Dr. Andrei Dragan, Asian Journal of Organic Chemistry, talked to Professor Jian-Mei Lu, College of Chemistry and Materials Engineering, Wenzhou University, China, about her latest article in the journal on the synthesis of novel NHC–Pd(II) complexes.
Professor Lu, could you start by briefly explaining the focus of your paper?
In this study, we wanted to develop a novel type of N-heterocyclic carbene-palladium(II)-2-methyl-4,5-dihydrooxazole complexes and investigate their application on the chemoselective mono-Suzuki–Miyaura coupling of dichlorobenzenes. The method can allow the conversion of easily available dichlorobenzenes into synthetically useful chlorobiphenyls.
What makes this method stand out compared to other chemoselective mono-Suzuki–Miyaura coupling reactions?
Usually, chemoselective mono-Suzuki–Miyaura coupling reactions were carried out for dibromobenzenes, iodobromobenzenes, and bromochlorobenzenes. Comparably, very little attention was paid to dichlorobenzenes, which are usually more attractive owing to their higher availability and lower cost. However, these are usually inert because of the stronger bond (C–Cl).
Recently, N-heterocyclic carbenes and their metal complexes have become a big challenge to phosphine–metal complexes because most phosphine ligands are air-, temperature-, and/or moisture-sensitive. Therefore, it is a very attractive challenge for synthetic organic chemists to develop stable, highly active N-heterocyclic carbene–palladium complexes by short synthetic routes and to use them in a highly chemoselective mono-Suzuki–Miyaura coupling of dichlorobenzenes.
How long did it take to put this manuscript together (from initial idea, to actual lab work and submission)?
About one and a half years.
What was the most challenging part of this project?
Although in our current method, the mono-chemoselectivity is satisfactory, disubstituted products are difficult to avoid in most cases even under our optimal conditions.
Have you attempted to catalyze any other reactions using your NHC–Pd(II) complexes?
We have used them in a mono-Buchwald–Hartwig coupling of dichlorobenzenes, but the effect was not as good as we thought.
Do you have any plans for future work extending from this study? If so, could you please provide some details?
Further applications of this type of NHC–Pd(II) complexes in the coupling of aryl chlorides are being done in our group. In addition, we may use these catalysts in other chemoselective C–C bond formations. Applications of the mono-Suzuki–Miyaura coupling products in materials chemistry are also underway.
The article they talked about
- Synthesis of N-Heterocyclic Carbene-Pd(II)-2-Methyl-4,5-Dihydrooxazole Complexes and Their Application Toward Highly Chemoselective Mono-Suzuki–Miyaura Coupling of Dichlorobenzenes,
Jian-Mei Lu, Kai-Xin Sun, Qian-Wei He, Bin-Bin Xu, Xiang-Ting Wu,
Asian J. Org. Chem. 2018.