2. Reviews on Platinum as Heck catalystMostly the studies on the heck reaction depend upon the reaction mechanism and the use of different catalyst type will redirect the mechanism towards different direction finally giving the similar type of product. So use of catalyst which can really shorten the reaction time and mechanism is the must and also the majority of the work on Heck reaction has been focused on the catalyst development.For any catalyst to be suitable for the Heck reaction the properties it should possess is its stability and its ability to make the reaction quick. This review discusses the simple N-heterocyclic carbine palladium based complexes as effective catalyst and it can be used in variety of cross coupling reactions and have been proved to a suitable choice phosphine ligands in homogeneous catalysis in different catalytic processes. The efficiency of this catalyst depends upon the binding ability for transition metal and their ability to stabilize and activate metal centers in different steps of organic synthesis. Also N/heterocyclic carbenes as ligands where ligands and metal complexes are selectively obtained and active towards Heck reaction giving TONs upto 1.
7*106.these ligands don’t only bind with the transition metal but also the main group elements.it has been explained as that bulky NHC ligands for successful reactions with catalysts made of these ligands. Palladium complexes are electron donating ligands such as carbenes, phospines.
Nitrogen donor ligands also increase the activity, stability and the selectivity properties of the catalysts. However, palladium nanoparticles can also act as pre catalyst by putting thecatalyst on a polymer support. Palladacycles are found to be active against a broad spectrum of reactions and its high activity at low palladium ligands ratio does increases its thermal capabilities as well. However, there are also some problems like scope, purity, and the time for developing high turnover for the cross coupling and Heck reactions. As compared to the most of the traditional catalyst , carbine ligands along with palladium nanoparticles do have high/TON and thus have more robust than most of the other phosphine ligands.
For heterogeneous catalysis, palladium catalysed coupling reactions are efficient and reliable for introducing of new carbon-carbon bonds onto molecules attached to a solid support. The main advantage of using palladium metal catalyst to heck reaction is the simplification of the procedure and the possibility of the recovery of the precious metal. For the industrial approach, there has been many developments on the mechanism of the palladium catalysed C-C bond formation and change in methodologies during its innovation and evolution.fig2: schematic representation of C-H activation and transmetallationHeck reaction has been a robust and efficient method for carbon-carbon bond formation and it could promise for new discoveries resulting in better and efficient catalyst formation and the great functional properties of palladium makes Heck reaction possible even on most sensitive substrates and it could also reduce the number of reaction steps by use of the palladium catalyst by concentrating on protection and deprotection procedures.
hence , the palladium catalysed heck reaction has been a integral part of pharmaceutical and industrial research and production.