Transition metal-catalyzed substitution of alcohols by N-nucleophiles (or N-alkylation of amines and related compounds with alcohols) avoids the use of alkylating agents by means of borrowing hydrogen (BH) activation of the alcohol substrates. Water is produced as the only by-product, which makes the “BH” processes atom-economic and environmentally benign. Diverse types of homogeneous organometallic and heterogeneous transition metal catalysts, and substrates such as N-nucleophiles including amines, amides, sulfonamides and ammonia, and various alcohols, can be used for this purpose, demonstrating the promising potential of “BH” processes to replace the procedures using traditional alkylating agents in pharmaceutical and chemical industries. Borrowing hydrogen activation of alcohols for C–N bond formation has recently been paid more and more attention, and a lot of new and novel procedures and examples have been documented. This critical review summarizes the recent advances in “BH” substitution of alcohols by N-nucleophiles since 2009. “Semi-BH” N-alkylation processes with or without an external hydrogen acceptor are also briefly presented. Suitable discussion of the “BH” strategy provides new principles for establishing green processes to replace the relevant traditional synthetic methods for C–N bond formation.

Substitution of alcohols by N-nucleophiles via transition metal-catalyzed dehydrogenation

Continuous flow synthesis. A pharma perspective.

Preface.- Acknowledgements.- 1: Introduction.- 1.1. Catalysis. 1.2. Homogeneous catalysis. 1.3. Historical notes on homogeneous catalysis. 1.4. Characterization of the catalyst. 1.5. Ligand effects. 1.6. Ligands according to donor atoms. 2: Elementary Steps.- 2.1. Creation of a 'vacant' site and co-ordination of the substrate. 2.2. Insertion versus migration. 2.3. beta-Elimination and de-insertion. 2.4. Oxidative addition. 2.5. Reductive elimination. 2.6. alpha-Elimination reactions. 2.7. Cycloaddition reactions involving a metal. 2.8. Activation of a substrate toward nucleophilic attack. 2.9. sigma-Bond metathesis. 2.10. Dihydrogen activation. 2.11. Activation by Lewis acids. 2.12. Carbon-to-phosphorus bond breaking. 2.13. Carbon-to-sulfur bond breaking. 2.14. Radical reactions. 3: Kinetics.- 3.1. Introduction. 3.2. Two-step reaction scheme. 3.3. Simplifications of the rate equation and the rete-determining step. 3.4. Determining the selectivity. 3.5. Collection of rate data. 3.6. Irregularities in catalysis. 4: Hydrogenation.- 4.1. Wilkinson's catalyst. 4.2. Asymmetric hydrogenation. 4.3. Overview of chiral bidentate ligands. 4.4. Monodentate ligands. 4.5. Non-linear effects. 4.6. Hydrogen transfer. 5: Isomerisation.- 5.1. Hydrogen shifts. 5.2. Asymmetric isomerisation. 5.3. Oxygen shifts. 6: Carbonylation of Methanol and Methyl Acetate.- 6.1. Acetic acid. 6.2. Process scheme Monsanto process. 6.3. Acetic anhydride. 6.4. Other systems. 7: Cobalt Catalysed Hydroformylation.- 7.1. Introduction. 7.2. Thermodynamics. 7.3. Cobalt catalysed processes. 7.4. Cobalt catalysed processes for higher alkenes. 7.5. Kuhlmann cobalt hydroformylation process. 7.6. Phosphine modified cobalt catalysts: the shell process. 7.7. Cobalt carbonyl phosphine complexes. 8: Rhodium Catalysed Hydroformylation.- 8.1. Introduction. 8.2. Triphenylphosphine asthe ligand. 8.3. Diphosphines as ligands. 8.4. Phosphites as ligands. 8.5. Diphosphites. 8.6. Asymmetric hydroformylation. 9: Alkene Oligomerisation.- 9.1. Introduction. 9.2. Shell-higher-olefins-process. 9.3. Ethene trimerisation. 9.4. Other alkene oligomerisation reactions. 10: Propene Polymerisation.- 10.1. Introduction to polymer chemistry. 10.2. Mechanistic investigations. 10.3. Analysis by 13CNMR spectroscopy. 10.4. The development of metallocene catalysts. 10.5. Agostic interactions. 10.6. The effect of dihydrogen. 10.7. Further work using propene and other alkenes. 10.8. Non-metallocene ETM catalysts. 10.9. Late transition metal catalysts. 11: Hydrocyanation of Alkenes.- 11.1. The adiponitrile process. 11.2. Ligand effects. 12: Palladium Catalysed Carbonylations of Alkenes.- 12.1. Introduction. 12.2. Polyketone. 12.3. Ligand effects on chain length. 12.4. Ethene/propene/CO terpolymers. 12.5. Stereoselective styrene/CO terpolymers. 13: Palladium Catalysed Cross-Coupling Reactions.- 13.1. Introduction. 13.2. Allylic reaction. 13.3. Heck reaction. 13.4. Cross-coupling reaction. 13.5. Heteroatom-carbon bond formation. 13.6. Suzuki reaction. 14: Epoxidation.- 14.1. Ethene and propene oxide. 14.2. Asymmetric epoxidation. 14.3. Asymmetric hydroxilation of alkenes with osmium tetroxide. 14.4. Jacobsen asymmetric ring-opening of epoxides. 14.5. Epoxidations with dioxygen. 15: Oxydation with Dioxygen.- 15.1. Introduction. 15.2. The Wacker reaction. 15.3. Wacker type reactions. 15.4. Terephthalic acid. 15.5. PPO. 16: Alkene Metathesis.- 16.1. Introduction. 16.2. The mechanism. 16.3. Reaction overview. 16.4. Well-characterised tungsten and molybdenum catalysts. 16.5. Ruthenium catalysts. 16.6. Stereochemistry. 16.7. Catalyst decomposition. 16.8. Alkynes. 16.9. Industrial applications. 17: Enantioselective Cyclopropanation.-

Piet W. N. M. Van Leeuwen. Homogeneous catalysis—understanding the art. Kluwer, Dordrecht, 2004, 407 pp; (UK). ISBN 1‐4020‐1999‐8

A series of new iridium(III) complexes containing bidentate N-heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHC?OR, R=H, Me) were prepared. The complexes catalyzed the ...

https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10.1002/chem.201201845

A highly active bifunctional iridium complex with an alcohol/alkoxide-tethered N-heterocyclic carbene for alkylation of amines with alcohols.

Separation/recycling methods for homogeneous transition metal catalysts in continuous flow

This paper reports the use of an immobilised ruthenium complex in a continuous flow process for the N -alkylation of morpholine with benzyl alcohol. The ruthenium-based catalyst was supported on a phosphine bound polymer. Screening experiments were first performed in a batch reactor, with a 16 vol% mixture of morpholine and benzyl alcohol (stoichiometric molar ratio of 1:1) in toluene as the solvent. Operating at 110 °C for 24 h, it was shown that high conversions (>99%) into the desired tertiary amine could be achieved. This reaction was then shown to be viable in a continuous flow reactor, where the catalytic polymer beads were retained in the bed. Operating at 150 °C and using p -xylene as a solvent, the conversion into the desired tertiary amine was shown to be as high as 98%. This approach is clearly very promising, as it provides a greener and more atom efficient route for the production of secondary and tertiary amines in the pharmaceutical industry.

Firas A Al Badran

Papers

Production of pharmaceuticals: Amines from alcohols in a continuous flow fixed bed catalytic reactor