2-Hydroxypyridine-Ligated Pd-complexes as pre-catalysts in Hydrogen Borrowing Chemistry α -Alkylation of Ketones Using Alcohols

Abstract

An efficient method for selective alpha-alkylation of ketones with alcohols was developed using
2-hydroxypyridine-based ligands coordinated by palladium as pre-catalysts. The reactions were
performed without additional additives under mild reaction conditions. The method is
environmentally friendly to build C-C bond as water is the only byproduct. This tandem reaction
proceeds via dehydrogenation reaction, aldol condensation and hydrogenation processes using
hydrogen borrowing from the alcohols. The pre-catalyst was characterized by NMR, IR and XRD.
Time profile study investigated by NMR and GC.

Popular Abstract

In certain parts of chemistry, it is important to be able to design organic molecules so that they
have exactly same structure that you are looking for. C-C bond formation is very important
reaction in synthesis of products such as pharmaceuticals, natural products, agrochemical and in
the plastics industry. There are variety of organic reactions that can be used to couple and build
molecules differently.
Recently, there has been great interest in using alcohols as starting materials for C-C bond
formation processes. As they are less toxic, cheap, environmentally friendly. Alcohols are readily
available alkylating agents however they are unreactive as alkylating agents because hydroxy
group cannot be easily replaced by nucleophilic reagents. The common ways to convert alcohols
to carbonyl compounds is by using wide range of oxidizing agents in stoichiometric and over
stoichiometric amount by using metal oxides or metal salts for oxidation. These procedures
produce heavy metal waste that is not compatible with environmental regulations. Therefore,
the search for environmentally friendly, selective, and efficient methods is a great challenge for
chemists. Metal catalyzed dehydrogenation or oxidative dehydrogenation have been found an
interesting alternative. Catalysis has become one of the cornerstones in organic synthesis, as it
increases the rate of a chemical reaction, theoretically without being consumed itself. This occurs
by lowering the activation energy compared to uncatalyzed reaction.
Transition metal catalyzed cross coupling reaction between alcohols and ketones is attractive
strategy for alpha alkylation of ketone. 2-Hydroxy pyridine ligands have been found to catalyze
hydrogenation and dehydrogenation reactions. Therefore, the aim of the project is to prepare 2-
hydroxy pyridine and quinoline ligands then coupled with palladium chloride to study
hydrogenation and dehydrogenation reactions between alcohols and ketones. An advantage of
this reaction is it follows borrowing hydrogen approach for α-alkylation of benzyl alcohol with
acetophenone and produces water as only byproduct which is in accordance with green
chemistry. The reaction is proceeding via hydrogen transfer strategy and alcohols are source of
hydrogen.
The reactions were performed without additional additives under mild reaction conditions using
KOtBu, 1-Pd catalyst in toluene at 120oC for 48 hours under nitrogen in carousal. The reaction
proceeds via dehydrogenation reaction, aldol condensation and hydrogenation processes using
hydrogen borrowing approach.

• author: Kanwal, Ayesha
• supervisor: Magnus Johnson
• organization: Department of Chemistry
• course: KEMR32 20172
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: Hydrogen Borrowing in activation of alcohols, Palladium in Catalysis, hydrogenation and dehydrogenation reactions, hydrogen borrowing concept for hydrogenation and dehydrogenation reactions, 2-hydroxyquinoline Ligand, 2-hydroxy pyridine ligands, inorganic chemistry, oorganisk kemi
• language: English
• id: 8933301
• date added to LUP: 2018-02-01 11:40:22
• date last changed: 2018-02-01 11:40:22