.D Thesis, IIT Guwahati 6 adducts, 46 metal-oxides, 47 metal hydrides, 48 metal-organic frameworks, 49 zeolites50 and organometallic complexes.51 Usually, carbon dioxide, 52 aldehydes, 53 ketones, 54 esters, 55 Amides, 56 acids, 56 alkynes, 57 alkenes, 58 nitro groups, 59 nitrile moieties60 and aromatic rings61 (Scheme 1.6) are mainly used as unsaturated substrates for hydrogenation.
Schematic representation of organometallic complex catalyzed hydrogenation of various unsaturated substrates
- Pincer complexes
- Synthesis protocol of several forms of pincer complexes
- Synthesis of pincer-iron(0) complex from its dichloride precursor
- Synthesis of pincer-iron dihydride complex from its dihalocomplex
- Dehydrogenation of alcohols
- Dehydrogenative coupling (N/C-alkylation) reaction
- Imine synthesis from alcohols and/or amines
- Heterocyclic derivative synthesis from amino alcohols with alcohols
Kanu Das, Ph.D Thesis, IIT Guwahati 10 gave monohydridoiron complex 1.71 (Scheme 1.8) which showed good hydrogenation activity. Kanu Das, Ph.D Thesis, IIT Guwahati 14 the PNN ruthenium catalyst resulted in extraordinary acceptorless dehydrogenation of alcohols to esters under mild conditions (Scheme 1.17).
Catalytic dehydrogenative coupling of secondary alcohol with amino alcohol by pincer complexes. 127-132
- Azines synthesis from alcohols with hydrazine
In this regard, Huang and co-workers reported a dehydrogenation coupling of primary amines with imines in the presence of pincer-Ru 1.116 with the liberation of ammonia (Scheme 1.22).126 On the other hand, Milstein and co-workers reported an environmental connection Benign imine synthesis with the release of molecular hydrogen from alcohols and amines by pincer-Ru 1.115. This reaction also tolerates a variety of alcohols and amines for the synthesis of imines with high turnover numbers (Scheme 1.22).94.
Pincer-ruthenium catalyzed primary amine synthesis starting from ammonia and alcohol. 142
- Hydrogenation of alkenes and alkynes
- Hydrogenation of carbon dioxide and its derivatives
- Hydrogenation of carbonate and carbamate derivatives
- Pincer-iron catalyzed 3-hydroxyacrylates production from aldehydes
- Olefin polymerizations by (bis)imino pincer-complexes
Guan and colleagues reported the first example of PNP pincer iron 1.182 catalyzed hydrogenation of unactivated esters to alcohols (Scheme 1.38).207. Peris and colleagues reported a CNC pincer ruthenium complex for the catalytic transfer hydrogenation of ketone in the presence of 0.1 M KOH in isopropanol (Scheme 1.39).88 In.
A few valuable transformations of olefins catalyzed by (bis)imino based pincer- iron complex. 223
- Objectives
- References
- Introduction
In this context, Celik235, 237 and Goldman235-237 have shown that the dehydrogenation of alkane to alkene is more favorable with a heterogeneous molecular catalyst (solid support on silica) than with its analogous homogeneous system (Scheme 1.44).235 They showed that the thermal cracking dodecene at 340 °C yielded two lighter olefins, which hydrogenate to give rise to lighter alkane via transfer hydrogenation. Chusov and colleagues reported a unique reaction pathway for the synthesis of higher order amines using carbonyls, amines and carbon monoxide as starting materials (Scheme 2.2).8 With this methodology, they demonstrated well the synthesis of higher order amines. excellent yields with sales as high as 2465 TON via a deoxygenative route using ruthenium trichloride as a catalyst precursor.
Ru-catalyzed reductive amination of carbonyl compounds in the presence of high pressure of carbon monoxide. 8
Gram-scale synthesis of Ladasten, an anxiolytic agent, has been reported and following this strategy reduces the cost-effectiveness of this reaction. Kanu Das, PhD Thesis, IIT Guwahati 47 Beller and co-workers demonstrated a facile reaction using commercially available Karstedt catalyst 2.7 with dppe ligand combination 2.6 under mild reaction conditions. Not surprisingly, this has become one of the popular routes to carry out N-alkylation (Scheme 2.1)6, since alcohols are readily available, less hazardous, and the reaction involves water as the only by-product with almost no waste generation (Scheme The first stage involves s metal-catalyzed dehydrogenation of an alcohol to form a metal-dihydride complex and the corresponding aldehyde or ketone, which proceeds to an uncatalyzed condensation reaction with an amine to form the corresponding imine.
Hydrogen-borrowing strategy for N-Alkylation
- Objectives
Kanu Das, Ph.D Thesis, IIT Guwahati 48 Scheme 2.5: Transition Metal Catalyzed N-Alkylation of Amines with Alcohols.16-23. Kanu Das, Ph.D Thesis, IIT Guwahati 50 sulfonamides with primary alcohols in the presence of K2CO3 and air (Scheme 2.9).92 Excellent yields (up to 99 TON) are obtained in this reaction, where active species appear to be a bissulfonylated amidine intermediate with the Cu(OAc)2/K2CO3/air system. Kanu Das, Ph.D Thesis, IIT Guwahati 51 scope.34, 43 The N-heterocyclic carbene (NHC) ligand 2.30-based ruthenium system catalyzed N-alkylation of amines with alcohols, exhibiting high activity and selectivity under low catalyst loading (scheme 2.11) .97.
Transition metal catalyzed N-alkylation using hydrogen-borrowing strategy
- Result and Discussions
- Synthesis of pincer bis(imino) ligands and their complexes
- Scope of the pincer-ruthenium catalyzed N-Alkylation reaction
Kanu Das, PhD Dissertation, IIT Guwahati 59 Table 2.2: N-Alkylation of Aniline with Benzyl Alcohol at Various Base and Catalyst Loadings 2.48d. Kanu Das, PhD Thesis, IIT Guwahati 61 Table 2.4: N-alkylation of various primary amines with multiple alcohols catalyzed by 2.48d.a. Moderate turns (products 2,50p and 2,50q, Table 2.4) were obtained when alcohols containing heterocyclic substituents were used as the alkyl precursor.
Schematic diagram of N-methylation of amine via various methodologies
Using an iron carbene complex, Darcel and co-workers reported the methylation of secondary amines under mild reaction conditions (Scheme 2.24). Yang and co-workers reported a one-pot ruthenium-catalyzed methylation of nitroarenes using methanol as the methylating agent (Scheme 2.25). Kanu Das, PhD Thesis, IIT Guwahati 66 pincer catalytic system is still important in amine methylation using methanol as alkylating agent.
Unexpected products obtained in N-methylation of 4-(trifluoromethyl)aniline
- Control experiment
- Plausible mechanism
- Computational study
Rests on minor peaks can also be assigned to several derivatives of 2.48d that are thought to be involved in the catalytic cycle (Scheme 2.29-2.30). The -hydride elimination of the benzyl oxide in complex 2.61c by TS-2.62c can lead directly to the formation of 2.66c together with benzaldehyde (2.29′) (purple dotted arrows, Scheme 2.30). Kanu Das, Ph.D Thesis, IIT Guwahati 74 and hydrogenation segment (Figure 2.7) was modeled by DFT studies.
Synthetic path for the formation of 2-substituted benzimidazoles
- Conclusion
- Experimental Section
- General methods and material
- General synthesis procedure for N-alkylation
- Computational Details
- References
- Introduction
- Objectives
- Result and Discussion
Gülcemal and colleagues reported the imidazol-2-ylidene ligand based iridium(I) 3.13 catalyzed β-alkylation of secondary alcohols with primary alcohols. Bera and colleagues reported Ir-N-heterocyclic carbene 3.14 catalyzed -alkylation of secondary alcohols with primary alcohols. Kundu and colleagues reported a series of tang ruthenium catalysts for -alkylation of secondary alcohols with primary alcohols.
Synthesis of pincer-ruthenium carbonyl complexes based on bis(imino) pyridine
- a (x mol %)
- Mechanism of β-alkylation of Alcohols Catalyzed by 3.30 and 3.31
Complex 3.31a crystallizes in the monoclinic space group P21/n−1 with two symmetrically nonequivalent molecules in the asymmetric unit. Complex 3.31a consists of one molecule of acetone and two molecules of water in the crystal lattice. This is supported by the fact that the entire RDS is present in the dehydrogenation segment (Scheme 3.16-17 and mechanistic studies below).
Scheme 3.16: Plausible mechanism involved catalytic dehydrogenation of alcohols and the formation of -alkylated ketone
- Quantum Mechanical Calculations on the NNN Pincer-Ruthenium (3.30/3.31) Catalyzed -Alkylation of Alcohols
- Conclusion
- Experimental Section
- General methods and materials
- Computational details
- References
- Introduction
This was followed by solvent evaporation to give a dark brown solid which was washed with dry diethyl ether (3 x 5 mL) followed by hexane (2 x 5 mL) to give 0.041 g of 3.31b as a tan solid in 81% yield . This was followed by solvent evaporation to give a dark brown solid which was washed with dry diethyl ether (3 x 5 mL) followed by hexane (2 x 5 mL) to give 0.047 g of 3.31c as a green colored solid in 80% yield. This was followed by solvent evaporation to give a dark brown solid, which was washed with dry diethyl ether (3 x 5 mL) followed by hexane (2 x 5 mL) to give 0.036 g of 3.31d as a yellowish-brown solid in 80% yield.
Fermentation performed by enzyme in the ABE process
The rapidly depleting fossil fuels in combination with the ever-increasing energy demand have triggered an intense search for the alternative energy resources.1 In addition to energy security, alternative energy sources are essential for the protection of the environment.2 Compared to conventional gasoline, ethanol is widely accepted to be a sustainable fuel given its easy availability through the crop fermentation process (ABE: Acetone-Butanol-Ethanol; process, Scheme 4.1).3-4. Kanu Das, Ph.D Thesis, IIT Guwahati 136 isobutyraldehyde and butyraldehyde.8 Further hydrogenation of butyraldehyde yields n-butanol (oxo synthesis; Scheme 4.2).8 Similarly, under low pressure and temperature, propylene has been converted to n- butanol using carbon monoxide and water.
Butanol synthesis from propylene
- Ethanol vs butanol
- Homogenous organometallic catalysts towards biofuel production
These limitations can be circumvented by using n-butanol, which not only has a higher energy density (86%), but is also non-corrosive while being immiscible with water (Table. Kanu Das, Ph.D.- thesis, IIT Guwahati 140 the composition of the catalyst and the density and strength of the associated base sites are very important.54 involving the conversion of bio-ethanol to bio-butanol with water as the only by-product has been widely explored.55- 58 Based on the hydrogen-borrowing (HB) strategy (Scheme 4.3), this reaction involves alcohol dehydrogenation to aldehyde, followed by aldol condensation and hydrogenation of the resulting higher ,-unsaturated aldehyde to the higher molecular weight alcohol product.
Hydrogen-borrowing strategy for the upgradation of ethanol to n-butanol
In this context, methods that upgrade ethanol either to n-butanol or to higher analogues with higher energy density24 are the subject of great interest. Kanu Das, Ph.D Thesis, IIT Guwahati 141 Wass and co-workers presented ruthenium-based complexes for catalyzing the ethanol upgrading reaction. Later, Wass and co-workers reported the use of ruthenium 6-complex 4.9 along with various bidentate ligands (4.11a-d) towards ethanol upgrading.
Pincer-Ru and pincer-Mn catalysts reported for the upgradation of ethanol to n- butanol
- Objective
- Result and discussion
- Synthesis of bis(benzimidazole) ligands and their complexes
- Catalytic transformation of ethanol to bio-butanol under thermal condition
Therefore, the optimization conditions were re-evaluated for ethanol upgrading using (Cy2NNN)RuCl2(CO) (4.20a) (Table 4.4) at 140 °C in the presence of various bases. Kanu Das, Ph.D Thesis, IIT Guwahati 147 Table 4.5: Guerbet reaction catalyzed by phosphine-based pincer-ruthenium complexes.a. Kanu Das, Ph.D Thesis, IIT Guwahati 148 Table 4.6: Guerbet reaction catalyzed by carbonyl-based pincer-ruthenium complexes.a.
Rate equation for the 4.22a catalyzed ethanol upgradations to n-butanol
- Catalytic transformation of ethanol to biobutanol under microwave condition The studies were initiated by repeating the best results reported in the above discussion, where,
- Mechanistic studies on the upgradation of ethanol catalyzed by pincer-ruthenium catalysts
Kanu Das, Ph.D Thesis, IIT Guwahati 153 Table 4.9: Upgrading of ethanol catalyzed by 4.22a under conventional and microwave heating.a. Various inorganic and organic bases have been screened for the Guerbet reaction in the presence of (Bim2NNN)RuCl2(CO) (4.22a) (Table 4.10). The initial rate of the 4.22a-catalyzed Guerbet reaction in the presence of NaOH was comparable to that carried out in the presence of NaOEt albeit with 50% of the productivity (entry 7 vs. 1, Table 4.10).
Mechanistic studies on the upgradation of ethanol catalyzed by pincer-ruthenium catalysts
- Upgradation of ethanol catalyzed by pincer-ruthenium catalysts immobilized on solid supports
The region of the corresponding 1 H NMR spectra representing the hydride signal is given in the inset. The evolution of H2 in these reactions has been confirmed by headspace GC analysis (Figure 4.11).70. Kanu Das, Ph.D Thesis, IIT Guwahati 166 Better results were obtained when 4.22c was heterogenized with a polar OH group in the para position of the arene ring.
Upgradation of ethanol catalyzed by phosphine based pincer-ruthenium catalysts immobilized on solid supports
- Experimental section
- Computational details
- References
During the reaction, the color of the reaction mixture changed from brown to pink. During the course of the reaction, the color of the reaction mixture changed from brown to straw color. During the reaction, the color of the reaction mixture changed from pink to brown.
