FULL PAPER Novel (N‐heterocyclic carbene)Pd(pyridine)Br 2 complexes for carbonylative Sonogashira coupling reactions: Catalytic efficiency and scope for arylalkynes, alkylalkynes and dialkynes Mansur Ibrahim | Imran Malik | Waseem Mansour | Muhammad Sharif | Mohammed Fettouhi | Bassam El Ali Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia Correspondence Bassam El Ali, Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia. Email: belali@kfupm.edu.sa Funding information NUS/KFUPM collaboration; King Abdulaziz City for Science and Technol- ogy, Grant/Award Number: 14‐PET165‐04 New N,N′‐substituted imidazolium salts and their corresponding dibromidopyridine–palladium(II) complexes were successfully synthesized and characterized. Reactions of palladium bromide with the newly synthesized N,N′‐substituted imidazolium bromides (2a and 2b) in pyridine afforded the corresponding new N‐heterocyclic carbene pyridine palladium(II) complexes (3a and 3b) in high yields. Their single‐crystal X‐ray structures show a distorted square planar geometry with the carbene and pyridine ligands in trans position. Both complexes show a high catalytic activity in carbonylative Sonogashira coupling reactions of aryl iodides and aryl diiodides with arylalkynes, alkylalkynes and dialkynes. KEYWORDS alkynones, aryl diiodides, carbonylative Sonogashira coupling, dialkynes, Pd–NHC complex 1 | INTRODUCTION Ynones (α,β‐acetylenic carbonyl compounds) are impor- tant structural moieties found in natural products, biologically active compounds and agrochemicals. [1] They are also precursors for the synthesis of a variety of organic compounds, especially aromatic heterocycles such as pyrazoles, [2,3] quinolones, [4] furans [5] and pyrimi- dines. [1,6–8] Traditional methods for the synthesis of ynones often involve multistep reactions and they are also associated with side reactions. [9] Another way for their synthesis is the catalytic carbonylative Sonogashira coupling reaction of aryl halides with terminal alkynes in the presence of palladium complexes. [10] This method offers access to a variety of ynones via a single step and under mild reaction conditions. Palladium‐catalysed carbonylation reactions are now widely recognized as a very important tool in industrial and organic chemistry. Palladium‐catalysed carbonylation chemistry allows the direct synthesis of carbonyl compounds using readily available feedstocks such as carbon monoxide (CO). [10–13] Several palladium complexes and supported palladium catalysts have been considered and tested in catalytic carbonylative Sonogashira coupling reactions. [14–36] However, the use of phosphine, the low catalyst activity, the relatively large loading of catalyst and the need for high CO pressure were drawbacks. [37–42] Recently, much attention has been paid to the devel- opment of N‐heterocyclic carbene (NHC) metal com- plexes, and notable advances have been made especially for their applications as organometallic catalysts. [43–58] This is attributed to the ability of NHC ligands to provide highly active and stable transition metal catalysts for var- ious organic transformations. The highly sigma‐donating NHC ligands prevent the formation of inactive palladium Received: 22 November 2017 Revised: 26 December 2017 Accepted: 26 December 2017 DOI: 10.1002/aoc.4280 Appl Organometal Chem. 2018;e4280. https://doi.org/10.1002/aoc.4280 Copyright © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/aoc 1 of 11