 Welcome to this course on transition metal organometallics in catalysis and biology. In this series of lecture, of late we are discussing oligomerization of alkenes and alkynes topic, and in that we have discussed about four kinds of oligomerization reaction starting with ethylene oligomerization. And this we have discussed with regard to shell higher olefin process or the shop process, which uses the nickel catalyst for carrying out this ethylene oligomerization. The main drawback, even though this is an industrial scale process, the main drawback is that it is not selective in the sense that it produces a broad range of distributions of ethylene oligomers of various chain length. This shop is an industrial process that includes ethylene oligomerization along with olefin isomerization and olefin metathesis together they constitute the process of shop, which is shell higher olefin process. Subsequently, we have also discussed another interesting reaction, which is ethylene trimerization, and this is done very selectively in which ethylene is trimerized to give one hexene, and this is a process that uses early transition metal Tantalum 3 catalyst for carrying out this one hexene at trimerization. The subsequent that we have also discussed another topic, which is a dimerization of propene dimerization, and this produces hexenes of different substitutions, and these branched hexenes when hydrogenated give a high quality petrol of very high anti-knocking attributes, and this also uses a nickel catalyst for carrying out such kind of transformation. Now, with this being discussed today, we are going to proceed further, and then we are going to discuss another interesting reaction, which is cyclotrimerization of butadiene, or maybe we can call it for the sake of butadiene cyclotrimerization. This produces cyclo-octa-dodeca-triene, and uses also a nickel catalyst. Now, if one were to look, we are going to be discussing about this topic in as a part of today's class. Now, in this connection, it is worth noting that if one were to look at all these oligomerization process, for example oligomerization, trimerization, drymerization, cyclotimerization, all of these process, then one would see that the metal of choice for such process is in fact nickel, which is a late transition metal, and also supposedly very electron rich. Now, this is an interesting observation as well as correlation that comes out of these oligomerization reactions. What it says is that olefin oligomerization is usually favored by electron rich late transition metals, whereas olefin polymerization is favored by early transition metal electron deficient early transition metals. This is a conventional wisdom in the area of olefin oligomerization and polymerization. From this perspective, this ethylene trimerization with tantalum III, which is an early transition metal stands out in the sense that there are some examples of even lower degree of polymerization like trimerization happening with electron deficient metal like tantalum. But note that the oxidation state of tantalum is not 5 and 3, so hence it is not really very electron deficient as it would have been if it were in the plus 5 oxidation state. Now, with that, we will be able to focus on today's discussion, which would be centered around this butadiene cyclotrimerization reaction and look at various ways that they form. One thing to note that in terms of application, before I proceed further in terms of application, this shop is where applied for preparing detergent ingredients application in the detergent industry, whereas this propene dimerization giving hexane branches, these are in automobile because they are used for producing petrol of high quality anti-knocking agents. This is an application in auto industry and this ethylene trimerization is providing very selective one-hexane, they are also used for commercial purpose. Also to note that this particular reaction which is propene dimerization having applications in high quality petrol of anti-knocking capacity, the activity of these catalysts is extremely high, the turnover number is quite comparable to that of a biological enzyme like catalase that carry out these kind of transformations. Having said that, here we have a system which is extremely efficient and has a very high turnover number with respect to similar to that or comparable to that of an enzyme catalase reaction. From that perspective, this catalyst or this process is quite remarkable fit that demonstrate the capability of organometallic catalysis in the world of chemical transformation. With that discussion, let us move on to this topic of today's discussion which is cyclotrimerization of butadiene. What we are going to primarily focus on is the mechanism in which how it works. The precursor is a nickel to allyl complex, this allyl complex that is the catalyst precursor and the oxidation state over here is a nickel 2. That in presence of butadiene undergoes reductive elimination of the two allyl moiety to give a diallyl compound as is shown here. The reductive elimination happens between this and this resulting in diallyl compound as is shown over here and it gives this nickel 0 species with 2 butadiene. So the oxidation state for this species is a nickel 0. Now that subsequently reacts with butadiene to give the species which is shown over here. Now this is the oxidation addition reaction of 2 butadiene moiety to form this b-sallyl ligand and the oxidation state of the nickel has become nickel 2 as a result of this oxidation reaction. Now this is in equilibrium this species which is a sigma bond and this is a pi bond which are now separated and at a very low temperature greater than minus 40 degree centigrade, the second insertion happens on to this ligand giving rise to this nickel 2 species which also is nickel 2 and then this is an important species which subsequently tremorizes at reaction above minus 40 degree centigrade to give the corresponding nickel 0. So this is a sort of reductive elimination process to give the nickel 0 species as is shown here and this is called nickel and this is a nickel 0 species which finally eliminates the butadiene tremor to give this cyclic tremor. This is called trans trans trans 159 cyclo dodeca triene. This gives cyclo dodeca triene and this butadiene 2 of them then enters the catalytic cycle. This is an interesting mechanism which has been proposed by Wilke in 1960 and this involves the formation of nickel as is shown over here, so this involves formation of nickel as is shown over here. The main feature is the transformation from nickel 2 into the catalytic cycle as well as nickel 0 or the nickel nickel in the 2 of the catalytic cycle. The other important thing is that these particular species was confirmed by preparing it separately and entering the catalytic cycle through these species which also gave the identical cyclo tremorized products. This is indeed a very good reaction that has been successfully carried out in which butadiene can be tremorized to give trans trans trans 159 cyclo dodeca triene as is shown over here. So, the key features of these cyclo tremorization reaction is given below the key features. The number one of the pre-catalyst is a bicellular complex of nickel. Then the second thing is the mechanism was validated by independently preparing one of the intermediate and then successfully entering the catalytic cycle. So another important attribute of this mechanism is for the metal for nickel change in coordination number from 3 to 4 and the oxidation state 0 to 2 are observed and the last but a very important attribute is nickel in nickel 0 stabilized by donor ligands are observed. These are the key attributes of this cyclo tremorization process which shows the feasibility of this nice reaction through the metal undergoing flexible displaying flexible coordination mode by changing the coordination number from 3 to 4 as well as flexible oxidation state by changing the oxidation state from 0 to 2 in the process naked nickel stabilized by alkene donors are formed and they are part of the catalytic cycle. Lastly the catalytic cycle is even validated by entering the catalytic cycle through one of the catalytic intermediates which were prepared independently. Now having said this even though this was a very nice and beautiful reaction in terms of the applications of organometallic catalysis are concerned however this reaction is not being used in industrial scale for producing this cyclo-dodeca trin or trimer of butadiene and this cyclo-dodeca trin in industry is prepared by Ziegler-Nutter process as is shown over here cyclo-dodeca trimerization of butadiene in industrial scale process use Ziegler-Nutter catalysis and this is shown below 3 butadiene with titanium tetrachloride R2L2Cl3 and this gives this cis trans trans 159 cyclo-dodeca trin that is further hydrogenated and then finally in presence of oxygen and the second with nitric acid is produced this acid is produced in large scale about 10,000 ton per year annually. So even though this will this method of producing butadiene trimerization is a very nice beautiful method but this is not being used in industry probably because of difficulty in handling the air sensitive nature of nickel zero intermediate that is produced in the process of cyclo trimerization of butadiene and hence Ziegler-Nutter catalysis used to produce this trans cyclo butadiene then which is then hydrogenated and subsequent oxidation and nitric acid produces this diacid about 10,000 ton annually in a large industrial scale. So with this I come to the conclusion of today's lecture. In today's lecture we have looked into cyclo trimerization of butadiene in the context of various other topics we are covering along the theme of olefin and alkyne oligomerization reaction. We have looked into the mechanism as proposed by Wilkie using an nickel catalyst and then we have also looked at the alternative pathway which is used in industry using Ziegler-Nutter catalysis using titanium tetrachloride to produce the cyclo trimerization of butadiene in large scale processes for making a diacid in about bulk quantity about 10,000 ton annually. So with this I come to the conclusion again one more time of today's lecture and I look forward to taking up the topic in bit more detail little bit remains on this olefin and alkyne oligomerization reaction and subsequently we will take up olefin polymerization reaction as we meet next till then goodbye and thank you.